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CYCLOPEDIA
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Applied Electricit)
» _. ' •
A Practice! Guide for
ELECTRICIANS, MECHANICS, ENGINEERS, STUDENTS,
TELEGRAPH AND TELEPHONE OPERATORS,
AND ALL OTHERS INTERESTED
IN ELECTRICITY
Prepared /n* // Corf\ of'
EXPERTS. ELECTRICAL KNGINKKRS AND DESIGNERS
Illustrated with over Two Thousand Engravings
AMRklC AN SCHOOL OI- ( tmkKSI'ONI )KN'Ch
AT
A K MO IK Ins i: 1 1 IK oh 'I'n hnh; ■■ y
CinCACO, V. - A
PVSIIC LIBRARY 1
1 ri4A5
AfCP, L?NOT AND
TILLjES f'_-. M-AliUflR
COPYKIGHT, 19U2, I'^US, r>iH, 19U6.
BY
AMERICAN SCHOOL OF CORRESPONDENCE.
• •
Writers and Collaborators
F. B. CROCKER, E. M., Ph. D.
Head of Dept. of Electrical EnglneerInK, ^-oluinbla University.
Past I'nisldent American Institute Electrical Engineers.
WILLIAM ESTY, S. B., M. A.
l»rnfess<»r of Electrical Engineering. Lehigh University.
DUGALD C. JACKSON, C. E.
Head of Dept. of Electrical Engineering. University of Wisconsin.
GEORGE C. SHAAD, B. S.
As.sistant Profes.sor of Electrical Engineering. T'niversity of Wisconsin.
H. C. CUSHING, JR.
Consulting Electrical Engineer. Author of " Standard Wiring for Electric
Light and Power."
CHARLES THOM
Chief Quadruples Department. Western Union Telegraph CJompany.
LAWRENCE K. SAGER, S. B., M. P. L.
Patent Attorney and Electrical Expert, formerly Assistant Examiner.
U. S. Patent Office.
WILLIAM C. BOYRER. M. E., M. M. E.
Formerly Assistant Superintendent of Construction, New York and New
Jersey Telephone Co.
LOUIS DERR, S. B., A. M.
Associate Professor of Physics, Ma.ssaohusetts Institute of Technology.
Writers and Collaborators— Continued
JOHN E. SNOW, A. M., M. S., E. E.
Associate Professor of Electrical Engineering. Armour Institute of
Technology. American Institute Electrical Engineers.
JAMES R. CRAVATH
Western Editor. "Street Rail w'ay Journal.'
JOHN C. SHERMAN, S. B.
Electrical Expert, formerly with Westlnghouse CompauleN.
HARRIS C. TROW, S. B.
Instructor in Electrical Engineering. American School of Correspondence,
American Institute Electrical Engineers.
R. F. SCHUCHARDT, B. S.
Testing Laboratory. Chicago Edison Company.
A. FREDERICK COLLINS,
Author of " Wireless Telegraphy, Its History, Theory and Practice."
PERCY H. THOMAS, S. B.
Chief Electrician. Cooper-Hewitt Electric C«).
ALFRED E. ZAPF, S. B., Managing Editor
Secretary American School of Correspondence,
Editor '-The Technical World."
A^uthorities Consulted
1 XT the preparation of these volumes the editors have received invaluable
assistance from the foremost enpfineering firms and manufacturers.
Grateful acknowledgment is here made for the valuable drawings, data,
ggestions, and criticisms which have enabled the editors to make these
volumes representative of the latest and best practice in the Design,
Construction, and Operation of Electrical Machinery and Instruments.
The standard technical literature of Europe and America has been freely
consulted in the preparation of these volumes. The editors desire to express
their indebtedness, particularly to the following eminent authorities,
whose well-known treatises should be in the library of every Electrician
and Engineer.
ELROY McKENDRIE AVERY, Ph. D., LL. D.
Author of EUementary Physics. Elements of Natural Philosophy, Physical Technics, Teacher's
Handbook of Chemistry. Complete Chemistry. First Principles of Natural Philosophy.
School Physics, Elementary Physics, First Lessons in Physical Science. School Chemistry.
GEORGE FREDERICK BARKER, M. D.. Hon. Sc. D., LL. D.
Emeritus Professor of Physics. University of Pennsylvania; Member, National Academy
Science; Late President. American Academy Arts and Sciences; American Chemical Society.
Author of Textbooks of Elementary Chemistry, Physics, etc.
WILLIAM M. BARR.
Member. American Society Mechanical Engineers.
Author of Boilers and Furnaces, Pumpinsr Machinery, Chimneys of Brick and Metal, etc.
FRANCIS BACON CROCKER, M. E., Ph. D.
Professor of Electrical Encrineerircr, Columbia Colleg-e. New York; Vice-President, Crocker-
Wheeler Electric Company; and
SCHUYLER S. WHEELER, D. Sc.
Electrical Expert of the Board of Electrical Control. New York City; Member American
Societies of Civil and Mechanical Ensrineers.
Joint Authors of Practical Manasrcment of Dynamos and Motors, Electric Lisrhting-.
J. A. FLEMING, M. A., D. Sc. (Lond.), F. R. S.
Professor of Electrical Engineerinar in University College, London; Late Fellow and Scholar of
St. John's College, CaR:bridfirc; Fellow of University Collesre. London; Member of the
Institution of Electrical Engineers; Member of the Physical Society of London; Member
of the Royal Institution of Great Britain, etc , etc.
Author of The Alternate Current Transformer, etc.
Authorities Consulted— Continued
HORATIO A. FOSTER.
Member of American Institute of Electrical Enffinecrs; Member of American Society of
Mechanical Entfineers; Consultinfir Enirineer.
Author of EUectrical En^rineer's Pocket-book.
J. FISHER-HINNEN.
Late Chief of the Drawing Department at the Oerlikon Works.
Author of Continuous Current Dynamos.
WILLIAM L. HOOPER, Ph. D.
Professor of Electrical Enflrineerinir. Tufts College; and
ROY T. WELLS, M. S.
Senior Fellow in Physics, Clark University. Joint Authors of Electrical Problems for Engineerinar
Students.
EDWIN JAMES HOUSTON, Ph. D.
Professor of Physics, Franklin Institute. Pennsylvania; Joint Inventor of Thompson-Houston
System of Arc Lighting; Electrical Expert and Consulting Engineer; and
' ARTHUR E. KENNELLY, D. Sc.
Joint Authors of Algebra Made Easy. Alternating Currents, Arc Lighting. Electric Heating,
Electricity Made Easy. Electric Motors, Electric Railways, Electrical Engineering
Leaflets, Electro-Dynamic Machinery, Electro-Therapeutics, Incandescent Lighting.
Interpretation of Mathematical Formulae. Magnetism, Recent Types of Dynamo-Electric
Machinery. Telephony.
DUGALD C. JACKSON, C. E.
Professor of Electrical Engineering in the University of Wisconsin; Member of the American
Society of Mechanical Engineering, American Institute of Electrical Engineers, etc;
JOHN PRICE JACKSON, M. E.
Joint Authors of Text-Book on Electro-MaKTo'i^m and the Construction of Dynamos, and
Alternating Currents and Alternating Current Machinery.
WILLIAM KENT, M. E.
Consulting Engineer; Member American Institute Mining Engineers: American Society
Mechanical Engineers.
Author of Strength of Materials. Strength of Wrought Iron and Chain Cables. The
Mechanical Engineers' Pocket Book. Steam Boiler Ecomxny.
LAMAR LYNDON, B. E., M. E.,
Consulting Electrical Engineer: Associate McTiber American Institute of EleclricAl Engi-
neers; Member American Electro Chemical Society
Author of Storage Battery Enginecrinjr.
Authorities Consulted -Continued
WILLIAM JOHN M ACQUORN RANKINE, LL. D. , F. R. S. S.
Civil Engineer: Late Resius Professor of Civil Ensineerinsr and Mechanics in University of
Glasffow, etc. etc.
Author of Applied Mechanics. The Steam Enirine. Civil Enffinee: inir. Useful Rules and
Tables, Machinery and Mill Work, A Mechanical Textbook.
KEMPSTER B. MILLER, M. E.
Consulting En^rineer and Telephone Expert.
Author of American Telephone Practice.
MAURICE A. OUDIN, M. S.
Member of American Institute of Electrical Ensrineers.
Author of Standard Polyphase Apparatus and Systems.
CECIL HOBART PEABODY, S. B.
Professor of Marine Ensrineerinfl: and Naval Architecture. Massachusetts Institute of Tech-
nology; and
EDWARD F. MILLER.
Assistant Professor of Steam EnKineerins: at the Masaachusotts Institute of Technolofry.
Joint Authors of Steam Boilers.
JOHN PERRY, M. E., D. Sc, F. R. S.
Professor of Mechanics and Mathematics. Royal College of Science, South K<'nsinKton.
Author of The Steam Engine, Practical Mechanics, and about 100 Scientific Papers.
BALFOUR STEWART, M. A., LL. D., F. R. S.
Late Professor of Physics. Victoria University, The Owens College, Manchester.
Author of Primer of Physics, Lessons in Elementary Physics.
. BALFOUR STEWART and W. W. HALDANE GEE, B. Sc.
Joint Authors of Lessons in Elementary Practical Physics.
SYLVANUS P. THOMPSON, D. Sc, B. A., F. R. S., F. R. A. S.
Principal and Professor of Physics in the City and Guilds of I^ndon Technical Collesre.
Author of Electricity and Mafirnetism, Dynamo-Electric Machinery. Polyphase Electric Current.**.
Electroma«rnet, etc.
ROBERT HENRY THURSTON, C. E., Ph. B., A. M., LL. D.
Late Director. Sibley Collesre, Cornell University.
Author of Friction and Lubrication, Materials of Ensrineerinsr. Manual of the Steam Engine.
History of the Steam Ensrine. Manual of Steam Boilers, etc., also alx>ut 300 Professional
and Scientific Papers. Editor of "Science" and of Johnston's Cyclopedia.
ROBERT WILSON.
Associate Institute Civil Enfirineers.
Author of Treatise on Steam Hollers, Common Sense for Gas Users, Boiler and Factory
Chimneys, etc.. etc.
Preface
REALIZING the great need for a more scientific knowl-
edge of electricity on the j)art of thousands of practical
^ men of limited technical education, an attempt has been
made in the following pages to give a presentation of the subject
which shall be easily understood by such men, and at the same time,
cover all the essential principles and methods. The principles
usually deduced by higher mathematics are here made clear by
careful explanation and a large number of diagrams drawn
especially for the text. Num<»rous engravings exemplify modern
practice, and fonn a pictorial index to the latest and best methods
of applyiiig electricity to lighting, railways, power transmission,
machine tools, etc.
^The Cyclopedia of Applied Electricity is based upon the method
which the American School of Correspondence has develo|)ed and
successfully used for many years in teaching practical electricians
the scientific principles underlying their work. It is compiled
from the most valuable of the School's Instruction Paj)ers and
forms a simple, practical, concise, and convenient reference work
for the shop, the library, the school, and the home.
^The success which the An'ierican School of Correspondence has
attained in teaching thousands of electricians is in itself the best
possible guarantee for the present work. Therefore, while these
volumes are a marked innovation in technical literature, represent-
ing as they do the best methods of a large numl)er of different
authors, each an acknowledged authority in his work, — they are
by no means an experiment, but are in fact the e ^ the most
successful method yet devised for the education of the busy
working man.
€LAniong the sections of most practical value are those on Alter-
nating (.'urrent Machinery, Storage Batteries, Electric Wiring,
Lighting, etc. In these pages the authors have succeeded in
presenting the subjects in such manner as to overcome the hitherto
insurmountable obstacle — higher mathematics. The rules and
formulae are presented in a very simple manner, and special effort
has been made to illustrate every principle by diagrams and prac-
tical examples.
CLXumerous examples for practice are inserted at intervals; these
with the test (questions, help the reader to fix in mind the essential
points, thus combining the advantages of a textbook with a refer-
ence work.
CCirateful acknowledgment is due to the corps of writers and
colla])orators who have jjrepared the many sections of this work.
Tlie hearty co-o{)erati()n of these men — engineers of wide prac-
tical ex|)erience, and teachers of acknowledged al>ility — has alone
made these volumes possible.
CThe Cyclojx^dia is jniblished in the belief tliat it will meet a
real need among designers, constructors and oj)erators of elec-
trical machinery. That it mav save many weary hours of search
amoncf the scattered textbooks and reference works of the day, —
books which beintr intended larcrely for col lew -trained men are
necessarily far from meeting the needs of the average practical
man. is the hope of the compilers and |)ublishers.
Contents
PART I.
Elements of Electricity
The Electric Current .
Electrical Measurements
Electric Wiring
The Electric Telegraph
Wireless Telegraph
The Telautograrh
Insulators .
Electric Welding
Test Questions .
Page 11
63
" 105
' 155
' 233
' 331
* 369
' 383
' 399
* 409
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J
ELEMENTS OF ELECTRICITY.
Electricity is an invisible agent whicli manifests itself in
various ways. The precise nature of electricity is not known,
but the effects produced by it, the methods of controlling it, and
the laws governing its action are becoming well known.
Electricity nuiy be considered under three heads : fii-st
mai^etism, — second, static electricity (where it ap}>eai*s as a
charge upon l)odies), — and third, — dynamic electricity (where
it appears as a current). The sciences which treat of the two
latter branches are called electrostatics and electrodynamics re-
spectively. These divisions of the subject, although covering
manifestations widely different, are closely related.
MAQNETISM.
Natural Mas^nets. Substances which have the property of
attracting pieces of iron are called magnets, A material possess-
ing this property was first found by the Ancients at Magnesiii, in
Asia Minor, from which fact arose the name magnet. The nat
ural magnet is an oxide of iron and is also called the lodestone.
lo is widely distributed in different parts of the world, but is not
always found possessing magnetic properties.
Artificial Mas^nets. When a bar of hard steel is rubbed with
a lodestone,* the steel will acquire the same magnetic property
and to a much greater extent. Such artificial magnets are there-
fore always used in place of lodestones.
Poles. When one end of a magnet is placed in iron filings
and afterwards withdrawn, the filings are attracted and cling to it
in great numbers. This is illustrated in Fig. 1. The filings
would be attracted to the opposite end and would cling to it in the
same way if it were placed in the filings. The middle of the bar,
however, does not have this property, and toward the ends the
power rapidly increases. The ends of the magnet, where the
attraction is the greatest, are called poles,
A common example of a magnet is the compjiss needle. It
is well known tliat such a needle always places itself so as ix> *^**«^
11
ELEMENTS OF ELECTRICITY.
north and south, and that the samo pole always points toward the
north. This is called the north seeking pole, while the other is
called the south seeking pole^ or simply the north and south pole
res|)ectively.
In the experiment with iron filings either of the magnetic poles
Fig. 1.
attracts them and there is apparently no difference between the
two poles. That there is a diil'erence, however, mjiy be shown by
experimenting with two compass needles. If the north poles of
two such needles be brought near each other, tliey will l)e repelled.
In the same way the south poles will repel each other. But when
IWifP.''.il'i:V.-.^'':.i^?;rr:i
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r.:i
TTTi
m
mMMME^WEMMi. \H'X:.M\'M^'yi^
Fig. 2.
the north pole of one needle is brought near the south pole of the
other, attraction takes place. This shows that like poles repel
each other, while unlike poles attract each other.
The fact that a compass needle always points north and
souths or approximately so, is because the earth itself is a great
kiagnet. The magnetic poles of the earth coincide very nearly
12
ELEMENTS OF ELECTRICITY.
with the geogmphical north and south poles. The geog^phical
north pole of the earth is unlike the north pole of a magnetic
needle, and hence attracts it.
The two poles always exist in a magnet. If, as illustrated
in Fig. 2, a single magnet be broken into several parts, the sepa-
rate part^ will then become individual magnets. Each portioi>
will have the same properties which the magnet as a whole pos
aessed. When the separate parts are placed together again tin-
many poles (if the small p()rtion8 will neutralize each other and
the complete magnet will act as before
r
Pig. S. Fig. 4.
Magnetic Field. T)ie space surrounding a magnet, called
the field, is subject to the influence of the magnet and is called its
magnetic field. The presence of such a field may l>e shown by a
simple experiment.
Suppose a sheet of paper lie placed upon a bar magnet
and iron filings spread evenly upon the paper ; by tapping
the paper lightly, the filings will form into a series of curved
lines extending from one pole to the other. The foTm of these
curves for a bar magnet is illuBtrated in Fig. 3. The formation
of these definite curves indicates that the magnetic fidld exerts its
influence in certain definite directions which are called the lines
of magnetic force, or simjily lines of force. The field »f a liorse-
shoe magnet is represented in Fig. 4, and that about the end of "
Wr magnet is represented itt Fig. 5.
8 ELEMENTS OF ELECTKICITT.
Magnetic Induction. It b because of tliis magnetic field that
miigneta have the power of attriicting pieces of iron. When a
piece of iinn is hrnught iindei- its iiifluenoe, it becomes a tempo-
rary magnet, and fur the time being has its two poles. If tlie
north pole of the permanent magnet is adjacent to the piece of
iron, a sonth pole nill \>e induced in the iron next to this north
pole and a north pole in the portion farthest fnim it. The attrac-
tion is tlien exactly similar to tlie attraction between two perma-
nent magnets when unlilie poles are brought together. This
action of develoiting magnetism in iron is called magnetic
induction.
The attraction of iron is therefore due to the fact that the
Fig. 6 F!g. 6.
magnet first magnetizes it and then attracts it. Wlieu the iron is
withdmwn from the magnetic inlluence it loses its magnetism.
Tlie exi>eriraent illustrated in Fig. 6 proves this to be true.
When the upper ring of soft iron is placed in contact with the
bar mi^et it becomes a magnet, having, say, a north pole
at tlie top and a south pole at the bottom. When another
ring is added, the first will in turn mduce a north pole at
the top and a south pole at the bottom of the second ring.
Wlien other rings are added, a similar action takes place and all
the rings are supported. If, liowe.ver, the first ring be removed,
the otiiers will immediately drop and will lose their magnetism.
Magnetic induction explains the formation of tufts of iron
(ihngs whicli become attaclicd to the poles oE magnets. The fil-
ings are temporarily converted into magnets ; these oat inductively
ELEMENTS OF ELECTRICITY.
on the adjacent parts, these again on following ones, and so on,
causing them all to be attracted. They have a bush-like appear-
ance, which is due to the repulsive action that the outside free
poles exert upon each other.
The attraction is greatest when the iron is in contact with
the magnet, but actual contact is unnecessary to cause attraction.
A sheet of glass, paper or wood, etc., may be placed between the
magnet and the iron, and attraction will still be present.
riaicnetic Substances. Substances which are attracted by
magnets when either pole is presented to them al*e called magnetic
sub8tances. Besides iron are included steel, nickel and cobalt in
this class. A magnet is attracted or repelled by another magnet
according to whether the poles near each other are unlike or like,
but magnetic substances are always attracted.
Retentivity. After a piece of soft iron is once magnetized it
will, when removed from the influence of the magnet, lose sub-
stantially all of its magnetism. On the other hand, a piece of
steel or nickel will not be magnetized as much as soft iron, but
will aftenvards retain much of its magnetism. It resists being
magnetized, and afterwards resists being demagnetized. This
power of resisting magnetization or demagnetization is called
retentivity. Steel has much greater retentivity than wrought
iron, and the harder the steel the greater is the retentivity.
riethods of riagnetization. Permanent magnets are usually
made from steel, and the following are the common methods of
magnetization:
Magnetization by single touch consists in moving the pole of
a powerful magnet from one end to the other of the bar to be
magnetized, and repeating this operation several times, always in
the same direction. The end of the bar touclied last by tlie mag-
net becomes of opposite polarity to the end of the magnet by
which it has been touched. This method produces only a weak
magnet, and is therefore used for small magnets only.
Magnetization by divided touch consists in placing the two
unlike poles of two magnets at the middle of the bar to be mag
netized, and in moving them simultaneously towards the opposite
ends of the bar. Each magnet is tlien placed in its original posi«
J5
ELEMENTS OF ELECTRICITT,
tion mud the op?rad->n repealed. The Iat becomes magnetiied
after repeating this fteverai times on both fact« •>£ the faftr.
In magnet izatiori by double t&m^k li.e nro magnets are placed
as before, with opposite p>les near each oiLer, at the middle of the
bar to be magnetized. Instead of moving ihem in oppoate direc-
tions toward the ends, thev are kept a: a nxed distance apart by
means of a piece of wood between thenu aii«i are simoltaneouslv
moved 6rst towanls one erid and then luck towaids the other,
relocating sereral times and stop[»ing at the middle.
Magnets lose mach of their magnetism when sobjected to
knocks or jais.
STATIC ELECTRICITY.
FrictkMi as a Source. There are ^cTeral sources of eleo-
tricity, snch as friction, chemical action, heat and induction.
Friction as a si»urce of electricity will n«»w Iv considered. This
relates to ele ;trieity existing as charge* upon Ixxiies, and is known
as ftatic electricity.
When a glass rod or stick of sealing-wax is mbbed with a
piece of flannel or silk, each acquires the projjerty of attracting
light Ixxlies such 4^ pieces of wooL paper, gi:>id leaf, etc After
criming into contact with such substances, however, they will be
reiK'lleil. This may be well observed by employing a pith ball
suspended by a fine thread, lis shown in Fii::. T. When the rod
of glass or wax is brought near the b;\ll it is stnmgly attracted*
After contact is made, the ball will be strongly repelled.
This repulsion is explaineil by the fact that when contact
is made between the ball and rod, the ball receives pi\rt of the
electricity from the rod. Both are then charged with the same
kind of electricity, and the rejx41ant action shows that two
bodies thus charged, repel each other.
Positive and Negative Electricity. Repulsion does not
always take place between bodies charged with electricity.
Either a stick of sealing-wax or a gltiss rod after being rubbed
with silk will attract the pith ball until contact has been miide,
and then will rei)el it The electricity developed in each of these
cases, however, is not the same. After the pith ball has been
toufrhed with an electrified glass rod, it will be attracted by the
electiified stick of sealing-wax; or if touched by the latter, it
16
ELEMENTS OF ELECTRICITY.
9
will be repelled by it, but will be attracted by the glass rocu
Such phenomena are explained by assuming that there are two
kinds of electricity, which have been designated as positive (-{-)
and negative ( — ) electricity.
When the glass rod is rubbed with silk it is said to possess a
positive charge, and when tlie wax is rubbed it is said to possess
a negative charge. The pith ball having been touched by the
ghsB rod is cliarged positively, and is therefore attracted by
the negatively charged sealing-wax, or upon receiving a negative
charge from the wax, it will be attracted by the glass.
This action is expressed in the following law :
Electric charges of the same sign repel each other; ihoBe of
opposite sign attract each other.
Production of Both Positive and Negative Electricity.
When two substtmces are rubbed together neitlier positive nor
negative electricity is produced
alone, but both are produced at
the same time and in equal quan-
tities. After the friction, a posi-
tive charge is found to exist upon
one surface and a negative cliarge
upon the other and in equal
quantities. In the case of glass
being rubbed by silk, the glass
acquires a positive charge and
the silk a negative charge. That
the charges are equal is proved
by the fact that if both of these
charged bodies are presented to
the pith ball at once, the latter will be neither attracted nor
repelled. Also if the charges of both the glass and silk are
imparted to a third body, the third body will have no resultant
charge, since the two quantities of electricity being equal and of
opposite sign, neutralize each other.
Whether a body receives a positive or negative charge
depends upon the material of the body with which it makes con-
tact. Thus glass when rubbed by silk is ^^ " •-"'^Iv charged, but
when robbed by wool the glass is negi 1. in tue
Big. 7.
10
ELEMENTS OF ELECTRICITY.
following list the arrangement is such that each substance, when
rubbed by one following it, will be positively electrified, but when
rubbed by one preceding it, will be negatively electrified: Fur,
wool, ivory, glass, silk, wood, metals, sealing-wax, sulphur, india-
rubber, celluloid.
Conductors and Insulators. Conductors are substances
which readily allow electricity to pass from one portion of them to
another; that is, they readily conduct electricity. Insulators^ or
non-conductors, are those substances which do not allow such free
passage of electricity, or which offer a certain resistance to its
passage* If one end of a glass rod is rubbed with silk or wool,
the end so rubbed will be electrified, but the other end will pos-
sess little or no charge. The electricity is not freely conducted
from one part to another. When a metallic substance is charged,
however, the electricity will be distributed uniformly over its
surface. All substances offer a certain amount of resistance to the
passage of electricity and no body entirely prevents its passage ; that
??, there is no perfect conductor, and there is no perfect insulator.
There is no definite line of distinction between conductoi's
and insulatora, and some substances, are neither, but may be
termed semi-conductors or partial conductoi>5. The ability of a
body to conduct electricity, that is, its conductivity^ also depends
upon its physical condition. For example, the conductivity of
most bodies depends largely upon the temperature. The following
list of substances is arranged in the order of increiising resistance.
Conductors* Part
Silver
Copper
Other metals
Charcoal
Water
The body
I Conductors,
Insulatars.
Cotton
Oils
Diy wood
Porcelain
Marble
Wool
Paper
Silk
Resin
Guttapercha
Shellac
Ebonite
Paraffin
Glass
Air
18
ELEMENTS OP ELECTRICITY.
11
From tbe preceding it is evident that silver is the best con-
ductor and air is the best insulator. Copper, on account of being
an excellent conductor and comparatively cheap, is used almost
entirely for conducting electricity from power stations or from
one point to another. Marble is a comparatively poor conductor
and is therefore largely used for switchboards. Porcelain and
glass, being good insulators and having other desirable properties
are much used for insulating conductors from their main sup
ports. Water is a fairly good conductor, and considerable diffi
culty is consequently experienced in securing good insulation in
damp places.
Distribution of Charge. An electrical charge upon a con-
ducting body is distributed over its surface. That it does not
reside within the body may
!\
Fig. a
be shown in several different
ways. For example, it is
inunaterial whether the in-
side of xjk conductor is com-
posed of wood or glass, or if
the conductor is hollow ; the
charge in any case is dis-
tributed over its surface.
The ball A and covei-s
B and (7, shown in Fig. 8,
may be used to prove this. Suppose the covei-s to be placed ovei
the ball and the whole to be electrified. When the covers are
removed, the entire charge will be found to remain wth them,
and none will exist upon the ball.
Suppose the hollow sphere in Fig. 9 to be charged. If a
conductor be inserted through the aperture and brought in cod
tact with the inside of the sphere and afterwards carefully with-
drawn, it will be found that it hiis received no charge. If touched
to the outside, however, the conductor will receive part of the
charge. The conductor used for this purpose may be a thin piece
of metal attached to an insulating handle. A metallic cylinder,
even of wire gauze, may be used in place of the sphere. To
prevent the charge from passing to the earth, the cylinder or
sphere must be insulated from the earth by a glass standard
1»
12
ELEMENTS OF ELECTRICITY.
We have seen that bodies charged with eleotiicity of lifee
sign repel eacli other. This inaj' be taken as the explanation of
the fact that a charge resides upon t!ie surface. As it tends to
repel itself, the chaise resides as far from the centre of the body
as possible.
Static Influence. When a charged body is placed near
bodies in a neutral sttite, it will act u[ion them in a manner siml
lar to tluit of a magnet upon soft iron. This action is said to be
due to iiiflnence or to electroatnttc iiiduclion.
Induction of this nature may be made evident by means of
a metal cylinder supported on a ghiss 8tiiud;iril, as sliowli in Fig.
to. The cylinder is supplied at each end with a pith ball sus-
pended by a thread. Suppose a sphere chained with positive
electricity and mounted upon an insuUtting standard be brought
near one end of the cylinder;
the pith balls will at once fly
outwardly, showing that the
cylinder is then chaiged. If
the sphere is removed, the pith
balls will fall towards the ends
of the cylinder again, showing
that it is once more in the
neutral state. Tliroughout this
action the spliei-e has neither
gained nor lost in the amount
of its chaige. Upon testing
the temporary charge on the
cylinder, it will l>e found that
at the end near the sphere the
electricityis neipitivewhile that
at tlie distant end is positive.
Bodies charged with eleetrieity are surrounded by an electric
field ill the same way that magnets are surrounded by a magnetic
field. With this in mind, the above experiment may be easily
understood. When the charged sphere is brought near the cylin-
der, the latter comes under the inflnenee of (he former's field.
The lines of force from the sphere will pass to the cylinder, and
therefore cause its electrification. Since unlike charges attract
Plg.«.
ELKMKNTS OF ELECTRICITY.
n
each other and like charges repel each other, the sphere attracts
a negative charge to the near end and repels a positive charge
to the distant end of the cylinder. When the sphei-e is removed,
the induced [)Ositive and negative charges neutmlize each other.
If the sphere possessed a negative charge, there would then be
induced a positive charge at the near end and a negative charge
at the distant end of the cylinder. The middle portion of the
cylinder, however, remains neutral, and the strength of the
charges increases gradually towards the ends. If the cylinder be
separated into two parts while under the influence of tlie charged
body, the induced charges cannot unite after tlie removal of the
sphere, and will then retain their charges.
In the experiment illustrated by Fig. 10, there is consider*
F\fr. 10.
able attraction exerted between the sphere and cylinder. The
unlike and adjacent charges attract each other, but the like
charges on the sphere and disbint end of the cylinder repel each
other- As the unlike charges are nearer each other than the like
charges, the attraction overbalances the repulsion and there is a
resultant attraction. This action is the same in effect Jis that of
magnets upon soft iron. There is firet the induction and then
the consequent attraction.
The greater the charge possessed by the sphere, the greater
will be the induced charge upon the cylinder. Also, the nearer
the two bodies are placed to each other, the greater becomes the
charge upon the cylinder, but the induced charge can never
exceed that on the sphere.
When the distance between the sphere and cylinder is grad
81
ELEMENTS OK EI.ECTKICITY.
ually decreased, the attraction between the unlike charges is in-
cresised. This will continue until the attraction is ko great that
the unlike cliai-ges abruptly unite, and in so doing cause u spatk
to appear in the small intervening space. The unlike charges are
thus neutralized, but the repelled cliarge will still remain upon
the cylinder.
Free and Bound Charge. Tiie two charges induced in the
cylinder may be called free and Iwuiid charges. The unlike in-
duced chargf. which is represented as negative iu Fig. 10, is
Ifeferred U> iis the bound eharge, because it is attracted by the
charge upon the sphei-e and
is thus confined. Therepelled
charge, however, may escape
^j^-^ ~~y^k ^y '^"y piith which is offered,
.'i'^TTT^^ and is therefore called the
free charge. Hence if cou-
tiict l)e made between the
cylinder and the earth, the
repelled charge will pass to
the ground and the attracted
charge will i-eniain. If the
contact with the earth is then
Fip. 11. broken and the sphere re-
moved, a resultant charge
will remain upon the cylinder, which will be opposite in kind to
that of the sphere. This resiiltuit induced charge will then
distribute itself nnifonnly over the cylinder and may be used
to induce other charges.
When bodiLS aie thus charged by induction, the charge is
always oppoMte m kind to that inducing it, Oti the other hand,
when bodies .ire chaiged by conduction or by making direct cnn-
tact, the chirge unpaitcd is of the same kind. Poor con ductora
are not readily icted upon by induction, since they present great
resistance to the passage of eleetiicity.
Electroscope. An electroscope is an instrument used for
detecting the presence and determining the kind of electricity in
any body. The gold-leaf electroscope .shown in Fig. 11 is one
of the common forms, and is a very sensitive instrument. It
ELEMENTS OF ELECTRICITY. 15
consiflis of a glass jar with a metal itwl passing through the stop*
per and terminating at the lower end in two strips of gold leaf,
and at the upper end in a metal plate or knob.
When a charged body is brought near the plate, an unlike
charge is induced therein, while a like charge is repelled to the
two strips of gold leivf. The two strips, being then similarly
charged, repel each other and diverge. When the charged body
is withdrawn, the strips will come together again. A rubbed
glass rod will cause the strips to diverge even when two or three
feet from the plate.
In order to determine the kind of electrification a body
possesses, the plate is fii*st touched by a body charged with a
known kind of electricity, say positive. The electroscope is then
charged with positive electricity and the strips of gold diverge.
The body to be tested is then brought near the plate. If the
gold leaves then diverge more, the body is charged with positive
electricity, but if they approach each
other, the body is charged with negative
electricity.
Electrophorus. This is an appara-
tus by which an unlimited number of
charges may be obtained from a single
charge. It consists of a round cake of
resinous material (Fig. 12), fonned in
a shallow metal pan, and a round metal
plate of slightly smaller diameter, pro-
vided with a glass handle. In using the
electrophorus, the resin is first rubbed with a woolen cloth or
with a cat's skin, and receives a charge of negative electricity.
The plate is then placed on the cake. Owing, however, to the
unevennesa of the resin, the plate comes in contact with only ?
few points, and on account of the non-conductivity of the resin,
the negative electricity of the cake does not pass to the plate.
On the contrary, it acts by induction on the plate and attracts a
positive charge to the under surface and repels a negative charge
to the upper. The plate is now touched with the finger, and
the induced negative electricity being repelled and free, passes
ofif. The plate then retains a bound charge of positive electric
16 ELEMENTS OF ELECTRICITY.
ity and, when raised from the cake, the charge distributes itself
uniformly over the surface. The charge is sufficient to yield
a spark when another conductor is brought near the plate.
The plate may then be replaced, touched, and when removed will
possess another charge. The original charge on the cake, how-
ever, remains substantially the same in amount.
It may appear from the above that there is a gain in energy
without a corresponding expenditure of work. This is not the
case, however, for every time the plate is raised, the attraction
between the unlike charges must be overcome and work is there-
fore expended in raising the plate.
Electric ilachines. The electrophorus is a very elementary
form of electric machine, but there are other types which are
much more powerful. One type operates upon the same princi-
Fi^. 13.
pies as the electrophorus; tlie initial charge induces othei
charges, which are conveyed by the moving parts of the machine
to some other part, where the induced cliarges may be accumu-
lated. In another type the electricity is produced by friction.
Fig. 13 illustrates the plate electric machine wliieh is of the fric-
tional type. The machine consists of a plate, A, of ghiss or
ebonite, havmg its shafts -B, provided with a handle, (7. A pair of
rubbers or cushions, D, press against opposite sides of tlie glass
and are in electrical connection with the insulated negative con-
ductor U. The cushions are usually made of leather and covered
with an amalgam of tin, zinc and mercury. The prime conductor
G is supported by an insulating standard and canies two arms.
M
ELEMENTS OF ELECTRICITY. 17
Hj which extend one on each side of the plate. These arms carry
teeth in the form of combs which extend inwardly, but are not in
contact with the plate. Electricity tends to escape from sharp or
pointed projections, and round, polished surfaces are best adapted
to retain a charge. A silk flap S is attached to the cushions and
partially covers the plate.
When the handle is turned, the frictional contact causes the
rubber to be negatively electrified and the plate positively. The
positive charge is carried around on the plate and acts inductively
upon the prime conductor 6?, repelling a positive charge to its
distant end and attracting a negative charge. The negative
electricity, being attracted by the positive charge on the plate,
passes readily to it by means of the combs 11^ and these charges
are thereby neutralized. Hence that portion of the plate which
has passed the combs retains no charge, but an induced, positive
charge accumulates on the conductor Q-, Upon passing the
cushions, that portion of the plate is recharged, and the action is
repeated. The lower half of the plate is therefore always charged,
and tlie other half is neutral. As each successive part of the plate
passes the cushion it receives a positive charge, which is neutnJ-
ized when it passes the combs. The flap aS' is used to reduce
electrical leakage from the plate. When positive electricity is to
be collected on (?, conductor E is put in connection with the earth
by means of a chain or wire, F, The negative electricity of the
ciLshions is thereby neutralized. Negative electricity may be col-
lected upon conductor E^ by connecting Q- to ground instead of
conductor E.
Condensers. A condenser is an apparatus for accumulating
a large quantity of electricity on a comparatively small surface.
The form may vary considerably, but in all cases it consists essen-
tially of two conductors separated by a non-conductor, and its
action depends upon induction.
In explaining the action of the condenser, the apparatus
SUuBtrated in Fig. 14 will be considered. The two plates A and
B are insulated conductoi-s, and C is a glass plate between them.
Each of the conductors has a pith ball a and b connected with it.
Let plate A at first be at such a distance from i? as to be out of
its sphere of influence. The plate B is then connected by the
IS ELEMENTS OF ELEOTItlCITT.
conductor x, to the positive conductor of an electrical macbitie,
and receives a positive cliarge, wliicli is distributed uniformly over
its surface. The pith bill or jKjiidnluui b will diverge widely, and
if connection with the charging machine then be broken, no change
in the distribution of the electricity occurs. However, when
plate A is placed in the position shown, tlie di^itribntion is consid-
erably elianged. This plate is connected to the eiirth by a con-
ductor y. The positive charge on Ji now actJ^ inductively across
the intervening space and glass-plate 0, repelling a positive charge
to the earth thvougli y, and attracting a negative charge which
resides iin tlie face n of plate A. TJiis negative chaise now
reacts upon the positive of plate B and attrsicts it. The uniform
distribution on this plate is then dLsturl)ed and the positive elec-
tricity accuninlates on the face m of plate B. Tliat the density of
charge on the otlier portions oE conductor B is diminished, is
shown by the fact that pendulum h diverges less. Owing to
there beirjg less electricity on portions of B than before, B can be
recharged until the pendulun) diverges as much as at firet. The
yig. 14.
effect of plate A, therefore, is to condease the electricity on face
m of plate B and tliiis increase its capacity for more electricity.
Electricity is then distributed over the entire surface of B, but is
much more dense on face w(. If the connections x and y be broken
and the plates sepanited so that they have no effect upon each
other, the positive charge will then be distributed equally over
the surface of B, and the negative charge equally over surface A.
This is shown by the penduhims diverging much more than
before.
The nearer the plates A and B are to each other, and the
greater their size, the greater the capacity of the apparatus ; that
is, the greater may be the charge ou B.
1 "'T^TTi^^^ '■'■ ^ i
ELEMENTS OK ELECTRICITY. 19
Leyden Jar. The Leyden j»r is the most convenient form
of condenser. It consists, as shown in Fig. 15, of a glass jar,
£oated within and without for about two-thirds of ita lieight with
tin foil. The stopper lias a metallic rod passing through it which
cominiinicates with the inner coating by means of a small chain.
The upper end of the rod tcnninates in a ktiob. The n|»per por-
tion of the jar, the stopper and the supporting rod are usually
coated with shellac to protect them from moisture. The inner
coating corresponds to the collecting plate B of Fig. 14, the glass
to the insulating plate Q and the outer coating to tlie condensing
olate A.
The jar is chared by holding the knob to the prime conduc-
tor of an electtical machine or other source of electricity, and con-
necting the outer coating to the earth by a w-ire or
chain, or by holding the jar in the hand. When the
knob is presented to tlie positive conductor of the
ranchine, positive electricity is accumulated on the
inner coating and negative electricity on the outer
coating. The positive chaise acts inductively
through the glass iind repels a positive chaise to the
earth and attracts a negative charge on the inner
face of the outer coating. The action of the jar is
therefore the same as that of the condenser previously t
The jar should be made of good glass, should be kept dry
and free from dust. The thinner the glass the greater is the
capacity, but if the glass is too thin it will not be effective in
insulating the chai-ges from each other. In such a case a spark
will pass from one coating to the other directly through the
glass.
The jar may be dischai^^ by connecting the inner and outer
coatings by a conductor. If the outer coating he held in one
hand, and the other hand be presented to tlie knob the pei'son will
experience a severe shock, iia the arms and body then provide a
path for the electricity to unite. To eliminate danger in dis-
charging, a pair of diechai-ging tongs should be used. These con-
sbt of jointed brass rods pi'ovide<l with knobs at the separable
ends and also provided with insulating handles. One of the
knobs is brought in contact with the outer coating and th''
iO ELEMENTS OF ELECTRICltV.
brought near the knob connected to the inner coating. A
bright spark then leaps between tliese two knobs and the dis-
charge is accomplished.
For the accumulation of powerful charges, a battery of jars
is used. This consists of several jars, which have all the inner
coatings or knobs connected together and all the outer coatings
connected together. The battery is charged and discharged in tlie
same manner as a single jar ; in fact, the Ixattery is equivalent to
a single jar having very large inner and outer coatings. Great
care must be taken in charging or discharging a battery, as a
shock received may be serious enough to prove fatal.
DYNAMIC ELECTRICITY.
Dynamic electricity, or electrodyniimics, considers the f!ow of
electricity in currents. In the ])receding pages the static charge
has been considered, but it has been shown that such a cliarge
may pass readily from one conducting body to another when a
suitable path is provided. If electricity could be su])plied just as
fast as it flowed away, llierc would be a continuous flow, or current
of electricity. Hence if one end of a wire is kept positive and the
other negative, electricity constantly flows from one end to the
other. This result may be ol)tained by chemical action, heat or
induction. The latter method, which includes the movement of
wires across a niagnetic field is used in the dynamo and is fully
considered in the following discussions. In all cases when a con-
tinuous current flows there must Ije a complete curcuit provided.
Voltaic Cell. A continuous current is obtained from the
voltaic cell, and the source of the elect ricty is the chemical action.
Such a cell is illustrated in Fig. lo. The glass jar ^1 contains
dilute sulphuric acid, in which are placed the copi)er plate C and
the zinc plate Z, When a wire connects the two plates as
shown, a continuous flow of electricity takes place (iis indicated
by the arrows) from the i;()[)pcr plate through the wire to the
zinc plate and through the Tupiid to the copper plate. The flow
of cuiTcnt tends to neutralize the difference in electrical condition
of the plates, but the chemical action within the jar maintains
this difference. This electrical difference between the plates is
called the potential dilference ; and the greater the amount of
2S
ELEMENTS OP ELECTRICITY.
21
potential difference, tiie gruater is said to be tlie presmire, electro-
motive force or voltage, wliicli eausea a current to flow. The
stren^h of the current passing depends directly upon the amount
of this electromotive force. The current .strength also depends
upon tlie amount of re*i»tanee to its flow. If the circuit is sliort and
miide up of good conductors, the current will be much stronger
than if it were long and made up of poor conductor.
Flow of Electricity. Electricity, altliough commonly de-
scribed and referred tons^flowHi^ thix)Ughacircuit does not actually
fiow. There is no transfer of matter along the circuit. A wire
carrying a current looks the same as one that is
not, and that electricity is present is only evident
by the heating, chemical or magnetic effectj* pro-
duced. It is convenient, however, to describe
electricity as flowing, and tliis term suffices for
all practical purposes.
In order to show the relation between elec-
tromotive force, current and resistance, electric-
ity flowing in u circuit is often compared to the
flow of water in a pipe which connects two
reservoirs containing water at different levels.
When a clear path is provided, the water will
flow from the reservoir at the higher level to the one at the
lower level, and the greater the difference in the levels the
greater is the pressure and consequent flow of water. Also
the water will flow much faster through a short large pipe,
than through a long and small one. Similarly, the greater the
pressure or electromotive force the stronger is the curient of
electricity, and the gieater the resistance of the ciicuit the
less the current. This analt^y must not be too closely applied,
however, for the reason that with water there is an aijtual transfer
of matter.
Internal and External Resistance. The oii-cuit shown in
Fig. 16 may be divided into two parts, — the Internal, which
inchides the plates and li(iuid, and the external circuit which con-
sists of the wire connecthig the platt-s. If this wire is small and
long, it will ha"e a high resistance and only a weak current will
flow. The resistance of liquids as compared with m
22
ELEMENTS OF ELKCTIirCITY.
siderable. The internal resistance of a cell may be reduced I>j
having the plates large and putting tliem close together. Gases
are poor cijndiictors of electriiiity, and hence the bubbles caused
by the chemical action and which cling to the plates, greatly
increase the internal resistance.
FiR. 17.
FiR. 18.
Chemical Action In the Ceil. The essential elements of a
voltiiie cell are: a plati^ which may \>e oxidized, such as zinc, a
liquid ea()al)le of acting im this plate, such as sulphuric acid, and
an inaf tive plate, sui-li its copjicr. Wlicn tlie wire connecting the
plates i.s bmkcn, there is no cun^ent, but npnii closing the cireuit
chemical action tiikcs place and a current flows. 'I'hc chemical
reactiim which occurs is represented as follows:
Zn + II^SO, = ZnSO, + H.^,
which is equivalent to saying that the zinc (Zn) combining with
the sulphuric iicid (lIjSO^), produces zinc sulphate (ZnSO,)
and free hydrogen gsts (H^). TJie liydTOgeii is given off as a gas
from tlie liquid and zinc sulphate reniiiins in solution. This
action takes place as h'ug as the current flows and depends upon
the amount of current flowing. Tlie zinc gradually dissolves into
the liquid and the latter gnidnally lieconies a solution of zinc
sulphate. When the liquid no longer contains any acid or when
the zinc is used up, the chcmiea] action ceases. The spent liquid
must then be replaced by a new acid solution and a new piece of
zinc substituted.
ELEMENTS OF ELECTRICITY. 23
Polarization. One great objection to the simple voltaic eel)
is that the current produced, rapidly decreases in strength after
the circuit is closed for a short time. This is due mainly to the
collection of hydrogen bubbles upon the surface of the copper
plate. This coating of bubbles hinders the direct contact of the
copper plate with the liquid as its effective area is reduced. This
also greatly increases the internal resistance of the battery.
When this accunmlation of hydrogen bubbles takes place,
the cell is said to be polarized. In order to reduce this Jiction
and so enable a cell to maintain a constant current for some time,
single fluid cells have been largely replaced by double fluid cellsc
In these the inactive plate, about which the bubbles would other-
wise collect, is placed in a liquid which chemically unites with the
hydrogen.
Among the numerous forms of cells now manufactured, the
following are described as being among the most ini[)ortimt.
5mee's Celh In this cell, which is illustrated in Fig. 17,
polarization is reduced by mechanical means. The cell consists
of a silver plate, coated with a deposit of finely divided platinum,
and suspended between two zinc plates in dilute sulphuric acid.
The middle plate has a roughened surface due to the deposit of
platinum, and the hydrogen bubbles therefore readily disengage
from its surface iuid pass off.
Bichromate Cell. This cell, shown in Fig. 18, has the zinc
plate suspended between two carbon plates which are joined
together at the top. The solution used is made up of dilute sul-
phuric acid and bichromate of potash. The latter substance
chemically unites with the free hydrogen and so prevents polari-
zation. This solution also attacks the zinc, even when the circuit
is open, and when not in use the zinc plate is raised above the
solution by the rod A.
Leclanche Cell. In place of the sulphuric acid solution, this
cell is provided with a solution of ammonium chloride (sal-
ammoniac), in which a zinc rod is placed. Within the jar contain-
ing this solution is placed a porous cup, as shown in Fig. 19.
This contains a rod of carbon, which is the inactive element, and
closely packed about it is black oxide of manganese and powdered
carbon. The oxide slowly gives off oxygen and ts
81
ELEMENTS OF ELECTRICITY.
accumulation of hydrogen about the carbon. The porous cup,
althougli it does not interfere with the passage of tlie current,
protects the zinc from the action of the oxide. This cell is much
used in connection with telephones and electric bells, or wliere it
is desired to use it for only a few miimtcH at a time. If used for
a long period, the current strengtli decreases, but quickly regains
its original power when the current is interrupted. Jt is therefore
well adapted for intermittent service.
Danlell Cell. The Daniell cell (Fig. 20) is made up of an
outer portion of copper, wliich serves as tiie inactive clement.
Within this is a saturated solution of copper sulphate, and crystals
Fig. 10.
Pig. 20.
of copper sulphate are provided in perforated cups at the top, so
that they may dissolve and keep the solution satui-ated. A porous
cup containing dilute sulphuric acid or zinc sulpjiate and a I'od of
zinc, completes the cell. The porous cup pi-otecta the zinc from
the copper sulphate solution, and this solution prevents the
Iiydriigen from acciinuilating ahout the copper. The hydrogen
unites chemically with the cojipcr sid])hate forming sulphuric acid
and free coj)per. The free copper is ihen dejiosited upon the out-
side copper portion. The action is represented as follows:
H„ + CuSO^ ^ H^SO, -f Cii,
which is equivalent to saying that hydrogen united with copper
sulphate ]>roduces sulphuric acid and copper.
This cell is very constant in its action because, as long as the
copper sulphate solution is saturated, no polarization can tiike
place. Tills cell is much used in telegraphy, and is kept on a
closed circuit, the interruption of the circuit being used to give
the signals, iusteiid of the closing of the cii-cuit.
ELEMENTS OF ELECTRICITY.
Qrove Cell. In the Grove cell (Fig, 21) a hollow cylinder
of zinc is placed in diliito sulphuric acid. Within this cylinder is
a porous cup containing strong nitric acid and a strip of platinum
for the inactive element. Polarization is prevented by the
hydrogen uniting with the nitric acid. This cell has a low inter-
nal resistance and l-jih produce a strong cun-ent for several hours.
Buns«n Cell. This is similar to the Grove cell, except that
the platinum ia replaced by a rod of carbon (Fig. 22). It has a
slightly higlier electromotive force tlian the Gi-ove cell and is less
expensive, but it has higher internal resistiiiici'.
Fig. 21.
Fig. 22.
Qravity Cell. Where one of the two liquids used in a cell
is heavier than the other, their iliffcience in speeirto gravity may
be depended upon to keep the liijuids Nei>arate, instead of using a
porous cup. The heavier liquid then remains at the bottom of the
cell and the ligliter oui; forms a layer above it. Fig. 23 shows
such a cell, which is the siinie jis the Daniell cell except that no
jrorous cup is used. A copjjer plate at the bottom ia surrounded'
by crystals of copper sulphate and covered with a solution of the
same. The zinc ii supported i\x>\e this and in a dilute solution
of sulphuric acid or zinc sul|iiiate The copper sulphate solution
being the heavier leinniiiB at the bottom and prevents polarization.
The two -solutions do not teniiin tntirely sejiarated, however, as
tlie heavier solution slowh diffu ts upward.
Dry Cell. 1» thi-. till, which i-. more lu'oporly called a moint
cell, the usual liquid solutions aie dispensed with, aud in place of
them the cell is urovided with t-ubstiuces c Auung
ELEMENTS OP ELECTRICITT.
Electromagnets may he made Tei'y powerful, and when made
in the form of a horseshoe have gteat lifting power. A faorae-
shoe electromagnet is shown in Fig. 27. The winding of the
two coils A and B mu^t be such that the ends of tbe horseshoe
have oppoaito polarity. This condition is fulfilled if the winding
Fig. 26.
on the two links is in the same direction, when the horseshoe is
straightened out.
ApplicatEons of Electromagnets. The gi-eat advantage in
using the fk'L-ti-rtniagiiet lies in the conti^ol of its magnetism.
When the cuvreiit is pawsing. the core is strongly magnetized, and
when no current flows it ceases to act as a magnet. Hence its
action may he conti-oUed by simply open-
ing (H' closing the circuit by a key or switch,
the source of the electricity being included
in the circuit. This control of the magnet
may !« accoiiiplislied at great distances
by merely extending the wires from the
coil to tlie distant point and operating the
switch or key at that point.
Ti'legraphic histriiments are eon-
slrufted upon Uiis principle, the closing
of a key at a dislant i>oint causing the
electromagnet to attnu't a piece of iron called its armature, sup-
ported near its i>(ilcs, iind so give a signal. When the current
et-ases to flow, the armature ia forced away from the poles by the
action of a spring;, the tiiice of the spring being overcome, how-
ever, wliencvcr the <'urrCMt iMisses.
Tiie eloclioniagnet is also used in electric liells. The arma-
ture carries a hammer which strikfs agiiinst tlie l)ell whenever the
armature is attracted, lly the rapid opening and closing of the
circuit, which is accomplished automatically, the hammer is made
Fis- 27.
ELEMKNTS OF ELECTRICITY.
to strike the bell repeatedly. Electrio clocks are also governed
by the action of electromagneta.
PRODUCTION OP CURRENTS BY INDUCTION.
We have seen that iwignets may induce magnetism in pieces
of soft iron and attnict thein. We have also seen that electric
charges may induce cliargce in other bodies. Induced currentg
may he produced by the relative movement of a magnetic field
and a neighboring conductor, or by the action of a current in
one conductor upon a neighboring conduct*n-. The production of
irtg.aa
induced currenta is therefore a very different phenomenon from
that of induced static charges.
Induction by riagnfts. Fig, 28 represents a coil B, having
connected in its circuit an instrument ff for the pui-pose of indi-
cating the presence of any current. The magnet A is adapted
to be thrust within the coil. Upon forcing the magnet rapidly
within the coil, the instrument will show that a momentiti-y cui'-
rent passes. Tlie current continues as long as the magnet is in
motion, and ceases as soon as the magnet is brouglit to rest. The
quicker the magnet moves tlic greiUer is the strength of the
induced current. Upon withdniwing the magnet a current Ls
also induced, and this flows in the opposite directinn t^ tlic former
current
ELEMENTS OF ELECTRICITY.
These induced currents are caused by the field surrounding
the magnet moving or cutting across the wires composing the coil.
If a current were passed tlirough the coil, it would create a
magnetic field, so on the otlier hand, the movement of a m^netio
field within the coil produces a current. It makes no difference
whether the magnet or the coil is moved, so long as there is
relative movement. This production of a current by the relative
movement of a magnetic field and a con-
ductor, is the fundajnental principle of all
dynamos.
Induction 1^ Currents. Asasuien-
oid is surrounded by a magnetic field
similar to tliat of a bar magnet, it follows
that if a solenoid cjirryiiig a current were
thrust within anotlier coil, induced cur-
rents wouUl be produced in the latter.
This experiment is illustrated in Fig. 29.
Tliese induced currents, as in the case
when the magnet is used, only How during
tlie motion of the solenoid. Wlion the
solcuoid is inserted, the induced current
flows in one direction and when with-
drawn, it flows in the opposite direc-tiim. Tlie insertion of the
solenoid induces a current which has a direction opposite to that
in the solenoid, and the withdrawal induces a current which has
the same direction us that in the solenoid.
Induction Coil. Suppose now that the two coils shown in
Fig. 29 are placed one within the other, there l>eing no current
passing, and that a curi'cnt is afterwards i>assed through the inner
coil. Upon permitting the passage of a current in the inner coil
a momentaiy current is induced in the outer coil, the same as
if a magnet had been thrust into the coil. This induced current
continues, however, only wliile the current in tlie inner coil is
increasing in value from zero to its noi'mal amount. As soon as
thisnonnal strength is reached the induced current ceases to flow.
Now when the circuit of the inner coil is broken and its current
ceases to flow, anotlier momeutaiy cuiTent is induced in the outer
coil, which has a dii-ection opposite to that formerly passed
ELEMENTS OF ELECTRICITY. 31
through it Such an instrument for producing induced currents
is called an induction coil. The coil through which the original
current is passed is called the primary coil, and that in which the
currents are induced is called the secondary coil. The induction
coil is the fundamental principle of tninsformers, commonly used
in long distiince power transmission.
Fig. 30 illustrates an induction coil having the two sets of
windings A and B and also supplied with a soft iron core C.
This iron core greatly increases the amount of imhiction.
The proiluction of induced currents by opening and closing,
or making and breaking the primary circuit, is similar in action
to thrusting a magnet within and Anthdrawing it from a coil.
When a magnet is used, the induction is caused by the magnetic
A A
A is secondary coll.
B is primary coll.
Fig. 30.
field moving across the wire composing the coil. Now when the
primary circuit is closed, a magnetic field is created, wliich is
equivalent to thrusting a magnet within the coil. The breaking
of the piimai-y circuit is equivalent to withdrawing the magnet,
and so induces a current. The current induced by closing the
primary circuit is opponite in direction to that of the primaiy
current, and that induced by breaking the primaiy ciivuit is in
the 9anie direction as the primary current. The induced currents
are only caused by the changing in strength of the magnetic field
surrounding tlie secondary ciix3uit. Therefore, wliile a constant
current is passing in the primai^y circuit, there will be no induced
currents. When the strengtli of the primary current clianges,
however, secondary currents will be induced. The strength of
these induced cun*ents will depend U[>on the abruptness of change
in the primary current, and their direction will depend upon
whether the primaiy current increases or decreases.
It should be remembered that before a current can flow there
89
ii
ELEMENTS OP ELECTRtClTr.
muist 1)0 a closed circuit, and iiti electromotive force. A current
flows in the secondary circuit only when it is closed, but the
electromotive force exists whether or not the secondary circuit is
closed. Strictly speaking the electromotive force is first produced
or generated, and the cui-reut then flows when the circuit is closed.
The viilue of the electromotive foi-ce generated in the secondary,
depends npon the nnmlifr of turos in the same ; a much higher
electromotive force being generated in a coil of a large numlier of ■
turns th in m a cnil of a few turns. This fact is of great pntctical
importance, for it thus prt^
vides a means of obtaining
very higli electromotive
forces.
Fig. 31 illustrates an
induction coil ari-anged to
generate a verj- high elee-
tjomotive force, and for
pniducing sparks between
widely scpamted points.
The priinaiy coil consists of a few turns of eoarae wire, and
about this is the sccondaiy coil made up of many thousand
turns of fine wire, all of which arc well insulated. In the
primary cin'uit are (■()inu'ctc<l a fi'w Grove's or liunsen"s cells
and a switch for in terra pting the circuit. The making and
breaking of the primary circuit generates n very high electro-
motive fo!x;e ill tlie secondary. Sparks of considerable IcTigth maj
be produced between the terminals of the sec<)ndary by this type
of coil, A condenser is used in connection with the device, in
order to decrease the electromotive fin-cc indnecd by closirjg the
primary circuit, and to increase that inilnced by opening the
primary circuit. The sparking thcrefoi-e {iccurs at tlu! breaking of
the primary cirLuit. A powerful induction coil made at London,
in which the sceondary coil contained 280 miles of wire wi>nnd in
3-10,000 tnnis. yields a spark 4-2.V in<-he3 in length, when worked
fay 30 drove's cells.
Mutual and Self-induction. Induction piivduced in one con-
ductor by currents in another, which has no electrical connec-
tion with the iiret, ia called mutual induction. We have seen
fiLEMENTS OF ELECTRICITt. 88
that mutual induction is caused by the cliangc* in strength of the
magnetic field surrounding the secondary coil. The primary coil
must necessarily be subject to the same change in field strength,
which is therefore acted upon inductively as well as the secondary
coil. This reaction tends to oppose any increase or decrease in
the primary current. It is greater for a coil having a large num-
ber of turns or one provided with an iron core. This inductive
action of a coil upon itself is called self-imluction. Electro-
magnets have very high self-induction. Upon closing the circuit
in such a coil its self-induction causes the current to increase in
strength very slowly, and upon opening the circuit self-induction
tends to prolong the current, and produces what is termed an
** extra current." The high electromotive force causing this extra
current, may be sufficient to give a dangerous shock, and produces
a bright spark where the circuit is opened.
HEATING EFFECTS OF CURRENT.
Heating: Depends upon Resistance. Wc have seen that
some substiinces are very good conductoi-s of electricity, that
others are fairly good and that others are very poor conductors.
That is, some substinces offer very much more resistance to the
flow of electricity than othei*s. In order to force the current
through this resistance, a certain amount of energy must be
expended and the greater the resistance, the greater is the amount
of energy required. The energy which is thus consumed, appears
in the form of heat. From every part of a circuit through which
a current is flowing, heat is dissipated, and this heating raises the
temperature of the circuit a certain aniount. A short, stout
copper wire has low resistiince, and so causes but little heat to be
generated. Also on account of its large radiating surface, this
heat is readily given off to the surrounding air, and therefore its
temperature is raised only to a small extent. A fine platinum
wire, however, has high resistance and but i^mall radiating surface,
hence if the same current be passed through this wire, it will come
to a high temperature and may even become incandescent.
The laws of heating in electrical circuits were first formulated
by Joule. Joule's law is as follows :
The number of heat units developed in a conductor is propor-
41
84
ELEMKNTS OF ELECTRICITY.
tiofial to its re^iHtance^ to the Sffiare of the current^ a7id to the time
that the current laifts.
The amount of lieat developed therefore increases in direct
proportion to the resistance, but increases as the square of the
current. Hence douhHng the resistance, doubles the heat gener-
ated, if the current remains the same, but doubling the cuiTent
increases tlie generation of heat four fold with the Sixme
resistance.
Applications. The heating of a wire cariying a current is
made use of for lighting j)urposos, and again for blasting, explod*
ing sul>marine mines, etc. Conducting wires are run from the
explosive material to a distant point, and include a battery and
Fij;. 32.
piece of fine platinum wire in the circuit. Some combustible
substance is placed around the platinum, and serves to ignite the
main charge when the ])latinum wire is luxated. Upon closing the
circuit this wire becomes hot and the cxph)sion takes place.
This principle of heating is also a[)plied to fuses^ used for
the protection of electric lighting or power circuits. The fuse
consists of an easily fusibh* nu'tal which is inserted in the circuit.
The passage of an excessive or dangerously large current heats
the fuse to its melting point and so breaks the circuit. The
cause of the large current may then be removed and a new fuse
inserted in place of the old one.
Electric welding is accomplished by passing a powerful cur-
42
THE MORTON-WIMSHURST-HOLTZ INFLUENCE MACHINE
.vr-ii-^rvit*]
ELEMENTS OF ELECTRICITY. 85
rent through two rods held together. The heating at the junction
softens the metal and the rods become welded.
The electrical heating of cars and of cooking utensils is
accomplished by passing a current through wires of high resist-
ance.
Thermo-Electric Currents. If the junction of two dissimilar
metals forming part of a circuit, is heated, a current is produced.
If a piece of bismuth and a piece of antimony be soldered together
and form part of a circuit, then if the junction be heated to a tem*
perature higher than that of the rest of the circuit, a current will
flow in the direction from bismuth to antimony thix)ugh the heated
section. If the junction be cooled below the temj^erature of the
rest of the circuit, a current will flow in the opposite direction.
The current will continue to flow as long as the difference in
temperature is maintained. Currents thus produced are called
thermo-electric currents. This phenomenon is commonly known
as the Seebeck effect f i-om the naiiie of its discoverer.
Alx)ut the only application'of the alx)ve phenomenon is made
to instruments for detecting very slight differences in temperature.
These ai*e arranged so that a very- small rise in temperature of a
bismuth aiid antimony junction, will generate a current which
may be measured by a sensitive instrument in the circuit. Other
metals may be used but the effect is not nearly so pronounced.
CHEHICAL EFFECTS OF CURRENTS.
Electrolysis. When a current of electricity is passed through
water from one terminal of a circuit to the other, the water is
decomposed into its constituent parts, hydrogen and oxygen. The
hydrogen gas rises in bubbles from one terminal and the oxygen
gas from the other. Fig. 32 illustrates an arrangement of appar-
atus by which this decomposition may be attained, and by which
the gases may be separately collected. The current from a couple
of cells is conducted through one wire to a vessel containing
water, then thi'ough the liquid and through the other wire to
the cells. Pure water is a poor conductor, and a few drops
of sulphuric or hydrochloric acid are added to increase its conduc-
tivity. The two terminals project through the bottom of the
vessel and over each of them is placed a tube * e upper
48
ae ELEMENTS OF ELECTRICITT.
end and filled with water. The gas given off from each '^rminal
rises and collects in the upper poition of the tubes. Oxygen
rises from the terminal by which the current enters the liquid
and hydrogen from the terminal by which it leaves. Oxygen is
therefore collected in one tube and liydrogen in the other. Two
volumes of liydrogen and one volume of oxygen unite to form
water, and hence in its decomposition, the volume of hydrogen col-
lected is twice that of the oxygen.
Other liquids may be decomposed by i)a8sing a current through
them, and this process of decomposition is called electrolt/sia.
Liquids which uvdy be decomposed in this manner are called
electrolytes. The terminals by which the current enters and
leaves the liquid are called electrodes, Tlie anode is that terminal
by which the current enters and the kathode is that by which it
leaves the liquid.
Some liquids such as oil, which is an ijisulator, and mercury
which is itself an element, cannot be decomposed by an electric
current. Dilute acids however, and solutions of metallic salts are
readily decomposed.
For an example of the decomposition of a salt we will take &
solution of copper sulpliate for the electrolyte. The .current from
a single cell is suiricient to decompose this salt. By passing the
current through tlie liquid, metallic copper is sepai-ated from its
compound and is deposited in a pure state u[)on the kathode.
The remainder of the compound unites with the water to form
sulphuric acid and oxygen. The latter rises in bubbles from the
anode. The final result therefore, is that the kathode i-eceives a
coating of pure copper and tlie liquid becomes dilute sulphuric
acid. It the anode consists of copper, it will dissolve into the
liquid forming copper sulphate as fiist as the pure copper \^
deposited upon the kathode. In this case the action of the cur-
rent is to transfer the copper from the anode to the kathode.
The amount of chemical action in an electrolytic cell depends
upoa the strength of current, and the lime it continues.
Electrotyping. The decomposition of salts by the electric
current has received \ most important application in electrometaU
lurgy. By this process exact reproductions may be made of
type, pltuiter casts, medals, etc. In the usual process a wax moold
44
ELEMENTS oK KLfccTltlClTV. 37
of the object is first made, and this is coated with gmphite or
powdered bronze to render it a good conductor. The mould is
then suspended in, and forms the kathode of an electrolytic cell.
For the formation of a copjjer electrotype, the anode is a plate of
copper and the electrolyte is copper sulphate. The passage of the
current produces an exact reproduction of the original object on
the wax mould. Even tlie faintest lines are accurately repioduced.
Electropiatinsr* l^y this process the cheaper ]iietals ma^
receive a thin coating of gold, silvtM*, nickel, etc. The objects to
he plated are suspended in the electrolytic cell and form the
kathode. In electro-gilding the electrolyte is a solution of double
cyanide of gold and potassium, and a plate of gold forms the
anode. This plate dissolves into the liquid as fast as the gold
coating is deposited upon the objects t(^ be coated. For electro-
silveiing a double cyanide of silver and potassium and a plate of
silver are used. Iron objects are usually coated with a copper
deposit before l)eing gilded, silvered or nickeled. Tlie copper
presents a l)etter surface for the otlier nieUils and givrs more
dunible results.
Accumulators, also called storage or secondary batteries,
consist of cells which are capable of giving out electrical energy,
in virtue of the chemical change caused by first passing a current
through them from an external source.
The simplest type of accumulator is called the Plantd battei-y
from the name of its inventor. This cell consists simply of lead
plates in dilute sulphuric acid. Tlie plates are ^'formed" or made
active by repeatedly " charging " and '* discharging " the cells.
That is, a current from an outside source is passed through the
cell from one plate to the other, and then by connecting the plates
by a wire a current will flow until the potential of each plate is
the same. By repeated charging and discharging, the capacity ol
the cell is greatly increased. No electricity is stored up by the
plates as with the Leyden jar, but the eflfect is due entirely to n
chemical change on the surface of the plates. By repeated cliarg
ings this chemical change penetrates deeper and deeper into tLt
plates and thus increases their capacity. The current received
from the cell flows in an opposite direction to that by which the
cell is charged.
45
s ELEMENTS OF ELECTRICITr.
THE TELEGRAPH.
Having considered tlie electromagnet and the effect pro-
duced in a core of soft iron, by a current of electricity which
parses through a coil of insulated wire surrounding it, we are pre-
pared to apply these principles to the electric telegraph.
Various devices have been tried, with more or less success,
for ti*ansniitting and recording signals from one point to another.
The apparatus used in one of these early attempts ciused
s[)arks from Leyden jai-s to pass thiough a circuit. Another was
o[)erated by means of a galvanometer nee<lle which was deflected
to the right or left.
None of these attempts were of any practical value except
that they served to lead up to the telegraph of the present day.
There are now two successful methods of operating telegraph lines;
namely the "Open Circuit" and the "Closed Circuit " systems.
The former is used in Europe and its chief advantage is that no
energy is consumed from the batteries except when signals are
actually being transmitted. The latter system which is used
almost entirely in America, has on tlie other hand, advantages
which offset this. On account of its greater importance in this
country we will consider more in detail the "Closed Circuit*'
system .
In its simplest form this system consists of three principal
parts connected in series in the circuit:
1. A key for transmitting the signals.
2. An instrument for receiving these signals.
3. A battery which furnishes the current to operate it.
The riorse Sounder. The instrument most commonly used
for receiving the signals is the Morse sounder, shown in Fig. 33.
It consists essentially of an inverted electromagnet E of the horse-
shoe type. This electromagnet differs somewhat from the one
shown in Fig. 27, in that it is made up of two cores and a yoke
or back strap B in oider to furnish a l)etter bearing for the electro-
magnet upon its base than would l)e possible with one having a
rounding back. Above the 2)oles of this magnet, an armature A
of soft iron is attached to a i)i voted lever L of non-magnetic
tn.iteriaU which is controlled by a spring S. When a current:
46
ELEMENTS OF ELECTIUClTi. 3-
passes thmugh the coils of thia electromagnet, tlie cores become
mi^etized and attract the armature downward. Just before !t
touches the poles of the electromagnet however, the lever to winch
it is attached, strikes a metallic stop F and a click is heard.
When the current ceases to fluw, tlie cores of the electi-omagnet
Fis-
lose their attractivo force. The armsitun; is then carrieil upward
by means of tlie spring wliicli acts nn the hivur to which the
armature is attached. The lever Uii'ii »trike.s a<;itinst another
stop D and another click is hciiid. The range uf t>trokc or play
of the lever is adjusted by net screws.
AHERICAN nOR5E CODE.
H .
If the duration of time of current flow is very short, tlie
interval of time between these two clicks will Iw correspondingly
short. The signal in this case would lie a "dot." If the inter-
val between the two clicks be longer, the signal would l>e a dash-
In this manner by a telegraphic code, consisting of different
signals made U]> of dots, spaces and ditshes for all tlie letters of
the alphebet and numbers, it is possible to .send and receive mea-
sles. Besids the "Sounder" described above in which the
40
ELEMENTS OF ELECTRICITY.
receiving operator depends entirely upon sound for the message,
there are also in use the *^ Embosser " and the " Ink Writer."
In the first a sharp point attached to the armature lever cuts
the dots or dashes in a strip of paper moved past it by clock
work ; in the second the dots and dashes are recorded on the
moving paper by an inked wheel. These last two methods are,
however, little used by expert o[)eratoi's.
The Horse Key. The Morse Key or instrument by which
the signals are controlled is sliown in Fig. 34.
M
Fig. 34.
It is composed of a invoted lever L fitted at one end with a
circular plate P on which the fingers of the o[)ei'ator rest. The
key is secured to the base by two thumb screws A and T, to
which the terminals of tlie circuit are attached. The screw A is
in electrical connection with the main body of the key, including
the lever. Tlie screw T is insulated from the rest of the key by
some ncju-conducti ng material, and terminates in a platinum {X)int.
On tlie underside of the lever and immediately above this
I)oint is another platinum tip wliicli, wlien the lever is pressed
down, makes cont-xct, tlius completing the circuit through the key.
The lever is kept in proper position when not in use, by a
spring D and the length of its stroke is controlled by an adjust-
able set screw. A switch S, for closing the circuit when the
instrument is not in use, completes this piece of apparatus.
The Battery. The battery used for operating the circuit is
either the Daniell cell sliown in Fig. 20 or the Gravity cell shown
in Fig:. 23. In thn *' Closed C'ircuit" system the batteries are
48
ELEMENTS OF ELECTRICITY. *1
required to furnish current nearly all the time and these cells are
remarkably well adapted for this purpose as they do not polarize
and require very little attention other than keeping them supplied
with copper sulphate and removing the zinc sulphate.
The number of cells used depends upon the length of the
line and resistance of the instruments in the circuit.
In actual practice there is a key and sounder at every station
on the line, all being connected in series together with a sufficient
number of cells to furnish the current. The switches of all the
keys being closed, a current will flow through the electromagnets
of all the soundei-s.
When an operator wishes to communicate with a certain
station, he opens the switch of his key, thus breaking the circuit
and he can then by means of the lever, call the station and send
any message he desires over the line. This message will, of
course be simultaneously signalled by all the soundei-s on the
circuit.
When the operator finishes his message he closes the switch
and is then prepared to receive the reply.
The Relay. In the case of long lines having many instru-
ments in series, the main current would not be strong enough to
properly operate the receiving sounder directly, and the relay
is then resorted to.
This instrument consists of a horizontal electromagnet, hav-
ing a large number of turns in its coils, in series with the main
line. It has an armature somewhat like that of the sounder
already described. It is however more delicately Imlanced so
that less magnetic force Ls required to attract it.
When the line current flows through the relay, this armature
is drawn against its stop, and thus it makes contact for a local
circuit including a Morse sounder and sufficient batteries to
work it.
In this manner, the main or line current, although not strong
enough to operate the sounder directly, can l)e made to control
the sounder in the local circuit, l>y means of the relay, the arma-
ture of which plays the siime part in the local circuit as does the
key in the main circuit when manipulated by the opemtor.
J.O
42
ELEMENTS OF ELECTRICITY.
THE TELEPHONE.
The modem telephone was invented in 1876 by Alexander
Graham Bell and Elisha Gray. Up to this time, many attempts to
perfect a successful speaking apimratus had been made but they
were all failures. One cause of lack of success was the fact that the
inventors had little or no knowledge of acoustics.
In order to understand the operation of the telephone, it is
necessary, fii*st of all, to understiiiid tlie principles underlying the
protluction of sound, or of acoustics. Sound is produced by vibra-
tions in tlie air set up by whatever may be the cause producing
the sound. These vibrations strike the eaitlrum, and the senssr
tion of sound is conveyed to the brain. The pitch depends upon
the rapidity of the vibration, the loudness upon the amplitude, and
the quality upon the form of the vibration.
The simplest sort of vibration is that set up by a musical tone,
and to give an idea of the rapidity of vibrations for a specific case
it may be stated that the musical tone known as middle C is set
up by 256 vibmtions per second. The vibrations set up by the
t
M
M.
r-±mm
m
c,
D.
Fig. as.
Toice in speaking are of a much more complex nature in every
way, and on this account the earliest telephones could reproduce
musical tones, but could not transmit speech.
The earlier telephones served to transmit and reproduce tlie
vibrations of the voice by means of electromagnetic induction. A
typical telephone circuit in its sim[)lest form is shown in Fig. 35.
There are two similar instruments, one at each end of tlie circuit;
we may consider one the ti*ansmitter and the other the receiver.
M and M^ are two permanent bar magnets on the ends of which
are coils of fine insulated wire. C and (^j. In front of the mag-
nets are thin elastic disks of .>lieet iron, D and I)^, commonly
known as the diaphmgms. Let us consider the left-hand instru-
50
ELEMENTS OF ELECTKICITY. 43
ment tlie tzaosnutter, and tbe other the receiyer. The penniment
ra^Det M sets np a certain number of magnetic lines of force
throu^ the coil C, and as the diaphragm D offers a path of lower
mimetic resistance than the air, manj of these lines pass through
it. When we speak close to the diaphragm D, tbe air \ibrati<Hi8
cause the diaphragm to vibrate. As it approaches tbe magnet M
more mimetic hnes pass throng the diapbtngm, and when it re-
cedes fewer lines jnss through it This action alters the number
of magnetic lines which jiam through tbe coil C, and hence alter-
nating currents are induced in it which are pro|>ortional in strength
to the rate of change of tbe number of lines.
These currents aUo pass through the coil C, at the receiving
end of the line, and according to the direction in which they flow
around the magnet M,, alternately add to or tend to neutralize its
strength. When the current strengthens the niiignet, it causes it
to attract its diaphragm D,, and when the current decreases the
strength of the m»gi)ct, tbe diaphragm moves away. In this man-
ner the diaphn^m at tbe receinng end is made to vibrate in exact
unison with tbe one at tbe transmitting end, and thus similar vi-
brations of the air are set up, reproducing tbe sounds spoken into
the transmitter.
Tbe above arrangement has ))een somewhat modified in the
telephone of the present day, and it has been found more con-
venient to have a separate transmitter at each end of the circuit
The transmittera now in use operate ■"" " "ly different princi-
ples, but the receiver is essentiallv
ELEMENTS OF ELECTKICmf,
Receivers. There are two coninKm forms of icceiver: the
»ioi;le-}^i1e and the i^ipolar type.
A flingle-[fnle receiver of the Bell type in shomi in se^MioD in
Fig. 36. It e'lnsJHtii of a Imnl rubher ca«e H, in which is placed
the laminated or L-<jnii>ou]id liar m<^iel of steel M. This m^net
is coin|K)Hed of two t;etji of liars Heparately m^tietized ; clamped
lietween tliein hy means of screws is tlie jxile piece of soft iroo A
at one einl and tin; Mmrk K at the other end. I'pon the jiole piece
is pluced a tmil ui tine insulated eopjier wire B; connectitm being
made from it to the liin<ling jMitits C C l>y means of heavy wires
Ij h. The hinding posts are attached to the end piece P, which
is held in place liy tlie screw S which tlireads into the block F,
and tlius ser%'es aUo to keep the nii^iet in position. The cap E
screws to tlie cose and supjMirts the diaphragm D, which is a flexi-
ble disk of soft innt. The diaphragm is placed a short distance io
front ()f the jmle pji-ci; of the magnet, and tlie portion directly
opposite it is free to vilirate.
This instrnmctil is U-iiig Kii|>p1airted to a great extent by the
r receiver, wliiih diR'crs from the King!c-iK)le receiver in that
the {icniianeiit magnet, iiiKlead of lieing straight,
IN eoiiNtnicted upon the horse-shoe principle.
Tliiu brings Imth [xtles in }>osition to act on the
diaphragm, giving increased strength of field, and
consequently making t)ie instrument more evident.
A soft-irnn jiolc piece is secured to each end of
Uic magnet, and a coil of insulated copper wire is
mounted on i-.if\i jiole jiiece.
At the |jiiMnt time the single-jwle receiver
IS soim tuij* s Usui for b«';tl work, wliile tlie bipolar
ivtr IS cinjilcM'd both f<)r this and for long-
dist.UKC Moik There is also another fonn of re-
tr known as tlie watch-case type, which is use*!
to some extent for desk sets and .it the exchange switch-l*oard.
Transmitters Tin, typt of telephone just descril>ed was
iiriginally used as the Iransnntter as well as the receiver, and for
short distiinces, in which tlie luie resistance was small, gave fairiy
ginxl results.
It is now tlto practice to use this instrument as the receiver
Fig ^7
ELEMENTS OF ELECTRICITY. 46
only, and to use a dififerent form of instrument, together with a bat-
tery, for the transmitter. The action of this transmitter depends
upon the fact, that if the resistance of a circuit is increased, the
current will be decreased, and if the resistance is decreased, the
current will be increased. This variation in resistance is produced
by varying the pressure between one or more carbon contacts. If
the jn-essure is increased, the resistance is decreased, and if the
pressure is decreased, the i-esistance is increased.
There are three types of transmitter: in the first but one
carlx)n contact is used lor varying the resistance, in tlie second
several contacts ai-e used, and in the third granular carbon is
employed, thus giving a very lai-ge number of contacts.
The Blake transmitter, a section of which is shown in Fig. 37,
is an example of the first type. This instrument, in common with
all other transmitters, has a diaphragm D somewhat similar to that
of the i-eceiver. This is supi)orted in a rubljer ring, and is lield In
place by two dumping springs not shown in the cut. Mounted
upon a light spring S, and i*esting against the back of the center
of this diaphragm, is the front electrode, which is a platinum pin.
Directly Imck of this piece of platinum, a carbon button B, which
forms -the other electrode, is supix)rted by means of a spring
(]J, so adjusted that the carbon button bears lightly against the
platinum pin. The tendency of the spring S is to press the plati-
num pin away from the diaphragm ; but this is overcome by the
stiffer spring C which bears in the opposite direction, and so keeps
the platinum in contact with the diaphragm. The electrode B is
mounted in a comparatively heavy socket of brass A. Both
electrodes can move freely with the vil)ratious of the diaphragm ;
but the carlxm, on account of the inertia due to the weight of the
brass socket, moves more slowly tFian the other. Any vibration
of the diaphragm will, therefore, result in a variation of the pres-
sure between the two electrodes, and thus vary the resistance of
the contact
The two springs S and C are insulated from each other, and
the current goes to the contact point by means of one spring and
leaves by the other. The adjustment of the pressure is effected
by means of the screw E, which bears against the lever L.
This transmitter is quite satisfactory for lines of mo<^
53
46
ELEMENTS OF ELEOTEICITY.
length, and is used to some extent at tlie present time. It is, how-
ever, somewhat difficult to keep in adjustment, and is not well
adapted for long-distance work.
