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UNIVERSITY  OF  CALIFORNIA 
AT   LOS  ANGELES 


^w 

/ 
iLtbrarp  of  electrical  Science 

I'OLUME   ONE 


A    DICTIONARY    OF 

E  LECTRIC AL 

WORDS,  TERMS  and  PHRASES 

BY 

EDWIN  J.   HOUSTON,   A.M.,  PH.D. 

EMERITUS   PROFESSOR    OF  NATURAL     PHILOSOPHY   AND   PHYSICAL   GEOGRAPHY 

IN   THE  CENTRAL    HIGH   SCHOOL     OF    PHILADELPHIA  J     PROFESSOR     OF 

PHYSICS    IN   THE   FRANKLIN    INSTITUTE     OF     PENNSYLVANIA  ; 

ELECTRICIAN    OF  THE   INTERNATIONAL    ELECTRICAL 

EXHIBITION,   ETC.,   ETC.,   ETC. 

P ART     ONE  —  A  to  S 


NEW     YORK 
P.    F.    COLLIER    fcf    SON 

1902 


COPYRIGHT  1889,  1892,  1894,  1897 
Bv  THE  W.  J.  JOHNSTON  COMPANY 

APPENDIX  B 

COPYRIGHT  1897 

BY  EDWIN  J.  HOUSTON 


S05T 
WtflcL 


PREFACE  TO  THE  FIRST   EDITION. 

THE  rapid  growth  of  electrical  science,  and  the  almost  daily  addition  to  it  of  new 
words,  terms  and  phrases,  coined,  as  they  too  frequently  are,  in  ignorance  of 
those  already  existing,  have  led  to  the  production  of  an  electrical  vocabulary  that  is 
already  bewildering  in  its  extent.  This  multiplicity  of  words  is  extremely  discourag- 
ing to  the  student,  and  acts  as  a  serious  obstacle  to  a  general  dissemination  of  elec- 
trical knowledge,  for  the  following  reasons  : 

1.  Because,  in  general,  these  new  terms  are  not  to  be  found  eve^  in  the  unabridged 
editions  of  dictionaries. 

2.  The  books  or  magazines,  in  which  they  were  first  jroposed,   are  either  inac- 
cessible to  the  ordinary  reader,  or,  if  accessible,   are  often  written  in  phraseology  un- 
intelligible except  to  the  expert. 

3.  The  same  terms  are  used  by  different  writers  in  conflicting  senses. 

4.  The  same  terms  are  used  with  entirely  different  meanings. 

5.  Nearly  all  the  explanations  in  the  technical  dictionaries  are  extremely  brief  as 
regards  the  words,  terms  and  phrases  of  the  rapidly  growing  and  comparatively  new 
science  of  electricity. 

In  this  era  of  extended  newspaper  and  periodical  publication,  new  words  are  often 
coined,  although  others,  already  in  existence,  are  far  better  suited  to  express  the  same 
ideas.  The  new  terms  are  used  for  a  while  and  then  abandoned  ;  or,  if  retained, 
having  been  imperfectly  defined,  their  exact  meaning  is  capable  of  no  little  ambiguity; 
and,  subsequently,  they  are  often  unfortunately  adopted  by^different  writers  with  such 
varying  shades  of  meaning,  that  it  is  difficult  to  understand  their  true  and  exact 
significance. 

Then  again,  old  terms  buried  away  many  decades  ago  and  long  since  forgotten,  are 
\   dug  up  and  presented  in  such  new  garb  that  their  creators  would  most  certainly  fail 
to  recognize  them. 

It  has  been  with  a  hope  of  removing  these  difficulties  to  some  extent  that  the  author 
r   has  ventured  to  present  this  Dictionary  of  Electrical  Words,  Terms  and  Phrases  to  his 
^$  brother  electricians  and  the  public  generally. 

He  trusts  that  this  dictionary  will  be  of  use  to  electricians,  not  only  by  showing  the 
sjt  wonderful  extent  and  richness  of  the  vocabulary  of  the  science,  but  also  by  giving  the 
eral  consensus  of  opinion  as  to  the  significance  of  its  different   words,   terms  or 
phrases.     It  is,   however,  to  the  general  public,   to  whom  it  is   not  only  a  matter  of 
interest  but  also  one  of  necessity  to  fully  understand  the  exact  meaning  of  electrical 
literature,  that  the  author  believes  the  book  will  be  of  the  greatest  value. 

In  order  to  leave  no  doubt  concerning  the  precise  meaning  of  the  words,  terms  and 
phrases  thus  defined,  the  following  plan  has  been  adopted  of  giving  : 
(i.)  A  concise  definition  of  the  word,  term  or  phrase. 

(2.)  A  brief  statement  of  the  principles  of  the  science  involved  in  the  definition. 
J— VOL.  1 

853927 


(3.)  Where  possible  and  advisable,  a  cut  of  the  apparatus  described  or  employed 
in  connection  with  the  word,  term  or  phrase  denned. 

It  will  be  noticed  that  the  second  item  of  the  plan  makes  the  Dictionary  ap- 
proach to  some  extent  the  nature  of  an  Encyclopedia.  It  differs,  however,  from 
an  Encyclopedia  in  its  scope,  as  well  as  in  the  fact  that  its  definitions  in  all  cases 
'  are  concise. 

Considerable  labor  has  been  expended  in  the  collection  of  the  vocabulary,  for 
which  purpose  electrical  literature  generally  has  been  explored.  In  the  alphabetical 
arrangement  of  the  terms  and  phrases  defined,  much  perplexity  has  arisen  as  to  the 
proper  catch-word  under  which  to  place  them.  It  is  believed  that  part  of  the 
difficulty  in  this  respect  has  been  avoided  by  the  free  use  of  cross  references. 

In  elucidating  the  exact  meaning  of  terms  by  a  brief  statement  of  the  principles 
of  the  science  involved  therein,  the  author  has  freely  referred  to  standard  textbooks  on 
electricity,  and  to  periodical  literature  generally.  He  is  especially  indebted  to  works 
or  treatises  by  the  following  authors,  viz.  :  S.  P.  Thompson,  Larden,  Gumming, 
Hering,  Prescott,  Ayrton,  Ayrton  and  Perry,  Pope,  Lockwood,  Sir  William  Thom- 
son, Fleming,  Martin  and  Wetzler,  Preece,  Preece  and  Sivewright,  Forbes,  Max- 
well, De  Watteville,  J.  T.  Sprague,  Culley,  Mascart  and  Joubert,  Schwendler, 
Fontaine,  Noad,  Smee,  Depretz,  De  la  Rive,  Harris,  Franklin,  Cavallo,  Grove, 
Hare,  Daniell,  Faraday  and  very  many  others. 

The  author  offers  his  Dictionary  to  his  fellow  electricians  as  a  starting  point  only. 
He  does  not  doubt  that  his  book  will  be  found  to  contain  many  inaccuracies,  ambig- 
uous statements,  and  possibly  doubtful  definitions.  Pioneer  work  of  this  character 
must,  almost  of  necessity,  be  marked  by  incompleteness.  He,  therefore,  invites 
the  friendly  criticisms  of  electricians  generally,  as  to  errors  of  omission  and  commis- 
sion, hoping  in  this  way  to  be  able  finally  to  crystallize  a  complete  vocabulary  of 
electrical  words,  terms  and  phrases. 

The  author  desires  in  conclusion  to  acknowledge  his  indebtedness  to  his  friends, 
Mr.  Carl  Henng,  Mr.  Joseph  Wetzler  and  Mr.  T.  C.  Martin,  for  critical  exami- 
nation of  the  proof  sheets ;  to  Dr.  G.  G.  Faught  for  examination  of  the  proofs  of 
the  parts  relating  to  the  medical  applications  of  electricity,  and  to  Mr.  C.  E.  Stump 
for  valuable  aid  in  the  illustration  of  the  book ;  also  to  Mr.  George  D.  Fowle, 
Engineer  of  Signals  of  the  Pennsylvania  Railroad  Company,  for  information  concern- 
ing their  System  of  Block  Signaling,  and  to  many  others. 

EDWIN  J.  HOUSTON. 

»      CENTRAL  HIGH  SCHOOL,  PHILADELPHIA,  PA., 
SEPTEMBER,  1889. 


PREFACE  TO  THE  SECOND  EDITION. 

THE  first  edition  of  the  "Dictionary  of  Electrical  Words,  Terms  and  Phrases"  met 
with  so  favorable  a  reception  that  the  entire  issue  was  soon  exhausted. 
Although  but  a  comparatively  short  time  has  elapsed  since  its  publication,  electrical 
progress  has  been  so  marked,  and  so  many  new  words,  terms  and  phrases  have  been 
introduced  into  the  electrical  nomenclature,  that  the  preparation  of  a  new  edition  has 
been  determined  on  rather  than  a  mere  reprint  from  the  old  plates. 

The  wonderful  growth  of  electrical  science  may  be  judged  from  the  fact  that  the 
present  work  contains  more  than  double  the  matter  and  about  twice  the  number  of 
definitions  that  appeared  in  the  earlier  work.  Although  some  of  this  increase  has 
been  due  to  words  which  should  have  been  in  the  first  edition,  yet  in  greater  part  it 
has  resulted  from  an  actual  multiplication  of  the  words  used  in  electrical  literature. 

To  a  certain  extent  this  increase  has  been  warranted  either  by  new  applications  of 
electricity  or  by  the  discovery  of  new  principles  of  the  science.  In  some  cases,  how- 
ever, new  words,  terms  or  phrases  have  been  introduced  notwithstanding  the  fact  that 
other  words,  terms  or  phrases  were  already  in  general  use  to  express  the  same  ideas. 

The  character  of  the  work  is  necessarily  encyclopedic.  The  definitions  are  given 
in  the  most  concise  language.  In  order,  however,  to  render  these  definitions  intel- 
ligible, considerable  explanatory  matter  has  been  added. 

The  Dictionary  has  been  practically  rewritten,  and  is  now,  in  reality,  a  new  book 
based  on  the  general  lines  of  the  old  book,  but  considerably  changed  as  to  order  of 
arrangement  and,  to  some  extent,  as  to  method  of  treatment. 

As  expressed  in  its  preface,  the  author  appreciates  the  fact  that  the  earlier  book 
was  tentative  and  incomplete.  Though  the  wide  scope  of  the  second  edition,  the 
vast  number  of  details  included  therein,  and  the  continued  growth  of  the  electrical 
vocabulary  must  also  necessarily  make  this  edition  incomplete,  yet  the  author  ventures 
to  hope  that  it  is  less  incomplete  than  the  first  edition.  He  again  asks  kindly  criti- 
cisms to  aid  him  in  making  any  subsequent  edition  more  nearly  what  a  dictionary  of 
so  important  a  science  should  be. 

The  order  of  arrangement  in  the  first  edition  has  been  considerably  changed.  The 
initial  letter  under  which  the  term  or  phrase  is  defined  is  in  all  caSjes  that  of  the  noun. 

For  example,  "Electric  Light  "  is  defined  under  the  term  "  Light,  Electric "  ; 

"  Diameter  of  Commutation  "  under  "Commutation,  Diameter  of , "  "Alter- 
nating Current  Dynamo- Electric  Machine"  under  "Machine,  Dynamo-Electric, 
Alternating  Current ."  As  before,  the  book  has  numerous  cross  references. 

Although  the  arrangement  of  the  words,  terms  and  phrases  under  the  initial  letter 
of  the  first  word,  term  or  phrase,  as,  for  example,  "  Electric  Light"  under  the  letter  E, 
might  possess  some  advantages,  yet,  in  the  opinion  of  the  author,  the  educational  value 


of  the  work  would  be  thereby  considerably  decreased,  since  to  a  great  extent  such  an 
arrangement  would  bring  together  incongruous  portions  of  the  science. 

Frequent  cross  references  render  it  possible  to  use  the  Dictionary  as  a  text-book  in 
connection  with  lectures  in  colleges  and  universities.  With  such  a  book  the  student  need 
nuke  notes  only  of  the  words,  terms  or  phrases  used,  and  afterwards,  by  the  use  of  the 
definitions  and  explanatory  matter  connected  therewith,  work  up  the  general  subject 
matter  of  the  lecture.  The  author  has  successfully  used  this  method  in  his  teaching. 

In  order  to  separate  the  definitions  from  the  descriptive  matter,  two  sizes  of  type 
have  been  used,  the  definitions  being  placed  in  the  larger  sized  type. 

In  the  descriptive  matter  the  author  has  not  hesitated  to  quote  freely  from  standard 
electrical  works,  electrical  magazines,  and  periodical  literature  generally.  Among  the 
numerous  works  consulted,  besides  those  to  which  reference  has  already  been  made 
in  the  preface  to  the  first  edition,  he  desires  to  acknowledge  his  indebtedness  espe- 
cially to  "The  Alternating  Current  Transformer,"  by  J.  A.  Fleming  ;  to  various  works 
of  John  W.  Urquhart ;  to  "Modern  Views  of  Electricity,"  by  Prof.  O.  J.  Lodge;  to 
"A  Text-book  of  Human  Physiology,"  by  Landois  &  Sterling;  and  to  "Practical 
Application  of  Electricity  in  Medicine  and  Surgery, "  by  Liebig  &  Rohe. 

The  cuts  or  diagrams  used  in  the  book  have  either  been  drawn  especially  for  the 
work  or  have  been  taken  from  standard  electrical  publications. 

The  chart  of  standard  electrical  symbols  and  diagrams  has  been  taken  from  Prof. 
F.  B.  Crocker's  paper  on  that  subject. 

The  definition  of  terms  used  in  systems  of  electric  railways  have  been  taken 
mainly  from  a  paper  on  "  Standards  in  Electric  Railway  Practice,"  by  O.  T.  Crosby. 

The  author  desires  especially  to  express  his  obligations  to  Prof.  F.  B.  Crocker  of 
the  Electrical  Engineering  Department,  Columbia  College,  New  York,  and  to  Carl 
Hering,  of  Philadelphia,  for  critical  examination  of  the  entire  manuscript  and  for  many 
valuable  suggestions  ;  also  to  The  Electrical  World  and  the  Electrical  Engineer  of  New 
York,  and  to  Prof.  Elihu  Thomson,  Edward  Caldwell,  T.  C.  Martin,  Dr.  Louis  Bell, 
Joseph  Wetzler,  Nikola  Tesla,  Wm.  H.  Wahl,  Prof.  Wm.  D.  Marks,  Prof.  A.  E. 
Dolbear,  C.  W.  Pike,  John  Hoskin,  and  numerous  others,  for  aid  in  connection  with 
new  words  or  phrases.  So  far  as  they  relate  to  the  medical  applications  of  electricity, 
the  proof  sheets  were  revised  by  Dr.  G.  G.  Faught,  of  Philadelphia. 

The  author  desires  to  thank  critics  of  the  first  edition  and  the  electrical  fraternity  in 
general  for  valuable  suggestions.  He  presents  this  second  e  lition  of  his  Dictionary  in  the 
hope  that  it  may  to  some  extent  properly  represent  the  vocabulary  of  electrical  science. 

CENTRAL  HIGH  SCHOOL,  EDWIN  J.   HOUSTON. 

PHILADELPHIA,  May,  1892. 


PREFACE  TO  THE  THIRD  EDITION. 

THE  second  edition  of  the  "Dictionary  of  Electrical  Words,  Terms,  and  Phrases" 
was  exhausted  in  such  a  comparatively  short  time  that  the  publishers  believed 
that  what  new  matter  might  be  required  for  a  third  edition  could  best  be  added  in 
the  form  of  an  appendix. 

Although  not  quite  two  years  have  elapsed  since  the  issue  of  the  second  edition, 
yet  the  growth  of  electrical  science  has  continued  at  so  rapid  a  pace,  and  new  words, 
terms,  and  phrases  have  of  necessity  been  introduced  so  rapidly,  that  fully  twenty  per 
cent.,  both  of  new  words  and  new  matter,  have  been  found  necessary  for  the  third 
edition.  Had  this  fact  been  known  in  time,  it  might  have  been  better  to  have 
developed  the  additional  matter  throughout  the  text,  rather  than  placing  it  at  the  end 
of  the  book  as  an  appendix. 

Should  a  demand  be  made  for  a  fourth  edition,  the  author  contemplates  re- 
writing and  re-arranging  the  entire  volume.  He  is  thoroughly  aware  of  the  inaccuracies 
and  incompleteness  of  many  of  the  definitions  in  the  second  edition,  and  hopes,  in 
the  event  of  a  demand  for  a  fourth  edition,  to  produce  a  volume  more  nearly  ap- 
proximating to  what  an  electrical  dictionary  should  be.  In  the  meantime,  he  again 
asks  the  kindly  criticisms  of  his  fellow  laborers  in  the  electrical  field  to  aid  him  in  the 
work. 

In  order  to  facilitate  the  use  of  the  cross-references,  all  words,  terms,  and  phrases 
referred  to  in  the  appendix  are  so  marked;  i.  e.,  (See  Appendix — Insulation,  Kilo- 
metric,  of  Cable. )  All  references  not  so  marked  will  be  found  in  the  main  text  of  the 
dictionary. 

The  author  desires  to  express  his  obligations  to  numerous  authors  and  technical 
journals  for  information  as  to  new  words,  terms,  and  phrases,  and  to  the  significance 
generally  given  to  them  in  actual  use.  He  desires  especially  to  acknowledge  his 
obligations  to  his  colleague,  Mr.  A.  E.  Kennelly,  and  to  Professors  R.  A.  Fessenden, 
C.  Wellman  Park;  to  Messrs.  C.  P.  Steinmetz,  J.  F.  Kelly,  O.  B.  Shallenberger,  Carl 
Hering,  H.  W.  Frye,  W.  D.  Weaver,  W.  F.  C.  Hasson,  Townsend  Wolcott,  J.  B. 
Cahoon,  and  many  others,  for  reading  of  proof  sheets  and  suggestions. 

The  author  presents  this  third  edition  of  the  Dictionary  with  the  hope  that  it 
may  prove  of  value  to  the  electrical  fraternity. 

EDWIN  J.  HOUSTON. 
PHILADELPHIA,  May,  1894. 


PREFACE  TO  THE  FOURTH  EDITION. 

TN  preparing  the  fourth  edition  of  his  "  Dictionary  of  Electrical 
1  Words,  Terms  and  Phrases,"  the  author  soon  found  that  the 
recent  marvellous  growth  in  the  electrical  vocabulary  was  such  that 
it  would  be  impossible  to  add,  in  the  shape  of  a  separate  appendix, 
the  new  words,  terms  and  phrases  only,  that  it  was  necessary  to 
introduce  into  the  book.  This  will  be  evident  from  the  fact  that 
the  added  words  exceed  in  number  those  already  contained  in  the 
first,  second  and  third  editions.  Since  it  was  deemed  inadvisable 
by  the  publisher  to  recast  the  entire  book,  the  only  course  left  open 
to  the  author  was  to  alphabetically  arrange  all  the  old  and  new 
words,  and  to  present  them  in  concise  definitions  without  any  ency- 
clopaedic matter,  referring  the  reader  to  the  matter  contained  in 
the  earlier  editions  for  illustration  and  detail. 

It  has  also  been  thought  advisable  to  introduce  a  change  in  the 
manner  of  arrangement,  the  words,  terms  and  phrases  being  alpha- 
betically arranged  according,  either  to  the  word,  or  to  the  first  word 
of  the  term  or  phrase.  This  has  permitted  the  entire  suppression 
of  all  cross  references,  which,  in  view  of  the  author's  past  expe- 
rience, he  believes  will  prove  an  advantage. 

The  author  desires  to  acknowledge  the  very  valuable  assistance 
afforded  him  by  his  colleague,  Dr.  A.  E.  Kennelly,  in  the  prepa- 
ration of  the  matter  for  the  fourth  edition,  both  in  collecting  new 
terms,  as  well  as  in  preparing  the  definitions,  and  reading  the 
proof. 

The  author  trusts,  that  the  fourth  edition  of  his  electrical  Diction- 
ary will  prove  of  benefit  not  only  to  the  electrical  world  but  to  the 
reading  public  generally. 

All  criticisms  will  be  gladly  received. 

EDWIN  J.  HOUSTON. 

PHILADELPHIA,  December,  1897. 


A     DICTIONARY 


OF 


ELECTRICAL 

WORDS,    TERMS    AND    PHRASES. 


A.  or  An. — An  abbreviation  sometimes  used 
in  medical  electricity  for  anode.  (See  Anode.) 

A.  C.  C. — An  abbreviation  used  in  medical 
electricity  for  Anodic  Closure  Contraction. 
(See  Contraction,  Anodic  Closure.) 

A.  D.  C. — An  abbreviation  used  in  medical 
electricity  for  Anodic  Duration  Contraction. 
(See  Contraction,  Anodic  Duration) 

A.  0.  C. — An  abbreviation  used  in  medical 
electricity  for  Anodic  Opening  Contraction. 
(See  Contraction,  Anodic  Opening.) 

Abscissa  of  Rectilinear  Co-ordinates. — A 
line  or  distance  cut  off  along  axis  of  abscissas. 

The  abscissa  of  the  point  D,  Fig.  i,  on  the  curve 
O  D  R,  is  the  distance  D  I,  or  its  equal  A  2, 
measured  or  cut  off  on  the  line  A  C,  the  axis  of 
abscissas;  or,  briefly,  A  2,  is  the  abscissa  of  the 
point  D. 

Abscissas,    Axis  of  — One    of   the 

axes  of  co-ordinates  used  for  determining  the 
position  of  points  on  a  curved  line. 

Thus  the  position  of 
the  point  D,  Fig.  i,  on 
the  curved  line  O  D  R, 
is  determined  by  the  per- 
pendicular distances,  D I 
and  D  2,  of  such  point 
from  two  straight  lines, 
A  B  and  A  C,  called  the 
ax  fs  of  co-ordinates.  AC,  A  2  C 

is  called  the  axis  of  ab-  F*-r;  **<**/ Co-ordinate*, 
scissas,  and  AB,  the  axis  of  ordinates.   The  point 


A,  where  the  lines  are  considered  as  starting  or 
originating,  is  called  fat  point  of  origin,  or,  gen- 
erally, the  origin. 

The  use  of  co-ordinates  was  first  introduced  by 
the  famous  mathematician,  Des  Cartes. 

Absolute.— Complete  in  itself. 

The  terms  absolute  and  relative  are  used  in 
electricity  in  the  same  sense  as  ordinarily. 

Thus,  a  galvanometer  is  said  to  be  calibrated 
absolutely  when  the  exact  current  strengths  re- 
quired to  produce  given  deflections  are  known  ; 
or,  in  other  words,  when  the  absolute  current 
strengths  are  known  ;  it  is  said  to  be  calibrated 
relatively  when  only  the  relative  current  strengths 
required  to  produce  given  deflections  are  known. 

The  word  absolute,  as  applied  to  the  units  em- 
ployed  in  electrical  measurements,  was  introduced 
by  Gauss  to  indicate  the  fact  that  the  values  of 
such  units  are  independent  both  of  the  size  of  the 
instrument  employed  and  of  the  value  of  gravity  at 
the  particular  place  where  the  instrument  is 
used. 

The  word  absolute  is  also  used  with  reference 
to  the  fact  that  the  values  of  the  units  could 
readily  be  redetermined  from  well  known  con- 
stants, in  case  of  the  loss  of  the  standards. 

The  absolute  units  of  length,  mass,  and  time 
are  more  properly  called  the  C.  G.  S.  units,  or 
the  centimetre-gramme-second  units.  (See  Units, 
Absolute.) 

An  absolute  system  of  units  based  on  the  milli- 
gramme ^  millimetre,  and  second,  was  proposed  by 
Weber,  and  was  called  the  millimetre -milli- 
gramme-second units.  It  has  been  replaced  by 


Abs.] 


[Ace. 


the  C.  G.  S.  units.  (See  Units,  Centimetre- 
Gramme- Second.  Units,  Fundamental.) 

Absolute  Block  System  for  Railroads.— 

(See  Block  System  for  Railroads,  Absolute) 

Absolute  Calibration.— (See  Calibration, 
Absolute) 

Absolute  Electrometer. — (See  Electrome- 
ter, Absolute?) 

Absolute  Galvanometer. — (See  Galva- 
nometer, Absolute?) 

Absolute  Unit  of  Current.— (See  Current, 
Absolute  Unit  of.)  • 

Absolute  Unit  of  Electromotive  Force.— 
(See  Force,  Electromotive,  Absolute  Unit 
of.) 

Absolute  Unit  of  Inductance.— (See  In- 
ductance, Absolute  Unit  of) 

Absolute  Unit  of  Resistance.— (See  Re- 
sistance, Absolute  Unit  of) 

Absolute  Unit  of  Self-induction.— (See 
Induction,  Self,  Absolute  Unit  of) 

Absolute  Units.— (See    Units,  Absolute.) 

Absolute  Vacuum. — (See  Vacuum,  Ab- 
solute) 

Absorption. — The  taking,  or,  literally, 
drinking  in,  of  one  form  of  matter  by  another, 
such  as  a  gas,  vapor  or  liquid  by  a  solid  ;  or 
of  the  energy  of  sound,  light,  heat,  or  elec- 
tricity by  ordinary  matter. 

Absorption,  Acoustic The  taking 

in  of  the  energy  of  sound  waves  produced  by 
one  sounding  or  vibrating  body  by  another 
vibrating  body. 

Acoustic  absorption  may  result  in  the  dissipa- 
tion of  the  absorbed  energy,  as  heat,  or  in  sym- 
pathetic vibrations.  (See  Vibrations,  Sympathetic.) 

Absorption,  Electric The  appar- 
ent soaking  of  an  electric  charge  into  the 
glass  or  other  solid  dielectric  of  a  Leyden  jar 
or  condenser.  (See  Condenser.) 

The  capacity  of  a  condenser  varies  with  the 
time  the  condenser  remains  charged  and  with  the 
time  taken  in  charging.  Some  of  the  charge 
acts  as  if  it  soaked  into  the  solid  dielectric,  and 
this  is  the  cause  of  the  residual  charge.  (See 
Charge,  Residual.)  Therefore,  when  the  con- 


denser is  discharged,  less  electricity  appears  than 
was  passed  in ;  hence  the  term  electric  absorption. 

Absorption,  Luminous The  ab- 
sorption of  the  energy  of  light  in  its  passage 
through  bodies. 

When  sunlight  falls  on  an  opaque  colored  body, 
such  for  example  as  a  red  body,  all  the  colors  but 
the  reds  are  absorbed.  yThe  reds  are  then  thrown 
off  and  thus  cause  the  color.  In  the  same  manner, 
when  sunlight  falls  on  a  transparent  colored  body, 
such  for  example  as  red,  all  colors  but  the  reds  are 
absorbed,  and  the  reds  are  transmitted. 

When  sunlight  falls  on  a  phosphorescent  body, 
a  part  of  the  light  is  absorbed  as  heat ;  another 
part  is  absorbed  by  the  molecules  being  set  into 
motion  sufficiently  rapid  to  cause  them  to  emit 
light  or  to  become  luminous. 

A  mass  of  glowing  gas  or  vapor  absorbs  waves 
of  light  of  the  same  length  as  those  it  itself  emits. 
This  is  the  cause  of  the  dark  lines  of  the  solar 
spectrum,  called  the  Fraunhoffer  lines. 

The  amount  of  light  absorbed  by  the  glass  globe 
of  an  incandescent  lamp,  according  to  Urquhart, 
is  as  follows,  viz.: 

Clear  glass 10  per  cent. 

Ground  glass 35        " 

Opalescent  glass 50        " 

Absorption,  Selective The  absorp- 
tion of  a  particular  or  selected  character  of 
waves  of  sound,  light,  heat,  or  electricity. 

Absorption,  Thermal The  ab- 
sorption of  heat  energy  in  its  passage  through 
a  body. 

The  phenomena  of  thermal  absorption  are 
similar  to  those  of  luminous  absorption.  A  sub- 
stance that  is  transparent  to  heat,  or  which  allpws 
heat  waves  to  pass  through  without  absorption, 
is  called  diathermanous,  or  diathermanic,  or 
is  said  to  be  transparent  to  heat. 

Absorptive  Power. — (See  Power,  Absorp- 
tive) 

Acceleration. — The  rate  of  change  of 
velocity. 

Acceleration  is  thus  distinguished  from  velocity: 
velocity  expresses  in  time  the  rate- of- change  of 
position,  as  a  velocity  of  three  metres  per  second ; 
acceleration  expresses  in  time  the  rate-of-change 
of  velocity,  as  an  acceleration  of  one  centimetre 
per  second. 

Since  all  matter  is  inert,  and  cannot  change  its 


Ace.] 


[Ace. 


condition  of  rest  or  motion  without  the  applica- 
tion of  some  force,  acceleration  is  necessarily  due 
to  some  force  outside  the  matter  itself.  A  force 
may  therefore  be  measured  by  the  acceleration  it 
imparts  to  a  given  mass  of  matter. 

Acceleration  is  positive  when  the  velocity  is  in- 
creasing, and  negative  when  it  is  decreasing. 

Acceleration,  Dimensions  of The 

value  of  the  acceleration  expressed  in  terms 
of  the  length  or  of  distance  by  the  time.  (See 
Acceleration,  Unit  of.} 

Acceleration,  Unit  of That  ac- 
celeration which  will  give  to  a  body  unit- 
velocity  in  unit-time;  as,  for  example,  one 
centimetre-per-second  in  one  second. 

Bodies  falling  freely  in  a  vacuum,  and  ap- 
proximately so  in  air,  acquire  an  acceleration 
which  in  Paris  or  London,  at  the  end  of  a  second, 
amounts  to  about  981  centimetres  per  second,  or 
nearly  32.2  ft.  per  second. 

V 
A  =  —  ,  or,  in  other  words, 

The  acceleration  equals  the  velocity  divided  by 
the  time. 

But,  since  velocity  equals  the  Distance,  or  the 

Length  traversed  in  a  Unit  of  Time,  V  =  t . 

L 
Therefore,  A  =  X  =  -I.  =  ^ ,  Or 


The  acceleration  equals  the  length,  or  the  dis- 
tance passed  through,  divided  by  the  square  of  the 
time  in  seconds. 

These  formulae  represent  the  Dimensions  of 
Acceleration. 

Accumulated  Electricity.— (See  Electri- 
city, Accumulated^} 

Accumulating1  Electricity. — (See  Electri- 
city, Accumulating?) 

Accumulation  of  Electricity.— (See  Elec- 
tricity, Accumulation  of.} 

Accumulator. — A  -word  sometimes  applied 
to  any  apparatus  in  which  the  strength  of  a 
current  is  increased  by  the  motion  past  it  of  a 
conductor,  the  currents  produced  in  which 
tend  to  strengthen  and  increase  the  current 
which  causes  the  induction. 


The  word  accumulator  is  sometimes  applied  to 
Sir  Wm.  Thomson's  Electric  Current  Accumu- 
lator. 

Current  accumulators  operate  on  the  reaction 
principle  of  dynamo-electric  machines.  In  this 
sense,  therefore,  a  dynamo-electric  machine  is  an 
accumulator.  (See  Machine,  Dynamo-Electric, 
Reaction  Principle  of.} 


Fig.  2.    Barltrw's  Whtel. 

The  copper  disc  D,  Fig.  2,  has  freedom  of 
rotation,  on  a  horizontal  axis  at  O,  in  a  magnetic 
field,  the  lines  of  force  of  which,  represented  by 
the  dotted  lines  in  the  drawing,  pass  downward 
perpendicularly  into  the  plane  of  the  paper. 

If,  now,  a  current  from  any  source  be  passed 
in  the  direction  A,  O,  B,  C,  A,  through  the  circuit 
A,  O,  B,  C,  A,  which  is  provided  with  spring 
contacts  at  O,  and  A,  the  disc  will  rotate  in  the 
direction  of  the  curved  arrow.  This  motion  is 
due  to  the  current  acting  on  that  part  of  the  disc 
which  lies  between  the  two  contacts — A  and  O. 
This  apparatus  is  known  as  Barlow's  Wheel. 

If,  when  no  current  is  passing  through  the 
circuit,  the  disc  be  turned  in  the  direction  of  the 
arrow,  a  current  is  set  up  in  such  a  direction  as 
would  oppose  the  rotation  of  the  disc.  (See 
Law,  Lenz's.) 

If,  however,  the  disc  be  turned  in  the  opposite 
direction  to  that  of  the  arrow,  induction  currents 
will  as  before  be  produced  in  the  circuit.  As 
this  rotation  of  the  disc  tends  to  move  the  circuit 
O  A,  towards  the  parallel  but  oppositely  directed 
circuit  B  C,  these  two  circuits  being  parallel  and 
in  opposite  directions  tend  to  repel  one  another, 
and  there  will  thus  be  set  up  induced  currents 
that  tend  to  oppose  the  motion  of  rotation,  and 
the  current  of  the  circuit  will  therefore  increase 
in  strength.  (See  Dynamics,  Electro.}  Should 
then  a  current  be  started  in  the  circuit,  and  the 
original  field  be  removed,  the  induction  will  be 
continued,  and  a  current  which,  up  to  a  certain 
extent,  increases  or  accumulates,  is  maintained  in 
the  circuit  during  rotation  of  the  disc.  (Larden.) 

Barlow's  Wheel,  when  used  in  this  manner,  is 
known  as  Thomsons  Electric  Current  Accumu- 
lator. 


Acc.] 


[Ace. 


Accumulator.  —  A  word  often  applied  to 
a  Leyden  jar  or  condenser,  which  permits  the 
gradual  collection  from  an  electric  source  of 
a  greater  charge  than  it  would  otherwise  be 
capable  of  containing. 

A  condenser.     (See  Condenser?) 

The  ability  of  a  source  to  accumulate  an  in- 
creased  charge  when  connected  to  a  condenser  is 
due  to  the  increased  capacity  which  a  plate  or 
other  conductor  acquires  when  placed  near 
another  plate  or  conductor.  (See  Condenser. 
Jar,  Leyden.} 

Accumulator,    Capacity    of  --  The 

capacity  of  a  condenser,  expressed  in  micro- 
farads.    (See  Condenser,  Capacity  of.) 

Accumulator  or  Condenser  ;  Laws  of  Ac- 
cumulation of  Electricity.—  Sir  W.  Snow 
Harris,  by  the  use  of  his  Unit-Jar  and  Elec- 
tric Thermometer,  deduced  the  following 
laws  for  the  accumulation  of  electricity,  which 
we  quote  from  Noad's  "  Student's  Text-Book 
of  Electricity,"  revised  by  Preece  : 

(l.)  "Equal  quantities  of  electricity  are  given 
off  at  each  revolution  of  the  plate  of  an  electrical 
machine  to  an  uncharged  surface,  or  to  a  surface 
charged  to  any  degree  of  saturation." 

(2.  )  "A  coated  surface  receives  equal  quantities 
of  electricity  in  equal  times  ;  and  the  number  of 
revolutions  of  the  plate  is  a  fair  measure  of  the 
relative  quantities  of  electricity,  all  other  things 
remaining  the  same." 

(3.)  "  The  free  action  of  an  electrical  accumula- 
tion is  estimated  by  the  interval  it  can  break 
through,  and  is  directly  proportional  to  the  quan- 
tity of  electricity." 

(4.)  "  The  free  action  is  inversely  proportional 
to  the  surface." 

(5.)  "  When  the  electricity  and  the  surface  are 
increased  in  the  same  ratio,  the  discharging  in- 
terval  remains  the  same  ;  but  if,  as  the  electricity 
is  increased,  the  surface  is  diminished,  the  dis- 
charging interval  is  directly  as  the  square  of  the 
quantity  of  electricity." 

(6.)  "  The  resistance  of  air  to  discharge  is  as 
the  square  of  the  density  directly.  " 

According  to  some  later  investigations,  the 
quantity  a  plane  surface  can  receive  under  a  given 
density  depends  on  the  linear  boundary  of  the 
surface  as  well  as  on  the  area  of  the  surface. 

"  The  amount  of  electrical  charge  depends  on 


surface  and  linear  extension  conjointly.  There 
exists  in  every  plane  surface  what  may  be  termed 
an  electrical  boundary,  having  an  important  rela- 
tion to  the  grouping  or  disposition  of  the  electric 
particles  in  regard  to  each  other  and  to  surrounding 
matter.  This  boundary  in  circles  or  globes  is 
represented  by  their  circumferences.  In  plane 
rectangular  surfaces,  it  is  by  their  linear  extension 
or  perimeter.  If  this  boundary  be  constant,  their 
electrical  charge  varies  with  the  square  root  of 
the  surface.  If  the  surface  be  constant  the  charge 
varies  with  the  square  root  of  the  boundary.  If 
the  surface  and  boundary  both  vary,  the  charge 
varies  with  the  square  root  of  the  surface  multi- 
plied into  the  square  root  of  the  boundary." 

These  laws  apply  especially  to  continuous  sur- 
faces taken  as  a  whole,  and  not  to  surfaces  divided 
into  separate  parts. 

By  electrical  charge  Harris  meant  the  quantity 
sustained  on  a  given  surface  under  a  given  elec- 
trometer indication  ;  by  electrical  intensity,  he 
meant  the  indication  of  the  electrometer  corre- 
sponding to  a  given  quantity  on  a  given  surface. 

(See  Condenser,  Capacity  of.  Capacity,  Elec- 
trostatic. Capacity,  Specific  Inductive.  ) 

Accumulators  of  this  character  are  now 
generally  called  Condensers.  (For  more  modern 
principles  concerning  their  construction  and 
capacity  see  Condenser.  Condenser,  Capacity  of.) 

Accumulator,  Secondary  or  Storage 
Cell  --  Two  inert  plates  partially  sur- 
rounded by  a  fluid  incapable  of  acting  cham- 
ically  on  either  of  them  until  after  the  passage 
of  an  electric  current,  when  they  become 
capable  of  furnishing  an  independent  electric 
current. 

This  use  of  the  term  accumulator  is  the  one 
most  commonly  employed.  A  better  term  for 
such  a  cell  is  a  secondary  or  storage  cell.  (See 
Cell,  Secondary  or  Storage.) 

Commercially,  an  accumulator  consists  of  a 
single  jar  and  its  electrolyte,  in  which  a  single 
set  of  positive  and  negative  plates  is  properly 
placed. 

Accumulator,  Water-Dropping  -- 
An  apparatus  devised  by  Sir  W.  Thomson  for 
increasing  the  difference  of  potential  between 
two  electric  charges. 

The  tube  X  Y,  Fig.  3,  connects  with  a  reser- 
voir of  water  which  is  maintained  at  the  zero 
potential  of  the  earth.  The  water  escapes  from 


Ach.] 

the  openings  at  C  and  D,  in  small  drops  and  falls 
on  funnels  provided,  as  shown,  to  receive  the 
separate  drops  and  again  discharge  them. 

The  vessels  A,  A',  and  B, 
B',  which  are  electrically 
connected  as  shown,  are 
maintained  at  a  certain  small  A  hj 
difference  of  potential,  as 
indicated  by  the  respective 
-f-  and  —  signs. 

Under  these  c  i  r  c  u  m  - 
stances,  therefore,  C  and  D,  A  ' 
will  be  charged  inductively  FiS-  3-  Water-Drop- 
with  charges  opposite  to  ting  Acatmulator- 
those  of  A  and  B,  or  with  —  and  -f-  electricities 
respectively.  As  the  drops  of  water  fall  on  the 
funnels,  the  charges  which  the  funnels  thus  con- 
stantly receive  are  given  up  to  B'  and  A',  before 
the  water  escapes.  Since,  therefore,  B,  B',  and 
A,  A',  are  receiving  constant  charges,  the  differ- 
ence of  potential  between  them  must  continually 
increase.  This  apparatus  operates  on  the  same 
principle  as  the  replenisher.  The  drops  of  water 
act  as  the  carriers,  and  A,  A',  and  B,  B',  as  the 
hollow  vessels.  (See  Replenisher.) 

Achromatic. — Free  from  false  coloration. 

Images  formed  by  ordinary  lenses  do  not  pos- 
sess the  true  colors  of  the  object,  unless  the  edges 
of  the  lenses  are  cut  off  by  the  use  of  a  diaphragm ; 
i.  f.,  an  opaque  plate  with  a  central  circular 
opening.  The  edges  of  the  lenses  disperse  the 
light  like  an  ordinary  prism,  and  so  produce  rain- 
bow colored  (prismatic)  fringes  in  the  image. 
The  use  of  an  achromatic  lens  is  to  obviate  this 
false  coloration. 

Achromatizable. — Capable  of  being  freed 
from  false  coloration. 

Achromatize. — To  free  from  false  color- 
ation. 

Achromatizing. — Freeing  from  false  color- 
ation. 

Acid,  Spent A  battery  acid,  or  other 

acid,  that  has  become  too  weak  for  efficient 
action. 

In  a  voltaic  cell  the  acid  of  the  electrolyte 
becomes  spent  by  combining  with  the  metal  of 
the  positive  plate. 

Acidometer. — A  special  form  of  hydrom- 
eter used  in  determining  the  specific  gravity 
of  the  acid  liquid  in  a  secondary  or  storage 


cell.     (See  Areometer  or  Hydrometer.     Cell. 
Storage?) 

The  scale  on  the  acidometer  tube  is  made  to  in- 
dicate the  density  according  to  the  distance  the 
floating  instrument  sinks  in  the  liquid. 

Aclinic  Line.— (See  Line,  Aclinic) 

Acoustic  Absorption. — (See  Absorption, 
Acoustic?) 

Acoustic  Engraving. — (See  Engraving, 
Acoustic?) 

Acoustic  Telegraphy. — (See  Telegraphy, 
Acoustic?) 

Acoustic  Tetanus. — (See  Tetanus,  Acous- 
tic:) 

Acoutemeter,  Electric An  ap- 
paratus for  electrically  testing  the  delicacy  of 
hearing. 

The  Acoutemeter  is  one  of  the  many  applica- 
tions of  Hughes'  sonometer.  It  consists  of  three 
flat  coils  placed  parallel  to  one  another  on  a  grad- 
uated rod,  passing  through  their  axes.  The 
central  coil,  which  is  used  as  the  primary  of  an 
induction  coil,  is  fixed.  The  other  two,  which  are 
employed  as  secondary  coils,  are  movable.  (See 
Sonometer,  Hughes*.  Coil,  Induction.  Micro- 
phone.} A  microphone,  electrical  tuning  fork, 
switches,  plugs,  and  other  accessories,  are  suitably 
placed  and  connected.  The  subject  whose  hear- 
ing is  to  be  tested  is  placed  with  his  back  to  tke 
apparatus,  and  with  two  telephone  receivers  tightly 
fixed  to  his  ears.  As  various  sounds  are  produced, 
the  outer  or  movable  coils  are  moved  gradually 
away  from  the  central  coil,  until  no  sound  is 
heard  in  the  telephone  receivers.  This  distance 
is  in  the  inverse  ratio  of  the  delicacy  of  hearing  of 
the  individual. 

Actinic  Photometer. — (See  Photometer, 
Actinic?) 

Actinic  Ray.— (See  Ray,  Actinic?) 

Actinism. — The  chemical  effects  of  light, 
as  manifested  by  the  decomposition  of  various 
substances. 

Under  the  influence  of  the  sun's  light,  the  car- 
bonic acid  absorbed  by  the  leaves  of  plants  is  de- 
composed in  the  living  leaves  into  carbon,  which  is 
retained  by  the  plant  for  the  formation  of  its 
woody  fibre  or  ligneous  tissue,  and  oxygen,  which 
is  thrown  off. 


Act,] 


[Act. 


The  bleaching  of  curtains,  carpets,  and  other 
fabrics  exposed  to  sunlight  is  caused  by  the  actinic 
power  of  the  light.  The  photographic  picture  is 
impressed  by  the  actinic  power  of  light  on  a  plate 
covered  with  some  sensitive  metallic  salt. 

Actinograph. — An  apparatus  for  measur- 
ing and  recording  the  intensity  of  the  chemi- 
cal effects  of  light. 

Actinography. — The  method  of  measuring 
and  recording  the  intensity  of  the  chemical 
effects  of  light. 

Actinometer. — A  word  sometimes  applied 
to  a  pyrheliometer.  (See  Pyrheliometer) 

Actinometer,  Electric An  appa- 
ratus for  electrically  measuring  the  intensity 
of  the  chemically  active  rays  present  in  any 
luminous  radiation. 

The  rays  from  the  luminous  source  are  per- 
mitted to  fall  on  a  selenium  resistance,  and  their 
intensity  determined  by  the  change  observed  in 
the  resistance  as  indicated  by  the  deflections  of  a 
galvanometer  placed  in  circuit  with  the  selenium 
resistance.  Or,  a  thermo-electric  pile  is  employed, 
and  the  amount  of  heat  present  determined  by  the 
indications  of  a  galvanometer  placed  in  its 
circuit. 

Action,  Cataphoric The  action 

of  electric  osmose  or  cataphoresis.  (See 
Cataphoresis.) 

Action  Currents. — (See  Currents,  Action?) 

Action,  Inductive,  Lines  of  — 

Lines  within  the  space,  separating  a  charge 
and  a  neighboring  body,  along  which  elec- 
trostatic inductive  action  takes  place. 

Lines  of  electrostatic  force. 

Lines  of  inductive  action  pass  through  the 
dielectric,  separating  the  two  bodies,  and  termi- 
nate on  the  surfaces  of  the  conductor.  According 
to  the  now  generally  received  notions,  the  elec- 
trostatic charge  exists  in  the  mass  of  the  dielectric, 
and  not  in  that  of  the  conductor.  The  lines  of 
inductive  action  terminate  against  the  surfaces, 
one  at  the  positive,  and  the  other  at  the  negative 
surface.  A  true  E.  M.  F.  exists  in  the  space 
traversed  by  lines  of  inductive  action.  A  con- 
ductor brought  into  this  space  becomes  electri- 
fied, or  is  strained  in  such  a  manner  that  a 
momentary  current  is  produced  by  the  rearrange- 


ment of  the  electrification  brought  about  by 
electrostatic  induction. 

Action,  Local,  of  Dynamo-Electric  Ma- 
chine   The  loss  of  energy  in  a  dy- 
namo-electric machine  by  the  setting  up  of 
eddy  currents  in  its  pole  pieces,  cores,  or 
other  conducting  masses.  (See  Currents, 
Eddy.} 

In  a  dynamo-electric  machine  local  action  is 
obviated  by  a.  lamination  of  the  pole  pieces,  arma- 
ture core,  etc.  (See  Core,  Lamination  of.) 

Action,   Local,   of  Voltaic    Cell 

An  irregular  dissolving  or  consumption  of  the 
zinc  or  positive  element  of  a  voltaic  battery,  by 
the  fluid  or  electrolyte,  when  the  circuit  is 
open  or  broken,  as  well  as  when  closed,  or  in 
regular  action. 

Local  action  is  due  to  small  particles  of  such 
impurities  as  carbon,  iron,  arsenic,  or  other 
negative  elements,  in  the  positive  plate.  These 
impurities  form  with  the  positive  element  minute 
voltaic  couples,  and  thus  direct  the  corrosive 
action  of  the  liquid  to  portions  of  the  plate  near 
them.  Local  action  causes  a  waste  of  energy. 
It  may  be  avoided  by  the  amalgamation  of  the 
zinc.  (See  Zinc,  Amalgamation  of.) 

Action,  Magne-Crystallic A   term 

proposed  by  Faraday  to  express  differences 
in  the  action  of  magnetism  on  crystalline 
bodies  in  different  directions. 

A  needle  of  tourmaline,  if  hung  with  its  axis 
horizontal,  is  no  longer  paramagnetic,  as  usual, 
but  diamagnetic.  The  same  is  true  of  a  crystal 
of  bismuth.  Faraday  concluded  from  these  ex- 
periments that  a  force  existed  distinct  from  either 
the  paramagnetic  or  the  diamagnetic  force.  He 
called  this  the  magne  crystallic  force. 

Pltlcker  infers  from  these  phenomena  that  a 
definite  relation  exists  between  the  ultimate  form 
of  the  particles  of  matter  and  their  magnetic  be- 
havior. The  subject  may  be  regarded  as  yet 
somewhat  obscure.  (See  Polarity,  Diamagnetic.} 

Action  of  a  Current  on  a  Magnetic  Pole. 

— (See  Current,  Action  of,  on  a  Magnetic 
Pole) 
Action,   Refreshing,  of  Current 

The  restoration,  after  fatigue,  of  muscular  and 
nervous  excitability  obtained  by  the  action  of 


Act.] 

voltaic  alternatives.     (See  Alternatives,  Vol- 
taic) 

Activity. — The  work  done  per  second  by 
any  agent.  (This  term  is  but  seldom  used.) 

Work-per-second,  or,  as  generally  termed 
in  the  United  States,  Power,  or  Rate  of 
Doing  Work.  (See  Power.) 

Activity,  Unit  of  —  —A  rate  of  work- 
ing that  will  perform  one  unit  of  work  per 
second. 

In  C.  G.  S.  units,  the  activity  of  one  erg  per 
second. 

The  C.  G.  S.  unit  of  activity  is  very  small. 
One  Watt,  the  practical  unit  of  activity  or  power, 
is  equal  to  ten  million  ergs  per  second.  (See 
Watt.) 

The  unit  of  activity  generally  used  for  mechan- 
ical power  is  the  horse-power,  or  746  watts. 
(See  Horse- Power.) 

Actual  Cautery.— (See  Cautery,  Actual) 

Acute  Angle. — (See  Angle,  Acute) 

Adapter. — A  screw  nozzle  fitted  to  an  elec- 
tric lamp,  provided  with  a  screw  thread  to  en- 
able it  to  be  readily  placed  on  a  gas  bracket 
or  chandelier  in  place  of  an  ordinary  gas 
burner. 

Adherence. — The  quality  or  property  of 
adhering.  (See  Adhesion) 

Adherence,  Magnetic Adhesion  be- 
tween surfaces  due  to  magnetic  attraction. 

Magnetic  adhesion  has  been  applied,  among 
other  things,  to  a  brake  action  on  car  wheels, 
either  by  causing  them  to  adhere  directly  to  the 
track  or  to  a  brake-block. 

Adhesion. — The  mutual  attraction  which 
exists  between  unlike  molecules.  (See  At- 
traction, Molecular?) 

The  phenomena  of  adhesion  are  due  to  the 
mutual  attraction  of  dissimilar  molecules. 

Adhesion,  Electric Adhesion  be- 
tween surfaces  due  to  the  attraction  of  unlike 
electrostatic  charges. 

Molecular  adhesion  must  be  distinguished  from 
the  attraction  which  causes  a  piece  of  dry  and 
warmed  writing  paper,  that  has  been  rubbed  by  a 
piece  of  india-rubber,  to  stick  to  a  papered  wall. 
In  this  latter  case  the  attraction  between  the  wall 


[Aer. 

and  the  paper  is  due  to  the  mutual  attraction  of 
two  dissimilar  electrostatic  charges.  Molecular 
adhesion  must  also  be  distinguished  from  the  at- 
traction of  opposite  magnetic  poles. 

Adhesion,  Galvanoplastic  --  The  ad- 

hesion of  a  galvanoplastic  deposit  or  coating 
to  surfaces  subjected  to  electroplating.  (See 
Plating,  Electro) 

Adiathermaiicy.  —  Opacity  to  heat. 

A  substance  is  said  to  be  diathermanous  when 
it  is  transparent  to  heat.  Clear,  colorless  crys- 
tals of  rock  salt  are  very  transparent  both  to  light 
and  to  heat.  Rock  salt,  covered  with  a  layer  or 
deposit  of  lampblack  or  soot,  is  quite  transparent 
to  heat.  An  adiathermanous  body  is  one  which 
is  opaque  to  heat. 

Heat  transparency  varies  ndt  only  with  differ- 
ent substances,  but  also  with  the  nature  of  the 
source  from  which  the  heat  is  derived.  Thus,  a 
substance  may  be  opaque  to  he  it  from  a  non- 
luminous  source,  such  as  a  vessel  filled  with  boil- 
ing water,  while  it  is  comparatively  transparent 
to  heat  from  a  luminous  source,  such  as  an  incan- 
descent solid  or  a  voltaic  arc. 

A  similar  difference  exists  as  regards  transpar- 
ency to  light.  A  colorless  glass  will  allow  light 
of  any  color  to  pass  through  it.  A  blue  glass  will 
allow  blue  light  to  pass  freely  through  it,  but  will 
completely  prevent  the  passage  of  any  red  light  ; 
and  so  with  other  colors. 

Adiathermauic.  —  Possessing  the  quality  of 
adiathermancy.  (See  Adiathermancy) 

Adjustable  Condenser.  —  (See  Condenser, 
Adjustable) 

Adjuster,  Cord  ---  A  device  for  ad- 
justing the  length  of  a  pendant  cord. 

Adjustment.  —  Such  a  regulation  of  any 
apparatus  as  will  enable  it  to  properly  perform 
its  functions. 

.Epinus'     Condenser.  —  (See      Condenser, 


Aerial  Cable.—  (See  Cable,  Aerial) 
Aerial  Cable,  Suspending  Wire  of  — 

(See  Wire,  Suspending,  of  Aerial  Cable) 
Aerial  Line.—  (See  Line,  Aerial.) 
Aerolites.  —  A  name  sometimes   given  to 

meteorites. 
Meteorites    are    masses   of  solids   which  pass 


Aff.] 


10 


[Ago. 


through  the  upper  portions  only  of  the  earth's 
atmosphere  on  their  approach  to  the  orbit  of  the 
earth,  or  which  fall  through  the  air  on  the  earth's 
surface  from  the  sky.  They  are  luminous  at 
night  and  are  followed  by  a  train  of  fire.  The 
luminosity  is  due  to  heat  produced  by  friction 
through  the  air.  Meteors  frequently  burst  from 
the  sudden  expansion  of  their  outer  portions. 

Some  meteorites  are  composed  of  nearly  pure 
iron  alloyed  with  nickel.  The  majority  of  them, 
however,  are  merely  stones  or  oxidized  sub- 
stances. Their  average  velocity  is  about  26  miles 
a  second. 

Affinity,  Chemical  —  —Atomic  attrac- 
tion. 

The  force  which  causes  atoms  to  unite  and 
form  chemical  molecules. 

Atomic  or  chemical  attraction  generally  results 
in  a  loss  of  the  characteristic  qualities  or  proper- 
ties which  distinguish  one  kind  of  matter  from 
another.  In  this  respect  chemical  affinity  differs 
from  adhesion,  or  the  force  which  holds  unlike 
molecules  together.  (See  Adhesion.  Attraction, 
Molecular.}  If,  for  example,  sulphur  is  mixed 
with  lampblack,  no  matter  how  intimate  the 
mixture,  the  separate  particles,  when  examined 
by  a  magnifying  glass,  exhibit  their  peculiar  color, 
lustre,  etc.  If,  however,  the  sulphur  is  chemi- 
cally united  with  the  carbon,  a  colorless,  transpar- 
ent, mobile  liquid,  called  carbon  bisulphide,  re- 
sults, that  possesses  a  disagreeable,  penetrating 
odor. 

Chemical  affinity,  or  atomic  combination,  is  in 
fluenced  by  a  variety  of  causes,  viz. : 

(I.)  Cohesion.  Cohesion,  by  binding  the  mole- 
cules more  firmly  together,  opposes  their  mutual 
atomic  attraction. 

A  solid  rod  of  iron  will  not  readily  burn  in  the 
flame  of  an  ordinary  lamp ;  but,  if  the  cohesion  be 
overcome  by  reducing  the  iron  rod  to  filings,  it 
burns  with  brilliant  scintillations  when  dropped 
into  the  same  flame.  In  this  case  the  increase  of 
surface  and  the  increased  temperature  of  the 
smaller  particles  also  contribute  to  the  result. 

(2.)  Solution.  Solution,  by  giving  the  molecules 
greater  freedom  of  motion,  favors  their  chemical 
combination. 

(3.)  Heat.  Heat  sometimes  favors  atomic  com- 
bination possibly  by  decreasing  the  cohesion,  and, 
possibly,  by  altering  the  electrical  relations  of  the 
atoms.  If  too  great,  heat  may  produce  decom- 
position. There  is  for  most  substances  a  critical 


temperature  below  wh^h  chemical  combination 
will  not  take  place.  (See  Thermolysis. ) 

(4.)  Light.  Decomposition,  or  the  lessening  of 
chemical  affinity,  through  the  agency  of  light,  is 
called  Actinism,  Light  also  causes  the  direct 
combination  of  substances.  A  mixture  of  equal 
volumes  of  hydrogen  and  chlorine  unites  explo- 
sively when  exposed  to  the  action  of  full  sunlight. 
(See  Actinism.) 

(5.)  Electricity.  An  electric  spark  will  cause 
an  explosive  combination  of  a  mixture  of  oxygen 
and  hydrogen.  Electricity  also  produces  chemi- 
cal decomposition.  (See  Electrolysis.) 

Helmholtz  accounts  for  the  electro-chemical 
attraction  of  oxygen  for  zinc  by  supposing  that  all 
substances  possess  a  definite  amount  of  attraction 
for  electricity,  and  that  the  attraction  of  zinc  in 
this  respect  exceeds  that  of  copper  and  the  other 
metals.  He  thus  regards  the  zinc  as  attracting 
its  electric  charge  rather  than  as  attracting  the 
oxygen.  Since  both  zinc  and  copper  are  dyad 
metals,  this  view,  as  will  be  seen,  is  at  variance 
with  later  views. 

Chemical  affinity  may  be  caused  by  the  opposite 
attractions  of  electrical  charges  naturally  possessed 
by  the  atoms  of  matter.  This  would  appear  to  be 
rendered  probable  by  the  law  of  electro-chemical 
equivalence.  (See  Equivalence,  Electro-Chemical, 
Law  of.  Electricity,  Atom  of.) 

After  Currents.— (See  Currents,  After.} 

Aging  of  Alcohol,  Electric (See 

Alcohol,  Electric  Aging  of.) 

Agonal.— Pertaining  to  the  agone.  (See 
Agone.) 

Agone. — A  line  connecting  places  on  the 
earth's  surface  where  the  magnetic  needle 
points  to  the  true  geographical  north. 

The  line  of  no  declination  or  variation  of 
a  magnetic  needle.  (See  Needle,  Magnetic, 
Declination  of.) 

As  all  the  places  on  the  earth  where  the  mag- 
netic needle  points  to  the  true  north  may  be  ar- 
ranged on  a  few  lines,  it  will  be  understood  that 
the  pointing  of  the  magnetic  needle  to  the  true 
geographical  north  is  the  exception  and  not  the 
rule.  In  many  places,  however,  the  deviation 
from  the  true  geograpical  north  is  so  small  that 
the  direction  of  the  needle  may  be  regarded  as 
approximately  due  north. 

Agonic. — Pertaining  to  the  agone. 


Air. 


11 


[Ala. 


Air-Blast  for  Commutators. — An  inven- 
tion of  Prof.  Elihu  Thomson  to  prevent  the 
injurious  action  of  destructive  flashing  at  the 
commutator  of  a  dynamo-electric  machine. 

A  thin,  forcible  blast  of  air  is  delivered  through 
suitable  tubes  at  points  on  the  three-part  commu- 
tator cylinder  of  the  Thomson- Houston  dynamo, 
where  the  collecting  brushes  bear  on  its  surface. 
The  effect  is  to  blow  out  the  arc  or  prevent  its  for- 
mation and  thus  avoid  its  destructive  action  on 
the  commutator  segments.  The  use  of  the  air- 
blast  also  permits  the  free  application  of  oil,  thus 
further  avoiding  wear. 


Fig.  4.    Air-Blast  on  Commuta 
The  blast-nozzles  are  shown  at  B3,  B8,  Fig.  4, 
near  the  collecting  brushes. 

The  air-supply  is  obtained  from  a  blower  at- 
tached directly  to  the  shaft  of  the  machine.  Its 
construction  and  operation  will  be  readily  under- 
stood from  an  inspection  of  Fig.  5,  in  which  the 


Fig.  f.      The  Thomson  Blower. 

top  is  removed  for  ready  examination  of  the 
interior  parts. 

Air  Churning. — (See  Churning,  Air) 

Air  Condenser. — (See  Condenser,  Air) 

Air  Field.— (See  Field,  Air) 

Air-Gap.— (See  Gap,  Air) 

Air-Line  Wire.— (See  Wire,  Air-Line) 

Air  Magnetic  Circuit.— (See  Circuit,  Air 
Magnetic) 

Air-Pump.— (See  Pump,  Air) 

Air-Pump,  Oeissler's  Mercurial 

(See  Pump,  Air,  Geissler's  Mercurial) 


Air-Pump,  Mechanical (See  Pump, 

Air,  Mechanical) 

Air-Pump,  Mercurial (See  Pump, 

Air,  Mercurial) 

Air-Pump,  Sprengel's  Mercurial 

(See  Pump,  Air,  SprengeFs  Mercurial) 

Air-Space  Cut-Out— (See  Cut-Out,  Air- 
Space) 

Alarm,  Burglar A  device,  generally 

electric,  for  automatically  announcing  the 
opening  of  a  door,  window,  closet,  drawer,  or 
safe,  or  the  passage  of  a  person  through  a 
hallway,  or  on  a  stairway. 

Electric  burglar-alarm  devices  generally  consist 
of  mechanism  for  the  operation  of  an  automatic 
make -and -break  bell  on  the  opening  or  closing  of 
an  electric  circuit.  The  bell  may  either  continue 
ringing  only  while  the  contact  remains  closed,  or, 
may,  by  the  throwing  on  of  a  local  circuit  or 
battery,  continue  ringing  until  stopped  by  some 
non-automatic  device,  such  as  a  hand-switch. 

The  alarm-bell  is  stationed  either  in  the  house 
when  occupied,  or  on  the  outside  when  the  house 
is  temporarily  vacated,  or  may  connect  directly 
with  the  nearest  police  station. 

Burglar-alarm  apparatus  is  of  a  variety  of 
forms.  Generally,  devices  are  provided  by  means 
of  which,  in  case  of  house  protection,  an  annunci- 
titor  shows  the  exact  part  where  an  entrance  has 
been  attempted.  (See  Annunciator,  Burglar- 
Alarm)  Switches  are  provided  for  disconnecting 
all  or  parts  of  the  house  from  the  alarm  when  so 
desired,  as  well  as  to  per- 
mit windows  to  be  partly 
raised  for  purposes  of  ven- 
tilation without  sounding 
the  alarm.  A  clock  is  fre- 
quently connected  with  the 
alarm  for  the  purpose  of 
automatically  disconnect- 
ing any  portion  of  the 
house  at  or  for  certain  in- 
tervals of  time. 

Fig.  6  shows  a  burglar-  Fig.  6.  Burglar-Alarm 
alarm  with  annunciator,  Annunciator. 

switches,  switch-key,  cut-off,  and  clock. 

Alarm,  Burglar,  Central-Station 

A  burglar-alarm,  the  contact  points  of  which 
are  placed  in  the  places  to  be  protected,  and 


Ala.] 


[Ate. 


connected  by  suitable  circuits  with    alarms 
placed  in  a  centrally  located  station. 

In  a  system  of  central-station  burglar-alarms,  a 
number  of  houses,  factories,  banks,  etc.,  are  all 
connected  telegraphically  with  the  nearest  police 
station,  or  other  central  station,  constantly  pro- 
vided with  police  officers.  A  series  of  contacts  are 
placed  on  doors,  windows,  safes  and  money  draw- 
ers, and  connected  with  alarms  and  annunciators 
placed  in  the  central  station.  An  unauthorized 
entrance,  therefore,  is  automatically  telegraphed 
to  the  central  station  and  its  exact  location  indi- 
cated on  the  annunciator.  Systems  of  central- 
station  fire-alarms  are  constructed  on  a  similar 
plan. 

Alarm,  Electric An  automatic  de- 
vice by  which  attention  is  called  to  the  occur- 
rence of  certain  events,  such  as  the  opening 
of  a  door  or  window;  the  stepping  of  a  person 
on  a  mat  or  staircase;  the  rise  or  fall  of  tem- 
perature beyond  a  given  predetermined  point; 
or,  a  device  intended  to  call  a  person  to  a  tel- 
egraphic or  telephonic  instrument. 

Electric-alarms  are  operated  by  means  of  the 
ringing  of  an  electro-magnetic  or  mechanical  bell, 


Fig.  7.    Electrically  Started  Mechanical  Alarm. 

which  is  electrically  called  into  action  by  either 
closing  or  opening  an  electric  circuit,  generally 
the  former. 

Electric-alarms  may  be  divided  into  two  classes, 
viz.: 

(I.)  Mechanically  operated  alarms,  or  those  in 


which  the  alarm  is  given  by  clock-work,  started 
by  means  of  an  electric  current. 

(2.)  Those  in  which  the  alarm  is  both  set  in  ac- 
tion and  operated  by  an  electric  current. 

In  Fig.  7  is  shown  the  general  construction  of 
an  electrically  started  mechanical  alarm.  The 
attraction  of  the  armature  B,  by  the  electro-mag- 
net A,  moves  the  armature  lever  pivoted  at  C, 
and  thus  releases  the  catch  e,  and  permits  the 
spring  or  weight  connected  with  the  clock  move- 
ment to  set  it  in  motion  and  strike  the  bell. 

Electrically  actuated  alarm-bells  are  generally 
of  the  automatic  make-and-break  form.  The 
striking  lever  is  operated  by  the  attraction  of  the 
armature  of  an  electro-magnet,  and  is  provided 
with  a  contact-point,  so  placed  that  when  the 
hammer  is  drawn  away  from  the  bell,  by  the  ac- 
tion of  a  spring,  on  the  electro-magnet  losing  its 
magnetism,  a  contact  is  made,  but  when  the  ham- 
mer is  drawn  towards  the  bell  the  contact  is  open- 
ed. When,  therefore,  the  hammer  strikes  the 
bell,  the  circuit  is  opened,  and  the  electro-magnet 
releases  its  armature,  permitting  a  spring  to  again 
close  the  contact  by  moving  the  striking  lever 
away  from  the  bell.  Once  set  into  action,  these 
movements  are  repeated  while  there  is  battery 
power  sufficient  to  energize  the  magnet. 

In  Fig.  8,  in  which  is  shown  an  electrically  ac- 
tuated alarm-bell,  the  battery  terminals  are  con- 


Fig.  8.    Automatic  Make-and-Break. 

..ected  with  the  right  and  left  hand  binding-posts, 
P  and  M.  The  hammer,  K,  is  connected  with  a 
striking  lever,  which  forms  part  of  the  circuit," 
and  which  is  attached  toihe  armature  of  the  elec 
tro-magnet  e.  A  metallic  spring,  g,  bears  against 
the  armature  when  the  latter  is  away  from  the 
magnet,  but  does  not  touch  the  armature  when 
it  is  moved  towards  the  magnet.  A  small  spring 
draws  the  lever  away  from  the  magnet  when  no 
current  is  passing.  The  movements  of  the  arma 


13 


[AlCo 


ture  thus  automatically  open  and  close  the  circuit 
of  the  electro-magnet. 

This  form  of  make-and-break  is  called  an  auto- 
matic make-and-break. 

Alarm,  Electrically  Operated  —     —An 

alarm  that  is  maintained  in  operation  by  the 
electric  current.  (See  Alarm,  Electric^) 

Alarm,  Electro-Mechanical  -  -  —A 
mechanically  operated  alarm  that  is  started 
or  set  in  operation  by  means  of  an  electric 
current.  (See  Alarm,  Electric^) 

Alarm,  Fire,  Automatic An  in- 
strument for  automatically  telegraphing  an 
alarm  from  any  locality  on  its  increase  in  tem- 
perature beyond  a  certain  predetermined  point. 

Fire-alarms  are  operated  by  thermostats,  or  by 
means  of  mercurial  contacts;  i.  e.,  a  contact 
closed  by  the  expansion  of  a  column  of  mercury. 
(See  Thermostat.  Contact,  Mercurial.) 

In  systems  of  fire-alarm  telegraphs,  the  alarm 
is  automatically  sounded  in  a  central  police  sta- 
tion and  in  the  district  fire-engine  house.  (See 
Telegraphy,  Fire-Alarm. ) 

Alarm,   Mercurial  Temperature 

An  instrument  for  automatically  telegraphing 
an  alarm  by  means  of  a  mercurial  contact  on 
a  predetermined  change  of  temperature. 

The  action  of  mercurial  contacts  is  dependent 
on  the  fact  that,  as  the  mercury  expands  more 
than  glass  by  the  action  of  heat,  the  mercury  level 
reaches  a  contact-point  placed  in  a  glass  tube  and 
thus  completes  the  circuit  through  its  own  mass, 
which  forms  the  other  or  movable  contact. 
Sometimes  both  contacts  are  placed  on  opposite 
sides  of  a  tube  and  are  closed  when  the  mercury 
reaches  them. 

Mercurial  temperature  or  thermostat  alarms 
are  employed  in  hot-houses,  incubators,  tanks 
and  buildings  for  the  purpose  of  maintaining  a 
uniform  temperature. 

Alarm,  Telegraphic  —  — An  alarm-bell 
for  calling  the  attention  of  an  operator  to 
a  telegraphic  instrument  when  the  latter  is  of 
the  non-acoustic  or  needle  type. 

In  acoustic  systems  of  telegraphy  the  sounds 
themselves  are  generally  sufficient. 

Alarm,  Telephonic An  alarm-bell 

for  calling  a  correspondent  to  the  receiving 
telephone. 


These  alarms  generally  consist  of  magneto- 
electric  bells.  (See  Bell,  Magneto-Electric.) 

Alarm,  Temperature  —  —An  electric 
alarm  automatically  operated  on  a  change  of 
temperature.  (See  Alarm,  Fire,  Automatic) 

Alarm,  Thermostat—  —An  electric 
alarm  that  is  thrown  into  action  by  a  thermo- 
stat. (See  Thermostat) 

Alarm,  Water  or  Liquid  Level 

A  device  for  electrically  sounding  an  alarm 
wnen  a  water  surface  varies  materially  from 
a  given  level. 

An  electric  bell  is  placed  in  a  circuit  that  is  au- 
tomatically closed  or  broken  by  the  movement  of 
contact-points  operated  by  the  change  of  liquid 
level. 

A  form  of  electric  alarm  for  a  water-level  is 
shown  in  Fig.  9.  The  float  is  provided  with 
contacts  for  closing  an  electric  circuit,  when  it 
either  rings  a  bell,  or,  by  its  action  on  some  form 
of  automatic  cut-off,  stops  the  water. 


Fig:  9.         Water- Level  Alarm.        Fig.  10. 

When  arranged  with  a  double  float,  as  shown 
in  Fig.  10,  the  alarm  may  be  made  to  signal 
either  a  too  high  or  a  too  low  water  level. 

Alarm,  Yale-Lock-Switch   Burglar  — 
— An   apparatus   whereby  the  opening  of  a 
door  by  an  authorized  party  provided  with  the 
regular  key  will  not  sound  an  alarm,  but  any 
other  opening  will  sound  such  alarm. 


Fig.  n.    Yale-Lock-Switch. 

A  Yale-lock  burglar-alarm  switch  is  shown  in 
Fig.  II. 

Alcohol,  Electric  Aging  of A  pro- 
cess for  the  rapid  aging  of  alcohol,  by  rx- 


Ale.] 


14 


[All. 


posing  it  to  the  action  of  electrically  produced 
ozone. 

Instead  of  the  ordinary  process  of  aging  alco- 
hol, by  exposing  it  in  partially  closed  vessels  to 
the  action  of  air,  it  is  exposed  to  the  action  of 
ozone,  electrically  produced. 

The  ozone  employed  is  obtained  in  substan- 
tially the  usual  way  by  the  passage  of  a  rapid 
succession  of  electric  sparks  through  air. 

Alcohol,  Electric  Rectification  of — 

A  process  whereby  the  bad  taste  and  odor  of 
alcohol,  due  to  the  presence  of  aldehydes, 
are  removed  by  the  electrical  conversion  of 
the  aldehydes  into  true  alcohols  through  the 
addition  of  hydrogen  atoms. 

An  electric  current  sent  through  the  liquid 
between  zinc  electrodes  liberates  oxygen  and  hy- 
drogen from  the  decomposition  of  the  water. 
The  nascent  or  atomic  hydrogen  converts  the 
aldehydes  into  alcohol  and  deprives  the  pro- 
ducts of  their  fusel  oil,  while  the  oxygen  forms 
insoluble  zinc  oxide. 

Algebraic  Co-efficient— (See  Co-efficient, 
Algebraic?) 

Algebraic  Notation.— (See  Notation,  Al- 
gebraic?) 

All-Night  Arc  Lamp.— (See  Lamp,  All- 
Night  Arc?) 

All-Night  Electric  Lamp.— (See  Lamp, 
All-Night  Arc.} 

Allotropic.— Pertaining  to  allotropy.  (See 
Allotropy.} 

Allotropic  State.— (See  State,  Allotropic). 

Allotropy. — A  variation  of  the  physical 
properties  of  an  elementary  substance  with- 
out change  of  composition  of  its  molecules.— 
(See  State,  Allotropic.) 

Alloy. — A  combination,  or  mixture,  of  two 
or  more  metallic  substances. 

Alloys  in  most  cases  appear  to  be  true  chemi- 
cal compounds.  In  a  few  instances,  however, 
they  may  form  simple  mixtures. 

The  composition  of  a  few  important  alloys  is 
here  given: 

Solder,  plumber's;  Tin  66  parts,  Lead 34  parts. 

Pewter,  hard;  Tin  92  parts,  Lead  8  parts. 

Britannia  metal;  Tin  100  parts,  Antimony  8 
parts,  Copper  4  parts,  Bismuth,  I  part. 


Type  metal;  Lead  80,  Antimony  20  parts. 
Brass,  white;  Copper  65,  Zinc  35  parts. 
Brass,  red;  Copper  90,  Zinc  I o parts. 
Speculum  metal ;  Copper  67,  Tin  33  parts. 
Bell  metal;  Copper  78,  Tin  22  parts. 
Aluminium  bronze;  Copper  90,  Aluminium  10 
parts. 

Alloy. — To  form  a  combination  or  mixture 
of  two  or  more  metallic  substances. 

Alloy,  German  Silrer  — An  alloy 

employed  for  the  wires  of  resistance  coils, 
consisting  of  50  parts  of  copper,  25  of  zinc, 
and  25  of  nickel. 

German  silver  wire  is  suitable  for  resistance 
coils,  because  its  resistance  varies  but  slightly  with 
changes  of  temperature.  It  is  cheaper  than  plati- 
num-silver alloy,  and  is  therefore  employed  ex- 
tensively. Platinum  silver  alloy,  however,  has 
more  resistance  for  a  given  size  of  wire,  and  its  re- 
sistance varies  somewhat  less  than  German  silver 
with  changes  of  temperature,  and  is  therefore  used 
where  greater  accuracy  is  desired. 

Alloy,  Palladium An  alloy  of  pal- 
ladium with  other  metals. 

Palladium  forms  a  number  of  useful  alloys  with 
various  metals.  Some  of  the  palladium  alloys  are 
as  elastic  as  steel,  are  unaffected  by  moisture  or 
ordinary  corrosive  agencies,  and  are  entirely  de- 
void of  paramagnetic  properties;  that  is  to  say, 
they  cannot  be  magnetized  after  the  manner  of 
iron. 

These  properties  have  been  utilized  by  their 
discoverer,  Paillard,  in  their  employment  for  the 
hair-springs,  escapements  and  balance  wheels  of 
watches,  in  order  to  permit  the  watches  to  be  car- 
ried into  strong  magnetic  fields  without  any  ap- 
preciable effects  on  the  rate  of  the  watch.  A 
number  of  careful  tests  made  by  the  author,  by 
long  continued  exposure  of  watches,  thus  pro- 
tected by  the  Paillard  alloys,  in  extraordinary 
fields,  show  that  the  protection  thus  given  the 
watches  enables  them  to  be  carried  into  the  strong- 
est possible  magnetic  fields  without  appreciably 
affecting  their  rate. 

The  Paillard  palladium  alloys  have  the  follow- 
ing composition,  viz.: 

Alloy  No.   i. 

Palladium 60  to  75  parts. 

Copper 151025  " 

Iron i  to    5  " 


All.] 


15 


[Alp. 


Alloy  No.  2. 
Palladium  ..............  50  to  75  parts. 

Copper  20  to  30      " 

jron  c  to  20      " 

Alloy  No.  j. 
Palladium  ..............  65  to  75      " 

, 

Copper  ................  151025  " 

Nickel  ................   ito    5  " 

Gold  ..................   ito    2*  « 

Platinum  ...............  i  to    2  " 

Silver  ..................  3toio  « 

Steel  ..............   i  to    5  " 

Alloy  No.  4. 

Palladium  ..............  45  to  50  " 

Silver  ..................  201025  " 

Copper  ................  l5to2S  <« 

Gold  ...................  2  to    5  " 

Platinum  ...............  2  to    5  " 

Nickel  .................  2105  " 

Steel  ...................    2  to     5  " 

The  great  value  of  the  palladium  alloys,  when 
employed  for  the  hair-springs  of  watches,  arises 
not  only  from  their  non  -magnetizable  properties, 
and  their  inoxidizability,  but  particularly  from  the 
fact  that  their  elasticity  is  approximately  the  same 
for  comparably  wide  ranges  of  temperature. 

Alloy,  Platinum-Silver  --  An  alloy 
consisting  of  one  part  of  platinum,  and  two 
parts  of  silver. 

Platinum-  silver  alloy  is  now  extensively  em- 
ployed  for  resistance  coils  from  the  fact  that 
changes  in  temperature  of  the  alloy  produce  but 
comparatively  small  changes  in  its  electrical  re- 
sistance.  (See  Alloy,  German  Silver.} 

Alphabet,  Telegraphic  --  An  arbi- 
trary  code  consisting  of  dots  and  dashes, 
sounds.deflections  of  a  magnetic  needle,  flashes 
of  light^  or  movements  of  levers,  following  one 
another  in  a  given  predetermined  order,  to 
represent  the  letters  of  the  alphabet  and  the 
numerals. 

Alphabet,     Telegraphic:     International 

n  A  T-i.          j       t     •        if       i 

Code  --  The  code  of  signals  for  letters, 

etc.,  employed  in  England  and  on  the  Euro- 
pean  continent  generally. 

Similar  symbols  are  employed  for  the  numerals 
and  the  punctuation  marks. 

It  will  be  observed  that  it  is  mainly  in  the 


characters  of  the  American  Morse,  in  which  spaces 
**  used>  that  the  Continental  characters  differ 
from  the  American.  This  is  due  to  the  use  of  the 
needle  instrument,  with  which  a  space  cannot  well 
be  represented.  A  movement  or  deflection  of  the 

S'nK'e  *"** 

Printing        Needle  Printing        .Needle 

*  —  x/  n—  <\ 

*  —  •'-  o   ---  "/ 
c~*  —  /X/N  p  ---  •  *''  x 
«—  '-  «    ----  ^ 


International  Telegraphic  Code. 

needle  to  the  left  signifies  a  dot;  a  movement  to 
the  right»  a  dash- 

Alphabet,    Telegraphic  :  Morse's  __ 

Varkms  ^        of   dots    and  dashes>  Qr 

deflections  of  a  ma  tic  needle  to  the  rf  ht 
^  ^  ^.^  represent  ^  lettere  Q£  ^ 

alphabet  or  other  signs. 

In  t^  Morse  alphabet  dots  and  dashes  are  em- 
ployed  in  recording  systems,  and  sounds  of 
varying  intervals,  corresponding  to  the  dots  and 
dashes,  in  the  sounder  system. 

A  dash  is  equal  in  length  of  time  to  three  dots. 
The  space  between  the  separate  characters  of  a 
single  letter  is  equal  to  one  dot,  except  in  the 
American  Morse,  in  which  the  following  letters 
contain  longer  spaces:  c>  o>  R?  Y>  and  z.  The 

lengthened  spaces  are  equal  to  two  dots.  L  is 
one  and  a  half  times  the  length  of  T. 

The  sound  produced  by  the  down  stroke  of  the 
sounding  lever  in  the  Morse  sounder  is  readily 
distinguishable  from  the  up  stroke.  When  these 
differences  are  taken  in  connection  with  the  inter- 
vals  between  successive  sounds  there  is  no  diffi- 

culty  in  reading  by  sound. 
(For  methods  of  recdving  the  alphabet>  see 

Sounder,  Morse  Telegraphic.  Recorder,  Morse. 
Recorder,  BaMs  Chemical.  Recorder,  Siphon. 
Relay.  Magnet,  Receiving.  )  In  the  needle  tele- 
graph,  the  code  is  similar  to  that  used  in  the  Morse 
Alphabet.  (See  Telegraphy,  Single-Needle.} 


Alt.] 


AMERICAN  MORSE  CODE. 
ALPHABET. 


h  ---. 


o  -  - 

P 

q 

r  -    -- 

s 

t  — 

u 

v 

w 


m 

&  -    --- 

NUMERALS. 
i 

2 

3 

4 

PUNCTUATION    MARKS. 


Period 

Comma 


Interrogation 

Exclamation 


Printing 


SingJe  Needle 
X  //// 

xx  /// 
xxx  // 
xxxx/ 


10 

Period  ------  NX    \\     \x 

Comma         ______  x  A  A  / 

Interrogation  ______  xx   /  /  \\ 

Exclamation  ______  /Ax// 

Colon  ______  ///NNN 

Semicolon     ______  /\/\/\ 

Alteration  Theory  of  Muscle  or  Nerve 
Current—  (See  Theory,  Alteration,  of 
Muscle  or  Nerve  Current?) 

Alternating  Arc.  —  (See  Arc,  Alternat- 
ing.} 

Alternating  Current  Circuit.—  (See  Cir- 
cuit, Alternating  Current?) 


16  [Alt. 

Alternating  Current  Condenser. — (See 
Condenser,  Alternating  Current?) 

Alternating  Current  Dynamo-Electric 
Machine. — (See  Machine,  Dynamo-Electric, 
Alternating  Current?) 

Alternating  Current  Electric   Motor.— 

(See  Motor,  Electric,  Alternating  Current?) 

Alternating  Currents. — (See  Currents, 
Alternating?) 

Alternating  Currents,  Distribution  of 
Electricity  by  —  —(See  Electricity,  Dis- 
tribution of,  by  Alternating  Currents?) 

Alternating  Discharge. — (See  Discharge, 
Alternating?) 

Alternating  Dynamo-Electric  Machine. — 
(See  Machine,  Dynamo-Electric,  Alternat- 
ing Current?) 

Alternating  Electrostatic  Field.— (See 
Field,  Alternating  Electrostatic?)  , 

Alternating  Electrostatic  Potential.— 
(See  Potential,  Alternating  Electrostatic?) 

Alternating  Field.— (See  Field,  Alternat- 
ing?) 

Alternating  Influence  Machine,  Wims- 
hurst's  —  — (See  Machine,  Wimshurst's 
Alternating  Influence?) 

Alternating  Magnetic  Field.— (See  Field, 
Alternating  Magnetic?) 

Alternating  Magnetic  Potential.— (See 
Potential,  Alternating  Magnetic?) 

Alternating  Potential.— (See  Potential, 
Alternating?) 

Alternating  Primary  Currents. — (See 
Currents,  Alternating  Primary?) 

Alternating  Secondary  Currents.— (See 
Currents,  Alternating  Secondary?) 

Alternation. — A  change  in  direction  or 
phase. 

Alternations. — Changes  in  the  direction  of 
a  current  in  a  circuit. 

A  current  that  changes  its  direction  300  times 
per  second  is  said  to  possess  300  alternations  per 
second. 

Alternations,  Complete  —  —A  change 
in  the  direction  of  a  current  in  a  circuit  from  its 


Alt] 


[A  mm. 


former  direction  and  back  again  to  that 
direction.  A  complete  to-and-fro  change. 

Complete  alternations  are  sometimes  indicated 
by  the  symbol  ~. 

Alternations,  Frequency  of  — A 

phrase  employed  to  denote  the  number  of  al- 
ternations per  second. 

Alternative  Path.— (See  Path,  Alterna- 
tive^ 

Alternatives,  Yoltaic A  term  used 

in  medical  electricity  to  indicate  sudden  re- 
versals in  the  polarity  of  the  electrodes  of  a 
voltaic  battery. 

An  alternating  current  from  a  voltaic  bat- 
tery, obtained  by  the  use  of  a  suitable  com- 
mutator. 

Sudden  reversals  of  polarity  produce  more 
energetic  effects  of  muscular  contraction  than  do 
simple  closures  or  completions  of  the  circuit. 

The  muscular  contraction  produced  by  a  voltaic 
current  is  much  stronger  when  the  direction  of  the 
current  is  rapidly  reversed  by  means  of  a  com- 
mutator than  when  the  current  is  more  slowly 
broken  and  the  poles  then  reversed. 

The  effect  of  voltaic  alternatives  is  to  produce 
quick  contractions  that  are  in  strong  contrast  to 
the  prolonged  contractions  that  result  from  the 
faradic  current.  In  the  faradic  machine,  the 
reversals  are  so  rapid  that  the  muscle  fails  to 
return  to  rest  before  it  is  again  contracted. 

Voltaic  alternatives  are  sometimes  indicated  by 
the  contraction  V.  A. 

Alternator. — A  name  commonly  given  to 
an  alternate  current  dynamo.  (See  Machine, 
Dynamo-Electric,  Alternating  Current?) 

Alternator,  Compensated  Excitation  of 

— An  excitation  of  an  alternating  current 
dynamo-electric  machine,  in  which  the  field  is 
but  partially  excited  by  separate  excitement, 
the  remainder  of  its  exciting  current  being 
derived  from  the  commuted  currents  of  a 
small  transformer  placed  in  the  main  circuit 
of  the  machine. 

The  object  of  compensated  excitation  of  an 
alternator  is  to  render  the  machine  self-governing. 

Amalgam. — A  combination  or  mixture 
of  a  metal  with  mercury. 

Amalgam,  Electric  — A  substance 


with  which  the  rubbers  of  the  ordinary  fric- 
tional  electric  machines  are  covered. 

Electric  amalgams  are  of  various  compositions. 
The  following  formula  produces  an  excellent 
amalgam  : 

Melt  together  five  parts  of  zinc  and  three  of 
tin,  and  gradually  pour  the  molten  metal  into 
nine  parts  of  mercury.  Shake  the  mixture  until 
cold,  and  reduce  to  a  powder  in  a  warm  mortar. 
Apply  to  the  cushion  by  means  of  a  thin  layer  of 
stiff  grease. 

Mosaic  gold,  or  bisulphide  of  tin,  and  powdered 
graphite,  both  act  as  good  electric  amalgams. 

An  electric  amalgam  not  only  acts  as  a  con- 
ductor to  carry  off  the  negative  electricity,  but, 
being  highly  negative  to  the  glass,  produces  a  far 
higher  electrification  than  would  mere  leather  or 
chamois. 

Amalgamate. — To  form  into  an  amalgam. 

Amalgamating. — Forming  into  an  amal- 
gam. 

Amalgamation. — The  act  of  forming  into 
an  amalgam,  or  effecting  the  combination  of 
a  metal  with  mercury. 

Amalgamation  of  Zinc  Plates  of  Yoltaic 
Cell.— (See  Plates,  Zinc,  of  Voltaic  Cell, 
Amalgamation  of,} 

Amber. — A  resinous  substance,  generally 
of  a  transparent,  yellow  color. 

Amber  is  interesting  electrically  as  being  be- 
lieved to  be  the  substance  in  which  the  proper- 
ties of  electric  attractions  and  repulsions,  imparted 
by  friction  or  rubbing,  were  first  noticed.  It  was 
called  by  the  Greeks  r/\Enrpov,  from  which  the 
word  electricity  is  derived.  This  property  was 
mentioned  by  the  Greek,  Thales  of  Miletus,  600 
B.  c.,  as  well  as  by  Theophrastus. 

American  System  of  Telegraphy.— (See 
Telegraphy,  American  System  of.) 

American  Twist-Joint— (See  Joint, 
American  Twist?) 

American  Wire  Gauge. — (See  Gauge, 
Wire,  American?) 

Ammeter. — A  form  of  galvanometer  in 
which  the  value  of  the  current  is  measured 
directly  in  amperes.  (See  Galvanometer?) 

An  ampere-meter  or  ammeter  is  a  commercial 
form  of  galvanometer  in  which  the  deflections*  of 


Amm.J 


18 


[Amp. 


a  magnetic  needle  are  calibrated  or  valued  in  am- 
peres. As  a  rule  the  coils  of  wire  in  an  ammeter 
are  of  lower  resistance  than  in  a  voltmeter.  The 
magnetic  needle  is  deflected  from  its  zero  position 
by  the  field  produced  by  the  current  whose  strength 
in  amperes  is  to  be  measured.  This  needle  is  held 
in  the  zero  position  by  the  action  of  a  magnetic 
field,  either  of  a  permanent  or  an  electro-magnet, 
by  the  action  of  a  spring,  or  by  a  weight  under  the 
influence  of  gravity.  There  thus  exist  a  variety 
of  ammeters,  viz. :  permanent-magnet  ammeters, 
electro-magnetic  ammeters,  spring  ammeters  and 
gravity  ammeters. 

In  the  form  originally  devised  by  Ayrton  and 
Perry,  the  needle  came  to  rest  almost  imme- 
diately, or  was  dead-beat  in  action.  (See  Damp- 
ing.') It  moved  through  the  field  of  a  permanent 
magnet.  The  instrument  was  furnished  with  a 
number  of  coils  of  insulated  wire,  which  could 
be  connected  either  in  series  or  in  multiple-arc  by 
means  of  a  commutator,  thus  permitting  the  scale 
reading  to  be  verified  or  calibrated  by  the  use  of  a 
single  voltaic  cell.  (See  Circuits,  Varieties  of. 
Commutator.  Calibration,  Absolute.  Calibra- 
tion, Relative.)  In  this  case  the  coils  were 
turned  to  series,  and  a  plug  pulled  out,  thus  intro- 
ducing a  resistance  of  one  ohm. 

c 


Fig.  ra.     Ayrton  and  Perry  Ammeter. 

Fig.  12  represents  an  ampere-meter  devised  by 
Ayrton  and  Perry.  A  device  called  a  commutator 
for  connecting  the  coils  either  in  series  or  parallel 
is  shown  at  C.  Binding-posts  are  provided  at 
P,  PS,  and  S.  The  dynamo  terminals  are  con- 
nected at  the  posts  P,  PS,  and  the  current  will 
pass  only  when  the  coils  are  in  multiple,  thus 
avoiding  accidental  burning  of  the  coils.  In  this 
case  the  entire  current  to  be  measured  passes 
through  the  coils  so  coupled.  The  posts  S  and 
PS,  are  for  connecting  the  single  battery  cell  cur- 
rent. 

A  great  variety  of  ampere-meters,  or  ammeters, 
have  been  devised.  They  are  nearly  all,  how- 


ever, constructed  on  essentially  the  same  general 
principles. 

Commercial  ammeters  are  made  in  a  great  va- 
riety of  forms.  When  the  currents  to  be  meas- 
ured are  large,  as  is  generally  the  case  in  electric 
light  or  power  stations,  they  consist  of  a  coil  of 
insulated  wire,  often  of  a  single  turn,  or  even  of 
but  a  part  of  a  turn,  having  a  balanced  core  of 
iron  or  steel  capable  of  moving  freely  within  it. 

Ammeter,      Electro-Magnetic A 

form  of  ammeter  in  which  a  magnetic  needle  is 
moved  against  the  field  of  an  electro-magnet 
by  the  field  of  the  current  it  is  measuring. 
(See  Ammeter?) 

Ammeter,  Gravity A  form  of  am- 
meter in  which  a  magnetic  needle  is  moved 
against  the  force  of  gravity  by  the  field  of  the 
current  it  is  measuring.  (See  Ammeter?) 

Ammeter,       Magnetic-  Vane An 

ammeter  in  which  the  strength  of  a  magnetic 
field  produced  by  the  current  that  is  to  be 
measured  is  determined  by  the  repulsion  ex- 
erted between  a  fixed  and  a  movable  iron 
vane,  placed  in  said  field  and  magnetized 
thereby.  (See  Voltmeter,  Magnetic- Vane.} 

Ammeter,     Permanent-Magnet A 

form  of  ammeter  in  which  a  magnetic  needle 
is  moved  against  the  field  of  a  permanent  mag- 
net by  the  field  of  the  current  it  is  measuring. 
(See  Ammeter?) 

Ammeter,  Reducteur  for (See  Re- 

ducteur,  or  Shunt  for  Ammeter?) 

Ammeter,  Spring A  form  of  am- 
meter in  which  a  magnetic  needle  is  moved 
against  the  action  of  a  spring  by  the  field  of 
the  current  it  is  measuring.  (See  Ammeter.} 

Amorphous. — Having  no  definite  crys- 
talline form. 

Mineral  substances  have  certain  crystalline 
forms,  that  are  as  characteristic  of  them  as  are  the 
forms  of  animals  or  plants.  Under  certain  cir- 
cumstances, however,  they  occur  without  definite 
crystalline  form,  and  are  then  said  to  be  amor- 
phous solids. 

Amperage. — The  number  of  amp&res  pass- 
ing in  a  given  circuit. 

The  current  strength  in  any  circuit  as  indi- 
cated by  an  ampere-meter  placed  in  the  circuit. 


Amp.] 


19 


[Amp. 


Ampere. — The  practical  unit  of  electric 
current. 

Such  a  rate-of-flow  of  electricity  as  trans- 
mits one  coulomb  per  second. 

Such  a  current  (or  rate-of-flow  or  trans- 
mission of  electricity)  as  would  pass  with  an 
electromotive  force  of  one  volt  through  a  cir- 
cuit whose  resistance  is  equal  to  one  ohm. 

A  current  of  such  a  strength  as  would 
deposit  .005084  grain  of  copper  per  second. 

A  current  of  one  ampere  is  a  current  of  such 
definite  strength  that  it  would  flow  through  a  cir- 
cuit of  a  certain  resistance  and  with  a  certain 
electromotive  force.  (See  Force,  Electromotive. 
Volt.  Resistance.  Ohm.} 

Since  the  ohm  is  the  practical  unit  of  resistance, 
and  the  volt  the  practical  unit  of  electromotive 
force,  the  ampere,  or  the  practical  unit  of  current, 
is  the  current  that  would  flow  through  unit  resist- 
ance, under  unit  pressure  or  electromotive  force. 

To  make  this  clearer,  take  the  analogy  of  water 
flowing  through  a  pipe  under  the  pressure  of  a 
column  of  water.  That  which  causes  the  flow  is 
the  pressure  or  head  ;  that  which  resists  the  flow 
is  the  friction  of  the  water  against  the  pipe,  which 
will  vary  with  a  number  of  circumstances.  The 
rate-of-flow  may  be  represented  by  so  many  cubic 
inches  of  water  per  second. 

As  the  pressure  or  head  increases,  the  flow  in- 
creases proportionally;  as  the  resistance  increases, 
the  flow  diminishes. 

Electrically,  electromotive  force  corresponds  to 
the  pressure  or  head  of  the  water,  and  resistance 
to  the  friction  of  the  water  and  the  pipe.  The 
ampere,  which  is  the  unit  rate-of-flow  per  second, 
may  therefore  be  represented  as  follows, 

viz. :      C  =  _,  as  was  announced  by  Ohm  in  his 
R 

law.     (See  Law  of  Ohm.} 

This  expression  signifies  that  C,  the  current  in 
amperes,  is  equal  to  E,  the  electromotive  force  in 
volts,  divided  by  R,  the  resistance  in  ohms. 

We  measure  the  rate-of-flow  of  liquids  as  so 
many  cubic  inches  or  cubic  feet  per  second — that  is, 
in  units  of  quantity.  We  measure  the  rate-of-flow 
of  electricity  as  so  much  electricity  per  second. 
The  electrical  unit  of  quantity  is  called  the  Coul- 
omb. (See  Coulomb.}  The  coulomb  is  such  a 
quantity  as  would  pass  in  one  second  through  a 
circuit  in  which  the  rate-of-flow  is  one  ampere. 

An  ampere  is  therefore  equal  to  one  coulomb  per 


The  electro-magnetic  unit  of  current  is  such  a 
current  that,  passed  through  a  conducting  wire 
bent  into  a  circle  of  the  radius  of  one  centimetre, 
would  tend  to  move  perpendicular  to  its  plane  a 
unit  magnetic  pole  held  at  its  centre,  and 
sufficiently  long  to  practically  remove  the  other 
pole  from  its  influence,  with  unit  force,  i.  <?.,  the 
force  of  one  dyne.  (See Dyne.)  The  ampere,  or 
practical  electro-magnetic  unit,  is  one-tenth  of 
such  a  current ;  or,  in  other  words,  the  absohite 
unit  of  current  is  ten  amperes. 

An  ampere  may  also  be  defined  by  the  chemical 
decomposition  the  current  can  effect  as  measured 
by  the  quantity  of  hydrogen  liberated,  or  metal 
deposited. 

Defined  in  this  way,  an  ampere  is  such  a  cur- 
rent as  will  deposit  .00111815  gramme,  or 
.017253  grain,  of  silver  per  second  on  one  of  the 
plates  of  a  silver  voltameter,  from  a  solution  of 
silver  nitrate  containing  from  15  to  30  per  cent,  of 
the  salt  (See  Voltameter],  or  which  will  decompose 
.00009326  gramme,  or  .001439  grain  of  dilute 
sulphuric  acid  per  second,  or  pure  sulphuric  acid 
at  59  degrees  F.  diluted  with  about  15  per  cent,  of 
water,  that  is,  dilute  sulphuric  acid  of  Sp.  Gr.  of 
about  I.I.  The  present  scientific  and  commercial 
practice  is  to  take  the  ampere  to  be  such  a  current 
as  will  deposit  4. 024  grammes  of  silver  in  one  hour. 

Ampere  Arc. — (See  Arc,  Ampere?) 
Ampdre-Feet.— (See  Feet,  Ampere.} 
AmpSre-Hour. — (See  Hour,  Ampere.} 

Ampere-Meter. — An  ammeter.  (See  Am- 
meter.} 

Ampere-Meter,  Balance  or  Neutral  Wire 

An  ampere-meter  placed  in  the  cir- 
cuit of  the  neutral  wire,  in  the  three-wire  sys- 
tem of  electric  distribution,  for  the  purpose  of 
showing  the  excess  of  current  passing  over 
one  side  of  the  system  as  compared  with  the_ 
other  side,  when  the  central  wire  is  no  longer 
neutral. 

Ampere-Minute. — (See  Minute,  Ampere} 
Ampere  Ring. — (See  king,  Ampere?) 
Ampere-Second. — (See  Second,  Ampere?) 
Ampdre  Tap7— (See  Tap,  Ampere?) 
Ampere-Turn. — (See  Turn,  Ampere?) 

Ampere-Turn,  Primary (See  Turn, 

Ampere,  Primary?) 


Amp.] 


20 


[Ane. 


Ampere-Turn,  Secondary  — (See 

Turn,  Ampere,  Secondary?) 

Ainpdre-Yolt. — A  watt,  or  the  -7-5^  of  a 
horse-power. 

This  term  is  generally  written  volt-ampere. 
(See  Volt-Ampere.} 

Ampdre-Winding. — (See  Winding,  Am- 
pere) 

Ampere's  Bule  for  Effect  of  Current  on 
Needle.— (See  Rule,  Amperes,  for  Effect  of 
Current  on  Needle?) 

Ampere's  Theory  of  Magnetism. — (See 
Magnetism,  Ampere's  Theory  of) 

Amperian  Currents. — (See  Currents,  Am- 
perian) 

Amplitude  of  Vibration  or  Wave.— (See 
Vibration  or  Wave,  Amplitude  of) 

Ammunition-Hoist,  Electric An 

electrically  operated  hoist  for  raising  ammu- 
nition to  the  deck  of  a  ship. 

In  the  electric  ammunition-hoist  the  electric 
motor  which  moves  the  hoist  is  made  to  follow  the 
motions  of  the  operator's  hand,  both  as  regards 
direction  and  speed.  The  motion  of  a  crank,  or 
wheel,  causes  a  switch  to  start  an  electric  motor  in 
a  certain  direction,  which  tends  to  close  the  switch, 
thus  necessitating  a  race  between  the  operator 
and  the  motor.  Shpuld  the  operator  begin  to 
close  the  switch  more  slowly,  the  motor  will  over- 
take him,  will  partially  close  the  switch,  and  thus 
*  lower  the  speed  of  the  motor. 

Analogous  Pole. — (See  Pole,  Analogous) 

Analysis. — The  determination  of  the  com- 
position of  a  compound  substance  by  separ- 
ating it  into  the  simple  or  elementary  sub- 
stances of  which  it  is  composed. 

Analysis,  Electric The  determin- 
ation of  the  composition  of  a  substance  by 
electrical  means. 

Various  processes  have  been  proposed  for  elec- 
tric analysis;  they  consist  essentially  in  decompos- 
ing the  substance  by  means  of  electric  currents, 
and  are  either  qualitative  or  quantitative.  (See 
Electrolysis . ) 

Analysis,  Electrolytic A  term 

sometimes  used  instead  of  electric  analysis. 
(See  Analysis,  Electric) 

Analysis,  Qualitative A  chemical 


analysis  which  merely  ascertains  the  kinds  of 
elementary  substances  present. 

Analysis,  Quantitative A  chemical 

analysis  which  ascertains  the  relative  propor- 
tions in  which  the  different  components  enter 
into  a  compound. 

Analyzable. — Separable  into  component 
parts. 

Analyze. — To  separate  into  component 
parts. 

Analyze,  Electrically To  separate 

electrically  into  component  parts. 

Analyzer,  Electric A  gridiron  of 

metallic  wires  which  is  transparent  to  electro- 
magnetic waves,  when  its  length  is  perpendic- 
ular to  them,  but  opaque  to  them — /.  e., 
possessing  the  ability  to  reflect  them — when 
rotated  90  degrees  from  its  former  position. 

The  electric  analyzer,  it  will  be  observed,  is 
analogous  to  an  analyzer  for  polarized  light.  A 
reflecting  surface,  for  example,  being  able  to  re- 
flect polarized  light  in  a  given  position,  and  unable 
to  reflect  it  when  rotated  90  degrees  from  such 
position,  is  capable  of  acting  as  an  analyzer  for 
pjlarized  light. 

Analyzer,  Gray's,  Harmonic  Telegraphic 

An  electro-magnet,  the  armature  of 

which  consists  of  a  steel  ribbon  stretched  in 
a  metallic  frame  and  capable  through  regula- 
tion, as  to  tension,  by  means  of  a  screw,  of 
being  tuned  to  a  certain  note. 

The  steel  ribbon  is  thrown  into  vibration  when- 
ever pulsations  from  the  transmitting  instruments 
are  sent  over  the  line  corresponding  to  the  rate  of 
motion  of  the  ribbon,  but  is  not  set  into  vibration 
by  any  others.  If,  therefore,  a  number  of  different 
analyzers,  tuned  to  different  notes,  are  placed  on 
the  same  line,  each  will  be  operated  only  by  the 
pulsations  sent  into  the  line  corresponding  to  its 
rate  of  motion,  and  thus  multiple  transmission  in 
the  same  direction  is  possible.  In  order  to 
strengthen  the  tones  of  the  analyzers,  each  is  pro- 
vided with  a  resonant  air  column.  (See  deton- 
ator. Telegraphy,  Multiplex) 

Analyzing. — Separating  into  component 
parts. 

Anelectric. — A  word  formerly  applied  to 
bodies  (conductors)  which  it  was  believed 
could  not  be  electrified  by  friction. 


Ane.] 


[Ani. 


This  term  is  now  obsolete.  Conductors  are 
easily  electrified,  when  insulated. 

Anelectrotonic  State.— (See  State,  Anelec- 
trotonic) 

Anelectrotonic  Zone. — (See  Zone,  Anelec- 
trotonic^) 

Anelectrotonus. — In  electro-therapeutics, 
the  decreased  functional  activity  which  occurs 
in  a  nerve  in  the  neighborhood  of  the  anode, 
or  positive  electrode,  when  applied  therapeu- 
tically.  (See  Electrotonus) 

Anemometer,  Electric An  appa- 
ratus to  electrically  record  or  indicate  the  direc- 
tion and  intensity  of  the  wind. 

In  the  electric  recording  anemometer,  the  force 
or  velocity  of  the  wind,  or  both,  are  recorded  on 
a  moving  sheet  of  paper,  on  which  the  time  is 
marked,  so  that  the  exact  time  of  any  given 
change  is  known. 

Anemoscope. — An  instrument  which  indi- 
cates, but  does  not  measure  the  intensity  or 
record  the  direction  of  the  wind. 

The  word  is  often,  though  improperly,  used  in- 
terchangeably for  anemometer. 

Angle. — The  deviation  in  direction  between 
two  lines  or  planes  that  meet. 

Angles  are  measured  by  arcs  of  circles.  The 
angle  at  B  A  C,  Fig.  13,  is  the  deviation  of  the 


straight  line  A  B,  from  A 
C.  In  reading  the  let- 
tering of  an  angle  the 
letter  placed  in  the  mid- 
dle indicates  the  angle 
referred  to.  Thus  B  A 

C,  means  the  angle  be-   D~ 

tween  A  B  and  A  C ;  B  A        Fig-  13-    Angles. 

D,  the  angle  between  B  A  and  A  D.    Angles  are 
valued  in  degrees,  there  being  360  degrees  in  an 
entire  circumference  or  circle.     Degrees  are  in- 
dicated thus:  90°,  or  ninety  degrees. 

Angle,  Acute An  angle  whose  value 

is  less  than  a  right  angle  or  90  degrees. 

B  A  E,  or  E  A  D,  in  Fig.  13,  is  an  acute  angle. 

Angle,  Complement  of  —  —What  an 
angle  needs  to  make  its  value  90  degrees,  or  a 
right  angle. 

Thus  in  Fig.  13,  B  A  E,  is  the  complement  of 
the  angle  E  A  D,  since  BAE4-EAD  =  9O 
degrees. 


Angle,   Obtuse An   angle   whose 

value  is  greater  than   a  right   angle   or  90 
degrees. 

E  A  C,  Fig.  13,  is  an  obtuse  angle. 

Angle  of  Declination  or  Variation. — (See 
Declination,  Angle  of.  Variation,  Angle  of.) 

Angle  of  Difference  of  Phase  Between 
Alternating  Currents  of  Same  Period. — 
(See  Phase,  Angle  of  Difference  of,  Between 
Alternating  Currents  of  Same  Period?) 

Angle  of  Dip.— (See  Dip.  Dip  or  Incli- 
nation, Angle  of) 

Angle  of  Inclination.— (See  Dip  or  Incli- 
nation, Angle  of) 

Angle  of  Lag  of  Dynamo-Electric  Ma- 
chine.— (See  Lag,  Angle  of,  of  Dynamo- 
Electric  Machine) 

Angle  of  Lead.— (See  Lead,  Angle  of) 

Angle  of  Variation.— (See  Variation, 
Angle  of.} 

Angle,  Plane An  angle  contained 

between  two  straight  lines. 

Angle,  Solid An  angle  contained 

between  two  surfaces. 

Angle,   Supplement  of What  an 

angle  needs  to  make  its  value  180  degrees,  or 
two  right  angles. 

Thus  in  Fig.  13,  E  A  C,  is  the  supplement  of 
E  A  D,  because  EAD-f-EAC  =  i8o  degrees, 
or  two  right  angles. 

Angle,  Unit An  angle  of  57.29578° 

or  57°  17'  44.8"   nearly. — (See   Velocity,  An- 
gular.) 

Angnlar  Currents. — (See  Currents,  An- 
gular.) 

Angular  Velocity.— (See  Velocity,  Angu- 
lar) 

Animal  Electricity.— (See  Electricity, 
Animal) 

Animal  Magnetism.— (See  Magnetism, 
Animal) 

Anion. — The  electro-negative  radical  of  a 
molecule. 

Literally,  the  term  ion  signifies  a  group  of 
wandering  atoms.  An  union  is  that  group  of 
atoms  of  an  electrically  decomposed  or  electro lyzed 


Ani.] 


[Ann. 


molecule  which  appears  at  the  anode.  (See 
Electrolysis.  Anode. ) 

As  the  anode  is  connected  with  the  electro- 
positive terminal  of  a  source,  the  anion  is  the 
electro-negative  radical  or  group  of  atoms,  and 
therefore  appears  at  the  electro-positive  terminal. 

A  kathion,  or  electro-positive  radical,  appears 
at  the  kathode,  which  is  connected  with  the 
electro-negative  terminal  of  the  battery.  Oxygen 
and  chlorine  are  anions.  Hydrogen  and  the 
metals  are  kathions. 

Anisotropic  Conductor. — (See  Conductor, 
Anisotropic?) 

Anisotropic  Medium. — (See  Medium, 
Anisotropic?) 

Annealing,  Electric  —  — A  process 
for  annealing  metals  in  which  electric  heating 
is  substituted  for  ordinary  heating. 

Annual  Inequality  of  Earth's  Magnet- 
ism.— (See  Inequality,  Annual,  of  Earth's 
Magnetism. 

Annual  Variation  of  Magnetic  Needle. 
— (See  Needle,  Magnetic,  Annual  Variation 
of.) 

Annunciator,  Burglar-Alarm An 

annunciator  used  in  connection  with  a  system 
of  burglar-alarms.  (See  Alarm,  Burglar?) 

Annunciator  Clock,  Electric  — -  — 
(See  Clock,  Electric  Annunciator?) 

Annunciator  Drop. — (See  Drop,  Annun- 
ciator?) 

Annunciator    Drop,  Automatic  — 
(See  Drop,  Automatic  Annunciator?) 

Annunciator,    Electro-Magnetic 

An  electric  device  for  automatically  indicating 
the  points  or  places  at  which  one  or  more 
electric  contacts  have  been  closed. 

The  character  of  the  annunciator  depends,  of 
course,  on  the  character  of  the  places  at  which 
these  points,  places  or  stations  are  situated. 

Annunciators  are  employed  for  a  variety  of 
purposes.  In  hotels  they  are  used  for  indicating 
the  number  of  a  room  the  occupant  of  which 
desires  some  service,  which  he  signifies  by  push- 
ing a  button,  thus  closing  an  electric  circuit. 
This  is  indicated  or  announced  on  the  annuncia- 
tor by  the  falling  of  a  drop,  on  which  is  printed  a 
number  corresponding  with  the  room,  and  by  the 


ringing  of  a  bell  to  notify  the  attendant.  The  num- 
ber is  released  by  the  movement  of  the  armature 
of  an  electro-magnet.  The  drops  are  replaced  in 
their  former  position  by  some  mechanical  device 
operated  by  the  hand.  In  the  place  of  a  drop  a 


Fig.  14.    Electro -Magnetic  Annunciator. 

needle  is  sometimes  used,  which,  by  the  attraction 
of  the  armature  of  an  electro-magnet,  points  to 
the  number  signaling. 

Annunciators  for  houses,  burglar-alarms,  fire- 
alarms,  elevators,  etc.,  are 
of  the  same  general  con- 
struction. 

Annunciators  are  general- 
ly operated  by  electro-mag- 
netic attraction  or  repulsion, 
and  are  therefore  some- 
times called  electro -magnetic 
annunciators. 

Fig.  14  shows  an  annun- 
ciator suitable  for  use  in 
hotels. 

The  numbers  28  and  85 
are  represented  as  having 
been  dropped  by  the  closing 
of  the  circuit  connected 
with  them. 

Annunciator,    Eleva- 
tor   — An  annuncia- 
tor   connected    with    an 
elevator  to    indicate   the 
floor  signaling. 
One  form  of  elevator  annunciator  is  shown  in 
Fig.  15. 


Fig.  z$.    Elevator 
Annunciator. 


Ann.] 


23 


[Ann. 


Annunciator,       Fire-Alarm An 

annunciator  used  in  connection  with  a  system 
of  fire-alarms. 
Annunciator,    Gravity-Drop An 

annunciator  whose  signals  are  operated  by 
the  fall  of  a  drop. 


Fig.  ib.    Gravity-Drop  Annunciator. 

A  form  of  gravity-drop  annunciator  is  shown 
in  Fig.  16.  The  armature  mechanism  for  the 
release  of  the  drop  will  be  understood  by  an  in- 
spection of  the  drawing. 

Annunciator,  Hotel An  annun- 
ciator connected  with  the  different  rooms  of  a 
hotel. 

A  hotel-annunciator  is  generally  provided  with 
a  return  bell  and  guest-call. 

Annunciator,  House An  annun- 
ciator connected  with  the  rooms  of  a  house. 

Annunciator,  Needle An  annun- 
ciator, the  indications  of  which  are  given  by 
the  movements  of  a  needle  instead  of  the  fall 
of  a  drop. 

A  form  of  needle-annunciator  is  shown  in 
Fig.  17. 

Annunciator,   Oral    or  Speaking    Tube 

An  annunciator  electrically  operated 


by  means  of  a  puff  of  breath   transmitted 
through  an  ordinary  speaking  tube. 

The  oral-annunciator  is  a  contrivance  whereby 
a  central  office  is  placed  in  communication  with  a 
number  of  speaking  tubes  coming  from  different 
points  in  a  hotel  or  other  place.  A  person 
in  any  room,  who  wishes  to  cpmmunicate 
with  the  central  office,  blows  through  the 
speaking  tube  in  his  room,  and  thus,  by 
effecting  an  electric  contact,  rings  a  bell  and 
operates  a  drop  at  the  annunciator,  thus  indicat- 
ing the  exact  tube  at  which  the  attendant  is  to 
receive  the  message.  The  attendant  can  thus  be 
placed  in  easy  communication  with  each  of  the 
rooms  whose  speaking  tubes  connect  with  the 
annunciator. 

Annunciator,  Pendulum  or  Swinging — 
—  An    annunciator,    the    indicating    arm  of 
which  consists  of  a  pendulous.or  swinging  arm, 


Fig.  77.    Needle- Annunciator. 

which,  when  at  rest,  points  vertically  down- 
ward, and  which  is  moved  to  the  right  or  left 
by  the  action  of  the  current. 

Pendulous,  or  swinging-annunciators  are  gen- 
erally so  arranged  as  to  need  no  replacement. 


Ano.] 


[App. 


On  the  cessation  of  the  current  the  indicator  arm 
drops  vertically  downward. 

A  relay  is  preferably  used  with  pendulum- 
annunciators,  since  the  rapid  makes  and  breaks 
of  the  current  by  the  bell  alarm  interfere  with 
their  satisfactory  action. 

Anodal. — Pertaining  to  the  anode.  (See 
Anode) 

Anodal  Diffusion.— (See  Diffusion, 


Anode. — The  conductor  or  plate  of  a  de- 
composition cell  connected  with  the  positive 
terminal  of  a  battery,  or  other  electric  source. 

That  terminal  of  an  electric  source  out  of 
which  the  current  flows  into  the  liquid  of  a 
decomposition  cell  or  voltameter  is  called  the 
anode. 

That  terminal  of  an  electric  source  into 
which  the  current  flows  from  a  decomposition 
cell  or  voltameter  is  called  the  kathode. 

The  anode  is  connected  with  the  carbon  or 
positive  terminal  of  a  voltaic  battery,  and  the 
kathode  with  the  zinc,  or  negative  terminal. 
Therefore  the  word  anode  has  been  used  to 
signify  the  positive  terminal  of  an  electric  source, 
and  kathode,  the  negative  terminal,  and  in  this 
sense  is  employed  generally  in  electro-thera- 
peutics. It  is  preferable,  however,  to  restrict  the 
use  of  the  words  anode  and  kathode  to  those 
terminals  of  a  source  at  which  electrolysis  is 
taking  place. 

The  terms  anode  and  kathode  in  reality  refer 
to  the  electro-receptive  devices  through  which 
the  current  flows.  Since  it  is  assumed  that  the 
current  flows  out  of  a  source  from  its  positive 
pole  or  terminal,  and  back  through  the  source  at 
its  negative  pole  or  terminal,  the  pole  of  any 
device  which  is  connected  with  the  positive  pole 
of  a  source  is  the  part  or  place  at  which  the 
current  enters  and  flows  through  it,  and  that 
connected  with  the  negative  pole,  the  part  at 
which  it  leaves.  Hence,  probably,  the  change 
in  the  use  of  the  words  already  referred  to. 

Since  the  anion,  or  the  electro-negative  radical, 
appears  at  the  anode,  it  is  the  anode  of  an  electro- 
plating bath,  or  the  plate  connected  with  the 
positive  terminal  of  the  source,  that  is  dissolved. 

When  the  term  anode  was  first  proposed  by 
Faraday,  voltaic  batteries  were  the  only  available 
electric  source,  and  the  term  referred  only  to  the 


positive  terminal  of  a  voltaic  battery  when 
placed  in  an  electrolyte. 

Anodic. — Pertaining  to  the  anode.  (See 
Anode) 

Anodic  Electro-Diagnostic  Reactions.— 

(See  Reactions,  Kathodic  and  Anodic  Elec- 
tro-Diagnostic?) 

Anodic  Opening  Contraction.— (See  Con- 
tration,  Anodic  Opening.) 

Anomalous  Magnet. — (See  Magnet,  An- 
omalous) 

Anomalous  Magnetization. — (See  Mag- 
netization, Anomalous) 

Anti-Induction  Cable (See  Cable, 

Anti-Induction) 

Anti-Induction  Conductor.  —  (See  Con- 
ductor, Anti-Induction) 

Antilogous  Pole.— (See  Pole,  Antilogous) 

Anvil. — The  front  contact  of  a  telegraphic 
key  that  limits  its  motion  in  one  direction. 
(See  Key,  Telegraphic) 

Aperiodic  Galvanometer. — (See  Galva- 
nometer, Aperiodic) 

Apparatus,  Faradic-Induction 

An  induction  coil  apparatus  for  producing 
faradic  currents. 

A  voltaic  battery  is  connected  with  the  primary 
of  an  induction  coil,  and  its  current  rapidly 
broken  by  an  automatic  break,  or  by  a  hand 
break.  The  alternating  or  faradic  currents  thus 
produced  in  the  secondary  coils  are  used  for 
electro-therapeutic  purposes.  (See  Coil,  Induc- 
tion.) 

Faradic-induction  apparatus  is  made  in  a  great 
variety  of  forms.  They  all  operate,  however,  on 
essentially  the  same  principles. 

Apparatus,  Faradic,  Magneto-Electric 

A  small  magneto-electric  machine 

employed  in  electro-therapeutics  for  producing 
faradic  currents. 

Magneto-electric  faradic  machines  consist  essen- 
tially of  a  coil  of  wire  wrapped  on  an  armature 
core  that  is  rotated  before  the  poles  of  permanent 
magnets.  No  commutator  is  employed,  since  it  is 
desired  to  obtain  rapidly  alternating  currents. 

Apparatus,  Interlocking  —  —Devices 
for  mechanically  operating  from  a  distant  signal 


App.] 


[Arc. 


tower,  railroad  switches  and  semaphore  signals 
for  indicating  the  position  of  such  switches, 
by  means  of  a  system  of  interlocking  levers, 
so  constructed  that  the  signals  and  the 
switches  are  so  interlocked  as  to  render  it 
impossible,  after  a  route  has  once  been  set  up 
and  a  signal  given,  to  clear  a  signal  for  a 
route  that  would  conflict  with  the  one  previ- 
ously set  up.  (See  Block  System  for  Rail- 
roads^) 

Apparatus,  Magneto-Electric  Medical 
A  term  applied  to  small  magneto- 
electric  machines  employed  in  medical  elec- 
tricity for  the  production  of  uncommuted 
or  faradic  currents.  (See  Apparatus,  Fara- 
dic,  Magneto-Electric) 

Apparatus,  Registering-,  Electric  — 

Devices  for  obtaining  permanent  records  by 
electrical  means. 

Apparatus,  Registering,  Telegraphic 

— A  name  sometimes  given  to  a  telegraphic 
recorder.  (See  Recorder,  Chemical,  Bain's, 
Recorder,  Morse.  Recorder,  Siphon?) 

Apparent    Co-efficient    of    Induction. — 

(See  Induction,  Apparent  Co-efficient  of.) 

Arago's  Disc. — (See  Disc,  Arago's) 

Arc.— A  voltaic  arc.     (See  Arc,   Voltaic) 

Arc. — To  form  a  voltaic  arc. 

A  dynamo-electric  machine  is  said  to  arc  at  the 
commutator,  when  the  current  passes  as  visible 
sparks  across  the  spaces  between  adjacent  seg- 
ments. 

This  action  at  the  commutator  is  more  gener- 
ally called  sparking  or  burning. 

Arc,  Alternating A  voltaic  arc 

formed  by  means  of  an  alternating  current. 

In  order  to  avoid  the  extinction  of  the  arc  a 
certain  number  of  alternations  per  second  is  nec- 
essary. The  alternating  arc  produces  a  loud 
singing  noise.  At  very  high  frequencies,  how- 
ever, the  noise  disappears. 

The  alternating  arc,  not  possessing  a  fixed  posi- 
tive crater,  requires  to  be  covered  by  a  good 
reflector  to  throw  the  light  downward. 

Arc,  Ampe're A  single  conductor 

bent  in  an  arc  of  a  circle,  and  used  in  electric 
balances  for  measuring  the  electric  current. 


Arc  Blow-Pipe.— (See  Blow-Pipe,  Elec- 
tric Arc.} 

Arc,  Compound An  arc  formed 

between  more  than  two  separate  electrodes. 

Arc,  Counter   Electromotiye    Force    of 

An  electromotive  force  generally  be- 
lieved to  be  set  up  on  the  formation  of  a 
voltaic  arc,  opposed  in  direction  to  the  electro- 
motive force  maintaining  the  arc.  (See  Force, 
Electromotive,  Counter?) 

This  counter  electromotive  force  is  believed  to 
have  its  origin  partly  in  the  energy  absorbed  at 
the  crater  of  the  positive  carbon,  where  the  car- 
bon is  volatilized,  and  given  out  at  the  nipple  on 
the  negative  carbon,  where  it  is  deposited  or 
solidified.  It  is  to  be  noted  in  this  connection 
that  the  apparent  resistance  of  the  carbon  voltaic 
arc  is  not  directly  proportional  to  the  length  of 
the  arc. 

Arc,  Electric A  term  sometimes 

used  for  the  voltaic  arc.  (See  Arc,  Voltaic) 

Arc,  Frying  of —  — A  frying  sound  at- 
tending the  formation  of  a  voltaic  arc  when 
the  carbons  are  too  near  together. 

The  cause  of  the  frying  sound  is  probably  the 
same  as  that  of  hissing.  (See  Arc,  Hissing  of '.) 

Arc,  Hissing  of A  hissing  sound 

attending  the  formation  of  voltaic  arcs  when 
the  carbons  are  too  near  together. 

The  cause  of  the  hissing  is  not  entirely  under- 
stood. Prof.  Elihu  Thomson  suggests  that  it  is 
due  to  a  too  rapid  volatilization  of  the  carbons. 

Arc  Lamp. — (See  Lamp,  Arc) 

Arc  Lamp,  Electric (See  Lamp, 

Electric  Arc) 

Arc  Lamp,  Triple  Carbon  Electric 

—(See  Lamp,  Arc,  Triple  Carbon  Electric) 

Arc  Lighting. — (See  Lighting,  Arc) 

Arc,  Metallic A  voltaic  arc  formed 

between  metallic  electrodes. 

When  the  voltaic  arc  is  formed  between  metallic 
electrodes  instead  of  carbon  electrodes,  a  flaming 
arc  is  obtained,  the  color  of  which  is  characteristic 
of  the  burning  metal ;  thus  copper  forms  a  brill- 
iant green  arc.  The  metallic  arc,  as  a  rule  is 
much  longer  than  an  arc  with  the  same  current 
taken  between  carbon  electrodes. 

Arc  Micrometer. — (See  Micrometer,  Arc) 


Arc.] 


[Arc. 


Arc,  Noisy A  voltaic  arc,  the 

maintenance  of  which  is  attended  by  frying, 
hissing,  or  spluttering  sounds. 

Arc,  (Juiet A  voltaic  arc  which  is 

maintained  without  sensible  sounds. 

Arc,  Roaring  of —  • — A  roaring  sound 
attending  the  formation  of  a  voltaic  arc  when 
the  carbons  are  too  near  together  and  a  very 
powt  rf ul  current  is  used. 

Arc,  Simple An  arc  formed  be- 
tween two  electrodes. 

Arc,  Spluttering  of A  spluttering 

sound  attending  the  formation  of  a  voltaic 
arc. 

Prof/Elihu  Thomson  suggests  that  the  cause  of 
spluttering  is  due  to  the  presence  of  impurities  in 
the  carbons,  or  from  the  sudden  evolution  of  gas 
from  insufficiently  baked  carbons. 

Arc,  Yoltaic  —  —The  brilliant  arc  or 
bow  of  light  which  appears  between  the  elec- 
trodes or  terminals,  generally  of  carbon,  of  a 
sufficiently  powerful  source  of  electricity,  when 
separated  a  short  distance  from  each  other. 

The  source  of  light  of  the  electric  arc  lamp. 

It  is  called  the  voltaic  arc  because  it  was  first 
obtained  by  the  use  of  the  battery  invented  by 
Volta.  The  term  arc  was  given  to  it  from  the 
shape  of  the  luminous  bow  or  arc  formed  between 
the  carbons. 

To  form  the  voltaic  arc  the  carbon  electrodes 
are  first  placed  in  contact  and  then  gradually 
separated.  A  brilliant  arc  of  flame  is  formed  be- 
tween them,  which  consists  mainly  of  volatilized 
carbon.  The  electrodes  are  consumed,  first,  by 
actual  combination  with  the  oxygen  of  the  air; 
and,  second,  by  volatilization  under  the  combined 
influence  of  the  electric  current  and  the  intense 
heat. 

As  a  result  of  the  formation  of  the  arc,  a  crater 
is  formed  at  the  end  of  the  positive  carbon,  and 
appears  to  mark  the  point  out  of  which  the 
greater  part  of  the  current  flows. 

The  crater  is  due  to  the  greater  volatilization 
of  the  electrode  at  this  point  than  elsewhere. 
It  marks  the  position  of  highest  temperature  of  the 
electrodes,  and  is  the  main  source  of  the  light  of 
the  arc.  When,  therefore,  the  voltaic  arc  is  em- 
ployed  for  the  purposes  of  illumination  with 
vertically  opposed  carbons,  the  positive  carbon 
should  be  made  the  upper  carbon,  so  that  the 


focus  of  greatest  intensity  of  the  light  may  be 
favorably  situated  for  illumination  of  the  space 
below  the  lamp.  When,  however,  it  is  desired  to 
illumine  the  side  of  a  building  above  an  arc  lamp, 
the  lower  carbon  should  be  made  positive. 

The  positive  carbon  is  consumed  about  twice  as 
rapidly  as  the  negative,  both  because  the  negative 
oxygen  attacks  the  points  of  the  positive  carbon.  ' 
and  because  the  positive  carbon  suffers  the  most 
rapid  volatilization. 

The  electric  current  passes  through  the  space 
occupied  by  the  voltaic  arc  because— 

(I.)  The  heated  arc  is  a  partial  conductor  of 
electricity. 

(2.)  Because  small  charges  of  electricity  are 
carried  bodily  forward  from  the  positive  to  the 
negative  carbon  through  the  space  of  the  voltaic 
arc,  by  means  of  the  minute  particles  which  are 
volatilized  at  the  positive  electrode. 

S.  P.  Thompson  has  shown  that  the  tempera- 
ture of  the  light-emitting  surface  of  the  carbon  is 
the  temperature  of  the  volatilization  of  carbon, 
and  is  therefore  constant/ 

Dr.  Fleming  found  that  "  A  rise  of  potential 
along  the  arc  takes 
place  very  suddenly, 
just  in  the  neighbor- 
hood of  the  crater. ' ' 

The   crater    in  the 
end  of  the  positive  car- 
bon is  seen  in  Fig.  18. 
On  the  opposed  end 
of  the  negative  carbon 
a  projection  or  nipple 
is  formed  by   the  de- 
posit of  the  electrical- 
ly volatilized  carbon. 
Fig.  r8.    Voltaic  Arc.        The  rounded    masses 
or  globules  that  appear  on  the  surface  of  the  elec- 
trodes are  due  to  deposits  of  molten  foreign  mat- 
ters in  the  carbon. 

The  carbon,  both  of  the  crater  and  its  opposed 
nipple,  is  converted  into  pure,  soft  graphite. 

Arc,  Voltaic,  Resistance  of—  —The 
resistance  offered  by  the  voltaic  arc  to  the 
passage  of  the  current. 

As  in  all  other  conductors,  the  ohmic  resistance 
of  the  arc  increases  with  its  length,  and  decreases 
with  its  area  of  cross-section.  The  apparent 
resistance,  however,  is  not  directly  proportional 
to  the  length.  An  increase  of  temperature  de- 
creases the  resistance  of  the  voltaic  arc. 


Arc.] 


[Arm. 


The  total  apparent  resistance  of  the  voltaic  arc 
is  composed  of  two  parts,  viz. : 

(I.)  The  true  ohmic  resistance.  (See  Resist- 
ance, Ohtnic.) 

(z.)  The  counter  electromotive  force,  or  spuri- 
ous resistance.  (See  Resistance,  Spurious.) 

Arc,  Watt A  voltaic  arc,  the  elec- 
tric power  of  which  is  equal  to  a  given  number 
of  watts. 

The  ordinary  long-arc,  as  employed  in  arc 
lighting,  has  a  difference  of  potential  of  about  45 
volts  and  a  current  strength  of  about  10  amperes. 
It  is,  therefore,  a  45O-watt  arc. 

Arch,   Auroral The  archlike  form 

sometimes  assumed  by  the  auroral  light.  (See 
Aurora  Borealis?) 

Arcing. — Discharging  by  means  of  voltaic 
arcs.  (See  Arc,  Voltaic?) 

Arcing  at  the  commutator  of  a  dynamo-electric 
machine  not  only  prevents  the  proper  operation 
of  the  machine,  but  eventually  leads  to  the  de- 
struction of  the  brushes  and  the  commutator. 

Areometer,  Bead  — A  form  of  are- 
ometer suitable  for  rapidly  testing  the  density 
of  the  liquid  in  a  storage  cell. 

The  bead  areometer  consists  of  a  glass  tube, 
open  at  both  top  and  bottom,  containing  a  few 
glass  beads,  so  weighted  as  to  float  at  liquid 
densities  such  as  1.105,  1.170,  1.190 
and  1. 200.  To  use  the  instrument, 
it  is  immersed  in  the  liquid  of  the 
storage  cell,  and  then  withdrawn. 
The  finger  being  kept  in  the  upper 
opening,  the  liquid  does  not  escape 
through  the  small  opening  at  the 
bottom.  The  density  is  then  ascer- 
tained by  noting  the  beads  that 
float. 

Areometer  or  Hydrometer. 
— An  instrument  for  determin- 
ing the  specific  gravity  of  a  liquid. 

A  common  form  of  hydrometer 
consists,  as  shown  in  Fig.  19,  of  a 
closed  glass  tube,  provided  with  a 
bulb,  and  filled  at  the  lower  end  V 

with  mercury  or  shot,  so  as  to  in-  ® 

sure  its    vertical     position    when  Fig.  19.    Hy- 
floating  in  a  liquid.     When  placed      drometer. 
in  different  liquids,  it  floats  with  part  of  the  tube 
out  of  the  liquid.     The   lighter  the  liquid,  the 
2— Vol.  1 


smaller  is  the  portion  that  remains  out  of  the 
liquid  when  the  instrument  floats.  The  specific 
gravity  is  determined  by  observing  the  depth  to 
which  the  instrument  sinks  when  placed  in  different 
liquids,  as  compared  with  the  depth  it  sinks  when 
placed  in  water. 

Areometry. — The  measurement  of  specific 
gravity  by  means  of  an  areometer. 

Argand  Burner,  Electric  Hand-Lighter 
-(See  Burner,  Argand,  Electric  Hand- 
Lighter?) 

Argand  Burner,  Electric  Plain-Pendant 
— (See  Burner,  Plain  Pendant,  Argand, 
Electric?) 

Argand  Burner,  Electric  Ratchet-Pen- 
dant —  —(See  Burner,  Ratchet-Pendant, 
Argand)  Electric?) 

Argyrometry. — The  art  of  determining 
the  weight  of  electrolytically  deposited  silver. 
(See  Balance,  Plating?) 

Arm,  Balance One  of  the  resist- 
ances of  an  electric  balance.  (See  Arms, 
Bridge  or  Balance.  Bridge,  Electric?) 

Arm,  Bridge  —  — A  bridge  arm.  (See 
Arms,  Bridge  or  Balance?) 

Arm,  Cross  —  — A  horizontal  beam  at- 
tached to  a  pole  for  the  support  of  the  in- 
sulators for  telegraph,  electric  light  or  'other 
electric  wires. 

A  telegraphic  arm.  (See  Arm,  Tele- 
graphic?) 

Arm,  Rocker  — An  arm  on  which  the 

brushes  of  a  dynamo  or  motor  are  mounted 
for  the  purpose  of  shifting  their  position  on 
the  commutator. 

Arm,  Semaphore The  movable 

arm  of  the  signal  apparatus  employed  in  block 
systems  for  railroads,  for  the  purpose  of  in- 
forming engineers  of  trains  of  the  condition 
of  the  road  as  regards  other  trains. 

In  the  absolute  block  system,  as  used  on  some 
roads,  there  are  two  positions  for  the  semaphore 
arm,  viz. : 

(i.)  For  Danger — when  in  a  horizontal  position,, 
or  at  90  degrees  with  the  vertical  supporting  pole. 

(2. )  Clear — when  dropped  below  the  horizontal 
position  through  an  angle  of  75  degrees. 

In  the  Permissive  Block  System,  a  third  position 


Arm.] 


[Arm. 


intermediate  between  the  ist  and  the  zd,  or  at  an 
angle  of  37  degrees  30  minutes  with  the  horizontal 
position,  is  used  for  caution.  (See  Block  System 
for  Railroads. ,) 

Arm,  Signal A  semaphore  arm. 

(See  Arm,  Semaphored) 

Arm,  Telegraphic  —  —A  cross-arm 
placed  on  a  telegraphic  pole  for  the  support 
of  the  insulators. 

These  arms  are  generally  called  cross-arms. 

Armature. — A  mass  of  iron  or  other 
magnetizable  material  placed  on  or  near  the 
pole  or  poles  of  a  magnet. 

In  the  case  of  a  permanent  magnet,  the  arma- 
ture, when  used  as  a  keeper,  is  of  soft  iron  and  is 
placed  directly  on  the  magnet  poles.  In  this  case 
it  preserves  or  keeps  the  magnetism  by  closing 
the  lines  of  magnetic  jorce  of  the  magnet  through 
the  soft  iron  of  the  armature,  and  is  then  called  a 
keeper.  (See  Force,  Magnetic,  Lines  of.} 

In  the  case  of  an  electro-magnet,  the  armature 
is  placed  near  the  poles,  and  is  moved  toward 
them  whenever  the  magnet  is  energized  by  the 
passage  of  the  current  through  the  magnetizing 
coils.  This  movement  is  made  against  the  action 
of  a  spring  or  weights,  so  that  on  the  loss  of 
magnetism  by  the  magnet,  the  armature  moves 
from  the  magnet  poles.  (See  Magnet,  Permanent. 
Magnet,  Keeper  of  .} 

When  the  armature  is  of  soft  iron  it  moves  to- 
ward the  magnet  on  the  completion  of  the  circuit 
through  its  coils,  no  matter  in  what  direction 
the  current  flows,  and  is  then  called  a  non-polar- 
ized armature.  (See  Armature,  Non-Polarized. ) 

When  made  of  steel,  or  of  another  electro-mag - 


Fig.2O.     Bi-polar  Armature. 

net,  it  moves  from  or  toward  the  poles,  accord- 
ing to  whether  the  poles  of  the  armature  are  of 
the  same  or  of  a  different  polarity  from  those  of 
the  magnet.  Such  an  armature  is  called  a 
polarized  armature.  (Set  Armature,  Polarized.) 


Armature,  Bi-polar An  armature 

of  a  dynamo-electric  machine  the  polarity  of 
which  is  reversed  twice  in  every  revolution 
through  the  field  of  the  machine. 

A  form  of  bi-polar  armature  is  shown  in  Fig.  20. 
The  word  bi-polar  armature  is  not  generally 
employed.  The  term  applies  rather  to  the  field- 
magnet  poles  than  to  the  armature. 

Armature  Bore. — (See  Bore,  Armature.} 

Armature  Bore,  Elliptical  —  —(See 
Bore,  Elliptical  Armature?) 

Armature  Chamber. — (See  Chamber, 
Armature?) 

Armature  Coils,  Dynamo  -  — (See 
Coils,  Armature,  of  Dynamo-Electric  Ma- 
chine?) 

Armature  Core,  Dynamo  -  — (See 
Core,  Armature,  of  Dynamo-Electric  Ma- 
chine?) 

Armature,  Cylindrical  —  — A  term 
sometimes  applied  to  a  drum  armature. 
(See  Armature,  Drum.  Armature,  Dy- 
namo-Electric Machine?) 

Armature,  Cylindrical  Ring.— A  ring 
armature  with  a  core  in  the  shape  of  a  com- 
paratively long  cylinder. 

Armature,  Disc An  armature  of  a 

dynamo-electric  machine,  in  which  the  arma- 
ture coils  consist  of  flat  coils,  supported  on 
the  surface  of  a  disc.  (See  Armature,  Dy- 
namo-Electric Machine?) 

Armature,  Dissymmetrical  Induction  of 

— Any  induction  produced  in  the  arma- 
ture of  a  dynamo-electric  machine  that  is  un- 
equal in  amount  on  opposite  halves,  or  in  sym- 
metrically disposed  portions  of  the  armature. 

Dissymmetrical  induction  in  the  armature  may 
cause  annoying  or  injurious  sparking  at  the  com- 
mutator. It  may  arise — 

(i.)  From  a  lack  of  symmetry  in  the  amount  of 
the  armature  windings. 

(2.)  From  a  lack  of  symmetry  in  the  arrange- 
ment of  the  armature  windings  on  the  armature 
core. 

(3. )  From  a  lack  of  symmetry  of  the  pole  pieces 
of  the  machine. 

(4.)  From  an  improper  position  of  the  brushes 


Aroi.] 


29 


[Arm, 


as  regards  the  neutral  point  on  the  commutator, 
causing  a  temporary  short-circuiting  of  one  or 
more  of  the  armature  coils. 

Armature,  Drum —  — An  armature  of 
a  dynamo-electric  machine,  in  which  the 
armature  coils  are  wound  longitudinally  over 
the  surface  of  a  cylinder  or  drum.  (See 
Armature,  Dynamo-Electric  Machine?) 

A  form  of  drum-armature  is  shown  in  Fig.  21. 


Fig.  21.    Drum- Armature. 

Armature,     Dynamo-Electric     Machine 

The  coils  of  insulated  wire  together 

with  the  iron  armature  core,  on  or  around 
which  the  coils  are  wound. 

That  part  of  a  dynamo-electric  machine  in 
which  the  differences  of  potential  which 
cause  the  useful  currents  are  generated. 

Generally,  that  portion  of  a  dynamo-elec- 
tric machine  which  is  revolved  between  the 
pole  pieces  of  the  field  magnets. 

The  armature  of  a  dynamo-electric  machine 
usually  consists  of  a  series  of  coils  of  insulated 
wire  or  conductors,  wrapped  around  or  grouped 
on  a  central  core  of  iron.  The  movement  of 
these  wires  or  conductors  through  the  magnetic 
field  of  the  machine  produces  an  electric  cur- 
rent by  means  of  the  electromotive  forces  so  gen- 
erated. Sometimes  the  field  is  rotated  ;  some- 
times both  armature  and  field  rotate. 

The  armatures  of  dynamo-electric  machines 
are  of  a  great  variety  of  forms.  They  may  for 
convenience  be  arranged  under  the  following 
heads,  viz.: 

Cylindrical  or  drum-armatures,  disc-arma- 
tures, pole  or-radial  armatures,  ring  armatures, 
and  spherical-  armatures .  For  further  particulars 
see  above  terms.  Armatures  are  also  divided 


into  classes  according  to  the  character  of  fee 
magnetic  field  through  which  they  move — viz.: 
unipolar,  bipolar,  and  multipolar- armatures. 

The  English  sometimes  use  the  word  cylindrical 
armature  as  a  synonym  of  ring-armature. 

A  unipolar-armature  is  one  whose  polarity  is 
never  reversed.  A  bipolar-armature  is  one  in 
which  the  polarity  is  reversed  twice  in  every 
rotation;  multipolar  armatures  have  their  po- 
larity reversed  a  number  of  times  in  every  rota- 
tion. 

The  term  armature  as  applied  to  a  dynamo- 
electric  machine  was  derived  from  the  fact  that 
the  iron  core  acts  to  magnetically  connect  the 
two  poles  of  the  field  magnets  in  the  same 
manner  that  an  ordinary  armature  connects  the 
poles  of  a  magnet. 

Armature,  Flat  Ring  —  —A  ring-arma- 
ture with  a  core  in  the  shape  of  a  short  cylin- 
drical ring. 

Armature,   Girder  —       — An  armature 

with  an  H  -shaped  or  girder-like  core. 

An  H -shaped  armature. 

Armature,  Intensity  —  —An  old  term 
for  an  armature  with  coils  of  many  turns  and 
of  a  comparatively  high  resistance. 

Armature,  Lamination  of  Core  of — 
— A  division  of  the  iron  core  of  the  armature 
of  a  dynamo-electric  machine  or  motor,  so  as 
to  avoid  the  formation  of  eddy-currents 
therein.  (See  Core,  Lamination  of.  Cur- 
rents, Eddy.) 

Armature,  Mnltipolar  —  —A  dynamo- 
electric  machine  armature  whose  polarity  is 
reversed  more  than  twice  during  each  rotation 
in  the  field  of  the  machine. 

Armature,  Neutral A  non-polarized 

armature.     (See  Armature,  Non-Polarized.) 

Armature,  Neutral-Relay A  relay 

armature,  consisting  of  a  piece  of  soft  iron, 
which  closes  a  local  circuit  whenever  its  elec- 
tro-magnet receives  an  impulse  over  the  main 
line.  (See  Artnature,  Polarized?) 

This  term  is  applied  in  contradistinction  to  a 
polarized  relay  armature. 

Armature,    Non-Polarized     — An 

armature  of  soft  iron,  which  is  attracted  toward 
the  poles  of  an  electro-magnet  on  the  comple 


Arm.] 


30 


[Arm. 


tion  of  the  circuit,  no  matter  in  what  direc- 
tion the  current  passes  through  the  coils. 

The  term  non-polarized  is  used  in  contradistinc- 
tion to  polarized  armature.  (See  Armature, 
Polarized.} 

Th.  non-polarized  armature  of  a  relay  magnet 
is  generally  called  the  neutral -relay  armature. 

Armature  of  a  Cable,  or  Cable-Armature. 

— A  term  sometimes  employed  for  the  sheath- 
ing or  protecting  coat  of  a  cable. 

The  term  armor  sheathing  or  coating  is  prefer- 
able. 

Armature  of  a  Condenser,  or  Condenser 
Armature. — A  term  sometimes  applied  to 
the  metallic  plates  of  a  condenser  or  Leyden 
jar. 

The  use  of  this  term  is  unnecessary  and  ill- 
advised.  The  term  coating  or  plate  would  appear 
to  be  preferable. 

Armature  of  Holtz  Machine,  or  Holtz- 
Machine  Armature. — The  pieces  of  paper 
that  are  placed  on  the  stationary  plate  of  the 
Holtz  and  other  similar  electrostatic  induction 
machines. 

Armature  Pockets.— (See  Pockets,  Arma- 
ture) 

Armature,  Polarized An  armature 

which  possesses  a  polarity  independent  of 
that  imparted  by  the  magnet  pole  near  which 
it  is  placed. 

In  permanent  magnets  the  armatures  are  made 
of  soft  iron,  and  therefore,  by  induction,  become 
of  a  polarity  opposite  to  that  ol  the  magnet  poles 
that  lie  nearest  them.  They  have,  therefore,  only 
a  motion  of  attraction  toward  such  pales.  (See 
Induction,  Magnetic. ) 

In  electro-magnets  the  armatures  may  either  be 
made  of  soft  iron,  in  which  case  they  are  attracted 
only  on  the  passage  of  the  current;  or  they  may 
be  formed  of  permanent  steel  magnets,  or  may  be 
electro-magnets  themsehes,  in  which  case  the  pas- 
sage of  the  current  through  the  coils  of  the  elec- 
tro-magnet, or  electro-magnets,  may  cause  either 
attraction  or  repulsion,  according  as  the  adjacent 
poles  are  of  opposite  polarity  or  are  of  the  same 
polarity. 

Armature,  Pole  —  — An  armature  the 
coils  of  which  are  wound  on  separate  poles 


that  project   radially  from  the  periphery  of  a 
disc,  drum  or  ring. 
A  pole-armature  showing  the  arrangement  of 


Fig.  Z2.    Pole- Armature. 

the  coils  and  their  connection  to  the  commutator 
segments  is  seen  in  Fig.  22. 

Armature,  Quantity An  old  term 

for  an  armature  wound  with  but  a  few  coils 
of  comparatively  low  resistance. 

Armature,  Radial  —  — A  term  some- 
times used  instead  of  pole-armature.  (See 
Armature,  Pole.) 

Armature,  Ring A  dynamo-electric 

machine  armature,   the   coils  of  which  are 
wound  on  a  ring-shaped  core. 
c 


Fig-  23-     Ring-Armature. 

A  ring-armature  is  shown  in  Fig.  23,  together 
with  the  disposition  of  the  coils  and  their  connec- 
tion to  the  segments  of  the  commutator. 

Armature,  Shuttle A  variety  of 

drum  armature  in  which  a  single  coil  of 
wire  is  wound  in  an  H -shaped  groove  formed 
in  a  bobbin  shaped  core. 

The  old  form  of  Siemens-armature. 

Armature,  Single-Loop A  closed 

conducting  circuit  consisting  of  a  single  loop, 
capable  of  revolving  in  a  magnetic  field  so  as 
to  cut  its  lines  of  force. 

Armature,  Spider. — (See  Spider,  Arma- 
ture) 


Arm.] 


31 


Arr. 


Armature,  Spherical A  dynamo- 
electric  machine  armature,  the  coils  of  which 
are  wound  on  a  spherical  iron  core. 

The  Thomson- Houston  dynamo,  which  is  the 
only  machine  employing  an  armature  of  this  type, 
has  its  armature  formed  by  wrapping  three  coils 
of  insulated  wire  on  a  core  of  iron  so  shaped  as 
to  insure  an  approximately  spherical  armature 
when  wrapped. 

Armature,  Toothed-Ring  —  — An  ar- 
mature, the  core  of  which  is  in  the  shape  of 
a  ring,  provided  with  a  number  of  teeth  in  the 
spaces  between  which  the  armature  coils  are 
placed. 

Armature,  Unipolar  —  — A  dynamo- 
electric  machine  armature  whose  polarity  is 
not  reversed  during  its  rotation  in  the  field 
of  the  machine. 

Armature,  Ventilation  of —  — A  pro- 
cess for  insuring  the  free  passage  of  air 
through  the  armature  of  a  dynamo-electric 
machine  in  order  to  prevent  overheating. 

Armor  of  Cable. — (See  Cable,  Armor  of.) 

Armored  Cable. — (See  Cable,  Armored?) 

Armored  Conductor. — (See  Conductor, 
Armored!) 

Arms,  Bridge  or  Balance  —  — The 
electric  resistances,  in  the  electric  balance  or 
bridge.  (See  Bridge,  Electric!) 


Zn    C 
Fig.  24.    Arms  of  Balance. 

An  unknown  resistance,  such,  for  example,  as 
D,  Fig.  24,  is  measured  by  proportioning  the 
known  resistances,  A,  C  and  B,  so  that  no  current 
flows  through  the  galvanometer  G,  across  the 
circuit  or  bridge  M  G  N. 

Arms,  Proportionate The  two  re- 
sistances or  arms  of  an  electric  bridge  whose 
relative  or  proportionate  resistances  only  are 
required  to  be  known  in  order  to  determine, 


in  connection  with  a  known  resistance,  the 
value  of  an  unknown  resistance  placed  in  the 
remaining  arm  of  the  bridge. 

Thus  is  Fig.  24,  A  and  B,  are  the  proportionate 
arms. 

Arrangement  or  Deyice,  Electromotive 

A  term  sometimes  employed  to  rep- 
resent a  dynamo-electric  machine,  voltaic  cell 
or  other  electric  source,  by  means  of  which 
electromotive  force  can  be  produced. 

Electric  sources  do  not  produce  electric  cur- 
rents, but  differences  of  potential  or  electro- 
motive force.  Electric  sources  are  therefore  very 
properly  termed  electromotive  devices. 

Arrester,  Lightning  —  — A  device  by 
means  of  which  the  apparatus  placed  in  any 
electric  circuit  is  protected  from  the  destruc- 
tive effects  of  a  flash  or  bolt  of  lightning. 

In  the  phenomena  of  lateral  induction  and 
alternative  path,  we  have  seen  the  tendency  of  a 
disruptive  discharge  to  take  a  short-cut  across  an 
intervening  air  space,  rather  than  through  a 
longer  though  better  conducting  path.  Most 
lightning  arresters  are  dependent  for  their  opera- 
tion on  this  tendency  to  lateral  discharge.  (See 
Induction,  Lateral.  Path,  Alternative.} 

A  form  of  lightning  arrester  is  shown  in  Fig.  25. 


Fig.  23-    Comb  Lightning- Arrester. 

The  line  wires,  A  and  B,  are  connected  by  two 
metallic  plates  to  C  and  D,  respectively. 

These  plates  are  provided  with  points,  as  shown, 
and  placed  near  a  third  plate,  connected  to  the 
ground  by  the  wire  G.  Should  a  bolt  strike  the 
line,  it  is  discharged  to  the  .earth  through  the 
wire  G. 

Various  forms  are  given  to  lightning  arresters 
of  this  type.  The  projections  are  sometimes  placed 
on  the  ground-connected  plate  as  well  as  on  the 
plates  connected  to  line  wires.  This  form  is 
sometimes  called  a  comb  arrester,  or  protector. 


Arr.] 


[Ast. 


Arrester,   Lightning,   Comb    -         —A 

term  sometimes  applied  to  a  lightning  ar- 
rester in  which  both  the  line  and  ground 
plates  are  furnished  with  a  series  of  teeth, 
like  those  on  a  comb.  (See  Arrester,  Light- 
ning) 

Arrester,  Lightning,  Counter-Electro- 
motive Force  —  — A  lightning  arrester, 
in  which  the  passage  of  the  discharge  through 
the  instruments  to  be  protected  is  opposed 
by  a  counter-electromotive  force,  generated 
by  induction  on  the  passage  of  the  discharge 
of  the  bolt  to  earth. 

The  counter-electromotive  force  lightning  ar- 
rester is  an  invention  of  Professor  Elihu  Thomson. 

It  assumes  a  variety  of  forms.  In  the  shape 
shown  in  Fig.  26,  the  line  circuit  of  the  dynamo, 


Fig.  26.     Counter-Electromotive  Force  Lightning 
Arrester. 

D,  has  one  end  connected  to  ground,  and  the 
other  end  has  two  conducting  paths  to  ground. 
One  of  these  paths  is  through  the  ordinary  comb- 
protector  at  P,  by  the  ground  plate  E;  this  cir- 
cuit includes  a  few  turns 
of  wire  C'.  The  other 
path  is  through  a  corres- 
ponding coil  C,  either 
interior  or  exterior  to  C', 
so  as  to  be  within  its  in- 
ductive field.  As  will  be 
[  E  I  seen  from  the  figure,  C,  is 

Fig.  27.  Counttr-Elec-  connected  through  the 
tromotive  force  Light-  machine  to  the  ground. 
ning  Arrester.  The  induction  coils  C 

and   C',    are    thoroughly    insulated    from     each 
other. 

Should  a  lightning  flash  or  other  static  discharge 
pass  through  the  circuit  C',  which  is  of  compara- 
tively low  self-induction,  a  counter-electromotive 
force  is  produced  in  the  other  coil  C,  which 
protects  the  line  circuit. 


In  the  form  of  lightning  arrester  shown  in 
Fig.  27,  the  coil  in  the  path  of  the  direct  light- 
ning discharge  is  formed  into  an  exterior  mesh  or 
net  work  surrounding  the  dynamo  to  be  pro- 
tected. In  this  case,  the  coils  of  the  dynamo  act 
as  the  secondary  coils  in  which  the  counter  elec- 
tromotive force  is  set  up. 

Arrester,  Lightning,  Transformer 

— A  form  of  lightning  arrester  designed  for 
the  protection  of  transformers. 

The  Thomson  arrester  for  transformers  oper- 
ates on  the  same  principle  as  his  arc-line  pro- 
tector. In  the  latter  the  arc,  when  formed, 
is  blown  out  by  the  action  of  the  field  of  an 
electro-magnet.  This  arc  is  formed  on  curved 
metallic  bows,  one  of  which  is  connected  to  line 
and  the  other  to  earth.  The  arc  is  formed  at  the 
smallest  interval  between  the  bows,  and  is  extin- 
guished by  being  driven  by  action  of  a  magnetic 
field  toward  greatest  interval. 

Arrester  Plate  of  Lightning  Protector.— 
(See  Plate,  Arrester,  of  Lightning  Pro- 
tector^ 

Arrester  Plates. — (See  Plates,  Arrester^ 

Articulate  Speech. — (See  Speech,  Articu- 
lated, 

Artificial  Carbons.— (See  Carbons,  Arti- 
ficial^ 

Artificial  Illumination.— (See  Illumina- 
tion, Artificial.} 

Artificial  Line.— (See  Line,  Artificial.} 

Artificial  Magnet— (See  Magnet,  Arti- 
ficial.} 

Asphyxia. — Suspended  respiration,  result- 
ing eventually  in  death,  from  non-aeration  of 
the  blood. 

In  cases  of  insensibility  by  an  electric  shock  a 
species  of  asphyxia  is  sometimes  brought  about. 
This  is  due,  probably,  to  the  failure  of  the  nerves 
and  muscles  that  carry  on  respiration.  The  exact 
manner  in  which  death  by  electrical  shock  results 
is  not  known.  (See  Death,  Electric. } 

Assy m  metrical  Resistance. — (See  Resist- 
ance, Assymmetrical.) 

Astatic. — Possessing  no  directive  power. 

Usually  applied  to  a  magnetic  or  electro-mag- 
netic-device which  is  free  from  any  tendency  to 
take  a  definite  position  on  account  of  the  earth's 
magnetism. 


Ast,] 


[Ato. 


Astatic  Circuit.— (See  Circuit,  Astatic} 

Astatic  Couple.— See  Couple,  Astatic.} 

Astatic  Galvanometer. — (See  Galvanom- 
ster,  Astatic.) 

Astatic  Needle.— (See  Needle,  Astatic.} 

Astatic  Pair.— (See  Pair,  Astatic} 

Astatic  System.— (See  System,  Astatic} 

Astronomical  Meridian. — (See  Meridian, 
Astronomical} 

Asymptote  of  Curve. — (See  Curve,  Asymp- 
tote of} 

Atmosphere,  An A  unit  of  gas  or 

fluid  pressure  equal  to  about  1 5  pounds  to  the 
square  inch. 

At  the  level  of  the  sea  the  atmosphere  exerts  a 
pressure  of  about  15  pounds  avoirdupois,  or, 
more  accurately,  14.73  pounds,  on  every  square 
inch  of  the  earth's  surface.  This  value  has  there- 
fore been  taken  as  a  unit  of  fluid  pressure. 

For  more  accurate  measurements  pounds  to  the 
square  inch  are  employed. 

In  the  metric  system  of  weights  and  measures 
an  atmosphere  is  considered  equal  to  1,033 
grammes  per  square  centimetre. 

Atmospheric  pressures  are  measured  by  instru- 
ments called  Manometers.  (See  Manometer.) 

Atmosphere,  Residual The  traces 

of  air  or  other  gas  remaining  in  a  space  which 
has  been  exhausted  of  its  gaseous  contents 
by  a  pump  or  other  means. 

It  is  next  to  impossible  to  remove  all  traces  of 
air  from  a  vessel  by  any  known  form  of  pump  or 
other  appliance.  (See  Vacuum,  Absolute.) 

Atmosphere,  The  — The  ocean  of 

.air  which  surrounds  the  earth. 

The  atmosphere  is,  approximately,  composed, 
by  weight,  of  oxygen  23  parts,  and  nitrogen  77 
parts.  Besides  these  there  are  from  4  to  6  parts 
in  10,000  of  carbonic  acid  gas  (or  about  a  cubic 
inch  of  carbonic  acid  to  a  cubic  foot  of  air),  and 
varying  proportions  of  the  vapor  of  water. 

The  oxygen,  nitrogen  and  carbonic  acid  form 
the  constant  ingredients  of  the  atmosphere,  the 
vapor  of  water  the  variable  ingredient.  There 
are  in  most  localities  a  number  of  other  variable 
ingredients  present  as  impurities. 

Atmospheric  Electricity. — (See  Electric- 
ity, Atmospheric.) 


Atmospheric  Electricity,  Origin  of 

— (See  Electricity,  Atmospheric,  Origin  of.) 

Atom. — The  smallest  quantity  of  elemen- 
tary or  simple  matter  that  can  exist. 

An  ultimate  particle  of  matter. 

Atom  means  that  which  cannot  be  cut.  It  is 
generally  believed  that  material  atoms  are  abso- 
lutely unalterable  in  size,  shape,  weight  and  den- 
sity ;  that  they  can  neither  be  cut,  scratched, 
flattened,  nor  distorted  ;  and  that  they  are  un- 
affected in  size,  density,  or  shape,  by  heat  or 
cold,  or  by  any  known  physical  force. 

Although  almost  inconceivably  small,  atoms 
nevertheless  possess  a  definite  size  and  mass. 
According  to  Sir  William  Thomson,  the  smallest 
visible  organic  particle,  1-4000  of  a  millimetre  in 
diameter,  will  contain  about  30,000,000  atoms. 

Atom,  Closed-Magnetic  Circuit  of  — 

(See  Circuit,  Closed-Magnetic,  of  Atom} 

Atom,  Gramme  -  — Such  a  number 
of  grammes  of  any  elementary  substance  as  is 
numerically  equal  to  the  atomic  weight  of 
the  substance. 

The  gramme-atom  of  a  substance  represents 
the  number  of  calories  required  to  raise  the  tem- 
perature of  one  gramme  of  that  substance  through 
I  degree  C.  (See  Heat,  Atomic.  Calorie.)  Thus, 
in  the  case  of  chlorine,  whose  atomic  weight  is 
35.5,  its  gramme-atom  is  35.5  ;  consequently 
35.5  small  calories  of  heat  would  be  required  to 
raise  one  gramme-atom  of  chlorine  through  i 
degree  C. 

Atom  of  Electricity.— (See  Electricity, 
Atom  of} 

Atom,  Vortex A  number  of  particles 

of  the  universal  ether  moving  in  the  manner 
of  a  vortex  ring. 

The  theory  of  vortex  atoms,  so  formed  from 
vortex  rings,  was  propounded  by  Sir  William 
Thomson  in  order  to  explain  how  a  readily  mov- 
able substance,  like  the  universal  ether,  could  be 
made  to  possess  the  properties  of  a  rigid  solid.  If 
it  be  granted  that  a  vortex  motion  has  once  been 
imparted  to  the  universal  ether,  Thomson  shows 
that  such  rings  would  be  indestructible.  (See 
Matter,  Thomson's  Hypothesis  of.) 

Atomic  Attraction.  —  (See  Attraction, 
Atomic} 


Ato.] 


34 


[All. 


Atomic  Capacity. — (See  Capacity,  Atom- 
ic) 

Atomic  Currents. — (See  Currents,  Atom- 
ic) 

Atomic  Energy. — (See  Energy,  Atomic) 
Atomic  Heat— (See  Heat,  Atomic) 

Atomic  or  Molecular  Induced  Currents. 

— (See    Currents,   Induced,   Molecular     or 
Atomic) 
Atomic  Weight.— (See  Weight,  Atomic) 

Atomicity. — The  combining  capacity  of 
the  atoms. 

The  relative  equivalence  of  the  atoms  or 
their  atomic  capacity. 

The  elementary  atoms  do  not  always  combine 
atom  for  atom.  Some  single  atoms  of  certain 
elements  will  combine  with  two,  three,  four,  or 
even  more  atoms  of  another  element. 

The  value  of  the  atomic  capacity  of  an  atom  is 
also  called  its  quantivalence  or  valency. 
Elements  whose  atomic  capacity  is — 

One,     are  called  Monads,     or  Univalent. 
Two,         "  Dyads,        "  Bivalent. 

Three,      "  Triads,        "  Trivalent. 

Four,         "  Tetrads,       "  Quadrivalent. 

Five,          "  Pentads,      "  Quinquivalent 

Six,  "  Hexads,      "  Sexivalent. 

Seven,       "  Heptads,    "  Septivalent. 

Atomization. — The  act  of  obtaining  liquids 
in  a  spray  of  finely  divided  particles. 

In  most  cases  the  term  is  not  literally  correct, 
as  each  of  the  smallest  particles  so  obtained  usu- 
ally consist  of  many  thousands  of  atoms. 

Atomize. — To  separate  into  a  fine  spray  by 
means  of  an  atomizer.  (See  Atomizer) 

Atomizer. — An  apparatus  for  readily  ob- 
taining a  finely  divided  jet  or  spray  of  liquid. 

A  jet  of  steam,  or  a  blast  of  air,  is  driven  across 
the  open  end  of  a  tube  that  dips  below  the  surface 
of  the  liquid  to  be  atomized.  The  partial  vacuum 
so  formed  draws  tip  the  liquid,  which  is  then 
blown  by  the  current  into  a  fine  spray. 

Attract. — To  draw  together. 
Attracted-Disc  Electrometer.— (See  Elec- 
trometer, Attracted-Disc) 

Attract  ins?. — Drawing  together. 


Attraction.— Literally  the  act  of  drawing 
together. 

In  science  the  name  attraction  is  given  to  a 
series  of  unknown  causes  which  effect,  or  are  as- 
sumed to  effect,  the  drawing  together  of  atoms, 
molecules  or  masses. 

Attraction  and  repulsion  underlie  nearly  all 
natural  phenomena.  While  their  effects  are  well 
known,  it  is  doubtful  if  anything  is  definitely 
known  of  their  true  causes. 

Since  attraction,  pure  and  simple,  necessitates 
the  belief  in  action  at  a  distance,  an  action  which 
is  now  generally  discredited,  we  must,  strictly 
speaking,  regard  the  term  attraction  as  being  but 
a  convenient  substitution  of  the  effect  for  the 
cause. 

It  would  appear  much  more  reasonable  to  re- 
gard the  effects  of  attraction  as  produced  by  a 
true  push  exerted  from  the  outside  of  the  bodies. 
According  to  this  notion,  two  masses  of  matter 
undergoing  attraction  are  pushed  together  rather 
than  drawn  or  attracted  together. 

It  has  been  suggested  that  gravitation  may  per- 
haps be  an  effect  of  a  longitudinal  motion  or  vibra- 
tory thrust  in  the  universal  ether.  If  this  is  the 
case,  and  the  ether  is  sensibly  incompressible,  the 
velocity  of  gravitation,  it  would  appear,  should  be 
almost  infinite. 

Attraction,  Atomic  —  —The  attraction 
which  causes  the  atoms  to  combine.  (See 
Affinity,  Chemical) 

In  the  opinion  of  Lodge,  atomic  attraction  is 
the  result  of  the  attraction  of  dissimilar  charges  of 
electricity  possessed  by  all  atoms,  which  are  capa  - 
ble  of  uniting  or  entering  into  chemical  combi- 
nation. (See  Electricity,  Atom  of) 

Attraction,  Capillary  —  —The  molec- 
ular attractions  that  are  concerned  in 
capillary  phenomena.  (See  Capillarity) 

Attraction,  Electro-Dynamic  —  —The 
mutual  attraction  of  electric  currents,  or  of 
conductors  through  which  electric  currents 
are  passing.  (See  Dynamics,  Electro) 

Attraction,  Electro-Magnetic  —  —The 
mutual  attraction  of  the  unlike  poles  of 
electro-magnets.  (See  Magnet,  Electro.} 

Attraction,  Electrostatic  -  —The 
mutual  attraction  exerted  between  unlike 
electric  charges,  or  bodies  possessing  unlike 
o'ectric  charges. 


Alt.] 


35 


[Aur. 


For  example,  the  pith  ball  supported  on  an  in- 
sulated string  is  attracted,  as  shown  at  A,  Fig.  28, 


Fig.  28.     Electrostati 
Attraction. 


Fig:  29.    Electrostati 
Repulsion. 


by  a  bit  of  sulphur  which  has  been  briskly  rubbed 
by  a  piece  of  silk.  As  soon,  however,  as  the  ball 
touches  the  sulphur  and  receives  a  charge,  it  is 
repelled,  as  shown  at  B,  Fig.  29. 

These  attractions  ai  d  repulsions  are  due  to  the 
effects  of  electrostatic  induction.  (See  Induction, 
Electrostatic.} 

Attraction,  Magnetic  —  —  The  mutual 
attraction  exerted  between  unlike  magnet 
poles. 

Magnetic  attractions  and  repulsions  are  best 
shown  by  means  of  the  magnetic  needle  N  S, 
Fig.  30.  The  N.  pole  of  an  approached  magnet 


Fig.  30.      Magnetic  Attraction. 

attracts  the  S.  pole  of  the  needle  but  repels  the 
N.  pole. 

The  laws  of  magnetic  attraction  and  repulsion 
may  be  stated  as  follows,  viz.: 

(i  )  Magnet  poles  of  the  same  name  repel  each 
other;  thus,  a  north  pole  repels  another  north 
pole,  a  south  pole  repels  another  south  pole. 


Fig.  31.     floating 
Magnet. 


(2.)  Magnet  poles  of  unlike  names  attract  each 
other;  thus  a  north  pole 
attracts  a  south  pole,  or 
a  south  pole  attracts  a 
north  pole. 

A  small  bar  magnet, 
N  S,  Fig.  31,  laid  on  the 
top  of  a  light  vessel  floating  on  the  surface  of  a 
liquid,  may  be  readily  employed  to  illustrate  the 
laws  of  magnetic  attraction  and  repulsion. 

Attraction,  Mass  —  —The  mutual  at- 
traction exerted  between  masses  of  matter. 
(See  Gravitation} 

Attraction,  Molar A  term  some- 
times employed  for  mass  attraction. 

Gravitation  is  an  example  of  mass  attraction, 
where  the  mass  of  the  earth  attracts  the  mass  of 
some  body  placed  near  it.  (See  Gravitation.} 

Attraction,  Molecular The  mutual 

attraction     exerted      between     neighboring 
molecules. 

The  attraction  of  like  molecules,  or  those  of  the 
same  kind  of  matter,  is  called  Cohesion  ;  that  of 
unlike  molecules,  Adhesion. 

The  tensile  strength  of  iron  or  steel  is  due  to 
the  cohesion  of  its  molecules.  Paint  adheres  to 
wood,  or  ink  to  paper,  by  cohesion  or  the  attrac- 
tion between  the  unlike  molecules. 

Attraction  of  Grayitation. — A  term  gen- 
erally applied  to  the  mutual  attraction  be- 
tween masses.  (See  Gravitation^) 

Attractions  and  Repulsions  of  Currents. 
— (See  Currents,  Attractions  and  Repulsions 
of} 

Audiphone. — A  thin  plate  of  hard  rubber 
held  in  contact  with  the  teeth,  and  maintained 
at  a  certain  tension  by  strings  attached  to  one 
of  its  edges,  for  the  purpose  of  aiding  the 
hearing. 

The  plate  is  so  held  that  the  sound-waves  from 
a  speaker's  voice  impinge  directly  against  its  flat 
surface.  It  operates  by  means  of  some  of  the 
waves  being  transmitted ,  to  the  ear  directly 
through  the  bones  of  the  head. 

The  audiphone  is  sometimes  called  a  denti- 
phone. 

Aural  Electrode. — (See  Electrode,  Aural} 

Aurora  Australis. — The  Southern  Light. 

A  name  given  to  an  appearance  in  the  south- 


Aur.] 


[Aut. 


ern  heavens  similar  to  that  of  the  Aurora 
Borealis.  (See  Aurora  Borealis.} 

Aurora  Borealis. — The  Northern    Light. 

Luminous  sheets,  columns,  arches,  or  pillars 
of  pale,  flashing  light,  generally  of  a  red  color, 
seen  in  the  northern  heavens. 

The  auroral  light  assumes  a  great  variety  of  ap- 
pearances, to  which  the  terms  auroral  arch,  bands, 
cor  once,  curtains  and  streamers  are  applied. 

The  exact  cause  of  the  aurora  is  not  as  yet 
known.  It  would  appear,  however,  beyond  any 
reasonable  doubt,  that  the  auroral  flashes  are  due 
to  the  passage  of  electrical  discharges  through  the 
upper,  and  therefore  rarer,  regions  of  the  atmos- 
phere. The  intermittent  flashes  of  light  are  prob- 
ably due  to  the  discharges  being  influenced  by  the 
earth's  magnetism. 

Auroras  are  frequently  accompanied  by  mag- 
netic storms.  (See  Storm,  Magnetic. ) 

The  occurrence  of  auroras  is  nearly  always 
simultaneous  with  that  of  an  unusual  number  of 
sun  spots.  Auroras  are  therefore  probably  con- 
nected with  outbursts  of  the  solar  energy.  (See 
Spots,  Sun.) 

The  auroral  light  examined  by  the  spectroscope 
gives  a  spectrum  characteristic  of  luminous  gaseous 
matter,  i.  e.,  contains  a  few  bright  lines;  but,  ac- 
cording to  S.  P.  Thompson,  this  spectrum  is  pro- 
duced by  matter  that  is  not  referable  with  cer- 
tainty to  that  of  any  known  substance. 

Whatever  may  be  the  exact  cause  of  auroras, 
their  appearance  is  almost  exactly  reproduced  by 
the  passage  of  electric  discharges  through  vacua. 

Aurora  Polaris. — A  general  term  some- 
times applied  to  aurora  in  the  neighborhood 
of  either  pole,  or  in  either  the  northern  or 
the  southern  hemisphere. 

Auroral  Arch. — (See  Arch,  Auroral?) 

Auroral  Bands. — (See  Bands,  Auroral} 

Auroral  Coronse. — (See  Corona,  Au- 
roral?) 

Auroral  Curtain. — (See  Curtain,  Au- 
roral.} 

Auroral  Flashes. — (See  Flashes,  Auroral.} 

Auroral  Light — (See  Light,  Auroral?) 

Auroral    Storm.— (See  Storm,  Auroral} 

Auroral  Streamer. — (See  Streamer,  Au- 
roral} 

Auroras    and    Magnetic   Storms,   Peri- 


odicity of Observed  coincidences  be- 
tween the  occurrence  of  auroras,  magnetic 
storms,  and  sun-spots. 

The  occurrence  of  auroras,  or  magnetic  storms, 
at  periods  of  about  eleven  years  apart,  corre- 
sponds to  the  well-known  eleven-year  sun-spot 
period. 

The  period  also  agrees  with  a  variation  in  the 
magnetic  declination  of  any  place,  which,  accord- 
ing to  Sabine,  occurs  once  in  every  eleven  years. 

Austral  Magnetic  Pole.— (See  Pole,  Mag- 
netic, Austral} 

Autographic  Telegraphy.  —  (See  Teleg- 
raphy, Autographic} 

Automatic  Annunciator  Drop.  —  (See 
Drop,  Annunciator,  Automatic} 

Automatic  Bell.— ,  See  Bell,  Automatic 
Electric} 

Automatic  Contact  Breaker.— (See  Con- 
tact Breaker,  Automatic} 

Automatic  Cut-Out.— (See  Cut-Out,  Au- 
tomatic} 

Automatic  Cut-Out  for  Multiple-Connect- 
ed  Electro-Receptive  Devices. — (See  Cut- 
Out,  Automatic,  for  Multiple-Connected 
Electro-Receptive  Devices} 

Automatic  Cut-Out  for  Series-Connected 
Electro-Receptive  Devices.  —(See  Cut-Out, 
Automatic ,  for  Series-Connected  Electro-Re- 
ceptive Devices} 

Automatic  Drop.  —  (See  Drop,  Auto- 
matic} 

Automatic  Electric  Burner. — (See  Burn- 
er, Automatic  Electric} 

Automatic  Electric  Safety  System  for 
Railroads. — (See  Railroads,  Automatic  Elec- 
tric Safety  System  for} 

Automatic  Fire-Alarm.  —  (See  Alarm, 
Fire,  Automatic} 

Automatic  Gas  Cut-Off.  — (See  Cut-Off, 
Automatic  Gas} 

Automatic  Indicator.  —  (See  Indicator, 
Automatic} 

Automatic  Make-and-Break.— (See  Make- 
and-Break,  Automatic} 

Automatic  Oiler. — (See  Oiler,  Automatic. 


Aut.] 


37 


[B.  A,  U. 


Automatic  Paper-Winder. — (See  Winder, 
Telegraphic  Paper.} 

Automatic  Regulation. — (See  Regulation, 
Automatic.) 

Automatic  Regulator. — (See  Regulator, 
Automatic?) 

Automatic  Search-Light.  —  (See  Light, 
Search,  Automatic?) 

Automatic  Switch  for  Incandescent  Elec- 
tric Lamp. — (See  Switch,  Automatic,  for 
Incandescent  Electric  Lamp?) 

Automatic  Telegraphy.  —  (S  e  e  Teleg- 
raphy, Automatic?) 

Automatic  Telephone  Switch.  —  (See 
Switch,  Telephone,  Automatic?) 

Automatic  Time  Cut-Outs.— (See  Cut- 
Out,  Automatic  Time?) 

Automatic  Variable  Resistance.— (See 
Resistance,  Variable,  Automatic?) 

Automatically  Regulable. — (See  Regula- 
ble, Automatically?) 

Automobile  Torpedo.— (See  Torpedo,  Au- 
tomobile?) 

Average  or  Mean  Electromotive  Force. — 
(See  Force,  Electromotive,  Average,  or 
Mean?) 

Axes  of  Co-ordinates. — (See  Co-ordinates, 
Axes  of?) 

Axial  Magnet.— (See  Magnet,  Axial?) 

Axis,  Magnetic The  line  around 

which  a  magnetic  needle,  free  to  move,  but 
which  has  come  to  rest  in  a  magnetic  field, 
can  be  turned  without  changing  the  set  or 
direction  in  which  it  has  come  to  rest. 

Axis,  Magnetic,  of  a  Straight  Needle 

— A  straight  line  drawn  through  the  magnet, 
joining  its  poles. 


The  magnetic  axis  of  a  straight  needle  may  be 
regarded  as  a  straight  line  passing  through  the 
poles  of  the  needle  and  its  point  of  support. 

The  magnetic  axis  may  not  correspond  with 
the  geometric  axis  of  the 
needle.  This  leads  to 
an  error  in  reading  the 
true  direction  in  which 
the  needle  is  pointing, 
which  must  be  cor- 
rected. Thus,  the  nee- 
dle N  S,  Fig.  32,  points 
to  31  degrees  on  the 
scale.  In  reality,  if  the 
magnetic  axis  of  the 
needle  lies  in  the  line 
N'  S',  the  true  deflec- 
tion of  the  needle  is  only 
28  degrees. 


Fig-.  33.     Magnet! 
Axis. 


Axis  of  Abscissas. — (See  Abscissas,  Axis 
of?) 

Axis  of  Ordinates.— (See  Ordinates,  Axis 
of?) 

Azimuth. — In  astronomy,  the  angular  dis- 
tance between  an  azimuth  circle  and  the 
meridian. 

The  azimuth  of  a  heavenly  body  in  the  North- 
ern Hemisphere  is  measured  on  the  arc  of  the 
horizon  intercepted  between  the  north  point  of 
the  horizon  and  the  point  where  the  great  circle 
that  passes  through  the  heavenly  body  cuts  the 
horizon. 

Azimuth  Circle.— (See   Circle,  Azimuth?) 

Azimuth  Compass. — (See  Compass,  Azi- 
muth?) 

Azimuth,  Magnetic The  arc  inter- 
cepted on  the  horizon  between  the  magnetic 
meridian  and  a  great  circle  passing  through 
the  observed  body. 


B. — A  contraction  used  in  mathematical 
writings  for  the  internal  magnetization,  or  the 
magnetic  induction,  or  the  number  of  lines  of 
force  per  square  centimetre  in  the  magnetized 
material. 

This  contraction  for  internal  magnetization  is, 


in  most  mathematical  treatises,  printed  in  bold- 
faced type. 

B.  A.  Ohm.— (See  Ohm,  B.  A?) 

B.  A.  U. — A  contraction  sometimes  em- 
ployed for  the  British  Association  unit  or  ohm. 


B.  W.  G.] 


[Bal. 


B.  W.  G.— A  contraction  for  Birmingham 
wire  gauge.  (See  Gauge,  Birmingham 
Wire.) 

A  contraction  sometimes  used  for  the  new 
British  wire  gauge. 

Back  Electromotive  Force.— (See  Force, 
Electromotive,  Back?) 

Back-Stroke  of  Lightning.— (See  Light- 
ning, Back- Stroke  of.) 

Bain's  Chemical  Recorder.— (See  Re- 
•corder,  Chemical,  Bain's.) 

Bain's  Printing  Solution.— (See  Solution, 
Bain's  Printing.) 

Balance  Arms. — (See  Arms,  Bridge  or 
Balanced) 

Balance,  Bi-fllar  Suspension An 

instrument  similar  in  construction  to  Cou- 
lomb's torsion  balance,  but  in  which  the 
needle  is  hung  by  two  separate  fibres  instead 
of  by  a  single  one.  (See  Balance,  Coulomb's 
Torsion.  Suspension,  Bi-filar.) 

Balance,  Centi-AmpSre An  arr- 

meter  in  the  form  of  a  balance,  whose  scale  is 
graduated  to  give  direct  readings  in  centi- 
amperes. 

Ampere  balances  giving  readings  in  various 
decimals  or  multiples  of  amperes  have  been  de- 
vised by  Sir  William  Thomson.  The  strength  of 
current  passing  is  determined  by  the  action  on  a 
movable  ring  or  coil,  placed  between  two  fixed 
rings  or  coils. 

The  movable  ring  is  in  a  horizontal  plane 
nearly  midway  between  the  two  fixed  rings. 
The  fixed  rings  are  traversed  by  the  current 
in  opposite  directions,  so  that  one  attracts 
and  the  other  repels  the  movable  ring.  The 
movable  ring  is  attached  to  one  end  of  a  horizon- 
tal balance  arm,  and  a  similar  movable  ring,  also 
provided  with  attracting  and  repelling  fixed  rings, 
is  attached  to  the  opposite  end  of  the  balance  arm. 
In  order  to  avoid  disturbance  of  horizontal  com- 
ponents of  terrestrial,  or  of  local  magnetic  force, 
the  current  is  sent  in  the  same  direction  through 
the  two  movable  rings.  The  balancing  is  effected 
by  means  of  a  weight,  sliding  on  a  nearly  hori- 
zontal arm  attached  to  the  balance.  A  counter- 
poi^e  weight  is  used  in  connection  with  the  sliding 
weight. 


A  standard   Thomson    centi-ampere    balance 
is  shown  in  Fig.  33.     In  measuring  a  current, 


F'S-  33-      Centi-Amplre  Balance. 
the  weight  is   moved  along  the  scale  until  the 
balance  comes  to  rest. 

Balance,  Composite — A    balance 

form  of  ammeter  devised  by  Sir  William  Thom- 
son, which  can  be  used  for  an  ampere-meter,  a 
watt-meter,  or  a  volt-meter,  according  to  the 
manner  in  which  its  sets  of  fine  and  coarse 
wire  coils  are  connected.  (See  Balance, 
Centi- Ampere.) 

Balance,  Coulomb's  Torsion An 

apparatus  to  measure  the  force  of  electric  or 
magnetic  repulsion  between  two  similarly 
charged  bodies,  or  between  two  similar  mag- 
net poles,  by  opposing  to  such  force  the  tor- 
sion of  a  thin  wire. 

The  two  forces  balance  each  other  ;  hence  the 
origin  of  the  name. 


Fig.  34.     Coulomb's  Torsion  Balance. 

Fig.    34  represents   a   Coulomb    torsion  bal- 
ance, adapted  to  the  measurement  of  the  force 


Bal.] 


39 


[Bal. 


of  electrostatic  repulsion.  A  delicate  needle  of 
shellac,  having  a  small  gilded  pith  ball  at  one  of 
its  ends,  is  suspended  by  a  fine  metallic  wire.  A 
proof -plane,  B,  is  touched  to  the  electrified  surface 
whose  charge  is  to  be  measured,  and  is  then 
placed  as  shown  in  the  figure.  (See  Plane,  Proof.) 
There  is  a  momentary  attraction  of  the  needle, 
anvx  t..^~«  a  repulsion,  which  causes  the  needle  to 
be  moved  a  ^.'^in  distance  from  the  ball  on  the 
proof-plane.  This  distance  is  measured  in  degrees 
on  a  graduated  circle  a  a,  marked  on  the  instru- 
ment. The  force  of  the  repulsion  is  calculated  by 
determining  the  amount  of  torsion  required  to 
move  the  needle  a  certain  distance  toward  the 
ball  of  the  electrified  proof-plane. 

This  torsion  is  obtained  by  the  movement  of  the 
torsion  head  D,  the  amount  of  which  motion  is 
measured  on  a  graduated  circle  at  D.  The 
measurement  is  based  on  the  fact  that  the  force  re- 
quired to  twist  a  wire  is  proportional  to  the  angle 
of  torsion. 

Balance,  Deci-Ampere An  ammeter 

in  the  form  of  a  balance,  whose  scale  is 
graduated  to  give  direct  readings  in  deci- 
amperes.  (See  Balance,  Centi-Ampere^) 

Balance,  Deka-Ampere  — An  am- 
meter in  the  form  of  a  balance,  whose  scale  is 
graduated  to  give  direct  readings  in  deka- 
amperes.  (See  Balance,  Centi-Ampere^) 

Balance,  Electric A  term  fre- 
quently used  for  Wheatstone's  electric  bridge. 
(See  Bridge,  Electric!) 

The  electric  bridge  is  sometimes  called  a  balance 
because,  when  in  use  in  measuring  resistances, 
one  resistance  or  set  of  resistances  balances  an- 
other resistance  or  set  of  resistances. 

Balance,  Hekto-Ampdre An  am- 
meter in  the  form  of  a  balance,  whose  scale 
is  graduated  to  give  direct  readings  in  hekto- 
amperes.  (See  Balance,  Centt'-Ampere.) 

Balance  Indicator.— (See  Indicator,  Bal- 
ance.) 

Balance,     Induction,     Hughes' 

An  apparatus  for  the  detection  of  the  presence 
of  a  metallic  or  conducting  substance  by  the 
aid  of  induced  electric  currents. 

Hughes'  induction  balance  is  shown  in  Fig.  35. 

A,  B,  C  and  D  are  bobbins,  wound  with  about 
300  feet  of  No.  32  copper  wire.  The  coils  are 


connected  as  shown,  A  and  B,  in  the  circuit  of  a 
battery,  and  C  and  D,  in  the  circuit  of  a  telephone. 
The  coils,  A  and  B,  and  C  and  D,  are  placed  at 


Fig  33.     Hughes'  Induction  Balance. 

such  a  distance  apart  as  to  prevent  any  mutual 
induction  occurring  between  them.  The  coils 
are  so  joined  that  the  direction  of  the  induction 
of  A,  on  C,  is  opposite  to  that  of  B,  on  D. 

The  coils,  A  and  B,  then  act  as  primaries,  and  C 
and  D,  as  secondaries.  In  the  battery  circuit  is  an 
interrupter  I,  which  is  caused  to  continually  make 
and  break  the  circuit. 

The  coils  are  so  adjusted  that  the  opposing 
secondary  coils  produce  but  little  noise  to  one 
listening  at  the  telephone.  This  can  readily  be 
done  by  the  adjusting  of  a  single  pair  of  coils. 

If  a  single  coin  or  mass  of  metal  be  introduced 
between  either  A  and  C,  or  B  and  D,  or  even 
above  one  of  the  coils,  as  at  d,  the  balance 
will  be  disturbed,  since  some  of  the  induction  is 
now  expended  in  producing  electric  currents  in 
the  interposed  metal,  and  a  sound  will  therefore 
be  heard  in  the  telephone.  But  if  precisely  similar 
metals  are  placed  in  similar  positions,  between  A 
and  C,  and  B  and  D,  no  sound  is  heard  in  the 
telephone,  since  the  inductive  effects  due  to  the 
two  metals  are  the  same. 

The  slightest  difference,  however,  either  in 
composition,  size  or  position,  destroys  the  balance, 
and  causes  a  sound  to  be  heard  in  the  telephone. 

A  spurious  coin  is  thus  readily  detected  when 
compared  with  a  genuine  coin. 

A  somewhat  similar  instrument  has  been  em- 
ployed to  detect  and  locate  a  bullet  or  other  for- 
eign metallic  substance  in  the  human  body. 

In  order  to  determine  the  amount  of  the  dis- 
turbance, an  instrument  called  a  sonometer  is  . 
used  (See  Sonometer,  Hughes'),  in  which  a  single 
secondary  coil,  placed  in  the  circuit  of  a  telephone, 
slides  on  a  graduated  bar  between  two  fixed 
primary  coils,  so  wound  as  to  exert  equal  and  op- 
posite inductions  on  the  secondary.  When,  there- 
fore, the  secondary  is  exactly  in  the  middle  of  the 


Bal.] 


40 


[Bal. 


graduated  bar,  and  consequendy  exactly  midway 
between  the  two  fixed  primary  coils,  no  sounds  are 
heard  in  the  telephone,  but  when  moved  to  one 
side  or  the  other  the  sounds  are  heard.  Switches 
are  so  arranged  that  the  telephone  can  be  readily 
switched  from  the  induction  balance  to  the  tele- 
phone, or  vice  versa.  When,  therefore,  a  metallic 
disc  is>  placed  in  one  of  the  coils  of  the  induction 
balance,  and  a  noise  is  heard  in  the  telephone, 
the  coil  of  the  sonometer  is  shifted  so  that  the 
noise  heard  in  this  telephone  is  judged  by  the 
ear  to  be  equal,  and  the  comparison  can  then  be 
made  by  means  of  simple  calculations. 

The  following  table  gives,  in  arbitrary  values, 
the  results  of  various  experiments  as  to  the  sensi- 
tiveness in  this  respect  of  discs  of  different 
metals,  of  various  sizes  and  shapes  : 

Silver,  chemically  pure 125 

Gold 117 

Silver,  commercial 115 

Aluminium 112 

Copper too 

Zinc 80 

Bronze 75 

Tin 74 

Iron,  ordinary 53 

German  silver 5° 

Iron,  pure 40 

Copper,  alloyed 40 

Lead ; 58 

Antimony 35 

Bismuth IO 

Zinc,  alloyed 6 

Carbon 2 

;  —(Fleming.) 

An  inspection  of  this  table  shows  that  the  values 
found  for  different  metals  do  not  correspond  with 
their  electric  conducting  power,  although,  roughly 
speaking,  the  best  conductors  stand  at  the  top  of 
the  table,  and  the  worst  at  the  bottom.  The 
effects  appear  to  be  dependent  for  their  action  on 
the  phenomena  of  magnetic  screening,  for — 

(i.)  If  slots  are  cut  in  the  middle  of  the  plate 
its  disturbing  action  is  either  removed  or  very 
much  decreased. 

(2.)  If  a  flat  coil  of  copper  wire  replaces  a  disc 
of  metal  no  effect  is  produced  on  the  induction 
balance  when  its  ends  are  open,  bui  when  closed 
the  coil  acts  just  like  a  disc,  or  continuous  plate 
of  metal. 

(3.)  The  difference  between  various  metals  in- 


serted as  discs  in  the  induction  balance  is  less  at 
high  speeds  of  reversal  than  at  low  speeds. 

Balance,  Kilo-Ampere — An  am- 
meter in  the  form  of  a  balance,  whose  scale  is 
graduated  to  give  direct  readings  in  kilo-am- 
peres. (See  Balance,  Centi- Ampere.} 

Balance  of  Induction  in  Cable.  _o 
Induction,  Balance  of,  in  Cab! .  J 

Balance,  Plating  —  — An  automatic 
device  for  disconnecting  the  current  from 
the  article  to  be  plated,  as  soon  as  a  certain 
increase  in  weight  has  been  obtained. 

The  objects  to  be  plated  are  suspended  at  one 
end  of  a  balance,  and  when  a  certain  increase  in 
weight  has  been  gained,  the  balance  tips  and 
breaks  the  circuit  Edison's  electric  meter  is 
based  on  this  principle. 

Balance,   Thermic,    or  Bolometer. — An 

apparatus  constructed  on  the  principle  of  the 
differential  galvanometer,  devised  by  Professor 
Langley  for  determining  small  differences  of 
temperature.  (See  Galvanometer,  Differen- 
tial) 

A  coil  composed  of  two  separately  insulated 
wires,  wound  together,  is  suspended  in  a  mag- 
netic field,  and  has  a  current  sent  through  it. 
Under  normal  conditions,  this  current  separates 
into  two  equal  parts,  and  runs  through  the  wires 
in  opposite  directions.  It  therefore  produces  no 
sensible  field,  and  suffers  no  deflection  by  the  field 
in  which  it  is  suspended. 

Any  local  application  of  heat  producing  a  dif- 
ference in  temperature  in  these  coils,  causing  a 
difference  in  resistance,  prevents  this  equality.  A 
field  is  therefore  produced  in  the  suspended  coil, 
which,  though  extremely  small,  is  rendered  meas- 
urable by  means  of  the  powerful  field  produced 
in  the  coil,  within  which  the  double  coil  is  sus- 
pended. 

Differences  of  temperature  as  small  as  one- 
fourteen  thousandth  of  a  degree  Fahrenheit  are 
detected  by  the  instrument. 

Balance,  Wheatstone's  Electric  —  —A 
name  often  given  to  the  electric  bridge  or 
balance.  (See  Bridge,  Electric.} 

Balanced-Metallic  Circuit.— (See  Circuit, 
Balanced-Metallic) 

Balanced  Resistances.— (See  Resistances, 
Balanced^ 


Bal. 


41 


[Bar. 


Balata. — An  insulating  material. 
Balata,  when  prepared  for  use  as  an  insulating 
material,  is  somewhat  like  gutta-percha. 

Ball,  Electric  Time  —  — A  ball,  sup- 
ported in  a  prominent  position  on  a  tall  pole, 
and  caused  to  fall  at  the  exact  hour  of  noon, 
or  at  any  other  predetermined  time,  for  the 
purpose  of  thus  giving  correct  time  to  an 
entire  neighborhood. 

The  release  of  the  ball  is  effected  by  the  closing 
of  an  electric  circuit,  either  automatically,  or 
through  the  agency  of  an  observer. 

Ball,  Fire A  term  sometimes  ap- 
plied to  globular  lightning.  (See  Lightning, 
Globular?) 

Ball  Lightning.— (See  Lightning,  Ball.} 
Ballistic  Curve.— (See  Curve,  Ballistic} 

Ballistic  Galvanometer.— (See  Galva- 
nometer, Ballistic.} 

Balloon,  Electric A  balloon,  or 

air  ship,  provided  with  electric  power  so  as 
to  be  able  to  be  steered  or  moved  against  the 
direction  of  the  wind. 

Electric  balloons  have  been  moved  against  the 
wind  and  steered  with  a  certain  amount  of  success, 
by  the  use  of  electric  motors  driven  by  storage 
batteries.  All  that  is  needed  to  make  aerial  navi- 
gation a  commercial  success  is  the  ability  to  ob- 
tain great  power  with  a  small  weight.  The  storage 
battery  does  this  to  a  limited  extent. 

Bearing  in  mind  the  high  efficiency  of  the  elec- 
tric motor,  it  would  appear  that  the  problem  of 
successful  aerial  navigation  will  be  solved  when 
the  discovery  is  made  of  means  for  directly  con- 
verting the  chemical  potential  energy  of  coal  into 
electrical  energy. 

Balloon  Signaling  for  Military  Pur- 
poses.— (See  Signaling,  Balloon,  for  Mil- 
itary Purposes} 

Balls,  Pith  —  —Two  balls  of  pith,  sus- 
pended by  conducting  threads  of  cotton  to 
insulated  conductors,  employed  to  show  the 
electrification  of  the  same  by  their  mutual 
repulsion. 

The  pith  balls  connected  with  the  insulated 
cylinder  A  B,  Fig.  36,  not  only  show  the  electri- 
fication of  the  cylinder,  but  serve  also  to  roughly 


indicate   the  peculiarities  of  distribution  of  the 
charge  thereon. 


Fig.  36.    Pith  Ball  Cylinder. 

Bands,        Anroral Approximately 

parallel  streaks  of  light  sometimes  seen 
during  the  prevalence  of  the  aurora.  (See 
Aurora  Borealis^) 

Bank  of  Lamps.— (See  Lamps,  Bank  of} 
Banked  Battery.— (See  Battery,  Banked} 

Bar,  Detorsion  —  —A  bar  placed  in  a 
magnetic  instrument  called  a  declinometer  for 
the  purpose  of  removing  the  torsion  of  the 
suspending  thread  of  the  magnet. 

The  detorsion  ^ar  of  the  declinometer  is  gen- 
erally made  of  gun  metal  of  the  same  weight  as 
that  of  the  suspended  magnet.  A  small  magnet 
is  placed  in  a  rectangular  aperture  in  the  middle 
of  the  bar. 

Bar  Electro-Magnet.— (See  Magnet, 
Electro,  Bar} 

Barad. — A  unit  of  pressure  proposed  by 
the  British  Association. 

One  barad  equals  one  dyne  per  square  centi- 
metre. 

Barometer. — An  apparatus  for  measuring 
the  pressure  or  weight  of  the  atmosphere. 

Barometric  Column. — (See  Column,  Baro- 
metric.) 

Bars,    Bus Omnibus     bars.     (See 

Bars,  Omnibus} 

Bars,    Krizik's — Cores    of    various 

shapes,  provided  for  solenoids,  in  which  the 
distribution  of  the  metal  in  the  bar  is  so  pro- 
portioned as  to  insure  as  nearly  as  possible  a 
uniform  attraction  or  pull  while  in  different 
positions  in  the  solenoid. 


Ban] 


42 


[Bat. 


Krizik's  bars  of  various  shapes  are  shown  in 
Fig.  37.     It  will  be  observed  that  in  all  cases  the 


Fig.  37.      Krizik's  Bars. 

mass  of  metal  is  greater  toward  the  middle  of 
the  core  than  near  the  ends. 

When  a  core  of  uniform  diameter  is  drawn  into 
a  solenoid,  the  attraction  or  pull  is  not  uniform  in 
strength  for  different  positions  of  the  bar.  When 
the  bar  is  just  entering  the  solenoid,  the  pull  is 
strongest ;  as  soon  as  the  end  passes  the  middle  of 
the  core  the  attraction  decreases,  until,  when  the 
centres  of  the  bar  and  core  coincide,  the  motion 
ceases,  since  both  ends  of  the  solenoid  attract 
equally  in  opposite  directions.  By  proportioning 
the  bars,  as  shown  in  the  figure,  a  fairly  uniform 
pull  for  a  considerable  length  may  be  obtained. 

Bars,      Negative-Omnibus — The 

bus-bars  that  are  connected  with  the  negative 
terminal  of  the  dynamos.  (See  Bars,  Omni- 
bus) 

Bars,  Neutral-Omnibus The  bus- 
bars that  are  connected  with  the  neutral 
dynamo  terminal  in  a  three-wire  system  of 
distribution. 

Bars,  Omnibus Heavy  bars  of  con- 
ducting material  connected  directly  to  the 
poles  of  dynamo-electric  machines,  in  electric 
incandescent  light  or  electric  railway  installa- 
tions, and  therefore  receiving  the  entire  current 
produced  by  the  machine. 

Main  conductors  common  to  two  or  more 
dynamos  in  an  electrical  generating  plant. 

The  terms  bus  and  omnibus  bars  refer  to  the 
fact  that  the  entire  or  whole  current  is  carried  by 
them. 

Bars,  Positive-Omnibus  —  —The  bus- 
bars that  are  connected  with  the  positive 
terminal  of  the  dynamos. 

Bath,  Bi-polar  —  — An  electro-thera- 
peutic bath,  the  current  applied  to  which 
enters  at  one  part  of  the  tub,  and  leaves  at 
another  part. 


The  electrodes  for  the  bi-polar  bath  consist  of 
suitably  shaped  copper  plates,  generally  called 
shovel  electrodes. 

Bath,  Copper—  —An  electrolytic  bath 
containing  a  readily  electrolyzable  solution 
of  a  copper  salt,  and  a  copper  plate  acting  as 
the  anode,  and  placed  in  the  liquid  near  the 
object  to  be  electro-plated,  which  forms  the 
kathode.  .(See  Plating,  Electro) 

The  sulphate,  the  cyanide  and  the  acetate  of  cop- 
per are  used  for  copper  baths.  The  use  of  the  sul- 
phate is  objectionable.  The  cyanide  is  expensive. 
The  acetate  is  therefore  very  generally  employed. 
Wahl  gives  the  following  formula  for  a  copper 
bath,  viz. : 

Water i  ,000  parts. 

Acetate   of  copper,  crystal- 
lized           20    " 

Carbonate  of  soda 20    " 

Bisulphite  of  soda 20    " 

Cyanide  of  potassium  (pure)         20    " 

Bath,  Electro-Plating  —  —Tanks  con- 
taining metallic  solutions  in  which  articles 
are  placed  so  as  to  be  electro-plated.  (See 
Plating,  Electro) 

Strictly  speaking  a  plating  bath  includes  not 
only  the  vessel  and  its  metallic  solution,  but  also 
the  metallic  plate  acting  as  the  anode  and  the 
article  to  be  plated  forming  the  kathode. 

Bath,  Electro-Therapeutic  —  — A  bath 
furnished  with  suitable  electrodes  and  used 
in  the  application  of  electricity  to  curative 
purposes. 

Such  baths  should  be  used  only  under  the  advice 
of  a  regular  physician. 

Bath,    Gold  — An   electrolytic    bath 

containing  a  readily  electrolyzable  solution  of 
a  gold  salt  and  a  gold  plate  acting  as  the 
anode,  and  placed  in  the  liquid  opposite  the 
object  to  be  plated,  which  forms  the  kathode. 
(See  Plating,  Electro) 

Electro  gilding  may  be  accomp'islied  either  with 
or  without  the  aid  of  heat.  Hot  gilding  appears 
to  give  a  smoother  and  cleaner  deposit. 

The  following  is  a  fairly  good  solution  for  a 
gold  bath: 

Water 1,000  parts. 

Cyanide  of  potassium,  pure. .        20     " 

Gold  10     " 

— (Wahl.) 


Bat.] 


43 


[Bat. 


The  gold  is  first  converted  into  neutral  chloride 
by  dissolving  it  in  25  parts  of  pure  hydrochloric 
acid  to  which  12.5  parts  of  pure  nitric  acid  has 
been  added.  When  the  gold  is  completely  dis- 
solved, the  liquid  is  heated  until  of  a  dark  red 
color,  in  order  to  expel  any  excess  of  acid. 

Bath,  Head,  Electric A  variety 

of  electric  breeze,  applied  therapeutically  to 
the  head  of  the  patient. 

The  patient  is  placed  on  an  insulating  stool  and 
connected  with  one  pole  of  an  electrostatic  induc- 
tion machine,  the  other  pole  of  which  is  con- 
nected to  a  circle  of  insulated  points  suspended 
over  the  head. 

Bath,  Hydro-Electric A  bath  in 

which  electro-therapeutic  treatment  is  given 
by  applying  one  electrode  to  the  metallic  lining 
of  the  tub,  and  the  other  electrode  to  the  body 
of  the  bather. 

Bath,  Multipolar-Electric An 

electro-therapeutic  bath,  in  which  more  than 
two  electrodes  are  employed. 

It  is  not  clear  that  the  multipolar-electric  bath 
possesses  any  decided  advantages  over  the  bi-polar 
bath. 

Bath,  Nickel An  electrolytic  bath 

containing  a  readily  electrolyzable  salt  of 
nickel,  a  plate  of  nickel  acting  as  the  anode 
of  a  battery  and  placed  in  the  liquid  near  the 
object  to  be  coated,  which  forms  the  kathode. 
(See  Plating,  Electro) 

The  double  sulphate  of  nickel  and  ammonium 
(from  5  to  8  parts  dissolved  in  100  parts  of  water) 
is  used  for  the  bath.  Some  prefer  to  add 
sulphate  of  ammonium  and  citric  acid  to  the  above 
solution. 

Bath,  Shower,  Electric A  shower 

bath  in  which  the  falling  drops  carry 'electric 
charges  to  the  patient  subjected  thereto. 

The  water  is  rendered  slightly  alkaline.  One 
pole  is  immersed  in  the  alkaline  water  and  the 
other  connected  to  a  metallic  stool  on  which  the 
patient  is  placed. 

Bath,  Silver An  electrolytic  bath 

containing  a  readily  electrolyzable  salt  of 
silver  and  a  plate  of  silver  acting  as  the 
anode  of  an  electric  source  and  placed  in  the 
liquid  near  the  object  to  be  coated,  which 
forms  the  kathode.  ^See  ^lating,  Electro?) 


The  double  cyanide  of  silver  and  potassium 
is  the  salt  usually  employed  in  the  silver  bath. 

The  following  bath  is  recommended  by  Rose- 
leur: 

Water 1,000  parts. 

Cyanide  of  potassium  (pure)        50     " 
Pure  silver 25     " 

The  silver  (granulated)  is  treated  with  pure  nitric 
acid  (43  degrees  Beaum€)  and  converted  into 
nitrate  of  silver.  The  solution  is  then  heated  to 
drynessand  subsequently  fused.  The  fused  nitrate 
so  obtained  is  dissolved  in  fifteen  times  its  weight 
of  distilled  water  and  treated  with  a  solution  of 
cyanide  of  potassium  (10  per  cent,  of  the  cyanide), 
by  means  of  which  silver  cyanide  is  thrown  down 
as  a  precipitate.  This  precipitate  is  then  sepa- 
rated and  washed.  It  is  added  to  the  1,000  parts 
of  water,  dissolved,  and  the  cyanide  of  potassium 
afterward  added,  thus  forming  the  double  cyan- 
ide required  for  the  bath. 

Bath,  Stripping  —  — A  bath  for  remov- 
ing an  electro-plating  of  gold,  silver,  or  other 
metal,  either  by  simple  dipping  or  by  electric 
action. 

Bath,  Ungilding  —  — A  stripping  bath 
suitable  for  the  removal  of  a  coating  of  gold. 
(See  Bath,  Stripping) 

Bath,  Unipolar-Electric An  electro- 
therapeutic  bath,  the  water  of  which  forms 
one  of  the  electrodes  of  the  source,  and  the 
other  electrode  is  attached  to  a  metallic  rod 
fixed  at  a  convenient  height  above  the  tub. 

The  bath  tub  is  formed  of  non-conducting  sub- 
stances. The  terminals  of  the  electrode  con- 
nected with  the  water  terminate  in  metal  plates 
located  at  suitable  points  in  the  tub.  The  cur- 
rent is  applied  by  the  patient  making  and  break- 
ing contact  at  the  vertical  metal  rod  with  his 
hands. 

The  unipolar-electric  bath  is  employed  instead 
of  local  galvanization  where  it  is  desired  to  limit 
the  application  to  especial  organs  or  particular 
parts  of  the  body.  In  general  galvanization  the 
patient  is  placed  on  an  electrode  of  large  sur- 
face, formed  of  a  large  spxjnge- covered  metallic 
plate,  on  which  he  sits  or  rests.  This  electrode  is 
connected  with  the  kathode  of  the  battery.  The 
anode  is  connected  with  a  large  sponge  electrode, 
which  is  moved  regularly  over  the  body  of  the 
patient;  sometimes  the  moistened  hand  of  the 
operator  is  used  in  place  of  the  sponge  electrode. 


Bat.] 


[Bat. 


Bath,  UnsilTering  —  — A  stripping  bath 
suitable  for  the  removal  of  a  coating  of  silver. 
(See  Bath,  Stripping^ 

Bathometer. — An  instrument  invented  by 
Siemens  for  obtaining  deep-sea  soundings 
without  the  use  of  a  sounding  line. 

The  bathometer  depends  for  its  operation  on 
the  varied  attraction  of  the  earth  for  a  suspended 
weight  in  parts  of  the  ocean  differing  in  depth. 
As  the  vessel  passes  over  deep  portions  of  the 
ocean,  the  solid  land  of  the  bottom,  being  further 
from  the  ship,  exerts  a  smaller  attraction  than  it 
would  in  shallow  parts,  where  it  is  nearer;  for, 
although  in  the  deep  parts  of  the  ocean  the  water 
lies  between  the  ship  and  the  bottom,  the  smaller 
density  of  the  water  as  compared  with  the  land 
causes  it  to  exert  a  smaller  attraction  than  in  the 
shallower  parts,  where  the  bottom  is  nearer  the 
ship.  The  varying  attraction  of  the  earth  is 
caused  to  act  on  a  mercury  column,  the  reading 
of  which  is  effected  by  means  of  an  electric  con- 
tact. 

Battery,  Banked  — A  term  some- 
times applied  to  a  battery  from  which  a  num- 
ber of  separate  circuits  are  supplied  with  cur- 
rents. 

The  term  banked-battery  is  sometimes  ap- 
plied to  a  multiple-arc  connected  battery. 

Battery,  Cautery  —  —A  term  some- 
times employed  in  electro-therapeutics,  for  a 
multiple  connected  voltaic  battery  adapted  for 
producing  electric  incandescence  for  cautery 
effects. 

Battery,  Closed-Circuit  -  —A  voltaic 
battery  which  may  be  kept  constantly  on 
closed-circuit  without  serious  polarization. 

The  gravity  battery  is  a  closed -circuit  battery. 
As  employed  for  use  on  most  telegraph  lines,  it  is 
maintained  on  a  closed  circuit.  When  an  operator 
wishes  to  use  the  line  he  opens  his  switch,  thus 
breaking  the  circuit  and  calling  his  correspondent. 
Such  batteries  should  not  polarize.  (See  Cell, 
Voltaic,  Polarization  of.) 

Battery,  Connection  of,  for  Quantity  — 

— A  term,  now  generally  in  disuse,  formerly 
employed  to  indicate  the  grouping  of  voltaic 
cells,  now  known  as  parallel  or  multiple. 

The  arrangement  or  coupling  of  a  number  of 
voltaic  cells  in  multiple  reduces  the  internal  resist- 


ance of  the  battery,  and  thus  permits  a  greater 
current,  or  quantity,  of  electricity  to  pass  ;  hence 
the  origin  of  the  term. 

Battery,  Dynamo The  combina- 
tion or  coupling  together  of  several  separate 
dynamo-electric  machines  so  as  to  act  as  a 
single  electric  source. 

The  dynamos  may  be  connected  to  the  leads 
either  in  series,  in  multiple,  in  multiple-series  or 
in  series-multiple. 

Battery,  Dynamo,  Electric  Machine  — 

— A  dynamo  battery.  (See  Battery,  Dy- 
namo?) 

Battery,  Electric A  general  term 

applied  to  the  combination,  as  a  single  source, 
of  a  number  of  separate  electric  sources. 

The  separate  sources  may  be  coupled  either  in 
series,  in  multiple,  in  multiple-series,  or  in  series- 
multiple.  (  See  Circuits,  Varieties  of.) 

The  term  battery  is  sometimes  incorrectly  ap- 
plied to  a  single  voltaic  couple  or  cell. 

Battery,  Floating,  De  la  Rive's  —     —A 

floating  voltaic  cell,  the  terminals  of  which  are 
connected  with  a  coil  of  insulated  wire,  em- 
ployed to  show  the  attractions  and  repul- 
sions between  magnets  and  movable  electric 
circuits. 

The  cell,  shown  in  Fig.  38,  consists  of  a  vol- 


Fig.  38.    Floating  Cell. 

taic  couple  of  zinc  and  copper,  the  terminals  of 
which  are  connected  to  the  circular  coil  of  insu- 
lated wire,  as  shown,  and  the  whole  floated  by 
means  of  a  cork,  in  a  vessel  containing  dilute  sul- 
phuric acid. 

When  the  current  flows  through  the  coil  in  the 
direction  shown  by  the  arrows,  the  approach  of 
the  N-seeking  pole  of  a  magnet  will  cause  the 
cell  to  be  attracted  or  to  move  towards  the  mag- 
net pole,  since  the  south  face  or  end  of  the  coil  is 
nearer  the  north  pole  of  the  magnet.  If  the  other 


Bat.] 


[Bat. 


end  were  nearer,  repulsion  would  occur,  the  cell 
turning  round  until  the  south  face  is  nearer  the 
magnet,  when  attraction  occurs. 

This  is,  strictly  speaking,  a  floating  cell,  and 
not  a  battery.  (See  Battery,  Voltaic.} 

Battery,  Galvanic Two  or  more 

separate  voltaic  cells  so  arranged  as  to  form 
a  single  source. 

This  is  more  correctly  called  a  Voltaic  Battery. 
(See  Battery,  Voltaic.) 

Battery,  Gas A  battery  in  which 

the  voltaic  elements  are  gases  as  distinguished 
from  solids. 

The  electrodes  of  a  gas  battery  generally  con- 
sist of  plates  of  platinum,  or  other  solid  substance 
which  possesses  the  power  of  occluding  oxygen 
and  hydrogen.  The  lower  parts  of  these  plates 
dip  into  dilute  sulphuric  acid,  and  the  upper  parts 
are  respectively  surrounded  by  oxygen  and  hydro- 
gen gas  derived  from  the  electrolytic  decompo- 
sition of  the  dilute  acid. 

A  gas  battery  consisting  of  plates  of  platinum 
dipping  below  into  acid  liquid,  and  surrounded 
in  the  space  above  the  liquid  by  hydrogen  and 
oxygen  H,  H'  and  O,  O',  etc.,  respectively  is 
shown  in  Fig.  39. 


Fig-  39-     Gas  Battery. 

In  charging  this  battery  an  electric  current  is 
sent  through  it  until  a  certain  quantity  of  the 
gases  has  been  produced.  If,  then,  the  charging 
current  be  discontinued,  a  current  in  the  oppo- 
site direction  is  produced  by  the  battery.  The 
gas  battery  is  in  reality  a  variety  of  storage  bat- 
tery. (See  Electricity,  Storage  of.  Cell,  Secon- 
dary. Cell,  Storage.") 

Gas  batteries  can  also  be  made  by  feeding  con- 
tinually into  the  cell  a  gas  capable  of  acting  on 
the  positive  elements. 

Battery  Gauge. — (See  Gaugi,  Battery?) 


Battery,  Leyden  Jar The  combina- 
tion of  a  number  of  separate  Leyden  jars  so 
as  to  act  as  one  single  jar. 

A  Leyden  jar  battery  is  shown  in  Fig.  40, 


Fig.  40,    Leyden  Jar  Battery. 


where  nine  separate  Leyden  jars  are  connected 
as  a  single  jar  by  joining  their  outer  coatings  by 
placing  them  in  the  box  P,  the  bottom  of  which 
is  lined  with  tin  foil.  The  inner  coatings  are 
connected  together  by  the  metal  rods  B,  as 
shown. 

A  discharging  rod  A,  may  be  employed  for 
connecting  the  opposite  coatings.  The  handles 
are  made  of  glass  or  any  other  good  insulating 
material. 

A  number  of  Leyden  jars  can  be  coupled  in 
series  by  connecting  the  inner  coating  of  the  first 
jar  to  the  outer  coating  of  the  second,  the  inner 
coating  of  the  second  to  the  outer  coating  of  the 
third,  and  so  on.  The  battery  so  obtained  is 
then  discharged  by  connecting  the  outer  coat, 
ing  of  the  first  jar  with  the  inner  coating  of  the 
last. 

Battery,  Local A  voltaic  battery 

used  at  a  station  on  a  telegraph  line  to 
operate  the  Morse  sounder,  or  the  register- 
ing or  recording  apparatus,  at  that  point 
only.  (See  Telegraphy,  American  or  Morse 
System  of.) 

The  local  battery  is  thrown  into  or  out  of  action 
by  the  telegraphic  relay.  (See  Relay.} 

Battery,  Magnetic -The  combina- 
tion, as  a  single  magnet,  of  a  number  of  sep- 
arate magnets. 

A  magnetic  battery,  or  compound  magnet,  is 


Bat.] 


[Bat. 


Fig,    J.T,       Magneti 
Battery,   or   Com 


shown  in  Fig.  41.  It  consists  of  straight  bars  of 
steel,  p,  p,  p,  with  their  similar  poles  placed  near 
together  and  inserted  in 
masses  of  soft  iron,  N  and 
S,  as  shown. 

Battery,  Main 

The  battery,  in  a  system 
of  telegraphic  communi- 
cation, that  is  employed 
for  sending  the  signals 
over  the  main  line,  as  dis- 
tinguished from  any  bat- 
tery employed  for  any 
other  particular  work, 
such,  for  example,  as  that 
of  the  local  battery.  (See 
Battery,  Local.) 

Battery,  Multiple-Con-       found  Magnet. 

nected A  battery  the  single  cells  of 

which  are  connected  to  one  another  and  to  the 
mains  or  conductors  in  multiple.  (See  Cir- 
cuit, Multiple) 

Battery,    Open-Circuit A   voltaic 

battery  which  is  normally  on  open-circuit, 
and  which  is  used  continuously  only  for  com- 
paratively small  durations  of  time  on  closed- 
circuit. 

Leclanche'-cells  form  an  excellent  open-circuited 
battery.  'They  have  a  comparatively  high  electro- 
motive force,  but  rapidly  polarize.  They  cannot 
therefore  be  economically  used  for  furnishing 
currents  continuously  for  long  durations  of  time. 
When  left  on  open-circuit,  however,  they  readily 
depolarize.  They  therefore  form  an  excellent 
battery  for  such  work  as  annunciator  bells,  burg- 
lar alarms,  etc.,  where  the  current  is  only 
required  for  short  periods  of  time,  separated  by 
comparatively  long  intervals  of  rest.  (See  Cell, 
Voltaic,  Leclanche.) 

Battery  Plates  of  Secondary  or  Storage 

Cell,    Forming    of (See   Plates    of 

Secondary  or  Storage  Cell,  Forming  of.) 

Battery,    Plunge A    number    of 

separate  voltaic  cells  connected  so  as  to  form 
a  single  cell  or  electric  source,  the  plates  of 
which  are  so  supported  on  a  horizontal  bar 
as  to  be  capable  of  being  simultaneously 
placed  in,  or  removed  from,  the  exciting 
liquid. 


The  plunge  battery  shown  in  Fig.  42,  consists 


Fig.  42.    Plunge  Battery, 

of  a  number  of  zinc-carbon  elements  immersed  in 
an  electrolyte  of  dilute  sulphuric  acid,  or  in  elec- 
tropoion  liquid,  contained  in  separate  jars,  J,  J. 
(See  Liquid,  Electropoion.) 

The  mode  of  support  to  the  horizontal  bar 
will  be  understood  from  an  inspection  of  the 
drawing. 

Battery,  Primary The  combina- 
tion of  a  number  of  separate  primary  cells  so 
as  to  form  a  single  source. 

The  term  primary  battery  is  used  in  order  to 
distinguish  it  from  secondary  or  storage  battery. 
(See  Cell,  Secondary.  Cell,  Storage.) 

Battery,  Secondary The  combina- 
tion of  a  number  of  separate  secondary  or 
storage  cells,  so  as  to  form  a  single  electric 
source.  (See  Electricity,  Storage  of.) 

Battery,  Selenium The  combina- 
tion of  a  number  of  separate  selenium  cells  so 
as  to  form  an  electric  source.  (See  Cell, 
Selenium.) 

Battery,  Series-Connected A  bat- 
tery, the  separate  cells  of  which  are  con- 
nected to  one  another  and  to  the  line  or 
conductor  in  series.  (See  Circuit,  Series.) 

Battery  Solution.— (See  Solution,  Bat- 
tery) 

Battery,  Split A  voltaic  batten' 

connected  in  series,  but  having  one  of  its 
middle  plates  connected  with  the  ground. 

By  the  employment  of  the  device  of  a  split- 
battery,  the  poles  of  the  battery  are  maintained 
at  potentials  differing  in  opposite  directions  from 
the  potential  of  ihe  earth. 

Battery,  Storage  —  —A  number  of 
separate  storage  cells  connected  so  as  to 
form  a  single  electric  source. 


Bat.] 


[Bel. 


A  cell  of  a  storage  battery  is  shown  in  Fig. 


43- 


Fig.  43.     Storage  Battery. 

Battery, '  Storage,  Element   of A 

single  set  of  positive  and  negative  plates  of  a 
storage  cell  connected  so  as  to  be  ready  for 
placing  in  the  acid  liquid  of  the  jar  or  cell. 

A  term  sometimes  applied  to  one  of  the 
storage  cells  in  a  storage  battery. 

This  latter  use  of  the  term  element  is  unfortu- 
nate, since  from  the  analogous  case  of  a  primary 
•cell,  an  element  would  consist  of  a  single  plate, 
either  positive  or  negative,  and  not  of  both.  That 
is,  every  voltaic  couple  consists  of  two  elements, 
the  positive  and  the  negative. 

Battery,    Thermo A   term    often 

applied  to  a  thermo-electric  battery.  (See 
Battery,  Thermo- Electric) 

Battery,     Thermo-Electric The 

combination,  as  a  single  thermo-electric  cell, 
of  a  number  of  separate  thermo-electric  cells 
or  couples.  (See  Couple,  Thermo-Electric) 

Battery,  Voltaic The  combina- 
tion, as  a  single  source,  of  a  number  of  sepa- 
rate voltaic  cells. 

Battery,  Water A  battery  formed 

of  zinc  and  copper  couples  immersed  in  an 
electrolyte  of  ordinary  water. 

Any  voltaic  couple  can  be  used,  the  positive 
element  of  which  is  slightly  acted  on  by  water. 
When  numerous  couples  are  employed  consider- 
able difference  of  potential  can  be  obtained. 

Water  batteries  are  employed  for  charging 
electrometers.  They  are  not  capable  of  giving 
any  considerable  current,  owing  to  their  great  in- 
ternal resistance. 


Bead  Areometer  or  Hydrometer. — (See 
Areometer,  Bead.) 

Bec-Carcel. — The  Carcel.  or  French  unit 
of  light.  (See  Carcel) 

Bell,  Automatic-Electric An  elec- 
tric bell  furnished  with  an  automatic  contact- 
breaker.  (See  Contact-Breaker,  Automatic) 

A  form  of  automatic-electric  bell  is  shown  m 
Fig.  44.  The  relation  of  the  electro- magnet,  its 
armature  and  the  bell 
lever,  will  be  readily 
understood  from  an  in- 
spection  of  the  draw- 
ing. 

Bell,  Call 

An  electric  bell  used 
to  call  the  attention 
of  an  operator  to  the 
fact  that  his  corre- 
spondent wishes  to 
communicate  with 
him. 

Bell,  Circular 

— A  bell  so  construct- 
ed that  all  its  moving 

parts  are  contained  in  Figt  44,  Automatic  EUctrii 
the  gong.  Bell. 

Bell,  Continuous-Sounding  Electric  — 

— An  electric  bell,  which,  on  the  completion 
of  the  circuit,  continues  striking  until  stopped 
either  by  hand  or  automatically. 

On  the  completion  of  the  circuit,  the  attraction 
of  an  armature  throws  a  catch  off  from  a  lever, 
and  thus  permits  the  lever  to  fall  and  complete  a 
contact  and  allows  the  current  to  ring  the  bell;  or 
the  bell  is  rung  by  clockwork,  which  is  thrown 
into  action  by  the  passage  of  a  current  through  an 
electro-magnet.  (See  Bell,  Electro-Mechanical.} 

Bell,    Differential     Electric An 

electric  bell,  the  magnetizing  coils  of  which 
are  differentially  wound.' 

Differential  winding  is  ot  advantage  where  a 
very  strong  current  is  required,  as  this  winding 
decreases  the  sparking  at  the  contacts,  on  the 
opening  of  the  circuit. 

Bell,  Electro-Magnetic,  Siemens-Arma- 
ture Form A  form  of  electro-mag- 


Bel.] 


48 


[Bel. 


netic  bell  in  which  the  movements  of  the  bell 
armature  are  obtained  by  the  reversal  of 
polarity  that  takes  place  when  alternating  cur- 
rents are  pass- 
ed  through  the 
coils  of  a  sim- 
ple, single  coil, 
Siemens  -  arma- 

ture>  Fig.  4$.  Siemens-Armature  Form 

The       details  of  Electro-Magnetic  Bell. 

will  be  readily  understood  from  an  examination 
of  Fig.  45. 

Bell,  Electro-Mechanical A  bell, 

the  striking  apparatus  of  which  is  driven  by 
a  weight  or  spring,  called  into  action  by  the 
movement  of  the  armature  of  an  electro- 
magnet. (See  Alarm,  Electric?) 

Bell,  Extension-Call A  device  for 

prolonging  the  sound  of  a  magneto  call. 

An  alarm  bell  is  automatically  connected  with 


Fig.  46.    Extension-Call  Bell. 

the  circuit  of  a  local  battery  by  means  of  the  cur- 
rent generated  by  the  magneto-call,  and  continues 
sounding  after  the  current  of  the  magneto  call 
has  ceased. 

A  form  of  extension-call  bell  is  shown  in  Fig.  46. 

Bell,  Indicating- An  electric  bell 

in  which,  in  order  to  distinguish  between 
different  bells  in  the  same  office,  a  number 
is  displayed  by  each  bell  when  it  rings. 

Bell,  Magneto-Electric An  electric 

bell,  the  curre.it  employed  to  operate  or 
strike  which  is  obtained  by  the  motion  of  a 
magneto-electric  machine. 

Bell,  Night In  a  telephone  ex- 
change, a  bell,  switched  into  connection  with 
the  shunted  circuit  of  an  annunciator  case,  and 
intended,  by  its  constant  ringing,  to  call  the 
attention  of  the  night  operator  to  the  falling 
of  a  drop. 


Bell,  Belay,  Electric  ---  An  electric 
bell  in  which  a  relay  magnet  is  employed  to 
switch  a  local  battery  into  the  circuit  of  the 
sounding  apparatus  of  the  bell. 

The  relay  bell  is  suitable  for  use  when  the  bell 
to  be  sounded  is  situated  at  a  great  distance.  As 
the  current  from  the  1  ine,  when  this  is  long,  is 
too  weak  to  ring  the  bell,  it  throws  into  action  a 
local  battery  by  the  action  of  a  relay. 

Relay  bells  were  used  in  the  early  forms  oi 
acoustic  telegraphs  as  employed  in  England  with 
relay  sounders. 

The  dots  and  dashes  of  the  Morse  alphabet  were 
indicated  by  the  sounds  of  two  bells,  a  tap  on 
one  bell  indicating  a  dot,  and  a  tap  on  the  other 
a  dash.  This  system  is  now  practically  aban- 
doned. 

Bell-Shaped  Magnet.—  (See  Magnet,  Sell- 


Bell,  Shunt,  Electric  --  An  electric 
bell,  the  magnetizing  coils  of  which  are  placed 
on  the  line  in  shunt. 

In  the  case  of  shunt-connected  electric  bells, 
one  of  the  bells  must  make  and  break  the  circuit 
for  all  the  rest.  The  series-connected  electric 
bell  is  used  where  the  distance  between  the  sepa- 
rate bells  is  great,  in  order  to  save  the  expense  of 
multiple  connections. 

In  most  cases,  where  a  number  of  electric  bells 
are  to  be  simultaneously  sounded,  connection  in 
multiple  is  adopted. 

Bell,  Single-Stroke  Electric  ---  An 

electric  bell  that  gives  a  single  stroke  only  for 
each  make  of  the  circuit. 


Kg.  47.     Single-Stroke  Bell. 

Since  the  bell  gives  a  single  stroke  for  each 
completion  of  the  circuit,  its  use  permits  of  ready 
communication  between  any  two  places  by  any 


Bel.] 


40 


[Bla. 


system  of  prearranged  signals.  A  buzzer  may  be 
used  for  the  same  purpose.  A  form  of  single- 
stroke  bell  is  shown  in  Fig .  47 .  On  completing  the 
circuit,  the  current,  through  its  coils,  attracts  the 
armature  and  causes  a  single  stroke  of  the  bell. 

Bell,  Telephone-Call  -  —A  call  bell 
used  to  call  a  correspondent  to  the  telephone. 

The  telephone-call  bell  is  generally  a  magneto- 
electric  bell. 

Bell,  Trembling A  name  some- 
times given  to  a  vibrating  or  an  automatic 
make-and-break  bell.  (^ezMake-and-Break, 
Automatic •) 

Bell,  Yibrating  —  — A  trembling  bell. 
(See  Bell,  Trembling) 

Bias  of  Relay  Tongue. — (See  Tongue, 
Relay,  Bias  of.} 

Bichromate  Toltaic  Cell.— (See  Cell,  Vol- 
taic, Bichromate.) 

Bi-fllar  Suspension. — (See  Suspension, 
Bi-filar.} 

Bi-fllar  Suspension  Balance.— (See  Bal- 
ance, Bi-filar  Suspension) 

Bi-fllar  Winding.— (See  Winding,  Bi- 
filar) 

Binary  Compound.— (See  Compound,  Bi- 
nary) 

Binding  Coils.— (See  Coils,  Binding) 

Binding-Post— (See  Post,  Binding) 

Binding-Screw.— (See  Screw,  Binding) 

Binding  Wire  for  Telegraph  Lines.— (See 
Wire,  Binding,  for  Telegraph  Lines) 

Biology,  Electro That  branch  of 

electric  science  which  treats  of  the  electric 
conditions  of  living  animals  and  plants,  and 
the  effects  of  electricity  upon  them. 

Electro-Biology  includes : 

(I.)  Electro-Physiology. 

(2.)  Electro-Therapy,  or  Electro-Therapeutics. 

Bioplasm.— Any  form  of  living  matter  pos- 
sessing the  power  of  reproduction. 

Bioscopy,  Electric The  determina- 
tion of  the  presence  of  life  or  death  by  the 
passage  of  electricity  through  the  nerves  and 
muscles. 

Bi-polar. — Having  two  poles. 


Bi-polar  Armature.  —  (See  Armature, 
Bi-polar) 

Bi-polar  Bath.— (See  Bath,  Bi-polar) 

Birmingham  Wire  Gauge.— (See  Gauge, 
Wire,  Birmingham) 

Bi-Telephone.— (See  Telephone,  Bi) 

Bitite. — A  variety  of  insulating  material. 

Black  Electro-Metallurgical  Deposit— 
(See  Deposit,  Black  Electro-Metallurgical) 

Black  Lead. — A  variety  of  carbon  em- 
ployed in  various  electrical  processes. 

Black  lead  is  also  termed  plumbago  or  graphite. 
(See  Plumbago.  Graphite) 

The  term  black  lead  is  a  misnomer,  since  the 
substance  is  carbon  and  not  lead.  The  term  is  an 
old  one,  and  is  still  very  generally  used. 

Blasting,  Electric  —  —The  electric 
ignition  of  powder  or  other  explosive  material 
in  a  blast.  (See  Fuse,  Electric) 

The  current  required  for  the  ignition  of  the 
fuse  is  generally  obtained  by  means  of  a  magneto- 
electric  machine.  In  the  form  of  magneto-blast- 
ing machine,  shown  in  Fig.  48,  the  movement 


Fig.  48.    Magneto-Blasting  Machine. 

of  the  handle  shown  at  the  top  of  the  figure 
causes  the  rapid  rotation  of  a  cylindrical  armature 
constructed  on  the  Wheatstone  and  Siemens  prin- 
ciple. The  magnets  are  of  iron,  and  are  furnished 


Ble.J 


50 


[Boa. 


with  coils  of  insulated  wire.  On  the  rotation  of 
the  armature  the  current  developed  therein  in- 
creases the  field  of  the  field  magnet,  and,  when 
of  the  proper  degree  of  intensity,  is  thrown  into  the 
outer  circuit,  and  ignites  the  fuse. 

Bleaching,  Electric Bleaching  pro- 
cesses in  which  the  bleaching  agents  are 
liberated,  as  required,  by  the  agency  of  electro- 
lytic decomposition. 

In  the  process  of  Naudin  and  Bidet,  the  cur- 
rent from  a  dynamo-electric  machine  is  passed 
through  a  solution  of  common  salt  between  two 
closely  approached  electrodes.  The  chlorine  and 
sodium  thus  liberated  react  on  each  other  and 
form  sodium  hypochloride,  which  is  drawn  off 
by  means  of  a  pump  and  used  for  bleaching. 
(See  Electrolysis.) 

Block,  Branch A  device  em- 
ployed in  electric  wiring  for  taking  off  a  branch 
from  a  main  circuit.  (See  Wiring.) 

A  form  of  branch-block,  with  its  fuses  attached, 
is  shown  in  Fig.  49. 


Fig.  49.   Branch-Black. 

Block,    Cross-Over A   device    to 

permit  the  safe  crossing  of  one  wire  over 
another  in  molding  or  cleat  wiring. 

Block,  Fuse A  block  containing 

a  safety  fuse  or  fuses  for  incandescent  light 
circuits.  (See  fuse,  Safety.) 

Block  System  for  Railroads.— (See  Rail- 
roads, Block  System  for.) 

Block  Wire.— (See  Wire,  Block) 

Blow-Pipe  Electric—  —A  blow-pipe 
in  which  the  air-blast  is  obtained  by  a  stream 
of  air  particles  produced  at  the  point  of  a 


charged    conductor    by    a    convection    dis- 
charge. 
The  candle  flame,  Fig.  50,  is  blown  in  the  di- 

P 


Fig.  50.     Convection  Blow-Pipe. 

rection  of  the  stream  of  air  particles  passing  off 
from  the  point  P.  (See  Convection,  Electric.) 

Blow-Pipe,  Electric-Arc A  de- 
vice of  Werdermann  for  cutting  rocks,  or 
other  refractory  substances,  in  which  the  heat 
of  the  voltaic  arc  is  directed*  by  means  of  a 
magnet,  or  a  blast  of  air,  against  the  substance 
to  be  cut. 

The  cartons  are  placed  parallel,  so  as  to  readily 
enter  the  cavity  thus  cut  or  fused.  This  inven- 
tion has  never  been  introduced  into  extensive 
practice. 

In  the  welding  process  of  Benardos  and 
Olzewski,  the  welding  temperature  is  obtained  by 
means  of  an  electric  arc  taken  between  two  suit- 
ably shaped  electrodes. 

In  t!ie  electric-arc 
blow  -  pipe,  shown  in 
Fig.  51,  the  voltaic  arc, 
taken  between  two  ver- 
tical carbon  electrodes, 
is  deflected  into  a  hori- 
zontal position  under  the 
influence  of  the  inclined 
poles  of  a  powerful  elec- 
tro-magnet. 

The  highly  heated  car- 
bon vapor  which  consti- 
tutes the  voltaic  arc  is  deflected  by  the  magnet  in 
the  same  direction  as  would  be  any  other  mov- 
able circuit  or  current. 

Board,     Cross-Connecting' In    a 

system  of  telegraphic  or  telephonic  communi- 
cation, a  board  to  which  the  line  terminals  are 
run  before  entering  the  switchboard,  so  as  to 


Fig.  5f.    Electric- Arc 
Blmv-Pipe. 


Boa.] 


51 


[Boa. 


readily  place  any  subscriber  in  connection 
with  any  desired  section  of  the  switchboard. 

Board,  Fuse A  board  of  slate  or 

other  incombustible  material  on  which  all 
the  safety  fuses  in  an  installation  are  as- 
sembled. 

The  fuse  board  is  used  for  avoiding  accidents 
from  the  firing  of  the  fuses. 

Board,  Hanger A  form  of  board 

provided  for  the  ready  placing  or  removal  of 
an  arc  lamp  from  a  circuit. 


Fig,  <fs*    Hanger- Board. 

A  hanger-board  contains  a  switch  or  cut-out  for 
the  ready  opening  or  closing  of  the  circuit.  A 
form  of  hanger-board  is  shown  in  Fig.  52. 

Board,  Key Any  board  to  which 

are  connected  electric  keys  or  switches. 

Board,  Legging-Key A  key  boaid 

employed  for  the  purpose  of  legging  an 
operator  into  a  circuit  connecting  two  or  more 
subscribers.  (See  Leg.) 

Board,  Multiple  Switch A  board 

to  which  the  numerous  circuits  employed  in 
systems  of  telegraphy,  telephony,  annunciator 
or  electric  light  and  power  circuits  are  con- 
nected. 

Various  devices  are  employed  for  closing  these 
circuits,  or  for  connecting  or  cross-connecting 
them  with  one  another,  or  with  neighboring  cir- 
cuits. 

A  multiple  switchboard,  for  example,  for  a  tele- 
phone exchange,  will  enable  the  operator  to  con- 
nect any  subscriber  on  the  line  with  any  other 
subscriber  on  that  line,  or  on  another  neighbor- 


ing line  provided  with  a  multiple  switchboard. 
To  this  end  the  following  parts  are  necessary: 

(I.)  Devices  whereby  each  line  entering  the  ex- 
change can  readily  have  inserted  in  its  circuit  a 
loop  connecting  it  with  another  line.  This  is 
accomplished  by  placing  on  the  switchboard  a 
separate  spring-jack  connection  for  each  sepa- 
rate line.  This  connection  consists  essentially 
of  one  or  two  springs  made  of  any  conducting 
metal,  which  are  maintained  in 
metallic  contact  when  the  plug 
key  is  not  inserted,  but  which  are 
readily  separated  from  one  another 
by  the  introduction  of  the  plug- 
key,  Fig.  53,  the  terminals,  a  and 
b,  of  which  are  insulated  from 
each  other,  and  are  connected  to 
the  ends  of  a  loop  coming  from 
another  line.  As  the  key  is  in-  Fis'53^e  Plug' 
serted,  the  metallic  spring  or 
springs  of  the  spring-jack  are  separated  and  the 
metallic  pieces,  a  and  b,  are  brought  into  good 
sliding  contact  therewith,  thus  introducing  the 
loop  into  the  circuit.  (See  Spring-  Jack.) 

(2.)  As  many  separate  annunciator-drops  as 
there  are  separate  subscribers.  These  are  pro* 
vided  so  as  to  notify  the  Central  Office  of  the  par- 
ticular subscriber  who  desires  a  connection. 
Alarm-bells  to  call  the  operator's  attention  to  the 
calling  subscriber,  or  to  the  falling  of  a  drop,  are 
generally  added.  (See  Bell,  Call.) 

(3. )  Connecting  cords  and  keys  for  connecting 
the  operator's  telephone,  and  means  for  ringing 
subscribers'  bells,  and  clearing  out  drops. 


Fig.  S4-    Multiple  Switchboard1  for  Electric  Light. 

In  Multiple  Switchboards  for  the  Electric  Light 
or  Distributing  Switches,  spring-jack  contacts  are 
connected  with  the  terminals  of  different  circuits. 


Boa.] 


[Bod. 


and  plug  switches  with  the  dynamo  terminals. 
By  these  means,  any  dynamo  can  be  connected 
with  any  circuit,  or  a  number  of  circuits  can  be 
connected  with  the  same  dynamo,  or  a  number 
of  separate  dynamos  can  be  placed  in  the  same 
circuit  without  interference  with  the  lights. 

Board,  Switch A  board  provided 

with  a  switch  or  switches,  by  means  of  which 
electric  circuits  connected  therewith  may  be 
opened,  closed,  or  interchanged. 

Board,  Switch,  Telegraphic A 

device  employed  at  a  telegraph  station  by 
means  of  which  any  one  of  a  number  of  tele- 
graph instruments,  in  use  at  that  station,  may 
be  placed  in  or  removed  from  any  line  con- 
nected with  the  station,  or  by  means  of  which 
one  wire  may  be  connected  to  another. 

The  ability  to  readily  connect  one  wire  with 
another  is  of  use  in  case  of  interruption  to  tele- 
graph lines,  in  which  case  a  through  circuit  may 
be  made  up  of  sections  of 
different  circuits. 

In  the  switchboard  shown 
fa  Fig.  55,  the  upper  left- 
hand  binding-post  is  con- 
nected to  earth;  the  four 
remaining  binding  -  posts 
are  connected  to  two  sepa-  Fig.  ss-  Telegraphic 
rate  instruments— the  sec-  Switchboard. 

ond  and  third  from  the  top  to  one  instrument, 
and  the  fourth  and  fifth  to  another  instrument. 
The  four  posts  at  the  top  of  the  figure  are  con- 
nected to  two  lines  running  east  and  west. 

Various  connections  are  made  by  the  insertion 
of  plug  keys  in  the  various  openings. 

Board,    Switch,    Trnnking   —A 

switchboard  in  which  a  few  subscribers  only 
are  connected  with  the  operator,  thus  enabling 
him  to  obtain  any  other  subscriber  by  means 
of  trunk  wires  extending  to  the  other  sections. 
(See  Wire,  Trunk) 

Boat,  Electric  —A  boat    provided 

with  electric  motive  power. 

Electric  power  has  been  applied  both  to  ordi- 
nary vessels  and  to  submarine  torpedo  boats. 

Boat,  Submarine  Electric A  boat 

capable  of  being  propelled  and  steered  while 
entirely  under  water. 

The  motive  power  of  such  boats  is  generally 


electricity.  The  requisite  buoyancy  is  obtained 
by  means  of  an  air  chamber.  Artificial  ventila- 
tion is  maintained,  the  fresh  air  requisite  for 
breathing  being  derived  from  a  compressed  air 
cylinder. 

Boat,  Torpedo  — A  boat  used  for 

carrying  and  discharging  torpedoes.  (See 
Torpedo) 

Bobbin,  Electric An  insulated  coil 

of  wire  for  an  electro-magnet. 

Body,  Charged A  body  containing 

an  electric  charge. 

Charges  are  bound  or  free.  '  (See  Charge, 
Bound.  Charge,  Free.} 

Body,  Electrified —A    body    con- 
taining an  electric  charge. 
Body,    Human,    Resistance    of  • 

The  resistance  which  the  human  body  offers  to 
the  passage  of  an  electric  current. 

The  resistance  of  the  human  body  to  the  passage 
of  a  current  varies  with  the  time.  The  re- 
sistance rapidly  decreases  after  a  short  time. 

"The  resistance  diminishes  because  of  the  con- 
duction of  water  in  the  epidermis  under  the  action 
of  the  constant  current  and  the  congestion  of  the 
cutaneous  blood  vessels  in  consequence  of  the 
stimulation. ' '  ( Landois  and  Stirling. ) 

The  resistance  also  varies  markedly  with  the 
condition  of  the  surface,  the  condition  of  the  skin, 
and  with  the  shape,  area,  position  and  material 
of  the  electrodes  by  which  the  current  is  led  into 
and  carried  out  of  the  parts.  It  very  seldom  is 
less  than  1,000  ohms  under  the  most  favorable 
conditions,  and  with  ordinary  contacts  is  many 
times  that  amount. 

The  muscles  offer  nearly  nine  times  the  resist- 
ance in  a  direction  transverse  to  the  fibres  than 
longitudinally  to  them.  (Hermann.) 

The  resistance  of  the  epidermis  is  greater  than 
that  of  any  other  tissue  of  the  body. 

The  human  body  probably  possesses  a  true 
assymmetrical  resistance;  that  is  to  say,  when 
taken  after  the  current  has  been  passing  for  some 
time,  its  resistance  is  different  in  different  direc- 
tions. This  variation  in  the  apparent  resistance 
is  believed  by  some  to  be  due  to  polarization 
effects. 

Body,  Insulated  —A  body  sup- 
ported on  an  insulator,  or  non-conductor  of 
electricity. 


Bod.] 


[Box. 


Body-Protector,  Electric  . —A  de- 
vice for  protecting  the  human  body  against  the 
accidental  passage  of  an  electric  discharge. 

To  protect  the  human  body  from  the  acciden- 
tal passage  through  it  of  dangerous  electric  cur- 
rents, Delany  places  a  light,  flexible,  conducting 
wire,  A  A  B  L  L,  in  the  posi- 
tion shown  in  Fig.  56,  for 
the  purpose  of  leading  the 
greater  part  of  the  current 
around  instead  of  through 
the  body.     The   body-pro- 
tector thus  provides  a  by- 
path, or  shunt  of  low  resist- 
ance, around  the  body,  and 
protects  it  from  the  effects 
of  an  accidental  discharge,     f'f-  S6.   Electric 
The  resistance  of  the  con-       Body-Protector. 
tacts  of  the  protecting  conductor  with  the  skin 
may  interfere  somewhat  with  the  efficacy  of  the 
device.     Inside  insulating  shoe-soles  for  lessening 
the  danger    from    accidental    contacts    through 
grounded  circuits  have  also  been  proposed. 

Boiler-Feed,  Electric   —A  device 

for  automatically  opening  a  boiler-feed  appar- 
atus electrically  when  the  water  in  the  boiler 
falls  to  a  certain  predetermined  point. 

Boiling  of  Secondary  or  Storage  Cell. — 
(See  Cell,  Secondary,  or  Storage,  Boiling  of,} 

Bole. — A  unit,  seldom  or  never  used,  pro- 
posed by  the  British  Association. 

One  bole  is  equal  to  one  gramme-kine.  (See 
Kine.) 

Bolometer.— An  apparatus  devised  by 
Langley  for  measuring  small  differences  of 
temperature. 

A  thermal  balance.  (See  Balance,  Ther- 
mic) 

Bpmbardment,   Molecular  — The 

forcible  rectilinear  projection  from  the  nega- 
tive electrode,  of  the  gaseous  molecules  of  the 
residual  atmospheres  of  exhausted  vessels  on 
the  passage  of  electric  discharges.  (See 
Matter,  Radiant,  or  Ultra-Gaseous) 

Bonsalite. — An  insulating  substance. 

Bore,  Armature •  —The  space  pro- 
vided between  the  pole  pieces  of  a  dynamo 
or  motor  for  the  rotation  of  the  armature. 


Boreal  Magnetic  Pole.— (See  Pole,  Mag~ 
netic,  Boreal?) 

Bot. — A  term  sometimes  used  as  a  con- 
traction for  Board  of  Trade  unit  of  electric 
supply,  or  the  energy  contained  in  a  current 
of  1 ,000  amperes  flowing  in  one  hour  under  a 
pressure  of  one  volt. 

The  term  appears  inadmissible.  If  used  at  all, 
it  should  be  B.  O.  T.  The  usage  of  giving  the 
names  of  distinguished  dead  electricians  to  new 
units  is  a  good  one,  and  should  be  followed  here. 

Boucherize. — To  subject  to  the  boucheriz- 
ing  process.  (See  Boucherizing?) 

Boucherizing. — A  process  for  the  preser- 
vation of  wooden  telegraph  poles,  by  inject- 
ing a  solution  of  copper  sulphate  into  the 
pores  of  the  wood.  (See  Pole,  Telegraphic?) 

Bound  Charge.— (See  Charge,  Bound) 

Box  Bridge.— (See  Bridge,  Box) 

Box,  Cable  —A  box  placed  on  a 

large  terminal  pole  and  provided  to  receive  the 
separate  conductors  where  the  air-line  wires 
join  a  cable. 

The  wires  are  distributed  in  the  cable  box  so 
as  to  be  readily  attached  to  the  air-line  wires. 

Box,  Cooling,  of  Hydro-Electric  Ma- 
chine. — A  box  provided  in  Armstrong's 
hydro-electric  machine  for  the  steam  to  pass 
through  before  leaving  the  nozzle. 

In  passing  through  the  cooling-box  some  of  the 
steam  suffers  condensation.  The  cooling-box, 
therefore,  always  contains  some  water,  the  pres- 
ence of  which  seems  to  be  necessary  to  the  opera- 
tion of  the  machine. 

Box,  Distributing,  of  Conduit. — A  name 
generally  applied  to  a  handhole  of  a  conduit. 
(See  Handhole  of  Conduit) 

Box,  Distribution,  for  Arc  Light  Cir- 
cuits.— A  device  by  means  of  which  arc 
and  incandescent  lights  may  be  simultane- 
ously employed  on  the  same  line  from  a  con- 
stant-current dynamo-electric  machine  or 
other  source  of  constant  currents. 

A  portion  of  the  line  circuit,  whose  difference 
of  potential  is  sufficient  to  operate  the  electro- 
receptive  device,  as,  for  example,  an  incandescent 
lamp,  is  divided  into  such  a  number  of  multiple 


Box.] 


[Box. 


circuits  as  will  provide  a  current  of  the  requisite 
strength  for  each  of  the  devices.  For  example,  if 
the  normal  current  on  the  line  is  seven  amperes, 
then  each  of  the  seven  multiple-connected  electro- 


Fig.  J7.     Series- Multiple  Circuit. 
receptive  devices  shown  in  Fig.  57  will  have  a  cur- 
rent of  one  ampere  passing  through  it,  provided 
the  resistance  of  each  branch  is  the  same, 

In  order  to  protect  the  remaining  devices  from 
variations  in  the  current  on  the  extinguishment  of 
any  of  the  devices,  automatic  cut-outs  are  pro- 
vided,  which  divert  the  current  thus  cut  off 
through  a  resistance  equivalent  to  that  of  the 
device. 

A  variety  of  distribution  boxes  are  in  use.  (See 
Circuits,  Varieties  of.) 

Box,    District-Call A    box    by 

means  of  which  an  electric  signal  is  auto- 
matically sent  over  a  telegraphic  line  and 
received  by  an  electro-magnetic  device  at  the 
other  end  of  the  line. 


motion  by  the  pulling  of  a  lever,  makes  and 
breaks  an  electric  circuit  and  sends  over  the  line 
a  succession  of  electric  impulses  of  varying  length, 
separated  from  one  another  by  varying  intervals 
of  time.  These  impulses  may  be  received  at  the 
central  station  as  a  series  of  dots  and  dashes,  or 
may,  by  means  of  a  Morse  sounder,  produce  suc- 
cessive sounds.  By  pulling  the  lever  or  handle 
through  different  distances,  different  signals  may 
be  sent  to  the  central  station  and  serve  as  calls  for 
various  services,  such  as  messenger  boys,  fire 
alarm,  police,  special,  etc. 

The  general  appearance  of  a  four-call  district 
box  is  shown  in  Fig.  58.  In  order  to  transmit 
a  call  for  any  particular  one  of  these  four  services 
the  handle  is  pulled  until  it  comes  opposite  to  the 
letters  indicating  the  required  service,  and  is  then 
released.  The  service  required  is  then  indicated 
at  the  receiving,  or  central  station,  through  the 
varying  signals  sent  over  the  line  by  the  move- 
ment of  the  break-wheel,  on  the  release  of  the 
handle. 

Box,  Fire-Alarm  Signal  —  —A  signal 
box  provided  for  the  purpose  of  automatically 
sending  an  alarm  of  fire. 

The  fire-alarm  box  shown  in  Fig.  59,  operates 


Fig.  38.    District  Call  Box. 

A  system  of  district  calls  includes  a  number  of 
call  boxes  connected  by  telegraphic  lines  with  a 
central  station,  A  wheel,  or  its  equivalent,  set  in 


Fig.  j-p.    Fire- Alarm  Signal-Box. 

on  the  same  principle  as  the  district  call  box.  The 
movement  of  the  handle  in  the  direction  of  the 
arrow  drives  a  wheel  that  makes  and  breaks  a 
circuit  at  certain  intervals. 

The  fire-alarm    signal    boxes    are    connected 


Box.] 


[Box. 


either  with  a  central  station,  or  with  the  engine 
houses  of  the  district  in  which  the  alarm  is 
sounded,  or  with  both. 

Box,  Fire- Alarm  Telegraph An 

automatic-call  signal-box  employed  for  send- 
ing an  alarm  of  fire  to  a  central  station. 

A  form  of  fire-alarm  telegraph  box  is  shown  in 
Fig.  60.  It  consists  essentially  of  a  circuit-breaker 


Fig.  6O.  Fire- Alarm  Telegraph  Box. 
that  is  moved  by  pulling  down  a  lever.  The 
release  of  the  lever  repeats  the  signal  to  the  fire 
department  at  the  central  station  a  certain  number 
of  times.  The  box  also  contains  a  relay  bell, 
lightning  arrester  and  signal-bell  key. 

Box,   Fishing A    term    sometimes 

used  instead  of  junction  box.  (See  Box, 
Junction. ) 

Box,  Flush A  box  or  space,  flush 

with  the  surface  of  a  road-bed,  provided  in  a 
system  of  underground  wires  or  conduits, 
to  facilitate  the  introduction  of  the  conduct- 
ors into  the  conduit,  or  for  the  examination 
of  the  conductors. 

Box,  Fuse The  box  in  which   the 

fuse-wire  of  a  safety-fuse  is  placed. 

The   fuse-box  should  be  formed  of  moisture- 
proof,  Incombustible,  insulating  materials. 

Box,    Junction A   moisture-proof 

box  provided  in  a  system  of  underground  con- 


the  feeders  and  the  mains,  and  from  which 
the  current  is  distributed  to  the  individual 
consumer.  (See  Feeder.  Main,  Electric^) 

A  form  of  junction  box  for  coupling  lengths  of 
conductors  is  shown  in  Fig.  6l. 

Box,  Patrol  Alarm An  automatic- 
signal  call-box  provided  for  use  on  the  out- 
side of  buildings. 

The  call-box  is  placed  inside  a  box,  the  outer 
door  of  which  is  furnished  with  a  Yale  lock. 


Fig.  6 1.     Junction  Box. 

ductors  to  receive  the  terminals  of  the  feed- 
ers, in  which  connection   is  made  between 


Fig.  62.    Patrol  Box. 

A  form  of  patrol  box  is  shown  in  Fig.  62. 

Box,  Resistance A  box  containing 

a  number  of  separate  coils  of  known  resist- 
ances employed  for  determining  the  value  of 
an  unknown  resistance,  and  for  other  pur- 
poses. (See  Bridge,  Electric,  Box  Form  of.) 

Box-Sounding  Relay.— (See  Relay,  Box- 
Sounding) 

Box-Sounding  Telegraphic  Relay.— (See 

Relay,  Box-Sounding  Telegraphic.) 

Box,  Splice A  box  provided  for 

holding  splice  joints  and  loops,  and  so  ar- 
ranged as  to  be  readily  accessible  for  exami- 
nation, re-arranging,  cross-connecting,  etc. 

Splice-boxes  vary  in  shape  and  construction 
according  to  the  purposes  for  which  they  are 
designed. 

Box,  Splice,  Four-way A  splice- 
box  piovided  with  four  ways  or  tubular  con- 
duits. 

Box,    Splice,   Two  Way A  splice- 


Box.J 


[Bra. 


box  provided  with  but  two  tubular  conduits  or 
ways. 

Box,    Tumbling A    rotating   box 

in  which  metallic  articles  that  are  to  be 
electroplated  are  placed  so  as  to  be  polished 
by  attrition  against  one  another. 

Boxing  the  Compass. — (See  Compass, 
Boxing  the?) 

Bracket,  Lamp,  Electric A  de- 
vice similar  to  a  bracket  for  a  gas  burner  for 
holding  or  supporting  an  electric  lamp. 


Fig.  63.    Lamp  Bracket.      Fig.  6  4.      Lamp  Bracket. 
Lamp  brackets  are   either  fixed  or  movable. 


Fig.  6j.    Lamp  Bracket,  Movable  Arms. 
Those  shown  in  Figs.  63  and  64  are  fixed.     That 
shown  in  Fig.  65  is  movable. 

Bracket,  Telegraphic A   support 

or  cross  piece  placed  on  a  telegraph  pole 
for  the  support  of  the  insulators  of  tele- 
graphic lines. 

Telegraphic  insulators  are  supported  either  on 
wooden  arms,  or  on  iron  or  metal  brackets. 

Fig.  66  shows  a  form  of  iron  bracket.     Fig.  67 
shows  a  form  of  wooden  arm. 


Fig.  66.    Telegraphic 
Bracket. 


Fig.  67.     Telegraphic 
Cross- Arm. 


Various  well  known  modifications  of  these 
shapes  are  in  common  use.  (For  details,  see  Fole, 
Telegraphic. ) 


Braid,  Tubular A  braid  of  fibrous 

insulating  material,  woven  in  the  form  of  a 
tube,  and  provided  for  drawing  over  a  splice 
after  two  wires  have  been  connected. 

Braided  Wire.— (See  Wire,  Braided) 

Brake,  Electro-Magnetic A  brake 

for  car  wheels,  the  braking  power  for  which 
is  either -derived  entirely  from  electro-magnet- 
ism, or  is  thrown  into  action  by  electro-mag- 
netic devices. 

Electro-magnetic  car  brakes  are  of  a  great  va- 
riety of  forms.  They  may,  however,  be  arranged 
in  two  classes,  viz. : 

(l.)  Those  in  which  magnetic  adhesion,  or  the 
magnetic  attraction  of  the  brake  to  the  wheels,  is 
employed. 

(2.)  Ordinary  brake  mechanism  in  which  the 
force  operating  the  brake  is  thrown  into  action  by 
an  electro-magnet. 

Brake,  Friction A  name  some- 
times given  to  a  Prony  brake.  (See  Brake, 
Prony.) 

Brake,  Magneto-Electric A  device 

for  checking  the  swing  of  a  galvanometer,  in 
which  a  slight  inverse  current  is  sent  through 
the  coils  of  the  galvanometer. 

The  Frey  magneto-electric  brake,  as  shown  in 
Fig.  68,  consists  of  a  small  coil,  connected  by  a 


Fig.  68.   Electric  Brakt. 

contact-key  with  the  galvanometer  terminals.  A 
small  adjustable  magnet  coil  is  provided  for 
regulating  the  action  ot  the  inverse  current.  To 
avoid  disturbance,  the  brake  is  placed  at  least 
4  or  5  feet  from  the  galvanometer.  Manipulation 
of  the  ordinary  galvanometer  key  attains  the  same 
end  in  a  much  simpler  manner. 

Brake,  Prony A  mechanical  de- 
vice for  measuring  the  power  of  a  driving 
shaft. 


Bra.j 


57 


[Bre. 


An  inflexible  beam,  Fig.  69,  is  provided  at  one 
end  with  a  clamping  device  for  clamping  the 
driving  shaft  or  pulley,  and  at  the  other  end  A, 
with  a  pan  for  holding  weights. 

If  the  brake  be  arranged  as  shown  in  Fig.  69, 
and  the  shaft  rotate  in  the  direction  of  the  arrow, 
the  tendency  will  be  to  carry  the  beam  around 
with  the  shaft,  placing  it  at  some  given  moment 


Fig,  69,    Pr any  Brake. 

in  the  position  shown  by  the  dotted  line.  If  a 
sufficiently  heavy  weight  be  placed  at  x,  in  a  pan 
hung  at  A,  the  beam  will  assume  a  position  ver- 
tically downwards.  If,  however,  the  torque,  or 


Fig.  70.    Prony 

twisting  force  of  the  driving  shaft,  be  balanced  by 
the  weight,  the  bar  will  remain  horizontal.  The 
power  can  then  be  calculated  by  multiplying  the 
weight  in  pounds  by  the  circumference  in  feet  of 
the  circle  of  which  the  bar  is  a  radius,  and  this 
product  by  the  number  of  turns  of  the  driving 
shaft  per  minute.  The  product  will  be  the  num- 

» V 


Fig.  7  TC    Prony  Brake. 

ber  of  foot-pounds  per  minute,  and,  when  divided 
by  33,000,  will  give  the  horse-power. 

Some  modified  forms  of  the  Prony  brake  are 
shown  in  Figs.  7°  and  71. 

A  simple  form  of  brake  consists  of  a  cord  passed 
over  the  pulley  of  the  machine  to  be  tested.  A 
weight  is  hung  at  one  end  of  the  cord.  The  other 


end  of  the  cord  is  attached  to  the  top  of  a  spring 
balance,  the  other  end  of  which  is  fastened  to  the 
floor.  A  reading  of  the  spring  balance  is  taken 
while  the  pulley  is  at  rest  and  when  it  is  in  motion, 
and  the  result  calculated. 

Branch. — A  term  applied  to  any  principal 
distributing  conductor  from  which  outlets 
are  taken  or  taps  made. 

Branch-Block.— (See  Block,  Branch) 

Branch  Conductors. — (See  Conductor, 
Branch) 

Branch  Fuse.— (See  Fuse,  Branch.} 

Branch,  Sub —A  distributing  con- 
ductor taken  from  a  branch. 

Branding,  Electric  -  -  — A  process 
whereby  the  branding  tool  is  heated  by  elec- 
trical incandescence  instead  of  by  ordinary 
heat. 

The  branding  tool  consists  essentially  of  a  small 
transformer  with  devices  for  regulating  the  cur- 
rent  strength  by  switches  and  choking  coils. 

Brassing,  Electro — Coating  a  sur- 
face with  a  layer  of  brass  by  electro-plating. 
(See  Plating,  Electro) 

The  plating  bath  contains  a  solution  of  copper 
and  zinc  ;  a  brass  plate  is  used  as  an  anode. 

Break. — A  want  of  continuity  in  a  circuit. 

Break,  Circuit  Loop  —  — A  device  for 
introducing  a  loop  in  any  part  of  a  line 
circuit. 

A  form  of  circuit  loop-break  is  shown  in  Fig.  72- 


Fig.  T3.     Circuit  Loop  Break. 

It  consists  essentially  of  a  rigid  frame  with  two 
porcelain  or  other  suitable  insulators  for  the  sup- 
port  of  the  loop  wires. 


Bre.] 


58 


[Bri. 


Break-Down  Switch.— (See  Switch,Break- 
Down?) 

Break-Induced  Current. — (See  Current, 
Break-Induced?) 

Break,  Mercury  —  —A  form  of  circuit 
breaker  operated  by  the  removal  of  a  conduc- 
tor from  a  mercury  surface. 

Mercury  breaks  assume  a  variety  of  forms.  One 
end  of  the  circuit  is  connected  with  the  mercury, 
and  the  other  with  the  conductor. 

Break  Shock.— (See  Shock,  Break\ 

Breaker,  Circuit Any  device  for 

breaking  a  circuit. 

Breaking  the  Primary.— (See  Primary, 
Breaking  the.) 

Breaking  Weight  of  Telegraph  Wires.— 
(See  Wires,  Telegraph,  Breaking  Weight 
of.) 

Breath  Figures.  — (See  Figures,  Breath?) 

Breeze,  Electric  —  — A  term  some- 
times employed  in  electro-therapeutics  for  a 
brush  discharge. 

One  of  the  electrodes,  consisting  of  a  single 
point  or  a  number  of  points,  is  held  near  the 
parts  to  be  treated  so  that  the  con vective  discharge 
is  received  thereon.  The  other  electrode  is  con- 
nected to  the  body  of  the  patient. 

Breeze,  Electro-Therapeutic  —       —An 

electric  breeze.     (See  Breeze,  Electric?) 

Breeze,  Head,  Electro-Therapeutic  — 
— A  form  of  electric  convective  discharge, 
or  electric  breeze,  applied  to  the  head.     (See 
Breeze,  Electric?) 

Breeze,  Static —  — An  electric  breeze 
obtained  by  the  convective  discharge  of  an 
electrostatic  charge. 

Bridge-Arms. — (See  Arms,  Bridge  or 
Balance?) 

Bridge,  Box A  box  of  resistance 

coils  so  arranged  as  to  be  capable  of  being 
used  directly  as  a  Wheatstone  electric  balance. 
(See  Bridge,  Electric,  Box  Form  of?) 

The  commercial  form  of  Wheatstone's 
balance. 

Bridge,  Electric  —A    device    for 

measuring  the  value  of  electric  resistances. 


The  electric  bridge  is  also  called  the  Electric 
Balance. 

This  is  called  a  bridge  because  the  wire  M,  G, 
N,  bridges  or  joins  points  of  equal  potential. 

A,  B,  C  and  D,  Fig.  73,  are  four  electric  re- 
sistances, any  one  of  which  can  be  determined  in 
ohms,  provided  the  absolute  value  of  one  of  the 
others,  and  the  relative  values  of  any  two  of  the 
remaining  three  are  known  in  ohms. 

A  voltaic  battery,  Zn  C,  is  connected  at  O 
and  P,  so  as  to  branch  at  P,  and  again  unite  at 


Zn   C 
Fig.  13.    Electric  Balance. 

Q,  after  passing  through  the  conductor  D  C,  and 
B  A. 

A  sensitive  galvanometer,  G,  is  connected  at 
M  N,  as  shown. 

The  passage  of  a  current  through  any  resistance 
is  attended  by  a  fall  of  potential  proportional  to 
the  resistance.  (See  Potential,  Electric.)  If,  then, 
the  resistances  A,  C  and  B,  are  so  proportioned 
to  the  value  of  the  unknown  resistance  D,  that  no 
current  passes  through  the  galvanometer  G,  the 
two  points,  M  and  N,  in  the  two  circuits,  Q  M  P 
and  Q  N  P,  are  at  the  same  potential.  That  is  to 
say,  the  fall  of  potential  along  Q  M  P  and  Q  N  P, 
at  the  points  M  and  N,  is  equal.  Since  the  fall 
of  potential  is  proportional  to  the  resistance,  it 
follows  that 

A  :  B  :  :  C  :  D, 
or  A  X  D  =  B  X  C, 

•">=(!) 

If  then  we  know  the  values  of  A,  B  and  C,  the 
value  of  D,  can  be  readily  calculated. 

T> 

By  making  the  value  iL  some  simple  ratio,  the 

value  of  D,  is  easily  obtained  in  terms  of  C. 

The  resistances  A,  B  and  C,  may  consist  of 
coils  of  wire  whose  resistance  is  known.  To 
avoid  their  magnetism  affecting  the  galvanometer 
needle  during  the  passage  of  the  current  through 
them,  they  should  be  made  of  wire  bent  into  two 


C. 


Bri.] 


59 


[Bri. 


parallel  wires  and  wrapped  in  coils  called  resist- 
ance  coils;  or  a  resistance  box  may  be  used.  (See 
Coil,  Resistance.  Box,  Resistance,) 

There  are  two  general  forms  of  Wheatstone's 
Bridge,  the  box  form,  and  the  sliding  form. 

Bridge,  Electric,  Armg  of The 

resistances  of  an  electric  bridge  or  balance. 
(See  Bridge,  Electric) 

Bridge,  Electric,  Box  Form   of — 

A  commercial  form  of  bridge  or  balance  in 
which  all  the  known  arms  or  branches  of  the 
bridge,  except  the  unknown  arm,  consist  of 
standardized  resistance  coils,  whose  values  are 
given  in  ohms.  (See  Coil,  Resistance?) 
The  box  form  of  bridge  or  balance  is  shown  in 


Fig.  74.    Box  Balance. 

perspective  in  Fig.  74,  and  in  plan  in  Fig.  75. 
The  bridge  arms,  corresponding  to  the  resistances 


Fig. 


Box  Balance. 


A  and  B,  of  Fig.  73,  consist  of  resistance  coils  of 
10,  100  and  1,000  ohms  each,  inserted  in  the 
arms  q  z,  and  q  x,  of  Fig.  75.  These  are 
called  the  froportional  coils.  The  arm  corre- 
sponding to  resistance  C,  of  Fig.  73,  is  composed 
of  separate  resistances  of  I,  2,  2,  5,  10,  10,  20,  50, 
loo,  100,  200,  500,  1,000,  1,000,  2,000  and  5,000 
ohms.  In  some  forms  of  box  bridges  additional 
decimal  resistances  are  added. 

The  resistance  coils  are  wound,  as  shown  in 
Fig.  76,  after  the  wire  has  been  bent  on  itself  in 
the  middle.  This  is  done  in  order  to  avoid  the 
effects  of  induction,  among  which  are  a  disturb- 
ing action  on  a  galvanometer  used  near  them, 
and  the  introduction  of  a  spurious  resistance  in 
the  coils  themselves.  (See  Resistance,  Spurious.} 

3—  Vol.  1 


To  avoid  the  effects  of  changes  of  resistance  oc- 
casioned by  changes  of  temperature,  the  coils  are 
made  of  German  silver,  or,  preferably,  of  alloys 
called  Platinoid  or  Platinum  silver.  Even  when 
these  alloys  are  used,  care  should  be  taken  not  to 
allow  the  currents  to  pass  continuously  through 
the  resistance  coils  longer  than  a  few  moments. 

The  coils,  C,  C',  are  connected  with  one  another 
in  series  by  soldering  their  ends  to  the  short 


Fig.  76. 


ce  Coils. 


thick  pieces  of  brass,  E,  E,  E,  Fig.  76.  On  the  in- 
sertion  of  the  plug-keys,  at  S,  S,  the  coils  are  cut- 
out by  short-circuiting.  Care  should  be  taken  to 
see  that  the  plug-keys  are  firmly  inserted  and  free 
from  grease  or  dirt,  as  otherwise  the  coil  will  not  be 
completely  cut  out.  As  each  plug-key  is  inserted 
it  should  be  turned  slightly  in  the  opening,  so 
as  to  insure  good  contact. 

The  following  are  the  connections,  viz.:  The 
galvanometer  is  inserted  between  q  and  r,  Fig.  77, 


Jit 

Fig.  77.     Electric  Balance. 

the  unknown  resistance  between  z  and  r ;  the  bat- 
tery  is  connected  tox  and  z.  ,  A  convenient  pro- 
portion being  taken  for  the  value  of  the  propor- 
tional coils,  resistances  are  inserted  in  the  arm  C, 
until  no  deflection  is  shown  by  the  galvanometer 
G.  The  similarity  between  these  connections  and 
those  shown  in  Fig.  75  will  be  seen  from  an 
inspection  of  Fig.  77.  The  arms,  A  and  B,  corre- 
spond to  q  x  and  q  z,  of  Fig.  75;  C,  to  the  arm 


Bri.] 


[Bri. 


x  r,  Fig.  75 ;  and  D,  to  the  unknown  resistance. 
We  then  have  as  before: 

A:B::C:D,  orAxD  =  BxC.  .-.  D  =  f—\  Q. 

The  advantage  of  the  simplicity  of  the  ratios,  A 
and  B,  or  10,  100  and  1,000  of  the  bridge  box, 
will  therefore  be  manifest.  The  battery  terminals 
may  also  be  connected  to  q  and  r,  and  the  gal- 
vanometer terminals  to  x  and  z,  without  disturb- 
ing the  proportions. 

Bridge,  Electric,  Commercial  Form  of 

A  name  sometimes  given  to  the  box 

form  of  Wheatstone's  electric  balance.  (See 
Bridge,  Electric,  Box  Form  of.) 

Bridge,  Electric  Duplex An  ar- 
rangement of  telegraphic  circuits  in  the  form 
of  a  Wheatstone  electric  bridge  for  the  pur- 
poses of  duplex  telegraphy.  (See  Teleg- 
raphy, Duplex,  Bridge  Method  of  ) 

Bridge,  Electric,  Proportionate  Arms 
of (See  Arms,  Proportionate) 

Bridge,  Electric,  Slide-Form  of 

A  balance  in  which  the  proportionate  arms  of 
the  bridge  are  formed  of  a  single  thin  wire,  of 
uniform  diameter,  generally  of  German  silver, 
of  comparatively  high  resistance.  The  length 
of  this  wire  is  usually  one  metre ;  hence  this 
apparatus  is  often  called  the  metre  bridge. 

A  Sliding  Contact  Key  slides  over  the  wire;  one 
terminal  of  the  key  is  connected  with  the  galva- 
nometer and  the  other  with  the  wire  when  the  key 
is  depressed.  As  the  wire  is  of  uniform  diameter 
the  resistances  of  the  arms,  A  and  B,  Fig.  78,  will 


Fig 


be  directly  proportional  to  the  lengths.  A  scale 
placed  near  the  wire  serves  to  measure  these 
lengths.  A  thick  metal  strip  connected  with  the 
slide  wire  has  four  gaps  at  P,  Q,  R  and  S. 

When  in  ordinary  use,  the  gaps  at  P  and  S,  are 
either  connected  by  stout  strips  of  conducting  ma- 
terial or  by  known  resistances,  in  which  latter  case 
they  act  simply  as  ungraduated  extensions  of  the 
slide  wire,  and,  like  lengthening  the  slide  wire, 
increase  the  sensibility  of  the  instrument. 


The  unknown  resistance  is  then  inserted  in  the 
gap  at  Q,  and  a  known  resistance,  generally  the 
resistance  box,  in  that  at  R.  The  galvanometer 
has  one  of  its  terminals  connected  to  the  metal 
strip  between  Q  and  R,  and  its  other  terminal  to 
the  sliding  key.  The  battery  terminals  are  con- 
nected to  the  metal  strips  between  P  and  Q,  and 
R  and  S,  respectively. 

These  connections  are  more  clearly  seen  in  the 
form  of  bridge  shown  in  Fig.  79.  The  slide  wire, 
w  w,  consists  of  three  separate  wires  each  a  metre 


Fig.  79.    SuU  Form  of  Bridge. 

in  length,  so  arranged  that  only  one  wire,  or  two 
in  series,  or  all  three  in  series,  can  be  used.  Mat- 
ters being  now  arranged  as  shown,  the  sliding 
key  is  moved  until  no  current  passes  through  the 
galvanometer  when  the  key  is  depressed. 

The  slide  form  of  bridge  is  not  entirely  satis- 
factory, since  the  uncertainty  of  the  spring-con- 
tact causes  a  lack  of  correspondence  between  the 
point  of  contact  and  the  point  of  the  scale  on 
which  the  index  rests. 

The  loss  of  uniformity  in  the  diameter  of  the 
wire,  due  to  constant  use,  causes  a  lack  of  corre- 
spondence between  the  resistance  of  the  wire  and 
its  length.  With  care,  however,  very  accurate 
results  can  be  obtained  by  the  slide  form. 

Bridge,  Inductance An  appara- 
tus for  measuring  the  inductance  of  a  circuit 
similar  to  a  Wheatstone  bridge.  (See /«</?/£•- 
tance) 

Professor  Hughes  employed  an  inductance 
bridge  of  the  following  description: 

Four  resistances,  Q,  S,  R  and  P,  arranged  as 
shown  in  Fig.  80,  form  the  bridge.  The  re- 
sistances, Q,  S  and  R,  consist  of  sections  of  Ger- 
man silver  wire,  one  metre  in  length,  each  of 
the  resistance  of  4  ohms.  P,  is  a  coil  of  wire  pos- 
sessing sensible  inductance.  The  object  of  tha 


Bri.] 


61 


[Bri, 


bridge  is  to  measure  the  value  of  this  inductance. 
I,  is  an  interrupter  placed  in  the  circuit  of  the 
battery  B. 

Suppose  the  interrupter,  I,  be  placed  in  the  tele- 
phone circuit  between  T  and  c.  By  shifting  the 
sliding  contact  so  as  to  alter  the  value  of  R,  a  bal- 


Fig.  80.     Inductance  Bridge. 

ance  can  be  effected  and  silence  obtained  in  the 
telephone. 

Now  remove  the  interrupter  and  place  it  in  the 
battery  circuit  between  b  and  a,  as  shown  in  Fig. 
80.  If  now,  the  interrupter,  I,  be  made  to  rapidly 
interrupt  the  battery  current,  this  balance  is 
destroyed,  and  cannot  be  again  obtained  by  any 
variation  in  the  value  of  the  resistance,  R. 

The  reason  of  this  is  evident.  On  the  closing 
or  opening  of  the  battery  current,  the  inductance 
of  P,  produces  a  counter  electromotive  force  in 
P,  which  produces  differences  of  potential  between 
a  and  c.  If  an  attempt  be  made  to  prevent  this, 


Fig.  St. 


Bridge. 


by  altering  the  value  of  R,  the  steady  balance  is 
destroyed,  and  the  telephone  wfll  be  traversed  by 
a  current  during  the  time  the  currents  have  be- 
come steady.  In  order  to  obtain  a  balance 
during  rapid  alternations  of  the  battery  current, 
Professor  Hughes  placed  a  pair  of  mutually  in- 


ductive  coils  in  the  battery  and  the  telephone 
circuits,  as  shown  in  Fig.  81. 

The  resistances,  Q,  S,  R  and  P,  are  the  same 
as  already  described.  The  mutually  inductive 
coils,  M1  and  M2,  are  placed  respectively  in  the 
telephone  and  battery  circuits  in  the  manner 
shown.  The  coil  M2,  in  the  battery  circuit  is 
fixed,  while  that  in  the  telephone  circuit  is  so 
arranged  that  it  can  be  maintained,  with  its  centre 
coincident  with  that  of  M3,  while  its  axis  can  be 
placed  at  any  desired  angle  with  M2.  When  the 
axes  of  the  coils  are  at  right  angles,  the  inductance 
is  zero.  When  they  are  co-linear,  the  inductance 
is  at  its  maximum. 

When  the  coils  Mlf  and  M8,  are  in  any  inter- 
mediate  position,  the  inductive  electromotive 
force  produced  in  the  telephone  circuit  can,  if 
the  value  of  R,  be  changed,  be  made  to  balance 
the  impulsive  electromotive  force  due  to  the  in- 
ductance of  P,  and  the  value  of  this  latter  can, 
therefore,  be  inferred. 

Bridge,  Magnetic An  apparatus  in- 
vented by  Edison  for  measuring  magnetic 
resistance,  similar  in  principle  to  Wheatstone's 
electric  bridge. 

The  magnetic  bridge  is  based  on  the  fact  that 
two  points  at  the  same  magnetic  potential,  when 
connected,  fail  to  produce  any  action  on  a  mag- 
netic needle.  The  magnetic  bridge  consists,  as 
shown  in  Fig.  82,  of  four  arms  or  sides  made  of 


Fig.  82.    Magnetic  Bridge. 

pure,  soft  iron.  The  poles  of  an  electro-magnet 
are  connected  to  projections  at  the  middle  of 
the  short  side  of  the  rectangle.  By  this  means 
a  difference  of  magnetic  potential  is  main- 
tained  at  these  points.  The»two  long  sides  are 
formed  of  two  halves  each,  which  form  the  four 
arms  of  the  balance.  Two  of  these  only  are 
movable. 

Two  curved  bars  of  soft  iron,  of  the  same  area 
of  cross-section  as  the  arms  of  the  bridge,  rest  on 
the  middle  of  the  long  arms,  in  the  arched  shape 
shown.  Their  ends  approach  near  the  top  of  the 


Bri.] 


[Bru. 


arch  within  about  a  half  inch.  A  space  is  hol- 
lowed out  between  these  ends,  for  the  reception  of 
a  short  needle  of  well-magnetized  hardened  steel, 
suspended  by  a  wire  from  a  torsion  head. 

The  movements  of  the  needle  are  measured  on 
a  scale  by  a  spot  of  light  reflected  from  a  mirror. 

The  electro-magnet  maintains  a  constant  dif- 
ference of  magnetic  potential  at  the  two  shorter 
ends  of  the  rectangle.  If,  therefore,  the  four 
bars,  or  arms  of  the  bridge,  are  magnetically 
identical,  there  will  be  no  deflection,  since  no 
difference  of  potential  will  exist  at  the  ends  of  the 
bars  between  which  the  needle  is  suspended.  If, 
however,  one  of  the  bars  or  arms  be  moved  even 
a  trifle,  the  needle  is  at  once  deflected,  the  motion 
becoming  a  maximum  when  the  bar  is  entirely 
removed.  If  replaced  by  another  bar,  differing 
in  cross-section,  constitution,  or  molecular  struc- 
ture, the  balance  is  likewise  disturbed. 

The  magnetic  bridge  is  very  sensitive.  It  was 
designed  by  its  inventor  for  testing  the  magnetic 
qualities  of  the  iron  used  in  the  construction  of 
dynamo-electric  machines. 

Bridge  Method  of  Duplex  Telegraphy.^ 

(See  Telegraphy,  Duplex,  Bridge  Method 
of.) 

Bridge  Method  of  Qnadrnplex  Teleg- 
raphy. — (See  Telegraphy,  Quadruples, 
Bridge  Method  of.) 

Bridge,   Metre A   slide   form    of 

Wheatstone's  electric  bridge,  in  which  the 
slide  wire  is  one  metre  in  length.  (See 
Bridge,  Electric,  Slide  Form  of.) 

Bridge,  Resistance A  term  some- 
times applied  to  an  electric  bridge  or  balance. 
(See  Bridge,  Electric) 

Bridge,   Reversible A   bridge  or 

balance  so  arranged  that  the  proportionate 
coils  can  be  readily  interchanged,  thus  per- 
mitting the  bridge  coils  to  be  readily  tested  by 
reversing. 

Bridge,   Wheatstone's    Electric 

A  name  given  to  the  electric  bridge  or  balance. 
(See  Bridge,  Electric) 

Bridges. — Heavy  copper  wires  suitably 
shaped  for  connecting  the  dynamo-electric 
machines  in  an  incandescent  light  station  to 
the  bus-rods  or  wires. 


Bright  Dipping.— (See  Dipping,  Bright?) 
Bright    Dipping   Liquid.— (See  Liquid, 
Bright  Dipping :) 

Britannia  Joint.— (See  Joint,  Britannia) 
Broken  Circuit.— (See  Circuit,  Broken) 

Bronzing,  Electro Coating  a  sur- 
face with  a  layer  of  bronze  by  electro-plating. 
(See  Plating,  Electro) 

The  plating  bath  contains  a  solution  of  tin  and 
copper. 

Bmsh-and-Spray  Discharge.— (See  Dis- 
charge, Brush-and-Spray) 

Brush  Discharge.  —  (See  Discharge, 
Brush) 

Brush  Electrode.— (See  Electrode,  Brush) 

Brush,  Faradic An  electrode  in 

the  form  of  a  brush  employed  in  the  medical 
application  of  electricity. 

The  bristles  are  generally  made  of  nickelized 
copper  wire. 

Brush-Holders  for  Dynamo-Electric  Ma- 
chines.— Devices  for  supporting  the  collecting 
brushes  of  dynamo-electric  machines. 

As  the  brushes  require  to  be  set  or  placed  on 
the  commutator  in  a  position  which  often  varies 
with  the  speed  of  the  machine,  and  with  changes 
in  the  resistance  of  the  external  circuit,  all  brush - 
holders  are  provided  with  some  device  for  moving 
them  concentrically  with  the  commutator  cylin- 
der. 

Brush  Rocker.— (See  Rocker,  Brush) 

Brush,  Scratch A  brush  made 

of  wire  or  stiff  bristles,  etc.,  suitable  for  clean- 
ing the  surfaces  of  metallic  objects  before 
placing  them  in  the  plating  bath. 

Scratch  brushes  are  made  of  various  shapes  and 
are  provided  with  wires  or  bristles  of  varying 
coarseness. 

Some  forms  of  scratch  and  finishing  brushes 
are  shown  in  Fig.  83.  They  are  circular  in  outline 


Fig.  83.     Scratch  Brushes. 

and  are  adapted  for  use  in  connection   with  a 
lathe. 


Bru.J 


63 


[Bui. 


Brush,      Scratch,      Circular  —A 

scratch  brush  of  a  circular  shape,  so  fitted  as 
to  be  capable  of  being  placed  in  a  lathe  and 
set  in  rapid  rotation. 

Brush,  Scratch,  Hand A  scratch 

brush  operated  by  hand,  as  distinguished 
from  a  circular  scratch  brush  operated  by  a 
lathe. 

Brushes,  Adjustment  of  Dynamo-Electric 

Machines Shifting  the  brushes  into 

the  required  position  on  thr  commutator 
cylinder,  either  non-automatically  by  hand,  or 
automatically  by  the  current  itself.  (See 
Regulation,  Automatic,  of  Dynamo-Electric 
Machines?) 

Brushes,  Carbon,  for  Electric  Motors 

Plates  of  carbon  for  leading  current 

to  electric  motors.  (See  Brushes  of  Dynamo- 
Electric  Machine?) 

These  are  generally  known  simply  as  brushes. 

Brushes,  Collecting,  of  Dynamo-Electric 

Machine Conducting  brushes  which 

bear  on  the  commutator  cylinder,  and  take  off 
the  current  generated  by  the  difference  of 
potential  in  the  armature  coils.  (See  Brushes 
of  Dynamo-Electric  Machine?) 

Brushes,  Lead  of The  angle  through 

which  the  brushes  of  a  dynamo-electric  ma- 
chine must  be  moved  forward,  or  in  the 
direction  of  rotation,  in  order  to  diminish 
sparking  and  to  get  the  best  output  from 
the  dynamo. 

