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A51

ALEXANDER GRAHAM BELL,
Inventor of the Electric Telephone,
Photophone, Induction Balance.
TELEPHONY
BY
WILLIAM C. BOYRER, M. E., M. M. E.
Formerly Division Engineer
New York and New Jersey Telephone Co.
INCLUDING SPECIAL ARTICLES
By
KEMPSTER B. MILLER
A. FREDRICK COLLINS
SAMUEL G. MC MEEN
H. S. DURANT

MOUNIV
Chicago
American School of Correspondence
at
Armour Institute of Technology
MCMV.

COPYRIGHT 1905 BY
AMERICAN SCHOOL OF CORRESPONDENCE
Entered at Stationers' Hall, London
All Rights Reserved
O
И ОПИ)
it
PUBLISHERS NOTE
'st's bo-1-9
T
a few years ago
elu
HE rapid development of Telephone Engineering within
the last few years has created a demand in this field for
trained men, whose education and knowledge of the sub-
ject must be no less complete than that required by the so-called
“heavy-current” engineers. It is becoming realized that the
problems presented in the installation, operation and maintenance
of a large telephone exchange lend themselves to scientific investi-
gation, and that progress is much more rapid from this standpoint
than by means of the empirical and haphazard methods in use
.
(In view of these facts and because of the ever increasing
importance of the telephone in business and social life this volume
has been prepared. It is made up of the Instruction Papers in
the Telephone Course of the American School of Correspondence,
covering the subjects of telephone instruments, pole line construc-
tion, the common battery system, intercommunicating sets,
telephone exchanges, operation, maintenance, and private branch
exchanges. A valuable feature of this work is the clear and
complete discussion of the methods of testing for and locating
faults in all parts of the system, together with a description of
the instruments used in such work. The above mentioned text
is supplemented by timely articles on such subjects as wireless
telephony, the automatic telephone, and telephone line protection.
( A characteristic of the entire work is its thoroughly practical
nature and the illustration of all principles explained, by means
of diagrams and circuits.

Reclair 4.942
193607
The successful engineer of to-day is neither the man who has
only a theoretical education to recommend him, nor the man
whose stock in trade consists solely of practical experience, but
he is rather the one who has both a theoretical and practical
knowledge of his subject. It is believed that this volume
presents a happy combination of the theoretical and practical,
a
so that it will have something to offer to the man whose educa-
tion is deficient from either standpoint, and if such is the case
no other excuse for its existence is necessary.
CHICAGO, August, 1905.

CONTENTS
TELEPHONE INSTRUMENTS.
Page 11
TELEPHONE LINES
71
TELEPHONE EXCHANGES
56
170
COMMON BATTERY SYSTEMS
236
TELEPHONE OPERATION
66
275
TELEPHONE MAINTENANCE.
305
AUTOMATIC TELEPHONE
365
WIRELESS TELEPHONY
375
TELEPHONE LINE PROTECTION.
387
66
QUALITY OF TELEPHONE SERVICE
395
AUTOMATIC V. MANUAL EXCHANGES.
403

REVIEW QUESTIONS
413

INDEX
427

MAIN EXCHANGE, CLEVELAND, OHIO.
Largest Four-Party Selective Ringing Switchboard in the World.
Kellogg Switchboard and Supply Co.
TELEPHONY

PART 1.
To properly understand the manner in which sound is trans-
mitted from one end of an electric circuit to the other, it will be
necessary to entirely get rid of a popular idea, and to fix clearly in
mind, at the outset, the process that actually takes place. The
popular idea referred to is, that the sound produced at one end of
a circuit actually travels over that circuit, in order to be heard at
the other end. That is erroneous; in reality the actual sound
produced at one end of the circuit, properly equipped with tele-
phone apparatus, travels no farther than it would if the telephone
apparatus were not present. What actually takes place is a process
conforming to the law of Conservation of Energy. It may be
described as follows: The sound energy produced in the presence
of the telephone apparatus is transformed by that apparatus into
electric energy, which, traveling to the distant end of the line, is
again retransformed by the distant apparatus into sound energy.
The sound energy thus reproduced, being an exact counterpart of
the original, produces on the human ear the same effect, and there-
fore can not be distinguished from it.
Nature of Sound. Sound may best be defined as the effect
produced on the ear drum by wave motions in the air particles.
Every-day experience offers many proofs of this statement. If a
man be observed while in the act of hammering nails into a
plank, it will be found that, at a distance of about ten feet,
the instant the hammer head strikes the nail a sensation is pro-
duced on the ear, which is recognized as the sound of the impact.
A little reflection will convince the observer that, although sepa-
rated from the point of impact by ten feet, the result of that
impact is transmitted in some manner through the intervening
space, and made to impress the ear with the sense of sound. In
11
4
TELEPHONY
c" CC
other words, the disturbance caused at the source of the sound is
carried through the intervening space, and in turn affects the
auditory nerves in such a manner as to produce sound. If no
intervening objects exist, such as a board fence or house, it will
be found that the sound may be heard with equal distinctness at
any point of a sphere whose radius is ten feet and whose center
lies at the point of impact. It therefore becomes established that
the disturbance caused by the hammer striking the nail is trans-
mitted with equal intensity along all lines radiating from the
point of impact.
Let the observer walk away from the man in question, con-
tinuing, however, to keep him under observation. He will note
that, as the distance increases
perceptibly, the sound of the
blow will no longer occur at the
same instant that the hammer
is seen to strike, but at an ap-
preciable time afterwards, and
this interval will increase with
the distance.
For a comparison between
the phenomenon of sound which
has just been observed, the work-
ings of which cannot be seen with
the eye, and some other phenom-
enon which can be seen, let us
Fig. 1.
consider what happens when a
stone is thrown into a pond whose surface is unrufled. Upon the
stone entering the water a disturbance is produced, which radiates
in waves in all directions. Any objects, such as chips of wood,
that
may be floating on the surface are agitated as the wave reaches
them. Those nearest the point where the stone enters the water
are set in motion sooner than those more remote. In fact, the
wave can be observed to progress from the center of disturbance
till it gradually dies out or strikes the shore.
From these simple observations, it is natural to imagine that
sound consists of a wave motion among the particles of air, which
motion progresses from the center of disturbance along the radii

A
El
B

12
TELEPHONY
5
OD
B
of a sphere. Other simple experiments will be made to prove that
sound does really consist of wave motion among air particles.
In Fig. 1 let A be a table upon which is fastened a vice B in
the jaws of which a flat piece of steel D is tightly held. If the
free end of C be drawn to one side, as shown at C', and then
allowed to go free, the elasticity of the metal will cause it to re-
turn to the vertical position, beyond which the kinetic energy due
to its motion will carry it to the other side, as shown at C". From
this position the elasticity will again cause it to return to the ver-
tical, beyond which the kinetic energy will again carry it to some
position between C and C. The elasticity will again cause it to
return to the vertical. This constantly decreasing motion will
continue until the piece of steel gradually comes to rest. It is
evident that the particles of air,
directly surrounding the bar,
will be given a similar motion
to that of the steel. If the
spring is made to move rapidly
enough, a sound will be heard.
Referring again to the piece
of steel: the motion of its end
from C to C' and back, or from
C' to C", is called a complete
vibration. The time taken to
make a complete vibration is
Fig. 2.
called a period of vibration.
To prove that sounding bodies are in a state of vibration the
following experiment is useful: In Fig. 2, let A be a glass bell-
shaped jar, and B a fixed steel point which is separated from the
surface of the jar by a very small space. If a resined violin bow
C be drawn across the edge of the jar till it emits a musical note,
a series of taps will be heard. They are caused by the glass bell,
in its vibration striking against the point. If a pith ball D, be
suspended so as to rest lightly against the side of the bell, it will
be violently thrown away from the jar when a musical note is
emitted.
If a glass plate A, Fig. 3, be secured at its center and sup-
ported on a table, it will, upon being agitated by a resined bow,

A
с
a
13
6
TELEPHONY

SASS
emit a musical note. Suppose sand be strewed on its surface. If
the plate is agitated, the sand will leave certain portions of the
plate bare, and collect in definite lines on different portions of the
plate. The lines so occupied by the sand are the places where the
different waves of vibration meet to form lines of rest.
The above experiments are sufficient to prove that all sound-
ing bodies are in a state of vibration, and that the phenomenon of
sound is caused by this vibration being carried in wave motion by
the air particles to the drum of the ear, and thence by the auditory
nerves to the center of sound in the brain.
The student must not suppose that the sense of sound is caused
by the particles of air, in actual contact with the sounding body,
being projected against the ear drum. Such is not the case, any
more than that the remote
chips in the pond are set in
motion by the particles of
water at the point where the
stone enters.
What actually
happens in the case of the
pond is that the particles of
water being thrown aside by
the stone, set up by means
of the elasticity of the wa-
ter a vibratory motion in
the adjacent particles. These
in turn set up the same
motion in those adjoining.
Successive particles are thus set in motion by their neighbors,
until the energy dies out, or until particles are reached which,
being adjacent to the shore, have no fellows to which to transmit
the vibration. The particles of water originally set in motion by
the stone, continue to oscillate with a decreasing amplitude, at or
very near their original locality, until they come to rest.
Similarly in the case of sound, the particles of air adjacent to
the disturbing body are set in motion, ard this motion is, through
the elasticity of the air particles, transmitted to those next adja-
cent. These in turn transmit it to their neighbors until the motion
dies out. When the particles of air adjacent to the ear drums are

A
et
Fig. 3.
14

TELEPHONY
7
set in motion, the sensation of sound is produced. The particles
disturbed remain in their original localities.
Air is not the only medium that will transmit sound. Metal,
wood, water, and even earth, are useful in this respect. But for
the present it will be sufficient to limit the discussion to sound
transmission through air.
Let us consider again the experiment of throwing a stone into
a pond. If the stone be of good size, such as is used in street
paving, the waves caused thereby will, upon close observation, be
found to be of different sizes. The largest wave will carry upon
its surface waves of less and less magnitude, down to the size of
ripples.
Nature of Sound Waves. The waves produced in water are
the result of the parti-
cles of water being dis-
ΑΑ Α'
M M' M"
turbed in a vertical di-
rection, and the direction
of wave propagation is
therefore at right angles
to the direction of the
displacement of the par-
Fig. 4.
ticles. In the case of
sound, the displacement of the air particles is in the same direc-
tion as that of the wave propagation. The displacement of
the air particles consists of an oscillation to and fro in the direc-
tion of the wave propagation. These oscillations produce alternate
pulses of condensation and rarefaction, which constitute the sound
B
B

wave.
To illustrate more fully, suppose that in Fig. 4, A represents
one of the prongs of a tuning fork which is vibrating in front of
the open end of a tube BB filled with air. As the prong A moves
toward the position A' it pushes before it the adjacent particles of
air, which in turn push their neighbors. The result is a pulse of
compression in front of the fork. When the prong A has reached
the position A’, it momentarily comes to rest, and consequently
ceases to act on the air particles. The particles of air beyond are
in a normal condition, because the pulse of compression has not
yet had time to travel any appreciable distance. As the prong of
15
8
TELEPHONY
the fork moves back from A' to A", a partial vacuum is formed,
and the air particles begin to move in the direction of the fork,
causing a pulse of rarefaction. By the time the prong has reached
the position A" and again comes to rest, the pulse of compression
has moved to some point as M. The shaded lies denote the
greater density of the air particles. With the pulse of rarefaction
being formed at the fork, the air particles tend to rush that way,
and by the time the fork has again reached the position A', and a
second pulse of compression formed, a pulse of rarefaction is found
at M' and the pulse of compression has moved to M". This oscil-
lation of the air particles continues in unison or harmony with that
of the prong of the fork, causing successive pulses of compression
and rarefaction to be sent through the air in the tube. The dis-
tance between the center of a wave of compression and a wave of
rarefaction is called one-half a wave length, while the distance
between two consecutive waves of compression is called a whole
wave length. A wave length may be defined as the distance
through which the pulse has traveled while the prong of the tuning
fork has made one complete vibration, during which time each
particle of air has gone through one complete cycle of changes,
both as regards motion and density. The period of vibration to
each particle is thus identical with the period of vibration of the
prong of the tuning fork. It has been proven by experiment
that the rate of sound traveling in air is 1,090 feet per second.
Now, if the tuning fork vibrates at the rate of 435 complete vibra-
tions per second, the period will be 57 second, and the wave
length will be 12039 = 2 feet and 6 inches, which is the wave
,
length in air for this note.
Noise and Musical Sound. Thus far the discussion has been
concerned only with sound waves of uniform length. It will be
necessary at this point to inquire more specifically into the nature
and construction of this wave. The discussion should be prefaced
by this definition: The difference between noise and musical
sound lies in the frequency of the disturbance. When the fre-
quency exceeds 16 impulses per second, the human ear is not
capable of distinguishing the separate impulses, but recognizes
them only as a continuous sound. This fact may be illustrated
by a piece of mechanism shown in Fig. 5, which consists of a
1
435
435

18
TELEPHONY
9
toothed wheel, which can be made to revolve, while a piece of
cardboard is firmly held in such a position that the teeth strike
against it as they pass. If the number of teeth on the wheel is
known, the number of revolutions of the wheel per second multi-
plied by the number of teeth will give the number of impulses
given to the card in the same time. Rotating the wheel slowly at
first, the separate impacts of the teeth against the cardboard are
plainly discernable. As the wheel rotates faster, the separate im-
pacts become less distinct, until when the number reaches 16 per
second they merge into one another and become a musical note.
If the speed of rotation be steadily increased from this point, the
musical sound becomes steadily shriller, until it becomes so shrill,

Fig. 5.
or, in other words, the frequency so high, that the ear is unable to
take any cognizance of it.
Musical sounds can be distinguished in three ways:
Loudness. This is the quality which, regarded subjectively,
measures the intensity with which a musical sound affects the
auditory nerve. This quality depends, for sounds of the same
pitch and quality, on the energy of the vibration of the air parti-
cles adjacent to the ear drum, and is proportional to the
the amplitude.
Pitch. This is the quality which distinguishes an acute
sound from a grave one; for example, a treble note from a bass
note. Pitch depends upon the frequency of vibration, rising as
the frequency rises. This point is illustrated by means of the
toothed wheel and the card.
Character. This is the quality which distinguishes between
the sound of the human voice and that of a cornet; or between
square of
17
10
TELEPHONY
.
a
that of a violin and that of a French horn. The terms poor, harsh,
rich, mellow, are used in this connection. The French call this
quality timbre; while the Germans use the term sound tint, or
sound flavor.
The point upon which the character of a sound depends was
made a special study by the celebrated German scientist, Alex-
ander Von Helmholz, and it may be explained as follows: The
first essential characteristic of a musical note is that each vibration
shall be exactly like its successor. In other words, the disturb-
ance must be periodic. It has been shown by the French mathe-
matician, Fourier, that any periodic vibration executed in one line
can be definitely resolved into simple vibrations of which one has
the same frequency as the given vibration, and the others have
frequencies 2, 3, 4, 5, etc., times as great. The theorem may be
briefly expressed by saying that every periodic vibration consists
of a fundamental simple vibration and its harmonics. As a result
of this reasoning, a sound wave caused by a musical note must
always be considered as consisting of one simple vibration, corre-
sponding in frequency to the pitch of the note, and several other
vibrations whose frequencies are multiples of the first or funda-
mental. This point is exceedingly important and should be clearly
understood. Speaking in the language of the musician, the funda-
mental vibration corresponding to the pitch of any note is called
the fundamental, while the accompanying vibrations of higher
frequency are called the over-tones. Helmholz determined that
the character of a note depended on the number of over-tones.
The vowel sounds used in speech are musical tones just as much
as those used in singing, only they are not sustained as long. The
laws governing their pitch intensity and character are therefore
the same as those already described. To sum up, then, when a
person is speaking, the surrounding air particles are agitated within
the range of the voice by a periodic vibration whose frequency, and
therefore wave length, corresponds to the pitch. Superimposed
upon this vibration are others whose frequencies are multiples of
the first and their wave lengths the corresponding fractions of the
first.
The Nature of Electricity. Up to this point the subject of
sound only has been considered. The object has been to fix clearly