The second type of transmitter mentioned is not much used
in this country, and a description need not be given.
The most common fonn of ti-ansmitter, and the one which is
mpidly replacing all otJiers, is the H minings or granular carbon
. type. This, as originally plmmed liy its inventor, consists of two
insulated plates of coiulucting niikteriiil wliich forms tlie elec-
trodes of the transmitter, tlie binico l)etween them being filled
v/iQi granular carbon. The general fonn of tliis instrument is
shown in Fig. 38. D is the diaphragm of metal or carbon which
is clamped between the body of the case C and the cap A by
means of screws. Another conducting plate B, of metal or
carbon, is placed in the buck of the case, and the spiicc Itetween
D and B is hllcd with gmnulHr carbon. The conducting plates
D and It form the electrodes <»r ter-
nunals of this ti-an&niitter. When the
diapliragm is Kj^keu agiiuist, it of
course vibrates, mid tluis varies the
pressure upon the numerous contact
points of the gi-aimlar carl)on through
which the ciirn^nt mnst flow to pass
from one elcctzald to the other, and
thus the resistance is varied ns in tlie
Blake instrument. Lm^rctin-ents can
used with the Unnniiigs tyjic of
transmitter tliati with other sorts, and
it has the fnrther advaiitiige of allou
ing a greater variation of resistance.
The transmitter which is used
almost entirely at tile present time is
known as tlie "solid back," being a
jnodilication of the Hunnings type just
described. The case, which is of metal
and hollowed out to contain the working parts of the instrument,
is enclosed by a brass cover, which also carries the moutli piece.
The metal diapliragm is supported in a ring of soft rubbe'
Hg. 38.
ELEMENTS OF ELECTRICITY. 47
attached to the back of the cover. The electrodes are enclosed
ill a luetal chamber \vhich is lined with insulating material,
rhis electrode ehaniljer is secured by means of a set screw to a
metal bridge which is attached to the back of the cover by means
of screws. Both electrodes are of carbon, being in the form
of discs somewhat smaller in diameter than the containing cham-
ber. The space between the electrodes is filled with granular car-
bon as is also the space between the circumference of the discs and
the insulated walls of the chamber. The rear electrode is mounted
upon a brass disc wliich is screwed to the back of the chamber,
tliereby holding the electrode securely in place. This electrode
being in metallic connection with the containing cliamber, is
in electrical connection, through the bridge and cover, with
the frame of the transmitter which thus becomes one of the
terminals.
The front electrode is also backed by a brass disc which is
attached to the metal diaphragm of the transmitter by means of a
stud which passes first through a mica washer that serves to en-
close the electrode chamlier, and then through the center of the
diaphragm. This stud is fitted with two tlireads, upon one of
which is screwed a nut which clamps the mica washer to the
electrode, and upon the otlier two nuts which clamp the electrode
to the diaplu-agm. A brass collar, which screws to the periphery-
of the electrode chamber, binds the mica washer securely against
it. Connection is made to the front electrode, which is the
second tenninal, by means of a fine wire brought out to a binding
post mounted upon an insulated block.
The vibrations of tlie diaphragm are communicated directly to
the front electrode, which thus varies the pressure upon the mass
of granular carbon and consequently serves to vary the resistance.
Two damping springs rest against the diaphragm, thus keeping
the amplitude of its vibrations within reasonable limits, and
checking tliem as soon as they have performed their part, leaving
the diaphragm reaily to obey the impulses due to the succeeding
sound waves.
This transmitter operates in a very satisfactory manner ; ex-
cellent contact is made between the carbon electrodes and the
particles of granular carbon. Packing of the granules is pre-
ss
46
ELEMENTS OF KLKCTUICITV.
vented on account of the space between the peripheiy of tlie
electrodes and the inner circumference of the chamber, which
contains granules tliat do not become lieated by the passage of
the current. Hence when the granules l)etween the electrodes
become heated they can expand into this jMirtion.
The transmittei-s of this type manufactured by different com-
panies vary slightly in minor details of construction, but all
ojierate u[)f)n pi*actieally the same principles.
Simple Telephone Circuit. The eailiest fonn of telephone cir-
cuit consisted simply of two Hell i*eceivers connected in series.
The one which was being used as a transmitter served as a very
small generator which sent alternatiniif mirrents over the line, and
these acted upon the instrument at the other end of the circuit,
which was, for the time being, used as a receiver.
After the invention of the carbon ti*ansmitter the circuit con-
sisted of a transmitter and receiver at each end of the line, to-
gether with the batteries wliich furnished the power, all coiniected
in series. Tliis arrangement did not give satisfactory results for
many reasons, but the use of tlie induction coil overcame the dif-
ficulties previously met with.
A typical circuit with the induction coil is shown in Fig. 39.
Here T is tlie transmitter, B the battery, P the primary and S tlie
secondary of the induction coil, and R tlie receiver. The primary
Fig ;IJ).
circuit contains the transmitter, batteries, and primary of the in-
duction coil, while the secondary circuit contiiins the receiver and
secondary coil. When the transmitter at one end of the line is
spoken into, the resistance of the j)rimary circuit is varied, and
this in turn vu'-^'es the sti*ength of the curi-ent pissing through the
56
ELEMENTS OF ELECTRICITY. 49
primary of the induction coil. Consequently alternating currents
are induced in the secondary coil which pass over the line and act
upon the receiver at Uie opposite end.
The action of tlie induction coil has already been described.
Tlie coil used in telephone work has a core made of soft iron
wires. Upon this is wound the primary coil, consisting of a com-
paratively small number of turns of coarse insulated copper wii-e,
and outside of this, and carefully insulated from it, is the secon-
dary coil in which are a great many turns of fine insulated copper
wire. Without the induction coil, it is probable that the long dis-
tance telephone in its present state of perfection would have been
impossible. Its use allows the resistance of tlie circuit in which
the transmitter acts to be very small ; with the result that the
effects of the variations in resistance due to the transmitter are
comparatively large. This low resistance also permits a larger
current to flow with a given number of cells of battery. The
electromotive force of the secondary current is high, thus being
well adapted to overcome the high resistance of the receivers,
secondary coils, and line wires. Still another advantiige lies in the
fact that if the transmitter were connected directly in the main
circuit, its effect would be to cause the current in tlie line to vary
in strengtli but not to change in direction. In other words, the
current would be undulating but not alternating. However, better
results are obtained if the current which actuates the receiver be
an alternating one, and this is of course the nature of the current
in the secondary of the induction coil.
Batteries. In telephone work the batteries are required to
iiirnish current for only short periods of time, and the Leclanche
cell is admirably adapted for the purpose. It requires very
little attention and will furnish a comparatively large current for
a short time. Moreover, although these batteries polarize in a
short time if kept on a closed circuit, they recover very quickly
when the circuit is opened.
The Fuller cell is also used to a considerable extent. In this
cell the plates are zinc and carbon ; dilute sulphuric acid is the
excitant, and either bichromate of sodium or bichromate of potas-
sium may be used as the de{X)hirizer. The zinc is placed in a
porous cup, in the bottom of which is a small quantity of
57
50 ELEMENTS OF ELECTRICITY.
which serves to amalgamate the surface of the zinc and thus pre-
vent local action between the zinc and the impurities which it
contains. This cup is then filled with a solution of sodium chlo-
ride (or common salt) dissolved in water. In tiie battery jar is
the solution of dilute sulphuric acid and bichromate of sodium or
potassium. The porous cup is put into the jar, and tiie carbon
suspended through an opening in the cover which fits over the
jar. This cell is excellent for telephone work ; it has a high
voltage, low internal i-esistance, and does not deteriorate on open
circuit.
Tlie gravity battery, already described, and the storage bat-
tery are used in telephone work when constant service is re-
quired. Dry cells ai*e also used extensively, particularly in
intercommunicating sets, on account of their cleanliness and
convenience.
The Magneto-Qenerator. The above-described equipment
serves to transmit and receive messages, but it is also necessary
to supply some sort of calling device. The simplest apparatus for
tliis purpose consists of an ordinary bell or buzzer operated from
batteries, and this system is used commoidy to-day for office sets
where the disUinee l)etvveen stations is small.
For long distances it is, however, impracticable to use this
system for calling, and recourse is had to the magneto, which is
described in another section. This consists of a generator having
l)ermanent field magnets and a shuttle armature which is wound
with many turns of fine insulated copper wire. The armature
is rotated at high speed by means of a small pinion on its shaft
which meshes with a larger gear which is turned by means of a
cnink. This machine furnishes an alternating current, and hence
it is necessary to use a polarized bell or ringer in connection with
it, so constructed as to operate with an alternating current
Magneto-generatore are designated by the resistance through
wliich they will ring, l)eing spoken of as a 10,000-ohm, 20,000-
ohm generator, etc.
At the exchange it is quite common to use a power-driven
magneto-generator, which may be driven from a small direct or
alternating current motor. Also in some cases the motor-generator
is used U' supply current for ringing purposes.
68
ss^
tOAl
ELEMENTS OF ELEf'TRiriTV.
Circuits of the Telephoiw. A complete telephone set is made
up of three distinct circuits : one for the calling Apparatus, one
for tlie transmitting a[i[>HratuR, and one for the receiving appa-
ratus. The calling ap^iaratus includes the generator and ringer,
the transmitting apparatus consists of the transmitter, iKitteries,
and priniar)", and the receiving apparatus consists of the receiver
and secondary of the induction coil.
When Ihe tele|>lione is not in use the calling apparatus must
lie connected with the line while the transmitting and receiving
ciixuiLs are hoth opiMi. On the other hand, when the telephone
is used fur bdking, tiie calling circuit shimld l>e <ii>ened, the tnuis-
mitting circuit should l>e closed,
and the receiving circuit should lie
connected to the line. Tliese re-
sults are accomplished autumati-
cally liy means of the switch-hook
uiMin wliich the n-ceiver is hung.
This hiM)k is depi-esscd when the
I'oceiver is in place, and miseil hy a
spring when it, is ivincivcfl. In this
maimer the desired cmmections are
maile at the ptujter time.
Thei-e are two types of tele-
phone, differing simiewhat in the
detiiils of their construction and
cininections, known as the series
telephone and tlie hriilged tele-
plu.ne. ^'''- ^'*-
The circuits of a series telephone are shown in Fig. 40. A
and B are the line terminals, and the ground connecti<m for
tlie lightning arrester. When the receiver is im the hook the
switch is in the position shown. The genemtor <i and ringer I)
are in series across the line, through contact point 1, the gen-
emtor l)eing antiimatically cut out hy the shunt E, when not in
use. When the receiver is n'nioved, the contact at 1 is hii>keii,
and contact is made at ix)int'» '2 and 3. The primary circuit is
then closed on itselt while tlie secondary circuit, <;oiitJniiing the
receiver and secondary of the induction coil, is cut in un the line.
62
ELEMENTS OF ELECTRICITY.
Below there are three pairs of binding posts, to one pair of
which the receiver R is connected, to another are connected the
terminals of the primary circuit containing the transmitter T, tlie
battery B, and primary P of the induction coil, while the second-
ary S of the induction coil is connected to the third pair.
Connection is made tf) tlie bell through the hinges of the
box upon the door of Nvhich it is mounted. It is customary to
use a ringer of 80 to 120 ohms resistance with series telephones.
On account of this low resistiince many "Series telephones eannnt
be bridged because it would be impossible to ring a numl)ei of
them in multiple. Moreover, many series telephones could not
be connected in series, because,
since all the ringers would be con-
stantly in the circuit, it would be
impossible to talk through them.
I G : p ^ Hence this type of telephone is
p 11 II J J Y used almost exclusively for city ex-
change work, not more than two
telephones being connected on a
line.
(h ^ (^ 65 — S i^ '^'^^ circuits of the bridged tel-
U J >S^ ephone are shown in Fig. 41. The
ringer coils ai*e permanently bridged
across the line. The generator is
also bridged, the circuit through it
being open when it is not in use,
but l)eing closed, usually automati-
^^' ' cally, when the genenitor is in oper-
ation. When tlie receiver is taken from the hook, contact is
made at points 1 and 2 for the primarv and secondary circuits as
in tlie series telephone.
The i:)ermanently bridged ringer does not interfere with the
action of the receiving circuit, since its coils have a resistance of
about IGOO ohms, and are wound so that their self-induction is
large. Thus they offer a high impedance to the currents in the
receiving circuit liecause of the extreme rapidity with which they
alternate. For tliis reason a number of these telephones can be
bridged upon one circuit, thus forming a party line.
60
KLKMENTS OF ELECTRU^ITY. 53
There are three general methods of constructing lines, namely,
the grounded circuit, the metallic circuit, and the common retuni.
In the connnon retuni the circuit is completed through a copper
wire instead of through the ground as in the grounded system,
thus eliminating the noise induced by earth currents.
61
THE ELECTRIC CURRENT.
Electromotive Force. When a difference of electrical poten-
tial exists between two i)oints, there is said to exist an electrO'
motive force^ or tendency to cause a current to flow from one point
to the other. In tlie voltaic cell one plate is at a different potential
from the other, which gives rise to an ehnrtromotive force between
them. Also in the induction coil, an electromotive force is created
in the secondary circuit caused by the action of the primary. This
electromotive force is analogous to the pressure^ caused by a dif-
ference in level of two lx)dies of water connected by a pipe. The
pressure tends to force the water through the pipe, and the
electromotive force tends to cause an electric current to flow.
The terms potential difference and electromotive force are
commonly used with the same meaning, but strictly speaking the
potential difference gives rise to the electromotive force. Electro-
motive force is commonly designated by the letters U. M. F. or
Bimply U. It is also referred to as pressure or voltage.
Current. A current of electricity flo\vs when two points, at
a difference of potential, are connected by a ^vire, or when the
circuit is otherwise completed. Similarly water flows from a high
level to a lower one, when a path is provided. In either case the
flow can take place only when the path exists. Hence to produce
a current it is necessary to have an electromotive force and a closed
circuit. The current continues to flow only as long as the electro-
motive force and closed circuit exist.
The strength of a current in a conductor is defined as the
^antity of electricity which passes any point in the circuit in a
unit of time.
Current is sometimes designated by the letter C, but the
letter /will be used for current througliout this and following
sections. The latter symbol was recommended by the Interna-
tional Electrical Congress held at Chicago in 1893, and has since
been universally adopted.
G3
THE ELECTlilC CUKKENT.
Resistance. Resistance is that property of matter in virtue
of which bodies oppose or resist the free flow of electricity. Water
passes with difficulty through a small pipe of great length or
through a pipe filled with stones or sand, but very readily through
a large clear pipe of sliort length. Likewise a small wire of con-
siderable length and made of poor conducting material offers gi-eat
resistance to the passage of electricity, but a good conductor of
si Drt length and large cross section offers very little resistance.
P^sistance is designated by the letter R.
Volt, Amipere and Ohm. The volt is the practical unit of
electromotive force.
The ampere is the practical unit of cuiTent.
The ohm is the practical unit of resistance. The microhm is
one milliontli of an ohm and the mejjohm is one million ghms.
The standard values of the above units were very accurately
determined by the International Electrical Congress in 1893, and
are as follows :
The International ohm, or true ohm, as nearly as known, is
tlie resistance of a uniform column of mercury 106.3 centimeters
long and 14.4521 grams in mass, at the temperatui'e of melting
ice.
The ami>ere is Uie strength of current which, when passed
through a solution of silver nitrate, under suitable conditions,
deposits silver at the rate of .001118 gram per second. Current
strength may be very accurately determined by electrolysis, and
it is used therefore in determining the standard unit.
The volt is equal to the E. M. F. which, when applied to a
conductor having a resistance of one ohm, will produce in it a
current of one ampere. One volt equals \i^^\ of the E. M. F. of
a Clark standard cell at 16° Centigrade.
RESISTANCE-
All substances resist the passage of electricity, but the resist-
ance offered by some is very much greater than that offered by
others. Metals have by far the least resistance and of these, silver
possesses the least of any. In other words, silver is the best con-
ductor. If the temperature remains the same, the resistance of ^
^\
THE ELECTRIC CURRENT.
conductor is not affected by the current passing through it. A
current of ten, twenty or any number of amperes may pass through
a circuit, but its resistance will be unchanged with constant tem-
perature. Resistance is affected by the temperature and also by
the degree of hardness. Annealing decreases the resistance of a
metal.
Conductance is the inverse of resistance ; that is, if a conduc-
tor has a resistance of R ohms, its conductance is equal to — .
^ R
Resistance Proportional to Length. The resistance of a
conductor is directly proportional to its length. Hence, if the
length of a conductor is doubled, the resistance is doubled, or if
the length is divided, say into three equal parts, then the resist-
ance of each part is one third the total resistance.
Example. — The resistance of 1288 feet of a certain wii-e is
6.9 ohms. What is the resistance of 142 feet of the same wire ?
Solution. — As the resistance is directly proportional to the
length we have the proportion,
required resistance : 6.9 : : 142 : 1283
required resistance 142
or.
6.9 1283
142
Hence^ required resistance = 6.9 X
1283
= .76 ohm (approx.)
Ans. .76 ohm.
Example. — The resistance of a wire having a lenj^th of 521
feet is .11 ohm. What length of the same wire will have a
resistance of .18 ohm?
Solution. — As the resistance is proportional to length, we
have the proportion,
required length : 521 : : .18 : .11
required length .18
or
521 .11
18
Hence, required length = 521 X - ---
^ 852 feet (approx.)
Ans. 852 feet.
05
THE ELKCTRIC CURRENT.
RMisUnce Invendy PropofftkMial to Crau-Sectioii. The
tenistance of a condactor is inTerselj pit^XMtioDal to its crasfr«ec-
tional area. Hence the greater the cross-section of a wire the less
is its resistance. Therefore, if two wires have the same length,
hot one has a cross-section three times that of the other, the
resistance of the former is one-third that of the latter.
Example. — The ratio of the cross-sectional area of one wirt
257
to that of another of the same lencfth and material is til — The
^ 101
resistance of the former is 16.3 ohms. What is the resistance of
the latter ?
Solution. — A» the resistances are inversely proportional to
the crofis-fiections, the smaller wire has the greater resistance, and
we have the proportion : -
required resist. : 16.3 : : 257 : 101
required resist. 257
^^^ W& 101
Hence, required resist. = 16.3 X — =-
^ 101
= 41.5 ohms (approx.)
Ans. 41.5 ohms.
Example. — If the resistance of a wire of a certain length
and having a cross-sectional area of .0083 square inch is 1.7 ohms,
what would be its resistance if the area of its cross-section were
.092 square inch ?
Solution. — Since increasing the cross-sectional area of a wire
decreases its resistance, we have the proportion,
required resist. : 1.7 : : .0083 : .092
required resist. _ .0083
1.7 ' .092
Henoe^ required resist. = 1.7 X *
= .15 ohm (approx.)
Ans. .15 ohm.
As the area of a circle is proportional to the square of its
diameter, it follows that the resistances of round conductors are
inversely proportional to the squares of their diameters.
Example. — The resistance of a certain wire having a diam.
iWi
THE ELECTRIC CURRENT.
eter of .1 inch is 12.6 ohms. What would be its resistance if the
diameter were increased to .32 inch ?
Solution. — The resistances being inversely proportional to
the squares of the diametei-s, we have,
required resbt. : 12.6 : : .1^ : .32*
required resist. _ .1^
12:6 ^M^^
car.
1 2
Hence, required resist. = 12.6 X --%.—
_ 12.6 X .01
^.1624~
=1.23 ohms (approx.)
Aus. 1.23 ohms.
Specific Resistance. The specific resistance of a substance
is the resistance of a portion of that substance of unit length and
unit cross-section at a standard tempeniture. The unit commonly
used is the centimeter or inch, and the tempeniture that of melting
ice. The specific i-esistance may therefore be said to be the
resistance (usually stated in microhms) of a centimeter cube or
inch cube at the temperature of melting ice. If the specific
resistances of two substances ai-e known then their relative resist-
ance is given by the ratio of the specific resistances.
Conductivity is the reciprocal of specific resistance.
Example. — A certain copper wire at the temperature of
melting ice has a resistance of 29.7 ohms. Its specific resistance
(resistance of 1 centimeter cube in microhms) is 1.594, and that of
platinum is 9.032. What would be the resistance of a platinum
wire of the same size and length of the copper wire, and at the
same temperature ?
Solution. — The resistance would be in direct ratio of the
specific resistances, and we have the proportion :
required resist. : 29,7 : : 9.032 : 1.594
Hence, required resist. =29.7 X ' ' "j *
= 168. ohms (approx.)
Ans. 168. ohms.
Calculation of Resistance. From the preceding pages it is
evident that resistance varies directly as the lengthy inversely as
87
THE ELECTRIC CURRENT.
the cross-eectional area, and depends upon the 8|)eeific resistance
of the materiaL This may be expressed conveuiently by the
formula,
A
in which R is the resistance, L the length of the conductor, A the
area of its cross section, and s the specific resistance of the
material.
Example. — A telegmph relay is wound with 1.800 feet of
wire .010 inch in diameter, vii>d has a resistance of 150 ohms.
What Avill be its resistance i{ wound with 400 feet of wire .022
inch ill diameter?
Solution. — If the wires were of equal length, we should
have the proportion,
Kequired resisUnce : 150 : : (.010)* : (.022)'
or, Required resistance = 150 X ->7VooTi = 30.99-f ohms.
For a wire 400 feet long, we have, therefore, by direct proportion,
Required resistance = ^ ^a- X 30.99 = 6.88-|—
• i,oUU
Ans. 6.88+ ohms.
If a circuit is made up of several different materials joined in
series with each other, the resistance of the circuit is equal to the
sum of the resistances of its several parts. In calculating the
resistance of such a circuit, tlie resistance of each part should first
l)e calculated, and the sum of these resistances will be the total
resistance of the circuit.
The table on page 9 gives the resistance of chemically pure
substances at 0° Centigrade or 32° Falirenheit in International
ohms. The fii*st column of numbers gives the relative resistances
when that of annealed silver is taken as unity. For example, mer-
cury has f)2.73 times the resistance of annealed silver. The
second and third colunins give the resistances of a foot of wire
.001 inch in diameter, and of a meter of wire 1 millimeter in
diameter, respectively. The fourth and fifth columns give
respectively the resistance in microhms of a cubic inch and cubic
centimeter, that is, the specific resistances.
60
THE ELECTWC CURRENT.
9
Table ShoirlBS Reladve Rcsistaaca •! CkeafcaUy Pare Sabstaacec at
Thirty^two Degrees Fabreolieit la lateraatieaal Ohms.
m* — M. ^ •
RclBtWe
RcsUtance.
1
ReaUiance
of awire '
1 foot long.
4101 inch In
diameter.
9.023
Beaiaianee
of a wire
1 meter long,
1 millimeter
in diameter.
Bealatance in
Microhma.
itetai.
Cubic
Inch.
.5904
Cubic Cen
timeter.
Silver, annealed.
1.000
.01911
1.500
C upper, annealed.
1.063
9.585
.02028
.6274
1.594
Silver, hard drawn.
1.086
9.802
.02074
.6415
1.629
Copper, hard drawn.
1.086
9.803
.02075
.6415
1.629
Gold, annealed.
1.369
12.35
.02613
.8079
2.052
Gold, hard drawn.
1.393
12.56
.02661
.8224
2.088
Aluminum, annealed
1.935
17.48
.03700
1.144
2.904
Zinc, pressed.
3.741
33.76
.07143
2.209
5.610
Platinum, annealed.
6.022
54.34
.1150
3.555
9.082
Iron, annealed.
6.460
58.29
.1234
3.814
9.689
Lead, pressed.
13.05
117.7
.2491
7.706
19.58
German silver.
13.92
125.5
.2659
8.217
20.87
Platinum-silver alloy
{\ platinum, ^ silver.)
Mercury.
16.21
146.3
.3097
9.576
24.32
62.73
570.7
1.208
37.05
94.06
It should be noted that the resistances in the above table are
for chemically pure substances, and also at 32^ Fahrenheit. A
very small portion of foreign matter mixed with a metal greatly
increases its resistance. An alloy of two or more metals always
has a higher specific resistance than that of any of its constituents.
For example, the conductivity of silver mixed with 1.2 per cent
in volume of gold, will be 69 when that of pure silver is taken as
100. Annealing reduces the resistance of metals.
The following examples are given to illustrate the use of the
table above in connection with the formula at the top of page 8,
and to show the application of preceding laws.
Example. — From the specific resistance of annealed alu-
minum as given in the next to tlio last column of tlie table,
calculate the resistance given in the second column of figures for
that substance.
Solution. — The resistance in microhms of a cubic inch of
annealed aluminum at 32^ F. is 1.144, which is equal to
j(K)0Q01144 ohms. The resistance oi a wire 1 foot long ^nd .001
ee
10 THE ELECTRIC CURRENT.
inch in diameter is required. In the formula on page 8, we
have s = .000001144, Z. = 1 foot = 12 inches and
A = = — = .0000007804 sq. m.
4 4
Substituting these values in the formula,
J? ^
A
we have,
Jl = .000001144 X ^^
.0000007854
= 17.48 ohms. Ans. 17.48 ohms.
Example. — The resistance in microhms of a cubic centimeter
of annealed platinum at 32° F. is 9.032. What is the i-esistance
of a wire of tlie same substance one meter long and one millimeter
in diameter at the same temi>erature ?
Solution. — In the formula for resistance we have the quan-
tities s = 9.032 microhms = .000009032 olmis ; i = 1 meter =
100 centimeters ; and
J ird^ 3.1416X.12 ..n^Tfi^A
A = = — = .007854 sq. cm.
4 4
the diameter being equal to 1 millimeter = .1 cm.
Substituting these values we have,
n = .000009032 X _12L_
.007854
= .1150 ohms. Ans. .115 ohms.
Example. — From tlie table the resistance of 1 ft. of pure
annealed silver wire .001 inch in diameter at 32° F. is 9.023
ohms. What is the resistance of a mile of wire of the same sub-
stance .1 incli in diameter at that temperature?
Solution. — As the resistance of wires is directly proportional
to their length and inversely proportional to the squares of their
diameU»rs, the required resisttmce is found by multiplying the
resistance per foot by 5,280 and the product by the inverse
squares of the dianietei's.
Therefore 7/ = 9.023 X 5280 X j -^^- j "
= 4.76 ohms (approx.)
Ans. 4.76 ohms.
70
THE ELECTRIC CUliUENT. 11
Example. — A mile and one-half of an annealed wire of pure
^ron has a resistance of 46.1 ohms. What would be the resist*
ance of hard drawn wire of pure copper of the same length and
diameter, assuming each to be at the temperature of melting ice?
Solution. — The only factor involved by this example is the
relative resistance of the two metals. From the table, page 9,
annealed iron has 6.460 and hard-drawn copper 1.086 times the
resistance of annealed silver. Hence the resistance of the copper
is to that of the iron as 1.086 is to 6.460, and the required resist-
ance is
J2= 46.1 X ^^ = 7.75 ohms (approx.)
Ans. 7.75 ohms*
Example. — If the resistance of a wire 7,423 feet long is
18.7 ohms, what would be its resistance if its length were reduced
to 6,253 feet and its cross-section made one half again as large ?
Solution. — As resistance \a directly proportional to the
length, and inversely proportional to the area of the cross-section,
die required resistance is
It = 18.7 X ^|||x 1= 10.5 ohms (approx.)
Ans. 10.5 ohms.
Resistance Affected by Heatlnsr. The resistance of metals
depends upon the temperature, and the resistance is increased by
heating. The heating of some substances, among which is carbon,
causes a decrease in their resistance. The resistance of the
filament of an incandescent lamp when lighted is only about half
as great as when cold. All metals^ however, have their resistance
increased by a rise in temperature. The percentage increase in
resistance with rise of temperatui*e varies with the different
metals, and varies slightly for the same metal at different tem-
peratures. The increase is practically uniform for most metals
throughout a considerable range of temperature. The resistance
of copper increases about .4 per cent, per degree Centigrade, or
about .22 per cent, per degree Fahrenheit. The percentage
increase in resistance for alloys is much less than, for the simple
metals. Standard resistance coils are therefore made of alloys, as
it is desirable that their resistance should be as nearly constant as
possible.
71
12
THE ELECTRIC CUKRENT.
The change in resistance of one ohm per degree rise in tem-
perature for a substance is called the temperature coefficient for
that substance. The following table gives the tempemture coeffi-
cients for a few substances.
TEHPERATURE COEFFICIENTS.
BI8B IN B. OP 1 OHM WBBW HBATBD:
MATSBIAX..
1© P.
1® <;.
Platinoid
.00012
.00022
Platinum-silver
.00014
.00026
German silver
.00022
.00040 w
Platinum
.0019
.0035
SUver
.0021
.0038
Copper, aluminum
.0022
.0040
Iron
.0026
.0046
If the resistance of a conductor at a certain temperature is
known, the resistance the conductor will have at a higher tem-
perature may be found by multiplying the temperature coellicient
for the substance, by the number of degrees increase and by the
resistiiuce at the lower tem{)erature, and adding to this result the
resistance at the lower temperature. The product of the temj)er-
ature coefficient by tlie nuniljer of degives increase gives the in-
crease in resistance of one olmi tln'ough lliat nnnilxjr of degrees,
and multiplying this by the number of ohms gives the increase in
resiaUince for the conductor. The result obtiiined is pnu:tically
correct for moder.ite rjinges of tempei-ature.
The above method of calculating the resistance of conductors
at increased tenij^e ratines is conveniently expressed by the follow-
ing foi inula:
i2a = 7?i (1 + a t)
where K^ is the resistance at the higher temperature, /f ^ that at
the lower temperature, a the temperature coefficient for the sub-
stance and t the number of degrees change.
From the preceeding formula it follows that if the resistance
at the higlH»r tempemture is known, that at the lower tem^Hii-ature
will ue triven by the formula :
* 1 +af
72
THE ELECTRIC CURRENT. IS
In calculating resistanceR at different temperatures, the tern
perature coefficient l)ased on the Fahrenheit scale should be used
if the number of degrees change is given in degrees Fahrenheit*
and that based on the Centigrade t>eale if given in degrees
Centigrade.
Example. — The resistance of a coil of German silver wire at
12** C. is 1304 ohms. What would be its resistance at a temper-
ature of 60** C?
Solution. — From the statement of the example 2t^ = 1304,
t=60 — 12 = 48, and from the table page 12, a = .0004.
Substituting these values in the first of the preceding formulas we
have,
JKj = 1804 (1 + .0004 X 48)
= 1304 X 1.0192
Bs 1329 ohms (approx.)
Ans. 1329 ohms.
Example. — If the resistance of a copper conductor at 95** F.
IS 48.2 ohms, what would be the resistance of the sjiine conductor
at 10** F.?
Solution. — In this case B^ = 48.2, t = 9') — 40 = o6»
and from the table a = .0022. Substituting these values in the
formula at the foot of page 12, we have,
^ _ 48.2 ^ 48.2
^ ~" i +r:00"22 X ;'>•') 1.121
= 4^5. ohms (approx.)
Ans. 43 ohms*
The first table on page 14 gives the resistance of the most
common sizes of copper wire Jiccording to tlie American or Brown
and Sharpe (B. & S.) gsuige. The resistance given is for pure
cop[>er wire at a temperature of 7'>^ F. or 24** C.
The first column gives the inuul)er of the wire, the second
the diameter in thousandths of an inch or mils, and the third the
diameter in millimeters. The fourth column gives tlie equivalent
number of wires each one mil or one thousiiiulth of an inch in
diameter. This is called the size of the wire in circular mils and
is equal to the square of the diameter in mils. The fifth cohunn
gives the ohms j^er thousand feet and the n*sistance p(ir niihi is
found by multiplying these values by 5.28. Ordinary counnerciiul
73
14
THE ELECTRIC CURRENT.
copper has a conductivity of about 95 to 97 per cent, of that of
pure copper. The resistance of commercial wire is therefore about
8 to 6 per cent, greater than the values given in the table. The
resistance for any metal other than copper may be found by mul-
tiplying the resistance given in the table by the ratio of the spec-
ific resistance of the given metal to the specific resistance of
copper.
American Wire Gauge (B. & 5.)
No.
Diameter in
Oiroalar
Mils.
Ohms
1000 Pi.
No.
Diameter in
Circular
Mils.
Ohma
Mils.
MUlim.
Mils.
MiUim.
lOfoPt.
0000
460.00
11.684
211600.0
.051
19
85.89
M2
1288.0
8.817
000
409.64
10.405
167805.0
.064
20
81.96
.812
1081.6
10.566
00
864.80
9.266
133079.4
.081
21
28.46
.723
810.1
1S4B3
824.05
8.254
105592.5
.102
22
25.85
.644
642.7
16.789
1
289.80
7.348
83694.2
.129
23
22.57
.578
609US
21.185
2
257.63
6.544
66373.0
.163
24
20.10
.611
404.0
86.713
8
229.42
5.827
52634.0
.205
26
17.90
.466
820.4
83.684
4
204.31
5.189
41742.0
.258
26
15.94
.406
864.0
42.477
6
181.94
4.621
33102.0
.826
27
14.19
.861
801US
68.668
6
162.02
4.115
26250.5
.411
28
12.64
.821
160.8
67.542
7
144.28
3.665
20816.0
.519
29
11.26
.286
196.7
85.170
8
128.49
3.264
16509.0
.654
80
10.03
.256
100.6
107.891
9
114.48
2.907
18094.0
.824
81
8.93
.227
79.7
185.4liS
10
101.89
2.588
10381.0
1.040
83
7.95
.202
68.2
170.765
U
90.74
2.805
8234.0
1.311
88
7.08
.180
60.1
215.818
18
80.81
2.053
6529.9
1.653
84
6.80
.160
80.7
871.668
18
71.96
1.828
5178.4
2.084
85
5.61
.148
81US
848.448
14
64.08
1.628
4106.8
2.628
86
6.00
.127
86.0
481.712
15
67.07
1.450
3256.7
3.314
87
4.45
.118
19.8
544.887
16
60.ra
1.291
2582.9
4.179
38
8.96
.101
16.7
686.511
17
45.26
1.160
2048.2
5.269
89
3.53
.090
12.6
865.046
18
40.80
1.024
1624.1
6.645
40
3.14
.080
9.9
1001.866
The following table gives the size of the English or Birming-
ham wire gauge. The H. & S. is however much more frequently
used in this country. The Brown and Sharpe gauge is a little
amaller than the Birmingham for corresponding numbers.
5tubs' or Birmingham Wire Gauge (B. W. Q.)
Mo.
Diameter in
No.
Diameter in
No.
Diameter in
Mils.
MiUim.
Mils.
9
Milllm.
Mils.
Millim.
0000
00
1
4
6
454
380
300
238
203
11.53
9.65
7.G2
6.04
6.16
8
10
12
14
16
165
134
109
83
65
4.19
3.40
2.77
2.11
1.65
18
20
24
SO
36
49
35
22
12
4
1.24
0.89
0.56
0.31
0.10
74
,TO.DB|«r21^
THE ELECTRIC CURRENT. 15
BXAflPLES FOR PRACTICE.
1. What is the resistance of an annealed silver wire 90 feet
long and .2 inch in diameter at 32° F.? Ans. .02+ ohm.
2. What is the resistance of 300 meters of annealed iron
wire 4 millimeters in diameter when at a temperature of O*' C?
Ans. 2.31+ ohms.
3. What in the resistance of 2 miles of No. 27 (B. & S.) pure
copp<»r wire at 75° F.? Ans. 565.+ ohms.
4. The resistance of a piece of copper wire at 32°F. is 3
ohms. What is its i-esistance at 49°F.? Ans. 3.11+ ohms.
5. The resistance of a copi^er wire at 52°F. is 7 ohms.
What is its resistance at 32°F.? Ans. 6.70+ ohms.
6. What is the resistance of 496 ft. of No. 10 (B. & S.)
pure copper wire at 45°F.? Ans. .483+ ohms.
On pages 16 and 17 is given a tiible disclasing among other
data the resistance of various primary cells. The resistance of a
circuit of which a battery forms a part> is made up of the external
resistance, or the resistance of outside wires and connections, and
the internal resistance, or the resistance of the battery itself.
The table referred to gives in the fii-st column the name of the
cell. In the second and third column a» pears the name of the
anode and kathode respectively. These terms are commonly
used with reference to electrolysis but may also be applied to
primary cells. The cuiTcnt passes f"'om the anode to the kathode
through the cell, and therefore wi i reference to the cell itself,
tlie anode may be considered the 2>ositive element and the kath-
ode the negative element. In regard to the outside circuit how-
ever, the current passes of course, from the kathode to the anode,
and hence with reference to the outside circuit the kathode is
positive and the anode negative ; ordinarily the external circuit
is considered. As the anode of almost all primaiy cells is zinc it
may readily be remembered that the current i)iisses from the other
element to the zinc through the external circuit. The fourth and
fifth columns of the table give the excitant and depolarizer respec-
tively. The sixth column gives the K. M. F. of each cell when H
is supplying no current, and the last cohnnn gives the internal
resistance in ohms.
76
le
THE ELECTKIC CURUENT.
TABLE IN RELATION TO PRIHARY CELLS, ELECTRO-
nOTIVE FORCE. RESISTANCE, ETC.
NAMB
OP
CELL.
ANODB.
KATHODB.
BZOXTANT.
DBPOLARISBB.
B. M. F.
IN
▼OLTS.
XITTBRNAL.
BB8I8T-
▲MCB IN
OBMB.
Volta
(WollM-
ton, etc.)
Smee
Law
Poggen-
dorff
(Grenet)
Poggen-
dorff
(Orenet)
two fluid
Grove
Bunseu
Leclanche
Lalande
Lalande—
Chaperou
Upward
ntch
Papst
Obach
(dry;
Daniell
(Meidin-
ger Min-
otto, etc.)
^e la Rue
Marie
Davy
Clark
Standard)
Weston
Zinc
Zinc
Zinc
Ziuc
Ziuc
Zinc
Zinc
Zinc
Zinc
Zinc
Zinc
Iron
Zinc
Zinc
Zinc
Zinc
Zinc
Cadmium
Copper
Platinized
Silver
Carbon
Graphite
(Carbon)
Graphite
(Carbon)
Platinum
Graphite
(Carbon)
Graphite
(Carbon)
(iraphite
(Carbon)
Graphite
(Carbon)
Graphite
(Carbon)
Graphite
(Carbon)
Graphite
(Carbon)
Copper
Silver
Graphite
(Carbon)
Mercury
Mercury
Solution of
Sulphuric Acid
(H, 8O4)
Solution of
Sulphuric Acid
(H, SO J
Solution of
Sulphuric Acid
(H, SOJ
Solution of
Sulphuric Acid
(H, SO J
Saturated Solu-
tion of Potas-
sium Dichro-
mate and
Sulphuric Acid
Sulphuric Acid
dilute (H. SO«)
Sulphuric Acid
dilute (HsSO«)
Ammonium
Chloride
(NH4 CI;
Caustic Potash
or Potassium
Hydrate (KOH)
Zinc Chloride
(ZnCl,)
Ammonium
Chloride
(NH, CI)
Ferric Chloride
(Fe, CI.)
Ammonium
Chloride
(NH4CI) in
Calcium Sul-
phate (CaSO«)
Zinc Sulphate
(Zn S6«)
Ammonium
Chloride
Sulphuric Acid
dilute (H. SO«)
Zinc Sulphate
(ZnSo«)
Cadmium Sul-
phate (CdSO^)
None
Nose
None
Potassium
Bichromate
(K, Cr, 0,>
None
Separate
Nitric Acid
(HNO,)
Ni tric Ac id
Chromic Acid
Manganese
Dioxide
(MnO,)
Cupric Oxide
Chlorine (CI)
Sodium & Potas-
sium Chlorates
(NaClOs-f
K CIO.)
(Fe, CI.)
Manganese
Dioxide
(MnO.)
Copper Sul-
phate (Cu SO«)
Silver Chloride
(Ag CI)
Paste of Sulph-
ate of Mercury
(Hg, SO4)
Mercurous Sul-
phate (Hga SO«)
Mercurous Sul-
phate (Hg, SO«)
lto05
ItoO^
ltoOU»
2.1
1.98
1.96
1.8 to 1.98
1.8
1.4 to 1.6
OA
0.8 to 0.98
2.0
1.1
0.4
1.46
1.079
1.08 to
1.42
1.62
1.484*
IM5
.00110 4)6
0.1 to 0.12
0.08 to 0.11
^.j_to0.12
1.13 to 1.1:
14
StoB
0.4toOj6
0.75 to 1
OJtoOJI
7e
Hie electric current.
ir
VAMB
OF
OSUU
A»ODl
KATHODE.
KZOITAHT.
DBPOI^RIBBa.
B. M. r.
IM
YOLTS.
XirrBBHAA
AKCB IB
OHMS,
Von
HelmholU
Chromic
Acid
single
fluid
Fuller
Gaiffe
Maiche
NiBQdet
Schana-
chieff
Skrivmnoff
Zinc
Zinc
Zinc
Zlno
Zfnc
flcrapa in
bath of
Mercury
Zinc
Zinc
Zinc
Mercury
Graphite
(Carbon)
Graphite
(Carbon)
SilTer
Platinized
Carbon
Graphite
(Carbon)
Graphite
(Carbon)
Silver
Zfnc Chloride
(Zn CI,)
Sulphuric and
Chromic Acids.
dilute mixed
Sulphuric Add
(H, SO J
Zinc Chloride
(Zn Cl,i
Common Salt
Solution t. e.
Sodium Chlo-
ride (NaCl)
Common Salt
Solution i. e.
Sodium Chlo-
ride (NaCl)
Mercurial
Solution
Caustic Potash
or Potassium
Hydrate (KOH)
Merourons
Chloride
(Hg. CM
None
Separate
Potassium
Dichromate
(K, Cr, O,)
Silver Chloride
(Ag CI)
None
Separate
Chloride of
Calcium
(Lime)
(Ca CI.)
None
Separate
Chloride of
Silver
(AgCl)
i.a
%A
1.0 to 1.6
1.S6
1^
JOUtoXS
OJStoO.7
ttot
6toe
0.06 to 0.78
1.6
* At 15 degrees Centigrade or 59 degrees Fahrenheit.
Resistances in last column measured in cells standing 6'^ X ^'*
onrvs LAW.
One of the most important and most used laws of electri-
city is that first formulated by Dr. G. S. Ohm^ and known as
Ohm's law. This law is as follows :
Ihe current is directly proportional to the electromotive force
and inversely proportional to the resistance.
That is, if the electromotive force applied to a cii^cuit is in-
creased, the current will be increased in the same proportion, and
if the resistance of a circuit is increased then the current will t)e
decreased proj)ortionally. Likewise a decrease in the electromotive
ror(*.e causes a propoi-tional decrease in current and a decrease in
resistance causes a propoitional increase in current. The current
depends only upon the electromotive force and resistance and in
the manner expressed by the above simple law. The Hw may be
expressed algebraically as follows :
current vanes as
el'^ctromotive force
resistance
• 77
18 THE ELECTRIC CtJRRENT.
The tmits of these quantities, the ampere, volt and ohm, have
been so chosen that an electromotive force of 1 volt applied to a
resistance of 1 ohm, causes 1 ampere of current to flow. Ohm's
law mav therefore be expressed by the following equation:
It
where lis the current in amperes, JS the electromotive force in
volts and H the resistance in ohms.
It is therefore evident, that if the electromotive force and
resistance are known the current may be found, or if any two of
the three quantities are known the third may be found. If the
current and resistance are known the electromotive force may be
found from the formula:
JB=IiI
and if the current and electromotive force are known, the resist-
ance may be found fit>m the formula:
Simple Applications. The following examples are given to
illustrate the simplest applications of Ohm's law.
Example. — If the E.M .F. applied to a circuit is 4 volts and
its resistance is 2 ohms, what current will flow?
Solution. — By the formula for current,
IwB — .ss— = 2 ampevea.
Ans. 2 amperes.
Example. — What voltage is necessary to cause a current of
28 amperes to flow through a resistance of 820 ohms?
Solution. — By the formula for E.M.F.,
JB=: RI= 820 X 28 = 18,860 volts.
Ans. 18,860 volts.
Example. — The E.M.F. applied to a circuit is 110 volts, and
it is desired to obtain a current of .6 ampere. What should ba
the resistance of the circuit?
Solution* — By the formula for resistance.
Ji = -J^= ^ =^ 188.+ ohms.
Ana 183 ohnu.
7S
THE ELECTRIC CURRENT. 19
Series Circuits. A circuit made up of sevei-al parts all
joined in series with each other, is called a series cii'cuit and the
resistance of the entire circuit is of course the sum of the separate
resistances. In calculating the current in such a circuit the
total resistance must first be obtained, and the current may then
be found by dividing the applied or total E.M.F. by the total
resistance. This is expressed by the formula,
j= I
Example. — Three resistance coils are connected in series with
each other and have a resistance of 8, 4 and 17 ohms respectively.
What current will flow if the E.M.F. of the circuit is 54 volts?
Solution. — By the preceding formula,
^=-^7+-^— +"^7^ 8 + 4 + n ^ 2g = 1.8+amperes.
Ans, 1.8+ amperes.
Example. — Six arc lamps, each having a resistance of 6
ohms, are connected in series with each other and the resistance
of the connecting wires and other aj)paratiis is 3.7 ohms. What
must be the pressure of the circuit to give a desired current of 9.6
amperes ?
Solution. — Tlie total resistance of the circuit is 7^ = (6 X 5)
-}- 3.7 = 33.7 ohms and the current is to l)e /= 9.G am{)ereB.
Hence by the formula for E.M.F.,
E=ni= 33.7 X 9.6 = 323.+ volts.
Ans. 323.+ volts.
Example. — The current passing in a certain circuit was 12
amperes and the E.M.F. was 743 volts. The circuit was made up
of 4 sections all coimected in series, and the resistance of tlnee
sections was 16, 9 and 26 ohms respectively. What was the
resistance of the fourtli section ?
Solution. — Let a; = the resistance of the fourtli section, then
^ =. 16 + 9 + 26 + J? =- 51 + 2r, / = 12, and E = 742. By
the formula for resistancie,
il =s _. or, 61 + a: — "Y^— 61.9 ohms (approx.)
79
20 THE ELECTRIC CURRENT.
If 51 + a; = 61.9 we have, by transposing 51 to the other
aide of the equation,
X = 61.9 — 51 = 10.9 ohms.
Ans. 10.9 ohms.
Example. — A curi-ent of 54 am{)eres flowed through a circuit
when the E.M.F. wjis 220 volts. What resistiince sliould Ije
added in series with the circuit to reduce the current to 19
amperes ?
Solution. — The resistance in the first case was,
220
7i = '^-^ =L 4.07 oluns (approx.)
The resistance in the second must be,
220
Ji = ^- = 11.58 ohms (approx.)
Tlie icipiircd resistance to insert in tlie circuit is tlie diflfer-
ence of these two resistances, or 11.58 — 4.07 = 7.51 ohms.
Ans. 7.51 ohms.
Fall of Potential in a Circuit. Fi^. 1 illustrates a series
circuit in whicli the resistances A^ -B, (7, D and U are connected
in series with cacli otlier and with the source of electricity.
If the K. M. F. is known, the curnMit may be found by divid-
ing the K. i\l. F. by tlie sum of all the resistiuices. Ohm's law
may, however, l)e a])plied to any part of a circuit se[>arately,
as well iis to tlie complete circuit. Suppose the resistances of
Ay -B, f, J> and 7? are 4, i^ <>, o and 4 ohms respectively, and
assume that the source has no resistance. Suppose the current
flowing to be 12 amperes. The K. M. F. necessary to force a
current of 12 anii)eres through the resistan(!c A of 4 ohms is, by
applying Ohm's law, (^(pial to JP=7r/— 4X 1 2 =: 48 volts.
Hence between the points a and h outside of the resistance -4,
there must be a difference of potential of 48 volts to force the
current through this resistance. Also to forcii the same current
through By the voltagt^ necessary is *> X 12 = 3*>. Similarly, for
each part (7, J) md /?, there are nnpiired 72, 36 and 48 volts
respectively.
As 48 volts are necessary for part A and 30 volts for i^irt J?,
it is evident that to force the current through both part^ a differ-
ence of potential of 48 + 3t) i^ 84 volts is required ; that is, the
TO
THE ELECTRIC CURRENT. 21
voltage between the points a and c must be 84 volts. For the
three parts A^ B and (7, 48 + 36 + 72 = 156 volts are necessary,
and for the entire circuit, 240 volts must be applied to give the
current of 12 amperes. From the above it is evident that there
is a gradual fall of potential throughout the circuit, and if the
voltage between any two points of the circuit be measured, the
E. M. F. obtained would depend upon the resistance included
between these two points. For example, the voltage between
points h and d would l)e found to be 72 -|- 36 = 108 volts, or
between d and e 36, volts, etc. From the pi-eceding it is apparent
that the fall of potential in a part of a circuit is equal to the
cujTent nmltiplied by the resistance of that part.
« E f .1 a A U
^/WVAAA— H| v^AAAA/^
AAAAAAAAA-— — —
« C ^
Fig. 1.
- This gradual fall of potential, or drop as it is commonly
called, throughout a circuit, enters into the ciilculations for the
size of conductoi-s or maiiLs supplying current to distant points.
The resistances of the conductors cause a cei-tain drop in trans-
mitting the current, dei)ending upon their size and length, and it
is therefore necessary that the voltage of machines at the supply
station shall be great enough to give the voltage necessary at the
receiving stations as well as the additional voltage lost in the
conducting mains.
For example, in Fig. 1 the voltage necessary between the
IK)int8 e and b is 144 volts, but to give this voltage the source
must supply in addition the voltage lost in parts A and Ey which
equals 96 volts.
Example. — ^The voltage required by 17 arc lamps connected
in series is 782 volts and the current is 6.6 amperes. The res'
81
22 THE ELECTRIC CURRENT.
ance of the connecting wires is 7 ohms. What must be the
E. M. F. applied to the circuit?
Solution. — The drop in the connecting wires is J? = 72/:=
7 X 6.6 = 46.2 volts. The E. M. F. necessary is therefore 782
4- 46.2 = 828.2 volts. Ans. 828.2 volts.
Example. — The source of E. M. F. supplies 114 volts to a
circuit made up of incandescent lamps and conducting wires.
The lam2)S require a voltage of 110 at their terminals, and take a
current of 12 am2)er(3S. What should be; llie resistance of the
conducting wires in order that the lamps will receive the necessary
voltage ?
Solution. — The allowable drop in the conducting wires b
114 — 110 = 4 volts. The current to pass through the wires is
12 amperes. Hence the resistance must be
^ = 5 = A- = -33 + ohms.
/ 12 ^
Ans. .88 -{- onms.
Divided Circuits. When a circuit divides into two or more
parts, it is called a divided circuit and each part will transmit a
portion of the current.
Such a circuit is illustrated in Fig. 2, the two branches being
represented by h and c. The current passes from the positive
l)ole of the battery througli a and then divides ; part of the
current passing througli h and part through c. The current then
unites ai;d ])assps through d to the negative pole of the battery.
The part c may bo considered Jis the main part of the circuit and
b as a by-pass about it. A branch
which serves as a by-pass to an-
other circuit is called a shunt
circuit, and the two branches are
said to be connected in parallel.
In considering the passage
^
-h
Fij:. 2. of a current through a circuit of
this sort, it may l)c necessary to determine liow much curient
will pass througli one branch and how much through the other.
Evidently this will depend upon the relative resistance of the two
branches, and more current will pass through the bmnch offering
the lesser resistance than thi-ou^^h the branch having the higher
82
THE ELECTUIC CUKKENT. 88
resistance. If the two parts have equal resistances, then one half
of the total current will pass througli each branch. If one branch
has twice the resistance of the other, then only one-half as much
of the total current will pass through that branch as through the
other ; that is, ^ of the total current will pass through the first
branch and the remaining | will pass through the second.
T/ie relative streuf/th of current in the (wo branches will he
inversely proportional to their renistancesy or directly proportional
to their conductancen.
SupiKJse the resistance of one bi-ancli of a divided circuit is
r^ (see Fig. 3), and that of the other is r^. Then by the pre-
ceding law,
current in r^ : current in r^ : : r^ : r^
Also,
current in r^ : total cun-ent : 2 r^ : r^ + ^i
and
curi-ent in r^ : total cun-ent : \ r^ • ^1 "f" ''2
Let /represent tlio toUil current, /^ tlie nirreiit through the
resistance r^ and /o the cun*ent tlii*ough the resistjince r^. Then
the two preceding proportions are expressed by the following
formulas :
»i = ~-^— and i^ = ^
Example. — The total current passing in a circuit \a 24
amperes. The circuit divides into two branches having resist-
ances of 5 and 7 ohms resi)ectively. What is the current in each
branch ?
Solution. — In this case /= 24, r^ = 5 and r.^ = 7. Sub-
stituting these values in the above formulas we have,
7ro 24 X 7 . .
tj = ?— = _ — _- = 14 amperes.
Tj + ''2 4" 7
and t« = ^ — = ^1 = 10 amperes.
* r^+ra 5 + 7
* ( In 5 ohm branch, 14 amperes.
* J In 7 ohm branch, 10 ampei-es.
Joint Resistance of Divided Circuits. As a divided circuit
83
24 THE ELECTRIC CUURENT.
offers two paths to the current, it follows that the joint resistance
of the two branches will be less than the resistance of either branch
alone. The ability of a circuit to conduct electricity is repre-
sented by its conductance, which is the reciprocal of resistance ;
and the conductance of a divided circuit is equal to the sum of
the conductances of its parts.
For example, in Fig. 3, the conductance of the upper bi*anch
equals — and that of the lower branch equals — . If R repre-
sents the joint resistance of the two parts then the joint conduct-
ance equals:
1 =^ JL + JL = '•i + ''2
B r^ r^ r^r^
Having thus obtained the joint conductance, the joint resist-
ance is found by taking the i*eciprocal of the conductance, that is«
R=-l±ll.
r^+r
2
This fornmla may be stated as follows :
The joint resistancfi of a divided circuit is equal to tlie product
qf tlie two separate resistances divided by their sum.
For example, suppose the resistance of each bi-auch to be
2 ohms. The conductance of the circuit will be,
— ==__ + _ ^ = 1, and hence iJ = 1 ohm*
Also by the preceding formula,
2 + 2
The resistance of a divided circuit in which each branch has
a i*esistance of 2 ohms is therefore 1 ohm.
Example. — The resistances of two separate conductors ai-e 8
M
THE ELECTRIC CUKRENT. S&
and 7 ohms respectivelj. What would be their joint resistance
if connected in parallel ?
Solution. — ^In this case r| ^ 3 and r^ = 7, hence bj the
formula,
B =s ^ ^ * = 2.1 ohms. Ans. 2.1 ohms.
3 + 7
Suppose, as illustrated in Fig. 4, the conducton> having
resistances equal to r^^ r^ and r.^ res|)ectively, are connected in
parallel. Tlie joint total condiietance will then lie equal to,
i_ = J-+JL + JL=''2^3+''i '■^ +''1 ''«
R ri r^ rg r^ r^ r^
and as tlie joint resistance is the recipnx^al of the joint conduct^
ance, the joint resistance R of the three branches is expressed by
the formula.
Example. — What is the joint resistance wlien connected in
pamllel, of three wires whose i-esiiective resistances are 41, 52 and
29 ohms resi)ectively ?
Solution. — In this case r^ = 41, r.^ = 52 and r^ ^ 29.
Hence, by the preceding fornmla,
R=z il_>^j:'r_>< -'^ = 12.X+ohms.
52 X 29 + 41 X 29 + 41 X 52 ^
Ans. 12.8 + ohms.
In general, for any nunil)er of contluctoi*s connected in
parallel, the joint resistance is found by taking the reciprocal oi
the sum of tHe reciprocals of the separate resistances.
Example. — A circuit is made up of five wires connected in
parallel, and their separate resistances are respectively 12, 21, 28,
8 and 42 ohms. What is the joint resistance?
85
26 THE ELECTRIC CURRENT.
Solution. — ^The eum of the conductances is:
12 ^ 21 ^ 28 ^ 8 ^ 42 iS8
Hence the joint resistance equals :
It = ---- = 3.1 + ohms. Ans. 8.1 + ohms.
53
If the resistance of each branch is known and also the poten-
tial difference between the points of union, then the current in
each branch may be found by applying Ohm's law to each branch
separately. For example, if this potential difference were 96
volts, and the separate resistances of the 4 branches were 8, 24, 3
and 48 ohms respectively, then the current in the respective
branches would be 12, 4, 32 and 2 amperes respectively.
If the current in each branch is known and also the poten-
tial difference Ix^tweeii the points of union, then the resistance of
each branch may likewise bt* found from Ohm's law.
The following examples are given to illustrate the applica-
tion of the preceding principles.
EXAMPLES FOR PRACTICE.
1. Two conductors having resistances of 71 and 19 ohms
respectively are connected in parallel, and the toted current pass-
ing in the circuit is S7 amperes. What current passes in the
conductor whose resistiince is 71 ohms? Ans. 7.8 -}- amperes.
2. What IS the joint resistance of two wires connected in
parallel if their separate resistances are 2 and 8 ohms respectively?
•
Ans. 1.6 ohms.
3. What is the joint resisbince of three wires when con-
nected in parallel, whose separate resistances are 5, 7 and 9 ohms
respectively ? Ans. 2.2 + ohms.
4. Three wires, the respective resistances of which are 8, 10
and 20 ohms, are joined in parallel. What is their joint resist-
ance ? Ans. 3.6 + ohms.
5. Four wires are joined in parallel, and their separate
resistances are 2, 4, G and ohms respectively. What is the
joint resistance of the conductor thus formed ?
Ans. .97 + ohm.
80
THE ELECTTRIC CURRENT. «
Battery Circuits. Fig. 5 illustrates a simple cirouit having
a single cell Q connected in series with a resistance. This is the
customary manner of representing a cell, the dhort, heavy line
representing the sine and the long light line representing the
copper or carbon plate. In determining the amount of current
which will flow in such a circuit, the total resistance of the circuit
must be considered. This is made up of the external resistance
It and the internal resistance r, or the resistance ^f the cell itHclf.
If -F represents the total E. M. P. of the cell, then the current
/which Till flow is expressed by the formula*
/= ^
It has been shown that whenever a curn>nt pfeunes through
any resistance, there is always a certain drop or fall of potential.
The total E. M. F. above referred to, expresses the total poten-
tial difference between the plates of the cell and is the E. M. F.
of the cell on iypen circuit. When
the current flows, however, there
is a fall of potential or loss of
voltage within the cell itself,
and hence the E. M. F. of the
cell on closed circuit is less cnaa
on open circuit. That is, if the Fig. 5.
voltage be measured when the
cell is supplying current, it will be found to be less than when
the voltage is measured on open circuit, or when the cell is sup-
pljring no current. The voltage on closed circuit is that available
for the external circuit, and is therefore called the external or
available voltage or E. M. F.
The external E. M. F. dej)end3 of course upon the strengtli
of current the cell is supplying, and may be calculated as
follows:
If the current passing is / and the resistance of the cell i.<
r, then from Ohm's law the voltage lost in the cell equals rl. If
J? represents the total E. M. F. of the cell and ^j the eaXemal
E. M. F., then,
E^^E—r£
87
28
THE ELECTRIC CURRENT.
Fig. 0.
The E. M. F. of a cell is understood to be the total E. M. F.
unless otherwise stated*
When two or more cells are interconnected they are said to
form a battery.
Fig. 6 illustrates three cells connected in series with each
other and with the external circuit. That is, the positive terminal
of one cell is connected to the negative of the next, and the posi-
tive of that cell to tlie negative of the adjacent, etc. Bj this
method of connecting, the E. M. F. of each cell is added to that
of the others, so that the total E. M. F. of the circuit is three
times that of a single cell. If one of the cells were connected ao
that its E. M. F. opposed that of
the other two, it would offset
the E. M. F. of one of the cells
and the resultant £. M. F. would
be that of a single cell. The con-
necting of cells in series as in
Fig. 6 not only increjises the E. M. F. of tiie circuit but alao
increases the internal resistance, the resistance of each cell being
added to that of the others. If E equals the E. M. F. of each
cell, r the internal resistance of each and R the external resist-
ance, tlien the current that will flow is expressed by the formula*
B + Zr
or for n cells connected in series the formula for current is,
j^_ nE
Fig. 7 illustrates two cells connected in parallel, and sup-
plying current to an ex-
-|- temal circuit. Here the
two positive terminals are
connected with each other
and also the two negative.
The E. M. F. supplied to
the circuit is equal to that
of a single cell only. In
fact connecting cells in parallel, is equivalent to enlarging the
FiK. 7.
88
THE ELECTRIC CrRREXT.
29
plates, and the only effect is to decraaae the internal reeiBtance.
It is evident that coupling two cells in parallel affords two
paths for the current and so decreases the resistance of the two
cells to one-half that of a single cell. The formula express-
ing the current that would flow in the external circuit with two
cells in parallel is therefore,
E
1 =
*+-^
or for n cells connected in parallel, the formula for current is.
y=
r.
£ +
r
Pig. 8.
Fig. 8 represents a combination of the series and parallel
method of connecting and represents four files of cells joined In
parallel and each file having four cells connected in series. The
E. M. F. of each file and consequently of the circuit is 4 K. The
resistance of each file is 4 r and that of all the tiles — ; — . Hence,
the formula for current is,
/ = -
iE
R
4/-
T
If there were n files connected in parallel and in cells were
so THE ELECTRIC CURRENT.
connected in series in each file, the formula expressing the current
in the external circuit would be.
n
where E is the E. M. F. of eaeli cell, R tlie external resistance,
and r the internal resistance of eacli cell.
The most advantageous inuthml of connecting cells depends
upon tlie results desired, tlie resistance of the cell and the external
resistance. Suppose it is desired to pass a current through an
external resistance of 2 ohms, and that Danieirs cells are to be
used each having an E. M. F. of I volt and an internal resistanoo
of 3 oil ins.
With one cell only in circuit, the current will be, ,
E 1 o
. = = .'J anu)ere,
H+r 2+ a ^ '
and with 5 cells all in series the current will te,
!yE 5
R
-r-^- = -y-r-^f ~ '^ a"n>«re (appwx.).
Therefore with 5 cells in series the current is only ,1 ampere
greater than with a single cell, and with 100 cells in series the
curivnt IS only,
100 E 100
y^ + ioor 'i^ + SM
= .33 ampere.
Hence with a comparatively low external resistance, there is but
little gain in current strength by the addition of cells in series.
This is due to the fact that^ although the E. M. F. is increased
1 volt by each cell, tlie resistance is increiised by 3 ohms.
Now suppose f) Dauiell cells to l)e connected in parallel with
the external circnit of 2 ohms. The E. M. F. of the circuit will
then Ixi that of a single cell and the current will !«,
E 1
= .4 ampere (nearly).
7^'v ^ 2+_
90
.TvP*;
THE ELECTlliaCUUKKr^T. U
and with 100 cells connected in parallel the current will be,
E 1
Ji -j- - 2 -^
3
=r .5 ampere (nearly).
100 • 100
A larger current Ls tliei-efore o])tained in this case by connect-
ing the cells in parallel than by connecting them in series.
With a large external resistance on the other hand, a larger
cun-ent Is obtained by connecting the cells in series. For example,
suppose the external resistiince to l)e 500 ohms. One cell will
then give a current of .00198 -|- am2)ere, and 5 cells in series will
give about ,0097 ampere, whereas 100 cells will give .125 ampei*e.
With 5 cells connected in parallel tlie current will be .00199 -f-
ampere, and with 100 cells the current will amount to approxi-
mately .002 ampere. With an external resistance of 600 ohms,
there is practically no advantage in connecting the cells in parallel.
The only effect of the latter method is to decrease the internal
resistance which is almost negligible in ciomparison with tlie
external resistance.
It may be sliown mathematically that for a given external
resistance and a given number of cells, tlie largest current is
obtained when the internal resistance is equal to the external
resistance. In order to obtain this result the values of m and n
in the formula on page 30, should be so chosen that equals
n
R. This arrangement, although giving the largest current
strength, is not the most economical. With the internal n^sist
ance equal to the external resistjince there is just as much energy
used up in the battery itself jis is expended usefully in the external
circuit.
In order to obtain the most economical arrangt nent, the
internal resistance should be made as small as possible, hat is.
all the cells should be connected in parallel. The loss of ^». wer
in the battery is then the smallest amount possible.
In order to obtain the quickest action of the current the cei.
should be connected in series. When the external circuit possesses
considenible self-induction, as is the case when electro Me
connected in the circuit, the action of the curreo
91
d-2 THE KLECTIMC CCHIiKNT.
This retardation may l)e decreased by having a high internal
resistance, which is obtained by connecting the cells in series.
Example. — Sixteen cells, each having an infernal rrsisUvnce of
.1 olim are to be connected with a circuit whose resistance is .4
ohm. How should the cells be connected to obtain the greatest
current?
Solution. — Here the external resistance 72, equals .4 ohm and
the resistance r of each cell equals .1 ohm. For maximum
cuiTent,
= B^ or = .4
n n
Therefore, w = 4 n
and as m n = 16, the only values of m and n which will be tme
for both of tliese equations are m = 8 and 7i = 2. Hence there
roust be 2 files of cells, with 8 cells in series in each file,
Ans. 2 files, 8 cells in each.
Example. — The external resistance in a circuit is 4 ohms.
The cells used each have an E. M. F. of 1.2 volts and an internal
resistance of 3.8 olnns. If 20 cells were used, which method of
connecting would supply the larger current, — 5 files with 4 cells
in series, or 4 files with T) cells in series?
1st Solution. — Applying the formula on page 30, we have
72 z= 4, i? = 1.2, r = 3.8 and with 5 files and 4 in series, 7/* = 4
and n = h. Hence, the current is,
m.E _ 4X1.2 _
_ = .681 + ampere.
2t -I- ''^L 4 + lAilL
n 5
With 4 liles and 5 cells in series, m = 5 and n = 4. Henc^*
the ^'^rrer , is,
^ ^ ^-^ = .685+ ampere.
4 I 5X_3^
Tlie larger current is therefore supplied by having 4 files
with 5 (!ells in series. Ans. 4 files, with 5 cells in series.
2nd Solution. — The maximum current is supplied when the
92
THE ELECTRIC CURRENT. 33
internal resistance equals Uie external resistance or when
n
With 5 files and 4 cells in series,
mr^ _ 4 X 3.8 ^ 3^^ ^^^^
n 5
and witli 4 files and 5 cells in series,
m r 5 X 3.8 . -- ,
— = = 4. To ohms.
n 4
The latter value is nearer to 4 ohms, which is the external resist-
ance, than is 3.04, hence the larger current will be supplied with
4 files and 5 cells in series. Ans. 4 files, with 5 cells in series.
Example. — It is de^sired to pass a current of .025 ampere
through an external resistiince of 921 ohms. The cells are to he
connected in series and eacli has an E. M. F. of .8 volt and an
intenml resistance of 1.3 ohms. What numl»er of cells must be
used ?
Solution. — From page 28, the general formula for cells in
series is,
7 _ nE
n -f n r
and in this case /= .02"), E= .8, «= 921 and r = 1.3. Substi-
tuting these values gives,
.025 = *^ ^
921 +/1I.3
Multiplying by 921 -|- ^••* ^* gives
23.025 + .0325/1 == .8n
Transposing .0325 n gives
.8/^— .0325/< = 23.025
or .7675 // = 23.025
lience, n zn 30
Ans. 30 cells.
EXAHPLES FOR PRACTICE.
I. Ten cells in series have an E. M. F. of 1 volt each and
93
34 THE ELECTRIC CUKRENT.
an internal resistance of .2 ohm. The external resistance is 8
ohnis. What is the current ? Ans. 2 amperes.
2. Six cells, ejich of which lias an E. M. F. of 1.2 volts and
* a resistance of 2 ohms, are connected in pamllel. With an external
resistance of 10 olims, wliat is tlie current? Ans. .116 -{-ampere.
3. What is the current supplied by the same cells if joined
in series and the external resistance is 20 ohms?
Ans. .225 amper 3.
4. A single cell whose E. M. F. on* open circuit is 1.41 volts
and whose internal resistance is .5 ohm is sup2jl3Mng a current of
.8 ampere. What is tiie available E. M. F. of the cell?
Ans. 1.26 volts.
5. What would be the available E. M. F. with 8 of the
cells referred to in example 4, when connected in series and sup-
plying the same current? Ans. 10.08 volts.
6. Eight Daniell cells (E. M. F. = 1.05, resistance = 2.5
ohms each) are joined in series. Three wires A^ B and C of 9,
36 and 72 ohms resistmce respectively are arranged to he connected
to the poles of the battery. Find the current when each wire is in-
serted sepai-ately, and when all three wires are connected in parallel.
Ans. Through A^ .29 ampere nearly ; through J5, .15 ampere ;
through C^ .091 4- i»'"U>ere ; and through all three, .31 -j- ampere.
7. A battery of 28 Bunsen cells (E. M. F. = 1.8, resistance
= .1 ohm each^ are to supply current to a circuit having an
external resistance of 30 ohms. Find the current (a) when all
the cells are joined in series, (ft) when all tlie cells are in parallel,
(c) when there are 2 files each having 14 cells in series, (d) when
there are 7 files each having 4 cells in series.
Ans. (a) 1.53 + ; (ft) .06 nearly; (<?) .82 + ; (d) .23 +
ampere.
QUANTITY, ENERGY AND POWER.
Quantity. The strength of a current is determined by the
amount of electricity which passes any cross section of the conduc-
tor in a second; that is, current strength expresses the rate at
which electricity is conducted. The q^mntity of electricity con-
veyed evidently depends upon the current strength and the time
the current continues.
94
THE ELECTRIC CURRENT. 85
The Coulomb. The coulomb is the unit of quantity and is
equal to the amount of electricity which passes any cross-section
of the conductor in one second when the current strength is one
ampere. If a curi-ent of one ampere flows for two seconds, the
quantity of electricity delivered is two coulombs, and if two
amperes flow for one second the quantity is also two coulombs.
With a current of four amperes flowing for three seconds, the
quantity delivei'ed is 12 coulomlis. The quantity of electricity in
CDulombs is therefore equal to the current strength in amperes
multiplied by the time in seconds, or
where Q i^ the quantity in coulombs, J the current in amperes and
t the time in seconds.
The coulomb is also called the ampere-second. The quantity
of electricity delivered in one hour when the current is one
ampere is called one ampere-hour. The ampere-hour is equal to
3,600 coulombs, as it is equal to one ampere for 3,600 seconds.
From the formula Q = It, it follows that
t I
Example. — A current of 18 amperes flows through a circuit
for 2^ hours. What quantity of electricity is delivered?
Solution. — Reducing 2| hours to seconds gives 8,100 seconds,
and 8,100 X 18 = 145,800. Ans. 145,800 coulombs.
Example. — What is the strength of current when 1^ ampere-
hours pass in a circuit in 89 seconds?
Solution. — One and one-half ampere-hours equal 5,400
coulombs and as current strength is expressed by quantity divided
by time, the current is 6,400 -7- 89 = 60. + amperes.
Ans. 60. + amperes.
EXAMPLES FOR PRACTICE.
1. How many coulombs are delivered in 9 minutes, when
the current is 17| amperes ? Ans. 9,450 coulombs.
2. What IS the current when 480 coulombs are delivered
per minute ? Aus. 8 but^-
96
36 THE ELECTRIC CURRENT.
3. In what time will 72,000 coulombs be delivered when the
curreut is 80 amperes? Ans. 15 minutes.
4. How many amiiore-lioura pass in a circuit in 2| hours
when the current is 22 ami)eres? Ans. 60.5 ampei*e-hours.
Energy. Whenever a current flows, a certain amount of
energy is expended, and this may 1x3 transformed into heat, or
mechanical work, or may produce chemical changes. The unit of
mechanical energy is the amount of work performed in raising a
mass of one pound through a distiiuce of one foot, and is called
the foot-[)ound. The work dono in raising any mass through any
height, is found by multi[)lying the number of pounds in that mass
by the numl>er of feet through which it is lifted. Electrical work
may be determined iu a corresponding manner by the amount of
electricity transferred through a difference of potential.
The Joule. The joule is the unit of electrical energy, and is
the work performed in tmnsferring one coulomb through a differ-
ence of potential of one volt. That is, the unit of electrical energy
is equal to the work performed in transferring a unit quantity of
electricity through a unit difference of potential. It is evident
that if 2 coulombs pass in a circuit and the difference of potential
is one volt, the energy expended is 2 joules. Likewise if 1 cou-
lomb passes and the potential difference is 2 volts, then the energy
ex{)ended is also 2 joules. Therefore, to find the number of joules
expended in a circuit, multiply the quantity of electricity by the
potential difference through which it is transferred. This is
expressed by the fornnda,
W= Q E, or W^lEt,
where TFis the work in joules, Q the ([uantity in coulombs, JS?the
I)Otential difference in volts, /the current in amperes and t the
time in seconds.
By Ohm's law ^= H I and by substituting this value of E
in the equation for energy, we obUiin the formula,
which may be used when the current, resistance, and time are
known, R l)eing the resistance in ohms.
Example. — With a potential difference of 97 volts and a cur^
rent of 14 amperes, what energy is expended in 20 minutes?
Solution. — Work is expressed by the product of the quantity
9Q
THE ELECTRIC CUliRENT. 37
and potential difference. The time in seconds equals 20 X 60 =
1200, and the work W=: 14 X 1200 X 97 = 1,629,600 joules.
Ans. 1,62J),600 joules.
Example. — The resistance of a circuit is .9 ohm, and the
current is 25 am[)eres. Wliat energy is exi)cnded in half an hour?
Solution. — Substituting these values of resistance, curr-ent
and time m the formula Wi^ I^ R ^ we have, TF— 25 ^ x .9 X
30 X OO = 1,012,500 joules. Ans. 1,012,500 joules.
Power. Power is the raU of doing work, and ex{)resses the
amount of work done in a certiiin time. The hoi'se-power is the
unit of mechanical energy, and is ecjual to «]3,000 foot-pounds per
minute or 550 foot-pounds per second. A certain amount of work
may l>e done in one hour or two houi*s, and in stilting the work
done to be so many foot-pounds or so many joules, the rate at
which the work is done is not expressed. Power on the other
liand, includes the rate of working.
It is evident that if it is known that a certain amount of work
is done in a certiiin time, the rate at which the work is done, or
the power, may be obtained by dividing the work by the time,
giving the work done i>er unit of time.
The Watt. The electrical unit of {)ower is the watt, and is
equal to one joule per second, that is, when one joule of work is
expended in one second, the power is one watt. If the number of
joules expended in a certain time is known, then the power in
watts is obtained by dividing the number of joules by the time in
seconds. The formulas for the work done in joules as given
on the preceding pages are,
Tr=7^^and W=I^ R i.
By dividing each of these by the time t^ we obtain the cor-
responding formulas for power as follows :
P=:.I E^ and P z=z I^ /?, where P is the power in watts, 1
the current in amperes, E the potential difference in volts, and R
the resistance in ohms.
The power is obtained therefore, by multiplying the current
by the voltage, or by multiplying the square of the current by the
resistance.
The watt is sometimes called the volUampere.
For large units the kilowatt is used^ and this is equal to 1,000
07
3>i THE ELECTRIC CUKKENT.
wattH. The common abbreviation for kilowatt is K. W. The
kilowatt-Jtour is a unit of energy, and is the energy expended in
OPe hour when the [x>wer is one kilowatt.
EXAHPLES FOR PRACTICE.
1. A current of 40 amiieres Ls su[)piied to a circuit and the
voltaic is 110. What is the jiower in watts? Aiis. 4400 \\'atU5.
li. What is th«5 power in kilowatts supplied to a number of
incandescent lamps when the current is 84 amperes and the volt-
ajfe (»f the circuit 97 '/ Ans. 8.1+ kilowatts.
.*>. A cinjuit luis a resistance of />0 ohms and the current is
VI aniiHires. What power is expended in the circuit?
Ans. 7.2 K. W.
4. The voltage (»f an incandescent lamp circuit is 220 volts,
and the resistance 2 ohms. What jKJWer is exi>ended in the cir-
cuit? Ans. 24.2 K. W.
NoTK. - - First fiinl current by Oliin's law.
Equivalence of Electrical Eners^y in Heat Units. When-
ever there is any resistance to the flow of a current there is always
a certjiin amount of ele(;trical eneigy transformed into heat. The
current in pjissin*^ through such resistance expends a certain
amount of encMgy in overcoming the resisUmce, and this energj- is
dissip:it(;(l as h(.»jit. The entire electrical energy of a circuit may
b(i transforuKMl into heat, as in a lamp circuit, or only part of the
energy may appear as heat, the remainder being transfonned into
mechanical or chcjmical work. The energy which appeal's as heat
raises the temperature of the circuit to an amount depending upon
its ladiating surface, and the temperature of the surrounding
medium.
When the resistance of a circuit and the current are known,
the electrical energy expendedinay l>e calculated by finding tlie
product of the s(]uare of tlie current, the resistance, and the time,
iis by the formula at the foot of i>age .'iO. All this energy is
transformed into lieat. Other work may be done by the current,
as would l>e the case if an electric motor were connected to the
circuit, but this requires additional energy to that which is dissi-
l)at('<l as heat. The formula referred to gives only the energy lost
as heat, which is the total energy when no other work is done.
98
THE ELECTRIC CURRENT. 89
This formula, which gives the energy in joules, is in accordance
with Joule's law, which is as follows :
Tlie number of heat units developed in a conductor is propor^
tianal to its resistance^ to the Sfjuare of the current^ and to the time
the current lasts.
As we have seen, the unit of electrical eneigy is the joule.
The conunon unit of heat is the calorie, which is the amC^unt of
heat necessary to raise the temperature of 1 gram of water througli .
1 degi-ee Centigrade. By careful investigations it has been found
that the joule is equivalent to .24 of a calorie ; that is, one joule
of electrical energy when transformed into heat is equal to .24
calorie. Electrical energy may therefore be expressed in heat
units by multiplying the number of joules by .24 ; that is,
U=r- XJtXtX. 24:
where U is the heat in calories.
As one joule is equivalent Ut .24 calorie, it follows that one
calorie is equivalent to 4.2 joules approximately.
EXAHPLES FOR PRACTICE.
1. How many calories will be develoi>ed by a current of 80
amperes flowing through a resistance of 12 ohms for 10 seconds?
Ans. 25,920 calories.
2. What amount of heat will a cuirent of 20 amperes
develop if it flows through a resistance of 80 ohms for 2 seconds ?
Ans. 15,360 calories.
Equivalent of Electrical Energy in /lechanical Units. The
common unit of mechanical energy is the foot-pound, and from
experiment it has been found that one joule is equivalent to
•7373 foot-pound; that is, the same amount of heat will be
developed by one joule as by .7373 foot-pound of work.
As one horse-power is equal to 550 foot-pounds per second, it
follows that this rate of working is equivalent to
650
* — = 746 joules j^er second (approx.).
.7373
Hence one horse-power is equivalent to 746 watts. There-
fore to find the equivalent of mechanical power in electrical
power iDultiply the horse-power by 746, and to And the equiva-
W
40 THE ELECTMC CURRENT.
lent of electrical power in mechanical ][>ower divide the number of
watts by 746.
EXAHPLES FOR PRACTICE.
1. A jHJwer of 287 ^vatts is equivalent to bow many horse-
power? Ans. .38-{- II. P.
2. Tlie voltage Hp[>Hed to a cii\!uit is 500 and the current is
196 am|>ere»s. Wliat is the equivalent horee-|K)wer of tlie circuit?
Ans. 181+ H. P.
3. What is tlie cijuivalent of 43 H. P. in kilowatts?
Ans. 32+ K. W.
4. How many horsc-iKiwer a[>[)roximately are equivalent to
one kilowatt? Ans. 1^ II. P.
THE SUPPLY OF ELECTRICAL ENERGY.
Electrical energj' is now made use of on such a large scale
for lighting, power, heating, etc., that it is generated or pro-
duced by machines of great ca{>acity. The dynamo is used for
this purpose and machines having a ca^>acity of several thousand
kilowatts are now common.
Central Stations. Large central stations or {>ower houses
are built at convenient places and here are collected the generat-
ing, controlling and measuring apparatus. Usually steam engines
or turbines are used to drive the dynamos, and from the latter,
large copper mains conduct the current to the switchboard located
mthin the station. Here ai-e assembled all the regulating devices,
instruments, and switches for the control of the 83r8tem. From
the switchboard conducting mains run out to various distant
points, where the energy is to be used, to the receiving apparatus,
such as electric motors, lamps, heating devices, etc. A complete
system is therefore made up of three subnli visions — the generat-
ing plant, the conducting mains, and the receiving apparatus.