The  necessity  for  the  lead  arises  from  the  coun- 
ter magnetism  or  magnetic  reaction  of  the  arma- 
ture, and  the  magnetic  lag  of  its  iron  core.  (See 
Lead,  Angle  of.) 

The  position  of  the  brushes  on  the  commutator 
to  insure  the  best  output  is  practically  the  same 
in  a  series  dynamo  for  any  current  strength. 
In  shunt  and  compound  dynamos  it  varies  with 
the  lead. 

Brushes  of  Dynamo-Electric  Machine.— 
Strips  of  metal,  bundles  of  wire,  slit  plates  of 
metal,  or  plates  of  carbon,  that  bear  on  the 
commutator  cylinder  of  a  dynamo-electric 
machine,  and  carry  off  the  current  generated. 

Rotary  brushes  consisting  of  metal  discs  are 
sometimes  employed.  Copper  is  almost  univer- 


Fig.  84.    Brushes 


sally  used  for  the  brushes  of  dynamo-electric 
machines.  Carbon  brushes  are  often  used  for 
dynamo-electric  motors. 

The  brush  shown  at  B,  Fig.  84,  is  formed  of 
copper  wires,  soldered 
together  at  the  non- 
bearing  end.  A  copper 
plate,  slit  at  the  bear- 
ing end,  is  shown  at  C, 
and  bundles  of  copper 
plates,  soldered  together 
at  the  non-bearing  end, 
are  shown  at  D. 

The  brushes  should 
bear  against  the  com- 
mutator cylinder  with 
sufficient  force  to  pre- 
vent jumping,  and  con- 
sequent burning,  and 
yet  not  so  hard  as  to 
cause  excessive  wear. 

Brushes,  Rotating,  of  Dynamo-Electric 

Machines Discs   of  metal,  employed 

in  place  of  the  ordinary  brushes  for  carry- 
ing off  the  current  from  the  armatures  of 
dynamo-electric  machines. 

Brushing,  Scratch Cleansing  the 

surface  of  an  article  to  be  electroplated,  by 
friction  with  a  scratch  brush. 

Scratch  brushing  is  generally  done  with  the 
brushes  wet  by  various  solutions. 

Buckling.— Irregularities  in  the  shape  of 
the  surfaces  of  the  plates  of  storage  cells,  fol- 
lowing a  too  rapid  discharge. 

Bug. — A  term  originally  employed  in  quad- 
ruplex  telegraphy  to  designate  any  fault  in 
the  operation  of  the  apparatus. 

This  term  is  now  employed,  to  a  limited  extent, 
for  faults  in  the  operation  of  any  electric  appa- 
ratus. 

Bug-Trap. — A  device  employed  to  over- 
come the  "  bug  "  in  quadruplex  telegraphy. 

Bulb,  Lamp  — The  chamber  or 

globe  in  which  the  filament  of  an  incan- 
descent electric  lamp  is  placed. 

The  chamber  or  globe  of  a  lamp  must  be  of 
such  construction  as  to  enable  the  high  vacuum 
necessary  to  the  operation  of  the  lamp  to  be  main- 
tained. 


Bun.] 


(54 


[Bur. 


Bunched  Cable.— (See  Cable,  Bunched?) 
Bunched    Cable,    Straightaway  — 

(See  Cable,  Bunched,  Straightaway?) 

Bunched  Cable,  Twisted  -  —(See 
Cable,  Bunched,  Twisted?) 

Bunsen  Yoltaic  Cell.— (See  Cell,  Voltaic, 
Bunsen's) 

Buoy,  Electric A  buoy  on  which 

luminous  electric  signals  are  displayed. 

Burglar  Alarm.— (See  Alarm,  Burglar?) 

Burglar  Alarm  Annunciator. — (See  An- 
nunciator, Burglar  Alarm?) 

Burglar  Alarm  Contacts. — (See  Contacts, 
Burglar  Alarm.) 

Burglar  Alarm,  Yale  Lock  Switch  for 

—(See  Alarm,  Yale-Lock-Switch  Burglar) 

Burner,  Argand  Electric An  ar- 

gand  gas-burner  that  is  lighted  by  means  of 
an  electric  spark. 

The  argand  electric  burner  assumes  a  variety 
of  forms,  such  as  the  plain  pendant,  the  ratchet- 
pendant  and  the  automatic.  They  are  also  used 
in  systems  of  multiple  gas  lighting. 

Burner,  Argand  Electric,  Automatic 

— An  argand  burner  arranged  for  automatic 
electric  lighting.  (See  Burner,  Automatic- 
Electric:) 

Burner,  Argand  Electric,  Hand-Lighter 

— A  plain-pendant  electric  burner 

adapted  for  lighting  an  argand  gas-burner. 
(See  Burner,  Plain-Pendant  Electric?] 

Burner,  Argand-Electric,  Plain-Pendant 

— A  plain-pendant  electric  burner 

adapted  for  lighting  an  argand  gas  burner. 
(See  Burner,  Plain-Pendant  Electric?) 

Burner,  Argand-Electric,  Ratchet-Pend- 
ant   A  ratchet-pendant  electric  burner 

adapted  for  lighting  an  argand  gas-burner. 
(See  Burner,  Ratchet-Pendant  Electric?] 

Burner,  Automatic-Electric An 

electric  device  for  both  turning  on  the  gas 
and  lighting  it,  and  turning  it  off,  by  alter- 
nately touching  different  buttons. 

The  gas-cock  is  opened  or  closed  by  the  motion 
of  an  armature,  the  movements  of  which  are  con- 
trolled by  two  separate  electro-magnets.  One 
push-button,  usually  a  white  one,  turns  the  gas  on 


by  energizing  one  of  the  electro-magnets  and, 
at  the  same  time,  lights  it  by  means  of  a  suc- 
cession of  sparks  from  a  spark  coil.  Another 
push-button,  usually  a  black  one,  turns  the  gas 
off  by  energizing  the  other  electro-magnet. 
The  turning  on  or  off  of  the  gas  is  accom- 
plished by  positive 
motions.  Automatic 
burners  are  also  made 
with  a  single  button. 

An  Argand  Electric 
Burner  is  shown  in 
Fig.  85. 

Burner,  Electric 
Candle  -  —A 
device  for  electri- 
cally lighting  a  gas 
jet  in  a  burner  sur- 
rounded by  a  por- 
celain tube  in  imita- 
tion of  a  candle. 

Electric  candle  bur- 
ners are  either  simple 
or  ratchet  candle  bur- 
ners. 

Burner,  Hand- 
Lighting  Electric 
A  name  sometimes  applied  to  a  plain- 
pendant  electric  burner.  (See  Burner,  Plain- 
Pendant  Electric?) 

Burner,    Jump-Spark  — A    term 

sometimes  applied  to  a  gas  burner  in  which 
the  issuing  gas  is  ignited 
by  a  spark  that  jumps  be- 
tween the  metallic  points 
placed  on  it. 

Jump-spark  burners  are 
used  in  systems  of  multiple 
gas  lighting.  (See  Light- 
ing,  Electric  Gas.) 

Burner,  Plain-Pen- 
dant Electric A 

gas  -  burner       provided 

with  a  pendant  for  the 

purpose  of  lighting  the 

gas  by  means  of  a  spark,  Fig.  8t>.  Plain. 

after  the  gas  has  been  Burner. 

turned  on  by  hand. 

The  gas  is  first  turned  on  by  hand  at  the  ordi- 


Fig.  Sj.    Argand  Electr 
Burner. 


Bur.] 


65 


[But 


nary  key,  and  is  then  lighted  by  pulling  the  pend- 
ant C,  Fig.  86.  A  spark  from  a  spark  coil  ignites 
the  gas. 

This  is  sometimes  called  an  electric  hund- 
Jighting  burner, 

Burner,  Ratchet-Pendant  Candle  Elec- 
tric   A  burner  for  both  lighting  and 

extinguishing  a  candle  gas  jet. 

Burner,  Ratchet-Pendant  Electric  — 

— A  gas-burner  in  which  one  pulling  of  a 
pendant  turns  on  the  gas  and  ignites  it  by 
means  of  an  electric  spark  from  a  spark  coil, 
and  the  next  pulling  of  the  pendant  turns  off 
the  gas. 

A  ratchet-wheel  and  pawl  are  operated  by  the 
motion  of  the  pendant.  The  first  pull  of  the 
pendant  chain  moves  the  ratchet  so  as  to  open  a 
four- way  gas  cock,  and  at  the  same  time  light 
the  gas  at  the  burner  tip  by  a  wipe-spark  from  a 
spark  coil.  On  the  next  pull  ot  the  pendant,  the 
four- way  cock  is  turned  so  as  to  turn  off  the  g?s. 
Alternate  pulls,  therefore,  light  and  extinguish 
the  gas. 

Burner,  Simple  Candle  Electric 

A  plain-pendant  electric  burner.  (See  Bur- 
ner, Plain  Pendant  Electric?) 

Burner,    Thumb-Cock    Electric  — 

An  electric  gas- 
burner,  in  which 
the  turning  of  an 
ordinary  thumb- 
cock  turns  on  the 
gas,  and  ignites  it 
by  a  spark  pro- 
duced by  a  wiping 
contact  actuated 
by  the  motions  of 
the  thumb-cock. 
A  form  of  thumb- 
cock  burner  is 
shown  in  Fig.  87. 

Burner,     Vi- 
brating-Elec- 

triC —An    Fig.  87.     Thumb- Cock  Burner. 

electric  gas-burner  in  which  the  gas  is  lighted 
after  it  is  turned  on  by  hand,  by  means  of  the 
spark  from  a  spark  coil  produced  on  the  rapid 


making  and  breaking  of  the  circuit  by  a 
vibrating  contact. 

The  vibrating-electric  burner  has  a  single  elec- 
tro-magnet. It  is  operated  by  means  of  a  button 
or  switch,  and  may  be  used  on  single  lights  or  on 
groups  of  lights.  It  bears  the  same  relation  to 
the  automatic  burner  that  the  plain-pendant 
burner  does  to  the  ratchet  burner. 

Burnetize. — To  subject  to  the  Burnetizing 
process.  (See  Burnetizing?) 

Burnetizing. — A  method  adopted  for  the 
preservation  of  wooden  telegraph  poles  by 
injecting  a  solution  of  zinc  chloride  into  the 
pores  of  the  wood.  (See  Pole,  Telegraphic?) 

Burning  at  Commutator  of  Dynamo. — 

An  arcing  at  the  brushes  of  a  dynamo-elec- 
tric machine,  due  to  their  imperfect  contact, 
or  improper  position,  which  results  in  loss  of 
energy  and  destruction  of  the  commutator 
segments. 

Bus. — A  word  generally  used  instead  of 
omnibus.  (See  Omnibus?) 

Bus-Bars.— (See  Bars,  Bus?) 

Bus-Rod  Wires.— (See  Wires  Bus-Rod.) 

Bus-Wire.— (See  Wire,  Bus?) 

Butt  Joint.— (See  Joint,  Butt?) 

Button,  Carbon  — A  resistance  of 

carbon  in  the  form  of  a  button. 

A  button  of  carbon  is  used  as  an  electric  resist- 
ance in  a  variety  of  apparatus;  its  principal  use, 
however,  is  in  the  transmitting  instrument  of  the 
electric  telephone.  In  the  telephone  transmitter, 
the  button  is  so  placed  between  contact-plates  that 
when  the  plates  are  pressed  together  by  the 
sound-waves,  the  electrical  resistance  is  decreased 
by  a  decrease  in  the  thickness  of  the  carbon  button, 
an  increase  in  its  density,  and  an  increase  in  the 
number  of  points  where  the  carbon  touches  the 
plates.  Rheostats,  or  resistances,  have  been 
made  by  the  use  of  a  number  of  carbon  buttons  or 
discs  piled  one  on  another  and  placed  in  a  glass 
tube.  Discs  of  carbonized  cloth  form  excellent 
resistances  for  such  purposes. 

Button,    Press A    push    button. 

(See  Button,  Push?) 

Button,  Push A  device  for  closing 


But] 


[Cab. 


In  electric   circuit   by  the   movement  of  a 
button. 
A  button,  when  pushed  by  the  hand,  closes  the 


Buzzer,  Electric A  call,  not  as 

loud  as  that  of  a  bell,  produced  by  a  rapid 


Fig.  88.    Push  Button.         Fig,  89.    Push  Button. 

contact,  and  thus  completes  a  circuit  in  which 
some  electro-receptive  device  is  placed.  This 
circuit  is  opened  by  a  spring, 
on  the  removal  of  the  pressure. 
Some  forms  of  push-buttons  are 
shown  in  Figs.  88,  89  and  90. 

A.floor-push  for  dining-rooms 
and  offices  is  shown  in  Fig. 
90. 

Fig.  88  shows  the  general 
appearance  of  an  ordinary  bell- 
push.  The  arrangement  of  the 
interior  spring  contacts  will  be 
understood  by  an  inspection  of  Fig.  91 


Fig.  9  /.     Spring  Contact  of  Bell  Push. 

automatic  make-and-break.    (See  Make-and' 
Break,  Automatic?) 

The  buzzer  is  generally  pkced  inside  a  resonant 


Fig.  90.    Floor 
Push. 


Fig.  92.    Buzzer. 

case  of  wood  in  order  to  strengthen  the  sound  by 
resonance.     A  form  of  buzzer  is  shown  in  Fig.  92. 


C. — An  abbreviation  for  centigrade. 

TIUS,  20  degrees  C.  means  20  degrees  of  the 
centigrade  thermometric  scale.  (See  Scale,  Cen- 
tigrade Thermometer.') 

C. — A  contraction  for  current. 

Generally  a  contraction  for  the  current  in 

amperes,  as  C  =  ^. 

C.  C. — A  contraction  for  cubic  centimetre. 
(See  Weights  and  Measures,  Metric  System 
of.) 

C.  G.  S.  Units.— A  contraction  for  centi- 
timetre-gramme-second  units.  (See  Units, 
Centimetre-Gramme-  Second.) 


C.  P. — A  contraction  for  candle  power. 
(See  Candle,  Standard.) 

Cable.— An  electric  cable.  (See  Cable, 
Electric.) 

Cable.— To  send  a  telegraphic  dispatch, 
by  means  of  a  cable. 

Cable,  Aerial A  cable  suspended 

in  the  air  from  suitable  poles. 

Cable,  Anti-Induction,  Waring 

A  form  of  anti-induction  cable. 

In  the  Waring  an ti- induction  cable  the  separate 
conductors  are  covered  with  a  fibrous  insulator, 
from  which  all  air  and  moisture  is  expelled,  and 
the  fibre  then  saturated  with  an  insulating  ma- 


Cab.] 


67 


[Cab. 


terial  called  ozite.  The  conductors  are  then  pro- 
tected from  the  inductive  effects  of  neighboring 
conductors  by  a  continuous  sheath  of  lead  alloyed 
with  tin. 

Where  the  cables  are  bunched,  the  bunches 
are  sometimes  again  surrounded  by  insulating 
material,  and  the  whole  then  covered  by  a  con- 
tinuous lead  sheathing  ;  generally,  however,  the 
separately  insulated  conductors  are  bunched, 
and  then  covered  by  a  single  sheathing  of  lead 
alloyed  with  tin. 

Cable,  Armature  of The  armor  of 

a  cable.  (See  Armature  of  a  Cable) 

Cable,  Armor  of The  protecting 

sheathing  or  metallic  covering  on  the  outside 
of  a  submarine  or  other  electric  cable. 

Cable,  Armored An  electric  cable 

provided,  in  addition  to  its  insulating  coat- 
ing, with  a  protective  coating  or  sheathing, 
generally  of  metal  tubing  or  wire. 

Cable-Box.— (See  Sox,  Cable.) 

Cable,  Bunched A  cable  contain- 
ing more  than  a  single  wire  or  conductor. 

Some  forms  of  bunched,  lead-covered  cables, 
are  bhown  in  Fig.  93. 


Fig.  93.     Bunched  Cables. 

Cable,  Bunched,  Straightaway 

A  bunched  cable  the  separate  conductors  of 
which  extend  in  the  direction  of  the  length  of 
the  cable  without  any  twisting,  being  placed 
in  successive  layers. 

In  arranging  the  separate  conductors  in  suc- 
cessive layers  an  advantage  is  gained  in  testing 
for  a  given  wire  in  order  to  make  a  loop,  splice, 
or  branch  with  the  next  adjoining  section.  This  is 
rendered  still  easier  by  giving  the  conductors 
of  the  successive  layers  some  distinctive  form  of 
braiding  in  the  fibrous  insulating  material,  or 
some  distinctive  color. 

Cable,     Bunched,    Twisted    —A 

bunched  cable,  the  separate  conductors  of 
which  are  twisted-pairs  placed  in  successive 
layers. 


Each  twisted-pair  of  a  bunched  cable  acts  as  a 
metallic  circuit,  and,  moreover,  possesses  the  ad- 
vantage of  avoiding  the  ill  effects  of  induction,  so 
disadvantageous  in  telephone  circuits. 

In  laying  up  the  twisted-pairs  in  successive 
layers  in  a  bunched  cable,  the  direction  of  twist- 
ing is  reversed  in  each  successive  layer.  This 
form  is  especially  desirable  on  all  long  cable  lines. 

In  the  case  of  twisted  cables  for  telephone  lines, 
the  twists  are  sometimes  made  as  frequent  as  one 
in  every  three  or  four  inches.  In  such  cases  the 
cross-talk  of  induction  is  inappreciable. 

Cable,  Capacity  of The  quantity 

of  electricity  required  to  raise  a  given  length 
of  a  cable  to  a  given  potential,  divided  by  the 
potential. 

The  amount  of  charge  for  a  given  potential 
that  any  single  conductor  will  take  up  with 
the  rest  of  the  conductors  grounded.  (See 
Capacity,  Electrostatic^) 

The  ability  of  a  wire  or  cable  to  permit  a 
certain  quantity  of  electricity  to  be  passed 
into  it  before  acquiring  a  given  difference  of 
potential. 

Before  a  telegraph  line  or  cable  can  transmit  a 
signal  to  its  further  end,  its  difference  of  potential 
must  be  raised  to  a  definite  amount  dependent  on 
the  character  of  the  instruments  and  the  nature  of 
the  system. 

The  first  effect  of  electricity  being  passed  into  a 
line  is  to  produce  an  accumulation  of  electricity 
on  the  line,  similar  to  the  charge  in  a  condenser. 
Cables  especially  act  as  condensers,  and  from  the 
high  specific  inductive  capacity  of  the  insulating 
materials  employed,  permit  considerable  induc- 
tion to  take  place  between  the  core  and  the 
metallic  armor  or  sheathing,  or  the  ground. 

The  capacity  of  a  cable  depends  on  the  capacity 
of  the  wire  ;  *.  e. ,  on  its  length  and  surface,  on 
the  specific  inductive  capacity  of  its  insulation, 
and  its  neighborhood  to  the  earth,  or  to  other 
conducting  wires,  casings,  armors,  or  metallic 
coatings.  Submarine  or  underground  cables 
therefore  have  a  greater  capacity  than  air  lines. 

This  accumulation  of  electricity  produces  a  re- 
tardation in  the  speed  of  signaling,  because  the 
wire  must  be  charged  before  the  signal  is  received 
at  the  distant  end,  and  discharged  or  neutralized 
before  a  current  can  be  sent  in  the  reverse  direc- 
tion. This  latter  may  be  done  by  connecting 
each  end  to  earth,  or  by  the  action  of  the  reverse 
current  itself. 


Cab.J 


[Cab. 


The  smaller  the  electrostatic  capacity  of  a  cable, 
therefore,  the  greater  the  speed  of  signaling.  (See 
Retardation. ) 

The  capacity  of  a  cable  is  measured  in  micro- 
farads. (See  Farad,  Micro.) 

Cable  Clip.— (See  Clip,  Cable) 

Cable-Core.— (See  Core  of  Cable) 

Cable,  Core-Ratio  of The  ratio  be- 
tween the  diameter  of  the  insulation  of  a  cable 
and  the  mean  diameter  of  the  strand. 

D 

The  core- ratio  is  represented  by  ^-;  where  D, 

is  the  diameter  of  the  insulation,  and  d,  the  mean 
diameter  of  the  strand.  Should  the  extreme 
diameter  of  the  strand  of  a  cable  be  used  in  cal- 
culations for  insulation  resistance,  inductive  capa- 
city, etc.,  erroneous  values  would  be  obtained. 
The  measured  diameter  of  the  copper  conductor 
is  consequently  decreased  some  five  per  cent.,  and, 
in  this  way,  correct  values  are  approximately 
obtained.—  (Clark  <&•>  Sabine.) 

Cable,  Duplex A  conductor  con- 
sisting of  two  separate  cables  placed  parallel 
to  each  other. 

The  duplex  cable  is  used  especially  in  the  al- 
ternating current  system. 

Cable,  Electric •  —The  combination 

of  an  extended  length  of  a  single  insulated 
conductor,  or  two  or  more  separately  insu- 
lated electric  conductors,  covered  externally 
with  a  metallic  sheathing  or  armor. 

Strictly  speaking,  the  word  cable  should  be 
limited  to  the  case  of  more  than  a  single  con- 
ductor. Usage,  however,  sanctions  the  employ- 
ment of  the  word  to  indicate  a  single  insulated 
conductor. 

The  conducting  wire  may  consist  of  a  single 
wire,  of  a  number  of  separate  wires  electrically 
connected,  or  of  a  number  of  separate  wires  in- 
sulated from  one  another. 

An  electric  cable  consists  of  the  following  parts, 
viz.: 

(i.)  The  conducting  wire  or  core. 

(2.)  The  insulating  material  for  separating  the 
several  wires;  and 

(3.)  The  armor  or  protecting  covering,  consist' 
Ing  of  strands  of  iron  wire,  or  of  a  metallic  coat- 
Ing  or  covering  of  lead. 

As  to  their  position,  cables  are  aerial,  sub- 
marine, or  underground.  As  to  their  purpose, 


they  are  telegraphic,  telephonic,  or  electric  light 
and  power  cables.  As  to  the  number  of  their 
conductors  they  are  single-wire  or  bunched 
cables.  Bunched  cables  are  straightaway  or 
twisted. 
Fig.  94  shows  a  form  of  submarine  cable  the 


Fig.  94.    Electric  Cablt. 

armor   of  which  is  formed  of  strands  of  iron 
wire. 
Cable,  Electric  Light  or  Power 

A  cable  designed  to  distribute  the  electric  cur- 
rent employed  in  electric  light  or  power  sys- 
tems. 

Electric  light  cables  are  generally  underground. 
They  may  be  submarine.  (See  Cable,  Electric.) 

Cable,  Flat A  cable,  the  separate 

conductors  of  which  are  laid-up  side  by  side 
so  as  to  form  a  flat  conductor. 

A  flat  cable  is  suitable  for  house  work  as  being 
less  objectionable  in  appearance  when  placed  OB 
the  outside  of  ceilings  or  walls. 

Cable,  Flat  Duplex A  flat,  laid-up 

cable  containing  two  wires. 

Cable-Grip.— (See  Grip,  Cable) 
Cable-Hanger.— (See  Hanger,  Cable) 

Cable-Hanger  Tongs.— (See  Tongs,  Cable- 
Hanger) 

Cable  Laid-TJp  in  Layers. — A  term  applied 
to  a  cable,  all  the  conducting  wires  of  which 
are  in  layers. 


Cab.] 


[Cab. 


Cable  Laid-TJp  in  Reversed  Layers. — A 
term  applied  to  a  cable  in  which  the  conduct- 
ors, in  alternate  layers,  are  twisted  in  opposite 
directions.  (See  Cable,  Bunched,  Straight- 
away) 

Cable  Laid-Up  in  Twisted  Pairs.— A  term 
applied  to  a  cable  in  which  every  pair  of  wires 
is  twisted  together.  (See  Cable,  Bunched, 
Twisted?) 

Cable  Lead.— (See  Lead,  Cable}. 

Cable,  Multiple-Core A  cable  corn- 

tainir.g  more  than  a  single  core. 

Cable-Protector.— (See  Protector,  Cable?) 

Cable-Serving.— (See  Serving,  Cable) 

Cable,  Single-Wire A  cable  con- 
taining a  single  wire  or  conductor. 

Cable,  Sub-Aqueous An  electric 

cable  designed  for  use  under  water. 

The  term  submarine  is  more  frequently  em- 
ployed. 

Cable,  Submarine A  cable  designed 

for  use  under  water. 

Submarine  cables  are  either  shallow-water,  or 
deep-sea  cables.  Gutta-percha  answers  admirably 
for  the  insulating  material  of  the  core.  Various 
other  insulators  are  also  used. 

Strands  of  tarred  hemp  or  jute,  known  as  the 
cable-serving,  are  wrapped  around  the  insulated 
core  in  order  to  protect  it  from  the  pressure  of  the 
galvanized  iron  wire  armor  afterwards  put  on. 
To  prevent  corrosion  the  iron  wire  is  covered 
with  tarred  hemp,  galvanized,  or  otherwise 
Coated. 

Submarine  cables  are  generally  employed  for 
telegraphic  or  telephonic  communication.  (See 
Cable,  Electric.') 

Cable,  Submarine,  .Deep-Sea A 

submarine  cable  designed  for  use  in  deep 
water. 

This  form  of  cable  is  not  so  heavily  armored  as 
the  shallow-water  submarine  cable. 

Cable,  Submarine,  Shallow- Water 

A  submarine  cable  designed  for  use  in  shallow 
water. 

This  cable  is  provided  with  a  heavier  armor  or 
sheathing  than  a  deep-sea  cable  to  protect  it 
from  chafing  due  to  the  action  of  the  waves  and 
tides  in  shallow  water.  (See  Cable^  Submarine.) 


Cable  Support,  Underground (See 

Support,  Underground  Cable.} 

Cable  Tank.-  (See  Tank,  Cable) 

Cable,  Telegraphic A  cable  de- 
signed to  establish  telegraphic  communication 
between  different  points. 

Telegraphic  cables  may  be  aerial,  submarine, 
or  underground.  (See  Cable,  Electric.) 

Cable,  Telephonic A  cable  de- 
signed to  establish  telephonic  communication 
between  different  points. 

Telephonic  cables  may  be  aerial,  submarine, 
or  underground,  (See  Cable,  Electric.) 

Cable-Terminal.— (See  Terminal,  Cabled 

Cable,  Torpedo —A  cable,  in  the 

circuit  of  which  a  torpedo  is  placed.  (See 
Torpedo,  Electric) 

Cable,  Twisted-Pair A  cable 

containing  a  single  twisted  pair,  suitable  for 
use  as  a  lead  and  return,  thus  affording  a 
metallic  circuit. 

Cable,  Two,  Three,  Four,  etc.,  Conductor 

A  cable  containing  two,  three,  four, 

or  more  separate  conducting  wires. 

Cable,  Underground An  electric 

cable  placed  underground. 

The  conducting  wires  of  an  underground  cable 
are  surrounded  by  a  good  insulating,  water-proof 
substance,  and  protected  by  a  sheathing  or  armor. 
A  coating  of  lead  is  very  generally  employed  for 
the  sheathing  or  armor.  Underground  cables,  in 
order  to  be  readily  accessible,  should  be  placed 
in  an  underground  conduit  or  subway.  (See 
Cable,  Electric,  Conduit^  Underground  Electric. 
Subway^  Electric.) 

Cable- Worming.— (See  Worming,  Cable) 

Cablegram. — A  message  received  by  means 
of  a  submarine  telegraphic  cable. 

Cables,  Lajlng-Up The  placing  or 

disposing  of  the  separate  cables  or  conduc- 
tors in  a  bunched  cable.1 

The  separate  conductors  in  cables  may  be  laid- 
up  "straightaway"  or  "twisted."  (See  Cable, 
Bunched*  Twisted.  Cable%  Bunched,  Straight- 
away. ) 

Cabling.— Sending  a  telegraphic  dispatch 
bv  means  of  a  cable. 


CaL] 


70 


[Cal. 


Calahaif  s  Stock  Printer.— (See  Printer, 
Stock,  Calahan's.) 

Calamine,   Electric A  crystalline 

variety  of  silicate  of  zinc  that  possesses  pyro- 
electric  properties.  (See  Electricity,  Pyro.) 

Cal-Electricity.— (See  Electricity,  Cal) 

Calibrate. — To  determine  the  absolute 
or  relative  value  of  the  scale  divisions,  or  of 
the  indications  of  any  electrical  instrument, 
such  as  a  galvanometer,  electrometer,  vol- 
tameter, wattmeter,  etc. 

Calibrating. — The  act  of  determining  the 
absolute  or  relative  value  of  the  deflections, 
or  indications  of  an  electric  instrument. 

Calibration,  Absolute The  deter- 
mination of  the  absolute  values  of  the  read- 
ing of  an  electrometer,  galvanometer,  volt- 
meter, amperemeter,  or  other  similar  instru- 
ment. 

The  calibration  of  a  galvanometer,  for  ex- 
ample, consists  in  the  determination  of  the  law 
which  governs  its  different  deflections,  and  by 
which  is  obtained  in  amperes,  either  the  absolute 
or  the  relative  currents  required  to  produce  such 
deflections. 

For  various  methods  of  calibration,  see  stan- 
dard works  on  electrical  testing,  or  on  elec- 
tricity. 

Calibration,  Invariable,  of  Galvanom- 
eter   In  galvanometers  with  absolute 

calibration,  a  method  for  preventing  the  oc- 
currence of  variations  in  the  intensity  of  the 
field  of  the  galvanometer,  due  to  the  neigh- 
borhood of  masses  of  iron,  etc. 

Calibration,  Relative The  deter- 
mination of  the  relative  values  of  the  reading 
of  an  electrometer,  voltmeter,  amperemeter, 
or  other  similar  instrument. 

Caliper,  Mi- 

erometer   

— A  name  some-' 
times  given  to  a 
vernier  wire 
gauge.  (See 
Gauge,  Vernier 

Wire)  Fig,  95.    Micrometer  Califer. 

A  form  of  micrometer  caliper  is  shown  in  Fig.  Q 


Call-Bell,    Extension (See  Sell, 

Extension  Call.) 
Call-Bell,    Magneto-Electric An 

electric  call-bell  operated  by  currents  pro- 
duced by  the  motion  of  a  coil  of  wire  before 
the  poles  of  a  permanent  magnet. 

A  well  known  form  of  magneto  call-bell  is  shown 


Fig.  96.    Magneto  Call  Bell. 

in  Fig.  96.  The  armature  is  driven  by  the  rota- 
tion of  the  handle. 

Call-Bell,  Telephone An  electric 

bell,  the  ringing  of  which  is  used  to  call  a 
person  to  a  telephone. 

Call,  Electric  Bell  —An  electric 

bell  sometimes  used  to  call  the  attention  of  an 
operator  to  the  fact  that  his  correspondent 
wishes  to  communicate  with  him,  or  to  notify 
an  attendant  that  some  service  is  desired. 

Call,  Messenger A  district  call- 
box.  (See  Box,  District  Call.) 

Call,  Thermo-Electric An  instru- 
ment for  sounding  an  alarm  when  the  tem- 
perature rises  above,  or  falls  below,  a  fixed 
point. 

In  one  form  of  thermo-electric  call  a  needle  is 
moved  over  a  dial  by  a  simple  thermic  device  and 
rings  a  bell  when  the  temperature  for  which  it 
has  been  se  is  attained.  The  thermo-call  is  appli- 
cable to  the  regulation  of  the  temperature  o/ 


Cal.] 


71 


[Cal. 


dwellings,  incubators,  hot  houses,  breweries,  dry- 
ing rooms,  etc. 

Callaud  Voltaic  Cell.— (See  CeH,  Vol- 
taic, Callaud's.} 

Calling-Drop.— (See  Drop,  Calling.} 

Calorescence.  —  The  transformation  of 
invisible  heat-rays  into  luminous  rays,  when 
received  by  certain  solid  substances. 

The  term  was  proposed  by  Tyndall.  The  light 
from  a  voltaic  arc  is  passed  through  a  hollow 
glass  lens  filled  with  a  solution  of  iodine  in  bisul- 
phide of  carbon. 

This  solution  is  opaque  to  light  but  quite  trans- 
parent to  heat. 

If  a  piece  of  charred  paper,  or  thin  platinum 
foil,  is  placed  in  the  focus  of  these  invisible  rays, 
it  will  be  heated  to  brilliant  incandescence.  (See 
Focus.) 

Caloric. — A  term  formerly  applied  to  the 
fluid  which  was  believed  to  be  the  cause  or 
essence  of  heat. 

The  use  of  the  word  caloric  at  the  present  time 
is  very  unscientific,  since  heat  is  now  known  to 
he  an  effect  of  a  wave  motion  and  not  a  material 
thing.  (SeeA^a/.) 

Calorie. — A  heat  unit. 

There  are  two  calories,  the  small  and  the  large 
calorie. 

The  amount  of  heat  required  to  raise  the  tem- 
perature of  one  gramme  of  water  from  o  degree 
C.  to  I  degree  C.  is  called  the  small  calorie. 

The  amount  of  heat  required  to  raise  1,000 
grammes,  or  a  kilogramme,  of  water  from  o  de- 
gree C.  to  I  degree  C.  is  called  the  great  calorie. 
The  first  usage  of  the  word  is  the  commoner. 

This  word  is  sometimes  spelled  calory. 

Calorie,  Great  — The  amount  of 

heat  required  to  raise  the  temperature  of  one 
kilogramme  of  water  from  o  degree  C.  to  I 
degree  C. 

Calorie,  Small  — The  amount  of 

heat  required  to  raise  the  temperature  of  one 
gramme  of  water  from  o  degree  C.  to  I 
degree  C. 

Calorimeter — An  instrument  for  measur- 
ing the  amount  of  heat  or  thermal  energy 
contained  or  developed  in  a  given  body. 

Thermometers  measure  temperature  only.     A 


thermometer  plunged  in  a  cup  full  of  boiling 
water  shows  the  same  temperature  that  it  would 
in  a  tub  full  of  boiling  water.  The  quantity  of 
heat  energy  present  in  the  two  cases  is  of  course 
greatly  different,  and  can  be  measured  by  a  cal- 
orimeter only. 

Various  forms  of  calorimeters  are  employed. 

In  order  to  determine  the  quantity  of  heat  in 
a  given  weight  of  any  body,  this  weight  may  be 
heated  to  a  definite  temperature,  such  as  the  boil- 
ing point  of  water,  and  placed  in  a  vessel  con- 
taining ice.  The  quantity  of  ice  melted  by  the 
body  in  cooling  to  the  temperature  of  the  ice,  is 
determined  by  measuring  the  amount  of  water 
derived  from  the  melting  of  the  ice.  Care  must 
be  observed  to  avoid  the  melting  of  the  ice  by  ex- 
ternal heat. 

In  this  way  the  amount  of  heat  required  to 
raise  the  temperature  of  a  given  weight  of  a  body 
a  certain  number  of  degrees,  or  the  capacity  of 
the  body  for  heat,  may  be  compared  with  the 
capacity  of  an  equal  weight  of  water.  This  ratio 
is  called  the  specific  heat.  (See  Heal,  Specific.) 

The  heat  energy,  present  in  a  given  weight  of 
any  substance  at  a  given  temperature,  can  be  de- 
termined by  means  of  a  calorimeter;  for,  since  a 
pound  of  water  heated  i°  F.  absorbs  an  amount 
of  energy  equal  to  772  foot-pounds,  the  energy  can 
be  readily  calculated  if  the  number  of  pounds  of 
water  and  the  number  of  degrees  of  temperature 
are  known.  (See  Heat,  Mechanical  Equivalent 
of-} 

Calorimeter,  Electric An  instru- 
ment for  measuring  the  heat  developed  in  a 
conductor  or  any  piece  of  electrical  apparatus, 
in  a  given  time,  by  an  electric  current. 


Fig.  97.    Electric  Calorimeter. 

A  vessel  containing  water  is  provided  with  a 
thermometer  T,   Fig.  97.     The  electric  currenl 


Cal.] 


[Can, 


passes  for  a  measured  time  through  a  wire  im- 
mersed in  the  liquid. 

The  quantity  of  heat  is  determined  from  the 
increase  of  temperature,  and  the  weight  of  the 
water  heated. 

According  to  Joule,  the  number  of  heat  units 
developed  in  a  conductor  by  an  electric  current 
is  proportional: 

(I.)  To  the  resistance  of  the  conductor. 

(2.)  To  the  square  of  the  current  passing. 

(3.)  To  the  time  the  current  is  passing. 

(See  Heat  Unit,  English.) 

The  heating  power  of  a  current  is  as  the  square 
of  the  current  only  when  the  resistance  remains 
the  same.  (See  Heat,  Electric.) 

Calorimetric. — Pertaining  to  or  by  means 

of  the  calorimeter. 

Calorimetric  measurement  is  the  measurement 
of  heat  energy  made  by  means  of  the  calorimeter. 
(See  Calorimeter.} 

Caloriinetrically. — In  a  Calorimetric  man- 
ner. 

Calorimetric  Photometer.— (See  Photom- 
eter, Calorimetric) 

Calorimotor. — A  name  applied  to  a  defla- 
grator.  (See  Deflagrator^ 

Calory. — A  term  used  for  calorie. 

Calorie  is  the  preferable  orthography.  (See 
Calorie.) 

Cam,  Electro-Magnetic A  form 

of  magnetic  equalizer,  which  depends  for  its 
operation  on  the  lateral  approach  of  a  suita- 
bly shaped  polar  surface.  (See  Equalizer, 
Magnetic?) 

Cam,  Listening In  a  telephone 

exchange  system,  a  metallic  cam  by  means  of 
which  an  operator  is  placed  in  circuit  with 
a  subscriber. 

Candle. — The  unit  of  photometric  intensity. 

Such  a  light  as  would  be  produced  by  the 
consumption  of  two  grains  of  a  standard 
candle  per  minute. 

An  electric  lamp  of  1 6  candle-power,  or  one  of 
2,coo  candle-power,  is  a  light  that  gives  respect- 
ively 16  or  2,000  times  as  much  light  as  one  stand- 
ard candle. 

Candle  Bnrner,  Electric (SeeJBur- 

ner.  Electric  Candle^ 


Candle,  Electric A   term  applied 

to  the  Jablochkoff  candle,  and  other  similai 
devices.  (See  Candle,  Jablochkoff,') 

Candle,  Foot A  unit  of  illumina- 
tion equal  to  the  illumination  produced  by  a 
standard  candle  at  tlv  distance  of  i  foot. 

According  to  this  unit,  the  illumination  pro- 
duced by  a  standard  candle  at  the  distance  of 
2  feet  would  be  but  the  one-fourth  of  a  foot- 
candle;  at  3  feet,  the  one-ninth  of  a  foot-candle, 
etc. 

The  advantage  of  the  proposed  standard  lies  in 
the  fact  that  knowing  the  illumination  in  foot- 
candles  required  for  the  particular  work  to  be 
done,  it  is  easy  to  calculate  the  position  and 
intensity  of  the  lights  required  to  produce  the 
illumination. 

Candle,  Jablochkoff An   electric 

arc  light  in  which  the  two  carbon  electrodes  are 
placed  parallel  to  each  other  and  maintained 
a  constant  distance  apart  by  means  of  a  sheet 
of  insulating  material  placed  between  them. 

The  Jablochkoff  electric  candle  consists  of  twa 
parallel  carbons,  separated  by  a  layer  of  kaolin  or 
other  heat-resisting  insulating  material,  as  shown 
in  Fig.  98.  The  current  is  passed  into  and  out  of 
the  carbons  at  one  end  of  the 
candle,  and  forms  a  voltaic  arc  at 
the  other  end.  In  order  to  start 
the  arc,  a  thin  strip  called  the 
igniter,  consisting  of  a  mixture  of 
some  readily  ignitable  substance, 
connects  the  upper  ends  of  the 
carbons. 

An  alternating  current  is  em- 
ployed with  these  candles,  thus 
avoiding  the  difficulty  which  Fig-  <)S  Ja" 
would  otherwise  occur  from  the  ******  Candu' 
more  rapid  consumption  of  the  positive  than  the 
negative  carbon.  (See  Current^  Alternating.) 

Candle,  Metre The  illumination  pro- 
duced by  a  standard  candle  at  the  distance  of 
one  metre.  (See  Candle,  Foot?) 

Candle-Power.— (See  Power,  Candle.) 

Candle-Power,  Bated (See  Power, 

Candle,  Rated.) 

Candle -Power,  Spherical (See 

Power,  Candle,  Spherical?) 

Candle,    Standard A  candle    of 


Cao.] 

definite  composition  which,  with  a  given  con- 
sumption in  a  given  time,  will  produce  a  light 
of  a  fixed  and  definite  brightness. 

A  candle  which  burns  120  grains  of  sperma- 
ceti wax  per  hour,  or  2  grains  per  minute,  will 
give  an  illumination  equal  to  one  standard  candle. 

Unless  considerable  care  is  taken,  erroneous  re- 
sults will  be  obtained  from  the  use  of  the  stand- 
ard candle.  According  to  SJingo  and  Brooker 
the  following  are  among  the  most  important 
causes  of  these  errors  : 

(i.)  Defective  forms  of  candle  which  cause  a 
varying  consumption  of  the  material  per  second, 
and  consequently  a  varying  light  for  the  standard 
candle. 

(2.)  Variations  in  the  composition  of  the  sper- 
maceti of  which  the  candle  is  composed.  Sper- 
maceti is  not  a  definite  chemical  compound,  but 
consists  of  a  mixture  of  various  substances ; 
therefore,  even  if  the  consumption  is  maintained 
constant,  the  light-giving  power  is  not  necessarily 
constant. 

(3.)  Variations  in  the  composition  and  charac 
ter  of  the  wick,  such  as  the  number  and  size  of 
the  threads  of  which  it  is  formed  and  the  closeness 
of  the  strands,  all  of  which  circumstances  influence 
the  amount  of  light  given  off  by  the  candle. 

(4.)  The  light  emitted  in  certain  directions  va- 
ries in  a  marked  degree  with  the  shape  of  the 
wick.  The  mere  bending  of  a  wick  may,  there- 
fore, cause  the  amount  of  light  to  vary  consider 
ably. 

(5.)  The  light  varies  with  the  thickness  of  the 
wick.  Thick  wicks  give  less  light  than  thin 
wicks. 

(6.)  The  light  given  by  the  standard  candle  va- 
ries with  the  temperature  of  the  testing-room. 
As  the  temperature  rises  the  light  given  by  the 
standard  candle  increases. 

(7.)  Currents  of  air.  by  producing  variations 
in  the  amount  of  melting  wax  in  the  cup  of  the 
candle,  vary  the  amount  of  light  emitted. 

These  difficulties  in  obtaining  a  fixed  amount  of 
light  from  a  standard  candle,  together  with  the 
difficulty  of  comparing  the  feeble  light  of  a  single 
candle  with  the  light  of  a  much  more  powerful 
source,  such  as  an  arc  lamp,  coupled  with  the 
additional  difficulty  arising  from  the  difference  in 
the  colors  of  the  lights,  have  led  to  the  use  of 
other  standards  of  light  than  those  furnished  by 
the  standard  candle. 

Caoutchouc,  or  India-Rubber.— A  resin- 


73 


[Cap. 


ous  substance  obtained  from  the  milky  juices 
of  certain  tropical  trees. 

Caoutchouc  possesses  high  powers  of  electric 
insulation,  and  is  used  either  pure  or  combined 
with  sulphur. 

Cap,  Insulator A  covering  or  cap 

placed  some  distance  above  an  insulator,  but 
separated  from  it  by  an  air  space. 

Insulator  caps  are  intended  for  protection  of  the 
insulators  from  injury  by  the  throwing  of  stones 
or  other  malicious  acts.  Insulator  caps  are  gen- 
erally made  of  iron.  They  are  highly  objection- 
able, owing  to  the  facility  they  offer  for  the  ac- 
cumulation of  dust  and  dirt. 

Capacity,  Atomic The  quantiva- 

lence  or  valency  of  an  atom.  (See  Atomi- 
city) 

Capacity,  Dielectric A  term  em- 
ployed in  the  same  sense  as  specific  inductive 
capacity.  (See  Capacity,  Specific  Indwtive.} 

Capacity,    Electro-Dynamic    —A 

term  formerly  employed  by  Sir  William 
Thomson  for  self-induction.  (See  Induction, 
Self.} 

Capacity,  Electrostatic The  quan- 
tity of  electricity  which  must  be  imparted  to  a 
given  body  or  conductor  as  a  charge,  in  order 
to  raise  its  potential  a  certain  amount.  (See 
Potential,  Electric.} 

The  electrostatic  capacity  of  a  conductor  is  not 
unlike  the  capacity  of  a  vessel  filled  with  a  liquid 
or  gas.  A  certain  quantity  of  liquid  will  fill  a 
given  vessel  to  a  level  dependent  on  the  size  or 
capacity  of  the  vessel.  In  the  same  manner  a 
given  quantity  of  electricity  will  produce,  in  a 
conductor  or  condenser,  a  certain  difference  of 
electric  level,  or  difference  of  potential,  dependent 
on  the  electrical  capacity  of  the  conductor  or 
condenser. 

Or,  taking  the  analogous  case  of  a  gas-tight 
vessel,  the  quantity  of  gas  that  can  be  forced  into 
such  a  vesssl  depends  on  the  size  of  the  vessel 
and  the  pressure  with  whfch  it  is  forced  in.  A 
tension  or  pressure  is  thus  produced  by  the  gas 
on  the  walls  of  the  vessel,  which  is  greater  the 
smaller  the  size  of  the  vessel  and  the  greater  the 
quantity  of  gas  forced  in. 

In  the  same  manner,  the  smaller  the  capacity 
of  a  conductor,  the  smaller  is  the  charge  required 


Cap.] 


[Cap. 


to  raise  it  to  a  given  potential,  or  the  higher  the 
potential  a  given  charge  will  raise  it. 

The  capacity  K,  of  a  conductor  or  condenser, 
is  therefore  directly  proportional  to  the  charge  Q, 
and  inversely  proportional  to  the  potential  V;  or, 

K.2. 

V 

From  which  we  obtain  Q  =  KV;  or, 

The  quantity  of  electricity  required  to  charge  a 
(onductor  or  condenser  to  a  given  potential  is 
tqual  to  the  capacity  of  the  conductor  or  condenser 
multiplied  by  the  potential  through  which  it  is 
raised. 

Capacity,  Electrostatic,  Unit  of 

Such  a  capacity  of  a  conductor  or  condenser 
that  an  electromotive  force  of  one  volt  will 
charge  it  with  a  quantity  of  electricity  equal 
to  one  coulomb. 

The  farad.    (See  Farad?) 

Capacity  of  Cable.— (See  Cable.  Capacity 

of) 

Capacity  of  Condenser. — (See  Condenser, 
Capacity  o/.) 

Capacity  of  Leyden  Jar.— (See  Jar, 
Leyden,  Capacity  of.) 

Capacity  of  Line.— (See  Line,  Capacity 

°tt 
Capacity  of  Polarization  of  a  Voltaic 

Cell.— (See  Cell,  Voltaic,  Capacity  of  Polar- 
ization of.) 

Capacity,  Safe  Carrying,  of  a  Conductor 

The  maximum  electric  current  the 

conductor  will  carry  without  becoming  unduly 
heated. 

Capacity,  Specific  Inductive 

The  ability  of  a  dielectric  to  permit  induction 
to  take  place  through  its  mass,  as  compared 
with  the  ability  possessed  by  a  mass  of  air  of 
the  same  dimensions  and  thickness,  under 
precisely  similar  conditions. 

The  relative  power  of  bodies  for  trans- 
mitting electrostatic  stresses  and  strains 
analogous  to  permeability  in  metals. 

The  ratio  of  the  capacity  of  a  condenser 
whose  coatings  are  separated  by  a  dielectric 
of  a  given  substance  to  the  capacity  of  a 
similar  condenser  whose  plates  are  separated 
by  a  plate  or  layer  of  air. 


The  inductive  capacity  of  a  dielectric  is  com- 
pared with  that  of  air. 

According  to  Gordon  and  others,  the  specific 
Inductive  capacities  of  a  few  substances,  com- 
pared  with  air,  are  as  follows: 

Air i. oo 

Glass 3.013  to  3.258 

Shellac 2.740 

Sulphur 2.580 

Gutta-percha 2.462 

Ebonite 2.284 

India-rubber 2.220  to  2.497 

Turpentine 2.160 

Petroleum 2.030  to  2.070 

Paraffin  (solid) 1.994 

Carbon  bisulphide 1.810 

Carbonic  acid 1.00036 

Hydrogen 0.99967 

Vacuum 0.99941 

Faraday,  who  proposed  the  term  specific  in- 
ductive capacity,  employed  in  his  experiments  a 
condenser  consisting  of  a  metallic  sphere  A,  Fig. 
99,  placed  inside  a  large 
hollow  sphere  B. 

The  concentric  space 
between  A  and  B  was  filled 
with  the  substance  whose 
specific  inductive  capacity 
was  to  be  determined. 

Capacity,       Specific 

Magnetic A  term 

sometimes  employed  in 
the  sense  of  magnetic 
permeability. 

Conductibility  for  lines 
of  magnetic  force  in  the 
same  sense  that  specific 
inductive  capacity  is  con- 
ductibility  for  lines  of 
electrostatic  force. 

This  term  has  received 
the  name  of  specific  mag-  'f  "' 
netic  capacity  in  order  to  distinguish  it  from  specific 
inductive  capacity.  The  velocity  of  propagation 
of  waves  in  any  elastic  medium  is  proportional  to 
the  quotient  obtained  by  extracting  the  square 
root  of  the  elasticity  of  the  medium  divided  by 
the  square  root  of  its  density;  or, 


Cap.] 


75 


[Car. 


Similarly,  the  speed  with  which  inductive  waves 
travel  depends  on  the  relation  between  the  elas- 
ticity and  the  density  of  the  medium.  Calling  ^, 

the  electric  elasticity,  then  its  reciprocal,  K,  corre- 
sponds with  the  dielectric  capacity.  The  elec- 
trical density,  /*,  corresponds  with  the  magnetic 
permeability.  The  velocity  of  wave  transmission 
is  therefore, 


Capacity,  Storage,  of  Secondary  Cell 

—  (See  Cell,  Secondary  or  Storage,  Capa- 
city of.) 

Capillarity. — The  elevation  or  depression 
of  liquids  in  tubes  of  small  internal  diameter. 

The  liquid  is  elevated  when  it  wets  the  walls, 
and  depressed  when  it  does  not  wet  the  walls  of 
the  rube. 

The  phenomena  of  capillarity  are  due  to  the 
mutual  attractions  existing  between  the  mole- 
cules of  the  liquid  for  one  another,  and  the 
mutual  attraction  between  the  molecules  of  the 
liquid  and  those  of  the  walls  of  the  tube. 

In  capillarity,  therefore,  the  approximately 
level  surface  caused  by  the  equal  attraction  of  all 
the  molecules  towards  the  earth's  centre  is  dis- 
turbed by  the  unequal  attraction  exerted  on  each 
molecule  by  the  walls  of  the  tube  and  by  the  re- 
maining molecules. 

Capillarity,  Effects  of,  on  Toltaic  Cell 

.  — Efrects  caused  by  capillary  action 
which  disturb  the  proper  action  of  a  voltaic 
cell. 

These  effects  are  as  follows: 

(i.)  Creeping,  or  efflorescence  of  salts.  (See 
Creeping,  Electric.  Efflorescence.) 

(2. )  Oxidation  of  contacts  and  consequent  in- 
troduction of  increased  resistance  into  the  battery 
circuit.  The  liquid  enters  the  capillary  spaces 
between  the  contact  surfaces  and  oxidizes  them. 

Capillary. — Of  a  small  or  hair-like  diame- 
ter or  size. 

A  capillary  tube  is  a  tube  of  small  hair-like  di- 
ameter. (See  Capillarity.) 

Capillary  Attraction.— (See  Attraction, 
Capillary) 


Capillary  Contact-Key.— (See  Key,  Cap- 
illary Contact?) 

Capillary  Electrometer.— (See  Electrom- 
eter, Capillary) 

Carbon. — An  elementary  substance  which 
occurs  naturally  in  three  distinct  allotropic 
forms,  viz.:  charcoal,  graphite  and  the  dia- 
mond. (See  Allotropy) 

Carbon-Brushes  for  Electric  Motors. — 

(See  Brushes,  Carbon,  for  Electric  Motors) 

Carbon  Button.— (See  Button,  Carbon) 
Carbon-Clutch  or  Clamp  of  Arc  Lamp. 

—(See  Clutch,  Carbon,  of  Arc  Lamp) 

Carbon-Electrodes  for  Arc  Lamps. — (See 
Electrodes,  Carbon,  for  Arc  Lamps) 

Carbon-Holders  for  Arc  Lamps. — (See 
Holders,  Carbon,  for  Arc  Lamps) 

Carbon  Points. — (See  Points,  Carbon) 

Carbon  Transmitter  for  Telephones. — 
(See  Transmitter,  Carbon,  for  Telephones) 

Carbonic  Acid  Gas.— (See  Gas,  Carbonic 
Acid) 

Carboning  Lamps. — (See  Lamps,  Carbon- 
ing) 

Carbonizable. — Capable  of  being  carbon- 
ized. (See  Carbonization,  Processes  of) 

Carbonization. — The  act  of  carbonizing, 
(See  Carbonization,  Processes  of) 

Carbonization,      Processes    of 

Means  for  carbonizing  material. 

The  carbonizable  material  is  placed  in  suitably 
shaped  boxes,  covered  with  powdered  plumbago 
or  lamp-black,  and  subjected  to  the  prolonged 
action  of  intense  heat  while  out  of  contact  with 
air. 

The  electrical  conducting  power  of  the  carbon 
which  results  from  this  process  is  increased  by  the 
action  ot  the  heat,  and,  probably,  also,  by  the  de- 
posit in  the  mass,  ot  carbon  resulting  from  the 
subsequent  decomposition  of  the  hydro-carbon 
gases  produced  during  carbonization. 

When  the  carbonization  is  for  the  purpose  of 
producing  conductors  for  incandescent  lamps,  in 
order  to  obtain  the  uniformity  of  conducting 
power,  electrical  homogeneity,  purity  and  high 
refractory  power  requisite,  selected  fibrous  ma- 
terial, cut  or  shaped  in  at  least  one  dimension 


€ar.J 


76 


[Car. 


prior  to  carbonization,  must  be  taken,  and  sub- 
jected to  as  nearly  uniform  carbonization  as  pos- 
sible. 

Carbonize. — To  reduce  a  carbonizable  ma- 
terial to  carbon.  (See  Carbonization,  Pro- 
cesses of.) 

Carbonized  Cloth  Discs  for  High  Resist- 
ances.— (See  Cloth  Discs  Carbonized,  for 
High  Resistances) 

Carbonizer.— Any  apparatus  suitable  for 
reducing  carbonizable  material  to  carbon. 

Carbonizing. — Subjecting  a  carbonizable 
substance  to  the  process  of  carbonization. 
(See  Carbonization,  Processes  of) 

Carbons,  Artificial Carbons  ob- 
tained by  the  carbonization  of  a  mixture  of 
pulverized  carbon  with  different  carbonizable 
liquids. 

Powdered  coke,  or  gas-retort  carbon,  some- 
times  mixed  with  lamp-black  or  charcoal,  is  made 
into  a  stiff  dough  with  molasses,  tar,  or  any  other 
hydro-carbon  liquid.  The  mixture  is  molded 
into  rods,  pencils,  plates,  bars  or  other  desired 
shapes  by  the  pressure  of  a  powerful  hydraulic 
press.  After  drying,  the  carbons  are  placed  in 
crucibles  and  covered  with  lamp-black  or  pow- 
dered plumbago,  and  raised  to  an  intense  heat  at 
which  they  are  maintained  for  several  hours.  By 
the  carbonization  of  the  hydro-carbon  liquids,  the 
carbon  paste  becomes  strongly  coherent,  and  by 
the  action  of  the  heat  its  conducting  power  in- 
creases. 

To  give  increased  density  after  baking,  the 
carbons  are  sometimes  soaked  in  a  hydro-carbon 
liquid,  and  subjected  to  a  re-baking.  This  may 
be  repeated  a  number  of  times. 

Carbons,  Concentric-Cylindrical 

A  cylindrical  rod  of  carbon  placed  inside  a  hol- 
low cylinder  of  carbon  but  separated  from  it 
by  an  air  space,  or  by  some  other  insulating, 
refractory  material. 

Jablochkoff  candles  sometimes  are  made  with  a 
solid  cylindrical  electrode,  concentrically  placed 
in  a  hollow  cylindrical  carbon. 

Carbons,  Cored A  cylindrical  carbon 

electrode  for  an  arc  lamp  that  is  molded 
around  a  central  core  of  charcoal,  or  other 
softer  carbon. 


Much  of  the  unsteadiness  of  the  arc  light  is  due 
to  changes  in  the  position  of  the  arc.  Cored  car- 
bons, it  is  claimed,  render  the  arc  light  steadier, 
by  maintaining  the  arc  always  at  the  softer  carbon 
and  hence  af.  the  central  point  of  the  electrode. 

A  core  of  harder  carbon,  or  other  refractory 
material,  is  sometimes  provided  for  the  negative 
carbon. 

Carbons,  Flashed Carbons  which 

have  been  subjected  to  the  flashing  pro- 
cess, (See  Carbons,  Flashing  Process  for) 

Carbons,  Flashing  Process  for A 

process  for  improving  the  electrical  uniformity 
of  the  carbon  conductors  employed  in  in- 
candescent lighting,  by  the  deposition  of  car- 
bon in  their  pores,  and  over  their  surfaces  at 
those  places  where  the  electric  resistance  is 
relatively  great. 

The  carbon  conductor  or  filament  is  placed  in 
a  vessel  filled  with  the  vapor  of  a  hydrocarbon 
liquid  called  rhigolene,  or  any  other  readily  de- 
composable hydrocarbon  liquid,  and  gradually 
raised  to  electric  incandescence  by  the  passage 
through  it  of  an  electric  current.  A  decomposi- 
tion of  the  hydrocarbon  vapor  occurs,  the  car- 
bon resulting  therefrom  being  deposited  in  and  on 
the  conductor. 

As  the  current  is  gradually  increased,  the 
parts  of  the  conductor  first  rendered  incandes- 
cent are  the  places  where  the  electric  resist- 
ance is  the  highest,  these  parts,  therefore,  and 
practically  these  parts  only,  receive  the  deposit 
of  carbon.  As  the  current  increases,  other 
portions  become  successively  incandescent  and 
receive  a  deposit  of  carbon,  until  at  last  the 
filament  glows  with  a  uniform  brilliancy,  in- 
dicative of  its  electric  homogeneity. 

A  carbon  whose  resistance  varies  considerably 
at  different  parts  could  not  be  successfully  em- 
ployed in  an  incandescent  lamp,  since  if  heated 
by  a  current  sufficiently  great  to  render  the  points 
of  comparatively  small  resistance  satisfactorily 
incandescent,  the  temperature  of  the  points  of 
high  resistance  would  be  such  as  to  lower  the  life 
of  the  lamp,  while  if  only  those  portions  were 
safely  heated,  the  lamp  would  not  be  economical. 
The  flashing  process  is  therefore  of  very  great 
value  in  the  manufacture  of  an  incandescent 
lamp. 

The  name  "  flashing  "  was  applied  to  the  pro- 
cess by  reason  of  the  flashing  light  emitted  by  the 


Car.] 


[Cas. 


carbons  when  they  have  been  sufficiently  treated. 
The  process  requires  so  little  time  that  the  dull  red 
which  first  appears  soon  flashes  to  the  full  lumin- 
osity required. 

The  term  "flashing"  is  sometimes  applied  to 
the  electrical  heating  to  incandescence,  while  the 
carbons  are  in  the  lamp  chambers,  and  on  the 
pumps.  This  flashing  is  for  the  purpose  of 
driving  off  all  the  gases  occluded  by  the  carbon, 
so  that  these  gases  may  be  carried  off  by  the 
operation  of  pumping.  This  process  is  more 
properly  called  the  process  for  driving  off  the 
occluded  gases. 

The  carbons  are  sometimes  flashed  in  the  liquid 
itself  instead  of  in  its  vapor. 

Carbons,  Paper Carbons,  of  textile 

or  fibrous  origin,  obtained  from  the  carboniza- 
tion of  paper. 

The  carbonization  of  paper  is  readily  effected 
by  submitting  the  paper  to  the  prolonged  action 
of  a  high  temperature  while  out  of  contact  with 
air. 

For  this  purpose  the  paper  is  packed  in  retorts 
or  crucibles,  and  covered  with  lamp-black,  or 
powdered  plumbago,  in  order  to  exclude  the  air. 

Since  paper  consists  of  a  plane  of  material  uni- 
formly thin  in  one  direction,  formed  almost  en- 
tirely of  fibres  of  pure  cellulose,  the  greatest 
length  of  which  extends  in  a  direction  nearly  par- 
allel to  that  in  which  the  paper  is  uniformly  thin, 
it  is  clear  that  sheets  of  this  substance,  when  car- 
bonized, should  yield  flexible  carbons  of  unusual 
purity  and  electrical  homogeneity,  since  such 
carbons  are  structural  in  character,  and  are  uni- 
formly affected  by  the  heat  of  carbonization  to  an 
extent  that  would  be  impossible  by  the  carboniza- 
tion of  any  material  in  a  mass. 

Carcase  of  Dynamo-Electric  Machine. — 
(See  Machine,  Dynamo-Electric,  Carcase  of.) 

Carcel. — The  French  unit  of  light.  The 
light  emitted  by  a  lamp  burning  42  grammes 
of  pure  colza  oil  per  hour,  with  a  flame  40 
millimetres  in  height. 

The  bec-carcel.  One  carcel  =  9.5  109.6  stand- 
ard candles. 

Carcel  Lamp.— (See  Lamp,  Carcel) 

Carcel  Standard  Gas  Jet.— (See/?/,  Gas, 
Carcel  Standard.) 

Card,  Compass A  card  used  in  the 

mariner's  compass,  on  which  are  marked  the 


four  cardinal  points  of  the  compass  N,  S,  E 
and  W,  and  these  again  divided  into  thirty- 
two  points  called  Rhumbs.  (See  Compass, 
Azimuth.) 

Cardew  Voltmeter.  —  (See  Voltmeter, 
Cardew.) 

Carriage,  Pen The  carriage  in  an 

electric  chronograph  which  holds  the  pen  and 
moves  over  the  sheet  of  paper  on  which  the 
record  is  made.  (See  Chronograph,  Elec- 
tric.) 

Carriers  of  Replenisher.— (See  Replen* 
isher,  Carriers  of.) 

Cascade,  Charging  Leyden  Jars  by 

— A  method  of  charging  jars  or  condensers 
by  means  of  the  free  electricity  liberated  by 
induction  from  one  coating,  when  a  charge  is 
passed  into  the  other  coating. 

The  jars  are  placed  as  shown  in  Fig.  100,  with 
the  inside  coating  of  the  first  jar  connected  with 
the  outside  coating  of  the  one  next  it.  There  is  in 


Fig.  100.  Cascade  Charging  of  Leyden  Jars. 
reality  no  increase  in  the  entire  charge  obtained 
in  charging  by  cascade,  since  the  sum  of  the 
charges  given  to  the  separate  jars  is  equal  to 
the  same  charge  given  to  a  single  jar  separately 
charged. 

The  energy  of  the  discharge  in  cascade  can  be 
shown  to  be  less  than  that  of  the  same  charge 
when  confined  to  a  single  jar.  This  i=  of  course 
to  be  expected,  since  it  is  energy  that  'P  charged 
in  the  jar  and  not  electricity,  and,  of  course,  the 
energy  charged  in  the  jar  can  never  exceed  the 
energy  employed  in  charging  the  jar.  There  is 
a  small  loss  for  each  jar,  and  this  increases  ne- 
cessarily with  each  jar  added. 

Cascade,  Connection  of  Electric  Sources 
in •  — A  term  sometimes  used  for  series- 
connection  of  electric  sources. 

The  term  series -connection  is  the  preferable 
one.  (See  Connection^  Series^) 

Case-Hardening,   Electric Super. 

ficially  converting  a  piece  of  wire  into  steel 
by  electrically  produced  heat. 


Cas.] 


78 


[Can. 


In  electric  case-hardening,  the  superficial  layers 
of  a  piece  of  iron  are  converted  into  steel  by 
electrically  heating  the  same,  while  surrounded 
by  a  layer  of  case-hardening  flux  and  carbonaceous 
substances  such  as  animal  charcoal,  shavings  of 
horn,  leather  cuttings  or  other  similar  substances. 

In  the  case  of  a  readily  oxidizable  metal  like 
iron,  oxidation  is  prevented  by  surrounding  the 
metal  by  a  hydrocarbon  gas,  which,  when  suffi- 
ciently heated,  deposits  on  the  surfaces  a  pro- 
tective coating  of  carbon.  This  layer  of  carbon 
gradually  carbonizes  the  iron. 

Case  Wiring.— (See  Wiring,  Case.) 

Cataphoresis.— A  term  sometimes  em- 
ployed in  place  of  electric  osmose.  (See  Os- 
mose, Electric?) 

The  word  cataphoresis  applies  to  the  cases  where 
medicinal  substances,  such  as  iodine,  cocoaine, 
quinine,  etc.,  are  caused  to  pass  through  organic 
tissues  in  the  direction  of  flow  of  an  electric  cur. 
rent,  or  from  the  anode  to  the  kathode.  This 
action  is  probably  due  to  an  electrolytic  action. 

Cataphoric  Action.— (See  Action,  Cata- 
phoric.) 

Catch,  Safety A  wire,  plate,  strip, 

or  box  of  readily  fusible  metal,  capable  of  con- 
ducting, without  fusing,  the  current  ordinarily 
employed  on  the  circuit,  but  which  fuses  and 
thus  breaks  the  circuit  on  the  passage  of  an 
abnormally  large  current. 

Safety -catches  are  generally  placed  on  multiple, 
arc  and  multiple -series  circuits.  (See  Fuse% 
Safety.) 

Catelectrotonns.— An  orthography  some- 
times applied  to  Kathelectrotonus.  (See 
Kathelectrotonus.) 

Cathetometer.— An  instrument  for  the  ac- 
curate measurement  of  vertical  height. 

The  cathetometer  consists  essentially  of  an 
accurately  divided  vertical  rod  which  carries  a 
sliding  support  for  a  telescope.  The  telescope  is 
provided  with  two  spider  lines  at  right  angles  to 
one  another,  so  placed  as  to  be  seen  in  front  of 
the  object  whose  height  is  to  be  measured.  From 
observations  taken  in  different  positions,  the 
measurement  of  the  true  vertical  height  is  readily 
obtained. 

Cathlon.— A  term  sometimes  used  instead 
ul  Kathion. 


More  correctly  written  Kathion.  (See 
Kathion) 

Cathode.— A  term  sometimes  used  instead 
of  Kathode. 

Catoptrics. — That  branch  of  optics  which 
treats  of  the  reflection  of  light. 

Causty,  Galvano A  term  some- 
times used  for  galvano-cautery.  (See  Cautery, 
Galvano) 

Cauterization.— The  act  of  cauterizing,  or 
burning  with  a  heated  solid  or  caustic  sub- 
stance. 

Cauterization,  Electric Subject- 
ing to  cauterization  by  means  of  a  wire  elec- 
trically heated.  (See  Cautery,  Electric.} 

Cauterize.— To  subject  to  cauterization,  or 
burning  with  a  heated  solid  or  caustic  sub- 
stance. 

Cauterizer,  Electric A  term  some- 
times applied  to  an  electric  cautery.  (See 
Cautery,  Electric.) 

Cautery,  Actual A  burning  or  sear- 
ing with  a  white-hot  metal. 

Cautery  Battery.— (See  Battery,  Cautery •.) 

Cautery,  Electric An  instrument 

used  for  electric  cauterization. 

In  electro-therapeutics,  the  application  ol 
variously  shaped  platinum  wires  heated  to  in- 
candescence by  the  electric  current  in  place 
of  a  knife,  for  removing  diseased  growths,  ot 
for  stopping  hemorrhages. 

The  operation,  though  painful  during  applies- 
tlon,  is  afterward  less  painful  than  that  with  a 
knife,  since  secondary  hemorrhage  seldom  occurs, 
and  the  wound  rapidly  heals. 

Electric  cautery  is  applicable  in  cases  where 
the  knife  would  be  inadmissible  owing  to  the 
situation  of  the  parts  or  their  surroundings. 

Cautery,  Galvano A  term  fre- 
quently employed  in  place  of  electric  cautery. 
(See  Cautery,  Electric) 

Cautery,  Galvano  Electric An 

electric  cautery.  (See  Cautery,  Electric) 

Cautery,  Galvano  Thermal A 

term  sometimes  used  for  an  electric  cautery. 
(See  Cautery,  Electric* 


tail,  f 


79 


[CeL 


Cautery-Knife  Electrode.— (See  Electrode 
Cautery- Knife.} 

Cautery,  Thermal  —A  cautery 

heated  by  heat  other  than  that  of  electric  ori- 
gin, as  distinguished  from  an  electric  cautery. 
(See  Cautery,  Electric) 

Ceiling  Rose.— (See  Rose,  Ceiling} 

Cell,  Depositing An  electrolytic 

cell  in  which  an  electro-metallurgical  deposit  is 
made  (See  Metallurgy,  Electro} 

Cell,  Electrolytic A  cell  or  vessel 

containing  an  electrolyte,  in  which  electrolysis 
is  carried  on. 

An  electrolytic  cell  is  called  a  voltanuter  when 
the  value  of  the  current  passing  is  deduced  from 
the  weight  of  the  metal  deposited. 

Cell,  Impulsion A  photo-electric 

cell  whose  sensitiveness  to  light  may  be  re- 
stored or  destroyed  by  slight  impulses  given 
to  the  plates,  such  as  by  blows  or  taps,  or  elec- 
tro-magnetic impulses. 

An  impulsion  cell  may  be  prepared  by  pasting 
pieces  of  tin-foil,  the  opposite  faces  of  which  are 
respectively  polished  and  dull,  on  the  opposite 
faces  of  a  plate  of  glass,  so  as  to  expose  dissimi- 
lar sides  to  the  light,  when  the  cells  are  dipped 
in  alcohol. 

Cell,  Photo-Electric A  cell  capa- 
ble of  producing  differences  of  potential 
when  its  opposite  faces  are  unequally  exposed 
to  radiant  energy. 

Photo -voltaic  cells  are  made  in  a  variety  of 
forms,  both  with  selenium  and  with  different  me- 
tallic substances.  (See  Cell,  Selenium.} 

Cell,  Porous  — A  jar  of  unglazed 

earthenware,  employed  in  double-fluid  voltaic 
cells,  to  keep  the  two  liquids  separated. 

The  use  of  a  porous  cell  necessarily  increases 
the  internal  resistance  of  the  cell,  from  the  de- 
crease it  produces  in  the  area  of  cross  section  of 
liquid  between  the  two  elements.  When  the  bat- 
tery is  dismantled,  the  porous  cells  should  be 
kept  under  water,  otherwise  the  crystallization  of 
the  zinc  sulphate  or  other  salt  is  apt  to  produce 
serious  exfoliation,  or  scaling  off,  or  even  to 
crumble  the  porous  cell. 

A  porous  cell  is  sometimes  called  a  diaphragm, 
but  only  properly  so  when  the  cell  is  reduced  to 
a  single  separating  plate.  (See  Cell,  Voltaic.} 


Cell,  Secondary  — A  term  sometimes 

used  instead  of  storage  cell. 

The  term  secondary  cell  is  used  in  contradis- 
tinction to  primary  or  voltaic  cell. 

Cell.  Secondary  or  Storage,  Boiling  of 

A   term  sometimes    applied   to   the 

gassing  of  a  storage  cell.  (See  Cell,  Storage, 
Gassing  of} 

Cell,  Secondary  or  Storage,  Capacity  of 

The  product  of  the  current  in  am- 
peres, by  the  number  of  hours  the  battery  is. 
capable  of  furnishing  said  current,  whea 
fully  charged,  until  exhausted. 

The  capacity  of  storage  cells  is  given  in  ampere- 
hours.  A  storage  battery  with  a  capacity  of  i,ooa 
ampere-hours  can  furnish,  say  a  current  of  fifty- 
amperes  for  twenty  hours,  or  a  current  of  one 
hundred  amperes  for  ten  hours ;  or  a  current  of 
twenty-five  amperes  for  forty  hours. 

Cell.  Secondary  or  Storage,  Gassing  of 

An  escape  of  gas  due  to  the  decom- 
position of  water  on  passage  of  too  strong  a 
charging  current. 

Cell,  Secondary  or  Storage,  Renovation 

of The   revivifying  or  recharging  of  a 

run-down,  or  discharged  storage  cell. 

Cell,  Secondary  or  Storage,  Time-Fall 

of  Electromotive  Force  of (See 

Force.  Electromotive  of  Secondary  or 
Storage  Cell,  Time-Fall,  of} 

Cell,  Secondary  or  Storage,  Time-Ris^ 

of  Electromotive  Force  of (See 

Force,  Electromotive  of,  Secondary  or 
Storage  Cell,  Time-Rise,  of} 

Cell,  Selenium A  cell  consisting 

of  a  mass  of  selenium  fused  in  between  two 
conducting  wires  or  electrodes  of  platinized 
silver  or  other  suitable  metal. 

A  convenient  manner  of  forming  a  selenium 
cell  is  to  wind  two  separate  spirals  of  platinized 
silver  wire  around  a  cylinder  of  hard  wood,  tak- 
ing care  to  maintain  them  a  constant  distance 
apart,  so  as  to  avoid  contact  between  them.  The 
space  between  these  wires  is  filled  with  fused  sele- 
nium, which  is  allowed  to  cool  gradually. 

Exposure  to  sunlight  reduces  the  resistance  of 
a  selenium  cell  to  about  one-half  its  resistance  ia- 


lei.] 


80 


[del. 


the  dark,  but  neither  the  resistance  nor  the  reduc- 
tion ratio  long  remains  constant. 

A  selenium  cell  produces  a  difference  of  poten- 
tial, or  electromotive  force,  when  one  of  its  elec- 
trode faces  is  exposed  to  light,  while  the  other  is 
kept  in  darkness. 

According  to  Von  Uljanin,  who  experimented 
with  selenium  melted  in  between  two  parallel 
platinized  piates,  cooled  under  pressure,  and  then 
reduced  from  the  amorphous  to  the  sensitive  crys- 
talline variety  by  gradual  cooling  after  two  or 
three  heatings  in  a  paraffine  bath  up  to  195  de- 
grees, the  following  peculiarities  were  observed: 

(I.)  Exposure  of  one  of  the  electrodes  to  sun- 
light produced  an  electromotive  force  which 
causes  a  current  to  flow  from  the  dark  to  the 
illumined  electrode. 

(2.)  The  maximum  electromotive  force  was 
o.i 2  volt. 

(3.)  The  electromotive  force  disappeared  instan- 
taneously and  completely  on  the  darkening  of  the 
electrodes^ 

(4.)  A  slight  difference  in  the  electromotive 
force  was  observed  when  the  positive  and  nega- 
tive electrodes  were  alternately  exposed  to  the 
light,  the  maximum  electromotive  force  being 
attained  by  the  exposure  of  the  negative  electrode. 
(5.)  If  both  electrodes  are  similarly  illumined 
the  resulting  current  strength  is  decreased  and 
may  reach  zero. 

(6.)  The  action  of  light  is  instantaneous. 
(7.)  Most  of  the  selenium  cells  experimented 
with  exhibited  an  electromotive  force  of  polariza- 
tion. 

(8.)  The  electromotive  force  of  polarization  is 
diminished  by  exposure  to  light. 

(9.)  The  electrical  resistance  and  sensitive- 
ness to  light  as  regards  the  production  of  an 
electromotive  force  decrease  with  time.  This 
is  probably  due  to  a  gradual  change  in  the  allo- 
tropic  state  of  the  selenium.  (See  State,  Allo- 
tropic.) 

(10.)  The  electromotive  force  produced  is  pro- 
portional  to  the  intensity  of  the  illumination  only 
when  the  obscure  rays  or  heat  rays  are  absent. 

(II.)  Of  different  wave  lengths  the  orange-yel- 
low rays  in  the  diffraction  spectrum,  and  the 
greenish-yellow  in  the  prismatic  ppectrum  pro- 
duced the  greatest  effect. 

Among  some  of  the  more  recent  applications 
of  selenium  cells  are  the  following: 

(i.)  A  selenium  cell  is  so  placed  in  a  circuit 
containing  an  electro-magnet  and  switch,  that  on 


one  of  its  electrodes  being  exposed  to  the  de- 
creased illumination  of  coming  night  it  automat- 
ically turns  on  an  electric  lamp,  and,  conversely, 
on  the  approach  of  daylight,  and  the  consequent 
illumination  of  the  electrode,  turns  it  off. 

(2.)  A  device  whereby  the  presence  of  light, 
as  for  example  that  carried  by  a  burglar,  auto- 
matically rings  an  alarm  and  thus  calls  the  atten- 
tion of  the  watchman  of  the  building. 

Cell,  Standard (See  Cell,  Voltaic, 

Standard?) 

Cell,  Storage Two  relatively  inert 

plates  of  metal,  or  of  metallic  compounds, 
immersed  in  an  electrolyte  incapable  of  acting 
considerably  on  them  until  after  an  electric 
current  has  been  passed  through  the  liquid 
from  one  plate  to  the  other  and  has  changed 
their  chemical  relations. 

A  single  one  of  the  cells  required  to  form 
a  secondary  battery. 

Sometimes,  the  jar  containing  a  single  cell 
is  called  a  storage  cell. 

This  latter  use  of  the  word  is  objectionable. 

A  storage  cell  is  also  called  an  accumulator. 

On  the  passage  of  an  electric  current  through 
the  electrolyte,  its  decomposition  is  effected  and 
the  electro-positive  and  electro- negative  radicals 
are  deposited  on  the  plates,  or  unite  with  them, 
so  that  on  the  cessation  of  the  charging  current, 
there  remains  a  voltaic  cell  capable  of  generating 
an  electric  current. 

A  storage  cell  is  charged  by  the  passage  through 
the  liquid  from  one  plate  to  the  other  of  an  elec- 
tric current,  derived  from  any  external  source. 
The  charging  current  produces  an  electrolytic  de- 
composition of  the  inert  liquid  between  the 
plates,  depositing  the  electro-positive  radicals,  or 
katkions,  on  the  plate  connected  with  the  negative 
terminal  of  the  source,  and  the  electro-negative 
radicals,  or  anions,  on  the  plate  connected  with 
the  positive  terminal. 

On  the  cessation  of  the  charging  current,  and 
the  connection  of  the  charged  plates  by  a  con- 
ductor outside  the  liquid,  a  current  is  produced, 
which  flows  through  the  liquid  from  the  plate 
covered  with  the  electro-positive  radicals,  to  that 
covered  with  the  electro -negative  radicals,  or  in 
the  opposite  direction  to  that  of  the  charging  cur- 
rent. 

The  simplest  storage  cell  is  Planters  cell,  which, 
as  originally  constructed,  consists  of  two  plates  of 


Cel.] 


81 


[Cel. 


lead  immersed  in  dilute  sulphuric  acid,  H2SO4. 
On  the  passage  of  the  charging  current,  the  plates 
A  and  B,  Fig.  101,  dipped  in  H2SO4,  are  covered 
respectively  with  lead  peroxide,  PbO2,  and  finely 
divided,  spongy  lead.  The  peroxide  is  formed  on 
the  positive  plate,  and  the  metallic  lead  on  the 
negative  plate.  The  acid  and  water  should  have 
a  specific  gravity  of  about  1.170.  When  the  cell 
is  fully  charged  the  acid  solution  loses  its  clear- 
ness and  becomes  milky  in  appearance,  and  the 


Figs.  10 1  and  102.    Storage  Cell. 

specific  gravity  increases  to  1. 195.  This  increase 
is  a  good  sign  of  a  full  charge. 

When  the  charging  current  ceases  to  pass,  the 
cell  discharges  in  the  opposite  direction,  viz., 
from  B'  to  A',  that  is,  from  the  spongy  lead  plate 
to  the  peroxide  plate  through  the  electrolyte,  as 
shown  in  Fig.  102. 

As  a  result  of  this  discharging  current  the  per- 
oxide, PbOg,  on  A',  gives  up  one  of  its  atoms  of 
oxygen  to  the  spongy  lead  on  B',  thus  leaving 
both  plates  coated  with  a  layer  of  PbO,  lead 
monoxide,  or  litharge.  When  this  change  is 
thoroughly  effected,  the  cell  becomes  inert,  and 
will  furnish  no  further  current  until  again  charged 
by  the  passage  of  a  current  from  some  external 
source. 

In  order  to  increase  the  capacity  of  the  storage 
cells,  and  thus  prolong  the  time  of  their  discharge, 
the  coating  of  lead  monoxide  thus  left  on  each 
of  the  plates,  when  neutral,  is  made  as  great  as 
possible.  To  effect  this,  a  process  called  '  'forming 
the  plates11  is  employed,  which  consists  in  first 
charging  the  plates  as  already  described,  and 
then  reversing  the  direction  of  the  charging  cur- 
rent,  the  currents  being  sent  through  the  cell  in 
alternately  opposite  directions,  until  a  consider- 
able  depth  of  the  lead  plates  has  been  acted  on. 

It  will  be  noticed  that  during  the  action  of  the 
charging  current,  the  oxygen  is  transferred  from 
the  PbO,  on  one  jjlate,  to  the  PbO,  on  the  other 
plate,  thus  leaving  one  Pb,  and  the  other  PbO,; 
and  that  on  discharging,  one  atom  of  oxygen  is 


transferred  from  the  PbOz,  to  the  Pb,  thus  leav- 
ing both  plates  covered  with  PbO.  In  reality 
this  is  but  the  final  result  of  the  action,  hydrated 
sulphate  of  lead,  PbO,  H4SO4,  being  formed, 
and  subsequently  decomposed.  Other  com- 
pounds are  formed  that  are  but  imperfectly  un- 
derstood. 

In  order  to  decrease  the  time  required  for  form- 
ing, accumulators,  or  secondary  cells,  have  been 
constructed,  in  which  metallic  plates  covered  with 
red  lead  Pb3O4  replace  the  lead  plates  in  the 
original  Plant<§  cell.  On  charging,  the  Pb8O4 
is  peroxidized  at  the  anode,  i.  e.,  converted  into 
PbOz,  and  deoxidized,  and  subsequently  con- 
verted into  metallic  lead  at  the  kathode.  Or,  in 
place  of  the  above  Pb3O4,  red  lead  is  placed  on 
the  anode  and  PbO,  or  litharge,  on  the  kathode. 

Plates  of  compressed  litharge  have  also  been 
recently  used  for  this  purpose.  Storage  cells  so 
formed  have  a  greater  storage  capacity  per  unit 
weight  than  those  in  which  a  grid  is  employed, 
but  a  higher  resistance. 

In  all  cases  where  a  metal  plate  is  employed 
various  irregularities  of  surface  are  given  to  the 
plates,  in  order  to  increase  their  extent  of  surface 
and  to  afford  a  means  for  preventing  the  separa- 
tion of  the  coatings.  The  metallic  form  thus 
provided  is  known  technically  z&z.grid. 

Unless  care  is  exercised,  the  plates  will  buckle 
from  the  difference  in  the  expansion  of  the  lead 
and  its  filling  of  oxide.  This  buckling  is  attended 
with  an  increase  in  the  resistance  of  the  cell  and 
the  gradual  separation  of  the  oxides  that  cover  ot 
fill  it. 

Cell,   Thermo-Electrlo A  name 

applied  to  a  thermo-electric  couple.  (See 
Couple,  Thermo-Electric^ 

Cell,  Voltaio The  combination  of 

two  metals,  or  of  a  metal  and  a  metalloid, 
which,  when  dipped  into  a  liquid  or  liquids 
called  electrolytes,  and  connected  outside  the 
liquid  or  liquids  by  a  conductor,  will  produce 
a  current  of  electricity. 

Different  liquids  or  gases  may  take  the  place  of 
the  two  metals,  or  of  the  metal  and  metalloid. 
(See  Battery ',  Gas.) 

Plates  of  zinc  and  copper  dipped  into  a  solu- 
tion of  sulphuric  acid  and  water,  and  connected 
outside  the  liquid  by  a  conductor,  form  a  simple 
voltaic  cell. 

If  the  zinc  be  of  ordinary  commercial  purity: 


Cel.] 


[Cel. 


and  is  not  connected  outside  the  liquid  by  a  con- 
ductor, the  following  phenomena  occur: 

(i.)  The  sulphuric  acid  or  hydrogen  sul- 
phate, HZSO4,  is  decomposed,  zinc  sulphate, 
ZnSO4,  being  formed,  and  hydrogen,  H,,  liber- 
ated. 

(2.)  The  hydrogen  is  liberated  mainly  at  the 
surface  of  the  zinc  plate. 

(3.)  The  entire  mass  of  the  liquid  becomes 
heated. 

If,  however,  the  plates  are  connected  outside 
the  liquid  by  a  conductor  of  electricity,  then  the 
phenomena  change  and  are  as  follows,  viz. : 

(i.)  The  sulphuric  acid  is  decomposed  as  be- 
fore; but, 

(2.)  The  hydrogen  is  liberated  at  the  surface  of 
the  copper  plate  only. 

(3.)  The  heat  no  longer  appears  in  the  liquid 
only,  but  in  all  parts  of  the  circuit. 

(4.)  An  electric  current  now  flows  through  the 
entire  circuit,  and  will  continue  so  to  flow  as  long 
as  there  is  any  sulphuric  acid  to  be  decomposed, 
and  zinc  with  which  to  form  zinc  sulphate. 

The  energy  which  previously  appeared  as  heat 
only,  now  appears  in  part  as  electric  energy. 

Therefore,  although  the  mere  contact  of  the 
two  metals  with  the  liquid  will  produce  a  differ- 
ence of  potential,  it  is  the  chemical  potential 
energy  which  became  kinetic  during  chemical 
combination  that  supplies  the  energy  required  to 
maintain  the  electric  current.  (See  Energy, 
Kinetic.  Energy,  Potential.) 

A  voltaic  cell  consists  of  two  plates  of  different 
metals,  or  of  a  metal  and  a  metalloid  (or  of  two 
gases,  or  two  liquids,  or  of  a  liquid  and  a  gas), 
each  of  which  is  called   a 
voltaic  element,  and  which, 
taken  together,  form  what  is 
called  a  voltaic  couple. 

The  voltaic  couple  dips  in- 
to a  liquid  called  an  electro- 
lyte,  which,  as  it  transmits 
the  electric  current,  is  de- 
composed by  it.  The  ele- 
ments are  connected  outside 
the  electrolyte  by  any  con- 
ducting material. 

Direction  of  the  Current.— la.  any  voltaic  cell 
the  current  is  assumed  to  flow  through  the  liquid, 
from  the  metal  most  acted  on  to  the  metal  least 
acted  on,  and  outside  the  liquid,  through  the  out- 
side circuit,  from  the  metal  least  acted  on  to  the 
metal  most  acted  on. 


Fig.  103.     Voltaic 
Couple. 


In  Fig.  103  a  zinc-copper  voltaic  couple  is 
shown,  immersed  in  dilute  sulphuric  acid.  Here, 
since  the  zinc  is  dissolved  by  the  sulphuric  acid, 
the  zinc  is  positive,  and  the  copper  negative  in 
the  liquid.  The  zinc  and  copper  are  of  opposite 
polarities  out  of  the  liquid. 

There  is  still  a  considerable  difference  of  opinion 
as  to  the  exact  cause  of  the  potential  difference  of 
the  voltaic  cell.  There  can  be  no  doubt  that  a 
true  contact  force  exists,  but  the  chemical  poten- 
tial energy  of  the  positive  plate  is  the  source 
of  energy  which  maintains  the  potential  differ- 
ence. 

The  difference  in  the  polarity  of  the  zinc  and 
copper  in  and  out  of  the  liquid  is  generally  de- 
nied by  most  of  the  later  writers  on  electricity, 
since  tests  by  a  sufficiently  delicate  electrometer 
show  that  the  entire  zinc  plate  is  negative  and 
the  entire  copper  plate  positive.  Remembering, 
however,  the  convention  as  to  the  direction  of 
the  flow  of  the  current,  since  the  current  flows 
from  the  zinc  to  the  copper  through  the  liquid, 
we  may  still  fairly  regard  the  zinc  as  positive  and 
the  copper  as  negative  in  the  liquid.  It  will  be 
remembered,  that  in  every  source  the  polarity 
within  the  source  is  necessarily  opposite  to  the 
polarity  outside  it.  The  copper  plate  is  there- 
fore called  the  negative  plate,  and  the  wire  con- 
nected to  its  end  out  of  the  liquid,  the  positive 
electrode.  Similarly,  the  zinc  plate  is  called  the 
positive  plate,  and  the  wire  connected  to  it  the 
negative  electrode. 

It  will  of  course  be  understood  that  in  the 
above  sketch  the  current  flows  only  on  the  com- 
pletion of  the  circuit  outside  the  cell;  that  is, 
when  the  conductors  attached  to  the  zinc  and 
copper  plates  are  electrically  connected. 

Amalgamation  of  the  Zinc  Plate. — When  zinc 
is  used  for  the  positive  element,  it  will,  unless 
chemically  pure,  be  dissolved  by  the  electrolyte 
when  the  circuit  is  open,  or  will  be  irregularly 
dissolved  when  the  circuit  is  closed,  producing 
currents  in  little  closed  circuits  from  minute  vol- 
taic couples  formed  by  the  zinc  and  such  impuri- 
ties as  carbon,  lead,  or  iron,  etc.,  always  found 
in  commercial  zinc.  (See  Action,  Local,  of  Vol- 
taic Cell.)  As  it  is  practically  impossible  to  ob- 
tain chemically  pure  zinc,  it  is  necessary  to  amal- 
gamate the  zinc  plate;  that  is,  to  cover  it  with  a 
thin  layer  of  zinc  amalgam. 

Polarization  of  the  Negative  Plate.— Since  the 
evolved  hydrogen  appears  at  the  surface  of  the 
negative  plate,  the  surface  of  this  plate,  unless 


Cel.J 


83 


means  are  adopted  to  avoid  it,  will,  after  a  while, 
become  coated  with  a  film  of  hydrogen  gas,  or 
as  it  is  technically  called,  will  become  polarized. 
(See  Cell,  Voltaic,  Polarization  of,) 

The  effect  of  this  polarization  is  to  cause  a  fall- 
ing off  or  weakening  of  the  current  produced  by 
the  battery,  due  to  the  formation  of  a  counter, 
electromotive  force  produced  by  the  hydrogen- 
covered  plate;  that  is  to  say,  the  negative  plate, 
now  being  covered  with  hydrogen,  a  very  highly 
electro-positive  element,  tends  to  produce  a 
current  in  a  direction  opposed  to  that  of  the 
cell  proper.  (See  Force,  Electromotive,  Coun- 
ter.) 

This  decrease  in  current  strength  is  rendered 
still  greater  by  the  increased  resistance  in  the  cell, 
due  to  the  bubbles  of  hydrogen,  and  to  the  de- 
creased electromotive  force,  due  to  the  increase 
in  the  density  of  the  zinc  sulphate,  in  the  case  of 
zinc  in  hydrogen  sulphate. 

In  the  case  of  storage  cells,  the  counter-elec- 
tromotive force  of  polarization  is  employed  as  the 
source  of  secondary  currents.  (See  Electricity, 
Storage  of.  Cell,  Secondary.  Cell,  Storage.) 

In  order  to  avoid  the  effects  of  polarization  in 
voltaic  cells,  and  thus  insure  constancy  of  cur- 
rent, the  bubbles  of  gas  at  the  negative  plate  are 
mechanically  carried  off  either  by  roughening  its 
surface,  by  forcing  the  electrolyte  against  the 
plate  as  by  shaking,  or  by  a  stream  of  air;  or  else 
the  negative  plate  is  surrounded  by  some  liquid 
or  solid  substance  which  will  remove  the  hydro- 
gen, by  entering  into  combination  with  it.  (See 
Cell,  Voltaic,  Polarization  of .) 

Voltaic  cells  are  therefore  divided  into  cells 
with  one  or  with  two  fluids,  or  electrolytes,  or 
into: 

(I.)  Single-fluid  cells;  and 

(2.)  Double-fluid  cells. 

Very  many  forms  of  voltaic  cells  have  been  de- 
vised. The  following  are  among  the  more  im- 
portant, viz.  :  Of  the  Single-Fluid  Cells,  the 
Grenet,  Poggendorff,  or  Bichromate,  the  Zinc- 
Copper,  the  Zinc-  Carbon  and  the  Smee.  Of  the 
Double-Fluid  Cells,  Grove's,  Bunsen's,  Callaud 
or  Gravity,  DanielFs,  Leclanche,  Siemens- Hals ke 
and  the  Meidinger, 

Of  all  the  voltaic  cells  that  have  been  devised 
two  only,  viz.,  the  Gravity,  a  modified  Daniell, 
and  the  Leclanche,  have  continued  until  now  in 
very  general  use,  the  gravity  cell  being  used  on 
closed-circuited  lines,  and  the  Leclanche  on  open- 
circuited  lines  ;  the  former  being  the  best  suited 


of  all  cells  to  furnish  the  continuous  constant  cur. 
rents  employed  in  most  systems  of  telegraphy, 
and  the  latter  for  furnishing  the  intermittent  cur- 
rents required  for  ringing  bells,  operating  annun- 
ciators, or  for  similar  work. 

Cell,  Voltaic,  Absorption  and    Genera- 

tion  of  Heat  in (See  Heat,  Absorption 

and  Generation  of,  in  Voltaic  Cell.) 

Cell,  Yoltaic,  Bichromate A  zinc- 
carbon  couple  used  with  an  electrolyte 
known  as  electropoion,  a  solution  of  bichro- 
mate of  potash  and  sulphuric  acid  in  water. 
(See  Liquid,  Electropoion^} 

Bichromate  of  sodium  or  chromic  acid  are 
sometimes  used  instead  of  the  bichromate  of 
potassium. 

The  zinc,  Fig.  104,  is  amalgamated  and  placed 
between  two  carbon  plates. 
The  terminals  connected 
with  the  zinc  and  carbon 
are  respectively  negative 
and  positive.  In  the  form 
shown  in  the  figure,  the  zinc 
plate  can  be  lifted  out  of 
the  liquid  when  the  cell  is 
not  in  action. 

The  bichromate  cell  is 
excellent  for  purposes  re- 
quiring strong  currents 
where  long  action  is  not 
necessary.  As  this  cell 
readily  polarizes  it  cannot 
be  advantageously  employ- 
ed continuously  for  any 
considerable  period  of  time.  It  becomes  depolar- 
ized, however,  when  left  for  some  time  on  open 
circuit 

The  following  chemical  reaction  probably  takes 
place  when  the  cell  is  furnishing  current,  viz. : 


jo  4.    Bichromate 
Cell. 


K8S04  -f  3ZnS04  +  Cr83(So4)  -j-  7H2O. 
This  cell  gives  an  electromotive  force  of  about 
1. 9  volts. 

Cell,  Voltaic,  Bunsen's A  zinc- 
carbon  couple,  the  elements  of  which  are 
immersed  respectively  in  electrolytes  of  dilute 
sulphuric  and  strong  nitric  acids. 

Bunsen's  cell  is  the  same  as  Grove's,  except 
that  the  platinum  is  replaced  by  carbon.  The 
zinc  surrounds  the  porous  cell  containing  the  car- 


Cel.] 


[Cel. 


bon.    The  polarity  is  as  indicated  in  Fig.  105. 
(See  Cell,  Voltaic,  Grove.) 


Fig.  1 03.    Bunsen  Cell. 

The  Bunsen  cell  gives  an  electromotive  force 
of  about  1.96  volts. 

Cell,  Voltaic,  Callaud's A  name 

sometimes  given  to  the  gravity  cell.  (See 
Cell,  Voltaic,  Gravity.) 

Cell,  Toltaic,  Capacity  of  Polarization  of 

The  quantity  of  electricity  required 

to  be  discharged  by  a  voltaic  cell  in  order  to 
produce  a  given  polarization.  (See  Cell,  Vol- 
taic, Polarization  of.) 

During  the  discharge  of  a  voltaic  cell  an  electro  - 
motive  force  is  gradually  set  up  that  is  opposed 
to  that  of  the  cell.  The  quantity  of  electricity 
required  to  produce  a  given  polarization  de- 
pends, of  course,  on  the  condition  and  size  of 
the  plates.  Such  a  quantity  is  called  the  capacity 
of  polarization. 

Cell,   Yoltalc,  Closed-Circuit A 

voltaic  cell  that  can  be  left  for  a  considerable 
time  on  a  closed  circuit  of  comparatively 
small  resistance  without  serious  polarization. 

The  term  closed-circuit  voltaic  cell  is  used  in 
contradistinction  to  open-circuit  cell,  and  applies 
to  a  cell  that  can  only  be  kept  on  closed  circuit 
for  a  comparatively  short  time. 

Daniell's  cell  and  the  gravity  cell  are  closed-cir- 
cuit cells.  Leclanchd's  is  an  open-circuit  celL 

Cell,  Voltaic,  Contact  Theory  of 

A  theory  which  accounts  for  the  production 
of  difference  of  potential  or  electromotive 
force  in  the  voltaic  cell  by  the  contact  of  the 
elements  of  the  voltaic  couple  with  one  an- 
other by  means  of  the  electrolyte. 


The  mere  contact  of  two  dissimilar  substances 
through  the  electrolyte  will  produce  a  difference 
of  potential,  but  the  cause  of  the  current  which  a 
voltaic  cell  is  able  to  maintain  is  the  chemical 
potential  energy  which  becomes  kinetic  during 
combination.  (See  Cell,  Voltaic.  Series, Contact,) 

Most  authorities  explain  the  difference  of 
potential  produced  by  the  contact  of  different 
metals  by  the  fact  that  the  metals  are  sur- 
rounded by  air.  They  point  out  the  fact  that  the 
order  of  the  metals  in  the  contact-series  is 
almost  identical  with  the  order  of  their  electro- 
chemical power  as  deduced  from  their  chemical 
equivalents,  and  their  heat  of  combination  with 
oxygen.  It  would  appear,  therefore,  that  the 
difference  of  potential  between  a  metal  and  the 
air  which  surrounds  it,  is  a  measure  of  the  tend* 
ency  of  the  metal  to  become  oxidized. 

The  origin  of  the  electromotive  force  of  a  zinc- 
copper  couple,  in  an  electrolyte  of  hydrogen  sul- 
phate, is  the  superior  affinity  of  the  zinc  for  the 
oxygen,  over  that  of  the  copper  for  the  oxygen. 

Cell,  Voltaic,  Creeping    in The 

formation,  by  efflorescence,  of  salts  on  the  sides 
of  the  porous  cup  of  a  voltaic  cell,  or  on  the 
walls  of  the  vessel  containing  the  electrolyte. 
Paraffining  the  portions  of  the  walls  out  of  the 
liquid,  or  covering  the  surface  of  the  liquid  with 
a  neutral  oil ,  obviates  much  of  this  d  ifficulty .  (See 
Efflorescence.) 

Cell,  Voltaic,  Daniell's A  zinc- 
copper  couple,  the  elements  of  which  are  im- 
mersed respectively  in  electrolytes  of  dilute 
sulphuric  acid,  and  a  saturated  solution  of 
copper  sulphate. 

In  the  form  of  Daniell's  cell,  shown  in  Fig.  106, 
the  copper  element  is  made  in  the  form  of  a  cylin- 
der c,  and  is  placed  in  a  porous  cell.  The  cop- 
per cylinder  is  provided  with  a  wire  basket  near 
the  top,  filled  with  crystals  of  blue  vitriol,  or  cop- 
per sulphate,  so  as  to  maintain  the  strength  of  the 
solution  while  the  cell  is  in  use.  The  zinc  is  in 
the  shape  of  a  cylinder  and  is  placed  so  as  to  sur- 
round the  porous  celL  This  cell  gives  a  nearly 
constant  electromotive  force. 

The  constancy  of  action  of  Daniell's  cell 
depends  on  the  fact  that  for  every  molecule  of 
sulphuric  acid  decomposed  in  the  outer  cell,  an 
additional  molecule  of  sulphuric  acid  is  supplied 
by  the  decomposition  of  a  molecule  of  copper  sul- 
phate  in  the  inner  cell.  This  will  be  better  un- 


Cel.] 


85 


ICel. 


derstood  from  the  following  reactions  which  take 

place,  viz.: 

Zn  +  H2S04  =  ZnS04  -f-  H, 
H»  -f  CuS04  =  H3S04  +  Cu. 
The  H8SO4,  thus  formed  in  the  inner  cell, 

passes  through  the  porous  cell,  and  the  copper  is 

deposited  on  the  surface  of  the  copper  plate. 


Fig  1 06.     Daniell  s  Cell. 

The  Daniell  cell  gives  an  electromotive  force 
of  about  1.072  volts. 

A  serious  objection  to  this  form  ot  cell  arises 
from  the  fact  that  the  copper  is  gradually  de- 
posited over  the  surface  and  in  the  pores  of  the 
porous  cell,  thus  greatly  increasing  its  resistance. 
This  difficulty  is  avoided  in  the  gravity  cell.  (See 
Cell,  Voltaic,  Gravity.) 

Cell,    Voltaic,    Double-Fluid A 

voltaic  cell  in  which  two  separate  fluids  or  elec- 
trolytes are  employed. 

One  of  the  elements  of  the  voltaic  couple  is 
dipped  into  one  ot  the  fluids  and  the  other  ele- 
ment into  the  other  fluid.  In  order  to  keep  the 
fluids  separate  and  distinct,  they  are  either  sep- 
arated by  means  of  porous  cells,  or  by  the  action 
of  gravity.  (See  Cell,  Porous.  Cell,  Voltaic, 
Gravity.) 

In  the  double-fluid  cell  the  negative  element  is 
surrounded  by  a  liquid  which  is  capable  ot  pre- 
Yenting  polarization  by  combining  chemically 
with  the  substance  that  tends  to  collect  on  its 
surface.  In  the  Daniell  cell  this  substance  is  the 
same  as  that  of  the  negative  plate.  (See  Cell, 
Voltaic^  Polarization  of.) 

Cell,  Yoltaic,  Dry A  voltaic  cell 

in  which  a  moist  material  is  used  in  place  of 
the  ordinary  fluid  electrolyte. 


The  term  dry  cell  is  in  reality  a  misnomer, 
since  all  such  cells  are  moistened  with  liquid 
electrolytes. 

The  dry  cell,  like  other  cells,  is  made  in  a 
variety  of  forms.  The  ab- 
sence of  free  liquid  permits 
the  cell  to  be  closed.  A  well 
known  form  of  dry  cell  is| 
shown  in  Fig.  107. 

Cell,  Yoltaic,  Effects  of  I 
Capillarity   in (See 

Capillarity,  Effects  of.  m  \ 
Voltaic  Cell.) 

Cell,  Yoltaic,  Exciting 
Liquid  of—  —The  elec- 
trolyte of  a  voltaic  cell.  ng,  f07.  Dry  ceil 

A  voltaic  cell  may  have  a  single  electrolyte,  in 
which  case  it  is  called  a  single-fluid  cell,  or  it  may 
have  two  electrolytes,  in  which  case  it  is  called  a 
double-fluid  cell. 

Cell,  Yoltaic,  Fuller's  Mercury  Bichro 
mate  — A  zinc-carbon  couple  im- 
mersed in  an  electrolyte  of  electropoion  liquid. 

The  zinc  is  attached  to  a  copper  rod  by  being 
cast  thereto,  and  is  placed  at  the  bottom  of  a 
porous  .cell,  where  it  is  covered  by  a  layer  of 
mercury.  The  carbon  plate  is  placed  in  electro- 


Pig.  M08     Fuller's  Mercury  Bichromate  Cell. 
poion  liquid,  diluted  with  wajer  in  the  proportion 
of  three  of  the  former  to  two  of  the  latter,,    The 
zinc  is  generally  placed  in  pure  water,  which 
rapidly  becomes  acid. 

The  mercury  effects  the  continuous  amalgama- 
tion of  the  zinc. 

A  Fuller  mercury  bichromate   cell   is  shown 
in  Fig.  108. 


Cel.J 


86 


[CeL 


Cell,  Toltaic,  Gravity A  zinc- 
copper  couple,  the  elements  of  which  are  em- 
ployed with  electrolytes  of  dilute  sulphuric  acid 
or  dilute  zinc  sulphate,  and  a  concentrated 
solution  of  copper  sulphate  respectively. 

The  use  of  a  porous  cell  is  open  to  the  objection 
of  increased  internal  resistance.  Moreover,  the 
porous  cell  is  apt  to  receive  a  coating  of  copper 
which  often  deposits  on  the  cell  instead  of  on  the 
copper  plate.  The  gravity  cell  was  devised  in 
order  to  avoid  the  use  of  a  porous  cell.  As  its 
name  indicates,  the  two  fluids  are  separated  from 
each  other  by  gravity. 

The  copper  plate  is  the  lower  plate,  and  is  sur- 
rounded  by  crystals  of  copper  sulphate.     The 
zinc,  generally  in  the  form  of  an  open  wheel,  or 
crow-foot,    is    sus- 
pended near  the  top 
of  the     liquid,    as 
shown  in  Fig.  109. 

When  the  cell  is 
set  up  with  sul- 
phuric acid,  the  re- 
actions are  the  same 
as  in  the  Daniell 
cell.  When  copper 
sulphate  and  zinc 
sulphate  alone  are 
used,  zinc  replaces 
the  copper  in  the 
copper  sulphate. 
The  action  is  then 
merely  a  substitution  process.  (See  Cell,  Voltaic, 
Daniels.) 

A  dilute  solution  of  zinc  sulphate  is  generally 
used  to  replace  the  dilute  sulphuric  acid.  It 
gives  a  somewhat  lower  electromotive  force,  but 
ensures  a  greater  constancy  for  the  cell. 

Cell,   Toltaic,    Grenet A    name 

sometimes  given  to  the  bichromate  cell.    (See 
Cell,  Voltaic,  Bichromate!) 

Cell,  Voltaic,  Grove A  zinc-plati- 
num couple,  the  elements  of  which  are  used 
with  electrolytes  of  sulphuric  and  nitric  acids 
respectively. 

The  zinc,  Z,  Fig.  HO,  is  amalgamated  and 
placed  in  dilute  sulphuric  acid,  and  the  platinum, 
P,  in  strong  nitric  add  (HNOt)  in  a  forous  tell 
to  separate  it  from  the  sulphuric  acid.  (See  C  ell, 
Porous.)  In  the  Grove  cell  the  current  is  moder- 
ately constant,  since  the  polarization  of  the  plati* 


Fig.  109.     The  Gravity  Cell. 


num  plate  is  prevented  by  the  nitric  acid,  which 
oxidizes  and  thus  removes  the  hydrogen  that 
tends  to  be  liberated  at  its  surface.  The  con- 
stancy of  the  current 
is  not  maintained  for 
any  considerable  time, 
since  the  two  liquids 
are  rapidly  decom- 
posed, or  consumed, 
zinc  sulphate  forming 
in  the  sulphuric  acid, 
and  water  in  the  nitric 
acid. 

The  chemical  reac- 
tions are  as   follows, 
viz.: 
Zn  +  HaSO4  = 

ZnSO4  +  H8; 
6H  -f  2HNO8= 

4H8O  -f-  2NO; 
2NO  +  O,  =  N804. 

Nitrate  of  ammo- 
nium is  sometimes  formed  when  the  nitric  acid 
becomes  dilute  by  decomposition.  The  reaction 
is  as  follows : 

2HNO,  -f  4H,  =  3H80  +  NH4NO,. 

The  cell  gives  an  electromotive  force  of  1.93 
volts. 

When  the  porous  cell  is  good,  the  resistance  of 
the  Grove  cell  may  be  calculated  according  to 
the  following  formula  of  Ayrton: 


Grove's  Cell. 


R  = 


ohms, 


where  d,  is  the  distance  in  inches  between  the 
platinum  and  zinc  plates,  and  A,  the  square  inches 
of  the  immersed  portion  of  the  platinum  plate. 

Cell,  Yoltaic,  LeclanchS A  zinc- 
carbon  couple,  the  elements  of  which  are  used 
in  a  solution  of  sal-ammoniac  and  a  finely 
divided  layer  of  black  oxide  of  manganese 
respectively. 

The  zinc  is  in  the  form  of  a  slender  rod  and 
dips  into  a  saturated  solution  of  sal-ammoniac, 
NH4C1. 

The  negative  element  consists  of  a  plate  of  car- 
bon, C,  Fig.  ill,  placed  in  a  porous  cell,  in  which 
is  a  mixture  of  black  oxide  of  manganese  and 
broken  gas-retort  carbon,  tightly  packed  around 
the  carbon  plate.  By  this  mean?  a  greatly  ex 
tended  surface  of  carbon  surrounded  by  black 


CeL] 

oxide  of  manganese,  MnO,,  is  secured.  The  entire 
outer  jar,  and  the  spaces  inside  the  porous  cell  are 
filled  with  the  solution  of  sal-ammoniac. 


Fig.  in.     The  Ledanchl  Cell. 


This  cell,  though  containing  but  a  single  fluid, 
belongs,  in  reality,  to  the  class  or  type  of  double- 
flwd  cells,  being  one  in  which  the  negative  ele- 
ment is  surrounded  by  an  oxidizing  substance, 
the  black  oxide  of  manganese,  which  replaces  the 
nitric  acid  or  copper  sulphate  in  the  other  double- 
fluid  cells. 

This  reaction  is  generally  given : 

Zn  +  4NH4C1  +  2Mn02  =  ZnCl,  -j-  2NH4Cl 
+  2NH8  -f-  Mn808  -1-  H80. 

This  reaction  is  denied  by  some,  who  believe 
the  following  to  take  place : 

Zn  +  2(NH4Cl)  =  ZnCla  +  aNH,  +  H2. 
The  ZnCl2  and  NH8  react  as  follows  : 
ZnCl,  -|-  2(NH3)  =  2  (NHZ)  ZnCl2  +  H,. 

2H  -f  2(Mn2O2)  =  H2O  -f  MnaO3; 
or,  possibly,  4H  -f  3MnOa  =  MnaO  -f-  2H,O. 

The  Leclanche'  cell  gives  an  electromotive  force 
of  about  1.47  volts.  It  rapidly  polarizes,  and 
cannot,  therefore,  give  a  steady  current  for  any 
prolonged  time.  When  left  on  open  circuit,  how- 
ever, it  quickly  depolarizes. 

Cell,  Toltaic,  Local  Action  of 

(See  Action,  Local,  of  Voltaic  Cell.) 

Cell,  Yoltaic,  Meidinger A  zinc- 
copper  couple,  the  elements  of  which  are  em- 
ployed with  dilute  sulphuric  acid,  or  solution 
of  sulphate  of  magnesia,  and  strong  nitric 
acid,  respectively. 

The  Meidinger  cell  is  a  modification  of  the 
Daniell  cell.  The  zinc-copper  couple  is  thus  ar- 
ranged :  Z  Z,  Fig.  112,  is  an  amalgamated  zinc 
ring  placed  near  the  walls  of  the  vessel,  A  A, 
constricted  at  b  b.  The  copper  element,  c,  is 
similarly  placed  with  respect  to  the  walls  of  the 
vessel  d  d.  The  glass  cylinder  h,  filled  with 


[Cel. 

crystals  of  copper  sulphate,  has  a  small  hole  in 
its  bottom,  and  keeps  the  vessel,  d  d,  supplied 
with  saturated  so-  4. 

lution  of  copper 
sulphate.  The  cell 
is  charged  with  di- 
lute sulphuric  acid, 
or  a  dilute  solution 
of  Epsom  salts,  or 
magnesium  sul- 
phate. 

Cell,    Voltaic, 
Open-Circuit 

A  voltaic 

cell  that  cannot  be 
kept  on  closed  cir- 
cuit, with  a  com- 
paratively small 

resistance,  for  any   Fig.  112.     The  Meidinger  Cell. 

considerable  time  without  serious  polariza- 
tion. 

A  Leclanch^  cell  is  an  open-circuit  cell.  The 
term  open-circuit  cell  is  used  in  contradistinc- 
tion to  closed-circuit  cell,  such  as  the  Daniell. 
^See  Cell,  Voltaic,  Closed-Circuit.) 

Cell,    Voltaic,   Poggendorff A 

name  sometimes  given  to  the  Grenet  cell.  (See 
Cell,  Voltaic,  Grenet.) 

Cell,  Voltaic,  Polarization  of The 

collection  of  a  gas,  generally  hydrogen,  on  the 
surface  of  the  negative  element  of  a  voltaic 
cell. 

The  collection  of  a  positive  substance  like  hydro- 
gen on  the  negative  element  or  plate  of  ?•  voltaic 
cell  sets  up  a  counter -electromotive  force,  which 
tends  to  produce  a  current  in  the  opposite  direc- 
tion to  that  produced  by  the  cell.  (See  Force, 
Electromotive,  Counter.) 

Polarization  causes  a  decrease  in  the  normal 
current  of  a  voltaic  cell: 

(l.)  On  account  of  the  increased  resistance  of 
the  cell  from  the  bubbles  of  gas  which  form  part 
of  its  circuit. 

(2.)  On  account  of  the  counter-electromotive 
force,  produced  by  polarization. 

There  are  three  ways  in  which  the  iH  effects  of 
the  polarization  of  a  voltaic  cell  can  be  avoided. 
These  are  : 

(i.)  Mechanical.  —  The  negative  plate  is  fur- 
nished with  a  roughened  surface  which  enables  the 


CeL] 


[Cel. 


bubbles  of  gas  to  escape  from  the  points  on  such  sur- 
face ;  or,  a  stream  of  gas,  or  air,  is  blown  through 
the  liquid  against  the  plate  and  thus  mechanically 
brushes  the  bubbles  off. 

(2.)  Chemical. — The  surface  of  the  negative 
plate  is  surrounded  by  some  powerful  oxidizing 
substance,  such  as  chromic  or  nitric  acid,  which 
is  capable  of  oxidizing  the  hydrogen,  and  thus 
thoroughly  removing  it  from  the  plate. 

The  oxidizing  substance  may  form  the  entire 
electrolyte,  as  is  the  case  of  the  bichromate  solution 
employed  in  the  zinc-carbon  couple.  Generally, 
however,  it  has  been  found  preferable  to  employ 
a  separate  liquid,  like  nitric  acid,  to  completely 
surround  the  negative  plate,  and  another  liquid  for 
the  positive  plate,  the  two  liquids  being  generally 
kept  from  mixing  by  a  porous  cell,  or  diaphragm. 
Such  cells  are  called  double-fluid  cells.  (See 
Cell,  Voltaic,  Double-Fluid.) 

(3.)  Electro-Chemical.—  This  also  necessitates  a 
double-fluid  cell.  The  negative  element  is  im- 
mersed in  a  solution  of  a  salt  of  the  same  metal  as 
that  forming  the  negative  plate.  Thus,  a  cop. 
per  plate,  immersed  in  a  solution  of  copper  sul- 
phate, cannot  be  polarized,  since  metallic  copper 
is  deposited  on  its  surface  by  the  action  of  the 
hydrogen  which  tends  to  be  liberated  there. 

The  constancy  of  action  of  a  Daniell  cell  depends 
on  a  deposition  of  metallic  copper  on  its  copper 
plate  as  well  as  on  the  formation  of  hydrogen 
sulphate,  and  the  solution  of  additional  copper 
sulphate  from  the  crystallized  salt  placed  in  the 
cell  (SeeO//,  Voltaic,  Daniell's.) 

Cell,  Voltaic,  Primary,  Exhaustion  of 

The  inability  of  a  primary  voltaic 

cell  to  furnish  any  further  current,  unless 
fresh  electrolyte,  or  fresh  positive  element,  or 
both,  are  supplied  to  it. 

In  the  case  of  exhaustion  of  a  primary  voltaic 
cell  the  stock  of  fresh  energy  is  supplied  to  the 
cell  from  the  chemical  potential  energy  of  the 
positive  element,  or  of  the  electrolyte  or  elec- 
trolytes. (See  Energy,  Chemical  Potential.) 

In  most  voltaic  cells  a  marked  decrease  in  the 
current  strength  is  observed  soon  after  the  cir- 
cuit is  closed,  and,  therefore,  long  before  the 
cell  is  exhausted.  This  decrease  is  due— 

(i.)  To  the  increased  internal  resistance  due  to 
the  bubbles  of  hydrogen  on  the  negative  plate. 

(2.)  To  the  counter-electromotive  force  of  po- 
larization, where  zinc  is  employed  with  an  elec- 
trolyte of  sulphuric  acid. 


(3.)  To  the  decrease  in  the  electromotive  force 
due  to  an  increase  in  the  density  of  the  zinc  sul- 
phate. 

Cell,  Voltaic,  Secondary,  Exhaustion  of 

The  inability  of  a  secondary  cell  to 

furnish  any  further  current,  unless  fresh 
electro-positive  and  electro-negative  materials 
are  formed  in  it  by  the  passage  of  the 
charging  current. 

In  the  case  of  the  exhaustion  of  a  secondary 
voltaic  cell,  the  stock  of  fresh  energy  supplied 
to  the  cell  is  derived  from  the  electric  energy 
of  the  charging  current.  (See  Energy,  Electric.) 

Cell,    Voltaic,    Siemens-Halske  - 
A  zinc-copper  couple,  the  elements  of  which 
are  employed  with  dilute  sulphuric  acid  and 
saturated  solution  of  copper  sulphate  respect- 
ively. 

The  Siemens-Halske  cell  is  a  modification  of 
Darnell's.  A  ring  of  zinc,  Z  Z,  Fig,  113,  sur- 


Fig   IT3.     Siemens-Halske  Cell. 

rounds  the  glass  cylinder,  c  c.  The  porous 
cell  is  replaced  by  a  diaphragm,  ff,  of  porous 
paper,  formed  by  the  action  of  sulphuric  acid  on 
a  mass  of  paper  pulp.  Crystals  of  copper  sul- 
phate are  placed  in  the  glass  jar,  c  c,  and  rest 
on  the  copper  plate,  k,  formed  of  a  close  copper 
spiral.  Terminals  are  attached  at  b  and  h.  The 
entire  cell  is  charged  with  dilute  sulphuric  acid. 
The  resistance  of  the  cell  is  high , 

Cell,  Voltaic,  Silver  Chloride A 

zinc  and  silver  couple  immersed  in  electro- 
lytes of  sal-ammoniac  or  common  salt  and 
silver  chloride. 


Cel.] 


89 


[Cel. 


The  zinc  acts  as  the  positive  element,  and  a 
silver  wire,  around  which  a  cylinder  of  fused 
silver  chloride  is  cast,  as  the  negative  element. 
The  zinc,  and  the  silver  wire  and  silver  chloride, 
are  placed  in  a  small  glass  test-tube  and  covered 
with  the  sal-ammoniac  or  common  salt,  and 
the  tube  closed  by  a  cork  of  paraffin,  to  prevent 
the  evaporation  of  the  electrolyte.  When  sal- 
ammoniac  is  used,  the  strength  of  the  solution  is 
that  obtained  by  dissolving  23  grammes  of  pure 
sal-ammoniac  in  I  litre  of  water.  The  silver 
chloride  acts  as  a  depolarizer. 

This  cell  is  used  as  a  standard  cell,  known  as 
De  la  Rue's  standard  cell,  from  its  inventor, 
Warren  De  la  Rue.  Its  electromotive  force  is 
1. 068  volts. 

Cell,  Voltaic,  Simple Any  voltaic 

cell  formed  of  a  single  couple  immersed  in  a 
single  exciting  liquid. 

Cell,  Voltaic,  Single-Fluid A  vol- 
taic cell  in  which  but  a  single  fluid  or  elec- 
trolyte is  used. 

Single-fluid  voltaic  cells  possess  the  disadvan- 
tage of  polarizing  during  action.  This  polariza- 
tion is  due  to  the  electro-positive  element  of  the 
electrolyte  collecting  on  the  surface  of  the  nega- 
tive plate,  or  within  its  mass.  For  example, 
where  dilute  sulphuric  acid  is  the  electrolyte, 
hydrogen  gas  collects  on  the  negative  plate  and 
lowers  the  electromotive  Jorce  produced  by  the 
cell,  by  a  counter -electromotive  force  thereby 
generated.  (See  Force,  Electromotive.  Force, 
Electromotive,  Counter.) 

Cell,  Voltaic,  Smee A  zinc-silver 

couple  used  with  an  electrolyte  of  dilute  sul- 
phuric acid,  H2SO4. 

A  form  of  Smee  cell  is  shown  in  Fig.  1 14.  Here 
the  plate  of  silver  is  placed  between  two  zinc 
plates. 

The  silver  plate  is  roughened  and  covered  with 
a  coating  of  metallic  platinum,  in  the  condition 
known  as  platinum  alack.  (See  Platinum  Black. ) 
This  cell  was  formerly  extensively  employed  in 
electro-metallurgy  but  is  now  replaced  by  dynamo- 
tlectric -machines.  (See  Metallurgy,  Electro. 
Machine,  Dynamo -Electric. ) 

A  zinc -carbon  couple  is  sometimes  used  to  re- 
place the  zinc-silver  couple.  A  couple  of  zinc- 
lead  is  also  used,  though  not  very  advanta- 
geously. 


The  Smee  cell  was  one  of  the  earliest  forms 
of  voltaic  cells. 

In  the  zinc-silver  couple  the  chemical  reaction 
that  takes  place   when  the 
cell  is  furnishing  current  is 
as  follows,  viz. : 
Zn  -f  HaS04  =  ZnS04 

+  H2. 

The  Smee  cell  gives  an 
electromotive  force  of  about 
.65  volt. 

Cell,  Voltaic,  Stand- 
ard   —A  voltaic  cell 

the  electromotive  force  of 
which  is  constant,  and  Fig.  IT 4.  Smee  Cell. 
which,  therefore,  may  be  used  in  the  measure- 
ment of  an  unknown  electromotive  force. 

Absolute  constancy  of  electromotive  force  is 
impossible  to  attain,  but  if  the  current  of  the 
standard  cell  is  closed  but  for  a  short  time  the 
electromotive  force  may  be  regarded  as  practically 
invariable. 

Cell,  Voltaic,  Standard,  Clark's 

The  form  of  standard  cell  shown  in  Fig.  115. 

Latimer    Clark's    standard    cell    assumes    a 
variety  of  forms.     The  H-form  is  arranged   as 
shown  in  Fig.  115.    The  vessel  to  the  left  con- 
tains, at  A,  an  amal- 
gam of  pure  zinc.   The 
other  vessel   contains, 
at  M,  mercury  covered 
with    pure  mercurous 
sulphate,      Hg8  SO4. 
Both  vessels  are  then 
filled,  above  the  level 
of  the  cross  tube,  with 
a  saturated  solution  of 
zinc  sulphate  Z,  Z,  to 
which  a   few    crystals 
of  the  same  are  added. 
Tightly    fitting    corks 
C,  C,  prevent  loss  by  Fig.  113.    Clark's  Stand- 
evaporation.  *rd  Cell. 

The  voltage  of  this  cell  in*  legal  volts  is  1.438 
[1—0.00077  (t—  IS  degrees  C.)]— (Ayrton.) 

The  value  t,  is  the  temperature  in  degrees  of 
the  centigrade  scale. 

Cell,  Voltaic,  Standard,  Kayleigh's  Form 

of  Clark's A  modified  form  of  Clark's 

cell. 


Ccl.] 


[Cel. 


Il(>_     Rayleigh'* 
Form     of    Clark's 

Standard  Cell. 


Lord  Rayleigh's  form  of  Clark's  standard  cell 
is  shown  in  Fig.  1  16.  The  electrodes  pass  respect- 
ively through  the  bottom  and  top  of  the  test  tube 
of  glass.  On  the  lower 
electrode  a  layer  of  mer- 
cury, Hg,  is  placed.  On 
this  rests  a  layer  of  mercu- 
rous  sulphate  paste  made 
sufficiently  semi-fluid  with 
a  solution  of  zinc  sulphate 
to  form  an  approximately 
level  surface.  The  zinc, 
Zn,  is  attached  to  the  up- 
per electrode  and  is  im- 
mersed in  this  semi-fluid 
paste. 

The  mercurous  sulphate 
appears  to  act  to  keep  the 
mercury  free  from  impuri- 
ties. 

The  electromotive  force  j 
of  this  cell  has  been  care- 
fully determined  by  Ray- 
leigh.     Its  value  in   true 

Volts  is  : 

E=  1.435  t1  —  -00077  (t  —  15)]  when  t,  is  the 
temperature  in  degrees  Centigrade. 

This  cell  is  often  called  Clark's  normal  element. 

Cell,  Voltaic,  Standard,  De  la  Rue's  - 
—  A  form  of  silver-chloride  cell.  (See  Cell, 
Voltaic,  Silver-Chloride.} 

Cell,  Voltaic,  Stand- 
ard, Fleming's  -- 
The  form  of  standard 
cell  shown  in  Fig.  117. 

The  U-tube,  Fig.  117, 
is  connected,  as  shown, 
by  means  of  taps,  with 
two  vessels  filled  with 
chemically  pure  solutions 
of  copper  sulphate  of  sp. 
gr.  i.i  at  15  degrees  C., 
and  zinc  sulphate  of  sp. 
gr.  1.4  at  15  degrees  C. 
respectively.  To  use  the 
cell  the  zinc  rod  Zn,  con- 
nected with  a  wire  pass- 
ing through  a  rubber 
stopper,  is  placed  in  the 
left-hand  branch.  The  tap  A,  is  opened  and 
the  entire  U-tube  is  filled  with  the  denser 
zinc  sulphate  solution.  The  tap  at  C,  is  then 


Fig.  z  if.    Fleming's 
Standard  Cell. 


opened,  and  the  liquid  in  the  right-hand  branch 
above  the  tap  is  discharged  into  the  lower  vessel, 
but,  from  this  part  only.  The  tap  C,  is  then 
closed,  and  the  tap  B,  opened,  and  the  lighter 
copper  sulphate  allowed  to  fill  the  right-hand 
branch  above  the  tapC.  The  copper  rod  Cu,  fitted 
to  a  rubber  stopper  and  connected  with  a  con- 
ducting wire,  is  then  placed  in  the  copper  solution. 

Tubes  are  provided  at  L  and  M,  for  the  recep- 
tion of  the  zinc  and  copper  rods  when  not  in  use. 
The  copper  rod  is  prepared  for  use  by  freshly 
electro-plating  it  with  copper.  The  electro- 
motive force  of  this  cell  is  1.074  volts.  If  the  line 
of  demarkation  between  the  two  liquids  is  not 
sharp,  the  arms  of  the  vessels  are  emptied,  and 
fresh  liquid  is  run  in. 

Cell,  Voltaic,  Standard,  Lodge's 

A  form  of  standard  Daniell  cell. 

Lodge's  standard  cell  is  shown  in  Fig.  118. 
Through  the  tube  T,  in  a 
wide  mouthed  bottle,  is 
passed  the  glass  tube,  in  the 
mouth  of  which  is  placed  a 
zinc  rod.  To  the  bottom  of 
the  tube  T,  a  small  test-tube 
t,  containing  crystals  of  cop  - 
per  sulphate,  is  fastened  by 
means  of  a  string  or  rubber 
band.  The  uncovered  end 
of  a  gutta-percha  insulated 
copper  wire  projects  at  the 
bottom  of  t,  through  a  tube 
in  a  tightly  fitting  cork,  and 
forms  the  copper  electrode.  The  bottle  is  partly 
filled  as  shown  with  a  solution  of  zinc  sulphate. 

The  internal  resistance  of  this  cell  is  so  high 
that  it  is  only  employed  in  the  use  of  zero  methods 
with  a  condenser. 

Cell,   Voltaic,   Standard,   Sir   William 

Thomson's   — A   form     of    standard 

Daniell  cell. 


Fig.  118.    Lodge's 
Form  of  Daniel!' t  Cell. 


Cu 


Fig.  u<).     Thomson's  Form  of  Daniell' s  Cell. 
Sir  Wm.  Thomson's  standard  cell  is  shown  in 
Fig .  1 1 9.  A  zinc  disc  is  placed  at  the  bottom  of  the 


Cel.] 

cylindrical  vessel  and  a  solution  of  zinc  sulphate 
of  sp.  gr.  1.2  poured  over  it.  By  means  of  the 
funnel  F,  a  half-saturated  solution  of  copper 
sulphate  is  carefully  poured  over  this  and  floats 
on  it  owing  to  its  smaller  density.  The  electro, 
motive  force  of  this  cell  is  1.072  true  volts  at 
15  degrees  C. 

Cell,Yoltaic,  Standardizing  a De- 
termining the  exact  value  of  the  electromotive 
force  of  a  voltaic  cell,  in  order  to  enable  it  to 
be  used  as  a  standard  in  determining  the 
electromotive  force  of  any  other  electric 
source. 

Cell,  Voltaic,  Two-Fluid A  term 

sometimes  employed  in  place  of  double-fluid 
cell.  (See  Cell,  Voltaic,  Double-Fluid) 

Cell,  Voltaic,  Water A  voltaic 

cell  in  which  the  exciting  liquid  is  merely 
water. 

Any  voltaic  couple  can  be  used,  the  positive 
element  of  which  is  acted  on  by  water.  (See 
Battery,  Voltaic.) 

Cell,    Voltaic,     Zinc-Carbon A 

cell  in  which  zinc  and  carbon  form  the  posi- 
tive and  negative  elements  respectively. 

A  name  sometimes  given  to  the  bichro- 
.nate  cell. 

Cell,  Voltaic,  Zinc-Copper A 

cell  in  which  zinc  and  copper  form  the  posi- 
tive and  negative  elements  respectively. 

Cell,  Voltaic  Zinc-Lead A  zinc- 
lead  couple  sometimes  used,  though  not  very 
advantageously,  to  replace  the  zinc-silver 
couple  in  a  Smee  cell.  (See  Cell,  Voltaic, 
Smee?) 

Cells,  Coupled A  number  of  sep- 
arate cells  connected  in  any  way  so  as  to 
form  a  single  source. 

Cells,  Voltaic,  Series-Connected 

A  number  of  separate  voltaic  cells  connected 
in  series  so  as  to  form  a  single  source.  (See 
Circuit,  Series.) 

Cement-Lined  Conduit.  —  (See  Conduit. 
Cement-Lined?) 

Cements,  Insulating  — Various 

mixtures  of  gums,  resins  and  other  substances, 
possessing  the  ability  to  bind  two  or  more 
4— Vol.  1 


[Ch* 

substances  together  and  yet  to  electrically  in- 
sulate one  from  the  other. 

Cent!. — (As  a  prefix) — The  one-hundredth 
part  of. 

Centi-Ampdre. — One-hundredth  of  an  am- 
pere. 

Centi-AmpSre  Balance. — (See  Balance. 
Centi-Ampere?) 

Centigrade  Thermometer  Scale.  —  (See 
Scale,  Centigrade  Thermometer?) 

Centigramme. — The  hundredth  of  a 
gramme 

One  centigramme  equals  0.1544  grains  avoir- 
dupoise.  (See  Weights  and  Measures^  Metric 
System  of.) 

Centilitre. — The  hundredth  of  a  litre. 

One  centilitre  equals  0.6102  of  a  cubic  inch. 
(See  Weights  and  Measures,  Metric  System  of.) 

Centimetre. — The  hundredth  of  a  metre. 

One  centimetre  equals  0.3937  inch.  (See 
Weights  and  Measures,  Metric  System  of.) 

Centimetre-Gramme-Second  Units. — (See 
Units,  Centimetre-Gramme-Second?) 

Central  Galvanization. — (See  Galvaniza- 
tion, Central?) 

Central  Station.— (See  Station,  Central?) 

Central  Station  Burglar  Alarm.— (See 
Alarm,  Burglar,  Central  Station?) 

Central  Station  Lighting.— (See  Light- 
ing, Electric  Central  Station?) 

Centre  of  Gravity.— (See  Gravity,  Centre 
of.) 

Centre  of  Oscillation.— (See  Oscillation, 
Centre  of.) 

Centre  of  Percussion.— (See  Percussion 
Centre  of) 

Centrifugal  Force.— (See  Force,  Centrifu- 
gal?) 

Centrifugal  Governor.-t-(See  Governor 
Centrifugal?] 

Chain  Lightning.  —  (See  Lightning, 
Chain?) 

Chain,  Linked  Magnetic  and  Electric 

A  chain  of  three  links,  the  separate 

links  of  which  consist  of  the  primary  circuit. 


Cha.j 


LCha. 


the  magnetic  circuit,  and  the  secondary  cir- 
cuit respectively,  of  an  induction  coil. 

The  conception  of  a  linked  magnetic  and  elec- 
tric chain,  in  studying  the  action  of  an  induction 
coil,  was  first  developed  by  Kapp.  A  linked 
magnetic  and  electric  chain  is  shown  in  Fig.  120. 


Fig.  120.    Linked  Magnttic  and  Electric  Chain. 

tf,  in  such  a  case,  the  magnetic  core  or  circuit  is 
of  varying  magnetization,  when  one  of  the  electric 
circuits  has  a  periodic  current  passed  through 
it,  the  various  phenomena  of  the  induction  coil 
are  produced.  (See  Coilt  Induction.) 

Chain,  Molecular A  polarized  chain 

oi  molecules  that  is  supposed  to  exist  in  an 
electrolyte  during  its  electrolytic  decomposi- 
tion, or  in  a  voltaic  cell  on  closing  its  circuit. 
(See  Hypothesis,  Grotthus.) 

Chain  Pull.— (See  Pull,  Chain) 

Chamber,  Armature The  armature 

bore.  (See  Bore,  Armature?) 

Chamber  of  Lamp.— (See  Lamp,  Cham- 
hrof.) 

Change,  Chemical Any  change  in 

matter  resulting  from  atomic  combination 
and  the  consequent  formation  of  new  mole- 
cules. 

Some  chemical  changes  are  caused  by  atomic 
combinations  and  the  formation  of  new  molecules. 
They  are  necessarily  attended  by  9  loss  of  the  spe- 
cific identity  of  the  substances  involved  in  the 
change.  Thus  carbon,  a  black  solid,  combined 
with  sulphur,  a  yellow  solid,  produces  carbon 
disulphide,  a  colorless,  odorous  liquid.  (See 
Atom.) 

Change,  Physical Any  change  in 

matter  resulting  from  a  change  in  the  relative 
position  of  its  molecules,  without  the  forma- 
tion of  new  molecules. 

Ice,  when  heated,  is  turned  into  water;  steel, 
when  stroked  by  a  magnet,  is  rendered  perma- 
nently magnetic;  a  piece  of  vulcanite  or  hard 


rubber  stroked  by  a  piece  of  cat  skin  becomes 
electrified.  In  all  these  cases,  which  are  instances 
of  physical  changes,  the  substances  retain  their 
specific  identity ,  This  is  true  in  all  cases  of  phys- 
ical changes.  (See  Molecule.) 

Changing-over  Switch. — (See  Switch, 
Changing-over?) 

Changing  Switch. — (See  Switch,  Chang- 
ing.'] 

Characteristic  Curve. — (See  Curve, 
Characteristic^) 

Characteristic  Curve  of  Parallel  Trans- 
former.— (See  Citrve,  Characteristic,  of 
Parallel  Transformer!) 

Characteristic  Curve  of  Series  Trans- 
former.— (See  Cur've,  Characteristic,  of 
Series  Transformer?) 

Characteristics  of  Sound. — (See  Sound, 
Characteristic  of.) 

Charge,  Bound The  condition  of 

an  electric  charge  on  a  conductor  placed  near 
another  conductor,  but  separated  from  it  by 
a  medium  through  which  electrostatic  induc- 
tion can  take  place.  (See  Induction,  Elec~ 
trostatic?) 

When  a  charged  conductor  is  placed  near  an- 
other conductor,  but  separated  from  it  by  a  di- 
electric or  medium  through  which  induction  can 
take  place,  a  charge  of  the  opposite  name  is  in- 
duced in  the  neighboring  conductor.  This  charge 
is  so  held  or  bound  on  the  conductor  by  the  mu- 
tual attraction  of  the  opposite  charge  that  it  is 
not  discharged  on  connection  with  the  earth 
unless  both  conductors  are  simultaneously  touched 
by  any  good  conductor.  The  bound  charge  was 
formerly  called  dissimulated  or  latent  electricity. 
(See  Electricity,  Dissimulated  or  Latent. ) 

Charge,  Density  of The  quantity 

of  electricity  per  unit  of  area  at  any  point  on 
a  charged  surface. 

Coulomb  used  the  phrase  surface  density  to 
mean  the  quantity  of  electricity  per  unit  of  area 
at  any  point  on  a  surface. 

Charge,  Dissipation  of  —  — The  gradual 
but  final  loss  of  any  charge  by  leakage,  which 
occurs  even  in  a  well  insulated  conductor. 

This  loss  is  more  rapid  with  negatively  charged 
conductors,  than  with  those  positively  charged. 


[Cha. 


Crookes,  of  England,  has  retained  a  charge  on 
conductors  for  years,  without  appreciable  leakage, 
by  placing  the  conductors  in  vessels  in  which  a 
high  vacuum  was  maintained.  (See  Vacuum, 
pi.) 

Charge,  Distribution  of The  vari- 
ations that  exist  in  the  density  of  an  electrical 
charge  at  different  portions  of  the  surface  of 
all  insulated  conductors  except  spheres. 

The  density  of  charge  varies  at  different  points 
of  the  surface  of  conductors  of  various  shapes.  It 
is  uniform  at  all  points  on  the  surface  of  a  sphere. 

It  is  greater  at  the  extremities  of  the  longer 
axis  of  an  egg-shaped  body,  and  greatest  at  the 
sharper  end. 

It  is  greater  at  the  corners  of  a  cube  than  at 
the  middle  of  a  side. 

It  is  greatest  around  the  edge  of  a  circular  disc. 

It  is  greatest  at  the  apex  oi  a  cone 

Charge,  Electric The  quantity  of 

electricity  that  exists  on  the  surface  of  an  in- 
sulated electrified  conductor. 

When  such  a  conductor  is  touched  by  a  good 
conductor  connected  with  the  earth,  it  is  <#*- 
charged.  (See  Condenser.) 

Charge,  Free The  condition  of  an 

electric  charge  on  a  conductor  isolated  from 
any  other  conductor. 

It  is  impossible  to  obtain  a  perfectly  free  charge, 
since  it  is  impossible  to  complete!;  isolate  an 
insulated  conductor.  The  charge,  however,  can 
be  comparatively  free. 

The  charge,  on  a  completely  isolated  conductor, 
readily  leaves  it  when  it  is  put  in  contact  with  a 
good  conductor  connected  with  the  ground.  (See 
Charge,  Bound.} 

Charge,   Induced   Electrostatic 

The  charge   produced  by  bringing  a  body 

into  an  electrostatic  fiel 

In  order  to  obtain  a  permanent  charge,  i.  e.,  a 
charge  which  will  be  maintained  when  the  body 
is  withdrawn  from  an  electrostatic  field,  it  is  nec- 
essary to  connect  the  body  with  the  earth  so  that 
it  may  lose,  or'part  with,  a  charge  of  the  same 
mame  as  the  inducing  charge.  Then,  on  the  with- 
drawal of  this  charge,  it  will  possess  a  charge  op- 
posite in  name  to  the  inducing  charge.  (See 
Condenser. ) 

Charge,  Influence A  charge  pro- 


duced by  electrostatic  induction.  (Sec  /«• 
duction,  Electrostatic) 

Charge,  Negative According  to  the 

double-fluid  hypothesis,  a  charge  of  negative 
electricity. 

According  to  the  single-fluid  hypothesis, 
any  deficit  of  an  assumed  electrical  fluid. 

Charge,  Positive According  to  the 

double-fluid  hypothesis,  a  charge  of  positive 
electricity. 

According  to  the  single-fluid  hypothesis, 
any  excess  of  an  assumed  electrical  fluid. 

Charge,  Residual The  charge  pos- 
sessed by  a  charged  Leyden  jar  for  a  few 
moments  after  it  has  been  disruptively  dis- 
charged by  the  connection  of  its  opposite 
coatings. 

The  residual  charge  is  probably  due  to  a  species 
of  dielectric  strain,  or  a  strained  position  of  the 
molecules  of  the  glass  caused  by  the  charge. 
Such  residual  charge  is  not  present  in  air  con« 
densers.  In  other  words,  a  Leyden  jar  does  not 
give  up  all  the  electric  energy  charged  in  it,  on  a 
Single  disruptive  discharge. 

Charge,  Return A  charge  induced 

in  neighboring  conductors  by  a  discharge  of 
lightning. 

Under  the  influence  of  induction  a  lightning 
stroke  produces  during  its  discharge  an  electric 
shock  in  the  human  body,  or  a  charge  in  neigh* 
boring  bodies,  which  is  called  the  back  or  re- 
turn stroke  of  lightning.  (See  Stroke^  Light- 
ning, Back  or  Return.} 

Charged  Body.— (See  Body,  Charged) 

Charging  Accumulators. — Sending  an 
electric  current  into  a  storage  battery  for  the 
purpose  of  rendering  it  an  electric  source. 

There  is,  strictly  speaking,  no  accumulation  of 
electricity  in  a  storage  battery,  such,  for  example, 
as  takes  place  in  a  condenser,  but  a  mere  storage 
of  chemical  energy,  which  may  .afterward  become 
electric.  (See  Cell,  Storage.) 

Charging  Leyden  Jars  1>7  Cascade.— (See 

Case  ad*,  Charging  Leyden  Jars  by) 

Chart,  Inclination A  map  or  chart 

on  which  the  isoclinic  lines  are  marked.  (See 
Map  or  Chart,  Inclination.  Lints,  Isocltnie) 


Cha.] 


94 


[Chr. 


Chart,  Isodynamie A  map  or  chart 

on  which  the  isodynamic  lines  are  marked. 
(See  Map  or  Chart,  Isodynamic.  Lines, 
Isodynamic?) 

Chart,  Isogonal An  isogonic  chart. 

(See  Map  or  Chart,  Isogonal) 

Chart,  Isogonic A  map  or  chart 

on  which  the  isogonic  lines  are  marked.  (See 
Map  or  Chart,  Isogonic.  Lines,  Isogonic) 

Chatterton's  Compound.  —  (See  Com- 
pound, Chatterton's) 

Chemical  Change. — (See  Change,  Chem- 
ical) 

Chemical  Effect.— (See  Effect,  Chemical) 

Chemical  Equivalent.— (See  Equivalent, 
Chemical) 

Chemical  Galvano-Cautery.— (See  Cau- 
tery, Galvano-Chemical) 

Chemical  Phosphorescence.— (See  Phos- 
phorescence, Chemical) 

Chemical  Photometer.,— (See  Photometer, 
Chemical) 

Chemical  Potential  Energy.— (See  En- 
ergy, Chemical  Potential) 

Chemical  Recorder,  Bain's (See 

Recorder,  Chemical,  Bains) 

Chemistry,  Electro That  branch 

of  electric  science  which  treats  of  chemical 
compositions  and  decompositions  effected  by 
the  electric  current.  (See  Electrolysis.  De- 
composition, Electrolytic) 

That  branch  of  chemistry  which  treats  of 
combinations  and  decompositions  by  means 
of  electricity. 

Electro-chemistry  treats  of  the  formation  of 
new  molecules,  by  the  combination  of  atoms  under 
the  electric  force,  as  well  as  the  decomposition  of 
molecules  by  electricity. 

The  action  of  a  series  of  sparks  passed  through 
air,  in  forming  nitric  acid,  is  an  instance  of  the 
former,  and  electrolytic  decompositions  fax  gen- 
eral afford  instances  of  the  latter. 

Chimes,  Electric Bells  rung  by 

the  attractions  and  repulsions  of  electrostatic 
charges. 

The  bells  B  and  B,  Fig.  121,  are  conductively 
connected  to  the  prime  or  positive  conductor  -\-, 


of  a  frictional  machine.  The  bell  C,  is  insulated 
from  this  conductor  by  means  of  a  silk  thread, 
but  is  connected  with  the  ground  by  the  metallic 
chain.  Under  these 
circumstances  th  e 
clappers,  1,  1,  insu- 
lated by  silk  threads, 
t,  t,  are  attracted  to 
B,  B,  by  an  induced 
charge  and  repelled 
to  C,  where  they  lose 
their  charge  only  to 
be  again  attracted  to 
B,  B.  In  this  way 
the  bells  will  con- 
tinue  ringing  as  long 
as  the  electric  ma- 
chine  is  in  operation. 

Choking  Coil.— (See  Coil,  Choking) 
Chronograph,  Electric •  —An  elec- 
tric apparatus  for  automatically  measuring 
and  registering  small  intervals  of  time. 

Chronographs,  though  of  a  variety  of  forms, 
generally  register  small  intervals  of  time  by 
causing  a  tuning  fork  or  vibrating  bar  of  steel, 
whose  rate  of  motion  is  accurately  known,  to 
trace  a  sinuous  line  on  a  smoke-blackened  sheet 
of  paper,  placed  on  a  cylinder  driven  at  a  uni- 
form rate  of  motion  by  clockwork.  If  the  fork 
is  known  to  produce,  say,  256  vibrations  per 
second  be  used,  each  sinuous  line  will  represent 
y|3  part  of  a  second. 


Fig.  tSf.  Electric  Chimes. 


Fig.  122.     Electric  Chronograph. 

An  electro-magnet  is  used  to  make  marks  on 
the  line  at  the  beginning  and  the  end  of  the 
observation,  and  thus  permit  its  duration  to  be 
measured. 

In  the  form  of  electric  chronograph  shown 


Clir.] 


95 


[Cir. 


in  Fig.  122,  an  electro-magnet,  the  armature  of 
which  carries  a  pen,  is  supported  on  a  carriage 
moved  by  clockwork  over  a  sheet  of  paper 
wrapped  on  a  rotating  cylinder.  A  clock  is  so 
connected  with  the  circuit  of  the  electro-magnet 
that  it  makes  or  breaks  the  circuit  at  the  end  of 
every  second  second,  and  so  moves,  or  displaces, 
the  armature,  as  to  cause  an  elevation  or  depres- 
sion in  the  otherwise  continuous  sinuous  line,  that 
would  be  drawn  on  the  paper  by  the  double 
motion  of  its  rotation  and  the  movement  of  the 
pen-carriage. 

When  it  is  desired  to  know  with  great  precision 
the  exact  time  of  occurrence  of  any  event, 
such,  for  example,  as  the  transit  of  a  star  over  the 
meridian,  the  observer,  who  carries  in  his  hand  a 
push  button,  or  other  form  of  electric  key,  closes 
or  opens  the  circuit  at  the  exact  moment  and  so 
superposes  an  additional  mark  on  the  sinuous 
line.  Since  the  exact  time  of  starting  the  clock 
is  known,  and  the  intervals  between  the  regular 
successive  marks  are  two  seconds  each,  it  is  easy  to 
estimate  from  its  position  between  any  two  such 
marks  the  exact  value  of  the  additional  mark  inter- 
posed. Fig.  122,  taken  from  Young,  shows  a  form 
of  chronograph  by  Warner  &  Swasey.  The  de- 
tails of  this  apparatus  will  be  understood  from 
an  inspection  of  the  drawing. 

Chronograph  Record. — (See  Record, 
Chronograph) 

Chronoscope,  Electric An  appa- 
ratus for  electrically  indicating,  but  not 
necessarily  recording,  small  intervals  of  time. 

This  term  is  often  used  for  chronograph. 

The  interval  of  time  required  for  a  rifle  ball 
to  pass  between  two  points  may  be  determined 
by  causing  the  ball  to  pierce  two  wire  screens 
placed  a  known  distance  apart.  As  the  screens 
are  successively  pierced,  an  electric  circuit  is 
thus  made  or  broken,  and  marks  are  registered 
electrically  on  any  apparatus  moving  with  a 
known  velocity. 

Cigar-Lighter,     Electric    —(See 

Lighter,  Cigar,  Electric) 

Cipher  Code.— (See  Code,  Cipher) 

Circle,  Azimuth The    arc   of  a 

great  circle  passing  through  the  point  of  the 
heavens  directly  overhead,  called  the  Zenith, 
and  the  point  directly  beneath,  called  the 

Nadir. 


Circle,  Dipping  — A  term  some- 
times applied  to  an  inclination  compass.  (See 
Compass,  Inclination) 

Circle,  Galvanic A  term  some- 
times used  for  galvanic  circuit.  (See  Circuit, 
Galvanic) 

Circle  of  Reference.— The  circle,  by  refer- 
ence to  which  simple  harmonic  motion  may 
be  studied,  by  comparison  with  uniform  mo- 
tion around  such  circuit.  (See  Motion, 
Simple  Harmonic) 

Circle,  Voltaic A  name  formerly 

employed  for  voltaic  cell  or  circuit.  (See 
Cell,  Voltaic.  Circuit,  Voltaic) 

Circuit,  Air-Magnetic That  part 

of  the  path  of  a  line  of  magnetic  induction 
which  takes  place  wholly  through  air. 

Circuit,  Alternating  Current A 

circuit  in  which  an  alternating  current  of 
electricity  is  flowing.  (See  Current,  Alter- 
nating) 

Circuit,  Astatic A  circuit  consist- 
ing of  two  closed  curves  enclosing  equal  sur- 
faces. 

Such    a    circuit   is  A 

not  deflected  by  the  *jL 

action  of  the  earth's  — »_|[l 

field.    The  circuit  dis-  J 
posed,   as    shown    in 
Fig.  1 23,  is  astatic  and 
produces    two    equal 
and  opposite  fields  at 
S  and  S'.     (See  Mag-    Fig.  123.    Astatic  Circuit, 
netism,  Ampere's  Theory  of.) 

Circuit,  Balanced-Metallic A  me- 
tallic circuit,  the  two  sides  of  which  have 
similar  electrical  properties. 

Circuit  Breaker.— (See  Breaker,  Circuit) 

Circuit,  Broken An  open  circuit. 

A  circuit,  the  electrical  continuity  of  which 
has  been  disturbed,  and  through  which  the 
current  has  therefore  ceased' to  pass. 

Circuit,  Closed A  circuit  is  closed, 

completed,  or  made  when  its  conducting 
continuity  is  such  that  the  current  can  pass. 

Circuit,    Closed    Iron-Magnetic 

The   name  applied  to  the  path  of   any  line 


dr.] 


96 


[Cir. 


of  magnetic  force,  which  takes  place  entirely 
through  iron,  steel,  or  other  paramagnetic  sub- 
stance. 
Circuit,  Closed-Loop  Parallel A 

variety  of  parallel  circuit  in  which  the  lead 
and  the  return  circuit  are  arranged  in  the 
form  of  concentric  circuits,  with  the  recep- 
tive devices  placed  radially  between  them. 

Circuit,  Closed-Magnetic A  mag- 
netic circuit  which  lies  wholly  in  iron  or  other 
substance  of  high  magnetic  permeability. 

All  lines  of  magnetic  force  form  closed  circuits. 
The  term  closed-magnetic  circuit  is  used  in  con- 
tradistinction to  a  divided  circuit,  or  one  in  which 
an  air  gap  exists  in  the  substance  of  high  mag- 


Fig.  124.*  Closed-Magnetic  Circuit. 
netic  permeability  forming  the  remainder  of  the 
circuit.  This  introduces  so  high  a  resistance  that 
such  a  circuit  is  sometimes  called  an  open-mag- 
netic circuit.  An  iron  ring,  such  as  shown  in 
Fig.  124,  forms  a  closed -magnetic  circuit. 

Circuit,  Closed-Magnetic,  of  Atom 

A  closed-magnetic  circuit,  or  closed  lines 
of  magnetic  force  supposed  to  lie  entirely  in 
the  atom  itself. 

The  assumption  of  closed  lines  of  magnetic 
force  in  atoms  or  molecules  was  made  in  order  to 
explain  the  original  polarity  of  the  same,  and  to 
account  for  some  of  the  other  phenomena  of 
magnetism. 

When  the  atom  is  subjected  to  a  magnetizing 
force,  such,  for  example,  as  the  field  of  an  electric 
current,  these  closed  lines  of  force  are  assumed 
to  open  out  and  produce  lines  of  polarized  atoms. 
According  to  Lodge,  for  every  single  line  of  force 
produced  by  the  current  passing  through  a  coil 
of  wire  surrounding  an  iron  core,  some  3,000 
lines  of  magnetic  force  are  added  to  it  from  the 
iron.  Therefore  an  iron  core  greatly  increases 
the  magnetic  strength  of  a  hollow  coil  of  wire. 


Circuit,  Closed-Magnetic,  of  Molecule 

— A  closed-magnetic  circuit  assumed  to  lie 
wholly  within  the  molecule. 

As  it  is  not  known  whether  the  assumed  mag. 
netic  circuit  lies  within  the  atom  or  the  molecule, 
it  is  called  indifferently  the  closed-atomic  or 
closed-molecular  circuit.  (See  Circuit,  Closed- 
Magnetic,  of  Atom.) 

Circuit,  Completed A  closed 

circuit. 

A  circuit,  the  conducting  continuity  of 
which  is  unbroken. 

A  completed  circuit  is  also  called  a  made  or 
closed  circuit. 

Circuit,  Compound A  circuit  con- 
taining more  than  a  single  source,  or  more 
than  a  single  electro-receptive  device,  or  both, 
connected  by  conducting  wires. 

The  term  compound  circuit  is  sometimes  ap- 
plied to  a  series  circuit.  (See  Circuit,  Series.) 
The  term,  however,  is  a  bad  one,  and  is  not 
generally  adopted. 

Circuit,  Constant-Current A  cir- 
cuit in  which  the  current  or  number  of  am- 
peres is  maintained  constant  notwithstanding 
changes  occurring  in  its  resistance. 

The  series-circuit,  as  maintained  for  arc-lamps, 
is  a  constant-current  circuit.  (See  Regulation, 
Automatic.) 

Circuit,  Constant-Potential  —  —A 
circuit,  the  potential  or  number  of  volts  of 
which  is  maintained  approximately  constant. 

The  multiple-arc  or  parallel  circuit  is  an  ap- 
proximately constant-potential  circuit. 

Circuit,  Derivative A  derived  or 

shunt  circuit.     (See  Circuit,  Shunt.) 

Circuit,  Derived 

A  term  applied  to  a  shunt 
circuit. 

If,  in  addition  to  the  galva- 
nometer G,  the  conductor  S, 
Fig.  125,  be  connected  with 
the  circuit  of  the  battery  B,  a 
derived  circuit  will  thus  be 
established,  and  a  current  will 
flow  through  S,  diminishing 
the  current  in  the  galvanom- 
eter. (See  Circuit,  Shunt.) 


J2j.  Derivtd 
Circuit. 


Cir.] 


97 


[Cir. 


Circuit,       Divided-Magnetic A 

magnetic  circuit  which  lies  partly  in  iron,  or 
qther  substance    of  high  magnetic    perme- 
ability, and  partly  in  air. 
A  divided-magnetic  circuit  is  shown  in  Fig.  126. 


Fig.  I2b.    Divided  Magnetic  Circuit. 
Where  the  iron  ring  is  separated  by  the  air  gap, 
a  high  magnetic  resistance  is  introduced,  owing 
to  the  fact  that  the  iron  is  at  these  points  replaced 
by  air,  whose  magnetic  reluctance  is  great. 

Circuit,     Double-Wire A    term 

sometimes  used  for  a  simple  multiple  circuit 
with  two  conductors  or  wires.  (See  Circuit, 
Multiple') 

The  term  double-wire  circuit  is  used  in  contra- 
distinction to  single-wire  circuit.  (See  Circuit, 
Single -Wire.-) 

Circuit,  Earth A  circuit  in  which 

the  ground  or  earth  forms  part  of  the  con- 
ducting path. 

Circuit,     Earth,     Telegraphic   — '- 

That  portion  of  a  telegraphic  circuit  which  is 
completed  through  the  earth  or  ground. 

Circuit,     Electric The    path  in 

which  electricity  circulates  or  passes  from  a 
given  point,  around  or  through  a  conducting 
path,  back  again  to  its  starting  point. 

All  simple  circuits  consist  of  the  following 
parts,  viz.: 

(I.)  Of  an  electric  source  which  may  be  a 
voltaic  battery,  a  thermopile,  a  dynamo-electric 
machine,  or  any  other  means  for  producing  elec- 
tricity. 

(2.)  Of  leads  or  conductors  for  carrying  the 
electricity  out  from  the  source,  through  whatever 
apparatus  is  placed  in  the  line,  and  back  again  to 
the  source. 

(3.)  Various  electro-receptive  devices,  such  as 
electro-magnets,  electrolytic  baths,  electric 
motors,  electric  heaters,  etc.,  through  which 


passes  the  current  by  which  they  are  actuated  or 
operated. 
Circuit,  Electrostatic The  circuit 

formed  by  lines  of  electrostatic  force. 

Lines  of  electrostatic  force,  like  lines  of  mag. 
netic  force,  form  closed  circuits.  Hence  the 
origin  of  the  phrase  electrostatic  circuit.  (See 
Force,  Electrostatic,  Lines  of.) 

Circuit,  External That  part  of  a 

circuit  which  is  external  to,  or  outside  the  elec- 
tric source. 

The  circuit  external  to  the  source  consists  of 
two  distinct  parts,  viz. : 

(i.)  The  conductors  or  leads. 

(2.)  The  electro-receptive  or  translating  de- 
vices. 

It  is  in  the  external  circuit  only  that  useful 
work  is  done  by  the  current. 

Circuit,  Forked A  term  sometimes 

used  in  telegraphy  for  a  number  of  circuits 
that  radiate  from  a  given  central  point. 

Circuit,  Galvanic A  term  some- 
times employed  instead  of  voltaic  circuit. 

The  term  galvanic  in  place  of  voltaic  is  unwar- 
ranted by  the  facts  of  electric  science.  (See  Cir- 
cuit, Voltaic. ) 

Galvani  thought  he  had  discovered  the  vital 
fluid  or  source  of  animal  life.  Volta  first  pointed 
out  the  true  explanation  of  the  phenomena  ob- 
served in  Galvani's  frog,  and  devised  means 
for  producing  electricity  in  this  manner.  The 
terms  voltaic  battery,  cell,  circuit,  etc.,  are  there- 
fore preferable. 

Circuit,  Ground A  circuit  in  which 

the  ground  forms  part  of  the  path  through 
which  the  current  passes. 

As  the  ground  is  not  always  a  good  conductor, 
the  terminals  should  be  connected  with  the  gas  or 
water  pipes,  or  with  metallic  plates,  called  ground 
plates.  Such  connection,  or  any  similar  ground 
connection,  is  usually  termed  the  ground  or  earth. 

Circuit,    Ground,   Telegraphic 

An  earth  circuit  used  in  any  system  of  telegra- 
phy. (See  Circuit,  Earth,  Telegraphic!) 

Circuit,  Grounded A  ground  cir- 
cuit. 

Circuit,  Incomplete An  open  01 

broken  circuit. 


Cir.] 

A  circuit  whose  conducting  continuity  is 
incomplete. 

Circuit,  Inductive Any  circuit  in 

which  induction  takes  place. 

Circuit,  Internal That  part  of  a 

circuit  which  is  included  within  the  electric 
source. 

The  electric  current  passing  through  the  inter- 
nal circuit  does  no  useful  work. 

Circuit,  Leg  of One  part  of  a 

twisted  or  metallic  circuit. 

Circuit,  Line The  wire  or  other 

conductors  in  the  main  line  of  any  telegraphic 
or  other  electric  circuit. 

Circuit,  Line,  Telegraphic The 

conductor  or  line  connecting  different  tele- 
graphic stations. 

Circuit,  Local-Battery The  cir- 
cuit, in  a  telegraphic  system,  in  which  is 
placed  a  local  battery  as  distinguished  from  a 
main  battery.  (See  Telegraphy \  American 
or  Morse  System  of.) 

Circuit,  Loop A  term  sometimes 

applied  to  a  circuit  in  parallel  or  multiple-arc. 
(See  Circuit,  Multiple^ 

Circuit  Loop  Break.— (See  Break,  Circuit 
Loop.) 

Circuit,  Made A  completed  circuit. 

A  circuit,  whose  conducting  continuity  is 
unbroken. 

A  made  circuit  is  often  called  a  completed  or 
closed  circuit.  (See  Circuit,  Closed.) 

Circuit,  Magnetic The  path  through 

which  the  lines  of  magnetic  force  pass. 

All  lines  of  magnetic  force  form  closed  circuits. 


[Cir. 

is  often  placed  around  the  magnet.  The  magnet 
is  then  said  to  be  iron-clad. 

The  armature  of  a  magnet  lowers  the  magnetic 
resistance  by  affording  a  better  path  for  the  lines 
of  magnetic  force  than  the  air  between  the 
poles. 

The  magnetic  circuit  always  tries  to  shorten  its 
path,  or  to  render  itself  as  compact  as  possible. 
This  is  seen  in  the  action  of  an  armature  drawn 
towards  a  magnet  pole. 

Circuit,     Main-Battery  —A    term 

sometimes  used  for  line  circuit.  (See  Circuit. 
Line)  . 

Circuit,  Metallic A  circuit  in  which 

the  ground  is  not  employed  as  any  part  of  the 
path  of  the  current,  metallic  conductors  being 
employed  throughout  the  entire  circuit. 

Circuit,  Multiple —A  compound  cir- 
cuit, in  which  a  number  of  separate  sources 
or  separate  electro-receptive  devices,  or  both, 
have  all  their  positive  poles  connected  to  a 
single  positive  lead  or  conductor,  and  all  their 
negative  poles  to  a  single  negative  lead  or 
conductor. 

The  connection  of  three  Bunsen  cells,  in  mul. 
tiple,  is  shown  in  Fig.  128,  where  the  three  car- 


Fig.  t2j.    Magnetic  Circuit. 

In  the  bar  magnet,  shown  in  Fig.  127,  part  of 
this  path  is  through  the  air.  In  order  to  reduce 
or  lower  the  resistance  of  a  magnetic  circuit,  iron 


Fig.  1 28.     Batteries  connected  in  a  Multiple  Circuit. 

bons,  C,  C,  C,  are  connected  together  so  as  to  form 
the  positive,  or  -\-  terminal  of  the  battery,  and 
the  three  zincs,  Zn,  Zn,  Zn,  are  similarly  con- 
nected together  so  as  to  form  the  negative,  or  — 
terminal. 

The  electromotive  force  is  the  same  as  that  of 
a  single  cell,  or  source.  The  internal  resistance 
of  the  source  is  as  much  less  than  the  resistance  of 
any  single  source  as  the  area  of  the  combined 
negative  or  positive  plates  is  greater  than  that  of 
any  single  negative  or  positive  plate ;  or,  in  othet 
words,  is  less  in  proportion  to  the  number  of  cells, 
or  other  separate  sources  so  coupled. 

The  connection  of  six  cells  in  multiple  or 
parallel  circuit,  is  shown  in  Fig.  129. 


Cir.J 


[Cir. 


In  the  case  of  the  six  cells,  the  current  would 
be, 

B 


where  E,  is  the  electromotive  force,  r,  the  in- 
ternal,  and  r',  the  external  resistance. 


1  H    fl2fi    031}    848    ISB    M 


Fig.  129.    Six  Cells  Connected  in  Multiple. 

In  the  case  of  voltaic  cells  the  effect  of  multiple 
connection  on  the  internal  resistance  of  the  source 
is  to  increase  the  area  of  cross-section  of  the 
liquid  in  the  dirert  proportion  of  the  number  of 
cells  added,  and  consequently  to  decrease  the  re- 
sistance in  the  same  proportion. 

When  strong  or  large  currents  of  low  electro- 
motive  force  are  required,  connections  in  multi- 
ple-arc are  generally  employed. 

The  multiple-arc  connection  was  formerly 
called  connection-f  or  -quantity.  This  term  is  now 
abandoned. 

The  total  resistance  for  the  parallel  circuit  is 
obtained  as  follows:  calling  the  separate  resist- 
ances of  the  separate  electro-receptive  devices, 
R',  R",  R'",  etc.,  etc.,  etc.,  total  resistance, 
R'  X  R"  X  R'" 


R= 


R'  R" 


R"  R'"       R'  R'" 


or,  what  is  the  same  thing,  the  conductivity  is  the 
sum  of  the  reciprocal  of  the  separate  resistances, 


Conductivity 

The  joint  resistance  of  only  two  separate  resist- 
ances joined  in  a  multiple-circuit  is  equal  to  the 
product  of  the  separate  resistances  divided  by 
their  sum. 

When  the  separate  resistances  joined  in  multiple 
arc  are  all  of  the  same  value,  the  joint  resistance  is 
equal  to  the  resistance  of  one  of  them  divided  by 
their  number. 

Circuit,  Multiple- Arc A  term  often 

used  for  multiple  circuit.     (See  Circuit,  Mul- 
tiple^ 

Circuit,  Multiple-Series  .  —A  com- 
pound circuit  in  which  a  number  of  separate 


sources,  or  separate  electro-receptive  devices, 
or  both,  are  connected  in  a  number  of  sepa- 
rate  groups    in  series,  and  these  separata 
groups  subsequently  connected  in  multiple. 
In  Fig.    130,  a  multiple-series  circuit  of  six 
_       _          _       _  c 


X 


Fig.  130.     Mulliple-Series-Connected  Cells. 

sources  is  shown,  in  which  three  separate  groups 
of  two  series-connected  cells  are  coupled  in  multi- 
ple. The  current  takes  the  paths  indicated  by  the 
arrows.  The  electromotive  force  of  the  source 
will  be  increased  in  proportion  to  the  number  of 
cells  in  series,  and  the  internal  resistance  de- 
creased in  proportion  to  the  number  in  parallel. 


Fig.  13  r.    Cells  Connected  in  Multiple-  Series. 
c_         3E 


In  Fig.  131,  six  cells  are  arranged  in  two 
groups  of  three  series-connected  cells,  and  these 
three  groups  connected  in  parallel. 

Calling  r,  the  resistance  of  each  separate  cell, 
the  total  resistance  for  the  multiple-series  circuit 
for  a  circuit  containing  three  cells  in  parallel  and 
two  in  series  is, 


for  three  in  series  and  two  in  parallel, 


If,   therefore,   the   circuit  of  this  battery  be 
closed  by  a  resistance  equal  to  r,  the  current 
would  be  in  the  case  of  Fig.  130, 
c_       2E 


Cir.] 


100 


[Cir. 


Circuit,  Negative  Side  of The  side 

olt  a  circuit  opposite  to  the  positive  side. 
(See  Circuit,  Positive  Side  of.) 

That  side  or  half  of  a  circuit  connected  to  or 
leading  from  the  positive  terminal  of  the  source  of 
Current. 

Circuit,  Open A  broken  circuit. 

A  circuit,  the  conducting  continuity  of 
which  is  broken. 

Circuit,  Open-Iron  Magnetic  — 

The  path  of  a  line  of  magnetic  induction, 
which  passes  partly  through  iron,  and  partly 
through  an  air  space. 

The  magnetic  circuit  is  always  closed,  that  is 
the  lines  of  magnetic  force  always  form  closed 
paths.  The  term  "  open  "  is  used  in  contradis- 
tinction only  to  "closed  "  iron  magnetic  circuit, 
in  which  the  entire  path  of  a  line  of  force  passes 
through  iron.  (See  Circuit,  Magnetic.) 

Circuit,  Parallel A  name  some- 
times applied  to  circuits  connected  in  mul- 
tiple. (See  Circuit,  Multiple.) 

Circuit,  Parallel-Tree A  form  of 

parallel  circuit  in  which  the  receptive  devices 
are  placed  in  parallel  between  the  leads  and 
returns,  and  the  branches  and  sub-branches 
arranged  in  a  tree-like  form. 

Circuit,  Positive  Side  of That  side 

of  a  circuit,  bent  in  the  form  of  a  circle,  in 
which,  if  an  observer  stood  with  his  head  in 
the  positive  region,  he  would  see  the  current 
pass  round  him  from  his  right  hand  towards 
his  ldt—(Dam'etZ.) 

Circuit,  Recoil A  term  sometimes 

applied  to  the  circuit  that  lies  in  the  alterna- 
tive path  of  a  discharge.  (See  Path,  Alter- 
native^ 

Circuit,  Return That  part  of  a 

circuit  by  which  the  electric  current  returns  to 
the  source. 

In  a  multiple-circuit  the  lead  that  is  con- 
nected to  the  negative  terminals  of  the 
separate  sources. 

Circuit,  Series A  compound  cir- 
cuit in  which  the  separate  sources,  or  the  sep- 
arate electro-receptive  devices,  or  both,  are  so 
placed  that  the  current  produced  in  each,  or 
passed  through  each,  passes  successively 


through  the  entire  circuit  from  the  first  to  the 
last. 

•  The  six  cells,  shown  in  Fig.  132,  are  connected 
in  series  by  joining  the  positive  pole  of  each  cell 
with  the  negative  pole  of  the  succeeding  cell,  the 
negative  and  positive  poles  at  the  extreme  ends 


Fig.  132.    Series  Circuit. 

being  connected  by  conductors  with  the  external 
circuit. 

The  connection  of  three  Leclanche'  cells  iit 
series  is  clearly  shown  in  Fig.  133.     The  carbons, 

-       C+Z«-         C> 


Altaic  Cells  Connected  in  Series. 


C,  C,  of  the  first  and  second  cells  are  connected  to 
the  zincs,  Zn,  Zn,  of  the  second  and  third  cells, 
thus  leaving  the  zinc,  Zn,  of  the  first  cell,  and  the 
carbon,  C,  of  the  third  cell,  as  the  terminals  of 
the  battery.  The  direction  of  the  current  is 
shown  by  the  arrows. 

The  resistance  of  such  a  connection  is  equal  to 
the  sum  of  the  resistances  of  all  of  the  separate 
sources. 

The  electromotive  force  is  equal  to  the  sum  of 
the  separate  electromotive  forces. 

If  the  electromotive  force  of  a  single  cell  is 
equal  to  E,  its  internal  resistance  to  r,  and  the 
resistance  of  the  leads  and  electro  -receptive  de- 
vices to  r',  then  the  current  in  the  circuit, 


If  six  of  such  cells  are  coupled  in  series,  the  cur- 
rent becomes 

6E 


If,  however,  the  internal  resistance  of  each  cell  be 
so  small  as  to  be  neglected,  the  formula  becomes 

r      6E- 
C=_, 


Cir.] 


101 


[Cir. 


or  the  current  is  six  times  as  great  as  with  one 
cell. 

The  total  resistance  of  the  separate  sources  or 
electro-receptive  devices  of  the  series  circuit  is 
as  follows,  calling  R',  R",  R'",  etc.,  the-separate 
resistance  and  R,  the  total  resistance, 
R  =  R'  -f  R"  +  R  "',  etc. 

The  series  connection  of  battery  cells  is  used 
on  telegraph  fines,  where  a  high  electromotive 
force  is  required  in  order  to  overcome  a  consider- 
able  resistance  in  the  circuit,  or  in  similar  cases 
where  the  resistance  in  the  external  circuit  is 
great,  on  account  of  a  number  of  electro-receptive 
devices  being  connected  to  the  line  in  series. 

The  series  connection  was  formerly  called 
connection  for  intensity.  The  term  is  now  aban- 
doned. 

Circuit,  Series-Multiple  --  A  com- 
pound circuit,  in  which  a  number  of  separate 
sources,  or  separate  electro-receptive  devices, 
or  both,  are  connected  in  a  number  of  sepa- 
rate groups  in  multiple-arc,  and  these  sepa- 
rate groups  subsequently  connected  in  series. 

In  the  series-multiple  circuit  the  resistance  of 
each  multiple  group  is  equal  to  the  resistance  of 
a  single  branch  divided  by  the  number  of  branches. 

If,  for  example,  r,  is  the  resistance  of  each  sepa- 
rate branch  of  say  seven  parallel  circuits  in  each 
of  the  separate  groups  of  multiple  circuits,  then 
the  resistance,  R,  of  each  separate  multiple 
group  is  —  • 


The  total  resistance  of  the  series-multiple  cir- 
cuit is  equal  to  the  sum  of  the  resistances  of  the 
separate  multiple  groups.  The  total  resistance  of 
the  three  groups  is  —  - 

R'  =  ^  +  JL  +  Jl^JL. 
777         7 

An  example  of  the  series-multiple  circuit  is 
shown  in  Fig.  134,  which  is  the  method  adopted 


Fig.  134-     Series-Multiple  Circuit. 
in  the  use  of  distribution  boxes.     Here  a  number 
c    multiple  groups  or  circuits  are  connected  with 
each  other  in  series,  as  shown.     (See  Box,  Dis- 
tribution, for  Arc  Light  Circuits. ) 

Circuit,  Short A  shunt,  or  by-path. 


of  comparatively  small  resistance,  around  the 
poles  of  an  electric  source,  or  around  any 
portion  of  a  circuit,  by  which  so  much  of  the 
current  passes  through  the  new  path,  as  vir- 
tually to  cut  out  the  part  of  the  circuit  around 
which  it  is  placed,  and  so  prevent  it  from  re- 
ceiving an  appreciable  current. 

Circuit,  Shunt A  branch  or  addi- 
tional circuit  provided  at  any  part  of  a  cir- 
cuit, through  which  the  current  branches  or 
divides,  part  flowing  through  the  original  cir- 
cuit, and  part  through  the  new  branch. 

A  shunt  circuit  is  in  multiple  circuit  with  the 
circuit  it  shunts. 

In  the  case  of  branch  circuits  each  of  the  cir- 
cuits acts  as  a  shunt  to  the  others.  Any  number 
of  additional  or  shunt  circuits  may  be  thus  pro- 
vided. (See  Lams,  JGrcAAofs.) 

Circuit,  Simple A  circuit  containing 

a  single  electric  source,  and  a  single  electro- 
receptive  device,  connected  by  a  conductor. 

The  term  simple  circuit  is  sometimes  applied 
to  a  multiple  circuit.  The  term  is  not,  however, 
a  good  one,  and  is  not  in  general  use. 

Circuit,  Single- Wire A  term  some- 
times used  for  a  grounded  circuit.  (See 
Circuit,  Grounded?) 

The  single-wire  circuit  is  sometimes  used  in  the 
distribution  of  incandescent  lamps  in  multiple-arc. 
One  pole  of  the  dynamo  is  put  to  ground,  and  the 
other  pole  to  a  single  wire  or  lead.  The  electro- 
receptive  devices  have  one  of  their  poles  con. 
nected  to  this  lead  and  the  other  pole  to  earth. 
The  single-wire  circuit  is  a  very  objectionable 
circuit  so  far  as  safety  is  concerned. 

It  is  frequently  used,  however,  in  the  wiring  of 
ships. 

Circuit,  Through A  telephonic  or 

telegraphic  circuit  that  has  been  completed 
through  to  a  given  station  by  cutting  out  inter- 
ruptions or  breaks  in  the  line  by  the  connec- 
tion together  of  sections  of  different  wires. 

Circuit,  Time-Constant   of —The 

time  in  which  a  current  due  .to  a  constant 
electromotive  force  will  rise  in  a  conductor 
to  a  definite  fraction  of  its  maximum  value. 
The  ratio  of  the  inductance  of  a  circuit  to 

its  resistance. 


Cir.J  1 

The  time  required  from  the  moment  of 
closing  the  circuit,  for  a  current  to  rise  to 

a  value  equal  to  e      *  of  the  full  value,  or 

.632  of  the  maximum  value. 

In  the  above,  e,  equals  2.71828,  or  the  base  of 
the  Napierian  system  of  logarithms. 

The  time-constant  is  proportional  to  the  con- 
ductivity of  the  circuit  and  its  formal  resistance. 

Approximately  the  time  constant  of  a  circuit  is 
the  time  from  closing  the  circuit,  in  which  the 
current  rises  to  two-thirds  of  its  maximum  value, 
this  maximum  value  being  determined  by  the 

formula,  C  =  -. 
R 

The  time- constant  of  a  circuit  may  be  reduced — 

(i.)  By  decreasing  the  self-induction  of  the  cir- 
cuit. 

(2.)  By  increasing  the  resistance. 

In  the  case  of  a  magnetic  conductor  the  time- 
constant  is  proportional  to  a  quantity  (the  perme- 
ability) which  is  determined  by  the  capacity  of 
the  conductor  to  utilize  part  of  the  energy  in 
producing  magnetization  of  its  substance.— (Flem- 
ing-) 

Circuit,  Voltaic The  path  through 

which  the  current  flows  out  from  a  voltaic  cell 
or  battery,  through  the  translating  devices 
and  back  again  to  the  cell  or  b?>tery. 

Circuits,  Forked A  term  employed 

in  telegraphy  to  indicate  circuits  that  radiate 
from  any  single  point. 

Forked  circuits  are  employed  in  simultaneously 
transmitting  messages  to  several  stations. 

Circuits,  Varieties  of » — Conducting 

paths  provided  for  the  passage  of  an  electric 
current. 

Electric  circuits  may  be  divided,  according  to 
their  complexity,  into— 

(i.)  Simple. 

(2.)  Compound. 

According  to  the  peculiarities  of  their  connec- 
tions, into — 

(i.)  Shunt  or  derived. 

(2.)  Series. 

(3.)  Multiple,  multiple-arc  or  parallel. 

(4.)  Multiple-series. 

(5.)  Series-multiple. 

Either  the  circuits,  the  sources,  or  the  electro- 


®  [Cle. 

receptive  devices  may  be  connected  in  series,  in 
multiple,  in  multiple-series  or  in  series-multiple. 

According  to  their  resistance,  circuits  are 
divided  into— 

(i.)  High-resistance. 

(2.)  Low-resistance. 

According  to  their  relation  to  the  electric 
source,  into — 

(I.)  Internal  circuits. 

(2.)  External  circuits. 

According  to  their  position,  or  the  work  done, 
circuits  are  divided  into  very  numerous  classes; 
thus,  in  telegraphy,  we  have  the  following,  viz.: 

(i.)  The  line-circuit. 

(2.)  The  earth  or  ground  circuit. 

(3.)  The  local-battery  circuit. 

(4.)  The  main -battery  circuit,  etc. 

Circular  Bell.— (See  Bell.  Circular) 
Circular  Units.— (See  Units,  Circular)' 

Circular  Units  (Cross-Sections),   Table 

of (See    Units,  Circular  (Cross-Sec- 

tions),  Table  of) 

Clamp,  Carbon A  carbon  clutch, 

(See  Clutch,  Carbon,  of  Arc  Lamp) 

Clamp  for  Arc  Lamps.— A  clamp  for 
gripping  the  lamp-rod,  /.  e.,  the  rod  that  sup- 
ports the  carbon  electrodes  of  arc  lamps. 
(See  Lamp,  Electric,  Arc.) 

Clamp,  Rod A  carbon  clutch.  (See 

Clamp  for  Arc  Lamps) 

Clark's  Compound. — (See  Compound, 
Clark's) 

Clark's    Standard    Voltaic    Cell.— (See 

Cell,  Voltaic,  Standard,  Clark's) 

Clark's    Standard    Voltaic    Cell,  Ray- 

leigh's  Form  of (See  Cell,    Voltaic, 

Standard,  Rayleigh's  Form  of  Clark's) 

Clay  Electrode.— (See  Electrode,  Clay) 

Cleansing,  Fire  —  —The  removal  of 
grease  from  metallic  articles,  that  are  to  be 
electro-plated,  by  subjecting  them  to  the  action 
of  heat. 

This  cleansing  is  for  the  purpose  of  obtaining  \ 
uniform,  adherent  coating. 

Clearance-Space.— (See  Stace.  Clearance) 


Cle.] 


103 


[Clo. 


Clearing-Out  Drops.— (See  Drops,  Clear- 
ing-Out) 

Cleat,  Crossing A  cleat  so  arranged 

as  to  permit  the  crossing  of  one  pair  of  wires 
under  or  over  another  pair  without  contact 
with  each  other. 

Cleat-Wiring.— (See  Wiring,  Cleat) 

Cleats,  Electric Suitably  shaped 

pieces  of  wood,  porcelain,  hard  rubber  or 
other  non-conducting  material  used  for  fasten- 
ing and  supporting  electric  conductors  to 
ceilings,  walls,  etc. 

A  simple  form  of  wooden  cleat  is  shown  in 
Fig.  135- 


.W 


Fig-  '35'     Wooden  Cleat. 

Clepsydra,  Electric An  instrument 

for  measuring  time  by  the  escape  of  water  or 
other  liquid  under  electrical  control. 

Climbers,  Pole 

—Devices  employed  by 
linemen  for  climbing 
wooden  telegraph  poles. 

A  climber  with  straps 
for  attachment  to  the  leg 
and  foot  is  shown  in  Fig. 
I36. 

Clip,  Cable A 

term  sometimes  used  for 
cable  hanger.  (See 
Hanger,  Cable?) 

Clock,  Electric 

— A  clock,  the  works  of 

which  are  moved,   COn-   Fig.  136.     Climber  and 

trolled,     regulated     or  *"**• 

wound,  either  entirely  or  partially,  by  the  elec- 
tric current. 

Electric  clocks  may  be  divided  into  three 
classes,  viz.: 

(i.)  Those  in  which  the  works  are  moved  en- 
tirely or  partially  by  the  electric  current. 

(2.)  Those  which  are  controlled  or  regulated 
by  the  electric  current 


Fig.  Jjf.     Controlling 
Clock. 


(3-)  Those  which  are  merely  wound  by  the 
current. 

A  clock  moving  independently  of  electric  power 
is  prevented  from  gain- 
ing or  losing  time,  by 
means  of  a  slight  re- 
tardation or  acceleration 
electrically  imparted . 
The  entire  motion  of 
the  balance  wheel  is 
sometimes  imparted  by 
electricity. 

An  example  of  one  of 
many  forms  of  controll- 
ing electric  clocks  is 
shown  in  Fig.  137, 
where  the  split  battery 
(See  Battery,  Split),  P 
N,  is  connected,  as 
shown,  to  the  spring 
contacts  S  and  S'.  In  this  way  currents  are  sent 
into  the  circuit  in  alternately  opposite  directions. 

The  pendulum  bob,  Fig.  138,  of  the  con- 
trolled  clock  is  formed  of  a  hollow  coil  of  insu- 
lated wire,  which  encircles  one  or  both  of  two 
permanent  magnets,  A  and  A',  placed  with  their 
opposite  poles  facing  each  other. 

When  the  pendulum  of  the  controlling  clock  is 
in  the  position  shown  in  Fig.  137,  the  current 
passes  in  the  direction  E  P  Sn  W,  etc.,  and  through 
the  coil  C,  Fig.  138.  When  the  pendulum  of  the 
controlling  clock  is  in  con- 
tact with  S',  the  current 
flows  through  Wn  S'  N  E, 
etc.,  and  through  the  coil 
C  in  the  opposite  direc- 
tion. In  this  manner  a 
slight  motion  forwards  or 
backwards  is  imparted  to 
the  pendulum,  which  is 
thus  kept  in  time  with  the 
controlling  clock. 

Mercury      contacts     are 
sometimes     employed     in 
place  of  the  springs  S  and 
S'.  Induction  currents  may  A 
also  be  employed. 

Clocks  of  non-electric  ac-  Fig.  138. 
tion  may  be  electrically 
controlled,  or  correctly  set  at  certain  intervals, 
either  automatically  by  a  central  clock,  or  by  the 
depression  of  a  key  operated  by  hand  from  an 
astronomical  observatory. 


Controlled 
Clock' 


Clo.] 


104 


[Clo, 


In  a  system  of  time-telegraphy,  the  controlling 
clock  is  called  the  master  clock,  and  the  con- 
trolled  clocks,  the  secondary  clocks. 

Secondary  clocks  are  generally  mere  dials,  con- 


Fig.  139.    Mechanism  of  Secondary  Clock. 

taining  step-by-step  movements,  for  moving  the 
hour,  minute  and  second  hands,  as  shown  in 
Fig.  139- 

In  Spellier's  clock,  a  series  of  armatures  H, 
Fig.    140,  mounted  on  the  circumference  of  a 

E 


Fig.  140.    Spellier's  Electric  Clock. 

wheel,  connected  with  the  escapement  wheel, 
pass  successively,  with  a  step-by-step  movement, 
over  the  poles  of  electro-magnets.  On  the  com- 
pletion of  the  circuit,  they  are  attracted  towards 
the  magnet,  and  on  the  breaking  of  the  circuit 
they  are  drawn  away  by  the  fall  of  the  weight  F, 
placed  on  the  lever  D,  pivoted  at  E.  A  pulley  at 
E,  runs  over  the  surface  of  a  peculiarly  shaped 
cog  on  the  escapement  wheel. 

Clock,  Electric  Annunciator A 

clock,  the  hands  or  works  of  which,  at  cer- 
tain predetermined  times,  make  electric  con- 
tacts and  thus  ring  bells,  release  drops,  trace 
records,  etc. 


Clock,  Electrical-Controlling In 

a  system  of  time  telegraphy,  the  master  clock, 
whose  impulses  move  or  regulate  the  second- 
ary clocks.  (See  Clock,  Electric.} 

Clock,  Electrically-Controlled In 

a  system  of  time  telegraphy,  a  secondary 
clock,  that  is  either  driven  or  controlled  by 
the  master  clock.  (See  Clock,  Electric.} 

Clock,  Electrolytic,  Tesla's A  time 

piece  in  which  the  rotation  of  the  wheel  work 
is  obtained  by  the  difference  in  weight  of  the 
two  halves  of  a  delicately  pivoted  and  well- 
balanced  wheel  placed  in  an  electrolytic 
bath. 

In  the  electrolytic  clock  of  Nikola  Tesla,  a  deli-  ' 
cately  formed  and  balanced  disc  of  copper  is  sup- 
ported on  a  horizontal  axis  at  right  angles  to  the 
shortest  distance  between  the  two  electrodes,  and 
placed  in  a  bath  of  copper  sulphate.  Its  two 
halves  become  respectively  electro-positive  and 
electro-negative  when  a  current  is  passed  through 
the  bath,  and  consequently  metal  is  deposited  on 
one  half  and  dissolved  from  the  other  half.  The 
rotation  of  the  disc  under  the  influence  of  gravity 
is  caused  to  mark  time. 

An  electrolytic  clock  could  therefore  be  made 
to  answer  roughly  as  an  electric  meter. 

Clock,  Master The  central  or  con- 
trolling clock  in  a  system  of  electric  time-dis- 
tribution, from  which  the  time  is  transmitted 
to  the  secondary  clocks  in  the  circuit.  (See 
Clock,  Electric.} 

Clock,  Secondary Any  clock  in  a 

system  of  time  telegraphy  that  is  controlled 
by  the  master  clock.  (See  Clock,  Electric.} 

Clock,  Self-Winding A  clock  that 

at  regular  intervals  is  automatically  wound  by 
the  action  of  a  small  electro-magnetic  motor 
contained  within  it. 

This  motor  is  usually  run  by  one  or  more  vol- 
taic cells,  concealed  in  the  case  of  the  clock. 

Cloged-Circuit.— (See  Circuit,  Closed) 

Closed-Circuit  Battery.— (See  Battery, 
Closed-Circuit) 

Closed-Circuit,  Single-Current,  Signal- 
ing   (See  Signaling,  Single-Current, 

Closed-Circuit^ 


Clo.] 


105 


[Coe. 


Closed-Circnit  Thermostat.— (See  Ther- 
mostat, Closed-Circuit) 

Closed-Circuit  Voltaic  Cell.— (See  Cell, 
Voltaic,  Closed-Circuit) 

Closed-Circuit  Voltmeter.— (See  Volt- 
meter, Closed-Circuit) 

Closed-Circuited. — Placed  in  a  closed  or 
completed  circuit. 

A  voltaic  battery,  or  other  source,  is  closed- cir- 
cuited when  its  poles  or  terminals  are  electrically 
connected  with  each  other. 

Closed-Circuited  Conductor.— (See  Con- 
ductor, Closed-Circuited) 

Closed-Circular  Current. — (See  Current, 
Closed-  Circular) 

Closed-Coil  Disc  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Closed-Coil  Disc) 

Closed-Coil  Drum  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Closed-Coil  Drum) 

Closed-Coil  Dynamo-Electric  Machine.— 
(See  Machine,  Dynamo-Electric,  Closed- 
Coil) 

Closed-Coil  Ring  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Closed-Coil  Ring) 

Closed-Iron-Circuit  Transformer.—  (See 
Transformer,  Closed-Iron-Circuit) 

Closed-Loop  Parallel-Circuit.— (See  Or- 
ttu't,  Closed-Loop  Parallel) 

Closed-Magnetic  Circuit. — (See  Circuit, 
Closed-Magnetic) 

Closed-Magnetic  Core. — (See  Core,  Closed- 
Magnetic) 

Closure. — The  completion  of  an  electric 
circuit. 

Cloth  Discs,  Carbonized,  for  High  Re- 
sistances   Discs  of  cloth  carbonized  by 

heating  to  an  exceedingly  high  temperature 
in  a  vacuum,  or  out  of  contact  with  air. 

After  carbonization  the  discs  retain  their  flex- 
ibility and  elasticity  and  serve  admirably  for  high 
resistances.  When  piled  together  and  placed  in 
glass  tubes,  they  form  excellent  variable  resist* 
>  vrhen  subjected  to  varying  pressure. 


Club-Footed     Magnet.  — (See     Magnet, 
Club-Footed) 
Clutch,  Carbon,  of  Arc  Lamp A 

clutch  or  clamp  attached  to  the  rod  or  other 
support  of  the  carbon  of  an  arc  lamp,  pro- 
vided for  gripping  or  holding  the  carbon. 
(See  Lamp,  Electric  Arc) 

Clutch  Rod.— (See  Rod,  Clutch) 

Coating,  Metallic A  covering  or 

coating  of  metal,  usually  deposited  from 
solutions  of  metallic  salts  by  the  action  of  an 
electric  current .  (See  Plating,  Electro) 

Coating  of  Condenser.— A  sheet  of  tin 
foil  on  one  side  of  a  Leyden  jar  or  condenser, 
directly  opposite  a  similar  sheet  on  the  other 
side  for  the  purpose  of  receiving  and  collecting 
the  opposite  charges.  (See  Jar,  Leyden. 
Condenser) 

Coatings  of  Leyden  Jar. — The  sheets  of 
tin  foil  or  other  conductor  on  the  opposite 
sides  of  a  Leyden  jar  or  condenser.  (See 
Jar,  Leyden.  Condenser) 

Code,  Cipher A  code  in  which  a 

number  of  words  or  phrases  are  represented 
by  single  words,  or  by  arbitrary  words  or  syl- 
lables. 

The  message  thus  received  requires  the  posses- 
sion of  the  key  to  render  it  intelligible. 

Code,Telegraphic The  pre-arranged 

signals  of  any  system  of  telegraphy.  (See 
Alphabet,  Telegraphic.  Alphabet,  Tele- 
graphic, Morse's.  Alphabet,  Telegraphic, 
International  Code) 

Co-efflcient,  Algebraic A  number 

prefixed  to  any  quantity  to  indicate  how 
many  times  that  quantity  is  to  be  taken. 

The  number  3,  in  the  expression  33,  is  a  co- 
efficient and  indicates  that  the  a,  is  to  be  taken 
three  times,  asa4-a4-a  =  3a. 

Co-efficient,  Economic,  of  a  Dynamo- 
Electric  Machine The  ratio  between 

the  electrical  energy,  or  the  electrical  horse- 
power of  the  current  produced  by  a  dynamo, 
and  the  mechanical  horse-power  expended  in 
driving  the  dynamo. 

The  economic  co-efficient  is  usually  called  the 
efficiency. 


Coe.] 


106 


[Coi. 


The  efficiency  may  be  the  commercial  effi. 
ciency,  which  is  the  useful  or  available  energy  in 
the  external  circuit  divided  by  the  total  mechan- 
ical energy;  or  it  may  be  the  electrical  efficiency, 
which  is  the  available  electrical  energy  divided 
by  the  total  electrical  energy. 

The  efficiency  of  conversion  is  the  total  elec- 
trical energy  developed,  divided  by  the  total 
mechanical  energy  applied. 

If  M,  equals  the  mechanical  energy, 
W,  the  useful  or  available  electrical  energy, 

and 
w,   the   electrical  energy   absorbed  by   the 

machine,  and 
m,  the  stray  power,  or  the  power  lost  in 

friction,  eddy  currents,  air  friction,  etc. 
Then,  since 


The  Commercial  Efficiency 

_  W_.        W 

~~  "M  ~~  W  +  w  -f  m" 
The  Electrical  Efficiency 
W 

The  Efficiency  of  Conversion 

^  W  +  w  =      W  -f  w 

M  W  +  w  -f  m' 

Co-efficient  of  Electro-Magnetic  Inertia. 

—  (See    Inertia,   Electro-Magnetic,  Co-effi- 
cient of.) 

Co-efficient  of  Expansion.  —  (See  Expan- 
sion, Co-efficient  of.) 

Co-efficient  of  Expansion,  Linear  -- 

(See  Expansion,  Linear,  Co-efficient  of) 

Co-efficient  of  Magnetic  Induction.  —  (See 
Induction,  Magnetic,  Co-efficient  of.) 

Co-efficient  of  Magnetization.  —  (See 
Magnetization,  Co-efficient  of.) 

Co-efficient  of  Mutual-  Inductance.  —  (See 
Inductance,  Mutual,  Co-efficient  of.) 

Co-efficient  of  Mutual-Induction.  —  (See 
Induction,  Mutual,  Co-efficient  of) 

Co-efficient  of  Self-induction.—  (See  In- 
duction, Self,  Co-efficient  of) 

Coercitive  Force.—  (See  Fora,  Coerci- 
tive) 

Coercive  Force.—  (See  Force,  Coercive) 

Coil,  Choking  --  A  coil  of  wire  so 


wound  on  a  core  of  iron  as  to  possess  high 
self-induction. 

Choking-coils  are  used  to  obstruct  or  cut  oft  an 
alternating  current  with  a  loss  of  power  less  than 
with  the  use  of  a  mere  ohmic  resistance. 

Fig.  141  shows  a  choking-coil.  It  consists  of 
a  circular  solenoid  of  insulated  wire,  wound 
on  a  core  of  soft  iron  wire.  A  thorough  divis- 
ion of  the  core  is  obtained  by  forming  it  of  coils 
of  insulated  iron  wire.  In  this  way,  no  eddy 
currents  are  produced  in  the  coil.  When  a  simple 
periodic  electromotive  force  is  applied  to  the 
terminals  of  such  a  coil,  if 
the  magnetic  permeability 
of  the  coil  is  constant,  a 
simple  periodic  current  is 
produced,  which  lags  be- 
hind the  phase  of  the  im- 
pressed electromotive  force 
by  a  constant  angle.  If  Fig.  14.1.  Choking- 
the  impressed  electromo- 
tive force  is  sufficiently  great  to  more  than  satu- 
rate the  core,  the  choking  coil  ceases  to  choke 
the  current.  The  higher  the  periodicity  the 
greater  is  the  choking  effect  of  a  given  coil,  or  the 
smaller  the  coil  may  be  made  to  produce  a  given 
effect. 

Since  an  open-magnetic  circuit  requires  a 
greater  current  to  saturate  it  than  a  closed-mag- 
netic circuit,  the  complete  throttling  or  choking 
power  of  such  a  coil  is  increased  by  forming  its 
core  of  a  closed -magnetic  circuit,  z\  e.,  of  a  circuit 
in  which  there  is  no  air  space  or  gap.  (See  Circuit, 
Divided-Magnetic.  Circuit,  Closed- Magnetic.) 

Coil,  Electric A  convolution  of  in- 
sulated wire  through  which  an  electric  current 
may  be  passed.  (See  Magnet,  Electro?) 

The  term  coil  is  usually  applied  to  a  number 
of  turns  or  to  a  spool  of  wire. 

Coil,  Impedance A  term  sometimes 

applied  to  a  choking-coil.  (See  Coil,  Chok- 
ing) 

Such  a  coil  has  a  high  self-induction.  Its  im- 
pedance is  therefore  high.  (See  Induction,  Self. 
Impedance. ) 

Coil,  Induction An  apparatus  con' 

sisting  of  two  parallel  coils  of  insulated  wire 
employed  for  the  production  of  currents  by 
mutual  induction.  (See  Induction,  Mutual. 
Induction,  Electro-Dynamic) 


Coi.] 


107 


[Coi. 


A  rapidly  interrupted  battery  current,  sent 
through  a  coil  of  wire  called  the  primary  coil, 
induces  alternating  currents  in  a  coil  of  wire  called 
the  secondary  coil. 

As  heretofore  made,  the  primary  coil  consists  of 
a  few  turns  of  a  thick  wire,  and  the  secondary 
coil  of  many  turns,  often  thousands,  of  fine  wire. 
Such  coils  are  generally  called  Ruhmkorff  coils, 
from  the  name  of  a  celebrated  manufacturer  of 
them. 

In  the  form  of  Ruhmkorff  coil,  shown  in  Fig. 
142,  the  primary  wire,  wound  on  a  core  formed 


Fig .  142.    Ruhmkorff  Coil. 

of  a  bundle  of  soft  iron  wires,  has  its  ends  brought 
out  as  shown  at  f,  f.  The  fine  wire,  forming  the 
secondary  coil,  is  wrapped  around  an  insulated 
cylinder  of  vulcanite,  or  glass,  surrounding  the 
primary  coil.  This  wire  is  very  thin,  and  in  some 
coils  is  over  one  hundred  miles  in  length. 

If  the  core  of  an  induction  coil  were  made  solid 
it  would  heat  considerably  and  therefore  cause  a 
loss  of  energy.  The  core  is  therefore  laminated, 
usually  by  forming  it  of  a  bundle  of  soft  iron  wire. 

Too  great  a  division  of  the  core,  however,  is 
inadvisable,  since,  although  the  eddy  currents 
therein  are  thereby  avoided,  yet,  too  great  a 
division  of  the  core  acts  practically  so  to 
decrease  the  magnetic  permeability  that  the 
greatest  efficiency  cannot  be  obtained. 

The  ends  of  the  secondary  coil  are  connected 
to  the  insulated  pillars  A  and  B. 

The  primary  current  is  rapidly  broken  by 
means  of  a  mercury  break,  shown  at  L  and  M. 

The  commutator,  shown  to  the  right  and  front 
of  the  base,  is  provided  for  the  purpose  of  cutting 
off  the  current  through  the  primary,  or  for  chang- 
ing its  direction.  When  a  battery  which  produces 
a  comparatively  large  current  of  but  a  few  volts 
electromotive  force  is  connected  with  the  pri- 
mary, and  its  current  rapidly  interrupted,  a 
torrent  of  sparks  will  pass  between  A  and  B, 
having  an  electromotive  force  of  many  thousands 
of  times  the  number  of  volts  of  the  primary  cur- 


rent, but  of  a  correspondingly  smaller  current 
strength. 

In  such  cases,  excepting  losses  during  conver. 
sion,  the  energy  in  the  primary  current,  or  C  E, 
is  equal  to  the  energy  in  the  secondary  current, 
or  C'  E'.  As  much  therefore  as  E',  the  electro- 
motive force  of  the  secondary  current,  exceeds  E, 
the  electromotive  force  of  the  primary  current, 
the  current  strength  C',  of  the  secondary,  will  ba 
less  than  the  current  strength  C,  of  the  primary. 
This  is  approximately  true  only,  and  only  in  in. 
duction  coils  possessing  a  closed  magnetic  circuit. 
(See  Transformer.') 

Fig.  143  shows  diagramatically  the  arrange. 


Fig.  143.     Circuit  Connections  of  Induction  Coil. 
ment  and  connection  of  the  different  parts  of  an 
induction  coil. 

The  core  II',  consists  of  a  bundle  of  soft  iron 
wires,  each  of  which  is  covered  with  a  thin  insu- 
lating layer  of  varnish  or  oxide.  A  primary  wire 
P  P,  consisting  of  a  few  turns  of  comparatively 
thick  wire,  is  wound  around  the  core,  and  a 
greater  length  of  thin  wire  S  S,  is  wound  upon  the 
primary.  This  is  called  the  secondary.  So  as 
not  to  confuse  the  details  of  the  figure  it  is  repre- 
sented as  a  few  turns. 

The  terminals  of  the  battery  B,  are  connected 
to  the  primary  wire,  through  the  automatic  inter- 
rupter, in  the  manner  shown.  It  will  be  seen  that 
the  attraction  of  the  core  I.I',  for  the  vibrating 
armature  H,  will  break  contact  at  the  point  o,  and 
cause  a  continued  interruption  of  the  battery 
current 

The  condenser  c  c',  is  connected  as  t>>.own.  It 
acts  to  diminish  the  sparking  at  the  contact  points 
on  breaking  contact,  and  thus,  by  making  the 
battery  current  more  sudden,  to  make  its  in- 
ductive action  greater. 

The  reactions  which  take  place  when  a  simple 


Coi.] 


108 


[Coi. 


periodic  electromotive  force  is  impressed  on  the 
primary  of  an  induction  coil  are  substantially 
thus  stated  by  J.  A.  Fleming  : 

(i.)  The  application  of  a  simple  periodic  im- 
pressed electromotive  force  produces  a  simple 
periodic  current,  moving  under  an  effective  elec- 
tromotive force  of  self-induction,  and  brings  into 
existence  a  counter-electromotive  force  of  self- 
induction,  which  causes  the  primary  current  to 
lag  behind,  by  an  angle  called  the  angle  of  lag. 

(2.)  The  field  around  the  primary,  and,  there- 
fore, the  induction  through  the  secondary,  is  in 
consonance  with  the  primary  current,  and  the  im- 
pressed electromotive  force  in  the  secondary  is 
in  quadrature  with  the  primary  current.  (See 
Consonance.  Quadrature,  In.} 

(3.)  The  secondary-impressed  electromotive 
force  gives  rise  to  a  secondary  current  moving 
under  an  effective  electromotive  force  and  creat- 
ing a  counter  electromotive  force  of  self-induc- 
tion. 

(4. )  This  secondary  current  reacts  in  its  turn 
on  the  primary,  and  creates  what  is  called  the 
back -electromotive  force,  or  the  reacting-induc- 
tive-electromotive  force  of  the  primary  circuit. 

(5.)  There  is  then  a  phase-difference  between 
the  primary  and  secondary  currents,  and  also  be- 
tween the  primary-impressed  electromotive  force 
and  the  primary  current. 

If,  as  in  Fig.  144,   two  electric  circuits   are 


Fig.  144.    Electric  and  Magnetic  Link. 

linked  with  a  magnetic  circuit,  and  a  small 
periodic  electromotive  force  be  impressed  on  the 
primary,  the  following  phenomena  occur: 

(I.)  A  periodic  primary  current  is  set  up  in 
the  primary  circuit,  which,  though  of  the  same 
periodic  time  as  the  impressed  electromotive 
force,  differs  from  it  in  phase. 

(2.)  A  wave  of  counter  electromotive  force  is 
produced  in  the  primary  circuit  by  the  inductive 
action,  which  does  not  coincide  either  with  the 
impressed  electromotive  force,  nor  with  the 
primary  current. 

(3.)  A  wave  of  magnetization  is  produced  in 
the  iron  core,  which  lags  behind  the  primary 


current  by  somewhat  less  than  90  degrees  of 
phase. 

(4.)  A  wave  of  impressed  electromotive  force 
is  produced  in  the  secondary  circuit,  due  to  and 
measured  by  the  rate  of  change  of  magnetic  in- 
duction in  the  core,  and  lagging  90  degrees,  o* 
more,  behind  the  magnetization  wave. 

(5.)  A  wave  of  secondary  current,  lagging  be- 
hind  the  secondary  electromotive  force  in  phase; 
except  where  the  circuit  consists  of  a  few  turns  o! 
conductor,  or  is  connected  with  an  external  cix  - 
cuit  of  practically  no  inductance. — (Fleming.) 

Coil,    Induction,    Inverted An 

induction  coil  in  which  the  primary  coil  is 
made  of  a  long,  thin  wire,  and  the  secondary 
coil  of  a  short,  thick  wire. 

By  the  use  of  an  inverted  coil,  a  current  of  high 
electromotive  force  and  comparatively  small  cur- 
rent strength,  /.  t.,  but  of  few  amperes,  is  con- 
verted or  transformed  into  a  current  of  compar- 
atively small  electromotive  force  and  large  cur- 
rent strength.  For  advantages  of  this  conversion 
see  Electricity*  Distribution  of,  by  Alternating 
Currents. 

Inverted  induction  coils  are  called  converters  or 
transformers.  (See  Transformer.) 

Coil,    Induction,   Medical An 

induction  coil  used  for  medical  purposes. 

A  form  of  induction  coil  used  for  medical  pur* 
poses  is  shown  in  Fig.  145. 


Fig.  145.    Medical  Induction  Cmt. 

Coil,  Induction,  Microphone Ar« 

induction  coil,  in  which  the  variations  in  the 
circuit  of  the  primary  are  obtained  by  means 
of  microphone  contacts.  (See  Microphone^ 

The  carbon -button  telephone  transmitter  is  a 
microphone  in  its  action,  its  electric  resistance 
varying  with  the  varying  pressure  caused  by  the 
sound  waves.  The  carbon-button  is  in  the  prim- 
ary  circuit  of  an  induction  coil,  variations  in 


Coi.] 


109 


[Coi. 


primary  of  which,  under  the  influence  of  the 
sound  waves,  produce  corresponding  variations 
in  the  currents  induced  in  the  secondary. 

Coil,  Kicking A  term  sometimes 

applied  to  a  Choking-Coil.  (See  Coil,  Chok- 
ing^ 

The  term  kicking-coil  has  arisen  from  the  fact 
that  the  impedance  due  to  self-induction  opposes 
the  starting  or  stopping  of  the  current  somewhat 
in  the  manner  of  an  opposing  kick. 

Coil,  Magnet A  coil  of  insulated 

wire  surrounding  the  core  of  an  electro-mag- 
net, and  through  which  the  magnetizing  cur- 
rent is  passed.  (See  Magnet,  Electro^) 

Coil,  Primary  -  —That  coil  or  con- 
ductor of  an  induction  coil  or  transformer, 
through  which  the  rapidly  interrupted  or  alter- 
nate inducing  currents  are  sent. 

In  the  Ruhmkorff  induction  coil  the  primary 
coil  consists  of  a  comparatively  short  length  of 
thick  wire,  the  secondary  coil  being  formed  of 
a  comparatively  great  length  of  fine  wire.  In 
the  transformer  or  converter,  the  primary  coil 
consists  of  wire  that  is  longer  and  thinner  than 
that  in  the  secondary  coil.  In  other  words,  the 
transformer  or  converter  consists  of  an  inverted 
induction  coil.  (See  Coil,  Induction.  Trans- 
former. ) 

Coil,  Reaction A  magnetizing  coil, 

surrounded  by  a  conducting  covering  or 
sheathing,  which  opposes  the  passage  of 
rapidly  alternating  currents  less  when  directly 
over  the  magnetizing  coil  than  when  a  short 
distance  from  it. 

A  term  often  used  for  choking-coil.  (See 
Coil,  Choking?) 

Coil,  Reaction,  Balanced A  coil 

employed  in  a 
system  of  distri- 
bution by  means 
of  transformers 
for  maintaining 
a  constant  cur- 
rent in  the  sec- 
ondary Circuit,  FiS-  Z4(>-  Balanced-Reaction  Grit. 

despite  changes  in  the  load  placed  therein. 
A  balanced -reaction  coil  is  shown  in  Fig.  146. 


A  reaction  coil  is  placed  in  the  circuit  of  lamps  in 
series  in  a  constant  potential  system.  The  sheath- 
ing of  this  coil  is  maintained  in  a  balanced  position 
by  the  counter  weight  P,  and  the  spring  S.  If  now 
a  lamp  is  extinguished  in  the  circuit,  the  increase 
of  current,  due  to  decreased  resistance,  causes  the 
sheath  to  be  deflected,  and,  thus  increasing  the 
self-induction  of  the  coil,  reduces  the  lamp  current 
to  its  normal  value. 

Coil,  Resistance A  coil  of  wire 

of  known  electrical  resistance  employed  for 
measuring  resistance. 

In  order  to  avoid  self-induction  and  the  mag- 
netizing effects  of  the  coils  on  the  needles  of  the 
galvanometer  used  in  electric  measurements,  as 
well  as  the  disturbing  effects  of  self-induction,  the 
wire  of  the  resistance  coil  is  doubled  on  itsell 
before  being  wound,  and  its  ends  connected 
with  the  brass  bars,  E,  E,  Fig.  147.  The  inser- 


Fig.  f4J.     Connections  of  Resistance  Coils. 

tion  of  the  plug -key  cuts  the  coil  out  of  the  cir- 
cuit by  short-circuiting.  (See  Box,  Resistance. 
Bridge.  Electric.  Coil,  Resistance,  Standard.) 

The  coils  are  made  of  German  silver,  or  plati- 
noid, the  resistance  of  which  is  not  much 
affected  by  heat. 

Coil,  Resistance,  Standard A  coil 

the  resistance  of  which  is  that  of  the  stand- 
ard ohm  or  some  multiple  or  sub-multiple 
thereof. 

The  standard  ohm,  as  issued  by  the  Electric 
Standards  Committee  of  England,  has  the  form 
shown  in  Fig.  148.  The  coil  of  wire  is  formed  of 
an  alloy  of  platinum  and  silver,  insulated  by  silk 
covering  and  melted  pararfine.  Its  ends  are  sol- 
dered to  thick  copper  rods,  r,  r',  for  ready  con- 
nection with  mercury  cups.  The  coil  is  at  B. 
The  space  above  it,  at  A,  is  filled  with  paraffine. 
A  hole,  at  t,  runs  through  the  coil  for  the  readv 


Coi.] 


110 


[Coi. 


insertion  of  a  thermometer.  The  lower  part  of 
the  coil,  B,  is  immersed  in  water  up  to  the  shoul- 
der of  A,  and  the  water  stirred  from  time  to 


Fig,  148.    Standard  Ohm. 

time.  Since  the  coil  is  heated  by  the  current,  sue- 
cessive  observations  should  be  at  least  ten  minutes 
apart.  Only  mild  currents  should  be  passed 
through  the  coils. 

Coil,  Resistance,  Standardized 

Resistance  coils  whose  resistances  have  been 
carefully  determined  by  comparison  with  a 
standard  ohm  or  other  standard  coils. 

Coil,  Ruhmkorff A  term  some- 
times applied  to  any  induction  coil,  the 
secondary  of  which  gives  currents  of  higher 
electromotive  force  than  the  primary.  (See 
Coil,  Induction?) 

Coil,  Secondary That  coil  or  con- 
ductor of  an  induction  coil  or  transformer, 
in  which  alternating  currents  are  induced  by 
the  rapidly  interrupted  or  alternating  currents 
in  the  primary  coil.  (See  Coil,  Induction. 
Transformer?) 

Coil,  Shunt  —  —A  coil  placed  in  a  de- 
rived or  shunt  circuit,  (See  Circuit,  Shunt) 

Coil,  Spark A  coil  of  insulated  wire 

connected  with  the  main  circuit  in  a  system 
of  electric  gas-lighting,  the  extra  spark  pro- 


Fig.  149.    Spark  Coil. 

duced  on  breaking  the  circuit  of  which  is  em- 
ployed for  electrically  igniting  gas  jets. 
Spark  coils  are  employed  where  the  number  of 


gas  jets  to  be  simultaneously  lighted  is  not  too 
great.  When  this  number  exceeds  certain  limits, 
the  spark  from  an  induction  coil  is  more  advan- 
tageously used. 

A  spark  coil  is  shown  in  Fig.  149. 

Coils,  Armature,  of  Dynamo-Electric 

Machine The  coils,  strips  or  bars  that 

are  wound  or  placed  on  the  armature  core. 

To  avoid  needless  resistance  the  wire,  or  other 
conductor,  of  the  armature  coils,  should  be  as 
short  and  thick  as  will  enable  the  desired  electro- 
motive force  to  be  obtained  without  excessive 
speed  of  rotation. 

The  armature  coils  should  enclose  as  many 
lines  of  force  as  possible  (/.  e.,  they  should  have 
as  nearly  a  circular  outline  as  possible).  In 
drum-armatures,  the  breadth  of  the  armature  is 
frequently  made  nearly  equal  to  its  length,  unless 
other  considerations  prevent. 

When  the  armature  wire  consists  of  rods  or 
bars,  it  should  be  laminated  or  slit  in  planes 
parallel  to  the  lines  of  force  so  as  to  avoid 
eddy  currents.  Other  things  being  equal,  the 


Fig.  1^0.    Series  Connection  of  Armature  Coils. 

greater  the  number  of  coils,  the  more  uniform 
the  current  generated.  The  separate  coils  should 
be  symmetrically  disposed;  otherwise  irregular  in- 
duction, and  consequent  sparking  at  the  commu- 
tator results. 

The  coils  of  pole-armatures  should  be  wound  near 
the  poles  rather  than  on  the  middle  of  the  cores. 
In  order  to  avoid  undue  heating,  spaces  for 
air  ventilation  are  not  inadvisable.  Various  con- 
nections of  the  armature  coils  are  used. 

In  some  machines  all  the  coils  are  connected  in 
a  closed  circuit.  In  some,  the  coils  are  independ- 
ent of  one  another,  and,  either  for  the  entire 
revolution,  or  for  part  of  a  revolution,  are  on  an 
open-circuit. 


Coi.] 


Ill 


[Col. 


In  alternating  current  dynamos  in  order  to  ob- 
tain the  rapid  reversals  or  alternations  of  current, 
which  in  some  machines  are  as  high  as  12,000 
per  minute,  a  number  of  poles  of  alternate  polar- 
ity are  employed.  The  separate  coils  that  are 
used  on  the  armature  may  be  coupled  either  in 
series  or  in  multiple-arc. 

Where  a  comparatively  low  electromotive  force 
is  sufficient,  such  as  for  incandescent  lamps  in 
multiple-arc,  the  separate  coils  are  united  in 
parallel;  but  for  purposes  where  a  considerable 
electromotive  force  is  necessary,  as  for  example, 
in  systems  of  alternate  current  distribution,  with 
converters  at  considerable  distances  from  the 
generating  dynamo,  they  are  often  connected  in 
series,  as  shown  in  Fig.  150. 

Coils,  Binding Coils  of  wire  wound 

on  the  outside  of  the  armature  coils,  and  at 
right  angles  thereto,  to  prevent  the  loosening 
of  the  armature  wires  by  the  action  of  cen- 
trifugal force. 

The  binding  coils  are  generally  made  of  hard 
brass  wire. 

Coils,  Compensating' A  term  some- 
times applied  to  the  series  coils  placed  on  a 
shunt-wound  dynamo. 

Coils,  Conjugate  —Two   coils   so 

placed,  as  regards  each  other,  that  an  interrup- 
tion of  the  current  in  one  produces  no  induced 
current  in  the  other. 

When  two  coils  are  conjugate  to  each  other,  the 
lines  of  force  of  one  do  not  pass  through  the  other. 
Consequently  such  coils  can  produce  no  induc- 
tion in  one  another. 

Coils,  Henry's A  number  of  sepa- 
rate induction  coils  so  connected  that  the 
currents  induced  in  the  secondary  wire  of 
the  first  coil,  are  caused  to  induce  currents 
in  the  secondary  wire  of  the  second  coil,  with  . 
whose  primary  it  is  connected  in  series,  and 
so  on  throughout  all  the  coils. 

A  series  of  three  of  Henry's  coils  is  shown  in 
Fig.  151.  An  intermittent  battery  current  is  sent 


secondary,  d,  of  the  second  coil,  is  connected  with 
the  primary,  e,  of  the  third  coil,  and  the  cur- 
rents finally  induced  in  f,  are  employed  for  any 
useful  purpose,  such  as  the  magnetization  of  a 
bar  of  iron  at  g. 

The  current  in  b,  is  sometimes  called  a  Secon- 
dary Current,  or  a  Current  of  the  Second  Order; 
that  induced  by  this  secondary  current  in  d,  is 
called  a  Tertiary  Current^  or  a  Current  of  the 
Third  Order  ;  that  in  f,  a  Current  of  the  Fourth 
Order.  Henry  carried  these  successive  induc- 
tions up  to  currents  of  the  Seventh  Order. 

Henry's  coils  in  reality  consist  of  separate  in- 
duction coils,  connected,  as  above  explained,  in 
series. 

In  Fig.   152,  the  tertiary  current  induced   in 


Fig,  I J '2.     Tertiary  Currents  of  Coils. 
IV,  may  be  employed  to  give  shocks  to  a  person 
grasping  the  handles,  e  and  f. 

Coils,  Proportional Pairs  of  re- 
sistance coils,  generally  of  10,  100  and  1,000 
ohms  each,  forming  the  proportional  arms  of 
the  balance  or  bridge,  and  employed  in  the  box, 
or  commercial  form  of  Wheatstone's  bridge. 
(See  Bridge,  Electric,  Commercial  Form 
of.} 

Cold,  Production  of,  by  Electricity 

— An  absorption  of  energy  and  consequent 
reduction  of  temperature  at  a  thermo-electric 
junction  by  the  passage  of  an  electric  current 
across  such  junction  in  a  certain  direction. 

When  an  electric  current  passes  across  a  thermo- 
electric junction,  the  junction  is  either  heated  or 
cooled.  In  the  case  of  an  antimony-bismuth 
couple,  if  the  current  passes  from  the  antimony 


Fig.  Jjr.    Henry's  Coils. 

into  a,  the  secondary,  b,  of  which  is  connected 
with  the  primary,  c,  of  the  second  coil.    The 


A  B 

Fig.  fjf.    Freezing  of  Water  by  Electricity. 

to  the  bismuth  the  junction  is  heated ;  if  it  passes 
from  the  bismuth  to  the  antimony  it  is  cooled. 
In  the  apparatus  shown  in  Fig.  153,  the  antimony- 
bismuth  couple  is  arranged  as  shown  for  the 


Col.] 


112 


[Com. 


freezing  of  water  by  means  of  the  electric  cur- 
rent. A  and  B,  represent  plates  of  antimony  and 
bismuth  respectively.  A  small  cavity,  at  E,  serves 
to  hold  a  drop  of  water.  When  a  current  has 
passed  in  the  direction  shown  by  the  arrows,  a 
drop  of  water,  previously  cooled  to  the  tempera- 
ture  of  melting  ice,  is  solidified  by  the  lowering 
of  the  temperature  at  the  junction. 

Collecting  Brushes  of  Dynamo-Electric 
Machine.  —  (See  Brushes,  Collecting,  of 
Dynamo-Electric  Machine?) 

Collectors,  Electric Devices  em- 
ployed for  collecting  or  taking  off  electricity 
from  a  moving  electric  source. 

Collectors  of  Electric  Frictional  Ma- 
chines.—The  metallic  points  that  collect  the 
charge  from  the  glass  plate  or  cylinder  of  a 
frictional  electric  machine. 

Collectors  of  Dynamo  Electric  Machines. 
— The  brushes  that  rest  on  the  commutator 
cylinder,  and  carry  off  the  current  generated 
on  the  rotation  of  the  armature. 

Collectors  are  properly  called  commutators 
when  they  are  employed  to  cause  an  alternate 
current  to  become  continuous,  or  to  flow  in  one 
and  the  same  direction. 

Colloids. — One  of  the  two  classes  into 
which  substances  are  separated  by  dialysis. 

By  dialysis  bodies  are  separated  into  crystal- 
loids,  or  bodies  capable  of  crystallizing,  and  col- 
loids or  jelly-like  bodies,  incapable  of  crystallizing. 
Colloids  possess  great  cohesion  and  but  slight 
diffusibility.  (See  Dialysis.) 

Colombin. — An  insulating  substance,  con- 
sisting of  a  mixture  of  sulphate  of  barium 
and  sulphate  of  calcium,  placed  between  the 
parallel  carbons  of  the  Jablochkoff  candle. 

Column,  Barometric A  column, 

usually  of  mercury,  approximately  30  inches 
in  vertical  height,  sustained  in  a  barometer, 
or  other  tube,  by  the  pressure  of  the  atmos- 
phere. 

The  space  above  the  barometric  column  con- 
tains a  vacuum  known  as  the  Torricellian  vac- 
uum. (See  Vacuum,  Torricellian.) 

Column,  Electric A  term  formerly 

applied  to  a  voltaic  pile.  (See  Pile,  Voltaic.} 

Colza  Oil.— (See  Oil,  Colza.) 


Combination  Gas  Fixtures— (See  Fix- 
tures, Gas,  Combination?) 

Combined  Tangent  and  Sine  Galvanom- 
eter.— (See  Galvanometer,  Combined  Tan« 
gent  and  Sine.) 

Comb  Lightning  Arrester. — (See  Arrester, 
Lightning,  Comb.) 

Comb  Protector.— (See  Protector,  Comb.) 

Commercial  Efficiency. — (See  Efficiency, 
Commercial?) 

Commercial  Efficiency  of  Dynamo. — 
(See  Efficiency,  Commercial,  of  Dynamo?) 

Commercial  Form  of  Electric  Bridge.— 
(See  Bridge,  Electric,  Commercial  Form  of.) 

Communicator,  Electric A  term 

formerly  employed  for  a  telegraphic  key.  (See 
Key,  Telegraphic?) 

Commutating  Transformers,  Distribu- 
tion of  Electricity  by (See  Elec- 
tricity, Distribution  of,  by  Commutating 
Transformers?) 

Commutation.— The  act  of  commuting,  as 
of  currents. 

Commutation,  Diameter  of —In  a 

dynamo-electric  machine  a  diameter  on  the 
commutator  cylinder  on  one  side  of  which 
the  differences  of  potential,  produced  by  the 
movement  of  the  coils  through  the  magnetic 
field,  tend  to  produce  a  current  in  a  direction 
opposite  to  those  on  the  other  side. 

That  diameter  on  the  commutator  cylinder 
of  an  open-circuited  armature  that  joins  the 
points  of  contact  of  the  collecting  brushes. 

Thus  in  Fig.  154,  the  directions  of  the  induced 
electromotive  forces  are  indicated  by  the  arrows. 
The  diameter  of  commutation  is  therefore  the  line 
n  n'.  The  term  neutral  line  is  also  sometimes 
given  to  this  line.  It  lies  at  right  angles  to  the 
line  of  maximum  magnetization  m  m. 

In  a  closed-circuited  armature,  that  is,  in  an  arm. 
ature  the  coils  of  which  are  connected  in  a  closed 
circuit,  the  collecting  brushes  rest  on  the  commu- 
tator cylinder  at  the  neutral  line,  or  on  the  diame* 
ter  of  commutation. 

In  an  open-circuited  armature,  however,  where 
the  coils  are  independent  of  each  other,  the 
collecting  brushes  must  be  set  at  m  m,  at  right 
angles  to  the  neutral  line  n  n.  The  term  diame- 


Com.] 


113 


[Com. 


ter  of  commutation  is,  therefore,  often  applied  to 
this  second  position.    According  to  this  use  of  the 


Fig.  134.    Diameter  of  Commutation. 
term,  the  diameter  of  commutation  is  that  diameter 
on  the  commutator  which  joins  the  points  of  con- 
tact  of  the  collecting  brushes. 

The  neutral  linenn',  Fig.  154,  it  will  be  noticed 
does  not  occupy  a  vertical  position,  but  is  dis- 
placed somewhat  in  the  direction  of  rotation,  thus 
necessitating  the  shifting  of  the  brushes  forward 
in  the  direction  of  rotation.  This  necessary  shift- 
ing of  the  brushes  is  known  technically  as  the 
lead  of  the  brushes.  (See  Lead,  Angle  of.) 

It  will  thus  be  seen  that  the  term  diameter  of 
commutation  is  used  in  two  different  senses. 

In  reality,  the  term  refers  to  the  position  of  cer- 
tain points  on  the  commutator  as  distinguished 
from  points  on  the  armature  coils.  On  the  com- 
mutator, the  diameter  of  commutation  is  the  line 
drawn  through  the  two  commutator  bars  at  which 
the  currents  from  the  two  sides  are  opposed  to 
each  other. 

It  is  evident  that  the  commutator  may  be  inten- 
tionally twisted  with  respect  to  the  armature,  so 
as  to  bring  its  diameter  of  commutation  into  any 
desired  convenient  position. 

Commutation,  Dissymmetry  of 

A  commutation  in  which  the  neutral  line  does 
not  coincide  with  a  diameter  of  the  commu- 
tator. (See  Commutation,  Diameter  of.) 

Commutator. — In  general,  a  device  for 
changing  the  direction  of  an  electric  current. 

Commutator,  Burning*  at Arcing 

and  consequent  destructive  action  on  the 
commutator  segments  of  a  dynamo-electric 
machine. 

When  the  arcing  is  pronounced,  the  intense 
heat  soon  destroys  the  commutator. 
Commutator  Cylinder,  Neutral-Line  of 

(See  Line,  Neutral,  of  Commutator 

Cylinder^ 


Commutator,  Dynamo-Electric  Machine 
— That  part  of  a  dynamo-electric  ma- 
chine which  is  designed  to  cause  the  alter- 
nating currents  produced  in  the  armature  to 
flow  hi  one  and  the  same  direction  in  the  ex- 
ternal circuit. 

One  end  of  an  armature  coil  is  connected  with 
A',  Fig.  155,  and  the 
other  with  A.  The  brushes 
are  so  set  that  A,  and  A', 
are  in  contact  with  B', 
and  B,  respectively,  as  .1 
long  as  the  current  flows 
in  the  same  direction  in  the 
armature  coil  connected 
therewith,  but  enter  into 
contact  with  B,  and  B',  Fig.  155.  Commutator 
when  the  current  changes  of  Dynamo  -  Electric 
its  direction,  and  continue  Machine. 
in  such  contact  as  long  as  it  flows  in  this  direc- 
tion. J3y  the  use  of  a  commutator  the  furrent 
•will  therefore  flow  throttgh  any  circuit  connected 
•with  the  brushes  in  one  and  tJie  same  constant 
direction. 


Two-fart  Commutator 

In  action,  the  commutator  is  subject  to  wear 
from  the  friction  of  the  brushes,  and  the  burning 
action  of  destructive  sparks.  The  commutator 


Fig.  1ST-     Two-part 
Commutator. 


Fig.  158.     Two-part 
Commutator. 


segments  are,  therefore,  made  of  comparatively 
thick  pieces  of  metal,  insulated  from  one  another 


Com.] 


114 


[Com. 


and  supported  on  a  commutator  cylinder  usually 
placed  on  the  shaft  of  the  armature. 

The  ends  of  the  armature  coils  are  connected 
to  commutator  strips  or  segments. 

The  number  of  metallic  pieces  or  segments,  A. 
and  A',  on  the  commutator  cylinder  depends  on 
the  number,  arrangement  and  connection  of  the 
armature  coils,   and  on  the 
disposition  of  the  magnetic 
field  of  the  machine. 

Figs.  156,  157  and  158 
show  the  connections  of  an 
armature  coil  to  the  plates  of 
a  two-part  commutator. 

A  four-part  commutator 
for  a  ring-armature,  and  the 
connections  of  the  coils 
thereto,  are  shown  in  Fig.  159. 

The  commutator  strips  may  either  connect  the 
separate  coils  in  a  closed-circuited  armature,  in 
which  the  coils  are  all  connected  with  one  an- 
other,  or,  in  an  open-circuited  armature,  in  which 
the  separate  coils  are  independent  of  one  another. 

Commutator,  RuhmkorfTs A  name 

given  by  Ruhmkorff  to  a  device  placed  on  his 
induction  coil  for  the  purpose  of  changing  or 
reversing  the  direction  of  the  battery  current 
through  the  primary. 

This  reverser  is  shown  in  Fig.  160.  (See 
Coil,  Ruhmkor/.} 


Fig.  1 60.    Ruhmkorjf's  Commutator 

Two  metallic  strips,  V,  V,  supported  on  a 
cylinder  of  insulating  material,  are  in  contact  with 
the  battery  terminals  A,  and  D,  through  Iwo 
vertical  springs  that  bear  on  them.  On  a  half 
rotation  of  the  cylinder  by  the  thumb  screw  L, 


the  strips  V,  V,  change  places  as  regards  the  ver- 
tical springs,  and  thus  reverse  the  direction  oi 
the  battery  current. 

Commuted  Currents.  —  (See  Currents, 
Commuted) 

Commuter,  Current Any  appa- 
ratus by  means  of  which  electrical  currents, 
flowing  alternately  in  different  directions, 
may  be  caused  to  flow  in  one  and  the  same 
direction. 

A  Commutator. 

Commuting.— Causing  to  flow  in  one  and 
the  same  direction. 

Commuting  Currents.  —  (See  Currents, 
Commuting) 

Compartment  Manhole  of  Conduit.— (See 
Manhole,  Compartment,  of  Conduit) 

Compass,  Azimuth A  compass 

used  by  mariners  for  measuring  the  horizon- 
tal distance  of  the  sun  or  stars  from  the  mag- 
netic meridian.  (See  Azimuth,  Magnetic) 

A  mariner's  Compass. 

A  single  magnetic  needle,  or  several  magnetic 
needles,  are  placed  parallel  to  one  another  on  the 
lower  surface  of  a  card,  called  the  compass  card. 
This  card  is  divided  into  the  four  cardinal  points, 
N,  S,  E  and  W,  and  these  again  subdivided  into 
thirty-two  points  called  Rhumbs. 

In  the  azimuth  compass  these  divisions  are  sup- 
plemented by  a  further  division  into  degrees. 

A  form  of  azimuth  compass  is  shown  in  Fig. 
l6l.  In  order  to  maintain  the  compass  box  in  a 


Fig.  1 6 1.    Azimuth  Compass. 

horizontal  position,  despite  the  rolling  of  the  ship, 
the  box,  A  B,  is  suspended  in  the  larger  box,  P 
Q,  on  two  concentric  metallic  circles,  C  D,  and 


Com. 


115 


[Com, 


E  F.  pivoted  on  two  horizontal  axes  at  right  angles 
to  each  other.  This  kind  of  support  is  technic- 
ally  termed  Gimbals.  Sights  G,  H,  are  provided 
for  measuring  the  magnetic  azimuth  of  any  ob- 
ject. 

Compass,  Boxing  the Naming, 

Consecutively,  all  the  different  points  or 
rhumbs  of  the  compass  from  any  one  of  them. 
(See  Compass,  Points  of.) 

Compass-Card.— (See  Card,  Compass) 

Compass,  Inclination A  magnetic 

needle  moving  freely  in  a  single  vertical  plane, 
and  employed  for  determining  the  angle  of 
dip  at  any  place. 

An  Inclinometer.    (See  Inclinometer^ 
A  dipping  circle.     (See  Circle,  Dipping) 
The  needle  M,  Fig.  162,  is  supported  on  knife 


Fig.  162.    Inclination  Cbmpast. 

tdges  so  as  to  be  free  to  move  only  in  the  vertical 
plane  of  the  graduated  vertical  circle  C  C.  This 
circle  is  movable  over  the  horizontal  graduated 
circle  H  H.  In  order  to  determine  the  true  angle 
of  dip,  the  vertical  plane  in  which  the  needle  is 
free  to  move  must  be  placed  exactly  in  the  plane 
of  the  magnetic  meridian. 

To  ascertain  this  plane  the  vertical  circle  is 
moved  until  the  needle  points  vertically  down- 
wards. It  is  then  in  a  plane  90  degrees  from  the 
magnetic  meridian.  The  vertical  circle  is  then 
moved  over  the  horizontal  circle  90  degrees,  in 
which  position  it  is  in  the  plane  of  the  magnetic 
meridian,  when  the  true  angle  of  the  dip  is  read  off. 

For  an  explanation  of  the  reason  of  thib  see 


Component^  Horizontal  and  Vertical,  of  tht 
Earth's  Magnetism. 

Compass,  Mariner's A  name  often 

applied  to  an  azimuth  compass.  (See  Com- 
fass,  Azimuth?) 

Compass,  Points  of The  thirty-two 

points  into  which  a  compass  card  is  divided. 

Sixteen  of  these  points  are  shown  in  Fig.  163. 


Fig.  163.    Points  of  Compass. 

The  position  of  the  remaining  points  will  be 
readfly  seen  by  an  inspection  of  the  figures. 
These  points  are  as  follows: 

1.  North.  17.  South. 

2.  N.  by  E.  18.  S.  by  W. 

3.  N.  N.  E.  19.  S.  S.  W. 

4.  N.  E.  by  N.  20.  S.  W.  by  S. 

5.  N.  E.  21.  S.  W. 

6.  N.  E.  by  E.  22.  S.  W.  by  W. 

7.  E.  N.  E.  23.  W.  S.  W. 
&  E.  by  N.  24.  W.  by  S. 
9.  East.  25.   West. 

10.  E.  by  S.  26.  W.  by  N. 

11.  E.  S.  E.  27.  W.  N.  W. 

12.  S.  E.  by  E.  28.  N.  W.  by  W. 

13.  S.  E.  29.  N.  W. 

14.  S.  E.  by  S  30.  N.  W.  by  N. 

15.  S.  S.  E.  31.  N.  N.  W. 

16.  S.  byE.  32.  N.byW. 

Boxing  the  Compass  consists  in  naming  aD 
these  points  consecutively  from  any  one  of  them. 

The  direction  in  which  the  ship  is  sailing  is  de. 
termined  by  means  of  a  point  fixed  on  the  inside  ol 
the  compass  box,  directly  in  the  line  of  the  ves- 
sel's bow. 

Compass,  Rhumbs  of  —  —The  points 
of  a  mariner*3  compass.  (See  Compass 
Points  <?/.) 


Com.] 


116 


[Com. 


Compensated   Alternator.— (See    Alter- 
nator, Compensated) 
Compensated  Excitation  of  Alternator. 

— (See  Alternator,  Compensated  Excita- 
tion of.) 

Compensating  Coils.— (See  Coils,  Com- 
pensating) 

Compensating  Magnet  — (See  Magnet. 
Compensating) 

Complement  of  Angle.— (See  Angle,  Com- 
plement of.) 

Completed-Circuit— (See  Circuit,  Com- 
pleted.) 

Component.— One  of  the  two  or  more  sep- 
arate forces  into  which  any  single  force  may 
be  resolved ;  or.  conversely,  the  separate  forces 
which  together  produce  any  single  resulting 
force. 

When  two  or  more  forces'act  simultaneously  to 
produce  motion  in  a  body,  the  -body  will  move 


,'D 


n 

Fig.  164.     Composition  of  Forcet. 

with  a  given  force  in  a  single  direction  called  the 
resultant.  The  separate  forces,  or  directions  of 
motion,  are  called  the  components* 

Two  forces  acting  simultaneously  on  a  body  at 
A,  Fig.  164,  tending  to  move  it  in  the  direction 

B  E 


Fig.tbf.    Rttfluiion  o/Fortts. 

of  the  arrows,  along  A  B,  and  A  C,  with  Intensl- 
tiesproportioned  to  the  lengths  of  the  lines  A  B, 
and  A  C,  respectively,  wfll  move  It  in  the  dlrec- 
tion  A  D,  obtained  by  drawing  B  D,  and  D  C, 


parallel  to  A  C,  and  A  B,  respectively,  and  then 
drawing  A  D,  through  the  point  of  intersection, 
D.  This  is  called  the  Composition  of  Forces. 
A  D,  is  the  resultant  force,  and  A  B  and  A  C, 
are  its  components. 

Conversely,  a  single  force,  acting  in  the  direc. 
tion  of  D  B,  Fig.  165,  against  a  surface,  B  C, 
may  be  regarded  as  the  resultant  of  the  two  sep- 
arate forces,  D  E,  and  D  C,  one  parallel  to  C  B, 
and  one  perpendicular  to  it.  D  E,  being  parallel 
to  C  B,  produces  no  pressure,  and  the  absolute 
effect  of  the  force  will,  therefore,  be  represented 
by  CD. 

This  separation  of  a  single  force  into  two  or 
more  separate  forces  is  called  the  resolution  of 
forces,  the  force,  D  B,  being  resolved  into  the 
components,  D  E  and  D  C. 

Component  Currents. — (See  Currents, 
Component) 

Component,  Horizontal,  of  Earth's  Mag- 
netism   That  portion  of  the  earth's 

directive  force  which  acts  in  a  horizontal  di- 
rection. 

That  portion  of  the  earth's  magnetic  force 
which  acts  to  produce,  motion  in  a  com- 
pass needle  free  to  move  in  a  horizontal  plane 
only. 

Let  A  B,  Fig.  166,  represent  the  direction  and 
magnitude  of  the  earth's  magnetic  field  on  a  mag- 
netic needle.  .  The  magnetic  force  will  lie  in  the 
plane  of  the   magnetic   merid- 
ian, which  will  be  assumed  to 
be  the  plane  of  the  paper  C  A 
D.    The  earth's  field,  A  B,  can 
be   resolved  into   two  compo- 
nents, A  D,  the  horizontal  com- 
ponent, and  A  C,  the  vertical 
component 

In  the  case  of  a  magnetic 
needle,  like  the  ordinary  com- 
pass needle,  which  is  free  to 
move  in  ahorizontal  plane  only, 
the  horizontal  component  alone 
directs  the  needle.  A  weight 
is  applied  to  balance  the  vertical  Magnetism . 
component. 

When  the  needle  Is  free  to  move  in  a  vertical 
plane,  and  this  plane  corresponds  with  that  of 
the  magnetic  meridian,  the  entire  magnetic  force, 
A  B,  acts  to  place  the  needle,  supposed  to  be 
properly  balanced,  in  the  direction  of  the  lines  of 
force  of  the  earth's  magnetic  field  at  that  point. 


Com.] 


117 


[Con. 


Component,  Tertical,  of  Earth's  Magnet- 

ism --  That  portion  of  the  earth's 
directive  force  which  acts  in  a  vertical  direc- 
tion. 

In  the  vertical  plane  at  right  angles  to  the  plane 
of  the  magnetic  meridian,  the  vertical  component 
alone  acts,  and  the  needle  points  vertically  down- 
wards,  in  no  matter  what  part  of  the  earth  it 
may  be.  In  Fig.  166,  A  C,  is  the  vertical  com- 
ponent of  the  earth's  directive  force. 

Composite  Balance.—  (See  Balance.  Com- 


Composite-Field  Dynamo.  —  (See  Dynamo. 
Composite-Field) 

Composition    of  Forces.—  (See    Forces, 

Composition  0f.) 

Compound  Arc.  —  (See  Arc,  Compoztnd^ 
Compound,  Binary  --  In  chemistry, 

a  compound  formed  by  the  union  of  two 

different  elements. 

Water  is  a  binary  compound,  being  formed  by 
the  union  of  two  atoms  of  hydrogen  with  one 
atom  of  oxygen.  Its  composition  is  expressed  in 
themical  symbols,  H2O,  which  indicates  that  two 
atoms  of  hydrogen  are  combined,  or  chemically 
united,  with  one  atom  of  oxygen.  Water  is 
therefore  a  binary  compound,  because  it  is  formed 
of  two  different  elementary  substances. 

Compound,  Chatterton's  --  A  com- 
pound for  cementing  together  the  alternate 
coatings  of  gutta-percha  employed  on  a  cable 
conductor,  or  for  filling  up  the  space  between 
the  strand  conductors. 

The  composition  of  Chatterton's  compound  is 
as  follows: 

Stockholm  tar  ........  I  part  by  weight. 

Resin  ...............  I     "  " 

Gutta-percha  .........  3     "'  " 

—(Clark  &•  Sabine.) 

Compound  Circuit.—  (See  Circuit,  Com- 
pound^ 

Compound,  Clark's  --  A  compound 
for  the  outer  casing  of  the  sheathing  of  sub- 
marine cables. 

The  composition  of  Clark's  compound  is  as  fol- 
lows: 


Mineral  pitch 65  parts  by  weight. 

Silica 4.30    «  •' 

Tar 5     «  «• 

— (Clark  S>  Sabine.) 

Compound  -  Horseshoe  Magnet.—  (See 
Magnet,  Compound-Horseshoe) 

Compound  Magnet. — (See  Magnet,  Com- 
pound?) 

Compound  Radical.— (See  Radical,  Com- 
pound?} 

Compound- Winding  of  Dynamo-Electric 
Machines.— (See  Winding,  Compound,  ef 
Dynamo- Electric  Machine?) 

Compound-Wound  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Compound-  Wound?) 

Compound-Wound  Motor.— (See  Motor, 
Compound-  Wound.) 

Concentration  of  Lines  of  Force.— (See 

Force,  Lines  of,  Concentration  of.) 
Concentric     Carbon     Electrodes.— (See 

Electrodes,  Concentric  Carbon.) 
Concentric  Cylindrical    Carbons.— (See 

Carbons,  Concentric  Cylindrical) 

Condenser. — A  device  for  increasing  the 
Capacity  of  an  insulated  conductor  by  bring- 
ing it  near  another  insulated  earth-connected 
conductor,  but  separated  therefrom  by  any 
medium  that  will  readily  permit  induction  to 
take  place  through  its  mass. 

A  variety  of  electrostatic  accumulator. 

If  the  conductor  A,   Fig.  167,  standing  alone 


Fig:  r67.    &pirtus  Air  Condenser. 
and  separated  from  other  conductors,   be  con- 
nected  with  an  electric  machine,  it  will  receive 
only  a  very  small  charge. 


Con.] 


118 


[Con. 


If,  however,  it  be  placed  near  C,  but  separated 
from  it  by  a  dielectric,  such  as  a  plate  of  glass 
B,  and  C,  be  connected  with  the  ground,  A,  will 
receive  a  much  greater  charge.  (See  Dielectric.') 

Suppose,  for  example,  that  A,  be  connected 
with  the  positive  conductor  of  a  frictional  electric 
machine,  it  will  by  induction  establish  a  negative 
charge  on  the  surface  C,  nearest  it,  and  repel 
a  positive  charge  to  the  earth.  The  presence  of 
these  two  opposite  charges  on  the  opposed  sur- 
faces of  A  and  C,  permits  A,  to  receive  a  fresh 
charge  from  the  machine.  (See  Induction, 
Electrostatic. ) 

The  charge  in  a  condenser  in  reality  resides 
on  the  opposite  surfaces  of  the  glass,  or  other 
dielectric  separating  the  metallic  coatings,  as  can 
be  shown  by  removing  the  coatings  after  charg- 
ing. 

The  condenser  resulted  from  the  discovery  of 
the  Leyden  jar.  (See  Jar^  Ley/den.} 

The  capacity  of  a  condenser  is  measured  in 
microfarads.  (See  Farad.} 

In  practice  condensers  are  made  of  sheets  of 
tin  foil,  connected  to  A  and  B,  respectively,  and 
separated  from  one  another  by  sheets  of  oiled 
silk,  paraffined  paper,  or  thin  plates  of  mica,  as 
shown  in  Fig.  168. 


Fig.  rb8.    Condenser. 

A  Leyden  jar  or  condenser  does  not  store  elec- 
tricity any  more  than  a  storage  battery  does. 
The  same  quantity  of  electricity  passes  out  of  the 
opposite  coating  of  the  jar  that  is  passed  into  the 
other  coating.  The  jar,  therefore,  possesses  no 
store  of  electricity.  What  it  really  possesses  is  a 
store  of  electrical  energy. 

According  to  Ayrton,  if  the  capacity  of  a  con- 
denser,'  in  farads,  be  F,  and  the  difference  of  po- 
tential, with  which  it  is  charged,  be  V,  volts,  the 
store  of  electric  energy  it  possesses,  or  the  work  it 
can  do  when  discharged,  is, 


In  order  to  obtain  a  comparatively  wide  range 
of  adjustability,  a  condenser  is  composed  of  say 
four  separate  sections:  consisting  of  one  of  2 
microfarads,  one  of  I  microfarad  and  two  of  } 
microfarad,  thus  making  in  all  4  microfarads. 

Condenser,  JEpinus A  name  given 

to  an  early  form  of  condenser.  (See  Con- 
denser?) 

Condenser,  Air  — A  condenser  in 

which  layers  of  air  act  as  the  dielectric. 

A  form  of  air  condenser  is  shown  in  Fig.  169. 


Work 


2.712 


foot-pounds. 


Condenser,  Adjustable A  con- 
denser, the  plates  of  which  can  be  readily 
adjusted  so  as  to  obtain  the  same  capacity 
as  that  of  the  conductor  to  be  measured. 


Fig.  769.    Air  Condenser. 

It  consists  essentially  of  one  set  of  thin  plates  of 
glass  partially  coated  on  both  sides  with  sheets  of 
tin  foil,  so  as  to  leave  uncoated  a  space  of  about 
one  inch  around  the  edge  of  the  glass.  The  glass 
plates  do  not  act  as  dielectrics,  but  merely  as  sup. 
ports  for  the  tin  foil,  hence  the  foil  on  both  sides 
of  the  plates  is  connected  electrically. 

Another  set  of  plates  alternating  with  the  above 
have  the  tin  foil  placed  over  the  whole  surface  of 
the  glass. 

These  plates  are  placed,  alternately,  over  one 
another  on  a  stand  between  guide  rods  of  vuIcan- 
ite  E,  E,  E,  E,  in  the  manner  shown,  and  are 
separated  from  one  another  by  fragments  of  glass 
of  the  same  thickness.  The  plates  with  the  foil 
over  their  entire  surface  are  all  connected  to-' 
gether  and  to  the  terminal  B,  to  form  the  outer 
coating,  and  the  plates  with  the  foil  over  nearly 
all  their  surfaces  are  all  connected  together  and 
to  the  terminal  A,  to  form  the  inner  coating  oi 
the  condenser. 

There  is  thus  formed  a  condenser  in  which 
practically  two  extended  conducting  surfaces  an 


Con.] 


119 


[Con. 


separated  from  each  other  by  a  thin  layer  of  air, 
which  acts  as  the  dielectric. 

Condenser,  Alternating-Current  -- 
A  condenser  suitable  for  use  in  connection  with 
a  system  for  the  distribution  of  electric  energy 
by  means  of  alternating  currents. 

Alternating-current  condensers  must  have  a  very 
thin  dielectric  in  order  to  avoid  too  great  bulk. 
This,  of  course,  introduces  a  difficulty  as  regards 
liability  of  failure  of  insulation,  which  must  be 
carefully  avoided. 

Condenser,  Armature  of  --  (See  Arm- 
ature of  a  Condenser?) 

Condenser,  Capacity  of  ----  The  quan- 
tity of  electricity  in  coulombs  a  condenser  is 
capable  of  holding  before  its  potential  in  volts 
is  raised  a  given  amount. 

The  ratio  between  the  quantity  of  electric- 
ity in  coulombs  on  one  coating  and  the  poten- 
tial difference  in  volts  between  the  two  coat- 
ings. —  (Ayrton.) 

The  capacity  is  directly  proportional  to  the 
charge  Q,  and  inversely  proportional  to  the  po- 
tential  V,  or, 


or,  since  Q  =  K  V,  the  quantity  of  electricity  re- 
quired  to  charge  a  condenser  to  a  given  potential 
is  equal  to  the  capacity  of  the  condenser  multi- 
plied by  the  potential  through  which  it  is  carried. 

The  capacity  of  a  condenser  increases  in  direct 
proportion  to  the  increase  in  the  area  of  its  coat- 
ings. 

When  the  Coatings  are  plane  and  parallel  to 
each  other,  the  capacity  of  the  condenser  is  in  the 
inverse  ratio  to  the  distance  between  the  coatings. 

Condenser,  Coating  of  --  (See  Coat- 
ing of  Condenser.} 

Condenser,  Plate  -  -A  condenser,  the 
metallic  coatings  of  which  are  placed  on 
suitably  supported  plates. 

Condenser,  Poles  of  -  -  —  (See  Poles  of 
Condenser.} 

Condenser,  Time-Constant  of  -- 
The  time  in  which  the  charge  of  a  condenser 
falls  to  the  1-2.71828  part  of  its  original 
value. 

Condensers,  Distribution  of  Electricity 
by  Means  of  --  .(See  Electricity.  Distrt 


button  of.  by  Alternating  Currents,  by  means 
of  Condensers .  Electricity,  Distribution  of, 
by  Continuous  Currents,  by  means  of  Con- 
densers!) 

Conduct.— To  pass  electricity  through  con- 
ducting substances. 

To  determine  the  general  direction  in  which 
electricity  shall  pass  through  the  ether  or 
dielectric  surrounding  the  so-called  conduct- 
ing substance.  (See  Conduction,  Electric.) 

Conductance. — A  word  sometimes  used  in 
place  of  conducting  power. 
Conductivity. 

Conductance,  Magnetic A  word 

sometimes  used  instead  of  magnetic  permea- 
bility. (See  Permeability  Magnetic.) 

The  magnetic  conductance  is  equal  to  the  total 
induction  through  the  circuit  divided  by  the 
magnetizing  force. 

Conducting  Cord.— (See  Cord,  Conduct- 
ing.) 

Conducting,  Electrical Possessing 

the  power  of  passing  electricity  through  any 
conducting  substance. 

Possessing  the  power  of  determining  the 
direction  in  which  electricity  shall  pass  through 
the  ether  surrounding  a  substance.  (See 
Conductor.) 

Conducting  Power.— (See  Power.  Con- 
ducting.) 

Conducting  Power  for  Electricity.— (Se* 

Power,  Conducting,  for  Electricity.) 

Conducting  Power  for  Lines  of  Mag 
netic  Force. — (See  Force,  Magnetic,  Lines 
of.  Conducting  Power  of.) 

Conducting    Power,   Tables   of 

(See  Power,  Conducting,  Tables  of.) 

Conduction  Current.— (See  Current,  Con- 
duction^ 

Conduction,  Disruptive A  species 

of  conduction  in  which  the  resistance  of  ?*•« 
conductor  is  suddenly  overcome. 

Disruptive  conduction  is  seen  in  the  disruptive 
discharge  of  a  condenser,  or  Leyden  jar. 

Conduction,      Electric The     so 


Con.] 


120 


[Con. 


called  flow  or  passage  of  electricity  through 
a  metallic  or  other  similarly  acting  substance. 

The  ability  of  a  substance  to  determine  the 
direction  in  which  electric  energy  shall  be 
transmitted  through  the  ether  surrounding  it. 

The  ability  of  a  substance  to  determine  the 
direction  in  which  a  current  of  electricity 
passes  from  one  point  to  another. 

When  a  conducting  wire  has  its  ends  connected 
with  an  electric  source,  a  current  of  electricity  is, 
in  common  language,  said  to  flow  through  the  wire, 
and  this  was  formerly  believed  to  be  a  correct 
statement.  According  to  modern  views,  however, 
the  electric  energy  is  believed  to  pass  through  the 
ether  or  other  dielectric  surrounding  the  con- 
ductor, the  so-called  conductor  forming  merely 
a  sink,  where  the  electrical  energy  dissipates 
itself.  The  conductor  simply  acts  to  direct  the 
current. 

Since,  however,  the  energy  practically  passes 
by  means  of,  and  in  the  general  direction  of  the 
conductor,  there  is  no  objection  in  speaking  of 
the  electricity  as  flowing  through  the  conductor. 

Conduction,  Electric,  Disruptive 

A  conduction  of  electric  energy  which  ac- 
companies a  disruptive  discharge.  (See 
Discharge,  Dismpti've^ 

Conduction,  Electric,  Metallic A 

conducting  of  electric  energy  of  the  same  char- 
acter as  that  which  occurs  in  metallic  sub- 
stances. 

Conduction,  Electrolytic A  terra 

sometimes  employed  to  indicate  the  passage 
of  electricity  through  an  electrolyte. 

There  is  no  passage  of  electricity  through  an 
electrolyte  in  the  same  sense  as  through  an  ordi- 
nary conductor. 

When,  through  electrolysis,  an  electromotive 
force  is  brought  to  bear  on  a  molecule  of  say 
HC1,  it  is  assumed  by  some  that  the  liberated 
hydrogen  atoms  travel  on  the  whole  in  one  di- 
rection, and  the  liberated  chlorine  atoms  in  the 
opposite  direction.  The  atoms  thus  moving 
through  the  liquid  may  by  their  electric  charges 
be  assumed  to  convey  electricity,  and  this  fact 
has  given  rise  to  the  term  electrolytic  conduc- 
tion. 

In  electrolytic  conduction  the  charges  are 
necessarily  equal,  but  the  speeds  of  their  motion 
are  unequal.  In  a  given  liquid,  each  atom  has 


its  own  rate  of  motion,  no  matter  with  what  it 
has  been  combined.  Hydrogen  travels  faster 
than  any  other  kind  of  atom.  The  conductivity 
of  a  liquid  depends  on  the  sum  of  the  speeds  with 
which  the  two  opposed  atoms  travel. 

This  assumed  double  stream  of  oppositely  mov- 
ing atoms  is  denied  by  most  physicists.  (See 
Hypothesis ,  Grot t hits.) 

Cond  uctive-Discharge. — (See  Discharge. 
Conductive^ 

Conductivity,  Electric The  recip- 
rocal of  electric  resistance. 

Since  the  conductivity  is  greater  the  less  the  re- 
sistance, the  conductivity  will  be  equal  to  the  recip. 
rocal  of  the  resistance,  and  may  be  so  defined.  The 

conductivity  is  therefore  equal  to  —  B 

•L 

Conductivity,  Equivalent A  con- 
ductivity equal  to  the  sum  of  several  conduc- 
tivities. 

Conductivity  per  Unit  of  Mass.— The  re- 
ciprocal of  the  resistance  of  a  substance  per 
unit  of  mass. 

Conductivity  per  Unit  of  Volume.— The 
reciprocal  of  the  resistance  of  a  substance 
per  cubic  centimetre  or  per  cubic  inch. 

The  resistance  is  measured  from  one  face  of 
the  cube  to  the  opposite  face. 

Conductivity  Resistance.— (See  Resist- 
ance, Conductivity?) 

Conductivity,  Specific The  par- 
ticular conductivity  of  a  substance  for  elec- 
tricity. 

The  specific  or  particular  resistance  of  a 
given  length  and  unit  of  cross-section  of  a 
substance  as  compared  with  the  same  length 
and  area  of  cross-section  of  some  standard 
substance. 

Conductivity,  Specific  Magnetic 

The  specific  or  particular  permeability  of  a 
substance  to  lines  of  magnetic  force. 

The  specific  magnetic  conductivity  is  measured 
by  the  ratio  of  the  magnetization  produced  to  tke 
magnetizing  force  which  produces  it. 

The  specific  magnetic  conductivity  is  the  an- 
alogue of  specific  inductive  capacity,  or  conduc- 
tivity for  lines  of  electrostatic  force.  It  is  also  th« 
analogue  for  specific  conducting  power  for  heat* 


Con.] 


121 


[Con. 


Conductor. — A  substance  which  will  per- 
mit the  so-called  passage  of  an  electric  current. 

A  substance  which  possesses  the  ability  of 
determining  the  direction  in  which  electricity 
shall  pass  through  the  ether  or  other  dielec- 
tric surrounding  it. 

Some  electrolytes,  such,  for  example,  as  vari- 
ous mixtures  of  sulphuric  acid  and  water,  possess 
a  true  power  of  conducting  electricity,  and  there- 
fore have  a  specific  resistance.  Generally,  how- 
ever, the  passage  of  the  electrolyzing  current  is 
regarded  as  different  from  that  of  a  current  which 
merely  heats  the  conductor. 

The  space  or  region  around  a  conductor 
through  which  an  electric  current  is  passing  has 
a  magnetic  field  produced  in  it. 

The  term  conductor  is  opposed  to  non-conductor, 
or  a  substance  which  will  not  permit  the  passage 
of  an  electric  current  through  it  after  the  manner 
of  a  conductor. 

The  terms  conductors  and  non-conductors  are 
only  relative.  There  are  no  such  things  as 
either  perfect  conductors  or  perfect  non-con- 
ductors. 

Conductors  in  general,  are  distinguished  from 
electrolytes,  in  that  the  latter  do  not  allow  the 
electricity  to  pass  save  by  undergoing  a  chemical 
decomposition. 

Conductor,  Anisotropic A  con- 
ductor which,  though  homogeneous  in  struc- 
ture like  crystalline  bodies,  has  different 
physical  properties  in  different  directions,  just 
as  crystals  have  different  properties  in  the 
direction  of  their  different  crystalline  axes. 

Anisotropic  conductors  possess  different  powers 
of  electric  conduction  in  different  directions. 
But  in  opposite  directions  along  the  same  axis  their 
conductivity  is  equal.  They  differ  in  this  respect 
from  isotropic  conductors.  (See  Conductor,  Iso- 
tropic.) 

Conductor,  Anti-Induction A  con- 
ductor so  constructed  as  to  avoid  injurious 
inductive  effects  from  neighboring  telegraphic 
or  electric  light  and  power  circuits. 

Such  anti-induction  conductors  sometimes  con- 
sist of  a  conductor  for  constant  currents  and  a 
metallic  shield  surrounding  the  conductor,  and 
designed  to  prevent  induction  from  taking  place 
in  the  wire  itself. 

The  anti-induction  conductor   generally  con- 


sists of  twin  conductors  surrounded  by  ordinary 
insulation  and  sometimes  enclosed  by  some  form 
of  metallic  shield,  in  order  to  prevent  the  action 
of  electrostatic  induction. 

When  a  periodic  current  is  to  be  transmitted 
through  a  conductor,  the  most  effective  way  of 
annulling  its  inductive  effects  on  neighboring  cir- 
cuits is  to  place  the  lead  of  the  conductor  in  the 
axis  of  another  conductor,  used  as  a  return.  In 
other  words,  to  employ  concentric  cylinders,  in- 
sulated from  one  another  and  from  the  earth. 
Under  these  conditions,  calling  the  current  in  one 
direction  positive,  and  in  the  other  direction 
negative,  the  shielding  action  will  be  perfect 
when  the  algebraic  sum  of  the  currents  in  the 
core  and  sheath  are  zero. 

The  same  effect  is  obtained  in  metallic  circuits, 
by  placing  the  leads  parallel  to  the  return,  and 
crossing  and  recrossing  the  wires  repeatedly. 
(See  Connection,  Telephonic  Cross.) 

Elihu  Thomson  renders  ordinary  telephone 
conductors,  arranged  as  single  lines  with  earth 
returns,  free  from  induction  by  means  of  the 
counter-electromotive  force  produced  in  a  coil  of 
wire  by  the  disturbing  cause. 

In  applying  this  system  to  the  case  of  an  elec- 
tric arc  or  power  line  passing  alongside  a  tele- 
phone line,  a  wire  coil,  whose  turns  are  pro- 
portioned in  number  to  the  induction  to  be  bal- 
anced, is  introduced  into  the  electric  light  line 
and  placed  near  another  coil  of  finer  wire  inserted 
as  a  loop  in  the  telephone  circuit.  The  second  coil 
is  placed  parallel  to  or  inclined  at  an  angle  to  the 
first  coil.  In  practice,  the  second  coil  is  inclined 
until  the  counter-induction  set  up  in  the  tele- 
phone wire  is  equal  to  that  produced  in  the  main 
line,  and  silence  is  thus  produced,  so  far  as  in- 
duction is  concerned,  in  the  telephone. 

Conductor,  Armored A  conduc- 
tor provided  with  a  covering  or  sheathing  of 
metal  placed  over  the  insulating  covering  for 
protection  from  abrasion  or  external  wear. 

Armored  conductors  are  used  in  situations 
where  the  conductor  is  exposed  to  abrasion  or 
other  external  wear. 

Conductor,  Branch  —A  conductor 

placed  in  a  shunt  circuit.  (See  Circuit, 
Shunt.) 

Conductor,   Closed-Circuited A 

conductor  connected  as  a  closed  or  com- 
pleted circuit. 


Con.] 


122 


[Con. 


Conductor,  Conjugate In  a  system 

of  linear  conductors,  any  pair  of  conductors 
that  are  so  placed  as  regards  each  other  that 
a  variation  of  the  resistance  or  the  electro- 
motive force  in  the  one  causes  no  variation  in 
the  current  of  the  other. 

Conductor,    Earth-Circuited    —A 

conductor  connected  to  the  ground,  or  to  an 
earth-connected  circuit. 

Conductor,  House-Service A  term 

employed  in  a  system  of  multiple  incan- 
descent lamp  distribution  for  that  portion  of 
the  circuit  which  is  included  between  the  ser- 
vice cut-out  and  the  centre  or  centres  of  dis- 
tribution, or  between  this  cut-out  and  one  or 
more  points  on  house  mains. 

Conductor,  Isotropic A  conduc- 
tor which  possesses  the  same  powers  of  elec- 
tric conduction  in  all  directions. 

An  electrically  homogeneous  conducting 
medium. 

Conductor,  Leakage A  conductor 

placed  on  a  telegraph  circuit  for  the  purpose 
of  preventing  the  disturbing  effects  of  leakage 
into  a  neighboring  line  by  providing  a  direct 
path  for  such  leakage  to  the  earth. 

The  leakage  conductor,  as  devised  by  Varley 
consists  of  a  thick  wire  attached  to  the  telegraph 
pole.  The  lower  end  of  the  conductor  is  grounded, 
and  its  upper  end  projects  above  the  top  of  the 
pole. 

There  exists  some  doubt  in  the  minds  of  expe- 
rienced telegraph  engineers  whether  it  is  well  to 
apply  leakage  conductors  to  telegraphic  or  tele- 
phonic lines  of  over  12  or  15  miles  in  length, 
since  such  conductors  greatly  increase  the  electro- 
static capacity  of  the  line,  and  thus  cause  serious 
retardation. 

Conductor,  Lightning  — A  term 

sometimes  used  for  a  lightning  rod.  (See 
Rod,  Lightning?) 

Conductor,  Open-Circuited A  con- 
ductor arranged  as  an  open  or  broken  circuit. 

Conductor,  Potential  of —The  rela- 
tion existing  between  the  quantity  of  elec- 
tricity in  a  conductor  and  its  capacity. 

A  given  quantity  of  electricity  will  raise  the 


potential  of  a  conductor  higher  in  proportion  as 
the  capacity  of  the  conductor  becomes  less. 

Conductor,    Potential    of,  Methods    of 

Tarying The  potential  of  a  conductor 

may  be  varied  in  the  following  ways : 

(I.)  By  varying  its  electric  charge. 

(2.)  By  varying  its  size  or  shape  without  alter- 
ing its  charge. 

(3.)  By  varying  its  position  as  regards  neigh- 
boring bodies. 

This  resembles  the  case  of  a  gas  whose  tension 
or  pressure  may  be  varied  as  follows,  viz. : 

(I.)  By  varying  the  quantity  of  gas. 

(z.)  By  varying  the  size  of  the  gas  holder  in 
which  it  is  kept,  and 

(3.)  By  varying  the  temperature. 

Difference  of  potential,  therefore,  correspondsr- 

(I.)  With  difference  of  level  in  liquids. 

(2. )  With  difference  of  pressure  in  gases. 

(3.)  With  difference  of  temperature  in  heat. 
— (Ayrton,) 

Conductor,    Prime —The  positive 

conductor  of  a  frictional  electric  or  electro- 
static machine.  (See  Machine,  Frictional 
Electric?) 

Conductor,    To  Short-Circuit  a 

To  shunt  a  conductor  with  a  circuit  of  com- 
paratively small  resistance. 

Conductor,  Underground An  elec- 
tric conductor  placed  underground  by  actual 
burial  or  by  passing  it  through  underground 
conduits  or  subways. 

Underground  conductors,  though  less  unsightly 
than  the  ordinary  aerial  conductors,  require  to 
be  laid  with  unusual  care  to  render  them  equally 
safe,  since,  when  contacts  do  occur,  all  the  wires 
in  the  same  conduit  are  apt  to  be  simultaneously 
affected,  thus  spreading  the  danger  in  many  dif- 
ferent directions.  They  are,  however,  less  liable  to 
dangers  arising  from  occasional  accidental  crosses 
or  contacts. 

Conductors,    Service Conductors 

employed  in  systems  of  incandescent  lighting 
connected  to  the  street  mains  and  to  the 
electric  apparatus  placed  in  the  separate 
buildings  or  areas  to  be  lighted. 

Conduit,   Cement-Lined A  cable 

conduit,  the  separate  ducts  of  which  are  sur- 
rounded by  any  suitable  cement. 


Con.] 


123 


[Con. 


Conduit,  Handhole  of (See  Hand- 
hole  of  Conduit) 

Conduit,  Manhole  of (See  Man- 
hole of  Conduit?) 

Conduit,  Multiple  —A  conduit 

formed  of  concrete  or  other  insulating  mate- 
rial, and  furnished  with  a  number  of  separate 
ducts. 

Conduit,  Open-Box  — A  conduit 

consisting  of  an  open  box  of  wood  placed  in 
a  trench  and  closed  with  a  wooden  cover 
after  the  introduction  of  the  cable. 

Cables  or  wires  may  be  drawn  through  such 
conduits  in  the  usual  manner. 

Conduit,  Rodding  a Introducing  a 

wire  or  rope  into  the  duct  of  a  closed  conduit 
preparatory  to  drawing  the  cable  through. 

Various  methods  are  in  use  for  rodding  a  con- 
duit  One  much  followed  consists  in  using  sec- 
tions of  gas  pipe,  the  ends  of  which  are  furnished 
with  screw  threads. 

The  sections  are  about  four  feet  in  length.  One 
section  is  pushed  into  the  duct  at  one  manhole 
and  the  successive  sections  are  introduced  into 
the  duct  and  screwed  onto  the  section  in  the  duct 
and  pushed  through  until  a  sufficient  length  is 
obtained  to  reach  the  next  manhole,  a  rope  or 
cable  is  then  pulled  through  from  one  manhole  to 
the  next. 

Conduit,  Underground  Electric 

An  underground  passageway  or  space  for 
the  reception  of  electric  wires  or  cables.  (See 
Subway,  Electric?) 

Congelation.— The  act  of  freezing,  or  the 
change  of  a  liquid  into  a  solid  on  loss  of  heat, 
or  change  of  pressure. 

Conjugate  Coils.— (See  Coils,  Conjugate) 

Connect. — To  place  or  bring  into  electric 
contact. 

Connecting. — Placing  or  bringing  into  elec- 
tric contact. 

Connection  for  Intensity. — Connection  in 
series.  (See  Connection,  Series) 

This  term  is  now  nearly  obsolete. 

Connection  for  Quantity. — Connection  in 
multiple.  (See  Connection,  Multiple) 

This  term  is  now  nearly  obsolete. 
5— Vol.  1 


Connection,  Mercurial —A  form 

of  readily  adjustable  connection  obtained  by 
providing  the  poles  of  one  piece  of  electric 
apparatus  with  cups  or  'cavities  filled  with 
mercury,  into  which  the  terminals  of  another 
piece  of  apparatus  are  dipped  in  order  to 
place  the  two  in  circuit  with  each  other. 

This  form  of  connection  is  used  particularly 
when  a  very  perfect  contact  or  one  free  from 
friction  is  desired. 

Connection,  Multiple Such  a  con- 
nection of  a  number  of  separate  electric 
sources,  or  electro-receptive  devices,  or  circuits, 
that  all  the  positive  terminals  are  connected 
to  one  main  or  positive  conductor,  and  all  the 
negative  terminals  are  connected  to  one  main 
or  negative  conductor. 

In  the  multiple  connection  of  a  number  of 
electro-receptive  devices,  when  the  devices  are 
connected  as  above  described  to  positive  and 
negative  leads  that  are  maintained  at  a  constant 
difference  of  potential,  the  current  passes  through 
the  devices  from  one  lead  to  the  other  by  branch- 
ing and  flowing  through  as  many  separate  cir- 
cuits as  there  are  separate  receptive  devices, 
and  the  opening  or  closing  of  one  of  these  cir- 
cuits does  not  affect  the  others.  (See  Circuits, 
Varieties  of. ) 

Connection,  Multiple-Series Such 

a  connection  of  a  number  of  separate  electric 
sources,  or  separate  electro-receptive  de- 
vices, or  circuits,  that  the  sources  or  devices 
are  connected  in  a  number  of  separate  groups 
in  series,  and  each  of  these  groups  connected 
to  main  positive  and  negative  conductors  or 
leads  in  multiple  arc.  (See  Circuits,  Varie- 
ties of) 

Connection  of  Battery  for  Quantity. — 
(See  Battery,  Connection  of ,  for  Quantity) 

Connection  of  Electric  Sources  in  Cas- 
cade.— (See  Cascade,  Connection  of  Electric 
Sources  in) 

Connection  of  Toltaic  Cells  for  Inten- 
sity.— (See  Intensity,  Connection  of  Voltaic. 
Cells  for) 

Connection,  Series The  connec- 
tion of  a  number  of  separate  electric 
sources,  or  electro-receptive  devices,  or  cir- 


Con.] 


124 


[Con. 


cuits,  so  that  the  current  passes  successively 
from  the  first  to  the  last  in  the  circuit.  (See 
Circuits,  Varieties  of.} 

Connection,  Series-Multiple Such 

a  connection  of  a  number  of  separate  electro- 
receptive  devices,  that  the  devices  are  placed 
in  multiple  groups  or  circuits,  and  these 
separate  groups  connected  with  one  another 
in  series. 

Connection,  Telephonic    Cross 

A  device  employed  in  systems  of  telephonic 
communication  for  the  purpose  of  lessening 
the  bad  effects  of  induction,  in  which  equal 
lengths  of  adjacent  parallel  wires  are  alter- 
nately crossed  so  as  to  alternately  occupy  the 
opposite  sides  of  the  circuit. 

Connector. — A  device  for  readily  con- 
necting or  joining  the  ends  of  two  or  more 
wires.  (See  Post,  Binding?) 

Connector,  Double 
A  form  of  bind- 
ing screw  suitable  for 
readily  connecting  two 
wires  together. 

A  form  of  double  con- 
nector is  shown  in  Fig. 
170. 

Conning  Tower.  — 
(See  Tower,  Conning.) 

Consequent  Points. — (See  Points,  Conse- 
quent) 

Consequent  Poles. — (See  Poles,  Conse- 
quent) 

Conservation  of  Energy. — (See  Energy, 
Conservation  of) 

Consonance,  "In  Consonance." — A  term 
employed  to  express  the  fact  that  one  simple 
periodic  quantity,  /.  e.,  a  wave  or  vibration, 
agrees  in  phase  with  another. 

Constant. — That  which  remains  invariable. 
Constant-Current. — (See    Current,    Con- 
stant) 

Constant-Current  Circuit.— (See  Circuit, 
Constant  Current) 

Constant-Current,  Distribution  of  Elec* 
trieity  by (See  Electricity,  Distri- 
bution of,  by  Constant  Currents) 


Fig.  i TO.    Double 
Connector. 


Constant,  Dielectric A  term  some- 
times employed  in  place  of  specific  inductive 
capacity.  (See  Capacity,  Specific  Inductive) 

Constant,     Galvanometer    —The 

numerical  factor  connecting  the  current  pass- 
ing through  a  galvanometer  with  the  deflec- 
tion produced  by  such  current. 

Sometimes  a  distinction  is  made  between  the 
galvanometer  constant  and  the  reduction  factor, 
the  former  being  used  to  indicate  the  relation 
between  the  current  and  the  geometrical  constant 
of  the  galvanometer,  while  the  latter  is  used  in 
the  sense  just  defined  of  galvanometer  constant. 

Constant  Inductance. — (See  Inductance, 
Constant) 

Constant  Potential.— (See  Potential, 
Constant) 

Constant-Potential  Circuit.— (See  Cir- 
cuit, Constant-Potential) 

Constant,  Time,  of  Electro-Magnet 

— The   time   required   for   the   magnetizing 

current  to  rise  to  the of  its  final  value. 

e 

Contact-Breaker,    Automatic A 

device    for    causing   an   electric    current  to 
rapidly  make  and  break  its  own  circuit. 

The  spring  c,  Fig.  171,  carries  an  armature  of 
soft  iron,  B,  and  is 
placed  in  a  circuit  in 
such  a  manner  that 
the  circuit  is  closed 
when  platinum  con- 
tacts placed  on  the 
ends  of  D  and  B, 
touch  each  other.  In 
this  case  the  arma- 
ture, B,  is  attracted  to 
the  core  A,  of  the 
electro-magnet,  thus 
breaking  the  circuit 
and  causing  the  magnet  to  lose  its  magnetism. 
The  elasticity  of  the  spring  C,  causes  it  to  fly  back 
and  again  close  the  contacts,  thus  again  energiz- 
ing the  electro-magnet  and  again  attracting  B, 
and  breaking  the  circuit.  The  makes  and  breaks 
usually  follow  each  other  so  rapidly  as  to  produce 
a  musical  note.  (See  Alarm,  Electric) 

Contact,  Dotting An  electric  con 


Ftg.  17  r.    Automatic 
Contact  Breaker. 


Con.] 


125 


[Con. 


tact  obtained  by  the  approach  of  one  con- 
tact point  towards  another. 

The  term  dotting  contact  is  used  in  contradis- 
tinction to  a  rubbing  contact.  The  rubbing 
contact  is  generally  to  be  preferred,  since  it  tends 
automatically  to  remove  dust  and  keep  the  con- 
tact surfaces  polished  and  free  from  oxides. 

Contact  Dynamo. — (See  Dynamo.  Con- 
tact) 

Contact  Electricity.  —  (See  Electricity, 
Contact.} 

Contact,  Fire- Alarm A  contact  so 

arranged  that  an  alarm  is  given  when  any 
predetermined  temperature  is  reached. 

Fire-alarm  contacts  are  generally  operated  by 
the  expansion  of  a  metal  or  of  a  conducting  fluid, 
such  as  mercury.  (See  Thermostat.) 

Contact  Force.— (See  Force,  Contact) 

Contact,  Fnll-Metallic A  contact, 

which  from  its  small  resistance  establishes  a 
good  or  complete  connection.  (See  Contact, 
Metallic) 

Contact,  Intermittent The  occa- 
sional contact  of  a  telegraphic  or  other  line 
with  other  wires  or  conductors  by  swing- 
ing, or  by  alternate  contraction  or  expansion 
under  changes  of  temperature. 

Contact,  Metallic A  contact  of 

a  metallic  conductor  produced  by  its  coming 
into  firm  connection  with  another  metallic 
conductor. 

Contact,  Partial  —A  contact  of  a 

telegraphic,  or  other  line,  arising  from  defect- 
ive insulation,  bad  earths,  or  connection  with 
an  imperfect  conductor. 

Contact,  Rolling -A  contact  con- 
nected with  one  part  of  an  electric  circuit, 
that  completes  the  circuit  by  being  rolled  over 
a  conductor  connected  with  and  forming 
another  part  of  the  circuit. 

Rolling  contacts  are  employed  on  electric  rail- 
roads. (See  Railroad,  Electric.) 

Contact,  Rubbing  —A  contact 

effected  by  means  of  a  rubbing  motion, 

Contact  Series.— (See  Series,  Contact!) 

Contact,  Sliding A  contact  con- 
nected with  one  part  of  a  circuit  that  closes 


or  completes  an  electric  circuit  by  being  slid 
over  a  conductor  connected  with  another 
part  of  the  circuit. 

Sliding  contacts  are  employed  in  electric  rail- 
roads, in  rheostats,  switches,  and  a  variety  of  other 
apparatus.  (See  Railroad,  Electric.  Rheostat. 
Key,  Discharge.) 

Contact,  Spring A  spring-sup- 
ported contact  connected  with  one  part  of  a 
circuit  that  completes  said  circuit  by  being 
moved  so  as  to  touch  another  contact  con- 
nected with  the  other  part  of  the  circuit. 

The  movement  required  to  bring  the  two  con- 
tacts together  may  be  non-automatic,  as  in  the  case 
of  a  push-button,  or  automatic,  as  in  the  case  of 
a  thermostat  (See  Button,  Push.  Thermostat.') 

Contact  Theory  of  Yoltaic  CelL— (See 

Cell,  Voltaic,  Contact  Theory  of) 

Contact,  Yibrating A  spring  con- 
tact, connected  with  one  part  of  a  circuit  and 
so  supported  as  to  be  able  to  vibrate  towards 
and  from  another  contact  connected  with 
another  part  of  the  circuit,  thus  automatically 
closing  and  opening  said  circuit. 

A  vibrating  contact  is  used  in  the  automatic 
contact-breaker  in  which  the  movement  of  aa 
armature  towards  an  electro-magnet  is  caused  to 
break  the  circuit  of  the  coils  of  the  electro-magnet, 
and,  on  its  movement  away  from  the  magnet,  to 
close  another  contact  which  again  completes  the 
circuit  of  the  electro-magnet.  (See  Coutect 
Breaker,  Automatic.) 

Contact,  Wiping A  contact  ob- 
tained by  a  wiping  movement  of  one  con- 
ductor against  another. 

The  spark  for  electrically  igniting  a  gas  jet  \s 
obtained  by  means  of  a  wiping  contact  of  a  spring 
moved  by  the  motion  of  the  pendant.  (See 
Burner,  Plain-Pendant  Electric. ) 

Contacts. — A  variety  of  faults  occasioned 
by  the  accidental  contact  of  a  circuit  with  any 
conducting  body. 

The  word  contacts  as  employed  above  is  in  die 
sense  of  accidental  contacts  as  distinguished  from 
predetermined  contacts. 

Contacts  of  an  accidental  character  are  of  the 
following  varieties,  viz.: 

(I.)  Full,  or  metallic,  as  when  the  circuit  is 


Con.] 


126 


[Con. 


Accidentally  placed  in  firm  connection  with  *n- 
other  metallic  circuit. 

(2.)  Portia/,  as  by  imperfect  conductors  being 
placed  across  wires,  or  bad  earths,  or  defective 
insulation. 

(3.)  Intermittent,  as  by  occasional  contacts  of 
swinging  wires,  etc. 

Contacts,  Burglar  •  Alarm  —  —Con- 
tacts fitted  to  windows,  doors,  tills,  steps, 
floors,  etc.,  so  that  a  movement  of  the  parts 
from  their  natural  position  gives  an  alarm  by 
sounding  a  conveniently  located  bell. 

Contacts,  Lamp Metallic  plates  or 

rings  connected  with  the  terminals  of  an  incan- 
descent lampf  or  ready  connection  with  the  line. 

Contacts,  Mercurial Electric  con- 

tacts  that  are  opened  or  closed  by  the  ex- 
pansion or  contraction  of  a  mercury  column. 

In  the  commonest  forms  of  mercurial  con- 
tacts, on  the  expansion  of  the  mercury  by  heat  it 
reaches  a  contact  point  placed  in  the  tube,  and 
thus  completes  the  circuit  through  it  own  mass. 

Or,  on  contraction  it  breaks  a  contact,  and  thus 
disturbing  an  electric  balance,  sounds  an  alarm. 

Continental  Code  Telegraphic  Alphabet. 
—(See  Alphabet.  Telegraphic,  International 
Code) 

Continuity  of  Current— (See  Current, 
Continuous.) 

Continuous  Current— (See  Current,  Con" 
tinuous) 

Continuous  Current,  Distribution  of 
Electricity  by (See  Electricity,  Dis- 
tribution of,  by  Constant  Currents) 

Continuous  Current,  Dynamo-Electric 
Machine (See  Machine,  Dynamo- 
Electric,  Continuous  Current) 

Continuous-Sounding  Electric  Bell.— 
(See  Bell,  Continuous-Sounding  Electric.) 

Continuous  Wires  or  Conductors.— (See 
Wires  or  Conductors,  Continuous) 

Contraction,  Anodic  Closure The 

muscular  contraction  observed  on  the  closing 
of  a  voltaic  circuit,  the  anode  of  which  is  placed 
over  a  nerve,  and  the  kathode  at  some  other 
part  of  the  body. 
This  term  is  generally  written  A.  C.  C. 


Contraction,  Anodic  Duration 

The  length  of  time  the  muscle  continues  in 
contraction  on  the  opening  or  closing  of  a 
circuit,  the  anode  of  which  is  placed  over  the 
part  contracted. 

This  term  is  generally  written  A.  D.  C. 

Contraction,   Anodic    Opening 

The  muscular  contraction  observed  on  the 
opening  of  a  voltaic  circuit,  the  anode  of  which 
is  placed  over  a  nerve,  and  the  kathode  at 
some  other  part  of  the  body. 

This  term  is  generally  written  A.  O.  C. 

When  the  anode  is  placed  over  a  nerve  and  a 
weak  current  is  employed,  if  the  circuit  be  kept 
closed  for  a  few  minutes,  it  will  be  noticed  that, 
on  opening  the  circuit  the  contraction  will  be 
much  greater  than  if  it  had  been  opened  after 
being  closed  for  only  a  few  seconds.  The  effect 
of  the  A.  O.  C.  therefore  depends  not  only  on  the 
current  strength,  but  also  on  the  time  during 
which  the  current  has  passed  through  the  nerve. 