18

TELEPHONY
11
in mind the fundamental principles of the wave theory. The ap-
plication will be seen when the action of the sound waves on the
telephone instrument is considered. However, it will now be
necessary
to inquire into the subject of the generation of electric
current. The flow of current in any circuit is given by Ohm's
E
law, which is expressed: I = in which I represents the current
R
in amperes, E the E. M. F. in volts acting in the circuit and
R the resistance of the circuit expressed in ohms. From this
equation it will be seen that to have a flow of current in an elec-
tric circuit, an E. M. F. or difference in potential is necessary.
Therefore, the first point to be considered is the method of gener-
ating this E. M. F. E. M. F. may be generated in three ways:
first, by chemical action between two or more bodies; second, by
the heating of the junction point of two dissimilar metals; third,
by the movement of a closed circuit in a magnetic field. For com-
mercial purposes the first and third methods only are common.
The second method is used only in laboratory experiments. The
apparatus by means of which chemical action generates electric
current is called a battery. A mechanism which is used to gen-
erate E. M. F. by moving a closed circuit in a magnetic field is
called a dynamo or generator.
Batteries are divided into two classes, Primary and Secondary.
A primary battery may be defined as one in which chemical action
takes place directly to produce the E. M. F., while in a secondary
battery the E. M. F. is produced by the chemical action set up
after a current of electricity has been passed through the cell for
some time. Secondary batteries are commonly called storage
batteries.
There are many types of primary batteries, each possessing
peculiar features. In telephone practice, however, the types avail-
able are limited to a few that meet the peculiar conditions required.
They are, first, the Gravity Battery; second, the Leclanche Battery;
third, the Fuller Battery; fourth, the Edison-Laland Battery; fifth,
some forms of dry battery.
Gravity Battery. In all forms of primary battery the E. M.
F. is generated by chemical action taking place between two dis-
similar bodies called the elements, which are surrounded by a


.
a
19
12
TELEPHONY
liquid called the electrolyte. The whole is encased in a glass jar.
The electrical potential generated in the cell depends on the nature
of the substances used as elements. In the gravity cell the ele-
ments consist of metallic zinc and metallic copper, and the electro-
lyte is a solution of copper sulphate in water. The generation of
E. M. F. is attended by certain chemical changes which take place
in the cell. The oxygen from the water attacks the zinc element
forming an oxide of zinc, which in turn combines with the sul-
phuric acid to form zinc sulphate, setting free the hydrogen. The
hydrogen thus released attacks the copper sulphate, displacing
the copper and forming sulphuric acid, and depositing the
copper in metallic form. The newly formed sulphuric acid again
attacks the oxide of zinc, forming additional zinc sulphate and
D
F
again releasing hydrogen, which in
turn displaces metallic copper as be-
fore. As a result of this chemical
action the elements remain in the
B
form of metallic zinc and metallic
copper.
А Polarization. By the term polar-
ization of a cell is meant the collect-
ing of bubbles of hydrogen on the
copper or negative element. These
hydrogen bubbles have an E. M. F.
opposite to that set up by the zinc
element, and as a result the two E. M.
Fig. 6.
F.'s of the cell, that due to the poten-
tial difference between the zinc and the copper, and that due to
the potential difference between the hydrogen bubbles and the
zinc, are opposed to each other. When this condition exists, the
cell is said to be polarized and the current ceases to flow. Since
the hydrogen gas does not collect on the copper plate, but is com-
,
bined with the sulphate, polarization does not take place in the
gravity cell.
Fig. 6 shows a cell of a gravity battery. Here the glass jar
is shown at A, the zinc element at B, and the copper
element at
C. To the copper element is riveted an insulated wire D, while
the zinc element is shaped to fit firmly over the top of the jar and


с
20
TELEPHONY
13
3
carries on its upper surface a binding post F. The copper sulphate
(blue crystals) is placed in the jar and sufficient water poured in
to bring the level just above the upper surface of the zinc. In
setting up batteries of this type from 3 to 3.1 pounds of copper
sulphate crystals are placed in the bottom of the jar surrounding
the copper element. The crystals should be small enough to pass
through a sieve with a 14-inch mesh, and should not be so small
as to pass through a 16-inch mesh. The water is then poured in
until the zinc element is submerged. The battery is then short-
circuited for about 24 hours. This short circuiting puts the cell
into action, with the result that zinc sulphate is formed. This zinc
sulphate solution gathers about the zinc element and therefore
forms the upper third of the electrolyte. The lower two-thirds of
the electrolyte is composed of copper sulphate solution which is
indicated by a deep blue color. When a cell of this type is in
good condition a distinct line separates the copper sulphate solu-
tion from the colorless zinc sulphate solution above. As the liquid
of the cell evaporates, the zinc sulphate is deposited over the edge
of the jar. In a short while this deposit, which is in the form of
white crystals, becomes very thick and reduces the efficiency of the
cell. To prevent this a layer of oil about } inch deep is placed on
the top of the electrolyte. This oil, by preventing evaporation,
makes it impossible for the zinc sulphate crystals to be deposited.
The E. M. F. of the gravity cell is 1.079 volts, and the internal
resistance varies between 2 and 3 ohms, depending on the size
of the plates, their nearness together, and the nature of the
electrolyte.
The Leclanche Cell. In this form of battery the elements
consist of zinc and carbon, the latter being encased in a porous
cup; the electrolyte is a solution of chloride of ammonium, com-
monly known as sal-ammoniac. The action in this cell during the
passage of the current is as follows: The chloride of ammonium
is decomposed, the chlorine leaving the ammonia and hydrogen to
unite with the zinc elements, forming chloride of zinc. The am-
monia is dissolved in the water. The hydrogen enters the porous
сир
and would soon polarize the cell by collecting on the carbon
plate were not some provision taken to prevent this action. Closely
packed around the carbon element within the porous cup are crys.

21
14
TELEPHONY
tals of peroxide of manganese, which yield up a part of their oxygen,
forming water by combination with the hydrogen. The peroxide
is thus reduced to a sesque-oxide of manganese. When the battery
is delivering its normal current, the hydrogen is set free in a
slightly larger quantity than can be absorbed by the manganese.
Polarization, therefore, takes place, although very slowly; it be-
comes noticeable where the cell has been in use for a very
time, and then quickly disappears upon the cell being cut out of
service. The E. M. F. of this type of cell is 1.47 volts, and its
internal resistance is about 1 ohm.


0
D
D
-A
B
IE
B
E
Fig. 7.
Fig. 8.
In Fig. 7 is shown a Leclanche cell, the jar being shown at A,
the zinc at B, the carbon at C and the porous cup at D.
This cell is being rapidly superseded by the Hayden cell.
The Fuller Cell. This type employes for its elements zinc
and carbon. The electrolyte consists of a solution of 3 parts
bichromate of potash, 1 part sulphuric acid and 9 parts water.
The zinc is placed in a porous cup in the bottom of which
is placed about 2 ounces of mercury. There is also placed in the
porous cup a solution of chloride of sodium in water, of sufficient
depth to completely cover the zinc. The mercury in the porous
cup is to keep the zinc thoroughly amalgamated, or coated with a
22

TELEPHONY
15
layer of mercury. If this were not done the impurities which are
always present, even in the best zinc, would, with dilute acid, set
up
chemical action in the zinc, thereby causing it to waste away,
thus reducing the efficiency of the cell. The bichromate of potash
is a combination of oxygen and the metals chromium and potas-
sium. When the circuit of the cell is completed and the current
flows, the sulphuric acid which passes through the porous cup
attacks the zinc, forming zinc sulphate and setting free the hydro-
gen. This hydrogen combines with the oxygen of the bichromate
of potash, thus preventing polarization.
The E. M. F. of the Fuller Cell is 2.028 volts, and its internal
resistance about .5 ohm. The Fuller battery is shown in Fig. 8.
The porous cup A is shown inside of the glass jar B; the carbon
C is equipped at the top with a binding post D. The zinc is
shown dotted inside of the porous cup and is also shown separately
at E.
O is a form of connector used with this type of cell on the
zinc element; one end is fastened to the wire attached to the zinc
and the other end holds the wire from the circuit. The two thumb
screws insure good contact.
Edison-Lalande Cell. The elements of this cell are zinc and
copper oxide, and the electrolyte is oxide of potassium or caustic
potash dissolved in water. Polarization is prevented by the decom-
position of the water of the solution, which results in the oxygen
combining with the zinc to form zinc oxide. This zinc oxide com-
bines with the potash to form a soluble double salt of zinc and
potash. The hydrogen of the water combines with the oxygen of
the
copper oxide to form water and deposit metallic copper. The
copper oxide used in this type of cell is formed by roasting copper
scraps, ground finely and formed into blocks. As in the case of
the gravity battery, a layer of oil is placed upon the top of the
solution, to prevent evaporation and the formation of “creeping
salts.” It also prevents the formation of carbon dioxide with the
potassium solution. In order to produce a minimum internal
resistance, a film of metallic copper is placed on the copper oxide
before the battery is put into use.
The E. M. F. of the cell is about .98 volt at starting, but falls
to .75 volt after the cell has been running for a short time. The
internal resistance, however, is very low, being about .025 ohm for

a
23
16
TELEPHONY
>
the largest cells. This type, owing to its low internal resistance,
is especially adapted to the production of strong currents.
Dry Battery. This type is made in several styles, all of which
use zinc and carbon for their elements. While the term “dry” is
applied to this cell, the application of the term is not strictly cor-
rect. However, the electrolyte is so prepared that it cannot be
spilled out of the jar, thus making it especially adapted for port-
The two typical forms of this cell are the Burnley and
the Gassner. In both these types the glass jar is replaced by a
able use.

B

F
B
LE
F
A
А
A
с
с
с
D
E
E
Fig. 9.
Fig. 10.
zinc cup, which serves the double purpose of being the retaining
cup and the positive element.
Burnley Cell. Here the carbon element is in the form of a
solid cylinder A, Fig. 9, which is provided with the usual binding
post B. Inside of the zinc cup is the electrolyte C, which is com-
posed of 1 part sal-ammoniac, 1 part chloride of zinc, 3 parts plas-
ter, 87 parts flour and 2 parts water. This compound, when
mixed, is a semi-liquid mass which quickly stiffens after being
poured into the cup. The depolarizing agent D is peroxide of
manganese, the same as used in the Leclanche cell, and is packed
,
around the carbon cylinder. The top of the cell is sealed with
bitumen E or its equivalent. The binding post F is fastened to the
24
TELEPHONY
17
zinc
cup.
It will be seen that the cell is proof against spilling.
The E. M. F. of this cell is 1.4 volts, while the internal resistance
is about 1 ohm.
Gassner Cell. This type is shown in Fig. 10, in which A
represents the zinc cup with its attached binding post B, C the
negative element which consists of carbon and manganese, and
carries at its top the binding post D. The electrolyte, shown at
E, consists of the following mixture: 1 part oxide of zinc, 1 part
sal-ammoniac, 3 parts plaster, 1 part chloride of zinc and 2 parts
water. No special depolarizing agent is needed, as the zinc oxide
tends to loosen the compound and make it porous, thus facilitating
the interchange of gases. The sealing compound is shown at F.


-А
B
B
E
E E
A
A
Fig. 11.
Fig. 12
Fig. 11 shows the general appearance of a dry battery, A being
the zinc cup with its binding post B, and C the end of the carbon
element with its binding post D. The sealing compound is shown
at E.
Wasteless Zinc. This is a type of zinc devised for use with
the gravity battery; it is shown in Fig. 12. The zinc is equipped
on the upper side with a conical-shaped projection A, and on the
under side with a similarly shaped depression B. When a zinc
has become so far eaten away as to be useless a new one is added,
25
18
TELEPHONY
and the projection on the old one is fitted into the depression in
the new one, so that it may remain in use until completely con-
sumed. The old zinc thus fitted into the new one is shown at C.
The general appearance of the cell is shown in Fig. 13. The
new zinc A is fastened to the supporting clamp B which rests
upon the edges of the jar. The old zinc is shown at C. By the
use of this type of zinc and the gaining of greater zinc surface the
internal resistance of the cell is reduced to .7 ohm.
Secondary or Storage Batteries. Thus far the only types of
batteries discussed are those which produce an E. M. F. from the

B

E
D
D
А
B
Yeeoo oo.99084004000
20000000
Fig. 13.
Fig. 14.
chemical changes which go on within the cell. A different type
of cell must now be considered. In this type a current of elec-
tricity is first used to produce certain chemical changes and store
up certain chemical affinities. These chemical affinities are then
allowed to act, and in so doing produce an E. M. F. This type of
cell is called a Storage or Secondary cell.
The most simple type of storage battery, and at the same time
the type most suited to illustrate the principle upon which it
works, is the one in which a current of electricity is made to pass
through water. The action of the current is to decompose the
water into its constituent elements hydrogen and oxygen. The
hydrogen is collected on the negative pole and the oxygen on the
positive. In Fig. 14 is shown a tank A containing water. The
two terminals of an electric circuit are introduced into the tubes
D and E at B and C. When the current passes, the water is

26

OUVIU
OMOLU JULIUDVIJULUI
VUUN JUVUU
FOR
.
O".
.O "O
mon..
WWWWWWWW
AMERICAN BELL-EXPRESS SWITCHBOABD.
American Electric Telephone Co.
TELEPHONY
19
B
-A
od
decomposed; hydrogen is collected in the upright arm D of the
tube, while oxygen is collected in the arm E. If, after the water
has been decomposed, the source of current is removed and the two
terminals or electrodes F and G connected, the gases in uniting to
again form water will generate an electric current. While this
form of storage battery is useful for illustrative purposes, it is
useless commercially.
The storage battery commonly used today consists of two ele-
ments of lead immersed in a solution of sulphuric acid and water.
In the early form, the elements consisted of thin sheets of metallic
lead. When a current of electricity passed through the cell, the
water in the sulphuric acid decom-
posed and the oxygen passed to the
positive plate and united with the
metallic lead to form on its surface a
red peroxide of lead. The hydrogen
was set free at the negative plate.
The charging current being discon-
A
tinued, the hydrogen retained at the
negative plate will be reduced on
discharge, and unite with the free A"
oxygen held by the positive plate.
The action will not cease when this
point is reached, but the lead peroxide
will be attacked on the positive plate,
and the metallic lead on the negative.
Fig. 15.
The forming of lead peroxide on the positive plate renders its
surface spongy and porous, and, presenting more surface, renders
it capable of forming and retaining a greater amount of lead
peroxide upon the second charge than upon the first. Consequently
this type of cell had to be charged and discharged several times
before the positive plate was sufficiently porous to bring the cell
up to its maximum efficiency. This charging and discharging
is called forming.
As the process of forming necessitated the waste of a great
deal of current, the chloride plate was introduced. It has proved
to be the best and is now used almost universally. It is con-
structed as follows: A specially prepared “tablet” is made by