Isolated Plants. Besides large centi-al stations which occupy
one or more entire buildings and which are usually built and
designed esi)ecially for such purpose, there are the comparatively
small and simple plants called isolated power plants. They are
purely local systems and supply energy to a single building, or to
buildings in the immediate vicinity. The generating apparatus
in this case is usually located in the basement of the building.
100
THE ELECTRIC CUllREXT. 41
Lai-ge hotels and office buildings ure frequently jirovided with
individual generating plants.
Losses in Energy. In o[)erating an electrical machine there
is always some loss in energy, that is, the machine does not give
out an amount of energy equivalent to the amount it receives.
Besides ordinary mechanical losses there is in addition the electi'i-
cal loss, which always occurs when a current fh»ws through any
resistance. This loss as previously explained, is equal U) the
square of the current multijjlied by the resistance.
The ratio of the auKmnt of energy which a machine gives
out, to the amount whicli it receives is called tiie commercial
efficiency of the macliine. For exanq)le, if the commercial eHi-
ciency of a dynamo is stated to l)e 80^, then 20% of the energy
given to the dynamo is lost, partly in overcoming friction and
partly in electrical losses.
Where electricity is transmitted some distiuice by means of
conducting mains, there takes place a loss in the line due to heat-
ing, which is fre(|uently tus much as 10%. Also at the receiving
station, if the electrical energy is converted into mechanical by
means of an electric motor, there will l>e a further loss.
Illustrative Example. For example, suppose it is desired to
ascertain the losses in a system which comprises a genenitor,
conducting mains and an electric motor. Su[)pose the efficiency
of the generator is 92% and that 1000 hoi-se-power are imparted
to it by the driving engine. The output of the dynamo will be
.92 X 1000, or 920 horse-power, and this is equivalent to
920 X 746, or 686,320 watts. The energy lost in the dynamo
will be 80 X 746, or 59,680 watts. We will assume the voltage
of the dynamo and the circuit to be 1000, and as the power in
watts is equal to the product of the voltage and current, the cur-
rent must be 686,320 -^ 1000, or 686 amperes approximately.
Now suppose the resistance of the conducting mains is equal
to .11 ohms. Knowing the current in the mains and the resis-
tance, tlie loss therein is obtained by applying the formula i^ R
giving 686^ X .11, or 51,765 watts. The energy available at the
receiving end of the line will therefore be 686,320 — 51,765, or
634,656 watts.
The remaining loss to be considered is that in the electric
101
42 THE ELECTRIC CURRENT.
motor. Assuming the efficiency of the motor to be 90%, the
I)ower lost therein will be .10 X 634,556, or 63,455 watts. The
output of the motor is therefore equivalent to 634,555 — 63,455,
or 571,100 watts. This in mechanical units is equal to 571,100 -r-
746, or 765 horse-power approximately.
Hence from an input of 1,000 horse-power at the generating
station, the work the motor is capable of performing at the receiv-
ing station is 765 horse-power. The efficiency of the entire
system under the assumed conditions is therefore 765 -7- 1,000, or
76.5%.
Among the great variety of generating machines, systems of
distribution and auxiliary devices, each hiis its particular advan-
tage for special conditions, and the selection of the type of ma-
chine and system of distribution depends almost entirely upon the
special circumstances. For example, a low voltage system is best
adapted for isolated plants, whereas for the transmission of power
long distances very high voltages are used. The various types of
machines, systems, etc., with their special advantages and disad-
vantages will be fully considered in the following Instruction
Papers.
10^
I ... -
.. v-lRX
«,.»*- •"
ELECTRICAL MEASUREMENTS.
ABSOLUTE AND PRACTICAL UN1T5,
Fundamental Units. All physical quantities such as volume,
Telocity, force, etc., are derived from, and can be expressed in
terms of the three fundamental quantities: len^h, mass, and
time. Each of these quantities is independent of the other, and
can only be measured ir terms of its own units.
The system of units in almost universal use by engineers and
upon which the electrical units are based, is the absolute or
Centimetre-Qramme-Second system, which is usually abbreviated
to the C. Q. 5. system. The fundamental units in this system
are: —
The Centimetre as a unit of ieni:th ;
The Oramme as a unit of mass ;
The Second as a unit of time.
The Poot-Pound-5econd system Ls also used to some extent,
Hiefootj poundj and second being the units of lengthy niass^ and
dme respectively.
Derived Units. From the three fundamental units length,
X, mass, Mt and time, T^ are derived all other physical quantities.
For example, the area of a rectangular surface is obtiiined by
multiplying the length by the width, or S = L X L =^ L^,
It is therefore evident that the only unit entering into the meiisure-
ment of surface is lengthy and that surface is measured by the pro-
duct of two lengths, or L^, Similarly, volume is measured by
the product of three lengths, or L^. Velocity which is the rate of
motion, or space covered per unit of time, is expressed by
^y^ , or -—- = X T~^. Hence the only quantities entering into
time T
the measurement of velocity are length and time, that is, length
an^ time are the dimensions of velocity. In a similar manner it
105
SYMBOLS OF PHYSICAL QUANTITIES.
Recommended by the Committee un Notation of the Chamlx^r o\
Delegates of the International Electrical Congresw of 1808.
With the Dames added in italics of the practical magnetic units provisionally
adopted hj the American Inst it ate of Electrical Engineers.
Sluuium OP Pols »«».......
MACMmc MoMirrr...^.....
luiBiniiy OP Maouktization.
TtXLD Iinx^fSlIT
Flux orfMACNcnc) Fokcx.
MACirrric I sv\:ctioh
MACirKTiziNC FoKcet. . . .^ . .
MACwrroMonvc Foacc.^...
tLMLVCTA»c% (Magnetic Re
SUTANCE)
(Macmstic) Pcrmxabiuty....
OfACKKTIC) SusctPTiMLirr...
i
^KUKmvrnr (Sricinc Mac-
Kmc Rk&isiamce).
Cto«lr«NMfa«tic.
iUntTA.^C
MutCnOMOTiVt FOKCK
l>irFsaBHcc OP Poicntial. ...
NTEKSmr OP CUKKCNT
QvAtnirr op Ei-ectiiicitt...
Capacity
Clsctkic KxEtny.
EttCTKlC POWEK..
RisisTiYiTY (SPEoric Rzsirr
ANCE)
Conductance
Conductivity (Specific Con
ductance)
CoKPPiciENT OP Induction (Ik
ouciancl) .^.— «...
Oil
a
*
30
IF
01
/«
X
U.u
/./
C.f
C,€
P
r
^,1
311 =
3:
#
X.
7»
mt
F
m
fX
L
r.
''=30
30
I
r ^ —
K =
£
U
p =
^/
R
IT
Q
' £.
BIT
£/
RS
L
1
1
r
p
#
1
j}jlt*T-*
A ttsmber.
Atmnbcr.
A number.
LT-*
VMT-*
VMT-*
L-^T
UT
L
•r-naC^CS.
Cabic
Cmtidwlffc per
Riiiin per second.
Ccaiifnetrc per second
per se cond.
Dyne.
£f( per wcow Q.
Djnc per
cead-
Camst,
CiOrrt.
Otrtitd,
of a
Mil
Sqnare
Cohic
Degree: aiipacc;
Mcueper
RevolaikMis (tnms) per
minntc.
Mef re per second per
second.
Craaine: kilogrmmne.
KilogrmmiDetre.
Kiloframmetrc per
second.
Ki|pfrsm per:
CSssus.
CSowr.
GiOert; l Ciafrt^CT^s!^
smpifcre-tums (a-c).
OtrsUd.
V<ilt.
Vole
Anp^.
Conlonb; anptee-boor
FaraO.
Joule ; wan<lioar.
Wau; kilowatu
OhaKeaUnccre.
Uho,
ficn^^a
|.V Ih Ihe uumber of windings, and L the length of the solenoid generating the mag-
netizing force.
106
ELECTRICAL MEASUREMENTS,
may be shown that every physical quantity such as force, work,
resistance, etc., may be expressed in terms of one or more of the
tfaree fundamental units.
A table of Symbols of Physical Quantities is given on page 4.
The first column gives the names of the physical quantities, the
fundamental, geometrical, mechanical, etc. The second column
gives the symbols for each of the physical quantities. In the third
column appears what are termed the defining equations, that is,
the equations which express the relation l)etween the different
quantities. The dimensions of the physical quantities are given
in thp fourth column. For example, the dimensions of velocity,
as we have seen, are L T~^. The fifth column contains the
names of the absolute or C. 0. S. units, and the sixth those of the
practical units.
Definitions of the absolute and practical electrical units are
given on the following pages, and are arranged so that they may
be easily refeiTed to.
The C. O, S. units upon which the electrical units depend
are as follows :
Surface. — The unit of surface is the square centimetre.
Volume. — The unit of volume is the cubic centimetre.
Velocity. — The unit of velocity is the velocity of a body
which moves through unit distance in unit time, or one centimetre
per second.
Acceleration. — The unit of accelenition is that acceleration
which imparts unit velocity to a body in unit time, or one
centimetre per second per second.
Force. — The unit of force is that force which, acting for one
second on a mass of one gramme, gives to it a velocity of one
centimetre per second. This unit is called one dyne.
Work. — The unit of work is the work done in overcoming a
force of one dyne through a distance of one centimetre. This unit
is called one erg.
Energy. — Since the energy of a iKxly is measured by its
abilitv to do work, the unit of energy is also the erg.
pi^^0|., — The unit of ])ower is the activity when one imit
work is done in a unit time, or one erg per second.
107
6 ELECTRICAL MEASITREMEirrS.
ABSOLUTE ELECTRICAL UNITS.
The magoetic units are as follows :
StreiiSth of Pole. — The unit magnetic pole is one of such a
atrength that when placed at a distance of one centimetre (in air)
from a similar pole of equal strength, it is repelled with a force of
one djTie.
riagnetlc Potential. — Magnetic potential is measured by the
work done on unit pole in moving it against the magnetic forces.
Difference of flagnetic Potential. — The unit difference of
magnetic {x>tential exists between two points, when it requires the
expenditure of one erff of work to bring a unit magnetic pole from
one point to the other against the magnetic forces.
Field Intensity. — The unit field intensity is that intensity of
field which acts on a unit pole with a force of one dyne. This
unit is called one gauss and is equal to one line of force per square
centimetre.
flagnetic Flux. — The unit of magnetic flux is that amount
of magnetism which passes through unit area of magnetic field
when the field intensity is unity. This unit is one magnetic line
and is called one weber.
riagnetomotive Force. — This is measured in the same units
as difference of magnetic potential. This upit is called one
S:ilbert.
Reluctance. — The unit of reluctance is that reluctance when
unit magnetomotive force generates in it a flux of one magnetic
line. Tiiis unit is called one oersted, and is the reluctance of a
cubic centimetre of air.
From the preceding magnetic units are derived the following
absolute electromagnetic units :
Intensity of Current. — A current of unit intensity is such
that whcni one centimetre length of its circuit is bent into an arc
of on(^ cM^niimetre radius, it exerts a force of one dyne on a unit
magnetic pole placed at its center.
Electromotive Force. — The unit difference of electromotive
force or i>ot(*ntial exists between two points when it requires the
exn(»n(liturt» of one en/ of work to bring a unit of positive electricity
irom one point to the other a;;ainst the electric force. A unit
108
ELECTRICAL MEAStJREMENTS.
electromotive force is generated by cutting one magnetic line per
second.
Resistance. — The unit of resistance is such a resistance that
unit difference of potential existing between its terminals, causes
a current of unit intensity to flow through it.
Quantity of Electricity. — The unit quantity of electricity is
that quantity which is conveyed by unit current in one second.
Capacity. — The unit capacity is such that unit quantity of
electricity charges it to unit potential difference.
Inductance. — The unit inductance is such that unit electro-
motive force is induced by the variation of the current at the rate
of one unit current per second.
PRACTICAL ELECTRICAL UNITS,
In practical work the resistance and electromotive forces com-
monly met with are usually so large that if the absolute electro-
ihagnetic C, G. S. units were used, the resulting numerical values
would be inconvenient. On the other hand, capacities are gener-
ally so small that their numerical values in C. Gr, S. units would
be very small fractions. For practical use therefore, certain mul-
tiples of the 0. O-. S, units of resistance and electromotive force,
and a submultiple of that of capacity have been chosen.
The following are the practical units :
Resistance. — The ohm = 10» (or 1,000,000,000) absolute
units of resistance. The International Oiim, which is equal to one
true ohm as nearly as known, is the resistance of a uniform column of
mercury 106.3 centimetres long and 14.4521 grammes in miiss, at
the temperature of melting ice. The megoiim is a resistance of
one million ohms.
Current. — The ampere = 10""^ (or one-tenth) absolute
units. This unit is practically represented by the unvarying cur-
rent which, when passed through a solution of silver nitrate in
water, deposits silver at the rate of .001118 gramme per second.
Electromotive Force. — The volt = lO^ (or 100,000,000)
absolute units, and is that E. M. F. which applied to one ohm will
produce in it a current of one ampere. The volt is equal to |xy$
of the E. M. F. of a Clark standard cell at 15° C.
100
ELECTRICAL MEASUREMENTBL
Qiumtity. — The ooolonb » lO^^ (or oiie4endi) absolute
nnit8 of quantity ; being tbe quantity of electricity oonTeyed by
one ampere in one second. Tbe ampere-hoar is the quantity of
electricity eonyeyed by one ampere in one hour.
Capacity. — The farad = 10~' (or one one-thousand-mil-
lionth) absolute unit of capacity ; and is the capacity of a con-
denser which is charged to a potential of one volt by one coulomb
of electricity. The microfafad is one millionth of a farad, and
:= 10"" 15 absolute units.
Work. — The joule = 10' absolute units of work (or
10,000.000 ergs) and is represented by the energy expendeil in
one second by one ampere fiassing through a resistance of one
ohm. The watt-hour is the energy expended in one hour when
the activity, or power, is one watt. The watt-hour is equal to
8,600 joules. The kilowatt-hour is the energy expended in one
liour when the activity is one kilowatt. The kilowatt-hour equals
8,«00,000 joules.
Power. — The watt = 10' absolute units of power (or
10,000,000 ergs per second), and is the power of a current of one
amjiere flowing under a pressure of one volt. This unit of power
is equal to one jouW 'per second^ and is approximately y Jj of one
liorse-power, or one horse-power is equal to 746 watts. The kilo-
watt is equal to one thousand watts.
Inductance. — The henry = 10« or (1,000,000,000) absolute
unit8 of induetance, and is the inductance in a circuit when the
K. M. F. induced is one volt, while the inducing current varies at
th'' rate of one ampere per second.
Values of the Ohm. — The difficulty in determining experi-
mentally the correct value of the ohm and volt has lead to the
ailo[)tion and use of several different values. Three of these are
tli'* British Association (B. A.) ohm and volt, the Legal ohm and
volt, and the International ohm and volt. The value of the
anii>ere has not changed materially because its absolute value may
\)it easily and accurately determined by means of the tangent
gjdvanometer.
The InU»rnational Electrical Congress held at Chicago in 1898
recommended the adoption of the International ohm and volt.
United Stiites, England, Germany, and other countries have now
110
ELECTRICAL MEASUREMENTS. »
adopted and legalized the International units, and the ohm and
other electrical units have probably now received their definite and
final values.
As the B. A. and L^al ohm are still in use to some extent,
it is well to know their values in terms of each other.
1 International ohm = 1.0137 B. A. ohms = 1.0028 Legal
ohms.
1 B. A. ohm = .9865 International ohm = .9893 L^al
ohm.
1 Legal ohm = .9972 International ohm = 1.0108 B. A.
ohms.
The International ohm represents the true ohm as nearly as
the latter is known (see p. 7).
The B. A. ohm is the mean resistance of six of the British
Association Committee's original ohm coils, now preserved in the
Cavendish Laboratory at Cambridge, England, and representing
the results of the Committee's experiments of 1865.
The Legal ohm is the resistance recommended to be legalized
as the standard unit of resistance by the Congress of Electricians
held at Paris in 1884. This unit was defined as the resistance of
106 centimetres of mercury, of one millimetre cross section, at
0^ C. It has never been legalized in this country but is still
employed in technical work to some extent.
ELECTRICAL HEASURINQ INSTRUMENTS.
Important Principles. When an electric current passes in a
conductor, the current causes the same to be surrounded by a mag-
netic field or by magnetic lines of force. These magnetic lines
encircle the conductor and their direction depends upon the direc-
tion of the current.
Owing to the presence of these *
magnetic lines a pivoted magnetic f ^ ft \
needle will be deflected when ^ *
placed near the conductor and will
tend to set itself at right angles to
the same. This phenomenon is
illustrated in Fig. 1, the arrows
indicating the direction in which ^*
the needle will turn. This direction depends not only upon
111
10
ELECTRICAL MEASUREMENTS.
the direction of coirent, but also whether the needle is above or
lielow the wire. If the direction of the corrent was from right to
\Ai ir. Fig. 1, then the needle would be deflected in an opposite
direction to tliat indicated. If the needle was above the wire and
the direction of the current remained as shown, then the needle
would Iv deflected again in an opposite direction.
A convenient rule for remembering the .direction of these
movement; is that suggesteil bv Ampere, whicli is as follows : Sup-
|x>se a man swimming in the wire with the current, then if he
faces the neeille, the north-peeking pole will be deflected towards
liis left hand.
If the wire jiasses over the needle and then back under
it, :iii shtu^ii in Fig. 2. the effect of the current in both parts
of the wire will be to deflect the
needle in the same direction. This
will be elt'ar l»y applying Amj^ere's
rule to the upjvr and lower parts of
the wire, the north-seeking pole in
eaeh ease being deflected as shown.
By passing the wire around the
needle several tunes, ov -n othe^ words
hy susj^ending the needle at the
cent«r of a coil of wire which carries a current, the deflection of the
nt*e<lle will be much inereasetl, as the effect of each turn is added*
t«» tliat of the others.
riiis may l>e more fully understood by considering Fig. 8.
XVhi'ii no eiirrent is passed through the coil, the needle will come
fo re.>t and phue itself ]>arallel to the lines of force of the earth's
nia;^'netisTn. The direetinn of these lines is nearly north and
soutli. Suppose tlie coil to be placed |>arallel to the needle and
tiio current tln*n pass«Ml through the coil. The needle will come
to rest in an olilique direction which will be the direction of the
r<,\sultant field due to the eurrent in the coil and to the earth's
magnetism. The less the sti*ength of the earth's magnetism and
the greater the strength of the field due to the current in the coil,
the gnat^M- will be the defleetion of the needle towards a position
at right angh'S to the coil. Hence the deflection may be increased
Fi?. 2.
113
ELECTRICAL MEASUREMENTS.
11
Fig. 8.
by increasing the number of turns or length of wire in the coil,
and by increasing the current.
Another phenomenon upon which many electrical instruments
depend is the deflection of a coil carrying a current. Such a coil,
as we have learned, is surrounded by a field similar to that of a
magnet, and therefore if it is
free to turn, it will take up a
position such that the magnetic
lines passing through it due to
the current, and the magnetic
lines of the earth's magnetism
will coincide in direction ; that
is, the coil will move so as to
Include a maximum number of
lines of force. The ends of the
coil will then point in a direction which is nearly north and south as
is the case with a compass needle. If the coil is in the neighborhood
of a powerful magnet the earth's magnetism will then have practically
no effect and the position of the coil will be almost entirely
influenced by the magnet. The movement of the coil may Ix*
caused by a fleld produced by another fixed coil as well as by a
permanent magnet.
Qalvanometers. Galvanometers are instruments used for
determining the strength or presence of an electric current. These
'instruments were formerly the only ones used to measure current
jtrengths, and are still largely used in the electrical laboratory for
accurately determining the strength of very small currents.
There are two general forms of these instruments ; in one the
strength of current is determined by the deflection of a magnetic
needle suspended at the center of a coil of wire through which the
current is passed ; in the other the current strength is determined
by the deflection of a movable coil carrying the current and which
is suspended between the poles of a fixed permanent magnet.
Tangent Qalvanometer. This form of galvanometer consists
of a coil of wire of many turns and of large radius having a mag-
netic needle supported or suspended at its center, as indicated in
Fig. 4. For accurate results the diameter of the coil must be
at least ten times the length of the needle. The needle is usually
113
12
ELECTRICAL MEASTTREMENTS.
Fig 4.
about one-half an inch in length and in order that its deflections
maj be easily determined, it carries a long light pointer which
swings over a graduated circle. In using the instrument care
must be taken to have the plane of the
coil in a vertical position and parallel to
the lines of force of the earth's magnetism.
Sine Galvanometer. The sine gal-
vanometer is similar in construction to the
tangent except that the coil is movable
about a vertical axis. Also the length of
the needle may be considerably greater thus
making the instrument more sensitive. In
measuring current strength by the sine
galvanometer the coil is first placed parallel
to the needle as in the case of the tangent
galvanometer, and the needle is then deflected by the passage of the
current. The coil itself is next turned about its vertical axis until it
is parallel with the deflected needle. Knowing the amount of deflec-
tion from the original position the value of the current may be
determined.
Astatic Galvanometer. This is a very sensitive form of
galvanometer owing to tlie use of what is known as an astatic pair
of needles. If two magnetic needles of equal strength and length
are held together with their opposite poles next to each other, as
indicated in Fig. 5, tht^y will l>e independ-
ent ot the earth's magnetism. One needle
will l>e acted upon to the same degree as
the other, and as they are opposite there
will l)e no resultant effect. Hence, if the
pair is suspended by a fine silk fibre the
needles may come to rest in any position.
Owing to the diflBculty of magnetizing two
needles to exactly the same strength, and of
joining them together so that they are parallel, such a pair of needles
will have a slKjht tendency to point north and south. If a coil of
wire is wound alK)ut one of the needles, as shown in Fig. 5, the pair
may be deflected by the passage of a very feeble current in the coil.
Fig. 5.
The current passing below one of the needles and above the other.
114
ELECTRICAL MEASUREMENTS.
IB
tends to deflect both in the same direction ; and as the action oi
the earth upon them is yery slight the deflection may be very
great. When the deflection is small the cuiTcnt is proportional to
the amount of deflection, hence if it is known that a certain cur-
rent deflects the pair 4**, then a current deflecting the needle 8^
will have twice the strength.
Thomson or ilirror Qalvanometer. This is the most sensi-
tive form of galvanometer, and is illustrated in Fig. 6. The
galvanometer is supported on three screw feet by which the instni-
ment may be leveled. The needles which are usually pieces of
steel watch-spring, form an astatic system and may consist of two ,
or more combinations. A small concave mirror is attached to the
upper combination and the whole is suspended by a very fine silk
or quartz fibre. A permanent magnet called the control or field
^^ii'sYz:
Fig. 6.
ma^et is supported above the galvanometer as shown. This may
be placed so as to counteract the earth's magnetism, and as it is
nearer the upper needle it also serves as a directing or controlling
magnet. If the field magnet is removed the magnetic system of
needles will come to rest as directed by the earth's magnetism
since the sj-stem cannot be perfectly astatic. The field magnet
may then be lowered in position until the earth's magnetism is
counteracted. It is then slightly niised, permitting a feeble direc-
tive force to act on the system. Deflection will then take place
with an exceedingly small current passing through the coil.
In using this instrument a line of light from a lamp is thrown
115
14 ELECTRICAL HEASUREMENT&
on the concave mirror of the galvaDometer which reflects it to a
graduated scale, as shown in the figure. The scale may be about
3 feet in length and situated about the same distance from the
galvanometer. The current is approximately proportional to the
deflection of the light on the scale when this deflection is small.
Usually one coil is used, one of the needles being suspended
at its center. Tlie coil is divided vertically into two separate parts
to ^ive access Uj the ne<*dle and mirror. For greater sensitiveness
two coils may Ije used one above the other, each of which has one
n(;('dl(j of the astatic pair suspended at its center. As each coil is
divided into two parts, such an instrument is usually called a four-
coil giilvanoineter.
Differential Galvanometer. This galvanometer is used for
the pur[Kj«e of comparing two currents. One coil may be used
having two similar independent windings or there may be two sep-
arate coils. If equal currents are passed through the windings in
opposite directif)n8 the resultant effect on the needle at the center
will he zero, and there will Ije no deflection. If the currents are
unequal the defl(?etion will be proportional to the difference
Iw'tween tlieni. A Thomson galvanometer may be made differen-
tial by connecting the coils so that the current passing through
one set will 1x3 opposite to that j)assing through the other.
Ballistic Galvanometer. The needle of this galvanometer is
Bo constiiicted as to have a slow period of oscillation, and there-
fore niav 1h* used to measure the stren^jth of currents which are of
short duration. The charge of a condenser may be measured by
dischar^nii^ it through this form of galvanometer. As the needle
is sh)\v to turn thcj varying impulses of the current of discharge
arc all()\vc<l to produce their full effect. The quantity of electricity
(h)\viii;r throu^^li the coil is determined from the maximum deflec-
tion of tli(; first swing.
D* Arson val Galvanometer. The D'Arsonval galvanometer is
quil/ii (lilTiTcnt from preceding forms in that the coil is suspended
and dclh'cted l)y the passage of a current. The arrangement is as
shown in Kig. 7. The eoil through which the current passes is
Bus[)cn(le<l between th(i poles of a strong, permanent, horse-shoe
magnet. The (!oil consisting of very fine wire is wound upon a
small rectangular frame and is suspended by thin platinum silver
116
ELECTRICAL MEASUREMENTS.
Fig. 7.
stiips. The current is passed into and out of the coil througb
tliese stripe. A small concave mirror is usually carried above the
coil as the deflection may then be more accurately determined.
Within the coil is fixed a cylindrical soft iron core which servee
to concentrate the lines of force passing
between the poles, and therein produces
11 strong magnetic field in which the coil
moves. The tendency of the coil to turn
so as to include the greatest number of
lines of force when a current is passed
through it, is resisted by the toraion of the
suspending wires. The deflection pro-
duced is directly proportional to the cui^
rent, the number of turns and the intensity
of the magnetic field. The magnet is built
up of laminations of hardened steel which
is treated so that it will maintain the
strength of ita magnetism.
The D'Arsonval galvanometer has sevend important advan-
tages over the Thomson and has largely repliu'ed the latter.
Owing to its strong magnetic field this galvauoiin'tcr is not
affected by the m^netism of the earth or other external magnet-
ism. It may therefore be used in close proximity to dynamos or
other machines without being affected by them. As the factors
upon which the deflection de[)ends maybe made invariable for long
jieriods of time, there is no necessity of frequently testing the
instrument.
Shunts. If a current is passed through a galvanometer and
a very large deflection is produced, there is liable to be a large
error in determining the strength of the current, as accurate results
are only obtained when the deflection is small. Moreover if a
large current is passed through the coil, the instrument will Ije
injured. It is therefore customary to use a shant al)out the gal-
vanometer. Part of the current then passes through the galva-
nometer and part through the shunt, the division of current lieing
inversely as the resistances of tlie two branches. If the resistiincra
of the shunt and galvanometer are known then the total current
may be easily calculated. For example if it was found that .008
16 ELECTRrCAL MEASUREMENTS.
ampere Aowf-d through the gialTaDometer and that the shunt resistr
ance w.i^ -^^ of tfivit of t:ie instrument, then the total current would
ije .S ::m[>ert; for the current passing through the shunt was 99
times as in^eat as that through the galvanometer and the total
current is the sum of the two, or 100 X -^*08 = .8 ampere.
Sliunts for galvanometere are adjustable so that the ratio of their
rfsUtance t* th;tt of the galvanometer is equal to ^J^, ^^g, or ^
as dvsi:e«l. With tliese ratios the total current passing will be
n.-s{K'Ct:v»-ly • q;al to 1.000. 100, or 10 times the value of that
pa>siiitr tlirr»-;t;Ii the galvanometer.
Wiien taking a measurement the shunt should be adjusted so
tliat oiiW a small p;»ition of the cuirent is at first allowed to pass
ilirouijh ti.e galvanometer. If the deflection is too small the
resistance of the siiunt mav be increased imtil a suitable deflection
is f»bt;iinetl. Wlieii the shunt circuit is broken the total current
passes throuirli the galvanometer obtaining the maximum deflection.
The n umber by which the current passing in the galvanome>
tcr is multiplied to obtain the total current is called the multipli/-
inff poivtr of the shunt. This is equal to one plus the ratio of the
galvanometer resLstance to the shunt resistance.
Voltmeters. Voltmeters are instruments used for measuring
the potential diffeivnc«* Ijetween two points in a circuit. They are
pn)vi<le<l with a M-ah- gnulnated in volts over which a pointer is
defleetel ; the f)osition of the pointer indicating the potential differ-
ence. 1 n many cases voltmeters depend upon the same principles as
^m1\ anometei-s. If a liigli resistance is connected in series with the
eoil of a galvanometer, only a small current will pass when the
jrjids from the coil and resistance are connected to points differing
c;!<atly in j)otential. The current will vary directly as the poten-
tial (liflVrenfM' and the defleetion of the needle will therefore \m
proportional to this difference.
Weston Voltmeter. This instrument is verj' much used and
is similar to the D'Ai-sonval galvanometer. The permanent mag-
net is horizontal instead of vertical, and is similar in shape to the
outline of ih<* brass eas(; which encloses the working parts. The
ma<^niet is provided with j)ole pieces which are carefully shaped*,
allowing the air gaj) lK»tween them and the coil to be small. Fi"*.
8 ilhiHtraUis tin; ariangcmcnt. Uetween the pole pieces If and 5
118
I
ELECTKICAL MEASUREMENTS.
b fixed a cylindrical piece of soft iron E serving to conduct the
lines of force. The coil F, wliich is wound upon an aluminum
fnmie, is suppoited Ly jewel bearings in-
serted in fixed hrasa cups A and B. A
directive force is given to the coil by two
delicate springs Oand D which are opposed
to each oUier. The coil carries ii light
pointer which swings o\er a scale grad-
uated in volta. A high lesistance is en-
closed within the case of tlie instrument
and is connected in series with the coiK.
the cuiTcnt being led to and from tlie
coil through the springs C .md I>.
A Weston portable voltmeter is
illustrated in Fig. 9. The lower rights
hand binding post is for the positive
terminal. If the negative terminiil is con- pi^r, b.
nected to the lower left-hand binding post
the upper graduation of the scale is used and readings may
taken up to 1.50 volts. If the negative terminal is connected to
the binding post marked 15, then the lower graduation of the
KLECTRICAL MEASt'KEAlENTS.
scale is nsed. the mn"""!"' d^ection indicating 15 volte. Wbeii
the latter couoection is made the resistance of the instnuuent is
only one tentti of what it is in the former case. The coirent in
the coil (for the same voltage) is therefore ten times as great and
the deflection ten times as much. The total resistance of the
instrument is about 17.000 ohms. This voltmeter can be used for
ver ' high voltages by oonnecting a latge resistance in seiies. If
a resistance ten times that of the voltmeter is connected in series
with the instroment, the defection will only be one tenth of what
it would be without this resistance, and hence the maximum
deflection will indicate 1,500 vol Is.
Ammeters. The only essential difference between a vcib-
meter and fui ampere-meter or ammeter, ia in the reustance of the
instrument. In a voltmeter it was desired that it should have a
ver^' bigu resistance so as to take onljr a Tery small current and
therefore consume unly i small amount of energy. In measur)ii<;
current strengtii however, the ammeter most be connected in
series in tlie main circuit, and
hence it is desirable tlutt its
resistance should he as low as
possible so that the enei^'
consumed (I^ R) will be
slight. The scale of the am-
meter is gradoated to indi-
cate amperes directly.
Tlie Weston ammeter is
veiy similar in form and con-
struction to the voltmeter,
except that in the former
instrument the moving coil is
connected in parallel with a
low resistance shunt tlin>iidi whioh the main current piisses. There-
fore tln> greater ibf umiu curreni, llie greater will be the current
lassing through tlu' coll. The Weston instnunenta are geneially
recognized as the most ai\'iii-it<- on the market. Besides the form of
iiistnimoiit illiisti-attvl in Fii,'. S^. the Weston voltmeters and amme-
ters «re made in ii form for station use. A station ammeter is
ilNistrntcd in Kig. 10. Tlu' eomuvtions to the instrument are made
Flp. 10.
KLKCTMCAL MEASUREMENTS.
Id
at the back of the switchboard. The instrument illustrated has
a translucent scale which is illuminated by an incandescent lamp
supported in the rear.
Electromagnetic Ammeters. Many ammeters have been
constructed upon the principle of the electromagnet. The Edison
pendulum ammeter is a simple example of this class. The aiTange-
ment is illustrated in Fig. 11. When the current to be measured
is passed through the coil it draws in the soft iron core C^ which
Fig. 11.
is pivoted at P. The needle is fixed to the core piece at P. The
core is drawn into the coil against the force of gravity, the weight
TT serving as an adjustment. The greater the current in the coil,
the greater is the deflection of the needle.
Instruments of this type are not veiy accurate especially at
low readings. There is some error due to hysteresis in the iron
core, which causes the readings to be too low for an increasing cur-
rent and too high for a decreasing current. The advantages of
this form of ammeter are simplicity and cheapness.
Current Balance. The Kelvin current balance is a very
accurate instrument for measuring current strength. It depends
for its action upon the force of attraction or repulsion exerted
between coils carrying a current. It consists of six coils two of
which A Am Fig. 12 are movable, and four, B B B B are fixed.
121
20
ELECTRICAL MEASUREMENTS.
llie movable coils may be considered as the scale pans of a balance,
being sup^x^rted at the center (7. The current passes through aU
of the coils in series the direction being such that the mutual
action causes one of the movable coils to rise and the other to
descend. This tendency is balanced by a sliding weight on the
arm, tho posititni of the slider when the arm is horizontal indicat-
ing the strength of current.
Electrodynamometer. This instrument is also used to
measure the strength of current by th& mutual
action of two coils carrying the current. The
\
^vcs5^ Siemens dynamometer represented in Fig. 18,
' ^ is one of the oldest and simplest of these.
r
B
fi
^
It consists of two coils A and B at right anglies
to each other, through which the current passes
in series. One of the coils, j4, is movable
and is sup[K)rted by a pivot bearing. A
spiral spring C is attached to this coil and tc
the ti^rsion head D. The eun^ent is intro-
duced through mercury cups in which the
terniinals are immersed. This coil carries a
pointt r which extends up and over a circular
scale. The toi*sion head also carries another
pointer. When a current is passed through
the coils, the movable one tends to move so
as to include the greatest number of lines
(^f force and to set itself parallel to the fixed
ioil. The toreion of the spring opposes this
movement. The tm-sion head is then turned until it exactly
counterbalances the turning moment of the coil, which is indicated
when its }>oiuti'r is at the zero reading of the scale. The angle
^
uv
-g
YVr, i:i.
isa
• T«T'f "-^'"^ '^^^^
{iii,A3>-« ^.::.« ■
ELECTRICAL MEASUREMENTS. 21
through which the torsion head is turned, as indicated by the
pointer, varies directly as the square of the current strength. The
scale may be graduated to read directly in amperes.
This instrument is serviceable for alternating currents as well
as direct, and has the further advantages of being very accurate
within certain ranges and of being very free from variable errors.
Cardew Voltmeter. The principle of this instrument depends
upon the heating effect of a current. A current passing in a wire
heats it and causes it to expand. In the Cardew voltmeter
the expansion and contraction of a long fine platinum silver wire
is made to move a pointer over a scale graduated in volts. The
gieater the potential difference at the ends of the wire, the greater
will be its current and the more it expands. The voltmeter may
be used for eitlier the direct or alternating current as the heating
effect is the same. The instrument is subject to many errors and
requiras therefore the greatest care in its manufacture. It is
somewhat awkward to use as it is about three feet in lengtli.
Another objection is the comparatively large amount of energy it
consumes.
Electrostatic Voltmeters. The principle that two oppositely
charged l)odies attract each other is applied in the electrostatic
voltmeter. The Thomson vertical electrostatic voltmeter is shown
in Fig. 14. It consists of two fixed parallel metallic plates J.,
between which is the movable plate B, The plate B is paddle
Bhaped and supported by two knife edges at its center. This plate
Oarries a pointer which swings over the scale, and is weighted
;^t the lower end to give it a directive force. To measure the dif-
^ei'ence of potential between two points, the fixed plates are elec tri-
vially connected to one point and the movable plate to the other.
"The two fixed plates then l>ecome charged with say positive
electricity, and the movable plate with negative electricity. The
-plate B is then attracted toward the fixed plates, and deflected
from the vertical position to an extent depending upon the differ-
ence in potential between them. The foi*ce of attraction varies as
the square of the difference of i)otential. The scale is graduated to
read directly in volts. It is immaterial whether the fixed plates
are charged positively and the movable plate negatively or if the
reverse is the case. The force of attraction in each case Ls the
liLECTBICAL MEASUKEMENTS.
some. The instrument may therefore be naed equally well i
idt^mating or direct currentB.
The electrostatic voltmeter is useful only in measuring poten-
tial differences greater than 5U volts. They cannot be made
delicate enough to measure below that figure with accuracy. They
are however, specially desirable in measuring high potential differ-
i.
enoes. They are simple in oonstruction and have the great a
tage that they consume uo energy, since bo carrent passes tliroiigh
the instrument.
Wattmeters. The power consumed in a circuit supplied
with a direct current is equal to the product of the amperes and
E, M. F, iu^-oIts. An instrument which measures electric^ energy-
most, therefore^, take these two factors into consideration.
The Siemens eleclrodTnaraometer may be adapted to measure
the numiRT of watts consumed in a oirvuit by ha\-ing one of the
o<mIs serve the purpose of a voltmeter, and the other timt of an
ammeter. If one of the coils is ti);t<Ie of high resistance, baviiig a
fcr,ECTI{10AL MEAStniEMKNTS. 25j
largi^ iiiimlx-r of tiim» of iinc wire hikI slmntitl iicnuts tJio circuit
termiiiali!, and the oilier coil iiiuilo of low roKpitiuicc, linving a few
turns of coai-sc wiro and <-iiiii)<H-te<l in serioH witli tlio circuit, then
the mutual action lictweeii tIi<'Hi will l)o proportional to the pro-
duct of tlie volte an<l itni|H'i-i'H. The angle through wliich thi;
toision head niuat Ik- tiirnod to hring tlie niovahlo coil Itaek at
right angle:) to the fixed coil will he ])i-ii|M>rtiomit In tin; eiiei^y
supplied to the circuit. The scale may Iw giwluivt<*d Ui lead di-
rcctlj- in wntts.
This instrument is more useful in ii)t<'rnating current work
than for direct currents. Multiplying the voltmeter and iinimeler
reiuliiigs together will give the curi-ect luiuiber of wjitls only in
the case of the direct current. W'itli the alteniatiiig cuin-nt this
product must be further multiplied hy what is known as tiw power
factor. The determination of the vjilne of this jHtwer factor is
fromewhst difficult. Tlic wattmeter, on tlic other hand, gives the
true watts directly, and, therefoiv, is veiy convenient for alternat-
ing cuiTents
Recording fleters. Kleetricjil instrunieuts are sometimes
made to give ii continuoua record of the volts, aui[)eres, or watts
of a circuit. This miiy l>e aec(iin]>liHhiHl liy attiichiug a [leii to the
indicating piii-t of the imstrunieiit ; then if a strip or cirtuitiir piece
of j«iper is moved Ity clockwork iH'neitth the pen, n line will be
traced showing the volts, an»iiei-e». or wntts at iiuy time. These
instruments cannot Ije made as sensitive as those which are not
recording and are therefore less accurate. They also consume
iiioi-e energy.
The Thomson is one of the Iwst recording wattmeters, and is
a motor of simple construction. It consists of two coansc wii-c
coils pla<-ed in series with, and a fine wire coil connected in
shunt around, the circuit whose jiowei' is to Iw ineaHurird. The
coarse wire coils form the field which causes the fine win^ coil to
revolve. The shunt coil is supiMirted in bearings and its lutation
is proitortional to the eiici-gy of the ciivuit. ,\ copjier disk in
mounted on the same shaft as the shunt coil and r»Hates lietwcen
the poles of a pennanent magnet. The t-urrents induced in this
disk serve as a drag, the drag being adjustfd to give a sijced pro-
portional to the watts Bup{ilied. The number of revolutions is
24
ELECTRICAL MEASUREMENTS.
recorded by clockwork and the instrument is graduated to indi-
cate watt-hours. '
Water Rheostats are very convenient for absorbing power
during electrical tests and are easily made adjustable. A very
sei-viceable form is illustrated in Fig. 15. It consists of a stout
barrel containing water thnmgh which the current is passed. The
current is introduced through the insulated wire A^ which is
attached to a terminal plate D. From this plate the current
passes to plate C and through the main B. The plates may l)e of
■Q perforated iron ; a stove grate serves very
well as it gives a large surface contact. To
the wire JB is attached a cord passing over
pulleys and having a counter-weight at its
other end. The plate C may then be raised
or lowered and will remain in any desired
position. The resistance of the rheostat
depends, of course, upon the distance Ijetween
the plates. Small pieces of wood should be
attached to one of the plates to prevent them
from accidentally coming into contact, and
so producing a short circuit. The conduc-
tivity of the water may Ikj greatly increased
F!-. 15.
by the ad<lition of sodium carbonate or sulphuric acid. A rheostat
constructed as above is capable of absorbing about 10 H. P.
Carbon Rheostats. These rheostats consist of a series of car-
bon blocks or plates in contact with each other through which the
current is passed. They are supported by some insulating mate-
rial such as slate, and arranged so that by turning a hand wheel
the blocks may l)e pressed closely together or allowed merely to
touch. Their resistance is varied in this manner as the closer the
plates the less is the resistance. A very exact adjustment may be
obtained by the use of these rheostats. Heating caused by the
continued passage of a current decreases their resistance.
Wire Rheostats usually consist of German silver wire sup-
ported on a frame and arranged so that the whole or parts may be
included in a circuit. This is accomplished by making contact at
different points along the wire, either by a switch or by sliding
clips.
126
ELECTRICAL MEASUREMENTS. 25
The wires are sometimes strung or wound on wooden frames,
and their carr}nng capacity is then limited by the charring of the
wood. A current of two amperes jxissing through Xo. 28 German
silver wire and a current of eleven anii^eres through Xo. 19 wire
will cause charring of pine wood.
Wire rheostats which are to carry large currents should not
be boxed in, as the free access of air greatly increases the carrying
capacity. By immersing wires in an oil bath, their carrying
capacity may be increased about four times. Overheating can be
prevented by running cold water through pipes immersed in the
oil.
Lamp Rheostats. Incandescent lamps are of ton used sis a
means of absorbing power or of obtiiining a certain E. M. F., or
currcnt strength. Such a rheostat may consist of any numl^er of
lani^ts arnmged .so that tliey may be connected in series or in
|)arallel between mains. The greater the numlier connected in
parallel the greater is the current taken from constiint }X)teni;ial
mains.
RESISTANCE MEASUREnE^r^.
Measurement of resistance is made by comparison with certain
standards of known resistance, the different methods of measure-
ment var}'ing to a great degree. The standard resistance coils are
made of such alloys as German silver,
platinum silver, or platinoid. These -^. sS
alloys have a high specific resistance ' — ■
and change their resistance with rise
in temperature to a much less extent
than other metals. It is of course *^Flg. leT
desirable that this change should be as
small as possible. The size and length of the coils are such that
they have resistances of a definite number of ohms at a certain
temperature. The coils are insulated with silk or paraffined cot-
ton and are very carefully wound. Each wire is doubled on itself
before being coiled up, and then wound as shown at A and B in
Fig. 16. Self-induction and consequent sparking on opening and
closing their circuit is thus avoided. The ends of the coils are
soldered to brass pieces as (7, 2>, U. Removable conical plugs F
127
26 ELECTRICAL .MEASUREMENTS,
and Q- of bnwH are iiiaWr to lit acciu-ately lietweeii the brass pieces.
When these ait* inserttnl a.s shown, th*^ coils will be short circuite<l
and a current will pass direcily through C\ F^ 2>, G and E with,
out going through the coils. If F is w^ithdrawn the coil .1 \\\\\
then be inseited in the circuit ; if (? is also withdrawn then coils .1
and B will both be inserted, as the current cannot pass from C to
jy without going through the coils.
Resistance boxes are constnurtcfl consisting of a large iiunil)er
of resistance coils, and of sucli resistances that by withdrawing
plugs varying resistances may be built up. A common form of
resistance box has coils of the following ohms resistance : 1 , 2, 2,
T), 10, 20, 20, 50, 100, 200, 200, 500, 1,000, 2,000. A resistance
of 497 ohms could be made up by withdrawing plugs corresponcL
ing to the coils 200+ 200 + 50 + 20 + 20 + T* + 2 = 497, or
768 by coils 500 + 200 + 50 + 10 + 5 + 2 -f- 1 = 7GS.
Resistance by Substitution. Hy Ohm's law the greater the
resistance inserted in a circuit tin? less liecomes the current, pro-
vided the E. M. F. remains constant. This gives us a simple
although not very accurate method of measuring electrical resist-
ance. If a battery of constant K. M. F., the unknown resistance,
and a simple galvanometer are connected in series, the §trengtb of
the current passing will be indicated by the latter. Suppose the
unknown resistanci* to Ik* replaced by known resistances, enouq-li
resishince coils In'ing inserted so that the deflection of the gjilva-
nometer u^mmUc* is the same as when the unknown resistance wius
in circuit. The current will then be the same, and as the E. M. F.
remains unchanged, the resistances nuist Ix* equal in each case.
The sum of the known resistance coils insei*ted will then be equal
to the unknowii resistance.
The advant^iges of this method are that it is mpid, and that
only crude api)aratus is r(*quired, as the galvanometer and resist-
ance box (?an he very simple in form. The resistance of the bat-
tery and galvanometer should l)e l)nt a few ohms, otherwise small
resistances cannot Ix' measured (dosely. Only small curivnts
should l)e used so that the error from heating may be negligible.
Wlieatstone Bridge. All ordinary meiisurements of resist-
ance are usually made by use of the Wlieatstone bridge.
128
ELECTRICAL MEASUREMENTS.
27
The principles of this instrument -will be understood from Fig.
17. Tliere are four amis to the bridge witli the resistances M^ iV^
X^ and P. From the points of junction A and C^ wires connect
with a lottery E. A galvanometer Gr is connected between the
junction points B and 7>. The current from the batterj*^ divides
at A and passes througli the resistances M and JV, and iVand P,
uniting again at (7. The fall of potential between A and C must
of course l)e the same in amount through the resistances ilf and X
Fi;^^ 17.
as through iVand P. If no current passes through the galvanom-
eter then the points B and D will be at tlie same potential, and
there will be the same fall of potential in the resistances M and N.
and in the re^sistances X and P, Under these circumstances the
ratio of the resistances of ilf to N will be the same as X to P, or
~N P*
If M^ N^ and P are known resistances, the resistance of -Y is
readily found by the formula.
The method of using the bridge will be better understood from
Fig. 18. The bridge arm iff has coils of 1, 10, 100 ohms resist-
ance, and arm i\r coils 10, 100, 1000. The series of coils P for
obtaining a balance usually has resistances of 1, 2, 2, 5, 10, 20, 20,
50, 100, 200, 200, 500, 1,000, 2,000 ohms, but coils up to 100
only are shown. There is a key K in the galvanometer circuit
and a key -ff in the battery circuit. The battery key iZ should
always be closed before the galvanometer key K^ and should be
129
28 ELECTRICAL MEASUREMENTS.
kept closed until after K is opened. This not only insures
steadiness in all curi*ents when the galvanometer circuit is closed,
but also protects the galvanometer from self-induction currents
which would occur if the battery circuit were closed after that of
the galvanometer. A reflecting galvanometer is used in making
accurate measurements.
In making a measurement of an unknown resistance it is first
necessary to gain a knowledge of its approximate resistance. For
this purpose the 100-ohm plug is withdrawn from both arms M
Fig. 18.
and iVJ the unknown resistance being connected at X. The ratios
of Mio iVwill then be unity, and hence for a balance the number
of ohms required in the resistance coils P will be the same as the
resistance X, The 1,000-ohm plug in P should first be drawn and
the keys depressed in their proper order for an instant only. The
galvanon)et(u- needle or mirror, as seen by the light reflected on
the scale, is deflected — say to the right, and the resistance is
probably too large. The plug is replaced and the 1-ohra coil with-
drawn. Ou depressing the keys suj^pose the spot of light is
deflected to the left. Then the 1-ohm is too small and the 1,000
ohms too large ; also in this case deflections to the right mean that
the resistance inserted is too laige, and deflections to the left
mean that the resistance inserted is too small. The 1-ohm plug
is now replaced, and 500. 200, etc., are successively tried until it
is found that 12 ohms is too large and 11 ohms too small, that is,
the unknown resistance is between 11 and 12 ohms.
Suppose that it is desired to find the correct value of the
unknown resistance to the second place of decimals. The ratio of
the arms Mio N must then be changed so that the resistance coils
130
ELECTRICAL MEASUREMENTS. 29
P will have a valae of between 1,100 and 1,200 ohms when a
balance is obtained. The ratio of JT to P will then be 11 to 1,1<^0
approximately, or about 1 to 1 00. To obtain a iKilunce the ratio
of the amis 3/ to iV must also lie 1 to lOO. Hence tlie 100-ohm
plugs withdrawn in the first determination are i-eplace*! and the
10-ohm plug withdrawn fi-om 3/ and the 1,000-ohm plug from N
giving the i*equired ratio. The same ratio could he obtained by
withdrawing the 1-ohm plug in 3/ and the 100-ohm plug in iV.
The bridge is now arranged for the final measurement. As
the resistance in P will now be over 1,100 ohms, the 1,000 and
100-ohm plugs are first removed. Suppose the 50-ohm plug to be
also removed, and a deflection to the right shows that this is too
great. The plug is i-eplaced and 20 withdrawn, which proves to
Ik» too small. The next twenty plug is also withdrawn and a de-
flection to the left shows the resistance to be still too small. The
5, 2 and 2-ohm plugs are successively withdrawn, the last two
ohms proving to l)e too greiit. This is replaced and the 1-ohm
plug withdrawn, and suppose no deflection is tlieu obtained. The
total number of ohms in P is noi ' 1,000 + 100 + 20 + 20 -f 5
-f 2 -f 1 = 1,148. The value oi X \s therefore i JS^ ,X 1,148
= 11.48 ohms.
The above example illustrates the general method of using the
bridge. Usually the resistance to be measured is known approxi-
mately and the required ratio between iJf and iVcan be determined
without making a preliminary measurement. The possible changes
in the ratio between 3f and JV gives the bridge a great range of
measurement. When iff is 1 and iVis 1,000 ohms, measurements of
resistance as small as .001 ohm may be made. Bridges are usu-
ally arranged with a reversing key so that 31 and iVmay be inter-
changed, hence ilf could be 1,000 and N 1, and measurements of
resistance as high as 4,110,000 ohms could be made with the
bridge we have considered.
Portable Testinsr Set. There are many different varieties of
bridges and their form always differs from that of the diagrams
in Figs. 17 and 18. A portable testing set including Wheatstone
bridge, galvanometer, battery, and keys, is illustrated in Fig. 19.
The rheostat of the bridge is made up of coils, 16 in number, of
denominations 1, 2, 3, 4, 10, 20, 30, 40, 100, 200, 300, 400, 1,000,
13;
80
ELECTRICAL MEASUREMENTS.
1', 000, S,000. 4,000 ohms — 11,110 ohma in all. Bridge coils are
1, 10, and 100 on one side and 10, 100, and 1,000 on the other.
A reversing key admits of any ratio being obtained in either direc-
tion so that the iiiiige of the t^et is from .001 to 11,110,000 ohms.
It is, however, impoesible to ronstruct a, portable galvanometer o(
sufficient sensitiveness for these mejis lire men ts, and the uctiiiil
hmits aM from .001 ohm to 300,000 or 400,000 ohms.
'J'he reversing key, shown in Fig.
20 consists of tlie blocks M, JV, J*,
and Xand two plugs whicli must botli
lie on one diagonal or the other. The
blocks are connected witli the resist-
ances indicated by their letters. In the left-hand figure M is
connected with Jf and JV" with P, and the bridge arms have the
relation
MX y itf .
N P
In the right-hand figure MU
N
Xi».
s connected with P and JVwith X, the
bridge arms then having the relation
The advantages of having a reversing key in the bridge arms are ;
the increase in range obtained, six coils being made to do the work of
eight, and also that any error in the initial adjustment of the bridge
ELECTRICAL MEASUREMENTS.
81
arms can be readily detected by having the two arms equal, balanc-
ing and reversing. Unless the resistance of the coils inserted in
-Wand iV are exactly equal, the system will lie unbalanced after
reversing.
The galvanometer, the needle and scale of which aiv shown at
the left in F'ig. 19, is of the D'Arsonval type, and the coil is
mounted in jewels. As this galvanometer is not affected by
external magnetic fields or el<*ctric currents, it is suitable for
dynamo or shop testing. The key for closing the galvanometer
circuit is shown in front at the right.
The battery is made up of six chloride of silver cells contained
in the cell box at the right ; flexible leads allow the total number
in use to be varied at will. The cells will last a number of months
even with daily use. The flexible coiniecting cords have their
terminal sockets combined with small binding posts so that con-
nection nuiy l)e made to an extra battery or other source of E. M. F.
if desired. The left-hand kev controls the batterv circuit.
A plan of the connections of this testing set is shown in Fig.
21 . The two lower rows of coils
(marked 1 to 4,000) are con-
nected beneath the top at the
right by a heavy (topp(*r rod and
constitut*^ the rheostat arm, or
what corresix^nds to P. By
withdrawing the proper plugs in
these rows any number of ohms
from 1 to 11,110 may be ^J^'- 21.
obtained. The upper row of coils consists of th(» two bridge arms,
iHf at the left and iVat the right, with the reversing key between
them. The two extremes of the upper row are joined by a heavy
copper connection and correspond to the point A in Fig. 17. The
upper block X of the reversing key is connected with the bind-
ing ix)st B^ the block P is joined to the left of the middles row
of coils while-th*^ other end of the rheostat combination is con-
nected with the binding post C, The resistiince to be measured is
connectt^d between the terminals B and C.
Example. — Suppose a balance is obtained — '^^ unknown
resistance connected between B and C, when with
•P- — St- .i _-»"~n: "X 1 *.•■
r I f y »> ♦ < j
% — j:-^
_r-_i-.r
* (i_ ®
@
K >0000O0(
'■rkii*nv<am iba* «m a«k f» MO
188
82 ELECTRICAL MEASUREMENTS.
drawn as shown in Fig. 21. What is the value of the unknown
resistance ?
Solution. — The reversing key is arranged so that M is con-
nected with P and N with JT, hence
In the figuie N = 100, M = 10, and P = 2,000 + 1,000 + 400
+ 800 + 100 + 30 + 3 + 2 z= 3,835. Therefore
X = Y^ X ^'^^^ = ^^'^^^ ol^^s-
Ans. 38,350 ohms.
Use and Care of Bridge. Befoi-e l)eginning a measurement
it is essential that each plug Ikj examined to see tliat it is firmly
twisted into place, also in rejilaciug a pluij tlie same care should be
used. A slight looseness will considerably inci-ease the contact
resistance and so introduce erroi-s in the result. For the same
reiuson the plug tapers should be kept clean and the top of the
briilge free from dust and moisture. Special care should be tiiketi
with the surfaces b(»tween adjacent blocks. The plugs should be
handled only by their vulcanite tops, and care should be taken not
to touch the blocks.
The plug tapei-s may l)e cleaned with a cloth moistened with
alcohol and then rubbed with powdered chalk or whiting. The
IK)wder should be entirely removed with a clean cloth before the
plugs are replac(»d. Sand paper or emery clotli should never be
used to clean the plugs or bridge blocks. If there are no idle
sockets for the reception of the plugs when they are withdrawn,
they should be stood on end or placed on a clean surface.
Slide Wire Bridge. The principle of this bridge is illustrated
in Fig. 22. The heavy lines represent heavy conducting straps of
low resistance. There are binding posts at the ends of each sec-
tion permitting resistances A, -B, li and ^V to be inserted as shown.
Between the ends (77) is stretched a German silver wire of uniform
cross section. A batteiy and galvanometer are connected as shown.
A balance is obtained by sliding the contact point J? along the
wire until a point is found when no current flows through the gal-
vanometer. Under tliese conditions the potential at U must be the
134
ELECTRICAL MEASUREMENTS. 88
same as that at F and as in the Wheatstone bridge the ratio of the
arms between the battery and galvanometer connections must be
equal, hence
The resistances a and h are easily obtjiined from the lengths
of the sections of the wire given by a scale fixed near the wire ;
Fig. 22.
then if the resistances of A^ J?, and R are known tliat of A' may
be calculated from the formula ^
A-f- a
If A and B are replaced by straps of negligible resistance then
the value of the unknown resistance may be found from the simple
ratio,
/J : A' : : a : 6, giving A' = — X -B.
a
Since the resistance of the wire is proportional to its length,
the lengths of the sections a and b may be read from the scale and
substituted in the latter formula.
This instrument is not well adapted for measuring resistances
greater than a few hundred ohms. For very accurate measure-
ments it is necessary to determine and allow for the resistiinces of
the leads from A to C and from B to D,
Example. — If a balance Is obtained with the bridge illustrated
in Fig. 22, when a is 68.4 centimetres, b 31. G centimetres, and R
150 ohms, what is the value of JT^ supposing A and B to be
of negligible resistance? Ans. 69.3 ohms approx.
High Resistance fleasurement. The standard and most
approved method of measuring resistances greater than five or ten
megohms is the direct deflection method. The main instruments
required are a sensitive Thomson galvanometer of high resistance,
135
ft4
ELECTRICAL MEASUREMENtS.
a variable shunt resistance for the galvanometer, a known resist-
ance of at least .1 megohm, and a source of constant E. M. F. of
100 volts or more. The connections are shown in Fig. 28. The
known resistance R is first connected in series with the galvanom-
eter Q and testing battery jB, through a key K. Care should be
taken that the insulation of the apparatus be very high. The
RorX
V\ii. 23.
shunt S IS adjusted to give a suitable deflection of the galvanometer
and from this deflection what is known sis the constant is calculated.
The value of this constant is the resistance that must be inserted
in the circuit to reduce the deflection to one scale division. The
value of the constant is therefore equal to the product of the known
resistance i?, the scale deflection rf, and the multiplying power of
the shunt w, or, conntant = R d m.
As an illustration su})p()se ^ = .1 megohm, d = 200 divi-
sions and 7w = 1,000 ; then constant = .1 X 200 X 1,000 = 20,000
megohms. This resistance would cause a deflection of only one
division, for if m = 1,000, then if the full current should be pissed
througli the galvanometer, tin* corresponding deflection would be
1,000 X 200 = 200,000 divisions, as the deflection maybe con-
sidered proportional to the current. The resistance producing this
supposed deflection is .1 megohm, therefore the resistance which
would produce a deflection of only 1 division would be 200,000
X .1, or JUS found above 20,000 megohms. This follows from
Ohm's law, for in order to reduce a deflection by 5^^^^^^ the cur-
i-ent must be redui^ed by oualuuij ^"^ consequently the resistance
inserted must be 200,000 times as great. This is true, however,
only in case the E. M. F. applied remains constant.
After the constant has been determined the known resistance
R is replaced by the unknown resistance A\ The galvanometer
186
ELECTIilCAL MEASUREMENTS.
36
shunt is readjusted if necessary and the deflection obtained is again
noted. The value of the unknown resistance is then found by
dividing the value of the constant by the product of the deflection
dj and the multiplying power m^ of the shunt used. To continue
our illustration suppose d^ = 50 divisions, and m^ = 10. The
deflection, if the full current went througli the galvanometer, would
be 50 X 10 = 500 divisions. A deflection of one division is pro-
duced with a resistance of 20,000 megohms, hence a resistance
producing a deflection of 500 divisions must be ^J^ of that; then
A^ = ^'^^-^ = 40 megohms. These steps may be combined and
the resistance given at once by the expression
R m d
X =
m^ d^
Example. — In a high resistance measurement by the alwve
method tlie known resistiince was .2 megohms, and gave a deflec-
tion cf 237 divisions, the multiplying power of the shunt l>eing
100. With the unknown resistance inserted, the deflection was
178 divisions with the full current passing through the galvanom-
eter. What was the value of this resistiinco?
Solution. — In the preceding formula R = .2, w = 100, rf =
237, and d^ = 178 ; also w^ = 1 as the shunt circuit was open.
Therefore,
^ .2 X 100 X 237 _ or « u
1 X 17 8 megohms.
Ans. 20. f) megohms.
Voltmeter Method. Another method of measuring high
resistance is tbiit in which a sensitive high resistance voltmeter
MA/WW
Fig 24.
such as the Weston is used. This method, however, is not so
accurate as the preceding and is not ada])ted to measurements of
resistance greater than a few megohms. The voItm<*ter is con
187
86 ELECTRICAL MEASUREMENTS.
nected in series with the unknown resistance and a source of
constant E. M. F. as shown in Fig. 24. With such an ari-aiige-
mtnt the resistance JC will be to the resistance of the voltmeter
Ry as the volts drop in ^ is to that in the voltmeter. The drop v
in the voltmeter is given by its reading and if the applied electro-
motive force V is known, the drop in ^will be V — r. We
tlierefore liave the proportion,
Ji : R I : V — V : r,
and X= ^~^ X R.
V
The voltage FJ which should be at least 100, may be first deter-
mined by measurement with the voltmeter.
Example. — A voltmeter having a resistance of 15,000 ohms,
was connected in series with an unknown resistance. The E. M. F.
applied to the circuit w<is 110 volts and the voltmeter indicated 6
volts. What was the value of the unknown resistance ?
Solution. — Applying the preceding formula
V = 110, t; = 6, and 5 = 15,000,
therefore
X = V^ ~ ^ X 15,000 = 260,000 ohms, or .26 megohms,
b
Ans. .26 megohms.
Insulation Resistance. The measurement of insulation resist-
ance is performed by either of the two preceding methods of meas-
uring high resistance. The voltmeter method is the simpler, but
since it cannot be used to meiisure resistances greater than a few
megohms, the direct deflection method proves to be the more val-
uable. The insulation of low potential circuits however, need not
exceed five megohms, and in testing such circuits the voltmeter
method may be used. If little or no deflection is obtained it is
then evident that the insulation is at legist several megohms, which
is all that is desired. As the insulation of high potential circuits
must bo greater than five or ten megohms the direct deflection
method should then be used.
The connections in testing the insulation of a circuit by these
two methods are similar to those shown m Figs. 23 and 24, the
resistance A'' being replaced by the insulation of the circuit. Thi»
is accomplished by connecting one wire to the line and the other to
\a&
ELECTRICAL MEASUREMENTS. 87
ground such as to a gas or water pipe. The insulation of the
line from the earth is then included in the testing circuit ; the cur-
rent passmg from the battery, or other source, through the volt-
meter or galvanometer to line, from line through the insulation to
ground, and then to the battery.
The insulation of a dynamo, that is, the resistance between
its conductors and its frame, is tested in a similar manner. This
resistance should be at least one megohm for a 110 volt machine
but two megohms is to be preferred and is customary. This insu-
lation is measured by connecting one wire to the frame and the
other to the binding post, brushes or commutator. Tlie insulation
is then included in the circuit. Insulation resistance decreases
with increase of temperature so that this test of a machine should
be made after a full load run of several hours.
The E. M. F. used should be constant and of one to two
hundred volts value. Secondary batteries are the best for this pur-
pose, but silver chloride testing cells are much used. The current
decreases from its value, at beginning the test, because of the
electrification or electrostatic charge of the insulation. For this
reason the deflection should not be read until after a certain period
of electrification — usually one minute. This action is quicker in
some materials than in others, and is also greater at low than at
liigh temperatures.
Insulation Resistance of Wire. The direct deflection method
is nsed to test the insulation of short lengths of wire. This is
sometimes necessary during manufacture or tq test the value of
different samples.
At least 200 feet of wire is used. This is made into a coil
and immersed in a tank of water. A few inches of the ends o{ the
wire are bared and twisted together ; a few feet extending outside
the tank. One wire of the testing circuit is connected to the ends
of the coil and the other to a metal plate also ininiorsed in the
water. The plate should be positive, and the current then passes
from this through the water and insulation to the core of the wire.
The galvanometer must be provided with a short circuiting key,
which is always closed when the battery key is operated, allowing
no current then to pass through the galvanometer. Cables in
water act like condensers when charged or discharged, and the
139
88 KLECTUICAL MEASUREMENTS.
large current would injure the galvanometer were it not short cir-
cuited.
The water should ]« at a temperature of 76® F., which is
generally accepted as tlie standard. A diflference of one degree in
the temperature will sometimes cause a difference of several per
cent in the insulation resistance. The cable should remain in the
water at least 24 hours before the test is made, and it is well to
Uike minute readings of the galvanometer during the first five min-
utes ehai^ng. The insulation resistance is usually calculated
fi-om the deflection taken at the end of five minutes charging
The length of time immersed, temperatui-e, E. M. F., and time of
charging should always be stilted in a report of a test. Knowing
the insulation resistance and length of the sample, the insulation
resistance per mile is found by multiplying this resistance by the
length expressed in miles. For example, if the insulation for a
length of .3 mile was found to be 1 ,800 megohms, then for a mile
of the cable the insulation would be only 1,800 X .3 = 540
megohms, for of coui-se the longer the cable, the less will be the
insulation resistance. The insulation of a good cable should lie
from 400 to 1,000 megohms per mile.
Example. — In measuring the insulation resistance of 250
feet of wire by the din^ct deflection method, the deflection after
liv(» minutes chai-ging of the cable was 15 scale divisions, the full
current parsing through the galvanometer. In determining the
constant the known resistance was .1 megohm, and the deflection
204 divisions, the multiplying power of the shunt l)eing 10,000.
(^ompute the value of the constant, the insulation i*esistAnce of the
sample, and the insulation per mile.
Solution. — As the constant is equal to the product of the
known resistance, deflection and multiplying power of the shunt,
we have,
coiutant = .1 X 204 X 10,000 = 204,000 megohms.
The insulation of the sample is equal to this resistance
divided by the product of the deflection after five minutes charging
and the multiplying power of the shunt then used. As the full
current passed through the galvanometer this latter quantity is
unity.
140
ELECTItlCAL MEASUKEMENTS. 39
The insulation is therefore
— -L — = 18,600 megohms.
15
The insulation per mile is
260
13,600 X -^ — = 644 megohms (nearly).
Resistance of Conductors. The conductivity resistance of
telegraph lines, cables, etc!., which are already installed, is meajs-
ured by use of the Wheatstone bridge. One end only of the con-
ductor whose resistance is to be mejusured is then at hand, and this
is joined to one of the tenninals of the bridge while the other
bridge terminal is connected to earth. The distant end of the wire
is also connected to eai-th and the measurement then made in the
usual manner.
The earth resistance between the two ends of the wire is then
included with the unknown resistance but the former is consid-
ered negligible. There are two factora, however, which may lead
to considerable error in the I'csult ; firat, the presence of earth cur-
rents, and second, the connections to earth may be defective.
When it is possible the loop test should be used. The distant
ends of two wires are then connected together while the near ends
are connected to the bridge terminals. The total resistance of the
two wires is then measured. This method does not, however, give
the resistance of a single wire. One of the best methods of obtain-
ing this is the following :
Three wires and three measurements are required. Let tlie
i^istances of the three wires 7, ^ and 3 be respectively r^, rg, and
^3 . First wires 1 and 2 are looped at their distant ends and sup-
pose their resistance is found to be 5j ; next wires 1 and 3 are
looped and their resistjince is found to be 72^ 5 finally r^ and r^ are
looped and their resistance is found to be B^. We then have
♦•i + ^2 = ^^
♦•i + ''8 = ^2
^^ding the equations and dividing by 2, we have
r
,+r,-\-r, = -1 -T- ^^, ^ ^.,
141
10
iripn»rrw&
r, = _- "^ — (r. -hr^
^ ^1 ~ ^ ~ -^ »
:^Tnriar'-v
^' — - /»».» -^ A^ i»
^1 = — T' ~—^
ami r, = -^^^ -_^_-r^L _ «^
The ifi:i*XiVuil j^TzciA ot die lotfC dine &nniiiiIaB emtam ooh
lrnr»n?n •-. x;uititi»»s .ixiti hf^ni!e die re«\Tiir»*ii re^fiscamce^ mar be WAiiij
The r»»siatAn«^t* of nearlr ail fieui coils of dmaiiios m^iv be
mejwnreri hy :iMe *>f uke VTheaott^ne bricfcie. SIiiiiLt field eoik of
n*) voir miuir.inem Ijav^ 4 resiat;uiee of from ai3iMre 5 ohms in hkip
marhin*^ z*'* !♦>'» or i"<> ofems in entail maefamesw High Tnitage
ma^h;r.r^^ ruiv^ a oor..^iilerabiv hi^er *fa.aiit field coil res£?tuice.
The merles ooil of crcatAnt ciirren.n »ivTiaxxu» have a rcsLstuiee of
1 r/i 2') ohrr.:^. Or. acnrr^.t: '-f the high self-indoctioii of field
''oi;:^ the ^'-^I'^'^nometer kry *hocld noc fee depressed until sooie
rirr.e afr>-r •i'.e r.-.tcterv rirrriiit L* oL:***^^
The ^irrr.At.irpr r'^^i.-t^noe of m*:♦^: macLinct? mar be measured
r,v t .-^ h;i i^''-*, V/.' i: i-^ tLi::allv much, more cr»nTeniect t*'* U5e the
^ !... ■■.: yr-r.^.^i,': "' rr.eth'^-d d*r!5criV>ed beloTv, measaring both car-
e^r.t H.:.'\ v /.u:.^e, and oht^iinin^ the r»?sistaaoe l«y simple divisioD.
IjfKatinz Faults. The I«x-atiiu^ of faults in telegraph lines
anrl r *?>>••» ofvn involvfr:^ a nrimber of measurements and consider-
aKl<- r/^U:,i.Hr.]^,n. Thf- riature of faults are so varied that one or
t7/r, rri'-th''yl--i r^nnot h^f applied t^^t all cases.
Th'- kind of a fault which is easiest to locale is where the
f'lrfMi^, ']-'. r:ornpl^'tely broken and the fault has no resistance. In
thlai 'a-'' t\>(: ^oFidnctivitv resistarK**- of the wire to the fault mavbe
ff»';nMr''l, iiT]f\ rlivifiing this t.y the conductivity resistance per
utiU. i/ivcA th<' dlnUmce in miles to the fault.
Th'r h/^ation of faults in dynamos is easily accomplished by
th^! r/rop (ST fall of potenfial method, A current from an independ-
ent wtwwA'. JH {jaHHed through the armature and connections, the
\4a
ELECTRICAL MEASUREMENTS. 41
t
armature being restrained from moving. The leads from a low
reading voltmeter are then applied to different sections of the cir-
cuit. The reading of the voltmeter gives of course, the drop in
volts in the section included between its terminals. For example,
the voltmeter leads may be successively applied to all adjacent
segments of the commutator. The potential difference between
adjacent segments should be equal ; thus a short cii*cuit would
be readily located by a decrease in the voltmeter reading.
When the current is passed through the field coils, the potential
difference at the terminals of each field coil should be nearly equal.
A \)ooT contact will be at once indicated by an increase in the
reading.
If the current is taken from 110 volt mains, the shunt coils
jmay be connected directly to them, but in testing the armature an
sidditional resistance should be connected in series to prevent a
^hort circuit. This extra resistance should be adjustable so that
"•ihe current may be i-egulated. A water rheostat or bank of incan-
descent lamps serve the purpose very well.
Resistance of Batteries. A very convenient method of
:3nieasuring the resistance of a cell or battery, is by means of an
ammeter and voltmeter. The E. M. F. on open circuit is first
ineasured by the voltmeter. Let this be E. The battery circuit is
then closed through an ammeter and suitable resistance ; the value
of the resistance being such that the output will be equal to the
value desired. The readings of the instruments then give the
current /, and the E. M. F. on closed circuit e. The drop of
potential in the battery is then equal to E — «, which is the
number of volts necessary to drive this current through the
battery. Therefore, by Ohm's law, the resistance of the bat-
tery is equal to — -y— •
Another method requires the use of a low reading voltmeter
and resistance box. The electromotive force E of the battery is
first measured by the voltmeter when the circuit is open. A known
resistance R is then connected in series with the cell and the
E.M. F. again measured. This voltage will be less than before,
as some E. M. F. is lost in the cell itself.
The drop in volts in the cell when the current is flowing is
143
43
ELECTRICAL MEASUREMENTS.
«;qaal to £ — e\ the drop in the resistance R is eqoal to e^ since
tills voltage is lost in the external circuit. Then if A^ is the
resistance of the cell we have the proportion,
X I Rii E — e I e^
as the resistances are proportional to the drop in volts.
Example. — The E. M. F. of a Daniell cell on open circuit
as measured by a voltmeter wjis found to be 1.08 volts. On closed
circuit with an external resist<ince of 15 ohms, the E. M. F. was
.90 volts. What was the internal resistance of the cell ?
Solution. — Here E = 1.08, e = .90, and R= 15. Sub-
stituting in the preceding proportion, we have,
X:15 : : 1.08 — .90 : .90.
Therefore, X= 3. Ans. 3 ohms.
nEASUREHENT OF ELECTROnOTIVE FORCE.
This is most easily accomplished by connecting the leads
from a voltmeter to the ix)ints ]>etween which the potential differ-
ence is to be measured ; the voltmeter forming a shunt circuit.
Weston portable voltmeters are to be recommended for accuracy
and permanency, the average error usually being less than .2 volt.
Potentiometer Method. This method is the standard for the
accurate comparison of electromotive forces, and is used for check-
ing standard cells against each other and for calibi-ating voltmeters.
II
B
Fiff. 25.
The connections are shown in Fig. 25. The potentiometer
P consists of a number of coils all connected in series giving a high
n^sistance. A sliding contact piece (7 Ls adjustable along P as in
the slide wire bridge, and the resistunco c»n either side of O may
\4A
ELECTRICAL MEASUREMENTS. 43
be read directly from a scale. A constant battery B having a
greater E. M. F. than that to be measured, is connected to the
ends of the resistance P, the positive pole of the Ijattery being con-
nected to the left-hand terminal of the potentiometer. Tlie positive
pole of the cell 2> to be tested, is also joined to the left-hand terminal.
The negative terminal of the cell is connected througli a galva-
nometer <r and a key to the contact piece C. A resistance S is
connected in series with the Ixitterv B in order to reduce the
potential difference across P to any desired amount
The determination is iiuulr as follows:
Before testing the cell 2> a standard cell of known E. M. F.
is first inserted in \t& place, and C adjusted until thei-e is no
deflection of the galvanometer upon closing the key. The cell
is connected so that its E. M. F. opposes that of the batter}-;
therefore, when no current flows through the galvanometer, the
E. M. F. of the cell must V)e e(|ual and opposite to the potential
difference l)etween the point C and the terminal at the left. The
resistance R^ included between these points is proportional to the
potential difference. The standard cell is then replaced by the
cell 2), and C again adjusted until there is no deflection of the
galvanometer. Let the resistance included be R. As the E. M. F.
of each cell is proportional to tlu» resistance included, we have,
E. M. F. of cell : E. M. F. of sfandanf cell : : R : R^.
The values of R and R^ are given dii'ectly by the potentio-
meter readings.
Condeiuer Method. A verv convenient nieth(Ml is that in
which a condenser is used. A condenser is first charged by :i
standard cell and then discharged througli a Iwillistie galvanonie.
ter. The condenser is then charged by the cell to lx> tested and
again discharged through the galvanometer. The E. M. F. of the
cells are proportional to the deflections of the galvanometer.
E. n. F. ol Alternating Currents. As the E. M. F. of alter-
nating currents changes from positive to negative and from nega-
tive to positive many times a second, it is evident that the alK>ve
methods which apply to direct currents cannot be adapted to alter-
nating cnrrents. Special forms of voltm ters and dynamometers
are therefoi-e necessary.
The electrostatic voltmeter is verv lar;Tjelv used in altcTnat-
145
u
ELECTRICAL
:4 4^ i 4,
ing (mment work. A» die force of attzau^tSoa between two plates
Ia the 3anif» whether one is ponitive and the odier negiitEve^ or one
negative and the other ponitive. it is evident that this Toltmeter is
equally well adapted for alternating or for direct eiizxents».
The ilynamometer is also used ia altematm^ ennent work.
For measuring E. M. F. the coils are given a hi^ least^nce or a
high resistance is piai^eii in .series with them. The Weston alternating
current voltmeter Is of the dynamometer type. In this instrument th«?
movable coil is mounted in bearings, the current being lead to and
from the coil by watch aprings as in. the direct current voltmeter.
Calibratmi of Veltaictefs. The errors in a voltmeter scale
which is already graduated, are very accurately determined by use
of the f)rjtentiometer. The connections, shown in Fig. 26, are
.similar to those in Fig. io required in measuring E. M. F. The
-$
\m
lolWlpi .
voltmeter Tto U- fralibrated Ls connected across the ends of the
p<»tentiom.ter, wliich should have a resistance of at least 10,000
<,l.rr..s. A con.suuit batterj- B which must have an E. M. F. greater
than that of th^- highest reading of the voltmeter is also connected
to' ty»f T>oteiitioincter terminals. The adjustable resistance S is
„b,mI to regulate the E. M. F. applied to the terminak of the
pr,t..ntiometer. Standitrd cells C. in series with a galvanometer
!,M/r.oni.er.t.rd as shown, the i^>sitive pole of the cells and bit-
L-ry are lK)tli coiine.cted to the same potentiometer termmal. A
rf.«-.HUiiri. should be connected in series with the cells and galva-
nometer to prevent polaiization during trial adjustments, and may
be Bhoit cin:uite<l durin^r the final adiustment.
To calibrate a voltmeter, .V is nrat adjusted unul a desired
\4A
ELECnueAL MEASUREMENTS. 45
deflection of the voltmeter is obtained. The contact key or slider
is then moved until such a point is found that closing the key
causes no deflection of the galvanometer. The E. M. F. of the
cells then exactly balances the potential difference between the
slider and left-hand terminal. The resistances r and R on either
side of the slider are then read from the instrument, and the true
potential difference across the ends of the potentiometer is calcu-
lated as follows : The drop in volts in r is equal to tlie E. M. F.
of the cells (X The drop in volts in ^ -j- r is the total E. M. F.
available. As the drop in volts is proportional to the resistance,
we have
total JS. M. F. : E. M. F, of C : : R ^ r : r,
therefore
total H. M. F. = -^-T X E.M.F.of C.
r
Example. — In calibrating a voltmeter the shunt S was
adjusted to give a voltmeter reading of 27.8 volts. Two standard
cells were used each having an E. M. F. of 1.435 volts. The total
resistance of the potentiometer was 10,000 ohms, and when a
balance was secured the value of r was 1,040 ohms. What cor-
rection should be applied to the voltmeter reading ?
Solution. — In this case 7? + r = 10,000, r = 1,040 and
E. M. F. of C = 2 X 1.435 z= 2.87. Substituting in the pre-
ceding formula,
total E. M.F. = ^yS- ^ ^'^'^ ^ -'^•^ ""^^^ (nearly).
The voltmeter i-eading is therefore too high by .2 volt.
Ans. — .2 volt.
By adjusting the shunt aS' the errors in various parts of the
scale may be determined and a table of corrections made.
If it is desired to graduate the scale so as to give correct read-
ings a slightly different method is employed. In such a case the
apparatus is adjusted to give a ix)tential difft»renee of a certain
number of volts at tlie terminals of the potentiometer, and the
position taken by the pointer of the voltmeter is marked that num-
ber of volts. By succeeding adjustments other points are located
along the scale, and this skeleton scale is then subdivided into
smaller divisions. Suppose a reading of 10 volts is desired. By
147
46 KLECTIilCAL MEASUREMENTS.'
moving the slider, r is given such a resistance that r : 10,000 : :
2.87 : 10, assuming the total resistance to be 10,000 ohms and
that the standard cells have an £. M. F. of 2.87 volts. The value
of r is then made equal to 2,870 ohms. The shunt S is then
iidjusted until there is no deflection of the galvanometer, which
gives a potential difference at the voltmeter terminals of 10 volts.
Similarly the correct position of the pointer for 20, 80, 40, etc.,
volts may be determined.
It is desirable to use several standard cells in series at C7, as
this gives a close average value and also gives larger readings on
the potentiometer. AVhen very accurate work is required the
standard cells should be placed in a water or oil bath and a cor-
rection for temperature made if necessary.
