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THE  LIBRARY 

OF 

THE  UNIVERSITY 
OF  CALIFORNIA 


PRESENTED  BY 

PROF.  CHARLES  A.  KOFOID  AND 
MRS.  PRUDENCE  W.  KOFOID 


MICHAEL   FAKADAY. 


MICHAEL   FAEADAY. 


LONDON:  PRINTED  BY 

8POTTISWOODE    AND    CO.,    NEW-STREET    SQUARB 
AND   PARLIAMENT    STREET 


F  A  K  A  D  A  Y 


AS 


A  DISCOVERER. 


BY     JOHN     TYNDALL. 

M 


LONDON : 
LONGMANS,     GKEEN,    AND     CO. 

1868. 


The  right  of  translation  it  reserved. 


.. 


F3T? 


NOTE. 

SOME  YEAKS  AGO  I  accompanied  Mr.  FAEADAY  to 
a  little  Photographic  Studio  in  Lambeth,  with  the 
view  of  exchanging  portraits.  The  Frontispiece  is 
engraved  from  one  of  the  negatives  taken  on  that 
occasion,  and  which  is  now  in  the  possession  of 
Dr.  Bence  Jones. 

The  portrait  facing  p.  79  is  from  a  Daguerreotype 
by  Claudet,  the  property  of  Mrs.  Faraday,  taken 
when  her  husband  was  about  fifty  years  old.  Its 
position  in  the  book  has  been  chosen  with  reference 
to  his  age. 

JOHN   TYNDALL. 

ROYAL  INSTITUTION: 
2lst  Feb.  1868. 


ivioG7892 


CONTENTS. 


PAGE 
PARENTAGE — INTRODUCTION    TO    THE     ROYAL    INSTITUTION — 

EARLIEST    EXPERIMENTS — FIRST    ROYAL    SOCIETY    PAPER — 
MARRIAGE       .  1 


EARLY  RESEARCHES — MAGNETIC  ROTATIONS — LIQUEFACTION 
OF  GASES — HEAVY  GLASS — CHARLES  ANDERSON — CONTRIBU- 
TIONS TO  PHYSICS  .  .  V  •  ;  '  .  .12 

DISCOVERY  OF  MAGNETO-ELECTRICITY  —  EXPLANATION  OF 
ARAGO'S  MAGNETISM  OF  ROTATION — TERRESTRIAL  MAG- 
NETO-ELECTRIC INDUCTION — THE  EXTRA  CURRENT  .  .  19 

POINTS   OF   CHARACTER  ';',.  .  .  .  .30 

IDENTITY  OF  ELECTRICITIES — FIRST  RESEARCHES  ON  ELECTRO- 
CHEMISTRY .  .  .  .  .  .  .41 

LAWS   OF  ELECTRO-CHEMICAL  DECOMPOSITION  .  .      53 

ORIGIN   OF  POWER  IN   THE  VOLTAIC   PILE  .•  .  .59 

RESEARCHES  ON  FRICTIONAL  ELECTRICITY — INDUCTION — CON- 
DUCTION —  SPECIFIC  INDUCTIVE  CAPACITY  —  THEORY  OF 
CONTIGUOUS  PARTICLES  ,  66 


yiii  CONTENTS. 

PAGE 
REST  NEEDED — VISIT   TO   SWITZERLAND  .  .      '          .      75 


MAGNETIZATION   OP  LIGHT         .  ...      79 

DISCOVERY  OP  DIAMAGNET1SM— RESEARCHES  ON  MAGNE-CRYS- 

TALLIC  ACTION  ....  .89 

SUPPLEMENTARY  REMARKS  .....  101 
MAGNETISM  OP  FLAME  AND  GASES — ATMOSPHERIC  MAGNETISM  .  108 
SPECULATIONS— NATURE  OP  MATTER— LINES  OP  PORCE  .  119 

UNITY    AND    CONVERTIBILITY   OF    NATURAL    FORCES— THEORY 

OF   THE  ELECTRIC   CURRENT  ....    133 

SUMMARY  .......    145 

ILLUSTRATIONS   OF  CHARACTER  .  .  .147 


FARADAY  AS  A  DISCOVERER. 


PARENTAGE  :  INTRODUCTION  TO  THE  ROYAL  INSTITU- 
TION: EARLIEST  EXPERIMENTS:  FIRST  ROYAL  SOCIETY 
PAPER  :  MARRIAGE. 

IT  has  been  thought  desirable  to  give  you  and  the 
world  some  image  of  MICHAEL  FARADAY,  as  a  scien- 
tific investigator  and  discoverer.  The  attempt  to 
respond  to  this  desire  has  been  to  me  a  labour  of 
difficulty,  if  also  a  labour  of  love.  For  however  well 
acquainted  I  may  be  with  the  researches  and  dis- 
coveries of  that  great  master — however  numerous  the 
illustrations  which  occur  to  me  of  the  loftiness  of 
Faraday's  character  and  the  beauty  of  his  life — still 
to  grasp  him  and  his  researches  as  a  whole ;  to  seize 
upon  the  ideas  which  guided  him,  and  connected 
them ;  to  gain  entrance  into  that  strong  and  active 
brain,  and  read  from  it  the  riddle  of  the  world — this 
is  a  work  not  easy  of  performance,  and  all  but  impos- 
sible amid  the  distraction  of  duties  of  another  kind. 
That  I  should  at  one  period  or  another  speak  to  you 

B 


2  FAEADAY  AS   A   DISCOVERER. 

regarding  Faraday  and  his  work,  is  natural,  if  not 
inevitable ;  but  I  did  not  expect  to  be  called  upon  to 
speak  so  soon.  Still  the  bare  suggestion  that  this  is 
the  fit  and  proper  time  for  speech  sent  me  imme- 
diately to  my  task:  from  it  I  have  returned  with 
such  results  as  I  could  gather,  and  also  with  the  wish 
that  those  results  were  more  worthy  than  they  are 
of  the  greatness  of  my  theme. 

It  is  not  my  intention  to  lay  before  you  a  life  of 
Faraday  in  the  ordinary  acceptation  of  the  term. 
The  duty  I  have  to  perform  is  to  give  you  some 
notion  of  what  he  has  done  in  the  world ;  dwelling 
incidentally  on  the  spirit  in  which  his  work  was 
executed,  and  introducing  such  personal  traits  as 
may  be  necessary  to  the  completion  of  your  picture 
of  the  philosopher,  though  by  no  means  adequate  to 
give  you  a  complete  idea  of  the  man. 

The  newspapers  have  already  informed  you  that 
Michael  Faraday  was  born  at  Newington  Butts,  on 
September  22,  1791,  and  that  he  fell  finally  asleep  at 
Hampton  Court,  on  August  25,  1867.  Believing,  as 
I  doa  in  the  general  truth  of  the  doctrine  of  here- 
ditary transmission  —  sharing  the  opinion  of  Mr. 
Carlyle,  that  '  a  really  able  man  never  proceeded 
from  entirely  stupid  parents  '  —  I  once  used  the 
privilege  of  my  intimacy  with  Mr.  Faraday  to  ask 
him  whether  his  parents  showed  any  signs  of  un- 


FARADAY  AS   A  DISCOVERER.  3 

usual  ability.  He  could  remember  none.  His  father, 
I  believe,  was  a  great  sufferer  during  the  latter  years 
of  his  life,  and  this  might  have  masked  whatever 
intellectual  power  he  possessed.  When  thirteen 
years  old,  that  is  to  say  in  1804,  Faraday  was 
apprenticed  to  a  bookseller  and  bookbinder  in 
Blandford-street,  Manchester-square:  here  he  spent 
eight  years  of  his  life,  after  which  he  worked  as  a 
journeyman  elsewhere. 

You  have  also  heard  the  account  of  Faraday's  first 
contact  with  the  Royal  Institution;  that  he  was 
introduced  by  one  of  the  members  to  Sir  Humphry 
Davy's  last  lectures;  that  he  took  notes  of  those 
lectures,  wrote  them  fairly  out,  and  sent  them  to 
Davy,  entreating  him  at  the  same  time  to  enable 
him  to  quit  trade,  which  he  detested,  and  to  pursue 
science,  which  he  loved.  Davy  was  helpful  to  the 
young  man,  and  this  should  never  be  forgotten :  he 
at  once  wrote  to  Faraday,  and,  afterwards  when  an 
opportunity  occurred,  made  him  his  assistant.*  Mr. 

*  Here  is  Davy's  recommendation  of  Faraday,  presented  to  the 
managers  of  the  Koyal  Institution,  at  a  meeting  on  the  18th  of  March, 
1813,  Charles  Hatchett,  Esq.,  in  the  chair  :— 

'  Sir  Humphry  Davy  has  the  honour  to  inform  the  managers  that  he 
has  found  a  person  who  is  desirous  to  occupy  the  situation  in  the  Insti- 
tution lately  filled  by  William  Payne.  His  name  is  Michael  Faraday. 
He  is  a  youth  of  twenty-two  years  of  age.  As  far  as  Sir  H.  Davy  has 
been  able  to  observe  or  ascertain,  he  appears  well  fitted  for  the  situa- 
tion. His  habits  seem  good ;  his  disposition  active  and  cheerful,  and 


4  FARADAY  AS  A   DISCOVERER. 

Gassiot  has  lately  favoured  me  with,  the  following 
reminiscence  of  this  time  : — 

'  Clapham  Common,  Surrey, 

'  November  28,  1867. 

6  MY  DEAR  TYNDALL, — Sir  H.  Davy  was  accustomed 
to  call  on  the  late  Mr.  Pepys,  in  the  Poultry,  on  his 
way  to  the  London  Institution,  of  which  Pepys  was 
one  of  the  original  managers ;  the  latter  told  me  that 
on  one  occasion  Sir  H.  Davy,  showing  him  a  letter, 
said,  "  Pepys,  what  am  I  to  do,  here  is  a  letter  from 
a  young  man  named  Faraday ;  he  has  been  attending 
my  lectures,  and  wants  me  to  give  him  employment 
at  the  Eayal  Institution— what  can  I  do?"  "  Do  ?  " 
replied  Pepys,  "put  him  to  wash  bottles;  if  he  is 
good  for  anything  he  will  do  it  directly,  if  he  refuses 
he  is  good  for  nothing."  "  No,  no,"  replied  Davy;  "  we 
must  try  him  with  something  better  than  that."  The 
result  was,  that  Davy  engaged  him  to  assist  in  the 
Laboratory  at  weekly,  wages. 

6  Davy  held  the  joint  office  of  Professor  of  Chemis- 
try and  Director  of  the  Laboratory;  he  ultimately 
gave  up  the  former  to  the  late  Professor  Brande,  but 
he  insisted  that  Earaday  should  be  appointed  Direc- 
tor of  the  Laboratory,  and,  as  Faraday  told  me,  this 

his  manner  intelligent.     He  is  willing  to  engage  himself  on  the  same 
terms  as  given  to  Mr.  Payne  at  the  time  of  quitting  the  Institution. 

'  Resolved, — That  Michael  Faraday  be  engaged  to  fill  the  situation 
lately  occupied  by  Mr.  Payne,  on  the  same  terms.' 


FARADAY   AS   A   DISCOVERER.  5 

enabled  him  on  subsequent  occasions  to  hold  a  defi- 
nite position  in  the  Institution,  in  which  he  was 
always  supported  by  Davy.  I  believe  he  held  tha* 
office  to  the  last. 

6  Believe  me,  my  dear  Tyndall,  yours  truly, 

'  J.  P.  GrASSIOT. 
'Dr.  Tyndall.' 

From  a  letter  written  by  Faraday  himself  soon 
after  his  appointment  as  Davy's  assistant,  I  extract 
the  following  account  of  his  introduction  to  the  Royal 

Institution : — 

'London,  Sept.  13,  1813. 

cAs  for  myself,  I  am  absent  (from  home)  nearly 
day  and  night,  except  occasional  calls,  and  it  is  likely 
shall  shortly  be  absent  entirely,  but  this  (having 
nothing  more  to  say,  and  at  the  request  of  my 
mother)  I  will  explain  to  you.  I  was  formerly  a 
bookseller  and  binder,  but  am  now  turned  philoso- 
pher,* which  happened  thus : — Whilst  an  apprentice, 
I,  for  amusement,  learnt  a  little  chemistry  and  other 
parts  of  philosophy,  and  felt  an  eager  desire  to  pro- 
ceed in  that  way  further.  After  being  a  journeyman 
for  six  months,  under  a  disagreeable  master,  I  gave 
up  my  business,  and  through  the  interest  of  a  Sir  H. 
Davy,  filled  the  situation  of  chemical  assistant  to  the 

*  Paraday  loved  this  word  and  employed  it  to  the  last ;  he  had  an 
intense  dislike  to  the  modern  term  physicist. 


6  FARADAY  AS  A  DISCOVERER. 

Royal  Institution  of  Great  Britain,  in  which  office  I 
now  remain ;  and  where  I  am  constantly  employed  in 
observing  the  works  of  nature,  and  tracing  the  man- 
ner in  which  she  directs  the  order  and  arrangement 
of  the  world.  I  have  lately  had  proposals  made  to 
me  by  Sir  Humphry  Davy  to  accompany  him  in  his 
travels  through  Europe  and  Asia,  as  philosophical 
assistant.  If  I  go  at  all  I  expect  it  will  be  in  October 
next — about  the  end ;  and  my  absence  from  home  will 
perhaps  be  as  long  as  three  years.  But  as  yet  all  is 
uncertain.' 

This  account  is  supplemented  by  the  following 
letter,  written  by  Faraday  to  his  friend  De  la  Rive,* 
on  the  occasion  of  the  death  of  Mrs.  Marcet.  The 
letter  is  dated  Sept.  2,  1858  :— 

c  MY  DEAR  FRIEND, — Your  subject  interested  me 
deeply  every  way;  for  Mrs.  Marcet  was  a  good 
friend  to  me,  as  she  must  have  been  to  many  of  the 
human  race.  I  entered  the  shop  of  a  bookseller  and 
bookbinder  at  the  age  of  13,  in  the  year  1804, 
remained  there  eight  years,  and  during  the  chief 
part  of  the  time  bound  books.  Now  it  was  in  those 
books,  in  the  hours  after  work,  that  I  found  the  be- 
ginning of  my  philosophy.  There  were  two  that 
especially  helped  me,  the  "Encyclopaedia  Britannica," 

*  To  whom  I  am  indebted  for  a  copy  of  the  original  letter. 


FARADAY   AS   A   DISCOVERER.  7 

from  which.  I  gained  my  first  notions  of  electricity, 
and  Mrs.  Marcet's  "  Conversations  on  Chemistry," 
which  gave  me  my  foundation  in  that  science. 

'  Do  not  suppose  that  I  was  a  very  deep  thinker, 
or  was  marked  as  a  precocious  person.  I  was  a  very 
lively  imaginative  person,  and  could  believe  in  the 
"  Arabian  Nights "  as  easily  as  in  the  "  Encyclo- 
psedia."  But  facts  were  important  to  me,  and  saved 
me.  I  could  trust  a  fact,  and  always  cross-examined 
an  assertion.  So  when  I  questioned  Mrs.  Marcet's 
book  by  such  little  experiments  as  I  could  find  means 
to  perform,  and  found  it  true  to  the  facts  as  I  could 
understand  them,  I  felt  that  I  had  got  hold  of  an 
anchor  in  chemical  knowledge,  and  clung  fast  to  it. 
Thence  my  deep  veneration  for  Mrs.  Marcet — first 
as  one  who  had  conferred  great  personal  good  and 
pleasure  on  me ;  and  then  as  one  able  to  convey  the 
truth  and  principle  of  those  boundless  fields  of  know- 
ledge which  concern  natural  things,  to  the  young, 
untaught,  and  inquiring  mind. 

'You  may  imagine  my  delight  when  I  came  to 
know  Mrs.  Marcet  personally ;  how  often  I  cast  my 
thoughts  backward,  delighting  to  connect  the  past 
and  the  present ;  how  often,  when  sending  a  paper 
to  her  as  a  thank-offering,  I  thought  of  my  first 
instructress,  and  such  like  thoughts  will  remain 
with  me. 


8  FARADAY   AS   A   DISCOVERER. 

'  I  have  some  such  thoughts  even  as  regards  your 
own  father  ;  who  was,  I  may  say,  the  first  who  per- 
sonally at  Geneva,  and  afterwards  by  correspondence, 
encouraged,  and  by  that  sustained,  me.' 

Twelve  or  thirteen  years  ago  Mr.  Faraday  and 
myself  quitted  the  Institution  one  evening  together, 
to  pay  a  visit  in  Baker-street.  He  took  my  arm  at 
the  door,  and,  pressing  it  to  his  side  in  his  warm 
genial  way,  said,  c  Come,  Tyndall,  I  will  now  show 
you  something  that  will  interest  you.'  We  walked 
northwards,  passed  the  house  of  Mr.  Babbage,  which 
drew  forth  a  reference  to  the  famous  evening  parties 
once  assembled  there.  We  reached  Blandford-street, 
and  after  a  little  looking  about,  he  paused  before 
a  stationer's  shop,  and  then  went  in.  On  entering 
the  shop,  his  usual  animation  seemed  doubled; 
he  looked  rapidly  at  everything  it  contained.  To 
the  left  on  entering  was  a  door,  through  which  he 
looked  down  into  a  little  room,  with  a  window 
in  front  facing  Blandford-street.  Drawing  me  to- 
wards him,  he  said  eagerly,  'Look  there,  Tyndall, 
that  was  my  working-place.  I  bound  books  in  that 
little  nook.'  A  respectable-looking  woman  stood 
behind  the  counter :  his  conversation  with  me  was 
too  low  to  be  heard  by  her,  and  he  now  turned  to  the 
counter  to  bny  some  cards  as  an  excuse  for  our  being 
there.  He  asked  the  woman  her  name — her  prede- 


FARADAY   AS   A   DISCOVERER.  9 

cessor's  name — his  predecessor's  name.  f  That  won't 
do/  he  said,  with  good-humoured  impatience ;  '  who 
was  his  .  predecessor  ? '  '  Mr.  Riebau,'  she  replied, 
and  immediately  added,  as  if  suddenly  recollecting 
herself,  £He,  sir,  was  the  master  of  Sir  Charles 
Faraday.5  ( Nonsense  ! '  he  responded,  ( there  is  no 
such  person.'  Great  was  her  delight  when  I  told 
her  the  name  of  her  visitor ;  but  she  assured  me  that 
as  soon  as  she  saw  him  running  about  the  shop,  she 
felt — though  she  did  not  know  why — that  it  must  be 
'  Sir  Charles  Faraday.' 

Faraday  did,  as  you  know,  accompany  Davy  to 
Rome :  he  was  re-engaged  by  the  managers  of  the 
Royal  Institution  on  May  15,  1815.  Here  he  made 
rapid,  progress  in  chemistry,  and  after  a  time  was 
entrusted  with  easy  analyses  by  Davy.  In  those 
days  the  Eoyal  Institution  published  '  The  Quarterly 
Journal  of  Science,'  the  precursor  of  our  own  '  Pro- 
ceedings.' Faraday's  first  contribution  to  science 
appeared  in  that  journal  in  1816.  It  was  an  analysis 
of  some  caustic  lime  from  Tuscany,  which  had  been 
sent  to  Davy  by  the  Duchess  of  Montrose.  Between 
this  period  and  1818  various  notes  and  short  papers 
were  published  by  Faraday.  In  1818  he  experi- 
mented upon  '  Sounding  Flames.'  Professor  Auguste 
De  la  Rive,  father  of  our  present  excellent  De  la 
Rive,  had  investigated  those  sounding  flames,  and 


10  FAEADAY  AS  A  DISCOVERER. 

had  applied  to  them  an  explanation  which  com- 
pletely accounted  for  a  class  of  sounds  discovered  by 
De  la  Eive  himself.  By  a  few  simple  and  conclusive 
experiments,  Faraday  proved  that  the  explanation 
was  insufficient.  It  is  an  epoch  in  the  life  of  a  young 
man,  when  he  finds  himself  correcting  a  person  of 
eminence,  and  in  Faraday's  case,  where  its  effect 
was  to  develop  a  modest  self-trust,  such  an  event 
could  not  fail  to  act  profitably. 

From  time  to  time  between  1818  and  1820  Faraday 
published  scientific  notes  and  notices  of  minor  weight. 
At  this  time  he  was  acquiring,  not  producing ;  work- 
ing hard  for  his  master  and  storing  and  strengthen- 
ing his  own  mind.  He  assisted  Mr.  Brande  in  his 
lectures,  and  so  quietly,  skilfully,  and  modestly  was 
his  work  done,  that  Mr.  Brande's  vocation  at  the 
time  was  pronounced  '  lecturing  on  velvet.'  In  1820 
Faraday  published  a  chemical  paper  '  on  two  new 
compounds  of  chlorine  and  carbon,  and  on  a  new 
compound  of  iodine,  carbon,  and  hydrogen.  This 
paper  was  read  before  the  Royal  Society  on  December 
21,  1820,  and  it  was  the  first  of  his  that  was  honoured 
with  a  place  in  the  '  Philosophical  Transactions.' 

On  June  12,  1821,  he  married,  and  obtained  leave 
to  bring  his  young  wife  into  his  rooms  at  the  Eoyal 
Institution.  There  for  forty-six  years  they  lived  to- 
gether, occupying  the  suite  of  apartments  which  had 


FARADAY  AS   A  DISCOVERER.  11 

been  previously  in  the  successive  occupancy  of  Young, 
Davy,  and  Brande.  At  the  time  of  her  marriage  Mrs. 
Faraday  was  twenty-one  years  of  age,  he  being  nearly 
thirty.  Regarding  this  marriage  I  will  at  present 
limit  myself  to  quoting  an  entry  written  in  Faraday's 
own  hand  in  his  book  of  diplomas,  which  caught  my 
eye  while  in  his  company  some  years  ago.  It  ran 
thus : — 

'  25th  January,  1847. 

'  Amongst  these  records  and  events,  I  here  insert 
the  date  of  one  which,  as  a  source  of  honour  and 
happiness,  far  exceeds  all  the  rest.  We  were  married 

on  June  12,  1821. 

c  M.  FARADAY.' 

Then  follows  the  copy  of  the  minutes,  dated  May 
21,  1821,  which  gave  him  additional  rooms,  and  thus 
enabled  him  to  bring  his  wife  to  the  Royal  Institu- 
tion. A  feature  of  Faraday's  character  which  I  have 
often  noticed  makes  itself  apparent  in  this  entry.  In 
his  relations  to  his  wife  he  added  chivalry  to  affection. 


12  FARADAY   AS  A   DISCOVERER. 


EAELY  EESEAECHES  :  MAGNETIC  ROTATIONS  :  LIQUE- 
FACTION OP  GASES  :  HEAVY  GLASS  :  CHAELES  AN- 
DEESON:  CONTEIBUTIONS  TO  PHYSICS. 

OEESTED,  in  1820,  discovered  the  action  of  a  voltaic 
current  on  a  magnetic  needle ;  and  immediately 
afterwards  the  splendid  intellect  of  Ampere  suc- 
ceeded in  showing  that  every  magnetic  phenomenon 
then  known  might  be  reduced  to  the  mutual  action 
of  electric  currents.  The  subject  occupied  all  men's 
thoughts  ;  and  in  this  country  Dr.  Wollaston  sought 
to  convert  the  deflection  of  the  needle  by  the  current 
into  a  permanent  rotation  of  the  needle  round  the 
current.  He  also  hoped  to  produce  the  reciprocal 
effect  of  causing  a  current  to  rotate  round  a  magnet. 
In  the  early  part  of  1821,  Wollaston  attempted  to 
realise  this  idea  in  the  presence  of  Sir  Humphry 
Davy  in  the  laboratory  of  the  Eoyal  Institution. 
This  was  well  calculated  to  attract  Faraday's  atten- 
tion to  the  subject.  He  read  much  about  it ;  and  in 
the  months  of  July,  August,  and  September,  he  wrote 
e  a  history  of  the  progress  of  electro-magnetism/ 
which  he  published  in  Thomson's  ( Annals  of  Phi- 
losophy.' Soon  afterwards  he  took  up  the  subject  of 
(  Magnetic  Eotations,'  and  on  the  morning  of  Christ- 
mas-day, 1821,  he  called  his  wife  to  witness  for  the 


FAEADAY   AS   A   DISCOVERER.  13 

first  time,  the  revolution  of  a  magnetic  needle  round 
an  electric  current.  Incidental  to  the  '  historic 
sketch/  he  repeated  almost  all  the  experiments  there 
referred  to ;  and  these,  added  to  his  own  subsequent 
work,  made  him  practical  master  of  all  that  was 
then  known  regarding  the  voltaic  current.  In  1821, 
he  also  touched  upon  a  subject  which  subsequently 
received  his  closer  attention — the  vaporization  of 
mercury  at  common  temperatures  ;  and  immediately 
afterwards  conducted,  in  company  with  Mr.  Stodart, 
experiments  on  the  alloys  of  steel.  He  was  accus- 
tomed in  after  years  to  present  to  his  friends  razors 
formed  from  one  of  the  alloys  then  discovered. 

During  Faraday's  hours  of  liberty  from  other 
duties,  he  took  up  subjects  of  inquiry  for  himself; 
and  in  the  spring  of  1823,  thus  self-prompted,  he 
began  the  examination  of  a  substance  which  had 
long  been  regarded  as  the  chemical  element  chlorine, 
in  a  solid  form,  but  which  Sir  Humphry  Davy,  in 
1810,  had  proved  to  be  a  hydrate  of  chlorine,  that  is, 
a  compound  of  chlorine  and  water.  Faraday  first 
analysed  this  hydrate,  and  wrote  out  an  account  of 
its  composition.  This  account  was  looked  over  by 
Davy,  who  suggested  the  heating  of  the  hydrate 
under  pressure  in  a  sealed  glass  tube.  This  was 
done.  The  hydrate  fused  at  a  blood-heat,  the  tube 
became  filled  with  a  yellow  atmosphere,  and  was 


14  FARADAY   AS   A   DISCOVERER. 

found  to  contain  two  liquid  substances.  Dr.  Paris 
happened  to  enter  the  laboratory  while  Faraday  was 
at  work.  Seeing  the  oily  liquid  in  his  tube,  he  rallied 
the  young  chemist  for  his  carelessness  in  employing 
soiled  vessels.  On  filing  off  the  end  of  the  tube,  its 
contents  exploded  and  the  oily  matter  vanished. 
Early  next  morning,  Dr.  Paris  received  the  following 
note : — 

6  DEAR  SIR, — The  oil  you  noticed  yesterday  turns 
out  to  be  liquid  chlorine. 

c  Tours  faithfully, 

<  M.  FARADAY.'  * 

The  gas  had  been  liquefied  by  its  own  pressure.  Fa- 
raday then  tried  compression  with  a  syringe,  and 
succeeded  thus  in  liquefying  the  gas. 

To  the  published  account  of  this  experiment  Davy 
added  the  following  note : — c  In  desiring  Mr.  Faraday 
to  expose  the  hydrate  of  chlorine  in  a  closed  glass 
tube,  it  occurred  to  me  that  one  of  three  things  would 
happen :  that  it  would  become  fluid  as  a  hydrate ; 
that  decomposition  of  water  would  occur;  ...  or 
that  the  chlorine  would  separate  in  a  fluid  state.' 
Davy,  moreover,  immediately  applied  the  method  of 
self-compressing  atmospheres  to  the  liquefaction  of 
muriatic  gas.  Faraday  continued  the  experiments, 

*  Paris  :  Life  of  Davy,  p.  391. 


FARADAY  AS   A   DISCOVERER.  15 

and  succeeded  in  reducing  a  number  of  gases  till 
then  deemed  permanent  to  the  liquid  condition.  In 
1844  he  returned  to  the  subject,  and  considerably 
expanded  its  limits.  These  important  investiga- 
tions established  the  fact  that  gases  are  but  the 
vapours  of  liquids  possessing  a  very  low  boiling-point, 
and  gave  a  sure  basis  to  our  views  of  molecular  ag- 
gregation. The  account  of  the  first  investigation 
was  read  before  the  Eoyal  Society  on  April  10,  1823, 
and  was  published,  in  Faraday's  name,  in  the  '  Phi- 
losophical Transactions.'  The  second  memoir  was 
sent  to  the  Eoyal  Society  on  December  19,  1844.  I 
may  add  that  while  he  was  conducting  his  first  ex- 
periments on  the  liquefaction  of  gases,  thirteen  pieces 
of  glass  were  on  one  occasion  driven  by  an  explosion 
into  Faraday's  eye. 

Some  small  notices  and  papers,  including  the 
observation  that  glass  readily  changes  colour  in 
sunlight,  follow  here.  In  1825  and  1826  Faraday 
published  papers  in  the  ( Philosophical  Transactions ' 
on  '  new  compounds  of  carbon  and  hydrogen,'  and 
on  *  sulphonaphthalic  acid.'  In  the  former  of  these 
papers  he  announced  the  discovery  of  Benzol,  which, 
in  the  hands  of  modern  chemists,  has  become  the 
foundation  of  our  splendid  aniline  dyes.  But  he 
swerved  incessantly  from  chemistry  into  physics; 
and  in  1826  we  find  him  engaged  in  investigating 


16  FAEADAY  AS   A  DISCOVERED. 

the  limits  of  vaporization,  and  showing,  by  exceed- 
ingly strong  and  apparently  conclusive  arguments, 
that  even  in  the  case  of  mercury  such  a  limit  exists ; 
much  more  he  conceived  it  to  be  certain  that  our 
atmosphere  does  not  contain  the  vapour  of  the  fixed 
constituents  of  the  earth's  crust.  This  question,  I 
may  say,  is  likely  to  remain  an  open  one.  Dr. 
Eankine,  for  example,  has  lately  drawn  attention  to 
the  odour  of  certain  metals ;  whence  comes  this 
odour,  if  it  be  not  from  the  vapour  of  the  metal  ? 

In  1825  Faraday  became  a  member  of  a  com- 
mittee, to  which  Sir  John  Herschel  and  Mr.  Dollond 
also  belonged,  appointed  by  the  Eoyal  Society  to 
examine,  and  if  possible  improve,  the  manufacture 
of  glass  for  optical  purposes.  Their  experiments 
continued  till  1829,  when  the  account  of  them  con- 
stituted the  subject  of  a  '  Bakerian  Lecture.'  This 
lectureship,  founded  in  1774  by  Henry  Baker,  Esq., 
of  the  Strand,  London,  provides  that  every  year  a 
lecture  shall  be  given  before  the  Eoyal  Society,  the 
sum  of  four  pounds  being  paid  to  the  lecturer.  The 
Bakerian  Lecture,  however,  has  long  since  passed 
from  the  region  of  pay  to  that  of  honour,  papers  of 
mark  only  being  chosen  for  it  by  the  council  of  the 
Society.  Faraday's  first  Bakerian  Lecture,  f  On  the 
Manufacture  of  Glass  for  Optical  Purposes,'  was  de- 
livered at  the  close  of  1829.  It  is  a  most  elaborate 


FAEADAY   AS   A   DISCOVEKER.  17 

and  conscientious  description  of  processes,  pre- 
cautions, and  results  :  the  details  were  so  exact  and 
so  minute,  and  the  paper  consequently  so  long,  thai 
three  successive  sittings  of  the  Eoyal  Society  were 
taken  up  by  the  delivery  of  the  lecture.*  This  glass 
did  not  turn  out  to  be  of  important  practical  use, 
but  it  happened  afterwards  to  be  the  foundation  of 
two  of  Faraday's  greatest  discoveries. f 

The  experiments  here  referred  to,  were  commenced 
at  the  Falcon  Glass  Works,  on  the  premises  of  Messrs. 
Green  and  Pellatt,  but  Faraday  could  not  conveniently 
attend  to  them  there.  In  1827,  therefore,  a  furnace 
was  erected  in  the  yard  of  the  Eoyal  Institution  ;  and 
it  was  at  this  time,  and  with  a  view  of  assisting  him 
at  the  furnace,  that  Faraday  engaged  Sergeant  An- 
derson, of  the  Royal  Artillery,  the  respectable,  truth- 
ful, and  altogether  trustworthy  man  whose  appearance 

*  Vis.  November  19,  December  3  and  10. 

t  I  make  the  following  extract  from  a  letter  from  Sir  John  Herschel, 
•written  to  me  from  Collingwood,  on  the  3rd  of  November,  1867 : — 

'  I  will  take  this  opportunity  to  mention  that  I  believe  myself  to  have 
originated  the  suggestion  of  the  employment  of  borate  of  lead  for  optical 
purposes.  It  was  somewhere  in  the  year  1822,  as  well  as  I  can  re- 
collect, that  I  mentioned  it  to  Sir  James  (then  Mr.)  South  ;  and,  in  con- 
sequence, the  trial  was  made  in  his  laboratory  in  Blackman  Street,  by 
precipitating  and  working  a  large  quantity  of  borate  of  lead,  and  fusing 
it  under  a  muffle  in  a  porcelain  evaporating  dish.  A  very  limpid 
(though  slightly  yellow)  glass  resulted,  the  refractive  index  1-866! 
(which  you  will  find  set  down  in  my  table  of  refractive  indices  in  my 
article  "  Light,"  Encyclopedia  Metropolitans).  It  was,  however,  too  soft 
for  optical  use  as  an  object-glass.  This  Faraday  overcame,  at  least  to 
a  considerable  degree,  by  the  introduction  of  silica.' 

C 


18  FARADAY   AS   A   DISCOVERER. 

here  is  so  fresh  in  our  memories.  Anderson  con- 
tinued to  be  the  reverential  helper  of  Faraday  and 
the  faithful  servant  of  this  Institution  for  nearly 
forty  years.* 

In  1831  Faraday  published  a  paper  '  On  a  peculiar 
class  of  Optical  Deceptions,'  to  which  I  believe  the 
beautiful  optical  toy  called  the  Chromatrope  owes  its 
origin.  In  the  same  year  he  published  a  paper  011 
Vibrating  Surfaces,  in  which  he  solved  an  acoustical 
problem  which,  though  of  extreme  simplicity  when 
solved,  appears  to  have  baffled  many  eminent  men. 
The  problem  was  to  account  for  the  fact  that  light 
bodies,  such  as  the  seed  of  lycopodium,  collected  at 
the  vibrating  parts  of  sounding  plates,  while  sand 
ran  to  the  nodal  lines.  Faraday  showed  that  the 
light  bodies  were  entangled  in  the  little  whirlwinds 
formed  in  the  air  over  the  places  of  vibration,  and 
through  which  the  heavier  sand  was  readily  projected. 
Faraday's  resources  as  an  experimentalist  were  so 
wonderful,  and  his  delight  in  experiment  was  so 
great,  that  he  sometimes  almost  ran  into  excess  in 

*  Regarding  Anderson,  Faraday  writes  thus  in  1845 : — '  I  cannot 
resist  the  occasion  that  is  thus  offered  to  me  of  mentioning  the  name  of 
Mr.  Anderson,  who  came  to  me  as  an  assistant  in  the  glass  experiments, 
and  has  remained  ever  since  in  the  laboratory  of  the  Royal  Institution. 
He  assisted  me  in  all  the  researches  into  which  I  have  entered  since 
that  time ;  and  to  his  care,  steadiness,  exactitude,  and  faithfulness  in 
the  performance  of  all  that  has  been  committed  to  his  charge,  I  am 
much  indebted. — M.IY  (Erp.  Researches,  vol.  iii.  p.  3,  footnote.) 


FAKADAY   AS   A   DISCOVERER.  19 

this  direction.  I  have  heard  him  say  that  this  paper 
on  vibrating  surfaces  was  too  heavily  laden  with 
experiments. 


DISCOVERY  OP  MAGNETO-ELECTRICITY:  EXPLANATION 
OP  ARAGO'S  MAGNETISM  OP  ROTATION  :  TERRES- 
TRIAL MAGNETO-ELECTRIC  INDUCTION:  THE  EXTRA 
CURRENT. 

The  work  thus  far  referred  to,  though  sufficient  of 
itself  to  secure  no  mean  scientific  reputation,  forms 
but  the  vestibule  of  Faraday's  achievements.  He  had 
been  engaged  within  these  walls  for  eighteen  years.* 
During  part  of  the  time  he  had  drunk  in  knowledge 
from  Davy,  and  during  the  remainder  he  continually 
exercised  his  capacity  for  independent  inquiry.  In 
1831  we  have  him  at  the  climax  of  his  intellectual 
strength,  forty  years  of  age,  stored  with  knowledge 
and  full  of  original  power.  Through  reading,  lec- 
turing, and  experimenting,  he  had  become  thoroughly 
familiar  with  electrical  science :  he  saw  where  light 
was  needed  and  expansion  possible.  The  phenomena 
of  ordinary  electric  induction  belonged,  as  it  were,  to 
the  alphabet  of  his  knowledge  :  he  knew  that  under 
ordinary  circumstances  the  presence  of  an  electrified 
body  was  sufficient  to  excite,  by  induction,  an  une- 

*  He  used  to  say  that  it  required  twenty  years  of  work  to  make  a 
man  in  Physical  Science  ;  the  previous  period  being  one  of  infancy. 

c  2 


20  FARADAY  AS  A   DISCOVERER. 

lectrified  body.  He  knew  that  the  wire  which  carried 
an  electric  current  was  an  electrified  body,  and  still 
that  all  attempts  had  failed  to  make  it  excite  in 
other  wires  a  state  similar  to  its  own. 