700
700
O00
04
000
G0004
OD0097
27
20
TELEPHONY
rolling into spiral form a strip of corrugated lead 4 inch in width;
the size of the spiral being Ğ inch in diameter. A sheet of metallic
lead is moulded under pressure around several of these tablets, the
whole presenting an appearance as shown in Fig. 15, where A, A',
etc., represent the tablets and B the lead plate. Each lead plate
is provided with a lug C for connecting two or more plates and
also to provide a terminal for the circuit.
The term 66 chloride” comes from the fact that the lead is
"
derived from lead chloride, but no chlorine is used in the manu-
- facture of the battery. In general the tablets for the positive
plates are made circular, while those used in the negative plates
are square. The plates intended for the positive element are im-
mersed in sulphuric acid, through which a current is passed in one
direction for about fifteen days. In so doing the lead of the tab-
lets is converted into lead peroxide or active material. They are
then ready to be set up in the cell with the negative plates.
There are two distinct chemical actions that take place in the
storage baitery; one during the charge and the other during dis-
charge. The sulphuric acid acts upon the lead of the negative
plate to form lead sulphate. When the charging current is passed,
this lead sulphate is broken up into lead peroxide, PbOn. This is
deposited upon the positive plate. The metallic lead is formed on
.
the negative plate. The sulphate is liberated into the electrolyte.
Expressing this chemical action as a chemical equation:
2 Pb S 0,= Pb + Pb 0, + 2 S 03
which means that the lead sulphate is broken up into Pb 0,, lead
peroxide, Pb lead and SO, the sulphate. This sulphate combining
with the water (HO) forms sulphuric acid, H, OSO,, or, as it is
generally written, H, SO
When the cell is discharged the reverse action takes place, and
one atom of oxygen leaves the lead peroxide to unite with the
hydrogen of sulphuric acid to form water. The sulphate in the elec-
trolyte unites with the lead monoxide to form sulphate of lead on the
negative plate; metallic lead is converted to sulphate on the positive.
Pb + Pb 0, + 2H, SO, = 2 H, O + 2 Pb SO,
It will be apparent from these considerations that during
charging the specific gravity of the solution increases, and that
while discharging the reverse takes place. The resistance of the
--
4
28
TELEPHONY
21
a
D
electrolyte varies with its density within certain limits, decreasing
as the density increases. The density of the electrolyte is very
important and should be watched with great care. It is measured
by an instrument called a hydrometer.
The hydrometer consists of a glass bulb (A Fig. 16) about 1
inch in diameter. To this bulb is attached a hollow glass stem B
about 5 or 6 inches long. A quantity of small shot is placed in
the bottom of the bulb, sufficient to sink it to the desired depth
in pure water. On the stem is a graduated scale D resembling
somewhat that of a thermometer. The height at which the instru-
ment floats will depend on the density of the liquid in which it is
placed. On a scale so marked that the point at which it floats in
pure water is 1,000, the density of the storage battery solution
would be 1,200. At the end of discharge the density falls
to about 1,190.
The E. M. F. of a cell when fully charged is 2.4
volts. In discharging it should never be allowed to fall
below 1.9 volts. The average voltage is about 2.1 volts.
The internal resistance of this class of cell is very low,
being about .02 ohm.
The capacity of a storage battery is rated in ampere-
hours. This means the ability to deliver a certain num-
ber of amperes for a given number of hours. For ex-
ample, if a cell delivered 10 amperes for 10 hours, its
capacity would be 10 x 10 = 100 ampere-hours. This
same cell would deliver 1 ampere for 100 hours.
Another property which a storage battery possesses
is the rate of charge and rate of discharge. This is meas- Fig 16..
ured in amperes. The battery above referred to has a rate of dis-
charge of 10 amperes.
On account of the losses in the battery, the charging rate
should always exceed the rate of discharge by about 10 per
cent. The rate of discharge should never be exceeded, as in
so doing the battery will certainly be injured. The trouble caused
by over-discharge is called buckling, and means á bending of the
positive plates. This bending is destructive in two ways: first, it
loosens the lead tablets; and second, it causes short circuits by the
bent plate touching the one next adjacent. When a plate becomes
B.
-A

29
22
TELEPHONY
А
B"
BY
bent it must be removed from the cell and straightened or a new
one substituted.
In setting up a storage battery, the plates must be carefully
dusted before they are placed in the jars, care being taken to sepa-
rate and insulate the negative from the positive elements. In the
smaller types, the plates are insulated by sheets of asbestos. In
the larger sizes, the insulation is secured by placing glass rods
between the plates, extending from the top to the bottom. The
plates having been placed in the
jar, the lugs are scraped clean, and
all those on the positive plates
CC
are soldered together, as are those
the negative elements. The
solution is then poured in and the
Fig. 17.
charge begun at once. The utmost
care should be taken not to leave the elements in the acid without
immediate charging, otherwise sulphating will take place. The
first charge should be carried on for a much longer time than
that normally required; for example, about 18 or 20 hours at
the normal rate for an 8-hour charge. The cell may then be
discharged at the normal rate until the voltage falls to 1.9 volts.
It should then receive the regular charge, after which it is ready
for work.
THUMANI

B
B
on
L
А
A
A"
A
A"
jeતું s[s[
B!
B"
B"
Вv
CI
Ć"
Arrangement of Cells Into Batteries. There are two ways
of grouping cells into batteries: first, in series, second, in multiple.
The first arrangement gives
a total E. M. F. equal to the
sum of the E. M. F's of each
cell. The method of connect-
ing cells in series is shown in
Fig. 17, in which A, A', A",
Fig. 18.
etc., represent a number of
gravity cells. It will be seen that the zinc element B of the
cell A is connected to the copper element C' of the cell A', while
the zinc element B' of the cell A" is connected to the copper ele-
ment C" of the cell A". This method is continued throughout;
the zinc element of the last cell and the copper element of the first
cell being connected to the line L. At this point it will be well

30
TELEPHONY
23
HHHHHH
H工​工​工​工
​HHHHHH
The copper
to remember that while the zinc element is electro-positive to the
copper, and the current in the cell passes from one to the other
with respect to the circuit; the copper element is the positive
terminal and the zinc the negative. As a result, the current flows
from the copper terminal of
the first cell to the zinc terminal
of the last, and so on through
each cell back to the first.
Fig. 18 shows the method
of connecting cells in parallel
or multiple.
Here the copper
elements C, C', C", etc., of the
Fig. 19.
cells A, A', A", etc., are connected, as are the zinc elements B, B', B',
etc.
terminal and the zinc terminal of cell A are con-
nected to the line. With this arrangement the effective E. M. F.
is that of one cell, but the current giving capacity is equal to that
of one cell multiplied by the number of cells. The reason is that
the internal resistanee of the whole battery is equal to that of one
cell divided by the number of cells.
We have already learned that the internal resistance decreases
with the increase in the area of the elements. It is evident that
under these conditions this area is equal to that of one element
multiplied by the number of cells. A combination of these two
arrangements can be obtained by connecting groups of cells in
multiple, each group being made
up of a number of cells connected
in series, as shown in Fig. 19.
s
Magnetism. So far the pro-
duction of E. M. F. by chemical
action has been considered. Let
Fig. 20.
now investigate the third
method of generating E. M. F. In this method a closed circuit is
made to move in a magnetic field. The machine constructed to
do this work is called a dynamo or generator. Before studying
the generator it is well to know something of magnetism and the
magnetic field. In Fig. 20 is shown a bar magnet, in whích N
and S represent the north and south poles, respectively. If this
magnet is placed upon a table and covered with a thin sheet of paper,

FILE
EN
us
31
24
TELEPHONY
A
с
fine iron filings shaken over the paper will arrange themselves in
curved lines radiating from each pole as shown. It will also be
observed that the tendency of the filings is to form closed curves
connecting the two poles. The space throughout which this effect
of the magnet is manifest is called the field; the curves which the
filings tend to form are called lines of force.
It is a well known fact that if a current is flowing through a
conductor AB, Fig. 21, it will be surrounded by circular lines of
force, as shown at C, C', C",
etc. These lines have their
-B
iunii
center coincident with the
axis of the wire. The num-
Fig. 21.
ber of these lines of force increases with the strength of current
flowing through the wire. If instead of being straight the wire is
wound about a soft iron core, the strength of the magnetic field
will be much greater for a given strength of current flow. For
a given kind of iron core the amount of magnetization is the
product of current strength
and the number of turns
divided by the length of the
iron core.
If the iron core
be extended so as to bring the
poles close together, as shown
in Fig. 22, the amount of
magnetization for a given
current strength will be still
greater. Such an arrangement
is called an electro-magnet.
If a closed conductor be
made to revolve in the field
of this magnet, so as to cut
the lines of force, as shown
at A, an E. M. F. will be gen-
Fig. 22.
erated therein and a current
will flow. If, again, this conductor be wound in many turns about
a soft iron core, the amount of current generated will be greater
for a given strength of field, since the number of convolutions
are increased, and the magnetic resistance is decreased by the


32
TELEPHONY
25
F
A
presence of the soft iron armature. Such an arrangement is called
a dynamo or generator. Fig. 23 shows the diagram of a dynamo.
The two field cores are shown at A and A', the yoke at B, the pole
pieces at C and C', and the armature at D. The space between
the surface of the armature and the pole pieces E and E' is called
the air gap. The field winding is shown at F and F', while the
armature coils are represented by G. H and H' are the brushes
which serve to collect the current from the armature.
The E. M. F. gen-
erated by a dynamo is
represented by the pro-
B
duct of the strength of
field, the number of
turns on half of the
armature and the speed
in turns per second.
When a dynamo deliv-
ers current, the effect-
A
ive E. M. F. is reduced
somewhat by the re-
sistance of the arma-
E'
When it is nec-
E
essary to provide a con-
stant potential from
H'
open circuit to full
load, it is advisable to
D
use the compound
winding, since by this
Fig. 23.
means, as the current
output increases by passing through the series coils, it assists the
shunt coils, increases the magnetic density and tends to keep the
E. M. F. constant.
A dynamotor is a combination of a dynamo and motor on
one shaft. This machine can be constructed so that the dynamo
and motor have independent fields and armatures mounted on the
same shaft; or in small machines one field and one armature is
provided, and on the armature are two windings, one of which is
used for the motor and the other for the dynamo. The commu-

G
ture.
с
H
c
33
26
TELEPHONY
tator of one winding is at one end of the shaft, and that of the
other winding is at the other end.
Alternating Current. So far, the generation of current flow-
ing under a constant E. M. F. has been considered. Let us now
consider the flow of current under a varying E. M. F. This force

M

B
D
А.
E
R
S
F
10
12_13
LAN
H
H
-
او
2
4
3
5
o
1
1
1
1
G
к
H
Н
M
Fig. 24.
may vary in many ways: it may start with a certain maximum
value and decrease to zero, or its variations may be irregular and
according to no law. The two classes of variable current to be
considered here are: one in which the direction of the E. M. F. is
periodically reversed; and one in which the E. M. F. is interrupted,
but always in the same direction. In the first case, the E. M. F.
rises from zero, attains a maximum in one direction, decreases to
zero again, and gradually increases to a maximum in the opposite
direction. This is called an alternating E. M. F., and the current
flowing under its impulse is termed an alternating current. The
second kind of variable E. M. F. will be discussed later. With an
alternating E. M. F. a thorough knowledge of the law of the varia-
tion is necessary.
Alternating current used for commercial purposes varies
according to the law of sines. This is illustrated by Fig. 24.
Suppose the circle M is described by the radius R which rotates
around the center 0, in the direction shown by the arrow head,
and from its extremity lines are drawn perpendicular to the hori-
zontal line HH' as S. The length of these lines will follow the
law of sines; that is, for any position of the radius the length of
the line dropped from its extremity perpendicular to HH' is pro-
portional to the sine of the angle that the radius makes with HH'.
Starting with R coincident with OH', the length of S is zero. As
the angle between R and OH' increases, the length of S increases
until it equals R for an angle of 90°. As the angle still further
increases, the length of S decreases, until at an angle equal to

34

TELEPHONY
27
180°, S is zero again. As R rotates below HH', S again increases
in length, until at an angle equal to 270°, S. again equals R. It
then decreases, reaching zero again for an angle of 360°, or when
R has completed its revolution. On the horizontal line 1-13, equal
distances, such as 1—2, 2—3, 3—4, etc., are measured off equal to
the angle made by R and HH' in successive units of time. From
these points ordinates are erected which are equal in length to S
for the corresponding angle; a line joining the extremities of these
lines will be a sine curve. It will be seen that this curve rises
from zero at 1 to a maximum at 4, corresponding to a rotation of
90° for R; it then decreases to zero at 180°. From this point it
again increases (but in the opposite direction) to a maximum at 10,
corresponding to a rotation of 270°, and again decreases to zero at
13, corresponding to a rotation of 360°. The current impelled by
this E. M. F. will also follow the sine law, and will vary in the
same manner.
The Induction Coil is designed to change a variable into an alter-
nating current. Whenever there is a change in a magnetic field, sur-
rounded by a closed coil, there will be a current induced in this coil. If
there are two coils wound around an iron core, and a variable current is
passed through one, the magnetic strength of the iron will change and this
will induce an electromotive force in both of the coils. In the coil carrying
the impressed current, the potential will be in a direction tending to cut
off the current. Such a potential is due to self induction, and is common
to all electro-magnets. If the second coil is closed, a current will flow
through it. The strength of the potential will depend upon the number
of turns upon this coil and the rate of change of the magnetic strength
of the core.
When the secondary is open, the counter electromotive force of
the primary coil is at its greatest, and consequently the amount of
current taken is a minimum, but when the secondary is closed the
action in this coil tends to neutralize the magnetic field, hence
the self induction is less and the impressed current is greater.
The coil which carries the impressed current is called the primary
coil, while the coil within which a current is induced is called the
secondary coil.
The core of the telephone induction coil is made up of fine
Norway or Swedish iron wire, No. 20 to No. 26 B. W. G., and
carefully annealed to prevent hysteresis. Each wire should be
35
28
TELEPHONY
carefully oxidized in order to form a resistance or partial insula-
tion between the individual wires.
As the current for talking is of very high frequency, it fol-
lows that if the iron is at all sluggish in its action, the transmis-
sion will be distorted so that speech will not be heard plainly. As
the core of a coil with a closed magnetic circuit is more sluggish
than one with an open magnetic circuit, and as a core composed of
a large amount of iron is more sluggish than one with a small
amount, it has been found that the coil with a straight core having
the lines pass through the air to complete the magnetic circuit, is
better than one wherein the lines of force are wholly confined to
an iron path, and that the diameter of the core need not be more
than from 1 to 1 an inch.
The size and number of turns of an induction coil are not
determined by a mathematical design, but almost wholly by experi-
ment. A coil must be designed for the instrument with which it
is to work, and for the service it is expected to give. As a general
rule, the winds of both of the coils are made as low in resistance as
is consistent with a proper number of turns and a reasonable sized
coil. The habit of judging an induction coil by its resistance is
wrong. There are many kinds of coils in use, but perhaps an
average for good practice is of the following dimensions :
Length of core 31 inches; diameter of core inch; length
of winding space 3 inches; primary 400 turns No. 22. B. & S.
gauge silk-covered copper wire; secondary 2,000 turns No. 28
B. & S. gauge silk-insulated copper wire.
Historical. Probably the first mention of the transmission
of speech to a distance is that of Robert Hooke, when in 1667 he
described how, by the aid of a tightly drawn string, he could trans-
mit sound to a very great distance. The distance over which he
propagated sound is not mentioned; but those who are familiar
with the lover's telephone, to which Robert Hooke's apparatus no
doubt bore a great resemblance, will probably limit the distance to
a little over 100 feet. In 1868 Philip Reis, of Friedrichsdorf,
Germany, invented an apparatus which, by the aid of the electric
current, would transmit sound to a distance. He called it the
Telephon. In 1876, patent specifications were filed simultaneously
at Washington by Alexander Graham Bell and Elisha Grey, and
16