Contraction  of  Lines  of  Magnetic  Force. 
— (See  Force,  Magnetic,  Contraction  of 
Lines  of) 

Contractures.  —  In  electro-therapeutics, 
prolonged  muscular  spasms,  or  tetanus,  caused 
by  the  passage  of  electric  currents. 

Contraplex  Telegraphy.— (See  Telegra- 
phy, Contraplex) 

Controlled  Clock.— (See  Clock,  Electric) 

Controller. — A  magnet,  in  the  Thomson- 
Houston  system  of  automatic  regulation, 
whose  coils  are  traversed  by  the  main  cur- 
rent, and  by  means  of  which  the  regulator 
magnet  is  automatically  thrown  into  or  out  of 
the  main  circuit  on  changes  in  the  strength 
of  the  current  passing.  (See  Regulation, 
Automatic) 

Controlling  Clock.— (See  Clock,  Electric) 

Controlling  Magnet— (See  Magnet,  Con- 
trolling) 

Convection  Currents.— (See  Currtnts.Con- 
vection) 

Convection,  Electric The  air  par- 
ticles, or  air  streams,  which  are  thrown  off 
from  the  pointed  ends  of  a  charged,  insulated 
conductor. 


Con.] 


[Cop. 


Convection  streams,  like  currents  flowing 
through  conductors,  act  magnetically,  and  are 
themselves  acted  on  by  magnets.  The  same  thing 
is  true  of  the  brush  discharge,  of  the  voltaic  arc, 
and  of  convective  discharges  in  vacuum  tubes. 

Convection,  Electrolytic A  term 

proposed  by  Helmholtz  to  explain  the  appa- 
rent conduction  of  electricity  by  an  electro- 
lyte, without  consequent  decomposition. 

Helmholtz  assumes  that  the  atoms  of  oxygen  or 
hydrogen,  adhering  to  the  electrodes  during  elec- 
trolysis, are  mechanically  dislodged  and  diffused 
through  the  liquid,  thus  carrying  off  the  elec- 
tricity by  the  charges  received  while  in  contact 
with  the  electrodes. 

Convection  of  Heat,  Electric  —  —(See 
Heat,  Electric  Convection  of.) 

Convection  Streams. — (See  Streams,  Con- 
vection^) 

Convective  Discharge. — (See  Discharge, 
Convective?) 

Conversion,  Efficiency  of,  of  Dynamo 

— The  total  electric  energy  developed  by  a 
dynamo,  divided  by  the  total  mechanical 
energy  required  to  drive  the  dynamo.  (See 
Co-efficient,  Economic,  of  a  Dynamo-Electric 
Machine?) 

The  efficiency  of  conversion 

W-f  w   _         W  + w 

M~~    ~~  W  +  w  +  m, 

where  W,  equals  the  useful  or  available  electrical 
energy,  M,  the  total  mechanical  energy,  w,  the 
electrical  energy  absorbed  by  the  machine,  and 
m,  the  stray  power,  or  the  power  lost  in  friction, 
eddy  currents,  air  friction,  etc. 

Converted  Currents. — (See  Currents, 
Converted.) 

Converter. — The  inverted  induction  coil 
employed  in  systems  of  distribution  by  means 
of  alternating  currents. 

A  term  sometimes  used  instead  of  trans- 
former. (See  Transformer?) 

Converter,  Closed-Iron  Circuit 

A  closed-iron  circuit  transformer.  (See 
Transformer,  Closed-Iron  Circuit.) 

Converter,    Constant-Current    — 

A  constant-current  transformer.  (See  Trans- 
former, Constant-Current.) 


Converter,  Efficiency  of The  effi- 
ciency of  a  transformer.  (See  Transformer, 
Efficiency  of.) 

Converter  Fuse. — (See  Fuse,  Converter.) 

Converter,  Hedgehog A  form  of 

transformer.  (See  Transformer,  Hedgehog.) 

Converter,  Multiple A  multiple 

transformer.  (See  Transformer,  Multiple.) 

Converter,  Open-Iron-Circuit An 

open-iron-circuit  transformer.  (See  Trans- 
former, Open-Iron-Circuit.) 

Converter,  Series A  series  trans- 
former. (See  Transformer,  Series.) 

Converter,  Step-down A  step-down 

transformer.  (See  Transformer,  Step-down.) 

Converter,  Step-up  — A  step-up 

transformer.  (See  Transformer,  Step-up?) 

Converter,  Welding  — A  welding 

transformer.  (See  Transformer,  IVelding.) 

Converting  Currents.— (See  Currents, 
Converting.) 

Cooling  Box  of  Hydro-Electric  Machine. 
—(See  Box,  Cooling,  of  Hydro-Electric 
Machine?] 

Co-ordinates,  Axes  of The  axes  of 

abscissas  and  ordinates. 

The  two  straight  lines,  usually  perpendicular 
to  each  other,  to  which  distances  representing 
values  are  referred  for  the  graphic  represen- 
tation of  such  values.  (See  Abscissas,  Axes  of.) 

Copper  Bath.— (See  Bath,  Copper?) 

Copper  Plating.— (See  Plating,  Copper?) 

Copper  Ribbon. — A  variety  of  strap  cop- 
per. (See  Copper,  Strap?) 

Copper,  Strap Copper  conductors 

in  the  form  of  straps  or  flat  bars. 

Strap  copper  is  used  on  the  armatures  of  some 
dynamos.  Heavy  copper  conductors  for  such 
purposes  are  divided  into  strap  copper  so  as  to 
avoid  eddy  currents.  The  straps  are  placed 
alongside  one  another  and  insulated  by  a  coating 
of  varnish. 

Copper  Wire,  Hard-Drawn (See 

Wire,  Copper,  Hard-Drawn?) 

Copper  Wire,  Soft-Drawn (See 

Wire,  Copper,  Soft-Drawn.) 


Cop.] 


128 


[Cor. 


Copper  Voltameter.— (See  Voltameter, 
Copper.) 

Coppered  Plumbago. — (See  Plumbago, 
Coppered.) 

Coppering,  Electro Electro-plating 

with  copper.  (See  Plating,  Electro.) 

Cord-Adjuster—  (See  Adjuster,  Cord.) 

Cord,  Conducting A  small  flexible 

cable,  usually  containing  several  conductors 
separated  from  one  another  by  insulating  ma- 
terial. 

Cord,  Electric A  flexible,  insulated 

electric  conductor,  generally  containing  at  least 
two  parallel  wires. 

Electric  cords  are  named  from  the  purposes  for 
which  they  are  employed,  battery  cords,  dental 
cords,  lamp  cords,  motor  cords,  switch  cords,  etc. 


Fig.   172.     Flexible  Cord. 

A  two-conductor  flexible  cord,  in  which  each 
cord  is  composed  of  a  number  of  bare  copper  wires 
placed  parallel  to  and  in  contact  with  one  another, 
is  shown  in  Fig.  172.  The  several  separate  wires 
give  flexibility  to  the  cord. 

Cord,  Pendant A  flexible  conductor 

provided  for  conveying  the  current  to  a  hang- 
ing electric  lamp  supported  by  it, 

Cords,  Telephone  —  — Flexible  con- 
ductors for  use  in  connection  with  a  tele- 
phone. 


Fig'  '73-     Telephone  Cards. 

Telephone  cords,  attached  to  an  articulating 
telephone,  are  shown  in  Fig.  173. 


Core,    Armature,    Filamentous 

An  armature  core,  the  iron  of  which  consists 
of  wire. 

Core,  Armature,  H An  armature 

core  in  the  shape  of  the  letter  H,  generally 
known  as  the  shuttle  armature,  and  some- 
times as  the  girder  armature. 

This  form  is  also  called  an  I  armature. 

The  H  armature  core  was  the  form  originally 
given  to  the  Siemens  armature.  In  this  form  a 
single  coil  of  wire  was  secured  on  the  cross-bar 
of  the  H  armature  core,  so  as  to  fill  up  the  entire 
space  inside  the  letter,  and  the  ends  of  the  wire 
connected  to  a  two-part  commutator, 

Core,  Armature,  Lamination  of 

The  subdivision  of  the  core  of  the  armature 
of  a  dynamo-electric  machine  into  separate 
insulated  plates  or  strips  for  the  purpose  of 
avoiding  eddy  or  Foucault  currents. 

This  lamination  must  always  be  perpendicular 
to  the  direction  of  the  eddy  currents  that  would 
^otherwise  be  produced.  (See  Currents,  Eddy.} 

Core,  Armature,  of  Dynamo-Electric 

Machine The  iron  core,  on,  or  around 

which,  the  armature  coils  of  a  dynamo-electric 
machine  are  wound  or  placed. 

The  armature  core  is  laminated  for  the  pur- 
pose of  avoiding  the  formation  of  eddy  or  Fou- 
cault currents. 

In  drum,  and"  in  ring-armatures,  the  laminae 
should  be  in  the  form  of  thin  insulated  discs  or 
plates  of  soft  iron;  in  pole-armatures  they  should 
be  in  the  form  of  bundles  of  insulated  wires. 

The  iron  in  the  cores  should  be  of  such  an  area 
of  cross-section,  as  not  to  be  readily  o  versa  turated. 

Core,    Armature,     Radially-Laminated 

An  armature  core,  the  iron  of  which 

consists  of  thin  iron  washers. 

Core,  Armature,  Ribbed A  cylin- 
drical armature  core  provided  with  longi- 
tudinal projections  or  ribs  that  serve  as 
spaced  channels  or  grooves  for  the  reception 
of  the  armature  coils. 

Core,  Armature,  Tangentiallj -Laminated 

— An  armature  core,  the  iron  of  which 

consists  of  a  coiled  ribbon. 

Core,  Armature,  Ventilation  of 

Means  for  passing  air  through  the  armature 


Cor.] 


129 


[Con. 


cores  of  dynamo-electric  machines  in  order  to 
prevent  undue  accumulation  of  heat. 

A  properly  proportioned  dynamo-armature 
may  need  no  ventilation,  since  in  such  the 
amount  of  heat  generated  is  small  as  compared 
with  the  extent  of  the  radiating  surface. 

Since,  however,  in  practice  all  armatures  tend 
to  heat  at  full  load,  especially  in  certain  installa- 
tions in  heated  situations,  ventilation  of  the  ar- 
mature is  desirable. 

Core,  Closed-Magnetic A  mag- 
netic core  so  shaped  as  to  provide  a  complete 
iron  path  or  circuit  for  the  lines  of  magnetic 
force  of  its  field. 

Core,  Laminated A  core  of  iron 

which  has  been  divided  or  laminated,  in  order 
to  avoid  the  injurious  production  of  Foucault 
or  eddy  currents. 

Core,  Lamination  of Structural 

subdivisions  of  the  cores  of  magnets,  arma- 
tures, and  pole-pieces  of  dynamo-electric 
machines,  electric  motors,  or  similar  appa- 
ratus, in  order  to  prevent  heating  and  subse- 
quent loss  of  energy  from  the  production  of 
local,  eddy  or  Foucault  currents. 

These  laminations  are  obtained  by  forming  the 
cores  of  sheets,  rods,  plates,  or  wires  of  iron  in- 
sulated from  one  another. 

The  cores  of  dynamo-electric  machine  arma- 
tures should  be  subdivided  in  planes  at  right 
angles  to  the  armature  coils;  or  in  planes  parallel 
to  the  direction  of  the  lines  of  force  and  to  the 
motion  of  the  armature;  or,  in  general,  in  planes 
perpendicular  to  the  currents  that  would  otherwise 
be  generated  in  them. 

Pole-pieces  should  be  divided  in  planes  per- 
pendicular to  the  direction  of  the  currents  in  the 
armature  wires. 

Magnet  cores  should  be  divided  in  planes  at 
right  angles  to  the  magnetizing  current. 

Core  of  Cable. — The  conducting  wires  of 
an  electric  cable.  (See  Cable,  Electric?) 

Core,  Open-Magnetic  — Any  mag- 
netic core  so  shaped  that  the  lines  of  magnetic 
force  of  its  field  complete  their  circuit  partly 
through  iron  and  partly  through  air. 

Core  Ratio  of  Cable.— (See  Cable,  Core 
Ratio  of.) 


Core,  Ring1 A  hollow,  cylindrical 

core  of  short  length. 

Core,  Ring,  Elongated A  hollow, 

cylindrical  core  of  comparatively  great  length. 

Core,  Solenoid A  core  so  arranged 

as  to  be  drawn  into  a  solenoid  on  the  passage 
of  the  current  through  its  coils,  and  to  be 
withdrawn  therefrom,  on  the  stopping  of  the 
current  by  the  action  of  a  spring  or  weight. 
(See  Solenoid?) 

Core,    Stranded,    of    Cable The 

conducting  wire  or  core  of  a  cable  formed  of 
a  number  of  separate  conductors  or  wires  in- 
stead of  a  single  conductor  of  the  same  weight 
per  foot  as  the  combined  conductors. 

Core   Transformer. — (See    Transformer, 

Core.} 

Cored  Carbons. — (See  Carbons,  Cored.) 

Cored  Electrodes.— (See  Electrodes, 
Cored.) 

Coronae,  Auroral A  crown-shaped 

appearance,  sometimes  assumed  by  the  auro- 
ral light.  (See  Aurora  JBorealis.) 

Corposant. — A  name  sometimes  given  by 
sailors  to  a  St.  Elmo's  Fire.  (See  Fire,  St. 
Elmo's.) 

Correlation  of  Energy. — (See  Energy, 
Correlation  0f.) 

Corresponding  Points.— (See  Points,  Cor- 
responding?) 

Cosine. — One  of  the  trigonometrical  func- 
tions. (See  Trigonometry?) 

Cotangent. — One  of  the  trigonometrical 
functions.  (See  Trigonometry?) 

Coulomb. — The  unit  of  electrical  quantity. 

A  definite  quantity  or  amount  of  the  thing 
or  effect  called  electricity. 

Such  a  quantity  of  electricity  as  would  pass 
in  one  second  in  a  circuit  whose  resistance  is 
one  ohm,  under  an  electromotive  force  of 
one  volt. 

The  quantity  of  electricity  contained  in  a 
condenser  of  one  farad  capacity,  when  sub- 
jected to  an  electromotive  force  of  one  volt. 

The  quantity  of  electricity  that  flows  per 
second  past  a  cross-section  of  a  conductor 


Con.] 


130 


[Coii. 


conveying  an  ampere.— (Ayrton.)  (See  Am- 
pere.  Farad.  Volt.) 

Coulomb's  Torsion  Balance. — (See  Bal- 
ance, Coulomb's  Torsion.) 

Coulomb-Volt.— A  Joule,  or  .7373  foot- 
pound. 

The  term  is  generally  written  volt-coulomb. 
(See  Volt-Coulomb.) 

Counter,  Electric A  device  for 

counting  and  registering  such  quantities  as 
the  number  of  fares  collected,  gallons  of  water 
pumped,  sheets  of  paper  printed,  revolutions 
of  an  engine  per  second,  votes  polled,  etc. 

Various  electric  devices  are  employed  for  this 
purpose.  They  are  generally  electro-magnetic 
in  character. 

Counter-Electromotive  Force.  —  (See 
Force,  Electromotive,  Counter?) 

Counter  Electromotive  Force  Lightning 
Arrester. — (See  Arrester,  Lightning,  Coun- 
ter-Electromotive Force.) 

Counter-Electromotive  Force  of  Convec- 
tive  Discharge. — (See  Force,  Electromotive, 
Counter,  of  Connective  Discharge?) 

Counter-Electromotive  Force  of  Mutual 
Induction. — (See  Force,  Electromotive, 
Counter,  of  Mutual  Induction?) 

Counter-Electromotive  Force  of  Self-in- 
duction.—(See  Force,  Electromotive,  Coun- 
ter, of  Self -Induction?) 

Counter-Electromotive  Force  of  Self-In- 
duction of  the  Primary.— (See  Force, 
Electromotive,  Counter,  of  Self-Induction  of 
the  Primary?) 

Counter-Electromotive  Force  of  Self-In- 
duction of  the  Secondary.— (See  Force, 
Electromotive,  Counter,  of  Self-induction  of 
the  Secondary?) 

Counter-Electromotive  Force  of  the 
Primary.— (See  Force,  Electromotive, 
Counter,  of  the  Primary?) 

Counter  Inductive  Effect.—  (See  Effect, 
Counter  Inductive?) 

Couple. — In  mechanics,  two  equal  parallel 
forces  acting  in  opposite  directions  but  not  in 
the  same  line,  and  tending  to  cause  rotation. 

The  moment,  or  effective  power  of  a  couple,  is 


equal  to  the  intensity  of  one  of  the  forces  multiplied 
by  the  perpendicular  distance  between  the  direc- 
tions of  the  two  forces. 

Couple,  Astatic  •  —Two  magnets  of 

exactly  equal  strength  so  placed  one  over  the 
other  in  the  same  vertical  plane  as  to  com- 
pletely neutralize  each  other. 

An  astatic  couple  has  no  directive  tendency.  A 
pair  of  magnets  combined  as  an  astatic  couple  is 
called  an  astatic  needle.  (See  Needle,  Astatic.) 

Couple,  Magnetic The  couple  which 

tends  to  turn  a  magnetic  needle,  placed  in  the 
earth's  field,  into  the  plane  of  the  magnetic 
meridian. 

If  a  magnetic  needle  is  in  any  other  position 
than  in  the  magnetic  meridian,  there  will  be  two 
parallel  and  equal  forces  acting  at  A  and  B,  Fig. 
174,  in  the  directions  shown  by  the  arrows. 
Their  effect  will  be  to  ro- 
tate the  needle  until  it 
comes  to  rest  in  the  mag- 
netic meridian  N  S. 

The  total  force  acting 
on  either  pole  of  a  needle 
free  to  move  in  any  direc- 
tion, is  equal  to  the 
strength  of  that  pole  mul- 
tiplied by  the  total  inten- 
sity of  the  earth's  field  at 
that  place  ;  or,  if  free  to  move  in  a  horizontal 
direction  only,  is  equal  to  the  intensity  of  the 
earth's  horizontal  component  of  magnetism  at 
that  place,  multiplied  by  the  strength  of  that  pole. 

The  effective  power  or  moment  of  a  magnetic 
couple  is  equal  to  the  force  exerted  on  one  of  the 
poles  multiplied  by  the  perpendicular  distance, 
P  Q,  between  their  directions. 

Couple,  Moment  of The  effective 

power  or  force  of  a  couple. 

The  moment  of  a  couple  is  equal  to  the  inten- 
sity  of  one  of  the  forces  multiplied  by  the  perpen- 
dicular  distance  between  the  direction  of  the 
forces. 

Couple,  Thermo-Electric Two  dis- 
similar metals  which,  when  connected  at  their 
ends  only,  so  as  to  form  a  completed  electric 
circuit,  will  produce  a  difference  of  potential, 
and  hence  an  electric  current,  when  one  of  the 
ends  is  heated  more  than  the  other. 

Thus  if  a  bar  of  bismuth  be  soldered  to  a  bar 


Fig.  174.    Magnttic 
Couple. 


Con.] 


131 


[Cre. 


of  antimony  the  combination  will  form  a  thermo- 
electric couple,  and  the  circuit  so  formed  will 
have  a  current  passing  through  it  when  one  junc- 
tion is  hotter  or  colder  than  the  other. 

There  is,  according  to  Lodge,  a  true  contact 
force,  at  a  thermo-electric  junction,  as  is  shown  by 
the  reversible  heat  effects  produced  when  an 
electric  current  is  passed  across  such  junction;  for, 
in  one  direction  more  heat  is  produced,  and  in  the 
opposite  direction  less  heat.  This,  as  is  well 
known,  differs  from  the  irreversible  heat  produced 
by  a  current  through  a  homogeneous  metallic 
conductor.  The  reversible  heat  effects,  or  as  they 
are  called  the  Peltier  effects,  may  overpower  and 
conceal  the  heating  effects.  But,  in  addition  to 
these  effects,  since  a  difference  of  potential,  called 
a  Thomson  effect,  exists  in  a  substance  unequally 
heated,  currents  are  so  produced,  and  these  are 
also  influential  in  causing  the  difference  of  poten- 
tial of  a  thermo-electric  couple. 

"  There  are  then,"  says  Lodge,  "  in  a  simple 
circuit  of  two  metals  with  their  junctions  at  differ- 
ent temperatures,  altogether  four  E.  M.  Fs.,  one 
in  each  metal,  from  hot  to  cold,  or  vice  versa,  and 
one  at  each  junction,  and  the  current  which  flows 
around  such  a  circuit  is  propelled  by  the  resultant 
of  these  four."  *  *  *  "These  four  forces, 
two  Thomson  forces  in  the  metals,  and  two  Peltier 
forces  at  their  junctions,  may  some  of  them  help 
and  some  hinder  the  current. "  *  *  *  "When- 
ever they  help,  the  locality  is  to  that  extent  cooled ; 
whenever  they  hinder,  it  is  to  that  extent 
warmed." 

The  action  of  a  thermo-electric  couple  in  pro- 
ducing a  difference  of  potential  is  therefore  a 
complicated  one,  and  depends  on  Peltier  and 
Thomson  effects,  as  well  as  on  the  thermo-electric 
effect.  (See  Effect,  Peltier.  Effect,  Thomson. 
Effect,  Tkermo-Electric.) 

Couple,  Yoltaic Two  materials, 

usually  two  dissimilar  metals,  capable  of 
acting  as  an  electric  source  when  dipped  in 
an  electrolyte,  or  capable  of  producing  a 
difference  of  electric  potential  by  mere  con- 
tact. 

Liquids  and  gases  are  capable  of  acting  as 
voltaic  couples. 

All  voltaic  cells  have  two  metals,  or  a  metal  and 
a  metalloid,  or  two  gaseous  or  liquid  substances 
which  are  of  such  a  character  that,  when  dipped 
into  the  exciting  fluid  one  only  is  chemically 
acted  on. 


Each  one  of  these  two  substances  is  called  an 
element  of  the  cell,  and  the  two  taken  collectively 
form  a  voltaic  couple. 

The  elements  of  a  voltaic  couple  may  consist  of 
two  gases  or  two  liquids.  (See  Battery,  Gas.) 

Coupled  Cells.— (See  Cells,  Coupled) 

Coupler,  Yoltaic Any  device  by 

means  of  which  voltaic  cells  may  be  readily 
coupled  or  connected  in  different  forms  of 
circuits.  (See  Circuits,  Varieties  of) 

Coupling  of  Voltaic  Cells  or  Other 
Electric  Sources. — A  term  indicating  the 
manner  in  which  a  number  of  separate 
electric  sources  may  be  connected  so  as  to 
form  a  single  source.  (See  Circuits,  Varie- 
ties of) 

Cramp,  Telegrapher's An  affec- 
tion of  the  hand  of  a  telegrapher  due  to  im- 
moderate and  excessive  use  of  the  same 
muscles,  somewhat  similar  to  the  disease 
known  as  writer's  cramp. 

Telegrapher's  cramp,  like  writer's  cramp,  may 
be  defined  as  a  professional  neurosis  of  co-ordina- 
tion. It  appears  not  only  in  certain  groups  of 
muscles,  but  is  limited  to  such  groups,  only  when 
they  are  performing  certain  complicated  opera- 
tions. For  example,  telegrapher's  cramp  is 
practically  a  paralysis  of  certain  muscles  of  the 
hand  and  wrist  of  the  operator.  These  muscles, 
when  called  on  to  perform  the  somewhat  delicate 
movements  required  in  sending  a  telegraphic  dis- 
patch, are  incapable  of  performing  their  proper 
functions,  but  when  called  on  to  perform  in  part 
other  similar  actions,  provided  all  these  actions 
are  not  required  to  be  used,  appear  to  be  un- 
affected. 

The  ability  of  the  operator  to  send  with  either 
hand  would  lessen  the  liability  to  this  disease. 

Crater  in  Positive  Carbon. — A  depression 
at  the  end  of  the  positive  carbon  of  an  arc 
lamp  which  appears  when  a  voltaic  arc  is 
formed.  (See  Arc,  Voltaic?) 

Creep,  Diffusion The  flow  of  an 

electric  current  in  portions  of  a  conducting 
substance,  outside  the  parts  that  lie  in  the 
direct  lines  between  the  points  where  the 
terminals  of  the  same  are  applied  to  the  con- 
ducting substance. 


Oe.J  132 

Creeping,  Electric A  term  some- 
times applied  to  the  creeping  of  a  current. 
(See  Current,  Creeping  of.) 

Creeping  in  Yoltaic  Cell.— (See  Cell,  Vol- 
taic, Creeping  in.) 

Creeping  of  Current. — (See  Current, 
Creeping  of,  Electric.) 

Creeping,  Saline The  formation 

of  salts  by  efflorescence  on  the  walls  of  a  solid 
immersed  in  a  solution  of  a  salt. 

Creosoting. — A  process  employed  for  the 
preservation  of  wood,  as,  for  example,  tele- 
graph poles,  by  injecting  creosote  into  the 
pores  of  the  wood.  (See  Pole,  Telegraphic.) 

Crith. — A  term  proposed  by  A.  W.  Hoff- 
man, as  a  unit  of  weight,  or  the  weight  of 
one  litre,  or  cubic  decimetre,  of  hydrogen  at 
O^  C.  and  760  mm.  barometric  pressure. 

Critical  Current.  —  (See  Current^  Crit- 
ical.) 
Critical    Current  of  a   Dynamo.— (See 

Current,  Critical,  of  a  Dynamo^ 

Critical  Distance  of  Lateral  Discharge 
through  Alternative  Path.— (See  Distance, 
Critical,  of  Lateral  Discharge  through 
an  Alternative  Path.) 

Critical  Speed  of  Compound-Wound  Dy- 
namo.—(See  Speed,  Critical,  of  Compound- 
Wound  Dynamo.) 

Crookes'  Dark  Space.— (See  Space,  Dark, 
Crookes'.) 

Crookes'  Electric  Radiometer.— (See  Ra- 
diometer, Electric,  Crookes'?) 

Cross  Arm. — (See  Arm,  Cress.) 

Cross-Connecting  Board. — (See  Board, 
Cross-Connecting?) 

Cross,  Electric A  connection,  gen- 
erally metallic,  accidentally  established  be- 
tween two  conducting  lines. 

A  defect  in  a  telegraph,  telephone  or  other 
circuit  caused  by  two  wires  coming  into 
contact  by  crossing  each  other. 

A  swinging  or  intermittent  cross  is  caused  by 
wires,  which  are  too  slack,  being  occasional^ 
blown  into  contact  by  the  wind. 


[Cro. 

A  weather  cross  arises  from  defective  action  ot 
the  insulators  in  wet  weather. 

Cross,  Swinging  or  Intermittent 

An  accidental  contact,  generally  metallic, 
caused  by  wires  being  brought  into  occasional 
contact  with  one  another,  or  with  some  other 
conductor,  by  the  intermittent  action  of  the 
wind. 

Cross,  Weather A  contact  or  leak 

occurring  in  a  telegraphic  or  other  line  dur- 
ing wet  weather,  from  the  defective  action  of 
the  insulators. 

Crossing  Cleat— (See  Cleat,  Crossing.) 

Crossing,  Live-Trolley A  device 

whereby  a  trolley  moving  over  a  line  that 
crosses  a  second  line  at  an  angle  is  enabled 
to  maintain  its  electrical  connection  with  the 
line  while  crossing. 

A  live-trolley  crossing  is  necessitated  where  one 
line  of  electric  railway  crosses  another.  The 
upper  line  must,  of  course,  provide  a  space  or 
opening  for  crossing  the  lower  line  at  the  points 
of  intersection.  This  is  effected  in  the  Bagnall 
live-trolley  crossing,  shown  in  Fig.  175,  by  attach - 


Fig'175-  Livt- Trolley  Crossing. 
ing  to  the  upper  trolley  wire  a  bridge  piece  of 
light  lathe  casting,  provided  at  its  centre  with  a 
gap  through  which  the  trolley  wire  passes.  This 
bridge  piece  is  insulated  from  the  trolley  wire  by 
means  of  a  disc  of  insulating  material  at  the  cen- 
tre of  the  bridge,  which  is  provided  with  a  hinged 
curved  lever,  that  in  its  normal  position  rests  un- 
der the  influence  of  gravity  in  the  position  shown 
in  the  figure.  The  passage  of  the  trolley  wheel 
along  the  wire  carries  the  line  under  it  and  thus 
bridges  the  gap,  as  shown  by  the  position  of  the 
dotted  lines. 

Crossing  Wires. — (See  Wires,  Crossing.) 

Cross-Over   Block.— (See   Slock,    Cross- 
Over.) 

Cross-Over,  Trolley A  device  by 

means  of  which  a  trolley  is  enabled  to  pass 
over  the  points  where  different  lines  cross  one 
another  without  serious  interruption. 


Cro.] 


133 


[Cur. 


A  trolley  cross-over,  for  trolley  lines,  is  shown 
in  Fig.  176. 


Fig.  176.     Trolley  Cross  Over. 

Crow-foot  Zinc.— (See  Zinc,  Crow-foot.') 

Crucible,  Electric A  crucible  in 

which  the  heat  of  the  voltaic  arc,  or  of  elec- 
tric incandescence,  is  employed  either  to  per- 
form difficult  fusions,  or  for  the  purpose  of 
effecting  the  reduction  of  metals  from  their 
cres  or  the  formation  of  alloys.  (See  Fur- 
nace, Electric?) 

Crystal.— A  solid  body  bounded  by  sym- 
metrically disposed  plane  surfaces. 

A  definite  form  or  shape  is  as  characteristic  of 
an  inorganic  crystalline  substance  as  it  is  of  an 
animal  or  plant.  Each  substance  has  a  form  in 
which  it  generally  occurs.  There  are,  however, 
certain  modifications  of  the  typical  forms  which 
cause  plane  surfaces  to  appear  curved,  and  the 
eymmetrical  airangement  of  the  faces  to  disap 
pear.  These  modifications  often  render  it  ex 
tremely  difficult  to  recognize  the  true  typical 
fornv 

For  the  different  fundamental  crystalline  forms, 
or  systems  of  crystals,  see  any  standard  work  on 
chemistry. 

Crystal,    Heniihedral   —A   crystal 

whose  shape  or  form  has  been  modified  by 
the  replacement  of  half  its  edges  or  solid 
angles, 

A  hemihedral  crystal  possesses  different  forms 
at  the  ends  or  extremities  of  its  axes.  Hemi 
hedral  Crystals,  when  unequally  heated,  develop 
electrical  charges. 

Electricity  produced  in  this  way  was  formerly 
called  pyro-electricity.  (See  Electricity,  Pyro.) 

Crystal,   Holohedral    —A    crystal 

whose  shape  or  form  has  been  modified  by 
the  replacement  of  all  its  edges  or  solid 
angles. 

Crystalline  Electro-Metallurgical  De- 
posit.—(See  Deposit.  Crystalline.  Electro- 
Met  allurgic  al.) 

Crystallization.— Solidification  from  a  state 
of  solution  or  fusion  in  a  definite  crystalline 
:orm 


The  crystallization  of  a  dissolved  solid  is  fa- 
vored by  any  cause  that  gives  increased  freedom 
of  movement  to  its  molecules,  such  for  example  as 
solution,  fusion,  sublimation,  or  precipitation, 

Crystallization  by  Electrolytical  Decom- 
position.— The  crystalline  deposition  of  vari- 
ous metals  by  the  passage  of  an  electric  cur- 
rent through  solutions  of  their  salts  under 
certain  conditions. 

A  strip  of  zinc  immersed  in  a  solution  of  sugar 
of  lead  (acetate  of  lead)  soon  becomes  covered 
with  bright  metallic  plates  of  lead,  that  are  elec- 
trolytically  deposited  by  the  weak  currents  due  to 
minute  voltaic  couples  formed  with  the  zinc  by 
particles  of  iron,  carbon,  or  other  impurities  in 
the  zinc.  The  deposit  assumes  at  times  a  tree- 
like growth,  and  is  therefore  called  a  lead  tree. 
(See  Couple,  Voltaic.} 

Crystallization,  Ele«tro  — —  —Crystalli- 
zation effected  during  elect  rolytic  deposition. 

Crystallize.— To  separate  from  a  liquid 
or  vapor,  in  the  form  of  a  crystalline  solid. 

Crystalloid.— Those  portions  of  a  mixed 
substance  subjected  to  dialysis,  that  are  capa- 
ble of  crystallization.  (See  Dialysis.) 

Cube,  Faraday's  —An  insulated 

room  cubic  in  shape,  covered  on  the  inside 
with  tin  foil,  which,  when  charged  on  the 
outside  gives  no  indications  to  an  observer  on 
the  inside,  though  furnished  with  delicate  in- 
struments. 

Faraday's  cube  illustrates  the  fact  that  an  elec- 
trostatic charge  resides  on  the  outside  of  an  insu- 
lated conductor.  (See  Net,  Faraday* s.) 

Cup,  Mercury A  cup  or  cavity 

filled  with  mercury  and  connected  with  the 
pole  of  an  electric  apparatus  for  the  ready 
placing  of  the  same  in  circuit  with  other  elec- 
tric apparatus. 

To  connect  apparatus  it  is  only  necessary  to 
insert  the  free  terminal  of  one  apparatus  in  the 
mercury  cup  of  the  other. 

Cup,  Porous A  porous  cell.  (See 

Cell,  Porous) 

Curb,  Double A  device  for  in- 
creasing the  speed  of  signaling,  by  means  of 
which  the  line  is  rid  of  its  charge  before  the 
next  signal  is  sent,  by  sending  an  opposite 
charge,  then  another  in  the  same  direction, 


Cur.] 


134 


[Cur. 


then  finally  another  in   the  same   direction 
before  connecting  with  the  ground. 

The  effect  of  the  third  charge  is  to  reduce  the 
potential  of  the  line  more  nearly  to  zero  at  the 
end  of  the  signal. 

Curb,  Single A  device  for  in- 
creasing the  speed  of  signaling  telegraphic- 
ally by  ridding  the  line  of  its  previous  charge 
by  sending  a  reversed  current  through  it  be- 
fore connecting  with  the  ground. 

In  single-curb  signaling  the  operator  in  dis- 
charging the  line  before  sending  another  signal 
through  it,  before  putting  the  line  to  earth,  re- 
verses the  battery,  and  then  connects  to  earth. 

Current,  Absolute  Unit  of A  cur- 
rent of  10  amperes.  (See  Ampere.  Units, 
Practical) 

A  current  of  such  a  strength  that  when 
passed  through  a  circuit  of  a  centimetre  in 
length  bent  in  the  form  of  an  arc  of  a  circle 
one  centimetre  in  radius,  will  act  with  the 
force  of  a  dyne  on  a  magnetic  pole  of  unit 
strength,  placed  at  the  centre  of  the  arc. 

The  ampere,  the  practical  unit  of  current,  is 
but  ^5  the  value  of  the  absolute  unit  of  current. 

Current,  Action  of,  on  a  Magnetic  Pole 
An  attraction  or  repulsion  depend- 
ent on  the  name  of  the  pole  and  the  direction 
of  the  current. 

Two  currents  of  electricity  attract  or  repel  each 
other  according  to  the  direction  in  which  they 
are  flowing,  and  the  mutual  positions  of  their 
circuits.  A  current  and  a  magnetic  pole  exert  an 
action  on  each  other  which,  strictly  speaking,  is 
neither  attraction  nor  repulsion,  but  which  is  ro- 
tation, that  may,  however,  be  regarded  as  being 
produced  by  the  combined  action  of  attraction 
and  repulsion. 

Current,  Alternating A  current 

which  flows  alternately  in  opposite  directions. 

A  current  whose  direction  is  rapidly  re- 
versed. 

The  non-commuted  currents  generated  by  the 
differences  of  potential  in  the  armature  of  a 
dynamo-electric  machine  are  alternating  or 
simple-periodic-currents. 

In  a  characteristic  curve  of  the  electromotive 
forces  of  alternating  currents,  positive  electro- 
motive forces,  or  those  that  would  produce  cur- 


rents in   a  certain  direction,   are  indicated  by 
values  above  a  horizontal  line,  and  negative  elec- 
tromotive forces,  by  values  below  the  line. 
The  curves  A  B  C,  and  C  D  E,  Fig.  177,  are 

B 


Fig.  177.     Curve  of  Electromotive  Forces  of  Alternating 
-Currents. 

often  called  phases,  and  represent  the  alternate 
phases  of  the  current. 

Current,  Alternative   —A  voltaic 

alternative.    (See  Alternatives,  Voltaic.) 
Current,    Assumed   Direction   of  Flow 

of The  direction  the  current  is  as- 
sumed to  take,  z*.  e.,  from  the  positive  pole  of 
the  source  through  the  circuit  to  the  negative 
pole  of  the  source. 

The  electricity  is  assumed  to  come  out  of  the 
source  at  its  positive  pole,  and  to  return  or  flow 
back  into  the  source  at  its  negative  pole.  This 
convention  as  to  the  direction  of  the  electric  cur- 
rent is  in  accordance  with  the  assumption  of  the 
direction  of  flow  of  lines  of  magnetic  forces. 

The  old  idea'of  a  dual  or  double  current  flowing 
in  opposite  directions  is  still  maintained  by  some. 
(See  Force,  Lines  of,  Direction  of.) 

Current,  Axial In  electro-thera- 
peutics a  current  flowing  in  a  nerve  in  the 
opposite  direction  to  the  normal  impulse  in 
the  nerve. 

Current,  Break-Induced The  cur- 
rent induced  by  a  current  in  its  own,  or  in 
another  circuit,  on  breaking  or  opening  the 
same. 

The  current  induced  in  the  secondary  on 
the  breaking  of  the  primary  circuit. 

The  break-induced  current  set  up  by  a  current 
in  its  own  circuit  is  sometimes  called  the  direct- 
induced  current. 

Lord  Rayleigh  has  shown  that  within  certain 
limits  the  break-induced  current  has  a  greater 
effect  in  magnetizing  steel  needles,  the  smaller 
the  number  of  turns  of  wire  in  the  secondary.  In 


Cur.] 


135 


[Cur. 


the  case  of  a  galvanometer,  it  is  well  known  that 
the  opposite  is  true.  The  deflection  of  the  gal- 
vanometer needle  depends  on  the  strength  of  the 
whole  current.  The  magnetizing  power  depends, 
for  the  greater  part,  on  the  strength  of  the  cur- 
rent at  the  beginning  of  its  formation. 

Current,  Closed-Circular A  cur- 
rent flowing  in  a  circular  circuit. 

A  small  closed-circular  current  may  be  replaced 
magnetically  by  a  thin  disc  of  steel,  magnetized  in 
a  direction  perpendicular  to  its  lace,  and  the  edge 
of  which  corresponds  to  the  edge  of  the  circular 
conductor. 

Current-Commuter.  —  (See  Commuter, 
Current?) 

Current,  Conduction —The  current 

that  passes  through  a  metallic  or  other  con- 
ducting substance,  as  contradistinguished 
from  a  current  produced  in  a  non-conductor 
or  dielectric.  (See  Current,  Displacement) 

Current,  Constant A  current  that 

continues  to  flow  in  the  same  direction  for 
some  time  without  varying  in  strength, 

This  term  is  sometimes  used  to  mean  a  con 
tinuous  or  direct  current  m  contradistinction  to 
an  alternating  current,  but  it  ought  to  be  applied 
only  to  unvarying  currents,  such,  for  example  as 
a  constant  current  of  10  ampdres. 

Current,  Continuous —An  electric 

current  which  flows  in  one  and  the  same 
direction. 

Although  the  term  continuous  current  is  used 
as  synonymous  with  constant  current,  it  is  not 
entirely  so;  a  continuous  current  flows  constantly 
in  the  same  direction.  A  constant  current  not 
only  flows  continuously  in  the  same  direction,  but 
maintains  an  approximately  constant  current 
strength 

This  term  continuous  current  is  used  in  the 
opposite  sense  to  alternating  current,  and  in  the 
same  sense  as  a  direct  current. 

Current,  Creeping  of  Electric 

A  change  in  the  direction  of  path  of  a  current 
from  the  direct  line  between  the  points  of 
connection  with  the  source. 

When  the  terminals  of  any  electric  source  are 
placed  in  contact  with  any  two  points  of  a  metallic 
sheet  of  conducting  material,  the  flow  of  the  cur- 
rent is  not  confined  to  the  direct  line  between  the 


points  of  contact,  but  creeps  or  diffuses  into  por- 
tions of  the  conducting  plate  surrounding  this 
direct  line.  (See  Current ',  Diffusion  of.) 

In  a  somewhat  similar  manner,  the  current 
is  said  to  creep,  or  to  establish  a  partial  short- 
circuit  around  the  poles  of  a  poorly  insulated 
voltaic  battery,  or  other  electric  source. 

Current,    Critical 

— The  current  at  which  a 
certain  result  is  reached, 

Current,  Critical,  of  a 

Dynamo That  value 

of  the  current  at  which  the 

characteristic  curve  begins 

to  depart  from    a    nearly     -^ 

straight  line.  —  (Silvanus  Fig  178.     Critical 

P.    Thompson.}  &**•  &  Dynatno 

In   Fig.    178    the    critical 

current  is  shown  in  three  different  cases,  as  oc- 
curring where  the  dotted  vertical  line  cuts  the 
characteristic  curves. 

The  speed  at  which  a  series  dynamo  excites 
itself  is  often  called  the  critical  speed. 

Current,    Demarcation  — A    term 

sometimes  applied  to  an  electric  current  ob- 
tained from  an  injured  muscle. 

"  Every  injury  of  a  muscle  or  nerve  causes  at 
the  point  of  injury  a  dying  surface,  which  benaves 
negatively  to  the  positive  intact  substance." — 
(Landois  dr»  Stirling.) 

Current  Density. — The  current  of  elec- 
tricity which  passes  in  any  part  of  a  circuit  as 
compared  with  the  area  of  cross-section  of 
that  part  of  the  circuit. 

In  a  dynamo- electric  machine  the  current  den- 
sity in  the  armature  wire  should  not,  according  to 
Silvanus  P.  Thompson,  exceed  2,500  ampdres 
per  square  inch  of  area  of  transverse  section  of 
conductor. 

The  current  density  in  a  dynamo  wire,  of 
necessity  depends  on  the  sectional  area  of  the 
coils.  If,  for  example,  a  current  of  50  ampdres 
be  safe  in  an  armature  section  of  eight  tu.us  it 
may  be  safely  increased  to  100  amperes  ii  the 
conductors  are  cross-  sectioned  so  as  to  make  but 
four  turns. — (Urquhart.) 

In  electro-plating,  for  every  definite  current 
strength  that  passes  through  the  bath,  or  in  other 
words,  for  a  definite  number  of  coulombs,  a 
definite  weight  of  metal  is  deposited,  the  charac- 


Cor.] 


136 


[Cur: 


ter  of  which  depends  on  the  current  density.  The 
character  of  an  electrolytic  deposit  will  therefore 
depend  on  the  current  density  at  that  part  of  the 
circuit  where  the  deposit  occurs. 

-The  following  table  from  Urquhart  gives  the 
practical  working  value  for  the  current  density 
for  electro-metallurgical  deposits  : 

CURRENT   DENSITY    (OR    AMPERES    ON 
CATHODE). 

Amperes 
Solution  of  per  square  foot. 

Copper,  acid  bath 5 . o  to  10.0 

Copper,  cyanide  bath 3.0  "     5.0 

Silver,  double  cyanide 2.0  "      5.0 

Gold,  chloride  in  cyanide i.o  "     2.0 

Nickel,  double  sulphate 6.0  "     8.0 

Brass,  cyanide 2.0  "     3.0 

Tin 

Current,  Diacritical  -  —Such  a 
strength  of  the  magnetizing  current  as  pro- 
duces a  magnetization  of  an  iron  core  equal 
to  half-saturation. 

The  diacritical  current  is  the  current  which, 
flowing  through  the  diacritical  number  of  ampere- 
turns,  will  bring  up  the  magnetism  produced  to 
half -saturation. 

The  diacritical  number  of  ampere-turns  is  such 
a  number  of  ampere-turns  as  would  reduce  the 
magnetic  permeability  to  half  its  iull  value. 

Current,  Diffusion  of A  term  em- 
ployed to  designate  the  difference  in  the 
density  of  current  in  different  portions  of  a 
conductor.  (See  Current,  Creeping  of,  Elec- 
tric.) 

Current,  Diffusion  of  Electro-Therapeu- 

fic The  difference  in  the  density  of 

current  in  different  portions  of  the  human 
body  between  the  electro-therapeutic  elec- 
trodes. 

When  the  electrodes  are  placed  at  any  two 
given  points  of  the  human  body,  the  current 
branches  through  various  paths,  extending  in  a 
general  direction  from  one  electrode  to  the  other, 
according  to  the  law  of  branched  or  derived  cir- 
cuits, and  flowing  in  greater  amount,  or  with 
greater  density  of  current,  tlirough  the  relatively 
better  conducting  paths.  (See  Current  Density.) 

This  is  sometimes  called  the  creeping  of  the 
current.  (See  Current,  Creeping  of  .) 

Current,  Direct  — A  current  con- 


stant in  direction,  as  distinguished  from  an 
alternating  current. 

A  continuous  current. 

Current,  Direct-Induced  —  — The  cur- 
rent induced  in  a  circuit  by  induction  on  it- 
self, or  self-induction,  on  breaking  or  opening 
the  circuit.  (See  Currents,  Extra?) 

This  is  called  the  direct-induced  current  because 
its  direction  is  in  the  same  direction  as  the  induc- 
ing current. 

Current,  Direction  of—  —The  direc- 
tion an  electric  current  is  assumed  to  take 
out  from  one  pole  of  any  source  through  the 
circuit  and  its  translating  devices  back  to  the 
source  through  its  other  pole. 

Conventionally,  the  current  is  assumed  to  come 
out  from  the  positive  pole  of  the  source  and  to  go 
back  to  the  source  at  the  negative  pole. 

Current,  Displacement  —  — The  rate 
of  change  of  electric  displacement. 

A  brief  conduction  current  produced  in  a 
dielectric  by  an  electric  displacement.  (See 
Displacement,  Electric?) 

This  is  called  a  displacement  current  in  order 
to  distinguish  it  from  a  conduction  current  in  any 
conductor. 

The  displacement  current  continues  while  the 
displacement  of  electricity  is  going  on.  Dis- 
placement currents  have  all  the  properties  of  con- 
duction currents,  and,  like  the  latter,  produce  a 
magnetic  field;  in  fact,  they  resemble  extremely 
brief  conduction  currents. 

The  difference  between  conducting  substances 
and  dielectrics,  lies  in  the  fact  that  the  conducting 
substances  do  not  possess  an  elastic  force,  en- 
abling them  to  resist  electric  displacement.  In 
other  words,  conducting  substances  possess  no 
electric  elasticity,  and  can  have  no  true  displace- 
ment current  established  in  them.  (See  Elasti- 
city, E let  trie.} 

A  displacement  current,  like  a  conduction  cur- 
rent, possesses  a  magnetic  field,  or  is  encircled  by 
lines  of  magnetic  force.  (See  Field,  Magnetic,  of 
an  Electric  Current. ) 

Current,  Electric  —  —The  quantity  of 
electricity  which  passes  per  second  through 
any  conductor  or  circuit. 

The  rate  at  which  a  definite  quantity  of  elec- 
tricity passes  or  flows  through  a  conductor  or 
circuit. 


Car.] 


137 


[Cur. 


The  ratio  existing  between  the  electro- 
motive force,  causing  the  current,  and  the 
resistance  which  may,  for  convenience,  be 
regarded  as  opposing  it,  expressed  in  terms 
of  quantity  of  electricity  per  second. 

The  unit  of  current,  or  the  ampere,  is  equal  to 
one  coulomb  per  second.  (See  Ampere.  Coulomb. ) 

The  word  current  must  not  be  confounded 
with  the  mere  act  of  flowing;  electric  current 
signifies  rate  of  flow,  and  always  supposes  an 
electromotive  force  to  produce  the  current,  and  a 
resistance  to  oppose  it. 

The  electric  current  is  assumed  to  flow  out 
from  the  positive  terminal  of  a  source^  through 
the  circuit  and  back  into  the  source  at  the  nega- 
tive terminal.  It  is  assumed  to  flow  into  the 
positive  terminal  of  an  electro-receptive  device 
such  as  a  lamp,  motor,  or  storage  battery,  and 
out  of  its  negative  terminal ;  or,  in  other  words, 
the  positive  pole  of  the  source  is  always  con- 
nected to  the  positive  terminal  of  the  electro-re- 
ceptive device. 

Professor  Lodge  draws  the  following  com- 
parison between  the  motions  of  ordinary  mat- 
ter, heat  and  electricity:  "Consider  the  modes 
in  which  water  may  be  made  to  move  from  place 
to  place;  there  are  only  two.  It  may  be  pumped 
along  pipes,  or  it  may  be  carried  about  in  jugs. 
In  other  words,  it  may  travel  through  matter,  or, 
it  may  travel  with  matter.  Just  so  it  is  with  heat, 
also.  Heat  can  travel  in  two  ways:  it  can  flow 
through  matter,  by  what  is  called  '  conduction, ' 
or,  it  can  travel  with  matter,  by  what  is  called 
'convection.'  There  is  no  other  mode  of  con- 
veyance of  heat."  *  *  *  "For  electricity 
the  same  is  true.  Electricity  can  travel  with 
matter,  or  it  can  travel  through  matter,  by  con- 
vection, or  by  conduction,  and  by  no  other  way." 

In  the  above,  the  radiation  of  heat  is  apparently 
lost  sight  of. 

In  the  opinion  of  some,  an  electric  current  con- 
sists of  two  distinct  currents,  one  of  positive  and 
the  other  of  negative  electricity,  flowing  in  oppo- 
site directions.  Each  of  these  currents  is  supposed 
to  be  equal  in  amount  to  the  other. 

The  electric  current  is  now  regarded  as  passing 
through  the  dielectric  surrounding  the  conductor, 
rather  than  through  the  conductor  itself.  (See 
Current,  Electric,  Method  of  Propagation  of, 
Through  a  Circuit.') 

The  current  that  flows  or  passes  in  any  circuit 
is,  in  the  case  of  a  constant  current,  equal  to  the 


electromotive    force,    or  difference    of  potential, 
divided  by  the  resistance,  as— 


f.  See  Law  of  Ohm.) 

Current,  Electric,  Method  of  Propagation 

of,  Through  a  Circuit When  an 

electric  current  is  propagated  through  a  wire 
or  other  conductor,  it  is  not  sent  or  pushed 
through  the  conductor,  like  a  fluid  through 
a  pipe  or  other  conductor,  but  is,  so  to  speak, 
rained  down  on  the  surface  of  the  conductor 
from  the  medium  or  dielectric  surrounding  it. 

Poynting,  who  has  carefully  studied  this  mat- 
ter, remarks  as  follows,  viz.:  "A  space  contain- 
ing electrical  currents  may  be  regarded  as  the 
field  where  energy  is  transformed  at  certain  points 
into  the  electric  or  magnetic  kind,  by  means  of 
batteries,  dynamos,  thermopiles,  etc.,  and  in 
other  parts  of  the  field  this  energy  is  being  again 
transformed  into  heat,  work  done  by  the  electro- 
magnetic forces,  or  any  other  form  yielded  by 
currents. 

"Formerly  the  current  was  regarded  as  some- 
thing traveling  in  the  conductor,  and  the  energy 
which  appeared  at  any  part  of  the  circuit  was 
supposed  to  be  conveyed  thither  through  the 
conductor  by  the  current  But  the  existence  of  in- 
duced currents  and  electro-magnetic  actions  have 
led  us  to  look  on  the  medium  surrounding  the 
conductor  as  playing  a  very  important  part  in  the 
development  of  the  phenomena.  If  we  believe  in 
the  continuity  of  the  motion  of  energy,  we  are 
forced  to  conclude  that  the  surrounding  medium 
is  capable  of  containing  energy,  and  that  it  is 
capable  of  being  transferred  from  point  to  point. 
We  are  thus  led  to  consider  the  problem,  how 
does  the  energy  about  an  electric  current  pass 
from  point  to  point;  by  what  paths  does  it  travel, 
and  according  to  what  laws?  Let  us  take  a  spe- 
cific case.  Suppose  a  dynamo  at  one  spot  gen- 
erates an  electric  current,  which  is  made  to  operate 
an  electric  motor  at  a  distant  place.  We  have 
here,  in  the  first  place,  an  absorption  of  energy 
from  the  prime  motor  into  the  dynamo.  We  find 
the  whole  space  between  and  around  the  conduct- 
ing wires  magnetized  and  the  seat  of  electro- 
magnetic energy.  We  have  further  a  retrans- 
formation  of  energy  in  the  motor.  The  question 
which  presents  itself  for  solution  is  to  decide  how 
the  energy  taken  up  by  the  dynamo  is  trans- 
mitted to  the  motor,  by  what  path  it  travels 


Cur.] 


138 


[Cur. 


and  according  to  what  laws  ?  Briefly  stated,  the 
tendency  of  recent  views  is  that  this  energy  is 
conveyed  through  the  electro-magnetic  medium 
or  ether,  and  that  the  function  of  the  wire  is  to 
localize  the  direction  or  to  concentrate  the  flow  in 
a  particular  path,  and  thus  provide  a  sink  or  place 
in  which  the  energy  can  be  dissipated.  *  *  *  " 

Taking  again,  for  instance,  the  case  of  the  dis- 
charge of  a  condenser  by  a  conductor.  He  says: 
"Before  the  discharge  we  know  that  the  energy 
resides  in  the  dielectric,  between  the  conducting 
plates.  If  these  plates  are  connected  by  a  wire, 
according  to  these  views,  the  energy  is  transferred 
outwards  along  the  electrostatic,  equipotential  sur- 
faces, and  moves  on  to  the  wire  and  is  there  con- 
verted into  heat.  According  to  this  view  we 
must  suppose  the  lines  of  electrostatic  induction, 
running  from  plate  to  plate,  to  move  outwards,  as 
the  dielectric  strain  lessens,  and  while  still  keep- 
ing their  ends  on  the  plates,  to  finally  converge 
in  on  the  wire  and  be  there  broken  up  and  their 
energy  dissipated  as  heat." 

In  other  words,  some  of  the  energy  of  the  ex- 
panding lines  of  induction  is  changed  into  mag- 
netic energy;  this  energy  is  contained  in  ring- 
shaped  tubes  of  force,  which  expand  outwards 
from  between  the  plates  and  then  contract  on 
some  other  part  of  the  conductor. 

The  time  of  the  discharge,  then,  consists  of  the 
following  steps,  viz. : 

(I.)  The  time  during  which  the  energy  of  the 
charge  is  nearly  all  electrostatic  and  is  repre- 
sented by  the  energy  contained  in  the  lines  or 
tubes  of  electrostatic  induction,  running  from 
plate  to  plate  of  the  condenser. 

(2.)  The  time  during  which  the  discharge  is  at 
its  maximum  and  the  energy  consists  of  two  parts, 
viz.:  energy  associated  with  the  outward  ex- 
panding lines  of  electrostatic  induction,  and  energy 
associated  with  the  closed  lines  or  tubes  of  mag- 
netic force,  which  at  first  are  expanding  and  after- 
wards contracting. 

(3.)  The  time  when  the  energy  has  been  ab- 
sorbed, or  the  period  in  which  the  energy  in  the 
wire  or  the  conductor  has  either  been  dissipated 
in  the  form  of  non -luminous  radiation  or  obscure 
heat. 

(4.)  The  time  during  which  this  non-luminous 
heat  gives  up  its  energy  again  to  the  surrounding 
medium  in  the  shape  of  heat  waves. 

Current,  Electro-Therapeutic  Polarizing 

The    current    which    produces    the 


phenomena  of  electrotonus.  (See  Electro- 
tonus.) 

Current,  Element  of A  term 

employed  in  mathematical  discussions  to  in- 
dicate a  very  small  part  of  a  current  for  ease 
in  considering  its  action  on  a  magnetic  needle 
or  other  similar  body. 

Current,  Faradic In  electro- 
therapeutics, the  current  produced  by  an  in- 
duction coil,  or  by  a  magneto-electric  machine. 

A  rapidly  alternating  current,  as  distin- 
guished from  a  uniform  voltaic  current. 

A  voltaic  current  that  is  rapidly  alternated  by 
means  of  any  suitable  key  or  switch  is  sometimes 
called  a  voltaic  alternative.  The  discharge  from 
a  Holtz  machine  is  sometimes  called  a  Franklinic 
Current.  (See  Alternatives,  Voltaic.  Current, 
Franklinic.} 

Current  •  Filaments.  —  (See  Filament, 
Current) 

Current,  Franklinic —A  term  some- 
times used  in  electro-therapeutics  for  a  cur- 
rent produced  by  the  action  of  a  frictional 
electric  machine. 

The  term,  Franklinic  current,  is  used  in  con- 
tradistinction to  Faradic  current,  or  that  produced 
by  induction  coils,  or,  in  contradistinction  to  a 
galvanic  or  voltaic  current,  or  that  produced  by 
a  voltaic  battery. 

Current,  Generation  of,  by  Dynamo-Elec- 
tric Machine  — The  difference  of 

potential  developed  in  the  armature  coils 
by  the  cutting  of  the  lines  of  magnetic 
force  of  the  field  by  the  coils,  during  the  rota- 
tion of  the  armature. 

If  a  loop  of  wire  whose  ends  are  connected  to 
the  two-part  commutator,  shown  in  Fig.  179,  be 
A 


Fig.  ifQ.    Induction  in  Armature  Loop. 

rotated  in  the  magnetic  field  between  the  magnet 
poles  N  and  S,  in  the  direction  of  the  large  arrow, 
differences  of  potential  will  be  generated  which 


Car,] 


139 


[Cur. 


will  cause  currents  to  flow  in  the  direction  indi- 
cated by  the  small  arrows  during  its  motion  past 
the  north  pole  from  the  top  to  the  bottom,  but  in  the 
opposite  direction  during  its  motion  past  the  south 
pole — from  the  bottom  to  the  top.  If,  now,  col- 
lecting brushes  rest  on  the  commutator  in  the 
positions  shown  in  the  Fig.  1 80.  the  vertical  line 
—18P1... 


Fig.  180.    Action  of  Commutator. 

of  the  gap  between  the  poles  corresponding  with 
the  vertical  gap  between  the  commutator  seg- 
ments, the  currents  generated  in  the  loop  will  be 
caused  to  flow  in  one  and  the  same  direction,  and 
B',  will  become  the  positive  brush,  since  the  end 
of  the  loop  is  connected  with  it  only  so  long  as  it 
is  positive.  As  soon  as  it  becomes  negative,  from 
the  current  in  the  loop  flowing  in  the  opposite 
direction,  the  other  end,  which  is  then  positive, 
is  connected  with  the  positive  brush. 

A  similar  series  of  changes  occur  at  the  nega- 
tive brush  B. 

Theoretically,  the  neutral  points,  where  the 
brushes  rest,  would  be  in  the  vertical  line  coincid  - 
ing  with  that  of  the  gap  between  the  poles.  An 
inspection  of  the  figure  shows  that  the  neutral 
line,  or  the  diameter  of  commutation,  is  dis- 
placed in  the  direction  of  rotation.  (See  Commu- 
tation, Diameter  of.)  The  displacement  of  the 
brushes,  so  necessitated,  is  called  the  lead. 

The  cause  of  the  lead  is  the  reaction  that  occurs 
between  the  magnetic  poles  of  the  field  magnets 


Fig  i8r  Cause  of  Lead  of  Brushes. 
and  those  of  the  armature,  the  result  of  which  is 
to  displace  the  field  magnet  poles,  and  to  cause  a 
change  in  the  density  in  the  field.  This  is  shown 
in  Fig.  181,  where  the  density  of  the  lines  offeree 
indicates  the  position  of  the  diameter  of  commu- 


tation as  being  near,  or  at  right  angles  to  the  di- 
ameter of  greatest  average  magnetic  density. 
(See  Lead,  Angle  of.  Lag,  Angle  of.) 

Current-Governor. — (See  Governor,  Cur- 
rent.) 

Current,  Homogeneous  Distribution  of 

Such  a  distribution  of  a  current  through 

any  conductor  in  which  there  is  an  equal 
density  of  current  at  all  portions  of  any 
cross-section  of  the  conductor. 

When  the  flow  of  a  constant  current  is  estab- 
lished in  a  solid  conducting  wire,  there  is  a 
homogeneous  distribution  of  current  in  that  con- 
ductor. 

Current,  Induced  — The  current 

produced  in  a  conductor  by  cutting  lines  of 
force. 

The  induced  current  results  from  differences  of 
potential  produced  by  electro-dynamic  induction. 
(See  Induction,  Electro- Dynamic.) 

Current  •  Induction.  —  (See  Induction, 
Current.) 

Current,  Intensity  of An  old 

term  sometimes  employed  to  indicate  the 
current  which  resulted  from  a  considerable 
difference  of  potential,  or  a  great  electromotive 
force. 

This  term  was  also  formerly  used  as  synony- 
mous with  strength  of  current. 

This  use  of  the  term  is  now  abandoned. 

Voltaic  batteries,  connected  in  series  so  as  to 
give  a  considerable  difference  of  potential,  were 
spoken  of  as  being  connected  for  intensity. 

This  term  has  also  been  used  for  the  quantity 
of  electricity  conveyed  per  second  across  a  unit 
area  of  cross -section. 

Intensity  of  current  is  more  properly  called 
density  of  current.  (See  Current  Density.) 

Current,  Intermittent A  current 

that  does  not  flow  continually,  but  which  flows 
and  ceases  to  flow  at  intervals,  so  that  elec- 
tricity is  practically  alternately  present  and 
absent  from  the  circuit. 

Current,  Inverse-Secondary The 

make-induced  current.  (See  Current,  Make- 
Induced?) 

Current.  Jacobi's  Unit  of -—Such 

a  current  that  when  passed  through  a  volta- 
meter will  liberate  a  cubic  centimetre  of 


Cur.J 


140 


[Cur. 


oxygen  and  hydrogen  at  O  degrees  C.  and 
760  mm.  barometric  pressure. 

One   Tacobi's    unit    of  current   equals    

10.32 
ampere.     (Obsolete.) 

Current,  Make-Induced  —The 

current  induced  by  a  current  in  its  own  circuit 
on  making  or  closing  the  same. 

The  current  produced  in  the  secondary  of 
an  induction  coil  on  the  making  or  com- 
pletion of  the  circuit  of  the  primary. 

The  make-induced  current  is  also  called  the 
inverse-secondary  current,  because  its  direction 
is  opposite  to  that  of  the  inducing  current. 

Current,  Make  or  Break  Induced,  Dura- 
tion of The  time  during  which  the 

induced  inverse  or  direct -secondary  currents 
continue. 

Blaserna  made  a  number  of  experiments,  which 
he  claims  shows  : 

(i.)  The  greater  the  distance  apart  of  the  pri- 
mary and  the  secondary,  that  is,  the  less  their 
mutual-induction,  the  less  the  maximum  value  of 
the  secondary  current,  and  the  greater  the  delay 
in  establishing  that  maximum. 

(2.)  The  delay  in  establishing  the  maximum  of 
the  break  or  direct -secondary  current  is  not  as 
great  as  in  the  case  of  the  make,  or  inverse-sec- 
ondary  current. 

(3.)  When  the  coils  are  near  together,  the  in- 
duced currents  at  starting  are  established  by  a 
series  of  electric  oscillations. 

(4  )  The  primary  current  establishes  itself  by  a 
series  of  electrical  oscillations. 

(5.)  That  the  interposition  of  dielectric  sub 
stances,  such  as  glass  between  ^.he  coils,  reduces 
the  time  between  tht  making  or  breaking  of  the 
primary  current  and  the  beginning  of  the  sec- 
ondary current.  This  last  conclusion  was  nega 
tived  by  some  experiments  of  Bernstein, 

Blaserna  determined  in  the  case  of  certain  ex  - 
periments  the  following  value  for  the  durations  of 
the  secondary  currents : 

In  verse -secondary  current  lasts  .000485  second. 

Direct -secondary  current  lasts  .000275  second. 

Helmholtz  contradicts  the  results  of  Blaserna, 
and  asserts  : 

(I.)  That  no  perceptible  difference  in  the  zero 
points  of  the  currents  is  produced  by  varying 
the  distance  between  the  primary  and  secondary . 

(2.)  That  the  sparks  produced  by  the  breaking 


of  the  primary  last  for  an  appreciable  time,  some 


thing  like  T545ff  to 


a  second. 


(3.)  The  duration  of  the  break-spark  is  never 
constant,  but  depends  in  great  part  on  the  amount 
of  platinum  given  off  from  the  contacts  at  each 
spark. 

Current-  Meter.—  A  form  of  galvanometer. 
(See  Galvanometer,} 

Current,  Momentary  -  —A  current 
that  continues  to  flow  but  for  a  short  time. 

Current,  Multi-Phase  -  —A  rotating 
current,  (See  Current,  Rotating.) 

Current,  Muscle  --  In  electro-thera- 
peutics, the  current  flowing  through  a  muscle. 

Muscle  currents  are  produced  either  by  stimu 
lation,  or  during  activity  of  a  muscle.  According 
to  L.  Hermann,  uninjured  muscles,  or  perfectly 
dead  muscles,  yield  no  currents,  but  such  cur- 
rents result  only  from  an  injury.  (See  Current, 
Demarcation  .  ) 

Current,  Non-  Homogeneous  Distribution 

of  -  —Such  a  distribution  of  current  pass- 
ing through  a  conductor  in  which  there  is  an 
unequal  density  of  current  at  all  portions  of 
any  cross-section  of  the  conductor. 

When  a  rapidly  alternating  current  is  passed 
through  any  solid  conductor,  the  current  density 
is  greater  at  the  surface  and  less  towards  the 
centre.  The  current  distribution  in  such  a  con  • 
ductor  is  non  homogeneous,  and  the  want  of  uni 
formity  of  current  density  is  greater  as  the  rapid 
ity  of  alternation  or  periodicity  is  greater. 

Current,  Outgoing  -  —The  current 
sent  out  over  the  line  from  a  station  provided 
with  a  duple  <  or  quadruplex  transmission,  as 
distinguished  from  the  received  current.  (See 
Current,  Received?) 

Current,  Periodic  -  —A  simple 
periodic  current.  (See  Currents,  Simple 
Periodic!) 

Current,  Periodic,  Power  of  --  An 

amount  of  work,  per  second,  equal  to  the 
product  of  the  electromotive  force  taken  at 
successive  moments  of  time  during  a  com- 
plete cycle,  multiplied  by  the  current  strength 
taken  at  the  corresponding  moments  during 
the  cycle. 
Since  the  electromotive  force  and  current  in 


Cur.] 


141 


[Cur. 


a  periodic  circuit  may  be  represented  by  two 
simple  harmonic  functions,  the  mean  value  of 
the  two,  when  of  different  amplitude  and  phase, 
is  equal  to  the  product  of  their  maximum  value 
by  the  cosine  of  their  difference  of  phase  divided 
by  two. 

Current,  Polarization In  electro- 
therapeutics, the  constant  current  which  when 
passed  through  a  nerve  produces  in  it  the 
electrotonic  stite.  (See  Elecfrolonus.} 

Current.  Pulsating A  pulsatory 

current.  (See  Current,  Pulsatory?) 

Current,  Pulsatory A  current,  the 

strength  of  which  changes  suddenly. 

The  pulsatory  current  usually  consists  of  sudden 
and  distinct  impulses,  or  rushes  of  current,  in 
contradistinction  to  an  undulatory  or  harmonically 
varying  current. 

Current,  Received The  current 

received  from  the  distant  end  of  the  line  at  a 
station  provided  with  a  duplex  or  quadruplex 
transmission  as  distinguished  from  the  out- 
going current. 

A  term  sometimes  used  in  telegraphy  to 
distinguish  between  currents  that  come  in  over 
the  line  from  a  distant  station,  and  those 
that  are  sent  out  to  a  distant  station. 

Current.  Rectilinear A  current 

flowing  through  straight  or  rectilinear  por- 
tions of  a  circuit. 

In  studying  the  effects  of  the  attractions  or  repul- 
sions produced  by  electric  currents  the  name  ex- 
pressing the  peculiarity  of  shape  of  any  part  of 
the  circuit  is  often  applied  to  the  current  flowing 
through  that  part  of  the  circuit.  Thus  we  speak 
of  a  rectilinear  current,  a  sinuous  current. 

Current,    Reverse-Induced  — -  — The 

current  induced  by  a  current  in  its  own  cir- 
cuit at  the  moment  of  making  or  closing  the 
circuit. 

The  current  induced  in  the  secondary  on 
closing  or  making  the  circuit  of  the  primary. 

This  is  called  the  reverse-induced  current,  be- 
cause its  direction  is  opposite  to  that  of  the  current 
in  the  inducing  circuit. 

Current,  Reversed A  current  whose 

direction  is  changed  at  intervals.  (See  Cur- 
rent, Alternating.} 


Current  Reverser.— (See  Reverser,  Cur- 
rent.} 

Current,  Reversing  a Changing  the 

direction  of  an  electric  current. 

Current,  Rotating A  term  applied 

to  the  current  which  results  by  combin- 
ing a  number  of  alternating  currents,  whose 
phases  are  displaced  with  respect  to  one  an- 
other. 

A  rotating  current  is  sometimes  called  a  poly- 
phase or  multiple-phase  current,  particularly  if 
there  are  three  or  more  currents  combined. 

The  rotating  current  is  employed  by  Tesla, 
Dobrowolsky  and  others  in  a  system  of  distribu- 
tion by  transformers  in  place  of  the  ordinary 
alternating  current.  In  practice,  three  alternating 
current  are  combined.  The  currents  and  their 
combination  are  obtained  by  means  of  a  specially 
constructed  alternator.  When  three  currents  are 
combined  the  displacement  between  each  set  of 
phases  is  120  degrees.  A  rotating  current,  unlike 
an  alternating  current,  possesses,  in  a  certain 
sense,  a  definite  direction  of  flow.  Its  effect  on  a 
magnetic  needle  is  to  cause  rotation.  Hence 
motors  constructed  on  the  principle  of  rotating 
currents  will  start  with  a  load. 

Current,    Rotatory  •  Phase  •  Alternating 

A  term    sometimes   employed  for   a 

rotating  electric  current.  (See  Current,  Ro- 
tating^) 

Current,  Secretion  •  — In  electro- 
therapeutics, a  current  following  stimulation 
of  the  secretory  nerves. 

Current,  Simple-Harmonic A  term 

sometimes  used  instead  of  simple-periodic 
current.  (See  Currents,  Simple  Periodic.} 

Current,  Sinuous A  term  some- 
times applied  to  currents  flowing  through  a 
sinuous  conductor. 

Sinuous  currents  exert  the  same  effects  of  attrac- 
tion or  repulsion  on  magnets,  or  on  neighboring 
circuits,  as  would  a  rectilinear  current  whose 
length  is  that  of  the  axis  of  such  sinuous  current. 

This  can  be  shown  by  approaching  the  circuit 
A'  B',  Fig.  182,  consisting  of  the  sinuous  con- 
ductor A',  and  rectilinear  conductor  B',  to  the 
movable  conductor  A  B  C,  on  which  it  produces 
no  effect.  The  current  A',  therefore,  neutral- 


Car.] 


142 


[Cur. 


izes  the  effects  of  the  current  B';  or,  it  is  equal  to 
it  in  effect. 


Fif.  182.    Rectilinear  Equivalent  of  Sinuous  Current. 

In  calculating  the  effects  of  sinuous  currents  it 
is  convenient  to  consider  them  as  consisting  of  a 


Fig.  183.    Sinuous  Currents. 
succession  of  short,  straight  portions  at  right  an- 
gles  to  one  another,  as  shown  in  Fig.  183. 

Current,  Steady A  current  whose 

strength  does  not  vary  from  time  to  time. 

In  a  steady  current  the  quantity  of  electricity 
flowing  through  each  unit  of  area  of  the  equi- 
potential  surface  of  the  conductor  is  the  same  for 
each  succeeding  interval  of  time.  Such  a  current 
is  sometimes  called  a  uniformly  distributed  cur- 
rent. 

Current  Streamlets.— (See  Streamlets, 
Current^ 

Current  Strength.— The  product  obtained 
by  dividing  the  electromotive  force  by  the 
resistance. 

The  current  strength  for  a  constant  current 
according  to  Ohm's  law  is— 

r_E 
C_R. 


Current  strength  is  proportional  to  the  amount 
of  the  magnetic  or  chemical  (electrolytic)  effects 
it  is  capable  of  producing. 

For  a  simple-periodic  current,  the  current 
strength  necessarily  varies  from  time  to  time. 

The  average  current  strength  of  a  simple- 
periodic  current  is  equal  to  the  average  impressed 
electromotive  force  divided  by  the  impedance. 
(See  Impedance. ) 

The  maximum  current  strength  is  equal  to  the 
maximum  impressed  electromotive  force  divided 
by  the  impedance. 

Current,    to    Transform    a To 

change  the  electromotive  force  of  a  current 
by  its  passage  through  a  converter, or  trans- 
former. 

To  convert  a  current. 

Current,  Transforming  a Chang- 
ing the  electromotive  force  of  a  current  by  its 
passage  through  a  converter  or  transformer. 

Current,    Undulating An   undu- 

latory  current.     (See  Currents,  Undulatory^ 

Current,  Uniformly-Distributed . 

A  term  sometimes  employed  in  the  same 
sense  as  steady  current.  (See  Current. 
Steady.) 

Current,  Unit  Strength  of Such 

a  strength  of  current  that  when  passed 
through  a  circuit  one  centimetre  in  length, 
arranged  in  an  arc  one  centimetre  in  radius, 
•will  exert  a  force  of  one  dyne  on  a  unit  mag- 
net pole  placed  at  the  centre. 

This  absolute  unit  is  equal  to  ten  amperes  or 
practical  units  of  current  (See  Ampere.) 

Current,    Variable    Period     of 

The  period  which  exists  while  an  electric 
current  is  being  increased  or  decreased  in 
strength,  or  while  it  is  being  reversed. 

Currents,  Action Physiological  cur- 
rents obtained  during  the  activity  of  a  muscle 
or  nerve. 

Currents,  After In  electro-thera- 
peutics, currents  produced  in  nervous  or 
muscular  tissue  when  a  constant  current, 
which  has  been  flowing  through  the  same, 
has  been  stopped. 

After  currents  are  due  to  internal  polarization. 

Currents,    Alternating-Primary — 

The  currents  employed  in  the  primary  of  a 


Cur.] 


143 


[Cnr. 


transformer  to  induce  alternating  currents  in 
the  secondary.  (See  Transformer) 

Currents,  Alternating-Secondary 

The  currents  induced  in  the  secondary  of  a 
transformer  by  the  alternating  currents  in  the 
primary.  (See  Transformer) 

Currents,  Alternating,  Shifting  of  Phase 

of (See  Phase,  Shifting  of,  of  Alter- 
nating Currents?) 

Currents,  Ampdrian The  electric 

currents  that  are  assumed  in  the  amperian 
theory  of  magnetism  to  flow  around  the  mole- 
cules of  a  magnet.  (See  Magnetism,  Amperes 
Theory  of.) 

The  amperian  currents  are  to  be  distinguished 
from  the  eddy,  Foucault,  or  parasitical  currents, 
since,  unlike  them,  they  are  directed  so  as  to  pro 
duce  useful  effects.  (See  Currents,  Eddy.) 

It  is  not  believed  that  the  amperian  currents 
are  produced  in  magnetizable  substances  by  the 
act  of  magnetization.  The  atoms  or  molecules 
were  magnetic  originally.  All  the  magnetizing 
force  does  is  to  arrange  the  molecules  or  atoms, 
or  to  set  them  in  one  and  the  same  direction. 

Currents,  Angular Currents  flow- 
ing through  circuits  that  cross  or  are  inclined 
to  one  another  at  any  angle,  (See  Dynamics, 
Electro) 

Currents,  Atomic A  term  some- 
times used  instead  of  molecular  or  amp&rian 
currents.  (See  Currents,  Amperian) 

Currents,   Attractions    and    Repulsions 

Of The  mutual  attractions  or  repul- 
sions exerted  by  currents  on  one  another 
through  the  interaction  of  their  magnetic 
fields.  (See  Dynamics,  Electro?) 

Currents,  Commuted Electric  cur- 
rents that  have  been  caused  to  flow  in  one 
and  the  same  direction.  (See  Commutator) 

Currents,  Commuting  — Causing 

several  currents  to  flow  in  one  and  the  same 
direction. 

Currents,  Component The  two  or 

more  currents  into  which  it  may  be  conceived 
that  a  single  current  can  be  divided,  so  as 
to  produce  the  same  effects  of  attraction  or 
repulsion  that  the  single  current  would  do. 


The  idea  of  component  currents  is  based  on  the 
similar  idea  of  the  components  of  any  single 
force. 

Currents,  Continuity  of The 

freedom  from  variation  in  current  strength  or 
current  direction. 

Currents,  Convection  — Currents 

produced  by  the  bodily  carrying  forward  of 
static  charges  in  convection  streams.  (See 
Streams,  Convection) 

In  a  convection  current,  the  static  charge  is-- 
bodily  carried  forward. 

Rowland  has  shown  experimentally  that  a. 
moving  electric  charge  is  the  equivalent  of  an 
electric  current.  He  rotated  a  gilded  ebonite 
disc  between  two  gilt  glass  discs,  near  which 
were  placed  a  number  of  delicate  magnetic 
needles.  When  certain  rapidity  of  rotation  was 
obtained,  the  discs  were  found  to  affect  the  mag- 
netic needles  the  same  as  would  a  current  of  elec- 
tricity flowing  in  a  circular  conductor,  whose- 
form  coincided  with  the  periphery  of  the  disc. 

Currents,  Converted Electric  cur- 
rents changed  either  in  their  electromotive 
force  or  in  their  strength,  by  passage  through 
a  converter  or  transformer.  (See  Trans- 
former) 

Currents,  Converting Changing 

the  electromotive  force  of  currents  by  their 
passage  through  a  converter  or  transformer. 
(See  Transformer) 

Currents,  Diaphragm Electric  cur- 
rents produced  by  forcing  a  liquid  through 
the  capillary  pores  of  a  diaphragm.  (See 
Osmose,  Electric) 

Currents,  Earth Electric  currents 

flowing  through  the  earth,  caused  by  a  differ- 
ence of  potential  at  different  parts. 

The  causes  of  these  differences  of  potential  are 
various  and  are  not  well  understood. 

Currents,  Eddy Useless  currents 

produced  in  the  pole  pieces,  armatures,  field- 
magnet  cores  of  dynamo-electric  machines  or 
motors,  or  other  metallic  masses,  either  by 
their  motion  through  magnetic  fields,  or  by 
variations  in  the  strength  of  electric  currents 
flowing  near  them. 

Sensible  eddy  currents  are  producd  in  the  mass 


Cnr.l 


144 


U'ur. 


of  the  conducting  wire  on  the  armature  of  a 
dynamo-electric  machine  when  the  wire  is  com- 
paratively heavy. 

Such  currents  are  called  eddy  currents,  local 
currents,  Foucault  currents^  or  parasitical  cur- 
rents. They  form  closed -circuits  of  comparatively 
low  resistance,  and  tend  to  cause  undue  heating  of 
armatures  or  pole  pieces.  They  not  only  cause  a 


Fig.  184.    Foveautt  Currents  in  PoCe  Pieces. 

useless  expenditure  of  energy,  but  interfere  with 
the  proper  operation  of  the  device. 

To  reduce  them  as  far  as  practicable,  the  pole 
pieces,  armature  cores  or  armature  wires,  are 
laminated.  (See  Core,  Lamination  of.) 

These  local  currents  are  perhaps  preferably 
called  Foucault  currents  when  they  take  place 
in  magnetic  cores,  pole  pieces  or  armature 
cores,  and  eddy  currents  when  they  occur  in  the 
armature  wire  or  conductor.  When  the  armature 
conductor  is  made  up  of  copper  bars,  for  exam- 
ple, the  eddy  currents  in  the  latter  are  usually 
considerable. 

Since  Foucault  currents  in  dynamo-electric  ma- 
chine cores  are  due  to  variations  in  the  magnetic 


Fig.  rSj.    Fouca»U  Currents  in  Pole  Pieces. 


strength  of  the  field  magnets,  or  of  the  arma- 
ture, they  will  be  of  greatest  intensity  when  the 
changes  in  the  magnetic  strength  are  the  greatest 
and  most  sudden. 

These  changes  are  most  marked,  and  conse- 
quently the  Foucault  currents  are  strongest  at  those 
corners  of  the  pole  pieces  of  a  dynamo  from  which 
the  armature  is  moved  in  its  rotation,  as  will  be 
seen  from  an  inspection  of  Fig.  184. 

Fig.  185,  shows  Foucault  currents  generated  in 
pole  pieces. 


Currents,    Eddy-Conduction —A 

term  employed  for  ordinary  eddy  currents  in 
conductors,  in  order  to  distinguish  them  from 
eddy-displacement  currents.  (See  Currents, 
Eddy-Displacement?) 

Currents,  Eddy  Deep  Seated Eddy 

currents  set  up  in  the  mass  of  a  conductor  sub- 
jected to  electro-dynamic  induction  in  con- 
tradistinction to  superficially  seated  eddy  cur- 
rents. (See  Currents,  Eddy,  Superficial^ 

Currents,    Eddy-Displacement    — 

Eddy  currents  produced  in  the  mass  of  a 
dielectric  or  insulator,  when  lines  of  magnetic 
or  electrostatic  force  pass  through  the  di- 
electric or  insulator. 

Eddy -displacement  currents  are  produced  in 
a  dielectric  or  non-conductor,  when  it  is  moved 
across  a  magnetic  field,  so  as  to  cut  the  lines  of 
magnetic  force. 

Eddy  displacement  currents  would  also  occur 
if  a  dielectric  is  subjected  to  varying  electrostatic 
induction. 

Currents,  Eddy,  Superficial Eddy 

currents  produced  in  conducting  substances 
that  are  limited  to  the  outer  layers  thereof. 

The  eddy  currents  produced  by  alternating 
currents  are  superficial  if  the  alternating  currents 
are  sufficiently  rapid.  The  oscillatory  currents  pro- 
duced during  the  discharge  of  a  Leyden  jar  are 
more  superficial  in  proportion  as  the  discharge 
takes  place  rapidly.  When  currents  are  pro- 
duced in  a  magnetizable  body  by  the  discharge 
of  a  Leyden  jar,  they  are  more  and  more  super- 
ficial, as  the  discharge  of  the  jar  is  more  and  more 
rapid.  The  reason  a  slow  discharge  of  a  jar  or 
condenser  produces  a  greater  magnetizing  effect 
is,  because  of  the  checking  or  screening  action 
the  superficial  eddy  currents  exert  on  the  interior 
of  the  mass  of  the  magnetizable  substance  when 
the  discharge  is  very  rapid. 

Currents,  Electrotonic In  electro- 
therapeutics, currents  due  to  internal  polariza- 
tion in  the  nerve  fibre  between  the  conduct- 
ing core  of  the  nerves  and  the  enclosing 
sheaths. 

Currents,  Extra Currents  pro- 
duced in  a  circuit  by  the  induction  of  the 
current  on  itself  on  the  opening  or  closing  of 


Car.] 


145 


ICur. 


the  circuit.  (See  Currents*  Extra.  Induc- 
tion, Self.) 

The  extra  current  induced  on  breaking,  flows 
in  the  same  direction  as  the  original  current  and 
acts  to  strengthen  and  prolong  it. 

The  extra  current  induced  on  making  or  com- 
pleting a  circuit  flows  in  the  opposite  direction 
to  the  original  current  and  tends  to  oppose  or  re  • 
tard  the  current. 

Both  of  these  currents  are  called  induced  or 
extra  currents.  The  former  is  called  the  direct- 
induced  current,  and  the  latter  the  reversed-in- 
duced  current.  (See  Current,  Direct-Induced. 
Current ',  Reversed-Induced.*) 

In  order  to  distinguish  this  induction  from  that 
produced  in  a  neighboring  conductor  by  the  pas- 
sage of  the  electric  current,  it  is  called  selj -induc- 
tion. (See  Induction,  Self.  Induction,  Afutttal.) 

The  effect  on  a  telegraphic  line  of  the  self-in- 
duced or  extra  currents  is  to  decrease  the  speed  ot 
signaling  by  retarding  the  beginning  of  a  signal, 
and  prolonging  its  cessation . 

The  greater  the  number  of  turns  of  wire  in  a 
circuit,  or  magnet,  and  the  greater  the  mass  of 
iron  in  its  core,  the  greater  the  strength  of  the 
extra  currents. 

Currents,  Foucault •  — A  name  some- 
times applied  to  eddy  currents,  especially  m 
armature  cores.  (See  Currents,  Eddy!) 

Currents,  Heating  Effects  of The 

heat  produced  by  the  passage  of  an  electric 
current  through  any  circuit.  (See  Heat,  Elec- 
tric) 

Currents,    Imbibition    — Currents 

produced  in  tissues  by  the  imbibition  or  ab- 
sorption of  a  fluid. 

Imbibition  currents  are  a  species  of  diaphragm 
currents.  The  absorption  of  a  fluid  at  the 
demarcation  surface  of  an  injured  nerve  or 
muscle,  or  at  the  contracted  portion  of  muscles, 
produces  imbibition  currents. 

Such  currents  are  also  produced  in  plants  by 

the  movement  of  fluids  produced  by  bending  the 

stalk  or  leaves,  or  by  active  movements  of  certain 

sensitive  plants. 

Currents,  Induced-Molecular  or  Atomic 

Currents    induced   in   the   atoms   or 

molecules  of  a  magnetizable  substance  on  its 
being  brought  into  a  magnetic  field. 

These  currents  are  called  induced-molecular 

or  induced-atomic  currents  in  order  to   distin- 


guish them  from  the  molecular,  atomic  or  amperian 
currents,  or  the  currents  which  are  assumed  to  be 
always"  present.  It  is  by  the  presence  of  these 
assumed  induced-molecular  currents  that  the 
phenomena  of  diamagnetism  are  explained  by 
Weber.  (See  Diamagnetism,  Weber's  Theory 
*f-) 

Currents,  Local A  name  sometimes 

applied  to  eddy  currents.  (See  Currents, 
Eddy.) 

Currents,  Molecular  or  Atomic 

A  term  sometimes  employed  for  amperian 
currents.  (See  Currents,  Amperian.) 

Currents,  Natural A  term  some- 
times applied  to  earth  currents.  (See  Cur- 
rents.  Earth) 

Currents,  Negative A  term  em- 
ployed in  single-needle  telegraphy  for  cur- 
rents sent  over  a  line  in  a  negative  direction 
by  depressing  a  key  that  connects  the  line 
with  the  negative  pole  of  a  battery  and  so 
deflects  the  needle  to  the  left.  (See  Teleg- 
raphy, Single-Needle) 

Currents,  Network  of  — -  — A  term 
sometimes  applied  to  a  number  of  shunt  or 
derived  circuits.  (See  Circuit,  Shunt.  Cir- 
cuit, Derived.  Laws,  Kirchhoff's) 

Currents  of  Motion. — A  term  sometimes 
employed  in  electro-therapeutics  for  the  cur- 
rents of  electricity  that  traverse  healthy 
muscle  or  nerve  tissue  during  the  sudden  con- 
traction or  relaxation  thereof. 

The  existence  of  these  currents  is  denied  by 
some. 

Currents  of  Rest. — A  term  sometimes  em- 
ployed in  electro-therapeutics  for  the  cur- 
rents of  electricity  that  traverse  healthy 
muscle  or  nerve  tissue  while  the  muscles  are 
passive. 

The  existence  of  these  currents  is  denied  by 
some. 

Currents,  Orders  of Induced  elec- 
tric currents  named  from  the  order  in  which 
they  are  induced,  as  currents  of  the  first, 
second,  third,  fourth,  etc.,  orders. 

An  induced  current  can  be  caused  to  induce  an- 
other current  in  a  neighboring  circuit,  and  this  a 
third  current,  and  so  on.  Such  currents  are  dis- 


Cur.] 


146 


[Cur. 


tinguished  by  the  term,  currents  of  the  second, 
third,  fourth,  etc.,  order.  (See  Coils,  Henry's.) 

Currents,  Parasitical A  name 

sometimes  applied  to  eddy  currents.  (See 
Currents,  Eddy.) 

Currents,  Positive A  term  em- 
ployed in  single-needle  telegraphy  for  currents 
sent  over  the  line  in  a  positive  direction  by  de- 
pressing a  key  that  connects  the  line  with 
the  positive  pole  of  a  battery  and  so  deflects 
the  needle  to  the  right.  (See  Telegraphy, 
Single-Needle) 

Currents,  Reversed A  name  some- 
times applied  to  alternating  currents.  (See 
Current,  Alternating.) 

Currents,  Secondary —The  currents 

produced  by  secondary  batteries  in  contra- 
distinction to  the  currents  produced  by 
primary  batteries. 

The  currents  produced  by  the  secondary 
conductor  of  an  induction  coil,  as  distinguished 
from  the  currents  sent  into  the  primaries. 

This  second  use  of  the  term  secondary  current 
is  more  usual. 

Currents,  Self-Induced —A  current 

produced  by  self-induction. 

An  extra  current.  (See  Induction,  Self. 
Currents,  Extra.) 

Currents,  Simple  Periodic Cur- 
rents, the  flow  of  which  is  variable,  both  in 
strength  and  duration,  and  in  which  the  flow 
of  electricity,  passing  any  section  of  the  con- 
ductor, may  be  represented  by  a  simple  peri- 
odic curve. 

A  current  of  such  a  nature  that  the  con- 
tinuous variation  of  the  flow  of  electricity 
past  any  area  of  cross-section  of  the  con- 
ductor, or  the  variations  in  the  electromotive 
force  of  which  can  be  expressed  by  a  simple- 
periodic  or  harmonic  curve.  (See  Curve, 
Simple-Harmonic^) 

Alternate  currents  are  simple-periodic  currents. 

The  average  current  strength  of  simple-periodic 
currents  is  equal  to  the  average  impressed  electro, 
motive  force  divided  by  the  impedance. 

The  transmission  of  rapidly  varying  or  sim- 
ple-periodic currents  through  conductors  differs 
very  greatly  from  the  transmission  of  steady  cur- 


rents. With  a  steady  current,  the  current  density 
is  the  same  for  all  areas  of  cross-section  of  the 
conductor.  For  a  rapidly  intermittent  current, 
the  current  density  is  greater  near  the  surface, 
and  when  the  rate  of  intermission  is  sufficiently 
great,  the  current  is  entirely  absent  at  the  centre 
of  the  conductor. 

Lord  Rayleigh  has  shown  that  when  the  rate  of 
intermission  is  1,050  per  second,  the  effective  re- 
sistance of  a  wire  l6omm.  in  length,  and  30  mm. 
in  diameter,  is  i .  84  times  its  resistance  to  steady 
currents.  He  found  that  the  increase  of  resist- 
ance is  greater  in  the  case  of  conductors  of  great 
diameter  than  in  those  of  small  diameter. 

As  regards  the  character  of  conductor  best 
suited  for  transmitting  rapidly  alternating  cur- 
rents, it  can  be  shown  : 

(I.)  That  for  transmitting  alternate  currents  of 
moderate  frequency,  say  of  about  1,000  per  sec- 
ond, copper  conductors  should  be  used  in  prefer- 
ence to  rods  of  iron. 

(2.)  That  the  conductor  should  be  in  the  form 
of  thin  strips,  or  if  tubular,  of  thin  walls. 

(3.)  That  the  mere  stranding  of  the  conductor, 
*'.  *.,  forming  it  of  separate  insulated  conductors 
connected  in  parallel,  will  be  of  no  effect  in  pre  • 
venting  the  current  from  acting  on  the  outside  of 
the  conductor,  unless  the  conductor  be  arranged 
in  the  form  of  a  cable,  in  which  one  part  forms  a 
lead,  and  another  part  the  return. 

Stephan  draws  the  following  analogy  between 
the  flow  of  alternating  currents  in  a  conductor 
and  the  flow  of  heat  in  a  hot  wire : 

' '  Suppose  a  wire  or  conductor,  uniformly  heated 
from  centre  to  circumference,  be  suddenly  taken 
into  a  space  where  the  temperature  is  high,  the 
outer  portions  of  the  wire  first  rise  in  temperature, 
and  afterwards  the  inner  portions.  In  the  case  of 
a  conductor  of  circular  cross-section,  the  heat 
penetrates  successive  concentric  layers.  The  same 
phenomena  occur  when  an  electromotive  force  is 
suddenly  set  up  between  the  ends  of  a  cylindrical 
conductor.  The  current  gradually  penetrates  the 
conductor  from  the  outside  to  the  centre. 

"  Now  suppose  the  heated  wire  is  carried  into  a 
cooler  space,  the  heat  waves  pass  out  radially 
from  the  centre  towards  the  circumference.  The 
cooling  wire  corresponds  to  the  case  of  a  con- 
ductor in  which  the  external  electromotive  force 
is  suddenly  removed." 

According  to  this  conception,  the  heat  conduct- 
ing power  of  any  substance  corresponds  to  its 
electrical  conducting  power. 


Cnr.] 


147 


[Cur. 


According  to  Stephan,  in  the  case  of  a  con- 
ductor of  iron  of  4  mm.  in  diameter,  traversed  by 
an  alternating  current  of  250  alternations  per 
second,  the  current  density  on  the  surface  is  about 
twenty-five  times  as  great  as  that  at  its  axis. 

Where  the  conductor  is  of  non-magnetic  mate- 
rial, the  difference  in  the  current  density  is  not  so 
marked. 

Rapidly  intermittent  currents  produce  a  real 
increase  in  the  resistance  of  the  conductor,  which 
must  not  be  confused  with  the  fact  that  the  impe- 
dance is  greater  than  the  ohmic  resistance,  but 
rather  as  an  actual  increase  in  the  rate  at  which 
energy  is  dissipated  per  unit  of  current. 

Since  current  density  is  greatest  at  the  outside 
portions  of  a  conductor,  and  the  central  portions 
are  nearly,  if  not  entirely,  deserted  by  the  cur- 
rent, we  may  regard  the  conductor  as  having 
the  ohmic  resistance  of  a  hollow  cylinder  of  the 
same  diameter  as  the  conductor,  with  a  cor- 
respondingly smaller  area  of  cross-section,  and 
therefore,  of  greater  ohmic  resistance  per  unit  of 
length. 

The  condition  of  affairs  in  the  case  of  a  con- 
ductor in  which  a  current  of  electricity  is  begin- 
ning to  flow,  is  now  very  generally  regarded 
somewhat  as  follows,  viz.: 

The  current  begins  at  the  surface  of  the  con- 
ductor, and  more  or  less  slowly  soaks  through 
towards  the  centre.  If  the  current  is  constant,  the 
current  soon  reaches  the  deepest  layers;  but,  if  it 
is  rapidly  intermittent,  before  it  can  soak  very  far 
into  the  conductor  towards  its  axis,  it  is  turned 
back  towards  the  surface,  and  so  becomes  con- 
fined to  layers  which  will  be  more  and  more  super- 
ficial, as  the  rapidity  of  reversal  increases. 

Therefore,  for  convenience,  we  may  regard  a 
solid  conductor,  through  which  a  rapidly  inter- 
mittent current  of  electricity  is  flowing,  as  being 
practically  converted  into  a  hollow  cylinder  of 
the  same  diameter  as  the  solid  conductor,  the 
area  of  cross-section  of  which  hollow  cylinder 
becomes  smaller  and  smaller,  as  the  rapidity  of 
alternation  is  increased. 

Another,  and  perhaps  the  more  correct  concep- 
tion of  the  condition  of  affairs  in  a  solid  conductor 
traversed  by  a  rapidly  alternating  current  of  elec- 
tricity, has  been  pointed  out  by  Maxwell,  and  after- 
wards by  Heavyside,  Rayleigh  and  Hughes.  This 
conception  is  to  regard  the  central  portions  of  the 
conductor  as  possessing  a  counter  electromotive 
force  greater  than  the  outer  portions.  The  entire 
current  flowing  across  any  section  of  a  conductor 


may  be  regarded  as  made  up  of  little  current 
streamlets,  parallel  to  one  another. 

The  central  streamlets,  or  filaments,  from  their 
mutual  induction  on  one  another,  experience  a 
greater  resistance  in  reaching  their  full  strength 
than  the  surface  filaments  do.  Taken  in  this 
sense,  we  may  state  generally  that  the  transmis- 
sion of  rapidly  alternating  currents  through  con- 
ductors depends  on  the  inductance,  rather  than 
on  the  resistance;  but  for  steady  currents,  it  de- 
pends more  on  the  resistance  than  on  the  induct- 
ance. 

In  periodic  or  oscillatory  currents,  as  those 
produced  by  the  discharge  of  a  Leyden  jar,  or 
condenser,  the  surface  streamlets  have  a  current 
density  far  greater  than  the  central  streamlets. 

The  true  or  ohmic  resistance  of  the  circuit  is  a 
minimum  when  the  current  is  uniformly  distrib- 
uted through  all  parts  of  the  cross-section  of  the 
conductor,  and  the  dissipation  of  energy  through 
the  generation  of  heat  is  less  than  for  any  other 
distribution. 

The  conception  of  a  periodic  current  flowing 
through  a  conductor,  starting  from  the  surface 
and  gradually  soaking  in  towards  the  centre, 
regards  the  energy  of  an  electric  current — not  as 
being  pushed  through  the  conductor,  as  water 
through  a  pipe,  but  as  actually  being  absorbed  at 
its  surface,  from  the  surrounding  dielectric,  or  as 
being,  so  to  speak,  rained  down  on  the  conductor 
from  the  space  outside  of  it. 

Currents,  Swelling In  electro- 
therapeutics, currents  that  begin  weak  and  are 
gradually  made  stronger  and  then  weaker. 

Currents,     Swelling-Faradic A 

term  employed  in  electro-therapeutics  for  fara- 
dic  currents  that  are  caused  to  gradually  in- 
crease in  strength  and  then  to  gradually  de- 
crease to  zero  strength. 

Currents, 'Transient Currents  that 

are  but  of  momentary  duration. 

Currents,  Undulatory Currents  the 

strength  and  direction  of  whose  flow  gradually 
change. 

The  term  undulatory  currents  is  used  in  con- 
tradistinction to  pulsatory  currents,  hi  which  the 
strength  changes  suddenly.  In  actual  practice, 
such  currents  differ  from  undulatory  currents 
more  in  degree  than  in  kind,  since,  when  sent 
into  a  line,  the  effects  of  retardation  tend  to 
obliterate,  to  a  greater  or  less  extent,  the  sudden 


Car.] 


148 


[Cur. 


differences  in  intensity  on  which  their  pulsatory 
character  depends. 

The  currents  produced  in  the  coils  of  the  Sie- 
mens magneto-electric  key,  in  which  the  me- 
chanical to-and-fro  motion  of  the  key  sends  elec- 
trical impulses  into  the  line,  are,  in  point  of  fact, 
undulatory  in  character,  when  they  follow  one  an- 
other rapidly. 

The  currents  in  most  dynamo-electric  machines, 
the  number  of  whose  armature  coils  is  compara- 
tively great,  are,  so  far  as  the  variations  in  their 
intensity  or  strength  are  concerned,  undulatory 
in  character  even  when  non--commuted. 

The  currents  on  all  telephone  lines  that  trans- 
mit articulate  speech  are  undulatory.  This  is 
true,  whether  the  transmitter  employed  merely 
varies  the  resistance  by  variations  of  pressure,  or 
actually  employs  makes-and-breaks  that  rapidly 
follow  one  another. — (See  Current,  Pulsatory. 
Current,  Intermittent.) 

Curtain.    Auroral   — A    sheet    of 

auroral  light  having  the  shape  of  a  curtain. 
(See  Aurora  B credits?) 

Curre,  Asymptote  of A  straight 

line  which  continually  approaches  a  curved 
line,  but  meets  or  becomes  tangent  to  such 
curved  line  only  at  an  infinite  distance. 

In  Fig.  186,  the  curve  C  D,  continually  ap- 
proaches the  asymptote  y  z,  but  never  meets  it. 

It  is  at  first  difficult  to  un- 
derstand how   one  line  can 
continually     approach      an- 
other and  yet  never  meet  it. 
But  it  will  be  readily  under- 
stood   if   it    is    remembered    v 
that  in  all  cases  of  asymp-  F*f-  *86> 
totic  approach  each  advance  °f  Curve' 

becomes  smaller  and  smaller. 

This  mathematical  conception  is  like  a  value 
which,  although  constantly  reduced  to  one-half 
of  its  former  value,  is  nevertheless  never  reduced 
to  zero  or  no  value. 

Curve,  Ballistic The  curve  ac- 
tually described  by  a  projectile  thrown  in 
any  other  than  a  vertical  direction  through 
the  air. 

The  path  of  a  projectile  in  a  vacuum  is  a  para- 
bola— that  is,  the  path  A  E  B,  Fig.  187.  In  air, 
the  effects  of  fluid  resistances  cause  the  projectile 
to  take  the  path  A  C  D,  called  a  ballistic  curve. 


The  ballistic  curve  has  a  smaller  vertical  height 
than   the  parabola.     The  projectile  also  has  a 


Fig.  187.    Ballistic  Curve. 

smaller  vertical  range.  Instead  of  reaching  the 
point  B,  it  continually  approaches  the  perpen- 
dicular E  F. 

Curve,  Characteristic A  diagram 

in  which  a  curve  is  employed  to  represent 
the  ratio  of  certain  varying  values. 

The  electromotive  force  generated  in  the  arma- 
ture coils  of  a  dynamo-electric  machine,  when  the 
magnetic  field  is  of  a  constant  intensity,  is  theo- 
retically proportional  to  the  speed  of  rotation.  In 
practice  this  is  modified  by  a  number  of  circum- 
stances. 

The  relation  existing  between  the  speed 
and  electromotive  force  may  be  graphically  rep- 
resented by  referring  the  values  to  two  straight 
lines,  one  horizontal  and  the  other  vertical,  called 
respectively  the  axes  of  abscissas  and  ordinates. 
(See  Abscissas,  Axis  of.}  If,  in  a  given  case,  the 
number  of  revolutions 
is  marked  off  along 

the     horizontal    line  J      ; 

from  the  point  o,  Fig.  I 


RerolutioM. 

Fig.  188.     Charactt 
Curve. 


188,  in  distances  from 
o,  proportional  to  the 
number  of  revolu- 
tions, and  the  corre- 
sponding electromo- 
tive forces  are  marked 
off  along  the  vertical  line  in  distances  from  o, 
proportional  to  the  electromotive  forces,  the 
points  where  these  lines  intersect  will  form  the 
characteristic  curve  as  shown  in  Fig.  188. 

Curre,  Characteristic,  of  Parallel  Trans- 
former   A  curve  so  drawn  that  its 

ordinate  and  abscissa  at  any  point  represent 
the  secondary  electromotive  force  and  the  sec- 
ondary current  of  a  multiple  connected  trans- 
former, when  the  resistance  of  the  secondary 
circuit  has  a  certain  definite  value. 

With  a  constant  electromotive  force  in  the  pri- 


Car.] 


149 


[Car. 


mary  circuit,  i.  e.,  with  the  transformers  in  parallel, 
the  characteristic  curve  is  a  straight  line  parallel 
to  the  axis  of  the  current.  This  curve,  as  shown 
in  Fig.  189,  is  practically  a  straight  line.  The  par- 
allel transformer  will  be 
practically  self-  regulatin  g 
under  a  constant  primary 
electromotive  force. 

According  to  Forbes,  if  Q' jj X 

a  transformer  has  its  lamp  p^gf  fg9.  character- 
load  in  parallel  with  the  istir  of  Parallel  Trans- 
secondary  circuit,  the  ex-  former. 
tinction  of  its  lamps  will  decrease  the  efficiency 
of  the  transformer.  The  efficiency  is  therefore 
less  for  light  loads  than  for  heavy  loads  of  parallel 
lamps  up  to  a  certain  point. 

Curre,  Characteristic,  of  Series  Trans- 
former  A  curve  so  drawn  that  its 

ordinate  and  abscissa  at  any  point  represent 
the  secondary  electromotive  force  and  second- 
ary current  of  a  series-connected  transformer, 
when  the  resistance  of  the  secondary  current 
has  a  certain  definite  value. 

Fig.   190  shows  characteristic  curve  of  a  series 


Fig.  i  go.     Characteristic  of  Series  Transformer. 

transformer.  O  a,  is  drawn  perpendicular  to  the 
line  representing  the  secondary  current,  and  a  b, 
perpendicular  to  O  a,  represents  the  correspond- 
ing secondary  electromotive  force.  The  various 
positions  of  b,  as  different  values  are  given  to  O  a, 
produce  the  elliptic  curve  which  is  the  character- 
istic curve  of  the  series  transformer. 

"  A  series  transformer, "  says  Fleming,  "with 
a  core  sufficiently  large  to  avoid  saturation,  can 
never  be  self-regulating  if  so  used.  It  can  only 
be  made  self-regulating  with  a  non  saturated  core, 
when  working  near  the  extremities  of  its  charac- 
teristic, either  with  a  small  secondary  current 
or  a  low  electromotive  force.  Both  of  these  con- 
ditions are  uncommercial." 

Curre,  Life,  of  Incandescent  Lamp 


—A  curve  in  which  the  life  of  an  electric 
lamp  is  represented  by  means  of  abscissas  and 
ordinates  proportional  to  the  life  in  hours  and 
the  candle-power  or  the  volts  respectively. 

Carre,  Logarithmic A  curve  in 

which  the  rate  of  increase  or  decrease  of  the 
ordinate  is  proportional  to  the  ordinate  itself. 

On  the  line  O  X,  Fig.  191,  mark  off  the  time 
Y- 


in  lengths,  reckoned  from  O.  Represent  the 
current  strength  by  lines  drawn  vertically  to  the 

jr 
time-line.     Let  O  Y,  equal  C  =  g- 

Applying  the  electromotive  force,  the  current 
grows  in  the  wire  as  represented  by  the  graphic 
curve. 

According  to  Fleming,  the  growth  of  this  cur- 
rent takes  place  according  to  the  following  law, 
viz. :  ' '  The  current  strength  at  any  instant, 
added  to  the  rate  of  growth  of  the  current  strength 
at  that  instant  multiplied  by  the  time-constant,  is 
equal  to  the  current  which  would  exist  if  induc- 
tion were  zero." 

Carve,  Permeability A  curve  repre- 
senting the  magnetic  permeability  of  a  mag- 
netic substance. 

There  is  a  certain  temperature  for  every  para- 
magnetic substance,  at  which  its  permeability  is 
no  greater  than  that  of  air.  This  temperature 
for  iron  is  reached  at  about  750  degrees  C. ;  for 
nickel,  at  about  400  degrees  C. 

Carve,      Simple-Harmonic   — The 

curve  which  results  when  a  simple-harmonic 
motion  in  one  line  is  compounded  with  a  uni- 
form motion  in  a  straight  line,  at  right  angles 
thereto. 

A  harmonic  curve  is  sometimes  called  a  curve 
of  sines,  because  the  abscissas  of  the  curve  are 
proportional  to  the  times,  while  the  ordinates  are 
proportional  to  the  sines  of  the  angles,  which  are 
themselves  proportional  to  the  times. 


Car.] 


150 


[Cut. 


Curves,  IsocluLsmeu Curves  drawn 

on  the  earth's  surface  between  zones  having 
equal  frequency  of  auroral  discharges. 

The  isochasmen  curves  are  nearly  at  right 
angles  to  the  magnetic  meridian. 

Curves,    Magnetic   — Curved    lines 

showing  the  direction  of  the  lines  of  mag- 
netic force  in  any  field,  formed  by  sprinkling 
iron  filings  on  a  sheet  of  paper  or  glass  held 
in  the  field  of  a  magnet,  and  gently  tapping 
the  support  so  as  to  permit  the  filing*  to  prop- 
-erly  arrange  themselves.  (See  Figures, 
Magnetic?) 

Cut-In,  To To  introduce  an  electro- 
receptive  device  into  the  circuit  of  an  electric 
source  by  completing  or  making  the  circuit 
through  it. 

Cut-Off,  Automatic  Gas A  device 

for  automatically  cutting  out  the  battery 
from  an  electric  gas-lighting  circuit  on  the 
accidental  grounding  of  the  circuit. 

Unless  the  battery  is  disconnected  from  the  cir- 
cuit on  the  establishing  of  a  ground,  the  battery 
will  polarize  and  soon  become  useless. 

Cut-Out,   A A  device  by  means  of 

which  an  electro-receptive  device  or  loop  may 
'be  thrown  out  of  the  circuit  of  an  electric 
source. 

In  any  system  of  light  or  power  distribution,  a 
cut-out  is  generally  placed  outside  a  building 
into  which  a  loop  or  branch  of  the  main  circuit 
runs,  so  as  to  permit  that  loop  or  branch  to  be 
readily  disconnected  therefrom.  In  the  same  way 
cut-out  keys  or  switches  are  generally  placed  in 
the  circuit  of  the  loop  and  each  electro-receptive 
device. 

Cut-Out,  Air-Space A    modified 

form  of  paper  cut-out,  in  which  the  disc  of 
paper  or  mica  is  replaced  by  the  resistance  of 
an  air-space. 

Although  the  resistance  of  an  air-space  is  so 
high  as  to  be  practically  immeasurable,  yet  it  is 
overcome  or  broken  by  a  much  lower  differ- 
ence  of  potential  than  an  equal  thickness  of 
paper  or  mica.  (See  Path,  Alternative.  Cut- 
Out,  Film.) 


Cut-Out,  Automatic Any  device 

that  will  automatically  cut-out,  or  remove,  a 
translating  device,  or  an  electric  source,  from 
an  electric  circuit,  whenever  any  predeter- 
mined effect  is  produced. 

Cut-Out,  Automatic,  for  Multiple-Con- 
nected Electro-Receptive  Devices 

A  device  for  automatically  cutting  an  electro- 
receptive  device,  such  as  a  lamp,  out  of  the 
circuit  of  the  leads. 

Automatic  cut-outs  for  incandescent  lamps, 
when  connected  to  the  leads  in  multiple-arc,  con- 
sist of  strips  of  readily  melted  metal  called  safety 
/uses,  which  on  the  passage  of  an  excessive  cur- 
rent fuse,  and  thus  automatically  break  the  cir« 


Fif.  f<?2.    Ceiling  Cut- Out. 

cuit   in    that    particular   branch.      (See    Catck, 
Safety.) 

A  form  of  ceiling  cut-out,  made  of  porcelain,  is 
shown  in  Fig.  192,  with  the  two  halves  separated 


Fif.  193.    Ceiling  Cut-Out. 

to  show  interior  details,  and  in  Fig.  193,  with  the 
two  halves  placed  together. 


CntJ 


151 


[Cyc. 


Cut-Oat,  Automatic,  for  Series-Connected 

Electro-Beceptire  Devices A  device 

whereby  an  electro-receptive  device,  such 
as  an  electric  arc  lamp,  is,  to  all  intents  and 
purposes,  automatically  cut  out,  or  removed 
from  the  circuit,  by  means  of  a  shunt  of  low 
resistance,  which  permits  the  greater  part  of 
the  current  to  flow  past  the  lamp. 

It  will  be  observed  that  the  lamp,  though  still  in 
the  circuit,  is  to  all  practical  intents  cut  out  from 
the  same,  since  the  proportion  of  the  current 
that  now  passes  through  it  is  too  small  to  oper- 
ate it. 

In  most  series  arc  lamps,  cut-outs  are  oper- 
ated by  means  of  an  electro-magnet  placed  in  a 
shunt  circuit  of  high  resistance  around  the  car- 
bons. If  the  carbons  fail  to  properly  feed,  the 
arc  increases  in  length  and  consequently  in  resist- 
ance. More  current  passes  through  the  shunt 
magnci,  until  finally,  when  a  certain  predeter- 
mined limit  is  reached,  the  armature  of  the  elec- 
tro-magnet is  attracted  to  the  magnet  pole  and 
mechanically  completes  the  short  circuit  past  the 
lamp. 

In  some  automatic  cut-outs  the  fusion  of  a 
readily  fused  wire,  placed  in  a  shunt  circuit 
around  the  carbons,  permits  a  spring  to  complete 
the  short  circuit. 

The  automatic  cut-out  prevents  the  accidental 
extinguishing  of  any  single  lamp  in  a  series  cir- 
cuit from  extinguishing  the  remaining  lamps  on 
that  circuit. 

Cut-Out,    Automatic     Time A 

device  arranged  so  as  to  automatically  cut  out 
a  translating  device,  or  an  electric  source,  from 
a  circuit,  at  the  end  of  a  certain  predetermined 
time. 

Cut-Out,    Duplex A   cut-out    so 

arranged  that  when  one  bar  or  strip  is  fused 
or  melted  by  an  abnormal  current  another  can 
be  immediately  substituted  for  it. 

Cut-Out,  Film A  cut-out  in  which 

a  film,  or  sheet  of  paper  or  mica,  is  interposed 
between  a  line  plate  and  an  earth  plate,  which, 
when  punctured  by  a  spark,  short  circuits  the 
instruments  on  the  line. 

Cut-Out,  Main-Line  —An  auto- 
matic cut-out  placed  on  the  main  line.  (See 
Cut-Out,  Automatic) 


A  form  of  main-line  cut-out  is  shown  in  Fig. 


Fig.  IQ4.    Main-Line  Cut-Out. 
194.     The  fuses  are  shown  as  attached  to  the  fuse- 
block. 

Cut-Out,  Paper A  term  sometimes 

employed  instead  of  film  cut-out.    (See  Cut- 
Out,  Film.') 

Cut-Out,  Rosette A  rosette  for  an 

electrolier,  containing   a  cut-out.     (See  Ro- 
sette.) 

Cut-Out,    Spring-Jack A    device 

similar  in  general  construction  to  a  spring- 
jack,  but  employed  to  cut  out  a  circuit. 

An  insulated  plug  is  thrust  between  spring 
contacts,  thus  breaking  the  circuit  by  forcing 
them  apart. 

Cut  Out,  To To  remove  an  elec- 
tro-receptive device  from  the  circuit  of  an 
electric  source  by  disconnecting  or  diverting 
the  circuit  from  it. 

Cutting:  Lines  of  Force.— (See  Force, 
Lines  of.  Cutting.} 

Cycle. — A  period  of  time  within  which  a 
certain  series  of  phenomena  regularly  recur, 
in  the  same  order. 

Cycle,  Magnetic A  single  round 

of  magnetic  changes  to  which  a  magnetizable 


Cyc.] 


152 


[Dam. 


substance,  such  as  a  piece  of  iron,  is  subjected 
when  it  is  magnetized  from  zero  to  a  cer- 
tain maximum  magnetization,  then  decreased 
to  zero,  reversed  and  carried  to  a  negative 
maximum,  and  then  decreased  again  to  zero. 

Cyclical  Magnetic  Yariation.— (See  Va- 
riation, Cyclical  Magnetic?) 

Cyclotrope. — A  name  proposed  in  place 
of  transformer  or  converter.  (See  Trans- 
former^) 

Cylinder,  Yortex A  number  of 

vortex  stream-lines  grouped  parallel  to  one 
another  about  a  straight  line  which  forms  the 
axis  or  core  of  the  vortex. 

Cylindrical  Armature. — (See  Armature, 
Cylindrical?) 

Cylindrical  Carbon  Electrodes.— (See 
Electrodes,  Cylindrical  Carbon?) 

Cylindrical  Electro-Magnet.— (See  Mag- 
net, Electro,  Cylindrical?) 


Cylindrical  Magnet— (See  Magnet,  Cyl- 
indrical?) 

Cylindrical  Ring  Armatnre.— (See  Arm- 
ature, Cylindrical  Ring?) 

Cymogene. — An  extremely  volatile  liquid 
which  is  given  off  from  crude  coal  oil  during 
the  early  parts  of  its  distillation. 

The  two  liquids  which  are  obtained  from  the 
condensation  of  the  vapors  given  off  during  the 
first  parts  of  the  distillation  of  coal  oil  are  called- 
cymogene,  and  rhigolene.  These  liquids  are  em- 
ployed on  account  of  their  extreme  volatility  for 
the  artificial  production  of  cold. 

Rhigolene  is  employed  by  some  for  the  treat- 
ment or  flashing  of  the  carbons  used  in  incan- 
descent lamps.  (See  Carbons,  Flashing  Process 
for.) 

Cystoscopy,  Electric — A  name  given 

to  Hitze's  method  of  ocular  examination 
of  the  human  bladder  by  electric  illumina- 
tion. 


Damped  Magnetic  Needle.— (See  Needle, 
Magnetic,  Damped.) 

Damper. — A  metallic  cylinder  provided  in 
an  induction  coil  so  as  to  partially  or  com- 
pletely surround  the  iron  core,  for  the  purpose 
of  varying  the  intensity  of  the  currents  induced 
in  the  secondary. 

The  metallic  cylinder  acts  as  a  screen  or  shield 
for  the  rapidly  alternating  currents  traversing  the 
field  of  the  primary.  (See  Screening,  Magnetic.) 
As  the  damper  is  pulled  out,  a  greater  length  of 
the  core  is  exposed  to  the  induction. 

Damper. — A  term  sometimes  applied  to  a 
dash-pot  or  other  similar  apparatus  provided 
for  the  purpose  of  preventing  the  too  sudden 
movement  of  a  lever  or  other  part  of  a  device. 
(See  Dash-Pot.) 

Some  form  of  damper  or  dash-pot  is  used  on 
most  electric  arc  lamps,  the  upper  carbon  of 
which  is  fed  by  a  direct  fall. 

The  double  use  of  this  word  is  unfortunate. 

Damping. — The  act  of  stopping  vibratory 
motion  such  as  bringing  a  swinging  mag- 


netic needle  quickly  to  rest,  so  as  to  deter- 
mine the  amount  of  its  deflection,  without 
waiting  until  it  comes  to  rest  after  repeated 
swingings  to  and  fro. 

Damping  devices  are  such  as  offer  resistance 
to  quick  motion,  or  high  velocities.  Those  gen- 
erally employed  in  electrical  apparatus  are  either 
air  or  fluid  friction,  obtained  by  placing  vanes 
on  the  axis  of  rotation,  or  by  checking  the  move- 
ments of  the  needle  by  means  of  the  currents  it 
sets  up,  during  its  motion,  in  the  mass  of  any  con- 
ducting metal  placed  near  it.  These  currents,  as 
Lenz  has  shown,  always  tend  to  produce  motion 
in  a  direction  opposed  to  that  of  the  motion  caus- 
ing them.  Bell-shaped  magnets  are  especially 
suitable  for  this  kind  of  damping.  (See  Magnet^ 
Bell  Shaped.) 

The  needle  of  a  galvanometer  is  dead-beat  when 
its  moment  of  inertia  is  so  small  that  its  oscillations 
in  an  intense  field  are  very  quick,  and  the  mirrcr, 
acting  as  a  vane,  causes  the  movements  to  die  out 
very  rapidly,  and  the  needle  therefore  moves 
sharply  over  the  scale  from  point  to  point  and 
comes  quickly  to  a  dead  stop.  When  the  needle 
or  swinging  coil  is  heavy  and  moves  in  an  intense 


Bam.] 


153 


[Dea. 


Geld,  as  in  the  Deprez-d'Arsonval  galvanometer, 
the  movements  are  dead-beat. 

Damping  by  means  of  pieces  of  India  rubber  is 
often  applied  to  telephone  diaphragms  to  prevent 
their  excessive  or  continued  vibration. 

Damping,  Electric A  term  some- 
times employed  to  express  a  decrease  in 
the  intensity  of  the  electric  oscillations  pro- 
duced in  a  conductor  by  electric  resonance, 
under  circumstances  where  higher  overtones 
are  set  up  in  the  conductor. 

Daniell's  Voltaic  Cell.— (See  Cell,  Vol- 
taic, Daniell's.} 

Dark-Space,  Crookes' (See  Space, 

Dark,  Crookes'.} 

Dark-Space,  Faraday's (See  Space, 

Dark,  Faraday's?) 

Dash-Pot. — A  mechanical  device  to  prevent 
too  sudden  motion  in  a  movable  part  of  any 
apparatus. 

The  dash-pot  of  an  automatic  regulator,  or  of 
an  arc -lamp,  is  provided  to  prevent  too  sudden 
movements  of  the  collecting  brushes  on  the  com- 
mutator cylinder,  or  the  too  sudden  fall  of  the 
upper  carbon.  Such  devices  consist  essentially  of 
a  loose  fitting  piston  that  moves  through  air  or 
glycerine. 

Dash-pots  are  species  of  damping  devices,  and, 
like  the  damping  arrangements  on  galvanometers 
or  magnet  needles,  prevent  a  too  free  movement 
of  the  parts  with  which  they  are  connected.  (See 
Damper.  Damping. } 

Day,  Normal  Magnetic A  day  dur- 
ing which  the  value  of  the  earth's  magnetic 
elements  does  not  vary  greatly  from  their 
mean  value.  (See  Elements,  Magnetic,  of  a 
Place^ 

Day  of  Disturbance,  Magnetic — 

A  day  during  which  the  mean  departure  of 
the  readings  of  a  declinometer  at  any  place, 
from  the  normal  monthly  value  at  that  place, 
is  once  and  a  half  the  average. — (Lloyd.} 

Dead-Beat. — Such  a  motion  of  a  galvanom- 
eter needle  in  which  the  needle  moves  sharply 
over  the  scale  from  point  to  point  and  comes 
quickly  to  rest.  (See  Damping!) 

Dead-Beat  Discharge.— (See  Discharge, 
Dead-Beat^ 


Dead-Beat    Galvanometer. — (See   Galva- 
nometer, Dead-Beat?)  / 
Dead  Dipping.— (See  Dipping,  Dead.} 
Dead  Earth.— (See  Earth,  Dead  or  Total.} 

Dead  Turns  of  Armature  Wire,  or  Dead 
Wire.— (See  Turns,  Dead,  of  Armature 
Wire.} 

Death,  Electric  — Death  resulting 

from  the  passage  of  an  electric  current 
through  the  human  body. 

The  exact  manner  in  which  an  electric  current 
causes  death  is  not  known.  When  the  current  is 
sufficiently  powerful,  as  in  a  lightning  flash,  or  a 
powerful  dynamo  current,  insensibility  is  prac- 
tically instantaneous. 

Death  may  be  occasioned: 

(I.)  As  the  direct  result  of  physiological  shock. 

(2.)  From  the  action  of  the  current  on  the  res- 
piratory centres. 

(3.)  From  the  actual  inability  of  the  nerves  or 
muscles,  or  both,  to  perform  their  functions. 

(4.)  From  an  actual  electrolytic  decomposition 
of  the  blood  or  tissues  of  the  body. 

(5.)  From  the  polarization  of  those  parts  of  the 
body  through  which  the  current  passes. 

(6.)  From  an  actual  rupture  of  parts  by  a  dis- 
ruptive discharge. 

The  current  required  to  cause  death  will  de- 
pend on  a  variety  of  circumstances,  among 
which  are: 

(i.)  The  particular  path  the  current  takes 
through  the  body,  with  reference  to  the  vital 
organs  that  may  lie  in  this  path. 

(2.)  The  freedom  or  absence  of  sudden  varia- 
tions of  electromotive  force. 

(3. )  The  time  the  current  continues  to  pass 
through  the  body. 

In  some  fatal  cases,  it  is  probably  the  extra- 
current,  or  the  induced-direct  current  on  break- 
ing, that  causes  death,  since,  as  is  well  known, 
its  electromotive  force  may  be  many  times 
greater  than  that  ot  the  original  current. 

A  comparatively  low-potential  continuous-cur- 
rent, cannot,  therefore,  be  properly  regarded 
as  entirely  harmless,  simply  because  its  electro- 
motive force  is  necessarily  small.  In  the  case  of 
alternating  currents  the  danger  increases  after  a 
certain  point  with  the  number  of  alternations  per 
second.  When,  however,  the  number  of  alter- 
nations per  second  reaches  a  given  number,  the 
danger  decreases  as  the  frequency  of  alternations 


Dec.] 


154 


[Deg. 


increases.  This  was  conclusively  shown  by  the 
independent  investigations  of  Tatum  and  Tesla. 

Decalescence. — A  term  proposed  by  Prof. 
Elihu  Thomson  for  an  absorption  of  sensible 
heat,  which  occurs  at  a  certain  time  during 
the  heating  of  a  bar  of  steel. 

Decalescence  will  thus  be  observed  to  be  the 
reverse  of  recalescence,  which  is  the  phenome- 
non of  the  emission  of  sensible  heat  at  a  certain 
time  during  the  cooling  of  a  heated  bar  of 
steel.  (See  Recalescence.) 

Deci  (as  a  prefix). — The  one-tenth. 

Deci-Ampe"re. — One-tenth  of  an  ampere. 

Deci-Ampdre  Balance. — (See  Balance, 
Deci- A  mpere) 

Deci-Lux.— The  one-tenth  of  a  lux.  (See 
Lux) 

Declination. — The  variation  of  a  mag- 
netic needle  from  the  true  geographical  north. 

The  magnetic  declination  is  east  or  west.  (See 
Needle,  Magnetic,  Declination  of) 

Declination,  Angle  of The  angle 

which  measures  the  deviation  of  the  mag- 
netic needle  to  the  east 
or  west  of  the  true  geo- 
graphical north. 

The  angle  of  variation 
of  a  magnetic  needle. 

In  Fig.  195,  if  N  S,  rep- 
resents the  true  north  and 
south  line,  the  angle  of  de- 
clination is  N  O  A,    and   Fig.  195.    Declination 
the  sign  of  the  variation  is  °f  Needle, 

east,  because  the  deviation  of  the  needle  is  to- 
ward the  east.  (See  Needle,  Magnetic,  Declina- 
tion of.) 

Declinometer. — A  magnetic  needle  suit- 
ably arranged  for  the  measurement  of  the 
value  of  the  magnetic  declination  or  varia- 
tion at  any  place. 

Decomposition. — In  chemistry  the  separa- 
tion of  a  molecule  into  its  constituent  atoms 
or  groups  of  atoms.  (See  Molecule.  Atom) 

Decomposition,  Electric Chem- 
ical decomposition  by  means  of  an  electric  dis- 
charge or  current. 

This  decomposition  may  result  from  an  increase 


of  temperature  produced  by  the  electric  discharge, 
or  from  the  passage  of  the  current.  In  the  latter 
case  it  is  more  properly  called  electrolytic  decom- 
position. 

Decomposition,  Electric,  Crystallization 

by (See  Crystallization    by  Electro- 

lytical  Decomposition?) 

Decomposition,  Electrolytic  —      — The 

separation  of  a  molecule  into  its  constituent 
atoms  or  groups  of  atoms  by  the  action  of 
the  electric  current. 

These  atoms  or  groups  of  atoms  are  either 
electro-positive  or  electro-negative  in  character. 
(See  Electrolysis.  Anion.  Kathion) 

De-energize. — To  deprive  an  electro-recep- 
tive device  of  its  operating  current. 

De-energizing. — Depriving  an  electro- 
receptive  device  of  its  operating  current. 

Deep-Seated  Eddy  Currents.— (See  Cur- 
rents, Eddy,  Deep-Seated) 

Deep-Water     Submarine      Cable.— (See 

Cable,  Submarine,  Deep- Sea) 

Deflagration,  Electrical  —  — The  fusion 
and  volatilization  of  metallic  substances  by  the 
electric  current. 

Deflagrator. — The  name  given  to  a  voltaic 
battery,  of  small  internal  resistance,  employed 
by  Hare  in  the  electric  deflagration  of  metal- 
lic substances. 

Deflection  Method.— (See  Method,  Deflec- 
tion) 

Deflection  of  Magnetic  Needle. — (See 
Needle,  Magnetic,  Deflection  of) 

Degeneration. — Such  a  degeneration  of  the 
muscular  or  cellular  structure  of  any  cell  or 
organ  that  incapacitates  it  from  performing  its 
functions. 

Degeneration  of  Energy. — (See  Energy, 
Degeneration  of) 

Degeneration,  Partial,  Reaction  of  — 
— That  form  of  alteration  to  electric  stimula- 
tion, in  which  the  nerves  show  no  abnormal 
reaction  to  electric  stimulation,  while  the 
muscles,  when  directly  stimulated  by  the  con- 
stant current,  exhibit  the  reaction  of  degen- 
eration. (See  Degeneration,  Reaction  of^ 


Deg.] 


155 


[Dep. 


Degeneration,    Reaction    of  —A 

qualitative     and     quantitative    alteration  of 
nerves  and  muscles  to  electric  stimulation. 

According  to  Landois  and  Stirling  the  following 
conditions  characterize  essentially  the  reaction  of 
degeneration  :  "The  excitability  of  the  muscles 
is  diminished  or  abolished  for  the  faradic  cur- 
rent, while  it  is  increased  for  the  galvanic  current 
from  the  third  to  the  fifty -eighth  day ;  it  again 
diminishes,  however,  with  variations,  from  the 
seventy-second  to  eightieth  day  ;  the  anodic  clos- 
ing contraction  is  stronger  than  the  kathodic 
closing  contraction."  *  *  *  "The  diminu- 
tion of  the  excitability  of  the  nerves  is  similar  for 
the  galvanic  and  faradic  currents. ' ' 

Deka  (as  a  prefix). — Ten  times. 

Deka-Amp&re. — Ten  amperes. 

Deka-Ampere  Balance. — (See  Balance, 
Deka- Ampere.) 

De  la  Rue's  Standard  Voltaic  Cell.— (See 
Cell,  Voltaic,  Standard,  De  la  Rue's.) 

Deliquescence. — The  solution  of  a  crystal- 
line solid  arising  from  its  absorption  of  vapor 
of  water  from  the  atmosphere. 

Demagnetizable. — Capable  of  being  de- 
prived of  magnetism. 

Demagnetization. — A  process,  generally  di- 
rectly opposite  to  that  for  producing  a  magnet, 
by  means  of  which  the  magnet  may  be  de- 
prived of  its  magnetism. 

A  magnet  may  be  deprived  of  its  magnetism, 
or  be  demagnetized — 

(i.)  By  heating  it  to  redness. 

(2. )  By  touching  to  its  poles  magnet  poles  of  the 
same  name  as  its  own. 

(3.)  By  reversing  the  directions  of  the  motions 
by  which  its  magnetism  was  originally  imparted, 
if  magnetized  by  touch,  by  stroking  it  with  a 
magnet  in  the  opposite  direction  from  that  which 
would  have  to  be  given  in  order  to  produce  the 
magnetization  which  is  to  be  removed  from  it. 

(4.)  By  exposing  it  in  a  helix  to  the  influence  of 
currents  which  will  impart  magnetism  opposite  to 
that  which  it  originally  possessed. 

Avria  claims  that  a  smaller  magnetizing  force  is 
required  to  demagnetize  a  needle  than  is  required 
to  magnetize  it. 

Demagnetization      of      Watches.— (See 

Watches,  Demagnetization  of.) 
o-Vol.  1 


Demagnetize. — To  deprive  of  magnetism. 

Demagnetizing. — Depriving  of  magnetiza- 
tion. 

Demarcation  Current. — (See  Current,  De- 
marcation.) 

Demarcation  Surface. — (See  Surface,  De- 
marcation^) 

Density,  Electric The  quantity  of 

free  electricity  on  any  unit  of  area  of  surface. 

The  density  is  said  to  be  positive  or  negative 
according  as  to  whether  the  charge  is  positive  or 
negative.  (See  Charge^  Density  of.  Plane, 
Magnetic  Proof.)  % 

Density,  Magnetic The  strength 

of  magnetism  as  measured  by  the  number  of 
lines  of  magnetic  force  that  pass  through  a 
unit  area  of  cross-section  of  the  magnet,  /.  e., 
a  section  taken  at  right  angles  to  the  lines  of 
force.  (See  Field,  Magnetic) 

Density  of  Charge. — (See  Charge,  Den- 
sity of.) 

Density  of  Current.  —  (See  Current 
Density?) 

Density  of  Field.— (See  Field,  Density  of.) 

Density,  Surface A  phrase  used 

by  Coulomb  to  mean  the  quantity  of  eiec- 
tricity  per  unit  of  area  at  any  point  on  a  sur- 
face. (See  Charge  Density.  Density^ 
Electric.) 

Dental-Mallet,  Electro-Magnetic 

A  mallet  for  filling  teeth,  the  blows  of  which 
are  struck  by  means  of  electrically-driven 
mechanism. 

Electro-magnetism  was  first  employed  for  this 
purpose  by  Bonwill,  of  Philadelphia. 

Dentiphone. — An  audiphone.  (See  Audi- 
phone) 

Depolarization. — The  act  of  reducing  or 
removing  the  polarization  of  a  voltaic  cell 
or  battery.  (See  Cell,  Voltaic,  Polarization 
of) 

Depolarize. — To  deprive  of  polarization. 

Depolarizing. — Depriving  of  polarization. 

Depolarizing  Fluid.— (See  Fluid,  De- 
polarizing.) 


Dep.J 


156 


[D«T. 


Deposit,    Black,    Electro-Metallurgical 

— A  crystalline  variety  of  electro- 
metallurgical  deposit.  (See  Deposit,  Electro- 
Metallurgical^ 

Deposit,  Crystalline,  Electro-Metallurgi- 

cal A    non-adherent,    non-coherent 

film  of  tlectrolytically  deposited  metal.  (See 
Deposit,  Electro-Metallurgical?) 

Deposit,    Electro-Metallurgical 

The  deposit  of  metal  obtained  by  any  electro- 
metallurgical  process. 

To  obtain  a  good  metallic  deposit  the  density 
of  the  current  must  be  regulated  according  to  the 
strength  of  the  metallic  solution  employed. 

Electro -metallurgical  deposits  are  either — 

(I . )  Reguline,  or  flexible,  adherent  and  strongly 
coherent  metallic  films,  deposited  when  neither 
the  current  nor  the  solution  is  too  strong;  or, 

(2.)  Crystalline;  or  non-adherent  and  non-co- 
herent deposits. 

The  crystalline  deposit  may  either  be  of  a  loose, 
sandy  character,  which  is  thrown  down  when  too 
feeble  a  current  is  used  with  too  strong  a  metallic 
solution,  or  it  may  consist  of  a  black  deposit,  which 
is  thrown  down  when  the  current  is  too  strong  as 
compared  with  the  strength  of  the  solution.  This 
latter  character  of  deposit  is  sometimes  technically 
called  burning,  and  takes  place  most  frequently 
at  sharp  corners  and  edges,  where  the  current 
density  is  greatest.  (See  Current  Density.) 

Deposit,  Electro-Metallurgical  Nodular 

A  coherent,  irregular  electro-metal- 
lurgical deposit  which  occurs  whenever  the 
current  density  falls  below  its  normal  value. 
Deposit,  Electro-Metallurgical,  Reguline 

A    flexible,    adherent    and   strongly 

coherent  film  of  metal  electrolytically  de- 
posited. (See  Deposit,  Electro-Metallur- 
gical) 

Deposit,    Electro-Metallurgical,    Sandy 

A  non-coherent  electro-metallurgical 

deppsit  which  occurs  whenever  the  current 
density  exceeds  its  normal  value. 
Depositing  Cell.— (See  Cell,  Depositing) 
Depositing  Tat— (See  Vat,  Depositing) 
Deposition,  Electric The  deposit- 
ing   of   a  substance,  generally  a  metal,  by 
the  action  of  electrolysis.    (See  Electrolysis) 


The  electric  deposition  of  a  metal  on  any  con- 
ducting  surface  is  sometimes  called  an  electro- 
metallurgical  deposition.  (See  Metallurgy, 
Electro.) 

Deprez-d'Arsonval  Galvanometer.— (Sec 

Galvanometer,  Deprez-d'Arsonval) 

Derivative  Circuit— (See  Circuit,  De- 
rivative) 

Derived  Circuit— (See  Circuit,  Derived) 

Derived  Units.— (See  Units,  Derived) 

Destructive  Distillation.— (See  Distilla- 
tion, Destructive) 

Detector  Galvanometer.— (See  Galva- 
nometer, Detector) 

Detector,  0 round In  a  system 

of  incandescent  lamp  distribution,  a  device 
placed  in  the  central  station,  for  showing  by 
the  candle-power  of  a  lamp  the  approximate 
location  of  a  ground  on  the  system. 

Fig.  196,  shows  a  form  of  ground -detector,  in 


Kg.  706.    Ground- Detector. 

which  a  small  transformer  is  placed  on  a  board  in 
connection  with  a  lamp  and  a  two-way  switch. 
One  terminal  of  the  primary  of  the  transformer  is 
put  to  ground,  while  the  other  can  be  connected 
by  means  of  the  switch  to  one  or  the  other  of  the 
two  primary  mains  of  the  distribution  circuit. 
Should  an  earth  exist  on  either  main,  then  when 
the  testing  transformer  has  its  pole  connected  to 
the  other  main,  the  lamp  in  its  secondary  circuit 
will  light  up,  providing  the  leak  is  of  sufficient 
magnitude  to  permit  a  sufficiently  great  current 
to  pass  through  the  primary  circuit. 

Detorsion  Bar. — (See  Bar,  Detorsion) 
Device,  Electro-Receptive Various 


De?.] 


157 


[Dey. 


devices  placed  in  an  electric  circuit,  and 
energized  by  the  passage  through  them  of  the 
electric  current. 

A  translating  device. 

The  following  are  among  the  more  important 
electro-receptive  devices,  viz. : 

(I.)  Electro  magnets. 

(2.)  Electric  motors. 

(3.)  Electro-magnetic  signal  apparatus. 

(4.)  Telegraphic  or  telephonic  apparatus. 

(5 . )  An  arc  or  incandescent  lamp. 

(6. )  An  electric  heater. 

(7. )  A  plating  bath  or  voltameter. 

(8.)  An  uncharged  storage  cell. 

(9.)  A  converter  or  transformer. 

ELECTRO-RECEPTIVE  DEVICES. 

Motion  Reproduced. 
(I.)  Electric  motor. 
(2.)  Telpherage  system. 
(3.)  Telephone  receiver. 
(4.)  Telegraphic  apparatus. 
(5.)  Telephote  receiver. 

Radiant  Energy  Produced. 
(6.)  Arc  or  incandescent  electric  lamp. 
(7.)  Electric  heater. 
(S.)  Electric  welder. 
(9.)  Leyden  jar  or  battery. 

Chemical  Decomposition  Effected, 
(10.)  Electrolytic  bath. 
(n.)  Uncharged  storage  battery. 

Electro-Magnetism  Produced. 
(12.)  Electro-magnet. 

Device,  Feeding,  of  an  Arc  Lamp 

A  device  for  maintaining  the  carbon  electrodes 
of  an  arc  lamp  at  a  constant  distance  apart 
during  their  consumption.  (See  Lamp, 
Electric  Arc,} 

Device,  Magneto-Receptive Any 

device  that  is  capable  of  being  energized 
when  placed  in  a  magnetic  field. 

The  term  magneto-receptive  device  is  used  in 
contradistinction  to  electro-receptive  device.  (See 
Device )  Electro- Receptive.") 

Device  or  Arrangement,  Electromotive 

A  term  sometimes  employed  instead 

of  an  electric  source.     (See  Source,  Electric. 

Arrangement  or  Device,  Electromotive^ 


Device,  Safety,  for  Arc  Lamps,  or  Series 
Circuits Any  mechanism  which  auto- 
matically provides  a  path  for  the  current 
around  a  lamp,  or  other  faulty  electro-recep- 
tive device  in  a  series  circuit,  and  thus  pre- 
vents the  opening  of  the  entire  circuit  on  the 
failure  of  such  device  to  operate.  (See  Lamp, 
Electric  Arc.) 

Device,  Safety,  for  Multiple  Circuits 

—A  wire,  bar,  plate  or  strip  of  readily 
fusible  metal,  capable  of  conducting,  without 
fusing,  the  current  ordinarily  employed  on  the 
circuit,  but  which  fuses  and  thus  breaks  the 
circuit  on  the  passage  of  an  abnormally  great 
current. 

The  terms  safety -catch,  safety-plug,  safety- 
strip  and  safety -fuse  are  also  used  for  this  safety 
device.  (See  Fuse,  Safety.} 

Device,  Translating-  — —  — A  term  em- 
bracing electro-receptive  and  magneto-recep- 
tive devices.  (See  Device,  Electro-Recep- 
tive) 

Translating  devices  are  placed  in  an  electric 
circuit,  and  when  traversed  by  the  current  effect 
a  change,  or  translation  in  the  form  of  the  electric 
energy  whereby  useful  work  is  accomplished. 

Translating  devices  depend  for  their  operation 
on  the  luminous,  heating,  magnetic,  or  chemical 
effects  of  the  current. 

Devices,  Electro-Receptive,  Multiple- 
Connected  — —  — A  connection  of  electro- 
receptive  devices,  in  which  the  positive  poles 
of  a  number  of  separate  devices  are  all  con- 
nected with  a  single  positive  lead  or  conduc- 
tor, and  the  negative  poles  all  connected  with 
a  single  negative  lead  or  conductor. 

The  multiple-arc-connection  of  electro-receptive 
devices  is  suitable  for  constant  potential  circuits,  or 
those  in  which  the  electromotive  force  is  main- 
tained approximately  constant.  In  such  circuits 
the  energy  absorbed  by  each  device  wilt  increase 
as  its  resistance  decreases,  since  the  energy  ab- 
sorbed is  proportional  to  the  current  passing. 
(See  Circuits,  Varieties  of.) 

Multiple-arc-connected  electro-receptive  devices 
are  employed  m  incandescent  lamp  distribution. 
Each  device  added  reduces  the  resistance  of  the 
entire  circuit. 


Dev.] 


158 


[Dia. 


Devices,  Electro-Receptive,Multiple-Arc- 

Counected A  term  used  in  place  of 

multiple-connected  electro-receptive  devices. 
(See  Devices,  Electro-Receptive,  Multiple- 
Connected?) 

Devices,  Electro-Receptive,  Multiple- 

Series-Connected — A  connection  of 

electro-receptive  devices  in  which  a  number  of 
separate  etectro-receptive  devices  are  con- 
nected in  groups  in  saries,  and  each  of  these 
separate  groups  afterwards  connected  in  mul- 
tiple-arc. 

The  multiple-series  connection  permits  electro- 
receptive  devices  to  be  placed  on  mains  whose 
electromotive  force  would  be  too  high  to  permit 
a  single  service  to  be  connected  directly  to  them. 
It  is  of  great  value  in  the  distribution  of  incandes- 
cent lamps  by  constant  currents,  since  by  per- 
mitting a  higher  electromotive  force  to  be  em- 
ployed on  the  main  conductors,  it  reduces  the 
dimensions  of  the  conductors  required  for  the 
economical  distribution  of  the  current.  (See 
Circuits ',  Varieties  of.) 

Devices,  Electro-Receptive,  Series-Con- 
nected   'The  connection  of  electro- 
receptive  devices  in  which  the  devices  are 
placed  consecutively  in  the  circuit,  so  that  the 
current  passes  successively  through  all  of 
them  from  the  first  to  the  last. 

The  series-connection  of  electro-receptive  de. 
vices  is  suited  to  cons  I  ant -current  circuits.  The 
work  done  in  the  device  is  developed  by  the  fall 
of  potential  in  each  device.  This  kind  of  con- 
nection is  used  in  most  systems  of  arc  light  and 
telegraphic  lines.  (See  Circuits,  Varieties  of  .) 

Devices,  Electro-Receptive,  Series-Mul- 
tiple-Connected   •  —A  connection  of 

electro-receptive  devices  in  which  a  number 
of  separate  electro-receptive  devices  are  joined 
in  separate  multiple  groups,  and  each  of  these 
groups  subsequently  connected  with  one  an- 
other in  series. 

The  effect  of  series-multiple  connections  is  to 
split  up  the  current  into  a  number  of  separate 
currents  of  smaller  strength,  but  of  the  same 
electromotive  force.  It  is  applicable  to  such  cases 
as  the  combination  of  arc  and  incandescent  lamps 
m  the  same  circuit.  (See  Circuits,  Varieties  of  .) 

Devices,      Translating,      Multiple-Con- 


nected —  — A  term  sometimes  used  for 
multiple-connected  electro-receptive  devices. 
(See  Devices,  Electro-Receptive,  Multiple- 
Connected^ 

Devices,  Translating,  Multiple-Arc-Con- 
nected  — A  term  used  in  place  of 

multiple-connected  electro-receptive  devices. 
(See  Devices,  Electro-Receptive,  Multiple- 
Connected^ 

Devices,  Translating,  Multiple-Series- 
Connected  •• — A  term  sometimes  used 

instead  of  multiple-series-connected  electro- 
receptive  devices.  (See  Devices,  Electro- 
Receptive,  Multiple-Series-Connected?) 

Devices,  Translating,  Series-Connected 
—A  term  sometimes  used  for  series- 
connected  electro-receptive  devices.  (See 
Devices,  Electro  -  Receptive,  Series  -  Con- 
nected^) 

Devices,  Translating,  Series-Multiple- 

Connected — A  term  sometimes  used 

for  series-multiple-connected  electro-recep- 
tive devices.  (See  Devices,  Electro-Recep- 
tive, Series-Multiple-Connected?) 

Dextrorsal  Helix.— (See  Helix,  Dex- 
trorsai?) 

Dextrorsal  Solenoid.— (See  Solenoid,  Dex* 
trorsaL} 

Diacritical  Current.— (Sae  Current,  Dia- 
critical?) 

Diacritical  Number.— (See  Number,  Dia- 
critical^) 

Diacritical  Point  of  Magnetic  Satura- 
tion.— (See  Saturation,  Magnetic,  Diacrit- 
ical Point  of.) 

Diagnosis,  Electro. — Diagnosis  by  means 
of  the  exaggeration  or  diminution  of  the  re- 
action of  the  excitable  tissues  of  the  body- 
when  subjected  to  the  varying  influences  of 
electric  currents. 

The  electric  current  has  also  been  applied  in 
order  to  distinguish  between  forms  of  paralysis, 
and  as  a  final  test  of  death. 

Diagnostic,  Electro Pertaining  to 

electro-diagnosis.  (See  Diagnosis,  Electro?) 

Diagometer,  Rousseau's An  ap- 
paratus m  which  an  attempt  is  made  to 


Dia.] 


159 


determine  the  chemical  composition  and  con- 
sequent purity  of  certain  substances  by  their 
electrical  conducting  powers. 

The  arrangement  of  the  apparatus  is  shown  in 
Fig    197.     A  dry  pile.  A,  has  its  negative,  or  — 


Fig.  K)7-     Rousseau' s  Diagometer . 

terminal,  m',  grounded.  Its  positive,  or  -j-  ter- 
minal is  connected  to  a  delicately  supported,  and 
slightly  magnetized  needle,  M,  terminated  by  a 
conducting  plate,  L.  Opposite  L,  and  at  the  same 
height,  is  a  fixed  plate  of  slightly  larger  size.  The 
needle  M,  when  at  rest  in  the  plane  of  the  magnetic 
meridian,  is  in  contact  at  L,  with  the  fixed  plate. 
If,  therefore,  the  upper  plate  of  the  pile  is  con- 
nected with  the  needle  M,  both  plates  are  similarly 
charged  and  repulsion  takes  place,  the  needle 
coming  to  rest  at  a  certain  distance  from  the  fixed 
plate. 

The  substance  whose  purity  is  to  be  determined 
is  placed  in  the  cup  G,  which  is  connected, 
through  L,  with* the  fixed  plate,  A  branch  wire 
from  the  -{-  terminal  of  the  pile  is  then  dipped  into 
the  substance  in  G,  and  its  purity  determined 
from  the  length  of  time  required  for  the  two  plates 
at  L,  to  be  t  ischarged  through  the  material  in  G. 

It  is  claimed  that  the  instrument  will  detect  the 
difference  between  pure  coffee  and  chicory.  Its 
practical  application,  however,  is  very  doubtful. 

Diagram,  Thermo-Electric  — A 

diagram  in  which  the  thermo-electric  power 
between  different  metals  is  designated  for 
different  temperatures. 

The  differences  of  potential,  produced  by  the 
mere  contact  of  two  metals,  varies,  not  only  with 
the  kind  of  metals,  and  the  physical  state  of  each 
metal,  but  also  with  their  temperature.  This 
difference  of  potential,  maintained  in  conse- 
quence of  the  difference  of  temperature  between 
the  junctions  of  a  thermo-electric  couple^  is  ap- 
proximately proportional  to  the  differences  of 
temperature  of  these  junctions,  if  these  differences 
are  not  great,  and  is  equal  to  the  product  of  such 


differences  of  temperature  and  a  number  depend  en  t 
on  the  metals  in  the  couple.     This  number  is 
called  the  thermo-electric  power.     (See    Couple^ 
Thermo-Electric.     Thermo-Electric  Power.) 
In  Fig.  198  (after    Tait),  the  thermo-electric 

0°c     K*.  100°c  lJO°e  200=,,  250°e  30<>o«  350°«  400°e  450",, 

M* 


Fig.  198.  Thermo-Electric  Diagram. 
power  is  shown  between  lead  and  iron,  and  lead 
and  copper.  The  numbers  at  the  top  of  the  table 
represent  degrees  of  the  centigrade  thermometer. 
Those  at  the  sides  represent  the  differences  of 
potential  in  micro -volts. 

The  thermo-electric  power  of  the  copper-iron 
couple  decreases  from  the  freezing  point  of  water, 
O  degrees  C.,  to  a  temperature  of  274.5  degrees 
C.,  when  it  becomes  zero.  Beyond  tha*  temper- 
ature the  thermo-electric  power  incre?  ,es,  but  in 
the  opposite  direction.  The  point  at  which  this 
occurs  is  called  the  neutral  point. 

Dial  Telegraph.— (See  Telegraphy,  Dial.) 

Dialysis.— The  act  of  separating  a  mixture 
of  crystalloids  and  colloids  by  diffusion 
through  a  membrane. 

If,  for  example,  the  contents  of  a  stomach,  in  a 
case  of  suspected  poisoning,  be  placed  in  a  vessel, 
the  bottom  of  which  is  formed  of  a  sheet  of 
parchment  paper  and  floated  in  water,  the 
crystalloid  or  substances  capable  of  crystalliz 
ing,  will  pass  into  the  water  and  the  colloid,  an 
uncrystallized  jelly-like  substance,  will  remain  in 
the  vessel.  This  process  has  been  used  to  detect 
the  presence  of  poison  in  the  stomach  in  post- 
mortem cases. 

Diamagnetic. — The  property  possessed  by 
•substances  like  bismuth,  phosphorus,  anti- 
mony, zinc  and  numerous  others,  of  being 
apparently  repelled  when  placed  between  the 
poles  of  powerful  magnets 

When  diamagnetic  substances  in  the  form  of 
rods  or  bars  are  placed,  as  in  Fig.  199,  between 
the  poles  of  a  powerful  electro-magnet,  they 
place  themselves  at  right  angles  to  the  poles,  or 
are  apparently  repelled. 

Paramagnetic  substances  like  iron  or  steel,  on 
the  contrary,  come  to  rest  under  similar  circum- 


Dia.] 


160 


[Dia. 


Fig.  799     Effect  of  Para- 
magnetism, 


stances  in  a  straight   line  joining  the  poles,   at 
right  angles  to  the  position  shown  in  Fig.  199. 

Paramagnetic  substances  are  sometimes  called 
ferro-magnetic,  or  substances  magnetic  after  the 
manner  of  iron.  This  word  is  unnecessary  and 
ill-advised.  The  term  sidero-magnetic,  which  has 
also  been  proposed  in  place  of  paramagnetic,  is 
also  unnecessary. 

Paramagnetic  substances  appear  to  concentrate 
the  lines  of  magnetic  force  on  them ;  that  is,  their 
magnetic  resistance  is 
smaller  than  that  of  the 
air  or  other  medium  in 
which  the  magnet  is 
placed.  They,  there- 
fore, come  to  rest  with 
their  greatest  dimen- 
sions in  the  direction  of 
the  lines  of  magnetic 
force. 

Diamagnetic  sub- 
stances  appear  to  have 
a  greater  nagnetic  re- 
sistance than  that  of 
the  air  around  them. 
They,  therefore,  come 
to  rest  with  their  least 
dimensions  in  the  direction  of  the  lines  of  mag- 
netic force. 

The  difference  between  paramagnetic  and  dia. 
magnetic  substances  is  generally  believed  to  be 
due  to  the  varying  resistance  these  substances 
thus  offer  to  lines  of  magnetic  force  as  compared 
with  that  offered  by  air  or  by  a  vacuum. 

Tyndall  comes  to  the  conclusion  as  the  result  of 
extended  experimentation:  «•  That  the  diamag- 
netic  force  is  a  polar  force,  the  polarity  of  dia- 
magnetic  bodies  being  opposed  to  that  of  para- 
magnetic ones  under  the  same  conditions  of 
excitement." 

This  view,  however,  is  not  generally  accepted 
by  scientists. 

Diamagnetism  is  also  possessed  by  certain  liquid 
and  gaseous  substances. 

Diamagnetic  Polarity.— (See  Polarity, 
Diamagnetic.} 

Diamagnetically. — In  a  diamagnetic  man- 
ner. 

Diamagnetism.— A  term  applied  to  the 
magnetism  of  diamagnetic  bodies.  (See  Dia- 
magnetic?) 


Diamagnetism,  Weber's  Theory  of • 

— A  theory  to  account  for  the  phenomena 
of  diamagnetism. 

Weber's  theory  of  diamagnetism,  like  Ampere's 
theory  of  magnetism,  supposes  that  magnetic 
substances  consist  of  originally  magnetized  mole- 
cules  or  atoms,  and  that  the  act  of  magnetization 
consists  of  polarizing  these  atoms  or  molecules, 
or  turning  them  in  one  and  the  same  direction. 
That  the  original  condition  of  the  molecules  or 
atoms  is  probably  due  to  the  passage  of  electricity, 
which  continually  circulates  through  their  mass, 
the  atoms  being  supposed  to  possess  perfect  con- 
ductivity. 

Suppose  the  substance  through  whose  mole- 
cules or  atoms  these  currents  are  flowing  be 
immersed  in  a  magnetic  field.  AH  of  the  mole : 
cules  or  atoms  which  can  turn  so  as  to  look  along 
lines  of  force  in  the  right  direction  will  have  the 
current  flowing  in  them  thereby  weakened  so  long 
as  they  remain  in  the  field.  When  drawn  out  of 
it,  however,  these  currents  will  regain  their  nor- 
mal  strength. 

Suppose  now  the  case  of  a  substance,  in  which 
the  currents  are  normal  'but  weak,  immersed  in  a 
strong  magnetic  field.  There  may  thereby  be 
effected  a  complete  reversal  of  the  direction  of 
these  currents,  and  others  may  be  produced 
which  flow  in  the  opposite  direction,  and  which 
will  continue  so  to  flow  as  long  as  the  substance 
remains  in  the  field.  Such  currents  would  then 
be  sufficient  to  explain  the  phenomena  of  diamag  - 
netic  action. 

An  electric  current  produced  in  a  circuit  near 
which  a  momentary  current  of  electricity  is  sud  • 
denly  brought  has  now  the  opposite  direction  to 
that  which  produces  it,  and  this  momentary  cur- 
rent  would  tend  to  produce  repulsion.  When, 


Fig.  200.     Weber's  Theory  of  Diamagnetism. 
too,  the  circuit  is  drawn  out  of  the  neighborhood 
in  which  another  current  is  flowing,  another  mo 


Bfau] 


161 


[Die. 


mentary  current  is  produced  in  the  same  direc- 
tion. This  produces  attraction. 

Now,  regarding  the  same  phenomena  from  the 
standpoint  of  lines  of  magnetic  force,  when  a 
conductor  through  which  a  current  is  passing  is 
placed  in  a  magnetic  field,  any  increase  in  the 
number  of  lines  of  magnetic  force  passing  through 
it  tends  to  move  the  conductor  out  of  the  magnetic 
field,  while  any  decrease  in  the  number  of  lines 
of  force  tends  to  move  the  conductor  into  the 
fieH.  To  experimentally  show  the  attractions 
and  repulsions  produced  by  magnetization  or 
demagnetization,  the  following  apparatus  may  be 
employed: 

A  stout  disc  of  copper,  Fig.  200,  is  supported 
on  a  horizontal  arm  in  the  position  shown  in  front 
of  the  pole  of  a  powerful  electro-magnet.  When 
the  current  is  sent  through  the  electro-magnet  the 
disc  of  copper  is  repelled  from  the  magnetic  pole. 
When  the  magnetism  is  being  destroyed  by  the 
opening  of  the  circuit  and  by  the  weakening  of 
the  current,  the  copper  disc  is  attracted. 

Diamagnetometer. — An  apparatus  de- 
signed for  studying  diamagnetism.  (See  Dta- 
magnetism. ) 

The  apparatus  for  the  study  of  paramagnetism 
generally  receives  simply  the  name  of  magnet- 
ometer. 

Diamagnets..—  Diamagnetic  substances 
subjected  to  magnetic  induction  and  formerly 
called  diamagnets  in  contradistinction  to  or- 
dinary magnets. 

Diamagnets  are  supposed  by  some  to  possess  a 
polarity  the  same  as  that  of  the  inducing  pole, 
instead  of  the  opposite  polarity,  as  in  paramagnetic 
substances.  (See  Diamagnetism.') 

Diaphragm. — A  sheet  of  some  solid  sub- 
stance, generally  elastic  in  character  and  cir- 
cular in  shape,  securely  fixed  at  its  edges  and 
capable  of  being  set  into  vibration. 

The  receiving  diaphragm  of  a  telephone  is 
generally  a  thin  plate  or  disc  of  iron,  fixed  at  its 
edges,  placed  near  a  magnet  pole  and  set  into 
vibration  by  variations  in  the  magnetic  strength 
of  the  pole,  due  to  variations  in  the  current  that 
is  passed  over  the  line. 

The  transmitting  diaphragm  of  the  telephone 
or  of  a  phonograph,  consists  of  a  plate  fixed  at  its 
edges  and  set  into  vibration  by  the  sound  waves 
striking  it. 


Diaphragm. — A  term  sometimes  employed 
for  a  plate  form  of  porous  cell. 

Diaphragm  Currents.— (See  Currents, 
Diaphragm.  Cell,  Porous?) 

Diaphragm  of  Voltaic  Cell.— A  term 
sometimes  used  for  the  porous  cell  of  a 
double  fluid  voltaic  cell  when  in  the  form  of 
a  plate. 

Dice-Box  Insulator. — (See  Insulator^ 
Dice-Box.) 

Dielectric. — A  substance  which  permits 
induction  to  take  place  through  its  mass. 

This  word  is  sometimes,  but  improperly,  writ- 
ten Di-Electric. 

The  substance  which  separates  the  opposite 
coatings  of  a  condenser  is  called  the  dielectric. 
All  dielectrics  are  non-conductors. 

All  non-conductors  or  insulators  are  dielectrics, 
but  their  dielectric  power  is  not  exactly  propor- 
tional to  their  non-conducting  power. 

Substances  differ  greatly  in  the  degree  or  ex- 
tent  to  which  they  permit  induction  to  take  place 
through  or  across  them.  Thus,  a  certain  amount 
of  inductive  action  takes  place  between  the  insu- 
lated metal  plates  of  a  condenser  across  the  layer 
of  air  between  them. 

A  dielectric  may  be  regarded  as  pervious  to 
rapidly  reversed  periodic  currents,  but  opaque  to 
continuous  currents.  There  is,  however,  some 
conduction  of  continuous  currents. 

According  to  Swinburne,  there  are  three  species 
of  conduction  that  may  take  place  in  dielectrics, 
all  of  which  produce  a  heating  of  the  dielectric, 
viz.: 

(i.)  Metallic  Conduction,  i.  e.,  such  a  conduc- 
tion as  takes  place  in  a  metal.  This  kind  of  con- 
duction arises  from  the  presence  of  metallic  par- 
ticles embedded  in  the  dielectric. 

(2.)  Disruptive  Conduction,  or  a  momentary 
current  accompanying  a  disruptive  discharge. 

(3.)  Electrolytic  Conduction,  •  or  that  kind  of 
conduction  which  accompanies  the  electrolysis 
of  a  conductor.  This  kind  of  conduction  may 
take  place  in  some  kinds  of  glass. 

Faraday  regarded  the  dielectric  as  the  true  seat 
of  electric  phenomena.  Conducting  substances 
he  considered  as  mere  breaks  in  the  continuity  of 
the  dielectric.  This  is  the  view  now  generally 
held. 

Dielectric  Capacity.— (See  Capacity,  Di- 
electric.) 


Die. 


162 


[Dim. 


Dielectric     Constant— (See     Constant. 
Dielectric.) 
Dielectric  Density  of  a  Gas.— (See  Gas, 

Dielectric  Density  of) 

Dielectric,  Polarization  of A 

molecular  strain  produced  in  the  dielectric  of  a 
Leyden  jar  or  other  condenser,  by  the  attrac- 
tion of  the  electric  charges  on  its  opposite 
faces,  or  by  the  electrostatic  stress.  (See 
Strain,  Dielectric) 

A  term  formerly  employed  in  place  of 
electric  displacement. 

Faraday,  in  his  study  of  the  action  of  induction, 
in  denying  the  possibility  of  action  at  a  distance, 
thought  that  the  dielectric  through  which  indue- 
tion  takes  place  was  polarized,  and  that  in  this 
way  the  induction  was  transmitted  across  the 
intervening  space  between  the  inducing  and  the 
induced  body,  by  the  action  of  the  contiguous 
particles  of  the  dielectric. 

The  polarization  of  the  glass  of  a  Leyden  jar, 
and  the  accompanying  strain,  are  seen  by  the 
frequent  piercing  of  the  glass,  and  by  the 
residual  charge  of  the  jar.  (See  Charge,  Resid- 
ual.} 

Dielectric  Resistance.— (See  Resistance, 
Dielectric) 

Dielectric  Strain.— (See  Strain,  Dielec- 
tric) 

Dielectric  Strength  of  a  Gas.— (See  Gas, 
Dielectric  Strength  of) 

Dielectric  Stress. — (See  Stress,  Dielec- 
tric) 

Difference  of  Potential.— (See  Potential, 
Difference  of) 

Differential  Electric  Bell.— (See  Bell, 
Differential  Electric) 

Differential  Galvanometer. — (See  Gal- 
vanometer, Differential) 

Differential  Inductometer. — (See  Induc- 
tometer,  Differential) 

Differential  Method  of  Duplex  Teleg. 
raphy.— (See  Telegraphy,  Duplex,  Differ- 
ential Method  of  ) 

Differential  Relay.— (See  Relay,  Differ- 
ential) 

Deferential  Thermo-Pile. — (See  Pile, 
T^'.-mo,  Differential) 


Differential  Voltameter.— (See    Voltam- 
eter, Siemens'  Differential.} 
Differentially     Wound     Motor.  —  (See 

Motor.  Differentially  Wound.) 

Diffusion,  Anodal A  term  applied 

to  the  introduction  of  any  drug  into  the  human 
body  by  electricity. 

The  cataphoretic  introduction  of  drugs 
into  the  body.  (See  Cataphoresis) 

A  sponge  or  other  similar  electrode,  saturated 
with  a  solution  of  the  drug,  is  connected  with 
the  anode  of  a  source  and  placed  over  the  part 
to  be  treated  and  its  kathode  connected  to 
another  part  of  the  body  in  a  nearly  direct  line 
with  the  anode  and  the  current  passed, 

Diffusion  Creep. — (See  Creep.  Diffusion) 

Diffusion  of  Electric  Current— (See 
Current,  Diffusion  of) 

Diffusion  of  Lines  of  Force.— (See  Force. 
Lines  of,  Diffusion  of) 

Dimensions  of  Acceleration.— (See  Ac- 
celeration, Dimensions  of) 

Dimensions  of  Units — (See  Units,  Dimen- 
sions of) 

Diminished  Electric  Irritability.— (See 
Irritability,  Electric,  Diminished) 

Dimmer A  choking  coil,  employed 

in  a  system  of  distribution  by  converters  or 
transformers,  for  regulating  the  potential  of 
the  feeders. 

The  dimmer  consists  essentially  of  a  choking 
coil  wound  around  a  laminated  ring  of  soft  iron, 


Fig.  20  T.  Rf action  Coil  Dimmer. 
and  provided  with  an  envelope  of  heavy  copper. 
The  copper  ring,  by  its  position  as  regards  the 
choking  coil,  adjusts  or  regulates  the  self-induc- 
tion of  the  coil,  and  consequently  regulates  the 
potential  of  the  feeders.  The  dimmer  is  used  in 
theatres  or  similar  situations  to  turn  the  lights  up 
or  down. 


Dio.] 


163 


[Dip. 


The  reaction  coil  or  dimmer  is  shown  in  Fig. 
201.  The  choking  coil  is  wound  on  a  ring  of 
iron.  The  copper  sheath  is  furnished  with  a 
handle  to  permit  its  position  to  be  readily 
changed  with  respect  to  the  coil  of  insulated  wire. 
A  laminated  iron  drum  is  supported  on  bearings 
inside  the  ring.  When  the  sheath  is  over  the 
coil,  the  coil  offers  but  a  small  resistance  to  the 
passage  of  the  current.  When  away  from  it  the 
self-induction  of  the  coil  is  increased. 

Dioptre. — A  unit  of  refracting  power. 

A  lens  of  one  dioptre  has  a  focal  length  of 
one  metre.  One  of  two  dioptres  has  a  focal 
length  of  50  centimetres;  one  of  four  dioptres 
25  centimetres.  This  is  also  spelled  dioptry. 

Dioptric. — Relating  to  dioptrics. 

Dioptrics. — The  science  which  treats  of 
the  refraction  of  light. 

Dioptry. — A  word  sometimes  used  for  di- 
optre. (See  Dioptre?) 

Dip,  Magnetic  —  — The  deviation  of  a 
magnetic  needle  from  a  true  horizontal  posi- 
tion. 

The  inclination  of  the  magnetic  needle  to- 
wards the  earth. 

The  magnetic  needle  shown  in  Fig.  202,  though 


//I 

Fig.  20  2.    Angle  of  Dip. 

supported  at  its  centre  of  gravity,  will  not  retain 
a  horizontal  position  in  all  places  on  the  earth's 
surface. 


In  the  northern  hemisphere  its  north-seeking 
end  will  dip  or  incline  at  an  angle  B  O  C,  called 
the  angle  of  dip.  In  the  southern  hemisphere 
its  south  seeking  end  will  dip. 

The  cause  of  the  dip  is  the  unequal  distance  of 
the  magnetic  poles  of  the  earth  from  the  poles  of 
the  needle. 

The  magnetic  equator  is  a  circle  passing 
around  the  earth  midway  (in  intensity)  between 
the  earth's  magnetic  poles.  There  is  no  dip  at 
the  magnetic  equator.  At  either  magnetic  pole 
the  angle  of  dip  is  90  degrees. 

Dip,  or  Inclination,  Angle  of 

The  angle  which  a  magnetic  needle,  free  to 
move  in  both  a  vertical  and  a  horizontal  plane, 
makes  with  a  horizontal  line  passing  through 
its  point  of  support. 

The  angle  of  dip  of  a  magnetic  needle. 
(See  Inclination,  Angle  of.} 

Diplex  Telegraphy.— (See  Telegraphy. 
Diplex) 

Dipping. — An  electro-metallurgical  process 
whereby  a  deposit  or  thin  coating  of  metal 
is  obtained  on  the  surface  of  another  metal 
by  dipping  it  in  a  readily  decomposable 
metallic  salt. 

Cleansing  surfaces  for  electro-plating  pro- 
cesses by  immersing  them  in  various  acid 
liquors. 

Dipping,  Bright Dipping  in  acid 

liquors  for  the  purpose  of  obtaining  a  bright 
electro-metallurgical  coating. 

Dipping  Circle.— (See  Circle,  Dipping^ 

Dipping,  Dead Dipping  in  acid 

liquors  for  the  purpose  of  obtaining  a  dead  or 
unpolished  surface  on  an  electro-metallurgical 
coating. 

Dipping,  Electro-Metallurgical — 

A  process  for  obtaining  an  electro-metallur- 
gical deposit  on  a  metallic  surface  by  dipping 
it  in  a  solution  of  a  readily  decomposable 
metallic  salt. 

A  bright,  polished  iron  surface,  when  simply 
dipped  into  a  solution  of  copper-sulphate,  re- 
ceives a  coating  of  metallic  copper  from  the  elec. 
trolytic  action  thus  set  up. 

This  process  is  known  technically  as  dipping. 
The  term  dipping  is  also  used  in  electro -metal- 
lurgy to  indicate  the  process  of  cleaning  the 


Dir.] 


164 


[Dis. 


articles,  that  are  to  be  electro-plated,  by  dipping 
them  in  various  acid  or  alkaline  baths. 

Direct  Current.— (See  Current,  Direct) 

Direct-Current  Electric  Motor.— (See 
Motor,  Electric,  Direct-Current) 

Direct  Electromotive  Force. — (See  Force, 
Electromotive,  Direct?) 

Direct  Excitation.— (See  Excitation, 
Direct) 

Direct-Induced  Current. — (See  Current, 
Direct-Induced) 

Direct,  or  Break-Induced  Current 

—(See  Current,  Direct.  Current,  Break- 
Induced) 

Direct  Working.— (See  Working,  Direct) 

Direction,  Negative,  of  Electrical  Con- 

Tection  of  Heat A  direction  in  which 

heat  is  transmitted  through  an  unequally 
heated  conductor  by  electric  convection, 
during  the  passage  of  electricity  through  the 
conductor,  opposite  that  of  the  current.  (See 
Heat,  Electric  Convection  of) 

Direction  of  Lines  of  Force.— (See  Force, 
Lines  of,  Direction  of) 

Direction,  Positive,  of  Electrical  Con- 

Tection    of    Heat A    direction    in 

which  heat  is  transmitted  through  an  un- 
equally heated  conductor  by  electric  convec- 
tion, during  the  passage  of  electricity  through 
the  conductor,  the  same  as  that  of  the  cur- 
rent. (See  Heat,  Electric  Convection  of) 

Direction,   Positive,  Round   a    Circuit 

In    a  plane  circuit  looked    at  from 

one  side,  a  direction  opposite  to  that  of  the 
hands  of  a  clock. 

This  is  a  convention  which  has  been  made  in 
order  to  conveniently  connect  the  direction  of  the 
electromotive  force  produced  by  induction,  with 
the  direction  of  the  induction. 

Direction,  Positive,  Through  a  Circuit 

In  a  plane    circuit,  looked  at  from 

one  side,  a  direction  through  the  circuit  away 
from  the  observer. 

Directive  Tendency  of  Magnetic  Needle. 
— (See  Needle,  Magnetic,  Directive  Ten- 
dency of) 

Disc,    Arago's A  disc    of    copper 


or  other  non-magnetic  metallic  substance, 
which,  when  rapidly  rotated  under  a  mag- 
netic needle,  supported  independently  of  the 
disc,  causes  the  needle  to  be  deflected  in  the 
direction  of  rotation,  and,  when  the  velocity 
of  the  disc  is  sufficiently  great,  to  rotate  with  it. 
Such  disc  is  shown  in  Fig.  203  at  b.  The  move- 


Fig.  203.    Arago's  Disc. 

ment  of  the  needle  is  due  to  electric  currents,  in- 
duced  by  the  disc  moving  through  the  field  of  the 
needle  so  as  to  cut  its  lines  of  magnetic  force.  To 
obtain  the  best  results  the  disc  must  move  very 
rapidly,  and  should  be  near  the  needle.  More- 
over, the  needle  should  be  powerful. 

This  effect  was  discovered  by  Arago,  in  1824. 
Since  a  magnetic  needle  moving  over  a  metalHc 
plate  produces  electric  currents  in  a  direction 
which  tends  to  stop  the  motion  of  the  needle,  a 
damping  of  the  motion  of  a  magnetic  needle  is 
sometimes  effected  by  causing  it  to  move  near  a 
metal  plate.  The  induced  currents,  which  the 
needle  produces  in  the  plate  by  its  motion  over  it, 
tend  to  retard  the  motion  of  the  needle.  (See 
Damping.  Law,  Lenz's.) 

Disc  Armature.— (See  Armature,  Disc) 

Disc,    Faraday's A    metallic  disc 

movable  in  a  magnetic  field  on  an  axis 
parallel  to  the  direction  of  the  field. 

Such  a  disc  is  shown  in  Fig.  204,  and  moves, 


Fig.  304-    Faraday's  Disc. 

as  will  be  seen,  so  as  to  cut  the  lines  of  magnetic 
force  at  right  angles. 

The  difference  of  potential  generated  by  the 
motion  of  such  a  disc  may  be  caused  to  produce 
a  current,  by  providing  a  circuit  which  is  com- 
pleted through  the  portion  of  the  disc  that  at  any 


Dis.] 


165 


[Dis. 


moment  of  its  rotation  is  situated  between  spring 
contacts  resting  on  the  axis  of  rotation  and  the 
circumference  of  the  disc,  respectively. 
In  Barlow's  or  Sturgeon's  wheel,  Fig.  205,  the 


Fig.  2  OS-    Barlow's  Wheel. 

wheel  itself  rotates  in  the  direction  shown,  when 
a  current  is  sent  through  it  in  a  direction  indicated 
by  the  arrows. 

Discharge. — The  equalization  of  the  dif- 
ference of  potential  between  the  terminals  of 
a  condenser  or  source,  on  their  connection  by 
a  conductor. 

The  removal  of  a  charge  from  the  surface 
of  any  charged  conductor  by  connecting  it 
with  the  earth,  or  another  conductor. 

The  removal  of  a  charge  by  means  of  a 
stream  of  electrified  air  particles. 

The  discharge  of  an  insulated  conductor,  a 
cloud,  a  condenser,  or  a  Leyden  battery,  is  oscil- 
latory. The  oscillatory  currents  continue  but  for 
a  short  time.  The  discharge  is  therefore  often 
spoken  of  as  producing  momentary  currents. 

The  discharge  of  a  voltaic  battery,  or  a  stor- 
age battery,  is  nearly  continuous,  and  furnishes  a 
current  which  is  practically  continuous,  as  dis- 
tinguished from  the  momentary  currents  produced 
by  the  discharge  of  a  condenser. 

A  discharge  may  be  alternating,  brush,  brush 
and  spray,  conductive,  convective,  dead-beat, 
disruptive,  flaming,  glow,  lateral,  oscillatory, 
periodic,  stratified,  streaming,  impulsive  and 
periodic. 

Discharge,  Alternating An  elec- 
tric discharge  which  changes  its  direction  at 
regular  intervals  of  time. 

A  periodic  discharge. 

Discharge,  Brush A  faintly  lu- 
minous discharge  that  occurs  from  a  pointed 
positive  conductor. 

The  brush  discharge  is  a  species  of  convective 
discharge.  In  it,  the  streams  of  electrified  air 
particles  assume  the  characteristic  brush  shape. 
(See  Discharge,  Convective. ) 


Discharge,    Brush-and-Spray A 

form  of  streaming  discharge  obtained  by  in- 
creasing the  frequency  of  the  alternations 
of  a  high  potential  current  which  assumes 
the  appearance  of  a  spray  of  silver-white 
sparks,  or  a  bunch  of  thin  silvery  threads 
around  a  powerful  brush. 

Some  idea  of  the  brush-and-spray  discharge 
may  be  obtained    from    Fig.   206,   taken  from 


Fig.  206.    Brush-and-Spray  Discharge  ( Tesla.). 
Tesla,  who  has  carefully  studied  these  phenom- 
ena. 

The  brush-and-spray  discharge  is  best  obtained, 
according  to  Tesla,  by  bringing  the  terminals 
of  a  source  of  rapidly  alternating  electrostatic 
currents  of  high  potential  somewhat  nearer  to- 
gether, when  the  streaming  discharge  has  been 
obtained,  and  preferably  increasing  the  frequency 
of  the  alternations. 

The  brush-and-spray  discharge,  when  power- 
ful, closely  resembles  a  gas  flame  from  gas  escap- 
ing under  great  pressure.  Says  Tesla:  "But 
they  do  not  only  resemble,  they  are  veritable 
flames,  for  they  are  hot.  Certainly  they  are  not 
as  hot  as  a  gas-burner,  but  they  would  be  so  if  the 
frequency  and  the  potential  would  be  sufficiently 
high." 

The  brush-and-spray  discharge,  at  higher  fre- 
quencies, passes  into  a  form  of  discharge  for  which 
Tesla  has  proposed  no  particular  name.  He  de- 
scribes this  form,  in  a  publication  of  a  lecture 
before  the  American  Institute  of  Electrical  Engi- 
neers, as  follows,  viz. : 

'•If  the  frequency  is  still  more  increased,  then 
the  coil  refuses  to  give  any  spark  unless  at  com- 
paratively small  distances,  and  the  fifth  typical 
form  of  discharge  may  be  observed  (Fig.  207). 
The  tendency  to  stream  out  and  dissipate  is  then 
so  great  that  when  the  brush  is  produced  at  one 
terminal  no  sparking  occurs,  even  if,  as  I  have  re- 
peatedly tried,  the  hand,  or  any  conducting  ob- 
ject, is  held  within  the  stream  ;  and,  what  is  more 


Dis.] 


166 


[Dis. 


singular,  the  luminous  stream  is  not  at  all  easily 
deflected  by  the  approach  of  a  conducting  body. 

"At  this  stage  the  streams  seemingly  pass  with 
the  greatest  freedom  through  considerable  thick- 
nesses of  insulators,  and  it  is  particularly  interest- 
ing to  study  their  behavior.  For  this  purpose  it 
is  convenient  to  connect  to  the  terminals  of  the 
coil  two  metallic  spheres,  which  may  be  placed  at 
any  desired  distance  ( Fig .  208) .  Spheres  are  pref - 


Fig.  207.    Fifth.  Typical  Farm  of  Discharge  ( Tetla). 

erable  to  plates,  as  the  discharge  can  be  better 
observed.  By  inserting  dielectric  bodies  between 
the  spheres,  beautiful  discharge  phenomena  may 
be  observed.  If  the  spheres  be  quite  close  and  a 
spark  be  playing  between  them,  by  interposing  a 
thin  plate  of  ebonite  between  the  spheres  the 
spark  instantly  ceases  and  the  discharge  spreads 
into  an  intensely  luminous  circle  several  inches  in 
diameter,  provided  the  spheres  are  sufficiently 
large.  The  passage  of  the  stream  heats,  and, 
after  a  while,  softens  the  rubber  so  much  that  two 


Fig.  208.    Luminous  Discharge  with  Interposed 
Insulators. 

plates  may  be  made  to  stick  together  in  this  man- 
ner. If  the  spheres  are  so  far  apart  that  no  spark 
occurs,  even  if  they  are  far  beyond  the  striking 
distance,  by  inserting  a  thick  plate  of  glass  the 
discharge  is  instantly  induced  to  pass  from  the 
spheres  to  the  glass  in  the  form  of  luminous 
streams.  It  appears  almost  as  though  these 


streams  pass  through  the  dielectric.  In  reality 
this  is  not  the  case,  as  the  streams  are  due  to  the 
molecules  of  the  air  which  are  violently  agitated 
in  the  space  between  the  oppositely  charged  sur. 
faces  of  the  spheres. 

"  When  no  dielectric  other  than  air  is  present, 
the  bombardment  goes  on,  but  is  toD  weak  tc 
be  visible;  by  inserting  a  dielectric  the  indiX 
tive  effect  is  much  increased,  and  besides,  the 
projected  air  molecules  find  an  obstacle  and  the 
bombardment  becomes  so  intense  that  the  streams 
become  luminous.  If  by  any  mechanical  means 
we  could  effect  such  a  violent  agitation  of  the 
molecules  we  could  produce  the  same  phenom- 
enon. A  jet  of  air  escaping  through  a  small 
hole  under  enormous  pressure  and  striking 
against  an  insulating  substance,  such  as  glass, 
may  be  luminous  in  the  dark,  and  it  might  be 
possible  to  produce  phosphorescence  of  the  glass 
or  other  insulators  in  this  manner. 

"  The  greater  the  specific  inductive  capacity  of 
the  interposed  dielectric,  the  more  powerful  the 
effect  p.  oduced.  Owing  to  this  the  streams  show 
themselves  with  excessively  high  potentials  even 
if  the  glass  be  as  much  as  one  and  one-half  to  two 
inches  thick.  But  besides  the  heating  due  to  bom- 
bardment, some  heating  goes  on  undoubtedly  in 
the  dielectric,  being  apparently  greater  in  glass 
than  in  ebonite.  I  attribute  this  to  the  greater 
specific  inductive  capacity  of  the  glass  in  conse- 
quence of  which,  with  the  same  potential  differ- 
ence, a  greater  amount  of  energy  is  taken  up  in  it 
than  in  rubber.  It  is  like  connecting  to  a  battery 
a  copper  and  a  brass  wire  of  the  same  dimen- 
sions. The  copper  wire,  though  a  more  perfect 
conductor,  would  heat  more  by  reason  of  its  tak- 
ing more  current.  Thus  what  is  otherwise  con- 
sidered a  virtue  of  the  glass  is  here  a  defect. 
Glass  usually  gives  way  much  quicker  than  ebo- 
nite ;  when  it  is  heated  to  a  certain  degree  tht 
discharge  suddenly  breaks  through  at  one  point, 
assuming  then  the  ordinary  form  of  an  arc." 

Discharge,  Conductive  -  —  A  dis- 
charge effected  .by  leading  the  charge  off 
through  a  conductor  placed  in  contac*  with 
the  charged  body. 

Discharge,  Conrective  -  —  A  dis- 
charge which  occurs  from  the  points  on  the 
surface  of  a  highly  charged  conductor, 
through  the  repulsion  by  the  conductor  of  air 
particles  that  in  this  manner  carry  off  minute 
charges. 


Dis.] 


167 


[Dis. 


A  convective  discharge,  though  often  attended 
by  a  feeble  sound,  is  sometimes  called  a  silent 
discharge,  in  order  to  distinguish  it  from  the 
noisy,  disruptive  discharge,  which  is  attended  by 
a  sharp  snap,  or  when  considerable,  by  a  loud 
report. 

A  convective  discharge  is  also  called  a  glow  or 
brush  discharge.  The  latter  is  best  seen  at  the 
small  button  at  the  end  of  the  prime  or  positive 
conductor  of  a  factional  electric  machine. 

The  positive  discharge  from  a  point  or  small 
rounded  conductor  is  always  brush-shaped;  the 
negative  discharge  is  always  star  shaped. 

In  rarefied  gases,  the  discharge  is  convective  in 
character  and  produces  various  luminous  effects 
of  great  beauty,  the  color  of  which  depends  on 
the  kind  of  gas,  and  the  size,  shape  and  material 
of  the  electrodes,  and  on  the  degree  of  the  vacuum . 
Thus  in  the  rarefied 
space  of  the  vessel  shown 
in  Fig.  209,  the  discharge  I 
becomes  an  ovoidal  mass 
of  light,  sometimes  called 
the  Philosopher's  Egg. 

When  the  discharges 
in  rarefied  gases  follow 
one  another  very  rapid- 
ly, alternations  of  light 
and  darkness,  or  stratifi- 
cations, or  stria  are  pro-  ] 
duced. 

The  breadth  of  the  I 
dark  bands  increases  as  j 
the  vacuum  becomes 
higher.  The  light  por- 
tions start  at  the  positive  I 
electrode,  and  are  hotter  f 
than  the  dark  portijns. 

The  effects  of  luminous 
convecti  ve  discharges  are 
best  seen  in  exhausted  glass  tubes,  called  Geissler 
tubes,  containing  residual  atmospheres  of  various 
gases.  (See  Tubes,  Geissler.) 

Discharge,  Dead-Beat A  non- 
oscillatory  discharge.  (See  Discharge, 
Oscillatory^) 

Discharge,  Disruptive A  sudden, 

and  more  or  less  complete,  discharge  that 
takes  place  across  an  intervening  non-con- 
ductor or  dielectric. 

A  mechanical  strain  of  the  dielectric  occurs, 
which  suddenly  breaks  down  as  it  were  and  per- 


mits the  discharge  to  pass  as  a  spark,  or  raplc* 
succession  of  sparks. 

In  air,  the  spark,  when  long,  generally  takes 
the  zigzag  path,  as  shown  in  Fig.  210. 

The  sparks  produced  by  disruptive   discharges 
consist  of  heated   gases, 
together  with  portions  of 
the   conductor   that  are 
volatilized  by  the  heat. 

The  discharge  of  a  Ley- 
denjar  or  condenser  may 
be  disruptive,  as  when 
the  discharging  rod  is 
held  with  one  knob  con- 
nected with  one  coating, 
and  the  other  near  the 
other  coating.  It  may 
be  gradual,  as  when  the 
two  coatings  are  alter- 
nately connected  with  the 
ground.  The  discharge 
of  a  Leyden  jar  as,  in- 
deed, the  disruptive  dis- 
charge in  general,  is  os- 
cillatory. 

The  stress  is  often  suf- 
ficient to  pierce  the  glass. 

Discharge,  Dura- 
tion of  —  The 

time  required  to  effect  a  complete  disruptive 
discharge. 

The  disruptive  discharge  is  not  instantaneous; 
some  time  is  required  to  effect  it.  Estimates  of 
the  duration  of  a  flash  of  lightning  based  on  the 
duration  of  a  Leyden  jar  discharge,  are  mislead- 
ing from  the  enormous  difference  in  the  quantity 
and  the  potential  in  the  two  cases.  The  fact  that 
the  disruptive  discharge  is  oscillatory  and  consists 
of  a  number  of  discharges  taking  place  in  alter, 
nately  opposite  directions  shows  that  the  discharge 
is  not  instantaneous. 

Leyden  jar  discharges,  are,  however,  accom- 
plished in  very  small  periods  of  time. 

Discharge,  Flaming The   white 

and  flaming  arc-like  discharge  that  occurs 
between  the  terminals  of  the  secondary  of  an 
induction  coil,  when,  with  a  great  number  of 
alternations  per  second,  the  current  through 
the  primary  is  increased  beyond  that  required 
for  the  sensitive-thread  discharge.  (See  Dis> 
charge,  Sensitive-  Thread!) 


Fig.  210.    Disruptive 
Discharge. 


Dis.] 


168 


[Dis. 


According  to  Tesla  the  flaming  discharge  is 
best  produced  when  the  number  of  alternations  is 
not  too  great  and  certain  relations  between  ca- 
pacity, self-induction  and  frequency  are  observed. 
These  relations  must  be  such  as  will  permit  the 
flow  through  the  circuit  of  the  maximum  current, 
and  thus  may  be  obtained  with  wide  variations  in 
the  frequency.  The  flaming  discharge  develops 
considerable  heat,  and  is  characterized  by  the 
absence  of  the  shrill  note  accompanying  less  pow- 
erful discharges.  This  is  probably  due  to  the 
enormous  frequency. 

Some  idea  of  the  flaming  discharge  may  be  had 


Fig.  si i.    Flaming  Discharge  ( Tesla). 
from  an  inspection  of  Fig.  211,  taken  from  Tesla. 

Discharge,  Glow A  form  of  con- 

vective  discharge.      (See  Discharge,   Con- 
nective) 

Discharge,  impulsive A  dis- 
charge produced  in  conductors  by  suddenly 
created  differences  of  potential. 

Impulsive  discharges  are  influenced  more  by  the 
inductance  of  a  conductor  than  by  its  true  ohmic 
resistance.  (See Inductance.  Resistance,  Ohmic.) 

A  mass  of  guncotton  simply  ignited  in  the 
open  air,  produces  but  little  effect  on  any  resisting 
object  placed  below  it.  If,  however,  itbe  rapidly 
ignited  by  means  of  a  detonator,  and  is  thus  fired 
with  much  greater  rapidity,  it  may  shatter  any- 
thing placed  beneath  it. 

In  a  similar  manner,  a  rapidly  discharged  cur- 
rent, or  impulsive  discharge,  produces,  through  the 
inductance  of  the  conductor,  a  series  of  effects 
somewhat  similar  to  the  above,  in  which  a  great 
impedance  is  produced  by  a  sudden  change  of 
direction. 

Discharge,    Induced    Currents,    Effects 

Produced    by    — Varying    classes  of 

effects  produced  by  the  discharges  of  induced 


The  effects  produced  by  discharges  of  induced 
currents  are  classified  by  Fleming  as  follows: 

(i.)  Effects  depending  on  the  entire  quantity  of 
the  discharge. 

a.  Galvanometric  effects. 

If  the  needle  of  the  galvanometer  has  a  period 
or  time  of  oscillation  that  is  long,  as  compared 
with  the  time  of  duration  of  the  discharge,  the  sine 
of  one-half  the  angle  of  deflection  is  proportional 
to  the  whole  quantity  of  the  discharge. 

b.  Electro-chemical  effects. 

The  quantity  of  an  electrolyte  broken  up  is 
proportional  to  the  quantity  of  electricity  which 
passes  through  it. 

(2.)  Effects  depending  on  the  average  of  the 
square  of  the  current  strength  at  any  instant  dur- 
ing the  discharge. 

a.  Heating  effects. 

The  rate  of  dissipation  as  heat,  according  to 
Joule's  law,  is  proportional  to  the  square  of  the 
current  strength  passing. 

b.  Electro-dynamic  effects. 

When  a  discharge  passes  through  a  circuit, 
part  of  which  is  fixed  and  part  movable,  the  forces 
of  attraction  and  repulsion  which  take  place  be- 
tween them  at  any  instant  are  proportional  to 
the  square  of  the  current  strength. 

(3.)  Effects  depending  on  rate  of  change  of 
the  current. 

a.  Physiological  effects. 

The  effect  of  the  discharge  in  producing  physi- 
ological shock  increases  with  the  suddenness  of 
the  discharge.  Of  two  discharges  which  reached 
the  same  maxima  that  which  reached  it  first  would 
produce  the  greatest  physiological  effect.  Recent 
investigations  by  Tesla  and  others  would  appear  to 
partly  disprove  the  above  statement 

b.  Telephonic  effects. 

The  telephone,  like  the  body  of  an  animal,  is 
affected  more  by  the  rate  of  change  than  by  the 
current  strength  at  any  instant. 

c.  Magnetic  effects. 

Rayleigh  has  shown  that  the  magnetic  effects  of 
the  discharge  depend  upon  the  maximum  current 
strength  during  the  discharge,  or  upon  the  initial 
current  strength,  in  cases  where  the  current  dies 
away  gradually.  Since  the  time  required  for  the 
permanent  magnetizing  of  a  steel  wire  is  small 
compared  with  the  duration  of  the  induced  cur- 
rent, the  amount  of  magnetism  acquired  depends 
essentially  on  the  initial  or  maximum  current 
strength  during  the  discharge,  irrespective  of  the 
time  during  which  said  discharge  lasts. 


Dis.] 


169 


[Dis. 


d.  Luminous  effects. 

These  are  also  dependent  in  the  case  of  induced 
discharges  on  the  rate  of  change  of  the  current. 

Discharge-Key. — (See  Key,  Discharged) 

Discharge,   Lateral  •  — A  discharge, 

taking  place  on  the  discharge  of  a  Leyden  jar, 
or  other  disruptive  discharge,  between  parts 
of  the  jar  or  conductors,  not  in  the  circuit  of 
the  main  discharge. 

If  a  charged  Leyden  jar  is  placed  on  an  insulat- 
ing stool,  and  is  then  discharged  by  the  discharg- 
ing rod,  the  lateral  discharge  is  seen  as  a  small 
spark  that  passes  between  the  outside  coating  of 
the  jar  and  a  body  connected  with  the  earth  at 
the  moment  of  the  discharge  through  the  rod. 

A  lateral  discharge  is  also  seen  in  the  sparks 
that  can  be  taken  from  a  conductor  in  good  con- 
nection with  the  earth,  by  holding  the  hand  near 
the  conductor,  while  it  is  receiving  large  sparks 
from  a  powerful  machine  in  operation.  These 
discharges  are  due  to  induction. 

If  a  Leyden  jar  be  discharged  by  means  of  a  con- 
ducting wire  bent  as  shown  in  Fig.  212,  in  which 


E 


Fig.    212. 

two  parts  of  the  circuit  are  closely  approached  as  at 
A,  whenever  a  spark  occurs  at  B,  another  spark 
produced  by  a  lateral  discharge  occurs  at  A. 
Although  the  resistance  of  the  metallic  circuit  is 
enormously  less  than  the  resistance  of  the  air 
space  through  which  the  lateral  discharge  occurs, 
yet  the  counter  electromotive  force  produced  in 
the  metallic  circuit  by  the  impulsive  discharge, 
renders  its  resistance  far  greater  than  that  of 
the  air  space.  The  path  of  a  lateral  discharge 
is  called  the  alternative  path.  (See  Path,  Al- 
ternative. ) 

Discharge,  Luminous  Effects  of  — • 

The  luminous  phenomena  attending  and  pro- 
duced by  an  electric  discharge. 

The  luminous  effects  vary  as  to  color,  intensity, 
shape  and  accompanying  acoustic  phenomena 
according  to  a  variety  of  circumstances,  the  prin- 
cipal of  which  are  as  follows,  viz. : 

(i.)  With  the  kind  of  gaseous  medium  through 
which  the  discharge  passes.  Thus,  a  spark  passed 
through  hydrogen  has  a  crimson  or  reddish  color; 


through  carbonic  acid  or  chlorine,  a  greenish 
color. 

(2.)  With  the  density  of  the  medium.  In  a 
partial  vacuum,  the  discharge  from  an  induction 
coil  becomes  an  ovoidal  mass  of  light.  As  the 
vacuum  increases,  the  light  at  first  grows  brighter, 
but  as  a  higher  vacuum  is  reached,  striae  of  al- 
ternate dark  and  light  bands  appear.  Finally, 
with  very  high  vacua  the  discharge  fails  to  pass. 
(See  Discharge^  Connective.) 

(3.)  With  the  nature  of  the  substances  forming 
the  points  from  which  the  discharge  is  taken. 
This  is  due  to  the  partial  volatilization  of  the  ma- 
terial of  the  electrodes. 

(4.)  With  the  kind  of  electricity,  *'.  <?.,  whether 
positive  or  negative.  A  positive  charge  assumes 
the  shape  of  a  fan;  a  negative  discharge,  that  of 
a  star. 

(5.)  On  the  density  of  the  discharge.  The  in- 
troduction of  a  Leyden  jar  or  condenser  in  the 
circuit  of  a  Holtz  machine,  for  example,  causes 
the  spark  to  change  from  the  faint  bluish  to  the 
silvery  white. 

(6. )  The  disruptive  discharge  through  air  is  at- 
tended by  snapping  or  crackling  sound,  which,  in 
the  case  of  lightning,  reaches  the  intensity  of  thun- 
der. When  the  disruptive  discharge  takes  place 
through  a  vacuum  a  faint  hissing  sound  is  heard, 
or  all  sound  may  entirely  disappear. 

(7. )  Luminous  effects  resulting  from  molecular 
bombardment  occurring  in  comparatively  high 
vacua.  These  luminous  effects  may  result : 

(a.)  From  actual  incandescence  of  some  refrac- 
tory material  produced  by  the  blows  of  the  mole- 
cules; or, 

(b.)  As  a  result  of  phosphorescence  or  fluores- 
cence due  to  such  blows. 

Canary  glass,  or  glass  stained  by  uranium  oxide, 
fluoresces  and  emits  a  yellowish  green  light;  solu- 
tion of  sulphate  of  quinine  emits  a  bluish  light. 

Discharge,    Non-Oscillatory A 

dead-beat  discharge.  (See  Discharge,  Dead- 
Beat.} 

Discharge,  Oscillating A  number 

of  successive  discharges  and  recharges  which 
occur  on  the  disruptive  discharge  of  a  Leyden 
jar,  or  condenser. 

A  discharge  which  periodically  decreases 
by  a  series  of  oscillations. 

A  discharge  which  produces  a  dying-away- 
backwards  and  forwards  current. 


Dis.] 


170 


[Dis 


The  disruptive  discharge  ot  a  Leyden  jar,  or 
condenser,  is  not  effected  by  a  single  rush  of  elec- 
tricity. When  discharged  through  a  compara- 
tively small  resistance,  a  number  of  alternate 
partial  discharges  and  recharges  occur,  which 
produce  true  oscillations  or  undulatory  discharges. 
These  oscillations  are  caused  by  the  induction 
of  the  discharge  on  itself,  and  are  similar  to  the 
self-induction  of  a  current. 

The  existence  of  the  oscillating  discharge  hi  the 
case  of  a  Leyden  jar  or  condenser,  proves,  in  the 
opinion  of  some,  that  electricity,  taken  along 
with  matter,  possesses  a  property  similar  to 
inertia. 

Discharge,    Oscillatory A    term 

sometimes  used  for  an  oscillating  discharge. 
{See  Discharge,  Oscillating) 

Discharge,  Periodic  — An  electric 

•discharge  which  changes  its  direction  at  reg- 
ular intervals  or  periods. 
An  alternating  discharge. 

Discharge,  Periodically-Decreasing 

— An  oscillating  discharge  whose  decrease  is 
periodic.  (See  Discharge,  Oscillating^ 

Discharge,  Sensiti re-Thread The 

thin,  thread-like  discharge  that  occurs  be- 
tween the  terminals  of  the  secondary  of  an  in- 
duction coil  of  high  frequency. 

The  sensitive-thread  discharge  occurs,  accord- 
ing to  Tesla,  when  the  number  of  alternations  per 


Fig.  2 13-    Sensitive-  Thread  Discharge  (  Tesla). 

second  is  high  and  the  current  through  the 
primary  small.  This  discharge  has  the  form  of 
a  thin,  feebly -colored  thread.  Though  very  sensi- 
tive, being  deflected  by  a  mere  breath,  it  is  never- 
theless quite  persistent,  if  the  terminals  be  at 
one-third  of  the  striking  distance  apart.  Tesla 
ascribes  its  extreme  sensitiveness,  when  long,  to 
the  motion  of  suspended  dust  particles  in  the  air. 
The  general  appearance  of  the  sensitive-thread 
discharge  is  shown  in  Fig.  213,  taken  from  Tesla. 


Discharge,  Silent A  name  given 

to  a  convective  discharge  in  order  to  distin- 
guish it  from  the  more  noisy  disruptive  dis- 
charge. 

The  convective  discharge  in  reality  is  attended 
by  a  feeble  sound,  which,  however,  is  quiet  when 
compared  with  the  more  pronounced  sound  of  the 
disruptive  discharge.  (See  Discharge,  Convec- 
tive.) 

Discharge,  Stratified The  form 

of  alternate  light  and  dark  spaces  assumed  by 
the  discharges  of  an  induction  coil  through  a 
partially  exhausted  gas.  (See  Tube,  Strati- 
fication^) 

The  striae  are  explained  by  Curtis  as  follows: 
"  Under  the  influence  of  the  electric  rhythm  of 
the  rapidly  following  discharges  the  molecules 
of  the  residual  gas  collect  in  alternately  dense 
and  rarefied  spaces.  The  light  bands  correspond  to 
the  spaces  where  the  molecules  are  comparatively 
crowded  together,  and  their  concomitant  friction 
produces  the  luminous  disturbance.  The  dark 
spaces  are  where  the  molecules  are  further  apart, 
and  where  their  collisions  are  consequently  less 
frequent. ' ' 

Discharge,  Streaming A  form  as- 
sumed by  the  flaming  discharge  between  the 
terminals  of  the  secondary  of  an  induction 
coil  when  the  frequency  of  the  alternations 
increases  beyond  a  certain  limit,  and  the 
potential  has  consequently  increased. 

The  streaming  discharge  partakes  of  the  general 
characteristics  of  the  flaming  discharge.  Lumi- 
nous streams  pass  in  abundance,  not  only  between 
the  terminals  of  the  secondary,  but,  according  to 
Tesla,  who  has  carefully  studied  these  phe- 
nomena, between  the  primary  and  the  secondary, 
through  the  insulating  dielectric  separating 


Fig.  214.     Streaming  Discharge  (Tesla). 

them.     The  streams  not  only  pass  between  the 
terminals,  but  also  issue  from  all  points  and  pro- 


Dis.] 


171 


[Dis. 


jections,  as  will  be  seen  from  Fig.  214,  taken  from 
Tesla. 

When  the  streaming  discharge  reaches  a  cer- 
tain higher  limit  it  becomes  a  brush-and  spray 
discharge.  (See  Discharge,  Brush-and- Spray.) 

The  streaming  discharge  obtained  from  an  in- 
duction coil  with  high  frequencies  differs  from  that 
of  an  electrostatic  machine  in  that  it  neither  pos- 
sesses the  violet  color  of  the  positive  static  dis- 
charge nor  the  brightness  of  the  negative,  but  is 
intermediate  in  color. 

Discharge,  Surging A  term  some- 
times applied  to  an  oscillatory  discharge.  (See 
Discharge,  Oscillatory?) 

Discharge,    to    Electrically To 

equalize  differences  of  potential  by  connecting 
them  by  means  of  a  conductor. 

Discharge,  Undnlatory A  dis- 
charge, the  strength  and  direction  of  which 
gradually  change.  (See  Currents,  Undn- 
latory?) 

Discharge,  Unidirectional  • — An 

electric  discharge  which  takes  place  from  the 
beginning  to  the  end,  in  one  and  the  same  di- 
rection. 

Discharge,  Telocity  of The  time 

required  for  the  passage  of  a  discharge 
through  a  given  length  of  conductor. 

According  to  modern  views  it  is  the  ether  sur- 
rounding the  wire  or  conductor  which  conveys 
the  electric  pulses.  All  the  energy  which  gets  into 
the  conductor  is  dissipated  as  heat. 

The  velocity  of  propagation  of  discharge  of  the 
pulses  produced  by  the  oscillating  discharge  of  a 
Leyden  jar  through  the  inter  atomic  or  inter- 
molecular  ether,  i.e. ,  through  the  fixed  ether  within 
different  substances,  varies  with  the  substance. 
Through  free  ether  the  velocity  is  that  of  light,  or 
185,000  miles  a  second. 

The  velocity  of  discharge  through  long  con- 
duct jrs  or  cables  is  much  lessened  by  incapacity 
of  the  cable,  and  the  effects  of  induction,  and  will 
therefore  vary  in  different  cases.  (See  Retard- 
ation.) 

Discharger,  Universal An  appa- 
ratus for  sending  the  discharge  of  a  powerful 
Leyden  battery  or  condenser  in  any  desired 
direction. 

The  universal  discharger  consists  essentially  of 


metallic  rods,  supported  on  insulated  pillars  and 
capable  of  ready  motion,  both  towards  and  from 
one  another,  as  well  as  in  vertical  and  horizon- 
tal planes.  The  object  which  is  to  receive  the 
discharge  is  placed  on  an  insulated  table  between 
the  rods,  and  the  latter  connected  with  the 
opposite  coatings  of  the  battery  or  condenser, 
when  the  discharge  passes  through  it. 

The  term  universal  discharger  is  sometimes  ap- 
plied to  the  discharging  tongs. 

Discharging,      Electrically The 

act  of  equalizing  differences  of  potential  by 
connection  with  a  conductor. 

Discharging  Bod.— (See  Rod,  Discharg- 
ing* 

Discharging  Tongs.— (See  Tongs,  Dis- 
charging?] 

Disconnect. — To  break  or  open  an  electric 
circuit. 

Disconnecter. — A  key  or  other  device  for 
opening  or  breaking  a  circuit. 

Disconnecting. — The  act  of  opening  or 
breaking  an  electric  circuit. 

Disconnection. — A  term  employed  to  des- 
ignate one  of  the  varieties  of  faults  caused 
by  the  accidental  breaking  or  disconnection 
of  a  circuit. 

Disconnections  of  this  kind  may  be  : 

(I.)  Total ;  as  by  a  switch  inadvertently  left 
open ;  or  by  the  accidental  breaking  of  a  part  of 
the  circuit. 

(2.)  Partial ;  as  by  a  dirty  contact;  a  loose,  or 
badly  soldered  joint;  a  poorly  clamped  binding 
screw;  a  loose  terminal,  or  a  bad  earth. 

(3.)  Intermittent;  as  by  swinging  joints,  alter- 
nate expansions  or  contractions  on  changes  of 
temperature;  the  collection  of  dust  and  dirt  in  dry 
weather,  and  then-  washing  out  in  wet  weather. 

Disconnection,       Intermittent 

Any  fault  in  a  line  which  occurs  at  intervals 
or  intermittently. 

Disconnection,  Partial A  partial 

fault  in  a  line  caused  by  any  imperfect  con- 
tact. 

Disconnection,  Total A  fault  in 

a  line  occasioned  by  a  complete  break  in  the 
circuit. 

Disguised  Electricity. -(See  Electricity, 


Dis.J 


172 


[Dis. 


Disjunctor.— A  device  employed  in  a  sys- 
tem for  the  distribution  of  electric  energy  by 
means  of  continuous  currents  by  condensers, 
for  the  purpose  of  periodically  reversing  the 
constant  current  sent  over  the  line.  (See 
Electricity,  Distribution  of,  by  Continuous 
Current  by  Means  of  Condensers?) 

Dispersion  Photometer. — (See  Photome- 
ter, Dispersion?) 

Displacement  Current. — (See  Current, 
Displacement?) 

Displacement,  Electric A  displace- 
ment of  electricity  in  a  uniform  and  non- 
crystalline  dielectric  when  lines  of  electro- 
static or  magnetic  force  pass  through  it. 

The  quantity  of  electricity  displaced  in  any 
homogeneous,  non-crystallizable  dielectric, 
by  the  action  of  an  electric  force  through 
the  unit  area  of  cross-section,  taken  perpen- 
dicular to  the  direction  of  the  electric  force. 

Electric  displacement  is  produced  under  an 
elastic  strain,  which  continues  only  while  the  elec- 
tric force  is  acting. 

Displacement,  Electric,  Lines  of 

Lines  of  electric  induction  along  which  elec- 
tric displacement  takes  place. 

Displacement,  Electric,  Oscillatory 

— A  displacement  of  electricity  in  a  di- 
electric or  non-conductor  of  an  oscillatory 
character. 

Displacement,  Electric,  Theory  of 

— A  theory  which  regards  the  electricity 
produced  on  an  insulated  conductor,  by  in- 
duction through  a  dielectric,  as  displaced  out 
of  the  dielectric  on  to  the  conductor,  or  into 
the  dielectric  from  the  conductor,  by  the  in- 
fluence of  the  electric  force. 

This  conception  was  introduced  into  science  by 
Maxwell,  after  a  careful  study  of  Faraday's  denial 
of  action  at  a  distance. 

Suppose  a  small  insulated  sphere  to  receive  a 
charge  of  electricity  -f  Q.  It  will,  by  induction, 
produce  an  equal  and  opposite  charge  —  Q,  on 
the  inner  surface,  and  a  similar  charge  on  the 
outer  surface  of  the  small  hollow  sphere,  placed 
near  it,  but  separated  by  the  dielectric.  There 
has,  therefore,  been  a  displacement  of  electricity 
through  the  dielectric.  The  medium  of  the 


dielectric  has  connected  the  two  bodies,  and  the 
phenomena  have  appeared  by  the  action  of  the 
electric  force  on  the  substance  of  the  dielectric; 
or,  in  other  words,  there  has  been  no  action  at 
a  distance. 

According  to  this  conception,  an  electric  cur- 
rent, called  a  displacement  current,  exists  in  the 
dielectric,  while  displacement  is  taking  place. 

Displacement  Waves. — (See  Waves,  Dis- 
placement.] 

Disruptive    Electric    Conduction.— (See 

Conduction,  Electric,  Disruptive?) 

Dissimulated   or   Latent    Electricity.— 

(See  Electricity,  Dissimulated  or  Latent?) 
Dissipation    of   Charge.— (See     Charge, 

Dissipation  of?) 
Dissipation    of  Energy. — (See    Energy, 

Dissipation  of.) 

Dissipation  of  Energy,  Hysteresial 

— (See  Energy,  Hysteresial,  Dissipation  of. 
Hysteresis.) 

Dissipation,  Specific  Hysteresial 

The  specific  loss  of  energy  by  hysteresis  in 
the  case  of  a  particular  substance.  (See 
Hysteresis.) 

Dissociate. — To  separate  a  compound  sub- 
stance into  its  constituents. 

Dissociation. — The  separation  of  a  chemi- 
cal compound  into  its  constituent  parts. 

Dissymmetrical  Induction  of  Armature. 

— (See  Armature,  Dissymmetrical  Induc- 
tion of.) 

Dissymmetrical  Magnetic  Field.— (See 
Field,  Magnetic,  Dissymmetrical.) 

Dissymmetry  of  Commutation.— (See 
Commutation,  Dissymmetry  of.) 

Distance,  Critical,  of  Lateral  Discharge 

Through  an  Alternative  Path The 

distance  at  which  a  discharge  will  take  place 
through  an  air  space  of  given  dimensions,  in 
preference  to  passing  through  a  metallic  cir- 
cuit of  comparatively  small  resistance. 

Distance,  Explosive A  term  some- 
times employed  for  sparking  distance.  (See 
Distance,  Sharking?) 

Distance,  Sparking The  distance 


Bis.] 


173 


[Dot 


at  which  electrical  sparks  will  pass  through 
an  intervening  air  space.  (See  Spark,  Length 
.of.) 

Distant  Station.— (See  Station,  Distant?) 

Distillation,  Destructive  -  —The 
action  of  heat  on  an  organic  substance, 
while  out  of  contact  with  air,  resulting  in  the 
decomposition  of  the  substance  into  simpler 
and  more  stable  compounds. 

The  different  products  resulting  from  destruc- 
tive distillation  may  be  successively  collected  by 
the  ordinary  processes  of  distillation. 

Distillation,  Dry A  species  of  de- 
structive distillation.  (See  Distillation,  De- 
structive?) 

Distillation,  Electric  -  —The  dis- 
tillation of  a  liquid  in  which  the  effects  of 
heat  are  aided  by  an  electrification  of  the 
liquid. 

Beccaria  discovered  that  a  liquid  evaporates  more 
rapidly  when  electrified  than  when  unelectrified. 
Crookes  has  shown  that  evaporation  is  aided 
by  negative  electrification,  or  that  evaporation 
takes  place  more  rapidly  at  the  negative  terminal 
during  a  discharge  than  at  the  positive.  (See 
Evaporation,  Electric. ) 

Distributing  Box  of  Conduit— (See  Box, 
Distributing,  of  Conduit?) 

Distributing  Station.— (See  Station,  Dis- 
tributing?) 
Distributing  Switch  for  Electric  Light. 

—{See  Switch,  Distributing,  for  Electric 
Lights.) 

Distribution-Box  for  Arc  Light  Circuits. 
— (See  Box,  Distribution,  for  Arc  Light 
Circuits?) 

Distribution,  Centre  of In  a  sys- 
tem of  multiple-distribution,  any  place  where 
branch  cut-outs  and  switches  are  located  in 
order  to  control  communication  therewith. 

The  electrical  centre  of  a  system  of  distri- 
bution as  regards  the  conducting  network. 

Distribution  of  Charge.— (See  Charge, 
Distribution  of?) 

Distribution  of  Electricity.— (See  Elec- 
tricity, Distribution  of) 


Distribution  of  Electricity  by  Alternate 
ing  Currents (See  Electricity,  Dis- 
tribution of,  by  Alternating  Currents.) 

Distribution  of  Electricity  by  Alternat- 
ing Currents  by  Means  of  Condensers. — 
(See  Electricity,  Distribution  of,  by  Alter- 
nating Currents  by  Means  of  Condensers.) 

Distribution  of  Electricity  by  Cammu- 
tating  Transformers.  —  (See  Electricity, 
Distribution  of,  by  Commutating  Trans- 
formers^) 

Distribution  of  Electricity  by  Constant 
Potential  Circuit.— (See  Electricity,  Multi- 
ple Distribution  of,  by  Constant  Potential 
Circuit?) 

Distribution  of  Electricity  by  Contin- 
uous Current  by  Means  of  Transformers.— 
(See  Electricity,  Distribution  of,  by  Contin- 
uous Current  by  Means  of  Transformers.) 

Distribution  of  Electricity  by  Motor- 
Generators. — (See  Electricity,  Distribution 
of,  by  Motor-Generators.) 

Distribution,  Series,  of  Electricity  by 
Constant  Current  Circuit.— (See  Electricity, 
Series  Distribution  of,  by  Constant  Current 
Circuit?) 

District  Call-Box.— (See  Box,  District 
Call?) 

Diurnal  Inequality  of  Earth's  Magnet- 
ism.— (See  Inequality,  Diurnal,  of  Earth's 
Magnetism?) 

Divided  Magnetic  Circuit.— (See  Circuit, 
Divided  Magnetic?) 

Door-Opener,  Electric  — A  device 

for  opening  a  door  from  a  distance  by  elec- 
tricity. 

Various  devices  consisting  of  electro-magnets, 
acting  against,  or  controlling  springs  or  weights, 
are  employed  for  this  purpose. 

Dosage,    Electro-Therapeutical 

The  apportioning  of  the  amount  of  the  cur- 
rent and  the  duration  of  its  application  to  the 
body  for  the  treatment  of  disease. 

Dosage,  Galvanic  — Electro-thera- 
peutical dosage.  (See  Dosage,  Electro- 
Therapeutical]  . 

Dotting  Contact.— (See  Contact,  Dotting.) 


Dou,J 


(Dr.). 


Double-Break     Knife     Switch.— (See 

Switch,  Double-Break  Knife?) 

Double-Carbon  Arc  Lamp. — (See  Lamp, 
Electric  Arc,  Double-Carbon) 

Double-Cone  Insulator. — (See  Insulator, 
Double-Cone?) 

Double-  Connector. — (See  Connector, 
Double) 

Double-Contact  Key.— (See  Key,  Double- 
Contact) 

Double-Cup  Insulator. — (See  Insulator, 
Double-Cup) 

Double-Curb.— (See  Curb,  Double) 

Double-Curb  Signaling.— (See  Signaling, 
Curb,  Double) 

Double-Current  Signaling.— (See  Signal- 
ing, Double-Current) 

Double-Current  Translator. — (See  Trans- 
lator, Double-Current) 

Double-Cur r ent  Transmitter. — (See 
Transmitter,  Double-Current) 

Double-Current  Working  —The 

employment,  in  systems  of  telegraphy,  by 
means  of  suitable  keys,  of  currents  from 
voltaic  batteries,  in  alternately  opposite 
directions,  thus  increasing  the  speed  of 
signaling.  (See  Working,  Reverse-Current) 

Double-Fluid  Electrical  Hypothesis.— 
(See  Electricity,  Double-Fluid  Hypothesis 
of) 

Double-Fluid  Voltaic  Cell.— (See  Cell, 
Voltaic,  Double-Fluid) 

Double-Magnet  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Double-Magnet) 

Double-Pen  Telegraphic  Register.— (See 
Register,  Double-Pen,  Telegraphic) 

D  o  u  b  1  e-Refraction. — (See  Refraction, 
Double) 

Double-Refraction,  Electric.— (See  Re- 
fraction, Double,  Electric) 

Double-Shackle  Insulator.— (See  Insula- 
tor, Double-Shackle) 

Double-Shed  Insulator.— (See  Insulator, 
Double-Shed) 


Double-Tapper  Key.— (See  Key,  Double- 
Tapper) 
DJ  able-Touch,  Magnetization  by 

A  method  for  producing  magnetization  by 
the  simultaneous  touch  of  two  magnet  poles. 
(See  Magnetization,  Methods  of) 

Double-Transmission. — (See  Transmis- 
sion, Double) 

Double-Trolley.— (See  Trolley,  Double) 

Doubler  of  Electricity.— An  early  form  of 
continuous  electrophorus.  (See  Electro- 
phorus.) 

Drifting  Torpedo.— (See  Torpedo,  Drift- 
ing) 

Drill,  Electro-Magnetic A  drill 

applied  especially  to  blasting  or  mining  opera- 
tions, operated  by  means  of  electricity. 

Drip  Loop.— (See  Loop,  Drip) 
Driven  Pulley.— (See  Pulley,  Driven) 
Driven  Shaft. — (See  Shaft,  Driven) 
Driving  Pulley. — (See  Pulley,  Driving) 
Driving  Shaft.— (See  Shaft,  Driving) 
Driving  Spider.— (See  Spider,  Driving) 

Drop,  Annunciator  — A  movable 

signal  operated  by  an  electro-magnet,  and 
placed  on  an  annunciator,  the  dropping  of 
which  indicates  the  closing  or  opening  of  the 
circuit  with  which  the  electro-magnet  is  con- 
nected. 

The  falling  of  the  drop  may  be  attended  by  the 
sounding"  of  a  bell  or  other  alarm,  or,  it  may  give 
a  silent  indication. 

Drop,  Annunciator,  Automatic A 

drop  for  an  annunciator,  which  on  the  closing 
of  a  circuit,  falls  and  holds  the  circuit  closed 
until  the  drop  is  raised. 

Drop,    Annunciator,  Gravity   -        — A 

drop  for  an  annunciator,  acted  on  by  gravity 
when  released  by  the  movement  of  the  arma- 
ture of  an  electro-magnet. 

Drop,  Automatic A  device  for  au- 
tomatically closing  the  circuit  of  a  bell  and 
holding  it  closed  until  stopped  by  resetting  a 
drop. 


Dro.J 


175 


[Dyn. 


The  automatic  drop  is  especially  applicable  to 
burglar  alarms.  On  the  opening  of  a  door  or 
shutter,  the  closing  of  the  circuit  moves  the 
armature  of  an  elec- 
tro -  magnet,  and, 
by  the  falling  of  a 
drop,  closes  the  cir- 
cuit and  holds  it 
closed  until  me- 
chanically opened 
by  the  replacing  of 
the  drop.  The 
general  appearance 
of  the  automatic 
drop  is  shown  in 
Fig.  215. 

Drop,   Calling- 

Ari    an-     Fig' 2*3'    Automatic  Dr°f- 

nunciator  drop  employed  to  indicate  to  the 
operator  in  a  telegraphic  or  telephonic  system 
that  one  subscriber  wishes  to  be  connected 
with  another. 

Drop  of  Potential.— (See  Potential,  Drop 
of-} 

Drops,   Clearing    Out  — Restoring 

the  drops  of  annunciators  to  their  normal 
position  after  they  have  been  thrown  out  of 
the  same  by  the  closing  of  the  circuits  of  their 
magnets. 

These  clearing-out  devices  as  placed  on  most 
forms  cf  annunciators  are  generally  mechanical  in 
operation. 

Drum  Armature. — (See  Armature, 
Drum.} 

Drum,  Electro-Magnetic A  drum, 

usied  in  feats  of  legerdemain,  operated  by 
an  automatic  electro-magnetic  make  and 
break  apparatus. 

Dry  Distillation.— (See  Distillation, 
Dry.} 

Dry  Electrode.— (See  Electrode,  Dry.} 

Dry  Pile.— (See  Pile,  Dry.} 

Dry  Voltaic  Cell.— (See  Cell,  Voltaic, 
Dry.} 

Dub's  Laws. — (See  Laws,  Dub's} 
Duplex  Cable.— (See  Cable,  Duplex) 
Duplex  Cut-Out.— (See  Cut-out,  Duplex) 


Duplex  Flat  Cable.— (See  Cable,  Flat 
Duplex) 

Duplex  Telegraphy.— (See  Telegraphy, 
Duplex) 

Duplex  Wire.— (See  Wire,  Duplex) 

Duration  of  Electric  Discharge.— (See 
Discharge,  Duration  of) 

Duration  of  Make-Induced  Current.— 
(See  Current,  Make  or  Break  Induced,  Du- 
ration of) 

Dust    Figures,  Lichtenberg's    

(See  Figures,  Lichtenberg's  Dust) 

Dyad. — A  chemical  element  which  has  two 
bonds  by  which  it  can  unite  or  combine  with 
another  element. 

An  element  whose  atomicity  is  bivalent. 

Dyeing,  Electric The  application 

of  electricity  either  to  the  reduction  or  the 
oxidation  of  the  salts  used  in  dyeing. 

GoppelsrSder,  in  his  processes  of  electric  dyeing, 
forms  and  fixes  aniline  black  on  cloth  as  follows, 
viz. :  the  cloth,  saturated  with  an  aniline  salt,  is 
placed  on  an  insulated  metallic  plate,  inert  to  the 
aniline  salt,  and  connected  with  one  pole  of  a 
battery  or  other  electric  source.  The  other  pole 
is  connected  with  a  metallic  plate  on  which  the 
required  design  is  drawn.  On  the  passage  of  the 
current,  the  design  is  traced  in  aniline  black  on 
the  cloth.  A  minute  or  two  suffices  for  the 
operation. 

A  species  of  electrolytic  writing  is  obtained  on 
cloths  arranged  as  above  by  substituting  a  carbon 
pencil  for  the  metallic  plate.  On  writing  with 
this  pencil,  as  with  an  ordinary  pencil,  the  pas- 
sage of  the  current  so  directed  is  followed  by  the 
deposition  of  aniline  black. 

By  means  of  a  somewhat  similar  process  writ- 
ing in  white  on  a  colored  ground  is  obtained. 

Dynamic  Electricity.— (See  Electricity, 
Dynamic?) 

Dynamics,  Electro That  branch 

of  electric  science  which  treats  of  the  action 
of  electric  currents  on  one  another  and  on 
themselves  or  on  magnets. 

The  principles  of  electro -dynamics  were  dis- 
covered by  Ampere  in  1821. 

A  convenient  form  of  apparatus,  for  showing 
experimentally  the  action  of  one  current  on 
another,  consists  of  two  upright  metallic  columns 


Dyn.J 


176 


[Dyn. 


or  pillars,  which  support  horizontal  metallic  arms 
containing  mercury  cups,  y,  and  c,  Fig.  216. 


.  216.     Deflection  of  a  Circuit  by  a  Current. 


The  circuit  is  bent  in  the  form  of  a  rectangle, 
circle  or  solenoid,  and  terminates  in  points  that 
dip  in  the  mercury  cups.  The  current  is  led  into 
and  out  of  the  apparatus  at  the  points  -f-  and — 
at  the  base  of  the  upright  supports. 

When  a  magnet,  or  another  circuit,  is  ap- 
proached to  the  movable  circuit  thus  provided, 
attractions  or  repulsions  are  produced  according 
to  th2  position  of  the  magnet,  or  the  direction  of 
the  currents  in  the  two  circuits. 

If  a  magnet  A  B,  Fig.  217,  be  placed,  as  shown, 


Fig.  217.     DtflectioH  of  Circuit  by  a  Magntt. 

below  the  movable  circuit  C  C,  the  circuit  will 
tend  to  place  itself  at  right  angles  to  the  axis  of 
the  magnet.  This  movement  is  the  same  as 
would  occur  if  electric  currents  were  circulating 
around  the  magnet  in  the  direction  of  the  assumed 
Amperian  currents.  It  also  illustrates  the  prin- 
ciple of  the  electric  motor.  (See  Magnetism,  Am- 
pere's  Theory  of.) 

Ampere  has  given  the  results  of  his  investigations 
as  to  the  mutual  attractions  and  repulsions  of  cur- 


rents  in    the    following    statements,    which   are 
known  as  Ampere's  Laws  : 

(I.)  Parallel  portions  of  a  circuit  attract  one 
another  if  the  currents  in  them  are  flowing  in  the 
same  direction,  and 
repel  one  another  if 
the  currents  are  flow- 
ng  in  opposite  direc- 
tions. 

A  current    flowing 

through  a  spiral  tends  A          B 

to  shorten  the  spiral  **•*'*•    Action  of  Solenoid 
from  the  attraction  of 
the  parallel  currents  in  contiguous  turns. 

Similar  poles  of  two  solenoids  repel  each  other, 
as  at  A,  A',  Fig.  218,  because,  when  opposed  to 
each  other,  the  currents  that  produce  these  poles 


Fig.  2IQ.     Ampere's  Stand. 

are  flowing  in  opposite   directions,  as  may  be 
seen  from  an  inspection  of  the  drawing. 

Dissimilar  solenoid  poles,  on  the  contrary,  at- 
tract each  other  as  at  A,  B,  in  Fig.  218,  since 


C 

Fig.  2 20.     Electro- Dynamic  Attraction. 

the  currents  which  produce  them  flow  in  the  same 
direction. 

In  Fig.  219,  a  form  of  Ampere's  stand  is  shown, 
in  which  one  of  the  circuits  is  in  the  form  of  the 


177 


coil  M  N  ;  its  action  on  the  movable  circuit  C  B, 
is  to  repel  it,  since  the  currents,  as  shown,  are 
flowing  in  an  opposite  direction  in  the  adjacent 
portions  of  the  fixed  and  movable  circuits. 

(2.)  Two  portions  of  a  circuit  intersecting  each 
Other  mutually  attract  each  other  when  the  cur- 
rents  in  both  circuits  flow 
either  towards  or  from 
the  point  of  intersection, 
but  repel  each  other  f 
they  flow  in  opposite  di- 
rections from  this  point. 

Thus,  in  Fig.  220,  the  ^/ 
currents  in  both  circuits  P 
P  Q  and  A.  B  C  D,  flow 
towards  and  from  the 
point  of  intersection  Y,  and  attract  one  another 
and  cause  a  motion  until  the  two  circuits  are 
parallel, 

If  the  currents  flow  in  opposite  directions  they 
repel  each  other,  and,  if  free  to  move,  will  come 
to  rest  when  parallel  to  each  other  ;  therefore, 
two  portions  of  a  circuit  crossing  each  other  tend 
to  move  until  they  are  parallel,  and  their  currents 
are  flowing  in  the  same  direction. 

(3.)  Successive  portions  of  the  circuit  of  the 
same  rectilinear  current ',  that  is,  a  current  flowing 
in  the  same  straight  line,  repel  one  another. 

A  circuit  O  A,  Fig.  221,  movable  on  O,  as  a 


Fig.  22  T.    Continuous 
Rotation  of  Current. 


Fig.  222.    Mutual  Action  of  Magnetic  Fields. 

centre,  will  be  continuously  rotated  in  the  direc- 
tion of  the  curved  arrow  by  the  rectilinear  cur- 
rent, P  Q;  for,  the  directions  of  the  currents  being 
as  shown  by  the  arrows,  there  will  be  attraction 
in  the  positions  (i)  and  (2),  and  repulsion  in  po- 
«ition(4). 

The  cause  of  the  mutual  attractions  and  repul- 
sions of  electric  circuits  will  readily  appear  from 
a  consideration  of  the  mutual  action  of  their 
magnetic  fields. 

Thus  an  inspection  of  Fig.  222  shows : 


(I.)  That  parallel  currents  flowing  in  the  same 
direction  attract,  because  their  lines  of  force  have 
opposite  directions  in  adjoining  parts  of  the  cir- 
cuit of  these  lines. 

(2.)  That  parallel  currents  flowing  in  opposite 
directions  repel,  because  their  lines  of  force  have 
the  same  directions  in  adjoining  parts  of  the  cir- 
cuit. 

These  laws  may  therefore  be  generalized  thus, 
viz. :  Lines  of  magnetic  force  extending  in  oppo- 
site directions  attract  one  another;  lines  of 
magnetic  force  extending  in  the  same  direction 
repel  one  another. 

Ampere  proved  that  a  circuit,  doubled  on  itself 
so  that  the  current  flows  in  opposite  directions  in 
the  two  parts,  exerts  no  force  on  external  objects. 
This  expedient  is  adopted  in  resistance  coils  to 
prevent  any  disturbance  of  the  galvanometer 
needles.  He  also  showed  that  a  sinuous  circuit, 
or  one  bent  into  zigzags,  produces  the  same  effects 
of  attraction  or  repulsion  as  it  would  if  it  were 
straight.  (See  Coil,  Resistance.) 

The  term  sinuous  current  is  sometimes  applied 
to  the  current  in  a  sinuous  circuit.  (See  Current, 
Sinuous.)  This  must  be  distinguished  from  the 
term  sinusoidal  current,  which  applies  to  fluctua- 
tions in  the  current  and  not  to  peculiarities  in  the 
shape  of  the  conductor. 

When  two  inclined  magnets,  free  to  move,  are 
left  to  their  mutual  attractions  and  repulsions,  they 
gradually  come  to  rest  with  their  axes  parallel  to 
each  other. 

Two  conductors  through  which  electric  cur- 
rents are  flowing  act  on  one  another  as  two 
magnets  would. 

A  conductor  conveying  a  current  of  electricity 
tends  to  rotate  round  a  magnetic  pole.  A  mag- 
netic pole  tends  to  rotate  continuously  round  an 
electric  current. 

The  motion  of  a  magnet  near  a  conductor 
produces  an  electromotive  force  in  that  conductor 
provided  the  conductor  cuts  the  lines  of  force. 

A  magnetized  substance  becomes  magnetized 
when  placed  in  a  magnetic  field. 

A  conductor  through  which  a  current  of  elec- 
tricity is  passing  tends  to  wrap  itself  around  a 
neighboring  magnetic  pole.  The  following  ex- 
periments illustrate  this  tendency : 

(I.)  The  experiment  suggested  by  Lodge:  A 
powerful  current  of  electricity  is  passed  through 
some  eight  feet  in  length  of  gold  thread  such  as 
is  employed  for  making  lace.  The  thread  is 
hung  in  a  vertical  position,  near  a  vertical  bar 


Dyn.] 


magnet.  As  soon  as  the  current  passes,  the 
thread  will  wrap  itself  around  the  -bar  magnet, 
one  half  of  it  twisting  itself  round  the  north  pole, 
the  other  half  round  the  south  pole. 

(2.)  The  experiment  suggested  by  Professor  S. 
P.  Thompson:  An  electric  current  is  sent  through 
a  stream  of  mercury  while  it  is  flowing  between 
two  poles  of  a  powerful  electro-magnet;  when 
the  current  is  sent  through  the  magnet,  the 
stream  is  twisted  in  spiral  directions  which  vary, 
either  with  the  direction  of  the  current,  or  with 
the  direction  of  the  magnetic  polarity. 

(3.)  Somewhat  similar  effects  can  be  shown  by 
the  rotation  of  a  stream  of  gas  round  a  magnetic 
pole  placed  in  an  exhausted  glass  receiver. 

Dynamo. — The  name  frequently  applied  to 
a  dynamo-electric  machine  used  as  a  gener- 
ator. (See  Machine,  Dynamo-Electric?) 

Dynamo  Balancing  Rheostat. — (See 
Rheostat,  Dynamo  Balancing?) 

Dynamo-Battery. — (See  Battery,  Dy- 
namo?) 

Dynamo  Brush  Trimmer. — (See  Trim- 
mer, Dynamo  Brush?) 

Dynamo,      Composite-Field — A 

dynamo  whose  field  coils  are  series  and 
separately  excited. 

Additional  separately  excited  coils  placed  on 
the  field  of  a  series  wound  dynamo  render  it  self- 
regulating. 

A  composite  dynamo  is  a  form  of  compounded 
dynamo. 

Dynamo,  Compound-Wound.— A  com- 
pound-wound dynamo-electric  machine.  (See 
Machine,  Dynamo-Electric,  Compound- 
Wound:) 

Dynamo,  Contact  —  — A  form  of  dyna- 
mo in  which  the  space  between  the  arma- 
ture and  field  magnet  poles  is  so  reduced  that 
they  actually  touch  one  another. 

In  contact  dynamos  both  field  and  armature 
revolve.  This  form  of  dynamo  has  not  been  very 
successful  in  practice. 

Dynamo-Electric  Machine.— (See  Ma- 
chine, Dynamo-Electric?) 

Dynamo-Electric  Machine,  Alternating 
Current  — (See  Machine,  Dynamo- 
Electric,  Alternating  Current?) 


Dynamo-Electric   Machine  Armature.— 

(See  Armature,  Dynamo-Electric  Machine?) 

Dynamo-Electric  Machine  Armature 
Coils. — (See  Coils,  Armature,  of  Dynamo- 
Electric  Machine?) 

Dynamo-Electric  Machine  Armature 
Core. — (See  Core,  Armature,  of  Dynamo- 
Electric  Machine?) 

Dynamo-Electric  Machine  Battery.— 
(See  Battery,  Dynamo-Electric  Machine?) 

Dynamo-Electric  Machine,  Bi-Polar 

— (See  Machine,  Dynamo-Electric,  Bi- 
Polar?) 

Dynamo-Electric  Machine,  Collecting 
Brushes  of —  — (See  Brushes,  Collecting, 
of  Dynamo-Electric  Machine?) 

Dynamo-Electric  Machine  Commutator 

(See  Commutator,  Dynamo-Electric 

Machine?) 

Dynamo-Electric  Machine,  Compound- 
Wound  — (See  Machine,  Dynamo- 
Electric,  Compound-  Wound?) 

Dynamo-Electric  Machine,  Generation  of 
Current  by  —  — 'See  Current,  Genera- 
tion of,  by  Dynamo-Electric  Machine?) 

Dynamo-Electric  Machine,  Field  Mag- 
nets —  —  ( See  Magnets,  Field,  of  Dynamo- 
Electric  Machine?) 

Dynamo-Electric  Machine,  Methods  ol 
Increasing  the  Electromotive  Force  Gene- 
rated by (See  Force,  Electromotive, 

Generated  by  Dynamo-Electric  Machine, 
Method  of  Increasing?) 

Dynamo-Electric  Machine,  Mouse-Mill, 
Sir  William  Thomson's  —  —(See  Ma- 
chine, Dynamo-Electric,  Mouse-Mill,  Sir 
William  Thomson's?) 

Dynamo-Electric  Machine,  Multipolar 
— (See  Machine,  Dynamo-Electric, 
Multipolar?) 

Dynamo-Electric  Machine,  Pole-Pieces  of 

(See  Pole-Pieces  of  Dynamo-Electric 

Machine?) 

Dynamo-Electric  Machine,  Reversibility 

of (See  Machine,  Dynamo-Electric, 

Reversibility  of?) 


Dyn.J 


179 


Dynamo-Electric  Machine,  Varieties  of 

•    — (See    Machine,    Dynamo-Electric, 

Varieties  of.} 

Dynamo,  Inductor A  dynamo- 
electric  machine  for  alternating  currents  in 
which  the  differences  of  potential  causing  the 
currents  are  obtained  by  magnetic  changes  in 
the  cores  of  the  armature  and  field  coils  by 
the  movement  past  them  of  laminated  masses 
of  iron  inductors. 

The  coils  corresponding  to  the  armature  and 
field  magnets  of  the  ordinary  dynamo  are  sta- 
tionary. The  laminated  masses  of  iron,  employed 
to  cause  magnetic  changes  in  the  cores  of  the  field 
and  armature  coils,  are  fixed  on  an  inductor  wheel 
which  is  rapidly  revolved  in  front  of  them.  The 
magnets  corresponding  to  the  field  magnets  are 
called  the  primary  poles,  and  are  magnetized  by 
an  exciter.  The  magnets  corresponding  to  the 
armature  are  called  the  secondary  poles  and  are 
placed  so  as  to  alternate  with  the  primary  poles. 
The  inductors  are  so  shaped  that  they  carry  the 
magnetism  of  one  pole  of  the  primary  magnet 
to  the  secondary  poles  when  the  inductor  is  in 
one  position,  and  of  the  opposite  pole  when  in  a 
slightly  different  position.  The  inductor  wheel 
therefore  acts  as  a  magnetic  commutator  and 
changes  the  position  of  the  secondary  magnet  as 
it  rotates,  thus  producing  electromotive  force. 
The  number  of  alternations  per  revolution  is 
equal  to  twice  the  number  of  inductors  placed  on 
the  inductor  wheel. 

Dynamo,  Inverted A  dynamo-elec- 
tric machine  in  which  the  armature  bore  or 
chamber  is  placed  below  the  field  magnet 
coils. 

The  term  inverted  is  used  in  contradistinction 
to  the  overtype  dynamo.  (See  -Dynamo,  Over- 
type.} 

Dynamo,  Mouse  Mill A  form  of 

dynamo-electric  machine  designed  by  Sir 
William  Thomson  to  act  as  the  replenisher  of 
one  of  his  electrometers.  (See  Replenisher •.) 

Dynamo,  Multiphase A  polyphase 

dynamo.  (See  Dynamo,  Polyphase.  Dyna- 
mo, Rotating  Current?) 

Dynamo,  Overtype A  dynamo- 
electric  machine,  the  armature  bore  or  cham- 
ber of  which  is  placed  above  the  field  magnet 
coils  instead  of  below  them  as  in  many  forms. 


The  overtype  form  of  dynamo  possesses  the 
advantage  of  better  avoiding  magnetic  leakage. 

Dynamo,  Polyphase A  name  some- 
times applied  to  a  rotating  current  dynamo. 
(See  Dynamo,  Rotating  Current!) 

Dynamo,  Pyromagnetic A  name 

sometimes  applied  to  a  pyromagnetic  gen- 
erator. (See  Generator,  Pyromagnetic!) 

Dynamo,  Rotary-Phase —A  term 

sometimes  employed  for  a  rotating  current 
dynamo.  (See  Dynamo,  Rotating  Current.} 

Dynamo,  Separately-Excited A 

separately-excited  dynamo-electric  machine. 
(See  Machine,  Dynamo-Electric,  Separ- 
ately-Excited^ 


A   series-wound 


Dynamo,  Series 

dynamo-  electric 
machine.  (SeeJ/a- 
chine,  Dynamo- 
Electric,  Series- 
Wound?) 

Dynamo,   Shunt 

— A  shunt- 
wound  dynamo- 
electric  machine. 
(See  Machine, 
Dynamo  -  Electric, 
Shunt-  Wound?] 

Dynamograph. 

—  A  term  some- 
times applied  to  a 
type-writing  tele- 
graph that  records 
the  message  in 
type-written  char- 
acters, both  at  the 
sending  and  the 
receiving  ends. 

Dynamometer.  ^ 
— A  name  given  to 

a  variety  of  appar-    /•£-.  223.    Parsons'  Dyna.- 
atus  for  measuring  mometer. 

the  power  of  an  engine  or  motor. 

In  all  dynamometers  the  strain  on  the  belt  or 
other  moving  part  is  measured,  say  in  pounds, 
and  the  speed  of  the  moving  part  is  also  measured 
in  feet  per  second.  The  product  of  the  strain  in 


Dyn.] 


180 


pounds  by  the  velocity  in  feet  per  second,  di- 
vided by  550,  will  give  the  horse  power. 

One  of  the  many  forms  of  dynamometers  is 
shown  in  Fig.  223.  It  is  known  as  Parsons'  Dy- 
namometer. 

The  driving  pulley  is  shown  at  A,  and  the 
driven  pulley  at  C.  Weights  hung  at  Q1?  are  va- 
ried so  as  to  maintain  the  axes  of  the  suspended 
pulleys,  D  and  B,  as  nearly  as  possible  at  the 
same  height.  Then  the  tension  Tx  and  T8,  on 
the  sides  O  and  O',  of  the  belts,  will  be  repre- 
sented by  the  following  equation  : 


from  which,  knowing  the  belt  speed,  the  horse 
power  may  be  deduced. 

There  are  several  other  forms  of  dynamometer, 
such  as  the  cradle  dynamometer,  in  which  the 
machine  is  supported  on  knife  edges  and  the 
torque  or  pull  exerted  on  or  by  the  machine  is 
balanced  by  weights  sliding  on  a  lever.  In  these 
dynamometers  the  power  is  transmitted  through 
them  and  they  are  therefore  called  transmission 
dynamometers. 

Dynamometer,  Electro A  form  of 

galvanometer  for  the  measurement  of  electric 
currents. 

In  Siemens'  Electro-Dynamometer,  shown  in 
Fig.  224,  there  are  two  coils  ;  a  fixed  coil,  C,  se- 
cured to  an  upright  support,  and  a  movable  coil, 
L,  consisting  often  of  but  a  single  turn  of  wire. 
The  movable  coil  is  suspended  by  means  of  a 
thread  and  a  delicate  spring,  S,  capable  of  being 
twisted  by  turning  a  milled  screw-head  through 
an  angle  of  torsion  measured  on  a  scale  by  means 
of  an  index  connected  to  the  screw-head.  The 
two  ends  of  the  movable  coil  dip  into  mercury 
cups  so  connected  that  the  current  to  be  measured 
passes  through  the  fixed  and  movable  coils  in 
series. 

When  ready  for  use  the  movable  coil  is  at  right 
angles  to  the  fixed  coil.  The  current  to  be  meas- 
ured is  then  sent  into  the  coils,  and  their  mutual 
action  tends  to  place  the  movable  coil  parallel  to 
the  fixed  coil  against  the  torsion  of  the  spring,  S. 
The  amount  of  this  force  can  be  ascertained  by 
determining  the  amount  of  torsion  required  to 
bring  the  movable  coil  back  to  its  zero  position. 


Since  the  same  cm-rent  passes  through  both  th« 
fixed  and  movable  coils,  and  they  both  act  on 
each  other,  the  deflecting  force  here  is  evidently 
proportional  to  the  square  of  the  strength  of  the 


Fig.  224.     Siemens'  Electro- Dynamomet, 


current  to  be  measured.  The  deflecting  force, 
and  consequently  the  current  strength,  is  there, 
fore  proportional  to  the  square  root  of  the  angle 
of  torsion,  and  not  directly  to  the  angle  of  tor- 
sion. 

Dyne.— The  unit  of  force. 

The  force  which  in  one  second  can  impart 
a  velocity  of  I  centimetre  per  second  to  a 
mass  of  I  gramme. 

The  dyne  is  the  unit  of  force,  or  a  force  capa- 
ble, after  acting  for  one  second  on  a  mass  of  i 
gramme,  of  giving  it  a  velocity  of  I  centimetre 
per  second.  The  -weight  of  a  body  in  dynes,  or  the 
force  with  which  it  gravitates,  is  equal  to  its 
mass  in  grammes,  multiplied  by  the  acceleration 
imparted  to  it  in  centimetres  per  second.  For 
this  latitude  the  acceleration  is  about  981  centi- 
metres per  second. 


181 


[Edd. 


E 


E.  —  A  contraction  sometimes  used  for 
earth. 

A  contraction  sometimes  used  for  electro- 
motive force,  or  E.  M.  F.,  as  in  the  well- 
known  formula  for  Ohm's  law, 


K.  M.  D.  P.  —  A  contraction  for  electro- 
motive difference  of  potential.  (See  Poten- 
tial, Difference  of,  Electromotive) 

Eo  M.  F.  —  A  contraction  generally  used  for 
electromotive  force.  (See  Force,  Electro- 
motived) 

Earth.  —  A  fault  in  a  telegraphic  or  other 
line,  caused  by  accidental  contact  of  the  line 
with  the  ground  or  earth,  or  with  some  con- 
ductor connected  with  the  latter. 

This  is  more  frequently  called  a  ground. 

Earths  are  of  three  kinds,  viz.: 

(I.)  Deader  Total  Earth. 

(2.)  Partial  Earth. 

(3.)  Intermittent  Earth. 

The  term  earth  is  also  applied  to  a  plate  buried 
in  the  ground,  and  intended  to  make  a  good  con- 
tact between  the  earth  and  a  wire  circuit,  which 
is  connected  with  the  plate. 

Earth  Circuit.—  (See  Circuit,  Earth) 

Earth-Circuited  Conductor.—  (See  Con- 
ductor, Earth-Circuited) 

Earth  Currents.  —  Electric  currents  flow- 
ing through  different  parts  of  the  earth  caused 
by  a  difference  of  potential  at  different  points. 

The  causes  of  these  differences  of  potential  are 
•various  and  are  not  well  understood. 

Earth,  Bead  or  Total  --  A  fault  in 
a  telegraphic  or  other  line  in  which  the  line 
is  thoroughly  grounded  or  connected  with 
the  earth. 

Dead  earih  is  sometimes  called  total  earth. 

Earth-Grounded  Wire.—  (See  Wire, 
Earth-Grounded.  ) 

Earth,  Intermittent  --  A  swinging 
earth.  (See  Earth,  Swinging  or  Intermit- 
tent^ 

Earth  or  Ground.—  That  part  of  the  earth 


or  ground  which  forms  part  of  an  electric 
circuit. 

A  circuit  is  put  to  earth  or  ground  when  the 
earth  is  used  for  a  portion  of  the  circuit. 

The  resistance  of  an  earth  connection  may  vary 
in  time  from  the  following  causes,  viz.: 

( I. )  The  corrosion  of  the  ground  plate.  This  is 
especially  apt  to  occur  in  the  case  of  a  copper 
plate. 

(2.)  From  polarization,  a  counter-electro- 
motive force  being  produced,  thus  introducing  a 
spurious  resistance  into  the  circuit.  (See  Resist- 
ance, Spurious.) 

Earth,  Partial A  fault  in  a  tele- 

graphic  or  other  line  in  which  the  line  is  in 
partial  connection  with  the  earth. 

The  term  partial  earth  is  used  in  contradistinc- 
tion to  dead  or  total  earth. 

Earth,  Return A  circuit  in  which 

the  return  current  passes  back  to  the  source 
through  the  earth. 

Earth,  Swinging  or  Intermittent 

— A  fault  in  a  telegraphic  or  other  line  in 
which  the  action  of  the  wind,  or  occasional 
expansion  by  heat,  brings  the  line  into  inter- 
mittent contact  with  the  earth. 

Earth,  Total A  term  sometimes 

used  for  dead  earth.  (See  Earth,  Dead  or 
Total) 

Ebonite. — A  tough,  hard,  black  substance, 
composed  of  india  rubber  and  sulphur,  which 
possesses  high  powers  of  insulation  and  of 
specific  inductive  capacity. 

Ebonite  is  often  called  vulcanite. 

Vulcanite  rubbed  with  cat-skin  acts  as  one  of 
the  best  known  substances  for  becoming  electri- 
fied by  friction.  For  this  purpose  both  substances 
should  be  thoroughly  dried. 

Economic  Co-efficient  of  Dynamo-Elec- 
tric Machine— (See  Co-efficient,  Economic, 
of  a  Dynamo-Electric  Machine) 

Eddy  Currents.— feee  Currents,  Eddy.) 

Eddy  Currents,  Deep-Seated (See 

Currents,  Eddy,  Deep-Seated) 

Eddy  Currents,  Superficial (See 

Currents,  Eddy,  Superficial) 


Edd.j 


182 


[Eft 


Eddy-Displacement  Currents.— (See  Cur- 
rents,  Eddy-Displacement.) 

Eel,  Electric An  eel  possessing 

the  power  of  giving  powerful  electric  shocks,. 

The  gymnotus  electricus. 

The  electricity  is  produced  by  an  organ  ex- 
tending the  entire  length  of 
the  body. 

According  to  Faraday,  the 
shock  given  by  a  specimen 
of  the  animal  examined  by 
him  was  equal  to  that  of  15 
Leyden  jars,  having  a  total 
surface  of  25  square  feet. 
Fig.  225  shows  the  general 
appearance  of  the  animal. 

Effect,  Acheson 

The  increase  in  the  electro- 
motive force  of  the  sec- 
ondary of  a  transformer  by 
the  action  of  the  changes 
in  temperature  of  its  core. 
(See  Electricity,  Cat.) 

Fig.  2ZS-    Electric 

Effect,   Chemical  Eel, 

—The  effect  occasioned  by  atomic  combina- 
tion, which  results  in  a  loss  of  those  properties 
or  peculiarities  by  which  the  substances  en- 
tering into  combination  are  ordinarily  recog- 
nized. 

Atomic  combination,  resulting  in  the  for- 
mation of  new  moleculeSo 

The  formation  of  new  molecules  necessitates  the 
possession  by  the  new  substance  of  properties  dis- 
tinct and  separate  from  those  of  its  constituents. 

Black  carbon,  and  yellow  sulphur,  for  example, 
both  solids,  unite  chemically  to  form  a  trans- 
parent colorless  liquid. 

Chemical  changes  differ  from  physical  changes, 
which  latter  can  occur  in  a  substance  without  the 
formation  of  new  molecules,  and  consequently 
without  the  loss  by  it  of  the  properties  it  ordi- 
narily possesses. 

Thus  a  sheet  ot'  vulcanite,  electrified  by  friction, 
still  retains  its  characteristic  density,  shape,  color, 
etc. 

Effect,  Counter-Inductive The 

opposal  of  current  or  charge  by  means  of  a 
counter-electromotive  force  produced  by  'n- 
duction. 


In  the  Thomson  counter-electromotive  force 
lightning  arrester,  a  counter-electromotive  force, 
produced  by  the  inductive  effects  of  the  passage 
of  the  bolt  to  earth,  protects  the  instrument  by 
opposing  the  passage  of  the  bolt.  (See  Arr  ester % 
Lightning,  Counter- Electromotive  Force.) 

Effect,  Edison An  electric  dis- 
charge which  occurs  between  one  of  the  ter- 
minals of  the  incandescent  filament  of  an 
electric  lamp,  and  a  metallic  plate  placed  near 
the  filament  but  disconnected  therefrom,  as 
soon  as  a  certain  difference  of  potential  is 
reached  between  the  lamp  terminals. 

The  effect  of  the  discharge  is  to  produce  a  cur- 
rent in  a  circuit  connected  to  one  pole  of  the  lamp 
terminals  and  the  metallic  plate,  as  may  be  shown 
by  means  of  a  galvanometer. 

Effect,  Electrotonic An  altered 

condition  of  excitability  of  a  nerve  produced 
when  in  the  electrotonic  state.  (See  Elec- 
trotonus.) 

Effect,  Faraday The  rotation  of 

the  plane  of  polarization  of  a  beam  of  plane 
polarized  light  by  its  passage  through  a 
magnetic  field. 

Lodge  suggests  the  following  explanation  for 
the  Faraday  effect :  As  is  well  known,  a  strongly 
magnetized  medium  possesses  a  different  magnetic 
susceptibility  to  additional  magnetizing  forces  in 
the  same  direction  than  it  does  in  the  opposite 
direction.  It  therefore  follows  that  the  vibra- 
tions are  resolved  into  two  opposed  circular  com- 
ponents, which  travel  through  the  medium  with 
different  rates  of  velocity,  since  one  tends  to  mag- 
netize it  and  the  other  to  demagnetize  it.  The 
plane  of  rotation  will  therefore  be  rotated. 

He  also  suggests  the  following  explanation  for 
the  Faraday  effect,  viz.:  He  assumes  that  the 
Amperian  molecular  currents  in  such  substances 
as  exhibit  rotation  in  a  magnetic  field  do  not 
consist  of  two  equal  and  opposite  electrical  cur- 
rents, but  that  one  of  the  currents  is  slightly 
stronger  than  the  other.  Suppose,  for  example, 
that  in  iron  the  positive  Amperian  current  is 
weaker  than  the  negative,  and  that  the  ether  as 
a  whole  is  rotating  with  the  negative  current. 
Any  ethereal  vibration  entering  such  a  medium 
will  begin  to  screw  itself  in  the  direction  opposed 
to  that  of  the  magnetizing  current.  In  copper, 
or  other  similar  substances,  the  rotation  should 
take  place  in  the  opposite  direction. 


Eff. 


183 


[Eff, 


Effect,  Ferranti •  —An  increase  in  the 

electromotive  force,  or  difference  of  potential, 
of  mains  or  conductors  towards  the  end  of  the 
same  farthest  from  the  terminals  that  are  con- 
nected with  a  source  of  constant  potential. 

The  Ferranti  effect  refers  to  the  increase  of  the 
electromotive  force  on  the  mains  employed  in 
systems  for  the  transmission  of  electrical  energy 
by  means  of  alternating  currents.  It  was  found, 
for  example,  in  the  currents  used  on  the 
mains  connected  with  one  of  Mr.  Ferranti' s  alter- 
nating dynamos  and  leading  to  the  town  of  Dept- 
ford,  that  instead  of  finding  a  drop  of  potential  at 
the  ends  of  the  mains  farthest  from  the  dynamo, 
as  was  expected,  a  notable  increase  in  the  poten- 
tial occurred.  These  effects  were  observed  dur- 
ing the  laying  of  the  mains.  Testing  the  poten- 
tial by  placing  an  incandescent  lamp  in  the  circuit 
across  the  mains,  the  increase  of  the  potential 
with  the  increase  of  the  length  of  the  main  was 
shown  by  the  increased  brilliancy  of  the  light  of 
the  incandescent  lamp. 

Various  explanations  have  been  given  as  the 
cause  of  the  Ferranti  effect. 

Effect,  Hall A  transverse  elec- 
tromotive force,  produced  by  a  magnetic 
field  in  substances  undergoing  electric  dis- 
placement. 

This  transverse  electromotive  force  is  probably 


Fig.  226.    Hall  Effect. 
due  to  magnetic  whirls,  in  a  manner  similar  to 
the  Faraday  effect. 

The  Hall  effect  is  produced  by  placing  a  very 
thin  metallic  strip,  conveying  an  electric  current, 
in  a  strong  magnetic  field. 

The  cross  A  B  C  D,  Fig.  226,  is  cut  out  of  a 


gold  leaf  or  other  very  thin  metallic  sheet.  The 
ends  A  and  B,  are  connected  with  the  terminals 
of  a  battery  S,  and  the  ends  C  and  D,  with  the 
galvanometer  G. 

None  of  the  battery  current  can  therefore  flow 
through  the  galvanometer. 

If,  now,  the  metallic  cross  be  placed  in  a  power- 
ful magnetic  field,  the  lines  of  force  of  which  are 
perpendicular  to  the  plane  of  the  cro^s,  the  deflec- 
tion of  the  galvanometer  needle  will  show  the 
existence  of  a  current,  which,  if  the  battery  cur- 
rent flows  in  the  direction  of  the  arrow,  or  from  A, 
to  B,  and  the  lines  of  magnetic  force  pass  through 
the  paper  from  the  front  to  the  back  of  the  sheet, 
when  the  cross  is  formed  of  gold,  silver,  platinum 
or  tin-foil,  will  flow  through  C  D,  from  C  to  D, 
but  in  the  opposite  direction  if  formed  of  iron. 
These  effects  cease  if  the  conductor  is  increased 
in  thickness  beyond  a  certain  extent. 

As  regards  the  production  of  the  Hall  effect  by 
the  influence  of  a  magnetic  field  on  conductors, 
Mr.  Shelford  Bidwell  suggests  that  since  magnet- 
ism affects  the  conductivity  of  metals  in  a 
complicated  manner,  it  is  possible  that  metallic 
substances  conveying  an  electric  current  in  a 
magnetic  field  are  more  or  less  strained  by  the 
mechanical  forces,  and  that,  therefore,  heat  may 
be  unequally  developed,  and  that  the  resistance 
thus  being  modified  in  places,  there  may  be  pro- 
duced disturbances  of  the  flow  which  may 
rapidly  produce  in  part  a  transverse  electromotive 
force. 

Effect,  Hall,  Real A  transverse  elec- 
tromotive force  produced  in  conductors  con- 
veying electric  currents,  by  magnetic  whirls, 
in  a  manner  similar  to  that  in  which  the  Far- 
aday effect  is  produced.  (See  Effect,  Fara- 
day) 

Effect,  Hall,  Spurious An  appa- 
rent transverse  electromotive  force  produced 
in  conductors  conveying  electric  currents  in 
magnetic  fields,  by  changes,  produced  by  mag- 
netism, in  the  conductivity  of  the  metals,  and 
the  consequent  production  of  local  distur- 
bances in  the  electrical  flow,  thus  resulting 
in  an  apparent  transverse  electromotive  force. 

Effect,  Impulsion The  restoration 

or  loss  of  sensitiveness  of  a  photo-voltaic  cell 
to  the  action  of  light,  produced  by  means  of 
an  impulse  such  as  that  of  a  tap  or  blow,  or 
electro-magnetic  impulse. 


Eff.] 


184 


[Eff. 


Effect,  Joule The  heating  effect 

produced  by  the  passage  of  an  electric  cur- 
rent through  a  conductor,  arising  merely  from 
the  resistance  of  the  conductor. 

The  rate  at  which  this  occurs  is  proportional  to 
the  resistance  of  the  conductor  through  which 
the  current  is  passing  multiplied  by  the  square 
of  the  current.  (See  Heat,  Electric. ) 

Effect,  Kerr A  term  applied  to 

the  electrostatic  optical  effect  discovered  by 
Dr.  Kerr,  viz.,  that  a  beam  of  plane  polarized 
light  is  elliptically  polarized  when  transmitted 
across  an  electrostatic  field. 

The  Kerr  effect  does  not  take  place  in  free  space, 
but  occurs  in  different  senses  or  directions  in  dif- 
ferent media. 

Like  the  Faraday  effect,  the  Kerr  effect  de- 
pends on  the  presence  of  a  dense  medium,  and  the 
direction  of  the  effect  depends  on  the  character  of 
the  medium. 

Effect,  Mordey  — A  term  some- 
times applied  to  a  decrease  in  the  value  of 
hysteresis  in  the  iron  of  a  dynamo  armature  at 
full  load. 

Effect,  Peltier The  heating  ef- 
fect produced  by  the  passage  of  an  electric 
current  across  a  thermo-electric  junction  or 
surface  of  contact  between  two  different  met- 
als. (See  Junction,  Thermo-Electric.) 

The  passage  of  the  current  across  a  thermo- 
electric junction  produces  either  heat  or  cold.  If 
heat  is  produced  by  its  passage  in  one  direction, 
told  is  produced  by  its  passage  in  the  opposite 
direction.  The  Peltier  effect  may,  therefore, 
mask  the  Joule  effect. 

The  Peltier  effect  is  the  converse  of  the  thermo- 
electric effect,  where  the  unequal  heating  of  metal- 
lic junctions  results  in  an  electric  current.  (See 
Effect,  Joule.  Effect,  Thomson.) 

The  quantity  of  heat  absorbed  or  emitted  by 
the  Peltier  effect  is  proportional  to  the  current 
strength,  and  not,  as  in  the  Joule  effect,  to  the 
square  of  the  current. 

Effect,  Photo-Yoltaic The  change 

in  the  resistance  of  selenium  or  other 
substances  effected  by  their  exposure  to 
light.  The  photo-voltaic  effect  is  seen  in 
the  case  of  the  selenium  cell.  (See  Cell, 
Selenium!) 


Effect,  Seebeck A  term  sometimes 

used  instead  of  thermo-electric  effect.  (See 
Effect,  Thermo-Electric.) 

This  term  has  nearly  passed  out  of  use. 

Effect,  Skin The  tendency  of  alter- 
nating currents  to  avoid  the  central  portions 
of  solid  conductors  and  to  flow  or  pass  mostly 
through  the  superficial  portions. 

The  so-called  skin  effect  is  more  pronounced 
the  more  frequent  the  alternations. 

Effect,  Thermo-Electric The  pro- 
duction of  an  electromotive  force  at  a 
thermo-electric  junction  by  a  difference  of 
temperature  between  that  junction  and  the 
other  junction  of  the  thermo-electric  couple. 
(See  Couple,  Thermo-Electric.  Junction, 
Thermo-Electric^) 

Effect,  Thomson — Th'e  production  of 

an  electromotive  force  in  unequally  heated 
homogeneous  conducting  substances. 

A  term  also  applied  to  the  increase  or  de- 
crease in  the  differences  of  temperature  in  an 
unequally  heated  conductor,  produced  by  the 
passage  of  an  electrical  current  through  the 
conductor. 

The  Thomson  effects  vary  according  to  whether 
the  current  passes  from  a  colder  to  a  hotter  part 
of  the  conductor,  or  the  reverse. 

The  Thomson  effects  differ  in  direction  in  differ- 
ent metals,  and  are  absent  in  lead.  Thomson  has 
pointed  out  the  similarity  between  this  species  of 
thermo-electric  phenomena,  and  convection  by 
heat,  or  the  phenomena  of  a  liquid  circulating  in 
a  closed  rectangular  tube,  under  the  influence  of 
differences  of  temperature,  in  which  the  heated 
fluid  gives  out  heat  in  the  cooler  parts  of  the  cir- 
cuit, and  takes  in  heat  in  the  -warmer  parts. 
This  would  presuppose  that  positive  electricity 
carries  heat  in  copper  like  a  real  fluid,  but  that 
in  iron  it  acts  as  though  its  specific  heat  were  a 
negative  quantity,  in  which  respect  it  is  unlike  a. 
true  fluid. 

"  We  may  express,"  says  Maxwell,  "  both  the 
Peltier  and  the  Thomson  effects  by  stating;  that 
when  an  electric  current  is  flowing  from  places  of 
smaller  to  places  of  greater  thermo-electric  power, 
heat  is  absorbed,  and  when  it  is  flowing  in  the 
reverse  direction  heat  is  generated,  and  this 
whether  the  difference  of  thermo-electric  power 
in  the  two  places  arises  from  a  difference  in  the 


Eff.] 


185 


[Ele. 


nature  of  the  metals,  or  from  a  difference  of  tem- 
perature in  the  same  metal." 

Effect,     Yoltaic A     difference     of 

potential  observed  at  the  point  of  contact  of 
two  dissimilar  metals. 

This  difference  of  potential  was  formerly  as- 
cribed to  the  mere  contact  of  dissimilar  metals, 
and  is  even  yet  believed  by  some  to  be  due  to 
such  contact.  It  is,  however,  perhaps  more  ac- 
curately ascribed  to  the  greater  affinity  of  oxygen 
of  the  air  for  the  positive  metal  than  for  the 
negative  metal;  that  is,  to  a  chemical  action  on 
the  positive  element  of  a  voltaic  couple. 

Effective  Electromotive  Force.— (See 
Force,  Electromotive,  Effective) 

Effective  Secondary  Electromotive 
Force. — (See  Force,  Electromotive,  Second- 
ary, Effectived) 

Effects  of  Capillarity  on  Voltaic  Cells.— 
(See  Capillarity,  Effects  of,  on  Voltaic  Cell) 

Efficiency,  Commercial —The  useful 

or  available  energy  produced  divided  by  the 
total  energy  absorbed  by  any  machine  or  ap- 
paratus. 

The  Commercial  Efficiency  = 
W  _  W 

M        W  -J-  w  -J-  m, 

when  W  =  the  useful  or  available  energy;  M  = 
the  total  energy;  w,  the  energy  absorbed  by  the 
machine,  and  m,  the  stray  power,  or  power  lost 
in  friction  of  bearings,  etc.,  air  friction,  eddy  cur- 
rents, etc. 

Efficiency,  Commercial,  of  Dynamo 

—The  useful  or  available  electrical  energy  in 
the  external  circuit,  divided  by  the  total 
mechanical  energy  required  to  drive  the 
dynamo  that  produced  it.  (See  Co-efficient, 
Economic,  of  a  Dynamo-Electric  Machine) 

Efficiency,  Electric The  useful  or 

available   electrical    energy  of    any  source, 
divided  by  the  total  electrical  energy. 
W 


The  electric  efficiency 


where  W, 


equals  the  useful  or  available  electrical  energy, 
and  w,  the  electrical  energy  absorbed  by  the 
machine. 

Efficiency  of  Conversion. — The  ratio  be- 
tween the  energy  present  in  any  result  and 
*he  energy  expended  in  producing  that  result. 


Efficiency  of  Conversion   of  Dynamo.— 

(See  Conversion,  Efficiency  of,  of  Dynamo^ 
Efficiency  of  Transformer. — (See  Trans- 
former, Efficiency  of.) 

Efficiency,  Quantity,  of  Storage  Battery 

The  ratio  of  the  number  of  ampere- 
hours  taken  out  of  a  storage  or  secondary 
battery,  to  the  number  of  ampere-hours  put  in 
the  battery  in  charging  it. 

Efficiency,  Real,  of  Storage  Battery 

— The  ratio  of  the  number  of  watt-hours 
taken  out  of  a  storage  battery,  to  the  number 
of  watt-hours  put  into  the  battery  in  charg- 
ing it. 

Efflorescence. — The  drying  of  crystals  by 
losing  their  water  of  crystallization  and  be- 
coming pulverulent  or  crumbling. 

The  term  is  sometimes  loosely  applied  to 
the  deposition  of  solid  matter  by  the  crystal- 
lization of  a  salt,  above  the  line  of  the  liquid, 
on  the  surface  of  a  vessel  containing  a  vaporiz- 
able  saline  solution. 

The  liquid,  by  capillarity  in  a  porous  vessel,  or 
by  adhesion  to  the  walls  of  an  impervious  vessel, 
rises  above  the  level  of  the  main  liquid  line,  and, 
evaporating,  deposits  crystals  on  the  vessel. 

This  process  is  technically  called  creeping,  and 
is  often  the  cause  of  much  annoyance  in  voltaic 
cells. 

Egg,  Philosopher's A  name  given 

to  the  ovoidal,  or  egg-shaped  mass  of  light 
that  appears  when  a  convective  discharge  is 
taken  between  two  electrodes  in  a  partial 
vacuum. 

The  philosopher's  egg  is  but  one  of  the  shapes 
assumed  by  the  convective  discharge.  (See  Dis- 
charge, Convective.) 

Elasticity,  Electric—  —The  quotient 
arising  from  dividing  the  electric  stress  by 
the  electric  strain. 

It  can  be  shown  mathematically  that  the  elec- 
tric elasticity  is  equal  to  4,  or  4  x  3. 1416,  divided 
by  the  specific  inductive  capacity. 

Electrepeter. — An  instrument  for  chang- 
ing the  direction  of  an  electric  current. 

The  old  term  for  switch,  key,  or  pole  changtr. 
(Obsolete.) 

Electric. — Pertaining  to  electricity. 


Ele.] 


186 


[Ele. 


Electric  Absorption.— (See  Absorption, 
Electric) 

Electric  Acoutemeter. — (See  Acouteme- 
ter,  Electric) 

Electric  Actinometer. — (See  Actinomeier, 
Electric) 

Electric  Adhesion. — (See  Adhesion,  Elec- 
tric) 

Electric  Aging  of  Alcohol.— (See  Alco- 
hol, Electric  Aging  of) 

Electric  Alarm.— (See  Alarm,  Electric) 

Electric  Alarm  Speaking-Tube  Mouth- 
Piece. — (See  Speaking-Tube  Mouth-Piece, 
Electric  Alarm) 

Electric  Amalgam. — (See  Amalgam, 
Electric) 

Electric  Ammunition  Hoist. — (See  Hoist, 
Ammunition,  Electric) 

Electric  Analysis.— (See  Analysis,  Elec- 
tric) 

Electric  Analyzer. — (See  Analyzer,  Elec- 
tric) 

Electric  Anemometer. — (See  Anemome- 
ter, Electric) 

Electric  Annealing. — (See  Annealing, 
Electric) 

Electric  Annunciator  Clock. — (See 
Clock,  Electric  Annunciator) 

Electric  Arc.— (See  Arc,  Electric) 

Electric  Arc  Blow-Pipe.—  ( See  Blow- 
Pipe,  Electric  Arc) 

Electric  Argand  Burner,  Hand-Lighter 
(See  Burner,  Argand  Electric,  Hand- 
Lighter) 

Electric  Argand  Burner,  Plain-Pendant 

— (See  Bttrner,  Argand  Electric, 

Plain-Pendant) 

Electric  Argand  Burner,  Ratchet-Pend- 
ant   (See  Burner,  Argand  Electric, 

Ratchet-Pendant) 

Electric  Balance.  -(See  Balance,  Elec- 
tric) 

Electric  Balloon.— (See  Balloon,  Elec- 
tric) 

Electric  Battery.— (See  Battery,  Elec- 
tric^ 


Electric  Bell,  Continuous-Sounding 

— (See  Bell,  Continuous-Sounding  Electric) 
Electric    Bell,  Differential.— (See  Bell, 
Differential  Electric) 

Electric    Bell,  Mechanical.— (See  Bell, 
Electro-Mechanical) 

Electric  Bell  Pull.— (See  Pull,  Bell,  Elec- 
tric) 

Electric  Bioscopy. — (See  Bioscopy,  Elec- 
tric) 

Electric  Bi-Polar  Bath.— (See  Bath,  Bi- 
Polar) 

Electric  Blasting.— (See  Blasting,  Elec- 
tric) 

Electric     Bleaching. — (See     Bleaching, 
Electric) 

Electric    Blow-Pipe.— (See     Blow-Pipe. 
Electric) 

Electric  Boat.— (See  Boat,  Electric) 
Electric  Bobbin.— (See  Bobbin,  Electric) 
Electric  Body-Protector.— (See  Body-Pro- 
tector, Electric) 

Electric  Boiler-Feed.— (See  Boiler-Feed, 
Electric) 

Electric  Branding. — (See  Branding,  Elec- 
tric) 

Electric  Breeze. — (See  Breeze,  Electric) 
Electric  Bridge.— (See  Bridge,  Electric) 
Electric  Buoy.— (See  Buoy,  Electric) 
Electric    Burner. — (See    Burner,   Auto- 
matic Electric) 

Electric  Buzzer.— (See  Buzzer,  Electric) 
Electric  Cable.— (See  Cable,  Electric) 
Electric  Calamine. — (See  Calamine,  Elec- 
tric) 

Electric  Call-Bell.— (See  Bell,  Call) 
Electric  Calorimeter. — (See  Calorimeter, 
Electric) 

Electric  Candle.— (See  Candle,  Electric) 
Electric     Case-Hardening.— (See     Case- 
Hardening,  Electric) 

Electric  Cauterization. — (See  Cauteriza' 
tion,  Electric) 

Electric     Cauterizer. — (See    Cauterizer, 
Electric) 


Ele.] 


187 


[Ele. 


Electric  Cautery.— (See  Cautery,  Elec- 
tric^ 

Electric  Charge-  (See  Charge, Electric?) 
Electric  Chimes.— (See  Chimes,  Electric.} 

Electric  Chronograph.— (See  Chrono- 
graph, Electric?) 

Electric  Chronoscope. — (See  Chronoscope, 
Electric?) 

Electric  Cigar-Lighter.— (See  Lighter, 
Cigar,  Electric?) 

Electric  Circuit.— ( See  Circuit,  Electric,) 

Electric  Cleats.— (See  Cleats,  Electric?) 

Electric  Clepsydra. — (See  Clepsydra,  Elec- 
tric?) 

Electric  Clock.-  (See  Clock,  Electric?) 

Electric  Coil.-  (See  Coil,  Electric?) 

Electric  Column.— (See  Column,  Elec- 
tric?} 

Electric  Communicator. — (See  Commu- 
nicator, Electric?) 

Electric  Conducting.— (See  Conducting, 
Electrical?) 

Electric  Conduction.— (See  Conduction, 
Electric.} 

Electric  Convection  of  Heat.— (See  Heat, 
Electric  Convection  of?) 

Electric  Cord.— (See  Cord,  Electric?) 

Electric  Counter. — (See  Counter,  Elec- 
tric?) 

Electric  Creeping. — (See  Creeping,  Elec- 
tric?) 

Electric  Cross.— (See  Cross,  Electric?) 

Electric  Crucible.— (See  Crucible,  Elec- 
tric?) 

Electric  Current.— (See  Current,  Elec- 
tric?) 

Electric  Cystoscopy. — (See  Cystoscopyt 
Electric?) 

Electric  Damping.— (See  Damping,  Elec- 
tric?) 

Electric  Death.— (See  Death,  Electric?) 

Electric    Decomposition. — (See    Decom- 
position, Electric?) 
1  -Vol.  1 


Electric  Density.— (See  Density,  Elec- 
tric?) 

Electric  Deposition.— (See  Deposition, 
Electric?) 

Electric  Determination  of  Longitude.— 
(See  Longitude,  Electric  Determination 
of.) 

Electric  Displacement. — (See  Displace- 
ment, Electric?) 

Electric  Distillation.— (See  Distillation, 
Electric?) 

Electric  Door-Bell  Pull.— (See  Pull, 
Electric  Door-Bell?) 

Electric  Double-Refraction.  —  (See 
Double-Refraction,  Electric?) 

Electric  Dyeing.— (See  Dyeing,  Electric?) 

Electric  Dynamometer,  Siemens'. — (See 
Dynamometer,  Electro?) 

Electric  Eel.— (See  Eel,  Electric?) 

Electric  Efficiency.— (See  Efficiency,  Elec- 
tric?) 

Electric  Elasticity.— (See  Elasticity,  Elec- 
tric?) 

Electric  Elevator.— (See  Elevator,  Elec- 
tric.) 

Electric  Endosmose.— (See  Endosmose, 
Electric?) 

Electric  Energy. — (See  Energy,  Electric?) 

Electric  Entropy.— (See  Entropy,  Elec- 
tric?) 

Electric  Escape. — (See  Escape,  Electric?) 

Electric  Etching.— (See  Etching,  Elec- 
tro?) 

Electric  Evaporation.— (See  Evapora- 
tion, Electric?) 

Electric  Excitability  of  Nerve  or  Mns- 
cular  Fibre.— (See  Excitability,  Electric, 
of  Nerve  or  Muscular  Fibre?) 

Electric  Exhaustion.— (See  Exhaustion, 
Electric?) 

Electric  Expansion.— (See  Expansion, 
Electric?) 

Electric  Exploder.— (See  Exploder,  Elec- 
tric Mine?) 


Ele.] 


188 


[Ele. 


Electric  Explorer.— (See  Explorer,  Elec- 
tric) 

Electric  Field.— (See  Field,  Electric) 
Electric    Figures,    Breath  -        —(See 
Figures,  Electric,  Breath) 

Electric  Figures,  Lichtenberg's  — 
(See  Figures,  Electric,  Lichtenberg's) 
Electric  Fishes.— (See  Fishes,  Electric) 
Electric  Fly.— (See  Fly,  Electric) 
Electric  Flyer.— (See  Flyer,  Electric) 
Electric  Fog.— (See  Fog,  Electric) 
Electric  Force.— (See  Force,  Electric) 
Electric  Furnace. — (See  Furnace,  Elec- 
tric) 

Electric  Fuse.— (See  Fuse,  Electric) 
Electric  Gas-Lighting.— (See  Gas-Light- 
ing, Electric) 

Electric  Gas-Lighting,  Multiple  — 
(See  Gas-Lighting,  Multiple  Electric) 

Electric  Gas-Lighting  Torch.— (See 
Torch,  Electric  Gas-Lighting) 

Electric  Gastroscope. — (See  Gastroscope, 
Electric) 

Electric  Gilding.— (See  Gilding,  Electric) 
Electric  Governor. — (See  Governor,  Elec- 
tric) 

Electric  Hand-Lighter  for  Argand 
Burner. — (See  Burner,  Argand  Electric 
Hand-Lighter) 

Electric  Head-Bath.— (See  Bath,  Head, 
Electric) 

Electric  Head-Light— (See  Head-Light, 
Locomotive,  Electric) 
Electric  Heat— (See  Heat,  Electric) 
Electric  Heater.— (See  Heater,  Electric) 
Electric  Horse  Power. — (See  Power, 
Horse,  Electric) 

Electric  Hydrotasimeter.— (See  Hydro- 
tasimeter,  Electric) 

Electric  Ignition.— (See  Ignition,  Elec- 
tric) 

Electric  Images.— (See  Images,  Electric) 
Electric  Incandescence. — (See  Incandes- 
cence, Electric) 


Electric  Indicator  for  Steamships. — (See 
Indicator,  Electric,  for  Steamships) 

Electric     Indicators. — (See     Indicators, 
Electric) 

Electric  Inertia,— (See  Inertia,  Electric) 

Electric     Insolation. — (See     Insolation, 
Electric) 

Electric  Installation.— (See  Installation, 
Electric) 

Electric     Insulation. — (See     Insulation, 
Electric) 

Electric    Irritability.— (See   Irritability, 
Electric) 

Electric  Jar.— (See  Jar,  Electric) 

Electric  Jewelry.— (See    Jewelry,   Elec- 
tric) 

Electric    Lamp,    Arc (See  Lamp, 

Electric,  Arc) 

Electric    Lamp-Bracket— (See   Bracket, 
Lamp,  Electric) 

Electric  Lamp,  Incandescent (See 

Lamp,  Electric,  Incandescent) 

Electric   Lamp,  Semi-Incandescent  — 
— (See  Lamp,  Electric,  Semi-Incandescent) 

Electric  Lamp,  Socket  for.— (See  Socket, 
Electric  Lamp) 

Electric    Launch. — (See    Launch,    Elec- 
tric) 

Electric    Letter-Box.— (See    Letter-Box, 
Electric) 

Electric  Light— (See  Light,  Electric) 

Electric  Lighting,  Central  Station  — 
— (See  Station,  Central) 

Electric   Lighting,   Isolated (See 

LigJtting,  Electric,  Isolated) 

Electric  Light  or  Power    Cable.— (See 
Cable,  Electric  Light  or  Power) 

Electric  Lock.— (See  Lock,  Electric) 

Electric   Locomotive. — (See  Locomotive. 
Electric) 

Electric  Log.— (See  Log,  Electric) 

Electric  Loom. — (See  Loom,  Electric) 

Electric  Loop.— (See  Loop,  Electric) 

Electric  Machine,  Frictional  —      —(See 
Machine,  Frictional  Electric) 


Ele.] 


189 


LEle, 


Electric  Main.— (See  Main,  Electric) 
Electric  Masses. — (See  Masses,  Electric.) 
Electric  Measurements. — (See  Measure- 
ments, Electric?) 

Electric     Megaloscope. — (See     Megalo- 
scope, Electric) 

Electric  Meter.— (See  Meter, .Electric) 
Electric  Mine-Exploder.— (See  Mine-Ex- 
ploder, Electro-Magnetic.     Fuse,  Electric) 

Electric  Motor.— (See  Motor,  Electric) 

Electric  Motor,  High-Speed  —     —(See 
Motor,  Electric,  High-Speed) 

Electric  Motor,  Low-Speed  —      —(See 
Motor,  Electric,  Low-Speed) 

Electric    Multipolar    Bath  -       —(See 

Bath,  Multipolar,  Electric) 

Electric  Musket.— (See  Musket,  Electric) 
Electric  Organ.— (See  Organ,  Electric) 
Electric  Oscillations.— (See  Oscillations, 
Electric) 

Electric  Osmose.— (See  Osmose,  Electric) 
Electric      Osteotome.— (See     Osteotome, 
Electric) 

Electric      Overtones.—  (See      Overtones, 
Electric) 

Electric  Pen.— (See  Pen,  Electric) 
Electric  Pendant— (See  Pendant,  Elec- 
tric) 

Electric   Pendani^Lamps.— (See  Lamps, 
Electric  Pendant) 

Electric     Pendulum. — (See     Pendulum, 
Electric) 

Electric  Permeancy. — (See  Permeancy, 
Electric) 

Electric   Phosphorescence. — (See    Phos- 
phorescence, Electric) 
Electric  Photometer.— (See  Photometer) 
Electric  Piano.— (See  Piano,  Electric) 
Electric  Plow.— (See  Plow,  Electric) 
Electric  Position-Finder.— (See  Finder, 
Position,  Electric) 

Electric  Potential.— (See  Potential,  Elec- 
tric) 


Electric  Power. — (See  Power,  Electric.} 
Electric  Probe.— (See  Probe,  Electric) 
Electric  Prostration. — (See  Prostration, 

Electric.} 
Electric     Protection.— (See    Protection, 

Electric,  of  Houses,  Ships  and  Buildings.} 
Electric    Protection    of    Metals.— (See 

Metals,  Electrical  Protection  of) 

Electric  Pulse.— (See  Pulse,  Electrical) 

Electric     Pyrometer,    Siemens'.— (See 

Pyrometer,  Siemens ' ,  Electric) 

Electric     Radiometer,   Crookes'  — 

(See  Radiometer,  Electric,  Crookes') 

Electric  Range-Finder.— (See  Finder, 
Range,  Electric) 

Electric  Ratchet-Pendant  for  Argand 
Burner. — (See  Burner,  Argand  Electric, 
Ratchet-Pendant) 

Electric  Bay. — (See  Ray,  Electric)- 

Electric  Reaction  Wheel.— (See   Wheel, 

Reaction,  Electric) 
Electric  Rectification  of  AlcohoL— (Sec 

Alcohol,  Electric  Rectification  of) 

Electric  Refining  of  Metals.— (See  Metals, 

Electric  Refining  of.) 

Electric   Register,    Watchman's  — 

(See  Register,  Watchman's  Electric) 

Electric    Registering    Apparatus.— (See 

Apparatus,  Registering,  Electric) 

Electric  Relay-Bell.— (See  Bell.  Relay, 
Electric) 

Electric  Repulsion. — (See  Repulsion, 
Electric) 

Electric  Resistance. — (See  Resistance, 
Electric) 

Electric  Resonance. — (See  Resonance, 
Electric) 

Electric  Retardation.— (See  Retardation, 
Electric.} 

Electric  Rings.— (See  Rings,  Electric) 

Electric  Safety  Lamps.— (See  Lamp, 
Electric  Safety.} 

Electric  Saw.— (See  Saw,  Electric) 


Ele.] 


190 


[Ele. 