What  was  the  reason  of  this  failure  ?  Faraday 
never  could  work  from  the  experiments  of  others, 
however  clearly  described.  He  knew  well  that  from 
every  experiment  issues  a  kind  of  radiation,  lumi- 
nous in  different  degrees  to  different  minds,  and 
he  hardly  trusted  himself  to  reason  upon  an  ex- 
periment that  he  had  not  seen.  In  the  autumn  of 
1831  he  began  to  repeat  the  experiments  with 
electric  currents,  which,  up  to  that  time,  had  pro- 
duced no  positive  result.  And  here,  for  the  sake  of 
younger  inquirers,  if  not  for  the  sake  of  us  all,  it  is 
worth  while  to  dwell  for  a  moment  on  a  power  which 
Faraday  possessed  in  an  extraordinary  degree.  He 
united  vast  strength  with  perfect  flexibility.  His 
momentum  was  that  of  a  river,  which  combines 
weight  and  directness  with  the  ability  to  yield  to 
the  flexures  of  its  bed.  The  intentness  of  his  vision 
in  any  direction  did  not  apparently  diminish  his 
power  of  perception  in  other  directions ;  and  when 
he  attacked  a  subject,  expecting  results,  he  had  the 
faculty  of  keeping  his  mind  alert,  so  that  results 
different  from  those  which  he  expected  should  not 
escape  him  through  pre-occupation. 


FARADAY   AS  A  DISCOVERER.  21 

He  began  his  experiments  'on  the  induction  of 
electric  currents '  by  composing  a  helix  of  two  insu- 
lated wires,  which  were  wound  side  by  side  round 
the  same  wooden  cylinder.  One  of  these  wires  he 
connected  with  a  voltaic  battery  of  ten  cells,  and  the 
other  with  a  sensitive  galvanometer.  When  con- 
nection with  the  battery  was  made,  and  while  the 
current  flowed,  no  effect  whatever  was  observed  at 
the  galvanometer.  But  he  never  accepted  an  experi- 
mental result,  until  he  had  applied  to  it  the  utmost 
power  at  his  command.  He  raised  his  battery  from 
10  cells  to  120  cells,  but  without  avail.  The  current 
flowed  calmly  through  the  battery  wire  without  pro- 
ducing, during  its  flow,  any  sensible  result  upon  the 
galvanometer. 

6  During  its  flow,'  and  this  was  the  time  when  an 
effect  was  expected — but  here  Faraday's  power  of 
lateral  vision,  separating,  as  it  were,  from  the  line  of 
expectation,  came  into  play — he  noticed  that  a  feeble 
movement  of  the  needle  always  occurred  at  the  mo- 
ment when  he  made  contact  with  the  battery ;  that 
the  needle  would  afterwards  return  to  its  former  posi- 
tion and  remain  quietly  there  unaffected  by  the 
flowing  current.  At  the  moment,  however,  when  the 
circuit  was  interrupted  the  needle  again  moved,  and 
in  a  direction  opposed  to  that  observed  on  the  com- 
pletion of  the  circuit. 


22  FAKADAY   AS   A   DISCOVERER. 

This  result,  and  others  of  a  similar  kind,  led  him 
to  the  conclusion  '  that  the  battery  current  through 
the  one  wire  did  in  reality  induce  a  similar  current 
through  the  other ;  but  that  it  continued  for  an  in- 
stant only,  and  partook  more  of  the  nature  of  the 
electric  wave  from  a  common  Ley  den  jar  than  of  the 
current  from  a  voltaic  battery.'  The  momentary 
currents  thus  generated  were  called  induced  currents, 
while  the  current  which  generated  them  was  called 
the  inducing  current.  It  was  immediately  proved  that 
the  current  generated  at  making  the  circuit  was 
always  opposed  in  direction  to  its  generator,  while 
that  developed  on  the  rupture  of  the  circuit  coin- 
cided in  direction  with  the  inducing  current.  It 
appeared  as  if  the  current  on  its  first  rush  through 
the  primary  wire  sought  a  purchase  in  the  secondary 
one,  and,  by  a  kind  of  kick,  impelled  backward 
through  the  latter  an  electric  wave,  which  subsided 
as  soon  as  the  primary  current  was  fully  established. 

Faraday,  for  a  time,  believed  that  the  secondary 
wire,  though  quiescent  when  the  primary  current 
had  been  once  established,  was  not  in  its  natural 
condition,  its  return  to  that  condition  being  declared 
by  the  current  observed  at  breaking  the  circuit.  He 
called  this  hypothetical  state  of  the  wire  the  electro- 
tonic  state  :  he  afterwards  abandoned  this  hypothesis, 
but  seemed  to  return  to  it  in  later  life.  The  term 


FARADAY   AS   A   DISCOVERER.  23 

electro-tonic  is  also  preserved  by  Professor  Du  Bois 
Eeymond  to  express  a  certain  electric  condition  of 
the  nerves,  and  Professor  Clerk  Maxwell  has  ably 
denned  and  illustrated  the  hypothesis  in  the  Tenth 
Volume  of  the  '  Transactions  of  the  Cambridge 
Philosophical  Society.' 

The  mere  approach  of  a  wire  forming  a  closed 
curve  to  a  second  wire  through  which  a  voltaic  cur- 
rent flowed  was  then  shown  by  Faraday  to  be  suf- 
ficient to  arouse  in  the  neutral  wire  an  induced 
current,  opposed  in  direction  to  the  inducing  cur- 
rent; the  withdrawal  of  the  wire  also  generated  a 
current  having  the  same  direction  as  the  inducing 
current ;  those  currents  existed  only  during  the  time 
of  approach  or  withdrawal,  and  when  neither  the 
primary  nor  the  secondary  wire  was  in  motion,  no 
matter  how  close  their  proximity  might  be,  no  in- 
duced current  was  generated. 

Faraday  has  been  called  a  purely  inductive  philo- 
sopher. A  great  deal  of  nonsense  is,  I  fear,  uttered 
in  this  land  of  England  about  induction  and  deduc- 
tion. Some  profess  to  befriend  the  one,  some  the 
other,  while  the  real  vocation  of  an  investigator,  like 
Faraday,  consists  in  the  incessant  marriage  of  both. 
He  was  at  this  time  full  of  the  theory  of  Ampere, 
and  it  cannot  be  doubted  that  numbers  of  his  ex- 
periments were  executed  merely  to  test  his  deductions 


^  FARADAY  AS   A   DISCOVERER. 

from  that  theory.  Starting  from  the  discovery  of 
Oersted,  the  celebrated  French  philosopher  had 
shown  that  all  the  phenomena  of  magnetism  then 
known  might  be  reduced  to  the  mutual  attractions 
and  repulsions  of  electric  currents.  Magnetism  had 
been  produced  from  electricity,  and  Faraday,  who  all 
his  life  long  entertained  a  strong  belief  in  such  re- 
ciprocal actions,  now  attempted  to  effect  the  evolu- 
tion of  electricity  from  magnetism.  Eound  a  welded 
iron  ring  he  placed  two  distinct  coils  of  covered  wire, 
causing  the  coils  to  occupy  opposite  halves  of  the 
ring.  Connecting  the  ends  of  one  of  the  coils  with  a 
galvanometer,  he  found  that  the  moment  the  ring- 
was  magnetized,  by  sending  a  current  through  the 
other  coil,  the  galvanometer  needle  whirled  round 
four  or  five  times  in  succession.  The  action,  as 
before,  was  that  of  a  pulse,  which  vanished  imme- 
diately. On  interrupting  the  circuit,  a  whirl  of  the 
needle  in  the  opposite  direction  occurred.  It  was 
only  during  the  time  of  magnetization  or  demagne- 
tization that  these  effects  were  produced.  The  in- 
duced currents  declared  a  change  of  condition  only, 
and  they  vanished  the  moment  the  act  of  magnetiza- 
tion or  demagnetization  was  complete. 

The  effects  obtained  with  the  welded  ring  were 
also  obtained  with  straight  bars  of  iron.  Whether 
the  bars  were  magnetized  by  the  electric  current,  or 


FAKADAY   AS   A   DISCOVERER.  25 

were  excited  by  the  contact  of  permanent  steel  mag- 
netSj  induced  currents  were  always  generated  during 
the  rise,  and  during  the  subsidence  of  the  magnetism. 
The  use  of  iron  was  then  abandoned,  and  the  same 
effects  were  obtained  by  merely  thrusting  a  perma- 
nent steel  magnet  into  a  coil  of  wire.  A  rush  of 
electricity  through  the  coil  accompanied  the  inser- 
tion of  the  magnet ;  an  equal  rush  in  the  opposite 
direction  accompanied  its  withdrawal.  The  precision 
with  which  Faraday  describes  these  results,  and  the 
completeness  with  which  he  defines  the  boundaries  of 
his  fact's,  are  wonderful.  The  magnet,  for  example, 
must  not  be  passed  quite  through  the  coil,  but  only 
half  through,  for  if  passed  wholly  through,  the 
needle  is  stopped  as  by  a  blow,  and  then  he  shows 
how  this  blow  results  from  a  reversal  of  the  electric 
wave  in  the  helix.  He  next  operated  with  the  power- 
ful permanent  magnet  of  the  Royal  Society,  and  ob- 
tained with  it,  in  an  exalted  degree,  all  the  foregoing- 
phenomena. 

And  now  he  turned  the  light  of  these  discoveries 
upon  the  darkest  physical  phenomenon  of  that  day. 
Aragp  had  discovered  in  1824,  that  a  disk  of  non- 
magnetic metal  had  the  power  of  bringing  a  vibrating 
magnetic  needle  suspended  over  it  rapidly  to  rest; 
and  that  on  causing  the  disk  to  rotate  the  magnetic 
needle  rotated  along  with  it.  When  both  were 


26  FARADAY   AS   A   DISCOVERER. 

quiescent,  there  was  not  the  slightest  measurable 
attraction  or  repulsion  exerted  between  the  needle 
and  the  disk;  still  when  in  motion  the  disk  was 
competent  to  drag  after  it,  not  only  a  light  needle, 
but  a  heavy  magnet.  The  question  had  been  probed 
and  investigated  with  admirable  skill  by  both  Arago 
and  Ampere,  and  Poisson  had  published  a  theoretic 
memoir  on  the  subject ;  but  no  cause  could  be 
assigned  for  so  extraordinary  an  action.  It  had  also 
been  examined  in  this  country  by  two  celebrated  men, 
Mr.  Babbage  and  Sir  John  Herschel ;  but  it  still  re- 
mained a  mystery.  Faraday  always  recommended  the 
suspension  of  judgment  in  cases  of  doubt.  '  I  have 
always  admired,'  he  says,  '  the  prudence  and  philo- 
sophical reserve  shown  by  M.  Arago  in  resisting  the 
temptation  to  give  a  theory  of  the  effect  he  had  dis- 
covered, so  long  as  he  could  not  devise  one  which 
was  perfect  in  its  application,  and  in  refusing  to 
assent  to  the  imperfect  theories  of  others.'  Now, 
however,  the  time  for  theory  had  come.  Faraday 
saw  mentally  the  rotating  disk,  under  the  operation 
of  the  magnet,  flooded  with  his  induced  currents, 
and  from  the  known  laws  of  interaction  between  cur- 
rents and  magnets  he  hoped  to  deduce  the  motion 
observed  by  Arago.  That  hope  he  realised,  showing 
by  actual  experiment  that  when  his  disk  rotated 
currents  passed  through  it,  their  position  and  direc- 


FARADAY   AS   A   DISCOVERER.  27 

tion  being  such  as  must,  in  accordance  with  the 
established  laws  of  electro- magnetic  action,  produce 
the  observed  rotation. 

Introducing  the  edge  of  his  disk  between  the 
poles  of  the  large  horseshoe  magnet  of  the  Eoyal 
Society,  and  connecting  the  axis  and  the  edge  of  the 
disk,  each  by  a  wire  with  a  galvanometer,  he  ob- 
tained, when  the  disk  was  turned  round,  a  constant 
flow  of  electricity.  The  direction  of  the  current  was 
determined  by  the  direction  of  the  motion,  the  cur- 
rent being  reversed  when  the  rotation  was  reversed. 
He  now  states  the  law  which  rules  the  production 
of  currents  in  both  disks  and  wires,  and  in  so  doing 
uses,  for  the  first  time,  a  phrase  which  has  since 
become  famous.  When  iron  filings  are  scattered 
over  a  magnet,  the  particles  of  iron  arrange  them- 
selves in  certain  determinate  lines  called  magnetic 
curves.  In  1831,  Faraday  for  the  first  time  called 
these  curves  6  lines  of  magnetic  force; '  and  he  showed 
that  to  produce  induced  currents  neither  approach 
to  nor  withdrawal  from  a  magnetic  source,  or  centre, 
or  pole,  was  essential,  but  that  it  was  only  necessary 
to  cut  appropriately  the  lines  of  magnetic  force. 
Faraday's  first  paper  on  Magneto-electric  Induction, 
which  I  have  here  endeavoured  to  condense,  was  read 
before  the  Eoyal  Society  on  the  24th  of  November, 
1831. 


28  FAKADAY  AS   A  DISCOVERER. 

On  January  12,  1832,  be  communicated  to  the 
Boyal  Society  a  second  paper  on  Terrestrial  Magneto- 
electric  Induction,  which  was  chosen  as  the  Bakerian 
Lecture  for  the  year.  He  placed  a  bar  of  iron  in  a 
coil  of  wire,  and  lifting  the  bar  into  the  direction 
of  the  dipping  needle,  he  excited  by  this  action  a 
current  in  the  coil.  On  reversing  the  bar,  a  current 
in  the  opposite  direction  rushed  through  the  wire. 
The  same  effect  was  produced,  when,  on  holding  the 
helix  in  the  line  of  dip,  a  bar  of  iron  was  thrust  into 
it.  Here,  however,  the  earth  acted  on  the  coil 
through  the  intermediation  of  the  bar  of  iron.  He 
abandoned  the  bar  and  simply  set  a  copper-plate 
spinning  in  a  horizontal  plane  ;  he  knew  that  the 
earth's  lines  of  magnetic  force  then  crossed  the  plate 
at  an  angle  of  about  70°.  When  the  plate  spun 
round,  the  lines  of  force  were  intersected  and  induced 
currents  generated,  which  produced  their  proper 
effect  when  carried  from,  the  plate  to  the  galvano- 
meter. 'When  the  plate  was  in  the  magnetic 
meridian,  or  in  any  other  plane  coinciding  with  the 
magnetic  dip,  then  its  rotation  produced  no  effect 
upon  the  galvanometer.' 

At  the  suggestion  of  a  mind  fruitful  in  suggestions 
of  a  profound  and  philosophic  character — I  mean 
that  of  Sir  John  Herschel — Mr.  Barlow,  of  Woolwich, 
had  experimented  with  a  rotating  iron  shell.  Mr. 


FARADAY   AS   A   DISCOVERER.  29 

Christie  had  also  performed  an  elaborate  series  of 
experiments  on  a  rotating  iron  disk.  Both  of  them 
had  found  that  when  in  rotation  the  body  exercised 
a  peculiar  action  upon  the  magnetic  needle,  deflect- 
ing it  in  a  manner  which  was  not  observed  during 
quiescence ;  but  neither  of  them  was  aware  at  the 
time  of  the  agent  which  produced  this  extraordinary 
deflection.  They  ascribed  it  to  some  change  in  the 
magnetism  of  the  iron  shell  and  disk. 

But  Faraday  at  once  saw  that  his  induced  currents 
must  come  into  play  here,  and  he  immediately  ob- 
tained them  from  an  iron  disk.  With  a  hollow  brass 
ball,  moreover,  he  produced  the  effects  obtained  by 
Mr.  Barlow.  Iron  was  in  no  way  necessary:  the 
only  condition  of  success  was  that  the  rotating  body 
should  be  of  a  character  to  admit  of  the  formation 
of  currents  in  its  substance :  it  must,  in  other  words, 
be  a  conductor  of  electricity.  The  higher  the  con- 
ducting power  the  more  copious  were  the  currents. 
He  now  passes  from  his  little  brass  globe  to  the  globe 
of  the  earth.  He  plays  like  a  magician  with  the 
earth's  magnetism.  He  sees  the  invisible  lines  along 
which  its  magnetic  action  is  exerted,  and  sweeping 
his  wand  across  these  lines  evokes  this  new  power. 
Placing  a  simple  loop  of  wire  round  a  magnetic 
needle  he  bends  its  upper  portion  to  the  west :  the 
north  pole  of  the  needle  immediately  swerves  to  the 


30  FARADAY  AS   A   DISCOVERER. 

east:  he  bends  his  loop  to  the  east,  and  the  north 
pole  moves  to  the  west.  Suspending  a  common  bar 
magnet  in  a  vertical  position,  he  causes  it  to  spin 
round  its  own  axis.  Its  pole  being  connected  with 
one  end  of  a  galvanometer  wire,  and  its  equator  with 
the  other  end,  electricity  rushes  round  the  galvano- 
meter from  the  rotating  magnet.  He  remarks  upon 
the  '  singular  independence '  of  the  magnetism  and  the 
body  of  the  magnet  which  carries  it.  The  steel  be- 
haves as  if  it  were  isolated  from  its  own  magnetism. 
And  then  his  thoughts  suddenly  widen,  and  he 
asks  himself  whether  the  rotating  earth  does  not 
generate  induced  currents  as  it  turns  round  its  axis 
from  west  to  east.  In  his  experiment  with  the  twirl- 
ing magnet  the  galvanometer  wire  remained  at  rest ; 
one  portion  of  the  circuit  was  in  motion  relatively 
to  another  portion.  But  in  the  case  of  the  twirling 
planet  the  galvanometer  wire  would  necessarily  be 
carried  along  with  the  earth ;  there  would  be  no  rela- 
tive motion.  What  must  be  the  consequence  ?  Take 
the  case  of  a  telegraph  wire  with  its  two  terminal 
plates  dipped  into  the  earth,  and  suppose  the  wire 
to  lie  in  the  magnetic  meridian.  The  ground  under- 
neath the  wire  is  influenced  like  the  wire  itself  by  the 
earth's  rotation ;  if  a  current  from  south  to  north  be 
generated  in  the  wire,  a  similar  current  from  south 
to  north  would  be  generated  in  the  earth  under  the 


FARADAY   AS   A   DISCOVERER.  31 

wire ;    these  currents  would  run  against   the  same 
terminal  plate,  and  thus  neutralize  each  other. 

This  inference  appears  inevitable,  but  his  profound 
vision  perceived  its  possible  invalidity.  He  saw  that 
it  was  at  least  possible  that  the  difference  of  con- 
ducting power  between  the  earth  and  the  wire  might 
give  one  an  advantage  over  the  other,  and  that  thus 
a  residual  or  differential  current  might  be  obtained. 
He  combined  wires  of  different  materials,  and  caused 
them  to  act  in  opposition  to  each  other :  but  found 
the  combination  ineffectual.  The  more  copious  flow 
in  the  better  conductor  was  exactly  counterbalanced 
by  the  resistance  of  the  worst.  Still,  though  ex- 
periment was  thus  emphatic,  he  would  clear  his  mind 
of  all  discomfort  by  operating  on  the  earth  itself. 
He  went  to  the  round  lake  near  Kensington  Palace, 
and  stretched  480  feet  of  copper  wire,  north  and 
south,  over  the  lake,  causing  plates  soldered  to  the 
wire  at  its  ends  to  dip  into  the  water.  The  copper 
wire  was  severed?  at  the  middle,  and  the  severed  ends 
connected  with  a  galvanometer.  ~No  effect  whatever 
was  observed.  But  though  quiescent  water  gave  no 
effect,  moving  water  might.  He  therefore  worked  at 
London  Bridge  for  three  days  during  the  ebb  and 
flow  of  the  tide,  but  without  any  satisfactory  result. 
Still  he  urges,  'Theoretically  it  seems  a  necessary 
consequence,  that  where  water  is  flowing  there  elec- 


32  FAEADAY  AS  A   DISCOVEREE. 

trie  currents  should  be  formed.  If  a  line  be  imagined 
passing  from  Dover  to  Calais  through  the  sea,  and 
returning  through  the  land,  beneath  the  water,  to 
Dover,  it  traces  out  a  circuit  of  conducting  matter 
one  part  of  which,  when  the  water  moves  up  or 
down  the  channel,  is  cutting  the  magnetic  curves  of 
the  earth,  whilst  the  other  is  relatively  at  rest. 
.  .  .  There  is  every  reason  to  believe  that  currents 
do  run  in  the  general  direction  of  the  circuit  des- 
cribed, either  one  way  or  the  other,  according  as  the 
passage  of  the  waters  is  up  or  down  the  Channel.' 
This  was  written  before  the  submarine  cable  was 
thought  of,  and  he  once  informed  me  that  actual 
observation  upon  that  cable  had  been  found  to  be 
in  accordance  with  his  theoretic  deduction.* 

*  I  am  indebted  to  a  friend  for  the  following  exquisite  morsel : — '  A 
short  time  after  the  publication  of  Faraday's  first  researches  in  magneto- 
electricity,  he  attended  the  meeting  of  the  British  Association  at  Oxford, 
in  1832. — On  this  occasion  he  was  requested  by  some  of  the  authorities 
to  repeat  the  celebrated  experiment  of  eliciting  a  spark  from  a  magnet, 
employing  for  this  purpose  the  large  magnet  in  the  Ashmolean  Museum. 
To  this  he  consented,  and  a  large  party  assembled  to  witness  the  ex- 
periments, which,  I  need  not  say,  were  perfectly  successful.  Whilst  he 
was  repeating  them  a  dignitary  of  the  University  entered  the  room,  and 
addressing  himself  to  Prof essorDani ell,  who  was  standing  near  Faraday, 
inquired  what  was  going  on.  The  Professor  explained  to  him  as  popu- 
larly as  possible  this  striking  result  of  Faraday's  great  discovery.  The 
Dean  listened  with  attention  and  looked  earnestly  at  the  brilliant  spark, 
but  a  moment  after  he  assumed  a  serious  countenance  and  shook  his 
head;  "I  am  sorry  for  it,"  said  he,  as  he  walked  away;  in  the  middle 
of  the  room  he  stopped  for  a  moment  and  repeated,  "  I  am  sorry  for  it ;  " 
then  walking  towards  the  door,  when  the  handle  was  in  his  hand  he 


FAEADAY  AS  A   DISCOVERER.  33 

Three  years  subsequent  to  the  publication  of  these 
researches,  that  is  to  say  on  January  29,  1835, 
Faraday  read  before  the  Eoyal  Society  a  paper  '  On 
the  influence  by  induction  of  an  electric  current 
upon  itself.'  A  shock  and  spark  of  a  peculiar  cha- 
racter had  been  observed  by  a  young  man  named 
William  Jen  kin,  who  must  have  been  a  youth  of 
some  scientific  promise,  but  who,  as  Faraday  once 
informed  me,  was  dissuaded  by  his  own  father  from 
having  anything  to  do  with  science.  The  investi- 
gation of  the  fact  noticed  by  Mr.  Jenkin  led  Faraday 
to  the  discovery  of  the  extra  current,  or  the  current 
induced  in  the  primary  wire  itself  at  the  moments  of 
making  and  breaking  contact,  the  phenomena  of 
which  he  described  and  illustrated  in  the  beautiful 
and  exhaustive  paper  referred  to. 

Seven-and-thirty  years  have  passed  since  the  dis- 
covery of  magneto-electricity ;  but,  if  we  except  the 
extra  current,  until  quite  recently  nothing  of  moment 
was  added  to  the  subject.  Faraday  entertained  the 
opinion  that  the  discoverer  of  a  great  law  or  principle 
had  a  right  to  the  'spoils' — this  was  his  term — 


turned  round  and  said,  "  Indeed  I  am  sorry  for  it ;  it  is  putting  new 
arms  into  the  hands  of  the  incendiary."  This  occurred  a  short  time  after 
the  papers  had  been  filled  with  the  doings  of  the  hayrick  burners.  An. 
erroneous  statement  of  what  fell  from  the  Dean's  mouth  was  printed  at 
the  time  in  one  of  the  Oxford  papers.  He  is  there  wrongly  stated  to 
have  said,  "It  is  putting  new  arms  into  the  hands  of  the  infidel." ' 

D 


34  FARADAY  AS   A   DISCOVERER. 

arising  from  its  illustration;  and  guided  by  the  prin- 
ciple lie  had  discovered,  his  wonderful  mind,  aided  by 
his  wonderful  ten  fingers,  overran  in  a  single  autumn 
this  vast  domain,  and  hardly  left  behind  him  the 
shred  of  a  fact  to  be  gathered  by  his  successors. 

And  here  the  question  may  arise  in  some  minds, 
What  is  the  use  of  it  all  ?  The  answer  is,  that  if 
man's  intellectual  nature  thirsts  for  knowledge,  then 
knowledge  is  useful  because  it  satisfies  this  thirst. 
If  you  demand  practical  ends,  you  must,  I  think, 
expand  your  definition  of  the  term  practical,  and 
make  it  include  all  that  elevates  and  enlightens  the 
intellect,  as  well  as  all  that  ministers  to  the  bodily 
health  and  comfort  of  men.  Still,  if  needed,  an 
answer  of  another  kind  might  be  given  to  the 
question  '  what  is  its  use?'  As  far  as  electricity  has 
been  applied  for  medical  purposes,  it  has  been  almost 
exclusively  Faraday's  electricity.  You  have  noticed 
those  lines  of  wire  which  cross  the  streets  of  London. 
It  is  Faraday's  currents  that  speed  from  place  to 
place  through  these  wires.  Approaching  the  point 
of  Dungeness,  the  mariner  sees  an  unusually  brilliant 
light,  and  from  the  noble  phares  of  La  Heve  the  same 
light  flashes  across  the  sea.  These  are  Faraday's 
sparks  exalted  by  suitable  machinery  to  sunlike 
splendour.  At  the  present  moment  the  Board  of 
Trade  and  the  Brethren  of  the  Trinity  House,  as 


FARADAY  AS   A   DISCOVERER.  35 

well  as  the  Commissioners  of  Northern  Lights,  are 
contemplating  the  introduction  of  the  Magneto-elec- 
tric Light  at  numerous  points  upon  our  coasts ;  and 
future  generations  will  be  able  to  refer  to  those 
guiding  stars  in  answer  to  the  question,  what  has 
been  the  practical  use  of  the  labours  of  Faraday  ? 
But  I  would  again  emphatically  say,  that  his  work 
needs  no  such  justification,  and  that  if  he  had  al- 
lowed his  vision  to  be  disturbed  by  considerations 
regarding  the  practical  use  of  his  discoveries,  those 
discoveries  would  never  have  been  made  by  him.  *  I 
have  rather,'  he  writes  in  1831,  *  been  desirous  of  dis- 
covering new  facts  and  new  relations  dependent  on 
magneto-electric  induction,  than  of  exalting  the  force 
of  those  already  obtained;  being  assured  that  the 
latter  would  find  their  full  development  hereafter.' 

In  1817,  when  lecturing  before  a  private  society  in 
London  on  the  element  chlorine,  Faraday  thus  ex- 
pressed himself  with  reference  to  this  question  of 
utility.  £  Before  leaving  this  subject,  I  will  point  out 
the  history  of  this  substance,  as  an  answer  to  those 
who  are  in  the  habit  of  saying  to  every  new  fact, 
"  What  is  its  use  ? "  Dr.  Franklin  says  to  such, 
"  What  is  the  use  of  an  infant  ?  "  The  answer  of  the 
experimentalist  is,  "  Endeavour  to  make  it  useful." 
When  Scheele  discovered  this  substance,  it  appeared 
to  have  no  use ;  it  was  in  its  infancy  and  useless 

D  2 


36  FARADAY  AS  A   DISCOVERER. 

state,  but  having  grown  up  to  maturity,  witness  its 
powers,  and  see  what  endeavours  to  make  it  useful 
have  done.5 

POINTS     OP     CHAEACTEE. 

A  point  highly  illustrative  of  the  character  of 
Faraday  now  comes  into  view.  He  gave  an  account 
of  his  discovery  of  Magneto-electricity  in  a  letter 
to  his  friend  M.  Hachette,  of  Paris,  who  communi- 
cated the  letter  to  the  Academy  of  Sciences.  The 
letter  was  translated  and  published  ;  and  immediately 
afterwards  two  distinguished  Italian  philosophers 
took  up  the  subject,  made  numerous  experiments,  and 
published  their  results  before  the  complete  memoirs 
of  Faraday  had  met  the  public  eye.  This  evidently 
irritated  him.  He  reprinted  the  paper  of  the  learned 
Italians  in  the  '  Philosophical  Magazine/  accom- 
panied by  sharp  critical  notes  from  himself.  He  also 
wrote  a  letter  dated  Dec.  1, 1832,  to  Gay  Lussac,  who 
was  then  one  of  the  editors  of  the  'Annales  de 
Chimie,'  in  which  he  analysed  the  results  of  the 
Italian  philosophers,  pointing  out  their  errors,  and 
defending  himself  from  what  he  regarded  as  impu- 
tations on  his  character.  The  style  of  this  letter  is 
unexceptionable,  for  Faraday  could  not  write  other- 
wise than  as  a  gentleman ;  but  the  letter  shows  that 
had  he  willed  it  he  could  have  hit  hard.  We  have 


FARADAY  AS  A   DISCOVERER.  37 

heard  much  of  Faraday's  gentleness  and  sweetness 
and  tenderness.  It  is  all  true,  but  it  is  very  incom- 
plete. You  cannot  resolve  a  powerful  nature  into 
these  elements,  and  Faraday's  character  would  have 
been  less  admirable  than  it  was  had  it  not  embraced 
forces  and  tendencies  to  which  the  silky  adjectives 
c  gentle '  and  '  tender '  would  by  no  means  apply. 
Underneath  his  sweetness  and  gentleness  was  the 
heat  of  a  volcano.  He  was  a  man  of  excitable  and 
fiery  nature  ;  but  through  high  self-discipline  he  had 
converted  the  fire  into  a  central  glow  and  motive 
power  of  life,  instead  of  permitting  it  to  waste  itself 
in  useless  passion.  '  He  that  is  slow  to  anger,'  saith 
the  sage,  '  is  greater  than  the  mighty,  and  he  that 
ruleth  his  own  spirit  than  he  that  taketh  a  city.' 
Faraday  was  not  slow  to  anger,  but  he  completely 
ruled  his  own  spirit,  and  thus,  though  he  took  no 
cities,  he  captivated  all  hearts. 

As  already  intimated,  Faraday  had  contributed 
many  of  his  minor  papers  —  including  his  first 
analysis  of  caustic  lime — to  the  e  Quarterly  Journal 
of  Science.'  In  1832,  he  collected  those  papers  and 
others  together  in  a  small  octavo  volume,  labelled 
them,  and  prefaced  them  thus : — 

'PAPERS,  NOTES,  NOTICES,  &c.  &c., 
published  in  octavo, 

np  to  1832. 
M.  FARADAY.' 


38  FARADAY   AS   A    DISCOVERER. 

'  Papers  of  mine,  published  in  octavo,  in  the  "  Quar- 
terly Journal  of  Science,"  and  elsewhere,  since  the 
time  that  Sir  H.  Davy  encouraged  me  to  write  the 
analysis  of  caustic  lime. 

'  Some,  I  think  (at  this  date),  are  good ;  others 
moderate;  and  some  bad.  But  I  have  put  all  into 
the  volume,  because  of  the  utility  they  have  been  of 
to  me — and  none  more  than  the  bad — in  pointing 
out  to  me  in  future,  or  rather,  after  times,  the  faults 
it  became  me  to  watch  and  to  avoid. 

£  As  I  never  looked  over  one  of  my  papers  a  year 
after  it  was  written  without  believing  both  in  philo- 
sophy and  manner  it  could  have  been  much  better 
done.  I  still  hope  the  collection  may  be  of  great  use 
to  me. 

'  M.  FAKADAY. 

'Aug.  18,  1832.' 

c  JSTone  more  than  the  bad  ! '  This  is  a  bit  of 
Faraday's  innermost  nature;  and  as  I  read  these 
words  I  am  almost  constrained  to  retract  what  I 
have  said  regarding  the  fire  and  excitability  of  his 
character.  But  is  he  not  all  the  more  admirable, 
through  his  ability  to  tone  down  and  subdue  that  fire 
and  that  excitability,  so  as  to  render  himself  able  to 
write  thus  as  a  little  child  ?  I  once  took  the  liberty 
of  censuring  the  conclusion  of  a  letter  of  his  to  the 


FARADAY   AS  A   DISCOVEREK.  39 

Dean  of  St.  Paul's.  He  subscribed  himself  '  humbly 
yours,'  and  I  objected  to  the  adverb.  c  Well,  but, 
Tyndall,'  he  said,  '  I  am  humble  ;  and  still  it  would 
be  a  great  mistake  to  think  that  I  am  not  also 
proud.'  This  duality  ran  through  his  character.  A 
democrat  in  his  defiance  of  all  authority  which 
unfairly  limited  his  freedom  of  thought,  and  still 
ready  to  stoop  in  reverence  to  all  that  was  really 
worthy  of  reverence,  in  the  customs  of  the  world  or 
the  characters  of  men. 

And  here,  as  well  as  elsewhere,  may  be  introduced 
a  letter  which  bears  upon  this  question  of  self- 
control,  written  long  years  subsequent  to  the  period 
at  which  we  have  now  arrived.  I  had  been  at 
Glasgow  in  1855,  at  a  meeting  of  the  British 
Association.  On  a  certain  day,  I  communicated  a 
paper  to  the  physical  section,  which  was  followed  by 
a  brisk  discussion.  Men  of  great  distinction  took 
part  in  it,  the  late  Dr.  Whewell  among  the  number, 
and  it  waxed  warm  on  both  sides.  I  was  by  no 
means  content  with  this  discussion ;  and  least  of  all, 
with  my  own  part  in  it.  This  discontent  affected  me 
for  some  days,  during  which  I  wrote  to  Faraday, 
giving  him  no  details,  but  expressing,  in  a  general 
way,  my  dissatisfaction.  I  give  the  following  extract 
from  his  reply : — 


40  FARADAY   AS   A   DISCOVERER. 

'  Sydenham,  6th  Oct.,  1855. 

CMT  DEAK  TYNDALL, — These  great  meetings,  of 
which  I  think  very  well  altogether,  advance  science 
chiefly  by  bringing  scientific  men  together  and  making 
them  to  know  and  be  friends  with  each  other ;  and  I 
am  sorry  when  that  is  not  the  effect  in  every  part  of 
their  course.  I  know  nothing  except  from  what  you 
tell  me,  for  I  have  not  yet  looked  at  the  reports  of 
the  proceedings ;  but  let  me,  as  an  old  man,  who 
ought  by  this  time  to  have  profited  by  experience,  say 
that  when  I  was  younger  I  found  I  often  misinterpret- 
ed the  intentions  of  people,  and  found  they  did  not 
mean  what  at  the  time  I  supposed  they  meant ;  and, 
further,  that  as  a  general  rule,  it  was  better  to  be  a 
little  dull  of  apprehension  where  phrases  seemed  to 
imply  pique,  and  quick  in  perception  when,  on  the 
contrary,  they  seemed  to  imply  kindly  feeling.  The 
real  truth  never  fails  ultimately  to  appear ;  and  op- 
posing parties,  if  WTong,  are  sooner  convinced  when 
replied  to  forbearingly,  than  when  overwhelmed.  All 
I  mean  to  say  is,  that  it  is  better  to  be  blind  to  the 
results  of  partisanship,  and  quick  to  see  good  will. 
One  has  more  happiness  in  oneself  in  endeavouring 
to  follow  the  things  that  make  for  peace.  You  can 
hardly  imagine  how  often  I  have  been  heated  in 
private  when  opposed,  as  I  have  thought  unjustly 


FAEADAY   AS  A   DISCO  VEEEE.  41 

and  superciliously,  and  yet  I  have  striven,  and  suc- 
ceeded I  hcpe,  in  keeping  down  replies  of  the  like 
kind.  And  I  know  I  have  never  lost  by  it.  I  would 
not  say  all  this  to  you  did  I  not  esteem  you  as  a  true 
philosopher  and  friend.* 

'  Yours,  very  truly, 

CM.  FAEADAY.' 


IDENTITY    OP    ELECTRICITIES  :    FIEST    EESEAECHES    ON 
ELECTEO-CHEMISTEY. 

I  have  already  once  used  the  word  e  discomfort '  in 
reference  to  the  occasional  state  of  Faraday's  mind 
when  experimenting.  It  was  to  him  a  discomfort  to 
reason  upon  data  which  admitted  of  doubt.  He 
hated  what  he  called  c  doubtful  knowledge,'  and  ever 
tended  either  to  transfer  it  into  the  region  of  un- 
doubtful  knowledge,  or  of  certain  and  definite  igno- 
rance. Pretence  of  all  kinds,  whether  in  life  or  in 
philosophy,  was  hateful  to  him.  He  wished  to  know 
the  reality  of  our  nescience  as  well  as  of  our  science. 


*  Faraday  -would  have  been  rejoiced  to  learn  that,  during  its  last 
meeting  at  Dundee,  the  British  Association  illustrated  in  a  striking 
manner  the  function  which  he  here  describes  as  its  principal  one.  In 
my  own  case,  a  brotherly  welcome  was  everywhere  manifested.  In 
fact,  the  differences  of  really  honourable  and  sane  men  are  never  beyond 
healing. 