36

TELEPHONY
29
-B
-В
(
B!
B!
B"
с
А
А!
in February of that year the patent was granted to Bell by the
United States of America for a speaking telephone. The question
of priority between these two inventors was made the subject
of a law suit, which ended in a compromise; one company buying
out the patents of both.
The Bell telephone, as first
made, consisted of two per-
manent magnets, of the form
B!
shown at A and A' in Fig. 25,
to each of which was attached
a harp of steel rods, B, B', B",
etc. Between the poles of
each permanent magnet was
an electro-magnet C C'; one
terminal of each coil being
Fig. 25.
connected together, while the
other terminals were grounded. When the rods of the harp attached
to A were made to vibrate the magnetic field of the electro-magnet
was disturbed, and currents were thereby induced in its coil. These
currents, flowing through the coil of the second magnet caused its
field to fluctuate, with the result that the harp attached to A' was
made to vibrate. The vibrations of the second harp were in unison
with those of the first, and the amplitude of the vibrations of the
first, determined the amplitude of the vibrations of the second;
because the strength of the induced currents depended upon the
amplitude of the vibrations of the first harp, while the amplitude
of the vibrations of the second harp depended upon the strength
of the induced currents. While this instrument was useful in
proving that sound could be produced at a distance, by means of
the electric current, it was useless as a means of transmitting
speech.
The second form adopted by Bell is shown in Fig. 26. In
this there was an electro-magnet A through which a current was
made to flow. Attached to a membrane of goldbeater's skin B,
was a piece of soft iron C which acted as an armature, the mem-
brane allowing it to vibrate in front of the pole of the electro-
magnet. The receiver was constructed as shown in Fig. 27, in
which A represents a vertical electro-magnet enclosed in a soft-
37
30
TELEPHONY
H
0
D
a
iron tube, upon the top of which is laid an armature B of
thin sheet iron. The transmitter was constructed to transmit artic-
ulate speech, since the vibrations of the soft-iron armature were
in unison with those of the membrane, which in turn, were in
unison with those of the voice.
The receiver also was capable of
giving out articulate speech.
In this form of apparatus a bat-
B
tery of cells was placed in the
circuit of each electro-magnet.
The instrument, however,
was further modified into the
Ti
form shown in Fig. 28. It con-
sisted of a permanent magnet of
Fig. 26.
the horse-shoe type, to the poles
of which were attached two coils B of fine wire. The thin soft-
iron diaphragm was mounted on a separate block as shown at C.
Through the opposite side of this block a hole was bored, and a
mouthpiece D fitted. The use of the permanent magnet rendered
the battery unnecessary.
Thus the first practical telephone was
produced.
The next step in the change
of the instrument was to mount
B
both the diaphragm and the per-
manent magnet in the same case,
so that the whole would be self-
-A
contained. The result is shown
in Fig. 29. It consisted of a
shell A, usually of hard rubber.
This shell contained a cavity M
at its upper end. Through the
Fig. 27.
center of this shell a permanent
magnet F was held in place by
the screw I and carried at its upper end the coil E of fine wire.
The terminals of this coil were brought down through the two chan-
nels G and G' to the two binding posts H and H'. The soft-iron
diaphragm is shown at M; it was held in place by the cap B
which is scooped out to form a mouthpiece. It will be seen


HO

38

TELEPHONY
31
that the essential parts were all contained within the shell. This
instrument is practically the same as the receiver in use to-day.
The principle upon which the Bell receiver operates deserves
a more detailed description than has yet been given. In Fig. 30,
A and A' represent two Bell telephones connected by a grounded
circuit L. Suppose that the receiver A is to be used to transmit
CB
В
D
Fig. 28.
M
F
sound to A'. The sound waves impinging upon the diapragm at
A cause it to vibrate in unison, which means that the vibration of
the diaphragm consists of a fundamental and overtones. The dia-
phragm so vibrating causes the same vibration
in the strength of the field of the permanent
magnet; this causes the same phenomenon to
В
occur in the induced current flowing through its
coil. The induced current, therefore, consists,
as did the original sound, of a fundamental and
E
overtones. This is equivalent to saying that the A-
A
electrical waves of induced currents consist of a
wave, equivalent in frequency to that of the
fundamental vibration, and superimposed upon
this wave are others whose periods of vibration
correspond to the frequencies of the overtones
of the original sound.
These electrical waves travel over the wire
and reach the coil on the permanent magnet at
Η' Η
H
A'. Here a reverse process of transformation
Fig. 29.
takes place; there is set up in the magnet a
vibrating magnetization, the vibrations consisting of a fundamental
whose frequency corresponds to that of the fundamental of the elec-
G'
G
H
39
32
TELEPHONY
trical wave, and therefore that of the original sound; while superim-
posed upon this are other vibrations whose frequencies correspond
to the overtones. This fluctuating magnetic field sets up an identi-
cal vibration in the diaphragm A' and therefore in the adjacent
air particles. As the air particles at the receiving station are set
in the same vibration as those at the transmitting station, the
resulting sound is identical. As a matter of fact, the ohmic re-
sistance of the line reduces the amplitude of the electrical waves,
so that the resultant sound is not as loud as the original. Addi-
tional losses take place at every transformation from sound to
magnetic, and from magnetic to electrical energy and the reverse,
These losses still further decrease the amplitude of the sound waves
at the receiving station, and, therefore, the loudness of the sound.

L
Α'
A
GROUND
GROUND
Fig. 30.
The self induction of the line and its static capacity tend to dis-
tort the form of the electrical wave so that the resultant sound
wave is not identical with the original. These points, however,
are of no importance in the present discussion and will be treated
later.
Although this explanation of the operation of the telephone
is accepted by most engineers as a good working theory, it has been
rejected by some scientists on the ground that the currents induced
in the coil are too feeble to cause a vibration of the diaphragm as
a whole. They contend that the induced currents in the coil cause
a vibration among the molecules of the iron core, which in turn
causes a vibration among the molecules of the diaphragm; and that
it is these molecular vibrations that cause the sonorous air vibrations
and not the vibration of the diaphragm as a whole. In support of
this theory Ader constructed a receiver without a membrane; and
Antoine Bregnet replaced the thin diaphragm by one whose thick-
ness was 14 centimeters. However, whether it be the vibrations
40

TELEPHONY
33
of the diaphragm as a whole, or only those of its molecules, has no
direct bearing on the theory of operation already described. To
show the extreme sensitiveness of the receiver, W. H. Preece made
one respond to a current which was .000,000,000,000,6 ampere,
which is equivalent to six ten thousand millionths of a milli-
ampere.
In the case of the receiver, it might be thought that a simple
electromagnet with soft iron core would do as well as that with a
permanent magnet. To be sure, such a magnet would work, but it
would not be as sensitive as that with the permanent magnet. It
has been established that the pull of a magnet upon its armature
is proportional to the square of the intensity of the magnetic force.
Let S be the strength of the permanent field, and suppose the change
due to an alternating current in the coil amounts to s, that is the
magnetic intensity is alternately increased and decreased by that
amount, so that at one time the intensity is S+s, and at another
S—8. The change in the stress upon the armature will therefore
vary between (S+s) and (S—s)"; the difference would then be 4Ss.
Now should there be no permanent magnetism, the intensity of the
force would vary between ts and —8, or a difference in tractive
effort of 2s. If S is larger than s, it follows that 4Ss must be
greater than 2s. If S=s, then 4Ss is twice 2s?. Now as S is always
larger than s, where there are feeble currents, it follows that a re-
,
ceiver is more sensitive with a permanent magnet than without.
Should the change in magnetic strength be greater than the
strength of a permanent magnet, there would be danger of demag-
netization. The permanent magnet exerts a constant pull upon the
diaphragm and tends therefore to prevent the diaphragm from
vibrating at its natural pitch, thus making the transmission plainer
and the articulation better.
It will be observed that the only force made use of in operat-
ing this form of the telephone is that of the sound waves at the
originating station. This force is very small and the resultant
forces are therefore of a like magnitude. It became obvious, there-
fore, that a mechanism must be devised to make use of some greater
force than that of the sound waves, if the telephone is to trans-
mit speech successfully over any considerable distance. The in-
strument invented to perform this work is called the microphone.
a
41
34
TELEPHONY
a
D
S
B
R
a
N
Microphone. If some mechanism could be devised which
would vary the current in harmony with the undulations of the
sonorous waves, and this varying current could, through the agency
of an induction coil, induce a current in the coil of the receiving
telephone, the problem would be solved. In 1877, Edison con-
ceived the idea of utilizing the fact that the resistance of carbon to
the flow of the electric current, depends upon the pressure; an in-
crease in pressure producing a decrease in the electric resistance.
The first carbon transmitter was constructed by Edison in
1877, and its present form is that shown in Fig. 31 in which A
represents an ebonite mouth piece and B a vibrating plate secured
firmly to the frame C. At D is shown a disc of prepared carbon,
about the size of a shilling which can be adjusted with respect to
the vibrating plate by means of
the screw E. Placed on the
F
A
upper surface of the carbon but-
ton, is a small platinum plate
with a rounded ivory button, by
means of which the vibrations
of the plate are communicated to MS
the carbon disc. There are two
binding posts MM', the first be-
Fig. 31.
ing insulated from the metallic
frame by the hard-rubber bushing N. Attached to the binding
post M is a metallic spring S which bears on the periphery of the
insulated ring R. The circuit goes from M through the spring S
to R thence to the platinum plate through the carbon disc, to the
screw, to the frame and out at the binding post M'.
It has already been stated that it was necessary to make use
of a current from a battery, the current varying in strength in
harmony with the sonorous vibrations, to obtain a greater amount
of energy for the transmission of sound than is contained in the
original sonorous waves. The transmitter just described is a
mechanism which performs this work. As the sound waves im-
pinge upon the diaphragm it vibrates in harmony with them caus-
ing a vibratory pressure to be exerted through the agency of the
ivory button upon the carbon disc. This vibratory pressure on
the carbon causes it to offer a vibratory resistance to the passage

63
M'
E

42

STERLING TELEPHONE FOR COMMON BATTERY OR CENTRAL ENERGY WORK
For Individual Lines, Two-Party and Four-Party Line Selective Ringing.

TELEPHONY
35
15
w
of a current of electricity; so that if the terminals of a battery are
connected to those of the transmitter, a vibratory or pulsating
current will flow through the circuit; and the vibrations of this
current will be in harmony with the original sound waves. It will
be evident that the sensitiveness of this instrument depends on the
ratio existing between the variation in the current and the total
value of the current flowing. This ratio in turn depends on the
proportion of the resistance of the carbon disc to the total resist-
ance in the circuit.
To illustrate, suppose that the resistance of the carbon disc
is 10 ohms, and the amplitude of the variation in the resistance
is 5 ohms. Suppose also that the resistance of the circuit ex-
clusive of the carbon disc is 5 ohms. With the transmitter in its
normal condition the total resistance in the circuit would be 15
ohms; and if a battery of 2 volts be used the amount of current
flow would be 23.133.
If the resistance of the carbon
disc is now decreased to 5 ohms,
the total resistance of the circuit
M
becomes 10 ohms, and the amount
of current flow is 25.2. In
other words, the current flow has
been increased from .133 to .2 or
Hilla
50 per cent. If on the other
hand with all other conditions
Fig. 32
remaining unchanged, the resistance of the circuit exclusive of the
carbon disc be 100 ohms the total resistance of the circuit would
vary between 110 and 105 ohms, and the current flow would there-
between .0181 and .019 or 5
When the transmitter was first invented it was to be con-
nected directly to the line causing the exciting current to flow to
the other station. The resistance of the circuit was thus added to
that of the transmitter, restricting the transmission to very short
distances as will be seen from the above. Edison overcame this
difficulty by including in the transmitter circuit the primary wind-
ing of an induction coil; the secondary winding being connected
to the line as shown in Fig. 32. The sensitiveness of the trans-
mitter therefore became independent of the length of the line.

10
fore vary
per cent.
43

36
TELEPHONY
The variable current of the transmitter circuit passing through
the primary winding of the induction coil, induces in its secondary
winding an alternating current of high tension, the alternations
being in harmony with the original sound vibrations. In this
manner the transmitter can be successfully used for very long lines.
.
Hughes Transmitter. In 1878, Professor Hughes devised a
transmitter which depended upon the variation in resistance of a
loose contact. This instrument was tried in several forms, one of
which is shown in Fig. 33. It consisted of a carbon pencil A
terminating at a point at each end, which rested in circular de-
pressions in two carbon blocks BB'. These blocks were fastened
rigidly to a thin board C and formed the terminals of the circuit.
B
mood
000000
A
с
eeeeee
relea
eccceee
B'
Fig. 33.
This instrument is very sensitive, responding to the slightest vi.
bration; it forms the basis of the transmitter of to-day.
The Blake Transmitter. In Fig. 34 is shown one of the more
recent forms of the transmitter, that tried by Blake. This instru-
ment is mounted in a wooden box shown in section at A and con-
sists of an iron ring having two projecting pieces B and B'. Upon
the upper projection is fastened an iron angle piece C by means
of a brass spring D. The lower end of C rests against the adjust-
ing screw E. Mounted on the iron ring is the diaphragm U
which consists of a circular iron disc surrounded by a rubber ring
44
TELEPHONY
37
I stretched over its periphery. It is held in position by two
springs M and M', Fig. 35, which are fixed to the ring A and
press the one directly upon the rubber ring and the other upon
the diaphragm itself. At the upper end of the angle piece C are
fixed two springs F and G, Fig. 34. Spring F is of thin flexible
steel and has at its free end a platinum contact. This free end
presses against the center of the diaphragm and the carbon disc K
is
pressed against it by means of the spring G which is attached
to the brass plate holding the disc. The springs F and G form
the terminals of the circuit which passes through the carbon disc.
By means of the adjusting screw E the pressure of the carbon disc
against the diaphragm can be varied. The two springs M and M*

B
А
0
0
D
o
o
F.
G
А
M
D
0
M
H
DE
0
e
B'
Fig. 34.
Fig. 35.
are to keep the diaphragm from singing or to make it “dead beat.”
This form of transmitter has been very successful in the past, but
has been superseded by others which will be described.
Berliner Transmitter. A form of transmitter which is of his-
toric interest is the Berliner transmitter, shown in Fig. 36.
It
consists of a wooden box A fitted with a screw cap B. On the
rim of A is fastened a brass ring C to which is clamped the carbon
diaphragm D consisting of a carbon plate which forms one elec-
trode. The carbon block E forms the second electrode, and has
in its lower surface three concentric grooves. This block is held
in position by the screw F, which has at its upper end a micro-
45
38
TELEPHONY
meter nut G. The end of this screw, which passes through the
carbon block, is turned down to receive a small rubber tube H
whose edge rests on the carbon plate and thus damps the vibra-
brations and makes it dead beat. A ring of felt 0 whose edge
rests on the carbon plate, surrounds the carbon block, thus forming
a closed chamber, which is filled with carbon granules. A cylin-
drical shank I is screwed to the cover B and to this a mouth piece
J is attached. The advantage of this transmitter is that the dia-
phragm is always horizontal, with the granules lying above it.
The granules are thus prevented from settling down when the
instrument is shaken. It is a very efficient transmitter and is
used largely in South America.
Hunnings Transmitter. In
G
this transmitter granular carbon
F
is used. The receptacle contain-
А
ing the carbon dust is held in
0
2,0
a horizontal position. A metal
C plate insulated from the frame,
but touching the carbon, forms
B' D'H
one of the electrodes, while the
B
frame forms the other. Al-
though this transmitter is very
sensitive, it is defective on ac-
count of the carbon granules
packing together. In this con-
dition the mobility of the parti-
cles is impaired, and the trans-
mitter rendered useless.
Solid-Back Transmitter.
Fig. 36.
The great disadvantage of the
granular carbon transmitter is
the tendency to “pack;" by this is meant the crowding together of
the granules into a compact mass, which greatly reduces the sensi-
tiveness. In fact, when the carbon becomes packed the transmit-
ter is useless. This packing can be readily overcome by striking
the side of the transmitter a sharp blow with the hand. This
practice however cannot be recommended, for in the hands
of a layman it is not conducive to the longevity of the instru-


46
TELEPHONY
39
32
a
ment. To reduce the packing to a minimum the solid back was
devised. This transmitter is shown in section in Fig. 37; it con-
sists of a thin brass chamber A which is made of 1-inch stock.
Securely fastened over the opening of this chamber is a heavier brass
disc B having a circular opening in its center, into which is screwed
a hard rubber mouth piece C. The diaphragm is a thin metal
disc having its edge covered with india rubber and securely fas-
tened to the inner surface of B by means of two springs shown at
A and B in Fig. 38. These are identical with the springs shown
in connection with the Blake transmitter.
The two electrodes consisting of two finely polished carbon
discs E and E', Fig. 37, are fastened to the inner side of a metallic
chamber which consists of two parts. The rear part F is in the
form of a circular cup which is firmly held, by means of a pin and
set screw, to the brass bridge G. The front part consists of a