Electric  Seismograph.— (See  Seismo- 
graph, Electric.} 

Electric  Shadow. — (See  Shadow,  Elec- 
tric} 

Electric  Shock.— (See  Shock,  Electric} 

Electric  Shower  Bath.— (See  Bath, 
Shower  Electric} 

Electric  Shunt  Bell.— (See  Bell,  Shunt, 
Electric} 

Electric  Single-Stroke  Bell.— (See  Bell, 
Single-Stroke  Electric} 

Electric  Siphon.— (See  Siphon,  Electric} 

Electric  Soldering.— (See  Soldering, 
Electric} 

Electric  Sphygmograph.— (See  Sphygmo- 
graph,  Electrical} 

Electric  Sterilization.— (See  Steriliza- 
tion, Electric} 

Electric  Storm.— (See  Storm,  Electric} 

Electric  Striw.— (See  Stria,  Electric} 

Electric  Submarine  Boat. — (See  Boat, 
Submarine,  Electric} 

Electric  Sunstroke.— (See  Sunstroke, 
Electric} 

Electric  Snrgings. — (See  Surgings,  Elec- 
tric} 

Electric  Swaging.— (See  Swaging,  Elec- 
tric} 

Electric  Tanning.— (See  Tanning,  Elec- 
tric.} 

Electric  Target— (See  Target,  Electric} 

Electric  Teazer.— (See  Teazer,  Electric 
Current} 

Electric  Telehydrobarometer.— (See  7V/- 
ehydrobarometer,  Electric} 

Electric  Tell-Tale  Signal.— (See  Signal, 
Electric  Tell-Tale} 

Electric  Tempering. — (See  Tempering, 
Electric.} 

Electric  Tension. — (See  Tension,  Elec- 
tric} 

Electric  Thermo-Call.— (See  Thermo- 
Call,  Electric} 

Electric  Thermometer. — (See  Thermom- 
eter, Electric} 


Electric      Throwback-Indicator.— ( See 
Indicator.  Electrical  Throwback} 

Electric  Time-Ball.— (See  Ball,  Electric 
Time} 

Electric  Time-Meter. — (See  Meter.  Elec- 
tric Time} 

Electric   Torpedo.— (See    Torpedo,  Elec- 
tric} 

Electric  Tower. — (See  Tower,  Electric} 

Electric  Tramway. — (See  Tramway,  Elec- 
tric} 

Electric  Transmitters.— (See   Transmit- 
ter, Electric} 

Electric  Trumpet— (See  Trumpet,  Elec- 
tric} 

Electric  Turn-Table. — (See  Turn-Table, 
Electric} 

Electric  Typewriter. — (See    Typewriter, 
Electric} 

Electric  Valve.— (See  Valve,  Electric} 

Electric  Valve  Burner,  Argand  — 
(See  Valve  Burner,  Argand  Electric} 

Electric  Varnish.— (See    Varnish,  Elec- 
tric} 

Electric  Vibrating  Burner.— (See  Burner 
Vibrating,  Electric} 

Electric  Volatilization.— (See  Volatiliza- 
tion, Electric} 

Electric  Water  or  Liquid  Level  Alarm.— 

(See  Alarm,  Water  or  Liquid  Level} 

Electric   Welding.— (See  Welding,  Elec- 
tric} 

Electric  Whirl.-(See  Whirl,  Electric} 

Electric  Whistle,  Automatic  Steam  — 
— (See    Whistle,    Steam,  Automatic    Elec- 
tric) 

Electric  Wood  Mouldings.— (See  Mould- 
ings, Electric   Wood} 

Electric  Work.— (See  Work,  Electric) 

Electrical    Controlling   Clock.— (See 
Clock,  Electrical  Controlling) 

Electrically. — In  an  electrical  manner. 

Electrically     Controlled    Clock.  —  (See 
Clock,  Electrically  Controlled) 


191 


[Ele. 


Electrically  Discharge,  To (See 

Discharge,  To  Electrically?) 

Electrically  Discharging. — (See  £>t's- 
charging,  Electrically?) 

Electrically  Energizing. — (See  Energiz- 
ing, Electrically?) 

Electrically  Operated  Alarm.— -(See 
Alarm,  Electrically  Operated?) 

Electrically  Retarding.— (See  Retard- 
ing, Electrically?) 

Electrician. — One  versed  in  the  principles 
and  applications  of  electrical  science. 

Electrician,   Electro-Therapeutical 

—A  medical  electrician. 

Electrician,  Medical One  skilled 

in  the  application  of  electricity  to  the  human 
body  for  diagnosis  or  curative  purposes. 

A  medicai  electrician  should  possess  a  full 
knowledge,  not  only  of  the  principles  and  appli- 
cations of  electric  science,  but  also  of  physics  and 
chemistry  and  of  the  medical  sciences. 

Electricity. — The  name  given  to  the  un- 
known thing,  matter  or  force,  or  both,  which 
is  the  cause  of  electric  phenomena. 

Electricity,  no  matter  how  produced,  is  oe- 
lieved  to  be  one  and  the  same  thing. 

The  terttuJriftioHaf-elfetrieity,  pyro-electricity, 
magneto  -electricity ',  -voltaic  or  galvanic  electricity •, 
thermo-electricity,  contact-electricity,  animal  or 
vegetable-electricity,  etc.,  etc.,  though  convenient 
for  distinguishing  LLeir  origin,  have  no  longer 
the  significance  formerly  attributed  to  them  as 
representing  different  kinds  of  the  electric  force. 
(See  Electricity,  Single-Fluid  Hypothesis  of.) 

Electricity,  Accumulated  — Elec- 
tricity collected  in  or  by  means  of  accumula- 
tors. 

Electricity,  Accumulating  —Ob- 
taining successively  increasing  electrical 
charges.  (See  Electricity,  Accumulation  of.) 

Electricity,  Accumulation  of A 

general  term  applied  indifferently  to — 

(l.)  The  gradual  collecting  of  electric 
energy  in  a  Leyden  jar  or  condenser. 

(2.)  The  increase  of  an  electric  charge  by 
the  action  of  various  devices  called  accumu- 
lators. 


(3.)  The  production  of  a  charge  by  the  use 
of  machines  called  influence  machines. 

(4.)  The  collection  of  electric  energy  in  the 
so-called  storage  batteries  or  accumulators. 

Electricity,  Animal  —Electricity 

produced  during  life  in  the  bodies  of  animals. 

All  animals  produce  electricity  during  life.  In 
some,  such  as  the  electric  eel  or  torpedo,  the 
amount  is  comparatively  large.  In  others,  it  is 
small. 

Some  of  these  animals,  when  of  full  size,  are  able 
to  give  very  severe  shocks,  and  use  this  curious 
power  as  a  means  of  defense  against  their  enemies. 

If  the  spinal  cord  of  a  recently  killed  frog  be 
brought  into  contact  with  the  muscles  of  the 
thigh,  a  contraction  will  ensue. — (Matteucci.) 

The  nerve  and  muscle  of  a  frog,  connected 
by  a  water  contact  with  a  sufficiently  delicate 
galvanometer,  show  the  presence  of  a  current 
that  may  last  several  hours.  Du  Bois-Reymond 
showed  that  the  ends  of  a  section  of  muscular 
fibres  art  negative,  and  their  sides  positive,  and 
has  obtained  a  current  by  suitably  connecting 
them. 

In  the  opinion  of  some  electro-therapeutists  no 
electric  current  exists  in  passive,  normal  nerve  or 
muscular  tissue.  In  an  injured  tissue  a  current, 
called  a  demarcation  current,  is  produced.  (See 
Current,  Demarcation.) 

All  muscular  contractions,  however,  apparently 
produce  electric  currents. 

In  electro-therapeutics,  it  is  probable  that 
greater  success  would  accrue  in  practice  if  the 
human  body  were  regarded  as  an  electric  source 
as  well  as  an  electro-receptive  device. 

Electricity,  Atmospheric The  free 

electricity  almost  always  present  in  the  atmos- 
phere. 

The  following  facts  have  been  discovered  con- 
cerning atmospheric  electricity,  viz. : 

(i.)  The  free  electricity  of  the  atmosphere  is 
generally  positive,  but  often  changes  to  negative 
on  the  approach  of  fogs  and  clouds. 

(2.)  It  exists  in  greater  quantity  in  the  higher 
regions  of  the  air  than  near  the  earth's  surface. 

(3.)  It  is  stronger  when  the  air  is  still  than 
when  the  wind  is  blowing. 

(4.)  It  is  subject  to  yearly  and  daily  changes 
in  its  intensity,  being  stronger  in  winter  than  in 
summer,  and  at  the  middle  of  the  day  than  eithex 
at  the  beginning  or  the  close. 


iws 


[£l<s 


Electricity,  Atmospheric,  Origin  of 

—The  exact  cause  of  the  free  electricity  of 
the  atmosphere  is  unknown. 

Peltier  ascribes  the  cause  of  the  free  electricity 
,>f  the  atmosphere  to  a  negatively  excited  earth, 
which  charges  the  atmosphere  by  induction.  (See 
Induction,  Electrostatic.)  Free  atmospheric  elec- 
tricity has  also  been  ascribed  to  the  evaporation 
of  water;  to  the  condensation  of  vapor;  to  the 
friction  of  the  wind;  to  the  'motion  ot  terrestrial 
objects  through  the  earth's  magneiic  field;  to  in- 
duction  from  the  sun  and  other  heavenly  bodies; 
to  differences  of  temperature;  to  combustion,  and 
to  gradual  oxidation  of  plant  and  animal  life.  It 
is  possible  that  all  these  causes  may  have  some 
effect  in  producing  the  free  electricity  of  the  at- 
mosphere. 

Whatever  is  the  cause  of  the  free  electricity  of  the 
atmosphere,  there  can  be  but  little  doubt  that  it 
is  to  the  condensation  of  aqueous  vapor  that  the. 
high  di/erence  of  potential  of  the  lightning  flash 
is  due.  (See  Potential,  Difference  of. )  As  the 
clouds  move  through  the  air  they  collect  the  free 
electricity  on  the  surfaces  of  the  minute  drops  of 
water  of  which  they  are  composed,  and  when 
many  thousands  of  these  subsequently  collect  in 
larger  drops  the  difference  of  potential  is  enor- 
mously increased  in  consequence  of  the  equally 
enormous  decrease  in  the  surface  of  any  single 
drop  over  the  sum  of  the  surfaces  of  the  drops 
that  have  coalesced  to  form  it. 

Electricity,   Atom  of A    quantity 

of  electricity  equal  in  amount   to   that  pos- 
sessed by  any  chemical  monad  atom. 

Professor  Lodge  points  out  the  fact  that  the 
charge  of  a  monad  atom  of  any  element  is  the 
smallest  charge  a  body  can  possess,  and  i>  possibly 
as  indivisible  as  the  atom  itself.  He  points  out  ihe 
fact  that  chemical  affinity  or  atomic  attraction  may 
bedue  to  the  electrical  attraction  of  atoms  contain- 
ing unlike  charges;  that  although  the  difference  of 
potential  between  the  atoms  is  small,  probably 
somewhere  between  I  and  3  volts,  the  distances 
separating  them  are  so  very  small  that  their 
mutual  attractive  force  must  be  almost  infinitely 
great. 

As  D'Auria  has  pointed  out,  if  the  centres  of  at- 
traction of  the  atoms  be  the  centres  of  the 
atoms  themselves,  then  the  atoms,  if  approached 
to  actual  contact,  would  be  separated  fom  one 
another  by  a  distance  equal  to  half  the  sum  of 
their  diameters.  If,  however,  the  centre  of  at- 


traction  be  situated  at  any  point  on  the  surface  of 
the  atoms  the  distance  of  separation  would  be- 
come equal  to  zero,  calling  d,  the  distance  be- 
tween them,  m  and  m1,  their  respective  masses, 
and  S,  a  co-effecient  varying  with  the  substance, 
and  f,  the  force  of  mutual  attraction,  then  : 


(m  m' 
~6T 


from  which  we  see  that  the  value  of  f  i  becomes 
infinite  when  the  atoms  are  in  contact. 

Electricity,  Cal  -  —Electricity  pro- 
duced by  changes  of  temperature  in  the  core 
of  a  transformer. 

The  changes  of  temperature  in  the  transformer 
core  can  produce  a  difference  of  potential  in  the 
secondary  circuit  which  increases  the  electro- 
motive force  induced  in  the  secondary  by  the 
variations  in  the  primary.  This  is  sometimes 
called  the  Acheson  effect.  (See  Effect,  Achesan.} 

Electricity,  Conservation  of A 

term  proposed  by  Lippman  to  express  the 
fact  that  when  a  body  receives  an  electric 
charge  in  the  open  air,  the  earth  and  heavenly 
bodies  receive  an  equal  and  opposite  charge, 
thus  preserving  the  sum  of  the  total  positive 
and  negative  electricities  in  the  universe. 

Electricity,  Contact  -  —Electricity 
produced  by  the  mere  contact  of  dissimilar 
metals. 

The  mere  contact  of  two  dissimilar  metals  re- 
sults in  the  production  of  opposite  electrical 
charges  on  their  opposed  surfaces,  or  in  a  differ- 
ence of  electric  potential  between  these  surfaces. 
The  cause  of  this  difference  of  potential  is  now 
very  generally  ascribed  to  the  voltaic  couple  being 
surrounded  by  the  atmosphere,  the  oxygen  of 
which  acts  more  energetically  on  the  positive 
element  than  it  does  on  the  negative  element. 

The  mere  contact  of  dissimilar  metals  cannot 
produce  a  constant  electric  current.  An  electric 
current  possesses  kinetic  energy.  To  produce  a 
constant  electri<"  current,  therefore,  energy  must 
be  expended. 

The  voltaic  pile  through  the  contact  of  dis- 
similar metals  produces  a  difference  of  potential, 
yet  the  cause  of  the  current  is  to  be  found  in 
chemical  action.  (See  Cell,  Voltaic.} 

Electricity,  Disgnised  -  —Dissimu- 
lated electricity.  (See  Electricity,  Dissimu- 
lated or  Latent?) 


193 


Electricity,  Dissimulated  or  Latent  -- 

—  The  condition  of  an  electric  charge  when 
placed  near  an  opposite  charge,  as  in  a  Leyden 
jar  or  condenser. 

In  this  case,  merely  touching  one  of  the 
charged  surfaces  will  not  effect  its  complete  dis> 
charge. 

Electricity  in  the  condition  of  a  bound  charge 
was  formerly  called  latent  electricity.  This  term 
is  now  in  disuse.  Such  a  charge  io  r.ow  called  a 
bound  charge.  (See  Charge,  Bound.  Chargt, 
Free.) 

Electricity,  Distribution  of  —  -  —Va- 
rious combinations  of  electric  sources,  circuits 
and  electro-receptive  devices  whereby  elec- 
tricity generated  by  the  sources  iS  carried  or 
distributed  to  more  or  less  distant  electro- 
receptive  devices  by  means  of  the  various  cir- 
cuits connected  therewith. 

A  number  of  different  systems  for  the  distribu- 
tion of  electricity  exist.  Among  the  most  import- 
ant are  the  following,  viz.  : 

(i.)  Direct  or  continuous-current  distribution. 

(2.)  Alternating-current  distribution. 

(3.)  Storage  battery  or  secondary  distribution. 

(4.  )  Distribution  by  means  of  condensers. 

(5.)  Distribution  by  means  of  motor-gener- 
ators. 

Electricity,  Distribution  of,  by  Alterna- 
ting Currents  --  A  system  of  electric 
distribution  by  the  use  of  alternating  currents. 

A  system  of  electric  distribution  in  which 
lamps,  motors,  or  other  electro-receptive  de- 
vices are  operated  by  means  of  alternating 
currents  that  are  sent  over  the  line,  but  which, 
before  passing  through  said  devices,  are  modi- 
fied by  apparatus  called  transformers  or  con- 
verters. 

Such  a  system  embraces  : 

(I.)  An  alternating-current  dynamo-electric 
machine  or  battery  of  machines.  v 

(2.)  A  conductor  or  line  wire  arranged  in  a 
metallic  circuit. 

(3.)  A  number  of  converters  or  transformers 
whose  primary  coils  are  placed  in  the  circuit  of 
the  line  wire. 

(4.  )  A  number  of  electro-receptive  devices 
placed  in  the  circuit  of  the  secondary  coil  of  the 
converter.  (See  Transformer.) 


Electricity,  Distribution  of,  by  Alterna- 
ting- Currents  by  Means  of  Condensers 

— A  system  of  alternate  current  distribution 
in  which  condensers  are  employed  to  trans- 
form current  of  high  potential  received  from 
an  alternating  current  dynamo  to  currents 
of  low  potential  which  are  fed  to  <he  lamps  or 
other  electro-receptive  devices. 

In  the  system  of  McElroy  the  conversion  from 
high  to  low  potential  is  obtained  by  making  the 
primary  plates  of  the  condensers  charged  by 
the  dynamo  smaller  than  the  secondary  plates, 
the  ratio  of  the  area  of  the  primary  plates  to  that 
of  the  secondary  plates  being  made  in  accordance 
with  the  ratio  of  conversion  desired. 

Electricity,  Distribution  of,  by  Commuta- 
ting-  Transformers A  system  of  elec- 
trical distribution  in  which  motor-generators 
are  used,  but  neither  the  armature  nor  the 
field  magnets  are  revolved,  a  special  commu- 
tator being  employed  to  change  the  polarity 
of  the  magnetic  circuits. 

Electricity,  Distribution  of,  by  Constant 

Currents A  system  for  the  distribution 

of  electricity  by  means  of  direct,  /.  e.,  con- 
tinuous, steady  or  non-alternating  currents, 
as  distinguished  from  alternating  currents. 

Distribution  by  means  of  direct  currents  may 
be  effected  in  ?,  number  of  ways  ;  the  most  im- 
portant are: 

(I.)  Distribution  with  constant  current  or 
series  -  distribution . 

(2.)  Distribution  with  constant  potential  or 
multip  le-  distribution. 

Strictly  speaking,  these,  as,  indeed,  all  systems, 
are  systems  for  the  distribution  of  electric  energy 
rather  than  the  distribution  of  electricity. 

In  a  system  of  series-distribution,  the  electro- 
receptive  devices  are  placed  in  the  main  line  in 
series,  so  that  the  electric  current  passes  succes- 
sively through  each  of  them.  In  such  a  system 
each  device  added  increases  the  total  resistance  of 
the  circuit  so  that  the  .total  resistance  is  equal  to 
the  sum  of  the  separate  resistances  on  the  line. 

In  order,  therefore,  to  maintain  the  current 
strength  constant,  independent  of  the  number  of 
devices  added  to  or  removed  from  the  circuit,  the 
electromotive  force  of  the  source  must  increase 
with  each  electro-receptive  device  added,  and  de- 
crease with  each  electro-receptive  device  taken 


Ele.] 


194 


[Ele. 


Out-  If  the  number  of  electro-receptive  devices 
be  great,  such  a  circuit  is  necessarily  character- 
ized by  a  comparatively  high  electromotive  force. 

Since  the  current  passes  successively  through 
all  the  electro-receptive  devices,  an  automatic 
safety  device  is  necessary  in  order  to  automatically 
provide  a  short  circuit  of  comparatively  low  resist- 
ance past  a  faulty  device,  and  thus  prevent  a 
single  faulty  device  from  invalidating  the  action 
of  all  other  devices  in  the  circuit 

Arc  lamps  are  usually  connected  to  the  line 
circuit  in  series. 

]na.sysi&motmultiple-distribution,  the  electro- 
deceptive  devices  are  connected  to  the  main  line 
or  leads  in  multiple-arc,  or  parallel,  so  that  each 
device  added  decreases  the  resistance  of  the  circuit. 
In  order,  therefore,  to  maintain  a  proper  current 
through  the  electro-receptive  devices,  the  mains 
must  be  kept  at  a  nearly  constant  difference  of 
potential.  The  electro-receptive  devices  employed 
in  such  a  system  of  distribution  are  generally  of 
high  electric  resistance,  so  that  the  introduction  or 
removal  of  a  few  of  the  electro-receptive  devices 
will  not  materially  alter  the  resistance  of  the  whole 
circuit,  and  will  not,  therefore,  materially  affect 
the  remaining  lights. 

In  this  system  automatic  safety  devices,  opera- 
ting by  the  fusion  of  a  readily  melted  alloy  or 
metal,  are  provided  for  the  purpose  of  preventing 
too  powerful  currents  from  passing  through  any 
branch  connected  with  the  main  conductors  or 
leads.  (See /%<£-,  Fusible.) 

Incandescent  lamps  are  generally  connected 
with  the  main  conductors  or  leads  in  parallel  or 
multiple-arc. 

Distribution  of  incandescent  lamps  by  series 
connections  is  sometimes  employed.  Such  lamps 
are  usually  of  comparatively  low  resistance,  and 
are  provided  each  with  an  automatic  cut-out, 
which  establishes  a  short  circuit  past  the  lamp  on 
its  failure  to  properly  operate. 

During  the  passage  of  an  electric  current 
through  any  series-distribution  circuit,  energy  is 
expended  in  different  portions  of  the  circuit,  in 
proportion  to  the  resistance  of  these  parts.  In 
any  system,  economy  of  distribution  necessitates 
that  the  energy  expended  in  the  electro-receptive 
devices  must  bear  as  large  a  proportion  as  prac- 
ticable to  the  energy  expended  in  the  source  and 
leads.  In  series-distribution,  this  can  readily  be 
accomplished  even  if  the  resistance  of  the  leads  is 
comparatively  high,  since  the  total  resistance  of 
the  circuit  increases  with  every  electro-receptive 


device  added.  Comparatively  thin  wires  can 
therefore  be  employed  for  a  very  considerable 
extent  of  territory  covered,  without  very  great 
loss. 

In  systems  of  multiple-distribution,  however, 
this  is  impossible  ;  for,  since  every  electro-recep , 
tive  device  added  decreases  the  total  resistance  of 
the  circuit,  unless  the  resistance  of  the  leads  is 
correspondingly  decreased  the  economy  becomes 
smaller,  unless  the  resistance  of  the  leads  was  orig<= 
inally  so  low  as  to  be  inappreciable  when  com- 
pared with  the  change  of  resistance. 

In  systems  of  distribution  by  alternating  cur- 
rents this  is  avoided  by  passing  a  current  of  but 
small  strength  and  considerable  difference  of 
potential  over  a  line  connecting  distant  points, 
and  converting  this  current  in  to  a  current  of  large 
strength  and  small  difference  of  potential  at  the 
places  where  it  is  required  for  use. 

Electricity,  Distribution  of,  by  Contin- 
uous Current,  by  Means  of  Condensers 

A  system  of  distribution  devised  by 

Doubrava,  in  which  a  continuous  current  is 
conducted  to  certain  points  in  the  line  where 
a  device  called  a  "  disjunctor  "  is  employed,  to 
reverse  it  periodically,  and  the  reversed  cur- 
rents so  obtained  directly  used  to  charge  con- 
densers in  the  circuit  of  which  induction  coils 
are  used. 

This  method  of  distribution  is  a  variety  of  dis- 
tribution by  means  of  constant  currents. 

The  condensers  are  used  to  feed  incandescent 
lamps  or  other  electro-receptive  devices. 

Electricity,  Distribution  of,  by  Continu- 
ous Current,  by  Means  of  Transformers 

— A  system  for  the  transmission  of  elec- 
tric energy  by  means  of  continuous  or  direct 
currents  that  are  sent  over  the  line  to  suitably 
located  stations  where  motor-dynamos  are 
used  for  transformers. 

The  dynamo  armature  is  used  with  two  sepa 
rate  circuits,  one  of  a  short  and  coarse  wire,  and 
one  of  a  long  fine  wire.  This  construction  will 
permit  the  conversion  of  a  high  to  a  low  potential 
or  vice  versa;  or  two  separate  dynamos  can  be 
placed  on  the  same  shaft  and  one  used  as  the 
motor. 

It  is  evident  that  a  motor  generator  can  be  con- 
structed to  convert  continuous  currents  into  alter- 
nate, or  alternate  currents  into  continuous  cur 


Ele.] 


195 


[Ele. 


rents.    In  this  last  case  the  armature  and  fixed 
circuits  must  be  kept  separate. 

Another  form  of  continuous  current  conversion 
is  effected  by  means  of  the  motion  of  a  commutator 
which  effects  a  rotation  of  magnetic  polarity  in  a 
double- wound  armature  of  fine  and  coarse  wire. 

Electricity,  Distribution  of,  by  Motor 
Generators A  system  of  electric  dis- 
tribution in  which  a  continuous  current  of 
high  potential,  distributed  over  a  main  line,  is 
employed  at  the  points  where  its  electric  en- 
ergy is  to  be  utilized  for  driving  a  motor, 
which  in  turn  drives  a  dynamo,  the  current  of 
which  is  used  to  energize  the  electro-recep- 
tive devices. 

This  method  of  distribution  is  a  variety  of  dis- 
tribution by  means  of  continuous  or  direct  cur- 
rents. 

In  another  system  of  distribution  by  means  of 
motor  generators,  the  motor  and  dynamo  are 
combined  in  one  with  a  double-wound  armature, 
the  fine  wire  coils  in  which  receive  the  high  po- 
tential driving  current  and  the  coarse  wire  coils 
furnish  the  low  potential  current  used  in  the  dis- 
tribution circuits. 

Electricity,  Double  Fluid  Hypothesis  of 
A  hypothesis  which  endeavors  to  ex- 
plain the  causes  of  electric  phenomena  by  the 
assumption  of  the  existence  of  two  different 
electric  fluids. 

The  double  fluid  hypothesis  assumes: 

(i.)  That  the  phenomena  of  electricity  are  due 
to  two  tenuous  and  imponderable  fluids,  the  posi- 
tive and  the  negative. 

(2.)  That  the  particles  of  the  positive  fluid  repel 
one  another,  as  do  also  the  particles  of  the  nega- 
tive fluid ;  but  that  the  particles  of  positive  fluid 
attract  the  particles  of  the  negative  and  vice  versa. 

(3.)  That  the  two  fluids  are  strongly  attracted 
by  matter,  and  when  present  in  it  produce  elec- 
trification. 

(4.)  That  the  two  fluids  attract  one  another  and 
unite,  thus  masking  the  properties  of  each. 

(5.)  That  the  act  of  friction  separates  these 
fluids,  one  going  to  the  rubber  and  the  other  to 
the  thing  rubbed. 

Professor  Lodge  is  disposed  to  favor  the  double 
rather  than  the  single  fluid  hypothesis.  He  states 
in  support  of  this  belief  the  following  facts,  viz.: 

(I.)  An  electric  wind  or  breeze  is  produced 
both  at  the  positive  and  negative  terminals  of  an 


electrical  machine,  and  this  whether  the  point  be 
attached  directly  to  these  terminals,  or  whether 
it  be  held  in  the  hand  of  a  person  near  them. 

(2.)  The  well  known  peculiarities  connected 
with  the  spark  discharge,  seen  in  Wheatstone's 
experiments  on  the  velocity  of  electricity. 

(3.)  An  electrostatic  strain  scarcely  affects  the 
volume  of  the  dielectric,  thus  suggesting  or  show- 
ing a  distorting  stress,  which  alters  the  shape  of 
the  substance  of  the  dielectric,  but  not  its  size. 

(4.)  The  effects  of  electrolysis  in  what  he  as- 
sumes the  double  procession  of  the  atoms  past 
each  other  in  opposite  directions. 

(5.)  The  phenomena  of  self-induction,  or  the 
behavior  of  a  thick  wire  on  an  alternating  current. 

(6.)  The  apparent  absence  of  momentum  in  the 
electric  current,  or  moment  of  inertia  in  an  elec- 
tro-magnet so  far  as  tested. 

Electricity,  Dynamic A  term  some- 
times employed  for  current  electricity  in  con- 
tradistinction to  static  electricity. 

Electricity,  Franklinic  —A  term 

sometimes  employed  in  electro-therapeutics, 
for  the  electricity  produced  by  a  factional 
or  an  electrostatic-induction  machine.  (See 
Current,  Franklinic!) 

Electricity,  Frictional Electricity 

produced  by  friction. 

This  term  as  formerly  employed  to  indicate 
static  charges  as  distinguished  from  currents,  is 
gradually  falling  into  disuse,  and  the  frictional 
electric  machines  are  being  generally  replaced  by 
continuous-induction  machines,  like  those  of 
Holtz,  TOpler-Holtz,  or  Wimshurst. 

The  character  of  the  charge  produced  by  fric- 
tion depends  on  the  nature  of  the  rubber  as  well 
as  on  that  of  the  thing  rubbed. 

In  the  following  table  the  substances  are  so  ar- 
ranged that  any  one  in  the  list  becomes  positively 
electrified  when  rubbed  by  any  which  follows  it: 

Positive. 
Cat's  fur. 
Polished  glass. 
Wool. 

Cork  at  ordinary  temperatures. 
Coarse  brown  paper. 
Cork  heated. 
White  silk. 
Black  silk. 
Shellac. 
Rough  glass. — (Forbes.") 


Ele.] 


196 


[Ele. 


Negative. 

It  will  be  seen  that  the  character  of  the  charge 
produced  by  friction  depends  on  the  character  of 
the  surfaces  rubbed.  This  is  seen  from  the  fore- 
going table,  where— 

(i.)  The  roughness  of  the  surface,  as  in  the 
case  of  glass,  produces  a  difference  in  the  nature  of 
the  charge;  thus,  rough  glass  is  at  the  bottom  of 
the  table,  and  smooth,  polished  glass  near  the  top. 

(2.)  The  state  of  the  surface  as  shown  by  the 
color.  Black  silk  rubbed  with  white  silk  is  nega- 
tive to  it. 

(3.)  The  state  of  the  surface,  as  varied  by  the 
temperature.  Hot  cork  receives  a  negative  charge 
when  rubbed  against  a  piece  of  cold  cork. 

Forbes  has  pointed  out  that  these  differences 
are  probably  due  to  the  change  produced  in  the 
ability  of  the  surface  to  radiate  heat  or  light.  A 
substance  or  body  which  radiates  the  most  light 
or  heat  is  negative.  Thus,  a  hot  body  radiates 
more  heat  than  a  cold  body,  and  is  negative  to  it. 
A  rough  surface  is  negative  to  a  smooth  surface 
because  it  radiates  more  heat  than  a  smooth  sur- 
face. For  the  same  reason  a  black  surface  is  neg- 
ative to  a  white  surface.  In  this  latter  case,  how- 
ever, the  black  surface  is  the  worse  radiator  of 
light. 

The  contact  of  dissimilar  substances  has  long 
been  considered  by  some  as  one  of  the  requisites 
for  the  ready  production  of  electricity  by  friction. 
In  fact,  the  production  of  electricity  by  friction 
has  been  ascribed  as  an  effect  due  to  a  true  contact 
force  at  the  points  of  junction  of  the  rubber  and 
the  thing  rubbed.  Others,  however,  deny  the 
existence  of  a  true  contact  force  of  this  nature. 
(See  Force,  Contact.) 

Electricity,  Galvanic A  term  used 

by  some  in  place  of  voltaic  electricity.  (See 
Electricity,  Voltaic) 

The  use  of  the  term  galvanic  electricity  would 
appear  to  be  less  logical  than  the  word  voltaic, 
since  Volta,  and  not  Galvani,  was  the  first  to  find 
out  the  true  origin  of  the  difference  of  potential 
produced  in  the  voltaic  pile. 

Electricity,  Hertz's  Theory  of  Electro- 
Magnetic  Radiations  or  Waves A 

theory,  now  generally  accepted,  which  regards 
light  as  one  of  the  effects  of  electro-magnetic 
pulsations  or  waves. 

The  recent  brilliant  researches  of  Dr.  Hertz,  of 
Carlsruhe,  show  that  when  an  impulsive  discharge 


is  passing  through  a  conductor,  ether  waves  are 
radiated  or  propagated  in  all  directions  in  the 
space  surrounding  the  conductor,  and  that  these 
waves  are  in  all  respects  similar  to  those  of  light, 
except  that  they  are  much  longer. 

The  electro-magnetic  waves  are  set  up  in  the 
luminiferous  ether,  and  move  through  it  wuh  the 
same  velocity  as  that  of  light.  Moreover,  electro- 
magnetic waves  possess  the  same  powers  of  reflec- 
tion, refraction,  interference,  resonance,  etc.,  etc., 
as  are  possessed  by  waves  of  light.  (See  Resona- 
tor,  Electric.} 

When  an  alternating  or  simple  faradic  current 
or  pulse  of  electricity  is  transmitted  from  one  end 
to  the  other  of  a  long  metallic  conductor,  the 
pulses  are  believed  to  travel  through  the  universal 
ether  surrounding  the  conductor  rather  than 
through  the  conductor  itself.  The  velocity  of  this 
propagation  in  free  ether  is  the  same  as  that  of 
light,  and,  indeed,  is  identical  with  that  of  light 
itself.  In  the  inter-atomic  or  inter-molecular 
ether,  whether  of  conductors,  or  of  dielectrics,  the 
velocity  of  propagation  varies  with  the  nature  of 
the  medium. 

The  waves  produced  by  electric  pulses  are  of 
much  greater  length  than  those  of  light. 

According  to  Lodge  a  condenser  of  the  capacity 
of  a  micro-farad,  if  discharged  through  a  coil  hav- 
ing the  self-induction  of  I  ohm,  will  give  rise 
to  waves  in  the  ether  1,200  miles  in  length,  and 
will  possess  a  rate  of  oscillation  equal  to  about  157 
complete  wave-lengths  per  second. 

A  common  pint  Ley  den  jar  discharged  through 
an  ordinary  discharging  rod,  will  produce  a  se- 
ries of  waves  about  15  to  20  metres  in  length, 
and  will  possess  a  rate  of  oscillation  equal  to  about 
ten  million  per  second. 

Lodge  calculates  that  in  order  to  obtain  the  short 
waves  requisite  to  influence  the  retina  of  the  eye, 
and  thus  produce  light,  the  circuit  in  which  the 
electrical  oscillations  take  place  must  have  at  least 
atomic  dimensions,  and  that  the  phenomena  of 
light  may  therefore  be  due  to  local  oscillations  or 
surgings  in  circuits  of  atomic  dimensions.  (See 
Light,  MaxwclPs  Electro-Magnetic  Theory  of.) 

Electricity,  Latent A  term  for- 
merly applied  to  bound  electricity. 

Electricity,  Magneto  —  —Electricity 
produced  by  the  motion  of  magnets  past  con- 
ductors, or  of  conductors  past  magnets. 

Electricity  produced   by  magneto-electric 


197 


[Ele. 


induction,     (See  Induction,  Electro-Dyna- 

Electricity,  Multiple-Distribution  of,  by 
Constant  Potential  Circuit Any 

system  for  the  distribution  of  continuous  cur- 
rents of  electricity  in  which  the  electro- 
receptive  devices  are  connected  to  the  leads 
in  multiple-arc  or  parallel.  (See  Electricity, 
Distribution  of,  by  Constant  Currents?) 

Electricity,  Natural  TJnit  of A 

term  sometimes  used  in  place  of  an  atom  of 
electricity. 

The  natural  unit  of  electricity  is  an  amount 
equal  to  the  charge  possessed  by  any  monad  atom 
of  a  chemical  element. 

The  natural  unit  of  electricity  is  equal  to  the 
hundred  thousand  millionth  of  the  ordinary 
electrostatic  unit,  or  less  than  a  hundred  tril- 
lionth  of  a  coulomb.  (See  Electricity,  Atom  of.) 

Electricity,  Negative One  of  the 

phases  of  electrical  excitement. 

The  kind  of  electric  charge  produced  on 
sesin  when  rubbed  with  cotton. 

Electricity,  Photo Electrical  dif- 
ferences of  potential  produced  by  the  action 
of  light 

Electricity,  Plant Electricity  pro- 
duced in  plants  during  their  growth. 

Electricity,  Positive One  of  the 

phases  or  electric  excitement. 

The  kind  of  electric  charge  produced  on 
cotton  when  rubbed  against  resin. 

Electricity,  Production  of,  by  Light 

— The  production  of  electric  differences  of 
potential  by  the  action  of  light. 

Hallwachs  nas  noticed  that  a  clean  metallic 
plate  oecomes  electrified  when  light  falls  upon  it. 

Differences  of  potential  are  produced  in  a 
selenium  cell  when  its  electrodes  are  unequally 
illumined.  A  thermo  cell  is  an  illustration  of  a 
difference  of  potential  produced  by  non-luminous 
radiation. 

Electricity,  Pyro Electricity  de- 
veloped in  certain  crystalline  bodies  by  un- 
equally heating  or  cooling  them. 

Tourmaline,  in  the  crystalline  state,  possesses 
Biis  property  in  a  marked  degree.  When  a 
crystal  of  tourmaline  is  heated  or  cooled,  it 


acquires  opposite  electrifications  at  opposite 
ends  or  poles. 

In  the  crystal  of  tourmaline  shown  in  Fig.  227, 
the  end  A,  called  the  analogous  pole,  acquires  a 
positive  electrification, 
and  the  end  B,  called  the 
antilogous  pole,  a  nega- 
tive electrification,  while 
the  temperature  of  the 
crystal  is  rising.  While 
cooling,  the  opposite 
electrifications  are  pro- 
duced. 

A  heated  crystal  of 
tourmaline,  suspended  by 
a  fibre,  is  attracted  or 
repelled  by  an  electrified 
body  or  by  a  second 
heated  tourmaline,  in  the  F'f-  *27-  Pyro  Electric 
same  manner  as  an  elec-  Crystal. 

trifled  body. 

Many  crystalline  bodies  possess  similar  prop- 
erties. Amnng  these  are  the  ore  of  zinc  known 
as  electric  calamine  or  the  silicate  of  zinc,  b  ra- 
cite,  quartz,  tartrate  of  potash,  sulphate  of 
quinine,  etc. 

Electricity,    Radiation     of The 

radiation  of  electric  energy  by  means  of  elec- 
tro-magnetic waves.  (See  Electricity,  Hertz's 
Theory  of  Electro-Magnetic  Radiations  or 
Waves.) 

Electricity,  Resinous A  term 

formerly  employed  in  place  of  negative  elec- 
tricity. 

It  was  at  one  time  believed  that  all  reii.ious 
substances  are  negatively  electrified  by  frict  0:1. 
This  we  now  know  to  be  untrue,  the  nature  of 
electrification  depending  as  much  on  the  char- 
acter of  the  rubber  as  on  the  character  of  the 
thing  rubbed.  Thus  resins  rubbed  with  cotto:i, 
flannel  or  silk,  become  negatively  excited,  but  w'  rn 
rubbed  with  sulphur  or  gun  cotton,  positively 
excited.  The  teims  positive  and  negative  are 
now  exclusively  employed. 

Electricity,  Series  Distribution  of,  by 
Constant  Current  Circuit Any  sys- 
tem for  the  distribution  of  constant  currents 
of  electricity  in  which  the  electro-receptive 
devices  are  connected  to  the  line-wire  or 
circuit  in  series.  (See  Electricity,  Distribu- 
tion of,  by  Constant  Currents?) 


file.] 


198 


[Elc. 


Electricity,  Single-Fluid  Hypothesis  of 

A  hypothesis  which  endeavors  to  ex- 
plain the  cause  of  electrical  phenomena  by 
the  assumption  of  the  existence  of  a  single 
electric  fluid. 

The  single-fluid  hypothesis  assumes: 

(i.)  That  the  phenomena  of  electricity  are  due 
to  the  presence  of  a  single,  tenuous,  imponder- 
able fluid. 

(2.)  That  the  particles  of  this  fluid  mutually 
repel  one  another,  but  are  attracted  by  all  matter. 

(3.)  That  every  substance  possesses  a  definite 
capacity  for  holding  the  assumed  electric  fluid, 
and,  that  when  this  capacity  is  just  satisfied  no 
effects  of  electrification  are  manifest. 

(4.)  That  when  the  body  has  less  than  this 
quantity  present,  it  becomes  negatively  excited, 
and  when  it  has  more,  positively  excited. 

(5.)  That  the  act  of  friction  causes  a  redistribu- 
tion of  the  fluid,  part  of  it  going  to  one  of 
the  bodies,  giving  it  a  surplus,  thus  positively 
electrifying  it,  and  leaving  the  other  with  a 
deficit,  thus  negatively  electrifying  it. 

The  single-fluid  hypothesis  has  been  provis- 
ionally accepted  by  some  with  this  modification, 
that  a  negatively  excited  body  is  thought  to  be 
the  one  which  contains  the  excess  of  the  assumed 
fluid,  and  a  positively  excited  body  the  one  which 
contains  the  deficit. 

They  make  this  change  on  account  of  the 
phenomena  observed  in  Crookes'  tube,  where 
the  molecules  of  the  residual  gas  are  observed  to 
be  thrown  oft"  from  the  negative  and  not  from  the 
positive  terminal.  (See  Tube,  Crookes\) 

Another  view  considers  electricity  to  be  due  to 
differences  of  ether  pressure,  electricity  being  the 
ether  itself,  and  electromotive  force,  the  differences 
of  ether  pressures.  Positive  electrification  is  as- 
sumed to  result  from  a  surplusage  of  energy,  and 
negative  electrification  from  a  deficit  of  energy. 

At  the  present  time  the  views  of  Hertz  are 
generally  accepted.  (See  Electricity,  Hertz's 
Theory  of  Electro-Magnetic  Radiations  or  Waves.} 

Electricity,  Specific    Heat   of A 

term  proposed  by  Sir  William  Thomson  to 
indicate  the  analogies  existing  between  the 
absorption  and  emission  of  heat  in  purely 
thermal  phenomena,  and  the  absorption  and 
emission  of  heat  in  thermo-electric  phe- 
nomena. (See  Heat,  Specific) 
As  we  have  already  seen  heat  is  either  given 


out  or  absorbed,  when  an  electric  current  passes 
from  one  metal  to  another  across  a  junction  be- 
tween them.  (See  Effect,  Peltier.} 

So,  too,  when  electricity  passes  through  an  un- 
equally heated  wire,  the  current  tends  to  increase 
or  decrease  the  differences  of  temperature,  ac- 
cording to  the  direction  in  which  it  flows,  and 
according  to  the  character  of  the  metal.  (See 
Effect,  Thomson.') 

" If  electricity  were  a  fluid,"  says  Maxwell, 
"running  through  the  conductor  as  water  does 
through  a  tube,  and  always  giving  out  or  ab- 
sorbing  heat  till  its  temperature  is  that  of  the 
conductor,  then  in  passing  from  hot  to  cold  it 
would  give  out  heat,  and  in  passing  from  cold  to 
hot  it  would  absorb  heat,  and  the  amount  of  this 
heat  would  depend  on  the  specific  heat  of  the 
fluid." 

Electricity,  Static A  term  applied 

to  electricity  produced  by  friction. 

The  term  static  electricity  is  properly  em- 
ployed in  the  sense  of  a  static  charge  but  not  as 
static  electricity,  since  that  would  indicate  a  par- 
ticular kind  of  electricity,  and,  as  is  now  gen- 
erally recognized,  electricity,  from  no  matter 
what  source  it  is  derived,  is  one  and  the  same 
thing. 

Electricity,  Storage  of A  term 

improperly  employed  to  indicate  such  a 
storage  of  energy  as  will  enable  it  to  directly 
reproduce  electric  energy. 

A  so-called  storage  battery  does  not  store  elec- 
tricity, any  more  than  the  spring  of  a  clock  can 
be  said  to  store  time  or  sound.  The  spring  stores 
muscular  energy,  i.  e.,  renders  the  muscular 
kinetic  energy  potential,  which,  again  becoming 
kinetic,  causes  the  works  of  the  clock  to  move 
or  strike. 

In  the  same  way  in  a  so-called  storage  battery, 
the  energy  of  an  electric  current  is  caused  to 
produce  electrolytic  decompositions  of  such  a 
nature  as  independently  to  produce  a  current  on 
the  removal  of  the  electrolyzing  current.  (See 
Cell,  Secondary.  Cell,  Storage.) 

Electricity,  Thermo Electricity 

produced  by  differences  of  temperature  at  the 
junctions  of  dissimilar  metals. 

If  a  bar  of  antimony  is  soldered  to  a  bar  of  bis- 
muth, and  the  free  ends  of  the  two  metals  art- 
connected  by  means  of  a  galvanometer,  an  appli- 
cation of  heat  to  the  junction,  so  as  to  raise  its 


Ele.j 


199 


temperature  above  the  rest  of  the  circuit,  will  pro- 
duce a  difference  of  potential,  which,  if  neutral- 
ized, will  cause  a  current  to  flow  across  the  junc- 
tion from  the  bismuth  to  the  antimony  (against 
the  alphabet,  or  from  B  to  A).  If  the  junction  be 
cooled  below  the  rest  of  the  circuit,  a  current  is 
produced  across  the  junction  from  the  antimony 
to  the  bismuth  (with  the  alphabet,  or  from  A  to  B). 
These  currents  are  called  thermo-electric  currents, 
and  are  proportional  to  the  differences  of  tem- 
perature. 

Even  the  same  metal,  in  different  physical 
states  or  conditions,  such  as  a  wire,  part  of  which 
is  straight  and  the  remainder  bent  into  a  spiral  as 
at  H  C,  Fig.  228,  if  heated  at  F  by  the  flame  of 


Fig.   228.     Thermo- Electricity. 
a  lamp  will  have  a  difference  of  potential  devel- 
oped in  it. 

The  same  thing  may  also  be  shown  by  placing 
a  Cylinder  of  bismuth  J,  Fig.  229,  in  a  gap  in  a 

A 


Fig.  229.     Thermo-Electric  Circuit. 

hollow  rectangle  of  copper  A  B,  inside  of  which 
a  magnetic  needle,  M,  is  supported. 

The  rectangle  of  copper  being  placed  in  the 
magnetic  meridian,  on  heating  the  junction  by  the 
flame  of  a  lamp  F,  the  needle  will  be  deflected 
by  a  current  produced  by  the  difference  of  tem- 
perature. 

Thermo-electricity  is  generally  obtained  by 
means  of  the  combination  of  a  thermo-electric 
couple,  in  a  thermo-electric  cell.  (See  Couple, 
Thermo -Electric.  Cell,  Thermo- Electric.) 

Since  the  difference  of  potential  produced  by 
a  single  thermo-electric  couple  is  small,  a  number 
of  such  couples  or  cells  are  generally  connected  in 


[Ele, 

(See 


series  to  produce  a  thermo-electric  battery. 
Battery ',  Thermo-Eleclric.) 
Electricity,    Unit   Quantity    of 

The  quantity  of  electricity  conveyed  by  unit 
current  per  second. 

The  practical  unit  quantity  of  electricity  is  the 
coulomb,  which  is  the  quantity  conveyed  by  a 
current  of  one  ampere  in  one  second. 

Electricity,  Unit  Quantity  of,  Natural 
The  quantity  of  electricity  pos- 
sessed as  a  charge  by  any  elementary  monad 
atom.  (See  Electricity,  Atom  of.) 

Electricity,  Tarieties  of A  classi- 
fication of  electricity  according  to  its  state  of 
rest  or  motion,  or  to  the  peculiarities  of  its 
motion. 

Lodge  classifies  the  different  varieties  of  elec- 
tricity as  follows,  viz. : 

(I.)  Electricity  at  Rest,  or  Static  Electricity. 

This  branch  of  electric  science  treats  of  phenom- 
ena belonging  to  stresses  and  strains  in  inflated 
media,  when  brought  into  the  neighborhood  of 
electric  charges,  together  with  the  modes  ot  ex- 
citing such  electric  charges,  and  the  laws  of  their 
interactions. 

(2.)  Electricity  in  Locomotion,  or  Current  Elec- 
tricity. 

This  branch  of  electric  science  treats  of  the  phe- 
nomena produced  in  metallic  conductors,  chem- 
ical compounds  and  dielectric  media,  by  the  pas- 
sage of  electricity  through  them,  and  the  modes 
of  exciting  electricity  into  motion,  together  with 
the  laws  of  its  flow. 

(3.)  Electricity  in  Rotation,  or  Magnetism. 

This  branch  of  electric  science  treats  of  the  phe- 
nomena produced  in  electricity  in  whirling  or 
vortex  motion,  the  manner  in  which  such  whirls 
may  be  produced,  the  strains  and  stresses  which 
they  produce,  and  the  laws  of  their  interactions. 

(4.)  Electricity  in  Vibration,  or  Radiation. 

This  branch  of  electric  science  treats  of  the  study 
of  the  propagation  of  periodic  or  undulatory  dis- 
turbances through  various  kinds  of  media,  the 
laws  regulating  wave  velocity,  wave  length,  re- 
flection, interference,  dispersion,  polarization  and 
other  similar  phenomena  generally  studied  under 
light. 

A  misleading  classification  of  electricity  is 
sometimes  made  according  to  the  sources  which 
produce  it.  This  is  misleading,  since  electricity, 
no  matter  how  produced,  is  one  and  the  same. 


Ele.] 


200 


[Ele. 


The  so-called  varieties  of  electricity  may  be  di- 
vided into  different  classes  according  to  the  nature 
of  the  source.  The  principles  of  these  are  as  fol- 
lows : 

(I.)  Frictional-Electricity,  or  that  produced  by 
the  fricti  >n  of  one  substance  against  another. 

(2.)  Voltaic-Electricity,  or  that  produced  by 
the  contact  of  dissimilar  substances  under  the  in- 
fluent of  chemical  action. 

(3.)  Thermo-Electricity,  or  that  produced  by 
differences  of  temperature  in  a  thermo  couple. 

(4.)  Pyro-Electricity,  or  that  produced  by  dif- 
ferences of  temperature  in  certain  crystalline 
solids. 

(5.)  Magneto-Electricity,  or  that  produced  by 
the  motion  of  a  conductor  through  the  field  of 
permanent  magnets.  This  is  a  variety  of  — 

(6.)  Dynamo-Electricity,  or  that  produced  by 
moving  conductors  so  as  to  cut  lines  of  magnetic 
force. 

(7.)  Vital-Electricity,  or  that  produced  under 
the  influence  of  life  or  accompanying  life. 

Electricity,  Yitreons A  term  for- 
merly employed  to  indicate  positive  elec- 
tricity. 

It  was  formerly  believed  that  the  friction  of 
glass  with  other  bodies  always  produces  the 
same  kind  of  electricity.  This,  however,  is  now 
known  not  to  be  the  case. 

The  term  is  now  replaced  by  positive  elec- 
tricity. (See  Electricity,  Resinous.) 

Electricity,  Voltaic Differences  of 

potential  produced  by  the  agency  of  a  vol- 
taic cell  or  battery. 

Electricity  is  the  same  thing  or  phase  of  energy 
by  whatever  source  it  is  produced. 

Electrics. — Substances  capable  of  becom- 
ing' electrified  by  friction. 

Substances  like  the  metals,  which,  when  held 
in  thj  hand  cou'd  not  be  electrified  by  friction 
were  f  irmcrly  ca'l^d  non-electrics. 

These  terms  were  used  by  Gilbert  in  the  early 
history  of  the  science. 

This  distinction  is  not  now  generally  employed 
since  conducting  substances  if  insulated,  maybe 
electrified  by  friction. 

Electriftable.— Capable  of  being  endowed 
with  electric  properties. 

Electrification.— The  act  of  becoming 
electrified. 

The  production  of  an  electric  charge. 


Electrified  Body.— (See  Body,  Electri- 
fied) 

Electrify. — To  endow  with  electrical  prop- 
erties. 

Electrine. — Relating  to  electrum,  or  am- 
ber. 

Electrization,  Therapeutical —Sub- 
jecting different  parts  of  the  human  body  to 
the  action  of  electric  currents  for  the  cure  of 
diseased  conditions. 

Electro-Biology.— (See  Biology,  Electro) 

Electro-Brassing.— (See  Brassing,  Elec- 
tro) 

Electro-Bronzing.— (See  Bronzing,  Elec- 
tro.) 

Electro  •  Capillary  Phenomena.— (See 
Phenomena,  Electro-Capillary) 

Electrocesis. — A  word  proposed  for  cur- 
ing by  electricity. 

Electro-Chemical  Equivalent,  —  (See 
Equivalent,  Electro-Chemical) 

Electro-Chemical  Meter.— (See  Meter, 
Electro-  Chemical) 

Electro-Chemical  Telephone.— (See  Tele- 
phone, Electro-Chemical) 

Electro-Chemistry.  —  (See  Chemistry, 
Electro) 

Electro-Chromic  Rings.— (See  Rings, 
Electro-Chromic) 

Electro-Contact  Mine.— (See  Mine,  Elec- 
tro-Contact) 

Electro-Coppering.  —  (See  Coppering, 
Electro) 

Electro-Crystallizal  ion.— (See  Crystalli- 
zation, Electro) 

Electrocution. — Capital  punishment  by 
means  of  electricity. 

Electrode. — Either  of  the  terminals  of  an 
electric  source. 

The  term  was  applied  by  Faraday  to  cither  of 
the  conductors  placed  in  an  electrolytic  bath  and 
conveying  the  current  into  it,  and  this  is  its  strict 
meaning.  The  terms  pole  or  terminal  apply  to 
the  ends  of  a  break  in  any  electric  circuit. 

Electrode,  Aural  —  — A  therapeutic 
electrode,  shaped  for  the  treatment  of  the 


Ele.] 


201 


[Ele. 


ear.  (See  Electrode,  Electro-Thera- 
peutic^) 

Electrode,    Brush A    therapeutic 

electrode  fashioned  like  a  wire  brush  or  other 
conducting  brush.  (See  Electrode,  Electro- 
Therapeutic^] 

Electrode,  Cautery-Knife  —  —A  knife- 
shaped  electrode,  that  is  rendered  incan- 
descent by  the  passage  of  the  electric  cur- 
rent. 

Electrode,  Clay A  therapeutic  elec- 
trode of  clay  shaped  to  fit  the  part  of  the 
body  to  be  treated.  (See  Electrode,  Electro- 
Therapeutic.} 

Electrode,  Disc A  disc-shaped  elec- 
trode employed  in  electro-therapeutics.  (See 
Electrode,  Electro-  Therapeutic!) 

Electrode,  Dry A  therapeutic  elec- 
trode applied  in  a  dry  state.  (See  Electrode, 
Electro-  Therapeutic!) 

Electrode,  Electro-Therapeutic  — 

In  electro-therapeutics  the  electrode  mainly 
concerned  in  the  treatment  or  diagnosis  of  the 
diseased  parts. 

Either  the  positive  or  the  negative  electrode 
may  be  the  therapeutic  electrode,  and  one  or  the 
other  is  employed  according  to  the  particular 
character  of  the  effect  it  is  desired  to  obtain. 
The  other  electrode  is  placed  at  any  convenient 
and  suitable  part  of  the  body,  and  is  called  the 
indifferent  electrode. 

The  therapeutic  electrode  is  generally  placed 
nearer  the  organ  or  part  to  be  treated  than  the 
indifferent  electrode. 

Electrode-Handle,  Pole-Changing  and 
Interrupting  —  — A  handle  provided  for 
the  ready  insertion  of  electro-therapeutic 
electrodes,  and  provided  with  means  for  inter- 
rupting or  changing  the  direction  of  the  cur- 
rent. 

Electrode,  Illumined  -  —That  elec- 
trode of  a  selenium  cell  which  is  exposed  to 
the  light.  (See  Cell,  Selenium!) 

Electrode,  Indifferent In  electro- 
therapeutics the  electrode  that  is  employed 
merely  to  complete  the  circuit  through  the 
organ  or  part  subjected  to  the  electric  cur- 


rent, and  is  not  directly  concerned  in  the 
treatment  or  diagnosis  of  the  diseased  parts. 
Either  the  positive  or  the  negative  electrode 
may  be  the  indifferent  electrode.  (See  Electrode, 
Electro-  Therapeutic.} 

Electrode,  Moist  —A  therapeutic- 
electrode  applied  in  a  moist  condition.  (See 
Electrode,  Electro-  Therapeutic!) 

Electrode,  Needle A  therapeutic 

electrode  in  the  shape  of  a  needle,  and  em- 
ployed for  electrolytic  treatment.  (See  Elec- 
trode, Electro-  Therapeutic!) 

Electrode,  Negative  —  —The  electrode 
connected  with  the  negative  pole  of  an  elec- 
tric source. 

Electrode,  Non-Illumined  -  —That 
electrode  of  a  selenium  cell  that  is  protected 
from  the  direct  action  of  light.  (See  Cell,  Sel- 
enium!) 

Electrode,   Non-Wasting A  term 

sometimes  applied  to  the  negative  electrode 
of  an  arc-lamp  when  made  of  iridium  or  other 
similar  material. 

Electrode,  Positive  —  —The  electrode 
connected  with  the  positive  pole  of  an  electric 
source. 

Electrode,  Rectal  -  —A  therapeutic 
electrode,  suitably  shaped  for  the  treatment  of 
the  rectum.  (See Elec trade,  Electro-Thera- 
peutic^ 

Electrode,  Sponge  —  — A  moistened 
sponge  connected  to  one  of  the  terminals  of 
an  electric  source  and  acting  as  the  electro- 
therapeutic  electrode. 

Electrode,  Urethral An  electro- 
therapeutic  electrode  suitably  shaped  for  the 
treatment  of  the  urethra.  (See  Electrode, 
Electro-  Therapeutic!) 

Electrode,  Yaginal An  electro- 
therapeutic  electrode  suitably  shaped  for  the 
treatment  of  the  vagina.  (See  Electrode, 
Electro-  Therapeutic!) 

Electro-Deposi's.— (See  Deposits,  Elec- 
tro^ 

Electrodes. — T^e  terminals  of  an  electric 
source. 
The  positive  electrode  is  sometimes  called  the 


Eie.J 


202 


[Ele. 


Anode,  and  the  negative  electrode  the  /Cathode. 
No  matter  for  what  purposes  employed,  they  are 
generally  in  electro-therapeutics  termed  electrodes. 
In  precise  use  these  terms  should  be  restricted 
to  the  electrodes  when  used  for  electrolytic  de- 
composition. 

The  electrodes  are  made  of  different  shapes  and 
of  different  materials  according  to  the  character  of 
the  work  the  current  is  to  perform. 

Electrodes,  Carbon,  for  Arc-Lamps 

Rods  of  artificial  carbon  employed  in  arc 
lamps. 

These  are  more  properly  called  simply  arc- 
lamp  carbons. 

Arc-lamp  carbons  are  moulded  into  the  shape 
of  rods,  from  plastic  mixtures  of  carbonaceous 
materials  and  carbonizable  liquids.  On  the  sub- 
sequent carbonization  of  these  rods  the  ingredients 
are  caused  to  cohere  in  one  solid  mass  by  the  de- 
posit of  carbon  derived  from  the  carbonizable 
materials.  (See  Carbons^  Artificial.) 

Carbons  for  arc-lamps  are  generally  copper- 
coated,  so  as  to  somewhat  decrease  their  resist- 
ance, and  insure  a  more  uniform  consumption. 
Arc-lamp  carbons  are  sometimes  provided  with  a 
central  core  of  softer  carbon,  which  fixes  the  po- 
sition of  the  arc  and  thus  insures  a  steadier  light. 
(S&  Zarbons,  Cored.) 

Electrodes,  Cored Carbon  elec- 
trodes of  a  cylindrical  shape  provided  with  a 
central  cylinder  of  softer  carbon. 

The  use  of  cored  electrodes  for  arc  lamps  is 
for  the  purpose  of  steadying  the  light  by  maintain- 
ing the  arc  in  a  central  position.  This  is  effected 
by  the  greater  vaporization  of  the  softer  carbon 
of  the  core. 

Electrodes,  Cylindrical  Carbon 

Carbon  cylinders  used  for  electrodes  of  arc- 
lamps,  or  for  battery  plates. 

Electrodes,  Electro-Therapentic 

Electrodes  of  various  shapes  employed  in 
electro-therapeutics. 

The  electro- therapeutic  electrode,  as  distin- 
guished from  the  indifferent  electrode,  is  especially 
shaped  for  the  particular  purpose  for  which  it  is 
designed. 

When  the  electricity  is  intended  to  affect  the 
skin  or  superficial  portions  of  the  body  only,  it  is 
applied  dry,  and  is  then  generally  metallic.  To 
reach  the  deeper  structures,  such  as  the  muscle 
or  nerve  trunks,  moistened  sponge  electrodes  are 


employed.  Before  their  use  the  skin  should  be 
thoroughly  moistened.  Sponge-electrodes  are 
generally  made  conducting  by  a  solution  of  some 
saline  substance,  such  as  common  salt. 

Electrodes,  Erb's  Standard  Size  of 

— Standard  sizes  of  electrodes  generally 
adopted  in  electro-therapeutics. 

The  following  standard  sizes  have  been  pro- 
posed by  Erb,  viz. : 

(i.)  Fine  electrode ^    centimetre  diameter. 

(2.)  Small       •«       ....2 

(3.)  Medium  '«       7.5  "  " 

(4.)  Large      "       ....6x2         "  «' 

(SO  Very  large  do. . .  .8  x  16      « 

Electrodes,     Non-Polarizable — 

Electrodes  employed  in  electro-therapeutics, 
that  are  so  constructed  as  to  avoid  the  effects 
of  polarization. 

Non-polarizable  electrodes  are  obtained  by 
employing  two  amalgamated  zinc  wires,  dipped 
into  saturated  solution  of  zinc  chloride  placed  in 
glass  tubes,  and  closing  the  lower  ends  of  the 
tubes  by  a  piece  of  potter's  clay.  The  contact  of 
an  electrode  so  prepared  with  the  tissues  of  the 
body  does  not  produce  a  polarization. 

Electro-Diagnosis.— (See  Diagnosis,  Elec- 
tro?) 

Electro-Diagnostic.  —  (See  Diagnostic, 
Electro?) 

Electro-Dynamic  Attraction.— (See  At- 
traction, Electro- Dynamic?) 

Electro-Dynamic  Capacity.—  (See  Ca- 
pacity, Electro-Dynamic?) 

Electro-Dynamic  Induction. — (See  Induc- 
tion, Electro- Dynamic?) 

Electro-Dynamic  Repulsion. — (See  Re- 
pulsion, Electro-Dynamic?) 

Electro-Dynamics.  —  (See  Dynamics, 
Electro?) 

Electro-Dynamometer. — (See  Dynamom- 
eter, Electro?) 

Electro-Etching.— Electric  etching.  (See 
Etching,  Electro) 

Electrogenesis. — Results  following  the 
application  of  electricity  to  the  spinal  cord  or 
nerve  after  the  withdrawal  of  the  electrodes. 

Electro-Gilding.— (See  Gilding,  Electro?, 


Ele.] 


203 


[Ele. 


Electro-Kinetics.— (See  Kinetics,  Elec- 
tro) 

Electrolier. — A  chandelier  for  holding 
electric  lamps,  as  distinguished  from  a  chan- 
delier for  holding  gas-lights. 

Electrology. — That  branch  of  science 
which  treats  of  electricity.  (Obsolete.) 

Electrolysis. —  Chemical  decomposition 
effected  by  means  of  an  electric  current. 

When  an  electric  current  is  sent  through  an 
electrolyte,  i.  e. ,  a  liquid  which  permits  the  cur- 
rent  to  pass  only  by  means  of  the  decomposition 
of  the  liquid,  the  decomposition  that  ensues  is 
called  electrolytic  decomposition, 

The  electrolyte  is  decomposed  or  broken  up 
into  atoms  or  groups  of  atoms  or  radicals,  called 
ions. 

The  ions  are  of  two  distinct  kinds,  viz. :  The 
electro-positive  ions,  or  kathions,  and  the  electro- 
negative  ions,  or  onions. 

Since  the  anode  of  the  source  is  connected  with 
the  electro-positive  terminal,  it  is  clear  that  the 
onions,  or  the  electro-negative  ions,  must  appear 
at  the  anode,  and  the  kathions,  or  electro-positive 
ions,  must  appear  at  the  kathode. 

Hydrogen,  and  the  metals  generally,  are 
kathions.  Oxygen,  chlorine,  iodine,  etc.,  are 
unions. 

The  vessel  containing  the  electrolyte,  in  which 
these  decompositions  take  place,  is  sometimes 
called  an  electrolytic  cell. 

An  electrolytic  cell  is  called  a  voltameter  when 
it  is  arranged  for  measuring  the  current  passing 
by  means  of  the  amount  of  decomposition  it 
effects.  (See  Voltameter.} 

Electrolysis  by  Means  of  Alternating 
Currents. — Electrolytic  decomposition  ef- 
fected by  means  of  alternating  currents. 

When  an  alternating  current  is  passed  through 
dilute  sulphuric  acid,  in  a  voltameter  provided 
with  large  platinum  electrodes,  no  visible  decom- 
position occurs.  If,  however,  the  size  of  the 
electrodes  be  decreased  below  a  certain  point, 
then  visible  decomposition  occurs. 

Verdet  showed  that  when  no  other  break  ex- 
ists in  the  circuit  of  the  alternating  current 
within  the  voltameter,  no  indications  of  elec- 
trolysis are  obtained,  unless  the  alternating 
current  is  very  powerful.  If,  however,  a  break  is 
made  in  the  secondary  circuit,  so  that  the  dis- 


charge has  to  pass  as  a  spark,  then  visible  signs 
of  electrolysis  are  produced  by  comparatively 
feeble  alternating  currents. 

When  electrolysis  occurs  by  means  of  alternat- 
ing currents — 

(I.)  The  gases  collected  at  both  electrodes 
have  the  same  composition. 

(2.)  Where  the  quantities  of  electricity  that  al- 
ternately pass  in  opposite  directions  are  unequal, 
the  electrodes  show  manifest  polarization,  and, 
when  connected  by  a  conductor,  yield  a  current 
like  a  secondary  battery. 

(3.)  The  electrodes  manifest  no  sensible  polari- 
zation where  the  quantities  of  electricity  that  al- 
ternately pass  in  opposite  directions  are  equal. 

Electrolysis,  Faraday's  Laws  of 

The  principal  facts  of  electrolysis  are  given 
in  the  following  laws: 

(I.)  The  amount  of  chemical  action  in  any 
given  time  is  equal  in  all  parts  of  the  circuit. 

(2.)  The  number  of  ions  liberated  in  a  given 
time  is  proportional  to  the  strength  of  the  cur- 
rent passing.  Twice  as  great  a  current  will 
liberate  twice  as  many  ions.  The  current  may 
be  regarded  as  being  carried  through  the  elec- 
trolyte by  the  ions:  since  an  ion  is  capable  of 
carrying  a  fixed  charge  only  of  -(-or  —  electri- 
city, any  increase  in  the  current  strength  necessi- 
tates an  increase  in  the  number  of  ions. 

(3.)  When  the  same  current  passes  successively 
through  several  cells  containing  different  elec- 
trolytes, the  weights  of  the  ions  liberated  at  the 
different  electrodes  will  be  equal  to  the  strength 
of  the  current  multiplied  by  the  electro-chemical 
equivalent  of  the  ion.  (See  Equivalence,  Elec- 
tro-Chemical, Law  of.} 

The  chemical  equivalent  is  proportional  to  the 
atomic  weight  divided  by  the  valency.  (See 
Equivalent,  Chemical.} 

The  electro-chemical  equivalent  of  any  element 
is  equal  to  the  weight  in  grammes  of  that  element 
set  free  by  one  coulomb  of  electricity,  and  is  found 
by  multiplying  the  electro-chemical  of  hydrogen 
by  the  chemical  equivalent  of  that  element.  (See 
Equivalent,  Electro-Chemical.} 

Electrolyte,  Polarization  of The 

formation  of  molecular  groups  or  chains,  in 
which  the  poles  of  all  the  molecules  of  any 
chain  are  turned  in  the  same  direction,  viz.: 
with  their  positive  poles  facing  the  negative 
plate,  and  their  negative  poles  facing  the 


Ele.] 


204 


[Ele, 


positive  plate.  (See  Cell,  Voltaic.  Hypoth- 
esis, Grotthus' ) 

Electrolytic  or  Electrolytical. — Pertain- 
ing to  electrolysis. 

Electrolytic  Analysis. — (See  Analysts, 
Electrolytic) 

Electrolytic  Cell.— (See  Cell,  Electro- 
lytic, Tesla's) 

Electrolytic  Clock.— (See  Clock,  Electro- 
lytic.) 

Electrolytic  Conduction.— (See  Conduc- 
tion, Electrolytic) 

Electrolytic  Convection.— (See  Convec- 
tion, Electrolytic) 

Electrolytic  Decomposition.— (See  De- 
composition, Electrolytic) 

Electrolytic  Hydrogen. — (See  Hydrogen, 
Electrolytic) 

Electrolytic  Writing.— (See  Writing, 
Electrolytic) 

Electrolytically. — In  an  electrolytic  man- 
ner. 

Electrolyzable. — Capable  of  being  elec- 
trolyzed,  or  decomposed  by  means  of  elec- 
tricity. 

Electrolyzed. — Separated  or  decomposed 
by  means  of  electricity. 

Electrolyzing. — Causing  or  producing 
electrolysis. 

Electro-Magnet. — (See  Magnet,  Electro) 

Electro-Magnetic  Ammeter. — (See  Am- 
meter, Electro-Magnetic) 

Electro-Magnetic  Annunciator. — (See 
Annunciator,  Electro-Magnetic) 

Electro-Magnetic  Attraction.— (See  At- 
traction, Electro-Magnetic) 

Electro-Magnetic  Bell-Call.— (See  Call, 
Bell,  Magneto-Electric) 

Electro-Magnetic  Bell,  Siemens'  Arma- 

tnre (See  Bell,  Electro-Magnetic, 

Siemens'  Armature  Form) 

Electro-Magnetic  Brake.— (See  Brake, 
Electro-Magnetic) 

Electro-Magnetic  Cam.— (See  Cam, 
Electro-magnetic) 


Electro-Magnetic     Dental-Mallet— (See 

Dental-Mallet,  Electro-Magnetic) 

Electro-Magnetic  Drill.— (See  Drill, 
Electro-Magnetic) 

Electro-Magnetic  Engine.— (See  Engine, 
Electro-Magnetic) 

Electro-Magnetic  Exploder.— (See  Ex- 
ploder, Electro-Magnetic) 

Electro-Magnetic  Eye.— (See  Eye,  Elec- 
tro-Magnetic) 

Electro-Magnetic  Impulse. — (See  Im- 
pulse, Electro-Magnetic) 

Electro-Magnetic  Induction. — (See  In- 
duction, Electro-Magnetic) 

Electro-Magnetic  Medium.— (See  Me- 
dium, Electro-Magnetic) 

Electro-Magnetic  Meter. — (See  Meter, 
Electro-Magnetic) 

Electro-Magnetic  Momentum  of  Sec- 
ondary Circuit. — (See  Momentum,  Elec- 
tro-Magnetic, of  Secondary  Circuit) 

Electro-Magnetic  Pop-Gun. — (See  Pop- 
Gun,  Electro-Magnetic) 

Electro-Magnetic  Radiation. —(See  Ra- 
diation, Electro-Magnetic) 

Electro-Magnetic  Repulsion. — (See  Re- 
pulsion, Electro- Magnetic) 

Electro-Magnetic  Resonator. — (See  Res- 
onator, Electro- Magnetic) 

Electro-Magnetic  Shunt.— (See  Shunt, 
Electro-Magnetic) 

Electro-Magnetic  Solenoid.— (See  Sole- 
noid, Electro-Magnetic) 

Electro-Magnetic  Strain.— (See  Strain, 
Electro-Magnetic) 

Electro-Magnetic  Stress. — (See  Stress, 
Electro-Magnetic) 

Electro-Magnetic  Theory  of  Light,  Max- 
well's —  —(See  Light,  Maxwell's  Elec- 
tro-Magnetic Theory  of) 

Electro-Magnetic  Vibrator.— (See  Vi- 
brator, Electro-Magnetic) 

Electro-Magnetic  Voltmeter.— (Sec  TW/- 
meter,  Electro-Magnetic) 


Ele.] 


205 


[Ele. 


Electro-Magnetic  Units.— (See  Units, 
Electro-Magnetic?) 

Electro-Magnetics.  —  (See  Magnetics, 
Electro?) 

Electro-Massage. — (See  Massage,  Elec- 
tro^ 

Electro-Mechanical  Alarm.—  (See  Alarm, 
Electro-Mechanical?) 

Electro-Mechanical  Gong.— (See  Gong, 
Electro-Mechanical?) 

Electro-Metallurgical  Crystalline  De- 
posit— (See  Deposit,  Crystalline,  Electro- 
Metallurgical?) 

Electro-Metallurgical  Galvanization.— 

(See  Galvanization,  Electro- Metallurgical?) 

Electro-Metallurgical  Nodular  Deposit. 

— (See      Deposit,     Electro  -  Metallurgical 
Nodular?) 

Electro  -  Metallurgical  Reguline  De- 
posit.—  (See  Deposit,  Electro-Metallurgical 
Reguline?) 

Electro-Metallurgical  Sandy  Deposit— 

(See  Deposit,  Electro-Metallurgical  Sandy?) 

Electro-Metallurgy.— (See  Metallurgy, 
Electro?) 

Electrometer. — An  apparatus  for  measur- 
ing differences  of  potential. 

Electrometers  operate,  in  general,  by  means 
of  the  attraction  or  repulsion  of  charged  conduc- 
tors on  a  suitably  suspended  needle  or  disc.  As 
no  current  is  required  to  flow  through  the  appa- 
ratus electrometers  are  especially  adapted  to  many 
cases  where  voltmeters  could  not  be  so  readily 
used. 

Electrometer,  Absolute An  elec- 
trometer the  dimensions  of  which  are  such 
that  the  value  of  the  electromotive  force  can 
be  directly  determined  from  the  amount  of 
the  deflection  of  the  needle. 

A  form  of  attracted-disc  electrometer. 
(See  Electrometer,  Attracted- Disc.} 

Electrometer,    Attracted-Disc A 

form   of  electrometer  devised  by  Sir  William 


Thomson,  in  which  the  force  is  measured  by 
the  attraction  between  the  two  discs. 

Thomson's  Attracted-Disc  Electrometer  is 
shown  in  Fig.  230.  It  consists  of  a  plate  C,  sus- 
pended from  the  longer  end  of  a  lever  1,  within  the 
fixed  guard  plate,  or  guard  ring  B,  immediately 
above  a  second  plate  A,  supported  on  an  insulated 
stand,  and  capable  of  a  measurable  approach 


Fig.  230.    Attracted-Disc  Electrometer. 

towards  C,  or  a  movement  away  from  it.  The 
plate,  C,  is  placed  in  contact  with  B,  by  means  of 
a  thin  wire.  By  means  of  this  connection  the 
distribution  of  the  charge  over  the  plate,  C,  is 
uniform.  The  electrostatic  attraction  is  meas- 
ured by  the  attraction  of  the  fixed  disc,  A,  on  the 
movable  disc,  C,  connected  respectively  to  the  two 
bodies  whose  difference  of  potential  is  to  be 
measured.  One  of  these  may  be  the  earth.  The 
fulcrum  of  the  lever  1,  is  formed  of  an  aluminium 
wire,  the  torsion  of  which  is  used  to  measure  the 
force  of  the  attraction;  or,  it  may  be  measured 
directly  by  the  counterpoise  weight  Q. 

This  instrument  is  sometimes  called  an  absolute 
electrometer,  because,  knowing  the  dimensions  <  i 
the  apparatus,  the  value  of  the  difference  of  poten- 
tial can  be  directly  determined  from  the  amount 
of  the  motion  observed. 

Electrometer,  Capillary An  elec- 
trometer in  which  a  difference  of  potential  i.c 


Fig.  231.     Capillary  Electrometer 

measured  by    the  movement   of  a   drop  of 
sulphuric  acid  in  a  tube  filled  with  mercury. 


206 


[Ele. 


A  form  of  capillary  electrometer  is  shown  in 
Vig.  231,  in  which  a  horizontal  glass  tube  with 
a  drop  of  acid  at  B,  has  its  ends  connected  with 
two  vessels  M  and  N,  filled  with  mercury.  If 
a  current  be  passed  through  the  tube,  a  move- 
ment of  the  drop  towards  the  negative  pole 
will  be  observed.  Where  the  electromotive 
force  does  not  exceed  one  volt,  the  amount  of 
the  movement  is  proportional  to  the  electro- 
motive force. 

Electrometer,  Quadrant An  elec- 
trometer in  which  an  electrostatic  charge  is 
measured  by  the  attractive  and  repulsive 
force  of  four  plates  or  quadrants,  on  a  light 
needle  of  aluminium  suspended  within  them. 

The  sectors  or  quadrants  are  of  brass,  and  are 
so  shaped  as  to  form  a  hollow  cylindrical  box 
when  placed  together.  The  four  sectors,  or  quad- 
rants, are  insulated  from  one  another,  but  the 
opposite  ones  are  connected,  by  a  conducting  wire, 
as  shown  in  Fig. 
232.  A  light  needle 
of  aluminium,  u, 
maintained  at  some 
constant  potential, 
by  connection  with 
the  inner  coating 
of  a  Leyden  jar,  is 
suspended,  gener- 
ally by  two  par-  Fig.  232-  Quadrant  Elec- 
allel  silk  threads,  trometer. 

so  as  to  freely  swing  inside  the  hollow  box.  This 
needle,  when  at  rest,  is  in  the  position  shown  by 
the  dotted  lines,  with  its  axis  of  symmetry  exactly 
under  one  of  the  slots  or  spaces  between  two 
Apposite  sectors.  (See  Suspension^  Bi- Filar.) 

The  quadrant  electrometer,  shown  in  Fig.  233, 
~.ias  one  of  its  quadrants  removed  so  as  to  show 
the  suspended  aluminium  needle. 

A  similar  form  of  instrument  is  shown  in  Fig. 
234,  with  all  the  quadrants  in  place,  and  the 
whole  instrument  covered  by  a  glass  shade. 

To  use  the  quadrant  electrometer  the  pairs  of 
sectors  are  connected  with  the  two  bodies  whose 
difference  of  potential  is  to  be  measured,  and  the 
deflection  of  the  needle  observed,  generally 
through  a  telescope,  by  means  of  a  spot  of  light 
reflected  from  a  mirror  attached  to  the  upper  part 
of  the  needle. 

Sometimes  the  segments  are  made  in  the  shape 
of  a  cylinder,  and  the  needle  in  the  shape  of  a 
suspended  rectangle. 


Electrometer,  Registering An  elec- 
trometer, the  deviations  of  the  needle  oi 
which  are  automatically  registered. 


Fig.  233.    Quadrant  Electrometer,  Showing  Suspended 
Needle. 

The  registration  of  this  class  of  electrometer  is 
obtained  by  means  of  photography.    The  spot  oi 


Fig.  234.     Quadrant  Electrometer. 

light,  reflected  from  the  mirror  of  the  electrometer, 
falls  on  a  fillet  of  sensitized  paper,  moved  by 
clockwork. 


Eh'.  I 


207 


[Ele. 


Electromotive   Arrangement  or  Device. 

— (Sae  Arrangement  or  Device,  Electromo- 
tive^ 

Electromotive  Difference  of  Potential.— 
(See  Potential,  Difference  of  Electromotive?) 

Electromotive  Force.— (See  Force,  Elec- 
tromotive^) 

Electromotive  Force,  Average (See 

Force,  Electromotive,  Average  or  Mean.) 

Electromotive  Force,  Back  or  Counter 
(See  Force,  Electromotive.  Sack.) 

Electromotive  Force,  Direct (See 

Force,  Electromotive,  Direct.) 

Electromotive  Force,  Inductive 

(See  Force,  Electromotive,  Inductive.) 

Electromotive  Force,  Secondary-Im- 
pressed    — (See  Force,  Electromotive, 

Secondary-Impressed.) 

Electromotive  Force,  Simple-Periodic 
— (See  Force,  Electromotive,  Simple- 
Periodic.) 

Electromotive  Force,  Transverse 

(See  Force,  Electromotive,  Transverse.) 

Electromotive  Impulse. — (See  Impulse, 
Electromotive?) 

Electro-Motograph. — (See  Motograph, 
Electro?) 

Electro-Muscular. — (See  Muscular,  Elec- 
tro?) 

Electro-Muscular  Excitation.— (See  Ex- 
citation* Electro-Muscular?) 

Electronecrosic. — Pertaining  to  capital 
punishment  by  means  of  electricity. 

Electronecrosis.— A  word  proposed  for 
capital  punishment  by  means  of  electricity. 

Electro-Negative  Ions.— (See  Ions,  Elec- 
tro-Negative?] 

Electronegatives. — The  atoms  or  radicals 
that  appear  at  the  anode  or  positive  terminal 
during  electrolysis. 

The  anions.     (See  Electrolysis.    Anton?) 

Electro-Nervous  Excitability.— (See  Ex- 
citability, Electro-Nervous?) 

Electro-  Nickeling.  —  (See  Nickeling, 
Electro?) 

Electro-Optics.— (See  Optics,  Electro?) 


Electrophanic. — Pertaining  to  capital  pun- 
ishment by  means  of  electricity. 

Electrophanical. — Pertaining  to  capital 
punishment  by  means  of  electricity. 

Electrophanize.-To  inflict  capital  pun- 
ishment by  means  of  electricity. 

Electrophany. — Capital  punishment  by 
means  of  electricity. 

The  word  electrophany  would  appear  to  be  far 
preferable  to  the  word  electrocution,  since  it  is  in 
accordance  with  etymological  usage,  while  elec- 
trocution is  not 

Electrophila. — A  devotee  of  electricity. 

Electrophobia. — A  word  proposed  for  fear 
of  electricity. 

Electrophoric. — Pertaining  to  an  electro- 
phorus.  (See  Electrophorus.?) 

Electrophorus. — An    apparatus    for    the 
production  of  electricity 
by  electrostatic    induc- 
tion.     (See   Induction, 
Electrostatic?) 

A  disc  of  vulcanite,  or 
hard  rubber  B,  contained 
in  a  metallic  form,  is  rub- 
bed briskly  by  a  piece  of 
cat's  skin  and  the  insu- 
lated metallic  disc,  A,  is  Fig.  233-  Eltdrophorus, 
placed  on  the  centre  of  the  Charging. 

vulcanite  disc,  as  shown  in  Fig.  235. 

The  negative  charge  produced  in  B,  by  fric- 
tion, produces  by  induction  a  positive  charge  on 
the  part  of  A,  nearest  it, 
and  a  negative  charge 
on  the  part  furthest  from 
it. 

In  this  condition,  if 
the  disc  be  raised  from 
the  plate  by  means  of  its 
insulating  handle,  as 
shown  in  Fig.  236,  no 
electrical  effects  will  be 
noticed,  since  the  two  op- 
posite and  equal  charges 
unite  and  neutralize  each  fv> 
other.  If,  however,  the 
disc  A,  be  first  touched  by  the  finger,  and  then 
raised  from  the  disc  B,  it  will  be  found  to  be  pos- 
itively charged. 


Electrophorus, 
Discharging, 


Kle.] 


208 


[Ele. 


E 1  e  c  t  r  o-Physiology.— (See  Physiology, 
Electro) 

Electropic  Medium.— (See  Medium,  Elec- 
tropic) 

Electro-Plating.— (See  Plating,  Electro) 

Electro-Plating  Bath.— (See  Bath,  Elec- 
tro-Plating) 

Electro-Pneumatic  Signals.— (See  Sig- 
nals, Electro-Pneumatic) 

Electro-Pneumatic  Thermostat.  —  (See 
Thermostat,  Electro-Pneumatic.} 

Electropoion  Liquid.— (See  Liquid,  Elec- 
tropoion) 

Electro-Positive  Ions.— (See  Ions,  Elec- 
tro-Positive) 

Electropositives. — The  atoms  or  radicals 
that  appear  at  the  kathode  or  negative  termi- 
nal of  any  source  during  electrolysis. 

Thekathions.  (See  Electrolysis.   Kathion) 

E 1  e  c  t  r  o-Prognosis. — (See  Prognosis, 
Electric) 

Electro-Puncture.— (See  Puncture,  Elec- 
tro) 

Electro-Receptive  Devices.— (See  Device, 
Electro-Receptive) 

Electro-Eeceptive  Devices,  Multiple-Arc- 
Connected  (See  Devices,  Electro- 
Receptive,  Multiple-Arc-Connected) 

Electro-Receptive  Devices,  Multiple-Se- 
ries-Connected —  —(See  Devices,  Elec- 
tro-Receptive, Multiple-Series-Connected) 

Electro-Receptive  Devices,  Series-Con- 
nected   (See  Devices,  Electro-Recep- 
tive, Series-Connected) 

Electro-Receptive  Devices,  Series-Mnl- 
tiple-Connected  —  —(See  Devices,  Elec- 
tro-Receptive, Series-Multiple-Connected) 

Electroscope.  -  An  apparatus  for  showing 
the  presence  of  an  electric  charge,  or  for  de- 
termining its  sign,  whether  positive  or  nega- 
tive, but  not  for  measuring  its  amount  or 
value. 

In  the  gold-leaf  electroscope,  two  gold  leaves, 
n,  n,  Fig.  239,  suspended  near  each  other,  show 
by  their  repulsion  the  presence  of  an  electric 
charge.  Two  pith  balls  may  be  used  for  the  same 
purpose. 


The  pith  balls  B,  B,  shown  in  Fig.  237,  form 
a  simple  electroscope.  If  repelled  by  a  charge, 
when  approached  by  a  similar  charge  in  S,  they 
will  at  once  be  still  further  repelled,  as  shown  by 
the  dotted  lines. 

To  use  an  electroscope  for  determining  the  sign  of 


Fig-  237-  &**  Bal1  Electroscopt. 
an  unknown  charge,  the  gold  leaves  or  pith  balls  are 
first  slightly  repelled  by  a  charge  of  known  name, 
as,  for  example,  positive,  applied  to  the  knob  C, 
Fig.  239.  They  are  then  charged  by  the  electrified 
body  whose  charge  is  to  be  determined.  If  they 
are  further  repelled,  its  charge  is  positive.  If 
they  are  first  attracted  and  afterwards  repelled, 
its  charge  is  negative. 

Two  posts  B,  Fig.  239,  connected  with  the 
earth,  increase  the  amount  of  divergence  by  in- 
duction. 

Electroscope,  Condensing,  Yolta's  -  — 

An  electroscope  employed  for  the  detection 
of  feeble  charges,  the  leaves  of  which  are 
charged  by  means  of  a  condenser. 

The  condensing  electroscope,  Fig.  238,  is 
formed  of  two  metallic 
plates,  placed  at  the 
top  of  the  instrument, 
and  separated  by  a 
suitable  dielectric. 
The  upper  plate,  P,  is 
removable  by  means 
of  the  insulated  han- 
dle, G. 

To  employ  the  elec 
troscope,  as  for  exam- 
ple, to  detect  the  free  ( 
charge  in  an  unequal- 
ly  heated  crystal  of 
tourmaline,  the  crystal  is  touched  to  the  lower 
plate,  while  the  upper  plate  is  connected  to  the 
ground  by  the  finger.  On  the  subsequent  re- 
moval of  the  upper  plate  an  enormous  decrease 


Condensing  Elec. 


Ele.J 


209 


[Ele. 


ensues  in  the  capacity  of  the  condenser,  and  the 
charge  now  raises    the    potential  of  the  lower 
plate,   and  causes  a  marked  divergence  of  the 
t  leaves  L,  L.     (See  Electricity,  Pyro.) 

Electroscope,  Gold-Leaf An  elec- 
troscope in  which  two  leaves  of  gold  are  used 
to  detect  the  presence  of  an  electric  charge, 
or  to  determine  its  character  whether  positive 
or  negative. 

When  a  charge  is  imparted  to  the  knob  C,  Fig. 
239,  the  gold  leaves  n,  n,  diverge.  This  will  oc- 
cur whether  the  charge  be 
positive  or  negative. 

To  determine  the  char- 
acter     of     an      unknown 
charge,  the  leaves  are  first 
caused  to  diverge  by  means  B| 
of  a  known  positive  or  neg- 
ative   charge.       The    un- 
known charge  is  then  given    Fig.  239-     Gold-Leaf 
to  the  leaves.     If  they  di-  Electroscope. 

verge  still  further,  then  the  charge  is  of  the  same 
name  as  that  originally  possessed  by  the  leaves. 
If,  however,  they  first  move  to- 
gether and  are  afterwards  re- 
pelled, the  charge  is  of  the 
opposite  name. 

Electroscope,  Pith  -  Ball 

—   An      electroscope 

which  shows  the  presence  of 
a  charge  by  the  repulsion  of 
two  similarly  charged  pith 
balls.  (See  Electroscope) 

Any  two  pith  balls,  suspend- 
ed by  conducting  threads,  but 
insulated  from  the  earth,  will 
serve  as  an  electroscope. 

Electroscope,  Quadrant, 
Henley's An  electro- 
scope sometimes  employed 
to  indicate  large  charges  of 
electricity. 

A  pith  ball  placed  on  a  light 
arm  A,  of  straw  or  other  simi- 
lar material,  Fig.  240,  is  pivoted 
at  the  centre  of  a  graduated 
circle  B.     The  arm,  C,  is  at-  Fig.  24.0.   Henley's 
tached  by  means  of  the  screw       Electroscope. 
to  the  prime  conductor  of  an  electric  machine. 
The  similar  charge  imparted   to  A,  by  contact 


with  C,  causes  a  repulsion  which  may  be  i 
ured  on  the  graduated  arc. 

This  instrument  approaches  the  electrometer  in 
the  character  of  its  operation,  since  by  its  means, 
approximately  correct  measurements  may  be  made 
of  the  value  of  the  repulsion.  It  should  not,  how- 
ever, be  confounded  with  the  quadrant  electrom- 
eter. (Set  Electrometer,  Quadrant.) 

Electroscopically. — By  means  of  the  elec- 
troscope. (See  Electroscope) 

Electroscopy. — The  art  of  determining  the 
kind  of  charge  a  body  possesses,  by  means 
of  an  electroscope. 

Electro  -  Sensibility.— (See  Sensibility, 
Electro) 

Electro-Silvering:.— (See  Silvering,  Elec- 
tro) 

Electro-Smelting.— {See  Smelting,  Elec- 
tro) 

Electrostatic  Attraction.— (See  Attrac- 
tion, Electrostatic) 

Electrostatic  Capacity.— (See  Capacity, 
Electrostatic) 

Electrostatic  Circuit.— (See  Circuit, 
Electrosta  tic  ) 

Electrostatic  Field.— (See  Field,  Electro- 
static) 

Electrostatic  Induction. — (See  Induction, 
Electrostatic) 

Electrostatic  Induction  Machine. — (See 
Machine,  Electrostatic  Induction) 

Electrostatic  Leakage. — (See  Leakage, 
Electrostatic) 

Electrostatic  Lines  of  Force.— (See  Force, 
Electrostatic,  Lines  of) 

Electrostatic  Repulsion.— (See  Repulsion, 
Electrostatic) 

Electrostatic  Screening.— (See  Screening, 
Electrostatic) 

Electrostatic  Stress.— (See  Stress,  Elec- 
trostatic) 

Electrostatic  Units.— (See  Units,  Electro- 
static) 

Electrostatics.— That  branch  of  electric 
science  which  treats  of  the  phenomena  and 
measurement  of  electric  charges. 


Ele.] 


210 


[Ele. 


The  principles  of  electrostatics  are  embraced 
in  the  following  laws,  viz.  : 

(i.)  Charges  of  like  name,  *.  *?.,  either  positive 
or  negative,  repel  each  other.  Charges  of  unlike 
name  attract  each  other. 

(2.)  The  forces  of  attraction  or  repulsion  be- 
tween two  charged  bodies  are  directly  propor- 
tional to  the  product  of  the  quantities  of  elec- 
tricity possessed  by  the  bodies  and  inversely 
proportional  to  the  square  of  the  distance  be- 
tween them. 

These  laws  can  be  demonstrated  by  the  use  of 
Coulomb's  torsion  balance.  (See  Balance,  Tor- 
sion.} 

Calling  q,  and  q1,  the  quantities  of  electricity 
possessed  by  the  two  bodies,  and  r,  the  distance 
between  them,  then,  if  f,  is  the  force  exerted  by 
their  mutual  action, 


Electro-Technics.—  (See  Technics,  Elec- 
tro.) 

Electrothanasing.—  Producing  death  by 
electricity. 

Electrothanasis.—  A  word  proposed  for 
death  by  electricity. 

The  death  referred  to  here  is  death  other  than 
that  caused  by  capital  punishment. 

Electrothanasise.—  To  produce  death  by 
electricity. 

The  death  here  referred  to  is  other  than  that 
caused  by  capital  punishment. 

Electrothanatose.—  To  cause  death  by 
electricity. 

Electrothanatosic.—  Pertaining  to  capital 
punishment  by  means  of  electricity. 

Electro  thanatosing.  —  Causing  death  by 
electricity. 

Electrothanatosis.  —  A  word  proposed  for 
death  by  electricity. 

The  death  here  referred  to  is  death  other  than 
that  caused  by  capital  punishment 

Electro-Therapeutic  Bath.—  (See  Bath, 
Electro-  Therapeutic) 

Electro-Therapeutic  Breeze.  —  (See 
Breeze,  Electro-  Therapeutic) 


Electro-Therapeutic  Diffusion  of  Cur- 
rent.—(See  Current,  Diffusion  of,  Electro- 
Therapeutic^) 

Electro-Therapeutic         Dosage. — (S  e  e 

Dosage,  Electro-  Therapeutical) 

Electro-Therapeutic       Electrode.— (See 

Electrode,  Electro-  Therapeutic.) 

Electro-Therapeutic     Electrodes.— (See 

Electrode,  Electro-  Therapeutic) 

Electro-Therapeutic      Galvanization. — 

(See  Galvanization,  Electro-  Therapeutical) 

Electro-Therapeutic         Head-Breeze. — 

(See  Breeze,  Head,  Electro-  Therapeutic) 

Electro-Therapeutics. — (See  Therapeu- 
tics, Electro) 

Electro-Therapeutist. — (See  Therapeu- 
tist, Electro) 

Electro-Therapy.— (See  Therapy,  Elec' 
tro) 

Electro-Thermal  Meter.— (See  Meter, 
Electro-  Thermal) 

Electro-Tinning.— (See  Tinning,  Elec- 
tro) 

Electrotisic. — Pertaining  to  capital  pun- 
ishment by  means  of  electricity. 

Electrotising.— Producing  capital  punish- 
ment by  means  of  electricity. 

Electrotisis. — A  word  proposed  for  capi- 
tal punishment  by  means  of  electricity. 

Electrotonic  Current. — (See  Current. 
Electrotonic) 

Electrotonic  Effect— (See  Effect,  Electro- 
tonic) 

Electrotonic  Excitability.-(See  Excita- 
bility, Electrotonic) 

Electrotonic  State.— (See  State,  Electro- 
tonic) 

Electrotonus.— A  condition  of  altered 
functional  activity  which  occurs  in  a  nerve 
when  subjected  to  the  action  of  an  electric 


Ele.J 


211 


[Ele. 


The  electrotonic  state  is  produced  by  the 
passage  through  a  nerve  of  a  constant  current 
Called  the  polarizing  current. 

Electrotonus  is  attended  by  the  modification  of 
the  nerve  in  the  following  respects,  viz. : 

(i.)  In  its  electromotive  force. 

(2.)  In  its  excitability. 

The  passage  of  the  constant  current  produces 
a  change  in  the  electromotive  force  of  that  part  of 
the  nerve  traversed  by  the  current. 

This  alteration  in  muscular  excitability  may 
consist  in  either  an  increased  or  a  decreased  func- 
tional activity.  The  decreased  functional  activity 
occurs  in  the  neighborhood  of  the  anode,  or  the 
positive  terminal,  and  is  called  the  anelectrotonic 
state.  The  increased  functional  activity  occurs  in 
the  neighborhood  of  the  kathode,  or  the  negative 
terminal,  and  is  called  the  kathclectrotonic  state. 
(See  Anelectrotomis.  Katheleclrotonus.) 

This  altered  functional  activity  affects  not  only 
the  intra-polar  parts  of  the  nerve,  or  that  part 
between  the  electrodes,  but  also  the  extra-polar 
portions,  or,  in  other  words,  the  remainder  of  the 
nerve. 

The  electrotonic  state  is  characterized  by  two 
varieties,  viz.:  those  in  which  the  electromotive 
force  of  the  nerve  is  decreased,  and  those  in  which 
the  electromotive  force  of  the  nerve  is  increased. 
These  varieties  of  electrotonus  are  called  respec- 
tively the  negative  and  positive  phase  of  electro- 
tonus. (See  Electrotonus,  Negative  Phase  of, 
Electrotonus,  Positive  Phase  of.} 

Electrotonus,  Negative  Phase  of 

A  decrease  in  the  electromotive  force  of  a. 
nerve  effected  by  sending  a  current  through 
the  nerve  in  the  opposite  direction  to  the 
nerve  current.  (See  Current,  Nerved) 

Electrotonus,  Positive  Phase  of 

An  increase  in  the  electromotive  force  of  a 
nerve  effected  by  sending  a  current  through 
the  nerve  in  the  same  direction  as  the  nerve 
current. 

The  increase  in  the  electromotive  force  not  only 
affects  the  portions  of  the  nerve  in  the  intra-polar 
regions,  but  in  the  extra-polar  regions  as  well. 

Electrotype. — A  type,  cast,  or  impression 
of  an  object  obtained  by  means  of  electro- 
metallurgy. (See  Metallurgy,  Electro.  Elec- 
trotypmg) 

Electrotyping,  or  the  Electrotype  Pro- 


cess   Obtaining    casts    or    copies    of 

objects   by  depositing   metals  in  molds  by 
the  agency  of  electric  currents. 

The  molds  are  made  of  wax,  or  other  plastic 
substance,  rendered  conducting  by  coating  it  with 
powdered  plumbago. 

The  mold  is  connected  with  the  negative 
battery  terminal,  and  placed  in  a  metallic  solu- 
tion, generally  of  copper  sulphate,  opposite  a 
plate  of  metallic  copper,  connected  with  the  posi- 
tive battery  terminal.  As  the  current  passes,  the 
metal  is  deposited  on  the  mold  at  the  kathode, 
and  dissolved  from  the  metallic  plate  at  the 
anode,  thus  producing  an  exact  copy  or  cast  and 
at  the  same  time  maintaining  constant  the  strength 
of  the  bath. 

Electrozemia.— A  word  proposed  for  capi- 
tal punishment  by  means  of  electricity. 

Electrum. — A  name  given  by  the  ancients 
to  various  substances  that  could  be  readily 
electrified  by  friction. 

The  term  electrum  included  a  number  of  sub- 
stances, but  was  applied  mainly  either  to  amber 
or  to  an  alloy  of  gold  and  silver. 

Element. — Any  kind  of  matter  which  can- 
not be  decomposed  into  simpler  matter. 

Matter  that  is  formed  or  composed  of  but 
one  kind  of  atoms. 

Oxygen  and  hydrogen  are  elements  or  varie- 
ties of  elementary  matter.  They  cannot  be  de- 
composed into  anything  but  oxygen  or  hydrogen. 
Water,  on  the  contrary,  is  compound  matter, 
since  it  can  be  decomposed  into  its  constituent 
parts,  oxygen  and  hydrogen. 

There  are  about  seventy  well-known  elements, 
some  of  which  are  very  rare,  occurring  in  ex- 
tremely small  quantities. 

The  evidence  of  the  true  elementary  condition 
of  many  of  the  elements  is  based,  to  a  great  ex- 
tent, on  the  fact  that  so  far  they  have  resisted  all 
efforts  made  to  decompose  them  into  simpler  sub- 
stances. We  should  bear  in  mind,  however,  that 
until  Davy's  use  of  the  voltaic  battery,  potash, 
soda,  and  many  other  similar  compounds  were  re- 
garded as  true  elements.  It  is  not  improbable 
that  many  of  the  now  so-called  elements,  may 
hereafter  be  decomposed  into  simpler  constitu- 
ents. 

The  following  table  gives  the  names,  chemical 


Ele.]  212 

symbols,  approximate  atomic  weights  and  equiva- 
lents of  the  principal  elements  : 


[Ele. 


Names  ot 
Elements. 

w" 

Approximate 
Atomic 
Weight. 

Chemical  Equivalent.* 

Aluminium  ....... 
Antimony  

At 

Sb. 
As. 

27. 

9             [compounds 
40  in  e>us,   24   in   fr 

Barium  

Ba. 

136.8 

68  4             '    S       U 

Beryllium  
Bismuth  

Be 
Bi. 
B. 

9.1 
207.5 

10.0 

4.1 
69.2 
3-6 

Cadmium  

Cd. 

79-8 
ni.  8 

79-8 

Caesium.  
Calcium...  

Cs. 
Ca. 
C. 

132.6 
40. 

li:S 

20 

6 

Cerium  
Chlorine  
Chromium  

Ce. 
Cl. 
Cr. 

140.4 

35-4 

§:« 

35-4 
26  (nous,  17.3  iafe 

Copper  
Didymium  

Cu. 
D 

144!  6 

31.6 

Erbium  
Fluorine  
Gallium  

E. 
F. 
Ga. 

165.9 
19. 
68.9 

19. 

Germanium.  ...... 
Glucmum  
Gold  
Hydrogen  

Ge. 
G. 

Au. 
H. 

72-3 

196.2  \i\ous,  65.4  In  ic 

I. 

Je'I 

Iridium  

Ir 

Fe 

192.7 

96.4,  64.2,  48.2 

28  in  out   18  6  in  ic 

Lanthanum  
Lead 

La. 

Pb 

138.5 

Lithium  

Li. 

Magnesium  
Manganese  

Hg 

«4- 
53-9 

12 

27 

M  olybdenum  
Nickel... 

Mo. 
Ni. 

95-5 

28 

Niobium  

Nb 

93.8 

N 

Osmium  

Os 

o 

* 

Oxygen  
Palladium  

0. 

Pd. 

16. 

8 

Phosphorus  
Platinum  

P. 

Pt. 

3'- 

6.2  in  phosphates 

K. 

Rhodium 

R 

Rubidium  
Ruthenium  
Samarium  

Rb. 
Ru. 
Sin. 
Sc. 

85 

104.3 
150.02 

85-3. 

52.1  mous,  34.7inz<r 

Selenium 

Se 

78!  8 

Silicon  
Silver  

bi. 

Ag- 

28.3 

107.7 

7- 
107.7 

Mrontium  
Sulphur  
Tantalum.  
Telluiium  .  .  . 

Sr. 
S. 
Ta. 
Te 

87-4 

128! 

23 
43-7 

Thallium  
Thorium  

Tl. 
Th. 

203.7 
233-4 

203.7  ino*j,67.9m*? 

Ti 

48. 

Tungsten  
Uranium  
Vanad.um  
Ytterbium  
Yttrium 

W. 

u. 

Va. 
Yb. 
y 

,83.6 
238-5 

'i'f 

91.8  mous 
119.2  in  ous 
ij.lino** 

Zinc  

Zn. 

64, 

Zirconium  

Zr. 

89.4 

*  Atotnzc wtigkt  divided  by  the  valency. 


Element,  Negative One  of   the 

substances  forming  a  voltaic  couple.  (See 
Couple,  Voltaic.} 

Element,  Negative,  of  a  Yoltaic  Cell 

— That  element  or  plate  of  a  voltaic  cell  into 
which  the  current  passes  from  the  exciting 
fluid  of  the  cell. 

The  plate  that  is  not  acted  on  by  the  elec- 
trolyte during  the  generation  of  current  by 
the  cell 

The  copper  or  carbon  plate,  respectively, 
in  a  zinc-copper  or  zinc-carbon  couple. 

It  must  be  carefully  borne  in  mind  that  the 
conductor  attached  to  the  negative  element  of  a 
voltaic  pile  is  the  positive  conductor  or  electrode 
of  the  pik,  since  the  current  that  flows  into  the 
plate  from  the  liquid  or  electrolyte  must  flow  out 
of  the  plate  where  it  projects  beyond  the  liquid. 

Element  of  Current— (See  Current,  Ele- 
ment of.) 

Element  of  Storage  Battery.— (See  Bat- 
tery, Storage,  Element  of.) 

Element,  Positive That  element  or 

plate  of  a  voltaic  cell  from  which  the  current 
passes  into  the  exciting  fluid  of  the  cell. 

The  element  of  a  voltaic  couple  which  is 
acted  on  by  the  exciting  fluid  of  the  cell. 
(See  Couple,  Voltaic^ 

Element,  Thermo-Electric One  of 

the  two  metals  or  substances  which  form  a 
thermo-electric  couple.  (See  Couple,  Ther- 
mo-Electric!) 

Element,  Toltaic One  of  the  two 

metals  or  substances  which  form  a  voltaic 
couple.  (See  Couple,  Voltaic!) 

Elements,   Electrical    Classification   of 

A  classification  of  the  chemical  ele- 
ments into  two  groups  or  classes  according 
to  whether  they  appear  at  the  anode  or  kathode 
when  electrolyzed. 

The  chemical  elements  may  be  arranged  into 
electro-positive  and  electro- negative  according  to 
whether,  during  electrolysis,  they  appear  at  the 
negative  or  positive  terminal  of  the  source  respec- 
tively. 

The  electro-positive  elements  or  radicals  are 
Called  kathions,  and  appear  at  the  kathode  or 
electro-negative  terminal.  The  electro-negative 


Ele.J 


213 


[Eue. 


dements  are  called  onions,  and  appear  at  the 
anode,  or  the  electro-positive  terminal.  (See 
AMT.J 

The  metals  generally  are  electro- positive;  oxy- 
gen,  chlorine,  iodine,  fluorine,  etc.,  are  electro- 
negative. 

Elements,  Magnetic,  of  a  Place 

The  values  of  the  magnetic  intensity,  the  mag- 
netic declination  or  variation,  and  the  mag- 
netic inclination  or  dip  at  any  place. 

Elevator  Annunciator. — (See  Annuncia- 
tor, Elevator?) 

Elevator,  Electric  —An  elevator 

operated  by  electric  power. 

Elongated  Ring  Core.— (See  Core,  Ring, 
Elongated?) 

Elongation,  Magnetic An  increase 

in  the  length  of  a  bar  of  iron  on  its  magnetiza- 
tion. 

This  increase  in  length  is  thought  to  greatly 
strengthen  Hughes'  theory  of  magnetism.  (See 
Magnetism,  Hughes'  Theory  of.) 

Elongation  of  Needle.— (See  Needle,  Elon- 
gation of.) 

Embosser,  Telegraphic An  appa- 
ratus for  recording  a  telegraphic  message  in 
raised  or  embossed  characters. 

Emptied.— A  term  sometimes  applied  to  a 
completely  discharged  secondary  or  storage 
cell. 

It  is  difficult  to  determine  exactly  when  a  stor- 
age cell  is  completely  emptied  or  "discharged." 
The  cell  is  generally  regarded  as  discharged 
when  its  voltage  falls  below  a  certain  point. 

Endosmose. — The  unequal  mixing  of  two 
liquids  or  gases  through  an  interposed  me- 
dium. 

The  presence  of  an  electric  current  affects  the 
endosmose.  (See  Currents,  Diaphragm.) 

Endosmose,  Electric. — Differences  in  the 
level  of  liquids  capable  of  mixing  through  the 
pores  of  a  diaphragm  separating  them,  pro- 
duced by  the  flow  of  an  electric  current 
through  the  liquid. 

Wiedemann,  who  investigated  these  phenom- 
ena, employed  a  porous  earthenware  vessel  closed 
at  the  bottom  and  terminated  at  its  upper  end  by 
a  glass  bell  provided  with  a  glass  tubulure,  to 


which  was  attached  a  horizontal  arm  for  the  es- 
cape of  the  liquid  raised  in  the  tubulure.  The 
battery  terminals  were  attached  to  platinum  elec- 
trodes placed  respectively  inside  the  porous  cell, 
and  in  a  vessel  of  water  outside  of  the  porous  cell, 
in  which  the  porous  cell  was  placed ;  on  the  passage 
of  the  current  from  the  outside  of  the  cell  to  the 
inside  the  liquid  rose  in  the  glass  tubulure  and  ran 
over  the  horizontal  tube  into  a  vessel  placed  ready 
to  receive  it. 

Energizing,  Electrically Causing 

electricity  to  produce  any  effect  in  an  electro- 
receptive  device. 

An  electro-magnet  is  energized  by  the  passage 
of  a  current  through  its  coils. 

Energy. — The  power  of  doing  work. 

The  amount  of  work  done  is  measured  by  the 
product  of  the  force,  by  the  space  through  which 
the  force  moves.  Thus  one  pound  raised  verti- 
cally through  ten  feet,  ten  pounds  raised  through 
one  foot,  or  five  pounds  raised  through  two  feet,  all 
represent  the  same  amount  of  work;  viz.,  ten  foot- 
founds. 

If  a  weight  of  ten  pounds  be  raised  through  a 
vertical  height  of  one  foot,  by  means  of  a  string 
passing  over  a  pulley,  there  will  have  befn  ex- 
pended an  amount  of  energy  represented  by  the 
work  often  foot-pounds.  If  the  weight  be  pre- 
vented in  any  way  from  falling,  as  by  securing 
the  string  to  a  fixed  support,  the  weight  will  have 
stored  in  it  an  amount  of  energy  equal  to  ten  foot- 
pounds,  and  if  permitted  to  fall,  will  be  capable 
of  doing  an  amountof  work  which,  leaving  out  air 
resistance  and  friction,  is  exactly  equal  to  that 
originally  expended  in  raising  it  to  the  position 
from  which  it  fell;  viz.,  ten  foot-pounds  of  work. 

Energy,  Actual Energy  actually 

employed  in  doing  ^work  as  distinguished 
from  energy  that  only  possesses  the  power  of 
doing  work,  but  not  actually  doing  such 
work. 

This  term  is  also  used  in  the  sense  of  kinetic 
energy  or  energy  due  to  motion,  but  kinetic  en- 
ergy is  no  more  actual  than  potential  energy. 

Energy,  Atomic •  — Chemical-potential 

energy.     (See  Energy,  Chemical-Potential.} 
Energy,  Chemical-Potential The 

potential  energy  possessed  by  the  elementary 
chemical  atoms.     (See  Energy,  Potential?) 
If  a  weight  of  one  pound  be  raised  vertically 


Ene.] 


214 


[Ene. 


against  the  earth's  attraction,  through  a  distance 
of  say  ten  feet,  and  placed  on  a  suitable  support, 
an  amount  of  energy,  equal  to  the  ten  foot-pounds 
of  work  done  on  the  weight,  becomes  potential. 

In  the  same  manner  if  the  elementary  atoms  of 
carbon  and  oxygen,  when  combined  so  as  to  form 
carbonic  acid,  are  raised  or  separated  from  one 
another  sufficiently  to  decompose  the  carbonic 
acid  and  separate  the  carbon  from  the  oxygen,  the 
amount  of  potential  energy  the  carbon  and  oxygen 
possess,  as  a  result  of  having  been  separated,  is 
equal  precisely  to  that  originally  required  to  sepa- 
rate them.  In  this  manner  each  chemical  element 
possesses  a  store  of  chemical-potential  energy 
peculiar  to  it,  and  any  element  with  which  it  may 
subsequently  enter  into  combination.  When  ele- 
ments combine  chemically  this  potential  energy  is 
expended  in  producing  heat. 

Energy,  Conservation  of The  in- 
destructibility of  energy. 

The  total  quantity  of  energy  in  the  universe  is 
unalterable. 

The  total  energy  of  the  universe  is  not,  how- 
ever, available  for  the  production  of  work  useful 
for  man. 

When  energy  disappears  in  one  form  it  reap- 
pears in  some  other  form.  This  is  called  the  con- 
servation  or  indestructibility  of  energy.  The  com  - 
monest  form  in  which  energy  reappears  is  as  heat, 
and  in  this  case  some  of  the  heat  is  lost  to  the 
earth  by  radiation.  This  degradation  or  dissipa- 
tion of  energy  causes  some  of  the  energy  of  the 
earth  to  become  non-available  to  man. 

Energy  is  therefore  available  and  non-available. 
(See  Entropy.) 

Energy,  Correlation  of A  term 

sometimes  applied  to  the  different  phases  un- 
der which  energy  may  appear. 

Since  energy  is  indestructible,  when  it  disap- 
pears in  one  form  or  phase,  it  must  reappear  in 
another  form  or  phase.  The  correlation  of  the 
different  phases  of  energy,  therefore,  necessarily 
follows  from  the  fact  that  all  energy  is  indestruc- 
tible. 

Energy,  Degradation  of Such  a 

dissipation  of  energy  as  to  render  it  non- 
available  to  man.  (See  Energy,  Conserva- 
tion of.  Entropy?) 

Energy,  Dissipation  of The  ex- 
penditure or  loss  of  available  energy. 


Energy,      Electric    —The    powei 

which  electricity  possesses  of  doing  work. 

In  the  case  of  a  liquid  mass  at  different  levels, 
the  liquid  at  the  higher  level  possesses  a  certain 
amount  of  potential  energy  measured  by  the 
quantity  of  the  liquid  at  the  higher  level,  and  the 
excess  of  its  height  over  that  of  the  lower  level; 
or,  by  the  difference  between  the  two  levels.  Any 
difference  of  level  will  produce  a  flow  of  the  liquid 
from  the  higher  to  the  lower  level,  and  during 
the  flow  of  this  current  of  liquid,  potential  energy 
will  be  lost,  and  a  certain  amount  of  work  will  be 
done. 

In  the  case  of  electricity,  the  difference  of  elec- 
tric level,  or  potential,  between  any  two  points  of 
a  conductor,  causes  an  electric  current  to  flow 
between  these  points  toward  the  lower  electric 
level,  during  which  electric  potential  energy  is 
lost,  and  work  is  accomplished  by  the  electric 
current.  (See  Potential,  Electric.} 

The  amount  of  this  electric  work  is  measured  by 
the  quantity  of  electricity  that  flows,  multiplied 
by  the  difference  of  potential  under  which  it 
flows.  (See  Joule.  Volt-Coulomb.) 

Electric  energy,  however,  is  generally  meas- 
ured in  electric  power,  or  rate  of  doing  electric 
work. 

Since  an  ampere  is  one  coulomb-per-second,  if 
we  measure  the  difference  of  potential  in  volts, 
the  product  of  the  amperes  by  the  volts  will  give 
the  electrical  power  in  volt-amperes,  or  watts,  or 
units  of  electric  power.  C  E  =  Watts.  (See 
Ampere.  Volt.  Watt.) 

One  horse -power  equals  550  foot-pounds  per 
second.  One  watt  or  volt-ampere  =  ,Jf  of  a 
horse-power,  or  one  horse-power  equals  746  volt 
amperes  or  watts,  therefore: 

The  current  in  amperes,  multiplied  by  the  dif- 
ference of  potential  in  volts,  divided  by  746, 
equals  the  rate  of  doing  work  in  horse-powers. 

Thus,  if  .7  ampere  is  required  to  operate  a 
16  candle,  no  volt,  incandescent  lamp,  it  requires 
4.8  watts  per  candle. 

One  Watt  —  44.2394  foot-pounds  per  minute. 

One  Watt  =  .737324  foot-pound  per  second. 

The  Heat  Activity,  or  the  heat-per-second 
produced  by  an  electric  current,  is  also  propor- 
tional to  the  product  C  E,  or  the  watts,  for  the 
heat  is  proportional  to  the  square  of  the  current 
in  amperes  multiplied  by  the  resistance  in  ohms, 
or  C*  R  =  the  watts.  (See  Calorimeter,  Elec- 
tric.) 


Ene.]  215 

By  Ohm's  Law  (See  Ohm's  Law} 

C  =  |-  (i),  or  C  R  =  E  (2), 
K. 

But  the  electric  power,  or  the  watts,  =  C  E    (3). 
If,  now,  we  substitute  the  value  of  E,  taken 
from  equation  (2)  in  equation  (3)  we  have 


[Ene. 


therefore  C"  R  =  Watts. 

To  determine  the  heating  power  of  a  current 
in  small  calories,  calling  H,  the  amount  of  heat 
required  to  raise  i  gramme  of  water  through  I  ° 
Cent.,  and  C,  the  current  in  amperes — 

H  =  C*  RX  -24. 
Or,  for  any  number  of  seconds,  /, 
H  =  C2  Rt  X  .24. 
(See  Cabrie.) 

But  from  Ohm's  Law. 


(i), 


and  the  formula  for  electric  power  or  the  watts 
=  C  E.  (2)  By  substituting  in  equation  (2) 
and  the  value  of  C,  in  equation  (i), 

C  E  =  E  X  —  =  5-*=  Watts. 
R        R 

That  is  to  say,  the  electric  power  in  any  part  of 
a  circuit  varies  directly  as  the  square  of  the 
electromotive  force. 

We,  therefore,  have  three  expressions  for  the 
value  of  the  watt,  or  the  unit  of  electric  power, 
•ro.: 

C  E  =  Watts.         (i) 
C»R  =  Watts.       (2) 

|^=  Watts.  (3) 

(li)  C  E  =  Watts;  or  the  electric  power  is  pro- 
portional  to  the  product  of  the  quantity  of  elec- 
tricity per-second,  that  passes,  in  amperes,  and 
the  difference  of  electric  potential  or  level, 
through  which  it  passes,  in  volts. 

(2.)  C»  R  =  Watts;  or  the  electric  power 
varies  directly  as  the  resistance  R,  when  the  cur- 
Tent  is  constant,  or  as  the  square  of  the  current, 
if  the  resistance  is  constant.  That  is  to  say,  if 
with  a  given  resistance  the  power  of  a  given 
current  has  a  certain  value,  and  the  current 
flowing  through  this  same  resistance  be  doubled, 
the  power  is  four  times  as  great,  or  is  as  the 
equare  of  the  current. 

E» 

(3.)  =-  =  Watts,  or  the  electric  power  is  in- 


versely  as  the  resistance  R,  when  the  electro- 
motive force  is  constant,  and  is  directly  propor- 
tional to  the  square  of  the  electromotive  force  if 
the  resistance  is  constant. 

A  circuit  of  one  ohm  resistance  will  have  a 
power  of  one  watt,  when  under  an  electromo- 
tive force  of  one  volt,  since  it  would  then  have 
a  current  of  one  ampere  flowing  through  it,  and 
C  E  =  i  .  If,  however,  the  resistance  be  halved 
or  becomes  .5  ohm,  then  two  amperes  pass,  or 
the  power  equals  2  watts. 

The  power  varies  as  the  square  of  the  electro- 
motive force  in  any  part  of  a  circuit,  when  tht 
resistance  is  constant  in  that  part.  Thus  2  am- 
peres,  and  2  volts,  in  a  circuit  of  one  ohm 
resistance,  give  a  power,  C  E=2X2=4  watts. 
If  now,  R,  remaining  the  same,  the  electro- 
motive force  be  raised  to  4  volts,  then  since  E,  is 
doubled,  C,  or  the  amperes,  is  doubled,  and  C 

=i6  watts,  or  --  =  —  =  16. 


Energy,  Electric,  Transmission  of  - 

—  The  transmission  of  mechanical  energy  be- 
tween two  distant  points  connected  by  an 
electric  conductor,  by   converting  the    me- 
chanical energy  into  electrical  energy  at  one 
point,    sending    the    current    so     produced 
through  the  conductor,  and  reconverting  the 
electrical  into  mechanical  energy  at  the  other 
point. 

A  system  for  the  electric  transmission  of  energy 
embraces: 

(i.)  A  conducting  circuit  between  the  two 
stations. 

(2.)  An  electric  source  or  battery  of  electric 
sources  or  machines  at  one  of  the  stations,  gener. 
ally  in  the  form  f  a  dynamo-electric  machine 
or  machines,  for  converting  mechanical  energy 
into  electric  energy. 

(3.)  Electro-receptive  devices,  generally  electric 
motors,  at  the  other  station  for  reconverting  the 
electric  into  mechanical  energy.  (See  Motor, 
Electric.) 

Energy,  Flow  of  --  The  flow  or  trans- 
mission of  energy  from  the  medium  or  die- 
lectric surrounding  a  conductor  which  is 
directing  a  current  of  electricity  on  to  the 
conductor.  (See  Law,  Poynt  ing's!) 

Energy,  Hysteresial,  Dissipation  of  - 

—  The   dissipation   of  energy  by  means  of 


Ene.] 


216 


[Ent. 


hysteresis.     (See    Energy,    Dissipation   of. 
Hysteresis?) 

Energy,  Kinetic Energy  which  is 

due  to  motion  as  distinguished  from  potential 
energy.     (See  Energy,  Potential!) 

Energy-Meter.— (See  Meter,  Energy?, 

Energy  of  Position.— (See  Position,  En- 
ergy  of.) 

Energy  of  Stress.— (See  Stress,  Energy 
of-) 

Energy,  Potential Stored  energy. 

Potency,  or  capability  of  doing  work. 

Energy  possessing  the  power  or  potency  of 
doing  work,  but  not  actually  performing  such 
work. 

The  capacity  for  doing  work  possessed  by 
a  body  at  rest,  arising  from  its  position  as 
regards  the  earth,  or  from  the  position  of  its 
atoms  as  regards  other  atoms,  with  which  it 
is  capable  of  combining. 

A  pound  of  coal,  if  raised  vertically  one  foot, 
possesses,  as  a  mere  weight,  an  amount  of  energy 
capable  of  doing  an  amount  of  work  equal  to  one 
foot-pound.  The  atoms  of  carbon,  however,  of 
which  it  is  composed,  have  been  raised  or  sepa- 
rated from  those  of  oxygen,  or  some  other  elemen- 
tary substance,  and  when  the  coal  is  burned,  or 
the  carbon  atoms  fall  towards  the  oxygen  atoms 
(*'.  e.,  unite  with  them),  the  coal  gives  up  the 
potential  energy  of  its  atoms  in  the  form  of  heat. 

All  elementary  substances  possess  in  the  same 
way  atomic  or  chemical-potential  energy,  or  the 
energy  with  which  they  tend  to  fall  together, 
or  enter  into  combination.  This  energy  varies  in 
amount  in  different  elements  and  becomes  kinetic, 
as  heat,  on  combination  with  other  elements.  (See 
Energy,  Chemical- Potential.) 

Energy,  Radiant Energy  trans- 
ferred to  or  charged  on  the  universal  ether. 

Radiant  energy  is  of  three  forms,  viz.: 
(I.)  Obscure  radiation,  or  heat. 
(2.)  Luminous  radiation,  or  light. 
(3.)  Electro-magnetic  radiation. 

Energy,  Static A  term  used  to  ex- 
press the  energy  possessed  by  a  body  at  rest, 
resulting  from  its  position  as  regards  other 
bodies,  in  contradistinction  to  kinetic  energy 
or  the  energy  possessed  by  a  body  whose 


atoms,  molecules  or  masses  are  in  actual 
motion. 

Potential  energy. 

The  general  term  for  static  energy  is  potential 
energy.  (See  Energy,  Potential.) 

Energy,  Storage  of —  —The  change 
from  any  form  of  kinetic  energy,  to  any  form 
of  potential  energy.  (See  Energy.  Kinetic. 
Energy,  Potential.) 

Engine,  Electro-Magnetic A  mo- 
tor whose  driving  power  is  electricity.  (See 
Motor,  Electric?) 

Engraving,  Acoustic Engraving 

by  the  human  voice. 

In  the  Phonograph,  Graphophone  and  Gramo- 
phone, a  diaphragm,  set  in  vibration  by  the 
speaker's  voice,  cuts  or  engraves  a  record  of  its 
to-and-fro  movements  on  a  sheet  of  tin  foil,  a 
cylinder  of  hardened  wax,  or  a  specially  coa.ted 
plate  of  metal  or  glass.  This  record  is  employed 
in  order  to  reproduce  the  speech.  (See  Phonograph. ) 

Engraving,  Electric A   method 

for  electrically  etching  or  engraving  a  me- 
tallic plate  by  covering  it  with  wax,  tracing 
the  design  on  the  wax  so  as  to  expose  the 
metal,  connecting  the  metal  with  the  positive 
terminal  of  a  battery,  and  placing  it  in  a 
bath  opposite  annther  plate  of  metal. 

By  the  action  of  electrolysis  the  metal  is  dis- 
solved from  the  exposed  portions  and  deposited 
on  the  plate  connected  with  the  other  terminal 
of  the  battery.  (See  Electrolysis. ) 

In  this  manner  the  design  is  obtained  in  the 
form  of  an  etching  or  cutting  of  the  plate. 

By  connecting  the  waxed  plate  to  the  negative 
terminal  of  the  electric  source,  the  metal  will  be 
deposited  on  the  exposed  portions  of  the  plate, 
thus  producing  the  design  in  relief.  Unless 
great  care  is  taken,  this  latter  method  is  not, 
however,  apt  to  produce  a  sufficiently  unif>>rm 
deposit  to  enable  the  plate  so  formed  to  bj  u-ed 
for  printing  from. 

Electric  engraving  is  sometimes  called  electro- 
etching. 

Entropy. — In  thermo-dynamics  the  non- 
available  energy  in  any  system. — (Clausiu* 
and  Mayer?) 

In  thermo-dynamics,  the  available  energy 
in  any  system. — ( Tait,  Thomson  and  Max 
well?) 


Ent.] 


217 


[Eqn. 


As  will  be  noticed,  this  term  is  used  in  entirely 
different  and  opposite  senses  by  different  scientific 
men.  The  latter  sense  is,  perhaps,  the  one  most 
generally  taken. 

Heat  energy  is  available  for  doing  useful  exter- 
nal work  only  when  the  source  of  heat  utilized  is 
hotter  than  surrounding  bodies,  that  is,  when  the 
heat  is  transferred  from  a  hotter  to  a  colder  body. 
When  all  bodies  have  acquired  the  same  temper- 
ature, they  can  do  no  more  external  work.  In 
the  various  transformations  of  energy  some  of  the 
energy  is  converted  into  heat,  and  this  heat  is 
gradually  diffused  through  the  universe  and  thus 
becomes  non-available  to  man.  Therefore,  the 
entropy  of  our  earth  is  decreasing. 

"Entropy,  in  thermo.dynami7s,"  says  Max- 
well, "is  a  quantity  relating  to  a  body  such  that 
its  increase  or  diminution  implies  that  heat  has 
entered  or  left  the  body.  The  amount  of  heat 
which  enters  or  leaves  the  body  is  measured  by  the 
product  of  the  increase  or  diminution  of  entropy 
into  the  temperature  at  which  it  takes  place." 

Entropy,  Electric  — A  term  pro- 
posed by  Maxwell  for  use  in  thermo-elec- 
tric phenomena  to  include  the  doctrine  of 
entropy  in  electric  science. 

"When  an  electric  current,"  says  Maxwell, 
"passes  from  one  metal  to  another,  heat  is 
emitted  or  absorbed  at  the  junction  of  the  metals. 
We  should,  therefore,  suppose  that  the  electric 
entropy  has  diminished  or  increased  when  the 
electricity  passes  from  one  metal  to  the  other,  the 
electric  entropy  being  different  according  to  the 
nature  of  the  medium  in  which  the  electricity  is, 
and  being  affected  by  its  temperature,  stress, 
strain,  etc." 

Equalizer,  Feeder An  adjustable 

resistance  placed  in  the  circuit  of  a  feeder  for 
the  purpose  of  regulating  the  difference  of 
potential  at  the  junction  box. 

Equalizer,  Magnetic A  device  for 

equalizing  the  otherwise  unequal  force  ex- 
erted between  a  magnet  pole  and  its  arma- 
ture at  varying  distances. 

Since  the  force  of  magnetic  attraction  increases 
rapidly  with  the  decrease  of  the  distance,  it  fol- 
lows that  any  force  sufficiently. great  to  cause  the 
motion  of  an  armature  towards  a  pole,  against  the 
force  of  gravity,  will  result  in  the  movement  of  the 
armature  to  the  pole,  and  that,  therefore,  no  dif- 
ferentiation as  to  the  final  result  will  be  produced 


by  a  powerful  current,  and  a  current  just  strong 
enough  to  start  the  action.  If,  however,  the 
armature  move  against  the  action  of  a  spring,  the 
latter  can  be  so  arranged  that  the  force  with 
which  it  opposes  the  motion  of  the  armature  in  • 
creases,  the  nearer  the  armature  is  to  the  pole, 
and  in  this  way  the  movement  of  the  armature 
can  be  made  proportional  to  the  strength  of  the 
current  energizing  the  electro-magnet. 

A  similar  method  consists  in  mechanical  devices 
that  cause  the  armature  to  work  with  lessened 
mechanical  advantage  as  it  approaches  the  pole. 

Or,  the  polar  surfaces  may  be  so  shaped  by  cut- 
ting, or  by  the  addition  of  suitable  projections, 
as  to  cause  the  approach  of  the  armature  to  be 
attended  by  a  nearly  constant  force. 

Equator,  Geographical An  imag- 
inary great  circle  passing  around  the  earth 
midway  between  its  poles. 

Equator,  Magnetic The  magnetic 

parallel  or  circle  on  the  earth's  surface  where 
a  magnetic  needle,  suspended  so  as  to  be  free 
to  move  in  a  vertical  as  well  as  in  a  horizontal 
plane,  remains  horizontal. 

An  irregular  line  passing  around  the  earth 
approximately  midway  between  the  earth's 
magnetic  poles.  (See  Dip  or  Inclination, 
Angle  of  ^ 

Equator  of  Magnet. — (See  Magnet,  Equa- 
tor of.) 

Equatorial. — Pertaining  to  the  equator. 

Equatorially. — In  the  direction  of  the 
equator. 

Equipotential  Surface  of  a  Conductor 
through  which  a  Current  is  Flowing. — 
(See  Surface,  Equipotential,  of  a  Conductor 
through  which  a  Current  is  Flowing?) 

Eqnipotential  Surface,  or  Level  Surface 
Of  Escaping  Fluid.— (See  Surface,  Equipo- 
tential, or  Level  Surface  of  Escaping  Fluid.) 

Equipotential  Surfaces,Electrostatic 

—  (See  Surfaces,  Equipotential,  Electro- 
static^ 

Eqnipotential    Surfaces,  Magnetic  — 
• — (See  Surfaces,  Equipotential,  Magnetic?} 

Equivalence,  Electro-Chemical,  Law  of 
The  amount  of  chemical  action  pro- 
duced by  an  electric  current,  passed  through 
various  chemical  substances,  is  proportional 
to  the  chemical  equivalent  of  each  substance, 


Equ.] 


218 


that  is,  to  its  atomic  weight,  divided  by  its 
valency.     (See  Valency.) 

Thus,  the  atomic  weight  of  oxygen  is  sixteen 
times  greater  than  the  atomic  weight  of  hydrogen. 
Oxygen  is  a  diad;  that  is,  has  twice  the  combin- 
ing power  of  hydrogen.  The  passage  of  a  given 
quantity  of  electricity  will  liberate  eight  times,  by 
weight,  as  much  oxygen  as  hydrogen ;  or,  to  put 
it  in  another  way,  the  passage  of  a  given  quan- 
tity of  electricity  will  liberate  two  atoms  of 
hydrogen  for  every  atom  of  oxygen. 

The  atomic  weight  of  chlorine  is  35.4.  The 
passage  of  a  given  amount  of  electricity  will 
liberate  a  weight  of  chlorine  35.4  greater  than  the 
weight  of  hydrogen;  or,  for  every  atom  of 
chlorine  it  will  liberate  one  atom  of  hydrogen. 
Here  the  passage  of  a  given  amount  of  electricity 
liberates  one  atom  of  the  monad  element  hydrogen 
for  every  atom  of  the  monad  element  chlorine. 

The  atomic  weight  of  gold  is  196.2,  and  its 
atomicity  or  valency  is  3.  The  passage  of  a 

given  amount  of  electricity  will  liberate  —  —  = 

65.4  in  ic  compounds  as  great  a  weight  of  the 
triad  element  gold  as  of  hydrogen ;  or,  will  liberate 
them  in  the  proportion  of  one  atom  of  gold  for 
every  three  atoms  of  hydrogen. 

Generalizing,  it  appears,  therefore,  that  the 
passage  of  the  same  quantity  of  electricity  through 
an  electrolyte  liberates  the  same  number  of  atoms 
of  a  monad  element,  no  matter  what  their  nature 
may  be.  It  liberates  one-half  as  many  of  the  diad 
atoms  as  it  does  of  the  monads,  and  one-third  as 
many  of  the  triad  atoms  as  of  the  monads. 

Professor  Lodge  points  out,  that  assuming  the 
truth  of  the  theory  that  a  current  of  electricity 
flows  in  an  electrolyte  by  means  of  a  true  electric 
convection,  each  atom  carrying  an  electric 
charge,  then  it  would  seem  that  every  monad 
atom  carries  an  equal  charge  of  electricity, 
whether  it  be  an  atom  of  hydrogen,  chlorine, 
potassium,  silver,  or  mercury.  That  each  diad 
element  carries  twice  as  much,  and  that  each 
triad  element  carries  three  times  as  much. 

In  general,  the  number  of  atoms  liberated  by  a 
given  current  of  electricity  is  equal  to  the  num- 
ber of  atoms  of  hydrogen,  divided  by  the  valency 
of  the  atom.  ' '  The  electric  charge, ' '  says  Lodge, 
•'belonging  to  each  atom  of  matter,  is  a  simple 
multiple  of  a  definite  quantity  of  electricity,  which 
quantity  is  an  absolute  constant,  quite  independent 
of  the  nature  of  the  particular  substance  to  which 
the  atom  belongs." 


The  specific  charge  thus  hypothetically  given  to 
each  atom  of  matter  is  believed  never  to  be  lost. 

Atoms  capable  of  entering  into  combination  are 
supposed  to  be  oppositely  charged,  and  chemical 
affinity  is,  according  to  this  supposition,  believed 
to  be  the  result  of  the  mutual  attractions  of  opposite 
electric  charges  naturally  and  originally  pos- 
sessed by  the  atoms  of  matter. 

Lodge  points  out  the  following  results  which 
naturally  flow  from  the  hypothesis  that  the  atoms 
of  matter  possess  definite  positive  and  negative 
charges  of  electricity,  viz. : 

(I.)  That  the  amount  of  electricity  possessed 
by  each  monad  atom  is  exceedingly  small,  being 
about  the  hundred  thousand  millionth  part  of 
the  ordinary  electrostatic  unit,  or  less  than  the 
hundred  trillionth  of  a  coulomb. 

(2.)  The  charge  being  small,  the  potential  is 
necessarily  low. 

Probably  something  between  one  and  three 
volts  is  a  high  difference  of  potential  between  two 
oppositely  charged  atoms. 

(3.)  The  nearness  of  the  attracting  atoms,  how- 
ever, can  cause  a  very  strong  electrostatic  attrac- 
tion between  them. 

(4. )  That  chemical  affinity,  or  atomic  attraction, 
is  caused  by  the  presence  of  these  electric  charges. 
(5.)  That  the  electrical  force  between  two 
atoms  at  any  distance  is  ten  thousand  million 
billion  billion  times  greater  than  their  gravitation 
attraction  at  the  same  distance,  or,  the  force  has 
an  intensity  per  unit  of  mass  capable  of  producing 
an  acceleration,  nearly  one  trillion  times  greater 
than  that  of  gravity  at  the  earth's  surface. 

Equivalent,  Chemical The  quo- 
tient obtained  by  dividing  the  atomic  weight 
of  any  elementary  substance  by  its  atomicity. 
(See  Weight,  Atomic.  Atomicity?) 

The  ratio  between  the  quantity  of  an  ele- 
ment and  the  quantity  of  hydrogen  it  is 
capable  of  replacing. 

That  quantity  of  an  elementary  substance 
that  is  capable  of  combining  with  or  replac- 
ing one  atom  of  hydrogen. 

The  chemical  equivalent  has  a  different  value 
from  the  atomic  weight  whenever  the  valency 
is  greater  than  unity.  Thus  the  atomic  weight 
of  gold  is  196.2,  but  since  in  ic  compounds  one 
atom  of  gold  is  capable  of  combining  with  three 
atoms  of  hydrogen,  the  weight  of  the  gold  equiva- 
lent to  that  of  one  atom  of  hydrogen  is  one-third 
of  196.2,  or  65.4. 


Eqn. 


219 


[Esc. 


Conductivity.— (See  Conduc- 
tivity, Equivalent?) 
Equivalent,  Electro-Chemical A 

number  representing  the  weight  in  grammes 
of  an  elementary  substance  liberated  during 
electrolysis  by  the  passage  of  one  coulomb  of 
electricity.  (See  Electrolysis.  Coulomb?) 

The  chemical  equivalent  of  a  substance 
multiplied  by  the  electro-chemical  equivalent 
of  hydrogen. 

The  electro- chemical  equivalent  is,  therefore, 
found  by  multiplying  the  electro-chemical  equiva- 
lent of  hydrogen  by  the  chemical  equivalent  of 
the  element. 

It  may  be  determined  experimentally  that  one 
coulomb  of  electricity,  expended  electrolytically, 
will  liberate  .0000105  gramme  of  hydrogen. 
Therefore  a  current  of  one  *mperet  or  one  coulomb- 
per-second,  will  liberate  .0000105  gramme  of  hy- 
drogen per  second.  The  number  .0000105  is  the 
electro-chemical  equivalent  of  hydrogen. 

In  the  same  manner  the  electro-chemical  equiva- 
lents of  the  other  elements  are  obtained  by  multi- 
plying the  electro-chemical  equivalent  of  hydrogen 
by  the  chemical  equivalent  of  the  substance. 

Thus,  the  chemical  equivalent  of  potassium  is 
-39.1,  therefore  its  electro-chemical  equivalent  is 
39.1  X  .0000105  =  .00041055.  By  multiplying 
the  strength  of  the  current  that  passes  by  the 
•electro-chemical  equivalent  of  any  substance  we 
obtain  the  weight  of  that  substance  liberated  by 
electrolysis.  (See  Equivalence,  Electro-Chemical, 
Law  of.} 

TO  determine  the  electro-chemical  equivalent 
of  the  other  elements  see  table  of  chemical  equiva- 
lents on  page  212. 

Equivalent,  Joule's The  mechan- 
ical equivalent  of  heat.  (See  Heat,  Mechan- 
ical Equivalent  of.) 

Equivalent  of  Heat,  Mechanical 

(See  Heat,  Mechanical  Equivalent  of.) 

Equivalent  Resistance. — (See  Resistance, 
Equivalent.) 

Equivolt. — A  term  proposed  by  J.  T. 
Sprague  for  the  unit  of  electrical  energy,  ap- 
plied especially  to  chemical  decomposition. 

Sprague  defines  an  equivolt  as  follows  :    ' '  The 
mechanical  energy  of  one  rolt  electromotive  force 
exerted  under  unit  conditions  through  one  equiva- 
lent of  chemical  action  in  grains." 
8— Vol.  1 


This  term  has  not  been  generally  accepted. 
(See  Volt -Coulomb.      Joule.) 
Erb's  Standard  Size  of  Electrodes.— (See 

Electrodes,  Erb's  Standard  Size  of.) 

Erg. — The  unit  of  work,  or  the  work  done 
when  unit  force  is  overcome  through  unit 
distance. 

The  work  accomplished  when  a  body  is 
moved  through  a  distance  of  one  centimetre 
with  the  force  of  one  dyne.     (See  Dyne.) 
A  dyne  centimetre. 

The  work  done  when  a  weight  of  one  gramme 
is  raised  against  gravity  through  a  vertical  height 
of  one  centimetre  is  equal  to  981  ergs,  because 
the  weight  of  one  gramme  is  i  X  981  dynes,  or 
981  ergs. 

The  following  values  for  the  erg,  the  unit  of 
work,  and  the  dyne,  the  unit  of  force,  are  taken 
from  Hering: 

I  erg   =  i  dyne  centimetre. 
i  erg   =  o.ooooooi  joule. 
981  ergs  =  i  gramme  centimetre. 
1,937.5  ergs  =  i  foot  grain. 
13,562,600  ergs  =  i  foot-pound. 

i  dyne   =  1 .0194  milligrammes. 
I  dyne    =  0.015731  grain. 
i  dyne   =  0.0010194  grammes. 
i  dyne   =  0.00003596  ounce  avoirdupois. 
63.568  dynes  =  I  grain. 
981  dynes  =  I  gramme. 

Ergmeter. — An  apparatus  for  measuring 
the  work  of  an  electric  current  in  ergs. 

Erg-ten. —  A  term  proposed  for  ten  million, 
ergs  or  i  X  10  10=  10,000,000,000. 

In  representing  large  numbers  containing  many 
ciphers  the  following  plan  is  generally  adopted  for 
representing  the  number  of  ciphers  that  are  to  be 
added  to  a  given  number.  Thus,  suppose  it  is 
desired  to  represent  the  number  3,800,000,000. 
When  written  38  X  lo8  it  indicates  that  38  is  to 
be  multiplied  by  lo8  or  100,000,000,  or,  in  other 
words,  that  38  is  to  be  followed  by  8  ciphers,, 
thus  3,800,000,000. 

A  negative  exponent,  as  3  X  io~8  represents 
the  corresponding  decimal  thus,  .00000003. 

I  erg  X  io10,  or  10,000,000,000  is  called  an 
erg-fen.  I  X  i°6  =  an  erg-six.  These  terms 
are  not  in  general  use.  Ten  meg -ergs  is  a  pref- 
erable phrase  to  an  erg-ten.  (See  Meg-erg. ) 

Escape,    Electric A    term    some- 


Esc.] 


220 


[Ev* 


times  employed  to  indicate  the  loss  of  charge 
on  an  insulated  conductor.  (See  Leakage, 
Electric^ 

Escaping  Fluid,  Flow-Lines  of  — 
(See  Flow-Lines  of  Escaping  Fluid.} 

Escaping  Fluid,  Stream-Lines  of  — 
(See  Stream-Lines  of  Escaping  Fluid.) 

Essential  Resistance. — (See  Resistance, 
Essential.). 

Etching,  Electro  — A  term  some- 
times employed  instead  of  electro-engraving. 
(See  Engraving,  Electric.) 

Etching,  Galvanic  —  — ElectroTEn- 
graving.  (See  Engraving,  Electric.) 

Ether.— The 'tenuous,  highly  elastic  fluid 
that  is  assumed  to  fill  all  space,  and  by  vibra- 
tions or  waves  in  which  light  and  heat  are 
transmitted. 

Although  the  existence  of  the  ether  is  assumed 
in  order  to  explain  certain  phenomena,  its  actual 
existence  is  very  generally  credited  by  scientific 
men,  and,  in  reality,  proofs  are  not  wanting  to 
fairly  establish  such  existence. 

Light  and  heat  are  believed  to  be  due  to  trans- 
verse vibrations  in  the  ether.  Magnetism  appears 
to  be  due  to  whirls  or  whirlpools,  and  an  elec- 
tric current  is  believed  by  some  to  be  due  to 
pulses  of  waves  of  ether  ^set  in  motion  by  differ- 
ences in  the  ether  pressures. 

It  is  not  correct  to  regard  the  luminiferous 
ether  as  possessing  no  weight,  or  as  being  im- 
ponderable. Maxwell  estimates  its  density  as 

?*- that  of  water.     It 

1,000,000,000,000,000,000,000 

is  very  readily  moved  or  set  into  vibration,  its 
rigidity  being  estimated  at  about  ,  ^^^ 

that  of  steel. 

According  to  the  speculations  of  some  physi- 
cists the  ether  is  not  discontinuous  or  granular, 
but  it  is  similar  to  what  might  be  regarded  as  an 
almost  impalpable  jelly. 

Ethereal.— Pertaining  to  the  universal 
ether. 

Eudiometer. — A  voltameter  in  which  sep- 
arate graduated  vessels  are  provided  for  the 
reception  and  measurement  of  the  gaseous 
products  evolved  during  electrolysis.  (See 
Voltameter.) 


In  all  cases  electrodes  for  eudiometers  must  be 
used  which  do  not  enter  into  combination  with  the 
evolved  gaseous  products.  In  the  case  of  oxygen 
and  hydrogen,  platinum  is  generally  used. 

A  form  of  eudiometer  is  shown  in  Fig.  241. 
Two  separate  glass  ves- 
sels, provided  at  the  top 
with  stop  cocks,  and 
open  at  their  lower 
ends,  rest  in  a  vessel  of 
water  A,  over  platinum 
electrodes,  connected 
electrically  with  binding 
posts  K,  K.  Both  ves- 
sels are  filled  with  water 
slightly  acidulated  with 
sulphuric  acid,  and, 
when  connected  with 
a  battery  of  sufficient 
electromotive  force  (not 
less  than  1.45  volts), 

electrolysis  takes  place,  Fig.  241.  Eudiometer. 
and  hydrogen  gas  collects  in  the  vessel  over 
the  platinum  electrode  connected  with  the  neg- 
ative battery  terminal,  and  oxygen  in  the  vessel 
over  the  electrode  connected  with  the  positive 
battery  terminal.  The  volume  of  the  hydrogea 
is  approximately  twice  as  great  as  that  of  the 
oxygen.  (See  Water,  Electrolysis  of.) 

The  proportion  is  not  exactly  2  to  i,  because, 

(I.)  Some  of  the  hydrogen  is  occluded  or  ab- 
sorbed by  the  platinum  electrode. 

(2.)  Some  of  the  oxygen  is  given  off  as  tri- 
atomic  oxygen,  or  ozone,  which  is  denser  and 
occupies  less  space  than  free  atomic  oxygen. 

Eudiometric. — Pertaining  to  the  eudiom- 
eter. (See  Eudiometer^ 

Eudiometrically.— By  means  of  the  eudi- 
ometer. 

Evaporation.— The  change  from  the  liquid 
to  the  vaporous  state. 

Wet  clothes  exposed  to  the  air  are  dried  by  the 
evaporation  of  the  water. 

Evaporation  is  greater: 

(I.)  The  more  extended  the  surfaces  exposed. 

(2.)  The  higher  the  temperature  of  the  air. 

(3.)  The  dryer  the  air,  or  the  smaller  the 
quantity  of  vapor  it  contains  already. 

(4.)  The  stronger  the  wind. 

(5.)  The  smaller  the  barometric  pressure. 

Evaporation,  Electric The  forma- 


EYH.] 


221 


LExc. 


tion  of  vapors  at  the  surfaces  of  substances 
by  the  influence  of  negative  electrification. 

The  term  electric  evaporation  was  proposed  by 
Crookes  (or  the  formation  of  metallic  vapors  of 
such  substances  as  metallic  platinum,  exposed  in 
high  vacua  to  the  effects  of  negative  electrifica- 
tion. He  shows  that  under  these  circumstances 
the  surface  molecules  of  the  platinum  lose  their 
power  of  cohering  and  fly  off  into  the  space 
around  them,  /.  t ,  suffer  true  evaporation.  This 
action  takes  place  under  atmospheric  pressures, 
butj  like  ordinary  evaporation,  is  greatly  facili- 
tated by  the  presence  of  a  high  vacuum. 

True  electric  evaporation  takes  place  with 
liquids  as  well  as  with  solids.  In  an  experiment 
with  water,  the  influence  of  the  kind  of  the  elec- 
trification was  clearly  shown.  A  vessel  of  water 

,A 


Fig.  242.  Electrical  Evaporation. 
exposed  to  the  air  was  first  positively  electrified, 
but  after  an  exposure  of  i|  hours  only  a  trifling 
evaporation  was  noticeable.  The  water  was 
then  negatively  electrified,  and  at  the  end  of  i^ 
kours  had  lost  -j^ViF  part  of  its  weight  more  than 
did  the  positively  charged  water. 

Professor  Crookes  experimented  with  cadmium, 
and,  in  order  to  show  that  electric  evaporation  is 
different  from  evaporation  produced  by  the  agency 
•f  heat,  tried  the  following,  viz. :  A  high  vacuum 
U-tube,  shaped  as  shown  in  Fig  242,  was  pro- 


243.     Electrical  Evaporation. 


Tided  with  platinum  poles  sealed  in  the  glass  at 
A  and  B.  Two  pieces  of  cadmium,  C  and  D, 
were  placed  in  the  tube  in  the  position  shown, 
and  the  Cube  uniformly  heated  by  means  of  %  gas- 
burner  ;.nd  air  bath,  and  maintained  at  a  constant 
temperature.  The  current  was  then  passed  for 
%bout  an  hour,  B,  being  made  the  negative  pole. 


No  metal  was  deposited  in  the  neighborhood  of 
the  positive  pole,  the  portions  of  the  tube  sur- 
rounding the  positive  pole  being  quite  clean, 
while  the  corresponding  portions  of  the  other  limb 
of  the  tube  were  thickly  coated,  as  shown  by  the 
shading  in  the  drawing. 

In  another  experiment,  in  which  the  tempera- 
ture was  kept  lower  than  in  the  preceding,  viz., 
just  below  the  melting  point  of  the  cadmium, 
after  the  current  had  passed  for  an  hour,  the  limb 
of  the  tube  through  which  the  current  had  passed 
had  received  a  thick  coating,  while  the  other  was 
nearly  free  from  coating,  as  shown  in  Fig.  243. 
Here  the  increase  in  the  amplitude  of  the  mole- 
cular oscillation  under  the  influence  of  the  elec- 
tricity is  manifest. 

Evaporation,  Electrification  by •  — 

An  increase  in  the  difference  of  potential  ex- 
isting in  a  mass  of  vapor  attending  its  sudden 
condensation. 

The  free  electricity  of  the  atmosphere  is  be- 
lieved by  some  to  be  due  to  the  condensation  of 
the  vapor  of  the  air  that  results  in  rain,  hail, 
clouds,  etc.  It  is  probable,  however,  that  the 
true  effect  of  condensation  is  mainly  limited  to 
the  increase  of  a  feeble  electrification  already 
possessed  by  the  air  or  its  contained  vapor.  The 
small  difference  of  potential  of  the  exceedingly 
small  drops  of  water  in  clouds  is  enormously  in- 
creased by  the  union  or  coalescing  of  many 
thousands  of  such  drops  into  a  single  rain  drop. 
(See  Electricity,  Atmospheric.} 

Exchange,  Telephonic,  System   of • 

— A  combination  of  circuits,  switches  and 
other  devices,  by  means  of  which  any  one  of 
a  number  of  subscribers  connected  with  a 
telephonic  circuit,  or  a  neighboring  telephonic 
circuit  or  circuits,  may  be  placed  in  electrical 
communication  with  any  other  subscriber 
connected  with  such  circuit  or  circuits. 

A  telephone  exchange  consists  essentially  of  a 
multiple  switchboard,  or  a  number  of  multiple 
switchboards,  furnished  with  spring-jacks,  an- 
nunciator drops,  and  suitable  connecting  cords.  A 
call  bell,  or  bells,  is  also  provided.  The  annun- 
ciator drops  are  often  omitted.  (See  Board^ 
Multiple  Switch.) 

Excitability.  Electric,  of  Nerve  or  Mns- 

cnlar  Fibre The  effect  produced  by  an 

electric  current  in  stimulating  the  nerve  of  a 


Exc.J 


[Exh. 


living  animal,  or  in  producing  an  involuntary 
contraction  of  a  muscle. 

Du  Bois-Reymond  has  shown  that  these  effects 
depend  : 

(i.)  On  the  strength  of  the  current  employed. 
The  excitability  occurs  only  when  the  current 
begins  to  flow,  and  when  it  ceases  flowing ;  or, 
when  the  electrodes  first  touch  the  nerves,  and 
when  they  are  separated  from  it.  Subsequent 
investigations  have  shown  that  this  is  true  only 
for  the  frog's  nerves,  and  is  true  for  the  human 
nerves  only  in  the  case  of  moderate  currents, 
strong  currents  producing  tetanus. 

(2.)  On  the  rapidity  with  which  the  current 
used  reaches  its  maximum  value,  that  is,  on  the 
rapidity  of  change  of  current  density,  (See 
Current  Density,") 

Excitability,  Electro-Nervous 

In  electro-therapeutics  the  electric  excitation 
of  a  nerve. 

Excitability,  Electrotonic  -  —The 
actual  excitability  of  a  nerve  when  in  the 
electrotonic  condition.  (See  Electrotonus, 
Anelectrotonus.  Kathelectrotonus) 

Excitability,  Faradic Muscular  or 

nervous  excitability  following  the  employment 
of  the  rapidly  intermittent  currents  produced 
by  induction  coils.  (See  Coil,  Induction,} 

Faradic  excitability  is  different  from  galvanic 
excitability,  or  that  produced  by  means  of  a  con  - 
tinuous  voltaic  current.  (See  Excitability,  Gal- 
vanic, ) 

Excitability,  Galvanic A  term 

sometimes  employed  for  electric  excitability 
of  nerve  or  muscular  fibre.  (See  Excitability, 
Electric,  of  Nerve  or  Muscular  Fibre?) 

Excitation,  Compensated,  of  Alternator. 
— (See  Alternator,  Compensated  Excitation 
of.) 

Excitation,  Direct The  excitement 

of  a  muscle  by  placing  an  electrode  on  the 
muscle  itself. 

Excitation,  Electro-Muscular  — 

In  electro-therapeutics  the  galvanic  or  faradic 
excitation  of  the  muscle,  or  its  excitation  by 
the  continuous  currents  of  a  voltaic  battery,  or 
the  alternating  currents  of  an  induction  coil. 

Excitation,  Faradic  —  —Excitation  of 
nuscle  or  nerve  fibre  by  means  of  rapidly 


alternating  currents  of  electricity.  (See 
Excitability,  Faradic) 

Excitation,  Indirect—  —The  excite- 
ment of  a  muscle  from  its  nerve. 

Exciter  of  Field.— (See  Field,  Exciter  of} 

Exciting  Liquid  of  Voltaic  Cell.— (See 
Cell,  Voltaic,  Primary,  Exciting  Liquid  of.) 

Execution,  Electric Causing  the 

death  of  a  criminal,  in  cases  of  capital  pun- 
ishment, by  means  of  the  electric  current. 

Electric  execution  has  been  adopted  by  the 
State  of  New  York,  in  accordance  with  the 
following  law  : 

"The  Court  shall  sentence  the  prisoner  to 
death  within  a  certain  week,  naming  no  day  or 
hour,  and  not  more  than  eight  nor  less  than  five 
weeks  from  the  day  of  sentence.  The  execution 
must  take  place  in  the  State  prison  to  which  con- 
victed felons  are  sent  by  the  Court,  and  the  execu- 
tioner must  be  the  agent  and  warden  of  the  prison. 

"No  newspaper  may  print  any  details  of  the 
execution,  which  is  to  be  inflicted  by  electricity. 
A  current  of  electricity  is  to  be  caused  to  pass 
through  the  body  of  the  condemned  of  sufficient 
intensity  to  kill  him,  and  the  application  is  to  be 
continued  until  he  is  dead." 

Exhaustion,  Electric  —  — Physiological 
effects  resembling  those  produced  by  sun- 
stroke, resulting  from  prolonged  exposure 
to  the  radiation  of  unsually  large  voltaic  arcs. 
(See  Sun- Stroke,  Electric} 

Exhaustion  Of  Primary  Voltaic  Cell.— 
(See  Cell,  Voltaic,  Primary,  Exhaustion  of} 

Exhaustion  of  Secondary  Voltaic  Cell.— 

(See  Cell,  Voltaic,  Secondary,  Exhaustion  of.) 

Exhaustion  of  Voltaic  Cell.— (See  Cell, 
Voltaic,  Exhaustion  of,) 

Exhaustion,  Reaction  of  —  — A  con- 
dition of  nervous  and  muscular  irritability  to 
electric  excitation  when  a  certain  reaction, 
produced  by  a  given  current  strength,  cannot 
be  reproduced  without  an  increase  of  current 
strength. 

The  reaction  of  exhaustion  may  be  regarded  as 
a  special  variety  of  the  reaction  of  degeneration. 
(See  Degeneration,  Reaction  of) 

The  reaction  of  degeneration  embraces  thf 
following  modifications  of  irritability,  viz.: 


Exp.J 


[Eye. 


(i.)  Disappearance  or  diminution  of  nervous 
irritability  to  both  galvanic  and  faradic  currents. 

(2.)  Disappearance  of  faradic  and  increase  of 
galvanic  irritability  of  muscles,  generally  associ- 
ated with  an  increase  of  mechanical  irritability. 

(3  )  Disappearance  of  faradic  and  increase  of 
galvanic  muscular  irritability  associated  generally 
with  increased  mechanical  irritability. 

(4.)  Tardy,  delayed  contraction  of  muscles  in- 
stead of  quick  reaction  of  normal  muscle. 

(5.)  Marked  modifications  of  normal  sequence 
of  contraction. — Liebig  6°  Rohe. 

Expanding       Magnetic       Whirl.— (See 

Whirl,  Expanding  Magnetic) 

Expansion,    Co-efficient    of  —The 

fractional  increase  in  the  dimensions  of  a  bar 
or  rod  when  heated  from  32  degrees  to  33 
degrees  F.  or  from  o  degree  to  I  degree  C. 

The  fractional  increase  in  the  length  of  the  bar 
is  called  the  Co-efficient  of  Linear  Expansion. 

The  fractional  increase  in  the  surface  is  called 
the  Co-efficient  of  Surf  ace  Expansion. 

The  fractional  increase  in  the  volume  is  called 
the  Co-efficient  of  Cubic  Expansion. 

Expansion,  Electric  —  — The  increase 
in  volume  produced  in  a  body  on  giving  such 
body  an  electric  charge. 

A  Leyden  jar  increases  in  volume  when  a 
charge  is  imparted  to  it.  This  result  is  due  to  an 
expansion  of  the  glass  due  to  the  electric  charge. 
According  to  Quincke,  some  substances,  such  as 
resinous  or  oily  bodies,  manifest  a  contraction  of 
volume  on  the  reception  of  an  electric  charge. 

Expansion  Joint  — (See  Joint,  Expan- 
sion?) 

Expansion,  Linear,  Co-efficient  of 

A  number  expressing  the  fractional  increase  in 
length  of  a  bar  for  a  given  increment  of  heat. 

The  co-efficients  of  expansion  of  a  few  sub- 
stances are  given  in  the  following  table: 

Temp. 
Aluminium 16  to  ico  degrees  C .  .0.0000235 


Copper 
German  silver 
Glass   
Iron  
Lead 

0 

o 
o 

13 

o 

ICO 
ICO 
IOO 
100 
IOO 

"  .  .0.0000167 
"  ..0.0000184 
"  .  .0.0000071 
"  .  .0.0000123 
"  .  .0.0000280 

Platinum  .... 
Silver  
Zinc... 

o 
o 
o 

IOO 
IOO 
IOO 

"  ..0.0000089 
"  ..0.0000194 
"  ..0.0000230 

(Anthony  &>  Brackett.) 


Exploder,  Electric  Mine A  small 

magneto-electric  machine  used  to  produce  the 
currents  of  high  electromotive  force  employed 
in  the  direct  firing  of  blasts. 

Exploder,  Electro-Magnetic A 

small  magneto-electric  machine  used  to  pro- 
duce the  currents  of  high  electromotive  force 
employed  in  the  direct  firing  of  blasts. 

Explorer,  Electric An  apparatus 

operated  by  means  of  induced  currents,  and 
employed  for  the  purpose  of  locating  bullets 
or  other  foreign  metallic  substances  in  the 
human  body.  (See  Balance,  Induction, 
Hughes') 

Explorer,  Magnetic  —  —A  small,  flat 
coil  of  insulated  wire,  used,  in  connection  with 
the  circuit  of  a  telephone,  to  determine  the 
position  and  extent  of  the  magnetic  leakage 
of  a  dynamo-electric  machine  or  other  similar 
apparatus.  (See  Magnetophone) 

Explosive  Distance. — (See  Distance,  Ex- 
plosive.) 

Extension  Call-Bell.— (See  Sell,  Exten- 
sion Call.) 

External  Circuit— (See  Circuit,  Exter- 
nal.) 

External  Secondary  Resistance.  —  (See 
Resistance,  External  Secondary.) 

Extra  Currents.— (See  Currents,  Extra) 

Extraordinary  Resistance. — (See  Resist- 
ance, Extraordinary) 

Extra-Polar  Region.— (See  Region,  Ex- 
tra-Polar) 

Eye,  Electro-Magnetic A  term  pro- 
posed for  a  certain  form  of  spark-micrometer 
employed  by  Hertz  in  his  experiment  on  elec- 
tro-magnetic radiation. 

This  apparatus  has  received  the  above  name 
because  it  enables  the  observer  to  see  or  localize 
an  electromagnetic  disturbance. 

The  particular  spark -micrometer  that  has  re- 
ceived the  name  of  the  electro-magnetic  eye  had 
the  form  of  a  circle  35  centimetres  in  radius,  and 
was  formed  of  a  copper  wire  2  millimetres  in  di- 
ameter. Like  all  spark-micrometer  circuits,  it 
had  its  terminals  separated  by  a  small  air-space. 

Eye,  Selenium An  artificial  eye  in 


Fac.] 

which  a  selenium  resistance  takes  the  place 
of  the  retina  and  two  slides  the  place  of  the 
eyelids. 

The  selenium  resistance  is  placed  in  the  circuit 
of  a  battery  and  a  galvanometer.  When  the 
slides  L,  L,  Fig.  244,  are  shut,  the  galvanometer 
deflection  is  less  than  when  they  are  open. 

The  opening  of  the  aperture  between  the  slides 
L,  L,  may  be  automatically  accomplished  by  the 
action  of  the  light  itself,  by  moving  them  by  an 
electro-magnet  placed  in  the  circuit  of  a  local  bat- 
tery, and  a  selenium  resistance  may  be  so  arranged 
that  when  light  falls  on  it  the  slides  L,  L,  are 
moved  together,  and  when  the  amount  of  such 
aght  is  small  they  are  moved  apart,  by  the  action 


224 


[Far. 


of  a  spring.     In  this  way  there  is  obtained   a 
device  roughly  resembling  the  dilatation  or  con- 


traction of  the  pupil  of  the  eye  from  the  action  of 
light  on  the  iris.     (See  Photometer,  Selenium.) 


Fac-Simile  Telegraphy,  or  Panteleg- 
raphy. — (See  Telegraphy,  Fac-Simile) 

Fahrenheit's  Thermometer  Scale. — (See 
Scale,  Thermometer,  Fahrenheit's?) 

Fall  of  Potential.— (See  Potential,  Fall 
of.) 

False  Magnetic  Pole (See  Pole, 

Magnetic,  False.) 

False  Resistance. — (See  Resistance, 
False.) 

False  Zero.— (See  Zero,  False.) 

Fan  Guard.— (See  Guard,  Fan.) 

Farad. — The  practical  unit  of  electric 
capacity. 

Such  a  capacity  of  a  conductor  or  condenser 
that  one  coulomb  of  electricity  is  required  to 
produce  in  the  conductor  or  condenser  a 
difference  of  potential  of  one  volt. 

As  in  gases,  a  quart  vessel  will  hold  a  quart  of 
gas  under  unit  pressure  of  one  atmosphere,  so,  in 
electricity,  a  conductor  or  condenser,  whose  capa- 
city is  one  farad,  will  hold  a  quantity  of  electricity 
equal  to  one  coulomb  when  under  an  electromotive 
force  of  one  volt. 

It  may  cause  some  perplexity  to  the  student  to 
understand  why  there  should  be  in  electricity  one 
unit  of  capacity  to  represent  the  size  of  the  vessel 
or  conductor,  and  another  to  represent  the 
amount  or  quantity  of  electricity  required  to  fill 


such  vessel.  But,  like  a  gas,  electricity  acts,  in 
effect,  as  if  it  were  very  compressible,  so  that  the 
quantity  required  to  fill  any  condenser  will  de- 

P'          N 


Fif.  245.  Elevation  of  Standardized  Condenser. 
pend  on  the  electromotive  force  under  which  it  is 
put  into  the  conductor  or  condenser. 

For    purposes  of  measurement,  capacities  of 
conductors  are  compared  with  those  of  condensers 


Fig.  24.6.    Plan  of  Standardized  Condenser. 

whose  capacities  are  known   in  microfarads,  or 
fractions    thereof.      The     microfarad,     or     tke 

of  a  farad,  is  used  because  of  the  very 

1,000,000 

great  size  of  a  farad. 


far,] 


[Fan. 


Fig.  245  shows  an  elevation,  and  Fig.  246  a 
plan  of  the  form  often  given  to  a  standardized 
condenser  or  microfarad.  The  condenser  is 
charged  by  connecting  the  terminals  of  the  elec- 
tric source  to  the  binding  posts  N  and  N.  It  is 
discharged  by  means  of  the  plug  key  P',  that 
connects  the  brass  pieces  A  and  B,  when  pushed 
firmly  into  the  conical  space  between  them. 

The  condenser  is  made  by  placing  sheets  of  tin 
foil  between  sheets  of  oiled  silk  or  mica  in  the 
box  and  connecting  the  alternate  sheets  to  one  of 
the  brass  pieces  B,  and  the  other  set  to  the  brass 
piece  A,  as  will  be  better  understood  from  an 
inspection  of  Fig.  247. 

5 


Fig.  247    Met kod  of  Construction  of  a  Condenser. 

Condensers  are  generally  made  of  the  capacity 
of  the  \  of  a  microfarad.  Sometimes,  however, 
they  are  made  so  that  either  all  or  part  of  the 
condenser  may  be  employed,  by  the  insertion  of 
the  different  plug  keys. 

The  form  of  condenser  shown  in  Fig.  248  is 


Fig.  248.  Standard  Condenser 

capable  of  ready  division  into  five  separate  val- 
ues, viz.:   .05,  .05,  .2,  .2  and  .5  microfarad. 

Farad,  Micro The  millionth  part 

of  a  farad.     (See  Farad.} 

Faraday  Effect.— (See  Effect,  Faraday) 
Faraday's  Cube.— (See  Cube,  Faraday's) 


Faraday's  Dark  Space.— (See  Space, 
Dark,  Faraday's) 

Faraday's  Net— (See  Net.  Faraday's) 

Faradic    Apparatus,    Magneto-Electric 

(See  Apparatus,  Faradic  Mag- 
neto-Electric) 

Faradic  Brush.— (See   Brush,  Faradic) 

Faradic  Current. — (See  Current  Fara- 
dic) 

Faradic  Excitation.— (See  Excitation, 
Faradic) 

Faradic     Induction     Apparatus.— (See 

Apparatus.  Faradic  Induction) 

Faradic  Irritability.— (See  Irritability, 
Faradic) 

Faradic  Machine.— (See  Machine,  Fara- 
dic) 

Faradization. — In  electro-therapeutics,  the 
effects  produced  on  the  nerves  or  muscles 
by  the  use  of  a  faradic  current,  in  order  to 
distinguish  such  effects  from  galvanization 
or  those  produced  by  a  voltaic  current.  (See 
Galvanization) 

Faradization,  General A  method 

of  applying  the  faradic  current  similar  to 
that  employed  in  general  galvanization. 
(See  Galvanization,  General) 

Faradization,  Local A  method  of 

applying  the  faradic  current  in  general  simi- 
lar to  that  employed  in  local  galvanization. 
(See  Galvanization,  Local) 

Fault. — Any  failure  in  the  proper  working 
of  a  circuit  due  to  ground  contacts,  cross- 
contacts  or  disconnections.  (See  Contacts. 
Cross) 

Faults  are  of  three  kinds,  viz.  : 

(i.)  Disconnections.     (See  Disconnection) 

(2.)  Earths.     (See  Earth) 

(3.)  Contacts.     (See  Contacts) 

Various  methods  are  employed  for  detecting 
and  localizing  faults,  for  the  explanation  of 
which  reference  should  be  had  to  standard  elec- 
trical works  on  testing  or  measurements. 

Fault,  Ironwork,  of  Dynamo A 

ground  or  connection  between  the  current  of 
a  dynamo  and  any  part  of  its  ironwork. 


Fan.] 


[Fie. 


If  the  dynamo  is  in  good  connection  with  the 
ground,  as  is  frequently  the  case  in  marine  plants, 
this  fault  is  the  same  as  a  ground. 

Faults,  Localization  of Determin- 
ing the  position  of  a  fault  on  a  telegraph  line 
or  cable  by  calculations  based  on  the  fall  in 
the  potential  of  the  line  measured  at  different 
points,  or  by  loss  of  charge,  etc. 

For  details,  see  standard  works  on  electrical 
measurements. 

Feed,  Clockwork,  for  Arc  Lamps 

An  arrangement  of  clockwork  for  obtaining 
a  uniform  feed  motion  of  one  or  both  elec- 
trodes of  an  arc  lamp. 

The  clockwork  is  automatically  thrown  into  or 
out  of  action  by  an  electro-magnet,  usually  placed 
in  a  shunt  circuit  around  the  carbons. 

Feed,  To To  supply  with  an  electric 

current,  as  by  a  dynamo  or  other  source. 

Feeder. — One  of  the  conducting  wires  or 
channels  through  which  the  current  is  dis- 
tributed to  the  main  conductors. 

Feeder,  Standard  or   Main —The 

main  feeder  to  which  the  standard  pressure 
indicator  is  connected,  and  whose  pressure 
controls  the  pressure  at  the  ends  of  all  the 
other  feeders. 

The  term  pressure  in  the  above  definition  is 
used  in  the  sense  of  electromotive  force  or  differ- 
ence  of  potential. 

Feeder-Wires.— (See  Wires,  Feeder) 
Feeders. — In  a  system  of  distribution  by 
constant  potential,  as  in  incandescent  elec- 
tric lighting,  the  conducting  wires  extend- 
ing between  the  bus-wires  or  bars,  and  the 
junction  boxes. 

A  feeder  differs  from  a  main  in  that  a  main 
consists  of  a  conductor  that  may  be  tapped  at  any 
point  to  supply  a  customer,  while  a  feeder  leads 
direct  from  the  dynamo  or  other  source  to  a  main 
and  is  not  tapped  at  any  point. 

Feeders,    Negative The    feeders 

that  are  connected  with  the  negative  terminal 
of  the  dynamo.  (See  Feeders?) 

Feeders,  Positive The  feeders  that 

are  connected  with  the  positive  terminal  of 
the  dynamo.  (See  Feeders?) 


Feeding  Device  of  Electric  Arc  Lamp.— 

(See  Device,  Feeding,  of   an    Arc  Lamp. 
Feed,  Clockwork,  for  Arc-Lamps?) 
Feeding-Wire.— (See  Wire,  Feeding) 

Feet,  Ampere The  product  of  the 

current  in  amperes   by  the  distance  in  feet 
through  which  that  current  passes. 

It  has  been  suggested  that  the  term  ampere- 
feet  should  be  employed  in  expressing  the  strength 
of  electro-magnetism  in  the  field  magnets  of 
dynamo-electro  machines  or  other  similar  ap- 
paratus. 

Ferranti  Effect— (See  Effect,  Ferranti) 
Ferro-Magnetic    Substance. — (See    Sub- 
stance, Ferro-Magnetic) 

Fibre,  Quartz A  fibre  suitable  for 

suspending  galvanometer  needles,  etc.,  made 
of  quartz. 

The  quartz  fibre  is  obtained  by  fusing  quartz  and 
drawing  out  the  fused  material  as  a  fine  thread, 
in  a  manner  similar  to  the  production  of  glass 
fibres.  Quartz  fibres  possess  marked  advantage 
over  silk  fibres,  in  that  they  are  5.4  times  stronger 
for  equal  diameters,  and  especially,  in  that  they 
return  to  the  zero  point,  after  very  considerable 
deflections. 

Quartz  fibres  are  readily  obtained  by  fusing 
quartz  pebbles  together  in  the  voltaic  arc,  and 
drawing  them  apart  with  a  rapid,  but  steady,  uni- 
form motion. 

Fibre  Suspension. — (See  Suspension, 
Fibre) 

Fibre,  Vulcanized A  variety  of  in- 
sulating material  suitable  for  purposes  not 
requiring  the  highest  insulation. 

Vulcanized  fibre  is,  however,  seriously  affected 
by  long  exposure  to  moisture. 

Fibrone. — An  insulating  substance. 
Field,  Air  —      — That  portion  of  a  mag- 
netic field  in  which  the  lines  of  force   pass 
through  air  only. 

Field,  Alternating An  electrostatic 

or  magnetic  field  the  positive  direction  of  the 
lines  of  force  in  which  is  alternately  reversed 
or  changed  in  direction. 

Field,  Alternating  Electrostatic  — 
An  electrostatic  field,  the  potential  of  which 
is  rapidly  alternating. 


Fie.] 


227 


[Fie. 


An  alternating  electrostatic  field  is,  according 
to  Tesla's  experiments,  produced  in  the  neighbor, 
hood  of  the  terminals  of  the  secondary  of  an  in- 
duction coil,  through  whose  primary,  alternations 
of  high  frequency  are  passing. 

Field,  Alternating  Magnetic.— A  mag- 
netic field  the  direction  of  whose  lines  of 
force  is  alternately  reversed. 

Field,  Density  of —  —The  number  of 
lines  of  force  that  pass  through  any  field,  per 
unit  of  area  of  cross-section. 

Field,  Electric A  term  sometimes 

used  in  place  of  an  electrostatic  field.  (See 
Field,  Electrostatic?) 

Field,  Electro-Magnetic The  space 

traversed  by  the  lines  of  magnetic  force  pro- 
duced by  an  electro-magnet.  (See  Field, 
Magnetic?) 

Field,  Electrostatic The  region  of 

electrostatic  influence  surrounding  a  charged 
body. 

Electrostatic  attractions  or  repulsions  take 
place  along  certain  lines  called  lines  of  electro- 
static force.  These  lines  of  force  produce  a  field 
called  an  electrostatic  field.  Electric  level  or 
potential  is  measured  along  these  lines,  just  as 
gravitation  levels  are  measured  with  a  plumb  line 
along  the  lines  of  gravitation  force.  (See  Poten- 
tial, Electric.) 

Work  is  done  when  a  body  is  moved  along  the 
lines  of  electrostatic  force  in  a  direction  from  an 
oppositely  charged  body,  or  towards  a  similarly 
charged  body,  just  as  work  is  done  against 
gravity  when  a  body  is  moved  along  the  lines  of 
gravitation  force,  away  from  the  earth's  centre, 
or  vertically  upwards. 

Field,  Exciter  of In  a  separately 

excited  dynamo-electric  machine,  the  dyna- 
mo-electric machine,  voltaic  battery,  or  other 
electric  source  employed  to  produce  the  field 
of  the  field  magnets.  (See  Machine,  Dyna- 
mo-Electric^) 

Field,  Intensity  of The  strength 

of  a  field  as  measured  by  the  number  of  lines 
of  force  that  pass  through  it  per  unit  of  area 
of  cross-section.  (See  Field,  Electrostatic. 
Field,  Magnetic?) 

Field,     Magnetic The    region    of 


magnetic  influence  surrounding  the  poles  of  a 
magnet. 

A  space  or  region  traversed  by  lines  of 
magnetic  force. 

A  place  where  a  magnetic  needle,  if  free 
to  move,  will  take  up  a  definite  position,  under 
the  influence  of  the  lines  of  magnetic  force. 

Unit  strength  of  magnetic  field  is  the  field 
which  would  be  produced  by  a  magnetic  pole  of 
unit  strength  at  unit  distance. 

Magnetic  attractions  and  repulsions  are  assumed 
to  take  place  along  certain  lines  called  lines  of 
magnetic  force.  The  directions  of  these  lines  in 
any  plane  of  a  magnetic  field  may  be  shown  by 
sprinkling  iron  filings  over  a  sheet  of  paper  held 
in  a  horizontal  position  to  a  magnet  pole  inclined 


*Fig.  249.    Magnetic  Field. 

to  the  paper  in  the  desired  plane  and  then  gently 
tapping  the  paper. 

The  groupings  of  iron  filings  so  obtained  are 
sometimes  called  magnetic  figures. 

The  directions  of  the  lines  of  force  thus  shown 
will  appear  from  an  inspection  of  Fig.  249,  taken 
in  a  plane  joining  the  two  poles  of  a  straight  bar 
magnet,  and  Fig.  250,  taken  in  a  plane  at  right 
angles  to  the  north  pole  of  a  straight  bar  magnet. 

In  Fig.  249,  the  repulsion  of  the  lines  of  force 
at  either  pole  is  shown  by  the  radiation  of  the 
chains  ot  magnetized  iron  particles.  The  mutual 
attraction  of  unlike  polarities  is  shown  by  the 
curved  lines. 

In  Fig.  250,  the  repulsion  of  the  similarly  mag- 
netized chains  is  clearly  shown. 

Lines  of  magnetic  force  are  assumed  to  pass 
out  from  the  north,  pole  and  back  again  into  the 
magnet  at  its  south  pole.  This  assumed  direction 


Fie.] 

is  called  the  direction  of  the  lines  of  magnetic 
force. 

Faraday  expressed  his  conception  of  lines  of 
magnetic  force  as  follows: 

"  Every  line  of  force  must  therefore  be  consid- 
ered as  a  closed  circuit,  passing,  in  some  part  of 
its  course,  through  a  magnet  and  having  an  equal 
amount  of  force  in  every  part  of  its  course.  There 


Fig.  230.    Magnetic  Field. 

exist  lines  of  force  within  the  magnet  of  the  same 
nature  as  those  without.  What  is  more,  they  are 
exactly  equal  in  amount  to  those  without.  They 
have  a  relation  in  direction  to  those  without'  and 
are,  in  fact,  continuations  of  them." 

When  a  conductor,  such  as  a  wire  through 
which  a  powerful  current  of  electricity  is  flowing, 
is  dipped  in  a  mass  of  iron  filings,  a  chain  of  iron 
filings  is  formed,  the  north  end  of  which  is  urged 
around  the  conductor  in  one  direction  and  the 
south  end  in  the  opposite  direction,  so  that  the 
movable  chain  of  filings  surrounds  or  grips  the 
conductor  in  concentric  rings  or  circles. 

The  density  of  a  magnetic  field  is  directly  pro- 
portional to  the  number  of  lines  of  force  per  unit 
of  area  of  cross-section. 

A  single  line  of  force,  or  a  unit  line  of  force,  is 
»uch  an  intensity  of  field  as  exists  in  each  square 
centimetre  of  cross-section  of  a  unit  magnetic 
field. 

A  magnetic  field  is  uniform,  or  possesses  uni- 
form intensity,  when  it  possesses  the  same  num- 
ber of  lines  of  force  per  square  centimetre  of  area 
of  cross-section. 

Field,  Magnetic,  Alternating The 

magnetic  field  produced  by  means  of  an 
alternating  current. 


Field,  Magnetic,  Dissymmetrical 

A  field  whose  lines  of  force  are  not  symmet- 
rically distributed  in  adjacent  halves. 

Field,  Magnetic,   Expanding  of — 

An  increase  in  the  length  of  the  lines  of  mag- 
netic force  in  any  field,  or  an  increase  in  the 
length  of  their  magnetic  circuit. 

Field,  Magnetic,  of  an  Electric  Current 
The  magnetic  field  surrounding  a  cir- 


Fig.  251.     Field  of  Current. 

cuit  through  which  an  electric  current  is  flow- 
ing. 

An  electric  current  produces  a  magnetic  field. 
This  was  discovered  by  Oersted 
in  1819,  and  may  be  shown  by 
sprinkling  iron  filings  on  a  sheet 
of  paper,  placed  on  the  wire 
conductor  conveying  the  cur- 
rent, at  right  angles  to  the  direc- 
tion in  which  the  current  is  pass- 
ing. Here  the  lines  of  force 
appear  as  concentric  circles,  ex- 
tending around  the  conductor, 
as  shown  in  Fig.  251.  Their 
direction,  as  regards  the  length 
of  the  conductor,  is  shown  in 
Fig.  252.  The  electric  current 
sets  up  these  magnetic  whirls 
around  the  conductor  on  its 
passage  through  it. 

The  direction  of  the  lines  of 
magnetic  force  produced  by  an      tion  of  Lines  oj 
electric  current,  and  hence  its      Force, 
magnetic  polarity,  depends  on  the  direction  in 
which  the  electric  current  flows.     This  directi^-i 


Fie. 


229 


[Fie. 


may  be  remembered  as  follows:  If  the  current 
flows  towards  the  observer,  the  directions  of  the 
lines  of  magnetic  force  is  opposite  to  that  of  the 
kands  of  a  watch,  as  shown  in  Fig.  253. 


Fig  233.    Direction  of  Lines  of  Force 

It  is  from  the  direction  of  the  lines  of  magnetic 
force  that  the  polanty  of  a  helix  carrying  a  cur- 
rent is  deduced.  (See  Solenoid,  Magnetic.  Mag. 
net,  Electro, ) 

A  magnetic  field  possesses  the  following  prop- 
erties, viz.: 

(I.)  All  magnetizable  bodies  are  magnetized 
when  brought  into  a  magnetic  field.  (See  Induc- 
tion, Magnetic.) 

(2.)  Conductors  moved  through  a  magnetic 
field  so  as  to  cut  its  lines  of  force  have  differences 
of  potential  generated  in  them  at  different  points, 
and  if  these  points  be  connected  by  a  conductor, 
an  electric  current  is  produced.  (See  Induction, 
Electro-Magnetic. ) 

Field,  Magnetic,  Pulsatory A  field, 

the  strength  of  which  pulsates  in  such  manner 
as  to  produce  oscillatory  currents  by  induc- 
tion. 

Field,  Magnetic,  Reversing That 

portion  of  the  field  of  a  dynamo-electric  ma- 
chine, produced  by  the  field-magnet  coils,  in 
which  the  currents  flowing  in  the  armature 
coils  are  stopped  or  reversed  after  the  coil  has 
passed  its  theoretical  position  of  neutrality. 

Sparkless  commutation  is  obtained  by  placing 
the  brushes  on  the  commutator  so  as  to  corre- 
spond with  the  reversing  field. 

Field,  Magnetic,  Shifting A  term 

proposed  by  Professor  Elihu  Thomson  to  ex- 
press a  field  of  magnetic  lines  of  changing 
position  with  respect  to  the  axis  of  the  pole 
from  which  they  emanate. 

*  .  A  shifting  magnetic  field  is  especially  a  phe- 
nomenon of  a  rapidly  alternating  magnetic  field 


occurring  in  a  substance  like  hardened  steel  in 
which  the  coercive  force  is  lairly  nigh.  It,  for 
example,  a  single  magnet  pole  of  an  electro- 
magnet, whose  coils  are  traversed  by  a  rapidly 
alternating  current  of  electricity,  is  placed  near  one 
end  of  a  steel  file,  the  changing  polarity  developed 
thereby  moves  or  shifts  trom  the  point  directly 
over  the  pole  towards  the  distant  end.  The 
presence  of  this  shifting  field  can  be  shown  by  the 
rotation  of  discs  of  copper  suitably  inclined  to  the  ' 
end  of  the  file.  In  a  similar  manner  a  prismatic 
mass  of  steel,  placed  with  one  of  its  flat  sides 
on  the  pole  of  a  rapidly  alternating  magnetic 
field,  will  have  a  magnetic  field  developed  in  it, 
which  will  move  or  shift  from  the  flat  base 
towards  the  upper  edge.  Movable  masses  of  good 
conducting  metal,  such  as  copper,  will  be  set  in 
rotation  in  a  direction  such  as  would  be  caused 
by  an  escape  of  gas  therefrom. 

The  shifting  magnetic  field  travels  from  the 
upper  portions  of  the  prism  just  as  a  stream  of 
escaping  gaseous  substance  would. 

Field,  Magnetic,  Spreading-Out A 

term  sometimes  used  to  represent  an  expand- 
ing magnetic  field.  (See  Field,  Magnetic, 
Expanding  of.) 

Field,  Magnetic,  Stray That  por- 
tion of  the  field  of  a  dynamo-electric  machine 
which  is  not  utilized  for  the  development  of 
differences  of  potential  in  the  armature,  be- 
cause its  lines  of  force  do  not  pass  through 
the  armature. 

Field,  Magnetic,  Strength  of  —     —The 

dynamic  force  acting  on  a  free  magnetic  pole, 
placed  in  a  magnetic  field. 

If  a  free  magnetic  pole  could  be  placed  in  a 
magnetic  field,  it  would  begin  to  move  towards 
the  opposite  pole  of  the  field,  under  its  magnetic 
attraction,  just  as  an  unsupported  body,  free  to 
move,  would  begin  to  fall  towards  the  earth. 
The  strength  of  a  magnetic  field  corresponds  to 
the  acceleration  of  the  force  of  gravity  in  the 
case  of  a  falling  body.  The  strength  of  the  mag- 
netic pole  corresponds  tto  the  mass  of  the  falling 
body.  The  force  impressed  m  the  case  of  the 
magnetic  field  is  equal  to  the  strength  of  the  pole 
multiplied  by  the  strength  of  the  field. 

Field,  Magnetic,  Symmetrical A 

field  whose  lines  of  force  are  symmetrically 
distributed  in  adjacent  halves. 


Fie.] 


[F1L 


Field,  Magnetic,  Uniform A  field 

traversed  by  the  same  number  of  lines  of 
magnetic  force  in  all  unit  portions  of  area  of 
cross-section.  (See  Field,  Magnetic^ 

Field,  Magnetic,  Waste A  term 

sometimes  employed  for  stray  field.  (See 
Field,  Magnetic,  Stray  ^ 

Field,  Rotating-Current A  mag- 
netic field  produced  by  means  of  a  rotating 
current.  (See  Current,  Rotating) 

Field,  Uniform  Density  of A  uni- 
form density  in  all  equal  areas  of  cross- 
section  of  field. 

Field,  Tortex-Ring The  field  of 

influence  possessed  by  a  vortex-ring. 

Professor  Dolbear  points  out  the  fact  that  the 
direction  of  the  rotation  of  a  fluid  constituting  a 
Tortex-ring  resembles  the  magnet  flux  in  a  mag- 
netic field,  and  shows,  from  the  action  of  such  rings 
on  one  another,  that  they  possess  a  true  field,  or 
atmosphere  of  influence  outside  their  actual 
bodies.  He  infers  that  such  rings  possess  true 
polarity,  since  the  motions  producing  them  have 
different  directions  on  opposite  sides  or  ends. 

Figure  of  Merit  of  Galvanometer. — (See 
Galvanometer,  Figure  of  Merit  of) 

Figures,  Breath Faint  figures  of 

condensed  vapor  produced  by  electrifying  a 
coin,  placing  it  momentarily  on  the  surface  of 
a  sheet  of  clean,  dry  glass,  and  then  breath- 
ing gently  on  the  spot  where  the  coin  was 
placed. 

The  moisture  collects  on  the  electrified  portions 
of  the  plate  and  lorms  a  iairly  distinct  image  ot 
the  coin. 

Figures,  Electric Figures  of  various 

shapes  produced  on  electrified  surfaces  by  the 
arrangement  of  dust  particles  or  vapor 
vesicles  under  the  influence  of  electric  charges. 

Electric  figures  are  ot  two  varieties,  viz. : 

(I.)  Dust  figures. 

(2.)  Breath  figures. 

Figures,    Lichtenberg's     Dust  - 

Figures  produced  by  writing  on  a  sheet  of  shel- 
lac with  the  knob  of  a  charged  Leyden  jar  and 
then  sprinkling  over  the  sheet  dried  and 
powdered  sulphur  and  red  lead,  which  have 


been  previously  mixed  together,  and  are  so 
rendered,  respectively  negative  and  positive. 

The  red  lead  collects  on  the  negative  parts  of 
the  shellac  surface,  and  the  sulphur  on  the  posi- 
tive parts,  in  curious  figures,  known  as  Lichten- 
berg's Dust  Figures,  one  of  which  is  shown  in 
Fig.  254. 


Fig'  254..    Lichtenberg's  Dust  Figures. 

These  figures  show  very  clearly  that  an  electric 
charge  tends  to  creep  irregularly  over  the  surface 
of  an  insulating  substance* 

Figures,  Magnetic A  name  some- 
times applied  to  the  groupings  of  iron  filings 
on  a  sheet  of  paper  so  held  in  a  magnetic  field 
as  to  be  grouped  or  arranged  under  the  in- 
fluence of  the  lines  of  force  of  the  same.  (See 
Field,  Magnetic.) 

Filament. — A  slender  thread  or  fibre. 
The  term  is  applied  generally  to  threads  or 
fibres  varying  considerably  in  diameter. 

Filament,  Current A  term  some- 
times employed  in  place  of  current  streamlet. 
(See  Streamlets  Current.) 

Filament,  Magnetic A  polarized 

line  or  chain  of  ultimate  magnetic  particles. 

This  is  sometimes  called  a  uniform  magnetic 
filament. 

A  bar-magnet  possesses  but  two  iree  poles. 
When  broken  ai  its  neutral  point  or  equator,  the 
bar  will  develop  iree  poles  at  the  broken  ends. 
This  is  explained  by  considering  the  magnet  to 
be  composed  of  a  number  of  separate  particles, 
separately  magnetized.  A  single  chain  or  fila- 
ment of  such  particles  is  called  a  magnetic 
filament.  (See  Magnet,  Neutral  Point  of.  Mag- 
netism, Hughes'  Theory  of.  Magnetism, 
Riving1  s  Theory  of.) 

Filament  of  Incandescent  Electric  Lamp, 


Fil.J 


231 


[Fir. 


— (See  Lamp,  Incandescent  Electric,  Fila- 
ment of.) 
Filament,  Uniform   Magnetic —A 

term  sometimes  applied  to  a  magnetic  fila- 
ment. (See  filament,  Magnetic.) 

Filaments,  Flashed Filaments  for 

an  incandescent  lamp,  that  have  been  sub- 
jected to  the  flashing  process.  (See  Carbons, 
Flashing  Process  for .) 

Filamentous  Armature  Core. — (See  Core, 
Armature,  Filamentous?) 
\  Film  Cut-Out— (See  Cut-Out,  Film.} 

Finder,  Induction  —  — A  term  some- 
times employed  for  a  magnetic  explorer. 

Finder,  Position,  Electric A  de- 
vice by  means  of  which  the  exact  position  of 
an  object  can  be  obtained. 

By  means  of  a  position-finder  a  gunner  can 
be  telephoned  or  otherwise  ordered  to  fire  at  ob- 
jects he  cannot  see,  and  yet  obtain  a  fair  degree 
of  accuracy. 

Finder,  Range,  Electric A  de- 
vice by  means  of  which  the  exact  distance  of 
an  enemy's  ship  or  other  target  can  be  readily 
determined. 

The  operation  of  an  electric  range-finder  is  based 
on  a  method  somewhat  similar  to  the  solving  of  a 
triangle  for  the  purpose  of  determining  distances. 
If  the  base  line  of  a  triangle  and  the  two  angles 
at  the  base  are  known,  the  other  two  sides  and 
the  included  angle  can  be  determined. 

In  the  range-finder,  the  resistance  of  a  German 
silver  wire  corresponds  to  the  graduated  arc  ot 
the  theodolite  used  to  measure  the  angles,  and  a 
rheostat,  as  a  receiving  instrument,  measures  the 
values  of  the  angles.  The  base  line  is  a  constant, 
so  that  the  receiving  instrument  is  marked  in 
yards  instead  of  angles.  To  use  the  range-finder, 
two  observers  watch  the  target  object  continu- 
ously through  a  telescope.  They  do  this  and 
nothing  else,  while  a  third  observer  watches  a 
galvanometer  and  so  alters  a  resistance,  by  moving 
a  contact  or  slide  key  along  a  resistance  wire,  as 
to  keep  the  needle  of  the  galvanometer  constantly 
at  zero.  The  exact  distance  being  thus  ascer- 
tained, the  gunner  can  make  the  proper  allowance 
in  firing. 

Finder,  Wire Any  form  of  galva- 
nometer used  to  locate  or  find  the  corre- 


sponding ends  of  different  wires  in  a  bunched 
cable. 

The  different  wires  in  a  cable  are  usually  tagged 
and  numbered  at  the  end  of  the  cable  and  at  the 
joints.  The  telephone  has  been  successfully  em- 
ployed as  a  wire  finder. 

Fire  Alarm  Annunciator. — (See  Annun- 
ciator, Fire  Alarm.) 

Fire  Alarm,  Automatic (See 

Alarm,  Fire  Automatic?) 

Fire  Alarm  Contact— (See  Contact,  Fire 
Alarm?) 

Fire  Alarm  Signal  Box.— (See  Box,  Fire 
Alarm  Signal.) 

Fire  Alarm  Telegraph  Box.— (See  Box, 
Fire  Alarm  Telegraph.) 

Fire  Ball.— (See  Sail,  Fire.) 

Fire  Cleansing.— (See  Cleansing,  Fire.) 

Fire   Extinguisher,    Electric A 

thermostat  or  mercury  contact,  which  auto- 
matically completes  a  circuit  and  turns  on  a 
water  supply  for  extinguishing  a  fire,  on  a 
certain  predetermined  increase  of  tempera- 
ture. 

Fire,  Hot,  St.  Elmo's A  term  pro- 
posed by  Tesla  for  a  form  of  powerful  brush 
discharge  between  the  secondary  terminals  of 
a  high  frequency  induction  coil.  (See  Dis- 
charge, Brush-and- Spray?) 

This  form  of  St.  Elmo's  fire  differs  from  the 
ordinary  form  in  being  hot.  Its  general  appear- 
ance is  shown  in  Fig.  255,  taken  from  Tesla. 


Fig.  253.    St.  Elmo's  Hot  Fire. 
Describing  its  production  he  says  :   '•  In  many  of 
these    experiments,   when  powerful  effects   are 
wanted  for  a  short  time,  it  is  advantageous  to  use 


Fir.] 


232 


[Flo. 


iron  cores  with  the  primaries.  In  such  case  a 
very  large  primary  coil  may  be  wound  and  placed 
side  by  side  with  the  secondary,  and,  the  nearest 
terminal  of  the  latter  being  connected  to  the 
primary,  a  laminated  iron  core  is  introduced 
through  the  primary  into  the  secondary  as  far  as 
the  streams  will  permit.  Under  these  conditions 
an  excessively  powerful  brush,  several  inches 
long,  which  may  be  appropriately  called  '  St. 
Elmo's  hot  fire, '  may  be  caused  to  appear  at  the 
other  terminal  of  the  secondary,  producing  strik- 
ing effects.  It  is  a  most  powerful  ozonizer  ;  so 
powerful  indeed,  that  only  a  few  minutes  are  suf- 
ficient to  fill  the  whole  room  with  the  smell  of 
ozone,  and  it  undoubtedly  possesses  the  quality  of 
exciting  chemical  affinities. " 

Fire,  St.  Elmo's Tongues  of  faintly 

luminous  fire  which  sometimes  appear  on  the 
pointed  ends  of  bodies  in  connection  with  the 
earth,  such  as  the  tops  of  church  steeples  or 
the  masts  of  ships. 

The  appearance  of  the  St.  Elmo's  fire  is  due  to 
brush  discharges  of  electricity. 

Fishes,  Electric A  term  applied  to 

various  fishes,  such  as  the  eel  and  the  ray, 
which  possess  the  ability  of  protecting  them- 
selves by  giving  electric  shocks  to  objects 
touching  them.  (See  Eel,  Electric!) 

Fishing  Box.— (See  Box,  Fishing) 

Fittings  or  Fixtures,  Electric  Light  — 

< —  The  sockets,  holders,  arms,  etc.,  required 
for  holding  or  supporting  incandescent  electric 
lamps. 

Fixed  Secondary.  —  (See  Secondary, 
Fixed.) 

Fixtures,  Telegraphic A  term  gen- 
erally limited  to  the  variously  shaped  supports 
provided  for  the  attachment  of  telegraphic 
wires. 

Fixtures,  Telegraphic  House-Top  — 
Telegraphic  fixtures  placed  on  the  roofs  of 
buildings  for  the  support  of  the  lines. 

Flaming  Discharge.  —  (See  Discharge, 
Flaming.) 

Flash,  Side A  sparking  or  lateral 

discharge  taking  place  from  the  sides  of  a 
conductor,  when  an  impulsive  rush  of  elec- 
tricity passes  through  it. 


The  phenomenon  of  siae  flashing  is  due  to  a 
lateral  discharge  which  takes  the  alternative  path, 
instead  of  a  path  of  much  smaller  obmic  re^ist- 
ance.  The  tendency  to  side  flash  results  from 
the  fact  that  the  metallic  circuit  possesses  induct- 
ance. (See  Path,  Alternative.  Discharge,  Lat- 
eral. Inductance. ) 

Flashed  Carbons.  —  (See  Carbons, 
Flashed.) 

Flashed  Filaments.  —  ( See  Filaments, 
Flashed) 

Flashes,  Auroral Sudden  variations 

in  the  intensity  of  the  auroral  light. 

Intermittent  flashes  of  auroral  light  that 
occur  during  the  prevalence  of  an  aurora. 
(See  Aurora  Borealis.) 

Flashing  of  Carbons,  Process  for  the 

— (See  Carbons,  Flashing  Process  for.) 

Flashing  of  Dynamo-Electric  Machine.— 

(See  Machine,  Dynamo-Electric,  Flashing 
of.) 
Flat  Cable.— (See  Cable,  Flat.) 

Flat  Duplex  Cable.— (See  Cable,  Flat 
Duplex.) 

Flat  Ring  Armature. — (See  Armature, 
Flat  Ring) 

Flats. — A  name  sometimes  applied  to  those 
parts  of  commutator  segments  the  surface  of 
which,  through  wear,  has  become  lower  than 
the  other  portions.  (See  Commutator) 

Fleming's    Gauss. — (See    Gauss,    Flem- 
ing's) 
Fleming's  Standard  Yoltaic  Cell.— (See 

Cell,  Voltaic,  Standard,  Fleming's) 
Flexible  Electric  Light  Pendant.— (See 

Pendant,  Flexible  Electric  Light) 
Flexible  Lead.— (See  Lead,  Flexible) 
Floating  Battery,   De    la   Rive's.— (See 

Battery  Floating,  De  la  Rives) 

Flow.— In     hydraulics,    the    quantity    of 

water  or  other  fluid  which  escapes  from  an 

orifice  in  a  containing  vessel,  or  through  a 

pipe,  in  a  given  time. 
Flow-Lines  of   Escaping    Fluid.  — Lines 

within  the  mass  of  a  fluid  in  motion,  drawn  at 


Flo.] 


[Fly. 


a.  number  of  points,  so  that  the  flow  at  any 
instant  is  tangential  at  such  points  to  the 
curved  path. 

Flow,  Magnetic  — The  magnetic 

flux.  (See  Flux,  Magnetic) 

Flow  of  Current,  Assumed  Direction  of 

— (See  Current,  Assumed  Direction 

of  Flow  of) 

Flow  of  Energy.— (See  Energy,  Flow  of?) 
Flow  of  Lines  of  Electrostatic  Force. — 

(See  Force,  Electrostatic,  Lines  of,  Assumed 
Flow  of) 

Flow  of  Magnetic  Induction. — (See  In- 
duction, Magnetic^  Flux  or  Flow  of) 

Fluid,  Depolarizing An  electro- 
lytic fluid  in  a  voltaic  cell  that  prevents  polari- 
zation. (See  Cell,  Voltaic,  Polarization  of) 

Fluid  Insulator.— (See  Insulator,  Fluid) 

Fluoresce.  —  To  become  self-luminous 
when  exposed  to  light. 

A  body  is  said  to  fluoresce  when  it  shines,  by 
means  of  the  light  it  produces.  In  this  respect  it 
differs  from  an  illumined  body,  which  shines  by 
reflected  light. 

Fluorescence. — A  property  possessed  by 
certain  solid  or  liquid  substances  of  becoming 
self-luminous  while  exposed  to  light. 

In  fluorescence  the  refrangibility  of  rays  of 
light  is  changed.  The  invisible  rays  beyond  the 
violet,  the  ultra-violet,  become  visible,  so  that 
the  light  is  transformed,  the  particles  absorbing 
one  wave  length  and  emitting  another.  (See  Incan- 
descence.} 

Canary  glass,  or  glass  colored  yellow  by  oxide 
•f  uranium,  or  a  solution  of  sulphate  of  quinine, 
possesses  fluorescent  properties.  The  path  of  a 
pencil  of  light  brought  to  a  focus  in  either  of  these 
substances,  or  a  beam  or  cone  of  light  passed 
through  them,  is  rendered  visible  by  the  particles 
lying  in  this  path  becoming  self-luminous.  The 
path  of  a  beam  of  light  entering  the  dusty  air  of 
a  darkened  chamber  is  visible  from  the  light  being 
diffused  or  scattered  in  all  directions  by  the  float- 
ing dust  particles. 

In  a  fluorescent  substance,  the  path  of  the  light 
is  also  rendered  visible  by  the  particles  which  lie 
in  its  path,  throwing  out  light  in  all  directions. 
There  is,  however,  this  difference,  that  in  the 


case  of  the  dust  particles  the  light  which  comes 
directly  from  the  beam  is  reflected  ;  while  in  the 
case  of  the  fluorescent  body  the  light  comes  from 
the  particles  themselves,  which  are  set  into  vibra- 
tion by  the  light  that  is  passing  through,  and  has 
been  absorbed  by  their  mass. 

Fluorescence  is,  therefore,  a  variety  of  phos- 
phorescence. (See  Phosphorescence.} 

Fluorescent.— Possessing  the  capability  of 
fluorescing. 

Fluorescing. — Exhibiting  the  property  of 
fluorescence. 

Flush  Box.— (See  Box,  Flush) 

FluTiograph. — An  apparatus  for  electri- 
cally registering  the  varying  height  of  water 
in  a  tidal  stream  or  in  the  ocean ;  or,  in  general, 
differences  of  water  levels. 

Flux,  Magnetic The  number  of 

lines  of  magnetic  force  that  pass  or  flow 
through  a  magnetic  circuit. 

The  total.number  of  lines  of  magnetic  force 
in  any  magnetic  field. 

The  magnetic  flux  is  also  called  the  magnetic 
flow. 

A  Committee  of  the  American  Institute  of 
Electrical  Engineers  on  "  Units  and  Standards  " 
proposed  the  following  as  the  definition  of  mag- 
netic flux. 

"  The  magnetic  flux  through  a  surface  bounded 
by  a  closed  curve  is  the  surface  integral  of  mag- 
netic induction  taken  over  the  bounded  surface, 
and  when  produced  by  a  current  is  also  equal  to 
the  line  integral  of  the  vector  potential  of  the  cur- 
rent taken  round  the  boundary." 

"  The  uniform  and  unit  time  rate  of  change  in 
flux  through  a  closed  electric  circuit  establishes 
unit  electromotive  force  in  the  circuit." 

Fluxes  range  in  present  practical  work  from 
100  to  100,000,000  C.  G.  S.  lines,  and  the  working 
units  would  perhaps  prefix  milli-  and  micro-. 

Flux  of  Magnetic  Induction.— (See  In- 
duction, Magnetic,  Flux  or  Flow  of) 

Flux  or  Flow  of  Magnetism. — (See  Mag- 
netism, Flux  or  Flow  of) 

Fly,  Electric A  wheel  or  other  de- 
vice driven  by  the  reaction  of  a  convective 
discharge.  (See  Flyer,  Electric.  Convec- 
tion, Electric.} 


Fly.] 


234 


[For. 


"Z 


Flyer,  Electric A  wheel  arranged 

so  as  to  be  set  into  rotation  by  the  escape  of 
convection  streams  from  its  points  when 
connected  with  a  charged  conductor. 

A  wheel  formed  of 
light  radial  armsP,  P,  P, 
etc.,  shaped  as  shown  in, 
Fig.  256,  and  capable  of 
rotation  on  the  vertical 
axis  A,  is  set  into  rapid 
rotation  when  connected 
with  the  prime  conduc- 
tor of  a  frictional  or  in- 
fluence machine,  through 
the  convection  streams  of 
air  particles,  which  are  Fig'  236-  Electric  Flyer. 
shot  off  from  the  points  or  extremities  of  the 
radial  arms.  The  wheel  is  driven  by  the  reac- 
tion of  these  streams  in  a  direction  opposite  to 
that  of  then- escape.  (See  Discharge,  Connective.) 

Focus. — A  point  in  front  or  back  of  a  lens 
or  mirror,  where  all  the  rays  of  light  meet  or 
seem  to  meet.  (See  Lens,  Achromatic.) 

Fog,  Electric A  dense  fog  which 

occurs  on  rare  occasions  when  there  is  an 
unusual  quantity  of  free  electricity  in  the 
atmosphere. 

During  these  electric  fogs  the  free  electricity  of 
the  atmosphere  changes  its  polarity  at  frequent 
intervals. 

Following  Horn  of  Pole  Pieces  of 
Dynamo-Electric  Machine.— (See  Horns, 
Following,  of  Pole  Pieces  of  a  Dynamo- 
JElectric  Machined) 

Foot-Candle.— (See  Candle,  Foot.) 

Foot-Pound. — A  unit  of  work.  (See 
Work.) 

The  amount  of  work  required  to  raise  I 
pound  vertically  through  a  distance  of  i  foot. 

The  same  amount  of  work,  viz.,  3  foot-pounds, 
is  done  by  raising  i  pound  through  a  vertical 
distance  of  3  feet,  or  3  pounds  through  a  verti- 
cal distance  of  I  foot. 

Apart  from  air  friction,  the  amount  of  work 
done  in  raising  I  pound  through  I  foot,  viz.,  I 
foot-pound,  is  the  same  whether  this  work  be 
done  in  one  second  or  in  one  day.  The  power , 
or  the  rate  of  doing  work,  is,  however,  very  dif- 
ferent in  the  two  cases.  (See  Power.) 

Force. — Any  cause  which  changes  or  tends 


to  change  the  condition  of  rest  or  motion  of 
a  body. 

Force,  Centrifugal  —  —The  force  that 
is  supposed  to  urge  a  rotating  body  directly 
away  from  the  centre  of  rotation. 

If  a  stone  be  tied  to  a  string  and  whirled  around, 
and  the  string  break,  the  stone  will  not  fly  off  di- 
rectly away  from  the  centre,  but  will  move  along 
the  tangent  to  the  point  where  it  was  when  the 
string  broke. 

The  centrifugal  force  in  reality  is  the  force 
which  is  represented  by  the  tension  to  which  the 
string  is  subjected  during  this  rotation. 

Force,  Coercitire A  name  some- 
times applied  to  coercive  force.  (See  Force, 
Coercive?) 

Force,  Coercive The  power  of  re- 
sisting magnetization  or  demagnetization. 

Coercive  force,  in  the  sense  of  resisting  demag- 
netization, is  sometimes  called  magnetic  reten- 
tivity. 

Hardened  steel  possesses  great  coercive  force; 
that  is,  it  is  magnetized  or  demagnetized  with 
difficulty. 

Soft  iron  possesses  very  feeble  coercive  force. 

It  is  on  account  of  the  feeble  coercive  force  of 
the  soft  iron  :ore  of  an  electro- magnet  that  its 
main  value  depends,  since  it  is  thereby  enabled  to 
rapidly  acquire  its  magnetization,  on  the  comple- 
tion of  a  circuit  through  its  coils,  and  to  rapidly 
lose  its  magnetization  on  the  opening  of  such 
circuit. 

Force,  Contact A  difference  of  elec- 
trostatic potential,  produced  by  the  contact  of 
dissimilar  metals. 

That  a  difference  of  potential  is  produced  by 
the  mere  contact  of  dissimilar  metals  is  now  gen- 
erally recognized.  Such  a  force  is  generally 
called  the  true  contact  force.  (See  Force,  True 
Contact. ) 

According  to  Lodge,  a  true  contact  force  has 
no  existence.  There  is  no  evidence,  he  thinks, 
of  a  peculiar  electromotive  force  at  the  point  of 
contact,  but  that  the  phenomena  are  due  simply 
to  the  fact  that  the  metals  are  immersed  in  air  or 
oxygen,  which  is  capable  of  combining  with  one 
of  them,  and  that,  therefore,  the  cause  of  the 
phenomena  is  the  greater  action,  for  instance,  of 
the  oxygen  of  the  air  on  the  zinc  than  on  the 
copper. 


For.] 


235 


[For. 


According  to  this  view,  the  voltaic  effect  is 
due  not  to  the  difference  of  potential  between 
the  zinc  and  copper,  but  to  the  difference  of  the 
action  of  the  air  or  moisture. 

Force  de  Cheral  or  Cheral  Vapeur.— 

The  French  term  for  horse-power. 

The  force  de  cheval  is  equal  to  75  kilogramme- 
metres  per  second,  or  32,549  foot-pounds  per 
minute. 

The  English  horse-power  is  equal  to  33,000 
foot-pounds  per  minute.  I  force  de  cheval  equals 
.98634 horse-power;  I  horse-power  equals  1.01385 
force  de  cheval. — (Hering.) 

Force,  Electric The  force  developed 

by  electricity. 

This  term  is  generally  limited  to  the  force  of 
attraction  or  repulsion  produced  by  an  electro- 
static charge. 

Force,  Electromotive The  force 

"starting  electricity  in  motion,  or  tending  to 
start  electricity  in  motion. 

The  force  which  moves  or  tends  to  move 
electricity. 

The  term  is  an  unfortunate  one.  Strictly  speak- 
ing, electromotive  force  is  not  a  force  at  all : 
at  least,  it  is  not  a  force  in  the  Newtonian  sense, 
where  force  is  only  that  which  acts  on  matter. 

The  term  electromotive  force  is  generally  writ- 
ten thus  :  E.  M.  F. 

The  unit  of  electromotive  force  is  the  volt. 

When  electric  induction  takes  place,  there 
results  a  change  in  the  distribution  of  the  thing 
called  electricity,  whereby  a  movement  occurs  that 
results  in  a  positive  and  a  negative  charge.  The 
cause  which  produces  this  movement  is  called  the 
electromotive  force. 

There  is  an  unfortunate  want  of  uniformity  at 
present  in  the  use  of  the  term  "electromotive 
force. ' '  By  some,  the  electromotive  force  is  re- 
garded as  something  which  causes  the  difference 
of  potential  ;  by  others  the  electromotive  force  is 
regarded  as  being  produced  by  the  difference  of 
potential;  and,  by  still  others,  electromotive  force 
is  regarded  as  the  entire  electric  moving  cause 
produced  by  any  source;  while  anything  less  than 
this  is  called  by  them  potential  difference. 

Those  who  regard  the  electromotive  force  as 
the  cause  which  produces  the  potential  difference 
look  on  the  electromotive  force  as  acting  within 


the  source  and  maintaining  a  potential  difference 
at  its  terminals. 

Silvanus  P.  Thompson  uses  the  term  electro- 
motive force  in  his  "Elementary  Lessons  in 
Electricity  and  Magnetism"  as  follows:  "The 
term  '  electromotive  force '  is  employed  to  denote 
that  which  moves  or  tends  to  move  electricity 
from  one  place  to  another.  For  brevity  we  some- 
times write  it  E.  M.  F.  In  this  particular  case  it 
is  obviously  the  result  of  difference  of  potential 
and  proportional  to  it  ;  just  as  in  water  pipes,  a 
difference  in  level  produces  a  pressure,  and  the 
pressure  produces  a  flow  as  soon  as  the  tap  is 
turned  on,  so  difference  of  potential  produces 
electromotive  force,  and  electromotive  force  sets 
up  a  current  as  soon  as  a  circuit  is  completed  for 
the  electricity  to  flow  through." 

Mascart  and  Joubert,  in  their  work  on  ' '  Elec- 
tricity and  Magnetism,"  Vol.  I.,  say:  "In  all 
cases  the  difference  of  potential  Vt  —  V2,  may  be 
considered  as  producing  the  motion  of  electrical 
masses  ;  it  is  often  called  the  electromotive  force. ' ' 

Maxwell,  in  his  "Elementary  Treatise  on  Elec- 
tricity," speaking  of  the  potential  differences 
which  may  be  shown  to  exist  at  the  terminals  of 
a  Daniell  voltaic  cell  when  on  open  circuit,  says  : 
' '  This  difference  of  potential  is  called  the  electro- 
motive force  of  a  Daniell  cell." 

Balfour  Stewart,  in  his  "  Electricity  and  Mag- 
netism," says :  •  "  This  difference  of  electric  level 
we  shall  call  E,  and,  indeed,  it  is  merely  a  manner 
of  expressing  the  cause  of  electromotive  force." 

Prof.  Fleming,  in  his  "Short  Lectures  to  Elec- 
trical Artisans,"  says:  "The  difference  of  elec- 
trical level  or  potential  must  be  caused  by  some 
electromotive  force  acting  in  the  conductor." 

Prof.  Anthony,  in  "A  Review  of  Modern 
Electrical  Theories,"  regards  the  potential  dif- 
ference as  due  to  electromotive  force.  He  says  : 
' '  Difference  of  potential  results  from  a  changed 
electrical  distribution,  an  electrical  strain,  and 
represents  the  tendency  to  return  to  the  state  of 
equilibrium.  Electromotive  force  is  the  some- 
thing from  without  that  produced  the  electric 
strain." 

Hering,  in  his  "Principles  of  Dynamo -Electric 
Machines,"  says  :  "  Difference  of  potential  is,  as 
the  name  implies,  the  difference  of  electrical  po- 
tential between  any  two  points  of  a  circuit,  and 
may,  therefore,  be  applied  to  that  at  the  poles  of 
a  machine,  battery  or  lamp,  or  at  the  ends  of 
leads,  or,  in  general,  to  any  two  points  in  a  cir- 
cuit. The  term  'electrom  >tive  torce,'  however, 


For.] 


236 


[For. 


applies  only  to  the  maximum  difference  ot  potential 
which  exists  in  the  circuit,  or,  in  other  words,  the 
total  generated  difference  of  potential." 

This  laht  paragraph  expresses  the  distinction 
between  the  two  terms  as  ordinarily  used  in  con- 
nection with  dynamos  and  batteries. 

Force,  Electromotive,  Absolute  Unit  of 
A  unit  of  electromotive  force  ex- 
pressed in  absolute  or  C.  G.  S.  units. 

The  one-hundred  millionth  part  of  a  volt, 
since  i  volt  equals  ios  C.  G.  S.  units  of  elec- 
tromotive force.  (See  Units,  Practical?) 

Force,  Electromotive,  Average  or  Mean 

The  sum  of  the  values  of  a  number  of 

separate  electromotive  forces  divided  by  their 
number. 

The  square  root  of  the  mean  square  of  the 
electromotive  force  of  an  alternating  or  vari- 
able current. 

When  a  wire  in  the  armature  of  a  dynamo- 
electric  machine  cuts  the  lines  of  magnetic  force 
in  the  field  of  the  machine,  the  electromotive 
force  produced  depends  on  the  number  of  lines 
of  force  cut  per  second.  This  will  vary  for  dif- 
ferent positions  of  the  coil.  The  mean  value  of 
the  varying  electromotive  forces  between  the 
brushes  is  the  average  electromotive  force. 

Force,  Electromotive,  Back—  —A 
term  sometimes  used  for  counter  electro- 
motive force. 

Counter  electromotive  force  is  the  preferable 
term.  (See  Force,  Electromotive,  Counter.) 

Force,    Electromotive,    Counter  — 
An  opposed  or  reverse  electromotive  force, 
which  tends  to  cause  a  current  in  the  oppo- 
site direction  to  that  actually  produced  by 
the  source. 

In  an  electric  motor,  an  electromotive  force 
contrary  to  that  produced  by  the  current 
which  drives  the  motor,  and  which  is  pro- 
portional to  the  velocity  attained  by  the 
motor. 

Counter  electromotive  force  acts  to  diminish 
the  current  in  the  same  manner  as  a  resistance 
would,  and  is  therefore  sometimes  called  spurious 
resistance  in  order  to  distinguish  it  from  an  ohmic 
or  true  resistance. 

Counter  electromotive  force  is  sometimes  ex- 
pressed in  ohms,  though  it  is  not  a  true  ohmic 
resistance.  (See  Resistance,  Spurious.) 


The  counter  electromotive  force  of  a  voltaic 
battery  is  due  to  the  polarization  of  the  cells. 
Since  this  force  is  due  to  the  current  in  the  cell,  it 
can  never  exceed  such  current  or  reverse  its  direc- 
tion. It  may,  however,  equal  it  and  thus  stop  its 
flow.  (See  Cell,  Voltaic,  Polarization  oj .) 

In  a  storage  cell,  the  charging  current  produces 
an  electromotive  force  counter  to  itself,  which,  as 
in  a  motor,  is  a  true  measure  of  the  energy  stored 
in  the  cell.  Economy  requires  that  the  electro- 
motive force  of  the  charging  current  should  be  as 
little  as  possible  greater  than  that  of  the  counter 
electromotive  force  of  the  cell  it  is  charging. 

In  a  voltaic  arc  a  counter  electromotive  force  is 
believed  to  be  set  up  by  polarization. 

Force,  Electromotive,  Counter,  of  Con- 

vective  Discharge Resistance  to  the 

passage  of  an  electric  discharge  through  a 
high  vacuum,  somewhat  of  the  nature  of  a 
counter  electromotive  force. 

The  resistance  to  the  passage  of  convective  dis- 
charges, therefore,  is  due  to  the  following  causes: 

(i.)  True  ohmic  resistance. 

(2.)  Counter  electromotive  force. 

Force,  Electromotive,  Counter,  of  Mutual 
Induction  —  — The  counter  electromotive 
force  produced  by  the  mutual  induction  of 
the  primary  and  secondary  circuits  on  each 
other. 

Force,  Electromotive,  Counter,  of  Self- 
induction  That  part  of  the  impressed 

electromotive  force  which  is  producing,  or 
which  tends  to  produce,  at  any  instant  a 
change  in  the  current  strength. 

Force,  Electromotive,  Counter,  of  Self- 
Induction  of  the  Primary  —  — A  counter 
electromotive  force  produced  in  the  primary 
circuit  of  an  induction  coil  by  the  action 
thereon  of  a  simple  periodic  electromotive 
force. 

The  counter  electromotive  force  produced 
in  the  primary  circuit  of  an  induction  coil  by 
the  application  of  a  simple  periodic  impressed 
electromotive  force  to  the  primary  circuit. 

Force,  Electromotive,  Counter,  of  Self- 
induction  of  the  Secondary  — A 

counter  electromotive  force  produced  in  ike 
secondary  by  the  periodic  variations  in  Ihe 
effective  electromotive  force  in  the  secondary. 


Tor.] 

Force,  ElectromotiYe,  Direct  — An 

electromotive  force  acting  in  the  same  direc- 
tion as  another  electromotive  force  already 
existing. 

The  term  direct  electromotive  force  is  em- 
ployed in  contradistinction  to  counter  electromo- 
tive force.  (See  Force,  Electromotive,  Counter. ) 

Force,  Electromotive,  Effective 

The  difference  between  the  direct  and  the 
counter  electromotive  force. 

Force,  Electromotive,  Effective,  of  Sec- 
ondary   — The  difference  between  the 

direct  and  the  counter  electromotive  force  in 
the  secondary  of  an  induction  coil. 

Force,  Electromotive,  Generated  by  Dy- 
namo-Electric Machine,  Method  of  Increas- 
ing   The  electromotive  force  of  a  dy- 
namo-electric machine  may  be  increased  in 
the  following  ways,  viz : 

(I.)  By  increasing  its  speed  of  rotation. 

(2.)  By  increasing  the  strength  of  the  magnetic 
field  in  which  the  armature  rotates. 

(3. )  By  increasing  the  size  of  the  field  through 
which  the  armature  passes  in  unit  time,  the  in- 
tensity remaining  the  same. 

(4.)  By  increasing  the  number  of  armature 
windings,  i.  e.,  by  making  successive  parts  of  the 
same  wire  pass  simultaneously  through  the  field. 

Force,  Electromotive,  Impressed 

The  electromotive  force  acting  on  any  cir- 
cuit to  produce  a  current  therein. 

The  impressed  electromotive  force  may  be  re- 
garded as  producing  two  parts,  viz. :  The  effective 
electromotive  force  and  the  counter  electromotive 
force. 

Force,  Electromotive,  Inductive  — 
A  term  sometimes  used  in  place  of  counter 
electromotive  force  of  self-induction. 

Force,  Electromotive,  Inverse An 

electromotive  force  which  acts  in  the  oppo- 
site direction  to  another  electromotive  force 
already  existing.  (See  Force,  Electromotive, 
Counter.} 

Force,  Electromotive,  Motor A 

term  proposed  by  F.  J.  Sprague  for  the  coun- 
ter electromotive  force  of  an  electric  motor. 
,(See  Force,  Electromotive,  Counter?) 

This  term  was  proposed  by  Sprague  as  express- 


237  [For. 

ing  the  necessity  for  the  existence  of  a  counter 
electromotive  force  in  an  electric  motor,  in  order 
to  permit  it  to  utilize  the  energy  of  the  electric 
current  which  drives  it 

Force,  Electromotive,  of  Induction 

— The  electromotive  force  developed  by  any 
inductive  action. 

In  a  coil  of  wire  undergoing  induction,  the 
value  of  the  induced  electromotive  force  does  not 
depend  in  any  manner  on  the  nature  of  the  ma- 
terial of  which  the  coil  is  composed . 

It  has  been  shown: 

(I.)  That  the  electromotive  force  of  induction  is 
independent  of  the  width,  thickness  or  material  of 
the  wire  windings.  —  (Faraday.) 

(2.)  That  it  is  dependent  on  the  form  of  the 
conductor,  and  the  character  of  the  change  it  ex- 
periences as  regards  the  magnetic  induction  which 
takes  place  through  it. 

Since  any  increase  in  the  strength  of  a  current 
flowing  through  a  coiled  circuit,  produces  a  coun- 
ter electromotive  force,  which  opposes  the  electro- 
motive force  producing  the  current,  it  is  clear 
that  the  impressed  electromotive  force  must  do 
work  against  this  counter  electromotive  force  all 
the  time  the  current  strength  is  increasing. 

The  movement  of  a  circuit  of  a  given  length 
through  a  given  field  with  a  given  velocity  pro- 
duces the  same  electromotive  force  whether  the 
circuit  be  formed  of  conducting  material  or  non- 
conducting material,  or  consists  of  an  electrolyte. 
Force,  Electromotive,  of  Secondary  or 

Storage  Cell,  Time-Fall  of A  gradual 

decrease  in  the  potential  difference  of  a  stor- 
age battery  observed  during  the  discharge  of 
the  same. 

When  a  secondary  or  storage  battery  is  first 
discharged,  a  slight  decrease  of  its  potential  dif- 
ference takes  place  and  a  potential  difference  of  a 
slightly  decreased  value  is  maintained  nearly  con- 
stant during  a  protracted  period  of  discharge. 
Force,  Electromotive,  of  Secondary  or 

Storage  Cell,  Time-Rise  of A  gradual 

increase  in  the  potential  difference  of  a 
secondary  or  storage  dell  observed  on  begin- 
ning the  discharge  after  a  prolonged  rest 

When  a  secondary  or  storage  cell  is  discharged 
and  then  given  a  prolonged  rest  by  opening  its 
circuit,  a  gradual  but  decided  rise  in  its  potential 
difference  is  observed  on  again  beginning  its  dis- 
charge. 


For.j 


238 


[For. 


Fore*,   Electromotive,  Photo An 

electromotive  force  produced  by  the  action  of 
light  on  selenium.  (See  Cell,  Selenium?) 

Force,  Electromotive,  Reacting  Induc- 
tive, of  the  Primary  Circuit The  back 

or  counter  electromotive  force  produced  in  the 
primary  circuit  by  the  current  set  up  by  in- 
duction in  the  secondary. 

Force,  Electromotive,  Secondary  Im- 
pressed   An  electromotive  force  pro- 
duced in  the  secondary  coil  or  circuit  by  a 
periodic  electromotive  force  impressed  on  the 
primary. 

Force,  Electromotive,  Simple-Periodic 

An  electromotive  force  which  varies 

in  such  manner  as  to  produce  a  simple 
periodic  current,  or  an  electromotive  force  the 
variations  of  which  can  be  correctly  repre- 
sented by  a  simple-periodic  curve. 

Force,  Electromotive,  Thermo An 

electromotive  force,  or  difference  of  potential, 
produced  by  differences  of  temperature 
acting  at  thermo-electric  junctions. 

Force,  Electromotive,  Transverse  — 

An  electromotive  force  excited  by  a  mag- 
netic field  in  a  substance  in  which  electric 
displacement  is  occurring. 

It  is  to  a  transverse  electromotive  force  that  the 
Hall  effect  is  due.  (See  Effect  %  Hall.} 

Force,  Electromotive,  Zigzag An 

electromotive  force,  the  curve  of  which  would 
have  the  general  form  of  a  zigzag. 

Force,  Electrostatic The  force  pro- 
ducing the  attractions  or  repulsions  of  charged 
bodies. 

Force,  Electrostatic,  Lines  of 

Lines  of  force  produced  in  the  neighborhood 
of  a  charged  body  by  the  presence  of  the 
charge. 

Lines  extending  in  the  direction  in  which 
the  force  of  electrostatic  attraction  or  repul- 
sion acts. 

An  insulated  charged  conductor  produces 
around  it  an  electrostatic  field,  in  a  manner  some- 
what similar  to  the  magnetic  field  produced  by 
a  magnet  or  an  electric  current.  (See  Field, 
Electrostatic.) 


Lines  of  electrostatic  force  pass  through  dielec- 
trics. Whether  the  force  acts  to  produce  electro- 
static induction,  by  means  of  a  polarization  of  the 
dielectric,  or  by  means  of  a  tension  set  up  in  the 
substance  of  the  dielectric,  is  not  known. 

Force,  Electrostatic,  Lines  of,  Assumed 

Flow  of A  mathematical  conception  in 

which  the  phenomena  of  electricity  are  com- 
pared with  the  similar  phenomena  of  heat. 

In  heat  no  flow  of  heat  occurs  over  isothermal 
surfaces,  or  surfaces  at  the  same  temperature. 
Between  different  isothermal  surfaces,  the  flow 
will  vary  with  the  power  of  heat  conduction.  In 
electricity,  no  flow  occurs  over  equipotential  sur- 
faces. Specific  inductive  capacity  corresponds  to 
heat  conductivity,  and  the  lines  of  force  to  the 
lines  of  heat  conduction.  (See  Capacity,  Specific 
Inductive. ) 

Force,  Lines  of,  Contraction  of — 

A  decrease  that  occurs  in  the  length  of  the 
circular  lines  of  force  that  surround  a  circuit 
through  which  an  electric  current  is  passing, 
while  the  current  is  decreasing  in  intensity  or 
strength. 

The  contraction  or  decrease  in  the  average 
diameter  of  the  circular  lines  of  force  of  an  elec- 
tric circuit  is  similar  to  the  expansion  or  growth 
of  lines  of  force,  excepting  that  the  movement  is 
one  of  decrease  in  diameter,  and  takes  place  in 
the  opposite  direction,  *'.  <?.,  towards  the  circuit, 
instead  of  away  from  it.  (See  Force,  Lines  of, 
Growth  or  Expansion  of.} 

Force,  Lines  of,  Cutting Passing  a 

conductor  through  lines  of  magnetic  force,  so 
as  to  cut  or  intersect  them. 

The  cutting  of  lines  of  magnetic  force  produces 
differences  of  potential.  This  is  true  whether  the 
conductor  moves  through  a  stationary  field  or 
whether  the  field  itself  moves  through  the 
stationary  conductor,  so  that  the  lines  of  force  and 
the  conductor  cut  one  another.  This  cutting  is 
mutual.  Each  line  of  force  cuts  and  is  cut  by  the 
circuit  Since  all  lines  of  force  form  closed-cir- 
cuits or  paths,  the  cutting  of  the  circuit  by  the 
lines  of  force,  or  the  reverse,  forms  a  link  or  chain, 
and  the  cutting  takes  place  at  the  moment  of 
linking  or  unlinking,  *'.  e.,  of  cutting. 

Force,  Lines  of,  Diffusion  of—  —The 
deflection  of  the  lines  of  magnetic  force  from 


For.  I 


239 


[For, 


their  ordinary   position,   between   the   poles 
that  produce  them. 

Force,  Lines  of,  Direction  of The 

direction  in  which  it  is  assumed  that  the  lines 
of  magnetic  force  pass. 

It  is  generally  agreed  to  consider  the  lines  of 
magnetic  force  as  coming  out  of  the  north  pole  of 
a  magnet  and  passing  into  its  south  pole,  as 
shown  in  Fig.  257. 


Fig.  237.     Direction  of  Lines  of  Force. 

This  is  sometimes  called  the  positive  direction 
of  the  lines  of  force  and  agrees  in  general  with  the 
direction  in  which  the  electric  current  is  assumed 
to  flow,  which  is  from  the  positive  to  the  nega- 
tive. That  is  to  say,  the  lines  of  magnetic  force 
are  assumed  to  flow  or  pass  out  of  the  north  pole 
and  into  the  south  pole  of  a  magnet.  Of  course 
there  is  no  direct  evidence  of  any  flow,  or  of  any 
particular  direction  characterizing  the  lines  of 
force.  (See  Field,  Magnetic.) 

The  lines  of  electrostatic  force  are  assumed  to 
pass  out  of  a  positively  charged  surface  and  into 
a  negatively  charged  surface. 

Force,  Lines  of,  Growth  or  Expansion  of 

The  increase  in  the  length  of  path 

through  which  lines  of  force  pass,  consequent 
on  an  increase  in  the  strength  of  the  mag- 
netization of  a  magnet,  or  on  an  increase  in 
the  strength  of  the  magnetizing  current. 

The  circular  lines  of  force  which  surround  a  con- 
ductor through  which  a  current  is  flowing,  may  be 
regarded  as  starting  from  the  surface  of  the  con- 
ductor and  growing  in  size  as  they  spread  out- 
wards, at  the  same  time  new  lines  of  force  being 
formed  in  their  places.  This  action  continues  while 
the  strength  of  the  current  is  increasing,  somewhat 
like  the  series  of  concentric  waves  which  are 
formed  on  the  surface  of  water,  when  a  stone  is 
dropped  into  it. 

In  their  growth  or  expansion  outwards  from 
the  conductor,  if  the  lines  of  force  cut  or  pass 
through  neighboring  conductors,  they  produce 


therein  differences  of  electric  ootential,  capable, 
on  being  connected  by  a  conductor,  of  produc- 
ing electric  currents. 

Force,  Lines  of,  Radiation  of —The 

passing  of  lines  of  force  out  of  the  north 
pole  of  a  magnet  or  solenoid. 

In  gross  matter  all  lines  of  magnetic  induction 
either  pass  through  magnetized  iron,  or  other 
paramagnetic  substance  which  surrounds  an 
electric  circuit.  Since  lines  of  force  pass  through 
a  vacuum,  the  ether  which  occupies  such  a  space 
must  also  be  regarded  as  permitting  the  passage 
of  lines  of  force. 

Force,  Loops  of A  term  sometimes 

employed  in  the  sense  of  lines  of  force.  (See 
Force,  Magnetic,  Lines  of.) 

The  term  "Lines  of  Force"  is  generally 
adopted  in  place  of  Faraday's  term  "Loops  of 
Force." 

Force,  Magnetic  —  —The  force  which 
causes  the  attractions  or  repulsions  of  mag- 
netic poles. 

Force,  Magnetic,  Line  of Arbitra- 
rily a  single  line  of  magnetic  force. 

Practically  the  lines  of  magnetic  force 
which  pass  through  a  unit  area  of  cross-sec- 
tion of  a  magnetic  field  of  unit  strength. 

Force,  Magnetic,  Lines  of Lines 

extending  in  the  direction  in  which  the  mag- 
netic force  acts. 

Lines  extending  in  the  direction  in  which 
the  force  of  magnetic  attraction  or  repulsion 
acts.  (See  Field,  Magnetic^ 

Faraday  regarded  the  lines  of  magnetic  force  as 
possessing  tension  along  one  direction.  Lines  of 
force  act  as  if  they  were  stretched  elastic  threads, 
possessed  of  the  property  of  lengthening  or  short- 
ening, and  of  repelling  one  another. 

Force,  Magnetic,  Lines  of,  Conducting 
Power  for A  term  employed  by  Fara- 
day for  magnetic  permeability.  (See  Perme- 
ability, Magnetic?) 

Force,    Magnetic,    Lines    of,    Positive 

Direction  of The  direction  in  which 

a  free  north-seeking  pole  would  move  along 
the  lines  of  force  when  placed  in  a  magnetic 
field. 


For.] 


240 


[For. 


Force,   Magnetic,  Telluric The 

earth's  magnetic  force. 

Force,  Magneto-Motive The  force 

that  moves  or  drives  the  lines  of  magnetic 
force  through  a  magnetic  circuit  against  the 
magnetic  resistance. 

A  Committee  of  the  American  Institute  of  Elec- 
trical Engineers  on  "Units  and  Standards"  pro- 
posed the  following  definition. 

The  magneto-motive  force  in  a  magnetic  cir- 
cuit is  47T  multiplied  by  the  flow  of  the  current 
linked  with  that  circuit.  The  magneto-motive 
force  between  two  points  connected  by  a  line  is 
the  line  integral  of  the  magnetic  force  along  that 
line.  Difference  of  magnetic  potential  constitutes 
magneto-motive  force. ' ' 

The  same  committee  gave  the  electro-magnetic 
dimensional  formula  L*  M*  T-I. 

The  flow  or  flux  of  lines  of  magnetic  force  in 
any  magnetic  circuit  is  proportional  to  the  mag- 
neto-motive force  divided  by  the  magnetic  resist- 
ance ;  or,  expressing  the  law  in  the  form  of  Ohm's 
law  for  current: 

Magnetic  Flux  =.  Magneto -Motive  Force 
Reluctance. 

In  this  formula  the  word  reluctance  is  used  in 
place  of  magnetic  resistance.  In  the  case  of  an 
electro-magnet,  the  magneto-motive  force  is  pro- 
portional to  the  strength  of  the  current  which  flows 
and  the  number  of  times  it  circulates ;  or,  more 
simply,  is  proportional  to  the  number  of  ampere 
turns.  (See  Turns,  Ampere.) 

Force,  Magneto-Motive,  Absolute  Unit  of 
— 4?r  multiplied  by  unit  current  of  one 
turn. 

Force,  Magneto-Motive,  Practical  Unit 

of A  value  of  the  magneto-motive  force 

equal  to  4*  multiplied  by  the  amperes  of  one 
turn,  or  to  iV  of  the  absolute  unit. 

Force,  Motor  Electromotive  —  -  — A 

term  proposed  by  F.  J.  Sprague  for  the 
counter  electromotive  force  of  a  motor. 

During  the  rotation  of  the  armature  of  an 
electric  motor  in  its  field,  a  counter  electromotive 
force  is  produced  in  its  coils,  which  acts  as  a 
spurious  resistance  and  opposes  the  flow  or  pass- 
age of  the  driving  current  through  its  coils.  As 
the  speed  of  the  motor  increases,  this  counter 
electromotive  force  increases  and  the  strength  of 
the  driving  current  decreases  until  a  certain 


Fig.  238.    Resolution  of 
Force. 


maximum  speed  is  reached,  when,  theoretically, 
no  current  passes. 

When  a  load  is  placed  on  the  electric  motor, 
the  speed,  and  consequently  the  counter  electro- 
motive force,  is  decreased  and  more  driving  cur- 
rent is  permitted  to  pass.  It  was  this  considera- 
tion, viz. :  that  the  load  automatically  regulates 
the  current  required  to  drive  the  motor,  that  led 
to  the  name  motor-electromotive  force.  (See 
Force,  Electromotive,  Counter.) 

Force,  Resolution  of The  separa- 
tion of  a  single  force,  acting  with  a  given 
intensity  in  a  given  direction,  into  a  number 
of  separate  forces  -, 
acting  in  some  other 
direction. 

Thus  the  force  D  B, 
Fig.  258,  acting  with 
the  intensity  and  in  the 
direction  shown,  may  c 
be  resolved  into  two 
component  forces,  D 
E  and  D  C,  acting  in  the  directions  and  having 
the  intensities  shown.  The  single  force  D  B,  has 
been  resolved  into  two  separate  forces  D  E  and 
CD. 

Force,  True  Contact A  force  or 

effect  entirely  distinct  from  the  voltaic  effect, 
which  exists  at  the  points  of  contact  be- 
tween two  dissimilar  metals. 

The  truth  of  the  existence  of  a  true  contact  force 
at  the  junction  of  dissimilar  metals  is  seen  by  the 
reversible  heat  effects  observed,  when  a  current 
of  electricity  is  passed  across  a  junction  of  two 
dissimilar  metals.  When  the  current  is  passed  in 
one  direction,  an  increase  of  temperature  is  pro- 
duced, but  when  passed  in  the  opposite  direction, 
a  decrease  of  temperature.  (See  Effect,  Peltier.) 

Hence  there  would  appear  to  be  a  force  existing 
at  the  junction,  helping  the  electricity  along  in 
one  direction,  but  opposing  it  in  the  opposite  di- 
rection. In  one  direction  the  electricity  does 
work  and  consumes  its  own  energy  in  so  doing. 
In  the  other  direction  it  opposes  the  passage  of 
the  current,  and  there  results  a  generation  of 
heat. 

Force,  Tubes  of Tubes  bounded  by 

lines  of  electrostatic  or  magnetic  force. 

Lines  of  force  never  intersect  one  another. 
Hence  a  tube  of  force  may  be  regarded  as  con- 


For.] 


241 


teining  the  same  number  of  lines  of  force  at  any 
and  every  cross-section. 

Tubes  of  electrostatic  force  always  terminate 
against  equal  quantities  of  positive  and  negative 
electricity  respectively.  They  terminate  when 
they  meet  a  conducting  surface. 

The  term  tubes  of  force  is  somewhat  mislead- 
ing, since  such  so-called  tubes  are  in  general 
cones  rather  .than  tubes. 

Force,  Twisting A  term  sometimes 

used  for  torque.     (See  Torque?) 

Force,  Unit  of A  force  which,  act- 
ing for  one  second  on  a  mass  of  one 
gramme,  will  give  it  a  velocity  of  one  centi- 
metre per  second. 

Such  a  unit  of  force  is  called  a  dyne.  (See 
Dyne.} 

Forces,  Composition  of Finding 

the  direction  and  intensity  of  a  single  force 
which  represents  the  total  effect  of  two  or 
more  forces  acting  simultaneously  on  a  body. 
(See  Component.) 

Forces,  Parallelogram  of  —  — A  paral- 
lelogram constructed  about  the  two  lines  that 
represent  the  direction  and  intensity  with 
which  two  forces  are  simultaneously  acting 
on  a  body,  in  order  to  determine  the  direction 
and  intensity  of  the  resultant  force  with 
which  it  moves. 

If  the  two  forces  A  C  and  A  B,  Fig.  259,  simul- 
taneously act  in  the  direc- 
tion  of  the  arrows  on  a 
body  at  A,  the  direction 
and  intensity  of  the  re- 
tultant  A  D,  is  deter- 
mined by  drawing  C  D 


f*f-  25Q-    Parallelo- 
gram of  Forces. 


and  B  D,  parallel  respectively  to  A  B  and  A  C. 
The  diagonal  A  D,  of  the  parallelogram  A  C  D  B, 
thus  produced,  gives  this  resultant.  (See  Com- 
ponent.) 

Fork,  Trolley The  mechanism 

which  mechanically  connects  the  trolley  wheel 
to  the  trolley  pole.  (See  Trolley.) 

Forked  Circuits.— (See  Circuits,  Forked?) 

Forked  Lightning.  —  (See  Lightning, 
Forked?] 

Formal  Inductance  of  Circuit— (See  In- 
ductance, Formal,  of  Circuit?) 


Forming  Plates  of  Secondary  or  Stor- 

age  Cells.— (See  Plates  of  Secondary  or  Stor- 
age Cells,  Forming  of.) 

Formulae. — Mathematical  expressions  for 
some  general  rule,  law,  or  principle. 

Formulae  are  of  great  assistance  in  science  in 
expressing  the  relations  which  exist  between  cer- 
tain forces  or  values,  and  the  effects  that  result 
from  their  operations,  since  they  enable  us  to  ex 
press  these  relations  in  clear  and  concise  forms. 

Thus  in  the  formulation  of  Ohm's  law: 

r  _E 
-R 

we  see  that  the  continuous  current  C,  in  any  cir- 
cuit, is  equal  to  the  electromotive  force  E,  divided 
by  the  resistance  R.  Again,  we  see  that  the  cur- 
rent is  directly  proportional  to  the  electromotive 
force,  and  inversely  proportional  to  the  resistance. 

Formulae  are  usually  written  in  the  form  of  an 
equation  and  therefore  contain  the  sign  of  equality 
or  =. 

Formulae,  Photometric (See  Pho- 
tometric Formula?) 

Foucault  Currents.— (See  Currents,  Fou- 
cault?) 

Four- Way  Splice  Box.— (See  Box,  Splice, 
Four-  Way?) 

Frames,  Sectional  Plating Frames 

employed  for  so  holding  the  objects  to  be 
plated  that  they  shall  receive  a  greater  depth 
of  deposit  on  certain  portions  of  their  surface 
than  elsewhere. 

Sectional  printing  frames  depend  for  their 
action  on  the  fact  that  the  portions  receiving  the 
greater  depth  of  deposit  are  nearer  one  of  the 
electrodes  than  the  rest  of  the  surface. 

Franklinic  Electricity.  —  (See  Elec- 
tricity, Franklinic?) 

Franklinization. — Electrization  by  means 
of  a  frictional  or  influence  machine  as  distin- 
guished from  faradization  or  electrization  by 
means  of  an  induction  coil. 

This  term  is  used  only  in 'medical  electricity. 

Free  Charge.— (See  Charge,  Free.} 

Free  Magnetic  Pole.— (See  Pole,  Mag- 
netic, Free.) 

Frequency  of  Alternations.— (See  Alter- 
nations, Frequency  of) 


FrL] 


242 


[Fun. 


Friction  Brake.-  (See  Brake,  Friction^ 
Frictional    Electrical     Machine.— (See 

Machine.  Frictional  Electric^ 

Frictional  Electricity.— (See  Electricity , 
Frictional?) 

Frog1,  Galvanoscopic The  hind  legs 

of  a  recently  killed  frog  employed  as  an  elec- 
troscope or  galvanoscope,  by  sending  an  elec- 
tric current  from  the  nerves  to  the  muscles. 
(See  Electroscope^ 

In  1786,  Luigi  Galvani  made  the  observation 
that  when  the  legs  of  a  recently  killed  frog  were 
touched  by  a  metallic  conductor  connecting  the 
nerves  with  the  muscles,  the  legs  were  convulsed 
as  though  alive.  He  repeated  this  experiment 
and  found  the  move- 
ments were  more  pro- 
nounced when  two  dis- 
similar metals,  such  as 
iron  and  copper,  were 
employed  in  the  manner 
shown  in  Fig.  260. 

The  classic  experi- 
ment created  intense 
excitement  in  the  scien- 
tific world,  and  Galvani 
at  first  believed  that  he 
had  discovered  the  true  vital  fluid  of  the  animal, 
but  afterwards  recognized  it  as  electricity,  which 
he  believed  to  be  obtained  from  the  body  of  the 
animal.  Volta  claimed  that  the  movements  were 
due  to  electricity  caused  by  the  contact  of  dissimi- 
lar metals,  and  thus  produced  his  famous  voltaic 
pile.  (See/*/*,  Voltaic.} 

Frog,  Trolley — The  name  given  to 

the  device  employed  in  fastening  or  holding- 
together  the  trolley  wires  at  any  point  where 
the  trolley  wire  branches,  and  properly  guiding 
the  trolley  wheel  along  the  trolley  wire  on  the 
movement  of  the  car  over  the  track. 

Frog,  Trolley,  Right-Hand A  trol- 
ley frog  used  at  the  point  where  the  branch 
trolley  wire  leaves  the  main  line  on  the  right 
of  the  direction  in  which  the  car  is  moving. 

Frog  Trolley,  Standard The  trol- 
ley frog  used  at  the  point  where  two  branch 
lines  make  equally  converging  angles  to  the 
main  line. 

Frog,  Trolley,  Three-Way A  trol- 


Fig.zbo.    Galvanoscopic 
Frog. 


ley  frog  used  where  the  line  branches  in  three 
directions. 

Frying  of  Arc.— (See  Arc,  Frying  of.} 
Fulgurite.— A  tube  of  vitrified  sand,  be- 
lieved to  be  formed  by  a  bolt  of  lightning. 

The  fulgurite  consists  of  an  irregular  shaped 
tube  of  glass  formed  of  sand  which  has  been 
melted  by  the  electric  discharge. 

Full  Contact-  (See  Contact,  Metallic.} 

Fuller's    Mercury    Bichromate  Voltaic 

Cell.— (See  Cell,  Voltaic,  Fuller's  Mercury 
Bichromate^ 

Fulminate.— The  name  of  a  class  of  highly 
explosive  compounds. 

Fulminating  gold,  silver  and  mercury  are 
highly  explosive  substances.  Fulminates  are 
employed  in  percussion  caps. 

Function,  Trigonometrical Cer- 
tain quantities,  the  values  of  which  are  de- 
pendent on  the  length  of  the  arcs  subtended 
by  angles,  which  are  taken  for  the  measures 
of  the  arcs  or  angles  instead  of  the  arcs 
themselves. 

The  trigonometrical  functions  are  the  sine,  the 
co-sine,  the  tangent,  the  co-tangent,  the  secant 
and  the  co-secant. 

These  are  generally  abbreviated  thus,  viz. :  sin., 
cos.,  tan.,  cot.,  sec.  and  co-sec. 

The  sine  of  an  angle  or  arc  is  the  perpendic- 
ular distance  from  one     L  C 
extremity  of  the  arc  to 
the     diameter     passing 
through   the    other  ex- 
tremity. 

Thus  in  Fig.  261  B  D,  G 
is  the  sine  of  the  angle 
B  O  A,   or  of  the  arc, 
B  A. 

The  co-sine  of  an  an  • 
gleor  arc  is  that  part  of  Fig-.  26 r.    Trigonometri- 
the  diameter  which  lies  cal  Functions. 

between  the  foot  of  the  sine  and  the  centre.  Thus, 
D  O,  is  the  co-sine  of  the  angle  B  O  A,  or  of  the 
arc  B  A. 

The  co-sine  of  an  arc  is  equal  to  the  sine  of  its 
complement.  Thus  E  O  B,  or  B  E,  the  comple 
ment  of  B  A,  has  for  its  sine  I  B,  which  is  equal 
to  O  D.  (See  Angle,  Complement  of .} 

If  the  arc  is  greater  than  a  right  angle,  or  90 


T/ 


Fnn.] 


243 


[Pus. 


degrees,  such,  for  instance,  as  the  angle  TOG, 
or  the  arc  B  E  F  G,  B  D,  is  its  sine.  This  is  also 
the  sine  of  B  O  A,  or  B  A,  which  is  the  supple- 
ment of  T  O  G,  or  B  E  F  G.  Hence  the  sine  of 
an  arc  is  equal  to  the  sine  of  its  supplement. 

The  same  is  true  of  the  co-sine. 

The  tangent  of  an  angle  or  arc  is  a  straight 
line  touching  the  arc  at  one  extremity,  drawn 
perpendicular  to  the  diameter  at  that  end  of  the 
arc,  and  limited  by  a  straight  line  connecting  the 
centre  of  the  circle  and  the  other  end  of  the  arc. 
Thus  C  A,  is  the  tangent  of  the  angle  B  O  A,  or 
the  arc  B  A. 

The  co-tangent  of  an  angle  or  arc  is  equal  to 
the  tangent  of  its  complement.  Thus  E  T,  is  the 
co-tangent  of  the  angle  B  O  A,  or  the  arc  B  A. 

The  tangent  of  an  angle  or  arc  is  equal  to  the 
tangent  of  its  supplement.  Thus  A  C,  is  the  tan- 
gent of  the  angle  B  O  A,  or  the  arc  B  A.  It  is 
also  equal  to  the  tangent  of  the  angle  B  O  G,  or 
the  arc  B  E  F  G,  the  corresponding  supplement  of 
the  angle  B'O  A,  or  the  arc  B  A. 

The  secant  of  an  angle  or  arc  is  the  straight 
line  drawn  from  the  centre  of  the  circle  through 
one  extremity  of  the  arc  and  limited  by  the  tan- 
gent  passing  through  the  other  extremity.  Thus 
O  C,  is  the  secant  of  the  angle  B  O  A,  or  of  the 
arc  B  A. 

The  secant  of  an  angle  or  arc  is  equal  to  the 
secant  of  its  supplement. 

The  co-secant  of  an  angle  or  arc  is  equal  to 
the  secant  of  its  complement. 

Thus  O  T,  is  the  co-secant  of  the  angle  BOA, 
or  of  the  arc  B  A. 

It  will  be  observed  that  the  co-sine,  the  co- 
tangent and  the  co-secant  a.e  respectively  the 
sine,  tangent  and  secant  of  the  complement  of 
the  arc,  or  in  other  words,  the  complement-sine, 
the  complement-tangent  and  the  complement- 
secant. 

Fundamental  Units.  -  (See  Units,  Funda- 
mental.') 

Furnace,  Electric  — A  furnace  in 

which  heat  generated  electrically  is  employed 
for  the  purpose  of  effecting  difficult  fusions 
for  the  extraction  of  metals  from  their  ores, 
or  for  other  metallurgical  operations. 

In  electric  furnaces,  the  heat  is  derived  either 
from  electric  incandescence  or  from  the  voltaic  arc. 
The  latter  form  is  frequently  adopted. 

The  substance  to  be  treated  is,  exposed  directly 


to  the  voltaic  arc.  In  some  forms  of  furnace  the 
crushed  ore  is  permitted  to  fall  through  the  arc, 
and  the  melted  matter  received  in  a  suitable  ves- 
sel in  which  the  separation  of  the  substances  so 
formed  is  afterwards  completed.  In  other  forms 
of  furnace,  the  ore  is  placed  between  two  elec- 
trodes of  carbon  or  other  refractory  substance, 
between  which  a  powerful  current  is  passed.  In 
the  Cowles  furnace,  when  aluminium  is  reduced, 
molten  copper  forms  an  alloy  with  the  aluminium 
as  soon  as  separated. 

Very  numerous  applications  of  electricity  to 
furnace  operations  have  been  made. 

Fuse  Block. — (See  Block,  Fuse.) 

Fuse  Board.— (See  Board,  Fuse.) 

Fuse  Box. — (See  Box,  Fuse.) 

Fuse,  Branch —A  safety  fuse  or 

strip  placed  in  a  branch  circuit.  (See  Fuse, 
Safety.) 

Fuse,  Converter A  safety  fuse  con- 
nected with  the  circuit  of  a  converter  or 
transformer. 

Fuse,  Electric A  device  for  elec- 
trically igniting  a  charge  of  powder. 

Electric  fuses  are  employed  both  in  blasting 
operations  and  for  firing  cannon. 

Electric  fuses  are  operated  either  by  means  of 
the  direct  spark,  or  by  the  incandescence  of  a 
thin  wire  placed  in  the  circuit.  They  are  there- 
fore either  high  tension,  or  low  tension  fuses. 

The  advantages  of  an  electric  fuse  consist  in 
the  fact  that  its  use  permits  the  simultaneous  fir- 
ing of  a  number  of  charges  in  a  mining  operation, 
thus  obtaining  a  greater  effect  from  the  explosion. 
A  fulminate  of  mercury  is  frequently  employed 
in  connection  with  some  forms  of  electric  fuses. 

Fuse,  Electric,   High-Tension A 

fuse  that  is  ignited  by  the  heating  power  of 
an  electric  spark. 

High-tension  fuses,  therefore,  require  a  high 
electromotive  force.  This  is  obtained  either  by 
means  of  induction  coils  or  by  some  form  of 
electrostatic  induction  machine. 

Fuse,  Electric,  Low-Tension A 

fuse  that  is  ignited  by  heating  a  wire  to  incan- 
descence by  the  passage  through  it  of  an 
electric  current. 

Fuse,  Electric,  Stratham's 


Fas.] 


244 


[GaL 


of  fuse,  in  which  the  ignition  is  effected  by  the 
electric  spark,  is  shown  in  Fig.  262. 

The  spark  passes  through  a  break  A  B,  in  the  in- 
sulated leads  D.  Since  gunpow- 
der is  not  readily  ignited  by  an 
electric  spark,  a  peculiar  priming 
material  is  employed  at  A  B,  in  the 
place  of  ordinary  powder. 

Fuse  Links.  —  (See   Links, 
Fuse.} 
Fuse,    Magazine   — A 

safety  fuse  so  arranged  as  to 
readily  permit  the  replacement 
of  the  fuse  when  burned  out. 

A  spool  contains  a  coil  of  fuse     Fig  z()3 
wire.      In    order    to   release    the    stratham's 
burned-out  fuse,   a  wedge-shaped         Fuse. 
device  is  provided  to  open  the  clamps  that  hold 
the  fuse  strip  to  release  the  portions  of  burned - 
out  fuse  left,  and  connection  with  the  fuse  strip 
is  severed  while  the  attachment  of  the  new  strip 
is  being  made. 

Fuse,  Main A  safety  fuse  or  strip 

placed  in  a  main  circuit.     (See  Fuse,  Safety?) 

Fuse,  Flat  ilium  •  — A  thin   platinum 

wire  rendered  incandescent  by  the  passage  of 
an  electric  current  and  employed  for  the  igni- 
tion of  a  charge  of  powder.  (See  Fuse, 
Electric?) 

Fuse,  Safety A  strip,  plate  or  bar 

of  lead,  or  some  readily  fusible  alloy,  that  au- 
tomatically breaks  the  circuit  in  which  it  is 
placed  on  the  passage  of  a  current  of  suf- 


ficient power  to  fuse  such  strip,  plate  or  bar, 
when  such  current  would  endanger  the  safety 
of  other  parts  of  the  circuit. 

Safety  fuses  are  often  called  safety  strips  or 
safety  plugs. 

Safety  fuses  are  made  of  alloys  of  lead,  and 
are  placed  in  boxes  lined  with  non-combustible 
material  in  order  to  prevent  fires  from  the  molten 
metal. 

Fig.  263  shows  a  fusible  strip  F,  connected  with 
leads  L,  L.  Safety  fuses  are  placed  on  all  branch 
circuits,  and  are  made  of  sizes  proportionate  to 
the  number  of  lamps  they  guard. 


Fig.  263.    Safety  fuse. 

Since  incandescent  lamps  are  generally  placed 
in  the  circuit  in  multiple- arc,  or  in  multiple-series, 
one  or  more  of  the  circuits  can  be  opened  by  the 
fusion  of  the  plug  without  interfering  with  the 
continuity  of  the  rest  of  the  circuits.  In  series 
circuits,  however,  such  as  arc-light  circuits,  when 
a  lamp  is  cut  out,  a  short  circuit  or  path  around 
it  must  be  provided  in  order  to  avoid  the  extin- 
guishing of  the  rest  of  the  lights. 

Fuse  Wire.— (See  Wire,  Fuse.) 

Fusible  Plug. — A  term  commonly  applied 
to  a  safety  plug.  (See  Fuse,  Safety 


Gains. — The  spaces  cut  in  the  faces  of 
telegraph  poles  for  the  support  or  placing  of 
the  cross  arms. 

Galvanic  Battery.— (See  Battery,  Gal- 
vanic.) 

Galvanic  Cell.— (See  Cell,  Voltaic.) 

Galvanic  Circle.— (See  Circle,  Galvanic.) 

Galvanic  Circuit— (See  Circuit,  Gal- 
vanic?) 


Galvanic  Dosage. — (See  Dosage,  Gal- 
vanic?) 

Galvanic  Electricity.— (See  Electricity, 
Galvanic?) 

Galvanic  Excitability  of  Nerve  or  Mus- 
oular  Fibre.— (See  Excitability,  Electric, 
of  Nerve  or  Muscular  Fibre) 

Galvanic  Irritability.— (See  Irritability, 
Galvanic) 


tfal.l 


245 


[Gal. 


Galvanic  Multiplier.— (See  Multiplier, 
Galvanic?) 

Galvanic  Polarization. — (See  Polariza- 
tion, Galvanic?) 

Galvanic  Taste.— (See  Taste,  Galvanic) 

Galvanism. — A  term  sometimes  employed 
to  express  the  effects  produced  by  voltaic 
electricity. 

Galvanization,  Central A  variety 

of  general  galvanization  in  which  the  kathode 
is  placed  on  the  epigastrium  and  the  anode 
moved  over  the  body. 

Galvanization,  Electro-Metallurgical 
The  process  of  covering  any  conduc- 
tive surface  with  a  metallic  coating  by  elec- 
trolytic deposition,  such,  for  example,  as  the 
thin  copper  coating  deposited  on  the  carbon 
pencils  or  electrodes  used  in  systems  of  arc 
lighting. 

The  term  is  borrowed  from  the  French,  in 
which  it  has  the  above  signification.  It  is  prefer- 
ably replaced  by  the  term  electro-plating.  (See 
Plating,  Electro.} 

The  term  galvanization  is  never  correctly  ap- 
plied to  the  process  for  covering  iron  with  zinc  or 
other  metal  by  dipping  the  same  in  'a  bath  of 
molten  metal. 

Galvanization,  Electro-Therapeutical 

—In  electro-therapeutics,  the  effects 

produced  on  nervous  or  muscular  tissue  by 
the  passage  of  a  voltaic  current. 

Galvanization,  General A  method 

of  applying  a  current  therapeutically  by  the 
use  of  electrodes  of  sufficient  size  to  direct 
the  current  through  practically  the  entire 
body. 

Galvanization,  Labile  -  — A  term 
employed  in  electro-therapeutics,  in  contradis- 
tinction to  stabile  galvanization,  to  designate 
the  method  of  applying  the  current  by  keep- 
ing one  electrode  at  rest  in  firm  contact  with 
one  part  of  the  body,  and  connecting  the  other 
electrode  to  a  sponge  which  is  moved  over 
the  parts  of  the  body  that  are  to  be  treated. 

Galvanization,  Local  — -> The  applica- 
tion of  galvanization  to  parts  or  organs  of  the 
body  in  contradistinction  to  general  galvani- 
zation. 


Galvanization,  Stabile A  term 

employed  in  electro-therapeutics  in  which  the 
current  is  caused  to  pass  continuously  and 
steadily  through  the  portions  of  the  body  un- 
dergoing galvanization. 

In  stabile  galvanization,  the  current  is  applied 
to  and  removed  from  the  body  gradually,  in  order 
to  avoid  shocks  at  the  beginning  and  end  of  the 
application. 

Galvanized  Iron. — (See  Iron,  Galvan- 
ized?) 

Galvano. — A  word  sometimes  used  in 
France  in  place  of  the  word  electro,  to  signify 
an  article  reproduced  in  copper  by  electro- 
metallurgy, especially  an  electrotype  or  wood- 
cut. 

Galvano-Causty. — (See  Causty,  Galvano?) 

Galvano-Cautery.— (See     Cautery,    Gal- 
vano?) 
Galvano-Cautery,     Chemical    — A 

term  sometimes  applied  to  electro  puncture 
or  the  application  of  electrolysis  to  the  treat- 
ment of  diseased  growths.  (See  Cautery, 
Electric.  Puncture,  Electro?) 

The  term  chemical  galvano-cautery  would  ap- 
pear to  be  poorly  chosen,  as  it  would  imply  the 
existence  of  a  cautery  action,  which  in  point  of 
fact  does  not  exist 

Galvano-Faradization. — In  electro-thera- 
peutics, the  simultaneous  excitation  of  a  nerve 
or  muscle  by  both  a  voltaic  and  a  faradic  cur- 
rent. 

Galvano-Magnet. — A  term  sometimes  used 
for  electro-magnetic. 

Electro  magnetic  is  by  far  the  preferable  term, 
and  is  almost  universally  employed  in  the  United 
States. 

Galvanometer. — An  apparatus  for  meas- 
uring the  strength  of  an  electric  current  by 
the  deflection  of  a  magnetic  needle. 

The  galvanometer  depends  for  its  operation  on 
the  fact  that  a  conductor,  through  which  an  elec- 
tric current  is  flowing,  will  deflect  a  magnetic 
needle  placed  near  it.  This  deflection  is  due  to 
the  magnetic  field  caused  by  the  current.  (See 
Field,  Magnetic,  of  an  Electric  Current.} 

This  action  of  the  current  was  first  discovered 
by  Oersted.  A  wire  conveying  a  current  in  the 


Gal.] 


246 


[GaL 


direction  shown  by  the  straight  arrow,  Fig.  264, 
or  from  +  to  — ,  will  deflect  a  magnetic  needle  in 
the  direction  shown  by  the  curved  arrows. 
The  following  rules  show  the  direction  of  the 


Fig   2t>-t.     Oersted's  Experiment. 
deflection  of  a  magnetic  pole  by  an  electrical  cur- 
rent: 

(I.)  Place  the  right  hand  on  the  conductor 
through  which  the  current  is  flowing,  with  the 
palm  facing  the  north  pole,  and  with  the  fingers 
pointing  in  the  direction  of  the  current.  The 
thumb  will  indicate  the  direction  in  which  the 
north  pole  tends  to  move. 

(2.)  Suppose  an  ordinary  corkscrew  so  placed 
along  the  conductor,  through  which  a  current  of 
electricity  is  passing,  that  when  twisted,  it  will 
move  in  the  direction  of  the  current.  The  han- 
dle will  then  turn  in  the  direction  in  which  the 
north  pole  of  the  magnet  tends  to  move. 

(3.)  Imagine  one  swimming  along  the  con- 
ductor in  the  direction  of  the  current  and  facing 
the  magnet.  The  north  pole  will  tend  to  move 
towards  the  left  hand  of  the  swimmer. 

Prof.  Forbes  has  shown  that  the  direction  of 
the  deflection  of  a  magnet  by  a  current  is  such 
A  B          C 


Fig.  265.     Antplre's  Apparatus. 
that  if  the  magnet  were  flexible,  it  would  wrap 
itself  round  the  current. 

If  the  wire  be  bent  in  the  form  of  a  hollow  rec- 
tangle F,  D,  E,  G,  Fig.  265,  and  the  needle,  M, 


be  placed  inside  the  circuit,  the  upper  and  lower 
branches  of  the  current  will  deflect  the  needle  in 
the  same  direction,  and  the  effect  of  the  current 
will  thus  be  multiplied.  Mercury  cups  are  pro- 
vided at  A,  B  and  C,  for  a  ready  change  in  the 
direction  of  the  current.  (See  Needle,  Astatic.") 

This  principle  of  the  multiplication  of  the  de- 
flecting power  of  a  current  was  first  applied  to  gal- 
vanometers by  Schweigger,  who  used  a  number  of 
turns  of  insulated  wire  for  the  purpose  of  obtain- 
ing a  greater  deflection  of  the  needle.  He  called 
such  a  device  a  multiplier.  In  extremely  sensi- 
tive galvanometers,  very  many  turns  of  wire  are 
employed,  in  some  cases  amounting  to  many 
thousands.  Such  galvanometers  are  of  high  re- 
sistance. Others,  of  low  resistance,  often  con- 
sist of  a  single  turn  of  wire  and  are  used  in  the 
direct  measurement  of  large  currents. 

A  Schweigger's  multiplier  or  coil  C,  C,  oi 
many  turns  of  insulated  wire,  is  shown  in  Fig.  266. 
The  action  of  such  a  coil  on  the  needle  M,  is  com- 
paratively great,  even  when  the  current  is  small. 


Fig.  266.     Schweigger's  Multiplier. 


In  the  case  of  any  galvanometer,  when  no  cur- 
rent  is  passing,  the  needle,  when  at  rest,  should  in 
general  occupy  a  position  parallel  to  the  plane  of 
the  coil.  On  the  passage  of  the  current,  the 
needle  tends  to  place  itself  in  a  position  at  right 
angles  to  the  direction  of  the  current,  or  to  the 
length  of  the  conducting  wire  in  the  coil.  The 
strength  of  the  current  passing  is  determined  by 
observing  the  amount  of  this  deflection  as  meas- 
ured in  degrees  on  a  graduated  circle  over  which 
the  needle  moves. 

The  needle  is  deflected  by  the  current  from  a 
position  of  rest,  either  in  the  earth's  magnetic 
field  or  in  a  field  obtained  from  a  permanent  or 
an  electro  magnet  In  the  first  case,  when  in  use 
to  measure  a  current,  the  plane  of  the  galvanom- 
eter coils  must  coincide  with  the  planes  of  the 
magnetic  meridian.  In  the  other  case,  the  instru- 


Gal.] 


247 


[Gal. 


ment  may  be  used  in  any  position  in  which  the 
needle  is  free  to  move. 

Galvanometers  assume  a  variety  of  forms  ac- 
cording either  to  the  purposes  for  which  they  are 
employed,  or  to  the  manner  in  which  their  deflec- 
tions are  valued. 

Galvanometer,  Absolute A  galva- 
nometer whose  constant  can  be  calculated 
with  an  absolute  calibration.  (See  Calibra- 
tion, Absolute?) 

Such  a  galvanometer  is  called  absolute  because 
if  the  dimensions  of  its  coil  and  needle  are  known, 
the  current  can  be  determined  directly  from  the 
observed  deflection  of  the  needle. 

Galvanometer,  Aperiodic A  gal- 
vanometer the  needle  of  which  comes  to  its 
position  without  any  oscillation. 

A  dead-beat  galvanometer.  (See  Galva- 
nometer, Dead-Seat.} 

Galvanometer,  Astatic A  galva- 
nometer, the  needle  of  which  is  astatic.  (See 
Needle,  Astatic.} 

Nobili's  astatic  galvanometer  is  shown  in  Fig. 
267.  The  astatic  needle,  suspended  by  a  fibre  b, 
has  its  lower  needle  placed  inside  a  coil,  a,  con- 
sisting of  many  turns  of  insulated  wire,  its  upper 
needle  moving  over  the  graduated  dial.  The  cur- 
rent to  be  measured  is  led  into  and  from  the 
coil  at  the  binding  posts,  x  and  y. 


Fig.  267.    Astatic  Galvanometer. 

In  this  instrument,  if  small  deflections  only  are 
employed,  the  deflections  are  sensibly  propor- 
tional to  the  strength  of  the  deflecting  currents. 

Galvanometer,  Ballistic A  galva- 
nometer designed  to  measure  the  strength  of 
currents  that  last  but  for  a  moment,  such,  for 
example,  as  the  current  caused  by  the  dis- 
charge of  a  condenser. 


The  quantity  of  electricity  passing  in  any  cir- 
cuit is  equal  to  the  current  multiplied  by  the  time. 
Since  the  current  caused  by  the  discharge  of  a 
condenser  lasts  but  for  a  small  time,  during  which 
it  passes  from  zero  to  a  maximum  and  back  again 
to  zero,  the  magnetic  needle  in  a  ballistic  galva- 
nometer takes  the  form  of  a  ballistic  pendulum, 
i.  <?.,  it  is  given  such  a  mass,  and  acquires  such  a 
slow  motion,  that  its  change  of  position  does  not 


Fig.  2b8.    Ballistic  Galvanometer. 

practically  begin  until  the  impulses  have  ceased 
to  act. 

.  In  the  ballistic  galvanometer  of  Siemens  and 
Halske,  the  coils  R,  R,  Fig.  268,  have  a  bell- 
shaped  magnet,  M,  suspended  inside  them  by 
means  cf  an  aluminium  wire.  The  magnet  is  pro- 
vided with  a  mirror  S,  for  measuring  the  deflec- 
tions. The  bell-shaped  magnet  is  shown  in  ele- 
vation at  M,  and  in  plane  at  n,  s. 

In  using  the  ballistic  galvanometer,  it  is  neces- 
sary to  see  that  the  needle  is  absolutely  at  rest  be- 
fore the  charge  is  sent  through  the  coils. 

A  form  of  ballistic  galvanometer  by  Nalder  is 
shown  in  Fig.  269. 

The  ordinary  form  of  compensating  magnet 
is,  in  this  galvanometer,  replaced  by  the  small  mag- 
net A,  capable  of  rotation  in  a  horizontal  plane,  but 
incapable  of  being  raised  or  lowered,  as  is  usual 
in  such  magnets.  This  form  of  compensating  mag- 
net possesses  the  advantage  of  being  able  to  alter 
the  direction  of  the  field  on  the  needle  system, 


Gal.] 


248 


[Oal. 


without  considerably  altering  its  intensity.  When 
the  galvanometer  is  for  ready  use  the  magnet  A,  is 
turned  until  the  needle  is  brought  to  zero.  The 


Fig.  269.    Nalder's  Galvanometer 
combined  field  of  earth  and  magnet  A,  are  then 
brought  to  the  degree  of  sensitiveness  required 


Fig.  270.    Nalder's  Galvanometer, 

by  rotating  magnet  B,  on  its  shaft,  or  altering 
its  distance  from  the  needle.  In  order  to  insure 
ease  in  replacing  the  fibre,  the  front  coil  is  hinged 
as  shown.  The  fibre  D,  is  supported  on  E,  one 
end  of  which  it  is  free  to  turn,  so  as  to  permit  of 
the  removal  of  torsion;  D,  being  twisted  can  be 
raised  or  lowered  at  E.  The  needle  system  with 
heavy  bell-shaped  magnet  is  shown  in  Fig.  270. 

Galvanometer,  Combined  Tangent  and 

Sine A  galvanometer  furnished  with 

two  magnetic  needles  of  different  lengths. 
The  small  needle  is  used  for  tangent  measure- 
ments, and  the  long  needle  for  sine  measure- 
ments. 

Galvanometer  Constant.— (See  Constant, 
Galvanometer?) 

Galvanometer,  Dead-Beat  —  —A  gal- 
vanometer, the  needle  of  which  comes  quickly 
to  rest,  instead  of  swinging  repeatedly  to-and- 
fro.  (See  Damping?) 

Galvanometer,  Deprez-D'Arsonval  

— A  form  of  dead-beat  galvanometer. 

The  movable  part  of  the  Deprez-D'Arsonval 
galvanometer  consists  of  a  light  rectangular  coil 


C,   Fig.  271,  of  many  turns  of  wire,  supported 

by  two  silver  wires  H  J  and  D  E,  between  tbe 

poles  of  a  strong  permanent  horseshoe  magaet 

A  A.     The  position  of 

the  coil  may  be  altered 

as  to  height  by  screws 

at  H  and  E.     The  sup- 

porting wires,  prevent 

by    their    torsion     the 

swinging  of  the  coil,  as 

does  also  the  cylinder 

of  soft  iron   B,  placed 

inside  the  coil,  and  sup- 

ported    independently 

of  it.      The  movements  If 

of  the  coil  are  observed 

by  means  of  a  spot  of 

light  reflected  from    a 

mirror  J,   attached    to 

the  wire  H  J. 

Galvanometer,  Detector  --  A  form  of 
galvanometer  employed  for  rough  testfa^ 
work. 

A  form  of  detector  galvanometer  is  show*  in 
Fig.  272. 


27  1-  Deprez-l?  Arson- 

val  Galvanometer. 


Fig.  2^  2.    Detector  Galvanometer. 

Galvanometer,  Differential  —  — A  gal- 
vanometer containing  two  coils  so  wound  as 
to  tend  to  deflect  the  needle  in  opposke 
directions. 

The  needle  of  a  differential  galvanometer  shows 
no  deflection  when  two  equal  currents  are  scat 
through  the  coils  in  opposite  directions,  since, 
under  these  conditions,  each  coil  neutralizes  the 
other's  effects.  Such  instruments  may  be  used 
in  comparing  resistances.  The  Wheatstoae 
Bridge,  however,  in  most  cases,  affords  a  prefer- 
able method  for  such  purposes.  (See  Bridge 
Electric.') 


Gal.] 


249 


[Gal. 


A  form  of  differential  galvanometer  is  shown  in 

Fig-  273- 

Sometimes  the  current  is  so  sent  through  the 
two  coils,  that  each 
coil  deflects  the  nee- 
dle in  the  same  di- 
rection. In  this  case 
the  instrument  is  no 
lunger  differential  in 
action. 

If  the  magnetic 
needle,  in  such  cases, 
is  suspended  at  the 
exact  centre  of  the 
line  which  joins  the 
centres  of  the  coils, 
the  advantage  is 
gained  by  obtaining 
a  field  of  more  nearly 
uniform  intensity  FiS-273-  Differential  Galva- 
arwund  the  needle. 

Galvanometer,  Figure  of  Merit  of 

The  reciprocal  of  the  current  required  to  pro- 
duce a  deflection  of  the  galvanometer  needle 
through  one  degree  of  the  scale. 

The  smaller  the  current  required  to  produce  a 
deflection  of  one  degree,  the  greater  the  figure 
of  merit,  or  the  greater  the  sensitiveness  of  the 
galvanometer. 

Galvanometer,  Marine  — A  galva- 
nometer devised  by  Sir  William  Thomson  for 
use  on  steamships  where  the  motion  of  mag- 
netized masses  of  iron  would  seriously  disturb 
the  needles  of  ordinary  instruments. 

An  unscreened  needle  would  be  so  much  af- 
fected by  the  motion  of  the  engines,  the  shaft  and 
the  screw,  as  to  be  useless  for  galvanometric 
measurement. 

The  needle  of  the  marine  galvanometer  is 
shielded  or  cut  off  from  the  extraneous  fields  so 
produced,  by  the  use  of  a  magnetic  screen  or 
shield,  consisting  of  an  iron  box  with  thick  sides, 
inside  of  which  the  instrument  is  placed. 

The  needle  is  suspended  by  means  of  a  silk 
fibre  attached  both  above  and  below,  in  line  with 
the  centre  of  gravity  of  the  needle.  In  this  man- 
ner, the  oscillations  of  the  ship  do  not  affect  the 
needle. 

Galvanometer,  Mirror A  galva- 
nometer in  which,  instead  of  reading  the  de- 
flections of  the  needle  directly  by  its  move- 


ments over  a  graduated  circle,  they  are  read 
by  the  movements  of  a  spot  of  light  reflected 
from  a  mirror  attached  to  the  needle. 

This  spot  of  light  moves  over  a  graduated 
scale,  or  its  movements  are  observed  by  means  of 
a  telescope. 


Fig.  274.    Mirror  Galvanometer. 

A  form  of  mirror  galvanometer  designed  by  Sir 
William  Thomson  is  shown  in  Fig.  274.  The 
needle  is  attached  directly  to  the  back  of  a  light, 
silvered  glass  mirror,  and  consists  of  several  small 
magnets  made  of  pieces  of  a  watch  spring.  The 
needle  and  mirror  are  suspended  by  a  single  sflk 
fibre  and  are  placed  inside  the  coil.  A  compen- 
sating magnet  N  S,  movable  on  a  vertical  axis,  is 
used  to  vary  the  sensitiveness  of  the  instrument. 
The  lamp  L,  placed  back  of  a  slot  in  a  wide 
screen,  throws  a  pencil  of  light  on  the  mirror  Q, 
from  which  it  is  reflected  to  the  scale  K. 

A  form  of  lamp  and  scale  with  slot  for  light  is 
shown  in  Fig.  275. 


Fig.  275.     Galvanometer  Lamp  and  Scale. 

Galvanometer,  Potential  —  —A  term 
sometimes  applied  to  a  voltmeter.  (See 
Voltmeter^ 

Galvanometer,  Reflecting A  term 

sometimes  applied  to  a  mirror  galvanometer. 
(See  Galvanometer,  Mirror?) 


Gal.] 


250 


[GaL 


Galvanometer,  Sensibility  of The 

readiness  and  extent  to  which  the  needle  of  a 
galvanometer  responds  to  the  passage  of  an 
electric  current  through  its  coils.  (See  Gal- 
vanometer.) 

Galvanometer-Shunt. — (See  Shunt,  Gal- 
vanometer^) 

Galvanometer,  Sine  — A  galva- 
nometer in  which  a  vertical  coil  is  movable 
around  a  vertical  axis,  so  that  it  can  be  made  to 
follow  the  magnetic  needle  in  its  deflections. 

In  the  sine  galvanometer,  the  coil  is  moved  so 
as  to  follow  the  needle  until  it  is  parallel  with  the 
coil.  Under  these  circumstances,  the  strength 
of  the  deflecting  currents  in  any  two  different 
cases  is  proportional  to  the  sines  of  the  angles  of 
deflection. 

A  form  of  sine  galvanometer  is  shown  in  Fig. 
276.  The  vertical  wire  coil  is  seen  at  M.  A 
needle  of  any  length  less  than  the  diameter  of  the 
coil  M,  moves  over  the  graduated  circle  N.  '  The 
coil  M,  is  movable  over  the  graduated  horizontal 
circle  H,  by  which  the  amount  of  the  movement 


Fig.  276.     Sine  Galvanometer. 

necessary  to  bring  the  needle  to  zero  is  measured. 
The  current  strength  is  proportional  to  the  sine 
of  the  angle  measured  on  this  circle,  through 
which  it  is  necessary  to  move  the  coil  M,  from  its 


position  when  the  needle  is  at  rest  in  the  plane  of 
the  earth's  magnetic  meridian,  until  the  needle 
is  not  further  deflected  by  the  current,  although 
parallel  to  the  coil  M. 

Galvanometer,  Tangent An  instru- 
ment in  which  the  deflecting  coil  consists  of 
a  coil  of  wire  within  which  is  placed  a  needle 
very  short  in  proportion  to  the  diameter  of 
the  coil,  and  supported  at  the  centre  of  the 
coil. 


Fig.  2TJ.      Tangent    Galvanometer. 

A  galvanometer  acts  as  a  tangent  galvanometer 
only  when  the  needle  is  very  small  as  compared 
with  the  diameter  of  the  coil.  The  length  of  the 
needle  should  be  less  than  one-twelfth  the  diameter 
of  the  coil. 

A  form  of  tangent  galvanometer  is  shown  in 
Fig.  277.  The  needle  is  supported  at  the  exact 
centre  of  the  coil  C. 

Under  these  circumstances,  the  strengths  of 
two  different  deflecting  currents  are  proportional 
to  the  tangents  of  the  angles  of  deflection.  Tan- 
gent  galvanometers  are  sometimes  made  with 
coils  of  wire  containing  many  separate  turns. 

Galvanometer,  Tangent,  Obach's 

A  form  of  galvanometer  in  which  the  deflect- 
ing coil,  instead  of  being  in  a  fixed  vertical 
position,  is  movable  about  a  horizontal  axis, 
so  as  to  decrease  the  delicacy  of  the  instru- 
ment, and  thus  increase  its  range  of  work. 

Galvanometer,  Torsion  —  — A  galva- 
nometer in  which  the  strength  of  the  deflecting 
current  is  measured  by  the  torsion  exerted  on 
the  suspension  system. 

A  ball-shaped  magnet,  shown  at  the  right  of 
Fig.  278,  is  suspended  by  a  thread  and  spiral 


Gal.] 


251 


[Gal. 


spring  between  two  coils  of  high  resistance, 
placed  parallel  to  each  other  in  the  positions 
shown.  On  the  deflection  of  the  magnet,  by  the 
current  to  be  measured,  the  strength  of  the  current 
is  determined  by  the  amount  of  the  torsion  re- 
quired to  bring  the  magnet  back  to  its  zero  point. 


Pig.  278.     Torsion  Galvanometer. 

The  angle  of  torsion  is  measured  on  the  horizontal 
scale  at  the  top  of  the  instrument. 

In  the  torsion  galvanometer,  unlike  the  electro- 
dynamometer,  the  action  between  the  coils  and  the 
movable  magnet  is  as  the  current  strength  causing 
the  deflection.  In  the  electro-dynamometer, 
since  an  increase  of  current  in  the  deflecting  coils 
also  takes  place  in  the  deflected  coil,  the  mutual 
action  of  the  two  is  as  the  square  of  the  current 
strength  causing  the  deflection. 

Galvanometer,  Upright A  gal- 
vanometer, the  needle  of  which  moves  in  a 
vertical  plane.  (See  Galvanometer,  Ver- 
tical. 

Galvanometer,  Yertical A  gal- 
vanometer the  needle  of  which  is  capable  of 
motion  in  a  vertical  plane  only. 

In  the  vertical  galvanometer,  the  north  pole  of 
the  needle  is  weighted  so  that  the  needle  as- 
sumes a  vertical  position  when  no  current  is  pass- 
ing. In  the  form  shown  in  Fig.  279,  two  needles 
9- Vol.  1 


are  sometimes  employed,  one  of  which  is  placed 
inside  the  coils  C,  C. 

The  vertical  galvanometer  is  not  as  sensitive  as 
the  ordinary  forms.  It  is  employed,  however, 
in  various  forms  for  an 
electric  current  indica- 
tor, or  even  for  a 
rough  current  meas- 
urer. 

Galvanometer 
Voltmeter. — An  in- 
strument devised  by 
Sir  William  Thom- 
son, for  the  meas- 
urement of  differ- 
ences of  electric 
potential. 


Fig.  279.     Vertical  Galva- 
nometer. 

This  instrument  is  so  arranged  that  by  a  single 
correction  for  the  varying  strength  of  the  earth's 
field  in  any  place,  the  results  are  read  at  once  in 
volts. 