42  FARADAY   AS   A    DISCOVERER. 

6  Be  one  thing  or  the  other,'  he  seemed  to  say  to  an 
unproved  hypothesis  ;  '  come  out  as  a  solid  truth,  or 
disappear  as  a  convicted  lie.5  After  making  the 
great  discovery  which  I  have  attempted  to  describe, 
a  doubt  seemed  to  beset  him  as  regards  the  identity 
of  electricities.  *  Is  it  right/  he  seemed  to  ask,  '  to 
call  this  agency  which  I  have  discovered  electricity 
at  all  ?  Are  there  perfectly  conclusive  grounds  for 
believing  that  the  electricity  of  the  machine,  the  pile, 
the  gymnotus  and  torpedo,  magneto-electricity  and 
thermo-electricity,  are  merely  different  manifesta- 
tions of  one  and  the  same  agent  ? '  To  answer  this 
question  to  his  own  satisfaction  he  formally  reviewed 
the  knowledge  of  that  day.  He  added  to  it  new 
experiments  of  his  own,  and  finally  decided  in  favour 
of  the  c  Identity  of  Electricities.'  His  paper  upon 
this  subject  was  read  before  the  Royal  Society  on 
January  the  10th  and  17th,  1833. 

After  he  had  proved  to  his  own  satisfaction  the 
identity  of  electricities,  he  tried  to  compare  them 
quantitatively  together.  The  terms  quantity  and  in- 
tensity, which  Faraday  constantly  used,  need  a  word 
of  explanation  here.  He  might  charge  a  single  Ley- 
den  jar  by  twenty  turns  of  his  machine,  or  he  might 
charge  a  battery  of  ten  jars  by  the  same  number  of 
turns.  The  quantity  in  both  cases  would  be  sensibly 
the  same,  but  the  intensity  of  the  single  jar  would  be 


FARADAY   AS   A   DISCOVERER.  43 

the  greatest,  for  here  the  electricity  would  be  less 
diffused.  Faraday  first  satisfied  himself  that  the 
needle  of  his  galvanometer  was  caused  to  swing 
through  the  same  arc  by  the  same  quantity  of  ma- 
chine electricity,  whether  it  was  condensed  in  a  small 
battery  or  diffused  over  a  large  one.  Thus  the  elec- 
tricity developed  by  thirty  turns  of  his  machine  pro- 
duced, under  very  variable  conditions  of  battery  sur- 
face, the  same  deflections.  Hence  he  inferred  the 
possibility  of  comparing  as  regards  quantity,  elec- 
tricities which  differ  greatly  from  each  other  in 
intensity. 

His  object  now  is  to  compare  frictional  with  vol- 
taic electricity.  Moistening  bibulous  paper  with  the 
iodide  of  potassium — a  favourite  test  of  his — and 
subjecting  it  to  the  action  of  machine  electricity, 
he  decomposed  the  iodide,  and  formed  a  brown  spot 
where  the  iodine  is  liberated.  Then  he  immersed  two 
wires,  one  of  zinc,  the  other  of  platinum,  each  TVth 
of  an  inch  in  diameter,  to  a  depth  of  -fths  of  an 
inch  in  acidulated  water  during  eight  beats  of  his 
watch,  or  ¥3¥ths  of  a  second;  and  found  that  the  needle 
of  his  galvanometer  swung  through  the  same  arc,  and 
coloured  his  moistened  paper  to  the  same  extent,  as 
thirty  turns  of  his  large  electrical  machine.  Twenty- 
eight  turns  of  the  machine  produced  an  effect  dis- 
tinctly less  than  that  produced  by  his  two  wires. 


44  FARADAY  AS  A  DISCOVERER. 

Now,  the  quantity  of  water  decomposed  by  the  wires 
in  this  experiment  totally  eluded  observation  ;  it  was 
immeasurably  small;  and  still  that  amount  of  de- 
composition involved  the  development  of  a  quantity 
of  electric  force  which,  if  applied  in  a  proper  form, 
would  kill  a  rat,  and  no  man  would  like  to  bear  it. 

In  his  subsequent  researches  £  On  the  absolute 
Quantity  of  Electricity  associated  with  the  Particles 
or  Atoms  of  matter,'  he  endeavours  to  give  an  idea 
of  the  amount  of  electrical  force  involved  in  the  de- 
composition of  a  single  .grain  of  water.  He  is  al- 
most afraid  to  mention  it,  for  he  estimates  it  at 
800,000  discharges  of  his  large  Leyden  battery. 
This,  if  concentrated  in  a  single  discharge,  would  be 
equal  to  a  very  great  flash  of  lightning ;  while  the 
chemical  action  of  a  single  grain  of  water  on  four 
grains  of  zinc  would  yield  electricity  equal  in  quan- 
tity to  a  powerful  thunderstorm.  Thus  his  mind 
rises  from  the  minute  to  the  vast,  expanding  involun- 
tarily from  the  smallest  laboratory  fact  till  it  em- 
braces the  largest  and  grandest  natural  phenomena.* 

*  Buff  finds  the  quantity  of  electricity  associated  with  one  milli- 
gramme of  hydrogen  in  water,  to  be  equal  to  45,480  charges  of  a  Leyden 
jar,  with  a  height  of  480  millimetres,  and  a  diameter  of  160  millimetres. 
Weber  and  Kohlrausch  have  calculated  that  if  the  quantity  of  electricity 
associated  with  one  milligramme  of  hydrogen  in  water,  were  diffused 
over  a  cloud  at  a  height  of  1,000  metres  above  the  earth,  it  would  exert 
upon  an  equal  quantity  of  the  opposite  electricity  at  the  earth's  surface 
an  attractive  force  of  2,268,000  kilogrammes.  (Electrolytische  Maas- 
i,  1856,  p.  262.) 


FARADAY  AS   A   DISCOVERER.  45 

In  reality,  however,  lie  is  at  this  time  only  clearing 
his  way,  and  he  continues  laboriously  to  clear  it  for 
some  time  afterwards.  He  is  digging  the  shaft, 
guided  by  that  instinct  towards  the  mineral  lode 
which  was  to  him  a  rod  of  divination.  (Er  riecht  die 
Wahrheit,'  said  the  lamented  Kohlrausch,  an  eminent 
German,  once  in  my  hearing : — '  He  smells  the  truth.' 
His  eyes  are  now  steadily  fixed  on  this  wonderful 
voltaic  current,  and  he  must  learn  more  of  its  mode 
of  transmission. 

On  May  23,  1833,  he  read  a  paper  before  the 
Royal  Society  e  On  a  new  Law  of  Electric  Conduc- 
tion.' He  found  that  though  the  current  passed 
through  water,  it  did  not  pass  through  ice : — why 
not,  since  they  are  one  and  the  same  substance? 
Some  years  subsequently  he  answered  this  question 
by  saying  that  the  liquid  condition  enables  the  mole- 
cule of  water  to  turn  round  so  as  to  place  itself  in 
the  proper  line  of  polarization,  while  the  rigidity  of 
the  solid  condition  prevents  this  arrangement.  This 
polar  arrangement  must  precede  decomposition,  and 
decomposition  is  an  accompaniment  of  conduction. 
He  then  passed  on  to  other  substances;  to  oxides  and 
chlorides,  and  iodides,  and  salts,  and  sulphurets,  and 
found  them  all  insulators  when  solid,  and  conductors 
when  fused.  In  all  cases,  moreover,  except  one — 
and  this  exception  he  thought  might  be  apparent 


46  FARADAY  AS   A   DISCOVERER. 

only — he  found  the  passage  of  the  current  across  the 
fused  compound  to  be  accompanied  by  its  decompo- 
sition. Is  then  the  act  of  decomposition  essential  to 
the  act  of  conduction  in  these  bodies  ?  Even  recently 
this  question  was  warmly  contested.  Faraday  was 
very  cautious  latterly  in  expressing  himself  upon  this 
subject ;  but  as  a  matter  of  fact  he  held  that  an  in- 
finitesimal quantity  of  electricity  might  pass  through 
a  compound  liquid  without  producing  its  decomposi- 
tion. De  la  Rive,  who  has  been  a  great  worker  on 
the  chemical  phenomena  of  the  pile,  is  very  emphatic 
on  the  other  side.  Experiment,  according  to  him 
and  others,  establishes  in  the  most  conclusive  man- 
ner that  no  trace  of  electricity  can  pass  through  a 
liquid  compound  without  producing  its  equivalent 
decomposition.* 

Faraday  has  now  got  fairly  entangled  amid  the 
chemical  phenomena  of  the  pile,  and  here  his  pre- 
vious training  under  Davy  must  have  been  of  the 
most  important  service  to  him.  Why,  he  asks, 
should  decomposition  thus  take  place  ? — what  force  is 
it  that  wrenches  the  locked  constituents  of  these 
compounds  asunder?  On  the  20th  of  June,  1833, 
he  read  a  paper  before  the  Eoyal  Society  '  On 
Electro-chemical  Decomposition,'  in  which  he  seeks 
to  answer  these  questions.  The  notion  had  been 

*  Faraday,  sa  Vie  et  ses  Travaux,  p.  20. 


FARADAY   AS   A   DISCOVERER.  47 

entertained  that  the  poles,  as  they  are  called,  of  the 
decomposing  cell,  or  in  other  words  the  surfaces 
by  which  the  current  enters  and  quits  the  liquid, 
exercised  electric  attractions  upon  the  constituents 
of  the  liquid  and  tore  them  asunder.  Faraday 
combats  this  notion  with  extreme  vigour.  Litmus 
reveals,  as  you  know,  the  action  of  an  acid  by 
turning  red,  turmeric  reveals  the  action  of  an  alkali 
by  turning  brown.  Sulphate  of  soda,  you  know,  is  a 
salt  compounded  of  the  alkali  soda  and  sulphuric 
acid.  The  voltaic  current  passing  through  a  solution 
of  this  salt  so  decomposes  it,  that  sulphuric  acid  ap- 
pears at  one  pole  of  the  decomposing  cell  and  alkali 
at  the  other.  Faraday  steeped  a  piece  of  litmus 
paper  and  a  piece  of  turmeric  paper  in  a  solution  of 
sulphate  of  soda  :  placing  each  of  them  upon  a  sepa- 
rate plate  of  glass,  he  connected  them  together  by 
means  of  a  string  moistened  with  the  same  solution. 
He  then  attached  one  of  them  to  the  positive  conduc- 
tor of  an  electric  machine,  and  the  other  to  the  gas- 
pipes  of  this  building.  These  he  called  his  'discharg- 
ing train.'  On  turning  the  machine  the  electricity 
passed  from  paper  to  paper  through  the  string, 
which  might  be  varied  in  -length  from  a  few  inches  to 
seventy  feet  without  changing  the  result.  The  first 
paper  was  reddened,  declaring  the  presence  of  sul- 
phuric acid  ;  the  second  was  browned,  declaring  the 


48  FARADAY  AS   A   DISCOVERER. 

presence  of  the  alkali  soda.  The  dissolved  salt, 
therefore,  arranged  in  this  fashion,  was  decomposed 
by  the  machine,  exactly  as  it  would  have  been  by  the 
voltaic  current.  When  instead  of  using  the  positive 
conductor  he  used  the  negative  ;  the  positions  of  the 
acid  and  alkali  were  reversed.  Thus  he  satisfied 
himself  that  chemical  decomposition  by  the  machine 
is  obedient  to  the  laws  which  rule  decomposition  by 
the  pile. 

And  now  he  gradually  abolishes  those  so-called 
poles,  to  the  attraction  of  which  electric  decom- 
position had  been  ascribed.  He  connected  a  piece  of 
turmeric  paper  moistened  with  the  sulphate  of  soda 
with  the  positive  conductor  of  his  machine  ;  then  he 
placed  a  metallic  point  in  connection  with  his  dis- 
charging train  opposite  the  moist  paper,  so  that  the 
electricity  should  discharge  through  the  air  towards 
the  point.  The  turning  of  the  machine  caused  the 
corners  of  the  piece  of  turmeric  paper  opposite  to  the 
point  to  turn  brown,  thus  declaring  the  presence  of 
alkali.  He  changed  the  turmeric  for  litmus  paper, 
and  placed  it,  not  in  connection  with  his  conductor, 
but  with  his  discharging  train,  a  metallic  point  con- 
nected with  the  conductor  being  fixed  at  a  couple 
of  inches  from  the  paper ;  on  turning  the  machine, 
acid  was  liberated  at  the  edges  and  corners  of  the 
litmus.  He  then  placed  a  series  of  pointed  pieces 


FARADAY  AS  A   DISCOVERER.  49 

of  paper,  each  separate  piece  being  composed  of  two 
halves,  one  of  litmus  and  the  other  of  turmeric 
paper,  and  all  moistened  with  sulphate  of  soda,  in 
the  line  of  the  current  from  the  machine.  The  pieces 
of  paper  were  separated  from  each  other  by  spaces 
of  air.  The  machine  was  turned ;  and  it  was  always 
found  that  at  the  point  where  the  electricity  entered 
the  paper,  litmus  was  reddened,  and  at  the  point 
where  it  quitted  the  paper,  turmeric  was  browned. 
(  Here,'  he  urges,  e  the  poles  are  entirely  abandoned, 
but  we  have  still  electro-chemical  decomposition.' 
It  is  evident  to  him  that  instead  of  being  attracted 
by  the  poles,  the  bodies  separated  are  ejected  by  the 
current.  The  effects  thus  obtained  with  poles  of  air 
he  also  succeeded  in  obtaining  with  poles  of  water. 
The  advance  in  Faraday's  own  ideas  made  at  this 
time  is  indicated  by  the  word  '  ejected.'  He  after- 
wards reiterates  this  view:  the  evolved  substances  are 
expelled  from  the  decomposing  body,  and  '  not  drawn 
out  by  an  attraction.9 

Having  abolished  this  idea  of  polar  attraction,  he 
proceeds  to  enunciate  and  develop  a  theory  of  his 

4 

own.  He  refers  to  Davy's  celebrated  Bakerian  Lec- 
ture, given  in  1806,  which  he  says  '  is  almost  entirely 
occupied  in  the  consideration  of  electro-chemical 
decompositions.'  The  facts  recorded  in  that  lecture 
Faraday  regards  as  of  the  utmost  value.  But  *  the 


50  FARADAY  AS  A   DISCOVERER. 

mode  of  action  by  which  the  effects  take  place  is 
stated  very  generally  ;  so  generally,  indeed,  that 
probably  a  dozen  precise  schemes  of  electro-chemical 
action  might  be  drawn  up,  differing  essentially  from 
each  other,  yet  all  agreeing  with  the  statement  there 
given.' 

It  appears  to  me  that  these  words  might  with 
justice  be  applied  to  Faraday's  own  researches  at 
this  time.  They  furnish  us  with  results  of  perma- 
nent value ;  but  little  h  elp  can  be  found  in  the  theory 
advanced  to  account  for  them.  It  would,  perhaps,  be 
more  correct  to  say  that  the  theory  itself  is  hardly 
presentable  in  any  tangible  form  to  the  intellect. 
Faraday  looks,  and  rightly  looks,  into  the  heart  of 
the  decomposing  body  itself;  he  sees,  and  rightly 
sees,  active  within  it  the  forces  which  produce  the 
» decomposition,  and  he  rejects,  and  rightly  rejects, 
the  notion  of  external  attraction ;  but  beyond  the 
hypothesis  of  decompositions  and  re-compositions, 
enunciated  and  developed  by  Grothuss  and  Davy, 
he  does  not,  I  think,  help  us  to  any  definite  con- 
ception as  to  how  the  force  reaches  the  decomposing 
mass  and  acts  within  it.  Nor,  indeed,  can  this  be 
done,  until  we  know  the  true  physical  process  which 
underlies  what  we  call  an  electric  current. 

Faraday  conceives  of  that  current  as  '  an  axis  of 
power  having  contrary  forces  exactly  equal  in  amount 


FARADAY  AS  A  DISCOVERER.  51 

in  opposite  directions ; '  but  this  definition,  though 
much  quoted  and  circulated,  teaches  us  nothing 
regarding  the  current.  An  i  axis '  here  can  only 
mean  a  direction ;  and  what  we  want  to  be  able  to 
conceive  of  is,  not  the  axis  along  which  the  power 
acts,  but  the  nature  and  mode  of  action  of  the  power 
itself.  He  objects  to  the  vagueness  of  De  la  Eive ; 
but  the  fact  is,  that  both  he  and  De  la  Eive  labour 
under  the  same  difficulty.  Neither  wishes  to  commit 
himself  to  the  notion  of  a  current  compounded  of  two 
electricities  flowing  in  two  opposite  directions ;  but 
the  time  had  not  come,  nor  is  it  yet  come,  for  the 
displacement  of  this  provisional  fiction  by  the  true 
mechanical  conception.  Still,  however  indistinct  the 
theoretic  notions  of  Faraday  at  this  time  may  be, 
the  facts  which  are  rising  before  him  and  around 
him' are  leading  him  gradually,  but  surely,  to  results 
of  incalculable  importance  in  relation  to  the  phi- 
losophy of  the  voltaic  pile. 

He  had  always  some  great  object  of  research  in 
view,  but  in  the  pursuit  of  it  he  frequently  alighted 
on  facts  of  collateral  interest,  to  examine  which  he 
sometimes  turned  aside  from  his  direct  course.  Thus 
we  find  the  series  of  his  researches  on  electro- 
chemical decomposition  interrupted  by  an  inquiry 
into  '  the  power  of  metals  and  other  solids,  to  induce 

E  2 


52  FARADAY  AS   A  DISCOVERER. 

the  combination  of  gaseous  bodies.'  This  in- 
quiry, which,  was  received  by  the  Royal  Society  on 
ISfov.  30,  1833,  though  not  so  important  as  those 
which  precede  and  follow  it,  illustrates  throughout 
his  strength  as  an  experimenter.  The  power  of 
spongy  platinum  to  cause  the  combination  of  oxygen 
and  hydrogen  had  been  discovered  by  Dobereiner  in 
1823,  and  had  been  applied  by  him  in  the  construc- 
tion of  his  well-known  philosophic  lamp.  It  was 
shown  subsequently  by  Dulong  and  Thenard  that 
even  a  platinum  wire,  when  perfectly  cleansed,  may 
be  raised  to  incandescence  by  its  action  on  a  jet  of 
cold  hydrogen. 

In  his  experiments  on  the  decomposition  of  water, 
Faraday  found  that  the  positive  platinum  plate  of 
the  decomposing  cell  possessed  in  an  extraordinary 
degree  the  power  of  causing  oxygen  and  hydrogen  to 
combine.  He  traced  the  cause  of  this  to  the  perfect 
cleanness  of  the  positive  plate.  Against  it  was  libe- 
rated oxygen,  which,  with  the  powerful  affinity  of  the 
'nascent  state,'  swept  away  all  impurity  from  the 
surface  against  which  it  was  liberated.  The  bubbles 
of  gas  liberated  on  one  of  the  platinum  plates  or 
wires  of  a  decomposing  cell  are  always  much  smaller, 
and  they  rise  in  much  more  rapid  succession  than 
those  from  the  other.  Knowing  that  oxygen  is  six- 
teen times  heavier  than  hydrogen,  I  have  more  than 


FARADAY  AS   A  DISCOVERER.  53 

once  concluded,  and,  I  fear,  led  others  into  the  error 
of  concluding,  that  the  smaller  and  more  quickly 
rising  bubbles  must  belong  to  the  lighter  gas.  The 
thing  appeared  so  obvious  that  I  did  not  give  myself 
the  trouble  of  looking  at  the  battery,  which  would 
at  once  have  told  me  the  nature  of  the  gas.  But 
Faraday  would  never  have  been  satisfied  with  a 
deduction  if  he  could  have  reduced  it  to  a  fact.  And 
he  has  taught  me  that  the  fact  here  is  the  direct  re- 
verse of  what  I  supposed  it  to  be.  The  small  bubbles 
are  oxygen,  and  their  smallness  is  due  to  the  perfect 
cleanness  of  the  surface  on  which  they  are  liberated. 
The  hydrogen  adhering  to  the  other  electrode  swells 
into  large  bubbles,  which  rise  in  much  slower  succes- 
sion ;  but  when  the  current  is  reversed,  the  hydro- 
gen is  liberated  upon  the  cleansed  wire,  and  then  its 
bubbles  also  become  small. 


LAWS   OP   ELECTRO-CHEMICAL   DECOMPOSITION. 

In  our  conceptions  and  reasonings  regarding  the 
forces  of  nature,  we  perpetually  make  use  of  symbols 
which,  when  they  possess  a  high  representative  value 
we  dignify  with  the  name  of  theories.  Thus,  prompted 
by  certain  analogies  we  ascribe  electrical  phenomena 
to  the  action  of  a  peculiar  fluid,  sometimes  flowing, 
sometimes  at  rest.  Such  conceptions  have  their 


54  FARADAY  AS  A   DISCOVERER. 

advantages  and  their  disadvantages ;  they  afford 
peaceful  lodging  to  the  intellect  for  a  time,  but  they 
also  circumscribe  it,  and  by-and-by,  when  the  mind 
has  grown  too  large  for  its  lodging,  it  often  finds 
difficulty  in  breaking  down  the  walls  of  what  has 
become  its  prison  instead  of  its  home.* 

No  man  ever  felt  this  tyranny  of  symbols  more 
deeply  than  Earaday,  and  no  man  was  ever  more  as- 
siduous than  he  to  liberate  himself  from  them,  and  the 
terms  which  suggested  them.  Calling  Dr.  Whewell 
to  his  aid  in  1833,  he  endeavoured  to  displace  by 
others  all  terms  tainted  by  a  foregone  conclusion. 
His  paper  on  Electro-chemical  decomposition,  re- 
ceived by  the  Royal  Society  on  January  9,  1834, 
opens  with  the  proposal  of  a  new  terminology.  He 
would  avoid  the  word  '  current '  if  he  could.f  He 
does  abandon  the  word  '  poles '  as  applied  to  the  ends 
of  a  decomposing  cell,  because  it  suggests  the  idea 
of  attraction,  substituting  for  it  the  perfectly  neutral 
term  Electrodes.  He  applied  the  term  Electrolyte  to 


*  I  copy  these  words  from  the  printed  abstract  of  a  Friday  evening 
lecture,  given  by  myself,  because  they  remind  me  of  Faraday's  voice, 
responding  to  the  utterance  by  an  emphatic  '  hear  !  hear  ! ' — Proceedings 
of  the  Eoyal  Institution,  vol.  ii.  p.  132. 

f  In  1838  he  expresses  himself  thus: — 'The  word  current  is  so  ex- 
pressive in  common  language  that  when  applied  in  the  consideration  of 
electrical  phenomena,  we  can  hardly  divest  it  sufficiently  of  its  meaning, 
or  prevent  our  minds  from  being  prejudiced  by  it.' — Exp.  Eesear.,  vol.  i. 
p.  515.  (§1617.) 


FARADAY  AS  A   DISCOVERER.  55 

every  substance  which  can  be  decomposed  by  the  cur- 
rent, and  the  act  of  decomposition  he  called  Electro- 
lysis. All  these  terms  have  become  current  in  science. 
He  called  the  positive  electrode  the  Anode,  and  the 
negative  one  the  Cathode,  but  these  terms,  though 
frequently  used,  have  not  enjoyed  the  same  currency 
as  the  others.  The  terms  Anion  and  Cation,  which 
he  applied  to  the  constituents  of  the  decomposed 
electrolyte,  and  the  term  Ion,  which  included  both 
anions  and  cations,  are  still  less  frequently  employed. 
Faraday  now  passes  from  terminology  to  research ; 
he  sees  the  necessity  of  quantitative  determinations, 
and  seeks  to  supply  himself  with  a  measure  of  voltaic 
electricity.  This  he  finds  in  the  quantity  of  water 
decomposed  by  the  current.  He  tests  this  measure  in 
all  possible  ways,  to  assure  himself  that  no  error  can 
arise  from  its  employment.  He  places  in  the  course 
of  one  and  the  same  current  a  series  of  cells  with 
electrodes  of  different  sizes,  some  of  them  plates  of 
platinum,  others  merely  platinum  wires,  and  collects 
the  gas  liberated  on  each  distinct  pair  of  electrodes. 
He  finds  the  quantity  of  gas  to  be  the  same  for  all. 
Thus  he  concludes  that  when  the  same  quantity  of 
electricity  is  caused  to  pass  through  a  series  of  cells 
containing  acidulated  water,  the  electro-chemical 
action  is  independent  of  the  size  of  the  electrodes. 
He  next  proves  that  variations  in  intensity  do  not 


56  FARADAY  AS   A  DISCOVERER. 

interfere  with  this  equality  of  action.  Whether  his 
battery  is  charged  with  strong  acid  or  with  weak ; 
whether  it  consists  of  five  pairs  or  of  fifty  pairs ;  in 
short,  whatever  be  its  source,  when  the  same  current 
is  sent  through  his  series  of  cells  the  same  amount 
of  decomposition  takes  place  in  all.  He  next  assures 
himself  that  the  strength  or  weakness  of  his  dilute 
acid  does  not  interfere  with  this  law.  Sending  the 
same  current  through  a  series  of  cells  containing 
mixtures  of  sulphuric  acid  and  water  of  different 
strengths,  he  finds,  however  the  proportion  of  acid  to 
water  might  vary,  the  same  amount  of  gas  to  be 
collected  in  all  the  cells.  A  crowd  of  facts  of  this 
character  forced  upon  Faraday's  mind  the  conclusion 
that  the  amount  of  electro-chemical  decomposition 
depends,  not  upon  the  size  of  the  electrodes,  not  upon 
the  intensity  of  the  current,  not  upon  the  strength 
of  the  solution,  but  solely  upon  the  quantity  of  elec- 
tricity which  passes  through  the  cell.  The  quantity 
of  electricity  he  concludes  is  proportional  to  the 
amount  of  chemical  action.  On  this  law  Faraday 
based  the  construction  of  his  celebrated  Voltameter, 
or  Measurer  of  Voltaic  electricity. 

But  before  he  can  apply  this  measure  he  must  clear 
his  ground  of  numerous  possible  sources  of  error. 
The  decomposition  of  his  acidulated  water  is  certainly 
a  direct  result  of  the  current ;  but  as  the  varied  and 


FARADAY  AS   A  DISCOVEKEK.  57 

important  researches  of  MM.  Becquei-el,  De  la  Rive, 
and  others  had  shown,  there  are  also  secondary  actions 
which  may  materially  interfere  with  and  complicate 
the  pure  action  of  the  current.  These  actions  may 
occur  in  two  ways  ;  either  the  liberated  ion  may  seize 
upon  the  electrode  against  which  it  is  set  free,  forming 
a  chemical  compound  with  that  electrode ;  or  it  may 
seize  upon  the  substance  of  the  electrolyte  itself,  and 
thus  introduce  into  the  circuit  chemical  actions  over 
and  above  those  due  to  the  current.  Faraday  sub- 
jected these  secondary  actions  to  an  exhaustive  ex- 
amination. Instructed  by  his  experiments,  and  ren- 
dered competent  by  them  to  distinguish  between 
primary  and  secondary  results,  he  proceeds  to  es- 
tablish the  doctrine  of  c  Definite  Electro-chemical 
Decomposition.' 

Into  the  same  circuit  he  introduced  his  voltameter, 
which  consisted  of  a  graduated  tube  filled  with  acidu- 
lated water  and  provided  with  platinum  plates  for 
the  decomposition  of  the  water,  and  also  a  cell  con- 
taining chloride  of  tin.  Experiments  already  referred 
to  had  taught  him  that  this  substance,  though  an  in- 
sulator when  solid,  is  a  conductor  when  fused,  the 
passage  of  the  current  being  always  accompanied  by 
the  decomposition  of  the  chloride.  He  wished  to 
ascertain  what  relation  this  decomposition  bore  to 
that  of  the  water  in  his  voltameter. 


58  FARADAY  AS   A    DISCOVERER. 

Completing  his  circuit,  he  permitted  the  current  to 
continue  until  (  a  reasonable  quantity  of  gas '  was 
collected  in  the  voltameter.  The  circuit  was  then 
broken,  and  the  quantity  of  tin  liberated  compared 
with  the  quantity  of  gas.  The  weight  of  the  former 
was  3-2  grains,  that  of  the  latter  0-49742  of  a  grain. 
Oxygen,  as  you  know,  unites  with  hydrogen  in  the 
proportion  of  8  to  1  to  form  water.  Calling  the  equi- 
valent, or  as  it  is  sometimes  called,  the  atomic  weight 
of  hydrogen  1,  that  of  oxygen  is  8  ;  that  of  water  is 
consequently  8  +  1  or  9.  Now  if  the  quantity  of 
water  decomposed  in  Faraday's  experiment  be  repre- 
sented by  the  number  9,  or  in  other  words  by  the 
equivalent  of  water,  then  the  quantity  of  tin  liberated 
from  the  fused  chloride  is  found  by  an  easy  calculation 
to  be  57'9,  which  is  almost  exactly  the  chemical  equi- 
valent of  tin.  Thus  both  the  water  and  the  chloride 
were  broken  up  in  proportions  expressed  by  their  re- 
spective equivalents.  The  amount  of  electric  force 
which  wrenched  asunder  the  constituents  of  the 
molecule  of  water  was  competent,  and  neither  more 
nor  less  than  competent,  to  wrench  asunder  the  con- 
stituents of  the  molecules  of  the  chloride  of  tin.  The 
fact  is  typical.  With  the  indications  of  his  volta- 
meter he  compared  the  decomposition  of  other  sub- 
stances both  singly  and  in  series.  He  submitted  his 
conclusions  to  numberless  tests.  He  purposely  intro- 


FARADAY  AS   A    DISCOVERER.  59 

duced  secondary  actions.  He  endeavoured  to  hamper 
the  fulfilment  of  those  laws  which  it  was  the  intense 
desire  of  his  mind  to  see  established.  But  from  all 
these  difficulties  emerged  the  golden  truth,  that  under 
every  variety  of  circumstances  the  decompositions  of 
the  voltaic  current  are  as  definite  in  their  character 
as  those  chemical  combinations  which  gave  birth  to 
the  atomic  theory.  This  law  of  Electro- chemical 
Decomposition  ranks,  in  point  of  importance,  with 
that  of  Definite  Combining  Proportions  in  chemistry. 

ORIGIN   OF   POWER   IN   THE   VOLTAIC    PILE. 

In  one  of  the  public  areas  of  the  town  of  Como 
stands  a  statue  with  no  inscription  on  its  pedestal, 
save  that  of  a  single  name,  '  Yolta.'  The  bearer  of 
that  name  occupies  a  place  for  ever  memorable  in  the 
history  of  science.  To  him  we  owe  the  discovery  of 
the  voltaic  pile,  to  which  for  a  brief  interval  we  must 
now  turn  our  attention. 

The  objects  of  scientific  thought  being  the  passion- 
less laws  and  phenomena  of  external  nature, one  might 
suppose  that  their  investigation  and  discussion  would 
be  completely  withdrawn  from  the  region  of  the  feel- 
ings, and  pursued  by  the  cold  dry  light  of  the  intel- 
lect alone.  This,  however,  is  not  always  the  case. 
Man  carries  his  heart  with  him  into  all  his  works. 


60  FARADAY  AS  A   DISCOVERER. 

You  cannot  separate  the  moral  and  emotional  from 
the  intellectual ;  and  thm  it  is  that  the  discussion 
of  a  point  of  science  may  rise  to  the  heat  of  a 
battle-field.  The  fight  between  the  rival  optical 
theories  of  Emission  anci  Undulation  was  of  this 
fierce  character;  and  scarcely  less  fierce  for  many 
years  was  the  contest  as  to  the  origin  and  mainten- 
ance of  the  power  of  the  voltaic  pile.  Yolta  himself 
supposed  it  to  reside  in  the  Contact  of  different 
metals.  Here  was  exerted  his  '  Electro-motive  force,' 
which  tore  the  combined  electricities  asunder  and 
drove  them  as  currents  in  opposite  directions.  To 
render  the  circulation  of  the  current  possible,  it  was 
necessary  to  connect  the  metals  by  a  moist  conduc- 
tor ;  for  when  any  two  metals  were  connected  by  a 
third,  their  relation  to  each  other  was  such  that  a 
complete  neutralization  of  the  electric  motion  was 
the  result.  Yolta's  theory  of  metallic  contact  was  so 
clear,  so  beautiful,  and  apparently  so  complete,  that 
the  best  intellects  of  Europe  accepted  it  as  the 
expression  of  natural  law. 

Yolta  himself  knew  nothing  of  the  chemical  phe- 
nomena of  the  pile;  but  as  soon  as  these  became 
known,  suggestions  and  intimations  appeared  that 
chemical  action,  and  not  metallic  contact,  might  be 
the  real  source  of  voltaic  electricity.  This  idea  was 
expressed  by  Fabroni  in  Italy,  and  by  Wollaston  in 


FARADAY  AS   A   DISCOVERER.  61 

England.  It  was  developed  and  maintained  by  those 
*  admirable  electricians/  Becquerel,  of  Paris,  and  De 
la  Rive,  of  Geneva.  The  Contact  Theory,  on  the 
other  hand,  received  its  chief  development  and  illus- 
tration in  Germany.  It  was  long  the  scientific  creed 
of  the  great  chemists  and  natural  philosophers  of 
that  country,  and  to  the  present  hour  there  may  be 
some  of  them  unable  to  liberate  themselves  from  the 
fascination  of  their  first-love. 

After  the  researches  which  I  have  endeavoured  to 
place  before  you,  it  was  impossible  for  Faraday  to 
avoid  taking  a  side  in  this  controversy.  He  did  so  in 
a  paper  '  On  the  Electricity  of  the  Voltaic  Pile,'  re- 
ceived by  the  Royal  Society  on  the  7th  April,  1834. 
His  position  in  the  controversy  might  have  been  pre- 
dicted. He  saw  chemical  effects  going  hand-in-hand 
with  electrical  effects,  the  one  being  proportional  to 
the  other;  and,  in  the  paper  now  before  us,  he  proved 
that  when  the  former  were  excluded,  the  latter  were 
sought  for  in  vain.  He  produced  a  current  without 
metallic  contact ;  he  discovered  liquids  which,  though 
competent  to  transmit  the  feeblest  currents — compe- 
tent therefore  to  allow  the  electricity  of  contact  to 
flow  through  them  if  it  were  able  to  form  a  cur- 
rent, were  absolutely  powerless  when  chemically  in- 
active. 

One  of  the  very  few   experimental    mistakes   of 


62  FAKADAY  AS  A  DISCOVERER. 

Faraday  occurred  in  this  investigation.  He  thought 
that  with  a  single  voltaic  cell  he  had  obtained  the 
spark  before  the  metals  touched,  but  he  subsequently 
discovered  his  error.  To  enable  the  voltaic  spark  to 
pass  through  air  before  the  terminals  of  the  battery 
were  united,  it  was  necessary  to  exalt  the  electro- 
motive force  .of  the  battery  by  multiplying  its 
elements;  but  all  the  elements  Faraday  possessed 
were  unequal  to  the  task  of  urging  the  spark  across 
the  shortest  measurable  space  of  air.  Nor,  indeed, 
could  the  action  of  the  battery,  the  different  metals 
of  which  were  in  contact  with  each  other,  decide  the 
point  in  question.  Still,  as  regards  the  identity  of 
electricities  from  various  sources,  it  was  at  that  day 
of  great  importance  to  determine  whether  or  not  the 
voltaic  current  could  jump,  as  a  spark,  across  an  in- 
terval before  contact.  Faraday's  friend,  Mr.  Gassiot, 
solved  this  problem.  He  erected  a  battery  of  4,000 
cells,  and  with  it  urged  a  stream  of  sparks  from  ter- 
minal to  terminal,  when  separated  from  each  other 
by  a  measurable  space  of  air. 

The  memoir  on  the  'Electricity  of  the  Voltaic 
Pile,'  published  in  1834,  appears  to  have  produced 
but  little  impression  upon  the  supporters  of  the  con- 
tact theory.  These  indeed  were  men  of  too  great 
intellectual  weight  and  insight  lightly  to  take  up,  or 
lightly  to  abandon  a  theory.  Faraday  therefore  re- 


FARADAY  AS  A   DISCOVERER.  63 

snmed  the  attack  in  a  paper  communicated  to  the 
Royal  Society,  on  the  6th  of  February,  1840.  In 
this  paper  he  hampered  his  antagonists  by  a  crowd  of 
adverse  experiments.  He  hung  difficulty  after  diffi- 
culty about  the  neck  of  the  contact  theory,  until  in 
its  eiforts  to  escape  from  his  assaults  it  so  changed 
its  character  as  to  become  a  thing  totally  different 
from  the  theory  proposed  by  Volta.  The  more  per- 
sistently it  was  defended,  however,  the  more  clearly 
did  it  show  itself  to  be  a  congeries  of  devices,  bearing 
the  stamp  of  dialectic  skill  rather  than  that  of  natural 
truth. 