B
B
EH
w
CO
A
L
E
Ρ' Η
-B'
Fig. 37
Fig. 38.
HH which is screwed to the front end of F. The front
carbon E' is securely fastened to a brass plate equipped with a
pin which fits a hole in the center of the diaphragm, and is held
in position by two small check nuts L L. A ring of mica ( O'
has its outer circumference securely held between the brass cap
H H and the edge of F, while the inner circumference is clamped
securely by the brass nut I. The brass plate and its attached carbon
disc are therefore insulated from the other electrode which makes con-
tact with the framework. The chamber P is nearly filled with finely-
granulated carbon which closes the circuit between the two plates.
brass
сар
47
40
TELEPHONY
A hard-rubber block is securely fastened to one side of the bridge
and has a hole drilled into which is fitted a copper bushing. This
bushing forms the contact for one side of the circuit, the terminal
being held in position in the hole by a small set screw. To a
small lug on this bushing is soldered a fine wire, the other end of
which is soldered to the brass nut 1. The other terminal of the
I.
circuit is on the frame of the transmitter.
Packing in transmitters is caused by the expansion of the
parts due to the heat generated by the current, and due to the
warm breath of the user. If the expansion of the parts tends to
throw the two electrodes together, the granules will pack, but if the
tendency in expansion is to separate the electrodes the transmitter
will not pack. The pressure of the damping springs is such that
.
any expansion of the diaphragm will be in a direction to separate
the electrodes. All of the best American transmitters are now
made of the same general pattern as the solid back.
Induction Coil. As the theory of induction coils has already
been discussed, let us now take up the special requirements of this
form of apparatus when used in connection with the transmitter.
It has already been shown that the circuit carrying the transmitter
must be so arranged that the resistance of the external portion
will be as low as possible. On the other hand the primary wind-
ing of the induction coil must have a sufficient number of turns to
produce the required magnetic field. It will be seen therefore that
the resistance of the winding of the primary coil must be very small
in proportion to that of the transmitter. The formula expressing
the magnetizing effect of a coil is as follows: H=1.26 s i u in
which H equals the strength of field in lines per square centi-
meter, s the number of turns of the coil per centimeter length;j,
the permeability of the iron core, and i the current strength in
amperes.
From this formula it will be seen that the greater the number
of turns and the greater the current strength, the greater will be
the strength of the resultant field. It has been shown, however,
that the resistance of the coil is limited by that of the transmitter,
and therefore the number of turns of the coil is limited by the
same factor. Since the quantity s cannot be increased at will, the
only way to increase H is by making i as large as possible; this is
a

48
TELEPHONY
41
done by increasing the number of cells used on the circuit. The
value of the quantity i has its limitations inasmuch as excessively
large currents tend to heat the carbon of the transmitter and throw
it out of adjustment.
By trial the following proportions have been found to give the
best results: In the Blake transmitter the resistance of the pri-
mary coil is 1.050 ohms and the E. M. F. used is about 3.2 volts.
In the solid-back transmitter, which is capable of carrying a heavier
current than the Blake, the resistance of the primary coil is cut
down to about 5 ohm. The potential used with this class of in-
strument is usually about 4 volts. The resistance of the solid-back
transmitter under normal conditions is about 10 ohms, but is often
as high as 30 ohms during use. The current density passing
through the transmitter is about .25 to .3 ampere. The mechani- .
cal construction of the induction coil depends upon the shape and
size of the instrument in which it is to be used; this has been dis-
cussed already.
An account of some of the more important tests will now be
given. The results are those of a series of tests made by the Swiss
government on ten different induction coils; the Blake transmitter
being taken as the standard instrument. The experiments were
made on five working circuits ranging in length from 5 to 107.4
kilometers in length. The induction coil used as a standard of
comparison was of American manufacture; with the primary coil
having a resistance of 1.05 ohms and the secondary a resistance of
180 ohms. The dimensions of the coils tested are given in the fol-
lowing table:

Number
of
Coil.
Number
of
Convolutions
Diam.
of
Wire.
m. m.
Resistance
ohms.
Number
Diam. Resistance
of
of
Convolutions. Wire.
ohms.
erororo
.5
.5
5
1
2
3
4
5
6
7.
8
9
10
61
62
62
116
230
232
295
368
368
1350
.25
.25
.25
.50
1.00
1.20
1.50
2 00
1.17
10 00
or stor er öror
1956
3191
4080
3952
3865
4420
4278
4735
4735
3950
.15
.15
.15
.15
.15
.15
.15
.15
.30
.15
听听​听听​听听​听听​凯西
​100
180
250
250
250
300
300
350
130.2
400
.5
1.5
49
42
TELEPHONY
By means of a suitable switch any one of the above coils
could be instantly cut into circuit at any time during the test so
that a comparison could be made with the standard in a short
enough time to enable the tester to retain the original impression.
In this manner each coil was compared with the standard. The
intensity and clearness of the standard coil is taken as one. The
results of the ten coils are shown in the following table:
INDUCTION COIL.
Length
in
Kilometers.
1 2
3
HA
4
5
6
7
8
9
10
.5
{
.3
.9
.7
.9
.9 1.5 1.3 1.5 1.3 1.3 1.7 .3
.9 1.3 1.0 .9 .9 1.0 1.0 3
Intensity
Clearness.
61.6
{0 1 3 3 2
.9 1.0 1.0 1.7 1.3 1.6 1.5 1.5 1.6 3
1.0 1.1 1.3 1.5 1.2 .9 .9 .9.9.5
79.1
.3 .9 .9 1.3 1.1 1.7 1.1 1.1 1.7.3
.7 1.0 1.0 1.5 1.3 1.3 1.1 1.0 1.4 .3

85.3
.7 1.0 .9 1.3 1.3 1.7 1.5 1.5 1,6 3 .3
.8 1.3 1.3 1.5 1.5 1.6 1.4 1.4 1.6 4
.2 .7 .6 1.2 1.0 1.5 1.6 1.6 1.7 ,3
.9 1.0 1.0 1.5 1.3 1.5 1.3 1.2 1.3 1
107.4
In the above table there are two sets of figures for each coil,
opposite every distance. The figures in the upper row denote the
intensity; those in the second row, the clearness. The table shows
that the same induction coil does not give equally good results on
all lines. For example, coil No. 1 has an intensity of .3 on a line
.5 kilometers long; while on a line 61.6 kilometers long this figure
rises to .9, almost equalling the standard. On the next longer
line, this quality falls to .3, but rises again to .7 on the
85.3 kilometer line. On the longest line it again falls to .2. Coil
No. 2 acts more uniformly in the point of clearness, being about
equal to the standard on all but the 85.3 kilometer line, where it
rises to 1.3. On the whole, coils No. 4 and No. 9 give the best
results for general use, and conform in point of make up to the
best practice of to-day.
Complete Telephone. Thus far we have discussed only the
two essential features of the telephone instrument—the transmitter,
or that which converts the sonorous vibrations into electrical
vibrations; and the receiver, or that which converts the electrical
50
TELEPHONY
43
A
GROUND
vibrations back into sonorous vibrations. Let us now take
.
up
the
telephone instrument, which makes use of these two essential
principles, together with some auxiliary features.
In addition to transmitting speech, a complete telephone
instrument must also be able to convey some sort of signal from
one end of the line to the other, in order to inform the party at the
distant end that attention is desired; it must also be able to
receive a signal thus transmitted from the distant end. In all
cases the bell is used as a means of receiving the signal, while a
small hand generator is used to transmit the signal to the distant
end. The method of connecting the bell and the generator has
given rise to two distinct classes of instruments, each possessing
distinctive features. These two classes are called the series tele-
phone and the bridging telephone.
The method of wiring up a series
instrument is shown in Fig. 39, in
A
which the line enters at A, and
terminates at a peculiar shaped G
switch C. This switch is so con-
my
structed that it moves in a vertical
co
direction and when in its upper
position makes contact with the
two points D and E. When de-
Ill
pressed, the contact with D and E
is opened and that with F closed.
Assuming the switch to be in the
Fig. 39.
latter position (closed) the circuit
passes through the contact point F to the generator B and bell coils
K and thence through the binding post A' to the other side of the
line in the case of a metallic circuit or to ground at G when the
earth is used as a return. It will be seen that under these condi-
tions the generator B and bell K are in series on the line. The
generator B is equipped with a shunt L which is closed when the
generator is out of use, thereby cutting the resistance of the
gen-
erator armature winding out of the circuit. When the handle of
the generator armature is revolved this shunt is automatically
opened so that the generator is ready for use.
Assume a line to be equipped at either end with a telephone

DI JE
AF
H
B
K
a
51
44
TELEPHONY
wired as shown in Fig. 39. If a call is sent from the distant end
by revolving the armature of the generator at that point, the
alternating current thus produced arrives at the binding post A,
passes through the bell K (by the route already shown) to the post
A' and returns. The bell is therefore sounded. Should the signal
be sent from this end, the armature of the generator is revolved, the
shunt L being opened thereby and the current flows out on the
line at A. It returns either metallic or through the earth to A',
thence through the bell K to the contact F, through the switch C
back to A.
When conversation is desired the switch is moved to its upper
position opening the contact at F and closing those at D and E.
The circuit from A passing through the switch C now follows the
path from the contact D through the receiver G and the secondary
winding I' of the induction coil back to A'. The circuit including
the transmitter passes from the battery J through the primary
winding I of the induction coil to the contact E, thence through
the switch C to the transmitter H returning to the opposite side of
the battery. The circuit including the bell is open at F. Assum-
ing that the switch of the telephone at the distant end of the line
is similarly adjusted, conversation is possible. Suppose that the
telephone at this end be used to transmit. The sonorous vibrations
impinging on the diaphragm of the transmitter H cause a variable
current to flow through the circuit in the manner described above.
This induces a current in the secondary winding I' which, flowing
'
out on the line, actuates the receiver at the distant end. If the
instrument at the distant end be used to transmit, the induced
current generated at that end flows over the line and actuates
the receiver at this end.
An examination of the circuit will show that whether the
instrument at this end be used to transmit or to receive, the induced
passes through the receiver. The same is true of the tele-
phone at the distant end. The sound produced in the receiver of
a telephone (when that telephone is used to transmit) is called a
side tone. Allusion will be made to this later on. Referring to
the switch C it will be seen that it is to close the bell circuit and
open the receiver and transmitter circuits when the instrument is
not in use. By this means the circuit containing the transmitter

current
52

TELEPHONY
45
battery J is opened during this period, the current ceases to flow
and the life of the battery is therefore prolonged. On the other
hand, the bell and the generator are in circuit ready to receive or
transmit a signal.
This form of instrument was designed before the bridging telephone,
and while it is well adapted to exchange work with one telephone on a
line or on private lines with but two instruments, it is not efficient when
there are more than two installed per line. It was, however, used some-
what for such service, all the instruments being connected in series with
each other. It will be seen that with the exception of the two telephones
in use on such a line that talking currents would have to pass through
the coils of the other bells, causing poor transmission.
The generator is shown in Fig. 40, being a dynamo with per-
manent field magnets bent into horseshoe shape, and their num-
A
A
A"
A"
B
42
mailla
DH-
M
D
F
Com
G+
I
HO
NO
R
0
B'
Ki
Fig. 40.
ber depends upon the strength of the field desired. The generator
.
used in the series telephone usually has three such magnets, while
those in bridging telephones usually have four, but sometimes
five, and even six.
Referring to Fig. 40, A A'A" A"" show the magnets with parts cut
away in order to expose the working of the crank shaft. The armature is
driven by means of a gear and pinion B B'. Fig. 41 shows the construc-
tion of the armature core. This core consists of thin sheets E of soft iron
mounted upon a shaft B. C is a steel pin inserted into the end of the
armature shaft. One end of the winding terminates at this pin, while
the other end is fastened directly to the body of the core. The coils are
wound lengthwise in the slots M M'.
In Fig. 40 springs C and D represent the shunt for a series
generator. When the crank G is turned, the shaft E moves to the
53
46
TELEPHONY
left, pressing the insulated tip T against the spring D, opening
the contact with C and placing the generator in action. The
spring C is in contact with the body of the generator, while D is
in contact with the pin J of the armature. The outside connections
are made at H and K. When the crank is released, the shaft E is
pulled to its normal position by the spring F and the generator again
becomes short circuited, or shunted out by the springs C and D.
The left-hand figure shows the spring arrangement for a
bridging generator. M and L are the two springs which are nor-
A

E
M'
M
Fig. 41.
mally separated; L is in contact with the pin R, while M is entirely
insulated. The insulated tip V of the shaft P moves the spring L
into contact with M and closes the circuit when the crank is turned.
Current passes from the armature tip R to spring L through the
contact to M out over the line from
connection N and back to the body
of the generator at 0.
An alternating current is given
by this generator. Fig. 42 shows
the arrangement of the armature
B
pinion, A represents the pinion, B
the driving gear, and C is the
spring, one end of which is at-
លាហលលលលលលលា
tached to the armature shaft and
the other end to the pinion. This
spring is for the purpose of making
the generator start easily, and also
Fig. 42.
to make it run smoothly and quietly.
The Bell. The bell used in telephones is what is known as the
polarized bell, because the armature is given a permanent polarity
by means of the permanent magnet. Fig. 43a shows a diagram of

tran
54
TELEPHONY
47
N
NE
IN'
S
Ş
this bell. A A' are two coils mounted upon a soft iron base D;
E is a permanent magnet mounted on the same base and extends
along one side of the coils to the top of the mechanism, where the
end is bent over the armature B. The armature is pivoted at the
point F, and the two ends are directly over the ends of the cores of the
coils. The clapper rod G extends from the center of the armature
and ends in a ball. As the armature swings back and forth on its
pivot the ball vibrates and strikes the bells placed on each side of it.
The permanent magnet magnetizes the ends S S' of the cores
to the same polarity, while the ends of the armature N N'are
given a polarity opposite to that of the cores.
If a current passes
through the coil in one direction, pole S would be made a north
pole, while pole S would become a
south pole. The permanent magnet
would make each end of the armature
north. The result is that S being
the same polarity as N, the armature
is repelled from that pole. S' being
made a south pole is of opposite
polarity to that of the armature, and
therefore attracts it; the armature is
thus thrown to one side. When the
current is reversed the armature is
thrown back to the first position.
Alternating current being used, the
Fig. 43a.
polarity of the coils is constantly changed, therefore, causing the
armature to vibrate.
The switch is shown in Fig. 436. When the instrument is
not in use the receiver is hung on the hook D; its weight brings
the switch to its lower position. When the receiver is removed

A
A
D
LE
AN
Fig. 436.
the spring G raises the hook and makes contact with the two upper
springs at F. When the receiver is on the hook, contact is made
with the lower spring, while the others are open.
55
48
TELEPHONY
D
The Receiver. It has been said that the receiver in use to-day
is practically the same as that of the original Bell telephone already
described; but this is true only in general because several import-
ant improvements have been made. Receivers may be divided
into two classes: single-pole and bi-polar. Bi-polar receivers are
more sensitive and are displacing the other type. One of these is
shown in Fig. 44. It consists of a hard-rubber shell shown at
G G', one end of which is enlarged to support the binding posts
D and D', and also to hold the screw B, which secures the permanent
horse-shoe magnet A made of hard steel. Fastened to the poles
of this magnet are two soft-iron cores E E', each one surrounded
by the exciting coil. From the two binding posts two heavy copper
wires C C lead to the terminals of the electro-magnetic coils II'.
The diaphragm O is held in place by the hard-rubber cap F.
In addition to the design of the receiver,
considerable experimenting has been done
to determine the best materials. For the
diaphragm, soft iron has been found to be
the most suitable on account of its sus-
ceptibility to magnet influences.
As to
size, it has been found that a diameter of
2.4 inches gives the best results. The
flexibility increases with the area of the
diaphragm. But while a certain degree of
G!
flexibility is desirable in order that the
whole diaphragm may be thrown into vi-
bration, an excess will cause the free vibra-
tions to become too marked, thereby reduc-
ing the clearness. To obtain the greatest
efficiency, the thickness of the diaphragm
should be from .008 to .012 inch. It
should be perfectly homogeneous, and se-
curely held about the rim. A thin layer
E"ο Έ
of varnish is used to prevent the metal from
Fig. 44
rusting. The inner surface of the dia
phragm should not make mechanical con-
tact with the poles of the receiver; there should be an air space
of
about 64 inch in order that the vibrations may not cause the metal