The above method of calibrating voltmeters is that used in
the laboratory for calibrating standaitl instruments. Station volt-
meters may then Ik? calibrated by direct comparison with such
standards.
The Clark Standard Cell. The ah^olute unit of E. M. F. is
that developed by a conductor when it cuts one line of force j>er
second, and the practical unit or volt is equal to 10^ absolute units.
In order to have some working standard, the volt is defined in
terms of the Clark cell. In this cell the negative element is a rod
of pure zinc in a solution of zuu) sulphate, and the positive element
is mercury in a paste of niercurous sulphate and zinc sulphate solu-
tion. This cell is the international stiindard of E. M. F. and if the
stiindard directions for setting it up are followed, the E. M. F. of
1.434 tnnf volts will be obtained if the temperature is 16® C. Tho
E. M.-F. decreases slightly with an increase of temperature, and if
the cell is at any othei? temperature, the correct E. M. F. is given
by the formula E = 1.434 — .0011 (t —15 ), where t is the tem-
j)erature in degrees Centigrade.
There are several other forms of cells used as standards, one
of the most reliable being the Carhai-t-Clark cell, which is illus-
trated in Fig. 27. Above a layer of mercury in the bottom of the
cell is the mercurous sulphate and zinc sulphate solution. A piece
of cork separates this from a solution of zinc sulphate above it, in
wliich the zinc is imuiersed. The s*-rength f)f this solution is deter-
mined by the fact that it is satunited at 0^ C. Contact is made
146
ELECTRICAL MEASUREMENTS.
with the meicDiy in t)ie bottom of the cell by a platlnuin vrire pass-
ii^ down through a small glass tube. The E. M. F. of tliis cell at
15° C. is 1.442 Tolts, the E. M. F. at other temperatureB being
given hj the formula
H = 1.442 j 1 — .00039 (t — 15)
Id the figure a Centigrade thermometer iu
attached to the cell.
In using a standard cell great rare
should be taken that only voiy .snmll cnr-
rents are allowed to jxiss tliroiigli it and
then only for a short perio<l. To prevent
polarization and n conseijiient decrease of
E. M. F. a high reliance whould l>e con-
nected in series, except for final adjust-
ments in zero methods. A short circuit is
likely to permanently injure a cell.
MEASUREHENT OF CURRENT.
One of the most accurate and universally applicable methods
of measuring current strength is to luca^^ure the potential difFer-
ence acroas^i known reisistanci- through which the <'iu'rt'iit is pass-
ing. The value of the current is then given by tlie formula
very large or very Bmall currents.
The simplest method of measuring current strength is by the
insertion of an ammeter in tlie circuit. Ammeters are usually
less reliable than voltmeters, but tiie imi>ortanee of obtaining cur-
rent strength accurately is usually less than that of E. At. V.
Alternating currents may be measured by tlie dynamometer,
current balance, measurement of E. M. F. across a known resist-
ance, and by some forms of ammeters.
Ammeter Calibration. A very convenient method of det«t^
mining the accuracy of ammeters is by measuring the potential
difference across a known resist^mce in the circuit. The connec-
tions are shown in Fig. 28. In circuit with the soun-e of E. M. V.
is the ammeter A, the known resistance A', and tlie resistance f
48
ELECTRFCAL MEASUREMENTS.
for varying the strength of the current. A standard voltmeter V
which has been accurately calibrated is connected across the
teiminals of the known resist-
ance. Dividing the voltmeter
reading by the value of 7?, de-
termines the current strength
and error of the ammeter.
Ammeters can also be
very accurately calibrated by
direct comparison with Thom-
son's current balance.
m\
"n
A/WWWl
Fig. 28.
MEASUREHENT OF ENERGY.
The wattmeter is used to indicate the power consumed in a
circuit. The dynamometer of the Siemens type is one of the most
common forms of wattmeter. The high resistance coil is shunted
across the pai-t of the circuit in which the energy consumed is to
be measured, and the low resistance coil connected in series.
With direct currents the energy consumed in watts is usually
obtaine(i from nuiltiplying the reading of a voltmeter shunted
across the teiminals, by the reading of an ammeter inserted in the
circuit.
MEASUREMENT OF QUANTITY.
As the unit of quantity is the ampere second or coulomb, it
may be measured by determining the current strength for a certain
length of time.
One method of measuring quantity which is largely used
dei)ends on the chemical action of a current when passed through
an electrolyte, the latter l)eing decomposed by the current. The
amount of this decomposition is directly proportional to the strength
of the current and to the time. Therefore the quantity of elec-
tricity will depend upon the amount of chemical decomposition.
The average current may be determiiu'd by dividing the quantity
by the time. Instruments arranged for measuring quantity or
current strength on this principle are termed voltameters.
The Edison chemical meter is the voltameter most generally
160
ELECTRICAL MEASUREMENTS. 49
used. This consists of a cell containing a solution of zinc sulphate,
and two zinc plates of a certain size at a fixed distance apart. A
low resistance shunt of German silver is connected in the main cir-
cuit and the cell is connected about this. If the ratio of the cell
resistance to that of the shunt is constant, then a certain fraction of
the total current >vill pass through the cell from which the whole
may be determined. Tliis ratio is about 1000. As the resistance
of tlie cell decreases with rise of temperatui-e, a resistance of
copper wire is inserted in series with it. The increase in resist-
ance of this with rise of temperature, just equals the decrease in
the resistance of the cell. The mtio of the resistances is thus
maintained constant. As the current passes from one zinc plate
to the other through the electrolyte, the positive plate gradually
goes into solution and loses in weight and the negative plate gradu-
ally gains in weight. By weighing the plates before and after
the passage of the current the quantity of electricity passed may
be determined. Usually the weight of the positive plate only is
taken, and its lost weight multiplied by a constant to give the
number of coulombs or ampere-hours.
The Forbes meter depends upon the heating effect of a cur-
rent to record the number of ampere-hours. The current Ls
passed through a number of fine wires connected in parallel. The
heating of these causes a rising curi-ent of warm air and this
rotates a spindle carrying light mica vanes. The uaml)er of
ampere-hours is determined from the number of revolutions of the
spindle.
If the potential of the circuit is constant the number of watt-
hours is found from the ampere-hours if the latter is multiplied by
the voltage of the circuit.
nEASUREMENT OF CAPACITY.
Capacity and its measurement becomes of considerable import-
ance in the case of submarine and underground cables. Such cables
actually become condensers, the internal wire forms the inner coat-
ing, the water the outer coating and the insulation forms the dielec-
tric between them. This presence of capacity in cables makes it
necessary to charge them before a signal is indicated at the distant
151
50
KLKCTiaCAL MKASUUKMENTS.
end, and thus cunses retiirdatioii in the transmission of signals and
also enfeebles the strength of the current at the distant station.
Ordinary condensers may be charged or discharged almost
Instantaneously. The charging and discharging of cables however,
i-equires so much time that the accurate measurement of their
capacity is very difficult. In discharging, a cable yields most of
its charge at first, and then gradually gives up the remainder.
Direct Deflection ilethod. In this method of measuring
capacity, which is the simplest and most generally employed, a
standard condenser is fii-st charged by a battery and then discharged
through a ballistic galvanometer. The condenser of unknov^n
capacity is then similarly charged and discharged. The capacities
of the two condensers are proportional to the galvanometer de-
Hections.
Example. — A condenser of .8 microfarad capacity was
charged by a battery and when discharged through a galvanome-
ter gave a detlection of 103 scale divisions. A condenser of
unknown capacity was then charged by the same battery and on
discharge gave a deflection of 128 divisions. What was the
unknown capacity ?
Sohition. — As the capacities are proportional to the deflec-
tions we have the proportion,
a; : .3 : : 128 : 103
or a: = j^f X .3 = .37 +
Ans. .37 + microfarad.
Divided Charge Method. This method gives more accurate
results tliaii the preceding and is often used in measuring the capa-
city of long cables. The
(connections are shown in
Fig. 29. The key k is first
depressed, charging a con-
denser Coi known capacity.
The key k is then opened
and the key K raised, dis-
charging the condenser
through the galvanometer
(r, giving a deflection D*
Cis th(Mi agam charged, k opened and K depressed. This connects
\\
{
Fis:. 20.
152
ELKCTKICAL MEASUREMENTS.
61
the standard condenser with the condenser c of unknown capacity,
and shares part of its charge with the same. The division of charge
is proportional to the capacities. By raising JTthe condenser C is
again discharged through the galvanometer, giving a deflection d.
As the deflections are proportional to the charge of C in each case,
the capacity of (7 is to that of c as the first deflection D is to the
decrease in deflection which represents the charge of Cj that is,
0: c:: I): D — d,
therefore,
D
I)
X O.
Bridge ilethod. In this method the capacities of a standard
and of any other condenser are bahmced in the arms of a bridge.
Fig. 30 illustrates the necessary connections. The standard C
and that of unknown capacity ^, form two arms of the bridge,
and the adjustable resistances 7? and r complete it When tho
key -ST is niised, current flows from the Iwittery and charges thfj
Fig. 30.
condensers; on depressing the key tlie condensers are discharged.
The resistances r and 7? are adjusted until during charging and
discharging there is no deflection of the galvanometer. The poten-
tial at D and ^ will then be the same, and the condensers are there
fore charged under the same potential ; the quantity of electricity
required to charge them will then be proportional to their capacL
ties. When there is no deflection of the galvanometer in charging
or discharging, the drop in the resistances r and 7? must be the
same. Suppose the capacity of c? to be larger than that of C: then
163
62
ELECTRICAL MEASUREMENTS.
in charging, the current passing through r must be greater than
that through 7?. As the drop is proportional to the product of
current and resistance ; then in order to have the same drop in r as
in y? if a larger current flows through r its resistance must be
less. The capacities of the condensers are therefore inversely as
these resistances, or
ex C I I R I r.
Example. — With condensers connected as shown in Fig. 30,
it was found thtit there was no deflection of the galvanometer when
r was 2,700 ohms and 7? 7,300 ohms. The capacity of the stand-
ard condenser was .2 microfarad. What was the capacity of c ?
Solution. — Substituting in the preceding proportion, we
have,
(? : .2 : : 7,300 : 2,700,
therefore c = .54. Ans. .54 microfarad.
Thomson's ilethod. If two condensers are charged with
Fig. 31.
equal quantities of electricity and then discharged by connecting
them in series -{- to — and — to +> the two charges will exactly
neutralize each other and no resultiint charge will remain. To
charge two condensers of unequal capacity with equal quantities
of electricity requires a higher E. M. F. at the terminals of the
smaller condenser, that is, the E. M. F. applied at the terminals
must be inversely as the capacities. If the ratio of the E. M. F.'s
is determined, then the ratio of the capacities of the condensers is
also obtained. These principles are involved in Thomson's method.
154
ELECTRIC WIRING*
INSTALLING THE DYNAHO.
Djiiamos should be located in a dry place so situated that
the surrounding atmosphere is cool. If the surrounding air is
warm, it reduces the safe carrying capacity of the machine and is
likely to allow such temperature to rise in the machine itself as to
burn out either armature or field, or both. A dvnamo should not
be installed where any hazardous process is carried on, nor where
it would be exposed to inflammable gases or flying combustible
materials, as the liability to occasional sparks from the conmiuta-
tor or brushes might cause serious explosions.
Wherever it is possible, d\nmmos should be raised or insu-
lated above the surrounding floor, on wooden base frames, which
should be kept filled to prevent the absori)tion of moisture, and
also kept clean and dry. When it is impracticable to insulate a
dynamo on account of its^reat weight, or for any other reason,
the Inspection Department of the Board of Fire Underwriters
having jurisdiction may, in writing, permit the omission of the
wooden base frame, in which case the frame should be permanent-
ly and eflfectively grounded. When a frame is grounded, the in-
sulation of the entire system depends upon the insulation of the
dynamo conductors from the frame, and if this breaks down the
system is grounded and should be remedied at once.
Qroundins^ Dynamo Frames can be effectually done by
firmly attaching a uire to the frame and to any main water pipe
inside the building. The wire should be securely fastened to the
pipe by screwing a brass plug into the pipe and soldering the wire
to this plug. WTien the dvnamo is direct driven, an excellent
ground is obtained through the engine coupling and the piping of
the engine and boiler.
Wherever high-potential machines have their frames ground-
ed, a small board walk should be built around them and raised
above the floor, on porcelain or glass insulators, in order that the
155
kLLcTKiC \mi:in6
«lviiaiiio U'whr umy Iw \ir** *<*'.* A ir*ui a >ln»ck wlicii ail j list iii<E^
bnushcs or working alx.iut ilic inacliiiK'.
SufSciont space ^iJou^l lie left on all siJes of llio <Iynamo and
<.*t»{>ecially at the coiiiriiiuator end, s^i that there may be ample
HMJin for removing armatures, e«.immutatrirs, or any other parts at
any time.
Circuit Brealcers and Fuses* Every ermstant-potential gen-
erator should \xi protectee! from excessive current by a safety fuse
or c-quivalent device of approve<l deriigii, in each wire lead, such
as a circuit breaker. The latter is preferable, on acc<^^>unt of its
being immeasurably more accurate and convenient for resetting.
Such device's should be jila^'od on or as near as possible to the
dynamo. When the nc-eds of the service make these devices im-
practicable, the InsfKfCtion Department having jurisdiction may,
in writing, mollify the rc*(iuireinents.
The lx*st practice is to place the fuses on the dynamo itself,
and the circuit breakers on the switchl)oanl.
Waterproof Covers should be provide*! for every d\Tiam
and placed over each machine as soon as it is shut dowii. Xegli-
jrence in this matter has caused man v an armature and fiehl coil
tc) burn out, as only a few drops of water are necessary to cause a
short circuit as soon as the machine is started up again, which
might do many d< liars' worth of damage, to say nothing of the
inconvenience caused by shutting off light or power when it is
•lost needed, and for an indefinite length of time.
Name -Plates. Every dynamo should Ik* provided with a
name-pliite, giving the nuikcr's name, the capacity in volts and
nnij)eres, and the normal s|)eed in revolutions per minute. This
will show <'xactly what the machine was designed for, and how it
should be run.
Wiring from Dynamos to switchboards should be in plain
, ight or rcndily accessible, and should l)e supported entirely
upon iHni combustible insulators, such as glass or porcelain; in no
(•ase should any wire romo in contact with anything except these
insulators, jiiid tli<' terminals upon the dynamos and switchl)oards.
When it becomes n<*cessarv to run th<*se wires through a wall or
IJotir, the holes must Im* prote<'ted by some approved uou-eombus-
106
ELECTKIC WlRIiVG
tible insulating tube, such as glass or porcelain, and in every case
the tube must be fastened so that it shall not slip or pull out.
Sections of any tubing, whether armored or otherwise, that are
chopped oflf for this pur|X)se, should not be used. All wires for
dynamos and switchboard work should be kept so far apart that
ihere is no liability of their coming in contact with one another,
and should be covered with non-intlammable insulating material
sufficient to prevent accidental contact, except that bus bars may
l>e made of bare metal so that additional circuits can be readily
attached. Wires must have amjde carrying caj)acity, so as not to
heat with the maximum current likely to flow through them under
natural conditions. (See ^'Capacity of Wires Table," page *^7.)
So much trouble in past years has arisen from faulty construction
of switchboards, and the apparatus i)laced ui)on them, that strict
requirements have been necessarily adopted by engineers as well
as insurance inspectors, and the following suggestions are recom-
mended by the latter :
The Switchboard should be so placed as to reduce to a min-
imum the danger of communicating fire to adjacent combustible
material, and, like the dynamo, should be erected in a dry place
and kept free from moisture. It is n(»cessary that it should be
accessible from all sides when the wiring is done on the back of
the board, but it may be placed against a brick or stone wall when
all wiring is on the face.
The board should be constructed wholly of non -combustible
material, but wdien this is impossible a hard-wood board made in
skeleton form, and well filled to prevent absorption of moisture, is
considered safe. Ev(*ry instrument, switch or apparatus of any
kind placed upon the switchboard should have its own non-com-
bustible insulating base. This is refpiired of every pioco of ap-
paratus connected in any way with any circuit. If it is found
impossible to place the resistance box or regulator (which should,
in every case, be made entirely of non-combustible material) upon
the switchboard, it must be placed at least one foot from com-
bustible material or separated therefrom by a non-inflammable,
non-absorptive insulating material. A slate slab is preferable.
Special attention is called to the fact that switchboards should not
157
6 ELECTKIC WIKING -
be built down to the floor, nor up to the ceiling, but a space of at
least ten or twelve inches should be left between the floor and the
board, and from eighteen to twenty-four inches between the ceil-
ing and the board, in order to prevent fire from communicating
from the switchboard to the floor or ceiling, and also to prevent
space being used for storage of rubbish and oily waste.
Lii^htnins: Arresters should be attached to each side of every
overhead circuit connected with the station.
It is recommended to all electric light and power companies
that arresters be connected at intervals over systems in such num-
bers and so located as to prevent ordinary discharges entering
(over the wires) buildings connected to the lines. They should
be located in readily accessible places away from combustible ma-
terials, and as near as practicable to the point where the wires
enter the building.
Station arresters should generally be placed in plain sight
on the switchboard. In all cases, kinks, coils and sharp bends in
the wires between the arresters and the outdoor lines should be
avoided as far as possible. Arresters should be connected with a
thoroughly good and permanent ground connection by metallic
strips or wires having a conductivity not less than that of a "No.
6 B. & S. copper wire, and running as nearly as possible in a
straight line from the arresters to the earth connection.
Ground wires for lightning arresters should not be attached
to gas pipes within the buildings.
It is often desirable to introduce a choke coil in circuit be-
tween the arresters and the dynamo. In no case should the
ground wire from a lightning arrester be put into iron pipes, as
these would tend to impede the discharge.
Unless a good, damp ground is used in connection with all
lightning arresters, they are practically useless.,^ Groimd con-
nections should be of the most approved construction, and should
be made where permanently clamp earth can be conveniently
reached. For a bank of arresters such as is commonly found in
a power house, the following instructions will be found valuable:
First, dig a hole six feet square directly under the arresters, until
permanently damp earth has been reached ; second, cover the hot-
l^S
ELECTRIC WIRING
torn of this hole with two feet of crushed coke or charcoal (about
pea size) ; third, over this lay twenty-five square feet of No. 16
copper plate; fourth, solder at least two ground wires, which
should not be smaller than No. G, securely across the entire sur-
face of the ground plate ; fifth, now cover the ground plate with
two feet of crushed coke or charcoal ; sixth, fill in the hole with
earth, using running water to settle.
All lightning arresters should be mounted on non-combustible
bases and be so constructed as not to maintain an arc after tho
discharge has passed ; they should have no moving parts.
Testing: of Insulation Resistance. All circuits except those
permanently grounded should be provided with reliable ground
detectors. Detectors which indicate continuously and give an in-
stant and permanent indication of a ground are preferable.
Ground wires from detectors should not be attached to gas pipes
within the building.
Where continuously indicating detectors are not feasible, the
circuits should be tested at least once per day.
Data obtained from all tests should be preserved for examin-
ation.
Storage or Secondary Batteries should be installed with as
much care as dynamos, and in wiring to and from them the same
precautions and rules should be adopted for safety and the pre-
vention of leaks. The room in wliich they are placed should l>e
kept not only dry, but exceptionally well aired, to carry off all
fumes which are bound to arise. The insulators for the support
of the secondary batteries should be glass or porcelain, as filled
wood alone would not be approved.
Care of Dynamos. A few suggestions as to the care of the
dynamo, as well as its installation, may be of value ; and one of the
important points under this head is that the driving power should
have characteristics of steadiness and regularity of speed, and
should always be sufficient to drive the d^^^amo with its full load,
besides doing the other work which it may be called upon to sus-
tain. TTnsatisfactory results are always obtained by attempting
to run a dynamo on an overloaded engine.
159
8 ELECTKIC WIRING
Wooden bed-plates are supplied, when ordered, for all dyna-
mos, except in the largest and direct-connected machines.
Most machines are fitted with a ratchet and screw bolt, so
that they may be moved backward or fonvard on the bed-plate in
a direction at right angles to the armature sliaft. By this means
the driving belt can be tightened or loosened at will, while the
machine is in operation. Care should be taken in tightening the
belt not to bind the bearings of the armature and force the oil
from between the surfaces of the shaft and boxes. Such practice
will inevitably cause heating of the bearings and consequent in-
jury.
Machines are usually assembled, unless ordered otherwise, so
that the aimaturc revolves clock-wise when the observer faces the
pulley end of the shaft. All bii)olar dynamos, however, may be
driven in either direction by reversing the brushes and changing
field connections.
The machine is provided with a pulley of the proper size to
transmit the power demanded, and a smaller one should not be
substituted unless approval be obtained from the makers.
When driving from a countershaft, or when belted directly
to the main shaft, a loose pulley or belt holder should be used, to
admit of starting and stopping the dynamo while the shafting is
running.
Belts. A thin double or heavy single belt should be used,
about a half inch narrower than the face of the pulley on the dy-
namo. An endless belt, one without lacing, gives the greatest
steadiness to the lights.
All bolts and nuts should be firmly screwed down. All
nuts which form part of electrical connections should receive
special attention.
The copper commutator brushes are carefully ground to fit
the commutator, and they should be set in the holders so as to
bear evenly upon its surface. On machines where two or more
brushes are supported on one spindle, the brushes on the same side
of the commutator must be set so that they touch the same s^
ments in the same manner. The brushes on the other side of the
commutator must be set to bear on the segments diametrically
190
£L£CTH1C WIIUjS'G
opposite. When the brushes are not so set it is impossible to run
tbe machine without sparking. A convenient method of deter-
mining the proper bearing point for the brushes is to set the toe
of one brush at the line of insulation, dividing two segments of
the commutator; then coimt the dividing lines for one-half the
way around the surface, and set the other brush or brushes at the
line diametrically o])posite the first. Thus, on the forty-four
segment commutator, after setting the tip of one brush at a line
of insulation, count around twenty-three lines, setting the other
brush at the twenty-third line, thus bringing the tij)s directly op-
])Osite each other. The angle which the brushes fuim with the
surface of the commutator should ha carefully noted, and the
brushes should not be allowed to wear so as to increase or decrease
this angle. Careless handling of the machine is at once indicated
by the brushes being worn either to a nearly square end, or to a
long taper in which the forward wires of the brush far outrun the
back or inside wires. Either condition will inevitably be attended
with excessive wear of both comnmtator and brushes.
After copper brushes are set in contact with the commutator,
the armature should never be rotated backward. If it is required
to turn the armature back, raise the brushes from the commutator
by the thumb screw on the holder provided for that purpose, be-
fore allowing such rotation. When starting a machine*, it is al-
ways better to let the brushes down upon the commutator after
the machine has started, rather than before, except when carbon
brushes are used.
BMring^s. See that the bearings of the machine are clean
and free from grit, and that the oil reservoirs are filled with a
good quality of lubricating oil. The oil reservoirs should always
be examined before starting, and all loose grit removed. After
starting the machine, the oil should be all drawn off at the end of
each dav's run for the first three or four davs, after which it mav
Iw assumed that any remaining grit has been carried off with the
oil, and it will onlv be necessary to add a little fresh oil once i^^
seven or ten days.
Starting: Up a Dynamo or ilotor. Fill the oil reservoirn
and see that the automatic oiling rings are free to move. In the
161
10 ELECTRIC WIBIXG
case of dviiainoe fitted with oil cape, stan the oil mnning at a
moderate rate. Too link oil will revolt in heating and injury of
the bearings, but, on the other hand, e^^cessive lubrication is un-
necessary, wasteful and s-^metime* pniJuctive of harm.
When the d\Tiamo is ready to be sianed, place the driving
belt on the pulley on the armature shaft, and then slip it from
the loose pulley or belt holder on to the driving pulley on the
coimtershaft. Tighten the belt by means of the ratchet on the
bed-plate, just sufficiently to keep it from slipping. Care should
be taken not to put more pr^^sure than is necessary on new bear-
ings; carelessness in this resj>ect is often followed by heating of
the boxes, and possible jx^rmaneut injury.
The brushes may now lie let dov^^l upon the commutator, and
the magnets will In? slowly energized. !Move the brushes slowly
backward or forward bv means of the v«»ke handle until there is
no sparking at the lower brushes. Clamp the yoke in this posi-
tion. If the top brushes then spark, move them slightly, one at a
time, forward or backward in the brush holder until their non-
sparking point is found.
The spring pressure exerted upon the commutator brushes
should be just sutlicient to produce a good contact without causing
cutting. If the brushes cut, the connnutator must be smoothed
by the use of sandpaper, not emery clofh.
The dynamo should run without load, at the speed given bv
the manufacturer, and this speed should Ix* unifonnly maintained
imder all conditions. In the case of incandescent dynamos, any
increase of speed above that given, shortens the life of the lam^s
while a variation below causes unsatisfactory lights.
Before the load is put on, the dynamo should \ye tested for
polarity. This can be done by holding a small pocket compass
near the field or pole piece. If the dynamo is connected to bo
run in multiple with another machine and happens to be polar-
ized wrong, it can be given the right polarity by lifting the brushes
from the commutator, closing the field switch and then closing
the double-pole switch used to throw it in multiple with the other
machine, which is supposed to be now running. After the cur-
rent has been allowed to pass through the fields for a few moments.
162
ELECTKIC WIBING 11
the double-pole 8^vitch can be thrown open, and if a test with the
compass is again made the polarity will be found to be right, and
the dynamo is ready to be started in the usual manner.
In starting for the first time a bipolar dynamo which is to be
run in multiple with a spherical armature dynamo^ the above in-
structions should always be followed.
If the dynamo is to be used in series with another on the
three-wire system, and is found to be polarized wrong, it can be
given the right polarity by making a temporary connection from
the positive brush of the new macliinc to the positive brush of the
machine already in operation; and also a temporary connection
from negative brush to negative brush, having first raised the
brushes from the commutator and closed the field switch. Keep
this connection for a few minutes, then open the field switch and
break the temporary connections.
Another test with the compass will show that the polarity of
the machine is now correct, and the dynamo is ready to be started
in the usual manner.
Assuming that the lamps and lines are all ready, the follow-
ing precautions must be observed when starting the dynamo:
Be very careful that the brushes are properly set and dia-
metrically opposite each other, as explained before.
Be sure that all connections are securely made, and all nuts
on the connection boards fimilv set.
»■
In cases where two or more dvnamos are connected in multi-
pie by the use of the equalizing connection, care should be taken
that the circuit wires from both positive brushes are connected to
the same side of the main line, while those from the negative are
connected to the other side.
A neat arrangement of the equalizing connection can be
made by using triple-pole switches on the switchboard, instead of
double-pole switches, and making the equalizing connections
through the center pole of the switch, instead of running a cable
direct from one dynamo to the other. This method is especially
desirable where three or more dynamos are run in multiple.
When dynamos are connected in series, as in the cases where
the three-wire system is in use, the leading wire from the positive
163
12 ELECTKIC W1K1^U
bnisli of one iiiacbiuc is connected to the negative brush of the
other. The other two brushes (negative and positive) are con-
nected to the main wire on the outside of the system, while the
third or center wire is connected to the conductor between the two
dvnanic^.
Dust or OriUy Substancet. AH insulations should be care-
full v eleaned yt ha A once a da v.
If any of tin* connections of the machine bec<jnie heated, ex-
amination will ^liow that the metal surfaces are not clean or not
in i»erfect contact. Avoid the use of water or ice on the bearings
in case of ac^jidentiil heating, as the water may get to the armr-
ture and injure the insulation.
The Commutator should be kept clean and allowed to pol-
ish or glaze itself while running. No oil is necessary, unless the
brushes cut, and then only at the point of cutting. A cloth
slightly greas^.'d with vaseline is best for the purj^se. Xever
use sandpapc^r on the commutator without first lifting the brushes.
Otherwise the grit will stick to the brushes and cut the c<jiiimu-
tator.
Brushes. Care should be taken to keep copper commiitator
brushes in good shf.pe, and not to allow them to be worn out of
square ; that is, loo much to one side, so that the end is not worn
at right angles to the lateral edges.
When the machine is not running, the brushes should always
be raised from the commutator. The brushes should be kept
carefully cleaned, and no oil or dirt allowed to accumulate upon
them. This can be done by washing them occasionally in benzine
or in a hot solution of soda ash.
^fannfaeturers usually furnish a gauge, which should hv
used occasionally to test the wearing of the brushes. If they are
found to be worn either too flat or too blunt, they should be filed
in proper shape, or, better still, ground on a grindstone. Carbon
brushes require less care. Spindles upon which the brush holders
are arranfijed to slide should be cleaned with emerv cloth often
enough to prevent tarnishing or the collection of dirt, which
might cause heating by impairing the electrical connection.
Brush holders that can be moved laterally on the spindle by
164
ELECTBIC WIBING 13
which they are supported^ should be so arranged that the top and
bottom brushes will bear on different parts of the length of the
commutator, for the purpose of distributing the wear more uni-
formly.
In case of a hot box the most natural thing to do is to shut
the machine down, but this should never be done until the fol-
lowing alternatives have been tried and failed :
First — Lighten the load.
Second — Slacken the belt.
Third — Loosen the caps on the boxes a little.
Fourth — Put more oil in bearings.
Fifth — If all the above fail to remedy the heating, use a
heavy lubricant, such as vaseline or cylinder oil. Sliould the
heating then diminish, the shaft must be polislied with crocus
cloth and the boxes scraped at the end of the (hiy.
Sixth — Under no conditions put ice upon the bearing, un-
less you are j)erfectly familiar with such a j)r(^K;e(liire.
Seventh — If it is absolutely necessary to shut (U>wn, get the
belt off as soon as possible, keej)ing the machine revolving mean-
while in order to prevent sticking, and at the same time take off
the caps of the bearings. Do not stop the flow of oil to the bear-
ings. When the caps have been taken off, stop the machine and
get the linings out immediately, and allow them to cool in the air.
Do not throw the linings into cold water, as it is liable to spring
them.
Scraping should be done only by an experienced person,
otherwise the linings may be ruined. Polish the shaft with cro-
cus cloth, or, if badly cut, file with a very fine file, and afterwards
polish with crocus.
Wipe the shaft, as well as the boxes, very carefully, as per-
haps grit has been the cause of the hot box. Inspect the bearings ;
see that they are in line, that the shaft has not been sprung, and
that the oil collar does not bear against the box.
Oily Waste should be kept in approved metal cans (made
entirely of metal, with legs raising them at least three inches
above the floor and with self-closing covers), and remover! daily.
A competent man should always be kept on duty where gen-
erators are operating.
165
14 ELECTRIC WISING
THE INSTALLATION OF MOTORS.
All motors should be insulated on floors or base frames, which
should be kept filled to prevent absorption of moisture ; also they
should be kept clean and dry. Where frame insulation is im-
practicable, the Inspection Department having jurisdiction may,
in writing, permit its omission, in whi*.h case the frame should be
permanently and effectively grounded.
A high-potential machine which on account of great weight
or for other reasons cannot have its frame insulated, should be
surrounded with an insulated platform. This may be of wood,
mounted on insulating supports, and so arranged that a man must
stand upon it in order to touch any part of the machine.
The leads or branch circuits should be designed to carry a
current at least fifty per cent greater than that required by the
rated capacity of the motor, to provide for the inevitable over-
loading of the motor at times, without over-fusing the wires.
The motor and resistance box should be protected by a cut-
out or circuit breaker, and controlled by a switdh, the switch
plainly indicating whether "on" or "off." Where one-fourth
liorse power or less is used on low-tension circuits a single-pole
switch will be accepted. The switch and rheostat should be lo-
cated wuthin sight of the motor, except in cases where special
permission to locate them elsewhere is given, in writing, by the
Inspection Department having jurisdiction.
In connection with motors the use of circuit breakers, auto-
matic starting boxes and automatic under-load switches is recom-
mended, wherever it is possible to install them.
Motors should not be run in series, multiple, or multiple-
series, except on constant-potential systems, and then only by
special permission of the Inspection Department having juris-
diction.
Like generators, they should be covered with a waterproof
cover when not in use, and if necessary, should be inclosed in an
^'^pproved case.
Motors, when combined with ceiling fans, should be hung
from insulated hooks, or there should be an insulator interposed
between the motor and its support.
\W
ELECTBIC WIEING 15
Every motor should be provided with a name-plate, giving
the maker's name, the capacity in volts and amperes^ and the
normal speed in revolutions per minute.
One rule at all times to be remembered in starting and
Stopping motors is, Switch first, rheostat last, which means, in
starting, close the switch first, and then gradually cut out all re-
sistance as the motor speeds up, and to stop the motor open the
switch first and then cut in all the resistance of the rheostat
which is in series with the motor armature.
When starting any new motor for the first time, see that the
belt is removed from the pulley and the motor started with no
load. Never keep the rheostat handle on any of its coils longer
than a moment, as they are not designed to regulate the speed of
the motor but to prevent too large a flow of current into the
armature before the latter has attained its full speed.
Fig. 1 shows a rheostat which is designed to protect auto^
matically the armature of a motor. The contact arm is fitted with
a spring which constantly tends to throw the arm on the "off
point" and open the circuit, but is prevented from so doing, while
the motor is in operation, by the small electro-magnet, shown on
the face of the rheostat, which consists of a low-resistance coil con-
nected in series with the field winding of the motor. This mag-
net holds the contact arm of the rheostat in the position allow-
ing the maximum working current to flow through the armature
while it is in operation.
If, for any reason, the current supplied to the motor be
momentarily cut off, the speed of the armature generates a coun-
ter current which also tends to hold the arm in position as long
as there is any motion to the motor armature ; but as soon as the
armature ceases to revolve, all current ceases to flow through the
electro-magnet, thereby releasing the rheostat handle, which flies
back to the "off point," as shown in the illustration, and the
motor armature is out of danger. Such a device is of great value
where inexperienced men have to handle motors, and are unaware
that the first thing to be done when a motor stops, for any reason
whatever, is to open the circuit, and then cut in all the resistance
in the rheostat to prevent too large an in-rush of current when
the motor is started up again.
ler
ELECTltlC WllUNQ
An nppr.ivt'il iii^mlkilion m rvcry detail; wiring connections for shunt-
lund 4-pole motor, using double-pole fu5e cut-out instead of circuit breaker.
tLECl'BlC WIlUNd It
«
The Circuit Breaker for under and over loads is also a most
v'a^luabie protection in such cases.
Motor Wiring Pormulae— ([Hroct Current). To find the
fii^e of wire, in circular mils, required to transmit any power
^r^^ distance at any required voltage and with any required loss,
^""^ have the following formula. Having found the required
^Vi^mber of circular mils, it is advisable to add 50 per cent more
•* <^r safety.
e ==: potential of motor. d= distance from generator to motor.
r= volts lost in lines. i*= efficiency of motor.
10.8 =^ resistance in ohms of 1 foot of 07 j)er cent
pure copper wire one mil in diameter.
_ h. p. of motor X 746 X 2d X 10.8
''•"'• eXvXk
To find size of wire from cm., see table, page 37.
AVERAGE MOTOR EFFICIENCY.
1 h. p 75 per cent
3 h. p 80 per cent
5 h. p 80 per cent
10 h. p. and over 00 per cent
Por !Most Cases — (Small Installations). The table and exam-
ples worked out on pages 38, 39 and 40 will give the desired
results without the above formula?.
To find current required by a motor when the horse power,
eflSciency and voltage are known, use the following formula :
Let C = current to be found. H. P. = horse power of motor.
E = voltage of motor cir- K = efficiency of motor,
cult.
H. P. X 746X100
^ E><K
Or, when possible, use table I.
By adding the volts indicated in table II. to the voltage of
the lamp or motor, the result shows the voltage at the dynamo for
losses indicated. Thus 10 per oeni on 110-volt system is: 12.22
volts added to 110 equal 122.22, showing that the dynamo must
generate 122.22 volts for a 10 per cent loss.
160
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171
30
ELECTItIC WIRING
OUTSIDE WIRINQ AND CONSTRUCTION.
Service Wires (those leading from the outside main wire
to the buildings and attached to same) should be "Rubber-Cov-
ered."
Line Wires, other than service wires, should have an approved
"weatherproof covering."
Bare Wires ma^ be used through uninhabited and isolated
territories free from all other wires, as in such places wire cover-
An approved
wound bipolar mo
m in every detail; wirins; connections for shunt-
r, using circuit breaker instead of double-pole fuse cut-out.
ing would be of little use, as it is not relied on for pole insulation,
and is not needed for other purposes, because the permanent
insulation of the wires from the ground is assured by the glass
or porcelain petticoat insulators to which the wires are secured.
Tie Wires should have an insulation equal to that of the
conductors they confine.
ELECTRIC WIRING
An approved installation in every detail, with wiring connections for shunt-
wound multipolar slow speed ceiling motor for direct connection to line shaft.
Using: both circuit breaker and double-pole fuse cut-out.
^
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ELECTEIC WlfilNQ 23
Space Between Wires for outside work, whether for high
or low tension, should be at least one foot, and care should be
exercised to prevent any possibility of a cross connection by
water. Wires should never come in contact with an\-thing except
their insulators.
Rool Structures. If it should become necessary to run
wires over a buildings the wires should be sui)ported on racks
which will raise them seven feet above flat roofs or at least one
foot above the ridge of pitched roofs. See Fig. 4.
Guard Arms. Whenever sharp corners are turned, each
cross arm should be provided with a dead insulated guard arm
to prevent the wires from (Iropi)ing down and creating trouble,
should their insulating support give way.
Petticoat Insulators should be used exclusively for all out-
side work, and esjx'cially on cross arms, racks, roof structures
and service bhx^ks. Porcelain knobs, cleats or rubber hooks
should never be used for this heavy outside work.
Splicins^ of two pieces of wire or cable should be done in
such manner as to Ix? mechanically and electrically secure with-
out solder. The joints should then be soldered to ])revent corro-
sion and consequent bad contact. All joints thus made should be
covered w^ith an insulation equal to that of the conductors.
Tree Wiring. Whenever a line passes through the branches
of trees, it should l)e properly supported by insulators, as shown
in Fig. 5, to prevent the chafing of the wure insulation and
grounding the circuit.
Service Blocks w^hicb are attached to buildings should have
at least two coats of waterproof paint to prevent the absorption
of moisture.
Entrance Wires. Where the service wires enter a build-
ing they should have drip loops outside, and the holes through
which the conductors pass should be bushed with non-combustible,
non-absorptive insulating tubes slanting upward toward the in-
side. See Fig. 6.
Telegrapli and Teleplione wires should never be placed on
the same cross-arm with light or power wires, especially when
alternating currents are used, as trouble will arise from induc-
175
ELECTRIC WIRING
INSULATOR WHEN
NECESSARY TO TIE L, ,„
TO TREE //J?
ELECTBIC WIBING 25
tion, unless expensive special construction, such as the transposing
of the lighting circuits, be resorted to at regular intervals. Even
under these conditions it is bad practice, as an accidental contact
with the lighting or power circuit might result in starting a
fire in the building to which the telephone line is connected. If,
however, it is necessary to place telegraph or telephone wires
on the same poles with lighting or power wires, the distance be-
tween the two inside pins of each cross-arm should not be less
than twenty-six inches, and the metallic sheaths to cables shoulc
be thoroughly and permanently connected to earth.
Transformers should not be placed inside of any buildings
except central stations, and should not be attached to the outside
walls of buildings, unless separated therefrom by substantial sup-
ports.
In cases where it is impossible to exclude the transformer
and primary wiring from entering the building, the transformer
should be located as near as pos-
sible to the point where the
primary wires enter the build-
ing, and should be placed in a
vault or room constructed of or
lined with fire- resisting mate-
pjg. g, rial, and containing nothing but
Porcelain tube, used where wires enter build- the transformer. In everv CaSC
ings, showing drip loop in wire. " ,
the transfonner must be insu-
lated from the ground and the room kept well ventilated. It is
of course the safest and best practice to place all transformers on
j)oles away from the building that is to be lighted, as illustrated
in Fig. 7.
The Qrounding of LowaPotentlal Circuits is allowed only
when such circuits are so arranged that under normal conditions
of service there will be no passage of current over the ground wnre.
In Direct-Current 3-Wire Systems the neutral wires may
be grounded, and when grounded the following rules should be
complied with:
1. They should be grounded at the central station on a
metal plate buried in coke beneath permanent moisture level, and
177
26
ELECTEIC WIBING
also through all avaitahle underground water and gaa pipe
Bystems.
2. In underground systems the neutral wire should also be
grounded at each distributing box through the box.
3. In overhead systems the neutral wire should be grounded
every 500 feet.
When grounding the neutral point of transformerB or the
J=L
M
PRIMARY CUT-OUT
\
^PRIMAFTT
BOLT TRANSFORMER
ro UPRIQHTS BEFOI —
RAISINO TO PLACE
o
tZJ
Fig. 7.
rk; icislaTIiiig transformer*.
neutral wire of distributing systems the following rule should
be complied with:
1. Transformers feeding two-wire systems should be
grounded at the center of the secondary coils, and when feeding
Eystems with a neutral wire, should have the neutral wire grounded
at the transformer, and at least every 500 feet for nndei^roand
Rystcms.
In making ground connections on low-potential circuits, the
ground wire in direct-current 3-wire systems should not at central
ELECTIUC WIRING 27
stations be smaller than the neutral wire, and not smaller than
No. 6 B. & S. elsewhere.
In Alternatlnr-Current Systems the ground wire should never
be less than No. 6 B. & S., and should always have equal carrying
capacity to the secondary lead of the transformer, or the combined
leads where transformers are banked.
These wires should be kept outside of buildings, but may be
directly attached to the building or pole, and should be carried
in as nearly a straight line as possible, all kinks, coils and sharp
bends being avoided.
The ground connection for central stations, transformer sub-
stations, and banks of transformers should be made through metal
plates buried in coke below permanent moisture level, and con-
nection should also be made to all available underground piping
systems, including the lead sheath of underground cables.
For individual transformers and building services the ground
connection may be made to water or other piping systems running
into the buildings. This connection may be made by carrying
the ground wire into the cellar and connecting on the street side
of meters, main cocks, etc., but connection should never be made
to any lead pipes which form part of gas services.
In connecting ground wires to piping systems, wherever pos-
sible, the wires should be soldered into one or more brass plugs
and the plugs forcibly screwed into a pipe fitting, or, where the
pipe is cast iron, into a hole tapped into the pipe itself. For
large stations, where connecting to underground pipes with bell
and spigot joints, it is well to connect to several lengths, as the
pipe joints may be of rather high resistance. Where such plugs
cannot be used, the surface of the pipe may be filed or scraped
bright, the wire wound around it, and a strong clamp put over the
wire and firmly bolted together.
Where groimd plates are used, a No. 16 copper plate, about
3 by 6 feet in size, with about two feet of crushed coke or char-
coal, about pea size, both under and over it, would make a ground
of sufficient capacity for a moderate-sized station, and would prob-
ably answer for the ordinary sub-station or bank of transformers.
For a large central station considerable more area might be neces-
170
ELECTRIC WIRING
ALTERNATrNQ
GROUND DETEOTon
FOR ONE CIRCUIT
TO GROUND
SSi^lvSS'-"-
OLA^
TO OROUNO
ALTERNATINQ
OR0UM> OCTECTOR
FOR TWO aRcurra
TO GROUND
IF THE LAMP BURNS A
GROUND IS INDICATED ON
THE OPPOSITE SIDE OF THE
, CIRCUIT FROM THAT TO
WHICH THE SWITOH IS
CONNECTED
Fig. 8.
Connections of GrouDd Deteclori.
ELEOTBIU WIBING 29
sary, depending upon the underground connections available.
The ground wire should be riveted to such a plate in a number of
places, and soldered for its whole length. Perhaps even better
than a copper plate is a cast iron plate, brass plugs being screwed
into the plate to which the wire is soldered. In all cases, the
joint between the plate and the ground wire should be thoroughly
protected against corrosion, by suitable painting with waterproof
paint or some equivalent.
Ground Detectors. Fig. 8 illustrates a few practical meth-
ods of detecting grounds on alternating and direct-current circuits
which have not been purposely grounded.
In using any one of these methods for detecting grounds,
always see that the circuit to ground is left open after testing the
outside circuits.
Some central station men are in the habit of leaving the
ground circuit closed on one side constantly in order that any
ground that might occur on the other side may be instantly
noticed. This, however, is bad practice, as it greatly reduces the
insulation of the whole system. Test all circuits at least once a
day.
\c is sometimes necessary to know just what the insulation
resistance of a line, or of the wiring in a building, is in ohms.
This can be found very readily, and closely enough for all prac-
tical purposes, by using a Weston volt meter in the following
manner :
Connect with a wire from one side of the circuit to one
binding post of the volt meter, and with another piece of wire con-
nect a water pipe to the other binding post of the volt meter. If
the needle or pointer shows any deflection we know there is a
ground, or leakage, on the opposite side of the circuit to which
the volt meter is connected.
The resistance of this ground leak may be found by the
following formula:
V
R == r ( 1) ohms when R —- resistance of ground leak
required, r = resistance of volt meter, V ^^ voltage between the
positive and negative sides of the line, v =^ reading in volts, on
the instrument, produced by the leakage.
181
30 ' ELECTRIC WIRING
Primary Wiring:. Primary wires should be kept at least
ten inches apart, and at that distance from conducting material
Primary wires carrying over 3,500 volts should not be brought
into or over any building other than the central power station or
sub-station.
Wires for Outside Use h^ve in most cases a "weatherproof"
insulation, except service wires, which should be "rubber-covered."
Any insulating covering for wires exposed to the weather on poles
is in a short time rendered useless. The real insulation of the
system will be found to be dependent upon the porcelain or glass
insulators.
POLES FOR LIGHT AND POWER WIRES.
It is essential to a proper installation that the poles receive
due consideration, a fact that is too often overlooked.
In selecting the style of pole necessary for a certain class of
work the conditions and circumstances should be considered.
Poles may be arranged in three classes, the size of wire which
they are to carry respectively being one of the important regulat-
ing circumstances.
First Class: Alternating-current plants for lighting small
towns. Main line of poles should consist of poles from 30 to 35
feet long, with G-ineli tops. These are strong enough for all the
weight that is placed upon them. No pole less than 30 feet
with 6-inch top should be placed on a corner for lamps. The
height of trees, of course, must be considered in many cases. For
the Edison municipal system, where more than one set of wires
are used for street lighting, a O-inch top should be the size of the
poles, the length being not less than 30 feet, and greater than this
if the streets be hilly and filled with trees.
Second Class: Town lighting by arc lights. All poles
should be at least 0-inch tops. The corner poles should be 6|-
inch tops; and wherever the cross-arms are placed on a pole at
different angles, the pole should be at least a 6^-inch top. A 30-
foot pole is sufficiently long for the main line, but it would be
advisable to place 35-foot poles on comers.
\8S&
ELECTEIO WIRING 31
Third Class: Where heavy wire^ such as No. 00, is used
for feeder wire, the poles should be at least 7-inch tops. Where
mains are run on the same pole line the strain is somewhat
lessened, and poles of smaller size will answer all purposes.
Cull Poles. The question as to what is a cull pole is some-
thing on which many authorities differ. Of course, if specifi-
cations call for a certain sized pole, parties supplying the poles
should be compelled to send the sizes called for. All poles that
are smaller at the top than the sizes agreed upon, are troubled
with dry rot, large knots and bumps, have more than one bend, or
have a sweep of over twelve inches, should certainly be classed
as cull poles. Specifications for electric light and power work
should be, and in many cases are, much more severe than those
required by telegraph lines. A cull pole, one of good material,
is the best thing for a guy stub, and is frequently used for this
purpose. A cedar pole is always preferable to any other, owing
to the fact that it is very light compared with other timber, and
is strong, durable and very long lived.
Pole Settins^. It seems to be the universal opinion of the
best construction men that a pole should be set at least five feet
in the ground, and six inches additional for every five feet above
thirty-five feet. Also additional depths on corners. Wherever
there is much moisture in the ground, it is well to paint the butt
end of the pole, or smear it with pitch or tar, allowing this
to extend about two feet above the level of the ground. This pro-
tects the pole from rot at the base. The weakest part of the pole
is just where it enters the ground. Never set poles farther than
125 feet apart; 110 feet is good practice.
Pole Holes should be dug large enough so that the butt of
the pole can be dropped straight in without any forcing, and
when the pole is in position only one shovel should be used to fill
in, the earth being thoroughly tamped do\vn with iron tampers
at every step until the hole is completely filled with solidly
packed earth. Where the ground is too soft for proper tamping,
a grouting composed of one part of Portland cement to two parts
of sand, mixed with broken stone, may be used to make an arti-
ficial foundation.
183
32
ELECTRIC WIBIXG
nci
^BOLT
BLOCK 24XX
X VARIES AS
THE DIAMETER
OF THE POLE.
JBOLT
FIG. 2
Fig. 9.
CONSTRUCTION WORK; POSITION OP CROSS-ARnS WHEN
TURNING CORNERS.
Wlirn rtinninR a heavy line wire it is necessary to use two cross-arms
fastened as shown ahove in Fig. 2. If lines are not heavy, only one cross-arm
will he necessary. In case lines cross the street diagonally, the arms where
the wires leave and those to which they run are both set at an angle. When
turning an abrupt comer only one arm is turned. The above cannot be used
where feeders tap into double branches. In such a case the method given
in Fig. 1 is used.
IM
BLECTKIC WIEINO
TABLE III.
k UcU W«rk.
650
100
Palatlng. When poles are to be painted, a dark olive greeo
color should be chosen, in order that they may be as inconspicuous
as possible. One coat of paint should be applied before the pole
is set, and one after the pole is set. Tops should be pointed to
shed water.
All poles 35 feet long and over must be loaded on two cars.
For chestnut poles add 50 per cent to weights as given iu
table.
Cross-Arms. The distance from the top of the pole to the
cross-aim should be equal to the diameter of pole at the top.
All cross-arms should be well painted with one coat of paint
before placing, and must be of standard size as shown in the
diagrams. Cross-arms of four or more pins should be braced,
using one or two braces as occasion demands. Cross-arms on one
pole should face those on the next, thereby making the cross-arms '
on every other pole face in one direction. All pins should have
their shanks dipped in paint and should be driven into the cross-
arm while the paint is wet. The upper part of the pin should
also be painted. Iron pins may be furnished for corners where
there is a heavy strain, but are not advised, it being preferable to
use the construction as shown in the diagrams. Put double arms
on the pole where feeder wires end.
Quard Irons. Guard irons should he placed at all angles in
lines, and on break-arms.
Steps. All junction and lamp poles should be stepped so
that the distance between steps on the same side of the pole will
not be over 36 inches. Poles carrying converters should also be
'if '
s.
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ELECTRIC WISING 35
Quys. All poles at angles in the line must be properly
guyed, using No. 4 B. & S. galvanized iron wire, or two No. 8
wires twisted. All junction poles should also be guyed. Never
attach a guy wire to a pole so that it prevents a cross-arm from
being removed.
For alternating work, double petticoat insulators are recom-
mended. Pole brackets, except in connection with the tree insu-
lators, should not ]yc used.
Tape should be secured at either end of a joint by a few
turns of twine. When looping for lamps, etc., leave coiled
sufficient wire, without waste, to reach lamp or building without
joints. In cutting arc or incandescent lamps into an existing
circuit, use a piece of "rubber-covered" wire. Feeder wires should
be strung on the cross-arms above the mains.
For good distribution, arc lamps should not be placed more
than 800 feet apart. The lamps may be brought nearer together
if a greater degree of illumination is desired.
Primary Wires on Poles. When running more than one
circuit of primarioF upon the same line of poles the wires of each
circuit should be run parallel and on adjacent pins, as shown
below, so as to avoid any fluctuation in the lamps due to induc-
tion. The lines lettered A and A are for circuit No. 1, and
B and B for circuit No. 2, etc.
A
A
B
B
When connecting transformers to 1^000-volt mains a doublo-
pole cut-out is placed in the primary circuit. For 2,000-volt cir-
cuits a single-pole cut-out should be placed in each side of the
line, thus avoiding any possible short circuit due to an arc being
established across the contacts of the double-pole cut-out. This,
owing to the greater diflFerence of potential between opposite poles,
is liable to occur when the fuses 'Tblow."
INSIDE WIRING.
Approved ••Rubber»Covered" Wire should be used exclu-
sively in all interior wiring. Although the Fire tJndenvr iters
I
18T
36 ELECTBIC WIBING
M
M
M
M
allow ''Slow Burning" weatherproof wire to be used in dry places
when wiring is entirely exposed to view and rigidly supported on
I>orcelain or glass insulators, "Rubber-Covered" wire is always
preferable.
The copper conductors, before being rubber covered, should
be thoroughly tinned, and the thickness of the rubber covering
should conform to the following table :
TABLE V.
RcqaUlto Thlcfcam af Rabker Covtrtaf for WItm.
For voltages up to 600:
From No. 18 to No. 16 inclusive, A in.
14 to •* 8 "A in.
7 to - 2 " tV in.
1 to " 0000 " A in.
0000 to " 500000 c ixL " A in.
•• 500000 c. m. to " lOOOOOO •• " A in.
Urgcr than " 1000000 " - J in.
For voltages between 600 and 3,500:
From No. 14 to No. 1 inclusive, A >"•
to " 500000 cm." A in. ) covered by
Larger than 500000 " " A in. > braid or tape.
••Slow Buminf Weatherproof" Wire should have an insu-
lation consisting of two coatings, the inner one to be fireproof
in character and the other to be weatherproof. The inner fire-
proof coating should comprise at least six-tenths of the total thick-
ness of the wall.
The complete covering should be of a thickness not less than
that given in the following table :
TABLE VI.
RM|Ml«ltc TbkkncM of Mow Burning: Weatbeiproof Insulatloa.
From No. 14 to No. 8 inclusive, A >n.
7 to " 2 "A »n.
2 to " 0000 " ^ in.
0000 to " 500000 c. m. " A in.
500000 c. m. to " 1000000 " " J^ in.
Larger than " 1000000 " " J in.
••Weatherproof" Wire, for out-door use, should consist of at
least three braids thoroughly impregnated with a dense moisture-
repellant which should stand a temperature of 180° Fahrenheit
without dripping. The thickness should correspond to that of
"Slow Burning Weatherproof" and the outer surface should be
thoroughly slicked do^vn.
Carrying Capacity of Wires. Table VII gives the safe
carrying capacity of wires fr'^m No. 18 B. & S. to cables of 2,-
000,000 circular mils.
IM
M
II
ELECTRIC WIRING
37
No wires smaller than Xo. 14 should be used except for
fixture wiring and peudauts, in which cases as small as No. 18
maj be used.
TABLE VII.
UU Cwrylag CapMlly tl WItm.
laiin Ko. B. A. 8. Diameter Mils. Araaarrulwllib. No. Ampsraa OpM
Wtxk. No. Amperes Cotieednl Work. Ohma Per 1000 Ft, Lba. ptC^UW
l»
1
H
II
Si
£
1^
13
11
i:
1
<l
1^
ii
D
1
^
^l
1"
i
r
7:;;
4J
.024
048
oioeoo
o:2(
.
B...
Bl
.583
4.0178
7.8;
2
S...
.267
3
.106
15 :«
a.,.
81
1530
1,5890
4
1..,
J234
■i
0...
!90S4s
9...
1 J»0
31
,7924
.■ioioj
1-f
I .SIO
41
3
.6aM
49. 9(
11
7...
3
,49S4
6...
S...
IB2
33.100
7;
: 31.141
00:2.'
4...
204
<l.T40
0;
0.
,24868
26.4C
22{
3...
52.0.^0
26
66,370
1:::
sat
83,090
15t
: 12308
253:43
0...
321
105.500
la;
125
,00827
319.7J
42:
00,,.
151
B2
20:
:0613
swill
0000:::
«6C
211,000
3ia
21:
,01904
040.73
Cabin .
300,000
40;
,0335;
933.
^i
BI4
59I
:o20i;
1553;
■sg
sei
681
44
.0166
863.
003
4S
g""
030
6 800!000
474!
-a
D9S
900,000
B2<
es
796.
1
6-S14
,0OOflOO
00(
03
.01006
106.
3
- 28
07
.0091
410.
B - 313
203
S ,300J)00
.0083
1
9 - 14S
3H
S .300.000
217
75
,00709
4038!
E
- 196
,400.000
as;
79
,00715
5
9 - 21
"St.
91- 285
45S
.flooiooo
908:
-s
91- 320
7 700.000
48t
91
-00588
278.
%
91- 367
7 ,800000
,00558
5B8.
127- 195
980
sees.
^■c
" ■
830
2 aiooolooo
681
,00500
208,
"2
127- 254
Tie Wires should have an insulation equal to that of the
conductors they confine.
5pliclng should be done in such manner as to make the wires
mechanically and electrically secure without solder; then they
should be soldered to insure preservation from corrosion and
from consequent heating due to poor contact.
88 ELECTBIC WIMNO
Stranded Wires should have their tips soldered before being
fastened under clamps or binding screws. When the stranded
wires have a conductivity greater than No. 10 B. & S. copper
wire, they should be soldered into lugs. All joints should be
soldered in preference to using any kind of splicing device.
WIrlns: Table. The following examples show the method of
using the table on page 40 :
1. What size of wire should we use to run 50 16-candle-
power lamps of 110 volts, a distance of 150 feet to the center of
distribution with the loss of 2 volts?
First multiply the amperes, which will be 25.5 (50 16-c. p.
110-v. lamps take 25.5 amperes, see table on page 57), by the dis-
tance, 150 feet, which will equal 3,825 ampere feet. Then refer
to the columns headed "Actual Volts Lost"; and as we are to
have a loss of two volts only, look down the column headed 2 until
you come to the nearest corresponding number to 3,825, and we
find that 3,000 is the best number to use. Put your pencil on
the number 3,900 and follow that horizontal column to the left
until you come to the vertical column headed "Size B. & S.," and
you find that a No. 4 B. & S. wire will be the proper size to use
in this case.
2. What size of wire should we use to carry current for a
motor that requires 30 amperes and 220 volts, and is situated 200
feet from the distributing pole, the "drop" in volts not to exceed
2 per cent?
First multiply 30 amperes by 200 feet, as we did in the first
example, and we get 6,000 ampere feet. Now look at the upper
left-hand comer of the table and vou will see a vertical column
headed "Volts." Go down this column until you come to 220,
and follow the horizontal column to the right until you come to the
figure 1.8, which is the nearest we can come to a 2 per cent loss
without a greater loss or "drop." Place your pencil on the figure
1.8 and follow down the vertical column of figures until you come
to the nearest corresponding figure to 6,000, which we find to be
6,200. Then wuth your pencil on this figure follow the horizontal
column to the left, and we find that a No. 5 B. & S. wire ^<* a
proper size to use for the above conditions.
too
ELECTBIC WIBINQ 89
B. Supposing we have occasion to inspect a piece of wiring,
and find a dynamo operating 50 16-c. p. 110-volt lamps at a dis-
tance of 150 feet, and our wire gauge shows that wire in use is a
No. 12 B. & S., at what loss, or "drop," are these lamps being
operated ?
First multiply the amperes, which will be 25.5 (50 16-c. p.
110-v. lamps take 25.5 amperes, see table on page 57), by the dis-
tance, 150 feet, and we get 8,825 ampere feet. As we find in
use a Xo. 12 B. & S. wire, we look for the vertical cohimn headed
"Size B. & S." and follow it down until we come to 12. With
our pencil on the figure 12 we travel along the horizontal line to
the right until we come to the jiearest corresponding number to
3,825, which we find to be 4,575. Then starting at this number
we travel up the vertical column and we find a loss of about 15
o.ctnal volts, or, practically, a 12 per cent loss, which would greatly
reduce the candle-power or brilliancy of the lamps.
Installation of Wires. All wiring should be kept free from
contact with gas, water or other metallic pij)iiig, or with any other
conductors or conducting material which it may cross, by some
continuous and firmly fixed non-conductor, creating a separation
of at least one inch. In wet places it should bo arranged so that
an air space will be left between conductors and pipes in crossing,
and the former must be run in such a way that they cannot come
in contact with the pipe accidentally.
Wires should be run over rather than under pipes upon
which moisture is likely to gather, or which by leaking might
cause trouble on a circuit. No smaller size than No. 14 B. & S.
gauge should ever be used for any lighting or power work, not that
it may not be electrically large enough, but on account of its
mechanical weakness and liability to be stretched or broken in
the ordinary course of usage. Smaller wire may be used for
fixture work, if provided with approved rubber insulation.
Wires should never be laid in or come in contact with plaster,
cement, or any finish, and should never be fastened by staples,
even temporarily, but always supported on porcelain cleats which
will separate the wires at least one-half inch from the surface
wired over and keep the wires not less than two and one-half
101
o
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ELECTKIC WIBINQ 41
inches apart. Three-wire cleats may be used when the neutral
wire is run in the center and at least two and one-half inches
separate the two outside or + and — ^ wires. This style of wiring
is intended for low-voltage systems (300 volts or less) ; and when
it is all open work, rubber-covered wire is not necessary, as
"weatherproof wire may be used. Weatherproof wire should
not be used in moulding. Wires should not be fished between
floors, walls or partitions, or in concealed places, for any great
distance, and only in places where the inspector can satisfy himself
that the rules have been complied with, as this style of work is
always more or less uncertain.
Twin wires should never be used, except in conduits or when
flexible conductors are necessary; they are always unsafe for
light or power circuits on account of the short distance between
them.
All wiring should be protected on side walls from mechanical
injury. This may be done by putting a substantial boxing about
the wires, allowing an air space of one inch around the con-
ductors, closed at the top (the wire passing through bushed holes)
and extending about five feet above the floor. Sections of iron-
armored conduit may be used, and in most cases are preferable,
as they take up but little room and are very rigid.
If, however, iron pipes are used with alternating currents,
the two or more wires of a circuit should always be placed in the
same conduit. If plain iron pipe be used the insulation of that
portion of each wire within the pipe should be reinforced by a
tough conduit tubing projecting beyond the iron tubing at both
ends about two inches.
When crossing floor timbers in cellars or in rooms where they
might be exposed to injury, wires should be attached, by their
insulating supports, to the under side of wooden strips not less
than one-half inch in thickness and not less than three inches
wide.
QBNBRAL VOKnVUE FOR LIGHT AND POWER WIRING.
c. m.=circular mils.
d = length of wire, in feet, on one side of circuit,
n = number of lamps in multiple.
198
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ELECTEIC WIKINQ 48
c = current in amperes per lamp.
V = volts lost in lines,
r == resistance per foot of wire to be u^ed.
10.8 ohms resistance of one foot of commercial copper wire
having a diameter of one mil and a temperature of 75° Fahren-
heit.
It is an easy matter to find any of the above values by the
following formuljc:
10.8 X2dXnXe
c»in, = ■—
i;
10.8 X2dXnXe cm. X v
^ cm. ^ 10.8X2dXn
cm X V cm, X v
n= ._ — 2d =
10.8 X2dXc 10.8 XcXn
r=
nXcX2d
v = nXcX2dXr e =
n" .. ^ ... 2d =
2dX7iXr
V
cX2dXr nXcXr
Arc LIsfht Wlrlns:* AH wiring in buildings for constant-
current series arc lighting should bo with approved rubber-cov-
ered wire, and the circuit arranged to enter and leave the building
through an approved double-contact service switch, which means
a switch mounted on a non-combustible, non-absorptive insulating
base and capable of closing the main circuit and disconnecting the
branch wires when turned "oflF." This switch must be so con-
structed that it will be automatic in action, not stopping l)etween
points w^hen started, must prevent an arc between points under all
circumstances, and must indicate, upon inspection, whether the
current is "on" or "off." Such a switch is ne^*essary to cut the
high voltage completely out of the building by firemen in case of
fire or when it becomes necessary to make any changes in the
lamps or wiring.
195
44 ELECTRIC WIHING
This class of wiring should never be concealed or encased
except when requested by the Electrical Inspector, and should
always be rigidly supported on porcelain or glass insulators whicl
will separate the wiring at least one inch from the surface wired
over, and which must be kept at least four inches from each othei
on all voltages up to 750, and eight inches apart when the voltages
exceed 750. No wires carrying a voltage of over 3,500 should
be carried into or over any buildings except central stations and
sub-stations. All arc light wiring should be protected on sidt
walls and when crossing floor timbers where wires are liable tc
injury. In mill-construction buildings, arc wires of No. 8 and
larger, where not liable to be disturbed, may be separated sis
inches for voltages up to 750, and ten inches for voltages above
750; may run from timber to timber, not breaking round; anC
may be supported at each timber only. In running along beami
or walls and ceilings they should be supported at intervals noi
exceeding four and one-half feet.
SPECIAL WIRINQ.
Special wiring for damp places such as breweries, packin]
houses, stables, dye houses, paper or pulp mills, or buildings espe
cially liable to moisture or acid or other fumes likely to injun
the wires or their insulation, should be done with approved rubber
covered wire, and rigidly supported on porcelain or glass insula
tors which separate the wires at least one inch from the surfao
wired over, and which must be kept apart at least two and one-hal
inches. The wire in such damp places should contain no splices
as it is almost impossible to tape a splice that will prevent aci<
fumes from getting at the copper surface.
Moulding Work should always be done with approved rubbe
covered wire to prevent leakage should the moulding becomi
damp.
This class of work should never be done in concealed or dam]
places, for fear that water may soak into the wood and cans
leakage of current between the wires, burning the wood and start
ing a fire. The action of the current in a case like this is to con
vert the wood very gradually into charcoal, then dry the water ou
and ignite the charcoal thus formed. Great care should be ol
\9^
ELECTRIC WIRING 45
served in driving nails into moulding, to avoid puncturing the
insulation and possibly grounding the circuit in a way that not
only might be difficult to locate, but might cause a concealed fire
back of the plastering or wood work to which the moulding is
attached.
Moulding should be of hard wood and made of two pieces,
a backing and capping, so constructed as to thoroughly encase the
wire. It should provide a one-half inch tongue between the con-
ductors and a solid backing, which under the grooves should be
not less than three-eighths of an inch in thickness and able to give
suitable protection from abrasion.
Concealed WIrInf or that which is to be run between
walls and floors and their joists, should always be done with ap-
proved rubber-covered wire, and should be rigidly supported on
porcelain or glass insulators which will separate the wires at least
.^te: ,.
Fig. 10.
Samples of approved moulding when filled and covered with at least
two coats of waterproof paint.
one inch from the surface wired over. The wires should be kept
at least ten inches apart, and where it is possible should be run
singly on separate timbers or joists. The insulators should be
placed not farther than four feet apart in any case, and where
there is any liability of the wires coming in contact with anything
else, due to a possible sagging, the supports should be placed much
closer together. In some cases where it is impossible to rigidly
support the wiring on porcelain or glass insulators in concealed
places,* the wires, if not exposed to moisture, may be fished on the
loop system if encased throughout in approved continuous fiexible
tubing or conduit. Fishing under floors or between walls is done
by boring holes at suitable distances apart and pushing a flat
spring wire from one hole toward the other and catching it with a
wire hook. The flexible conduit and wires may then be pulled
into place.
197
46 ELECTRIC WIRING
Although this fished work may be passed when the sur-
rounding conditions are, at the time of inspection, perfectly satis-
factory, it should be avoided, as trouble will arise in this class of
work sooner than in any other, when all conditions arc equal.
Iiuulated Metal Conduits — (Specifications). The metal
covering or pipe should be of sufficient thickness to resist pene-
tration by nails, etc., or the same thickness as ordinary gas pipe
of the same size.
It should not be seriously affected externally by burning out
a wire inside the tube when the iron pipe is connected to one side
of the circuit.
The insulating lining should be firmly attached to the pipe,
and should not crack or break when a length of conduit is uni-
formly bent at a tcmj)erature of 212 degrees Fahrenheit, to an
angle of 1)0 degrees, with a curve having a radius of 15 inches, for
pipes of 1 inch or less, or a radius of fifteen times the diameter of
the pipe for larger sizes.
The insulating lining should not soften injuriously at a tem-
perature below 212 degrees Fahrenheit, and should leave water in
which it has been boiled, practically neutral.
The insulating lining should be at least one-thirty-second of
an inch in thickness; and the materials of which it is composed
should be of such a nature as will not have a deteriorating effect
on the insulation of the conductor, and be sufficiently tough and
tenacious to withstand the abrasion test of drawing in and out of
some long lengths of conductors.
The insulating lining should not be mechanically weak after
three days' submersion in water, and, when removed from the
pipe entire, should not absorb more than ten per cent of its weight
of water during 100 hours of submersion.
All elbows should be made for the purpose, and not bent from
lengths of pipe. The radius of the curve of the inner edge of
any elbow should not be less than three and one-half inches.
There should not be more than the equivalent of four quarter
bends from outlet to outlet, the bends at outlets not being counted.
Each length of conduit, whether insulated or uninsulated,
should have the maker's name or initials stamped in the metal or
\^%
ELECTBIC WIBINO 47
attached to it in some satisfactory manner, so that it may be read-
ily seen, thus rendering it possible to place the responsibility for
pieces not up to standard.
Uninsulated fletal Conduits or plain iron or steel pipes may
be used instead of the insulated metal conduits, if made equally
as strong and thick as the ordinary form of gas pipe of the same
size, provided their interior surfaces arc smooth and free from
burrs. To prevent oxidation, the pipe should be galvanized,
or the inner surfaces coated or enameled with some substance
which will not soften so as to become sticky and prevent the wire
from being withdrawn from the pipe. Elbows must be made for
the purpose, and not bent from lengths of pipe. The radius of
curves and number of bends from outlet to outlet should be the
same as given under Insulated Metal Conduits. This bare iron
or steel pipe should never contain any but a special extra insu-
lated wire as hereinafter described :
Conduit Wire for Insulated Hetal Conduits, wliether single
or twin conductors, should be standard rubber-covered wire as
described on page 35 ; and where concentric wire is used in insu-
lated metal conduits, it should have a braided covering between
the outer conductor and the insulation of the inner conductor, and
in addition should comply with and be able to withstand the test
of standard rubber-covered wire.
Conduit Wire for Uninsulated Metal Conduits should not
only have a standard rubber insulation as required for Insulated
Metal Conduits, but in addition should have a second outer fibrous
covering at least one-thirty-second inch in thickness, and suffi-
ciently tenacious to withstand the abrasion of being hauled
through the metal conduit. When concentric conductors are to
be used in uninsulated metal conduits, thcv not onlv should
comply with the requirements when used in insulated metal con-
duits, but, in addition, should have a second outer fibrous covering
at least one-thirty-second of an inch in thickness and sufficiently
tenacious to withstand the abrasion of being hauled through the
metal conduit.
Interior Conduit Installation. All conduits should be con*
tinuouQ from one junction box to another or to fiz^ ^ tlie
100
48 ELECTRIC WIKING
conduit tube should properly enter all fittings, otherwise the con-
ductors are not perfectly protected, and water is much more
liable to gain an entrance into the conduit. No conduit with an
inside diameter of less than five-eighths inch should be used.
The entire conduit system for a building should be com-
pletely installed before a single wire is drawn in ; and all ends of
conduits should extend at least one-half inch beyond the finished
surface of walls or ceilings, except that, if the end is threaded and
a coupling screwed on, the conduit may be left flush with the
surface, and the coupling may be removed when work on the
building is completed.
After all conductors have been drawn or pushed in, all outlets
should be plugged up with special wood or fibrous plugs made in
parts to fit around the wire, and the outlet then sealed with a good
compound to keep out all moisture. All jdints should bo made
air-tight and moisture-proof.
The metal of every conduit system should be effectually and
permanently grounded. The conduit is likely to be more or less
grounded, and a positive ground is necessary for the same reason
that a positive ground is required for generator frames when it is
impossible to insulate them perfectly.
Conduit Wiring. The reason why standard rubber covered
wire, and not weatherproof, should be used in conduits, is that the
best possible insulation is desirable for this class of work, as the
insulating lining of the conduit may be defective in places, and
there is a possibility of dampness getting into the conduit.
Xo wires should be drawn in until all mechanical work on
the building is done.
Wires of different circuits should not be drawn in the same
conduit.
For alternating systems, the two or more wires of a circuit
should be drawn in the same conduit, in order to avoid trouble
from inductive losses, which, under certain conditions, would
cause a heating of the iron conduit to a dangerous degree. This
trouble from induction becomes very much less if the wires are
in the same conduit; less still, if the wires are twisted together;
and disappears almost entirely if concentric wire is used.
200
ELECTBIC WIRING 49
Even in direct-current work it is advisable to place the two
wires of a circuit in the same conduit, as in so doing the direct
current may be changed for the alternating current without the
necessity of rewiring, which would be necessary if only a single
wire were placed in a conduit.
Fixtures, when supported from the gas piping of a build-
ing, should be insulated from the gas-pipe system by means of
approved insulating joints placed as close as possible to the ceiling,
and the wires near the gas pipe above the insulating joint should
be protected from possible contact by the use of porcelain tubes.
All burrs or fins should be removed from the fixtures before
the wires are drawn in. The tendency to condensation within
the pipes should be guarded against by sealing the upper end of
the fixture.
In combination fixtures, where the wiring is concealed
between the inside pipe and outer casing, the space between pipe
and casing should be at least a quarter of an inch to allow plenty
of room for the insulation of the wires without jamming.
Fixtures should be tested for "contacts" between conductors
and fixtures, for "short circuits" and for ground connections, be-
fore being connected to the supply conductors.
Ceiling blocks of fixtures should be made of insulating
material ; if not, the wires in passing through the plate should be
surrounded by porcelain tubes.
Rosettes. These fittings should not be located where inflam-
mable flyings or dust will accumulate on them. Bases should be
high enough to keep the wires and terminals at least one-half inch
from the surface to which the rosette is attached.
Terminals with a turned up lug to hold the wire or cord
should be used, and in no case must the wire be cut or injured.
Fused rosettes are not advised for use where cords can be properly
protected by line cut-outs. If fused rosettes are used, the next
fuses back should not be over 25 amperes capacity.
Fixture Wirinf should be done with fixture wire, which has
a solid insulation with a slow-burning, tough, outer covering, the
whole at least one-thirty-second of an inch in thickness, and
having an insulation resistance between conductors, and between
Ml
60 ELECTBIC WIBING
either conductor and the ground, of at least one megohm per mile,
after one week^s submersion in water at 70 degrees Fahrenheit,
and after three minutes' electrification with 550 volts.
Although No. 18 (B. & S. gauge) is allowable in fixture
work, it is never advisable to use smaller than No. 16, for
mechanical reasons. Supply conductors, and especially the splices
to fixture wires, should be kept clear of the grounded part of gas
pipes, and where shells are used the latter should have area
enough to prevent pressing the wires against the gas pii^e when
finally in place. Where fixtures are wired on the outside, it is
advisable to use cord for attaching the wires to the fixture, and
not short bits of wire, as the latter might produce a short circuit
or ground.
Flexible Cord should be made of a number of copper strands;
no single strand should Ix) larger than No. 26 or smaller than No.
30 (n. & S. gauge), and each conductor should be covered by an
approved iiisuhition and l>e protected from mechanical injury by
a tough, braided, outer covering. When used for pendant lamps it
should bang frooly in air and be so placed that there is no chance
of its coming in contact with anything excepting the lamp socket
to whioli it is attacluMl and the rosotto from which it hangs. Each
stranded conductor should have a carrying capacity equivalent to
not loss than a No. 38 (13. & S. gauge) wire. The covering of the
stranded wires for flexible cord should first have a tight, close
wind of fine cotton, which is intended to prevent any broken
strand from piercing the insulation and causing a short circuit or
ground. Secondly, it should have a solid waterproof insulation
at least one-thirty-second of an inch thick, and should show an
insulation resistance of 50 megohms per mile throughout two
weeks' submersion in water at 70 degrees Fahrenheit. The outer
protecting l)raiding should be so put on and sealed in place that
when cut it will not fray out.
Flexible cord should not be used as a support for clusters,
' as it is not strong enough, and it should never be used for any-
thing other than pendants, wiring of fixtures and portable lamps,
portable motors, or small, light electrical apparatus.
Flexible eord should never be used in show windows, as a
2oa
\ .. . . - ."*•.» •••' .* \li ii t
ELECTBIC WIBINQ
51
Insulating bus'
sockets and desk s^
Flexible ^o
of the socket,
bushing in the S( ' ^
the cord comes
rosette, in orde^
defective piece might cause a short circuit and set fire to flimsy
material or decorations. Many fires have been caused by the use
of flexible cord in show wirdows, where handkerchiefs, decora-
tions, etc., have been pinned to the cord. When the current is
"turned on" short circuits are caused by the pins, and a fire is
the result.
s should be used where cords enter lamp
' lamps.
uld be so suspended that the entire weight
nd shade will bci borne by knots under the
^ , and above the point where
•ough the coiling block or
.lat the strain may be taken
from the joints and binding screws. It is good
practice always to solder the ends of flexible
cords which are going under binding screws, as
it holds the strands together and prevents the
pressure of the screws from forcing the strands
from under them and against the shell of the
socket, causing a grounded shell or short circuit.
Where it lx?comes necessary to solder a
great number of ends, as niav be required when
wiring a factory, use a small i)ot of melted
solder and dip the ends of the wire, which have all been previously
cut to the proper length.
Standard Lamp Sockets should be plainly marked 50 candle*
power, 250 volts, and with either the manufacturer'^ name or
registered trade mark. The inside of the shell of the socket
should have an insulating lining which should absolutely prevent
the shell from becoming part of the circuit, even though a wire or
strand inside the socket should become loose or come out from
under a binding screw. This insulating lining should be at least
one-thirty-second of an inch thick and of a tough and tenacious
material.
Special Lamp Sockets. In rooms where inflammable gases
may exist, both the socket and lamp should be enclosed in a vapor-
tight globe, supported on a pipe-hanger, and wired with "Rubber-
Fig. 11.
Waterproof keyless
socket, to be used in
dve houses or damp
places.
52 ELECTBIC WIRING
Covered'* wire soldered directly to the circuit. No fuses or
switches of any sort should be used in such cases, as the slightest
arc might produce dangerous explosions or fires. See Fig. 11,
In damp or wet places, such as dye houses, breweries, eta, a
waterproof socket such as shown on page 51 should be used.
Waterproof sockets should be hung by separate stranded rubber-
covered wires, not smaller than No. 14 (B. & S.). These wires
should be soldered direct to the circuit wires, but supported inde-
pendently of them. All sockets for the above conditions should
be keyless.
Stranded Wires in every case should be soldered together
before being clamped under binding screws, and when they have
a conductivity greater than No. 10 (B. & S.) copper wire they
should be soldered into lugs. Stranded wires if not thus stiffened
before being clamped under binding posts, are liable to be pressed
out or easily worked loose, making a poor contact, which causes
heating, a possibility of arcing or a complete bum oait, or fusing
of the wire at this point.
Bushings. All wires should be protected when passing
through walls, partitions or floors, by non-combustible, non-
absorptive insulating tubes, such as glass or porcelain. Each
bushing should be long enough to go clear through and allow a
projection of at least a quarter of an inch on both ends. Bush-
ings should be long enough to bush the entire length of the hole
in one continuous piece; or else the hole should first be bushed
by a continuous waterproof tube, which may be a conductor, such
as iron pipe, and the tube then should have a non-conducting bush-
ing pushed in at each end so as to keep the wire absolutely out of
contact with the conducting pipe.
Automatic Cut-outs such as circuit breakers and fuses should
be placed on all service wires as near as possible to the point
where they enter the building, on the inside of the walls, and
arranged to cut off the entire current from the building.
The cut-out or circuit breaker should always be the first
thing that the senn'ce wires are connected to after entering the
building; the switch next, and then the other fixtures or devices
in their order. This arrangement is made so that the cut-out or
804
ELECTBIC WIRING 53
circuit breaker will protect all wiring in the building, and the
opening of the switch will disconnect all the wiring.
These automatic cut-outs should not, however, be placed in
the immediate vicinity of easily ignitible stuff, nor where exposed
to inflammable gases or dust, or to flyings of combustible material,
as the arcing produced whenever they break the circuit might
cause a fire or explosion. When they are exposed to dampness
they should be inclosed in a waterproof box or mounted on
porcelain knobs. All cut-outs and circuit breakers should be sup-
ported on bases of non-combustible, non-absorptive insulating
material. Cut-outs should be provided with covers when not
arranged in approved cabinets, so as to obviate any danger of the
melted fuse metal coming in contact with any ignitible substance.