In  conclusion,  Faraday  brought  to  bear  upon  it  an 
argument  which,  had  its  full  weight  and  purport 
been  understood  at  the  time,  would  have  instantly 
decided  the  controversy.  (  The  contact  theory,'  he 
urged,  i  assumes  that  a  force  which  is  able  to  over- 
come powerful  resistance,  as  for  instance  that  of  the 
conductors,  good  or  bad,  through  which  the  current 
passes,  and  that  again  of  the  electrolytic  action 
where  bodies  are  decomposed  by  it,  can  arise  out  of 
nothing :  that  without  any  change  in  the  acting  mat- 
ter, or  the  consumption  of  any  generating  force,  a 
current  shall  be  produced  which  shall  go  on  for  ever 
against  a  constant  resistance,  or  only  be  stopped,  as 
in  the  voltaic  trough,  by  the  ruins  which  its  exertion 
has  heaped  up  in  its  own  course.  This  would  indeed 


64  FARADAY  AS   A  DISCOVERER. 

be  a  creation  of  power,  and  is  like  no  other  force  in 
nature.  We  have  many  processes  by  which  the/orra 
of  the  power  may  be  so  changed,  that  an  apparent 
conversion  of  one  into  the  other  takes  place.  So  we 
can  change  chemical  force  into  the  electric  current, 
or  the  current  into  chemical  force.  The  beautiful 
experiments  of  Seebeck  and  Peltier  show  the  conver- 
tibility of  heat  and  electricity ;  and  others  by  Oersted 
and  myself  show  the  convertibility  of  electricity  and 
magnetism.  But  in  no  case,  not  even  in  those  of  the 
Gymnotus  and  Torpedo,  is  there  a  pure  creation  or  a 
production  of  power  without  a  corresponding  exhaustion 
of  something  to  supply  it.9 

These  words  were  published  more  than  two  years 
before  either  Mayer  printed  his  brief  but  celebrated 
essay  on  the  Forces  of  Inorganic  Nature,  or  Mr. 
Joule  published  his  first  famous  experiments  on  the 
Mechanical  Value  of  Heat.  They  illustrate  the  fact 
that  before  any  great  scientific  principle  receives  dis- 
tinct enunciation  by  individuals,  it  dwells  more  or 
less  clearly  in  the  general  scientific  mind.  The  in- 
tellectual plateau  is  already  high,  and  our  disco- 
verers are  those  who,  like  peaks  above  the  plateau, 
rise  a  little  above  the  general  level  of  thought  at  the 
time. 

But  many  years  prior  even  to  the  foregoing  ut- 
terance of  Faraday,  a  similar  argument  had  been 


FAKADAY  AS   A   DISCOVERER.  65 

employed.  I  quote  here  with  equal  pleasure  and 
admiration  the  following  passage  written  by  Dr. 
Eoget  so  far  back  as  1829.  Speaking  of  the  contact 
theory,  he  says  : — '  If  there  could  exist  a  power 
having  the  property  ascribed  to  it  by  the  hypothesis, 
namely,  that  of  giving  continual  impulse  to  a  fluid 
in  one  constant  direction,  without  being  exhausted 
by  its  own  action,  it  would  differ  essentially  from 
all  the  known  powers  in  nature.  All  the  powers 
and  sources  of  motion  with  the  operation  of  which 
we  are  acquainted,  when  producing  these  peculiar 
effects,  are  expended  in  the  same  proportion  as  those 
effects  are  produced ;  and  hence  arises  the  impos- 
sibility of  obtaining  by  their  agency  a  perpetual 
effect  j  or  in  other  words  a  perpetual  motion.  But 
the  electro-motive  force,  ascribed  by  Yolta  to  the 
metals,  when  in  contact,  is  a  force  which  as  long 
as  a  free  course  is  allowed  to  the  electricity  it  sets 
in  motion,  is  never  expended,  and  continues  to  be 
excited  with  undiminished  power  in  the  production 
of  a  never-ceasing  effect.  Against  the  truth  of  such 
a  supposition  the  probabilities  are  all  but  infinite.' 
When  this  argument,  which  he  employed  indepen- 
dently, had  clearly  fixed  itself  in  his  mind,  Faraday 
never  cared  to  experiment  further  on  the  source  of 
electricity  in  the  voltaic  pile.  The  argument  appeared 


66  FARADAY  AS   A   DISCOVERER. 

to  him  ( to  remove  the  foundation  itself  of  the  contact 
theory,'  and  he  afterwards  let  it  crumble  down  in 


peace.* 


RESEAECHES  ON  FEICTIONAL  ELECTRICITY:  INDUCTION: 
CONDUCTION  :  SPECIFIC  INDUCTIVE  CAPACITY  : 
THEOEY  OP  CONTIGUOUS  PAETICLES. 

The  burst  of  power  which  had  filled  the  four  pre- 
ceding years  with  an  amount  of  experimental  work 
unparalleled  in  the  history  of  science  partially  sub- 
sided in  1835,  and  the  only  scientific  paper  con- 
tributed by  Faraday  in  that  year  was  a  comparatively 
unimportant  one,  '  On  an  improved  Form  of  the 
Voltaic  Battery.'  He  brooded  for  a  time  :  his  expe- 
riments on  electrolysis  had  long  filled  his  mind ;  he 

*  To  account  for  the  electric  current,  which  was  really  the  core  of  the 
whole  discussion,  Faraday  demonstrated  the  impotence  of  the  Contact 
Theory  as  then  enunciated  and  defended.  Still,  it  is  certain  that  -two 
different  metals,  when  brought  into  contact,  charge  themselves,  the  one 
with  positive  and  the  other  with  negative  electricity.  I  had  the  pleasure 
of  going  over  this  ground  with  Kohlrausch  in  1849,  and  his  experi- 
ments left  no  doubt  upon  my  mind  that  the  contact  electricity  of 
Volta  was  a  reality,  though  it  could  produce  no  current.  With  one 
of  the  beautiful  instruments  devised  by  himself,  Sir  William  Thomson 
has  rendered  this  point  capable  of  sure  and  easy  demonstration ;  and 
he  and  others  now  hold  what  may  be  called  a  contact  theory,  which, 
while  it  takes  into  account  the  action  of  the  metals,  also  embraces  the 
.chemical  phenomena  of  the  circuit.  Helmholtz,  I  believe,  was  the  Jfirst 
to  give  the  contact  theory  this  new  form,  in  his  celebrated  essay,  Veber 
die  Erhaltung  der  Kraft,  p.  45. 


FARADAY  AS  A   DISCOVERER.  67 

looked,  as  already  stated,  into  the  very  heart  of  the 
electrolyte,  endeavouring  to  render  the  play  of  its 
atoms  visible  to  his  mental  eye.  He  had  no  doubt 
that  in  this  case  what  is  called  ( the  electric  current ' 
was  propagated  from  particle  to  particle  of  the  elec- 
trolyte; he  accepted  the  doctrine  of  decomposition 
and  recomposition  which,  according  to  Grothuss  and 
Davy,  ran  from  electrode  to  electrode.  And  the 
thought  impressed  him  more  and  more  that  or- 
dinary electric  induction  was  also  transmitted  and 
sustained  by  the  action  of ( contiguous  particles.9 

His  first  great  paper  on  frictional  electricity  was 
sent  to  the  Royal  Society  on  November  30,  1837. 
We  here  find  him  face  to  face  with  an  idea  which 
beset  his  mind  throughout  his  whole  subsequent  life, 
— the  idea  of  action  at  a  distance.  It  perplexed  and 
bewildered  him.  In  his  attempts  to  get  rid  of  this 
perplexity,  he  was  often  unconsciously  rebelling 
against  the  limitations  of  the  intellect  itself.  He 
loved  to  quote  Newton  upon  this  point :  over  and 
over  again  he  introduces  his  memorable  words,  c  That 
gravity  should  be  innate,  inherent,  and  essential  to 
matter,  so  that  one  body  may  act  upon  another  at 
a  distance  through  a  vacuum  and  without  the  media- 
tion of  anything  else,  by  and  through  which  this 
action  and  force  may  be  conveyed  from  one  to  an- 
other, is  to  me  so  great  an  absurdity,  that  I  believe 


68  FARADAY  AS  A   DISCOVERER. 

no  man  who  has  in  philosophical  matters  a  compe- 
tent faculty  of  thinking,  can  ever  fall  into  it.  Gravity 
must  be  caused  by  an  agent  acting  constantly  ac- 
cording to  certain  laws ;  but  whether  this  agent  be 
material  or  immaterial,  I  have  left  to  the  considera- 
tion of  my  readers.'  * 

Faraday  does  not  see  the  same  difficulty  in  his 
contiguous  particles.  And  yet,  by  transferring  the 
conception  from  masses  to  particles,  we  simply  lessen 
size  and  distance,  but  we  do  not  alter  the  quality  of 
the  conception.  Whatever  difficulty  the  mind  ex- 
periences in  conceiving  of  action  at  sensible  dis- 
tances, besets  it  also  when  it  attempts  to  conceive 
of  action  at  insensible  distances.  Still  the  investiga- 
tion of  the  point  whether  electric  and  magnetic  effects 
were  wrought  out  through  the  intervention  of  con- 
tiguous particles  or  not,  had  a  physical  interest 
altogether  apart  from  the  metaphysical  difficulty. 
Faraday  grapples  with  the  subject  experimentally. 
By  simple  intuition  he  sees  that  action  at  a  distance 
must  be  exerted  in  straight  lines.  Gravity,  he 
knows,  will  not  turn  a  corner,  but  exerts  its  pull 
along  a  right  line ;  hence  his  aim  and  effort  to  as- 
certain whether  electric  action  ever  takes  place  in 
curved  lines.  This  once  proved,  it  would  follow  that 
the  action  is  carried  on  ly  means  of  a  medium  sur- 

*  Newton's  third  letter  to  Bentley. 


FARADAY  AS  A   DISCO VEEER.  69 

rounding  the  electrified  bodies.  His  experiments  in 
1837  reduced,  in  his  opinion,  this  point  to  demon- 
stration. He  then  found  that  he  could  electrify,  by 
induction,  an  insulated  sphere  placed  completely  in 
the  shadow  of  a  body  which  screened  it  from  direct 
action.  He  pictured  the  lines  of  electric  force  bend- 
ing round  the  edges  of  the  screen,  and  reuniting  on 
the  other  side  of  it ;  and  he  proved  that  in  many 
cases  the  augmentation  of  the  distance  between  his 
insulated  sphere  and  the  inducing  body,  instead  of 
lessening,  increased  the  charge  of  the  sphere.  This 
he  ascribed  to  the  coalescence  of  the  lines  of  electric 
force  at  some  distance  behind  the  screen. 

Faraday's  theoretic  views  on  this  subject  have  not 
received  general  acceptance,  but  they  drove  him  to 
experiment,  and  experiment  with  him  was  always 
prolific  of  results.  By  suitable  arrangements  he 
placed  a  metallic  sphere  in  the  middle  of  a  large 
hollow  sphere,  leaving  a  space  of  something  more 
than  half-an-inch  between  them.  The  interior  sphere 
was  insulated,  the  external  one  uninsulated.  To  the 
former  he  communicated  a  definite  charge  of  electri- 
city. It  acted  by  induction  upon  the  concave  surface 
of  the  latter,  and  he  examined  how  this  act  of  in- 
duction was  effected  by  placing  insulators  of  various 
kinds  between  the  two  spheres.  He  tried  gases, 
liquids,  and  solids,  but  the  solids  alone  gave  him 


70  FARADAY  AS  A   DISCOVERER. 

positive  results.  He  constructed  two  instruments  of 
the  foregoing  description,  equal  in  size  and  similar  in 
form.  The  interior  sphere  of  each  communicated 
with  the  external  air  by  a  brass  stem  ending  in  a 
knob.  The  apparatus  was  virtually  a  Ley  den  jar,  the 
two  coatings  of  which  were  the  two  spheres,  with  a 
thick  and  variable  insulator  between  them.  The 
amount  of  charge  in  each  jar  was  determined  by 
bringing  a  proof-plane  into  contact  with  its  knob,  and 
measuring  by  a  torsion  balance  the  charge  taken 
away.  He  first  charged  one  of  his  instruments,  and 
then  dividing  the  charge  with  the  other,  found  that 
when  air  intervened  in  both  cases,  the  charge  was 
equally  divided.  But  when  shellac,  sulphur,  or  sper- 
maceti was  interposed  between  the  two  spheres  of 
one  jar,  while  air  occupied  this  interval  in  the  other, 
then  he  found  that  the  instrument  occupied  by  the 
'solid  dielectric'  takes  more  than  half  the  original 
charge.  A  portion  of  the  charge  was  absorbed  by 
the  dielectric  itself.  The  electricity  took  time  to 
penetrate  the  dielectric.  Immediately  after  the  dis- 
charge of  the  apparatus,  no  trace  of  electricity  was 
found  upon  its  knob.  But  after  a  time  electricity 
was  found  there,  the  charge  having  gradually  re- 
turned from  the  dielectric  in  which  it  had  been  lodged. 
Different  insulators  possess  this  power  of  permitting 
the  charge  to  enter  them  in  different  degrees.  Faraday 


FARADAY   AS  A   DISCOVERER.  71 

figured  their  particles  as  polarized,  and  lie  concluded 
that  the  force  of  induction  is  propagated  from  par- 
ticle to  particle  of  the  dielectric  from  the  inner  sphere 
to  the  outer  one.  This  power  of  propagation  possessed 
by  insulators  he  called  their  '  Specific  Inductive  Ca- 
pacity.9 

Faraday  visualizes  with  the  utmost  clearness  the 
state  of  his  contiguous  particles ;  one  after  another 
they  become  charged,  each  succeeding  particle  de- 
pending for  its  charge  upon  its  predecessor.  And 
now  he  seeks  to  break  down  the  wall  of  partition 
between  conductors  and  insulators.  (  Can  we  not,'  he 
says,  'by  a  gradual  chain  of  association  carry  up 
discharge  from  its  occurrence  in  air  through  sper- 
maceti and  water,  to  solutions,  and  then  on  to  chlo- 
rides, oxides,  and  metals,  without  any  essential 
change  in  its  character?'  Even  copper,  he  urges, 
offers  a  resistance  to  the  transmission  of  electricity. 
The  action  of  its  particles  differs  from  those  of  an 
insulator  only  in  degree.  They  are  charged  like  the 
particles  of  the  insulator,  but  they  discharge  with 
greater  ease  and  rapidity ;  and  this  rapidity  of  mole- 
cular discharge  is  what  we  call  conduction.  Con- 
duction then  is  always  preceded  by  atomic  induction ; 
and  when,  through  some  quality  of  the  body  which 
Faraday  does  not  define,  the  atomic  discharge  is 


72  FARADAY   AS   A  DISCOVERER. 

rendered  slow  and  difficult,  conduction  passes  into 
insulation. 

Though  they  are  often  obscure,  a  fine  vein  of 
philosophic  thought  runs  through  those  investiga- 
tions. The  mind  of  the  philosopher  dwells  amid 
those  agencies  which  underlie  the  visible  phenomena 
of  Induction  and  Conduction;  and  he  tries  by  the 
strong  light  of  his  imagination  to  see  the  very  mole- 
cules of  his  dielectrics.  It  would,  however,  be  easy 
to  criticise  these  researches,  easy  to  show  the  loose- 
ness, and  sometimes  the  inaccuracy,  of  the  phraseo- 
logy employed ;  but  this  critical  spirit  will  get  little 
good  out  of  Faraday.  Eather  let  those  who  ponder 
his  works  seek  to  realise  the  object  he  set  before 
him,  not  permitting  his  occasional  vagueness  to  in- 
terfere with  their  appreciation  of  his  speculations. 
We  may  see  the  ripples,  and  eddies,  and  vortices  of 
a  flowing  stream,  without  being  able  to  resolve  all 
these  motions  into  their  constituent  elements ;  and 
so  it  sometimes  strikes  me  that  Faraday  clearly  saw 
the  play  of  fluids  and  ethers  and  atoms,  though  his 
previous  training  did  not  enable  him  to  resolve  what 
he  saw  into  its  constituents,  or  describe  it  in  a  man- 
ner satisfactory  to  a  mind  versed  in  mechanics.  And 
then  again  occur,  I  confess,  dark  sayings,  difficult  to 
be  understood,  which  disturb  my  confidence  in  this 
conclusion.  It  must,  however,  always  be  remembered 


FARADAY   AS  A   DISCOVERER.  73 

that  lie  works  at  the  very  boundaries  of  our  know- 
ledge, and  that  his  mind  habitually  dwells  in  the 
'  boundless  contiguity  of  shade '  by  which  that  know- 
ledge is  surrounded. 

In  the  researches  now  under  review  the  ratio  of 
speculation  and  reasoning  to  experiment  is  far  higher 
than  in  any  of  Faraday's  previous  works.  Amid 
much  that  is  entangled  and  dark  we  have  flashes 
of  wondrous  insight  and  utterances  which  seem  less 
the  product  of  reasoning  than  of  revelation.  I  will 
confine  myself  here  to  one  example  of  this  divining 
power:  By  his  most  ingenious  device  of  a  rapidly 
rotating  mirror,  Wheatstone  had  proved  that  elec- 
tricity required  time  to  pass  through  a  wire,  the  cur- 
rent reaching  the  middle  of  the  wire  later  than  its 
two  ends.  '  If,'  says  Faraday,  c  the  two  ends  of  the 
wire  in  Professor  Wheatstone's  experiments  were 
immediately  connected  with  two  large  insulated  me- 
tallic surfaces  exposed  to  the  air,  so  that  the  primary 
act  of  induction,  after  making  the  contact  for  dis- 
charge, might  be  in  part  removed  from  the  internal 
portion  of  the  wire  at  the  first  instance,  and  disposed 
for  the  moment  on  its  surface  jointly  with  the  air  and 
surrounding  conductors,  then  I  venture  to  anticipate 
that  the  middle  spark  would  be  more  retarded  than 
before.  And  if  those  two  plates  were  the  inner  and 
outer  coatings  of  a  large  jar  or  Ley  den  battery,  then 


74  FARADAY  AS  A   DISCOVERER. 

the  retardation  of  the  spark  would  be  much  greater.' 
This  was  only  a  prediction,  for  the  experiment  was 
not  made.*  Sixteen  years  subsequently,  however, 
the  proper  conditions-  came  into  play,  and  Faraday 
was  able  to  show  that  the  observations  of  Werner 
Siemens,  and  Latimer  Clark,  on  subterraneous  and 
submarine  wires  were  illustrations  on  a  grand  scale, 
of  the  principle  which  he  had  enunciated  in  1838. 
The  wires  and  the  surrounding  water  act  as  a  Leyden 
jar,  and  the  retardation  of  the  current  predicted 
by  Faraday  manifests  itself  in  every  message  sent  by 
such  cables. 

The  meaning  of  Faraday  in  these  memoirs  on  In- 
duction and  Conduction  is,  as  I  have  said,  by  no 
means  always  clear ;  and  the  difficulty  will  be  most 
felt  by  those  who  are  best  trained  in  ordinary  theoretic 
conceptions.  He  does  not  know  the  reader's  needs, 
and  he  therefore  does  not  meet  them.  For  instance, 
he  speaks  over  and  over  again  of  the  impossibility  of 
charging  a  body  with  one  electricity,  though  the  im- 
possibility is  by  no  means  evident.  The  key  to  the 
difficulty  is  this.  He  looks  upon  every  insulated  con- 
ductor as  the  inner  coating  of  a  Leyden  jar.  An  in- 
sulated sphere  in  the  middle  of  a  room  is  to  his  mind 

*  If  Sir  Charles  Wheatstone  could  be  induced  to  take  up  his  mea- 
surements once  more,  varying  the  substances  through  which,  and  the 
conditions  under  which  the  current  is  propagated,  he  might  render  great 
service  to  science,  both  theoretic  and  experimental. 


FAKADAY  AS   A   D1SCOVEREE.  75 

such,  a  coating ;  the  walls  are  the  outer  coating,  while 
the  air  between  both  is  the  insulator,  across  which 
the  charge  acts  by  induction.  Without  this  reaction 
of  the  walls  upon  the  sphere  you  could  no  more, 
according  to  Faraday,  charge  it  with  electricity  than 
you  could  charge  a  Ley  den  jar,  if  its  outer  coating 
were  removed.  Distance  with  him  is  immaterial. 
His  strength  as  a  generalizer  enables  him  to  dissolve 
the  idea  of  magnitude;  and  if  you  abolished  the 
walls  of  the  room — even  the  earth  itself — he  would 
make  the  sun  and  planets  the  outer  coating  of  his 
jar.  I  dare  not  contend  that  Faraday  in  these  me- 
moirs made  all  his  theoretic  positions  good.  But  a 
pure  vein  of  philosophy  runs  through  these  writings  ; 
while  his  experiments  and  reasonings  on  the  forms 
and  phenomena  of  electrical  discharge  are  of  im- 
perishable importance. 

EEST   NEEDED — VISIT    TO    SWITZERLAND. 

The  last  of  these  memoirs  was  dated  from  the 
Royal  Institution  in  June,  1838.  It  concludes  the 
first  volume  of  his  6  Experimental  Eesearches  on 
Electricity.'  In  1840,  as  already  stated,  he  made  his 
final  assault  on  the  Contact  Theory,  from  which  it 
never  recovered.*  He  was  now  feeling  the  effects  of 
the  mental  strain  to  which  he  had  been  subjected  for 

*  See  note,  p.  66. 


76  FARADAY  AS  A   DISCOVERER. 

so  many  years.  During  these  years  lie  repeatedly 
broke  down.  His  wife  alone  witnessed  the  extent  of 
his  prostration,  and  to  her  loving  care  we,  and  the 
world,  are  indebted  for  the  enjoyment  of  his  presence 
here  so  long.  He  found  occasional  relief  in  a  theatre. 
He  frequently  quitted  London  and  went  to  Brighton 
and  elsewhere,  always  choosing  a  situation  which 
commanded  a  view  of  the  sea,  or  of  some  other 
pleasant  horizon,  where  he  could  sit  and  gaze  and 
feel  the  gradual  revival  of  the  faith  that 

'Nature  never  did  betray 
The  heart  that  loved  her.' 

But  very  often  for  some  days  after  his  removal  to  the 
country  he  would  be  unable  to  do  more  than  sit  at  a 
window  and  look  out  upon  the  sea  and  sky. 

In  1841,  his  state  became  more  serious  than  it  had 
ever  been  before.  A  published  letter  to  Mr.  Richard 
Taylor,  dated  March  11,  1843,  contains  an  allusion 
to  his  previous  condition.  '  You  are  aware,'  he  says, 
6  that  considerations  regarding  health  have  prevented 
me  from,  working  or  reading  on  science  for  the  last 
two  years.'  This,  at  one  period  or  another  of  their 
lives,  seems  to  be  the  fate  of  most  great  investigators. 
They  do  not  know  the  limits  of  their  constitutional 
strength  until  they  have  transgressed  them.  It  is, 
perhaps,  right  that  they  should  transgress  them,  in 


FARADAY  AS  A   DISCOVERER.  77 

order  to  ascertain  where  they  lie.  Faraday,  however, 
though  he  went  far  towards  it,  did  not  push  his 
transgression  beyond  his  power  of  restitution.  In 
1841  Mrs.  Faraday  and  he  went  to  Switzerland,  under 
the  affectionate  charge  of  her  brother,  Mr.  George 
Barnard,  the  artist.  This  time  of  suffering  throws 
fresh  light  upon  his  character.  I  have  said  that 
sweetness  and  gentleness  were  not  its  only  consti- 
tuents ;  that  he  was  also  fiery  and  strong.  At 
the  time  now  referred  to,  his  fire  was  low  and  his 
strength  distilled  away ;  but  the  residue  of  his  life 
was  neither  irritability  nor  discontent.  He  was  unfit 
to  mingle  in  society.,  for  conversation  was  a  pain  to 
him ;  but  let  us  observe  the  great  Man-child  when 
alone.  He  is  at  the  village  of  Interlaken,  enjoying 
Jungfrau  sunsets,  and  at  times  watching  the  Swiss 
nailers  making  their  nails.  He  keeps  a  little  journal, 
in  which  he  describes  the  process  of  nailmaking,  and 
incidentally  throws  a  luminous  beam  upon  himself. 

'August  2nd,  1841. — Clout  nailmaking  goes  on 
here  rather  considerably,  and  is  a  very  neat  and 
pretty  operation  to  observe.  I  love  a  smith's  shop 
and  anything  relating  to  smithery.  My  father  was 
a  smith.9 

From  Interlaken  he  went  to  the  Falls  of  the  Giess- 
bach,  on  the  pleasant  lake  of  Brientz.  And  here  we 


78  FARADAY   AS   A    DISCOVERER. 

have  him  watching  the  shoot  of  the  cataract  down 
its  series  of  precipices.  It  is  shattered  into  foam  at 
the  base  of  each,  and  tossed  by  its  own  recoil  as 
water-dust  through  the  air.  The  sun  is  at  his  back, 
shining  on  the  drifting  spray,  and  he  thus  describes 
and  muses  on  what  he  sees : — 

*  August  12th,  1841. — To-day  every  fall  was  foaming 
from  the  abundance  of  water,  and  the  current  of 
wind  brought  down  by  it  was  in  some  places  too 
strong  to  stand  against.  The  sun  shone  brightly, 
and  the  rainbows  seen  from  various  points  were  very 
beautiful.  One  at  the  bottom  of  a  fine  but  furious 
fall  was  very  pleasant, — there  it  remained  motionless, 
whilst  the  gusts  and  clouds  of  spray  swept  furiously 
across  its  place  and  were  dashed  against  the  rock. 
It  looked  like  a  spirit  strong  in  faith  and  steadfast 
in  the  midst  of  the  storm  of  passions  sweeping  across 
it,  and  though  it  might  fade  and  revive,  still  it  held 
on  to  the  rock  as  in  hope  and  giving  hope.  And  the 
very  drops,  which  in  the  whirlwind  of  their  fury 
seemed  as  if  they  would  carry  all  away,  were  made 
to  revive  it  and  give  it  greater  beauty.' 


FROM  A  PEIOTOO-HAFH  BY  Ct.AS.UET 


London  Lougmar,.';   &  C° 


FARADAY    AS   A   DISCOVERER.  79 


MAGNETIZATION   OP   LIGHT. 

But  we  must  quit  the  man  and  go  on  to  the  dis- 
coverer: we  shall  return  for  a  brief  space  to  his 
company  by-and-by.  Carry  your  thoughts  back  to 
his  last  experiments,  and  see  him  endeavouring  to 
prove  that  induction  is  due  to  the  action  of  con- 
tiguous particles.  He  knew  that  polarized  light  was 
a  most  subtle  and  delicate  investigator  of  molecular 
condition.  He  used  it  in  1834  in  exploring  his  elec- 
trolytes, and  he  tried  it  in  1838  upon  his  dielectrics. 
At  that  time  he  coated  two  opposite  faces  of  a  glass 
cube  with  tinfoil,  connected  one  coating  with  his 
powerful  electric  machine  and  the  other  with  the 
earth,  and  examined  by  polarized  light  the  condition 
of  the  glass  when  thus  subjected  to  strong  electric 
influence.  He  failed  to  obtain  any  eifect,  still  he 
was  persuaded  an  action  existed,  and  required  only 
suitable  means  to  call  it  forth. 

After  his  return  from  Switzerland  he  was  beset  by 
these  thoughts  ;  they  were  more  inspired  than  logi- 
cal :  but  he  resorted  to  magnets  and  proved  his  in- 
spiration true.  His  dislike  of  c  doubtful  knowledge  ' 
and  his  eiforts  to  liberate  his  mind  from  the  thraldom 
of  hypotheses  have  been  already  referred  to.  Still 
this  rebel  against  theory  was  incessantly  theorizing 


80  FAEADAY  AS   A   DISCOVERER. 

himself.  His  principal  researches  are  all  connected 
by  an  undercurrent  of  speculation.  Theoretic  ideas 
were  the  very  sap  of  his  intellect — the  source  from 
which  all  his  strength  as  an  experimenter  was  de- 
rived. While  once  sauntering  with  him  through  the 
Crystal  Palace,  at  Sydenham,  I  asked  him  what 
directed  his  attention  to  the  magnetization  of  light. 
It  was  his  theoretic  notions.  He  had  certain  views 
regarding  the  unity  and  convertibility  of  natural 
forces;  certain  ideas  regarding  the  vibrations  of 
light  and  their  relations  to  the  lines  of  magnetic 
force;  these  views  and  ideas  drove  him  to  investi- 
gation. And  so  it  must  always  be :  the  great  experi- 
mentalist must  ever  be  the  habitual  theorist,  whether 
or  not  he  gives  to  his  theories  formal  enunciation. 

Faraday,  you  have  been  informed,  endeavoured  to 
improve  the  manufacture  of  glass  for  optical  pur- 
poses. But  though  he  produced  a  heavy  glass  of 
great  refractive  power,  its  value  to  optics  did  not. 
repay  him  for  the  pains  and  labour  bestowed  on  it. 
Now,  however,  we  reach  a  result  established  by 
means  of  this  same  heavy  glass,  which  made  ample 
amends  for  all. 

In  November,  1845,  he  announced  his  discovery  of 
the  '  Magnetization  of  Light,  and  the  Elumination  of 
the  Lines  of  Magnetic  Force.'  This  title  provoked 
comment  at  the  time,  and  caused  misapprehension. 


FARADAY   AS   A   DISCOVERER.  81 

He  therefore  added  an  explanatory  note;  but  the 
note  left  his  meaning  as  entangled  as  before.  In. 
fact  Faraday  had  notions  regarding  the  magnetiza- 
tion of  light  which  were  peculiar  to  himself,  and 
untranslatable  into  the  scientific  language  of  the 
time.  Probably  no  other  philosopher  of  his  day 
would  have  employed  the  phrases  just  quoted  as 
appropriate  to  the  discovery  announced  in  1845.  But 
Faraday  was  more  than  a  philosopher;  he  was 'a 
prophet,  and  often  wrought  by  an  inspiration  to  be 
understood  by  sympathy  alone.  The  prophetic  ele- 
ment in  his  character  occasionally  coloured,  and  even 
injured,  the  utterance  of  the  man  of  science ;  but 
subtracting  that  element,  though  you  might  have 
conferred  on  him  intellectual  symmetry,  you  would 
have  destroyed  his  motive  force. 

But  let  us  pass  from  the  label  of  this  casket  to  the 
jewel  it  contains.  '  I  have  long,'  he  says,  f  held  an 
opinion,  almost  amounting  to  conviction,  in  common, 
I  believe,  with  many  other  lovers  of  natural  know- 
ledge, that  the  various  forms  under  which  the  forces 
of  matter  are  made  manifest  have  one  common 
origin;  in  other  words,  are  so  directly  related  and 
mutually  dependent,  that  they  are  convertible,  as  it 
were,  into  one  another,  and  possess  equivalents  of 
power  in  their  action.  .  .  .  This  strong  persuasion,' 
he  adds,  c  extended  to  the  powers  of  light.'  And 


82  PABADAY   AS   A   DISCOVERER. 

then  lie  examines  the  action  of  magnets  upon  light. 
From  conversation  with  him  and  Anderson,  I  should 
infer  that  the  labour  preceding  this  discovery  was 
very  great.  The  world  knows  little  of  the  toil  of 
the  discoverer.  It  sees  the  climber  jubilant  on  the 
mountain  top,  but  does  not  know  the  labour  expended 
in  reaching  it.  Probably  hundreds  of  experiments 
had  been  made  on  transparent  crystals  before  he 
thought  of  testing  his  heavy  glass.  Here  is  his 
own  clear  and  simple  description  of  the  result  of 
his  first  experiment  with  this  substance  : — ( A  piece 
of  this  glass,  about  two  inches  square,  and  0*5 
of  an  inch  thick,  having  flat  and  polished  edges, 
was  placed  as  a  diamagnetic*  between  the  poles  (not 
as  yet  magnetized  by  the  electric  current),  so  that 
the  polarized  ray  should  pass  through  its  length ; 
the  glass  acted  as  air,  water,  or  any  other  trans- 
parent substance  would  do ;  and  if  the  eye-piece 
were  previously  turned  into  such  a  position  that  the 
polarized  ray  was  extinguished,  or  rather  the  image 
produced  by  it  rendered  invisible,  then  the  intro- 
duction of  the  glass  made  no  alteration  in  this  re- 
spect. In  this  state  of  circumstances,  the  force  of 

*  '  By  a  diamagnetic,'  says  Faraday,  '  I  mean  a  body  through  which 
lines  of  magnetic  force  are  passing,  and  which  does  not  by  their  action 
assume  the  usual  magnetic  state  of  iron  or  loadstone.'  Faraday  sub- 
sequently used  this  term  in  a  different  sense  from  that  here  given, 
as  will  immediately  appear. 


FARADAY   AS   A    DISCOVERER.  83 

the  electro-magnet  was  developed  by  sending  an 
electric  current  through  its  coils,  and  immediately 
the  image  of  the  lamp-flame  became  visible,  and 
continued  so  as  long  as  the  arrangement  continued 
magnetic.  On  stopping  the  electric  current,  and  so 
causing  the  magnetic  force  to  cease,  the  light  in- 
stantly disappeared.  These  phenomena  could  be 
renewed  at  pleasure,  at  any  instant  of  time,  and 
upon  any  occasion,  showing  a  perfect  dependence  of 
cause  and  effect.' 

In  a  beam  of  ordinary  light  the  particles  of  the 
luminiferous  ether  vibrate  in  all  directions  perpen- 
dicular to  the  line  of  progression ;  by  the  act  of  polar- 
ization, performed  here  by  Faraday,  all  oscillations 
but  those  parallel  to  a  certain  plane  are  eliminated. 
When  the  plane  of  vibration  of  the  polarizer  co- 
incides with  that  of  the  analyzer,  a  portion  of  the 
beam  passes  through  both ;  but  when  these  two 
planes  are  at  right  angles  to  each  other,  the  beam 
is  extinguished.  If  by  any  means,  while  the  po- 
larizer and  analyzer  remain  thus  crossed,  the  plane 
of  vibration  of  the  polarized  beam  between  them 
could  be  changed,  then  the  light  would  be,  in  part  at 
least,  transmitted.  In  Faraday's  experiment  this  was 
accomplished.  His  magnet  turned  the  plane  of  po- 
larization of  the  beam  through  a  certain  angle,  and 
thus  enabled  it  to  get  through  the  analyzer;  so 

c  2 


84  FARADAY  AS   A   DISCOVERER. 

that  '  the  magnetization  of  light  and  the  illumina- 
tion of  the  magnetic  lines  of  force '  becomes,  when 
expressed  in  the  language  ot  modern  theory,  the  ro- 
tation of  the  plane  of  polarization. 

To  him,  as  to  all  true  philosophers,  the  main  value 
of  a  fact  was  its  position  and  suggestiveness  in  the 
general  sequence  of  scientific  truth.  Hence,  having 
established  the  existence  of  a  phenomenon,  his  habit 
was  to  look  at  it  from  all  possible  points  of  view,  and 
to  develop  its  relationship  to  other  phenomena.  He 
proved  that  the  direction  of  the  rotation  depends 
upon  the  polarity  of  his  magnet;  being  reversed 
when  the  magnetic  poles  are  reversed.  He  showed 
that  when  a  polarized  ray  passed  through  his  heavy 
glass  in  a  direction  parallel  to  the  magnetic  lines  of 
force,  the  rotation  is  a  maximum,  and  that  when  the 
direction  of  the  ray  is  at  right  angles  to  the  lines  of 
force,  there  is  no  rotation  at  all.  He  also  proved  that 
the  amount  of  the  rotation  is  proportional  to  the  length 
of  the  diamagnetic  through  which  the  ray  passes. 
He  operated  with  liquids  and  solutions.  Of  aqueous 
solutions  he  tried  150  and  more,  and  found  the  power 
in  all  of  them.  He  then  examined  gases  ;  but  here 
all  his  efforts  to  produce  any  sensible  action  upon  the 
polarized  beam  were  ineffectual.  He  then  passed 
from  magnets  to  currents,  enclosing  bars  of  heavy 
glass,  and  tubes  containing  liquids  and  aqueous  solu- 


FARADAY   AS   A   DISCOVERER.  85 

tions  within  an  electro-magnetic  helix.  A  current 
sent  through  the  helix  caused  the  plane  of  polari- 
zation to  rotate,  and  always  in  the  direction  of  the 
current.  The  rotation  was  reversed  when  the  current 
was  reversed.  In  the  case  of  magnets,  he  observed 
a  gradual,  though  quick,  ascent  of  the  transmitted 
beam  from  a  state  of  darkness  to  its  maximum  bril- 
liancy, when  the  magnet  was  excited.  In  the  case  of 
currents,  the  beam  attained  at  once  its  maximum. 
This  he  showed  to  be  due  to  the  time  required  by  the 
iron  of  the  electro-magnet  to  assume  its  full  magnetic 
power,  which  time  vanishes  when  a  current,  without 
iron,  is  employed.  f  In  this  experiment,'  he  says,  '  we 
may,  I  think,  justly  say  that  a  ray  of  light  is  elec- 
trified, and  the  electric  forces  illuminated.'  In  the 
helix,  as  with  the  magnets,  he  submitted  air  to  mag- 
netic influence  £  carefully  and  anxiously,'  but  could 
not  discover  any  trace  of  action  on  the  polarized  ray. 
Many  substances  possess  the  power  of  turning 
the  plane  of  polarization  without  the  intervention 
of  magnetism.  Oil  of  turpentine  and  quartz  are 
examples  ;  but  Faraday  showed  that,  while  in  one  di- 
rection, that  is,  across  the  lines  of  magnetic  force,  his 
rotation  is  zero,  augmenting  gradually  from  this  until 
it  attains  its  maximum,  when  the  direction  of  the  ray 
is  parallel  to  the  lines  of  force ;  in  the  oil  of  turpen- 
tine the  rotation  is  independent  of  the  direction  of 


86  FARADAY  AS   A   DISCOVERER. 

the  ray.  But  lie  showed  that  a  still  more  profound 
distinction  exists  between  the  magnetic  rotation  and 
the  natural  one.  I  will  try  to  explain  how.  Suppose 
a  tube  with  glass  ends  containing  oil  of  turpentine  to 
be  placed  north  and  south.  Fixing  the  eye  at  the 
south  end  of  the  tube,  let  a  polarized  beam  be  sent 
through  it  from  the  north.  To  the  observer  in  this 
position  the  rotation  of  the  plane  of  polarization,  by 
the  turpentine,  is  right-handed.  Let  the  eye  be  placed 
at  the  north  end  of  the  tube,  and  a  beam  be  sent 
through  it  from  the  south  ;  the  rotation  is  still  right- 
handed.  Not  so,  however,  when  a  bar  of  heavy  glass  is 
subjected  to  the  action  of  an  electric  current.  In  this 
case  if,  in  the  first  position  of  the  eye,  the  rotation  be 
right-handed,  in  the  second  position  it  is  left-handed. 
These  considerations  make  it  manifest  that  if  a  polar- 
ized beam,  after  having  passed  through  the  oil  of 
turpentine  in  its  natural  state,  could,  by  any  means, 
be  reflected  back  through  the  liquid,  the  rotation 
impressed  upon  the  direct  beam  would  be  exactly 
neutralized  by  that  impressed  upon  the  reflected  one. 
.Not  so  with  the  induced  magnetic  effect.  Here  it  is 
manifest  that  the  rotation  would  be  doubled  by  the 
act  of  reflection.  Hence  Faraday  concludes  that 
the  particles  of  the  oil  of  turpentine  which  rotate  by 
virtue  of  their  natural  force,  and  those  which  rotate 
in  virtue  of  the  induced  force,  cannot  be  in  the  same 


FAEADAY  AS   A   DISCOVERER.  67 

condition.  The  same  remark  applies  to  all  bodies 
which  possess  a  natural  power  of  rotating  the  plane 
of  polarization. 