A  coil  of  insulated  wire  shown  at  A,  Fig.  280, 
has  a  resistance  of  over  5,000  ohms.  A  magnetic 
needle,  formed  of  short  parallel  needles  placed 
above  one  another,  and  called  a  magnetometer 
needle,  is  attached  to  a  long  but  light  aluminium 
index,  moving  over  a  graduated  scale.  A  mova- 
ble, semi-circular  magnet  B,  called  the  restoring 
magnet,  is  placed  over  the  needle,  and  is  used 
for  varying  the  effect  of  the  earth's  field  at  any 
point.  The  sensitiveness  of  the  instrument  may 
be  varied  either  by  the  restoring  magnet  or  by 
sliding  the  magnetometer  box  nearer  to  or  further 
away  from  the  coil. 

The  voltmeter  galvanometer  depends  for  its 
operation  on  the  fact  that  when  a  galvanometer 
of  sufficiently  high  resistance  is  introduced  be- 


Fig.  280.     Galvanometer  Voltmeter. 

tween  any  two  points  in  a  circuit,  the  current  that 
passes  through  it,  and  hence  the  defiection  of  its 
needle,  is  directly  proportional  to  the  difference 
of  potential  between  such  two  points. 


tiaL] 


[Gas. 


Galvanometers  for  the  commercial  measure- 
ments of  currents  assume  a  variety  of  forms. 
They  are  generally  so  constructed  as  to  read  off 
the  amperes,  volts,  ohms,  watts,  etc.,  directly. 
They  are  called  amperemeters  or  ammeters,  volt- 
meters, ohmmeters,  wattmeters,  etc.  For  their 
filler  description  reference  should  be  had  to 
standard  works  on  electrical  measurement. 

Galranometric. — Of  or  pertaining  to  the 
galvanometer.  (See  Galvanometer?) 

Galvanometrical. — Of  or  pertaining  to  the 
galvanometer.  (See  Galvanometer?) 

Galranometrically. —  In  a  galvanometric 
manner. 

Galyano-Plastics.— (See  Plastics,  Gal- 
vano.) 

Galvanoplasty. — The  art  of  galvano- 
plastics.  (See  Plastics,  Galvano?) 

Galrano-Puncture.— (See  Puncture,  Gal- 
vano?) 

Galvanoscope. — A  term  sometimes  im- 
properly employed  in  place  of  galvanometer. 

A  galvanoscope,  strictly  speaking,  is  an  instru- 
ment intended  rather  to  show  the  existence  of  an 
electric  current  than  to  measure  it  in  degrees. 
It  may,  however,  be  roughly  calibrated,  and  then 
it  differs  from  a  galvanometer  only  in  delicacy 
and  accuracy. 

Galvano-Therapentics. — A  term  some- 
times used  for  electro-therapeutics. 

Electro- therapeutics  is  by  far  the  preferable 
term  and  is  almost  universally  employed  in  the 
United  States. 

Gap,  Air A  gap,  or  opening  in 

a  magnetic  circuit  containing  air  only.  (See 
Gap,  Air,  Magnetic?) 

The  air  gap  between  two  magnetic  poles  may 
be  regarded  as  the  space  in  which  an  armature 
acting  as  a  magneto- receptive  device  is  placed, 
which  by  the  action  upon  it  of  the  lines  of  mag- 
netic force  passing  through  the  gap  has  differ- 
ences of  potential  generated  in  its  coils  of  insulated 
wire. 

Gap,  Air,  Magnetic A  gap  filled 

with  air  which  exists  in  the  opening  at  any 
part  of  a  core  of  iron  or  other  medium  of  high 
permeability. 

The  space  between  the  pole  pieces  and  arma- 


ture core  is  called  the  air  gap  in  dynamos  or 
motors  even  though  partly  filled  with  copper  con-, 
ductors.  It  is  also  called  the  interference  space. 

The  gap  or  air  space  of  an  electro-magnet  de- 
creases the  strength  of  its  magnetization  be- 
cause—- 
The increased  reluctance  of  the  air  gap  causes 
a  decrease  in  the  number  of  lines  of  magnetic 
force  which  pass  through  the  magnetic  circuit. 

Gap,  Spark A  gap  forming  part  of 

a  circuit  between  two  opposing  conductors, 
separated  by  air,  or  other  similar  dielectric 
which  is  closed  by  the  formation  of  a  spark 
only  when  a  certain  difference  of  potential 
is  attained. 

Gap,  Wire-Gauge  -  —(See  Gauge, 
Wire,  Gap.) 

Gas-Battery. — (See  Battery,  Gas.) 

Gas  Burner,  Argaml,  Plain-Pendant, 

Electric  — (See  Burner,  Argand 

Electric,  Plain-Pendant?) 

Gas  Burner,  Argand,  Ratcliet-Pendant, 
Electric (See  Burner,  Argand  Elec- 
tric, Ratchet-Pendant?) 

Gas  Burner,  Automatic  Electric • 

(See  Burner,  Automatic  Electric?) 

Gas  Burner,  Plain-Pendant,  Electric 
— (See  Burner,  Plain-Pendant  Elec- 
tric?) 

Gas  Burner,  Ratchet-Pendant,  Electric 
(See  Burner,  Ratchet-Pendant  Elec- 
tric?) 

Gas,  Carbonic  Acid A  gaseous  sub- 
stance formed  by  the  union  of  one  atom  of 
carbon  with  two  atoms  of  oxygen. 

Carbonic  acid  gas  is  formed  during  the  com- 
bustion of  carbon  by  a  sufficient  supply  of  air. 

Gas,  Dielectric  Density  of  —  —A  term 
sometimes  emploved  instead  of  dielectric 
strength  of  gas.  (See  Gas,  Dielectric 
••  Strength  of?) 

Gas,  Dielectric  Strength  of The 

strain  a  gas  is  capable  of  bearing  without 
suffering  disruption,  or  without  permitting  a 
disruptive  discharge  to  nass  through  it. 

The  dielectric  strength  of  a  gas  depends — 

(I.)  On  the  nature  of  the  gas. 

(2.)  On  its  pressure. 


Gas.] 


253 


[Gau. 


It  has  been  calculated  roughly  that  it  requires 
40,000  volts  per  centimetre  to  pass  a  disruptive 
discharge  through  dry  air  at  ordinary  pressures. 

Gas-Jet,    Carcel    Standard (See 

Car  eel  Standard  Gas- Jet) 

Gas-Jet  Photometer.— (See  Photometer) 

Gas-Lighting,  Electric The  electric 

ignition  of  a  gas-jet  from  a  distance. 

Gas-Lighting,  Multiple  Electric 

A  system  of  electric  gas-lighting  in  which  a 
number  of  gas-jets  are  lighted  by  means  of 
a  discharge  of  high  electromotive  force, 
derived  from  a  Ruhmkorff  coil  or  a  static 
induction  machine. 

Such  devices  are  operated  by  means  of  minute 
electric  sparks  which  are 
caused  to    pass    through 
the  escaping  gas-jets. 

The  spark  for  this  pur- 
pose is  obtained  either  by 
means  of  the  extra  current 
from  a  spark  coil,  by  means 
of  an  induction  coil  or  by 
static  discharges.  (See 
Currents,  Extra.  Coil, 
Spark.  Coil,  Induction.) 

A  gas  tip  for  use  in  multiple  gas-lighting  ap- 
paratus is  shown  in  Fig.  281.  The  spark  is 
formed  immediately  over  the  slot  in  the  burner, 
and  therefore  ignites  the  escaping  gas. 

Gas,  Occlusion  of The  absorption 

or  shutting  up  of  a  gas  in  the  pores,  or  on  the 
surfaces  of  various  substances. 

Carbon  possesses  in  a  marked  degree  the  prop- 
erty of  occluding  or  absorbing  gases  in  its  pores. 
These  occluded  gases  must  be  driven  out  from  the 
carbon  conductor  employed  in  an  incandescent 
lamp,  since  otherwise  their  expulsion ,  on  the  in- 
candesence  of  the  carbon,  consequent  on  the  light- 
ing of  the  lamp,  will  destroy  the  high  vacuum  of 
the  lamp  chamber  and  thus  lead  to  the  ultimate 
destruction  of  the  filament  (See  Lamp,  Electric, 
Incandescent) 

Gassing. — The  evolution  of  gas  from  the 
plates  of  a  storage  or  secondary  cell. 

Gastroscope.— An  electric  apparatus  for 
the  illumination  and  inspection  of  the  human 
stomach. 


The  light  is  obtained  by  means  of  a  platinum 
spiral  in  a  glass  tube  surrounded  by  a  layer  of 
water  to  prevent  undue  heating.  The  platinum 
spiral  is  placed  at  the  extremities  of  a  tube,  pro- 
vided with  prisms,  and  passed  into  the  stomach 
of  the  patient.  A  separate  tube  for  the  supply 
of  air  for  the  extension  of  the  stomach  is  also 
provided. 

Gastroscopy. — The  examination  of  the 
stomach  by  the  gastroscope.  (See  Gastro- 
scope) 

Gauge,  Battery. — A  form  of  portable  gal- 
vanometer, suitable  for  ordinary  testing  work. 
A  form  of  battery  gauge  is  shown  in  Fig.  282. 


Fig.  s82.    Battery  Gauge. 

Gauge,  Electrometer A  device  em- 
ployed in  connection  with  some  of  Sir  Wil- 
liam Thomson's  electrometers  to  ascertain 
whether  the  needle,  connected  with  the  layer 
of  acid  that  acts  as  the  inner  coating  of  the 
Leyden  jar  used  in  connection  therewith,  is  at 
its  normal  potential. 

Gauge,  Wire,  American A  name 

sometimes  applied  to  the  Brown  &  Sharpe 
Wire  Gauge.    (See  Ganges,  Wire,  Varieties 

of) 

Gauge,  Wire,  Birmingham A  term 

sometimes  applied  to  one  of  the  English  wire 
gauges. 

Gauge,  Wire,  Gap A  wire  gauge  in 

which  gaps  are  left  for  the  introduction  of  the 
wire  to  be  measured. 


Gail.] 


254 


[dan. 


Gauge,  Wire,  Micrometer A  gauge 

employed  for  accurately  measuring  the  di- 
ameter of  a  wire  in  thousandths  of  an  inch, 
based  on  the  principle  of  the  vernier  or  mi- 
crometer. (See  Fig.  283.) 

The  wire  to  be  measured  is  placed  between  a 
fixed  support  B,  and  the  end  C,  of  a  long  mova- 
ble screw,  which  accurately  fits  a  threaded  tube  a. 
A  thimble  D,  provided  with  a  milled  head,  fits 
over  the  screw  C,  and  is  attached  to  the  upper 
part.  The  lower  circumference  of  D,  is  divided 
into  a  scale  of  twenty  equal  parts.  The  tube  A,  is 
graduated  into  divisions  equal  to  the  pitch  of  the 
screw.  Every  fifth  of  these  divisions  is  marked 
as  a  larger  division. 

The  principle  of  the  operation  of  the  gauge  is 
as  follows:  Suppose  the  screw  has  fifty  threads  to 
the  inch,  the  pitch  of  the  screw,  or  the  distance 
between  two  contiguous  threads,  is  therefore  ^ 
or  .02  of  an  inch. 

One  complete  turn  of  the  screw  will,  therefore, 
advance  the  slteve  D,  over  the  scale  a,  the  .02  of 
an  inch.  If  the  screw  is  only  moved  through 
one  of  the  twenty  parts  marked  on  the  end  of 
the  thimble  or  sleeve  parts,  or  the  ^  of  a  com- 


plete  turn,  the  end  C,  advances  towards  B,  the 

sV  of  A»  *'•  '•»  TffW  or  -001  inch- 

Suppose  now  a  wire  is  placed  between  B  and 
C,  and  the  screw  advanced  until  it  fairly  fills  the 


Fig.  283.     Vernier  Wire  Gattg>e. 
space  between  them,  and  the  reading  shows  two 
of  the  larger  divisions  on  the  scale  a,  three  of  the 
smaller  ones  and  three  on  the  end  of  the  sleeve 
D,  then 

Two  large  divisions  of  scale  a =     .2      inch 

Three  smaller  divisions  of  scale  a..  =     .06       " 
Three  divisions  on  circular  scale 
onD =     .003     " 

Diameter  of  wire .263 

Serious  inconvenience  has  arisen  in  practice 


NEW  LEGAL  STANDARD  WIRE  GAUGE  (ENGLISH). 
Tables  of  Sizes,  Weights,  Lengths  and  Breaking  Strains  of  Iron  Wire. 


Size  oi 
Wire 
Gauge 

Diameter. 

i 

Sectional 
area  in 
sq.  inches. 

Weight  of 

Length  of 
Cwt. 

Breaking  Strains. 

Size  on 
Wire 
Gauge. 

Inch. 

Millimetres. 

100  yards. 

Mile. 

Annealed. 

Bright. 

Lbs. 

Lbs. 

Yards. 

Lbs. 

Lbs. 

5/0.  ••• 

.500 
.464 
•432 

XI. 

.1963 
.1691 
.1466 

144. 

34°4 
2930 
2541 

I 

10470 
9017 
7814 

15700 
13525 
11725 

$ 

5/o 

4/0.       . 

.400 

XO.2 

.1257 

123. 

2179 

*    91 

6702 

10052 

4/o 

•37* 
.348 

h 

.1087 
.0051 

107. 
§3- 

25 

1649 

xos 

5796 
5072 

8694 
7608 

3/o 

2/0 

*£  : 

.324 

8.3 

.0824 

81. 

1429 

38 

4397 

6595 

I/O 

i. 

a. 
3« 

.252 

7.6 

.0707 
.0598 
.0499 

69. 
58. 
49- 

1225 
•g 

61 

28 

377° 

23 

5655 
4785 

2 

3 

4- 

.232 

5-9 

5-4 
4-9 

.0423 
•°353 
.0290 

41- 

11: 

III 

502 

269 

322 
393 

38 

1544 

&4 

4 
1 

1: 

.192 

?• 

•35 

4-5 

•0243 

24. 

22 

467 

!298 

1946 

7 

8. 

.160 

4-1 

.0201 

*9- 

48 

566 

1072 

1608 

X 

9- 

.144 

3-7 

.0163 

16. 

700 

869 

1303 

9 

to. 

.128 

3-3 

.0129 

12. 

23 

882 

687 

1030 

10 

i. 

•  1x6 

3- 

.0106 

xo. 

83 

1077 

564 

845 

it 

2. 

.104 

2.6 

•°°85 

8-4 

48 

1333 

454 

680 

12 

3- 

.002 

2.3 

.0066 

6-5 

14 

1723 

355 

532 

13 

4- 

.080 

a. 

.0050 

5- 

88 

2240 

268 

402 

14 

I: 

.072 
.064 

.8 
.6 

.0041 

.0032 

4- 

3-2 

56 

2800 
3500 

218 
172 

326 
257 

11 

7. 

.056 

.4 

.0025 

42 

4667 

"97 

'7 

8. 

.048 

.2 

.0018 

i  .8 

32 

6222 

97 

'45 

A 

19. 

.040 

.0013 

I  .2 

21 

9333 

67 

100 

'9 

»o. 

.036 

id 

.0010 

*' 

18 

II200 

55 

82 

20 

(Issued  by  the  Iron  and  Steel  Wire  Manufacturers'  Association.) 


(Jan.] 


255 


[Gau. 


from  the  numerous  arbitrary  numbers  of  sizes  of 
wires  employed  by  different  manufacturers. 
These  differences  are  gradually  leading  to  the 
abandonment  of  arbitrary  sizes  for  wires  and  em- 
ploying in  place  thereof  the  diameters  directly  in 
inches  or  thousandths  of  an  inch. 

Gauge,  Wire,  Round —A  device  for 

accurately  measuring  the  diameter  of  a  wire. 

The  round  wire  gauge  shown  in  Fig.  284  is 
very  generally  used  for  telegraph  lines.  Notches 


Fig.  284.    Round  Wire  Gauge. 

for  varying  widths,  cut  in  the  edges  of  a  circular 
plate  of  tempered  steel,  serve  to  approximately 
measure  the  diameter  of  a  wire,  the  sides  of  the 
wire  being  passed  through  the  slots.  Numbers, 
indicating  the  different  sizes  of  the  wire,  are 
affixed  to  each  of  the 
openings. 

Gauge,  Wire,  Self- 
Registering  A 

wire  gauge  arranged 
to  give  the  exact  di- 
ameter of  the  wire  to 
be  measured  directly 
without  calculation. 

A  form  of  self -register- 
ing wire  gauge  is  shown 
in  Fig.  285.  The  wire 
or  plate  is  inserted  in  the 
gap  between  a  fixed  and 
a  movable  plate.  The 


Fig.  28s.     Wire  and 
Plate  Gauge. 


Gauge,  Wire,  Standard A  wire 

gauge  adopted  by  the  National  Telephone 
Exchange  Association  at  Providence,  R.  I., 
and  by  the  National  Electric  Light  As- 
sociation, at  Baltimore,  Md.,  in  February, 
1886. 

The  value  of  the  standard  as  compared  with 
the  other  gauges  will  be  seen  from  an  inspection 
of  the  table  in  this  column: 

Gauges,    Wire,  Tarieties  of The 

following  table  gives  a  comparison  of  the 
principal  wire  gauges  in  use. 

COMPARISON   OF  THE    DIFFERENT  WIRE 
GAUGES. 


numbers  corresponding  to  the  diameter  of  the 
wire  or  plate  are  shown  on  one  side  of  the  gauge 
and  the  gauge  numbers  on  the  other  side. 


.40964 
.3648 
•32495 
.2893 
•25763 
.22942 

.2043! 
.18194 
. 16202 
.14428 


071961 
.064084 
.057068 
.05082 
•045257 
.040303 
.035390 


.022571 

.0201 
.0179 

.01394 
.014195 
.012641 
.011257 
.010025 
.008928 


.006304 

.005614 

.005 

.004453 

.003965 

•003531 

.003144 


a 


.46 
•43 
•393 
.362 
•331 
•307 
.283 


.225 

.207 
.192 
•i?7 
.  i62 
.148 
•'35 


.072 
.063 
.052 
.047 
.o4I 
.035 
.033 
.028 
.025 
.023 


•o  5 
.o  4 
.0135 


•0095 

:^S 
.008 
.0075 
.007 


ron 
ton, 


en 

;. 


Tren 
Co., 


•MS 
•13 

•«75 
.105 

•0925 


•0525 

•045 

.039 

•034 

.03 

•27 

.024 

.0215 

.'oil 


.013 

.012 
.Oil 

:3 

.00725 
.0065 
•00575 
.005 


.018 
.0164 
.o,48 
.0136 

.0124 

.0116 


.006 

.0052 
.0048 


it 


.083 


•0155 
•01375 
.01235 

.01135 
.01025 

.0095 
.009 

.0075 
.0065 
•00575 

•0045 


256 


[Gi 


NUMBER,    DIAMETER,    WEIGHT,    LENGTH    AND   RESISTANCE    OF    PURE    COPPER 

WIRE. 

American  Gauge. 


No. 

Diameter. 
Inches. 

Wetght.sp.gr.  =8.889. 

Length. 

Resistance  of  Pure  Copper  at  70°  Fahrenheit. 

Grs.  per  It. 

Lbs.  per  ,,ooo 
feet. 

Ft.  per  Ib. 

Ohms  per  1,000  ft. 

Feet  per  ohm. 

Ohms  per  Ib. 

0000.  .. 

.46000 

4475-33 

640.40 

,.56 

.051 

,9605.69 

.0000798 

000... 

.40964 

3549.07 

507.0, 

i-97 

.064 

I5547.87 

.000127 

00... 

.36480 

28,4.62 

402.09 

2-49 

.081 

,2330.36 

.000202 

0... 

.32486 

2233.28 

319.04 

3-13 

.102 

0783.63 

.000320 

I... 

.28930 

,770.13 

252.88 

3-95 

.129 

7754-66 

-00051 

2.  .  . 

•25763 

1403.79 

2OO-54 

4.99 

•l63 

6,49.78 

.0008,1 

3... 

.22942 

11,3.20 

159-03 

6.29 

.205 

4876.73 

.001289 

4... 

.2043, 

882.85 

,.26.12 

7-93 

.259 

3867.62 

.00205 

.,8194 

700.10 

,00.0, 

,0.00 

.326 

3067.06 

.00326 

6.  .  . 

.  16202 

555-  o 

79-32 

12.6, 

2432.22 

.00518 

I*" 

•  14429 

440-27 

O2.9O 

15-90 

.519 

1928.75 

.00824 

8... 
9... 

.12849 
•"443 

349-18 
276.94 

49.88 
39-56 

£3 

•654 
.824 

1529-69 
12,3.22 

.013,1 

.02083 

10... 

.10190 

219.57 

3'-37 

31.88 

1.040 

961.91 

-03314 

XI.  .. 

.09074 

174-15 

24.88 

40.20 

I.3II 

762.93 

.05269 

12. 

.0808, 

,38.11 

19-73 

50.69 

I-653 

605.03 

.08377 

13... 
14... 

.07,96 
.06408 

•8:8 

15-65 

12.41 

63.91 
80.59 

2.084 
2.628 

479.80 
380.51 

•13321 

.21,8 

«... 

.05707 

68.88 

9.84 

,01.63 

3-3H 

301-75 

.3368 

16... 

3-:: 
19... 

.05082 
-04525 

43-32 
34-35 
26  49 

7.8! 
6.19 
4.9, 

3-78 

128.14 

161.53 

203.76 

264  .  26 

4-179 
5-269 
6.645 
8.6,7 

239.32 
,89.78 
,50.50 
116.05 

•5355 
•  8515 
'•3539 
2.2772 

30... 
31... 

.02846 

31.  6l 

i  .13 

3.09 
2-45 

324.00 
408.56 

10.  566 

,3.323 

94.65 
75.06 

5.443 

22'.  .  . 

•025347 

i  -59 

1.94 

5'5-i5 

16.799 

59-53 

8.654 

23... 

.022572 

10.77 

1-54 

649.66 

2,.  l8S 

47-20 

24... 

.0201 

•54 

1.22 

819.2, 

26.713 

37-43 

2,;  885 

25... 

.0,79 

.78 

•97 

,032.96 

33  684 

29.69 

34-795 

26... 
27... 

•01594 
.014,95 

3 

•77 
.6, 

1302.6, 
1642.55 

42-477 
53-563 

23 

55-331 
87.979 

28... 
29... 

.0,2641 
.01,258 

£ 

"S 

2071.22 
26,1.82 

67.542 
85.,  70 

M-8, 

139.893 
222.449 

30... 

.010025 

•13 

.30 

3293-97 

107.391 

9-31 

353-742 

31... 

.008928 

.69 

•  24 

4,52.22 

,35.402 

7-39 

562  .  22  I 

33... 

.00795 

•34 

.19 

5236.66 

170.765 

5.86 

894.242 

33-  •• 

.00708 

.06 

•*5 

660.271 

215.3,2 

4.64 

M2I.646 

34--- 

.0063 

.84 

8328.30 

271-583 

3.68 

2261.82 

35-  •• 

.00561 

•67 

.10 

10501  .  35 

342.413 

2.92 

3596.104 

36... 
37-  •• 

.005 
•00445 

•53 
•42 

.08 

.06 

13258.83 
16691.06 

43I-7I2 
544-287 

1:11 

9084.71 

38... 

.003965 

•34 

.°5 

20854.65 

686.5,, 

,.46 

14320.26 

39-  •• 

•003531 

.27 

.04 

26302.23 

865.046 

,.,6 

22752.6 

40... 

.003,44 

.2, 

.03 

33I75-94 

,091.865 

.92 

36223.59 

Gauss. — The  unit  of  intensity  of  magnetic 
field. 

The  term  gauss  for  unit  of  intensity  of  mag- 
netic field  was  proposed  by  S.  P.  Thompson  as 
being  that  of  a  field  whose  intensity  is  equal  to 
lo8  C.  G.  S.  units,  that  is,  lo1*  lines  of  force  per 
square  centimetre. 

J.  A.  Fleming  proposes,  for  the  value  of  the 
gauss,  such  strength  of  field  as  would  develop  an 
electromotive  force  of  one  volt  in  a  wire  one 
million  centimetres  in  length,  moving  through 
such  a  field  with  unit  velocity. 

Fleming's  value  for  the  gauss  was  assumed  on 
account  of  the  small  value  of  the  gauss  proposed 


by  S.  P.  Thompson.  It  is  one  hundred  times 
greater  in  value  than  Thompson's  gauss. 

Sir  William  Thomson  proposes,  for  the  value  ol 
the  gauss,  such  an  intensity  of  magnetic  field  as  is 
produced  by  a  current  of  one  weber  (ampere)  at 
the  distance  of  one  centimetre. 

Gauss,  Fleming's Such  a  strength 

of  magnetic  field  as  is  able  to  develop  an 
electromotive  force  of  one  volt  in  a  wire  one 
million  centimetres  in  length  moved  through 
the  field  with  unit  velocity.  (See  Gauss.) 

Gauss,  S.  P.  Thompson's  —  —Such  a 
strength  of  magnetic  field  that  its  intensity 
is  equal  to  10"  C.  G.  S.  units.  ,  (See  Gauss.) 


Oau.] 


257 


[Gen. 


Gauss,  Sir  William  Thomson's 

Such  an  intensity  of  magnetic  field  as  would  be 
produced  by  a  current  of  one  ampere  at  the 
distance  of  one  centimetre.  (See  Gauss.) 

Geissler  Mercurial  Pump. — (See  Pump, 
Air,  Geissler,  Mercurial.} 
Geissler  Tubes. — (See  Tubes,  Geissler.} 

General  Faradization. — (See  Faradiza- 
tion, General.) 

General  Galvanization. — (See  Galvaniza- 
tion, General.} 

Generation  of  Current  by  Dynamo-Elec- 
tric Machine. — (See  Current,  Generation  of, 
by  Dynamo-Electric  Machined) 

Generator,  Dynamo-Electric An 

apparatus  in  which  electricity  is  produced  by 
the  mechanical  movement  of  conductors 
through  a  magnetic  field  so  as  to  cut  the 
lines  of  force. 

A  dynamo-electric  machine.  (See  Machine, 
Dyna  mo-Electric?) 

A  dynamo  electric  machine  operates  on  the 
general  principles  of  electro-dynamic  induction. 
Strictly  speaking,  however,  in  a  dynamo-electric 
generator  the  conductors  are  actually  moved 
through  the  lines  of  force.  In  this  respect,  there- 
fore, a  dynamo-electric  generator  differs  from  a 
transformer,  in  which  the  lines  of  force  are  moved 
through  the  conductor.  (See  Induction,  Electro- 
Dynamic.  Transformer.  Induction,  Mutual.) 

Generator,  Motor A  dynamo-elec- 
tric generator  in  which  the  power  required  to 
drive  the  dynamo  is  obtained  from  an  elec- 
tric current. 

Motor  generators  are  used  in  systems  of  elec- 
trical distribution  for  the  purpose  of  changing 
the  potential  of  the  current.  They  consist  of 
dynamos,  the  armatures  of  which  are  furnished 
with  two  separate  windings,  of  fine  and  coarse 
wire  respectively.  One  of  these,  generally  the 
fine  wire,  receives  the  driving  or  motor  cur- 
rent, usually  of  high  potential,  and  the  other, 
the  coarse  wire,  furnishes  the  current  used,  usu- 
ally of  low  potential. 

The  advantage  of  having  the  windings,  which 
receive  the  driving  current,  of  fine  wire,  is  to 
enable  a  current  of  high  potential  to  be  dis- 
tributed over  the  line  from  distant  stations  to 


places  where  it  is  desired  to  use  the  energy  of  the 
current  at  a  much  lower  potential. 

Motor  generators  often  consist  simply  of  two 
distinct  machines  mechanically  connected,  one 
acting  as  a  motor  and  the  other  as  a  dynamo. 

Motor  generators  are  sometimes  called  dynamo- 
motors  or  dynamotors. 

Aldrich  draws  the  following  distinction  between 
a  dynamo-motor  and  a  dynamotor  : 

(I.)  A  dynamo-motor  is  an  energy  transformer 
with  the  dynamo  and  motor  in  the  same  electric 
circuit. 

(2.)  A  dynamotor  is  an  energy  transformer  with 
the  dynamo  and  motor  in  the  same  magnetic  cir- 
cuit. 


Fig.  286.    Edison's  Pyro-Magnetic  Generator. 

Generator,  Pyro-Magnetic An  ap* 

paratus  for  producing  electricity  directly  from 
heat  derived  from  the  burning  of  fuel. 


Gen.] 


258 


[Gil. 


The  operation  of  the  pyro-magnetic  generator 
is  dependent  upon  the  fact  that  any  variation  in 
the  number  of  lines  of  magnetic  force  that  pass 
through  a  conductor  will  develop  differences  of 
electric  potential  therein.  Such  variations  may 
be  effected  either  by  varying  the  position  of  the 
conductor  as  regards  the  magnetic  field,  or  by 
varying  the  magnetic  field  itself.  The  latter 
method  of  generating  differences  of  potential  is 
utilized  in  the  pyro-magnetic  generator,  and  is 
effected  in  it  by  varying  the  magnetization  of  rolls 
of  thin  iron  or  nickel  by  the  action  of  heat. 

A  form  of  pyro-magnetic  generator  devised  by 
Edison  is  shown  in  Figs.  286  and  287. 


Fig.  287,    Edison's  Pyro- Magnetic  Generator. 

This  apparatus  is  sometimes  called  a  pyro- 
magnetic  dynamo. 

Eight  electro-magnets  are  provided,  each  with 
an  armature  consisting  of  a  roll  of  corrugated 
iron.  Each  of  these  armatures  is  provided  with 
a  coil  of  insulated  wire  wound  on  it  and  pro- 
tected by  asbestos  paper.  The  armatures  pass 
through  two  iron  discs  as  shown.  The  armature 
coils  are  connected  in  series  in  a  closed-circuit, 
the  wires  from  the  coils  being  connected  with 
metallic  brushes  that  rest  on  a  commutator  sup- 
ported on  a  vertical  axis.  A  pair  of  metallic 
rings  is  provided  above  the  commutator  to  carry 
off  the  current  generated. 

The  vertical  axis  is  provided  below  with  a  semi- 
circular screen  called  a  guard  plate  which  rotates 
with  the  axis  and  cuts  off  or  screens  one-half  the 
iron  armatures  from  the  heated  air. 

When  the  axis  is  rotated,  the  difference  in  the 


magnetization  of  the  armatures,  when  hot  and 
cold,  develops  electromotive  forces  which  result 
in  the  production  of  an  electric  current. 

Generator,  Secondary A  term  fre- 
quently employed  for  a  converter  or  trans- 
former. 

The  word  transformer  is  now  almost  univer- 
sally employed.  (See  Transformer.) 

Generator,  Watt A  term  sometimes 

employed  for  stating  the  power  in  watts  that 
any  electric  source  is  capable  of  producing. 

Estimating  the  power  of  a  dynamo-electric 
machine  by  the  number  of  watts  it  is  capable  of 
producing  is  very  convenient  in  practice,  and  is 
now  very  generally  adopted.  A  dynamo  capable 
of  furnishing  a  difference  of  potential  of  1,000 
volts,  and  a  current  of  10  amperes,  would  be  said 
to  be  a  10,000  watt-generator. 

The  term  watt-generator,  though  applicable  to 
the  case  of  any  electric  source,  is  in  practice 
generally  limited  to  the  case  of  dynamo-electric 
machines  or  secondary  batteries. 

Generators,  Motor,  Distribution  of  Elec- 
tricity by (See  Electricity,  Distribu- 
tion of,  by  Motor  Generators?) 

Geographical  Distribution  of  Thunder 
Storms. — (See  Storms,  Thunder,  Geograph- 
ical Distribution  of.) 

Geographical  Equator. — (See  Equator, 
Geographical?) 

Geographical  Meridian. — (See  Meridian, 
Geographical?) 

German  Silver  Alloy.— (See  Alloy,  Ger- 
man Silver?) 

Gilding,  Electric The  electrolytic 

deposition  of  gold  on  any  object. 

Electro-plating  with  gold.  (See  Plating, 
Electro) 

The  surfaces  of  the  object  to  be  gilded  are 
made  electrically  conducting,  if  not  already  so, 
and  are  then  connected  to  the  negative  terminal 
of  a  voltaic  cell  or  other  source,  and  immersed  in 
a  plating  bath  containing  a  solution  of  a  salt  of 
gold,  directly  opposite  a  plate  of  gold,  connected 
with  the  positive  terminal  of  the  source.  The 
objects  to  be  plated  thus  become  the  kathode,  and 
the  plate  of  gold  the  anode  of  the  plating  bath. 
On  the  passage  of  a  suitable  current,  the  gold  is 
dissolved  from  the  plate  at  the  anode  and  deposited 


Oil.] 


259 


[Gov. 


on  the  object  at  the  kathode.     (See  Bath,  Gold. 
Kathode.     Anode.} 

Gilt  Plumbago.— (See  Plumbago,  Gilt.) 

Gimbals. — Concentric  rings  of  brass,  sus- 
pended on  pivots  in  a  compass  box,  and  on 
which  the  compass  card  is  supported  so  as  to 
enable  it  to  remain  horizontal  notwithstand- 
ing the  movements  of  the  ship.  (See  Com- 
pass, Azimuth.) 

Each  ring  is  suspended  on  two  pivots  placed 
directly  opposite  each  other,  that  is,  at  the  ends 
of  a  diameter,  which  in  one  ring  is  at  right  angles 
to  that  in  the  other. 

Girder  Armature. — (See  Armature,  Gir- 
der) 

Globe,  Vapor,  of  Incandescent  Lamp 
A  glass  globe  surrounding  the  cham- 
ber of  an  incandescent  electric  lamp,  for  the 
purpose  of  enabling  the  lamp 'to  be  safely 
used  in  an  explosive  atmosphere,  or  to  permit 
the  lamp  to  be  exposed  in  places  where  water 
is  liable  to  fall  on  it. 

Such  a  vapor  globe  is  shown  in  Fig.  288.  In 
the  event  of  accidental  breakage  of  the  outside 
globe,  the  lamp  chamber 
proper  prevents  the  igni- 
tion of  the  explosive 
gases.  In  such  cases, 
however,  the  outer  pro- 
tecting chamber  should 
be  promptly  replaced. 

In  some  forms  of  vapor 
globes,  a  valve  is  pro- 
vided, opening  outwards, 
in  order  to  permit  the  ex- 
panded air  to  escape 
when  a  given  pressure  is 
reached,  and  yet,  at  the 
same  time,  to  prevent  the 
entrance  of  gas  or  vapor 
from  without. 

Glow  Discharge.— 
(See  Discharge,  Glow.) 

Glow  Lamp. — (See  Lamp,  Electric  Glow.) 

Gold  Bath.— (See  Bath,  Gold.) 

Gold-Leaf  Electroscope.— (See  Electro- 
scope, Gold-Leaf) 

Gold-Plating.-(See  Plating,  Gold.) 

Gong,  Electro-Mechanical A  gong 


Fig-  288      Vapor  Globe. 


struck  or  operated  by  mechanical  force  at 
times  which  are  dependent  on  the  passage  of 
an  electric  current. 

The  motive  power  is  the  mechanical  force,  de- 
veloped by  a  bent  spring,  the  fall  of  a  weight, 
etc. ,  and,  by  suitable  mechanism,  is  permitted  to 
act  only  on  the  passage  of  an  electric  current. 

Governor,  Centrifugal A  device  for 

maintaining  constant  the  speed  of  a  steam 
engine  or  other  prime  mover,  despite  sudden 
changes  in  the  load  or  work. 

In  a  ball  governor,  any  increase  in  speed 
causes  the  balls  to  fly  out  from  the  centre  of  rota- 
tion by  centrifugal  force.  This  motion  is  utilized 
to  control  a  valve  or  other  regulating  device.  If 
the  speed  of  the  engine  falls,  the  balls  move 
towards  the  centre,  shifting  the  valve  or  regulat- 
ing device  in  the  opposite  direction. 

Governor,  Current A  current  regu- 
lator. 

A  device  for  maintaining  constant  the  cur- 
rent strength  in  any  circuit. 

Current  governors  are  either  automatic  or  non- 
automatic.  (See  Regulation,  Automatic.) 

Governor,  Electric A  device  for 

electrically  controlling  the  speed  of  a  steam 
engine,  the  direction  of  current  in  a  plating 
bath,  the  speed  of  an  electric  motor,  the  re- 
sistance of  an  electric  circuit,  the  flow  of 
water  or  gas  into  or  from  a  containing  vessel, 
or  for  other  similar  purposes. 

The  particular  form  assumed  by  the  apparatus 
varies  with  the  character  of  the  work  it  is  intended 
to  accomplish.  In  some  cases  an  ordinary  ball 
or  centrifugal  governor  is  employed  to  open  or 
close  a  circuit;  or,  a  mass  of  mercury  in  a  rotat- 
ing vessel  is  caused,  at  a  certain  speed,  to  open  or 
close  a  circuit;  or,  the  resistance  of  a  bundle  of 
carbon  discs  is  caused  to  vary,  either  by  pressure 
produced  by  centrifugal  force,  or  by  the  move- 
ment of  an  armature. 

Governor,  Periodic A  name  ap- 
plied by  Ayrton  &  Perry  to  a  form  of  gover- 
nor for  an  electric  motor,  in  which  the  cur- 
rent is  automatically  cut  out  for  a  certain 
portion  of  each  revolution. 

Governor,  Spasmodic A  name 

given  by  Ayrton  &  Perry  to  a  form  of  gover- 
nor for  an  electric  motor,  in  which  the  cur- 


Gov.J 


260 


[Gra- 


rent  is  automatically  cut  off  in  proportion  as 
the  work  is  cut  off. 

The  spasmodic  governor  consists  essentially  of  a 
cone  dipping  into  the  surface  of  mercury  in  a  rotat- 
ing vessel.  As  the  speed  of  the  governor  increases 
on  a  lightening  of  the  load,  the  surface  of  the  mer- 
cury is  curved  by  the  increased  centrifugal  force, 
until  finally  the  mercury  leaves  the  contact  point 
and  thus  cuts  off  the  current. 

Governor,  Steam,  Electric A  de- 
vice used  in  connection  with  a  valve  to  so 
electrically  regulate  the  supply  of  steam  to  an 
engine,  that  the  engine  shall  be  driven  at 
such  a  speed  as  will  maintain  either  a  con- 
stant current  or  a  constant  potential. 

In  the  electric  governor,  the  steam  valve  is 
operated  by  an  electro-magnet,  whose  coils,  in 
the  case  of  a  constant  current  machine,  are  of 
thick  wire  placed  in  the  main  circuit,  and,  in 
that  of  a  constant  potential  machine,  are  of  thin 
wire  placed  in  a  shunt  around  the  mains. 

Gradnators. — Devices,  generally  electro- 
magnetic, employed  in  systems  of  simultane- 
ous telegraphic  and  telephonic  transmission 
over  the  same  wire,  so  inserted  in  the  line  cir- 
cuit as  to  obtain  the  makes  and  breaks  re- 
quired in  a  system  of  telegraphic  communi- 
cation so  gradually  that  they  fail  to  sensibly 
influence  the  diaphragm  of  a  telephone  placed 
in  the  same  circuit. 

Gramme. — A  unit  of  weight  equal  to 
I5-43235  grains. 

The  gramme  is  equal  to  the  weight  of  one  cubic 
centimetre  of  pure  water  at  the  temperature  of  its 
maximum  density.  It  has  various  multiples  and 
decimal  divisions— of  the  former,  the  kilogramme 
or  one  thousand  grammes  is  the  most  frequently 
used;  of  the  latter,  the  centigramme  or  the  one- 
hundredth  of  a  gramme,  and  the  milligramme  or 
the  one -thousandth  of  a  gramme.  (See  Weights 
and  Measures i  Metric  System  of.) 

Gramme  Atom.— (See  Atom,  Gramme?) 

Gramme  Molecnle.— (See  Molecule. 
Gramme?) 

Gramophone. — An  apparatus  for  record- 
ing and  reproducing  articulate  speech.  (See 
Phonograph .) 

Gramophone  Record. — (See  Record, 
Gramophone?) 


Graphite.— A  soft  variety  of  carbon  suit- 
able for  writing  on  paper  or  similar  surfaces. 

Graphite  is  the  material  that  is  employed  for 
the  so-called  black  lead  of  lead  pencils.  It  is 
sometimes  called  plumbago.  Strictly  speaking, 
the  term,  graphite  is  only  applicable  to  the  variety 
of  plumbago  suitable  for  use  in  lead  pencils. 

Graphite  is  used  for  rendering  surfaces  to  be 
electro-plated,  electrically  conducting,  and  also  for 
the  brushes  of  dynamos  and  motors.  For  the 
latter  purpose  it  possesses  the  additional  advantage 
of  decreasing  the  friction  by  means  of  its  marked 
lubricating  properties. 

Graphophone,  Micro A  modifica- 
tion of  the  phonograph  in  which,  instead  of  a 
single  diaphragm,  a  number  of  separate  non- 
metallic  diaphragms  are  caused  to  act  on  a 
single  diaphragm  to  record  the  speech,  so  that 
the  separate  diaphragms  can  be  thrown  into 
strong  vibration  when  reproducing  the  speech. 

Graphophone,  Phonograph A  term 

sometimes  applied  to  the  graphophone.  (See 
Graphophone,  Micro.  Phonograph^) 

Graphophone  Record. — (See  Record, 
Graphophone?) 

Gray's  Harmonic  Telegraphic  Analyzer. 
— (See  Analyzer,  Grays  Harmonic  Tele- 
graphic?) 

Gray's  Harmonic  Telegraphy.— (See  Te- 
legraphy, Grays  Harmonic  Multiple?) 

Gravitation. — A  name  applied  to  the  force 
which  causes  masses  of  matter  to  tend  to 
move  towards  one  another. 

This  motion  is  assumed  to  be  that  of  attraction, 
that  is,  the  bodies  are  assumed  to  be  drawn  to- 
gether. It  is  not  impossible,  however,  that  they 
may  be  pushed  together. 

Gravitation,  like  electricity,  is  well  known,  so 
far  as  its  effects  are  concerned ;  but,  as  to  the  true 
cause  of  either,  particularly  the  former,  we  are  in 
comparative  ignorance. 

The  general  facts  of  gravitation  may  be  suc- 
cinctly stated  by  the  following  law,  generally 
known  as  Newton's  law. 

Every  particle  of  matter  in  the  universe  is  at- 
tracted by  every  other  particle  of  matter,  and 
itself  attracts  every  other  particle  of  matter,  with 
a  force  which  is  directly  proportional  to  the  pro- 
duct of  the  masses  of  the  two  quantities  of  matter 


tira.] 


261 


[Gna. 


and  inversely  proportional  to  the  square  of  the 
distance  between  them. 

Gravity  Ammeter. — (See  Ammeter,  Grav- 
ity) 

Gravity,  Centre  of The  centre  of 

weight  of  a  body. 

Bodies  supported  at  their  centres  of  gravity  are 
in  equilibrium,  since  their  weight  is  then  evenly 
distributed  around  the  point  of  support. 

Gravity-Drop  Annunciator.— (See  An- 
nunciator, Gravity-Drop?) 

Gravity,  Voltaic  Cell (See  Cell, 

Voltaic,  Gravity?) 

Gravity  Voltmeter. — (See  Voltmeter, 
Gravity?) 

Great  Calorie. — (See  Calorie,  Great '.) 

Grenet  Voltaic  Cell.— (See  Cell,  Voltaic, 
Grenet?) 

Grid. — A  lead  plate,  provided  with  perfor- 
ations, or  other  irregularities  of  surface,  and 
employed  in  storage  cells  for  the  support  of 
the  active  material. 

The  support  provided  for  the  active  material 
on  the  plate  of  a  secondary  or  storage  cell. 

The  grid  receives  its  name  from  its  resemblance 
to  a  gridiron.  The  active  material  is  generally 
maintained  on  the  grid  by  means  of  variously 
shaped  apertures  or  holes.  These  are  generally 
larger  near  the  centre,  so  as  to  prevent  the  falling 
out  of  the  material  after  it  has  been  hardened  by 
compression.  (See  Cell,  Secondary.  Cell,  Star- 

<«*•) 

Various  forms  have  been  given  to  the  grid. 
The  object  of  these  iForms,  in  general,  is  to  in- 
sure the  retention  of  the  active  material  by  the 
grid. 

The  grids  are  preferably  suspended  from  suit- 
able supports  fastened  to  the  top  of  the  battery 
jars,  instead  of  resting  on  the  bottom  of  the  bat- 
tery jars. 

Grip,  Cable A  grip  provided  for 

seizing  the  end  of  a  cable  when  it  is  to  be 
drawn  into  a  duct  or  conduit. 

Grove's  Yoltaic  CelL— (See  Cell,  Voltaic, 
Grove.} 

Grothuss'  Hypothesis.— (See  Hypothesis, 
Grothuss'.} 


Ground  Circuit— (See  Circuit,  Ground} 

Ground  Detector. —(See  Detector, 
Ground?) 

Ground  or  Earth.— A  general  term  for 
the  earth  when  employed  as  a  conductor,  or 
as  a  large  reservoir  of  electricity. 

The  term  ground  is  also  applied  to  a  fault 
caused  by  an  accidental  and  undesired  connection 
between  an  electric  circuit,  line  or  apparatus  and 
the  ground.  (See  Fault.} 

Ground  Plate  of  Lightning  Protec- 
tor.— (See  Plate,  Ground,  of  Lightning 
Protector?] 

Ground-Return. — A  general  term  used 
to  indicate  the  use  of  the  ground  or  earth 
for  a  part  of  an  electric  circuit. 

The  earth  or  ground  which  forms  part  of 
the  return  path  of  an  electric  circuit. 

The  ground-return  is  generally  used  in  the 
Morse  system  of  telegraphy  as  practiced  in  the 
United  States. 

Ground-Wire.— The  wire  or  conductor 
leading  to  or  connecting  with  the  ground  or 
earth  in  a  grounded  circuit. 

This  is  sometimes  called  an  earth-grounded 
wire. 

A  circuit  is  grounded  when  it  is  completed  in 
part  by  the  ground  or  earth. 

Grounded  Circuit.— (See  Circuit, 
Grounded?) 

Growth  or  Expansion  of  Lines  of  Force. 

— (See  Force,  Lines  of,  Growth  or  Expan- 
sion of?) 

Guard,  Fan — A  wire  netting  placed 

around  the  fan  of  an  electric  motor  for  the 
purpose  of  preventing  its  revolving  arms 
from  striking  external  objects. 

Guard,  Lightning A  term  some- 
times used  for  lightning  rod.  (See  Rod, 

Lightning?) 

Guard,  Transformer,  Lightning 

A  transformer  lightning  arrester.  (See  Ar* 
rester,  Lightning,  Transformer?) 


Gua.] 


262 


[Hal. 


Guard,  Wire  Shade A  guard  of 

wire  netting  provided  for  the  protection  of  a 
shade. 

A  form  of  wire  shade  is  shown  in  Fig.  289. 


Fig.  289.     Wire  Shade  Guard. 

Gutta-Percha. — A  resinous  gum  obtained 
from  a  tropical  tree,  and  valuable  electrically 
for  its  high  insulating  powers. 

Gutta-percha  readily  softens  by  heat,  but  on 


cooling  becomes  hard  and  tough.  Unlike  India- 
rubber,  it  possesses  but  little  elasticity.  Its 
specific  inductive  capacity  is  4.2,  that  of  air  being 
I,  and  of  vulcanized  rubber,  2.94.  (See  Capacity, 
Specific  Inductive.) 

Gutta-percha  is  obtained  largely  from  the  East 
Indies,  from  a  tree  which  yields  a  brownish  gum. 
It  is  a  fibrous  and  tenacious  substance  with  but 
little  flexibility,  and  is  unaffected  by  acids.  Oils 
produce  less  effect  upon  it  than  on  India-rubber. 

Gutta-percha  is  one  of  the  best  insulating  mate- 
rials known  for  sub-aqueous  cables. 

Gymnotns  Electricus.— The  electric  eel. 
(See  Eel,  Electric) 

Gyrometer.— A  speed  indicator.  (See  In- 
dicator, Speed^ 


H. — A  contraction  for  the  horizontal  inten- 
sity of  the  earth's  magnetism. 

H. — A  contraction  proposed  for  one  unit 
of  self-induction. 

H. — A  contraction  used  in  mathematical 
writings  for  the  magnetizing  force  that  exists 
at  any  point,  or,  generally,  for  the  intensity  of 
the  magnetic  force. 

The  letter  H,  when  used  in  mathematical 
writings  or  formulae  for  the  intensity  of  the 
magnetic  force,  is  always  represented  in  bold  or 
heavy  faced  type,  thus  :  H . 

H-Armature    Core. — (See    Core,  Arma- 
ture, H.) 
Hail,  Assumed  Electric  Origin  of 

A  hypothesis,  now  generally  rejected,  framed 
to  explain  the  origin  of  the  alternate  coatings 
of  ice  and  snow  in  a  hail  stone,  by  the  alter- 
nate electric  attractions  and  repulsions  of 
the  stones  between  neighboring,  oppositely 
charged,  snow  and  rain  clouds. 

It  is  now  generally  recognized  that  the  electric 
manifestations  attending  hail  storms  are  the 
effects  and  not  the  causes  of  the  hail.  (See  Para- 
grtfts.) 

Hair,  Electrolytic  Removal  of 

The  permanent  removal  of  hair  from  any  part 


of  the  body,  by  the  electrolytic  destruction  of 
the  hair  follicles. 

A  platinum  negative  electrode  is  inserted  in  the 
hair  follicle  and  the  positive  electrode,  covered  with 
moist  sponge  or  cotton,  is  held  in  the  hand  of  the 
patient.  A  current  of  from  two  to  four  milli.am- 
peres  from  a  battery  of  from  eight  to  ten  Le- 
clanche  elements  is  then  passed  for  from  ten  to 
thirty  seconds.  A  few  bubbles  of  gas  appear, 
and  the  hairs  are  then  removed  from  the  follicles 
by  a  pair  of  forceps.  (See  Milli-  Ampere. ) 

When  the  work  is  properly  done  there  is  no 
destruction  of  the  skin  and  therefore  no  marks  or 
scars. 

In  the  removal  of  hair  from  the  face,  it  is  pref- 
erable that  the  current  should  slowly  reach  its 
maximum  strength. 

Half-Shades  for  Incandescent  Lamps. 
— Sbr/tes  for  incandescent  electric  lamps,  in 
which  one-half  of  the  lamp  chamber  proper 
is  covered  with  a  coating  of  silver,  or  other 
reflecting  surface  for  reflecting  the  light,  or  is 
ground  for  the  purpose  of  diffusing  the  light. 

The  half-shade  is  applicable  to  cases  where  it 
is  desired  to  throw  out  the  light,  not  in  all  direc- 
tions, but  on  one  side  only  of  any  plane.  Some- 
times the  dividing  plane  is  taken  parallel  to  the 
length  of  the  incandescing  filament  and  sometimes 
at  right  angles  to  it.  When  the  lamp  is  placed 


Hal.J 


[ttea. 


within  a  surrounding  globe  the  reflecting  surface 
may  be  placed  on  this  globe  instead  of  on  the 
lamp  chamber. 

Hall  Effect.-(See  Effect,  Hall.} 

Halle)  an  Lines.— (See  Lines,  Halleyan) 

Halpine-Savage  Torpedo.— (See  Torpedo, 
Halpine-Savage) 

Hand  hole  of  Conduit.— A  box  or  opening 
communicating  with  an  underground  cable, 
provided  for  readily  tapping  the  cable,  and 
of  sufficient  size  to  permit  of  the  introduction 
of  the  hand. 

Hand-Lighting  Argand  Electric  Burner. 
— (See  Burner,  Argand  Electric,  Hand- 
Lighter) 

Hand-Lighting  Electric  Burner.— (See 
Burner,  Hand-Lighting  Electric) 

H  a  n  d  •  R  e  gulation.— ( See  Regulation, 
Hand) 

Hand-Regulator.— (See  Regulator, 
Hand) 

Hanger-Board. — (See  Board,  Hanger) 

Hanger,  Cable A  hanger  or  hook 

suitably  secured  to  the  cable  and  designed  to 
sustain  the  weight 
of  the  cable  by 
intermediately  sup- 
porting it  on  iron  or 
steel  wires  strung 
above  the  cable. 

A  cable  hanger  or 
cable  clip  is  shown  in 
Fig.  290.  The  mode 
of  supporting  the  cable 
C,  by  the  hanger  hook 
H,  will  be  readily  un- 
derstood from  an  in- 
spection  Of  the  figure.  &**<><>•  Cable  Hanger. 

The  weight  per  foot  of  an  aerial  cable  is  gener- 
ally so  great  that  the  poles  or  supports  would  re- 
quire to  be  very  near  together,  unless  the  device 
of  intermediate  supports,  by  means  of  cable  clips 
or  hangers,  were  adopted. 

Hanger,  Double-Curve  Trolley A 

trolley  hanger  generally  employed  at  the  ends 
of  single  and  double  curves,  and  on  inter- 
mediate points  on  double  track  curves,  sup- 
ported by  lateral  strain  in  opposite  directions. 


Hanger,  Single-Carre  Trolley A 

trolley  hanger  supported  on  a  single  track 
curve,  except  at  the  ends  and  on  the  inside 
curve  of  a  double  track  line,  by  lateral  strain 
in  one  direction. 

Hanger,  Straight-Line  Trolley A 

trolley  hanger  on  a  straight  trolley  line  suit- 
ably supported  by  a  span  wire  so  as  to  have 
a  vertical  strain  only. 

Hanger,  Trolley A  device  for  sup- 
porting and  properly  insulating  trolley  wires. 

Hard-Drawn  Copper  Wire.— (See  Wire, 
Copper,  Hard-Drawn) 

Harmonic  Receiver.— (See  Receiver,  Har- 
monic) 

Harmonic  Telegraphy.— (See  Telegraphy. 
Gray's  Harmonic  Multiple) 

Head  Bath,  Electric (See  Bath. 

Head,  Electric) 

Head  Breeze,  Electro-Therapeutic 

(See  Breeze,  Head,  Electro-Therapeutic.) 

Head  Light,  Locomotive,  Electric 

An  electric  light  placed  in  the  focus  of  a  par- 
abolic reflector  in  front  of  a  locomotive  eajine. 

The  lamp  is  so  placed  that  its  voltaic  ar  is  a 
little  out  of  the  focus  of  the  reflector,  so  Mar.  by 
giving  a  slight  divergence  to  the  reflected  light, 
the  illumination  extends  a  short  distance  on  either 
side  of  the  tracks. 

Heat. — A  form  of  energy. 

The  phenomena  of  heat  are  due  to  a  vbratory 
motion  impressed  on  the  molecules  of  matter  by 
the  action  of  some  form  of  energy. 

Heat  in  a  body  is  due  to  the  vibrations  or 
oscillations  of  its  molecules.  Heat  is  transmitted 
through  space  by  means  of  a  wave  motion  in  the 
universal  ether.  This  wave  motion  is  the  same 
as  that  causing  light. 

A  hot  body  loses  its  heat  by  producing  vave 
motion  in  the  surrounding  ether.  Tin  ...ess 
is  called  radiation.  (See  Radiation.) 

The  energy  given  off  by  a  heated  body  .  >)ing 
is  called  radiant  energy. 

Radiant  energy  is  transmitted  by  means  of 
ether  waves;  it  is  of  two  kinds,  viz. : 

(l.)  Obscure  Heat,  or  heat  which  does  not 
affect  the  eye,  although  it  can  impress  a  photo- 
graphic image  on  a  sufficiently  sensitive  photo- 
graphic  plate. 


Hca.J 


264 


[Hea, 


(z.)  Luminous  Heat,  or  heat  which  accompanies 
tight  (Sze  Energy,  Radiant.) 

Heat  is  conducted,  or  transmitted  through 
bodies,  with  different  degrees  of  readiness. 

Some  bodies  are  good  conductors  of  heat, 
others  are  poor  conductors. 

Heat  is  transmitted  through  liquids  by  means 
of  currents  occasioned  by  differences  in  density 
caused  by  differences  ot  temperature.  These 
currents  are  called  convection  currents. 

Heat  is  measured  as  to  its  relative  degree  of  in- 
tensity  by  the  thermometer.  It  is  measured  as  to 
its  amount  or  quantity  by  the  calorimeter.  (See 
Thermometer,  ELctric.  Calorimeter.} 

The  heat  unit  n.ost  commonly  employed  is, 
perhaps,  the  calorie,  or  the  amount  of  heat  re- 
quired to  raise  one  gramme  of  water  one  degree 
centigrade. 

Another  heat  unit,  very  generally  employed  in 
the  United  States  and  England,  is  the  quantity  of 
heat  required  to  raise  one  pound  of  water  one  de- 
gree Fahrenheit.  This  is  called  the  English  heat 
unit  (See  Calorie.  Units,  Heat.  Joule.  Volt- 
Coulomb.) 

Heat,  Absorption  and  Generation  of,  in 

Voltaic  Cell The  heat  effects  which 

attend  the  action  of  a  voltaic  cell. 

The  chemical  action  of  the  exciting  liquid  or 
electrolyte  on  the  positive  plate  or  element  of  a 
voltaic  cell,  like  all  cases  of  chemical  combination, 
is  atiend>  d  by  a  development  of  heat. 

When,  however,  the  circuit  of  the  cell  is  closed, 
the  energy  liberated  during  the  chemical  combi- 
nation appears  as  electricity,  which  develops  heat 
in  all  parts  of  the  circuit.  (See  Heat,  hlectric. 
Cell,  Voltaic.) 

Heat,  Atomic A  constant  product 

obtained  by  multiplying  the  specific  heat  of 
an  elementary  substance  by  its  atomicwetght. 
(See  Weight,  Atomic.) 

Dulong  and  Petit  have  discovered  the  remark- 
able fact  that  the  product  of  the  specific  heat  of 
all  elementary  substances  by  their  atomic  weights 
•s  nearly  the  same.  The  product  is  called  the 
atomic  heat,  and  is  about  equal  to  6.4. 

Dulong  and  Petit's  law  may  be  stated  as  fol- 
ows,  viz. :  All  elementary  atoms  require  the  same 
quantity  of  heat  to  heat  them  to  the  same  number 
of  degrees. 

The  atomic  heat  of  any  body  divided  by  its 
specific  heat  gives  its  atomic  weight. 


The  heat  imparted  to  any  body  performs  three 
kinds  of  work,  viz. : 

(I.)  That  expended  in  external  work,  such, 
for  example,  as  in  overcoming  the  atmospheric 
pressure. 

(2.)  That  expended  in  internal  work,  or  in 
overcoming  the  attractions  of  the  atoms  and  driv- 
ing them  apart 

(3.)  That  expended  in  overcoming  the  temper- 
ature, or  the  true  specific  heat,  or  heat  expended 
in  increasing  the  molecular  vis-viva. 

The  expenditure  of  energy  is  greatest  in  the 
third  head.  The  exact  value  of  the  three  factors 
is  as  yet  unknown,  and  in  the  opinion  of  Weber 
and  others  the  correctness  of  Dulong  and  Petit's 
law  cannot  be  regarded  as  being  satisfactorily 
established. 

Regnault  has  proved  that  Dulong  and  Petit's  law 
is  true  for  compound  bodies,  i.  e.,  in  all  compounds 
of  similar  composition  the  product  of  the  specific 
heat  by  the  total  chemical  equivalent  is  constant. 

The  following  table  from  Anthony  and  Bracket 
illustrates  the  law  of  Dulong  and  Petit: 


Elements. 

Specific  Heat 
of  Equal  Weight. 

Atomic 
Weight. 

Product  of 
Specific 
Heat  into 
uomic 
Weight. 

Iron 

Copper  
M-rcury  
Silver  
Gold 

0.0314  (Solid) 
0.057 

63.17 
199.71 
107.67 

6.001 
6.   28 
6-   37 

Tin  
Lead  

0.056 

117.7 

6.  91 

6     83 

Zinc 

,-  ^' 

"This  product -the  atomic  heat  of  elements, 
the  molecular  heat  of  compounds —has  the  follow- 
ing physical  meaning:  Of  any  substance  whose 
atomic  or  molecular  weight  we  kn>>w,  we  may 
take  a  number  of  grammes  numerically  equal  to 
the  atomic  or  molecular  weight;  lor  example, 
35-5  grammes  of  chlorine,  1 6  grammes  of  marsh 
gas;  we  may  call  such  quantity  the  gramme  atom 
or  the  gramme  molecule  of  the  substance.  The 
atomic  heat  or  the  molecular  heat  of  a  substance 
is  the  number  of  calories  of  heat  necessary  to 
raise  the  temperature  of  a  gramme  atom  or  a 
gramme  molecule  of  the  substance  through  i 
d  eg  ree  C . "  — ( Daniell. ) 

Heat,  Electric  —  —The  heat  developed 
by  the  passage  of  an  electric  current  through 
a  conductor. 


Hea.J 


265 


[lie*. 


Heat  is  developed  by  the  passage  of  a  current 
through  any  conductor,  no  matter  what  its  resist- 
ance may  be. 

If  the  conductor  is  of  considerable  length,  and 
of  good  conducting  power,  the  heat  developed  is 
not  very  sensible,  since  it  is  spread  over  a  consid- 
erable area,  and  is  rapidly  lost  by  radiation. 

H,  the  heat  generated  in  any  conductor  of  a 
resistance  R,  by  the  passage  through  it  of  an  elec- 
tric current  C,  is  equal  to 

H  =  C3  R,  in  watts. 

But  one  watt  =  .24  small  calorie  per  second. 

Therefore,  the  heat  which  is  generated, 
H  =  C2  R  X  .24  calories  per  second. 

For  the  case  of  a  uniform  wire  of  circular  cross- 
section  the  resistance  R,  in  ohms  is  directly  pro- 
portional to  the  length  1,  and  inversely  propor- 
tional to  the  area  of  cross  -section  jrr8,  or 


The  temperature  to  which  a  wire  of  a  given  re- 
sistance is  raised,  will  of  course  vary  with  the 
mass  of  the  wire,  its  radiating  surface,  and  its 
specific  heat  capacity.  If  the  same  number  of 
heat  calories  are  generated  in  a  small  weight  of  a 
conductor,  whose  radiating  surface  is  small,  the 
resulting  temperature  will  of  course  be  far  higher 
than  if  generated  in  a  larger  mass  provided  with 
a  much  greater  radiating  surface.  In  general, 
however,  its  temperature  increases  as  the  square 
of  the  current  strength  when  the  resistance  is  con- 
stant, and  increases  as  the  resistance  of  ihe  wire 
per  unit  of  length  is  greater. 

The  temperature  a  wire  acquires  by  the  passage 
of  a  current  through  it  varies  inversely  as  the 
third  power  of  the  radius.  If  two  wires  of  the 
same  material  have  the  same  lengths,  but  different 
radii,  the  temperature,  acquired  by  the  pas- 
sage of  an  electric  current,  will  depend  on  the 
heat  developed  per  second,  less  that  radiated  per 

second.  Since  the  former  varies  as  —^  and  the 
latter  as  r,  that  is,  as  1  X  2jrr,  the  temperatures 
attained  vary  as  L,  and  not  as  _£,  as  frequently 

stated.  —  (Larden.) 

The  current  required  to  raise  the  temperature 
of  a  bare  copper  wire  a  given  number  of  degrees 
above  the  temperature  of  the  air  is  given  in  the 
following  tab1*  • 


BARE  COPPER  WIRES. 

Current  required  to  increase  the  temperature  of  a  copper 
wire  t°  Centigrade  above  the  surrounding  air,  the 
copper  wire  being  bright  polished  or  blackened. 


Centimetres 

and  Mils 

(thousandths  of 
an  inch). 

t  =  i°  C. 

t  =  9'C. 

t  =  2S«C. 

Cm. 

Mils. 

Bright 

Black 

Bright 

Black 

Bright 

Black 

.1 

40 

I  0 

1.4 

3.0 

4.1 

4.8 

6.6 

,2 

80 

2.8 

3-9 

8-3 

11.5 

r3-5 

18.7 

•3 

•4 

120 

160 

5-2 

7- 

15-3 
23-6 

31.2 
32.7 

33 

34-4 
S3-o 

200 

II.  I 

15- 

33-o 

45-7 

53-5 

74-1 

240 

14.6 

20. 

43-4 

60.0 

7°-3 

97-4 

•7 

18.5 

25- 

S46 

75.6 

88.7 

123 

31Q 

22.6 

31- 

66.7 

92.4 

108 

150 

•9 

35° 

26.() 

37- 

79.6 

129 

179 

i. 

39° 

3T*5 

43-6 

93-3 

129 

210 

790 

89.2 

123 

264 

428 

593 

4- 

1180 
157° 

164 
252 

327 

349 

746 

671 
1035 

787 

,090 
'675 

5- 

1970 

353 

488 

i°43 

1444 

,699 

2343 

2360 

463 

642 

1828 

2225 

3080 

7. 

2760 

584 

808 

1728 

2392 

2803 

3882 

8. 

3150 

714 

O88 

2922 

3422 

474  « 

9- 

3540 

8si 

1.78 

2519 

,486 

4088 

S6SO 

10. 

394° 

997 

1380 

2950 

4084 

4788 

6626 

Diameter  in 
Cent  metres 

CURRENT  IN  AMPERES. 

and  Mils 

(thousandths  of 

an  inch). 

t  =  49°  C. 

t  =  Sz"  C. 

Cm. 

Mils. 

Bright. 

Black. 

Bright. 

Black. 

.1 

40 

6-5 

8.9 

7-9 

II.  O 

•  2 

80 

18.3 

25-3 

22.4 

31.0 

-3 
-4 

1 

120 

160 

aoo 
240 

33-5 
5i-7 
72.2 
94-9 

46.4 
99-9 

ii 

116 

:78 

280 
310 

3 

165 

202 

"47 
179 

3 

•9 

174 

24I 

214 

296 

I.O 

39° 

204 

25  i 

347 

2.0 

790 

577 

79i 

709 

081 

3.O 

1180 

1061 

i468 

1303 

1803 

4.0 

1570 

'633 

2260 

2006 

2776 

1970 

2283 

3i6o 

2802 

3880 

7.0 

2360 
2760 

3°oo 

4154 

36*5 
4642 

Sioo 

6426 

315° 

4620 

6396 

5671 

7850 

9.0 

354° 

55" 

7630 

6769 

9370 

10.  0 

3940 

6425 

8935 

7926 

10973 

34-4 

— (Forbes.) 

Heat,  Electric   Convection  of  —   — A 

term  employed  to  express  the  dissymmetrical 
distribution  of  temperature  that  occurs  when  a 


Hea.] 


266 


[Hea. 


current  of  electricity  is  sent  through  a 
metallic  wire,  the  middle  of  which  is  main- 
tained at  a  constant  temperature,  and  the 
ends  at  the  temperature  of  melting  ice. 

The  distribution  of  heat  during  the  pas- 
sage of  a  current  through  an  unequally 
heated  conductor. 

If  the  central  portions  of  a  metallic  bar  are 
heated  the  curve  of  heat  distribution  is  sym- 
metrical. On  sending  an  electric  current  through 
the  wire  it  is  heated  according  to  Joule's  law, 
and  the  curve  of  heat  distribution  is  still  sym- 
metrical. But  the  current  in  passing  from  the 
colder  to  the  hotter  parts  of  the  wire  produces 
an  additional  heating  effect  at  this  point,  and  in 
passing  from  the  warmer  to  the  colder  parts  of 
the  wire  produces  a  cooling  effect.  (See  Effect, 
Peltier.  Effect,  Thomson.)  The  curve  of  heat 
distribution  is  then  no  longer  symmetrical.  The 
term  Electrical  Convection  of  Heat,  has  been 
given  to  the  dissymmetrical  distribution  of  heat 
so  effected. 

Sir  William  Thomson,  who  studied  these 
effects,  found  that  the  electrical  convection  of 
heat  in  copper  takes  place  in  the  opposite 
direction  to  that  in  iron;  that  is  to  say,  the  elec- 
trical convection  of  heat  is  negative  in  iron,  (i.  e., 
the  direction  is  opposite  to  that  of  the  current), 
and  positive  in  copper. 

Heat,  Irreversible Heat  pro- 
duced in  a  homogeneous  conductor  by  the 
passage  of  electricity  through  it. 

This  heat,  according  to  Joule's  law,  is  propor- 
tional to  the  square  of  the  current,  and  is  produced 
no  matter  in  what  direction  the  current  is  pass- 
ing. In  this  respect  it  is  unlike  the  heat  pro- 
duced by  the  passage  of  electricity  through  a 
heterogeneous  conductor,  in  which  case  heat  is 
developed  or  liberated  only  by  the  passage  of  the 
current  in  a  given  direction  :  on  the  passage  of  the 
current  in  the  opposite  direction,  heat  being 
absorbed  and  the  temperature  lowered.  (See 
Heat,  Reversible.} 

Heat  Lightning.— (See  Lightning,  Heat.) 

Heat,  Luminous A  variety  of  radi- 
ant energy  which  affects  the  eye,  as  light. 

Radiant  heat  and  light  are,  in  reality,  different 
effects  produced  by  one  and  the  same  cause,  viz., 
by  vibrations  or  waves  in  the  universal  ether. 
In  general  the  waves  producing  heat  are  of 


greater  length  and  smaller  frequency  than  are 
those  producing  light. 

Heat,  Mechanical  Equivalent  of — 

The  amount  of  mechanical  energy,  converted 
into  heat,  that  would  be  required  to  raise  the 
temperature  of  I  pound  of  water  i  degree 
Fahr. 

The  mechanical  equivalence  between  the 
amount  of  energy  expended  and  the  amount 
of  heat  produced,  as  measured  in  heat  units. 

Joule's  experiments,  the  results  of  which  are 
generally  accepted,  gave  772  foot-pounds  as  the 
energy  equivalent  to  that  expended  in  raising  the 
temperature  of  I  pound  of  water  I  degree  Fahr. 

Heat,  Molecular The  number  of 

calories  of  heat  required  to  raise  the  tempera- 
ture of  one  gramme-molecule  of  any  sub- 
stance i  degree  C.  (See  Molecule,  Gramme. 
Heat,  Atomic.) 

Heat,  Obscure A  variety  of  radiant 

energy  which  does  not  effect  the  eye. 

Radiant  heat  is  sometimes  divided  into  lumi- 
nous heat  and  obscure  heat.  (See  Heat,  Lumi- 
nous.) 

Heat,  Red The  temperature  at 

which  a  body,  whose  temperature  is  gradually 
increasing,  begins  to  glow  or  to  emit  red  rays 
of  light. 

When  a  refractory  solid  body  is  gradually 
heated  to  incandescence,  the  red  waves  of  light 
are  first  emitted,  then  the  orange,  and  successively 
afterwards  the  yellow,  green,  blue,  indigo  and 
violet,  when  the  body  emits  white  light  or  is 
white  hot. 

Heat,  Reversible The  heat  pro- 
duced in  a  heterogeneous  conductor  by  the 
passage  through  it  of  an  electric  current  in  a 
certain  direction. 

Reversible  heat  is  produced  at  the  junction  of 
two  metals,  where  a  difference  of  potential  exists 
between  them,  or  where  their  heterogeneity  is 
greatest.  It  is  called  reversible  because  it  de- 
pends upon  the  direction  in  which  the  current 
is  passing.  If  the  current  be  passed  in  a  certain 
direction  across  the  junction,  heat  is  liberated; 
while,  if  it  be  passed  in  the  opposite  direction, 
heat  is  absorbed,  or  cold  results. 

Reversible  heat  effects  are  seen  in  the  Peltier 
effect.  (See  Effect,  Peltier.) 


Hea.] 


267 


[Hel. 


Heat,  Specific The  capacity  of  a 

substance  for  heat  as  compared  with  the 
capacity  of  an  equal  quantity  of  some  other 
substance  taken  as  unity. 

Water  is  generally  taken  as  the  standard  for 
comparison,  because  its  capacity  for  heat  is  greater 
than  that  of  any  other  common  substance. 

Different  quantities  of  heat  are  required  to 
raise  the  temperature  of  a  given  weight  of  dif- 
ferent substances  through  I  degree.  The  spe- 
cific heats  of  substances  are  generally  compared 
with  water  or  with  hydrogen,  the  capacity  of 
these  substances  for  heat  being  very  great. 

According  to  Dulong  and  Pettit,  the  specific 
heat  of  all  elementary  atoms  is  the  same.  For 
example,  the  heat  energy  of  an  atom  of  hydrogen 
is  equal  to  that  of  an  atom  of  oxygen,  but  since 
a  given  mass  of  hydrogen,  under  similar  condi- 
tions of  temperature  and  pressure,  contains  sixteen 
times  as  many  atoms  as  an  equal  mass  of  oxygen, 
therefore,  when  compared  weight  for  weight, 
hydrogen  has  a  specific  heat  sixteen  times  greater 
than  that  of  oxygen. 

Or,  in  general,  comparing  equal  weights,  the 
specific  heat  of  an  elementary  substance  is  in- 
versely proportional  to  its  atomic  weight.  (See 
Heat,  Atomic.} 

Heat,  Specific,  of  Electricity (See 

Electricity,  Specific  Heat  of.) 

Heat  Unit— The  quantity  of  heat  required 
to  raise  a  given  weight  of  water  through 
a  single  degree. 

There  are  a  number  of  different  heat  units. 
The  most  important  are: 

(I.)  The  British  Heat  Unit,  or  Thermal  Unit,  or 
the  amount  of  heat  required  to  raise  I  pound 
of  water  I  degree  Fahr.  This  unit  represents  an 
amount  of  work  equal  to  772  foot-pounds. 

(2.)  The  Greater  Calorie,  or  the  amount  of  heat 
required  to  raise  the  temperature  of  1,000 
grammes  of  water  I  degree  C.  (See  Calorie.) 

(3.)  The  Smaller  Calorie,  or  the  amount  of  heat 
required  to  raise  the  temperature  of  one  gramme 
of  water  I  degree  C. 

(4.)  The  Joule,  or  the  quantity  of  heat  developed 
in  one  second  by  the  passage  of  a  current  of  one 
ampere  through  a  resistance  of  one  ohm. 

l  joule  equals  .0002407  large  calories. 

I  joule  equals  .  2407  small  calories. 

I  foot-pound  equals  1.356  joules. 


I  pound-Centigrade  equals  1884.66  joules. 

I     "  '•       1389.6  foot  pounds. 

I      "       Fahrenheit      -1       1047.03  joules. 

Heat  Unit,   English (See    Units, 

Heat) 

Heat  Unit  or  Calorie.— (See  Calorie) 
Heat  Unit  or  Joule.— (See  Joule) 

Heat,  White The  temperature  at 

which  light  of  all  wave  lengths  from  the  red 
to  the  violet  is  emitted  from  a  heated  body, 
and  the  body,  therefore,  glows  with  a  white 
light. 

A  solid  substance  heated  to  white  incandescence 
emits  a  continuous  spectrum,  *'.  e.,  a  spectrum  in 
which  all  the  wave  lengths  of  light  from  the  red 
to  the  violet  are  present. 

Heater,  Electric A  device  for  the 

conversion  of  electricity  into  heat  for  purposes 
of  artificial  heating. 

Electric  heaters  consist  essentially  of  coils  or 
circuits  of  some  refractory  metal  through  which 
the  current  is  passed.  These  coils  or  circuits  are 
surrounded  by  air  or  finely  divided  solids,  and  are 
placed  inside  metallic  boxes  or  radiators,  which 
throw  off  or  radiate  the  heat  produced. 

When  employed  for  the  heating  of  liquids  the 
coils  are  placed  directly  in  the  liquid  to  be 
heated,  or  are  surrounded  by  radiating  boxes 
placed  in  the  liquid. 

Heating  Effects  of  Currents.— (See  Cur- 
rents, Heating  Effects  of) 

Hedgehog  Transformer. —  (See  Trans- 
former, Hedgehog) 

Hecto-Ampdre One  hundred  am- 
peres. 

Heliograph.—  An  instrument  for  tele- 
graphic communication  that  operates  by  em- 
ploying flashes  of  light  to  represent  the  dots 
and  dashes  of  the  Morse  alphabet,  or  the 
movements  of  the  needles  of  a  needle  tele- 
graph to  the  right  or  the  left.  (See  Alphabet, 
Telegraphic) 

The  flashes  of  light  are  thrown  from  the  sur- 
face of  a  plane  mirror.  Motions  to  the  right  or 
left  may  be  employed  in  order  to  distinguish 
between  the  dots  and  dashes,  or  the  same  may  be 
effected  by  the  relative  durations  of  the  flashes  of 


Hel.] 


268 


[Hol. 


light,   or  by   the  intervals    between    successive 
flashes. 

Telegraphic  communication  has  been  carried 
on  betweeh  steamers  during  foggy  weather  by 
means  of  their  fog  horns;  or  between  locomotives 
by  their  steam  whistles. 

Helix,  Dextrorsal A  name  some- 
times applied  to  a  dextrorsal  solenoid.  (See 
Solenoid,  Dextrorsal?) 

The  magnetic  polarity  of  a  helix  or  solenoid 
depends  not  only  on  the  direction  in  which  the 
current  is  passed,  but  also  on  the  direction  in 
which  the  wire  is  coiled  or  wound .  (See  Magnet, 
Electro.} 

Helix,  Sinistrorsal A  name  some- 
times applied  to  a  sinistrorsal  solenoid.  (See 
Solenoid,  Sinistrorsal?) 

Hemihedral  Crystal.— (See  Crystal,  Hem- 
ihedral.) 

Henry,  A  —  — The  practical  unit  of  self- 
induction. 

It  has  been  generally  agreed  in  the  United 
States  to  call  the  practical  unit  of  self-induction 
a  henry,  in  place  of  a  secohm  or  quadrant. 
The  name  henry  should  be  adopted,  not  only  by 
American  electricians,  but  also  by  those  of  other 
countries,  since  the  terms  secohm  or  quadrant 
are  contrary  to  the  generally  adopted  usage  of 
employing  for  such  the  names  of  distinguished 
electricians,  who  have  passed  from  their  labors. 

The  fact  that  of  all  discoverers  in  the  field  of  self- 
induction,  none  possesses  so  great  a  claim  as  that  of 
Prof.  Henry,  must  be  generally  acknowledged. 
As  early  as  1832  he  published  in  Silliman's  Jour- 
nal a  paper  in  which  he  described  experiments, 
showing  clearly  that  the  spark  obtained  by  break- 
ing the  current  of  a  battery,  in  which  along  wire 
was  interposed,  was  greater  than  when  a  short 
wire  was  employed,  and  that  this  increased  length 
of  spark  was  further  increased  by  coiling  the  wire, 
and  that  the  phenomena  were  ascribed  to  the  ac- 
tion of  the  current  on  itself. 

A  committee  of  the  American  Institute  of 
Electrical  Engineers,  after  careful  consideration, 
recommended  to  the  Institute  that  the  value  of 
the  practical  unit  of  inductance  should  be  equal  to 
lo»  C.  G.  S.  units  of  inductance,  usually  ex- 
pressed by  a  length  equal  to  one  earth  quadrant 
or  1,000,000,000  centimetres. 

The  value  of  the  practical  unit  of  inductance, 
or  the  "henry,"  may  in  some  cases  be  too  high  for 


convenience;  in  such  cases  it  may  be  expressed 
by  some  fractional  dimension,  such,  for  example, 
as  milli-henry. 

Hercules  Stone.  — (See  Stone,  Hercules.} 
Herinetical    Seal.— (See   Seal,  Hermeti- 
cal.} 

Hertz's  Theory  of  Electricity.— (See  Elec- 
tricity, Hertz's  Theory  of.) 

Heterostatic.— A  term  applied  by  Sir 
William  Thomson  to  distinguish  a  form  of 
electrometer  in  which  the  electrification  is 
measured  by  determining  the  mutual  influ- 
ence of  the  attraction  exerted  by  the  charge 
to  be  measured  and  the  attraction  of  an  oppo- 
site charge  imparted  to  the  instrument  by  a 
source  independent  of  the  charge  to  be  meas- 
ured. 

The  term  heterostatic  distinguishes  this  form  of 
electrometer  from  an  idiostatic  instrument,  or  one 
in  which  the  measurement  is  effected  by  deter- 
mining the  repulsion  between  the  charge  to  be 
measured  and  the  repulsion  of  a  charge  of  the 
same  name,  i.  e.,  positive  or  negative,  imparted 
to  the  instrument  from  an  independent  source. 
(See  Electrometer.) 

Hick's  Automatic    Button    Repeater.— 

(See  Repeaters,  Telegraphic?) 

High-Bars. — A  term  applied  to  those  com- 
mutator segments,  or  parts  of  commutator 
segments,  which,  through  less  wear,  faulty 
construction  or  looseness,  are  higher  than  ad- 
joining portions.  (See  Commutator.) 

High-Frequency  Currents,  Electric  Light- 
ing by (See  Lighting,  Electric,  by 

High-Frequency  Currents?) 

High  Resistance  Magnet— (See  Magnet, 
High  Resistance?) 

High  Speed  Electric  Motor.— (See  Mo- 
tor, Electric,  High  Speed?) 

High  Tension  Electric  Fuse.— (See  Fuse, 
Electric  High  Tension?) 

Hissing  of  Arc. — (See  Arc,  Hissing  of.) 

Holder  for  Safety  Fuse. — A  box  or  other 
receptacle  of  refractory  material  for  holding 
a  safety  fuse,  and  catching  the  molten  metal 
when  fused. 

The  holder  or  fuse  box  is  provided  to  prevent  the 


Hoi.] 


269 


[Eor. 


molten  metal  of  the  fuse  from  setting  fire  to  any 
combustible  material  on  which  it  might  other- 
wise fall. 

Holders,  Carbon,  for  Arc  Lamps  — 
A  clutch  or  clamp  attached  to  the  end  of  the 
lamp  rod  or  other  support,  and  provided  to 
hold  the  carbon  pencils  used  on  arc  lamps. 
(See  Lamp,  Arc,  Electric!) 

Holders  for  Brushes  of  Dynamo-Electric 
Machine.— A  device  for  holding  the  collect- 
ing brushes  of  a  dynamo-electric  machine. — 
(See  Machine,  Dynamo-Electric!) 

Hole,  Armature A  term  sometimes 

applied  for  armature  bore  or  chamber.  (See 
Bore,  Armature!) 

Hole,  Armature  Bore,  Elliptical  — 
An  armature  bore  or  chamber  ellipsoidal  in 
shape. 

Holohedral  Crystal.— (See  Crystal,  Holo- 
hedral.) 

Holtz  Machine.— (See  Machine,  Holtz.) 

Home  Station.— (See  Station,  Home.) 

Homogeneous  Current  Distribution. — 
(See  Current,  Homogeneous  Distribution  of.) 

Hood  for  Electric  Lamp. — A  hood  pro- 
vided for  the  double  purpose  of  protecting  the 


Fig.  2QT.     Arc  Lamp  Hood. 

body  of  an  electric  lamp  from  rain  or  sun, 
and  for  throwing  its  light  in  a  general  down- 
ward direction. 

Hoods  for  arc  lamps  are  generally  conical  in 
shape. 


A  form  of  hood  for  an  exposed  arc  lamp  is 
shown  in  Fig.  291. 

Horizontal  Component  of  Earth's  Mag- 
netism.— (See  Component,  Horizontal,  of 
Earth's  Magnetism,) 

Horns,  Following,  of  Pole  Pieces  of 
a  Dynamo  -  Electric  Machine The 

edges  or  terminals  of  the  pole  pieces  of  a  dy- 
namo-electric machine  towards  which  the 
armature  is  carried  during  its  rotation. 


According  to  S.  P.  Thompson,  the  following 
horns,  b,  d,  Fig.  292,  are  those  towards  which 
the  armature  is  carried  ;  the  leading  horns,  a,  c, 
those  from  which  it  is  carried. 

As  the  change  in  the  magnetic  intensity  is  more 
sudden  when  the  armature  is  moved  from  the 
pole  pieces,  and  least  when  moved  towards  them, 
it  is  clear  that  the  leading  horns  in  a  dynamo - 
electric  machine,  and  the  following  horns  in  an 
electric  motor,  become  heated  during  rotation  by 
the  production  of  Foucault  currents.  (See  Cur. 
rents,  Foucault.  Machine,  Dynamo  Electric.) 

Horns,  Leading,  of  Pole  Pieces  of  a  Dy- 
namo-Electric Machine The  edges 

or  terminals  of  the  pole  pieces  of  a  dynamo- 
electrical  machine  from  which  the  armature 
is  carried  during  its  rotation. 

Thus,  in  Fig.  292,  a  and  c,  are  the  leading  horns 
of  the  pole  pieces. 

Horns  of  Pole  Pieces  of  Dynamo-Electric 
Machine.— The  edges  of  the  pole  pieces  of  a 
dynamo-electnc  machine  towards  or  from 
which  the  armature  is  carried  during  its  rota- 
tion. 

These  are  called  the  following  and  the  leading 
horns. 


Horse-Power. — A  commercial    unit 
powe-  or  rate  of  doing  work. 


for 


Hor.] 


270 


[Hoa 


A  rate  of  doing  work  equal  to  33,000  pounds 
raised  i  foot  per  minute,  or  5  50  pounds  raised 
I  foot  per  second. 

A  rate  of  doing  work  equal  to  4,562.33 
kilogrammes  raised  i  metre  per  minute. 

A  careful  distinction  must  be  drawn  between 
work  and  power.     The  same  amount  of  work 
is  done  in  raising    I    pound    through   10  feet 
whether  it  be  done  in  one  minute  or  in  one  hour. 
The  power  expended  or  the  rate  of  doing  work 
is,  however,  quite  different,  being  in  the  former 
case  sixty  times  greater  than  in  the  latter. 
I  horse-power  =  550  foot-pounds  per  second. 
"  =33,000  foot-pounds  per  min- 

ute. 
"  =  4,562.33   kilogramme-metres 

per  minute. 

««  =  745.941  watts. 

"  =  1.01385  metric  horse-power. 

Horse-Power,  Electric (See  Power, 

Horse,  Electric) 

Horse-Power  Hour. — (See  Hour,  Horse- 
Power). 

Horse-Power,  Metric A  unit  of 

power  in  which  rate  of  doing  work  is  equal 
to  75  kilogramme-metres.  (See  Horse- 
Power.) 

Horseshoe  Electro-Magnet. — (See  Mag- 
net, Electro,  Horseshoe.) 

Horseshoe  Magnet. — (See  Magnet,  Horse- 
shoe.) 

Hot,  Red Sufficiently  heated  to 

emit  red  light  only.  (See  Heat,  Red.) 

Hot  St.  Elmo's  Fire.— (See  Fire,  Hot.  St. 
Elmo's) 

Hot,  White Sufficiently  heated  to 

emit  all  the  colored  lights  of  the  spectrum. 
(See//«z/,  White.) 

Hotel  Annunciator. — (See  Annunciator, 
Hotel.) 

Hour,  Ampere  — • A  unit  of  electrical 

quantity  equal  to  one  ampere  flowing  for  one 
hour. 

The  ampere-hour  is  in  reality  a  unit  of  quanti- 
ty like  the  coulomb.  It  is  used  in  the  service  of 
electric  currents,  and  is  equal  to  the  product  of 
the  current  delivered  by  the  time  in  hours.  The 
ampere  hour  is  not  a  measure  of  energy,  but  when 


combined  with  the  volt,  and  expressed  in  watt 
hours,  it  is  a  measure  of  energy. 

The  capacity  of  any  service  for  maintaining  a 
flow  of  current  is  measured  in  ampere-hours. 
Thus,  if  any  service,  such  as  a  primary  or  sec- 
ondary battery,  has  a  capacity  of  80  ampdre- 
hours,  it  will  supply  8  amperes  for  ten  hours,  or 
it  may  give  10  amperes  for  eight  hours. 

The  storing  capacity  of  accumulators  is  gener 
ally  given  in  ampere-hours.  The  same  is  true  ol 
primary  batteries. 

One  coulomb  equals  .0002778  ampere-hours. 

One  ampere-hour  equals  3,600  coulombs. 

Hour,  Horse-Power A  unit  of  work. 

An  amount  of  work  equal  to  one  horse- 
power for  an  hour. 

One  horse- power  is  equal  to  1,980,000  foot- 
pounds, or  745.941  watt  hours. 

Hour,  Kilo- Watt A  unit  of  electri- 
cal power  equal  to  a  kilo-watt  maintained  for 
one  hour. 

Hour,  Lamp Such  a  service  of  elec- 
tric current  as  will  maintain  one  electric  lamp 
during  one  hour. 

The  number  of  lamp-hours  is  obtained  by  mul- 
tiplying the  number  of  lamps  by  the  average 
number  of  hours  during  which  the  lamps  are 
burning. 

The  use  of  lamp-hours  is  for  the  purpose  of 
estimating  the  current  supplied  to  a  consumer  by 
counting  the  number  of  hours  each  lamp  is  in. 
service. 

To  convert  lamp-hours  to  watt-hours,  multiply 
the  number  of  lamp-hours  by  the  number  of 
watts  per  lamp.  The  watt  hours,  divided  by  746^ 
will  then  give  the  electrical  horse-power  hours. 
(Seeffour,  Watt.) 

Hour,  Watt A  unit  of  electrical 

work. 

An  expenditure  of  an  electrical  work  of 
one  watt  for  one  hour. 

Lamp-hours  are  converted  to  watt-hours  by 
multiplying  the  number  of  lamp-hours  by  the 
number  of  watts  per  lamp.  (See  Hour,  Lamp.) 

House  Annunciator. — (See  Annunciator. 
House.) 

House  Main.— (See  Main,  House.) 
House-Service  Conductor.—  (See  Conduc- 
tor, House-Service.) 


Hon.] 


271 


[Hyp. 


House-Top  Fixtures,  Telegraphic 

(See  Fixtures,  Telegraphic  House-  Top.) 

House  Wire.— (See  Wire,  House.) 

Hughes'  Electro-Magnet— (See  Magnet, 
Electro,  Hughes') 

Human  Body,  Electric  Resistance  of 

— (See  Body,  Human,  Resistance  of) 

Hydro-Electric  Bath.— (See  Bath,  Hydro- 
Electric) 

Hydro-Electric  Machine,  Armstrong's 
(See  Machine,  Armstrong's  Hydro- 
Electric) 

Hydrogen,  Electrolytic Hydrogen 

produced  by  electrolytic  decomposition. 

It  is  the  electrolytic  hydrogen  liberated  in  a 
voltaic  cell  at  the  surface  of  the  negative  plate, 
which  causes  polarization  and  consequent  de- 
crease in  the  resulting  current  strength,  by  rea- 
son both  of  the  counter-electromotive  force  it 
produces  and  the  increased  resistance  it  produces 
in  the  cell. 

Electrolytic  hydrogen  is  atomic  hydrogen;  i.  e., 
hydrogen  with  its  bonds  open  or  free.  It  there- 
fore possesses  much  stronger  chemical  affinities 
than  does  molecular  hydrogen.  Electrolytic 
oxygen  which  is  evolved  at  the  same  time  as  the 
electrolytic  hydrogen  has  been  successfully  em- 
ployed in  electric  bleaching.  Hydrogen  per- 
oxide is  also  formed  and  acts  as  a  bleaching  agent. 

Hydrometer  or  Areometer. — An  appa- 
ratus for  determining  the  specific  gravity  of 
liquids.  (See  Areometer  or  Hydrometer) 

Hydro-Plastics.— (See   Plastics,  Hydro) 

Hydro-Plasty. — The  art  of  hydro-plastics. 
(See  Plastics,  Hydro) 

Hydrotasimeter,  Electric An  elec- 
trically operated  apparatus  designed  to  show 
at  a  distance  the  exact  position  of  any  water 
level. 

In  most  forms  of  the  electric  hydrotasimeter  a 
float  placed  in  the  liquid  and  connected  with  an 
electric  circuit  breaks  this  circuit,  and,  at  intervals, 
sends  positive  impulses  into  the  line  when  rising 
and  negative  impulses  when  falling.  These  are 
registered  by  means  of  an  index  moved  by  a  step- 
by-step  motion,  positive  currents  moving  it  hi 
one  direction  and  negative  currents  moving  it  in 
the  opposite  direction. 


Hygrometer. — An  apparatus  for  determin- 
ing the  amount  of  moisture  in  the  air. 

Hygrometrical. — Of  or  pertaining  to  the 
hygrometer. 

Hygrometrically. — In  the  manner  of  the 
hygrometer. 

Hypothesis. — A  provisional  assumption  of 
facts  or  causes  the  real  nature  of  which  is 
unknown,  made  for  the  purpose  of  studying 
the  effects  of  such  causes. 

When  the  facts  assumed  by  a  hypothesis  can 
be  shown  to  be  presumably  true  the  hypothesis 
becomes  a  theory.  A  theory,  therefore,  gives  a 
more  correct  expression  of  the  relations  between 
the  causes  and  effects  of  natural  phenomena  than 
does  a  hypothesis. 

Hypothesis,  Double-Fluid  Electric 

—(See  Electricity,  Double-Fluid  Hypothesis, 
of) 

Hypothesis,  Grothiiss' A  hypothe- 
sis proposed  by  Grothiiss  to  account  for  the 
electrolytic  phenomena  that  occur  on  closing 
the  circuit  of  a  voltaic  cell. 

Grothttss'  hypothesis  assumes: 

(I.)  That  before  the  electric  circuit  is  closed 
the  molecules  of  the  electrolyte  are  arranged  in 
an  irregular  or  unpolarized  condition,  as  repre* 


Fig.  293.  GrothVus-  Hypothesis  of  Electrolytic  Polari- 
zation. 

sented  at  (i),  Fig.  293.  These  molecules  are 
shaded  as  shown  in  Fig.  294,  to  indicate  their  com- 
position and  polarity. 

(2.)  When  the  circuit  is  closed  and  a  current 


Hyp.] 


272 


[Hys. 


begins  to  pass,  a  polarization  of  the  electrolyte,  as 
shown  at  (2),  ensues,  whereby  all  the  negative 
ends  of  the  molecules  of  hydrogen  sulphate,  o 
sulphuric  acid,  are  turned  towards  the  positive 
or  zinc  plate,  and  all  the  positive  ends  towards 
the  negative  or  copper  plate.  This,  as  will  be 
seen,  will  turn  the  SO4  ends  towards  the  zinc, 
and  the  H2  ends  towards  the  copper. 

(3.)  A  decomposition  of  the  polarized  chain, 
whereby  the  SO4 
unites  with  the  zinc 
and  the  H£  liberated  / 
reunites  with  the  SO4 
of  the  molecule  next 
to  it  in  the  chain,  and 
its  liberated  Ha  with  Fig,  294.  Conventionalized 
the  one  next  to  it,  and  Molecule. 

so  on  until  the  last  liberated  Hz  in  the  chain  is 
given  off  at  the  surface  of  the  copper  or  negative 
plate.  This  leaves  the  chain  of  molecules  as 
shown  at  (3). 

(4.)  A  semi-rotation  of  the  molecules  of  the 
chain,  as  at  (3),  until  they  assume  the  position 
shown  at  (4).  This  rotation  is  required,  since  all 
the  molecules  in  (3)  are  turned  with  their  similar 
poles  towards  similarly  charged  battery  plates. 

Hypothesis,   Single-Fluid  Electric  — 

—(See  Electricity,  Single-Fluid  Hypothe- 
sis of.) 

Hypothetical. — Of  or  pertaining  to  a  hy- 
pothesis. 

Hypsometer. — An  apparatus  for  determin- 
ing the  height  of  a  mountain  or  other  eleva- 
tion by  ascertaining  the  exact  temperature  at 
which  water  boils  at  such  elevation. 

The  use  of  a  thermometer  to  measure  the 
height  of  a  mountain  or  other  elevation  is  based 
on  the  fact  that  a  given  decrease  in  the  tempera- 
ture of  the  boiling  point  of  water  invariably  at- 
tends a  given  decrease  in  the  atmospheric  press- 
ure. Therefore,  as  the  observer  goes  further 
above  the  level  of  the  sea,  the  boiling  point  of 
water  becomes  lower,  and  from  this  decrease  the 
height  of  the  mountain  or  other  elevation  may  be 
calculated. 

HypsometricaL— Of  or  pertaining  to  the 
hypsometer. 

Hypsometrically.— -In  the  manner  of  the 
hypsometer. 


Hysteresial  Dissipation  of  Energy. — (See 
Energy,  Hysteresial  Dissipation  of.} 

Hysteresis.  —  Molecular  friction  to  mag- 
netic change  of  stress. 

A  retardation  of  the  magnetizing  or  de- 
magetizing  effects  as  regards  the  causes 
which  produce  them. 

The  quality  of  a  paramagnetic  substance 
by  virtue  of  which  energy  is  dissipated  on  the 
reversal  of  its  magnetization. 

The  ratio  of  magnetic  induction  to  the  mag- 
netizing force  producing  it,  or,  in  other  words, 
the  magnetic  permeability,  is  greater  when  the 
magnetizing  force  is  decreasing,  than  when  it  is 
increasing.  This  phenomenon  is  seen  in  the  well 
known  retention  of  magnetism  in  iron  after  the 
withdrawal  of  the  force  causing  the  magnetization, 
and  was  called  by  Ewing  hysttresis,  from 
'vdr-£fJ£(o,  to  lag  behind. 

If  a  curve  is  constructed  in  which  the  hori- 
zontal abscissas  represent  the  magnetizing  force, 
or  the  magnetizing  current  to  which  they  are 
proportional,  and  the  vertical  ordinates  the 
number  of  lines  of  induction  passing  through  the 
body  that  is  being  magnetized,  both  in  the  case 
of  gradually  increasing  and  gradually  decreasing 
currents,  the  curve  will  be  found  to  have  greater 
values  for  the  decreasing  than  for  the  increasing 
current  Constructing  a  curve  in  this  manner  for 
the  case  of  a  ring  of 
iron,  which  has  been 
first  suddenly  magnet- 
ized and  then  demag- 
netized, taking  the 
magnetizing  force  along 
the  line  F  H,  Fig. 
295,  and  the  result- 
ing magnetization 
along  the  line  M  N,  a 
loop  is  formed  in  the 
curve,  as  shown  in  the 
figure.  The  arrows 
show  the  direction  of  j?ig.  395.  Curves  of  Hys. 
the  magnetizing  force;  teresis  (Ewing}. 

the  shaded  area  the  work  done  due  to  hysteresis. 

The  area  of  this  loop  represents  the  amount  of 
energy  pur  unit  of  volume  expended  in  perform- 
ing a  magnetic  cycle,  *  e.,  in  carrying  the  iron 
ring  through  a  magnetization  and  subsequent 
demagnetization. 

The  physical  meaning  of  the  loop  is  that  a  lag- 


273 


[Hys. 


ging  of  magnetization  has  occurred.  This  lag- 
ging of  the  magnetization  is  due  to  hysteresis. 
Ewing  gives  the  value  for  the  energy  in  ergs 
dissipated  per  cubic  centimetre,  for  a  complete 
magnetic  cycle  for  a  number  of  substances,  as 
follows  : 

Energy  dissipated 
in  ergi  per  cubic 
centimetre,  during 
a  complete  cycle  of 
doubly  reversed 
strong  magnetiza- 
Somple  of  Iron  operated  upon.  don. 

Very  soft  annealed  iron 9,30x5  ergs. 

Less  soft  annealed  iron 16,300  ' ' 

Hard  drawn  steel  wire 60.000  " 

Annealed  steel  wire 70,500  " 

Same  steel,  glass  hard 76,000  ' ' 

Piano-forte    steel     wire,   normal 

temper 116,000  " 

Same,  annealed , 94,000  ' ' 

Same,  glass  hard 117,000  " 

Approximately  28  foot-pounds  of  energy  are 
required  to  make  a  double  reversal  of  strong 
magnetization  in  a  cubic  foot  of  iron.  Energy 
expended  in  this  way  takes  the  form  of  heat. 
This  heat,  however,  is  to  be  distinguished  from 
heat  produced  by  Foucault  currents. 

According  to  Ewing,  hysteresis  is  greatly  de- 
creased by  keeping  the  iron  in  a  state  of  mag- 
netic vibration.  In  this  way,  the  energy  dis- 
sipated in  a  complete  magnetic  cycle  is  corre- 
spondingly decreased.  This  observation  of  Ewing 
agrees  with  the  prior  observation  of  Hughes,  who 
noticed  that  tapping  or  twisting  a  bar  of  iron 
greatly  accelerates  the  removal  of  its  residual 
magnetism. 

The  phenomena  of  hysteresis,  according  to 
Fleming,  accounts  for  part  of  the  energy  which 
is  dissipated  in  a  dynamo-electric  machine: 

(i.)  In  the  field  magnets. 

In  an  ordinarily  constructed  continuous- current 
dynamo,  work  is  done  in  magnetizing  the  field 
magnets,  not  only  to  give  the  iron  its  initial  mag- 
netism, but  also  to  constantly  reproduce  the  mag- 
netism which  the  machine  loses  by  reason  of  the 


continual  vibrations  to  which  it  is  subjected  dur- 
ing its  run.  If  sufficient  residual  magnetism 
were  retained,  on  the  withdrawal  of  the  magneti- 
zing torce  there  would  be  no  necessity  for  the 
current  in  the  field  magnets ;  but,  since  this  is 
removed  by  even  a  small  vibration,  the  energy  of 
the  exciting  current  must  needs  be  expended. 

(2.)  In  the  armature  of  the  dynamo. 

The  soft  iron  of  the  core  is  subjected  to  succes- 
sive magnetizations  and  demagnetizations.  Ac- 
cording to  Fleming,  in  the  case  of  a  core  having 
a  volume  of  9,000  cubic  centimetres,  with  fifteen 
reversals  per  second,  the  loss  is  equal  to  about  £ 
horse-power. 

Hysteresis,  Static  —  —That  quality  in 
iron,  or  other  paramagnetic  substance,  by 
virtue  of  which  energy  is  dissipated  during 
every  reversal  of  its  magnetization. 

Static  hysteresis  is  so  named  in  order  to  dis- 
tinguish it  from  viscous  hysteresis.  (See  Hystere- 
sis, Viscous.) 

Hysteresis,  Viscous The  time-lag 

observed  in  magnetizing  a  bar  of  iron, 
which  is  referable  neither  to  induction  in  the 
iron,  nor  to  self-induction  in  the  magnetizing 
current,  but  to  the  magnetic  viscosity  of  the 
substance. 

A  sluggishness  exhibited  by  iron  for  mag- 
netization or  demagnetization  due  to  magnetic 
viscosity. 

The  difference  between  static  and  viscous 
hysteresis  is  thus  stated  by  Fleming  in  consider- 
ing the  analogous  mechanical  case  of  lifting  a 
weight  in  a  viscous  fluid.  "Apart  from  fluid 
resistance,  the  work  done  in  lifting  the  weight 
against  gravity,  say  one  hundred  times,  is  a  hun- 
dred times  the  work  required  to  be  spent  to  lift 
it  once  ;  but  if  fluid  resistance  comes  into  play, 
and  if  this  varies  as  the  square  of  the  velocity  of 
the  moving  body,  then  the  total  work  done  in 
lifting  the  weight  through  the  fluid  will  be  de- 
pendent also  upon  the  rate  at  which  the  cycle  is 
performed." 


274 


[111. 


I.  H.  P. — A  contraction  for  indicated  horse- 
power, or  the  horse-power  of  an  engine  as 
obtained  by  the  means  of  an  indicator  card. 

I.  W.  G.— A  contraction  for  Indian  wire 
gauge. 

Idio-ElectricSo — A  name  formerly  applied 
to  such  bodies  as  amber,  resin  or  glass,  which 
are  readily  electrified  by  friction,  and  which 
were  then  supposed  to  be  electric  in  them- 
selves. 

This  distinction  was  based  on  an  erroneous 
conception,  and  the  word  is  now  obsolete. 

Idiostatic.— A  term  employed  by  Sir  Wil- 
liam Thomson  to  designate  an  electrometer 
in  which  the  measurement  is  effected  by  de- 
termining the  repulsion  between  the  charge 
to  be  measured  and  that  of  a  charge  of  the 
same  sign  imparted  to  the  instrument  from 
an  independent  source.  (See  Heterostatic) 

Idle  Poles.— (See  Poles,  Idle) 

Igniter,  Jablochkoff A  small  strip 

of  carbon,  or  some  carbonaceous  material 
that  is  readily  rendered  incandescent  by  the 
current,  placed  between  the  free  ends  of  the 
parallel  carbons  of  a  Jablochkoff  candle,  for 
the  establishment  of  the  arc  on  the  passage 
of  the  current. 

The  igniter  is  necessary  in  the  Jablochkoff  elec- 
tric candle,  since  the  parallel  carbons  are  rigidly 
kept  at  a  constant  distance  apart  by  the  insulat- 
ing material  placed  between  them,  and  cannot 
therefore  be  moved  together  as  in  the  case  of  the 
ordinary  lamp.  (See  Candle,  Jablochkoff.) 

Ignition,  Electric The  ignition  of 

a  combustible  material  by  heat  of  electric 
origin. 

The  electric  ignition  of  wires  is  generally  ac- 
complished by  electric  incandescence.  Ignition 
may  be  accomplished  by  the  heat  of  the  voltaic 
arc.  (Seefftat,  Electric.  Furnace,  Electric,} 

The  ignition  of  combustible  gases  is  accom- 
plished by  the  heat  of  the  electric  spark.  (See 
Burner,  Automatic,  Electric.) 

Illumination.  Artificial The  em- 
ployment of  artificial  sources  of  light. 


A  good  artificial  illuminant  should  possess  the 
following  properties,  viz. : 

(i.)  It  should  give  a  general  or  uniform  illumi- 
nation  as  distinguished  from  sharply  marked 
regions  of  light  and  shadow. 

To  this  end  a  number  of  small  lights  well  dis- 
tributed are  preferable  to  a  few  large  lights. 

(2.)  It  should  give  a  steady  light,  uniform  in 
brilliancy,  as  distinguished  from  a  flickering, 
unsteady  light.  Sudden  changes  in  the  intensity 
of  a  light  injure  the  eyes  and  prevent  distinct 
vision. 

(3.)  It  should  be  economical,  or  not  cost  too 
much  to  produce. 

(4.)  It  should  be  safe,  or  not  likely  to  cause 
loss  of  life  or  property.  To  this  intent  it  should, 
if  possible,  be  inclosed  in  or  surrounded  by  a 
lantern  or  chamber  of  some  incombustible  mate- 
rial, and  should  preferably  be  lighted  at  a  dis- 
tance. 

(5.)  It  should  not  give  off  noxious  fumes  or 
vapors  when  in  use,  nor  should  it  unduly  heat 
the  air  of  the  space  it  illumines. 

(6.)  It  should  be  reliable,  or  not  apt  to  be  un- 
expectedly extinguished  when  once  lighted. 

The  electric  incandescent  lamp  is  an  excellent 
artificial  illuminant. 

(i.)  It  is  capable  of  great  subdivision,  and  can, 
therefore,  produce  a  uniform  illumination. 

(2. )  It  is  steady  and  free  from  sudden  changes 
in  its  intensity. 

(3.)  It  compares  favorably  in  point  of  economy 
with  coal  oil  or  gas,  provided  its  extent  of  use  is 
sufficiently  great. 

(4.)  It  is  safer  than  any  known  illuminant, 
since  it  can  be  entirely  inclosed  and  can  be 
lighted  from  a  distance  or  at  the  burner  without 
the  dangerous  friction  match. 

The  leads,  however,  must  be  carefully  insu- 
lated and  protected  by  safety  fuses.  (See  Fuse, 
Safety.} 

(5.)  It  gives  off  no  gases,  and  produces  far  less 
heat  than  a  gas-burner  of  the  same  candle  power. 

It  perplexes  many  people  to  understand  why 
the  incandescent  electric  light  should  not  heat 
the  air  of  a  room  as  much  as  a  gas  light,  since  it 
is  quite  as  hot  as  the  gas  light.  It  must  be  re- 
membered, however,  that  a  gas-burner,  when 
lighted,  not  only  permits  the  same  quantity  of 


111.] 


275 


[Imp. 


gas  to  enter  the  room  which  would  enter  it  if 
the  gas  were  simply  turned  on  and  not  lighted, 
but  that  this  bulk  of  gas  is  still  given  off,  and  is, 
indeed,  considerably  increased  by  the  combina- 
tion of  the  illuminating  gas  with  the  oxygen  of  the 
atmosphere ;  and,  moreover,  this  great  bulk  of 
gas  escapes  as  highly  heated  gases.  Such  gases 
are  entirely  absent  in  the  incandescent  electric 
light,  and  consequently  its  power  of  heating  the 
surrounding  air  is  much  less  than  that  of  gas 
lights. 

(6.)  It  is  quite  reliable,  and  will  continue  to 
burn  as  long  as  the  current  is  supplied  to  it. 

Illumination,  Lighthouse,  Electric 

— The  application  of  the  electric  arc  light 
to  lighthouses. 

A  powerful  arc  light  is  placed  in  the  focus  of 
the  dioptric  lens  now  commonly  employed  in 
lighthouses.  Since  the  consumption  of  the  carbon 
electrodes  would  alter  the  position  of  the  focus  of 
the  light,  electric  lamps  for  such  purposes  are 
constructed  to  feed  both  of  their  carbons,  instead 
of  the  upper  carbon  only,  as  in  the  case  of  the 
ordinary  arc  lamp.  Such  lamps  are  called  focus- 
ing lamps. 

Illumination,  Unit  of A  standard 

of  illumination  proposed  by  Preece,  equal  to 
the  illumination  given  by  a  standard  candle 
at  the  distance  of  12.7  inches. 

According  to  Preece,  the  illumination  of  the 
average  streets  of  London,  where  gas  is  employed, 
is  equal  to  about  one- tenth  of  this  standard  in  the 
neighborhood  of  a  gas  lamp,  and  about  one- 
fiftieth  in  the  middle  space  between  two  lamps. 

The  term  unit  of  illumination,  in  place  of  in- 
tensity of  light,  was  proposed  by  Preece  in  order 
to  avoid  the  very  great  difficulty  in  determining 
the  intensity  of  a  light  in  a  street  or  space  where 
there  were  a  number  of  luminous  sources,  and 
where  the  directions  of  incidence  of  the  different 
lights  vary  so  greatly. 

A  carcel  standard  at  the  distance  of  a  metre 
will  illumine  a  surface  to  the  same  intensity  of 
illumination  as  a  standard  candle  at  the  distance 
of  12.7  inches.  (See  Candle,  Foot.) 

Illumined  Electrode.— (See  Electrode, 
Illumined?) 

Imbibition  Currents.— (See  Currents,  Im- 
bibition^ 

Images,  Electric A  term  some- 


times applied  to  the  charge  produced  on  a 
neighboring  surface  by  induction  from  a 
known  charge. 

A  positive  charge  produces,  by  induction,  on  a 
flat  metallic  surface  near  it,  a  negative  charge 
which  is  distributed  with  varying  density  over  the 
surface,  but  acts  electrically  as  would  an  equal 
quantity  of  negative  electricity  placed  back  of  the 
plate  at  the  same  distance  the  positive  charge  is 
in  front  of  it.  The  correspondence  of  this  charge 
with  the  image  of  an  object  seen  in  a  plane  mirror, 
has  led  to  the  term  electric  image. 

Maxwell  defines  electric  image  as  follows:  "  An 
electric  image  is  an  electrified  point,  or  system  of 
points,  on  one  side  of  a  surface,  which  would  pro- 
duce,  on  the  other  side  of  that  surface,  the  same 
electrical  action  which  the  actual  electrification  oi 
the  surface  really  does  produce. ' ' 

Impedance.— Generally  any  opposition  to 
current  flow. 

The  sum  of  the  ohmic  resistance  and  the 
spurious  resistance  of  a  circuit  measured  in 
ohms. 

A  quantity  which  is  related  to  the  strength 
of  the  impressed  electromotive  force  of  a  sim- 
ple periodic  or  alternating  current,  in  the  same 
manner  that  resistance  is  related  to  the  steady 
electromotive  force  of  a  continuous  current. 

In  the  case  of  steady  currents,  the  current 
strength  is  equal  to  the  electromotive  force  dl. 
vided  by  the  resistance;  or, 

_  Electromotive  force 

Current  strength  = =— : 

Resistance. 

In  the  case  of  a  simple  periodic  or  alternating  cur* 
rent,  the  average  current  strength  is  equal  to  the 
average  impressed  electromotive  force  divided  by 
the  impedance;  or, 
Average  current  strength  = 

Average  impressed  electromotive   force 
Impedance. 

Since  impedance,  like  true  resistance  of  the  cir- 
cuit, can  be  measured  in  ohms,  it  is  sometimes 
called  the  virtual  resistance. 

Impedance  is  a  quantity  equal  to  the  square 
root  of  the  sum  of  the  squares  of  the  inductive 
resistance  of  the  circuit  and  the  ohmic  resistance. 

In  the  case  of  simple  periodic  or  alternating 
currents,  the  average  current  strength  is  equal  to 
the  average  impressed  electromotive  force,  divided 
by  the  impedance;  the  maximum  current  strength 


lmp.J 


276 


[Inc. 


it 


is  equal  to  the  maximum  impressed  electromotive 
force,  divided  by  the  impedance. 

The  impedance  of  a  circuit  can  be  repre- 
sented geometrically  as  fol 
lows:  Draw  a  right  angled 
triangle  (Fig.  296),  the  base 
of  which  represents  the 
ohmic  resistance  of  the  cir- 
out,  and  the  perpendicular, 
the  inductive  resistance; 
then  the  hypothenuse  will 
represent  the  impedance. 

Since  the  ohmic  resistance  equals  R,  and  the  in- 
ductive resistance  equals  the  inductance  L,  mul- 
tiplied by  2  it  n,  in  which  n,  is  the  frequency,  the 
value  of  the  impedance  is  equal  to 


Representation  of  I 


Impedance  Coil.  —  (See  Coil,  Impedance.) 

Impedance,    Impulsive    or   Oscillatory 

--  The  impedance  which  a  conductor 
offers  to  an  impulsive  or  oscillatory  dis- 
charge. 

The  impulsive  impedance  varies  in  simple  pro- 
portion to  the  frequency  of  the  periodic  current. 
It  depends  on  the  form  and  size  of  the  circuit,  but 
it  is  independent  of  its  resistance  or  permeability. 

Imponderable.  —  That  which  possesses  no 
weight. 

A  term  formerly  applied  to  the  luminiferous 
or  universal  ether,  but  now  generally  aban- 
doned. 

It  is  very  questionable  whether  it  is  possible  for 
any  form  of  matter  to  be  actually  imponderable 
or  to  possess  no  attraction  for  other  matter. 

An  imponderable  fluid,  as,  for  example,  the 
universal  ether,  as  the  term  is  now  generally  em- 
ployed, is  a  fluid  whose  weight  is  comparatively 
small  and  insignificant,  and  not  a  fluid  an  infinite 
quantity  of  which  would  be  entirely  devoid  of 
weight. 

Impressed  Electromotive  Force.  —  (See 
Force,  Electromotive,  Impressed.) 

Impulse,  Electro-Magnetic  --  An  im- 
pulse produced  in  the  ether  surrounding  a 
conductor  by  the  action  of  an  impulsive  dis- 
charge, or  by  a  pulsating  field. 

Impulse,  Electromotive  --  An  im- 
pulse producing  an  impulsive  rush  of  elec- 
tncity. 


The  term  is  employed  to  distinguish  between 
the  ordinary  electromotive  force  which  produces  a 
steady  current  of  electricity  and  an  electromotive 
impulse  which  produces  an  impulsive  rush  of  elec- 
tricity or  impulsive  discharge. 

Impulsion  Cell.— (See  Cell,  Impulsion.) 

Impulsion  Effect— (See  Effect,  Impul- 
sion?) 

Impulsive  Impedance. — (See  Impedance, 
Impulsive  or  Oscillatory) 

Incandesce. — To  shine  or  glow  by  means 
of  heat. 

Incandescence. — The  shining  or  glowing  of 
a  substance,  generally  a  solid,  by  reason  of  a 
sufficiently  high  temperature. 

Incandescence,  Electric  —  — The  shin- 
ing or  glowing  of  a  substance,  generally  a 
solid,  by  means  of  heat  of  electric  origin. 

Electric  incandescence  of  solid  substances  differs 
from  ordinary  incandescence,  in  the  fact  that  un- 
less the  substance  is  electrically  homogeneous 
throughout,  the  temperature  is  not  uniform  in  all 
parts,  but  is  highest  in  those  portions  where  the 
resistance  is  highest  and  the  radiation  smallest. 

The  deposition  of  carbon  in  and  on  a  carbon 
conductor  by  \h.s  flashing  process  is  quite  different 
as  performed  by  electrical  incandescence,  than  it 
would  be  if  the  carbons  were  heated  by  ordinary 
furnace  or  other  heat.  (See  Carbons,  Flashing 
Process  for.) 

Incandescence,  Thermal The  shin- 
ing or  glowing  of  a  substance,  generally  a 
solid,  by  means  of  heat  other  than  that  of 
electric  origin. 

Incandescent. — Shining  or  glowing  with 
heat. 

Incandescent  Ball  Electric  Lamp.— (See 
Lamp,  Electric,  Incandescent  JBall.) 

Incandescent  Electric  Lamp,  Life  Curve 

of (See  Curve,  Life,  of  Incandescent 

Lamp.) 

Incandescent  Electric  Lamp,  Life  of  — 
— (See  Lamp,  Electric,  Incandescent,  Life 
of.) 

Incandescent  Straight  Filament  Lamp. 
— (See  Lamp,  Incandescent,  Straight 
ment.\ 


Inc.J 


277 


[Ind 


Incandescing.— Glowing  or  shining  by 
means  of  heat. 

Inclination,  Angle  of  —  —The  angle 
which  a  magnetic  needle,  free  to  move  in  a 
vertical  and  horizontal  plane,  makes  with  a 
horizontal  line  passing  through  its  point  of 
support. 

The  angle  of  magnetic  dip. 

A  magnetic  needle,  supported  at  its  centre  of 
gravity,  and  capable  of  moving  freely  in  a  ver- 
tical as  well  as  in  a  horizontal  plane,  does  not 
retain  a  horizontal  position  at  all  parts  of  the 
earth's  surface. 

The  angle  which  marks  its  deviation  from  the 
korizontal  position  is  called  the  angle  of  dip  or 
inclination.  (See  Dip,  Magnetic.) 

Incandescent      Electric      Lamp.  —  (See 

Lamp,  Electric,  Incandescent.) 

Inclination  Chart.— (See  Chart,  Inclina- 
tion.) 

Inclination  Compass. — (See  Compass,  In- 
clination.) 

Inclination,  Magnetic — The  an- 
gular deviation  from  a  horizontal  position  of 
a  freely  suspended  magnetic  needle.  (See 
Dip,  Magnetic.  Chart,  Inclination^ 

Inclination  Map. — (See  Map  or  Chart, 
Inclination?] 

Inclination  of  Magnetic  Needle. — (See 
Needle,  Magnetic,  Inclination  of) 

Inclinometer. — A  name  sometimes  given 
to  an  inclination  compass.  (See  Compass, 
Inclination.) 

Incomplete  Circuit. — (See  Circuit,  In- 
complete.) 

Increased  Electric  Irritability.— (See 
Irritability,  Electric,  Increased?) 

Increment  Key. — (See  Key,  Increment?] 

Increment  Key  of  a  Qnadruplex  Tele- 
graphic System. — (See  Key,  Increment,  of 
Quadruplex  Telegraphic  System.) 

India  Rubber. — A  resinous  substance  ob- 
tained from  the  milky  juices  of  several  tropi- 
cal trees. 

India  rubber  or  caoutchouc  is  obtained  from 
tfhe  Siphonia  elastica  of  South  America. 


India  rubber  is  quite  elastic  and  possesses  high 
powers  of  electric  insulation.  When  vulcanized 
or  combined  with  sulphur,  it  still  retains  its 
powers  of  electric  insulation  in  a  high  degree. 
In  this  state  it  is  highly  electrified  by  friction. 
(See  Caoutchouc.) 

Indicating  Bell.— (See  Bell,  Indicating?] 

Indicator,  Automatic Any  auto- 
matic device  for  electrically  indicating  the 
number  of  times  a  circuit  has  been  opened  or 
closed,  and  thus  the  number  of  times  a  given 
operation  has  occurred  which  has  caused  the 
opening  or  closing  of  such  circuit. 

An  annunciator  with  an  automatic  drop  is 
sometimes  called  an  automatic  indicator.  (See 
Annunciator,  Electro-Magnetic.  Annunciator 
Drop,  Automatic.) 

Indicator,  Electric A  name  ap- 
plied to  various  devices,  generally  operated 
by  the  deflection  of  a  magnetic  needle,  or  the 
ringing  of  a  bell,  or  both,  for  indicating,  at 
some  distant  point,  the  condition  of  an  electric 
circuit,  the  strength  of  current  that  is  passing 
through  it,  the  height  of  water  or  other  liquid, 
the  pressure  on  a  boiler,  the  temperature,  the 
speed  of  an  engine  or  line  of  shafting,  the 
working  of  a  machine  or  other  similar  events 
or  occurrences. 

A  term  sometimes  used  in  place  of  annun- 
ciator. (See  Annunciator, Electro-Magnetic.) 

Indicators  are  of  various  forms.  They  are 
generally  electro-magnetic  in  character.  They 
are  automatic  in  action. 

Indicator,  Electric  Circuit A  de- 
vice, generally  in  the  form  of  a  vertical  gal- 
vanometer, employed  to  indicate  the  presence 
and  direction  of  a  current  in  a  circuit,  and 
often  to  roughly  measure  its  strength.  (See 
Galvanometer,  Vertical.) 

Indicator,  Electric,  for  Steamships  — 

— An  electric  indicator  operated  by  circuits 
connected  with  the  throttle  valve  and  revers- 
ing gear  of  the  steam  engine. 

The  signal  "stop,"  for  example,  sent  by  the 
navigating  officer  to  the  engineer,  causes  him  to 
close  the  throttle.  This  act  places  the  indicator 
needle  at  "etop,"  and  thus  informs  the  officer 
that  his  signal  has  been  obeyed.  In  the  same 


Ind.] 


278 


[Ind. 


manner,  the  opening  of  the  throttle  sets  the  in- 
dicator  needle  to  "ahead,"  etc. 

Indicator,  Electric    Throwback 

An  annunciator  with  a  drop  that  is  electrically 
replaced.  (See  Annunciator,  Electro-Mag- 
netic^ 

Indicator,    Lamp An    apparatus 

used  in  the  central  station  of  a  system  of  in- 
candescent lamp  distribution  to  indicate  the 
presence  of  the  proper  voltage  or  potential 
difference  on  the  mains. 
c 


Fig.  397.    Edison-Howell  Lamp  Indicator. 

The  lamp  indicator  of  Edison  and  Howell  is 
shown  in  Fig.  297.  It  consists  essentially  of  a 
Wheatstone  bridge  with  the  resistances  arranged 
as  shown.  A  galvanometer  at  G,  serves,  by  the 
movements  of  its  magnetic  needle,  to  act  as  an 
indicator.  This  needle  remains  at  zero,  when 
the  potential  difference  is  the  exact  voltage  re- 
quired on  the  circuit  with  which  the  indicator  is 
connected.  The  incandescent  lamp  at  L,  being 
one  of  the  resistances,  and  being  constantly 
traversed  by  the  current,  will  have  a  fixed  resist- 
ance for  the  temperature  at  which  it  is  designed 
to  run.  The  other  resistances  are  so  proportioned 
as  to  insure  the  needle  at  G,  remaining  at  zero. 
If,  however,  the  potential  varies,  the  temperature 
of  the  lamp  L,  varies,  and,  being  carbon,  its  re- 
sistance also  varies,  a  rise  of  temperature  cor- 
responding to  a  fall  of  lamp  resistance,  which 
destroys  the  balance  of  the  bridge  and  deflects 
the  galvanometer  needle.  The  attendant  then 
regulates  the  potential  to  bring  the  needle  back  to 
zero. 

Indicator,  Mechanical  Throwback 

— An  annunciator  with  a  mechanical  drop. 
(See  Annunciator,  Electro-Magnetic.  An- 
nunciator, Drop.  Annunciator,  Gravity) 

Indicator,  Pendulum An  annun- 
ciator, the  indicating  arm  of  which  is  operated 


by  means  of  a  pendulum.  (See  Annunciator, 
Pendulum) 

Indicator,  Potential An  apparatus 

for  indicating  the  potential  difference  between 
any  points  of  a  circuit. 

A  voltmeter  is  a  potential  indicator.  It  is, 
however,  more  than  an  indicator,  since  it  gives 
the  value  of  the  potential  difference  in  volts.  (See 
Voltmeter. )  A  lamp  indicator  is  a  potential  in- 
dicator. (See  Indicator ',  Lamp) 

Indicator,  Semaphore An  annun- 
ciator in  which  a  gravity  drop  or  shutter  is 
caused  to  fall  by  the  action  of  the  electric 
current,  thus  exposing  a  number  of  other 
signals  back  of  the  drop  or  shutter. 

Indicator,  Speed A  name  some- 
times applied  to  a  tachometer.  (See  Tachom- 
eter) 

A  form  of  speed  indicator  is  shown  in  Fig. 
298.  The  endless  screw  drives  the  wheel  when 
the  triangular  point  is  held  firmly  against  the 
centre  of  the  revolving  shaft  or  pulley. 


Fig.  298.    Speed  Indicator. 

Indicator,  Voltaic  Battery A  de- 
vice for  indicating  the  condition  of  a  voltaic 
battery. 

Indifferent  Point.— (See  Point,  Indif- 
ferent) 

Indirect  Excitation.— (See  Excitation, 
Indirect) 

Induced  Atomic  Currents.— (See  Cur- 
rents, Induced,  Atomic  or  Molecular) 

Induced  Current. — (See  Current,  In- 
duced) 

Induced  Direct  Current. — (See  Current, 
Direct,  Induced) 

Induced  Electrostatic  Charge.  — (See 
Charge,  Induced  Electrostatic) 

Induced  Molecular  Currents. — (See  Cur- 
rents, Induced  Molecular) 


Ind.] 


279 


[Ind. 


Induced  Rererse  Currents.— (See  Cur- 
rent, Reverse,  Induced!) 

Inductance  • The  induction  of  a 

circuit  on  itself,  or  on  other  circuits. 

Self-induction. 

A  term  now  generally  employed  instead  of 
self-induction. 

That  property  in  virtue  of  which  a  finite 
electromotive  force,  acting  on  a  circuit,  does 
not  immediately  generate  the  full  current  due 
to  its  resistance,  and  when  the  electromotive 
force  is  withdrawn,  time  is  required  for  the 
current  strength  to  fall  to  zero. — (Fleming?) 

A  quality  by  virtue  of  which  the  passage  of 
an  electric  current  is  necessarily  accompanied 
by  the  absorption  of  electric  energy  in  the 
formation  of  a  magnetic  field. 

The  inductance  of  a  circuit  depends: 

(i.)  On  the  form  or  shape  of  the  circuit. 

(2.)  On  the  magnetic  permeability  of  the  space 
surrounding  the  circuit. 

(3.)  On  the  magnetic  permeability  of  the  circuit 
itself. 

For  the  variations  of  current  strength  in  elec- 
tric circuits,  inductance  is  not  unlike  mass,  or 
moment  of  inertia,  as  regards  variations  of  velo- 
city. Time  is  required  to  produce  velocity  in  a 
heavy  body  by  the  action  of  any  force;  so  also 
time  is  required  to  produce  a  current  by  the 
action  of  an  electromotive  force. 

The  electro-magnetic  energy  present  in  any 
given  current  is  equal  to  the  square  of  the  current 
multiplied  by  the  inductance.  Since  one  of  these 
factors  (the  current  strength)  represents  the 
force,  the  other,  the  inductance,  must  have  the 
dimension  of  a  distance  or  length.  Inductance, 
therefore,  is  measurable  in  units  of  length.  If 
the  circuits  are  formed  of  magnetizable  materials, 
the  inductance  of  a  circuit  is  the  ratio  between  the 
total  inductance  taking  place  through  the  circuit 
to  the  current  producing  it. 

If  the  circuit  is  formed  entirely  of  non-magnetic 
material,  surrounded  entirely  by  materials  of 
constant  magnetic  permeability  (such  as  air,  in- 
sulators and  diamagnetic  materials  generally),  the 
inductance  is  a  constant  quantity  and  depends 
only  on  the  form  or  shape  of  the  circuit.  In  this 
case,  the  total  inductance  through  the  circuit  is  pro- 
portional to  the  magnetizing  force,  and  the  mag- 
netic resistance,  or  the  magnetic  conductance  of 
the  magnetic  circuit,  is  equal  to  the  total  induc- 


tion through  the  circuit,  divided  by  the  magnetiz- 
ing force. 

In  cases  where  the  magnetic  circuit  is  partly  or 
wholly  of  paramagnetic  substances,  where  the 
induction  bears  no  constant  ratio  to  the  magnetiz- 
ing force,  and  where  the  induction  takes  place 
partly  or  wholly  in  media  of  variable  permeability, 
the  co-efficient  of  self- induction,  or  the  inductance, 
must  be  denned  in  three  ways: 

(i.)  As  the  ratio  between  the  counter  electro- 
motive force  in  any  circuit  and  the  time  rate  of 
variation  of  the  current  producing  it. 

(2.)  As  the  ratio  between  the  total  induction 
through  the  circuit  and  the  current  producing  it. 

(3.)  As  the  energy  associated  with  the  circuit 
in  the  form  of  magnetic  field,  due  to  unit  current 
in  that  circuit,  or  as  the  co-efficient  by  which  half 
the  square  of  the  current  must  be  multiplied  to 
obtain  the  electro-kinetic  energy  of  the  circuit  at 
that  instant.  —  (Fleming.) 

A  flat  sheet  or  strip  of  metal  possesses  less  in- 
ductance than  a  round  conductor  of  equal  cross- 
section. 

This  may  be  explained  by  conceiving  that  a 
flat  conductor  presents  a  greater  absorption  sur- 
face to  the  dielectric. 

Therefore,  the  perfect  form  for  a  conductor 
transmitting  rapidly  alternating  currents  is  that 
of  a  flat  sheet  or  strip  of  copper,  or  preferably  a 
copper  tube. 

The  experiments  of  Hughes  show  that  the  in- 
ductance of  a  conductor  may  be  regarded  as  an 
effect  due  to  the  time  required  for  the  rapidly 
periodic  current  to  penetrate  the  conductor,  and 
that  the  decrease  in  the  inductance,  produced  by 
forming  the  conductor  of  a  strip  or  bar,  is  due 
to  the  decreased  distance  the  current  has  to  pass 
to  the  inner  parts. 

Inductance,  Absolute  Unit  of A 

unit  of  length  equal  to  one  centimetre. 

A  length  equal  to  an  earth  quadrant  or  IO» 
centimetres  is  called  the  practical  unit  of  induct- 
ance. The  practical  unit  of  inductance  was  form- 
erly called  a  secohm  or  quadrant  It  is  now  gen- 
erally called  a  henry.  (See  Henry,  A.) 

Inductance  Bridge. — (See  Bridge,  In- 
ductance,) 

Inductance,  Co-efficient  of A  con- 
stant quantity,  such  that  when  multiplied  by 
the  current  strength  passing  in  any  coil  or  cir- 
cuit, will  represent  numerically  the  induction 
through  the  coil  or  circuit  due  to  that  current 


Ind.] 


280 


rind. 


A  term  sometimes  used  for  co-efficient  of 
self-induction.  (See  Induction,  Co-efficient 
of.) 

Inductance,  Constant The  induct- 
ance which  occurs  in  circuits  formed  wholly 
of  non-magnetic  materials,  immersed  in  or 
surrounded  by  media  of  constant  magnetic 
permeability  or  magnetic  conductance  for 
lines  of  magnetic  force.  (See  Permeability, 
Magnetic?) 

When  the  lines  of  magnetic  force  pass  through 
such  materials  as  ordinary  insulators,  or  diamag- 
netic  materials,  such  as  copper,  the  inductance  is 
constant,  provided  the  geometric  form  of  the  cir- 
cuit remains  the  same. 

Inductance,   Formal,  of  Circuit 

That  part  of  the  counter  electromotive  force 
of  a  circuit  which  depends  on  the  form  of  the 
circuit. 

Inductance,  or  Self-induction,  Practical 

Unit  of A  length  equal  to  the  earth 

quadrant  or  lo'1  centimetres. 

The  absolute  unit  of  inductance  is  equal  to  I 
centimetre. 

Inductance,  Oscillatory,  Electric 

Inductance  produced  by  electric  oscillations. 

Inductance,  Unit  of A  term  now 

generally  used  for  unit  of  self-induction. 

The  value  of  the  inductance  may  be  given 
either  in  absolute  or  in  practical  units  of  induct 
ance.  The'absolute  unit  of  inductance  is  equal 
to  a  length  of  one  centimetre.  The  practical  unit 
of  inductance  is  equal  to  1,000,000,000  centi- 
metres or  IO1  centimetres. 

The  practical  unit  of  inductance  was  formerly 
called  a  secohm.  The  term  henry  is  generally 
used  for  this  unit.  (See  Henry,  A.) 

Inductance,  Variable The  induc- 
tance which  occurs  in  circuits  formed  partly 
or  wholly  of  substances  like  iron  or  other 
paramagnetic  substances,  the  magnetic 
permeability  of  which  varies  with  the  inten- 
sity of  the  magnetic  induction,  and  where  the 
lines  of  force  have  their  circuit  partly  or 
wholly  in  such  material  of  variable  magnetic 
permeability. 

Induction. — An    influence   exerted   by  a 


charged  body  or  by  a  magnetic  field  on  neigh- 
boring bodies  without  apparent  communica- 
tion. 

A  medium  is  necessary  to  connect  the  body 
producing  the  induction  and  that  in  which  the 
induction  is  produced.  (See  Induction,  Electro- 
static. Induction,  Magnetic.  Induction,  Electro- 
Dynamic.} 

Induction,  Apparent  Co-efficient  of — 

— A  term  sometimes  used  for  co-efficient  of 
apparent  magnetic  induction.  (See  Induc- 
tion, Magnetic,  Apparent  Co-efficient  of.) 

It  is  called  the  apparent  co  efficient  of  induction 
because  its  value  is  different  from  what  it  would 
be  if  the  eddy  currents  were  entirely  suppressed. 
The  eddy  currents  increase  the  resistance  of  the 
primary  and  decrease  its  inductance. 

Induction-Balance,  Hughes'  —  —(See 
Balance,  Induction,  Hughes'?) 

Induction,  Balance  of,  in  Cable  — 
The    removal    of    induction   in   a   cable   by 
neutralization  by  the  presence  of  equal  and 
opposite  effects. 

A  balance  is  obtained  of  the  inductive  effects  of 
the  neighboring  conductors,  whether  in  the 
bunched  cable  or  outside  of  it. 

Induction-Bridge.— (See  Bridge,  Induc- 
tance?) 

Induction,  Coefficient  of  —  — A  term 
sometimes  used  for  co-efficient  of  magnetic 
induction.  (See  Induction,  Magnetic,  Co~ 
efficient  of.) 

Induction  Coil.— (See  Coil,  Induction?) 

Induction    Coil,    Inyerted  — (See 

Coil,  Induction,  Inverted.     Transformer?) 

Induction,  Current A  term  some- 
times used  for  voltaic  induction.  (See  Induc- 
tion, Voltaic.  Induction,  Electro-Dynamic?] 

Induction,  Dissymmetrical,  of  Armature 

An  induction  produced  by  the  passage 

of  a  different  number  of  lines  of  magnetic 
force  through  adjoining  halves  of  the  arma- 
ture. 

Induction,  Electro-Dynamic Elec- 
tromotive forces  set  up  by  induction  in  con- 
ductors which  are  either  actually  or  practically 
moved  so  as  to  cut  the  lines  of  magnetic 
force. 


Ind.j 


281 


[In<L 


These  electromotive  forces,  when  permitted  to 
act  through  a  circuit,  produce  an  electric  current. 

Electro-dynamic  induction  may  be  produced  in 
any  circuit  in  two  ways: 

(i.)  By  causing  expanding  or  contracting  lines 
of  magnetic  force  to  pass  through  that  circuit. 

(2.)  By  causing  the  circuit  or  conductor  to  pass 
through  the  lines  of  magnetic  force. 

In  all  cases  the  lines  of  force  are  made  to  pass 
through  the  conductor  or  wire. 

There  are  four  cases  of  electro -magnetic  induc- 
tion: 

(I.)  That  in  which  expanding  or  contracting 
lines  of  magnetic  force,  produced  by  rapidly  vary- 
ing the  current  in  any  circuit,  are  caused  to  pass 
through  or  cut  that  circuit  and  consequently  to 
produce  differences  of  potential  therein. 

(2.)  That  in  which  expanding  or  contracting 
lines  of  magnetic  force  produced  by  any  circuit  by 
the  rapidly  varying  strength  of  the  electric 
current  passing  through  that  circuit,  are  caused 
to  pass  through  another  neighboring  circuit  and 
thus  produce  differences  of  potential  therein. 

(3.)  That  produced  by  moving  a  conductor 
through  a  magnetic  field  so  as  to  cut  its  lines  of 
magnetic  force.  In  this  way  the  strength  of  the 
magnetic  field  may  remain  practically  constant, 
but  this  strength  as  regards  the  field  of  the  fixed 
conductor  is  varying,  as  the  magnet  producing 
such  a  field  is  moved  toward  or  from  such  cir- 
cuit, and  m  this  way  differences  of  potential  are 
produced  in  the  circuit. 

(4.)  That  "produced  by  moving  an  inducing  field 
past  a  fixed  conductor.  This  may  be  accom- 
plished by  moving  an  electro-magnet,  an  electric 
circuit,  or  a  permanent  magnet  past  the  conductor 
in  which  the  difference  of  potential  is  to  be  in- 
duced. 

There  are  therefore  four  distinct  varieties  of 
electro-dynamic  induction: 

(i.)  Self-induction  or  inductance.  (SeeSnduct- 
ance.) 

(2.)  Mutual  induction,  or,  as  it  is  sometimes 
called,  voltaic  current  induction.  (See  Induction^ 
Mutual.} 

(3.)  Electro-magnetic  induction,  or,  as  it  is 
sometimes  called,  dynamo-electric  induction. 

(4.)  Magneto-electric  induction. 

If  the  terminals  of  a  voltaic  cell  be  connected 
with  the  ends  of  a  comparatively  long  coil  of  in- 
sulated wire,  no  appreciable  spark  will  be  observed 
on  closing  the  cell,  because  the  current  induced 
by  self-induction  is  in  the  opposite  direction  to  the 


current  of  the  cell  and  weakens  it.  On  breaking 
contact,  however,  a  spark  is  readily  observed. 
This  is  due  to  the  induced  current  on  breaking, 
which,  flowing  in  the  same  direction  as  the  cur- 
rent of  the  cell,  strengthens  it. 


Fig.  299.    Mutual  In 

The  coil  B,  Fig.  299,  consists  of  two  parallel 
coils  of  insulated  wire,  the  terminals  of  one  of 
which,  called  the  primary  coil,  are  connected 
with  the  battery  cell  P  N,  and  those  of  the 
other,  called  the  secondary  coil,  with  the  galva- 
nometer G. 

Under  these  circumstances  it  is  found: 

(i.)  That  at  the  moment  of  closing  the  circuit 
through  the  primary  coil,  a  momentary  current 
is  produced  in  the  secondary  coil  in  a  direction 
opposite  to  that  of  the  current  through  the  primary, 
as  is  shown  by  the  direction  of  the  deflection  of 
the  needle  of  the  galvanometer. 

(2.)  At  the  moment  of  breaking  the  circuit 
through  the  primary  coil,  an  induced  current  is 
produced  in  the  secondary  coil  in  the  same  direc- 
tion as  that  flowing  thYough  the  primary  coil. 

(3.)  These  induced  currents  are  momentary, 
and  continue  in  the  secondary  only  while  the  in- 
tensity of  the  current  in  the  primary  is  varying, 
*.  t.,  while  variations  are  occurring  in  the  strength 
of  the  magnetic  field  in  which  the  secondary  coil 
is  placed,  therefore  while  the  expanding  or  con- 
tracting lines  of  force  are  passing  through  the  sec- 
ondary coil. 

If,  for  instance,  when  the  current  is  established 
in  the  primary  coil,  and  no  current  exists  in  the 


Fig.  300.    Mutual  Induction. 

secondary,  the  intensity  of  the  current  in  the 
primary  be  varied  by  establishing  a  shunt  circuit 
across  the  battery  terminals,  as  by  placing  a  short 
wire  d,  Fig.  300,  in  the  mercury  cups  g,  g,  thus 


£nd.] 


282 


[Ind. 


decreasing  the  intensity  of  the  current  in  the 
primary,  an  induced  current  will  be  set  up  in  the 
secondary  circuit  in  the  same  direction  as  the 
primary  current. 

From  all  of  these  phenomena,  we  see  that  any 
increase  of  current  in  a  conductor  produces  in  a 
neighboring  conductor  an  induced  inverse  current, 
or  one  in  the  opposite  direction  to  the  inducing 
current,  while  a  decrease  of  such  current  produces 
a  direct  induced  current,  or  one  in  the  same 
direction  as  the  inducing  current. 

If  the  induction  coil  be  made,  as  in  Fig.  301, 
with  its  primary  coil  movable  into  and  out  of  the 
secondary  coil,  then  the  following  phenomena  will 
occur: 

(I.)  When  the  primary  coil  is  moved  toward 
the  secondary  coil  an  inverse  current  is  induced 
in  the  secondary ;  and, 

(2.)  When  the  primary  coil  is  moved  away  from 
the  secondary  coil  a  direct  current  is  induced  in 
the  secondary. 

The  movements  of  permanent  magnets  towards 
or  from  a  coil  will  also  produce  an  Induced  cur- 
rent. 

If,  for  example,  the  apparatus  be  arranged  as 
in  Fig.  302,  then: 


These  facts  may  be  expressed  by  the  following 
laws  : 
(I.)  &ny  increase  in  thenumber  of  lines  of  force 


Fig.  $OI.    Electro- Dynamic  Induction. 

(I.)  A  motion  of  the  magnet  towards  the  coil 
produces  an  induced  current  in  the  coil  in  one 
direction,  and 

(2.)  Its  motion  away  from  the  magnet  produces 
an  induced  current  in  the  coil  in  the  opposite 
direction. 

The  directions  of  these  induced  currents  are 
respectively  inverse  and  direct  as  compared  with 
the  direction  of  the  amperian  currents  which  are 
assumed  to  produce  the  magnetic  poles  of  perma- 
nent magnets,  or  of  the  currents  that  actually 
produce  electro-magnets.  (See  Magnetism,  Am- 
fitrSs  Theory  of.} 


Fig.  302.    Magneto-Electric  Induction. 

which  pass  through  a  circuit  produces  an  inverse 
current  in  that  circuit,  while  any  decrease  in  the 
number  of  such  lines  of  force  which  pass  through 
any  circuit  produces  a  direct  current  in  that 
circuit. 


D/HECT/OA 
Of  UN£ 

OF 
MOTION 


303.     Fleming's  Rule. 


(2.)  The  intensity  of  the  induced  current,  or, 
more  correctly,  the  difference  of  potential  pro- 
duced, is  proportional  to  the  rate  of  increase  or 
decrease  of  the  lines  of  force  passing  through  the 
circuit. 

A  conductor,  therefore,  when  moved  through 


283 


[Ind. 


a  magnetic  field  so  as  to  cut  the  lines  of  magnetic 
force,  will  have  a  difference  of  potential  generated, 
and  if  its  circuit  is  closed  so  that  the  difference  of 
potential  can  neutralize  itself,  it  will  have  a  cur- 
rent produced  in  it  by  induction. 

A  simple  but  effective  manner  of  remembering 
the  direction  of  such  currents  is  that  proposed  by 
Fleming. 

If  the  hand  be  held  with  the  fingers  extended, 
as  in  Fig.  303,  and  the  direction  of  the  forefinger 
represent  the  positive  direction  of  the  lines  of 
force,  *.  e.,  those  coming  out  of  the  N.  pole  of  a 
magnet,  then,  if  a  wire  or  other  conductor  be 
moved  in  the  direction  in  which  the  thumb  points, 
so  as  to  cut  these  lines  of  force  at  right  angles, 
that  is,  if  the  conductor  have  its  length  moved 
directly  across  these  lines,  it  will  have  an  induced 
current  developed  in  it  in  the  direction  in  which 
the  middle  finger  points.  (See  Force,  Lines  of, 
Direction  of.) 

Or,  the  same  thing  can,  perhaps,  be  even  more 
readily    remembered  by         p 
cutting  a  piece  of  paper 
In  the   shape  shown  in-w 
Jig.  304,  marking  it  as  H 
shown,  and  then  bending  ^ 
the  arm  P,  upward  at  the  ji 
dotted  line,  so  as  to  form  Q 
three  axes  at  right  angles 
to  one  another. 

As  has  been  already 
remarked,  a  difference  of 
potential,  and  not  a  cur-  , 
rent,  is  produced  by  mov- 
ing a  conductor  through 
a  magnetic  field  so  as  to  ~     _"       F2emin  's  Rule 
cut  its  lines  of  force. 

It  can  be  shown  that  in  order  to  generate  a  dif- 
ference of  potential  of  one  -volt,  100,000,000  C.  G. 
S.  lines  of  force  must  be  cut  per  second. 

In  electro-dynamic  induction,  the  induced  cur- 
rent is  produced  by  the  energy  absorbed  in  moving 
the  conductor  through  the  magnetic  field.  Lenz 
has  shown  that  in  all  cases  of  electro-dynamic 
induction,  produced  by  the  movement  either  of 
the  circuit  or  of  the  magnet,  the  current  induced 
in  the  circuit  is  in  such  a  direction  as  to  produce 
a  magnet  pole  which  would  tend  to  oppose  the 
motion. 

Induction,    Electro-Magnetic A 

variety  of  electro-dynamic  induction  in  which 
electric  currents  are  produced  by  the  motion 
10_ Vol.  l 


«,_, 


Direction  of 
Motion. 


of  electro-magnets  or  electro-magnetic  sole- 
noids. (See  Induction,  Electro-Dynamic.) 

Induction,  Electrostatic The  pro- 
duction of  an  electric  charge  in  a  conductor 
brought  into  an  electrostatic  field. 

If  the  insulated  conductor  A  B,  Fig.  305,  be 
brought  into  the  positive  electrostatic  field  of  the 
insulated  conductor  C,  then, 

(I.)  A  charge  will  be  produced  on  A  and  B,  as 
will  be  indicated  by  the  divergence  of  the  pith 
balls. 

(2.)  This  charge  is  negative  at  the  end  A, 
nearest  C,  and  positive  at  the  end  B,  furthest 
from  C,  as  can  be  shown  by  an  electroscope.  (See 
Electroscope. ) 


(3.)  The  charges  at  A  and  B,  are  equal  to  each 
other  ;  for,  if  the  conductor  A  B,  be  removed  from 
the  field  of  C,  without  touching  it,  the  opposite 
charges  completely  neutralize  each  other. 

(4.)  If,  however,  the  conductor  A  B,  be  touched 
at  any  place  by  a  conductor  connected  with  the 
earth,  it  will  lose  its  positive  charge,  and  will 
remain  negatively  charged  when  removed  from 
the  field  of  C.  It  is  in  this  manner  that  an  electro- 
phorus  is  charged.  (See  Electrophorus. ) 

(5.)  The  amount  of  the  charges  produced  in  the 
conductor,  A  B,  can  never  be  greater  than  that 
in  the  inducing  body  C.  That  is  to  say,  the 


Kg.  306.    Induction  Precedes  Attraction. 
negative  electricity  at  A,  may  be  sufficient  in 
ampunt  to  neutralize  the  positive  charge  on  C,  if 
allowed  to  do  so.     In  point  of  fact  the  charge  in- 


Ind.J 


284 


[Ind. 


duced  is  less  in  amount  than  the  inducing  charge, 
according  to  the  distance  between  C  and  A,  and 
the  nature  and  condition  of  the  medium  which 
separates  them. 

The  attraction?  of  light  bodies  by  charged  sur- 
faces are  due  to  the  opposite  charge  produced  on 
those  parts  of  thf  light  bodies  that  are  nearest  the 
charged  body 

The  pith  ball  B,  Fig.  306,  suspended  by  a  silk 
thread  between  an  insulated  positively  charged 
conductor  A,  and  the  uninsulated  conductor  C, 
will  receive  by  induction  a  negative  charge  on 
the  side  nearest  A,  and  a  positive  charge  on  the 
side  nearest  C.  It  is  therefore  attracted  to  A, 
where,  receiving  a  positive  cnarge,  it  is  repelled  to 
C,  where  it  is  discharged  and  again  assumes  a 
vertical  position.  Induction  again  occurs,  and 
consequent  attraction  and  repulsion.  These 
movements  follow  one  another  so  long  as  a  suffi- 
cient charge  remains  in  A. 

Induction,    Faradic,    Apparatus 

(See  Apparatus,  Faradic  Induction.) 

Induction-Finder. — (See  Finder,  Induc- 
tion^ 

Induction,  Lateral An  induction 

observed  between  closely  approached  portions 
of  a  circuit  through  which- an  impulsive  dis- 
charge, such  as  the  disruptive  discharge  of  a 
Leyden  jar,  is  passed  as  a  long  spark,  thereby 
making  the  resistance  of  the  circuit  high. 

A  long  copper  wire,  bent  in  the  form  of  a  rec- 
tangle, has  its  free  ends  near  their  extremities 
bent  so  as  to  approach  within  half  an  inch  of  each 
other.  One  of  the  ends  of  the  wire  is  provided 
with  a  metallic  ball  and  the  other  end  connected 
with  the  earth.  If,  now,  a  Leyden  jar  charge  is 
passed  through  the  wire  by  connecting  the  outer 
coating  with  the  end  of  the  earth-connected  wire 
and  holding  the  inside  coating  near  the  knob,  a 
spark  will  pass  through  the  half  inch  of  space  be- 
tween the  approached  portions  of  the  circuit. 

This  discharge  is  due  to  what  was  formerly 
called  lateral  induction.  The  discharge  of  a 
Leyden  jar  is  an  oscillatory  discharge,  and  it 
passes  through  the  intervening  air  space  instead 
of  through  the  conductor  because  the  resistance 
of  the  latter  to  the  rapid  alternations  produces  a 
counter  electromotive  force  which  acts  as  a  re- 
sistance whose  value  is  greater  than  that  of  the 
airspace  itself.  (See  Path,  Alternative.) 


Induction,  Magnetic The  produc- 
tion of  magnetism  in  a  magnetizable  substance 
by  bringing  it  into  a  magnetic  field. 

Suppose  a  small  portion  of  a  magnetizable  body 
is  placed  in  a  magnetic  field  produced  in  a  gap 
separating  two  closely  approximated  poles.  To 
simplify  matters,  suppose  this  small  portion  to  be 
a  free  unit  pole.  It  will  be  acted  on  by  two 
forces: 

(I.)  The  force  due  to  the  magnetic  field. 

(2.)  The  force  dae  to  the  free  magnetism, 
which  appears  at  the  surface  of  the  gap  or  cut. 

The  force  on  the  unit  pole  is  compounded  of 
these  two  separate  forces,  and  is  called  the  magnetic 
induction  of  the  space.  Magnetic  induction  is, 
therefore,  strictly  speaking,  a  quantity. 

The  direction  of  magnetic  force  and  the  mag- 
netic induction  are  the  same  in  an  air  space  out- 
side a  magnet.  Within  a  bar  of  iron  or  other 
paramagnetic  material,  under  induction  in  a  mag- 
netic field,  the  magnetic  force  at  any  point  is  due 
not  only  to  the  external  or  original  field,  but  also 
to  the  field  produced  by  the  polarity  induced, 
which  acts  opposed  to  the  magnetic  force  at 
points.  Magnetic  force  and  magnetic  induction 
are  identical  only  where  there  is  no  magnetism.— 
(Fleming.) 

When  a  magnetizable  body  is  brought  into  a. 
magnetic  field  the  following  phenomena  occur, 
viz.: 

(i.)  The  lines  of  magnetic  force  pass  through 
the  body  and  are  condensed  upon  it.  (See  Field^ 
Magnetic.  Paramagnetic.) 

(2.)  If  the  body  is  free  to  move  around  an  axis, 
but  is  not  free  to  move  bodily  towards  the  magnet 
pole,  il  will  come  to  rest  with  its  greatest  extent 
or  length  in  the  direction  oi  the  lines  of  force; 
i.  f.t  in  the  direction  in  which  it  will  offer  the 
least  resistance  to  the  lines  oi  force  that  thread 
through  it. 

(3. )  The  body  will  therefore  become  a  magnet, 
its  south  pole  being  situated  where  the  lines  of 
force  enter  it  and  its  north  pole  where  they  pass 
out  from  it.  Since  the  lines  of  magnetic  force 
are  assumed  to  come  out  of  the  north  pole  of  a 
magnet  and  to  enter  its  south  pole,  if  a  magnet- 
izable substance  is  brought  near  a  north  pole, 
the  lines  of  force  from  that  north  pole  will  enter 
it  at  those  parts  nearest  such  north  pole,  thereby 
rendering  such  points  south,  and  will  pass  out  of 
its  further  end,  which  will  thereby  become  north. 

(4.)  The  intensity  of  the  induced  magnetism 


Tnd.] 


285 


will  depend  on  the  number  of  lines  of  force  that 
pass  through  it. 

(5.)  The  direction  of  the  axis  of  magnetization 
will  depend  on  the  directions  in  which  the  lines 
«f  force  thread  through  the  body.  (See  A.\  is, 
Magnetic.) 


Fig.  307.    Magnetic  Induction. 

If  abarofiron,  N'  S'  ,Fig.  307,  be  brought  near 
the  magnetized  bar,  N  S,  poles  will  be  produced 
in  it  by  induction,  as  may  be  shown  by  throwing 
iron  filings  on  it. 

The  nearer  the  body  to  be  magnetized  is  brought 
to  the  magnetizing  pole  the  greater  will  be  the 
number  of  lines  of'torce  that  thread  through  it. 
Consequently,  the  intensity  of  the  induced  mag- 
netism will  be  greater  ;  this  will  be  greatest  when 
the  bodies  actually  touch  each  other. 

The  production  of  magnetism,  therefore,  by 
contact  or  touch  is  only  a  special  case  of  the  pro- 
dtiction  of  magnetization  by  induction. 

The  attraction  of  a  magnetizable  body  by  a 
magnet  pole  is  caused  by  the  mutual  attraction 
which  exists  between  the  pole  produced  by  induc- 
tion and  the  pole  producing  the  induction.  This, 
it  will  be  seen,  is  similar  to  the  attraction  caused 
by  an  electric  charge. 

The  following  terms  are  given  by  Fleming  as 
employed  in  the  same  sense  as  magnetic  induc- 
tion of  an  area: 

(I.)  The  number  of  unit  tubes  of  induction 
passing  through  the  area. 

(2.)  The  number  of  lines  of  force  (induction) 
passing  through  the  area. — (Faraday.) 

(3.)  The  total  magnetic  induction  through  the 
area. — (Maxwell. ) 

(4.)  The  flux  or  flow  of  magnetic  induction 
through  an  area. — (Mascart  6°  Joubert.} 

(5.)  The  surface-integral  of  magnetic  induction 
over  an  area. — (Fleming.} 

Induction,  Magnetic,  Apparent  Co-effi- 
cient of •  — The  co-efficient  of  induction 

as  influenced  by  the  presence  of  eddy  cur- 
rents. 

This  is  called  the  co-efficient  of  apparent  in- 
duction, because  its  value  is  not  the  same  as  it 
would  be  if  the  eddy  currents  were  entirely  sup- 
nressed. 


The  value  of  the  co-efficient  of  apparent  induc- 
tion depends  on  the  amount  of  the  retardation  of 
the  magnetism;  or,  what  is  the  same  thing,  on, 
the  strength  of  the  eddy  currents. 

Induction,  Magnetic,  Co-efficient  of 

— A  term  sometimes  used  instead  of  magnetic 
permeability.  (See  Permeability,  Magnetic?) 

The  ratio  existing  between  the  number  of 
lin.es  of  magnetic  induction  that  pass  through 
any  area  of  cross-section  of  a  magnetic  cir- 
cuit and  the  magnetizing  force  producing 
such  induction. 

If  B,  equals  the  magnetic  induction,  or  the  num- 
ber of  lines  of  force  that  pass  through  any  area  of 
cross-section,  and  H,  equals  the  magnetizing  force, 
and  //,  equals  the  permeability,  or  the  co-efficient 
of  magnetic  induction;  then, 
_B_ 

Induction,    Magnetic,    Dynamic 

The  induction  which  takes  place  in  the  field 
of  a  magnet  whose  field  is  moving  as  regards 
the  body  in  which  induction  is  occurring. 

This  movement  of  the  field  may  be  attained, 

(i.)  By  the  movement  of  the  magnet. 

(2.)  By  the  movement  of  the  body  in  which 
induction  is  taking  place. 

(3.)  By  the  expansion  or  contraction  of  the  lines 
of  magnetic  force  produced  by  variations  of  the 
strength  of  the  magnetic  field;  or,  in  other  words, 
by  the  movement  of  the  field.  (See  Induction, 
Electro-Dynamic. ) 

Induction,  Magnetic,   Flux  or  Flow  of 

A  term  employed  in  the  same  sense 

as  the  magnetic  induction  which  takes  place 
through  any  given  area. 

The  flux  or  flow  of  magnetic  induction  is  equal 
to  the  magnitude  of  the  area  multiplied  by  the 
normal  induction  which  takes  place  in  one  unit 
of  that  area. 

Induction,  Magnetic,  Lines  of • 

Lines  which  show  not  only  the  direction  in 
which  magnetic  induction  takes  place,  but 
also  the  magnitude  of  the  induction. 

A  line  of  induction  may  be  regarded  as  a  line 
along  which  induction  takes  place,  or  as  the  axis 
of  a  tube  of  induction. 

This  term  is  often  loosely  used  for  lines  of  force. 

Induction,  Magnetic,  Static The 


Ind.j 


286 


[Ind. 


induction  which  takes  place  in  the  field  of  a 
magnet  whose  field  is  stationary  as  regards 
the  body  in  which  induction  is  occurring. 

The  term  static  magnetic  induction  is  used  in 
contradistinction  to  dynamic  magnetic  induction 
which  occurs  in  a  moving  field.  (See  Induction, 
Electro-Dynamic. ) 

Induction,  Magnetic,  Surface-Integral 

of A  term  employed  in  the  same  sense 

as  the  magnetic  induction  which  takes  place 
over  a  given  area. 

Induction,  Magneto  •  Electric A 

variety  of  electro-dynamic  induction  in  which 
electric  currents  are  produced  by  the  motion 
of  permanent  magnets,  or  of  conductors  past 
permanent  magnets.  (See  Induction,  Elec- 
tro-Dynamic?) 

Induction,  Mutual Induction  pro- 
duced by  two  neighboring  circuits  on  each 
other  by  the  mutual  interaction  of  their  mag- 
netic fields.  (See  Induction,  Electro-Dy- 
namic. Currents,  Extra?) 

Induction  produced  in  neighboring  charged 
conductors  by  the  mutual  interaction  of  their 
electrostatic  fields.  (See  Field,  Electro- 
static?) 

The  mutual  induction  of  two  conductors  or  cir- 
cuits, is  equal  to  the  ratio  of  the  induction  which 
takes  place  through  one  of  the  circuits,  to  the 
strength  of  current  in  the  other  circuit,  which  is 
producing  the  induction 

Induction,  Mutual,  Co-efficient  of 

The  quantity  which  represents  the  number 
of  lines  of  force  which  are  common  to  or 
linked  in  with  two  circuits,  which  are  pro- 
ducing mutual  induction  on  each  other. 

The  maximum  value  the  co-efficient  of  mutual 
induction  can  have,  is  equal  to  the  square  root  of 
the  product  of  the  inductance  of  the  two  circuits, 
or  "yii  X  N,  in  which  L  and  N,  are  the  constant 
co-efficients  of  self-induction  of  the  two  circuits. 

Induction,  Mutual,  Loops  of Loops 

or  lines  of  induction  produced  in  any  circuit 
by  variations  141  the  intensity  of  the  current 
flowing  in  a  neighboring  circuit. 

The  lines  of  induction  produced  by  a  circuit,  in 
which  a  current  of  electricity  is  flowing,  are 
closed  loops  or  circles  surrounding  the  circuit 
once  or  more.  The  wire  or  circuit  is  formed  by 


coiling  a  conductor  a  number  of  times  in  a  cir- 
cular  coil,  and  this  circular  coil  is  placed  near 
another  coil  in  which  a  varying  current  is  flowing. 

As  the  lines  of  induction  grow  or  increase, 
they  cut  the  circular  coil,  forming  lines  of  induc- 
tion in  the  shape  of  loops,  a  number  of  which  pass 
around  it.  They  are  called  loops  of  mutual  in- 
duction. 

Induction,  Open-Circuit The  in- 
duction produced  in  an  open  circuit  by  means 
of  electric  pulses  in  neighboring  circuits. 

The  researches  of  Hertz  have  shown  that  when 
an  impulsive  discharge,  or  an  oscillatory  dis- 
charge, occurs,  an  induction  occurs  even  in  open 
circuited  conductors.  He  shows  that  these  induc- 
tive effects  are  due  to  electro-magnetic  waves  or 
oscillations  set  up  in  the  surrounding  ether, 
which  are  propagated  through  free  ether  with  the 
velocity  of  light.  When  these  electro-magnetic 
waves  or  radiations  impinge  on  any  circuit,  if  it? 
dimensions  be  such  that  sympathetic  vibration? 
can  be  excited  therein,  such  vibrations  are  set  up 
and  cause  similar  phenomena  to  those  of  the  ex- 
citing cause,  viz.,  oscillatory  discharges  or  elec- 
tro-magnetic vibrations.  Hertz  calls  these  sym- 
pathetic circuits,  resonators,  from  their  resem- 
blance to  acoustic  resonators.  (See  Resonators, 
Electric.) 

Induction,  Oscillatory A  name 

sometimes  applied  to  open-circuit  induction. 
(See  Induction,  Open-Circuit?) 

Induction,  Reflection  of A  term 

proposed  by  Fleming  to  express  an  action 
which  resembles  a  reflection  of  inductive 
power. 

The  coils  A  and  B,  Fig.  308,  are  arranged  a3 


I'l'l 

f.joS.     Reflection  of  Induction. 

shown,  so  as  to  act  as  the  primary  and  secondary 
respectively  of  an  induction  coil,   and  are  placed 


Ind.] 


287 


[Ind. 


conjugate  or  perpendicular  to  each  other.  (See 
Coils,  Conjugate.)  Therefore,  no  sounds  are 
heard  in  the  telephone  T,  when  the  current  is 
rapidly  reversed.  If,  however,  a  plate  of  copper, 
C,  is  placed  in  the  position  shown,  then  sounds 
are  heard  in  the  telephone.  The  action  here 
resembles  a  reflection  of  the  inductive  action  from 
A  to  B,  by  means  of  the  plate  C.  The  explana- 
tion is,  of  course,  simple.  Though  A,  can  exert 
no  action  on  B,  because  the  two  coils  are  conju- 
gate to  each  other,  yet  A,  can  produce  secondary 
currents  in  C ;  and  these  reacting  on  B,  produce 
tertiary  currents  in  C,  and,  therefore,  sounds  in 
the  telephone. 

Induction,  Self Induction  produced 

in  a  circuit  at  the  moment  of  starting  or  stop- 
ping the  currents  therein  by  the  induction  of 
the  current  on  itself.  (See  Currents,  Extra.) 

A  coil  having  unit  self-induction,  is  sometimes 
said  to  have  one  tube  of  induction,  or  line  of  force 
added  to  its  field  for  each  increase  of  one  unit  of 
current. 

Induction,  Self,  Absolute  Unit  of 

A  term  sometimes  employed  for  absolute  unit 
of  inductance.  (See  Inductance,  Absolute 
Unit  of.) 

Induction,  Self,  Ayrton  &  Perry's 
Standard  of A  standard  for  the  com- 
parison of  values  of  self-induction. 

The  standard  of  self-induction  of  Ayrton  & 
Perry  consists  of  three  bobbins  of  wire,  two  fixed 
and  one  movable.  The  movable  bobbin  is  so  ar- 
ranged as  to  be  capable  of  motion  through  1 80 
degrees  within  the  fixed  bobbins.  The  coils  are 
wound  on  the  surface  of  the  zone  of  a  sphere. 

This  apparatus  permits  of  the  ready  compari- 
son of  the  self-induction  in  different  circuits,  or  in 
ihe  same  circuit  under  different  conditions. 

Induction,  Self,  Co-efficient  of 

The  number  of  lines  of  force  the  current  would 
induce  or  enclose  in  itself  when  the  current 
flowing  through  it  is  equal  to  one  absolute 
unit. 

A  term  sometimes  employed  in  the  sense 
of  inductance  of  a  circuit 

The  co-efficient  of  self-induction  is  defined  by 
Fleming  as  follows  :  "In  the  case  of  circuits  con- 
veying electric  currents,  which  are  wholly  made 
of  non-magnetic  material,  and  wholly  immersed 


in  a  medium  of  constant  magnetic  permeability, 
the  total  induction  through  the  circuit  per  unit  of 
current  flowing  in  that  circuit,  when  removed 
from  the  neighborhood  of  all  other  magnets  and 
circuits,  is  called  the  co-efficient  of  self-induction; 
otherwise  the  ratio  of  the  numerical  values  of  the 
electro-magnetic  momentum  of  such  circuit,  and 
the  current  flowing  in  it,  when  totally  removed 
from  all  other  currents  and  magnets,  is  the  nu- 
merical value  of  the  inductance  of  the  circuit." 

Since  the  magnetic  lines  due  to  a  current  in  a 
circuit  thread  through  the  convolutions  of  the  cir- 
cuit itself,  any  variation  in  the  current  induces 
a  difference  of  potential  in  the  circuit  itself,  since 
the  lines  of  force  produced  by  the  current  in  the 
circuit  pass  through  or  cut  the  circuit. 

The  ratio  between  this  self-induced  electromo- 
tive force,  and  the  rate  of  change  in  the  current 
which  causes  it,  is  called  the  co-efficient  of  self- 
induction.- -(5.  P.  Thompson.) 

For  a  given  coil  the  co-efficient  of  self-induction 
is,  according  to  S.  P.  Thompson  : 

(I.)  Proportional  to  the  square  of  the  number 
of  convolutions. 

(2.)  Is  increased  by  the  use  of  an  iron  core. 

(3.)  If  the  magnetic  permeability  is  assumed  as 
constant,  the  co-efficient  of  self-induction  is  nu- 
merically equal  to  the  product  of  the  number  of 
lines  of  magnetic  force  due  to  the  current,  and 
the  number  of  times  they  are  enclosed  by  the 
circuit. 

Induction,  Self,  Magnetic  •  —A  re- 
tardation in  the  appearance  of  magnetization, 
after  the  application  of  the  magnetizing  force, 
due  to  the  influence  of  the  magnetic  lag. 

Magnetic  retardation. 

This  retardation  in  the  magnetization  has  re- 
ceived the  name  of  magnetic  self-induction  or  re- 
tardation because  it  corresponds  to  the  retarda- 
tion in  the  starting  or  stopping  of  a  current,  in  a 
conducting  circuit,  due  to  the  self-induction  of  the 
current. 

Induction,  Self,  Unit  of The  unit 

of  inductance.  (See  Inductance,  Unit  of) 

The  unit  of  self-induction  is  now  generally 
called  the  unit  of  inductance. 

Induction,    Symmetrical,  of  Armature 

An  induction  produced  by  the  simul- 

tane  ous  passage  of  the  same  number  of  lines 
of  magnetic  force  through  adjoining  halves  of 
the  armature. 


Ind.] 


288 


[lad. 


Induction  Telegraphy,  Current  Indue- 
tion  System  of (See  Telegraphy,  In- 
duction, Current  Induction  System  of,) 

Induction  Telegraphy,  Static  Induction 
System  of (See  Telegraphy,  Induc- 
tion, Static  Induction  System  of) 

Induction  Top.— (See  Top,  Induction) 

Induction,  Total   Magnetic  —The 

total  magnetic  induction  of  any  space  is  the 
number  of  lines  of  magnetic  induction  which 
pass  through  that  space,  where  the  magnetiz« 
able  material  is  placed,  together  with  the  lines 
added  by  the  magnetization  of  the  magnetic 
material. 

Induction,  Tubes  of A  portion  of 

a  magnetic  field  containing  a  number  of 
closely  contiguous  lines  of  induction  termi- 
nated by  equipotential  surfaces,  or  surfaces 
perpendicular  to  the  lines  of  induction. 

Tubes  of  induction  possess  the  following  char- 
acteristics : 

(I.)  The  product  of  a  normal  cross-section  of  a 
tube  and  the  mean  magnetic  induction  which 
takes  place  over  that  section  is  the  same  for  all 
tross-sections  of  the  tube.  In  other  words,  the 
flux  or  flow  of  induction  is  constant  throughout 
the  entire  length  of  the  tube. 

(2.)  The  normal  cross-section  of  any  equipoten- 
tial surface  at  any  point  of  a  tube  of  induction  is 
inversely  proportional  to  the  magnetic  induction 
at  that  point. 

(3.)  All  tubes  of  induction  form  endless  tubes. 
This  is  necessary,  since  all  lines  of  induction  form 
closed  circuits. 

(4.)  All  tubes  of  induction  may  be  expressed 
by  a  single  line  of  induction,  which,  in  the  case  of 
a  uniform  field,  occupies  the  centre  of  the  tube. 
(See  Force,  Tubes  of.) 

Induction,  Toltaic A  variety  of 

electro-dynamic  induction  produced  by  cir- 
cuits on  themselves  or  on  neighboring  circuits. 

Mutual  induction.  (See  Induction,  Elec- 
tro-Dynamic.) 

This  kind  of  induction  is  usually  called  current 
induction. 

Induction,  Unipolar A  term  some- 
times applied  to  the  induction  that  occurs 
when  a  conductor  is  so  moved  through  a 


magnetic  field  as  to  continuously  cut  its  lines 
of  force. 
If  the  conducting  wire,  ABC,  Fig.  309,  be  ro- 


3°<)'  Unipolar  Induction. 
tated  (in  a  direction  toward  the  observer)  around 
the  pole  N,  of  a  magnet,  it  will  continuously  cut 
its  lines  of  magnetic  force  in  practically  the  same 
direction,  and  will  therefore  produce  a  difference 
of  potential  that  will  result  in  a  continuous  cur- 
rent in  the  direction  of  the  arrows.  The  end  A, 
is  supported  in  a  recess  in  N,  while  the  end  near 
C,  slides  on  a  projection  on  the  middle  of  the 
magnet. 

Unipolar  induction  occurs  in  the  case  of  Stur- 
geon's wheel,  in  which  a  metallic  disc  mounted 
on  an  axis  is  rotated  between  the  poles  of  a  mag- 
net so  as  to  cut  the  lines  of  magnetic  force.  In 
this  case  a  difference  of  potential  is  generated 
which  will  produce  a  current  that  flows  from  the 
axis  to  the  periphery,  provided  contact  points  are 
placed  on  the  axis  of  rotation  and  the  periphery 
of  the  disc  connecting  these  parts  of  the  disc  in  a 
closed  circuit 

Unipolar  dynamos  operate  by  the  continuous 
cutting  of  lines  of  magnetic  force. 

Strictly  speaking,  there  is  no  such  thing  as  a 
unipolar  dynamo  or  unipolar  induction,  since  a 
single  magnetic  pole  cannot  exist  by  itself.  Con- 
tinuous cutting  of  lines  of  magnetic  force,  how- 
ever, can  exist,  and  produces,  unlike  the  ordinary 
bipolar  induction,  a  continuous  current  without 
the  use  of  a  commutator. 

Inductionless  Resistance.  — (See  Resist- 
ance, Inductionless) 

Inductive  Capacity,  Specific (See 

Capacity,  Specific  Inductive) 

Inductive  Circuit.— (See  Circuit,  Indue- 


Ind.j 


289 


[Ine. 


Inductive    Electromotive   Force.— (See 

Force,  Electromotive.  Inductive) 

Inductive  Retardation.— (See  Retarda- 
tion, Inductive.) 

Inductive  Resistance. — (See  Resistance, 
Inductive.) 

Inductivity,  Specific  Magnetic 

A  term  sometimes  employed  for  specific  mag- 
netic conductivity.  (See  Conductivity.  Spe- 
cific Magnetic?) 

Indnctometer,    Differential An 

apparatus  for  measuring,  by  means  of  a  gal- 
vanometer, the  momentary  currents  produced 
by  the  discharge  of  a  cable. 

Currents  produced  by  the  discharge  of  a  cable 
are  of  so  short  a  duration  that  they  do  not  pro- 
duce  much  more  than  a  momentary  effect  on  a 
galvanometer  needle. 

The  inductive  charge  in  a  cable,  or  the  quan- 
tity of  electricity  produced  in  it  by  induction,  is: 

(i.)  Directly  as  the  electromotive  force  of  the 
charging  battery; 

(2.)  Inversely  is  the  square  root  of  the  thick« 
ness  of  the  coating  of  gutta-percha  or  other  insu- 
lating material  between  the  conducting  wires  and 
the  metallic  sheathing; 

(3.)  Directly  as  the  square  root  of  the  diameter 
of  the  copper  wire  of  the  conductor;  and 

(4. )  Dependent  on  the  specific  inductive  capa- 
city of  the  insulating  material  employed  in  the 
cable. 

In  order  to  cause  the  cable  discharge  to  more 
thoroughly  affect  the  galvanometer  needle,  Mr. 
Latimer  Clark  employed  a  differential  instrument 
with  a  large  battery  and  three  reversing  keys,  by 
means  of  which  he  gave  a  rapid  succession  of 
charges  to  the  cable.  He  called  the  instrument  a 
Differential  Inductometer. 

Inductophone,,— A  device,  suggested  by 
Mr.  Willoughby  Smith,  for  obtaining  electric 
communication  between  moving  trains  and 
fixed  stations  by  means  of  the  currents  devel- 
oped by  induction  in  a  spiral  of  wire  fixed  on 
the  moving  engine,  by  its  motion  past  spirals 
on  the  line,  into  which  intermittent  currents 
are  passed. 

The  spiral  on  the  engine  is  placed  in  the  circuit 
of  a  telephone.  (See  Telesratk  .  7  ductive.) 


Inductor  Dynamo.— (See  Dynamo,  Induc- 
tor.) 

Inductor inm. — A  name  sometimes  applied 
to  a  Ruhmkorff  induction  coil.  (See  Coil, 
Induction.) 

Inequality,  Annual,  of  Earth's  Magnetic 

Tariatiou    or  Inclination Annual 

variations  in  the  value  of  the  magnetic  varia- 
tion or  inclination  at  any  place.  (See  Varia- 
tion, Magnetic.  Inclination,  Magnetic) 

Inequality,  Annual,  of  Earth's  Magnet- 
ism   Variations  in  the  value  of  the 

earth's  magnetism  during  the  earth's  revolu- 
tion depending  on  the  position  of  the  sun. 

Annual  variations  in  the  earth's  magnetism. 
(See  Variations,  Magnetic,  Annual) 

Inequality,  Diurnal,  of  Earth's  Magnetic 

Variation  or  Inclination Diurnal 

variations  in  the  value  of  the  earth's  magnetic 
variation  or  inclination.  (See  Variation, 
Magnetic.  Inclination,  Magnetic) 

Inequality,  Diurnal,  of  Earth's  Magnet- 
ism   Inequalities  or  variations  in  the 

value  of  the  earth's  magnetism,  dependent  on 
the  position  of  the  sun  during  the  earth's 
rotation. 

Inequality,  Lunar,  of  Earth's  Magnetic 
Variation  or  Inclination Small  va- 
riations in  the  value  of  the  magnetic  variation 
or  inclination,  dependent  on  the  position  of 
the  moon  as  regards  the  magnetic  meridian. 

Inequality,  Lunar,  of  Earth's  Magnet- 
ism   Small  variations  in  the  value  of 

the  earth's  magnetism  dependent  on  the  po- 
sition of  the  moon  as  regards  the  magnetic 
meridian. 

Inertia. — The  inability  of  a  body  to  change 
its  condition  of  rest  or  motion,  unless  some 
force  acts  on  it. 

The  inertia  of  matter  is  expressed  in  Newton's 
first  law  of  motion,  as  follows  : 

"Every  body  tends  to  preserve  its  state  of  rest 
or  of  uniform  motion  in  a  straight  line,  except  in 
so  far  as  it  is  acted  on  by  an  impressed  force." 

All  matter  possesses  inertia. 

Inertia,  Electric A  term  some- 
times employed  instead  of  electro-magnetic 
inertia.  (See  Inertia,  Electro-Magnetic?) 


Ine.J 


290 


[Ins. 


A  term  employed  to  indicate  the  tendency 
of  a  current  to  resist  its  stopping  or  starting. 

By  self-induction  an  electromotive  force  is  pro- 
duced in  a  wire  or  other  conductor  at  the  moment 
of  starting  the  current  in  it  that  tends  to  oppose 
the  starting  of  such  current,  and  also  an  electro- 
motive force  at  the  moment  of  stopping  the  cur- 
rent, in  such  a  direction  as  to  prolong  or  continue 
the  current.  In  other  words,  self-induction  tends 
to  retard  the  rise  or  fall  of  the  current. 

Fleming  traces  the  following  comparison  be- 
tween the  moment  of  inertia  of  a  rotating  wheel 
and  the  energy  of  its  rotation  on  the  one  side,  and 
the  inductance  of  a  circuit  and  the  electro-mag- 
netic energy  of  the  circuit  on  the  other. 

(I.)  The  angular  momentum  of  a  fly-wheel  is 
equal  to  the  numerical  product  of  its  moment  of 
inertia  and  the  angular  velocity  of  the  wheel. 
Similarly  the  electro-magnetic  momentum  is  equal 
to  the  product  of  the  inductance  of  the  circuit  by 
the  current  flowing  through  it  at  any  instant. 

(2.)  The  rate  of  change  of  the  angular  mo- 
mentum of  the  wheel,  at  any  instant,  is  a  measure 
of  the  rotational  force  of  the  couple  acting  at  that 
instant 

Similarly  the  rate  of  change  of  the  electro-mag- 
netic momentum  of  the  circuit  is  the  measure  of 
the  electromotive  force  acting  on  it  so  far  as 
mere  change  of  current  is  concerned,  and  irre- 
spective of  that  part  of  the  electromotive  force  re- 
quired to  overcome  the  ohmic  resistance. 

An  electric  current  does  not  start  or  stop  in- 
stintaneously.  It  requires  time  to  do  either,  just 
as  a  stream  of  water  or  other  fluid  does,  and  it  is 
this  property  which  is  referred  to  by  the  term 
electric  inertia.  Inertia  does  not  appear  to  be 
possessed  by  electricity  apart  from  matter.  "It 
is  doubtful,"  says  Lodge,  "whether  electricity 
of  itself,  and  disconnected  from  matter,  has  any 
inertia  " 

Inertia,  Electro-Magnetic A  term 

sometimes  employed  instead  of  inductance, 
or  the  self-induction  of  a  current.  (See  In- 
ductance. Inertia,  Electric?) 

Inertia,  Electro-Magnetic,  Co-efficient  of 

A  term  sometimes  employed  in  place 

of  the  co-efficient  of  inductance  or  self-induct- 
ance of  a  circuit. 

Inertia,  Magnetic The  inability  of 

a  magnetic  core  to  instantly  lose  or  acquire 
magnetism. 


A  magnet  core  tends  to  continue  in  the  mag- 
netic state  in  which  it  was  placed. 

The  magnetic  inertia  is  sometimes  called  the 
magnetic  lag. 

To  decrease  the  magnetic  inertia,  the  strength 
of  the  magnetizing  current  is  increased  and  the 
length  of  the  iron  core  decreased.  The  iron 
should  also  be  quite  soft.  (See  Lag,  Magnetic. 
Force,  Coercive.} 

Inferred  Zero. — (See  Zero,  Inferred) 

Infinity  Plug.— (See  Plug,  Infinity) 

Influence. — A  term  sometimes  used  instead 
of  electrostatic  induction.  (See  Induction, 
Electrostatic) 

The  word  influence  is  used  by  some  to  apply 
to  the  case  of  electrostatic  induction,  as  distin- 
guished from  electro-magnetic  or  magnetic  induc- 
tion. 

Influence  Charge. — (See  Charge,  Influ- 
ence) 

Influence  Machine. — (See  Machine,  In- 
fluence) 

Inker,  Morse A  form  of  tele- 
graphic ink-writer.  (See  Ink-  Writer,  Tele- 
graphic) 

Ink-Writer,  Telegraphic — A  device 

employed  for  recording  the  dots  and  dashes 
of  a  telegraphic  message  in  ink  on  a  fillet  or 
strip  of  paper. 

A  telegraphic  ink-xvriter  is  a  form  of  telegraphic 
recorder.  (See  Recorder,  Morse) 

Inside  Wiring.— (See  Wiring,  Inside) 

Insolation,  Electric A  term  some- 
times employed  for  electric  sunstroke,  or 
electric  prostration.  (See  Sunstroke,  Elec- 
tric. Prostration,  Electric) 

Installation. — A  term  embracing  the 
entire  plant  and  its  accessories  required  to 
perform  any  specified  work. 

The  act  of  placing,  arranging  or  erecting 
a  plant  or  apparatus. 

Installation,  Electric The  estab- 
lishment of  any  electric  plant. 

An  electric  light  installation,  for  example,  in- 
eludes  the  steam  engine  and  boilers,  or  other 
prime  movers,  the  dynamo-electric  machines,  the 
line  wires  or  leads,  and  the  lamps. 

Insulated  Body.— (See  Body,  Insulated) 


Ins.] 


291 


[Ins. 


Insulating  Cements. — (See  Cements,  In- 
sulating.) 

Insulating  Sleeve. — (See  Sleeve,  Insula- 
ting.) 

Insulating  Stool.— (See  Stool,  Insula- 
ting.) 

Insulating  Tape.— (See  Tape,  Insula- 
ting.) 

Insulating  Tube.— (See  Tube,  Insula- 
ting.) 

Insulating  Tarnish.— (See  Varnish,  Elec- 
tric.) 

Insulation,  Electric — Non-conduct- 
ing material  so  placed  with  respect  to  a  con- 
ductor as  to  prevent  the  loss  of  a  charge,  or 
the  leakage  of  a  current. 

In  the  case  of  coils  the  character  of  the  insula- 
tion of  the  coil  of  wires  through  which  the  cur- 
rent is  to  pass  must  be  considered  from  the  stand- 
point of  the  cooling  of  the  coil  by  radiation. 

In  considering  the  safest  and  most  economical 
current  density  to  employ  in  any  dynamo  or 
motor,  the  depth  of  the  coil,  *'.  <«•.,  the  thickness  of 
its  coils,  must  be  considered,  as  well  as  the  char- 
acter of  the  materials  employed  for  the  insulation. 
Such  substances  as  silk  or  wool,  which  are  char- 
acterized by  low  heat  conduction,  retain  the  heat 
longer  than  cotton.  Hence  the  depth  of  a  silk 
covered  coil  should  necessarily  be  less  than  that  of 
one  covered  with  cotton. 

Insulation  Joint. — (See  Joint,  Insula- 
tion.) 

Insulation,  Porous  — -  — An  insulating 
material  containing  air  or  gas  placed  between 
the  conductor  and  the  insulating  covering. 

A  strip  of  perforated  paper  is  used  for  cover- 
ing the  bare  conductor,  and  the  insulating  ma- 
terial is  placed  on  the  outside  of  this  ;  or,  a  cord 
is  wrapped  separately  around  che  conductor,  and 
the  insulating  material  is  placed  on  the  outside  of 
this.  By  these  means,  as  will  be  seen,  a  layer  of 
air  exists  between  the  conductor  and  its  insulating 
covering. 

Insulation  Resistance. — (See  Resistance, 
Insulation.) 

Insulation,  Static — A  term  em- 
ployed in  electro-therapeutics  for  a  method 
of  treatment  by  convection  stream0  or  dis- 


charges, in  which  the  patient  is  seated  on  an 
insulated  stool  connected  to  one  pole  or 
electrode  of  an  influence  marline,  while  the 
other  pole  or  electrode  is  connected  to  the 
ground. 

Insulator  Cap.— (See  Cap,  Insulator) 

Insulator,  Dice-Box A  name  some- 
times applied  to  a  double-cone  insulator.  (See 
Insulator,  Double-Cone.) 

Insulator,  Double-Cone An  insu- 
lator in  which  the  line  wire  passes  through  and 
is  supported  by  means  of  a  tube  consisting  of 
two  inverted  cones  joined  at  their  smaller 
bases. 

Insulator,  Double-Cup An  insula- 
tor consisting  of  two  funnel-shaped  cups, 
placed  in  an  inverted  position  on  the  sup- 
porting pin  and  insulated  from  one  another 
by  a  free  air  space,  except  near  the  ends, 
which  are  cemented. 

The  wire  is  wrapped  in  a  groove  on  the  outside 
of  the  outer  cup.  This  possesses  the  advantage 
of  exposing  it  to  the  rain,  which  thus  cleanses  the 
insulator  and  improves  its  power  of  insulation. 
The  inner  cup  is  supported  on  a  pin  and  the  outer 
cup  cemented  to  it.  Any  leakage  must,  there- 
fore, pass  over  the  entire  surface  of  both  cups. 

Insulator,  Double-Shackle A  form 

of  insulator  used  in  shackling  a  wire,  consist- 
ing of  two  single-shackle  insulators. 

Insulator,  Double-Shed A  double- 
cup  insulator.  (See  Insulator,  Double-Cup.) 

Insulator,  Fluid An  insulator  pro- 
vided with  a  small,  internally  placed,  annular, 
cup-shaped  space,  filled  with  an  insulating 
oil,  thus  increasing  the  insulating  power  of  the 
support. 

The  line  wire  is  wrapped  in  a  groove  on  the 
outside  of  the  insulator.  Any  surface  leakage 
between  the  wire  and  ground  in  wet  weather 
must  occur  between  the  outer  surface  of  the  insu- 
lator, which  is  kept  cleansed  by  the  rain,  and  the 
inner  surface,  where  it  is  supported  by  the  pin. 
But  to  do  this,  the  current  must  cross  the  oil  in 
the  cup,  which,  from  its  high  power  of  insulation, 
effectually  prevents  leakage. 

Insulator,  Invert   — An   insulator 


I -is.] 


292 


[Int, 


placed  on  the  top  of  the  wire  instead  of  under- 
neath it,  as  was  formerly  done. 

Insulator,  Oil A  fluid  insulator 

filled  with  oil.  (See  Insulator,  Fluid.). 

Insulator  Pins. — (See  Pins,  Insulator.} 

Insulator,  Single-Shackle A  form 

of  insulator  used  for  shackling  a  wire.  (See 
Shackling  a  Wire) 

Insulator,  Single-Shed  —  —An  insula- 
tor with  a  single  inverted  cup. 

The  wire  is  wrapped  around  a  groove  on  the 
outside  of  the  cup,  where  it  is  exposed  to  the 
cleansing  action  of  the  rain.  The  cup  is  inverted 
and  supported  on  a  pin,  to  which  it  is  screwed  and 
cemented. 

Insulator,  Telegraphic  or  Telephonic 
A  non-conducting  support  of  tele- 
graphic, telephonic,  electric  light  or  other 
wires. 

Insulators  are  generally  made  of  glass,  earthen- 


Fig.3io.     Glass 
Insulator. 


Fig.  311.     Porcelain 
Insulator. 


ware,  porcelain  or  hard  rubber,  and  assume  a 
variety  of  forms,  some  of  which  are  shown  in  Figs. 
310,  311  and  312.  Of  whatever  material  they  are 
made,  it  is  necessary  that  the 
surface  on  which  the  wire  rests, 
or  around  which  it  is  wrapped, 
should  be  smooth,  so  as  to  avoid 
abrasion,  either  of  its  insulat 
ing  covering  or  of  the  wire  it- 
self. 

Two  things  are  to  be  con- 
sidered in  the  selection  of  an 
insulator,  viz. : 

(I.)  The  insulating  power  of 
the  material  of  which  the  in- 
sulator is  composed,  so  as  to  Fig.  3 12.  Hard 
reduce  the  leakage  as  much  as  Rubber  Insulator. 
possible.  (See  Leakage,  Electric.} 

(2.)  The  tensile  strength  of  the  material,  so 


that  in  case  of  heavy  wires  no  breaks  may  resuk 
from  the  fracture  of  the  insulator 

Some  forms  of  insulators  are  shown  hi  Figs. 
310,  311  and  312..  They  are  screwed  to  the  pins 
by  the  threads  shown.  The  insulating  materials 
of  which  they  are  formed  are  of  glass,  porcelain 
and  hard  rubber  respectively. 

Insulator,  Window-Tube A  tube 

of  vulcanite  or  other  insulating  material  pro- 
vided for  the  insulation  of  a  wire  entering  a 
room. 

The  wire  conductor  passes  through  the  middle 
of  the  tube,  which  is  firmly  faxed  in  an  opening 
passing  through  the  window  frame. 

Insulator,  Z A  form  of  double-cup 

insulator  in  which  the  insulating  material, 
earthenware  or  porcelain,  is  made  in  a  single 
piece,  instead  of  in  two  separate  pieces. 

The  body  of  the  insulator  is  conical  in  form, 
and  the  interior  air  space  presents  a  shape  ap- 
proximately that  of  the  letter  Z. 

The  double  form  is  used  in  order  to  diminish 
the  leakage. 

Intensity    Armature. — (See    Armature, 
Intensity} 
Intensity,  Connection  of  Toltaic  Cells  for 

— A  term  formerly  employed  for  series- 
connected  voltaic  battery  cells.  (Obsolete.) 

Intensity,  Magnetic  < — Density  of 

magnetic  induction. 

Magnetic  flux  per  square  centimetre. 

A  committee  of  the  American  Institute  of  Elec- 
trical Engineers  on  "Units  and  Standards,"  pro- 
poses the  following  definition  for  magnetic  inten- 
sity: 

The  induction  density  at  a  point  within  an  ele- 
ment of  surface  is  the  surface  differential  at  that 
point. 

The  practical  unit  of  magnetic  intensity  is 
lo«  or  100,000,000  C.  G.  S.  lines  per  square  cen- 
timetre. 

In  practice,  excluding  the  earth's  field,  intensi- 
ties range  from  too  to  20,000  C.  G.  S.  lines  per 
square  centimetre,  and  the  working  unit  should, 
perhaps,  have  the  prefix  milli  or  micro. 

Intensity,  Magnetic,  Pole  of The 

earth's  magnetic  poles  as  determined  by 
means  of  the  oscillations  of  a  magnetic 
needle. 


Int.] 


293 


[Ion. 


The  points  of  the  earth's  greatest  magnetic 
intensity. 

Intensity  of  Current. — (See  Current,  In- 
tensity of.} 

Intensity  of  Field.— (See  Field,  Inten- 
sity of  ) 

Intensity  of  Light— (See  Light.  Inten- 
sity oj '.) 

Intensity  of  Magnetization.— (See  Mag- 
netization, Intensity  of) 

Intensity,  Photometric,  Unit  of 

The  amount  of  light  produced  by  a  candle 
that  consumes  two  grains  of  spermaceti  wax 
per  minute.  (See  Candle!) 

Inter  Air  Space.— (See  Space,  Inter  Air) 

Intercrossing. — In  a  system  of  telephonic 
communication,  a  device  for  avoiding  the  dis- 
turbing effects  of  induction  by  alternately 
crossing  equal  sections  of  the  line.  (See 
Connection,  Telephonic  Cross.} 

Interference  of  Electro-Magnetic 
Waves. — (See  Waves,  Electro-Magnetic, 
Interference  of.) 

Interlocking  Apparatus.— (See  Appa- 
ratus Interlocking) 

Intermittent  Contact— (See  Contact.  In- 
termittent) 

Intermittent  Cross.— A  form  of  electric 
cross.  (See  Cross,  Electric) 

Intermittent  Current— (See  Current,  In- 
termittent) 

Intermittent  Disconnection.— (See  Dis- 
connection, Intermittent) 

Intermittent  Earth.— (See  Earth,  Inter- 
mittent) 

Internal  Circuit— (See  Circuit,  In- 
ternal) 

Internal  Polarization  of  Moist  Bodies.— 
(See  Polarization,  Internal,  of  Moist 
Bodies) 

Interrupter.— Any  device  for  interrupting 
or  breaking  a  circuit. 

Interrupter,  Automatic An  auto- 
matic contact  breaker,  (See  Make-and- 
Break,  Automatic) 


Interrupter,  Reed A  term  some- 
times applied  to  a  tuning-fork  interrupter. 
(See  Interrupter,  Tuning-Fork) 

Interrupter,  Tuning-Fork —An  in- 
terrupter in  which  the  successive  makes  and 
breaks  are  produced  by  the  vibrations  of  a 
tuning-fork  or  reed. 

The  tuning-fork  or  reed  is  maintained  in  vibra- 
tion by  any  suitable  means.  Such  interrupters 
are  applied  to  various  uses.  Synchronous  mul- 
tiplex telegraphy  affords  an  example  of  such  uses. 

Invariable  Calibration  of  Galvanometer. 

— (See  Calibration,  Invariable,  of  Galva- 
nometer) 

Inverse  Electromotive  Force. — (See  Force, 
Electromotive,  Inverse) 

Inverse  or  Make-Induced  Current — (See 
Current,  Make-Induced) 

Inverse  Secondary  Current— (See  Cur- 
rent, Inverse  Secondary) 

Inversion,  Thermo-Electric An 

inversion  of  the  thermo-electric  electromotive 
force  of  a  couple  at  certain  temperatures. 
(See  Diagram,  Ther mo-Electric) 

Invert  Insulator.— (See  Insulator,  In- 
vert) 

Inverted  Induction  Coil.— (See  Coil. 
Induction,  Inverted) 

Inverted  Type  of  Dynamo. — (See  Dy- 
namo, Inverted) 

Invisible  Electric  Floor  Matting.— (See 
Matting,  Invisible  Electric  Floor) 

Ions. — Groups  of  atoms  or  radicals  which 
result  from  the  electrolytic  decomposition  of 
a  molecule. 

The  ions  are  respectively  electro-positive  and 
electro-negative.  The  electro-positive  ion  ap- 
pears at  the  plate  connected  with  the  electro- 
negative terminal^  or  at  the  kathode,  and  is  called 
the  kathion. 

The  electro-negative  ion  appears  at  the  plate 
connected  with  the  electro-positive  terminal,  or 
at  the  anode,  and  is  called  the  anion,  (See 
Electrolysis.  Kathion.  Anion.} 

Ions,  Electro-Negative •  —The  neg- 
ative atoms,  or  groups  of  atoms,  called  rad- 
icals, into  which  the  molecules  of  an  electro- 


lon.J 


294 


[ISO. 


lyte  are  decomposed  by  electrolysis.     (See 
Electrolysis^ 

The  electro-negative  ions  are  called  the  anions, 
because  they  appear  at  the  anode  of  a  decompo- 
sition cell.  (See  Anions,  Anode.} 

Ions,  Electro-Positive  -  —The  pos- 
itive atoms,  or  groups  of  atoms,  called  rad- 
icals, into  which  the  molecules  of  an  electro- 
lyte are  decomposed  by  electrolysis.  (See 
Electrolysis?) 

The  electro-positive  ions  are  called  the  kathions, 
because  they  appear  at  the  kathode  of  a  decom- 
position cell.  (SeeJEStfifah  Kathode.} 


Iron-Clad  Electro-Magnet.—  (See  Mag- 
net, Electro,  Iron-Clad?) 

Iron-Clad  Magnet.—  (See  Magnet,  Iron- 
Clad) 

Iron  Core,  Effect  of,  on  the  Magnetic 
Strength  of  a  Hollow  Coil  of  Wire  — 

An  increase  in  the  number  of  lines  of  mag- 
netic force,  beyond  those  produced  by  the 
current  itself,  due  to  the  opening  out  of  the 
closed  magnetic  circuits  in  the  atoms  or 
molecules  of  the  iron. 

The  atoms  or  molecules  of  the  iron  possess 
naturally  closed  magnetic  circuits,  or  closed  lines 
of  magnetic  force,  lying  entirely  within  the  mass 
of  the  iron.  When  the  iron  is  placed  in  a  magnetic 
field,  these  minute  closed  circuits  open  out  and 
are  added  to  the  lines  of  force  produced  by  the 
circuit  itself.  The  opening  out  of  these  closed 
atomic  or  molecular  lines  of  magnetic  force  is  at- 
tended by  the  formation  of  lines  of  polarized 
molecules  or  atoms. 

Roughly  speaking,  according  to  Lodge,  for 
each  single  line  of  magnetic  force  produced  by  the 
electric  current,  there  are  some  3,000  lines  of 
magnetic  force  added  to  it  from  the  iron,  the  ex- 
act number  varying  with  the  kind  of  iron,  the 
physical  condition  of  the  iron  and  the  degree  of 
magnetization. 

Iron,  Galvanized  --  Iron  covered  by 
a  layer  of  zinc  by  dipping  it  in  a  bath  of 
molten  zinc. 

The  process  of  galvanizing  iron  is  designed  to 
Vrevent  the  corrosion  or  rusting  of  the  iron  on 
exposure  to  the  air.  (See  Metals,  Electrical  Pro- 
tection  of.} 

The  word  galvanized  probably  had  its  origin  in 


an  assumed  galvanic  or  voltaic  action,  in  causing 
the  zinc  to  adhere  to  the  iron.  The  true  galvanic 
or  voltaic  action,  viz.,  the  galvanic  protection, 
comes  after  the  galvanizing  process  is  completed. 

Iron-Work  Fault  of  Dynamo. — (See 
Fault,  Iron-  Work,  of  Dynamo?) 

Irreversible  Heat.— (See  Heat,  Irreversi- 
ble?) 

Irritability,  Electric  -  —Irritability 
of  nervous  or  muscular  tissue  by  an  electric 
discharge. 

Irritability,  Electric,  Diminished  — 
A  decreased  irritability  of  nervous  or  muscu- 
lar tissue,  produced  by  an  electric  current  of 
given  strength. 

Diminished  electric  irritability  is  often  present 
in  certain  diseases  of  the  motor  apparatus. 

Irritability,  Electric,  Increased 

An  irritability  of  nervous  or  muscular  tissue 
produced  by  a  much  weaker  electric  current 
than  that  required  to  produce  it  in  normal 
tissue. 

Irritability,     Faradic Muscular 

contractions  produced  by  the  action  of  a 
faradic  current  on  a  nerve. 

The  action  of  the  faradic  current  is  to  cause  a 
prolonged  tonic  contraction,  which  continues 
while  the  current  continues.  Though  the  natural 
action  is  to  produce  a  contraction,  followed  by  a 
relaxation  on  each  make  and  break,  yet  the  makes 
and  breaks  follow  one  another  so  rapidly  that  the 
relaxation  has  not  time  to  occur  before  the  next 
contraction  follows. 

Irritability,    Galvanic Muscular 

contractions  produced  by  the  action  of  a  gal- 
vanic current. 

The  action  of  a  galvanic  current  is  to  cause  a 
single,  quick,  momentary  contraction  of  a  muscle 
on  each  starting  or  completion  of  the  circuit. 

The  contractions  are  stronger  in  the  case  of 
galvanic  currents  when  the  direction  of  the  cur 
rent  is  reversed  with  a  commutator  instead  of  by 
an  actual  break  at  the  poles.  Such  a  break  is 
called  a  voltaic  alternative,  and  the  currents  so  pro- 
duced voltaic  alternatives.  (See  Alternatives, 
Vottaic.} 

Isobaric  Lines. — (See  Lines,  Isobaric?) 

Isobars. — Lines  connecting  places  on  the 


ISO.] 


295 


[Jar. 


earth's  surface  which  have  the  same  barome- 
tric pressure. 

The  isobaric  lines  are  generally  corrected  for 
differences  of  elevation  of  the  surface. 

Isobars  are  often  called  isobaric  lines. 

A  study  of  the  isobaric  lines,  or  isobars,  is  of 
great  assistance  in  making  forecasts  or  predictions 
of  coming  changes  in  the  weather. 

Isocnasmen  Curres.  —  (See  Curves,  Iso- 
chasmen) 

Isochronism.  —  Equality  of  time  of  vibra- 
tion or  motion. 

Isochronize.  —  To  produce  equality  of 
Jime  of  vibration  or  motion.  —  (See  Isochron- 


Isochronizing. —  Producing  equality  of 
time  of  vibration  or  motion.  (See  Isochron- 
ism) 

Isochronous  Yibrations  or  Oscillations. 
—  (See  Vibrations  or  Oscillations,  Isochron- 
Mtf.) 

Isoclinic  Chart.—  (See  Chart,  Inclina- 
tion) 

Isoclinic  Lines.  —  (See  Lines,  Isoclinic) 

Isodynamic  Chart.  —  (See  Chart,  Isody- 
namic) 


Isodynamic  Lines. — (See  Lines,  Isody- 
namic) 

Isodynamic  Map. — (See  Chart,  Isody- 
namic) 

Iso-Electric  Points.— (See  Points,  Iso- 
Electric) 

Isogonal. — Pertaining  to  the  isogonic  lines. 

Isogonal  Lines. — (See  Lines,  Isogonal) 

Isogonal  Map  or  Chart.— (See  Map  or 
Chart,  Isogonal) 

Isogonic.— Pertaining  to  the  isogonal  lines. 

Isogonic  Chart — (See  Chart,  Isogonic) 

Isogonic  Lines. — (See  Lines,  Isogonic) 

Isogonic  Map.— (See  Map,  Isogonic) 

Isolated  Electric  Lighting.— (See  Light- 
ing, Electric,  Isolated) 

Isolatine. — A  kind  of  insulating  material. 

Isothermal  Surfaces.— (See  Surfaces,  Iso- 
thermal) 

Isotropic  Conductor. — (See  Conductor, 
Isotropic) 

Isotropic  Medium.— (See  Medium,  Iso- 
tropic) 


J. — A  contraction  proposed  for  Joule. 

Jablochkoff  Candle.— (See  Candle,  Jab- 
tochkoff) 

Jacketed  Magnet.— (See  Magnet,  Jack- 
eted) 

Jacobi's  Law. — (See  Law,  Jac obi's) 

Jar,  Electric  — A  name  formerly 

given  to  the  Leyden  jar. 

Jar,  Leyden A  condenser  in  the 

form  of  a  jar,  in  which  the  metallic  coatings 
are  placed  opposite  each  other  on  the  outside 
and  the  inside  of  the  jar  respectively. 

The  metal  coatings  should  not  extend  to  more 
than  two-thirds  of  the  height  of  the  jar,  the  rest 
of  the  glass  being  varnished  to  avoid  the  creeping 
of  the  charges  over  the  glass  in  damp  weather. 
The  inside  coating  is  connected  by  means  of  a 


metallic  chain  to  a  knob  on  the  top  of  the  jar,  as 
shown  in  Fig.  313.  The  conductor  supporting 
the  knob  passes  through  a  dry  cork  or  plug  of 
some  insulating  material. 

To  charge  the  jar,  the  outside  coating  is  con- 
nected with  the  earth,  as 
by  holding  it  in  the  hand, 
and  the  outside  coating 
is  connected  with  the 
conductor  of  a  machine. 
(See  Condenser.  Accu- 
mulator. ) 

The  inner  coating  of 
the  jar  is  usually  con- 
nected with  the  knob  by 
means  of  a  chain  or  wire  Ke'3*3' 
as  shown  above.  This  necessitates  a  support  for 
the  ball  and  stem,  which  is  generally  obtained  by 
a  cork  or  wooden  plug  inserted  in  the  mouth  of 


Jar.T 


296 


[Jet. 


the  jar.  Such  a  form,  however,  is  extremely  ob- 
jectionable, since,  although  the  top  of  the  jar  be 
Covered  with  shellac  varnish  to  avoid  leakage,  it 
affords  fcut  a  poor  insulation  in  damp  weather,  be- 
cause both  the  metallic  rod  supporting  the  ball  and 


Sir  WiUiam  Thomsons  Leydt*  Jar. 
the  damp  wood  or  cork  are  in  connection  with  the 
glass  and  thus  facilitate  leakage. 

To  overcome  these  objections  a  form  of  jar  has 
been  devised  by  Sir  William  Thomson,  in  which  the 
knob  is  supported  on  three  feet,  which  rest  on  the 
inner  coating.  In  this  form  the  uncoated  glass 
<:an  be  readily  kept  dry  and  clean.  This  form  is 
;shown  in  Fig.  314. 

A  layer  of  sulphuric  acid  is  sometimes  employed 
for  the  inner  coating  of  the  Leyden  jar.  This 
serves  the  double  purpose  of  acting  as  a  coating 
,and  an  absorber  of  moisture  during  damp 
weather. 

Jar,    Leyden,    Capacity  of The 

quantity  of  electricity  a  Leyden  jar  will  hold 
at  a  given  difference  of  potential. 

The  capacity  of  a  jar  is  equal  to  the  quantity 
of  electricity  divided  by  the  difference  of  potential 
such  quantity  produces  in  the  jar;  or  the  capacity 

=  ^j,  where  Q  =  the  quantity,  and  V,  the  differ- 
ence of  potential. 

Jar,  Leyden,  Coatings  of (See 

Coatings  of  Leyden  Jar.) 

Jar,  Lightning A  Leyden  jar,  the 

coatings  of  which  consist  of  metallic  filings. 

As  the  discharge  passes,  an  irregular  series  of 
sparks  appear,  which  somewhat  resemble  in  their 
shape  a  lightning  flash.  Hence  the  origin  of  the 
term. 

Jar  of  Secondary  Cell. — The  containing 


vessel  in  which  the  plates  of  a  single  secondary 
cell  are  placed. 

Jar,  Porons A  porous  cell.     (See 

Cell,  Porous.) 

Jar,    Scintillating A  Leyden  jar. 

the  coatings  of  which,  instead  of  being  formed 
of  continuous  sheets  of  tin-foil  or  other  con- 
ducting substances,  are  formed  of  small  pieces 
of  such  substances,  placed  at  regular  intervals 
on  the  glass  or  dielectric  so  as  to  leave  a  small 
space  between  them. 

Such  a  jar  has  received  the  name  of  scintillat- 
ing jar,  because  when  discharged  by  connecting 
its  two  opposite  coatings  the  discharge  appears  as 
minute  sparks,  which  jump  across  the  space 
between  the  metallic  pieces. 

Jar,  Unit A  small  Leyden  jar  some- 
times employed  to  measure  approximately  the 
quantity  of  electricity  passed  into  a  Leyden 
battery  or  condenser. 

As  shown  in  Fig.  315,  the  unit  jar  consists  of  a 
small  Leyden  jar  j,  whose  outer  coating  is  con- 
nected with  a  sliding  metallic 
rod  b,  provided  at  each  end 
with  a  rounded  knob,  and  the 
inner  coating  of  which  is  con- 
nected with  a  metallic  knob  c, 
placed  as  shown,  inside  a 
glass  jar  d,  opposite  a  ball  on 
the  lower  end  of  b. 

When,  now,  the  inside  of 
the  unit  jar,  or  the  end  con- 
nected with  c,  is  connected 
with  the  charging  source,  such 
as  a  machine,  and  the  outside 
at  a,  is  connected  with  the  jar 
or  jars  to  be  charged,  for 
every  spark  that  passes  be- 
tween d  and  c,  a  definite  quantity  has  passed  a. 

The  value  of  this  unit  charge  may  be  varied  by 
varying  the  distance  between  d  and  c. 

The  smaller  the  unit  jar  is  in  proportion  to  the 
jar  to  be  charged,  and  the  shorter  the  distance 
between  c  and  d,  the  more  reliable  are  the  com- 
parative results  obtained. 

Jars,  Leyden,  Charging,  by  Cascade 

— (See  Cascade,  Charging-  Leyden  Jars  by.) 

Jet,  Cfas,  Carcel  Standard  -  —A 
lighted  gas  jet  employed  for  determining  the 
candle-power  of  gas  by  measuring  the  height 


Unit  Jar. 


Jet.] 


297 


[Joi. 


of  a  jet  of  gas  burning  under  a  given  press- 
ure, and  used  in  connection  with  the  light  of 
a  larger  gas  burner,  burning  under  similar 
conditions,  for  the  photometric  measurement 
of  electric  lights. 


The  twisted  joint  is  sometimes   subsequently 
soldered. 


Fig  3ib.    Seven-  Car  eel 
Standard  Gas  Jet. 


Fig.  317.    Carcel  Candle 
Burner-. 


In  Fig.  316  is  shown  a  section  of  a  seven-carcel 
standard  gas  jet,  and  in  Fig.  317,  a  section  of  a 
candle  burner,  connected  within  the  same  service 
pipe.  The  gas  for  both  burners  is  received  in  a 
chamber,  from  whence  it  passes  by  an  opening  to 
the  burner,  under  the  constant  pressure  obtained 
by  the  weight  of  the  bell  C,  and  the  tube  A.  The 
burner  shown  in  Fig.  317,  which  is  used  as  the 
standard  of  comparison,  will  give  a  candle-power 
determined  from  the  height  of  the  jet  of  the 
burning  gas.  This  height  is  measured  in  milli- 
metres by  the  motion  of  a  circular  screen. 

The  determination  of  the  candle-power  of  gas  by 
means  of  a  jet  photometer  is  only  approximately 
correct,  unless  many  precautions  are  taken. 

Jet  Photometer.— (See  Photometer,  Jet^ 

Jewelry,  Electric  —  — Minute  incan- 
descent electric  lamps  substituted  for  the 
rarer  gems  in  articles  of  jewelry. 

The  lamps  are  lighted  by  means  of  small  pri- 
mary or  storage  batteries,  carried  in  the  pocket  or 
elsewhere  on  the  person. 

Joint,  American  Twist A  tele- 
graphic or  telephonic  joint  in  which  each  of 
the  two  wires  is  twisted  around  the  other. 
(See/0/«/,  Telegraphic  or  Telephonic^ 


Fig.  318.    America*  Twist  Joint. 

The  American  twist  joint  is  shown  in  Fig.  318. 
This  joint  is  easily  made  and  is  very  serviceable. 

Joint,  Bell-Hanger's A  joint  for 

telegraphic  or  telephonic  wires  in  which  the 
ends  are  merely  looped  together.  (See  Joint, 
Telegraphic  or  Telephonic!) 

Joint,  Britannia A  telegraphic  or 

telephonic  joint  in  which  the  wires  are  laid 
side  by  side,  bound  together  and  subsequently 
soldered.  (See  Joint,  Telegraphic  or  Tele- 
phonic^ 


Fig.  319.    Brit: 


Joint. 


The  Britannia  joint  is  shown  in  Fig.  319.  No, 
16  wire,  B.  W.  G.,  is  used  as  the  binding  wire. 

Joint,  Butt An  end-to-end  joint. 

A  joint  effected  in  wires  by  placing  the 
wires  end  on  and  subsequently  soldering. 

Butt  joints  are  formed  by  bringing  the  ends  to 
be  joined  together  and  securing  them  while  in 
such  position. 

Joint,  Butt  and  Lap,  of  Belts The 

joint  in  a  leather  belt,  employed  for  transmit- 
ting power  from  a  line  of  shafting  where  the 
ends  are  simply  brought  together  and  laced, 
is  called  a  butt  joint,  in  contradistinction  to  a 
lap  joint,  or  a  joint  formed  by  placing  one  end 
of  the  belt  over  the  other  and  lacing  or  rivet- 
ing the  two. 

In  using  delicate  galvanometers,  the  slightest 
change  in  the  speed  of  the  engine  driving  the 
dynamo-electric  machine  producing  the  current, 
causes  an  annoying  fluctuation  of  the  needle  that 
prevents  accurate  reading,  when  lap  joints  are  used 
in  the  belt  instead  of  butt  joints,  unless  the  former 
are  very  carefully  made.  Lap  joints  may  also  cause 
a  flickering  in  the  lights.  When,  however,  lap 
joints  are  made  by  cutting  the  belt  by  an  oblique 
section  and  properly  securing  them  so  that  their 


Joi.] 


[Joi. 


elevation  at  the  joint  is  no  greater  than  elsewhere, 
the  lap  joint  is  preferable  to  the  butt  joint. 

Joint,  Expansion A  joint  for  under- 
ground conductors,  tubes  or  pipes,  exposed 
to  considerable  changes  of  temperature,  in 
which  a  sliding  joint  is  provided  to  safely 
permit  a  change  of  length  on  expansion  or 
contraction. 

Joint,  Insulation A  joint  in  an  insu- 
lating material  or  covering  in  which  a  conti- 
nuity is  insured  in  the  conducting  as  well  as 
the  insulating  substance. 

Joint,  Lap A  joint  effected  by  over- 
lapping short  portions  near  the  ends  of  the 
things  to  be  joined,  and  securing  them  while 
in  such  position. 

Joint,  Lap,  for  Wires A  joint 

effected  between  two  wires  by  overlapping 
their  ends  and  subsequently  soldering. 

Joint,  Magnetic The  line  of  junc- 
tion between  two  separate  parts  of  magnetiza- 
ble materal. 

Magnetic  joints  should  be  of  such  a  nature  as 
to  permit  the  passage  of  the  lines  of  magnetic 
force  with  the  least  increase  in  the  resistance  of 
the  magnetic  circuit 

Magnetic  joints  in  the  field  magnets  of  a  dynamo- 
electric  machine  should  be  as  few  as  possible,  since 
the  resistance  of  the  best  magnetic  joint  to  the 
passage  of  the  lines  of  force  is  necessarily  greater 
than  that  of  the  same  material  without  such 
joints. 

Joint,  Metallic  Conducting A  joint 

in  a  conductor  in  which  a  continuity  of  con- 
ducting power  is  secured. 

Joint  Resistance  of  Parallel  Circuits.— 

($&i  Resistance,  Joint,  of  Parallel  Circuits^ 

Joint,  Sleeve A  junction    of    the 

ends  of  conducting  wires  obtained  by  passing 
them  through  tubes  and  then  twisting  and 
soldering. 

All  joints  should  be  soldered,  but  in  so  doing 
care  must  be  taken  that  the  soldering  liquid  or 
solid  employed  is  free  from  acids  or  other  corro- 
sive materials,  and  that  all  traces  of  the  soldering 
liquid  or  solid  are  removed  from  the  wire  before 
the  joint  is  covered  with  insulating  material. 
Kerite,  okonite  or  other  insulating  tape,  should 


preferably  be  wrapped  around  the  joint  after 
it  is  soldered. 

In  making  a  joint  in  a  gutta-percha  covered 
wire,  such  as  a  submarine  cable,  the  following 
method  may  be  employed:  The  bared  and 
cleansed  wires  are  twisted  together  and  soldered. 
The  soldered  joint  is  then  covered  with  a  layer 
of  plastic  insulating  material  made  of  a  mixture 
of  gutta-percha,  tar  and  rosin.  (See  Chatterton's 
Compound.)  In  order  to  insure  a  good  junction 
between  this  and  the  gutta-percha  covering  on  the 
rest  of  the  wire,  the  outer  surface  of  the  gutta- 
percha  is  removed  for  about  two  inches  from  each 
side  of  the  joint,  so  as  to  remove  its  oxidized  sur- 
face. After  the  coating  is  put  on,  it  is  warmed 
gently  by  a  warm  joining  tool,  not  by  the  flame 
of  a  lamp.  A  sheet  of  -warmed  gutta-percha  is 
then  wrapped  around  the  joint,  and  while  it  and 
the  joint  are  still  hot,  another  coating  of  the 
plastic  insulating  material  is  applied.  Successive 
layers  of  gutta-percha  and  some  other  insulating 
material  are  generally  applied  in  the  case  of  sub- 
marine cables. — (Culley.) 

Joint,  Telegraphic,  Mclntire's  Parallel 

Sleeve A  joint  for  telegraphic  or  other 

wires,  in  which  the  ends  to  be  joined  are 
slipped  into  parallel  sleeves  or  tubes,  which 
are  afterward  twisted  around  each  other. 

A  general  view  of  the  parallel  sleeve  joint,  both 
before  and  after  twisting,  is  shown  in  Fig.  320. 


Fig.  320.    Mclntirfs  Parallel  Sleeve  Joint. 

The  twisting  is  done  by  means  of  the  specially 
devised  twisting  clamp  shown  in  Fig.  321. 


Fig.  321.  Tansting  CZamf/or  Mclntire's  Parallel  Joint. 

Joint,  Telegraphic  or  Telephonic 

A  juncture  of  the  ends  of  two  electric  con- 
ductors so  as  to  insure  a  permanent  junc- 
tion whose  resistance  shall  not  be  appreci- 
ably greater  per  unit  of  length  than  that  of 
the  rest  cf  the  wire. 


Joi.J 


299 


[Kao. 


In  making  a  joint,  care  should  always  be  taken 
to  scrape  the  insulating  material  from  the  wires 
and  clean  their  surfaces  before  twisting  them  to- 
gether. 

Telegraph  wires  were  formerly  joined  by  the 
ordinary  bell- hangers' joint;  that  is,  the  wires  were 
simply  looped  together.  The  constant  vibrations 
to  which  the  wires  are  subjected  caused  such  a 
joint  to  be  abandoned  and  an  improvement  intro- 
duced by  bolting  the  ends  together,  as  shown  in 
Fig.  322. 


Fig.  332.     Teleg, 


Joint. 


Joint,  Testing  of Ascertaining  the 

resistance  of  the  insulating  material  around 
a  joint  in  a  cable. 

The  resistance  of  the  insulating  material  of  a 
cable  at  a  joint  is  necessarily  high,  since  the 
joint  forms  but  a  small  part  of  length  of  the  cable. 
It  should  not,  however,  be  large  as  compared  with 
an  equal  length  of  another  part  of  the  cable  with 
a  perfect  core. 

Two  methods  for  testing  cable  joints  are  gener- 
ally employed,  viz. : 

(I.)  A  conductor  is  charged  through  the  joints 
for  a  given  time,  and  the  deflection  obtained  by 
its  discharge  compared  with  the  discharge  of  the 
same  condenser  charged  for  an  equal  length  of 
time  through  a  few  feet  of  perfect  cable. 

(2.)  A  charged  conductor  is  permitted  to  dis- 
charge itself  through  the  joint,  and  the  amount 
lost  in  a  given  time  noted. 

For  description  of  different  methods,  see 
Kempe's  "  Handbook  of  Electrical  Testing." 

Joulad. — A  term  proposed  for  the  Joule. 


This  term  is  not  generally  adopted.  (See 
Joule.} 

Joule.  —  The  unit    of   electric   energy  or 
work. 

The  volt-coulomb. 

The  amount  of  electric  work  required  to 
raise  the  potential  of  one   coulomb  of  elec- 
tricity one  volt. 

The  joule  may  be  regarded  as  a  unit  of  energy 
or  work  in  general,  apart  from  electrical  work  or 
energy. 

i  joule  .....  ,  ....  =  10,000,000  ergs. 

I  joule  ..........  =  .  73732  foot-pounds. 

I  joule  ..........  =  I  volt-coulomb. 

I  joule  ..........  =  .24  calorie. 

4.2  joules  .........  =  i  small  calorie. 

i  joule  per  second  =  i  watt. 

The  British  Association  proposed  to  call  one 
joule  the  work  done  by  one  watt  in  one  second. 

Joule,  as  a  Heat  Unit.—  The  quantity  of 
heat  developed  by  the  passage  of  a  current 
of  one  ampere  through  a  resistance  of  one 
ohm. 


Joule  Effect.—  (See  Effect,  Joule) 

Joule's    Cylindrical    Electro-Magnet— 

(See  Magnet,  Electro,  Joules  Cylindrical?) 

Joule's  Law.  —  (See  Laws  of  Joule) 
Junction  Box.  —  (See  Box,  Junction) 
Jump-Spark    Burner.  —  (See     Burner, 

fump-Spark) 
Junction,  Thermo-Electric.  —  A  junction 

between  any  thermo-electric   couple.    (See 

Cell,  Thermo-Electric^ 


K. — A  contraction  for  electrostatic  capa- 
city. (See  Capacity,  Electrostatic) 

K.  C.  C. — In  electro-therapeutics,  a  brief 
method  of  writing  kathodic  closure  contrac- 
tion, or  the  effects  of  muscular  contraction 
observed  at  the  kathode  on  the  closure  of  a 
circuit. 

K.  D.  C. — In  electro-therapeutics,  a  brief 
method  of  writing  kathodic  duration  con- 


traction, or  the  effects  of  muscular  contrac- 
tion observed  at  the  kathode  after  the  current 
has  been  passing  for  some  time. 

K.  W. — A  contraction  for  kilo-watt.  (See 
Watt,  Kilo) 

Kaolin. — A  variety  of  white  clay  some- 
times employed  for  insulating  purposes. 

Jablochkoff  sometimes  employed  kaolin  be- 
tween the  parallel  carbons  of  his  electric  candle 


Kap.] 


[Key. 


for  the  purpose  of  insulating  them  from  each 
other.  He  also  devised  an  electric  lamp  in  which 
a  spark  of  considerable  difference  of  potential, 
obtained  from  an  ordinary  induction  coil,  was 
caused  to  raise  a  surface  of  kaolin  to  incan- 
descence by  passage  over  it. 

Kapp  Lines.— (See  Lines,  Kapp) 

Kartavert — A  kind  of  insulating  material. 

Katelectrotonus. — A  word  sometimes  used 
instead  of  kathelectrotonus.  (See  Kathe- 
lectrotonus) 

Kathelectrotonic  State.  —  (See  State, 
Kathelectrotonic) 

Eatheleetrotonic  Zone.  —  (See  Zone, 
Kathelectrotonic) 

Kathelectrotonus. — In  electro-therapeu- 
tics, the  condition  of  increased  functional  ac- 
tivity that  occurs  in  a  nerve  in  the  neighbor- 
hood of  the  kathode  or  negative  electrode. 
(See  Electrotonus.) 

Kathion. — The  electro-positive  ion,  atom 
or  radical  into  which  the  molecule  of  an 
electrolyte  is  decomposed  by  electrolysis. 
(See  Electrolysis.  Ions.] 

Kathion  is  sometimes  written  cathion. 

In  electrolysis  the  kathion,  or  the  electro-posi- 
tive ion  or  radical,  appears  at  the  kathode  or 
electro-negative  electrode.  Similarly,  the  anion, 
or  the  electro-negative  ion  or  radical,  appears  at 
the  anode  or  the  electro-positive  electrode. 

Kathodal. — Pertaining  to  the  kathode. 
(See  Kathode) 

Kathode. — The  conductor  or  plate  of  an 
electro-decomposition  cell  connected  with  the 
negative  terminal  or  electrode  of  a  battery  or 
other  source. 

The  word  kathode  is  sometimes  applied  to  the 
negative  terminal  of  a*battery  or  source,  whether 
connected  with  a  decomposition  cell  or  not.  It 
is  preferable,  however,  to  restrict  its  use  to  de- 
composition cells.  (See  Anode.) 

The  word  kathode  is  sometimes  written  cathode. 

Kathodic.— Pertaining  to  the  kathode. 
(See  Kathode) 

Kathodic  Electro-Diagnostic  Reactions. 
—(See  Reactions,  Electro-Diagnostic) 

Keeper  of  Magnet— (See  Magnet,  Keeper 


Kerite. — An  insulating  material. 
Kerr  Effect— (See  Effect,  Kerr) 
Key  Board.— (See  Board,  Key) 

Key,  Capillary  Contact A  form  of 

fluid  contact  in  which  the  circuit  is  closed  or 
broken  by  means  of  a  wire  which  is  dipped 
into  or  removed  from  the  surface  of  a  mass 
of  mercury. 

In  order  to  avoid  an  increase  in  the  resistance 
of  the  circuit,  due  to  the  formation  of  oxide  of 
mercury,  the  contact  surface  of  the  mercury  is 
kept  covered  with  a  layer  of  dilute  alcohol. 

Key,  Discharge •  A  key  employed  to 

enable  the  discharge  from  a  condenser  or 
cable  to  be  readily  passed  through  a  galva- 
nometer for  purposes  of  measurement. 

Key,  Discharge,  Kempe's A  dis- 
charge key  constructed  as  shown  in  Fig.  323. 


.  323.     Kempe's  Discharge  Key. 


The  solid  lever,  hinged  at  one  extremity,  plays 
between  two  contacts  connected  to  two  terminals, 
and  has  two  finger  triggers  at  its  free  end  marked 
"Discharge"  and  "Insulate,"  connected  respec- 
tively to  two  ebonite  hooks.  The  hook  attached 
to  that  marked  "  Discharge  "  is  a  little  higher  than 
the  other,  so  that  when  the  lever  is  caught  against 
it,  the  key  rests  in  an  intermediate  position  be- 
tween the  contacts,  and,  when  caujht  against  the 
lower  trigger,  it  rests  against  the  bottom  contact. 
When  in  the  last  position,  a  depression  of  tke 
"  Insulate  "  trigger  causes  the  lever  to  spring  np 
against  the  second  hook,  thus  insulating  it  from 
either  contact,  and  on  the  depression  of  the  '«  Die- 
charge  "  trigger,  the  lever  springs  up  against  the 
top  contact. 

Key,  Discharge,  Webb's  --  A  dk- 
charge  key  constructed  as  shown  in  Fig.  324. 

A  horizontal  lever  L,  Fig.  324,  passing  between 
two  contacts  and  hinged  at  J,  is  pressed  upward 
by  a  spring.  The  free  end  of  this  lever  termi- 
nates in  two  steps,  i  and  2.  A  vertical  lever,  pro- 


301 


[Key. 


vided  with  an  insulating  handle,  is  jointed  at  J', 
aadhasat  C,  a  projecting  metallic  tongue  that 
engages  in  the  upper  step  when  the  lever  H,  is 
vwtical,  and  on  the  lower  step  when  it  is  slightly 
naored  from  the  free  end. 

When  the  projection  C,  rests  on  the  lower  step 
2,  the  lever  L,  is  intermediate  between  the  top 
and  bottom  contacts,  and  is,  therefore,  discon- 


pieces,  I,  2,  3  and  4,  serve  to  make  contacts  with 
apparatus  used  in  connection  with  the  key. 

The  battery  circuit  is  connected  to  I  and  2, 
and  the  galvanometer  to  3  and  4,  so  that  the  bat- 
tery circuit  is  closed  first,  and  the  galvanometer 
afterwards.  This  form  of  key  is  used  in  connec- 
tion with  the  Wheatstone  Bridge. 

Key,  Double-Contact,  Lambert's 

A  key  used  in  cable-work,  and  constructed 
as  shown  in  Fig.  326. 


Fig.  324.      Webb's  Disdiarge  Key. 

nected  from  either  of  them;  but,  when  it  rests  on 
the  upper  step,  it  is  in  contact  with  the  lower 
contact. 

When  the  lever  H,  is  so  moved  as  to  have  the 
projection  C,  away  from  both  steps,  the  lever  L, 
is  pressed  by  its  spring  against  the  upper  contact. 

The  battery  terminals  are  connected  with  the 
condenser  terminals  when  the  lever  L,  is  touching 
the  lower  contact,  but  when  the  lever  L,  touches 
the  top  contact,  the  condenser  is  connected  with 
the  galvanometer  terminals. 

Key,  Double-Contact  Form  of  Bridge, 

Spragne's A  key  designed  to  succes- 
sively close  two  separate  circuits. 


i     2 

Fig.  325. 


3  4, 

Spragve's  Double-Contact  Key. 


Sprague's  double-contact  key  is  shown  in  Fig. 
325.  On  depressing  K,  the  contacts  c,  c,  are  first 
closed  and  afterwards  contacts  at  c',  c'.  Metallic 


In  Thomson's  method  for  the  determination  of 
electrostatic  capacity,  the  capacity  of  the  cable 
is  compared  with  that  of  a  condenser  containing 
a  known  charge.  These  two  charges  are  so  con- 
nected electrically  as  to  discharge  into  and 
neutralize  each  other  if  equal,  but  if  not,  to  pro- 
duce a  galvanometer  deflection  by  a  charge 
equal  to  their  difference. 

A  Lambert  double  contact  key  is  shown  in  Fig. 
326.  The  connections  are  such  that  the  pushing 
forward  of  K,  depresses  keys  that  permit  a  bat- 
tery to  simultaneously  charge  the  condenser  and 
the  cable.  On  drawing  K,  back,  the  two  charges 
are  allowed  to  mix.  Then  on  depressing  K,  the 
difference  of  the  charges,  if  any,  is  discharged 
through  the  galvanometer. 

Key,  Double-Tapper The  key  used 

in  a  system  of  needle  telegraphy  to  send 
electric  impulses  through  the  lines  in  alter- 
nately opposite  directions.  (See  Telegraphy, 
Single-Needle^ 

Key,  Increment A  telegraphic  key 

so  connected  that  an  increase  or  increment 
in  the  line  current  occurs  whenever  the  key  is 
depressed. 

The  increment  key  is  used  in  duplex  and  quad- 
ruplex  systems  of  telegraphic  transmission. 

Key,  Increment,  of  Quadruples  Tele- 
graphic System A  key  employed  to 

increase  the  strength  of  the  current  and  so 
operate  one  of  the  distant  instruments  in  a 


Key.] 


302 


[Key. 


quadruplex  system  by  an  increase  in  the 
strength  of  the  current.  (See  Telegraphy, 
Quadruplex^) 

Key,  Magneto-Electric A  tele- 
graph key  for  sending  an  electric  impulse 
into  a  line,  so  arranged  that  a  coil  of  wire  on 
an  armature  connected  with  the  key  lever  is, 
by  the  movements  of  the  key,  moved  toward 
or  from  the  poles  of  a  permanent  magnet,  the 
movements  of  the  key  thus  producing  the 
currents  sent  into  the  line. 

Key,  Plug A  simple  torm  of  key  in 

which  a  connection  is  readily  made  or  broken 
by  the  insertion  of  a  plug  of  metal  between 
two  metallic  plates  that  are  thus  introduced 
into  a  circuit. 

A  form  of  plug  key  is  shown  in  Fig.  327. 


Fig.  327-    Plus  Key. 

Key,  Reversing A  key  inserted  in 

the  circuit  of  a  galvanometer  for  obtaining 
deflections  of  the  needle  on  either  side  of  the 
galvanometer  scale. 

A  form  of  reversing  key  is  shown  in  Fig.  328. 
The  galvanometer  terminals  are  connected  to  the 
binding  posts  2  and  3,  and  the  circuit  terminals 
to  the  other  two  posts.  On  depressing  K,  the 


Fig.  328.    Reversing  Key. 

current  flows  m  one  direction  and  on  depressing 
K',  it  flows  in  the  opposite  direction.  Clamps, 
operated  by  handles,  are  provided  so  as  to  close 
either  of  the  keys  permanently,  if  so  desired. 


Key,  Reversing,  of  Quadruples  Tele- 
graphic System A  key  employed  to 

reverse  the  direction  of  the  current  and  so 
operate  one  of  the  distant  instruments,  in  a 
quadruplex  system,  by  a  change  in  the 
direction  of  the  current.  (See  Telegraphy, 
Quadruplex.) 

Key,  Short-Circuit A  key  which 

in  its  normal  condition  short  circuits  the  gal- 
vanometer. 


Ftg.  329.    Short-  Circuit  Key. 

Such  a  short-circuit  key  is  provided  for  the 
purpose  of  protecting  the  galvanometer  from  in- 
jury by  large  currents  being  accidentally  passed 
through  its  coils.  In  the  form  shown  in  Fig.  329, 
the  spring  S,  rests  against  a  platinum  contact ; 
but  when  depressed  by  the  insulated  head  at  K, 
it  rests  against  an  ebonite  contact,  and  throws 
the  galvanometer  into  the  desired  circuit. 

The  key  is  provided  with  double  binding  posts 
at  P  and  N,  for  convenience  of  attachment  to  re- 
sistance coils,  batteries,  etc. 

In  the  form  of  a  short-circuit  key  shown  in  Fig. 
330,  a  catch  is  provided  for  the  purpose  of  keep- 
ing the  key  down  when  once  depressed.  Its 
arrangement  will  be  readily  understood  from  an 
inspection  of  the  figure. 


Fig.  330.     Short-Circuit  Key. 

Key,  Sliding-Contact The  key  em- 

ployed  in  the  slide  form  of  Wheatstone 
bridge,  to  make  contact  with  the  wire  over 
which  the  sliding  contact  passes.  (See 
Bridge,  Electric,  Slide  Form  of^ 


Key.] 


303 


[Kit. 


Key,  Stationary  Floor An  electric 

key  or  push  button  placed  on  the  floor  so  as 
to  be  reatlily  closed  by  the  foot. 

This  form  of  key  is  especially  suitable  for  use 
in  connection  with  an  electric  bell  and  annuncia- 
tor for  readily  calling  an  attendant.  (See  Annun- 
ciator, Electro-Magnetic.) 

Key,  Telegraphic The  key  em- 
ployed for  sending  over  the  line  the  successive 
makes  and  breaks  that  produce  the  dots  and 
dashes  of  the  Morse  alphabet,  or  the  deflec- 
tions of  the  needle  of  the  needle  telegraph. 
(See  Telegraphy,  American  System,  of.} 

Kick.— A  recoil. 

Kicking  Coil.— (See  Coil,  Kicking.} 

Kilo  (as  a  prefix}. — One  thousand  times. 

Kiloampere. — One  thousand  amperes. 

Kiloampgre  Balance.— (See  Balance, 
Kiloampere.} 

Kilodyne. — One  thousand  dynes.  (See 
Dyne.} 

Kilogramme. — One  thousand  grammes, 
or  2.2046  pounds  avoirdupois.  (See  Weights, 
French  System  of.} 

Kilojoule. — One  thousand  joules. 

Kilometre. — One  thousand  metres. 

Kilowatt. — One  thousand  watts. 

Kilowatt  Hour.— (See  Hour,  Kilowatt.} 

Kine. — A  unit  of  velocity  proposed  by  the 
British  Association. 

A  kine  equals  I  centimetre  per  second. 

Kinetic  Energy. — (See  Energy,  Kinetic.} 

Kinetic  Theory  of  Matter.— (See  Matter, 
Kinetic  Theory  of.} 

Kinetics,  Electro A  term  some- 
times applied  to  the  phenomena  of  electric 
currents,  or  electricity  in  motion,  as  distin- 
guished from  electrostatics,  or  the  phenom- 
ena of  electric  charges,  or  electricity  at  rest. 

Kinetograph. — A  device  for  the  simultane- 
ous reproduction  of  a  distant  stage  and  its 
actors  under  circumstances  such  that  the 
actors  can  be  heard  at  any  distance  from  the 
theatre. 

The  sounds  heard  by  the  distant  audience  are 
actual  reproductions  of  those  uttered  during  the 


performance,  though  not  at  the  time  of  their 
utterance.  The  appearance  of  the  stage  and  its 
actors  represents  the  appearance  of  a  previous 
reproduction  of  the  play  or  opera  or  other  per- 
formance, as  taken  by  means  of  a  Kodak  camera 
with  a  film  cylinder  and  drop  shutter,  operated 
by  an  electric  motor,  exposing,  say,  forty  plates 
a  second.  By  means  of  a  projecting  lantern  these 
photographic  pictures  are  thrown  on  a  curtain  on 
a  stage  at  the  distant  theatre  in  regular  order  of 
sequence,  while  a  loud- speaking  phonograph 
puts  song  and  speech  into  the  mouths  of  the 
mimic  actors  and  thus  gives  the  phantom  stage 
the  semblance  of  life  and  reality. 

Kite,  Franklin's A  kite  raised  in 

Philadelphia,  Pa.,  in  June,  1752,  by  means  of 
which  Franklin  experimentally  demonstrated 
the  identity  between  lightning  and  electricity, 
and  which,  therefore,  led  to  the  invention  of 
the  lightning  rod. 

It  is  true  that  Dalibard,  on  the  loth  of  May, 
1752,  prior  to  Franklin's  experiment,  succeeded 
in  drawing  sparks  from  a  tall  iron  pole  he  had 
erected  in  France.  This  experiment  was,  how  - 
ever,  tried  at  the  suggestion  of  Franklin,  to  whom 
it  must  properly  be  ascribed. 

A  description  of  this  kite  is  given  by  Franklin 
in  the  following  letter: 

Letter  XI,  from  BENJ.  FRANKLIN,  Esq.,  of  Phil- 

adelphia,  to  PETER  COLLINSON,  Esq., 

F.  R.  S.,  London. 

"OCT.  19,  1752. 

"As  frequent  mention  is  made  in  public  papers, 
from  Europe,  of  the  success  of  the  Philadelphia 
experiment  for  drawing  the  electric  fire  from 
clouds  by  means  of  pointed  rods  of  iron  erected 
on  high  buildings,  etc.,  it  may  be  agreeable  to 
the  curious  to  be  informed  that  the  same  experi- 
ment has  succeeded  in  Philadelphia,  though 
made  in  a  different  and  more  easy  manner,  which 
is  as  follows: 

"  Make  a  small  cross  of  two  light  strips  of  cedar, 
the  arms  so  long  as  to  reach  to  the  four  corners  of  a 
large  thin  handkerchief  when  extended ;  tie  the 
corners  of  the  handkerchief  to  the  extremities  of 
the  cross,  so  you  have  the  body  of  a  kite,  which, 
being  properly  accommodated  with  a  tail,  loop 
and  string,  will  rise  in  the  air  like  those  made  of 
paper,  but  this,  being  of  silk,  is  fitter  to  bear  the 
wet  and  wind  of  a  thunder  gust  without  tearing. 
To  the  top  of  the  upright  stick  of  the  cross  is  to 


KnLJ 


304 


[Lag. 


be  fixed  a  very  sharp  pointed  wire  rising  a  foot 
OT  more  above  the  wood.  To  the  end  of  the 
twine,  next  the  hand,  is  to  be  tied  a  silk  ribbon, 
and  where  the  silk  and  twine  join,  a  key  may  be 
fastened.  This  kite  is  to  be  raised  when  a  thun- 
der gust  appears  to  be  coming  on,  and  the  per- 
son who  holds  the  string  must  stand  within  a 
door  or  window,  or  under  some  cover,  so  that 
the  silk  ribbon  may  not  be  wet,  and  care  must  be 
taken  that  the  twine  does  not  touch  the  frame  of 
the  door  or  window.  As  soon  as  any  of  the 
thunder  clouds  come  over  the  kite  the  pointed 
wire  will  draw  the  electric  fire  from  them,  and 
the  kite,  with  all  the  twine,  will  be  electrified, 
and  the  loose  filaments  of  the  twine  will  stand 
out  every  way,  and  be  attracted  by  an  approach- 
ing finger.  And  when  the  rain  has  wet  the  kite 
and  twine  so  that  it  can  conduct  the  electric  fire 
freely,  you  will  find  it  stream  out  plentifully  from 
the  key  on  the  approach  of  your  knuckle.  At 
this  key  the  phial  may  be  charged,  and  from 
electric  fire  thus  obtained  spirits  may  be  kindled, 
and  all  the  other  electric  experiments  be  per- 
formed, which  are  usually  done  by  the  help  of  a 


rubbed  glass  globe  or  tube,  and  thereby  the 
sameness  of  the  electric  matter  with  that  of  light- 
ning completely  demonstrated. 

"B.  FRANKLIN." 

Knife  Break  Switch.— (See  Switch,  Knife 
Break) 

Knot  or  Nautical  Mile.— A  length  equal 
to  6,087  feet. 

The  English  statute  mile  is  equal  to  5,280  feet. 
The  value  of  the  nautical  mile  is  therefore  in  excess 
of  that  of  the  statute  mile. 

Kohlrausch's  Law.  —  (See  Law  of  Kohl- 

rausch.) 

Krizik's  Bars.— (See  Bars,  Krizik's) 
Kyanized. — Subjected    to    the    kyanizing 

process.     (See  Kyanizing?) 

Kyanizing. — A  process  employed  for  the 
preservation  of  wooden  telegraphic  poles  by 
injecting  a  solution  of  corrosive  sublimate 
into  the  pores  of  the  wood.  (See  Pole,  Tele- 
graphic?) 


L. — A  contraction  for  co-efficient  of  in- 
ductance. (See  Inductance,  Co-efficient  of.) 

L. — A  contraction  for  length. 

Labile  Galvanization.— (See  Galvaniza- 
tion, Labile.) 

Lag,  Angle  of The  angle  through 

which  the  axis  of  magnetism  of  the  armature 
of  a  dynamo-electric  machine  is  shifted  by 
reason  of  the  resistance  its  core  offers  to  sud- 
den reversals  of  magnetization. 

An  armature  of  a  bi-polar  dynamo -electric  ma- 
chine has  its  magnetism  reversed  twice  in  every 
rotation.  The  iron  of  the  core  resists  these  mag- 
netic reversals.  The  result  of  this  resistance  is  to 
shift  the  axis  of  magnetism  in  the  direction  of  ro- 
tation. The  angle  through  which  the  axis  has 
thereby  been  shifted  is  called  the  angle  of  lag. 

The  term,  angle  of  lag,  is  sometimes  incorrectly 
applied  so  as  to  include  a  similar  result  produced 
by  the  magnetization  due  to  the  armature  current 
itself.  It  is  this  latter  action  which,  in  armatures 
With  soft  iron  cores,  is  the  main  cause  of  the  angle 


of  lead.  (See  Brushes,  Lead  of.  Lead,  Angle 
of.) 

Lag,  Angle  of,  of  Current An 

angle  whose  tangent  is  equal  to  the  ratio  of 
the  inductive  to  the  ohmic  resistance. 

An  angle,  the  tangent  of  which  is  equal  to 
the  inductive  resistance  of  the  circuit,  divided 
by  the  ohmic  resistance  of  the  circuit. 

An  angle,  the  co-sine  of  which  is  equal  to 
the  ohmic  resistance  of  the  circuit,  divided 
by  the  impedance  of  the  circuit. 

Lag,  Magnetic A  magnetic  viscos- 
ity as  manifested  by  the  sluggishness  with 
which  a  magnetizing  force  produces  its  mag- 
netizing effects  in  iron. 

The  tendency  of  the  iron  core  of  a  magnet, 
or  of  the  armature  of  a  dynamo-electric  ma- 
chine, to  resist,  and,  therefore,  retard  mag- 
netization. 

This  retardation,  or  lag,  is  called  the  magnetic 
lag. 

The  lead  necessary  to  give  the  brushes  of  a  dy- 
namo-electric machine  to  insure  quiet  action  has  by 


Lam.] 


Borne  been  erroneously  ascribed  to  the  magnetic 
lag.  The  lead,  though  due  to  lag  in  part,  in  reality 
is  mainly  due  to  the  resultant  magnetization  of 
the  armature  both  by  the  field  magnets  and  by  its 
own  current.  (See  Lead,  Angle  of.)  This  dis- 
placement of  the  brushes  is  measured  by  an  angle 
sometimes,  though  erroneously,  called  the  angle 
of  lag.  (See  Lag,  Angle  of.) 

Lamellar  Distri- 
bution of  Magnet- 
ism.—(See  Magnet- 
ism, Lamellar  Dis- 
tribution of.} 

Laminated  Core. 
— (See  Core,  Lami- 
natedl) 

Laminating  Core. 
— (See  Core,  Lami- 
nation of.) 

Lamination  of 
Armatnre  Core.  — 
(See  Core,  Armature, 
Lamination  0f.) 

Lamination  of 
Cores.  —  (See  Core, 
Lamination  of.) 

Lamp,     Ail-Night 

A  term  some- 
times applied  to  a 
double  -  carbon  arc 
lamp.  (See  Lamp, 
Electric  Arc,  Double- 
Caroon.) 

A  form  of  all-night 
arc  lamp  is  shown  in 
Fig.  331.  When  the 
consumption  of  the  first 

pair    of    carbons    has  Kg.  331.    Au-Night  Arc 
reached  a  certain  limit  Lamp. 

the  current  is  automatically  switched  over  to  the 
other  pair. 

Lamp,  All-Night  Electric A  lamp 

provided  with  carbon  electrodes  so  as  to  burn 
all  night  without  recarboning. 

A    double-carbon     electric     lamp,       (See 
Lamp,  All-Night) 

Lamp,  Arc An   electric  lamp,  the 

source  of  whose  light  is  a  voltaic  arc. 


305  [Lam. 

Lamp,   Arc,  Electric An  electric 

lamp  in  which  the  light  is  produced  by  a  vol- 
taic arc  formed  between  two  or  more  carbon 
electrodes. 

The  carbon  electrodes  are  placed  in  various 
positions,  either  parallel,  horizontal,  inclined 
to  one  another  or  vertically  one  above  the  other. 
The  latter  is  the  form  most  generally  adopted, 
since  it  permits  the  ready  feeding  of  the  upper 
carbon. 

The  carbons  are  maintained  during  their  con- 
sumption at  a  constant  distance  apart,  by  the  aid 
of  various  feeding  devices.  Such  devices  are  op- 
erated generally  by  trains  of  wheel- work,  by  me- 
chanical or  electrical  motors,  or  by  the  simple 
action  of  a  spring,  by  gravity  or  by  the  attraction 
of  a  solenoid. 

The  carbon  pencils  or  electrodes  are  held  in 
carbon  holders,  consisting  of  clutches  or  clamps, 
attached  to  the  end  of  the  lamp  rods. 

When  the  lamp  is  not  in  operation  the  carbons 
are  usually  in  contact  with  one  another;  but,  on 
the  passage  of  the  current,  they  are  separated 
the  required  distance  by  the  action 
of  an  electro-magnet  whose  coils 
are  traversed  by  the  direct  or  main 
current. 

In  order  to  maintain  the  elec- 
trodes a  constant  distance  apart, 
the  upper  carbon  in  some  lamps  is 
held  in  position  by  the  operation  of 
a  clutch,  or,  in  others,  by  a  detent, 
that  engages  in  a  toothed  wheel. 
The  position  of  this  clutch  or  de- 
tent is  controlled  by  the  action  of 
an  electro-magnet  whose  coils  are 
usually  situated  in  a  shunt  or  de- 
rived circuit,  of  high  resistance, 
around  the  electrodes.  When  the 
carbons  are  at  their  normal  dis- 
tance apart,  the  shunt  current  is 
not  of  sufficient  strength  to  move 
the  clutch  or  detent  from  the  position  in  which 
it  prevents  the  downward  motion  of  the  upper 
carbon  rod.  When,  however,  by  the  burning 
or  consumption  of  the  carbons,  the  resistance 
of  the  arc  has  increased  to  an  extent  which  can 
be  predetermined,  the  increased  current  that  is 
thereby  passed  through  the  shunt  circuit  is  now 
sufficiently  strong  to  release  the  clutch  or  de- 
tent, thus  permitting  the  fall  or  feed  of  the  upper 
carbon.  In  a  well  designed  lamp  this  occurs 


Lam.] 


306 


[Lam. 


so  gradually  as  to  produce  no  perceptible  effect 
on  the  steadiness  of  the  light. 

Arc  lamps  are  generally  placed  in  series  circuits, 
that  is,  in  circuits  in  which  the  current  passes  suc- 
cessively through  all  the  lamps  in  the  circuit,  and 
returns  to  the  source.  In  order  to  avoid  the  break- 
ing  of  the  entire  circuit  through  the  extinguish- 
ing of  a  single  arc,  on  the  breaking  of  its  cir- 
cuit, an  automatic  safety  device  is  provided  for 
each  lamp.  This  safety  device  consists  essentially 
of  an  electro-magnet  so  placed  in  a  shunt  circuit, 
that,  as  the  resistance  of  the  arc  becomes  too 
great,  the  increased  current,  which  will  then  flow 
through  the  coils  of  the  electro-magnet,  at  last 
produces  a  movement  of  its  armature  which  closes 
a  short  circuit  around  the  lamp,  and  thus  cuts  it 
out  of  the  circuit. 

Arc  lamps  assume  a  great  variety  of  forms.  A 
well  known  form  is  shown  in  Fig.  332. 

Lamp,  Arc,  Triple  Carbon An  arc 

lamp  in  which  three  carbon  electrodes  are 
used. 

The  positive  carbons  consist  of  two  ordinary 
cylindrical  carbons,  placed  parallel  to  each  other. 
The  negative  carbon  is  shaped  like  the  figure  8. 
The  arc  is  established  between  one  of  the  positive 
carbons  and  the  corresponding  side  of  the  nega- 
tive carbon.  The  feeding  of  the  lamp  is  attended 
by  a  shifting  back  and  forth  of  the  arc  between 
the  positive  carbons  and  from  side  to  side  of  the 
negative  carbons. 

The  design  of  the  triple  carbon  arc  lamp  is  to 
produce  a  lamp  of  long  life. 

Lamp    Bracket,    Electric 

—  (See  Bracket,  Lamp, 

Electric) 

Lamp  Bulb.— (See  Bulb, 
Lamp) 

Lamp,  Carcel An 

oil  lamp  employed  in  France 
as  a  photometric  standard. 

Fig.  333  shows  a  formofcar- 
cel  lamp.  Like  the  standard 
candle,  the  carcel  is  a  standard 
only  when  it  consumes  a  given 
weight  of  the  light-producing 
substance  in  a  given  time, 

Lamp,  Chamber  of ' 

The  glass  bulb  or  chamber  of 
an  incandescing  electric  lamp 
in  which  the  incandescing 


conductor     is 


placed,  and  in  which  is  maintained  a  high 
vacuum. 

The  transparency  of  the  lamp  chamber  and 
consequently  the  efficiency  of  the  lamp  may  de- 
crease— 

( I . )  From  the  settling  of  dust  or  dirt  on  its  outer 
walls. 

(2.)  From  the  deposit  of  carbon  or  metal  on  its 
inner  walls. 

To  obviate  the  first  cause  of  diminished  trans- 
parency the  outside  of  the  lamp  chamber  should 
be  frequently  cleansed.  The  diminished  trans- 
parency, due  to  the  second  cause,  cannot  be 
removed.  When  it  has  reached  a  certain  point,  it 
is  more  economical  to  replace  the  old  lamp  by  a 
new  lamp. 

In  a  properly  made  lamp  the  dimming  of  the 
lamp  chamber  is  not  apt  to  occur  unless  a  stronger 
current  than  the  normal  current  is  passed  through 
the  lamp. 

Lamp  Clamp.  —  (See  Clamp  for  Arc 
Lamps) 

Lamp,  Contact A  form  of  semi- 
incandescent  electric  lamp  in  which  a  carbon 
pencil  is  pressed  against  a  slab  of  carbon  or 
other  refractory  material. 

The  source  of  light  in  an  electric  contact  lamp 
is  twofold,  viz.: 

(i.)  A  minute  arc  formed  at  the  points  of  im- 
perfect contact. 

(2.)  The  incandescence  of  the  carbon  pencil, 
and  the  points  of  the  slab  of  carbon  against  which 
it  is  pressed. 

Lamp  Contacts.— (See  Contacts,  Lamp.) 

Lamp,  Electric,  Arc,  Carbon  Elec- 
trodes for (See  Electrodes,  Carbon, 

for  Arc  Lamps) 

Lamp,  Electric,  Arc,  Differential 

An  arc  lamp  in  which  the  movements  of 
the  carbons  are  controlled  by  the  differential 
action  of  two-magnets  opposed  to  each  other, 
one  of  whose  coils  is  in  the  direct  and  the 
other  in  a  shunt  circuit  around  the  carbons. 

Sometimes  the  differential  coils  are  placed  on 
the  same  magnet  core. 

Lamp,  Electric,  Arc,  Donble  Carbon 

— An  electric  arc  lamp  provided  with  two 
pairs  of  carbon  electrodes,  so  arranged  that 
when  one  pair  is  consumed,  the  circuit  is  auto- 
matically completed  through  the  other  pair. 


lam.! 


307 


[Lam. 


Lamp,  Electric  Glow A  "erm  em- 
ployed mainly  in  Europe  for  an  incandescent 
electric  lamp.  (See  Lamp,  Electric,  Incan- 
descent^ 

Lamp,  Electric,  Incandescent An 

electric  lamp  in  which  the  light  is  produced 
by  the  electric  incandescence  of  a  strip  or 
filament  of  some  refractory  substance,  gener- 
ally carbon. 

The  carbon  strip  or  filament  is  usually  bent  into 
the  form  of  a  horseshoe  or  loop,  and  placed  inside 
a  glass  vessel  called  the  lamp  chamber.  The 
lamp  chamber  is  exhausted  by  means  of  a  mercury 
pump,  generally  to  a  fairly  high  vacuum. 

Jn  order  to  insure  the  complete  removal  from 
the  lamp  chamber  of  all  the  air  it  originally  con- 
tained,  the  carbon  strips  that  are  placed  within  it 
are  maintained  at  a  high  temperature  during  the 
process  of  exhaustion.  This  temperature,  in 
practice,  is  obtained  by  sending  the  current 
through  the  carbon  strip  as  soon  as  nearly  all 
the  air  is  removed.  Towards  the  end  of  the 
pumping  operation  the  current  is  increased  so 
as  to  raise  the  carbons  to  their  full  bril- 
liancy. 

The  lamp  chamber  is  also  maintained  at  a 
fairly  high  temperature. 

To  insure  this  heating  of  the  walls  of  the  lamp 
chamber  by  the  incandescent  carbons  during 
pumping,  for  the  purpose  of  driving  off  all  the 
air  adhering  to  the  walls  of  the  chamber,  they  are 
sometimes  covered  with  some  readily  removable 
preparation  of  lamp  black. 

The  operation  of  driving  off  the  gases  absorbed 
by  the  carbons  is  termed  the  occluded  gas  process, 
and  is  essential  to  the  successful  sealing  of  an 
incandescent  lamp.  By  its  means,  a  considerable 
quantity  of  air  or  other  gaseous  substances  shut 
up  or  occluded  by  the  carbon  is  driven  out  of  the 
raroon,  which  it  would  be  impossible  to  get  rid  of 
by  the  mere  operation  of  pumping.  In  order  to 
insure  the  success  of  the  operation,  it  is  necessary 
that  the  heating  must  take  place  while  the  lamp 
is  being  exhausted,  since  otherwise  the  expelled 
gases  -would  be  re-absorbed.  (See  Gas,  Occlu- 
lion  of. ) 

Both  the  exhaustion  and  the  incandescence  con. 
tinue  up  to  the  moment  the  lamp  chamber  is 
hermetically  sealed;  otherwise,  some  of  the  air 
might  remain  in  the  lamp  chamber. 

The  lamp  chamber  is  hermetically  sealed, 
usually  by  the  fusion  of  the  glass  in  the  manner 


adopted  in    the    sealing    of   Geissler    tubes    or 
Crookes'  radiometers. 

For  the  preparation  of  the  carbon  strip,  its 
carbonization  and  the  flashing  of  the  strip,  see 
Carbonization,  Processes  of.  Carbons,  Flashing 
Process  for. 

The  ends  of  the  carbon  strip, 
or  filament,  are  attached  to  lead- 
ing-in  wires  of  platinum  that  pass 
through  the  glass  walls  of  the 
lamp  chamber,  and  are  fused 
therein  by  melting  the  glass 
around  them  in  the  same  manner 
as  are  the  leading-in  wires  of  the  I 
Geissler  tubes  and  other  similar 
apparatus. 

Incandescent  lamps  are  gener- 
ally connected  to  the  leads  or  cir-  Fig.  334.  In  can- 
cuits  in  multiple-arc  or  in  multi-   <*««*'  Electric 
pie-series.     They  are,  however,          •£«*»/• 
sometimes  connected  to  the  line  in  series.     (See 
Circuits,  Varieties  of.) 

In  the  case  of  multiple-arc  or  multiple-series 
connection,  the  resistance  of  the  filament  is  com- 
paratively high.  In  the  case  of  series-connec- 
tion the  resistance  is  comparatively  low. 

Incandescent  electric  lamps  assume  a  variety  of 
different  forms.  In  all  cases,  however,  the  shape 
of  the  filament  is  such, 
that  the  leading-in 
wires  that  carry  the 
current  to  and  from 
the  filament  shall  en- 
ter and  leave  the  lamp 
chamber  at  points  that 
are  comparatively 
near  together.  This 
is  for  the  purpose  of 
avoiding  the  unneces- 
sary production  of 
shadows. 

Commercial  incan- 
descent electric  lamps 
are  generally  marked 
with  the  potential  dif- 
ference in  volts  that 
must  be  applied  at  the 
terminals  in  order  to 
furnish  the  current 
necessary  to  properly 
operate  them.  If  this 
potential  difference  is 
made  greater,  the  can- 


Lam.] 


[Lam. 


ffle-power  of  the  lamp  is  greatly  increased,  but  its 
life  greatly  decreased. 

The  lamp  chamber  is  more  liable  in  such  cases 
to  become  less  transparent  from  the  deposit  of  a 
thin  layer  of  carbon  or  metal  on  its  inner  surfaces. 

In  the  Swan  lamp  the  filament  is  made  of  cot- 
ton thread.  These  threads  are  immersed  in  a 
mixture  of  two  parts  of  sulphuric  acid  and  one  of 
water,  which  converts  the  cellulose  of  the  thread 
into  artificial  parchment.  The  filaments  are  rap- 
idly washed  as  soon  as  they  are  removed  from  the 
sulphuric  acid  until  all  traces  of  the  acid  are  re- 
moved. They  are  then  passed  through  discs  so 
as  to  insure  a  uniform  area  of  cross-section,  and 
are  then  wrapped  on  rods  of  carbon  or  earthen- 
ware of  the  required  outline,  packed  in  a  crucible 
filled  with  powdered  charcoal,  and  carbonized. 

The  form  generally  given  to  the  Swan  filament 
is  that  shown  in  Fig.  335. 

Lamp,  Electric,  Incandescent  Ball  - 

—  An  incandescent  electric  lamp  in  which 
the  light  is  produced  by  a  sphere  or  ball  of 
carbon  placed  in  an  exhausted  receiver  of 
glass. 

When  subjected  to  the  effects  of  electrostatic 
waves  of  high  frequency  of  alternation,  such  a 
lamp  becomes  luminous 
from  the  incandescence  of 
the  carbon  ball  or  sphere. 
Tesla's  incandescent  ball 
electric  lamp  is  a  modifica- 
tion of  his  straight  filament 
lamp.  (See  Lamp,  Incan- 
descent,  Straight  Filament  .) 

The  construction  of  Tes- 
la's ball  incandescent  elec- 
tric lamp  will  be  readily 
understood  from  an  inspec- 
tion of  Fig.  336. 

Lamp,  Electric,  In- 
candescent,  Half-Shades 

for  --  (See    Half- 
Shades  for  Incandescent  Lamps?) 

Lamp,   Electric,  Incandescent,   Life  of 

--  The  number  of  hours  that  an  incan- 
descent electric  lamp,  when  traversed  by  the 
normal  current,  will  continue  to  afford  a  good 
commercial  light. 

The  failure  of  an  electric  incandescent  lamp 
results  either  from  the  volatilization  or  rupture 
of  the  carbon  conductor,  or  from  the  failure  of  the 


vacuum  of  the  lamp  chamber.  Since  the  em- 
ployment of  the  flashing  process,  and  the  process 
for  removing  the  occluded  gases,  it  is  not  unusual 
for  incandescent  lamps  to  have  a  life  of  several 
thousand  hours.  (See  Carbons,  Flashing  Pro- 
cess for .) 

The  life  of  an  incandescent  electric  lamp  should 
not  be  considered  as  continuing  until  the  filament 
actually  breaks.  As  soon  as  the  lamp  chamber 
has  become  covered  with  such  a  deposit  of  car- 
bon or  coating  of  metal  as  to  considerably  de- 
crease the  amount  of  light  which  passes  through 
the  chamber,  the  lamp  should  be  considered  as 
useless. 

Lamp,  Electric,  Incandescent,  Three- 
Filament,  for  Multi-Phase  Circuits 

— An  incandescent  lamp  for  use  on  multi- 
phase circuits,  provided  with  three  leading-la 
wires,  connected  to  the  free  ends  of  three 
filaments,  the  other  ends  of  which  are  con- 
nected in  a  common  joint. 

When  properly  acting,  the  current  passing 
through  each  filament  should,  at  any  instant, 
equal  the  sum  of  the  currents  in  the  other  two 
filaments,  which,  as  is  well  known,  is  the  property 
of  any  three-phase  circuit. 

Lamp,  Electric,  Ontrigger  for  f  — 

(See  Outrigger  for  Electric  Lamp.) 

Lamp,  Electric,  Pendant An  in- 
candescent electric  lamp  suspended  by  flexible 
twin-wire. 

Lamp,  Electric,  Safety An  in- 
candescent electric  lamp,  with  thoroughly 
insulated  leads,  employed  in  mines,  or  other 
similar  places,  where  the  explosive  effects  of 
readily  ignitable  substances  are  to  be  feared. 

Such  lamps  are  often  directly  attached  to  a 
portable  battery,  in  which  case  they  can  be  read- 
fly  carried  about  from  place  to  place. 

Lain]),  Electric,  Semi-Incandescent 

— An  electric  lamp  in  which  the  light  is  due 
to  the  combined  effects  of  a  voltaic  arc  and 
electric  incandescence. 

In  the  Reynier  semi-incandescent  lamp,  shown 
in  Fig.  337,  a  thin  pencil  of  carbon  C,  is  gently 
pressed  against  a  block  of  graphite  B.  A  lateral 
contact  is  provided  at  L,  through  a  block  o* 
graphite  I,  by  means  of  which  the  current  xs  COO- 


Lam.] 


309 


[Lam. 


•veyed  to  the  lower  part  only  of  the  movable  rod 
C,  which  part  alone  is  rendered  incandescent. 
In  this  lamp,  the  light  is  due  both  to  the  incan. 

•  C 


&*£•  337'    Semi- Incandescent  Lamp, 
descence  of  the  rod  C,  and  to  the  small  arc  formed 
at  J,  between  its  lower  end  and  the  contact  block 
B,  though  mainly  from   the  latter.    The  semi- 
incandescent  electric  lamp  has  not  as  yet  been  in- 
troduced  to  any  considerable  extent. 
Lamp,  Electric,  Series-Connected  Incan* 

descent An  incandescent  electric  lamp 

adapted  for  use  in  series  circuits. 


Fig.  338.    Series  Incandescent  Electric  Lamp. 

A  form  of  series  incandescent  lamp,  attached 
to  pendant  and  shade,  is  shown  in  Fig.  338. 

In  the  series  connected  incandescent  lamp,  un- 
ite the  multiple-connected  incandescent  electric 
lamp,  the  resistance  of  the  filament  is  low.  This 
is  done  .in.  order  to  prevent  the  total  resistance  of 


the  circuit  from  requiring  too  high  an  electro- 
motive force  for  operation.  In  order  to  preserve 
the  continuity  of  the  circuit  on  the  failure  of  any 
lamp  to  operate,  some  form  of  automatic  cut-out 
is  employed.  This  is  generally  some  form  of 
film  cut-out.  (See  Cut-Out,  Film.} 

Lamp  Hour. — (See  Hour,  Lamp.} 

Lamp,  Incandescent,  Electric  Filament 

Of A  term  now  generally  applied  to  the 

incandescing  conductor  of  an  incandescent 
electric  lamp,  whether  the  same  be  of  very 
small  cross-section  or  of  comparatively  large 
cross-section. 

The  term  filament  is  properly  applied  to  a  con- 
ductor containing  fibres  or  filaments  extending  in 
the  general  direction  of  the  length  of  the  incan- 
descing conductor.  Such  a  conductor  is  made  of 
carbonizable  fibrous  material,  cut  or  shaped  prior 
to  carbonization  so  as  to  have  its  fibres  extend- 
ing with  their  greatest  length  in  the  direction  of 
length  of  the  filament. 

Lamp,  Incandescent,  Straight  Filament 

An    incandescent    electric    lamp    in 

which  a  straight  filament,  placed  in  an  ex- 
hausted glass  chamber,  is  rendered  luminous 
by  the  effects  of  electro- 
static waves  or  thrusts  of 
high  frequency. 

The  straight  filament  in 
candescent  lamp  is  the  in- 
vention of  Tesla.  One 
form  of  such  a  lamp  is 
shown  in  Fig.  339. 

The  glass  globe  b,  of  the 
lamp  is  provided  with  a 
cylindrical  neck,  inside  of 
which  is  placed  a  tube  m, 
of  conducting  material,  on 
the  side  and  over  the  end 
of  the  insulating  plug  n. 

The  light-giving  fila. 
ment  e,  is  a  straight  car- 
bon stem,  connected  to  the 
plate  by  a  conductor  cov- 
ered with  a  refractory  in- 
sulating material  k.  An 
insulated  tube-socket  p, 
provided  with  a  metallic  lining  s,  serves  to  sup 
port  the  lamp  and  connect  it  with  one  pole  of  the 
source  of  current.  It  will  be  noticed  that  the  coat 


339-      Tesla's 
Straight  Filament  In- 
candescent Lamp. 


Lam.] 


310 


[Law. 


ings  s  and  m,  form  the  plates  of  a  condenser. 
The  other  terminal  of  the  machine  may  be  con- 
nected to  the  metal  coated  walls  of  the    room, 
or  to  metallic  plates  suspended  from  the  ceiling. 
Lamp  Indicator.—  (See  Indicator,  Lamp?) 

Lamp,  Pilot  --  In  systems  for  the 
operation  of  electric  lamps,  an  incandescent 
lamp  employed  in  a  station  to  indicate  the 
difference  of  potential  at  the  dynamo  ter- 
minals, by  means  of  the  intensity  of  its  emitted 
light. 

Lamp  Bod.—  (See  Rod,  Lamp) 
Lamp    Socket     Switch.—  (See     Switch, 
Lamp  Socket?) 

Lamps,  Bank  of  -  •  —A  term  applied 
to  a  number  of  lamps,  equal  to  about  half  the 
load,  that  were  formerly  placed  in  view  of  the 
attendant  in  circuit  with  a  dynamo  that  is  to 
be  placed  in  a  parallel  circuit  with  another 
dynamo,  one  of  the  lamps  of  which  is  also 
in  view. 

When  the  lamps  "in  bank  "  were  judged  to  be 
of  the  same  brilh'ancy  as  the  one  fed  by  the  other 
dynamo,  the  attendant  switched  the  dynamo  par- 
allel with  the  other,  and  at  the  same  time  cut  off 
the  bank  of  lamps  from  the  switched  in  dynamo. 

The  method  is,  however,  wrong.  The  proper 
way  is  to  make  the  voltage  of  the  dynamo  equal 
to  that  of  the  circuit.  Then  connect  it  and 
finally  raise  its  electromotive  force  until  it  takes 
its  share  of  the  load. 

Lamps,  Carboning  --  Placing  carbons 
in  electric  arc  lamps. 

When  the  carbons  are  consumed,  the  lamp 
requires  recarboning.  The  old  carbon  ends  are 
replaced  by  new  carbons,  and  the  lamp  rods 
cleansed. 

Large  Calorie.  —  (See  Calorie,  Great?) 

Latent  Electricity.  —  (See  Electricity, 
Latent?) 

Lateral  Discharge.  —  (See  Discharge, 
Lateral.) 

Lateral  Induction.  —  (See  Induction,  Lat- 
eral?) 

Lateral  Leakage  of  Lines  of  Magnetic 
Force.—  (See  Leakage,  Lateral,  of  Lines  of 
Magnetic  Force?} 


Lateral  Magnetic  Leakage.—  (See  Leak- 
age, Lateral,  of  Lines  of  Magnetic  Force.) 

Latitude,  Magnetic  --  The  distance 
a  place  is  situated  north  or  south  of  the  mag- 
netic equator. 

All  places  that  have  the  same  magnetic  latitude 
have  the  same  value  for  the  magnetic  inclination 
and  magnetic  intensity,  or  are  on  the  same  isocli- 
nal and  isodynamic  lines.  The  magnetic  latitude 
is  the  same  at  all  points  of  a  magnetic  parallel. 

Launch,  Electric  --  A  boat,  the  mo- 
tive power  for  which  is  electricity,  suitable  for 
launching  from  a  ship. 

Up  to  the  present  time  electric  launches  have 
been  propelled  by  means  of  electric  motors,  driven 
by  means  of  powerful  storage  batteries. 

A  form  of  electric  launch  constructed  for  the 
English  Government  is  shown  in  Fig.  340.  It  is 


Fig  34-O-    Electric  Launch. 

48^  feet  in  length  over  all,  by  8  feet  9  inches 
beam,  with  an  average  draft  of  2  feet  3  inches. 
Its  speed  is  8  knots  per  hour.  It  will  carry  forty 
fully  equipped  soldiers. 

Law,  Jacobi's  -  -  —  The  maximum  work 
done  by  a  motor  is  reached  when  the  counter- 
electromotive  force  is  equal  to  one-half  of  the 
impressed  electromotive  force,  or, 


Law,  Joule's  ---  Tha  heating  power  of 
a  current  is  proportional  to  the  product  of 
the  resistance  and  the  square  of  the  current 
strength.  (See  Heat,  Electric?) 

Law,  Natural  --  A  correct  expression 
of  the  order  in  which  the  causes  and  effects 
of  natural  phenomena  follow  one  another. 

The  law  of  gravitation,  for  example,  correctly 
•  expresses  the  order  of  sequence  of  the  phenomena 
which  result  when  unsupported  bodies  fall  to  the 
earth.  It  should  be  carefully  borne  in  mind,  how- 
ever, that  natural  laws  cannot  be  regarded  as 
explaining  tiie  ultimate  causes  of  natural  phcnc- 


Law.] 


311 


[Lai 


mena,  but  merely  express  their  order  of  occur- 
rence or  sequence. 

We  are  ignorant,  for  example,  of  the  true  cause 
of  gravitation  and  are  only  acquainted  with  its 
effects.  This  is  true  of  all  ultimate  physical 
causes,  save  for  our  belief  in  their  origin  in  a 
Divine  will. 

Law  of  Electro-Chemical  Equivalence. 
—(See  Equivalence,  Electro-Chemical,  Law 
of.) 

Law  of  Kohlrausch. — In  electrolytic  con- 
duction, each  atom  has  a  rate  of  motion  for 
a  given  liquid,  which  is  independent  of  the 
element  with  which  it  may  have  been  com- 
bined. 

In  the  following  table,  the  rate  of  motion  of 
various  kinds  of  atoms  through  nearly  pure  water 
for  a  difference  of  potential  of  one  volt  per  linear 
centimetre,  is  given: 

H 1. 08    centimetres  per  hour. 

K 0.205  centimetre  " 

Na 0.126  "  " 

Li 0.094  "  " 

Ag 0.166  "  " 

C 0.213 

1 0.216  "  " 

NO8 0.174 

Law  of  Ohm,  or  Law  of  Current 
Strength. — The  strength  of  a  continuous 
current  is  directly  proportional  to  the  differ- 
ence of  potential  or  electromotive  force  in  the 
circuit,  and  inversely  proportional  to  the  re- 
sistance of  the  circuit,  /'.  e.,  is  equal  to  the 
quotient  arising  from  dividing  the  electromo- 
tive force  by  the  resistance. 


F*S-  34  r.     Current  Strength  in  Circuit. 
Ohm's  law  is  expressed  algebraically  thus: 

C  =  5;  or,  E  =  C  R. 
R 

If  the  electromotive  force  is  given  in  volts,  and 
the  resistance  in  ohms,  the  formula  will  give  the 
current  strength  directly  in  amperes. 


The  resistance  of  any  electric  circuit,  as,  for 
example,  that  shown  in  Fig.  341,  consists  of  three 
parts,  viz.: 

(i.)  The  internal  resistance  of  the  source,  r. 

(2.)  That  of  the  conducting  wires  or  leads,  r'; 
and 

(3.)  That  of  the  electro-receptive,  r",  energized 
by  the  current.  Ohm's  law  applied  to  this  case 
would  be: 


-  r  +  r'  +  r". 

That  is,  the  resistance  of  the  entire  circuit  is 
equal  to  the  sum  of  the  separate  resistances  of  its 
different  parts. 

Since  C=  5,  (x);  then  E  =  C  R,  (2); 
R 

and  R  =  5,  (3). 

But,  since  a  current  of  one  ampere  is  equal  to 
one  coulomb  per  second,  then,  in  order  to  deter- 
mine in  coulombs  the  quantity  of  electricity  pass- 
ing in  a  given  number  of  seconds,  it  is  only  neces- 
sary to  multiply  the  current  by  the  time  in  seconds, 
orQ  =  CT(4). 

Hence,  referring  to  the  above  equations  (i), 
(2),  (3)  and  (4);  according  to  Ohm's  law: 

(I.)  The  current  in  amperes  is  equal  to  the 
electromotive  force  in  volts  divided  by  the  resist- 
ance w\ohms. 

(2.)  The  electromotive  force  in  volts  is  equal  to 
the  product  of  the  current  in  amperes  and  the 
resistance  in  ohms. 

(3.)  The  resistance  in  ohms  is  equal  to  the  elec- 
tromotive force  in  volts  divided  by  the  current  in 
amperes. 

(4.)  The  quantity  of  electricity  in  coulombs  is 
equal  to  the  current  in  amperes  multiplied  by  the 
time  in  seconds. 

Law  of  Volta,  or  Law  for  Contact-Series. 

— A  law  for  the  differences  of  electric  potential 
produced  by  the  contact  of  dissimilar  metals 
or  other  substances. 

"  The  difference  of  potential  between  any  two 
metals  is  equal  to  the  sum  of  the  differences  of 
potential  between  the  intervening  substances  in 
the  contact  series"  (See  Electricity,  Contact. 
Series,  Contact.) 

Law,  Pfliiger's A  given  tract  of 

nerve  is  stimulated  by  the  appearance  of 
kathelectrotonus  and  the  disappearance  of  an- 
eiectrotonus ;  not,  however,  by  the  disap- 


Law.J 


312 


[Law, 


pearance  of  kathelectrotonus  nor  by  ihe  ap- 
pearance of  anelectrotonus. — (Landois  and 
Stirling!) 

Law,  Pointing's At  any  point  in 

a  magnetic  field,  or  a  conductor  conveying 
current,  the  energy  moves  perpendicularly  to 
the  plane  containing  the  lines  of  electric  force 
or  the  lines  of  magnetic  force,  and  the  amount 
of  energy  crossing  the  unit  of  area  of  this 
plane  per  second  is  equal  to  the  product  of 
the  intensities  of  the  two  forces  multiplied  by 
the  sine  of  the  angle  between  them,  divided 
by  4*. 

If  E,  represents  the  electric  force  of  a  small  body 
charged  with  positive  electricity,  and  H,  the 
magnetic  force  or  forces  of  a  smaller  free  unit 
north  pole,  and,  if  these  forces  at  any  point  in 
the  magnetic  field  are  inclined  at  an  angle,  0, 
then  e,  the  flow  of  energy  per  second  at  this  point, 
in  a  direction  t>erpendicular  to  the  planes  of  E  and 
His, 

EH  sin.  9 

e  =  -^T— 

There  is,  therefore,  a  difference  in  the  direction 
of  the  flow  of  electricity  and  the  flow  of  electric 
energy.  Electricity  may  be  conceived  as  passing 
through  the  conductor  something  like  water 
through  a  pipe,  but  electrical  energy  does  not 
travel  in  this  way.  Electrical  energy  travels 
through  the  surrounding  dielectric,  which  is 
thereby  strained,  and  it  propagates  this  strain 
from  point  to  point  until  it  reaches  the  conductor 
and  is  there  dissipated. 

Law,  Yoltametric The    chemical 

action  produced  by  electrolysis  in  any  elec- 
trolyte is  proportional  to  the  amount  of  elec- 
tricity which  passes  through  the  electrolyte. 

This  is  called  the  Voltametric  law,  because  any 
vessel  containing  an  electrolyte,  and  furnished 
with  electrodes,  so  that  electrolysis  may  take  place 
on  the  passage  of  the  current,  and  is  provided 
with  means  for  measuring  the  amount  of  the 
electrolysis  which  occurs,  is  called  a  Voltameter. 
(See  Voltameter.  Electrolysis.} 

Laws,  Ampere's,  or  Laws  of  Electro- 
Dynamic  Attraction  and  Repulsion  — 

Laws  expressing  the  attractions  and  repul- 
sions of  electric  circuits  on  one  another  or 
en  magnets. 


Laws,  Dub's The  magnetism  ex- 
cited at  any  transverse  section  of  a  magnet  is 
proportional  to  the  square  root  of  the  distance 
between  the  given  section  and  the  near  end 
of  the  magnet." 

*'  The  free  magnetism  at  any  given  trans- 
verse section  of  a  magnet  is  proportional  to 
the  difference  between  the  square  root  of  half 
the  length  of  the  magnet  and  the  square  root 
of  the  distance  between  the  given  section  and 
the  nearest  end." 

Laws,  Kirchhofifs   —The  laws  for 

branched  or  shunted  circuits. 

These  laws  may  be  expressed  as  follows: 

(I.)  In  any  number  of  conductors  meeting  at  a 
point,  if  currents  flowing  to  the  point  be  considered 
as  -j->  and  those  flowing  away  from  it  as  — ,  the 
algebraic  sum  of  the  meeting  currents  witt  be 
zero. 

This  is  the  same  thing  as  saying  as  much  elec- 
tricity must  flow  away  from  the  point  as  flows  to- 
ward it. 

(2.)  In  any  system  of  closed  circuits  the  alge- 
braic sum  of  the  products  of  the  currents  into  the 
resistances  is  equal  to  the  electromotive  force  in 
the  circuit. 

In  this  case  all  currents  flowing  in  a  certain 
direction  are  taken  as  positive,  and  those  flowing 
in  the  opposite  direction  as  negative.  All  elec- 
tromotive forces  tending  to  produce  currents  in 
the  direction  of  the  positive  current  are  taken  as 
positive,  and  those  tending  to  produce  currents  in 
the  opposite  direction,  as  negative. 

E 

This  follows  from  Ohm's  law;  for,  since  C  =  — , 

R 

the  electromotive  force  E  =  CR,  and  this  is  tr»e, 
no  matter  how  often  the  circuit  is  branched. 

Laws,  Lenz's Laws  for  determining 

the  directions  of  currents  produced  by  electro- 
dynamic  induction. 

The  direction  of  the  currents  set  up  by  electra- 
dyriamic  induction  is  always  such  as  to  oppose 
the  tiotions  by  which  such  currents  were  pro- 
duced. 

Laws  of  Becquerel,  or  Laws  of  Mag- 
neto-Optic Rotation. — Laws  for  the  mag- 
neto-optic rotation  of  the  plane  of  polarization 
of  light.  (See  Rotation,  Magneto-Optic>. 

Laws  of  Coulomb,  o»*  Laws  of  Electro- 


Law.] 


313 


[Lea. 


static  and  Magnetic  Attractions  and  Re- 
pulsions. — Laws  for  the  force  of  attraction 
and  repulsion  between  charged  bodies  or  be- 
tween magnet  poles. 

The  fact  that  the  force  of  electrostatic  attrac- 
tion or  repulsion  between  two  charges,  is  directly 
proportional  to  the  product  of  the  quantities  of 
electricity  of  the  two  charges  and  inversely  propor- 
tional to  the  square  of  the  distance  between  them, 
is  known  as  Coulomb"1 's  Law.  Coulomb  also  as- 
certained that  the  attractions  and  repulsions  be- 
tvreen  magnet  poles  are  directly  proportional  to  the 
product  of  the  strength  of  the  two  poles,  and  in- 
versely proportional  to  the  square  of  the  distance 
between  them.  This  is  also  called  Coulomb's 
Law. 

Coulomb's  law,  in  order  to  be  accurate,  must 
take  into  account  the  specific  inductive  capacity 
of  the  intervening  medium.  The  correct  expres- 
sion for  the  force  between  two  quantities  q  and  q', 
of  electricity  -would  be,  therefore, 

'-3ft 

-where  K,  is  equal  to  the  specific  inductive  capacity 
of  the  medium  separating  the  two  charges. 

In  a  similar  manner  when  the  force  is  exerted 
between  two  magnet  poles,  to  be  accurate,  we  must 
take  into  account  the  magnetic  permeability  of 
the  medium  between  the  two  magnets.  The  cor- 
rect  expression  for  the  force  between  two  magnet 
poles  is,  therefore, 

mm; 
r*j*  ' 
-when  //,  is  the  magnetic  permeability. 

Laws  of  Faraday,  or  Laws  of  Electrolysis 

Laws  for  the   effects  of  electrolytic 

decomposition.     (See  Electrolysis.) 

These  laws  are  as  follows: 

(I.)  The  amount  of  an  electrolyte  decomposed 
is  directly  proportional  to  the  quantity  of  elec- 
tricity which  passes  through  it ;  or,  the  rate  at 
which  a  body  is  electrolyzed  is  proportional  to 
the  current  strength  producing  such  electrolysis. 