Cut-outs should operate successfully under the most severe
conditions they arc liable to meet with in practice, on short cir-
cuits, with fuses rated at 50 per cent above, and with a voltage
25 per cent above, the current and voltage for which they are de-
signed. Circuit breakers should also be designed to operate suc-
cessfully under the severe conditions liable to be met with in prac-
tice, or at 50 per cent above the current and with a voltage of 25
per cent above that for which they are designed. All cut-outs and
circuit breakers should be plainly marked, and where it will
always be visible, with the name of the maker as well as the cur-
rent and voltage for which the device is designed.
Cut-outs or circuit breakers should be placed at every point
where a change is made in the size of wire, unless such a device
in the larger wire will protect the smaller. They should never
be placed in canopies or shells of fixtures, but should be so placed
that no set of incandescent lamps, whether grouped on one fixture
or several fixtures or pendants, requiring a current of more than
six amperes, should be dependent upon one cut-out. Special per-
mission may be given in writing by the Inspection Department
having jurisdiction, in case extra large or special chandeliers are
to be used. Fused rosettes, when used with fiexible cord pendants,
are considered as equal to a cut-out. Fuses for cut-outs should
not have a capacity to exceed the carrying capacity of the wire;
and where circuit breakers are used they should not be set more
805
6i
ELECTBIC WIRING
than 30 per cent above the allowable carrying capacity of the
wire, unless a fusible cut-out is also installed in the circuit.
Circuit breakers open at exactly the current they are act for,
and instantly ; therefore it is necessary to get them considerably
above the ordinary amount of current required, to keep tUem from
constantly opening on slight fluctuations. When this is the case
a double-pole fusible cut-out should be added to protect the wire
from a heavy, steady current, which may be maintained just
below the oi)Ciiiug jioint of the circuit breaker. The fuse requires
a little time to heat, and therefore would not blow out with a
momentary rise of current which might open the circuit breaker
if set as low aa necessary to protect the wire, which may be of a
size only large enough for the figured amount of current under
ordinary conditions of operation. If, however, in the ease of
motor wiring, the size of wire is 50 per cent above the figured
size for the molor's average current, as it should be, then the
introduction of a fusible cut-out in addition to the circuit breaker
is unnecessary.
Intulatlng Joints should be made entirely of material that
will resist the action of illuniiualing gases, and that will not give
way or soften under the heat of an ordinary gas flame, or leak
under a moderate prrasure.
They should be so arranged that a deposit of moisture will
not destroy the insulating effect, and should have an insulation
resistance of at least 250,000 ohms between the gas pipe attach-
ments, and be sufficiently strong to resist the strain they will be
liable to be subjected to in being installed.
ELECTHIC WISING 66
Insulating joints should not contain any soft rubber in their
composition. The insulating material should be of some hard
and durable material, such as mica. See Fig. 12.
Insulatioii Resistance. The wiring in any building should
test free from grounds, i. e., the complete installation should have
an insulation between conductors and between all conductors and
the ground (not including attachments, sockets, receptacles, etc.),
of not less than the following:
Up to—
5 amperes 4,000,000
10 amperes 2,000,000
25 amperes 800,000
50 amperes 400,000
100 amperes 200,000
200 amperes 100,000
400 amperes 50,000
800 amperes 25,000
1,000 amperes 12,500
AH cut-outs and safety dovices in j)lace in the above.
Where lamp sockets, receptacles and electroliers, etc., are
connected, one-half of the above will be required.
Knife Switches. Switches should be placed on all service
wires, either overhead or underground, in a readily accessible
place, as near as possible to the j)oint where the wdres enter the
building, and arranged to cut oflF the entire current.
Knife switches should alwavs be installed so that the handle
will be up when the circuit is closed, so that gravity will tend to
open rather than close the switch. They should never be single-
pole except when the circuit which they control is carrying not
more than six 16-candle-power lamps or their equivalent.
Double-pole switches are always preferable to single-pole,
as they absolutely disconnect the part of the circuit out of use.
Flush Switches. Where gangs of flush switches are used,
whether with conduit systems or not, the switches should be
enclosed in boxes constructed of, or lined with, fire-resisting
material.
Where two or more switches are placed under one plate, the
box should have a separate compartment for each switch. No
push buttons for bells, gas lighting circuits, or the like, should
be placed in the same wall plates with switches controlling
electric light or power wiring.
207
56 ELECTIUC WIBINQ
Snap Switches, like knife switches, should always be
mounted on non-combustible, non-absorptive, insulating bases,
such as slate or 2>orcelain, and should have carrying capacity
sufficient to prevent undue heating.
When used for service switches they should indicate at sight
whether the current is "on" or **ofF." Indicating switches should
be used for all work, to prevent mistakes and possible accidents.
The fact that lights do not burn or the motor does not run is not
necessarily a sure sign that the current is off.
Every switch, like every piece of electrical apparatus, should
be plainly marked, where it is always visible, with the maker's
name and the current and voltage for which it is designed.
On constant - potential systems, these switches, like knife
switches, should operate successfully at 50 per cent overload in
amperes with 25 per cent excess voltage, under the most severe
conditions they are likely to meet with in practice. They should
have a firm contact, should make and break readily, and not stop
when motion has once been imparted to the handle. When this
style of switch is used for constant-current systems, they should
close the main circuit and disconnect the branch wires when
turned "off;'' should be so constructed that they will be auto-
matic in action, not stopping between points when started; and
should prevent an arc between the points under all circumstances.
They should also indicate at sight whether the current is "on"
or "off."
Incandescent Lamps. Table X is compiled from a series of
careful tests on a number of incandescent lamps taken from a
large stock at random.
Poor regulation of voltage results in more trouble with
incandescent lamps and their users than any other fault in electric
lighting service.
Some men act on the theory that so long as the life of a lamp
is satisfactory, an increase of voltage, either temporary or perma-
nent, will increase the average light. The fact is that when
lamps are burned above their normal rating the average candle-
power of all the lamps on the circuit is decreased.
Excessive voltage is thus a double error — it decreases the
20^
ELEGTBIC WIRING
67
TABLE X.
Volts.
CP.
Amp.
Watts
Per Lamp.
Watts
Per C P,
Hoc
Res.
52
10
.67
85
8.50
77.61
«
16
1.08
56
48.14
M
20
1.34
70
88.80
«
24
1.62
84
82.09
M
82
2.15
112
24.18
M
50
8.36
175
15.47
«
100
6.73
850
7.72
«
150
10.09
525
, 5.15
104
10
.34
35
3.50
805.88
M
16
.54
56
M
192.59
«
20
.67
70
M
185.22
«
24
.81
84
«
128.89
M
82
1.08
112
M
96.29
M
50
1.68
175
M
61.90
«
100
8.36
350
M
80.95
«
150
5.05
525
M
90.59
110
10
.32
85
8.50
848.75
16
.51
56
«
215.68
20
.64
70
M
171.87
24
.76
84
<«
144.73
82
1.02
112
«•
107.84
50
1.59
175
M
691.82
100
8.18
850
M
84.59
150
4.77
525
M
23.06
S20
16
.291
64
4.00
756.01
«
82
.582
128
<i
879.81
total light of the lamps, and increases the power consumed. If
increased light is needed, 20-candle-power lamps should be in-
stalled instead of raising the pressure. Their first cost is the
same as 16-candle-power lamps; they take but little more current
than 16-candle-power lamps operated at high voltage and give
greater average light.
Increased pressure also decreases the commercial life of the
lamp, and this decrease is at a far more rapic' the
increase of pressure, as shown in the following: t*
200
68 ELECTRIC WIHINQ
shows the decrease in life of standard 3.1-watt lamps due to
increase of normal voltage.
Per Cent of
Normal Voltage. Life Factor.
100 J.000
101 818
102 681
103 662
104 452
105 374
106 310
From this tabic it is seen that 3 per cent increase of voltage
halves the life of a lamj), while 6 per cent increase reduces the life
by two thirds.
Intensity or Brilliancy. The average brilliancy of illumi-
nation required will depend on the use to which the light is put.
A dim light that would be very satisfactory for a church would
be wholly inadequate for a library and equally unsuitable for a
ballroom.
The illumination given by one candle at a distance of one
foot is called the "candle-foot" and is taken as a unit of intensity.
In general, intensity of illumination should nowhere be less than
one candle-foot, and the demand for light at the present time
quite frequently raises the brilliancy to double this amount. As
the intensity of light varies inversely with the square of the dis-
tance, a 16-candle-power lamp gives a candle-foot of light at a
distance of four feet. A candle-foot of light is a good intensity
for reading purposes.
Assuming the 16-candle-power lamp as the standard, it is
generally found that two IG-candle-power lamps per 100 square
feet of floor space give good illumination, three very bright and
four brilliant. These general figures will be modified by the
height of ceiling, color of walls and ceiling, and other local condi-
tions. The lic;hting effect is reduced, of course, by an increased
height of ceiling. A room with dark walls requires nearly three
times as many lights for the same illumination as a room with
walls painted white. With the amount of intense light available
in arc and incandescent lighting, there is danger of exceeding,
"the limits of effective illumination" and producing a "glaring
intensity" which should be avoided as carefully as too little
intensity of illumination.
210
ELECTJilC WmiNO 69
Distribution concerns the arrangement of the various sources
of light and the determination of their candle - power. The
object should be to "secure a uniform brilliancy on a certain
plane, or within a given space. A room uniformly lighted, even
though comparatively dim, gives an eflFect of much better illumi-
nation than where there is great brilliancy at some points and
comparative darkness at others. The darker parts, even though
actually light enough, appear dark by contrast, while the lighter
parts are dazzling. For this reason naked lights of any kind are
to be avoided, since they must appear as dazzling points in con-
trast with the general illumination."
Ttie Arran^ment of ttie Lamps is de^iendent very largely
upon existing conditions. In factories and shops, lamps should
be placed over each machine or bench so as to give the necessary
light for each workman. In the lighting of halls, public build-
ings and large rooms, excellent efTects are obtained by dividing
the ceilings into squares and placing a lamp in the center of each
square. The size of square depends on the height of ceiling and
on the intensity of illumination desired. Another excellent method
consists in placing the lamps in a border along the walls near the
ceiling.
For the illumination of show windows and for display effects,
care must be taken to illuminate by reflected light. The lamps
should be so placed as to throw their rays upon the display w^ith-
out casting any direct rays on the observer.
The relative value of high candle-power lamps in comparison
wuth an equivalent number of 16-caiidle-power lamps is worthy of
r.otice. Large lamps can be efficiently used for lighting large
areas, but in general a given area will be much less effectively
lighted by high candle-power lamps than by an equivalent number
of IG-candle-power lamps. For example, sixteen 64-candle-power
lamps distributed over a large area will not give as good general
illumination as sixty-four 16-candle-power lamps distributed over
the same area. High candle-power lamps are useful chiefly when
a brilliant light is needed at one point, or where space is limited
and an increase in illuminating effect is desired.
The Relative Value of ttie Arc and Incandescent Systems
of Lighting is frequently difficult to determine. Incandescent
211
flO
ELECTRIC WIBING
TABLE XI.
TMtcd Piue Wlrs.
"
Chase-Shawmut Co.,
Boston.
Carry inif
Capacity.
Amperes.
Standard
Length.
Inches.
Diameter
in Mils.
Feet
Per Pound.
X
]>^
10
2,700
H
1%
17
950
1
l}^
20
670
IK
1>^
23
510
2
IK
25
480
8
IK
27
870
4
IK
80
800
5
2
85
812
6
2
88
504
7
2
44
021
8
2
47
120
9
2
54
98
10
2
58
80
12
8
62
70
14
8
68
60
15
8
70
52
16
8
73
49
18
8
78
48
20
86
86
26
90
82
80
100
26
85
110
22
40
122
18
45
126
17
60
147
12.5
60
6
160
10.8
TO
6
172
9.0
75
6
178
8.8
80
5
190
7.6
90
6
198
6.7
100
5
220
6.6
%Vl
ELECTRIC WIEINQ 61
lamps have the advantage that they can be distributed so as to
avoid the shadows necessarily cast by one single source of light.
Arc lamps used indoors with ground or opal globes cutting off
half the light^ have an eflBciency not greater than two or three
times that of an incandescent lamp. Nine 50-watt, 16-candle-
power lamps consume the same power as one full 450-watt arc
lamp. It has been found that unless an area is so large as to
require 200 or 300 incandescent lights distributed over it, arc
lamps requiring equal total power will not light the area with so
uniform a brilliancy.
Fuses should have contact surfaces or tips of harder metal,
having perfect electrical connection with the fusible part of the
strip.
The use of the hard metal tip is to afford a strong mechanical
bearing for the screws, clamps or other devices provided for
holding the fuse.
Fuses should be stamped with al)out 80 jx^r cent of the
maximum current they can carry indefinitely, thus allowing about
25 per cent overload before the fuse molts.
With naked open fuses of ordinary shapes and not over 500
amperes capacity, the maximum current wliich will melt them in
about five minutes may be safely taken as the melting point, as
the fuse practically reaches its maximum temperature in this
time. With larger fuses a longer time is necessary.
The following table shows the minimum break distance, and
the separation of the nearest metal parts of opposite polarity, for
open-link fuses when mounted on slate or marble bases, for differ-
ent voltages and different currents :
Separation of nearest
metal parts of Minimum
125 Volts OR Less. opposite polarity, break distance.
10 amperes or less H inch H inch
11— 100 amperes 1 inch ^ inch
101—300 amperes 1 inch 1 inch
125 TO 250 Volts.
10 amperes or less. .... ^ V/i inch
11 — 100 amperes , V4 inch
101 — 300 amperes 'nch
Pose Terminals shoi^^'^ ^s name or
initials, or some knowr
62 ELECTRIC WIRING
Fuse Wire, Table XI shows the sizes of fuse wire and thje
approximate current-carrying capacity of each size.
Fuses have been known to blow out simply from the heat due
to poor contact when nowhere near their current-carrying capacity
had been reached. They should be so put up and protected that
nothing will tend to rupture them except an excessive flow of
current. No fuse of the larger sizes ever blew out without
causing a greater or less fire risk.
Fuses blow out or melt from excessive heat, and nothing
else, and are therefore not as instantaneous in their action as a
circuit breaker, which is constantly cared for and kept clean.
Central stations or large isolated plants subject to greatly varying
loads should have their lines and generators protected by both
fuses and magnetic circuit breakers as a double protection against
excessive current.
The lengths of fuses and distances between terminals are
important points to be considered in the proper installation of
these electrical "safety valves." No fuse block should have its
terminal screws nearer together than one inch on 50 or 100-volt
circuits, and one inch additional space should always be allowed
between terminals for every 100 volts in excess of this allowance.
For example, 200-volt circuits sliould have their fuse terminals
2 inches apart, 300-volt 3 inches, and HOO-volt 5 inches. This
rule will prevont the burning of the terminals on all occasions of
rupture from maximum current, and this maximum current
means a "short circuit." Good contact is absolutely essential in
the installation and maintenance of fuses. See that the copper
tips to all fuses arc well soldered to the fuse wire, and further-
more see that the binding screw or nut is firmly set up against
this copper tip when the fuse is placed in circuit; a lOO-ampere
fuse can be readily "blown" by 25 amperes if the above pre-
cautions are not carried out. Poor contact in every case can
cause a heating beyond the carrying capacity of the largest fuses.
On the other hand, much damage can be done by using too short
fuses and too large terminals, as the radiation of heat from the
short piece of fuse wire to the heavy metal terminals and set
screws or nuts can very easily raise the current-carrying capacity
2\4
ELECTEIC WIEING
63
of a fuse designed to carry 50 amperes to 100 amperes^ or even
more. All open-link fuses should be placed in cut-out cabinets
when possible.
Cut-out Cabinets should be so constructed, and cut-outs so
arranged, as to obviate any danger of the melted fuse metal com-
ing in contact with any substance which might be ignited thereby.
A suitable box may be made of marble, slate or wood,
strongly put together, the door to close against a rabbet so as to be
perfectly dust tight, and it should be hung on strong hinges and
held closed by a strong hook or catch. If the box is wood the
inside should be lined with sheets of asbestos board about one-
sixteenth of an inch in thickness, neatly put on and finnly
secured in place by shellac and tacks. The wires should enter
through holes bushed with porcelain bushings, the bushings tightly
fitting the holes in the box, and the wires tightly fitting the bush-
ings (using tape to bind up the wire, if necessary), so as to keep
out the dust.
The Enclosed Fuse, or "Cartridge Fuse" (see Fig. 13), con-
sists of a fusible strip or wire placed inside of a tubular hold-
ing jacket filled with porous or powdered insulating material
through which the fuse wire is suspended from end to end and
which surrounds the fuse wire. The wire, tube and filling are
made into one complete, self-contained device with brass or copper
terminals or ferrules at each end, the fuse wire being soldered
Fig. 13.
Enclosed Fuse.
to the inside of the ferrules. When an inclosed fuse "blows'* by
excess current or short circuit the gases resulting are taken up by
the filling, the explosive tendency is reduced and flashing and
arcing are eliminated.
Incandescent Lamps in Series Circuits should be wired with
819
a
Sou
< S o
Fuse
Length,
Inches.
:i5
to U9 lO
SS
Tube
Diam.,
Inches.
:«^
:iR
»l 2^ :st
»H
Tube
Length,
Inches.
mI\ i^M *X«
CO CD CD
9
Class,
Amps.
03
1
8
35-50
60-75
80-100
o
T
o
>
1
Fuse
Length,
Inches.
CO
CO
:*^ ^ :s^
CO 00 CO
CO
CO -^
00 QO
Tube
Diam.,
Inches.
;^
:«^
>5t bt
W^ 1-H
1-H
C4 04
*-
Tube
Length,
Inches.
>!t :3t ^
iO CD CD
CD
CD O
as ss
Class,
Amps.
o
1
1-H
30-50
60-100
125-150
250400
500-600
CO
H
O
>
tf»
1
Fuse
Length,
Inches.
-
^H
:^ ^s :*^
1-H 1-H 1-H
>1t
1-H
^ ^ :*^
C4 09 C4
2 2**
Tube
Diam.,
Inches.
X
:^
^ >?t ;^
1-H
«-i «-i 09
•
Tube
Length,
Inches.
"!S >?t :?^
CO CO '^
*^ MhB J0
-^ mt^ "Vi
^ ^ CD
:?^ :s^ :j^
kO aO 00
Class,
Amps.
^H
3
20-30
35-50
60-100
s
1-H
J,
1-H
175-225
250-400
500-600
Hi
o
>
o
•i
1
2\0
ELECTBIC WIBINQ 65
the same precaution as for series arc lighting and each lamp
should be provided with an automatic cut-ofif.
Each lamp should be suspended from an approved hanger
board by means of a rigid tube, to prevent the wires from constant
swinging.
No electro-magnetic device for switches and no system of
multiple, series, or series-multiple lighting in this class of work
should be used. Under no circumstances should incandescent
lamps in series circuits be attached to gas fixtures, as the high
voltage necessarily employed in this class of lighting should be
kept as far as possible from gas piping, which is so thoroughly
grounded or likely to be.
When incandescent lamps are used for decorative purposes,
as in the use of miniature colored lamps, and it is necessary to
run two or more in series, permission should always be secured,
in writing, from the Inspection Department having jurisdiction.
Arc Lamps should be carefully isolated from inflammable
material, should be provided at all times with a glass globe sur-
rounding the arc and securely fastened upon a closed base. No
broken or cracked globes should be used, as they are designed to
prevent hot bits of carbon from falling to the floor should they
fall from the carbon holder. All globes for inside work should be
covered with a wire netting having a mesh not exceeding one and
one-quarter inches, to retain the pieces of the globe in position
should the latter become broken from any cause. A globe thus
broken should be replaced at once. When arc lamps are used
in rooms containing readily inflammable material they should
be provided with approved spark arresters, which should be made
to fit so closely to the upper orifice of the globe that it would be
impossible for any sparks thrown off by the carbons to escape.
It is safer to use plain carbons and not copper-plated ones in such
rooms, or better still, an enclosed arc lamp, one having its carbons
enclosed in a practically tight glass globe which is inside the
outer globe. Where hanger-boards are not used arc lamps should
be hung from insulating supports other than thei'' ' '^^ors.
All arc lamps should be provided with rel
vent carbons from falling out in case the '^
•^•.•fV,
817
66 ELECTRIC WIRING
and all exposed parts should be carefully insulated f roiD the cir-
cuit. Each lamp for constant-current systems should be provided
with an approved hand switch, and also an automatic switch that
will shunt the current around the carbons, so that the lamp will
thus cut itself out of circuit should the carbons fail to feed
properly. If the hand switch is placed anywhere except on the
lamp itself, it should comply in every respect with the require-
ments for switches on hanger-boards as described under the latter
heading.
Arc Lig:ht Wirin^^, All wiring for high-potential arc light-
ing circuits should be done with "Rubber-Covered" wire. Tlie
wires should be arranged to enter and leave the building through
an approved double-contact service switch, which should close the
main circuit and disconnect the wires in the building when turned
"off." These switches should be so constructed that they will be
automatic in their action, not stopping between points when
started, and preventing arcing between points under any circum-
stances, and should indicate plainly whether the current is "on"
or "off." Never use snap switches for arc lighting circuits. All
arc light wiring of this class should be in plain sight and never
enclosed except when required, and should be supported on porce-
lain or glass insulators which separate the wires at least one inch
from the surface wired over. The wires should be kept rigidly at
least eight inches apart, except of course within the lamp, hanger-
board, or cut-out box or switch. On side walls the wiring should
be protected from mechanical injury by a substantial boxing
retaining an air space of one inch around the conductors, closed
at the top (the wires passing through bushed holes), and extend-
ing not less than seven feet above the floor. When crossing floor
timbers in cellars or in rooms, where they might be exposed to
injury, wires should \ye attached by their insulating supports to
the under side of a wooden strip not less than one-half an inch
in thickness.
Arc Lamps on Low-Potential Circuits should have a cut-out
for each lamp or series of lamps. The branch conductors for
such lamps should have a carrying capacity about 50 per cent in
excess of the normal current required by the lamp or lamps^ to
%\A
ELECTKIC WIRING 67
provide for the extra current necessary wlien the lamps are started,
or, should a carbon become stuck, to prevent <»ver-fusing the
wires. If any resistance coils are necessary for adjustment or
roguhition, they should 1k' enclosed in non-condmstible material
and be treated as sources of heat ; it is i)referable that such
resistance coils Ik? placed within the metal framework of the
lamp itself. Incandescent lamps should never l)e used for resist-
ance devices. These lamps slmuhl be i)rovided with globes and
spark arresters, as in the case of arc lami)s on high-potential series
circuits, except when the enclosed arc lamps are used.
Economy Coils, or compensator coils, for arc lamps should
be mounted on glass or porcelain, allowing an air space of at least
one inch between frame and support, and in general should be
treated like sources of heat.
Hanger-Boards should l)e so constructed that all wires and
eirrrent-carrying devices thereon will be exposed to view and
thoroughly insulated on non-combustibh*, non-absorptive insulat-
ing substance, such as porcelain.
All switches attached to the hanger-board should be so con-
structed that they will be automatic in their action, cutting off
both poles to the lamp, not stopping between j)oint3 when started,
and preventing an arc between points under all circumstances.
Electric Heaters slK>u]d always be treated as sources of heat
and kept away from inflammable materials. Kach heater should
have a cut-out and indicating switch, and all attachments from
the feed wires to the heater should be kept in plain sight, easily
accessible and protected from interference. Each beater should
have a name-plate giving the maker's name and the normal capac-
ity in volts and amperes.
Approved Apparatus and Supplies. Every article or fitting
intended for use in electrical wiring or construction or in con-
nection therewith should, before being manufactured or placed
upon the market, Ik? examined and approved by tin* Underwriters'
National Electric Association for use under the rules and require-
ments of the National Board of Eire Underwriters and placed
upon their official list of "approved" electrical fittings.
Any new article, therefore, or mo<lification of an old article,
210
68 ELEOTiUC WIBIX'G
iiiH'iidt'tl to be iilucrd in {jjC'iieral electrical use, shuiild lirst be st
fur exiiiiiiunliiiii ijuj test \u ihe liiburatur^' of the £)leclrii
Biireuu of tlic JS'iLtiuiial JJuard of Firo Uiitlerwr iters, G7 Ei
Twenty-first street, t'hieago, 111.
If the article is ii])iiruvc(l it will be placed upon the list
fittings, which list is revised quarterly. When buying electrii
sniijilieti of any deserij)tion make sure that they have been i
proved. If there is any question about it, make your supj
dealer give yi>u a s"ii'*'"t<'<-' that tlioy %*'ill be approved by t
Fire Underwriiers' Inajwctor if installed in aeeordanco with t
rnles ami requirenientH uf the Xatiwnal lioard of Underwriters.
Electrical Inspection. The principal points regarding t
safe iiisiallntiin of dynamos, uiolor-*, (intsido and inside wirii
as required by the insurance underwritei-a, have been set forth
this jiajier. There will probably arise questions whieh cam
be settled by n'ference to the suggestions herein contained, a
therefore a great deal lias to lie left to the judgment of the a
strucfing engineer and inspector. In every such case the Insp
tion Department having jurisdiction should be consulted w
porfcet assurance that riotlnng unreasonable will ever be demanc
in the way of sjiceial constnictioii.
Every jiiccc <>{ wiring ov electrical construction wo
whether open or cuiicrid.'d, sbnuld Ix' and usually is inspect
and notice, Iherefore, shcmld always he sent by the contractor
engineer to the board having jiii-isditMion, ininiodiatcly npon cfl
plelion of any work.
Xcgligcni-e in this matter has frequently caused floors to
torn up when donbtfid work lias In'en 8uspe<;ted, and at the c
of the parties who installed llie wiring.
The insurance ins]»eeliir cannot order any piece of wiri
taken out or altered, hut always reports whether or not the pb
is installed in a manner which will reduce the fir<^ risk to a mi
mum. If the inspector has occasion to roconnnend any chan
which ho considers for the safely of the building, and si
changes are not immediately made, he recniumcnds that the ins
ance rate on Ihe building be so raised that it will, in tbe end,
found ad\'isable lo attend to his suggestions, which are in ev
case reasonable.
ELECTRIC BELL WIRING.
In wiring for electric bells to be operated by batteries, the
danger of causing tires from short circuits or poor contacts does
not exist as in the case of wiring for light and power, because tlie
current strength is so small. Neither is the bell-fitter responsible
to city inspe<.*tors or fire underwriters. On this account, bell
litting is too often done in a careless and slovenly manner, caus-
ing the aj)paratU8 to give unsatisfactory results and to require
frequent repairs, so that the expense and inconvenience in the end
far more than offset any time saved by doing an inferior grade of
work. Hence, at the outset it is well to state that as much care
shouhl be taken in the matter of joints and insuhition of bell
wiring as in wiring for light or power.
If proj)erly installed, the electric bell forms a reliable and yet
inexjKMisive means of signaling, and is far su])erior to any other.
On this account practically every new building is litted through-
out with electric bells.
In addition to the necessity of thoroughness already men-
tioned, care should be taken to use only reliable a])paratus which
must be installed in accordance with the fundamental principles
on which its satisfactory operation depends.
WIRE.
The common sizes of wire in use for bell work are Nos.
18, 20, and 22. In general, however. No. 20 will be found satis-
factory as it is usually sutKciently large, while in many cases No.
22 is not strong enough from a mechanical standpoint.
It is important that the wires should be well insulated to pre-
Fig. 1.
vent accidental contacts with the staples or other wires
all the wire should be tinned, as this prevents *'
IxMng acted uj)on by the sulphur in the insula^
itates soldering. The inner coating of insB
881
2
ELECTRIC BELL WIRING
iiidia rubl>er, surrounded by several longitudinal strands of cotton,
outside of wbieh are wound several strands of colored cotton laid
on spirally. Tbis is next immersed in melted pamtMn wax and
polisbed by friction. A short length of approved electric btdl wire
is shown in Fig. 1.
When ordering wire, it is well to have it furnished in several
different colors as this greatly facilitates both the original instal-
lation and later repairs, because in this way one line may be dis-
tinguished from another, taps from main lines, etc. Moreover, a
faulty wire having been found, it is possible to identify it at any
desired section of its length.
METHODS OF WIRING.
In running wires, the shortest and most direct route should,
of course, be taken between the battery, bells, and bell pushes.
There are two cases to be considered. The better method is that
in which the wires are run before the building is completed, and
the wiring should be done as soon as the roof is on and the walls
are up. In this case the wires are usually run in zinc tubes
secured to the walls with nails. The tubes should be from | inch
^e— ^ to i inch in diameter, preferably
U the latter. It is better to place
I the wires and tubes simultane-
^ ^ ^ ously, but the tubes may be put
in place first and the wires drawn
in afterward, although this latter
plan has the objection that the insulation is liable to become
abraded when the wires are drawn in. In joining up two lengths
of tul)e, the end of one piece should be opened up w'ith the pliers
so that it may receive the end of the other tube, which should also
be opened up, but to a less extent, to prevent wear upon the
insulation. Specially prepared paper tubes are sometimes substi-
tuted for the zinc.
If the building is completed l)efore the wiring is done, the
concealed method descrii)ed above cannot be used, and it is neces-
sary to run the wires along the walls supported by staples, where
they will be least conspicuous. Fig. 2 shows ordinary double-
pointed tacks. Fig. 3 shows an insulating saddle staple which
Fig. 2.
mst
ELECTRIC BELL WIRING
Fifi. 3.
is to be recom mended. Two wires ehould never )m> ei-cured under
the same staple if it can possibly Iw Kvoiiled. ow.in^ to tbo danger
of short circuits. With a little
care it is Dsually possible to con-
ceal the wiring behind the picture
niouIding,»long the skirting- l«»inl,
and beside the door poets, bu t where
it ie impossible to conceal it, a light
ornamental casing to match the
linish of the room, may l>e used.
It is sometimes advisable to ii»e
twin wires or two insulated wires nm in the eanie outfr rovering.
In some cases it is well to run the wires under tin; Ihiors,
laying them in notches in the tops of the joists or in holes bored
about two inches below the tups of tlie joists.
JOINTS.
When making a joint, care should l>e taken to have a tinu,
clean connection, both mechanically and elt-ctriciilly, and this must
always be soldered to prevent corrosion. The insulatidn should
be stripped off the ends of the wires to W: joined, fur a distanct.) of
about 2 inches, and the wires made bright by seiitping or sandpa-
S=^S^^J^
Fig.
pcring. They should then W-- twisteii tightly ajxl evenly together
as shown in Fig. 4.
Next comes the operatiuii of soldering, whidi is abHulutely
necessary if a |iennanent joint fruni an el <.'<.■ tricxl HtKiid|)oiMt is to
be obtained. A joint made without solder nmv 1h' electrically
sound at first, but its resiHtanee rajiidly increases, due to deteri-
oration of the joint. As has already liecn stated, the wires should
be made bright and clean l>efore they are twisted together.
Soldering fluids should never be used, l>eeause they cause corrosion
of the wire. The U-st flux to use is n'sin or composite candle.
The soldering should always Iw done with a copper bit rather than
with a blowpipe or wirenmn's torch.
ELECTRIC BELL WIRING
A convenient form of soldering tool consists of a small copper
bit having a semicircular notch near the end. This bit should, of
course, be well tinned. It is then heated over a spirit lamp, or
wireman's torch, and the notch filled with soft solder. Lay the
joint, which has previously been treated with the flux, in this
notch and turn it so that the solder runs completely around among
the spirals of the joint. The loose solder should be shaken oflf or
removed with a bit of rag. When the joint is set, it should Ix?
insulated with rubber tape, so that it will be protected as j)erfectly
as the other j)ortions.
It is often possible to save a considerable length of wire and
amount of labor by using a ground return, which, if properly
arranged, will give very satisfactory results, although a complete
metallic circuit is always to be preferred. Where water or gas
mains are available, a good ground may be ob-
tained by connecting to them, being sure to
have a good connection. This may be se-
cured by scra])ing a portion of the pipe
perfectly bright and clean and then winding
this with bare wire; the whole is then well
soldered. An end should be left to which
the wire from the bell circuit is twisteil and
Onl/n soldered. If such mains are not available,
^y-^ a good ground can be obtained by connecting
the wire from the bell circuit, as descrilxKl
above, to a pump pipe. In the absence of
water and gas mains, and of a pump pipe,
ji ground may be obtained l)y burying l)ene^th
permanent moisture level a sheet of copper
or lead, having at least five Sijuare feet of surface, to which the
return wire is connected. The ground plate should be covered
with coke nearly to the surface; the hole should then be filled in
with ordinary soil well rammed.
OUTFIT.
The three essential parts of the electric bell outfit are the bell
push, which furnishes a means of opening and closing the circuit
at will, the battery, which furnishes the current for operating the
-"innnr^R
Fig. 5.
824
ELECTRIC BELL WIRING
;iiplete circuit, let
Fig. i
bell, aDd tbe bell itself. Beforw clisciissiug tlie (.-oiiit>i nation of
tbese jiieL'ea of apjaratus in tlw
tbe individual parts in order,
A b«ll push is bIiowii diagraniniaticatly
ilhistratioii P is the push liiittoii; wlieii
tliis is pressed upon it briu<rs tbe jKiiiit
of the spring S in contact with tbe metal
strip It, thus closing the circuit with which
it is conneot«d in series. Xorrnally the
springs are separated as shown, and the
circuit is accordingly open.
IJell pushes are made in various de-
signs and styles, from the simple wooileii
push shown in Fig. 11 to very elaborate niid expensive iirticleB.
Fig. 7 shows four cast hroH7A! pushes of neat appi'arance and mod-
erate price.
Batteries. Klectrio WIls are nearly always o]>erated on tbe
open circuit plan, and lience the Imttery used is generally of tbe
open circuit ly|)e, sucb as the Leclaucbe cell, which is used very
largely except for heavy work. This is a zinc-carbon cell in which
tbe excitant is sal-ammoniac dissolved .ill water. Polarization is
prevented liy peroxide of manganese, which gives up part of its
oxygen, combining with the hydrogen set frw and forming water.
6
ELECTRIC BELL WIRING
Dry Batteries are also frequently used for bell work, their
princijxal advantage l)eing cleanliness, as tliey cannot spill. Dry
cells are really a iiiodilication of the I-<eclanche type, as they use
zinc and carbon plates and sal-anuuoniac as the exciting agent.
The Burnley cell, which is one of the principal ty{K*s of dry cell,
has an electrolyte conn)08ed of sal-aniinoniac, chloride of zinc,
plaster, Hour, and water. Tbis compound when mixed is a semi-
liquid mass which quickly stiffens after being poured into tbe cup.
The depolarizing agent is peroxide of manganese, the same as is
used in the Ijeclanche cell, this l)eing packed around the carbon
cylinder. The top of the cell is sealed
with bitumen or some similar substance.
For very heavy work the Edison-
Lalande and the Fuller types of cell are
best suited, while for closed circuit work
the gravity cell is most satisfactory.
Bell. It is a well-known fact that
if a current of electricity flows through
a coil of wire wound on an iron core,
the core becomes magnetized and is ca-
pable of attracting any magnetic sub-
stances to itself. The operation of the
electric bell, like that of so many other
pieces of electrical apparatus, depends
upon this fact. A diagrammatic repre-
sentation of an electric bell is shown in
Fig. 8, in which M is an electromagnet
composed of soft- iron cores on wliich are wound coils of insulated
wire. The armature is mounted upon a spring K, and carries a ham-
mer H at its end for strikintr theironir. On the back of the armature
is a spring wliich makes contact at 1) with the back stop T. The
action of the b(»ll is as follows: AVhen the circuit is closed throuuh
the bell a current flows from terminal 1, around the coils of the
magnet, through the spring K and contact ])oint D, through the
back stop T, to terminal 2. In flowing around the electromagnet the
current magnetizes its core, which conseijuently attracts the arma-
ture. This causes the hammer II to strike the gong. While in
this position the contact at D is broken, the current ceases to flow
Ki^r. H.
226
ELECTRIC BELL WIRIXG
around tliu electromagnet and tliu cores consequently loet; tlieir
attraotivo forte. The arniiitiire is llieii carrieil liaek to its oriiriiiHl
|H)Hitioii by the spring K, making eonlai-t at I), aii<t the iiroceKK iH
repeated. Tlie hKuinier will tliiix vihnttu and tlie U^ll coiitinne to
rinft as lontr as the eirciiit is elowd.
The ty|)e of l>i']l descrihed atxive is the one iiiost eiiinnioiily
HBed. Such Wis are iiimle in a frrcut viirictyof eliajK-s and styles,
the priws varyinf^ aceordini;h-. It is iinjKirtant lliiit platinnni
tips lie furnished at the eontnet point I>, Kif^. H, tn [irevent eor-
Fin- ». Fin- liJ.
rosion. Tim hells on tlie uiarki't ttnliiy are of Iwo elasses, the iron
box hell and the u-mNlcn Ih)\ U-ll. A U-ll oF llie -wooden hox type is
shown in Kig. 11, and u liifjher frrade U-ll of the iron franie skeleton
type 18 shown in Fig. 10. liells without covers shouhl never he nsed,
ae duet will settle on the eontaels and interfere with their action.
CIRCIJITS.
The po3siliIe conihiriatiuns of the varions psirt^ into complete
circuits are so variwl that it would Iw impossible to descriln! thi'in
R
ELECTRIC BELL WIRING
all; in fact, almost every one is to a certain extent a special
problem. It is, however, possible to give typical circuits the
underlying principles of which can be applied successfully to any
particular case.
Fig. 11 shows a bell circuit in its simplest form, in which P
represents the push, Ji the bell, and C the batterj-; all connected
in series. The circuit is normally open at P, and hence no cur-
rent Hows to exhaust the batteries.
AVhen P is pressed, the circuit,
otherwise complete, is closed and
current passes through the M\
causing it to ring, as already ex-
plained. For instance, the push
might be located l)eside the front
door, the bell in the kitchen and the
battery in the cellar; the location de{)ending on the results desired
and conditions to be met. The wire l>etween P and C may, if
necessary, Ix^ dispensed with and connection made to ground at G
and (i, as shown by the dotted lines.
¥\ii. 12 shows an arrantrement by means of which one l)ell B
^="G
Fig. 11.
=" G
u
B
^
P P'
^l
■<§^
Fitr. 12.
Fig. 13.
uv<\\ be controlled by either of tlu^ j)ushes P or P. This system
may be*, extended to any number of pushes similarly connected.
A method for ringing two bells simultaneously from one push
is shown in Fig. 13, where both bells I] and B' will ring from push
P. Bells, if connected in this manner, should have as nearly as
possible the same resistance, otherwise the bell of lower resistance
will take so much current that there will not be a sufficient amount
left for the other. Also, the batteries must be of greater current
capacity as the amount of curnMit taken is, of course, doubled. This
svstem can be extended to any numl)er of bells connected in this
way, up to the limit of caj)acityof the battery to ring them. Figs.
228
ELECTRIC BELL WIRING
12 and 13 may be combined so that two or more bells may be
rung from any one of two or more pushea.
In Fig. 14 is shown a scheme for ringing either bell, li or B',
from one push and one battery by means of the two-point switch
Fig. u.
S. When the arm of the switcli is on contact 1, the |iiihIi will
ring bell B, and when on coiitnet 2 it will ring bell IV.
Ill Fig. 15 is shown a method of connecting Iiells in sei-tes so
that C and B' may be rung from P. If all the t>ells 80 connected
were of the vibrating tyjx', they would not work Batisfactorily, as
it would be impossible to time them so that the vilirations would
keep step, heuce only one bell should
be of the vibrating type, and the others
should have the circuit breakers short-
circuited, the vibrating l>ell serving as
interrupter for the whole series. Obvi-
onslv this system requires a higher volt-
age than jmrallel connection, and the
cells must be of sufficient E.M.F. to
ring the bells satisfactorily. Several
bells may be connected in this way, if
desired, up to the limit of vol' ' '''e
battery.
Oftentimes a liell is to
For instance, the l>ell i-
10
ELECTRIC BELL WIRING
Reveral floors, or tlie l>ell in the office of a hotel may Ihj niiif^ from
any one of siiveral different rooms. In tliis ease it is necessary to
have some device to indicate from which push the l>ell was run<r.
The annunciator furnishers this information very wc^ll. A three-
station annunciator is sliown in Fig. 1(5. The connections for an
annunciator are shown in V\fr, 17 where A represents tlu^ anun-
ciator, B tlie l)ell, C the battery, and J*', P-, and P* the j)uslie?.
For instance, wlien P' is presseil, the current passes through the
electromagnet controlling j)oint 1 on the annunciator which causes
^
B
' (o) P% P%
FiK. 17.
the arrow to be turned and at the same time the bell rings. After
the attendant has noted the signal, the arrow is restored to its
normal position by ju-essing a lever on the bottom of the anuun-
ciator box.
The electric burghir alar in fiiriiishcs a V(mt etticient ])rotec-
tion and is an application of tlu^ principles already described. Tlie
circuit, instead of being conijileted by a j)ush, is completed by
contacts ])laced on the doors or windows so that the oi)ening of
either will cause the bell to rintr. The same device^ may be used
on money-drawers, snfes, etc.
In the case of tin* electric tin' alarm, the sicrnal niiiv be crjven
either autoiriatically when the temperature reaches a certain detrree,
•■I ?r>
or pushes may be placed in convenient locations to be o{H*rated
manually. The pushes should be protected by glass so that tliev
will not be tampered with, it being necessary to break the glass
to give the alarm.
230
THI RIW YORK
PUBLIC LIBRARY
ArrOR, LBMOZ
THE ELECTRIC TELEGRAPH,
Apparatus and the riorse Code.
In order to get the beginner's point of view, it is taken for
granted that the re«ider knows nothing oi electricity or the prac-
tice of telegraphy. If there is a sh'i^^it knowledge of either of
these, so nmch the Ixitter; bnt as a starting-[)oint, we will con-
sider that altogether familiar nse of the electric cnrrent in the
ringing of a door-lndl by pressing on a button. In so doing the
new arrival ^'telegraphs " the fact to the housc^hold, and asks for
admission, and those within respond to his message, although
neither the one nor the other may know a dot from a dash.
The simple combination of batteiy, wire and apparatus by which
this action is carried on is as truly a telegra})]i circuit as is the
longest in the land, and a glance at its elements will serve as a
stepping stone to the more complex apparatus of the electric
telegraph.
The different parts of the electric-bell device may be seen in
their relation one to the oth(»r by reference to Fig. 1. In the center
is the push-button P, pressing upon which brings the point of
spring S into contact with the metal strip R. On one side is the
cell A, with its two poles C and Z ; on the other is the bell, with
its electromagnet M, its armature hinged upon a spring K, carry-
ing a hammer H, to strike the bell. Attached to the back of the
armature is a spring, making contact at D v/ith a biick-stop T.
These parts are so adjusted that when the armature is attracted
by the magnet the contact at D is broken. Looking now at the
diagram, if the wiring is traced from the point C back to the
point Z, but one break will be found in the continuous contact of
the wire with the different parts, and that is between the spring
S and the strip R.
If, by means of the push-button, S is forced against R, the
break is closed ; the current spetjds from the point C of the
233
THE ELECTRIC TELEGRAPH.
througli the wire lock to the imtiit Z, olijii^fuig tlie elect romagiiet
M, which iUti-iicts iirmatiire-ciiirying haniiuer 11. But by this move-
ment the rontiict, and therefore tlie electric circuit, is broken at
I>, tlie ciiiTctit cea-scs, elect I'oiiiiijriiet M relejises the liammer H;
contiict of the Hrniiitiire nml liatk-st^ip at D is thus restored ; mag-
net M is a<^iiii i'h.irg(.'cl, attracting Uie armiittii'c; the i-esult lieiiig
a vibmtioii of the hammer, coiiliniicil a» long iis aiiring S is kept
ill contact witli R. The ent-rgy is derived fi-om the cell, but the
control oE it lies in the pusli-biittoii; and the effect of the making
and breaking of the circnit at R is such as to appeal to tlie ear.
By means not very different the same organ is addi-essed in tel^
niphy; but tlie appeal is of a kind legible only to the expert.
The bell devi;;e serves the further purpose of bringing the learner
face to face, at tlie outset, with the fact of the inconceivable speed
of the energy he is employing, — a fe;iture which allies it to light
in the velocity of its movement.
Having now gjiincd a general idea of the action of a current
in moving an armature, we will siipjiosc? that tiie reader, if hi a city,
hiw stepped into one of the many biHTicii ofRces of a great tele-
graph company, or it may Iw into a town or village ofliec of the
same, and for the lirst timn is fciking notice of the outfit. In
sncb an oHhie tliem will be seen (sc.-ured t-o the wall) a small
switcblmard, but the interest <!i'Titei-s oil the l^ilite or desk, where
there ai-e usually Ihitte forms of apparatus, kiiown as the relay.
THE ELECTRIC TELEGI^APII.
key and sounder, with the wires connecting the various parts.
On the window-sill, or under the table, is the battery of one or
two cells, for the operation of the sounder, shown in the Instruc-
tion Paper " Elements of Electricity." The uninitiated, listening
to its clicks for the first time, naively expresses surprise that they
" can make nothing of them." This set of appanitus, installed
in thousands of small offices all over the continent, and duplicated
many times in the large offices, is shown in outline in Fig. 2,
The relav, described in '" Elements of Electricitv," is not heard
at all ; the main battery which operates it may be scores of miles
away ; the current from it has its path in the main, or air, line
ON ^Ol£S
Me.
LOCAL BATTCf^Y
L.„_H|,|_..
FJtL2..
MA//V L /NC
OH fOLta
coming in from the pole in the street. Passing through the coils
of the relays and the keys, it makes its exit througli the office
window, to resume its place on the poles which suppoit it to the
terminus of the line.
Examining Fig. 2 and comparing it with the bell-ringing
device shown in Fig. 1, we find the cells of battery and the wir-
ing common to both ; the sounder corresponds to the bell proper ;
the key marked K answers to the push-button. The dotted lines
in Fig. 2 represent the ^ local " circuit, and the cells are the
** local " battery, so called because its action is confined to the
.235
6
THE ELECTRIC TELEGRAPH.
place (Latin, locus) or station with which it is immediately con-
nected. See the " Gravity Cell " in Elements of Electricity; the leads
from the two polos beincr shown. If the wlierefore of this pair of
conductors and their connected parts is understood, the method of
Morse telegraphy is within easy distance; and with the little light
gained from the comparison of the electric bell with the telegraph
circuits we may take a step further in advance. For closer
examination, therefore, this local circuit and its parts are repro-
duced on a larger scale in Fig. 3 and with more lettering. Each
of the two cells of batteiy is surmounted by two projections called
poles, — the terminal connections of two dissimilar substances, as
copper and zinc, or zinc and carbon. The cell is explained in
D
F^3
"Elements of Electricity;" all that need be noted now is that
by outwardly joining up the cells so that the unlike sul)stances
are in metallic contact, a current is the result. Fii-st the carlwn
terminal or pole of one cell is connected to the zinc pole of the
other; then from the cfirbou polo C of cell A runs a wire (dotted
line) which can be traced through the coil of magnet M ; thence
to the armature D, and local points at P of the relay R back to
the zinc pole Z of cell B. Of relay R only the moving parts are
shown. The thumbscrews, wherever found, have connected to
them wires from the different parts of the instrument, and are
merely conveniences for making contact with the outside wiring.
2^Q
THE ELECTRIC TELEGRAPH.
Besides the biitteiy of two cells and the conducting wires (dotted
lines), the circuit, as already intimated, inchides an electromagnet,
consisting of a pair of upright coils (only one is shown), which,
with the surmounting armature F and its adjacent parts, consti-
tutes the sounder S. Each of the two upright coils of wire has
a core of soft iron with a strip of iron X, joining them under-
neath. Close to the upper ends of the cores, but not touching, is
a strip of soft iron F, called the armature, secured to a lever L,
moving on trunnions T, at one end, lis free end moving Ijctween
two stops, the spring J serving for its adjustment. The move-
ment of armature D of relay R is also limited by stoi)S, and, trac-
ing our dotted line circuit, we find a point 1% where the circuit
may be "broken " by withdrawing armatnre D from the front-stop
H ; just as in the case of the push-button, the circuit is " made "
by pressure on the button, and '-broken " by the witlidrawal of it.
In other words, in tliis armature I), with its front and back stop,
and spring K, we have a telegraph key in a form tlie simplest and
most easily understood, but not the most easily openit^Ml.
In a local circuit arranged as in Fig. 8, whtMi armature D of
relay R rests against its front-stop H, the current magnetizes the
cores of electromagnet M of the sounder; armature F is strongly
attracted thereto, making a sliaip click as it strikes the down-stop
N; a reverse or upward movement is determined by spring J if
armature D of the relay is withdrawn from the front-stop, giving
a sound less sharp than in the downward movement. The differ-
ence in sound between the front and back-stroke of the lever is
something of which the learner must early take note, because the
front is the marking stroke, or the one from which he reads, tlie
back-stroke being unintelligible. In the former ease (armature 1)
against the front-stop), the circuit is said to be "made" or
"closed;" in the latter it is "broken " or "open.'* Cl)sed and
open are the terms in general use among telegrapliers. In the
case of the electric bell, the push-button puts us in control of the
energy which attracts the hammei- to the gong. In the lo(»al
arrangement we h.ave l^en considering, the control of the sounder
S lies in the armature D, wliether moved by the finger, or in the
usual way by the current.
In this dotted-Iine arrangement the wires are the carriers or
237
8 THE ELECTRIC TELEGKAPII.
conductors of an energy which has its source in chemical action
in the cells. In the poverty of language it is said to ** flow " or
"run " within the cell from the zinc to the copper plate, or from
zinc to carbon; and in the external |K)rtion (dotted line) from cop-
per or carbon to zinc. Moving thus along the conducting wire and
through the connected instruments it is called a current (Liitin,
curro^ to run) and in doing so it is said to make a "circuit,**
which may vary in length from a few feet to hundreds of miles.
Its velocity is such that wherever a fitting pathway is afforded, it
seems not so much to flow as to be omnipresent. In a series of
tests made in New York l)y the United States Coast Sui-vey, two
separate wires were obtained to San Francisco, where they were
joined, or, as telegraphers say, "looped." To each of the New
York ends of the wire, instruments were connected, and signals
sent on the one wire returned on tlie other in a space of time just
perceptible. The current had traversed the continent and back
in a small fraction of a second, — a kind of movement which the
words *" flow " and " run " hardly describe.
It is the purpose of this description, to explain to the
reader how it is that the signals heard on the sounder can have a
meaning to tlie operator; how it is that the down and up move-
ment of the lever of tlie key K, V'v^, 3, can transmit intellicrence
to a distant stiition; then, briefly at fii-st, but later on more com-
pletely, to instrui^t him in the method of operation, use and
adjustment of eacli instrument in the set, so that in a reasonable
period of time he will himself be able to sr^nd and receive the
signals which bt»fore were unintelligible. At this point a num-
ber of questions iiiay susjf<^est thcMuselves to the thoughtful stu-
dent. Some of tlu?m, it may be, eannot be answered; others may
belong to the theory of the art; but our present aim is entirely
practical, the point being to beget in the student the ability to
translate writing and speech into tlie " Morae " language ; the
consideration even of the main-line circuit is therefore deferred.
Summing up the examination of tlie local circuit there art
(1) The cells of battery as the source of energy,
(2) The conducting wires,
(3) The sounder S, consisting of an upright electromagnet
having for an armature a movable lever ; and
2»&
THE ELECTIilC TELEGRAPH.
9
(4) A point P in the circuit at which, by a movement of the
armature D of relay R, we can control at will the annature of
sounder S.
In speaking of the relay R, Fig. 3, and its armature, the
remark was made that in it we have a telegmph key in form tho
simplest and most easily understood, but not the most easily oper-
ated. Remove the dotted line wires from the timmbscrews of
relay R and insert them, as in Fig. 4, in the tenninals of a key
K', described in *' Elements of P^leetricMty." We now have a ** learn-
er's outfit '' — battery, key, pounder and eonneetint; wires. Even with
LCAR/>f£/i's oar^/T
these, signalling to considerable distances can be carried on, and
the medium for it is the Morse Telegraph Code, whose elements
and their combinations to form letters are now to be taken up.
THE nORSE CODE.
It is taken for granted now that the student is provided with
"a learner's outfit," comprising the apparatus shown in Fig. 4.
The key K is provided with a curved arm E, hinged at V. By
moving this to the right the key is opened. If, by tapping on the
rubber knob of the lever, dots are made on the open key, it will be
found that the armature of the sounder follows its movements.
Having attained thus the control of an electromagnet, only a time
element is needed in connection with the movements of the key to
939
10 THE ELECTRIC TELEGRAPH.
produce intelligible signals. In other words, if the open key is
closed, by depressing the lever, now for a short, now for a longer
time, or if the time between the moments of depression is varied,
it is possible, by assigning the letters of the alphabet to different
combinations of these movements, to make the instrument spell out
the words of a language. To this end there was devised a system of
dots, sj)ace8 and dasliea, so arranged and combined that, singly or
in groups, they are made to represent the different letters, figures
and characters of the English language. If the learner (the key
being open) hits the rubber knob a short, sharp blow with the
finger, the sounder will give two clicks, one with the downwiird
motion of the armature and one with the upward. Tlie former
has a sharp click, the latter a dull sound called the "back-stroke."
The signal thus formed is called a dot, and its prolongation by a
longer depression of tlie key is a dasli; the down-stroke of the
armature marks the beginning of a dot or dasli, and the up or
backstroke its end. In the movements for the production of the
signals the time unit is the dot; by its duration all the dashes
and spaces are measured. The single dot, produced as described,
is the signal for tlie letter E, the letter in most frequent use hav-
ing assigned to it an element the simplest and most easily formed.
Prolong the dot to twice the time and we have the dash — the
signal for tiie letter T; to four times the time, a longer dash,
forming the letter L ; to five times the time, and we have the sig-
nal for a cipher (0). To the hand the only difference between a
dot and a dash is a longer depression of the key ; to the ear the
difference is in the interval between the down and up, or back-
stroke of the armature. If the back-stroke were absent it would
be impossible to distinguish E, T and L one from the other. It is
not an uncommon thing for even the experienced o[>erator to
"get the back-stroke," in which case he dampens the up-stroke of
the sounder with his finger until the ear catches the down-stroke
again.
In the selection of the combinations which make up the code
of signals, the principle, " the easy signal for the frequent letter, '*
is observed throughout. The time value of the dot is constant,
but the dasli and space have each three different lengtlis. Two
dots separated by a space of time approximately equal to a dot
^tA!^
THE ELECTBIO TELEGRAPH. 11 ^H
A
V
I
I
"
I
B
■ I
1
1
w
1
1
I
C
1
I
X
1
I
I
I
D
I ■
1
Y
■
I
■
E
z
1
I
■
F
1
i.
1
I
■
G
1 1
1 1
1
1
■
■
1
I
H
1
1
I I
2
3
1
I
1
1
1
J
1 I
4
1
■
1
K
1 I
5
1
1
1
■ 1
L
6
1
■
I
1
1
M
■ ■
■
7
1
■
■
1
N
I I
8
1
■
I
1
3
1
■
1
1
P
Q
■
1 I
1
■
■
1
1
■
1
R
1
1
■
■ 1
I
1
I
1
s
I
I
?
1
■
1
1
1
T
1
I
I
1
■ I
U
■
■■
r
1
1
■ 1
I
1
12
THE ELECTRIC TELEGRAPH.
represent the letter I, but two dots separated by a space equal in
time to two dots represent O. The former is a mere interval, the
latter is called the letter space ; the word and sentence space are
multiples of it — usually twice for the former and thrice for the
latter. In naming the elements of the signal for the letter O,
for example, they are read " dot, space and dot."
The entire scheme of the Morse Code, with its dots, spaces
and dashes, their combinations and their relative time values com-
puted according to the unit of time — the dot — and the letters,
figures and characters they represent, is shown graphically in the
accompanying chart, which the student must now, for a time at
least, make his constant guide and reference.
Fig. 6.
That we are able to present the alphabet in this preferred
form is due to the courtesy of the D. Van Nostrand Company of
New York, publishers of " Modern Practice of the Electric Tele-
graph " by F. L. Pope, to which manual, for details of nearly
every topic in connection with telegraphy, the student is referred.
In this connection it may bo of interest to state that the
Morse Code, in tlie form in which it is now used, is the work of
Alfred Vail of Morristowii, N. J., and that in the selection of the
signals for the different letters he was aided, so the story goes, by
a chance visit to a printing-office, where he noticed that in the
type cases the size of the different compartments was determined
by the frequency of the use of the letter.
The attention of the learner having been called to the rela-
tive time values of the elements which go to make up the signals,
he is now in a position to attempt for himself the making of them,
and to take his first step as a sender. His instrument for th'«
2ASL
THE ELECTRIC TELEGRAPH. 18
purpose is the key, with regard to which it has already been
explained that it is merely a convenient device for the admission
and non-admission of the current to the electromagnet of the
sounder, according to a prearranged code. A suggestion as to
the manner of holding the key can be gained from the cut (Fig.
5) given herewith. In it will be noticed the thumb pressing
lightly upward against the rubljer knob, the fore and second
fingera curved, their tips slightly enibeddcid in the knob, the
wiust kept well Jibove the lino of the lever. Tliis illustration,
long familiar to telegrapliei*s from its use in advertisements, and
known among them as the " Catlin grip/' is not intended for exact
imitation. As in the case of handwriting, individual proclivities
will assert themselves; but if the learner infers from it how to
gain a firm command of the key, without cramping the fingers and
forearm, he will have leanied all that the text-book or a teacher can
tell him.
At this stage some learners simply place the code chart before
them and beginning at A, with its dot and dash, plod through the
entire alphabet; then back and forth over the same ground, until
they have obtained a certain mastery of the signals ; and many good
operators have learned in just this way. The writer has heard Mr.
James D. Reid, "the father of telegraphers," relate that even on
his way to assume his firet position he re-enforced his limited prac-
tice by tapping out the alphabet with a pencil or a knife on the
Mdndow of the railway coach or on the arm of a seat. But it
seems more in keeping with ujvto-date methods of instruction pur-
sued in other branches to give to the exercises now to be entered
upon a growing and developing character. With this end in view
the different combinations of dot, space and dash are classified and
arranged in six different modes — the signals for letters, figures, and
common punctuation points only being considered at present. A
mere glance at the chart will indicate to the eye the differences
already noted in the lengths of the daslx^s ; thc^ letter L is repre-
sented by a dash twice as long, as T ; and the signal for a cipher
is a dash two and a half times as long as T. It is as well for the
beginner to observe these relative lengths; but in actual work the
daalies undergo some shortening without danger of error.
248
14 THE ELECTRIC TELEGRAPH.
1. Dot only, . E •• I ... S •••• H ••••• P
2. Dash only, — T L cipher U 5
I>aragraph
3. Dot preceding the dash, • — A •• — U ••• — V •••• — 4
. W
4. Dot following the dash, — . N — .. D — ... B — — ..7
— .».. S .G .exclamation
6. A combination of (3) and (4) . — .F — . — .J — .-K
— •• — 9 . — . — comma .• •• period
— .. — • interrogation
6. Dot and space, .. • C • . O . •• R •• .. Y ... . Z •...<$;
The method to be followed by the student looks to the repe-
tition of tlie signals for these letters and characters, first in direct
order as given, and then in reverse. In this way his work is
graduated, and his ear will soon become accustomed to the diflfer-
cnce as the elements increase or diic reuse. Especially is this true in
regard to the first mode ; and in connection with the second it is to
be noticed that while the dot always has the same time value, the
dash, as already stated, luis thiee different values, as indicated by
the length of the lines for T, L, and ciplier in the chart. The T
dash repeated gives us the letter M ; used thrice, the Fig. 5, and
four times, the signal for a paragraph.
The tliird mode includes those letters and characters in which
a dfish or dashes is preceded by a dot or dots. They represent
the letters A, U, V, VV, Fig. 4. And for mode four we have a
reversal of the elements in the preceding one ; dot follows dash,
and signals are thus composed for letters N, D, B, G, Figs. 7 and
8, and the exclamation point.
In the fifth mode the order is miscellaneous ; and the more
complex and difficult signals thus obtained, have assigned to them
the letters least often used. They are F, J, K, Q, X, figures
1, 2, 3, 9, the commv, the period and interrogation. Last come
the so-called spaced letters — of all the signals, requiring in their
formation and grouping the most care. They are C, O, R, Y, Z,
& ; and their persistent repetition, both singly and in combinations
of short words, is enjoined upon the student.
The telegraphic equivalents of all the letters, figures and
more common punctuation marks having l)een given, attention is
next called to groups of letters having signals somewhat similar.
M4
THE ELECTRIC TELEGRAPH. 15
For the letters and characters in these groups the student can find
for himself the signals in the code card. He can, by inspection,
determine for himself the exact difference in each case, as, for in-
sUmce, in the first of the following groups A differs from I by the
change of a dot into a dash. 1. I, A, S, U, H, V.
2. A, F, X, comma, W, !•
3. U, Q, 2, period, 8.
4. K, J, 9, ?, G, 7, !
The signals for these letters and charactei-s having by repe-
tition Ijecome familiar to the ear, the combination of letters into
words, may next bo taken up. In the coui*se of the plodding thus
far pursued, the leanier may begin to think that the slow analysis
by the brain and the mcntid noting of every signal must be an
irksome task. But he will find as he advances that by degrees
the analysis l)ecomes mechanical; c(Mtain sounds come to mean
letters, groups of sounds, words. The real alphabet of the expert
telegraplier is largely one of words ; to him tlie clicking of the
sounder is a language, and its interpretation as easy as that of
speech. It is therefore witli the comlnnatioii of letters into words
tluit we have now to do. And in pursuance of the i)rogressive plan
the exercises revert at this point to the order in which the signals
were classified ; that is, words are made up first of dot letters,
then of dash letters, and so on.
1. Of the dot lettei-s can be formed the words is, she, ship,
hips, his, pies, sip, pipe, sheep.
As it is not possible to furnish many words made up exclu-
sively of the letters in each group, single letters from other groups
are here and there borrowed to make up some exercise words ; as
for instance, in the old-time favorites with learners, pippin and
Mississippi, in which N and M Ixilong to another group.
Exercises in words containing dot letters :
Dishes, dispel, high, dipped, Spanish, spite, shipshape, dimin-
ish, dishevel, phase, diipple, hiss, hissing.
2. Dash letters : Met, tell, till, time, mill, pellmell, metal,
limit, telltale, mamma, mammal, minimum, little, time, tittle,
tattle, emit, timid, multiple, multitude, dimmed, mallet, skillet,
skimmed.
M5
16 THE ELECTRIC TELEGRAPH.
8. Dot before dash letters : Awe, awful, awl, law, mauve,
value, valve, wave, Eva, vault, view, lava, vamp, haul, pawl,
squaw.
4. Dash before dot letters : Bend, bidden, gilded, laden,
dined, begemmed, dunned, dabble, nab, ban, Denbigli, Big Indian,
quagga.
5. Combination of (3) and (4): Julep, jungle, junk, Fiji
king, fast bind, fast find, quit, equal, quaff, quake, exit, exist, ex-
queen, exquisite, exhaust, skiff, piquant. Affix a k to kin and
it is kink, bequeath, quaint, mujik, Ajax, Xanthine, jejune, jujube,
keg, fix.
Thus far no words containing a spaced letter have been ad-
mitted. The hand and ear are thus first accustomed to the sisrnals
whose elements are separated by a uniform interval of time. By
reference to the code card the learner will notice the difference in
tlie spacing between s and c, i and o, s and r, h and y, h and z.
The addition of the spaced lettera makes the alphabet complete,
and a numlx3r of excellent practice words omitted heretofore are
now available.
6. Spaced letters : Or, err, to err is human, errant, comer,
Corcyra, correct the error, eczenii, corollary, co-operate, Corcoran
& ('o., coon, raccoon, circus, circle, cycle, bicycle, cuiTcnt^ currant,
cracker, firecracker, (;lirouicle, coccyx, buzzard, zyrcon, correlate,
physics, phantasmagoria, rhododendron, corrupt, cohesion, cordu-
roy, road, dory, hippo[)otamus. There is no royal road to leam-
mg. The voice said Cry. What shall I cry ? According to
Sinbad the sailor, the roc's egg was enormous in size. Llewelljm,
sassafras, crown, point, parallelogram, oyster, eyelet, icicle, ice-
cream, puzzle, bamboozle, binocular, verdict, door, category, oracle,
rollicking, moored, marooned, j)irate, gyratory, circumstance, cir-
cumgyratory, paraphernalia, jiffy, clfigy, equinox, quiz. Quixotic.
Peter Piper's peacock picked a peck of pepper out of a pewter
platter.
A few easy messages of ordinary commercial form are here
introduced, attention being called to the fact that the destination
o(»,cupies a line by itself. This is done so that the distributors in
the larger oflSces can catch the '• place to " at a glance.
84e
THE ELECTRIC TELEGRAPH. 17
116 B. B N MB 11 Paid.
RECEIVED It tlw . . . BUILDING, . . Broadway, N. Y. July 12, 1902 >
Dated B^ir Harbor, Me., 12.
To The o . Faulkner ,
Jenkintown, Pa. i
Can give same room as last year — twenty-
eight dollars. Answer.
(Sig.) J. S. LYMAN.
7 Paid.
RECEIVED at the . . . BUILDING, . . Broadway N. Y. July 12, 1902.
Dated Kingston Depot, N. Y . , 12.
To Mexican Gulf Agricultural Co.,
Dallas, Tex.
Arrive there Monday morning, 8.55.
(Sig.) ALLEN.
184 U D B 20 D. H.
RECEIVED at the . . . BUILDING, . . Broadwaj, N. Y. July 12, 190 2
Dated MajDaroneck, N. Y., 12.
Xo G. P. -Harriman,
Pullman Co . ,
Detroit, Mich. »
Empire Coupler Co. shipped car load of
couplers to-day in D. L. & W. car 58,051.
(Sig.) H. M. WYATT.
847
18 THE ELECTRIC TELEGRAPH.
In the top line the first space contains the number, and gen-
erally the call of the sending station ; the second and tliird spaces,
the signals of the sending and receiving operators; the fourth, the
check. In practice the signature is also on a line by itself.
By attention to the response of the sounder as he forms the
lettere on the key, the learner has now to some extent familiar-
ized himself with the sound of the signals as he translates their
form, as printed in the code card, into the key movements neces-
sary to produce the dot, space, and dash. Reading the signals as
they are embossed on paper by a *' register," except for some
special uses, has become obsolete in telegraphy, so that it is with
the sound that the learner has entirely to deal ; and the signals
from which he must copy are those of a hand not his own on a
distant key. In this, as in handwriting, there are individual
differences ; and the query whether operators can recognize one
another over the wire by their "Morse" can bo answered affirm-
atively. Since much depends on the initial practice in the
formation of his style, the learner should, if possible, at the out-
set take a few lessons from an operator. That these remarks
are practical and not perfunctory, the writer has personal- knowl-
edge at tlic present time of the contemphited removal of ope-
rators from some important circuits because of their defective
sending. To aid in the formation of a coiTert style the signals
have been })resenled in a graded form, beginning with the dot,
which is the unit of time, passing on to the dash, then to tho
various C()ml)inati()ns of dots and dashes, and lastly of dots and
spaces; all with a view to their reproduction in words, phrases
cand sentences.
The Automatic Sounder Method. It was intimated that, for
bejrinners, it was advisable to observt^ closely the relative lentrth
of the sijruals as indicated by the chart, esptKiially the dashes,
and that, on this account, it would be well for them to take a few
It^ssons from an o[)erat()r at the outset. In order, however, to do
away with the necessity for this, there is broutrht to their notice a
(hnice of ^Mr. II. AV. Elani of \'al[)araiso, Indiana, for the repro-
duction of signals the same in eiftH't as if sent by hand, thus sun-
plying in a trreat measure the truidance of an experi(Miced teacher.
848
THE ELECTRIC TELEGRAPH
19
The apparatus is constnicttHl by tht; National Automatic
Transmitter Cmiijmny and ia fiirnishe<i to sliiilonts hy tho Aiiicri.
caD iScliool of Corrc-sponJonee. In addition to tlit; ap|)arutns
itself, the student is supplied with a set of rwords rcpri'st-nting
the letters and characters in the Morse cod<' ; the ap|)arutiid repro-
duces them in such a manner that, in tht- furmativo pi'ritxl, the
learner may accustom his ear to the si>rnals as maile hy tm ex|MTt.
These records are exact reproductions of the chariM-tcrs as made hy
hand; having been trananiUteii to the ret-ordinfj jx'rforator by
an expert o[)tTator throu;fh tlio use of an ordinary telcjirapb
key. So natural are the messai^es thus rcprdduci'd thiit thw indi-
viduality of the sender's *• wire-writinfj" can W detecteil.
T/iff AjjjMtrutiis. In the form furnishiil to students it is
mounted on a base, llA by
12 inches, made of (juarter-
sawed oak, finely tinishiHl;
and coniprises a learner's
outfit consisting of a key,
sounder and battery such
as havB been previously
described; with clock-work
and circuit-breaking mech-
anism througbwbich moves
a strip of perforated taj)e.
To the axle of the clock-
work, where it projects
through the frame, is af-
fixed a friction wheel
which imjiarts its motion to the tiijMi.
AUTO-ALPHABET INSTRUMI
i>.I the
.',1 by
Between the wheel ;i
tajw bolder is a curved pad against which the tiipe is [in-s.
an arm pivoted nearer to the end next the jiad which we will Ciill
A; the other end we will call B. A alight delhrlion, tlu-refon-.
of end A is quite niarke<l at end li; the movement of the hitler
is limited by a stop similar to the armaturi' of a relay. Like
the relay also, at its end IJ the pivoted arm and the «ti>p make
connection with the poles of a local battery, so that when contact
is made between the arm and the stop, the circuit through the
sounder is closed; when the contact is broken the sounder is ojwn.
20 THE ELECTRIC TELEGRAPH
The slight movement of the arm needed to operate the sounder is
effected by runnincr the perforated tape between the end A of the
arm, and the curved pad; when the end A is against the paper the
souudtjr is oj)en; it is closed whenever end A drops into an open-
ing.
In the tape the student will readily see that the smallest
openings re])resent the dots of the Morse code; the larger ones the
dashes of dilferent lentrths.
Keleasing the brake with which the mechanism is provideil,
the paper moves forward, imparting to the pivoted arm a series of
mt)vements which the souiKler translates to the ear; the perforated
tape acts as an automatic circuit breaker, protlucing the signals on
the sounder precisely as the key does, and with greater accuracy
as to relative units of time. Li effect the signals are being sent
by hand; to have them at his command is a great advantage to
the beginner, some of whose tendencies to error are set forth in a
later paragr4iph.
The course comj)rises a series of records capable of repro-
ducing the work of an expcTt as effectively as if he were listen-
inix to the actual workintr of a wire. Another advantaire lies in
the fact that the speed with which the messages are sent can
be varitnl over a w i(U^ i'ancr(» i^o i]i it the student can use a slow
S])ec(l wliiMi lirst taking up tlie work and, as he becomes more
exjH'rt, can incicasc tliis to keep ])ace with his advance. The
instrument can jdso be niadt* to re|)eat any triven messat{e as manv
times as tlie stud<'nt dt^sires.
To insure good results the local ])oints, where the arm touches
tiie front slop, sluwild be ke]>t clean; and it uuiy be necessary at
tinu's to pa.'-s a line lile lie;]itly between tluMu. The cUK*kwork
needs no attention beyond the windintr up. and an occasional
oilin<r.
'i'ht^ parts of the learner's out lit have been described else-
wh.ere, and in such a manner as should make clear how closely it
resembles the local circuit of the regular Morse Line. In placing
the tape, see that the sio:nals read in the direction away from the
1 c? %■'
markino- arm. The speed should be slow at first; the learner
should note the perforations and mentally name the letters and
characters as they pass toward the arm, so that when the sounder
260
THE ELECTRIC TELEGRAPH 21
reconls tbeni, the ear will associate the sounds with the sitrnals.
A iiuinl>er of these strips are furnished the student; but the
one with which he should lirst familiarize himself is that in which
the exercises follow tlie course indicated l)elow; the words are
grouped according to the six modes just indicated; they are made
up first of dot letters, then of dash letters, and so on. In pursu-
ance of this plan the particular ta|H* in (juestion is perforated to
render the following :
Is she ship his pies sip pipi^ sheep.
The learner may, if he chooses, stop the movement at this
point, and, going back to the word " is," reproduce the series any
desired number of times. Following u]K)n the word '*shet*p-' the
sounder will reproduce the following words composed for the most
part of dots:
Dishes dispel high dipped Spanish s])ite shipshape diminish
pippin Mississippi dishevel phase dapple hiss hissing
Following upon this the sounder will render the exercise
words in paragraph 2: Met tell till time mill pellmell metal limit
telltale mamma mammal minimum little time tittle tattle emit
timid multiple multitude dimmed mallet skillet skimmed; par-
agraph 3: Awe awful awl law mauve value valve wave Eva
vault view lava vamp haul pawl squaw, and so on through par-
agraphs 4 and 5.
Paragraph fi: Or err to err is human errant corner Corcyra
correct the error eczema corollary co-operat«^ Corcoran ct Co. coon
racoon circus circle cycle bicycle current currant cracker lire-
cracker chronicle coccyx buzziird zyrcon correlate physics phan-
tasmagoria rhododendron corrupt cohesion corduroy road dory'
hippopotamus. There is no royal road to learning.
Some Faults of the Beginner. The learner may now, with
key in hand held in the manner indicated, traverse once more the
ground over which he has gone; but this time, he goes along with
the notations of certain incorrect tendencies and faults which mark
the beginner's work. lie can take up those letters whose t^lements
are simple dots, viz., e, i, s, h, p, and j)ractice on the words already
furnished, or u[)on combinations of his own. He will be interested
at this point, to know that some experienced operators C4innot make
the five dots which form the letter J^, and that nuiny more
251
22 THE ELECTRIC TELEGRAPH.
cannot make the six dots of the figure 6. If the learner would
avoid the ** seven,*' " eight,** and ** ten-dot ** habit, he should start
in slowly, giving definite values to his dots, making the inter-
vals uniform, until some approach to precision is reached. Avoid
shortening or clipping the final dot, and make sure by actual
count at first that the correct number for each character is made.
Following upon the dot mode are the four short dash charac-
ters for the letters T and M, the figure 5, the paragraph ; and the
elongated dash characters for L and cipher. Here, again, a ten-
dency to shorten or lengthen the terminal dash and to space
unduly the successive dashes should be guarded against. It is
well to ol>serve at first the relative time value of the dashes, but
in practice the cipher and L dashes approach one another very
closely without inconvenience. Occurring alone or among other
letters the long dash is translated as L ; among figures it is read
as cipher. As between T and L, the usual inclination among
learners is to make the T too long and the L too short.
In the next mode, in wliich the dot or dots occur first, the
tendency is to separate too much the dot and dash elements.
The interval between them should be appreciable to the ear, but
no more. The places of these elements are reversed in the fourth
mode to form the letters N, D, B, the figures 7 and 8, and the
exclamaticn point. The first two should offer no diflBculty, but
B, 7 and 8 are troublesome, tlie tendency being to add in each
ease to the prescribed number of dots. There are operators who
make the figure 8 for B, and a dasli and five dots for 8 ; but no
one careful of his work allows himself to fall into this habit.
Then there is that couibiniition of the dot and dash elements
which gives us the letters F, J, K, Q, A, figures 1, 2, 3, 9, the
comma and the period. Of these, J and K are usually considered
the most difFicult, the tendency being to make a double N of the
J, and the dashes of unequal length in both. The last mode
brings us to the test of a good sender, in the deftness with which
he makes the spaced letters unmistakable to the receiver; and he
does this by such slight modifications of the space as the exigen-
cies of the different combinations call for. The space in these
characters is a prolonging of the necessary interval between the
elements, and it should be just enough in excess of it to make
258
THE ELECTRIC TELEGRAPH. 23
the letters O, C, Z, for instance, distinguishable from I, S
and H ; and the spaces between the successive letters of a group
of spaced letters should be slightly greater than the ordinary let-
ter space. Some unfamiUar words, such as coerce, offer such a
succession of spaced letters that it is usual for careful o[)erator8 to
repeat the word thus: coerce? coerce — the interrogation point
implying " Did you get it correctly ? " It sliould liardly bo neces-
sary to warn the learner against the stereotyped niistjike of
beginners — that of going over a great deal of ground and doing
nothing thoroughly. The real progress lies in correct work ivs
one goes along, and accuracy at first in tlie formation of the sig-
nals will lay the foundation for safe and rapid work. The stu-
dent has already been apprised, by means of three examples, what
the ordinary message form is ; but something more than " a
learner's outfit" is needed for the exchange of messages. The
point has now been reached for the consideration of the main-line
circuit, to which the electric bell and the local circuit have
formed a kind of introduction.
THE MAIN-LINE CIRCUIT.
As compared with the local circuit, or learner's outfit, no new
///T£/fMSD/>^T£
OMUAiC OR OUAfD
principle is involved in its operation. The local circuit, with its
few yards of connecting wire, has all the essential features of the
longest Morse line working single ; the differences are merely
those of adaptation to new conditions.
First to be made clear is the difference between a metallic
863
u
THE ELECTRIC TELEGRAPH.
and a ground circuit, as exempliBed in a local and a main-line ;
and the location of the latter battery with respect to the
the main line. Reverting now to the battery in the local circuit
(Figs. 3 and 4), it will be noticed that, where the sides of the
cells adjoin, the two unlike poles are connected by a sliort piece
of wire. This, with the longer piece passing through the instru-
ments and connecting the other poles, forms what is called a
metallic circuit, because the entire path of the current is of metal.
If the short piece of wire between the cells be broken in two and
both ends sunk in the damp earth, the circuit will be found intact
as before, the current finding a path through the ground; and in-
stead of a metallic we have what is called a. "ground," or (in
England) "eiirth" circuit. At tliis stage we must content our-
selves with the fact that the earth acts af a return wire; the
reason for it In-longs to the theory of electricity. The main line
is a ground circuit, not a motallie one; and the location of tlie
main batteries relatively to the rest of the circuit is made plain in
Fig. 6. In it are shown two terminal stations, each %vith main
battery, relay R and kpy K ; and between them is an intermedi-
ate station. The circuit here shown may be hundreds of miles in
THE ELECTRIC TELEGRAPH.
25
length. The cells at each terminal are usually about 150 in num-
ber ; at terminal A in the drawing the copper pole is grounded,
and the zinc goes to the main line ; at terminal C these conditions
are reversed.
Between the terminals there may be a score or more of inter-
mediate stations, of which only one (B) is represented in the
drawing; and as its position in regard to the main line is made
clear, the details of an intermediate sUition, hitherto passed over,
are now to be described. For this purpose attention is called
to Fig. 7, in which is shown, more in detiiil than in Fig. 2, an
intermediate or way-station, with its main lines appearing at
the top, its switchboard, relay, key, sounder and local circuit
(dotted line) all complete. As compared with the " learner's out-
M
O
D
M'
TO
sQ
RELAY
TO
eO
KEY
TO
GROUND
fit** the additional parts are the relay and switchboard Sw. The
wires marked " main line " are identical with those extending in
either direction from station B in Fig. 6. In connection with
relay R, Fig. 7, the dotted lines which are seen in Fig. 4 inserted
in a key are replaced in the thumbscrews of the relay ; and the
armature and front stop of the relay are again a part of the local
circuit. The coils of the relay cores, of which the thumbscrews
Y Y are the terminals, form part of the main circuit, just as the
coils of the somider in Figs. 3 and 4 form pait of the local cir-
cuit; but in the construction of the relay as compared with the
sounder, some new features mav be noted. Tht; latter instrument
is operated by a battery close at hand, for which (mly a few yards
of wire are required ; but the relay is only one of a number of
256
26 TIIE ELECTRIC TELEGRAPH.
similar instruments operated by a battery or batteries through
hundreds of miles of wire — a problem in which the matter of
economy is also a factor. The cells of battery at each main line
tei-minal was given as 150; but even with this number a meter
inserted in the main line of an ordinary telegraph circuit would
show a very feeble current. If an ordinary sounder were " cut in "
on sucli a line, there would be no response of the armature to the
opening and closing of the circuit, for the reason that the wind-
ing of its coils is not suited to the conditions. But in the relay,
in order to obtain a sufficient amount of magnetism, the coils are
wound with many more turns of much smaller wire. To make
room for the additional turns, the soft iron cores are made longer;
because of their length they are placed parallel with the base
instead of standing up, and the other parts are made to corre-
spond. The winding of the relay coils has its terminals in thumb-
screws Y Y, Fig. 7 ; and if from one of them the main line wire
is detached and tapped firmly against the thumbscrew, not only
will armature D of relay R respond to the action, but all the
relays on tlie line, be they two or twenty, open and close in unison
with the non-contact or contact of the detached wire with the
thumbscrew. Then because tlie movement of the armature of the
relay opens and closes the local circuit of each and every relay
along the line, the sounder in each local circuit moves in unison
with the home relay — a result brought about by merely tapping
the thumbscrew of the home relay with the main line wire tem^Ky-
rarily detached from it. But the detaching and tapping method
litis been resorted to only to emphasize for the learner the essential
features of a telegraph circuit. In piractice the tapping is done
nuicli more conveniently with the key, with whose use the learner
is presumed to be already somewhat familiar. And as he either
has one in his possession, or the use of one, he can examine its
construction for himself, so that a description of it here is unneces-
sary. With the key in the main line circuit to do tlie work done
by detacjhing the wire from the relay, it is plain that all the
instruments in the circuit can be controlled by the movements of
the key ; when the operator opens the key by moving the curved
ann from under the spur (see Fig. 4), all the relays instantly
o|)en ; when he depresses the lever they all as instantly close. This
THE ELECTRIC TELEGRAPH. 27
result is possible because of the velocity of the current — the time
consumed in traversing five hundred miles being inappreciable.