And  then  he  proceeded  with  exquisite  skill  and  in- 
sight to  take  advantage  of  this  conclusion.  He  sil- 
vered the  ends  of  his  piece  of  heavy  glass,  leaving, 
however,  a  narrow  portion  parallel  to  two  edges  dia- 
gonally opposed  to  each  other  unsilvered.  He  then 
sent  his  beam  through  this  uncovered  portion,  and 
by  suitably  inclining  his  glass  caused  the  beam 
within  it  to  reach  his  eye,  first  direct,  and  then  after 
two,  four,  and  six  reflections.  These  corresponded  to 
the  passage  of  the  ray  once,  three  times,  five  times, 
and  seven  times  through  the  glass.  He  thus  estab- 
lished with  numerical  accuracy  the  exact  proportion- 
ality of  the  rotation,  to  the  distance  traversed  by  the 
polarized  beam.  Thus  in  one  series  of  experiments 
where  the  rotation  required  by  the  direct  beam  was 
12°,  that  acquired  by  three  passages  through  the 
glass  was  36°,  while  that  acquired  by  five  passages 
was  60°.  But  even  when  this  method  of  magnifying 
was  applied,  he  failed  with  various  solid  substances 
to  obtain  any  effect ;  and  in  the  case  of  air,  though 
he  employed  to  the  utmost  the  power  which  these  re- 
peated reflections  placed  in  his  hands,  he  failed  to 
produce  the  slightest  sensible  rotation. 

These  failures  of  Faraday  to  obtain  the  effect  with 


88  FARADAY   AS   A   DISCOVERER. 

gases,  seem  to  indicate  the  true  seat  of  the  phenome- 
non. The  luniimferous  ether  surrounds  and  is  influ- 
enced by  the  ultimate  particles  of  matter.  The  symme- 
try of  the  one  involves  that  of  the  other.  Thus,  if  the 
molecules  of  a  crystal  be  perfectly  symmetrical  round 
any  line  through  the  crystal,  we  may  safely  conclude 
that  a  ray  will  pass  along  this  line  as  through  ordi- 
nary glass.  It  will  not  be  doubly  refracted.  Prom 
the  symmetry  of  the  liquid  figures,  known  to  be  pro- 
duced in  the  planes  of  freezing,  when  radiant  heat  is 
sent  through  ice,  we  may  safely  infer  symmetry  of 
aggregation,  and  hence  conclude  that  the  line  per- 
pendicular to  the  planes  of  freezing  is  a  line  of  no 
double  refraction :  that  it  is,  in  fact,  the  optic  axis  of 
the  crystal.  The  same  remark  applies  to  the  line  join- 
ing the  opposite  blunt  angles  of  a  crystal  of  Iceland 
spar.  The  arrangement  of  the  molecules  round  this 
line  being  symmetrical,  the  condition  of  the  ether  de- 
pending upon  these  molecules  shares  their  symmetry; 
and  there  is,  therefore,  no  reason  why  the  wave- 
length should  alter  with  the  alteration  of  the  azi- 
muth round  this  line.  Annealed  glass  has  its  mole- 
cules symmetrically  arranged  round  every  line  that 
can  be  drawn  through  it ;  hence  it  is  not  doubly  re- 
fractive. But  let  the  substance  be  either  squeezed  or 
strained  in  one  direction,  the  molecular  symmetry,  and 
with  it  the  symmetry  of  the  ether,  is  immediately 


FARADAY   AS   A   DISCOVERER.  89 

destroyed  and  the  glass  becomes  doubly  refractive. 
Unequal  .heating  produces  the  same  effect.  Thus 
mechanical  strains  reveal  themselves  by  optical 
effects  5  and  there  is  little  doubt  that  in  Faraday's 
experiment  it  is  the  magnetic  strain  that  produces 
the  rotation  of  the  plane  of  polarization.* 


DISCOVERY     OP     DIAMAGNETISM     RESEARCHES     ON 
MA3NE-CRYSTALLIC    ACTION. 

Faraday's  next  great  step  in  discovery  was  an- 
nounced in  a  memoir  on  the  c  Magnetic  Condition 
of  all  Matter,'  communicated  to  the  Royal  Society 
on  December  18,  1845.  One  great  source  of  his 
success  was  the  employment  of  extraordinary  power. 
As  already  stated,  he  never  accepted  a  negative 
answer  to  an  experiment  until  he  had  brought  to 
bear  upon  it  all  the  force  at  his  command.  He  had 
over  and  over  again  tried  steel  magnets  and  ordinary 

*  The  power  of  double  refraction  conferred  on  the  centre  of  a  glass 
rod,  when  it  is  caused  to  sound  the  fundamental  note  due  to  its  longi- 
tudinal vibration,  and  the  absence  of  the  same  power  in  the  case  of 
vibrating  air  (enclosed  in  a  glass  organ-pipe),  seems  to  be  analogous  to 
the  presence  and  absence  of  Faraday's  effect  in  the  same  two  substances. 

Faraday  never,  to  my  knowledge,  attempted  to  give,  even  in  conver- 
sation, a  picture  of  the  molecular  condition  of  his  heavy  glass  when 
subjected  to  magnetic  influence.  In  a  mathematical  investigation  of 
the  subject,  published  in  the  Proceedings  of  the  Royal  Society  for  1856, 
Sir  William  Thomson  arrives  at  the  conclusion  that  the  '  diamagnetic ' 
is  in  a  state  of  molecular  rotation. 


90  FARADAY  AS  A   DISCOVEEER. 

electro-magnets  on  various  substances,  but  without 
detecting  anything  different  from  the  ordinary  at- 
traction exhibited  by  a  few  of  them.  Stronger  coer- 
cion, however,  developed  a  new  action.  Before  the 
pole  of  an  electro-magnet,  he  suspended  a  frag- 
ment of  his  famous  heavy  glass ;  and  observed  that 
when  the  magnet  was  powerfully  excited  the  glass 
fairly  retreated  from  the  pole.  It  was  a  clear  case 
of  magnetic  repulsion.  He  then  suspended  a  bar  of 
the  glass  between  two  poles  ;  the  bar  retreated  when 
the  poles  were  excited,  and  set  its  length  equatorially 
or  at  right  angles  to  the  line  joining  them.  When 
an  ordinary  magnetic  body  was  similarly  suspended, 
it  always  set  axially,  that  is,  from  pole  to  pole. 

Faraday  called  those  bodies  which  were  repelled 
by  the  poles  of  a  magnet,  diamagnetic  bodies ;  using 
this  term  in  a»sense  different  from  that  in  which  he 
employed  it  in  his  memoir  on  the  magnetization  of 
light.  The  term  magnetic  he  reserved  for  bodies 
which  exhibited  the  ordinary  attraction.  He  after- 
wards employed  the  term  magnetic  to  cover  the  whole 
phenomena  of  attraction  and  repulsion,  and  used  the 
word  paramagnetic  to  designate  such  magnetic  action 
as  is  exhibited  by  iron. 

Isolated  observations  by  Brugmanns,  Becquerel,  le 
Baillif,  Saigy,  and  Seebeck,  had  indicated  the  exist- 
ence of  a  repulsive  force  exercised  by  the  magnet  on 


FARADAY   AS   A   DISCOVERER.  91 

two  or  three  substances ;  but  these  observations, 
which  were  unknown  to  Faraday,  had  been  permitted 
to  remain  without  extension  or  examination.  Having 
laid  hold  of  the  fact  of  repulsion,  Faraday  imme- 
diately expanded  and  multiplied  it.  He  subjected 
bodies  of  the  most  various  qualities  to  the  action  of 
his  magnet: — mineral  salts,  acids,  alkalis,  ethers, 
alcohols,  aqueous  solutions,  glass,  phosphorus,  resins, 
oils,  essences,  vegetable  and  animal  tissues,  and 
found  them  all  amenable  to  magnetic  influence.  No 
known  solid  or  liquid  proved  insensible  to  the  mag- 
netic power  when  developed  in  sufficient  strength. 
All  the  tissues  of  the  human  body,  the  blood — though 
it  contains  iron — included,  were  proved  to  be  dia- 
magnetic.  So  that  if  you  could  suspend  a  man 
between  the  poles  of  a  magnet,  his  extremities  would 
retreat  from  the  poles  until  his  length  became  equa- 
torial. 

Soon  after  he  had  commenced  his  researches  on 
diamagnetism,  Faraday  noticed  a  remarkable  phe- 
nomenon which  first  crossed  my  own  path  in  the 
following  way :  In  the  year  1849,  while  working  in 
the  cabinet  of  my  friend,  Professor  Knoblauch,  of 
Marburg,  I  suspended  a  small  copper  com  between 
the  poles  of  an  electro-magnet.  On  exciting  the 
magnet,  the  coin  moved  towards  the  poles  and  then 
suddenly  stopped,  as  if  it  had  struck  against  a 


92  FARADAY  AS   A   DISCOVERER. 

cushion.  On  breaking  the  circuit,  the  coin  was  re- 
pelled, the  revulsion  being  so  violent  as  to  cause  it 
to  spin  several  times  round  its  axis  of  suspension. 
A  Silber-groschen  similarly  suspended  exhibited  the 
same  deportment.  For  a  moment  I  thought  this  a 
new  discovery ;  but  on  looking  over  the  literature  of 
the  subject,  it  appeared  that  Faraday  had  observed, 
multiplied,  and  explained  the  same  effect  during 
his  researches  on  diamagnetism.  His  explanation 
was  based  upon  his  own  great  discovery  of  magneto- 
electric  currents.  The  effect  is  a  most  singular 
one.  A  weight  of  several  pounds  of  copper  may  be 
set  spinning  between  the  electro-magnetic  poles ; 
the  excitement  of  the  magnet  instantly  stops  the 
rotation.  Though  nothing  is  apparent  to  the  eye, 
the  copper,  if  moved  in  the  excited  magnetic  field, 
appears  to  move  through  a  viscous  fluid ;  while,  when 
a  flat  piece  of  the  metal  is  caused  to  pass  to  and  fro 
like  a  saw  between  the  poles,  the  sawing  of  the  mag- 
netic field  resembles  the  cutting  through  of  cheese  or 
butter.*  This  virtual  friction  of  the  magnetic  field 
is  so  strong,  that  copper,  by  its  rapid  rotation  between 
the  poles,  might  probably  be  fused.  We  may  easily 
dismiss  this  experiment  by  saying  that  the  heat  is 
due  to  the  electric  currents  excited  in  the  copper. 
But  so  long  as  we  are  unable  to  reply  to  the  question, 

*  See  Heat  as  a  Mode  of  Motion,  third  edition,  §  36. 


FAEADAY   AS  A  DISCO  VEEEE.  93 

'What  is  an  electric  current?'  the  explanation  is 
only  provisional.  For  my  own  part,  I  look  with 
profound  interest  and  hope  on  the  strange  action 
here  referred  to. 

Faraday's  thoughts  ran  intuitively  into  experi- 
mental combinations,  so  that  subjects  whose  capacity 
for  experimental  treatment  would,  to  ordinary  minds, 
seem  to  be  exhausted  in  a  moment,  were  shown  by 
him  to  be  all  but  inexhaustible.  He  has  now  an 
object  in  view,  the  first  step  towards  which  is  the 
proof  that  the  principle  of  Archimedes  is  true  of 
magnetism.  He  forms  magnetic  solutions  of  various 
degrees  of  strength,  places  them  between  the  poles 
of  his  magnet,  and  suspends  in  the  solutions  various 
magnetic  bodies.  He  proves  that  when  the  solution 
is  stronger  than  the  body  plunged  in  it,  the  body, 
though  magnetic,  is  repelled ;  and  when  an  elongated 
piece  of  it  is  surrounded  by  the  solution  it  sets,  like 
a  diamagnetic  body,  equatorially  between  the  excited 
poles.  The  same  body  when  suspended  in  a  solution 
of  weaker  magnetic  power  than  itself,  is  attracted  as 
whole,  while  an  elongated  portion  of  it  sets  axially. 

And  now  theoretic  questions  rush  in  upon  him. 
Is  this  new  force  a  true  repulsion,  or  is  it  merely  a 
differential  attraction  ?  Might  not  the  apparent  re- 
pulsion of  diamagnetic  bodies  be  really  due  to  the 
greater  attraction  of  the  medium  by  which  they  are 


94  FARADAY   AS   A   DISCOVERER. 

surrounded?  He  tries  the  rarefaction  of  air,  but 
finds  the  effect  insensible.  He  is  averse  to  ascribing 
a  capacity  of  attraction  to  space,  or  to  any  hypothe- 
tical medium  supposed  to  fill  space.  He  therefore 
inclines,  but  still  with  caution,  to  the  opinion  that 
the  action  of  a  magnet  upon  bismuth  is  a  true  and 
absolute  repulsion,  and  not  merely  the  result  of  dif- 
ferential attraction.  And  then  he  clearly  states  a 
theoretic  view  sufficient  to  account  for  the  pheno- 
mena. '  Theoretically,'  he  says,  '  an  explanation  of 
the  movements  of  the  diamagnetic  bodies,  and  all 
the  dynamic  phenomena  consequent  upon  the  action 
of  magnets  upon  them,  might  be  offered  in  the  sup- 
position that  magnetic  induction  caused  in  them  a 
contrary  state  to  that  which  it  produced  in  ordinary 
matter.'  That  is  to  say,  while  in  ordinary  magnetic 
influence  the  exciting  pole  excites  adjacent  to  itself 
the  contrary  magnetism,  in  diamagnetic  bodies  the 
adjacent  magnetism  is  the  same  as  that  of  the 
exciting  pole.  This  theory  of  reversed  polarity, 
however,  does  not  appear  to  have  ever  laid  deep 
hold  of  Faraday's  mind ;  and  his  own  experiments 
failed  to  give  any  evidence  of  its  truth.  He  there- 
fore subsequently  abandoned  it,  and  maintained  the 
non-polarity  of  the  diamagnetic  force. 

He  then  entered  a  new,  though  related  field  of  in- 
quiry.    Having  dealt  with  the  metals  and  their  coin- 


FARADAY  AS   A   DISCOVERER.  95 

pounds,  and  having  classified  all  of  them  that  came 
within  the  range  of  his  observation  under  the  two 
heads  magnetic  and  diamagnetic,  he  began  the  in- 
vestigation of  the  phenomena  presented  by  crystals 
when  subjected  to  magnetic  power.  The  action  of 
crystals  had  been  in  part  theoretically  predicted  by 
Poisson,*  and  actually  discovered  by  Pliicker,  whose 
beautiful  results,  at  the  period  which  we  have  now 
reached,  profoundly  interested  all  scientific  men. 
Faraday  had  been  frequently  puzzled  by  the  deport- 
ment of  bismuth,  a  highly  crystalline  metal.  Some- 
times elongated  masses  of  the  substance  refused  to 
set  equatorially,  sometimes  they  set  persistently  ob- 
lique, and  sometimes  even,  like  a  magnetic  body, 
from,  pole  to  pole.  e  The  eifect,'  he  says,  '  occurs 
at  a  single  pole ;  and  it  is  then  striking  to  observe 
a  long  piece  of  a  substance  so  diamagnetic  as  bismuth 
repelled,  and  yet  at  the  same  moment  set  round  with 
force,  axially,  or  end  on,  as  a  piece  of  magnetic  sub- 
stance would  do.'  The  effect  perplexed  him ;  and 
in  his  efforts  to  release  himself  from  this  perplexity, 
no  feature  of  this  new  manifestation  of  force  escaped 
his  attention.  His  experiments  are  described  in  a 
memoir  communicated  to  the  Royal  Society  on  De- 
cember 7, 1848. 

I  have   worked  long   myself  at  magne-crystallic 

*  See  Sir  Wm.  Thomson  on  Magne-crystallic  Action.   Phil.  Mag.  1851. 


96  FARADAY   AS   A   DISCOVERER. 

action,  amid  all  the  light  of  Faraday's  and  Pliicker  s 
researches.  The  papers  now  before  me  were  objects 
of  daily  and  nightly  study  with  me  eighteen  or  nine- 
teen years  ago  ;  but  even  now,  though  their  perusal 
is  but  the  last  of  a  series  of  repetitions,  they  astonish 
me.  Every  circumstance  connected  with  the  sub- 
ject; every  shade  of  deportment;  every  variation  in 
the  energy  of  the  action ;  almost  every  application 
which  could  possibly  be  made  of  magnetism  to  bring 
out  in  detail  the  character  of  this  new  force.,  is 
minutely  described.  The  field  is  swept  clean,  and 
hardly  anything  experimental  is  left  for  the  gleaner. 
The  phenomena,  he  concludes,  are  altogether  dif- 
ferent from  those  of  magnetism  or  diamagnetism  : 
they  would  appear,  in  fact,  to  present  to  us  c  a  new 
force,  or  a  new  form  of  force,  in  the  molecules  of 
matter,'  which,  for  convenience  sake,  he  designates 
by  a  new  word,  as  '  the  magne-crystallic  force.' 

He  looks  at  the  crystal  acted  upon  by  the  -magnet. 
From  its  mass  he  passes,  in  idea,  to  its  atoms,  and  he 
asks  himself  whether  the  power  which  can  thus  seize 
upon  the  crystalline  molecules,  after  they  have  been 
fixed  in  their  proper  positions  by  crystallizing  force, 
may  not,  when  they  are  free,  be  able  to  determine 
their  arrangement  9  He,  therefore,  liberates  the 
atoms  by  fusing  the  bismuth.  He  places  the  fused 
substance  between  the  poles  of  an  electro-magnet, 


FARADAY   AS   A   DISCOVERER.  97 

powerfully  excited ;  but  lie  fails  to  detect  any  action. 
I  think  it  cannot  be  doubted  that  an  action  is  exerted 
here,  that  a  true  cause  comes  into  play :  but  its  mag- 
nitude is  not  such  as  sensibly  to  interfere  with  the 
force  of  crystallization,  which,  in  comparison  with 
the  diamagnetic  force,  is  enormous.  '  Perhaps,'  adds 
Faraday,  '  if  a  longer  time  were  allowed,  and  a  per- 
manent magnet  used,  a  better  result  might  be  ob- 
tained. I  had  built  many  hopes  upon  the  process.' 
This  expression,  and  his  writings  abound  in  such,  il- 
lustrates what  has  been  already  said  regarding  his  ex- 
periments being  suggested  and  guided  by  his  theoretic 
conceptions.  His  mind  was  full  of  hopes  and  hypo- 
theses, but  he  always  brought  them  to  an  experi- 
mental test.  The  record  of  his  planned  and  executed 
experiments  would,  I  doubt  not,  show  a  high  ratio 
of  hopes  disappointed  to  hopes  fulfilled ;  but  every 
case  of  fulfilment  abolished  all  memory  of  defeat; 
disappointment  was  swallowed  up  in  victory. 

After  the  description  of  the  general  character  of 
this  new  force,  Faraday  states  with  the  emphasis 
here  reproduced  its  mode  of  action :  '  The  law  of 
action  appears  to  be  that  the  line  or  axis  of  MAGNE- 
CETSTALLIC  force  (being  the  resultant  of  the  action  of 
all  the  molecules)  tends  to  place  itself  parallel,  or  as  a 
tangent,  to  the  magnetic  curve,  or  line  of  magnetic  force, 
passing  through  the  place  where  the  crystal  is  situated.9 

H 


98  FARADAY  AS  A   DISCOVERER 

The  magne-crystallic  force,  moreover,  appears  to 
him  '  to  be  clearly  distinguished  from  the  magnetic 
or  diamagnetic  forces,  in  that  it  causes  neither 
approach  nor  recession,  consisting  not  in  attraction 
or  repulsion,  but  in  giving  a  certain  determinate 
position  to  the  mass  under  its  influence.'  And  then 
he  goes  on  '  very  carefully  to  examine  and  prove  the 
conclusion  that  there  was  no  connection  of  the  force 
with  attractive  or  repulsive  influences.'  With  the 
most  refined  ingenuity  he  shows  that,  under  certain 
circumstances,  the  magne-crystallic  force  can  cause 
the  centre  of  gravity  of  a  highly  magnetic  body  to 
retreat  from  the  poles,  and  the  centre  of  gravity  of  a 
highly  diamagnetic  body  to  approach  them.  His 
experiments  root  his  mind  more  and  more  firmly  in 
the  conclusion  that  it  is  c  neither  attraction  nor  re- 
pulsion causes  the  set,  or  governs  the  final  position  ' 
of  the  crystal  in  the  magnetic  field.  That  the  force 
which  does  so  is  therefore  '  distinct  in  its  character 
and  effects  from  the  magnetic  and  diamagnetic  forms 
of  force.  On  the  other  hand,'  he  continues,  '  it  has 
a  most  manifest  relation  to  the  crystalline  structure 
of  bismuth  and  other  bodies,  and  therefore  to  the 
power  by  which  their  molecules  are  able  to  build  up 
the  crystalline  masses.' 

And  here  follows  one  of  those  expressions  which 
characterize  the  conceptions  of  Faraday  in  regard  to 


FARADAY   AS   A   DISCOVERER.  99 

force  generally : — c  It  appears  to  me  impossible  to 
conceive  of  the  results  in  any  other  way  than  by  a 
mutual  reaction  of  the  magnetic  force,  and  the  force 
of  the  particles  of  the  crystal  upon  each  other.'  He 
proves  that  the  action  of  the  force,  though  thus 
molecular,  is  an  action  at  a  distance  ;  he  shows  that 
a  bismuth  crystal  can  cause  a  freely  suspended  mag- 
netic needle  to  set  parallel  to  its  magne-crystallic 
axis.  Few  living  men  are  aware  of  the  difficulty  of 
obtaining  results  like  this,  or  of  the  delicacy  neces- 
sary to  their  attainment.  '  But  though  it  thus  takes 
up  the  character  of  a  force  acting  at  a  distance,  still 
it  is  due  to  that  power  of  the  particles  which  makes 
them  cohere  in  regular  order  and  gives  the  mass  its 
crystalline  aggregation,  which  we  call  at  other  times 
the  attraction  of  aggregation,  and  so  often  speak  of 
as  acting  at  insensible  distances.'  Thus  he  broods 
over  this  new  force,  and  looks  at  it  from  all  possible 
points  of  inspection.  Experiment  follows  experiment, 
as  thought  follows  thought.  He  will  not  relinquish 
the  subject  as  long  as  a  hope  exists  of  throwing  more 
light  upon  it.  He  knows  full  well  the  anomalous 
nature  of  the  conclusion  to  which  his  experiments 
lead  him.  But  experiment  to  him  is  final,  and  he 
will  not  shrink  from  the  conclusion.  '  This  force,' 
he  says,  6  appears  to  me  to  be  very  strange  and 
striking  in  its  character.  It  is  not  polar,  for  there 

H    2 


100  FARADAY  AS   A   DISCOVERER. 

is  no  attraction  or  repulsion.5  And  then,  as  if  startled 
by  his  own  utterance,  he  asks — ( What  is  the  nature 
of  the  mechanical  force  which  turns  the  crystal 
round,  and  makes  it  affect  a  magnet  ?  '  .  ,  .  i  I 
do  not  remember,'  he  continues,  f  heretofore  such  a 
case  of  force  as  the  present  one,  where  a  body  is 
brought  into  position  only,  without  attraction  or  re- 
pulsion.' 

Pliicker,  the  celebrated  geometer  already  men- 
tioned, who  pursued  experimental  physics  for  many 
years  of  his  life  with  singular  devotion  and  suc- 
cess, visited  Faraday  in  those  days,  and  repeated 
before  him  his  beautiful  experiments  on  magneto- 
optic  action.  Faraday  repeated  and  verified  Pliicker's 
observations,  and  concluded,  what  he  at  first  seemed 
to  doubt,  that  Pliicker's  results  and  magne-crystallic 
action  had  the  same  origin. 

At  the  end  of  his  papers,  when  he  takes  a  last  look 
along  the  line  of  research,  and  then  turns  his  eyes  to 
the  future,  utterances  quite  as  much  emotional  as 
scientific  escape  from  Faraday.  '  I  cannot,'  he  says, 
at  the  end  of  his  first  paper  on  magne-crystallic 
action,  '  conclude  this  series  of  researches  without 
remarking  how  rapidly  the  knowledge  of  molecular 
forces  grows  upon  us,  and  how  strikingly  every  in- 
vestigation tends  to  develop  more  and  more  their 
importance,  and  their  extreme  attraction  as  an  object 


FARADAY   AS   A   DISCOVERER.  101 

of  study.  A  few  years  ago  magnetism  was  to  us  an 
occult  power,  affecting  only  a  few  bodies,  now  it  is 
found  to  influence  all  bodies,  and  to  possess  the  most 
intimate  relations  with  electricity,  heat,  chemical 
action,  light,  crystallization,  and  through  it,  with  the 
forces  concerned  in  cohesion;  and  we  may,  in  the 
present  state  of  things,  well  feel  urged  to  continue  in 
our  labours,  encouraged  by  the  hope  of  bringing  it 
into  a  bond  of  union  with  gravity  itself.' 


SUPPLEMENTARY    REMARKS. 

A  brief  space  will,  perhaps,  be  granted  me  here  to 
state  the  further  progress  of  an  investigation  which 
interested  Faraday  so  much.  Drawn  by  the  fame  of 
Bunsen  as  a  teacher,  in  the  year  1848  I  became  a 
student  in  the  University  of  Marburg,  in  Hesse  Cassel. 
Bunsen  behaved  to  me  as  a  brother  as  well  as  a 
teacher,  and  it  was  also  my  happiness  to  make  the 
acquaintance  and  gain  the  friendship  of  Professor 
Knoblauch,  so  highly  distinguished  by  his  researches 
on  Eadiant  Heat.  Pliicker's  and  Faraday's  investi- 
gations filled  all  minds  at  the  time,  and  towards  the 
end  of  1849,  Professor  Knoblauch  and  myself  com- 
menced a  joint  investigation  of  the  entire  question. 
Long  discipline  was  necessary  to  give  us  due  mastery 
over  it.  Employing  a  method  proposed  by  Dove,  we 


102  FARADAY  AS  A   DISCOVERER. 

examined  the  optical  properties  of  our  crystals  our- 
selves ;  and  these  optical  observations  went  hand  in 
hand  with  our  magnetic  experiments.  The  number  of 
these  experiments  was  very  great,  but  for  a  consider- 
able time  no  fact  of  importance  was  added  to  those 
already  published  At  length,  however,  it  was  our 
fortune  to  meet  with  various  crystals  whose  deport- 
ment could  not  be  brought  under  the  laws  of  magne- 
crystallic  action  enunciated  by  Pliicker.  We  also 
discovered  instances  which  led  us  to  suppose  that  the 
magne-crystallic  force  was  by  no  means  independent, 
as  alleged,  of  the  magnetism  or  diamagnetism  of  the 
mass  of  the  crystal.  Indeed,  the  more  we  worked  at 
the  subject,  the  more  clearly  did  it  appear  to  us  that 
the  deportment  of  crystals  in  the  magnetic  field  was 
due,  not  to  a  force  previously  unknown,  but  to  the 
modification  of  the  known  forces  of  magnetism  and 
diamagnetism  by  crystalline  aggregation. 

An  eminent  example  of  magne-crystallic  action  ad- 
duced by  Pliicker  and  experimented  on  by  Faraday, 
was  Iceland  spar.  It  is  what  in  optics  is  called  a 
negative  crystal,  and  according  to  the  law  of  Pliicker, 
the  axis  of  such  a  crystal  was  always  repelled  by  a 
magnet.  But  we  showed  that  it  was  only  necessary 
to  substitute,  in  whole  or  in  part,  carbonate  of  iron 
for  carbonate  of  lime,  thus  changing  the  magnetic, 
but  not  the  optical  character  of  the  crystal,  to  cause 


FARADAY   AS  A   DISCOVERER.  103 

the  axis  to  be  attracted.  That  the  deportment  of 
magnetic  crystals  is  exactly  antithetical  to  that  of 
dianiagnetie  crystals  isomorphous  with  the  magnetic 
ones,  was  proved  to  be  a  general  law  of  action.  In 
all  cases,  the  line  which  in  a  diamagrietic-crystal  set 
equatorially,  always  set  itself  in  an  isomorphous  mag- 
netic crystal  axially.  By  mechanical  compression 
other  bodies  were  also  made  to  imitate  the  Iceland 
spar. 

These  and  numerous  other  results  bearing  upon 
the  question  were  published  at  the  time  in  the  c  Phi- 
losophical Magazine  '  and  in  'Poggendoff's  Annalen; ' 
and  the  investigation  of  diamagnetism  and  magne- 
crystallic  action  was  subsequently  continued  by  me 
in  the  laboratory  of  Professor  Magnus  of  Berlin.  In 
December,  1851,  after  I  had  quitted  Germany,  Dr. 
Bence  Jones  went  to  the  Prussian  capital  to  see  the 
celebrated  experiments  of  Du  Bois  Reymond ;  and  in- 
fluenced, I  suppose,  by  what  he  heard,  he  afterwards 
invited  me  to  give  a  Friday  evening  discourse  at  the 
Royal  Institution.  I  consented,  not  without  fear  and 
trembling.  For  the  Royal  Institution  was  to  me  a  kind 
of  dragon's  den,  where  tact  and  strength  would  be 
necessary  to  save  me  from  destruction.  On  February 
11,  1853,  the  discourse  was  given,  and  it  ended  hap- 
pily. I  allude  to  these  things,  that  I  may  mention 
that  though  my  aim  and  object  in  that  lecture  was 


104  FARADAY   AS   A   DISCOVERER. 

to  subvert  the  notions  both  of  Faraday  and  Pliicker, 
and  to  establish  in  opposition  to  their  views  what 
I  regarded  as  the  truth,  it  was  very  far  from  pro- 
ducing in  Faraday  either  enmity  or  anger.  At  the 
conclusion  of  the  lecture,  he  quitted  his  accustomed 
seat,  crossed  the  theatre  to  the  corner  into  which  I 
had  shrunk,  shook  me  by  the  hand,  and  brought  me 
back  to  the  table.  Once  more,  subsequently,  and  in 
connection  with  a  related  question,  I  ventured  to 
diifer  from  him  still  more  emphatically.  It  was 
done  out  of  trust  in  the  greatness  of  his  character ; 
nor  was  the  trust  misplaced.  He  felt  my  public 
dissent  from  him;  and  it  pained  me  afterwards  to 
the  quick  to  think  that  I  had  given  him  even  mo- 
mentary annoyance.  It  was,  however,  only  momen- 
tary. His  soul  was  above  all  littleness  and  proof  to 
all  egotism.  He  was  the  same  to  me  afterwards  that 
he  had  been  before;  the  very  chance  expression  which 
led  me  to  conclude  that  he  felt  my  dissent,  being  one 
of  kindness  and  affection. 

It  required  long  subsequent  effort  to  subdue  the 
complications  of  magne-crystallic  action,  and  to 
bring  under  the  dominion  of  elementary  principles 
the  vast  mass  of  facts  which  the  experiments  of 
Faraday  and  Pliicker  had  brought  to  light.  It  was 
proved  by  Eeich,  Edmond  Becquerel,  and  myself, 
that  the  condition  of  diamagnetic  bodies,  in  virtue  of 


FARADAY   AS   A   DISCOVERER.  105 

which,  they  were  repelled  by  the  poles  of  a  magnet, 
was  excited  in  them  by  those  poles ;  that  the  strength 
of  this,  condition  rose  and  fell  with,  and  was  propor- 
tional to,  the  strength  of  the  acting  magnet.     It  was 
not  then  any  property  possessed  permanently  by  the 
bismuth,  and  which  merely  required  the  development 
of  magnetism  to  act  upon  it,  that  caused  the  repul- 
sion ;  for  then  the  repulsion  would  have  been  simply 
proportional  to  the  strength  of  the  influencing  mag- 
net, whereas  experiment  proved  it  to  augment  as  the 
square  of  the  strength.     The  capacity  to  be  repelled 
was  therefore  not  inherent  in  the  bismuth,  but  in- 
duced.    So  far  an  identity  of  action  was  established 
between  magnetic  and  diamagnetic  bodies.      After 
this  the  deportment  of  magnetic  bodies,  '  normal ' 
and  ' abnormal';   crystalline,  amorphous,  and  com- 
pressed,   was    compared    with   that   of    crystalline, 
amorphous,  and  compressed  diamagnetic  bodies ;  and 
by  a  series  of  experiments,  executed  in  the  laboratory 
of  this  Institution,  the  most  complete  antithesis  was 
established  between  magnetism  and  diamagnetism. 
This  antithesis  embraced  the  quality  of  polarity, — -the 
theory  of  reversed  polarity,  first  propounded  by  Fara- 
day, being  proved  to  be  true.     The  discussion  of  the 
question  was  very  brisk.    On  the  Continent  Professor 
Wilhelm  Weber  was  the  ablest  and  most  successful 
supporter  of  the  doctrine  of  diamagnetic  polarity; 


106  FARADAY   AS   A    DISCOVERER. 

and  it  was  with  an  apparatus,  devised  by  him  and 
constructed  under  his  own  superintendence,  by  Leyser 
of  Leipzig,  that  the  last  demands  of  the  opponents 
of  diamagnetic  polarity  were  satisfied.  The  es- 
tablishment of  this  point  was  absolutely  necessary 
to  the  explanation  of  magne-crystallic  action. 

With  that  admirable  instinct  which  always  guided 
him,  Faraday  had  seen  that  it  was  possible,  if  not 
probable,  that  the  diamagnetic  force  acts  with  dif- 
ferent degrees  of  intensity  in  different  directions, 
through  the  mass  of  a  crystal.  In  his  studies  011 
electricity,  he  had  sought  an  experimental  reply  to 
the  question  whether  crystalline  bodies  had  not  dif- 
ferent specific  inductive  capacities  in  different  direc- 
tions, but  he  failed  to  establish  any  difference  of  the 
kind.  His  first  attempt  to  establish  differences  of 
diamagnetic  action  in  different  directions  through 
bismuth,  was  also  a  failure ;  but  he  must  have  felt 
this  to  be  a  point  of  cardinal  importance,  for  he 
returned  to  the  subject  in  1850,  and  proved  that 
bismuth  was  repelled  with  different  degrees  of  force 
in  different  directions.  It  seemed  as  if  the  crystal 
were  compounded  of  two  diamagnetic  bodies  of  dif- 
ferent strengths,  the  substance  being  more  strongly 
repelled  across  the  magne-crystallic  axis  than  along 
it.  The  same  result  was  obtained  independently,  and 
extended  to  various  other  bodies,  magnetic  as  well  as 


FARADAY  AS   A   DISCOVERER.  107 

diamagnetic,   and  also  to  compressed  substances,  a 
little  subsequently  by  myself. 

The  law  of  action  in  relation  to  this  point  is,  that 
in  diamagnetic  crystals,  the  line  along  which  the 
repulsion  is  a  maximum,  sets  equatorially  in  the 
magnetic  field;  while  in  magnetic  crystals  the  line 
along  which  the  attraction  is  a  maximum  sets  from 
pole  to  pole.  Faraday  had  said  that  the  magne- 
crystallic  force  was  neither  attraction  nor  repulsion. 
Thus  far  he  was  right.  It  was  neither  taken  singly, 
but  it  was  both.  By  the  combination  of  the  doctrine 
of  diamagnetic  polarity  with  these  differential  at- 
tractions and  repulsions,  and  by  paying  due  regard 
to  the  character  of  the  magnetic  field,  every  fact 
brought  to  light  in  the  domain  of  magne-crystallic 
action  received  complete  explanation.  The  most 
perplexing  of  those  facts  were  shown  to  result 
from  the  action  of  mechanical  couples,  which  the 
proved  polarity  both  of  magnetism  and  diamagnetism 
brought  into  play.  Indeed  the  thoroughness  with 
which  the  experiments  of  Faraday  were  thus  ex- 
plained, is  the  most  striking  possible  demonstration 
of  the  marvellous  precision  with  which  they  were 
executed. 