с
a
G
T
58

TELEPHONY
49
to strike the poles. The resistance of the coils, varies between
75 ohms and 135 ohms, and equally good results have been obtained
with the one as with the other. Most receivers now in use have
a resistance which varies between 75 and 80 ohms.
The single pole receiver is similar to that shown in Fig.
44. For operators, a receiver has been designed to be fastened on
the head by a steel spring. This type is called a head receiver.
One of these is shown in Fig. 45. It will be seen that the body
of the receiver is flat, due to a shortening of the magnetic circuit.
The steel spring clip is made in one piece, as shown in Fig. 45, or
a double piece as in Fig. 46. This receiver is the same as that
already described, and is usually of the bi-polar type.
Let us now consider the form of the coils placed upon the pole
pieces. The induced currents passing through these coils, which
for convenience sake may be called the talking currents, are very
small in intensity, varying between .0001 to .00001 ampere; as a
result the magnetic influences produced thereby are also very weak.
Fig. 45.
Fig. 46.
Therefore to make them effective, the coil windings must be
placed as near the iron cores as possible. Only very fine silk-
.
covered wire is permissible—that having a diameter of from .004
to .006 inch. About 710 turns are used in each coil—a total of
1,420 turns. In a single pole receiver, the 1,420 turns are wound
on one coil. For a single-pole receiver, the shape of the coil is
circular, while those of the bi-polar receiver are elliptical.
The Bridging Telephone. Let A and B, Fig. 47, represent
two telephone stations on a line. Assume both of these stations
equipped with series bells. If now it is desired to connect an
additional telephone to the line, the difficulty will at once become
57

50
TELEPHONY
apparent. If the third station be cut in as shown at C the three
bells will be bridged across the line. With the low resistance to
which the series bells is wound (80 ohms) the third bell would
shunt so much current from the other two that they would ring
very faintly. A more serious condition: during conversation
between any two of the stations, the bell of the third one would
still be bridged across the line. The result would be that so much
of the talking current would be shunted by the bell that conversa-
tion would be possible only on lines of a few hundred feet in
length. If more telephones were added to the line, the effect
would be still more marked. On a very short line it might be
possible to operate three telephones wired in this way, but it would
be impossible to operate a greater number. Even with the best
conditions the results with the three telephones would be far from
satisfactory.
HE
1200
11:00
B
Fig. 47.
A
To make the use of more than two telephones on a line possible,
and to overcome the difficulties described, the bridging bell was
invented by Mr. J. J. Carty, Chief Engineer of the New York
Telephone Company. The principle of this bell is best explain
by quoting from the patent specifications, which call for a "bell of
high impedance, permanently bridged across the telephone circuit.”
The bell having a high impedance, does not shunt out an appreciable
amount of current. The original bridging bell was wound to a
resistance of 1,000 ohms, and to-day this figure is the standard.
The number of turns on the bell coils is much greater than with
the series bells, therefore the current density necessary to produce
the ringing is much less than with the other type. Again, the
,
58

parte
U
STEP ANG
W
STERLING TELEPHONE FOR BRIDGING AND FARMERS' LINES
For Straight Bridging Party Line, Two-Party and Four-Party Line Selective,



TELEPHONY
51
impedance of the bell coils is so high, compared with that of the
circuit through the telephone receivers, that the amount of talking
current shunted is inappreciable.
The method of connecting up the telephone with the bridging
bell is shown in Fig. 48, in which A represents the generator, B
the bell coils, H the receiver, C the secondary winding of the
induction coil, D the primary winding, E the transmitter battery,
F the transmitter and G the hook switch. It will be seen that the
generator A together with the bell coils B are permanently bridged
across the line. The generator armature is provided with an
A
मीन
ТВ
B
H
с
H
C
my
ww
TV 2 w
TV 2 w
G
D
D
G
G
E
ES
J
da
od
F
Fig. 48.
automatic switch, which leaves the armature coils on open circuit
during the time that the generator is out of use. Upon turning
the crank the coil is cut into circuit. The only difference between
the wiring of this telephone and that with the series bell, is in the
switch. It will be observed that with the bridging bell the hook
switch is not provided with a lower contact. The only contacts
are those marked 1 and 2, which form the circuit for the receiver
and the transmitter. As in the case of the telephone equipped
with the series bell, these two contacts are opened when the switch
moves to its lowest position, and are again closed when the switch
returns to its highest position. With this form three or more can
be connected to a line without interfering with the transmission.
The greatest number of telephones of this type that can be success-
fully operated on one line will be treated more in detail later.
59
52
TELEPHONY
While the essential parts of a telephone remain unchanged,
the method of assembly or mechanical construction differs consid-
erably in different types of the instrument. In this respect telephone
instruments may be divided into four classes: The framework of
the desk cabinet telephone is made up in the form of a desk, so
that the person using it may sit down and write.
With the wall
cabinet telephone, the subscriber stands up, but also has a surface
to write on. These two types are so constructed that a cabinet is

M
A
-B
с
CS
E
A
16
R
B
Fig. 49.
Fig. 50,
provided for the reception of the battery. With wall telephones
the transmitter, induction coil, bell and generator are mounted
upon a back board to fasten on the wall at any desired height.
A small shelf is usually provided for writing. The transmitter of
the desk stand telephone is mounted on a metallic arm provided
with the hook switch. This stand is portable and constructed to
set on a desk or table. The box containing the bell and generator
is usually mounted separately as is also the induction coil.
60
TELEPHONY
53
In Fig. 49 will be seen an illustration of a desk cabinet set,
of one of the most approved types. It consists of a desk-like
structure, upon which is mounted a cabinet A A'equipped with a
glass front through which are seen the generator B, the bells C
and the induction coil F. The switch D has its hook end pro-
jecting through a slot in the side of the cabinet; and the pivot end
can be seen through the glass cover. The receiver E is seen in its
position on the hook, and is connected (by the flexible cord I) to
two binding posts, one of which forms the line terminal, and the
other the terminal of the secondary winding of the induction coil.
This cord is made up of two conductors of fine copper tinsel, thor-
oughly insulated by close cotton braiding, and together enclosed
in a cover of heavy cotton braid. The transmitter which is of the

1
2
A All
B
D
E
B
с
mm
my
sum
S
olol
WO
Х
7
3
4
K
Fig. 51.
solid-back type is seen at 0. It is mounted on a supporting arm
S which is fastened to the top of the cabinet. The circuit from the
primary winding of the induction coil is made through the flexible
cord M, which is constructed of very fine copper strands, insulated
with silk and cotton winding and covered with a close heavy silk
braiding. The transmitter is fastened to the arm by means of a
milled-head screw, so that it can be adjusted to the proper height.
The return circuit is through an insulated wire attached to a bind-
ing post placed on the foot of the arm. An enlarged view of the
arm is shown Fig. 50. The binding post is seen at A and the
milled-head screw,for securing the transmitter, at B. The flexible
cord is seen at C, The batteries are held in a cabinet, which is
closed by a movable door R.
61
54
TELEPHONY
The plan of the wiring is shown in Fig. 51. Here the line
wires 1 and 2 are run to the binding posts A and A', A being
wired directly to the binding post B. The post A' is wired directly
to the switch S. Ths binding post B' is wired to the secondary
coil, and its other terminal to the contact point 5. The contact
point 6 is wired directly to the primary coil, whose other terminal
is wired to the binding post 7, thence down to the batteries placed
in the cabinet as described, from which the wire comes up to the

A
B
А
o
B
Fig. 53.
C
D
binding post 3. The flexible cord M,
Fig. 49, runs from the post 3 to the
transmitter K, the return circuit
go-
ing to binding post 4, which in turn
is wired permanently to the switch S.
The receiver is shown at C, and the
receiver cord at D. The bell coils I
are bridged across the line at A and
A'. The generator E is bridged
across the bell coils. All
permanent
wiring is done with No. 19 B & S
gauge rubber-covered wire laid in
Fig. 52.
channels.
The telephone of the wall-cabinet type consists of the same
essential features as the desk-cabinet set. The induction coil, gen-
erator, bell and switch are mounted in the cabinet which has a
glass front. The transmitter arm is of the same type, but shorter
than that used on the desk-cabinet sets. The battery cabinet is
made in three compartments, one above the other, each one large
enough to hold one Fuller battery.
In Fig. 52 is shown a wall set. It consists of a back board
62

TELEPHONY
55
AA upon which are mounted the magneto-bell box B, and the
transmitter C with its supporting arm. The bottom third of the
back board is flared out to accommodate the battery box D. This
box is designed to hold three Leclanche batteries. When Fuller
batteries are used, a separate bat-
tery box is provided which is placed
on the floor. In the instrument
shown, the induction coil is mount-
ed in the magneto box; the trans-
mitter arm being merely a sup-
port. In Fig. 53 is shown a trans-
mitter arm which has a metallic
receptacle A for the induction coil.
Both styles of arms are pivoted at
B for the adjustment of the height.
Fig. 54 shows a modification
of the wall set in which the battery
box is so designed that the cells
may be placed one above the other.
The back board can then be made
narrower thus saving wall space.
The magneto-generator box is
also shown. Fig. 55 shows a
slightly modified form which is
used by the Bell companies for
series telephones. The hook switch
A is pivoted at B and its heel is
equipped with a platinum point C,
which, when the switch is in the
upward position, makes a contact
with two springs, one of which is
seen at D. Beneath the heel of
Fig. 54.
the switch is a hard-rubber block E which presses against the two
springs and breaks the contact when the switch is depressed.
Beneath the switch is a spring F which presses the hook upward
when the receiver is removed. Fastened to the under side of the
switch is a small hard-rubber block G which insulates the spring
when the switch is at its highest point. Just in front of G is a
이 ​이
​63
56
TELEPHONY
wedge-shaped projection H having a platinum point which makes
contact with F when the switch is at the lowest position, thus
closing the bell circuit. At the end of the crank shaft opposite
the crank will be seen a small pin I, which, when resting against
J, closes the shunt on the armature. Upon revolving the crank,
this point is automatically drawn away from J thus opening the
circuit. At the top of the box are three binding posts marked L
P and L. The two marked L being for the line wires while P is

6ODO
CO
COD
8
0
Leo
O
PE
o
ATHY
A
B'E
S
Foor
B
Fig. 55.
connected to ground, when the instrument is used on a grounded
circuit. At the bottom of the box are three pairs of posts, two
marked T for the receiver cords; two marked B for the primary
circuit and two marked M for the secondary. The wiring is the
same as for the series bell. From the switch A projects a german-
silver strip S to which is soldered all permanent connections.
In Fig. 56 is shown the form of bridging bell used by the
Bell companies. It is made up in the same form as the series
bell. It will be observed however that the spring under the switch
always makes metallic contact. Since there is no connection on
this spring there is no necessity for insulating it from the switch.
The pin at the end of the crank shaft remains normally separated
64
TELEPHONY
57
from its contact, being automatically closed as the crank is turned.
The bell coils on this bell are longer than those shown in Fig. 55.
This is for the accommodation of the extra wire. Of the six
binding posts on the bottom of the box, two (marked R) are
for the receiver cords; one marked P for the primary coil; one
marked B for the battery; and two marked S for the secondary
coil. Both of thyse magneto boxes are designed for wall sets where
the induction coil is in the transmitter arm.

5
O
2
M
cer
R
R
P.
B
S
Fig. 56.
In Fig. 57 is shown one of the types of desk-stand sets. The
transmitter is supported on a metallic shank A provided with a
heavy base B. The shank is hollow and the hook switch passes
through a slot, making all connections inside. The receiver cord
is shown at D, and makes connections inside of the base. With
this style a separate magneto box is used, which may or may not
contain the induction coil.
The plan of wiring is shown in Fig. 58 where R and S denote
the terminals of the primary and secondary winding of the induc-
tion coil respectively; the post between them being dead and used
as a connector only. One side of the transmitter circuit is wired
65
58
TELEPHONY
to the switch by means of a flexible cord; connection to the other
side being made through the frame and the contact 1. The receiver
circuit is completed through the flexible cord A to the contact 2.
In other respects the circuit is the same as that already described
for a bridging bell. This type of telephone is used with either a
bridging or series bell.
Special designs are sometimes made to meet requirements.
One of these is shown in Fig. 59. It is of the wall type, and the
bell, induction coil, generator and accessories are placed in a cabinet,
on the door of which is mounted the transmitter arm. The trans-

А
R
S
FA
D
பார்
B
Fig. 57.
Fig. 58.
mitter current is furnished by two dry cells. This is a very com-
pact and convenient form of instrument.
Relative Merits of Transmitter Batteries. It must be remem-
bered that the microphone, consisting of the transmitter, battery
and induction coil, depends for its operation upon the fluctuation
of the current flow in the circuit. For its operation, this fluctu-
ation must be in harmony with the sonorous vibrations. Since
any fluctuation of the current produces an induced current on the
line, and therefore a corresponding sonorous vibration at the
receiving end, it is absolutely necessary for the proper working of
this apparatus that the fluctuations be produced solely by the
change in resistance of the transmitter. In other words, the
battery must give an absolutely constant current and all connections
66

TELEPHONY
59
on the circuit must be perfect. Therefore, a cell adapted for a
transmitter circuit must give constant E. M. F. In this respect
the Gravity, Fuller, Leclanche, Edison-Lalande, and the two types
of the dry cell already described are equal when in good condition.
The Gravity battery is the least likely to produce fluctuations
in the E. M. F. by getting out of order. If the zinc, however, is

BV
eje
HO
өне
Fig. 59.
allowed to become very dirty from creeping-salt deposit, a fluctua-
tion of the E. M. F. is produced, which renders conversation over
very long lines impossible. There are no cases recorded where
this effect has been noticed with batteries having oil on the surface.
Impurities in the zinc tend rather to retard the creation of
zinc sulphate, and therefore lower the E. M. F. of the cell. The
principle source of trouble with this type of cell is the collection
of dirt on the zinc element, which interferes with the creation of
67
60
TELEPHONY
2
a
zinc sulphate, thereby reducing the E. M. F. of the cell. The
zinc should, therefore, be kept clean.
With the Fuller cell, care must be taken to preserve the amal-
gamation. To do this a little mercury is placed in the bottom of
the porous cup, so that it can always be in contact with the zinc.
Should the supply of zinc amalgam give out, severe local action
would be set up by the contact of the chromate of potash solution
and such impurities as iron and other metals. This local action
would set up varying E. M. F.'s which would be in opposition to
that of the cell. When the zinc is placed in the porous cup, care
should be taken not to bend the copper wire at the edge of the
battery cover.
If this is done the zinc cannot feed down as it
becomes used. The wire should be allowed to extend straight out
three or four inches before being bent over. This type of cell
becomes exhausted quicker than the Gravity battery, and ordinarily
about five renewals a year are required. The zincs must be replaced
about two or three times a year.
In the Leclanche battery, the zinc is placed in contact with the
active electrolyte, but it is purer than that used in the two cells
already described. The zinc is amalgamated when first introduced.
As it becomes eaten away, zinc chloride crystals form, with the
result that unless replaced by new, a loud hissing will result.
Dry cells have largely superseded wet cells for all local battery
work. They are cheaper, easier to maintain, and when properly
designed and manufactured, have longer life under the same con-
ditions than the Leclanche cell.
To sum up, the Gravity battery is best adapted where the
cost of maintenance and renewal is high. They are used on the
operators' transmitter circuit in country and suburban exchanges.
For the proper E. M. F. three cells are connected in series. The
Fuller battery is best adapted for intermittent work at points near
the supplies. Two cells in series are sufficient for ordinary use.
The Leclanche battery is used on the transmitter circuit of sub-
scriber telephones in thinly populated districts, where the cost of
renewal is high, and the number of long distance connections small.
Three cells in series are commonly used. On long distance lines
three cells of the Fuller battery are commonly used on the sub-
scribers' telephones.