(2.)  If  the  same  current  be  passed  through  dif- 
ferent electrolytes,  the  quantity  of  each  ion 
evolved  is  proportional  to  its  chemical  equivalent. 

Laws  of  Joule.— Laws  expressing  the  de- 
velopment of  heat  produced  in  a  circuit  by  an 
electric  current. 

Tliese  laws  may  be  expressed  as  follows  : 

(I.)  The  amount  of  heat  developed  in  any  cir- 


cuit is  proportional  to  its  resistance,  providing 
the  current  strength  is  constant. 

(2.)  The  amount  of  heat  developed  in  any  cir- 
cuit is  proportional  to  the  square  of  the  current 
passing,  providing  the  resistance  is  constant. 

(3.)  The  amount  of  heat  developed  in  any  cir- 
cuit is  proportional  to  the  time  the  current  con- 
tinues. 

Or,  H  =  Cs  RtX0.24. 

Where  H,  equals  the  heat  in  small  calories,  C, 
equals  the  current  in  amperes,  R  equals  the  re- 
sistance in  ohms,  t,  equals  the  time  in  seconds, 
and  0.24,  the  heat-units  per  second  developed  in 
a  resistance  of  I  ohm  by  the  passage  of  I  am- 
pere. 

Lay  Torpedo.— (See  Torpedo,  Lay.) 

Layer,  Crookes'  -  —A  layer,  or 

stratum,  of  the  residual  atmosphere  of  a 
vacuous  space,  in  which  the  molecules,  recoil- 
ing from  a  heated  or  electrified  surface,  do 
not  meet  other  molecules,  but  impinge  on  the 
walls  of  the  vessel  directly  opposite  such 
heated  or  electrified  surface. 

A  Crookes  layer  may  result  as  the  effect  of 
two  different  causes,  viz. : 

(I.)  The  rarefaction  of  the  gas  is  such  that  the 
distance  between  the  walls  of  the  vessel  and  the 
heated  surface  is  less  than  the  mean-free-path  of 
the  molecules. 

(2.)  The  wall  is  so  near  the  heated  surface  that 
the  distance  between  the  two  is  less  than  the  ac- 
tual mean-free-path  of  the  molecules.  Under 
these  last-named  circumstances  Crookes'  layers 
may  result,  whatever  be  the  density  of  the  gas. 

Laying-Up  Cables.— (See  Cables,  Lay- 
ing-Up.) 

Lead,  Angle  of  —  —The  angular  devia- 
tion from  the  normal  position,  which  must  be 
given  to  the  collecting  brushes  on  the  com- 
mutator cylinder  of  a  dynamo-electric  ma- 
chine, in  order  to  avoid  destructive  burning, 
(See  Commutator,  Burning  at.) 

The  necessity  for  giving  the  collecting  brushes 
a  lead,  arises  both  from  the  magnetic  lag  and  from 
the  distortion  of  the  field  of  the  machine  by  the 
magnetization  of  the  armature  current.  The 
angle  of  lead  is,  therefore,  equal  to  the  sum  of  the 
angle  of  lag,  and  the  angular  distortion  due  to  th  e 
magnetization  produced  by  the  armature  current . 


Lea.] 


314 


[Lea. 


Lead,  Cable A  lead  containing  a 

conductor  formed  of  several  stranded  con- 
ductors, as  distinguished  from  a  wire  lead  or 
a  lead  containing  a  single  conductor. 

Lead,  Flexible A  conductor  formed 

of  a  number  of  small  stranded  conductors  for 
the  purpose  of  obtaining  flexibility. 

Lead,  Flexible  Twin A  flexible 

conductor  in  which  two  parallel  and  sepa- 
rately insulated  wires  are  placed. 

Lead  of  Brushes  of  Dynamo-Electric 
Machine. — The  angular  deviation  from  the 
normal  position,  which  it  is  necessary  to  give 
the  brushes  on  the  commutator  of  a  dynamo- 
electric  machine,  in  order  to  obtain  efficient 
action.  (See  Lead,  Angle  of.) 

Lead  Scoring  Tool.— (See  Tool,  Scoring, 
Lead) 

Lead  Sleeve.— (See  Sleeve,  Lead.) 

Lead,  Tee.— (See  Tee,  Lead) 

Lead,  Wire A  lead  consisting  of  a 

single  conductor,  as  distinguished  from  a 
cable  lead,  or  a  lead  containing  a  number  of 
stranded  conductors. 

Lead  Wire.— (See  Wire,  Lead) 

Leading  Horn  of  Pole  Pieces  of  Dynamo- 
Electric  Machine. — (See  Horns,  Leading,  of 
Pole  Pieces  of  a  Dynamo-Electric  Machine) 

Leading-Ill  Wires.— (See  Wires,  Lead- 
ing-In) 

Leading-Up  Wires.— (See  Wires,  Lead- 
ing- up) 

Leads. — The  conductors  in  any  system  of 
electric  distribution. 

In  distribution  by  parallel,  the  conductors 
through  which  the  current  flows  from  the  source 
are  sometimes  called  the  leads  in  contradis- 
tinction to  those  through  which  it  returns  to 
the  source. 

The  leads,  or  main  conductors,  in  a  multiple 
system  of  electric  lighting,  must  maintain  a  con- 
stant potential  at  the  lamp  terminals.  The  dimen- 
sions of  the  leads  are,  therefore,  so  proportioned  as 
to  absorb  as  small  an  amount  of  potential  as  pos- 
sible. Since,  in  incandescent  lighting,  where  the 
lamps  are  connected  to  the  leads  in  multiple-arc, 
the  total  resistance  of  the  lamps  is  comparatively 


small,  the  resistance  of  the  leads  must  be  quite 
small  in  order  to  avoid  a  marked  drop  of  poten- 
tial. Comparatively  large  conductors  must, 
therefore,  be  used. 

The  main  conductor  for  series  circuits,  such  as 
for  arc-lights,  has  in  all  parts  the  same  current 
strength.  Since  the  sum  of  the  resistances  of  the 
lamps  in  such  a  circuit  is  quite  high,  a  compara- 
tively high  resistance  in  the  conductor  may  be 
employed  without  a  proportionally  large  absorp- 
tion of  potential.  Comparatively  small  conduc- 
tors can  therefore  be  used.  (See  Electricity,  Dis- 
tribution of,  by  Constant  Currents.  Electricity, 
Distribution  of,  by  Alternating  Currents) 

Leads,  Armature,  Twist  in  —  —A  dis- 
placement of  the  ends  of  the  wires  connected 
to  the  commutator  segment,  with  respect  to 
the  position  of  the  coils  on  the  armature,  for 
the  purpose  of  obtaining  a  more  convenient 
position  for  the  diameter  of  commutation, 
that  is,  for  the  collecting  brushes. 

Leak,  Oscillatory -A  leak  or  grad- 
ual loss  of  electricity  which  takes  place  in 
alternately  opposite  directions. 

Leak,  Unidirectional — A  gradual 

loss  or  leakage  of  electricity  which  takes  place 
in  one  and  the  same  direction. 

The  term  has  been  employed  to  distinguish 
such  a  leak  from  an  oscillatory  leak. 

Leakage  Conductor.— (See  Conductor, 
Leakage) 

Leakage,  Electric The  gradual 

dissipation  of  a  current  due  to  insufficient  in- 
sulation. 

Some  leakage  occurs  under  nearly  all  circum- 
stances. On  telegraphic  lines,  during  wet 
weather,  the  leakage  is  often  so  great  as  to  inter- 
fere with  the  proper  working  of  the  lines. 

Leakage,  Electrostatic •  —The  grad- 
ual dissipation  of  a  charge  due  to  insufficient 
insulation. 

The  leakage  of  a  well  insulated  conductor, 
placed  in  a  high  vacuum,  is  almost  inappreciable. 
Crookes  has  maintained  electric  charges  in  high 
vacua  for  years  without  appreciable  loss. 

Leakage,  Lateral,  of  Lines  of  Magnetic 
Force The  failure  of  lines  of  magnetic 


Lea.] 


315 


[Leu. 


force  to  pass  approximately  parallel  to  one 
another  through  a  bar  of  iron  or  other  mag- 
netizable material,  when  it  has  come  to  rest 
in  a  magnetic  field  in  which  it  is  free  to 
move. 

The  escape  of  the  lines  of  magnetic  force 
from  the  sides  of  a  bar  or  other  similar 
magnet,  instead  of  from  the  poles  at  the 
end. 

When  a  bar  of  magnetizable  material,  sus- 
pended so  as  to  be  free  to  move,  comes  to  rest  in 
a  magnetic  field  in  which  it  is  undergoing  mag- 
netization, it  has  its  greatest  length  parallel  to 
the  direction  of  the  lines  of  force.  If  the  bar  is  a 
long,  thin,  straight  bar,  the  lines  of  force  do  not 
all  pass  in  or  come  out  at  its  ends.  On  the  con- 
trary, many  of  these  lines  of  force  or  induction 
pass  in  or  come  out  at  other  points.  The  mag- 
metic  induction  is,  therefore,  unequal  at  different 
sections  of  the  bar.  In  other  words,  the  mag- 
netic flux  or  intensity  is  not  constant  per  unit  of 
all  cross-sections  of  such  bar. 

Leakage,  Magnetic A  useless  dis- 
sipation of  the  lines  of  magnetic  force  of  a 
dynamo-electric  machine,  or  other  similar 
device,  by  their  failure  to  pass  through  the 
armature  where  they  are  needed. 

Useless  dissipation  of  lines  of  magnetic 
force  outside  that  portion  of  the  field  of  a 
dynamo-electric  machine  through  which  the 
armature  moves. 

Such  a  leakage  can  be  detected  by  an  instru- 
ment called  a  magnetophone.  (See  Magneto- 
phone.} 

Magnetic  leakage  results  in  lowering  the  effi- 
ciency of  the  dynamo.  (See  Co-efficient,  Econo- 
mic, of  a  Dynamo-Electric  Machine. ) 

Leclanche-'s  Voltaic  Cell.— (See  Ceff, 
Voltaic,  Lcclancht) 

Leg. — In  a  system  of  telephonic  exchange, 
where  a  ground  return  is  used,  a  single  wire, 
or,  where  a  metallic  circuit  is  employed,  two 
wires,  for  connecting  a  subscriber  with  the 
main  switchboard,  by  means  of  which  any 
subscriber  may  be  legged  or  placed  directly 
in  circuit  with  two  or  more  other  parties. 

Leg  of  Circuit.— (See  Circuit,  Leg  of.) 

Legal  Earth  Quadrant— (See  Quadrant, 

Legal  Earth.) 

H_Vol.  i 


Legal  Ohm.— (See  Ohm,  Legal) 

Legging-Key  Board.— (See  Board,  Leg- 
ging-Key) 

Length  of  Spark.— (See  Spark,  Length 

Lens,  Achromatic A  lens  the 

images  formed  by  which  are  free  from  the 
false  coloration  produced  in  other  lenses  by 
dispersion. 

An  ordinary  lens  can  be  rendered  approxi- 
mately achromatic  by  the  use  of  a  diaphragm. 
Achromatic  lenses  generally  consist  of  the  com 

D 


A 

Fig.  342.    Equal  and  Opposite  Refracting  Angles. 

bination  of  a  double  convex  lens  of  flint  glass  am? 
a  concave  lens  of  crown  glass. 

The  ray  of  light  entering  the  prism  A  B  Cj 

Fig.  342,  suffers  dispersion  (separation  into  pris- 

matic   colors).      This  dispersion   in   the  samr 

B 


A  C 

Fig.  3  43-    Principle  of  Achromatism. 

medium  is  proportional  to  the  angle  g,  between 
the  incident  and  emergent  faces,  called  the  re- 
fracting angle. 

If,  now,  another  prism  B  C  D,  of  the  same  ma- 
terial, with  a  refracting  angle  g',  equal  to  g,  is 
combined  with  the  first  prism  in  the  manner 
shown  in  Fig.  342,  it  will  produce  an  equal  but 
opposite  dispersion,  so  that  the  ray  of  light  will 
emerge  at  R',  free  from  rainbow  tints,  but  par- 
allel to  its  original  direction. 

The  variety  of  glass  called  crown  glass  pro- 
duces only  half  as  great  dispersion  of  light  as  the 
variety  called  fiint  glass,  under  the  same  refract- 


ten.]  316 

ing  angle  g.  If  the  prism  A  B  C,  of  crown  glass, 
Fig.  343,  whose  angle  g,  is  twice  as  great  as  the 
refracting  angle  g  ,  of  the  prism  B  C  D,  of  flint 
glass,  be  placed  together  in  the  manner  shown, 
then  the  ray  R,  will  be  transmitted  at  R',  free  from 
color,  but  will  not  emerge  par  ailed  to  its  original 
direction  ;  in  other  words,  it  suffers  refraction  or 
bending.  Consequently  such  a  combination  can 
be  used  to  free  a  pencil  of  light  from  false  colora- 
tion and  yet  permit  it  to  undergo  refraction, 
and  thus  act  as  a  lens.  (See  Refraction.") 

The  construction  ot  achromatic  lenses  is  based 
on  this  principle. 

The  crown  glass  is  generally  made  with  two 


fig.  344.     Piano-Convex 
Achromatic  Lens. 


345.    Ach 
Lens. 


convex  surfaces  ;  the  flint  glass,  with  one  con- 
cave and  one  plane  surface,  as  shown  in  Fig. 
344- 

Sometimes  both  surfaces  of  the  flint  glass  are 
made  curved,  as  in  Fig.  345. 

Lenz's  Law. — (See  Law,  Lenz's.) 

letter  Box,  Electric  -  —A  device 
that  announces  the  deposit  of  a  letter  in  a 
box  by  the  ringing  of  a  bell,  or  by  the  move- 
ment of  a  needle  or  index. 

These  devices  generally  act  by  the  closing  or 
opening  of  an  electric  circuit  on  the  fall  of  the 
letter  into  the  box. 


Leyden  Jar. — (See  Jar,  Ley  den.} 

Leyden  Jar  Pattery.— (See  Battery,  Ley- 
den  Jar!) 

Lichtenberg's  Dust  Figures.— (See  Fig- 
ures, Lichtenberg' s  Dust.) 

Life  Curve  of  Incandescent  Electric 
Lamp. — (See  Curve,  Life,  of  Incandescent 
Electric  Lamp.) 

Life  of  Electric  Incandescent  Lamp. — 
(See  Lamp,  Incandescent,  Life  of.) 

Light,  Auroral  —  — The  light  given  off 
during  the  prevalence  of  an  aurora.  (See 
Aurora  Eorealis.) 

Light,  Electric  —  —Light  produced  by 
the  action  of  electric  energy. 

Electric  light  is  produced  by  electric  energy  in 
various  ways,  the  most  important  of  which  are  as 
follows,  viz.: 

(I.)  By  the  passage  of  an  electric  discharge 
through  a  gas  or  vapor,  either  in  a  rarefied  condi- 
tion, at  ordinary  atmospheric  pressure,  or  at  pres- 
sures higher  than  that  of  the  ordinary  pressure. 
In  any  of  these  cases  the  gas  or  vapor  is  heated  to 
incandescence  by  the  passage  of  the  discharge. 

(2.)  By  the  incandescence  of  a  solid  by  the 
heating  power  of  the  current,  as  in  the  incandes- 
cent lamp. 

(3.)  By  the  incandescence  of  a  solid  by  the  ac- 
tion of  a  rapidly  alternating  electrostatic  field,  as 
in  Tesla's  incandescent  lamp. 

\4. )  By  the  volatilization  of  a  solid  and  the  form- 
ation thereby  of  a  voltaic  arc. 

(5.)  By  the  combination  of  the  effects  of  incan- 
descence and  the  voltaic  arc. 

The  amount  of  light  produced  in  proportion  to 
the  amount  of  energy  expended  to  produce  it 
is  probably  least  in  the  case  of  light  produced 
by  the  sparks  of  a  Wimshurst  or  Holtz  machine, 
or  as  in  (i),  than  in  any  other  case  in  which  electric 
energy  acts  to  produce  luminous  energy. 

Light,  Electric,  Pumping  of  —  —(See 
Pumping  of  Electric  Light) 

Light,  Intensity  of—  —The  brilliancy 
or  illuminating  powtr  of  a  light  as.  measured 
by  a  photometer  in  standard  candles  or  other 
standard  units.  (See  Photometer.  Candle, 
Standard) 

Light,  Maxwell's  Electro  -  Magnetic 
Theory  of  — A  hypothesis  for  the 


Us.] 


317 


cause  oi  light  proposed  by  Maxwell,  based 
on  the  relations  existing-  between  the  phe- 
nomena of  light  and  those  of  electro-magnet- 
ism. 

Maxwell's  electro-magnetic  theory  of  light  as- 
sumes that  the  phenomena  of  light  and  magnet- 
ism are  each  due  to  certain  motions  of  the  ether, 
electricity  and  magnetism  being  due  to  its  rota- 
tions, and  light  to  oscillations,  or  its  to-and-fro 
motions. 

Maxwell  proposed  this  theory  to  show  that  the 
phenomena  of  light,  heat,  electricity  and  magnet- 
ism could  all  be  explained  by  one  and  the  same 
cause,  viz.,  a  vibratory  or  oscillatory  motion  of 
the  particles  of  the  hypothetical  ether.  Maxwell 
died  before  completing  his  hypothesis,  and  it  has 
never  since  been  sufficiently  developed  to  thor- 
oughly entitle  it  to  the  name  of  a  theory.  This 
theory  has  more  recently  been  elaborated  by 
Hertz.  (See  Electricity,  Hertz's  Theory  of  Elec- 
tro-Magnetic Radiations  or  Waves) 

There  are,  however,  numerous  considerations 
which  render  it  probable  that  electric  and  mag- 
netic phenomena,  like  those  of  light  and  heat, 
have  their  origin  in  a  vibratory  or  oscillatory  mo- 
tion of  the  luminiferous  ether.  A  few  of  these, 
as  pointed  out  by  Maxwell,  S.  P.  Thompson, 
Lodge,  Larden  and  others,  are  as  follows: 

(i.)  It  is  possible  that  the  thing  called  elec- 
tricity is  the  ether  itself,  negative  electrification 
consisting  in  an  excess  of  the  ether,  and  positive 
electrification  in  a  deficit.  (See  Electricity,  Sin- 
gle-Fluid Hypothesis  of. ) 

(2.)  It  is  possible  that  electrostatic  phenomena 
consist  in  a  strain  or  deformation  of  the  ether. 
A  dielectric  may  differ  from  a  conductor  in  that 
the  former  may  have  such  an  attraction  for  the 
ether  as  to  give  it  the  properties  of  an  elastic 
solid,  while  in  the  latter  the  ether  is  so  free  to 
move  that  no  strain  can  possibly  be  retained  by 
it.  (See  Dielectric.  Conductor.) 

(3.)  Dielectrics  are  transparent  and  conductors 
are  opaque. 

There  are  exceptions  to  this  in  the  case  of  vul- 
canite and  many  other  excellent  dielectrics.  Nor 
should  this  similarity  be  expected  to  be  general  in 
view  of  the  well  known  differences  that  exist  be- 
tween diathermancy  and  transparency. 

(4.)  It  is  possible  that  an  electric  current  con- 
sists of  a  real  motion  ot  translation  of  the  ether 
through  a  conductor. 

(5.)  It  is  possible  that  electromotive  force  re- 


sults from  differences  of  ether  pressures.  This 
would  of  course  follow  from  (4). 

(6.)  The  vibrations  of  light  are  propagated  in 
a  direction  at  right  angles  to  the  direction  in 
which  the  light  is  moving.  The  magnetic  field 
of  a  current  is  propagated  in  planes  at  right 
angles  to  the  direction  in  which  the  current  is 
flowing. 

(7.)  It  is  possible  that  lines  of  electrostatic  and 
magnetic  force  consist  of  chains  of  polarized  ether 
particles. 

(8. )  The  velocity  of  propagation  of  light  agrees 
very  nearly  with  the  velocity  of  propagation  of 
electro-magnetic  induction.  (See  Ratio  Velocity.) 

(9. )  In  certain  axial  crystals  the  difference  of 
transparency  in  the  direction  of  certain  axes, 
corresponds  with  the  direction  in  which  such 
crystals  conduct  electricity. 

Recent  investigations  render  it  almost  certain 
that  light  and  electro-magnetic  waves  or  radia- 
tions are  one  and  the  same,  and,  therefore,  have 
the  same  velocity  of  propagation  through  free 
ether.  Through  fixed  ether,  that  is,  through  the 
ether  that  exists  between  the  molecules  of  differ- 
ent kinds  of  matter,  as  is  well  known,  the  velocity 
of  propagation  differs  with  different  substances. 
(See  Electricity,  Hertz's  Theory  of  Electro-Mag- 
netic Radiations  or  Waves. ) 

Light,    Northern (See    Aurora 

Eorealis.) 

Light,  Platinum-Standard The 

light  emitted  by  a  surface  of  platinum  one 
square  centimetre  in  area,  at  its  temperature 
of  fusion. 

This  is  called  the  Violle  Standard  and  is  ex- 
tensively used  in  France. 

Light,  Search,  Automatic A  search 

light  in  which  a  parallel  or  slightly  diverging 
beam  of  light  is  automatically  caused  to 
sweep  the  horizon,  and  thus  disclose  the  ap- 
proach of  a  torpedo  boat  or  other  similar 
danger. 

This  is  called  an  automatic  search  light  because 
it  may  be  caused  to  automatically  sweep  the  hori- 
zon, instead  of  being  manipulated  by  hand,  as 
usual. 

Light,  Search,  Electric An  electric 

arc  light  placed  in  a  focusing  lamp  before  a 
lens  or  mirror,  so  as  to  obtain  either  a  parallel 
beam  or  a  slightly  divergent  pencil  of  light 


318 


for  lighting  the  surrounding  space  for  pur- 
poses of  exploration. 

Light,  Southern —(See  Aurora 

Australis?) 

Light,  Tail A  light  displayed  at  the 

rear  end  of  trains  in  order  to  avoid  rear  colli- 
sions. (See  Railroads,  Block  System  for.} 

Lighter,  Cigar,  Electric An  ap- 
paratus for  electrically  lighting  a  cigar. 

A  cigar  lighter  consists  essentially  of  a  wire  or 
rod  of  refractory  substance,  rendered  incandes- 
cent by  the  passage  of  a  current  obtained  from  a 
voltaic  battery,  secondary  generator,  or  other 
electric  source. 

Lighter,  Electric,  Argand A  name 

sometimes  given  to  an  argand  electric  plain- 
pendant  burner.  (See  Burner,  Argand- 
Electric,  Plain-Pendant?) 

Lighter,  Electric,  Argand  Talve 

A  name  sometimes  given  to  an  argand  elec- 
tric ratchet-pendant  burner.  (See  Burner, 
Argand-Electric,  Ratchet-Pendant!) 

Lighthouse  Illumination,  Electric 

^-(See  Illumination,  Lighthouse,  Electric) 

Lighting,  Arc Artificial  illumina- 
tion obtained  by  means  of  an  arc  light. 

The  term  arc  lighting  is  used  in  contradistinc- 
tion to  incandescent  lighting.  In  the  United 
States,  and,  indeed,  generally,  a  number  of  arc 
lights  are  placed  in  series  on  the  line  circuit,  con- 
nected  generally  with  a  series  dynamo.  Each 
of  the  lamps  is  provided  with  a  safety  cut-out, 
which  cuts  out  or  removes  a  defective  lamp  from 
the  circuit  by  automatically  turning  or  switching 
the  current  through  a  shunt  of  low  resistance. 

Lighting,  Electric,  by  High  Frequency 

Currents A  system  of  electric  lighting, 

in  which  rods,  bars  or  filaments  of  carbon  or 
other  refractory  substances  are  raised  to  in- 
candescence when  placed  in  a  rapidly  alternat- 
ing electrostatic  field. 

This  system  of  electric  lighting  was  invented 
by  Nikola  Tesla.  Its  general  principles  will  be 
understood  from  an  inspection  of  Fig.  346. 

G,  is  a  dynamo  producing  alternating  currents 
.  of  comparatively  low  potential.  A  portion  of  its 
current  P,  acting  as  the  primary  of  an  induction 
coil,  induces  alternating  currents  of  high 


potential  in  the  secondary  circuit  S,  which, 
charging  the  condenser  C,  is  disruptively  dis- 
charged into  the  circuit  A,  provided  with  an  air 
gap  at  A'  through  P'.  The  inductive  action 
of  P',  on  S',  produces  oscillatory  currents  of 


Tesla' s  High  Frequency  Currents 
System  of  Light  ing. 

enormous  frequency  and  potential  in  the  second- 
ary circuits  connected  therewith.  In  the  ap- 
paratus shown  in  Fig.  346,  two  incandescent 
electric  lamps  are  connected  with  the  secondary 
circuit,  one  with  a  single  straight  filament,  and 
the  other  with  a  ball  conductor.  The  other 
terminal  of  S',  is  connected  to  the  walls  of  the 
room  to  be  lighted.  (See  Lamp,  Incandescent, 
Straight  Filament.  Lamp,  Electric,  Incandes- 
cent Ball.} 

Lighting,  Electric,  Central  Station 

— The  lighting  of  a  number  of  houses  or  other 
buildings  from  a  single  station,  centrally  lo- 
cated. 

Central  station  lighting  is  distinguished  from  iso- 
lated lighting  by  the  fact  that  a  number  of  sepa- 
rate buildings,  houses  or  areas,  are  lighted  by  the 
current  produced  at  a  single  station,  centrally 
located,  instead  of  from  a  number  of  separate 
electric  sources  located  in  each  of  the  houses,  etc., 
to  be  lighted.  (See  Electricity,  Distribution  of.) 

Lighting,  Electric  Gas Igniting 

gas  jets  by  means  of  electric  discharges. 

Electric  sparks  are  caused  to  pass  through  a 
jet  of  escaping  gas,  and  thus  to  light  it.  These 
sparks  are  obtained  from  a  spark-coil,  *.  e.,  a 
coil  of  insulated  wire  connected  in  series  with 
the  circuit  so  as  to  produce  an  extra  current  on 
the  sudden  breaking  of  the  circuit,  the  discharge 
of  which  produces  a  spark  capable  of  igniting  the 
gas.  In  cases  where  a  number  of  burners  are  to 
be  simultaneously  lighted  the  sparks  required  for 


Lig.] 


319 


[Lig. 


lighting  the  gas  are  obtained  from  the  secondary 
of  an  induction  coil  (See  Burner,  Automatic 
Electric.) 

Lighting,   Electric,    Isolated A 

system  of  electric  lighting  where  a  separate 
electric  source  is  placed  in  each  house  or 
area  to  be  lighted,  as  distinguished  from  the 
central  station  lighting,  where  electric  sources 
are  provided  for  the  production  of  the  current 
required  for  an  entire  neighborhood. 

Lighting,  Electric,  Long-Arc  System  of 

A  system  of  electric  lighting  in  which 

long  arcs  are  maintained  between  the  carbon 
electrodes. 

Lighting,    Electric,    Short-Arc    System 

A  system  of  electric  lighting  in  which 

short  voltaic  arcs  are  maintained  between  the 
carbon  electrodes. 

Systems  of  short  arcs  require  an  electromotive 
force  of  about  25  volts,  which  is  about  one-half 
that  employed  in  long  arcs.  To  develop  an 
equal  amount  of  heat  energy  in  a  short  arc  as  in 
a  long  arc,  therefore,  requires  that  the  current  be 
of  double  strength. 

The  greater  part  of  the  light  of  a  voltaic  arc 
is  given  off  from  a  tiny  crater,  which  is  formed  in 
the  end  of  the  positive  carbon.  In  the  short- arc 
system  the  crater  lies  so  near  the  negative  carbon 
that  much  of  its  light  is  necessarily  obscured,  and 
troublesome  shadows  are  sometimes  produced. 
The  long-arc  system  avoids  these  difficulties. 

Lightning. — The  spark  or  bolt  that  results 
from  the  disruptive  discharge  of  a  cloud  to 
the  earth,  or  to  a  neighboring  cloud.  (See 
Electricity,  Atmospheric.  Kite,  Franklin's?) 

Lightning  Arrester. — (See  Arrester, 
Lightning?) 

Lightning,    Back-Stroke   of An 

electric  discharge,  caused  by  an  induced 
charge,  which  occurs  after  the  direct  dis- 
charge of  a  lightning  flash. 

The  shock  is  not  caused  by  the  lightning  flash 
itself,  but  most  probably  by  a  charge  which  is  in- 
duced in  neighboring  conductors  by  the  discharge. 
A  similar  effect  may  be  noticed  by  standing  near 
the  conductor  of  a  powerful  electric  machine, 
when  shocks  are  felt  at  every  discharge. 

The  back-stroke  has  been  ascribed  by  many  to 


the  oscillations  by  which  a  disruptive  discharge 
is  effected.  (See  Discharge,  Oscillating.) 

The  effects  of  the  return  shock  are  sometimes 
quite  severe.  They  are  often  experienced  by 
sensitive  people,  on  the  occurrence  ot  a  lightning 
discharge,  at  a  considerable  distance  from  the 
place  where  the  discharge  occurred. 

In  some  instances,  the  return  stroke  has  been 
sufficiently  intense  to  cause  death.  In  general, 
however,  its  effects  are  much  less  severe  than 
those  of  the  direct  lightning  discharge. 

Lightning,  Ball A  name  some- 
times given  to  globular  lightning.  (See 
Lightning,  Globular?) 

Lightning,  Chain A  variety  of 

lightning  flash  in  which  the  discharge  takes 
a  rippling  path,  somewhat  resembling  a 
chain. 

Lightning  Conductor.— (See  Rod,  Light- 
ning?) 

Lightning,  Forked A  variety  of 

lightning  flash,  in  which  the  discharge,  on 
nearing  the  earth  or  other  object,  divides  into 
two  or  more  branches. 

Lightning,  Globular A  rare  form 

of  lightning,  in  which  a  globe  of  fire  appears, 
which  quietly  floats  for  a  while  in  the  air  and 
then  explodes  with  great  violence. 

The  exact  cause  of  globular  lightning  is  un- 
known. Phenomena  allied  to  it,  however,  have 
been  observed  by  Plants  during  the  series  dis- 
charge of  his  rheostatic  machine.  Similar  pheno- 
mena are  sometimes,  though  rarely,  observed 
during  the  discharge  of  a  powerful  Leyden  battery. 
Sir  Wm.  Thomson  ascribes  the  effect  to  an  optical 
illusion  due  to  the  persistence  of  the  visual  impres- 
sion of  a  bright  flash.  This,  however,  would  not 
account  for  the  explosion  which  almost  invariably 
attends  globular  lightning. 

Lightning  Guard.— (See  Guard,  Light- 
ning?) 

Lightning,  Heat—  —A  variety  of 
lightning  flash  in  which  the  discharge  lights 
up  the  surfaces  of  the  neighboring  clouds. 

Sheet  lightning  is  unaccompanied  by  thunder. 
It  may  be  regarded  as  a  brush  discharge  from  one 
cloud  to  another. 

Heat  lightning  is  a  variety  of  sheet  lightning. 
(See  Lightning,  Sheet.) 


320 


[Lin. 


Lightning  Jar.— (See  Jar,  Lightning) 
Lightning,    Return-Stroke    of—     —A 

term  sometimes  applied  to  the  back-stroke  of 
lightning.  (See  Lightning,  Back-Stroke  of.} 

Lightning  Rod.— (See  Rod,  Lightning) 

Lightning  Rod  for  Ships.— (See  Rod, 
Lightning,  for  Ships.) 

Lightning,  Sheet A  variety  of 

lightning  flash  unaccompanied  by  any  thunder 
audible  to  the  observer,  in  which  the  entire 
surfaces  of  the  clouds  are  illumined. 

The  cause  of  sheet  lightning  has  been  ascribed 
to  reflection  from  clouds  of  lightning  flashes 
that  occur  too  far  below  the  horizon  either  to 
permit  them  to  be  directly  seen,  or  the  thunder 
to  be  heard. 

If  a  Geissler  tube,  which  contains  several  con- 
centric tubes,  be  charged  by  a  Holtz  machine, 
and  then  touched  at  different  parts  by  the  hands, 
a  succession  of  luminous  discharges  will  be  seen 
in  the  dark,  that  bear  a  remarkable  resemblance 
to  the  flashes  of  heat  or  sheet  lightning. 

Lightning  Stroke.— (See  Stroke,  Light- 
ning.) 

Lightning  Stroke,  Back  or  Return 

— (See  Stroke,  Lightning,  Back  or  Return) 

Lightning,  Summer A  name  some- 
times given  to  heat  lightning.  (See  Light- 
ning, Heat) 

Lightning,  Volcanic The  lightning 

discharges  that  attend  most  volcanic  erup- 
tions. 

Volcanic  lightning  is  possibly  sometimes  due  to 
the  friction  of  volcanic  dust  particles  against  one 
another,  or  against  the  air,  but  is  more  probably 
caused  by  the  sudden  condensation  of  the  water 
vapor  that  is  generally  disengaged  during  volcanic 
eruptions. 

Lightning,  Zigzag  —  —The  common- 
est variety  of  lightning  flashes,  in  which  the 
discharge  apparently  assumes  a  forked  zig- 
zag, or  even  a  chain-shaped  path. 

This  form  is  seen  in  the  discharge  of  a  Holtz 
machine,  or  of  a  Ruhmkorff  Induction  Coil. 

Photographic  pictures  of  such  lightning  dis- 
charges appear  to  show  that  these  discharges  are 
in  reality  zigzag  curves,  rather  than  sharp  angu- 
lar zigzags. 


Limiting  Stop.— (See  Stop,  Limiting) 

Limb,  Rheoscopic A  term  some- 
times applied  to  a  sensitive  nerve  muscle  prep- 
aration, employed  to  detect  the  presence  of 
an  electric  current.  (See  Frog,  Galvano- 
scope) 

Line. — A  wire  or  other  conductor  connect- 
ing any  two  points  or  stations. 

Line,  Aclinic A  line  connecting 

places  on  the  earth's  surface  which  have  no 
magnetic  inclination. 

The  magnetic  equator  of  the  earth.  (See 
Equator,  Magnetic) 

Line  Adjuster. — An  instrument  invented 
by  Delany  for  overcoming  the  effects  of  leak- 
age on  the  adjustment  of  the  relays  in  a  way 
line. 

When  any  key  is  opened,  the  line  circuit  is 
simultaneously  broken  at  both  ends  so  that  there 
is  a  moment  of  no  current,  which  causes  all  the 
relays  to  respond. 

Line,  Aerial An  air  line  as  dis- 
tinguished from  an  underground  conductor. 

Line,  Agonic A  line  connecting 

places  on  the  earth's  surface  where  the  mag- 
netic needle  has  no  declination,  or  where  it 
points  to  the  true  geographical  north.  (See 
Agonic) 

Line,  Artificial A  line  so  made  up 

by  condensers  and  resistance  coils  as  to  have 
the  same  inductive  effects  on  charging  or  dis- 
charging as  an  actual  telegraph  line. 

In  duplex  telegraphy  by  the  differential  method, 
the  artificial  line  used  must  have  its  capacity 
balanced  against  that  of  the  line,  so  as  to  avoid 
the  effects  of  self-induction,  and  other  effects  pro- 
duced by  charging  and  discharging. 

Line,  Capacity  of  —  —The  ability  of  a 
line  or  cable  to  act  like  a  condenser-  and 
therefore  like  it  to  possess  a  capacity.  (See 
Cable,  Capacity  of) 

Line  Circuit.— (See  Circuit,  Line) 

Line  Circuit,  Telegraphic (See 

Circuit,  Line,  Telegraphic) 

Line,  Neutral,  of  a  Magnet A  line 

joining  the  neutral  points  of  a  magnet  o«f 


Lin.J 


321 


[Lin. 


points  approximately  midway  between  the 
poles. 

This  is  sometimes  called  the  equator  of  the 
magnet. 

The  neutral  point  is  the  point  where  the  lines 
of  force  outside  the  magnet  extend  parallel  to  the 
surface  of  the  magnet. — (Hering.) 

Line,  Neutral,  of  Commutator  Cylinder 

A  line  on  the  commutator  cylinder  of 

a  dynamo-electric  machine  connecting  the 
neutral  points,  or  the  points  of  maximum 
positive  and  negative  difference  of  potential. 
(See  Mac/izne,  Dynamo-Electric.} 

Line  of  Least  Sparking.— (See  Sparking, 
Least  Line  of.) 

Line,  Single-Wire A  term  some- 
times used  for  a  solid-wire  conductor.  (See 
Line,  Solid.) 

Line,  Solid  — A  line  formed  of  a 

single  conductor,  as  distinguished  from  a  line 
formed  of  several  conductors  or  by  a  stranded 
cable. 

Line,  Stranded A  line  formed  of 

several  strands  or  separate  conductors  twisted 
into  one. 

Line,  Telegraphic,  Telephonic,  etc. 

— The  conducting  circuit  provided  for  the 
transmission  of  the  electric  impulses  or  cur- 
rents employed  in  any  system  of  electric 
transmission. 

Line,  Telpher The  conducting  line 

used  in  a  system  of  telpherage.  (See  Tel- 
pherage.) 

Line,  Through A  line  extending 

between  two  terminal  points,  as  distinguished 
from  a  line  containing  way  stations. 

Line,  Trunk In  a  system  of  tele- 
phonic communication  any  line  connecting 
distant  stations  and  used  by  a  number  of 
subscribers  at  each  end  for  purposes  of  inter- 
communication. 

Line,  Way A  line  communicating 

with  way  stations. 

Line  Wire.— (See  Wire,  Line.) 

Lineman.— One  who  puts  up  and  repairs 
line  circuits  and  attends  to  the  devices  con- 
nected therewith. 


In  a  system  of  electric  lighting  the  lineman 
attends  to  carboning  the  lamps,  cleaning  the 
lamp  rods,  and,  generally,  to  the  minor  details  of 
the  lines,  insulators  and  the  electro- receptive  de- 
vices placed  on  the  line. 

Lines,  Halleyan A  term  sometimes 

applied  to  the  isogonal  lines. 

The  isogonal  lines  are  sometimes  called  the 
Halleyan  lines,  from  Halley,  who  published  the 
first  chart  of  such  lines  in  the  year  1701. 

Lines,  Isobaric Lines  connecting 

places  on  the  earth's  surface  which  simulta- 
neously have  the  same  barometric  pressure. 

The  isobaric  lines  are  sometimes  called  isobars. 

Lines,  Isoclinic  —  —Lines  connecting 
places  that  have  the  same  angle  of  magnetic 
dip  or  inclination.  (See  Dip,  Magnetic) 

Lines,  Isodynamic Lines  connect- 
ing places  which  have  the  same  total  mag- 
netic intensity. 

The  magnetic  intensity  of  a  place  is  determined 
by  the  number  of  oscillations  that  a  small  mag- 
netic needle,  moved  from  its  position  of  rest  in 
the  magnetic  meridian  of  any  place,  makes  in  a 
given  time.  This  method  is  similar  to  that  em- 
ployed for  determining  the  intensity  of  gravity  at 
any  place  by  observing  the  number  of  oscillations 
that  a  pendulum  of  a  given  length  makes  in  a 
given  time  at  that  place.  If,  for  example,  a  mag- 
netic needle  at  one  place  makes  211  oscillations  in 
ten  minutes,  and  245  in  the  same  time  at  another 
place,  then  the  relative  intensities  of  magnetism 
at  these  places  are  as  the  squares  of  those  num- 
bers, or  as  44,521  :  60,025,  or  as  I  :  1.348. 

Lines,  Isogonal Lines  connecting 

places  that  have  the  same  magnetic  declina- 
tion.    (See  Declination^) 

Lines,  Isogonic A  term  sometimes 

used  for  isogonal  lines.    (See  Lines,  Isogonal^} 

Lines,  Isothermal Lines  connect- 
ing points  or  places  which  have  the  same 
mean  temperature. 

Lines,  Kapp A  term  proposed  by 

Mr.  Gisbert  Kapp  for  a  unit  of  lines  of  mag- 
netic force. 

One  Kapp  line  =  6,000  C.  G.  S.  magnetic  lines. 

Since  there  are  6.4514  square  centimetres  in  a 
square    inch,    i    Kapp    line    per    square    inch 
6,000 
'-45 14 


Lin.] 


322 


[Loc. 


The  total  number  of  Kapp  lines  passing  through 
a  magnet  and  air  space  is  equal  to  the  ampere 
turns  divided  by  the  total  magnetic  reluctance  in 
the  magnetic  circuit. — (Urquhart.) 

Lines  of   Electric   Displacement.— (See 

Displacement,  Electric,  Lines  of.) 

Lines  of  Electrostatic  Force.— (See  Force, 
Electrostatic,  Lines  of.) 

Lines  of  Force,  Cutting  —  —(See  Force, 
Lines  cf,  Cutting?) 

Lines  of  Force,  Direction  of  —  —(See 
Force,  Lines  of,  Direction  of.) 

Lines  of  Inductive  Action.— (See  Action, 
Inductive,  Lines  of) 

Lines  of  Magnetic  Force. — (See  Force, 
Magnetic,  Lines  of.) 

Lines  of  Magnetic  Force,  Conducting 

Power  for (See  Force,  Magnetic, 

Lines  of.  Conducting  Power  for.) 

Lines  of  Magnetic  Induction. — (See  In- 
duction, Magnetic,  Lines  of.) 

Lines,  Overhead  —  — A  term  applied 
to  telegraph,  telephone  and  electric  light  or 
power  lines  that  run  overhead,  in  contradis- 
tinction to  similar  lines  placed  underground. 

Lines,  Vortex-Stream Lines  ex- 
tending in  the  direction  in  which  the  particles 
of  a  fluid  are  moving. 

A  vortex  stream  is  supposed  to  be  composed  of 
a  number  of  vortex-stream  lines. 

Linked  Magnetic  and  Electric  Chain.— 
(See  Chain,  Linked  Magnetic  and  Electric.) 

Links,  Fuse  —  — Strips  or  plates  of 
fusible  metal  in  the  form  of  links,  employed 
for  safety  fuses  for  incandescent  or  other 
circuits. 

Liquid,  Bright  Dipping  —  —A  liquid 
used  in  electro-plating  for  dipping  articles 
preparatory  to  electro-plating,  so  as  to  insure 
a  bright  plating  deposit  on  them  when  after- 
wards subjected  to  the  plating  process. 

A  bright  dipping  liquid  is  prepared  by  the  ad- 
dition of  I  volume  of  common  table  salt  to  a 
mixture  of  loo  volumes  each  of  sulphuric  and 
nitric  acids.  For  small  objects  or  articles  of 
copper,  or  other  readily  corroded  metals,  the 


above  solution  is  diluted  by  the  addition  of  one- 
eighth  its  volume  of  water. 

Liquid,   Electropoion A  battery 

liquid  consisting  of  i  pound  of  bichromate 
of  potash  dissolved  in  10  pounds  of  water,  to 
which  2±  pounds  of  commercial  sulphuric 
acid  has  been  gradually  added. 

This  liquid  is  employed  with  the  carbon-zinc 
cell  or  the  bichromate  of  potash  cell. 

Liquid,  Exciting,  of  Voltaic  Cell  — 

The  electrolyte  or  liquid  in  a  voltaic  cell, 
which  acts  on  the  positive  plate. 

Liquid  Level  Alarm. — (See  Alarm,  Water 
or  Liquid  Level.) 

Liquid  Resistance  Load. — (See  Load 
Liquid  Resistance?) 

Liquid,  Stripping A  liquid  em- 
ployed to  remove  a  coating  of  one  metal 
from  the  surface  of  another,  without  affecting 
the  other  metal. 

The  character  of  the  stripping  liquid  used  will 
depend  on  the  kind  of  metal  to  be  removed,  and 
whether  the  stripping  is  to  be  accomplished  by 
solution  effected  by  chemical  action,  or  by  electro- 
lytic action. 

Liquid,  Specific  Resistance    of  - 
(See  Resistance,  Specific,  of  Liquid.) 

Liquor,  Spent  —  —Any  liquor,  such  as 
that  in  the  acid  or  other  baths  used  in  electro- 
plating, that  has  become  weakened  by  use. 

Listening  Cam. — (See  Cam,  Listening?) 

Load,  Liquid  Resistance  —  —  An  artk 
ficial  load  for  a  dynamo-electric  machine, 
consisting  of  a  mass  of  liquid  interposed  be- 
tween electrodes. 

A  liquid  is  generally  rendered  better  conduct- 
ing by  the  addition  of  a  small  quantity  of  soluble 
salt,  such,  for  example,  as  sulphate  of  soda. 

Local  Action  of  Dynamo-Electric  Ma- 
chine.— (See  Action,  Local,  of  Dynamo- 
Electric  Machine?) 

Local  Action  of  Voltaic  Cell.— (See  Ac* 
tion,  Local,  of  Voltaic  Cell.) 

Local  Battery.— (See  Battery  Local.) 

Local  Battery  Circn't— (See  Circuit 
Local-Battery?) 


Loc.] 


323 


[Loo. 


Local  Currents. — (See  Currents,  Local.) 

Local  Faradization. — (See  Faradization, 
Local) 

Local  Galvanization. — (See  Galvaniza- 
tion, Local.) 

Localization  of  Faults.— (See  Faults, 
Localization  of.) 

Lock,  Electric A  lock  that  is  au- 
tomatically unlocked  by  the  aid  of  electricity. 

The  electric  lock  is  so  arranged  that  the  action 
of  a  push  button  at  a  distance  unlocks  the  door. 
A  speaking  tube  communicates  with  the  house, 
and  the  pressing  of  a  push  button  on  any  floor  of 
the  house  unlocks  the  door.  The  mere  shutting 
of  the  door  locks  it. 

A  form  of  electric  lock  is  shown  in  Fig.  347. 


-  347-     Electric  Lock. 


Locomotive,  Electric  --  A  railway 
engine  whose  motive  power  is  electricity. 
(See  Railroads,  Electric) 

Locomotive  Head  Light,  Electric  -- 

(See  Head  Light,  Locomotive) 

Lodestone.  —  A  name  formerly  applied  to 
an  ore  of  iron  (magnetic  iron  ore)  ,  that  natu- 
rally possesses  the  power  of  attracting  pieces 
of  iron  to  it. 

Lodestone,  or  magnetic  iron  ore,  must  be  re- 
garded as  a  magnetizable  substance  that  has  be- 
come permanently  magnetic  from  its  situation  in 
the  earth's  magnetic  field.  Such  beds  of  ore 
concentrate  the  lines  of  the  earth's  magnetic  field 
on  chem,  and  thus  become  magnetic. 


Lodge's  Standard  Voltaic  Cell.  —(See 
Cell,  Voltaic,  Standard,  Lodge's) 

Log,  Electric An  electric  device 

for  measuring  the  speed  of  a  vessel. 

A  log,  operated  by  the  rotation  of  a  wheel,  is 
caused  to  register  the  number  of  its  rotations  by  a 
step-by-step  recording  apparatus  operated  by 
breaks  in  the  circuit,  made  during  the  rotation 
of  the  wheel,  at  any  given  number  of  turns,  say 
loo,  or  some  other  convenient  multiple.  Such  a 
log  may  be  kept  constantly  in  the  water,  and  ob- 
served when  required,  or  it  can  be  caused  to 
make  a  permanent  record  of  its  actual  speed  at 
any  time  during  the  entire  run. 

Logarithm, — The  exponent  of  the  power 
to  which  it  is  necessary  to  raise  a  fixed  num- 
ber, in  order  to  produce  a  given  number. 

A  table  of  logarithms  enables  the  operations  of 
multiplication,  division,  the  raising  of  powers, 
and  the  extraction  of  roots,  to  be  readily  per- 
formed by  simple  addition,  subtraction,  multi- 
plication or  division,  respectively.  When  thor- 
oughly understood,  logarithms  greatly  reduce  the 
labor  of  mathematical  calculations.  For  the  man- 
ner in  which  they  are  used,  the  student  is  referred 
to  any  standard  work  on  mathematics. 

Logarithmic  Curve. — (See  Curve,  Loga- 
rithmic) 

Long-Coil  Magnet. — (See  Magnet,  Lcng- 
Coil.) 

Long-Core  Electro-Magnet. — (See  Mag- 
net, Electro,  Long-Core.) 

Long-Shunt  Compound- Wound  Dynamo- 
Electric  Machine. — (See  Machine,  Dyna- 
mo-Electric, Compound-  Wound,  L  o  ng- 
Shunt.) 

Longitude,   Electric   Determination    of 

The  determination  of  the  longitude  of 

a  place,  by  differences  in  time  between  it  and 
a  place  on  the  prime  meridian,  as  simultane- 
ously determined  telegraphically. 

In  determinations  of  this  character  allowance 
must  be  made  for  the  retarding  effects  of  long 
telegraphic  lines,  or  cables. 

Loom,  Electric A  device  by  means 

of  which  Jacquard  cards  in  the  ordinary  loo' 
are  replaced  by  a  simple  perforated   metal 
plate,  the  perforations  in  which  correspond 
to  those  in  the  Jacouard  card. 


Loo.] 


[Lnx. 


The  necessary  movements  are  effected  by 
means  of  electro-magnets. 

Loop  Break.— A  device  for  introducing  a 
loop  in  a  break  made  at  any  part  of  a  circuit. 

The  rigidity  of  the  line  wire,  between  the  points 
of  attachment  of  the  loop  introduced,  is  main- 
tained by  means  of  some  inflexible  non-conducting 
material  inserted  in  the  break. 

Loop  Circuit— (See  Circuit,  Loop.} 

Loop,  Drip An  inclined  loop  placed 

where  the  outside  conductors  enter  a  build- 
ing. 

The  inclination  is  upwards  towards  the  point 
of  entrance  to  the  building.  This  device  of 
a  drip  loop  is  adopted  for  the  purpose  of  prevent- 
ing the  rain  water  from  flowing  along  the  inclined 
wire  into  the  building.  This  is  effected  by  making 
the  wire  incline  from  the  building,  thus  throwing 
the  drainage  from  the  building. 

Loop,  Electric A  portion  of  a  main 

circuit  consisting  of  a  wire  going  out  from 
one  side  of  a  break  in  the  main  circuit  and 
returning  to  the  other  side  of  the  break. 

Loops  are  employed  for  the  purpose  of  con- 
necting a  branch  telegraph  office  with  the  main 
line;  for  placing  one  or  more  electric  arc  lamps 
on  the  main  line  circuit;  for  connecting  a  mes- 
senger call  or  telephone  circuit  with  a  main  line; 
and  for  numerous  similar  purposes. 

Loops  of  Force. — (See  Force,  Loops  of.) 

Loops  of  Mutual  Induction. — (See  Induc- 
tion, Mutual,  Loops  of.) 

Low-Resistance  Magnet.— (See  Magnet, 
Low-Resistance.) 

Low-Tension  Electric  Fuse. — (See  Fuse, 
Electric,  Low-  Tension.) 

Loxodrograph. — An  apparatus  for  electri- 
cally recording  on  paper  the  actual  course  of 
a  ship  by  the  combined  action  of  magnetism 
and  photography. 

Luces.— Plural  of  lux.    (See  Lux.) 

Luminescence.— A  limited  power  of  emit- 
ting light,  possessed  by  certain  bodies  which 
have  previously  acquired  potential  energy  by 
exposure  to  light  or  radiant  energy. 

The  term  luminescence  was  proposed  by  E. 
Wiedemann  to  cover  the  case  of  the  emission  of 


light  under  circumstances  differing  from  the  emis- 
sion or  radiation  of  light  by  incandescence.  Lu- 
minescence applies  to  the  case  of  a  radiation, 
generally  selective  in  character,  that  is  apparently 
due  to  effects  allied  to,  or  the  same  as,  those  of 
fluorescence  and  phosphorescence.  For  example, 
magnesium  oxide  or  zinc  oxide,  when  heated 
above  a  certain  critical  temperature,  radiates  far 
more  light  than  equally  hot  carbon. 

The  spectrum  of  such  luminescent  light  is  espe- 
cially rich  in  certain  wave  lengths.  The  ability 
of  the  substance  to  continue  to  furnish  this  extra 
light  is,  however,  limited.  After  a  comparatively 
short  time,  the  additional  light,  or  selective  radia- 
tion, disappears.  The  luminescent  light  is  appa- 
rently due  to  molecular  potential  energy  stored  in 
the  substance  during  its  exposure  to  light.  Lumi- 
nescence may  be  developed  in  bodies  in  the  fol- 
lowing manner,  viz. : 

(I.)  By  heat. 

(2.)  By  chemical  action. 

(3.)  By  friction. 

(4. )  By  exposure  to  the  sun,  or  by  actual  impact 
of  light  waves. 

(5.)  By  electricity.  . 

(6.)  By  vital  forces,  as  in  the  fire  fly,  or  the 
glow  worm. 

Luminescence,  Rejuvenation  of 

Reimparting  by  exposure  to  light,  or  any  other 
suitable  means,  the  power  of  luminescence  to 
a  substance  after  it  has  lost  this  power. 

Luminous  Absorption. — (See  Absorption, 
Luminous.) 

Lunar  Inequality  of  Earth's  Magnetic 
Variation  or  Inclination.  —(See  Inequality, 
Lunar,  of  Earth's  Magnetic  Variation  or 
Inclination.) 

Lunar  Inequality  of  Earth's  Magnetism. 

— (See  Inequality,  Lunar,  of  Earth's  Mag- 
netism.) 

Lux.— A  name  proposed  by  Preece  for  the 
unit  of  intensity  of  illumination. 

The  illumination  given  by  a  standard 
candle  at  the  distance  of  12.7  inches. 

The  illumination  given  by  I  carcel  at  the 
distance  of  r  metre. 

The  illumination  given  by  a  lamp  of  10,000 
candles  at  105.8  feet.  (See  Illumination 
Unit  of.) 


325 


[Mac. 


M. — A  contraction  sometimes  used  to  ex- 
press a  gaseous  pressure  of  the  .oooooi  'of 
an  atmosphere. 

I, coo, oc»  M.  equals  760  mm.  of  mercury  or  I 
atmosphere  of  pressure. 

A  vessel  containing  air,  which  has  been  ex- 
hausted to  the  .oooooi  of  its  pressure  at  760 
mm.,  or  one  atmosphere,  has  a  pressure  or  ten- 
sion  of  I  M. 

This  contraction  is  used  by  Crookes  in  his  re- 
searches on  the  properties  of  radiant  matter.  (See 
Matter,  Radiant,  or  Ultra  Gaseous. ) 

yu. — A  contraction  used  in  mathematical 
writings  for  magnetic  permeability,  or  the 
specific  conductibility  of  any  substance  for 
lines  of  magnetic  force. 

mm. — A  contraction  for  millimetre.  (See 
Weights,  French  System  of.} 

M.  P.  H. — A  contraction  sometimes  used  in 
railroad  work  to  indicate  miles  per  hour. 

Machine,  Armstrong's  Hydro-Electric 

A  machine  for  the  development  of 

electricity  by  the  friction  of  a  jet  of  steam 
passing  over  a  water  surface. 

Steam  generated  in  a  suitably  insulated  boiler, 


Fig.  348.     Armstrong's  Hydro- Electric  Machine. 

Fig.  348,  is  allowed  to  escape  through  a  tortuous 
nozzle,  from  a  series  of  apertures  opposite  a 
pointed  comb,  attached  to  an  insulated  conductor. 


The  cooling  of  the  steam  during  its  passage 
through  a  flat  box,  termed  the  cooling  box,  con- 
nected with  the  nozzles,  causes  a  partial  condensa- 
tion, so  that  the  box  always  contains  a  small 
quantity  of  water. 

The  friction  of  the  drops  of  water  against  the 
orifice,  and,  possibly,  their  friction  against  the 
water  surface  itself,  are  the  cause  of  the  electricity 
produced. 

A  conductor  connected  with  the  pointed  comb 
furnishes  positive  electricity.  The  boiler  fur- 
nishes negative  electricity.  The  hydro-electric 
machine  is  not  a  very  economical  source  of  elec- 
tricity, and  is  'only  employed  for  experimental 
purposes.  1 1  was  discovered  accidentally  through 
a  shock  given  to  an  engineer,  who  placed  his 
hand  in  a  jet  of  steam  escaping  from  a  leaking 
boiler  he  was  endeavoring  to  mend.  The  causes 
were  first  studied  by  Sir  Wm.  Armstrong,  who, 
in  1840,  devised  the  apparatus  just  described. 

Machine,  Dynamo-Electric  — A 

machine  for  the  conversion  of  mechanical 
energy  into  electrical  energy,  by  means  of 
magneto-electric  induction. 

The  term  is  also  applied  to  a  machine  by 
means  of  which  electrical  energy  is  converted 
into  mechanical  energy  by  means  of  magneto- 
electric  induction.  Machines  of  the  latter  class  are 
generally  called  motors,  those  of  the  former, 
generators, 

Prof.  S.  P.  Thompson  defines  a  dynamo-elt-c- 
tric  machine  as  follows,  viz.:  "A  machine  for 
converting  energy  in  the  form  of  mechanical 
power  into  energy  in  the  form  of  electric  currents, 
or  vice  versa,  by  the  operation  of  setting  con- 
ductors (usually  in  die  form  of  coils  of  copper 
wire)  to  rotate  in  a  magnetic  field,  or  by  vary- 
ing a  magnetic  field  in  the  presence  of  conduc- 
tors." 

The  term  dynamo  was  first  applied  to  such 
machines,  because  in  the  form  in  which  this 
machine  first  appeared,  viz.:  the  series- wound 
machine,  it  was  self-exciting,  or  required  no  ex- 
citement other  than  what  it  received  by  the  rota- 
tion of  its  armature  in  the  field  of  its  magnets, 
or,  indeed,  in  the  field  of  the  earth.  (See  Machine, 
Dynamo -Electric,  Reaction  Principle  of. ) 

A  dynamo -electric  generator,  or  a  dynamo-elec 


Mac.]  326 

*ric  machine  proper,  consists  of  the  following 
parts,  viz.: 

(i.)  The  revolving  portion,  usually  the  arma- 
ture, in  which  the  electromotive  force  is  developed, 
which  produces  the  current. 

It  must  be  borne  in  mind  that  it  is  not  current, 
but  difference  of  electric  potential ',  or  electromotive 
forte,  that  is  developed  by  any  electric  source 
from  which  a  current  is  obtained.  For  ease  of 
reference,  however,  we  will  speak  of  an  electric 
current  as  being  generated  by  the  armature,  or  by 
the  source.  No  ambiguity  will  be  introduced  if 
the  student  bears  the  above  in  mind. 

(2.)  The  field magnets,  which  produce  the  field 
in  which  the  armature  revolves. 

(3.)  h2  pole  pieces,  or  free  terminals  of  the  field 
magnets. 

(4.)  The  commutator,  by  which  the  currents  de- 
veloped in  the  armature  are  caused  to  flow  in 
one  and  the  same  direction.  In  alternating 
machines,  and  in  some  continuous  current  dynamos 
this  part  is  called  the  collector,  and  does  not  rec- 
tify the  currents. 

(5.)  The  collecting  brushes,  that  rest  on  the 
commutator  cylinder  and  take  off  the  current 
generated  in  the  armature. 

Machine,  Dynamo-Electric,  Alternating- 

Current A  dynamo-electric  machine 

in  which  alternating  currents  are  produced. 

The  field  magnets  may  be  either  permanent 
jnagnets  or  electro-magnets.  When  electro-mag  - 
aets  are  used,  their  coils  may  be  separately  ex- 
cited by  another  machine  whose  current  is  con- 
tinuous; or,  they  may  be  excited  by  the  commuted 
.  irrent  of  a  separate  coil  on  the  armature ;  or,  they 
may  be  partly  excited  by  commuted  currents  and 
partly  by  commuted  currents  from  a  transformer, 
placed  in  the  main  circuit  of  the  dynamo. 

Machine,  Dynamo-Electric,  Armatnre  of 

(See    Armature,    Dynamo- Electric 

Machine) 

Machine,  Dynamo-Electric,  Bed-Piece  of 

The  frame  or  base  on  which  a  dynamo 

is  supported. 

The  bed-piece  is  sometimes  called  the  dynamo 
frame  or  base. 

Machine,  Dynamo-Electric,  Bi-Polar 

— A  dynamo-electric  machine,  the  armature 
of  which  rotates  in  a  field  formed  by  two 
magnet  poles,  as  distinguished  from  a  ma- 


[Mac. 


chine  the  armature  of  which  rotates  in  a  field 
formed  by  more  than  two  magnet  poles. 

A  dynamo-electric  machine  whos<.  armature 
rotates  in  the  field  formed  by  more  than  two 
P9les  is  called  a  multi-polar  machine.  (See  Ma- 
chine,  Dynamo-Electric,  Multi-Polar;) 

Machine,    Dynamo-Electric,  Carcass  of 

--  A  term  sometimes  used  in  place  of 
the  field  magnet  frame  of  a  dynamo-electric 
machine.  (See  Machine,  Dynamo-Electric, 
Frame  of) 

The  term,  field  magnet  frame,  would  appear 
to  be  the  preferable  term.  The  term,  however, 
is  used  in  France,  and  is  derived  from  the 
French  word  for  skeleton. 

Machine,  Dynamo-Electric,   Closed-Coil 

--  A  dynamo-electric  machine,  the 
armature  coils  of  which  are  grouped  in  sec- 
tions, communicating  with  successive  bars  of 
a  collector,  so  as  to  be  connected  continu- 
ously together  in  a  closed  circuit. 

The  Gramme  dynamo  and  most  continuous- 
current  dynamos  are  closed-coil  dynamos. 

Machine,  Dynamo-Electric,  Closed-Coil 
Disc  --  A  closed-coil  dynamo-electric 
machine,  the  armature  core  of  which  is  disc- 
shaped. 

Machine,  Dynamo-Electric,  Closed-Coil 
Drum  --  A  closed-coil  dynamo-electric 
machine,  the  armature  core  of  which  is 
drum-shaped. 

Machine,  Dynamo-Electric,  Closed-Coil 
Ring  --  A  closed-coil  dynamo-electric 
machine,  the  armature  core  of  which  is  ring- 
shaped. 

Machine,  Dynamo-Electric,  Collectors 
--  (See  Collectors  of  Dynamo-Electric 
Machines)  t 

Machine,  Dynamo-Electric,  Compound 
Winding  of  --  (See  Winding,  Com- 
pound, of  Dynamo-Electric  Machine) 

Machine,  Dynamo-Electric,  Compound- 
Wound  --  Machines  whose  field  mag- 
nets are  excited  by  more  than  one  circuit  of 
coils,  or  by  more  than  a  single  electric 
source. 

The  object  of  compound  winding  is  to  make 


327 


[Mac. 


the  dynamo  self-regulating  under  changes  in  its 
working  load.  A  shunt-wound  dynamo  renders 
both  series  and  multiple  circuits  approximately 
constant  as  regards  their  working.  Multiple  cir- 
cuits, however,  require  great  constancy  of  poten- 
tial, and  for  this  purpose  the  compounding  of  the 
dynamos  is  necessary . 

In  the  compound  dynamo,  the  shunt  coils  are 
superposed  on  the  series  coils,  or  are  used  in  con- 
nection with  them.  The  shunt  coils  consist  of  a 
much  greater  number  of  convolutions  of  fine  wire 
than  the  series  coils,  which  are  of  coarse  wire. 

Separate  excitation  is  sometimes  compounded 
either  with  series  or  with  shunt  field  magnet 
coils. 

Compound  dynamos  are  of  two  classes,  viz. : 

(r.)  Those  designed  to  produce  a  constant 
potential,  and 

(2. )  Those  designed  to  produce  a  constant  cur- 
rent 

For  Constant  Potential  : 

In  the  long-shunt  compound-wound  dynamo, 
the  terminals  of  the  shunt  coil  are  connected  with 
the  binding  posts  of  the  machine.  As  the  cur- 
rent leaves  the  armature  it  has  two  paths  to  take  : 
one,  the  thick  series  coils,  to  the  external  circuit, 
and  the  other  the  finer  and  longer  shunt  coils. 
The  resistance  of  the  shunt  coils  is  greater  than 
that  of  the  armature.  Current  variations  in  the 
armature  will,  therefore,  produce  no  appreciable 
effect  on  the  magnetizing  power  of  the  shunt, 
which  acts  as  a  nearly  uniform  exciter  of  the  field. 

In  a  shunt-wound  dynamo  connected  to  a 
multiple  circuit,  the  introduction  of  an  additional 
number  of  receptive  devices  into  the  circuit  re- 
quires more  current,  and  this  would  tend  to  cause 
a  slight  drop  in  the  potential.  The  object  of  the 
series  coils  is  to  prevent  this  drop.  The  series 
coils,  therefore,  act  as  compensators.  If  the 
coils  are  too  powerful  the  compensation  will 
have  the  effect  of  increasing  the  potential. 

The  combination  of  a  series  and  separately  ex- 
cited machine  is  shown  in  Fig.  351.  The  field  is 
in  series  with  the  armature,  but  has  also  an  ad- 
ditional and  separate  excitation. 

The  combination  of  a  series  and  shunt  machine 
insures  the  excitation  of  the  field  both  by  the 
main  and  by  the  shunted  current.  Such  a  com- 
bination  is  shown  in  Fig.  353. 

For  Constant  Current : 

The  combination  of  shunt  and  separately  ex. 
cited  machines  is  shown  in  Fig.  356.  In  this 
machine  the  field  is  excited  by  means  of  a  shunt 


to  the  external  circuit,  and  by  a  current  produced 
by  a  separate  source. 

The  combination  of  a  series  and  magneto  ma- 
chine is  shown  in  Fig.  352.  This,  also,  is 
designed  to  give  a  constant  current. 

Machine,  Dynamo-Electric,  Compound- 
Wound,  Long-Shunt A  compound- 
wound  dynamo-electric  machine,  in  which 
the  shunt-field  magnet  coils  form  a  shunt  to 
the  binding  posts  of  the  machine. 

In  the  short-shunt  compound-wound  dynamo- 
electric  machine,  the  ends  of  the  shunt  coil  are 
connected  to  the  brushes  of  the  machine. 

Machine,  Dynamo-Electric,  Compound- 
Wound,  Short-Shunt A  compound- 
wound  dynamo-electric  machine  in  which  the 
shunt-field  magnet  coils  form  a  shunt  to  the 
armature  only,  as  distinguished  from  the 
armature  and  series  coils  combined. 

In  the  short-shunt  dynamo-electric  machine, 
the  ends  of  the  shunt  coil  are  connected  t  >  the 
brushes  of  the  machine,  and  not  to  the  binding 
posts  of  the  machine,  or  to  the  external  circuit,  as 
in  the  long-shunt  machine. 

Machine,  Dynamo-Electric,  Continuous- 
Current  A  dynamo-electric  machine, 

the  current  of  which  is  commuted  so  as  to 
flow  in  one  and  the  same  direction,  as  dis- 
tinguished from  an  alternating  dynamo. 

Machine,  Dynamo-Electric,  Double-Mag- 

net A  term  sometimes  applied  to  a 

dynamo-electric  machine,  the  field  magnets 
of  which  have  two  consequent  poles. 

Machine,  Dynamo-Electric,  Economic 
Co-efficient  of A  name  formerly  ap- 
plied to  the  efficiency  of  a  dynamo-electric 
machine.  (See  Machine,  Dynamo-Electric, 
Efficiency  of.) 

Machine,  Dynamo-Electric,  Efficiency 

of The  ratio  between  the  electric 

energy  or  the  electrical  horse-power  produced 
by  a  dynamo,  and  the  mechanical  energy  or 
horse-power  expended  in  driving  the  dynamo. 

The  Efficiency  may  be  the  Commercial  Effi- 
ciency, which  is  the  useful  or  available  energy  in 
the  external  circuit  divided  by  the  total  mechan- 
ical energy  ;  or  it  may  be  the  Electrical  Efficiency- , 
which  is  the  available  electric  energy  divided  by 
the  total  electric  energy. 


Mac.] 


328 


[Mac. 


The  Efficiency  of  Conversion  is  the  total  elec- 
trical   energy    developed,   divided  by  the  total 
mechanical  energy  applied. 
If  M,  equals  the  mechanical  energy, 

W,  the  useful  or  available  electrical  energy, 

and 

w,  the  electrical  energy  absorbed  by  the  ma- 
chine, and 

m,  the  Stray  Power,  or  the  power  lost  in 
friction,  eddy  currents,  air  friction,  etc. 
Then,  since 

M  =  W  +  w  +  m, 

W 
Commercial  Efficiency . .  =  — — 


Machine,    Dynamo-Electric,    Open-Coil 

A    dynamo-electric     machine,     the 

armature  coils  of  which,  though  connected  to 


W 


W 


Electrical  Efficiency 

W  -f  w    • 

Efficiency  of  Conversion  =W  +  W-    W  +  w 

M        W+  w  +  m 

Machine,  Dynamo-Electric,  Flashing  of 

A  name  given  to  long  flashing  sparks 

at  the  commutator,  due  to  the  short  cir- 
cuiting of  the  external  circuit  at  the  com- 
mutator, by  arcing  over  the  successive  com- 
mutator insulating  strips. 

Machine,  Dynamo-Electric,  Frame  of 
The  bed-piece  that  supports  a  dyna- 
mo-electric machine. 

The  frame  is  sometimes  called  the  dynamo  bed- 
piece. 

The  word  frame  is  sometimes  applied  to  the 
field  magnet  cores  and  yokes. 

Machine,  Dynamo-Electric,  Local  Action 
of (See  Action,  Local,  of  Dynamo- 
Electric  Machine^ 

Machine,  Dynamo-Electric,  Mouse-Mill, 
Sir  Wm.  Thomson's A  dynamo- 
electric  machine  designed  by  Sir  Wm. 
Thomson,  named  from  the  resemblance  of 
its  armature  to  a  mouse  mill. 

The  armature  conductor  of  this  dynamo  con- 
sists of  parallel  bars  of  copper,  arranged  on  a 
hollow  cylinder,  like  the  bars  on  a  mouse  mill. 

Machine,  Dynamo-Electric,  Mnltipolar 

— A  dynamo-electric  machine,  the 

armature  of  which  revolves  in  a  field  formed 
by  more  than  a  single  pair  of  poles. 

This  form  is  usually  adopted  for  large  machines 
as  being  more  economical. 

Fig-  349  shows  a  multipolar  dynamo  with  four 
poles. 


Fig.  349.     Multipolar  Dynamo  with  Four  Poles. 


the  successive  bars  of  the  commutator,  are  not 
connected  continuously  in  a  closed  circuit. 

The  Brush  and  the  Thomson-Houston  arc  dy- 
namos are  open-coil  machines. 

Machine,    Dynamo-Electric,     Open-Coil 

Disc An   open-coil    dynamo-electric 

machine,   the    armature   of    which   is   disc- 
shaped. 

Machine,    Dynamo  Electric,    Open-Coil 

Dram An  open-coil  dynamo-electric 

machine,  the  armature  core  of  which  is  drum- 
shaped. 

Machine,    Dynamo-Electric,    Open-Coil 

Ring An   open-coil   dynamo-electric 

machine,  the  armature  core  of  which  is  ring- 
shaped. 

Machine,    Dynamo-Electric,   Output    of 

The  electric  power  of  the  current  gen- 
erated by  a  dynamo-electric  machine  ex- 
pressed in  volt-amperes,  watts  or  kilo-watts. 
S.  P.  Thompson  suggests  that  dynamo- electric 
machines  be  rated  as  to  their  practical  safe  ca- 
pacity in  units  of  output  of  1,000  watts,  or  one 
kilo-watt.  According  to  this,  an  8-unit  machine 
might  give,  say,  100  ampdres  at  a  difference  of 
potential  of  80  volts,  or  2,000  amperes  at  a  differ- 
ence of  potential  of  4  volts.  Such  a  unit  would  be 
far  more  expressive  than  the  usual  method  ot  rat- 
ing a  machine  as  having  a  capacity  of  such  and 
such  a  number  of  lights. 

Machine,     Dynamo-Electric,    Reaction 
Principle  of The  mutual  interaction 


Mac.J 


329 


[Mac. 


between  the  current  generated  in  the  armature 
coils  of  a  dynamo-electric  machine  and  the 
field  of  the  machine,  each  strengthening  the 
other  until  the  full  working  current,  which 
the  machine  is  capable  of  developing,  is 
produced,  i 

When  the  armature  of  a  series  or  shunt  dynamo 
commences  to  rotate,  the  differences  of  potential 
generated  in  its  coils  are  very  small,  since  the 
field  of  the  magnet  is  weak,  being  merely  the 
residual  magnetism.  The  current  so  produced 
in  the  armature,  circulating  through  the  field 
magnet  coils,  increases  the  intensity  of  the  mag- 
netic field  of  the  machine,  and  this,  reacting  on 
the  armature,  results  in  a  more  powerful  current 
through  it.  This  current  again  increases  the 
strength  of  the  magnetic  field  of  the  machine, 
which  again  reacts  to  increase  the  current 
strength  in  the  armature  coils,  and  this  continues 
until  the  machine  is  producing  its  full  output. 

A  dynamo-electric  machine  very  rapidly 
"builds  «/,"  or  reaches  its  maximum  current 
after  starting.  The  reaction  principle  was  dis- 
covered by  Soren  Hjorth,  of  Copenhagen. 

Machine,  Dynamo-Electric,  Reversibility 

of The  ability  of  a  dynamo  to  act  as 


3*0.    Separately  Excited  Dynamo 


a  motor  when  traversed  by  an  electric  cur- 
rent.    (See  Motor,  Electric.} 

Machine,  Dynamo-Electric,  Separate 
Coil  -  —  A  dynamo-electric  machine  in 
which  the  field  magnets  are  excited  by  means 


of  coils  on  the  armature,  separate  and  dis- 
tinct from  those  which  furnish  current  to  the 
external  circuit. 

Machine,  Dynamo-Electric,  Separately 

Excited A  dynamo-electric  machine 

in  which  the  field  magnet  coils  have  no  con- 
nection with  the  armature  coils,  but  receive 
their  current  from  a  separate  machine  or 
source. 

A  separately  excited  dynamo-electric  machine 
is  shown  in  Fig.  350. 

Separate  excitation  for  constant  current  ma- 
chines has  not  come  into  any  extended  use  in  the 
United  States. 

Machine,  Dynamo-Electric,  Series  and 
Magneto  — A  compound-wound  dy- 
namo-electric machine  in  which  the  arma- 
ture circuit  of  a  magneto-electric  machine  is 
connected  in  series  with  the  armature  and 
field  magnet  circuits  of  a  series  dynamo. 

The  circuit  connections  of  a  series  and  magneto 
dynamo  are  shown  in  Fig.  351. 


fig  35  r.    Series  and  Magneto  Dynamo. 

Machine,  Dynamo-Electric,  Series  and 
Separately  Excited  -  — A  compound- 
wound  dynamo-electric  machine  in  which 
there  are  two  separate  circuits  on  the  field 
magnet  cores,  one  of  which  is  connected  in 
series  with  the  field  magnets  and  the  exter- 
nal circuit,  and  the  other  with  some  source 
by  which  it  is  separately  excited. 


Mac.] 


330 


[Mac. 


A  series  and  separately  excited  compound- 
wound  dynamo-electric  machine  is  shown  in 
Fig.  3S2. 


Fig,  332.    Series  and  Separately  Excited  Dynamo, 
This  machine  is  employed  for  maintaining  a 

constant  potential  at  its  terminals. 
Machine,  Dynamo-Electric,  Series   and 

Shunt  Wound  — A  compound-wound 


Fig,  3 S3>    Series  and  Shunt-  Wound  Dynamo. 

dynamo-electric  machine  in  which  the  field 
magnets  are  wound  with  two  separate  coils, 
one  of  which  is  in  series  with  the  armature 
and  the  external  circuit,  and  the  other  in 
shunt  with  the  armature. 


This  is  usually  called  a  compound- wound  ma- 
chine. (See  Machine,  Dynamo -Electric,  Com- 
pound- Wound.) 

A  compound-wound  series  and  shunt  dynamo- 
electric  machine  is  shown  in  Fig.  353.  This  ma- 
chine is  designed  to  maintain  constant  potential 
at  its  terminals. 

There  are  two  varieties  of  series  and  shunt- 
wound  dynamos,  viz. : 

(I.)  Long-shunt  compound-wound  dynamo. 

(2.)  Short-shunt  compound-wound   dynamo. 

(See  Machine,  Dynamo-Electric,  Compound- 
Wound,  Long- Shunt,  Machine,  Dynamo-Electric, 
Compound-Wound,  Short -Shunt.) 

Machine,  Dynamo-Electric,  Series- Wound 

A  dynamo-electric  machine,  in  which 

the  field  circuit  and  the  external  circuit  are 


D    D    D    D 

i    &£•  35 *•    Serie*  Dynamo. 

connected  in  series  with  the  armature  circuit, 
so  that  the  entire  armature  current  must  pass 
through  the  field  coils. 

A  series  dynamo -electric  machine  is  shown  in 
Fig.  354.  Here  the  armature  circuit,  the  field 
circuit  and  the  external  circuit  are  all  connected 
in  series. 

Since  in  a  series-wound  dynamo  the  armature 
coils,  the  field  and  the  external  series  circuit  are  in 
series,  any  increase  in  the  resistance  of  the  external 
circuit  will  decrease  the  electromotive  force  from 
the  decrease  in  the  magnetizing  currents.  A  de- 
crease in  the  resistance  of  the  external  circuit  will, 
in  a  like  manner,  increase  the  electromotive  force 
from  the  increase  in  the  magnetizing  current 


Mac.] 


331 


[Mac. 


The  use  of  a  regulator  avoids  these  changes 
the  electromotive  force. 


355-     Series  Dynamo. 

The  dynamo  shown  in  Fig.  355  is  series  con- 
nected.  The  armature  is  ring  shaped.  The 
armature  core  consists  of  a  ring  made  of  soft  iron 
wire.  The  field  is  bi-polar,  and  is  obtained  by 
the  use  of  four  magnet  coils  and  two  consequent 
poles. 

Machine,  Dynamo-Electric,  Shunt  and 
Separately  Excited A  compound- 
wound  dynamo-electric  machine,  in  which 


Fig.  Sft>.    Shunt  and  Separately  Excited  Dynmmo. 

the  field  is  excited  both  by  means  of  a 
shunt  to  the  armature  circuit,  and  by  a 
current  produced  by  a  separate  source. 
A   shunt  and    separately  excited    compound- 


wound  dynamo -electric  machine  is  shown  in  Fig. 
356.  This  machine  maintains  a  constant  current 
in  its  circuit,  notwithstanding  changes  in  its  ex- 
ternal circuit. 

Machine,  Dynamo-Electric,  Shunt- Wound 

-A  dynamo-electric  machine  in  which 

the  field  magnet  coils  are  placed  in  a  shunt 
to  the  armature  circuit,  so  that  only  a 
portion  of  the  current  generated  passes 
through  the  field  magnet  coils,  but  all  the 
difference  of  potential  of  the  armature  acts 
at  the  terminals  of  the  field  circuit. 

A  shunt  dynamo-electric  machine  is  shown  in 
Fig-  357- 


D      D    D    D 

fig-  S57'    Shunt  Dynamo, 

In  a  shunt  dynamo-electric  machine,  an  in- 
crease  in  the  resistance  of  the  external  circuit  in- 
creases the  electromotive  force,  and  a  decrease  in 
the  resistance  of  the  external  circuit  decreases  the 
electromotive  force.  This  is  just  the  reverse  of 
the  series-wound  dynamo. 

In  a  shunt- wound  dynamo  a  continuous  balanc- 
ing of  the  current  occurs.  The  current  dividing 
at  the  brushes  between  the  field  and  the  external 
circuit  in  the  inverse  proportion  to  the  resistance 
of  these  circuits,  if  the  resistance  of  the  external 
circuit  becomes  greater,  a  proportionately  greater 
current  passes  through  the  field  magnets,  and  so 
causes  the  electromotive  force  to  become  greater. 

If,  on  the  contrary,the  resistance  of  the  external 
circuit  decreases,  less  current  passes  through  the 
field,  and  the  electromotive  force  is  proportion- 
ately decreased. 


Mae.] 


[Mac. 


In  a  shunt-wound  dynamo  the  resistance  of  the 
shunt  should  be  at  least  four  hundred  times  that 
of  the  armature.  It  is  sometimes  as  much  as  one 
thousand  times  as  great. — (Urqukart.) 

To  obtain  complete  regulation  of  the  machine 
some  form  of  compounding  is  necessary.  (See 
Machine,  Dynamo-Electric,  Compound-  Wound. ) 

Machine,  Dynamo-Electric,  Single  Mag- 
net   A  dynamo-electric  machine,  in 

which  the  field  magnet  poles  are  obtained 
by  means  of  a  single  coil  of  insulated  wire, 
instead  of  by  more  than  a  single  coil. 

Machine,  Dynamo-Electric,  Sparking  of 
An  irregular  and  injurious  oper- 
ation of  a  dynamo-electric  machine,  at- 
tended with  sparks  at  the  collecting 
brushes. 

Sparking  consists  in  the  formation  of  small 
arcs  under  the  collecting  brushes.  One  cause  of 
sparking  is  to  be  found  in  the  brushes  leaving 
one  commutator  strip  before  making  connection 
with  the  next  strip. 

Sparking  from  this  cause  may  be  avoided  by  so 
placing  the  brushes  as  to  cause  them  to  bridge 
over  the  space  between  two  consecutive  bars, 
thus  permitting  them  to  touch  one  bar  before 
leaving  the  other.  Two  brushes,  electrically  con- 
nected, are  sometimes  employed  for  this  purpose, 
or  the  slots  between  contiguous  bars  are  slightly 
inclined  to  the  axis  of  rotation. 

Sparking  causes  a  burning  of  the  commutator 
strips,  and  an  irregular  consumption  of  the 
brushes,  both  of  which  produce  further  irregu. 
larities  by  the  wear  of  the  brushes  against  the 
commutator  bars. 

At  the  moment  the  brush  touches  two  contigu- 
ous commutator  bars,  it  short  circuits  the  coil 
terminating  at  those  bars.  On  the  breaking  of 
this  closed  circuit,  a  spark  appears  under  the 
brushes.  This  spark  is  often  considerable,  since 
from  the  comparatively  small  resistance  of  the 
coil,  it  is  apt,  when  short-circuited,  to  produce  a 
heavy  current  if  not  exactly  at  the  neutral  point. 

Another  cause  of  sparking  is  to  be  found  in  the 
self-induction  of  the  armature  coils.  The  extra 
current  on  breaking  forms  an  injurious  spark 
under  the  brushes.  This  spark  may  be  consid- 
erable, since  the  current  produced  in  the  coil  on 
momentarily  short  circuiting  it  by  the  brushes 
simultaneously  touching  the  adjoining  commu- 
tator currents  may  be  large. 

Sparking  occurs  when  the  brushes  are  not  set 


close  to  the  neutral  line.  Since  the  principal 
cause  for  the  change  in  the  lead  of  the  brushes  is 
the  magnetizing  effect  of  the  armature  coils,  it  is 
preferable  to  make  the  number  of  windings  of 
these  as  few  as  possible,  and  to  obtain  the  neces- 
sary differences  of  potential  by  increasing  the 
speed  of  rotation  and  the  strength  of  the  mag- 
netic field  of  the  machine.  Short  armature  coils 
also  lessen  the  sparking  due  to  self-induction. 

Sparking  at  the  brushes  is  also  caused  by  the 
jumping  of  improperly  supported  or  constructed 
brushes. 

When  the  brushes  are  not  set  close  to  the  neu- 
tral point,  \wb%  flashing  sparks  are  apt  to  occur. 

A  lack  of  symmetry  of  winding  of  the  arma- 
ture coils  will  necessarily  be  attended  bj  injurious 
flashing,  from  the  impossibility  of  properly  ad- 
justing the  brushes. 

Machine,  Dynamo-Electric,  Synchroniz- 
ing   Adjusting  the  phases  of  two 

alternating  current  dynamos  so  as  to  per- 
mit their  being  coupled  or  joined  in  par- 
allel. 

Machine,  Dynamo-Electric,  to  Short  Cir- 
cuit a To  put  a  dynamo-electric  ma- 
chine on  a  circuit  of  comparatively  small 
electric  resistance. 

Machine,  Dynamo- Electric,  Unit  of  Out- 
put of A  unit  for  the  electric  power 

furnished  by  the  current  of  a  dynamo- 
electric  machine. 

A  unit  of  output  equal  to  1,000  watts 
or  i  kilowatt. 

A  machine  furnishing  a  current  of  100  amperes 
at  a  difference  of  potential  of  80  volts,  would 
have  an  output  of  8,000  watts,  and  would, 
therefore,  be  rated  as  an  8-unit  machine. 

Machine,  Electric,  Rubber  of  —  -A 
cushion  of  leather  covered  with  an  electric 
amalgam,  and  employed  to  produce  elec- 
tricity by  its  friction  against  the  plate  or 
cylinder  of  a  frictional  electric  machine. 
(See  Machine,  Frictional  Electric. ) 

Machine,  Electrostatic  Induction  of 

A  machine  in  which  a  small  initial  charge 
produces  a  greatly  increased  charge  by  its 
inductive  action  on  a  rapidly  rotated  disc 
of  glass  or  other  dielectric. 

An  excellent  type  and  example  of  such  a  ma- 
chine is  found  in  the  Holtz  machine,  which  con- 


Mac.]  333 

sists  of  the  following  parts,  as  shown  in  Fig.  358, 
viz.; 

(i.)  A  stationary  glass  plate  A,  fixed  at  its 
edges  to  insulated  supports- 

(2.)  A  movable  plate  B,  capable  of  rapid  rota- 
tation  on  a  horizontal  axis,  by  a  driving  pulley. 


[Mac. 


Fig.  358.     Holtz  Electric  Machine. 

(3.)  Armatures  of  varnished  paper  f,  f',  placed 
on  opposite  sides  of  the  fixed  plate  at  holes  or 
windows  P,  P',  cut  in  the  plate.  The  armatures 
are  placed  on  the  side  of  the  fixed  plate  away  from 
the  moving  plate,  or  on  the  back  of  the  plate,  so  that 
the  plate,  on  its  rotation,  moves  towards  tongues  of 
paper  attached  to  the  middle  of  the  armatitre. 

(4.)  Metal  combsplaced  in  front  of  the  movable 
disc  opposite  the  armatures,  and  connected  with 
the  brass  balls  m,  n,  one  of  which  is  movable 
towards  and  from  the  other  by  means  of  a  suitably 
supported  insulating  handle  connected  with  it. 

A  small  initial  charge  is  given  to  one  of  the 
armatures  by  holding  a  plate  of  electrified  vul- 
canite against  it,  and  rotating  the  machine  -while 
the  balls  m,  n,  are  in  contact.  As  soon  as  the  ma- 
chine is  charged  the  balls  are  gradually  separated, 
when  a  torrent  of  sparks  will  pass  between  them 
so  long  as  the  plate  is  rotated. 

W  hen  the  balls  are  separated  too  far  the  sparks 
cease  to  pass.  The  balls  must  then  be  again 
brought  into  contact  and  gradually  separated  as 
before. 

The  Holtz  machine  can  be  regarded  as  a  re- 
volving electrophorus  provided  with  means  for 
constantly  discharging  and  recharging  the  upper 
metallic  plate.  (See  Electrophorus.} 

The  action  of  the  machine  is  well  described  by 
S.  P.  Thompson  in  his  "Elementary  Lessons  on 
Electricity  and  Magnetism,  "  as  follows: 

"Suppose  a  small  +  charge  to  be  imparted  at 
the  outset  to  the  right  armature  f  ;  this  charge  acts 


inductively  across  the  discs  upon  the  metallic 
comb,  repels  electricity  through  it,  and  leaves  the 
points  negatively  electrified.  They  discharge 
negatively  electrified  air  upon  the  front  surface  of 
the  movable  disc ;  the  repelled  charge  passes 
through  the  brass  rods  and  balls,  and  is  dis- 
charged through  the  left  comb  upon  the  front  side 
of  the  movable  disc.  Here  it  acts  inductively 
upon  the  paper  armature,  causing  that  part  of  it 
which  is  opposite  itself  to  be  negatively  charged 
and  repelling  a  -f  charge  into  its  farthest  part, 
viz.,  into  the  tongue,  which  being  bluntly  pointed, 
slowly  discharges  a  -f  charge  upon  the  back  of  the 
movable  disc.  If  now  the  disc  be  turned  round, 
this  -(-  charge  on  the  back  comes  over  from  the 
left  to  the  right  side,  in  the  direction  indicated  by 
the  arrow,  and,  when  it  gets  opposite  the  comb, 
increases  the  inductive  effect  of  the  already  exist- 
ing -f  charge  on  the  armature,  and  therefore 
repels  more  electricity  through  the  brass  rods  and 
knob  into  the  leit  comb.  Meantime  the  —  charge, 
which  we  saw  had  been  induced  in  the  left  arma- 
ture, has  in  turn  acted  on  the  left  comb,  causing 
a  -j-  charge  to  be  discharged  by  the  points  upon 
the  front  of  the  disc ;  and  drawing  electricity 
through  the  brass  rods  and  knobs,  has  made  the 
right  comb  still  more  highly  — ,  increasing  the 
discharge  of  — ly  electrified  air  upon  the  front 
of  the  disc,  neutralizing  the-)-  charge  which  is  be- 
ing conveyed  over  from  the  left.  These  actions  re- 
sult in  causing  the  top  half  of  the  moving  disc  to 
be  — ly  electrified.  The  charges  on  the  front 
serve,  as  they  are  carried  round,  to  neutralize  the 
electricities  let  off  by  the  points  of  the  combs, 
while  the  charges  on  the  back,  induced  respect- 
ively in  the  neighborhood  of  each  of  the  arma- 
tures, serve,  when  the  rotation  of  the  disc  con- 
veys them  round,  to  increase  the  inductive  influ- 
ence of  the  charge  on  the  other  armature." 

The  student  will  be  aided  in  following  Prof. 
Thompson's  explanation  by  the  diagrammatic 
sketch,  shown  in  Fig.  359.  Here  the  rotating  plate 
is  shown  for  convenience  in  the  form  of  a  cylinder. 
The  armatures  are  shown  on  the  back  of  the  plate 
at  f  and  f,  opposite  the  brass  collecting  combs  P' 
and  P,  with  their  discharging  rods  and  balls  a,  a. 

The  effect  of  the  positive  charge  given  to  the 
right  hand  armature  f',  directly  through  the 
comb  P',  rods  a,  a,  comb  P,  to  left  hand  arma- 
ture f,  is  readily  seen.  The  rotation  of  the  plate 
being  in  the  direction  of  the  curved  arrows  the 
charging  of  the  front  of  the  plate  by  convection 
streams  from  the  combs,  and  the  back  of  the  plate 


Vac.] 


334 


[Mac. 


from  the  points  of  the  paper  armatures,  as  well  as 
the  character  of  the  charge,  will  be  understood. 
There  thus  results,  as  is  shown,  a  positive  charge 
on  both  the  front  and  back  of  the  upper  half  of 

•fe. 
•fe, 


Fig,  JSQ.  Plait  ofHoltz  Machine. 
the  rotating  plate,  and  a  negative  charge  on  both 
sides  of  its  lower  half.  A  reversal  of  polarity  of 
the  plate  occurs  at  the  line  P  a  a  P'.  Sometimes 
the  reversal  does  not  occur,  and  the  machine  either 
loses  its  charge  entirely,  or  in  part.  A  conductor 
S  S,  furnished  with  points,  is  sometimes  provided 
to  lessen  the  chances  of  lack  of  reversal. 

Machine,  Faradic A  machine    for 

producing  faradic  currents. 

There  are  two  varieties  of  faradic  machines, 
viz.:  magneto-faradic  apparatus  and  simple  in. 
duction  apparatus. 

Machine,    Frictional     Electric A 

machine  for  the  development  of  electricity 
by  friction. 

A  frictional  electric  machine  consists  of  a  plate 
or  cylinder  of  glass  A,  Fig.  360,  capable  of  rota- 
tion on  a  horizontal  axis. 

A  rubber  formed  of  a  chamois  skin,  covered 
with  an  amalgam  of  tin  and  mercury,  is 
placed  at  B.  By  the  rotation  of  the  plate  the 


Fig.  360.  Frictional  Electric  Machine. 
rubber  becomes  negatively  and  the  glass  posi- 
tively excited.  An  insulated  conductor  D,  called 
the  prime  or  positive  conductor,  provided  with  a 
comb  of  points,  becomes  positively  charged  by  in- 
duction. The  machine  will  develop  electricity 


best  if  a  conductor  attached  to  the  rubber  is  con- 
nected with  the  ground,  as  by  a  chain. 

Machine  t  Holt* A  particular  form 

of  electrostatic  induction  machine.     (See 
Machine,  Electrostatic  Induction. ) 

Machine,  Influence An    electrical 

machine    depending    for    its   action   on 
electrostatic  induction. 

The-  Wimshurst  and  Holtz  machines  are  influ- 
ence  machines.  (See  Machine,  Electrostatic  In- 
duction. Machine,  Wimshurst  Electrical.  Ma- 
chine, Holts.} 

Machine,  Influence,  Wimshurst's  Alter- 
nating   An  electrostatic  induction 

machine  by  means  of  which  a  series  of 
rapidly  alternating  charges  are  produced. 

Although  such  a  machine  furnishes  a  torrent  of 
sparks  between  its  terminals,  yet  it  is  unable  to 
furnish  a  permanent  charge  to  a  Leyden  jar 
or  condenser,  since  its 
oscillatory  discharges, 
continually  undo  at  any 
small  interval  of  time 
what  was  done  at  the 
preceding  interval,  and 
thus  leave  the  jar  un- 
charged. 

Machine,    Magneto 

Blasting    —A 

magneto-e  1  e  c  t  r  i  c 
machine  employed 
for  generating  the 

j  •        i        Fig  301-    Magneto-Electric 

current  used  m  elec-    *        Mac\int, 
trie  blasting. 

Machine,  Magneto-Electric A  ma- 
chine in  which  there  are  no  field  magnet 
coils,  the  magnetic  field  of  the  machine 
being  due  to  the  action  of  permanent 
steel  magnets. 

A  dynamo  in  which  currents  are  produced  by 
the  motion  of  armature  coils  past  permanent  mag- 
nets. (See  Machine,  Dynamo-Electric. ) 

A  magneto-electric  machine  is  shown  in  Fig. 
361. 

Another  form  of  magneto-electric  machine  is 
shown  in  Fig.  362. 

This  latter  form  of  machine  is  known  as  a  hand 
generator,  in  contradistinction  to  one  driven  by 
power  and  called  a  power  generator. 


Mac.] 


335 


[Mac. 


The  field  is  obtained  by  means  of  a  number  of 
separate  permanent  magnets  so  combined  as  to 


Fig.  362.    Magneto- Electric  Machine. 
act  as  a  single  magnet.     The  armature  is  rotated 
by  hand. 

Machine,  Mouse-Mill A   form    of 

convection  induction  machine,  invented 
by  Sir  William  Thomson  to  act  as  the  re- 
plenisher  of  his  electrometer.  (See  Ma- 
chine, Electrostatic  Induction. ) 

Machine,  Rheostatic A    machine 

devised  by  Plante  in  which  continuous 
static  effects  of  considerable  intensity  are 
obtained  by  charging  a  number  of  con- 
densers in  multiple-arc  and  discharging 
them  in  series. 

The  condensers  are  charged  by  connecting 
them  with  a  number  of  secondary  or  storage  bat- 
teries. 

Machine  Telegraphy. — (See  Telegraphy, 
Machine. ) 

Machine,  Toppler-Holtz A  modified 

form  of  Holtz  machine  in  which  the  initial 
charge  of  the  armatures  is  obtained  by  the 
friction  of  metallic  brushes  against  the 
armatures. 

Machine,   Wimshurst  Electrical 

A  form  of  convection  electric  machine 
invented  by  Wimshurst. 

Like  the  Holtz  machine,  the  Wimshurst  ma- 
chine is  a  convection  induction  machine.  It  is, 
however,  more  efficient  in  action,  and  will  prob- 
ably soon  supersede  the  former  machine.  The 
Wimshurst  machine  consists  of  two  shellac-var- 
nished glass  plates  that  are  rapidly  rotated  in  op- 
posite directions.  Thin  metallic  strips  are  placed 
on  the  outside  of  each  of  the  plates,  in  the  radial 
positions  shown  in  Fig.  363.  These  strips  act 


both  as  inductors  and  carriers ;  the  carriers  of 
one  plate  acting  as  inductors  to  the  other  plate. 

Two  curved  brass  rods,  terminating  in  fine  wire 
brushes  that  touch  the  plates,  are  placed  as  shown, 
one  at  the  front  of  the  plate;  and  one  at  the  back, 
at  right  angles  to  each  other.  Pairs  of  conduct- 


Fig.  363.    The  Wimshurst  Electrical  Machi. 


ors,  connected  together,  provided  with  collecting 
points,  are  placed  diametrically  opposite  each 
other,  as  shown.  Sliding  conductors,  terminated 
with  metallic  balls,  are  provided  for  discharging 
the  conductors.  Leyden  jars,  the  inner  coatings 
of  which  are  connected  with  two  discharging 
rods,  and  the  outer  coatings  together,  may  be  em- 
ployed in  this  as  in  the  Holtz  machine. 

The  exact  action  of  this  machine  is  not  thor- 
oughly understood. 

Machines,  Dynamo-Electric,  Varieties  of 

Dynamo-electric  machines  may  be 

divided  into  classes  according  to — 

(I.)  The  manner  in  which  the  magnetism  of 
the  field  magnets  is  obtained. 

(2.)  The  character  of  their  armatures. 

(3.)  The  nature  of  the  current  obtained, 
whether  continuous  or  alternating. 

(4.)  The  form  of  their  field  magnets. 

(5.)  The  nature  of  their  magnetic  fields. 

(6.)  The  manner  in  which  the  current  of  the 
field  magnets,  the  armature  and  the  external 
circuits  are  connected. 

Mack A  term  proposed  by  Mr. 

Oliver  Heaviside  for  a  unit  of  self-induc- 
tion. 

The  term  Mack  is  derived  from  Maxwell.  The 
unit  of  self-induction  has  also  been  a  secohm  and 
a  quadrant. 


Mad.] 


336 


[Mag. 


The  term  Max  would  seem  to  be  indicated. 
In  the  United  States  the  unit  of  selt -induction  is 
called  a  Henry,  after  Prof.  Joseph  Henry.  (See 
Henry,  A.) 

Made  Circuit.— (See  Circuit,  Made.} 

Magazine  Fuse.— (See  Fuse,  Magazine. ) 

Magne-Crystallic  Action.-(See  Action, 
Magne-Crystallic. ) 

Magnet.— A  body  possessing  the  power 
of  attracting  the  unlike  pole  of  another 
magnet  or  of  repelling  the  like  pole ;  or 
of  attracting  readily  magnetizable  bodies 
like  iron  filings  to  either  pole. 

A  body  possessing  a  magnetic  field. 
(See  Field,  Magnetic.) 

The  lines  of  force  are  assumed  in  passing 
through  the  magnetic  field  to  come  out  at  the  north 
pole  of  the  magnet  and  to  go  in  at  the  south  pole. 
All  lines  of  force  form  closed  magnetic  circuits.  If 
a  magnetizable  body  is  brought  into  a  magnetic 
field,  the  lines  of  magnetic  force  are  concentrated 
on  it  and  pass  through  it.  The  body  therefore  be- 
comes magnetic.  The  intensity  of  the  resulting 
magnetism  depends  on  the  number  of  lines  of 
force  that  pass  through  the  body,  and  the  polar- 
ity on  the  direction  in  which  they  pass  through  it. 

A  magnetized  bar  cannot  be  regarded  as  a 
source  of  energy  in  itself.  Energy  must  be  ex- 
pended to  magnetize  the  iron,  and  must  also  be 
expended  to  demagnetize  it. 

Magnet,  Anomalous A  magnet  pos- 
sessing more  than  two  free  poles. 

There  is  no  such  thing  as  a  unipolar   magnet. 

8 


f'f-  3&4-    Anomalous  Magnet. 

All  magnets  have  two  poles.  Sometimes,  how- 
ever, several  magnets  are  so  grouped  that  there 
appear  to  be  more  than  two  poles  in  the  same 
magnet. 

D 


It  is  clear,  however,  that  the  central  pole  is  in 
reality  formed  of  two  juxtaposed  negative  poles, 
and  that  ABC  actually  consists  of  two  magnets 
with  two  poles  to  each. 

The  magnet  A  B  C  D  Fig.  365,  which  in  like 
manner  appears  to  possess  four  separate  poles,  in 
reality  is  formed  of  three  magnets  with  two  poles 
to  each. 

Since  unlike  magnetic  poles  neutralize   each 
other,  it  is  clear  that  only  similar  poles  can  thus 
be  placed  together  in  order  to  produce  addition- 
al magnet  poles. 
S 


Fig.  363.    Anomalous  Magnet. 
Thus,  in  Fig.  364,  the  magnet  ABC   appears 
to  possess  three  poles,   two  positive  poles  at  A 
and  C,  and  a  central  negative  pole  at  B. 


Fig.  366.    Anomalous  Magnet. 

The  six-pointed  star  shown  in  Fig.  366,  is  an 
anomalous  magnet  with  apparently  seven  poles. 
The  formation  of  the  central  N-pole,  as  is  evi- 
dent from  an  inspection  of  the  drawing,  is  due  to 
the  six  separate  north  poles,  n,  n,  n,  n,  n,  n,  of 
the  six  separate  magnets  Sn,  Sn,  etc.  Such  a 
magnet  would  be  formed  by  touching  the  star  at 
the  point  N,  with  the  S-pole  of  a  sufficiently 
powerful  magnet. 

The  extra  poles  are  sometimes  called  con- 
sequent poles.  Their  presence  may  be  shown  by 
means  of  a  compass  needle",  or  by  rolling  the 
magnet  in  iron  filings,  which  collect  on  the  poles. 

Magnet,  Artificial  —  -A  magnet  pro- 
duced by  induction  from  another  magnet, 
or  from  an  electric  current. 

Any  magnet  not  found  in  nature  is  called  an 
artificial  magnet. 

Magnet,  Axial  —  —A  name  sometimes 
given  to  a  solenoid  with  an  axial  or 
straight  core. 

Magnet,  Bell-Shaped A  modifica- 
tion of  a  horseshoe  magnet  in  which  the 
approached  poles  are  semi-annular  in 
shape,  and  form  a  split  tube. 

Bell- shaped  magnets  are  used  in  many  galra- 


Mag.] 

nometers,  because  they  can  be  readily  dampened 
by  surrounding  them  by  a  mass  of  copper.  The 
needle  in  its  motion  produces  currents  that  tend 
to  oppose,  and,  therefore,  to  stop  its  motion. 
(See  Laws,  Lenz's.)  • 

Magnet,  Club-Footed An  electro- 
magnet whose  core    is  in  the  form  of  a 
horse-shoe  and  is  provided  with  a  mag- 
netizing coil  on  one  pole  only. 
Magnet  Coil.— (See  Coil,  Magnet.} 

Magnet,  Compensating — A  magnet 

placed  over  a  magnetic  needle,  generally 
over  the  magnetic  needle  of  a  galvanome- 
ter, for  the  purpose  of  varying  the  direc- 
tion and  intensity  of  the  magnetic  force  of 
the  earth  on  such  needle.  (See  Galvanom- 
eter, Reflecting.} 

A  magnet,  called  a  compensating  magnet,  is 
sometimes  placed  on  a  ship,  near  the  compass 
needle,  for  the  purpose  of  neutralizing  the  local 
variations  produced  on  the  compass  needle  by 
the  magnetism  of  the  ship. 

Magnet,  Compound A  number  of 

single  magnetsplaced  par. 
allel  and  with  their  similar  i 
poles  facing  one  another, 
as  shown  in  Fig.  367. 

Compound  magnets  are 
stronger  in  proportion  to  their 
weight  than  single  magnets. 
Magnet,  Compound 
Horseshoe A  horse- 
shoe magnet  composed 
of  several  separate  horse- 
shoe magnets  placed  with  S[ 
their  similar  poles  to- 
gether. 

A  compound  horseshoe  magnet  is  shown  in 
Fig.  368. 

A  horseshoe  magnet  possesses  greater  portative 
power  than  a  straight  bar  magnet  of  the  same 
weight.  (See  Power,  Portative.) 

(i.)  Because  its  opposite  poles  are  nearer  to- 
gether; and 

(2.)  Because  the  magnetic  resistance  of  its 
circuit  is  less,  the  lines  of  magnetic  force  closing 
through  the  armature,  and  thus  concentrating 
the  magnetic  attraction  on  the  armature. 

Electro-magnets  are  generally  made  of  the 
horseshoe  shape. 


337  [Mag. 

Magnet,   Controlling    — A    name 

sometimes  applied  to  the  controller  in  the 
Thomson-Houston  automatic  system  of 
current  regulation.  (See  Controller.) 

Generally  any  mag. 
net  which  controls 
some  particular  ac- 
tion. 

Magnet,  Cylindri- 
cal— -—A  magnet 
in  the  shape  of  a 
cylinder. 

A  helix  or  solenoid 
through  which  a  cur- 
rent of  electricity  is 
passing  is,  so  far  as  ex- 
ternal space  is  con- 
cerned, the  exact  mag- 
netic equivalent  of  a 
cylindrical  magnet. 

Magnet,  Damping 

Any  magnet 

employed    for    the 

,    ,         ,   .          Fig  368.     Compound  Horst- 
pUrpOSC  Of  Checking  shoe  Magnet. 

the  velocity  of  motion  of  a  moving  body 
or  magnet. 

Dampening  magnets  generally  act  by  the  resist- 
ance which  they  offer  to  the  passage  of  a 
metallic  disc,  so  moved  as  to  cut  the  lines  offeree 
of  their  field. 

Magnet,  Electro A  magnet  pro- 
duced by  the  passage  of  an  electric  current 
through  a  coil  of  insulated  wire  surround- 
ing a  core  of  magnetizable  material. 

The  magnetizing  coil  is  called  a  helix  or  sole- 
noid. (See  Magnetism,  Amptre's  Theory  of.) 

Strictly  speaking,  the  .  term  electro-magnet  is 
limited  to  the  case  of  a  magnet  provided  with  a 
soft  iroh  core,  which  enables  it  to  rapidly  acquire 
its  magnetism  on  the  passage  of  the  magnetizing 
current,  and  as  rapidly  to  lose  its  magnetism  on 
the  cessation  of  such  current. 

An  electric  current  passed  around  a  bar  ot 
magnetizable  material,  in  the  manner  and  direc- 
tion shown  in  Fig.  369,  will  produce  the  polarity 
N  and  S,  at  its  ends  or  extremities  as  marked. 

The  directions  of  the  currents  required  to  pro- 
duce N  and  S,  poles  respectively  are  shown  in 
Fig.  370. 

The  cause  of  this  difference  of  polarity  will  be 
readily  understood  from  a  study  of  the  direction 


Mag.] 


338 


[Mag. 


of  lines  of  magnetic  force  in  the  field  produced 
by  an  electric  current. 


309.    Polarity  of  Current. 

The  direction  of  this  polarity  may  be  predicted 
by  the  following  modification  of  a  rule  by  Ampere: 

Imagine  yourself  swimming  in  the  wire  in  the 
direction  of  the  current ;  if,  then,  your  face  is 


Fig.  370.    N»rtk  and  South  Magnet  Poles. 

turned  toward  the  bar  that  is  being  magnetized, 
its  North  seeking  pole  will  be  on  your  left. 


S       S 


-  37*'    Deflection  of 
Magnetic  Needle. 


B 

Fig.  373.    Defection  of 
Magnetic  Needle. 

If,  for  example,  the  conductor  A  B,  be  traversed 
by  a  current  in  the  direction  from  B,  to  A,  as 
shown  in  Fig.  371,  the  north  pole  N,  of  the 
needle  N  S,  placed  under  the  conductor,  is  de- 
flected, as  shown,  to  the  left  of  the  observer,  who 
is  supposed  to  be  swimming  in  the  current,  facing 
the  needle.  It  the  current  flow  in  the  opposite 


direction,  as  from  A,  to  B,  as  shown  in  Fig.  372, 
the  N,  pole  of  the  needle  is  deflected  as  shown, 
but  still  to  the  left  of  the  observer  supposed  to  be 
swimming  as  before. 

In  any  electric  circuit,  the  lines,  of  magnetic 
force,  produced  by  the  passage  of  the  current,  form 
circles  around  the  circuit  in  planes  at  right  angles 
to  the  direction  of  the  current,  as  shown  in  Fig. 
373.  The  direction  of  these  lines  of  force  is  the 
same  as  that  of  the  hands  of  a  watch,  if  the  cur- 
rent be  supposed  to  flow  away  from  the  observer. 
(See  Field)  Magnetic ,  of  an  Electric  Current.1) 


Fig-  373'    Direction  of  Line*  of  Force. 

Remembering  now  that  the  lines  of  force  are 

supposed  to  come  out  at  the  north  pole  of  a  magnet, 

and  to  pass  in  at  the  south  pole,  it  is  evident  that 

if  the  current  flows  in  the  direction  shown  in  Fig. 


Fig.  374.    Direction  of  Lines  of  Force. 

374,  the  lines  of  force  will  come  out  at  the  north 
pole  and  pass  in  at  the  south  pole. 

Since  in  a  right-handed  helix  the  wire  passes 
around  the  axis  in  the  opposite  direction  to  that 
in  which  it  passes  in  a  left-handed  helix,  it  is 
evident  that  the  helices  shown  in  Fig.  375  at  i, 
and  2,  will  produce  opposite  polarities  at  the 
points  of  entrance  and  exit  by  a  current  flowing 
in  the  direction  of  the  arrows. 

If  the  current  be  sent  through  the  right-handed 
helix,  shown  at  I,  from  b,  to  a,  that  is,  from  the 
left  to  the  right  in  the  figure,  a  south  pole  will  be 
produced  at  b,  and  a  north  pole  at  a.  If,  how- 
ever, it  be  sent  from  a,  to  b,  the  polarity  will  be 
reversed. 

If  the  current  be  sent  through  the  left-handed 


Mag.] 


339 


[Mag. 


helix,  shown  at  2,  from  a,  to  b,  that  is,  from  the  left 
to  the  right  in  the  figure,  a  north  pole  will  be  pro- 
duced at  a,  and  a  south  pole  at  b.  If,  however,  it 
be  sent  in  the  opposite  direction,  the  polarity  will 
be  reversed. 

Therefore,  in  an  electro-magnet,  on  the  core 
of  which  several  layers  or  thicknesses  of  wire  are 
wound,  in  which  the  current  flows  through  one 
layer,  in,  say  a  direction  from  right  to  left,  the  cur- 
rent  must  return  through  the  next  layer  in  the 
opposite  direction,  or  from  left  to  right.  The 
polarities  of  the  same  extremities  of  the  helices 
are,  however,  the  same  in  all  cases,  since  the 
layers  are  successively  right  and  left  handed 
to  the  current.  The  winding  shown  at  3,  pro- 
duces consequent  poles. 

The  following  laws  express  the  more  important 
principles  concerning  electro-magnets : 

(i.)  The  magnetic  intensity  (strength)  of  an 
electro-magnet  is  nearly  proportional  to  the 
strength  of  the  magnetizing  current,  provided  the 
core  is  not  saturated. 

(2.)  The  magnetic  strength  is  proportional  to 
the  number  of  turns  of  wire  in  the  magnetizing 
coil ;  that  is,  to  the  number  of  ampere  turns.  (See 
Turns,  Amp&re.') 

(3.)  The  magnetic  strength  is  independent  of 
the  thickness  or  material  of  the  conducting  wires. 

These  laws  may  be  embraced  in  the  more  gen- 
eral statement  that  the  strength  of  an  electro- 


Fig.  375-    Right-Handed,  Left- Handed  and  Anomalous 
Helices, 

magnet,  the  size  of  the  magnet  being  the  same, 
is  proportional  to  the  number  of  its  ampere  turns. 
(See  Turns,  Amptre.) 

A  short  interval  of  time  is  required  for  a  cur- 
rent to  thoroughly  magnetize  a  powerful  electro- 
magnet. 

A  few  moments  are  also  required  for  a  power- 
ful magnet  to  thoroughly  lose  its  magnetism.  At 
the  same  time  electro-magnets  are  capable  of 
acquiring  or  losing  their  magnetism  with  very 
great  rapidity.  It  is,  in  fact,  on  this  ability  pos- 
sessed to  so  remarkable  a  degree  by  soft  iron,  that 


he  value  of  an  electro-magnet  for  many  purposes 
depends.  (See  Lag,  Magnetic.) 

A  difference  exists  between  the  action  of  a  mag- 
netized disc  and  a  hollow  coil  of  wire  through 
which  a  current  of  electricity  is  passing.  So 
far  as  the  space  outside  either  is  concerned,  the 
action  is  the  same,  but  the  coil  is  penetrable  on 
the  inside  and  the  disc  is  not,  and  for  the  inside  of 
the  space,  therefore,  there  is  a  difference  in  the  ac- 
tion. 

Magnet,  Electro,  Bar An  electro- 
magnet, the  core  of  which  is  in  the  form  of 
a  straight  bar  or  rod. 

Magnet,  Electro,  Cylindrical An 

electro-magnet,  the  core  of  which  consists 
of  a  hollow  cylinder  provided  with  a  slot 
extending  parallel  to  its  axis. 

The  gap  in  the  cylinder  suffices  for  the  placing 
of  the  magnetizing  coils,  and  forms  the  poles. 
This  form  of  electro-magnet  was  devised  by 
Joule.  Its  construction  will  be  understood  from 
an  inspection  of  Fig.  376. 


Fig.  376.     Cylindrical  Electro- Magntt. 

Magnet,  Electro,  Horseshoe  — An 

electro-magnet,   the  core  of  which  is  in 
the  shape  of  a  horseshoe  or  U. 
Magnet,   Electro,   Hughes' An 

electro-magnet  in  which  a  U-shaped  per- 
manent magnet  is  provided  with  pole 
pieces  of  soft  iron,  on  which  only  are 
placed  the  magnetizing  coils. 

A  quick  acting  electro-magnet,  in 
which  the  magnetizing  coils  are  placed  on 
soft  iron  pole  pieces  that  are  connected 
with  and  form  the  prolongations  of  the 
poles  of  a  permanent  horseshoe  magnet. 

Hughes  devised  this  form  of  electro-magnet  in 
order  to  obtain  the  best  effects  from  currents  of 
but  short  duration. 

He  thus  obtained  a  quick  acting  magnet,  neces- 
sary to  insure  the  success  of  his  system  of  printing 
telegraph,  where  the  magnetizing  currents  at 
times  have  a  duration  of  but  the  .20  of  a  second. 


Mag.] 


340 


[Mag. 


J77.     Iron-Clad 
'-Magnet. 


Magnet,    Electro,    Joule's     Cylindrical 

An  electro-magnet  provided  with 

a  hollow  cylindrical  core.  (See  Magnet, 
Electro,  Cylindrical. ) 

Magnet,   Electro,   Iron-Clad  —An 

electro-magnet  whose  magnetizing  coil  is 
almost  entirely  surrounded  by  iron. 

The  effect  of  the  iron  casing  is  to  greatly  re- 
duce the  magnetic  re- 
sistance of  the  circuit. 
A  form  of  iron-clad  elec- 
tro-magnet is  shown  in 
Fig.  377.  Here  one  of 
the  poles  is  connected 
with  a  casing  of  iron, 
external  to  the  coils,  and 
is  thus  brought  nearer  to 
the  other  pole. 

Magnet,     Electro, 
Long-Core  —    — An  electro-magnet  with 
a  long  core  of  iron. 

A  long-core  electro-magnet  magnetizes  and 
demagnetizes  much  more  slowly  than  a  short- 
core  electro-magnet. 

Magnet,  Electro,  Short-Core An 

electro-magnet  with  a  short  core  of  iron. 

A  short-core  electro-magnet  possesses  the 
power  of  being  magnetized  and  demagnetized 
much  more  rapidly  than  a  long-core  magnet. 

Magnet,  Electro,  Yoked  Horseshoe 

A  horseshoe  electro-magnet,  in  which  the 
two  straight  limbs  are  formed  of  two 
straight  rods  or  bars,  yoked  together  at  one 
pair  of  ends  by  a  yoke  or  bar  of  iron. 

In  some  cases  the  magnetizing  coils  are  placed 
on  each  of  the  limbs.  Sometimes,  however,  a 
single  coil  is  placed  at  the  middle  of  the  yoke 
and  the  limbs  are  left  bare. 

Even  with  the  closest  possible  fitting  the  re- 
sistance of  the  magnetic  circuit  is  much  greater 
in  this  form  of  electro-magnet,  owing  to  the 
smaller  permeability  of  the  air  gap  at  the  joints, 
than  it  would  be  if  the  entire  core  were  made  of 
a  single  piece  of  iron.  A  yoked  electro- magnet 
is,  however,  more  convenient  to  make  and  use. 

Magnet,  Electro,  Zigzag  —  -A  multi- 
polor  electro-magnet,  the  magnetizing 
coils  of  which  are  separately  wound  in 
grooves  cut  in  the  face  of  straight  or 
curved  bars. 


3  7  8.     Zigzag  Electro- 
Magnet. 


A  form  of  zigzag  electro-magnet  devised  by 
Joule  is  shown  in  Fig.  378.  The  spiral  char- 
acter of  the  winding 
produces  the  alternate 
North  and  South  polari- 
ties shown  in  the  figure. 

Magnet,  Equator  of 
— A  point  ap- 
proximately midway 
between  the  poles  ofa 
straight  bar  magnet, 
or  nearly  midway 
from  the  poles  of  a  horseshoe  magnet  if 
measured  along  the  bar  from  each  pole. 

This  term  was  proposed  by  Dr.  Gilbert.  It  is 
now  almost  entirely  displaced  by  the  term  neutral 
point. 

Magnet,  High-Resistance  —  —A  term 
sometimes  used  in  place  of  long-coil  mag- 
net whose  coils  have  a  high  electric  resist- 
ance. (See  Magnet,  Long -Coil.} 

The  term  long -coil  magnet  is,  perhaps,  the 
preferable  one,  because  the  resistance  of  a  coil, 
per  se,  has  nothing  to  do  with  its  magnetizing 
power,  which  is  determined  by  its  ampere  turns. 
(See  Turns,  Ampere.  Magnet,  Long-Coil.} 

Magnet,  Horseshoe magnetized 

bar  of  steel  or  iron  bent  in  the  form  ofa 
horseshoe  or  letter  U. 

Magnet,  Iron-Clad A  magnet  whose 

magnetic  resistance  is  lowered  by  a  casing 
of  iron  connected  with  the  core  and  pro- 
vided for  the  passage  of  the  lines  of  mag- 
netic force.  (See  Magnet,  Tubular. ) 

Magnet,  Jacketed A  term  some- 
times applied  to  a  form  of  iron-clad  mag- 
net. (See  Magnet,  Iron-Clad.} 

Magnet,  Keeper  of A  mass  of  soft 

iron  applied  to  the  poles  of  a  magnet 
through  which  its  lines  of  magnetic  force 
pass.  (See  Field,  Magnetic.} 

The  keeper  of  a  magnet  differs  from  its  arma- 
ture in  that  the  keeper  while  acting  as  such  is 
always  kept  on  the  poles  to  prevent  loss  of  mag- 
'  netization,  while  the  armature,  besides  acting  as 
a  keeper,  may  be  attracted  towards,  or,  if  an 
electro,  magnet,  be  repelled  from  the  magnet 
poles.  While  performing  its  functions  the  keeper 
is  always  fixed,  the  armature  generally,  though 


341 


[Mag. 


not  always,  is  in  motion.  A  keeper  is,  of  course, 
only  used  with  permanent  magnets. 

Opinion  is  divided  as  to  the  efficacy  of  the 
keeper  in  preventing  loss  of  magnetization  in 
certain  cases. 

Magnet,  Long  Coil  -An  electro- 

magnet whose  magnetizing  coil  consists 
of  many  turns  of  thin  wire. 

Magnet,  Low-Resistance A  term 

sometimes  used  in  place  of  short-coil 
magnet.  (See  Magnet,  Short-Coil) 

This  term,  short-coil  magnet,  is  the  preferable 
one. 

Magnet,  Marked  Pole  of A  name 

formerly  applied  to  that  pole  of  a  magnet 
which  points  approximately  to  the  geo- 
graphical north. 

If  the  pole  of  the  magnet  that  points  to  the 
geographical  north  be  in  reality  the  north  pole 
of  the  magnet,  then  the  earth's  magnetic  pole  in 
the  Northern  Hemisphere  is  of  south  magnetic 
polarity.  In  the  United  States,  and  Europe 
generally,  this  is  regarded  as  the  fact. 

The  French,  however,  formerly  called  the 
pole  ot  the  needle  that  points  to  the  earth's  geo- 
graphical north,  the  south  or  austral  pole.  In 
America  and  England  it  is  called  the  north  pole, 
the  marked  pole,  or  the  north-seeking  pole,  and 
the  Northern  Hemisphere  is  assumed  to  possess 
south  magnetic  polarity.  (See  Pole,  Magnetic, 
Austral.  Pole,  Magnetic,  Boreal.) 

Magnet,  Moment  of  —  —The  effective 
force  of  a  magnetic  couple  as  obtained  by 
multiplying  one  of  the  forces  of  the  couple 
by  the  perpendicular  distance  between 
the  directions  of  the  forces. 

The  moment  of  a  magnet  is  equal  to  the  prod- 
uct of  the  volume  of  the  magnet  and  the  in- 
tensity  or  magnetization,  or  simply  its  magnetiza- 
tion. 

Magnet,  Natural A  name  some- 
times given  to  a  lodestone.  (See  Lode- 
stone.  ) 

Magnet,  Central  Line  of  —  —(See  Line, 
Neutral,  of  a  Magnet.) 

Magnet,  Permanent A  magnet  of 

hardened  steel  or  other  paramagnetic  sub- 
stance which  retains  its  magnetism  for  a 
long  time  after  being  magnetized. 


A  permanent  magnet  is  distinguished,  in  this 
respect,  from  a  temporary  magnet  of  soft  iron, 
which  loses  its  magnetization  very  shortly  alter 
being  taken  from  the  magnetizing  field. 

Magnet,  Portative  Power  of  —  —The 
lifting  power  of  a  magnet. 

The  portative  or  lifting  power  of  a  magnet, 
depends  on  the  form  of  the  magnet,  as  well  as  on 
its  strength.  A  horseshoe  magnet,  for  example, 
will  lift  a  much  greater  weight  than  the  same 
magnet  if  in  the  form  of  a  straight  bar. 

This  is  due  not  only  to  the  mutual  action  of  the 
approached  poles,  but  also  to  the  decreased  re- 
sistance of  the  magnetic  circuit,  and  to  the  greater 
number  of  lines  of  magnetic  force  that  pass 
through  the  armature.  The  portative  power  is 
proportional  to  the  area  of  contact  and  the  square 
of  the  magnetic  intensity,  the  formula  being 

P  =      A  XB* 

8  7T    X    98l, 

in  which  P,  is  the  lifting  power  in  grammes,  AT 
the  area  of  contact  in  square  centimetres,  and  B, 
is  the  number  of  lines  of  force  per  square  centi- 
metre. 

Magnet  Operation (See  Operation, 

Magnet. ) 

Magnet,  Receiving A  name  some- 

times  given  to  the  relay  of  a  telegraphic 
system.  (See  Relay.) 

In  general,  any  magnet,  used  directly  in 
the  receiving  apparatus,  at  the  receiving 
end  of  a  line  connecting  a  system  of  elec- 
tric communication  between  transmitting 
and  receiving  instruments. 

Magnet,  Regulator A  magnet,  the 

operation  of  which  is  to  automatically 
effect  any  desired  regulation. 

The  magnet  in  the  Thomson-Houston 
system  of  automatic  regulation,  by  means 
of  which  the  commutator  collecting 
brushes  are  automatically  shifted  to  such 
positions  on  the  commutator  as  will  main- 
tain the  current  practically  constant,  de- 
spite the  changes  in  the  resistance  of  the 
circuit  external  to  the  machine.  (See 
Regulation,  Automatic.) 

Magnet,  Relay  —  -An  electro-magnet, 
whose  coils  are  connected  to  the  main  line 
of  a  telegraphic  circuit,  and  the  movements 


Mag.] 


342 


[Mag. 


of  whose  armature  is  employed  to  bring  a 
local  battery  into  action  at  the  receiving 
station,  the  current  of  which  operates  the 
register  or  sounder. 

Magnet,  Short-Coil An  electro- 
magnet whose  magnetizing  coil  consists 
of  a  few  turns  of  short,  thick  wire. 

Magnet,  Simple A  simple  mag- 
netized bar. 

The  term  simple  magnet  is  used  in  contradis- 
tinction to  compound  magnet.  (See  Magnet, 
Compound.) 

Magnet,  Sluggish A  magnet  that 

magnetizes  or  demagnetizes  sluggishly. 

An  electro-magnet  becomes  sluggish  when  sur- 
rounded by  a  sheathing  of  copper,  on  account  of 
the  currents  induced  in  the  sheathing  in  a  direc- 
tion opposite  to  those  passing  through  the  mag- 
netizing coil. 

Magnet,  Solenoidal A  thin,  uni- 
formly magnetized  straight  bar  of  steel,  of 
such  a  length  that  its  poles,  situated  at 
extremities  or  ends  of  its  longer  axis,  act 
on  external  objects  as  if  equal  and  oppo- 
site quantities  of  magnetism  were  con- 
centrated at  such  extremities. 

It  derives  its  name  solenoidal  from  the  simi- 
larity between  its  action  and  that  of  a  solenoid. 
Unless  very  carefully  magnetized,  a  magnet  will 
not  act  as  a  solenoid  magnet.  (See  Magnet, 
Electro.  Magnetism,  Solenoidal  Distribution  of.) 

Magnet,  Tabular A  form  of  horse- 
shoe magnet,  in  which  one  pole  is  brought 
near  the  opposite  pole  by  a  hollow  cylin- 
der or  tube  of  iron,  which  is  placed  in  con- 
tact with  one  of  the  magnetic  poles,  so  as 
to  completely  surround  the  other,  except 
in  the  plane  of  cross-section  of  that  pole. 

A  form  of  iron-clad  magnet.  (See 
Magnet,  Iron- Clad.) 

There  is  thus  obtained  a  magnet,  with  two  con- 
centric poles,  one  solid  and  the  other  annular, 
the  portative  power  of  which  is  much  greater  than 
that  of  a  horseshoe  magnet  of  equal  dimensions. 

Magnet,  Field,  of  Dynamo-Electric  Ma- 
chine   One  of  the  electro-magnets 

employed  to  produce  the  magnetic  field 
of  a  dynamo-electric  machine. 


The  field  magnets  consist  of  a  suitable  frame . 
or  core,  on  which  the  field  magnet  coils  are 
wound. 

The^/fc/rf  magnet  cores  are  made  of  thick  and 
solid  iron,  as  soft  as  possible.  They  should  con- 
tain plenty  of  iron  in  order  to  avoid  too  ready 
magnetic  saturation. 

All  edges  and  corners  are  to  be  avoided,  since 
they  tend  to  cause  an  irregular  distribution  of  the 
field. 

The  field  magnets  should  in  general  have  suffi- 
cient magnetic  strength  to  prevent  the  magnet- 
izing effect  of  the  armature  from  unduly  influ- 
encing the  field,  and  thus,  by  causing  too  great  a 
lead,  produce  injurious  sparking. 

Magnetic  or  Magnetical.— Pertaining  to 
magnetism. 

Magnetic  Adherence.— (See  Adherence, 
Magnetic. ) 

Magnetic  Air  Circuit.— (See  Circuit,  Air, 
Magnetic. ) 

Magnetic  Air  Gap— (See  Gap,  Air,  Mag- 
netic. ) 

Magnetic  Attraction.— (See  Attraction, 
Magnetic, ) 

Magnetic  Axis.— (See  Axis,  Magnetic.) 

Magnetic  Axis  of  a  Straight  Needle.— 

(See  Axis,  Magnetic,  of  a  Straight  Needle.) 

Magnetic  Azimuth. -(See  Azimuth,  Mag- 
netic. ) 

Magnetic  Battery.— (See  Battery,  Mag- 
netic.) 

Magnetic  Bridge,— (See  Bridge,  Mag- 
netic.) 

Magnetic  Circuit.— (See  Circuit,  Mag- 
netic.) 

Magnetic  Closed-Circuit.-(See  Circuit, 
Closed  Magnetic. ) 

Magnetic  Conductance.- (See  Conduct- 
ance, Magnetic.) 

Magnetic  Core,  Closed (See  Core, 

Closed-Magnetic. 

Magnetic  Core,  Open (See  Core, 

Open-Magnetic. ) 

Magnetic  Couple.-(See  Coupe,  Mag- 
netic.) 


Mag.] 


343 


Magnetic  Curves.—  (See  Curves,  Mag- 
netic. ) 

Magnetic  Day  of  Disturbancc.-(See  Day 
of  Disturbance,  Magnetic. ) 

Magnetic  Declination.  —  (See  Declina- 
tion.} 

Magnetic  Density.— (See  Density,  Mag- 
Wtic. } 

Magnetic  Dip.— (See  Dip,  Magnetic.} 

Magnetic  Elements  of  a  Place.  — (See 
Elements,  Magnetic,  of  a  Place. } 

Magnetic  Equalizer.  —  (See  Equalizer, 
Magnetic. } 

Magnetic  Explorer. —(See  Explorer,  Mag- 
netic. ) 

Magnetic,  Ferro Magnetic  after 

the  manner  of  iron  or  other  paramagnetic 
body.  (See  Paramagnetic.} 

Magnetic  Field.— (See  Field,  Magnetic.} 

Magnetic  Field,  Reversing. (See 

Field,  Magnetic,  Reversing.} 

Magnetic  Field,  Shifting. (See 

Field  Magnetic,  Shifting.} 

Magnetic  Figures.— See  Figures,  Mag- 
netic. Field,  Magnetic.} 

Magnetic  Filament.  —  (See  Filament 
Magnetic.} 

Magnetic  Flow.— (See Flow,  Magnetic.} 

Magnetic  Flux.— (See    Flux,  Magnetic.} 

Magnetic  Force.— (See  Force,  Magnetic. } 

Magnetic  Inclination.— (See  Inclination, 
Magnetic. } 

Magnetic  Induction.  —  (See  Induction, 
Magnetic.) 

Magnetic  Induction,  Dynamic. 

(See Induction,  Magnetic,  Dynamic.) 

Magnetic  Induction,  Static. (See 

Induction,  Magnetic,  Static} 

Magnetic  Inertia.— (See  Inertia,  Mag- 
netic.} 

Magnetic  Intensity.  —  (See  Intensity, 
Magnetic. } 

Magnetic  Joint.— (See  Joint,    Magnetic.} 


Magnetic  Lag. — (See  Lag,  Magnetic} 

Magnetic  Latitude. — (See  Latitude,  Mag- 
netic.} 

Magnetic  Leakage. — (See  Leakage,  Mag- 
netic.} 

Magnetic  Lines  of  Force.— (See  Force, 
Magnetic,  Lines  of.} 

Magnetic  Mass. — (See  Mass,  Magnetic. ) 

Magnetic  Memory.— (See  Memory,  Mag- 
netic. ) 

Magnetic  Meridian.  —  (See  Meridian, 
Magnetic.} 

Magnetic  Moment.— (See  Moment,  Mag- 
netic.} 

Magnetic  Normal  Day.— (See  Day,  Nor- 
mal, Magnetic.) 

Magnetic  Observatory.  —  (See  Observa- 
tory, Magnetic. 

Magnetic  Output— (See  Output,  Mag- 
netic. ) 

Magnetic  Parallel.— (See  Parallels,  Mag- 
netic. ) 

Magnetic  Permeability.  —  (See  Permea- 
bility, Magnetic.) 

Magnetic  Permeance. — (See  Permeance, 
Magnetic.) 

Magnetic  Permeation. — (See  Permeation, 
Magnetic. ) 

Magnetic  Poles.— (See  Poles,  Magnetic.) 

Magnetic  Poles,  False, (See  Pole, 

Magnetic,  False.) 

Magnetic  Proof  Piece.— (See  Piece,  Mag- 
netic Proof.) 

Magnetic  Proof  Plane.— (See  Plane, 
Proof,  Magnetic.) 

Magnetic  Reluctance.— (See  Reluctance, 
Magnetic. ) 

Magnetic  Repulsion.  —  (See  Repulsion, 
Magnetic.) 

Magnetic  Resistance.  —(See  Resistance, 
Magnetic.) 

Magnetic  Retardation.  —  (See  Retarda- 
tion Magnetic.) 


Mag.] 


344 


[Mag. 


Magnetic  Retentirity.-(See  Retentwity, 
Magnetic.} 

Magnetic  Saturation.— (See  Saturation, 
Magnetic.) 

Magnetic  Screen  or  Shield.- (See  Screen 
or  Shield,  Magnetic. ) 

Magnetic  Screening.  —  (See  Screening, 
Magnetic.) 

Magnetic,  Self  Induction.— (See  Induc- 
tion, Self,  Magnetic.) 

Magnetic  Shells.— (See  Shells,  Magnetic.) 
Magnetic  Shunt.— (See  Shunt,  Magnetic. ) 

Magnetic  Sidero A  term  proposed 

by  S.  P.  Thompson  to  replace  the  term 
ferro-magnetic.    (See  Magnetic,  Ferro.) 

Magnetic  Solenoid. -(See  Solenoid,  Mag- 
netic. ) 

Magnetic  Sounds.— (See  Sounds,  Mag- 
netic. ) 

Magnetic  Spin.— (See  Spin,  Magnetic.) 
Magnetic    Storm.— (See     Storm,     Mag- 
netic.) 

Mignetic  Strain. —  (See  Strain,  Mag- 
netic.) 

Magnetic  Stress.— (See  Stress,  Magnetic. ) 
Magnetic   Susceptibility. -(See    Suscepti- 
bility, Magnetic. ) 

Magnetic  Theodolite.  —  (See  Theodolite, 
Magnetic  ) 

Magnetic  Unit  Pole.— (See  Pole,  Unit, 
Magnetic. ) 

Magnetic  Units.— (See    Units,  Magnetic) 

Magnetic- Vane  Ammeter.— (See  Ammeter, 
Magnetic-  Vane. ) 

Magnetic  Vane  Voltmeter.  -  (See  Volt- 
meter, Magnetic-  Vane.) 

Magnetic  Variations.  —  (See  Variations, 
Magnetic. ) 

Magnetic  Variation  Transit. -(See  Tran- 
sit, Magnetic  Variation.) 

Magnetic  Variometer.— (See  Variometer, 
Magnetic.) 


Magnetic  Viscosity.-  (See  Viscosity,  Mag- 
netic.) 

Magnetic  Whirl.— (See  Whirls,  Magnetic.) 

Magnetic  Whirl,  Expanding  —(See 

Whirl,  Magnetic,  Expanding.) 

Magnetics,  Electro That  branch  of 

electric  science  which  treats  of  the  rela- 
tions that  exist  between  electric  circuits 
and  magnets. 

Magnetism.  —  That  branch  of  science ' 
which  treats  of  the  nature  and  properties 
of  magnets  and  the  magnetic  field.  (See 
Field,  Magnetic.) 

A  property  or  condition  of  matter  at- 
tended by  the  existence  of  a  magnetic 
field. 

Magnetism,  Ampere's  Theory  of A 

theory  or  hypothesis  proposed  by  Ampere, 
to  account  for  the  cause  of  magnetism,  by 
the  presence  of  electric  currents  in  the 
ultimate  particles  of  matter. 


f  •  37  Q*     Unmagnetized 
Bar  (after  Am  fire}. 


Fig.  380.      Magnetized 
Bar  (after  Amptre) . 


This  theory  assumes  : 

(I.)  That  the  ultimate  particles  of  all  magneti- 
zable  bodies  have  closed  electric  circuits  in  which 
electric  currents  are  continually  flowing. 

(2.)  That  in  an  unmagnetized  body  these  cir  - 
cuits  neutralize  one  another  because  they  have 
different  directions. 

(3.)  That  the  act  of  magnetization  consists  •> 
such  a  polarization  of  the  particles  as  will  cause 
these  currents  to  flow  in  one  and  the  same  direc- 
tion,  magnetic  saturation  being  reached  when  all 
the  separate  circuits  are  parallel  to  one  another. 

(4.)  That  coercive  force  is  due  to  the  resistance 
these  circuits  offer  to  a  change  in  the  direction 
of  their  planes. 

Figs.  379  and  380  show  the  circular  paths  of 
some  of  these  circuits.  Fig.  379  shows  the  as- 


Mag.] 


345 


[Mag. 


sumed  condition  of  an  unmagnetized  bar.  Fig. 
380  the  assumed  condition  of  a  magnetized 
bar. 

A  careful  inspection  of  the  figures  will  show  that 
in  a  magnetized  bar  all  the  separate  currents  flow 
in  the  same  direction.  All  the  circuits  except 
those  on  the  extreme  edge  of  the  bar  will,  there- 
fore, have  the  currents  flowing  in  them  in  opposite 
directions  to  that  in  their  neighboring  circuits, 
and,  therefore,  will  neutralize  one  another .  There 
will  remain,  Jurwever,  a  current  in  a  circuit  on  the 
outside  of  the  bar,  which  must  therefore  be  re- 
garded as  the  magnetizing  current. 

Guided  by  these  considerations,  Ampere  pro- 
duced a  coil  of  wire,  called  a  solenoid,  which  is 
the  equivalent  of  the  magnetizing  circuit  assumed 
by  his  theory. 

It  therefore  follows  that  an  electric  current  sent 
through  a  coil  of  insulated  wire  surrounding  a 
rod  or  bar  of  soft  iron,  or  other  readily  magnet- 
izable material,  will  make  the  same  a  magnet.  A 
magnet  so  produced  is  called  an  electro-magnet. 
(See  Magnet,  Electro.} 

The  magnetizing  coil  is  called  a  helix  or  sole- 
noid. See  Solenoid,  Electro -Magnetic.") 

The  polarity  of  the  magnef  depends  on  the 
direction  of  the  current,  or  on  the  direction  of 
winding  of  the  helix  or  solenoid.  (See  Solenoid, 
Sinistrorsal.  Solenoid,  Dextrorsal.) 

The  improbability  of  an  electric  current  con- 
tinually flowing  in  a  circuit  without  the  expendi- 
ture of  energy,  has  led,  perhaps,  the  majority  of 
scientific  men  to  reject  Ampere's  theory  of  mag- 
netism. 

Lodge,  however,  does  not  agree  with  the  ma- 
jority of  physicists  in  regarding  a  constant  flow 
of  electricity  through  the  molecules  of  magnetiza- 
ble substances  as  an  impossibility.  On  the  sup- 
position that  the  atoms  or  molecules  possess 
no  resistance,  the  current  would  flow  through 
them  lorever.  He  says:  "To  all  intents  and  pur- 
poses certainly  atoms  are  infinitely  elastic,  and 
why  should  they  not  also  be  infinitely  conducting  ? 
Why  should  the  dissipation  of  energy  occur,  in 
respect  to  an  electric  current  circulating  wholly 
inside  an  atom?  There  is  no  reason  why  it 
should.  " 

Magnetism,  Animal A  term  some- 
times applied  to  hypnotism  or  artificial 
somnambulism. 

Magnetism,  Earth's,  Theories  as  to  Cause 
of The  various  theories  or  hypotheses 


respecting  the  cause  of  the  earth's  magnet- 
ism. 

Any  theory  or  hypothesis  which  shall  satisfac- 
torily  explain  the  cause  of  the  earth's  magnetism 
must  account  for  the  following  phenomena,  viz.  ; 

(l.)  Variations  in  the  intensity  of  the  earth's 
magnetic  field. 

(2.)  Variations  in  the  earth's  magnetic  inclina- 
tion, declination  and  intensity. 

The  following  hypotheses  have  been  proposed: 

1st.  That  the  earth's  magnetism  is  due  to  the 
circulation  round  the  earth  of  electric  currents 
produced  by  differences  of  temperature  which  the 
earth's  surface  acquires  from  exposure  to  the  sun 
during  its  rotation. 

As  the  earth  rotates  from  west  to  east,  the  area 
of  greatest  heat  would  move  round  the  earth  in 
the  opposite  direction,  or  from  east  to  west.  If 
now  those  differences  of  temperature  could  pro- 
duce, in  a  manner  not  as  yet  explained,  thermo- 
electric currents  circulating  round  the  earth  from 
east  to  west,  such  currents  would  produce,  in  the 
Northern  Hemisphere  of  the  earth,  south  mag- 
netic polarity,  and  in  the  Southern  Hemisphere 
north  magnetic  polarity,  which  would  account  for 
the  magnetic  polarity  of  the  earth. 

Differences  in  the  intensity  of  the  earth's  mag- 
netic field,  and  in  the  inclination  and  direction  of 
its  lines  ot  magnetic  force,  would  be  explained, 
according  to  this  hypothesis,  by  the  differences  in 
the  amount  of  the  solar  radiation  at  different 
times. 

The  objection  to  this  theory  is  to  be  found  in 
the  fact  that  by  far  the  larger  part  of  the  earth's 
surface  at  the  Equator  is  composed  of  water,  so 
that  the  differences  of  potential  at  such  parts, 
produced  by  the  differences  of  temperature,  are 
not  readily  set  up  in  the  earth's  crust,  if,  indeed, 
they  are  set  up  at  all. 

2d.  That  the  earth's  magnetism  is  due  to  in- 
duction from  an  already  magnetized  sun.  This 
theory  was  brought  forward  by  Secci  and  others. 
It  is  not  generally  credited. 

3d.  A  theory  proposed  by  Biglow,  which  ac- 
counts for  the  earth's  magnetism  by  rotation  in 
the  magnetic  field  of  the  sun's  light  and  radia- 
tion. 

Biglow  believes  that  the  earth's  magnetism  is 
due  to  its  rotation  in  the  magnetic  field  of  the 
sun's  light.  As  the  sun's  light  illumines  one-half 
of  the  earth's  surface,  the  earth's  rotation  causing 
different  portions  of  the  surface  to  pass  through 


Mag.] 


346 


[Mag. 


this  illumiru  d  area,  produces,  in  Prof.  Biglow's 
opinion,  th  #e  differences  in  the  direction  and  in- 
tensity of  the  magnetic  lines  of  the'  earth's  field 
that  correspond  to  differences  in  the  earth's  mag- 
netic intensity,  declination  and  inclination. 

It  will  be  observed  that  in  all  these  theories  the 
sun  is  the  prime  factor  in  the  production  ol  the 
earth's  magnetism. 

The  evident  connection  between  the  earth's 
magnetism  and  the  solar  radiation  is  established 
from  the  well  known  connection  between  the  so- 
called  magnetic  storms  and  variations  in  the  in- 
tensity of  the  earth's  magnetism. 

Magnetic  storms  are  always  attended  by  out- 
bursts of  solar  energy,  known  technically  as 
sun  spots.  A  series  of  observations  on  the  num- 
bers and  frequency  of  sun-spots,  plotted  in  the 
form  of  a  curve,  the  ordinates  of  which  represent 
the  times  of  occurrence  of  the  spots  and  the 
abscissas,  the  number  of  such  spots,  prove  that 
such  curve  agrees,  in  a  remarkable  manner,  with 
a  similar  curve  representing  the  variations  of  the 
earth's  magnetic  field. 

An  evident  connection,  too,  exists  between  the 
earth's  magnetism  and  the  prevalence  of  the 
aurora  borealis. 

MairnetUin,  Electro Magnetism 

produced  by  means  of  electric  currents. 

The  discovery  by  Oersted,  in  1820,  of  the  ac- 
tion of  an  electric  current  on  a  magnetic  needle, 
was  almost  immediately  followed  by  the  simul- 
taneous and  independent  discoveries  by  Arago 
and  Davy,  of  the  method  of  magnetizing  iron 
by  the  passage  of  an  electric  current  around  it. 

These  observations  were  first  reduced  to  a 
theory  by  Ampere  (See  Magnetism,  Ampere's 
Theory  of.  Magnet ',  Electro.) 

Magnetism,  Ewing's  Theory  of A 

theory  of  magnetism  proposed  by  Prof. 
Ewing,  based  on  the  assumption  of  orig- 
inally magnetized  particles. 

Ewing's  theory  of  magnetism  assumes  that  the 
ultimate  particles  ot  matter  are  naturally  mag- 
netic and  possess  polarity.  In  this  respect  Ewing's 
theory  agrees  with  the  theories  of  Hughes  and 
Weber.  Ewing  does  not  believe,  however,  in  the 
necessity  for  the  assumption  of  any  arbitrary  re- 
straining or  constraining  force  to  the  movements 
of  these  ultimate  magnetic  particles  other  than 
those  due  to  their  own  mutual  magnetic  attractions 
and  repulsions.  He  assumes  that  in  a  magnet, 


the  centres  about  which  the  molecular  magnets 
rotate  are  maintained  at  constant  distances  from 
one  another,  save  only  as  they  are  affected  by  the 
action  of  strain. 

He  has  experimentally  demonstrated  the  prin- 
ciples of  his  theory  by  means  of  a  model  in  which 
a  number  of  small  magnetic  needles  are  so  sup- 
ported as  to  be  capable  of  free  motion  in  a  hori- 
zontal plane,  when  under  varying  magnetic 
forces. 

According  to  Ewing,  "magnetic  hysteresis" 
is  not  the  result  of  any  quasi  frictional  resistance 
to  molecular  rotation,  but  arises  from  a  molecule 
moving  from  one  position  of  stable  equilibrium  to 
another  position  of  stable  equilibrium  through  a 
position  of  unstable  equilibrium.  "  This  pro- 
cess "  says  Ewing,  "considered  mechanically,  is 
not  reversible.  The  forces  are  different  for  the 
same  displacement,  going  and  coming,  and  there 
is  dissipation  of  energy.  In  the  model,  the  energy 
thus  expended  sets  the  little  bars  swinging,  and 
their  swings  take  some  time  to  subside.  In  the 
actual  solid,  the  energy  which  the  molecular 
magnet  loses  as  it  swings  through  unstable  posi- 
tions, generates  eddy  currents  in  surrounding 
matter.  Let  the  magnets  of  the  model  be 
furnished  with  air  vanes  to  damp  their  swings 
and  the  correspondence  is  complete." 

In  Hughes'  modification  of  Weber's  theory  of 
magnetism,  it  was  held,  that  when  magnetized 
iron  was  suddenly  demagnetized  by  torsion  or 
flexure,  it  lost  its  magnetization  because  the  mo- 
lecular magnets  came  to  rest  in  closed  chains,  which 
produced  no  external  effects.  Experimentation 
with  Ewing's  model  of  a  magnet  shows  that  when 
the  separate  magnets  after  having  been  placed  in 
any  particular  grouping  are  permitted  to  come  to 
rest  free  from  any  external  magnetic  force,  they  do 
not  arrange  themselves  in  closed  chains,  but  in 
general  the  tendency  appears  to  be  the  formation 
of  lines  consisting  of  two,  three  or  more  magnets, 
each  member  of  a  line  being  strongly  controlled 
by  its  next  member  in  that  line,  but  influenced 
by  the  neighbors  which  lie  off  the  line  on  either 
side. 

The  fact  that  a  given  force,  suddenly  applied, 
produces  more  magnetic  induction  than  when 
gradually  applied,  and  leaves  less  residual  mag- 
netism when  suddenly  than  when  gradually  re- 
moved, is  presumably  due  to  the  inertia  of  the 
molecules. 

The  influence  of  mechanical  vibration  in  in- 
creasing the  magnetic  susceptibility  and  decreas- 


Mag.] 


34? 


[Mag; 


ing  the  magnetic  retentiveness,  is  ascribed  by 
Ewing  to  the  fact  that  the  vibrations  cause 
periodic  variations  in  the  distances  between  the 
centres  of  rotation  of  the  magnetic  molecules; 
thus  making  the  molecular  magnets  respond  more 
readily  to  changes  of  magnetic  force  during  the 
time  they  are  moving  away  from  one  another, 
when  their  magnetic  stability  is  less,  but  also  in- 
creasing the  ease  with  which  they  respond  to 
changes  of  magnetic  force,  by  causing  them  to 
swing. 

Ewing  discusses  the  theoretical  effects  of  tern- 
perature  on  magnetism  as  follows,  viz. :  Suppose 
a  moderate  magnetizing  force  to  be  applied  so 
that  nothing  like  saturation  is  obtained,  if  now 
the  temperature  be  raised ;  then 

(i.)  The  magnetic  permeability  increases  until 
the  temperature  reaches  a  certain  (high)  critical 
value. 

(2.)  At  this  temperature  there  is  suddenly  an 
almost  complete  disappearance  of  magnetic 
quality. 

He  explains  these  facts  as  follows,  viz.:  An 
increase  of  temperature  by  increasing  the  distance 
between  the  molecular  centres  causes  a  decrease 
In  their  stability. 

The  loss  of  magnetic  qualities,  when  a  certain 
temperature  is  reached,  is,  he  believes,  due  to  the 
fact  that  at  such  temperatures  the  magnetic 
molecules  are  set  into  actual  rotation,  when, 
naturally,  all  traces  of  polarity  would  disappear. 

Ewing's  theory  of  magnetism  also  accounts  to 
a  considerable  extent  for  the  effects  of  stress  and 
consequent  elastic  strain  on  the  magnetic  qualities 
of  iron,  nickel  and  cobalt. 

The  following  general  summary  of  his  theory 
is  taken  mainly  from  Prof.  Ewing's  original 
articles  as  published  in  the  Journal  of  the  Society 
of  Arts: 

(i.)  That  in  considering  the  magnetization  of 
iron  and  other  magnetic  metals  to  be  caused  by 
the  turning  of  permanent  molecular  magnets,  we 
may  look  simply  to  the  magnetic  forces  which 
the  molecular  magnets  exert  upon  one  another  as 
the  cause  of  their  directional  stability.  There  is 
no  need  to  suppose  the  existence  of  any  quasi- 
elastic  directing  force,  or  any  quasi-frictional  re- 
sistance to  rotation. 

(2. )  That  the  intermolecular  magnetic  forces  are 
sufficient  to  account  for  all  the  general  character- 
istics of  the  process  of  magnetization,  including 
the  variations  of  susceptibility  which  occur  as 
the  magnetizing  force  is  increased. 

12— Vol.  1 


(3.)  That  the  intermolecular  magnetic  forces 
are  equally  competent  to  account  for  the  known 
facts  of  retentiveness  and  coercive  force,  and  the 
characteristics  of  cyclic  magnetic  processes. 

(4. )  The  magnetic  hysteresis  and  the  dissipation 
of  energy  which  hysteresis  involves  are  due  to 
molecular  instability,  resulting  from  intermolec- 
ular magnetic  actions,  and  are  not  due  to  any- 
thing  in  the  nature  of  frictional  resistance  to  the 
rotation  of  the  molecular  magnets. 

(5.)  That  this  theory  is  wide  enough  to  admit  an 
explanation  of  the  differences  in  magnetic  quality 
which  are  shown  by  different  substances,  or  by 
the  same  substance  in  different  states. 

(6. )  That  it  accounts  in  a  general  way  for  the 
known  effects  of  vibration,  of  temperature,  and 
of  stress,  upon  magnetic  quality. 

(7.)  That,  in  particular,  it  accounts  for  the 
known  fact  that  there  is  hysteresis  in  the  relation 
of  magnetism  to  stress. 

(8.)  That  it  further  explains  why  there  is  in 
magnetic  metals  hysteresis  in  physical  quality 
generally  with  respect  to  stress. 

(9.)  That,  in  consequence,  any  (not  very  small) 
cycle  of  stress  occurring  in  a  magnetic  metal  in- 
volves dissipation  of  energy. 

It  can  be  demonstrated  by  means  of  experi- 
ments with  a  model  constructed  according  to 
Ewing's  hypothesis,  that  this  hypothesis  comes 
nearer  than  any  which  had  been  proposed  before 
in  explaining  the  following  effects: 

(I.)  The  behavior  of  a  piece  of  iron  when 
placed  in  a  magnetic  field  whose  strength  is  made 
to  pass  through  a  cycle  of  changes. 

(2.)  That  nearly  all  reversals  of  sign  on  the 
change  of  the  magnetizing  force  are  accompanied 
by  small  changes  in  the  magnetization. 

(3.)  That  a  piece  of  iron  submitted  to  vibra- 
tions or  mechanical  shocks,  is  magnetized  and 
demagnetized  more  readily  and  with  a  smaller 
hysteresial  area  than  if  it  had  remained  undis- 
turbed by  vibrations. 

(4.)  The  phenomenon  of  "time  lag  "in  mag- 
netization. 

(5.)  The  phenomena  of  stress,  both  those  which' 
occur  when  a  body  has  first  been  placed  in  a 
magnetic  field  and  the  stress  made  to  vary,  and 
those  which  occur  when  a  body  is  first  placed  in 
a  constant  stress  and  the  magnetizing  force  is 
made  to  vary. 

(6.)  The  effects  of  heat  on  magnetization,  both 
as  regards  the  effect  of  comparatively  low  heating 
on  increase  of  magnetic  susceptibility,  and  the 


Mag.] 


348 


[Mag. 


effect  of  excessive  heating  to  decrease  the  sus- 
ceptibility. 

The  author  is  indebted  for  the  above  summary 
of  demonstrable  facts  to  a  paper  recently  read  be- 
fore the  Electrical  Section  of  the  Franklin  Insti- 
tute, by  Prof.  Henry  Crew. 

Magnetism,  Flux  or  Flow  of  —  —The 
quantity  of  magnetism,  or  the  number  of 
lines  of  force  which  pass  in  any  magnetic 
circuit  under  a  given  magneto-motive  force, 
against  a  given  magnetic  reluctance. 

Magnetism,  Galvano A  term  some- 
times used  for  electro-magnetism. 

Electro-magnetism  is  by  far  the  preferable 
term,  and  is  almost  universally  used  in  the  United 
States. 

Magnetism,  Horizontal  Component  of 

Earth's (See  Component,  Horizontal, 

of  Earth's  Magnetism^) 

Magnetism,  Hughes'  Theory  of A 

theory  propounded  by  Hughes  to  account  for 
the  phenomena  of  magnetism  apart  from  the 
presence  of  electric  currents. 

Hughes'  theory,  or,  more  strictly  speaking, 
hypothesis  of  magnetism,  though  very  similar  to 
that  of  Ampere,  does  not  assume  the  improbable 
condition  of  a  constantly  flowing  electric  current. 

Hughes'  hypothesis  assumes: 

(I.)  That  the  molecules  of  matter,  and,  per- 
haps, more  probably,  the  atoms,  possess  naturally 
opposite  magnetic  polarities,  which  are  respect- 
ively +  and  — ,  or  N  and  S. 

(2.)  That  these  molecules,  when  arranged  in 
closed  chains  or  circuits,  are  capable  of  neutral- 
izing one  another  so  far  as  external  action  is  con- 
cerned. 


and  that,  therefore,  the  substance  can  possess  no 
magnetic  properties  so  far  as  external  action  is 
concerned. 


i: 


'n\ 


Fig,  381.     Closed  Molecular  Chain. 

Two  such  arrangements  or  groupings  are 
shown  in  Figs.  381  and  382.  It  will  be  observed 
that  the  magnetic  chain  or  circuit  is  complete, 


Fig.  382.     Closed  Groupings. 

(3.  )  That  the  act  of  magnetization  consists  in 
such  a  rotation  of  the  molecules  that  a  polariza- 
tion of  the  substance  is  effected—  that  is,  the 
molecules  are  rotated  on  their  axes  so  that  one  set 
of  poles  tend  to  point  in  one  direction  and  the 
other  set  of  poles  in  the  opposite  direction. 

Partial  magnetization  consists  in  partial  polari- 
zation. Magnetic  saturation  is  reached  when  the 
polarization  is  complete.  (See  Saturation,  Mag- 
netic.) 

Coercive  force  is  the  resistance  the  body  offers 
to  the  polarization  or  rotation  of  its  molecules. 
(See  Force,  Coercive.) 

Hughes'  hypothesis  of  magnetism  would  ap- 
pear to  be  strengthened  by  the  following  facts: 

(I.)  A  bar  of  steel  or  iron  is  sensibly  elongated 
on  being  magnetized.  This  would  naturally  re- 
sult if  the  molecules  be  supposed  to  be  longer  in 
one  direction  than  in  any  other. 

(2.)  A  tube,  furnished  at  its  ends  with  plates  of 
flat  glass  and  filled  with  water  containing  finely 
divided  magnetic  oxide  of  iron,  is  nearly  opaque 
to  light  when  unmagnetized,  but  will  permit  some 
light  to  pass  through  it  when  magnetized. 

(3.  )  A  magnet,  if  cut  at  its  neutral  point,  will 
possess  opposite  polarities  at  the  cut  ends;  and, 
no  matter  to  what  extent  this  subdivision  is  car- 
ried, the  particles  will  still  possess  opposite  polar- 
ities. 

These  facts  are,  however,  also  explained  by 
Ampere's  hypothesis  of  magnetism,  with,  how- 
ever, the  improbable  assumption  of  a  constantly 
flowing  current  in  each  molecule. 

The  following  experiment  by  Von  Betz  tends 
somewhat  to  confirm  Hughes'  hypothesis: 

He  placed  a  powerful  horseshoe  magnet  in  a 
solution  of  iron  and  deposited  a  bar  or  plate  of 
metallic  iron  between  the  poles  by  electrolysis. 
Here  the  molecules,  at  the  time  of  their  deposi- 
tion, were  subjected  to  a  polarizing  force  which 
tended  to  place  them  all  in  the  same  direction, 
and,  as  the  solution  from  which  they  were  ob- 
tained permitted  great  freedom  of  motion,  they 
were  all  presumably  deposited  in  lines  parallel  to 
one  another.  When  this  bar  of  iron  was  subse 


Mag.] 


349 


[Mag. 


quently  magnetized  it  was  found  to  be  much  more 
powerful  in  comparison  to  its  size  than  any  other 
magnet. 

Mr.  Shelford  Bidwell  has  shown  that  the  act  of 
magnetization  produces  a  shortening  rather  than 
a  lengthening  of  the  magnetizable  material. 
When  the  magnetization  is  moderate  there  is  a 
true  lengthening  of  the  material,  but  when  a 
more  powerful  magnetizing  force  is  exerted  a 
true  contraction  or  shortening  is  observed. 


Fig.  383.    Bidwell  Apparatus. 

The  Bidwell  apparatus  is  shown  in  Fig.  383. 
The  bar  of  iron  to  be  magnetized  is  shown  at 
R  R.  The  magnetization  is  obtained  by  means  of 
the  coil  of  wire  C.  The  upper  end  of  the  bar 
presses  against  the  rod  L,  fulcrumed  at  F.  The 
other  end  of  the  bar  bears  against  a  pivoted 
mirror  M,  from  which  a  spot  of  light  is  reflected. 

In  the  case  of  the  magnetization  of  nickel,  the 
experiments  of  Bidwell  showed  the  existence  of 
contraction  for  both  weak  and  strong  currents. 
This  contraction  is  much  greater  than  in  the  case 
of  iron. 

Magnetism,  Lamellar  Distribution  of 

— The  distribution  of  magnetism  in 

magnetic  shells. 

A  term  sometimes  applied  to  such  a  dis- 
tribution of  magnetism  in  a  plate,  that  the 
magnetized  particles  are  arranged  with  their 
greatest  length  in  the  direction  of  the  thick- 
ness of  the  plate,  so  that  the  poles  are  situ- 
ated at  the  faces  of  the  plate,  and  conse- 
quently the  extent  of  such  polar  surfaces  is 
great  when  compared  with  the  thickness  of 
the  plate. 

The  term  lamellar  distribution  of  magnetism  is 
used  in  contradistinction  to  solenoidal  distribution. 
(See  Magnetism,  Solenoidal  Distribution  of  .) 

A  thin  sheet  or  disc  of  magnetized  material 
whose  opposed  extended  faces  are  of  opposite 


magnetic  polarities,  and  the  extent  of  whose  sur- 
face is  very  great  as  compared  with  its  thickness, 
is  sometimes  called  a  magnetic  shell. 

The  field  produced  by  a  magnetic  shell  is  ex- 
actly similar  to  that  produced  by  a  closed  voltaic 
circuit,  the  edges  of  the  space  inclosed  by  which 
correspond  to  the  edges  of  the  magnetic  shell. 

The  magnetic  intensity,  or  the  number  of  lines 
of  force  per  unit  area  of  cross-section,  is  equal 
over  all  parts  of  the  surface  of  a  simple  magnetic 
shell. 

A  magnetic  shell  may  be  conceived  as  consist- 
ing of  a  very  great  number  of  short,  straight 
magnetic  needles,  placed  side  by  side,  with  their 
north  poles  terminating  at  one  of  the  faces  of  the 
sheet  and  their  south  poles  at  the  opposite  face, 
the  breadth  of  the  sheet  being  very  great  as  com- 
pared with  its  thickness.  Such  a  distribution  of 
magnetism  is  known  as  a  lamellar  distribution. 

Magnetism,  Residual The  magnet- 
ism remaining  in  the  core  of  an  electro-mag- 
net on  the  opening  of  the  magnetizing  cir- 
cuit. 

The  small  amount  of  magnetism  retained 
by  soft  iron  when  removed  from  any  mag- 
netizing field. 

When  hard  iron  or  steel  is  removed  from  a  mag- 
netizing field  it  retains  nearly  all  its  magnetism. 
Such  magnetism  is  also,  in  reality,  residual  mag- 
netism, but  the  term  is  generally  limited  to  the 
case  of  soft  iron. 

Magnetism,  Solenoidal  Distribution  of 

A  term  sometimes  applied  to  such 

a  distribution  of  magnetism  in  a  bar  that 
the  magnetized  particles  are  arranged  with 
their  poles  in  the  direction  of  the  length  of  the 
bar,  the  ends  of  which  are  of  opposite  mag- 
netic polarities,  and  the  extent  of  whose  sur- 
faces is  small  as  compared  with  the  length 
of  the  bar. 

The  term  solenoidal  distribution  is  used  in  con- 
tradistinction to  lamellar  distribution .  (See  Mag- 
netism, Lamellar  Distribution  of. ) 

Magnetism,  Strength  of A  term 

sometimes  used  in  the  sense  of  intensity  of 
magnetization.  (See  Magnetization,  Inten- 
sity of.} 

The  term,  strength  of  magnetism,  is  sometimes 
used  for  flux  or  quantity  of  magnetism. 

Intensity  of  magnetization,  is  the  preferable 
term. 


Mag.] 


350 


[Mag. 


Magnetism,  Terrestrial A  name 

applied  to  the  magnetism  of  the  earth. 

Terrestrial  magnetism  has  been  ascribed  to  a 
variety  of  causes.  (See  Magnetism,  Earth's, 
Theories  as  to  Cause  of. ) 

Magnetism,    Vertical     Component     of 

Earth's (See    Component,     Vertical, 

of  Earth's  Magnetism?) 

Magnetite. — Magnetic  oxide  of  iron,  or 
Fe3  O4f  found  in  nature,  as  an  ore  or  mineral. 

Lode-stone  consists  of  pieces  of  magnetized 
magnetite. 

Magnetizable. — Capable  of  being  magnet- 
ized after  the  manner  of  a  paramagnetic  sub- 
stance like  iron. 

The  most  magnetizable  metals  are  iron,  nickel, 
cobalt  and  manganese.  (See  Paramagnetism.) 

Magnetization.— The  act  of  calling  out  or 
of  endowing  with  magnetic  properties. 

Magnetizable  substances  are  magnetized  by 
being  placed  in  magnetic  fields.  (See  Field,  Mag- 
netic.  Magnetization,  Methods  of  .) 

The  act  of  initial  magnetization  is  not  exactly 
the  same  as  the  act  of  subsequent  magnetization. 

A  piece  of  steel,  which  has  once  been  magnet- 
ized and  subsequently  demagnetized,  is  a  thing  en- 
tirely distinct,  as  regards  its  magnetization,  from 
a  piece  of  steel  which  has  never  before  been  mag- 
netized, and  such  a  piece  can  never  be  placed  ex- 
actly in  the  same  position  as  regards  a  magnet- 
izing force,  unless  it  is  actually  melted  and  recast, 
or,  perhaps,  maintained  for  a  comparatively  long 
time  at  a  white  heat. 

Magnetization,    Anomalous The 

magnetization  obtained  from  an  oscillatory 
discharge,  such  as  that  of  a  Leyden  jar. 

In  1842,  Henry  described  the  real  character  of 
anomalous  magnetization,  and  showed  that  there 
was  nothing  anomalous  in  such  magnetization,  but 
rather  in  the  fact  that  the  magnetizing  currents 
possessed  no  simple  direction.  He  remarks  on 
this  subject  as  follows: 

"This  anomaly,  which  has  remained  so  long 
unexplained,  and  which,  at  first  sight,  appears  at 
variance  with  all  our  theoretical  ideas  of  the  con- 
nection of  electricity  and  magnetism,  was,  after 
considerable  study,  satisfactorily  referred  to  an 
action  ot  the  discharge  of  a  Leyden  jar  which  had 
never  before  been  recognized.  The  discharge, 


whatever  may  be  its  nature,  is  not  correctly  rep- 
resented (employing  the  simplicity  of  Franklin) 
by  the  single  transfer  of  an  imponderable  fluid 
from  one  side  of  the  jar  to  the  other  ;  the  phe- 
nomena require  us  to  admit  the  existence  of  a 
principal  discharge  in  one  direction  and  then 
several  reflex  actions  backward  and  forward,  each 
more  feeble  than  the  preceding,  until  the  equi- 
librium is  obtained.  All  the  facts  are  shown  to 
be  in  accordance  with  the  hypothesis,  and  a  ready 
explanation  is  afforded  by  it  of  a  number  of  phe- 
nomena which  are  to  be  found  in  the  older  works 
on  electricity,  but  whi:h  have  until  this  time  re- 
mained unexplained." 

Magnetization  by  Touch. — The  produc- 
tion of  magnetism  in  a  magnetizable  sub- 
stance by  touching  it  with  a  magnet. 

There  are  three  methods  of  magnetization  by 
touch,  viz.: 

(i.)  Single  touch. 

(2.)  Separate  touch. 

(3.)  Double  touch. 

In  single  touch,  the  magnetization  of  a  bar  of 
iron  or  other  magnetizable  material  is  effected  by 
the  touch  of  a  single  magnet. 

In  Single  Touch,  the  magnetizing  magnet  is 
drawn  over  the  bar  to  be  magnetized  from  end  to 
end  and  returned  through  air,  the  stroke  being 
repeated  a  number  of  times.  The  end  of  the 
bar  the  magnet  leaves  is  magnetized  oppositely 
to  the  magnetizing  pole. 

By  some  writers  the  method  of  single  touch  is 
described  as  that  effected 
by  placing  the  magnet- 
izing magnet  N  S  (Fig. 
384)  on  the  middle  of 
the  bar  to  be  magnetized, 
and  drawing  it  to  the 
end  and  returning 
through  the  air  as  be-  |+N  s— ) 

fore,  and  then  reversing  •* 

the   pole,  placing    it    on    F'£-  3^4-    Magnetization 

the   middle  of  the  bar          by  SinSl,  Touch. 
and  drawing   it  towards  the    other  end.     The 


Fig.  j<?/.    Magnetization  by  Separate  Touch. 

former  would,  however,  appear  to  be  the  better 
use  of  the  term  single  touch. 

In  Separate  Touch,  two  magnetizing  bars  are 
placed  with  their  opposite  poles   at  the   middle 


Mag.] 


351 


of  the  bar  to  be  magnetized  and  drawn  away  from 
each  other  towards  its  ends,  as  shown  in  Fig. 
385.  This  motion  is  repeated  a  number  of  times, 
the  poles  being  each  time  returned  through  the 
air. 

In  the  above,  as  in  all  cases  of  magnetization 
by  touch,  better  effects  are  produced,  if  the  bar 


Fig.  386.    Magnetization  by  Double  Touch. 
to  be  magnetized  is  rested  on  the  opposite  poles 
of  another  magnet,  or,  as  shown  in  Fig.  386, 
placed  near  them. 

In  Double  Touch  the  two  magnets  are  placed 
with  their  opposite  poles  together  on  the  middle 
of  the  bar  to  be  magnetized,  as  shown  in  Fig. 
386.  They  are  then  moved  to  one  end  of  the  bar, 
when,  instead  of  removing  them  and  passing  them 
back  through  the  air  to  the  other  end,  they  are 
moved  over  the  surface  of  the  bar  to  be  magnet- 
ized to  the  other  end,  and  these  to-and-fro  mo- 
tions are  repeated  a  number  of  times.  The  mo- 
tion is  stopped  at  the  middle  of  the  bar,  when  the 
magnetizing  magnets  are  moving  in  the  opposite 
direction  to  that  at  which  they  began  to  move. 
This  insures  an  equal  number  of  strokes  to  the 
two  halves  of  the  bar.  The  method  of  double 
touch  produces  stronger  magnetization  than 
either  of  the  other  methods,  but  does  not  effect 
such  an  even  distribution  of  the  magnetism,  and 
therefore  is  not  applicable  to  the  magnetization 
of  needles. 

A  variety  of  double  touch  is  shown  in  Fig.  387, 
where  four  bars,  to  be  magnetized,  are  placed  in 
the  form  of  a  hollow  rectangle,  with  only  their 
ends  touching  at  their  edges,  the  angular  spaces 


F'f-  387-    Magnetization  by  Double  Touch. 
at  the  corners  being  filled  with  pieces  of  soft  iron. 
The  horseshoe  magnet  N  S,  is  then  moved  around 
the  circuit  several  times  in  the  same  direction. 
This  is  believed  to  produce  a  more  uniform  mag- 


netization than  the  ordinary  method  of  double 
touch. 

Magnetization,    Co-efficient  of  --  A 

number  representing  the  intensity  of  magnet- 
ization produced  in  a  magnetizable  body, 
divided  by  the  magnetizing  force  H. 

Calling  k,  the  co-efficient  of  magnetization  ;  I, 
the  intensity  of  the  resulting  magnetization,  and 
H,  the  magnetizing  force  producing  it,  then 


The  co-efficient  of  magnetization  is  sometimes 
called  the  magnetic  susceptibility. 

A  paramagnetic  body  when  placed  in  a  mag- 
netic field  concentrates  the  lines  of  magnetic  force 
on  it,  or  causes  them  to  pass  through  it.  The 
intensity  of  the  magnetization  so  produced  de- 
pends, therefore, 

(I.)  On  the  intensity  of  the  magnetizing  field. 

(2.)  On  the  ability  of  the  metal  to  concentrate 
the  lines  of  force  on  it;  that  is,  on  the  nature  of 
the  metal,  or  on  its  magnetic  permeability.  (See 
Permeability,  Magnetic.  Paramagnetism.  Dia- 
magnetism.) 

The  intensity  of  magnetization  will,  therefore, 
be  equal  to  the  product  of  the  co-efficient  of  mag- 
netization and  the  intensity  of  the  magnetizing 
field.  It  will,  also,  of  course,  depend  on  the  area 
of  cross-section  of  the  magnetized  body. 

The  co-efficient  of  magnetization  of  paramag- 
netic bodies  is  said  to  be  positive,  and  that  of  dia- 
magnetic  bodies  to  be  negative,  because  paramag- 
netic bodies  concentrate  the  lines  of  magnetic 
force  on  them,  while  diamagnetic  bodies  appear 
to  repel  the  lines  of  force.  (See  Paramagnetic. 
Diamagnetic.  ) 

Magnetization,  Critical  Current  of  — 

•  —  The  current  at  which  any  certain  or  definite 
effect  of  magnetization  is  produced. 

Magnetization,    Intensity  of  --  A 

quantity  showing  the  intensity  of  the  magnet- 
ization produced  in  a  substance. 

A  quantity  showing  the  intensity  with 
which  a  magnetizable  substance  is  mag- 
netized. 

The  intensity  of  magnetization  depends: 

(I.)  On  the  intensity  of  the  magnetizing  field. 

(2.)  On  the  magnetic  permeability,  or  on  the 
conducting  power  of  the  substance  for  lines  of 
magnetic  force. 


Mag.] 


352 


[Mag. 


The  greater  the  strength  of  the  magnetizing 
field,  and  the  greater  the  magnetic  permeability, 
the  greater  is  the  intensity  of  the  magnetization 
produced. 

When,  therefore,  a  magnetizable  substance  is 
placed  in  a  magnetizing  field,  the  intensity  of  the 
magnetization  will  depend  on  the  magnetic  sus- 
ceptibility of  the  substance;  that  is,  on  the  ratio  of 
the  induced  magnetization  to  the  magnetizing  force 
producing  it. 

Soft  iron  has  a  high  co-efficient  of  magnetization, 
or  its  magnetic  susceptibility  is  high.  (See  Sus- 
ceptibility, Magnetic.  Magnetization,  Co-efficient 
of.) 

The  intensity  of  magnetization  through  a  sub- 
stance is  measured  by  dividing  the  magnetic 
moment  by  the  magnetic  volume. 

If  a  bar  of  soft  iron  is  placed  with  its  greatest 
length  extending  in  the  direction  of  the  lines  of 
force  in  a  magnetic  field,  it  will  have  induced  in 
it  a  certain  intensity  of  magnetization  which  may 
be  expressed  as  follows: 

m  .  1 
Intensity  of  Magnetization  =  yoiume  =  k  H, 

where  m,  equals  the  strength  of  the  magnet ;  1,  its 
length  ;  k,  the  co-efficient  of  magnetization,  and 
H,  the  intensity  of  the  magnetizing  field. — (S.  P. 
Thompson.) 

"  The  moment  of  a  magnet,  or  of  any  element 
of  a  magnet,  may  be  considered  numerically  to  be 
made  up  of  two  factors,  one,  its  volume,  and  the 
other  its  intensity  of  magnetization,  or  simply 
its  magnetization,  and  hence,  for  a  uniformly  mag- 
netized small  linear  needle,  we  may  define  the 
intensity  of  its  magnetization  by  saying  that  it  has 
magnetic  moment  of  unit  volume."— (Fleming.) 

Magnetization,  Maximum A  term 

sometimes  used  for  magnetic  saturation. 

Urquhart  states,  as  the  result  of  numerous  ex- 
periments, that  the  number  of  lines  of  magnetic 
force  that  usually  pass  through  a  bar  of  soft  iron 
I  square  centimetre  in  area  of  cross- section,  when 
magnetized  to  a  maximum,  is  equal  to  32,000. 
Ewing  gives  the  number  in  the  particular  case  of 
a  very  extraordinary  magnetization  as  being  equal 
to  45>3S°  Per  square  centimetre  area  of  cross- 
section. 

Magnetization,  Methods  of Mag- 
netization effected  either  by  induction  from 
another  magnet,  or  by  means  of  induction  by 
an  electric  current. 


The  substance  to  be  magnetized  is  brought  into 
a  magnetic  field,  so  that  the  lines  of  magnetic 
force  pass  through  it.  All  methods  of  magnet- 
ization may  be  divided  into  methods  of  magnetiza- 
tion by  toitch.  and  magnetization  by  the  electfic 
current.  (See  Magnetization  by  Touch.) 

Magnetization,  Permanent,  Intensity  of 

A  term  employed  for  the  intensity  of 

a  permanent  magnetization  produced  in  hard 
steel,  as  distinguished  from  the  magnetization 
temporarily  produced  in  soft  iron.  (See  Mag- 
netization, Intensity  of.) 

Magnetization,  Temporary,  Intensity  of 

The  intensity  of  the  magnetization 

temporarily  induced  in  a  bar  of  soft  iron,  as 
distinguished  from  permanent  magnetization 
induced  in  hard  steel.  (See  Magnetization, 
Intensity  of.) 

Magnetization,  Time-Lag  of A  lag 

which  appears  to  exist  between  the  time  of 
action  of  the  magnetizing  force  and  the  ap- 
pearance of  the  magnetism. 

The  time  which  must  elapse  in  the  case  of 
a  given  paramagnetic  substance  before  a  mag- 
netizing force  can  produce  magnetization. 

In  the  opinion  of  some  physicists  there  is  no 
such  thing  as  a  true  magnetic  time-lag,  the  ap- 
parent time-lag  being  due  entirely  either  to  hys- 
teresis or  to  eddy  currents.  According  to  them, 
while  the  magnetizing  force  is  increasing,  it  pro- 
duces, in  the  iron,  reversely-directed  surface - 
eddy-currents,  which  produce  a  reversed  or 
opposed  magnetizing  force  in  the  more  deeply 
seated  layers  of  the  iron,  the  time-lag  being  due 
to  the  interval  which  is  required  for  these  eddy 
currents  to  die  away  and  thus  permit  the  mag- 
netizing force  to  produce  its  full  magnetization. 

According  to  others,  however,  a  true  time- 
lag  does  exist  entirely  apart  from  the  existence  of 
surface-eddy-currents. 

Magnetize. — To  endow  with  magnetic 
properties. 

Magnetized. — Endowed  or  impressed  with 
magnetic  properties. 

Magnetizing. — Causing  or  producing  mag- 
netism. 

Magneto-Blasting  Machine.— (See  Ma- 
chine,  Magneto-Blasting.) 


Mag.] 


353 


[Mag. 


Magneto-Electric  Bell.— (See  Bell,  Mag- 
neto-Electric?) 

Magneto-Electric  Brake. — (See  Brake, 
Magneto-Electric) 

Magneto-Electric  Call-Bell.— (See  Call- 
Bell.  Magneto-Electric) 

Magneto-Electric  Faradic  Apparatus.— 

(See  Apparatus,  Faradtc,  Magneto-Elec- 
tric) 

Magneto-Electric  Induction.— (See  In- 
duction, Magneto- Electric.) 

Magneto-Electric  Machine.— (See  Ma- 
chine, Magneto-Electric) 

Magneto-Electric  Medical  Apparatus.— 
(See  Apparatus,  Magneto- Electric  Medi- 
cal) 

Magneto-Electricity.—  (See  Electricity, 
Magneto) 

Magnetograph.— The  permanent  record 
obtained  from  the  action  of  a  self-recording 
magnetometer.  (See  Magnetometer,  Self- 
Recording) 

Magnetometer.— An  apparatus  for  the 
measurement  of  magnetic  force. 


Fig  388.    Magnetometer, 

In  some  magnetometers  the  magnetic  force  is 
measured  by  the  torsion  of  a  wire,  as  in  the  tor- 
•ion  balance.  ($•&&  Balance,  Coulomb's  Torsion) 


The  magnetometer  shown  in  Fig.  388,  consists 
of  a  magnetized  bar  suspended  by  two  wires  pasfr- 
i ng  over  a  pulley,  as  shown.  The  magnet  is  held 
by  the  frame  S  S,  provided  with  a  graduated  scale 
K.  The  mirror  S,  is  supported  by  a  vertical  post 
attached  to  the  frame,  and  serves  to  reflect  a  scale 
placed  below  a  distant  reading  telescope.  This 
form  of  magnetometer,  is  called  the  bifilar  mag- 
netometer, and  was  the  one  used  by  Gauss  in  his 
study  of  the  earth's  magnetism. 

A  variety  of  forms  have  been  given  to  delicate 
magnetometers.  Some  are  self-recording.  (See 
Magnetometer,  Self -Recording.) 

Magnetometer,  Differential A  form 

of  magnetometer  in  which  the  principles  of  the 
differential  galvanometer,  as  applied  to  the 
electric  circuit,  are  applied  to  the  magnetic 
circuit. 

The  differential  magnetometer  of  Eickemeyer  is 
shown  in  Figs.  389  and  390.  Its  principles  of 
operation  will  be  understood  from  the  following 
considerations. 

Referring  to  Fig.  389.  Suppose  Ft  and  F2  are 
two  electromotive  forces  connected  in  series,  and 
x  and  y,  two  resistances  to  be  compared.  Each  of 
the  resistances  x  and  y,  is  shunted  respectively  by 
two  conductors  a  and  b,  whose  resistance  we 
wish  to  compare.  Since  the  action  of  each  of 
them  on  the  galvanometer  G,  is  opposite,  its  nee- 
dle remains  at  zero,  when  the  current  in  a,  is 
equal  to  the  current  in  b. 

If,  instead  of  electric  circuit,  we  take  the  idea 
of  magnetic  circuit  or  the  number  of  lines  of 
magnetic  force,  and  instead  of  potential  difference, 


fig-  38<)  •    Eickemeyer' s  Differential  Magnetometer. 

magneto-motive  force,  and  instead  of  electric  re- 
sistance, magnetic  resistance,  we  have  the  princi- 
ples on  which  the  Eickemeyer  differential  magnet- 
ometer is  founded. 

The  magnetic  circuit  of  the  differential  magnet- 
ometer consists  of  two  pieces  of  soft  iron,  shaped 


Mag.J 


354 


as  shown  at  Fj  and  F2,  Fig.  390.  A  magnetic 
coil  C,  surrounds  the  middle  portion  of  each  cir- 
cuit as  shown.  The  operation  as  described  by 
Mr.  Chas.  Steinmetz,  from  whom  the  above  de- 
scription is  mainly  taken,  is  as  follows,  viz. :  "The 
front  part  Sj  of  the  left  iron  piece  becomes  south, 
and  the  back  part  nx  north  polarity;  the  front 
part  of  the  right  iron  piece  n2  becomes  north,  and 
the  back  part  south;  and  the  lines  of  magnetic 
force  travel  in  the  front  from  the  right  to  the  left, 
from  ns  to  Sj ;  in  the  back  the  opposite  way,  from 
the  left  to  the  right,  or  from  nx  to  S;,  either 
through  the  air,  or,  when  n2  and  Sj,  or  nx  and  s2> 
are  connected  by  a  piece  of  magnetizable  metal, 
through  this  and  through  the  air. 

In  the  middle  of  the  coil  C,  stands  a  small  soft 
iron  needle  with  an  aluminum  indicator,  which 
plays  over  a  scale  K,  and  is  held  in  a  vertical 
position  by  the  lines  of  magnetic  force  of  the  coil 
C,  itself,  deflected  to  the  left  by  the  lines  of  mag- 
netic force  traversing  the  front  part  of  the  instru- 
ment from  na  to  s15  deflected  to  the  right  by  the 
lines  traversing  the  back  from  nx  to  s2.  This 
needle  shows  by  its  zero  position  that  the  mag- 
netic flow  through  the  air  in  front  from  n3  to  sx 
has  the  same  strength  as  the  magnetic  flow  in  the 
back  from  n1  to  sa  through  the  air. 

Now  we  put  a  piece  of  soft  iron  x  on  the  front 
of  the  instrument.  A  large  number  of  lines  go 
through  x,  less  through  the  air  from  na  to  sa ;  but 
all  these  lines  go  from  n ,  to  s2  through  the  air 
at  the  back  part  of  the  magnetometer,  the  front 
part  and  back  part  of  the  instrument  being  con- 
nected in  series  in  the  magnetic  circuit.  There- 
fore the  needle  is  deflected  to  the  right  by  the 
magnetic  flow  in  the  back  of  the  instrument. 

Now,  we  put  another  piece  of  iron,  y,  on  the 
back  part  of  the  instrument,  then  equilibrium 
would  be  restored  as  soon  as  the  same  number  of 
lines  of  magnetic  force  go  through  x,  as  through 
y,  because  then  also  the  same  number  of  lines  go 
through  air  in  the  front  as  in  the  back.  As  will 
be  noted,  the  air  here  takes  the  place  of  the  resist- 
ances a  and  b,  influencing  the  galvanometer 
needle  G,  as  in  the  diagram  Fig.  389. 

The  operation  of  the  instrument  is  exceedingly 
simple  and  is  as  follows  :  Into  the  coil  C,  an  elec- 
tric current  is  sent  which  is  measured  by  the  am- 
meter A,  and  regulated  by  the  resistance-switch 
R.  Then  the  needle,  which  before  had  no  fixed 
position,  points  to  zero. 

Now,  we  lay  the  piece  of  iron,  the  magnetic 
properties  of  which  we  want  to  determine,  on  the 


back  part  of  the  instrument.  The  needle  is  de- 
flected to  the  left.  On  the  front  of  the  instrument 
we  put  Norway  iron  rods  of  known  cross-section 
and  known  conductivity,  until  equilibrium  is 
again  restored.  Then  the  iron  in  the  front  has 
the  same  magnetic  resistance  as  the  iron  in  the 
back,  and  the  ratio  of  the  cross-sections  gives 
directly  the  ratio  of  the  conductivities  ;  so  that 
by  a  single  reading  the  magnetic  conductivity  of 
any  piece  of  iron  can  be  compared  with  that  of 
the  Norway  iron  standard. 

For  absolute  determinations,  the  iron  is  turned 
off  into  pieces  of  exactly  4  square  centimetres 
cross-section  and  20  centimetres  in  length,  both 
ends  fitting  into  holes  in  large  blocks  of  Norway 
iron,  which  are  laid  against  the  pole  pieces  of  the 
magnetometer,  so  that  the  transient  resistance 
from  pole  face  to  iron  is  eliminated. 


Fig.  3QO.    Eickemeyer\i  Differential  Magnetometer, 

Magnetometer,  Self-Recording—     —A 

self-recording  apparatus,  by  means  of  which 
the  daily  and  hourly  variations  of  magnetic 
needles  in  the  earth's  field,  at  any  locality,  are 
continuously  registered. 

The  self-recording  magnetometer  employed  in 
the  observatory  at  Kew,  consists  essentially  of 
means  of  obtaining  a  photographic  record  of  a 
spot  of  light  reflected  from  a  mirror,  attached  to 
the  needle  whose  variations  are  to  be  recorded. 
The  photographic  record  is  received  on  a  strip  of 
sensitized  paper,  maintained  in  uniform  and  con- 
tinuous motion  by  means  of  suitable  clock-work. 
The  record  so  obtained  is  called  a  magneto- 
graph. 

Magneto-Motive  Force.  —  (See  Force, 
Magneto-Motive.) 


Mag.] 


355 


[Mak. 


Magneto-Motive  Force,  Absolute  Unit  of 

(See  Force,  Magneto-Motive,  Abso- 
lute Unit  of.} 
Magneto-Motive  Force,  Practical  Unit  of 

(See  Force,  Magneto-Motive,  Prac- 
tical Unit  of.) 

Magneto-Optic  Rotation.— (See  Rotation, 
Magneto-Optic?) 

Magnetophone. — A  species  of  magnetic 
siren  in  which  sounds  are  produced  in  an 
electro-magnetic  telephone  by  the  periodic 
currents  produced  in  its  coils  by  the  rotation 
of  a  perforated  metallic  disc  in  a  magnetic 
field. 

As  the  speed  of  the  disc  increases,  the  pitch  of 
the  note  increases.  The  apparatus  was  invented 
by  Prof.  Carhart,  in  1883.  A  similar  apparatus 
is  useful  in  studying  the  distribution  of  the  mag- 
netic field  of  a  dynamo-electric  machine.  In  this 
case,  a  small,  thin  coil  of  insulated  wire  is  held  in 
the  different  regions  around  the  machine,  while 
the  telephone  is  held  to  the  ear  of  the  observer. 
Magnetic  leakage,  or  useless  dissipation  of  lines 
of  magnetic  force  outside  the  field  proper  of  the 
machine,  is  at  once  rendered  manifest  by  the 
musical  note  caused  by  variations  in  the  intensity 
of  the  field. 

Since  the  intensity  of  the  note  heard  will  vary 
according  to  the  intensity  of  the  field,  and  also 
according  to  the  position  in  which  the  coil  is  held, 
such  a  coil  becomes  a  magnetic  explorer,  and  by 
its  use  the  distribution  and  varying  intensity  of  an 
irregular  field  can  be  ascertained.  Its  use  is 
especially  advantageous  in  proportioning  dynamo - 
electric  machines  and  electric  motors.  (See  Ex- 
plorer, Magnetic. ) 

Magneto-Receptive  Device. — (See  Device, 
Magneto-Receptive?) 

Magneto-Static  Current  Meter.  —  (See 
Meter,  Current,  Magneto-Static?) 

Magneto-Static  Screening.— (See  Screen- 
ing, Magneto-Static?) 
Magneto-Statics.— (See  Statics,  Magneto?) 

Magneto-Therapy. — (See  Therapy,  Mag- 
neto?) 

Main  Battery.— (See  Battery,  Main?) 
Main-Battery     Circuit  —  (See    Circuit, 
Main-Battery?) 


Main,  Electric The  principal  con- 
ductor in  any  system  of  electric  distribution. 

Main  Feeder.— (See  Feeder,  Standard  or 
Main?) 

Main  Fuse.— (See  Fuse,  Main?) 

Main,  House A  term  employed  in 

a  system  of  multiple  incandescent  lamp  dis- 
tribution for  the  conductor  connecting  the 
house  service  conductors  with  a  centre  of 
distribution,  or  with  a  street  main. 

Main-Line  Cut-Out  —  (See  Cut-Out,  Main- 
Line?) 

Main,  Street In  a  system  of  incan- 
descent lamp  distribution  the  conductors  ex- 
tending in  a  system  of  networks  through  the 
streets  from  junction  box  to  junction  box, 
through  which  the  current  is  distributed 
from  the  feeder  ends,  through  cut-outs,  to 
the  district  to  be  lighted,  and  from  which 
service  wires  are  taken. 

Main,  Sub A  name  sometimes 

given  to  the  distributing  conductor  that  is 
connected  directly  to  a  main. 

The  branch  nearest  the  main.  (See 
Branch?) 

Main  Wire.— (See  Wire,  Main?) 

Mains  of  Electric  Railroads.— The  wires 
or  conductors  used  for  carrying  the  current 
from  the  feeders  through  the  tap  wires  to  the 
trolley  wires. 

Make. — A  completion  of  a  circuit. 

Make-ami- Break. — The  periodic  alternate 
completion  and  opening  of  a  circuit. 

Make-and-Break,  Automatic A 

term  sometimes  employed  for  such  a  combi- 
nation of  contact  points  with  the  armature  of 
any  electro-magnet,  that  the  circuit  is  auto- 
matically made  and  broken  with  great  rapidity. 

An  automatic  make-and-break  is  used  in  most 
forms  of  electric  alarms  in  connection  with  some 
form  of  electric  bell.  (See  Alarm,  Electric.) 

It  is  also  used  in  the  Ruhmkorff  ind  action  cofl 
in  order  to  produce  the  variations  in  the  primary 
circuit.  (See  Coil,  Induction?) 

Make-Induced  Current.  —  (See  Current, 
Make-Induced?\ 


Mat,] 


356 


[Mar. 


Making    the    Primary.— (See    Primary, 
Making  the.) 
Mallet,    Electro-Magnetic    Dental  

—(See  Dental-Mallet,  Electro-Magnetic.) 

Mangin  Projector. — (See  Projector,  Man- 
gin^ 

Man-Hole,  Compartment,  of  Conduit 

— A  man-hole  provided  with  suitably  sup- 
ported shelves  or  compartments,  guarded  by 
locked  doors  that  protect  different  cable  sec- 
tions. 

Man-Hole  of  Conduit. — An  opening  of 
sufficient  size  to  admit  a  man,  communi- 
cating from  the  surface  of  the  roadbed  with 
an  underground  conduit. 

Manipulator,  Breguet's The  send- 
ing instrument  employed  by  Breguet  in  his 
system  of  step-by-step  or  dial  telegraphy. 
(See  Telegraphy,  Step-by-Step.) 

Manometei. — An  apparatus  for  measuring 
the  tension  or  pressure  of  gases. 

Manometers  are  either  mercurial  or  metallic. 
Mercurial  manometers  are  of  two  classes,  viz., 
manometers  with  free  air  and  manometers  with 
compressed  air. 

Manometers  measure  the  pressure  of  gases 
either  in  atmospheres,  i.  e.,  in  multiples  or  deci- 
mals of  15  pounds  to  the  square  inch,  or  in  inches 
of  mercury. 

Map  or  Chart,  Inclination A  chart 

or  map  on  which  lines  are  drawn,  showing 
the  lines  of  equal  dip  or  inclination,  or  the 
isoclinic  lines. 

An  inclination  chart  is  shown  in  Fig.  391. 

It  will  be  seen  that  the  magnetic  equator,  or 
line  of  no  dip,  does  not  correspond  with  the  geo- 
graphical equator,  being  generally  north  of  the 
equator  in  the  Eastern  Hemisphere,  and  south  of 
h  in  the  Western.  The  figures  attached  to  the 
lines  indicate  the  value  of  the  angle  of  dip. 

Map  or  Chart,  Isodynamic  —     — A  map 

of  the  earth  on  a  mercator's  projection,  on 
which  isodynamic  lines  are  drawn. 

An  isodynamic  chart  is  shown  in  Fig.  392.  It 
will  be  observed  that  the  isodynamic  lines  do  not 
exactly  coincide  with  the  isoclinic  lines,  since  the 
line  of  least  magnetic  intensity  does  not  correspond 
with  the  line  of  the  magnetic  equator. 

The  point  of  least  magnetic  intensity  is  found  at 


about  lat.  20  degrees  S.,  and  Ion.  35  degrees  VV. 
The  point  of  greatest  magnetic  intensify  is  found 
at  about  lat.  52  degrees  N.  and  Ion.  92  degrees 
W. 

Another,  though  weaker  point  of  magnetic  in- 
tensity, is  found  in  Siberia.  These  are  distin- 
guished from  the  true  magnetic  poles  by  the  term 
Poles  of  Intensity. 

The  Poles  of  Verticity,  as  determined  by  the 
dipping  needle,  and  the  Poles  of  Intensity,  as  de- 
termined by  the  needle  of  oscillation,  therefore  do 
not  coincide  in  the  Northern  Hemisphere. 

Map  or  Chart,  Isogonal A  term 

sometimes  used  for  an  isogonic  map  or  chart. 

Map  or  Chart,  Isogonic  —  —A  chart 
on  which  the  isogonal  lines  are  marked. 

An  isogonic  map  or  chart  is  sometimes  called 
a  declination  map  or  chart. 

In  the  declination  or  variation  chart,  shown  in 
Fig.  393,  the  region  of  western  declination  is  in  • 
dicated  by  the  shading.  There  is  a  remarkable 
oval  patch  in  the  northeastern  part  of  Asia,  in 
which  the  declination  is  west  A  similar  oval  of 
decreased  inclination  is  seen  in  the  Southerm 
Pacific. 

The  entire  earth  acts  like  a  huge  magnet  with 
south  magnetic  polarity  in  the  Northern  Hemi- 
sphere. 

It  is  not  known  whether  the  earth  possesses 
but  a  single  pair  of  magnetic  poles  or  more 
than  a  single  pair.  The  variations  in  the  dec- 
lination, and  in  the  intensity  of  its  magnetism, 
due  to  the  position  of  the  sun,  •ss  well  as  the 
marked  magnetic  disturbances  that  accompany 
the  occurrence  of  sun  spots,  would  appear  to  con- 
nect the  earth's  magnetism  in  some  manner  witk 
the  solar  radiation.  (See  Magnetism,  Earth's, 
Theories  as  to  Cause  of.) 

Marine  Galvanometer. — (See  Galvanom- 
eter, Marine?) 

Mariner's  Compass. — (See  Compass,  Azi- 
muth.) 

Marked  Pole  of  Magnet— (See  Magnet, 
Marked  Pole  of.) 

Markers. — Colored  flags,  or  signal  lights, 
generally  green,  displayed  in  systems  of 
block  railway  signaling  at  the  ends  of 
trains,  in  order  to  avoid  accidents  from  trains 
breaking  in  two.  (See  Railroads,  Block 
System  for.) 


357 


[Mar. 


Mar.] 


358 


[Mar. 


Har.] 


359 


[Mar. 


g  g 


S  S 


Mas.] 


360 


[Mat. 


Mass. — The  quantity  of  matter  contained 
in  a  body. 

Mass  must  be  carefully  distinguished  from 
weight.  The  weight  of  a  given  quantity  of 
matter  depends  on  the  attraction  which  the  earth 
possesses  for  it,  and  this,  on  the  earth' s  surface, 
varies  with  the  latitude,  being  greatest  at  the 
poles  and  least  at  the  equator.  It  also  varies 
with  different  elevations  above  the  level  of  the  sea. 
The  mass,  however,  is  the  same  under  all  circum- 
stances, whether  for  different  latitudes  or  alti- 
tudes, on  the  earth's  surface. 

Mass  Attraction.— (See  Attraction,  Mass.) 

Mass,  Magnetic  —  —A  quantity  of  mag- 
netism which  at  unit  distance  produces  an 
action  equal  to  unit  force. 

Mass,  Unit  of The  quantity  of  mat- 
ter which  under  certain  conditions  will  balance 
the  weight  of  a  standard  gramme  or  pound. 

The  gramme  is  equal  to  the  one-thousandth 
part  of  a  piece  of  platinum  called  the  kilogramme, 
deposited  as  a  standard  in  the  archives  of  the 
French  Government,  and  intended  to  be  equal  to 
the  mass  of  I  cubic  centimetre  of  water  at  the  tem- 
perature of  its  maximum  density. 

Massage. — A  treatment  for  the  purpose 
of  effecting  changes  in  general  nutrition  or 
.action  of  particular  parts  of  the  body,  by 
kneading,  rubbing,  friction,  etc. 

Massage,  Electro The  application 

•of  electricity  to  the  body  during  its  massage. 

Connections  are  established  between  the  patient 
and  a  battery  by  connecting  one  electrode  of  a 
source  to  the  kneading  instrument,  and  the  other 
electrode  to  the  body  of  the  patient. 

Masses,  Electric A  mathematical 

conception  for  such  quantities  of  electricity 
as  at  unit  distance  will  produce  an  attrac- 
tion or  repulsion  equal  to  unit  force. 

Electrical  masses  are  assumed  to  be  equal  when 
they  produce  on  two  identical  bodies  of  sn»all 
dimensions  charges  of  the  same  electric  force. 

Master  Clock.— (See  Clock,  Master.) 
Materials,  Insulating Non-con- 
ducting substances  which  are  placed  around  a 
conductor,  in  order  that  it  may  either  retain 
an  electric  charge,  or  permit  the  passage  of 


an  electric  current  through  the  conductor 
without  sensible  leakage. 

Various  gases,  liquids  or  solids  may  be  em- 
ployed as  insulators.  A  very  high  vacuum  affords 
the  best  known  insulation. 

Matter. — Anything  which  occupies  space  in 
three  directions  and  prevents  other  matter  from 
simultaneously  occupying  the  same  space. 

Matter  is  composed  of  atoms,  which  unite  to 
form  molecules.  (See  Atom.  Molecule. ) 

Matter,  Elementary Matter  which 

cannot  be  decomposed  into  simpler  matter. 

Varieties  of  elementary  matter  are  called 
elements.  (See  Element. ) 

Matter,    Kinetic     Theory    of—     —A 

theory  which  assumes  that  the  molecules  of 
matter  are  in  a  constant  state  of  motion  or 
vibration  towards  or  from  one  another  in 
paths  that  lie  within  the  spheres  of  their 
mutual  attractions  or  repulsions. 

The  molecules  of  gases  have  great  freedom 
of  motion,  and  are  so  far  removed  from  one 
another  as  to  be  but  little,  if  any,  influenced  by 
their  mutual  attractions.  They  are  therefore 
assumed  to  move  in  straight  lines  with  very  great 
velocity  until  they  collide  against  one  another,  or 
against  the  sides  of  the  containing  vessel,  when 
they  are  reflected  and  again  move  in  straight  lines 
in  a  new  path. 

Matter,  Radiant,  or  Ultra-Gascons  — 

• — A  term  proposed  by  Crookes  for  the 
peculiar  condition  of  the  gaseous  matter  which 
constitutes  the  residual  atmospheres  of  high 
vacua. 

This  is  now  generally  recognized  as  a  fourth 
state  of  matter,  these  four  states  being: 

(i.)  Solid. 

(2.)  Liquid. 

(3.)  Gaseous. 

(4. )  Ultra-gaseous  or  radiant. 

The  peculiar  properties  of  radiant  matter  are 
seen  in  the  mechanical  effects  of  the  localized 
pressures  produced  when  such  residual  atmos- 
pheres are  locally  heated  or  electrified. 

In  Creoles'  radiometer,  vanes  of  mica,  silvered 
on  one  face  and  covered  with  lampblack  on  the 
opposite  face,  are  supported  on  a  vertical  axis  so 
as  to  be  capable  of  rotation  and  placed  in  a  glass 
vessel  in  which  a  high  vacuum  is  maintained.  On 


Mat.] 


361 


[Mat. 


exposing  the  instrument  to  the  radiation  from  a 
candle  or  gas  flame,  a  rapid  rotation  takes  place. 
^See  Radiometer,  Crookes'.) 

The  explanation  is  as  follows :  The  lampblack 
covered  surfaces  absorb  the  radiant  heat,  and  be- 
coming heated,  the  molecules  of  gas  in  the  residual 
atmosphere  are  shot  violently  from  them,  and  by 
their  reaction  drive  the  vanes  around  in  the 
Opposite  direction  to  that  from  which  they  are 
thrown  off.  The  molecules  are  also  shot  off  from 
the  silvered  surfaces,  but,  as  these  are  cooler,  the 
effect  is  not  as  great  as  at  the  blackened  surfaces. 

In  a  gas,  at  ordinary  pressure,  the  heated  sur- 
faces are  also  bombarded  by  other  molecules  of 
the  gas,  but  in  high  vacua  the  mean  free  path  of 
the  molecules  is  so  great  that  there  is  no  interfer- 
ence, a  Crookes'  layer  existing  between  the  vanes 
and  the  walls  of  the  glass  vessel.  (See  Layer^ 
Crookes\} 

When  a  Cr cokes'  tube  is  furnished  with  suit- 
able electrodes,  and  electric  discharges  are  sent 
through  it  between  these  electrodes,  a  stream  of 
molecules  is  thrown  off  in  straight  lines  from  the 
stir  face  of  the  negative  electrode. 

Some  of  the  effects  of  this  molecular  bombard- 
ment are  seen  by  the  use  of  the  apparatus  shown 
in  Fig.  394.  When  the  positive  and  negative 


fig.  394.    Effects  of  Molecular  Bombardment. 

terminals  are  arranged  as  shown,  the  paths  of  the 
molecular  streams  are  seen  as  luminous  streams 
whose  directions  are  those  shown  in  the  figures. 

The  figure  on  the  left  shows  the  path  taken  in 
a  low  -vacuum.  Streams  pass  from  the  negative 
electrode  to  each  of  the  positive  electrodes. 

The  figure  on  the  right  shows  the  discharge  in 
a  high  vacuum.  Here  the  streams  pass  off  at 
right  angles  to  the  face  of  the  negative  electrode, 


ana  proceed  therefrom  in  straight  lines,  inde- 
pendently of  the  position  of  the  positive  electrode. 
Since,  therefore,  the  negative  electrode  at  a,  is  in 
the  shape  of  a  concave  mirror,  the  luminous 
particles  converge  to  a  focus  near  the  centre  of 
the  glass  vessel,  and  then  diverge  to  the  opposite 
wall. 

Refractory  substances  placed  at  such  a.  focus  of 
molecular  bombardment,  as  shown  in  Fig.  395,  are 
rendered  incandescent. 

In  a  similar  manner,  phosphorescent  substances 
exposed  to  such  molecular  streams  emit  a  beauti- 


Forces  of  Molecular.  Bombardment. 


ful  phosphorescent  light.  (See  Phosphorescence, 
Electric.} 

Matter,  Thomson's  Hypothesis  of  — 

A  hypothesis  as  to  the  structure  of  matter 
suggested  by  Sir  William  Thomson,  in  order 
to  show  how  the  extremely  tenuous  ether 
might  possess  rigidity. 

The  fact  that  the  ether,  although  a  fluid  sub- 
stance, possesses  the  properties  of  a  rigid  solid, 
has  given  no  little  trouble  to  physicists.  Thomson 
explains  this  rigidity  of  the  ether  as  being  due  to 
a  rapid  motion  in  its  fluid  particles. 

A  perfectly  flexible  rubber  tube  filled  with 
water  or  other  fluid,  possesses,  when  at  rest,  a 
very  great  degree  of  flexibility.  When  in  mo- 
tion, however,  the  tube  becomes  more  and  more 
rigid,  as  the  flow  increases  in  rapidity.  Thorn- 


Mat.] 


362 


son  imagines  the  ether  to  be  set  in  motion  in 
minute  vortex  rings,  and  shows  that  a  readily 
movable  fluid  body,  like  ether,  once  set  in  such 
motion  should  possess  the  properties  of  a  solid. 
In  a  perfect  fluid,  such  as  ether,  these  vortex 
rings  once  formed,  would  be  practically  imperish- 
able or  indestructible. 

Thomson  regards  the  atoms  of  matter  as  con- 
sisting of  such  vortex  rings.  Vortex  rings  can  be 
formed  in  the  air  by  cutting  a  circular  aperture 
in  the  end  of  a  pasteboard  box,  and  tapping 
sharply  against  the  end  of  the  box.  In  order  to 
render  the  rings  visible,  the  box  may  be  previously 
filled  with  smoke. 

Vortex  rings  formed  in  smoky  air  differ  from 
vortex  rings  in  the  ether,  in  the  fact  that  air  is 
not  a  perfect  fluid,  while  ether  is.  Air  vortex 
rings  increase  in  size  and  decrease  in  energy. 
Vortex  rings  of  the  ether  would  not  vary  in  size. 

According  to  Thomson's  vortex  theory  of 
matter,  the  atoms  of  matter  are  the  same  as  the 
ether  which  surrounds  them.  They  cannot  be 
produced  in  ether  by  any  known  way;  therefore, 
they  cannot  be  manufactured,  or,  as  it  were, 
created.  Nor,  on  the  other  hand,  can  they  be 
destroyed ;  in  other  words,  they  are  indestruct- 
ible. They  are  elastic,  capable  of  definite  vibra- 
tions, possess  all  the  properties  of  matter  save,  in 
the  opinion  of  some,  the  very  important  prop- 
erty of  gravitation.  As  Prof.  Lodge  points  out, 
the  fact  that  this  property  is  not  present  should 
cause  Sir  William  Thomson's  theory  of  matter  to 
"be  accepted  with  considerable  hesitation. 

Matthiessen's  Metre-Gramme  Standard. 

—(See  Metre-Gramme  Standard,  Matthies- 
sen's.) 

Matthiessen's  Mile  Standard.— (See  Mile 
Standard,  Matthiessen's) 

Matting,  Invisible  Electric  Floor  

— A  matting  or  other  floor  covering,  provided 
with  a  series  of  electric  contacts,  which  are 
closed  by  the  passage  of  a  person  walking 
over  them. 

This  matting  is  provided  as  an  adjunct  to  a 
system  of  burglar  alarms.  The  electric  bell  or 
annunciator,  connected  with  the  different  con- 
tacts, is  disconnected  during  the  day-time,  or  while 
the  rooms  are  occupied.  (See  Alarm,  Burglar. ) 

Maximum  Magnetization.— (See  Mag- 
ttetization,  Maximum) 


Mclntire's  Parallel  Sleeve  Telegraphic 
Joint— (See  Joint,  Telegraphic,  Mclntires 
Parallel  Sleeve) 

Measurements,  Electric  — Deter- 
minations of  the  values  of  the  electromotive 
force,  resistance,  current,  capacity,  energy, 
etc.,  in  any  electric  circuit. 

Electric  measurements  may  be  either  qualitative 
or  quantitative. 

In  qualitative  electric  measurements  the  rela- 
tive values  only  are  obtained;  in  quantitative 
measurements  the  actual  values  are  obtained. 

Mechanical  Alarm,  Electric  —  —(See 
Alarm,  Electro-Mechanical.} 

Mechanical  Electric  Bell.— (See  Btll, 
Electro-Mechanical?) 

Mechanical  Equivalent  of  Heat.— (See 
Heat,  Mechanical  Equivalent  of} 

Mechanical  Mine.— (See  Mine,  Mechani- 
cal} 

Mechanical  Throwback  Indicator.  — 
(See  Indicator,  Mechanical  Throwback) 

Medical  Induction  Coil.— (See  Coil,  In- 
duction Medical) 

Medical  Magneto-Electric  Apparatus. — 
(See  Apparatus,  Magneto-Electric  Medi- 
cal) 

Medium,  Anisotropic A  medium 

in  which  equal  stresses  do  not  produce  equal 
strains  when  applied  in  different  directions. 

A  medium,  homogeneous  in  structure  like 
crystalline  bodies,  but  possessing  different 
powers  of  specific  inductive  capacity  in  differ- 
ent directions. 

An  eolotropic  medium.  (See  Medium, 
Eolotropic) 

The  latter  term  is  used  to  distinguish  it  from 
an  isotropic  medium.  (See  Medium,  Isotropic) 

Medium,  Eolotropic A  medium 

in  which  equal  stresses  do  not  produce  the 
same  strains  when  applied  in  different  direc- 
tions. (See  Medium,  Isotropic) 

Medium,  Electro-Magnetic Any 

medium  in  which  electro-magnetic  phenom- 
ena occur. 

The  medium  through  which  electro-magnetic 
waves  are  propagated  is  now  universally  re- 


Med.] 


363 


[Met. 


garded  as  the  luminiferous  or  universal  ether. 
(See Electricity,  Hertz's  Theory  of  Electro-Mag- 
netic Radiations  or  Waves.} 

Medium,  Isotropic A  medium  in 

which  equal  stresses  applied  in  any  direction 
produce  equal  strains. 

A  transparent  medium  which  possesses  the 
same  optical  or  electric  properties  in  all  di- 
rections. 

An  optically  homogeneous,  transparent 
medium. 

Such  media  are  called  isotropic  to  distinguish 
them  from  anisotropic  or  eolotropic,  or  those  in 
which  equal  stresses  produce  unequal  strains  in 
different  directions.  .(See  Medium,  Anisotropic. 
Medium,  Eolotropic. ) 

Meg  or  Mega  (as  a  prefix).— 1,000,000 
times  ;  as,  megohm,  1,000,000  ohms  ;  mega- 
volt,  i  ,000,000  volts. 

Megaloscope,  Electric An  appara- 
tus for  the  medical  exploration  of  the  cavities 
of  the  body. 

The  light  necessary  for  exploration  is  obtained 
from  a  small  incandescent  lamp  placed  at  the 
extremity  of  a  tube,  suitably  shaped  for  introduc- 
tion into  the  special  organ  for  which  it  is  devised. 
The  organ  so  illumined  throws  its  light  on  a 
prism,  by  means  of  which  the  light  is  caused  to 
pass  through  a  series  of  lenses  by  which  it  is 
viewed. 

Megavolt. — 1,000,000  volts. 
Megohm. — 1,000,000  ohms. 

Meidinger  Toltaic  Cell.— (See  Cell,  Vol- 
taic, Meidinger.} 

Memory,  Magnetic A  term  pro- 
posed by  J.  A.  Fleming  for  coercive  force. 

Soft  iron  has  but  a  feeble  memory  of  its  past 
magnetization. 

Mercurial  Connection. — (See  Connection, 
Mercurial?) 

Mercurial  Contact.  —  (See  Connection, 
Mercurial?) 

Mercurial  Temperature  Alarm. — (See 
Alarm,  Mercurial  Temperature) 

Mercury  Break. — (See  Break,  Mercury?) 

Mercury  Cup. — (See  Cup,  Mercury?) 


Meridian,  Astronomical A  great 

circle  passing  through  any  point  in  the 
heavens,  and  the  North  and  South  poles  of 
the  heavens. 

The  astronomical  meridian  corresponds  to  the 
geographical  meridian.  The  former  is  considered 
as  passing  around  the  dome  of  the  heavens;  the 
latter,  around  the  surface  of  the  earth.  In  order 
to  locate  any  point  in  the  heavens,  a  great  circle 
of  the  heavens  is  caused  to  pass  through  that  point 
and  through  the  astronomical  North  and  South 
poles. 

Meridian,  Geographical The  geo- 
graphical meridian  of  a  place  is  a  great  circle 
passing  through  that  place  and  the  North  and 
South  geographical  poles  of  the  earth. 

Meridian,  Magnetic The  magnetic 

meridian  of  any  place  is  the  meridian  which 
passes  through  the  poles  of  a  magnetic  needle 
at  that  place  when  in  a  position  of  rest  under 
the  free  influence  of  the  earth's  magnetism. 

The  plane  of  the  magnetic  meridian  at  any  place 
is  a  vertical  plane  passing  through  the  poles  of  a 
magnetic  needle  in  a  position  of  rest  under  the 
free  influence  of  the  earth's  magnetism  at  that 
place. 

The  magnetic  meridian  may  be  regarded  as  the 
vertical  plane  in  which  a  freely  suspended  mag- 
netic needle  comes  to  rest  in  the  earth's  magnetic 
field. 

Meridional. — Pertaining  to  the  meridian. 
Message  Wire.— (See  Wire,  Message?) 
Messenger  Call. — (See  Call,  Messenger) 
Metallic  Arc.— (See  Arc,  Metallic?) 
Metallic   Circuit.— (See   Circuit,  Metal- 
lic) 

Metallic  Coating.— (See  Coating,  Metal- 
lic) 

Metallic  Conducting  Joint.— (See  Joint, 
Metallic  Conducting.} 

Metallic  Contact.— (See  Contact,  Metal- 
lic.} 

Metallic  Electric  Conduction.  —  (See 
Conduction,  Electric,  Metallic?) 

Metallization. — The  rendering  of  a  non- 
conducting surface  electrically  conducting  by 
covering  it  with  a  metallic  coating,  so  as  to 


Met.] 


364 


[Met. 


enable  it  to  readily  receive  a  metallic  coating 
by  electro-plating.     (See  Plating,  Electro?) 

Metallochromes.  —  A  name  sometimes 
given  to  Nobili's  rings.  (See  Rings,  No- 
bt'lz's.) 

Metalloid. — A  name  formerly  applied  to  a 
non-metallic  body,  or  to  a  body  having  only 
some  of  the  properties  of  a  metal,  as  carbon, 
boron,  oxygen,  etc. 

The  term  is  now  but  little  used. 

Metallurgy,  Electro That  branch 

of  applied  science  which  relates  to  the  elec- 
trical reduction  or  treatment  of  metals. 

Metallurgical  processes  effected  by  the 
agency  of  electricity. 

Electro-Metallurgy  embraces : 

(I.)  The  reduction  of  metals  from  their  ores, 
either  directly  during  fusion  by  the  heat  of  the 
voltaic  arc,  or  the  heat  of  incandescence,  or  by 
the  electrolysis  of  solutions  of  their  ores,  or  ores 
in  the  fused  state.  (See  Electrolysis.  Furnace, 
Electric.) 

(2.)  Electroplating. 

(3.)  Electrotyping. 

The  application  of  electricity  to  the  reduction 
of  metals  is  carried  on  in  the  electric  furnace  for- 
the  reduction  of  the  aluminium  ores,  for  example. 

Metals,  Electric  Deflagration  of  — 
The  volatilization  of  metals  by  electric  in- 
candescence. 

Metals,    Electric    Refining    of  - 
Purifying  metals  by  means  of  electricity. 

Different  methods  are  employed  for  the  electric 
refining  of  metals.  They  are  generally  electro- 
lytic in  character. 

Metals,  Electrical  Protection  of — 
The  protection  of  a  metal  from  corrosion  by 
placing  it  in  connection  with  another  metal, 
which,  when  exposed  to  the  corroding  liquid, 
vapor  or  gas,  will  form  with  the  metal  to  be 
protected  the  positive  element  of  a  voltaic 
couple. 

The  negative  element  of  a  voltaic  couple  is 
protected  by  the  presence  of  the  positive  element, 
which  is  alone  corroded.  This  method  has  been 
adopted  with  considerable  success  to  electrically 
protect  metals  from  corrosion. 

The  following  are  examples  of  this  protection  : 

(I.)  Davy    proposed    to    protect    the    copper 


sheathing  of  ships  from  corrosion  by  attaching 
pieces  of  zinc  to  the  copper  sheathing.  This 
succeeded  too  well,  since  the  copper  salts  which 
were  formerly  produced,  and  acted  as  a  poison 
to  the  marine  plants  and  animals,  being  now 
absent,  permitted  these  organisms  to  thrive  to 
such  an  extent  as  to  seriously  foul  the  ship's 
bottom. 

(2.)  A  ring  of  zinc  attached  to  a  lightning  rod, 
near  its  points,  has,  it  is  claimed,  the  power  of 
protecting  the  points  from  corrosion. 

(3.)  Iron  bars  of  railings,  if  sunk  or  embedded 
in  zinc,  are  preserved  from  corrosion  near  the 
junction  of  the  two  metals,  but  if  sunk  in  lead  are 
rapidly  corroded,  because  iron  is  electro-positive 
to  lead,  but  electro-negative  to  zinc. 

(4.)  Tinned  iron  rapidly  corrodes  or  rusts 
when  the  iron  is  exposed  to  the  atmosphere  by  a 
scratch  or  abrasion,  because  the  iron  is  electro- 
positive to  tin.  Nickel-plated  iron,  for  the  same 
reason,  rusts  rapidly  on  the  exposure  of  an 
abraded  surface. 

(5.)  Zinced  or  galvanized  iron,  or  iron  covered 
with  a  deposit  of  zinc,  is  protected  from  corro- 
sion because  the  zinc,  being  positive  to  iron,  can 
alone  be  corroded,  and  the  zinc  is  also  protected 
in  part  by  the  coating  of  insoluble  oxide  that  is 
formed. 

Meteorites. — Aerolites.     (See  Aerolites.} 

Meter,  Ampere  — (See  Ampere- 
Meter.  Ammeter.) 

Meter,  Current A  term  now  ap- 
plied to  an  electric  meter  or  galvanometer 
which  measures  the  current  in  amperes,  as 
distinguished  from  one  which  measures  the 
energy  in  watts. 

This  term  is  sometimes  loosely  applied  to  a 
galvanometer. 

The  term  galvanometer  is  preferable.  (See 
Galvanometer. ) 

Meter,  Current,  Magneto-Static  —     —A 

current  meter  in  which  a  small  steel  magnet, 
or  system  of  magnets,  is  suspended  at  the 
centre  of  the  uniform  magnetic  field  produced 
by  the  combined  influence  of  two  coils  and 
two  systems  of  powerful  permanent  magnets. 

Meter,  Electric Any  apparatus  for 

measuring  commercially  the  quantity  of  elec- 
tricity that  passes  in  a  given  time  through 
any  consumption  circuit. 


Met.J 


365 


[Met. 


Electric  meters  are  constructed  in  a  great 
variety  of  forms;  they  may,  however,  be  ar- 
ranged under  the  following  heads  : 

(I. )  Electro-Magnetic  Meters,  or  those  in  which 
the  current  passing  is  measured  by  the  electro- 
magnetic effects  it  produces. 

In  such  meters  the  entire  current  may  pass 
through  the  meter. 

(2.)  Electro-Chemical  Meters,  or  those  in  which 
the  current  passing  is  measured  by  the  electroly- 
tic decomposition  it  effects. 

In  these  meters,  a  shunted  portion  only  of  the 
current  is  usually  passed  through  a  solution  of  a 
metallic  salt,  and  the  current  strength  calculated 
from  the  amount  of  electrolytic  decomposition 
thus  effected. 

(3.)  Electro-  Thermal  Meters,  or  those  in  which 
the  current  passing  is  measured  by  a  movement 
effected  by  the  increase  in  temperature  of  a  resist- 
ance through  which  the  current  is  passed,  or  by 
the  amount  of  a  liquid  evaporated  by  the  heat 
generated  by  the  current. 

(4.)  Electric- Time  Meters,  or  those  in  which 
no  attempt  is  made  to  measure  the  current  that 
passes,  but  in  which  a  record  is  kept  of  the  num- 
ber of  hours  that  an  electric  lamp,  motor  or 
other  electro-receptive  device  is  supplied  with 
current. 

Edison's  electric  meter  is  of  the  second  class. 
It  consists  of  two  voltameters,  or  electrolytic  cells, 
containing  zinc  sulphate,  in  which  two  plates  of 
chemically  pure  zinc  are  dipped.  The  current 
that  passes  is  determined  by  the  amount  of  the 
variation  in  weight  of  the  zinc  plates.  To  deter- 
mine this,  the  plates  are  weighed  at  stated  in. 
tervals :  one  plate  every  month,  the  other  plate, 
which  is  intended  to  act  as  a  check  on  the  first, 
only  once  in  three  months.  Some  difficulty  has 
been  experienced  in  the  employment  of  meters  of 
this  class,  from  the  variations  in  the  value  of  the 
shunt  resistance,  due  to  variations  in  the  condi- 
tion and  temperature  of  the  electrolytic  cell. 
The  use  of  a  compensating  resistance,  however, 
has,  it  is  claimed,  removed  this  objection.  (See 
Voltameter.) 

Meter,  Electric-Time  —  — An  electric 
meter  in  which  the  current  passing  is  esti- 
mated by  recording  the  number  of  hours  that 
an  electric  lamp  or  other  electro-receptive 
device  is  supplied  with  a  known  current. 
i  (See  Meter,  Electric.} 


Meter,  Electro-Chemical An  elec- 
tric meter  in  which  the  current  passing  is 
measured  by  the  electrolytic  decomposition  it 
effects.  (See  Meter,  Electric^ 

Meter,  Electro-Magnetic An  elec- 
tric meter  in  which  the  current  passing  is 
measured  by  the  electro-magnetic  effects  it 
produces.  (See  Meter,  Electric?) 

Meter,  Electro-Thermal An  elec- 
tric meter  in  which  the  current  passing  is 
measured  by  means  of  the  heat  generated  by 
the  passage  of  the  current  through  a  resist- 
ance. (See  Meter,  Electric^ 

Meter,  Energy A  term  sometimes 

applied  to  a  watt  meter.  (See  Meter, 
Watt.} 

Meter,  Milli-Ampe're An  ampere 

meter  graduated  to  read  milli-amperes. 

Meter,  Watt An  instrument  gener- 
ally consisting  of  a  galvanometer  constructed 
so  as  to  measure  directly  the  product  of  the 
current,  and  the  difference  of  potential. 

Since  the  watt  is  equal  to  the  product  of  the 


Fig.  39  6.     Watt  Meter. 

current  by  the  electromotive  force,  if  the  current 
and  electromotive  force  are  simultaneously  meas- 
ured, their  product  gives  directly  the  watts. 
The  scale  reading  of  a  watt  meter  may  be  grad- 
uated so  as  to  give  the  watts  directly. 

A  watt  meter  consists  essentially  of  a  thick  wire 
coil,  placed  in  series  in  the  circuit  whose  electric 
power  is  to  be  measured,  and  a  thin  wire  coil 


Met.] 


366 


[Mic. 


placed  in  a  shunt  around  the  circuit  to  be  meas- 
ured. These  two  coils,  instead  of  acting  on  a 
needle,  act  on  each  other,  and  the  amount  of  this 
deflection  will,  therefore,  be  proportional  to  the 
watts  present. 
A  form  of  watt  meter  is  shown  in  Fig.  396. 

Method,  Deflection A  method  em- 
ployed in  electrical  measurements,  as  distin- 
guished from  the  zero  method,  in  which  a 
deflection,  produced  on  any  instrument  by  a 
given  current,  or  by  a  given  charge,  is  utilized 
for  determining  the  value  of  that  current  or 
charge. 

The  conditions  remaining  the  same,  the  same 
Current  or  charge  will  produce  the  same  deflection 
at  any  time.  Different  deflections  produced  by 
currents  or  charges,  the  values  of  which  are  un- 
known, are  determined  by  certain  ratios  existing 
between  the  deflections  and  the  currents  or 
charges.  These  ratios  are  determined  experi- 
mentally by  the  calibration  of  the  instrument. 
(See  Calibrate.) 

Deflection  methods  are  opposed  to  zero  or  null 
methods,  in  which  latter  a  balance  of  opposite 
electromotive  forces,  or  a  proportionally  equal 
fall  of  electric  potential,  is  ascertained  by  the 
failure  of  a  delicately  poised  needle  to  be  moved 
by  a  current  or  a  charge. 

Method,  Null  or  Zero Any  method 

employed  in  electrical  measurements,  in  which 
the  values  of  the  electromotive  force  in  volts, 
the  resistance  in  ohms,  or  the  current  in  am- 
p&res,  or  other  similar  units,  are  determined 
by  balancing  them  against  equal  values  of  the 
same  units,  and  ascertaining  such  equality,  not 
by  the  deflections  of  the  needle  of  a  galvano- 
meter, or  of  an  electrometer,  but  by  the  ab- 
sence of  such  deflections. 

The  advantage  of  zero  methods  is  iound  in  the 
fact  that  the  galvanometer  or  electrometer  may 
then  be  made  as  sensitive  as  possible,  which  is  not 
otherwise  the  case,  since  great  deflections  are 
generally  to  be  avoided,  especially  in  tangent 
galvanometers.  (See  Galvanometer.  Electrom- 
eter.} 

Method  of   Magnetization  by  Touch.— 

(See  Magnetization  by  Touch.) 

Methven's  Screen.— (See  Screen,  Meth- 
•ven  's.) 


Metre  Bridge.— (See  Bridge,  Metre.) 
Metre  Candle.— (See  Candle,  Metre.} 
Metre-Gramme  Standard,  Matthiessen's 

A  unit  of  resistance. 

The  resistance  of  a  wire  one  metre  in 
length,  and  of  such  a  diameter  as  would  cause 
the  wire  to  weigh  one  gramme. 

One  metre-gramme  of  pure  hard  drawn  cop  per 
has  a  resistance  of  .1469  B.  A.  units  at  zero  de- 
grees C.  as  determined  by  Matthiessen  (Phil. 
Mag.,  May,  1865). 

Metre-Millimetre A  resistance  unit 

of  length  of  a  wire  or  other  conductor  of  the 
length  of  one  metre  and  of  the  area  of  cross- 
section  of  one  square  millimetre. 

According  to  the  report  of  the  Committee  of  the 
American  Institute  of  Electrical  Engineers  of  1890, 
on  a  Standard  Wiring  Table,  a  metre-millimetre 
of  pure  soft  copper  wire  has  a  resistance  of  .02057 
B.  A.  units  at  zero  degrees  C.  From  the  corre- 
sponding term,  milfoot,  millimetre-metre  would 
appear  to  be  the  preferable  term. 

Metric  Horse-Power. — (See  Horse-Power, 
Metric.) 

Metric  System  of  Weights  and  Meas- 
ures.— (See  Weights  and  Measures,  Metric 
System  of.} 

Mho. — A  term  proposed  by  Sir  Wm. 
Thomson  for  the  practical  unit  of  conductiv- 
ity. 

Such  a  unit  of  conductivity  as  is  equal  to 
the  reciprocal  of  I  ohm. 

The    conducting   power  is  equal  to or  the 

R 
reciprocal  of  the  resistance. 

The  word  mho,  as  is  evident,  is  obtained  by  in- 
verting the  order  of  sequence  of  the  letters  in  the 
word  ohm. 

Mica. — A  mineral  substance  employed  as 
an  insulator. 

Mica  is  a  silicious  mineral.  It  occurs  of  vary- 
ing degrees  of  transparency,  and  splits  or  cleaves 
readily  into  transparent  laminae.  It  is  a  good 
non-conductor,  is  fairly  fire-proof,  and  is  not 
hydroscopic. 

Mica  is  used  extensively  in  insulating  the  me- 
tallic segment  of  commutators  of  motors  and 
dynamo-electric  machines  and  in  various  other 
electric  work. 


Mic.] 


36? 


Mica,  Moulded An  insulating  sub- 
stance consisting  of  finely  divided  mica  made 
into  a  paste,  with  some  fused  insulating 
substance,  and  moulded  into  any  desired 
shape. 

Finely  divided  mica  mixed  with  gum-shellac 
rendered  plastic  by  means  of  heat,  forms  a  good 
insulating  substance. 

Micro  (as  a  prefix). — The  one-millionth; 
as,  a  microfarad,  the  millionth  of  a  farad ;  a 
microvolt,  the  one-millionth  of  a  volt. 

Micro-Farad.— (See  Farad,  Micro) 

Micro-Graphophone. — A  modified  form  of 
phonograph  in  which  several  independent 
non-metallic  diaphragms  are  used  instead  of 
the  single  diaphragm  of  the  phonograph.  (See 
Graphophone,  Micro.) 

Micrometer,  Arc An  apparatus  for 

the  accurate  measurement  of  the  length  of  a 
voltaic  arc  by  means  of  a  micrometer. 

The  distance  between  two  carbon  electrodes — 
one  movable  and  the  other  fixed — placed  inside  a 
glass  vessel,  is  accurately  determined  by  means  of 
a  micrometer  placed  on  the  movable  electrode. 
The  operation  is  similar  to  that  of  the  •vernier 
•wire  gauge. 

Micrometer,  Spark A  term  some- 
times applied  to  Hertz's  electric  resonator. 
(See  Resonator,  Electric?) 

Micron. — A  measure  of  length. 

The  one-millionth  part  of  a  metre. 

The  micron  is  equal  to  .00004  of  an  inch,  very 
nearly. 

Microphone.— An  apparatus  invented  by 
Prof.  Hughes  for  rendering  faint  or  distant 
sounds  distinctly  audible. 

The  microphone  depends  for  its  operation  on 
variations  produced  in  the  resistance  of  the  circuit 
of  a  battery,  or  other  electric  source,  by  means  of 
a  loose  contact.  These  variations  in  the  resist- 
ance are  caused  to  produce  corresponding  move- 
ments in  the  diaphragm  of  a  receiving  telephone. 

The  loose  contact  may  take  a  variety  of  forms. 
Originally  it  was  made  in  the  form  shown  in  Fig. 
397,  in  which  a  small  piece  of  carbon  E,  pointed 
at  both  ends,  is  inserted  in  holes  near  the  ends  of 
cross-pieces  of  carbon  B  and  C.  The  thin  upright 
board  A,  on  which  these  are  supported,  acts  as  a 


sounding  board  or  diaphragm,  and  its  movements 
by  sound  waves  are  at  once  audible  to  a  person 
listening  at  the  receiving  telephone.  The  walk- 
ing of  a  fly  over  the  sounding  board  is  heard  as  a 
loud  sound. 

The  forms  of  transmitting  telephones  invented 
by  Reis,  Edison,  Blake,  Berliner  and  others,  are 
in  reality  varieties  of  microphones. 


Fig-  397-    Microphone. 

Microphone  Relay.— (See  Relay,  Micro- 
phoned) 

Micro-Seismograph. — (See  Seismograph 
Micro) 

Microtasimeter. — An  apparatus  invented 
by  Edison  to  measure  minute  differences  of 
temperature,  or  of  moisture,  by  the  resulting 
differences  of  pressure. 

A  change  of  temperature,  or  moisture,  is  caused 
to  produce  variations  in  the  resistance  of  a  button 
of  compressed  lampblack,  placed  in  the  circuit  of 
a  delicate  galvanometer.  The  apparatus,  though 
of  surprising  delicacy,  is  scarcely  capable  of  prac- 
tical application,  from  the  fact  that  the  resistance 
of  the  carbon  does  not  resume  its  normal  value  on 
the  removal  of  the  pressure. 

Micro-Volt— (See  Volt,  Micro.) 

Mil.— A  unit  of  length  equal  to  the  TTTOT  of 
an  inch,  or  .001  inch,  used  in  measuring  the 
diameter  of  wires. 

Mil,  Circular A  unit  of  area  em- 
ployed in  measuring  the  areas  of  cross-sec- 
tions of  wires,  equal  to  .78540  square  mil. 

The  area  of  a  circle  one  mil  in  diameter. 


Mil.] 


368 


[Min. 


One  circular  mil  equals  .000000785  square  inch. 

The  area  of  cross-section  of  a  circular  wire  in 
circular  mils  is  equal  to  the  square  of  its  diameter 
expressed  in  mils.  (See  Units  ^  Circular.} 

Mil-Foot. — A  resistance  unit  of  length  of 
one  foot  of  wire  or  other  conductor  of  one 
mil  diameter. 

The  resistance  of  a  mil-foot  of  soft  copper  wire 
or  wire  i  foot  long  and  .001  of  an  inch  in  diam- 
eter is  equal  to  9.720  B.  A.  units  at  O  degrees  C. 

Mil,  Square A  unit  of  area  em- 
ployed in  measuring  the  areas  of  cross-sec- 
tions of  wires,  equal  to  .000001  square  inch. 

One  square  mil  equals  1.2732  circular  mil. 

Mile,  Nautical  -  —A  knot,  or  a  dis- 
tance of  6,087  feet,  or  very  nearly  1.15  statute 
miles. 

The  -gifloo  of  the  earth's  equatorial  cir- 
cumference, or  the  -gV  of  a  degree  of  longi- 
tude at  the  equator,  or  about  2,029  yards. 

A  nautical  or  geographical  mile  being  the 
syiinr  of  24,899  miles,  has  a  value  somewhat 
greater  than  that  of  the  statute  mile. 

Mile  Standard,  Matthiessen's A 

standard  of  resistance  equal  to  the  resistance 
of  one  mile  of  pure  copper  wire  iV  inch  in 
diameter  at  15.5  degrees  C. 

Matthiessen's  mile  standard  has  a  resistance  of 
13.59  B.  A.  units  at  15.5  degrees  C. 

Mile,  Statute  —  — The  ordinary  unit  of 
distance  on  land,  equal  to  5,280  feet. 

Milli  (as  a  prefix). — The  one-thousandth 
part. 

Milli- Ampere. — The  thousandth  of  an  am- 
pere. 

Milli-Calorie. — The  smaller  calorie.  (See 
Calorie,  Small.) 

Milli-Oerstedt— The  one-thousandth  of 
an  Oerstedt. 

Mimosa  Sensitive— A  sensitive  plant 
whose  leaves  fold  or  shut  up  when  touched. 

The  fibres  of  all  the  sensitive  plants,  such,  for 
example,  as  the  above,  the  Venus'  Fly-trap,  etc., 
like  all  muscular  fibre,  and  indeed  all  protoplasm, 
suffer  contraction  when  traversed  by  electric  cur- 
rents. 

Mine,  Electro-Contact A  sub- 
marine mine  that  is  fired  automatically  on 
the  completion  of  the  current  of  a  battery 


placed  on  the  shore  through  the  closing  of 
floating  contact  points  by  passing  vessels. 
(See  Mine,  Submarine!) 

Mine  Exploder,  Electro-Magnetic 

A  form  of  electro-magnetic  exploder.  (See 
Exploder,  Electro-Magnetic.) 

Mine,  Mechanical A  submarine 

mine  that  is  fired  when  struck  by  a  passing 
ship  by  the  action  of  some  contrivance  con- 
tained within  the  torpedo  itself,  and  having 
no  connection  whatever  with  the  shore. 

Mine,  Observation A  variety  of 

submarine  mine  that  is  fired  when  the 
enemy's  vessels  are  observed  to  be  within  the 
destructive  area  of  the  mine.  (See  Mine, 
Submarine.) 

Various  means  are  adopted  for  obtaining  the 
current  required  for  firing  such  mines.  A  suffi- 
ciently powerful  battery  is  generally  used.  An 
electro-magnetic  mine  exploder  may,  under  cer- 
tain circumstances,  be  employed.  (See  Mine 
Exploder,  Electro-Magnetic. ) 

Mine,  Submarine A  mass  of  gun- 
cotton  or  other  explosive  contained  in  a 
water-tight  vessel  and  placed  under  water  so 
as  to  be  exploded  on  the  passage  over  it  of 
an  enemy's  vessel. 

A  submarine  mine  is  a  stationary  torpedo  ar- 
ranged for  the  defense  of  a  harbor.  A  harbor 
is  protected  by  a  number  of  mines  which  are  so 
arranged  as  to  be  readily  exploded  by  the  passage 
of  an  enemy's  ship,  but  safely  crossed  by  other 
vessels. 

Submarine  mines  consist  essentially  of  gun- 
cotton  or  other  explosives  contained  in  water-tight 
vessels  anchored  in  very  carefully  located  posi- 
tions, and  connected  with  the  shore  by  means  of 
cables. 

An  operating-room  at  the  shore  end  of  the 
cable  is  furnished  with  batteries,  measuring  in- 
struments, contact  keys,  etc.,  etc.,  by  means  of 
which  the  mines  can  be  exploded  by  the  trans- 
mission of  an  electric  current  through  the  cables; 
or,  the  mines  are  furnished  with  automatic  cir- 
cuit closers  in  which  two  central  points  are  closed 
by  the  passage  of  the  vessel.  In  ordinary  times 
this  current  is  too  weak  to  ignite  the  fuse,  and 
merely  closes  a  relay  in  the  operating-room, 
which  in  turn  directs  a  current  through  a  bell  or 
indicator,  but,  of  course,  too  weak  to  fire  the  fuse. 


Hiii.] 


[Mom. 


In  times  of  war,  however,  the  relay  sends  a 
current  through  the  cable  sufficiently  strong  to 
heat  a  platinum  indium  fuse,  ignite  a  fulminate  of 
mercury  cap,  and  thus,  by  the  detonation  of  the 
primer  of  dry  gun-cotton,  explode  the  full  charge 
of  damp  gun-cotton  in  the  torpedo  or  mine. 

Mine,  Subterranean  --  A  mass  of 
gun  powder,  gun-cotton  or  other  explosive, 
placed  under  ground  in  vessels  suitable  for 
protection  against  moisture,  and  fitted  with 
electrically  connected  electric  fuses,  which  are 
either  exploded  automatically  by  the  move- 
ment of  an  enemy  over  them,  or  by  an  oper- 
ator placed  at  a  safe  distance  within  an  en- 
trenchment. 


—  One  ampere  flow- 
(See Hour,  Ampere?) 

A  unit  of  electrical 


Minute,  Ampere 

ing  for  one  minute. 

Minute,  Watt 

work. 

The  expenditure  of  an  electrical  power  of 
one  watt  for  one  minute. 

The  watt-minute  is  equal  to  60  joules.  This 
unit  of  electrical  work  is  seldom  used. 

Miophone.  —  An  apparatus  invented  by 
Boudet  based  on  the  use  of  the  microphone, 
and  designed  for  the  medical  examination  of 
the  muscles. 

Mirror  Galvanometer.  —  (See  Galvanom- 
eter, Mirror?) 

Moist  Electrode.—  (See  Electrode,  Moist?) 

Moisture,  Eifect  of,  on  Electrical  Phe- 
nomena -  —  The  influence  of  moisture 
on  the  surfaces  of  insulators  in  causing  the 
loss  or  dissipation  of  an  electric  charge. 

This  loss  is  more  rapid  with  negatively  charged 
bodies  than  with  those  positively  charged. 

Molar  Attraction.  —  (See  Attraction, 
Molar?) 

Molecular.  —  Pertaining  to  the  molecule. 
(See  Molecule?) 

Molecular  Attraction.—  (See  Attraction, 
Molecular?) 

Molecular  Bombardment.—  (See  Bom- 
bardment, Molecular?) 

Molecular  Chain.—  (See  Chain,  Molecu- 
lar?) 


Molecular  Currents.— (See  Currents, 
Molecular  or  Atomic?) 

Molecular  Currents,  Induced (See 

Currents,  Induced  Molecular  or  Atomic?) 

Molecular  Range. — (See  Range,  Molecu- 
lar?) 

Molecular  Repulsion. — (See  Repulsion 
Molecular?) 

Molecular  Rigidity.  —  (See  Rigidity, 
Molecular?) 

Molecular  Theory  of  Muscle  and  Nerve 
Currents.— (See  Theory,  Molecular,  of  Mus- 
cle and  Nerve  Currents?) 

Molecule. — A  group  of  atoms  whose 
chemical  bonds  or  affinities  are  mutually 
satisfied. 

The  smallest  quantity  of  a  compound  sub- 
stance that  can  exist  as  such. 

Water  is  a  compound  substance  formed  of  two 
atoms  of  hydrogen  combined  with  one  atom  of 
oxygen.  The  molecule  of  water,  therefore,  or 
the  smallest  quantity  of  water  that  can  exist,  must 
contain  two  atoms  of  hydrogen  and  one  of  oxygen. 

The  molecule  of  hydrogen  consists  of  two  atoms 
of  hydrogen.  Since  hydrogen  is  a  monad,  or  an 
element  whose  atomicity  is  one,  it  can  combine 
with  one  atom  of  hydrogen  and  form  a  molecule, 
since  then  its  bonds  will  be  fully  satisfied.  (See 
Atomicity.} 

Molecule,    Closed-Magnetic    Circuit    of 

— (See   Circuit,   Closed-Magnetic,  of 

Molecule?) 

Molecule,  Gramme The  weight  of 

any  substance  taken  in  grammes  numerically 
equal  to  the  molecular  weight. 

Moment,  Magnetic The  sum  of  the 

two  forces  of  the  directive  couple  multiplied 
by  half  the  perpendicular  distance  between  the 
directions  of  these  forces ;  or,  in  other  words, 
the  moment  of  a  magnet  is  equal  to  its  length 
multiplied  by  the  intensity  of  the  magnetism 
of  one  of  its  poles.  (See  Couple,  Magnetic?) 

Moment  of  Couples. — (See  Couple,  Mo- 
ment of?) 

Momentary  Current. — (See  Current,  Mo- 
mentary?) 

Momentum,  Electro-Magnetic,  of  Sec- 
ondary Circuit  — A  quantity  equal  to 


Moii.] 


370 


[Mot. 


the  co-efficient  of  mutual  induction,  multi- 
plied by  the  current  strength  in  the  primary, 
when  the  primary  current  is  fully  established. 
When  the  primary  current  is  fully  established, 
the  number  of  lines  of  force  which  pass  through 
the  secondary  circuit  is  equal  to  the  co-efficient  of 
mutual  induction,  multiplied  by  the  strength  of 
the  primary  current. 

Monophotal  Arc-Light  Regulator.— (See 
Regulator,  Monophotal  Arc-Light?) 
Mordey  Effect. — (See  Effect,  Mordey?) 
Morse  Alphabet.— (See  Alphabet,    Tele- 
graphic: Morse's?) 

Morse  Inker.— (See  Inker,  Morse.) 
Morse  Recorder. — (See  Recorder,  Morse?) 
Morse  Register. — (See  Register,  Morse?) 
Morse     System     of    Telegraphy.— (See 
Telegraphy,  Morse  System  of.) 

Morse's  Telegraphic  Alphabet.— (See  Al- 
phabet, Telegraphic  :  Morse's?) 

Morse's  Telegraphic  Sounder.— (See 
Sounder,  Morse  s  Telegraphic?) 

Motion,  Energy  of  —  — A  term  some- 
times applied  to  actual  or  kinetic  energy  in 
contradistinction  to  potential  energy.  (See 
Energy,  Actual?) 

Motion,  Simple-Harmonic Motion 

which  repeats  itself  at  regular  intervals,  taking 
place  backwards  or  forwards,  and  which  may 
be  studied  by  comparison  with  uniform  mo- 
tion round  a  circle  of  reference. — (Daniell?) 
c 


Fig.  398.     Simple-Harmonic  Motion. 

Motion  which  is  a  simple  periodic  function 
of  the  time. 

Suppose  a  pendulum  be  set  swinging  in  a  cer- 
tain path.  If  the  path  of  such  a  pendulum,  or, 
as  it  is  generally  called,  a  conical  pendulum,  be 


looked  at  from  above  or  from  below,  it  will  appear 
to  be  circular;  if  observed  from  one  side  it  will 
appear  elliptical,  and  this  elliptical  path  will  ap- 
pear longer  and  narrower  as  the  eye  of  the  ob- 
server approaches  the  level  of  the  plane  in  which 
the  bob  moves,  when  the  bob  will  appear  to 
travel  backwards  and  forwards  in  a  straight  line. 
The  bob  will  appear  to  be  moving  faster,  when  it 
is  moving  right  across  the  field  of  view. 

Let  the  circle  Q  C  R  (Fig.  398)  be  the  path  in 
which  the  bob  moves,  and  let  Q  A,  A  B,  B  C,  C  o, 
etc.,  be  equal  distances  in  such  path.  Let  the 
lines  A  a,  B  b,  C  c,  o  O,  etc.,  be  drawn  perpendicu- 
lar to  the  line  Q  R.  Then  when  looked  at,  with 
the  eye  on  the  level  of  the  plane  in  which  the  bob 
travels,  the  line  Q  R,  will  be  the  path  in  which 
the  bob  appears  to  move  backwards  and  for- 
wards, and  the  lines,  Q  a,  a  b,  b  c,  c  O,  etc.,  will 
represent  the  spaces  apparently  traversed  in 
equal  intervals  of  time. 

The  circle  Q  o  R,  is  called  the  circle  of  refer- 
ence. 

Motion,  Simple-Harmonic,  Amplitude  of 

The  length  of   the  swing  from    the 

median  position  to  its  extreme  position,  in 
either  direction. 

The  line  O  Q,  or  O  R,  in  the  circle  of  reference 
Q  O  R  (Fig.  398). 

Motion,  Simple-Harmonic,  Negative  Di- 
rection of  —  — The  motion  which  a  body, 
with  a  simple-harmonic  motion,  has  when  it 
appears  to  move  from  left  to  right. 

Motion,  Simple-Harmonic,  Period  of 

— The  interval  of  time  which  elapses  between 
two  successive  passages  of  a  moving  particle, 
over  the  same  point,  in  the  same  direction. 

The  period  of  simple-harmonic  motion  repre- 
sents the  time  of  one  complete  motion  around  a 
circle  called  the  circle  of  reference.  (See  Motion, 
Simple -Harmonic. ) 

Motion,  Simple-Harmonic,  Phase  of 

— The  position  of  a  point  executing  a  simple 
harmonic  motion,  expressed  in  terms  of  the 
interval  of  time  which  has  elapsed  since 
such  point  last  passed  through  the  middle' 
of  its  path  in  the  positive  direction. — (An- 
thony &•  Brackett?) 

The  exact  position  of  a  particle  executing  a 
simple-harmonic  motion  for  any  instant  of  time 
can  be  readily  expressed  in  terms  of  the  phase. 


Mot.] 


371 


[Mot. 


Motion,  Simple-Harmonic,  Positive 

Direction  of The  motion  which  a 

body  moving  in  simple-harmonic  motion  has, 
when  it  appears  to  move  from  right  to  left. 

Motion,  Simple-Periodic A  term 

sometimes  employed  in  the  sense  of  simple- 
harmonic  motion.  (See  Motion,  Simple- 
Harmonic,} 

Motion,  Simple-Sine —A  term  some- 
times employed  in  the  sense  of  simple-har- 
monic motion.  (See  Motion,  Simple-Har- 
monic^) 

Motograph,  Electro An  apparatus 

invented  by  Edison  whereby  the  friction  of  a 
platinum  point  against  a  rotating  cylinder  of 
moist  chalk,  is  reduced  by  the  passage  of 
an  electric  current. 

This  result  is  due  to  electrolytic  action  at  the 
points  of  contact,  varying  the  friction. 

The  electro-motograph,  though  less  certain  in 
its  action  than  an  electro-magnet,  may  replace  it 
in  certain  electric  apparatus. 

The  detailed  construction  of  the  electro-moto- 
graph will  be  understood  from  an  inspection  of 
Fig-  399- 

The  lever  A,  pivoted  with  a  universal  joint  at 
C,  has  a  metallic  point  at  its  free  extremity  F, 
resting  on  a  strip  of  moistened  paper  N,  and  held 
against  it  with  some  pressure  by  the  action  of  the 
spring  S.  The  paper  N,  rests  on  the  metallic 
drum  G,  over  which  it  is  moved  on  the  rotation 
of  the  drum  by  clockwork.  A  spring  R,  acts  to 
move  the  lever  A,  in  a  direction  opposite  to  that 
in  which  it  tends  to  move  by  the  rotation  of  the 
drum  G. 

The  main  battery  L,  is  connected  at  its  negative 
pole  to  the  point  F,  and  at  its  positive  pole,  through 
the  key  K,  to  the  metallic  drum  G.  The  local  bat- 
tery L  B,  is  connected  through  the  sounder  X,  to 
the  contacts  D  and  X. 

When  the  key  K,  is  open,  the  friction  of  F,  on 
the  paper  N,  is  sufficient  to  move  the  lever  A,  to 
the  right  so  as  to  close  the  circuit  of  the  local 
battery,  but  when  the  key  K,  is  depressed,  the 
current  of  L,  passing  through  the  paper,  decom- 
poses the  chemicals  with  which  it  is  moistened, 
lessens  the  friction  of  the  point  F,  and  permits  the 
spring  B,  to  draw  the  lever  A,  to  the  left,  thus 
opening  the  circuit  of  the  local  battery  L  B. 

The  movements  of  the  key  are  therefore  repro- 
duced by  the  armature  of  the  electro-magnet  X. 


An  excellent  loud  speaking  telephone  has  been 
devised  by  Edison  on  the  principle  of  the  electro- 
motograph. 


Fig.  399.    Electro-Motograph. 

Motor,  Compound- Wound An  elec- 
tric motor  whose  field  magnets  are  excited  by 
a  series  and  a  shunt  wire.  (See  Machine, 
Dynamo-Electric,  Compound-  Wound.) 

Motor,  Differentially  Wound  -  —A 
compound-wound  motor,  in  which  the  cur- 
rent in  the  shunt  coils  opposes  in  its  magnet- 
izing effects  the  current  in  a  series  coil,  so 
that  the  efficient  magnetizing  effect  produced 
is  the  difference  in  the  magnetizing  effect  of 
the  two  coils. 

Motor,  Electric A  device  for  trans- 
forming electric  power  into  mechanical 
power. 

All  practical  electric  motors  depend  for  their 
operation  on  the  tendency  to  motion  in  a  mag- 
netic field  of  a  conductor  carrying  a  current  or 
on  magnetic  attraction  or  repulsion.  The  entire 
magnetism  may  be  produced  by  the  current,  or 
part  may  be  obtained  from  permanent  magnets, 
and  the  rest  from  electro-magnets. 

A  dynamo-electric  machine  will  act  as  a  motor 
if  a  current  is  sent  through  it.  Such  a  motor  is 
sometimes  called  an  electro-motor.  The  term 
electric  motor  would,  however,  appear  to  be  the 
preferable  one. 

In  all  cases  the  rotation  is  in  such  a  direction  as 
to  induce  in  the  armature  an  electromotive  force 
opposed  to  that  of  the  driving  current  ;  this  is 
therefore  called  the  counter  electromotive  force. 

A  magneto-dynamo,  or  a  dynamo  the  field  of 
which  is  obtained  from  permanent  magnets,  or  a 
separately  excited  dynamo,  will  operate  as  a 
motor  when  a  current  is  sent  through  its  arma- 
ture, and  will  turn  it  in  the  opposite  direction  to 
that  required  to  drive  it  in  order  to  produce  a 
current  in  the  same  direction. 

A  series  dynamo  will  operate  as  a  motor  when 


Mot.] 


372 


[Mot. 


a  current  is  sent  through  it.  If  the  current  is 
sent  through  it  in  the  opposite  direction  to  that 
which  it  produces  when  in  operation  as  a  gener- 
ator, the  polarity  of  the  field  is  reversed  and  the 
dynamo  will  turn  as  a  motor  in  the  opposite  direc- 
tion to  that  required  to  produce  the  current.  If 
the  current  is  reversed,  the  polarity  of  both  the 
field  and  the  armature  is  again  reversed,  and  the 
dynamo  still  rotates  as  a  motor  in  the  opposite 
direction  to  that  in  which  it  is  rotated  as  a 
generator. 

A  series  dynamo,  therefore,  always  rotates  as  a 
motor  in  a  direction  opposite  to  that  of  its  rotation 
as  a  generator. 

When,  however,  the  polarity  of  the  field  only 
is  reversed  by  changing  the  connection  between 
the  armature  and  the  field,  the  rotation  is  in  the 
same  direction. 

A  shunt  dynamo  operated  as  a  motor  will  also 
turn  in  but  one  direction,  but  this  direction  is  the 
same  as  that  in  which  it  turns  when  operating 
as  a  generator;  for  if  the  direction  of  the  current 
in  the  armature  is  the  same  as  in  a  generator, 
that  in  the  shunt  is  reversed. 

A  compound  wound  dynamo  will  move  in  a 
direction  opposite  to  that  of  its  motion  as  a  gene- 
rator if  the  series  part  is  more  powerful  than  the 
shunt,  and  in  the  same  direction  if  the  shunt  part 
is  more  powerful  than  the  series.  To  use  a  com- 
pound-wound dynamo  as  a  differential  motor  the 
connections  need  not  be  changed.  For  a  cumu- 
lative motor  it  is  necessary  to  reverse  the  connec- 
tions of  the  series  coils. 

Alternating-Current  Dynamo. — The  current 
from  an  alternating-current  dynamo,  if  sent 
through  another  similar  alternating-current  dy- 
namo running  at  the  same  speed,  will  drive  it  as  a 
motor.  Such  a  machine  possesses  the  disadvan- 
tage of  requiring  to  be  maintained  at  a  speed  de- 
pending on  that  of  the  driving  dynamo,  and  also 
that  it  requires  to  be  brought  to  nearly  this  speed 
before  the  driving  current  is  supplied  to  it.  As  a 
result  of  this  last  requirement,  variations  in  the 
load  are  apt  to  stop  the  motor.  Considerable 
improvements,  however,  are  being  introduced 
into  alternate -current  motors,  by  which  these 
difficulties  are  almost  entirely  removed. 

An  alternating  current  sent  through  any  self- 
exciting  dynamo-electric  machine,  such  as  a 
shunt  or  series  machine,  will  drive  it  continu- 
ously as  a  motor.  The  sudden  reversals  in  the 
magnetization  of  its  cores  will,  however,  unless 
Xhe  cores  are  thoroughly  laminated,  set  up  power- 


ful eddy  currents  that  will  injuriously  heat  the 
machine,  and  there  is  also  excessive  sparking  at 
the  brushes. 

The  reversibility  of  any  dynamo -electric  ma- 
chine, or  its  ability  to  operate  as  a  motor  if  sup- 
plied with  a  current,  leads  to  a  fact  of  great 
importance  in  the  efficiency  of  electric  motors, 
viz. :  that  during  rotation  there  is  induced  in  the 
armature  during  its  passage  through  the  field  of 
the  machine,  an  electromotive  force  opposed  co 
that  produced  in  the  armature  by  the  driving 
current,  or  a  counter  electromotive  force.  (See 
Resistance,  Spurious.  Force,  Counter  Electro- 
motive.) This  counter  electromotive  force  acts 
as  a  spurious  resistance,  and  opposes  the  passage 
of  the  driving  current,  so  that,  as  the  speed  of  the 
electric  motor  increases,  the  strength  of  the  driv- 
ing current  becomes  less,  until,  when  a  certain 
maximum  speed  is  reached,  very  little  current 
passes.  In  actual  practice,  this  maximum  speed 
is  not  attained,  or  is  only  momentarily  attained, 
and  a  small,  nearly  constant,  current  is  expended 
in  overcoming  friction  at  the  bearings,  air  fric- 
tion, etc. 

When,  however,  the  load  is  placed  on  the 
motor,  that  is,  when  it  is  caused  to  do  work,  the 
speed  is  reduced  and  the  counter  electromotive 
force  is  decreased,  thus  permitting  a  greater  cur- 
rent to  pass.  The  fact  that  the  load  thus  auto- 
matically regulates  the  current  required  to  drive 
the  motor,  renders  electric  motors  very  economi- 
cal in  operation. 

The  relations  between  the  power  required  to 
drive  the  generating  dynamo,  and  that  produced 
by  the  electric  motor,  are  such  that  the  maximum 
work  per  second  is  done  by  the  motor  when  it 
runs  at  such  a  rate  that  the  counter  electro- 
motive force  it  produces  is  half  that  of  the  current 
supplied  to  it.  The  maximum  work  or  activity  of 
an  electric  motor  is  therefore  done  when  its  theo- 
retical efficiency  is  only  50  per  cent  This, 
however,  must  be  carefully  distinguished  from 
the  maximum  efficiency  of  an  electric  motor.  A 
maximum  efficiency  of  100  per  cent,  can  be  at- 
tained theoretically  ;  and,  in  actual  practice,  con- 
siderably over  90  per  cent,  is  obtained.  In  such 
cases,  however,  the  motor  is  doing  work  at  less 
than  its  maximum  power. 

This  is  Jacobi's  law  of  maximum  effect,  but 
does  not  apply  to  actual  motors  on  account  of  the 
limitations  of  current  carrying  capacity.  For 
example,  a  motor  of  9  horse  power  and  90  per 
cent,  efficiency  loses  I  horse-power  in  heat  within 


Mot.] 


373 


[Mot 


itself.  Hence,  if  run  according  to  Jacobi's  law, 
it  would  only  produce  the  same  amount,  i.  e.,  I 
horse-power  in  useful  work  instead  of  9.  More 
than  this  would  overheat  it. 

An  efficiency  of  100  per  cent,  is  reached  when 
the  counter  electromotive  force  of  the  motor  is 
equal  to  that  of  the  source  supplying  the  driving 
current.  Supposing  now  the  driving  machine  to 
be  of  the  same  type  as  the  motor,  and  the  two 
machines  are  running  at  the  same  speed.  If 
now  a  load  is  put  on  the  motor  so  as  to  reduce  its 
speed,  and  thus  permit  it  to  produce  a  counter 
electromotive  force  of  but  90  per  cent.,  its 
efficiency  will  be  but  90  per  cent.  In  such  a 
case,  therefore,  the  efficiency  is  represented  by 
the  relative  speeds  of  the  generator  and  the 
motor. 

Motor,    Electric,     Alternating-Current 

An  electric  motor  driven  or  operated 

by  means  of  alternating  currents.  (See 
Motor,  Electric?) 

Dr.  Louis  Duncan  divides  alternating  motors 
into  two  classes,  viz. : 

(I.)  Those  in  which  there  is  but  one  trans- 
formation in  the  machine,  viz.,  that  of  the  electric 
energy  of  the  armature  current  into  the  mechani- 
cal energy  of  the  armature's  rotation. 

(2.)  Those  in  which  there  are  two  transforma- 
tions, viz.: 

(a.)  The  transformation  of  electrical  energy 
from  the  main  current  to  electrical  energy  in  the 
armature  current. 

(b.)  The  transformation  of  the  electric  energy 
of  the  armature  current  into  mechanical  energy. 

Alternating  motors  of  the  first  type  are  found 
in  the  ordinary  alternating -current  dynamo  re- 
versed. Those  of  the  second  type  in  Tesla's  or 
Thomson's  motors. 

Motor,  Electric,  Direct-Current  — 

An  electric  motor  driven  or  operated  by 
means  of  direct  or  continuous  electric  cur- 
rents, as  distinguished  from  a  motor  driven 
or  operated  by  alternating  currents.  (See 
Motor,  Electric} 

Motor,  Electric,  High-Speed  —  —The 
ordinary  electric  motor. 

The  term  high-speed  electric  motor  is  used  in 
contradistinction  to  low-speed  electric  motor. 
(See  Motor,  Electric,  Low -Speed.} 

Motor,    Electric,    Low-Speed A 


slow-speed  motor.  (See  Motor,  Electric, 
Slow-Speed^) 

Motor,    Electric,  Overload  of A 

load  greater  than  that  which  an  electric  motor 
can  carry  while  at  its  greatest  efficiency  of 
operation,  or  a  load  which  causes  injurious 
heating  of  a  motor. 

Motor,  Electric,  Reversing  Oear  of  — 

— Apparatus  for  so  reversing  the  direction  of 
the  current  through  an  electric  motor  as  to  re- 
verse the  direction  of  its  rotation.  (See  Rail- 
road, Electric} 

Motor,  Electric,  Slow-Speed  —      —An 

electric  motor  so  constructed  as  to  run  with 
fair  efficiency  at  slow  speed. 

The  electric  motor  develops  a  counter  electro- 
motive fcwve  when  in  motion,  which,  of  course, 
increases  with  the  increase  of  motion.  The  elec- 
tric motor  has,  as  generally  constructed,  its  great- 
est efficiency  at  high  speed.  When  used  on  street 
railroads,  the  high  speed  requires  to  be  decreased 
by  various  forms  of  reduction  gear.  The  loss  of 
power  which  all  such  gear  involve,  together  with 
the  noise  attending  their  use,  render  any  decrease 
in  speed  that  can  be  obtained  on  the  part  of  the 
motor,  without  serious  loss  of  efficiency,  desir- 
able. 

Motor-Electromotive  Force.— (See  Force, 
Motor  Electromotive.} 

Motor,     Pyromagnetie A  motor 

driven  by  the  attraction  of  magnet  poles  on 
a  movable  core  of  iron  or  nickel  unequally 
heated. 

The  intensity  of  magnetization  of  iron  decreases 
with  an  increase  of  temperature,  iron  losing  most 
of  its  magnetization  at  a  red  heat.  A  disc  of  iron 
placed  between  the  poles  of  a  magnet,  so  as  to 
be  capable  of  rotation,  will  rotate,  if  heated  at  a 
part  nearer  one  pole  than  the  other,  since  it  be- 
comes less  powerfully  magnetized  at  the  heated 
part. 

In  the  form  of  pyromagnetic  motor  devised  by 
Edison,  and  shown  in  Fig.  400,  in  elevation,  and 
in  Fig.  401,  in  vertical  section,  the  disc  of  iron  is 
replaced  by  a  series  of  small  iron  tubes,  or  di- 
vided annular  spaces,  heated  by  the  products  of 
combustion  from  a  fire  placed  beneath  them.  In 
order  to  render  this  heating  local,  a  flat  screen  is 
placed  dissymmetrically  across  the  top  to  prevent 


Mot.] 


374 


[Mov. 


the  passage  of  air  through  the  portion  of  the  iron 
tubes  so  screened.  The  air  is  supplied  to  the 
furnace  by  passing  down  from  above  through  the 


Fig,  400.    Pyromagnctic  Motor. 

tubes  so  screened.  This  is  shown  in  the  draw- 
ings, the  direction  of  the  healing  and  the  cooling 
air  currents  being  indicated  by  the  arrows.  The 


Fig.  401.     Pyromagnttic  Motor. 

supply  of  a?r  from  above  thus  insures  the  more 
rapid  cooling  of  the  screened  portion  of  the 
tubes. 

Motor,      Rotating-Current An 

electric  motor  designed  for  use  with  a  rotat- 
ing electric  current. 


Unlike  alternating. current  motors,  rotary-cur- 
rent motors  will,  like  continuous-current  motors, 
readily  start  with  a  load.  (See  Current,  Rotating. ) 

Motor,  Series-Wound An  electric 

motor  in  which  the  field  and  armature  are 
connected  in  series  with  the  external  circuit  as 
in  a  series  dynamo.  (See  Machine,  Dynamo- 
Electric,  Series-  Wound?) 

Motor,  Shunt- Wound An  electric 

motor  in  which  the  field  magnet  coils  are 
placed  in  a  shunt  to  the  armature  circuit. 
(See  Machine,  Dynamo-Electric,  Shunt- 
Wound) 

Motor  Standards.  —  (See  Standards, 
Motor) 

Moulded  Mica.— (See  Mica,  Moulded) 

Moulding,  Electric  Wood  —  —  Mould- 
ing of  dried,  non-conducting  wood,  provided 
with  longitudinal  grooves  for  the  reception 
and  support  of  electric  wires  or  conductors. 

Wood  mouldings  are  employed  for  the  protec- 
tion and  concealment  of  electric  conductors. 

Moulding 
Moulding) 

Mouse-Mill 
Mouse-Mill) 

Mouse-Mill  Machine.  —  (See  Machine, 
Mouse-Mill) 

Mouth  Pieces.— (See  Pieces,  Mouth) 

Movable  Secondary.  —  (See  Secondary, 
Movable) 

Mover,  Prime In  a  system  of  dis- 
tribution of  power  the  motor  by  which  sec- 
ondary motors  or  movers  are  driven. 

In  a  steam  plant,  the  steam  engine  is  the  prime 
mover;  the  shafts  or  machines  driven  by  tlu  main 
shaft  are  sometimes  called  the  secondary  m  vers. 
The  main  shaft  is  called  the  driving  shaf.  Its 
motion  is  carried  by  means  of  be'ts  to  other 
shafts,  called  driven  shafts  The  pulleys  on  the 
driving  or  driven  shafts  a>e  called  respectively 
the  driving  and  driven  pulleys. 

Movers,  Secondary The  shafts  or 

machines  driven  by  the  main  shafts  in  order 
to  distinguish  them  from  the  steam  engine  or 
other  mover  which  drives  it.  (See  Mover, 
Prime.} 


Wiring.  —  (See       Wiring, 
Dynamo.  —  (See    Dynamo, 


Mill.] 


375 


[Mul. 


Multi-Cellular  Electrostatic  Yoltmeter. 

— (See   Voltmeter,  Multi-Cellular  Electro- 
static^) 

Multiphase  Current.— (See  Current,  Mul- 
tiphase^) 

Multiphase  Dynamo.  —  (See  Dynamo, 
Multiphase?) 

Multiphase  System.— (See  System,  Multi- 
phased) 

Multiple-Arc  Circuit.  —  (See  Circuit, 
Multiple-Arc?) 

Multiple-Arc-Connected  Electro-Recep- 
tive Devices. — (See  Devices,  Electro-Recep- 
tive, Multiple- Arc-Connected?) 

Multiple-Arc-Connected  Sources.— (See 
Sources,  Multiple-A  re-  Connected?) 

Multiple-Arc-Connected  Translating  De- 
vices.— (See  Devices,  Translating,  Mul- 
tiple-Arc-Connected?) 

Multiple-Brush  Rocker. — (See  Rocker, 
Multiple-Brush?, 

Multiple-Brush  Yoke.— (See  Yoke,  Mul- 
tiple-Pair Brush?) 

Multiple  Cable  Core.— (See  Cable,  Mul- 
tiple-Core?) 

Multiple  Circuit.— (See  Circuit,  Mul- 
tiple?) 

Multiple  Conduit— (See  Conduit,  Mul- 
tiple?, 

Multiple-Connected  Battery.— (See  Bat- 
tery, Multiple-Connected?) 

Multiple-Connected  Electro-Receptive 
Devices.— (See  Devices,  Electro-Receptive, 
Multiple-  Connected?) 

Multiple-Connected  Electro-Receptive 
Devices,  Automatic  Cut-Out  for  —  — (See 
Cut-Out,  Automatic, for  Multiple-Connected 
Electro-Receptive  Devices?) 

Multiple-Connected  Translating  Devices. 
— (See  Devices,  Translating,  Multiple-Con- 
nected?) 

Multiple  Connection.  — (See  Connection, 
Multiple?) 


Multiple  Distribution  of  Electricity  by 
Constant  Potential  Circuits.— (See  Elec- 
tricity, Multiple  Distribution  of,  by  Constant 
Potential  Circuits?) 

Multiple        Electric-Gaslighting.— (See 

Gaslighting,  Multiple  Electric?, 

Multiple-Series.— A  multiple  connection 
of  series  groups.  (See  Connection,  Series 
Multiple?) 

Usage  in  regard  to  this  terra  is  divided.  By 
some  the  term  multiple-series  is  applied  to  a  series 
connection  of  parallel  groups.  This  is  done  on 
account  of  the  order  of  the  words,  multiple-series 
indicating,  it  is  claimed,  a  series  connection  of 
multiple  groups. 

Multiple-Series  Circuit— (See  Circuit, 
Multiple-  Series?) 

Mtiltiple-Series-Connected  Electro-Re- 
ceptive Devices. — (See  Devices,  Electro- 
Receptive,  Multiple-  Series-  Connected?) 

Multiple  -  Series   Connected     Sources. — 

(See  Sources,  Multiple- Series-Connected?) 

Multiple-Series-Connected    Translati  ng 

Devices. — (See  Devices,  Translating,  Mul- 
tiple- Series-  Connected?) 

Multiple-Series  Connection.— (See  Con- 
nection, Multiple- Series.} 

Multiple-Switch  Board.  — (See  Board, 
Multiple-Switch?) 

Multiple  Transformer.  —  (See  Trans- 
former, Multiple?) 

Multiple  Transmission.— (See  Trans- 
mission, Multiple?) 

Multiple  Working  of  Dynamo-Electric 
Machines. — (See  Working,  Multiple,  of 
Dynamo-Electric  Machines?) 

Multiplex  Telegraphy.  —  (See  Teleg- 
raphy, Multiplex?, 

Multiplicator. — A  word  sometimes  used 
for  multiplier. 

Multiplier,  Galvanic  —  —A  term  for- 
merly applied  to  a  galvanometer.  (See  Gal- 
vanometer?) 

Multiplier,  Schweigger's The 

name  first  given  to  a  coil  consisting  of  a 


Mul.] 


376 


[Nee. 


number  of  turns  of  insulated  wire,  provided 
for  the  purpose  of  increasing  the  strength  of 
the  magnetic  field  produced  by  an  electric 
current,  and  consequently  the  amount  of  its 
deflecting  power  on  a  magnetic  needle. 

Schweigger's  multiplier  was  in  fact  an  early 
form  of  galvanometer.  (See  Galvanometer.') 

Multiplying  Power  of  Shunt.  —  (See 
Shunt,  Multiplying  Power  of.} 

Multipolar  Armature. — (See  Armature, 
Multipolar) 

Multipolar  Dynamo-Electric  Machine.— 
(See  Machine,  Dynamo-Electric,  Multipo- 
lar) 

Multipolar-Electric  Bath.— (See  Bath, 
Multipolar  Electric.} 

Muscle  Current. — (See  Current,  Muscle?) 

Muscles,  Electrical  Excitation  of 

(See  Excitation,  Electro- Muscular) 


Muscular,    Electro Pertaining    to 

the  influence  of  electricity  on  the  muscles. 

Muscular  or  Nerve  Fibre,  Excitability 

of (See    Excitability,     Electric,    of 

Nerve  or  Muscular  Fibre) 

Muscular   Pile,    Matteucci's (See 

Pile,  Muscular,  Matteucci's) 

Musket,  Electric A  gun  in  which 

the  charge  is  ignited  by  a  platinum  wire  ren- 
dered incandescent  by  the  action  of  a  bat- 
tery placed  in  the  stock  of  the  gun. 

Mutual  Inductance. — (See  Inductance) 

Mutual      Induction.  —  (See     Induction, 
Mutual.} 

Mutual  Induction,  Co-efficient   of  

— (See  Induction,  Mutual,  Co-efficient  of) 

Myria  (as  a  prefix). — A  million  times. 


N 


N. — A  contraction  employed  in  mathe- 
matical writings  for  the  whole  number  of 
lines  of  magnetic  force  in  any  magnetic  cir- 
cuit. 

N. — A  contraction  for  North  Pole. 

This  N,  may  be  distinguished  from  the  N,  used 
for  expressing  the  whole  number  of  lines  of  mag- 
netic force,  by  making  the  former  light  and  the 
latter  heavy. 

N.  H.  P. — A  contraction  for  Nominal 
Horse-Power. 

Nominal  horse-power  is  a  somewhat  indefi- 
nite term  for  a  quantity  dependent  on  the  length 
of  stroke  and  the  dimensions  of  the  cylin- 
der. This  quantity  is  a  dependent  one,  be- 
cause it  varies  necessarily  with  the  type  of  en- 
gine. 

Nascent  State.— (See  State,  Nascent) 

Natural  Currents.— (See  Currents,  Nat- 
ural) 
Natural  Law.— (See  Law,  Natural) 

Natural  Magnet— (See  Magnet,  Nat- 
ural) 


Natural  Unit  of  Electricity.— (See  Elec- 
tricity, Natural  Unit  of) 
Natural  Unit  of  Quantity  of  Electricity, 

— (See  Electricity,  Unit  Quantity  of,  Natu- 
ral) 

Nautical  Mile.— (See  Mile,  Nautical) 

Needle  Annunciator. — (See  Annunciator, 
Needle) 

Needle,  Astatic A  compound  mag- 
netic needle  of  great  sensibility,  possessing 
little  or  no  directive  power. 

An  astatic  needle  consisting  of  two  separate 
magnetic  needles,  rigidly  connected  together 
and  placed  parallel  and  directly  over  each 
other,  with  opposite  poles  opposed. 

An  astatic  needle  is  shown  in  Fig.  402.  The 
two  magnets  N  S,  and  S'  N',  are  directly  opposed 
in  their  polarities,  and  are  rigidly  connected  to- 
gether by  means  of  the  axis  a,  a.  So  disposed, 
the  two  magnets  act  as  a  very  weak  single  needle 
when  placed  in  a  magnetic  field. 

Were  the  two  magnets  N  S,  and  S'  N',  of  ex- 
actly equal  strength,  with  their  poles  placed  in 
exactly  the  same  vertical  plane,  they  would  com- 
pletely neutralize  each  other,  and  the  needle 


Nee.] 


377 


[Nee. 


would  have  no  directive  tendency.    Such  a  sys- 
tem would  form  an  Astatic  Pair  or  Couple. 
In  practice  it  is  impossible  to  do  this,  so  that  the 


Fig.  402.     Astat:c  Needle. 

needle  has  a  directive  tendency,  which  is  often 
east  and  west. 

The  cause  of  the  east  and  west  directive  ten- 
dency of  an  unequally  bal- 
anced astatic  system  will 
be  understood  from  an  in- 
spection of  Fig.  403.  Un- 
less the  two  needles,  N  S, 
and  S'  N',  are  exactly  op-  ;5 

posed,  they  will  form  a  fig-  403-  Astatic  Pair. 
single  short  magnet,  N  N  NN,  S  S  S  S,  the  poles 
of  which  are  on  the  sides  of  the  needle.  The 
system  pointing  with  its  sides  due  north  and 
south  will  appear  to  have  an  east  and  west  direc- 
tion. 

The  principal  use  of  the  astatic  needle  is  in  the 
astatic  galvanometer,  in  which  the  needle  is  de- 
flected by  the  passage  of  an  electric  current 
through  a  conductor  placed  near  the  needle. 
Therefore  it  is  evident  that  one  of  the  needles 
must  be  outside  and  the  other  inside  the  coil.  In 
the  most  sensitive 
form  of  galvanome- 
ter there  is  also  a 
coil  surrounding  the 
upper  needle,  the 
two  coils  being  op- 
positely connected, 
so  that  the  deflection 
on  both  needles  is  in 
the  same  direction, 
and  the  deflecting  F'f-  404-  Astatic  System. 
power  is  equal  to  the  sum  of  the  two  coils,  while 
the  directive  power  of  the  needles  is  the  differ- 
ence of  their  magnetic  intensities. 

In  the  astatic  system,  as  shown  in  Fig.  404,  the 
current,  which  flows  above  one  needle,  flows  be- 
iow  the  other,  and  therefore  deflects  both  needles 


in  the  same  direction,  since  their  poles  point  in 
opposite  directions. 

In  some  galvanometers  a  varying  degree  of 
sensitiveness  is  obtained  by  means  of  a  magnet, 
called  a  compensating  magnet,  placed  on  an  axis 
above  the  magnetic  needle.  As  the  compensat- 
ing magnet  is  moved  towards  or  away  from  the 
needle  the  effect  of  the  earth's  field  is  varied,  and 
with  it  the  sensitiveness  of  the  galvanometer. 
Such  a  magnet  may  form  with  the  needle  an 
astatic  system.  (See  Magnet,  Compensating. 
Galvanometer,  Astatic.  Galvanometer,  Mirror. 
Multiplier,  Schweigger'1  s~]. 

Needle  Electrode.— (See  Electrode,  Nee- 
dle^ 

Needle,  Elongation  of A  phrase 

sometimes  used  for  the  angular  deflection  of 
a  needle. 

Needle,  Magnetic A  straight  bar- 
shaped  needle  of  magnetized  steel,  poised 
near  or  above  its  centre  of  gravity,  and  free 
to  move  either  in  a  horizontal  plane  only,  or 
in  a  vertical  plane  only,  or  in  both. 

A  magnetic  needle  free  to  move  in  a  vertical 
plane  only  is  called  a  dipping  needle.  A  mag- 
netic needle  free  to  move  in  a  horizontal  plane 
only,  as  shown  in  Fig.  405,  is  the  form  employed 


Fig.  405.     Magnetic  Needle. 

in  the  mariner's  compass.     This  form  of  magnetic 
needle  is  the  one  most  commonly  employed. 

For  use  as  a  mariner's  compass  the  needle  is 
supported  on  gimbals  and  placed  in  a  box  pro- 
vided with  a  card  on  which  are  marked  the 
points  of  the  compass.  (See  Compass,  Azimuth. 
Compass,  Points  of.) 

Needle,  Magnetic,  Annual  Variations  of 
Variations  in  the  value  of  the  mag- 


Nee.J 


378 


[Nee. 


netic  declination  that  take  piace  at  regular 
periods  of  the  year. 

The  annual  variations  of  the  magnetic  field  were 
discovered  by  Cassini  in  1786. 

Needle,   Magnetic,    Daily    Variation  of 

Variations  in  the  value  of  the  magnetic 

declination  that  take  place  at  different  periods 
of  the  day. 

It  was  noticed,  for  example,  in  London  that  the 
north  pole  of  the  magnetic  needle  begins  to  move 
westward  between  7  and  8  A.  M.  and  continues 
this  movement  until  I  P.  M.,  when  it  begins  to 
move  towards  the  east  until  near  10  p.  M.,  when 
it  again  begins  its  westward  course. 

Needle,    Magnetic,    Damped    —A 

magnetic  needle  so  placed  as  to  quickly  come 
to  rest  after  it  has  been  set  in  motion.  (See 
Damping?) 

Magnetic  damping  is  readily  effected  by  caus- 
ing the  needle  to  move  near  a  metallic  plate.  On 
the  motion  of  the  needle  the  currents  set  up  in  the 
plate  by  dynamo-electric  induction  tend,  accord- 
ing to  Lenz's  law,  to  oppose  the  motions  pro- 
ducing them.  (See  Induction,  Electro-Dynamic. 
Laws,  Lenz^s.) 

Needle,  Magnetic,  Declination  of  — 

The  angular  deviation  of  the  magnetic  needle 
from  the  true  geographical  north. 

The  variation  of  the  magnetic  needle. 

The  declination  of  the  magnetic  needle  is  either 
E.  orW.  (See  Declination,  Angle  of .) 

Decliaation,  or  variation,  is  different  at  dif- 
ferent parts  of  the  earth's  surface. 

Lines  connecting  places  which  have  the  same 
value  and  direction  for  the  declination  are  called 
isogonal  lines.  A  chart  on  which  the  isogonal 
lines  are  marked  is  called  a  variation  chart. 

The  value  of  the  declination  varies  at  dif- 
ferent times.  These  variations  of  the  declination 
are: 

(i.)  Secular,  or  those  occurring  during  great 
intervals  of  time.  Thus,  in  London,  in  1580  the 
magnetic  needle  had  a  variation  of  about  n 
degrees  east.  This  eastern  declination  decreased 
in  1622  to  6  degrees  E.,  and  in  1680  the  needle 
pointed  to  the  true  north.  In  1692  the  declina- 
tion was  6  degrees  W.;  in  1730,  13  degrees  W.; 
in  1765,  20  degrees  W. ;  and  in  1818  the  needle 
reached  its  greatest  western  declination  and  is 


now  moving  eastwards.  The  declination,  how- 
ever, is  still  west. 

(2.)  Annual,  the  needle  varying  slightly  in  its 
declination  during  different  seasons  of  the  year. 

(3.)  Diurnal,  the  needle  varying  slightly  in  its 
declination  during  different  hours  of  the  day. 

(4.)  Irregular,  or  those  which  occur  during 
the  prevalence  of  a  magnetic  storm. 

It  has  been  discovered  that  the  occurrence  of  a 
magnetic  storm  is  simultaneous  with  the  occur- 
rence of  an  unusual  number  of  sun  spots.  (See 
Spots,  Sun.) 

Needle,  Magnetic,  Deflection  of  — 

The  movement  of  a  needle  out  of  a  position  of 
rest  in  the  earth's  magnetic  field  or  in  the 
field  of  another  magnet,  by  the  action  of  an 
electric  current  or  another  magnet. 

The  deflection  of  the  needle  is  sometimes  called 
its  elongation.  This  latter  term  is,  however,  but 
little  used,  and  is  unnecessary. 

Needle,    Magnetic,     Dipping A 

magnetic  needle  suspended  so  as  to  be  tree 
to  move  in  a  vertical  plane,  employed  to  de- 
termine the  angle  of  dip  or  the  magnetic  in- 
clination. (See  Dtp,  Magnetic.  Inclination, 
Magnetic.  Inclinometer.  Chart,  Inclina- 
tion.) 

A  dipping  needle  is  shown  in  Fig.  406.    The 


Fig.  406.    Dipping  Needle. 

angle  B  O  C,  which  marks  the  deviation  of  the 
needle  from  the  horizontal  position,  is  called  the 
angle  ot  dip. 


Nee.] 


379 


[Neg. 