It should now be plain to the learner how it is that the control of
a key at any point in the circuit enables him to exchange signals
with a distant station ; and, in doing so, he " telegraphs " or, as the
word means, writes at a distance ; for telegraphy is distance writ-
ing, just as telephony is distance speaking.
Mention may be made here of a new form of key which
in its construction and operation is a radical departure from
the form hitherto in general use. The handling of the ordinary
key for any length of time is a serious tax on the muscles
of the forearm, resulting in some instances in an ailment known
as *' telegrapher s cramp." The new form of key was devised
with a view to relieve the strain on the forearm by a form of lever
which is not only initially different from the ordinary one, but
admits of being instantly shifted into various positions, as the
sender feels the need.
THE SWITCHBOARD.
One part of the apparatus of a way-station remains to be de-
scribed ; it is called the " switchboard," and is usually secured to
the wall over the operating desk. It enables the operator to
change the arrangement of the wires leading from the desk with
respect to tlie main line, and to the ground. It is simply a board
of well-seasoned wood, fitted in front with metal strips running
vertically and terminating in thumbscrews; horizontally across
the board are rows of small circles of metal, called discs, whose
stems pass through the board, at whose back each row is connected
together with a wire terminating in tlmmbscrews in front and at
one side of the board. The strips and discs are so constructed
with reference to each other, that connection can be made between
them by a metal peg having a short handle of rubl)er. The switch-
board is seen in position in Fig. 7, but is reproduced on a larger
scale in Fig. 8. The different rows of discs (each row having a
connecting wire at the back) have their terminals in the thumb-
screws 3, 4, 5, 6, of which 4 and 5 make direct connection with
the relay and key, and 6 makes connection with the ground.
Suppose the way-stiition to be between Now York and Albany;
267
28 THE ELECTTRIC TELEGRAPH.
let M represent the main line from Nev York, making connecti
with the thumbscrew 1 ; and M' the wire to Albany connecti:
with 2. Look briefly at a few changes in the connections tl
can be made by means of two raeiat pegs. Supjxtse each of t
discs in a given row to be nambired as shown on the right of th
row. Connect with i>egs 1, 3 and 3, 2. In this case the curre
would simply piss fntm bir to bar across the middle disc 3 wil
cut affecting the iiistramenti at all ; and in this position of t'
pegs they are said to b3 '* cut out." Move the peg in 1, 3 to 1,
and the mi:n line circuit is op>n because there ia connection on
between discs of the sasne row. Move tlie peg in 3, 2 to 5, 2 ar
the current h:i3 to p^KS tlirouTh key and relay in going from oi
upright b,»r to tiio other, and the apparatus ia said to be " cut in
The drawing represents the switchboard in its simplest form, ai
the operations inUcatcd are the most ordinary; but if the Ieam<
will bear in mind that the discs are connected with each oth
only in straight lines across the board, he can trace out for himse
other peg connections of discs and bars and the changes tht
bring about in the circuit. For instance, discs 6 all connect wil
the ground. ReraoYe the peg from 1, 4 to 1, 6 and from 5, 2 1
6, 2 ; the wire from both directions is now grounded, with tl
result that there are now two independent circuits — one in eac
direction from the way-station whose operator could now woi
with either New York or Albany, but tlie stations named woul
be cut off one from the otlier. Restom the pegs to their origin
TOSition in 1, 3 luid 3, 2, and the terminal stations can work wil
each other, but the way-station is once more '■ cut out." This
the position in wliich the pegs should l>e placed when the operab
leaves t!ie office, oi' during a thunderstorm. But for the lati
incident there is generally arranged a " cut out " outside the offio
Many intermediate stations iiavo more than one wire and switcl
board to correspond, and it would be jioasible to fill pages wil
the combinations that might be effected ; but suflicient cxplanatic
hiis been given to indicate the method which, when once unde
Htuod, can easily !» cxtt'ndcii and applied to suit larger needs.
In the caro and adjustment of his instruments' the operat
should see that the local points of his relay and the points of h
key are clean ; he should bo on his guard to see that the armatu
THE ELECTRIC TELEGRAPH. 29
of his relay or sounder does not hit upon the soft iron of the cores.
A good way to assure himself of this is to pass a piece of paper at
times between the armature and the core. Instructions in the
care of the local battery are now in order ; but they differ with
the kind of battery used, and are usually furnished in the book of
rules of each company.
The purpose up to this point has been to give the reader an
idea of the apparatus employed in telegraphy. It has been em-
pliasized thus far that the essential features of the local circuit,
viz., battery, electro-magnets, and connecting wires, are all repro-
duced in the main circuit, the differences being only those of
adaptation to new conditions.
With this statement a reversion is now made to the practical
— to the matter of the exchange of messages, of which some
examples of the ordinary form have already been given. The
greater part of the business handled by the commercial companies
is of the kind exhibited ; but the work of the operator would be
easy if it consisted in exchanging only such messages as the sam-
ples. In addition to the ordinary form, there are those known
among telegraphers by the following terms : Wire, service, for-
warded message, repeated back, government, grain, transfer, cipher,
number group, circular, C. N. D. (Commercial News Department),
.marine, and railway D. H. Then there is the press service, mak-
ing use, in some cases, of fixed forms for a baseball score, golf
score, and the like. Of ordinary press matter the volume on cer-
tain occasions, such as a presidential convention, is great. At the
present time much of the press matter is handled on wires leased
from the telegraph companies by the press associations, and their
carrying capacity is increased by the use of a code which enables
an operator to transmit as fast as an expert typewriter, at his
highest speed, can copy. Of code telegraphy, some details will be
given later on. In addition to all these the art has been special-
ized by railway companies in the movement of their trains and
traffic, also by brokers and large commercial houses, to such an
extent that even an expert operator must serve an apprenticeship
in order to fit himself for the rapid work in these specialized forms.
Of the different kinds of messages just enumerated, the first
two designations are self-explanatory, the former having to do
30 TilK ELECTKIC TELEGUAPH.
with the assignment, arrangement, and cross-connection of wires ;
the latter with the forwarding, re-addressing, and delivery of tele-
grams. Service messages have to do with the movement of the
despatch from the customer to the hands of the party addressed,
and, if errors have been made, with their correction.
The following are examples of this form of message :
Marietta Pa ofs.
Give full address Oswald Denberg. We fail to locate
your msg date signed National El. Co. S. Y. S. (sig) Munn,
New York.
The use of abbreviations ^^411 be noted ; and for some con-
stantly recurring phrases, such as •'•see your service," only the
initials are used. " Give better address '' is similarly represented
by G. B. A.
Munn, N. Y.
Pis D. W. C. from original yours today Carnegie Steel
Co. signed Union National Bank, A. L. Dignam Cashier.
Same reaches us dated Waterbury Conn. ; Carnegie say think
should be dated Watertown N. Y. Advise my care.
(sig) Phila., Pa.
In this case a ^ duplicate with care " is requested.
An extra-date message is one that litis been redeived by mail
at, say, Albany office ; or, having come over another line, has been
handed in to be sent forward, and takes this form :
116A hn Mo 15 Paid
lierlin, N. Y. Oct. 20, via Albany Oct. 26
Adam Brown,
Bridgeport, Conn.
Have been unexpectedly detained. Meet me next
Monday at ten. H. Brosnan.
In this case the five words " Berlin N. Y. Oct. 26 " are added
in and chargcid for as part of the message. It is customary when
the i)arty to whom a messiij^^e is addressed has left town, to for-
ward it to a given address, in which case the forwarding station,
with tin* word via^ appeal's in the date, and the originating sta-
tion and date are charged for, the same as in the example just
given.
^''.casionally the sender of a message, to insure its correct-
260
THE ELECTiaC TELEGRAPH. 31
ness, requests a repetition, in which ciise the words " repeat back "
are inserted in the check and included in the count. For such
repetition a charge of a rate and a half is made. A '' night mes-
sage " does not differ in form from the examples of paid messages
already given, except that it is always copied on a blank printed
in red ink, and in the check is inserted the word ^' night," which
is not counted. In all collect messages, whether day or night, the
word "collect " is counted as if part of the body of the message.
Government messages are exchanged between the officials of
the United States government and its employees, and differ from
the ordinary form in that the address and signature are counted
as part of the body of the message, thus :
197W Kn Mg 28 Paid Gov't
Washington, D. C. June 24
Col. H. K. Ames
Memphis, Tenn.
Forward to New Orleans all the tents and rations you
can spare in aid of the flooded district.
(sig) E. M. Harrison,
Commissary General.
The text or body of this message contains only seventeen
words ; but the count of every word in the address and signature
makes the check twenty-eight.
A prominent feature of commercial telegi-aphy at the present
day is the facilities provided for the quick interchange of messages
between Produce, Stock, and Cotton Exchanges in cities remote
from each other, the circuit arrangements being such that the
members of these bodies can carry on their trading with a celerity
and correctness that leave little to be improved upon. Many of
these traders have their own private wires ; but the greater part
of this chiss of business is carried on by the New York Produce
Exchange with the different grain centres, such as Buffalo, Toledo,
Detroit, Chicago, Duluth. In the forms of messages hitherto
given each message is preceded by its number, the signals of the
sending and receiving operators, and the cheek. In the exchange
of grain orders all this, with the exception of the number, is dis-
261
32 THE ELECTRIC TELEGRAPH.
pensed with. To show the difference in usage between the ordi-
nary and the exchange form, a message is given in both :
B123 Da Mo 7 Paid
Ex Chicago, May 18
J. C. Ladenberg,
New York.
Sell five July com at sixty half.
(sig) M. J. Allen.
In practice this would be transmitted in abbreviated form,
thus:
B186 7 Pd.
Ex. J. C. L. Sell etc. (sig) M. J. A.
Such work, of course, calls for experience on the part of the
operator and great familiarity with the names of his patrons;
these being granted, the volume of business that can be handled
during exchange hours is large.
There has been evolved in connection with the telegraph ser-
vice a great convenience to the business community in the order
by wire to pay to one party money deposited by another — a trans-
action possible between . cities on opposite sides of the continent.
The instrument of this exchange is a message called a '* transfer,"
of which the following is the common form :
B171 Dq Rn 17 Free
Hartford, Conn. June 19
J. D. Mallory,
Henderson, Texas.
Pay to N. D. Ililliard, Hotel Baldwin, gilt bald edge-
ways from E. L. Adams, Jr., Hartford. Vigilant
(sig) H. N. Tallman,
Transfer Agent.
It is a curious fact in connection with the "transfer" that
in place of tlie very commonly used D. H. for "deadhead" in the
check, the word " free " has always been retained. It is said that
the use of this rather grim j)lirase with the meaning ** no charge "
dates as far back as tlie Roman times, when free admission to the
circus and the theatres was gained by the presentation of a carved
death's head furnished l)y the authorities.
MA
THE ELECTRIC TELEGRAPH. 33
THE CIPHER nESSAOE.
In the above message it will be noticed that the amount to be
paid is indicated by words without mesining to the outsider ; and
it concludes with ^ Vig^ant," which is understood to mean *^ iden-
tification is required." The " transfer " is, therefore, in part a
cipher — a form of message much in favor among ptitrons of the
telegraph. It involves the representation of a word or phrase by
a word arbitrarily chosen, and therefore understood only by those
concerned ; and this is very nearly the dictionary definition of the
word "cipher" used in the sense of a secret writing. Its use in
telegraphy serves the double purpose of economy and secrecy;
and incidentally some forms of it greatly tax the patience of the
operator. As the meaning of the cipher is the concern only of
the correspondents, there may be as many systems sis there are
patrons ; but among business men the phrases in common use be-
came so numerous that cipher-making itself became a business.
At the present time quite a number of systems are in use ; so that,
to carry on a secret telegraphy, the patron needs only to buy two
copies of any preferred code — one for himself, and one for his cor-
respondent. As the words representing the different phrases are
generally chosen arbitrarily, any number of English words chosen
at random might be taken to form the text of a " cipher " message.
But portions of two or three with fictitious addresses, are here
given to bring the learner into touch with the reality.
B67 Ha Ks 10 Paid
New York, June^lO
L. M. Hazeltine,
Boulder, Col.
Metemperic entire peasoup velvetleaf bondmaid eighteen
birthsongs thalarctos each periwig.
(sig) Alplia.
B68 Pq An 11 Collect
North Adams, Mass. June 21
C. K. Thurber & Co.
New York.
Admixed unaided unbias aleak unapplied fetch andiron
marauding maroon hairpin.
(sig) E. M. Seymour.
268
34 THE ELECTRIC TELEGRAPH.
In this last, as in all messages similarly checked, the word
** collect" is counted. Of the more difficult forms of cipher that
in use by the large business houses of the West famishes two
examples :
C18 Mo Ns 20 Paid
Kansas City, Mo. June 21
L. M. Wetstein,
New York.
Molucris morbescunt desque cow dexterous demulsion
facial gildos holzstoss hoodwink hymniferohamauxmarandara
vetader no vetachtig motandos fatichera koinplot salami.
(sig) Robum.
D21 Aj So 15 Collect
Indianapolis, Ind. June 24
R. A. Clarkson,
Middletown, N. Y.
Asander unbespeak umsetzbar unbeing boneless mar-
agnoii monarch cervelat disallowed each car alamoth arrodeth
absorb.
(sig) Schievelin.
Quite commonly these messages contain sevenil hundred words,
and no knowledge of Englisli or of any other language is of much
aid to the receiving operator ; he must watcli for each letter, and
pen or typewrite the signals as they arrive. It should be apparent
at a glance wliat an indispensable aid to this work the typewriter
is. By means of it these unintelligible words are copied in a man-
ner that makes them unmistakable to the reader, and the receiver
has no need to rosoit to the old expedient of "writing in'' the
Morse characters under the letters imperfectly formed by the pen.
The Cable Messag^e. The high tolls charged for cable ser-
vice makes the use of cipher in their composition very common.
The address and signature of each message is counted, and the
former is often transmitted as a cipher word, which is duly registered
for reference when needed ; for instance, Havicam, London, might
stand for Ilaviland, Campbell & Co., at any address in that city
they chose to give. A single example only of a cable message
need be given, as the one form is quite generally followed.
264
THE ELECTRIC TELEGRAPH. 35
52 Yv Kn Duluth 10
Richfig,
Rotterdam.
Ascanilota apilatori makobojoss Koln luhoto
schizandra pythao (sig) Blockland.
Several of the words, it \*ill be noticed, contain just ten letters.
This is tlie pennissable limv*"- for one word ; if exceeded, tlie word is
counted as two, except in case of the destination, as Constantinople.
The correct handling of cables involves many matters of detiil in
regard to the '' count " which requires some little practice to master
properly.
A unique form of cipher deserving of mention here, makes a
message to consist entirely of groups of figures, usually five in a
group and in this form: 17641, 75089, 84356, 09543, and so on
through hundreds of groups. For the nought beginning the last
group the signals for TW — dash, dot, dash, dash — are sometimes
used. This form of cipher seems to be much used in correspond
ence between the different governments and their representatives
and agents.
The circular message, as its name indicates, has a number of
addresses with a common text^ or body. For this form the senders
generally avail themselves of the night-rate service. Except for
the plurality of the addresses, each one of which in sending is
separately numbered, it does not usually differ in form from the
ordinary message.
The ••€ N. D." The Commercial News Department message
is as unique in appearance as it is different in form from the others.
The department is an agency for systemized and detailed advice
in matters of commercial interest as they transpire in the different
exchanges, and in sporting matters to individual patrons and cus-
tomer. For transmission by the operator the message is usually
written either on a pink blank or on a sheet of yellow manifold.
One such, picked up at random, reads : '* Add Charleston. Quiet
8| Sales 50 . . . 2.31 " This is a quotation of cotton, and the
time when written takes the place of the signature. Another
reads:
" Detroit close 2.25
" Dw 84b Red & m 81 N 76 U 75^ . . . 1.15 "
866
36 THE ELECTRIC TELEGRAPa
To tlie initiated this means : Cash wheat 84 bid ; Red and mixed 81
July 76 September 75|. 1.15 is the Detroit time; 2.25 is the
time received, in New York. Another, addressed to a summer
hotel on Long Island, reads : •
"Stocks A81|; St 175; MP109f ; USS37| ; U 105 . . .
10,16 A.M.," in which A stands for Atchison, Topeka and Santa
F(5 ; St for St. Paul, and so on through the list.
These brief examples give the merest hint of the traffic of
this elaborate system ; and so diversified are its forms it takes
weeks and in some Ciises months of training to make even a
skilled operator master of the service.
The Marine Message. The natural interest of the friends of
those at sea in the sighting of their ships, and their desire to know
the probable time of their arrival at the dock in New York, led to
the organization of tlie Marine Department, which, on payment of
a certain sum, furnishes the information in the following form :
Marine Department, New York, June 2.
George Homer, 351 West 14th St., New York.
Steamer " Columbia " will arrive, unless detained at quaran-
tine, al)out 6.30 P.M. (Sig.) Manager Marine Department.
This service is almost tis old as the telegmph itself, and it remains
to be seen how far the windless system will modify it. It is cer-
tainly in this direction that the latter system should first make
itself felt.
Of the railway I). 11. a short example has already been given
as one of the three si)ecimens of tlio ordinary message. Its marks
are the use of initials and groups of figures in which each digit is
counted as a wend. Thity are fre([uently of great length, and re-
quire some care in copying in onh^r not to lose the count.
Abbreviated Telegraphy. A notable development of the art
in connection with the fast-sj)eed press work involves the use of
abbreviations according to a system, and is known among the
craft as Code Tel(;graphy. It was always more or less the custom
among press operators to abbreviate familial' and frequently recur-
ring words and phrases w\wn stMiding to experienced mates ; but
the intrrduetion of the typewritor gave such impetus to the aii;
t^dt a CO lified Moi-se, at the present time, is not far behind the
speed of ordinary speech. Beginning with the Moise alphabet,
266
THE ELECTRIC TELEGRAPH.
37
figures and onlinary punctuation marks, tlio code system first pro-
vides an extended system of fiunctuation coveriiig all tlio charac-
ters and marks that commonly occur in print, as follows : (See
page 34.)
For an apostrophe the signal is the same as that given in this
I
Dash-
Hyphen -
Pounds
Shillings
»
Capital
Colon qudtotlon :"
Parerflhesia ( )
Underline
Quotation beginning "
Quotation end "
<Iu(rt'n within quot'n
Cipher beginning
group o( figures
[ ]
i
chart for quotation within a quotation ; a parenthesis hegins with
Pn, and ends with Pq ; a fraction, as |, is transmitted 3e4 ; a deci-
mal, as 89.92, S9dot92 ; omitted words are indicated by a series of
x's; and in sending one or more lines of verse a paragraph mark
( ) closes each Uue.
38 THE ELECTRIC TELEGRAPH.
The system in general use among operators is the Phillips
Code, from its inventor, Mr. Walter P. Phillips, general manager
of the United Press ; and in its arrangement it advances of course
from the simple to the complex. Single letters are first made to
represent common words and phrases : B, be ; C, see ; F, of the ;
K, out of the ; Q, on the ; and so on through a list that need not
be reproduced here, because the entire code can be purchased in
book form and contains, besides tlie code itself, hints for the mem-
orizing and pro[)er use of it. Tlie single letter list is followed by
the two-letter and three-letter contractions; and the learner will
think it is a far cry from the jog trot of the ordinary text to such
expedients as " fap " for " filed a petition, " '' sak " for *'shot and
killed," and "sbl" for "struck by lightning." The typewriter
alone makes the use of such abbreviations possible. In order that
beginners may catch the spirit of the system, the following exer-
cise is written in the code text and then given in full :
" Bt Lufa Pic is smhw Lafa Pic stil. Its tmsfmatn into chp
lodgmts is gradl tho su. T sieg gos stedly on, btt bsiegd hvn yet
sucmbd. Ey y t hansm cariags tt rol up & dwn its aves gro fuer
and fuer si ey y its pavmts worn bi t fet o ded & gon Nikrbokrs
r m fqd bi shaby Gennns or slatrnly Italns."
"But Lafayette Phicc is somehow Lafayette Place still. Its
transformation into cheap lodgments is gradual though sure. The
siege goes steadily on, but the besieged have not yet succumbed.
Every year the handsome carriages that roll up and down its
avenues grow fewer and fewer; every year its pavements, worn by
the feet of dead and gone Knickerbockers, are more frequented by
shabby Germans or slatternly Italians."
Messages for Practice. To extend the student's practice, and
further to familiarize him witli tlie aj)])earance and wording of the
different forms of messa<j;es, the followinjr &jK*cimen3 have been
selected. They are arranired ])romiscuously, so as to afford exer-
cise in naming the dilFerent kinds; attention should also be given
to the different ways of counting in cable, government, collect
messages, etc.
AllGP Ilk AVn 18 Free.
Portland Me. 27
J. E. Bierhardt, Transfer Agent,
Home, N. Y.
268
THE ELECTRIC TELEGRAPH 39
Pay W. L. Dumont, Arion Club, Central Hotel, Rome N. Y.
Japan Alms, indent from Abner Gaylord, Portland. Caution.
(sig) Wm. Ellerby, T. A.
57 Av Uc 20 Collect
Tb Hartford Conn 4
Adam Mason & Co.,
Ottumvva, Iowa.
Manifoldly mensural parks nacrite distrust nacori cryintr
naively medium mensural nalul)u monitory treble namesake monk
rudeness Naaman tourmaline, Hawaii
(si^) IL. M. Allen & Co.
158N X Ks 17 Paid
Norfolk Va. 4
Chandler Elevatintr Co.
Great Bend Ind.
Skeptic W. H. McAlpin border route Norfolk western on
tantrum tread affordincr chucklinc/ offers chubby alfray more
(slg) L. W. Jay iSc Co.
14 Wd Fr 121)11.
Marine I)oi)'t, X. Y. 21»
M. B. Goldfogle,
International Ilotcl, N. Y. ("itv.
Steamer Campania will arrive^, unlt?ss detained at Quarantine,
about 8 A. M. tomorrow.
(sig) Manager, Marine l)e[)'t.
273 W 125th St. N. V.
I). F. S. Delivered ok your 23 today to S. S. Cooper
sined Atkinson. (sig) Phila
In this case " DFS " means destroy former service.
Danville N. J.
Yes have collected 25 cts for msg to Dickerson sined Hall
(sig) Garfield N. J.
191 Kf Gs 10 Paid 8 Extra
Str. Campania off Sagaponack L. I. Nov. 21)
via New York 29
Morris, 21 Flushing Ave.
Jamaica L. I.
All well. Dock early Sunday. Don't come down
(sig) II. N. lleldman
269
40 THE ELECTRIC TELEGRAPH
The above resembles one received by the " Wireless " and
transferred by them to land lines at New York.
133 Ro Py 22 Paid Gov't
Washington D. C. 29
Morning Register,
Dallas, Texas.
Showers Sunday warmer except on the coast; Monday fair in
northwest; showers in east and south portions.
(sig) Wells.
119 Fs Ki 11 Paid
Winnipeg Man 29
Lindsay & McDonald
Valley Stream, L. I.
Offer saltcat to saltpeter scalene throe garrulity en route or
gallate. (sig) Bobb & Parrish.
174 Wr Ta 6 Collect.
South Bend Ind 4
Champion Beef (^o.
Pine Island N. Y.
Enkindle gratefully erupt none trundle.
(sig) Baker Packing Co.
114 Gu Ps 8 Paid Night
Xtnv Orleans 29
Mrs. S. Dorner, llS West 111) St
New York.
Will be homo Monday afternoon . Tell Ella. Love.
(sig) Joe.
128 F Kn Cable
Havana 6
Hammond,
Calumet (Mich)
Candelabra domiseda 780 calefying.
In the above, the State in parenthesis is supplied by the land
line clerk, and is not counted; the group of figures is one word.
193 Yv Wr 12 Paid Repeat back
Philadelphia 31
R. B. Dicrnam
New Orleans.
Elmpole arundelian bags parable admit actuality rampal-
lian Ilalpen aliped bags. (sig) C. Emslie & Co.
2,10
THE ELECTRIC TELEGRAPH 41
In this case the words " repeat back " are counted and charged.
... ... ... 7 Paid Charge
Newark N. J. 29
Adams Ilich & Co. Memphis Tenn.
A. N. Harriman Louisville Ky.
F. J. Farjeon Mobile Ala.
Walter N. Davis St Louis Mo.
No reds; best Jerseys eight twenty five.
(sig) C. W. Allison.
In transmitting messages like the above each operator num-
bers and times the address of the one which goes on his particular
wire; then passes it on to another and so on until all, sometimes
scores in number, have been sent.
To Albany N. Y. Dec. 15
B83 487J
34 484" (sig) 10.18
To Salida Colo.
N. Y. Metal Ex. Pig lead 412i
London Silver 22| (sig) 9.10
To New Orleans and Mobile.
C. Adam
31 - m - 30 (Sig) 11.43
174 Eo Fc 44 Dll
Bridgeport Conn 29
Agent L. S. Rli. (;o.
Cleveland Ohio.
From Paterson to Cleveland Juno 1st in D L car 27052
one case brass tubes number 2590 consigned Schneider & Fen-
kamp covered by Lackawanna line waybill 2774 advise date
arrival and delivery quick. (sig) R. J. (^amp
By way of introduction to the next topic — Railway Teleg-
raphy — the above series of specimen messages concludes with one
more example of a railway DII.
37 Av Tv 36 DH
Springfield Mass 20
E. H. Palmer,
Buffalo, N. Y.
871
42 THE ELECTRIC TELEGRAPH
File W, Adams to East Buffalo Wb 111 Dec 8 Christmas
trees for D. H. Croley Dunkirk N. Y. deld N. Y. C Dec. 9 on
B & A 2718. Please advise delivery. liush.
(sig) H. C. McCarthy.
Railway Telegraphy. It is well known that the first tele-
graph line built in the United States was intended for commercial
work; but the new art had not loner to wait before it was enlisted
in the service of the railway. Along their right of way the latter
erected poles for the accommodation of their wires to which the
commercial companies soon made additions; and, except in the
larger towns and cities, one man usually did the work of both.
As railways extended and towns multiplied, the work of the latter
differentiated from that of the former so that today there are two
well defined divisions in the craft; interchange going on between
them, however, all the time.
In many places even yet by agreement between companies the
railway operator covers the service for the commercial; the latter
likewise transmits in great numbers over its wires the service mes-
sages of the railway, examples of which have just been given. As
compared with these, the student will find that the railway mes-
sage usually takes an ampler form, more nearly approaching that
of a letter. In railwav work all messacjes are '^ service," and
concern the movement of freight and passenger traffic, and the
dispatching of trains. All the stock phrases in use are shorteneil;
initials, figures, and abbreviations occur in nearly every line; the
*' count" which serves as a safeguard to the commercial operator
is dispensed with, so that there is all the more need for the
operator to be on his guard against omissions.
Again, mention was made in connection with commercial
messages of the use ot for//i.s for races, games, and the like; in
railway service this is a marked feature, their number in the case
of some leading railways exceeding one hundred.
Then, thirdly, in connection with the purely telegraphic part
of the service is the very important work of handling the train
orders; first as received from the dispatcher, and then repeated
back with the signatures of the reci])ients.
On a single track railway a crossing order, at one time, com-
monly ran thus: —
272
THE ELECTRIC TELEGRAPH 43
To Conductor and Driver Train No. 21
Train twenty-one will meet and pass Special Freight, Con-
ductor Holmes at 31
(sig) IL M. Wallace.
H. M. Wallace
32 Train twenty-one will meet, etc.
(sig) Conductor and Driver.
More recent usage however is indicated by the following
forms; in connection with which it may be premised that the aim
is simply to acquaint the student and prospective railwav operator
with the forms of the messages he will be called upon to handle;
but, in order to make them intelligible, some details of the train
despatcher's work must accompany them. This can be set down
as consisting, for the most part, of (1) orders fixing meeting
points for trains; (2) fixing the point for one train to pass and
run ahead of another; (3) giving a train the right over an oppos-
ing train; (4) giving regular trains the right over a specified
train; (5) providing for the use of a section of double track as
single track; (C) providing for a single movement against the
current of trafiic on double track. Then there are (7) time
orders; (8) orders for sections; (9) for extra trains; (10) for
work extras, or auxiliaries; (11) holding orders; (12) orders
annulling or cancelling a regular train; (13) annulling an order
or part of an order; and, (14) orders superseding an order, or
part of an order.
From the list of train movement forms thus indicated, some
of the more important, viz., the first, second, fifth, eighth, ninth
items are selected for illustration; the names chosen for the
stations are fictitious; but the forms are those in actual use on
some of the leading trunk lines.
Suppose a single track, of which Balmain and Allaire are
terminals; Eden and Canton are intermediate stations. Train 334
going south is late; it is desired to advance on its time train 331
going north, Eden being the regular meeting place. The des-
patcher calls up Balmain, Allaire, and Eden and sends the follow-
ing; C and E being the stereotyped abbreviation for Conductor
and Engineer:
31 No. .. Operator, Eden.
31 No .... C & E No. 334, Allaire.
31 No. C &E No. 331, Balmain.
273
U THE ELECTRIC TELEGRAPH
No. 381 has right of track from Eden to Canton
sig W. L. D. Sup't.
Each operator copying this message mnst repeat it back to the
despatcher, and each one must listen to its repetition by the others.
Another form of crossing order for two trains, one at Eden
the other at Balmain, would run thus:
31 No . . ! . . C & E No. 332 Eden.
31 No C & E No. 329 Balmain.
No. 332 and 329 will meet at Carrolton.
In this and the examples to follow a signature is taken for
granted.
For the next movement, viz., the passing of one train by
another, the procedure is less formal. It is desired that train 001
should allow No. 1 to pass. In this instance the co-operation of
the signal towers, having control of the switches and side-tracks,
is enlisted. The despatcher calls up the tower, say at Breslin, and
tells the operator that train GOl is next to him, and that he is to
side-track it for No. 1. The next tower beyond, say Ashley, is
then notified that 001 is in the siding at Breslin for No. 1, so that
he may know which train to look for first. Or, the passing may
be arranged for in a formal manner:
31 No ( ' vfc E Extra :)\n, Breslin.
31 No. . . . C it E No. 0, Breslin.
Extra 51)4 will run ahead of No. Breslin to Dexter.
In this ease the speed of No. (> must not exceed that of Extra
59-t between the points named.
The fifth item presu]>poses the blockade of one of the two
tracks by a wreck — an incident by no means exceptional; the
situation beintr indicated in the cut: —
TRAIN N0.6 ^^^^ X WRECK ^^^ — *- EAST
CARLSBAD ^^ ^-^.^ ."" ^^''DANBURY
.^_ ^
WEST
Tlie station next east of Danbury is Berber. The procedure
is then: —
31 No C it E all west bound trains, Berber.
)U No C it E all west bound trains, Danbury.
31 No C & E Train No. 8, Carlsbad.
274
THE ELECTRIC TELEGRAPH 45
No. 8 Engine 914 will use west lK)und track from Carls-
bad to Danbun'i and has riirht of track over all west
bound trains.
This message is rej)eated back by all three stations; and
under its provisions no west bound trains can pass Danbury until
No. 8, Engine 914, has passed east.
Durincr the summer season it is a common incident of the
despatchers work to be called u{>on to divide into sections trains
that, by the addition of extra coaches, have l>ecome too heavy for
one engine. The two, and sometimes three, sections must be so
protected one by the other that, so far as their right of wav is con-
cerned, they are substantially one train. Let us suppose train
No. 8 at Corbin, going east, has too many coaches for one engine
31 No C ct E Xo. s, Corbin.
No. 8 will carry signals from Corbin to JersL»y City for
Engine iu2.
Engine 672 then takes the second section, and proceeds to its
destination under protection of the signal. If a third section is
necessary a message similar to the foregoing would be addressed:
31 No C it E second section No. 8 entrine 072.
A third engine namvxl in this message then proceeds under
the protection of the foregoing with a third section of the traii\.
The above is the method of procedure in case the need for the
third section did not appear until after the first section had left
Corbin. Otherwise the division into three sections would take
this form:
31 No C ife E Engines 671, (572, 891, Corbin.
Engines 671, 672, 891 will run as first, second, and
third section of No. 8 from Corbin to Jersey City.
This form implies the carrying of signals, one for the other,
as prescribed by rule; and trains carrying such signals are
regarded by other parts of the running service as practically one
train.
For the starting of extra trains the signal ** 19 " is used
instead of " 31 " and the order runs thus:
19 No C & E Engine 587, Jersey City.
Engine 587 will run extra from Jersey City to Bt^rl^er
276
46 THE ELECTRIC TELEGRAPH
If a regular train is late, and it is desired to giv^e this extra
a right to the time of the regular, it is done by inserting in the
above message " No. 3 will run 30 minutes late from Jersey City
to Berber." All these orders are copied on manifold paper; one
copy is furnished to the conductor, another to the driver, while a
third is filed by the operator for his guidance and future refer-
ence. These examples could be multiplied indefinitely, but it is
believed these citations are sufficient to indicate to the learner the
kind of service expected of the railway operator in co-operation
with the work of the train despatcher.
276
THE ELECTRIC TELEGRAPH.
PART II.
The principal topics considered in Part I, were the ''learner's
outfit"; the "one-wire" office with its relay, key, sounder, and
local circuit: and the switchboard for the cuttincr in and out of
instruments, and the cross-connection of wires. There are scores
of such offices, called branches, in the larger cities; and every
town throuc{hout the land has at least one.
An advance is now made to the more complex equipment of
a junction station, or town office, to which a score or more of wires
converge, and from which they radiate in all directions.
Instead of a '' one- wire " set, there may now be noticed on
the desks or tables, six, eight, or ten relays and keys; the sounders,
possibly less in number than the relays, are operated by a current
furnished by storage cells to which energy is sup{)liec^ by an electric
light circuit. The clock on the wall is probably of the " electric "
pattern with two Leclanche cells inside. On a shelf are probably
two or three sets of apparatus called repeaters; on another table
are the duplexes or, it may be a quadruplex, whose princij)les and
manner of operation need careful consideration; and in place of
the diminutive single-wire switch of the city branch, or country
office, is its more ambitious counterpart with fittings for some
thirty, forty, or fifty wires. The handling and care of such a plant
calls for skill and experience to which many a commercial operator,
doing the work merely of a sender and receiver, is a stranger.
A consideration of the apparatus and methods of work in this
larger office is the purpose of this paper; and the apparatus first to
Ixj studied is the switchboard. The one shown in Part I is a
" single- wire intermediate"; but to accommodate the thirty or more
wires now in view a greatly enlarged form is needed. The de-
scription of the small switchboard should be re-read, noting that in
an intermediate switch two vertical strips are needed for a wire; that
is, one strip for each direction of the wire, say north and south; in
the switch of a terminal office a wire occupies only one strip.
ITTT
48 THE ELECTRIC TELEGRAPH
Of the former class a common pattern is shown in Fig. 9; the
diagram representing three pairs of strips out of a 50-8trip switch
for the accommodation of 23 wires; the gap in the middle repre-
sents 19 omitted pairs; the pair on the extreme right has a special
use which will be explained later. In all respects the numbers on
the small switch shown in Fig. 8, Part I, have been duplicated,
except that the top row of discs is reserved for the ground wire;
and for a review we shall go over, on this larger board, all the
steps taken in connection with the smaller one.
In Fig. 9 the strips are numbered, for convenience, at the
lower end from left to right; the disc rows are indicated by the
figures down the center. In some patterns of boards the 8tri|)s are
so shaped at the bottom that to join them up in pairs a peg can be
inserted. The switch is supposed to be at a station intermediate
between Cincinnati and Chicago; strips 3 and 4 accommodate
wire 1 South and 1 North respectively; strips 5 and 6, wire 2
South and 2 North; and so on. Disc rows 4 and 5 are connected
on the left with one set of instruments; rows 6 and 7 with another
set. In the drawing they are shown close to the board, but in
practice the instruments are usually at some distance from the
board on a desk to which the connections are made by means of
office wire. Supj)ose, first, that the instruments are to be "cut
out". Connect with a pe<^, strip 3 and disc 3; and strip 4 with
the same disc 3; wire 1 lias now no connection with either instru-
ment, the current sinij)ly crosses on the disc from strip to strip.
Move the peg in strip 3 to strip 3 disc 4; there is now no connec-
tion between disc rows 3 and 4, and the circuit in wire No. 1 is
broken. Move the peg in disc 3 strip 4 to disc 5 strip 4; the cur-
rent in wire 1 will pass through the relay and key connected up
to disc rows 4 and 5; and the instruments are now said to be "cut
in". In this larger board the ground wire occupies the top disc
row, instead of the bottom, so that the discs marked 6 can be used
the same as any other numbered row.
Reverting now to the changes indicated in Part I, page 25;
for the sake of practice, move the peg from strip, or bar, 3 disc 4
to bar 3 disc (i ; and the peg from bar 4 disc 5 to bar 4 disc G; the
wire from each direction is grounded. There are now two inde-
pendent circuits each with a battery at one terminal only; Cincin-
278
THE ELECTRIC TELEGRAPH
49
nati and Chicago are cut off one from tlif otlitr; the way-station
iiistranients also are cut out. In order to -t-iit in" on the south
section of wire Jso, 1, remove the pei; from Iwr 3 disc tt and
insert it in bar 3 disc 5; put a peg in bar 1 disc 4, and another in
J^L ft.
;o;
p
p
p
p
p
p
p
c
p
P
p
p
p
p
p
P
p
P
po;
00
00
00
00
00
00
00
00
po
00
po
po
00
po
po
po
po
00
00
00
poi
8 3 4 5 6 45 16 47 18 D
Pig. 9.
bar 1 disc G. The current from Cincinnati must now pasa through
the relay and key at the Bide of the swituhbuard before reaching
the ground at bar 1 disc G. The peg having been restored to bar
3 disc G, the same set of instruments, or a different set connecting
with disc rows 6 and 7, can, in a similar manner, bo cnt in on the
north section. Bestore the pegs to bars 3 and 4 disc 3, and the
50 THE ELECTKIC TELEGRAPH
terminals Cincinnati and Chicago can now work with each other,
but neither of the instruments at the side of the switchboard is in
the circuit.
The letters D F on the extreme right hand of Fig. 9 stand for
the words " double flip " — a device more commonly used in a termi-
nal than in an intermediate oflice; but it may as well be explained
here. In a board like that in Fig. 9, whether terminal or inter-
mediate, each strip has underneath it a "flip", or spring- jack for
the insertion of a wedge; usually the pairs of strips on the extreme
left and right are set apart and joined in pairs by a wire behind
the board. Strips 49 and 50 are practically one bar wnth two flips
at the lower end — hence the name. A board like that in Fig. 9 is
often part of a larger system ; it may have a similar section on the
right and left. The "double flip" enables the switch operator to
desk and furnish battery to a wire coming in on another section,
by running along on one of the disc rows. The twin discs shown
in Fig. 9 have reference also to the presence of a companion section
on the right-hand side; in such a case the discs on the extreme
right of Fig. 9, row for row, would be connected with it; and, by
inserting a peg between the twin discs, rows of like number in the
separate sections may be joined, making them continuous across
as many sections as desired.
Besides the cutting in and out of his own instruments, it is
one of the duties of the intermediate station operator correctly to
cross -connect wires at the request of the wire chiefs. lie may be
asked, for instance, to connect 1 North to 2 South, and 2 North to
1 South. Ilemove the pegs from bar 3 disc 3, and bar 4 disc 3.
Peg bar 4 disc 2; bar 5 disc 2. Peg bar disc 3; bar 3 disc 3.
The current on 1 North crosses disc 2 to 2 South; the current on
1 South crosses disc 3 to 2 North. While this cross-connection
stands, care must be taken to connect no other wires on either of
the disc rows 2 or 3. The test station may have instruments, as
shown in Fig. 9, connected up to disc rows G and 7. If it is de-
sired to put this instrument in circuit on the wire 2 North to 1
South, remove the pegs from bar disc 3, and from bar 3 disc 3.
Peg bar disc 0, and bar 3 disc 7. To facilitate the correct trac-
ing of the difl'erent disc rows, it is common to alternate four rows
of specially marked discs with four plain ones. To make any
280
THE ELECTBIC TELEGRAPH 51
cross-connections and combinations of wires that may be needed,
the operator needs only to get clearly before him the relation of
bars and discs one to the other, remembering that the several rows
of discs have no connection with each other or with the bars except
by means of pegs.
Recent Form of Switchboard. Tlie pattern shown in Fig. 9,
although in very general use, has some defects for which a remedy
is sought by a change of form. The connections for 'Mn" and ''out'*
on the top side only of the board require two strips to a wire — an
arrangement which is wasteful of space. There has recently
l>een installed in a suburban test office near New York an entirely
new form of switchboard for intermediate stations in which the
wires pass in at one side and out at the other. A 50- wire board
of this pattern is seven feet in height, and thirty-three inches in
width. The lower part resembles somewhat a long-distance tele-
phone cabinet; the shelf is thirty inches from the floor, and the
Q(aQzziz]>g> II » oCmO^O QQQ QijiOntJJ ^\\^<l O^l
Fig. 10.
space underneath is taken up with the slack of the cords. On top
of the cabinet are strips, like that shown in Fig. 10, placed one
above the other to the number of say fifty, supjx)rted at the corners
by four vertical bars of angle iron resting on the floor. The strips
are of wood, one inch wide, each consisting of three parts. On
each of the end parts are a fuse and carbon ])late lightning
arrester; in the middle part are four holes. A, B, C, D, for type
jacks, and three discs. Between the holes for the type jacks is a
tag for marking; the wires in the drawing are 1 West and 1 East.
Extending up both sides of the switch are the wires contained in
cables, parting with their conductors one by one and making con-
nections with the fuses at each end of the strip.
The middle portion of each strip is ten inches long; and a
side elevation is shown in Fig. 11. The four type jacks are con-
nected in series as represented; between the two inner ones are
three discs — the middle one grounded; a peg inserted on one side
or the other of the center disc will ground the wire in the direction
281
52
THE ELECTllIC TELEGRAPH
desired. The ioner pair of jacks is for patcbing. In bnilding up
the switchboard the strip next above the one shown would be 2
West and 2 East. Each cord is fitted with an automatic slack
take-up, as shown, and cross-connections are made by lueans of
single cords and connection pings F and H. To cross-connect 1
East to 2 West it is only required to place one of the plugs F in
the patching jack marked 1 East, and the other plug H in the
jack 2 West. In tlie diagram 1 West appears grounded by lueane
of peg E. The outside pair of jacks is used for inserting loops;
also to cnt in test and desk instruments. The disadvantage iu this
form of switcliboard is that the continuity of the wire depends on
the perfect contact of the fonr springs with the pius behind them.
Figs, 10, 11. 12 and 13 are from a "Pocket Edition of Dia-
grams" by Willis II. Jones. They are reproduced through the
courtesy of the publisher of Thv T-U'ifrajih Aije.
An inspection of the diiigrams in Part I yields a fair infer-
ence that each relay must have its own sounder; but tbe opening
THE ELECTRIC TELEGRAPH
53
lines of this paper in which it is said that tho sounders, [)Ossi])Iy
less in number than the relays, are operattKl by a storacre current,
hint at a departure from this rule. In former days the telegraplier
sometimes made his first efforts at invention in a j)lan to economize,
by making one sounder do duty, at different times, for three or
more relays. But the field of devices for locals is well covered
Fig. 12.
now; one of the results is shown in Ficr. 12 whicli represt^nts an
arrangement of circuits in which one sounder can, by niejins of a
switch, 1x3 worked in connection with tliree relays. Tlie diagram
needs no description, but the connections should bt» traced in each
case; the lever resting on the right, middle, or left |K)intfl cuts in
the cor res j)on ding relays, in each cane forming an in(ie|K*n(lent local
circuit. At ju.nction stations, where j)assing trains are likely to
make considerable noise, one sounder may be insuilicient; in this
■pmr;
-^
^^f-
case an extra one with a l(K*al circuit of its own is sonietinirs |)ro-
vided. In Fig. 13 is shown how such an additional eoininon
sounder may be used in connection with three (lifbM'ent circuits,
each sounder having a battery of its own.
For local systems of this kind tlie form of battery most com-
monly used is that shown in " Elements of Klectricity ", called the
Daniell, or "blue-stone", cell. l>(?tter still is the mo<lilication of
it shown in the same j)a|)er known as tlu^ ** gravity " cell in which
288
» THE EXfTTRIC TELEGRAPH
iihe iia>s cam be m JcsirtL 'Hb^ iau die odu^. that no ponioo of
ibAc airol needs co ha khrov^ kw^t or w«}CmL Bat noC even the
loal tjttnrTT fvsiem. h^ «9e&f«<i die spirit of cimage: uid in huuit
nntaxlj-^tn^^^Kd o£>x9 die zfiue and copper tjpe Eias beeo replswd
bv the acocaet a^L m oZctL The luune implies the giviag oat of
ft enrrwit in-rv-ti fr-xn »ain±er sooice — ^atnUy a dTiuzno — bni
the E'fea r^niiir^ n.ci': =:.jtili«si:f>ia. u will >ppev later oo.
Fig. U.
In Fifi- 14 is shown a etor^e wll ejstfin fed hy h dMiamo
whidi is al^o the source of t'iier<rr for an electric- light plant.
TIitTn an; two Btorafp; cells, one of which, B Fig. 14. ia in the same
circuit with, ami receives the current in the same manner as, the
IiiniiiH. The other cell, B', ia disconnected for the time being from
tin; (lyiiumo, and is represented as supplying the current for a
nunilfer of sounders arranged in multiple on the lower right. It
THE ELECTHrC TELEGRAPH
will be apparent on examination that the mt-thud of connecting up
the lamps io one circuit and the sounders in the other. is the same.
In the opening paragraphs of " The Electric Current " the stu-
dent has learned something of the laws of resistance. His attention
is called at this point to the difference bi-tween the series and multi-
ple arrangement of sounders. In the former, the resistance in ohms
offered by the coils is the resistance of one sounder >iruft/jt/i«'l
by the number of sounders;
in the multiple system it is
the resistance of one sounder
divided by the nuinlMT. A
pair of knife switches, S and
S', shown in Fig. 14, is the
means by which storage cell
B,' when it is exliansted, can
be cot in on tbesaniecin^'uit
with the lamps; its place in
operating the souiultrs is
then taken by the freshly
charged cell If. In Fig. 15
the construction and action
of the double knife switcli is
clearly shown, A\Tien turned
from the position they bold
io the diagram they make a
new series of connections
with the ri'sult alR-ady in- FIe- l-'i,
dicated.
The Dynamo in Telegraphy. Within littk- itiont tlian h qniir-
ter of a century this appliance, regarded at tiret somewhat as a
curiosity, has advanced to the place of an indiflj>enaal>le and well-
nigh omnipresent help in the mechanical and technical world. In
countless shops and factories its familiar hum and vari-culored
sparking can be detected in out-of-the-way corners; while in power
houses its more developed and, in some caws, giant form fully
justifies the remark of the scientist Faraday when he saw the first
dynamo in operation: "That was my child; but you have made a
man of him," In the field of telegraphy its principal uses are to
56 THE ELECTRIC TELEGRAPH
chai^ storage cells, and supply current for the iubid lines. In
the former operation, the cell is said to be fed by the dynanio;
and, as already illustrated, it is commonly carried on in com-
bination with the supply for an electric-lighting system. The
"feeding" consists of a chemical change in the cell, whose ele-
ments, when the charging ceases, give up in the form of electricity
the energy thus imparted,
Aa the dynamo is the source of enei^ for the storage cell,
and for the operation of the different forme of main line apparatus,
the need arises for a brief statement of the principles underlying
its construction. In bo doing, some words and phrases not hitherto
used come into view; and a definition of them, in connection with
familiar forms, is first in order.
The C'lrijn in the electromagnet of the sounder, as the etu-
deut knows, attract the armature. The free ends of the cores
are the poles; and if a penknife is placed near, it is drawn
towards the core with a force that increases as the distance
lessens. Similarly, if a small piece of metal is held near the
poles of a toy magnet in tlio horst^shoe form, the attraction is
marked. The space between the poles alike of the electro-
THE ELECTRIC TELEGRAPH
57
magnet and the toy magnet seems full of invisible stresses whose
mechanical effect is like that of thousands of stretched rub-
ber threads which tend constantly to contract. These stresses are
called lines of force; and the space in which their influence is felt
is called the field of force. These lines are inseparable from every
form of magnet, permanent or electro; in the case of the earth,
which is itself a great magnet, their effects are seen in the action
of the magnetic needle placing itself parallel to the lini^s of force
betwt^en the north and south poles; in the case of an ordinary mag-
net, the lines seem to appropriate
to themselves any material which
will shorten their journey through
the air space; and, if the piece of
metal is free to move, the linf^s
tend to place it in the position
which will shorten their pathway
the most. Another, and the most
common, name for the space oc-
cupied by the lines of force is the
7na^netic field. It is graphically
shown in Fig. 16 in which is
represented also the simplest form
of dynamo. The arrows represent the lines of force between the
magnetic poles ; and, revolving therein, is shown a single conductor
cutting the lines of force at right angles. Now conies the prin-
ciple which underlies the generation of the electric current by means
of the dynamo: If a closed conductor is rajn'dly revolved in a mag-
netic field an electric current is set up in the conductor. The
collector rings and brushes conduct to the outside circuit the cur-
rent thus generated.
In Fig. 17 there is shown in outline form a simple dynamo;
the yoke Y connects the field pieces FF, uj)on which are wound
the field coils; the latter is charged ])y an external current in the
direction of the arrows. In an intense magnetic field, between the
pole pieces N and S, is the armature. It is made up of the core
and a complete circle of conductors like the one shown in Fig. 10;
a large number of conductors being ni»eded to generate a contin-
uous current. The conductors are made to tenninate in a series
Fig. 17.
287
58 THE ELECTRIC TELEGRAPH
of etripu separated hy iusulattng material, and bound together in
a cylinder to form the commutator marked C; the collecting brushes
BB eorrtapond to the copper and zinc poles of a voltaic cell.
A gas or steam engine is usually the motive power for a dyQanio;
a common ty])e is shown in Fig. 18 with the belt pulley at the
left; in this form it illustrates the definition of a dynamo given in
the text Ixxjks as "a machine for converting mechanical enei^-
applii-d at the pulley into electrical energy given off at the
brushes."
One use of the machine, namely, to furnish current for a sys-
tem of local instruments, is illustrated in Fig. 11, but its more
important function in telegraphy is the supply of the current for
the main lines. The different circuits to lie supplied may vary in
length from 50 to SOO miles; and, as nearly the same quantity of
currunt^say j'^ of au ampere — is required in each case, the volt-
age, or pressure, must vary accordingly.
A series of dynamos connected together u[)ou the same prin-
ciple as a series of cells in a battery is outlined in Fig. 19, showing
how this may he dune. One terminal of machine A is grounded,
and from the connecting points of the brushes the wirea 1, 2, 3, 4,
THE ELECTRIC TELEGRAPH
and 5 are led to the horizontal rows of discs on the tfmiiiial switch-
board. Ill practice they are commonly made a part of the larger
board similar to that shown in Fig, 0; but, for the sake of clear-
ness, it is represented here as distinct. Each vertical bar repre-
sents a main line wire; the horizontal lines are rows of discs to
which are connected the wires carrj-iiig the curront for distribu-
tion. In Fig. lU wire 1, connected to one of the disc rows, fur-
nishes 70 volts (the voltage of a Grove cell is about 1.5); wire 2,
140 volts; 3, 200 volts; 4, 2fiO volts; 5, 325 volts. It is neces-
sary only to connect, with a peg, a disc and bar to supply any wire
with any desired voltage. A plant of the capacity indicated in
the diagram can be made to fnrniKli ciirR-nt for 1,000 lines, yet its
compactness is such that it may be installed in a small room.
\>^.\ aROUNO
The advantages of tJie dyDunio over (lin voltaic cell are:
(1) Its low internal reslstant-e making puHMlliie Die HU|>|ily uf ik>
many wires.
(2) Economy in maluteuance.
(3) The Bpa<;e occupied is much leHS.
(4) It does away with the unhealthy conditions ufa fume-laden
battery room.
The Open Circuit System. Jieforo dealing with the topic of
Single-Line Repeaters, let ns discuss a system much used in Eng-
land, known as the "open circuit", as distinguished from the one
in general nse in the United States, Canada, and Mexico, descril>ed
in connection with Fig. 0, Part I. Tliis is known as the "closed
circuit", in which the circuit is first broken by opening the key
switch as de3cril>ed, and the signals are transmitted in the manner
DOW familiar to the student. The open circuit system is illnRtrated
60
THE ELECTRIC TELEGRAPH
in Fig. 20; in it may be noted the difference in the connections of
the key as compared with those of the American system. In the
latter, as may be seen by reference to Fig. 6, Part I, the battery,
key, and relay coils are in series; in the former, the ground con-
nection divides, one branch passing through the relay coils to a
point in the base of the key against which the lever carrying the
main line normally rests. The other branch connects the battery
to a different point of the base. It may be seen from the diagram
that when both keys are making contact wuth the backstop there is
no current on the line, and the relays are open. Depress one of
1
T_
nil-, I.
Fig. 20.
the keys and tlie current, passing directly to the line, closes the
relay at the distant station.
In this arrantrenient there are two advantages over the Ameri-
can, or closed circuit, system:
(1) The battery is in use only when signals are transmitted.
(i!) l^y tlie cutting out of the relay at the sending station the resist-
ance of the circuit is reduced.
The disadvantao-es are:
(1) Tlie operator liears his own sending on the key only.
(1!) The system does not admit the cutting in of intermediate
stations.
The closed circnit arrangement allows as many as twenty-five
or thirty ollices between terminals; and the batteries, placed one
at each end of the line, are more likely to receive skilled attention.
290
THE ELECTRIC TELEGRAPH 61
SINGLE-LINE REPEATERS.
In the junction station, or town office, wo now have in mind
a set, or sets, of repeaters — an important feature in the equip-
ment, and the one next to be considered. The limit of the Morse
single line, in good weather, is ordinarily about 450 mik^s; it is
one-half or one-third of that in rainy spells when extra repeaters
are cut in. The repeater is a means by which the relay at a dis-
tant terminal of one circuit is made to operate a key in a second
circuit. The distant relay of the second circuit may operate a key
in a third; and so on. The circuit of say 1,500 miles has thus the
advantage of batteries at needed intervals; the distance between
repeaters being determined by the conditions already indicated;
and it has not been found expedient to exceed very much the dis-
tance first given.
There are many different forms of repeaters; and from among
the score or more that have been in use at different times selection
is made of the three commonly regarded as the best — the Milliken,
Atkinson, and Weiny-Phillips. The same result is attained in
each, but by somewhat different means; all three are of the auto-
matic class — so called because they permit the terminals to break
without the aid of an attendant.
Fig. 21 shows the Milliken repeater in theory. It consists of two
relays of special construction, two transmitters, two main batteries,
M B, a pair of local batteries, L and L', and a pair of extra locals.
Tracing the connections of the local batteries, they are found to be
wired through the local points of relays E and W, one for each;
and through the coils of transmitters T and T'. The extra locals
are wired through the back contacts of transmitters T and T'; and
in the same circuit are the coils E' and W. In the construction
of the relay the peculiarity is that, in combination with the electro-
magnet and upright armature of the ordinary relay, there is an extra
magnet with a pendent, or hanging armature marked P in one and
P' in the other, Each one is so placed that, w^hen released from its
magnet, the tension of a spring forces it against the upright arma-
ture and holds the local points closed '" '^ the student in
tracing out the different connections <*ircuits are
marked by dot and dash lines; the la lines;
the main lines are in full lines. ^ est
THE ELECTRIC TELEGRAPH
THE ELECTRIC TELEGRAPH 63
are supposed to extend in each direction to terminals, it may be,
400 miles distant. When the circuits are at rest, the armatures
of the instruments are attracted by their respective cores, and are
said to be closed.
Kecall now the definition of a repeater, and notice in the
description to follow how the transmitter in the East set acts as a
key in the West wire, and v!ce verm. Suppose the distant East
station opens and writes; the operator opens the local points of
relay E, and this opens transmitter T; through its tongue and
post passes the West wire, and it, therefore, is opened. Tlie open-
ing of the West wire should open relay W and transmitter T'; and
the opening of transmitter T' would open the East wire which
passes through its tongue and post. But the opening of the East
wire when the distant East is sending is just what the re])eater is
intended to prevent. When transmitter T opens, the extra mag-
net W', held closed by battery h through the back points of the
transmitter, also opens; the pendent armature P is released, falls
back, and holds closed, by the tension of its spring, the upright
armature of electromagnet W. This prevents the opening of
transmitter T'; and the East wire is not allowed to open in the
latter instrument. Transmitter T' can be opened only l)y o])ening
a key in the West wnre, either at the repeater (key not shown in
diagram) or, normally, at the distant West station.
When the distant West writes, the action begins with the
West relay W the same course as that just descril)ed; in this case
the pendent armature P' holds closed the transmittter T, and the
West wire passing through its tongue and post.
The Atkinson Repeater. Probably the best of all the re-
peaters in general use is the Atkinson, the theory of which is shown
in Fig. 22. The apparatus consists of two relays of the common
type, two transmitters, two main batteries, a pair of local, and an-
other pair of extra local, batteries. The local batteries belong to
circuits which, it will be noticed, are marked one with dots, the
other with dots and dashes, the same as in the Milliken repeater.
On the East set the battery is marked MB, relay E, extra sounder
E' (operated by battery J'), and transmitter T; the West set is
lettered to correspond. The wires marked East and West extend,
of course, in each direction to distant terminals. & dis-
64
THE ELECTRIC TELEGRAPH
"5
• mm
2IM
THE ELECTRIC TELEGRAPH 65
taut East opens his key; he thereby opens in rapid succession relay
E and transmitter T, which, in turn opens the West wire and relay
W. The opening of the local points of the latter instrument would
ordinarily open transmitter T, and therefore the East wire which
passes through the tongue and post of transmitter T'. But here
again the opening of the East wire, when the East side is sending,
is prevented by a device characteristic of this repeater. When
transmitter T opens, the current passing through Wis broken;
the armature of W' is released and, falling against the backstop, it
bridges the points of relay W, so that transmitter T' is held closed
and, with it, the East wire. As in the Milliken, transmitter T' can
only be opened by opening the key on the West wire either at the
repeater or, normally, at the distant West station.
When the latter opens his key the action begins, as already de-
scribed, with the West relay W and follows precisely the same order,
in the latter case the magnet E' holds closed transmitter T. Notice
that, in describing the action of this repeater, the language used is
very similar to that employed in connection with the Milliken.
These two forms of repeater afford illustration sufficient for a
good understanding of the principle; one more kind is added be-
cause, up to a recent date it was in general use by one of the large
telegraph companies; and, more esj^ecially, l>ecau8e its construc-
tion involves the principle of differentiation in magnet coils which
plays so important a part in duplex telegraphy. A description
therefore forms a convenient stepping stone to the subject of mul-
tiplex work, which opens up a new and interesting field.
A theoretical diagram of the Weiny-Phillips repeater is
shown in Fig. 23. As in the Milliken, there are three distinct
sets of circuits in duplicate; that is, one set represents the East
the other the West side of the apparatus; and in all three diagrams.
Figs. 21, 22, and 23, the parts performing like functions are sim-
ilarly outlined and lettered. The connections of the main line
(full line), and of the local (dotted) circuits are identical with those
of the Milliken. But, instead of the extra magnets E' and W' and
the pendent armatures P and P' of the repeater last named, there
is a device which effects the same end; and, for the reason already
indicated, it requires some attention because of the new principle
involved.
295
66
THE ELECTRIC TELEGRAPH
V.:ir~3- :^-^
'g
Si
is-yy
2Q6
THE ELECTRIC TELEGRAPH 67
In E' and W we have an iron shell enclosing a* straight iron
core and its winding. The combination of shell and core j)erforms
the same functions as the parallel cores in the common tyj)e of
relay. Trace the wire from battery b to the core W; at a point
jnst above the core the circuit splits; one part winds round the
core to the left, and goes to the middle point of the lever of the
transmitter; thence back to the zinc pole of battery h. The other
part goes to the right, and back to transmitter T at the under-stop
of the lever. Each division of the matrnet coil contains the same
numl)er of turns of wire round core W. When transmitter T is
closed, since the lever makes contact with the under-stop, the cur-
rent from battery h traverses the coils of core W in op|X)site direc-
tions; the result being that no magnetic pull is produced in the
core. But note the effect when transmitter T is 0{R*n. One of the
circuits that passes round the core is open; the neutralization of
the current in the other division of the circuit is impossible; the
core at once becomes an electromagnet capa])le of holding the
armature at the needed moment. A winding of this kind allows
the core to be energized by the difference in the strength of the
currents in the two divisions; such a core is said to l)e differentially
wound. If currents equal in quantity pass round the coils of core
W in opposite directions, their magnetic eifects are nil; if the
currents are unequal, or if one current is nothing and the other any
given quantity, the core is energized and will attract its armature.
Notice now the o]x»ration of this repeater, in effect identical
with that of the others. The distant East station opens his key;
this opens relay E, then transmitter T, the opening of which opens
the West wire passing through the points of transmitter T. The
opening of the West wire would open relay W, transmitter T', and
therefore the East wire which passes through its points. The last
opening is the one the repeater is planned to avert. When trans-
mitter T opens, one circuit round the core of W' is opened; the
core is energized and holds the armature of relay W closed, so that
transmitter T*, through whose points passes the East wire, does
not open.
When the distant West breaks and sends, the same action be-
gins with the West relay and follows the same course. '^" 'dis-
tant East and West can then work with one another 1
297
68
THE ELECTRIC TELEGRAPH
repeater, and have the benefit of the main line batteries at the
repeating station. This is the sole purpose of a repeater; in every
other respect it is a disadvantage, introducing in a circuit two sets
of apparatus which need careful adjustment and considerable at-
tention.
MULTIPLEX TELEGRAPHY.
The Stearns Duplex. In the description of the Weiny-
Phillips repeater, the differential winding of a single core was
illustratc»d; and the fact explained that such a magnet is operated
by the difference in the strengths of the currents passing through
the coils. If the two cores of a single-line instrument are wound
in the manner described, we have a form of relay known as the
d
-= \f^^ ,,
D/f
LfN€
M/1IN LINE
\tp H
O-^ G^ ^G G^ ^G
Fig. 24.
Stearns differential; with this and a few accessories a line can be
made to carry signals in opposite directions at the same time. In
other words, the wire can be duplexed; and the theory of it can be
explained and understood from the diagram, Fig. 24, in which the
apparatus and connections for both terminals are shown. I) R
and I)' R' are the differential relays; the gap between them is sup-
]K)sed to be bridged by the main-line wire, which may be 450 or
500 miles long.
In addition to the relays and batteries, the essentials for each
terminal are a transmitter, rheostat, some resistance coils, and a
condenser. Each of these may l)e seen in its place in the diagram;
the rheostat marked in full, the others with the first letter of the
288
MS MEW TORC
rWUCUBRAAl
IX
^•WHDATIOKS
THE ELECTRIC TELEGRAPH 69
name; the local circuits for the relays are not shown. One j)ole
of each battery is grounded; the other makes contact with th<^ j)08t
P of the transmitter; and, as the sets are duplicates, one only needs
to be described.
The lever of transmitter T makes contact with the ground
through a coil c r, which compensates for the internal resistance
of the battery, making the resistance of the circuit the same whether
the transmitter is closed or o|)en. The lever carries, on an insu-
lating pedestal, a spring or tongue ^, to which is attached the line
wire; it makes contact with the post P (battery) wlien the trans-
mitter is closed, and with the lever (ground) when the transmitter
is open. This instrument is seen to be a device for transferring
tlie line wire from the battery to the ground contact without inter-
rupting the circuit; and it is o{)erated, as shown, by means of a
key in a local circuit. The line wire can Ije traced from the
tongue t to the point of division — technically known as **the split";
the little semicircle in the diagram indicates in every case no con-
nection with the wire underneath; each division of the circuit
passes through two spools of the relay; one branches off to the
main line, the other through the rheostat to the ground. By
way of introduction to the apparatus last named, take tlie case
of a motorman of a trolley car in motion. His left hand con-
trols a radial arm surmountincr a box which extends down to
the platform, and contains a numl>er of leiigtlis of coiled wire
through which the current passes on its way from the trolley wire to
the motor. Every move of the radial arm in one direction or the
other means more or Ic^ss of current, and therefore more or less of
speed in the motor. The coils resist the j)assage of the current, and
the box is therefore a current retarder, or rlieostat, whidi is the
same thing. In a similar manner, either l)y a radial arm or, more
commonly in a duplex, by means of jx»gs making contact between
discs in which the resistance coils terniinatt*, thi^ current may be
recrulated in. the circuit of which the set of coils marked '* rheostat"
is a part; that portion of the circuit from tlie point of division to
the ground being called the artificial line.
Tlie purpose of the rheostat is to divide the current })as8ing
through the relay coils equally l)etween thi^ main and artificial
lines; and, as already intimated in connection with the repeater,
299
70 THE ELECTRIC TELEGRAPH
this can be done by making tbo resistance in tbe rheostat eqiia
tliat of the 400 or 500 miles of wire in the main line — aiiywl
from 5,000 to 10,000 ohms. When this condition ia estnblis
it doi's not matter, within working limits, what the eizo of Imtl
is; the current will j>as8 throvigh the relay with no appreeii
magnetic uffwt n^Kin it; and the dnplex is said to be "Imlanced
How to Balance. Sup|)OBe the terminals to be providt^i v
diiplux sets and batteries as shown in the diagram, and a main
connecting them. First approximate the balance by pegging
rluM)Stat to 5,(HK) or C,0(K) ohms in clear weather for a lino
miles long. Ask the distant oHice to "open". Notice in com
tiun with transmitter T' that this opening gronnde the wire at
distant end. Tliere is now no battery on the line but your o
lower the tension on the spring 8 ji and, by means of the p
yar; the resistance in the rheostat (the liome key being clo!
until the cores of the relay show no appreciable attraction for
Rrninturi'. This done, open and close the key a nuniK-r of tin
sli"ht click of the sounder with each movement of the key
proUhly l>e heard— an effect which it is necessary to elimiii
It is with the dynamic, or current, form that, np to this time
have l>een dealing; but the false signal jui^t mentioned in con
tion with the dnplex brings to notice, for the first time, electn
in the form of -/..-v/,.. upon the wire, and therefore calle.1 st
It i.R'sents itself as a disturbing element in connection with dn
k- and the renuily fur it is a movement in the artificial
round the reluv coil, in » dinction opivosite to that which oa
,1k- -kivk': tl"- "'-^"^ f^"" FO^l'"^"'? '^ '^ *^'*" «PI«*™t"^ '" *M
,„.,rfcM C. for condenser.
For •. ^latenient of what static ehi-tricity is. and certain f
Klemeiits of Khi-tricity"". In the diag
of the
ibeel^ottin foil: the sjwees mica, paral
1., .,., »I.i.l. .n»k.- >•'•"■"' ""'■ ""■ *■'"'"'"'■ ^'"' ,''
THE ELECTRIC TELEGRAPH
/I
of an adjustable set of coils r, the charge and discharge can be
assimilated to that of the main line.
On the condensers commonly used in telegraphy the discs are
usually five in number, and are marked 40, 32, 16, 8, 4 to denote
the percentage of tin-foil area connected to the disc. If pegs are
inserted uniting the bar with discs marked 4, 10, and 40, 00 per
cent of the capacity is in use^and the charge and discharge will be
in just that proportion. A condenser usually bears a stamp as
2.5 M F, or 3 M F. The M F stands for micro-farad, which is the
practical unit of capacity; and is about equal to that of three miles
of an Atlantic cable.
With the duplex in operation there is, on the closing of the
transmitter, a charge through each pair of relay coils and, on the
opening of the transmitter, a discharge through each pair of relay
coils the same in quantity and at the same instant; and in each
case the movement in one pair of relay coils neutralizes that in
the other.
When the "kick" has been cleared, the distant station is
asked to write; and it will be found that the outgoing signals do
not interfere with the incoming, because the duplex has had a
static, in addition to its first, or ohmic, balance. The distant
station then goes through with the same process, and the sets are
ready for service.
All the accessories having been described, it remains to trace
in detail the effects of the currents on the relays in every position
possible to the transmitters. In the diagram, on the left, the l)at.
tery has zinc to the post and copper to the ground; at the other
terminal, on the right, copper is to the post and zinc to the ground.
The duplex would work if the batteries had like poles to the line;
but we shall consider them in the manner shown. In operation,
four conditions are possible, and they maybe ttibulated as follows:
T closed
Topen
T closed
Topen
T' closed
T' closed
T' open
T' open
+ to line
G ** "
G " *'
D' R' closed
I)' R' open
I)' R' closed
D' R' open
DR closed
I)R closed
DR open
I)R open
It will appear from this that the differential relay at one ter-
minal obeys the transmitter at the other. We shall see how this
801
72 THE ELECTRIC TELEGRAPH
works out in practice. A line 450 miles long usually has a voltage
of at least 150 at each terminal; and, as only 25 cells are represented
in the diagram, each cell must be supposed to represent 6 volts.
First, when T and T' are closed; the batteries unite their
energies, giving on the main line a current of ^^^ ampere, or 40
milliamperes. Ori the artificial line, in the relay coils at each ter-
minal, there is a current from the battery at that terminal through
a resistance in the rheostat equal to that of the line, say 20 milli-
amperes, because the voltage in each case is only one-half that of
the united batteries on the main line. In the coils of each relay
there is a difference of 20 ma and both remain closed.
Next, open transmitter T. The battery at the left is cut off, and
the line is grounded through a compensating resistance C R equal
to the internal resistance of the battery. On the artificial line in
relay D K there is no current; on the main line there is a current
of 20 ma from the distant battery; relay D R remains closed. On
the artificial line in relay D' R' there is a current of 20 ma which
neutralizes the current of 20 ma on the main line, and the relay
D'll' opens; in other words, it obey& transmitter T.
Next, close transmitter T and open T'. This is the phase
shown in the diagram, and it should be traced with special care.
The line is now grounded through the tongue f and lever of T' on
the right; and the only current on the wire is from the battery at the
other end. At the terminal where T' is there is no current on the
artilieial line, and the current of 120 ma on the main line closes
the relay !>' K'. l>ut at the other terminal, where T is, the cur-
rent in the coils of the artificial line neutralizes the current on the
main line, and the relay D K opens; in other words, it obeys trans-
mitter T'.
Lastly, when both transmitters are open. The battery at each
terminal is off; there is no current in either the main or artificial
line at either terminal, and the relays stand o|)en. In this way are
verified the results set down in the table; the relay in each case is
unresponsive to the home instrument, but responsive to the distant
transmitter; and signalling in opposite directions at the same time
is prHctiea])le.
In explanation of the j)art j)layed by the condenser in the
long distance du])Iex, it may be said that when current flows in a
302
THE ELECTRIC TELEGRAPH 73
wire, a portion of it collects and becomes static on the conducting
material; and it will discbarge instantly in any direction a path
offers. In duplex work, the transmitter makes a line contact first
with the battery, then with the ground; the conditions are present
for a static charge and discharge of the wire; and the extent to
which it is capable of these effects is called its eleCtro-static ca-
pacity. On short lines it is small; so that, in the duplexing of
such wires, the 'kick' is not noticeable; but there is a difference
between a main line wire 450 miles in length, and the fine wire
with which the coils of the rheostat are wound. So far as rexffit-
auc<^ to the current is concerned, the coils in the box are capable
of reproducing exactly the conditions on the wire; but the main
line wire has electro-static ca|)acity; the fine wire of the rheostat
coils has not. The initial charge in the line, therefore, will not,
unless the condenser is used, be offset by an opposite movement in
the artificial line; nor, at the termination of the signal, when the
line is moved from the battery to the ground, will the discharge
be offset by an opposite movement in the artificial line. A form
of duplex was invented in Germany, and known in America as
early as 1855; but it was worked only on comparatively short
lines. The duplexing of long lines by the aid of the condenser
was made practical in 1872; and the credit is due to Jo8e{)h B.
Stearns of Boston. His was one of the notable achievements in
the history of telegraphy, for by means of it the value of most of
the wires of the telegra{)h companies was doubled at a stroke.
In the diagram. Fig. 24, there is indicated a connection from
each transmitter through a coil c r to the ground at h, Before
leaving the subject of the Stearns duplex, it is proposed to make
a change in this circuit, and note results with a view to future
reference and use. In each circuit move the wire from the point
J to the point i'. When the transmitters are closed the c r cir-
cuits are open, so that the change to 1/ makes no difference on the
line; but when a transmitter is open, the line has in circuit about
one-third of the battery before it reaches the ground. Under these
conditions, instead of the main and artificial lines being free of cur-
rent, there would be on the main line coils in each relay, say 10 ma
of current; and opposed to it in the artificial line coils about 8 ma.
The difference (8 ma) would be suflrtcient to close the relays; but,
303
74 THE ELECTRIC TELEGRAPH
according to the four-phase table, when the transmitters are open
the relays should be open. Under these conditions, to open the
relays it would be necessary to increase the tension on the arma-
ture spring. Now, if for any reason, we wish to maintain a weak
current always on the line we could use for the purpose a por-
tion of the battery, and counteract the effects of it by giving the
8[)riug Hj) sufficient tension to overcome the magnetism induced
by the weak current; or, as the operators express it, the relay can
be '* turned up" al>ove the weak current. This done, the opera-
tion of the duplex can be carried on as usual; the only difference
is that the springs of tlie relays have tension sufficient to make
them unresponsive to the weak currents. It is possible, therefore,
to work a duplex of the Stearns pattern when the connections are
such that the movement of each transmitter sends alternately to
the line the whole battery and only one-third of it. This state-
ment made, let us leave it for the present. It will be fitted into its
place later, when we come to deal with the quadruplex in connec-
tion with which the statement just made plays an important part.
It remains only to gather up the terms and phrases used in
describing the duplex; from this time on they must be a part of
our vocabulary. We have had to do with the differential winding
of a single core, the diiferential relay, main line, artificial line,
rheostat, conqKMisating resistance, transmitter, condenser, retarda-
tion coils marked /• /', internal resistance (usually of a battery), the
split, the balance, tension (of a spring), the static and its kick,
charge and discharge, electrostatic capacity. If the reader will
note in the diagram, as far as possible, each object named, he
should get a better idea of its theory and function than could l)e
obtained from a deiinition.
It thus a[)j)ears that the characteristic instrument of the
Stearns du])lex is a relay, in apfX'arance not very different from
the ordinary relay of the single-line ty])e; it can be constructed
from it by a change in the winding from the simple to the differ-
ential form as represented in the diagram. Fig. 24. For the sake of
simplicity all the thumbscrew connections, the front and back
stop, and a])paratus of the local circuit are omitted from the draw-
ing; only the essential parts — the differential coils with the
armature and spring — are shown. It will be noticed that the
804
THE ELECTRIC TELEGRAPH 75
main line has a number of turns around one core, then around the
other; the same with the artificial line. In practice, the points
where the main and artificial lines enter and leave the instrument
are fitted with four thumbscrews; two more are provided for the
local points — one making connection with the armature, and the
other with the front stop — forming parts of a local circuit as in
the ordinary single-line relay. These omitted parts will be sup-
plied in Fig. 29; but in dealing with first principles the fewer the
details the better.
The Polar Duplex. In the same manner as we took the
single-line relay and changed it to one of the differential type, so
now it is proposed to take the latter, to make some changes in its
construction; and, with a view to one more advance, to introduce
a different form of armature and note the results. The yoke
which, in the working instrument, joins the cores at the ends
furthest from the armature is supposed to be removed; next take
away the armature and turn end to end the cores that faced it, so
that the coils, instead of lying parallel, are in a straight line.
With a space of one-ijuarter or one-third inch between them they
will present the appearance shown in Fig. 25, in w^liich C and Z,
C and Z' represent the terminals of the coils; one core is marked
D A, the other B E; and for observation the student is supposed
to take up a position in the space between the cores. First, a cur-
rent in the wire C Z encircles the core D A in a direction opposite
to that of the hands of a clock, that is, from right to left, then it
encircles the core B E in the direction of the hands of a clock, that
is from left to right. If the student will imagine himself in place
between the letters A and B he can readily understand this.
Heretofore we have been content merely to state the fact of
the attraction of a magnet for its armature; the point has now
been reached where it is necessary to state the law of the formation
of magnetic poles in cores around which a current is passing. In
"Elements of Electricity" are shown magnets marked N and S;
in the text relating to the same it is explained that N stands for
north -seeking, S for south-seeking; and tliere is further stated the
law that like poles repel, while unlike poles attract, each other.
Reverting now to what was said of the ])assing of a current round
a core, let us, for the sake of brevity, call the directions just men-
30ft
76
THE ELECTRIC TELEGRAPH
tioned an ti -clockwise and clockwise. At the end of the core, at
which one is looking "end on", magnetic poles are formed accord-
ing to this law: When the current passes an ti -clockwise N
polarity is induced in the near end, S polarity in the far end; when
the current passes clockwise, S polarity is induced in the near end,
N polarity in the far end. In the instance showm in Fig. 25 in
the line C Z, there will be formed at A and D, K and S poles
respectively; at B and E, S and N poles respectively. There is
therefore on one side of the space between the cores an N mag-
netic pole; on the other side an S pole; it remains to provide
something on which they may act.
F'lfr. 20.
Ill Fi<^. 20 let S be tlie end of a jR^rnianent magnet semicir-
cular in sliape; a strip of soft iron for an armature is so pivoted
tliat it can move freely between tlie stops at the upper end. In
tlie armature tlie induced ])oles are marked with the small letters
jf and s\ in accordance with the principle stated in "Elements of
Electricitv". With no current in tlie wire C'Z', a current in the
wire in the direction C to Z will induce, according to the clock
rule, at A, N magnetism; at B, S magnetism. The N pole, ac-
cording to a law already stated, attracts the .«? pole of the armature;
the S pole repels it; the armature is strongly moved towards front
stop K. The current ceases, let us su])p()se; but the armature has
no spring, and its jiosition remains unchanged until a current flows
throuixh the same wire in a direction from Z to C Under its
inHuence there is formed at J^, an N pole; at A, a S pole; the
effect on the .y juile of the armature is to move it from the front to
306
THE ELECTRIC TELEGRAPH
tliw back stop. Every time the ciirreut cliaDges its direction the
armature cliaiiges its position from one stop to another; and we
have & jiiilar relay. It is one in which a magnetized armature is
moved from point to [>oint under the influence of magnetic poles
chatigin<; as the effect of changes in the direction of the current
around tlie cores.
One step more and we have a differential polar relay. In the
diagram, Fig. 21) ia an extra wire with a number of turns around
each core. Its terminals are C Z'; but it is so wound that a cur-
reut from C to Z' passes round the cores in a direction different
from that in the line C to Z. The current from C passes first
[IMi]
Fig. 26.
clockwise, then anti-cloi-kwise around the cores; and from what
has been said it is plain that if currents of e^jual strength flow in
the wires C Z and C Z' they will induce at A and B magnetic poles
such that they will neutralize each other; provided, of course, there
is the same number of turns in each coil. The effect on the anna-
tore will, in that case, be nil. But if the currents in C Z and C Z'
are not equal, the armature will obey the stronger current with a
pull determined by the difference between the two. The result is
a differential polar relay, by means of which that very perfect
Bystein of signalling in opposite directions — the polar duple.x^is
possible. The relay is made in different forms, but it consists
essentially of a permanent magnet in which is pivoted a strip or
tube of soft iron called the armature. This is placed Iwtween two
cores around which are wound, in the manner shown i" '" "^
THE ELECTRIC TELEGRAPH
two independent cirenita. Tlie windings terminate in four thumb-
screws, with two more fur tlie local points, making six tbumbscrevB
for the polar relay. The spools may be wonnd in varioDS ways;
the wires may be laid sidti by sidu thronghout the length of each
core; or, aa in the diagram. Fig. 27, in i^qiial comfHirtiiienta eejm-
rati'd lij discs at ri^lit angles to the core. In the relays most eoni-
iiioiily imed each division of a sjiool contains 2,4(10 turns of wire,
and has a resistaucn of 200 ohms; so that, in each circuit there is in
THE ELECTRIC TELEGRAPH 79
the relay coils, a resistance of 400 ohms. This is equal to 42 miles
(very nearly) of No. 6 iron wire, such as is commonly used in the
construction of telegraph lines.