108  FARADAY   AS   A   DISCOVERER. 

MAGNETISM  OP  FLAME  AND  GASES — ATMOSPHERIC 
MAGNETISM. 

When  an  experimental  result  was  obtained  by 
Faraday  it  was  instantly  enlarged  by  his  imagina- 
tion. I  am  acquainted  with  no  mind  whose  power 
and  suddenness  of  expansion  at  the  touch  of  new 
physical  truth  could  be  ranked  with  his.  Sometimes 
I  have  compared  the  action  of  his  experiments  on 
his  mind  to  that  of  highly  combustible  matter  thrown 
into  a  furnace ;  every  fresh  entry  of  fact  was  accom- 
panied by  the  immediate  development  of  light  and 
heat.  The  light,  which  was  intellectual,  enabled 
him  to  see  far  beyond  the  boundaries  of  the  fact 
itself,  and  the  heat,  which  was  emotional,  urged  him 
to  the  conquest  of  this  newly-revealed  domain.  But 
though  the  force  of  his  imagination  was  enormous, 
he  bridled  it  like  a  mighty  rider,  and  never  permitted 
his  intellect  to  be  overthrown. 

In  virtue  of  the  expansive  power  which  his  vivid 
imagination  conferred  upon  him,  he  rose  from  the 
smallest  beginnings  to  the  grandest  ends.  Having 
heard  from  Zantedeschi  that  Bancalari  had  esta- 
blished the  magnetism  of  flame,  he  repeated  the 
experiments  and  augmented  the  results.  He  passed 
from  flames  to  gases,  examining  and  revealing  their 
magnetic  and  diamagnetic  powers  ;  and  then  he  sud- 


FARADAY  AS   A   DISCOVERER.  109 

denly  rose  from  his  bubbles  of  oxygen  and  nitrogen 
to  the  atmospheric  envelope  of  the  earth  itself,  and  its 
relations  to  the  great  question  of  terrestrial  magne- 
tism. The  rapidity  with  which  these  ever-augment- 
ing thoughts  assumed  the  form  of  experiments  is 
unparalleled.  His  power  in  this  respect  is  often  best 
illustrated  by  his  minor  investigations,  and,  perhaps, 
by  none  more  strikingly  than  by  his  paper  '  On  the 
Diamagnetic  Condition  of  Mame  and  Gases,'  pub- 
lished as  a  letter  to  Mr.  Richard  Taylor,  in  the 
'  Philosophical  Magazine '  for  December,  1847. 
After  verifying,  varying,  and  expanding  the  re- 
sults of  Bancalari,  he  submitted  to  examination 
heated  air-currents,  produced  by  platinum  spirals 
placed  in  the  magnetic  field,  and  raised  to  incan- 
descence by  electricity.  He  then  examined  the 
magnetic  deportment  of  gases  generally.  Almost 
all  of  these  gases  are  invisible  ;  but  he  must,  never- 
theless, track  them  in  their  unseen  courses.  He 
could  not  effect  this  by  mingling  smoke  with  his 
gases,  for  the  action  of  his  magnet  upon  the  smoke 
would  have  troubled  his  conclusions.  He,  therefore, 
'  caught '  his  gases  in  tubes,  carried  them  out  of  the 
magnetic  field,  and  made  them  reveal  themselves  at 
a  distance  from  the  magnet. 

Immersing   one '  gas    in   another,  he   determined 
their  differential  action  5  results  of  the  utmost  beauty 


1.10  FARADAY   AS  A   DISCOVERER. 

being  thus  arrived  at.  Perhaps  the  most  impor- 
tant are  those  obtained  with  atmospheric  air  and 
its  two  constituents.  Oxygen,  in  various  media, 
was  strongly  attracted  by  the  magnet ;  in  coal-gas, 
for  example,  it  was  powerfully  magnetic,  whereas  ni- 
trogen was  diamagnetic.  Some  of  the  effects  obtained 
with  oxygen  in  coal-gas  were  strikingly  beautiful. 
When  the  fumes  of  chloride  of  ammonium  (a  diamag- 
netic substance)  were  mingled  with  the  oxygen,  the 
cloud  of  chloride  behaved  in  a  most  singular  manner. 
— '  The  attraction  of  iron  filings,'  says  Faraday,  '  to 
a  magnetic  pole  is  not  more  striking  than  the  ap- 
pearance presented  by  the  oxygen  under  these  cir- 
cumstances.' 

On  observing  this  deportment  the  question  imme- 
diately occurs  to  him, — can  we  not  separate  the 
oxygen  of  the  atmosphere  from  its  nitrogen  by  mag- 
netic analysis?  It  is  the  perpetual  occurrence  of 
such  questions  that  marks  the  great  experimenter. 
The  attempt  to  analyze  atmospheric  air  by  magnetic 
force  proved  a  failure,  like  the  previous  attempt  to 
influence  crystallization  by  the  magnet.  The  en- 
nornious  comparative  power  of  the  force  of  crystal- 
lization was  then  assigned  as  a  reason  for  the  in- 
competence of  the  magnet  to  determine  molecular 
arrangement ;  in  the  present  instance  the  magnetic 
analysis  is  opposed  by  the  force  of  diffusion,  which  is 


FARADAY   AS   A   DISCOVERER.  Ill 

also  very  strong  comparatively.  The  same  remark 
applies  to,  and  is  illustrated  by,  another  experiment 
subsequently  executed  by  Faraday.  Water  is  dia- 
niagnetic,  sulphate  of  iron  strongly  magnetic.  He 
enclosed  c  a  dilute  solution  of  sulphate  of  iron  in  a 
tube,  and  placed  the  lower  end  of  the  tube  between 
the  poles  of  a  powerful  horseshoe  magnet  for  days 
together,3  but  he  could  produce  '  no  concentration  of 
the  solution  in  the  part  near  the  magnet.'  Here  also 
the  diffusibility  of  the  salt  was  too  powerful  for  the 
force  brought  against  it. 

The  experiment  last  referred  to  is  recorded  in  a 
paper  presented  to  the  Eoyal  Society  on  the  2nd 
August,  1850,  in  which  he  pursues  the  investigation  of 
the  magnetism  of  gases.  Newton's  observations  on 
soap-bubbles  were  often  referred  to  by  Faraday.  His 
delight  in  a  soap-bubble  was  like  that  of  a  boy,  and 
he  often  introduced  them  in  his  lectures,  causing 
them,  when  filled  with  air,  to  float  on  invisible  seas 
of  carbonic  acid,  and  otherwise  employing  them  as  a 
means  of  illustration.  He  now  finds  them  exceed- 
ingly useful  in  his  experiments  on  the  magnetic  con- 
dition of  gases.  A  bubble  of  air  in  a  magnetic  field 
occupied  by  air  was  unaffected,  save  through  the  feeble 
repulsion  of  its  envelope.  A  bubble  of  nitrogen,  on 
the  contrary,  was  repelled  from  the  magnetic  axis 
with  a  force  far  surpassing  that  of  a  bubble  of  air. 


112  FARADAY   AS  A   DISCOVERER. 

The  deportment  of  oxygen  in  air  '  was  very  impres- 
sive, the  bubble  being  pulled  inward,  or  towards  the 
axial  line,  sharply  and  suddenly,  as  if  the  oxygen 
were  highly  magnetic.' 

He  next  labours  to  establish  the  true  magnetic 
zero,  a  problem  not  so  easy  as  might  at  first 
sight  be  imagined.  For  the  action  of  the  magnet 
upon  any  gas,  while  surrounded  by  air,  or  any  other 
gas,  can  only  be  differential;  and  if  the  experiment 
were  made  in  vacuo,  the  action  of  the  envelope,  in 
this  case  necessarily  of  a  certain  thickness,  would 
trouble  the  result.  While  dealing  with  this  sub- 
ject, Faraday  makes  some  noteworthy  observations 
regarding  space.  In  reference  to  the  Torricellian 
vacuum,  he  says,  '  Perhaps  it  is  hardly  necessary  for 
me  to  state  that  I  find  both  iron  and  bismuth  in 
such  vacua  perfectly  obedient  to  the  magnet.  From 
such  experiments,  and  also  from  general  observations 
and  knowledge,  it  seems  manifest  that  the  lines  of 
magnetic  force  can  traverse  pure  space,  just  as  gravi- 
tating force  does,  and  as  statical  electrical  forces  do, 
and  therefore  space  has  a  magnetic  relation  of  its 
own,  and  one  that  we  shall  probably  find  hereafter 
to  be  of  the  utmost  importance  in  natural  phenomena. 
But  this  character  of  space  is  not  of  the  same  kind 
as  that  which,  in  relation  to  matter,  we  endeavour  to 
express  by  the  terms  magnetic  and  diamagnetic.  To 


FARADAY  AS   A   DISCOVERER.  113 

confuse  these  together  would  be  to  confound  space 
with  matter,  and  to  trouble  all  the  conceptions  by 
which  we  endeavour  to  understand  and  work  out  a 
progressively  clearer  view  of  the  mode  of  action,  and 
the  laws  of  natural  forces.  It  would  be  as  if  in 
gravitation  or  electric  forces,  one  were  to  confound 
the  particles  acting  on  each  other  with  the  space 
across  which  they  are  acting,  and  would,  I  think, 
shut  the  door  to  advancement.  Mere  space  cannot 
act  as  matter  acts,  even  though  the  utmost  latitude 
be  allowed  to  the  hypothesis  of  an  ether ;  and  admit- 
ting that  hypothesis,  it  would  be  a  large  additional 
assumption  to  suppose  that  the  lines  of  magnetic 
force  are  vibrations  carried  on  by  it,  whilst  as  yet  we 
have  no  proof  that  time  is  required  for  their  propa- 
gation, or  in  what  respect  they  may,  in  general  cha- 
racter, assimilate  to  or  differ  from  the  respective  lines 
of  gravitating,  luminiferous,  or  electric  forces.' 

Pure  space  he  assumes  to  be  the  true  magne- 
tic zero,  but  he  pushes  his  inquiries  to  ascertain 
whether  among  material  substances  there  may  not 
be  some  which  resemble  space.  If  you  follow  his 
experiments,  you  will  soon  emerge  into  the  light  of 
his  results.  A  torsion  beam  was  suspended  by  a 
skein  of  cocoon  silk ;  at  one  end  of  the  beam  was 
fixed  a  cross-piece  1 J  inches  long.  Tubes  of  exceed- 
ingly thin  glass,  filled  with  various  gases,  and  herme- 

i 


114  FARADAY  AS   A   DISCOVERER. 

tically  sealed,  were  suspended  in  pairs  from  the  two 
ends  of  the  cross-piece.  The  position  of  the  rotating 
torsion-head  was  such  that  the  two  tubes  were  at 
opposite  sides  of,  and  equidistant  from,  the  magnetic 
axis,  that  is  to  say  from  the  line  joining  the  two 
closely  approximated  polar  points  of  an  electro  mag- 
net. His  object  was  to  compare  the  magnetic  action 
of  the  gases  in  the  two  tubes.  When  one  tube  was 
filled  with  oxygen,  and  the  other  with  nitrogen,  on 
the  supervention  of  the  magnetic  force,  the  oxygen 
was  pulled  towards  the  axis,  the  nitrogen  being 
pushed  out.  By  turning  the  torsion-head  they  could 
be  restored  to  their  primitive  position  of  equidistance, 
where  it  is  evident  the  action  of  the  glass  envelopes 
was  annulled.  The  amount  of  torsion  necessary 
to  re-establish  equi-distance  expressed  the  magnetic 
difference  of  the  substances  compared. 

And  then  he  compared  oxygen  with  oxygen  at 
different  pressures.  One  of  his  tubes  contained  the 
gas  at  the  pressure  of  30  inches  of  mercury,  another 
at  a  pressure  of  15  inches  of  mercury,  a  third  at  a 
pressure  of  10  inches,  while  a  fourth  was  exhausted 
as  far  as  a  good  air-pump  renders  exhaustion  pos- 
sible. (  When  the  first  of  these  was  compared  with 
the  other  three,  the  effect  was  most  striking.'  It 
was  drawn  towards  the  axis  when  the  magnet  was 
excited,  the  tube  containing  the  rarer  gas  being 
apparently  driven  away,  and  the  greater  the  differ- 


FARADAY   AS   A   DISCOVERER.  115 

ence  between  the   densities  of  the  two  gases,  the 
greater  was  the  energy  of  this  action. 

And  now  observe  his  mode  of  reaching  a  material 
magnetic  zero.  When  a  bubble  of  nitrogen  was 
exposed  in  air  in  the  magnetic  field,  on  the  super- 
vention of  the  power,  the  bubble  retreated  from  the 
magnet.  A  less  acute  observer  would  have  set  nitro- 
gen down  as  diamagnetic ;  but  Faraday  knew  that  re- 
treat, in  a  medium  composed  in  part  of  oxygen,  might 
be  due  to  the  attraction  of  the  latter  gas,  instead  of 
to  the  repulsion  of  the  gas  immersed  in  it.  But  if 
nitrogen  be  really  diamagnetic,  then  a  bubble  or  bulb 
filled  with  the  dense  gas  will  overcome  one  filled 
with  the  rarer  gas.  From  the  cross-piece  of  his  tor- 
sion-balance he  suspended  his  bulbs  of  nitrogen,  at 
equal  distances  from  the  magnetic  axis,  and  found 
that  the  rarefaction,  or  the  condensation  of  the  gas 
in  either  of  the  bulbs  had  not  the  slightest  influence. 
When  the  magnetic  force  was  developed,  the  bulbs 
remained  in  their  first  position,  even  when  one  was 
filled  with  nitrogen,  and  the  other  as  far  as  possible 
exhausted.  Nitrogen,  in  fact,  acted  'like  space  it- 
self ; '  it  was  neither  magnetic  nor  diamagnetic. 

He  cannot  conveniently  compare  the  paramagnetic 
force  of  oxygen  with  iron,  in  consequence  of  the 
exceeding  magnetic  intensity  of  the  latter  substance ; 
bat  he  does  compare  it  with  the  sulphate  of  iron, 

I  2 


116  FARADAY  AS  A  DISCOVERER. 

and  finds  that,  bulk  for  bulk,  oxygen  is  equally  mag- 
netic with  a  solution  of  this  substance  in  water 
*  containing  seventeen  times  the  weight  of  the  oxy- 
gen in  crystallized  proto- sulphate  of  iron,  or  3 -4  times 
its  weight  of  metallic  iron  in  that  state  of  combina- 
tion.' By  its  capability  to  deflect  a  fine  glass  fibre, 
he  finds  that  the  attraction  of  his  bulb  of  oxygen, 
containing  only  0*117  of  a  grain  of  the  gas,  at  an 
average  distance  of  more  than  an  inch  from  the 
magnetic  axis,  is  about  equal  to  the  gravitating 
force  of  the  same  amount  of  oxygen  as  expressed  by 
its  weight. 

These  facts  could  not  rest  for  an  instant  in  the 
mind  of  Faraday  without  receiving  that  expansion  to 
which  I  have  already  referred.  '  It  is  hardly  neces- 
sary,' he  writes,  c  for  me  to  say  here  that  this  oxygen 
cannot  exist  in  the  atmosphere  exerting  such  a  re- 
markable and  high  amount  of  magnetic  force,  with- 
out having  a  most  important  influence  on  the  dis- 
position of  the  magnetism  of  the  earth,  as  a  planet ; 
especially,  if  it  be  remembered  that  its  magnetic 
condition  is  greatly  altered  by  variations  of  its 
density  and  by  variations  of  its  temperature.  I  think 
I  see  here  the  real  cause  of  many  of  the  variations 
of  that  force,  which  have  been,  and  are  now  so  care- 
fully watched  on  different  parts  of  the  surface  of  the 
globe.  The  daily  variation,  and  the  annual  variation, 


FARADAY   AS   A   DISCOVERER.  117 

both  seem  likely  to  come  under  it ;  also  very  many 
of  the  irregular  continual  variations,  which  the  pho- 
tographic process  of  record  renders  so  beautifully 
manifest.  If  such  expectations  be  confirmed,  and 
the  influence  of  the  atmosphere  be  found  able  to 
produce  results  like  these,  then  we  shall  probably 
find  a  new  relation  between  the  aurora  borealis  and 
the  magnetism  of  the  earth,  namely,  a  relation  esta- 
blished, more  or  less,  through  the  air  itself  in  con- 
nection with  the  space  above  it ;  and  even  magnetic 
relations  and  variations,  which  are  not  as  yet  sus- 
pected, may  be  suggested  and  rendered  manifest  and 
measurable,  in  the  further  development  of  what  I 
will  venture  to  call  Atmospheric  Magnetism.  I  may 
be  over-sanguine  in  these  expectations,  but  as  yet  I 
am.  sustained  in  them  by  the  apparent  reality,  sim- 
plicity, and  sufficiency  of  the  cause  assumed,  as  it  at 
present  appears  to  my  mind.  As  soon  as  I  have 
submitted  these  views  to  a  close  consideration,  and 
the  test  of  accordance  with  observation,  and,  where 
applicable,  with  experiments  also,  I  will  do  myself 
the  honour  to  bring  them  before  the  Royal  Society.' 

Two  elaborate  memoirs  are  then  devoted  to  the 
subject  of  Atmospheric  Magnetism;  the -first  sent  to 
the  Royal  Society  on  the  9th  of  October,  and  the 
second  on  the  19th  of  November,  1850.  In  these 
memoirs  he  discusses  the  effects  of  heat  and  cold 


118  FAKADAY  AS   A   DISCO VEEER. 

upon  the  magnetism  of  the  air,  and  the  action  on 
the  magnetic  needle,  which  must  result  from  thermal 
changes.  By  the  convergence  and  divergence  of  the 
lines  of  terrestrial  magnetic  force,  he  shows  how  the 
distribution  of  magnetism,  in  the  earth's  atmos- 
phere, is  affected.  He  applies  his  results  to  the  ex- 
planation of  the  Annual  and  of  the  Diurnal  Variation : 
he  also  considers  irregular  variations,  including  the 
action  of  magnetic  storms.  He  discusses,  at  length, 
the  observations  at  St.  Petersburg,  Greenwich,  Ho- 
barton,  St.  Helena,  Toronto,  and  the  Cape  of  Good 
Hope ;  believing  that  the  facts,  revealed  by  his  ex- 
periments, furnish  the  key  to  the  variations  observed 
at  all  these  places. 

In  the  year  1851,  I  had  the  honour  of  an  interview 
with  Humboldt,  in  Berlin,  and  his  parting  words  to 
me  then  were,  c  Tell  Faraday  that  I  entirely  agree 
with  him,  and  that  he  has,  in  my  opinion,  completely 
explained  the  variation  of  the  declination.'  Eminent 
men  have  since  informed  me  that  Humboldt  was 
hasty  in  expressing  this  opinion.  In  fact,  Faraday's 
memoirs  on  atmospheric  magnetism  lost  much  of 
their  force — perhaps  too  much — through  the  impor- 
tant discovery  of  the  relation  of  the  variation  of  the 
declination  to  the  number  of  the  solar  spots.  But  I 
agree  with  him  and  M.  Edmond  Becquerel,  who 
worked  independently  at  this  subject,  in  thinking, 


FARADAY   AS  A  DISCOVERER.  119 

that  a  body  so  magnetic  as  oxygen,  swathing  the 
earth,  and  subject  to  variations  of  temperature,  diur- 
nal and  annual,  must  affect  the  manifestations  of 
terrestrial  magnetism.*  The  air  that  stands  upon  a 
single  square  foot  of  the  earth's  surface  is,  according 
to  Faraday,  equivalent  in  magnetic  force  to  81601bs. 
of  crystallized  protosulphate  of  iron.  Such  a  sub- 
stance cannot  be  absolutely  neutral  as  regards  the 
deportment  of  the  magnetic  needle.  But  Faraday's 
writings  on  this  subject  are  so  voluminous,  and  the 
theoretic  points  are  so  novel  and  intricate,  that  I 
shall  postpone  the  complete  analysis  of  these  re- 
searches to  a  time  when  I  can  lay  hold  of  them  more 
completely  than  my  other  duties  allow  me  to  do  now. 

SPECULATIONS  :    NATTJEE    OP    MATTER  :    LINES    OP 
FOECE. 

The  scientific  picture  of  Faraday  would  not  be  com- 
plete without  a  reference  to  his  speculative  writings. 
On  Friday,  January  19,  1844,  he  opened  the  weekly 
evening-meetings  of  the  Royal  Institution  by  a  dis- 
course entitled  £A  speculation  touching  Electric 
Conduction  and  the  nature  of  Matter.'  In  this  dis- 
course he  not  only  attempts  the  overthrow  of  Dalton's 
Theory  of  Atoms,  but  also  the  subversion  of  all  ordi- 

*  This  persuasion  has  been  greatly  strengthened  by  the  recent  perusal 
of  a  paper  by  Mr.  Baxendell. 


120       .  FARADAY   AS   A    DISCOVERER. 

nary  scientific  ideas  regarding  the  nature  and  rela- 
tions of  Matter  and  Force.  He  objected  to  the  use  of 
the  term  atom : — c  I  have  not  yet  found  a  mind,'  he 
says,  c  that  did  habitually  separate  it  from  its  accom- 
panying temptations ;  and  there  can  be  no  doubt  that 
the  words  definite  proportions,  equivalent,  primes, 
&c.,  which  did  and  do  fully  express  all  the  fads  of 
what  is  usually  called  the  atomic  theory  in  chemistry, 
were  dismissed  because  they  were  not  expressive 
enough,  and  did  not  say  all  that  was  in  the  mind  of 
him  who  used  the  word  atom  in  their  stead.' 

A  moment  will  be  granted  me  to  indicate  my  own 
view  of  Faraday's  position  here.  The  word  c  atom' 
was  not  used  in  the  stead  of  definite  proportions, 
equivalents,  or  primes.  These  terms  represented 
facts  that  followed  from,  but  were  not  equivalent 
to,  the  atomic  theory.  Facts  cannot  satisfy  the 
mind :  and  the  law  of  definite  combining  proportions 
being  once  established,  the  question  'why  should 
combination  take  place  according  to  that  law  ? '  is 
inevitable.  Dalton  answered  this  question  by  the 
enunciation  of  the  Atomic  Theory,  the  funda- 
mental idea  of  which  is,  in  my  opinion,  per- 
fectly secure.  The  objection  of  Faraday  to  Dalton, 
might  be  urged  with  the  same  substantial  force 
against  Newton :  it  might  be  stated  with  regard  to 
the  planetary  motions  that  the  laws  of  Kepler  re- 
vealed the  fads ;  that  the  introduction  of  the  prin- 


FARADAY   AS   A   DISCOVERER.  121 

ciple  of  gravitation  was  an  addition  to  the  facts. 
But  this  is  the  essence  of  all  theory.  The  theory  is 
the  backward  guess  from  fact  to  principle;  the  con- 
jecture, or  divination  regarding  something,  which 
lies  behind  the  facts,  and  from  which  they  flow  in 
necessary  sequence.  If  Dalton's  theory,  then,  ac- 
count for  the  definite  proportions  observed  in  the 
combinations  of  chemistry,  its  justification  rests  upon 
the  same  basis  as  that  of  the  principle  of  gravi- 
tation. All  that  can  in  strictness  be  said  in  either 
case  is  that  the  facts  occur  as  if  the  principle 
existed. 

The  manner  in  which  Faraday  himself  habitually 
deals  with  his  hypotheses  is  revealed  in  this  lecture. 
He  incessantly  employed  them  to  gain  experimental 
ends,  but  he  incessantly  took  them  down,  as  an  ar- 
chitect removes  the  scaffolding  when  the  edifice  is 
complete.  'I  cannot  but  doubt,'  he  says, '  that  he  who 
as  a  mere  philosopher  has  most  power  of  penetrating 
the  secrets  of  nature,  and  guessing  by  hypothesis  at 
her  mode  of  working,  will  also  be  most  careful  for 
his  own  safe  progress  and  that  of  others,  to  distin- 
guish the  knowledge  which  consists  of  assumption, 
by  which  I  mean  theory  and  hypothesis,  from  that 
which  is  the  knowledge  of  facts  and  laws.'  Faraday 
himself,  in  fact,  was  always  '  guessing  by  hypothesis,' 
and  making  theoretic  divination  the  stepping-stone 
to  his  experimental  results. 


122  FARADAY    AS   A   DISCOVERER. 

I  have  already  more  than  once  dwelt  on  the  vivid- 
ness with  which  he  realised  molecular  conditions  ;  we 
have  a  fine  example  of  this  strength  and  brightness 
of  imagination  in  the  present  '  speculation.'  He 
grapples  with  the  notion  that  matter  is  made  up  of 
particles,  not  in  absolute  contact,  but  surrounded 
by  inter-atomic  space.  '  Space,'  he  observes,  '  must 
be  taken  as  the  only  continuous  part  of  a  body 
so  constituted.  Space  will  permeate  all  masses  of 
matter  in  every  direction  like  a  net,  except  that  in 
place  of  meshes  it  will  form  cells,  isolating  each  atom 
from  its  neighbours,  itself  only  being  continuous.' 

Let  us  follow  out  this  notion ;  consider,  he  argues, 
the  case  of  a  non-conductor  of  electricity,  such  for 
example  as  shell-lac,  with  its  molecules,  and  in- 
termolecular  spaces  running  through  the  mass.  In 
its  case  space  must  be  an  insulator ;  for  if  it  were  a 
conductor  it  would  resemble  'a  fine  metallic  web,'  pene- 
trating the  lac  in  every  direction.  But  the  fact  is  that 
it  resembles  the  wax  of  black  sealing-wax,  which  sur- 
rounds and  insulates  the  particles  of  conducting  car- 
bon, interspersed  throughout  its  mass.  In  the  case  of 
shell-lac,  therefore,  space  is  an  insulator. 

But  now,  take  the  case  of  a  conducting  metal.  Here 
we  have  as  before,  the  swathing  of  space  round  every 
atom.  If  space  be  an  insulator  there  can  be  no  trans- 
mission of  electricity  from  atom  to  atom.  But  there 


FARADAY  AS   A   DISCOVERER.  123 

is  transmission  ;  hence  space  is  a  conductor.  Thus  he 
endeavours  to  hamper  the  atomic  theory.  '  The  rea- 
soning,' he  says,  'ends  in  a  subversion  of  that  theory 
altogether ;  for  if  space  be  an  insulator  it  cannot  exist 
in  conducting  bodies,  and  if  it  be  a  conductor  it  can- 
not exist  in  insulating  bodies.  Any  ground  of  rea- 
soning,' he  adds,  as  if  carried  away  by  the  ardour  of 
argument,  '  which  tends  to  such  conclusions  as  these 
must  in  itself  be  false.' 

He  then  tosses  the  atomic  theory  from  horn  to  horn 
of  his  dilemmas.  What  do  we  know,  he  asks,  of  the 
atom  apart  from  its  force  ?  You  imagine  a  nucleus 
which  may  be  called  a,  and  surround  it  by  forces 
which  may  be  called  m ;  '  to  my  mind  the  a  or  nucleus 
vanishes,  and  the  substance  consists  in  the  powers  of 
m.  And  indeed  what  notion  can  we  form  of  the 
nucleus  independent  of  its  powers  ?  What  thought 
remains  on  which  to  hang  the  imagination  of  an  a 
independent  of  the  acknowledged  forces? '  Like  Bos- 
covich  he  abolishes  the  atom,  and  puts  a  '  centre  of 
force '  in  its  place. 

With  his  usual  courage  and  sincerity  he  pushes  his 
view  to  its  utmost  consequences.  *  This  view  of  the 
constitution  of  matter,'  he  continues,  '  would  seem  to 
involve  necessarily  the  conclusion  that  matter  fills 
all  space,  or  at  least  all  space  to  which  gravitation 
extends;  for  gravitation  is  a  property  of  matter 


124  FARADAY  AS  A  DISCOVERER. 

dependent  on  a  certain  force,  and  it  is  this  force  which 
constitutes  the  matter.  In  that  view  matter  is  not 
merely  mutually  penetrable  ;*  but  each  atom  extends, 
so  to  say,  throughout  the  whole  of  the  solar  system, 
yet  always  retaining  its  own  centre  of  force.' 

It  is  the  operation  of  a  mind  filled  with  thoughts 
of  this  profound,  strange,  and  subtle  character  that 
we  have  to  take  into  account  in  dealing  with  Fara- 
day's later  researches.  A  similar  cast  of  thought 
pervades  a  letter  addressed  by  Faraday  to  Mr.  Eichard 
Phillips,  and  published  in  the  'Philosophical  Maga- 
zine' for  May,  1846.  It  is  entitled  'Thoughts  on  Ray- 
vibrations,'  and  it  contains  one  of  the  most  singular 
speculations  that  ever  emanated  from  a  scientific 
mind.  It  must  be  remembered  here,  that  though 
Faraday  lived  amid  such  speculations  he  did  not  rate 
them  highly,  and  that  he  was  prepared  at  any  mo- 
ment-to  change  them  or  let  them  go.  They  spurred 
him  on,  but  they  did  not  hamper  him.  His  theo- 
retic notions  were  fluent ;  and  when  minds  less 
plastic  than  his  own  attempted  to  render  those 
fluxional  images  rigid,  he  rebelled.  He  warns  Phil- 
lips, moreover,  that  from  first  to  last,  'he  merely 
threw  out  as  matter  for  speculation  the  vague  im- 

*  He  compares  the  interpenetration  of  two  atoms  to  the  coalescence 
of  two  distinct  waves,  which  though  for  a  moment  blended  to  a  single 
mass,  preserve  their  individuality,  and  afterwards  separate. 


FAEADAY   AS  A   DISCOVEREK.  125 

pressions  of  his  mind;  for  he  gave  nothing  as  the 
result  of  sufficient  consideration,  or  as  the  settled 
conviction,  or  even  probable  conclusion  at  which  he 
had  arrived.' 

The  gist  of  this  communication  is  that  gravitating 
force  acts  in  lines  across  space,  and  that  the  vibrations 
of  light  and  radiant  heat  consist  in  the  tremors  of 
these  lines  of  force.  '  This  notion,'  he  says,  '  as  far 
as  it  is  admitted,"  will  dispense  with  the  ether,  which, 
in  another  view,  is  supposed  to  be  the  medium  in 
which  these  vibrations  take  place.'  And  he  adds 
further  on,  that  his  view  '  endeavours  to  dismiss 
the  ether  but  not  the  vibrations.'  The  idea  here 
set  forth  is  the  natural  supplement  of  his  previous 
notion,  that  it  is  gravitating  force  which  constitutes 
matter,  each  atom  extending,  so  to  say,  throughout 
the  whole  of  the  solar  system. 

The  letter  to  Mr.  Phillips  winds  up  with  this  beau- 
tiful conclusion : — 

'  I  think  it  likely  that  I  have  made  many  mistakes 
in  the  preceding  pages,  for  even  to  myself  my  ideas 
on  this  point  appear  only  as  the  shadow  of  a  specu- 
lation, or  as  one  of  those  impressions  upon  the  mind 
which  are  allowable  for  a  time  as  guides  to  thought 
and  research.  He  who  labours  in  experimental 
inquiries,  knows  how  numerous  these  are,  and  how 


126  FARADAY  AS  A  DISCOVERER. 

often  their  apparent  fitness  and  beauty  vanish  before 
the  progress  and  development  of  real  natural  truth.' 

Let  it  then  be  remembered  that  Faraday  entertained 
notions  regarding  matter  and  force  altogether  dis- 
tinct from  the  views  generally  held  by  scientific  men. 
Force  seemed  to  him  an  entity  dwelling  along  the  line 
in  which  it  is  exerted.  The  lines  along  which  gra- 
vity acts  between  the  sun  and  earth  seem  figured 
in  his  mind  as  so  many  elastic  strings  :  indeed  he 
accepts  the  assumed  instantaneity  of  gravity  as  the 
expression  of  the  enormous  elasticity  of  the  '  lines 
of  weight.'  Such  views,  fruitful  in  the  case  of 
magnetism,  barren,  as  yet,  in  the  case  of  gravity, 
explain  his  efforts  to  transform  this  latter  force. 
When  he  goes  into  the  open  air  and  permits  his 
helices  to  fall,  to  his  mind's  eye  they  are  tearing 
through  the  lines  of  gravitating  power,  and  hence 
his  hope  and  conviction  that  an  effect  would  and 
ought  to  be  produced.  It  must  ever  be  borne  in 
mind  that  Faraday's  difficulty  in  dealing  with  these 
conceptions  was  at  bottom  the  same  as  that  of 
Newton ;  that  he  is  in  fact  trying  to  overleap  this 
difficulty,  and  with  it  probably  the  limits  prescribed 
to  the  intellect  itself. 

The  idea  of  lines  of  magnetic  force  was  sug- 
gested to  Faraday  by  the  linear  arrangement  of 


FARADAY  AS  A   DISCOVERER.  127 

iron  filings  when  scattered  over  a  magnet.  He 
speaks  of  and  illustrates  by  sketches,  the  deflec- 
tion, both  convergent  and  divergent,  of  the  lines  of 
force,  when  they  pass  respectively  through  magnetic 
and  diamagnetic  bodies.  These  notions  of  concen- 
tration and  divergence  are  also  based  on  the  direct 
observation  of  his  filings.  So  long  did  he  brood  upon 
these  lines ;  so  habitually  did  he  associate  them  with 
his  experiments  on  induced  currents,  that  the  asso- 
ciation became  e  indissoluble,'  and  he  could  not  think 
without  them.  '  I  have  been  so  accustomed/  he 
writes,  ( to  employ  them,  and  especially  in  my  last 
researches,  that  I  may  have  unwittingly  become  pre- 
judiced in  their  favour,  and  ceased  to  be  a  clear- 
sighted judge.  Still,  I  have  always  endeavoured  to 
make  experiment  the  test  and  controller  of  theory 
and  opinion  ;  but  neither  by  that  nor  by  close  cross- 
examination  in  principle,  have  I  been  made  aware  of 
any  error  involved  in  their  use.' 

In  his  later  researches  on  magne-crystallic  action, 
the  idea  of  lines  of  force  is  extensively  employed ;  it 
indeed  led  him  to  an  experiment  which  lies  at  the 
root  of  the  whole  question.  In  his  subsequent  re- 
searches on  Atmospheric  Magnetism  the  idea  receives 
still  wider  application,  showing  itself  to  be  wonder- 
fully flexible  and  convenient.  Indeed  without  this 
conception  the  attempt  to  seize  upon  the  magnetic 


128  FARADAY  AS  A  DISCOVERER. 

actions,  possible  or  actual,  of  the  atmosphere  would 
be  difficult  in  the  extreme ;  but  the  notion  of  lines  of 
force,  and  of  their  divergence  and  convergence,  guides 
Faraday  without  perplexity  through  all  the  intricacies 
of  the  question.  After  the  completion  of  those  re- 
searches, and  in  a  paper  forwarded  to  the  Royal 
Society  on  October  22, 1851,  he  devotes  himself  to  the 
formal  development  and  illustration  of  his  favour- 
ite idea.  The  paper  bears  the  title,  (  On  lines  of 
magnetic  force,  their  definite  character,  and  their 
distribution  within  a  magnet  and  through  space.' 
A  deep  reflectiveness  is  the  characteristic  of  this 
memoir.  In  his  experiments,  which  are  perfectly 
beautiful  and  profoundly  suggestive,  he  takes  but  a 
secondary  delight.  llis  object  is  to  illustrate  the 
utility  of  his  conception  of  lines  of  force.  'The 
study  of  these  lines,'  he  says,  ( has  at  different  times 
been  greatly  influential  in  leading  me  to  various 
results  which  I  think  prove  their  utility  as  well  as 
fertility.' 

Faraday  for  a  long  period  used  the  lines  of  force 
merely  as  'a  representative  idea.'  He  seemed  for  a 
time  averse  to  going  further  in  expression  than  the 
lines  themselves,  however  much  further  he  may 
have  gone  in  idea.  That  he  believed  them  to 
exist  at  all  times  round  a  magnet,  and  irrespec- 
tive of  the  existence  of  magnetic  matter,  such  as 


FAEADAY   AS  A  DISCOVERER.  129 

iron  filings,  external  to  the  magnet,  is  certain. 
No  doubt  the  space  round  every  magnet  presented 
itself  to  his  imagination  as  traversed  by  loops  of 
magnetic  power;  but  he  was  chary  in  speaking 
of  the  physical  substratum  of  those  loops.  Indeed 
it  may  be  doubted  whether  the  physical  theory  of 
lines  of  force  presented  itself  with  any  distinctness 
to  his  own  mind.  The  possible  complicity  of  the 
luminiferous  ether  in  magnetic  phenomena  was  cer- 
tainly in  his  thoughts.  '  How  the  magnetic  force,' 
he  writes,  '  is  transferred  through  bodies  or  through 
space  we  know  not ;  whether  the  result  is  merely 
action  at  a  distance,  as  in  the  case  of  gravity ;  or  by 
some  intermediate  agency,  as  in  the  case  of  light, 
heat,  the  electric  current,  and  (as  I  believe)  static 
electric  action.  The  idea  of  magnetic  fluids,  as  ap- 
plied by  some,  or  of  magnetic  centres  of  action,  does 
not  include  that  of  the  latter  kind  of  transmission, 
but  the  idea  of  lines  of  force  does.'  And  he  continues 
thus  : — '  I  am  more  inclined  to  the  notion  that  in  the 
transmission  of  the  [magnetic]  force  there  is  such 
an  action  [an  intermediate  agency]  external  to  the 
magnet,  than  that  the  effects  are  merely  attraction 
and  repulsion  at  a  distance.  Such  an  affection  may  be 
a  function  of  the  ether  j  for  it  is  not  at  all  unlikely  that, 
if  there  be  an  ether,  it  should  have  other  uses  than  simply 
the  conveyance  of  radiations.9  When  he  speaks  of  the 


130  FARADAY  AS  A   DISCOVERER. 

magnet  in  certain  cases,  '  revolving  amongst  its  own 
forces/  he  appears  to  have  some  conception  of  this 
kind  in  view. 