Needle,  Magnetic,  Directive  Tendency  of 

The  tendency  of  a  magnetic  needle  to 

move  so  as  to  come  to  rest  in  the  direction  of 
the  lines  of  the  earth's  magnetic  field. 

The  directive  power  of  the  magnetic  needle  is 
due  to  the  attraction  of  the  earth's  magnetic  poles 
for  the  poles  of  the  needle,  or  to  the  action  of  the 
earth's  magnetic  field.  Since  the  force  of  the 
earth's  magnetism  forms  a  couple,  there  is  no 
tendency  for  the  needle  to  move  bodily  forward 
towards  either  of  the  earth's  poles.  Its  tendency 
is  merely  to  rotate  until  it  comes  to  rest  within 
the  lines  of  the  earth's  magnetic  field,  entering  at 
its  south  pole,  passing  through  its  mass  and 
coming  out  at  its  north  pole. 

Of  course  this  would  be  true  in  the  case  of  a 
directing  magnet  only  when  it  is  at  a  great  dis- 
tance from  the  needle.  Otherwise,  there  would 
be  motion  towards  the  poles  as  well  as  rotation. 

Needle,  Magnetic,  Inclination  or  Dip  of 

The  deviation  of  a  mechanically  bal- 
anced magnetic  needle  from  a  horizontal  po- 
sition. 

The  direction  of  a  magnetic  needle  in  all  parts 
of  the  earth,  except  at  the  magnetic  equator, 
differs  from  a  level  or  horizontal  position.  One 
of  its  ends  inclines  or  dips  towards  the  ground. 
(See  Dip,  Magnetic.  Needle,  Magnetic ;  Dipping.) 

Needle,  Magnetic,  Orientation  of 

The  coming  to  rest  of  a  magnetic  needle  in 
the  earth's  magnetic  field. 

Needle,  Magnetic,  Variation  of 

The  angular  deviation  of  a  magnetic  needle 
from  the  true  geographic  north. 

The  declination  of  the  magnetic  needle. 
(See  Declination?) 

Needle  of  Oscillation. — A  small  magnetic 
needle  employed  for  measuring  the  intensity 
of  a  magnetic  field  by  counting  the  number  of 
oscillations  the  needle  makes  in  a  given  time, 
when  disturbed  from  its  position  of  rest  in 
such  field.  (See  Magnetization,  Intensity  of. 
Lines,  Isodynamic.) 

This  use  of  a  magnetic  needle  in  determining 
the  magnetic  intensity  of  any  place  is  analogous 
to  the  use  of  the  pendulum  in  determining  the  in- 
tensity of  gravity  at  any  place. 

Suppose,  for  example,  that  at  a  certain  place  the 
needle  made  245  oscillations  in  ten  minutes,  and 
13— Vol.  1 


that  at  another  place  it  made  211  in  the  same 
time.  Then  the  relative  intensities  at  these  two 
places  would  be  as  the  square  of  these  two  num- 
bers, or  as  I  :  1.3482. 

Needle,  Telegraphic A  needle  em- 
ployed in  telegraphy  to  represent  by  its  move- 
ments to  the  left  or  right  respectively  the  dots 
and  dashes  of  the  Morse  alphabet.  (See 
Telegraphy,  Needle  System  of.) 

Needle,  Throw  of A  phrase  some- 
times used  for  the  angular  deflection  of  a 
needle,  particularly  when  the  needle  is  swing- 
ing. 

The  displacement  of  the  magnetic  needle  is^ 
called  the  deflection,  the  elongation,  or  the  throw. 
The  first  will  appear  to  be  the  preferable  term 
when  the  needle  comes  to  rest  in  a  displaced  posi- 
tion. 

Negative  Charge.— (See  Charge,  Nega- 
tive.) 

Negative  Direction  of  Electrical  Con- 
vection of  Heat. — (See  Direction,  Negative,, 
of  Electrical  Convection  of  Heat?) 

Negative  Direction  of  Simple-Harmonic 
Motion.— (See  Motion,  Simple-Harmonic, 
Negative  Direction  of.) 

Negative  Electricity.— (See  Electricityt 
Negative.) 

Negative  Electrode.— (See  Electrode* 
Negative?) 

Negative  Element  of  a  Voltaic  Cell.— 
(See  Element,  Negative,  of  a  Voltaic  Cell) 

Negative  Feeders. — (See  Feeders,  Nega- 
tive?) 

Negative  Omnibus  Bars.— (See  Bars^ 
Negative  Omnibus?) 

Negative  Phase  of  Electrotonus.— (See 
Electrotonus,  Negative  Phase  of.) 

Negative  PJate  of  Storage  Battery.— 
(See  Plate,  Negative,  of  Storage  Cell?) 

Neg-ative  Plate  of  Voltaic  Cell.— (See 
Plate,  Negative,  of  Voltaic  Cell?) 

Negative  Pole.— (See  Pole,  Negative?) 

Negative  Potential.— (See  Potential,  Neg- 
ative?) 

Negative  Side  of  Circuit— (See  Circuit. 
Negative  Side  of.) 


Neg.] 


380 


[Nig. 


Negative  Wire.— (See  Wire,  Negative.} 

Negatively. — In  a  negative  manner. 

Negatively  Excited. — Charged  with  nega- 
tive electricity.  (See  Electricity,  Negative?) 

Nerve  or  Muscular  Fibre,  Excitability 
of  —  — (See  Excitability,  Electric,  of 
Nerve  or  Muscular  Fibred) 

Nerves,  Action  of  Electricity  on  — 

Stimulating  and  other  actions  produced  in 
nerves  by  the  passage  of  electricity  through 
them,  dependent  on  the  direction  and  char- 
acter of  the  current.  (See  Electrotonus. 
Galvanization.  Faradization.  Galvano- 
Faradization?) 

Net,    Faraday's An  insulated  net 

of  cotton  gauze,  or  other  similar  material, 
capable  of  being  turned  inside  out  without 
being  thereby  discharged,  employed  for  de- 
monstrating that  in  a  charged,  insulated  con- 
ductor the  entire  charge  is  accumulated  on 
the  outer  surface  of  the  conductor. 


.      Fig.  407.    Faraday's  Net. 

Faraday's  net,  as  shown  in  Fig.  407,  consists 
of  a  bag  N,  of  cotton  gauze,  or  mosquito  netting, 
supported  on  an  insulating  stand  I.  When  tested 
by  a  proof  plane,  no  free  electric  charge  is  found 
on  the  inside,  though  such  a  charge  is  readily 
detected  by  the  same  means  on.  the  outside.  By 
the  aid  of  the  silk  strings  S,  S,  the  bag  can  be 
turned  inside  out,  when  the  charge  will  then  all 
be  found  on  the  then  inside,  or  the  now  outside . 
Faraday  was  in  the  habit  of  protecting  his 
delicate  electroscopes  against  outside  electrifica- 
tion by  covering  them  with  gauze.  To  properly 
act  as  an  electric  screen,  the  gauze  should  be  con- 
nected  with  the  earth. 

Faraday  constructed  a  small  insulated  room, 


twelve  feet  in  height,  breadth  and  depth,  covered 
on  the  inside  with  tin-foil,  and,  on  charging  this 
room  from  the  outside,  he  was  unable  to  detect 
the  presence  of  any  charge  on  the  inside,  even  by 
the  aid  of  his  most  delicate  instruments.  This 
room  is  often  referred  to  as  Faraday's  Cube. 

Nets,  Torpedo  —  — Steel  wire  netting 
suspended  from  or  attached  to  a  ship's  side 
for  the  purpose  of  ensuring  protection  against 
moving  torpedoes. 

Network  of  Currents. — (See  Currents, 
Network  of.  Laws,  Kirchhoff's?) 

Neutral  Armature. — (See  Armature, 
Neutral?) 

Neutral  Feeder.  —  The  feeder  that  is 
connected  with  the  neutral  or  intermediate 
terminal  of  the  dynamos  in  a  three-wire  sys- 
tem of  distribution.  (See  Feeders?) 

Neutral  Line  of  Commutator  Cylinder. 

— (See  Line,  Neutral,  of  Commutator 
Cylinder?) 

Neutral  -  Omnibus  Bars.  —  (See  Bars, 
Neutral-Omnibus.) 

Neutral  Point.— (See  Point,  Neutral.) 

Neutral  Points  of  a  Dynamo-Electric 
Machine.— (See  Points,  Neutral,  of  Dynamo- 
Electric  Machine?) 

Neutral  Points  of  Magnet.— (See  Points, 
Neutral,  of  Magnet?) 

Neutral  Points  of  Thermo-Electric  Dia- 
gram.— (See  Points,  Neutral,  of  Thermo- 
Electric  Diagram?) 

Neutral-Relay  Armature.— (See  Arma- 
ture, Neutral-Relay?) 

Neutral  Section  of  Magnet.— (See  Sec- 
tion, Neutral,  of  Magnet?) 

Neutral  Wire.— (See  Wire,  Neutral?) 

Neutral  Wire  Ampere-Meter. — (See  Am- 
pere-Meter, Balance  or  Neutral  Wire?) 

New  Ohm.— (See  Ohm,  New?) 

Nickel  Bath.- (See  Bath,  Nickel.) 

Nickeling,  Electro  —  —Electroplating 
with  nickel.  (See  Plating,  Electro?) 

Nickel-Plating.-(See  Plating,  Nickel?) 

Night  BelL-(See2te//, 


Nod.] 


381 


[Nou 


Nodal  Point.— (See  Point,  Nodal) 

Nodes,  Electrical  —  —  Points  in  an  open 
circuited  conductor,  through  which  electrical 
oscillations  are  passing,  which  possess  a  con- 
stant mean  value  of  potential,  while  the  poten- 
tial at  its  ends  alternates  between  two  fixed 
limits. 

Points  on  a  conductor  where  the  strength 
of  the  induced  oscillatory  current  is  equal  to 
zero. 

The  nodal  points  on  a  conductor  through  which 
electrical  oscillations  are  passing  therefore  cor- 
respond closely  to  the  nodes  on  a  vibrating  wire 
or  cord. 

Dr.  Hertz  employed  the  following  appara- 
tus in  order  to  show  the  position  of  two  nodes 
in  a  conductor:  An  induction  coil,  A,  had  its  sec- 
ondary terminals  connected  as  shown  in  Fig.  408, 


-©- 


Fig.  408.      Nodes  in  Condttctor. 

to  two  metallic  spheres,  C  and  C ' .  The  spark  mi- 
crometer circuit,  a  c  d  b,  was  placed  near  it,  as 
shown,  and  the  sparking  distance  of  the  secondary 
circuit  of  the  induction  eoil  adjusted,  so  that  the 
spark  micrometer  circuit  was  in  unison  with  it. 
When  sparks  were  passed  between  the  terminals 
of  the  induction  coil  A,  sparks  passed  between  the 
terminals  I  and  2,  at  M,  under  the  influence  of 
resonant  action. 

If,  now,  a  second  micrometer  circuit,  e  g  h  f, 
exactly  similar  to  a  c  d  b,  was  added,  as  shown  in 
the  figure,  and  the  two  joined  near  the  terminals  i 
234,  by  conducting  wires,  as  shown,  the  entire 
system  of  the  micrometer  circuit  formed  a  closed 
metallic  circuit,  the  fundamental  vibration  of 
which  would  have  two  nodes,  one  at  the  middle 
point  of  c  d,  and  the  other  at  g  h.  The  inter- 
nodes  would  be  at  the  junctions  I  3,  and  2  4,  and 
under  these  circumstances  a  true  resonant  ac- 
tion existed  between  the  secondary  circuit  and  the 
micrometer  circuit,  as  was  shown  by  the  fact  that 
any  alteration  in  the  circuit  e  g  h  f ,  whether  by 


increasing  or  decreasing  its  length,  diminished 
the  sparking  distance.  Since  the  conductor  con- 
necting points  2,  and  4,  was  in  the  position  of 
the  node,  where  the  strength  of  the  excited  oscil- 
latory current  was  zero,  its  removal  from  between 
these  points  should  have  no  influence  on  the 
intensity  of  the  vibration.  This  was  found  on 
trial  to  be  the  case.  Electrical  vibrations  may 
therefore  be  excited  by  electrical  resonance  in 
conductors  corresponding  not  only  to  the  simple 
fundamental  note  or  vibration,  but  also  to  the 
higher  electrical  overtones. 

The  apparatus  shown  in  Fig.  409,  from  Tesla, 
illustrates  the  phenomena  of  alternative  path,  as 
well  as  electric  nodes.  The  terminals  of  an  in- 
duction coil  are  connected,  as  shown,  to  a  con- 
denser and  to  a  thick  copper  conductor.  Though 
the  two  incandescent  lamps  are  placed  as  shown, 
yet  they  are  raised  to  luminosity  by  a  species  of 
brush  discharge  that  passes  through  them,  al- 
though they  would  be  short  circuited  to  any  cur- 
rent but  an  oscillatory  discharge. 


Fig.  409.    Nodes  in  a  Conductor. 

Nodular  Deposit,  Electro-Metallurgical 

(See  Deposit,  Electro-Metallurgical 

Nodular.} 
Noisy  Arc.— (See  Arc,  Notsv^ 


Norn.] 


382 


[Num. 


Nominal  Candle-Power.  —  (See  Power, 
Candle,  Nominal?) 

Non-Automatic  Variable  Resistance.— 
(See  Resistance,  Variable,  Non-Automatic.} 

Non-Conductors.  — Substances  that  offer 
so  great  resistance  to  the  passage  of  an  elec- 
tric current  through  their  mass  as  to  practi- 
cally exclude  a  discharge  passing  through 
them. 

Non  conductors  are  called  insulators,  because 
they  electrically  insulate  substances  placed  on  or 
surrounded  by  them. 

The  terms  non-conductors  or  insulators  are 
ordinarily  used  in  a  relative  sense  to  mean  bodies 
which  allow  no  practical  or  appreciable  current 
to  pass  through  them,  since  there  are  no  sub- 
stances known,  apart,  perhaps,  from  the  universal 
ether,  that  absolutely  prevent  the  flow  of  an  elec- 
tric current,  the  difference  of  potential  of  which 
is  sufficiently  great 

The  entire  absence  of  ordinary  matter,  as  in  the 
case  of  a  high  vacuum,  appears  to  render  a  high 
vacuum  very  nearly,  if  not  entirely,  an  absolute 
insulator. 

Non-Electrics.— A  term  formerly  applied 
to  substances  like  metals  or  other  conductors 
which  appeared  not  to  become  electiified  by 
friction. 

The  term  non-electric,  was  used  in  contradis- 
tinction to  electrics,  or  substances  readily  elec- 
trified by  friction.  The  distinction  no  longer 
holds,  since  non- electrics,  ifinsulated,  are  readily 
•electrified  by  friction. 

Non-Homogeneous  Current-Distribu- 
tion.— (See  Current,  Non-Homogeneous, 
Distribution  of.) 

Non-Illumined  Electrode.— (See  Elec- 
trode, Non-Illumined) 

Non-inductive  Resistance.— (See  Resist- 
ance, Non-inductive.) 

|    Non-Oscillatory    Discharge.— (See    Dis- 
charge, Non-Oscillatory.) 
'    Non-Polarized   Armature.— (See  Arma- 
ture, Non-Polarized.) 

Non-Polarizable  Electrodes.— (See  Elec- 
trodes, Non-Polarizable) 

Non-Wasting  Electrode.-  (See  Elect;  ->de, 
Won-  Wasting) 


Normal  Day,  Magnetic  --  (See  Day, 
Normal  Magnetic) 

Northern  Light.—  The  Aurora  Borealis. 
'(See  Aurora  Borealis) 

Notation,  Algebraic  --  A  system  of 
arbitrary  symbols  employed  in  algebra. 

The  following  brief  description  of  the  notation 
employed  in  algebra  is  for  the  use  of  the  non- 
mathematical  reader. 

Quantities  are  represented  in  algebra  by  let. 
ters,  such  as  a,  and  b,  x,  and  y,  etc. 

Addition  is  represented  thus:  a  +  b. 

Subtraction  is  represented  thus:  a  —  b. 

Multiplication  is  represented  thus:  a  X  b,  or 
simply  by  writing  the  letters  next  to  each  other  ab. 

Division  is  represented  thus:  a  -=-  b,  or  3 

An  Exponent,  or  figure  placed  to  the  right  of  a 
letter,  above  it  as  a8,  indicates  that  the  quantity 
represented  by  a,  is  to  be  multiplied  by  itself  three 
times,  as  a  X  a  X  a,  or  a  a  a. 

A  Co-efficient,  or  figure  placed  to  the  left  of  a 
quantity,  indicates  the  number  of  times  that  quan- 
tity is  to  be  taken;  thus,  3  a,  indicates  that  a  is  to 
be  added  three  times,  tnus:  a  -f  a  -|-  a,  or  3  X  a. 

A  Radical  Si%n  or  Root,  thus  \/a,  or  8v/a> 
indicates  that  the  square  root  of  the  quantity  at 
is  to  be  taken.  In  the  same  manner  3  v/li,  indi- 
cates that  the  cube  root  of  a  is  to  be  taken. 

These  expressions  are  sometimes  written  a%  or 


Equality  is  indicated  thus:  a*^a  XaXa,  or 


A  negative  exponent  a~»  indicates  _i,  or  is  the 

a2 

exponent  of  the  reciprocal  of  the  quantity  indi- 
cated. 

Null  or  Zero  Method.—  (See  Method, 
Null  or  Zero) 

Null  Point.—  (See  Point,  Null) 

Number,  Diacritical  --  Such  a  num- 
ber of  ampere-turns  at  which  a  given  core 
would  receive  a  magnetization  equal  to  half 
saturation. 


Obs.J 


[Ohm. 


n. — A  contraction  for  megohm.  (See 
Ohm,  Meg) 

(a. — A  contraction  for  ohm.     (See  Ohm.} 

Obscure  Heat.— (See  Heat,  Obscure) 

Observation  Mine. — (See  Mine,  Observa- 
tion?) 

Observatory,  Magnetic An  obser- 
vatory in  which  observations  of  the  variations 
in  the  direction  and  intensity  of  the  earth's 
magnetic  field  are  made. 

Magnetic  observatories  are  generally  furnished 
with  self-registering  magnetic  apparatus,  such  as 
magnetographs,  magnetometers,  inclinometers. 
(See  Magnetometer.  Magnetograph.  Inclinome- 
ter.) 

Magnetic  observatories  are  generally  con- 
structed entirely  of  non-magnetic  materials;  that 
is,  of  such  materials  as  are  destitute  of  paramag- 
netic properties. 

Obtuse  Angle.— (See  Angle,  Obtuse) 

Occlusion  of  Gas.— (See  Gas,  Occlusion 
of) 

Odorscope. — An  apparatus  in  which  the 
determination  of  an  odor  was  attempted  by 
the  measurement  .of  the  effect  the  odorous 
vapor,  or  effluvia,  produced  on  a  variable 
contact  resistance. 

The  microtasimeter  was  used  in  connection 
with  the  odorscope.  (See  Diagometer,  ftous- 
seau's.  Microtasimeter.') 

Oerstedt,  An A  proposed  term  for 

the  unit  of  electric  current,  in  place  of  an 
ampere. 

The  term  has  not  been  adopted. 

Ohm. — The  unit  of  electric  resistance. 

Such  a  resistance  as  would  limit  the  flow 
of  electricity  under  an  electromotive  force  of 
one  volt  to  a  current  of  one  ampere,  or  to  one 
coulomb  per  second.  (See  Unit,  B.A.  Ohm, 
Legal.  Ohm,  Standard) 

A  value  equal  to  io9  absolute  electro-mag- 
netic units. 

A  value  which  is  represented  by  a  velocity 
of  io ,  or  i, 000,000,000  centimetres  per  second. 


It  may  be  difficult  at  first  to  see  how  resistance 
can  be  correctly  represented  by  a  velocity.  The 
following  consideration  may  render  this  clear  : 
The  formula  for  calculating  the  velocity  Is 

D 
V  =  vp  or  the  velocity  equals  the  distance  passed 

through  in  unit  time.  Now,  by  examining  the 
formula  for  the  value  of  the  resistance,  expressed 
in  terms  of  the  electro-magnetic  units  (see 
Units,  Electro-Magnetic,  Dimensions  of),  it  may 
be  seen  to  be  that  resistance  = 


Electromotive  force 
Current. 


But  this  value  is  of  the  nature  of  a  velocity, 
being  equal  to  the  length,  divided  by  the  time. 
Resistance,  therefore,  has  the  dimensions  of  a 
velocity.  . 

This  is  clearly  expressed  by  Silvanus  P.  Thomp- 
son in  his  "Elementary  Lessons  in  Electricity 
and  Magnetism,"  as  follows,  viz.:  "  Suppose  we 
have  a  circuit  composed  of  two  horizontal  coils, 
C  S,  and  D  T  (Fig.  410),  I  centimetre  apart, 
joined  at  C  D,  and  completed  by  means  of  a 
sliding  piece,  A  B.  Let  this  variable  circuit  be 
placed  in  a  uniform  magnetic  field  of  unit  inten- 
sity, the  lines  of  force  being  directed  vertically 
downwards  through  the  circuit. 

".If,  now,  the  slider  be  moved  along  towards 
S  T,  with  a  velocity  of  n,  centimetres  per  second, 
the  number  of  additional  lines  of  force  embraced 
by  the  circuit  will  increase  at  the  rate  of  n,  per 
second  ;  or,  in  other  words,  there  will  be  an  in- 


Fig. 410.     Resistance  as  a  I'clocily. 

duced  electromotive  force  impressed  upon  the  cir- 
cuit, which  will  cause  a  current  to  flow  through 
the  slider  from  A  to  B.  Let  the  rails  have  no 
resistance,  then  the  strength  of  the  current  will 
depend  on  the  resistance  of  A  B.  Now,  let  A  B, 
move  at  such  a  rate  that  the  current  shall  be  of 
unit  strength.  If  its  resistance  be  one  absolute 
(electro-magnetic)  unit,  it  need  only  move  at  the 
rate  of  i  centimetre  per  second.  If  its  resistance 
be  greater,  it  must  move  with  a  proportionately 


Ohm.] 


384 


[Ohi 


greater  velocity  ;  the  velocity  at  which  it  must 
move  to  keep  up  a  current  of  unit  strength  being 
numerically  equal  to  its  resistance.  The  resist- 
ance known  as  "  i  ohm  "  is  intended  to  be  so9  ab- 
solute electro -magnetic  units,  and,  therefore,  is 
represented  by  a  velocity  of  io9  centimetres,  or 
10,000,000  metres  (/  earth-qitadrant)  per 
second." 

Ohm,  B.  A. —A  contraction  for 

.British  Association  ohm. 

Ohin,  Board  of  Trade A  unit  of  re- 
sistance as  determined  by  a  committee  of  the 
English  Board  of  Trade. 

A  committee  consisting  of  Sir  W.  Thomson, 
Lord  Rayleigh,  Dr.  J.  Hopkinson  and  other 
authorities  appointed  by  the  Board  of  Trade 
(England)  has  recently  recommended  that  the 
ohm  be  taken  as  the  resistance  of  a  column  of 
mercury  106.3  centimetres  in  length  and  one 
square  millimetre  area  of  cross-section  at  o  de- 
grees C.  and  since  this  value  agree's  with  the  best 
experimental  results,  it  will  probably  be  generally 
and  finally  adopted. 

Ohm,    British    Association The 

British  Association  unit  of  resistance, 
adopted  prior  to  1884. 

The  value  of  the  unit  of  electric  resistance,  or 
the  ohm,  was  determined  by  a  Committee  of  the 
British  Association  as  being  equal  to  the  resistance 
at  o  degree  C.  of  a  column  of  mercury  I  square 
millimetre  in  area  of  cross-section  and  104.9 
centimetres  in  length.  This  length  was  taken  as 
coming  nearest  the  value  of  the  true  ohm  de- 
auced  experimentally  from  certain  theoretical 
considerations.  Subsequent  re-determinations 
showed  the  value  so  obtained  to  be  erroneous. 

The  value  of  the  ohm  is  now  taken  internation- 
ally, as  adopted  by  the  International  Electric 
Congress  in  1884,  as  the  resistance  of  a  column 
of  mercury  106  centimetres  in  length,  and  I 
square  millimetre  in  area  of  cross-section.  This 
last  value  is  called  the  legal  ohm,  to  distinguish  it 
from  the  B.  A.  ohm,  which,  as  above  stated,  is 
equal  to  a  mercury  column  104.9  centimetres  in 
length.  Usage  now  sanctions  the  use  of  the 
word  ohm  to  mean  the  legal  ohm. 

This  value  of  the  legal  ohm  is  provisional  until 
the  exact  length  of  the  mercury  column  can  be 
inally  determined.  (See  Ohm,  Board  of  Trade. ) 

The  following  are  the  relative  values  of  these 
wuts,  viz.: 


i  legal  ohm =  1.0112  B.  A.  ohm. 

"       "     =  i. 0600  Siemens  unit. 

i  B.  A.  ohm =    .9889  legal  ohm. 

i       "       "    =  1.0483  Siemens  unit. 

i  Siemens  unit =    .9540  B.  A.  ohm. 

"  "    =    .9434  legal  ohm. 

Ohm,   Legal The    resistance  of  a 

column  of  mercury  i  square  millimetre  in 
area  of  cross-section,  and  106  centimetres  in 
length,  at  the  temperature  of  o  degree  C.  or 
32  degrees  F.  (See  Unit,B.  A.) 

i  ohm  =  1.00112  B.  A.  units.  This  value  of 
the  ohm  was  adopted  by  the  International  Elec- 
tric Congress,  in  1884,  as  a  value  that  should  be 
accepted  internationally  as  the  true  value  of  the 
ohm.  This  value,  however,  was  provisional,  and 
was  never  actually  legalized.  It  will  probably  be 
replaced  by  the  new  (106.3  cm.)  ohm.  (See 
Ohm,  Board  of  Trade.} 

Ohm,  Meg One  million  ohms. 

Ohm,  New A  term  sometimes  used 

for  the  Board  of  Trade  ohm.  (See  Ohm, 
Board  of  Trade?) 

Ohm,  Standard A  length  of  wire 

having  a  resistance  of  the  value  of  the  true 
or  legal  ohm,  employed  in  standardizing  re- 
sistance coils. 

The  standard  ohm,  as  issued  by  the  Electric 
Standards  Committee  of  England,  has  the  form 


Fig.  411.     Standard  Ohm. 

shown  in  Fig.  411.  The  coil  of  wire  is  formed 
of  an  alloy  of  platinum  and  silver,  insulated  by 
silk  covering  and  melted  paraffine.  Its  ends  are 
soldered  to  thick  copper  rods  r,  r',  for  ready 
connection  with  mercury  cups.  The  coil  is  at 
B.  The  space  above  it  at  A,  is  filled  with  parafnae, 
except  at  the  opening  t,  which  is  provided  for 
the  insertion  of  a  thermometer. 


Ohm.] 


385 


[Ope. 


Ohm,   True An  ohm    having    the 

true  theoretical  value  of  the  ohm.    (See  Ohm.*) 

Ohmage.— The  value  of  the  resistance  of 
a  circuit  expressed  in  ohms. 

Ohmic  Resistance.  —  (See  Resistance, 
Ohmic  or  True) 

Obmmeter. — A  commercial  galvanometer, 
devised  by  Ayrton,  for  directly  measuring  by 
the  deflection  of  a  magnetic  needle,  the  re- 
sistance of  any  part  of  a  circuit  through 
which  a  strong  current  of  electricity  is 
flowing. 

Ayrton's  ohmmeter  is  represented  diagram- 
matically  in  Fig.  412.  Two  coils  C  C,  and  c  c, 


Fig.  412.    Ayrton's  Ohmmeter. 

consisting  of  a  short  thick  wire,  and  a  long  thin 
wire,  respectively,  are  placed  at  right  angles  to 
each  other,  and  act  on  a  soft  iron  needle  situated 
as  shown.  The  short,  thick  wire  coil  C  C,  is  con- 
nected in  series  with  the  resistance  O,  to  be 
measured.  The  long,  fine  wire  coil,  of  knmvn 
high  resistance,  is  placed  as  a  shunt  to  the  un- 
known resistance. 

Under  these  circumstances,  it  can  be  shown 
that  the  action  on  the  needle  is  that  due  to  the  ratio 
of  the  difference  of  potential  at  the  terminals  of 
the  unknown  resistance  and  the  current  strength 

•p* 
in  the  thick  wire  coil,  or  R  =  __,   as  may  be 

deduced  from  Ohm's  law. 

The  coils  are  so  proportioned  that  the  current 
when  flowing  through  the  short  thick  wire  moves 
the  needle  to  the  zero  of  the  scale,  while  the  long 
thin  wire  produces  a  deflection  directly  propor- 
tional to  the  resistance. 

Ohm's  Law.— (See  Law  of  Ohm.) 

Oil,  Colza An  oil  obtained  from  the 

seed  of  the  Brassica  oleracea,  a  species  of 
cabbage. 

Colza  oil  is  extensively  used  for  purposes  of  il- 
lumination and  in  the  carcel  standard  lamp.  (See 
Lamp,  Carcel.) 


Oil  Cup. — A  cup  containing  oil  for  lubri 
eating  machinery. 

Oil  Insulator. — (See  Insulator,  Oil.) 

Oil  Transformer.— (See  Transformer, 
Oil.) 

Oiler,  Automatic An  oil  cup  or  res- 
ervoir that  automatically  spreads  oil  over  the 
bearings  of  m.  chinery  in  motion. 

Okonite. — A  variety  of  insulating  material. 

Omnibus  Bars. — (See  Bars,  Omnibus.) 

Omnibus  Wires.— (See  Wires,  Omnibus.) 

Opacity,  Selective  —  — Opaque  in  a  cer- 
tain direction  or  directions  only. 

Certain  substances  are  opaque  to  polarized  light 
in  certain  planes  only.  Thus,  a  plate  of  tourma- 
line permits  light  polarized  in  a  certain  plane 
freely  to  pass  through  it,  but  is  entirely  opaque 
in  a  plane  at  right  angles  thereto. 

S.  P.  Thompson  and  Lodge  have  shown  that 
such  crystals  of  tourmaline  possess  curious  prop- 
erties in  regard  to  the  conduction  of  heat.  While 
warming,  the  crystal  conducts  heat  better  in  a  cer- 
tain direction  than  in  the  opposite  direction.  While 
cooling,  exactly  the  opposite  effects  are  observed. 
In  the  same  manner,  while  the  crystal  is  rising  in 
temperature,  there  is  an  accumulation  of  positive 
electricity  at  one  end,  and  negative  at  the  other. 
While  the  crystal  is  cooling,  the  reverse  is  true. 

Open-Box  Condait.— (See  Conduit,  Open- 
Sox.) 

Open  Circuit.— (See  Circuit,  Open.) 

Open-Circuit  Electric  Oscillations.— 
(See  Oscillations,  Open-Circuit,  Electric) 

Open-Circuit  Induction.— (See  Induction, 
Open-Circuit) 

Open-Circuit  Oscillation,  Period  of  — 
— The  time  in  which  the  oscillations  set  up  in 
a  circuit   by  electrical  resonance  require  to 
make  a  complete  one  to-and-fro  motion. 

The  period  of  an  open-circuit  electric  oscillation 
is  determined  by  the  product  of  the  co-efficients 
of  self-induction  of  the  conductor,  and  does  not 
depend  on  the  composition  of  the  terminals.  It  is 
practically  independent  of  their  resistances. 

Open-Circuit  Single-Current  Signaling.— 
(See  Signaling,  Single-Current,  Open- 
Circuit) 


Ope.] 


386 


[Ore. 


Open-Circuit  Voltaic  Cell.— (See  Cell, 
Voltaic,  Open-Circuit} 

Open-Circuit  Voltmeter.— (See  Volt- 
meter, Open-Circuit.} 

Open-Circuited. — Put  on  an  open  circuit. 

Open-Circuited  Conductor. — (See  Con- 
ductor, Open-Circuited} 

Open-Circuited  Thermostat. — (See  Ther- 
mostat, Open-Circuit} 

Open-Coil  Drum  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Open-Coil  Drum} 

Open-Coil   Dynamo-Electric  Machine. — 

(See  Machine,  Dynamo-Electric,  Open-Coil} 

Open-Coil  Ring  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Open-Coil  Ring} 

Open-Iron-Circuit      Transformer.— (See 

Transformer,  Open-Iron-Circuit} 

Open-Iron  Magnetic  Circuit. — (See  Cir- 
cuit, Open-Iron  Magnetic} 

Open  Magnetic  Core.— (See  Core,  Open- 
Magnetic} 

Opening  Shock.— (See  Shock,  Opening} 

Operation,  Magnet The  use  of  a 

magnet  for  the  purpose  of  removing  particles 
of  iron  from  the  human  eye. 

Optical  Strain.— (See  Strain,  Optical} 

Optical  Strain,  Electro-Magnetic 

(See  Strain,  Optical  Electro-Magnetic} 

Optical  Strain,  Electrostatic  —  — (See 
Strain,  Electrostatic,  Optical} 

Optics,  Electro  -  —That  branch  of 
electricity  which  treats  of  the  general  relations 
that  exist  between  light  and  electricity. 

The  phenomena  of  electro-optics  may  be  ar- 
ranged under  the  following  heads,  viz. : 

(I.)  Electrostatic  stress,  produced  by  an 
electrostatic  field  causing  an  optical  strain  in  a 
transparent  medium,  whereby  such  medium 
acquires  the  property  of  either  rotating  the  plane 
of  polarization  of  a  beam  of  plane  polarized  light, 
or  of  doubly  refracting  light. 

(2.)    Electro  magnetic    stress    produced   by  a 


magnetic  field  causing  an  optical  strain  in  a  trans- 
parent medium,  whereby  such  medium  acquires 
the  property  of  either  rotating  the  plane  of  polar- 
ization, or  of  doubly  refracting  light.  (See  Re- 
fraction, Double,  Electric.) 

(3.)  Changes  in  the  electric  resistance  of  bodies 
caused  by  the  action  of  light.  (See  Cell,  Sele- 
nium. ) 

(4.)  The  relation  existing  between  the  values  of 
the  index  of  refraction  of  a  transparent  medium 
and  its  specific  inductive  capacity.  (See  Refrac- 
tion. Capacity,  Specific  Inductive} 

This  relation  has  been  shown  to  be  as  follows  : 

The  specific  inductive  capacity  is  approxi- 
mately equal  to  the  square  of  the  index  of  re- 
fraction. 

(5.)  The  relation  existing  between  the  velocity 
of  light  and  the  value  of  the  ratio  of  electrostatic 
and  the  electro-magnetic  units,  thus  giving  a 
basis  for  an  electro-magnetic  theory  of  light. 
(See  Light,  Maxwell's  Electro-Magnetic  Theory 
of.) 

Polarized  light  reflected  from  the  surface  of  a 
magnet,  although  it  penetrates  the  substance  to 
but  a  trifling  extent,  yet  has  its  plane  of  polariza- 
tion distinctly  rotated  by  the  magnetic  whirls  in 
the  iron. 

Oral  or  Speaking-Tube  Annunciator.— 

(See  Annunciator,  Oral  or  Speaking-  Tube.) 
Ordinate. — A  distance  taken  on  a  per- 
pendicular line  called  the  axis  of  ordinates,  in 
contradistinction  to  the  axis  of  abscissas. 
(See  Ordinates,  Axis  of} 

Thus  in  Fig.  413,  D  i,  is  the  ordinate  of  the 
point  D,  in  the  curve  O  D  R. 

Ordinates,  Axis  of One  of  the  axes 

of  co-ordinates  used 
for  determining  the 
position  of  the  points 
in  a  curved  line. 

Thus  in  Fig.  413  the 
line  A  B,  is  called  the  axis 
of  ordinates  because  it  is 
the  line  on  which  the  or- 


dinate 2  D,  is  measured.    pig,4J3,    Axisof0rdi- 

Ores,     Electric 

Treatment  of —      — Processes  for  the   ex- 
traction of  metals  from  their  ores. 

These  processes  are  referable  to  three  dis- 
tinct classes,  viz. : 


Org.] 


387 


[Osm. 


(i.)  Those  in  which  the  reduction  is  effected  by 
means  of  heat  of  electric  origin. 

(2.)  Those  in  which  the  reduction  is  effected  by 
the  combined  action  of  heat  and  electrolysis. 

(3.)  Those  in  which  the  reduction  is  effected  by 
means  of  electrolysis  only. 

Organ,  Electric A  wind  organ,  in 

which  the  escape  of  air  into  the  different 
pipes  is  electrically  controlled. 

In  an  electric  organ,  the  keys,  instead  of  oper- 
ating levers,  as  usual,  to  admit  the  passage  of  air 
into  the  pipes,  merely  complete  the  circuit  of  a 
battery  through  a  series  of  controlling  electro-mag- 
nets. With  such  an  arrangement,  the  keyboard 
can  be  placed  at  any  desired  distance. 

Electric  organs  have  been  constructed,  in  which 
a  chemical  or  mechanical  record  is  made  of  the 
notes  struck  by  the  performer,  as  well  as  the 
musical  value  of  such  notes.  By  such  a  device 
the  musical  creations  of  a  composer  are  perma- 
nently recorded  in  characters  that  are  capable  of 
interpretation  by  a  compositor  skilled  in  musical 
notation. 

Orientation  of  Magnetic  Needle.— (See 
Needle,  Magnetic,  Orientation  of.) 

Origin,  Point  of  —  —The  point  where 
the  axes  of  co-ordinates  start  or  originate. 
(See  Co-ordinates,  Axes  of.} 

Orthogonal. — Rectangular,  or  right-an- 
gled. 

Oscillating  Discharge.— (See  Dis&harge, 
Oscillating?) 

Oscillating  Needle.— (See  Needle  of 'Oscil- 
lation^) 

Oscillation,  Centre  of A  point  in 

a  body  swinging  like  a  pendulum,  which  is 
neither  accelerated  nor  retarded,  during  its 
oscillations,  by  the  portions  of  the  pendulum 
that  are  situated  respectively  above  or  below  it. 

If  all  the  mass  were  concentrated  at  the  centre 
of  oscillation  the  time  of  oscillation  would  be  the 
same. 

The  centre  of  oscillation  is  always  below  the 
centre  of  gravity.  The  vertical  distance  between 
the  centre  of  oscillation  and  the  point  of  support 
of  a  pendulum,  determines  the  virtual  length  of 
the  pendulum,  and  hence  its  number  of  vibra- 
tions per  second.  (See  Pendulum,  Laws  of. ) 


Oscillations,  Electric The  series 

of  partial,  intermittent  discharges  of  which 
the  apparent  instantaneous  discharge  of  a 
Leyden  jar  through  a  small  resistance  actu- 
ally consists. 

These  partial  discharges  produce  a  series  of 
electric  oscillations  of  the  current  in  the  circuit  of 
the  discharge,  which  consist  of  true  to-and-fro 
or  backward -and-forward  motions  of  the  elec- 
tricity. This  phenomenon  was  discovered  by 
Joseph  Henry. 

Oscillations,  Open-Circuit,  Electric 

— Electric  oscillations  produced  in  open  cir- 
cuits by  the  presence  of  electric  pulses  in 
neighboring  circuits. 

Oscillatory  Discharge.— (See  Discharge, 
Oscillatory?) 

Oscillatory  Electric  Displacement.— (See 
Displacement,  Electric,  Oscillatory?) 

Oscillatory  Electromotive    Force. — An 

electromotive  force  which  is  rapidly  periodic. 

Oscillatory  Inductance. — (See  Induc- 
tance, Oscillatory,  Electric?) 

Oscillatory  Induction. — (See  Induction, 
Oscillatory?) 

Osmose. — The  unequal  mixing  of  liquids  of 
different  densities  through  the  pores  of  a 
separating  medium. 

If  a  solution  of  sugar  and  water  be  placed  in  a 
bladder,  the  neck  of  which  is  tied  to  a  straight 
glass  tube,  and  the  bladder  is  then  immersed  in  a 
vessel  of  pure  water  with  the  tube  in  a  vertical 
position,  the  two  liquids  will  begin  to  mix,  the 
sugar  and  the  water  passing  through  the  bladder 
into  the  pure  water,  and  the  pure  water  passing 
into  the  sugar  and  water  in  the  bladder.  This 
latter  current  is  the  stronger  of  the  two,  as  will  be 
shown  by  the  water  rising  in  the  vertical  glass 
tube. 

The  stronger  of  the  two  currents,  that  is,  the 
one  directed  towards  the  higher  level,  or  the  one 
which  produces  the  higher  level,  is  called  the  en- 
dosmotic  current,  and  the  weaker  current  the 
exosmotic  current. 

Osmose,  Electric A  difference  of 

liquid  level  between  two  liquids  placed  on 
opposite  sides  of  a  diaphragm  produced  by 
the  passage  of  a  strong  electric  current 


Osm.J 

through  the  liquids  between  two  electrodes 
placed  therein. 

The  higher  level  is  on  the  side  towards  -which  the 
current  flows  through  the  diaphragm,  thus  appa- 
rently indicating  an  onward  motion  of  the  liquid 
with  the  current,  or,  in  other  words,  the  liquid  is 
higher  around  the  kathode  than  around  the  anode. 
The  difference  of  level  is  most  marked  when 
poorly  conducting  liquids  are  employed. 

As  a  converse  of  this,  Quincke  has  shown  that 
electric  currents  are  setup  when  a  liquid  is  forced 
by  pressure  through  a  porous  diaphragm.  The 
term  diaphragm  currents  has  been  proposed  for 
these  currents.  Their  electromotive  force  depends 
on  the  nature  of  the  liquid,  on  the  material  of  the 
diaphragm,  and  on  the  pressure  that  forces  the 
liquid  through  the  diaphragm.  (See  Phenomena, 
Electro-Capillary.  Currents,  Diaphragm.} 

Osmotic.— Of  or  pertaining  to  osmose. 
(See  Osmose?} 

Osteotome,    Electric A  revolving 

electrically  propelled   saw,   employed  in  the 
surgical  cutting  of  bones. 

An  electric  osteotome  consists  essentially  of  a 
form  of  revolving  engine  known  as  a  dental  en- 
gine, furnished  with  a  circular  saw,  or  other  ro- 
tary cutter,  driven  or  propelled  by  electricity. 

Outgoing  Current— (See  Current,  Out- 
going) 

Outlet. — In  a  system  of  incandescent  lamp 
distribution  the  places  in  a  building  where 
the  fixtures  or  lamps  are  attached. 

The  outlets  are  left  in  a  building  by  the  wire- 
man  for  the  electric  fixtureman  to  attach  the  de- 
vice intended  to  be  used  on  the  circuits  so  pro- 
vided. 

Output,  Magnetic The  product  of 

the   magnetic  flux  by  the  magneto-motive 
force. 

Output  of  Dynamo-Electric  Machine.— 

(See  Machine,  Dynamo-Electric,  Output  of.) 

Outrigger  for  Electric  Lamp.— A  device 
for  suspending  an  electric  arc  lamp  so  as  to 
cause  it  to  stand  out  from  the  wall  of  a 
building. 

An  outrigger  and  hood  with  lamp  attached  are 
shown  in  Fig.  414. 


[Ozo. 

Outrigger  Torpedo.  —  (See  Torpedo,  Out- 
rigger.) 

Over-Compounded.— The  compounding  of 
a  dynamo-electric  machine  so  as  to  produce 


Fig.  414.     Outrigger  and  Hood. 

an  increase  of  voltage  under  increase  of  load. 
Over-compounding  is  generally  employed  for 
compensating  for  drop  or  loss  of  potential  in  the 
line  or  conductor,  and  is  adjusted  to  a  definite 
percentage  of  increase  from  light  to  full  load  in 
accordance  with  the  amount  of  drop,  or  loss,  for 
which  such  compensation  was  designed. 

Overhead  Lines. — (See  Lines,  Overhead.) 

Overhead  System,  Continuous,  of  Motive 
Power  for  Electric  Railroads  —  —  (See 
Railroads,  Electric,  Continuous  Overhead 
System  of  Motive  Power  for) 

Overload  of  Electric  Motor.— (See  Motor, 
Electric,  Overload  oj r.) 

Overtones.— Additional,  faint  tones,  ac- 
companying nearly  every  distinct  musical 
tone,  by  the  presence  of  which  the  peculiarity 
or  quality  of  such  tone  is  produced.  (See 
Sound,  Characteristics  of.) 

Overtones,  Electric Electric  vibra- 
tions produced  in  open-circuited  conductors 
by  electric  resonance,  of  higher  rates  than  the 
fundamental  vibrations.  , 

The  existence  of  electrical  overtones  necessitates 
the  existence  of  electric  nodes.  (See  Nodes,  Elec- 
trical. ) 

Overtype  Dynamo.—  (See  Dynamo,  Over- 
type) 

Ozite. — An  insulating  substance. 

Ozokerite. — An  insulating  substance. 


Uzo.J 


389 


[Par. 


Ozone. — A  peculiar  modification  of  oxygen 
which  possesses  more  powerful  oxidizing 
properties  than  ordinary  oxygen. 

Ozone  is  now  generally  believed  to  be  tri- 
atomic  oxygen,  or  oxygen  in  which  the  bonds  are 
closed,  thus: 


O- 


The  peculiar  smell  observed  when  a  torrent  of 
electric  sparks  passes  between  the  terminals  of 
a  Holtz  machine,  or  a  Ruhmkorff  coil,  is  caused 
by  the  ozone  thus  formed. 

In  a  similar  manner  ozone  is  formed  in  the  at- 


mosphere during  the  passage  through  the  air  of  a 
flash  of  lightning. 

During  the  so-called  electrolysis  of  water,  a  com- 
pound formed  by  the  union  of  two  volumes  of 
hydrogen  with  one  volume  of  oxygen,  some  of  the 
oxygen  is  given  off  in  the  form  of  ozone.  Since 
ozone  has  a  somewhat  smaller  volume  than  that 
of  the  oxygen  forming  it,  the  volume  of  the 
oxygen  liberated  is  somewhat  less  than  half  the 
volume  of  the  hydrogen. 

There  are  a  number  of  different  forms  of  ap- 
paratus designed  for  the  production  of  ozone. 
They  consist  essentially  either  of  means  for  pass- 
ing a  torrent  of  electric  sparks  through  air  or  for 
producing  a  species  of  polarization  in  the  air. 


P.  D.  or  p.  d. — A  contraction  frequently  em- 
ployed for  difference  of  potential.  (See  Poten- 
tial, Difference  of.} 

Pacinotti  Projections. — (See  Projections, 
Pacinotti.) 

Pacinotti  King.— (See  Ring,  Pacinotti^ 

Pair,  Astatic A  term  sometimes 

applied  to  an  astatic  couple.  (See  Couple, 
Astatic?) 

Palladium. — A  metal  of  the  platinum 
group. 

Metallic  palladium  has  a  tin-white  color,  and, 
when  polished,  a  high  metallic  lustre.  It  is 
tenacious  and  ductile,  and,  like  iron,  can  be 
welded  at  a  white  heat.  It  is  very  refractory  and 
possesses  in  a  marked  degree  the  power  of  ab- 
sorbing or  occluding  hydrogen  and  other  gases. 
It  is  not  affected  by  oxygen  at  any  temperature, 
nor  readily  affected  by  ordinary  corrosive  agents. 

Palladium  Alloy.— (See  Alloy,  Pal- 
ladium^) 

Pane,  Magic A  condenser  formed 

of  a  sheet  of  glass  covered  on  one  side  with 
pieces  of  tin- foil  with  small  spaces  between 
them  pasted  in  some  design  on  the  glass. 

On  the  discharge  of  a  Leyden  jar  through  these 
metallic  pieces,  the  design  is  seen  as  a  series  of 
minute  sparks,  which  bridge  the  spaces  between 
the  adjacent  pieces  of  foil. 


Pantelegraphy. — A  system  for  the  tele- 
graphic transmission  of  charts,  diagrams, 
sketches  or  written  characters. 

Pantelegraphy  is  more  frequently  called  fac- 
simile telegraphy.  (See  Telegraphy,  Fac- Simile.) 

Paper  Carbons.— (See  Carbons,  Paper.) 

Paper  Cut-Out.— (See  Cut-Out,  Paper?) 

Paper  Perforator.— (See  Perforator, 
Paper.) 

Paper  Winder,  Automatic  —  —A  de- 
vice, driven  by  clockwork,  for  automatically 
delivering  the  paper  fillet  on  which  a  tele- 
graphic message  is  received. 

Parabolic  Reflector.— (See  Reflector, 
Parabolic.) 

Parafflne.  —  A  name  given  to  various 
solid  hydrocarbons  of  the  marsh  gas  series, 
that  are  derived  from  coal  oil  or  petroleum  by 
the  action  of  nitric  acid. 

Paraffine  possesses  excellent  powers  of  insula- 
tion, and  forms  a  good  dielectric  medium.  Dried 
wood,  boiled  in  melted  paraffine,  forms  a  fair  in- 
sulating material. 

Paraffine  Wire.— (See  Wire,  Paraffine?) 

Paraffining. — Covering  or  coating  with 
paraffine. 

The  paraffine  is  applied,  while  melted  by  heat, 
either  by  means  of  a  brush,  or  by  dipping  the 
article  in  the  fused  mass. 


Par.] 


390 


[Par. 


Care  must  be  taken  in  paraffining  wooden  or 
other  absorbent  articles,  to  dry  them  before  im- 
mersing in  the  melted  paraffine,  since,  if  water  be 
present,  steam  is  formed  explosively,  and  the 
melted  paraffine  scattered  in  all  directions. 

Paragreles. — Lightning  rods,  intended  to 
protect  fields  against  the  destructive  action  of 
hail.  (See  Hail,  Assumed  Electrical  Ori- 
gin of.) 

It  was  formerly  believed  that  hail  is  caused  by 
electricity.  It  is  now  generally  believed  that  the 
electricity  in  hail  storms  is  caused  by  the  hail. 
It  will,  therefore,  readily  be  understood  that  para- 
greles  can  afford  no  real  protection. 

Parallax. — The  apparent  angular  displace- 
ment of  an  object  when  seen  from  two  dif- 
ferent points  of  view. 

In  reading  the  exact  division  on  a  scale  to  which 
a  needle  points,  care  must  be  taken  to  look  di- 
rectly down  on  the  needle,  and  not  sideways,  so 
as  to  avoid  the  error  of  displacement  due  to 
parallax. 

Parallel  Circuit— (See  Circuit,  Parallel.) 
Parallel  Series.— (See  Series,  Parallel) 

Parallelogram  of  Forces. — (See  Forces, 
Parallelogram  of.) 

Parallels,  Magnetic Lines  connect- 
ing places  on  the  earth's  surface  at  right 
angles  to  the  isogonal  lines,  or  lines  of  equal 
declination  or  variation. 

The  magnetic  parallels  are  at  right  angles  to 
the  magnetic  meridians.  The  magnetic  parallels 
lie  in  planes  parallel  to  the  magnetic  equator. 
(See  Needle,  Magnetic,  Declination  of.  Meridian, 
Magnetic. ) 

Paramagnetic.— Possessing  properties  or- 
dinarily recognized  as  magnetic. 

Possessing  the  power  of  concentrating  the 
lines  of  magnetic  force. 

Paramagnetic  is  a  term  employed  in  contra- 
distinction to  diamagnetic.  (See  Diamagnetic.) 
A  paramagnetic  substance,  cut  in  the  form  of  a 
bar  whose  length  is  much  greater  than  its  breadth 
and  thickness,  will,  when  suspended  in  a  magnetic 
field  in  the  manner  shown  in  Fig.  415,  take  up  a 
position  of  rest  with  its  greatest  length  in  the  direc- 
tion of  the  lines  of  force,  i.  e.,  will  point  axially. 


In  other  words,  the  lines  of  force  will  so  pass 
through  the  paramagnetic  substance  as  to  reduc? 
the  magnetic  resistance  of  the  circuit  as  much  as 
possible. 

Paramagnetic  substances,  therefore,  concen- 
trate the  lines  of  force  on  them.  (See  Resistance, 
Magnetic.) 

Diamagnetic  substances,  on  the  contrary,  when 
placed  as  shown  in  Fig.  415,  assume  a  position  of 
rest  with  their  least  dimensions  in  the  direction  of 
the  lines  of  force,  i.  e. 
they  point  equatorially. 
This  is  the  position  in 
which  they  are  placed 
by  the  lines  of  force,  in 
order  to  insure  the  least 
magnetic  resistance  in 
the  circuit  of  these  lines. 
The  magnetic  resistance 
of  diamagnetic  sub- 
stances is  great  as  com- 
pared with  that  of  par- 
amagnetic substances. 

The  term  f err o -mag- 
netic has  been  proposed 
for  paramagnetic.  If 
another  term  be  required,  which  is  doubtful, 
sidero -magnetic,  proposed  by  S.  P.  Thompson, 
would  appear  to  be  preferable.  (See  Magnetic, 
Ferro.  Magnetic,  Sidero.') 

Tyndall  believes  that  the  magnetic  polarity 
possessed  by  diamagnetic  substances  is  the  result 
of  a  distinct  polar  force,  different  in  its  nature 
from  ordinary  magnetism.  His  views,  in  this  re- 
spect, are  not  generally  accepted.  (See  Polarity, 
Diamagnetic. ) 

Paramagnetically. — In  a  paramagnetic 
manner.  (See  Paramagnetism.) 

Paramagnetism. — The  magnetism  of  a 
paramagnetic  substance. 

Parasitical  Currents. — (See  Currents, 
Parasitical.) 

Paratonnfire. — A  French  term  for  light- 
ning rod,  sometimes  employed  in  English 
technical  works. 

Lightning  rod  would  appear  to  be  the  prefer- 
able term. 

Partial  Contact— (See  Contact,  Partial) 

Partial  Disconnection.— (See  Disconnec- 
tion, Partial) 


Par.] 


391 


[Fen. 


Partial  Earth.— (See  Earth,  Partial) 

Partial  Reaction  of  Degeneration. — (See 
Degeneration,  Partial  Reaction  of) 

Passive  State.— (See  State,  Passive) 

Path,  Alternative The  path  or 

circuit  taken  by  an  impulsive  discharge,  in 
preference  to  another  path  or  circuit,  open  to 
the  discharge,  although  of  enormously  smaller 
ohmic  resistance. 

The  alternative  path  is  the  path  taken  by  the 
discharge  produced  by  what  was  formerly  called 
lateral  induction. 

The  explanation  of  the  reason  the  discharge 
takes  the  alternative  path  is  that  the  counter- elec- 
tromotive force  of  self-induction  of  the  circuit, 
produced  by  the  impulsive  discharge,  is  so  great 
as  to  make  the  path  of  the  circuit  itself,  although 
formed  of  conducting  materials,  practically  non- 
conducting. 

If  a  Leyden  jar  is  provided  with  discharge  wires 
or  conductors,  as  shown  is  Fig.  416,  a  discharge 


would  pass  across  an  air  space  in  preference  to 
a  metallic  circuit,  was  greater  for  a  thick  copper 


Fig.  416.    Phenomena  of  Alternative  Puth. 

taking  place  at  A,  is  accompanied  simultaneously 
by  an  even  longer  spark  at  B,  between  the  ends 
of  two  long  open-circuit  leads. 

To  explain  in  a  general  manner  the  phenomena 
of  the  alternative  path,  we  may  say  that  the  dis- 
charge at  A,  gives  rise  to  electric  oscillations  in  the 
leads  connected  with  B,  and  that  there  are  sent  out 
into  the  surrounding  medium  radiations  of  pre- 
cisely the  same  nature  as  those  which  produce 
light,  only  of  a  wave  length  so  long  as  to  be  un- 
able to  produce  on  the  eye  the  effects  of  light. 

If  the  space  between  the  balls  at  B,  is  too  great 
for  the  discharge  to  take  place,  the  wires  glow 
and  throw  out  minute  sparks  or  brushes  of  light. 

The  action  of  the  ordinary  lightning  arrester 
depends  on  the  principle  of  the  alternative  path. 
The  resistance  of  the  metallic  circuit,  composed 
of  the  line  and  the  instruments,  is  so  great  in  the 
case  of  the  impulsive  discharge  of  a  lightning 
flash,  that  the  discharge  takes  place  between  a 
series  of  points  connected  with  the  line  plate  and 
another  series  of  points  connected  with  the  ground 
plate.  (See  Arrester,  Lightning. ) 

Dr.  Lodge,  who  has  studied  the  principle  of 
alternative  path  in  the  case  of  lightning  rods, 
finds  that  the  distance  at  which  the  discharge 


Fig.  417.    Edison  Electric  Pen, 

rod,  40  feet  long,  than  for  an  iron  rod  of  No.  27 
B.  W.  G.  of  33.03  ohmic  resistance. 

Patrol  Alarm  Box. 

—(See  Box,  Patrol 
Alarm) 

Peltier   Effect  — 

(See  Effect,  Peltier) 

Pen    Carriage.— 

(See  Carriage,  Pen) 

Pen,  Electric  - 

—  A  device  for  mani- 
fold copying,  in  which 
a  sheet  of  paper  is 
made  into  a  stencil  by 
minute  perforations 
obtained  by  a  needle 
driven  by  a  small 
electric  motor  and  the 
stencil  afterwards  em- 
ployed in  connection 
with  an  inked  roller 
for  the  production  of 
any  required  number 
of  copies. 

Mechanical  pens  are 
constructed  on  the  same 
principle,  the  perfora- 
tions being  obtained  by 
mecnamcal  instead  of 
by  electric  power. 

In  the  Edison  electric 
pen,  Fig.  417,  the 
forations  are  made  by  an  electric  motor  driven 
by  a  voltaic  battery.  The  manifold  press  with 
its  inked  pad  is  shown  to  the  left  of.the  figure. 

Pendant  Cord.—  (See  Cord,  Pendant) 
Pendant,  Electric  --  A  hanging  fix- 


Electric  Pendant. 


Pen.] 


392 


[Per. 


ture  provided  with  a  socket  for  the  support  of 
an  incandescent  lamp. 

A  form  of  electric  pendant  is  shown  in  Fig. 
418. 

Pendant,  Flexible  Electric  Light  — 
— A  pendant  for  an  incandescent  lamp  formed 
by  the  flexible  conductors  which  support  the 
lamp. 

The  advantages  procured  by  a  flexible  pendant 
are  evident  in  that  both  the  length  of  the  flexible 
conductor  from  which  the  lamp  is  hanging  and 
position  of  the  lamp  can  be  changed  considerably. 

Pendnlnm  Annunciator. — (See  Annun- 
ciator, Pendulum  or  Swinging?) 

Pendulum,  Electric A  pendulum 

so  arranged  that  its  to-and-fro  mojtions  send 
electric  impulses  over  a  line,  either  by  making 
or  breaking  contacts. 

An  electrical  tuning  fork  whose  to-and-fro 
movements  are  maintained  by  electric  im- 
pulses. 

Electric  pendulums  are  employed  in  systems 
for  the  electrical  distribution  of  time. 

Sometimes  instead  of  using  true  pendulums  for 
such  purposes,  coils,  mounted  on  tuning  forks,  or 
on  the  ends  of  flexible  bars  of  steel,  called  reeds, 
are  used  for  the  purpose  of  establishing  cur- 
rents, or  modifying  the  currents  that  are  already 
passing  in  a  circuit.  The  movement  of  a  mag- 
netic diaphragm,  as  in  the  case  of  a  telephone 
diaphragm,  towards  and  from  a  coil  of  wire,  is 
.another  illustration  of  an  electric  pendulum. 

Electric  tuning-fork  pendulums  are  employed 
in  Delany's  system  of  synchronous-multiplex  teleg- 
raphy, and  in  Gray's  harmonic-multiple  teleg- 
raphy. (See  Telegraphy,  Synchronous-Multi- 
plex, Delany"1*  System.  Telegraphy,  Gray's  Har- 
monic. Multiple.) 

Pendulum,  Laws  of  -  —The  laws 
which  express  the  peculiarities  of  the  motion 
of  a  simple  pendulum. 

A  simple  penduhim  is  one  in  which  the  entire 
•weight  is  considered  as  concentrated  at  a  single 
point,  suspended  at  the  end  of  a  weightless,  in- 
flexible and  inextensible  line. 

The  following  are  the  laws  of  the  simple  pen- 
dulum : 

(I.)  Oscillations  of  small  amplitude  are  approx- 
imately isochronous;  that  is,  are  made  in  times 
that  are  sensibly  equal.  (See  Vibration  or  Wave, 
Amplitude  of .  Isochronism.) 


(2.)  In  pendulums  of  different  lengths,  the 
duration  of  the  oscillations  is  proportional  to  the 
square  root  of  the  length  of  the  pendulum. 

(3.)  In  the  same  pendulum,  the  length  being 
preserved  invariable,  the  duration  of  the  oscilla- 
tion is  inversely  proportional  to  the  square  root 
of  the  intensity  of  gravity. 

The  intensity  of  gravity,  at  any  latitude,  may 
be  determined  by  the  number  of  oscillations  of  a 
pendulum  of  a  given  length.  In  the  same  man- 
ner the  intensity  of  a  magnetic  field,  or  the  in- 
tensity  of  magnetization  of  a  magnet,  may  be  de- 
termined by  the  needle  of  oscillation,  by  observing 
the  number  of  oscillations  a  needle  makes  in  a 
given  time  when  disturbed  from  its  position  of 
rest.  (See  Needle  of  Oscillation.) 

Since  a  simple  physical  pendulum  is  a  physical 
impossibility,  the  -virtual  length  of  a  pendulum, 
that  is,  the  vertical  distance  between  its  point  of 
support  and  the  centre  of  oscillation,  is  taken  as 
the  true  length  of  the  pendulum. 

If  the  irregularly  shaped  body,  shown  in  Fig. 
419,  whose  centre  of  gravity  is  at  G,  is  made  to 
swing  like  a  pendulum,  either  on 
S,  or  O,  its  oscillations  will  be 
performed  in  equal  times,  and 
the  body  will  act  as  a  simple 
pendulum,  whose  virtual  length 
is  S  O. 

If,  while  suspended  at  S,  it  be 
struck  at  O,  it  will  oscillate 
around  S,  without  producing  Fig.  4It)_  Centre 
any  pressure  on  the  supporting  of  Oscillation. 
axis  at  S,  on  which  it  turns.  If  floating  entirely 
submerged  in  a  liquid,  a  blow  at  O,  would  cause 
it  to  move  in  a  straight  line  in  the  direction  of 
the  blow,  without  rotation. 

The  point  O,  is  called  the  centre  of  percussion, 
or  the  centre  of  oscillation.  The  centre  of  oscil- 
lation is  always  below  the  centre  of  gravity. 

Pentane  Standard. — (See  Standard,  Pen- 
tane?) 

Percussion,  Centre  of That  point  in 

a  body  suspended  so  as  to  move  as  a  pendu- 
lum at  which  a  blow  would  produce  rotation, 
but  no  forward  motion,  or  motion  of  transla- 
tion. 

Perforator,  Paper  —  — An  apparatus 
employed  in  systems  of  automatic  telegraphy 
for  punching  in  a  fillet  of  paper  the  circular  or 
elongated  spaces  that  produce  the  dots  and 


Per.] 


393 


[Per. 


dashes  of  the  Morse  alphabet,  when  the  fillet  is 
drawn  between  metal  terminals  that  form  the 
electrodes  of  a  battery.  (See  Telegraphy, 
Automatic.) 

Perforator,  Pneumatic  -  —A  paper 
perforator  operated  by  means  of  compressed 
air.  (See  Perforator,  Paper.) 

Period  of  Open-Circuit  Oscillation.— (See 
Open-Circuit  Oscillation,  Period  of) 

Period  of  Simple-Harmonic  Motion.— 
(See  Motion,  Simple-Harmonic,  Period  of) 

Period  of  Vibration.— (See  Vibration, 
Period  of) 

Period,  Vibration  —  —The  period  of  a 
single  or  a  whole  vibration  in  a  conductor,  in 
which  an  oscillatory  vibration  is  being  pro- 
duced by  electrical  resonance  when  respond- 
ing to  its  fundamental  vibration. 

Hertz  gives  the  following  value  for  the  vibration 
period:  Calling  T,  the  single  or  half  vibration 
period ;  L,  the  co-efficient  of  self-induction  in  abso- 
lute magnetic  measure,  and  therefore  expressed  in 
centimetres;  C,  the  capacity  of  the  terminals,  in 
electrostatic  measure,  and  therefore  also  expressed 
in  centimetres;  v,  the  velocity  of  light  in  centi- 
metre-seconds, then,  when  the  resistance  of  the  con- 
ductor is  small,  T  =  it  ^L  C. 
v 

Periodic  and  Alternate  Discharge.— (See 

Discharge,  Periodic.  Discharge,  Alternat- 
ing^ 

Periodic  Current,  Power  of —  —The 
rate  of  transformation  of  the  energy  of  a  cir- 
cuit traversed  by  a  simple  periodic  current. 


Fig.  420.  Power  of  Periodic  Current.— (Fleming.) 
If  the  thin  line  in  the  curve,  Fig.  420,  repre- 
sents the  impressed  electromotive  force  in  an  in- 
ductive circuit,  and  the  thick  line  the  correspond- 
ing current,  then,  at  any  instant,  say  at  the  point 
M,  the  rate  at  which  energy  is  being  expended  on 
the  circuit,  is  equal  to  the  ordinate  P  M,  multi- 
plied by  the  ordinate  Q  M.  The  mean  power  is 


the  mean  of  all  such  products  taken  at  points  of 
time  very  near  together. 

The  power  of  a  periodic  current,  or  the  work 
expended  per  second  on  such  a  circuit,  is  equal 
to  half  the  product  of  the  maximum  values  of  the 
current,  at  any  instant,  and  the  maximum  value 
of  the  impressed  electromotive  force,  multiplied 
by  the  cosine  of  the  angle  of  lag. 

Periodic      Governor. — (See       Governor, 
Periodic) 
Periodically    Decreasing    Discharge. — 

(See  Discharge,  Periodically  Decreasing) 

Periodicity. — The  rate  of  change  hi  the 
alternations  or  pulsations  of  an  electric  cur- 
rent. 

Periodicity  of  Auroras  and  Magnetic 
Storms.  —  (See  Auroras  and  Magnetic 
Storms,  Periodicity  of) 

Permanency,  Electric The  prop- 
erty possessed  by  most  metallic  substances, 
while  in  the  solid  state,  of  retaining  a  constant 
electric  conducting  power  at  the  same  tem- 
perature. 

The  electric  permanency  of  hard  drawn  wire  is 
small,  since  such  wire  becomes  gradually  an- 
nealed, and  thus  changed  in  its  electric  resist- 
ance. 

Matthiessen  showed  that  some  specimens  of 
annealed  German  silver  wire  increased  in  their 
conducting  power  at  the  rate  of  about  .02  per 
cent,  yearly. 

Permanent  Intensity  of  Magnetization. 

— (See  Magnetization,  Permanent,  Intensity 
of) 

Permanent  Magnet  Voltmeter. —  (See 
Voltmeter,  Permanent  Magnet.) 

Permanent  State  of  Charge  on  Telegraph 
Line. — (See  State,  Permanent,  of  Charge  on 
Telegraph  Line) 

Permeability  Curre.— (See  Curve,  Per- 
meability) 

Permeability,  Magnetic  —  —  Conducti- 
bility  for  lines  of  magnetic  forces. 

The  ratio  existing  between  the  magnetiza- 
tion produced,  and  the  magnetizing  force  pro- 
ducing such  magnetization. 

If  n  equals  the  permeability,  B,  the  magnetiza- 


Per.] 


394 


[Phe. 


tion  produced,  or  the  intensity  of  magnetic  induc- 
tion, and  H,  the  magnetizing  force;  then, 

HI 

The  permeability  of  non-magnetic  materials, 
such  as  insulators,  or  non-magnetic  metals,  such  as 
copper,  etc.,  is  assumed  to  be  practically  equal  to 
that  of  air,  or  to  unity. 

The  magnetic  permeability  decreases  as  the 
magnetization  increases.  When  a  piece  of  iron 
has  been  magnetized  up  to  a  certain  intensity,  its 
permeability  becomes  less  for  any  further  magnet- 
ization; or,  the  substance  shows  a  tendency  to 
reach  magnetic  saturation.  In  good  iron,  this 
limit  is  reached  at  about  125,000  lines  of  force  to 
the  square  inch  of  rea  of  cross  section. 

The  magnetic  permeability  varies  greatly,  not 
only  with  different  specimens  of  iron,  but  also  with 
the  previous  history  of  the  iron,  as  to  whether  or 
jiot  it  has  before  been  subjected  to  magnetization  or 
demagnetization,  and  also  as  to  whether  the  value 
of  the  permeability  is  taken  while  the  magnetiza- 
•tion  is  increasing  or  decreasing. 

Permeameter. — An  apparatus  devised  by 
S.  P.  Thompson,  for  roughly  measuring  the 
magnetic  permeability. 

Thompson's  permeameter  consists  essentially  of 
a  rectangular  piece  of  soft  iron,  provided  with  a 
elot,  for  the  reception  of  the  magnetizing  coil.  A 
hole  bored  in  one  end  of  the  block  serves  to  receive 
Ihe  bar  or  rod  of  iron  whose  permeability  is  to  be 
determined.  On  the  magnetization  of  the  bar  to 
be  tested,  the  square  root  of  the  force  required  to 
jdetach  the  rod  from  the  lower  surface  of  the  iron 
block,  is  a  measure  of  the  permeation  of  the  lines 
of  magnetic  forces  through  its  end  faces. 

Permeance,  Magnetic Magnetic 

permeability.    (See  Permeability,  Magnetic?) 

Permeating,  as    of   Lines   of  Force.— 

The  passing  of  lines  of  force  through  a  mag- 
netic substance.  (See  Permeability,  Mag- 
jvertc.) 

Permeation,  Magnetic The  pass- 

»cc  of  lines  of  magnetic  force  through  any 
permeable  substance. 

Permissive  Block  System  for  Railroads. 

— (See  Railroads,  Permissive  Block  System 
.for.) 


Pfliiger's  Law. — (See  Law,  PJlugers?) 
Phantom  Wires.— (See  Wires,  Phantom^ 

Phase,  Angle  of  Difference  of,  between 
Alternating  Currents  of  Same  Period 

The  angle  which  measures  the  shift- 
ing of  phase  of  a  simple  periodic  current  with 
respect  to  another  due  to  lag  or  other  cause. 

Phase,  Shifting  of,  of  Alternating  Cur- 
rent • A  change  in  phase  of  current 

due  to  magnetic  lag  or  other  causes. 

Phase  of  Tibration.— (See  Vibration, 
Phase  of.) 

Phelps'  Stock  Printer.— (See  Printer, 
Stock,  Phelps'.) 

Phenomena,  Electro-Capillary  — 

Phenomena  observed  in  capillary  tubes  at 
the  contact  surfaces  of  two  liquids. 

Where  acidulated  water  is  in  contact  with 
mercury,  each  liquid  possesses  a  definite  sur- 
face tension,  and  each  a  definite  shape  of  sur- 
face. The  two  liquids,  however,  do  not  actually 
touch,  there  being  a  small  interval  or  space  be- 
tween them.  This  space  acts  as  a  minute  accu- 
mulator. But  the  liquid  and  water,  being  different 
substances  in  contact,  possess  different  potentials. 
Any  cause  which  alters  the  shape  of  these  con- 
tact surfaces,  and  consequently  the  extent  of  the 
spaces  between  them,  necessarily  alters  the  capa- 
city of  the  condenser,  and  consequently  the  dif- 
ference of  potential.  Therefore  the  mere  shaking 
of  the  tube,  or  heating  it,  will  produce  electric 
currents  from  the  resulting  differences  of  po- 
tential. Conversely,  an  electric  current  sent 
across  the  contact-surfaces  will  produce  motion  as 
a  result  of  a  change  in  the  value  of  the  surface 
tension.  An  electro-capillary  telephone  has  been 
constructed  on  the  former  principle,  and  an 
electrometer  on  the  latter.  (See  Electrometer, 
Capillary.) 

Phenomena,  Porret An  increase 

in  the  diameter  of  a  nerve  fibre  in  the  neigh- 
borhood of  the.  positive  pole  when  traversed 
by  a  voltaic  current. 

When  a  voltaic  current  passes  through  fresh 
living  substance  the  contents  of  the  muscular  fibre 
exhibit  a  streaming  movement  in  the  direction  the 
current  is  flowing,  viz.,  from  the  positive  to  the 


Phe.] 


395 


[Pho. 


negative.  This  causes  the  fibre  to  swell  up  or 
increase  in  diameter  at  the  negative  electrode. 

Pherope. — A  name  sometimes  applied  to 
a  telephote.  (See  Telephote} 

Phial,  Leyden A  name  sometimes 

applied  to  a  Leyden  jar.  (See/ar,  Leyden} 

Philosopher's  Egg.— (See  Egg,  Philoso- 
phers) 

Phonautograph.— An  apparatus  for  the 
automatic  production  of  a  visible  tracing  of 
the  vibrations  produced  by  any  sound. 

Phonautographic  apparatus  consists  essentially 
of  devices  by  which  the  sound  waves  are  caused 
to  impart  their  to-and- fro  movements  to  a  dia- 
phragm, at  the  centre  of  which  a  pencil  or  tracing 
point  is  attached.  The  record  is  received  on  a 
sheet  of  paper,  or  wax,  or  on  a,  smoked  glass  or 
other  suitable  surface. 

Leon  Scott's  Phonautograph,  which  is  among 
the  forms  best  known,  consists  of  a  hollow  coni .  al 


Fig.  421.    Scott's  Phonautograph. 

vessel  A,  Fig.  421,  with  a  diaphragm  of  parch- 
ment stretched  tightly  like  a  drumhead  over  its 
smaller  aperture  B.  A  tracing  point  attached  to 
the  centre  of  the  diaphragm,  traces  a  sinuous 
line  on  the  surface  of  a  soot-covered  cylinder  C, 
that  is  uniformly  rotated  under  the  tracing  point. 
As  the  cylinder  is  advanced  a  short  distance  with 
every  rotation,  a  sinuous  spiral  line  is  traced  on 
the  surface. 

Phone. — A  term  frequently  used  for  tele- 
phone. 

Phonic  Wheel.— (See  Wheel,  Phonic.} 

Phonogram.— A  record  produced  by  the 
phonograph.  (See  Phonograph} 

Phonograph.— An  apparatus  for  the  re- 
production of  articulate  speech,  or  of  sounds 


of  any  character,  at  any  indefinite  time  after 
their  occurrence,  and  for  any  number  of  times. 
In  Edison's  phonograph  the  voice  of  the 
speaker,  received  by  an  elastic  diaphragm  of  thin 
sheet  iron  or  other  similat  material,  is  caused  to 
indent  a  sheet  of  tin-foil  placed  on  the  surface  of 
a  cylinder  C,  Fig.  422,  that  is  maintained  at  a 
uniform  rate  of  rotation  by  the  crank  at  W.  In 


Fig.  422- 

the  form  shown  in  Fig.  422,  the  motion  is  by  hand. 
In  a  later  improved  form  the  cylinder  is  driven  by 
means  of  an  electric  motor  or  by  clockwork. 

In  order  to  reproduce  the  speech  or  other 
sounds  the  phonogram  record  is  placed  on  the 
surface  of  a  cylinder  similar  to  that  on  which  it 
was  received  (or  is  kept  on  the  same  surface), 
and  the  tracing  point,  placed  at  the  beginning  of 
the  record  and  being  maintained  against  it  by 
gentle  pressure,  is  caused,  by  the  rotation  of 
cylinder,  to  follow  the  indentations  of  the  phono- 
gram record.  As  the  point  is  thus  moved  up  and 
down  the  hills  and  hollows  of  the  record  surface, 


Fig.  423.    EdL 


iproved  Phonograph. 


the  diaphragm,  to  which  it  is  attached,  is  given  to- 
and-fro  motions  that  exactly  correspond  to  the 
to-and -fro  motions  it  frad  when  impressed  origin- 
ally by  the  sounds  it  recorded  on  the  phono- 
gram record.  A  person  listening  at  this  dia- 


Pho.] 


[Pho. 


phragm  will  therefore  hear  an  exact  reproduction 
of  the  sounds  originally  uttered. 

In  this  manner  the  voices  of  relatives,  dis- 
tinguished singers  or  statesmen  can  be  preserved 
for  future  generations. 

In  Edison's  improved  phonograph  the  record 
surface  consists  of  a  cylinder  of  hardened  wax.  The 
rotary  motion  of  the  cylinder  is  obtained  by  means 
of  an  electric  motor.  Two  diaphragms  are  used, 
one  for  recording,  and  one  for  reproducing  the 
sound  waves.  As  shown  in  Fig.  423,  the  record- 
ing diaphragm  is  in  position  against  the  cylinder. 
The  recording  diaphragm  is  made  of  malleable 
glass.  The  reproducing  diaphragm  is  formed  of 
bolting  silk  covered  with  a  thin  layer  of  shellac. 

In  the  Graphophone  of  Bell  and  Tainter  the 
point  attached  to  the  diaphragm  is  caused  to  cut 


Fif.424.    Bell  and  Tainter 's  Graphophone. 
or  engrave  a  cylinder  of  hardened  wax.    Two 
separate  diaphragms  are  employed,  one  for  speak- 
ing, and  the  other  for  hearing. 

The  recording  surface  is  made  of  a  mixture  of 
beeswax  and  paraffine.  A  uniformity  of  rotation  of 
the  cylinder  is  obtained  by  means  of  a  motor  pro- 
vided with  a  suitable  governor.  An  ordinary  con- 
versation of  some  five  minutes,  it  is  claimed,  can 
be  recorded  on  the  surface  of  a  cylinder  6  inches 
long  and  I  \  inch  in  diameter. 

In  the  Gramophone  of  Berliner,  a  circular  plate 
of  metal,  covered  with  a  film  of  finely  divided  oil 


or  grease,  receives  the  record  in  a  sinuous,  spiral 
line.  This  record  is  subsequently  etched  into  tie 
metal  by  any  suitable  means,  or  is  photographic- 
ally reproduced  on  another  sheet  of  metal. 

Glass  covered  with  a  deposit  of  soot  is  some- 
times employed  for  the  latter  process.  The  ap- 
paratus is  shown  in  Fig.  425,  as  arranged  for  the 
reproduction  of  speech. 

In  Mr.  Berliner's  apparatus,  the  record  surface 
is  impressed  by  a  point  attached  to  the  trans- 
mitting diaphragm,  in  a  direction  parallel  to  tke 
record  surface,  and  not,  as  in  the  instrument  of 
Mr.  Edison,  in  a  direction  at  right  angles  to  the 
same.  This  method  would  appear  to  be  the  best 
calculated  for  a  more  exact  reproduction  of  ar- 
ticulate speech,  since  it  permits  comparatively 
loud  speaking  or  singing,  without  interfering 


Fig.  423.    Berliner's  Gramophone. 

with  the  quality  of  the  reproduced  sounds.  Since 
the  resistance  to  indentation,  or  vertical  cutting, 
increases  more  rapidly  than  the  increase  in  the 
amplitude  of  vibration  of  the  cutting  point,  it 
follows  that  the  louder  the  sounds  recorded  by  the 
phonograph  or  graphophone,  the  less  complete 
would  be  the  quality  of  the  reproduced  sounds, 
or  the  less  the  probability  of  the  peculiarities  of 
the  speaker's  voice  being  recognized.  In  order 
to  avoid  this,  the  speaker  in  the  phonograph  and 
the  graphophone  speaks  in  an  ordinary  conversa- 
tional tone  only.  (See  Vibration  or  Wave,  Am- 
plitude of ) 

For  purposes  of  dictation,  and,  indeed,  most 
commercial  purposes,  this  is  rather  an  advantage 
than  otherwise. 

Phonograph  Record.  —  (See  Record 
Phonograph.) 

Phonoplex. — Literally  sound  folds. 

A  system  of  telegraphy.  (See  Telegraphy, 
Phonoplex.) 


Pho.] 

Phonoplex  Telegraphy.  —  (See  Telegra- 
phy, Phonoplex^ 

Phonopore. — A  modified  form  of  har- 
monic telegraph. 

Fhonozenograph. — An  instrument  devised 
by  De  Feltre  to  indicate  the  direction  of  a 
distant  sound. 

A  Deprez-D'Arsonval  galvanometer,  a  Wheat- 
stone's  bridge,  and  a  microphone  of  peculiar  con- 
struction, are  placed  in  the  circuit  of  a  voltaic 
battery  and  a  receiving  telephone.  The  observer 
determines  the  direction  of  the  distant  sound  by 
means  of  the  sounds  heard  under  different  condi- 
tions in  the  telephone. 

Phosphoresce. — To  emit  phosphorescent 
light. 

Phosphorescence. — The  power  of  emitting 
light,  or  becoming  luminous  by  simple  ex- 
posure to  light. 

Bodies  that  possess  the  property  of  phosphor- 
escence, when  exposed  to  a  bright  light  acquire 
the  power,  when  subsequently  carried  into  the 
dark,  of  continuing  to  emit  light,  for  periods 
varying  from  a  few  seconds  to  several  hours. 
The  diamond,  barium  and  calcium  sulphides, 
dry  paper,  silk,  sugar,  and  compounds  of  ura- 
nium, are  examples  of  phosphorescent,substances. 

The  effects  of  phosphorescence  appear  to  be 
due,  in  some  cases,  to  sympathetic  vibrations  set 
up  in  the  molecules  of  the  phosphorescent  body 
by  the  exciting  light  (See  Vibrations,  Sympa- 
thetic.} 

In  other  cases,  however,  that  are  not  exactly 
understood,  the  wave  length  of  the  emitted  light 
is  more  rap  LI  than  that  of  the  exciting  light. 

The  fire-fly,  the  glow-worm,  and  decaying 
animal  or  vegetable  matter,  exhibit  a  species  of 
phosphorescence  that  appears  to  be  due  to  the  ac- 
tual oxidation  or  gradual  burning  of  a  peculiar, 
specific,  chemical  substance. 

Phosphorescence  may  therefore  be  divided  into 
two  classes,  viz. : 

(I.)  Physical  phosphorescence,  or  that  produced 
by  the  actual  impact  of  light,  and, 

(2.)  Chemical  pJwsphorescence,  or  that  caused 
by  actual  chemical  combination  or  combustion  of 
a  specific  substance.  This  is  sometimes  called 
spontaneous  phosphorescence. 

Physical  phosphorescence  may  be  produced  in 
a  variety  of  ways,  viz.: 


897 


[Pho. 


(I.)  By  an  Elevation  of  Temperature: 
A  variety  of  fluorspar,  called  chlorophane, 
shines  with  a  beautiful  greenish  blue  light  when 
heated  to  less  than  a  red  heat.  Here  the  non- 
luminous  rays  are  apparently  transformed  into 
luminous  rays. 

A  phosphorescent  substance  like  fluorspar 
eventually  loses  its  ability  to  phosphoresce.  It 
regains  it,  however,  on  exposure  to  the  light,  i.  t., 
if  such  an  exhausted  body  be  exposed  to  sunlight  it 
again  phosphoresces  on  exposure  to  non-luminous 
heat.  The  light  emitted,  during  phosphorescence 
by  heat,  is,  probably,  wholly  due  to  potential 
energy  acquired  during  exposure  to  the  light. 
(See  Luminescence.)  The  phosphorescence  by 
heat  exhibited  by  fluorspar  is  sometimes  called 
fluorescence.  It  is  preferable,  however,  to  call 
the  phenomena  phosphorescence.  (See  Fluores- 
fence.) 

(2.)  By  Mechanical  Effects: 

The  flashes  of  light  emitted  during  the  attri- 
tion or  friction  of  some  bodies,  when  not  traceable 
directly  to  electricity,  are,  most  probably,  to  be 
ascribed  to  phosphorescence. 

(3.)  By  Molecular  Bombardment. 

The  molecular  bombardment  due  to  the  mole- 
cules of  residual  gas  shot  off  from  the  negative 
electrode  of  an  exhausted  receiver  through  which 
an  electric  discharge  is  passing,  produces  many 
brilliant  effects  of  phosphorescence. 

(4.)  By  Electricity. 

An  electric  spark  produces  phosphorescence  in 
such  substances  as  canary  glass,  solution  of  sul- 
phate of  quinine,  etc.,  etc. 

(5.)  Exposure  to  Sunlight,  or,  in  fact,  to  any 
light. 

The  different  rays  of  the  sun  are  not  equally 
able  to  excite  phosphorescence.  As  a  rule  the 
violet  or  ultra  violet  rays  excite  the  greatest  phos- 
phorescence. The  light  excited  is  often,  though 
not  always,  of  a  greater  wave  length  than  the 
exciting  light. 

Phosphorescent  paints  for  rendering  the  posi- 
tion of  a  push  button,  electric  call,  match  safe, 
gas  pendant  or  some  other  similar  object  visible 
at  night,  consist  essentially  of  sulphides  of  cal- 
cium or  barium,  or  of  mixtures  of  the  same. 

Phosphorescence,  Chemical A 

variety  of  phosphorescence,  in  which  the  emit- 
ted light  is  produced  by  the  actual  combustion 


398 


[Pho. 


of  a  specific  chemical  substance  by  the  oxygen 
of  the  air. 

Chemical  phosphorescence  is  seen  in  the  fire- 
fly and  the  glow-worm.  (See  Phosphorescence.} 

Phosphorescence,  Electric Phos- 
phorescence caused  in  a  substance  by  the 
passage  of  an  electric  discharge. 

The  phosphorescent  material  is  placed  in  an 
exhausted  glass  tube,  as  shown  in  Fig.  426,  and 
submitted  to  the  action  of  a  series  of  discharges, 
as  from  a  Ruhmkorff  coil,  or  Holtz  machine. 
The  violet-blue  light  of  such  discharge  is  very 
efficient  in  producing  phosphorescence.  Phosphor- 
escence is  thus  effected  by  subjecting  the  phos- 
phorescent material  to  the  molecular  bombard- 
ment which  is  produced  by  such  discharges  in  a 
high  vacuum.  (See  Bombardment,  Molecular.) 


Fig.  426.    Electric  Phosphorescence. 

Phosphorescence,  Physical  —  — Phos- 
phorescence produced  in  matter  by  the  actual 
impact  of  light  waves  resulting  in  a  vibratory 
motion  of  the  molecules  of  sufficient  rapidity 
to  cause  them  to  emit  light. 

Physical  phosphorescence  is  distinguished  from 
chemical  phosphorescence  in  that  in  the  former 
the  energy  required  to  produce  molecular  vibra- 
tions is  imparted  by  the  light  to  which  the  phos- 
phorescent body  is  exposed,  while  in  chemical 
phosphorescence  the  energy  producing  the  light 
is  derived  from  the  chemical  potential  energy 
of  the  specific  substance  burned.  (See  Phosphor- 
escence. ) 

Phosphorescent — Possessing  the  proper- 
ties or  qualities  of  phosphorescence. 

Phosphorescing. — Emitting  phosphores- 
cent light.  (See  Phosphorescence?) 

Phosphorescope. — An  apparatus  for  meas- 
uring the  phosphorescent  power  of  any  sub- 
stance. (See  Phosphorescence?) 


Phosphorus.  Electric    Smelting  of 

—  An  electric  process  for  the  direct  production 
of  phosphorus. 

In  the  electric  smelting  of  phosphorus,  the 
crude  material,  consisting  of  a  mixture  of  bones  or 
animal  phosphates  and  carbon,  is  fed  into  a  space 
between  two  electrodes  connected  to  the  poles  of 
a  source  of  powerful  alternating  currents.  The 
apparatus  is  similar  in  general  to  the  Cowles  fur- 
nace for  the  reduction  of  aluminium.  The  heat 
produced  by  the  alternating  currents  decomposes 
the  phosphates,  and  the  volatilized  phosphorus 
is  condensed  in  suitable  chambers. 

Photochronograph. — An  electric  instru- 
ment for  automatically  recording  the  transit 
of  a  star  across  the  meridian. 

In  a  small  camera  connected  with  the  eye- piece 
of  the  transit  instrument  is  placed  a  sensitized 
plate. 

A  sidereal  clock  has  an  electric  attachment  to 
its  pendulum,  so  made  that  a  shutter  alternately 
exposes  and  conceals  the  photographic  plate,  and 
thus  permits  the  image  of  a  star  to  be  formed  on 
the  plate  at  intervals  during  its  passage  across 
the  field  of  the  telescope.  An  image  of  the  spider 
lines  is  afterwards  fixed  on  the  plate  by  the  light 
of  a  lamp,  held  for  a  few  moments  before  the  ob- 
ject glass  of  a  telescope.  A  shutter  is  provided, 
by  means  of  which  this  light  is  prevented  from 
falling  on  the  trail  of  the  star  across  the  field  of 
the  glass.  In  this  manner  the  time  of  passage  of 
the  star  across  the  meridian  is  automatically  re- 
corded on  the  photographic  plate. 

The  photochronograph  is  also  adapted  for 
similarly  automatically  recording  the  transit  or 
passage  of  any  heavenly  body  across  any  imagin- 
ary line  in  the  heavens. 

Photo-Electric  Cell.— (See  Cell,  Photo- 
Electric?) 

Phot  o-Electricity.  —  ( See  Electricity, 
Photo:) 

Photo-Electromotive  Force. — (See  Force, 
Electromotive,  Photo?) 

Photometer. — An  apparatus  for  measuring 
the  intensity  of  the  light  emitted  by  any 
luminous  source. 

There  are  various  methods  for  measuring  the 
intensity  of  a  beam  of  light  passing  through  any 
given  space,  or  emitted  from  any  luminous 


Pho.] 


399 


[Pho. 


source;  these  methods  are  embraced  in  the  use 
of  the  following  apparatus: 

( I . )  Calorimetric  Photometer,  in  which  the  light 
to  be  measured  is  absorbed  by  the  face  of  a 
thermo-electric  pile,  and  the  electric  current 
thereby  produced  is  carefully  measured.  Since 
obscure  radiation  or  heat  will  also  thus  produce 
an  electric  current,  it  is  necessary  first  to  absorb 
all  the  heat  by  passing  the  beam  of  light  through 
an  alum  cell. 

(2.)  Actinic,  or  Chemical  Photometers,  in  which 
the  intensity  of  the  light  is  estimated  by  a  com- 
parison of  the  depth  of  coloration  produced  on  a 
fillet  of  photographic  paper  under  similar  con- 
ditions of  exposure  to  a  standard  light,  and  the 
light  to  be  measured. 

The  combination  of  pure  hydrogen  and  chlorine, 
or  the  decomposition  of  pure  mercurous  chloride, 
have  been  employed  for  the  purpose  of  determin- 
ing the  intensities  of  two  lights  by  measuring  the 
amount  of  chemical  action  effected. 

(3.)  Shadow  Photometers,  in  which  a  shadow 
produced  by  the  light  to  be  measured  is  compared 
with  a  shadow  produced  by  a  standard  candle. 
(See  Candle,  Standard.} 


Fig.  427.     The  Shadow  Photometer. 

Rumford's  photometer,  shown  in  Fig.  427,  is 
an  example  of  this  form  of  instrument.  The 
standard  candle,  shown  at  L,  casts  a  shadow  C", 
of  an  opaque  rod  C,  on  the  screen  at  B. 

The  Hght  to  be  measured  L',  is  moved  away 
from  the  screen  until  its  shadow  C',  on  the  screen 
at  A,  is  judged  by  the  eye  to  be  of  the  same 
depth.  The  distance  between  the  screen  and  the 
lights  is  then  measured  in  straight  lines.  The 
relative  intensities  of  the  two  lights  are  then  pro- 
portional to  the  squares  of  their  distances.  If,  for 
example,  the  candle  be  at  10  inches  from  the 
screen,  and  the  lamp  at  40  inches,  then  the 
intensities  are  as  io8 :  4O2  or  as  100  :  1,600,  or  the 
lamp  is  a  16  candle-power  lamp. 


This  photometer  is  based  on  the  fact  that  the 
shadow  of  each  source  is  illumined  by  the  light 
of  the  other  source. 

These  results  are  more  accurate  if  the  two 
shadows  are  adjoining  or  nearly  adjoining. 

(4.)  Translucent-Disc  Photometers.— -The  light 
to  be  measured  and  a  standard  candle  are  placed 
on  opposite  sides  of  a  sheet  of  paper  the  centre  of 
which  contains  a  grease  spot.  The  standard 
candle  is  kept  at  a  fixed  distance  from  the  paper 
and  both  it  and  the  paper  are  moved  towards  or 
from  the  light  to  be  measured  until  both  sides  of 
the  paper  are  adjudged  to  be  equally  illumined. 

In  Bunsen's  photometer  a  vertical  sheet  of 
paper  with  a  grease  spot  at  its  centre,  is  exposed 
to  the  illumination  of  a  standard  candle  on  one 
side,  and  the  light  to  be  measured  on  the  other. 

The  sheet  of  paper  is  placed  inside  a  dark  box 
provided  with  two  plane  mirrors  placed  at  such 
an  angle  to  the  paper  that  an  observer  can  readily 
see  both  sides  of  the  paper  at  the  same  time. 

This  box  can  be  slid  along  a  graduated,  hori- 
zontal scale  towards,  or  from,  the  light  to  be 
measured,  and  carries  with  it  the  standard  candle 
mounted  on  it  at  a  constant  distance  of  io  inches. 
If  the  box  is  too  near  the  light  to  be  measured, 
the  grease  spot  appears  brighter  on  the  side  of  the 
sheet  of  paper  nearest  the  candle.  If  too  near 
the  candle,  it  appears  brighter  on  the  side  of  the 
sheet  of  paper  nearest  the  light  to  be  measured. 
The  position  in  which  the  spot  appears  equally 
bright  on  both  sides,  is  the  position  in  which  both 
sides  of  the  paper  are  equally  illumined,  and  the 
relative  intensities  of  the  two  lights  are  then 
directly  as  the  squares  of  their  distances  from  the 
sheet  of  paper. 

Shadow,  and  translucent-disc  photometers 
being  dependent  on  equal  illumination,  are  re- 
liable only  when  the  color  of  the  lights  compared 
is  the  same.  For  the  determination  of  the  photo- 
metric intensity  of  very  bright  lights,  the  standard 
candle  is  replaced  by  a  carcel  lamp,  a  standard 
gas  jet,  or  by  the  light  emitted  by  a  given  mass 
of  platinum,  heated  to  incandescence  by  a  given 
current  of  electricity.  (See  Lamp,  Carcel.  Gas- 
Jet,  Carcel  Standard.  Light,  Platinum  Stand- 
ard.) 

Preece's  photometer  belongs  to  the  class  of 
translucent  disc  photometers.  A  tiny  incandes- 
cent lamp  is  placed  in  a  box,  the  topof  which  has 
a  white  paper  screen  on  which  is  a  grease  spot. 
The  box  is  placed  in  the  street  where  the  intensity 
of  illumination  is  to  be  measured,  and  the  inten- 


Pho.J 


400 


[Pho. 


sity  of  the  light  of  the  incandescent  lamp  is 
varied  until  the  grease  spot  disappears.  The 
current  of  electricity  then  passing  through  the 
incandescent  lamp  acts  as  the  measure  of  the 
illumination. 

In  the  case  of  the  shadow  photometer,  or  of 
Bunsen's  photometer,  if  the  intensity  of  illumina- 
tion is  the  same,  the  relative  intensities  of  the  two 
lights  may  be  determined  as  follows: 

Calling  I,  and  i,  respectively  the  relative  inten- 
sities of  the  standard  light,  and  the  light  to  be 
measured,  and  D,  and  d,  their  respective  dis- 
tances from  the  screen,  then 

I  :  i  :   :  D»   :  d2,  or  I  X  d*  =  i  X  D2; 

that  is,  i  =  I  (^-)  - 

Or ,  the  intensity  of  the  light  to  be  measured  is 
(— - \  times  the  intensity  of  the  standard  light. 

If,  for  example,  D  and  d,  represent  10  and  100 
inches,  respectively,  the  intensity  of  i,  is  100  times 
the  intensity  I,  the  standard  light. 

(5.)  Dispersion  Photometers.  -A  class  of  pho- 
tometers in  which,  in  order  to  more  readily  com- 
pare or  measure  a  very  bright  or  intense  light, 
like  that  of  an  arc  lamp,  the  intensity  of  the  light 
is  decreased  by  dispersion  a  readily  measurable 
amount. 

Ayrton  S*  Perry's  Dispersion  Photometer. — A 
photometer  in  which,  in  order  to  bring  an  in- 
tensely bright  light,  like  an  electric  arc  light,  to 


Fig.  428.    Ayrton  &•  Perry's  Dispersion  Photometer. 

such  an  intensity  as  will  permit  it  to  be  readily 
compared  with  a  standard  candle,  its  intensity  is 
weakened  by  its  passage  through  a  diverging 
(concave)  lens. 

Ayrton  &  Perry's  dispersion  photometer  is 
shown  in  two  different  positions,  Figs.  428  and 
429.  The  apparatus  is  supported  on  a  trip  >d 
stand  E,  arranged  so  as  to  obtain  exact  leveling. 


A  plane  mirror  H,  movable  around  a  pin  placed 
directly  under  its  centre,  can  be  rotated  and  thus 
reflect  the  light  after  its  passage  through  the 
diverging  lens,  while  still  maintaining  its  distance 
from  the  electric  light 

The  horizontal  axis  of  this  mirror  is  inclined 
45  degrees  to  its  reflecting  surface  in  order  to 
avoid  errors  arising  from  varying  absorption  at 
different  angles  of  reflection. 

The  inclination  of  the  beam  to  the  horizontal 
is  indicated  by  means  of  an  index  attached  to  the 
mirror  and  moving  over  the  graduated  circle  G. 

A  black  rod  A,  casts  its  shadow  on  a  screen  of 
white  blotting  paper  B.  A  standard  candle, 
placed  in  the  holder  D,  casts  its  shadow  alongside 
the  shadow  cast  by  the  electric  light.  The  lens 
is  now  displaced  until  the  shadow  of  the  electric 
light  is  of  the  same  intensity  as  that  of  the  candle, 
when  viewed  successively  through  sheets  of  red 
and  green  glass. 

A  graduated  scale  serves  to  mark  the  distances 
of  the  candle  and  the  lens,  respectively,  from  the 
screen,  from  which  data  the  intensity  ot  the 
electric  light  may  be  calculated. 


Fig.  429.    Ayrton  and  Perry's  Dispersion  Photometer. 

(6.)  Selenium  Photometers .  —  Instruments  in 
which  the  relative  intensities  of  two  lights  are  de- 
termined by  the  variations  produced  in  a  selenium 
resistance. 

In  Siemens'  Selenium  photometer  a  selenium 
cell  is  employed  in  connection  with  an  electric 
circuit  for  determining  the  intensity  of  light. 

The  tube  A  B,  Fig.  430,  is  furnished  at  A,  with 
a  diaphragm,  and  at  B,  with  a  selenium  plate, 
connected  by  wires  G  G,  with  the  circuit  of  a 
battery  and  a  galvanometer. 

A  graduated  scale  L  M,  bears  the  standard 
candle  N.  The  tube  A  B,  is  capable  of  rotation 
on  the  vertical  axis  F.  A  reflecting  mirror  gal- 
vanometer is  used  in  connection  with  the  selenium 
photometer.  The  light  to  be  measured  is  placed 


Pho.] 


401 


[Pho. 


at  right  angles  to  the  scale  L  M,  and  the  tube  A 
B,  directed  towards  it,  and  the  galvanometer  de- 
flection compared  with  the  deflection  obtained 
when  turned  towards  the  standard  candle. 

(7.)  Gas-Jet  Photometers, — Instruments  in 
which  the  candle-power  of  a  gas-jet  is  determined 
by  measuring  the  height  at  which  the  jet  burns 
when  under  unit  conditions  of  volume  and  press- 
«re  of  gas  consumed. 


Fig.  4.30.     Siemens'  Selenium  Photometer. 

In  determining  the  candle-power  of  an  intense 
light  like  the  electric  arc  light,  a  large  gaslight 
is  used  instead  of  a  standard  candle,  and  the 
photometric  power  of  this  gaslight  is  carefully 
determined  by  comparison  witha  gas-jet  photom- 
eter. (See  Jet,  Gas,  Carcel Standard.} 

Photometer,  Actinic A  photom- 
eter in  which  the  intensity  of  any  light  is  meas- 
ured by  the  amount  of  chemical  decomposi- 
tion it  effects.  (See  Photometer) 

In  some  actinic  photometers  the  intensity  of  the 
light  to  be  measured  is  determined  by  the  com- 
parison of  the  depth  of  coloration  of  a  sensi- 
tized film  under  similar  conditions  of  exposure 
to  a  standard  light  and  the  light  to  be  measured. 

Photometer,  Calorimetric A  pho- 
tometer in  which  the  light  to  be  measured  is 
absorbed  by  the  face  of  a  thermo-electric  pile, 
and  the  intensity  of  the  light  estimated  from 
the  strength  of  the  electric  current  thereby 
produced. 

In  order  to  avoid  the  error  arising  from  the 
current  produced  from  the  absorption  of  the  ob- 
scure radiation  from  the  light,  all  the  heat  is  first 
absorbed  by  passing  the  light  through  an  alum 
cell.  (See  Photometer.') 

Photometer,  Chemical A  photom- 
eter in  which  the  intensity  of  the  light  to  be 


measured  is  determined  from  the  amount  of 
chemical  action  effected  in  a  given  time. 

Photometer,  Dispersion A  photom- 
eter in  which  the  light  to  be  measured  is  de- 
creased in  intensity  a  known  amount  so  as  to 
more  readily  permit  it  to  be  compared  with  a 
standard  light  of  much  smaller  intensity. 
(See  Photometer) 

Photometer,  Electric An  electrical 

instrument  for  measuring  the  intensity  of 
illumination. 

A  form  of  electric  photometer  invented  by  C. 
R.  Richards  depends  for  its  indications  on  the 
variations  that  occur  in  the  resistance  of  a  wire  on 
change  of  temperature.  An  irom  wire,  whose 
change  of  temperature  is  utilized  for  measuring 
the  intensity  of  any  light  to  whose  radiations  it  is 
opposed,  is  covered  by  a  deposit  of  lampblack. 
On  exposure  to  the  light  whose  intensity  is  to 
be  measured,  the  light  is  absorbed  by  the  lamp- 
black and  an  increase  in  temperature  occurs. 

In  order  to  get  rid  of  the  heat  rays  that  are 
associated  with  the  light  rays,  the  rays  before 
falling  on  the  soot-covered  wire  are  caused  to  pass 
through  a  solution  of  alum  ;  the  intensity  of  the 
light  is  then  calculated  by  reference  to  the  change 
in  the  resistance  of  the  soot-covered  wire,  which 
is  made  one  of  the  arms  of  a  Wheatstone  bridge. 

Photometer,  Gas-Jet — A  photom- 
eter in  which  the  candle-power  of  a  gas  jet  is 
estimated  from  a  measurement  of  the  height 
at  which  the  jet  burns  under  unit  conditions 
of  volume  and  pressure.  (See  Photometer) 

Photometer,  Jet An  apparatus  for 

determining  the  candle  power  of  a  luminous 
source  by  means  of  the  height  of  a  jet  of  the 
gas,  whose  candle-power  is  being  determined, 
when  burning  under  constant  conditions  as 
to  pressure,  etc.  (See  Jet,  Gas,  Carcel 
Standard.) 

Photometer,  Selenium  — A  photom- 
eter in  which  the  intensity  of  a  light  is  esti- 
mated by  the  comparison  of  the  changes  in 
the  resistance  of  a  selenium  resistance  suc- 
cessively exposed  under  similar  conditions  to 
this  light  and  to  a  standard  light.  (See 
Photometer) 

Photometer,  Shadow A  photom- 
eter in  which  the  intensity  of  the  light  to  be 


JPho.] 


402 


[Pho. 


measured  is  estimated  by  a  comparison  of 
the  distances  at  which  it  and  a  standard  light 
produce  a  shadow  of  the  same  intensity. 
(See  Photometer^) 

Photometer,  Translucent  Disc A 

photometer  in  which  the  light  to  be  measured 
is  placed  on  one  side  of  a  partly  translucent 
and  partly  opaque  disc,  and  a  standard  can- 
dle is  placed  on  the  opposite  side,  and  the  in- 
tensity of  the  light  estimated  by  the  distances 
of  the  light  from  the  disc  when  an  equal  illu- 
mination of  all  parts  of  the  disc  is  obtained. 
(See  Photometer) 

When  the  illumination  of  the  opposite  sides  of 
such  a  disc  is  "equal,  the  relative  positions  of  the 
transparent  and  opaque  portions  of  the  disc  are 
indistinguishable. 

Photometer,  Varley's •  — A  form  of 

photometer  in  which  the  intensity  of  the  light 
to  be  measured  is  determined  from  the  rel- 
ative openings  of  two  concentric  circular 
diaphragms  placed  in  two  rotating  discs,  and 
through  which  the  standard  light  and  the 
light  to  be  measured  respectively  pass. 

The  general  arrangement  of  Varley's  photo- 
meter  is  shown  in  Fig.  431.  The  concentric  cir- 


ring  is  fully  open,  the  ether  is  completely  closed-, 
or,  if  one  ring,  say  the  outer,  is  opened  160  de- 
grees, the  inner  is  opened  20  degrees.  The 
quantity  of  light  then  which  passes  through  the 
outer  ring  from  the  light  to  be  measured  is  eight 
times  that  passed  through  the  inner  ring.  The 
circle  is  divided  into  2,000  parts,  instead  of  into 
360  degrees,  and,  by  means  of  a  vernier,  these 
parts  are  further  divided  into  10  parts,  permitting 
a  reading  of  the  20,000  divisions. 

Two  collimeters  placed  in  front  of  the  disc, 
project  a  disc  with  a  black  centre,  and  a  luminous 
spot  respectively.  The  discs  are  regulated  until 
the  light  projected  on  the  screen  produces  a  uni- 
form disc.  This  is  readily  ascertained,  since  if 
one  or  the  other  predominate,  a  disc  with  gray 
spot,  or  a  gray  marginal  ring  with  a  bright  spot, 
will  appear. 

The  general  appearance  of  the  circular  dia- 
phragm, corresponding  to  different  relative  posi- 
tions of  the  two  discs,  is  shown  in  Fig.  432. 


43  1.    Parley's  Photometer. 


cular  apertures  extend  circumferentially  180  de- 
grees,  and  are  reversed  so  that  when  one  half 


Fig.  4.32.    Circular  Diaphragm  of  Varley's  Photometer. 

Photometric.— Of  or  pertaining  to  the 
photometer.  (See  Photometer^ 

Photometrically. — In  a  photometric  man- 
ner. 

Photophone. — An  instrument  invented  by 
Bell  for  the  telephonic  transmission  of  artic- 
ulate speech  along  a  ray  of  light  instead  of 
along  a  conducting  wire. 

A  beam  of  light,  reflected  from  a  diaphragm 
against  which  the  speaker's  voice  is  directed,  is 
caused  to  fall  on  a  selenium  resistance  inserted  in 
the  circuit  of  a  voltaic  battery,  and  a  telephone. 
The  changes  thus  effected  in  the  resistance  of  the 
circuit  by  the  varying  amounts  of  light  reflected  on 
the  selenium  resistance  from  the  diaphragm,  while 
moving  to-and-fro  under  the  influence  of  the  speak- 
er's voice,  produce  in  the  receiving  telephone  a 
series  of  to-and  fro  movements  similar  to  those  im- 
pressed on  the  transmitting  diaphragm.  One  lis- 
tening at  the  telephone  can  hear  whatever  has  been 
spoken  in  the  neighborhood  of  the  transmitting 
diaphragm.  Telephonic  communication  can, 
therefore,  by  such  means  be  carried  on  aiong  » 


Pho.] 


403 


[Pie. 


ray  or  beam  of  light,  theoretically  through  any 
distance.  (See  Resistance,  Selenium.) 

A  block  of  vulcanite  or  of  certain  other  sub- 
stances  may  be  used  as  the  receiver,  since  it  has 
been  discovered  that  a  rapid  succession  of  flashes 
of  light  produces  an  audible  sound  in  small  masses 
of  these  substances. 

The  term  sonorescence  has  been  proposed  for 
the  property  possessed  by  such  substances  of 
emitting  sounds  when  subjected  to  such  inter- 
mittent flashes  of  light.  (See  Sonorescence.) 

Photophore,  Trouye's — An  appa- 
ratus in  which  the  light  of  a  small  incandescent 
electric  lamp  is  employed  for  purposes  of 
medical  exploration. 

A  small  incandescent  lamp  is  placed  in  a  tube 
containing  a  concave  mirror  and  a  converging 
lens. 

Photo-Telegraphy. — The  electric  produc- 
tion of  pictures,  writing,  charts  or  diagrams 
at  a  distance. 

Photo-Telegraphy  is  sometimes  called  telepho- 
tography ;  it  is  a  species  of  fac-simile  telegraphy. 
(See  Telegraphy,  Fac- Simile.  Telephotography.) 

Photo- Voltaic  Effect.— (See  Effect,  Photo- 
Voltaic^ 

Physical  Change.— (See  Change,  Phy- 
sical.) 

Physical  Phosphorescence. — (See  Phos- 
phorescence, Physical.) 

Physiological. — Pertaining  to  physiology. 

Physiological  Rheoscope. — (See  Rheo- 
scope.  Physiological,} 

Physiologically. — In  a  physiological  man- 
ner. 

Physiology,  Electro The  study  of 

electric  phenomena  of  living  animals  and 
plants. 

Living  animals  and  plants  present  electric 
phenomena,  due  to  the  electricity  naturally  pro- 
duced  by  them.  It  is  the  province  of  electro- 
physiology  to  ascertain  the  causes  and  effects  of 
these  phenomena. 

Piano,  Electric A  piano  in  which 

the  strings  are  struck  by  hammers  actuated 
by  means  of  electro-magnets,  instead  of  by 
the  usual  mechanical  action  of  levers. 


An  electric  piano-action  is  mainly  useful  in  per- 
mitting the  instrument  to  be  played  at  any  dis- 
tance from  the  key-board,  it  is  also  of  value 
from  the  ease  it  affords  in  recording  the  pieces 
played. 

It  fails,  however,  to  properly  preserve  the  vari- 
ous modulations  of  force  so  requisite  for  brilliant 
instrumentation. 

Pickle. — An  acid  solution  in  which  me- 
tallic  objects  are  dipped  before  being  gal- 
vanized, or  electroplated,  in  order  to 
thoroughly  cleanse  their  surfaces. 

The  pickle  used  for  the  preparation  of  iron  for 
galvanization  is  a  weak  solution  of  sulphuric  acid 
in  water.  Various  acids,  or  acid  liquids,  are  em- 
ployed  for  insuring  the  thorough  cleansing  of 
metallic  surfaces  so  necessary  in  order  to  ensure 
an  even,  uniform,  adherent  coating  of  metal  by 
the  process  ot  electroplating.  (See  Plating, 
Electro.) 

Piece,  Magnetic  Proof A  para. 

magnetic  rod,  ellipsoid  or  sphere  employed 
for  ascertaining  the  distribution  of  magnetism 
over  a  magnet  by  the  force  required  to  de- 
tach the  same.  (See  Paramagnetic^) 

Prof.  S.  P.  Thompson  points  out  the  fact 
that  the  presence  of  the  proof-piece  so  alters  the 
distribution  of  magnetism  on  the  magnet  to  be 
measured  as  to  render  this  method  unreliable. 
He  also  shows  that  the  force  required  for  detach- 
ment depends  on  the  magnetic  permeability  of 
the  proof-piece,  as  well  as  on  its  shape  and  its 
position  in  the  magnetic  circuit 

Pieces,  Month Openings  into  air 

chambers,  generally  circular  in  shape,  placed 
over  the  diaphragms  of  telephones,  phono- 
graphs, gramophones  or  graphophones  to 
permit  the  ready  application  of  the  mouth  in 
speaking,  so  as  to  set  the  diaphragm  into 
vibration. 

The  mouth -piece  may  be  also  utilized  by  the 
ear  of  an  observer  listening  so  as  to  be  affected 
by  its  vibrations. 

Pieces,  Pole,  of  Dynamo-Electric  Ma- 
chine   Masses  of  iron  connected  with 

the  poles  of  the  field  magnet  frames  of 
dynamo-electric  machines,  and  shaped  to 
conform  to  the  outline  or  contour  of  the 
armature. 


PH.] 


404 


LPil. 


The  pole  pieces  are  made  in  a  variety  of  forms, 
but  in  all  cases  are  so  shaped  as  to  conform  to  the 
outline  of  the  space  in  which  the  armature  rotates. 

The  pole  pieces  are  brought  as  near  as  possible 
to  the  armature,  so,  as  to  increase  the  intensity  of 
the  magnetic  induction.  The  intervening  air 
space  should  be  as  thin  as  possible,  but  of  as  large 
an  area  as  convenient. 

The  opposite  pole  pieces  should  not  have  their 
extensions  brought  too  near  together,  as  this  will 
permit  of  serious  loss  through  magnetic  leakage. 
The  distance  between  them  should  be  as  many 
times  the  depth  of  the  armature  windings  as 
possible.  (See  Leakage,  Magnetic. ) 

Rounded  edges  are  preferable  to  sharp  edges 
for  the  same  reason. 

Pile,  Dry A  voltaic  pile  or  battery 

consisting  of  numerous  cells,  the  voltaic 
couple  in  each  of  which  consists  of  sheets  of 
paper  covered  with  zinc-foil  on  one  side  and 
black  oxide  of  manganese  on  the  other. 

Various  modifications  of  the  above  form  have 
been  made. 

The  term  dry-pile  is  a  misnomer,  since  all  such 
piles  contain  substances  moistened  by  liquid 
electrolytes. 

Pile,  Muscular,  Matteueci's  —  — A  vol- 
taic battery  or  pile,  the  elements  of  which  are 
formed  of  longitudinal  and  transverse  sections 
of  muscle  alternately  connected. 

Matteucci's  experiments  appear  to  show  that 
the  lower  the  animal  is  in  the  scale  of  creation, 
the  stronger  is  the  current  produced,  and  the 
longer  its  duration.  Du  Bois-Reymond  has 
shown  that  the  muscular  current  is  not  due  to 
contact,  but  to  the  differences  of  electric  poten- 
tial naturally  possessed  by  the  muscles  them- 
selves. 

The  nerves  also  possess  the  power  of  producing 
differences  of  electromotive  force,  and  hence  cur- 
rents. (See  Electrotonus. ) 

Pile,  Thermo,  Differential  —  —A  ther- 
mopile in  which  the  two  opposite  faces  are 
exposed  to  the  action  of  two  nearly  equal 
sources  of  heat  in  order  to  determine  accu- 
rately the  differences  in  the  thermal  intensities 
of  such  sources  of  heat. 

Pile,  Thermo-Electric  —  — A  number 
of  separate  thermo-electric  couples,  united  in 


series,  so  as  to  form  a  single  thermo-electric 
source.  (See  Couple,  Thermo-Electric?) 

A  thermo-electric  pile  is  sometimes  called  a 
thermo-electric  battery. 

Fig.  433  shows  Nobili's  thermopile,  in  whick 
a  number  of  bismuth- 
antimony  thermo-elec- 
tric couples  connected 
in  a  continuous  se- 
ries, as  shown  partly 
in  Fig.  434,  are  insu- 
lated from  one  another, 
except  at  their  junc- 
tions, and  packed  in  a 
metallic  box,  supported 
as  shown  in  Fig.  433. 

The  free  terminals  of  Fig.  433.  fher mo- Electric 
the  series  are  con-  Pile- 

nected  to  binding  posts.  Differences  of  tem- 
perature between  the  two  faces  of  the  pile,  where 
the  junctions  are  exposed,  result  in  a  difference 
of  potential  equal  to  the  sum  of  the  differences  of 
potential  of  all  the  thermo-electric  couples. 

A  careful  inspec- 
tion will  show  that 
the  junctions  are 
formed  successively 
at  opposite  faces  of 
the  pile,  so  that  if 
the  junctions  be 
numbered  succes- 
sively, the  even  junc- 
tions will  come  at 
one  face,  and  the 


Fig-  434-    Series-Connected 
Thermo-Electric  Couples. 


odd  junctions  at  the  other.  This  is  necessary 
in  order  to  permit  all  the  thermo-electric  couples 
to  add  their  differences  of  potential ;  for,  if,  as 
in  Fig.  435,  a  thermo-electric  chain  be  formed, 


Fig-  435-     Thermo-Electric  Circuit. 


no  currents  will  result  from  equally  heating  any 
two  consecutive  junctions  J,  J,  of  the  metals  A 
and  B,  since  the  electromotive  forces  so  produced 
oppose  each  other. 

Thermopiles  have  been  constructed  by 
Clamond,  of  couples  of  iron  and  an  alloy  of  zinc 
and  antimony,  of  sufficient  power  to  produce  a 
voltaic  arc  whose  illuminating  power  equaled  40 


PH.] 


405 


[Pla. 


carcel  burners.  Many  practical  difficulties  exist 
which  will  have  to  be  surmounted,  however,  before 
such  piles  can  be  employed  as  commercial  electric 
sources. 

Pile,  Yoltaic A  battery  consisting 

of  a  number  of  voltaic  couples  connected  so 
as  to  form  a  single  electric  source. 

A  form  similar  to  Volta's  original  pile,  consist- 
ing of  alternate  discs  of  copper  and  zinc,  separated 
from  each  other  by  discs  of  wet  cloth,  and  piled 
•n  one  another,  so  as  to  form  a  number  of  separate 
voltaic  couples  connected  in  series,  is  shown  in 
Fig.  436.  The  thick  plates  marked  Zn,  are  of 
zinc  ;  the  copper  plates,  marked  Cu,  are  much 


Fig.  436.     Voltaic  Pile. 

thinner.  The  discs  of  moistened  cloth  are  shown 
at  d  d.  One  end  of  such  a  pile  would  then  be 
terminated  by  a  plate  of  copper,  and  the  other 
by  a  plate  of  zinc.  The  copper  end  forms  the 
positive  electrode,  and  the  zinc  end  the  negative 
electrode.  (See  Cell,  Voltaic.} 

Pilot  Lamp.— (See  Lamp,  Pilot.) 

Pilot  Transformer. — (See  Transformer, 
Pilot.) 
Pilot  Wires.— (See  Wires,  Pilot.) 


Pin,  Insulator A  bolt  by  means 

of  which  an  insulator  is  attached  to  the  tele- 
graphic support  or  arm. 

The  insulator  pins  or  bolts  are  generally  fixed  to 
the  insulator  by  means  of 
screw  threads  turned  on 
their  ends.  They  are  then, 
cemented  to  the  insulators  by 
any  suitable  moisture-proof 
cement. 

The  pin  and  insulator  con- 
nected  to  one  another  by 
means  of  a  screw  thread  are 
shown  in  Fig.  437. 

Pin,  Switch  -      —A 

metallic  pin  or  plug  pro- 
vided for  insertion  in  a 
telegraphic  switch  board. 
A  form  of  switch  pin  is 
shown  in  Fig.  438.  The 
metallic  end  is  conical  in 
form,  and  is  provided  with 
two  longitudinal  slots  at  Fig.  437.  Insulator 
right  angles  to  each  other  in  Pi*. 

order  to  insure  a  light  spring  connection  with 
the  metallic  contact  plate  in  which  the  pin  is  in- 
serted. 

Pith. — A  light,  cellular  material,  forming  the 
central  portions  of  most  exogenous  plants. 

An  excellent  pith,  suitable  for 
electrical  purposes,  is  furnished  by 
the  dried  interior  of  the  elder- berry 
stick. 

Pith  Ball.— (See  Balls,  Pith.) 
Pith  -  Ball    Electroscope.  — 

(See  Electroscope,  Pith-Ball) 

Pivot  Suspension.— (See  Sus- 
pension, Pivot) 

Plain-Pendant  Argand  Elec- 
tric Burner.  —  (See  Burner, 
Plain-Pendant  Electric) 

Plain-Pendant  Electric  Burner.  — (See 

Burner,  Plain-Pendant  Electric) 

Plane  Angle.— (See  Angle,  Plane) 

Plane,   Proof A   small   insulated 

conductor  employed  to  take  test  charges  from 
the  surfaces  of  insulated,  charged  conductors. 


Pla.] 


406 


[Pla. 


The  proof-plane  is  used  in  connection  with 
some  form  of  electrometer.  (See  Balance,  Cou- 
lomb''s  Torsion.) 

Plane,  Proof,  Magnetic A  small 

coil  of  wire  placed  in  the  circuit  of  a  delicate 
galvanometer,  and  used  for  the  purpose  of 
exploring  a  magnetic  field. 

When  the  coil  is  suddenly  inverted  in  a  mag- 
netic field,  if  a  long-coil  galvanometer  provided 
with  a  heavy  needle  is  used,  the  number  of  lines 
of  force  which  pass  through  the  area  of  cross-sec- 
tion of  the  coil  will  be  proportional  to  the  sine  of 
half  the  angle  of  the  first  swing  of  the  needle. 

Plant.— A  word  sometimes  used  for  in- 
stallation, or  for  the  apparatus  required  to 
carry  on  any  manufacturing  operation. 

An  electric  plant  includes  the  steam  engines 
or  other  prime  motors,  the  generating  dynamo  or 
dvnamos,  the  lamps  and  other  electro-receptive 
devices,  and  the  circuits  connected  therewith. 

Plant  Electricity.  —  (See  Electricity, 
Plant.  Plants,  Electricity  of.) 

Plants,  Electricity  of—  —Electricity 
produced  naturally  by  plants  during  their  vig- 
orous growth. 

DuBois-Reymond  and  others  have  shown  that 
plants  while  in  a  vigorous  vital  state  are  active 
sources  of  electricity. 

If  one  of  the  terminals  of  a  galvanometer  be 
inserted  into  a  fruit  near  its  stem,  and  the  other 
terminal  into  the  opposite  part  of  the  fruit,  the 
galvanometer  at  once  shows  the  presence  of  an 
electric  current. 

Buff  has  shown  that  the  roots  and  interior  por- 
tions of  plants  are  always  negatively  charged, 
while  the  flowers,  fruits  and  green  twigs  are  posi- 
tively charged. 

Plant  tissue  or  fibre,  like  the  muscular  fibre  of 
animals,  exhibits  in  many  cases  a  true  contraction 
on  the  passage  through  it  of  an  electric  current. 
This  is  seen  in  the  Mimosa  sensitiva,  or  Sensitive 
Fern,  in  the  Venus'  Fly-Trap,  and  in  several  other 
species  of  plants. 

Pouillet  concludes  from  numerous  observations 
that  the  free  positive  electricity  of  the  atmosphere 
is  partly  due  to  the  vapors  disengaged  by  grow- 
ing plants. 

The  peculiar  geographical  distribution  of  thun- 
der storms,  however,  does  not  favor  this  assump- 


tion. (See  Storm,  Thunder,  Geographical  Dis- 
tribution of.) 

Plastics,  Galvano A  term  some- 
times employed  for  electrotyping,  that  is 
where  the  deposits  are  sufficiently  thick  to 
permit  of  ready  separation  from  the  object 
which  forms  the  mould. 

Literally,  the  cold  moulding  or  shaping  of 
metals  by  electrotyping.  (See  Plating,  Elec- 
tro. Metallurgy,  Electro}) 

The  word  galvano-plastics  is  sometimes  used 
as  synonymous  with  electrotyping,  electro-plat- 
ing, or  electro-metallurgy  generally. 

Plastics,  Hydro The  art  of  elec- 
trically shaping  or  depositing  metals  in  the 
wet  by  electrotyping.  (See  Plastics,  Gal- 
vano.) 

Plate,  Arrester,  of  Lightning  Protector 

That   plate   of   a  lightning  protector 

which  is  directly  connected  with  the  circuit 
to  be  protected,  as  distinguished  from  the  plate 
that  is  connected  with  the  ground.  (See 
Arrester,  Lightning?) 

Plate  Condenser.— (See  Condenser,  Plate.) 
Plat-,  Ground,  of  Lightning  Arrester — 

— That  plate  of  a  comb  lightning  arrester 
which  is  connected  to  the  earth  or  ground. 
(See  Arrester,  Lightning,  Comb.) 

Plate,  Negative,  of  Storage  Cell  — 
That  plate  of  a  storage  cell  which,  by  the 
action  of  the  charging  current,  is  converted 
into  or  partly  covered  with  a  coating  of  spongy 
lead. 

That  plate  of  a  storage  battery  which  is 
connected  with  the  negative  terminal  of  the 
charging  source,  and  which  is  therefore  the 
negative  pole  of  the  battery  on  discharging. 

The  usage  is  the  reverse  of  that  in  the  case  of 
the  primary  battery. 

Plate,  Negative,  of  Yoltaic  Cell 

The  electro-negative  element  of  a  voltaic 
couple.  (See  Couple,  Voltaic.) 

That  element  of  a  voltaic  couple  which  is 
negative  in  the  electrolyte  of  the  cell.  (See 
Electrolyte.) 

The  negative  plate  of  a  voltaic  cell  is  the  plate 
not  acted  on  by  the  electrolyte.  In  a  zinc  carbon 


Pla.] 


407 


[Pla. 


couple  in  dilute  sulphuric  acid,  the  carbon  plate 
is  the  negative  plate.  (See  Cell,  Voltaic.) 

The  negative  plate  is  to  be  carefully  distin- 
guished from  the  Negative  pole,  which  is  the  ter- 
minal connected  to  the  positive  plate.  The 
terminal  connected  to  the  negative  plate  is  the 
positive  pole.  (See  Cell,  Voltaic.) 

Plate,  Positive,  of  Storage  Battery 

— That  plate  of  a  storage  battery  which  is 
converted  into,  or  covered  by,  a  layer  of  lead 
peroxide,  by  the  action  of  the  charging  current. 

That  plate  of  a  storage  battery  which  is 
connected  with  the  positive  terminal  of  the 
charging  source  and  which  is,  therefore,  the 
positive  pole  of  the  battery  on  discharging. 

It  will  be  noticed  that  the  usage  in  this  respect 
is  the  reverse  of  that  in  the  case  of  primary  bat- 
teries, in  which  the  positive  plate  is  positive  in 
the  liquid  only;  the  end  which  projects  from  the 
liquid,  or  the  terminal  connected  with  it  being 
negative. 

In  storage  batteries,  the  positive  plate  is  con- 
nected with  the  positive  pole.  (See  Battery, 
Storage.  Cell,  Voltaic.) 

Plate,  Positive,  of  Toltaic  Cell — 

The  electro-positive  element  of  a  voltaic 
couple.  (See  Couple,  Voltaic) 

That  element  of  a  voltaic  couple  which  is 
positive  in  the  electrolyte  of  the  cell.  (See 
Electrolysis?) 

The  positive  plate  of  a  voltaic  cell  is  the  plate 
out  from  which  the  current  flows  through  the 
electrolyte. 

The  zinc  plate  of  a  zinc-carbon  couple  is  the 
positive  plate.  (See  Cell,  Voltaic. ) 

The  current  leaves  the  cell,  however,  to  flow  or 
pass  through  the  external  circuit  at  the  wire  or 
terminal  connected  with  the  negative  plate.  (See 
Cell,  Voltaic.} 

Plate,    Primary,   of   Condenser 

That  plate  of  a  condensing  transformer  in 
which  the  inducing  charge  is  placed  in  order 
to  induce  a  charge  of  different  potential  in  the 
secondary  plate. 

Plate,   Secondary,  of  Condenser  — 

That  plate  of  a  condensing  transformer  in 
which  the  induced  charge  is  produced  by  the 
induction  of  a  charge  on  the  primary  plate. 
Plate,  Zinc,  of  Yoltaic  Cell.  Amalgama- 


tion of Covering   the  surface  of  the 

zinc  plate  of  a  voltaic  cell  with  a  thin  layer  of 
amalgam  in  order  to  avoid  local  action.  (See 
Action,  Local,  of  Voltaic  Cell.  Zinc,  Amal- 
gamation of.) 

Plates,  Arrester A  term  sometimes 

applied  to  the  two  plates  of  an  ordinary  comb 
lightning  arrester.  (See  Arrester,  Lightning, 
Comb.) 

The  plate  that  is  connected  to  the  line  to  be 
protected,  is  more  correctly  called  the  arrester 
plate,  and  that  connected  to  the  ground  the  ground 
plate. 

Plates  of  Secondary  or  Storage  Cell, 
Forming  of  —  — Obtaining  a  thick  coating 
of  lead  peroxide  on  the  lead  plates  of  a  storage 
battery,  by  repeatedly  sending  the  charging 
current  through  the  cell  alternately  in  opposite 
directions. 

The  effect  of  sending  a  current  between  two 
lead  plates  immersed  in  dilute  sulphuric  acid,  is  to 
coat  one  of  the  plates  with  lead  peroxide.  On  the 
sending  of  the  current  in  the  opposite  direction, 
the  other  plate  is  coated  with  lead  peroxide.  If 
now  the  current  is  sent  in  the  opposite  direction, 
more  peroxide  is  deposited  on  one  of  the  plates, 
and  the  peroxide  at  the  other  plate  is  converted 
into  spongy  lead. 

At  the  end  of  charging,  the  battery  will  form 
an  independent  source  of  current.  (See  Cell, 
Storage.) 

Platform,  Pole A  platform,  capable 

of  supporting  several  men,  placed  on  a  termi- 
nal pole  provided  with  a  cable  box,  for  the 
purpose  of  affording  a  ready  means  of  inspect- 
ing and  arranging  the  conductors  in  the  box. 

Plating  Balance.— (SeeBalance,  Plating.} 

Plating  Bath,  Electro  —  —  (See  Bath, 
Electro-Plating) 

Plating,    Copper  — Electro-plating 

with  copper.  (See  Plating,  Electro.  Bath, 
Copper) 

Plating,  Electro The  process  of 

covering  any  electrically  conducting  surface 
with  a  metal  by  the  aid  of  the  electric 
current. 

By  the  aid  of  electro-plating,  the  baser  metals 
are  covered  w.th  silver,  gold  or  platinum,  or  with 
any  other  metal,  such  as  nickel  or  copper. 


Pla.] 


408 


[Pla. 


The  process  of  electro-plating  is  carried  on  as 
follows: 

The  object  to  be  plated  is  connected  with  the 
negative  terminal  of  a  battery  and  placed  in  a  so- 
lution of  the  metal  with  which  it  is  to  be  plated, 
opposite  a  plate  of  that  metal  connected  to  the 
positive  terminal  of  the  battery.  If,  for  example, 
the  object  is  to  be  plated  with  copper,  it  is  pi  iced 
in  a  solution  of  copper  sulphate  or  blue  vitriol, 
opposite  a  plate  of  copper.  By  this  arrangement 
the  object  to  be  plated  forms  the  kathode  of  the 
plating  bath,  and  the  plate  of  copper  forms  the 
anode. 

On  the  passage  of  the  current  the  copper  sul- 
phate (Cu  SO4)  is  decomposed,  metallic  copper 
being  deposited  in  an  adherent  layer  on  the  arti- 
cles attached  to  the  kathode,  and  the  acid  radical 
(SO4)  appearing  at  the  anode,  where  it  combines 
with  one  of  the  atoms  of  the  copper  plate.  Since 
for  every  molecule  of  copper  sulphate  decomposed 
in  the  electrolyte,  a  new  molecule  of  copper  sulphate 
is  thus  formed,  by  the  gradual  solution  of  the  copper 
anode,  the  strength  of  the  solution  in  the  bath  is 
maintained  as  long  as  any  of  the  copper  plate  re- 
mains at  the  anode,  and  the  ordinary  activity  of 
the  cell  is  not  otherwise  interfered  with. 

When  any  other  metals,  such  as  gold,  silver  or 
nickel,  for  example,  are  to  be  deposited,  suitable 
solutions  of  their  salts  are  placed  in  the  bath,  and 
plates  of  the  same  metal  hung  at  the  anode. 

The  character  and  coherence  of  the  metallic 
coatings  thus  obtained  depend  on  the  nature  and 
strength  of  the  plating  bath,  and  on  the  density 
of  the  current  employed.  The  size  and  position 
of  the  anode,  as  compared  with  the  size  and  posi- 
tion of  the  objects  to  be  plated,  must  therefore  be 
carefully  attended  to,  as  well  as  the  strength  of 


F'g-  439'    Electro-Plating 

the  metallic  solution  and   the  current  strength 
passing.     (See  Current  Density.) 

Fig.   439,  shows  a  bath  arranged   for   silver- 
plating. 

The  anode  consists  of  a  plate  of  silver.     The 


spoons,  forks,  etc.,  to  be  plated  are  immersed  in 
a  suitable  silver  solution  and  connected  with  tke 
kathode. 

The  electro-plating  process  when  employed  for 
the  production  of  electrotype  plates  is  called 
electrotyping.  Here  the  object  is  to  obtain  a  re- 
production in  metal  of  any  particular  form,  such 
as  of  type  or  of  some  natural  object.  It  was 
called  by  Jacobi  the  galvanoplastic  process.  The 
term  electrotyping  is,  however,  more  generally 
adopted.  (See  Electrotyping,  or  the  Electrotype 
Process.} 

Plating,  Gold  —  —Electro-plating-  with 
gold.  (See  Plating,  Electro.  Bath,  Gold.} 

Plating,     Nickel Electro  -  plating- 

with  nickel.  (See  Plating,  Electro.  BathT 
Nickel} 

Plating,  Sectional Plating  an  article 

with  a  greater  thickness  of  metal  at  certain 
points  than  at  the  rest  of  the  surface. 

Sectional  plating  is  employed  for  such  objects 
as  spoons,  etc.,  which  are,  by  this  method,  given 
a  greater  thickness  of  deposit  at  the  under  portions 
of  the  bowl  and  handle,  where  the  spoon  usually 
rests,  and  is,  therefore,  exposed  to  the  greatest 
wear. 

Sectional  plating  is  effected  by  means  of  sec- 
tional plating  frames.  (See  Plating,  Electro . 
Frames,  Sectional  Plating. ) 

Plating,  Silver  .  —  —Electro-plating: 
with  silver.  (See  Plating,  Electro.  Bath, 
Silver) 

Platinoid.— An  alloy  consisting  of  German 
silver  containing  i  or  2  per  cent,  of  metaJKc 
tungsten. 

Platinoid  is  suitable  for  use  in  resistance  coils  on 
account  of  the  comparatively  small  influence  pro- 
duced on  its  electric  resistance  by  changes  of 
temperature. 

Its  resistance  is  60  per  cent,  higher  than  that 
of  German  silver. 

Platinum. — A  refractory  and  not  readily 
oxidizable  metal,  of  a  tin-white  color. 

The  co-efficient  of  expansion  of  platinum  by 
heat  is  very  nearly  that  of  ordinary  glass.  Pla- 
tinum is,  therefore,  generally  employed  for  the 
leading-in  conductors  of  an  incandescent  lamp. 
These  conductors  are  fused  into  the  glass  of  the 
lamp  chamber.  On  the  heating  of  the  wires  by 


Pla.] 


409 


[Pla. 


the  current,  the  glass  expands  equally  with  the 
wires,  and  the  vacuum  in  the  lamp  chamber  is 
not,  therefore,  injured. 

Platinum  Alloy.— (See  Alloy,  Platinum- 
Silver^ 

Platinum  Black. — Finely  divided  platinum 
that  possesses,  in  a  marked  degree,  the  power 
of  absorbing  or  occluding  gases. 

Platinum  black  is  obtained  by  the  action  of 
potassium  hydrate  on  platinum  chloride.  Unlike 
metallic  platinum  it  is  of  a  black  color. 

Platinum  Fuse.— (See  Fuse,  Platinum^ 

Platinum-Silver  Alloy.— (See  Alloy,  Plat- 
inum-Silver?) 

Platinum  Standard  Light.- (See  Light, 
Platinum  Standard?) 

Platymeter. — An  instrument  invented  by 
Sir  William  Thomson  for  comparing  the 
capacities  of  two  condensers. 

Plow. — The  sliding  contacts  connected  to 
the  motor  of  an  electric  street  car,  and  placed 
within  the  slotted  underground  conduit,  and 
provided  for  the  purpose  of  taking  off  the 
current  from  the  electric  mains  placed  therein, 
as  thevcontacts  are  pushed  forward  over  them 
by  the  motion  of  the  car. 

Similar  contacts,  placed  in  the  rear  of  the  motor 
car  and  drawn  after  the  train,  form  what  is  techni- 
cally known  as  the  sled,  or  when  rolling  on  over- 
head wires  as  trolleys.  (See  Railroad,  Electric.) 

Plow,  Electric A  plow  driven  by 

an  electric  motor  placed  either  on  a  wagon  to 
which  the  plow  is  attached,  or  by  a  stationary 
electro-motor,  by  the  aid  of  cords  or  other 
flexible  belts. 

One  of  the  first  practical  applications  of  the  elec- 
tric transmission  of  energy  was  for  the  operation 
of  a  plow,  dnven  electrically,  by  an  electric  current 
generated  at  some  distance,  and  transmitted  to 
the  electric  motor  by  suitable  conductors. 

Plucker  Tube.— (See  Tube,  Plucker.) 

Plug. — A  piece  of  metal  in  the  shape  of  a 
plug,  provided  for  making  or  breaking  a  cir- 
cuit by  placing  in,  or  removing  from,  a  con- 
ical opening  formed  in  the  ends  of  two 
closely  approached  pieces  of  metal  which  are 


connected  with  the  circuits  to  be  made  or 
broken. 

As  the  plug  is  inserted  in  the  opening  it  bridges 
over  the  opening  and  thus  closes  the  circuit  con- 
nected with  the  separate  pieces  of  metals.  Oa 
removing  the  plug  the  circuit  is  opened  or  broken. 

Plug. — In  telegraphy,  an  inexpert  operator. 

Plug,  Double A  plug  so  constructed 

that  when  inserted  in  a  spring-jack  it  makes 
two  connections,  one  at  its  point  and  one  at 
its  shank.  (See  Spring-Jack.) 

Plug,  Fusible A  term  sometimes 

applied  to  a  safety  fuse.  (See  Plug,  Safety?) 

Ping,  Infinity — A  plug  hole  in  a  box 

of  resistance  coils,  in  which  the  two  pieces  of 
brass  it  connects  are  not  connected  by  any 
resistance  coil,  and  which,  therefore,  leaves, 
when  withdrawn,  an  open  circuit  of  an  in- 
finite resistance. 

Plug,  Safety A  wire,  bar,  plate  or 

strip  of  readily  fusible  metal,  capable  of  con- 
ducting, without  fusing,  the  current  ordinarily 
employed  on  the  circuit,  but  which  fuses,  and 
thus  breaks  the  circuit,  on  the  passage  of  an 
abnormal  current.  (See  Fuse,  Safety?) 

A  safety  plug  is  only  used  on  circuits  in  which 
the  electro-receptive  devices  are  connected  with 
the  leads  in  multiple.  In  this  case  the  fusing  of 
the  safety  plug,  and  the  consequent  opening  of  the 
circuit  with  which  it  is  connected,  does  not  affect 
the  rest  of  the  circuit.  On  series-connected  circuits 
a  different  form  of  safety  device  is  used.  (See 
Cut -Out,  Automatic,  for  Series -Connected  Elec- 
tro-Receptive Devices. ) 

Plug,  Short-Circuiting A  plug  by 

means  of  which  one  part  of  a  circuit  is  cut 
out  by  being  short-circuited. 

Plug  Switch.— (See  Switch,  Plug) 

Plug,  Wall A  plug  provided  for 

the  insertion  of  a  lamp  or  other  electro-re- 
ceptive device  in  a  wall  socket,  and  thus  con- 
necting it  with  a  lead. 

Plugging.— Completing  a  circuit  by  means 
of  plugs. 

Pings,  Grid Plugs  of  active  ma- 
terial that  fill  the  spaces  or  apertures  in  the 
lead  grid  or  plate  of  a  storage  battery. 


Plu.] 


410 


[Poi. 


The  active  material  forming  the  plugs  is  placed 
in  the  spaces  in  the  grid  while  in  the  plastic  con- 
dition. On  the  subsequent  hardening  of  this  ma- 
terial, these  grid  plugs  cannot  readily  fall  out, 
since  the  spaces  are  so  shaped  that  their  interior 
portions  are  01  greater  diameter  than  at  the  sur- 
face of  the  plates. 

Plumbago. — An  allotropic  modification  of 
carbon. 

Plumbago,  the  material  commonly  known  as 
black  lead,  is  the  same  as  graphite.  Powdered 
plumbago  is  employed  in  electrotyping  processes 
for  rendering  non-conducting  surfaces  electrically 
conducting.  For  this  purpose  powdered  plum- 
bago is  dusted  on  the  surfaces,  which  thus  acquire 
the  power  of  receiving  a  metallic  lustre  by  fric- 
tion. Stove  polishes  are  formed  of  mixtures  of 
plumbago  and  other  cheap  materials.  (See 
Graphite.) 

Strictly  speaking,  the  term  graphite  is  properly 
applied  to  such  varieties  of  plumbago  as  are  suit- 
able for  direct  use  for  writing  purposes,  as  in  lead 
pencils. 

Plumbago,  Coppered Powdered 

plumbago  coated  with  copper,  for  use  in  the 
metallization  of  objects  to  be  electro-plated. 
(See  Metallization) 

Plumbago,  Gilt Powdered  plum- 
bago whose  conducting  power  for  electricity 
has  been  increased  by  coating  it  with  metallic 
gold. 

Gilt  plumbago  is  used  for  rendering  non-con- 
ducting surfaces  electrically  conducting  and  thus 
preparing  them  for  electro-plating. 

To  prepare  gilt  plumbago,  dissolve  in  i  oo  parts 
of  sulphuric  ether  I  part  of  chloride  of  gold,  mix 
in  this  60  parts  of  powdered  plumbago,  and  ex- 
pose to  air  and  light  until  all  ether  has  volatilized. 
Then  dry  in  an  oven. 

Plumbago,  Silvered — Powdered 

plumbago  coated  with  metallic  silver  for  use 
in  the  metallization  of  objects  to  be  electro- 
plated. 

Plunge  Battery.— (See  Battery,  Plunge) 

Pneumatic  Perforator. — (See  Perforator, 
Pneumatic?)  B 

Pneumatic  Signals,  Electro—  —(See 
Signals,  Electro-Pneumatic^) 

Pockets,  Armature  —  — Spaces  pro- 
vided in  an  armature  for  the  reception  of  the 


armature  coils.  (See  Coils,  Armature,  of 
Dynamo-Electric  Machine) 

Poggendorff's  Voltaic  Cell.— (See  Cell, 
Voltaic,  Poggendorff's.} 

Point,  Carbon A  term    formerly 

applied  to  the  carbon  electrodes  used  in  the 
production  of  the  voltaic  arc. 

Point,  Indifferent A  point  in  the 

intra-polar  regions  of  a  nerve  where  the  ane- 
lectrotonic  and  kathelectrotonic  regions  meet, 
and  where  the  excitability  is  therefore  un- 
changed. 

This  is  sometimes  called  the  neutral  point. 

Point  of  Lightning  Rod.  — (See  Rod, 
Lightning,  Points  on.} 

Point  of  Origin.— (See  Origin,  Point  of.) 

Point,  Neutral  — In  electro-thera- 
peutics, a  term  sometimes  used  instead  of  in- 
different point.  (See  Point,  Indifferent) 

Point,  Nodal The  null  point  in  a 

circuit  traversed  by  electric  oscillations.  (See 
Point,  Null.) 

Point,   Null Such  a  point   on    a 

micrometer  circuit,  that  when  joined 
nected  with  the  second- 
ary circuit  of  an  in- 
duction coil,  the  sparks 
in  the  micrometer  cir- 
cuit are  either  very 
greatly  decreased  or 
are  entirely  absent. 

The  null  point  on  the 
micrometer  circuit  is  situ- 
ated  symmetrically  with 
respect  to  the  micrometer 
knobs. 

If  the  induction  coil  A, 
Fig.  440,  has  its  second- 
ary circuit  connected  as  o 
shown  with  the  microm-  Fig.  440.  Xull  Point. 
eter  circuit  at  the  point  e,  situated  at  the  centre 
of  the  micrometer  circuit,  the  point  will  be  a  null 
point,  and  the  effects  of  sparks  at  the  micrometer 
knobs,  at  M,  will  be  greatly  decreased.  Under 
the  conditions  shown  in  the  figure,  the  electrical 
oscillations  in  the  micrometer  circuit  must  be  re- 
garded as  in  the  condition  of  stationary  waves  or 
vibrations.  It  would  seem,  therefore,  that  defi- 
nite waves  or  vibrations  are  set  up  in  the  microm- 


PoL] 


411 


[Pol. 


eter  circuit,  in  the  same  way  as  are  the  vibra- 
tions produced  in  an  elastic  bar  set  in  vibration 
by  a  violin  bow,  or  by  a  blow  from  a  hammer. 

Points,  Consequent The  points  or 

places  in  an  anomalous  magnet  where  the 
consequent  poles  are  situated.  (See  Magnet, 
Anomalous.  Pole,  Anomalous?) 

Points,  Corresponding — Points 

where  the  lines  of  electrostatic  force  sur- 
rounding an  insulated  charged  conductor 
enter  the  surfaces  of  neighboring  conductors. 

Points  on  the  surface  of  a  body  placed  in 
an  electrostatic  field  where  the  lines  of  elec- 
trostatic force  enter  its  surface,  and  thus  pro- 
duce a  charge  equal  and  opposite  to  that 
of  the  surface  of  the  body  at  the  points  from 
which  they  came. 

Corresponding  points  receive,  in  accordance 
with  the  laws  of  electrostatic  induction,  charges 
equal  and  opposite  to  those  of  the  surfaces  from 
which  the  lines  of  electrostatic  force  originate. 

Points,  Electric    Action    of The 

effect  of  points  placed  on  an  insulated, 
charged  conductor,  in  slowly  discharging  the 
conductor  by  electric  convection.  (See  Con- 
vection, Electric?) 

The  cause  of  this  action  of  points  is  to  be  at- 
tributed to  the  increased  density  of  a  charge  on 
the  surface  of  a  conductor  at  the  points  and  the 
consequent  production  of  convection  streams  of 
air,  which  thus  gradually  carry  off  the  charge. 
(See  Charge,  Distribution  of.) 

Points,  Iso-Electric A  term  some- 
times used  in  electro-therapeutics  for  points 
of  equal  potential. 

Points,  Neutral,  of  Dynamo-Electric  Ma- 

chino Two  points  of  greatest  differ- 
ence of  potential,  situated  on  the  commutator 
cylinder,  at  the  opposite  ends  of  a  diameter 
thereof,  at  which  the  collecting  brushes  must 
rest  in  order  to  carry  off  the  current  quietly. 

These  are  called  the  neutral  points  because  the 
coils  that  are  short-circuited  by  the  brushes  Jie  in 
the  magnetically  neutral  points  of  the  armature. 
(See  Line,  Neutral,  of  Commutator  Cylinder.) 

Points,  Neutral,  of  Magnet  —  —Points 
approximately  midway  between  the  poles  of 
14— Vol.  1 


a  magnet.  (See  Line,  Neutral,  of  a  Magnet. 
Magnet,  Equator  of.) 

Points,  Neutral,  of  Thermo-Electric  Dia- 
gram   The  points  on  a  thermo-electric 

diagram  where  the  lines  representing  the 
thermo-electric  powers  of  any  two  metals 
cross  one  another. 

A  mean  temperature  for  any  two  metals  in 
a  thermo-electric  series,  at  which,  if  their  two 
junctions  are  slightly  over  and  slightly  under 
the  mean  temperature  (the  one  as  much 
above  as  the  other  is  below),  no  effective 
electromotive  force  is  developed.  (See  Dia- 
gram, Thermo-Electric.  Couple,  Thermo- 
Electric^ 

Points  or  Rhumbs  of  Compass.— (See 
Compass,  Points  of.) 

Polar  Region.— (See  Region,  Polar.) 

Polar  Tips.— (See  Tips,  Polar) 

Polarity,  Diainagnetic A  polar- 
ity the  reverse  of  ordinary  magnetic  polarity, 
the  existence  of  which  was  assumed  by  Fara- 
day to  explain  the  phenomena  of  diamag- 
netism.  (See  Diamagnetism.) 

Faraday  assumed  that  diamagnetic  substances, 
when  brought  into  a  magnetic  field,  acquired 
north  magnetism  in  those  parts  that  were  nearest 
the  north  pole,  instead  of  south  magnetism,  as 
with  ordinary  magnetic  substances.  The  north 
pole  thus  obtained  would,  he  thought,  explain 
the  apparent  repulsion  of  a  slender  rod  of  any  di  - 
amagnetic  material  delicately  suspended  in  a 
strong  magnetic  field,  and  cause  it  to  point  equa- 
torially,  or  with  the  lines  of  force  passing  through 
its  least  dimensions.  This  supposition  was  subse- 
quently abandoned  by  Faraday.  It  has  recently 
been  revived  by  Tyndall.  (Soe  Diamagnetism.) 

The  action  of  a  diamagnetic  body,  when  placed 
in  a  magnetic  field,  is  now  generally  ascribed  to 
the  fact  that  the  atmosphere,  by  which  such  body 
is  surrounded,  is  more  powerfully  paramagnetic 
than  the  diamagnetic  substance.  The  diamag- 
netic substance  conies  to  rest  in  an  equatorial  posi 
tion,  because  in  that  position  there  is  the  greatest 
length  of  air  in  the  path  of  the  magnetic  lines, 
which  has  a  smaller  magnetic  resistance  than  the 
diamagnetic  substance. 

Polarity,  Magnetic The  polarity 

acquired  by  a  magnetizable  substance  when 
brought  into  a  magnetic  field. 


Pol.] 


412 


[Pol. 


The  direction  of  magnetic  polarity,  acquired  by 
a  substance  when  brought  into  a  magnetic  field, 
depends  on  the  direction  in  which  the  lines  of 
magnetic  force  pass  through  it.  Where  these 
lines  enter  the  substance  a  south  pole  is  pro- 
duced, and  where  they  pass  out,  a  north  pole  is 
produced.  The  axis  of  magnetization  lies  in  the 
direction  of  the  lines  of  force  as  they  pass 
through  the  body,  and  the  intensity  of  magnetiza- 
tion depends  on  the  number  of  these  lines  of 
force  which  pass  through  the  body. 

The  cause  of  magnetic  polarity  is  not  definitely 
known.  Hughes'  hypothesis  attributes  it  to  a 
property  inherent  in  all  matter.  Ampere  at- 
tributes it  to  closed  electric  circuits  in  the  ultimate 
particles.  Whatever  its  cause,  it  is  invariably 
manifested  by  a  magnetic  field,  the  lines  of  force  of 
which  are  assumed  to  have  the  direction  already 
mentioned.  (See  Magnetism,  Hughes'1  Theory 
of.  Magnetism,  Ampere's  Theory  of.  Magnet- 
ism,  Living's  Theory  of.} 

Polarization,  Galvanic  —  —A  term 
sometimes  applied  to  the  polarization  of  a 
voltaic  cell.  (See  Cell,  Voltaic,  Polariza- 
tion of.) 

Polarization,  Internal,  of  Moist  Bodies 

A    polarization    exhibited    by    such 

moist  bodies  as  the  nerves,  muscular  fibres, 
the  juicy  parts  of  vegetables  and  animals,  or 
in  general  by  all  bodies  possessing  a  firm  struc- 
ture filled  with  a  liquid,  on  the  passage 
through  them  of  a  strong  electric  current. 

Polarization,  Magnetic  Rotary  — 
The  rotation  of  the  plane  of  polarization  of  a 
beam  of  plane-polarized  light  consequent  on 
its  passage  through  a  plate  of  glass  subjected 
to  the  stress  of  a  magnetic  field.  (See  Rota- 
tion, Magneto-Optic?) 

Polarization  of  Dielectric.— (See  Dielec- 
tric, Polarization  of.) 

Polarization  of  Electrolyte.— (See  Elec- 
trolyte, Polarization  of.) 

Polarization  of  Voltaic  Cell.— (See  Cell, 
Voltaic,  Polarization  of.) 

Polarized  Armature. — (See  Armature, 
Polarized) 

Polarized  Relay.— (See  Relay,  Polarized?) 

Polarizing  Current  —  (See  Current , 
Polarization?) 


Polarizing  Electro-Therapeutic  Current. 

—(See  Current,  Electro-Therapeutic  Polar- 
izing) 

Pole,  Analogous That  pole  of   a 

pyro-electric  substance,  like  tourmaline,  which 
acquires  a  positive  electrification  while  the 
temperature  of  the  crystal  is  rising.  (See 
Electricity,  Pyro.) 

Pole,  Anomalous A  name  some- 
times given  to  those  parts  or  poles  in  an 
anomalous  magnet  which  consist  of  two  simi- 
lar free  poles  placed  together.  (See  Magnet, 
Anomalous) 

Pole,  Antilogous  —  —That  pole  of  a 
pyro-electric  substance,  like  tourmaline,  which 
acquires  a  negative  electrification  when  the 
temperature  of  the  crystal  is  rising,  and  a 
positive  electrification  when  it  is  falling.  (See 
Electricity,  Pyro) 

Pole,  Armature  —  — (See  Armature, 
Pole) 

Pole  Changer. — A  switch  or  key  for  chang- 
ing or  reversing  the  direction  of  current  pro- 
duced by  any  electric  source,  such  as  a  bat- 
tery 

The  commutator  of  a  Ruhmkorff  coil  is  a  sim- 
ple form  of  pole  changer.  It  is,  however,  usu- 
ally called  a  commutator.  (See  Coil,  Induction. ) 

Pole-Changing  and  Interrupting  Elec- 
trode Handle.— (See  Electrode-Handle, 
Pole-Changing  and  Interrupting) 

Pole-Changing  Switch.— (See  Switch, 
Pole-  Changing) 

Pole  Climbers.— (See  Climbers,  Pole) 

Pole,  Consequent  —  — A  magnet  pole 
formed  by  two  free  north  or  two  free  south 
poles  placed  together.  (See  Magnet,  Anom- 
alous) 

Pole,  Magnetic,  Austral  —  —A  name 
formerly  employed  in  France  for  the  north- 
seeking  pole  of  a  magnet. 

That  pole  of  a  magnet  which  points  to  the 
earth's  geographical  north. 

It  will  be  observed  that  the  French  regarded  the 
magnetism  of  the  earth's  Northern  Hemisphere 


Pol.] 


413 


[Pol. 


as  north,  and  so  named  the  north-seeking  pole  of 
the  needle  the  austral  or  south  pole. 

The  north-seeking  pole  of  the  magnet  is  some- 
times called  the  boreal  or  north  pole.  (See  Pole, 
Magnetic,  Boreal.} 

Pole,  Magnetic,  Boreal  — A  name 

formerly  employed  in  France  for  the  south- 
seeking  pole  of  a  magnet,  as  distinguished 
from  the  austral  or  north-seeking  pole. 

That  pole  6f  a  magnet  which  points  to- 
ward the  geographical  south. 

If  the  earth's  magnetic  pole  in  the  Northern 
Hemisphere  be  of  north  magnetism,  then  the  pole 
of  a  needle  that  points  to  it  must  be  of  the  oppo- 
site polarity,  or  of  south  magnetism.  In  this 
country  we  call  the  end  which  points  to  the  north, 
the  north-seeking  pole  or  marked  pole.  In 
France  the  end  which  points  to  the  north  was 
formerly  called  the  austral  pole.  Austral  means 
south  pole.  (See  Pole,  Magnetic,  Austral.} 

Pole,  Magnetic,  False A  term  pro- 
posed by  Mascart  and  Joubert  to  designate 
the  place  or  places  on  the  earth  which  appar- 
ently act  as  magnetic  poles,  in  addition  to 
the  two  true  magnetic  poles,  near  the  earth's 
geographical  poles. 

According  to  these  authorities,  the  earth  pos- 
sesses two  magnetic  poles  only,  viz.,  a  negative 
polte  in  the  Northern  Hemisphere  and  a  positive 
pole  in  the  Southern  Hemisphere.  The  addi- 
tional poles  are  called  by  them  the  false  magnetic 
poles. 

Pole,  Magnetic,  Free A  pole  in  a 

piece  of  iron,  or  other  paramagnetic  sub- 
stance, which  acts  as  if  it  existed  as  one  mag- 
netic pole  only. 

A  free  magnetic  pole  has  in  reality  no  physical 
existence.  The  conception,  however,  is  of  use  in 
describing  certain  magnetic  phenomena.  If  the 
bar  of  iron  be  so  long  as  to  practically  place  one 
pole  beyond  the  sensible  action  of  the  other,  either 
pole  may  be  regarded  as  a  free  pole. 

Pole,  Magnetic,  Marked  —  — That  pole 
of  a  magnetic  needle  which  points  approxi- 
mately to  the  earth's  geographical  north. 
(Obsolete.) 

The  north-seeking  pole  of  a  magnetic  needle. 

Pole,  Magnetic,  North  -  —That  pole 
of  a  magnetic  needle  which  points  approxi- 
mately to  the  earth's  geographical  north. 


The    north-seeking    pole    of    a  magnetic 
needle. 
Pole,  Magnetic,  North-Seeking 

That  pole  of  a  magnetic  needle  which  points 
approximately  towards  the  earth's  geographi- 
cal north. 

Pole,  Magnetic,  Salient A  term 

sometimes  applied  to  the  single  poles  at  the  ex- 
tremities of  an  anomalous  magnet,  in  order  to 
distinguish  them  from  the  double  or  consequent 
pole  formed  by  the  juxtaposition  of  two  simi- 
lar magnetic  poles.  (See  Magnet,  Anoma- 
lous^) 

Pole,  Magnetic,  South  —  — That  pole 
of  a  magnetic  needle  which  points  approxi- 
mately towards  the  earth's  geographical  south. 

The  south-seeking  pole  of  a  magnetic 
needle. 

Pole,  Magnetic,  South-Seeking  - 

That  pole  of  a  magnetic  needle  which  points 
approximately  toward  the  geographical  south. 

Pole,  Negative  -  —That  pole  of  an 
electric  source  through  which  the  current  is 
assumed  to  enter  or  flow  back  into  the  source 
after  having  passed  through  the  circuit  ex- 
ternal to  the  source. 

Pole-Pieces  of  Dynamo-Electric  Machine. 

— (See  Pieces,  Pole,  of  Dynamo-Electric 
Machine?) 

Pole  Platform.— (See  Platform,  Pole} 

Pole,  Positive—  —That  pole  of  an 
electric  source  out  of  which  the  electric  cur- 
rent is  assumed  to  flow. 

Pole  Steps. — Short  rods  or  bars  shaped  so 
as  to  be  readily  inserted  in  holes  near  the 
base  of  telegraph  or  electric  light  poles,  so  as 
to  serve  as  steps  to  enable  a  lineman  to  reach 
the  permanently  placed  steps. 

Permanent  steps  are  placed  only  at  some  dis- 
tance from  the  ground,  in  order  to  prevent  the 
ready  climbing  of  the  poles  by  unauthorized 
persons. 

Pole,  Telegraphic A  wooden  or  iron 

upright  on  which  telegraphic  or  other  wires 
are  hung. 

Wooden  poles  are  generally  round. 


Pol.] 


414 


[Pol. 


The  terminal  pole,  or  the  last  pole  at  each  end 
of  the  line,  or  where  the  wires  bend  at  an  angle 
of  nearly  90  degrees,  is  made  larger  than  usual 
and  is  often  cut  square. 

The  holes  for  the  poles  must  be  dug  in  the  true 
line  of  the  wires,  and  not  at  an  angle  to  such  line. 
As  little  ground  should  be  disturbed  in  the  dig- 
ging as  possible.  Earth  borers,  or  modifications 
of  the  ordinary  ship  auger,  are  generally  em- 
ployed for  this  purpose.  When  the  pole  is  placed 
in  position  the  ground  should  be  rammed  or 
punned  around  the  pole. 

In  setting  the  pole,  it  is  generally  buried  at  least 
5  feet  in  the  ground.  In  England  the  poles  are 
planted  to  a  depth  of  about  one-fifth  of  their 
length.  In  embankments  and  loose  ground,  they 
are  planted  deeper  than  in  more  solid  earth.  On 
curves,  the  poles  should  be  inclined  a  little  so  as 
to  lean  back  against  the  lateral  strain  of  the  wire, 
since  by  the  time  the  ground  has  completely  set, 
the  strain  of  the  wire  will  have  pulled  them  into 
an  erect  position. 

Care  must  be  taken  to  so  plant  the  poles  on 
that  side  of  a  road  or  railway  that  the  prevailing 
winds  will  blow  them  off  the  roadbed,  should  it 
overturn  them.  As  to  location,  the  top  of  steep 
cuttings  is  preferable  to  the  slope.  In  all  exposed 
positions,  it  is  preferable  to  strengthen  the  poles 
by  stays  attached  to  both  sides. 

Where  the  number  of  wires  is  unusually  large, 
heavy  timber,  or  in  case  of  its  absence,  double 


Fig.44'-     Telegraphic 
Brackets. 


Fig.  442.     Telegraphic 
Arms* 


poles  suitably  braced  together,  must  be  employed. 
In  long  lines  the  poles  should  all  be  numbered  in 
order  to  afford  ease  of  reference  in  case  of  repair. 

When,  even  with  the  best  punning,  and  other 
precautions,  the  pole  is  judged  to  be  unable  to 
resist  the  strain  on  it,  stays  and  struts  are  em- 
ployed. A  stay  is  used  when  it  is  desired  to  re- 
move the  pull  or  tension  from  the  pole  ;  a  strut, 
when  it  is  desired  to  remove  the  thrust  or  pressure. 

The  arms  or  brackets,  or  the  cross-pieces  that 


support  the  insulators,  should  all  be  placed  on 
the  same  side  of  the  poles.  Some  common  forms 
of  brackets  are  shown  in  Fig.  441,  and  of  tele- 
graphic arms  in  Fig.  442. 

Saddle  brackets  should  be  placed  on  alternate 
sides  of  the  poles.  When  the  strain  on  an  insula- 
tor is  too  great,  on  account  of  the  wire  going  off 
at  a  sharp  angle,  a  shackle  is  used.  This  is  a 
special  form  of  insulator  which  confines  the  strain 
to  one  spot. 


-  443-    Double  Shackles. 

A  form  of  double  shackle  is  shown  in  Fig. 
443.  The  wire  passes  around  the  recess  at  B, 
between  the  two  insulators. 

On  curves,  or  in  any  situation  where  there  is  a 
probability,  in  case  of  the  breaking  of  an  insula- 

"6 


Fig.  444.    Hook  Guard. 

tor,  of  a  wire  getting  into  a  dangerous  position, 
guards  should  be  employed. 

Guards  are  of  two  kinds,  viz.:  hoop  guards 
and  hook  guards.  A  form  of  hook  guard  is 
shown  in  Fig.  444. 

When  wooden  poles  are  employed  various  pre- 
servative methods  are  adopted  to  protect  the 
wood  from  decay,  which  is  very  apt  to  occur, 
especially  where  the  pole  enters  the  ground. 
Some  of  these  forms  are  as  follows,  viz.  : 

( I . )  Charring  and  tarring  the  butt  end  of  the 
pole  where  it  enters  the  ground,  so  as  to  expel 
the  sap  and  destroy  injurious  plant  or  animal 
germs. 


Pol.] 


415 


[For. 


The  charred  end  is  then  cleansed  and  dipped 
in  a  mixture  of  tar  and  slaked  lime. 

(2.)  Burnetizing,  or  the  introduction  of 
chloride  of  zinc  into  the  pores  of  the  wood,  by 
placing  the  poles  in  an  open  tank  filled  with  a 
solution  of  this  salt. 

(3.)  Kyanizing,  or  the  similar  introduction  of 
corrosive  sublimate,  or  mercuric  chloride. 

(4.)  Boucher izing,  or  the  injection  of  a  solution 
of  copper  sulphate  into  the  pores  of  the  wood. 

(S-)  Creosoting,  or  the  application  of  creosote 
to  well  seasoned  poles. 

Pole,  Telegraphic,  Punning  of  — 

Ramming  or  packing  the  earth  around  the 
base  of  a  telegraph  pole  for  the  purpose  of 
more  securely  fixing  it  in  the  ground. 

Pole,  Telegraphic,  Terminal The 

pole  at  either  end  of  a  telegraphic  line. 

As  the  first  or  last  pole  in  a  telegraphic  line  is 
not  supported  on  opposite  sides  by  the  line  wires, 
it  is  generally  made  stouter  than  the  intermediate 
poles,  and  greater  care  is  taken  to  fix  it  securely 
in  the  ground. 

Pole,  Testing A  term  sometimes 

employed  in  electro-therapeutics  for  the  in- 
different pole  or  electrode.  (See  Electrode, 
Indifferent) 

Pole,  Trolley The  pole  which  sup- 
ports the  trolley  bearing  and  rests  on  the 
socket  in  the  trolley  base  frame  in  an  over- 
head wire  electric  railway  system. 

Pole,  Unit,  Magnetic A  magnetic 

pole  of  such  a  strength  that  it  would  act  with 
a  unit  or  dyne  of  force  on  another  unit  pole  at 
a  distance  of  one  centimetre. 

Poles,  Consequent The  name  given 

10  single  magnetic  poles  formed  by  two  free 
N.  poles  or  two  free  S.  poles  placed  together. 
(See  Magnet,  Anomalous) 

Poles,  Idle Poles  or  electrodes  in 

Crookes'  tubes,  between  which  discharges  are 
not  taking  place. 

The  idle  poles  have  no  connection  with  the  in- 
duction coils  or  other  sources  from  which  the  elec- 
tric discharges  are  obtained.  These  poles  are  pro- 
vided for  attaching  galvanometer  wires,  etc.,  in  the 
study  of  the  Edison  effect,  or  for  the  study  of  the 


electrical  condition  of  the  dark  space  and  other 
regions  of  the  atmosphere  of  the  tube. 

Poles,  Magnetic The  two  points 

where  the  lines  of  magnetic  force  pass  from 
the  iron  into  the  air,  and  from  the  air  into 
the  iron. 

The  two  points  in  a  magnet  where  the 
magnetic  force  appears  to  be  concentrated. 

In  reality  the  magnetic  force  is  most  concen- 
trated at  the  neutral  points  of  a  m  agnet,  through 
which  all  the  lines  of  force  pass. 

All  magnets  possess  at  least  two  poles,  one 
positive  or  north,  and  the  other  negative  or  south. 

The  lines  of  magnetic  force  are  assumed  to 
come  out  of  a  magnet  at  its  north  pole,  and  to 
enter  it  at  its  south  pole. 

Poles,  Magnetic,  of  Verticity  —  —(See 
Verticity,  Poles  of,  Magnetic) 

Poles  of  Condenser. — The  terminals  of  a 
condenser.  (See  Condenser) 

Poles  of  Magnetic  Intensity.— (See  In- 
tensity, Magnetic,  Pole  of) 

Polyphase       Current.— (See       Current, 
Multi-Phase) 
Polyphotal  Arc  Light  Regulators.— (See 

Regulator,  Polyphotal  Arc-Light) 

Popgun,  Electro-Magnetic A  mag- 
netizing coil,  provided  with  a  tubular  space 
for  the  insertion  of  a  core,  much  shorter  than 
the  length  of  the  coil,  which,  when  the  ener- 
gizing current  is  passed  through  the  coil, 
is  thrown  violently  out  from  the  coil. 

The  movement  and  consequent  expulsion  of  the 
core  is  due  to  the  action  of  the  lines  of  magnetic 
force  which  complete  their  circuit  through  the 
core. 

Porcelain. — A  variety  of  insulating  ma- 
terial. 

A  translucent  variety  of  earthenware. 
Porous  Cell.— (See  Cell,  Porous) 
Porous  Cup.— (See  Cup,  Porous) 
Porous     Insulation. — (See     Insulation, 
Porous) 

Porous  Jar. — (See  far,  Porous.) 
Porret's  Phenomena. — (See  Phenomena, 
Porret) 


For.] 


416 


FPos. 


Portatiye  Power.— (See  Power,  Porta- 
tive^ 

Portelectric. — An  electric  carrier. 

A  system  of  electric  transportation  by 
means  of  the  successive  attractions  of  a  num- 
ber of  hollow  helices  of  insulated  wire  on  a 
hollow  solenoidal  iron  car. 

The  solenoidal  car  forms  the  movable  core  of  the 
helical  coils.  As  it  moves  through  these  coils  it 
automatically  closes  the  circuit  of  an  electric  cur- 
rent through  the  coils  in  advance  of  it  and  opens 
the  circuit  of  the  coils  in  its  rear.  In  this  way  the 
solenoidal  car  advances  in  a  line  coincident  with 
the  axis  of  the  helical  coils,  being  virtually  sucked 
through  them  by  their  magnetic  attractions.  This 
system  of  electric  propulsion  is  unique  in  systems 
of  electric  traction.  The  motor  becomes  a  mere 
mass  of  iron  or  other  paramagnetic  material. 
The  system  is  suitable  for  the  carriage  of  mail  or 
other  comparatively  light  articles  at  a  high  speed. 

In  an  experimental  plant  at  Dorchester,  Mass., 
a  track  of  2,784  feet  in  length  was  laid  in  the  ap- 
proximate form  of  an  oval.  The  track  was 
formed  by  an  upper  and  lower  rail  of  steel,  suit- 
ably supported  by  stringers. 

The  car,  which  forms  the  movable  core  of  the 
solenoidal  coils,  was  of  wrought  iron,  and  was 
cylindrical  in  shape,  with  conical  ends.  It  was 


placed  on  the  top  of  the  carrier  and  connected  the 
several  helices    successively    with    the    electric 


Fig.  4*5.    Portelectric  Track. 

12  feet  in  length  and  10  inches  in  diameter,  and 
weighed  about  500  pounds.  It  would  carry  about 
10,000  letters.  It  had  two  flanged  wheels  above 
and  two  below. 

The  solenoidal  coils,  by  the  attractive  power  of 
which  the  core  was  moved,  embraced  the  track 
and  the  movable  core  or  carrier.  They  were 
fixed  along  the  track  at  intervals  of  6  feet  from 
centre  to  centre.  Each  coil  was  formed  of  630 
turns  of  No.  14  copper  wire.  The  upper  track 
rail  is  divided  into  sections  which  form  conductors 
for  the  driving  current.  A  central  wheel  was 


Fig.  446.    Portelectric  Cay. 


source  as  the  carrier  was  drawn  forward.  A 
speed  of  about  34  miles  an  hour  was  reached. 

A  section  of  the  track  is  shown  in  Fig.  445,  and 
the  shape  and  general  structure  of  the  carrier  in 
Fig.  446. 

Portrait,  Electric  —  —A  portrait 
formed  on  paper  by  the  electric  volatilization 
of  gold  or  other  metal. 

An  electric  portrait  is  obtained  by  cutting  on 
a  thin  card  a  portrait  in  the  form  of  a  stencil.  A 
sheet  of  gold  leaf  is  then  placed  on  one  side  of  the 


Fig.  447.    Electric  Portrait. 

paper  stencil,  and  a  sheet  of  paper  on  the  othet 
side  ;  sheets  of  tin -foil  are  then  placed  on  the  out, 
side,  as  shown  in  Fig.  447,  and  the  whole  firmly 
pressed  together.  If,  now,  a  disruptive  discharge 
is  passed  through  from  one  sheet  of  tin-foil  to  the 
other,  the  gold  leaf  is  volatilized,  and  a  purplish 
stain  is  left  on  the  paper  of  the  outlines  of  the 
stenciled  card,  thus  forming  an  electric  portrait. 

Position,  Energy  of A  term  used 

for  stored  energy,  or  potential  energy.  (See 
Energy,  Potential?) 

Positive  Direction  of  a  Simple-Harmonic 
Motion. — (See  Motion,  Simple-Harmonic, 
Positive  Direction  o^ 


Fos.] 


417 


[Pot. 


Positive  Direction  of  Lines  of  Magnetic 
Force. — (See  Force,  Magnetic,  Lines  of, 
Positive  Direction  of.) 

Positive  Direction  of  the  Electrical  Con- 
vection of  Heat. — (See  Direction,  Positive, 
»f  Electrical  Convection  of  Heat?) 

Positive  Direction  Round  a  Circnit. 
—(See  Direction,  Positive,  Round  a  Cir- 
cuit) 

Positive  Direction  Through  a  Circnit 
— (See  Direction,  Positive,  Through  a  Cir- 
cuit) 

Positive  Electricity. — (See  Electricity, 
Positive) 

Positive  Electrode.  — (See  Electrode, 
Positive) 

Positive  Feeders.— (See  Feeders,  Posi- 
tive) 

Positive-Omnibus  Bars.— (See  Bars,  Posi- 
tive Omnibus) 

Positive  Phase  of  Electrotonns.— (See 
Electrotonus,  Positive  Phase  of) 

Positive  Plate  of  Storage  Battery.— (See 
Plate,  Positive,  of  Storage  Battery) 

Positive  Plate  of  Voltaic  Cell.— (See 
Plate,  Positive,  of  Voltaic  Cell) 

Positive  Pole.— (See  Pole,  Positive) 

Positive  Potential.— (See  Potential,  Posi- 
tive) 

Positive  Side  of  Circuit— (See  Circuit, 
Positive  Side  of) 

Positively.— In  a  positive  manner. 

Positively  Excited. — Excited  or  charged 
with  positive  electricity.  (See  Electricity, 
Positive) 

Post,  Binding  — A  device  for  con- 
necting the  terminal  of  an  electric  source 
with  the  terminal  of  an  electro-receptive  de- 
vice, or  for  connecting  different  parts  of  an 
electric  apparatus  with  one  another. 

The  conducting  or  circuit  wire  is  either  intro- 
duced in  the  opening  a,  or  c',  Fig.  448,  and 
clamped  by  the  screw  b,  or  b',  or  is  placed  in 
the  space  d,  d,  and  kept  in  place  by  means  of  a 
thumbscrew.  Sometimes  two  openings  are 
provided  at  c,  and  c',  for  the  purpose  of  connect- 
ing two  wires  together. 


A  device  for  coupling  or  connecting  the  ends 
of  two  wires  to  each  other.  It  is  then  called  a 
coupler.  (See  Couple,  Voltaic) 


Fig.  448.    Binding  Posts. 

Pot,  Porous  —  —The  porous  jar  or  cell 
of  a  voltaic  cell.  (See  Cell,  Porous) 

Potential,  Alternating—  —A  poten- 
tial, the  sign  or  direction  of  which  is  alter- 
nately changing  from  positive  to  negative. 

An  alternating  potential  may  be  obtained  either 
in  the  case  of  an  electrostatic  field,  or  in  that 
of  a  magnetic  field. 

Potential,  Alternating  Electrostatic 

— The  potential  of  a  charge  that  is  under- 
going rapid  alternations. 

Potential,  Alternating,  Magnetic 

The  difference  of  magnetic  potential  pro- 
duced by  alternating  electric  currents. 

Potential,  Constant  —  —A  potential 
which  remains  constant  under  all  conditions. 

A  machine  or  other  electric  source  is  said  to 
have  a  constant  potential  when  it  is  capable, 
while  in  operation,  of  maintaining  a  constant 
difference  of  electric  pressure  between  its  two 
terminals  on  changes  of  load.  (See  Circuit, 
Constant-Potential. ) 

Potential,  Difference  of A  term 

employed  to  denote  that  portion  of  the 
electromotive  force  which  exists  between 
any  two  points  in  a  circuit. 

The  difference  of  potential  at  the  poles  of  any 
electric  source,  such  as  a  battery  or  dynamo,  is 
that  portion  of  the  total  electromotive  force 
which  is  available,  and  is  equal  to  the  total 
electromotive  force,  less  what  is  lost  in  the 
source. 

Some  difference  of  opinion  exists  as  to  the  exact 
meaning  that  is  attached  to  the  phrase  difference 
of  potential. 

A  positively  electrified  body  is  said  to  have  a 
higher  electric  potential  than  the  earth,  whose 
potential  is  taken  as  zero. 


Pot] 


418 


[Pot 


Potential,  Difference  of,  Methods  of 
Measuring Methods  employed  for  de- 
termining differences  of  potential. 

These  methods  are  as  follows: 

(I.)  By  the  Method  of  Weighing,  that  is,  by 
obtaining  the  weight  required  to  overcome  the 
attraction  between  two  oppositely  charged  plates, 
or  oppositely  energized  coils;  or  by  measuring 
the  repulsion  between  similarly  charged  surfaces, 
or  similarly  energized  coils. 

(2.)  By  the  Use  of  Electrometers,  or  apparatus 
designed  for  measuring  differences  of  potential. 
(See  Electrometers. ) 

(3.)  By  the  Use  of  Galvanometers. 

Differences  of  potential,  in  the  case  of  currents, 
may  be  determined  from  the  quantity  of  electri- 
city which  flows  per  second  through  a  given 
circuit,  that  is,  by  the  number  of  amperes,  just 
as  the  pressure  of  water  at  any  point  in  the  side 
of  a  containing  vessel  can  be  determined  by  the 
quantity  of  water  that  flows  per  second.  Differ- 
ence of  potential  in  the  case  of  currents,  there- 
fore, may  be  measured  by  any  galvanometer 
which  measures  the  current  directly  in  amperes, 
provided  the  resistance  of  the  circuit  is  known. 

Potential,  Drop  of A  term  some- 
times used  instead  of  fall  of  potential.  (See 
Potential,  Fall  of.) 

Potential,  Electric The  power  of 

doing  electric  work. 

Electric  level. 

Electric  potential  can  be  best  understood  by 
comparison  with  the  case  of  a  liquid  such  as 
water. 

The  ability  of  a  water  supply  or  source  to  do 
work  depends: 

(l.)  On  the  quantity  of  water. 

(2. )  On  the  level  of  the  water,  as  compared  with 
some  other  level ;  or,  in  other  words,  on  the  dif. 
ference  between  the  two  levels, 

In  z  like  manner  the  ability  of  electricity  to  do 
work  depends: 

(i.)  On  the  quantity  of  electricity. 

(2.)  On  the  electric  potential  at  the  place  where 
the  electricity  is  produced,  as  compared  with  that 
at  some  other  place;  or,  in  other  words,  on  the 
difference  of  potential. 

In  the  case  of  water  flowing  through  a  pipe, 
when  its  flow  has  been  fully  established,  the  quan- 
tity which  passes  in  a  given  time  is  the  same  at 
any  cross-section  of  the  pipe. 


In  the  case  of  electricity,  the  quantity  of  elec- 
tricity flowing  through  any  conductor,  or  part  of 
a  circuit,  is  the  same  at  any  cross-section.  A  gal- 
vanometer introduced  into  a  break  in  any  part  of 
the  conductor  would  show  the  same  strength  of 
current. 

But,  though  the  quantity  of  water  which  passes 
is  the  same  at  any  cross-section  of  a  pipe,  the 
pressure  per  square  inch  is  not  the  same,  even  in 
the  case  of  a  horizontal  pipe  of  the  same  diameter 
throughout,  but  becomes  less,  or  suffers  a  loss  of 
head,  or  difference  of  pressure,  at  any  two  points 
along  the  pipe.  This  difference  of  pressure  causes 
the  flow  of  water  between  these  two  points  against 
the  resistance  of  the  pipe. 

So,  too,  in  the  case  of  a  conductor  carrying  aa 
electric  current,  when  the  full  current  strengtk 
has  been  established,  the  quantity  of  electricity 
that  passes  is  the  same  at  all  cross-sections. 


Fig.  449-    Hydraulic  Gradient. 

The  electric  pressure  or  potential,  however, 
is  by  no  means  the  same  at  all  points  in  the 
conductor,  but  suffers  a  loss  of  electric  head  or 
level,  in  the  direction  in  which  the  electricity  is 
flowing.  It  is  this  electric  head  or  level,  or  dif- 
ference of  electric  potential,  that  causes  the  elec- 
tricity to  flow  against  the  resistance  of  the  con 
ductor. 

These  analogies  can  be  best  shown  by  the  fol- 
lowing illustration: 

In  Fig.  449,  a  reservoir,  or  source  of  water,  at 
C,  communicates  with  the  horizontal  pipe  A  B, 
furnished  with  open  vertical  tubes  at  a,  b,  c,  d,  e, 
f,  g,  and  B.  If  the  outlet  at  B,  is  closed,  the  level 
of  the  water  in  the  communicating  vessels  is  the 
same  as  at  the  source;  but  if  the  liquid  escape 
freely  from  B,  the  level  of  the  water  in  the  branch 
pipes  will  be  found  on  the  inclined  dotted  line,  or 
at  a',  b',  c',  d',  e',  f,  g',  which  may  be  called 
the  hydraulic  gradient. 

The  pressure  per  square  inch,  at  any  cross  sec 
tion  of  the  horizontal  pipe,  which  is  measured  by 
the  height  of  the  liquid  in  the  vertical  pipe  at  that 
point,  decreases  in  the  direction  in  which  the  liquid 
is  flowing.  The  force  that  urges  the  liquid 


Pot] 


419 


I  Pot. 


through  the  pipe  between  any  two  points,  may 
be  called  the  liquid-motive  force  (Fleming)  and  is 
measured  by  the  difference  of  pressure  between 
these  points. 

In  Fig.  450,  the  dynamo-electric  machine  at  D, 
has  its  negative  pole  grounded,  and  its  positive 
pole  connected  to  a  long  lead,  A  B,  the  positive 
pole  of  which  is  also  grounded.  A  fall of poten- 
tial^ represented  by  the  inclined  dotted  line, 
occurs  between  A  and  B,  in  the  direction  in  which 
the  electricity  is  flowing. 


Fig-.  4  jo.     Fall  of  Electric  Potential. 

The  dynamo-electric  machine  may  be  regarded 
as  a  pump  that  is  raising  the  electricity  from  a 
lower  to  a  higher  level,  and  passing  it  through 
the  lead  A  B.  The  electric  pressure  or  potential 
producing  the  flow  is  greatest  near  the  dynamo  and 
least  at  the  further  end,  the  differences  at  the 
points  a,  b,  c,  d,  e,  f,  and  g,  being  represented  by 
the  vertical  lines  a  a',  bb',  c  c',  d  d',  ee',  f  f,  and 

gg'- 

The  electricity  flows  between  any  two  points  as 
a  and  b,  in  the  conductor  A  B,  in  virtue  of  the 
difference  of  electric  pressure  or  potential  be- 
tween these  two  parts,  or  the  difference  between 
a  a'  and  b  b'. 

Differences  of  potential  must  be  distinguished 
from  differences  in  electric  charge,  or  electrostatic 
density.  If  two  conductors  at  different  potentials 
are  connected  by  a  conductor,  a  current  will  flow 
through  this  conductor.  When  their  potential  is 
the  same,  no  current  flows.  The  density  of  a 
charge  is  the  quantity  of  electricity  per  unit  of 
area. 

The  electric  potential  is  the  same  at  all  points 
of  an  insulated  charged  conductor;  the  density  is 
different  at  different  points,  except  in  the  case  of 
a  sphere.  The  potential,  however,  is  the  same, 
since  no  current  flows,  or  the  charge  does  not  re- 
distribute itself.  The  density  on  an  insulated, 
isolated  sphere,  is  uniform  over  all  parts  of  the 
surface,  and  its  potential  is  the  same  at  all  points. 
If  now  the  sphere  be  approached  to  another  body, 
its  density  will  vary  at  different  parts  of  its  sur- 


face, and  while  the  charge  ic  redistributing  itself 
so  as  to  produce  these  differences  in  density  the 
potential  will  vary.  As  soon,  however,  as  this 
redistribution  is  effected  and  no  further  current 
exists,  the  potential  is  the  same  over  all  points, 
though  the  density  differs  at  different  points. 

An  electric  source  not  only  produces  but  also 
maintains  a  difference  of  potential.  In  the  case 
of  the  flow  of  liquid  in  a  pipe,  if  a  continuous 
current  of  the  liquid  be  maintained  from  the 
higher  level  in  the  reservoir  to  a  lower  level,  as, 
for  example,  by  means  of  a  pump,  it  must  flow 
through  the  pump  to  the  reservoir,  from  the  lower 
level  towards  the  higher  level.  In  case  of  an 
electric  source,  since  the  thing  called  electricity 
flows  through  a  closed  circuit,  if  its  direction  of 
flow  in  that  part  of  the  circuit  external  to  the 
source — *.  e. ,  in  the  external  or  useful  current — 
be  from  a  higher  to  a  lower  level,  then  its  flow 
through  the  remainder  of  the  circuit — i.  e., 
through  the  source — must  be  from  the  lower  to  the 
higher  level.  Since,  however,  the  electrical  po- 
tential of  a  body  represents  the  work  the  elec- 
tricity is  capable  of  doing,  the  work  done  by  the 
electricity  may  be  regarded  as  being  that  done 
when  it  passes  from  the  higher  to  the  lower  level. 

Potential,      Electrostatic    —The 

power  of  doing  work  possessed  by  a  unit 
quantity  of  positive  electricity  charged  or  re- 
siding on  an  insulated  body. 

Potential,   Electrostatic,    Difference  of 

Difference  of  potential  of  an  electric 

charge.  (See  Potential,  Difference  of. 
Electrostatics) 

Potential  Energy.— (See  Energy,  Poten- 
tial) 

Potential,  Fall  of A  decrease  of 

potential  in  the  direction  in  which  an  elec- 
tric current  is  flowing,  proportional  to  the  re- 
sistance when  the  current  is  constant.  (See 
Potential,  Electric?) 

Potential  Galvanometer. — (See  Galva- 
nometer, Potential) 

Potential  Indicator.— (See  Indicator, 
Potential) 

Potential,  Magnetic The  amount 

of  work  required  to  bring  up  a  unit  north- 
seeking  magnetic  pole  from  an  infinite  dis- 
tance to  a  given  point  in  a  magnetic  field. 


Pot.] 


420 


[Pow. 


Potential    of    Conductor,    Methods    of 

Varying (See  Conductor,  Potential 

of,  Methods  of  Varying?) 

Potential  of  Conductors. — (See  Conduc- 
tor, Potential  of.) 

Potential,  Negative That  potential 

in  the  circuit  external  to  the  source  towards 
which  the  electric  current  flows. 

Generally  the  lower  potential,  or  lower 
level. 

Potential,  Positive  —  —That  potential 
in  the  circuit  external  to  the  source,  from 
which  the  electric  current  flows. 

The  higher  potential  or  higher  level. 

Potential,  Uniform  -  —A  potential 
that  does  not  vary. 

A  constant  potential.  (See  Potential,  Con- 
stant.) 

An  electric  source  is  said  to  generate  a  uniform 
potential  when  it  maintains  a  constant  difference 
of  potential  at  its  terminals. 

Potential,  Unit  Difference  of  - 
Such  a  difference  of  potential  between  two 
points  that  requires  the  expenditure  of  one 
erg  of  work  to  bring  a  unit  of  positive  elec- 
tricity from  one  of  these  points  to  the  other, 
against  the  electric  force.  (See  Erg?) 

The  practical  unit  of  difference  of  potential  is 
the  volt.  (See  Volt.) 

Potential,  Zero An  arbitrary  level 

from  which  electric  potentials  are  measured. 

As  we  measure  the  heights  of  mountains  from 
the  arbitrary  mean  level  of  the  sea,  so  we  measure 
electric  levels  from  the  arbitrary  level  of  the  po- 
tential of  the  earth. 

Potentiometer. — An  apparatus  for  the 
galvanometric  measurement  of  electromotive 
forces,  or  differences  of  potential,  by  a  zero 
method.  (See  Method,  Null  or  Zero.) 

In  the  potentiometer  the  difference  of  potential 
to  be  measured  is  balanced  or  opposed  by  a 
known  difference  of  potential,  and  the  equality 
of  the  balance  is  determined  by  the  failure  of  one 
or  more  galvanometers,  placed  in  shunt  circuits, 
to  show  any  movement  of  their  needles. 

The  principle  of  operation  of  the  potentiometer 
will  be  understood  from  an  inspection  of  Fig.  45 1 . 
A  secondary  battery  S,  has  its  terminals  con- 


nected to  the  ends  of  a  uniform  wire  A  B,  of  high 
resistance  called  the  potentiometer  wire.  There 
will,  therefore,  occur  a  regular  drop  or  fall  of  po- 
tential along  this  wire,  which,  since  the  wire  is 
uniform,  will  be  equal  per  unit  of  length.  This 
drop  of  potential  can  be  shown  by  connecting  the 
terminals  of  a  delicate  galvanometer,  generally  of 
high  resistance,  to  different  parts  of  the  wire, 
when  the  deflection  of  the  needle  will  be  propor- 

S 


Fig.  {jr.     Potentiometer. 

tional  to  the  drop  of  potential  between  the  tw» 
points  of  the  wire  touched.  If,  now,  the  terminals 
of  a  standard  cell  be  inserted  in  the  circuit  of 
the  galvanometer,  so  as  to  oppose  the  current 
taken  from  the  potentiometer  wire,  and  the  con- 
tacts of  the  potentiometer  wire  be  slid  along  the 
wire  until  no  deflection  of  the  galvanometer  needle 
is  produced,  the  drop  of  potential  between  these 
two  points  on  the  wire  will  be  equal  to  the  differ- 
ence of  potential  of  the  standard  cell.  (See  Cell, 
Voltaic,  Standard.) 

Suppose,  now,  it  be  desired  to  measure  the  dif- 
ference of  potential  between  two  points  a  and  b, 
on  the  wire  C,  through  which  a  current  is  flow- 
ing. Connect  the  points  b  and  d,  and  a  and  c,' 
as  shown,  with  the  delicate  high  resistance  gal- 
vanometer G,  in  either  of  them.  Now  slide  c, 
towards  d,  until  the  needle  of  G,  shows  no  deflec- 
tion. The  potential  between  a  and  b,  is  then 
equal  to  that  between  c  and  d. 

Potentiometer  Wire.— (See  Wire,  Po- 
tentiometer?) 

Power. — Rate  of  doing  work. 

Mechanical  power  is  generally  measured  in 
horse  power,  which  is  equal  to  work  done  at  the 
rate  of  550  foot-pounds  per  second.  • 

The  C.  G.  S.  unit  of  power  is  one  erg  per 
second. 

The  practical  unit  of  power  is  the  watt,  or 
10,000,000  ergs  per  second.  The  kilowatt  is 
even  more  frequently  used  as  the  unit  of  power 
than  the  watt.  (See  Power,  Unit  of.) 

Power,  Absorptive The  property 


Pow.] 


421 


[Pow. 


possessed  by  many  solid  bodies  of  taking  in 
and  condensing  gases  within  their  pores. 

Carbon  possesses  marked  absorptive  powers. 
The  absorption  of  gases  in  this  manner  by  solid 
bodies  is  known  technically  as  the  occlusion  of 
gases.  (See  Gas,  Occlusion  of.) 

One  volume  of  charcoal,  at  ordinary  tempera- 
tures and  pressures,  absorbs  of 

Ammonia 90    volumes 

Hydrochloric  acid 85  " 

Sulphur  dioxide  65  " 

Hydrogen  sulphide 55  " 

Nitrogen  monoxide 40  " 

Carbonic  acid  gas 35  " 

Ethylene       35 

Carbon  monoxide 9-42      " 

Oxygen 9.25      " 

Nitrogen 6.50      " 

Hydrogen 1.25      " 

— (Satissure.) 

Power,  Candle An  intensity  of 

light  emitted  from  a  luminous  body  equal  to 
the  light  produced  by  a  standard  candle. 
(See  Candle,  Standard.) 

The  light-giving  power  of  one  standard 
candle. 

Power,  Candle,  Nominal A  term 

sometimes  applied  to  the  candle-power  taken 
in  a  certain  favorable  direction. 

This  term  is  generally  used  in  arc  lighting. 
In  the  ordinary  arc  lamp  the  greatest  amount  of 
light  is  emitted  at  a  particular  point,  viz.,  from 
the  crater  in  the  upper  or  positive  carbon.  (See 
Arc,  Voltaic.) 

Power,  Candle,  Rated A  term 

sometimes  used  for  nominal  candle-power. 

Power,  Candle,  Spherical  -  —The 
average  or  mean  value  of  candle  power 
taken  at  a  number  of  points  around  the  source 
of  light. 

Power,  Conducting  —  —The  ability  of 
a  given  length  and  area  of  cross-section  of  a 
substance  for  conducting  light,  heat,  elec- 
tricity or  magnetism,  as  compared  with  an 
equal  length  and  area  of  cross-section  of 
some  other  substance  taken  as  a  standard. 

Power,  Conducting,  for  Electricity  — 

—The  ability  of  a  given  length  and  area  of 


cross-section  of  a  substance  to  conduct  elec- 
tricity, as  compared  with  an  equal  length  and 
area  of  cross-section  of  some  other  substance, 
such  as  pure  silver  or  copper. 

No  substance  is  known  that  does  not  offer  some 
resistance  to  the  passage  of  an  electric  current. 

The  following  table  is  taken  from  Sylvanus  P. 
Thompson's  « «  Elementary  Lessons  in  Electricity 
and  Magnetism": 


GOOD  CONDUCTORS. 


Silver, 
Copper, 


Other  metals, 
Charcoal. 


PARTIAL  CONDUCTORS. 


Water, 

The  human  body, 

Cotton, 


Wood, 
Marble, 
Paper. 


NON-CONDUCTORS. 


Oils, 

Porcelain, 
Dry  wood, 
Silk, 
Resins, 


Gutta-percha, 

Shellac, 

Ebonite, 

Paraffme, 

Glass, 


Dry  air. 


Heat  decreases  the  conducting  power  of  ele- 
mentary substances.  This  decrease  in  the  con- 
ducting power  is  approximately  proportional  to 
the  increase  of  temperature.  Carbon  is  an  ex- 
ception to  the  law,  being  a  better  conductor  at  a 
red  or  white  heat  than  when  cold. 

The  resistance  of  some  alloys,  such  as  German 
silver  and  platinoid,  is  but  little  affected  by  mod- 
erate changes  of  temperature.  These  alloys  are, 
therefore,  employed  in  the  construction  of  resist- 
ance coils. 

At  a  red  heat  insulators  become  fairly  good 
conductors  of  electricity. 

At  very  low  temperatures  the  conducting 
powers  of  the  metals  increase. 

Wroblewski  has  shown  that  at  extremely  low 
temperatures  copper  increases  in  its  conducting 
power  for  electricity.  He  cooled  copper  to  — 200 
degrees  C.,  the  temperature  of  the  solidification 
of  nitrogen,  and  found  that  at  this  temperature 
its  conducting  power  increased  to  about  nine  times 
its  conducting  power  at  O  degrees  C. 

It  may  be  remarked  here  that  at  exceedingly 
low  temperatures  a  metal  would  take  in  or  absorb 
heat  from  the  surrounding  medium  with  very 
great  rapidity.  In  this  sense  it  might  be  said  that 


Pow.] 


423 


[Pow. 


its  conducting  power  for  heat  was  greatly  in- 
creased. 

Kohlrausch  estimates  the  conducting  power  of 
distilled  water  at  .000000000025,  that  of  mer- 
cury being  taken  as  unity. 

The  best  conductors  of  electricity  are  the  best 
conductors  of  heat. 

This  fact  is  well  illustrated  by  the  following 
table  from  Ayrton : 

RELATIVE  CONDUCTIVITIES  PER  CUBIC  UNIT. 

Name  of  Metal.  Electricity.  Heat. 

Silver,  annealed 100  100 

Copper,       ««        94.1  74-8 

Gold,  •«       73  54.8 

Platinum 16.6  94 

Iron 15.5  10.1 

Tin 11.4  15.4 

Lead 7.6  7.9 

Bismuth i.i  1.8 

The  electric  conductivity  of  porous  conductors 
decreases  much  more  rapidly  than  the  heat  con- 
ductivity. 

Practically  perfect  insulators  for  electricity  can 
be  obtained,  but  are  unknown  for  heat. 

Edlund  believes  the  universal  ether  to  be  al- 
most a  perfect  conductor.  He  bases  this  belief 
on  the  phenomena  of  sun  spots,  the  occurrence  of 
which  is  almost  immediately  followed  by  the 
occurrence  of  magnetic  disturbances  on  the 
earth. 

Lodge  regards  the  luminiferous  ether  as  being 
almost  a  perfect  non-conductor,  because  he  thinks 
that  conductors  must  be  opaque.  It  may  be  sug- 
gested in  this  connection  that  Edlund's  hypothesis 
as  to  the  conductibility  of  magnetic  effects  through 
the  ether  is  also  capable  of  an  explanation  by  the 
effects  of  magnetic  induction. 

The  conducting  power  for  alternating  currents 
is  not  the  same  as  for  steady  currents.  When 
the  alternations  become  very  high,  the  difference 
between  these  conducting  powers  of  the  metals 
becomes  almost  inappreciable. 

Iron  is  an  enormously  worse  conductor  of 
electricity  than  copper  for  rapidly  alternating 
currents,  at  least  when  the  alternations  are  not 
too  great.  When,  however,  the  alternations  are 
extremely  high,  such  as  those  which  are  produced 
by  the  discharge  of  a  Leyden  jar  or  lightning 
flash,  the  iron  is  as  good  a  conductor  as  the  cop- 
per. The  reason  for  this  is  evident.  The  dis- 
charge in  such  cases  keeps  to  the  extreme  outer 


layer  of  the  conductor,  so  that  the  composition  of 
the  substance  is  practically  of  no  effect. 

Hughes  has  shown  that  the  resistance  of  an  iron 
telephone  line  of  the  usual  diameter,  to  periodic 
currents  of  about  100  per  second,  is  somewhat 
more  than  three  times  its  resistance  for  steady 
currents. 

There  is  no  such  thing  as  conduction  of  elec- 
tricity in  gases.  Electricity  makes  its  way  through 
a  gas  by  a  sudden  piercing  of  the  dielectric,  or,  in 
other  words,  by  a  disruptive  discharge.  (See 
Discharge,  Disruptive.}  In  such  a  disruptive 
discharge  it  may  be  assumed  that  the  gas  be- 
comes a  conductor  of  electricity  while  the  dis- 
charge is  passing.  It  would  then  partake  of  the 
nature  of  an  electrolytic  conductor,  since  the  dis- 
charge takes  place  by  means  of  a  true  locomotion 
of  atoms.  (See  Conduction,  Electrolytic.) 

Power,  Conducting,  for  Heat The 

ability  of  a  substance  to  transmit  heat  through 
its  mass. 

The  metals  are  good  conductors  of  heat  They 
are  also  good  conductors  of  electricity.  The 
conducting  powers  for  heat  and  electricity  are 
nearly  identical.  As  the  temperature  of  a  body 
increases,  its  conducting  power  for  heat  is  de- 
creased. Carbon  forms  an  exception  to  this 
statement. 

The  flow  of  heat  across  a  wall  formed  of  a 
homogeneous  material,  the  exposed  faces  of  which 
are  of  equal  extent  and  are  maintained  at  a  con- 
stant difference  of  temperature,  takes  place  in 
accordance  with  the  following  laws : 

(i.)  The  rate  of  flow  across  all  perpendicular 
sections  is  the  same. 

(2.)  A  uniform  drop  of  temperature  occurs 
from  one  side  of  the  wall  to  the  other  in  the  direc- 
tion in  which  the  flow  is  taking  place. 

(3.)  The  rate  of  flow  is  proportional  to  the  dif- 
ference in  temperature. 

The  similarity  between  the  laws  of  the  flow  of 
heat  under  the  circumstances  just  named  and  the 
flow  of  electricity  through  a  conductor  is  evident ; 
the  electrical  current  being  the  same  in  all  parts 
of  the  circuit,  a  drop  of  potential  occurring  in 
the  direction  in  which  the  current  is  moving, 
and  the  flow  being  proportional  to  the  difference 
of  potential. 

Power,    Conducting,  Tables   of 

Tables    in    which    the    relative    conducting 


Pow.] 


423 


[Pow, 


powers  of  different  substances  are  given.  (See 
Resistance,  Tables  of.) 

Power,  Electric Power  developed 

by  means  of  electricity. 

Power,  Electric,  Distribution  of 

The  distribution  of  electric  power  by  means 
of  any  suitable  system  of  generators,  connect- 
ing circuits  and  electric  motors. 

Power,  Electric  Transmission  of 

The  transmission  of  mechanical  energy  by 
converting  it  into  electric  energy  at  one  point 
or  end  of  a  line,  and  reconverting  it  into 
mechanical  energy  at  some  other  point  on  the 
line.  (See  Energy,  Electric,  Transmission 
of) 

Power,  Horse A  rate  of  doing  work 

equal  to  550  foot-pounds  per  second,  or  33,- 
ooo  foot-pounds  per  minute. 

I  horse-power=745.94  X  io7  ergs  per  second. 

(See  Erg.) 

««  =745.941  watts.      (See  Watt.) 

"  -=42.746  lb.    Fahr.    heat    units 

per     min.      (See     Units, 
Heat.) 

"  =23.748  lb.  Cent,  heat  units  per 

min.     (See  Units,  Heat.) 

Power,   Horse,  Electric Such  a 

rate  of  doing  electric  work  as  is  equal  to 
746  watts  or  746  volt-coulombs  per  second. 

This  rate  is  equivalent  to  33,000  foot-pounds 
per  minute,  or  550  foot-pounds  per  second. 

Just  as  I  pound  of  water  raised  through  the 
vertical  distance  of  I  foot  requires  the  expendi- 
ture of  a  foot-pound  of  energy,  so  I  coulomb  of 
electricity  acting  through  the  difference  of  poten- 
tial of  I  volt  requires  a  certain  amount  of  work 
to  be  done  on  it.  (See  Coulomb.  Volt.  Po- 
tential, Electric.} 

This  amount  is  called  a  volt-coulomb  or  joule, 
and  measured  in  foot-pounds  is  equal  to  .737324 
foot-pounds.  The  volt-coulomb,  or  joule,  isthere- 
fore  the  unit  of  electric  work,  just  as  the  foot- 
pound is  the  unit  of  mechanical  work. 

The  electric  work  of  any  circuit  in  joules  is 
equal  to  the  product  of  the  volts  by  the  coulombs. 

If  we  determine  the  rate  per  second  at  which 
the  coulombs  pass,  and  multiply  this  product  by 
the  volts,  we  have  a  quantity  which  represents  the 
electrical  power,  or  rate  of  doing  electrical  work. 


But  i  ampere  is  equal  to  I  coulomb  per  second; 
therefore,  if  we  multiply  the  current  in  am- 
peres by  the  difference  of  potential  in  volts,  the 
product  is  equal  to  the  electrical  power  or  rate  of 
doing  electrical  work. 

The  product  of  an  ampere  by  a  volt  is  called 
a  volt-ampere,  or  a  watt. 

One  watt  =  .0013406  horse-power,  or 

One  horse-power  =  745.941  watts. 

C*  F* 
Therefore  the  electrical  horse-power  =  — •?' 

where  C  =  the  current  in  amperes  and  E  =  the 
difference  of  potential  in  volts. 

Power,    Multiplying,     of  Shunt 

(See  Shunt,  Multiplying  Power  of  .) 

Power  of  Periodic  Current— (See  Cur- 
rent, Periodic,  Power  of.) 

Power,  Portative The  carrying 

power  of  a  magnet.  (See  Magnet,  Porta- 
tive Power  of.) 

Power,  Projecting,  of  Magnet The 

power  a  magnet  possesses  of  throwing  or  pro- 
jecting its  lines  of  magnetic  force  across  an 
intervening  air  space  or  gap. 

The  greater  the  air  space  the  greater  the  mag- 
netic reluctance,  and  consequently  the  greater  the 
magnetizing  force  required  to  overcome  it.  Mag- 
nets of  great  projecting  power  are  generally  of 
great  length,  to  accommodate  the  long  coils  of 
wire  required. 

Power,  Resuscitating,  of  Secondary  Bat- 
tery Cell The  power  possessed  by  an 

apparently  completely  discharged  secondary 
or  storage  cell  of  furnishing  additional  current 
after  a  protracted  rest. 

This  resuscitating  power  is  probably  due  to 
depolarization.  It  is  therefore  present  in  primary 
as  well  as  in  secondary  batteries. 

Power,  Stray That  part  of  the 

power  employed  in  driving  a  dynamo,  which 
is  lost  through  friction,  air  churning  or  air 
currents,  eddy  currents,  hysteresis,  etc. 

Power,  Thermo-Electric A  num- 
ber which,  when  multiplied  by  the  difference 
of  temperature  of  a  thermo-electric  couple, 
will  give  the  difference  of  potential  thereby 
generated  in  micro-volts.  (See  Diagram. 
Thermo-Electric.) 


Pow.] 


424 


[Pri. 


Power,  Units  of Various  units  em- 
ployed in  the  measurement  of  power. 

The  following  table  of  units  of  power  is  taken 
from  Heringls  work  on  dynamo-electric  machines. 

Unit  of  Power. 

I  erg  per  second. .  =  .000000 1  watt. 
I  watt,  or   I   volt- 
ampere,     or      I 
joule  per  second, 
or  I  volt-coulomb 

per  second =  icoooooo  ergs  per  second. 

=  44.2394    foot-pounds   per 

min. 
"  =6.11622    kilogram  -  metres 

per  min. 
«  =  .0573048  Ib.-Fah. ,  heat  unit 

per  min. 
"  =  .318360  Ib.-Cent.,  heat  unit 

per  min. 
"  =  .0144402  klgr.-Cent.   heat 

unit  per  min. 

"  =  .0013592     metric    horse- 

power. 

"  =  .0013406  horse-power. 

I  foot-pound    per 

min =  226043  erSs  Per  second. 

"  =  .0226043  watt. 

"  =  .13825  kilogram-metre  per 

min. 

"  =  .00003072     metric    horse- 

power. 

"  =  .000030303  horse-power. 

I  kilogram- metre 

per  min =  1635000  ergs  per  second. 

"  =  .163500  watt. 

=  7.23314    foot-pounds   per 

min. 
•«  =.0002222     metric     horse- 

power. 

=  .0002 192  horse-power. 
I  metric  horse- 
power, or  I 
French  horse- 
power, or  I  che- 
Tal-vapeur,  or  I 
force  de  cheval, 
or  i  Pferdekraft.  =  735  75  x  io»  ergs  per 

second. 

=  735-750  watts. 
=  32549.0    foot-pounds    per 

min. 
"  =  4500  kilogram-metres  per 


I  metric  h.-p.,  etc.  =42.162  Ib.-Fah.,  heat  units 

per  min. 
"  =  23.423  Ib.  -Cent.,  heat  units 

per  min. 
"  =  10.625     klg.-Cent.,     heat 

units  per  min. 

=  .98634    horse-power    heat 
units  per  min. 

I  horse-power =745.94    x     io7    ergs    per 

second. 

"          =745.941  watts. 

=  33000  foot  pounds  per  min. 

"          =  4562.33    kilogram  -  metres 

per  min. 

"          =  42.746  Ib.-Fah.,  heat  units 

per  min. 

"          =  23.748  Ib.-Cent,  heat  units 

per  min. 

"         =  10.772     klg.  -  Cent.,    heat 

units  per  min. 

"          =  1.01385      metric       horse- 
power. 
I    lb.-Fih.,    heat 

unit  per  min =  17.45  X  io7  ergs  per  sec. 

"  =  17.4505  watts. 

=  .23718  metric  horse-power. 
"  =  .023394  horse-power. 

I  Ib.  Cent.,    heat 

unit  per  min =  31.41  x  io7  ergs  per  sec. 

"  =31.4109  watts. 

=  .04269  metric  horse  power. 
"  =  .042109  horse-power. 

I  klgr.-Cent.,  heat 

unit  per  min =  69.25  x  io7  ergs  per  sec. 

"  =  69.249  watts. 

=  .094 1 2  metric  horse-power. 
"  =  .092835  horse-power. 

Poynting's  Law.— (See  Law,  Poynting's.) 

Practical  Unit  of  Inductance,  or  Self- 
induction.—  (See  Inductance,  or  Self -Induc- 
tion, Practical  Un  it  of.) 

Practical  Unit  of  Magneto-Motive  Force. 

— (See  Force,  Magneto-Motive,  Practical 
Unit  of.) 

Practical  Units.— (See  Units,  Practical) 

Pressel. — A  press  switch  or  push  connected 
to  the  end  of  a  flexible,  pendant  conductor. 
Pressure  Wires. — (See  Wires,  Pressure.) 
Primary  Battery. — (See  Battery,  Prim- 
ary.) 


Pri.] 


425 


[Pro. 


Primary,  Breaking  the Breaking 

or  opening  the  circuit  of  the  primary  of  an 
induction  coil.  (See  Primary,  The.) 

Primary  Coil.— (See  Cot'l,  Primary.) 

Primary,  Making  the Closing  or 

completing  the  circuit  of  the  primary  of  an 
induction  coil.  (See  Primary,  The.) 

Primary  Plate  Condenser.— (See  Plate, 
Primary,  of  Condenser?) 

Primary  Spiral.— (See  Spiral,  Primary) 

Primary,  The That  conductor  in 

an  induction  coil,  or  transformer,  which  re- 
ceives the  impressed  electromotive  force,  or 
which  carries  the  inducing  current. 

On  changes  in  the  current  intensity  in  the 
primary,  currents  are  induced  in  the  secondary. 
(See  Induction,  Electro-Dynamic.  Coil,  Induc- 
tion. Transformer. ) 

Prime  Conductor.  —  (See  Conductor, 
Prime) 

Prime  Motor.— (See  Mover,  Prime) 

Prime  Mover.— (See  Mover,  Prime) 

Printer,  Stock,  Callahan's A  form 

of  printing  telegraph  used  in  sending  stock 
quotations  telegraphically.  (See  Telegraphy, 
Printing.  Ticker,  Stock) 

Printer,  Stock,  Phelps' A  form  of 

printing  telegraph  used  in  sending  stock  quo- 
tations telegraphically.  (See  Ticker,  Stock. 
Telegraphy,  Printing) 

Probe,  Electric A  metallic  con- 
ductor inserted  in  the  body  of  a  patient  in 
order  to  ascertain  the  exact  position  of  a 
bullet,  or  other  foreign  metallic  substance. 

Two  conductors  are  placed  parallel  to  each 
other,  and  are  separated  at  the  extremity  of  the 
probe  by  any  suitable  insulating  material.  On 
contact  with  the  metallic  substance,  an  electric 
bell  is  rung  by  the  closing  of  the  circuit,  or  the 
same  thing  is  more  readily  detected  by  the  de- 
flection of  the  needle  of  a  galvanometer,  or  by  a 
telephone  placed  in  the  circuit. 

Process,  Electrotyping (See  Elec- 

trotyping,  or  the  Electrotype  Process) 

Processes  of  Carbonization.— (See  Car- 
bonization, Processes  of) 


Production  of  Electricity  by  Light.-. 

(See  Electricity,  Production  of,  by  Light) 
.  Prognosis,  Electric In  electro- 
therapeutics, a  prognosis,  or  prediction  of  the 
fatal  or  non-fatal  termination  of  a  disease, 
from  an  electro-diagnosis  based  on  the  exag- 
gerated or  diminished  reactions  of  the  excit- 
able tissues  of  the  body  when  subjected  to 
the  varying  influences  of  electric  currents. 
(See  Diagnosis,  Electro) 

Projections,  Pacinotti  —Radial 

projections  or  teeth  in  an  armature  core  ex- 
tending from  the  central  shaft,  so  as  to  form 
slots,  pockets,  or  armature  chambers,  for  the 
reception  of  the  armature  coils. 

The  term  Pacinotti  projections  was  given  to 
these  teeth  because  they  were  first  introduced  by 
Pacinotti  in  his  dynamo-electric  machine. 

Projector,  Mangin A  special  form 

of  search  light. 

The  Mangin  reflector  consists  of  a  concavo- 
convex  mirror,  the  convex  surface  of  which  is 
silvered  and  acts  as  a  reflector.  The  radii  ot 
curvature  of  the  two  surfaces  are  such  that  the 
light  undergoes  the  two  refractions,  i .  e.,  on  en- 
tering and  on  passing  out  of  the  mirror,  in  such  a 
manner  as  to  pass  out  of  the  mirror  in  absolute 
parallelism,  and  thus  destroy  all  aberration. 


Fig.  452.     Mangin  Projector. 

The  Mangin  projector  is  shown  in  longitudinal 
and  in  cross-section  in  Fig.  452,  and  the  projector 
>  B,  is  placed  in  one  end  of  the  cylinder  A,  furnished 
with  the  openings  for  the  ventilation  of  the  cham- 
ber. 

The  cylinder  is  supported  on  trunnions,  and  by 
means  of  screws  can  be  given  any  desired  inclina- 
tion, in  a  manner  which  will  be  readily  under- 
stood from  an  inspection  of  the  drawing. 

The  source  of  light  is  an  arc  lamp  of  the  focus- 
ing type.  A  small  disc  is  placed  in  front  of  the 


Pro.] 


[Pui. 


arc  in  order  to  stop  the  direct  light  from  the  arc 
which  would  have  divergent  rays.  The  door  C, 
is  formed  of  a  number  of  cylindrical  lenses,  placed 
parallel  to  one  another,  which  cause  the  rays  to 
diverge  horizontally,  when  so  desired. 

Prony  Brake.— (See  Brake,  Prony.} 
Proportional  Coils.— (See  Coils,  Propor- 
tional.} 

Proportionate  Arms.— (See  Arms,  Pro- 
portionate.} 

Proportionate  Arms  of  Electric  Bridge. 

— (See  Arms,  Proportionated) 

Prostration,  Electric Physiological 

exhaustion  or  prostration,  resembling  that 
produced  by  sunstroke,  resulting  from  pro- 
longed exposure  to  the  radiation  of  an  unusu- 
ally large  voltaic  arc.  (See  Sunstroke, 
Electric.} 

Protection,  Electric,  of  Houses,  Ships 

and  Buildings  Generally Means  for 

protection  against  the  destructive  effects  of  a 
lightning  discharge,  consisting  essentially  in 
the  use  of  lightning  rods.  (See  Rod,  Light- 
ning) 

Protection,  Electric,  of  Metals 

(See  Metals,  Electrical  Protection  of.} 

Protective  Sheath.— (See  Sheath,  Pro- 
tective?) 

Protector,  Cable A  device  for  the 

safe  discharge  of  the  static  charge  produced 
on  the  metallic  sheathing  of  a  cable,  or  on 
conductors  surrounding  or  adjacent  to  the 
cable,  consequent  on  changes  in  the  electro- 
motive force  applied  to  the  conducting  core  of 
such  cable. 

The  cable  protector  is  provided  for  the  purpose 
of  preventing  the  discharge  of  the  charge  from 
piercing  and  thus  injuring  the  insulation  of  the 
cable  itself. 

Protector,  Comb A  term  some- 
times applied  to  a  lightning  protector  or  ar- 
rester, in  which  both  the  line  and  ground 
plates  are  furnished  with  a  series  of  teeth, 
like  those  on  a  comb.  (See  Arrester,  Light- 


Protector,  Voltaic  Battery A  de- 
vice for  automatically  disconnecting  a  voltaic 
battery,  whenever  the  circuit  in  which  it  is 
placed  becomes  grounded. 

The  battery  protector  is  used  in  systems  of  elec- 
tric gaslighting,  where,  unless  great  care  is  exer- 
cised in  insulating  the  circuits, considerable  annoy- 
ance is  often  experienced  from  the  readiness  with 
which  grounds  are  established.  This  arises  from 
the  high  electromotive  force  of  the  spark  ob- 
tained from  the  spark  coil,  piercing  the  insula- 
tion and  establishing  a  ground  through  the  gas 
pipes. 

Protoplasm,  Effects  of  Electric  Currents 

on Contractions  observed  in  all  pro- 
toplasm on  the  passage  of  an  electric  current 
through  it. 

Protoplasm,  the  basis  of  plant  and  animal  life, 
or  the  jelly-like  matter  that  fills  all  organic  cells, 
whatever  may  be  the  origin  of  such  cells,  suffers 
contraction  when  traversed  by  an  electric  cur- 
rent. 

An  increased  activity  in  the  movements  of  a 
form  of  microscopic  life  called  the  amoeba  is  occa- 
sioned by  slight  shocks  from  an  induction  coil  ; 
stronger  discharges  produce  tetanic  contractions, 
with,  in  some  cases,  expulsion  of  food  or  even  of 
the  nucleus.  A  uniform  strength  of  current  pro- 
duces contraction  and  imperfect  tetanus. 

Pull. — A  contact  maker,  similar  in  general 
construction  to  a  push  button,  but  operated 
by  means  of  a  pulling  rather  than  a  pushing 
force. 

The  pull  is  preferable  to  the  push  in  exposed 
positions,  such  as  outer  doors,  where  moisture  is 
apt  to  injure  pushes. 

Pull,  Chain A  chain  pendant  at- 
tached to  a  pendant  burner  for  the  move- 
ment of  the  wipe-spark  spring  and  the 
ratchet  in  an  electrically  lighted  gas  burner. 

Pull,  Door  Bell,  Electric A  cir- 
cuit-closing device  attached  to  a  bell  pull  and 
operated  by  the  ordinary  motion  of  the  pull 

Pull,  Electric  Bell A  circuit-clos- 
ing device  operated  by  a  pull. 

Fig.  453  shows  a  form  of  electric  bell  pull.  On 
pulling  the  bell  handle,  contact  springs,  that 
rest  on  a  ring  of  insulating  material  when  the 


PuL] 


427 


[Pum, 


pull  is  in  its  normal  position,  are  brought  into  con- 
tact with  a  metal  ring,  thus  completing  the  cir- 


-  453  •    Electric  Bell  Pull. 


«uit.     The  bell  pull  is  often  used  to  replace  the 
ordinary  push  button. 

Pulley,  Driven  --  A  pulley  attached 
to  the  driven  shaft.     (See  Mover,  Prime?) 

Pulley,  Driving  --  A  pulley  attached 
to  the  driving  shaft.     (See  Mover,  Prime?} 

Pulsating  Current.—  (See  Current,  Pul- 


Pulsation.  —  A  quantity  of  the  nature  of 
an  angular  velocity,  equal  to  2  it  multiplied 
by  the  frequency  of  the  oscillation,  or,  equal 
to  z  Tt  divided  by  the  duration  of  a  single 
period. 

Pulsatory  Current.—  (See  Current,  Pul- 
satory?) 

Pulsatory  Magnetic  Field.—  (See  Field, 
Magnetic,  Pulsatory?) 

Pulse,  Electrical  --  An  electric  oscil- 
lation. 

A  momentary  flow  of  electricity  from  a 
conductor,  which  gradually  varies  from  the 
zero  value  to  the  maximum,  and  then  to  the 
zero  value  again,  like  a  pulse  or  vibration  in 
an  elastic  medium. 

Electric  pulses  are  set  up  in  conductors  con- 
nected with  the  coatings  of  a  Leyden  jar,  on  the 
discharge  of  the  same.  Such  pulses  produce  a 
series  of  electrical  oscillations,  which  move  alter- 
nately backwards  and  forwards,  until  the  dis- 
charge  is  gradually  dissipated.  (See  Oscillations  , 
Electric.) 

The  circumstances  influencing  the  rate  of 
propagation  of  an  electric  pulse  through  different 
parts  of  a  closed  circuit,  according  to  Lodge,  are— 


(I.)  The  extra  inertia,  or  the  so-called  magnetic 
susceptibility  in  the  conducting  substance,  es- 
pecially at  its  outer  parts. 

(2. )  An  undue  constriction  or  throttling  of  the 
medium  through  which  the  disturbance  is  pass- 
ing. 

(3.)  The  nature  of  the  insulating  medium. 

Pump,  Air,  Geissler  Mercurial 

A  mercurial  air  pump,  in  which  the  vacuum 
is  attained  by  the  aid  of  a  Torricellian  vacuum. 

In  the  Geissler  Mercury  Pump,  Fig.  454,  a 
vacuum  is  obtained  by  means  of  the  Torricellian 
vacuum  produced  in 
a  large  glass  bulb  that 
forms  the  upper  ex- 
tremity of  a  barome- 
tric column.  The 
lower  end  of  this  tube 
or  column  is'  con- 
nected with  a  reser- 
voir of  mercury  by 
means  of  a  flexible 
rubber  tube.  To  fill 
the  bulb  with  mer- 
cury the  reservoir  is 
raised  above  its  level, 
*.  e.,  above  thirty 
inches,  the  air  it  con- 
tains being  allowed  to 
escape  through  an 
opening  governed  by 
a  stopcock.  The  ves- 
sel to  be  exhausted  is 
connected  with  the 
bulb,  and  by  means 
of  a  two-way  exhaus- 
tion cock,  communi-  Fig.  434.  Getssler1 's  Mer- 
cation  can  be  made  curial  Air  Pump. 

with  the  bulb,  when  it  contains  a  Torricellian 
vacuum,  and  shut  off  from  it  while  its  air  is  being 
expelled. 

In  actual  practice  the  mercury  is  mechanically 
pumped  into  the  barometric  column,  and  the 
valves  are  opened  either  by  hand,  or  automati- 
cally by  electrical  means. 

Pump,  Air,  Mechanical A  mechan- 
ical device  for  exhausting  or  removing  the  air 
from  any  vessel. 

An  excellent  form  of  air  pump  is  shown  in  Fig. 
455,  which  is  a  drawing  of  Bianchi's  pump. 

Three  valves,  all  opening  upwards,  are  placed 


Pum.] 


428 


Barrel  of 
Bianchi's  Air  Pump. 


at  the  top  and  bottom  of  the  cylinder,  and  in  the 
piston,  respectively.  These  valves  are  mechan- 
ically opened  and  closed  at  the  proper  moment 
by  the  movements  of  the  piston,  i.  e.,  their  action 
is  automatic.  This  enables  a  much  higher  vacuum 
to  be  obtained  than  when  the  valves  open  and 
close  by  the  tension  of  the  air. 

Mechanical  pumps  are  unable  to  readily  pro- 
duce the  high  vacua  employed  in  most  electric 
lamps.  Mercury  pumps 
are  employed  for  this 
purpose.  (See  Pump, 
Air,  Mercurial.) 

Pump,  Air,  Mer- 
curial   A  de- 
vice for  obtaining  a 
high  vacuum  by  the 
use  of  mercury. 

Mercury  pumps  are 
in  general  of  two  types 
of  construction,  viz.  : 

(i.)  The  Geissler 
pump. 

(2.)  The  Sprengel  pump.  (See  Pump,  Air, 
Geissler  Mercurial.  Pump,  Air,  SprengePs 
Mercurial.} 

I'  11  m  p,  Air,  Sprengel's  Mercurial 

A  mercurial  air  pump  in  which  the  vacuum 
is       obtained       by 
means    of   the  fall 
of  a  stream  of  mer- 
cury. 

In  the  Sprengel 
mercury  pump,  Fig. 
456,  the  fall  of  a  mer- 
cury stream  causes 
the  exhaustion  of  a 
reservoir  connected 
with  the  vertical 
tube,  by  the  mechan- 
ical action  of  the 
mercury  in  entang- 
ling bubbles  of  air. 
These  bubbles  are 
largest  at  the  begin- 
ning of  the  exhaus- 
tion, but  become 
smaller  and  smaller  Fig.  456.  SfrengeCt  Mer- 
near  the  end,  until,  curial  Air  Pump. 

at  last,  the  characteristic  metallic  click  of  mer- 
cury or  other  liquid  falling  in  a  good  vacuum 


is  heard.  The  exhaustion  may  be  considered  as 
completed  when  the  bubbles  entirely  disappear 
from  the  column. 

The  Sprengel  pump  produces  a  better  vacuum 
than  the  Geissler  pump,  but  is  slower  in  its 
action. 

In  actual  practice,  the  mercury  that  has  fallen 
through  the  tube  is  again  raised  to  the  reservoir 
connected  to  the  drop  tube  by  the  action  of  a 
mechanical  pump. 

Pumping  of  Electric  Lights.— A  term 
sometimes  applied  to  a  pulsating  or  period- 
ical increase  and  decrease  in  the  brilliancy  of 
the  light. 

This  action  is  generally  due  to  the  periodic  slip- 
ping of  the  belt  or  other  driving  mechanism.  In 
the  case  of  arc  lamps  it  may  also  be  caused  by  the 
improper  action  of  the  feeding  device  of  the 
lamp. 

Puncture,  Electro The  application 

of  electrolysis  to  the  treatment  of  aneurisms 
or  diseased  growths. 

The  blood  is  decomposed  by  the  introduction 
of  a  fine  platinum  needle  connected  with  the 
anode  of  a  battery,  and  insulated,  except  near  its 
point,  by  a  covering  of  vulcanite. 

The  kathode  is  a  sponge-covered  metallic  plate. 

Puncture,  Galvano A  term  some- 
times applied  to  electro-puncture.  (See 
Puncture,  Electro.) 

Punning  of  Telegraph  Pole.— (See  Pole, 
Telegraphic,  Punning  of) 

Push. — A  name  sometimes  applied  to  a 
push  button,  or  to  a  floor  push.  (See  Push, 
Floor.  Button,  Push.) 

Push  Button.— (See  Button,  Push.) 

Push-Button  Kattler,  —  (See  Rattler, 
Push-Button) 

Push,  Floor A  push  button  placed 

on  the  floor  of  a  room  so  as  to  be  readily 
operated  by  means  of  the  foot.  (See  But- 
ton, Push) 

Pyknometer. — A  term  sometimes  used 
for  the  specific  gravity  bottle  employed  in 
determining  the  specific  gravity  of  a  liquid. 

Pyrheliometer. — An  apparatus  for  mea- 
suring the  energy  of  the  solar  radiation. 


429 


[Qua. 


The  pyrheliometer  consists  essentially  of  a 
short  cylinder,  the  area  of  whose  base  is  accu- 
rately determined.  The  cylinder  being  filled  with 
a  known  weight  of  water,  the  water  surface  is  ex- 
posed for  a  definite  time  to  the  sun's  radiation, 
and  the  increase  in  temperature  carefully  deter- 
mined. The  product  of  the  weight  of  the  water 
thus  heated  by  the  increase  in  degrees,  gives 
the  number  of  heat  units,  from  which  the  total 
energy  absorbed  is  readily  calculable.  In  order 
to  avoid  loss  by  reflection  or  diffusion  from  the 
water  surface,  it  is  covered  by  a  layer  of  lamp- 
black. (See  Units,  Heat.  Calorimeter.) 

Pyro  -  Electricity.  —  (See  Electricity, 
Pyro.) 

Pyro-Magnetic  Generator  or  Dynamo.— 
(See  Generator,  Pyro-Magnetic!) 

Pyro-Magnetic  Motor. — (See  Motor,  Pyro- 
Magnetzc.) 

Pyrometer. — An  instrument  for  deter- 
mining temperatures  higher  than  those  that 
can  be  readily  measured  by  thermometers. 

Pyrometers  are  operated  in  a  variety  of  ways. 
A  common  method  is  by  the  expansion  of  a  metal 
rod. 

Pyrometer,  Siemens'  Electric An 

apparatus  for  the  determination  of  tempera- 


ture by  the  measurement  of  the  electric  resist- 
ance of  a  platinum  wire  exposed  to  the  heat 
whose  temperature  is  to  be  measured. 

The  platinum  wire  is  coiled  on  a  cylinder  of 
fire-clay,  so  that  its  separate  convolutions  do  not 
touch  one  another.  It  is  protected  by  a  platinum 
shield,  and  is  exposed  to  the  temperature  to  be 
measured  while  inside  a  platinum  tube. 

The  resistance  of  the  platinum  coil  at  O  degree 
C.  having  been  accurately  ascertained,  the  temper- 
ature to  which  it  has  been  exposed  can  be  calcu- 
lated from  the  change  in  its  resistance  when  ex- 
posed to  the  unknown  temperature. 

Pyrometer,    Siemens'    Water—     —A 

pyrometer  employed  for  determining  the  tem- 
perature of  a  furnace,  or  other  intense  source 
of  heat,  by  calorimetric  methods,  t.  e.,  by  the 
increase  in  the  temperature  of  a  known 
weight  of  water,  into  which  a  metal  cylinder 
of  a  given  weight  has  been  put,  after  being 
exposed  for  a  given  time  to  the  source  of 
heat  to  be  measured. 

When  copper  cylinders  are  employed,  the  in- 
strument possesses  a  range  of  temperature  of 
1, 800  degrees  F. ;  when  a  platinum  cylinder  is 
used,  it  has  a  range  of  2,700  degrees  F. 


Q. — A  contraction  for  electric  quantity. 

Quad. — A  contraction  sometimes  em- 
ployed in  place  of  quadruplex  telegraphy. 
(See  Telegraphy,  Quadruplex!) 

Quadrant. — A  term  proposed  for  the  unit 
of  self-induction. 

An  earth  quadrant  is  equal  to  io9  centi- 
metres. 

In  the  United  States  the  word  henry  is  used 
for  the  unit  of  self-induction.  (See  Henry,  A.) 

Quadrant  Electrometer.— (See  Electro- 
meter, Quadrant!) 

Quadrant  Electroscope,  Henley's.— (See 
Electroscope,  Quadrant,  Henley's!) 

Quadrant,  Legal A  length  equal  to 

9,978  kilometres,  instead  of  the  assumed 
10,000  kilometres. 


Quadrant,  Standard A  length  equal 

to  10,000  kilometres. 

Quadrature,  In A  term  employed 

to  express  the  fact  that  one  simple  periodic 
quantity  lags  90  degrees  behind  another. 

The  electromotive  force  of  s-elf-induction  is  said 
to  be  in  quadrature  with  the  effective  electro- 
motive force  or  current. 

Quadruple v  Telegraphy,  Bridge  Method 

of (See  Telegraphy,  Quadruplex, 

Bridge  Method  of.) 

Qualitative  Analysis.  —  (See  Analysis, 
Qualitative.) 

Quality  or  Timbre  of  Sound.— (See  Sound, 
Quality  or  Timbre  of.) 

Quantitative  Analysis.— (See  Analysis, 
Quantitative.) 


[Bad. 


Quantity  Armature.  —  (See  Armature, 
Quantity.) 

Quantity,  Connection  of  Battery  for 

(See  Battery,  Connection,  of,  for 

Quantity) 

Quantity  Efficiency  of  Storage  Battery. 
—(See  Efficiency,  Quantity,  of  Storage  Bat- 
tery.) 

Quantity,  Unit  of  Electric A 

definite  amount  or  quantity  of  electricity 
called  the  coulomb.  (See  Coulomb.) 

Although  the  exact  nature  of  electricity  is  un- 
known, yet,  like  a  fluid  (a  liquid  or  gas),  electricity 
can  be  accurately  measured  as  to  quantity. 


A  current  of  I  ampere,  for  example,  is  a 
current  in  which  one  coulomb  of  electricity  passes 
in  every  second. 

A  condenser  of  the  capacity  of  i  farad,  is 
large  enough  to  hold  I  coulomb  of  electricity 
if  forced  into  the  condenser  under  an  electro- 
motive force  of  I  volt.  (See  Capacity,  Electro- 
static. Farad.  Volt.  Amptre.) 

Quiet  Arc.— (See  Arc,  Quiet) 

Quiet  Discharge. — (See  Discharge,  Si- 
lent) 

Qnicking  Solution.  —  (See  Solution, 
Quicking) 


R. — A  contraction  used  for  ohmic  resist- 
ance. ' 

p. — A  contraction  used  for  specific  resist- 
ance. 

Radial  Armature.—  (See  Armature, 
Radial.) 

Radially  Laminated  Armature  Core.— 
(See  Core,  Armature,  Radially-Laminated.) 

Radiant  Energy.— (See  Energy,  Radiant.) 

Radiant  Matter.— (See  Matter,  Radiant, 
or  Ultra-Gaseous) 

Radiate. — To  transfer  energy  by  means  of 
waves. 

Radiating.— Transferring  energy  by  means 
of  waves. 

Radiation. — Transference  of  energy  by 
means  of  waves. 

When  an  elastic  body  is  set  into  vibration, 
whether  it  be  the  vibrations  that  produce  light, 
heat  or  electricity,  energy  is  charged  on  the 
body,  and  the  body  will  then  continue  to  vibrate 
until  it  imparts  to  some  medium  surrounding  it 
an  amount  of  energy  exactly  equal  to  that  orig- 
inally imparted  to  itself. 

In  the  case  of  a  sonorous  body  the  energy  is 
transferred  from  the  vibrating  body  to  the  air 
around  it.  For  example,  in  the  case  of  an  elastic 
metallic  wire  set  into  vibration,  the  wire  will  con- 
tinue to  vibrate  until  it  does  as  much  work  on 
the  surrounding  air  as  was  originally  done  on  it, 
in  order  to  set  it  into  vibration. 


In  the  case  of  a  heated  body  the  energy  is 
transferred  from  the  body  to  the  luminiferous 
ether  around  it.  For  example,  in  the  case  of  the 
same  wire  heated  above  the  temperature  of  the 
air,  the  energy  imparted  to  the  molecules  of  the 
metal  by  the  source  of  heat  causes  them  to 
move  towards  and  from  one  another.  These 
to-and-fro  motions  of  the  molecules  cause  the 
surrounding  ether  to  be  set  into  waves,  and  as 
much  energy  is  imparted  to  the  ether,  as  was 
originally  imparted  to  the  'vire  in  order  to  heat  it. 

In  the  case  of  a  luminous  body  the  energy  is 
transferred  from  the  body  to  the  luminiferous 
ether.  For  example,  if  the  wire  is  heated  to 
luminosity  by  a  certain  amount  of  energy  im- 
parted to  it,  the  surrounding  ether  is  now  set 
into  waves  of  both  light  and  heat,  which  differ 
from  one  another  only  in  their  wave  length,  and 
the  luminous  body  will  continue  to  radiate  light 
and  heat  until  it  imparts  to  the  surrounding 
ether  an  amount  of  energy  exactly  equal  to  that 
originally  imparted  to  it 

So,  too,  in  the  case  of  a  Ixxly  charged  with 
electricity.  If  disruptively  discharged,  the  im- 
pulsive rush  of  electricity,  so  produced,  causes  the 
energy  charged  on  it  to  be  radiated  as  electro- 
magnetic waves  into  the  surrounding  ether.  The 
discharging  body  is,  to  all  intents  and  purposes,  in 
the  same  condition  as  the  vibrating  elastic  wire, 
and  dissipates  or  radiates  its  energy  in  much  the 
same  manner. 

Radiation,  Electro-Magnetic 

The  sending  out  in  all  directions  from  a  con- 


Bad.] 


431 


[Had. 


ductor,  through  which  an  oscillating  discharge 
is  passing,  of  electro-magnetic  waves  in  all 
respects  similar  to  those  of  light  except  that 
they  are  of  much  greater  length.  (See  Elec- 
tricity, Hertz's  Theory  of  Electro-Magnetic 
Radiations  or  Waves.) 

Radiation  of  Electricity.— (See  Electri- 
city, Radiation  of) 

Radiation  of  Lines  of  Force.— (See  Force, 
Lines  of,  Radiation  of.) 

Radical,  Compound A  group  of 

unsaturated  atoms. 

A  group  of  elementary  atoms,  some  of  the 
bonds  of  which  are  open,  or  not  connected 
or  joined  with  the  bonds  of  other  atoms. 
(See  Atomicity?) 

For  example,  hydroxyl,  HO,  is  a  compound 
radical,  with  one  of  the  two  bonds  of  the  diad 
oxygen  atom,  open  or  unsaturated. 

Radical,  Simple An  unsaturated 

atom  with  its  bond  or  bonds  free. 

A  single  unsaturated  atom  as  distinguished 
from  an  unsaturated  group  of  atoms. 

Radicals. — Unsaturated  atoms  or  groups  of 
atoms,  in  which  one  or  more  of  the  bonds  are 
left  open  or  free. 

Radicals  are  either  Simple  or  Compound. 

The  radical  may  be  regarded  as  the  basis  to 
which  other  elements  may  be  added,  or  as  the 
nucleus  around  which  they  may  be  grouped. 

Thus  H8O,  forms  a  complete  chemical  molecule, 
because  the  bonds  of  all  its  constituent  atoms  are 
saturated,  thus  H  —  O  —  H.  But  H  —  O  — ,  or 
hydroxyl,  is  a  radical,  because  its  oxygen  atom 
possesses  one  unsaturated  or  free  bond.  By 
combining  with  the  radical  (NOS),  it  forms  nitric 
acid,  thus  H  —  O  —  (NO8)  or  H  NO,. 

During  electrolysis,  the  molecules  of  the  elec- 
trolyte are  decomposed  into  two  groups  of  simple 
or  compound  radicals,  called  ions.  These  ions  are 
respectively  electro-positive  and  electro-negative, 
and  are  called  kathions  and  onions.  (See  Ions. 
Electrolysis.} 

Radiometer,  Crookes' An  appara- 
tus for  showing  the  action  of  radiant  matter 
in  producing  motion  from  the  effects  of  the 
reaction  of  a  stream  of  molecules  escaping 
from  a  number  of  easily  moved  heated  sur- 
faces. (See  Matter,  Radiant,  or  Ultra- 
Gaseous) 


Radiometer,   Electric,  Crookes 

A  radiometer  in  which  the  repulsion  of  the- 
molecules  of  the  residual  atmosphere  takes, 
place  from  electrified  instead  of  from  heated! 
surfaces.  (See  Radiometer,  Cxookes'.) 

Radio-Micrometer,  Boys' An  elec- 
trical apparatus  for  measuring  the  intensity 
of  radiant  heat. 

The  action  of  the  radio-micrometer  depends  oni 
the  deflection,  by  a  magnetic  field,  of  a  suspended 
thermo-electric  circuit  composed  of  three  metals, 
viz. :  two  bars  of  antimony  and  bismuth,  or  of 
their  alloys,  which  are  soldered  side  by  side  to- 
the  end  of  a  minute  disc  or  strip  of  copper  foil,  as- 
shown  in  Fig.  457.  This  disc  or  foil  of  copper  is, 


F*g-  457-    Boyf  Radio-Micrometer. 

provided  for  the  purpose  of  receiving  the  radia- 
tion that  is  to  be  measured.  The  upper  ends  ot 
the  thermo-couple  are  soldered  to  the  ends  of  a 
long,  narrow,  inverted  U-shaped  piece  of  copper 
wire,  which  completes  the  thermo-electric  circuit. 

The  absorption  of  radiant  energy  by  the  cop- 
per disc  connected  to  the  thermo-electric  couple 
produces  an  electric  current,  and  the  circuit, 
being  suspended  in  a  magnetic  field,  is  at  once 
deflected  to  a  degree  dependent  on  the  intensity 
of  the  radiation,  or  of  the  current  generated  at 
the  thermo-electric  junction. 

The  means  adopted  for  the  suspension  of  the 
system  are  shown  in  Figs.  457  and  458.  A 
small  piece  of  straight  wire  is  soldered  to  the  up-  - 


Rad.] 


432 


[Rai. 


QUARTZ 
IBRE 


771 


GLASS 
TUBE 


per  end  of  the  copper  stirrup,  which  completes 
the  tbenno-electric  circuit.  This  wire  is  cemented 
to  the  lower  end  of  a  glass  tube,  the  upper  end 
of  which  is  provided  with  a  mirror,  and  the  whole 
suspended,  as  shown,  by  a 
quartz  fibre  in  the  field  of  a 
powerful  magnet. 

In  a  radio- micrometer  made 
by  Prof.  Boys,  the  minuteness  of 
the  suspended  circuit  may  be 
judged  from  the  following  ac- 
tual dimensions,  viz. :  Thermo- 
electric bars,  £  x  -fa  x  5^ff  inch  ; 
copper  circuit  of  number  36 
copper  wire,  i  inch  long  and 
about  ^j  inch  wide ;  copper 
heat-receiving  surface,  black- 
ened on  the  face  exposed  to  the 
radiation,  -fa  inch  in  diameter, 
or  i  x  <V  inch;  receiver,  ^  inch 
square,  ffa  inch  thick  ;  quartz 
fibre  4  inches  long,  ^Jtns  inch  in 
diameter. 

This  instrument,  when  pro- 
perly adjusted  for  extreme  sen- 
sitiveness, should  give  clear  in- 
dications when  the  blackened 
surface  is  warmed  but  the  Fig.  "45 8.  Boys' 
ttVTtTfvv  degree  Centigrade.  It  Radio-Micrometer. 
will  respond  to  the  heat  radiated  on  the  surface 
of  a  half  penny  from  a  candle  flame  at  a  dis- 
tance of  1,530  feet. 

In  order  to  avoid  the  disturbance  due  to  the 
magnetic  qualities  of  the  antimony  and  bismuth 
bars,  the  central  portions  of  the  metallic  block, 
inside  which  the  system  is  suspended,  is  made 
of  iron,  as  shown  by  the  heavier  shading  in 
Fig.  457- 

This  mass  of  iron  serves  as  a  magnetic  screen 
to  the  thermo-electric  bars,  but  permits  the  action 
of  the  field  on  the  circuit. 

Radiophone. — A  name  sometimes  given  to 
the  photophone.  (See  Photophone^ 

Radiophony.— The  production  of  sound  by 
a  body  capable  of  absorbing  radiant  energy 
when  an  intermittent  beam  of  light  or  heat 
falls  on  it. 

The  action  of  radiant  energy,  when  absorbed 
by  matter,  is  to  cause  its  expansion  by  the  conse- 
quent increase  of  temperature.  This  occurs  even 
when  the  body  is  but  momentarily  exposed  to  a 


COPPER 
WIRE 


Bi. 
Cu. 


flash  of  light,  but  the  instantaneous  expansion 
thus  produced  immediately  dies  away,  and  by 
itself  is  indistinguishable.  If,  however,  a  suffi- 
ciently rapid  succession  of  such  flashes  fall  on  the 
body,  the  instantaneous  expansions  and  contrac- 
tions produce  an  appreciable  musical  note. 

The  sounds  so  produced  have  been  utilized  by 
Bell  and  Tainter  in  the  construction  of  the  Phtto- 
phone.  (See  Photophone.} 

Railroad,  Electric A  railroad,  or 

railway,  the  cars  on  which  are  driven  or  pro- 
pelled by  means  of  electric  motors  connected 
with  the  cars. 

The  electric  current  that  drives  the  motor  is 
derived  either  from  storage  batteries  placed  on 
the  cars,  or  from  a  dynamo-electric  machine,  or 
battery  of  dynamo-electric  machines,  conveniently 
situated  at  some  point  on  the  road.  The  current 
from  the  dynamo  is  led  along  the  line  by  suitable 
electric  conductors  and  is  passed  into  the  electric 
motor  as  the  car  runs  along  the  tracks  in  various 
ways,  viz. : 

Systems  for  the  electric  propulsion  of  cars  may, 
therefore,  be  divided  into  the  dependent  system,  in 
which  the  driving  current  is  obtained  from  conduc- 
tors placed  somewhere  outside  the  cars,  and  the 
independent  system,  where  the  current  is  derived 
from  primary  or  secondary  batteries  placed  on 
the  cars.  (See  Railroads,  Electric,  Dependent 
System  of  Motive  Power  for.  Railroads,  Electric, 
Independent  System  of  Motive  Power  for.) 

In  the  dependent  system,  the  conductors  which 
supply  the  car  with  current  are  placed  either 
overhead,  on  the  surface  of  the  road-bed  or  un- 
derground. Thus  arise  three  divisions  of  the 
dependent  system: 

(I.)  The  Surface  System. 

(2.)  The  Underground  System. 

(3.)  The  Overhead  System. 

(I.)  The  Surface  System..— By  placing  one  or 
both  rails  in  the  circuit  of  the  dynamo  and  taking 
the  current  from  the  tracks  by  means  of  sliding 
or  rolling  contacts  connected  with  the  motor. 

(2.)  The  Underground  System.  —  By  placing  the 
conducting  wires  parallel  to  each  other  in  a  longi- 
tudinally slotted  underground  conduit  in  the  road- 
bed, and  provided  with  two  central  plates,  insu- 
lated from  one  another  and  connected  respectively 
to  the  motor  terminals,  and  taking  the  current 
by  means  ot  a  traveling  brush  or  roller,  called  a 
plow,  sled  or  shoe.  On  the  movement  ot  the  car 
over  the  track,  these  traveling  contacts  touch  the 


Rai.] 


433 


[1UI. 


two  parallel  line  conductors  in  the  conduit  and 
fake  the  electric  current  therefrom.  (See  Plow. 
Sled.} 

(3.)  The  Overhead  System.— Ky  placing  the 
(ine  conductors  on  poles  along  the  road,  and 
taking  the  current  therefrom  by  means  of  suitable 
traveling  contacts  called  trolleys,  or  by  sliders. 

Where  a  single  conductor  is  employed,  the  re- 
turn conductor  generally  consists  of  the  track 
itself,  or  of  the  track  and  ground.  (See  Trolley.) 

The  first  method,  viz.,  that  of  using  the  tracks 
alone  as  conductors,  is  not  much  employed. 

The  use  of  the  track  and  ground  as  a  return  for 
the  current  is  now  very  generally  employed. 

In  some  systems  the  track  is  divided  into  sec- 
tions which  are  successively  brought  into  connec- 
tion with  the  main  conductors  by  contacts  effected 
by  the  attraction  between  magnets  carried  on  the 
car  and  contact  pieces  of  magnetic  material  placed 
below  the  surface.  The  rail  section  thus  tempo- 
rarily energized  is  placed  in  connection  with  the 
motor. 

In  order  to  regulate  the  speed,  various  devices 
are  employed  to  vary  the  current  strength  in  the 
motor  circuit.  These  devices  consist  essentially 
of  rheostats  or  resistances  introduced  into,  or  re- 
moved from,  the  motor  circuit  on  the  movement 
by  hand  of  a  lever  that  forms  part  of  the  circuit, 
over  contact  plates  connected  to  the  resistance 
coils. 

In  order  to  change  the  direction  of  the  car,  the 
direction  of  rotation  of  the  electric  motor  is 
changed.  This  is  effected  by  some  form  of  re- 
versing gear  or  mechanism  that  changes  the  di- 
rection of  rotation  of  the  motor,  either  by  shifting 
the  brushes,  by  changing  the  field,  or  by  any 
other  means.  (See  Telpherage.  Motor,  Elec. 
trie.  Rheostat.} 

Railroads,  Absolute  Block   System  for 

— A  block  system   in  which  one  train 

only  is  permitted  to  occupy  a  given  block  at 

any  time.  (See  Railroads,  Block  System  J "or .) 

Railroads,  Automatic  Electric  Safety  Sys- 
tem for A  system  for  automatically 

preventing  the  approach  of  two  trains  at  any 
speed  beyond  a  predetermined  distance  of 
each  other. 

The  system  consists  essentially  in  the  automatic 
closing  of  the  circuit  of  an  electric  motor  placed 
on  the  locomotive  between  the  steam  dome  and 
the  sand  box.  This  motor  is  in  circuit  with  a 
local  battery  placed  on  the  cow-catcher,  and  in- 


troduced in  the  circuit  of  the  motor  by  a  magnet 
placed  on  the  cow-catcher,  as  shown  in  Fig.  459, 


-  459-    Locomotive  with  Safety  System. 
which  represents  a  locomotive  provided  with  this 
system. 

The  magnet  is  on  open  circuit  with  generators 
placed  on  the  rear  car  of  a  second  train,  or  with 
generators  at  a  bridge  or  crossing. 

By  means  of  double  sectional-conductors  placed 
along  the  track,  the  generators  are  automatically 
closed  through  the  magnet,  one  conductor  being 
in  permanent  connection  with  the  magnet,  while 
the  other  is  connected  to  the  generator  in  the  rear 
car  of  a  second  train,  at  a  switch  or  crossing.  The 
other  terminals  of  the  magnet  and  generators  are  in 
permanent  electricial  connection  with  the  rails, 
which  are  employed  as  return  ground  conductors. 

Fig.  460  shows  the  application  of  the  safety 
electric  system  to  a  bridge. 


Fig.  460.     Safety  System  for  Bridge. 

Fig.  461  shows  the  application  of  the  safety 
system  at  grade  crossing. 


Fig,  4.61.    Safety  System  for  Grade  Cresting : 

The  author  is  indebted  to  Mr.  E.  P.  Thompson 
for  cuts  and  general  description. 

Railroads,  Block  System  for A  sys- 
tem for  securing  safety  from  collisions  of  mov- 
ing railroad  trains  by  dividing  the  road  into  a 
number  of  blocks  or  sections  of  a  given 
length,  and  so  maintaining  telegraphic  com- 
munication between  towers  located  at  the 
ends  of  each  of  such  blocks  as  to  prevent, 


Rai.] 


[Rai. 


by  the  display  of  suitable  signals,  more  than 
one  train  or  engine  from  being  on  the  same 
block  at  the  same  time. 

There  are  two  kinds  of  railway  block  systems 
in  common  use,  viz.: 

(I.)  The  Absolute  Block  System. 

(2.)  The  Permissive  Block  System. 

In  the  absolute  system,  which  is  the  safer,  one 
train  only  is  permitted  on  any  particular  block  at 
a  given  time. 

In  the  permissive  block  system  more  than  one 
train  is  permitted,  under  certain  circumstances 
and  conditions,  to  occupy  the  same  block  simul- 
taneously, each  train  then  being  notified  of  the 
fact  that  it  is  not  alone  on  the  block. 

The  absolute  block  system,  though  expensive 
to  construct  and  maintain,  is  the  only  one  that 
should  be  permitted  by  law  to  exist  on  roads  whose 
traffic  exceeds  a  certain  amount. 

An  absolute  block  system  is  employed  on  the 
London  Underground  Railroad,  and  on  the  Penn- 
sylvania Railroad  Systems. 

The  system  in  use  on  the  New  York  Division 
of  the  Pennsylvania  Railroad  is  as  follows  : 

The  road  between  Philadelphia  and  Jersey  City 
is  divided  into  some  seventy  sections,  the  length 
of  each  section  being  dependent  on  the  amount  of 


Fig.  462.    Block  Tower. 

daily  traffic  ,  thus,  between  Jersey  City  and  New- 
ark, where  the  traffic  is  great,  there  are  some 
fifteen  sections,  although  the  distance  is  only  7.9 
miles. 

In  each  block-tower  there  are  connections  with 
three  separate  and  distinct  telegraph  lines  or  cir- 
cuits, viz. : 

(i.)  A  line  or  wire  called  the  train  wire,  con- 
necting the  block-tower  with  the  General  Dis- 
patcher's office  at  Jersey  City.  This  line  is  used 
for  sending  train  orders  only. 

(2.)  A  line  or  wire  called  the  block  wire,  con- 


necting  each  block-  tower  with  the  next  tower  on 
each  side  of  it. 

(3.)  A  line  or  wire  called  the  message  wire,  and 
used  for  local  traffic  or  business. 

The  general  arrangement  of  the  block  -tower  is 
shown  in  Fig.  462. 

Each  of  the  block-towers  is  sufficiently  elevated 
above  the  road-bed  to  afford  the  operator  an  un- 
obstructed view  of  the  tracks. 

The  operator,  having  ascertained  the  actual 
condition  of  the  track,  either  by  observation  or  by 
telegraphic  communication  with  the  stations  on 
either  side  of  him,  gives  notice  of  this  condition  to 
all  trains  passing  his  station  by  the  display  of 
certain  semaphore  signals. 

The  semaphore  signals  as  used  on  the  Penn- 
sylvania Railroad  are  shown  in  Figs.  463  and  464. 

The  form  shown  in  Fig.  463  is  used  in  the  abso- 


Fig.  4(13.  Semaphore  Signal— Absolute  System. 
lute  system,  and  that  shown  in  Fig.  464  in  the  per- 
missive system.  These  signals  consist  essentially 
of  an  upright  support  provided  with  a  movable 
arm  A  B,  called  the  semaphore  arm,  capable  of 
being  set  in  any  of  two  or  three  positions.  The 
semaphore  signal  is  placed  outside  the  signal 
tower,  often  several  hundred  feet  away,  but  is 
readily  set  from  the  tower  in  any  of  the  desired 
positions  by  the  operator,  by  the  movement  of 
rods  connected  with  levers. 

In  the  permissive  system,  the  semaphore  arm 
can  be  set  in  three  positions,  viz. : 

(I.)  In  a  horizontal  position,  or  where  the 
semaphore  arm  makes  an  angle  of  90  degrees  with 
the  upright. 

(2.)  Or  it  may  be  dropped  down  from  the 
horizontal  position  through  an  angle  of  75 
degrees,  as  shown  in  Fig.  463. 

(3.)  Or  it  may  occupy  a  position  exactly  inter- 


Rai.] 


435 


[Rai. 


mediate  between  the  first  and  second,  or  37°  30' 
below  the  horizontal,  as  shown  in  Fig.  464. 

Position  No.  i  is  the  danger  signal,  and  when 
it  is  displayed  the  train  may  not  enter  the  block 
it  governs. 

Position  No.  2  shows  that  "the  track  is  clear, 
and  that  the  train  may  safely  enter  the  block  it 
governs. 

Position  No.  3,  which  is  used  in  the  permissive 
block  system,  only  signifies  caution,  and  permits 
the  train  to  cautiously  enter  the  block  and  look 
out  for  further  signals. 

The  semaphore  arm  consists  of  a  light  wooden 
arm,  II  inches  wide  by  5^  feet  in  length,  painted 
red  or  other  suitable  color  that  can  be  easily  dis- 
tinguished by  daylight. 

By  night  the  positions  of  the  semaphore  arm 
are  indicated  by  colored  lights.  These  lights  are 


| 
!  LEY 

Fig.  464.    Semaphore  Signal — Per  missive  System. 

operated  as  follows,  viz. :  in  the  absolute  system, 
the  semaphore  arm  A  B,  pivoted  at  A,  bears  at 
its  shorter  end  a  disc  or  lens  of  red  glass  R,  and, 
in  the  permissive  system,  below  this  another  disc 
or  lens  of  green  glass  G.  An  oil  lantern,  pro- 
vided with  an  uncolored  glass  lens,  is  so  sup- 
ported on  a  bracket  fastened  to  the  upright  that 
when  the  semaphore  arm  points  to  danger  the 
red  glass  is  immediately  in  front  of  the  lantern  ; 
when  it  points  to  caution,  the  green  glass  is  in 
front  of  the  lantern;  but  when  it  points  to  safety, 
the  lantern  is  left  uncovered  save  by  its  uncolored 
glass. 

At  night,  therefore,  when  the  semaphore  arm 
is  set  to  danger,  a  red  light  is  displayed;  when  it 
points  to  caution,  a  green  light  is  displayed;  and 
when  it  points  to  safety,  a  white  light  is  displayed. 

In  some  systems  the  position  of  the  semaphore 


arm  is  shown  at  night  by  means  of  light  reflected 
from  a  parabolic  mirror,  at  the  focus  of  which  the 
signal  lantern  is  placed.  This  method  possesses 
the  advantage  over  other  systems'of  rendering  it 
very  improbable  that  the  engineer  would  mistake 
an  ordinary  light  for  a  signal  light. 

The  green  light  is  only  used  in  the  permissive 
block  system.  In  the  absolute  block  system,  the 
semaphore  arm  has  two  positions  only  ;  viz.,  dan- 
ger, or  horizontal,  and  safety,  or  75  degrees  below 
the  horizontal. 

A  single  arm  is  used  when  it  is  intended  to 
govern  a  single  track  only.  Where  the  condition 
of  a  number  of  tracks  is  to  be  indicated,  several 
arms  are  employed,  one  above  the  other. 

When  semap  r.ore  signals  are  placed  on  each  side 
of  a  double-track  road,  the  semaphore  arm  point- 
ing to  the  right  of  the  vertical  support  governs 
the  line  running  to  the  right. 

When  the  semaphore  signals  are  placed  at 
junctions  or  switch-crossings,  the  operator  in  the 
signal-tower  opens  or  closes  the  switches  from 
the  tower  by  the  movements  of  levers  that  set  the 
switches,  and  then  displays  the  proper  semaphore 
signal  for  that  crossing  or  route  ;  red,  or  danger, 
if  the  route  is  blocked,  and  white,  or  safety,  if  it 
is  clear.  Here  the  interlocking  apparatus  is  em- 
ployed, which  consists  in  devices  by  means  of 
which,  when  a  route  has  once  been  set  up  and  a 
signal  given  for  that  route,  the  switches  and  sig- 
nals are  so  interlocked  that  no  signal  can  pos- 
sibly be  given  for  a  conflicting  route. 

The  signals  or  switches  are  operated  by  means- 
of  iron  rods  passing  over  rollers  or  pulleys. 
These  rods  are  attached  by  suitable  connections 
to  the  switch  or  semaphore  signals,  and  are 
operated  by  means  of  levers  from  the  signal- 
tower.  Switches  can  be  operated  as  far  as  1,000 
feet  from  the  tower;  signals,  as  far  as  2,500  feet. 

Colored  switch-signals  are  placed  opposite  the 
end  of  the  switches  to  indicate  the  positions  of 
the  switch.  These  signals  consist  of  red  and 
white  discs  for  day,  and  a  lantern  provided  with 
red  and  white  glasses  for  night.  When  the 
switch  on  any  line  is  open,  the  switch-signal  shows 
red;  when  shut,  it  shows  white.  These  switch- 
signals  are  only  used  in  the  yards. 

No  passenger  train  is  permitted  on  a  block, 
after  another  train  has  passed  the  signal  station, 
until  a  dispatch  has  been  received  from  the 
station  ahead  that  the  train  has  passed  and  the 
block  is  thus  cleared. 

As  an  additional  precaution  against  rear  col- 


RaL] 


436 


[Rai. 


lisions,  tail-lights  are  displayed  at  the  ends  of  the 
trains.  These  consist  of  lanterns  placed  on  each 
side  of  the  rear  end  of  the  last  car.  These 
lanterns  are  furnished  with  three  glass  slides. 
The  side  of  the  lantern  towards  the  rear  of  the 
car  shows  a  red  light;  that  to  the  front  and  side 
of  the  car  shows  a  green  light.  The  engineer, 
looking  out  of  the  cab,  can  thus  see  a  green  light, 
which  serves  as  a  "marker"  and  indicates  to 
him  that  his  train  is  intact  By  day  a  green  flag, 
placed  in  the  same  position  as  the  lantern,  serves 
the  same  purpose  as  a  marker.  An  observer  on 
the  track,  or  in  the  tower,  sees  the  red  lights  on 
the  rear  of  the  train  when  it  has  passed. 

Freight  trains  are  now  run  on  separate  tracks, 
except  in  places  where  the  extra  tracks  are  not 
yet  completed.  Here  they  do  not  run  on  schedule 
time,  but  are  permitted  to  follow  one  another  at 
intervals  that  depend  on  the  condition  of  the 
tracks  as  shown  by  the  signals  displayed. 

Railroads,  Electric,  Continuous  Over- 
head System  of  Motive  Power  for 

A  variety  of  the  dependent  system  of  motive 
power  for  electric  railroads  in  which  a  con- 
tinuous bare  conductor  is  connected  with  the 
terminals  of  a  generating  dynamo,  and  sup- 
ported overhead  by  suitable  means,  and  a 
traveling  wheel  or  trolley  is  moved  over  the 
same  by  the  motion  of  the  car,  in  order  to 
carry  off  the  current  from  the  line  to  the  car 
motor.  (See  Railroads,  Electric,  Depend- 
ent System  of  Motive  Power  for.) 

Railroads,  Electric,  Continuous  Surface 
System  of  Motive  Power  for  —  -  A 
variety  of  the  dependent  system  of  motive 
power  for  electric  railroads,  in  which  the  ter- 
minals of  the  generating  dynamo  are  con- 
nected to  the  continuous  bare  metallic  con- 
ductor that  extends  along  the  entire  track  on 
the  surface  of  the  roadway  or  street,  and  from 
which  the  current  is  taken  off  by  means  of  a 
traveling  conductor  connected  with  the  mov- 
ing car.  (See  Railroads,  Electric,  Continu- 
ous Underground  System  of  Motive  Power 
for.) 

Railroads,  Electric,  Continuous  Under- 
ground System  of  Motive  Power  for  — 
A  variety  of  the  dependent  system  of  motive 
power  for  electric  railways,  in  which  a  con- 
tinuous  bare    conductor  is  placed    under- 


ground in  an  open  slotted  conduit,  and  the 
current  taken  off  from  the  same  by  means  of 
sliding  or  rolling  contacts  carried  on  the  mov- 
ing car.  (See  Railroads,  Electric,  Depend- 
ent System  of  Motive  Power  for) 

Railroads,  Electric,  Dependent  System 
of  Motive  Power  for  —  —A  term  now 
generally  used  for  a  system  of  motive  power 
for  the  propulsion  of  electric  railway  cars,  in 
which  the  electric  current  is  taken  from  wires 
or  conductors  connected  with  electric  sources 
external  to  the  cars. 

A  dependent  system  of  motive  power  for  elec- 
tric railways  includes  three  distinct  varieties, 
namely  : 

(i.)  The  Underground  System. 

(2.)  The  Surface  System. 

(3.)  The  Overhead  System. 

In  all  of  these  systems  the  bare  conductor  con- 
nected with  the  terminals  of  a  generating  dynamo 
may  form  either  one  continuous  wire  or  it  can 
be  divided  into  separate  portions  or  sections. 

The  underground  system  embraces  two  distinct 
varieties  : 

ist.  A  continuous  bare  conductor  placed  in  an 
open  slotted  conduit. 

2d.  A  sectional  bare  conductor  placed  in  an 
open  slotted  conduit. 

In  the  first  variety  of  the  underground  system, 
bare  conductors  are  placed  in  an  open  slotted 
conduit,  and  connected  with  the  terminals  of  a 
dynamo-electric  machine  which  generates  the 
current  that  is  to  be  employed  for  the  propulsion 
of  the  cars.  Traveling  contacts  placed  on  the 
car  and  connected  with  an  electric  motor,  carry 
off  the  current  from  the  bare  conductor  by  rolling 
or  sliding  over  it. 

In  the  second  variety  of  the  underground  sys- 
tem, a  section  of  a  bare  conductor,  or  bare  metal- 
lic points  that,  on  the  passage  of  the  car  over 
them  are  automatically  connected  with  the  gen- 
erating dynamo,  replace  the  continuous  metallic 
conductors  of  the  first  system. 

In  the  surface  system,  the  wires  or  conductors 
that  are  connected  with  the  generating  dynamo, 
instead  of  being  placed  in  the  underground  open 
slotted  conduit,  are  placed  directly  on  the  surface 
of  the  street  or  roadbed  and  the  current  carried 
off  from  the  same  by  suitable  contacts  placed  on 
the  car. 

In  most  cases,  however,  in  which  the  surface 
system  is  adopted,  the  conductors  that  are  con- 


Rai.] 


437 


[Rai. 


nected  with  the  generating  dynamo  do  not  ex- 
tend throughout  the  entire  length  of  the  track, 
but  are  limited  to  sections  of  the  track  that  are 
suitably  connected  with  the  generating  dynamo. 
In  some  of  these  systems  arrangements  are 
devised,  by  which  the  car,  as  it  passes  over  the 
track,  automatically  connects  these  sections  with 
the  generating  dynamo  while  passing  over  the 
same,  and  disconnects  them  after  such  sections 
have  been  passed. 

The  overhead  system  embraces  two  varieties: 

(i.)  A  continuous  trolley  wire. 

(2.)  A  divided  or  sectional  trolley  wire. 

In  the  continuous  trolley  wire  system,  the  cur- 
rent is  taken  off  from  the  continuous  wire  by 
means  of  a  trolley  wheel  that  moves  over  the 
trolley  wire. 

Such  a  system  is  especially  suitable  for  suburban 
districts  or  small  towns.  In  such  a  system  the 
trolley  wire  is  connected  with  a  number  of  feeder 
wires  that  either  extend  from  the  generating  sta- 
tion the  entire  length  of  the  line,  and  are  con- 
nected with  such  line  at  suitable  points;  or,  sepa- 
rate feeders  extend  from  the  station  to  points  on 
the  line  where  they  are  tapped  into  the  trolley 
wire. 

In  the  divided  or  sectional  trolley  wire  system 
the  wire  is  divided  into  suitable  sections,  and 
feeders  extend  the  entire  length  of  the  line  and 
are  connected  to  the  central  points  of  each  section; 
or,  the  feeders  extend  the  entire  length  of  the 
line  and  tap  into  both  ends  of  the  section. 

The  author  is  indebted  to  G.  W.  Mansfield  for 
the  principal  facts  contained  in  the  above  descrip- 
tive matter. 

Eailroads,  Electric,  Divided  Overhead 
System  of  Motive  Power  for A  sec- 
tional overhead  system  of  motive  power  for 
electric  railroads.  (See  Railroads,  Electric, 
Sectional  Overhead  System  of  Motive  Power 
for,} 

Railroads,  Electric,  Divided  Surface 
System  of  Motive  Power  for A  sec- 
tional system  of  motive  power  for  electric 
railroads.  (See  Railroads,  Electric,  Sec- 
tional Surface  System  of  Motive  Power 
for.} 

Railroads,  Electric,  Divided  Under- 
ground System  of  Motive  Power  for 

— A  sectional  system  of  motive  power  for 
electric  railroads.  (See  Railroads,  Electric, 


Sectional  Underground  System  of  Motive 
Power  for.} 

Railroads,  Electric,  Double-Trolley  Sys- 
tem for A  system  of  electric  railroad 

propulsion,  in  which  a  double  trolley  is  em- 
ployed to  take  the  driving  current  from  two 
overhead  trolley  wires. 

The  double-trolley  system  differs  from  the 
single-trolley  system  in  that  it  employs  no  earth 
return.  The  parallel  wires  also  avoid  the  effects 
of  injurious  induction  in  neighboring  telegraph 
or  telephone  wires.  (See  Railroads,  Electric, 
Dependent  System  of  Motive  Power  for.) 

Railroads,  Electric,  Independent  System 

of  Motive  Power  for A  term  for  the 

electric  propulsion  of  railway  cars  by  means 
of  primary  or  storage  batteries  placed  on  the 
car  and  directly  connected  with  the  motor. 

This  is  called  the  independent  system,  because, 
unlike  the  dependent  system,  the  energy  required 
for  the  propulsion  of  the  car  is  obtained  directly 
from  the  energy  of  the  electric  source  placed  on 
the  car,  instead  of,  as  in  the  dependent  system, 
outside  of  the  car. 

Railroads,  Electric,  Sectional  Overhead 

System  of  Motive  Power  for A  variety 

of  the  dependent  system  of  motive  power  for 
electric  railroads,  in  which  sections  of  bare 
conductors  are  supported  overhead  on  poles 
placed  along  the  railroad  track,  and  the  cur- 
rent taken  off  from  the  same  by  means  of 
traveling  conductors  such  as  the  trolley 
wheel,  which  is  moved  over  the  trolley  wire 
by  the  motion  of  the  car. 

Various  systems  are  employed  for  connecting 
the  different  sections  of  the  trolley  wire  by  means 
of  feeder  wires  with  the  generating  dynamo. 
(See  Railroads,  Electric,  Dependent  System  of 
Motive  Power  for.) 

Railroads,  Electric,  Sectional  Surface 
System  of  Motive  Power  for —  — A 

variety  of  the  dependent  system  of  motive 
power  for  electric  railroads  in  which  conduc- 
tors are  placed  on  the  roadbed  or  along  the 
track,  and  the  current  taken  off  from  the  same 
by  means  of  contacts  connected  with  the  mov- 
ing car,  and  so  arranged  as  to  automatically 
switch  in  such  bare  sections  on  the  passage 


Kai.] 


438 


[Ray. 


of  the  car  over  them,  and  to  switch  them  out 
as  the  car  leaves  them.  (See  Railroads, 
Electric,  Dependent  System  of  Motive  Power 
Jor!) 

Railroads,  Electric,  Sectional  Under- 
ground System  of  Motive  Power  for 

— A  variety  of  the  dependent  system  of 
motive  power  for  electric  railroads  in  which  a 
sectional  conductor  is  placed  underground  in 
a  slotted  conduit,  and  the  current  taken  from 
the  same  by  means  of  sliding  or  rolling  con- 
tacts connected  with  the  moving  car.  (See 
Railroads,  Electric,  Dependent  System  of 
Motive  Power  for!) 

Railroads,  Electric,  Section  Line  of 

— Any  part  of  the  overhead  electric  conduc- 
tors insulated  from  other  parts  so  as  to  permit 
its  supply  of  electric  power  to  be  separately 
.controlled. 

Railroads,  Electric,  Signal  Service  Sys- 
tem for The  system  of  electric  signals 

used  on  railways  for  ascertaining  the  condition 
•of  the  roads,  sending  instructions  to  engineers, 
and  conveying  intelligence  generally  from 
stations  along  the  road  to  the  running  trains. 

Railroads,  Electric,  Single-Trolley  Sys- 
tem   A  system  of  electric  railroad 

propulsion  in  which  a  single  trolley  is  em- 
ployed to  take  the  driving  current  from  a 
single  overhead  trolley  wire. 

The  earth,  or  a  conductor  placed  along  the 
.track  on  the  roadbed,  acts  as  the  return.  (See 
Railroads,  Electric,  Dependent  System  of  Mo- 
live  Power  far.) 

Railroads,  Permissive  Block  System  for 

A  block  system  in  which  more  than 

-one  train  is  permitted  under  given  conditions 
to  occupy  the  same  block  simultaneously. 
(See  Railroads,  Block  System  for!) 

Railway,  Electric An  electric  rail- 
road. (See  Railroad,  Electric!) 

Range,  Molecular The  distance  at 

which  the  molecules  of  matter  exert  a  sensi- 
ble attraction  for  one  another. 

This  distance  has  been  estimated  in  the  case  of 
zinc  and  oxygen  as  equal  to  about  the  ten-mil- 
lionth of  a  millimetre. 


Ratchet-Pendant  Argand-Electric  Burner. 

— (See  Burner,  Argand-Electric,  Ratchet- 
Pendant^ 

Ratchet-Pendant  Electric  Burner.— (See 

Burner,  Ratchet- Pendant,  Electric!) 

Ratchet-Pendant  Electric  Candle  Burner. 
—(See  Burner,  Ratchet-Pendant  Candle 
Electric!) 

Ratio,  Telocity  • —A  ratio,  in  the 

nature  of  a  velocity,  that  exists  between  the 
dimensions  of  the  electrostatic  and  the  elec- 
tro-magnetic units. 

This  ratio  will  be  understood  from  the  com- 
parison of  the  following  units.  In  each  case  the 
numerator  gives  the  dimensions  in  the  electro- 
static and  the  denominator  the  dimensions  in  the 
electro-magnetic  system : 


Quantity, 


Here  the  value  of  the  ratio,  viz.,  the  length 
divided  by  the  time,  is  clearly  in  the  nature  of  a 

velocity,   for  V  =  —    . 


Potential. 


Capacity, 


Resistance, 


-i  T 


=  V«    . 


T» 


A  remarkable  similarity  exists  between  the 
value  of  the  -velocity  expressed  in  C.  G.  S.  units, 
and  the  velocity  of  light,  which  is  of  great  signifi- 
cance in  the  electro-magnetic  theory  of  light.  (See 
Light,  MaxwelPs  Electro-Magnetic  Theory  of.) 

The  velocity  of  light  is  2.9992  X  io10  cen 
timetres  per  second. 

The  velocity  ratio,  v,  is  2.9800  X  io10  centi- 
metres per  second. 

Rattler,  Push-Button  --  A  device 
connected  with  a  push  button  to  show  that 
the  bell  connected  at  a  distant  point,  in  the 
circuit  of  a  push  button,  rings  when  the  button 
is  pressed. 

Ray,  Actinic  --  A  ray  of  light  or  other 
form  of  radiant  energy  that  possesses  the 


Kay.] 


439 


[Rec. 


power  of  effecting   chemical  action.      (See 
Decomposition?) 

All  rays  of  light,  and  even  some  of  those  in- 
visible to  the  human  eye,  are  actinic  to  some 
particular  chemical  substance  or  another. 
Whether  the  ether  waves  produce  the  effects  of 
heat,  of  light  or  of  chemical  decomposition  de- 
pends on  the  nature  of  the  material  on  -which 
they  fall,  as  well  as  on  the  character  of  the  waves 
themselves. 

Ray,  Electric  (Raia   torpedo) A 

species  of  fish  named  the  ray,  which,  like  the 
electric   eel,   pos- 
sesses the  power 
of  producing  elec- 
tricity. 

The  electric  or- 
gan is  situated  at 
the  back  of  the 
head,  and  consists 
of  hundreds  of  poly- 
gonal, cellular 
laminae,  supplied 
with  numerous 
nerve  fibres,  as 
shown  in  Fig.  465. 
(See  Fishes.  Elec- 
tric.) 

Rayleigh's 
Form  of  Clark's 
Standard  Voltaic 
Cell.— (See  Cell, 
Voltaic,  Stand- 
ard, Rayleigh's 
Form  of  Clark's)  &g-  4<>5-  The  *«'<*  Torpedo. 
Reaction. — In  electro-therapeutics  mus- 
cular contractions  following  the  closing  or 
opening  of  an  electric  circuit. 

Reaction  Coil.— (See  Coil,  Reaction.) 

Reaction  of  Degeneration. — (See  Degen- 
eration, Reaction  of) 

Reaction  of  Exhaustion.— (See  Exhaus- 
tion, Reaction  of.) 

Reaction  Principle  of  Dynamo-Electric 
Machines. — (See  Machine,  Dynamo-Elec- 
tric, Reaction  Principle  of) 

Reaction  Telephone.  —(See  Telephone, 
Reaction?) 


Reaction  Time. — (See  Time,  Reaction)    • 

Reaction     Wheel,    Electric (See 

Wheel,  Reaction,  Electric.) 

Reactions,  Kathodic  and  Anodic  Electro- 
Diagnostic  The  reactions  which  oc- 
cur at  the  kathode  or  anode  of  an  electric 
source  placed  on  or  over  any  part  of  a  living 
body. 


Fig.  466.     Kathodic  and  Anodic  Reactions. 

Fig.  466,  from  De  Watteville's  "  Medical  Elec- 
tricity" represents  what  he  assumes  takes  place  at 
the  points  of  entrance  and  exit  of  the  current  in  a 
nerve  submitted  to  the  action  of  the  anode  of  an 
electric  source.  Two  zones  are  formed,  an  anodic 
and  a  kathodic  zone;  the  virtual  anode  is  formed 
by  the  portion  of  the  skin  nearer  the  nerve,  and 
the  virtual  kathode  by  the  adjoining  muscies. 
There  are  thus  formed  two  zones  of  influence — 
one  immediately  around  the  anode,  called  the 
polar  or  anodic  electrotonic  zone,  and  one  sur- 
rounding this  and  including  the  virtual  kathode, 
and  called  the  peripolar,  or  kathelectrotonic  zone. 

Reading  Telescope.  —  (See  Telescope, 
Reading) 

Real  Efficiency  of  Storage  Battery.— 
(See  Efficiency,  Real,  of  Storage  Battery.) 

Real  Hall  Effect.— (See  Effect,  Hall, 
Real) 

Recalescence. — The  property,  possessed 
by  incandescent  steel  when  cooling,  of 
again  becoming  incandescent  after  a  certain 
degree  of  cooling  has  been  reached. 

The  property  of  recalescence  was  first  pointed 
out  by  Barrett. 

A  steel  wire  heated  at  the  middle  or  near  one 
end  to  a  bright  red,  and  allowed  to  cool  in 
a  dim  light,  will  cool  until  a  low  red  heat  is 
reached,  when  it  will  be  observed  to  reheat  at 
some  point  in  the  originally  heated  portion.  This 
reheating  is  manifested  by  a  brighter  red  spot 


Rec.] 


440 


[Rec. 


which  moves  along  the  portion  originally  heated. 
This  reheating  is  called  recalescence,  and  is  due 
to  latent  heat  (potential  energy),  which,  disap- 
pearing when  the  bar  was  heated,  again  becomes 
sensible  (kinetic  energy)  on  cooling. 

The  temperature  at  which  recalescence  takes 
place  is  sensibly  the  temperature  at  which  heated 
steel  regains  its  magnetizability. 

Received  Current.  —  (See  Current,  Re- 
ceived^ 

Receiver,  Gramophone  --  The  re- 

ceiver employed  in  the  gramophone.  (See 
Gramophone?) 

Receiver,  Graphophone  --  The    re- 

ceiver employed  in  the  graphophone.  (See 
Phonograph?) 

Receiver,  Harmonic  --  A  receiver, 
employed  in  systems  of  harmonic  telegraphy, 
consisting  of  an  electro-magnetic  reed,  tuned 
to  vibrate  to  one  note  or  rate  only.  (See  Te- 
legraphy, Gray's  Harmonic  Multiple.) 

Receiver  Magnet.  —  (See  Magnet,  Receiv- 
ing) 

Receiver,  Phonographic  —  —The  ap- 
paratus employed  in  a  telephone,  phono- 
graph, graphophone  or  gramophone  for  the 
reproduction  of  articulate  speech.  (See 
Phonograph.) 

Receiver,  Telephonic  --  The  receiver 
employed  in  the  telephone.  (See  Tele- 
phone) 

Receptive  Device,  Electro  —  —(See 
Device,  Electro-Receptive?) 

Receptive  Device,  Magneto  —  —(See 
Device,  Magneto-Receptive^) 

Reciprocal  ---  The  reciprocal  of  any 
number  is  the  quotient  arising  from  dividing 
unity  by  that  number. 

Thus,  for  example,  the  reciprocal  of  4,  is  \  or 
.250. 

The  conducting  power  of  any  circuit  is  equal 
to  the  reciprocal  of  its  resistance  ;  or,  in  other 
words,  the  conducting  power  is  inversely  propor- 
tional to  the  resistance. 


The  following  table  contains   the  reciprocals 
of  the  numerals  up  to  100  : 

TABLE  OF  RECIPROCALS. 


Re- 

Re- 

Re- 

Re- 

Re- 

cipro- 

No. 

cipro- 

No. 

cipro- 

No. 

cipro- 

No. 

cipro- 

cal. 

cal. 

cal. 

cal. 

cal. 

0.5000 

n 

0.0455 

42 

0.0338 

02 

0161 

82 

0    22 

0-3333 

23 

0.0435 

43 

0.0233 

f>3 

0159 

•3 

O  2O 

0.2500 

M 

.0417 

4 

.0227 

<>4 

56 

«4 

o   19 

0.2000 

25 

.0400 

\ 

.0222 

6S 

54 

B5 

o  18 

o.   667 

20 

.0385 

6 

.0217 

00 

52 

86 

o     6 

o.  429 

27 

.0370 

7 

.O2I3 

"7 

49 

«7 

o     5 

o.   250 

28 

•0357 

8 

.0208 

oS 

47 

Bfl 

O     4 

O.     Ill 

20 

•°345 

9 

.O2O4 

69 

45 

By 

OJ    2 

0.     OOO 

30 

•0333 

5° 

.0200 

70 

43 

90 

0       I 

0.0909 

3' 

.0323 

3* 

.OI96 

71    o.     41 

9* 

O      O 

0.0833 

32 

•0313 

52 

.0192 

72 

39 

9- 

0  oq 

0.0769 

S3 

•0-303 

53 

.0,89 

73 

37 

M 

0  c8 
o  06 

0.0667 

35 

.0286 

55 

.0182 

75 

33 

9S 

0.0625 

P 

.0278 

5'' 

•  0179 

7« 

32 

0<> 

0104 

0.0588 

37 

.0270 

57 

•0175 

77 

3° 

97. 

0103 

0.0556 

38 

.0263 

P 

.0172 

7» 

9K 

0102 

0.0526 

39 

.0256 

59 

.0169 

79 

27 

)9 

oior 

0.0500 

40 

.0250 

do 

.0167 

So 

25 

0100 

0.0476 

4> 

.0244 

<ii 

.0164 

9t 

23 

—(Clark  &  Sabine. ) 
Recoil  Circuit— (See  Circuit,  Recoil.) 

Record,    Chronograph A    record 

made  by  means  of  a  chronograph  for  the  pur- 
pose of  measuring  and  recording  small  inter- 
vals of  time.  (See  Chronograph^  Electric) 

Record,  Gramophone  —  — The  irregular 
indentations,  cuttings  or  tracings  made  by  a 
point  attached  to  the  diaphragm  spoken 
against,  and  employed  in  connection  with  the 
receiving  diaphragm  for  the  reproduction  of 
articulate  speech. 

Record,  Graphophone  —  —The  record 
made  by  the  movement  of  the  diaphragm  of 
the  graphophone.  (See  Phonograph) 

Record,  Phonographic  —  — The  record 
produced  in  a  phonograph,  for  the  subse- 
quent reproduction  of  audible  articulate 
speech. 

Record,  Telephonic  -  —The  record 
produced  by  the  diaphragm  of  a  receiving 
telephone. 

Various  methods  have  been  proposed  for  ob- 
taining telephonic  records,  but  none  of  them 
have  yet  been  introduced  into  actual  commercial 
use. 