A differential polar relay, then, is one whose armature, polar-
ized by contact with a permanent magnet, is o|>erated by the differ-
ence in the strength of the currents, the direction of whose course
is constantly being changed.
The instrument by which the direction of the current is
reversed at will is called a jxde chanrjer^ which, with the polar
relay, the dynamos, lamps, and dynamo switch connected up, is
shown in P'ig. 27. These, with the rheostat and condenser described
in connection with the Stearns apparatus, form a duplex set for one
terminal. There is shown in the drawing one set for each ter-
minal, and, for convenience in description, the left-hand station is
called Pittsburg; the other Fort Wayne. The latter, as compared
with the former, shows a different arrangement of battery and pole
changer, of which explanation will be made later on. The Pitts-
burg pole changer is o[)erated by means of electromagnets. These
are part of a local circuit (not shown) and controlled by a key in
the same way as the sounder in the learner's outfit. To the end
posts of the pole changer are connected wires from dynamos sup-
plying, let us suppose, a 200- volt current. It is made to pass
through lamps and a switch; negative to the left, positive to the
right. To the center lever of the switch is connected the main
line. With the center bar of the switch to the left, connection is
made with the lever of the pole changer, so that when the latter
is closed a zinc current goes to the main line; when open, copper.
The lamps are placed between the dynamo and pole changer so
that in case of a short circuit, by the lever of the pole changer
accidentally making contact with both posts, a resistance of 1,200
ohms will be interposed until the short circuit can be broken and
thus injury to the dynamo is prevented. The purpose of the
dynamo switch is to provide means for readily cutting off the cur-
rents from the pole changer when any cleaning of the points or
adjustment is required, or in case of a short circuit through the
lever. With the center bar of switch A turned to the right, the
main line goes to the groimd through a resistance equal to that of
each lamp, or 600 ohms; it makes no difference, therefore, in the
soo
80 THE ELECTRIC TELEGRAPH
resistajwe of the main line whether the center bar is to the left or
to the right. From the switch the wire may be traced to the
'split' near the polar relay. At this point, as in the Stearns
duplex, the current divides; one-half of the Pittsburg battery pass-
ing through two coils to the main line; the other half also through
two coils to the rheostat, thence to the ground. The function of
the rheostat, and its companion, the condenser, was ex]>Iained in
connection with the Stearns duplex; and it might be well to review
that part of the text.
Woisv to Balance. First approximate the balance by pegging
or unpegging the rheostat to about 5,000 ohms for a line 450
miles long; in wet weather two-thirds of that. Ask the distant
station — in this case. Fort Wayne — to ground; ground also at
Pittsburg — the home station. Adjust, by means of the set screws,
the armature of the polar relay so that it remains on one stop or
the other as placed, or else vibrates freely under the Influence of
the slight current which the nearness of other wires on the poles
may induce. Turn tlie switch from the ground to the pole
changer connection. There is now on the wire no current of any
account but your own; and the rheostat must now be so adjusted
that the current from the home battery — in this case the Pittsburg
— divides equally between the main and artificial lines. When it
does this the armature of the home relay will vibrate freely as before.
In other words, the home current has no effect on the arma-
ture and the relay stands ready to respond to the current from the
distant, or Fort Wayne, battery. Tell him to ''cut in"; he does
tin's l)v movincr the lever of switch F from the right to the left-
hand lower point; and when his key is closed your relay should
close. Kow, if you open and close your pole changer by means of
your key the static "kick" will probably be noticed; and the
remedy for it is the same as that descril>ed in connection with the
Stearns duplex. This done, the ''kick" disappears; the distant
station writes, and it will be found that the signals sent from the
home station by reversing the pole changer do not interfere with
the incoming signals. Fort Wayne then asks you to ground and
proceeds to balance his end; the duplex is then ready for service.
In the hands of experts the operation of balancing both ways does
not ordinarily re(juire more than three minutes.
310
THE ELECTRIC TELEGRAPH 81
The right hand, or Fort Wayne, terminal shows an arrange-
ment of battery and pole changer in vogue for many years before
the use of the dynamo current in telegraphy; and it still obtains
in a few places where a machine current is not available. The
diagram represents the combination of a chemical battery of say
150 cells and the old-fashioned continuity-preserving, or clock-
face, pole changer. The latter is retained here and described be-
cause it is also as an essential part of the phonoplex — the topic
with which this book deals last.
In the diagram only the clock-face portion is shown; the part
G', in the center, represents the end of a lever operated like that
shown in the Pittsburg pole changer, making contact with the
ground. The poles of the battery connect with two springs as
shown; the latter with the point-bearing blocks, Q and K are
suitably insulated from the supporting material which is usually
of brass. Q and R are connected to each other and to the main
line. The connections made when the lever is closed are shown in
the diagram. The left-hand spring is grounded, lifting it up from
Q; the right-hand s])ring is free from the ground, but is making
contact between the line and the zinc pole of the battery. AVhen
the pole changer is open, the center block drops down; the line
makes connection with copper; zinc goes to the ground. In both
forms of pole changer the results are therefore the same — zinc
to the line when closed; copper when open — and this is the rule
for their arrangement in practice. Care must evidently be taken
for the adjustment of the pole changer in either form. '^ Clean
and close" is the rule for placing of the points — as close, that is,
as they can be worked without short-circuiting and sparking. Of
pole changers and sounders alike the armatures must not be al-
lowed to beat upon the magnets; to make sure they do not, a piece
of paper should at times be passed between them.
As in the Stearns duplex, the polar duplex in operation has
combinations of current four in number; and a description of the
latter will not be complete without giving in detail the reason for
the response of the relays in each combination. In advanced
telegraphy there is no instrument in more general use than the
polar relay; the principles involved are everywhere used; and a
thorough understanding of them is necep ^stery of the
|i
82 THE ELECTRIC TELEGRAPH
more complex forms of apparatus and their latest applica-
tions. The changes in magnetic poles, as the result of changes in
the direction of the current, will occupy our attention now; but
before entering upon this we must consider the conditions which
determine the direction of the current.
Much has been said about positive and negative currents, and
the signs + and — are conventionally used to represent them;
but these terms are not meant to convey the idea of strong and
weak; a negative current may be strong or weak the same as a
positive. In surveying it is convenient to consider "sea level" as
a zero point from which to measure heights or depths, so in elec-
trical potential the earth is taken as a neutral point and arbitrarily
called zero; a current flowing into it is called positive; a current
flowing from it, negative. If this seems unsatisfactory', perhaps
an analogy may help us. Suppose we regard the air at rest as
zero. Confine a rotating fan within a closed iron frame with a
single tubular opening. Revolve the fan and, at the opening, a
pressure will at once be felt of say 50 pounds to the inch. A few
feet away the pressure will be 25; further away 15; and soon
until no disturbance of the air is felt; the pressure is practically
zero. Reverse the direction of the fan's motion so that instead of
])re8sure outward there is suction inward, and at like distances
effects like those just mentioned will be felt, but in an opposite
sense. At the optMiing the suction is 50; whereas before there was
an outward pressure of 50. In the one case we have the air at
rest, the pressure, and the suction; these have their electrical anal-
ogies in the earth considered as zero potential; the positive cur-
rent, which always sets towards the earth; and the negative, which
always sets from it. The common direction of a thunderbolt is
from a cloud to the earth, in this case the cloud must be posi-
tively charged; but instances have occurred where the direction of
the bolt was from the earth to the cloud; in which case the cloud
was negatively charged. In other words, and for the present pur-
pose, the direction of the current is always + to zero, + to — , and
zero to — ; or, as stated, always from the higher potential to the
lower. It is taken for granted that the same amount of current is
supplied to the line at each terminal; in a duplex circuit 400 or
450 miles in length this is generally 150 or 200 volts. With these
^\^
Pl
5h key.
To line.
FtW relay.
1
Closed
Closed
2
Open
+
Open
3
Closed
Closed
4
Open
+
Open
THE ELECTRIC TELEGRAPH 83
statements in raind the investigation of the combinations possible
in duplex telegraphy may be taken up.
FtW key. To line. Pgh relay.
Closed — Closed
Closed — Closed
Open + Open
Open + Open
In phases 1 and 4, the two stations present like poles to the
main line; in phases 2 and 3 unlike poles.
Coinhhidtton^ orplutMe 1. Pole changers at terminals closed;
zinc to the main line. In the diaorram, the main line is solid
black; the artificial line is dotted. AVith like poles of equal
strength to the main line there is no current on the solid black
line. Under these conditions on the artificial (dotted) line a cur-
rent sets in from the ground through the rheostat, along the dotted
line, through the pole changer to the zinc ( — ) of the dynamo in
accordance with the law just stated. In the Pittsburg relay it
forms first an N magnetic pole on the end of the core at M; then
an S pole at O. If we enclose an N thus N to represent the
polarity of the Pittsburg armature, the magnetic conditions may
be graphically represented: K closing the relay in accordance
s
with the law that like poles repel, unlike poles attract each other.
Similarly, at the Fort Wayne end, by means of a current from the
ground to the zinc of the battery the magnetic conditions are:
8
S also closing the relay.
n
Comhinatioii 2 shows Pittsburg +, Fort Wayne — to line;
current direction on the main line is from Pittsburg to Fort
Wayne. On Pittsburg artificial (dotted) line, current is from +
to ground through the rheostat; on Fort Wayne artificial line it is
from ground through the rheostat to — of the battery, the same
as in combination 1. But the current on the main line is twice
that on either of the artificifi^ ^^nes; because in the former case
the current is from + to ' ' *^<^r case it is from +
to ground at one term — at the other.
84 THE ELECTRIC TELEGRAPH
The magnetic poles induced in the cores by the current on the main
line are therefore twice as strong as those induced in the cores by
the current on the artificial line. If we represent the magnetism
induced by the main line current by a capital, and that induced
by the artificial line current by a small letter, and indicate the
polarity of the armature as before, the magnetic conditions in
the Pittsburg relay may be typographically represented thus: N
nS
the stronger poles closing the relay; in the Fort Wayne relay
S the stronger poles opening the relay.
Combinatlo7i 3, Pittsburg — to line; Fort Wayne + to
line. Current in opposite direction to that in combination 2; but
on main line twice as strong as on either artificial line; in the
Pittsburg relay the conditions are N opening it; in the Fort
^71
Wayne relay 8 closing it.
Cfunhi nation 4. + to the main line at each end; no current
oil the inuiii line; relays actuated as in combination 1 l)y curreut
.y
in artificiiil line; in Pittsburo; relay N opening it; in Fort Wayne
n
n
relay S also opening it. Tin* Fort Wayne relay might have an N
armature the same as Pittsbnrtr, but it was purposely made differ-
ent to afford exercise in tracincr out the effect of the current.
The student should now l)e master of at least the theory of
tlie two forms of the duplex — the original Stearns and the later
and more ])erfect polar. The former came into general use in
1872, the latter about 1880. In making comparison between the
two it can be seen that the su])eriority of the polar duplex lies in the
^\<v
4
" 1
THE ELKCTRIC TELEGRAPH K>
relay whose action is determined, not, as in the Stearns, by a cur-
rent attracting the armature in one direction and a spring drawing
it in the other, but by a current directing its movement first to
the front then to the back stop. This makes the polar duplex
almost independent of weather conditions. The occasions are rart»,
the relay being so sensitive, when sufficient current does not gt^t
|)ast the escape to record the signals. The resistance of 450 or
500 miles of No. gauge iron wire is, in dry weather, about 5,000
ohms; in damp or rainy weather this is often reduced to two-thirds,
or even one-half. This is a good point to remember in adjusting
the rheostat to get into coniinunication initially with a distant
station before the correct balance is taken. Less condenser, also,
is nee<led in moist weather than in dry, because a part, sometimeft
nearly all, of the static charge escaj)e8 into the moist air.
With a clear wire and apparatus in good condition, the |X)lar
duplex is a well-nigh perfect in.strument capable of a sjhhhI, when
working the ilorse system, equal to that of the fastest typewriter;
and when operated by the AVheatstone Automatic system it has
attained a speed of 250 words a minute each way -nearly ten
times as fast as the ordinary SjR^ed by hand.
THE QUADRUPLEX.
The quadruplex — among telegraj)liers known always as the
quad — permits the exchange of four messages at the same time;
two in each direction. In the diagram, Fig. 28, presenting the
theory of the quad, there is much that will seem familiar to the
student; the text has beim so arranged and the drawings so nuide
as to give the impression of previous acquaintance. The neutral
relays are a reproduction of the instruments made prominent in the
Stearns duplex; the polar relays are those which we have just studitnl
in the polar duplex. The rheostats — the same in principle as those
already shown — are represented by a simj)le coil ; and, shunting each,
is the now familiar condenser, H and J, each with its retardation
coil lie. The batteries and ])ole changers are a reproduction of
those shown in connection with the polar duplex.
At the left hand, or Pittsburg, end the dynamo switch has
been omitted for the sake of simj)licity; everything, in fact, has
been left out except the parts needetl to illustrate the fundamental
315
86 THE ELECTETC TELEGRAPH
principles on wliich tbe quad is arraaged. The details which
make the quad appear so complicated can be filled in later. In
the dit^ram the one new feature is the introduction at each end ol
a transmitter in combination with the pole changer; at the Pitts-
tmrg end it is between tlie pole changer and the split; at the Fort
Wajue end Iwtween the battery and the pole changer.
THE ELECTRIC TELEGRAPH 87
We have seen that it is the function of the pole changer to
alter the direction of the current; it is the function of a ti'ans-
mitter, like those shown in Fig. 28, to alter the streiujth of the
current within certain well-defined limits. Now the pole changers
are evidently in position for the purpose of operating the polar
relays; the transmitters can therefore be in place only to operate
the neutral relays. The instruments heretofore designated as polar
and neutral are also called polar and common; the sides on which
they are worked are sometimes called by the numbers 1 and 2, and
sometimes by the letters A and B.
From what has been said, the student may already have in-
ferred that a neutral relay is one operated by the strength of the
current without reference to its direction; he knows that a polar
relay is operated by the direction of the current without reference,
within reasonable limits, to its strength; and in the annhi nation
of these two ^>>/v'//<v^>»/r.v lies the theory of the quad, as it is com-
monly known. There are other forms of the (juad; Init our present
business is with the one still in general use.
The student is now asked to recall and review an experiment
made in connection with the Stearns duplex, and intended for
introduction at this point. It was made clear that, by the simple
expedient of "turning up" on the relay spring, the Stearns duplex
could be operated even when a weak current remained continu-
ously on the main line; or, as it was expressed in a former para-
graph, "If, for any reason, we desired to maintain a weak current
on the line, we could use therefor a portion of the battery and
counteract the effects of the weak portion by giving the spring
sufficient tension to overcome the magnetism induced by it."
The need has now arisen for maintaining at least a portion of
the current continuously on the line; and the reason for it is
that changes in the direction of a comparatively weak current
will operate a polar relay as readily as the reversals of a current
three or four times as strong. The neutral relay can be made
unresponsive to the weak current, but responsive to a strong cur-
rent without reference to its direction; in other w^ords, the quad-
ruple is merely a combination of the Stearns duplex, in a form
modified as shown in the t^xt. with the polar duplex. It re-
mains only to explain so ination.
90 TETE ELECTRIC TELEGRAPH
the direction of the current is changed it is pUin there must be a
very brief moment of time when there is no current on the line; at
such moments there is a tendency on the part of the armature of
the neutral relay to fall away from the magnets. If the local con-
tact were on the front stop this would record a false signal: and
the greater the length of the wire worked in the quad the more
apparent is the interval.
On all long-distance quads, with a view to eliminate the false
signal, there is interposed (see P'ig. 29) Ijetween the relay and the
recording sounder, what is called a repeating sounder; the device
however, is not an entire success, and the signals on the common
side lack firmness to an extent which afifects the speed.
Troubles of the Quad. It is usual in text books dealing with
this subject to devote considerable space to the troubles of the
quad. An expert quad man is not he who sets up quadruplexes —
that is generally done by the office lineman — it is one who keeps
the quad in working 6ha[)e, and who, when any stoppage or defect
arises, can locate the trouble and remove it. In the language of
the craft, a defect in the set is called a ''bug'';. and those who
deal with them are known as ''bug hunters." It would be possible
to fill a IxKjk the size of this with the ailments of the quad; how to
locuite and renie<Jy tbein; the reader might study it attentive! v,
but if his knowledge of the principles underlying the quad arrange-
ment was hazy he inif/ht, and prol>ably would, l)e worsted! bv the
very first trouble he met; on the other hand, if he is thoroughly
versed, as it has l)een the aim in these pages to make him, in first
f)riiicij)les, each exf)erience of trouble and its removal will prepjire
liiin to coj)ewith the one that next presents itself. A prime quali-
fication for anyone who aspires to be a defect hunter is a j>ersist-
ence in the search which never flags until the root of the trouble
has been found and removed.
A very insidious defect in a quad, because, slight at first, it
may gradually grow worse, is that of uneven ness in the coils, pro-
ducing wliat is called a **loj)-sided" relay. It is well to make
tests, at stated times, of the relay coils with a current other than
tliat of the quad. It need hardly l>e said that the batteries for tlie
quad must l>e kej)t up to the standard; that the ground wires and
their resistance coils, which are a part of the circuit when a bal-
THE ELECTRIC TELEGRAPH 89
the upper core S polarity; in the lower N ; the effect of these on the
S armature is to close it; the effect of the transmitter closed at
Pittsburg is to close the Fort Wayne neutral relay. The number of
phases or combinations jyossible to the eight instruments (four at
each end) of the quad is sixteen; and one of these has been traced
out with the results described. The general result in every case
is that the Fort Wayne neutral relay obeys the Pittsburcr trans-
mitter; the Fort Wayne j)olar relay obeys the Pittsburg pole
chancrer, and ^v^v vn'sii.
How to Balance. The operation of balancing the quad is the
same as that followed in connection with the polar duplex, except
that the static is eliminated by watehintr its effect on the neutral
relay instead of the polar. Approximate the resistance in the rhe-
ostat to that of the main line: Pittsburcr then asks Fort Wayne for
his ground, and goes on the ground himself. Center the relay so
that the armature remains on the front or l)ack stop as placed; or
vibrates freely under the influence of slight extraneous currents.
Turn on the home, or Pittsburg, battery and adjust the rheostat until
the polar relay vibrates freely as l)efore. Now wedge the sounder of
the polar relay in order to silence it temporarily. Turn down on the
spring of the neutral relay; close the transmitter and dot slowly on
the pole changer. Commonly a kick will be felt on the neutml relay
which can be removed by adjusting the plugs on the condensers;
turn down further on the spring and readjust the condensers; turn
down still more if necessary and readjust the plugs until all trace
of the kick is removed. Now restore the spring to its normal pull,
and ask Fort Wayne to cut in. Ask him to write on the common,
or No. 2, side and dot on the polar side. Pittsburg does the same,
and, if his balance is correct, the signals from Fort Wayne on each
side of the quad will be clear-cut and readable. Pittsburg now
grounds for Fort Wayne, who goes through the same routine, and
tests the result in the same way. This done, the quad is ready for
service and is cajmble during a day of 9i hours of carrying 300
messages each way on the polar side, and 250 each way on the
common side.
The slower work on the No. 2 side has its source in a defect
in the quad which has never been entirely overcome. In the
operation of the pole changer, even of the clock-face kind, when
319
92 THE ELECTRIC TELEGRAPH
gives fairly satisfactory results. In an office where two quad set? are
available, and occasional cessation in their use gives opjiortuiiitY,
the following plan for familiarizing one's self with the cjuad and
its troubles is suggested by an expert. Select a station 2(Nj miles
away and ask him to "loop'\ that is to join together, two wiivs
which you name. Connect the two wires to adjacent sets in your
own office. Balance them as though they were distant sets. Now
introduce into one set any form of interference or disconnection
that would V>e likely to occur in practice, and observe the effect on
the other set; exf^erience may be gained in this way that would aid
in the location of trouble when it occurs in practice.
Duplex Repeater. In wires worked on the duplex or quadru-
plex system, the static capacity of the wire places a limit on the
numl>er of straight miles a circuit can be worked. But the dis-
tance between stations can l>e greatly extended by the use of
rej)eaters in which, by a fjerfectly simj)le arrangement of local
circuits, the [Kjle changer of a second circuit is controlled by the
relay points of the first, and Vf^^e vtrxa. For example, in the text,
a duplex Pittsburg to Fort Wayne was described; call it the first
circuit. Yov a second circuit suf^pose Fort Wayne has a duplex to
Chicago, and that Pittsburg wishes to be put through direct. By
nieaii=? of Hwitcli- jacks and cord?? provided for the purpose. Fort
Wayne makes the electroniairnels of the j>ole changer of his
nortliern set a j)art of tlie local circuit which passes through the
points of the pohir relay of his Pittsburg, or eastern, set; he also
makes the electromaf^nets of tlu^ i>ole chantrer of his eastern set a
part of the local circuit which passes through the points of the
j>olar relay of his northern set; Pittsburg and (-hicago can then
work duplex. The longest regular circuit in the United States is
that worked l>etween New York and San Francisco with six re-
peaters; another long circuit is that between New York and Heart's
Content, Newfoundland, witli re]K\aters at Boston, St. John, and
North Sydney. In a few seconds these two circuits could l>e
rejieatered at New York; San Francisco and Heart's Content could
then work dnplex through nine repeaters — a circuit from ocean to
ocean where the continent is widest.
The Repeatin^^ Sounder, pnjih.r Lni,^,x. Fig. 21) shows the
local connections of the common side of a quad and the method of
329
TnE ELECTRIC TELEGRAPH
r
)
^
5 I
cp o- '
^-» l«
&-•
91 THE ELECTRIC TELEGRAPH
current supply which, it is seen, is from two independent sources.
The common side is shown preferably because it exhibits, in place,
the repeating sounder, to which reference was made in a preceding
paragraph, in the receiving, or relay, side. The current supply is
a 6-volt dynamo, from one pole of which a wire extends through a
fuse to the armature of the neutral relay. From the biicl\ not the
front, stop of the relay it passes through the coils of the repeating
sounder, through another fuse, back to the dynamo, thus complet-
ing a metallic circuit. Wlien the neutral relay is on the front stop,
the reptatiny sounder is open; but its points, between the lever and
the up stop, are closed, permitting the 23-volt current to close the
other sounder from which the signals are read. When the neutral
relay j)oint8 open, the re|)eating sounder is closed, but the receiv-
ing sounder is open; the reason for this arrangement has already
been given in the text on the quad.
The regular local system of a duplex, or one side of a quad-
ruplex, is not a metallic circuit; it is a grounded system supplied,
as the drawing shows, by a 23-volt dynamo. The reason for the
ground arrangement is that in all the principal offices by far the
greater number of the duplex and quadruplex sets are fitted up so
that while the sets themselves are in the main oftice, where they
can receive exj)ert attention, they can be operated in branch offices
by means of what are called ** loops", or ''legs". By suitable
switches the loops can be cut in or out as desired.
The current from the 23-volt dvnamo runs first to a fuse block
(not shown) ; thence to a small 3-point switch, the lever of which,
if turned to the left, connects the battery with the set; if turned to
the right it connects the set with the ground. The latter connec-
tion is made in ''setting up" a duplex repeater. With the lever
to the left, the current is seen in the drawing to divide at the point
S; one branch can be traced through the points of the repeating
sounder, through the coils of the receiving sounder; thence (with
the lever of the 0-point switch to the right) through a lamp of
al)out 1M> ohms resistance to the ^rround. The other branch can l>e
traced through the coils of the transmitter; through two keys;
thence (the lever of the T). point switch to the right) through a lamp
to the ground. The ])ur])ose of the lamps is to make the resistance
in the circuits the same in either position of the levers of the G-
^lf>k
THE ELECTRIC TELEGRAPH 95
point switch. Above this switch are the connections and outfit of
a branch office for the operation of a duplex; or, what is known as
a duplex loop. It shows one wire connecting a lamp and the coils
of a sounder to the ground ; another wire connecting a lamp, sounder
and key to the ground for the sending side; the first mentioned
sounder is that of tlie receiving side. To cut them in, turn the
levers of the 6 -point switcli to the left; the relay then operates a
receiving sounder in both main and branch offices; the branch office
can operate the transmitter and work duplex with another city or
a branch office therein similarly equipped. The word "loop",
though commonly used in this connection, is a misnomer. In
telegraphy, loops connect an outlying office, which may be rods or
miles away, with a single Morse circuit. To do this, the pair of
wires leading to the distant relay, which makes the loop properly
so called, terminates in a wedge which can be inserted in the spring-
jack of any wire in the main switch. In the duplex arrangement
the wires operating the branch instruments are merely extensions
of the sending and receiving sides of the local system.
There are many matters of detail in connection with the setting-up
and operation of a quad which do not properly fall within the scope of
this work. For special works on the dux)lex and quadruplex the reader is
referred to Thorn and Jones' Telegraphic Coniiections ; to Jones' Pocket
Edition of Diagrams ; and to Maver's American Telegraphy: Jts Systems
and Operation.
THE PHONOPLEX.
Among contrivances for increasing telegraphic facilities a
worthy place is occupied by the device known as the Phonoplex —
an invention of Mr. Thomas A. Edison. In its mode of operation
it will be found to differ materially from anything heretofore pre-
sented; its essential feature being the superposition, without
noticeable interference, of the high-tension impulses of a magnetic
coil upon the current or currents of the Morse system. Even when
all the wires on the route are crossed or grounded, not excepting
the one upon which the phonoplex is working, it admits of service-
able operation.
It can be worked in connection with the duplex and quadru*
plex systems; but its usefulness is greatest as an adjunct to the
Bingle-line service of the railw in a sphere where
THE ELECTRIC TELEGRAPH
tlio luiTdiier oJ \iin'? is usiiiilly liiiiitiHl, an extra circuit which is
at 111! tiTTit'S availiililf. Tin- iijijjiirutiiri is uiiapted for use l)etween
iiitentifiliate. as well as iH-twceii tiTiiiiiiuI, poiiite; but the diagram
(Fig. 80) prcsi'iits. and (lie ti-xt ileHfriU'S, the arrangement of a
tenniiial titatiuii where thi> single wire lakes ittt battery. As it
THE ELECTRIC TELEGRAPH 97
embodies some new features, the details require more than usual
length in their description. Referrinir now to the diagram — on
the right is seen the spring- jack of a terminal switch, showing
main battery and line connections. Two wetlgt^s are inserte<l in
the jack; one carries the conductors to the phonoplex; the other
cuts in a main-line key and relay which are bridginJ by condens-
ers; the bridging arrangement obtains also at everj' intermeiliate
station. This use of coiulensers makes feasible the o|)eration of the
phonoplex in the j)resence of cross^*d and groundtHl wires — a feature
to which reference has already been made.
.Tlie phonoplex requires for its ojvration, two batteries — one,
B, of at least live 2-volt cells, and one, L'^ of three cells; a key
and transmitter, each of jx*culiar construction; a small rheostat
containing five coils of two ohms each; a simple magnetic coil,
bridged by a condenser of small capacity, to quicken the impulses
sent out from the coil; an ordinarv Morse relay and condenser;
and, lastly, the characteristic j)hono])lex instrument itself, marked
P in the diagnim. The latter consists of a circular wooil base
supporting an uj)right cylinder containing an elongjited hor8e8ln)e
magnet, U])on e'lcli pole of which is wound a small coil of insulated
copper wire. Above the poles, and covering them, is a metallic
diaphragm like that usihI in the telephone. A 8j)lit steel ring 11
rests upon this diaphragm, or moves freely uj)on a threaded verti-
cal pin N, at the top of which is placed an adjustable nut. tiich
agitation of the diaphragm causes the steel ring to be thrown up
against the nut, producing an excellent imitation of the well-known
"click" of the sounder. Between mamietic coil M and the nniin
battery is an ordinary 150-ohm Morse relay C II, which acts as a
choke-coil; to it is tapjR^d a condenser C\ and a ground. \ih is a
small adjustable resistance box containing five coils of about 2
ohms each. Tliis resistance is introduced into one of the circuits
bridging the magnetic coil, in order to weaken the current so that
one stroke of the j)hone recorder may be distinguished from the
other; otherwise the ** back -stroke" eifect would ensue, and the
signals would not be readable. Of the wires bridging the magnetic
coil two, on the left-hand side, terminate in springs between which
moves the hammer-headed lever of the transmitter ojHTated in the
usual manner by means of local battery L^>, and key K. The lower
327
98 THE ELECTRIC TELEGRAPH
end of the hammer-head also has an attachment which aots on
spring z for a purpose which will be explained later.
It is difficult to represent in a diagram the insulated portions
of key K; in order to understand its working a detailed description
is necessary. The key and its attachments control two independ-
ent circuits. The ordinary circuit-closing switch is absent; the
local circuit (dotted) is always *' open '* except when signals are
being sent. One conductor of the local circuit makes connection
with the anvil post W which is insulated from the base, and is
fixed underneath the lever. To the further end of the lever is at-
tached the other end of the local circuit conductor, so that when
the key is depressed, the transmitter is closed. To the near end
of the base of the key is connected a wire leading to the lever of
the transmitter T. Attached to the base by means of a screw,
which serves also as a pivot, is a curved arm A, at the pivoted
end of which is a curved spur 8 reaching across the base of the
key. At 2 and 1) are small spurred thumbscrews attached to, but
insulated from the base; so that, in the position shown in the dia-
gram, the arm A puts 2 in contact with the base; but if the arm
is withdrawn from 2 a sufficient distance then makes contact
with the base through the spur s.
To understand the working of the apparatus it must be borne
in mind that the transmitter, unlike that of the Stearns duplex,
produces the effects of dots and dashes by the *' breaks", and not
by contacts. In the diagram, the lever of key K, and that of trans-
mitter T are open; the current from B Hows from + to 2, throucrh
the base of K and the lever of T, through spring x and the coil M,
to - of battery MB, thereby charging the coil with the full strength
of B. The act of depressing the key lever breaks the contact at a?,
coil M discharges, and a loud "^snap" is heard in the distant
phone or phones. When the lever T strikes the upper spring y,
the current flows through y instead of ;/;, thence through resistance
R//, charging coil M less strongly than before; so that, when the
upward movement, or 0{)ening, of the key breaks the contact at y,
a less pronounced snap is heard on the distant phone; thus obviat-
ing, as already stated, the effect of the '* back-stroke".
It will be noticed that, during this sending operation, the
curved arm is to the right, which is the position of an ordinary
^Vt^
THE ELECTRIC TELEGRAPH 99
key when an operator is sending. When he begins to receive on
the phone, he moves the curved arm to the left, which movement
corresponds to the "closing" of an ordinary key; but in this case
the movement simply disconnects the battery B from the trans-
mitter, and the spur s makes connection between and the base,
shunting the magnetic coil, so that the phone may be affected by the
maximum of charge and discharge from the distant magnetic coil.
One feature remains to be described. Leading from the ter-
minals of the phone may be noticed a shunt circuit (in dots and
dashes) terminating in spring 2 and a contact point above. The
position of spring s is such that when the transmitter is open and
its lever in a downward position, the shunt circuit is 0{)en; but
when the hammer end of lever T is raised, and so long as it remains
so, the phone is shunted. This automatic shunting of the phone
during the time when the lever is "breaking" the charging cur-
rents of the coil, obviates annoyance from the discharges of magnetic
coil M to the oj)erator who is sending in proximity to the home
phone.
WIRELESS TELEGRAPHY.*
HISTORY.
The practice of signaling through space may be traced back
through the ages to the beginning of the history of mankind, for
the earliest records indicate that the survival of the fittest sent
powerful sounds from his lips through the air, and that for longer
distances he employed fire to propagate light waves through the
subtler medium of the ether.
As civilization advanced, the necessity of transmitting intelli-
gence to a longer distance and with a broader interpretation, led
to the introduction of many forms of intercommunication, made
possible by the invention of writing and the use of semaphores, but
these were not without their special limitations since the former con-
sumed time in transportation and the latter could be operated only
where a direct visual line between the sender and receiver •was
possible.
With the advent of experimental electricity and the knowledge
of its properties for traversing long lengths of wire with practically
the speed of light, came the burning desire to utilize it for the
transmission of messages, but we need not here dwell upon the
remarkable events that gave us the electric telegraph, the sub-
marine cable and the s])eaking telephone, for these do not form a
part of the subject herein treated; but instead we shall follow the
evolution of that allied and newer branch of the art called wireless
tele(/raj>/ii/.
For at least a century before an electric impulse, representing
a signal, had actually been transmitted and received without inter-
vening and connecting wires coupling the two opposite but com-
plementary instruments, the subject was a favorite one with the
physicist, and it is not unlikely that the ancient Greeks who wit-
nessed Thale's experiment of transferring energy from electrified
♦Prepared especially for the Cyclopedia of Apr
A. Frederick Collins, Author of '* Wireless Telegraphy
and Practice."
881
WIRELESS TELEGRAPHY
amber to neutral paper, dreamed of the bridging of greater dis-
tances by the same mysterions influence.
The first recorded instance, however, in which a definite
scheme was proposed having for its object the telegraphing without
wires by electricity, was that given by Silva, a Spanish physicist,
who read a paper " On the Application of Electricity to Telegraphy"
before the Academy of Sciences on Dec. 10, 1795, at Barcelona.
In this prophetic memoir, he advocated that a given area of earth
be positively electrified at Mellorca and that a similar area of
earth be charged to the opposite sign at Alicante; the sea connect-
ing these two cities would then act as a conductor when the electric
difference of potential would be restored, and by a proper translat-
ing device the transfer of energy could be indicated.
Conductivity Method. The first experiment resulting in the
successful transmission of electricity between two j)oints without
an artificial connection may be as-
/ .^ ,^' — V, cribed with considerable certainty,
::r"-^^-^^^N "^ \ to Steinheil of Bavaria, who made
'''^~"^"* \ \ X % tlie important discovery that the
earth could be utilized in place of
the usual return conductor of a
wire telegraph line. After ascer-
t;iininop the fact that current trav-
ersinor such a circuit flowed in
V. ~ \ ^>\~ '- -''.'/ i u n u inerable cu r ved 1 i nes between
"---"' tlie terminals of the line wire eni-
Fi^'. 1. CniKiuctivity MHhod. bedded in the earth, Steinheil then
found that I)y ])lacing a similar |)air
of earth plates, 8, 3' and 4, 4', likewise connected together and
having a galvanometer 5 interposed in the circuit, parallel with
the first, which included a battery and a key 2, as shown in
Fig. 1, there was a sulHcient dis])ersion or leakage of the current
from the one to affect the other to the extent of deflecting the
needle of the galvanometer. The dotted lines represent currents
in the earth.
These y)ioneer experiments were made in 1838, the discoverer
having ])roven it possible to obtain calculations at a distance of at
least 50 feet, this forming the basis of what is now known as the
/ ' • 1 ' ' I . ' ' • I L
332
WIRELESS TELEGRAPHY
(Hsjpersion or conductivity method of wireless telegraphy. This
mode of transmission has been thoroughly tested by many investi-
gators since its inception until 1S92 when Preece, of England,
obtained results from Lavernoch Point to Steepholm in the Bristol
Channel, a distance of nearly five and a half miles.
The invention of the telephone receiver by Bell opened fresh
fields in the realm of sicrnaliiig through space, owing to its extraor-
dinary sensitiveness; and by means of this remarkable instrument
an effort was made to determine the inductive effects of telephone
circuits. This was attempted in 1877, by Saches, of Austria, who
arranged two parallel circuits, each forming a loop 120 meters in
length with a distance of 20 meters separating them. A current
from three cells was employed for exciting the first circuit, and
this was found ample to j)roduce distinctly audible signals in the
telephone receiver.
Induct! vity Method. Following these researches, Trowbridge,
of Boston, carried on a large number
of experiments in electromagnetic
induction, the arrangement of which
is illustrated in Fig. 2. In this
method, two coils of wire 3 and 4,
formed of many turns, are placed in
parallel, or in a plane with each other ; rig. 2. luductivuy Method.
a battery and key 2 are connected
in series with one coil and a telephone receiver 5 in the comple-
mentary loop of wire. When the coils are adjusted several yards
apart, the *Mnake and break " of the sending circuit by the key
causes the electric energy to be transformed into curved magnetic
lines which thread through the receiving coil producing in the
latter an electromotive force proportional to the rate at which they
link with it. Trowbridge believed that this inductive method^ as
it is termed, could be made to operate effectively between vessels
separated by a distance of at least a mile.
Electrostatic Method. A curious coincidence is now pre-
sented in the electrostatic method evolved (patented and experi-
mented with by Dolbear, of Boston, in 1880) since it is an almost
exact counterpart of that proj)ose<l l)y Silva in 1795, for the anna-
ratus of the former is designed to fulfill the precise fi
d33
WreELESS TELEGRAPHY
reqaircd by the hypothesis of the latter, that is, the charging of
the earth at the sending and receiving stations to opposite signs.
The sending instrument, indicated diagrainmatically in Fig. 3,
consisted of a small induction coil 3, the primary winding of which
was connected with a battery 1, an interrupter, and a key 2, while
the terminals of the secondary coil were connected with a condenser
4 and the earth 5, respectively; the receiver was formed of a con.
denser 10, one side being connected to a battery 9, which in turn
r^'
11
(m-^
A
o-s-
6
Electrostatic Method.
Fig. 3.
led to a second condenser 8, thence to a static telephone receiviT?,
the terminal connecting to a plate 6 in the earth. Edison followed
with a somewhat similar arrangement in 1891, except that he em-
ployed ajrial wires with plates of metal at the top, which served as
capacity areas, instead of the condensers described above. Tliere is
no authentic record of the performance of either of these devices.
Electric Wave Method. All the methods described above
have their especial limitations, and these are so tightly drawn that
none of them have ever approximated a utility of the slightest
commercial importance; work, however, continued along these
lines, but during the past fifty years an entirely new method has
been unfolding, a method at once marvelous in conception, beauti-
ful in theory, perfect in formation, and startling in its final results;
this is the vlcctrfHiiiff/nctlc mave method.
The fundamental principles upon which this method is based
may be said to have begun in 1078 when Iluygens, aDutch niathe-
«M
WIRELESS TELEGRAPHY
matician, conceived the hypothesis that all space not taken up by
gross matter was filled with a highly attenuated subtle substance
named ether, and by which he was enabled to account logically for
all the phenomena of light.
Faraday, in 1845, not only believed in Iluygen'sluminiferous
ether but demonstrated by ex|)eriment that electric and magnetic
forces were propagated through the same medium. This physical
evidence was resolved into a mighty theoretical system by Maxwell
who determined mathematically the relations between all the
varied phenomena juvsented by. these different, yet allied, sciences.
The last link in the chain necessary to establish absolutely
these great fundamental truths was supplied by Hertz, of Karlsruhe,
Germany, in 1888, who succeeded in producing electromagnetic,
or, as he termed them simply, electric waves, which followed every
known law of light, such as rectilinear propagation, refraction,
polarization, etc. The electric waves discovered by Hertz are, of
course, much longer than those of light, and being much too long
Hertz's Kloetromagnetle Wave Method.
F'lfr. i.
to affect the eye, they are invisible; every known test, however,
only served to offer additional proof that the Hertzian waves are
transverse vibrations in the ether, and that they are propagated
through spac(^ at a velocity equal to that of light.
The a{)paratus Hertz emj)loyed in producing and receiving
electric waves is shown in Fig. 4. The sending apparatus A com-
335
6
WIRELESS TELEGRAPHY
prises an induction coil 3 energized by a battery 2, and operated by
a key 1; the high-tension terminals are connected to an oscillator
formed of two brass spheres a, a attached to large metal sheets J, J
by brass rods; this is the arrangement by which the waves were
radiated. The spark-gap is show^n at d. Tlie receiver B is simply
a loop of wire with the free ends brought nearly together, and when
the waves impinged upon it, their presence was indicated by the
passage of minute sparks in the gap formed between the ends.
Here then was a complete apj)aratus for fulfilling the condi-
tions of signaling through space without wires; but many improve-
ments were needed before an efficient system could be produced
capable of operating on a commer-
cial scale. For instance, the metal
ring receiver of Hertz required too
much energy to affect it at any great
distance, but this defect was over- .
come by Branly, of Paris, who found,
CYoctric Ball
o o
BoLttery
Pig. 5. Popofl's Receiver
FiR. 6. Marconi's Transmitter.
in 1890, that metal filings enclosed in a tube, termed by him a
vfnUo -conductor^ were marvelously sensitive to enfeebled electric
waves impinging uj)on them. In 1S95, Popoff, o'f lUissia, com-
bined with a cohertv 1, as Pranly's detector had been re-named,
an electric bell, the hammer 7 of which also served as a tapper
to de-cohere the filings, a sensitive relay and a local battery 5,
as illustrated in Fig. 5; one terminal of the coherer was connected
to a rod 2 elevated in the air while the opposite terminal 3 led to the
%aft
WIRELESS TELEGRAPHY
earth. This formed a self-acting receiver, but was used by bim in
the study of atmospheric electricity. The spark-gap is shown at 4.
This was the state of the art when Marconi, of Italy, in 1895
began his experiments wich a view to long-distance transmission.
In his earlier trials in Italy, the young man employed the induc-
tion coil and oscillator in transmitting, just as Hertz did before
him, but later he ascertained that if one side of the oscillator was
connected to a wire 1 suspended in the air, and the opposite side
was connected to the earth 2, as in Fig. 0, the energy would be
radiated in the form of electric waves to much greater distances
than was possible with the simple oscillator designed by Hertz.
The receiver used by Marconi in connection with his transmitter
was very like that of Topoff except that he added a Morse register
and adjusted the mechanism to imprint the received impulses in
dots and dashes in accordance with the simials transmitted.
Tlie results attained by Marconi bring the history of wireless
telegraphy to the time of its commercial adoption in 1897. Since
then there has been a multitude of workers, all of whom have bent
their efforts to eliminatins: its defects, and these men and their
work will lind f place in the succeeding pages of this text.
PRINCIPLES.
Ether. The lirst principles uj)on which the theoretical struc-
ture of wireless telegraphy is based are identical to those evolved
by Faraday and Maxwell to account for all the phenomena of light,
since in either case the waves are electromagnetic in character and
are transverse vibrations in and of the ether.
In accepting the hypothesis of an all-pervading substance,
termed the electromagnetic medium, it is neither necessary to
know its essential form nor its composition, for just as sound may
be sent through the air without a knowledge of its constituent
parts, so also may electric waves be propagated likewise through
the ether. But if the laws of either sound or electric waves are to
be deduced then some of the characteristics of the medium in which
they are set up and through which they travel must be known, and
in working out the system of sequences that governs the action of
light, mathematicians come to conclude that ether is a highly
attenuated substance, that it possesses elasticity and rigidity, that
337
WIRELESS TELEGRAPHY
It has density and that it is incompressible. Thus it will be
observed that ether is closely related to electricity yet it partakes
of some of the properties of gross matter, and while Sir Oliver
Lodge has pointed out that electricity may be a product of shearing
the ether, J J. Thomson has done much to indicate that corpuscular
matter is of etheric origin.
The* constants of the ether have been determined empirically
and its specific inductive capacity is taken at 1 which is expressed
symbolically by the letter K, while its density is assumed to Ihj
about 936 one-sextillionths that of water and is represented by the
Greek letter fi. Now /x divided by K equals the velocity of light
and all other forms of electromagnetic energy or ^ = 186,500
miles per second.
Air Waves and Electric Waves.
Fig. 7.
Electric Waves. Undulatory, or wave, motion through the
air and that taking j)laco in the ether are different in that the first
consists of longitudinal thrusts due to one molecule of matter
striking another, while in the latter the motion is caused by trans-
verse vibrations taking place across the line of propagation due to
polarized stresses in the ether as shown in Fig. 7, A and IJ resjK*ct-
ively. Ii'/ertrom(/fj/n t!r^ or to use the common abbreviated term,
clertrlr v^aocfi^ are, however, like sound waves in a number of
limiting cases, as for instance, they may vary greatly in length and
yet the speed at which they travel in their resjHJctive mediums
remains constant; again, just as in air, waves of different lengths
produce different tones when they impinge on the ear. waves in
ether, of very short but varying lengths, reflect dissimilar colors,
the violet beintr the shortest and the red the lonuest visible waves.
An electric wave a little loncrerthan the red is invisible to the
eye, but its effects may be felt in the form of radiant heat. Ifetween
the short, radiant heat waves and the long electric waves produced
saa
WIRELESS TELEGRAPHY
by the disrQptivB discharge of an electric epartc there is a wide gap,
jet they are identical except when their lengths are considered.
Because they are invisible and the senses of man incapable of
perceiving them except by the aid of some exterior physical means,
the existence of electric waves iiad not been proven by experiment
until 1888, when Hertz demonstrated their characteristics, showed
a method for producing them, and a simple means by which they
coold be detected and their effects observed.
Electric waves of whatever length are the result of charges of
electricity in rapid motion; if the charge of an atom is set into vibra-
tion it will emit a very short wave length, say 271 ten-milliontha
of an inch which is that of red light, but if a pint Leyden jar is dis-
charged its oscillations will send out waves 50 or GO feet in length.
Electric Oscillations, i^tncu all waves in ether are dae to
transverse vibrations tbey should follow the same physical laws,
.J I,
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' —
J
Pnlltrlznl Elwlrlc WaveB.
l-'iK. 8.
and to prove that the long electric waves were identical with those
of light, Hertz reproduwd all the known optical experimeDts;
showing that waves from bis oscillator traveled in straight lines,
by reflecting them from the siu-faces of metals; that they could be
refracted, by passing them through huge prisms of pitch; he
formed shadows by intercepting them with his own body and other
objects; and finally he polarized them by means of a grid made of
a number of [laralle! wires as shown in Fig. 8.
Disruptive Dischat^e. To set into vibration the electric
charge of an atom for the purpose of producing light, it is usual
10 WIRELESS TELEGRAPHY
to employ heat, but to obtain long electric waves for experimental
purposes or for wireless telegraphy there is only one method known
to science and that is by discharging a charged Leyden jar or other
oscillator formed of opposite metal conductors B, B' and separated
by a spark-gap as shown in Fig. 9; this form of oscillator is
© 1 ° °^ ®
Open Circuit Oscillator.
Figr. 9.
chargeil by an induction coil or other high-tension apparatus.
When the spark takes place, the opposite sides or arms of the
ost^'illator discharge into each other, thus e<|ualizing their diflFerence
of |H>tential through the s|>ark or disruptive discharge.
Tlie moment the sjvirk occurs, the static charge of the oscilla-
tor is changeil into kinetic energy' which surges through the system
to and fro, like a straight steel spring
suddenlv released; but while the enercr>-
of a spring is damped out in the making
/I of air waves, the electric oscillations are
f 1 /\yy^.^ traiisforiiuxl into electric waves in the
1/ ether, but in Unh cases the enercry de-
creases in gei>metric progression from
inaxiiiia tozeroasuescrn>eii m the curve,
FiiT. UK
For this rt-ason tlit* wavt»s ean In* eniitteil only nerii^icallv.
and U*fon.» another tniin of wavt»s can l»i» starteil, the oscillator
must Ih* nvhariTiHl, ami this rvtniiivs lime. The cliaririnir is done
antomaticaliv bv havjiiix i1k» terminals of an induction coil ct>n-
nev^'titl with the arms of the oscillator so that as Si>on as the c^scil-
latory currents si*t up by the sj^iirk have damj»ed out their eiierg\*
in electric waves, the hiirh -tension current ireueratt^d bv the coil
will instamiv nvliarixt* the iiscillator to its nuiximum caiwcitv.
• ~ I •
when it will aijtiiii )»rt-ak dowii the thin tilni of air and the cycle of
o{ieniiii»ns will l»e rr|vateil.
To determine the leuixth of an electric wave, it is necessan* to
know not only its vek^'ity. which has In.'en previously calculated.
^M^
WIRELESS TELEGRAPHY
bat also the jwrioJ of OBcillation of tlie system radiatirif^ tlie waves;
the latter depends upon the constants of the oscillator circuit, that
is, its capacity 0, its indnctance L, and its resistance R. These
factors are Id turn governed by its length and other dimensions,
and the time of oscillation T may he found by the formula T ^=
2 R V LC; the resistance may he considered negligible in a
simple open circnit where oscillations are of sufficient frecjuency
to send ont electric waves. The lengtli of the wave is easily fonnd
by dividing the velocity d hy the miirilier of wtivfs //, or — = the
wave length.
Electric waves
emitted by a simple
oscillator of the
Hertz tyje give rise
to free spherical
waves in space, and
the writer has ever
advocated the theory
that this is the form
of waves radiated hy
the serial wire and
earthed -oscillator
system of a wireless
telegraph transmit-
ter, while Blondel,
Taylor, and Fesseri-
den have promul-
gated a theory in Fig. ll. Electric wave Propanatloli.
which the waves are
as8umt.-d to he hemispherical or half-waves which slide over the
surface of the earth or sea; the illustrations, Fig. 11, A and B
respectively, show graphically tbewe two view-points.
Having ascertained the process by which low-voltage direct
currents are trjinBforme<I into currents of high frequency and
potential, and bow these oscillations radiate tlieir energy into space
in the form of electric waves, the final fundamental principles
inTolre their reception and indication. While all insnlating
» ■''-
■'•' '^.•- i«-ij:'
:^:..-ri4:'^:
-t-^ .*-
L^
1»
J. ■
.M«l '
k* *
rr
^hMM^
a. -Y«i>- r-
- * ft * «^
^4. •» "Ha;
— . -r I -^ — ~-r.
V*:
•;i:
~" , ,, • "XT' " '
■ - --«•
.L
.-'~ ••r'l'".-"' f"~ • "*
• - u'^ I' ■ r . I ».;^-.
^" ■ ■ ■ •
- ••-
• ■ I
, I .
■j
.\
ii. - :u..r-:.
I- ' — ,*" J ..-•- ~\"'.^.i'^ i
WIRELESS TELEGRAPHY
13
single cell E, and a galvanometer, or a telephone receiver F, as in
Fig 13; D and D represent the capacity plates and B, B the
internal circuit. It is obvious that when the filings cohere, the
current from the cell will readily flow through the circuit including
the galvanometer, its needle will then be deflected and it will so
continue until the filings are restored to their normally high resist-
ance, which condition may be easily attained by merely tapping
the tube with a pencil; in practice, the decohesion of the particles
is usually effected autoriiatieally by an electro-mechanical device.
In commercial wireless telegraphy, the atrial wire at the send-
ing station is connected with the earth through the medium of a
spark-gap, as A in Fig. 14, which constitutes the circuit wherein the
current oscillates. At the receiving station, the coherer is connected
to the lower terminal of the vertical wire and to the free end of the
wire leading to the earth, as indicated at B, forming the resonator.
Marconi ascertained that the energy of the waves did not
diminish in intensity when the distance w^as increased if the length
OO
O
o
|2
J
■^E^
r
H-0J
Fig. 15.
of the ferial wires were increased as the square of the distance, that
is, by doubling the height of the wires the waves would be trans-
mitted to four times the distance, the initial energy remaining the
same. These are the first principles of the action of electric waves
and the operation of the earliest and most simple forms of wireless
ti)legraph systems, while those of a later and more complex nature
depend on electrical resonance and electro- mechanics.
It has been previously shown that the length of an electric
wave depended upon the coetticients of the oscillator, and it has
also been pointed out that a resonator in the field of force would
have oscillations produced in it by the impinging waves.
843
U WIKELESS TELEGRAPHY
Resonance. Now it is well kDOwn that when an oscillator
and a resonator have exactly the same electrical dimensions, that
is. inductance, cajwicity, and resistance, the currents set up in the
rt*souator will be much stronger than where the circuits are not in
rt^souance with each other. By applying the laws of resonance to
wireless telegraphy, inventors have striven to produce the same con-
ditions on a commercial scale that have been obtained in the labora-
tory in onler to provide a method capable of signaling selectively.
The oscillators and resonators previously described were of the
"j»tti'C*/'c»i't tyjie, having two oppositely disposed arms; but for
r\*sonance etfects c^'^st'l-L-'i^-utt oscillators and resonators, illus-
tniteil diagrammatioally in Fig. 15, at A and B respectively, give
the maximum results. Conversely, open-circuit oscillators are the
Ivst nidiators of electric waves, damping out the energy in two or
thnv swiiiiTs while the closed -circuit type permits the current to
oscillate for a long jvriod of time and consequently very feeble
eUvrric waves are eiuitied. Uence wireless telegraphy systems
with ojvn circuits srive the l>est results over long distances, but as
those art* co-resonanr, in vinue of the capacity of the earth with
whioh thoy are connected, every receiver is in syntony with every
rnmsmitter, and therefore they have
: ^^ individual selective properties.
Tile eiTorts to combine open and
o.ost-i circuits to obtain the advan-
::-.^vs of lonvT-distance transmission
.,1 st'!t-^-::ve sitrualiucr has led to
:i::y ::.i:enious relations and thepro-
•:::.:: j:: of several syntonic systems.
r_-
APPARATUS.
> _ . ■
. ,1..^ .V
T:.r :ii : tirurus comprising the
lt ei'iisists of a source of
oltvtrov.v^:''. '. :\v\,v, a " .-lu^v . r ivv.a: . \ :i kt-v. an induction coil or
• • •
:rin-:\^r:.-, :\ :i:.v; ar. o<v-i.:-.:.'r. Ti.e :i' ; !::i::v.V5 formintja receiver
of ti.e si-:.j!c<: :y:e i:o'.::io :» a:.--,- cvtrcior, a ceil, a telephone
rtwivtr. rr. i a rvsor;i:-^-: '••. tie tcirirr :%:.J more «.%>:iiplex systems.
s relay, a :;ij«jvr, a:.vi a Alor>e rii:::?:^ r w^re added-
944
WIRELESS TELEGRAPHY
IS
Induction Coll. TLere are two incthodB of transfortiiing low-
[Hiieiilitil intu tiigh-pntt'iitial currents. Tln> Ural ie by iiifaDS of
■ n iiiiliiftitin '■'•H ami tLo second is liy using a tr-UDtformer, Tbe
iiidiictioii coil dilFert'iitiuti^a this npparatiis from that known
I tranefonner; the former Iwing supplied witli an interrupter
[ a condenser iind energizetl by a low-voltage diretit ciirrcni.
Idle the latter has neither of tbe derioea just cited and is ojMTa'ed
I low-voltagH alternating current.
Tlie iudiu'tion foil, Fig. Ifi, is niado up of an iron core 4,
fined of a number of soft iron wir«H having wound around them
I layers of ht-avy wire o, called ihv jntninnj oil or t ri/hirliir,
9 end of the primary leads direct to the battery 1, the other con-
Bting with an interrupter 3. a simple mechanism for automat-
llj making and breaking the current, which is in tarn connected
» opposite pole of the generator. Around the "make and
ink" a condenser 2 is connected in shunt, assuming the contacts
» intprrnpter to be closed, but when ojjen the condenser is iu
» witli the jtrimary coil.
16 WIRELESS TELEGRAPHY
Onteitle tht? ])riiiiar^ coil mid well insulated from it is tha
0ei^yiuIuTy coll tl, biiilt up of several thousaud fwt of very fine win»
and thoroughly insulated with a compound of reaiu aud beesvm.
Thtf termiiialB of ibe secondary connect to the opposite arins 8, 8
of tJie oacillator. In operation, when the primary coil is euer^zwl
by the cnrrent, the core becomes
uiajjnetized and it>agnetic flux sur-
rounds the coil in a direction par-
alleling its axis. Tliis causes a
current to be induced in one direc.
tion in the secondary. When the
\~\\ £ < S3 interrupter breaks the circuit, a
Y V ^ T current ia induced in the opposilo
I ^ ^ 4- direction; this is repented auto-
matically several hundred times
[KT minute resulting in a high-teu-
sion alternating-current flow at the
terminals of the secondary coil and
which is utilized for chaining the
oscillator. Fig. 17 is a photographic illustration of an induction coil.
Transformer. In n later method, shown in Fig. 18, the primary
winding 2 of an ordinary commercial oil transformer is coaoecttMl
Fig. 18. Transtormer TrAaxll
'^jtsJ^iBr^.^
to the terminals of an alternating-current generator 1, of say, 60
cycles and 500 volts. The ends of the secondary of the coil 3 are
joiutnl to a battery of Leyden jars 4, 4, When in action, the
WIRELESS TELEGRAPHY
n
reversals of the t;iirreiil in the primary of the transformer induce
alternating currents iu the secondary coil having the same puriod.
but enormonsly increased potential, the tranaformer giving alx)ut
Ti-leerapb Key.
25,000 volts at the secondary terininala. This low- frequency,
high-potential current charges theLfsydcn jars to the limit of their
capacity, when they discharge through the spark-gap of the oscil-
lator, n is the earthed terminal and 7 the rerial wire.
Keys. In order to hreak up the current arbitrarily into dots
and dashes, a telegraph key is interjiosed in the primary eircnit;
the keys nsually employed are constructed like an ordinary tele-
graph key, init are very much larger, like the one in Fig. 19, as the
cnrrents to Iw broken are often in excess of 746 M'atts or one elec-
trical horae-power. Another form of key, designed to be operated
with the rapidity of the ordinary Morse key, is constructed bo tiiat
the heavy curreut id broken under oil.
IS
WIKELESS TELEGRAPH!
The spark-gap, dividing the aerial wire and the earthed ter-
minal ia nsually formed of two spheres or discs so that the length
of the disruptive dischai^ may be reguLited at will.
Wave Detectors. Of the reoeivincr devices the wave detectors
are the most inipiortant. These comprise two general classes; those
of the first class are v^Atage-operatt:*! and are of the coherer type,
in which the resistance is lowered by the potential of the oscilla-
tions, and the anti -coherer type in which the resistance is increased
by the oscillations. Those of the second class are cwrrt «^-/yx nrtt*1
detectors where the current strencrth of the oscillations varies the
resistance of a fine wire or liquid through heat losses by radiation.
A coherer of the filings type is shown in
Fig. 2<>; two silver conductor plugs with plat-
inum wire tenninals are forced into a piece of
glass tubing leaving a space or pocket for the
Fit: 21. F^'.-^iKU-n
lJ;irr»M.r
Fiu. 23. Polanztti K»*lay.
fiUncji? iiiarlt* with a coarse file from nickel a«<l silver in ilu» proix)r.
tions of 00 j)er (vnt of the former and 10 j)er cent of the latter; the
tube is then adjusted, tlie air is exhausted with a niercurv pump, and
the tip sealed off. Ant'i-cnh, lu r>i are made by substitutiui; oxide
of lead for the ordinary filin<rs l)etween the eontluetor iducrs; the
current from the l(K*al cell causes minute thn»ads of metal to l»e
built up between the Jjlut^s by electrolysis, and these are <lisrupted
by the electric oscilhitions. Atiftt.mht r* rs an* those that m^ no
Uij)ping to brin<^ them back to their normal resistance after the
effects of cohesion, l)Ut are restore*! automatically in virtue of their
inherent properties.
348
A l/<trrvtf.f or ciirrt<nt-openitn<i wave detector is illustrated
in Fig. 21 ; it is made of a little loop uf silver wire having h diairi-
eter of .002 inch with & core of plHtioum wire 1 drawn down to
.00006 inch in diameter; the tip of the silver loop ia then dissolvM
away exposing tlie plalimiiii tilament; ihia done, the ends of tb(
li>op are attached to the luadiiig-iii wires 2, 2 sealed in a glass liuln
■which IB liimlly enclosed iu a ailver case. The silver shell is show
«t y and the glass globe at 4. A new form of barretter ein-J
ploys a very airiall eolinim of nitric acid and a minute platiiiiintl
I immersed in the liqnid ao that the resistant-e of the latter is I
concentrated closely to the point. Anti- and auto-coherera andl
barretters can be used only in connection witli a telephone receiver, J
I'ig. 23.
IT tlteir resistance variations are too limited In |H-rmit the n^Ifiy^
Hlo U» actnatcd; the tilings coherer ia the only tyjM* of detector]
Piknown that can l>e emjiloyed in combination with a relay. 1
Relays. Of relays there are several forms, but tho jxrltirisedM
mrnla-j/, showu in Fig. 2*2, ia ihe only one sensitive enuiigh to bol
1 in eonjnnction with a cuhei-er for long-diatanc*? work. Al
■ polartJced relay is providi-d with a [lerrnarieully magnetized aririk'
iJlure 3 instead of the aoft iron one of the ordinary inslrnment; it
a two magnets, one an electromagnet 2, 2 and the other n |ier.
WDt magnet 1, 1; by this arrangemeot, when no current ig
20
WIRELESS TELEGRAPHY
pasgini; tbron<rb the coiU of the flMMrotnagnet, tlie poles will 1>e
Dortb; but wlieQ the cnrrvDt dows. oiii? of the poles is more
Etronglv iii>i>riietized while tlie other cliKiir^s its polarity to sooth.
There are several luoditicatiuiis of the polarized relay, bat their
principles of o|>er»tiuii are the same. Fig. 23 shows the type used
in win-less-tele<rraph receivers.
De-Coherer. Xext in iiiiportance is ih© tapper, or de-coherer,
for restoring the filings after tlie oscillating current has cohered
them. The con .-^t met ion of a tapper is much like that of the ordi-
nary electric bell with an au.
toiuatic contact breaker; but
different from the latter in
that the Lauimer of the tap.
{ler has a very low time con-
stant so that its vibrations
can l>e very rapid. Snch a
tapfter is shown in Fig. 24,
ami is, it will I»e observed,
provided with a devii-e for
siipjiortiiig and wljnsting the
tniliercr so that the strength
of the stroke of the Imiiiiiier
niiiy Ih- varitnl at will.
There are several instru-
nri'tits for tninslaliiig the rt.>-
(.■I'ivi-d inipntses into readable
Morse, as for instance, the
pdvan<iiiifter, the telephone
ri'ceivfr, the ordinary sounder
giiLiI tiic Morse register. The
>ll kiioMii tliiit they need not
eiiiiilc<vi'<l where it is desirable
tliR'o former appliances
be descriJM-d here. The
to have a |)eriiiiirieiit reconi uf tlif receivdl
idea imiy be g!iiiii-<l of its c-onstnu'tion ami
to Fig. h.
Register. Tlic r.jfister is an eh-elro-meclianical apparatus
ciimjirising n spring motor, t!i>' jmrjKi.-'e of wliich is to draw a tajie
of pajRT nnili-r an inked disc ojH-ruted by an ehH:tro magnet.
iicswige. and n general
ijiemtion by referring
When a current is passing through the coils of the electromagnet^ 1
the inked disc, which in att&clied to the armature, is drawn intov
contact with the paper and held there until the current e
this way the dot and dash
code is formed and im-
printed on the tape.
The above appliances
are the principal ones mak-
ing up the ordinary wire-
less telegraph systenia, hut
there are a number of othep
and minor devices utilized
to render more accurate the
working of the iustru-
mente. One of these ia the
clinking ceil, made of a
long, fine insulated wire
doubled back on itself and
then wound on a woodun
epijol aa shown in Fig. 2)i;
these coils are interposed
iu the local circuits of the
receiver to cut offhigli-fre-
WIRELESS TELEGRAPHY
qiieney currents wliich may be set np by eparking. either ii
culierer or between the relay contat-tB,
Oscillation Triin.sJ'iiniiers are need in many systeins of receat
desigij; these are constructed for etepping up or down high-fn--
queiiey and high- potential
electric oscillations, itiid
are employe*! in liotli tlic
Si'iidinf/ anil the receivinir
(.-iivuita. The transmittiiif!
transformera have au in-
diiirtor or primary of thrve
or four turns of hea\'y wire
wound nuti'iili' tlie ge<ron(l-
ary ooil which la formed of
IJiirty or forty turns of tim-
wiro. when the coils ar*'
llien immersed iu oil; two
views of a typical traus-
former are iltnstrated in
I'.iim UIgb Polvntlal TraDsfi
Fig 27.
Fig. 27. Smaller traneformers are often employed in the receiving
ciiviiita, and consist of simply a primary and at
lateid in the usual manner.
WIRELESS TELEGRAPHY 23
Inductance coih and ctpnihn^ers are also largely used in wire-
less telegraph practice for the purpose of increasing the inductance
and capacity of the oscillators and therefore the waves emitted by
them. They are also useful for tuning a closed -circuit to an open-
circuit as well as to obtain resonance l)etween the transmitter and
receiver. Inductance coils are formed of a larw numl>er of turns
of heavy wire with sliding contacts so that any desired value of
inductance may be procured. Condensers for providing suitable
caj)acitie3 can Ix? made up of Ix^ydt^n jars or metal sheets immersed
in oil where high tensions are emj>loveil, but in receiving circuits,
those of the ordinarv mica tviK.* are used. Fiiiallv where detectors
of the coherer tyj>e are utilized a metal case is providiM.1 which
encloses not only the coherer but the relav, tap|KM', and local cells
leaving the register alone expostnl. The object of the scrtvning
box is to protect the delicate and sensitive instruments from the
powerful oscillations of the transmitter in the immediate vicinity.
AVith an understanding of the subsidiary aj)j)aratus compris-
ing the component parts of transmitters and receivers and the
principles involved, it is now easy to follow the intricacies of the
various systems that complete the art of wireless telegraphy.
SYSTEnS.
The many different systems for sending messages through
space without wires may be classified under two general heads,
namely, those designed without regard to selectivity, and those
where electrical resonance has been broucrht to bear in onler to
prevent interference. Those of the first class are termed non-ayn-
tonic and those of the second class syntonic systems.
riarconi. First form. The first comj)lete system of windless
telegraphy was conceived and patented by William JIarconi, who,
by employing greater power, larger radiating surfaces and improv-
ing its details, was enabled to increase its effective range from ;UH)
feet to 2,000 miles. His first apparatus w^as simply an o|K»n. circuit
apparatus of the non-syntonic type as a reference to the diagram
Fig. 28, will show.
The transmitter A includes an induction coil 1, energized by a
battery 2, the current being broken up into the Morse cinle by the
key 3; the coil is equipped with a spring interruj)ter i; the ter-
r%m.€%
24
WIRELESS TELEGRAPHY
minals of the Becondary are connected to either side of the spark-
gap 5, which witli the atrial wire G and the earthed temiinal 7,
forms the oscillator system. The receiver B is made up of a
coherer 1, the polarized relay 2, and the cell 3, all of which are
connected in series and comprise the first internal circuit. The
second internal circuit includes the contact points of the relay 2,
the Morse register 4, the battery 5, and the tapper 6; the tapper
^^ o o
5
J
iJ
HI
4-
10
Diagraiii of (l^i^iIlal Marconi TraiismllttT aud H«*celver.
Fig. 28.
and register may he in t^eries or jmnillel; the jerial wire 9 and the
earthed terminal 10 form the resonator. Choking coils 7 and 8
are placed in tlie lirst internal cireiiit hetween the coherer and the
relay to ])revent oscillations from the resonator from wasting their
energy in the relay coils, as well as to j)revent those originatinir at
the contacts of the relay from actin^r on the coherer. To the frtv
ends of the atrial wiri»s were attached laim» sheets of metal termed
caj)acity areas, l)ut these are no longer deemed necessary. A pho-
tograph of a Marconi station at Hahylon, Long Island, is given in
Fig. 21).
Lodge. To Sir Oliver Lodge is due the credit of haviniT
evolved the first syntonic electric wave aj)j)aratus haseil on the laws
of resoiianc(», and since nearly all the succeeding systems utilize
these principles a brief review of his arrangement may prove use-
^^%
UoTconl Wireless Telegrapb Sfstum.
Fig. 29.
ftil. In thia systotn, instead of the usual serial and earth wires,
two conical metal capacity areas are Bubstitiited; in Fig. 30, A, 1,
and 3 represent the areas wliich are charged Ijj- an induction coil
I.odgB Synionk' Systpiii.
Klg. 30.
26
WIRELESS TELEGRAPHY
3 and which discharge through the spark-gap 4; the value of
capacity can be changed by means of the adjustable condensers 5
and 6; the values of inductance are also made variable by the coils
7 and 8; the resistance of the circuit is negligible; it is obvious
that a wave of predetermined length may now be obtained since it
depends on the period of oscillation and this on the inductance and
capacity of the circuit. The capacity areas are insulated from the
post which supports them. The receiver B is formed of two similar
capacity areas 1 and 2, and these are connected through the pri-
mary of an oscillation transformer 3, the secondary of which -t
leads to the coherer 5; the relay, tapper, and roister are not
shown but operate as previously described.
Dia^raininatio VIow of Slaby-Arco Multiplo-Tuned Wireless-Telegraph
Traiisinliier and Keceiver.
Fipr. 31.
The 5laby-Arco System, of (Tormaii manufacture, is now
extensivi'ly iist'd in tlio UnitiHl States Navy, and though retaining
the lerial wires and earthed terminals it is based on certain res-
onance phenomena as will bo seen. When an oscillation is set up
in a wire, it will emit a wave four times its own length; if the wire
is connected directly to the earth, as shown in Fig. 31, the greatest
amplitude will be at the free end of the wire while the nodal point
will be at the earthed end as indicated by the dotted lines. If, in
the transmitter A, the earthed radiating wire 1 is connected to the
spark-gap 2 and to the earth 3 through the inductance coil 4 and
the condenser 5, then a coml)ination of an open and a closed circuit
^&^
WIRELESS TELEGRAPHY
27
is formed. Biiice the earth serves to elose tbtt circuit conlnlDing the
spark-gap. Asgiiming ttiat tlie iiidiietauee 4 and the eiijiavity 5 is
ei|nal to that of the wire C, then oecillaliotia set up in the former
will be impressed upon the latter which will radiate the energy iu
electric wave^. In tlie receiver B siiiiilur conditions prevail; 1 is
the receiving lerial wire or a/iU'itii'i, the oscillatiou having it^
greatest loop at rt, 2 is the nodal point forming an open-circuit
resonator; a closed resonator circuit is forinod by the inductance
1-8, the coherer 4, condenser 5, .and the earth 0; the point oF greatest
~ mplitudu of the oscillations is arranged to correspond with the
»herer which ivceives the inaxiuiuni potential n
lotted lines. A photograph of the complete ;
idicati-d in the
eiiown iu
narwjni. St:a>iid /»-■///. In
problem of selectivity, Marconi prod'
Hvking a solution for the
;ed a second system in wliich
he eliminated the lerial wire, as iu Lodge's scheme, but since
grounded terminals were essential to long-distance transmissio
he retained these features. Fig. .S3 is a diagrammatic view of tha
rita
db
28
WIRELESS TELEOBAPHT
5 4
n
FlfT. 33. Diagram of Marconi Selective Wireless-
Ti'li'uraph System.
arrangement; the oscillator and resonator are compoand, that is,
each is of the nature of an open and a closed circuit. The trans-
mitter A shows two concentric cylinders 1 and 2, separated by an
air space and forming
1 — 1^ in reality a huge Leyden
jar. The inner cylinder
leads to earth and is also
connected to the outer
cylinder through the
spark-gap 4 and the in-
ductance coil 6. The
receiver B has a similar
cylinder 1 and 2; the
outer is connected to the
inner through the pri-
mary of a small oscil-
lation -tninsformer 4 and inductance 5; the coherer 6 is connected to
the Bccoiidiiry coil thus forming another closed circuit. These cyl-
inders do not radiate their energy in two or three swings, yet the
oscillations are not sustained to such a point as to enfeeble the
emitted waves; when syntonized to
each otlicr, selectivity may be ob-
tained within certain limits.
Braun-Siemens and Halske.
One of the bent theoretical syntonic
systems is the Hraun -Siemens and
Ilalske of (iermany. ()j)])0sitely
disposed to the one just descrilnd,
Dr. Ijraiin has retained the atrial
wires, but discarded the earthed
ttM'ininals. The arrangement is
shown (rrapliicallv in Fijr. Hi, The
fact that the terial wire is one-fourtli
the lencrth of the emitted wave, that
th(^ oscillations in one circuit can be Fl>r. 34. Schematic Arranpement of
- f 1 • . .1 • '. 1 Uriiun s Wireless-Teleirraph Svstera.
transformed into another Circuit, and *
that a closed circuit is a ])ersistent oscillator while an open circuit
is a strong radiator led to the design of the following apparatus:
ll!
B
7
i
^
11-12
\
A-
I
7
at^s
WIRELESS TELEGRAPHY
^11
Fig. -J^.
lu tlie Iniiisiiiitler A, llie aecoiidai'y of an indiictiuri foil 1,
largeB the oscillator system of whicli tlie B[«irk-ga]» 2, the t-on-
deDsera 3 3, and the primary 4 of a bigli-tetision transformer are
the complement; llie transformer ia shown in Fig. 27. The soc-
ondary 5 of the transformer connects with the eerial radiating wire
6, while the lower wire 0' is made ei^nal in length or it may \w tin
inductance coil and capacity equal to that of the lerial wire, Tlio
receiver B has a similar serial wire one Fourth ( -r ) thi^ h-ngtli uF
30 WIRELESS TELEGRAPHY
tbe received wave luogtli connected witli a closed resonator circuit
formed of tlie cundensere H, 8 and the primary of a small oscilla-
tion transformer 9; the antenna 7 is balanced by an equal amount
of cajjacity and inductance at its lower end 7'; the coherer 12 ie
placed in one arm of an open-circuit resonator; the secondary 11,
of the transformer connecting witii an opposite arm of equal elec-
trical dimensions, completes the apparatus. Fig. 35 is a photo-
graphic reprodnction of the Bnnin-Siemena and Halske system.
Fig. »i.
Fesscndcn. An Aiiicricaii system dfsigned liy Itegiiiald A.
Fosst'ndi'ii is almwn in Fig, itii; it cuiitains Si-veral novel features,
as the use of a ciirri'iit-opi'riitvd wave detector, inventeti liy I'rof.
FcBaendeii and terrm.-d by him ii barretter. The tuning of the cir-
cuitK is accom|ilislu4.l liy a grid formed of wires immersLHl in oil
that gives a variable ciipacity and inductance without the nae of
WISELESS TELEGRAPHY
1
^gjy^
f
I PBBBOndon Tunpd System.
■ Fig, 37.
■ coils or condensers. By means of eliding coiitaels on tlio wires,
the ofM'n-firvuit oscillator may be tuned to the closed-iiirfnit Ryateni
BO that hoth have exactly the same period.
By referring to the diagram the arrangement will become
clear. In this drawing the transmitter and receiver are combined
as they are in practice, since the same (Brial and ejirth wires serve
for sending and iiidicating the waves. The itrial wire 1 Is snp-
plied with energy from the induction coil 2 throngh tiie spark-gap
3; one side of the gap leads to the key 4, making connection with
the tuning grid wires 5; these can be adjusted hy the sliding con-
tacts 0, ([ dually leading to the earth at 11. Tlie receiving devices
comprise a condenser 7 and a tuning grid 9 whicJi connects with
the barretter 10 through a holder containing a number of them at
17, an electro) ti ague t automatically breaking the circuit in which
they are phiced by the operation of the induction coil ; the resonator
circuit is completed hy antenna 1 and tlie earth 11; the variation
WIRELESS TELEGHAFHT
Pig. 38.
of tLe current is rend by ineans of & telt^plione roceiTur 12. The
a])paratus is very compact as Fig. 3? showe, it is rapid iu operfttiOD
;iiid accurate in its translations.
American De Forest. Another sy8t<>m nsing Uie teleijbane
receiver as a means of indication ia the American 0p Fori'st. TbiB
was tlie first coiiinieroial system to employ an alteruating-ctirrent
generator and an oil transformer to ciiHt-ge tiie oscillator Gystein.
4
4
«
• -l
I 4-
I .-
WIRELESS TELEGRAPHY
The transmitter A, Fig. 38, includes an alternatiug-current gener.
ator 1, an ordinary Morae key 2, with contacts breaking under oil,
and a transformer 3. The serial wire 4 and earthed wire o form a
simple o]>en -circuit OBcillator through the spark-gap (!; this system
is supplied with energy liy the condensers 7 and 8 which are
charged by the secondary of the transformer. The receiver in its
simplest form compriaea a self- restoring detector invented by Dr.
De Forest and E. H. Smythe, called an electrolytic responfJer —
previously descrilied under "Principles" — a cell and a telephone
receiver. In practice, it takes on the form shown at D; two
responders 1', 1" are connected with the jerial wire and earth; the
DeForetl Beoelvat.
Pig. 4ft
internal circuit includes the respouders 1', 1", the choke coils 3',
2", a resistance of 5,000 ohms 3, battery 4, condenser C, telephone
receiver C, antenna 7. ground 8, and shniit switches 9', 9". This
system baa met wilb favor at home and abroad dne largely to Its
simplicity and efficiency. Fig. 39 illuatrates the transmitter and
Fig. 411 the receiver.
Branly-Popp. Especial interest is attached to the Branly-
Popp system in virtue of the fact that Prof. Branly is the original
inventor of the coherer. The chief feature of the newly-designed
apparatus is a tripod coherer and the elimination of the regulation
M
WIEELESS TELEGRAPHY*
tapping device. Fig, 41 is a diagram of the coiiuections and Fig.
42 sbuwB the apparatus. The transmitter is of the nsual iodnctioD-
coil, open-eiivitit oscillator type. The coherer consists of tlirw
highly iKilisbed tapering steel legs, the lop-er poJate of which arc
Uliigraiii Branlf-Popp Sy-ttent.
Fig. «.
slightly oxidized. The legs are fastened to a metal disc at the t
the points resting on a polished stee! plate. In ihe jihotograpli i'
will be observed that the coherer is placed immediately back of the
WIRELESS TELEX3RAPHY
35
electromagnets of the Morse register, and when the armature la
attracted by thu magnets, a projecting haminor serves to lap tlm
coherer, restoriiifj the high resistance between the points and mak-
ing the plate reaiiy for the succeeding impnlse.
Lortge-MiiirSeaa SyBtei
Fig. «.
Lodee-nuirhead. Another recent example of the advances
in wireless telegriipJi practice is the Lodge-Muirhead system, the
acheniatic arrangement U-ing shown in Fig. 43 and thtj complete
apparatus in Fig. 41. The combiDatiou of open and closed oscil-
lator and resonator circuits will be recognized as well as the iudif"
ance coils and condensers for obtaining resonance effects. The
receiver embocJies a new rotating mercury coherer, in which a pol-
ished steel disc is made to revolve so that its edge runs in, and
therefore forms contact with, a column of mercury. Instead of a
WIRELESS TELEGRAPHY
Bent liy an antomatic or innchine tran sin i tier,
operatfd key may be used if desired.
I^ileplione receirer or
a MurBO register, a
Byplioii recorder such
■ as is used for receiv.
iiig cable mesaagea ia
,, einpluyed and, owing
to tlie conipHrativi'Iy
wide variations of re-
sistivity of the co-
herer, tbia enablfS
thein lo be traiinected
direct, tbns dning
away with the usual
1 relay. The equip.
irietit also iriclndes a
perforator, for pre-
paring tho ineasagca
so ihat tliey may Iw
. although a manually
WIRELESS TELEGRAPHY
37
Bull. In all the foregoing systems, where electric signaling
was one of the objects to be attained, the desired results were
striven for by utilizing the laws of electrical resonance. The solv-
ing of the difficult problems of syntonization has, however, been
attempted along other and more concrete lines embracing electro-
mechanics of which the followinor inventions of Anders Bull are
the best examples. In this system, the transmitter consists of a
</ ffipe/'itcr &nd an induction coil shown in Figs. 45 and 40; when
in ojHjration its function is to send out a fixed number of wave im-
\>27
23^(
1
r '
1
1
^
1
»^ -»
^*
L.
n
-f-
•
A
Receiver, Showing Connection Between Coherer Keluy, Morse* Ke>;lster,* antl Collector.
Fi^. 47.
pulses per given period of time; these waves actuate different re-
ceivers adjusted in accordance with the j)re-arranged time intervals.