A  great  part  of  the  investigation  completed  in 
October,  1851,  was  taken  up  with  the  motions  of 
wires  round  the  poles  of  a  magnet  and  the  converse. 
He  carried  an  insulated  wire  along  the  axis  of  a 
bar  magnet  from  its  pole  to  its  equator,  where  it 
issued  from  the  magnet,  and  was  bent  up  so  as  to 
connect  its  two  ends.  A  complete  circuit,  no  part  of 
which  was  in  contact  with  the  magnet,  was  thus  ob- 
tained. He  found  that  when  the  magnet  and  the 
external  wire  were  rotated  together  no  current  was 
produced  ;  whereas,  when  either  of  them  was  rotated 
and  the  other  left  at  rest  currents  were  evolved. 
He  then  abandoned  the  axial  wire,  and  allowed  the 
magnet  itself  to  take  its  place ;  the  result  was  the 
same.*  It  was  the  relative  motion  of  the  magnet 
and  the  loop  that  was  effectual  in  producing  a  cur- 
rent. 

The  lines  of  force  have  their  roots  in  the  magnet, 
and  though  they  may  expand  into  infinite  space, 
they  eventually  return  to  the  magnet.  Now  these 
lines  may  be  intersected  close  to  the  magnet  or  at  a 
distance  from  it.  Faraday  finds  distance  to  be  per- 

*  In  this  form  the  experiment  is  identical  with  one  made  twenty 
years  earlier.  See  page  30. 


FARADAY  AS  A   DISCOVERER.  131 

fectly  immaterial  so  long  as  the  number  of  lines  in- 
tersected is  the  same.  For  example,  when  the  loop 
connecting  the  equator  and  the  pole  of  his  bar- 
inagnet  performs  one  complete  revolution  round  the 
magnet,  it  is  manifest  that  all  the  lines  of  force  issuing 
from  the  magnet  are  once  intersected.  Now  it  matters 
not  whether  the  loop  be  ten  feet  or  ten  inches  in 
length,  it  matters  not  how  it  may  be  twisted  and 
contorted,  it  matters  not  how  near  to  the  magnet  or 
how  distant  from  it  the  loop  may  be,  one  revolution 
always  produces  the  same  amount  of  current  elec- 
tricity, because  in  all  these  cases  all  the  lines  of  force 
issuing  from  the  magnet  are  once  intersected  and 
no  more. 

From  the  external  portion  of  the  circuit  he  passes 
in  idea  to  the  internal,  and  follows  the  lines  of  force 
into  the  body  of  the  magnet  itself.  His  conclusion 
is  that  there  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  in  fact  are  continuations  of  them.  .  .  *  Every 
line  of  force,  therefore,  at  whatever  distance  it  may 
be  taken  from  the  magnet,  must  be  considered  as 
a  closed  circuit,  passing  in  some  part  of  its  course 
through  the  magnet,  and  having  an  equal  amount  of 
force  in  every  part  of  its  course.' 

K    2 


132  FARADAY  AS  A   DISCOVERER. 

All  the  results  here  described  were  obtained  with 
moving  metals.  'But,'  he  continues  with  profound 
sagacity,  '  mere  motion  would  not  generate  a  relation, 
which  had  not  a  foundation  in  the  existence  of  some 
previous  state;  and  therefore  the  quiescent  metals 
must  be  in  some  relation  to  the  active  centre  of  force,' 
that  is  to  the  magnet.  He  here  touches  the  core  of 
the  whole  question,  and  when  we  can  state  the  con- 
dition into  which  the  conducting  wire  is  thrown 
before  it  is  moved,  we  shall  then  be  in  a  position  to 
understand  the  physical  constitution  of  the  electric 
current  generated  by  its  motion. 

In  this  inquiry  Faraday  worked  with  steel  magnets, 
the  force  of  which  varies  with  the  distance  from  the 
magnet.  He  then  sought  a  uniform  field  of  magnetic 
force,  and  found  it  in  space  as  affected  by  the  magnet- 
ism of  the  earth.  His  next  memoir,  sent  to  the 
Royal  Society,  December  31, 1851,  is  con  the  employ- 
ment of  the  Induced  Magneto-electro  Current  as  a 
test  and  measure  of  magnetic  forces.'  He  forms 
rectangles  and  rings,  and  by  ingenious  and  simple 
devices  collects  the  opposed  currents  which  are  de- 
veloped in  them  by  rotation  across  the  terrestrial  lines 
of  magnetic  force.  He  varies  the  shapes  of  his  rec- 
tangles while  preserving  their  areas  constant,  and 
finds  that  the  constant  area  produces  always  the  same 
amount  of  current  per  revolution.  The  current  de- 


FARADAY  AS  A   DISCOVERER.  133 

.pends  solely  on  the  number  of  lines  of  force  inter- 
sected, and  when  this  number  is  kept  constant  the 
current  remains  constant  too.  Thus  the  lines  of  mag- 
netic force  are  continually  before  his  eyes,  by  their 
aid  he  colligates  his  facts,  and  through  the  inspira- 
tions derived  from  them  he  vastly  expands  the 
boundaries  of  our  experimental  knowledge.  The 
beauty  and  exactitude  of  the  results  of  this  investi- 
gation are  extraordinary.  I  cannot  help  thinking 
while  I  dwell  upon  them,  that  this  discovery  of  mag- 
neto-electricity is  the  greatest  experimental  result 
ever  obtained  by  an  investigator.  It  is  the  Mont 
Blanc  of  Faraday's  own  achievements.  He  always 
worked  at  great  elevations,  but  a  higher  than  this 
he  never  subsequently  attained. 


UNITY   AND    CONVERTIBILITY   OP    NATURAL    FORCES  : 
THEORY   OF    THE    ELECTRIC    CURRENT. 

The  terms  unity  and  convertibility,  as  applied  to 
natural  forces,  are  often  employed  in  these  investi- 
gations, many  profound  and  beautiful  thoughts  re- 
specting these  subjects  being  expressed  in  Faraday's 
memoirs.  Modern  inquiry  has,  however,  much  aug- 
mented our  knowledge  of  the  relationship  of  natural 
forces,  and  it  seems  worth  while  to  say  a  few  words 
here,  tending  to  clear  up  certain  misconceptions 


134  FARADAY  AS  A   DISCO VEEEK. 

which  appear  to  exist  among  philosophic  writers 
regarding  this  relationship. 

The  whole  stock  of  energy  or  working-power  in  the 
world  consists  of  attractions,  repulsions,  and  motions. 
If  the  attractions  and  repulsions  are  so  circumstanced 
as  to  be  able  to  produce  motion,  they  are  sources 
of  working-power,  but  not  otherwise.  Let  us  for 
the  sake  of  simplicity  confine  our  attention  to  the 
case  of  attraction.  The  attraction  exerted  between 
the  earth  and  a  body  at  a  distance  from  the  earth's 
surface  is  a  source  of  working-power ;  because  the 
body  can  be  moved  by  the  attraction,  and  in  falling 
to  the  earth  can  perform  work.  When  it  rests  upon 
the  earth's  surface  it  is  not  a  source  of  power  or 
energy,  because  it  can  fall  no  further.  But  though 
it  has  ceased  to  be  a  source  of  energy,  the  attraction 
of  gravity  still  acts  as  &  force,  which  holds  the  earth 
and  weight  together. 

The  same  remarks  apply  to  attracting  atoms  and 
molecules.  As  long  as  distance  separates  them,  they 
can  move  across  it  in  obedience  to  the  attraction, 
and  the  motion  thus  produced  may,  by  proper  appli- 
ances, be  caused  to  perform  mechanical  work. 
When,  for  example,  two  atoms  of  hydrogen  unite 
with  one  of  oxygen,  to  form  water,  the  atoms 
are  first  drawn  towards  each  other — they  move, 
they  clash,  and  then  by  virtue  of  their  resiliency, 


FARADAY   AS   A   DISCOVERER.  135 

they  recoil  and  quiver.  To  this  quivering  motion 
we  give  the  name  of  heat.  Now  this  quivering 
motion  is  merely  the  redistribution  of  the  motion 
produced  by  the  chemical  affinity ;  and  this  is  the  only 
sense  in  which  chemical  affinity  can  be  said  to  be 
converted  into  heat.  We  must  not  imagine  the  chemi- 
cal attraction  destroyed,  or  converted  into  anything 
else.  For  the  atoms,  when  mutually  clasped  to  form 
a  molecule  of  water,  are  held  together  by  the  very 
attraction  which  first  drew  them  towards  each  other. 
That  which  has  really  been  expended  is  the  pull 
exerted  through  the  space  by  which  the  distance 
between  the  atoms  has  been  diminished. 

If  this  be  understood,  it  will  be  at  once  seen  tha,t 
gravity  may  in  this  sense  be  said  to  be  convertible 
into  heat ;  that  it  is  in  reality  no  more  an  outstand- 
ing and  inconvertible  agent,  as  it  is  sometimes  stated 
to  be,  than  chemical  affinity.  By  the  exertion  of  a 
certain  pull,  through  a  certain  space,  a  body  is  caused 
to  clash  with  a  certain  definite  velocity  against  the 
earth.  Heat  is  thereby  developed,  and  this  is  the 
only  sense  in  which  gravity  can  be  said  to  be  con- 
verted into  heat.  In  no  case  is  the  force  which  pro- 
duces the  motion  annihilated  or  changed  into  any- 
thing else.  The  mutual  attraction  of  the  earth  and 
weight  exists  when  they  are  in  contact  as  when  they 
were  separate ;  but  the  ability  of  that  attraction  to 


136  FARADAY  AS  A   DISCOVERER. 

employ  itself  in  the  production  of  motion  does  not 
exist. 

The  transformation,  in  this  case,  is  easily  followed 
by  the  mind's  eye.  First,  the  weight  as  a  whole  is 
set  in  motion  by  the  attraction  of  gravity.  This 
motion  of  the  mass  is  arrested  by  collision  with  the 
earth;  being  broken  up  into  molecular  tremors,  to 
which  we  give  the  name  of  heat. 

And  when  we  reverse  the  process,  and  employ 
those  tremors  of  heat  to  raise  a  weight,  as  is  done 
through  the  intermediation  of  an  elastic  fluid  in  the 
steam-engine,  a  certain  definite  portion  of  the  mole- 
cular motion  is  destroyed  in  raising  the  weight.  In 
this  sense,  and  this  sense  only,  can  the  heat  be  said 
to  be  converted  into  gravity,  or  more  correctly,  into 
potential  energy  of  gravity.  It  is  not  that  the  de- 
struction of  the  heat  has  created  any  new  attraction, 
but  simply  that  the  old  attraction  has  now  a  power 
conferred  upon  it,  of  exerting  a  certain  definite  pull 
in  the  interval  between  the  starting-point  of  the 
falling  weight  and  its  collision  with  the  earth. 

So  also  as  regards  magnetic  attraction :  when  a 
sphere  of  iron  placed  at  some  distance  from  a  mag- 
net rushes  towards  the  magnet,  and  has  its  motion 
stopped  by  collision,  an  effect  mechanically  the  same 
as  that  produced  by  the  attraction  of  gravity  occurs. 
The  magnetic  attraction  generates  the  motion  of  the 


FARADAY  AS  A  DISCOVERER.  137 

mass,  and  the  stoppage  of  that  motion  produces  heat. 
In  this  sense,  and  in  this  sense  only,  is  there  a  trans- 
formation of  magnetic  work  into  heat.  And  if  by 
the  mechanical  action  of  heat,  brought  to  bear  by 
means  of  a  suitable  machine,  the  sphere  be  torn  from 
the  magnet  and  again  placed  at  a  distance,  a  power 
of  exerting  a  pull  through  that  distance,  and  produc- 
ing a  new  motion  of  the  sphere,  is  thereby  conferred 
upon  the  magnet;  in  this  sense,  and  in  this  sense 
only,  is  the  heat  converted  into  magnetic  potential 
energy. 

When,  therefore,  writers  on  the  conservation  of 
energy  speak  of  tensions  being  '  consumed '  and 
'  generated,'  they  do  not  mean  thereby  that  old 
attractions  have  been  annihilated  and  new  ones 
brought  into  existence,  but  that,  in  the  one  case, 
the  power  of  the  attraction  to  produce  motion  has 
been  diminished  by  the  shortening  of  the  distance 
between  the  attracting  bodies,  and  that  in  the  other 
case  the  power  of  producing  motion  has  been  aug- 
mented by  the  increase  of  the  distance.  These  re- 
marks apply  to  all  bodies,  whether  they  be  sensible 
masses  or  molecules. 

Of  the  inner  quality  that  enables  matter  to  attract 
matter  we  know  nothing ;  and  the  law  of  conserva- 
tion makes  no  statement  regarding  that  quality. 
It  takes  the  facts  of  attraction  as  they  stand,  and 


138  FARADAY  AS  A  DISCOVERER. 

affirms  only  the  constancy  of  working-power.  That 
power  may  exist  in  the  form  of  MOTION  ;  or  it  may 
exist  in  the  form  of  FORCE,  with  distance  to  act 
through.  The  former  is  dynamic  energy,  the  latter 
is  potential  energy,  the  constancy  of  the  sum  of  both 
being  affirmed  by  the  law  of  conservation.  The  con- 
vertibility of  natural  forces  consists  solely  in  trans- 
formations of  dynamic  into  potential,  and  of  potential 
into  dynamic,  energy,  which  are  incessantly  going 
on.  In  no  other  sense  has  the  convertibility  of  force, 
at  present,  any  scientific  meaning. 

By  the  contraction  of  a  muscle  a  man  lifts  a 
weight  from  the  earth.  But  the  muscle  can  con- 
tract only  through  the  oxidation  of  its  own  tissue  or 
of  the  blood  passing  through  it.  Molecular  motion 
is  thus  converted  into  mechanical  motion.  Supposing 
the  muscle  to  contract  without  raising  the  weight, 
oxidation  would  also  occur,  but  the  whole  of  the  heat 
produced  by  this  oxidation  would  be  liberated  in  the 
muscle  itself.  Not  so  when  it  performs  external  work ; 
to  do  that  work  a  certain  definite  portion  of  the  heat 
of  oxidation  must  be  expended.  It  is  so  expended 
in  pulling  the  weight  away  from  the  earth.  If  the 
weight  be  permitted  to  fall,  the  heat  generated  by  its 
collision  with  the  earth  would  exactly  make  up  for 
that  lacking  in  the  muscle  during  the  lifting  of  the 
weight.  In  the  case  here  supposed,  we  have  a  con- 


FARADAY   AS   A  DISCOVEKER.  139 

version  of  molecular  muscular  action  into  potential 
energy  of  gravity ;  and  a  conversion  of  that  potential 
energy  into  heat;  the  heat,  however,  appearing  at 
a  distance  from  its  real  origin  in  the  muscle.  The 
whole  process  consists  of  a  transference  of  molecular 
motion  from  the  muscle  to  the  weight,  and  gravitat- 
ing force  is  the  mere  go-between,  by  means  of  which 
the  transference  is  effected. 

These  considerations  will  help  to  clear  our  way  to 
the  conception  of  the  transformations  which  occur 
when  a  wire  is  moved  across  the  lines  of  force  in  a 
magnetic  field.  In  this  case  it  is  commonly  said  we 
have  a  conversion  of  magnetism  into  electricity.  But 
let  us  endeavour  to  understand  what  really  occurs. 
For  the  sake  of  simplicity,  and  with  a  view  to  its 
translation  into  a  different  one  subsequently,  let  us 
adopt  for  a  moment  the  provisional  conception  of  a 
mixed  fluid  in  the  wire,  composed  of  positive  and 
negative  electricities  in  equal  quantities,  and  there- 
fore perfectly  neutralizing  each  other  when  the  wire 
is  still.  By  the  motion  of  the  wire,  say  with  the 
hand,  towards  the  magnet,  what  the  Germans  call  a 
Scheidungs-Kraft — a  separating  force — is  brought  into 
play.  This  force  tears  the  mixed  fluids  asunder,  and 
drives  them  in  two  currents,  the  one  positive  and 
the  other  negative,  in  two  opposite  directions  through 
the  wire.  The  presence  of  these  currents  evokes  a 


140  EAR  AD  AY   AS   A   DISCOVERER. 

force  of  repulsion  between  the  magnet  and  the  wire ; 
and  to  cause  the  one  to  approach  the  other,  this  re- 
pulsion must  be  overcome.  The  overcoming  of  this 
repulsion  is,  in  fact,  the  work  done  in  separating  and 
impelling  the  two  electricities.  When  the  wire  is 
moved  away  from  the  magnet,  a  Scheidungs-Kraft,  or 
separating  force,  also  comes  into  play ;  but  now  it  is 
an  attraction  that  has  to  be  surmounted.  In  sur- 
mounting it,  currents  are  developed  in  directions 
opposed  to  the  former ;  positive  takes  the  place  of 
negative,  and  negative  the  place  of  positive ;  the  over- 
coming of  the  attraction  being  the  work  done  in  sepa- 
rating and  impelling  the  two  electricities. 

The  mechanical  action  occurring  here  is  different 
from  that  occurring  where  a  sphere  of  soft  iron  is 
withdrawn  from  a  magnet,  and  again  attracted. 
In  this  case  muscular  force  is  expended  during  the 
act  of  separation ;  but  the  attraction  of  the  magnet 
effects  the  reunion.  In  the  case  of  the  moving  wire 
also  we  overcome  a  resistance  in  separating  it  from 
the  magnet,  and  thus  far  the  action  is  mechanically 
the  same  as  the  separation  of  the  sphere  of  iron. 
But  after  the  wire  has  ceased  moving,  the  attraction 
ceases  ;  and  so  far  from  any  action  occurring  similar 
to  that,  which  draws  the  iron  sphere  back  to  the 
magnet,  we  have  to  overcome  a  repulsion  to  bring 
them  together. 


FARADAY  AS   A  DISCOVERER.  141 

There  is  no  potential  energy  conferred  either  by 
the  removal  or  by  the  approach  of  the  wire,  and  the 
only  power  really  transformed  or  converted,  in  the 
experiment,  is  muscular  power.  Nothing  that  could 
in  strictness  be  called  a  conversion  of  magnetism 
into  electricity  occurs.  The  muscular  oxidation  that 
moves  the  wire  fails  to  produce  within  the  imiscle  its 
due  amount  of  heat,  a  portion  of  that  heat  equi- 
valent to  the  resistance  overcome,  appearing  in  the 
moving  wire  instead. 

Is  this  effect  an  attraction  and  a  repulsion  at  a 
distance?  If  so,  why  should  both  cease  when  the 
wire  ceases  to  move?  In  fact,  the  deportment 
of  the  wire  resembles  far  more  that  of  a  body 
moving  in  a  resisting  medium  than  anything  else ; 
the  resistance  ceasing  when  the  motion  is  sus- 
pended. Let  us  imagine  the  case  of  a  liquid  so 
mobile  that  the  hand  may  be  passed  through  it  to 
and  fro,  without  encountering  any  sensible  re- 
sistance. It  resembles  the  motion  of  a  conductor  in 
the  unexcited  field  of  an  electro-magnet.  Now,  let 
us  suppose  a  body  placed  in  the  liquid,  or  acting  on 
it,  which  confers  upon  it  the  property  of  viscosity  ; 
the  hand  would  no  longer  move  freely.  During  its 
motion,  but  then  only,  resistance  would  be  encoun- 
tered and  overcome.  Here  we  have  rudely  repre- 
sented the  case  of  the  excited  magnetic  field,  and  the 


142  FARADAY  AS   A   DISCOVERER. 

result  in  both,  cases  would  be  substantially  the  same. 
In  both  cases  heat  would,  in  the  end,  be  generated 
outside  of  the  muscle,  its  amount  being  exactly 
equivalent  to  the  resistance  overcome. 

Let  us  push  the  analogy  a  little  further ;  suppose 
in  the  case  of  the  fluid  rendered  viscous,  as  assumed 
a  moment  ago,  the  viscosity  not  to  be  so  great  as  to 
prevent  the  formation  of  ripples  when  the  hand  is 
passed  through  the  liquid.  Then  the  motion  of  the 
hand,  before  its  final  conversion  into  heat,  would 
exist  for  a  time  as  wave-motion,  which,  on  subsiding, 
would  generate  its  due  equivalent  of  heat.  This  in- 
termediate stage,  in  the  case  of  our  moving  wire,  is 
represented  by  the  period  during  which  the  electric 
current  is  flowing  through  it ;  but  that  current,  like 
the  ripples  of  our  liquid,  soon  subsides,  being,  like 
them,  converted  into  heat. 

Do  these  words  shadow  forth  anything  like  the 
reality?  Such  speculations  cannot  be  injurious  if 
they  are  enunciated  without  dogmatism.  I  do  con- 
fess that  ideas  such  as  these  here  indicated  exercise 
a  strong  fascination  on  my  mind.  Is  then  the 
magnetic  field  really  viscous,  and  if  so,  what  sub- 
stance exists  in  it  and  the  wire  to  produce  the  visco- 
sity? Let  us  first  look  at  the  proved  effects,  and 
afterwards  turn  our  thoughts  back  upon  their  cause. 


FARADAY  AS   A   DISCOVERER.  143 

When  the  wire  approaches  the  magnet,  an  action  is 
evoked  within  it,  which  travels  through  it  with  a 
velocity  comparable  to  that  of  light.  One  substance 
only  in  the  universe  has  been  hitherto  proved  compe* 
tent  to  transmit  power  at  this  velocity ;  the  lumini- 
ferous  ether.  Not  only  its  rapidity  of  progression  but 
its  ability  to  produce  the  motion  of  light  and  heat, 
indicates  that  the  electric  current  is  also  motion.* 
Further,  there  is  a  striking  resemblance  between  the 
action  of  good  and  bad  conductors  as  regards  electri- 
city, and  the  action  of  diathermanous  and  adiather- 
manous  bodies  as  regards  radiant  heat.  The  good 
conductor  is  diathermanous  to  the  electric  current ;  it 
allows  free  transmission  without  the  development  of 
heat.  The  bad  conductor  is  adiathermanous  to  the 
electric  current,  and  hence  the  passage  of  the  latter 
is  accompanied  by  the  development  of  heat.  I  am 
strongly  inclined  to  hold  the  electric  current,  pure 
and  simple,  to  be  a  motion  of  the  ether  alone ;  good 
conductors  being  so  constituted  that  the  motion  may 
be  propagated  through  their  ether  without  sensible 
transfer  to  their  atoms,  while  in  the  case  of  bad 

*  Mr.  Clerk  Maxwell  has  recently  published  an  exceedingly  im- 
portant investigation  connected  with  this  question.  Even  in  the  non- 
mathematical  portions  of  the  memoirs  of  Mr.  Maxwell,  the  admirable 
spirit  of  his  philosophy  is  sufficiently  revealed.  As  regards  the  em- 
ployment of  scientific  imagery,  I  hardly  know  his  equal  in  power  of 
conception  and  clearness  of  definition. 


144  FARADAY  AS  A   DISCOVERER. 

conductors  this  transfer  is  effected,  the  transferred 
motion  appearing  as  heat.* 

I  do  not  know  whether  Faraday  would  have  sub- 
scribed to  what  is  here  written;  probably  his  habitual 
caution  would  have  prevented  him  from  committing 
himself  to  anything  so  definite.  But  some  such 
idea  filled  his  mind  and  coloured  his  language 
through  all  the  later  years  of  his  life.  I  dare  not  say 
that  he  has  been  always  successful  in  the  treatment 
of  these  theoretic  notions.  In  his  speculations  he 
mixes  together  light  and  darkness  in  varying  pro- 
portions, and  carries  us  along  with  him  through 
strong  alternations  of  both.  It  is  impossible  to 
say  how  a  certain  amount  of  mathematical  train- 
ing would  have  affected  his  work.  We  cannot  say 
what  its  influence  would  have  been  upon  that  force 
of  inspiration  that  urged  him  on ;  whether  it  would 
have  daunted  him,  and  prevented  him  from  driving 
his  adits  into  places,  where  no  theory  pointed  to  a 
lode.  If  so,  then  we  may  rejoice  that  this  strong 
delver  at  the  mine  of  natural  knowledge  was  left  free 
to  wield  his  mattock  in  his  own  way.  It  must  be 
admitted,  that  Faraday's  purely  speculative  writings 
often  lack  that  precision  which  the  mathematical 

*  One  important  difference,  of  course,  exists  between  the  effect  of 
motion  in  the  magnetic  field,  and  motion  in  a  resisting  medium.  In  the 
former  case  the  heat  is  generated  in  the  moving  conductor,  in  the  latter 
it  is  in  part  generated  in  the  medium. 


FARADAY  A3  A   DISCOVERER.  145 

habit  of  thought  confers.  Still  across  them  flash 
frequent  gleams  of  prescient  wisdom  which  will  ex- 
cite admiration  throughout  all  time ;  while  the  facts, 
relations,  principles,  and  laws  which  his  experiments 
have  established  are  sure  to  form  the  body  of  grand 
theories  yet  to  come. 

SUMMARY. 

When  from  an  Alpine  height  the  eye  of  the 
climber  ranges  over  the  mountains,  he  finds  that  for 
the  most  part  they  resolve  themselves  into  distinct 
groups,  each  consisting  of  a  dominant  mass  sur- 
rounded by  peaks  of  lesser  elevation.  The  power 
which  lifted  the  mightier  eminences,  in  nearly  all 
cases  lifted  others  to  an  almost  equal  height.  And 
so  it  is  with  the  discoveries  of  Faraday.  As  a 
general  rule,  the  dominant  result  does  not  stand 
alone,  but  forms  the  culminating  point  of  a  vast  and 
varied  mass  of  inquiry.  In  this  way,  round  about  his 
great  discovery  of  Magneto-electric  Induction,  other 
weighty  labours  group  themselves.  His  investi- 
gations on  the  Extra  Current;  on  the  Polar  and 
other  Condition  of  Diamagnetic  Bodies  ;  on  Lines  of 
Magnetic  Force,  their  definite  character  and  distri- 
bution ;  on  the  employment  of  the  Induced  Magneto- 
electric  Current  as  a  measure  and  test  of  Magnetic 
Action ;  on  the  Eevulsive  Phenomena  of  the  mag- 

L 


146  FARADAY   AS   A   DISCOVERER. 

netic  field,  are  all,  notwithstanding  the  diversity  of 
title,  researches  in  the  domain  of  Magneto-electric 
Induction. 

Faraday's  second  group  of  researches  and  dis- 
coveries embrace  the  chemical  phenomena  of  the 
current.  The  dominant  result  here  is  the  great  law 
of  definite  Electro-chemical  Decomposition,  around 
which  are  massed  various  researches  on  Electro- 
chemical Conduction,  and  on  Electrolysis  both  with 
the  Machine  and  with  the  Pile.  To  this  group  also 
belong  his  analysis  of  the  Contact  Theory,  his 
inquiries  as  to  the  Source  of  Yoltaic  Electricity,  and 
his  final  development  of  the  Chemical  Theory  of 
the  pile. 

His  third  great  discovery  is  the  Magnetization 
of  Light,  which  I  should  liken  to  the  Weisshorn 
among  mountains — high,  beautiful,  and  alone. 

The  dominant  result  of  his  fourth  group  of  re- 
searches is  the  discovery  of  Diamagnetism,  an- 
nounced in  his  memoir  as  the  Magnetic  Condition  of 
all  Matter,  round  which  are  grouped  his  inquiries  on 
the  Magnetism  of  Flame  and  Gases;  on  Magne- 
crystallic  action,  and  on  Atmospheric  Magnetism, 
in  its  relations  to  the  annual  and  diurnal  variation  of 
the  needle,  the  full  significance  of  which  is  still  to  be 
shown. 

These    are    Faraday's  most   massive   discoveries, 


FARADAY  AS   A   DISCO VEREE.  147 

and  upon  them  his  fame  must  mainly  rest.  But 
even  without  them,  sufficient  would  remain  to  secure 
for  him  a  high  and  lasting  scientific  reputation. 
We  should  still  have  his  researches  on  the  Lique- 
faction of  Gases;  on  Frictional  Electricity;  on  the 
Electricity  of  the  Grymnotus  ;  on  the  source  of  Power 
in  the  Hydro-electric  machine,  the  two  last  investi- 
gations being  untouched  in  the  foregoing  memoir; 
on  Electro-magnetic  Rotations ;  on  Regelation ;  all 
his  more  purely  Chemical  Researches,  including  his 
discovery  of  Benzol.  Besides  these  he  published  a 
multitude  of  minor  papers,  most  of  which,  in  some 
way  or  other,  illustrate  his  genius.  I  have  made 
no  allusion  to  his  power  and  sweetness  as  a  lecturer. 
Taking  him  for  all  and  all,  I  think  it  will  be  con- 
ceded that  Michael  Faraday  was  the  greatest  experi- 
mental philosopher  the  world  has  ever  seen ;  and  I 
will  add  the  opinion,  that  the  progress  of  future 
research  will  tend,  not  to  dim  or  to  diminish,  but  to 
enhance  and  glorify  the  labours  of  this  mighty  in- 
vestigator. 

ILLUSTRATIONS  OP  CHARACTER. 

Thus  far  I  have  confined  myself  to  topics  mainly 
interesting  to  the  man  of  science,  endeavouring, 
however,  to  treat  them  in  a  manner  unrepellent  to 
the  general  reader  who  might  wish  to  obtain  a  notion 

L  2 


]48  FARADAY  AS   A   DISCOVERER. 

of  Faraday  as  a  worker.  On  others  will  fall  the 
duty  of  presenting  to  the  world  a  picture  of  the  man. 
But  I  know  you  will  permit  me  to  add  to  the 
foregoing  analysis  a  few  personal  reminiscences  and 
remarks,  tending  to  connect  Faraday  with  a  wider 
world  than  that  of  science — namely,  with  the  general 
human  heart. 

One  word  in  reference  to  his  married  life,  in 
addition  to  what  has  been  already  said,  may  find  a 
place  here.  As  in  the  former  case,  Faraday  shall  be 
his  own  spokesman.  The  following  paragraph, 
though  written  in  the  third  person,  is  from  his 
hand : — '  On  June  12,  1841,  he  married,  an  event 
which  more  than  any  other  contributed  to  his 
earthly  happiness  and  healthful  state  of  mind.  The 
union  has  continued  for  twenty- eight  years  and  has 
in  no  wise  changed,  except  in  the  depth  and  strength 
of  its  character.' 

Faraday's  immediate  forefathers  lived  in  a  little 
place  called  Clapham  Wood  Hall,  in  Yorkshire. 
Here  dwelt  Robert  Faraday  and  Elizabeth  his  wife, 
who  had  ten  children,  one  of  them,  James  Faraday, 
born  in  1761,  being  father  to  the  philosopher.  A 
family  tradition  exists  that  the  Faradays  came  origi- 
nally from  Ireland.  Faraday  himself  has  more  than 
once  expressed  to  me  his  belief  that  his  blood  was  in 
part  Celtic,  but  how  much  of  it  was  so,  or  when  the 


FARADAY  AS  A   DISCOVERER.  149 

infusion  took  place,  he  was  unable  to  say.  He  could 
imitate  the  Irish  brogue,  and  his  wonderful  vivacity 
may  have  been  in  part  due  to  his  extraction.  But 
there  were  other  qualities  which  we  should  hardly 
think  of  deriving  from  Ireland.  The  most  prominent 
of  these  was  his  sense  of  order,  which  ran  like  a 
luminous  beam  through  all  the  transactions  of  his 
life.  The  most  entangled  and  complicated  matters 
fell  into  harmony  in  his  hands.  His  mode  of  keeping 
accounts  excited  the  admiration  of  the  managing 
board  of  this  Institution.  And  his  science  was  simi- 
larly ordered.  In  his  Experimental  Researches,  he 
numbered  every  paragraph,  and  welded  their  various 
parts  together  by  incessant  reference.  His  private 
notes  of  the  Experimental  Researches,  which  are 
happily  preserved,  are  similarly  numbered :  their  last 
paragraph  bears  the  figure  16,041.  His  working 
qualities,  moreover,  showed  the  tenacity  of  the  Teu- 
ton. His  nature  was  impulsive,  but  there  was  a  force 
behind  the  impulse  which  did  not  permit  it  to  retreat. 
If  in  his  warm  moments  he  formed  a  resolution,  in 
his  cool  ones  he  made  that  resolution  good.  Thus 
his  fire  was  that  of  a  solid  combustible,  not  that  of  a 
gas,  which  blazes  suddenly,  and  dies  as  suddenly 
away. 

And  here  I  must  claim  your  tolerance  for  the  limits 
by  which  I  am  confined.     No  materials  for  a  life  of 


150  FARADAY  AS   A   DISCOVERER. 

Faraday  are  in  my  hands,  and  what  I  have  now  to 
say  has  arisen  almost  wholly  out  of  our  close  personal 
relationship. 

Letters  of  his,  covering  a  period  of  sixteen  years, 
are  before  me,  each  one  of  which  contains  some 
characteristic  utterance; — strong,  yet  delicate  in 
counsel,  joyful  in  encouragement,  and  warm  in  affec- 
tion. Eeferences  which  would  be  pleasant  to  such 
of  them  as  still  live  are  made  to  Humboldt,  Biot, 
Dumas,  Chevreul,  Magnus,  and  Arago.  Accident 
brought  these  names  prominently  forward;  but  many 
others  would  be  required  to  complete  his  list  of  con- 
tinental friends.  He  prized  the  love  and  sympathy 
of  men — prized  it  almost  more  than  the  renown 
which  his  science  brought  him.  Nearly  a  dozen 
years  ago  it  fell  to  my  lot  to  write  a  review  of  his 
'  Experimental  Researches  '  for  the  '  Philosophical 
Magazine.'  After  he  had  read  it,  he  took  me  by  the 
hand,  and  said,  '  Tyndall,  the  sweetest  reward  of  my 
work  is  the  sympathy  and  good  will  which  it  has 
caused  to  flow  in  upon  me  from  all  quarters  of  the 
world.'  Among  his  letters  I  find  little  sparks  of 
kindness,  precious  to  no  one  but  myself,  but  more 
precious  to  me  than  all.  He  would  peep  into  the 
laboratory  when  he  thought  me  weary,  and  take  me 
upstairs  with  him  to  rest.  And  if  I  happened  to  be 
absent  he  would  leave  a  little  note  for  me,  couched 


FAEADAY   AS  A   DISCOVERER.  151 

in  this  or  some  other  similar  form  : — '  Dear  Tyndall 
—I  was  looking  for  you,  because  we  were  at  tea — we 
have  not  yet  done — will  you  come  up  ?  '  I  frequently 
shared  his  early  dinner ;  almost  always,  in  fact,  while 
my  lectures  were  going  on.  There  was  no  trace  of 
asceticism  in  his  nature.  He  preferred  the  meat  and 
wine  of  life  to  its  locusts  and  wild  honey.  Never 
once  during  an  intimacy  of  fifteen  years  did  he  men- 
tion religion  to  me,  save  when  I  drew  him  on  to  the 
subject.  He  then  spoke  to  me  without  hesitation  or 
reluctance  ;  not  with  any  apparent  desire  to  ' improve 
the  occasion,'  but  to  give  me  such  information  as  I 
sought.  He  believed  the  human  heart  to  be  swayed 
by  a  power  to  which  science  or  logic  opened  no 
approach,  and  right  or  wrong,  this  faith,  held  in  per- 
fect tolerance  of  the  faiths  of  others,  strengthened 
and  beautified  his  life. 

From  the  letters  just  referred  to,  I  will  select  three 
for  publication  here.  I  choose  the  first,  because  it 
contains  a  passage  revealing  the  feelings  with  which 
Faraday  regarded  his  vocation,  and  also  because 
it  contains  an  allusion  which  will  give  pleasure  to  a 
friend. 


'Ventnor,  Isle  of  Wight,  June  28,  1854. 

'  MY  DEAR  TYNDALL,— You  see  by  the  top  of  this 
letter  how  much  habit  prevails  over  me  ;  I  have  just 


152  FARADAY   AS   A   DISCOVERER. 

read  yours  from  thence,  and  yet  I  think  my  self  there. 
However,  I  have  left  its  science  in  very  good  keeping, 
and  I  am  glad  to  learn  that  you  are  at  experiment 
once  more.  But  how  is  the  health  ?  Not  well,  I  fear. 
I  wish  you  would  get  yourself  strong  first  and  work 
afterwards.  As  for  the  fruits,  I  am  sure  they  will  be 
good,  for  though  I  sometimes  despond  as  regards 
myself,  I  do  not  as  regards  you.  You  are  young, 
I  am  old.  .  .  .  But  then  our  subjects  are  so  glorious, 
that  to  work  at  them  rejoices  and  encourages  the  feeblest; 
delights  and  enchants  the  strongest. 

6 1  have  not  yet  seen  anything  from  Magnus. 
Thoughts  of  him  always  delight  me.  We  shall  look 
at  his  black  sulphur  together.  I  heard  from  Schon- 
bein  the  other  day.  He  tells  me  that  Liebig  is  full 
of  ozone,  i>e.  of  allotropic  oxygen. 