68



(v)
EXTENSION NIGHT
BELL TO BE
PLACED IN
ANOTHER ROOM
IF DESIRED
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121
ol
183
SL
137
o21
BARS 16 & 17 ARE
NOT FURNISHED EXCEPT
WHEN TRANSFER JACKS
AND LAMPS ARE USED
BARS 10 & 11 ARE NOT
FURNISHED EXCEPT
WHEN SWITCHING KEY
13 USED
127
170
188
(x)
178
(w)
D
021
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xlu
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towo
TOBAR 2 IN NEXT CABINET
TOISAR 1 IN NEXT CABINET
TOBAR 3 IN NEXT CABINET
CP
ЕР
-P
PT
TO NEXT Pag.
To 5
TO 4
TO 12
TO 3
TO 19
To 15
TO 1
YO17
P27
P.
I U
PUT IN BY K.5.& 5.CO BETWEEN
ALL POSITIONS OF ANY ONE bheia
CABINET, BUT WILL HAVE TO
BE PUTIN BY TELCO
HOV. 16-CP LAMPS
FROM ONE CABINET TO
ANOTHER
POWER
IGEN
TO GENERATOR ALSO WHEN
4.PARTY LINE SELECTIVE
RINGING IS FURNISHED
NOTE 7 CELLS FULLER BATTERY ARE
USEP INSTEAD OF 15-CELLS DRY
BATTERY WHEN TRANSFER
JACKS ARE FURNISHED.
11111111111111111
tolat
021
олон
DOBO
NOTE- THESE WIRES ARE ALWAYS
2.ORY CELLS
FOR BUZZER.
15-CELLS DRY BATTERY
OR T CELLS FULLER BATTERY
3-CELLS GRAVITY 3. CELLS GRAVITY
2
BATTERY
BATTERY
TRANSMITTER BATTERIES
WIRING OF CORD CIRCUIT,
Kellogg Express Switchboard

TELEPHONY.
PART II.
TELEPHONE LINES.
The fundamental principles upon which the telephone works
having been grasped, and the development of the complete tele-
phone traced to its culminating point, it now becomes necessary
to take up the subject of the nature of the line or circuit over
which the talking current is transmitted, from the originating to
the receiving end. Before the subject of line construction is
taken up, however, it will be necessary to become familiar with
с
O
O
6
Ξα
e
Fig. 60.
the nature of the work required of the line, together with its dis-
position and arrangement, in order that the proper connections
may be made in the quickest and most economical manner.
Telephone lines must not only be so constructed mechani-
cally and electrically as to carry properly the talking current, but
also be so distributed as to afford, at a minimum expense of mate-
rial and labor, access to all points to which access is desired.
The work of arranging lines with the object mentioned above is
called distribution, and is based upon the following principles :
The simplest method of distribution that can be conceived is
that in which two telephones are connected together by a line
either grounded or metallic, as shown in Figs. 60 and 61. In Fig.
60, a and b represent two telephones connected by the line c, the
return circuit being made through the ground between the points
a
71
62
TELEPHONY
d and e.
In Fig. 61, a and b again represent two telephones; but
here they are connected by a metallic circuit c. The relative
merits of the grounded and the metallic circuits will be discussed
later.

с
Fig. 61.
With the arrangements shown in Figs. 60 and 61, evidently
communication can be established only between the two points a
and b, either in one direction or in the other. If it be desired to
establish communication with a third point, a third telephone may

с
O
a
Fig. 62.
be bridged upon the line as shown at d in Fig. 62. In this case,
communication can be established between a and b, a and d, or 6
and d. If a fourth point is to be brought into communication,
this can be done as shown in Fig. 63, where e represents the addi-
tional telephone bridged on the line at this point. If the new

с
O
a
d
e
6
Fig. 63.
points of communication lie beyond a or b, the line can be ex-
tended accordingly and the additional telephone bridged on as
before.
It is evident that the flexibility of this system is limited by
72

TELEPHONY
63
the greatest number of telephones that can be bridged on a line
without cutting down the talking current to such an extent as to
render transmission unsatisfactory, or the ringing current to such
an extent as to render the amount of signaling current that
passes through each bell insufficient to ring it. Besides these two
considerations, there is an additional one — namely, the fact that
-
a signal cannot be sent from any one station to any other with-
out it being received at the remaining stations. Nor can conver-
sation be carried on between any two stations without the
possibility of it being overheard at the others, or without pre-
4

1
2
3
α
с
2
3
e
Fig. 64
cluding the possibility of independent conversation being carried
on between any of the others. It will be obvious that if each of
the telephones be connected to a separate line, and if these lines
be run to a common point at which is placed suitable apparatus
for their connection together in any desired order, the above-
mentioned difficulties will be overcome. In Fig. 64 is shown such
an arrangement, where the four telephones a, b, c, and d are con-
nected respectively to the lines 1, 2, 3, and 4, which lines run to
the common point e. By means of suitable apparatus placed at e,
the circuit 1 can be connected to circuit 2, 3, or 4, and communi-
cation thus established for a with either b, c, or d as desired.
Similar connections can be made for b, c, and d.
So far as the problems of transmission are concerned, the
number of telephones that can be connected to the common point
e is unlimited ; nor would the problems of line construction have
73
64
TELEPHONY
any bearing on the subject. The point to which these lines are
run is called an exchange or central office. An employee must
be placed in the exchange to make the connections required; and
in order to attract the attention of this person, each line is
equipped with a signal so designed as to be operated automati-
cally by the generator at the telephone.
The lines above described are called subscriber or sub-station
lines from the fact that they connect the subscriber telephones to
the exchange. By some telephone engineers the subscriber tele-
phones are called sub-stations, whence the additional title.

3
5
12
w
34
6
24
2
8
CD
e
5
13
12
6.
9
SIO
ID
8
a
b
Fig. 65.
There are limitations to the number of subscriber telephones that
can advantageously be connected to one and the same exchange,
and among these limitations one of the most important is the cost
of the line construction. To illustrate this point, in Fig. 65 let a
and 6 be two towns situated in proximity to each other, and
suppose that telephone communication is first established in the
town a. After a while the inhabitants in town b desire to have
communication. If only three or four people in the latter town
desire service, it will probably be most economical to connect
them by direct lines to the exchange in a. As the number of
subscribers increases, however, a time will arrive when it will be
most advantageous to establish an exchange in b and connect to it
all the subscriber telephones in this town. Then, to afford means
of establishing communication between the two towns, a number
of lines will be built between the two exchanges.
The point at which it becomes most economical to open a
new exchange in the town b will depend on the following factors :
74



IL
AMERICAN EXPRESS ELECTRIC FLASH-LIGHT TRANSFER SWITCHBOARD
American Electric Telephone Co.

TELEPHONY
65
е
Assuming the quality of line construction to be standard, the
number of telephones that could be most economically operated
through the exchange at a would vary inversely as the distance
between the two towns. It would vary directly with the cost of
establishing and maintaining an exchange at b, which would itself
depend on the cost of rent and the operator's salary. It would
be influenced also by the number of communications established
between the two towns.
In Fig. 65 the numbers 1, 2, 3, etc. represent the subscriber
stations in each of the towns, while the two lines e and e' represent
the two circuits joining the exchanges. The lines that so connect
the two exchanges are called trunk lines. When a toll rate is
charged for communicating over these trunk lines, they are called
toll lines. In large cities, where the cost of line construction is
high, it is advantageous to have several exchanges connected by
trunk lines as shown in Fig. 65.
It will be obvious that each subscriber line may be connected
to as many telephones as it will carry under the limitations of
transmission and signaling described above. Such an arrange-
ment would be obtained by extending the line c, Fig. 63, to the
exchange. In practice this is constantly done. Exclusive of toll
lines, trunk lines never terminate in more than two stations, one
at each end. Toll lines, on the other hand, are sometimes con-
nected to three or more stations.
In the most advanced practice
the location of the business and its
probable growth are determined be-
6
forehand as accurately as possible,
and the distribution of subscriber
lines is made from these data. In this
way the work of subscriber-line con-
struction can be pushed in advance
of daily needs. The largest com-
panies plan subscriber-line require-
ments for two or three years in
Fig. 66.
advance of actual needs. Under these
conditions the subscriber lines are built to predetermined
points of distribution. The idea will be better understood

.3
e
0
5
n
75

66
TELEPHONY
are
6.
10
9
ways. Either
by reference to Fig. 66, where a represents an exchange situated
in a large town or city. Let 1, 2, 3, 4, and 5 represent centers
of distribution, that is, points about which the subscriber tele-
phones cluster. To handle this business properly, lines, whose
number would depend upon
1234567891011
the number of subscribers,
would be run out to these
points as shown. To pro-
vide for cases in which
more than one telephone
is connected to a circuit,
some of the lines
equipped with branches as
shown at b, c, d, etc. in the
figure. These branches are
made in two ways.
a certain number of wires
are turned aside at the
branching point, or the re-
quired number of wires are
bridged off the lines at
that point. This is illus-
trated in Fig. 67, where
the figures 1 to 11 repre-
sent metallic lines emerg-
ing from an exchange. At
the point a the lines 8 to
11 are turned aside and
proceed to the point b.
1234567
This is a split branch. At
the point c the lines 1
to 4 are bridged to lines
of the same number and proceed to d. This is a bridging
branch. The lines 1 to 7 proceed to the main point of distribu-
tione.
The points b and d are branch points of distribution.
Should it be required to connect a subscriber telephone at d to the
same line as is already connected to a telephone at e, this could
readily be done by connecting the two telephones to one of the lines
-
2
d
e
Fig. 67.
76

TELEPHONY
67
1 to 4. Should it be required to connect a subscriber telephone at
b to the same line as that carrying a telephone at e or d, the bridge
would have to be made at the central office. This is sometimes ad-
vantageous. The centers of distribution, whether main or branch,
should be so located that the distance from any one of them to the
most remote subscriber telephone is not over 300 feet. In most
cases this can be accomplished. This condition enables a subscriber
telephone to be connected to the exchange by merely running from
it a line to the distribution point. Such a line can be run in from
2-hour to two hours' time, and can be readily removed at small cost
should occasion require. This line is called the bridle or drop line.
Looked at from the standpoint of distribution, therefore, telephone
lines are divided into two classes : Subscriber lines and Trunk
lines. Each partakes of distinctive features to be described later.
LINE CONSTRUCTION.
The subject of distribution having been understood, it is now
time to consider the methods adapted for line construction and to
describe fully the nature of the materials required in this work.
Looked at from the standpoint of construction, telephone lines may
be divided into two classes: Open-wire lines and Cable lines.
Open-wire lines are those in which each wire is run independently
of its neighbors, and insulated from them by sufficient air space. .
The wires are tied to glass insulators which are placed on wooden
pins set in holes on a wooden cross-arm. This cross-arm is fastened
to a pole set in the ground, and at a sufficient height not to obstruct
traffic. Cable lines are those in which the wires, each insulated by
a suitable covering, are twisted together in cable form and securely
bound. The cable may be covered with a layer of tape saturated
with tar, or may be encased in a lead pipe. Both classes have spe-
cial spheres of usefulness and are of equal importance. The open-
wire line is used almost exclusively in country districts, and to a
large extent in suburban districts. It is also used in small cities
and, in a few instances, in large cities.
The cable line has the advantage of being capable of use for
either overhead or underground work. In Fig. 68 is shown the top
of a pole equipped with two cross-arms, each accommodating ten
pins. The pole is shown at a, and the two cross-arms at b and c.
a
a
77
68
TELEPHONY
The cross-arms are fastened to the pole by means of bolts which
pass through the pole, being secured by nuts resting on washers as
shown at f and fl. The cross-arm is held rigid by two cross-arm
braces, as e and d, which are secured to the cross-arm by two car-
riage bolts, as g and g', and to the pole by a drive-screw, as h. The
spacing of the cross-arms is 2 feet and that of the pins 12 inches.
Upon these pins are placed glass insulators, as shown at i and j.
The insulators are constructed with a semicircular depression
as shown, which is for the reception and securing of the wire.
a

4-12"
Rj i
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Fig. 68
For use in climbing the pole, steps are driven on opposite sides,
as shown at m and n. The cross-arm bolts with their washers, the
cross-arm braces, the carriage bolts, the drive-screws, the pole
steps, the pins, and the insulators are referred to as pole fittings,
and will be discussed under that heading in this book.
The Pole. This is the most important feature of the
open-
wire lines, and since it has to bear the load of the wires under all
conditions it is essential that the wood used be selected with the
utmost care. In America the following woods are used for this
purpose :
Norway pine
Chestnut......
Cypress
White cedar
10 years.

lasts 6 years.
16 years.
12 years.
65
78
TELEPHONY
69
In former days white cedar was the favorite wood among tele-
phone engineers on account of its combination of strength and
lightness. Chestnut, however, on account of its durability and
toughness, is coming to replace cedar; and the Bell companies,
in building new lines or rebuilding old ones, use this wood almost
exclusively. Juniper is also coming into favor, being used exten-
sively in the South. Although not quite so strong as chestnut, it
gives very good results.
Everybody is familiar with the annual rings exhibited by a
cross-section of a tree when sawed through. These are caused by
the difference in the rate of growth of the tree in spring and in
autumn. In spring, when the ground is soft and the leaves fully
developed, the rate of growth is quicker than in the fall, when the
conditions are the reverse. As a result the wood grown in the
earlier season is less dense than that formed under more adverse
conditions. The annual rings consist therefore of nothing more
than layers of porous spring wood alternating with layers of dense
fall wood. Trees planted in barren soil grow less rapidly than
those in more fertile soil, and for the reason explained above con-
tain a greater percentage of dense wood. They are what is tech-
nically known as “slow growth” timber and are the best suited
for telephone poles.
Whatever kind of wood is selected, it should have the follow-
ing qualities: It should be live and green, reasonably straight,
well proportioned from butt to top, and free from loose knots, and
should have the hard knots trimmed close. The pole should be
squared at both ends. The size of pole required will depend on
the number of wires to be carried and on the height of the ob-
stacles, if any, to be overcome. The shortest pole, however,
should be of sufficient height to have the lowest wire at least 20
feet above the ground.
The size of the diameter of the pole will depend upon its
height, for the higher the pole the greater the load it will have to
support and therefore the greater will be the strength required.
Attempts have been made to figure out the required shape and
size that a pole must have to be of the most economical volume to
support the required load. Results, however, have shown that if
a pole has the ordinary taper, all that is required is to specify that
>

79

70
TELEPHONY
it shall have a circumference of 22 inches at the top, or be about
7 inches in diameter. The diameter at the butt will then be of
the proper dimensions no matter what the height of the pole may
be. The following table gives the requisite dimensions of cedar,
chestnut, and juniper poles for pole lengths ranging from 30 to 90
feet :
TABLE I.
Pole Dimensions.
CEDAR POLES.
LENGTH.
CIRCUMFERENCE CIRCUMFERENCE 6 FEET FROM
AT TOP
BUTT NOT LESS THAN
30 feet.
35
40
22 inches.
22
22
22
22
36 inches.
38
43
47
50
45 66
50
66
CHESTNUT POLES.
66
66
30 feet.
35
40
45
50
55
60
65
70
75
80
85
90
66
22 inches.
22
22
22
22
22
22
22
22
22
22
22
22
36 inches.
40
43
47
50
53
56
59
62
65
69
72
75
66
66
JUNIPER POLES.
30 feet.
35
40
45
50
22 inches.
22
22
22
22
37 inches.
40
44
48
52
66
The following table gives the weight of cedar and Norway
pine poles for lengths between 25 and 85 feet. The diameter at
the top for the cedar poles is approximately 7 inches, varying
between 5 and 7 inches. For the Norway pine poles the diameter
of the pole at the top is 7 inches in every case.
80
TELEPHONY
71
TABLE II.
Pole Weights.
CEDAR POLES.