When the key closes the circuit of the l)attery 1 and the ek^ctro-
magnet 2, the armature of the latter releases a clutch on the disc
3 from the pin 4; the disc is rotated by a frictional shaft 5 making
five revolutions per second. Every revolution of the disc causes
the pin 6 to close the circuit including the battery 7 and the elec-
tromagnet 8; the dispenser proper consists of a disc having attached
thereto four hundred straight steel springs 0, their free ends passing
through a radial slot in the upjuT revolving disc 10; a brass ring 11
serves as a guide for the spring points and when the disc revolves
867
WIBELESS TELEGBAPHT
I
uMftchanlcnl Syawm, Reiflvtr.
Pig. 48.
they slide withiu a TJ-sbaped groove 12 if attracU-d by the mi^et
or within tlie ring itself when there ie no magnetic pull upon them.
A bronze are 13 causes the springs toltend toward the magnet 14,
and being energized by the battery, tln-y slide into the groove
where they finally close the circuit of the magnet 20 einntmllirip
the induetioii coil 23, As the disc rotates, the springs make eon-
tact with projections extending around the fraiue at certain prede-
termined intervals and in this way waves of prescril>ed frequency
are consequently emitted.
^V^le^ these jieriodically emitted waves 'impinge upon the an-
tenna of the reeeiving apparatus, Fig. 47. the coherer closes the
circuit of the relay magnets 23; and the tapper 24, and the collector
magnet 25 are brought into action. The mechanism of the col-
lector is exactly like that of the disperser and can therefore he
instantly converted into a disperser. The discs of the dispi-rser
and collector revolve synchronously, hence if five electric wave
series are transmitted, five springs will close the eircnit at given
intervals of time; the spring points 27 of the collector having the
same relative arrangement as in the disperser the impulses o])erate
similar contacts controlling the Morse register 28. In this eystem
interference is not obviated, yet any one of a number of ri>ceivers
in the same field of action may be operated to the exclusion of all
others. The Bull receiver is shown in Fig. 48.
THE TELAUTOGRAPH.*
Electrical transmission of handwriting has engaged a certain
amount of attention ever since telegraphic transmission of printed
characters was successfnllv carried out.
As early as ISSi), Cow[)er and Robertson brought the writing
telegraph' into a fairly operative form. This instrument was
adapted to operate several receivers in series in "reporting"
service, where the regular news ticker service was unobtainable or
too expensive. The system was put to some use, chietly in Pitts-
burtj and vicinity.
The writing was received on a paper tajH% advanced at con-
stant speed by clockwork. No pen -lifting device was provided
and the words were connected together by a mark of the j)en,
making figure work poor. As the characters were formed by the
combination of the pen motion and the tape motion, a certain
amount of j)ractice and skill was required to produce a legible
message.
The electrical features were as follows : two independent vari-
able currents were obtained from the transmitter; these passed
over lines to the receiver where they traversed two electromagnets
set at ricrht antrles to each other, and so influenced their effect
upon a common armature as to cause the receiver-pen rod to re-
produce the motion of the transmitter pencil.
It will be noted that this principle is nearly identical with
that of Gruhu's Telechipograph,- recently described in the tech-
nical j)ress, the main differences being that the telechipograj)h
writes upon a larger field and uses a beam of light, and photo-
graphic record instead of a pen with ink record.
Following the writing telegraph. Professor Elisha Gray con-
structed, at his Chicago laboratory, an instrument which wrote
upon stationary paper, and which he called a telautograph. It
1. Wm. MiivtT. Jr.. American Teltgraphy.
2. Scientific American. August, 1903.
♦Prepared by James Dixon, E.E., and read by him before ti 'n.slltuuj
Qt Electrical Engineers, October 28th. 1904. Reprinted by special
969
THE TELAUTOGRAPH
required four line wires and operattKl as follows: by means of
cords and drums the motions of the transmitting stylus were
resolved into tw^o component rotary motions which were used
to operate two mechanical interrupters in the primary circuits of
two induction coils. The relations of the parts were such that a
motion of the transmitting stylus amounting to one-fortieth of an
inch caused a complete make-and-break at one or both of the inter-
rupters.
Tlie line currents w^ere the impulses produced in the second-
ary circuits of the induction coils. These impulses passed over
lines to tw^o electromechanical escajx^ments in the receiver. By
means of cords and drums, their motions were combined and
caused to act upon the receiver pen. By the use of relays and
condensers and a local battery at each receiver, the paj)er was
advanced when necessary and the pen lifted from and lowered to
the paper. The mechanical ditHculties met with in perfecting this
instrument were very great, and in the apparatus exhibited at the
World's Fair in Chicago in 1893 the escapement mechanism was
brought to a perfection thought impossible of attainment only a
short time before. The writing showed a saw-tooth or step-by-
step character due to the action of the escapements. The instru-
ment was abandoned on account of the number of line wires
required, limited sptvd, numerous fine adjustments, and cost and
difficulty of manufacture.
In 1SU3, while still working at the escapement device, Pro-
fessor Gray patented a variable-current instrument,' using two
line wires, which worked, in a general way, like the present telau-
tograph. The motions of the transmitter pencil were resolved
into two components which were used to vary two line currents,
the variable resistances being carbon rods dipping into tubes of
mercury. The receiver contained two D'zVrsonval movements, to
the moving elements of which the pen -arms were attached. Pro-
fessor Gray never developed this instrument much beyond the
laboratorv stacre, ])rol)ablv <>n account of his firm belief in the
esca[)einent type.
Foster llitchie, at that time an assistant to Professor Gray,
gave considerable attention to this patent and ])erfected an instru-
1. U. S. Patent 4di,\)6Q, April 1, 1893.
^1^
THE TELAUTOGRAPH
meot based on it. lie uhtaiiied a piitt'iit fur iiitproveinents' and
has produced an instniiiient tliat opt^rates in a fairly eatisfactory
manner' under certain favoral)le foiiditJona,
The telantograjili has bi«n broufrht to its present state chietiy
through ex [leri mental work done by, or niider the personal direc-
tion of, Mr. George L. Tiffany, to whom several patents'' for
improvements have been granted, Mr. Tiffany's instrument oper-
ates upon the variable-current jirineiple and iuclndes a number of
interesting features, among them what may be called a straight-line
D'Arsonval movement, which is used to operate the receiver.
Transmitter
Line Wires
The operation may be brietly described thus: at the transmit-
ter a pencil is attached by rtxla to two lever-arms which carry
contact-rollers at their ends. These rollers bear against the snr-
faces of two current-carrying rheostatt;, connectt'd to a constant-
pressure source of direct current. The writing cuneiits jjass from
the rheostats to the rollers and from them to the Hue wires. "When
the pencil is moved, aa in writing, the positionti of the rollers uj>on
the rheostats are changti], and currt'iits of varying strength go out
upon the Hue wires. At the rit'eiver these currents jiass through
two vertically movable coils, suspended by springs in niagnetic
1. U. S. Pal. eM,82H, AllR. 28, IWO.
2. Elic. Wortilnnd Kngiietr.Df;.*, lOun, Vol. XXXVI., No. 23.
s. u. s. Patents «e8.itee to eee,eus lucm^ive, i''>.'b. so, luui.
THE TELAUTOGRAPH
fields, and the coils move up or down according to the strengths
of the line currents. The motions of the coils are communicated
to levers similar to those at the transmitter, and on these levers is
mounted the receiver pen, which, by the motions of the coils, is
caused to duplicate the motions of the sending pencil. Fig. 1
shows the circuits of the instrument.
Many of the principles and devices in the instruments are of
considerable interest. The method by which the variable cun-ents
are obtained is the laboratory arrangement for securing a variable
j)re8sure from a direct-current, constant-pressure circuit; that is,
the line circuit (of constant resistance) is connected as a shunt
around that part of the rheostat between the moving roller and the
ground or return. Motion of the roller varies the amount of resist-
ance in series with the line and also the amount in parallel with it
and tine gradations are easily obtained, giving smooth motion of
the receiver pen. In this way a variable pressure is impressed on
the line circuit, giving a variable current. In all the other variable-
current instruments, a constant pressure was impressed on the line
and a resistance in series with the line varied to give the desired
variations in current. One result of the shunting method is a bet-
ter form of rheostat, more easy of construction and handling, in
which, also, the heatincr is better distributed.
The rheostats are wound upon castings of I cross-section, with
the turns of wire lyintj close tom'ther on the inner or contact-face.
After windintr, tlie insulation on this face is saturated with Q\ne,
wliich is allowed to harden and is then scraped olF, taking the
insulation with it, and giving a surface where contact is possible
on every turn of the wire. This gives a rheostat of a large nuni-
]>er of small steps, of good mechanical construction, and of low
cost.
The receiver operates with wliat may be called a straight-line
d'Arsonval movement. The moving element or coil is wound uix)n
a co])per shell for damping effect. The magnetic circuit is so ar-
ranged that one pole surrounds the other, forming an annular air-
gap of short length and large cross-section in wliich the direction
of the flux is radial. The field is electronuij^netic and is hio-hlv
excited, to secure uniformity. The coil, suspended in the annular
space, moves up or down with little friction, as it touches the
Z1^
THE TELAUTOGRAPH
Bides of the space of the core very lightly if at all. The principle
is the well-known one that a current-carrying coil, in a magnetic
field, tends to place itself with re8{)ect to the field so that the flux
enclosed by the coil shall be a niaxinium.
The current for operating is taken from the ordinary lighting
mains, preferably at about 115 volts. Satisfactory operation has
resulted with pressures from 80 up to 250. At 115 volts, receiver
and transmitter each re(piire a])out one ampere while in operation.
Fairly steady pressure is necessary as the receiver, being in effect
a voltmeter, is rather sensitive to sudden changes, the effect being
slight distortion of tbe message.
X master-switch at the transmitter is provided to do all neces-
sary switching of line and power circuits, to make needed changes
in connections and to cut off current when not writing. A relay
in one of the lines closes the power circuit of the receiver when-
ever the transmitter at the distant station is switched on, and serves
to prevent waste of current when not in operation.
Attached to the master-switch is a mechanical device which
shifts the transmitter paper the space of one line of ordinary writing
for each stroke of the switch. The relay mentioned controls the elec-
trical receiver paper shifter and, as each stroke of the switch causes
a stroke of the relay, the receiver [)aper is shifted an amount equal
to that at the transmitter. The writing space is about two inches
long and five inches wide, allowing for three or four lines of writ-
ing. When tilled by messages, a few strokes of the switch serve
to bring fresh ])aj>er into position at both rea^ver and transmitter.
To prevent switching on of the transmitter while its home re-
ceiver is receiving a message from the distant station, an electro-
magnet lock is connected in the receiver power circuit, controlled l)y
the relay, which locks the home transmitter in the '*off" j)Osition
until the distant transmitter is switched off. If l>oth transmitters
were switched on at once, neither station would receive any mes-
sage; the lock is provided to render this condition impossible.
The ink suj)ply is most im|)ortant, and is arranged for as fol-
lows: at the left of the receiver platen is a bottle with a hole in
the front near the lx)ttom. Wlien Hlled with ink and tightly corked
the ink dcjes not run out of this hole because of the pressure of the
87S
6 THE TELAUTOGRAPH
atmosphere. The iuk is accessible for the pen at the hole and the
surface of ink exposed to evaporation is small.
The pen is made of a piece of German silver bent double, after
the manner of a ruling pen, and makes a uniform line in any direc-
tion over the paper. It takes up its supply by capillary attraction,
from the hole in the front of the bottle. When the receiver is
switched off, retractile springs draw the pen-arms to stops so
arranged as to bring the pen exactly in front of the hole in the
bottle, and when the pen-lifter armature is released the pen is
caused to insert its tip in the opening. Tims a fresh tilling of iuk
is obtained each time the paper is shifted. When not in use the
pen rests in the ink, always ready to write.
For the prevention of mechanical shocks to the necessarily
light moving system of the receiver, it has been necessary to sup-
ply means to prevent the switching on or off of the transmitter,
and by that action of the receiver, when the transmitter pencil is
"out in the field"; that is, at a position other than that corre-
sponding to the opening in the receiver ink-bottle; as in that case
the receiver pen would instantly jump to a similar position. This
position is called the 'Minison point," a term having its origin in
the days of the '*self-])ro[)ellor " escapement telautograph. By
placing a catch, rcKnisod only by ])n^ssure of the j^encil-point u|X)n
it, at tlu^ transMiitttM' unison point, thodcsiriHl result is accomplished
and tli<^ tninsmittcr niastiM'-switrli can not ])e switched either '-off
or "on" unli'ss tlit* ]K*ncil lu^ placed at the unison point and held
tlnTii until th(^ strokti of the switch is completed. In this cjise, as
evt»rywhere, the ap|)aratus is made strong enough to stand any
possible shocks, altliono;]i every ])reeaution is taken to prevent their
occurrence. Aside from the shock to the moving system these
jumps might shakt^ the ink supply out of the ])eri and prevent the
recordintr of the niessam*.
The ])en -lifter is a magnet phiced liack of the receiver writing
phittMi, an<l carrying u|)on its armature a rod adapted to engage
with the pen -arm rods and raise tlie pen clear of the paj)er when
the nuurnet is ener<nzed. This matrnet is controlled from the
transmitter as follows: bequeath the transmitter platen is a spring-
contact, op(Mied by pressure of the j)encil upon the paj)er, and
closed by a spring when the ])encil is raised. An induction coil
374
THE TELAUTOGRAPH
having an interrupter in its primary circuit is so connecteil to this
spring-contact that wlien the pencil is raiscnl the primary winding
is short-circuited. The induction coil has two independent sec-
iC^
f.-m
7 3 J-; f
yty^yu
}U^^^ XrTr-//-/f^^
SA^rPLE OF WRITING
Made pspeclnlly for tho American School of CorrosixHulence ovrr a distanco of alxmt W
miles. Ac ihc left Is .^hown the original, at tlio rl^fht the ropriHliu'tiou.
ondary windincrs through which the two variable line currents jiass
before leavinrr the transmitter. The etTect of the induction coil
and its interrupted primary current is to induce, in the two line
876
8 THE TELAUTOGRAPH
currents, superimposed vibrations or ^'ripples" when the pencil is
pressed down on the paper and the spring- contact is open. When
the contact is closed, by its spring, and the primary winding is cut
out, no vibrations are produced in the line currents. In one of the
line wires, at the receiver, is placed a relay upon whose sheet-iron
diaphragm armature is mounted a loose contact, consisting of two
platinum -silver contacts in series, sealed in a glass tube, to pre-
vent oxidation. A local circuit contains the winding of the jien-
lifter magnet and this loose contact.
When the vibrations are present in the line current, due to
the pressure of the pencil upon the paper and consequent openiDg
of short circuit of the primary of the induction coil, the diaphragm
of the relay is shaken, the loose contact opened, and the pen-lifter
de-energized, its armature being drawn back by a spring and the
pen being allowed to rest against the paper. When there are no
vibrations in the line currents due to the raising of the pencil from
the paper, the relay diaphragm is at rest, the pen -lifter is energized,
and the pen is lifted clear of the paper.
The superimposed vibrations used for operating the pen-lifter
have another minor effect. The suspended coils, and through
them the entire moving system of the receiver, are kept in a state
of very sli<rht niee'lumical vibration wliile the pen is on the paper.
This aids the How of ink from tlie pen -point, assists the j)en in
passing over any rono;liness or irregularity in the surface of the
paper, and nKiterially reduces friction in the joints and pivots uf
the movinir system, and results in better writintr. In some of the
later instruments, the two relays, that for nen-liftincr and that for
paper-sliifting and power-switching, are combined in a single
piece of ap[)aratus.
For signaling, a pusli-l)utton is placed upon the transmitter
and a call -bell or buzzer is mounted on the receiver. This circuit
is disconnected by the nuister-switch while a messao-e is ])eini''
written. {Spring reels are attached when needed to roll up the
received messages for preservation and future reference.
The ordinary arrangements for operation are as follows: the
instruments may be operated singly, upon a private line having an
instrument at each end, or on an exchanm^ systeni where a switch-
board provides for connection. Working in this way, satisfactory
STe
THE TELAUTOGRAPH
writing has bt^n obuinud with a reBistance in eac-h line wire oF
1,0(X) olitiia and an optruting presaiire of 110 volta. Multiple
ojteralion can tje carrirtl out to a limited extent, tbree receivers
being at present the inaximuin iminber that can be operated at
once, in mulliply, using 110 volts. This allows of placing a
8Upervisoi"j uiachiin- upon a line.
Wben no response to messages beyond a bell signal is required,
and the same message is to be sent to a number of stations, a series
rH| J^ltfJBBp
Fig. 2.
arrangement of receivers is used. With a transmitting pressni*
of 110 viiits a maxiniiim of seven reeeivera can l>e Of>erated from a
single pair of transmitting rheostats and rollers. This number
may be iriereased hy increasing the jn-essure or by adding addi-
tional rheostats and rollers, ojieratetl hy the same j»encil. I'sing
lx)tli these methods a maximum of 50 or more receivers may be
operated at once.
Instances in actual commercial use of the arrangements of
inatruinenta mentiuuMl are: private lines; the transmission of mail
and other orders from office to factory or yards; investigation of
cliecka over lines between jwying tidlersaiid bookkeepers in banking
concerns, and transmission of messages, usually in cipher, between
brokerage firms and cable or telegraph offices. A few momenta'
10 THE TELAUTOGRAPH
thought will bring to mind many places where a telautograph
private line could l^ used to save time and trouble, especially
where accurate transmission of iigures is essential.
Multiple operation may be resorted to when a third station
upon a line desires a record, accessible at any time, of what is being
sent, as, for instance, when one of the officers of a bank desires to
know what passes between his bookkeepers and paying tellers.
(Jn such a line the third station receives all messages and can write
to either or both of the other stations, should the necessity arise.
Series operation may be used when several stations are to
receive the same message and no response except a bell signal is
required, as in sending orders in a hotel or club from dining roono
to kitchen, pantry and wine room; in ** reporting " or news service?,
or for bulletin work, such as the announcement of arrival ^t^d
departure of trains to a number of stations in a large railway
station or freight depot. Fig. 2 shows the standard commercial
instrument.
One of the most important uses for series systems has been
found in the U. S. Coast Defense Service, in sending ballistic
data, such as range and azimuth of target, or character of pro-
jectile, from j)osit ion -finding stations to the gunners. This is
called ''fire -control connminication " and is installed in the forts
by the U. S. SiVnal Corps. In a paper presented by Col. Samuel
Reher on *• Electricity in tlic Si(j;nal Corps,"* will Ixj found a
dcscrij)tion of the position-fiiulinti; systems. The desired character-
istics of a system of communication for sendincr this data to the
(runs are stated as foUows:
'*Tlie system that will siiecessfully solve this problem must be sim-
ple in coiistruclion, jiiocliaiiically slroiitr ^q as not to be artecteii by the
l)last, as the receivers are ])lace<l close to the Kii^^s, ra})id in operation, and
give a character of record that ran l)e read without liability of error/'
Since that paper was prepared, it has been decided that the
receivtM-s must he mounted directly on the trun-carriai^e and can
hav(> no shelter other than that afforded hy their own cases. Add
to these re(juirements the facts that the instruments must l)e careil
for hy post electricians, an<l operated by enlisted artillerymen;
that nu?ssao;es must lu^ visible at night; and the operation must be
1. TUANSACTIONS. A. I. E. E.. Vol. XIX., pp. 723 and 721.
S78
THE TELAUTOGRAPH
U
iadepeDiJent of rain, ealt mists, eold, he&t, ur tropical iusecte, and
it is apparent tbat no easy problem is presented.
A special type of telHiitoirrapli lias lieeu desigin?d for tliiB Berv-
icB aud lias l>et-ii adopted liy the U, S. SignHl (.'orps' for Hm-
eontrul column nidation.
In this service "telautograph," the rather delicate pen-lifter
relay is elimiiiiitcd and the receiver [leii-lifters are ojieruted over a
third line wire by the transmitter platen ewitcli dii'ectly.
Kach gun receiver is enclosed in a watwr-tight brass case, sns-
j»;ndtHi by springs from the gun carriage directly in front of the
gunner. Tlie parts are as far as possible made "brntally slntrig,"
and the couat ruction is as simple as |)0ssible.
The desired rapidity of operation ia inherent to the telauto.
graph, and accnrncy of record is ensured by careful writing and by
the use of a "home" receiver, mounted at the transmitter wliere
the operator can see it plainly, which is connected in series with
1. THAHBACnoSH, A. I. E. E., VoL ZtX., p. 073,
12 THE TELAUTOGRAPH
the gun receivers and records the messages as actually sent over
the line.
Freezing of ink is prevented by the addition of alcohol; and
rain, mists, and insects, as well as the eifects of the blast, are shut
out by the metal case. A heavy glass window is placed in the
case so that messages can l)e read without ojxi^ning the case.
A small incandescent lamp inside the case lights automatic-
ally when the receiver is writing and may be lighttnl by }»ressing
a Ijutton at other times, thus providing for visibility at night.
Fig. 8 shows the army ty[)e of receiver mounting.
On warships there is a somewhat similar service to he ren-
dered and the performance of this should fall to the army ty|>e of
tehiutograph.
Connnercial service has given op|K)rtunity for the installation
of a considerable number of private line telautographs in actual
use, and at least three of each of the other typical installations are
in oj K-ration at the present time.
Much of the improvement in details of construction and reli-
ability in operation has resulted from ex{)erience gained in efforts
to perfect the service of these commercial plants. The experience
leading up to the special army type of telautograph has extended
over a period of about five years and in the present instrument all
tiu» re(|uirenients, unusually severe as they are, have been success-
fully fullilled.
\*»
*■ 1.-^ -
■J ••"!;>'
INSULATORS FOR TRANSMISSION LINES.
Line insnlators. pins, and oross-arins all ctq to make up patbi^
of more or less eoiHluetivitv Unween the wires of a transmission
circuit. The amount of current tlowintr alonix these iiaths fnmi
one conductor to anotht-r in any ca.-t' will depend on the combined
resistance of the insulators, pins, and cross-arm at each |x)le.
As a general rult-, the wires of high-voltage transmission cir-
cuits are used l»are l)ecause continuous coverings would add materi-
ally to the cost with only a triHintj increase in effective insulation
against high voltages. In some instances the wires of high-pres-
sure transmission line$ have individual coverings for short dis-
tances where thev enter larj/e cities, but often this is not the case.
At Manchester. New IIani[»shire. bare conductors from water-power
plants enter the sul>station. well within the city limits, at 12,000
volts. From the water jMjwer at C'hambly the bare 25,000-volt
circuits, after crossinc; the St. l^wrenee River over the x/reat Vic-
toria Bridge, pass overhead to a terminal house near the water
front in Montreal. In order to reach the General Electric Works,
the 30,000-volt circuits from Spier Falls enter the city limits of
Schenectady, New York, with bare overhead conductors.
Where transmission lines pass over a territory exposed to cor-
rosive gases, it is sometimes desirable to give each wire a weather-
proof covering. An instance of this sort occurs near Niagara Falls
where the aluminum conductors forming one of the circuits to
Buffalo are covered with a braid that is saturated with asphaltum.
Each path, formtH.1 by the surface of the insulators of a line
and the pins and cross-arm by which they are supported, not only
wastes the energy representtHl by the leakage current passing over
it, but may lead to the charring and burning of the pins and cross-
arm by this current. To prevent such burning, the main reliance
is to Ixj placed in the surface resistance of the insulators rather
than that of pins and cross-arms. These insulators should be made
of glass or porcelain, as far as past experience is a guide, and
should be used dry, that is, without oil. In 8om«^ ' ' *wirly
INSULATORS
transinissiou lines, insulators were used on which the lower edges
were turned inward and upward so that a circular trough was
formed beneath the body of the insulator, and this trough was filled
with heavy petroleum. It was found, however, that this trough of
oil served to collect dirt and thus tended to lower the insulation
between wire and cross-arm, so that the practice was soon aban-
doned, (flass and j)orcelain insulators are rivals for use on high-
tension lines and each has advantages of its own. Poroelaiu
insulators are much stronger mechanically than are those of glass,
and are not liable to crack because of unequal internal expansion,
a result sometimes met with where glass insulators are exposed to
a hot morning sun. In favor of glass insulators it may be said
that their insulating properties are quite uniform, and that, nnlike
porcelain, their internal defects are generally apparent on inspec-
tion. In order to avoid internal defects in large porcelain insula-
tors, it has been found necessary to manufacture some designs in
several parts, and then cement the parts of each insulator leather.
Defective insulators may be divided into two classes — those
that the line voltage will puncture and break, and those that
permit an excessive amount of current to pass over their sur&oes
to the pins and cross-arms. Where an insulator is punctured and
broken, the pin, cross-arm, and ])ole to which it is attached, are
lia])Ie to h(* buriu'd ii|). If tlie leakage of current over the surface
of an insulator is lar^e, not only may the loss of enercjv on the
line where tlu' insulator is used be serious, but this energy follows
the ])ins an<l c-ross-arni in its j)atli from wire to wire, and gradually
chars the lornier, or both, so that they are ultimately set on fire or
break throutxh lack of mechanical strength. The discharge over the
surface of an insulator nuiy ))e so larire in amount as to have a dis-
ruptive character, and thus to be readily visible. More frequently
this surface leakao;e of current over insulators is of the invisible
and silent sort that nevertheless may be sufHcient in amount to char,
weaken, and even ultimately set lire to pins and cross-arms.
All insulators, whether made of glass or porcelain, should be
tested electrically to determine their ability to resist puncture, and
to hold l)ack the surface leakage of current, before they are put
into ])ractical use on high-tension lines. Experience has shown
that inspection alone cannot be de[)ended on to detect defective
SM
INSULATORS
S
glues ineulntors that will fail when put into service on high-voltage
lines. Electrical testing of insulators serves well to determine the
vollape to which they may lie subjected in practical eerviee with
liuii' (i;uit:iT <<f [luiichin' hy lin- (iisriiptivo passage of current
INSULATOR. ARC TO MKTAI. I'lN AT W
prBi'liilltttloB "i luoh i*r minule. Dliinietir 11".
mt' iibore hotliontBl. Helglit IJ".
DuraMoD o( IflHt. Ifi minutes. WulKblSa lbs.
lySULATORS
through their substance. It is also possible to determine the volt-
af^* that will canse a disniptive discharge of current over the
surface of an insulator, when the outer part of this surface is either
wet or drj'. This is as far as electrical tests are usually carried,
but it seems desirable that such tests should also determine the
amount of silent, invisible leakage over the surface of insulators
lK>th when they are wet and when they are dry, at the voltage
which their circuits are intended to carry. Such a test of silent
leakage is important because this sort of leakage chars and weakens
insulator pins, and sets fire to them and cross-arms, besides repre-
senting a waste of energy.
The voltage employed to test insulators should vary in amount
according to the purpose for which any particular test is made.
Glass and porcelain, like many other solid insulators, will with-
stand a voltage during a few minutes that will cause a puncture
if continued indefinitely. In this respect these insulators are
unlike air, which allows a disruptive discharge at once when the
voltage to which it is exposed reaches an amount that the air can-
not permanently withstand. Because of this property of glass and
porcelain insulators, it is necessary in making a puncture test, to
employe voltage much higher than that to which they are to be
permanently exposed. In good practice it is thought desirable to
test iiisuljitors for puncture with at least twice the voltage of the
circuits vvlii('li they will be required to permanently support ou
transnilHsion lines.
For tht» first transmission line from Niagara Falls to Buifalo,
which was designed to operate at 11,000 volts, the j)orcelain insu-
lators were tested for puncture with a voltage of 40,000, or nearly
four times that of the circuits they were to support.
Porcelain insulators for the second line between Niagara Falls
and IhilTalo, after the voltage of transmission had been raised to
22,000, were given a puncture test at 00,000 volts. Of these in-
sulators tested at 00,000 volts only about 3 per cent proved to be
defective. These puncture tests were carried out by placing each
insulator upside down in an open pan containing salt water to a
depth of two inches, partly filling the pin hole of the insulator with
salt water, and then connecting one terminal of the testinrj circuit
with a rcMJ of metal in the pin hole, and the other terminal with
386
INSULATORS 5
the pan. Alternatinfj current was en)pIoy«J in these tests, as is
nsually the ease, arxl they are mentioned in Voluuie XVITI, Trans-
actions A.LE.E., pajjes 514 to 52(1. For the transinisBiun lines
between Spier Falls, Sehenectady, Albany, and Troy, where the
eoiooo TO ac^ooo volts.
SHOWING CAVE TROUSHS.
voltage IB 30,000 tlie insulators were required to withstand a punc-
turing test with 75,(MIO volls for a period of five ininates, after
they had l>eon soaked in water for 24 hours.
INSULATORS
Tlierf is some difference of opinion as to the proper duration
of a punctiiring test, llie practice in eoiiie cases being to contirine
the test for only one minnte on each insulator, while in other cases
tho time runs up to live minutes or more. Aa a rule, the higher
the testing voltage compared with that under which the insnlatora
will be regularly nsed.
the shorter should be
the period of test. In-
stead of being tested in
Bait water as above de-
scribed, an insnlator may
be screwed onio an iron
))in of a size that tits ite
threads, and then one
b-ide of the testing cir-
I uit put in contact witb
ihi> pin, and the otlier
side connected wilh the
wire groove of the in-
'^ulnior. Care should be
i!."ii where an iron pin
used cither in testing
tipr regular line work,
I [ the pin is not
■ I. wed hard up against
till' top of the iiisulator.
Its this tends to crack
off the top, especially
when the pin and insu-
lator are raised in tem-
perature. Iron expands
at a mnch higher rate
than glass or porcelain.
and it is desirable, where an iron pin is screwed into the insulator,
to place a washer of leather or cork over the top of the pin bo that
the iron will not press hard against the inside of the insulator top.
lu this way a little room for expansion is provided liy compression of
the washer. There eeems to be some reason to think that an insula-
INSDLATORS
tor will pnnctcre more readily when it ia exposed to severe median-
ical strt'ss by tlie expansion of tlie iron pin oil which it is mounted.
Teals of insulators are iisimlly made with nttemating cnrrent,
and the form of the voltage curve is important, especially where
the test is made to determine what voltage will arc over the surface
of the insulator from the line wire to the pin. The square root of
the moan square for two
curves of alteruatiug vol- |
tage, aa read by a volt-
meter, may be the same I
though the maximum volt-
ages of the two curves
differ widely. In tests fur
the puncture of insulators,
the average alternating
voltage applied is more I
important than the maxi-
mum voltage shown by the
highest points of the pres-
sure curve, because of the
influence of the time ele-
ment with glass and porce-
lain. On the other hand,
when the test is to deter-
iiiioe tlie average voltage at
which current will arc over
the insHlatop surface from
the line wire to the pin, the
maximumvalueof the pres-
sure curve should he taken
into consideration becausf
air has no time element,
but permits a disruptive
discharge under a merely
instantaneous voltage.
Alternators used in transmission systems usually conform
approximately to a sine curve in the iuatantaneoua values of the
pressures they develop, and it is therefore desirable that tests on line
IXSl'LATORS
inBulatora be made witli voltages whose values follow the sine curve.
Either a single transformer or several trausfoniierB in aeries may
be employed to step up to the required voltage, but a siDgle traDS-
former will iianally give belter regulation and greater accuracy.
An air gap between needle ])oints is nut a very satisfacIoiT nieaiiB
by whit'L to detenniue the
average voltage on a testing
circuit, txH-'aose, as already
jHjinted out, the sparking
distance between thunnedle
points dejkends mainly on
the niii\imnm instantane-
ous values of the voltage,
which may vary with the
loud on the generator and
the saturation of its mag-
nets. For accurate results
a etep-down voltmeter
transformer should be used
on ihe testing circuit.
An insulator that re-
sists a puncture test per-
fectly may fail badly when
sul>jected to a test as to the
voltage that will arc over
its surface from line-wire
to pin. Tliia arc-over test
should be made with the
outer surface of the insu-
ktorboth wetanddry. For
the pur[)Oseof this test the
insulator should Ik? screwed
unto an iron pin, or onto a
wooden pin that has been covered with tinfoil. One wire of the
testing circuit should then be secured in the groove of the insulator,
which should preferably be on top. and the other wire should be
connected to the iron or tinfoil of the j)in. The voltage that will
arc over the surface of an insulator from the line wire to the pin
INSULATORS
depends on the conditions of that surface and of the air. In light
air, such as is found at great elevations, an arc will jump a greater
distance than in dry air near the sea level. A fog increases the
distance that a given voltage will jump between a line-wire and
its insulation pin, and a heavy rain lengthens the distance still
further. The heavier the downpour of rain the greater is the dis-
tance over the outside surface of an insulator that a given voltage
will arc over. The angle at which the falling water strikes the
insulator surface also has an influence on the voltage required to arc
over that surface, a deviation from a downjK)ur perpendicular to
the plane of the lower edge of the petticoat of the insulator seeming
to increase the arcing distance for a given voltage.
An insulator should be given an arc-over test under condi-
tions that are approximately the most severe to be met in practice.
These conditions can |)erhaps be fairly represented by a downpour
of water that amounts to a depth of one inch in five minutes for
each S(|uare inch of the plane included by the edge of the largest
petticoat of the insulator, when the direction of the falling water
makes an angle of 45 degrees with that plane. A precipitation of
one inch in depth on a horizontal plane during live minutes seems
to be a little greater than any recorded by the United States
Weather Bureau. Under the severe conditions just named, the
voltage required to arc over the insulator surface from line-wire to
pin should be somewhat greater at least than the normal voltage
of the circuit where the insulator is to be used. For the trans-
mission line between Spier P'alls and Schenectady, on which the
maximum voltage is 30,000, the insulators were required to stand
a test of 42,000 volts when wet, without arcing over from line-
wire to pin. In these wet tests the water should be sprayed evenly
onto the insulator surface like rain, and the quantity of water
that strikes the insulator, in a given time, should be measured.
When the outside of an insulator is wet, it is evident that
most of the resistance between the line wire and the insulator pin
must be offered by the inside surface of the petticoat of the insula-
tor and by the air l>etween the lower edge of the petticoat and the
pin or cross-arm. P'or this reason an insulator that is to with-
stand a very high voltage so that no arc will be formed over its
wet outside surface, must have not only a wide, dry surface under
391
10 INSULATORS
its petticoat, but also a long distance through the air between the
lower wet tnlge of the insulator and the pin or cross-arm. In
some tests of line insulators reported in Volume XX, Transactions
A.I.E.E., pages 521 to 525, the results show that the voltage required
to arc over from line-wire to pin dej)end8 on the shortest distance
l)etween them, rather than on the distance over the insulator sur-
face. Three insulators, numbered 4, 5, and 7 in the trial, were in
each case tested by a gradual increase of voltage until a discharge
took place between the wire and j)in. The pins were coated with
tinfoil, and the testing voltage was applit*d to the tie wire on each
insulator and to the tinfoil of its pin. Insulators 4, 5, and 7 per-
mitted arcs from wire to pin when expostni to 78,800, 74,7(K), and
74,700 volts resj)ectivt*ly, the surfaces of all being dry and clean.
The shortest distances l>etween wires and pins over insulator sur-
face and through air were ()|, 0|, and 7^ inches respi^ctively for
the three insulators, so that the arcintr voltages amounted to 11,140,
Or? '
11,1)52. and 1»,471> j)er inch of these distances. Measured along
their surfaces the distances l>etween wires and pins on these three
insulators were S, 11 1, and 15 A inches resj)ectively, so that the
tliRv arcing voltages, which were nearly equal, amounted to 0,225,
(),()4(>,and 4,Sll) jht inch of these distances. These figures make
it plain that the aiviiijx Voltaire for each insulator depends on the
shortt\-t di.-taiict* ovt*r its surface and tliroutrh the air, from wire
to pin. It iiiiixlit l)e fXpectt-d that the voltage in any case would
arc etiual dislaiK-es ovtM' cK^an. drv insulator surface or throucrh the
air, and the t'XptM'iiiuMits ju?t naint-d iiulicate that this view is ap-
proxiinati'ly convrt. The sj»arkino distance through air In^tween
needle jH)iiits, wliich is givater than that U'tween smooth surfaces,
is 5.S5 inchrs with Iujmm) v,ihs. and 7.1 inches with sO.OOO volts
accoriling to tiu* n-pnrt in A'oliniie XIX, A.I.E.E., page 721.
Comparing tlu'M' di>tan(.-rs with the shortest distances l)etween
wires ami piii> in the tt*st.^ of iIl^lllators numl)ered 4, 5, and 7.
which ImoUc ilowTi at 7;^.'^nO to 7 k7tH> volts when drv, it seems
*hal a tii\en Vf»itajj:e will are somewhat further over clean, drv
ula(i>r surface than it will throni^h air. This view finds support
n the fad tlial only a part of each of tlie ^hortest distances
WiHMi wire and pin was over insulator surface, the remainder
iiig through air alone.
398
INSULATORS 11
The fact that the dry part of the surface of an insulator and
the air between its lower wet edge and the pin or cross-arm oifer
most of the resistance between the line-w-ire and the pin and cross-
arm, is plainly brought out by the results of the tests above men-
tioned, in the cases of insulators numl>ered 4 and 7. While 73,800
volts were required to arc from line wire to pin when the entire
insulator was dry and clean, the arc was formed at only 53,400
volts during a moderate rain storm, in the case of number 4 insu-
lator. With insulator number 7 the arcinc; voltajre was 74,700
when the entire surface* was clean and dry, but the arc from wire
to pin was started with r)2,S0() volts dnring a moderate rain.
Number 5 insulator seems to present an erratic result, for when
dry and clean the arc jnmpcd from wire to pin at 74,700 volts, and
yet during a moderate rain no arc was formed until a voltage of
70,400 was reached. For each of the seven insnlators on which
tests are reported as above, the voltage required to arc from line-
wire to pin was nearly or quite as great during a dry-snow storm
as when the insulator surface was clean and dry. When the insu-
lators were covered with wet snow their surface insulation broke
down at voltages that were within 10 per cent above or below the
arcing voltages during a moderate rain in five cases. With two
insulators the arcing voltages, when they were covered with wet
snow, were only about 00 j)er cent of the voltages necessary to
break down the surface insulation between wire and pin during a
moderate rain.
AVhen the outside surface of an insulator is wet, as during a
moderate rain, it seems that the under surface of the insulator, and
the distance through air from the lower wet edge of the insulator
to the pin or cross-arm, make up most of the insulation that pre-
vents arcing over from the wire to the j)in or cross-arm. It further
appears that it is useless to extend the distance across the dry
under surface of the insulator indefinitely without a corresponding
increase of the direct distance throutjh air from the lower wet
edge of the insulator to the wood of cross-arm or pin. Insulator
number 7 in the tests under consideration had a diameter at the
lower edge of its outer petticoat of 7 inches, and was mounted on
a standard wooden pin. The diameter of this pin iii the })lane of
the lower edge of the insulator was probably about 1^ inches, so
808
12 INSULATORS
that the radial distance through air from this edge to the pin must
have been 2^ inches approximately. During a moderate rain the
surface insulation of this insulator broke down and an arc was
formed from wire to pin with 52,800 volts. The sparking distance
between needle points at 50,000 volts is 3.55 inches, according to
Volume XIX A.I.E.E., page 721 and must be shorter between
smooth surfaces, such as the wire and pin in question, so that
nearly all of the 52,800 volts in this case must have been required
to jump the 2J inches of air, leaving very little to overcome the
slight resistance of the wet outside surface of the insulator. On
this insulator the surface distance from wire to pin was 15J inches,
while the shortest breaking distance was only 7^ inches, so that
the distance across the dry under surface of the insulator must
have been 15A - (7J - 2|) = 10-A inches approximately. It is
evidently futile to put a path lOJ inches long across dry insulator
surface in parallel with a path only 2 J inches long in air, as an arc
will certainly jump this shorter path long before one will be
formed over the longer. The same line of reasoning applies to
number 3 insnlator in this test, which had a diameter of (r^ inches,
a surface distance from wire to pin of 13 inches and a minimum
distance of 7| inches, and whose surface insulation ])r()ke down at
48,()0() volts during a moderate rain. The absolute necessity of in-
creasing the distance between the lower wet edcres of insulators and
the pins and cross-arm, as well as the distance across the dry under
surfaces of insulators, has led to the adoption of the so-callt»d
umbrella tyj)e for some high-voltage lines. In this type of insu-
later the main or outer petticoat is given a relatively great
diameter, and instead of being bell -shaped is only moderately con-
cave on its under side. With an, insulator of this tvjK^ mounted on
a large, long pin, the lower edge of the umbrella-like ])etticoat may
be far removed from the T)in and cross-arm. Eenealh the larcre
petticoat of such insulators for high voltages there are usually one
or more smaller petticoats or sleeves that run down over the pin, and
increase the distance between it and the lower edtre of the larcrest
petticoat, if this distance is measured entirely through the air.
The inner petticoat or sleeve that runs down over the pin and
sometimes reaches nearly to the cross-arm, of course becomes wet
on its outside surface and at its lower edge during a rain, but
^^4
INSULATORS
18
Insulators on Transmission Lines.
Location of Line.
Voltage
of
Line.
Material
of
Insulator.
Porcelain
Porcelain
Glass
Porcelain
Glass
Porcelain
Porcelain
Glass
Porcelain
Porcelain
Porcelain
Glass
Inches
Diameter
of
Insulator.
Inches
Height
Insulator.
Electra to San Francisco
60,000
60,000
50,000
50,000
40,fX)0
:i3,(X)0
30,000
25,000
25,0(X)
22,000
13,(XX)
12,0(X)
11
11
9
10
7
71/
*/2
5
11>^
Colgate to Oakland, Cal
11%
Canon Ferry to Butte
12
Shawinigan Falls to Montreal
Provo around Utah Lake
13
5^
I^nta Ana River to Las Angeles
Spier Falls to Schenectady
4
r.%
7
Apple River Falls to St. Paul
Chambly to Montreal
Niagara Falls to Buffalo
Portsmouth to Pelham, N. H
Garvins Falls to Manchester, N. H.. .
3%
45i
between this lower wet part of the inner petticoat, or sleeve, and
the lower wet edge of the larger outside petticoat, there is a wide,
dry strip of insulator surface. A result is that an arc over the
surface of the outside petticoat can only reach the wet edge of the
sleeve by crossing the strip of dry under surface or jumping
through the air.
The same type of insulator is used on the 60,000-volt lines
between Electra and San PVancisco, and between Colgate and
Oakland, each insulator having an outer petticoat 11 inches diam-
eter and one inner petticoat or sleeve 6i inches diameter. This
inner petticoat runs down the pin for a distance of 7i inches below
the outer petticoat. Slightly different pins are used for mounting
Insulators on Transmission Lines.
Location of Line.
£leetra to San Francisco
Colgate to Oakland
Canon Ferry to Butte
Shawinigan to Montreal
Santa Ana River to Los Angeles. . .
Spier Falls to Schenectady
Niagara Falls to Buffalo
Chambly to Montreal
Inches
Inches
Inches
from
from
from
lop of
outside
lowest
insulator
petticoat
petticoat
to
'9
to
cross-arm.
cross-arm.
cross-arm.
HX
11
3X
15
UK
4
i'iX
->%
^X
M'A
n%
3K
3%
9.%
3?i
10%
7%
iX
10
5>^
3
Wi
4%
2
Inches
from edge
of outside
to edge
of lowest
petticoat.
7X
3%
2%
2J<
On each of the lines named in this table the wires are strung on the
tops of their insulators.
AQR
U INSULATORS
the insulators od the two transmission lines just named, so that
on the former the distance through air from the lower edge of the
outer petticoat to the cross-arm is 11 inches, and on the latter the
corresponding distance is 11^ inches. On the Electra line the
lower edge of the inner petticoat of each insulator is about 3}
inches, and on the Colgate line about 4 inches above the cross-arm.
The Canon Ferry line is carried on insulators, each of which
has three short petticoats, and a long separate sleeve that runs
down over the pin to within li inches of the cross-arm. This
sleeve makes contact with its insulator near the pin hole and elec-
trically may be considered a part of it. The outside petticoat of
each insulator on this line is 7| inches above the cross-arm, and 6|
inches above the lower end of the sleeve. Both the main insu-
lator and the sleeve in this case are of glass.
White porcelain insulators are used to support the 50,000-
volt Sliawinigan line and are of a design that has not come iuto
general use elsewhere. Each of these insulators has three petti-
coats ranged about a central stem so that their lower edges are 4i
inches, 9 inches and 13 inches respectively, below the top. The
highest petticoat is 10 inches, the intermediate 9 J inches, and the
lowest 4| inches in diameter. The height of this insulator is 13
inches, coinpaivd witli 11| inches for those used on the Electra
and Colgate lines, and 12 inches for the combined insulator and
sleeve used on the Canon Ferry line. AVhen mounted on its pin,
this insulator on the Sliawinigan line holds its wire 10| inches
above the cross-arm, compared with a corresjyonding distance of
14 A inches on tlie Klectra, 15 inches on the Colgate, and Vii
inches on the Canon Ferry line. The two upper petticoats on each
of these insulators are much less concave than the lowest one, and
the e(lo-t»s of all three stand resj)ectively ll'J, T|, and 8| inches
above the cross-arm. From the edge of the top to the edge of the
bottom j)etticoat, the distance is S\ inches.
Of the three transmission lines above named, that oj)erate at
50 to 00 thousand volts, that between IShawinigan Falls and Mon-
treal leads as to distances between the line-wire and insulator pet-
ticoats, and the cross-arm. On the Santa Ana line, where the
voltage is 8.5,000, the insulator is of a more ordinary type, being
of porcelain, ^V^l inches in diameter, 4| inches high, and having the
^^^
INSULATORS
16
lower edges of ite three j>etticoat3 in the same plaae. Each of
these iosiilators holds its wire 8§ iaches above the crosa-arm, and
has all of its petticoats 3^ incites above the cross-arm. Unlike the
^rxS^Jo^^-v^Sr ^^^..^^o.^^
^fz
three insulators just describt-d, which are inoimted on wooden pins,
this Santa Aim insulator has a pin with an iron core, wooden thread
16 INSULATORS
and porcelain base. This base extends up from the cross-arm a dis-
tance of 8^ inches, and the wooden sleeve, in which the threads for
the insulator are cut, runs down over the central bolt of the pin to
the top of the porcelain base, which is | inch below the petticoats.
Tie 30,000.volt lines from Spier Falls are carried 10| inches
above their cross-arms by triple petticoat porcelain insulators.
Each of these insulators is 8^ inches in diameter, 6| inches high,
and is built up of three parts cemented together. A malleable-
iron pin cemented into each insulator with pure Portland cement
carries with it the outside petticoat 7^ inches, and its lowest petti-
coat 4J inches above the cross-arm. When the voltage on the
Spier Falls lines was raised from about 13,000 to from 26,500 to
30,000, the circuits being carried in part by one-piece porcelain
insulators, a number of these insulators were punctured at the
higher pressures, and some cross-arms and poles were burned as a
result. No failures resulted on those parts of these lines where
the three-part insulators were in use. The second pole line between
Niagara Falls and Buffalo was designed to carry circuits at 22,000
volts, or twice that for which the first line was built. Porcelain
insulators were employed on both of these lines, but while the
11,000-volt line was carried on three-petticoat insulators, each
with a diameter of 7 inches and a heiffht of 5i inches, the 22,000-
volt line was mounted on insulators each 7i inches in diameter and
7 inches h\(r\\^ with only two petticoats. The older insulator had
its petticoats 2 inches above the cross-arm, and the lower petticoat
of the new insulator is 3 inches above the arm. These two insu-
lators illustrate the tendency to lengthen out along the insulator
axis as the voltage of the circuits to be carried increases.
For future work at still higher voltages, the advantage as to
both first cost and insulating qualities seems to lie with insulators
that are very long in an axial direction, like those on the Shawinigan
line, and which have their petticoats arranged one l)elow the other
and all of about the same diameter, rather than with insulators of
the umbrella type, like those on the Electra and Colgate lines.
^d^
ELECTRIC WELDING DEVELOPMENT.
The art of welding iron is probably as old as the earliest pro-
dnctioD of that metal by man; in fact, the reduction of iron in the
primitive forges demanded the union by welding of the reduced
particles, for no true fusion could have resulted, the percentage of
carbon present being too low. Until the closing years of the last
century iron was the only weldable metal, if we except gold and
platinum, — too expensive for common application.
The fact that nearly pure iron, so difficult to melt, becomes
quite plastic at high temperatures, while the oxide or black scale
melts long before the metal itself becomes fluid, thus providing a
liquid flux which is squeezed out during the process of union,
accounts for the unique position which iron held until recent
years. When, however, the heating effects of electric current
energy, so jR^rfectly under control, were applied to weld metals, a
metal or alloy which would not weld became the exce[)tion, instead
of the rule, as before. Much of the former work of the smithy
fire is now accomplished by the electric welding transformer, and
although many metals are easily manipulated by the electric proc-
ess, iron, of course, still occupies, as ever, the principal place.
The electric weld is becoming a more and more important
factor in many industries. During recent years the extension of
its application has been steady, and each year has witnessed its
entrance into new fields. Sometimes, indeed, new manufactures,
or new ways of obtaining results have been based upon its use.
The electric welds under consideration are the results of that oper-
ation of uniting two pieces of metal by what is known as the
Thomson process, first brought out by the writer and rendered
available in commercial practice a considerable number of years
ago. The rapidity, flexibility, cleanliness, neatness, accuracy, and
economy of the electric process has won for it such an important
standing in the arts that many future extensions in its application
are assured.
Note : This article by Prof. Elihu Thomson, the inventor of the sys-
tem of Electric Welding, first appeared in Cassiers' Magazine, and is here
reprinted by special permission.
ELECTRIC WELDING
The UBiforniity of the work, the control of the operation, the
extreme localisatioti of the heat to the particular parts to \m
uoitecl, aiKl the fact that the process is uot limited to iron and
Hteel, but can deal etpially well with other metals, such aa cop[>er.
brass, bronzes, and even lead, are characteristics of the electric
weldiit^ operation.
The Electric Welder. In its simplest fonn, an eletrtric
welder consists of n B[iw.-i«l transformer, the primary circuit of
wbieh receives current from an electriu station or dynamo gener-
ator, at a voltage usually from one hundred to five hundred
times that required to make a we!d. The cupper secondary circuit
of the transformer is generally only a single turn of very large
section, so that it may develop an extremely heavy current at from
two to four voltB. — an electric pressure so low that it cannot give
the least effect of shock, and one for which there is no difficulty
ring perfect insulation. The
clamps or viaea, attached to or carrieil npuu the terminals of the
■ELECTRIC WTXDTyO
I
^^P))inglH-tiirii si-i'undarj' circuit. The control of tbu clampiag tlevi<.*ei
BDil the current switcli is eitlier iiianiial, or. in some cases, yiitircly 1
automatic. Without attempting to enumerate the many apjtiiea- [
ttioiia of electric welding in the arts, we may refer to a few j
Bxauiplefl. '
Applications. In the waggon and carriage indiiBtry the proc-
BBB ia applied in the production of tires of all Bectiona, axles, hub,
■poke and sand bands, Hfth wheels, ehifting rails, steps, shaft iron,
Btc., while it has found a large use iu the welding into continnoua ,
Btrips or bands of the wires inclosed in rubber tirea for holding :
them in place. The larger part of the dash-frairies used in car-
riages iu the United States are now probably made by electric 1
■welding, whilo iron and steel agricultural wheels are built up, or
Iftve their parts united, by electric welds.
To ennmerate the inuiiy applications to the bicycle industry !
troald he almost to catalogue most of the metal parts of this use-
ELECTRIC WELDING
fal machine. It mnet be borne in mind, too, that a welding
machine, slightly modified, is equally applicable for locally heat-
ing parts in electric brazing or hard soldering, for upsetting, and
for bending or shaping. Bicycle crank hangers, pedals, seat-posts,
fork and fork ends, frames and brake parts thus become products
in which the welding transformer has its part. It has found a
useful field also in tool manufacture, such as drills, reamers, taps,
band and circular saws, drawing knives, carpenter's squares,
printer's chases, etc., etc., and electric welding has a closely related
use in the production of machine parts. Cam shafts and crank-
shafts are made from drop forgings welded together, teeth are
inserted into gear wheels, and teeth are welded to saw bodies,
including stone saws. Such things as inking rolls in printing
machines and fallers for looms are additional examples.
In the wire industry the part played by electric welding is
already quite important, and becomes steadily more so. Besides
the mere simple joining of wires of iron, steel or copper into lona
lengths, the welding of wire or strip into hoops for barrels, tubs,
pails, etc., is supplanting the older forms. Numerous machines
are in operation turning out electrically- welded wire fence, much
as a loom turns out cloth. In pij)e bending and coiling, as in
uniting ordinary lengths of pipe into very long lengths without
screw joints, tlie electric, weld has a special adaf)tal)ility. Hun-
dreds of miles of street railwjiy rails have been welded into contin-
uous lentftlis and now exist in niany cities. Where rails are
horuled only, the electric welder assists in the production of brazed
or welded bonds.
It is a wide rano;e In'tween bnckh^s, tyj>ewriter bars and
umbrella rods to the local annealing of armour plates on warships,
Init tlie electric welder covers that ranrre. It is no wider, how-
ever, than that from fine wires of a diameter of one-fiftieth of an
inch up to heavy steel wire for the armour of submarine cables,
and again up to street railway rail joints.
In recent years, elaborate machinery, for the actual produc-
tion on a large scale of steel tnbing from flat stock or skelp by the
progressive welding of a longitndinal seam, has been put into
o[)eration. Tlie long strip, or skelp, is rolled up so that its edges
meet. In this condition it enters between the weldinor rolls, which
402
pass tbe Iwjatili;! ciirri-nt locally scroas thu wlgea to weld tlit'in, and
tlitt opi^i-utiori ia progressive from one end of iho pifK) to the ollivr
as it is fed into the mai-hine. The result is a [)i|)e of which tlie
walls aru of even thickut-ss and the diameter uniform. This piiHi
cau be afterward drawn, if needed, lo the exact size desired. Very
thin pijw can be made of steel, the longitudinal seatn or weld in
which is a delicate Ix'ad along the length,— a Ix^aiuiful [iroduct,
for the extreme localisiition of the heat has allowed preservation of
surface and finish of the metal outside the joint. Taijer lubes,
6 ELECTRIC WELDING
8iich as are used for bicycle front forks and the like, are easily
made.
A similar machine for large work has lately been constmcted,
and l>y its use large diameter tubes or shells, up to 16 inches in
<liameter, are produced from sheet steel or iron. The accompany-
ing illustration shows such a machine ready for operation. The
welding transformer is at the top of the machine, and the second-
ary circuit has for its terminals two copper rolls inclined to each
other on two nearly horizontal shafts adjustable in position over
the work. Below are the guitle rolls, one on each side on vertical
shafts, and between these tlie sliell to be welded passes with its
meeting edges uj)jHTinost and in contact with the copper contact
rolls. As the metal shell [)asses along under these rolls the joint
■
is j)rogressive]y heated by the welding current crossing it, and the
weld Is finisluKJ by the side pressure of the guiding rolls. The
process, as well as the resulting welded product, is unique.
For a considerable time past, welding machines have been
applied to the pro<luction of bands or tires from stock of varying
width, thickness, and sectional form. More rec^ently the practice
of welding plain bands or cylindrical rings, and afterwards rolling
them with the form of section desired, has been largely adopted;
such as, for example, in the ])r(Kiuction of automobile wheel rims,
ban<ls for roviniJ" cans, stove rinrrs. etc.
\vr\ (litftMvnt from this is the formation of crankshafts, now
demanded in <n't'at numbers for entwines of automobiles. These
are made from drop forgings and
^
m c
3E^
round shaft stock by unitintr the
pieces, as in the annexed sketch,
and afterwards lightly machin-
ing and tinirhing the approxi-
mately correct shaft, as j)roduce(l by wehling.
Jiesides the banding of wire or strip of such comparatively
frail containing vessels as barrels or pails, the electric weld finds
application in the forming and capj)ing of metal vessels for with-
standing high pressures, such as soda-water cylinders, carbonic
acid reservoirs, and steel ])ott]es for nitrous oxide gas.
One of the most interestinjr of the more recent apj)lications is
that of welding hollow steel handles on cutlery, such as table
404
ELECTRIC WELDING
knives and forks. The operation is remarkable for the celerity
and neatness of the work, the articles being finiEihed by silver-
plating and polishing, as usnal. The hollow handle is drawn from
thin steel, and united to the knife blade or to tbe fork, as the case
may be, in a special welding machine, there being no brazing or
other o[>eration of joint -forming required. There ia, indeed, no
limit to the delicacy of the work which may be undertaken, pro-
vided only the welding apparatus is equally refined.
Adjustments. In the siuipler types of electric welders,
especially where the machine is designed to do a variety of work,
perhaps of different forma or sizes of pieces, or both, the adjust-
ments are usually manual; that is to say, the operatJons of olamp-
8 ELECTRIC WELDING
ing the pieces and applying the electric current and mechanical
pressure are each controlled by the operator. In other cases, such
as in the welding of copper or aluminium wire, the machine is, at
least in part, automatic. The pressure is automatically applied
and the welding current is cut oflP automatically upon the com-
pletion of the joint; the placing of the pieces in the clamps and
the switching on of the current is. in this case, manually per-
formed.
In other, more completely automatic, types, particularly
adapted for rapid repetition of the same operation on identical
pieces, the machine runs continuously, and its sequence of actions
is definitely determined by the construction. In such cases a
source of power, as by a belt, drives the machine, the movement
so imparted having the effect of clamping the pieces as they are
fed to the machine, puttincr on the current, applying the pressure,
cutting off the current and releasing the pieces.
The mechanism which has been developed for these purposes
displays, in many instances, much ingenuity. In these machines
the duty of the attendant is limited to the mere placing of the pieces
between the clamping jaws, just before they are clamped, and the
work is characterised by rapidity and by uniformity of the results.
More completely automatic still are machines for the produc-
tion of wire fencincx and for the consecutive weldinnr of the links
of chains. In these the operation, once started, goes on uninter-
ruptedly 80 long as the work holds out, or until the stock under-
going operation is exhausted. In the fence machines, of which
fifteen are now in existence, galvanised iron wires are fed from
reels parallel to one another, at distances apart depending on the
mesh desired. These may correspond to the warp in weaving.
Transversely to these, and at intervals corresponding to the mesh
selected, are fed wires, cut from a reel, which transverse wires are
the verticals in the finished fence itself and correspond to the weft
in weaving. A series of small welders are automatically brought
into operation to weld each transverse wire to the longitudinals
where the two cross. This done, the web so formed moves for-
ward, the operation repeats itself, and so on continuously. The
welding is, in this case, practically instantaneous, and all of the
movements of the machine are entirely automatic.
406
EXfCTBIC WELDIXO 9
Id tfaia wAj it is possible for a eiagle tnachiiie to tarn oat
many thousands of ttx^l of fencing per dar with a widtb of meah
from 2 or 3 inches np. l/ea vire is 09«d tbAn vbers the jointa
are made by twists or loops, and tlie stability or fixedness of pon-
tion of snoJi joints as are made is mncb more assorcd.
Kl.EfTTRIC CHAJN-WELDINO MACHINE.
Joints, 'Wliilti in irinat cHses of electrie welding th» joint
foniiB wbat la known as a liiitt weld, with a burr or exteusioii of
metal at tlio joint, whit-li, according to conditions, is either allowed
to remain or is forged down or dressed off, there ia no difficulty in
making lap welda electrically, and some of the recent work of the
electric welder ia of that character. While, too, the usual welding
ELEfCTHIC WTLDING
concerns pieces of tbe eanie metal, as iron to iron, eteel to steel, or
copper to copper, combination welds of different metals are made
with facility in many cases, as when brass and iron are united.
In tbe working of high-carbon steels the usual precautioDB to
prevfiit Luriiiiitj ur injury to tht) metal are, of course, rtiquired;
HOLUi OP l-.I.F.I-riiU-M.l.Y-Wy.LDKD WIDL FKVCE.
but, on account of the delicacy of heat control, they are more easily
adupti-d.
Quite recently automatic chain welders have been put into
use, and electrically- welded chain work will probably aoon attaio
an importance not second to the other priucipal applications
which have been briefly descrilied.
REVIEW ijIESTIOXS.
PRACTICAL TEST ^JCESTIONSL
la the f-'Tr^y.'^ s-xzicr.s of this CjvloivHiia
cucieroua ulj-:ra::vt? v\.i::.: lv> nro workrd o;.: in
detail ir. or-ir-r to sho-^v :Le a; jiioation cf tho v:iru^;;s
methoiisar.d pr:r. :;le>. Av.voii.j>ar.yir.i: t':.t<o ary
exar:.i''.'.-s f.r ; ra.tice whi..h will aid the n^ador iu
tixicg the j.-rir.cij'!t-3 in niir.d.
In the fullowinsr pases are triven a Iari^> numln^r
of te=it questions and jtrc.iilems whioh atTorvl a valu-
able means of testinc the reader's knowKnlire of iho
suhjecta treated. Thoy will l>e found exoellent prav*
tice for those preimringf for Colloire, Civil Service,
or Engineer's License. In some oasos nunierioal
answers are sriven as a further aid in this work.
■ •*
REVIEW QUESTIONS
ON THS RTTBJKOT OF*
ELEMENTS OF ELECTRICITY
1. What is a magnetic substance?
2. Name the essential elements of a voltaic cell.
3. Upon what does the capacity of a condenser depend?
4. If it were desired to reduce the magnetism in a piece of
steel, how could this l)e acconn)lished?
r>. What is a loadstone ?
6. What is the effect of self-induction upon the current?
7. How may the internal resistance of a c(»ll Ih^ made of
small amount?
8. Why does the compass needle point approximately north
and south ?
9. What is an electro-magnet?
10. Describe the process of electrotyping.
11. If one end only of a glass rod is rubbed with silk, will
or will not the unrubbed end l)e charged by electricity, and why ?
12. How may it be shown that the poles of a mjignet are
dissimilar?
13. Name a few applications of the heating effects of cur-
rents.
14. What is the source of electricity in the voltaic cell ?
15. How may it be proved that the charges produced by
frictional contact, although different in kind are equal in amount?
16. Give a definition of an accumulator.
17. What substance is the best conductor of electricity, and
what one is the best insulator ?
18. Suppose a piece of ivory and a piece of sulphur to be
rubbed with silk. After a suspended pith ball has been touched
411
ELEMENTS OP ELECTRICTTr.
by the sulphur, will it be attracted or repelled by the ivory, and
why?
19. What is an electroscope ?
20. Explain how polarization is overcome in double fluid
cells.
21. How may it be shown that the field of a magnet exerts
Its influence in certain definite directions ?
22. What are the essential parts of a condenser?
23. How may it be shown that the charge upon a body
resides upon its surface?
24. What is meant by the terms ** primary coil " and **seo
ondary coil " ?
25. How does the construction of the relay differ from that
of the sounder ?
26. Why does attraction take place between a charged liody
and a conductor brought within its inductive influence?
27. In what manner does polarization decrease the power of
a cell?
28. State three ways in which a current may be induced in
a coil of wire.
29. What is meant by electrolysis ? What is an electrolyte?
An anode? A kathode?
30. Upon what main factors does the amount of charge in-
duced by a charged body upon a conducting body depend ?
31. State Joule's law.
32. How may it be shown that a wire carrying a current is
surrounded by a magnetic field ?
33. (a) When glass is rubbed by wool, which substance
receives a ix)sitive charge, and which one a negative charge? (J)
Does the charge produced on the glass exceed in quantity thai
produced on the wool?
34. Why is it possible to obtain very high electromotive
forces by means of the induction coil ?
35. Explain why there is no gain in energy by use of the
electrophorus without a con*esponding expenditure o{ work.
<v\st
REVIEW QUESTIONS
OX THE SITBJKCX OF
THE f:lectric current
1. (a) Explain wliat is meant by electromotive force, (h)
What is its unit of measurement, and by what value is it repre-
sented?
2. (a) What is necessary to cause an elect rii* current to
flow? (J) What Is meant by tJie strength of a current? (c)
What is its unit of measurement, and by wliat value is it repre-
sented ?
3. What is the unit of resistiince and bv what value is it
represented?
4. Uix)n what three general factoi*s does resistance de[>end ?
5. What length of cupper wire 2 milliiuctci*s in diameter
will have the same resistance as 12 yards, 1 millimeter in diameter?
Ans. 48 vards.
6. State Ohm's law.
7. Two wires, whose resistances are respectively 28 and 24
ohms, are placed in parallel in a circuit so that the current divides,
part passing through each. What resistance is otYercd by them to
the current? Ans. 1 2.02 -j olmus.
8. Fifty Grove's cells (E. M. F. = 1.8 volts) are in series,
and united by a wire of 15 ohms resistance. If the internal resist-
ance of each cell is .3 ohm, what is the current ? Ans. {\ amperes.
9. (a) What is the unit of quantity of electricity? (A)
Define the ampere-hour.
10. What is the power in watts when 4000 jouU>s of work
are done in 50 minutes? Ans. l.JiJi + watt*».
11. How many horse-power are equivalent to 88 kilowatts?
Ans. 111 + hoi-se-power.
413
THE ELECTRIC CURRENT.
12. What is a shunt circuit?
18. A current of 18 amperes flows in a circuit whose resisti
ance is 116 ohms. What is the voltage? Ans. 2088 volta.
14. The resistance of 812 feet of a certain wire is 2.08
ohms. What would be the resistance of 240 feet of the same
wire? Ans. 1.6 ohms.
15. A total current of 56 amperes passes through a divided
circuit having the resistance of its branches equal to 28 and 4
ohms respectively. What is the current in each branch?
. In the 28-ohm branch, 7 amperes.
In the 4-ohm branch, 49 amperes.
16. What is the value of the current when 4 ampere-hoars
are delivered in a circuit in 20 minutes? Ans. 12 amperes.
17. (a) Define the joule. (6) Define the watt.
18. A 220-volt circuit supplies a current of 18 amperes.
What is the power in kilowatts? Ans. 8.96 K. W.
19. If the resistance of a certain wire is 2.3 ohms per 1000
feet, how many feet of the wire will be required to make up a
resistance of 17.8 ohms? Ans. 7739 + feet
20. What is the resistance of a wire having a diameter of
.2 inch if the resistance of the same length of similar wire having
a diameter of .04 inch is 64.2 ohms? Ans. 2.56 -J- ohms.
21. Define specific resistance.
22. The resistance of a circuit is 1.8^ohms and the voltage
is 110. Wliat is the current? Ans. 61 -f- amperes.
23. A circuit conti\ins a voltaic cell generating an electro-
motive force of 1 volt. Its electrodes are connected by three
wires in parallel of 2, 3, and 4 ohms resistance respectively. The
resistance of the cell is -^ ohm. What is the current?
Ans. 1 ampere.
24. Eight cells each having an E. M. F. of .9 volt and an
internal resistance of .6 ohm are connected in parallel, and the
external resistance is 3.4 ohms. Find the current.
Ans. .26 ampere (approx.).
25. What quantity of electricity will be conveyed by a cur-
rent of 40 amperes in half an hour? Ans. 72,000 coulombs.
26. The resistance of a circuit is 10 ohms, and the current
is 33 amperes. What is the power in watts ? Ans. 10,890 watte.
\\\
THE ELECTRIC CTRRENT.
27. How many wmtts are eqaiTalent to 14 hor»e-power?
Aii5. 10.444 watts.
28. Five condactors haTuig resistances respectively equal
to 14, 3, 20, 31 and 8 ohms are joined in series, and the E. M. F.
applied to the circuit is 50 volts. W^at is the current ?
Ans. .l>o amperes.
29. (a) Define conductance. (6) Define conductivity.
30. What is the resistance of 10 feet of annealeil gold wire
.001 inch in diameter at 32^ F., if the resistance of an inch cube
of the substance at 32^ F. is .8079 microhm? Ans. 123 -|- ohms.
31. A copper wire has a resistance of 13.5 olims at 43^ F.
What is its resistance at 57^ F ? Ans. 13.91 -j-or nearly 14 olims.
32. WTiat must be the resistance of a 220-volt circuit if the
current is to be 70 amperes? Ans. 8.14 -\- ohms.
33. The E. M. F. applied to a circuit is 582, and tlie cur-
rent is 8 amperes. A number of lamps connected in tlie circuit
require a total drop of 522 volts. Find tlie resistance of tlie
remaining portion of the circuit. Ans. 7.5 ohms.
34. A circuit is made up of six wires connected in parallel
and having resistances of 72, 60, 21, 36, 40 and 210 ohms resi>ec-
tively. Find their joint resistance. Ans. 7.3 -|- ohms.
35. When a cell, which has an internal resistance of 1.39
ohms and an E. M. F. on open circuit of 1.32 volts, is supplying a
current of .29 ampere, what is its available E. M. F. ?
Ans. .92 volts (approx.).
36. With a current of 20 amperes how much time will be
required to deliver 4,000 coulombs. Ans. 3 minutes, 20 seconds.
37. The voltage of a circuit is 103 and the current is .6
ampere. What energy is expended in a minute and a half?
Ans. 4635 joulofl.
38. The resistance of a coil of platinoid wire at 98"* (/. is
8014 ohms. What resistance would the coil have at IS'' C. ?
Ans. 2962 ohms (approx.).
39. What is the resistance of 28 feet of No. 6 (li. ^ S.)
pure copper wire at 90** F. ? Ans. .0118 -j- olim.
40. If a resistance of 116 ohms l>e inserted i i a circuit, and
it is desired to maintain a constant current of 9.6 amporeH, liow
much must the voltage of the circuit \)e increasf»d ?
Ann lUn I snhM.
41 A
THE ELECTRIC CURRENT.
41. When a current of 14 amperes flows in a circuit whosd
resistance is 54 ohms, what energy in Jdlowatt-hours is expended
in half an hour? Ans. 5.292 kilowatt-hoois.
42. Explain the difference between the kilowatt and the
kilowatt-hour.
43. What number of calories will be developed by a current
of .14 ampere flowing through a >vire of 4 ohms resistance for 5
minutes ? Ans. 5.6 -}- calories, .
44. The voltage applied to a circuit in which three wires
are connected in parallel is 107. Find the current in each branch
if the separate resistances are respectively 43, 9 and 25 ohms.
In 43-ohm branch, 2.4 -}- amperes.
Ans. In 9-ohm branch, 11 -}- amperes.
In 25-ohm branch, 4.2 -}- amperes,
45. How many hoi-se-power are equivalent to 1048 watts?
Ans. 1.4 -}- horse-power.
46. If the resistance of 1 foot of annealed silver wire .001
inch in diameter at 32° F. is approximately 9.02 ohms, what is
the resistance of 4 miles of the wire .01 inch in diameter at a
temperature of 90° F. ? Ans. 2137 + ohms.
47. Twenty large Leclanche cells (E. M. F. = 1.5 volts,
resistiinco =i 0.") ohm eacli) are in a circuit in which the external
resistance is lo ohms. Find the strength of current which flows
(«) wlieii the eells are joined in series; (ft) when all the cells are
in j)arallel ; (r ) wlien tliere avo. 2 files each having 10 cells in
series ; and (^ci) when there are 4 liles each having 5 cells in series.
Ans. Amperes (a) l.f); (ft) 0.149; (c) 1.2; (</) 0.706.
48. How many kilowatts are equivalent to 150 horse-^wwer?
Ans. 111.9 K. W.
40. If a current of 9.3 amperes flows when the voltage of a
circuit is 110, how much resistance must be inserted in the circuit
to reduce tlie current to 3.4 amperes ? Ans. 20 4-ohms (approx.).
r>0, A current of 26 amperes is flowing in a circuit which
has a voltiige of 500. What is the equivalent power in mechani-
cal units ? Ans. 17.4 + horse-powar.
4\G
REVIEW QUESTIONS
ON THB HUDJKOT OF
ELECTRICAL MEASUREMENTS.
1. What is the distinction between fundamental and
m
derived units?
2. What is meant by the dimensions of a physical quan-
tity?
3. Describe a method of calibrating ammeters.
4. Explain why a voltmeter should have a high resistance
and an ammeter a low resistance.
5. The ohm is equal to how many absolute units of resist
ance?
6. Upon what factors does the deflection of a galvanome*
ter needle depend?
7. How may the resistance of a water rheostat be varied?
8. It is known that a coil of wire has an approximate resist-
ance of 200 ohms, and it is desired to find its correct resistance
tothe first decimal place by using the Wheatstone bridge. What
should be the ratio of the bridge arms?
9. State the difference between the two general classes of
galvanometers.
10. Give the advantages of the D'Arsonval galvanometer.
11. How many B. A. ohms are equal to 96 International
ohms?
12. A galvanometer has a resistance of 5940 ohms and iti
shunt 60 ohms. What is the multiplying power of the shunt ?
13. (a) What is the value of the kilowatt-hour? (^) How
UT
ELECTRICAL MEASUREMENTS.
many kilowatt-hourB are expended by a current of 60 amperes in
8 hours and 45 minutes, the E. M. F. being 110 volts?
Ans. 24.75 kilowatts-hours.
14. When using the Wheatstone bridge why should the
galvanometer key be closed after and opened before the battery
key?
15. Explain why an astatic pair of needles is very sensitive
to a slight current when the coil carrying the same is wound about
one of the needles.
16. How may a galvanometer be used as a voltmeter ?
17. Explain the principle of a differential galvanometer.
18. The E. M. F. of a Leclanche cell on open circuit as
sriven by a voltmeter was 1,64 volts. After closing the cell
through a certain exteiiial resistance, its E. M. F. fell to 1.10
volts, the current being .4 ampere. What was the resistance of
the cell?
19. Describe the Weston voltmeter.
20. In Fig. 21 suppose the reversing key to be changed, and
that a balance is obtained when M = 1, iV = 100, and P =
j^^OOO + 400 4-200 + 30 + 3 + 2. What is the value of the
resistance measured?
21 . What are the disadvantages of electromagnetic ammeters ?
22. In testing the insulation of a circuit by the voltmeter
method, the voltmeter reading was 4.5 volts and the applied
E. M. F. 220 volts. What was the insulation resistance in meg-
ohms, the voltmeter resistimce being 17,000 ohms?
23. In making a high resistance measurement by the direct
deflection method, the deflection obtained with .1 megohm resist-
ance was 250 divisions. The unknown resistance gave a deflec-
tion of 20 divisions. In the former case the multiplying power of
the shunt was 1000, and in the latter the shunt circuit was open.
What was the unknown resistance ?
24. What method should be used in testing the insulation
of a 1,000 volt circuit?
25. (a) l)escril)e an electrosUitic voltmeter. (6) Give its
advantages and disadvantages.
26. How b quantity determined by the Edison chemical
meter?
\\%
REVIE\r QCESTIOXS
O^ T-HK Sr'BJKCT- O:
ELECTRIC WIRIXG,
1. Under wha: o-::i::i>L^ is "nshiiiii'* of wir^^ alUnved I
Explain the ['r*:or^^.
2. In e«>n«i.i:t w-rk b«'.v many i|v.ar:cr Kiuls an^ allo\\*od
from outlet to •jiriet '
3. Tell what V..U can a':-*ii* tl* \ii»li <.^•rti.
4. Where >L«>uld cm-t:»ii:s or cirv'uii breakers Iv Kx^atini for
house wiring t
5. What must he the vohaire of the ilynamo in orvlor to sujv-
ply lamps or motors in a 110 volt system, with a o jvr ivnt Kv^f
6. What is a cull i^Ae I
7. When a high-|H»tential machine has its frame i::nmnihHl»
what precautions should be taken for the j>i\>tirtiou of tlie At-
tendant ?
8. What can vou sav al)out the rules to be fi^Uowtnl when
installing wires ?
9. Give a rule for the proper depth to which to s(^t a ptdo.
10. IIow would you ground a dynamo frame i
11. What is the least allowable radius of eurvatun^ in ooh
duit work ?
12. State the ride to be followed in starting or nti^pping
motors.
13. What is the objection to putting tlu* ground win^ fnun ii
lightning arrester into an iron ])ip(»'i(
14. State briefly the recpiirenuMitH for interior wiring in tho
case of series arc lighting work.
din
ELECTBIC WIRING
16. Describe the care which should be given to the brushes
to keep them in good condition.
16. Describe a piece of apparatus for protecting the arma-
ture of a motor.
17. Why should standard rubber-covered wires be used in
conduit work ?
18. What is the least space that should be left between
(a) The switchboard and the floor?
(b) The switchboard and the ceiling?
19. What is the largest permissible current dependent upon
one cut-out ?
20. What insulation resistance is required between gas pipe
attachments and an insulating joint ?
21. Under what conditions should the frame of a dynamo be
grounded ?
22. What kind of wire must be used in moulding work ?
23. What can you say about wiring for damp places ?
24. In which direction does the armature of a generator
usually revolve ?
25. Determine by use of table on page 40 what size of wire
should be used to supply 75 16-candle-power incandescent lights,
110 volts, loss 3 volts, and at a distance of 200 feet to center of
distribution.
26. What is the best material for poles?
27. Describe a method of setting the brushes so that they
will be diametrically opposite each other.
28. In splicing two pieces of wire, what precautions are
necessary ?
29. What size of wire will be required to supply a 10-horse-
power motor on a 500-volt circuit at a distance of 200 feet with 15
volts' drop ?
30. What current is taken by the motor referred to in Ques-
tion 29 ?
31. Describe the connections for the three-wire system.
32. Determine by formula the size of wire for 40 16-candle-
power incandescent lights on a 110-volt circuit with 5 volts* drop
at a distance of 150 feet.
^"^o
ELECTRIC WIRING
33. Under what conditions may the neutral of a three-wire
system be grounded ?
34. What is the smallest sized wire that should be used for
interior wiring?
35. In ease of hot box, what should be done before deciding
that it is necessary to shut down ?
3G. What are the objections to using excessive volcage for
incandescent ligliting circuits ?
37. Describe with sketch the direct-current ground detector.
38. If iron pipe be used with alternating current, should the
two or more wires of a circuit l>c placed in the same conduit, or
in separate conduits ?
39. In wiring a building, what is the least insulation re-
sistance allowed between conductors and the ground for 100
amperes ?
40. If a d\Tiamo is to be run in parallel with another ma-
chine and its polarity is wrong, how can this be remedied?
d.91
REVIEW QUESTION'S
OM vrnm BUBamavp ov*
THE ELECTRIC TELEORAPH!.
1. Give examples of the different kinds of messages.
2. Wherein does the construction of the relay differ from
that of the sounder? Why?
3. How many copies are made of train orders? Why?
4. How does the count of a government message differ
from that of an ordinary message? Of a cable message?
5. How could signals be transmitted without a key ?
6. (a) What is Code telegraphy? (b) Give a brief example.
7. In copying a message why is the destination placed on
a line by itself?
8. (a) Give three points of difference between commercial
and railway telegraphy, (b) What is the important feature of a
railway operator's work?
9. In the switchboard, what is the only means of electrical
connection between the bars and discs?
10. Name the apparatus used in a one-wire office.
11. What are the parts of the sounder?
12. (a) What are the six different classes in which the
signals of the Morse code can be arranged? (b) Give examples.
13. What part of the relay does the work of a key for the
local circuit?
14. (a) In the Auto-Alphabet instrument what determines
the movement of the local points? (b) What care must be taken
with regard to them?
15. (a) What are the elements of the Morse code? (b) Which
is the time unit?
16. (a) How would you transform the local circuit into a
learner's outfit?
^TH
RKVIEW QUESTIONS
0>r TMK HUHJBOfr OB*
THE ELECTRIC TELEORAPH
1. What test can be apj)lied to make sure that the armature
of an electromagnet does not touch the core ?
2. What is the essential feature of the Phonoplex ? How
are the signals produced i
8. What are the principal uses of the dynamo in telegraphy?
4. What two forms of ap|)aratu3 are combined to form the
quadruplex i
5. [a) What is static electricity ? (J) IIow are the effects
of the discharge on the duplex relay overcome?
f). If the transmitters are open in the Stearns duplex, admit-
ting a small proportion of each battery to line, how can the effect
on the relay be overcome?
7. What is the only means of electrical connection in the
switchboard between the rows of discs and the strips?
8. How is the home relay in the Stearns duplex made unre-
sponsive to the home battery?
9. What is the function of the transmitter in the quadruplex
as compared with that of the pole changer?
10. What is the rule for determining the polarities in a core
around which a current is passing?
11. What would be the resistance of six four-ohm sounders
in series? In multiple?
12. What is a rheostat and what part does it play in the
duplex ?
13. How could a test of the short and long end of the quad
battery be made without a meter?
14. What is meant by a differential relay?
483