'  Good-bye  for  the  present. 

f  Ever,  my  dear  Tyndall, 
6  Yours  truly, 
CM.  FARADAY.' 

The  contemplation  of  Nature,  and  his  own  rela- 
tion to  her,  produced  in  Faraday  a  kind  of  spiritual 
exaltation  which  makes  itself  manifest  here.  His 
religious  feeling  and  his  philosophy  could  not  be  kept 
apart ;  there  was  an  habitual  overflow  of  the  one  into 
the  other. 


FAKADAY  AS   A  DISCOVERER.  153 

Whether  he  or  another  was  its  exponent,  he  ap- 
peared to  take  equal  delight  in  science.  A  good 
experiment  would  make  him  almost  dance  with 
delight.  In  November,  1850,  he  wrote  to  me  thus  : — 
c  I  hope  some  day  to  take  up  the  point  respecting  the 
magnetism  of  associated  particles.  In  the  mean 
time  I  rejoice  at  every  addition  to  the  facts  and 
reasoning  connected  with  the  subject.  When  science 
is  a  republic,  then  it  gains :  and  though  I  am  no 
republican  in  other  matters,  I  am  in  that.'  All  his 
letters  illustrate  this  catholicity  of  feeling.  Ten  years 
ago,  when  going  down  to  Brighton,  he  carried  with 
him  a  little  paper  I  had  just  completed,  and  after- 
wards wrote  to  me.  His  letter  is  a  mere  sample  of 
the  sympathy  which  he  always  showed  to  me  and  my 
work. 

« Brighton,  December  9,  1857. 

c  MY  DEAR  TYNDALL, — I  cannot  resist  the  pleasure 
of  saying  how  very  much  I  have  enjoyed  your  paper. 
Every  part  has  given  me  delight.  It  goes  on  from 
point  to  point  beautifully.  You  will  find  many  pencil 
marks,  for  I  made  them  as  I  read.  I  let  them  stand, 
for  though  many  of  them  receive  their  answer  as 
the  story  proceeds,  yet  they  show  how  the  wording 
impresses  a  mind  fresh  to  the  subject,  and  perhaps 
here  and  there  you  may  like  to  alter  it  slightly,  if 
you  wish  the  full  idea,  i.e.  not  an  inaccurate  one,  to 


154  FARADAY  AS   A   DISCOVERER. 

be  suggested  at  first ;  and  yet  after  all  I  believe  it  is 
not  your  exposition,  but  the  natural  jumping  to  a 
conclusion  that  affects  or  has  affected  my  pencil. 

6  We  return  on  Friday,  when  I  will  return  you  the 
paper. 

6  Ever  truly  yours, 

6  M.  FARADAY.' 

The  third  letter  will  come  in  its  proper  place  to- 
wards the  end. 

While  once  conversing  with  Faraday  on  science,  in 
its  relations  to  commerce  and  litigation,  he  said  to 
me,  that  at  a  certain  period  of  his  career,  he  was 
forced  definitely  to  ask  himself,  and  finally  to  decide 
whether  he  should  make  wealth  or  science  the  pursuit 
of  his  life.  He  could  not  serve  both  masters,  and  he 
was  therefore  compelled  to  choose  between  them. 
After  the  discovery  of  magneto-electricity  his  fame 
was  so  noised  abroad,  that  the  commercial  world 
would  hardly  have  considered  any  remuneration  too 
high  for  the  aid  of  abilities  like  his.  Even  before  he 
became  so  famous,  he  had  done  a  little  '  professional 
business.'  This  was  the  phrase  he  applied  to  his 
purely  commercial  work.  His  friend,  Eichard 
Phillips,  for  example,  had  induced  him  to  undertake 
a  number  of  analyses,  which  produced,  in  the  year 
1830,  an  addition  to  his  income  of  more  than  a 


FAEADAY   AS  A   DISCOVERER.  155 

thousand  pounds  ;  and  in  1831,  a  still  greater  addi- 
tion. He  had  only  to  will  it  to  raise  in  1832  his 
professional  business  income  to  5,OOOZ.  a  year.  In- 
deed, this  is  a  wholly  insufficient  estimate  of  what  he 
might,  with  ease,  have  realised  annually  during  the 
last  thirty  years  of  his  life. 

While  restudying  the  Experimental  Eesearches 
with  reference  to  the  present  memoir,  the  conver- 
sation with  Faraday  here  alluded  to  canie  to  my 
recollection,  and  I  sought  to  ascertain  the  period 
when  the  question,  '  wealth  or  science,'  had  presented 
itself  with  such  emphasis  to  his  mind.  I  fixed  upon 
the  year  1831  or  1832,  for  it  seemed  beyond  the 
range  of  human  power  to  pursue  science  as  he  had 
done  during  the  subsequent  years,  and  to  pursue 
commercial  work  at  the  same  time.  To  test  this 
conclusion  I  asked  permission  to  see  his  accounts, 
and  on  my  own  responsibility,  I  will  state  the  result. 
In  1832,  his  professional  business-income,  instead  of 
rising  to  5,0001,  or  more,  fell  from  1,090?.  4s.  to  155Z. 
9s.  From  this  it  fell  with  slight  oscillations  to  92Z.  in 
1837,  and  to  zero  in  1838.  Between  1839  and  1845,  it 
never,  except  in  one  instance,  exceeded  221. ;  being 
for  the  most  part  much  under  this.  The  exceptional 
year  referred  to  was  that  in  which  he  and  Sir  Charles 
Lyell  were  engaged  by  Government  to  write  a  report 
on  the  Haswell  Colliery  explosion,  and  then  his 


156  FARADAY  AS   A   DISCOVERER. 

business  income  rose  to  1121.  From  the  end  of  1845 
to  the  day  of  his  death,  Faraday's  annual  professional 
business  income  was  exactly  zero.  Taking  the  dura- 
tion of  his  life  into  account,  this  son  of  a  blacksmith, 
and  apprentice  to  a  bookbinder,  had  to  decide 
between  a  fortune  of  150,000?.  on  the  one  side,  and 
his  undowered  science  on  the  other.  He  chose  the 
latter,  and  died  a  poor  man.  But  his  was  the  glory 
of  holding  aloft  among  the  nations  the  scientific 
name  of  England  for  a  period  of  forty  years. 

The  outward  and  visible  signs  of  fame  were  also 
of  less  account  to  him  than  to  most  men.  He  had 
been  loaded  with  scientific  honours  from  all  parts  of 
the  world.  Without,  I  imagine,  a  dissentient  voice, 
he  was  regarded  as  the  prince  of  the  physical  in- 
vestigators of  the  present  age.  The  highest  scien- 
tific position  in  this  country  he  had,  however,  never 
filled.  When  the  late  excellent  and  lamented  Lord 
Wrottesley  resigned  the  presidency  of  the  Royal 
Society,  a  deputation  from  the  council,  consisting  of 
his  Lordship,  Mr.  Grove,  and  Mr.  Gassiot,  waited 
upon  Faraday,  to  urge  him  to  accept  the  president's 
chair.  All  that  argument  or  friendly  persuasion 
could  do  was  done  to  induce  him  to  yield  to  the 
wishes  of  the  council,  which  was  also  the  unanimous 
wish  of  scientific  men.  A  knowledge  of  the  quick- 
ness of  his  own  nature  had  induced  in  Faraday  the 


FARADAY  AS   A   DISCOVERER.  157 

liabit  of  requiring  an  interval  of  reflection,  before  lie 
decided  upon  any  question  of  importance.  In  the 
present  instance  he  followed  his  usual  habit,  and 
begged  for  a  little  time. 

On  the  following  morning,  I  went  up  to  his 
room,  and  said  on  entering  that  I  had  come  to 
him  with  some  anxiety  of  mind.  He  demanded 
its  cause,  and  I  responded  'lest  you  should  have 
decided  against  the  wishes  of  the  deputation  that 
waited  on  you  yesterday.'  '  You  would  not  urge 
me  to  undertake  this  responsibility/  he  said.  '  I 
not  only  urge  you,'  was  my  reply,  c  but  I  consider  it 
your  bounden  duty  to  accept  it.'  He  spoke  of  the 
labour  that  it  would  involve ;  urged  that  it  was  not 
in  his  nature  to  take  things  easy;  and  that  if  he 
became  president,  he  would  surely  have  to  stir  many 
new  questions,  and  agitate  for  some  changes.  I 
said  that  in  such  cases  he  would  find  himself  sup- 
ported by  the  youth  and  strength  of  the  Eoyal 
Society.  This,  however,  did  not  seem  to  satisfy  him. 
Mrs.  Faraday  came  into  the  room,  and  he  appealed 
to  her.  Her  decision  was  adverse,  and  I  deprecated 
her  decision.  (  Tyndall,'  he  said  at  length,  '  I  must 
remain  plain  Michael  Faraday  to  the  last;  and  let 
me  now  tell  you,  that  if  I  accepted  the  honour  which 
the  Royal  Society  desires  to  confer  upon  me,  I  would 
not  answer  for  the  integrity  of  my  intellect  for  a 


158  FARADAY   AS   A   DISCOVERER. 

single  year.'  I  urged  him  no  more,  and  Lord 
Wrottesley  had  a  most  worthy  successor  in  Sir  Ben- 
jamin Brodie. 

After  the  death  of  the  Duke  of  Northumberland, 
our  Board  of  Managers  wished  to  see  Mr.  Faraday 
finish  his  career  as  President  of  the  Institution, 
which  he  had  entered  on  weekly  wages  more  than 
half  a  century  before.  But  he  would  have  nothing 
to  do  with  the  presidency.  He  wished  for  rest,  and 
the  reverent  affection  of  his  friends  was  to  him  in- 
finitely more  precious  than  all  the  honours  of  official 
life. 

The  first  requisite  of  the  intellectual  life  of  Fara- 
day was  the  independence  of  his  mind ;  and  though 
prompt  to  urge  obedience  where  obedience  was  due, 
with  every  right  assertion  of  manhood  he  intensely 
sympathized.  Even  rashness  on  the  side  of  honour 
found  from  him  ready  forgiveness,  if  not  open 
applause.  The  wisdom  of  years,  tempered  by  a 
character  of  this  kind,  rendered  his  counsel  pecu- 
liarly precious  to  men  sensitive  like  himself.  I  often 
sought  that  counsel,  and,  with  your  permission,  will 
illustrate  its  character  by  one  or  two  typical  in- 
stances. 

In  1855,  I  was  appointed  examiner  under  the 
Council  for  Military  Education.  At  that  time,  as 
indeed  now,  I  entertained  strong  convictions  as  to 


FARADAY   AS   A   DISCOVERER.  159 

the  enormous  utility  of  physical  science  to  officers  of 
artillery  and  engineers,  and  whenever  opportunity 
offered,  I  expressed  this  conviction  without  reserve. 
I  did  not  think  the  recognition,  though  considerable, 
accorded  to  physical  science  in  those  examinations 
at  all  proportionate  to  its  importance ;  and  this  pro- 
bably rendered  me  more  jealous  than  I  otherwise 
should  have  been  of  its  claims. 

In  Trinity  College,  Dublin,  a  school  had  been 
organized  with  reference  to  the  Woolwich  examina- 
tions, and  a  large  number  of  exceedingly  well-in- 
structed young  gentlemen  were  sent  over  from  Dublin, 
to  compete  for  appointments  in  the  artillery  and 
engineers.  The  result  of  one  examination  was  par- 
ticularly satisfactory  to  me;  indeed  the  marks  ob- 
tained appeared  so  eloquent,  that  I  forbore  saying 
a  word  about  them.  My  colleagues,  however,  followed 
the  Usual  custom  of  sending  in  brief  reports  with 
their  returns  of  marks.  After  the  results  were  pub- 
lished, a  leading  article  appeared  in  6  The  Times,'  in 
which  the  reports  were  largely  quoted,  praise  being 
bestowed  on  all  the  candidates,  except  the  excellent 
young  fellows  who  had  passed  through  my  hands. 

A  letter  from  Trinity  College  drew  my  attention 
to  this  article,  bitterly  complaining,  that  whereas  the 
marks  proved  them  to  be  the  best  of  all,  the  science 
candidates  were  wholly  ignored.  I  tried  to  set 


160  FARADAY  AS   A   DISCOVERER. 

matters  right  by  publishing,  on  my  own  responsi- 
bility, a  letter  in  '  The  Times.'  The  act  I  knew 
could  not  bear  justification  from  the  War-Office  point 
of  view ;  and  I  expected  and  risked  the  displeasure 
of  my  superiors.  The  merited  reprimand  promptly 
came.  c  Highly  as  the  Secretary  of  State  for  War 
might  value  the  expression  of  Professor  TyndalPs 
opinion,  he  begged  to  say  that  an  examiner,  appointed 
by  His  Royal  Highness  the  Commander-in-Chief,  had 
no  right  to  appear  in  the  public  papers  as  Professor 
Tyndall  has  done,  without  the  sanction  of  the  War 
Office.'  Nothing  could  be  more  just  than  this  re- 
proof, but  I  did  not  like  to  rest  under  it.  I  wrote  a  re- 
ply, and  previous  to  sending  it  took  it  up  to  Faraday. 
We  sat  together  before  his  fire,  and  he  looked  very 
earnest  as  he  rubbed  his  hands  and  pondered.  The 
following  conversation  then  passed  between  us  : — 

F.  You  certainly  have  received  a  reprimand, 
Tyndall ;  but  the  matter  is  over,  and  if  you  wish  to 
accept  the  reproof,  you  will  hear  no  more  about  it. 

T.  But  I  do  not  wish  to  accept  it. 

F.  Then  you  know  what  the  consequence  of  send- 
ing that  letter  will  be  ? 

T.  I  do. 

F.  They  will  dismiss  you. 

T.  I  know  it. 

F.   Then  send  the  letter  ! 


FAEADAY  AS  A  DISCOVERER.  161 

The  letter  was  firm,  but  respectful;  it  acknow- 
ledged the  justice  of  the  censure,  but  expressed 
neither  repentance  nor  regret.  Faraday,  in  his  gra- 
cious way,  slightly  altered  a  sentence  or  two  to  make 
it  more  respectful  still.  It  was  duly  sent,  and  on 
the  following  day  I  entered  the  Institution  with  the 
conviction  that  my  dismissal  was  there  before  me. 
Weeks,  however,  passed.  At  length  the  well-known, 
envelope  appeared,  and  I  broke  the  seal,  not  doubt- 
ing the  contents.  They  were  very  different  from 
what  I  expected.  e  The  Secretary  of  State  for  War 
has  received  Professor  TyndalTs  letter,  and  deems  the 
explanation  therein  given  perfectly  satisfactory.'  I  have 
often  wished  for  an  opportunity  of  publicly  acknow- 
ledging this  liberal  treatment,  proving,  as  it  did, 
that  Lord  Panmure  could  discern  and  make  allow- 
ance for  a  good  intention,  though  it  involved  an 
offence  against  routine.  For  many  years  subse- 
quently it  was  my  privilege  to  act  under  that  ex- 
cellent body,  the  Council  for  Military  Education. 

On  another  occasion  of  this  kind,  having  en- 
couraged me  in  a  somewhat  hardy  resolution  I  had 
formed,  Faraday  backed  his  encouragement  by  an 
illustration  drawn  from  his  own  life.  The  subject 
will  interest  you,  and  it  is  so  sure  to  be  talked 
about  in  the  world,  that  no  avoidable  harm  can  arise 
from  its  introduction  here. 


162  FARADAY   AS   A   DISCOVERER. 

In  the  year  1835,  Sir  Eobert  Peel  wished  to  offer 
Faraday  a  pension,  but  that  great  statesman  quitted 
office  before  he  was  able  to  realise  his  wish.  The 
Minister  who  founded  these  pensions  intended  them, 
I  believe,  to  be  marks  of  honour  which  even  proud 
men  might  accept  without  compromise  of  indepen- 
dence. When,  however,  the  intimation  first  reached 
Faraday,  in  an  unofficial  way,  he  wrote  a  letter 
announcing  his  determination  to  decline  the  pension ; 
and  stating  that  he  was  quite  competent  to  earn  his 
livelihood  himself.  That  letter  still  exists,  but  it  was 
never  sent,  Faraday's  repugnance  having  been  over- 
ruled by  his  friends.  When  Lord  Melbourne  came 
into  office,  he  desired  to  see  Faraday ;  and  probably 
in  utter  ignorance  of  the  man — for,  unhappily  for 
them  and  us,  Ministers  of  State  in  England  are  only 
too  often  ignorant  of  great  Englishmen — his  Lord- 
ship said  something  that  must  have  deeply  displeased 
his  visitor.  The  whole  circumstances  were  once 
communicated  to  me,  but  I  have  forgotten  the  de- 
tails. The  term  '  humbug,'  I  think,  was  incau- 
tiously employed  by  his  Lordship,  and  other  ex- 
pressions were  used  of  a  similar  kind.  Faraday 
quitted  the  Minister  with  his  own  resolves,  and  that 
evening  he  left  his  card  and  a  short  and  decisive  note 
at  the  residence  of  Lord  Melbourne,  stating  that  he 
had  manifestly  mistaken  his  Lordship's  intention  of 


FARADAY   AS   A   DISCOVERER.  163 

honouring  science  in  his  person,  and  declining  to 
have  anything  whatever  to  do  with  the  proposed 
pension.  The  good-humoured  nobleman  at  first  con- 
sidered the  matter  a  capital  joke ;  but  he  was  after- 
wards led  to  look  at  it  more  seriously.  An  excellent 
lady,  who  was  a  friend  both  to  Faraday  and  the 
Minister,  tried  to  arrange  matters  between  them  ;  but 
she  found  Faraday  very  difficult  to  move  from  the 
position  he  had  assumed.  After  many  fruitless  efforts, 
she  at  length  begged  of  him  to  state  what  he  would 
require  of  Lord  Melbourne  to  induce  him  to  change 
his  mind.  He  replied,  CI  should  require  from  his 
Lordship  what  I  have  no  right  or  reason  to  expect 
that  he  would  grant — a  written  apology  for  the 
words  he  permitted  himself  to  use  to  me.'  The 
required  apology  came,  frank  and  full,  creditable,  I 
thought,  alike  to  the  Prime  Minister  and  the  Phi- 
losopher. 

Considering  the  enormous  strain  imposed  on  Fara- 
day's intellect,  the  boy-like  buoyancy  even  of  his 
later  years  was  astonishing.  He  was  often  prostrate, 
but  he  had  immense  resiliency,  which  he  brought 
into  action  by  getting  away  from  London  whenever 
his  health  failed.  I  have  already  indicated  the 
thoughts  which  filled  his  mind  during  the  evening  of 
his  life.  He  brooded  on  magnetic  media  and  lines  of 
force ;  and  the  great  object  of  the  last  investigation 


164  FARADAY  AS  A  DISCOVEEER. 

lie  ever  undertook  was  the  decision  of  the  ques- 
tion whether  magnetic  force  requires  time  for  its 
propagation.  How  he  proposed  to  attack  this  sub- 
ject we  may  never  know.  But  he  has  left  some 
beautiful  apparatus  behind;  delicate  wheels  and 
pinions,  and  associated  mirrors,  which  were  to  have 
been  employed  in  the  investigation.  The  mere  con- 
ception of  such  an  inquiry  is  an  illustration  of  his 
strength  and  hopefulness,  and  it  is  impossible  to  say 
to  what  results  it  might  have  led  him.  But  the 
work  was  too  heavy  for  his  tired  brain.  It  was  long 
before  he  could  bring  himself  to  relinquish  it,  and 
during  this  struggle  he  often  suffered  from  fatigue  of 
mind.  It  was  at  this  period,  and  before  he  resigned 
himself  to  the  repose  which  marked  the  last  two 
years  of  his  life,  that  he  wrote  to  me  the  following 
letter — one  of  many  priceless  letters  now  before  me 
— which  reveals,  more  than  anything  another  pen 
could  express,  the  state  of  his  mind  at  the  time.  I 
was  sometimes  censured  in  his  presence  for  my 
doings  in  the  Alps,  but  his  constant  reply  was,  '  Let 
him  alone,  he  knows  how  to  take  care  of  himself.' 
In  this  letter,  anxiety  on  this  score  reveals  itself,  for 
the  first  time. 


FARADAY  AS   A   DISCOVERER.  165 

'Hampton  Court,  August  1,  1861. 

DEAR  TYNDALL, — I  do  not  know  whether 
my  letter  will  catch  yon,  bnt  I  will  risk  it,  thongh 
feeling  very  unfit  to  communicate  with  a  man  whose 
life  is  as  vivid  and  active  as  yonrs ;  bnt  the  receipt 
of  yonr  kind  letter  makes  me  to  know  that  thongh  I 
forget,  I  am  not  forgotten,  and  thongh  I  am  not  able 
to  remember  at  the  end  of  a  line  what  was  said  at 
the  beginning  of  it,  the  imperfect  marks  will  convey 
to  yon  some  sense  of  what  I  long  to  say.  We  had 
heard  of  yonr  illness  through  Miss  Moore,  and  I  was 
therefore  very  glad  to  learn  that  yon  are  now  quite 
well ;  do  not  run  too  many  risks,  or  make  your  hap- 
piness depend  too  much  upon  dangers,  or  the  hunt- 
ing of  them.  Sometimes  the  very  thinking  of  you, 
and  what  you  may  be  about,  wearies  me  with  fears, 
and  then  the  cogitations  pause  and  change,  but 
without  giving  me  rest.  I  know  that  much  of  this 
depends  upon  my  own  worn-out  nature,  and  I  do  not 
know  why  I  write  it,  save  that  when  I  write  to  you 
1  cannot  help  thinking  it,  and  the  thoughts  stand 
in  the  way  of  other  matter. 


*  See  what  a  strange  desultory  epistle  I  am  writing 


166  FARADAY   AS   A   DISCOVERER. 

to  you,  and  yet  I  feel  so  weary  that  I  long  to  leave 
my  desk  and  go  to  the  couch. 

'  My  dear  wife  and  Jane  desire  their  kindest  re- 
membrances :  I  hear  them  in  the  next  room  :    .  .  .  . 
I  forget  —but  not  you,  my  dear  Tyndall,  for  I  am 
'  Ever  yours, 

*  M.  FARADAY.' 

This  weariness  subsided  when  he  relinquished  his 
work,  and  I  have  a  cheerful  letter  from  him,  written 
in  the  autumn  of  1865.  But  towards  the  close  of 
that  year  he  had  an  attack  of  illness,  from  which  he 
never  completely  rallied.  He  continued  to  attend 
the  Friday  Evening  Meetings,  but  the  advance  of 
infirmity  was  apparent  to  us  all.  Complete  rest 
became  finally  essential  to  him,  and  he  ceased  to  ap- 
pear among  us.  There  was  no  pain  in  his  decline  to 
trouble  the  memory  of  those  who  loved  him.  Slowly 
and  peacefully  he  sank  towards  his  final  rest,  and 
when  it  came,  his  death  was  a  falling  asleep.  In 
the  fulness  of  his  honours  and  of  his  age  he  quitted 
us ;  the  good  fight  fought,  the  work  of  duty — shall  I 
not  say  of  glory — done.  The  6  Jane  '  referred  to  in 
the  foregoing  letter  is  Faraday's  niece,  Miss  Jane 
Barnard,  who  with  an  affection  raised  almost  to 
religious  devotion,  watched  him  and  tended  him  to 
the  end. 


FARADAY   AS   A   DISCOVERER.  167 

I  saw  Mr.  Faraday  for  the  first  time  on  my  return 
from  Marburg  in  1850.  I  came  to  the  Royal  Insti- 
tution, and  sent  up  my  card,  with  a  copy  of  the  paper 
which  Knoblauch  and  myself  had  just  completed. 
He  came  down  and  conversed  with  me  for  half-an- 
hour.  I  could  not  fail  to  remark  the  wonderful  play 
of  intellect  and  kindly  feeling  exhibited  by  his  coun- 
tenance. When  he  was  in  good  health  the  question 
of  his  age  would  never  occur  to  you.  In  the  light 
and  laughter  of  his  eyes  you  never  thought  of  his 
grey  hairs.  He  was  then  on  the  point  of  publishing 
one  of  his  papers  on  Magne-crystallic  action,  and  he 
had  time  to  refer  in  a  nattering  note  to  the  memoir 
I  placed  in  his  hands.  I  returned  to  Germany, 
worked  there  for  nearly  another  year,  and  in  June 
1851  came  back  finally  from  Berlin  to  England. 
Then,  for  the  first  time,  and  on  my  way  to  the  meet- 
ing of  the  British  Association,  at  Ipswich,  I  met  a 
man  who  has  since  made  his  mark  upon  the  intel- 
lect of  his  time ;  who  has  long  been,  and  who  by  the 
strong  law  of  natural  affinity  must  continue  to  be,  a 
brother  to  me.  We  were  both  without  definite  out- 
look at  the  time,  needing  proper  work,  and  only 
anxious  to  have  it*  to  perform.  The  chairs  of  Na- 
tural History  and  of  Physics  being  advertised  as 
vacant  in  the  University  of  Toronto,  we  applied  for 
them,  he  for  the  one,  I  for  the  other ;  but,  possibly 


168  FARADAY  AS  A   DISCOVERER. 

guided  by  a  prophetic  instinct,  the  University  au- 
thorities declined  having  anything  to  do  with  either 
of  us.  If  I  remember  aright,  we  were  equally  un- 
lucky elsewhere. 

One  of  Faraday's  earliest  letters  to  me  had  refer- 
ence to  this  Toronto  business,  which  he  thought  it 
unwise  in  me  to  neglect.  But  Toronto  had  its  own 
notions,  and  in  1853,  at  the  instance  of  Dr.  Bence 
Jones,  and  on  the  recommendation  of  Faraday  him- 
self, a  chair  of  physics  at  the  Royal  Institution  was 
offered  to  me.  I  was  tempted  at  the  same  time  to 
go  elsewhere,  but  a  strong  attraction  drew  me  to  his 
side.  Let  me  say  that  it  was  mainly  his  and  other 
friendships,  precious  to  me  beyond  all  expression, 
that  caused  me  to  value  my  position  here  more 
highly  than  any  other  that  could  be  offered  to  me  in 
this  land.  Nor  is  it  for  its  honour,  though  surely 
that  is  great,  but  for  the  strong  personal  ties  that 
bind  me  to  it,  that  I  now  chiefly  prize  this  place. 
You  might  not  credit  me  were  I  to  tell  you  how 
lightly  I  value  the  honour  of  being  Faraday's  succes- 
sor compared  with  the  honour  of  having  been  Fara- 
day's friend.  His  friendship  was  energy  and  in- 
spiration ;  his  '  mantle '  is  a  burden  almost  too  heavy 
to  be  borne. 

Sometimes  during  the  last  year  of  his  life,  by  the 


FAEADAY   AS   A   DISCOVERER.  169 

permission  or  invitation  of  Mrs.  Faraday,  I  went 
up  to  his  rooms  to  see  him.  The  deep  radiance, 
which  in  his  time  of  strength  flashed  with  such  ex- 
traordinary power  from  his  countenance,  had  sub- 
sided to  a  calm  and  kindly  light,  by  which  my  latest 
memory  of  him  is  warmed  and  illuminated.  I  knelt 
one  day  beside  him  on  the  carpet  an-d  placed  my 
hand  upon  his  knee;  he  stroked  it  affectionately, 
smiled,  and  murmured,  in  a  low  soft  voice,  the  last 
words  that  I  remember  as  having  been  spoken  to  me 
by  Michael  Faraday. 

It  was  my  wish  and  aspiration  to  play  the  part  of 
Schiller  to  this  Goethe ;  and  he  was  at  times  so 
strong  and  joyful — his  body  so  active,  and  his  intel- 
lect so  clear — as  to  suggest  to  me  the  thought  that 
he,  like  Goethe,  would  see  the  younger  man  laid  low. 
Destiny  ruled  otherwise,  and  now  he  is  but  a 
memory  to  us  all.  Surely  no  memory  could  be  more 
beautiful.  He  was  equally  rich  in  mind  and  heart. 
The  fairest  traits  of  a  character  sketched  by  Paul, 
found  in  him  perfect  illustration.  For  he  was 
6  blameless,  vigilant,  sober,  of  good  behaviour,  apt  to 
teach,  not  given  to  filthy  lucre.'  He  had  not  a 
trace  of  worldly  ambition ;  he  declared  his  duty 
to  his  Sovereign  by  going  to  the  levee  once  a 
year,  but  beyond  this  he  never  sought  contact  with 


170  FARADAY  AS  A   DISCOVERER. 

the  great.  The  life  of  his  spirit  and  of  his  intel- 
lect was  so  full,  that  the  things  which  rnen  most 
strive  after  were  absolutely  indifferent  to  him. 
'Give  me  health  and  a  day,'  says  the  brave  Emer- 
son, 'and  I  will  make  the  pomp  of  emperors 
'  ridiculous.'  In  an  eminent  degree  Faraday  could 
say  the  same.  What  to  him  was  the  splendour 
of  a  palace  compared  with  a  thunderstorm  upon 
Brighton  Downs?  —  what  among  all  the  appli- 
ances of  royalty  to  compare  with  the  setting  sun? 
I  refer  to  a  thunderstorm  and  a  sunset,  because 
these  things  excited  a  kind  of  ecstasy  in  his  mind, 
and  to  a  mind  open  to  such  ecstasy  the  pomps  and 
pleasures  of  the  world  are  usually  of  small  ac- 
count. Nature,  not  education,  rendered  Faraday 
strong  and  refined.  A  favourite  experiment  of  his 
own  was  representative  of  himself.  He  loved  to  show 
that  water  in  crystallizing  excluded  all  foreign  ingre- 
dients, however  intimately  they  might  be  mixed  with 
it.  Out  of  acids,  alkalis,  or  saline  solutions,  the 
crystal  came  sweet  and  pure.  By  some  such  natural 
process  in  the  formation  of  this  man,  beauty  and 
nobleness  coalesced,  to  the  exclusion  of  everything 
vulgar  and  low.  He  did  not  learn  his  gentleness  in 
the  world,  for  he  withdrew  himself  from  its  culture; 
and  still  this  land  of  England  contained  no  truer 


FARADAY   AS  A   DISCOVERER.  171 

gentleman  than  he.  Not  half  his  greatness  was  in- 
corporate in  his  science,  for  science  could  not  reveal 
the  bravery  and  delicacy  of  his  heart. 

But  it  is  time  that  I  should  end  these  weak  words, 
and  lay  my  poor  garland  on  the  grave  of  this 

Just  and  faithful  knight  of  God. 


LONDON:  PRINTED  BY 

SPOTTISTVOODB   AND    CO.,  XEW-STREET  SQUARE 
AND  PARLIAMENT   STREET. 


ILLUSTRATED 

CHARTS  OF  NATURAL  HISTORY, 

DESIGNED  AND  ENGRAVED  BY  J.  W.  LOWRY,  P.E.G.S. 

I.  The  Vegetable  Kingdom.  II,  Recent  Shells.  III.  Worms,  Crustacea,  Spiders, 
Scorpions,  etc.  IV.  Insects.  V.  Fishes.  VI.  Reptiles.  VII.  Birds.  (VIII. 
Mammalia,  just  ready).  IX.  Characteristic  British  Fossils,  stratigraphically 
arranged. 

London :  Society  for  Promoting  Christian  Knowledge. 

I.     Chart  of  Fossil  Crustacea  (with  descriptive  Catalogue.)     II.  Chart  of  Characterises 
British  Tertiary  Fossils,  stratigraphically  arranged. 

LONDON:    J.    TENNANT,    149,    STRAND,  W.C- 

E.  STANFOKD,  6,  CHARING  CROSS,  S.W. 


fT^HERE  are  few  men  who  have  done  more  to  promote  a  taste  for 
JL  Natural  History — especially  among  young  people — than  Mr.  J.  W. 
Lowry.  His  Natural  History  Charts,  though  designed  and  engraved 
by  himself,  have  all  been  carried  out  under  the  direction  of  able 
naturalists,  in  the  several  branches  of  which  they  treat,  among  these  may 
be  named  such  men  as  the  late  Mr.  Henfrey  and  Dr.  S.  P.  Woodward, 
Mr.  Adam  White,  Dr.  Baird,  Mr.  Gosse,  and  Mr.  George  Gray. 

Visual  education  is  not  only  the  first  form  of  training  by  which  the 
attention  of  youth  is  attracted,  but  it  is  also  that  which  remains  longest 
impressed  upon  our  mental  retina.  These  charts  are  calculated,  how- 
ever, to  afford  education  of  a  still  higher  character,  and  to  pupils  of  all 
ages ;  they  are  admirably  fitted  for  the  school  and  class-room,  and  every 
teacher  of  Natural  History  should  possess  a  copy  of  each,  nor  can  a  museum 
be  complete  without  these  admirable  and  instructive  guide-maps. 

The  Chart  of  Fossil  Crustacea  by  Messrs.  J.  W.  Salter  and  H.  Wood- 
ward, gives  a  conspectus  of  a  single  class,  arranged  not  only  in  strati- 
graphical  series,  but  in  zoological  order.  It  contains  nearly  500  figures, 
and  is,  moreover,  accompanied  by  a  short  descriptive  catalogue. 4> 

That  of  Characteristic  British  Tertiary  Fossils  is  an  elaborate  view  of 
the  topmost  or  newest  section  of  the  Chart  of  British  Fossils,  and  holds 
the  same  relation  to  it  which  a  map  of  Europe  does  to  a  map  of  the 
World.  It  contains  upwards  of  800  figures  of  characteristic  shells  and 
other  organisms  found  in  the  series  of  formations  of  Cainozoic  or  Tertiary 
age,  which  have  been  engraved  by  Mr.  Lowry  expressly  for  this  work, 
and  selected  by  him  with  great  care,  assisted  by  Messrs.  Kobt.  Etheridge. 
Searles  V.  Wood,  Fred.  E.  Edwards,  and  other  geologists  of  eminence, 
and  contains  a  mass  of  information  never  before  collected  in  so  compact 
a  form  for  reference.  Every  specimen  is  not  only  named,  but  has  its 
natural  size  indicated  against  it,  if  it  be  enlarged  or  reduced.  Those 
Crag  species  which  occur  in  more  than  one  bed  are  also  marked  by  the 
initial  letter  of  the  beds  in  which  they  have  been  found,  thus  giving 
the  range  of  each. 

We  strongly  recommend  these  charts  to  all  lovers  of  Natural  History, 
but  would  especially  call  the  attention  of  geologists  to  this  new  and 
interesting  CHART  OF  CHARACTERISTIC  BRITISH  TERTIARY  FOSSILS. — See 
GEOLOGICAL  MAGAZINE,  No.  28.  Oct.,  1866,  p.  464. 

*  For  a  full  description  of  this  Chart  of  Fossil  Crustacea,  see  British  Association  Reports, 
Sections  C.  and  D.  Birmingham,  1865  ;  and  GEOLOGICAL  MAGAZINE,  Vol.  II.,  p.  468. 


CHART  OF  THE 
CHABACTEKISTIC 

BRITISH    TERTIARY    FOSSILS, 

STRATIGRAPHICALLY  ARRANGED. 

(CONTAINING  UPWARDS  OF  800  FIGURES). 

COMPILED  AND  ENGEAVED  BY  J,  W,  LOWRY, 

ASSISTED    BY    R.   ETHERIDGE,    ESQ.,    F.R.S.E.,    F.G.S.,  AND    OTHER 
PALAEONTOLOGISTS. 

FIGURES       DRAWN       BY      C.      R.      BONE. 

This  Chart  contains  figures  of  organic  remains,  from  the  PLEISTOCENE 
(Land,  Fresh- water,  and  Marine) ;  the  CRAG,  and  EOCENE  formations, 
the  latter  divided  into  upper,  middle,  and  lower,  according  to  the  divi- 
sions adopted  by  the  Geological  Survey  of  Great  Britain. 
PRICE:  Mounted  on  linen  to  fold  in  Case,  or  mounted  on  Boilers  and 
Varnished,  10s. ;  mounted  to  fold  in  thin  cover,  7s.  Qd. 


ALSO, 
A  CHART    OF    THE 

GENERA  OF  FOSSIL  CRUSTACEA, 

SHOWING  THE  RANGE  IN  TIME  OF  THE  SEVEEAL  ORDERS, 

WITH  RECENT  TYPES, 
CCXNTT-AJCN'rN'a     60O     FIGURES, 

Accompanied  by  a  descriptive  Catalogue  giving  Localities,  &c.f  &c. 

ARRANGED   AND   DRAWN   BY   J.   W.   SALTER,   F.G.S., 

AND  HENRY  WOODWARD,  F.G.S.,  &  F.Z.S. 
ENGRAVED       BY       J.       "W.       IL,  O  W  R  Y. 

Besides  being  Stratigraphically  Arranged,  as  shown  by  horizontal  lines 

marking  the  different  Formations,  this  Chart  is  intended  to  show  at  a 

glance  the  development  in  Geological  time  of  the  different  orders  of  the 

class  Crustacea,  by  curved  and  nearly  vertical  lines,  which  separate  the 

various  orders,  and  show  in  what  formations  they  first  came  into  existence 

(as  far  as  our  knowledge  yet  extends),  and  where  they  ceased  to  live. 

PRICE  :  Mounted  to  fold  in  Case  with  Descriptive  Catalogue,  10s.  Qd. 

Mounted  on  Rollers  Varnished,  with  Descriptive  Catalogue,  13s. 

LONDON: 

Published  by  J,  TENNANT,  Mineralogist  to  the  dueen,  149,  Strand, W.C. 
AND  E.  STANFORD,  6,  CHARING  CROSS,  S.W. 


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