Recorder,  Chemical,  Bain's  —  — An  ap- 
paratus for  recording  the  dots  and  dashes  of 


Ree,] 


441 


[Eec. 


a  Morse  telegraphic  dispatch,  on  a  sheet  of 
chemically  prepared  paper. 

A  fillet  of  paper  soaked  in  some  chemical  sub- 
stance, such  as  ferro-cyanide  of  potassium,  is 
moved  at  a  uniform  rate  between  the  two  ter- 
minals of  the  line,  one  of  which  is  iron  tipped,  so 
that  on  the  passage  of  the  current,  a  blue  dot,  or  a 
dash,  will  be  made  on  the  paper  according  to  the 
length  of  time  the  current  is  passing. 

In  order  to  insure  a  moist  condition  of  the  paper 
fillet,  some  deliquescent  salt,  like  ammonium 
nitrate,  is  generally  mixed  with  the  ferro-cyanide 
of  potassium. 


Fig.  467.    B, 


A  Bain  recorder  is  shown  in  Fig.  467.  A,  is 
a  drum  of  brass,  tinned  on  the  outside.  The 
paper  fillet  is  drawn  from  the  roll  and  kept 
pressed  against  the  cylinder  A,  by  a  s'mall  wooden 
roller  B.  The  needle,  which  is  a  metallic  point, 
is  placed  in  connection  with  one  end  of  the  line 
wire,  and  the  brass  drum  is  connected  with  the 
other  end  through  the  earth.  Care  must  be  ob- 
served to  connect  the  needle  point  with  the  posi- 
tive electrode,  as  otherwise  the  paper  will  not  be 
marked.  (See  Electrolysis.) 

The  Bain  recorder  is  now  almost  entirely  re- 
placed by  the  Morse  sounder.  (See  Sounder, 
Morse  Telegraphic.) 

Recorder,  Morse An  apparatus  for 

automatically  recording  the  dots  and  dashes 
of  a  Morse  telegraphic  dispatch,  on  a  fillet  of 
paper  drawn  under  an  indenting  or  marking 
point  on  a  striking  lever,  connected  with  the 
armature  of  an  electro-magnet. 

This  apparatus  is  sometimes  called  a  Morse 
register. 

The  Morse  recording  or  registering  apparatus 
is  shown  in  Fig.  468. 

The  paper  fillet  passes  between  a  pair  of  rollers 
r,  driven  by  the  clockwork  W.  The  upper  roller 
is  provided  with  a  groove,  so  that  the  movement 
of  the  stylus  at  the  bent  end  of  the  lever  L,  by  the 


electro-magnet  M,  moving  its  armature  attached 
to  the  lever  L,  may  indent  or  emboss  the  paper 
fillet.  When  no  current  is  passing,  the  armature 
of  the  magnet  and  the  lever  L,  are  drawn  back  by 
the  action  of  an  adjustable  spring  at  n. 


Fig.  468.     Morse  Recorder. 

In  the  drawing,  the  ordinary  Morse  sounder  is 
shown  on  the  right.  The  sounder  has  almost 
entirely  replaced  the  recording  apparatus. 

Recorder,  Siphon An  apparatus 

for  recording  in  ink  on  a  sheet  of  paper,  by 
means  of  a  fine  glass  siphon  supported  on  a 
fine  wire,  the  message  received  over  a  cable. 

One  end  of  the  siphon  dips  in  a  vessel  of  ink. 
The  record  is  received  on  a  fillet  of  paper  moved 
mechanically  under  the  siphon.  The  ink  is  dis- 
charged from  the  siphon  by  electric  charges  im- 
parted to  the  ink  by  a  static  electric  machine. 


Fig.  469.  The  Siphon  Recorder. 
In  the  annexed  sketch  of  the  siphon  recorder, 
Fig.  469,  a  light  rectangular  coil  b  b,  of  very  fine 
wire,  is  suspended  by  a  thin  wire  f  f ,  between  the 
poles  N,  S,  of  a  powerful  compound  permanent 
magnet,  and  moving  on  the  vertical  axis  of  the 
supporting  wire  f  f,  and  adjustable  as  to  tension, 
at  h.  A  stationary  soft  iron  core  a,  is  magnetized 


SI    PHON     RECORDER 

Fig.  470.    Record  of  Siphon  Recorder. 

by  induction  and  strengthens  the  magnetic  field 
of  N,  S.     The  cable  current  is  received  by  the 


Rec.] 


[Ref. 


coil  b  b,  through  the  suspending  wire  f  f ,  and  is 
moved  by  it  to  the  right  or  the  left,  according  to 
its  direction,  to  an  extent  that  depends  on  the 
current  strength. 

The  fine  glass  siphon  n,  which  dips  into  a 
reservoir  of  ink  at  m,  is  capable  of  movement  on 
a  vertical  axis  1,  and  is  moved  backwards  or  for- 
wards, in  one  direction  by  a  thread  k,  attached 


S    E    T   T    L     ED' 

Fig.  47 1.    Record  of  Siphon  Recorder. 
to  b,  and  in  the  opposite  direction  by  a  retractile 
spring  attached  to  an  arm  of  the  axis  1. 

As  the  paper  is  moved  under  the  point  of  the 
siphon,  an  irregular  curved  line  is  marked  thereon. 

Two  records  as  actually  received  by  a  siphon 
recorder  are  shown  in  the  Figs.  470  and  471. 
Movements  upwards  correspond  to  the  dots,  and 
downwards  to  dashes. 

Rectification  of  Alcohol,  Electric  — 
—(See  Alcohol,  Electric  Rectification  of.) 

Rectified. — Turned  in  one  and  the  same 
direction. 

The  alternate  currents  in  a  dynamo-electric 
machine  are  rectified  or  caused  to  flow  in  one  and 
the  same  direction  by  means  of  a  commutator. 

The  word  commuted,  generally  used  in  this 
connection,  would  appear  to  be  preferable  to  the 
word  rectified.  (See  Commutator.) 

Rectilinear  Co-ordinates,  Abscissa  of 

— (See  Abscissa  of  Rectilinear  Co-ordinates?) 

Rectilinear  Current — (See  Current,  Rec- 
tilinear?) 

Red  Heat— (See  Heat,  Red.) 

Red  Hot— (See  Hot,  Red.) 

Redncteur  or  Resistance  for  Voltmeter. 
— A  coil  of  known  resistance  as  compared 
with  the  resistance  of  the  coils  of  a  voltmeter, 
and  connected  with  them  in  series  for  the 
purpose  of  increasing  the  range  of  the  instru- 
ment. (See  Voltmeter.) 

Rednctenr  or  Shunt  for  Ammeter.— A 
shunt  coil  connected  in  multiple  with  the  coils 
of  an  ammeter  for  the  purpose  of  changing 
the  value  of  the  readings. 

The  ratio  of  the  resistance  of  the  reducteur  and 
the  ammeter  coils  is  known.  A  reducteur  in- 
creases  the  range  of  current  measured  by  the  am- 


Refiuiug  of  Metals,  Electric The 

refining  of  metals  by  the  application  of  elec- 
trolysis. 

When  certain  precautions  are  taken,  metals 
thrown  down  from  their  solutions,  are  obtained  in 
a  chemically  pure  condition.  This  fact  is  utilized 
in  the  electrical  refining  of  metals.  If,  for  exam- 
ple, a  plate  of  impure  copper  is  to  be  refined 
electrolytically,  it  is  used  as  the  anode  of  a  copper 
bath,  and  placed  opposite  a  thin  plate  of  pure  cop- 
per forming  the  kathode.  The  passage  of  the 
current  gradually  dissolves  the  copper  from  the 
plate  at  the  anode,  and  deposits  it  in  a  chemically 
pure  condition  on  the  plate  at  the  kathode. 

Somewhat  similar  principles  are  employed  for 
electrically  refining  other  metals. 

Reflect. — To  throw  off  from  a  surface,  ac- 
cording to  the  laws  of  reflection,  as  of  waves 
in  an  elastic  medium.  (See  Reflection,  Laws 
of) 

Reflecting. — Throwing  off  from  a  surface, 
according  to  the  laws  of  reflection.  (See 
Reflection,  Laws  of.) 

Reflecting  Galvanometer. — (See  Gal- 
vanometer, Reflecting.) 

Reflection.— The  throwing  back  of  a  body 
or  wave  from  a  surface  at  an  angle  equal  to 
that  at  which  it  strikes  such  surface.  (See 
Reflection,  Laws  of.) 

Reflection,  Laws  of The  laws  gov- 
erning the  reflection  of  light 

(I.)  The  angle  of  reflection,  or  the  angle  in- 
cluded between  the  reflected  ray  and  the  perpen- 
dicular to  the  reflecting  surface  at  the  point  of 
incidence,  is  equal  to  the  angle  of  incidence,  or 
the  angle  included  between  the  striking  ray  and 
the  perpendicular  to  the  reflecting  surface  at  the 
point  of  incidence. 

(2.)  The  plane  of  the  angle  of  incidence  co- 
incides with  the  plane  of  the  angle  of  reflection. 

Reflection  of  Electro-Magnetic  Wares. 

— (See  Waves,  Electro-Magnetic,  Reflection 
of) 

Reflection  of  Induction. — (See  Induc- 
tion, Reflection  of) 

Reflector. — A  plane  or  curved  surface, 
capable  of  regularly  reflecting  light. 

Reflector,  Parabolic A  reflector, 


Ref.j 


443 


[Reg. 


or  mirror,  the  reflecting  surface  of  which  is 
a  paraboloid,  or  such  a  surface  as  would  be 
obtained  by  the  revolution  of  a  parabola 
about  its  axis. 

A  parabolic  curve,  which  may  be  regarded  as 
a  section  of  a  parabola,  is  shown  in  Fig.  472. 
A  parabola  has  the  following  properties:  If  lines 
F  P,  F  P,  etc.,  be  drawn  from  the  point  F, 
called  the  focus,  to  any  point,  P,  P,  etc.,  in  the 
curve,  and  the  lines  Pp,  Pp,  Pp,  etc.,  be  then 
drawn  severally  parallel  to  the  axis,  V  M,  then 
all  such  angles,  F  P  p,  F  P  p,  will  be  bisected  by 
verticals  to  tangents  at  the  point  P,  P,  and  P. 

Therefore,  if  a  light  be  placed  at  the  focus  of  a 
parabolic  reflector,  all  the  light  reflected  from  the 
surface  of  the  parabola  will  pass  off  sensibly  par- 
allel to  the  axis  V  M. 

In  Locomotive  Head  lights,  a 
lamp  is  placed  at  the  focus  of 
a  parabolic  reflector,  and  the 
parallel  beam  so  obtained  is 
utilized  for  the  illumination  of 
the  track.  In  a  search  light  an  v  1 
electric  arc  lamp  is  placed  at 
the  focus  of  a  parabolic  reflec- 
tor,  or  at  the  focus  of  a  lens. 

A    parabolic    reflector     is 
used  for  search  lights,   some-  Fig.  472.    Parabolic 
times  in  connection  with  an  Reflector. 

arc  lamp.  A  focusing  arc  lamp  must  be  used  for 
this  purpose,  so  as  to  maintain  the  voltaic  arc  at 
the  focus  of  the  parabolic  reflector,  notwithstand- 
ing the  unequal  consumption  of  the  positive  and 
negative  carbons.  (See  Arc,  Voltaic.) 

Refract. — To  change  the  direction  of  waves 
in  any  elastic  medium  in  accordance  with 
the  laws  of  refraction.  (See  Refraction.) 

Refracting. — Changing  the  direction  of 
waves  in  an  elastic  medium  in  accordance 
with  the  laws  of  refraction. 

Refraction. — The  bending  of  a  ray  of 
sound,  light,  heat,  or  electro-magnetism  at 
the  surface  of  any  medium  whose  density 
differs  from  that  through  which  such  ray 
was  previously  passing. 

Rays  of  sound,  light,  heat  or  electro-mag- 
netism are  transmitted  or  propagated  in  straight 
lines  as  long  as  the  density  of  the  homogeneous 
medium  through  which  they  are  passing  under- 
goes no  change.  That  is,  as  long  as  the  medium 


is  homogeneous  or  isotropic.  (See  Medium,  Iso- 
tropic.)  As  the  rays  enter  the  surface  of  a 
medium  which  differs  in  density  from  that  through 
which  they  have  been  passing,  they  are  bent  or 
refracted  at  the  surface  of  such  a  medium. 

This  bending  takes  place  towards  a  perpen- 
dicular to  the  refracting  surface  at  the  point  of  in- 
cidence, when  the  medium  into  which  the  rays  are 
entering  is  of  greater  density  than  that  they  are 
leaving,  and  from  the  perpendicular  when  the 
medium  they  are  entering  is  of  less  density  than 
that  they  are  leaving. 

•  The  refraction  or  bending  of  the  ray  is  caused 
by  the  difference  in  the  velocity  with  which  the 
waves  are  propagated  through  the  two  media. 

There  is  no  refraction  or  deviation  when  the 
two  rays  enter  the  new  medium  at  right  angles 
to  its  surface,  or  when  there  is  no  angle  of  inci- 
dence. 

Refraction,  Double — The  property 

possessed  by  certain  substances  of  splitting 
up  a  ray  of  light  passed  through  them  into 
two  separate  rays,  and  thus  doubly  refracting 
the  ray. 

Certain  specimens  of  calc  spar  possess  the  prop- 
erty of  double  refraction.  Each  of  the  two  rays 
into  which  the  original  ray  is  separated  is  polar- 
ized. Such  calc  spar  is  called  doubly  refracting 
calc  spar. 

Refraction,  Double,  Electric The 

property  of  doubly  refracting  light  acquired 
by  some  transparent  substances  while  in  an 
electrostatic  or  electro-magnetic  field. 

Transient  or  momentary  powers  of  double 
refraction,  acquired  by  a  transparent  sub- 
stance while  placed  in  an  electric  field. 

The  intensity  of  double  refraction  is  propor- 
tioned to  the  square  of  the  electric  force. 

The  action  of  an  electric  field  in  endowing  a 
substance  with  the  power  of  double  refraction 
while  kept  in  such  field,  is  due  to  the  strain  pro- 
duced by  the  electrostatic  stress  of  the  field. 

A  similar  transient  power  of  double  refraction 
is  acquired  by  many  bodies  when  subjected  to 
the  strain  produced  by  a  simple  mechanical 
stress. 

Refreshing  Action  of  Current.— (See  Ac- 
tion, Refreshing,  of  Current?) 

Region,  Extra-Polar A  term  ap- 
plied in  electro-therapeutics  to  the  region 


Beg.] 


444 


[Beg. 


which  lies  outside  or  beyond  the  therapeutic 
electrode. 

The  term  extra-polar  region  is  used  in  contra- 
distinction to  polar  region.  (See  Region,  Polar.) 

Region,  Polar A  term  applied  in 

electro-therapeutics  to  that  region  or  part  of 
the  body  which  lies  directly  below  the  thera- 
peutic electrode. 

Register,  Double-Fen  Telegraphic 

— A  telegraphic  register  provided  with  two 
separate  styluses  or  pens  for  recording  the 
telegraphic  message  on  a  fillet  of  paper.  (See 
Register,  Telegraphic) 

Register,  Morse A  name  sometimes 

given  to  a  Morse  recorder.  (See  Recorder, 
Morse.) 

Register,  Telegraphic An  appa- 
ratus employed  at  the  receiving  end  of  a  tele- 
graphic line  for  the  purpose  of  obtaining  a 
permanent  record  of  the  telegraphic  dispatch. 

The  telegraphic  register  consists  essentially  of 
means  whereby  a  fillet  or  tape  of  paper  is  drawn 
mechanically  under  a  pen  or  stylus  attached  to 
the  armature  of  an  electro-magnet  and  moving 
therewith. 

The  pen  or  stylus  presses  against  the  paper 
whenever  the  armature  is  attracted  to  the  elec« 
tro-magnet,  and  is  held  there  while  the  cur- 


Fig-  473  f**~  Writing  Register. 
rent  is  passing  through  the  coils  of  the  electro- 
magnet. By  these  means  the  dots  and  dashes  of 
the  telegraphic  alphabet  are  recorded  on  the 
paper  fillet  as  embossed  or  printed  dots  and 
dashes.  The  Morse  register  is  an  apparatus  of 
this  description.  (See  Recorder,  Morse.) 

A  form  of  ink-writing  telegraphic  register  is 
«howninFig.  473.    It  is  self-starting. 


Register,  Time,  for  Railroads A 

telegraphic  recording  apparatus  or  register 
designed  to  record  all  telegraphic  messages 
transmitted  over  a  line. 

The  record  is  received  on  an  endless  band  or 
fillet  of  paper.  It  is  useful  in  case  of  disputes  as 
to  the  time  certain  messages  were  sent  over  the 
line. 

Register,  Watchman's  Electric 

A  device  for  permanently  recording  the  time 
of  a  watchman's  visit  to  each  of  the  dif- 
ferent localities  he  is  required  to  visit  at  stated 
intervals. 

These  registers  are  of  a  variety  of  forms.  They 
consist,  however,  in  general,  of  a  drum  or  disc  of 
paper  driven  by  clockwork,  on  which  a  mark  is 
made  by  a  stylus  or  pencil,  operated  on  the  clos- 
ing of  a  circuit  by  the  pressing  of  a  push  button 
or  the  pressing  of  a  key  by  the  watchman  at  each 
station. 

Registering  Apparatus,  Electric 

(See  Apparatus,  Registering,  Electric?) 

Registering  Electrometer.— (See  Elec- 
trometer, Registering?) 

Regulable,  Automatically Capa- 
ble of  being  automatically  regulated.  (See 
Regulation,  Automatic?) 

Regulate,  Automatically To  regu- 
late in  an  automatic  manner.  (See  Regula- 
tion, Automatic) 

Regulation,  Automatic Regulation 

automatically  effected. 

Regulation,  Automatic,  of  Dynamo-Elec- 
tric Machine Such  a  regulation  of  a 

dynamo-electric  machine  as  will  automati- 
cally preserve  constant  either  the  current  or 
the  potential  difference. 

The  automatic  regulation  of  dynamo-electric 
machines  may  be  accomplished  in  the  following 
ways,  viz.: 

(I.)  By  a  Compound  Winding  of  the  Machine. 

This  method  is  particularly  applicable  to  con- 
stant-potential  machines.  By  this  winding,  the 
magnetizing  effect  of  the  shunt  coils  is  maintained 
approximately  constant,  while  that  of  the  series 
coils  varies  proportionally  to  the  load  on  the  ma- 
chine. 

The  series  coils  are  sometimes  wound  close  to 


Reg.] 


445 


[Beg. 


the  poles  of  the  machine,  and  the  shunt  coils 
nearer  the  yoke  of  the  magnets.  Custom,  how- 
ever, varies  in  this  respect,  and  very  generally 
the  shunt  coils  are  placed  nearer  the  poles  than 
the  series  coils.  (See  Machine,  Dynamo-Electric, 
Compound-  Wound?) 

(2.)  By  Shifting  the  Position  of  the  Collecting 
Brushes. 

In  the  Thomson-Houston  system  of  current 
regulation,  the  current  is  kept  practically  con- 
stant by  the  following  devices:  The  collecting 
brushes  are  fixed  to  levers  moved  by  the  regula- 
tor magnet  R,  as  shown  in  Fig.  474,  the  arma- 
ture of  which  is  provided  with  an  opening  for  the 
entrance  of  the  paraboloidal  pole  piece  A.  A 
dash-pot  is  provided  to  prevent  too  sudden  move- 
ment. 

When  the  current  is  normal,  the  coil  of  the 
regulator  magnet  is  short-circuited  by  contact 
points  at  S  T,  which  act  as  a  shunt  of  very  low  re- 
sistance. These  contact  points  are  operated  by 
the  solenoid  coils  of  the  controller,  traversed  by 
the  main  current.  The  cores  of  this  solenoid  are 
suspended  by  a  spring.  When  the  current  be- 
comes too  strong,  the  contact  point  is  opened, 
and  the  current,  traversing  the  coil  of  the  regu- 
lar magnet  A,  attracts  its  armature,  which  shifts 
the  collecting  brushes  into  a  position  in  which  a 
smaller  current  is  taken  off. 

A  carbon  shunt,  r,  of  high  resistance,  is  pro. 
vided  to  lessen  the  spark  at  the  contact  points  S 
T,  which  occurs  on  opening  the  circuit. 


Fig.  474.     Thomson-Houston  Regulator. 

In  operation  the  contact  points  are  continually 
opening  and  closing,  thus  maintaining  a  practi- 
cally constant  current  in  the  external  circuit. 

(3.)  By  the  Automatic  Variation  of  a  Resist- 
ance shunting  the  field  magnets  of  the  machine, 
as  in  the  Brush  system. 

In  Fig.  475  the  variable  resistance  C,  forms  a 
part  of  the  shunt  circuit  around  the  field  mag- 
nets F  M.  This  resistance  is  formed  of  a  pile  of 
carbon  plates.  On  an  increase  of  the  current, 
such,  for  example,  as  would  result  from  turning 
out  some  of  the  lamps,  the  electro-magnet  B, 


placed  in  the  main  circuit,  attracts  its  armature 
A,  and,  compressing  the  pile  of  carbon  plates  C, 
lowers  their  resistance,  thus  diverting  a  propor- 
tionally larger  portion  of  the  current  from  the 
field  magnet  coils  F  M,  and  maintaining  the  cur- 
rent practically  constant. 

In  some  machines  the  same  thing  is  done  by 
hand,  but  this  is  objectionable,  since  it  requires 
the  presence  of  an  attendant. 

(4.)  By  the  Introduction  of  a  Variable  Resist- 
ance into  the  shunt  circuit  of  the  machine,  as  ia 
the  Edison  and  other  systems. 


Fig-  47 S-    The  Brush  Regulator. 

This  resistance  may  be  adjusted  either  auto- 
matically  by  an  electro-magnet  whose  coils  are 
in  an  independent  shunt  across  the  mains,  or  may 
be  operated  by  hand. 

In  Fig.  476,  the  variable  resistance  is  shown 
at  R,  the  lever  switch  being  in  this  case  operated 
by  hand  whenever  the  potential  rises  or  falls  be- 
low the  proper  value. 


Fig.  476.     The  Edison  Regulator. 

The  machine  shown  is  thus  enabled  to  main- 
tain a  constant  potential  an.  the  leads  to  which  the 
lamps  L,  L,  L,  etc.,  are  connected  in  multiple  arc. 

(5.)  Dynamometric  Governing,  ID  which  a 
series  dynamo  is  made  to  yield  a  constant  cur- 
rent by  governing  the  steam  engine  that  drives 
it,  by  means  of  a  dynamometric  governor.  This 
governor  operates  by  maintaining  a  constant 
torque  or  turning  moment,  instead  of  by  means  of 


Beg.] 


446 


[Bel. 


the  usual  centrifugal  governor  which  maintains  a 
constant  speed. 

(6.)  Electric  Governing  of  the  Drivi ng  Engine, 
in  which  the  governor  is  regulated  by  the  cur- 
rent itself  instead  of  by  the  speed  of  rotation,  as 
usual. 

Regulation,  Hand Such  a  regula- 
tion of  a  dynamo-electric  machine  as  will  pre- 
serve constant,  either  the  current  or  the 
potential,  said  regulation  being  effected  by 
hand  as  distinguished  from  automatic  regu- 
lation. 

Regulator,  Automatic  — A  device 

for  securing  automatic  regulation  as  dis- 
tinguished from  hand  regulation.  (See 
Regulation,  Hand.  Regulation,  Automatic.) 

Regulator,  Hand  — A  resistance 

box,  the  separate  coils  or  resistances  of  which 
can  be  readily  placed  in  or  removed  from  a 
circuit  by  means  of  a  hand-moved  switch. 

The  term  hand  regulator  is  used  as  distin- 
guished from  automatic  regulator.  (See  Regu- 
lator, Automatic.  Regulation,  Automatic.) 

Regulator  Magnet.— (See  Magnet,  Regu- 
lator) 

Regulator,  Monophotal  Arc-Light  

— A  term  sometimes  employed  for  an  electric 
arc  lamp  in  which  the  whole  current  passes 
through  the  arc-regulating  mechanism,  and 
which  is  usually  operated  singly  in  circuit 
with  a  dynamo. 

Regulator,  Polyphotal  Arc-Lamp 

A  regulator  for  an  arc  lamp  suitable  for 
maintaining  a  number  of  lamps  in  series  cir- 
cuit with  the  dynamo. 

Polyphotal  regulators  differ  from  monophotal 
regulators  in  that  their  regulating  electro -mag- 
nets are  energized  by  a  shunt  circuit  around  the 
electrodes  of  the  lamp,  while  in  monophotal  regu- 
lators such  electro-magnets  are  placed  in  the  di- 
rect circuit  The  terms  monophotal  and  poly- 
photal  are  not  generally  used  in  America. 

Regnline  Electro-Metallurgical  Deposit. 

—(See  Deposit,  Electro-Metallurgical,  Reg- 
uline) 

RejnTenation  of  Luminescence. — (See 
Luminescence,  Rejuvenation  of) 


Relative  Calibration.— (See  Calibration, 
Relative) 

Relay. — An  electro-magnet,  employed  in 
systems  of  telegraphy,  provided  with  contact 
points  placed  on  a  delicately  supported  arma- 
ture, the  movements  of  which  throw  a  battery, 
called  the  local  battery,  into  or  out  of  the 
circuit  of  the  receiving  apparatus. 

A  relay  is  sometimes  called  a  receiving  magnet. 


Fig.  477 •     Telegraphic  Relay. 

The  use  of  a  relay  permits  much  smaller  cur- 
rents to  be  used  than  could  otherwise  be  done, 
since  the  electric  impulses,  on  reaching  a  distant 
station,  are  required  to  do  no  other  work  than 
attracting  a  delicately  poised  movable  contact, 
and  thus,  by  throwing  a  local  battery  into  the 
circuit  of  the  receiving  apparatus,  to  cause  such 
local  battery  to  perform  the  work  of  register- 
ing. Its  use  is  especially  required  in  the  Morse 
system  of  telegraphy  in  order  to  cause  the  sounder 
to  be  distinctly  heard. 

A  form  of  relay  that  is  much  used  is  shown  in 
Fig-  477- 

The  electro-magnet  M,  is  wound  with  many 
turns  of  very  fine  wire.  In  the  form  used  by  the 
Western  Union  Telegraph  Company,  there  are 
about  8, 500  turns,  having  resistance  of  150  ohms. 
A  screw  m,  is  provided  for  moving  the  electro- 
magnet M,  a  slight  distance  in  or  out,  for  the  pur- 
poses of  adjustment  A  semi-cylindrical  arma- 
ture A,  of  soft  iron,  is  attached  to  the  insulated 
armature  lever  a,  the  lower  end  of  which  is  sup- 
ported by  a  steel  arbor,  which  is  pivoted  between 
two  set  screws. 

A  retractile  spring  S',  regulable  at  S,  is  pro, 
vided  for  moving  the  armature  away  from  the 
electro-magnet.  There  are  four  binding  posts, 
two  of  which  are  placed  in  the  circuit  of  the 
electro-magnet,  and  two  hi  that  of  the  local  bat- 
tery. The  ends  of  the  line  wire  are  connected 
with  the  former,  and  the  receiving  instrument 
placed  in  the  circuit  of  the  latter.  A  platinum 


Rel.] 


447 


[Rel. 


contact  is  placed  on  the  end  of  a  screw  supported 
at  F,  opposite  a  similar  contact,  near  the  end  a, 
of  the  armature  lever.  The  contact  is  regulable 
by  means  of  a  screw  c. 

On  the  energizing  of  the  electro-magnet,  the 
attraction  of  its  armature  closes  the  platinum 
contact,  and,  by  thus  completing  the  circuit  of  the 
local  battery,  causes  an  attraction  of  the  armature 
of  the  receiving  apparatus.  On  the  cessation  of 
the  current  in  the  main  line,  the  spring  S',  pulls 
the  armature  away  from  the  magnet,  breaks  the 
circuit  of  the  local  battery,  and  thus  permits  a 
similar  spring  on  the  receiving  instrument  to  pull 
its  armature  away.  Thus  all  the  movements  of 
the  armature  of  the  relay  are  reproduced  with  in- 
creased intensity  by  the  armature  of  the  receiving 
instrument. 

The  connections  of  the  relay  to  the  local  bat- 
tery  and  the  registering  apparatus,  will  be  better 
understood  from  an  inspection  of  Fig.  478,  which 
represents  a  form  of  relay  much  used  in  Germany. 


Relay,  Differential A  telegraphic 


Fig.  47 S.     Telegraphic  Relay,  German  Pattern. 

The  retractile  spring  f,  is  regulated  by  the  up- 
and-down  movements  of  its  lower  support,  which 
slides  in  the  vertical  pillar  S.  The  line  wire  is 
shown  at  m  m,  connected  at  one  end  to  earth  by 
a  ground  wire. 

The  registering  apparatus  R,  is  connected  in 
the  circuit  of  the  local  battery  L,  as  shown. 
The  contacts  are  made  by  the  end  B,  of  the  lever 
B  B',  attached  to  the  armature  A,  of  the  electro- 
magnet M  M. 

Relay  Bell.— (See  Bell,  Relay,  Electric) 

Relay,  Box-Sounding  Telegraphic  

— A  relay  the  magnet  of  which  is  surrounded 
by  a  resonant  case  of  wood  for  the  purpose 
of  increasing  the  intensity  of  the  sound  made 
by  the  armature  of  the  magnet. 

A  form  of  box-sounding  relay  is  shown  in  Fig. 
479- 


Fig.  479.     Box-Sounding  Relay 


relay  containing  two  differentially  wound  coils 
of  wire  on  its  magnet  cores. 

When  the  currents  which  pass  through  these 
two  coils  are  of  the  same  strength,  there  is  no 
movement  of  the  armature,  since  the  fields  of  the 
two  coils  neutralize  each  other. 

The  differential  relay  is  used  in  the  differential 
method  of  duplex  and  quadruplex  telegraphy. 
(See  Telegraphy,  Duplex  Differential  Method  of. 
Telegraphy,  Quadruplex  Differential  Method  of  .) 

Relay  Magnet. — A  name  sometimes  given 
to  a  relay.  (See  Relay,) 

Relay,  Microphone A  device  for 

automatically  repeating  a  telephonic  message 
over  another  wire. 


Ftg .  480.    Microphone  Relay. 

A  form  of  microphone  relay  is  shown  in  Figs. 
480  and  481. 

Several  minute  microphones  mounted  on  the 


Fig.  481.    Microphone  Relay. 

diaphragm  of  the  telephone  whose  message  is  to 
be  repeated,  so  vary  the  resistance  of  a  local  bat- 
tery included  in  their  circuit  as  to  automatically 
repeat  the  articulate  speech  received. 

The  microphones  may  be  connected  either  in 


Rel.] 


448 


[Rel. 


multiple  arc  or  in  series,  as  shown  respectively  to 
the  left  and  right  in  Fig.  480. 

Relay,  Pocket  Telegraphic A  form 

of  telegraphic  relay  of  such  small  dimensions 
as  to  permit  it  to  be  readily  carried  in  the 
pocket. 

Relay,  Polarized A  telegraphic  re- 
lay provided  with  a  permanently  magnetized 
armature  in  place  of  the  soft  iron  armature  of 
the  ordinary  instrument. 

In  the  form  of  polarized  relay  shown  in  Fig. 
482,  N  S,  is  a  steel  magnet,  whose  magnetism  is 
consequently  permanent,  with  its  north  and  south 
poles  at  N,  and  S,  respectively.  The  cores  of 
the  electro-magnet  m,  m',  are  of  soft  iron,  and, 
since  they  rest  on  the  north  pole  of  the  permanent 
steel  magnet,  the  poles,  brought  very  near  to- 
gether by  the  armatures  at  n,  n',  will  be  of  the 
same  polarity  as  N,  when  no  current  is  passing 
through  the  coils  m,  m' ;  but  when  such  current 
does  pass,  one  of  these  poles  becomes  of  stronger 
north  polarity,  while  the  other  changes  its  polar- 
ity to  south. 

By  these  means  to-and  fro  movements  of  the 
armature  lever,  with  its  contact  point,  are  effected 
without  the  use  of  a  retractile  spring  ;  movement 
in  one  direction  occurring  on  the  closing  of  the 
circuit  due  to  the  electro-magnetism  developed 


Fig.  482.    Polarized  Relay. 

by  the  coils  m,  m',  and  movement  in  the  opposite 
direction,  on  the  losing  of  this  magnetism  on 
breaking  the  circuit,  by  the  permanent  magnet- 
ism of  the  steel  magnet  N  S. 

These  movements  are  imparted  to  the  soft  iron 
lever  c,  c',  pivoted  at  B,  and  passing  between  the 
closely  approached  soft  iron  poles  at  n,  n'.  This 
lever  rests  at  the  end  c',  against  a  contact  point 


when  moved  in  one  direction,  and  against  an  in- 
sulated point  when  moved  in  the  opposite  direc- 
tion. It  rests  against  the  insulated  point  when 
no  current  is  passing  through  the  coils  m,  m'. 

If  the  armature  lever  were  placed  in  a  position 
exactly  midway  between  the  poles  n,  and  n',  it 
would  not  move  at  all,  being  equally  attracted  by 
each;  but  if  moved  a  little  nearer  one  pole  than 
the  other,  it  would  be  attracted  to,  and  rest 
against,  the  nearer  pole. 

When  alternating  currents  are  employed  on 
the  line,  the  lever  c,  c',  must  be  adjusted  as  nearly 
as  possible  in  the  middle  of  the  space  between  n 
and  n',  in  which  case  it  will  remain  on  the  side  to 
which  it  was  last  attracted,  until  a  current  in  the 
opposite  direction  moves  it  to  the  other  side. 


Fig-  483.     A  Detail  of  the  Polarized  Relay. 

The  space  between  the  magnet  poles  n,  n', 
and  the  contacts  of  the  armature  lever  at  D,  and 
D',  are  shown  in  detail  in  Fig.  483,  which  is  a 
plan  of  Fig.  482.  The  binding  posts  for  the  line 
battery  are  shown  at  L  B,  i,  and  2,  and  those 
for  the  local  battery  at  A  and  B.  The  dotted 
lines  show  the  connections. 

Since  the  polarized  relay  dispenses  with  the  re- 
tractile spring,  it  is  far  more  sensitive  than  the 
ordinary  instrument.  Once  adjusted,  no  further 
regulation  is  required,  in  which  respect  it  differs 
very  decidedly  from  non. polarized  relays. 

There  are  other  forms  of  polarized  relays,  but 
the  above  will  suffice  to  illustrate  the  general 
principle  of  their  operation. 

Relay  Shunt,  Steam's (See  Shunt, 

Relay,  Steam's?) 

Reluctance,  Magnetic A  term  re- 
cently proposed  in  place  of  magnetic  resist- 
ance to  express  the  resistance  offered  by  a 


Rel.] 


449 


[Rep. 


medium  to  the  passage  through  its  mass  of 
lines  of  magnetic  force. 

The  term  reluctance,  in  the  sense  of  resistance 
to  passage  of  lines  of  magnetic  force,  has  been 
proposed  in  place  of  resistance,  for  the  purpose 
of  carrying  out  the  conception  of  regarding  the 
flow  of  lines  of  force  in  a  magnetic  circuit  as 
being  due  to  a  magneto-motive  force,  and  being 
opposed  by  a  reluctance  of  the  substances  form- 
ing such  circuit  to  the  passage  of  such  lines. 

According  to  this  conception, 

The  magnetic  flux  = 

The  magneto-motive  force 
The  reluctance. 

Reluctance,   Magnetic,  Unit  of 

Such  a  magnetic  reluctance  in  a  closed  cir- 
cuit that  permits  unit  magnetic  flux  to 
traverse  it  under  the  action  of  unit  magneto- 
motive force. 

In  present  practical  work  reluctances  vary 
from  100,000  to  100,000,000  of  the  practical 
units. 

Reluctivity. — A  term  proposed  for  mag- 
netic reluctance.  (See  Reluctance,  Mag- 
netic^) 

This  term  is  not  generally  adopted. 

Removable  Key  Switch.— (See  Switch, 
Removable  Key.) 

Renovation  of  Secondary  Cell.— (See 
Cell,  Secondary  or  Storage,  Renovation  of.) 

Renovation  of  Secondary  or  Storage 
Cell.— (See  Cell,  Secondary  or  Storage, 
Renovation  of)  •• 

Reofore.— A  rheophore.    (See  Rheophore) 

Repeaters,  Telegraphic Tele- 
graphic devices,  whereby  the  relay,  sounder 
or  registering  apparatus,  on  the  opening  and 
closing  of  another  circuit,  with  which  it  is 
suitably  connected,  is  caused  to  repeat  the 
signals  received. 

Repeaters  are  employed  to  establish  direct 
communication  between  very  distant  stations,  or 
to  connect  branch  lines  to  the  main  line. 

Fig.  484,  shows  Wood's  Button  Repeater.  This 
repeater  consists  simply  of  a  three-point  switch 
L,  capable  of  being  placed  on  the  points  I,  2  and 
3  ;  and  a  ground  switch  at  4.  The  circuits  are 
arranged  between  the  sounders  S,  S',  relays 


M,  M',  main  batteries  B,  B',  and  the  two  main 
lines  E,  and  W,  in  the  manner  shown. 


Fig.  484.     WootFs  Button  Repeater. 

If  the  lever  L,  is  in  the  position  shown  in  the 
drawing,  the  lines  E  and  W,  form  independent 
circuits. 

If  the  ground  switch  4  is  closed,  and  the  lever 
L,  is  placed  on  2,  2,  the  eastern  line  repeats  into 
the  western.  If  the  lever  L,  is  placed  on  the 
plates  3,  3,  the  western  line  repeats  into  the 
eastern. 

This  repeater  is  non- automatic  and  can  be 
worked  in  but  one  direction  at  a  time  ;  moreover, 
it  requires  the  services  of  an  attendant. 

The  automatic  repeater  can  be  operated  in  both 
directions,  and  dispenses  with  the  constant  ser- 
vices of  an  attendant  at  the  repeating  station. 

In  sending  a  dispatch  through  a  repeater,  the 
dots  and  dashes  are  prolonged  so  as  to  give  the 
lever  of  the  repeating  instrument  time  in  which 
to  move  backwards  and  forwards. 


Fig.  485.    Hick's  Automatic  Button  Repeater. 

In  Hick's  Automatic  Repeater,  shown  in  Fig. 
485,  the  switch  or  circuit- changer  is  automatic  in 
its  action. 

The  relay  magnets  are  shown  at  M,  M',  the 
sounders  at  R  and  R'  ;  f,  f ,  are  platinum  con- 
tacts  operated  by  levers  1  and  1',  and  L  and  L', 
are  extra  local  magnets,  that  act  on  armatures 


Rep.] 


450 


[Rep. 


placed  directly  opposite  the  armatures  of  the  relay 
magnets. 

The  extra  local  magnet  L,  is  cut  out  of  the 
circuit  of  B',  the  extra  local  battery,  when  the 
main  circuit  is  broken,  and  the  armature  is  in 
contact  with  c.  As  soon  as  this  happens,  how- 
ever, the  spring  s,  drawing  away  the  armature, 
and  thus  opening  the  short-circuit  of  no  resist- 
ance between  c  and  a,  establishes  a  circuit 
through  L.  On  a,  coming  in  contact  with  c,  the 
circuit  is  again  broken. 

The  tension  of  the  spring  s,  is  so  regulated  that 
a  very  rapid  vibration  of  a,  is  maintained  so  con- 
stantly, that  it  is  impossible  to  close  the  main  cir- 
cuit when  L,  is  not  cut  out.  The  armature  a, 
will  therefore  respond  to  very  weak  impulses  of 
the  relay  magnet 

On  breaking  the  western  main  circuit  N,  the 
lever  a,  vibrates  very  rapidly.  The  lever  1,  of  the 
sounder  R,  first  breaks  the  circuit  of  L,  and  after- 
wards that  of  the  eastern  main  circuit  E,  which 
passes  through  M.  Both  L'  and  M',  being 
broken,  a  slight  tension  of  s',  will  hold  a,  in 
place,  thus  avoiding  the  breaking  of  the  western 
main  circuit  through  the  closing  of  the  local  cir- 
cuit through  R.  On  the  closing  of  the  western 
circuit,  the  reverse  of  these  operations  occurs. 

The  author  has  taken  the  above  explanation 
mainly  from  Pope's  work  on  "Modern  Practice 
of  the  Electric  Telegraph." 

Repeating  Sounder. — (See  Sounder,  Re- 
peating^) 

Replenisher.— A  static  influence  machine 
devised   by  Sir  William 
Thomson    for  charging 
the    quadrants    of    his 
quadrant  electrometer. 

Two    brass    carriers    C 
and  D,  shown  in  Fig.  486, 
are  electrically  fixed  to  the 
end  of  the    vulcanite  rod 
E,  which  is  capable  of  ro- 
tation by  the  thumb  screw 
at   M,    in    the    direction 
shown  by  the  arrow.    Hol- 
low   metal   half-cylinders,  p. 
A  and  B,  act  as  inductors, 
a  strip  of  brass  fixed  around  Fig.48(>.    The  Rephn- 
the  edges  of  a  piece  of  vul- 
canite P,  connecting  the  metallic  springs  S,  and 
S',  as  shown. 

The  action  of  the  replenisher  is  readily  under- 


stood from  the  following  considerations,  as  sug- 
gested by  Ayrton  in  his  "Practical  Electricity  "  : 

A  and  B,  Fig.  487,  are  two  insulated  hollow 
metallic  vessels  having  a  small  difference  of  po- 
tential between  them,  A,  being  the  higher.  C, 
and  D,  are  two  small  uncharged  conductors  held 
by  insulating  strings.  If  C  and  D,  be  held  near 
A  and  B,  as  shown,  the  potential  of  C,  will,  by 
induction,  be  raised  somewhat  above  that  of  D, 
so  that  when  connected  by  a  conductor,  such  as 
the  metallic  wire  W,  a  small  quantity  of  positive 
electricity  will  flow  from  C,  to  D,  thus  leaving  D, 
positively,  and  C,  negatively  charged. 

If,  now,  C  and  D,  are  removed  from  W,  and 
placed  in  the  bottom  of  B  and  A,  as  shown  in 
Fig.  488,  the  difference  of  potential  between  A, 
and  B,  will  be  thereby  increased,  and  if  they  are 
then  withdrawn,  and  totally  discharged,  and 


Fig.  487.    Action  of  Replenisher. 
again  placed  in  the  first  position  shown,  an  ad- 
ditional charge  can  be  given  to  A  and  B,  and  this 
can  be  repeated  as  often  as  desired. 

In  the  replenisher,  A  and  B,  correspond  to  the 
vessels  A  and  B  ;  the  brass  carriers  C  and  D, 
to  the  balls  C  and  D,  and  the  spring  S  S,  and  M, 


Fig.  488.    Action  of  Replenisher. 
to  the  wire  W.     No  initial  charge  need  be  given 
to  A  and  B,  since  they  are  invariably  found  to 


Rep.] 


451 


[Res. 


be  at  a  sufficient  difference  of  potential  to  build 
up  the  charge. 

Replenisher,  Carriers  of The 

moving  conductors  of  a  replenisher  which 
carry  the  charges  and  thus  permit  of  an  ac- 
cumulation of  such  charges.  (See  Re- 
plenisher?) 

Repulsion,  Electric The  mutual 

driving  apart  or  tendency  to  mutually  drive 
apart  existing  between  two  similarly  charged 
bodies,  or  the  mutual  driving  apart  of  similar 
electric  charges. 

Repulsion,  Electro-Dynamic The 

mutual  repulsion  between  two  electric  circuits 
whose  currents  are  flowing  in  opposite  direc- 
tions. 

Parallel  currents  flowing  in  opposite  directions 
repel  one  another,  because  their  lines  of  magnetic 
force  have  the  same  direction  in  adjoining  parts  of 
the  circuit.  (See  Dynamics,  Electro.) 

Repulsion,  Electro-Magnetic —The 

mutual  repulsion  produced  by  two  similar 
electro-magnetic  poles. 

Repulsion,  Electrostatic  —The 

mutual  repulsion  produced  by  two  similar 
electric  charges. 

Repulsion,  Magnetic The  mutual 

repulsion  exerted  between  two  similar  mag- 
netic poles. 

Repulsion,  Molecular The  mutual 

repulsion  existing  between  molecules  arising 
from  their  kinetic  energy.  (See  Matter,  Ki- 
netic Theory  of.) 

Residual  Atmosphere — (See  Atmosphere, 
Residual.) 

Residual  Charge.— (See  Charge,  Resid- 
ual.) 

Residual  Magnetism.— (See  Magnetism, 
Residual.) 

Resin. — A  general  term  applied  to  a  variety 
of  dried  juices  of  vegetable  origin. 

Resins  are,  in  general,  transparent,  inflamma- 
ble solids,  soluble  in  alcohol,  and,  in  general, 
excellent  non-conductors  of  electricity.  Rosin  is 
one  of  the  varieties  of  resin. 

Resinous  Electricity.— (See  Electricity, 
Resinous.) 

Resistance. — Something  placed  in  a  circuit 
for  the  purpose  of  opposing  the  passage  or 


flow  of  the  current  in  the  circuit  or  branches 
of  the  circuit  in  which  it  is  placed. 

The  electrical  resistance  of  a  conductor  is 
that  quality  of  the  conductor  in  virtue  of 
which  there  is  a  fixed  numerical  ratio  be- 
tween the  potential  difference  of  the  two 
opposing  faces  of  a  cubic  unit  of  such  con- 
ductor, and  the  quantity  of  electricity  which 
traverses  either  face  per  second,  assuming  a 
steady  flow  to  take  place  normal  to  these 
faces,  and  to  be  uniformly  distributed  over 
them,  such  flow  taking  place  solely  by  an  elec- 
tromotive force  outside  the  volume  considered. 

The  term  is  used  in  the  first  definition  in  the 
concrete  sense  of  something  intended  for  or  used 
as  a  resistance.  For  the  physical  definitions  and 
facts  see  Resistance,  Electric. 

Gases  offer  very  high  resistance  to  the  flow  of 
an  electric  current.  Their  non-conducting  power 
causes  the  increase  of  resistance  which  attends 
the  polarization  of  a  voltaic  cell.  (See  Cell, 
Voltaic,  Polarization  of.) 

Resistances  consist  of  coils,  strips,  bars  or 
spirals  of  metal,  or  plates  of  carbon,  or  metallic 
powders,  powdered  or  granulated  carbon,  or 
liquids. 

Resistance,  Absolute  Unit  of The 

one  thousand  millionth  of  an  ohm.  (See 
Ohm.  Units,  Practical.) 

Resistance,  Assymmetrical Con- 
ductors or  parts  of  conductors,  which  offer  a 
greater  resistance  to  the  flow  of  an  electric 
current  in  one  direction  than  in  another. 

Assymmetrical  conductors  are  unknown,  so  far 
as  structural  peculiarities  are  concerned,  but  can 
be  obtained  by  the  use  of  counter  electromotive 
forces,  acting  as  resistance.  This  term  was  pro- 
posed by  Wilke  in  discussing  the  obtaining  of 
continuous  currents  by  commutatorless  dynamo- 
electric  machines. 

The  resistance  of  the  human  body  is  possibly  an 
assymmetrical  resistance. 

An  evident  application  of  an  assymmetrical  re- 
sistance is  to  direct  alternating  currents  so  as  to 
cause  the  current  that  passes  to  flow  in  and  to  the 
same  direction. 

Resistance,  Balanced A  resistance 

so  placed  in  a  circuit  as  to  be  balanced  or 
made  equal  to  another  resistance  connecter] 
therewith. 


Res.] 


453 


[Res, 


Resistance,  Balanced,  for  Dynamos 

— A  resistance  that  possesses  a  range  suf- 
ficient tq  balance  one  dynamo  against  another 
with  which  it  is  desired  to  run  in  parallel. 
— (  Urquhart) 

Resistance  Box.— (See  Box,  Resistance) 

Resistance  Bridge.— (See  Bridge,  Resist- 
ance?) 

Resistance  Coil.— (See  Coil.  Resistance) 

Resistance  Coil,  Standard (See 

Coil,  Resistance,  Standard) 

Resistance,  Conductivity The  re- 
sistance offered  by  a  substance  to  electric 
conduction,  or  to  the  passage  of  electricity 
through  its  mass. 

Resistance,    Dielectric A  term 

sometimes  employed  for  the  resistance  of  a 
dielectric  to  mechanical  strains  produced  by 
electrification. 

The  dielectric  resistance  of  the  glass,  or  other 
dielectric  of  a  Leyden  jar  or  condenser,  is  fre- 
quently overcome  by  the  passage  of  the  charges 
on  the  conducting  surfaces,  and  the  glass  is  thus 
pierced. 

The  term  dielectric  resistance  would  appear 
to  be  badly  chosen;  for,  like  all  substances,  dielec- 
trics possess  a  true  ohmic  resistance,  which  in- 
creases with  the  increase  of  length,  and  decreases 
with  the  increase  of  area  of  cross-section. 

The  resistance  of  the  dielectric,  however,  differs 
from  the  ordinary  ohmic  resistance  of  conductors, 
in  that  the  resistance  of  the  dielectric  is  suddenly 
overcome,  and  the  discharge  passes  disruptively 
as  a  spark. 

Resistance,  Effect  of  Heat  on  Electric 

Nearly  all  metallic   conductors  have 

their  electric  resistance  increased  by  an  in- 
crease of  temperature. 

The  carbon  conductor  of  an  incandescent  elec- 
tric lamp,  on  the  contrary,  has  its  resistance 
decreased  when  raised  to  electric  incandescence. 
The  decrease  amounts  to  about  three-eighths  of  its 
resistance  when  cold. 

The  effects  of  heat  on  electric  resistance  may  be 
summarized  as  follows: 

(i.)  The  electric  resistance  of  metallic  conduc- 
tors increases  as  the  temperature  rises.  In  some 
alloys  this  increase  is  small. 

(2.)  The  electric  resistance  of  electrolytes  de- 
creases as  the  temperature  rises. 


(3.)  The  electric  resistance  of  dielectrics  and 
non-conductors  decreases  as  the  temperature  rises. 

RESISTANCE  AND   CONDUCTIVITY   OF    PURE 
COPPER  AT  DIFFERENT  TEMPERATURES. 


.00381 

.00756 
oii35 


02280 

, 02663 
03048 
03435 
03822 
.04*99 
.04599 
.04990 
.05406 
•05774 


1. 00000 

.99624 
.99250 
.98878 
.98508 
98139 
•97771 
.97406 
•  97048 
96679 
.96319 

•9597° 
.95603 
•95247 
.94893 
.94541 


.06168 
06563 
.06959 
•07350 
.07742 
.08164 
•08553 
.08954 
•09365 
.09763 

0567 
1972 

i3«» 
1782 


•93494 
•93H8 
.92814 
•62452 


.91445 
.91110 

. 90776 
•9°443 
.00113 
.§9784 
.89457 


—(Latimer  Clark.} 

Resistance,  Electric  — —  —The  ratio  be- 
tween the  electromotive  force  of  a  circuit 
and  the  current  that  passes  therein. 

The  reciprocal  of  electrical  conductivity. 
Resistance  can  be  defined  as  the  reciprocal  of 
electrical    conductivity,  because    even   the   best 
electrical  conductors  possess  appreciable  resist- 
ance. 

Ordinarily  the  resistance  of  a  circuit  may  be 
conveniently  regarded  as  that  which  opposes  or 
resists  the  passage  of  the  current.  Strictly  speak- 
ing, however,  this  is  not  true,  since  from  Ohm's 
law  (See  Law  of  Ohm,  or  Law  of  Current 
Strength) 

E 

C  =  — ,  from  which  we  obtain 
R 
E 
R  =  — ,  which  shows  that  resistance  is  a 

C 

ratio  between  the  electromotive  force  that  causes 
the  current  and  the  current  so  produced. 

Resistance  may  be  expressed  as    a  velocity. 
The   dimensions  of  resistance  in  terms  of  the 
electro-magnetic  units  are 
L 


(See  Units,  Electro- Magnetic.)  But  these  are  the 
dimensions  of  a  velocity,  which  is  the  ratio  of  the 
distance  passed  over  in  unit  time.  Resistance  may 
therefore  be  expressed  as  a  velocity. 


Res.] 


453 


"The  resistance  known  as  'one  ohm*  is  in- 
tended  to  be  io»  absolute  electro-magnetic  units, 
and,  therefore,  is  represented  by  a  velocity  of  lo9 
centimetres  or  10,000,000  metres  (one  earth  quad- 
rant) per  second." — (Sylvanus  Thompson.) 

Resistance  may  be  represented  by  a  velocity, 
one  ohm  being  the  resistance  of  a  wire,  which, 
if  moved  through  a  unit  field  of  force  at  the  rate 
of  1,000,000,000  (lo9)  centimetres  per  second  will 
have  a  current  of  one  ampere  generated  in  it. 
(See  Resistance,  Ohmic.  Resistance,  Spurious.) 

The  true  value  of  the  ohm  is  exactly  lo9  centi- 
metres. The  material  standards  employed,  *.  e., 
the  B.  A.  and  "legal "  ohms,  are  not  absolutely 
of  this  value. 

One  mil-foot  of  soft  copper  at  10.22  degrees  C. 
or  50.4  degrees  F.  has  the  standard  resistance  of 
exactly  10 legal  ohms;  at  15.56  or  59.9  degrees 
F.,  it  has  a  resistance  of  10.20  legal  ohms,  and 
at  23.9  degrees  C.  or  75  degrees  F.,  10.53  legal 
ohms. 

RESISTANCE. 

Resistance  of  Wires  of  Pure  Annealed  Copper  at  o"  C. 
(Density  =  8.9.) 


II 

I 

& 


175 

,35-28 

t.l5 
62.93 

40.23 
33.82 
27-95 
22.7 
17.89 
15-75 

g:L 

10. 06 

8.47 

5:8 

2.13 
2.52 
i-74 

':8 
.7181 
.4026 
.2797 
.179 
.1007 
.0699 
.0447 
.0252 


Resistance  of  Wire   of  Pure  An- 
nealed Copper  at  O  degree  C. 


5-7 
7-4 
9-5 

12.5 

16 

,9.8 

25 


too 

119 
144 

I73 

•H 

294 

& 

90.. 
•S* 


5590 


Ohms 


3.6 
4.2 


9.1 


25 
32 
42 

II 
122.4 

177-9 

228.5 
357 


1428 
2056 
3213 


Metres 
dhm. 


944.38 

563.92 
439-07 

Ii'  S 
36.08 


24-9 

09-75 

95-651 

82.4 

70.247 

59.024 

48.782 

39-515 

31.225 

% 
•Kg 

5-622 
4-377 
3.801 
1.945 
1.245 

.'486 
.311 

.^l 


Ohms 

Kilogramme. 


.00456 
.00784 

.0128 

.0222 
•0365 


•574 
.763 
1.03 
1.42 

"•95 
4.19 
7.21 
12.3 

22.78 

46.8! 

110.41 

222.55 

367-2 

895.36 

1,857.6 

4,489 

29^549 

78,943 
227,515 
142,405 


The  following  table,  based  on  Matthiessen's 
measurements,  gives  the  relative  resistances  of 
equal  lengths  and  cross-sections  of  a  number  of 
different  substances  used  in  electricity  as  com- 
pared with  silver. 

LEGAL  MICROHMS. 


Resistance  i 

n  Microhms 

at  o  dc 

greeC. 

W               "vr 

Relative 

OF>  -METAL. 

Resistance. 

Cubic 
Centimetre. 

Cubic  Inch. 

Silver,  annealed... 

T.CO4 

O.592X 

i 

Copper,  annealed. 

1.598 

O.6292 

i!o63 

Silver,  hard  drawn 
Copper,  h'rd  dr*wn 

Jl34 

0.6433 
0.6433 

,.086 
i.  086 

Gold,  annealed.... 
Gold,  hard  drawn. 
Aluminium,  ann'ld 

2.094 
2.912 

0.8102 
0.8247 
1.147 

1.369 
J-393 
'•935 

Zinc,  pressed  
Platinum,  annealed 

5.626 
9.057 

2.215 

3-565 

3-741 

6.022 

Iron,  annealed  
Nickel,  annealed.  . 

9.716 
12.47 

3.825 
4.907 

6.460 
8.285 

Tin,  pressed  

13.21 

8.784 

Lead,  pressed  
German  silver  

19.63 
20.93 

1:5 

I3-05 

Antimony,  pressed 

35-50 

13.98 

62   71 

Bismuth,  pressed.  . 

94.32 
131.2 

s^s5 

02.73 
87.23 

—(Hosfitalier.) 


—(Ayrton.) 

The  above  resistances  are  for  chemically  pure 
substances  only.  Slight  impurities  produce  a  very 
considerable  increase  in  the  resistance. 

Resistance,  Electric,  of  Liquids  -- 

The  resistance  offered  by  a  liquid  mass  to 
the  passage  of  an  elec- 
tric current 

As  a  rule  the  electric  re- 
sistances  of  liquids,  with 
the  single  exception  of  mer- 
cury, are  enormously  high- 
er than  those  of  metallic 
bodies. 

To  roughly  determine 
the  resistance  of  a  liquid, 
a  section  is  taken  between 
two  parallel  metallic  plates 
A  and  B,  Fig.  489,  placed 
as  shown  in  the  figure,  and 
an  electric  current  is  pass- 
ed between  them. 

In  order  to  accurately 
vary  the  size  of  the  plates 
immersed  in  the  liquid,  and 
hence  the  area  of  cross-section  of  the  liquid  con- 
ductor,  as  well  as  the  distance  between  the  plates, 
the  apparatus  shown  in  Fig.  490  may  be  used,  in 


489-    RetistanceoJ 
Liquid. 


Res.]  454  [Res. 

TABLE  OF  CONDUCTING  POWERS  AND  RESISTANCES  IN  OHMS— B.  A.  UNITS. 


NAMES  OF  METALS. 

Conducting 
power  at  o  de- 
gree C. 

Resistance  of  a 
wire  one   foot 
long  weighing 
one  grain. 

Resistance  of  a 
wire  one  metre 
ong  weighing 
one  gramme. 

Resistance  of  a 
wire    one  foot 
long  nfou  >nch 
in  diameter. 

Resistance  of  a 
wir   one  metre 
on      one  milli- 
me    e  in  diam- 
eter. 

Approximate 
percentage  of 
variation   in   re- 
sistance for  t  de- 
gree of  tempera- 
ture at  20  deg. 

0.2214 
0.2421 

o.  1544 
0.1689 

9.936 
9.151 
9.718 
9.940 
12.52 
12.74 
17.72 
32.22 
55-09 
59-40 
75-78 
80.36 
119.39 
216.0 
798-0 
600.0 

143-35 
127.32 
66.10 

.01937 

.02057 
.02104 
.02650 
.02697 

0-377 

Silver,  hard  drawn  

100.  CO 

Copper,  hard  drawn  

99-55 

0.2106 
0.5849 
0.5950 
0.06822 
0.5710 
3.536 
1.2425 
1.0785 

l:% 
3.324 

5-°54 
18.740 

0.1469 
0.4080 
0.4150 
0.05759 
0.3983 
2.464 
0.7522 
0.8666 
0.9.84 
2.257 
2.3295 
3-525 
13.071 

8.959 
1.850 
1.668 

0-355 

77.96 

29.02 

•°l& 

:'Ji 
.2527 

•457' 
1.689 
1.270 

0.3140 
0.2695 
0.1399 

0.365 

16.81 
13  ii 

12    36 

832 
462 

I  24 

Nickel,  annealed  
Tin,  pressed  

0.365 
0.387 
0.389 
0-354 
0.072 

0.065. 

Antimony,  pressed  

Platinum  -  silver,      alloy, 

German    silver,  hard  or 

Gold,  silver,  alloy,  hard 

2.391 

which  these  distances  are  readily  adjustable,  as 
shown. 

Resistance,  Equivalent A  single 

resistance  which  may  replace  a  number  of 
separate  resistances  in  a  circuit  without  alter- 
ing the  value  of  the  current  traversing  it. 

Resistance,  Essential  —A  term 

sometimes  used  instead  of  internal  resist- 
ance. 


Kg.  490. 


Apparatus  for   Measuring  Resistance   of 
Liquid. 


Resistance,  External  Secondary A 

term  proposed  by  Du  Bois  Reymond  for  the 
change  in  the  resistance  of  a  circuit  external  to 
the  electric  source  when  cataphoric  action 
takes  place.  (See  Action,  Cataphoric^) 

"  If  the  copper  electrodes  of  a  constant  battery 
be  placed  in  a  vessel  filled  with  a  solution  of 
cupric  sulphate  and  from  each  electrode  there 
projects  a  cushion  saturated  with  this  fluid,  then, 


on  placing  a  piece  of  muscle,  cartilage,  vegetable 
tissue,  or  even  a  prismatic  strip  of  coagulated 
albumen  across  these  cushions,  we  observe,  that 
very  soon  after  the  circuit  is  closed,  there  is  a 
considerable  variation  of  the  current.  *  *  * 
This  phenomenon  is  called  '  external  secondary 
resistance.'  " — (Landois  and  Sterling.) 

Resistance,  Extraordinary A  term 

sometimes  employed  instead  of  external  re- 
sistance. (See  Resistance,  External  Secon- 
dary.) 

Resistance,  False A  resistance  aris- 
ing from  a  counter  electromotive  force  and 
not  directly  from  the  dimensions  of  the  circuit, 
or  from  its  specific  resistance. 

The  false  resistance  of  any  circuit  is  sometimes 
called  its  spurious  resistance.  (See  Force,  Electro- 
motive, Counter.  Resistance,  Spurious.) 

Resistance,  Inductionless A  term 

sometimes  used  instead  of  non-inductive  re- 
sistance. (See  Resistance,  Non-inductive.) 

Resistance,  Inductive A  resistance 

which  possesses  self-induction. 

Resistance,  Insulation The  re- 
sistance of  a  line  or  conductor  existing  be- 
tween the  line  or  conductor  and  the  earth 
through  the  insulators,  or  between  the  two 


Res.] 


455 


[Bes. 


wires  of  a  cable  through  the  insulating 
material  separating  them. 

The  insulation  resistance  of  a  telegraph  line  is 
the  resistance  that  exists  between  the  line  and  the 
earth,  through  its  insulators.  The  insulation  re- 
sistance will  decrease  as  the  length  of  line  in- 
creases, since  for  any  increase  in  the  number  of 
poles  and  insulators  there  is  a  proportional  in- 
crease in  the  area  of  cross-section  of  the  insula- 
ting supports. 

If  the  insulation  resistance  is  1  ,000,000  ohms 
per  mile,  in  a  line  200  miles  in  length,  the  insula- 
tion resistance  is  only  5,000  ohms,  that  is, 

1,000,000 

•I-  —  :  -  =  5,000  ohms. 

200 

Resistance,  Joint,  of  Parallel  Circuits 

--  The  joint  resistance  of  two  parallel 
circuits  is  determined  by  means  of  the  follow- 
ing formula  : 


Where  R  =  the  joint  resistance  of  any  two  cir- 
cuits whose  separate  resistances  are  respectively 
r  and  r'. 

When  there  are  three  resistances  r,  r'  and  r*, 
in  parallel,  the  joint  resistance, 

R=  r  r'  r< 

r  r'  -j-  r  r"  -j-  r'  r"  " 

(See  Circuits,  Varieties  of.  ) 

Resistance,  Magnetic  --  The  recipro- 
cal of  magnetic  permeability  or  conduct!- 
bility  for  lines  of  magnetic  force. 

Resistance  offered  by  a  medium  to  the 
passage  of  the  lines  of  magnetic  force  through 
it. 

The  magnetic  resistance  of  the  circuit  of  the 
lines  of  force  is  reduced  by  forming  the  circuit  of 
a  medium  having  a  high  magnetic  permeability, 
such  as  soft  iron.  This  is  accomplished  by  the 
armature  or  keeper  of  a  magnet,  or  by  the  iron  in 
an  iron-clad  magnet.  (See  Magnet,  Iron-Clad.} 

Resistance,     Measurement    of  -- 

Methods  employed  for  determining  the  re- 
sistance of  any  circuit  or  part  of  a  circuit. 

Numerous  methods  are  employed  for  this  pur- 
pose. Among  these  are  : 

(I.)  The  use  of  'a  resistance  box  -with  a  Wheat. 
stone  bridge,  by  opposing  or  balancing  the  un- 
known resistance  against  a  known  resistance. 
(See  Balance,  Wheatstone'1  s  Electric.) 


(2.)  The  differential  galvanometer.  (See  Gal- 
vanometer, Differential^ 

(3.)  The  method  of  substitution. 

(4.)  Comparison  of  the  deflections  of  a  gal~ 
vanometer. 

Method  of  Substitution. — A  resistance-box  R, 
Fig.  491,  galvanometer  G,  and  the  resistance  x, 
that  is  to  be  measured,  are  placed  in  the  direct 
circuit  of  the  battery  B,  by  means  of  conductors 
of  such  thick  wire  that  their  resistance  can  be 
neglected. 

The  deflection  of  the  galvanometer  is  first 
measured  with  x,  in  circuit,  and  no  resistance  in 
the  box  R.  The  resistance  x,  is  then  cut  out  of 
the  circuit  by  placing  a  thick  copper  wire  across 
the  terminals  of  the  mercury  cups  at  mm',  and 
resistances  unplugged  in  R,  until  the  same  deflec- 
tion is  obtained.  Then,  if  the  electromotive  force 
of  the  battery  has  remained  constant,  the  resist- 
ances unplugged  equal  the  unknown  resistance. 

For  full  description  of  the  various  methods  of 
determining  resistance  the  reader  is  referred  to 
•l  Ayr  ton's  Practical  Electricity,'*  "Kempe's 
Handbook  of  Testing"  or  other  standard  books 
on  electrical  measurements. 


Fig.  49  z.    Substitution  Method. 

When  several  resistances  are  placed  in  series  in 
any  circuit,  by  measuring  the  difference  of  poten- 
tial at  their  terminals,  their  values  can  be  deter- 
mined by  simple  calculation,  being  directly  pro- 
portional  to  these  differences  of  potential. 

This  method  is  especially  applicable  to  the 
measurement  of  such  low  resistances  as  the  arma- 
tures of  dynamo-electric  machines. 

Resistance,  Non-inductive A  re- 
sistance in  which  self-induction  is  practically 
absent. 

An  incandescent  lamp  filament  is  practically  a 
non-inductive  resistance  when  compared  with  a 
coil  on  the  helix  of  an  electro-magnet. 

Resistance  of  Human  Body.— (See  Body, 
Human,  Resistance  of.) 


Res.] 


456 


[Res. 


Resistance  of  Toltalc  Arc.— (See  Arc, 
Voltaic,  Resistance  of.) 

Resistance,  Ohmic The  true  resist- 
ance of  a  conductor  due  to  its  dimensions 
and  specific  conducting  power,  as  distin- 
guished from  the  spurious  resistance  produced 
by  a  counter  electromotive  force.  (See  Force, 
Electromotive,  Counter.  Resistance,  Spuri- 
ous.) 

The  term  ohmic  resistance  must  be  regarded  as 
a  pleonasm.  Its  use  can  only  be  permitted  in 
contradistinction  to  counter  electromotive  force 
resistance.  True  and  spurious  resistance  would 
seem  preferable. 

Resistance  or  Cell,  Selenium A 

mass  of  crystalline  selenium,  the  resistance  of 
which  is  reduced  by  placing  it  in  the  form  of 
narrow  strips  between  the  edges  of  broad 
conducting  plates  of  brass. 

The  selenium  employed  for  this  purpose  is  the 
vitreous  variety  which  has  been  fused  and  main* 
tained  for  several  hours  at  about  220  degrees  C., 
by  means  of  which  its  resistance  is  reduced. 

By  exposure  to  sunlight,  the  resistance  of  a 
selenium  cell  is  decreased  fully  one-half  its  re- 
sistance  in  the  dark.  The  selenium  cell  is  used 
in  the  photophone.  (See  Photophone.) 

Resistance  or  Reducteur  for  Voltmeter. 

— (See  Reducteur  or  Resistance  for  Volt- 
meter!) 

Resistance,   Secondary A  term 

sometimes  used  in  place  of  external  secon- 
dary resistance.  (See  Resistance,  External 
Secondary?) 

Resistance  Slide.— (See  Slide,  Resist- 
ance^ 

Resistance,  Specific The  particular 

resistance  which  a  substance  offers  to  the 
passage  of  electricity  through  it. 

In  absolute  measure,  the  resistance  in  ab- 
solute units  between  the  opposite  faces  of  a 
centimetre  cube  of  the  given  substance. 

In  the  practical  system  the  resistance  given 
in  ohms. 

Resistance,  Specific  Conduction 

A  term  sometimes  used  instead  of  specific 
resistance.  (See  Resistance,  Specific) 


Resistance,  Specific,  of  Liquids 

The  resistance  of  a  given  length  (one  centi- 
metre) and  area  of  cross-section  (one  square 
centimetre)  of  any  liquid  as  compared  with 
the  resistance  of  an  equal  length  and  cross- 
section  of  pure  silver. 

The  resistance  of  a  few  common  liquids  and  so- 
lutions  is  here  given  from  Lupton: 

Water,  pure,  at  75  degrees  C..I.I88  X  IO»  ohms, 
*'.  e.,  118,800,000. 

Water  at  4  degrees  C 9.100  X  K>«     •• 

Water  at  II  degrees  C 3.400X10*     •• 

Dilute  hydrogen  sulphate  (sul- 
phuric acid)  at  18  degrees 
C.,  5  per  cent,  acid 4.88 

Dilute  hydrogen  sulphate  at 
1 8  degrees  C.,  3  per  cent, 
acid i  .38  ohms. 

Nitric  acid  at  18  degrees  C., 

density  1.32 l.6l      «« 

Saturated  solution  of  copper 
sulphate  (blue  vitriol)  at  10 
degrees  C 29.30  «« 

Saturated  solution  of  zinc  sul- 
phate at  14  degrees  C 21.50  «« 

Hydrochloric  acid,  20  per  cent, 
acid,  at  18  degrees  C 1.34  " 

Sal  ammoniac,  25  percent,  salt  2.53      «« 

Common  salt,  saturated,  at  13 
degreesC ...5.30  " 

It  will  be  observed  that  the  resistance  varies 
considerably  with  differences  of  temperature. 

Resistance,  Spurious A  false  re- 
sistance arising  from  the  development  of  a 
counter  electromotive  force.  (See  Resist- 
ance, False.  Force,  Electromotive,  Coun- 
ter) 

The  spurious  resistance  is  also  called  the  false 
resistance,  in  order  to  distinguish  it  from  the  true 
or  ohmic  resistance.  (See  Resist ance*  Electric.) 

Resistance,  Standard A  resistance 

used  for  comparison  with  or  the  determina- 
tion of  unknown  resistances. 

A  committee  appointed  by  the  American  Insti. 
tute  of  Electrical  Engineers  in  1890  reported  the 
following  values  for  the  standard  resistance  of 
copper  wire;  at  O  degree  C.  in  B.  A.  U.  and  legal 
ohms,  viz.: 


Res.] 


457 


[Res. 


STANDARD  RESISTANCE  AT  o*  C. 

B.  A.  U.    Legal  Ohms. 
'  Meter-mfllimetre, " 

"  soft  copper "...       .02057  .02034 

Cubic  centimetre...  .000001616  .000001598 
"Mil-foot" 9.720  9.612 

Resistance,  Tables  of Tables  in 

which  the  resistance  of  equal  lengths  and 
•:ross-sections  of  different  substances  is 
given  in  ohms,  or  other  units  of  resistance. 

Resistance  Thermometer. — (See  Ther- 
mometer, Electric  Resistance!) 

Resistance,  Transition  — A  term 

sometimes  used  in  electre-therapeutics  for  a 
change  in  the  value  of  the  resistance  caused 
by  polarization. 

Whenever  an  electric  current  passes  through 
a  fluid  substance  and  decomposes  the  fluid,  the 
decomposition  products  collect  on  the  electrodes 
and  produce  an  increase  in  the  resistance  of  the 
circuit. 

Resistance,  True The  resistance 

which  a  conductor  offers  to  the  passage  of  a 
current  by  reason  of  its  dimensions  and  spe- 
cific conducting  power,  as  distinguished  from 
a  spurious  resistance  produced  by  a  counter 
electromotive  force. 

The  true  resistance  is  sometimes  called  the 
ohmic  resistance. — (See  Resistance^  Spurious. 
Resistance,  Ohmic.) 

Resistance,  Unit  of Such  a  resist- 
ance that  unit  difference  of  potential  is  re- 
quired to  cause  a  current  of  unit  strength 
to  pass.  (See  Ohm.  Potential,  Electric. 
Potential,  Difference  of.) 

Resistance,  Unit  of,  Absolute The 

one  thousand  millionth  of  an  ohm.  (See 
Ohm.  Units,  Practical.) 

Resistance,  Unit  of,  Jacobi's The 

electric  resistance  of  25  feet  of  a  certain 
copper  wire  weighing  345  grains. 

Another  unit  of  electric  resistance  proposed 
by  Jacobi  was  the  resistance  of  a  copper  wire 
one  metre  in  length  and  one  millimetre  in  diame- 
ter. 

Resistance,  Unit  of,  Matthiessen's 

—The  resistance  of  one  statute  mile  of  pure 
annealed  copper  wire  iV  inch  in  diameter  at 


15.5  degrees  C,  and  determined  by  him  to  be 
13.59  B.  A.  ohms. 
Resistance,  Unit  of,  Varley's The 

resistance  of  one  statute  mile  of  a  special 
copper  wire  ^  inch  in  diameter. 

Varley's  unit  was  afterwards  adjusted  by  him 
to  equal  25  Siemens  Mercury  Units. 

Resistance,  Variable A  resistance 

the  value  of  which  can  be  readily  varied. 
Variable  resistances  are  either  : 
(I.)  Automatically  variable  resistances;  or 
(2.)  Non-automatically  variable  resistances. 

Resistance,  Variable,  Automatic 

A  resistance  the  value  of  which  can  be  auto* 
matically  varied. 

A  pile  of  carbon  plates  resting  on  one  another, 
in  loose  contact,  offers  a  high  resistance,  but  when 
compressed  as  by  an  electro-magnet  their  resist- 
ance is  lowered.  Brush  employs  such  an  auto- 
matic resistance  in  the  regulation  of  his  dynamo- 
electric  machine.  (See  Regulation,  Automatic.) 

Resistance,  Variable  Non-Automatic 

— A  resistance  the  value  of  which  is  regulated 
by  hand.  (See  Rheostat.) 

Resistance,  Virtual A  term  some- 
times employed  instead  of  impedance.  (See 
Impedance.) 

Resonance,  Electric The  setting 

up  of  electric  pulses  in  open-circuited  con- 
ductors, by  the  action  of  pulses  in  neighboring 
conductors. 

Electric  resonance,  like  acoustic  resonance, 
takes  place  when  a  correspondence  exists  between 
the  time-rate  of  vibration  of  the  body  producing 
the  resonance,  and  the  body  in  which  the  reso- 
nance is  produced.  In  other  words,  when  the 
wave  lengths  are  the  same  in  the  two  bodies,  or 
when  the  wave  length  in  one  is  equal  to  a  half 
wave  length,  or  some  definite  multiple  of  a  half 
wave  length  of  the  other. 

Partial  resonance  may  occur,  when  there  is  a 
small  difference  between  the  wave  lengths  of  the 
two  bodies.  Beyond  certain  limits,  however,  this 
is  so  small  as  to  be  practically  absent. 

When  an  electrical  pulse  is  started  in  a  con. 
ductor  by  the  discharge  of  a  Leyden  jar,  a  side  flash 
spark  is  obtained  in  the  alternative  path,  between 
the  discharge  points.  The  length  of  this  spark  has 
its  greatest  value,  when  the  time  required  for  the 


Res.] 


458 


pulse  to  travel  backwards  and  forwards  along  the 
conducting  wires,  is  exactly  equal  to  the  time  of 
a  complete  oscillation  in  the  circuit,  or  when  the 
length  of  the  open-circuit  wires  is  equal  to  half  a 
wave  length,  or  some  multiple  of  half  a  wave 
length. 

The  fact  that  the  length  of  the  spark  is  greatest 
when  certain  relations  exist  between  the  dimen- 
sions of  the  two  circuits,  shews  that  the  time-rate 
of  an  electrical  pulse  in  any  circuit  depends  on 
the  dimensions  of  that  circuit. 

In  the  case  of  acoustic  resonance,  in  order  that 
one  tuning  fork  may  be  able  to  excite  vibrations  in 
another,  the  fork  producing  or  exciting  the  vibra- 
tion must  be  strictly  in  unison  with  the  fork  in 
which  the  vibrations  are  excited,  and  any  varia- 
tions produced  in  the  rate  of  vibration  of  the 
sounding  fork,  by  overloading  it,  or,  in  other 
words,  by  altering  its  dimensions,  checks  the 
effects  of  its  resonance. 

In  a  similar  manner,  any  alterations  in  the  di. 
mansions  of  the  circuit,  checks  or  diminishes  the 
effects  of  electric  reson- 
ance in  a  neighboring  cir- 
cuit, which  was  previously 
in  unison  with  it.  This 
has  been  experimentally 
shown  by  Hertz  as  fol- 
lows: 

An  induction  coil  A, 
Fig.  492,  has  the  terminals 
of  its  secondary  connected 
to  an  open  rectangular  cir- 
cuit provided  with  spark- 
ing terminals,  I,  and  2, 
called  a  spark  micrometer. 
Under  certain  conditions, 
when  the  discharge  oc- 
curs at  the  terminals  B, 
of  the  ordinary  discharger,  sparks  are  produced 
by  electric  resonance  in  the  electric  resonator 
formed  by  the  spark  micrometer  at  M. 

Supposing,  now,  that  a  certain  character  of  sparV 
is  obtained  at  the  terminals  B,  that  is,  a  cei_ 
tain  velocity  of  electrical  pulsations  is  obtained 
which  depends  on  the  nature  of  the  spark  ;  sup- 
pose, moreover,  that  the  dimensions  of  the  spark 
micrometer  or  electric  resonator  are  such  that  the 
greatest  length  of  spark  is  obtained.  Then,  any 
alteration  in  the  character  of  these  sparks,  be- 
tween the  terminals  at  B,  varies  the  intensity  of 
She  sparks  in  the  spark  micrometer. 

X&  for  example,   the  apparatus  be  arranged 


Fig.  493.    Electrical 
Resotiaitct. 


as  shown  in  Fig.  493,  in  which  one  of  the  sec- 
ondary terminals  of  the  induction  coil  has  con- 
nected with  it  a  copper  wire  i  g  h.  The  sparks  at 
M,  decrease  considerably.  When,  however,  the 
conductor  C,  is  connected  with  the  free  end  H, 
of  this  additional  conductor,  then  this  effect  is 
not  observed,  as  is  shown  by  the  fact  that  when 
the  conductor  C,  is  attached  at  the  point  G,  it 
produces  no  effect  on  it. 


Fig.  493.    Electric  Resonanct. 

In  another  experiment  with  the  same  apparatus, 
matters  may  be  arranged  that  the  sparks  in  the 
micrometer  circuit  pass  singly.  When,  now,  an- 
other conductor  C',  is  attached  to  K,  a  stream  of 
sparks  immediately  passes. 

It  would  appear,  therefore,  from  the  above  ex- 
periments, that  when  two  circuits  are  taken, 
having  as  nearly  as  possible  the  same  vibration 
periods,  any  alteration  in  the  dimensions  of  either 
will  prevent  one  from  producing  electrical  reso- 
nance in  the  other. 

In  the  above  experiments  Hertz  demonstrated 
the  following  facts,  viz., 

(I.)  The  sparks  in  the  micrometer  circuit  are 
smaller  when  the  discharges  take  place  between 
points,  or  a  point  and  a  plate,  instead  of  between 
knobs. 

(2.)  The  micrometer  sparks  are  feebler  in  rare- 
fied gas  than  in  air  at  ordinary  pressures. 

(3.)  Extremely  slight  differences  in  the  nature 
of  secondary  sparks  produce  considerable  differ- 
ence in  the  length  of  the  micrometer  sparks. 

Hertz  found  the  above  results  were  obtained 
when  the  secondary  sparks  were  of  a  brilliant 
color,  and  were  attended  by  a  sharp  crack. 

(4.)  The  length  of  the  spark  in  the  micrometei 


Res.] 


459 


circuit  varies  with  the  length  of  the  micrometer 
circuit. 

This,  of  course,  follows  from  the  fact  that  any 
alteration  of  the  length  in  the  micrometer  circuit, 
produces,  by  electrical  retardation,  a  correspond- 
ing  alteration  in  the  time  of  the  electrical  pulses. 

(5.)  No  effect  is  produced  in  the  length  of  the 
micrometer  spark  by  variations  in  the  material, 
the  resistance,  or  the  diameter  of  the  wire  forming 
the  micrometer  circuit. 

This  is  probably  because  the  rate  of  propaga- 
tion of  electrical  pulses  along  a  conductor,  de- 
pends mainly  on  the  capacity  of  the  conductor, 
and  on  its  co-efficient  of  self-induction,  and  only 
to  a  slight  extent  on  its  resistance. 

(6.)  The  length  of  wire  connecting  the  microm- 
eter circuit  with  the  secondary  circuit  has  but 
little  effect,  provided  such  length  does  not  exceed 
a  few  metres. 

Local  disturbances,  therefore,  must  traverse 
conductors  without  undergoing  any  appreciable 
change. 

(7. )  The  position  of  the  point  on  the  micrometer 
circuit  connected  with  the  secondary  circuit,  is  of 
the  greatest  importance. 

When  the  point  on  the  micrometer  circuit  is 
situated  symmetrically  with  respect  to  the  two  mi- 
crometer knobs,  variations  of  potential  will  reach 
the  terminals  in  the  same  phase,  and  there  will  be 
but  little  effect,  as  seen  by  the  sparks  between  the 
micrometer  knobs.  Such  a  point  on  the  microm  j 
eter  knobs  is  called  the  null  point,  or  it  is  called  as 
in  a  corresponding  case  in  acoustics,  a  nodal  point. 
(See  Point,  Null.  Point ',  Nodal.} 

(8.)  When  the  conductors  are  of  sufficient 
length,  their  approach  produces  disturbances  in 
a  previously  adjusted  and  quiet  spark  microm- 
eter, just  as  the  approach  of  a  conductor  would. 

Probably  one  of  the  most  curious  effects  con- 
nected with  the  phenomena  of  electrical  resonance 
is  that  pointed  out  by  Lodge,  viz. :  that  when  the 
spark  from  a  secondary  circuit  is  so  placed  that 
the  light  is  visible  from  a  micrometer  circuit,  the 
effects  of  the  discharge  are  greatly  increased. 
Lodge  also  found  that  the  light  from  burning 
magnesium  wire,  or,  in  general,  light  rich  in  the 
ultra-violet  rays,  produces  the  same  effect. 

Resonator,  Electric An  apparatus 

employed  by  Hertz  in  his  investigations  on 
electric  resonance.  (See  Resonance,*  Elec- 
tric) 

An  «l«ctric  resonator  consists  essentially  of  an 


[Ret. 

open-tircuited  conductor,  or  circuit  of  such  dimen- 
sions that  electro-magnetic  waves  or  pulses  are 
propagated  through  it  at  the  same  rate  as  those 
which  are  occurring  in  a  neighboring  circuit 
from  which  electro-magnetic  radiation  is  tak- 
ing place.  Under  these  circumstances  electro- 
magnetic pulses  are  set  up  sympathetically  by 
resonance  in  the  open  circuit  of  the  resonator,  like 
the  sympathetic  vibrations  in  a  tuning  fork,  when 
placed  near  another  vibrating  tuning  fork,  which 
is  giving  off  sound  waves  of  exactly  the  same 
period  of  vibration  as  its  own. 

Resonator,  Electro-Magnetic A 

term  applied  to  the  Hertz  spark  micrometer, 
in  which  electro-magnetic  waves  are  produced 
by  electric  resonance.  (See  Resonance,  Elec- 
tric?) 

Resultant. — In  mechanics,  a  single  force 
that  represents  in  direction  and  intensity  the 
effects  of  two  or  more  separate  forces. 

The  separate  forces  are  called  the  components. 
(See  Components.} 

Retardation.— A  decrease  in  the  speed  of 
telegraphic  signaling  caused  either  by  the 
induction  of  the  line  conductor  on  itself,  or 
by  mutual  induction  between  it  and  neighbor- 
ing conductors,  or  by  condenser  action,  or  by 
all. 

The  line  must  receive  a  certain  charge  before 
a  current  sent  into  it  at  one  end  can  produce  a 
signal  at  the  other  end.  This  charge  will  de- 
pend on  the  length  and  surface  of  the  wire,  on  the 
neighborhood  of  the  wire  to  the  earth  or  other 
wires,  and  on  the  nature  of  the  insulating  mate- 
rial between  the  wire  and  neighboring  conductors. 
This  results  in  a  charge  given  to  the  wire  which 
is  lost  as  a  current  for  signaling.  The  greater  the 
electrostatic  capacity  of  the  line  wire,  the  greater 
will  be  the  retardation  in  signaling.  (See  Capa* 
city,  Specific  Inductive.  Dielectric.  Capacity., 
Electrostatic.  Induction,  Electro-Dynamic.} 

Retardation  in  signaling  is  produced  by  the 
following  causes : 

(I.)  Self-induction  which  produces  extra  cur- 
rents.  (See  Induction,  Self.  Currents,  Extra.} 

The  extra  current  on  making,  retards  the  be- 
ginning of  the  signal ;  the  extra  current  on  break- 
ing, retards  its  stopping. 

(2.)  Mutual  Induction  between  the  line  con- 
ductor and  neighboring  conductors. 


Itet] 


460 


[Rhe. 


(3.)  The  Magnetic  Inertia  or  Lag,  or  the  time 
required  to  magnetize  or  demagnetize  the  core  of 
the  electro-magnetic  receptive  devices  used  on 
the  line. 

(4. )  By  Condenser  Action,  the  cable  acting  as  a 
condenser. 

Retardation,  Electric A  retarda- 
tion in  the  starting  or  stopping  of  an  electric 
current,  arising  from  self-induction.  (See  In- 
duction, Self.  Retardation?) 

Retardation,  Inductive A  retarda- 
tion in  the  appearance  of  a  signal  at  the  dis- 
tant end  of  a  cable,  produced  by  the  action  of 
induction.  (See  Retardation?) 

Retardation,  Magnetic  — A  retarda- 
tion in  the  magnetization  or  demagnetization 
of  a  substance  due  to  magnetic  lag.  (See 
Retardation.  Lag,  Magnetic?) 

Retarding,  Electrically Decreas- 
ing the  speed  of  telegraphic  signaling,  by 
means  of  induction.  (See  Retardation?) 

Retentivity,  Magnetic A  term  pro- 
posed by  Lamont  in  place  of  coercive  force, 
or  the  power  possessed  by  a  magnetizable 
substance  of  resisting  magnetization  or  de- 
magnetization. (See  Force,  Coercive?) 

Return  Circuit— (See  Circuit,  Return?) 

Return,  Earth (See  Earth  Re- 
turn?) 

Return  Ground.— (See  Ground-Return?) 

Return  Wire  or  Conductor.— (See  Wire, 
Return?) 

Returns. — In  a  system  of  distribution,  those 
conductors  through  which  the  current  flows 
back  from  the  electro-receptive  devices  to 
the  source.  (See  Leads?) 

The  word  returns  is  sometimes  used  in  a  sys- 
tem of  distribution  by  parallel  circuits,  to  distin 
guish  between  the  conductor  by  which  the  cur- 
rent goes  back  or  returns  from  the  receptive  de- 
vices to  the  dynamo,  and  the  conductor  that  leads 
it  to  the  receptive  devices.  The  term  leads  is, 
however,  often  applied  to  both  conductors. 

Reverse-Induced  Current. — (See  Current, 
Reverse-Induced?) 


Reversed  Currents.— (See  Currents,  Re- 
versed?) 

Reverser,  Current A  switch,  or 

other  apparatus,  designed  to  reverse  the  di- 
rection of  a  current. 

Reversible  Bridge.— (See  Bridge,  Rever- 
sible?) 

Reversible  Heat— (See  Heat,  Reversible?) 

Reversibility  of  Dynamo.— The  ability 
of  a  dynamo  to  operate  as  a  motor  when  tra- 
versed by  an  electric  current.  (See  Motor, 
Electric?) 

Reversing  Gear  of  Electric  Motor. — (See 
Motor,  Electric,  Reversing  Gear  of.) 

Reversing  Key.— (See  Key,  Reversing.) 

Reversing  Key  of  Quadruple*  Tele- 
graphic System.— (See  Key,  Reversing,  of 
Quadruplex  Telegraphic  System?) 

Reversing  Magnetic  Field.— (See  Field, 
Magnetic,  Reversing?) 

Rheochord. — A  word  formerly  employed 
instead  of  rheostat.  (See  Rheostat?) 

Rheometer.— A  word  formerly  employed 
for  any  device  for  measuring  the  strength  of 
a  current 

This  word  is  now  obsolete  and  is  replaced  by 
the  word  galvanometer.  (See  Galvanometer.) 

Rheomotor. — A  word  formerly  employed 
to  designate  any  electric  source. 

This  word  is  now  obsolete,  and  replaced  by 
the  various  names  of  the  different  electric  sources. 
(See  Source,  Electric.) 

Rheophore. — A  word  formerly  employed  to 
indicate  a  portion  of  a  circuit  conveying  a  cur- 
rent and  capable  of  deflecting  a  magnetic 
needle  placed  near  it.  (Obsolete.) 

Rheoscope. — A  word  formerly  employed  in 
place  of  the  present  word  galvanoscope,  for 
an  instrument  intended  to  show  the  presence 
of  a  current,  or  its  direction,  but  not  to 
measure  its  strength.  (Obsolete.) 

Rheoscope,  Physiological  —  — A  sensi- 
tive nerve-muscle  preparation  employed  to 
determine  the  presence  of  an  electric  current. 
(See  Frog,  Galvanoscope?) 


Rhe.] 


461 


[Kin. 


A  term  sometimes  applied  m  electro-thera- 
peutics to  the  frog's  legs  preparation  adapted 
to  show  the  presence  of  any  electric  current. 

The  physiological  rheoscope  is  adapted  to 
show  the  presence  of  an  electric  current  without 
the  use  of  a  galvanometer.  On  the  passage  of 
the  electric  current  the  frog's  legs  twitch  con- 
vulsively. 

Rheostat. — An  adjustable  resistance. 

A  rheostat  enables  the  current  to  be  brought 
to  a  standard,  i.  e.,  to  a  fixed  value,  by  adjusting 
the  resistance;  hence  the  name. 

The  term  rheostat  is  applied  generally  to  a 
readily  variable  resistance,  the  varying  values  of 
which  are  known. 

Rheostat,  Dynamo-Balancing An 

adjustable  resistance  whose  range  is  sufficient 
to  balance  the  current  of  one  dynamo  against 
another  with  which  it  is  required  to  run  in 
parallel. 

Rheostat,  Water A  rheostat   the 

resistance  of  which  is  obtained  by  means  of  a 
mass  of  water  of  fixed  dimensions.  (See 
Rheostat^ 

Rheostat,  Wheatstone's A  form  of 

apparatus  sometimes  employed  for  an  adjust- 
able resistance. 

This  apparatus  is  very  seldom  employed  in 
accurate  work. 

The  parallel  cylinders  A  and  B,  Fig.  494,  are 
formed  respectively  of  conducting  and  non-con- 
ducting materials,  the  bare  wire  on  which  can  be 
wound  from  either 
cylinder  to  the  other. 
When  introduced  into 
a  circuit,  only  the  re- 
sistance of  that  part 
of  the  wire  that  is  on 
B,  is  introduced  into 
the  circuit,  since  the 
bare  wire  on  A,  is 
short-circuited  by  the 
metallic  cylinder. 
This  rheostat  is  not 
very  suitable  for  accurate  measurements,  owing 
to  the  difficulty  of  invariably  obtaining  reliable 
contacts. 

Rheostatic  Machine.— (See  Machine, 
Rheostatic) 


Fig.  494.     Wheatstoiu?  s 
Rheostat. 


Rheotome. — A  word  formerly  employed 
for  any  device  by  means  of  which  a  circuit 
could  be  periodically  interrupted. 

This  word  is  now  obsolete,  and  is  replaced  by 
interrupter.  (See  Interrupter.) 

Rheotrope. — A  word  formerly  employed 
for  any  device  by  which  the  current  could 
be  reversed. 

This  word  is  now  obsolete  and  replaced  by 
commutator  or  current  reverser.  (See  Reverser, 
Current.) 

Rhigolene. — A  highly  volatile  hydro-car- 
bon obtained  during  the  distillation  of  coal 
oil,  and  employed  in  the  flashing  treatment  of 
carbons  for  incandescent  lamps.  (See  Car- 
bons, Flashing  Process  for.) 

Rhumbs  of  Compass. — (See  Compass, 
Rhumbs  of.*) 

Ribbed  Armature  Core.— (See  Core, 
Armature,  Ribbed') 

Ribbon  Copper.— (See  Copper,  Ribbon) 

Right-Handed  Solenoid.— (See  Solenoid, 
Right-Handed.) 

Right-Hand  Trolley  Frog.— (See  Frog, 
Trolley,  Right-Hand.} 

Rigidity,  Molecular  — Resistance 

offered  by  the  molecules  of  a  substance  to 
rotation  or  displacement. 

The  molecular  rigidity  of  a  magnetizable  sub- 
stance was  until  recently  considered  to  be  the 
cause  of  the  differences  of  coercive  force  or  mag- 
netic retentivity  possessed  by  different  substances. 
The  general  acceptance  of  Ewing's  theory  of 
magnetism  has,  of  course,  caused  the  above  view 
to  be  considerably  modified.  (See  Magnetism, 
Swing's  Theory  of.  Force,  Coercive.  Retentiv- 
ity, Magnetic.) 

Ring,  Ampere The  turn  or  turns 

of  wire  used  in  electric  balances  for  the  meas- 
urement of  electric  current. 

Ring  Armature. — (See  Armature,  Ring.) 

Ring  Armature  Core.-  (See  Core,  Arma- 
ture, of  Dynamo-Electric  Machine?) 

Rings,  Electric A  term  sometimes 

used  instead  of  Nobili's  rings.  (See  Metal- 
lockromes.) 


Kin.] 


462 


[Rod. 


Rings,  Electro-Chromic  --  A  term 
sometimes  applied  to  metallochromes.  (See 
Metallochromes?) 

Rings,  Nobili's  --  A  term  sometimes 
used  for  metallochromes.  (See  Metallo- 
chromes?) 

Roaring  of  Arc.  —  (See  Arc,  Roaring  of.) 

Rocker  Arm.—  (See  Arm,  Rocker^ 

Rocker,  Brnsh  --  In  a  dynamo-elec- 
tric machine  or  electric  motor,  any  device  for 
shifting  the  position  of  the  brushes  on  the 
cummutator  cylinder. 

Rocker,  Multiple-Pair  Brush—  —A 
term  sometimes  used  for  multiple-pair  brush 
yoke.  (See  Yoke,  Multiple-Pair  Brush.) 

Rocker,  Single-Brush  --  A  device 
by  means  of  which  a  single  pair  of  brushes 
are  so  supported  on  a  dynamo-electric  ma- 
chine or  electric  motor,  as  to  be  capable 
of  being  readily  shifted  into  the  desired 
position  on  the  commutator  cylinder. 

Rocker,  Single-Pair  Brush  --  -A 
term  sometimes  used  for  single-pair  brush 
yoke.  (See  Yoke,  Single-Pair  Brush.) 

Rod  Clamp.—  (See  Clamp,  Rod^ 

Rod,  Clutch  --  A  clutch  or  clamp  pro- 
vided in  an  arc  lamp  to  seize  the  lamp  rod  and 
thus  arrest  its  fall,  during  feeding,  beyond  a 
certain  predetermined  point. 

The  clutch  or  clamp  is  caused  to  release  or  hold 
the  lamp  rod  by  the  action  of  an  electro-magnet 
placed  in  a  shunt  circuit  around  the  electrodes. 
(See  Lamp,  Arc,  Electric.') 

Rod,  Discharging  --  A  jointed  rod 
provided  at  both  ends 
with  balls  and  con- 
nected at  the  middle  by 
a  swinging  joint  which 
permits  the  balls  to 
move  towards  or  from 
one  another,  employed 
for  the  disruptive  dis- 
charge of  Leyden  bat- 
teries or  condensers. 

,~          T-*  .     7  r^- 

(See  Discharge,  Dts- 
ruptive.    Jar,  Leyden?) 
The  insulated  handles  H,  H,  Fig.  495,  permit 


495-    Discharging 

yj  Rodi 


the  balls  at  M,  M,  to  be  readily  applied  to  the 
opposite  coatings  of  the  jar  or  condenser. 

The  name  discharging  tongs  is  sometimes  ap- 
plied to  this  apparatus. 

Rod,  Lamp A  metallic  rod  pro- 
vided in  electric  arc  lamps  for  holding  the 
carbon  electrodes. 

When  the  upper  carbon  only  is  fed,  as  is  the 
case  in  most  arc  lamps,  there  is  usually  but  one 
lamp  rod  provided.  The  clutch  or  clamp  of  the 
feeding  device  acts  against  this  rod,  which  must 
of  necessity  be  at  least  as  long  as  the  upper  carbon. 
(See  Lamp,  Arc,  Electric.) 

Rod,  Lightning  — A  rod,  or  wire 

cable  of  good  conducting  material,  placed  on 
the  outside  of  a  house  or  other  structure,  in 
order  to  protect  it  from  the  effects  of  a  light- 
ning discharge. 

Lightning  rods  were  invented  by  Franklin. 
The  results  of  a  very  extended  inquiry  on  the 
subject,  leave  no  room  for  doubt  that  a  lightning 
rod,  properly  placed  and  constructed,  affords  an 
efficient  protection  to  the  buildings  on  which 
it  is  placed. 

To  insure  this  protection,  however,  the  fol- 
lowing conditions  were,  until  very  recently,  gen- 
erally insisted  on  in  order  to  permit  the  rod  to 
properly  act,  viz. : 

(I.)  The  rod,  generally  of  iron  or  copper, 
should  have  such  an  area  of  cross- section  as  to 
enable  it  to  carry  without  fusion  the  heaviest  bolt 
it  is  liable  to  receive  in  the  latitude  in  which  it  is 
located. 

When  of  iron,  the  area  of  cross-section  should 
be  about  seven  times  greater  than  when  of 
copper. 

(2.)  The  rod  should  be  continuous  throughout, 
all  joints  being  carefully  avoided. 

When  joints  are  used,  they  should  be  made  of  as 
low  resistance  as  possible,  and  should  be  pro- 
tected against  corrosion. 

(3.)  The  upper  extremity  of  the  rod  should 
terminate  in  one  or  more  points  formed  of  some 
metal  that  is  not  readily  corroded,  such  as  pla- 
tinum or  nickel. 

(4.)  The  lower  end  of  the  rod  should  be  car- 
ried down  into  the  earth  until  it  meets  perma- 
nently  damp  or  moist  ground,  where  it  should 
be  attached  to  a  fairly  extended  metallic  surface 
buried  in  the  ground. 

Metallic  plates  will  answer  for  grounding  the 


Rod.] 


463 


[Rod. 


rod,  but,  if  gas  or  water  pipes  are  available,  the 
rod  should  be  placed  in  good  electrical  connec- 
tion therewith,  by  wrapping  it  around  and 
soldering  it  to  such  pipes. 

This  fourth  requirement  is  of  great  importance 
to  the  proper  action  of  a  lightning  rod,  and  un- 
less thoroughly  fulfilled,  may  render  the  rod 
worthless,  no  matter  how  carefully  the  other  re- 
quirements are  attended  to.  When  a  bolt  strikes 
a  lightning  rod  which  is  not  properly  grounded, 
the  discharge  is  almost  certain  to  destroy  the 
building  to  which  the  rod  is  connected. 

(5.)  The  rod  should  not  be  insulated  from  the 
building,  unless  to  prevent  stains  from  the  oxi- 
dation of  the  metal.  On  the  contrary,  the  rod 
should  be  directly  connected  with  all  masses  of 
metal  in  its  path,  such  as  tin  roofs,  gutter  spouts, 
metallic  cornices,  etc.  In  this  way  only  can  dan- 
gerous disruptive  lateral  discharges  from  the  rod 
to  such  masses  of  metal  be  avoided. 

(6.)  The  rod  should  project  above  the  roof  or 
highest  part  of  the  building,  or,  in  other  words, 
the  height  of  the  rod  should  bear  a  certain  pro- 
portion to  the  size  of  the  building  to  be  pro- 
tected. 

A  rod  will  protect  a  conical  space  around  it, 
the  radius  of  whose  base  is  equal  to  the  vertical 
height  of  the  rod  above  the  ground,  but  whose 
sides  are  curved  inwards  instead  of  being  straight. 
Where  the  building  is  very  high,  a  number  of 
separate  rods  all  connected  to  one  another  should 
be  employed. 

A  lightning  rod  sometimes  fails  to  protect  a 
house  or  barn,  from  the  fact  that  a  heated,  ascend- 
ing current  of  air  from  a  fire  in  the  house,  or 
from  the  gradual  heating  of  green  hay  or  grain  in 
the  barn,  acting  as  a  conductor,  increases  the  vir- 
tual height  of  the  house  beyond  the  ability  of  its 
rods  to  protect  it. 

(7.)  A  stranded  conductor  is  much  better  than 
an  equal  cross-section  of  a  solid  rod  of  the  same 
metal. 

A  copper  tape  is  better  than  a  copper  rod  for 
lightning  rods,  because  a  rapidly  periodic  current, 
whose  periodicity  is  sufficiently  great,  passes 
practically  over  the  surface  of  the  conductor  only. 
Considering  an  electric  current  as  taking  its 
energy  from  the  surrounding  dielectric,  a  tape  is 
better,  because  the  surface  which  absorbs  the 
energy  is  greater  in  the  case  of  a  tape  than  of  a 
solid  rod.  (See  Law,  Pointing's.) 

A  lightning  rod  more  frequently  acts  to  quietly 
discharge  an  impending  cloud  by  connective  dis- 


charge than  by  an  actual  disruptive  discharge  of 
the  same.  (See  Discharge,  Convective.  Dis- 
charge, Disruptive.') 

Lightning  rods  should  be  frequently  tested  to 
see  that  no  breaks  or  oxidation  of  their  joints- 
have  occurred. 

Professor  Lodge  takes  exception  to  some  of  the 
heretofore  generally  received  notions  concerning 
the  action  of  lightning  rods.  He  distinguishes 
between  two  distinct  kinds  of  discharge  that  may 
occur  between  a  charged  cloud  and  the  earth, 
viz.: 

(l.)  A  steady  strain  or  current. 

(2.)  An  impulsive  rush  or  oscillatory  discharge, 

A  discharge  by  a  steady  strain  or  current  oc- 
curs when  the  cloud  gradually  approaches  a  point 
on  the  earth ;  or,  in  the  case  of  the  cloud  being 
stationary,  when  it  receives  its  charge  gradually 
by  the  approach  of  another  cloud. 

In  steady  discharge,  the  lightning  rod,  with  its 
pointed  end,  either  quietly  discharges  the  cloud 
by  a  convective  discharge,  or  by  a  harmless  con- 
ductive discharge  through  the  rod,  after  a  spark 
has  passed  disruptively  between  the  cloud  and 
the  rod.  (See  Discharge,  Convective.  Dis- 
charge, Conductive.  Discharge,  Disruptive. ,) 

The  impulsive  discharge  or  rush  occurs  when- 
ever the  cloud  that  discharges  to  the  earth  re- 
ceives its  charge  suddenly,  as  by  the  discharge 
into  it  of  a  neighboring  cloud,  or  when  a  bound 
charge,  produced  by  the  presence  of  a  neighbor- 
ing charged  cloud,  is  suddenly  liberated  by  dis- 
harge,  and,  thus  becoming  free,  impulsively  dis- 
charges to  the  earth. 

In  all  cases  of  an  impulsive  discharge  or  rush,  a 
counter  electromotive  force  is  set  up  in  the  rod, 
which  resists  the  discharge  through  the  rod  and 
causes  the  electricity  to  rush  back  and  spit  off  in 
lateral  discharges.  In  this  case  the  conducting 
power  of  the  rod  has  no  effect  in  facilitating  the 
discharge.  Indeed,  the  smaller  its  resistance,  and 
the  longer  the  oscillations  last,  the  greater  the 
danger  from  lateral  discharges.  (See  Discharge, 
Lateral.  Path,  Alternative.) 

The  following  principles  advanced  by  Lodge 
differ  from  the  views  heretofore  generally  re- 
ceived, viz.: 

(i.)  Iron  is  a  better  substance  for  a  lightning 
rod  than  copper,  because  it  is  equally  as  good  a 
conductor  as  copper  for  very  rapidly  alternating 
currents,  and  is  more  difficult  to  fuse. 

(2.)  All  neighboring  metallic  conductors  should 
be  connected  to  earth.  These  connections  should 


Rod.] 


464 


[Rot. 


preferably  be  by  separate  conductors  rather  than 
by  the  rod  itself. 

(3.)  The  lightning  conductors  should  have  a 
good  separate  earth,  but  should  be  connected  to 
water  pipes,  gas  pipes,  etc.,  if  near  them,  by  an 
underground  connection. 

(4.)  The  lightning  conductor  should  be  de- 
tached from  the  building  and  not  close  against  it. 

(5.)  The  rod  should  be  of  flat  section,  or  a 
stranded  conductor. 

Bod,  Lightning,  for  Ships A 

system  of  rods  designed  to  afford  electric 
protection  for  vessels  at  sea. 

Since  the  lightning  discharge  takes  place  be- 
tween the  points  of  greatest  difference  of  poten- 
tial, and  these  points  are  generally  the  cloud 
and  the  nearest  point  of  the  earth,  tall  objects  are 
especially  liable  to  be  struck. 

Ships  at  sea  should,  therefore,  be  thoroughly 
protected  from  lightning. 

In  Harris'  system  of  lightning  protection  for 
ships,  the  rods  are  connected  with  a  series  of 
copper  plates  and  rods  so  placed  on  the  masts  as 
to  readily  yield  to  strains.  These  plates  or  rods 
are  electrically  connected  with  the  copper  sheath- 
ing of  the  vessel  and  with  all  large  masses  of 
metal  in  the  vessel.  This  latter  precaution  is 
especially  necessary  in  the  case  of  men-of-war, 
in  order  to  protect  the  powder  magazine. 

Harris'  method  for  the  lightning  protection  of 
ships  was  adopted  only  after  very  considerable 
opposition.  It  proved,  however,  so  efficacious  in 
practice  that  serious  effects  of  lightning  on  vessels 
so  protected  are  now  almost  unknown.  In  1845, 
Harris  received  the  honor  of  knighthood  from 
the  English  Government  for  his  services  in  this 
respect 

Rod,  Lightning,  Points  on Points 

of  inoxidizable  material,  placed  on  lightning 
rods,  to  effect  the  quiet  discharge  of  a  cloud  by 
convection  streams.  (See  Rod,  Lightning. 
Convection,  Electric?) 

Bod,  Thunder A  term  formerly 

used  for  lightning  rod.  (See  Rod,  Light- 
ning) 

Bods,  Bus Heavy  copper  rods  em- 
ployed in  a  central  or  distributing  station,  to 
which  all  the  terminals  of  the  generating  dy- 
namos are  connected,  and  from  which  the  cur- 
rent passes  to  the  different  points  of  the  dis- 
tribution system  over  the  feeders. 


Bus  rods  are  often  called  bus  bars  or  bus  wires. 
(See  Wires,  Bus.) 

Bodding  a  Conduit— (See  Conduit,  Rod- 
ding-  a.} 

Boiling  Contact— (See  Contact,  Rolling.} 

Rose,  Ceiling An  ornamental  ceil- 
ing plate  through  which  an  electric  conductor 
passes. 

Bosette. — An  ornamental  plate  provided 
with  contacts  connected  to  the  terminals  of 
the  service  wires,  and  placed  in  a  wall  for  the 
ready  attachment  of  the  incandescent  lamp. 

A  word  sometimes  used  in  place  of  rose. 

Bosette  Cut-Out— (See  Cut-Out,  Rosette) 

Botary  Magnetic  Polarization.— (See 
Polarization,  Magnetic  Rotary.) 

Botary-Phase  Current — (See  Current, 
Rotating.) 

Botary-Phase  Dynamo. — (See  Dynamo, 
Rotary-Phase) 

Botary-Phase  Motor.— (See  Motor,  Ro- 
tating Current.) 

Botary-Phase  Transformer.— (See  Trans- 
former, Rotary-Phase.) 

Botating  Brushes  of  Dynamo-Electric 
Machine.— (See  Brushes,  Rotating,  of 
Dynamo-Electric  Machines.) 

Botating  Current— (See  Current,  Rota- 
ting) 

Botating  Current  Field.— (See  Field, 
Rotating  Current) 

Botating  Current  Motor.— (See  Motor, 
Rotating  Current) 

Botating  Current  Transformer.— (See 
Transformer,  Rotatory  Current) 

Botation,  Electro-Magnetic —A 

rotation  obtained  by  electro-magnetic  attrac- 
tions and  repulsions.  (See  Disc,  Arago's. 
Disc,  Faraday's.  Motor,  Electric.) 

Botation,  Magneto-Optic  —  —A  rota- 
tion of  the  plane  of  polarization  of  a  beam 
of  polarized  light  on  its  passage  through  a 
transparent  medium  when  placed  in  a  strong 
magnetic  field. 

The  medium  only  possesses  such  properties 
while  in  the  field. 


Rub.] 


465 


[Sai. 


In  a  ray  of  ordinary  light  the  vibrations  of  the 
ether  particles  are  at  right  angles  to  the  direction 
of  the  ray,  or  to  the  direction  in  which  the  light 
is  moving.  But  the  vibrations  occur  indiscrimi- 
nately in  all  planes  passing  through  the  line  of 
direction.  Under  certain  circumstances,  all  the 
ether  particles  may  be  caused  to  move  in  planes 
that  are  parallel  to  one  another.  Such  a  beam  of 
light  is  called  a  plane  polarized  beam, 

A  plane  polarized  beam  of  light,  when  passed 
through  many  transparent  substances,  will  have 
its  ether  particles  vibrating  in  the  same  plane 
when  it  emerges  from  the  medium,  as  it  had  before 
it  entered.  Some  transparent  substances,  how- 
ever, possess  the  property  of  rotating  or  turning 
the  plane  of  polarization  of  the  light  to  the  right 
M  N 


Fig.  496.    Magneto- Optic  Rotation. 
or  to  the  left.    This  property  is  called  respec- 
tively right-handed  rotary  polarization,  and  left- 
handed  rotary  polarization. 

Many  substances  that  ordinarily  possess  no 
power  of  rotary  polarization  acquire  this  power 
when  placed  in  a  magnetic  field.  This  property 
of  a  magnetic  field  was  discovered  by  Faraday. 


The  effect  is  to  be  ascribed  to  the  strain  produced 
in  the  transparent  medium  by  the  stress  of  the 
magnetic  field.  It  may  be  caused  in  solid  bodies 
by  mechanical  force. 

The  apparatus  for  demonstrating  the  rotation 
of  the  plane  of  polarization  by  a  magnetic  field  is 
shown  in  Fig.  496. 

A  powerful  electro-magnet,  M,  M,  is  provided 
with  a  hollow  core.  The  substance  c,  is  placed 
in  the  field  produced  by  the  approached  poles, 
and  its  action  on  the  light  of  a  lamp,  placed  at 
the  end  1,  is  observed  by  suitable  apparatus  at  a. 

'Rubber    of    Electrical    Machine.— A 

cushion  of  leather,  covered  with  an  electric 
amalgam,  and  employed  to  produce  electricity 
by  its  friction  against  the  plate  or  cylinder  of 
a  frictional  electric  machine.  (See  Machine, 
Fractional  Electric.) 

Rubbing  Contact— (See  Contact,  Rub- 
bing.) 

Ruhnikorff  Coil.— (See  Coil,  Ruhmkorff) 

RuhmkorflTs  Commutator.— (See  Com- 
mutator, Ruhmkorjf ~'s) 

Rule,  Ampere's,  for  Effect  of  Current  on 

Needle A  magnetic  needle,  when 

placed  near  a  conductor  through  which  a 
current  is  flowing,  has  its  north  pole  deflected 
to  the  left  of  the  observer,  who  is  supposed 
to  be  swimming  with  the  current  and  facing 
the  needle. 


s 


S.— A  contraction  employed  for  second. 

S.  H.  M. — A  contraction  employed  for 
simple  harmonic  motion. 

S.  N.  Code. — A  contraction  for  single  needle 
code. 

S.  W.  G.— A  contraction  for  Standard  Wire 
Gauge. 

Saddles,  Telegraphic B  rackets 

placed  on  the  top  of  telegraphic  poles  for 
the  support  of  the  insulators. 

Saddle  brackets  are  usually  employed  for  the 
wire  attached  to  the  top  of  a  telegraph  pole.  (See 
Pole,  Telegraphic.) 


Safe  Carrying  Capacity  of  a  Conductor. 

-  (See  Capacity,  Safe  Carrying^  of  a  Con- 
ductor?) 

Safety  Catch.— (See  Catch,  Safety) 
Safety  Device  for  Multiple  Circuits.— (See 
Device,  Safety,  for  Multiple  Circuits) 
Safety  Fuse.— (See  Fuse,  Safety.) 
Safety  Lamp,  Electric  —     —(See  Lamp, 
Electric  Safety) 

Safety  Plug.— (See  Plug,  Safety.) 
Safety  Strip.— (See  Strip,  Safety.) 
Saint  Elmo's  Fire.— (See  Fire,  St.  El- 
mo's) 


Sal.] 


466 


[Sch. 


Salient  Magnetic  Pole.— (See  Pole,  Mag- 
netic, Salient?) 
Saline  Creeping.— (See  Creeping,  Saline.} 

Salts,  Electrolysis  of The  decom- 
position of  a  salt  into  its  electro-positive  and 
negative  radicals  or  ions.  (See  Electrolysis.} 

Sandy    Deposit,    Electro-Metallurgical 

(See  Deposit,  Electro-Metallurgical, 

Sandy.} 

Saturated  Solution.— (See  Solution,  Sat- 
urated.} 

Saturation,  Magnetic The  max- 
imum magnetization  which  can  be  imparted 
to  a  magnetic  substance. 

The  condition  of  iron,  or  other  paramag- 
netic substance,  when  its  intensity  of  mag- 
netization is  so  great  that  it  fails  to  be  further 
sensibly  magnetized  by  any  magnetic  force, 
however  great. 

When  the  core  of  an  electro-magnet  is  saturated 
by  the  passage  of  an  electric  current,  the  only 
further  increase  of  its  magnetization  that  is  possi- 
ble, is  that  due  to  the  magnetic  field  of  the  in- 
creased current  which  may  be  sent  through  its 
coils.  This  is  comparatively  insignificant. 

A  permanent  magnet  is  sometimes  said  to  be 
super-saturated,  that  is,  to  have  received  more 
magnetism  than  it  can  retain  for  any  considerable 
time  after  its  magnetization. 

In  the  saturated  field  magnets  of  a  dynamo-elec- 
tric machine  the  magnetic  density  is  seldom  taken 
at  a  larger  value  than  16,000  lines  per  square  cen- 
timetre of  area  of  cross-section.  But  this  is  only 
practical  saturation,  since  Ewing  has  forced 
45,300  lines  per  square  centimetre  by  using  an 
enormously  high  magnetizing  force  (H  =  24,500). 

Saturation,  Magnetic,  Diacritical  Point 

of A  term  proposed  by  S.  P.  Thomp- 
son for  such  a  value  of  the  co-efficient  of 
magnetic  saturation,  that  the  core  is  mag- 
netized to  exactly  one-half  its  possible  max- 
imum 'of  magnetization. 

Saw,  Electric A  platinized  steel 

wire,  employed  while  incandescent  for  cut- 
ting hard  substance. 

Scale,  Tangent A  scale  designed 

for  use  with  a  galvanometer,  on  which  the 
values  of  the  tangents  are  marked,  instead  of 


equal  degrees  as  ordinarily,  thus  avoiding  the 
necessity  of  finding  from  tables  the  tangents 
corresponding  to  the  degrees. 

Such  a  scale  may  be  constructed  as  follows: 
Draw  the  tangent  B  T,  to  the  circle,  Fig.  497, 
and  lay  off  on  it  any  number  of  equal  divisions 
or  parts,  as,  for  example,  the  thirty  shown  in  the 
annexed  figure.  Connect  these  parts  with  the 
centre  C,  of  the  circle.  The  arc  of  the  circle  will 


Fig-  497-     Tangent  Scale. 

thus  be  divided  into  parts  proportional  to  the 
value  of  the  tangents  of  the  angles. 

These  parts  are  more  nearly  equal  the  nearer 
they  are  to  B,  and  grow  smaller  and  smaller  the 
further  they  are  from  B.  In  tangent  galva- 
nometers it  is  therefore  very  difficult  to  accurately 
determine  the  current  strength  when  the  deflec- 
tions of  the  needle  are  very  large. 

Scale,  Thermometer,  Centigrade A 

thermometer  scale,  in  which  the  length  of  the 
thermometric  tube  between  the  melting  point 
of  ice  and  the  boiling  point  of  water  is  divided 
into  one  hundred  equal  parts  or  degrees. 

Centigrade  degrees  are  indicated  by  a  C.,  thus 
O  degree  C,  or  100  degrees  C.,  to  distinguish  them 
from  Fahrenheit  degrees  that  are  marked  F. 
In  the  Fahrenheit  scale  the  freezing  point  of 
water  is  taken  at  32  degrees,  and  the  boiling  point 
at  2 12  degrees. 

Scale,  Thermometer,    Fahrenheit's 

— A  thermometer  scale  in  which  the  length 
of  the  thermometer  tube  between  the  melting 
point  of  ice  and  the  boiling  point  of  water  is 
divided  into  180  equal  parts  called  degrees. 

Fahrenheit  degrees  are  indicated  by  an  F., 
thus,  32  degrees  F. 

The  freezing  point  of  water  in  Fahrenheit's 
scale  is  marked  32  degrees  F.,  and  the  boiling 
point  of  water  is  marked  212  degrees  F. 

Schiseophone.— An  electro-mechanical  ap- 
pliance for  detecting  flaws  and  internal  de- 
fects in  rails  or  other  metallic  masses. 

The  schiseophone  consists  essentially  in  the 
combination  of  a  microphone  and  telephone  with 
a  mechanical  hammer  and  induction  balance. 


Sch.] 


467 


[Scr. 


Schweigger's  Multiplier.— (See  Multi- 
plier, Schweigger's^) 

Scintillating  Jar.— (See  Jar,  Scintillat- 
ing^ 

Scratch  Brush.— (See  Brush,  Scratch^ 

Scratch  Brush,  Circular (See 

Brush,  Scratch,  Circular?) 

Scratch  Brush,  Hand (See  Brush, 

Scratch,  Hand.) 

Scratch  Brushing. — (See  Brushing, 
Scratch.) 

Screen,  Electric A  closed  conduc- 
tor placed  over  a  body  to  screen  or  protect  it 
from  the  effects  of  external  electrostatic  fields. 

An  electric  screen  is  sometimes  called  an  elec- 
tric shield. 

The  ability  of  a  closed,  hollow  conductor  to  act 
as  a  screen,  arises  from  the  fact  that  all  points  on 
its  inner  surface  are  at  the  same  potential,  and 
therefore  are  not  affected  by  an  increase  or  de- 
crease in  the  potential  of  the  outside  of  the  con- 
ductor as  compared  with  that  of  the  earth.  (See 
Net,  Faraday's.} 

No  considerable  thickness  is  required  for  the 
efficient  operation  of  an  electric  screen. 

Screen,  Magnetic A  hollow  box 

whose  sides  are  made  of  thick  iron,  placed 
around  a  magnet  or  other  body  so  as  to  cut 
it  off  or  screen  it  from  any  magnetic  field  ex- 
ternal to  the  box. 

Magnetic  screens  are  placed  around  delicate 
galvanometers  to  avoid  any  variations  in  their 
field  due  to  extraneous  masses  of  iron  or  neigh- 
boring magnets.  They  are  also  sometimes  placed 
around  watches  to  shield  or  screen  the  works 
from  the  effects  of  magnetism. 

To  act  effectively,  when  the  external  fields  are 
at  all  powerful,  magnetic  screens  must  be  made 
of  thick  iron.  They  differ  in  this  respect  from 
electrostatic  shields,  which  will  afford  protection 
against  electrostatic  charges  although  they  may 
be  but  mere  films. 

Screen,  Methven's A  vertical  rec- 
tangular metallic  screen  used  in  connection 
with  a  standard  argand  burner,  for  furnish- 
ing a  standard  amount  of  light  for  photo- 
metric purposes. 

In  a  rectangular  screen  a  small  vertical  slot  is 
made  of  such  dimensions  as  to  permit  an  amount 


of  light  to  pass  just  equal  to  two  standard  candles. 
The  proper  burning  of  the  argand  lamp  is  de- 
termined by  supplying  sufficient  gas  to  produce 
a  flame  exactly  3  inches  high.  The  glass 
chimney  used  in  the  burner  is  6  inches  high, 
and  is  provided  with  two  horizontal  wires  placed 
on  each  side  of  the  burner  at  the  required  height. 

Methven's  screen  possesses  the  advantage  of 
being  easily  used  and  of  furnishing  a  reliable 
standard  of  light.  Extended  experiments  made 
with  it  appear  to  show  that  the  amount  of  light 
produced  depends  rather  on  the  height  of  the 
gas  flame  than  on  the  quality  of  the  gas  itself. 
In  using  Methven's  screen  care  should  be  taken 

(i.)  To  see  that  the  gas  flame  is  of  exactly  the 
required  height. 

(2.)  That  the  chimney  on  the  lamp  is  quite 
clean. 

(3.)  That  the  top  of  the  flame  is  as  regular  as 
possible. 

As  this  last  point  is  almost  impossible  to  obtain  in 
actual  practice,  the  flame  is 
adjusted  so  that  the  highest 
point  extends  about  one- 
eighth  of  an  inch  above  the 
height  of  the  horizontal 
wires. 

(4.)  That  the  lamp  and 
apparatus  be  permitted  to 
acquire  its  normal  temper- 
ature before  the  readings 
are  taken. 

Fig.  498  shows  the  con- 
struction of    the   ordinary 
Methven  standard   screen. 
The  vertical    slot  in    the 
screen  is  placed  as  shown 
before  the  standard  argand    Fis-  4<)8- 
burner.     Horizontal   wires 
for  the  adjustment  of  the  height  of  the  flame  are 
placed  one  on  each  side  of  the  gas  chimney. 

Screening,  Electrostatic Screening 

or  shielding  from  the  inductive  effects  of  a 
charge. 

A  continuous  metallic  surface  surrounding  an 
air  space  to  be  shielded,  completely  protects  any 
body  placed  within  such  air  space  from  electro- 
static influence.  (See  Cube,  Faraday's.) 

Screening,  Magnetic  — Preventing 

magnetic  induction  from  taking  place  by  in- 
terposing a  metallic  plate,  or  a  closed  circuit 
of  insulated  wire,  between  the  body  producing 


Methven's 
Standard  Scran. 


Scr.] 


468 


[Scr. 


the  magnetic  field  and  the  body  to  be  mag- 
netically screened. 

A  magnetic  needle  is  screened  from  the  action 
of  the  earth's  field  by  placing  it  inside  a  hollow 
iron  box,  which  prevents  the  lines  of  force  of  the 
earth's  field  from  passing  through  it  by  concen- 
trating them  on  itself.  This  action  is  dependent 
on  the  fact  that  iron  is  paramagnetic  and  there- 
fore offers  the  lines  of  force  less  resistance 
through  its  mass  than  elsewhere.  A  plate  of 
copper  would  not  effect  any  such  magnetic 
shielding  or  screening. 

In  any  magnetic  field,  however,  in  which  the 
strength  of  the  field  is  undergoing  rapid,  periodic 
variations,  a  plate  of  copper  or  other  electric 
conductor  may  act  as  a  screen  to  protect  neigh- 
boring conductors  from  the  effects  of  magnetic 
induction,  and  its  ability  to  thoroughly  effect 
such  a  screening  will  depend  directly  on  its 
conducting  power. 

If,  for  example,  the  copper  plate  c  (Fig.  499), 
be  interposed  between  a  coil  of  copper  ribbon  a, 
and  the  fine  wire  coil  b,  it  will  greatly  reduce  the 
intensity  of  the  induced  currents,  produced  when 
rapidly  alternating  currents  are  sent  through  a. 
If,  however,  the  copper  plate  be  slit,  as  shown  to 
the  right  at  a,  the  screening  effect  is  lost,  but  is 
regained  if  the  slit  be  connected  by  a  conductor. 
Similarly  a  flat  coil  of  insulated  wire  effects  no 
screening  action  when  open,  but  when  closed  acts 
as  the  uncut  copper  plate. 

Here  the  screening  action  is  due  to  thp  fact 
that  the  energy  of  the  field  is  spent  in  producing 
eddy  currents  in  the  interposed  metal  screen  or 
coils.  If  the  metal  screen  is  discontinuous  in  the 
direction  in  which  the  eddy  currents  tend  to  flow, 
the  inability  of  the  screen  to  absorb  the  energy  as 
eddy  currents  prevents  its  action  as  a  screen. 


induction  from  occurring  in  a  neighboring  con- 
ductor, by  interposing  some  conducting  substance 
in  which  eddy  currents  can  be  freely  established. 

As  to  the  efficiency  of  the  screening  action,  if  the 
makes-and-breaks  do  not  follow  one  another  very 
rapidly,  the  following  principles  can  be  proved  : 

(I.)  If  the  screening  material  have  absolutely 
no  electrical  resistance  it  will  effect  a  perfect  mag- 
netic screening  when  placed  between  the  primary 
and  secondary,  no  matter  what  its  thickness 
may  be. 

(2.)  If  the  screen  have  a  finite  conductivity, 
the  screening  will  be  imperfect,  unless  the  thick- 
ness of  the  material  employed  is  considerable. 

If,  however,  the  makes-and-breaks  follow  one 
another  very  rapidly,  then 

The  screening  effect  of  even  imperfect  conduc- 
tors will  become  manifest  with  comparatively 
thin  screens  of  metal. 

As  to  magnetic  screening,  therefore,  it  follows 
that  the  less  the  conductivity,  the  greater  must 
be  the  speed  of  reversal,  in  order  that  the  screen- 
ing action  may  be  effective. 

Where  a  screen  of  iron  is  employed,  an  ad- 
ditional effect  is  produced  by  the  fact  that  the 
small  magnetic  resistance  of  the  metal,  or  its  con- 
ductivity for  lines  of  magnetic  force,  causes  the 
lines  of  induction  to  pass  through  its  mass,  and 
thus  effect  a  screening  action  for  the  space  on  the 
other  side.  This  action  is,  by  some,  called  mag- 
netic screening. 

In  the  case  of  iron  screens,  considerable  thick- 
ness is  required  in  the  metal  plate,  in  order  to 
obtain  efficient  screening  action  of  this  latter 
character.  On  account  of  this  action  of  iron,  in 
conducting  away  lines  of  force,  a  much  smaller 
speed  of  reversal  is  required,  in  order  to  obtain 
effective  screening  action,  where  plates  of  iron 
are  used,  than  in  the  case  of  plates  of  other 
metal. 

The  apparatus  shown  in  Fig.  500  was  employed 


Fig>  499- 

The  word  magnetic  screening  is  generally  em- 
ployed in  the  latter  sense  of  preventing  magnetic 


Fig.  500.     Willoitghby  Smith's  Apparatus. 

by  Mr.  Willoughby  Smith,  in  studying  the  effects 
of  magnetic  screening. 

The  flat  coils  A,  and  B,  were  employed  for  the 
primary  and  secondary  coils  respectively,  and 
were  connected  to  the  battery  C,  and  the  galva- 


Sep.] 


469 


[Sec. 


nometer  F,  as  shown.  Current  reversers,  D  and 
E,  were  so  arranged  as  to  reverse  galvanometer 
and  battery  alternately,  and  so  cause  the  oppo- 
site induced  currents  to  affect  the  galvanometer  in 
the  same  direction.  If  the  commutators  were 
caused  to  reverse  the  current  slowly,  a  plate  of 
copper  interposed  between  A  and  B,  produced 
but  little  effect  on  the  galvanometer,  but  if  the  re- 
versers were  driven  at  a  very  rapid  rate,  a  marked 
decrease  of  deflection  occurred. 

The  screening  action  of  the  metals,  or  their 
ability  to  diminish  the  galvanometer  deflection, 
is  in  the  order  of  their  electrical  conductivity,  ex- 
cept in  the  case  of  iron,  which,  as  we  have  seen 
already,  has  an  additional  screening  power,  due 
to  its  conducting  away  the  lines  of  magnetic  force. 

It  follows  from  the  preceding  principles  that 
the  use  of  lead  covered  cables,  for  the  conveyance 
of  periodic  currents,  of  the  frequency  of,  say,  sixty 
to  one  hundred  alternations  per  second,  is  of  but 
little  or  no  advantage  for  protecting  neighboring 
telephones  from  inductive  action,  because 

(i.)  Lead  is  a  poor  conductor. 

(2.)  The  rapidity  of  alternation  is  too  slow. 

J.  J.  Thomson  made  some  experiments  with 
electrical  oscillations  produced  by  resonance,  of 
about  ios  in  frequency.  He  obtained  this  fre- 
quency of  oscillation  from  oscillations  set  up  in 
the  primary  of  an  induction  coil,  in  a  secondary 
circuit  of  suitable  dimensions.  The  presence  of 
these  secondary  vibrations  or  waves  was  shown 
by  means  of  the  sparks  seen  at  the  terminals  of  a 
spark-micrometer  circuit.  Under  these  circum- 
stances he  found  that  the  interposition  of  a  thin 
sheet  of  tin  foil  or  gold  leaf  at  once  completely 
stopped  the  secondary  sparks  by  the  shielding 
action  it  exerted. 

Screening,  Magnetostatic Screen- 
ing from  the  inductive  effect  of  a  stationary 
magnetic  field. 

Magnetostatic  screening  differs  from  electrostatic 
screening  in  that  the  plate  of  iron  or  other  para- 
magnetic material  surrounding  the  space  to  be 
screened  must  have  a  fairly  considerable  thick- 
ness. This  arises  from  the  fact  that  the  magnetic 
susceptibility  of  the  substance  is  not  infinitely 
great. 

Screw,  Binding A  name  some- 
times applied  to  a  binding  post.  (See  Post, 
Binding.} 

Seal,  Hermetical Such  a  sealing  of 


a  vessel,  designed  to  hold  a  vacuum,  or  gas- 
eous atmosphere  under  pressures  greater  or 
less  than  that  of  the  atmosphere,  as  will  pre- 
vent either  the  entrance  of  the  external  at- 
mosphere into  the  vessel,  or  the  escape  of  the 
contained  gas  into  the  atmosphere. 

Hermetical  sealing  may  be  accomplished  either 
by  the  use  of  suitable  cements,  or  by  the  direct 
fusion  of  the  walls  of  the  containing  vessel.  The 
latter  method  is  generally  employed. 

Search    Light,    Automatic (See 

Light,  Search,  Automatic) 

Search  Light,  Electric (See  Light, 

Search,  Electric) 

Secohm. — The  practical  unit  of  self-induc- 
tion, or  the  practical  unit  of  inductance, 

The  secohm  is  equivalent  to  a  length  equal  to 
that  of  an  earth  quadrant,  or  lo1  centimetres. 

The  word  secohm  is  a  contraction  for  second, 
ohm,  and  implies  the  fact  that  the  product  of  the 
ohm  and  the  second  are  taken. 

The  word  henry  is  now  generally  used  in  the 
United  States  for  secohm.  (See  Henry.) 

Secohmmeter. — An  apparatus  for  measur- 
ing the  co-efficient  of  self-induction,  mutual 
induction  and  capacity  of  conductors.  (See 
Secohm,  Induction,  Mutual.  Induction, 
Self.) 

The  principle  of  the  secohmmeter  depends 
upon  successively  performing  the  cycle  of  magnetic 
operations,  by  making  and  breaking  the  circuit 
of  a  galvanometer  by  means  of  a  commutator 
capable  of  working  at  a  definite  speed. 

Second,  Ampdre One  ampere  flow- 
ing for  one  second.  (See  Hour,  Ampere.) 

Second,  Watt A  unit  of  electrical 

work. 

A  watt -second  equals  the  work  due  to  the  ex- 
penditu  re  of  an  electrical  power  of  one  watt  for 
one  second.  It  is  the  same  as  a  volt-coulomb. 

The  watt-second  and  the  H.  P.  hour,  etc., 
Work^ 
Time 
therefore,  power  X  time  =  work. 

Secondary  Battery.— (See  Battery,  Sec- 
ondary.) 

Secondary  Battery,  Cell  of —(See 

Cell,  Secondary.} 


are  units  of  work,  since  Power 


Sec.] 


470 


[Sec. 


Secondary  Cell.— (See  Cell,  Secondary) 

Secondary  Cell,  Jar  of (See  Jar  of 

Secondary  Cell.) 

Secondary    Clock.— (See  Clock.  Second- 
ary.) 
Secondary  Coil.— (See  Coil,  Secondary) 

Secondary  Currents. — (See  Currents, 
Secondary) 

Secondary,  Fixed The  secondary 

of  an  induction  coil,  that,  as  is  common  in 
such  coils,  is  fixed,  as  contradistinguished 
from  a  movable  secondary.  (See  Secondary, 
Movable) 

Secondary  Generator.— (See  Generator, 
Secondary) 

Secondary  Impressed  Electromotive 
Force. — (See  Force,  Electromotive,  Second- 
ary Impressed) 

Secondary,  Movable The  second- 
ary conductor  of  an  induction  coil,  which,  in- 
stead of  being  fixed  as  in  most  coils,  is  mova- 
ble. 

The  peculiar  movements  observed  in  the 
secondary  of  an  induction  coil  when  the  second- 
ary  is  free  to  move,  have  been  carefully  studied 
by  Prof.  Elihu  Thomson.  The  secondaries 
employed  for  this  purpose  are  in  the  shape  of 
rings,  discs,  spheres,  wedges,  bars,  wheels,  etc., 
etc. 

The  primary  is  in  the  form  of  a  straight  cylin- 
drical coil  surrounding  a  straight  core.  The  coils 
are  traversed  by  rapidly  alternating  currents  and 
possess  considerable  impedance. 

Among  the  many  phenomena  concerning  the 
behavior  of  movable  secondaries  in  such  a  rapidly 
alternating  field  are  the  following,  viz. : 

(i.)  A  metallic  ring,  resting  on  lugs  attached 
to  the  coils  of  the  primary,  is  thrown  violently  off 
the  magnet  on  the  passage  of  alternating  currents 
through  the  primary. 

(2.)  Two  metallic  rings  of  the  same  diameter 
brought  into  the  field  are  mutually  attracted  to 
each  other,  with  sufficient  force  to  sustain  the 
weight  of  one  of  the  rings  when  the  other  ring  is 
held  in  the  field. 

(3.)  Metallic  spheres  are  set  into  rotation  when 
so  held  near  the  primary  pole  as  to  be  shielded 


from  the  action  of  part  of  the  rapidly  alternating 
field.  When  held  on  one  side  of  the  pole,  this 
rotation  occurs  in  the  opposite  direction  to  that 
when  held  on  the  opposite  side. 

(4.)  Metallic  discs  similarly  placed  are  simi- 
larly set  into  rotation. 

(5.)  The  speed  of  rotation  of  spheres  or  discs 
varies  in  different  positions. 

(6.)  Spheres  or  discs  of  diamagnetic  substances 
attain  their  maximum  rotation  when  held  in  posi- 
tion at  right  angles  to  those  of  paramagnetic  sub- 
stances. 

(7.)  Bars  of  steel  or  substances  possessing  high 
coercive  power,  placed  dissymmetrically  on  the 
primary  as  regards  their  centres  of  gravity,  ex- 
hibit the  phenomena  of  a  shifting  magnetic  field. 
(See  Field,  Magnetic,  Shifting) 

(8.)  A  wedge-shaped  piece  of  steel  placed  with 
a  flat  face  on  the  primary,  exhibits  a  shifting 
magnetic  field,  and  acts  on  movable  metallic 
masses  near  it,  just  as  though  a  fluid  substance 
was  escaping  with  great  velocity  from  its  edges. 

Secondary  Movers.— (See  Movers,  Second- 
ary.) 

Secondary    Plate    of    Condenser.— (See 

Plate,  Secondary,  of  Condenser) 

Secondary  Spiral.— (See  Spiral,  Second- 
ary) 

Secretion  Current. — (See  Current,  Secre- 
tion) 

Section  Line  of  Electric  Railway.— (See 

Railroads,  Electric,  Section  Line  of) 

Section,  Neutral,  of  Magnet A 

section  passing  through  the  neutral  line  or 
equator  of  a  magnet.  (See  Line,  Neutral, 
of  a  Magnet.  Magnet,  Equator  of) 

Section,  Trolley A  single  contin- 
uous length  of  trolley  wire,  with  or  without 
its  branches. 

Sectional  or  Divided  Overhead  System 
of  Motive  Power  for  Electric  Railroads. — 

(See  Railroads,  Electric,  Sectional  Over- 
head System  of  Motive  Power  for)  . 

Sectional  or  Divided  Snrface  System  of 
Motive  Power  for  Electric  Railroads. — 

(See  Railroads,  Electric,  Sectional  Surf  ace 
System  of  Motive  Power  for) 


Sec.] 


471 


[Sep. 


Sectional  or  Divided  Underground 
System  of  Motive  Power  for  Electric  Rail- 
roads.— (See  Railroads,  Electric,  Sectional 
Underground  System  of  Motive  Power  for,} 

Sectional  Plating.— (See  Plating,  Sec- 
tional.} 

Sectional  Plating  Frame.— (See  Frames, 
Sectional  Plating?) 

Seebeck  Effect.— (See  Effect,  Seebeck) 

Seismograph,  Electric An  appa- 
ratus for  electrically  recording  the  direction 
and  intensity  of  earthquake  shocks. 

Seismograph,  Micro An  electric 

apparatus  for  photographically  registering 
the  vibrations  of  the  earth  produced  by  earth- 
quakes or  other  causes. 

The  micro-seismograph  consists  essentially  of  a 
microphone  placed  on  the  ground  and  connected 
with  a  telephone.  A  small  concave  mirror  mova- 
ble about  a  horizontal  axis  is  supported  on  a 
plate  of  aluminium  supported  on  a  platinum  wire 
connected  with  the  diaphragm  of  the  telephone. 
The  movements  of  the  diaphragm  of  the  telephone 
are  permanently  recorded  on  a  strip  of  sensitized 
paper  that  is  moved  before  the  mirror. 

Selective  Absorption.— (See  Absorption, 
Selective} 

Selenium. — A  comparatively  rare  element 
generally  found  associated  with  sulphur. 

Selenium  Battery.— (See  Battery,  Selen- 
ium^) 

Selenium  Cell.— (See  Cell,  Selenium} 

Selenium  Eye. — (See  Eye,  Selenium} 

Selenium  Photometer.— (See  Photometer, 
Selenium} 

Self-Induced  Current.— (See  Currents, 
Self-Induced) 

Self-Induction.— (See  Induction,  Self} 

Self-Induction,  Co-efficient  of (See 

Induction,  Self  Co-efficient  ef.} 

Self-Recording  Magnetometer. — (S  e  e 
Magnetometer,  Self-Recording) 

Self-Registering  Wire  Gauge.  —  (See 
Gauge,  Wire,  Self -Registering) 

Self-Winding  Clock.— (See  Clock,  Self- 
Winding) 


Semaphore. — A  variety  of  signal  apparatus 
employed  in  railroad  block  systems. 

The  semaphore  used  on  the  Pennsylvania  Rail- 
road consists  of  a  wooden  post,  in  the  neighbor- 
hood of  twenty  feet  in  height,  on  which  a  wooden 
arm  or  blade,  six  feet  in  length  and  a  foot  in 
width,  is  displayed. 

When  the  block  is  clear,  during  the  day  the 
arm  is  placed  pointing  downwards  at  an  angle  of 
75  degrees  with  the  horizontal ;  during  night 
semaphore  displays  a  white  light.  When  the 
block  is  not  clear,  the  arm  or  blade  is  placed  in  a 
horizontal  position  by  day,  or  displays  a  red  light 
at  night.  (See  Railroads,  Block  System  for.} 

Semaphore  Arm.— (See  Arm,  Semaphore) 

Semaphore  Indicator.— (See  Indicator, 
Semaphore) 

Sender,  Zinc A  device  employed 

in  telegraphic  circuits,  by  means  of  which,  in 
order  to  counteract  the  retardation  produced 
by  the  charge  given  to  the  line,  a  momen- 
tary reverse  current  is  sent  into  the  line  after 
each  signal. 

A  zinc  sender  generally  consists  of  a  low  resist- 
ance Siemens  relay  introduced  between  the  line 
and  the  front  contact  of  the  signaling  key. 

Sensibility,  Electro An  effect  pro- 
duced on  a  sensory  nerve  by  its  electrization. 

Sensibility  of  Galvanometer. — (See  Gal- 
vanometer, Sensibility  of) 

Sensitive  Thread  Discharge.— (See  Dis- 
charge, Sensitive  Thread) 

Separate  Coil  Dynamo-Electro  Machine. 
— (See  Machine,  Dynamo-Electric,  Separate 
Coil) 

Separate  Touch,  Magnetization  by 

—(See  Touch,  Separate) 

Separately  Excited  Dynamo.— (See  Dy- 
namo, Separately  Excited) 

Separately  Excited  Dynamo-Electric 
Machine. — (See  Machine,  Dynamo-Electric, 
Separately  Excited) 

Separator. — An  insulating  sheet  of  ebonite, 
or  other  similar  substance,  corrugated  and 
perforated  so  as  to  conform  to  the  outline  of 
the  plates  of  a  storage  battery,  and  placed 
between  them  at  suitable  intervals,  in  such  a 


Sep.] 


472 


[Ser. 


manner  as  to  avoid  short-circuiting,  without 
impeding  the  free  circulation  of  the  liquid. 

Series  and  Magneto  Dynamo-Electric 
Machine.— (See  Machine,  Dynamo-Electric, 
Series  and  Magneto!) 

Series  and  Separately  Excited  Dynamo- 
Electric  Machine. — (See  Machine,  Dynamo- 
Electric,  Series  and  Separately  Excited?) 

Series  and  Shunt-Wound  Dynamo-Elec- 
tric Machine. — (See  Machine,  Dynamo- 
Electric,  Series  and  Shunt-  Wound) 

Series  Circuit— (See  Circuit,  Series) 

Series-Connected  Battery.— (See  Battery, 
Series-Connected.) 

Series-Connected  Electro-Receptive  De- 
vices.—(See  Devices,  Electro-Receptive,  Se- 
ries-Connected. ) 

Series-Connected  Electro-Receptive  De- 
vices, Automatic  Cut-out  for  — (See 

Cut-out,  Automatic,  for  Series-Connected 
Electro-Receptive  Devices) 

Series-Connected  Sources. — (See  Sources, 
Series-Connected) 

Series-Connected  Translating  Devices. 
— (See  Devices,  Translating,  Series-Con- 
nected.) 

Series-Connected  Voltaic  Cells.— (See 
Cells,  Voltaic,  Series-Connected) 

Series  Connection.— (See  Connection, 
Series) 

Series,  Contact A  series  of  metals 

arranged  in  such  an  order  that  each  becomes 
positively  electrified  by  contact  with  the  one 
that  follows  it. 

The  contact  values  of  some  metals,  according 
to  Ayrton  and  Perry,  are  as  follows: 

CONTACT  SERIES. 
Difference  of  Potential  in  Volts. 
Zinc ) 


Lead. 

Lead 

Tin 

Tin 

Iron 

Iron 

Copper 

Copper 

Platinum 

Platinum 

Carbon  . . . 


.210 
.069 

•3»3 
.146 
.238 
•"3 


The  difference  in  potential  between  zinc  and 
carbon  is  equal  to  1.089,  and  is  obtained  by  add- 
ing the  successive  differences  of  potential  between 
the  intermediate  couples,  thus: 
.210+.  069+.3I3  +  .  14  6+  .238-1-113=1.089. 

This  fact  is  known  technically  as  Volt  a' s  Law, 
which  may  be  formulated  as  follows: 

The  difference  of  potential,  produced  by  the  con- 
tact of  any  two  metals,  is  equal  to  the  sum  of  the 
differences  of  potentials  between  the  intervening 
metals  in  the  contact  series. 

Series  Distribution  of  Electricity  by 
Constant  Currents. — (See  Electricity,  Se- 
ries Distribution  of,  by  Constant  Current 
Circuit) 

Series-Multiple. — A  series  of  multiple 
connections.  (See  Circuit,  Series-Multiple) 

Series-Multiple  Circuit— (See  Circuit, 
Series-Multiple) 

Series  -  Multiple-Connected  Electro-Re- 
ceptive Devices. — (See  Devices,  Electro-Re- 
ceptive, Series-Multiple-  Connected) 

Series-Multiple-Connected  Sources.  — 
(See  Sources,  Series-Multiple-Connected) 

Series-Multiple-Connected  Translating 
Devices. — (See  Devices,  Translating,  Series- 
Multiple-Connected) 

Series-Multiple  Connection.— (See  Con- 
nection, Series-Multiple) 

Series,  Parallel  —  — A  term  some- 
times applied  to  a  multiple-series  connection. 
(See  Connection,  Multiple-Series) 

Series,  Thermo-Electric  —  —A  list  of 
metals  so  arranged  according  to  their  ther- 
mo-electric powers,  that  each  metal  in  the 
series  is  electro-positive  to  any  metal  lower  in 
the  list. 

Series-Transformer. — (See  Transformer, 
Series) 

Series  Turns  of  Dynamo-Electric  Ma- 
chine.— (See  Turns,  Series,  of  Dynamo- 
Electric  Machine) 

Series  Winding.— (See  Winding,  Series) 

Series-Wound  Dynamo.— (See  Dynamo, 
Series) 

Series-Wound  Dynamo-Electric  Machine. 
— (See  Machine,  Dynamo-Electric,  Series- 
Wound) 


Sen] 


473 


Series-Wound  Motor.— (See  Motor,  Se- 
ries- Wound.) 

Service  Conductors. — (See  Conductors, 
Service.) 

Service,  Street In  a  system  of  in- 
candescent lamp  distribution  that  portion  of 
the  circuit  which  is  included  between  the 
main  and  the  service  cut-out. 

Serving,    Cable The   covering   of 

hemp  or  jute  spun  around  the  insulated  core 
of  a  cable  to  act  as  a  protection  against  the 
pressure  of  the  iron  wire  which  forms  the 
armor  of  the  cable. 

Shackling  a  Wire. — Inserting  an  insula- 
tion between  the  two  ends  of  a  cut  wire. 

Shaded  or  Screened. — Cut  off  or  screened 
from  the  effects  of  an  electrostatic  or  mag- 
netic field.  (See  Screening,  Magnetic.  Screen, 
Magnetic.  Screen,  Electric.) 

Shadow,  Electric  —  — A  term  some- 
times used  for  molecular  shadow.  (See 
Shadow,  Molecular.) 

Shadow,  Molecular The  compara- 
tively dark  space  on  those  parts  of  the  walls 
of  Crookes'  tubes,  which  have  been  protected 
from  molecular  bombardment  by  suitably 
placed  screens. 


[She. 

(See  Phos- 


Fig.  501.     Molecular  Shadow. 

If  a,  in  the  Crookes  tube,  shown  in  Fig.  501, 
be  connected  with  the  negative  pole  of  an  elec- 
tric source,  and  the  cross-shaped  mass  of  alu- 
minium at  b,  be  connected  with  the  positive  elec- 
trode, on  the  passage  of  a  series  of  rapid 
discharges,  phosphorescence  is  produced  by  the 
molecular  bombardment  from  a,  in  all  parts  of 
the  vessel  opposite  a,  except  those  lying  in  the 


projection  of  its  geometrical  shadow. 
phorescence,  Electric.} 

Shadow  Photometer.— (See  Photometer, 
Shadow?) 

Shaft,  Driven A  shaft  which  re- 
ceives its  power  from  the  driving  shaft.  (See 
Mover,  Prime.) 

Shaft,  Driving The  main  line  of 

shafting  which  takes  its  power  directly  from 
the  prime  mover. 

Shallow-Water  Submarine  Cable.— (See 

Cable,  Submarine,  Shallow-  Water.) 

Sheath,  Protective A  device  at- 
tached to  a  transformer  or  converter,  to  pre- 
vent any  connection  from  taking  place  between 
the  high-potential  primary  circuit  and  the 
low-potential  secondary  circuit. 

The  protective  sheath  devised  by  Prof.  Elihu 
Thomson  consists  essentially  in  an  earth -con- 
nected copper  strip  or  divided  plate  interposed 
between  the  windings  for  the  secondary  and  pri- 
mary circuit.  Should  the  primary  circuit  lose  its 
high  insulation  it  becomes  grounded. 

Sheet,  Current  — The  sheet  into 

which  a  current  spreads  when  the  wires  of 
any  source  are  connected  at  any  two  points 
near  the  middle  of  a  very  large  and  thin  con- 
ductor. 

A  continuous  electric  current  does  not  flow 
through  the  entire  mass  of  a  conductor  in  any 
single  line  of  direction.  If  the  terminals  of  any 
source  are  connected  to  neighboring  parts  of  a 
greatly  extended  thin  conductor,  the  current 
spreads  out  in  a  thin  sheet  known  as  a  cur- 
rent sheet,  and  instead  of  flowing  in  a  straight 
line  between  the  points,  spreads  over  the  plate 
in  curved  lines  of  flow,  which,  so  far  as  shape  is 
concerned,  are  not  unlike  the  lines  of  magnetic 
force. 

Sheet  Lightning.  —  (See  Lightning, 
Sheet) 

Shellac. — A  resinous  substance  possessing 
valuable  insulating  properties,  which  is  ex- 
uded from  the  roots  and  branches  of  certain 
tropical  plants. 

The  specific  inductive  capacity  of  shellac  as 
compared  with  air  is  2.74. 


She.] 


474 


[Shu. 


Shell,  Magnetic A  sheet  or  layer 

consisting  of  magnetic  particles,  all  of  whose 
north  poles  are  situated  in  one  of  the  flat 
surfaces  of  the  layer,  and  the  south  poles  in 
the  opposite  surface.  (See  Magnetism,  La- 
mellar Distribution  of.) 

Shell  Transformer.— (See  Transformer, 
Shell.) 

Shield,  Magnetic,  for  Watches A 

hollow  case  of  iron,  in  which  a  watch  is  per- 
manently kept,  in  order  to  shield  it  from  the 
influence  of  external  magnetic  fields.  (See 
Screen,  Magnetic.) 

Shifting  Magnetic  Field.— (See  Field, 
Magnetic,  Shifting.) 

Shifting  Zero.— (See  Zero,  Shifting.) 

Ships,  lightning  Rods  for (See 

Rod,  Lightning,  for  Ships.) 

Ship's  Sheathing,  Electric  Protection  of 

Attaching  pieces  of  zinc  to  the  copper 

sheathing  of  a  ship  for  the  purpose  of  prevent- 
ing the  corrosion  of  the  copper  by  the  water. 
(See  Metals,  Electrical  Protection  of.) 

Shock,  Break A  term  sometimes 

employed  in  electro-therapeutics  for  the 
physiological  shock  produced  on  the  opening 
or  breaking  of  an  electric  circuit. 

Shock,  Electric  —  —The  physiological 
shock  produced  in  an  animal  by  an  electric 
discharge. 

Shock,  Opening The  physiological 

shock  produced  on  the  opening  or  breaking 
of  an  electric  circuit. 

Shock,  Static A  term  employed  in 

electro-therapeutics  for  a  mode  of  applying 
Franklinic  currents  or  discharges,  by  placing 
the  patient  on  an  insulating  stool  and  apply- 
ing one  pole  of  a  static  machine  provided 
with  small  condensers  or  Leyden  jars,  to  an 
insulated  platform  on  which  the  patient  is 
placed,  while  the  other  pole  is  applied  to  the 
body  of  the  patient  by  the  operator. 

The  electrode  applied  to  the  body  of  the  pa- 
tient is  provided  with  a  ball  electrode.  Shocks 
are  given  to  the  patient  on  the  approach  of 
this  electrode  by  the  discharge  of  the  Leyden 
jars. 


Short-Arc  System  of  Electric  Lighting. 

—(See  Lighting,  Electric,  Short-Arc  Sys- 
tem.) 

Short-Circuit.— To  establish  a  short  cir- 
cuit. (See  Circuit,  Short.) 

Short-Circuit  Key.— (See  Key,  Short- 
Circuit) 

Short-Circuiting  —  Establishing  a  short 
circuit.  (See  Circuit,  Short.) 

Short-Circuiting  Plug.— (See  Plug, 
Short-Circuiting.) 

Short-Coil  Magnet— (See  Magnet,  Short- 
Coil.) 

Short-Core  Electro-Magnet. — (See  Mag- 
net, Electro,  Short-Core.) 

Short-Shunt  Compound-Wound  Dyna- 
mo-Electric Machine.— (See  Machine,  Dy- 
namo-Electric, Compound-  Wound,  Short- 
Shunt^ 

Shunt— An  additional  path  established 
for  the  passage  of  an  electric  current  or  dis- 
charge. 

Shunt — To  establish  an  additional  path 
for  the  passage  of  an  electric  current  or  dis- 
charge. 

Shunt  and  Separately  Excited  Dynamo- 
Electric  Machine. — (See  Machine,  Dynamo- 
Electric,  Shunt  and  Separately  Excited?) 

Shunt  Circuit— (See  Circuit,  Shunt.) 

Shunt  Dynamo-Electric  Machine.— (See 

Machine,  Dynamo-Electric,  Shunt-  Wound.) 

Shunt    Electric   Bell (See    Bell, 

Shunt,  Electric) 

Shunt,  Electro-Magnetic In  a  sys- 
tem of  telegraphic  communication  an  electro- 
magnet whose  coils  are  placed  in  a  shunt 
circuit  around  the  terminals  of  the  receiving 
relay. 

The  electro-magnetic  shunt  operates  by  its 
self-induction.  Its  poles  are  permanently  closed 
by  a  soft  iron  armature  so  as  to  reduce  the  resist- 
ance of  the  magnetic  circuit  (See  Induction, 
Self.) 


Shu.] 


475 


[Shu, 


On  making  the  circuit  in  the  coils  of  a  receiv- 
ing relay,  a  current  is  produced  in  the  coils  of  the 
electro  magnetic  shunt  hi  the  opposite  direction 
to  the  relay  current;  and,  on  breaking  the  circuit 
in  the  relay,  a  current  is  produced  in  the  coils  of 
the  electro-magnetic  shunt  hi  the  same  direction 
as  the  current  in  the  relay. 

The  connection  of  the  coils  of  the  electro-mag- 
netic shunt  with  those  of  the  receiving  relay,  how- 
ever, is  such  that  on  making  the  circuit  in  the 
relay  the  current  in  the  shunt  coils  flows  through 
the  relay  in  the  same  direction,  and  on  breaking 
the  circuit  it  flows  in  the  opposite  direction. 
Therefore  this  shunt  produces  the  following  effects : 

(i.)  At  the  commencement  of  each  signal  in 
the  receiving  relay,  it  produces  an  induced  cur- 
rent in  the  same  direction  which  strengthens  the 
current  in  the  relay. 

(2.)  At  the  ending  of  each  signal  in  the  receiv- 
ing relay,  it  produces  a  current  in  the  opposite 
direction,  which  hastens  the  motion  of  the  tongue 
of  the  polarized  relay.  (See  Relay,  Polarized. ) 

Shunt,    Galvanometer A   shunt 

placed  around  a  sensitive  galvanometer  for 
the  purpose  of  protecting  it  from  the  effects 
of  a  strong  current,  or  for  altering  its  sensi- 
bility. (See  3hunt) 

The  current  which  will  flow  through  the  shunt 
wire  depends  on  the  relative  resistance  of  the  gal- 
vanometer and  of  the  shunt.  In  order  that  only 

total  curtent  shall  pass 
through  the  galvanome- 
ter, it  is  necessary  that 
the  resistances  of  the 
shunt  shall  be  the  ^  -fo, 
or  ^-g ,  of  the  galvanom- 
eter resistance. 

Fig.  502  shows  a 
shunt,  in  which  the  re- 
sistances, as  compared 
with  that  of  the  galva- 
nometer, are  those  above 
referred  to.  The  galva- 
nometer terminals  are  Fig.  302.  Galvanometer 
connected  at  N,N.  Plug  Shunt. 

keys  are  used  to  connect  one  or  another  of  the 
shunts  with  the  circuit.  (See  Shunt,  Multiplying 
Power  of.) 

Shunt,    Magnetic  —     —An    additional 
path  of  magnetic  material  provided  in  a  mag- 
16— Vol.  1 


netic  circuit  for  the  passage  of  the  lines  of 
force. 
Shnnt,  Multiplying  Power  of __A 

quantity,  by  which  the  current  flowing  through 
a  galvanometer  provided  with  a  shunt,  must 
be  multiplied,  in  order  to  give  the  total  cur- 
rent. 

The  multiplying  power  of  a  shunt  may  be  de- 
termined from  the  following  formula,  viz. : 

A=  (j^-)  X  C,  in  which  ^li  =  the  mul- 
tiplying power  of  a  shunt  whose  resistance  is  s; 
g,  is  the  galvanometer  resistance;  C,  the  current 
through  the  galvanometer,  and  A,  the  total  cur- 
rent passing;  s  and  g,  are  taken  in  ohms,  and  C 
and  A,  in  ampSres. 

Suppose,  for  example,  that  but  ^  the  entire 
current  is  to  flow  through  the  galvanometer;  then 
the  resistance  of  the  shunt  must  evidently  be  \  g, 
for, 

s  I      _   r 

s-f-g ~~  i~+9 ~~  io' 

or,  io  s  =  s -f  g.  10  s  —  s  =  g  .•.  9  s=g;  or, 
s=(i)g- 

Shunt  or  Rednctenr  for  Ammeter. — (See 
Reducteur  or  Shunt  for  Ammeter?) 

Shunt.  Ratio.— The  ratio  existing  between 
the  shunt  and  the  circuit  which  it  shunts 
(See  Shunt,  Multiplying  Power  of.) 

Shunt,  Relay,  Stearns' A  shunt 

employed  in  the  differential  method  of  duplex 
telegraphy  to  short-circuit  the  relay  and  then 
permit  the  line  current  to  be  cut  off  directly 
after  it  has  completed  its  work  in  closing  the 
local  circuit. 

The  use  of  the  relay  shunt  permits  the  slacken.- 
ing  of  the  armature  spring  of  the  relay,  because 
the  decreased  duration  of  the  line  current  does 
not  produce  so  strong  a  magnetization  of  the 
iron. 

Shunt-Turns  of  Dynamo-Electric  Ma- 
chine.—(See  Turns,  Shunt,  of  Dynamo- 
Electric  Machine.) 

Shunt-Wound  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Shunt-  Wound.) 

Shunt-Wound  Motor.  —  (See  Motor, 
Shunt-  Wound) 


Shn.] 


476 


[Sig. 


Shunting.— Establishing  a  shunt  circuit. 

Shuttle  Armature.— (See  Armature, 
Shuttle) 

Side  A,  of  Quadruples  Table.— (See  Table. 
Quadruplex,  A,  Side  of.) 

Side  B,  of  Quadruplex  Table.— (See  Table. 

Quadruplex,  B,  Side  of) 

Side  Flash.— (See  Flash,  Side) 

Sidero-Magnetic.— (See  Magnetic,  Side- 
ro) 
Siemens'  -  Armature     Electro-Magnetic 

Bell. — (See  Bell,Electro-Magnetic,  Siemens' 
Armature  Form) 

Siemens'  Differential  Voltameter.— (See 
Voltameter  Siemens'  Differential) 

Siemens'  Electric  Pyrometer.— (See  Py- 
rometer, Siemens'  Electric) 

Siemens-Halske  Voltaic  CeU.— (See  Cell. 
Voltaic,  Siemens-Halske) 

Siemens1  Water  Pyrometer.— (See  Py- 
rometer, Siemens'  Water) 

Signal  Arm.— (See  Arm,  Signal) 

Signal,  Electric  Tell-Tale An 

electrically  operated  signal,  generally  silent, 
whereby  the  appearance  of  a  white  or  colored 
disc,  on  a  black  or  otherwise  uniformly 
colored  surface,  indicates  the  occurrence  of 
a  certain  predetermined  event. 

Signal  Service  for  Electric  Railways.— 
(See  Railroads,  Electric,  Signal  Service 
System  for) 

Signals,  Electro-Pneumatic  —  —Sig- 
nals operated  by  the  movements  of  dia- 
phragms or  pistons  moved  by  compressed 
air,  the  escape  of  which  is  controlled  electri- 
cally. 

Signaling,  Balloon,  for  Military  Pur- 
poses   Transmitting  intelligence  of  the 

movements  of  an  enemy's  army  obtained  from 
observations  made  in  balloons  by  means  of  tel- 
ephone circuits  connected  with  the  balloon. 

Signaling,  Curb  —In  cable  teleg- 
raphy a  system  for  avoiding  the  effects  of 
retardation  by  rapidly  discharging  the  cable 
before  another  electric  impulse  is  sent  into 


it,  by  reversing  the  battery,  before  connecting 
it  to  earth,  and  then  connecting  to  earth  be- 
fore beginning  the  next  signal. 

Signaling,  Double-Curb In  curb 

signaling,  a  method  by  which  the  cable,  after 
being  connected  with  the  battery  for  sending 
a  signal,  is  subjected  to  a  reverse  battery,  but 
instead  of  being  put  to  earth  after  this  con- 
nection, as  in  single-curb  signaling,  the  bat- 
tery is  again  reversed  and  connected  to  earth. 

The  time  during  which  the  cable  is  connected 
to  the  reversed  battery  before  being  put  to  earth, 
that  is,  the  time  during  which  it  receives  the 
positive  and  negative  currents,  may  be  made  of 
any  suitable  duration. 

Signaling,  Double-Current  —  —Signal- 
ing by  means  of  currents  that  alternately 
change  their  direction. 

Double-current  signaling  was  devised  by  Var- 
ley  in  order  to  avoid  the  effects  of  the  induction 
of  underground  conductors  on  Morse  tele- 
graphic apparatus.  The  idea  of  reversing  the 
direction  of  the  current  was  to  hasten  the  dis- 
charge of  the  wire,  which  was  prolonged  by  in- 
duction. Double- current  working,  however, 
possesses  other  advantages,  and  is  used  in  duplex 
and  quadruples  transmission. 

Signaling,  Single-Curb  —In  curb 

signaling,  a  method  by  which  the  cable,  after 
connection  with  the  battery  for  sending  a 
signal,  is  subjected  to  a  reverse  battery  cur- 
rent, and  then  put  to  earth  before  again  being 
connected  to  the  battery  for  sending  the  next 
signal. 

Signaling,  Single-Current  —  —Signal- 
ing by  making  or  breaking  the  circuit  of  a 
single  current. 

Single-current  signaling  is  of  two  kinds,  viz.: 

(I.)  Open-Circuit  Signaling,  in  which  the  bat- 
teries are  fixed  at  each  station,  and  are  in  circuit 
only  when  signaling. 

(2.)  Closed-Circuit  Signaling,  where  the  bat- 
teries are  divided,  one  half  generally  being  at  each 
end  of  the  line,  and  so  connected  that  both  sets 
flow  in  the  same  direction. 

Signaling,  Single-Current,  Closed-Circuit 

A  system  of  single-circuit  signaling  in 

which  the  sending  batteries  are  placed  at 
each  end  of  the  line  and  are  so  connected  as 


477 


[Sin. 


to  remain  always  in  circuit.     (See  Signaling, 
Single-Current) 
Signaling,  Single-Current,  Open-Circuit 

A  system  of  single-current  signaling 

in  which  the  sending  batteries,  fixed  at  each 
station,  are  in  circuit  during  signaling  only. 
(See  Signaling,  Single-Current) 

Signaling,  Velocity  of  Transmission  of 

The  speed  or  rate  at  which  successive 

signals  can  be  sent  on  any  line  without  the 
retardation  producing  serious  interference. 
(See  Retardation) 

Silent  Discharge.— (See  Discharge,  Si- 
lent) 
Silver  Bath.— (See  Bath,  Silver) 

Silver  Chloride  Voltaic  Cell.— (See  Cell, 
Voltaic,  Silver  Chloride) 

Silver  Plating.— (See  Plating,  Silver) 

Silver  Voltameter.— (See  Voltameter, 
Silver) 

Silvered  Plumbago.— (See  Plumbago,  Sil- 
vered) 

Silvering,  Electro Covering  a  sur- 
face with  a  coating  of  silver  by  electro-plat- 
ing. (See  Plating,  Electro) 

Electro-plating  with  silver. 

Silnrns  Electricus.— The  electric  eel. 
(See  Eel,  Electric) 

Simple  Arc. — (See  Arc,  Simple) 

Simple  Circuit— (See  Circuit,  Simple) 

Simple  Electric  Candle-Burner.— (See 
Burner,  Simple  Candle  Electric) 

Simple-Harmonic  Current— (See  Cur- 
rent, Simple-Harmonic) 

Simple-Harmonic  Curve. — (See  Curve, 
Simple-Harmonic) 

Simple-Harmonic  Motion.— (See  Motion, 
Simple-Harmonic) 

Simple  Magnet— (See  Magnet,  Simple) 

Simple-Periodic  Current. — (See  Cur- 
rents, Simple-Periodic) 

Simple-Periodic  Electromotive  Force. 
— (See  Force,  Electromotive,  Simple- 
Periodic) 


Simple-Periodic  Motion.— (See  Motion, 
Simple-Periodic) 

Simple  Radical.— (See  Radical,  Simple) 

Simple-Sine  Motion.— (See  Motion, 
Simple-Sine) 

Simple  Voltaic  Cell.— (See  Cell,  Voltaic, 
Simple) 
Simplex  Telegraphy. — (See  Telegraphy, 

Simplex) 

Sims-Edison  Torpedo.— (See  Torpedo, 
Sims-Edison) 

Sine  Galvanometer. — (See  Galvanometer, 
Sine) 
Single-Brush     Rocker.— (See     Rocker, 

Single-Brush) 

Single-Cup    Insulator. — (See  Insulator, 
Single-Shed) 
Single  Curb.— (See  Curb,  Single) 

Single-Current  Signaling.— (See  Signal- 
ing, Single-Current) 

Single-Curve     Trolley      Hanger. — (See 

Hanger,  Single-Curve  Trolley) 

Single-Fluid  Hypothesis  of  Electricity. 

—(See  Electricity,  Single-Fluid  Hypothesis 

of) 
Single-Fluid  Voltaic     Cell.— (See    Cell, 

Voltaic,  Single-Fluid) 

Single-Loop  Armature. — (See  Armature, 
Single-Loop.) 

Single-Magnet  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Single- Magnet) 

Single-Pair  Yoke.— (See  Yoke,  Single- 
Pair) 

Single-Shackle  Insulator.— (See  Insula- 
tor, Single-Shackle) 

Single-Shed  Insulator.— (See  Insulator, 
Single-Shed) 

Single-Stroke  Electric  Bell.— (See  Bell, 
Single-Stroke  Electric) 

Single  Touch.— (See  Touch,  Single) 

Single-Wire  Cable.— (See  Cable,  Single- 
Wire) 


Sin.] 


478 


[Sme. 


Single-Wire  Circuit.— (See  Circuit, 
Single-  Wire.*) 

Sinistrorsal  Solenoid  or  Helix.— (See  So- 
lenoid, Sinistrorsal) 

Sinuous  Currents. — (See  Current,  Sinu- 
ous') 

Siphon,  Electric  — A  siphon  in 

which  the  stoppage  of  flow,  due  to  the 
.gradual  accumulation  of  air,  is  prevented  by 
electrical  means. 

In  the  electric  siphon,  an  opening  is  provided 
at  the  highest  part  of  the  bend  of  the  siphon  tube, 
and  a  chamber  is  attached  thereto,  provided  with 
a  float.  Contact  points  are  so  connected  with  the 
float  that  when  it  falls,  contact  is  made,  and  when 
it  rises,  contact  is  broken. 

The  closing  of  the  circuit,  on  the  fall  of  the 
float,  operates  an  electric  motor  which  drives  an 
air  pump  which  exhausts  the  air  from  the  siphon. 
Or  the  float  being  raised  in  the  siphon,  the  con- 
tact is  broken  and  the  operation  of  the  pump  is 
stopped. 

Siphon  Recorder.— (See  Recorder,  Si- 
phon) 

Sir  William  Thomson's  Standard  Cell.— 
(See  Cell,  Voltaic,  Standard,  Sir  William 
Thomson's?) 

Skin  Effect.— (See  Effect,  Skin.) 

Skin,  Faradization  of —The  thera- 
peutic treatment  of  the  skin  by  a  faradic  cur- 
rent. 

For  efficient  faradization  the  skin  should  be 
thoroughly  dried  and  a  metallic  brush  or  elec- 
trode employed.  For  very  sensitive  parts,  as, 
for  example,  the  face,  the  hand  of  the  operator, 
first  thoroughly  dried,  is  to  be  preferred  as  an 
electrode. 

Skin,  Human,  Electric  Resistance  of 

— The  electric  resistance  offered  by  the 
skin  of  the  human  body. 

The  electric  resistance  of  the  skin  is  subject  to 
marked  differences  in  different  parts  of  the  body, 
where  its  thickness  or  continuity  varies.  It 
varies  still  more  with  variations  in  its  condition  of 
moisture.  Even  in  the  same  individual  the  re- 
sistance varies  materially  under  apparently 
.similar  conditions. 

•Sleeve,  Insulating A  tube  of  treated 

paper  or  other  insulating  material,  provided 


for  covering  a  splice  in  an  insulated  con- 
ductor. 

Sleeve  Joint— (See  Joint,  Sleeve.) 

Sleeve,  Lead A  lead  tube  provided 

for  making  a  joint  in  a  lead-covered  cable. 

Sled. — The  sliding  contacts  drawn  after  a 
moving  electric  railway  car  through  the  slotted 
underground  conduit  containing  the  wires  or 
conductors  from  which  the  driving  current  is 
taken. 

Slide  Bridge.— (See  Bridge,  Electric, 
Slide  Form  of) 

Slide,  Resistance A  rheostat,  in 

which  the  separate  resistances  or  coils  are 
placed  in  or  removed  from  a  circuit  by  means 
of  a  sliding  contact  or  key. 

Apparatus  employed  in  telegraphy  for 
charging  a  conductor  to  a  given  fraction  of 
the  maximum  potential  of  the  battery  so  as 
to  adjust  its  charge  in  order  to  balance  the 
varying  charge  of  a  cable. 

The  resistance  slide  consists  essentially  of  a  set 
of  resistance  coils  of  high  insulation  and  of  equal 
resistance.  Suppose,  for  example,  ten  such  equal 
coils  to  be  connected  in  series,  then  if  connected 
to  the  charging  battery  the  potential  will  vary  by 
one-tenth  at  the  junction  between  each  pair.  A 
condenser,  therefore,  will  be  charged  to  any 
number  of  tenths  of  the  potential  of  the  charging 
battery  by  connecting  it  at  suitable  points. 

A  second  set  of  coils  of  equal  resistance  is  ar. 
ranged  so  as  to  subdivide  any  of  the  lower  coils, 
thus  permitting  an  adjustment  to  within  a  hun- 
dredth of  the  potential  of  the  battery. 

Slide  Wire.— (See  Wire,  Slide) 
Sliding  Contact— (See  Contact,  Sliding) 

Slow-Speed  Electric  Motor. — (See  Motor, 
Electric,  Slow-Speed) 

Sluggish  Magnet— (See  Magnet,  Slug- 
gish) 

Small  Calorie.— (See  Calorie,  Small) 

Smee  Yoltaic  Cell.— (See  Cell,  Voltaic, 
Smee) 

Smelting,  Electro The  separation 

or  reduction  of  metallic  substances  from  their 
ores  by  means  of  electric  currents. 


Sna. 


479 


[Sol. 


Snap  Switch.— (See  Switch,  Snap.} 

Soaki  iiir-I  n. — A  term  sometimes  employed 
by  telegraphers  to  represent  the  gradual 
penetration  of  an  electric  charge  by  a  neigh- 
boring dielectric. 

An  electric  displacement  occurs  in  the  neigh- 
boring dielectric,  and  produces  thereby  what  is 
generally  called  the  residual  charge. 

Soaking-Out.— A  term  sometimes  em- 
ployed by  telegraphers  to  represent  a  gradual 
discharge  which  occurs  in  the  case  of  a 
charged  conductor  in  a  neighboring  dielec- 
tric. 

When  a  condenser,  or  other  similar  conductor, 
is  discharged,  the  discharge  is  not  instantaneous. 
The  charge  which  soaked  in,  gradually  recovers, 
or  soaks- out. 

Socket,  Electric  Lamp A  support 


Fig.  303.    Lamp  Socket. 

for  the  reception  of  an  incandescent  electric 
lamp. 

Incandescent  lamp  sockets  are  generally  made 
so  that  the  mere  insertion  of  the  base  of  the  lamp 


Fig.  304.    Lamp  Socket. 

in  the  socket  completes  the  connection  of  the  lamp 
terminals  with  the  terminals  of  the  socket.     The 


socket  terminals  are  connected  with  the  leads  that 
supply  current  to  the  lamp ;  the  removal  of  the 
lamp  from  the  socket  automatically  breaks  its  cir- 
cuit. The  socket  is  generally  provided  with  a  key 
for  turning  the  lamp  on  or  off  without  removing 
it  from  the  socket. 

Figs.  503  and  504  show  forms  of  lamp  sockets 
for  incandescent  lamps  and  the  details  of  the  key 
for  connecting  or  disconnecting  the  lamp  with  the 
leads. 

Socket,  Wall  —  —A  socket  placed  in  a 
wall  and  provided  with  openings  for  the  inser- 
tion of  a  wall  plug  with  which  the  ends  of  a 
flexible  twin-lead  are  connected. 

A  wall -socket  permits  the  temporary  connec- 
tion of  a  portable  electric  lamp,'  a  push  button  or 
other  device  with  the  conductor  or  lead. 
.  Soft-Drawn  Copper  Wire.— (See   Wire, 
Copper,  Soft-Drawn?) 

Soldering,  Electric A  process  for 

obtaining  metallic  joints,  in  which  heat  gen- 
erated by  the  electric  current  is  used  to  melt 
the  solder  in  the  place  of  ordinary  heat. 

Solenoid. — A  cylindrical  coil  of  wire  the 
convolutions  of  which  are  circular. 

An  electro-magnetic  helix.  (See  Solenoid, 
Electro-Magnetic,  or  Electro-Magnetic 
Helix.) 

A  solenoid  is  termed  dextrorsal  or  sinistrorsal 
according  to  the  direction  in  which  its  wire  is 
wound.  (See  Solenoid,  Dextrorsal.  Solenoid, 
Sinistrorsal.) 

Solenoid  Core. — The  core,  usually  of  soft 
iron,  placed  within  a  solenoid  and  magnetized 
by  the  magnetic  field  of  the  current  passing 
through  the  solenoid. 

The  soft  iron  core  of  a  solenoid  differs  from 
that  of  an  electro-magnet  in  the  fact  that  the  core 
of  the  solenoid  is  movable,  while  that  of  the  elec- 
tro-magnet is  fixed.  (See  Magnet,  Electro.) 

In  order  to  obtain  a  nearly  uniform  pull  in  its 
various  positions  in  the  solenoid,  the  soft  iron  cores 
are  made  of  a  shape  which  insures  a  greater  mass 
of  metal  towards  the  middle  of  the  core.  (See 
Bars,  KriziVs.) 

Solenoid,  Dextrorsal  —  — A  solenoid 
in  which  the  winding  is  right-handed.  (See 
Solenoid,  Practical!) 

Solenoid,  Electro-Magnetic,  or  Electro- 
Maguetic  Helix The  name  given  to 


Sol.] 


480 


[8W. 


a  cylindrical  coil  of  wire,  each  of  the  convo- 
lutions of  which  is  circular. 

A  circuit  bent  in  the  form  of  a  helix,  supported 
at  its  two  extremities,  as  shown  in  Fig.  505,  and 
traversed  by  an  electric  current,  will  move  into 
the  magnetic  meridian  of  the  place,  and,  if  free  to 
move  in  a  vertical  plane,  will  come  to  rest  in  the 
line  of  the  magnetic  inclination  or  dip  of  the  place. 

A  solenoid  traversed  by  an  electric  current  ac- 
quires thereby  all  the  properties  of  a  magnet,  and 
is  attracted  and  repelled  by  other  magnets.  Its 
poles  are  situated  at  the  ends  of  the  cylinder  on 
which  the  solenoid  may  be  supposed  to  be  wound. 

Solenoid,  Ideal A  solenoid  con- 
sisting of  a  cylinder  built  up  of  a  number  of 
true  circular  currents,  with  all  faces  of  like 
polarity  turned  in  the  same  direction  and 
entirely  independent  of  one  another. 

The  practical  solenoid  differs  from  the  ideal 
solenoid  in  that  the  successive  circular  circuits  or 
currents  are  all  connected  with  one  another  in 
series. 

The  polarity  of  a  solenoid  depends  on  the  direc- 
tion of  the  current  as  regards  the  direction  in 
which  the  solenoid  is  wound. 

This  solenoid  is  sometimes  called  an  electro- 
•utgnetic  solenoid  or  helix,  in  order  to  distinguish 


Fig.  sos-    Practical  Solenoid. 
it  from  a  solenoidal  magnet.     (See  Magnet,  Sole- 


move,  will  come  to  rest  in  the  plane  of  the  mag- 
netic meridian  when  traversed  by  an  electric 
current. 

It  will  also  be  attracted  or  repelled  by  the  ap. 
proach  of  a  dissimilar  or  similar  magnet  pole 
respectively,  as  shown  in  Fig.  505. 

Solenoid,  Left-Handed  —  — A  sinistror- 
sal  solenoid  or  one  in  which  the  winding  is 
left-handed.  (See  Solenoid,  Practical.} 

Solenoid,  Magnetic A  spiral  coil 

of  wire  which  acts  like  a  magnet  when  an 
electric  current  passes  through  it. 

The  magnetic  solenoid  must  be  distinguished 
from  a  solenoidal  magnet.  (See  Magnet,  Sole- 
noidal. Solenoid,  Electro-Magnetic,  or  Electro- 
Magnetic  Helix.} 

Solenoid,  Practical The  name  ap- 
plied to  the  ordinary  solenoid  in  order  to  dis- 
tinguish it  from  the  ideal  solenoid.  (See 
Solenoid,  Ideal.} 

A  Practical  Solenoid  consists,  as  shown  in  Figs. 


Fig.  so  6.    Practical  Solenoid. 

505  and  506,  of  a  spiral  coil  of  wire  in  which  the 
successive  circular  circuits  are  connected  to  oae 
another  in  series. 


A  solenoid,  if  suspended  so  as  to  be  free  to 


.  Right-Handed  HeKx.    Fig. 308.  Left-Handed 
Helix.    Fig.  309.    Helix,  with  Consequent  Polet. 
The  polarity  of  the  solenoid  depends  on  tke 
direction  of  the  current,   and  therefore  on  the 
direction  of  winding.     In  any  solenoid,  however, 
the  polarity  may  be  reversed  by  reversing  tke 
direction  of  the  current     (See  Magnet,  Electr*.) 
A  Right- Handed,  or  Dextrorsal  Solenoid,  iso«e 
wound  in  the  direction  shown  in  Fig.  507  at  i. 


Sol.] 


481 


[Sou. 


A  Left -Handed,  or  Sinistror sal  Solenoid,  is  one 
wowid  in  the  direction  shown  in  Fig.  508  at  2. 

The  solenoid  shown  in  Fig.  509  at  3,  is  wound 
so  as  to  produce  consequent  poles.  (See  Poles, 
Consequent.) 

Solenoid,  Right-rfanded A  dex- 

trorsal  solenoid,  the  winding  in  which  is  right- 
banded.  (See  Solenoid,  Practical.) 

Solenoid,  Sinistrorsal  —  —A  solenoid 
in  which  the  winding  is  left-handed.  (See 
Solenoid,  Practical.) 

Solenoidal. — Pertaining  to  a  solenoid. 

Solid  Angle.— (See  Angle,  Solid.) 

Solid  Line.— (See  Line,  Solid.) 

Solution. — A  liquid  in  which  another  sub- 
stance, generally  a  solid,  is  dissolved. 

The  liquid  may  contain  either  a  solid,  another 
liquid,  or  a  gas. 

Solution,  Bain's  Printing The 

solution  used  in  Bain's  chemical  telegraph. 

Bain's  solution  is  made  by  mixing  together  one 
part  of  a  saturated  solution  of  potassium  ferro- 
cyanide,  with  two  parts  of  water. 

Solution,  Battery The  exciting 

liquid  for  voltaic  cells.  (See  Cell,  Voltaic.) 

Solution,  Chemical,  Bain's—  — A  solu- 
tion employed  in  connection  with  Bain's  re- 
cording telegraph.  (See  Recorder,  Chemical, 
JBain's) 

Solution,  Qnicking A  solution  of 

a  salt  of  mercury,  in  which  objects  to  be  elec- 
tro-plated are  dipped  after  cleansing,  just 
before  being  placed  in  the  plating  bath. 

If  the  articles  have  been  properly  cleansed,  im- 
mersion in  the  quicking  solution  will  cover  them 
with  a  uniform,  silver-like  coating,  which  will  in- 
sure an  adherent,  uniform  coating  in  the  plating 
bath. 

Solution,  Saturated A  solution  in 

which  as  much  of  the  solid  or  other  substance 
has  been  dissolved  in  the  liquid  as  it  will  take 
at  a  given  temperature. 

Solution,  Super-Saturation  of 

The  condition  assumed  by  a  warmed  satu- 
rated solution  of  a  salt,  when  placed  in  a 
closed  vessel  out  of  contact  with  the  air,  and 
allowed  to  cool  without  being  shaken. 

Un^er  the  above  circumstances  the  solution 
may  be  cooled  without  depositing  any  crystals. 


Such  a  solution  is  said  to  be  super-saturated.  It 
will  immediately  deposit  crystals  if  a  crystal  of  the 
salt  dissolved  or  a  crystal  of  an.  isomorphous  salt 
be  dropped  in  the  solution,  or  often  if  merely 
shaken. 

It  is  important  in  standard  voltaic  cells  in 
which  zinc  sulphate  is  used,  that  the  solution  be 
saturated  but  not  super-saturated. 

Sonometer,  Hughes' An  apparatus 

for  determining  the  amount  of  inductive  dis- 
turbance in  an  induction  balance,  by  compar- 
ing the  sounds  heard  in  a  telephone,  as 
a  result  of  such  induction,  with  the  sounds 
heard  in  the  same  telephone  under  circum- 
stances in  which  the  amount  of  disturbance 
is  directly  measurable. 

An  apparatus  devised  by  Professor  Hughes  to 
be  used  in  connection  with  the  induction  balance, 
in  order  to  measure  the  amount  of  disturbance  of 
balance  produced  therein  in  any  particular  case. 

Sonorescence. — A  term  proposed  for  the 
sounds  produced  when  a  piece  of  vulcanite  or 
any  other  solid  substance  is  exposed  to  a 
rapid  succession  of  flashes  of  light.  (See 
Photophone) 

Sound. — The  sensation  produced  on  the 
brain,  through  the  ear,  by  the  vibrations  of  a 
sonorous  body. 

The  sound  waves  that  are  capable  of  pro- 
ducing the  sensation  of  sound  on  the  brain 
through  the  ear. 

The  word  sound  is  therefore  used  in  science  in 
two  distinct  senses,  viz. : 

(i.)  Subjectively,  as  the  sensation  produced  by 
the  vibrations  of  a  sonorous  body. 

(2.)  Objectively,  as  the  waves  or  vibrations  that 
are  capable  of  producing  the  sensation  of  sound. 

Sound  is  transmitted  from  the  vibrating  body 
to  the  ear  of  the  hearer  by  means  of  alternate  to- 
and-fro  motions  in  the  air,  occurring  in  every 
direction  around  the  vibrating  body  and  forming 
spherical  waves  called  waves  of  condensation  and 
rarefaction.  Unlike  light  and  heat,  these  waves 
require  a  tangible  medium  such  as  air  to  trans- 
mit them. 

Sound,  therefore,  is  not  propagated  in  a. 
vacuum.  The  vibrations  of  sound  are  longi- 
tudinal, that  is,  the  to-and-fro  motions  occur  in 
the  same  direction  as  that  in  which  the  sound  is 
traveling.  The  vibrations  of  light  are  transverse, 


Sou.] 


482 


[Son. 


that  is,  the  to-and-fro  motions  are  at  right  angles 
to  the  direction  in  which  the  light  is  traveling. 

Sound. — (Objectively.)  The  waves  in  the 
air  or  other  medium  which  produce  the  sen- 
sation of  sound. 

Sound.— (Subjectively.)  The  effect  pro- 
duced on  the  ear  by  a  vibrating  body. 

Sound,  Absorption  of Acoustic  ab- 
sorption.    (See  Absorption,  Acoustic?) 
Sound,    Characteristics    of The 

peculiarities  that  enable  different  musical 
sounds  to  be  distinguished  from  one  another. 

The  characteristics  of  musical  sounds  are: 

(l.)  The  Tone  or  Pitch,  according  to  which  a 
sound  is  either  grave  or  shrill. 

(2.)  The  Intensity  or  Loudness,  according  to 
which  a  sound  is  either  loud  or  feeble. 

(3.)  The  Quality  or  Timbre,  the  peculiarity 
which  enables  us  to  distinguish  between  two 
sounds  of  the  same  pitch  and  intensity,  but 
sounded  on  different  instruments,  as  for  example, 
on  a  flute  and  on  a  piano. 

Sound,  Quality  or  Timbre  of That 

peculiarity  of  a  musical  note  which  enables 
us  to  distinguish  it  from  another  musical  note 
of  the  same  tone  or  pitch,  and  of  the  same 
intensity  or  loudness,  but  sounded  on  another 
instrument. 

The  middle  C,  for  example,  of  a  pianoforte,  is 
readily  distinguishable  from  the  same  note  on  a 
flute,  or  on  a  violin ;  that  is  to  say,  its  quality  is 
different.  The  differences  in  the  quality  of  musi- 
cal sounds  are  caused  by  the  admixture  of  addi- 
tional sounds  called  overtones  which  are  always 
associated  with  any  musical  sound. 

Briefly,  nearly  all  so-called  simple  musical 
sounds  are  in  reality  chords  or  assemblages  of  a 
number  of  different  musical  sounds. 

In  the  case  of  the  many  different  notes  that  are 
present  in  an  apparently  simple  note  or  tone,  one 
of  the  notes  is  far  louder  than  all  the  others  and  is 
called  the  fundamental  tone  or  note,  and  is  what 
is  recognized  by  the  ear  as  the  note  proper.  The 
others  are  called  the  overtones.  The  overtones 
are  too  feeble  to  be  heard  very  distinctly,  but 
their  presence  gives  to  the  fundamental  note  its 
own  peculiar  quality.  In  the  case  of  a  note 
sounded  on  the  flute,  these  overtones  are  dif- 
ferent either  in  number  or  in  their  relative  intensi- 
ties from  the  same  note  sounded  on  another  instru- 


ment Their  fundamental  tones,  however,  are 
the  same. 

The  peculiarities  which  enable  us  to  distinguish 
the  voice  of  one  speaker  or  singer  from  another 
are  due  to  the  presence  of  these  overtones.  The 
overtones  must  be  correctly  reproduced  by  the 
diaphragm  of  the  telephone,  or  phonograph, 
graphophone,  or  gramophone,  if  the  articulate 
speech  is  to  be  correctly  reproduced  wit'n  all  its 
characteristic  peculiarities. 

Sounder,  Morse  Telegraphic An 

electro-magnet  which  produces  audible 
sounds  by  the  movements  of  a  lever  attached 
to  the  armature  of  the  magnet. 

The  Morse  sounder  has  new  almost  entirely 
supplanted  the  paper  recorder  or  register.  On 
short  lines  it  is  placed  directly  in  the  telegraphic 
circuit.  On  long  lines  it  is  operated  by  a  local 
battery,  thrown  into  or  out  of  the  action  by  the 
relay.  (See  Relay.} 


Pig.  fro.    Morse  Sounder. 

The  Morse  sounder,  shown  in  Kg.  510,  con- 
sists of  an  upright  electro-magnet  M,  whose  soft 
iron  armature  A,  is  rigidly  attached  to  the  striking 
lever  B,  working  in  adjustable  screw  pivots  as 
shown.  The  free  end  of  the  lever  is  limited  in  its 
strokes  by  two  set  screws  N,  N.  The  lower  of 
these  screws  is  set  so  as  to  limit  the  approach  of 
the  armature  A,  to  the  poles  of  the  electro-magnet; 
the  upper  screw  is  set  so  as  to  give  the  end  B, 
sufficient  play  to  produce  a  loud  sound.  A  re- 
tractile spring,  attached  to  the  striking  lever  near 
its  pivoted  end,  and  provided  with  regulating 
screw  S  S,  pulls  the  lever  back  when  the  current 
ceases  to  flow  through  M. 

The  dots  and  dashes  of  the  Morse  alphabet  are 
reproduced  by  the  sounder,  as  audible  signals, 
that  are  distinguished  by  the  operator  by  means 
of  the  different  sounds  produced  by  the  up  and 
down  stroke  of  the  lever  as  well  as  by  the  differ 


Sou.] 


483 


[Sou. 


ence  in  the  intervals  of  time  between  the  succes- 
sive signals. 

Another  form  of  telegraphic  sounder,  similar 
in  its  general  construction  to  that  already  de- 
scribed, is  shown  in  Fig.  511. 


Fig.  311.    Telegraphic  Soun 

Sounder,  Repeating- A  telegraphic 

sounder  which  repeats  the  telegraphic  dis- 
patch into  another  circuit. 

Sounds,     Magnetic Faint     clicks 

heard  on  the  magnetization  of  a  readily  mag- 
netizable substance. 

One  of  the  earlier  forms  of  Reis'  telephone, 
operated  by  means  of  a  rapid  succession  of  these 
faint  magnetic  sounds. 

Source,  Electric Any  arrangement 

capable  of  maintaining  a  difference  of  poten- 
tial or  an  electromotive  force. 

The  following  are  the  more  important  electric 
sources,  arranged  according  to  the  character  of 
the  energy  which  is  converted  into  electric 
energy. 

ELECTRIC  SOURCES. 

1.  Voltaic  Cell  or  Primary 

Battery. 

2.  Charged  Storage  Cell  or 

Secondary  Battery. 

3.  Thermo  Cell  or  Thermo 

Battery. 

4.  Selenium  Cell   or   Sele- 

nium Battery. 

5.  Magneto  -  Electric    Ma- 

chine. 

6.  Dynamo-Electric       Ma- 

chine. 

7.  Frictional    Electric    Ma- 

chine. 

8.  Electrostatic      Induction 

Machine. 

9.  Magneto -Electric     Tele- 

phone Transmitter. 


Chemical  Poten- 
tial Energy. 


Radiant  Energy. 


Mechanical 
Energy. 


10.  Pyromagnetic  Generator. 

11.  Animal  or  Plant Vital  Energy. 


Heat  and  Mechan- 
ical Energy. 


Sources,  Multiple-Arc-Connected 

A  term  sometimes  applied  to  sources  connect- 
ed in  multiple.  (See  Sources,  Multiple-Con- 
nected) 

Sources,  Multiple-Connected The 

connection  of  a  number  of  separate  sources 
so  as  to  form  a  single  source  by  joining  the 
positive  poles  of  all  the  separate  sources  to  a 
single  positive  lead  or  conductor,  and  all  the 
negative  poles  to  a  single  negative  lead  or 
conductor. 

The  multiple  connection  of  sources  results  in 
each  of  the  sources  discharging  its  current  into 
the  main  conductor  in  a  direction  parallel  to 
that  of  the  other  sources. 

The  electromotive  force  in  the  same  is  that  of 
any  single  source,  but  the  resistance  of  the  com- 
bined source  decreases  with  each  source  added. 
Supposing  the  resistance  of  each  source  be  the 
same,  then  if  ten  such  sources  are  connected  in 
multiple-arc,  the  resistance  of  the  combined  source 
is  but  one-tenth  the  resistance  of  a  single  source. 
(See  Circuit,  Multiple.) 

Sources  are  combined  in  multiple-arc  whenever 
the  current  furnished  by  the  separate  sources  is 
insufficient  to  properly  operate  the  electro-recep- 
tive or  translating  device  with  which  it  is  con- 
nected. 

Sources,  Multiple-Series-Connected 

— The  conection  of  a  number  of  separate 
sources  so  as  to  form  a  single  source  by  con- 
necting a  number  of  the  sources  in  groups 
in  series,  and  joining  these  groups  together 
in  multiple-arc. 

The  battery  of  sources  obtained  by  connecting 
a  number  of  separate  sources  in  multiple-series 
will  have  an  electromotive  force  equal  to  the 
sum  of  the  separate  electromotive  forces  of  the 
sources  connected  in  any  of  the  separate  series- 
connected  groups. 

The  current  produced  will  be  greater  in  propor- 
tion to  the  number  of  separate  groups  in  parallel. 
The  internal  resistance  will  be  increased  in  pro- 
portion  to  the  number  of  coils  in  series,  and  de- 
creased in  proportion  to  the  number  of  groups  in 
multiple-arc  or  parallel. 

Sources  are  connected  in  multiple-series  when 
both  the  electromotive  force  and  the  current  of 
any  single  source  are  insufficient  to  operate  the 
electro-receptive  or  translating  device.  (See 
Circuit,  Multiple- Series.) 


Sou.] 


484 


[Spa. 


Sources,  Parallel  •  Connected A 

term  sometimes  applied  to  multiple-connected 
sources.  (See  Sources,  Multiple-Connected?) 

Sources,  Series-Connected The 

connection  of  a  number  of  separate  electric 
sources  so  as  to  form  a  single  source,  in 
which  the  separate  sources  are  placed  in  a 
single  line  or  circuit  by  so  connecting  their  op- 
posite poles  that  the  current  produced  in  each 
passes  successively  through  each  of  the 
sources. 

The  series-connection  of  sources  results  in  an 
electromotive  force  equal  to  the  sum  of  the  sepa- 
rate electromotive  forces  produced  by  each 
source— that  is,  a  rise  of  potential  occurs  with  each 
source  added.  This  connection  increases  the  re- 
sistance of  the  circuit  by  the  amount  of  the  resist- 
ance of  each  source  introduced  into  the  circuit. 
The  value  of  the  resulting  current  depends  on  the 
total  electromotive  force  and  resistance  of  the 
series-connected  sources. 

Sources  are  connected  in  series  when  the 
electromotive  force  furnished  by  a  single  source 
is  insufficient  for  the  character  of  work  required 
to  be  done.  (See  Circuit ',  Series.) 

Sources,  Series-Mnltiple-Connected 

— The  connection  of  a  number  of  separate 
electric  sources,  so  as  to  form  a  single  source, 
in  which  the  separate  sources  are  connected 
in  a  number  of  separate  multiple  groups  or 
circuits,  and  these  groups  or  circuits  separ- 
ately connected  together  in  series.  (See  Cir- 
cuit, Series-Multiple?} 

Southern  Light. — A  name  sometimes  given 
to  the  Aurora  Australis.  (See  Aurora  Aus- 
iralis.) 

Space,  Clearance The  space  be- 
tween the  revolving  armature  of  a  dynamo- 
electric  machine,  or  electric  motor,  and  the 
polar  faces  of  the  pole  pieces. 

Space,  Dark,  Crookes'  -  —A  dark 
space  surrounding  the  negative  electrode  in  a 
rarefied  space  through  which  electric  dis- 
charges are  passing. 

Crookes'  dark  space  .lies  immediately  between 
the  negative  electrode  and  its  glow  or  luminous 
discharge.  It  differs,  therefore,  from  Faraday's 
dark  space,  which  lies  between  the  luminous  dis- 
charges of  the  negative  and  positive  electrodes. 


The  radius  of  Crookes'  dark  space  increases 
with  the  degree  of  exhaustion.  It  varies  also 
with  the  character  of  the  residual  gas,  with  the 
temperature  of  the  negative  electrode,  and  some- 
what with  the  intensity  of  the  spark.  When  the 
vacuum  becomes  sufficiently  high,  the  dark  space 
fills  the  entire  tube  through  which  the  discharges 
are  passing. 

Crookes  has  found  that  in  the  case  of  substances 
that  become  phosphorescent  under  the  electric 
discharge,  phosphorescence  best  takes  place  whem 
the  body  is  placed  on  the  boundary  of  the  dark 
space. 

Space,  Dark,  Faraday's The  gap 

in  the  continuity  of  the  luminous  discharges 
that  occurs  between  the  glow  of  the  positive 
and  negative  electrodes. 

Faraday's  dark  space  is  seen  in  a  partially  ex- 
hausted tube  through  which  the  discharges  of 
an  induction  coil  are  passing.  It  occurs  in  as 
low  a  vacuum  as  6  millimetres  of  mercury. 
As  the  vacuum  becomes  higher,  the  length  of  tke 
dark  space  increases. 

Space,  Inter-Air A  term  some- 
times employed  for  the  air  space  between  the 
outer  surface  of  the  revolving  armature  of  a 
dynamo-electric  machine  and  the  adjacent 
faces  of  the  pole  pieces.  (See  Space,  Clear- 
ance?) 

Space,  Interferric A  term  some- 
times used  for  air  gap.  (See  Gap,  Air.) 

Span  Wire.— (See  Wire  Span.) 

Spark  Coil.— (See  Coil.  Spark) 

Spark  Gap.— (See  Gap,  Spark) 

Spark.  Length  of The  length  of 

spark  that  passes  between  two  charged  con- 
ductors depends  : 

(I.)  On  the  difference  of  potential  between 
them. 

(2.)  On  the  character  of  the  gaseous  medium 
that  separates  the  two  conductors. 

(3.)  On  the  density  or  pressure  of  the  gaseous 
medium  between  the  conductors. 

Up  to  a  certain  pressure,  a  decrease  in  the 
density  causes  an  increase  in  the  length  of  the 
distance  the  spark  will  pass.  When  this  limit  is 
reached,  a  further  decrease  of  density  decreases 
the  length  of  spark.  A  high  vacuum  prevents 
the  passage  of  a  spark  even  under  great  differ- 
ence* of  potential. 


Spa.] 


485 


[Spa. 


(4.)  On  the  kind  of  material  that  forms  the 
electrodes  between  which  the  charges  pass. 

(5.)  On  the  shape  of  the  charged  conductor. 

(6. )  On  the  direction  of  the  current. 

Sparks  from  the  prime  conductor  are  denser 
and  more  powerful  than  those  from  the  negative 
conductor. 

It  will  be  observed  that  the  length  of  the  spark 
practically  depends  mainly  on  two  circumstances, 
Tiz.,  on  the  differences  of  potential  of  the  oppo- 
site charges,  and  the  conducting  power  of  the 
medium  that  separates  the  two  bodies. 

Spark,  T-Shaped A  variety  of 

three-branched  spark  obtained  by  the  dis- 
charge of  a  Leyden  jar  through  a  peculiar 
form  of  induction  coil.  (See  Spark,  Three- 
Branched^ 

Spark,  Three-Branched A  pecu- 
liar form  of  branched  spark  obtained  by  the 
discharge  of  a  Leyden  jar  through  a  peculiar 
form  of  induction  coil. 

The  three- branched  spark  was  obtained  by 
Elihu  Thomson  by  the  use  of  the  following  appa- 
ratus: The  discharges  of  a  Leyden  jar,  charged  by 
a  Topler-Holtz  machine,  were  sent  through  an  in- 
duction coil,  the  primary  and  secondary  of  which 


fig.  J 1 2.    Apparatus  for  Three-Branched  Sparks. 
•were  of  few  turns.    The  circuit  connections  were 
as  shown  in  Figs.  512  and  513,  and  the  apparatus 
is  described  by  Thomson  as  follows: 

"A  double  coil  was  made,  Fig.  512,  in  which 
the  inner  turns  were  about  twelve  and  the  outer 
turns  twenty.  These  were  kept  separate  from  each 
other  and  a  branch  wire  taken  from  the  line  and 
slid  from  point  to  point  on  the  outer  wire  enabled 
the  effective  length  'of  the  same  to  be  adjusted. 
The  inner  coil  was  connected  through  a  small 
spark  gap,  as  at  A,  to  the  outer  coating  of  a  Ley- 
den jar,  while  the  wire  L,  was  brought  near  the 
pote  of  the  jar,  which  was  continually  being 


charged  from  a  TOpler-Holtz  machine.  The 
discharge,  in  passing  from  the  knob  of  the  jar  to 
the  wire  L,  representing  the  line,  passed  by  the 


OiO 


Fig- 3  z 3.  Apparatus f  or  T  and  Y  Shaped  Stark*. 
inner  coil.  When  a  certain  length  of  the  outer 
coil  was  employed,  only  a  very  short,  almost  im- 
perceptible spark  was  obtainable  at  a.  If  the 
balance  of  the  turns  were  disturbed  by  including 
more  or  less  than  the  proper  number  of  the  outer 
turns,  not  only  did  a  vigorous  spark  occur,  but 
the  gap  at  a,  could  be  quite  considerably  extended, 
in  accordance  with  the  amount  of  departure  taken 
from  the  proper  number  of  turns  required  to  pro- 
duce the  balance.  This  ex- 
periment indicates  that  it  is 
possible  to  make  a  selective 
path  for  the  Leyden  jar  dis- 
charge, and  to  have  a  struc- 
ture so  proportioned  that 
the  discharges  reaching  line 
will  pass  to  earth  without  FiS-  Si4.  Thrt*- 
tending  to  go  through  the  cir-  Branched  Sparks 
cuit  of  the  dynamo.  1'he  action  is  apparently 
due  to  a  balance  of  electromotive  forces  such 
that  the  discharge  which  tends  to  pass  from  the 
line  in  going  to  earth  induces  in  the  coil  con- 
nected to  the  dynamo  a  counter  electromotive 
force  which  nearly  wipes  out  the  potential  of  the 
discharge  before  it  reaches  the  dynamo.  This 
balance  of  inductive  effects  is  certainly  very  strik- 
ing, and  once  obtained,  it  is  disturbed,  as,  in  the 
experiments,  by  changing  the  relative  lengths  o| 
the  coils  in  inductive  relation  through  so  small 
an  amount  as  an  inch  or  two. 

"  It  may  be  mentioned  here  that  some  curious 


Spa.] 


486 


[Spe. 


effects  of  spark  were  obtained  in  these  experi- 
ments. When  a  disturbance  of  the  balance  ex- 
ists and  a  spark  is  obtained  at  a,  the  character  of 
the  spark  is  different  from  that  of  the  Leyden  jar 
discharge.  It  appears  to  be  less  luminous,  the 
noise  less  sharp,  and  its  color  would  indicate  a 
greater  power  of  volatilizing  metal  and  perhaps  a 
greater  duration.  It  is  in  part,  no  doubt,  due  to 
a  current  local  to  the  coils  in  series  with  one  an- 
other. 

' :  Another  curious  effect  was  the  production  of 
T-shaped  and  Y"snaPe(i  sparks,  or  three- 
branched  sparks  (such  as  are  shown  in  Figs.  513 
and  514.)" 

"  These  were  obtained  by  separating  the  elec- 
trodes at  A,  an  inch  and  a  half  or  thereabouts, 
and  bringing  the  third  electrode  from  the  outer 
coil  to  the  position  shown  in  Fig.  513.  The  dis- 
charges were  now  obtained  as  before  from  the 
charged  jar.  In  this  case  the  discharge  appears 
to  split  and  unite  in  air,  producing  the  curious 
shaped  sparks  shown.  It  would  seem  that  to  ob- 
tain these  effects — particularly  the  sparks  which 
were  three- branched  from  a  common  point  in  the 
centre  between  the  discharge  electrodes— the 
dielectric  air  must  break  down  simultaneously  be- 
tween the  three  electrodes.  It  would  easily  ex- 
plain the  "["-shapes  to  assume  the  straight  part 
above  to  form  first,  and  the  cross  or  transverse 
spark  to  strike  from  the  side  of  this  spark  to  the 
third  electrode." 

Spark  Tube.— (See  Tube,  Spark.} 

Spark,  Wipe In  an  electric  gas- 
lighting  pendant  burner,  a  spark  obtained 
from  a  spark  coil  by  the  wiping  contact  of  a 
spring,  moved  by  the  pulling  of  the  pendant. 
(See  Burner,  Ratchet-Pendant,  Electric?) 

Spark,  Y-Shaped A  variety  of  three- 
branched  spark  obtained  by  the  discharge  of 
a  Leyden  jar  through  a  peculiar  form  of  induc- 
tion coil.  (See  Spark,  Three-Branched) 

Sparking  Discharge.— (See  Discharge, 
Disruptive?) 

Sparking  Distance.— (See  Distance, 
Sparking?) 

Sparking,  Line  of  Least The  line 

on  a  commutator  cylinder  of  a  dynamo  con- 
necting the  points  of  contact  of  the  collecting 
brushes  where  the  sparking  is  a  minimum. 

In  some  forms  of  dynamos  the  line  of  least 


sparking  lies  parallel  to  the  lines  of  magnetic 
force  of  the  field. 

In  most  forms,  however,  it  is  at  right  angles  to 
such  lines.  The  exact  position  of  all  these  lines 
is  changed  by  the  angular  lead  of  the  brushes. 
(See  Lead,  Angle  of.) 

Sparking  of  Dynamo-Electric  Machine.— 

(See  Machine,  Dynamo-Electric,  Sparking 
of.) 

Spar  Torpedo.— (See  Torpedo,  Spar.) 

Spasmodic  Governor. — (See  Governor, 
Spasmodic.) 

Speaking-Tube  Annunciator.— (See  An- 
nunciator, Oral  or  Speaking-  Tube?) 

Speaking-Tube  Mouth   Piece,    Electric 

Alarm A  mouth  piece  for  a  speaking 

tube,  so  arranged,  that  the  movement  of  a 
pivoted  plate  covering  the  mouth  piece  au- 
tomatically rings  a  bell  at  the  other  end  of 
the  tube. 

Specific  Conduction  Resistance.— (See 
Resistance,  Specific  Conduction?) 

Specific  Conductivity. (See  Conduc- 
tivity, Specific?) 

Specific  Heat— (See  Heat,  Specific?) 

Specific  Heat  of  Electricity.— (See  Elec- 
tricity, Specific  Heat  of.) 

Specific  Hysteresial  Dissipation.— (See 
Dissipation,  Specific  Hysteresial.) 

Specific  Inductive  Capacity.— (See  Ca- 
pacity, Specific  Inductive.) 

Specific  Magnetic  Capacity.— (See  Ca- 
pacity, Specific  Magnetic.) 

Specific  Magnetic  Conductivity.— (See 
Conductivity,  Specific  Magnetic.) 

Specific  Magnetic  Inductivity.— (See  In- 
ductivity,  Specific  Magnetic?) 

Specific  Resistance.— (See  Resistance, 
Specific?) 

Specific  Resistance  of  Liquids.— (See 
Resistance,  Specific,  of  Liquids?) 

Speech,  Articulate The  successive 

tones  of  the  human  voice  that  are  necessary 
to  produce  intelligible  words. 

The  phrase  articulate  speech  refers  to  the  join- 
ing or  articulation  of  the  successive  sounds  in- 
volved in  speech.  The  receiving  diaphragm  of  a 


Spe.] 

telephone  is  caused  to  reproduce  the  articulate 
speech  uttered  near  the  transmitting  diaphragm. 

Speed,  Critical,  of  Compound-Wound 
Dynamo  —  —The  speed  at  which  both  the 
series  and  shunt  coils  of  the  machine  give  the 
same  difference  of  potential  when  the  full  load 
is  on  the  machine,  as  the  shunt  coil  would  if 
used  alone  on  open-circuit. 

Speed  Indicator.— (See  Indicator,  Speed?) 

Speeding.— Varying  the  number  of  revolu- 
tions per  minute. 

The  speeding  of  a  dynamo  is  for  the  purpose 
of  obtaining  the  current  requisite  to  properly 
operate  the  electro -receptive  device  placed  in  its 
circuit. 

Spent  Acid.— (See  Acid,  Spent?} 

Spent  Liquor. — (See  Liquor,  Spent.) 

Spherical  Armature. — (See  Armature, 
Spherical.) 

Sphygmogram. — A  record  made  by  a 
sphygmograph.  (See  Sphygmograph?) 

Sphygmograph. — An  instrument  for  re- 
cording the  peculiarities  of  the  normal  or 
abnormal  pulse. 

Sphygmograph,  Electrical An  in- 
strument for  electrically  recording  the  peculi- 
arities of  the  pulse. 

Sphygmophone.— An  apparatus  in  which 
a  microphone  is  employed  for  the  medical 
examination  of  the  pulse.  (See  Microphone?) 

Spider,  Armature A  light  frame- 
work or  skeleton  consisting  of  a  central  sleeve 
or  hub  keyed  to  the  armature  shaft,  and  pro- 
vided with  a  number  of  radial  spokes  or  arms 
for  fixing  or  holding  the  armature  •  core  to 
the  dynamo-electric  machine. 

Spider,    Driving Radial   arms  or 

spokes  connected  to  the  armature  of  a  dynamo- 
electric  machine  and  keyed  to  the  shaft  so  as 
to  act  as  a  driving  wheel  for  the  armature. 

Spin,  Magnetic A  term  sometimes 

employed  instead  of  magnetic  field. 

The  term  magnetic  spin  is  sometimes  used  in- 
stead  of  magnetic  field  because  the  magnetism  is 
now  generally  believed  to  be  due  to  the  effects  of 
a  rotary  motion  or  spin  in  the  surrounding  uni- 
versal ether. 


487 


[Spo. 


Spiral,  Primary The  primary  of  an 

induction  coil  or  transformer.     (See  Trans- 
former.   Coil,  Induction?) 

Spiral,  Roget's  —  —A  suspended  wire 
spiral  conveying  a  strong  electric  current  and 
devised  to  show  the  attractions  produced  by 
parallel  currents  flowing  in  the  same  direc- 
tion. 

The  lower  end  of  the  wire  spiral  dips  into  a 
mercury  cup.  On  the  passage  of  the  current,  the 
attraction  of  the  neighboring  turns  of  the  spiral 
for  each  other  shortens  the  length  of  the  spiral 
sufficiently  to  draw  it  out  of  the  mercury  and  thus 
break  the  circuit.  When  this  occurs  the  weight 
of  the  spiral  causes  it  to  fall  and  again  re-estab- 
lish the  circuit.  A  rapid  automatic-make-and- 
break  is  thus  established,  accompanied  by  a  brill- 
iant spark  at  the  mercury  surface  due  to  the  ex. 
tra  spark  on  breaking. 

Spiral,  Secondary The  secondary 

coil  of  an  induction  coil  or  transformer.     (See 
Transformer.    Coil,  Induction?) 

Splice  Box.— (See  Box,  Splice?] 
Split  Battery.— (See  Battery,  Split.) 
Split  Lead  Tee.— (See  Tee,  Split  Lead.) 
Spluttering  of  Arc.— (See  Arc,  Splutter- 
ing of.) 

Spots,  Sun Dark  spots,  varying  in 

number  and  position,  which  appear  on  the 
face  of  the  sun  and  are  believed  by  some  to  be 
caused  by  huge  vortex  motions  in  the  masses 
of  glowing  gas  that  surround  the  sun's  body. 
Sun  spots  occur  in  greater  number  at  intervals 
of  about  every  eleven  years. 

Their  occurrence  is  generally  attended  with 
unusual  terrestrial  magnetic  variations.  (See 
Storm,  Magnetic.) 

In  the  opinion  of  most  astronomers  the  sun 
spots  mark  depressions  in  the  atmosphere  of  the 
sun.  Their  exact  causes  are  unknown,  though 
they  appear  to  be  dependent  on  a  local  cooling 
or  condensation  of  the  sun's  atmosphere. 

When  observed  through  a  telescope  the  sun 
spot  appears  as  a  dark  region  surrounded  by  a 
less  dark  region.  Though  darker  by  contrast 
with  tht  rest  of  the  sun's  face,  yet  such  spots  are 
in  reality  much  brighter  than  the  most  brilliant 
arc  light.  The  outline  of  the  sun  spot  is  quite 
irregular. 


Spr.] 

Spreading-Ont  Magnetic  Field.— (See 
Field,  Magnetic,  Spreading-Out) 

Sprengel  Mercury  Pump.— (See  Pump, 
Air,  SprengeFs  Mercurial?) 

Spring  Ammeter.  —  (See  Ammeter, 
Spring) 

Spring  Contact.— (See  Contact,  Spring) 

Spring,  Hold-Off A  spring  which 

acts  to  keep  one  thing  away  from  another  in 
opposition  to  some  force  tending  to  keep  it  in 
•  contact  with  such  a  thing. 

Spring,  Hold-On A  spring  which 

acts  to  keep  one  thing  against  another  in  op- 
position to  some  force  tending  to  pull  it 
away. 

A  hold-on  spring  is  sometimes  employed  in  a 
dynamo-electric  machine  for  the  purpose  of  keep- 
ing the  collecting  brushes  in  proper  pressure 
against  the  segments  of  the  commutator. 

Spring-Jack. — A  device  for  readily  insert- 
ing a  loop  in  a  main  electric  circuit.  The 
spring-jack  is  generally  used  in  connection 
with  a  multiple  switch  board.  (See  Board, 
Multiple  Switch) 

Spring-Jack  Cut-Out— (See  Cut-Out, 
Spring-Jack) 

Spnrious  Hall  Effect— (See  Effect,  Hall, 
Spurious) 

Spurious  Resistance.— (See  Resistance, 
Spurious) 

Stabile  Galvanization.— (See  Galvaniza- 
tion, Stabile) 

Staggering. — A  term  sometimes  applied  to 
the  position  of  the  brushes  on  a  commutator 
cylinder,  in  which  one  brush  is  placed  slightly 
in  advance  of  the  other  brush  so  as  to  bridge 
over  a  break. 

When  a  break  occurs  in  the  circuit  ot  the  arma- 
ture wires,  the  device  of  staggering  the  brushes  is 
adopted  for  temporarily  bridging  over  the  break. 
When  a  break  occurs,  the  rewinding  of  the  arma- 
ture is  the  only  radical  cure. 

Standard  Candle.— (See  Candle,  Stand- 
ard) 


488 


[Sta. 


Standard  Carcel  Gas  Jet.— (See  Jet,  Gas, 
Carcel  Standard) 

Standard,  Dynamo The  supports 

for  the  bearings  of  a  dynamo-electric  ma- 
chine. 

Standard  Earth  Quadrant.— (See  Quad- 
rant, Standard) 

Standard  of   Self-induction,  Ayrton  & 

Perry's (See  Induction,  Self,  Ayrton 

6-  Perry's  Standard  of) 

Standard  Ohm.— (See  Ohm,  Standard) 

Standard,  Pentane A  standard 

source  of  light  used  in  photometric  measure- 
ments, in  place  of  a  Methven  screen. 

The  pentane  standard  is  constructed  in  general 
in  the  same  manner  as  the  Methven  standard. 
In  place,  however,  of  ordinary  coal  gas,  a  mixture 
of  pentane  and  air  is  used.  Pentane  is  a  variety 
of  coal  oil  left  after  several  distillations  of  ordinary 
crude  oil.  It  distills  at  a  temperature  not  greater 
than  50  degrees  centigrade. 

The  mixture  for  burning  consists  of  about 
twenty  volumes  of  air  to  seven  volumes  of  pen- 
tane. A  burner  of  the  pentane  standard  is  some- 
what similar  to  the  Methven  standard,  but  differs 
in  a  number  of  minor  details. 

Standard  Resistance  CoiL— (See  Coil, 
Resistance,  Standard) 

Standard  Size  of  Electrodes,  Erb's 

—(See  Electrodes,  Erb's  Standard  Size  of) 

Standard  Voltaic  CelL— (See  Cell.  Voltaic, 
Standard) 
Standard  Voltaic  Cell,  Clark's 

(See  Cell,  Voltaic,  Standard,  Clark's) 

Standard  Voltaic  Cell,  Clark's,  Rayleigh's 
Form  of (See  Cell,  Voltaic,  Stand- 
ard, Rayleigh's  Form  of  Clark's) 

Standard  Voltaic  Cell,  Fleming's 

(See  Cell,  Voltaic,  Standard,  Fleming's) 

Standard  Voltaic  Cell,  Lodge's 

(See  Cell,  Voltaic,  Standard,  Lodge's) 

Standard  Voltaic  Cell,  Sir  William 
Thomson's (See  Cell,  Voltaic,  Stand- 
ard, Sir  William  Thomson's) 

Standard  Wire  Gauge.— (See  Gauge, 
Wire,  Standard) 


Sta.] 


489 


[Sta. 


Standardizing  a  Toltaic  Cell.— (See  Cell, 
Voltaic,  Standardizing  a.) 

Standards,  Motor  —  —A  name  applied 
to  the  supports  for  the  bearings  of  an  electric 
motor. 

State,  Allotropic A  modification 

of  a  substance,  in  which,  without  changing 
its  chemical  composition,  it  assumes  a  condi- 
tion in  which  many  of  its  physical  and  chem- 
ical properties  are  different  from  those  it  or- 
dinarily possesses. 

Thus  the  element  carbon  occurs  in  three  widely 
different  allotropic  states,  viz.: 

(I.)  As  charcoal,  or  ordinary  carbon; 

(2.)  As  graphite,  or  plumbago;  and 

(3.)  As  the  diamond. 

State,  Anelectrotonic The  condi- 
tion of  decreased  functional  activity  which 
occurs  in  a  nerve  in  the  neighborhood  of  the 
anode  or  positive  terminal  of  a  source  to 
whose  influence  it  is  subjected.  (See  Anelec- 
trotonus^) 

State,  Electrotonic A  peculiar 

state  supposed  by  Faraday  to  exist  in  a  wire  or 
other  conductor,  whereby  differences  of  po- 
tential are  produced  by  means  of  its  move- 
ment through  a  magnetic  field. 

In  his  early  researches  Faraday  regarded  this 
State  as  a  necessary  condition  in  which  a  wire  or 
conductor  must  exist,  prior  to  its  movement 
through  a  magnetic  field,  in  orde  to  have  a  dif- 
ference of  potential  produced ;  but  at  a  later  day 
he  abandoned  this  idea,  and  explained  the  true 
causes  of  electrodynamic  induction.  (See  In- 
duct  ion,  Electro- Dynamic.) 

The  term  electrotonic  state  is  to  be  carefully  dis- 
tinguished from  electrotonus,  or  the  change  pro- 
duced in  the  functional  activity  of  a  nerve  by  an 
electric  current.  (See  Electrotonus.) 

State,  Kathelectrotonic The  con- 
dition of  increased  functional  activity  of  a 
Herve  in  the  neighborhood  of  the  kathode  or 
negative  terminal  of  a  source  to  whose  in- 
fluence it  is  subjected.  (See  Kathelectro- 
tonus.} 

The  kathelectrotonic  state  is  one  of  the  states 
or  conditions  of  electrotonus  or  altered  functional 
activity  produced  in  a  nerve  by  an  electric  cur- 
rent. (See  Electrotonus.) 


State,    Nascent A  term  used  in 

chemistry  to  express  the  s'tate  or  condition  of 
an  elementary  atom  or  radical  just  liberated 
from  chemical  combination,  when  it  possesses 
chemical  affinities  or  attractions  more  ener- 
getic than  afterwards. 

According  to  Grothiiss'  hypothesis,  during  the 
decomposition  of  a  chain  of  polarized  molecules, 
such  for  example  as  in  the  case  of  hydrogen  sul- 
phate, Hs  SO4,  in  a  zinc-copper  voltaic  cell,  the 
two  atoms  of  hydrogen  H8,  liberated  by  the  com- 
bination of  the  SO4,  with  an  atom  of  zinc,  Zn,  pos- 
sess a  stronger  affinity  for  the  SO4  of  the  molecule 
next  to  it,  than  does  its  own  H8,  and  thus  liber- 
ates  its  two  atoms  of  hydrogen,  which  in  turn 
unite  with  the  SO4,  of  the  next  molecule  in  the 
polarized  chain,  and  this  continues  until  the  two 
atoms  of  hydrogen  liberated  from  the  last  mole- 
cule in  the  chain  are  given  off  at  the  copper  plate. 
(See  Hypothesis,  Grothuss\) 

The  peculiar  properties  characteristic  of  the 
nascent  state  of  elements  is  doubtless  due  to 
the  fact  that  the  elements  are  then  in  a.  free 
state,  with  their  bonds  open  or  unsatisfied,  and 
therefore  possess  greater  affinities  than  when  they 
are  united  in  molecules.  Thus  H — ,  H — ,  or 
atomic  hydrogen,  should  possess  different  affinities 
than  H— H,  or  molecular  hydrogen. 

State,  Passive The  condition  of  a 

metallic  substance  in  which  it  may  be  placed 
in  liquids  that  would  ordinarily  chemically 
combine  with  it,  without  being  attacked  or 
corroded. 

It  is  very  doubtful  whether  metallic  bodies  can 
be  properly  regarded  as  possessing  an  actual 
passive  state.  Iron,  for  example,  which  is  one  of 
the  metals  that  is  said  to  be  capable  of  assuming 
this  so-called  passive  state,  can  be  placed  in  this 
condition  by  immersing  it  for  a  few  moments  in 
concentrated  nitric  acid,  and  subsequently  wash- 
ing it  It  will  then,  unlike  ordinary  iron,  neither 
be  attacked  by  concentrated  nitric  acid,  nor  will 
it  precipitate  copper  from  its  solutions.  This 
condition  is  now  generally  believed  to  be  due  to 
the  formation  of  a  thin  coating  of  magnetic  oxide 
on  its  surface. 

Many  of  the  instances  of  the  so-called  passive 
state  are  simply  cases  of  the  well  known  electrical 
preservation  of  metals  that  form  the  negative 
element  of  a  voltaic  combination,  under  which 
circumstances  the  positive  element  only  of  the 


Sta.J 


490 


ISte 


voltaic  couple  is  chemically  attacked  by  the  elec- 
trolyte. (See  Cell,  Voltaic.  Metals,  Electrical 
Protection  of. ) 

State,  Permanent,  of  Charge  on  Tele- 
graph Line The  condition  of  the 

charge  on  a  telegraph  wire  when  the  current 
reaching  the  distant  end  has  the  same 
strength  as  at  the  sending  end. 

State,  Tariable,  of  Charge  of  Telegraph 

Line The  condition  of  the  charge  on 

a  telegraph  wire  while  the  strength  of  the 
current  is  increasing  up  to  the  full  strength 
in  all  parts. 

The  duration  of  the  variable  state  is  directly  as 
the  length  of  the  line,  the  electrostatic  capacity 
and  the  total  resistance.  It  is  increased  by  leak- 
age, by  static  capacity  and  by  the  effects  of  the 
extra  current.  (See  Currents,  Extra.) 

Static  Breeze.— (See  Breeze,  Static.) 

Static  Electricity.  —  (See  Electricity, 
.Static) 

Static  Energy.— (See  Energy,  Static) 

Static  Hysteresis.  —  (See  Hysteresis, 
Static) 

Static  Insulation.  —  (See  Insulation, 
.Static) 

Static  Magnetic  Induction.- (See  Induc- 
tion, Magnetic,  Static) 

Static  Shock.— (See  Shock,  Static) 

Statics. — The  science  which  treats  of  the 
relations  that  must  exist  between  the  points 
of  application  of  forces  and  their  direction 
and  intensity,  in  order  that  equilibrium  may 
result. 

Statics,  Electro—  —That  branch  of 
electric  science  which  treats  of  the  phenome- 
na and  measurement  of  electric  charges. 

Some  of  the  more  important  principles  of  elec- 
trostatics are  embraced  in  the  following  laws: 

(I.)  Charges  of  like  name,  i.  f.,  either  positive 
•r  negative,  repel  each  other.  Charges  ot  unlike 
name  attract  each  other. 

(2.)  The  forces  of  attraction  or  repulsion  be 
tween  two  charged  bodies  are  directly  proper 
tional  to  the  product  of  the  quantities  of  electricity 
possessed  by  the  bodies  and  inversely  proportional 
to  the  square  of  the  distance  between  them. 


These  laws  can  be  demonstrated  by  the  use  of 
Coulomb's  torsion  balance.  (See  Balance,  Cou- 
lomb'1 s  Torsion.") 

Statics,   Magneto That  branch  of 

magnetism  which  treats  of  magnetic  attrac- 
tions and  repulsions,  the  distribution  of  lines 
of  magnetic  force  and  other  facts  regarding 
fixed  magnets. 

Station,  Central A  station,  cen- 
trally located,  from  which  electricity  for  light 
or  power  is  distributed  by  a  series  of  con- 
ductors radiating  therefrom. 

Station,  Distant A  term  applied  by 

an  operator  to  the  distant  end  of  the  line  in 
order  to  distinguish  it  from  his  own  end. 

Station,   Distributing  -       —A   station 
from  which  electricity  is  distributed. 
A  central  station. 

Station,  Home A  term  applied  by 

an  operator  to  his  end  of  the  line,  in  order  to 
distinguish  it  from  the  other  or  distant  sta- 
tion. 

Station,  Transforming -In  a  system 

of  distribution  by  transformers  or  converters 
a  station  where  a  number  of  transformers  are 
placed,  in  order  to  supply  a  group  of  houses 
in  the  neighborhood.  (See  Transformer. 
Electricity,  Distribution  of,  by  Alternating 
Currents) 

Stationary  Floor  Key.— (See  Key,  Sta- 
tionary Floor) 

Stationary  Torpedo.— (See  Torpedo,  Sta- 
tionary) 

Stay  Rods,  Telegraphic Metal  rods 

attached  to  a  telegraph  pole,  and  securely 
fastened  in  the  ground  in  order  to  counteract 
the  effects  of  a  pull  or  tension  on  the  poles. 
(See  Pole,  Telegraphic) 

Stay  rods  should  be  used  in  all  exposed  situa 
tions,  or  where  the  poles  are  exposed  to  severe 
strains. 

Steady  Current— (See  Current,  Steady.} 

Stearns'  Relay  Shunt.— (See  Shunt.  Re- 
lay, Stearns .) 

Steel,  Qualities  of.  Requisite  for  Mag- 
netization —  —  Qualities  which  must  be 


Ste.] 


491 


[Sto. 


possessed  by  steel  in  order  to  permit  it  to  per- 
manently retain  a  considerable  magnetization. 

For  the  purposes  of  permanent  magnetization 
steel  should  possess  the  following  qualities: 

It  should  be  hard  and  fine  grained.  Hard  cast 
steel  answers  the  purpose  very  well.  Scoresby 
showed  that  an  intimate  relation  exists  between 
the  quality  of  the  iron  from  which  the  steel  is 
made,  and  the  ability  of  the  steel  to  take  and  re- 
tain considerable  magnetism. 

The  steel  should  be  hardened  as  high  as  possi- 
ble and  the  temper  afterwards  drawn  by  heat  to 
a  violet-straw  color.  Practice  is  not  uniform  in 
this  respect,  the  exact  color  varying  with  the 
quality  of  the  steel. 

An  admixture  with  the  steel  of  about  -^  of  one 
per  cent  of  tungsten  is  said  to  increase  its  mag- 
netic powers. 

Cast  steel  is  not  generally  employed  for  mag- 
nets, wrought  steel  being  generally  preferred. 

Step-by-Step,  or  Dial  Telegraphy.— (See 
Telegraphy,  Step-by-Step) 

Step-Down  Transformer. — (See  Trans- 
former, Step-Down?) 

Step-Up  Transformer. — (See  Transform- 
er, Step-Up) 

Sterilization,  Electric—  —Sterilizing 
a  solution  by  depriving  it  of  whatever  germs 
it  may  contain  by  means  of  electrical  cur- 
rents. 

The  following  experiments  were  recently  made 
on  sterilization  by  means  of  electric  currents: 
The  fluid,  with  the  culture,  was  placed  in  a  glass 
test  tube,  wound  about  with  a  wire  coil  connected 
either  with  a  dynamo  or  accumulator  or  other 
electric  source.  Some  increase  in  temperature 
was  made,  but  never  over  98°  Fahr..  When  a 
Wrrent  1.25  volts,  2.5  amperes  passed,  a  com- 
plete sterilization  of  Micrococus  Prodigiosus  oc- 
curred at  the  end  of  twenty -four  hours. 

Blood  and  water  containing  pathogenic  germs 
was  sterilized  in  five  to  thirty  minutes.  The 
above  described  effects  would  appear  to  be  mag- 
netic rather  than  electric. 

Sticking. — A  word  applied  by  telegraphers 
to  the  failure  of  the  positive  pole  relay  arma- 
ture to  leave  the  magnet  pole  on  the  cessation 
of  the  current. 

In  telegraphy,  when  from  any  cause  a  circuit 
is  imperfectly  broken  by  an  operator's  key,  or  at 


the  points  of  contact  of  a  relay  or  other  instru- 
ment, such  failure  is  called  sticking.  When  an  arc 
is  formed  at  the  points  of  a  relay  where  the  local 
circuit  is  made  and  broken,  the  relay  "sticks." 
The  arc  is  caused  by  burning  of  the  platinum 
points.  Sticking  may  be  a  result  of  a  too  weak 
retractile  spring. 

Stone,  Hercules A  name  given  by 

the  ancients  to  the  lodestone.  (See  Lode- 
stoned) 

Stool,  Insulating A  stool  provided 

with  insulating  supports  of  vulcanite  or  other 
insulator,  employed  to  afford  a  ready  insulat- 
ing stand  or  support. 

Stop,  Limiting A  stop  set  so  as  to 

limit  the  motion  of  an  electrically  vibrating  or 
oscillating  bar  to  any  predetermined  extent. 

Such  limiting  stops  are  common  on  telegraphic 
and  various  other  electrical  apparatus. 

Stopping-Off. — A  process  employed  in 
electro-plating,  in  which  a  metallic  article,  al- 
ready electro-plated  over  its  entire  surface,  is 
electro-plated  with  another  metal  over  certain 
parts  only. 

The  process  of  stopping-off  consists  of  covering 
the  parts  which  are  to  receive  the  metallic  coat- 
ing, with  various  stopping-off"  varnishes.  By  this 
means  articles  can  be  electro-plated  on  parts  of 
their  surfaces  with  gold  and  on  the  remainder 
with  silver.  The  whole  surface  is  first  silvered 
and  the  portions  intended  to  be  afterwards  gilded 
are  then  stopped- off  and  the  object  placed  in  the 
gilding  bath. 

Stopping-Off  Tarnish.— (See  Varnish, 
Stopping-Off.} 

Storage  Battery.— (See  Battery,  Storage) 

Storage  Capacity  of  Secondary  Cell.— 
(See  Cell,  Secondary  or  Storage,  Capacity 
of) 

Storage  Cell.— (See  Cell,  Storage) 

Storage  of  Electricity.— (See  Electricity, 
Storage  of) 

Storm,  Auroral A  term  sometimes 

employed  to  express  an  unusual  prevalence 
of  auroras. 

Storm,  Electric An  unusual  con- 
dition of  the  atmosphere  as  regards  the  quan- 
tity of  its  free  electricity. 


Sto.J 


492 


Dttr. 


A  thunder  storm  is  a  variety  of  electric  storm. 
(See.Stor»*,  Thunder.) 

Storm,  Magnetic Irregularities  oc- 
curring in  the  distribution  of  the  earth's 
magnetism,  affecting  the  magnetic  declina- 
tion, dip,  and  intensity. 

Magnetic  storms  have  been  observed  to  accom- 
pany auroral  displays,  and  to  be  coincident  with 
the  occurrence  of  sun  spots^  or  unusual  outbursts 
of  solar  activity. 

The  coincidence  of  magnetic  storms  and  out- 
bursts of  solar  activity  is  unquestioned.  Wolf, 
of  Zurich,  has  shown  by  a  comparison  of  nu- 
merous observations  of  sun  spots,  the  unques- 
tioned correspondence,  in  the  times  of  their 
greatest  activity,  which  occur  every  n.i  years, 
with  the  time  of  occurrence  of  an  unusual  number 
of  sun  spots.  He  has  placed  these  results  in  the 
form  of  curves.  Those  shown  in  Fig.  515  are 
taken  from  observations  at  Paris  and  Prague. 
The  full  lines  represent  the  periods  of  sun  spots. 
The  dotted  lines  the  periods  of  magnetic  storms. 


Fig'  SIS-     Wolfs  Sun  Spot  Numbers. 

Storm,  Thunder A  storm  during 

which  electrical  discharges  accompanied  by 
thunder  take  place  between  two  clouds  or  be- 
tween a  cloud  and  the  earth.  (See  Elec- 
tricity. Atmospheric.  Storms,  Thunder, 
Geographical  Distribution  of.) 

Storms,  Thunder,  Geographical  Dis- 
tribution of The  following  general 

facts  as  to  the  geographical  distribution  of 
thunder  storms,  show  the  intimate  relation 
between  the  frequency  of  thunder  storms  and 
the  tune  and  place  of  the  condensation  of 
vapor. 

(I.)  Thunder  storms  seldom,  if  ever,  occur  in 
the  polar  regions. 

This  is  probably  because   the  rainfall   in  the 


polar  regions  results  from  the  condensation  of  tka 
vapor  that  was  formed  in  the  equatorial  or  tem- 
perate regions,  so  that  a  considerable  time 
elapses  between  the  evaporation  and  condensa- 
tion. 

(2.)  Thunder  storms  seldom,  if  ever,  occur  in 
rainless  districts,  owing  probably  to  the  absence 
of  the  condensation  of  vapor. 

(3.)  Thunder  storms  are  most  frequent  and 
violent  in  the  equatorial  regions,  where  the  rain- 
fall results  from  the  condensation  of  the  vapor  by 
the  action  of  ascending  currents,  conveying  the 
vapor  almost  immediately  after  its  formation  into 
the  upper  and  colder  regions  of  the  atmosphere. 

(4.)  Thunder  storms  occur  in  regions  beyond 
the  tropics,  at  those  seasons  of  the  year  when  the 
rainfall  results  from  the  condensation  of  the  vapor 
shortly  after  the  time  of  its  formation,  viz.,  in  the 
temperate  zones  in  the  hotter  parts  of  the  year. 

Straight-Line     Trolley    Hanger.— (See 

Hanger,  Straight-Line  Trolley!) 
Straightaway     Bunched     Cable.— (See 

Cable,  Bunched,  Straightaway^) 

Strain,  Dielectric The  strained 

condition  hi  which  the  glass,  or  other  dielec- 
tric of  a  condenser,  is  placed  by  the  charging 
of  the  condenser. 

The  deformation  of  a  body  under  the  in- 
fluence of  a  stress.  (See  Stress.) 

The  stress  in  this  case,  *.  *•.,  the  force  produc- 
ing the  deformation  or  strain,  is  the  attraction,  of 
the  opposite  charges.  This  stress,  in  the  case  of 
a  Leyden  jar,  is  often  sufficiently  great  to  cause 
a  rupture  of  the  glass. 

Strain,  Electro-Magnetic The  de- 
formation produced  by  an  electro-magnetic 
stress.  (See  Stress,  Electro-Magnetic^ 

Strain,  Electrostatic,  Optical—  —A 
strain  or  deformation  produced  in  a  plate  of 
glass,  or  other  transparent  solid,  by  subject- 
ing it  to  the  stress  of  an  electrostatic  field. 
(See  Stress,  Electrostatic^ 

To  obtain  the  electrostatic  stress,  holes  are 
drilled  in  the  plate  of  glass,  and  wires  from  a 
Holtz  machine  or  induction  coil  placed  therein, 
the  wires  being  separated  by  a  thin  layer  of  glass. 

The  glass,  on  being  traversed  by  a  beam  of 
plane  polarized  light,  rotates  the  plane  of  polar- 
ization of  the  light  in  the  same  direction  as  the 
glass  would  if  subjected  to  a  strain  in  the  direc- 


Str.] 


[StP. 


rttH  of  the  lines  of  electric  force.   (See  Rotation, 
Magneto-Optic.') 

Strain,  Magnetic  --  The  deformation 
produced  in  the  air-gap  between  two  dissimi- 
lar magnetic  poles,  or  in  any  substance  placed 
therein,  by  the  stress  of  the  lines  of  magnetic 
force  bridging  such  gap. 

Strain,  Optical  --  A  deformation  or 
akeration  of  volume  produced  in  a  plate  of 
glass,  or  other  transparent  medium,  by  the 
action  of  any  stress.  (See  Strain,  Electro- 
Magnetic.  Strain,  Electrostatic,  Optical!) 

Strain,  Optical  Electro-Magnetic  — 
A  strain  produced  in  a  plate  of  glass  or  other 
transparent  medium  by  placing  it  in  a  mag- 
netic field.     (See  Stress,  Electro-Magnetic. 
Rotation,  Magneto-Optic!) 

Optical  strain,  whether  electrostatic  or  mag- 
netic, or  even  mechanical,  often  causes  a  medium 
to  acquire  the  power  of  double  refraction  or  ro~ 
tary  polarization.  (See  Refraction,  Double, 
Electric.  Rotation,  Magneto-Optic.) 

Stranded  Core  of  Cable.—  (See  Core, 
Stranded,  of  Cable!) 

Stranded  Line.—  (See  Line,  Stranded!) 

Strap  Copper.—  (See  Copper,  Strap.) 

Straps  and  Climbers.  —  Devices  employed 
by  linemen  for  climbing  wooden  telegraph 
poles. 

Stratham's  Electric  Fuse.—  (See  Fuse, 
Electric,  Stratham's!) 

Stratification  Tube.—  (See  Tube,  Stratifi- 


Stratified  Discharge.—  (See  Discharge, 
Stratified.) 

Stray  Field.—  (See  Field,  Magnetic, 
Stray.) 

Stray  Power.  —  (See  Power,  Stray!) 

Stream-Lines  of  an  Escaping  Fluid.— 
Lines  which  show  the  actual  path  of  the 
particles  of  an  escaping  fluid. 

When  the  escape  has  reached  a  steady  condi- 
tion, the  stream-lines  correspond  to  the  flow  lines. 

Streamers.—  Pillars  or  parallel  flashing 
columns  of  light  frequently  seen  during  the 
prevalence  of  an  aurora.  (See  Aurora  Bo- 
realis^ 


Streamers,  Auroral A  term  some- 
times applied  to  the  flashing  columns  or  pillars 
of  light  that  are  thrown  out  in  the  shape  of 
streams,  from  portions  of  the  sky  during  the 
prevalence  of  an  aurora.  (See  Aurora  Bo- 
realis.) 

Streaming  Discharge.— (See  Discharge, 

Streaming.) 

Streamlets,  Current A  theoretical 

conception  of  a  series  of  parallel  current 
streams  or  current  filaments,  flowing  through 
a  solid  conductor. 

In  the  case  of  uniform  distribution  of  an  elec- 
tric current  where  the  current  density  is  the  same 
for  all  areas  of  cross- section,  these  current  stream- 
lets are  all  of  the  same  strength. 

In  the  case  of  rapidly  alternating  currents, 
however,  the  current  streamlets  are  of  greater 
strength  near  the  surface.  When  the  rate  of  al- 
ternation is  sufficiently  great,  they  are  almost 
entirely  absent  at  the  central  parts. 

The  conception  of  current  streamlets  is  made 
in  order  to  account  for  the  increase  in  the  resist- 
ance of  a  solid  conductor  through  which  rapidly 
alternating  currents  of  electricity  are  passing. 
(See  Currents,  Simple-Periodic.) 

Streams,    Convection Streams    of 

electrified  air  or  other  gaseous  or  vaporous 
particles  given  off  from  the  pointed  ends  of 
charged,  insulated  conductors.  (See  Con- 
vection, Electric!) 

Street  Mains.— (See  Main,  Street.) 
Street  Service.— (See  Service,  Street) 

Strength,  Field The  intensity  or 

total  flux  of  magnetism  of  a  dynamo. 

This  term  is  also  sometimes  roughly  used  for 
the  current  strength  in  the  field  magnet  circuit  of 
a  dynamo-electric  machine. 

Strength    of     Current— (See     Current 

Strength!) 

Strength  of  Magnetic  Field.— (See  Field, 
Magnetic,  Strength  of!) 

Strength  of  Magnetism.— (See  Magnetism, 
Strength  of!) 

Stress.— The  pressure,  pull,  or  other  force 
producing  a  deformation  or  strain. 


Str. 


494 


[Sub. 


Stress,  Dielectric The  force  pro- 
ducing the  deformation  or  strain  in  a  dielec- 
tric. 

A  dielectric  strain,  in  the  case  of  a  Leyden  jar 
or  condenser,  is  sometimes  sufficiently  great  to 
pierce  the  dielectric. 

Stress,  Electro-Magnetic The  force 

or  pressure  in  a  magnetic  field,  which  produces 
a  strain  or  deformation  in  a  piece  of  glass  or 
other  similar  substance  placed  therein.  (See 
Strain,  Optical  Electro-Magnetic) 

Stress,  Electrostatic The  force  or 

pressure  in  an  electrostatic  field,  which  pro- 
duces strain  or  deformation  in  a  piece  of  glass 
or  other  substance  placed  therein.  (See 
Strain,  Electrostatic,  Optical?) 

Stress,  Energy  of A  term  some- 
times used  in  place  of  potential  energy.  (See 
Energy,  Potential) 

Stress,  Magnetic The  force  acting 

to  produce  a  strain  in  the  air-gap  between 
two  dissimilar  magnet  poles  by  the  action  of 
the  lines  of  magnetic  force,  bridging  such  air 
gap- 

Striae,  Electric Parallel  streaked 

bands,  consisting  of  alternate  light  and  dark 
spaces,  produced  in  tubes  containing  low 
vacua,  by  the  passage  of  rapidly  alternating 
currents  through  them.  (See  Tube,  Strati- 
fication) 

Strip,  Safety A  strip  or  bar  used  as 

a  safety  fuse.    (See  Fuse,  Safety) 

Stripping.— Dissolving  the  metal  coating 
from  a  silver-plated  or  other  metal-plated  ar- 
ticle. 

The  object  of  the  "stripping  "  process  is  tore- 
cover  silver  from  imperfectly  plated  ware,  or 
from  old  ware  which  is  to  be  replated. 

Stripping  of  silver  is  accomplished  either  in  the 
cold  or  by  aid  of  heat,  by  the  use  of  the  following 
solutions,  viz.: 
Concentrated  sulphuric  acid, 

(Baume',  66  degrees) ico  parts. 

Concentrated  nitric  acid, 

(Baume,  40  degrees) 10      " 

The  objects  are  suspended  in  this  liquid,  which, 
provided  it  be  not  diluted  with  water,  possesses 
the  property  of  dissolving  the  silver  without 
touching  the  metal  underneath. 


Stripping  Baths. — (See  Bath,  Strip- 
ping) 

Stripping  Liquid. — (See  Liquid,  Strip- 
ping) 

Stroke,  Lightning A  disruptive 

discharge  between  two  oppositely  charged 
clouds,  or  between  a  cloud  and  the  earth. 
(See  Discharge,  Disruptive) 

Stroke,  Lightning,  Back  or  Return  — 

— An  electric  shock,  caused  by  an  induced 
charge,  produced  by  the  discharge  of  a  light- 
ning flash. 

The  shock  is  not  caused  by  the  lightning  flash 
itself,  but  by  a  charge  which  is  induced  in  neigh- 
boring conductors  by  the  discharge.  These  in- 
duced effects  are,  in  fact,  effects  of  electro-dy- 
namic induction.  (See  Induction,  Electro-Dy- 
namic) A  similar  effect  may  be  noticed  by 
standing  near  the  conductor  of  a  powerful  electric 
machine,  when  shocks  are  felt  at  every  discharge. 

The  effects  of  the  return  shock  are  sometimes 
quite  severe.  These  effects  are  often  experienced 
by  sensitive  people  on  the  occurrence  of  a  light- 
ning  discharge  at  a  considerable  distance. 

In  some  instances  the  return  stroke  has  been 
sufficiently  intense  to  cause  death.  In  general, 
however,  the  effects  are  much  less  severe  than 
those  of  the  direct  lightning  discharge. 

Struts  for  Telegraphic  Poles.— Inclined 
wooden  or  iron  poles,  applied  to  telegraph 
poles  in  order  to  support  the  thrust  or  press- 
ure acting  on  them.  (See  Pole,  Tele- 
graphic) 

Sturgeon's  or  Barlow's  Wheel.— A  wheel 
capable  of  rotation  on  a  horizontal  axis,  which, 
when  placed  between  the  poles  of  a  magnet, 
rotates  when  a  current  is  passed  through  it 
between  the  axis  and  the  circumference. 

Sub-Aqueous  Cable.— (See  Cable,  Sub- 
Aqueous) 

Sub-Branch.— (See  Branch,  Sub) 

Sub-Main.— (See  Main,  Sub) 

Submarine  Boat.— (See  Boat,  Sub- 
marine, Electric) 

Submarine  Cable.— (See  Cable,  Sub- 
marine) 

Submarine  Mine.— (See  Mine,  Sub- 
marine) 


Sub.] 


495 


[Sur. 


Submarine  Telegraphy. — (See  Teleg- 
raphy, Submarine?) 

Substance,    Ferro-Magnetic    —A 

term  proposed  in  place  of  paramagnetic,  for 
substances  that  are  magnetic  after  the  man- 
ner of  iron.  (See  Paramagnetic^ 

Subterranean  Mine.  (See  Mine,  Sub- 
terranean^) 

Subway,  Electric An  accessible 

underground  way  or  passage  provided  for  the 
reception  of  electric  wires  or  cables. 

Underground  electric  conductors,  like  all  elec- 
tric conductors,  are  liable  to  faults,  crosses,  etc. 
Unless  they  are  readily  accessible,  very  serious 
loss  and  damage  may  occur  before  the  fault  is 
located  and  corrected. 

Sulphating. — A  name  applied  to  one  of  the 
sources  of  loss  in  the  operation  of  a  storage 
battery,  by  means  of  the  formation  of  a  coating 
of  inert  sulphate  of  lead  on  the  battery  plates. 

The  addition  of  a  solution  of  sulphate  of  soda 
to  the  sulphuric  acid  liquid  is  claimed  to  have  the 
effect  of  decreasing  the  extent  of  the  sulphating. 

Summer  Lightning. — (See  Lightning, 
Summer?) 

Sun  Spots.— (See  Spots,  Sun.) 

Sunstroke,  Electric,  or  Electric  Prostra- 
tion or  Insolation Physiological 

effects,  similar  to  those  produced  by  exposure 
to  the  sun,  experienced  by  those  exposed  for 
a  long  while  to  the  intense  light  and  heat  of 
the  voltaic  arc. 

Electric  sunstroke  is  sometimes  called  electric 
insolation,  or  electric  prostration. 

The  effects  of  electric  sunstroke  were  first 
noticed  by  Desprez  in  his  classic  experiments  on 
the  fusion  or  volatilization  of  carbon. 

On  undue  exposure  to  an  intense  electric  light 
the  eyes  are  irritated  and  the  skin  burned  as 
by  the  sun.  In  some  cases  it  is  claimed  that  the 
effects  of  sunstroke,  or  excessive  production  of 
heat,  as  in  true  insolation,  are  produced.  In  the 
applications  of  electricity  to  electric  furnaces, 
these  same  effects  have  been  noticed  in  an  inten- 
sified degree. 

From  some  recent  investigations  it  would  ap- 
pear that  these  effects  are  to  be  ascribed  to  the 
light  rather  than  to  the  heat 


The  symptoms  are  as  follows:  Pain  in  the 
throat,  face  and  temples,  followed  by  a  coppery 
red  color  of  the  skin,  irritation  and  watering  of 
the  eyes,  when  the  symptoms  disappear.  The 
skin  peels  off  in  about  five  days. 

Superficial  Eddy  Currents.— (See  Cur- 
rents, Eddy,  Superficial.) 

Super-Saturation      of     Solution.— (See 

Solution,  Super-Saturation  of.) 

Supplement  of  Angle. — (See  Angle,  Sup- 
plement of.) 

Supply,  Unit  of,  Electrical A  unit, 

provisionally  adopted  in  England  by  the 
Board  of  Trade,  equal  to  1,000  amperes  flow- 
ing for  one  hour  under  an  electromotive  force 
of  one  volt. 

This  would,  of  course,  equal  1,000  watt-hours, 
and  would  be  the  same  as  ico  amperes  flowing 
for  ten  hours  under  one  volt. 

One  unit  of  electrical  supply  is  equal  to  1.34 
actual  horse-power  expended  for  one  hour,  and 
will  feed  13.4  Swan  lamps  of  21  candle-power  for 
one  hour.  It  is  equal  in  illuminating  power  in 
Swan  lamps  to  the  light  produced  by  ico  cubic 
feet  of  gas  consumed  in  twenty  14-candle  burners 
in  one  hour. 

The  unit  of  electrical  supply  is  called  a  "Board 
of  Trade  unit,"  a  B.  O.  T.  unit,  or  simply  a  bot. 
It  is  equal  to  one  kilo-watt  hour. 

Support,  Tripod  Eoof  —  — A  support 
for  a  housetop  telegraphic  line. 

The  tripod  roof  support,  as  its  name  indicates, 
consists  of  a  three-legged  support  for  any  suitable 
insulator. 

A  common  form  is  shown  in  Fig.  516. 

Support,  Underground  Cable A 

support  provided  for  holding  a  cable  where 
it  passes  around  the  side  of  a  man-hole,  un- 
derground conduit,  or  other  similar  location. 

Surface,  Demarcation The  surface 

at  which  a  demarcation  current  is  generated. 

The  surface  which  marks  the  point  of  in- 
jury in  a  muscle  or  nerve. 

Demarcation  currents  in  electro-therapeutics, 
are  currents  produced  in  injured  nerves  or 
muscles.  They  are  probably  due  to  the  chemical 
changes  that  take  place  between  the  injured  and 
the  uninjured  tissues.  The  demarcation  surface  is 


Sun] 


496 


[Sur. 


the  surface  separating  parts  in  a  normal  condi- 
tion from  those  in  an  abnormal  condition. 

An  injury  to  a  muscle  or  nerve  causes  or  pro- 
duces at  such  surface  a  dying  substance  which  is 


Kg.  Si  6.     Tripod  Roof  Support. 
negative  to  the  uninjured,  normal  or  positive  sub- 
stance.    Such  a  surface  results  in  a  demarcation 
current. 

Surface  Density.— (See  Density,  Surface) 

Surface,  Equipotential,  of  a  Conductor 
Through  Which  a  Current  is  Flowing 

— A  surface  described  within  the  mass  of  a 
conductor,  conveying  an  electric  current,  at 
points  perpendicular  to  the  direction  of  the 
flow,  all  possessing  the  same  potential. 

Surface,  Eqnipotential,  or  Level  Surface 
of  Escaping  Fluid—  —A  surface  de- 
scribed within  the  mass  of  a  fluid  in  motion 
at  all  places  perpendicular  to  the  stream  lines 
passing  such  surface. 

Surface  Integral  of  Magnetic  Induction. 
— (See  Induction,  Magnetic,  Surf  ace-Inte- 
gral of) 

Surfaces,  Eqnipotential,  Electrostatic 

Surfaces,  all  the  points  of  which  are 

at  the  same  electric  potential.  (See  Poten- 
tial, Electric) 


Electric  surfaces  perpendicular  to  the  lines 
of  electric  force  over  which  a  quantity  of 
electricity,  considered  as  being  concentrated 
at  a  point,  may  be  moved  without  doing 
work.  (See  Field,  Electrostatic.) 

Equipotential  surfaces  correspond  with  a  water 
level,  over  which  a  body  may  be  moved  horizon- 
tally without  doing  any  work  against  the  force  of 
gravity. 

In  the  case  of  the  charged  insulated  sphere, 
shown  in  Fig.  517,  the  equipotential  surfaces, 
represented  by  the  circles,  are  concentric, 

Hi, 


Fig.  Jf?.    Equipotential  Surfaces. 

Surfaces,   Eqnipotential,  Magnetic  

— Surfaces  surrounding  the  poles  of  a  mag- 
net, or  system  of  magnets,  where  the  mag- 
netic potential  is  the  same.  (See  Potential, 
Magnetic) 

Magnetic  equipotential  surfaces  extend  in  a 
direction  perpendicular  to  the  lines  of  magnetic 
force.  (See  field,  Magnetic.) 

No  work  is  required  in  order  to  move  a  unit 
pole  over  equipotential  magnetic  surfaces,  be- 
cause in  so  doing  it  cuts  no  lines  of  magnetic 
force.  Work,  however,  is  done  when  the  motion 
is  from  one  equal  potential  surface  to  another. 

Equipotential  surfaces,  whether  electric  or  mag- 
netic, cannot  intersect  one  another,  since  their 
potential  is  the  same  at  all  points. 

Surfaces,  Isothermal Surfaces  con- 
necting points  in  a  body  which  have  the  same 
temperature. 

Surging  Discharge.— (See  Discharge, 
Surging) 

Surgings,  Electric Electric  oscilla- 
tions set  up  in  a  charged  conductor  that  is 
undergoing  rapid  discharge. 

These  surgings  produce  waves  in  the  surround- 
ing ether  that  travel  outwards  with  the  velocity  of 


8ns.] 


497 


[8ns. 


light.  (See  Electricity,  Hertz's  Theory  of  Elec- 
tro-Magnetic Radiations  or  Waves.  ) 

Susceptibility,  Magnetic  --  The  ratio 
existing  between  the  induced  magnetization 
and  the  magnetic  force  producing  such  mag- 
netism, or  the  intensity  of  magnetism  divided 
by  the  magnetic  force. 

Susceptibility  relates  to  the  poles  produced  in  a 
body  by  a  magnetizing  force,  whereas  permea- 
bility refers  its  power  to  conduct  lines  of  force. 
When  the  inducing  field  has  unit  strength  of 
magnetization,  the  magnetic  susceptibility  will 
measure  directly  the  strength  of  the  magnetiza- 
tion. 

When  a  bar  of  iron  is  placed  in  a  magnetic 
field,  it  is  threaded  by  the  lines  of  magnetic  force, 
and  thus  becomes  magnetized  by  induction.  This 
induction  will  necessarily  depend  both  on  the 
number  of  lines  of  force  in  the  magnetizing  field 
and  on  the  magnetic  permeability  of  the  magnet- 
ized body;  or,  in  other  words,  the  induction  is 
equal  to  the  product  of  the  intensity  of  the  mag- 
netizing field  and  the  magnetic  permeability  of 
the  body  in  which  the  induction  occurs. 

The  magnetic  susceptibility  is  sometimes  called 
the  Co-  efficient  of  Magnetization;  calling  K,  the 
•usceptibility,  H,  the  magnetizing  force,  and  I,  the 
intensity  of  the  resulting  magnetization;  then 


The  magnetic  permeability  is  sometimes  called 
the  Co-efficient  of  Magnetic  Induction,  calling  fj., 
the  permeability,  B,  the  magnetic  induction  and 
H,  the  magnetic  force  producing  the  induction  ; 
then 


Suspending  Wire  of  Aerial  Cable.—  (See 

Wire,  Suspending,  of  Aerial  Cable.) 
Suspension,  Bifilar  --  The  suspen- 


sion  of  a  needle  by  two 
parallel  wires  or  fibres,              ' 
as  distinguished   from 
a  suspension  by  a  sin- 
gle wire  or  fibre. 
M         & 

< 

I 

L 

b'        N, 

shown  in  Fig.  5  1  8.     The 
two  threads,  a  b  and  a' 
b',  are  connected  to  the  Fig-Si*-    Bifilar  Svsfie*. 
needle  MN,  so  as  to  per- 

mit  it  to  hang  in  a  true  horizontal  position.    Any 


twisting,  around  the  imaginary  axis  c  c',  causes 
the  lines  of  suspension,  ab  and  a  b',  to  tend  to 
cross  one  another  and  so  shorten  the  axis  c  c'. 

Harris, -who  was  the  first  to  employ  the  bifilar 
suspension,  showed  that  the  reactive  force  im- 
parted to  the  suspension  threads  by  turning  the 
needle,  was: 

(i.)  Directly  proportional  to  the  distance  be- 
tween the  threads. 

(2.)  Inversely  as  their  lengths. 

(3.)  Directly  proportional  to  the  weight  of  the 
suspended  body. 

(4.)  Proportional  to  the  angle  of  twist  or  torsion 
of  the  threads  on  each  other. 

Any  deflection  of  the  needle  shortens  the  verti- 
cal distance  between  the  points  of  support  and 
the  needle,  and  so  tends  to  lift  the  needle.  The 
motions  are  therefore  balanced  against  the  force 
of  gravity  instead  of  against  the  torsion  of  the 
fibre. 

Suspension,  Combined  Fibre  and  Spring 

— The  suspension  of  a  needle  by  the 

combined  use  of  a  spiral  spring  and  a  single 
fibre. 

In  this  form  of  suspension  the  spring  is  intro- 
duced between  the  fibre  and  the  needle.  It  is 
valuable  for  marine  galvanometers  and  other  ap- 
paratus exposed  to  tilting  or  rolling  motions,  be- 
cause it  permits  the  instrument  to  be  tilted 
through  several  degrees  without  causing  any  con- 
siderable variation  in  the  deflections  produced  by 
the  current  or  the  charge. 

Suspension,  Fibre Suspension  of  a 

needle  by  means  of  a  fibre  of  unspun  silk  or 
other  material. 

A  fibre  suspension  generally  means  a  single 
fibre  or  thread.  It  may,  however,  be  applied  to 
a  bifilar  suspension.  (See  Suspension,  Bifilar.) 

A  fibre  suspension  is  to  be  preferred  to  a  pivot 
suspension,  since  it  eliminates  all  friction .  It  has, 
however,  the  disadvantage  of  necessitating  level- 
ing screws. 

Suspension,  Knife-Edge  —  —The  sus- 
pension of  a  needle  on  knife  edges  that  are 
supported  on  steel  or  agate  planes. 

A  suspension  of  this  kind  is  used  in  the  dip- 
ping needle,  since  it  permits  of  freedom  of  mo- 
tion in  a  single  vertical  plane  only. 

Suspension,  Pivot Suspension  of  a 

needle  by  means  of  a  jeweled  cup  and  a  me- 
tallic pivot. 


Swa.] 


498 


[Swi. 


The  jeweled  cup  is  placed  above  the  centre  of 
gravity  of  the  needle,  and  is  supported  on  a  steel 
point.  As  a  rule,  compass  needles  have  this 
variety  of  support. 

Swage. — A  particular  form  of  anvil  on 
which  highly  heated  metallic  plates  are  shaped 
by  hammering  them  into  forms  the  same  as 
that  of  the  anvil  on  which  they  are  placed. 

Swage. — To  fashion  heated  metallic  plates 
by  hammering  them  into  the  form  of  an  anvil 
on  which  they  are  supported. 

Swaging. — Fashioning  highly  heated  me- 
tallic plates  into  any  desired  form  by  ham- 
mering while  on  suitable  dies. 

Swaging,  Electric The  forming  or 

shaping  of  metallic  plates  by  hammering 
them  against  suitable  anvils  or  dies  while 
softened  by  electrical  heating. 

The  electro-swaging  apparatus  consists  of  a 
welding  transformer  provided  with  a  movable 
clamp.  The  pressure  required  for  the  swaging 
is  attained  by  the  use  of  steam  admitted  into  a 
cylinder  by  a  lever  which  operates  a  four-way 
valve. 

The  rod,  bar,  or  plate  of  metal  to  be  shaped  or 
swaged,  is  first  heated  by  the  passage  of  a  pow- 
erful heating  current,  obtained  preferably  from  a 
welding  transformer,  one  of  the  clamps  of  which 
is  movable.  When  the  metal  is  suitably  softened 
by  the  passage  of  the  current,  it  is  then  subjected 
to  swaging. 

Swelling  Current.— (See  Currents,  Swell- 
ing-.) 

Swelling  Faradic  Current.— (See  Cur- 
rents, Swelling  Faradic?) 

Swinging  Annunciator. — (See  Annuncia- 
tor, Pendulum  or  Swinging?) 

Swinging  Cross. — (See  Cross,  Swinging 
or  Intermittent^) 

Switch,  Automatic,  for  Incandescent 

Electric  Lamps A  device  by  which 

incandescent  electric  lamps  can  be  lighted  or 
extinguished  at  a  distance  by  means  of  push 
buttons. 

The  automatic  switch  for  incandescent  lamps 
corresponds  in  electric  lighting  to  the  automatic 
gaslighting  device  in  systems  of  electric  gaslight- 
ing.  It  consists  essentially  of  two  electro- 
magnets, one  for  turning  the  switch  which  lights 


the  lamp  by  cutting  them  into  the  circuit  of  the 
lighting  mains  or  conductors,  and  the  other  for 
extinguishing  them,  by  cutting  them  out.  These 
electro-magnets  are  operated  by  two  push  buttons, 
a  black  one  to  extinguish  the  lamp  and  a  white 
button  to  light  it. 

The  details  of  the  automatic  switch  are  shown  in 
Fig.  520.  ThemainsM1  andM2,  areconnected  to 
one  set  of  contacts,  and  the  branches  containing 


Fig-  5IQ-    Automatic  Switch. 
the  lamps  to  be  lighted,  to  the  contacts  between 
them.     The  push  buttons,  P1andP2,  are  con- 
nected by  their  wires   to  the  main  M1   and  the 
branch  B1. 

These  buttons  are  made  respectively  positive 
and  negative,  and  are  marked  +  and  — .  The 
third  wire  of  the  push  button  is  connected  as 
shown  to  the  lamp  L,  and  the  switch  magnet, 
SM. 

When  the  contact  is  closed  atP1,  the  arma- 
ture of  S  M,  closes  the  contact  through  C. 
When  the  button  is  released,  connection  is  estab- 


Fig.  J20.     Automatic  Switch, 

lished  between  the  magnet  and  the  lamp  L,  in 
series.  This  is  for  the  purpose  of  cutting  down 
the  circuit  to  the  -^  of  an  ampere,  and  thus  per- 
mitting a  thin  wire  to  serve  between  the  button 
and  the  switch  magnet. 

When  the  button,  Pf,  is  closed  the  lamps  are 
turned  out. 
Switch  Board.— (See  Board,  Switch^ 

Switch  Board,    Multiple    -(See 

Board,  Multiple  Switch^ 


Swi.] 


499 


[Swi. 


Switch  Board,  Telegraphic  —(See 

Board,  Switch,  Telegraphic) 

Switch  Board,    Trunking —(See 

Board,  Switch,  Trunking) 

Switch,    Break-Down A   special 

switch,  employed  in  small  three-wire  systems, 
for  connecting  the  positive  and  negative  bus- 
wires  in  such  a  manner  as  to  practically 
convert  it  into  a  two-wire  system  and  permit 
the  system  to  be  supplied  with  current  from 
a  single  dynamo.  (See  Wires,  Bus) 

Switch,  Changing A  switch  de- 
signed to  throw  a  circuit  from  one  electric 
source  to  another. 

A  changing  switch,  for  example,  is  of  use  in 
disconnecting  a  circuit  from  one  dynamo  and 
connecting  it  to  another;  or,  in  other  words,  to 
suddenly  transfer  the  load  from  one  dynamo  to 
another. 

Switch,  Changing-Orer A  term 

sometimes  applied  to  a  changing  switch. 
(See  Switch,  Changing!) 

Switch,  Distributing A  multiple 

switch  board.  (See  Board,  Multiple  Switch!] 

Switch,     Distributing,    for      Electric 

Lights A    switch    employed    in  a 

system  of  arc  lighting  by  series-distribu- 
tion, by  means  of  which  any  particular 
dynamo-electric  machine  or  a  number  of 


FSf.  321.    Dmtble-Break  Knife  Switch. 

separate  dynamo-electric  machines  can 
be  connected  with  the  same  circuit  without 
interfering  with  the  lights.  (See  Board,  Mul- 
tiple Switch) 

Switch,    Donble-Break A  term 

sometimes  used  for  double-pole  switch.  (See 
Switch,  Double-Pole.) 


Switch,  Double-Break  Knife A 

knife  switch  provided  with  double-break  con- 
tacts. 

A  double-break  knife  switch  is  shown  in  Fig. 
521. 

Switch,    Double-Pole A    switch 

that  makes  or  breaks  contact  with  both  poles 
of  the  circuit  in  which  it  is  placed. 

A  switch  consisting  of  a  combination  of 
two  separate  switches,  one  connected  to  the 
positive  lead  and  the  other  to  the  negative 
lead. 

Double-pole  switches  are  used  in  most  systems 
of  incandescent  lighting  in  order  to  insure  the 
thorough  separation  of  the  circuit  from  the  main 
conductor  or  leads  when  cut  out  and  to  diminish 
the  spark. 

Switch,  Feeder The  switch  em- 
ployed for  connecting  or  disconnecting  each 
conductor  of  a  feeder  from  the  bus-bars  in  a 
central  station. 

Switch,  Four-Point A  switch  by 

which  a  circuit  can  be  completed  through 
four  central  points. 

Switch,  Knife A  switch   which  is 

opened  or  closed  by  the  motion  of  a  knife 


Pig.  522.    Lamp-Socket  Switch. 

contact  which  moves  between  parallel  contact 
plates. 

A  knife-edge  switch.  (See  Switch,  Knife- 
Edge) 

Switch,  Knife-Break A  knife 

switch.  (See  Switch,  Knife) 

Switch,  Knife-Edge A  term  some- 
times used  in  place  of  knife  switch.  (See 
Switch,  Knife) 


Swi.] 


500 


[Swi 


Switch,  Lamp-Socket A  switch 

placed  in  the  socket  of  an  incandescent  lamp 
and  provided  for  throwing  the  lamp  in  and 
out  of  the  circuit. 

A  form  of  lamp  socket  switch  is  shown  in  Fig. 
522.  Its  operation  will  be  understood  from  an 
inspection  of  the  drawing. 

Switch  Pin.— (See  Pin,  Switch^ 

Switch,  Plug1 A  switch  in  which  a 

metal  plug  is  withdrawn  to  throw  into  a  cir- 
cuit a  coil  or  other  device,  the  ends  of  which 
are  connected  to  metallic  blocks  that  are  suf- 
ficiently near  together  to  be  joined  and  short- 
circuited  by  the  insertion  of  the  plug. 

Switch,  Pole-Changing A  switch 

employed  for  changing  the  direction  of  the 
current  in  any  circuit. 

A  form  of  pole-changing  switch  is  shown  in  Fig. 
523. 


Fig.  J2J.    Pole-Changing  Switch. 

If  the  two  outer  contacts  are  connected  to  the 
same  pole  as  the  source,  as,  for  example,  the 
positive,  and  the  two  intermediate  contacts  are 
connected  to  the  other  pole,  or  to  the  negative, 
then  in  the  position  shown  in  the  cut,  the  current 
will  flow  through  any  receptive  device  connected 
with  the  switch,  in  one  direction,  but  if  the 
switch  is  moved  to  the  left,  it  will  flow  in  the  op- 
posite direction. 

Switch,  Removable  Key A  plug 

switch.  (See  Switch,  Plug.) 

Switch,  Reversing A  switch  for 

reversing  the  direction  of  the  battery  current 
through  a  galvanometer. 

A  simple  reversing  switch  consists  of  four  in- 
sulated brass  segments  mounted  on  a  plate  of 
ebonite  and  furnished  with  openings  between 
them  for  plug  connections. 

The  battery  terminals  are  connected  to  two  di- 
agonally opposite  segments,  as  B,  and  D,  Fig. 
524,  and  the  leading  wires  of  the  galvanometer, 


01-  other  instrument,  to  the  other  segments,  as  C 
and  A.  If,  now,  the  plugs  are  placed  between  B 
and  C,  and  A  and  D,  the  battery  current  flows 
in  one  direction.  If,  however,  the  plugs  arft 


Fig-  524.    Reversing  Switch. 

placed  between  A  and  B,  and  C  and  D,  the  bat- 
tery current  will  flow  in  the  opposite  direction. 

The  battery  current  is  cut  off  if  one  plug  is  re- 
moved. In  practice,  however,  it  is  preferable  t» 
remove  both  plugs,  so  as  to  avoid  any  current 
from  want  of  sufficient  insulation. 

Switch,  Snap A  switch  in  whick 

the  transfer  of  the  contact  points  from  one 
position  to  another  is  accomplished  by  means 
of  a  quick  motion  obtained  by  the  operation 
of  a  spring. 

The  object  of  the  snap  switch  is  to  prevent  the 
switch  resting  in  any  half  way  position,  and  thus 
preventing  the  establishing  of  an  arc. 

Switch,  Telephone,  Automatic —A 

device  for  automatically  transferring  the  con- 
nection of  the  main  line  from  the  call  bell  t« 
the  telephone  circuit. 

In  most  telephone  circuits,  as  now  arranged, 
the  automatic  switch,  besides  transferring  the  main 
line  from  the  call  bell  to  the  telephone  circuit, 


Fig- 5 25-     Automatic   Telephone  Switch. 
closes  the  local  battery  circuit  of  the  transmitter 
on  the  removal  of  the  telephone  from  its  support- 
ing hook. 


Swi.] 


501 


[Synu 


The  means  whereby  this  is  accomplished  are 
shown  in  Fig.  525.  On  the  removal  of  the  tele- 
phone from  the  hook  L,  the  lever  is  pulled  up- 
wards by  the  spring  Z,  thus  closing  the  contacts  I, 
2  and  3,  by  which  the  local  battery  S,  is  closed 
through  the  circuit  of  the  transmitter,  the  tele- 
phone disconnected  from  the  circuit  of  the  call  bell 
M,  B,  and  connected  with  the  circuit  of  the  trans- 
mitter. On  replacing  the  telephone  on  the  hook 
L,  its  weight  depresses  the  lever,  breaking  con- 
nection with  I,  2  and  3,  and  establishing  connec- 
tion with  the  call  circuit. 

Switch,  Three-Point A  switch  by 

means  of  which  a  circuit  can  be  completed 
through  three  different  contact  points. 

Switch,  Time An  automatic  switch 

in  which  a  predetermined  time  is  required 
either  to  insert  a  resistance  in  or  remove  it 
from  a  circuit. 

Switch,  Two-Point A  switch  by 


means  of  which  a  circuit  can  be  completed 
through  two  different  contact  points. 

Switch,  Two- Way A  switch  pro- 
vided with  two  contacts  connected  with  two 
separate  and  distinct  circuits. 

Switch,  Yale-Lock,  for  Burglar  Alarm 

(See  Alarm,  Yale-Lock  Switch 

Burglar?) 

Switched-In. — Placed  in  a  circuit  by  means 
of  a  switch.  (See  Closed-Circuited) 

Switched-Out— Cut  out  of  a  circuit  by 
means  of  a  switch.  (See  Open-Circuited,) 

Symbols  and  Diagrams,  Standard  Elec- 
tric   Standard  symbols  and  diagrams 

used  in  electro-technics. 

The  standard  electric  diagrams  and  symbols 
shown  on  pages  501,  and  502,  were  arranged  by 
Prof.  F.  B.  Crocker,  and  are  reproduced  from 
the  Electrical  Engineer. 


SYMBOLS   COMMONLY 
MECHANICAL. 


USED  IN  ELECTRICAL  WORK. 
ELECTRICAL. 


MAGNETIC. 


or  I.  Length  D.  Diameter 

orm.  Mass  r.  Radius 

ort.  Time  H.P.      Horse povie. 

Velocity  I.H.P.  Indicated  " 

frt  Force  B.II.P.  Brake       " 

Acceleration  r.p.m.  Revolutions 

due  to  gravity.  per  min. 

or-n.  Work.  C.G.S.  Centimetre 
Power. 
CUlb.  Footpound. 


E.07-E.M.F.  Electromotive    T.  Volt 


force 

P.D.  Potential  different 
C.   Current 
B.  Resistance 
p.  Specific  resistance 
Q.   Quantity 
K.  Electrostatic  capacity. 


gramme  second  L>  inductance  (Coeffic.  of) 
(System)  i<^j.^.m.f^ 


A.W.G.  Amer 


Wire  Gauge 


A.M.  Amperemeter. 

T.M.  Voltmeter 

F.M.  Field  Magnet 

+  Positive  pole  or  termin 

—  Negative  "    " 


amp.  Ampere 
w.  Ohm 
0.  Megohm. 
B.A.U.  Brit.  As 
mfd.  Microfarad 
b.orhj.     Henry 
z.  Electrochemical 

equivalent 
J.   Joule 
E.W.  Kilowatt 


N.  North  pole 
S.  South  pole 
m.  Strength  of  pole 
H.  Magnetizinsforce 
Unit  (C.G.S.) 

B.  Magnetic  induction 

(C.G.S.  lines) 
\.  Intensity  of  mag- 
netization 

*  MaSmea^y' 
K.  Magnetic  sus- 
ceptibility 
H.  Horizontal 

intensity  of  Earth' t 

magnetism 


Sym.J 


502 


tSym. 


Mont  Telfffraph  System 


Crocker's  Ckart  o/  Standard  Electric  Symbols  and  Diagrams. 


Sym.] 


503 


[Sys. 


Symmetrical  Induction  of  Armature. — 

(See  Induction,  Symmetrical,  of  Armature.") 
Symmetrical     Magnetic      Field.— (See 

Field,  Magnetic,  Symmetrical.) 
Sympathetic    Electrical    Vibrations.— 

(See  Vibrations,  Sympathetic  Electrical.) 

Sympathetic  Vibrations. -(See  Vibra- 
tions, Sympathetic.) 

Synchronism. — The  simultaneous  occur- 
rence of  any  two  events. 

A  rotating  cylinder,  or  the  movement  of  an 
index  or  trailing  arm,  is  brought  into  synchronism 
with  another  rotating  cylinder  or  another  index 
or  trailing  arm,  not  only  when  the  two  are  mov- 
ing with  exactly  the  same  speed,  but  when  in  ad- 
dition they  are  simultaneously  moving  over  simi- 
lar portions  of  their  respective  paths. 

In  the  Breguet  Step-by-Step  or  Dial  Telegraph 
(See  Telegraphy,  Step -by -Step),  the  movements  of 
the  needle  on  the  indicator  are  synchronized  with 
the  movements  of  the  needle  on  the  manipulator. 
In  systems  of  Fac- Simile  Telegraphy  the  move- 
ments of  the  transmitting  apparatus  are  syn- 
chronized with  those  of  the  receiving  apparatus. 

In  Delany's  Synchronous  Multiplex  Telegraph 
System,  the  trailing  arm  that  moves  over  a  cir- 
cular table  of  contacts  at  the  transmitting  end, 
is  accurately  synchronized  with  a  similar  trailing 
arm  moving  over  a  similar  table  at  the  receiving 
end. 

Delany,  who  was  the  first  to  obtain  rigorous 
synchronism  at  the  two  ends  of  a  telegraphic 
line  hundreds  of  miles  in  length,  accomplishes 
this  by  the  use  of  La  Cour's  phonic  wheel, 
through  the  agency  of  correcting  electric  im- 
pulses, automatically  sent  in  either  direction  over 
the  main  line,  when  one  trailing  arm  gets  a  short 
distance  in  advance  or  back  of  the  other. 

With  alternating  current  dynamos,  where  one 
dynamo  is  feeding  incandescent  lamps  connected 
to  the  leads  in  multiple,  and  it  is  desired  to 
couple  another  alternating  current  dynamo  in 
parallel  with  the  first,  it  is  necessary  to  obtain  a 
complete  synchronism  of  the  two  dynamos  before 
coupling  them,  since  otherwise  the  lamps  will 
show  variations  in  their  light,  and  the  machine 
may  suffer. 

Sjnchronizable. — Capable  of  being  syn- 
chronized. (See  Synchronism?) 

Synchronize. — To  cause  to  occur  or  act 
simultaneously.  (See  Synchronism?) 


Synchronized. — Caused  to  occur  or  act 
simultaneously.  (See  Synchronism!) 

Synchronizing  Dynamo-Electric  Ma- 
chine.— (See  Machine,  Dynamo-Electric, 
Synchronizing?) 

Synchronous  Multiplex  Telegraphy.— 
(See  Telegraphy,  Synchronous  Multiplex, 
Delany's  System.) 

System,  Astatic An  astatic  com- 
bination of  magnets. 

An  astatic  needle  consists  of  an  astatic  system 
of  two  magnetic  needles.  The  needles  are 
rigidly  fixed  together  with  their  opposite  poles 
facing  each  other.  The  two  needles  form  an  as- 
tatic pair  or  couple.  (See  Needle,  Astatic.) 

System,  Block,  for  Railways  —  —(See 
Railroads,  Block  System  for?) 

System,    Centimetre  -  Gramme  -  Second 

(See  Units,  Centimetre  -  Gramme  - 

Second?) 

System,    Continuous    Underground,    of 

Motive  Power  for  Electric  Railroads 

— (See  Railroads,  Electric,  Continuous  Un- 
derground System  of  Motive  Power  for?) 

System,  Dependent,  of  Motive  Power  for 

Electric  Railroads (See  Railroads, 

Electric,    Dependent    System    of    Motive 
Power  for?) 

System,  Independent,  of  Motive  Power 
for  Railroads (See  Railroads,  Elec- 
tric, Independent  System  of  Motive  Power 
for) 

System,  Multiphase A  term  fre- 
quently applied  to  a  system  of  rotating  elec- 
tric currents.  (See  Current,  Rotating.) 

System  of  Distribution  of  Electricity  by 
Commntating  Transformers. — (See  Elec- 
tricity, Distribution  of,  by  Commutating 
Transformers?) 

System  of  Distribution  of  Electricity  by 
Condensers. — (See  Electricity,  Distribution 
of,  by  Alternating  Currents  by  Means  of 
Condensers.  Electricity,  Distribution  of,  by 
Continuous  Current  by  Means  of  Condens- 
ers?) 

System  of  Distribution  of  Electricity  bf 
Means  of  Alternating  Currents.— (See  Elee- 


504 


[fai. 


tricity,  Distribution  of,  by  Alternating  Cur- 
rents,") 

System  of  Distribution  of  Electricity  by 
Motor  Generators.— (See  Electricity,  Dis- 
tribution of,  by  Motor  Generators.) 

System,  Three-Wire A  system  of 

electric  distribution  for  lamps  or  other  trans- 
lating devices  connected  in  multiple,  in  which 
three  wires  are  used  instead  of  the  two  usually 
employed. 

In  the  three-wire  system  two  dynamos  are  gen- 
erally employed,  which  are  connected  with  one 
another  in  series. 

The  three  conductors  are  connected  as  shown 
in  Fig.  527,  the  central  conductor  to  the  junction 
of  the  two  dynamos  and  the  two  others  to  their 
free  terminals,  and  the  difference  of  potential  be- 
tween the  central  and  the  two  outer  conductors 
is  maintained  the  same.  The  lamps,  or  other 
electro-receptive  devices,  are  placed  in  multiple- 
arc  between  either  branch,  and  so  distributed 
that  the  current  in  each  branch  is  the  same. 
When  such  balance  is  established  no  current 
flows  through  the  central  or  neutral  conductor. 
But  when  that  balance  is  disturbed,  the  surplus 
current  in  one  branch  is  taken  up  by  the  central 
conductor. 

The    three-wire    system    effects  considerable 


economy  in  the  weight  of  wire  required.  Since  in 
the  multiple-series-connection  of  electro-receptive 
devices  whatever  difference  of  potential  is  im- 
pressed on  the  mains  is  fed  to  each  device,  no 
higher  difference  of  potential  can  be  employed  on 
the  mains  than  that  which  the  devices  are  capa- 
ble of  taking.  In  the  case  of  an  incandescent 
lamp,  if  such  difference  be  exceeded,  too  strong 
a  current  is  passed  through  the  lamps  wiik  a 
consequent  decrease  in  their  life. 

In  the  three-wire  system  of  distribution  a  higfcer 
difference  of  potential  can  be  maintained  on  fke 
mains  than  is  required  for  any  lamp  placed  in 


<a 


li 


>  S>7'     Three-  Wi> 


0" 

System. 


connection  therewith,  and  in  this  manner  a  c*»- 
siderable  saving  is  effected  in  the  cot  of  the  leads. 


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