LENGTH.
DIAMETER AT
TOP.
WEIGHT.
60
66
.
<<
66
25 feet.
25
30
30
35
35
40
40 €
45
45
50
50
55
55
5 inches,
6
6
7
6
7
6
7
6
66
200 pounds.
275
325
450
500
600
700
800
950
1,100
1,250
1,450
1,500
1,800
66
06
65
Ovo
6
7
6
7
64
66
NORWAY PINE POLES.
66
<<
65
40 feet.
45
50
55
60
65
66
70
75 65
80
85
7 inches.
7
7
7.
7
7
7
7
7
7
1,100 pounds.
1,200
1,350
1,500
1,700
2,000
2,400
2.800
3,400
3,800
66
65
66
In Fig. 69 is shown a standard pole for any required length.
The top is cut into a wedge shape with an angle of 90° between
the two sides. This is called "framing,” and is done to throw off
water. At a, a', a', etc., are shown rectangular depressions called
gains. The center of the first gain is 10 inches below the top of
the pole, and the succeeding gains are 24 inches apart. These
.
gains are cut in a vertical line down one side of the pole, with
their faces at right angles to the direction of the wires. The
frame at the top of the pole has its edge parallel to the direction
of the wires. The gains are cut 44 or 41 inches broad and 14 inches
deep. They are for the reception of the cross-arms.
Many attempts have been made with more or less success, to
treat poles artificially so as to protect them against the action of
the weather. One method is to expel the sap, and fill the pores
81
72
TELEPHONY
90°
-
日
​24
24
24"
*
with creosote, or dead oil of tar. The results have been only
measurably successful, as the creosote, though adding to the life
of the pole, reduces its strength. The general practice is to paint
the pole thoroughly after it has been placed. The frame and the
gains are treated to three coats of the best white lead.
종
​The point at which the pole is most liable to
decay is at the surface of the ground. This is
because at this point the action of the dampness
in the ground and in the air is greatest. Various
methods have been devised for protecting poles at
X-/ole
this point, such as coating with tar and the like,
but the general practice today is to depend
altogether on paint. Poles should be cut about
one year before they are to be used, and should
be peeled of bark as soon as possible after they
are cut. Square and hexagonal poles are some-
times used, but only in extraordinary cases, such
tim as when passing through a town where the inhabit-
ants are particular about appearances. They are
usually creosoted though sometimes painted. Poles
occasionally have hollow hearts, by which term is
meant the condition where a pole has decayed at
its axis. This condition is very hard and some-
times impossible to detect, but on the other hand
does not materially weaken the pole until it has
progressed very far.
Lamhl
The Cross-Arm. The cross-arm is next in
Fig. 69.
importance to the pole, and the utmost care should
be taken in the selection of the material for its construction, and
in the proper design. Three kinds of wood are used in the con-
struction of cross-arms : Norway pine, cypress, and yellow pine.
The same dimensions are used with all three. Cross-arms made
out of Norway pine and cypress are painted, but when yellow pine
is used they are usually creosoted.
The process of creosoting is as follows: The timber is sub-
jected to either live or superheated steam for from 3 to 6 hours,
depending on the condition of the timber. The temperature of
the timber must not exceed 250° Fahrenheit. The steam is then
24
82
TELEPHONY
73
withdrawn, and the timber placed in a vacuum of 26 inches until
the water and sap have been removed. The chamber containing
the timber is next filled with the dead oil of tar at a temperature
of not less than 120° F nor more than 250° F, and pressure is
applied until the requisite amount of oil has been forced into the
timber.
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Fig. 70.
Cross-arms are of two sizes. The Standard cross-arm, for
general use, is shown in Fig. 70. The Terminal cross-arm, for
use, as its name indicates, at terminal points, is shown in Fig. 71.
Whatever the kind of wood used, it should be thoroughly seasoned,
straight-grained, and free from injurious shakes or unsound knots.
Referring to Fig. 70 the elevation of the cross-arm is shown above,
while the plan is shown below. The length over all is 10 feet.
The top is arched, as will be seen in the end view at d, to throw off
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Fig. 71.
water. A A space 9 inches long in the center of the arm is flattened
as shown at c. This is done to prevent the water running into the
gain. The pin holes are shown both in plan and in elevation at a,
a', a", etc. They are 19 inches in diameter and are spaced 12
inches on centers. The center of the end pin is 4 inches from the
end of the arm.
The distance between the two pins nearest the

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74
TELEPHONY
One,
pole is 16 inches. Looking at the elevation it will be seen that
there are three holes bored through the axis of the arm.
shown at b', is inch in diameter and is in the center of the arm.
The other two, shown at b and 6", are 3 inch in diameter and are
spaced 182 inches on each side of the center hole. The center
hole is for the reception of the cross-arm bolt, while the other two
are to receive the carriage bolts for fastening the cross-arm braces.
The cross-sectional dimensions of the arm are 4 inches high by 31
inches wide, the height to the top of the arch being 41 inches.
The terminal cross-arm is shown in Fig. 71, the upper view
being the elevation, while the lower one is the plan. It will be
seen that the length over all is 8 ft., or two feet shorter than in case
of the standard cross-arm. The cross-sectional dimensions are
larger than those of the standard arm, being 32 inches wide by 41
inches high, with a height of 4; inches to the top of the arch.
The spacing of the pin holes is 9 inches as against 12 inches for
the standard arm. Three holes, shown at 6,5,6", are bored through
the axis, having the same dimensions and the same location as
those already shown in the standard arm. The terminal cross-arm
is made heavier than the other, for the reason that it is used on the
pole where the line terminates, and has therefore to bear a greater
strain than the arms used at other points of the line. In shape
and method of construction, the terminal cross-arm is the same as
the standard. The pin holes are 132 inches in diameter, for the
accommodation of a larger-sized pin than those used on the stand-
ard arm.
Pins. Fins used in telephone work are made either of oak
wood or of locust. Orange wood is used somewhat throughout the
South and makes a very good pin, but with this exception locust
or oak wood are used. Pins are of two classes : Standard pins and
Transposition pins. Both of these classes of pins are made in
two sizes, one to fit the holes on a standard cross-arm, and the other
to fit those on a terminal cross-arm. In Fig. 72 is shown a stand-
ard pin, that marked A being for a terminal cross-arm, while that
marked B is for a standard cross-arm, the difference between the
two lying solely in the girth dimensions. The upper part of the
pin, for a distance of 24 inches from the top, is threaded for
the reception of the glass insulator,
Below the threaded por-

84

TELEPHONY
75
61
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tion is a taper-shaped hood c, which terminates in an overhang
shown at e. The part below this is in the form of a conical-shaped
shank, with its greatest diameter above and its smallest below.
The shank a or b is introduced
into the hole on the cross-arm,
and makes a binding fit when
the overhang e touches the top
At of the arm. This overhang is
designed to throw off water and
prevent its running down into
the hole. To hold it securely
to the arm a tenpenny nail is
Hť
driven through the side of the
cross-arm and the pin.
A transposition pin for a
14
standard and a terminal cross-
arm is shown in Fig. 73. It
Fig. 72.
will be observed that the main
difference between the transposition pins and the standard pins lies
in the fact that the threaded portion is longer in the former than
in the latter. The standard pin
is threaded to a point 27 inches
from the top, while the transpo-
sition pin is threaded to a point
31 inches from the top. The
extra amount of threaded sur-
face on the transposition pin is
for the accommodation of the
transposition insulator, to be
shown directly. The diameter
of the threaded portion of the
pins, whether transposition or
standard, and whether used on a
standard or on a terminal cross-
arm, is only one inch, the object,
k Fig. 73.
being to obviate the necessity of
having two sizes of insulators. The strain on a pin comes on the
section just below the overhang or hood, so that there is no necessity

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TELEPHONY
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of increasing the diameter of the threaded portion on the pins used
on a terminal cross-arm.
Insulators. With the exception of that portion of the line
known as the drop line or bridle wire, the material used in America
in making insulators is glass. In Europe, porcelain is used more
extensively. Porcelain has some advantages over glass as a
material for makinginsulators, and on the other hand, glass possesses
some advantages over porcelain. Porcelain, when new, has an
insulation resistance about 5 or 6 times
greater than that of glass. However, in
cities or near factories or railroads, the
insulators soon become coated with a thin
film of dust, so that the insulating powers
b of the two materials soon become equal.
d Porcelain is more expensive than glass, and
its glazed surface soon becomes cracked
under the influence of cold, thus allowing
rain to soak into the interior portion and
Fig. 74.
greatly reduce the insulating power. Porce-
lain is more durable than glass and less likely to succumb to
mechanical injury. It is also less hydroscopic; that is to say, it
does not so readily condense the moisture in the air into a thin
film on its surface. Glass, however, possesses one peculiar advan-
tage over porcelain, which in America it is not well to overlook.
Cocoons and spider webs are much less likely to form on glass
insulators than on porcelain because glass is transparent and does
not offer the shade that seems to be desired by worms and spiders
for this work. The fact that glass is cheaper than porcelain and
offers quite as good a resistance under every-day working conditions,
has caused engineers to adopt it generally for open-wire line
construction.
Various forms of glass insulators have been put on the market
from time to time, each possessing advantages; but after much
experience the form shown in Fig. 74 has been found to be the
best suited for general use. It is made as light as possible consis-
tent with strength and durability, and is of such a shape as to
secure the wire properly and, in addition, offer the greatest insula-
tion resistance. In shape it is like a thick inverted cup, with a

86

TELEPHONY
77
2
CV
16
V
a
as
Y-
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heavy bottom a. The bottom is bored out and threaded as shown
at b, to receive the threads on the pin. Around the sides is a
semicircular depression c c', which is designed to receive the wire.
The side of the cup d d', called the “petticoat," is brought down a
good distance to offer as long a path as possible over the surface
of the glass to the pin. When screwed on the pin, the hood occu-
pies the greater portion of the space e, so that the current, in
order to reach the ground, must pass down the outside of the
glass, around the edge, and up on
2 -
the inner side to the pin. In-
sulation resistance like any other
resistance increases with the length
of the path traversed. Hence the mo
necessity of bringing the sides of
the insulator as far down
possible. The sides of the insula-
tor also form a shield for the pin,
and protect it from rain. The
inloo
principal dimensions are given in
the diagram.
In Fig. 75 is shown the most
generally adopted form of trans-
3
position insulator. It consists in
substance of two glasses, one above
Fig. 75.
the other, each one being of the
same general design illustrated in Fig. 74. The lower glass b is
screwed on the pin first, a hole in its top allowing it to descend
to the bottom of the thread. The upper one is then screwed into
place. The upper one should be so designed that when screwed
tight a space of 3 inch will exist between its lower surface and the
upper surface of the lower glass. By this means the surface path
to ground is broken and the insulation resistance increased.
Transposition glasses are sometimes made in one piece, but they
fail in so far as they do not possess this feature.
Pole Fittings.-Cross-Arm Bolts. As has already been said,
the cross-arm is fastened to the pole by means of a cross-arm bolt.
In Fig. 76 is shown a standard cross-arm bolt. It is an iron bolt
made of -inch stock and cut with a standard thread to a point 5

3
16
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32
87
78
TELEPHONY
inches from one end. It is made in five sizes of the following
lengths : 10-inch, 13-inch, 14-inch, 15-inch, and 16-inch, to be used
10"-13-14-15-16"
5"
10
ในปอ
TI
Fig. 76.
3
a
yhi
according to the size of the pole. The head of the bolt is 1 inch
square and linch thick, and the nut is inch thick and 1 inch
5
square. It is thoroughly galvanized, including the thread. In
Fig. 77 is shown an iron washer 24 inches by 24 inches and of
86-inch stock thoroughly galvanized. Through its center is a hole
a"
" of 4-inch diameter. Two of these washers
-24
are used with each bolt, one to go under
the head and the other under the nut.
Cross-Arm Braces. In Fig. 78 is
shown a cross-arm brace. It is made out
of iron or low carbon steel thoroughly
galvanized, 28 inches long, 11 inches wide,
Fig. 77.
and į inch thick. One inch from each
end is a hole, that at one end being 32 inch in diameter for
the reception of the fetter drive-screw which holds it to the pole,
and the other 15 inch in diameter for the reception of the carriage
bolt which secures it to the cross-arm.
Carriage Bolts. In Fig. 79 is shown a carriage bolt. It is
made in two sizes, one 4 inches long for use on standard arms, and

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pa-
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28"
hole
15
32
hole az
17"
32
Fig. 78.
a
the other 42 inches long for use on terminal arms. One end is
threaded to a length of 14 inches for the accommodation of a nut.
In connection with this bolt are used two iron washers of the type
shown in Fig. 80: they are 14 inches in diameter and 1 inch thick,
3
with a half-inch hole in the center. Both carriage bolt and washers
a
88

TELEPHONY
79
OU
are thoroughly galvanized. One washer is placed under the bolt-
head, and the other under the nut.
Fetter Drive-Screws. In Fig. 81 is shown a fetter drive-
screw. It is made of low car-
4" 4" —
bon steel thoroughly galvanized,
and threaded to a point about
3 inches from the end. The
Fig. 79.
end is pointed so that it may be
driven into the wood with a hammer. These screws are used to
fasten the cross-arm braces to the pole.
Pole Steps. In Fig. 82 is shown a pole step. It is made of
thoroughly galvanized iron or low carbon steel
10 inches long and of -inch stock. One end
5
is turned up as shown at a, to prevent the
foot from slipping off as the pole is ascended ES
or descended. The other end is cut with a
fetter thread for a distance of about 3 inches,
Fig. 80.
and the end is pointed so that it may be driven
into the pole.
Under the head of pole fittings comes a lot of apparatus that
will be described now, but whose method of use will be touched
on later. In this lot are the fol-
5"
lowing articles: guy rods, thimbles,
ย
rock eye-bolts, and guy clamps.
ーーーー​」
These articles are used in strength-
Fig. 81.
ening a pole line against excessive
strains.
Guy Rods. In Fig. 83 will be seen a standard guy
rod.
It is
made of 2-inch iron thoroughly galvanized, and has one end threaded
for a distance of 3 inches. The opposite end is bent into the form
- 10"
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Balco
w LIST
Fig. 82.
of an “eye” and welded at a. The length over all is 8 feet. In
practice this rod is used to secure guy wires to the ground.
Thimbles. A standard thimble is of the shape and dimen-
89
80
TELEPHONY
sions given in Fig. 84. It is made of malleable iron thoroughly gal-
vanized. Its use will be explained later.
Rock Eye-Bolts. In Fig. 85 is shown a standard rock eye-
bolt. It is made of a bar of 5 inch wrought iron thoroughly gal-
3
ALO
1
1
kmit
KODIO
G
1
1
6'
3'
8'-0"-
-
Fig. 83.
vanized, and bent double so as to form an eye at a. The length
when formed is 24 inches. Its use will be explained later.
Guy Clamps. The standard guy clamp, used in securing guy
wire, is shown in Fig. 86. It consists of two pieces of malleable

3".
Fig. 84.
iron thoroughly galvanized, and held together by three bolts. The
adjacent surfaces of these two pieces are cut, each with two pecu-
liarly shaped grooves, shown in section at a b, a' b',and in plan at d
and e. Each one of these grooves is tapered. The two grooves on one
piece taper in opposite directions. When the two pieces are placed
together, each groove tapers in the opposite direction to that one
90


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North Electric Co.
TELEPHONY
81
directly over it. In this way, when the bolts are tightened, a bind.
ing strain is placed upon the guy wire, holding it firmly. The de-
tail of the bolt and nut is shown in Fig. 86a. The clamp assembled
is shown in Fig. 866.
Laying out the Line. Before constructing a pole line the
3

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isico
kolt
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fisico
24" -
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inlole
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Fig. 85.

first work is to determine the most feasible route to be followed.
In doing this a great many factors have to be taken into consider-
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Fig. 86.
ation. In general the shortest route should be selected. In doing
this, however, the nature of the ground should not be overlooked.
Very hard, rocky ground is to be avoided owing to the amount of
blasting and hard work it entails in digging the holes. On the
other hand very soft earth, such as marsh or swampy ground,
91

82
TELEPHONY
should be avoided on account of the cost and delay in building
artificial foundations, and also on account of the liability of the
poles to settle and fall in spite of the best of foundations. The
best soil for a pole line is either sharp sand, or loamy or clayey soil,
on account of the ease in digging and the firmness with which it
can be packed down when the pole is set.
There is another factor, however, which is far more potent in
deciding the course of a pole line, and it is one which does not lend
itself to any mathematical solution. That is the right of way.
Before a pole line can be built on a road or public thoroughfare,
Dora
N60
Fig. 86 a.
Fig. 86 6.
the consent of the property owners along the road must be obtained
or a franchise from the town or city must be had. In the major-
ity of cases, particularly in small towns and in the country, both
must be obtained. The right of way should also include the right
to trim any and all trees that may protrude their branches through
the line. The route to be selected is the best one according to the
above considerations along which a right of way can be obtained.
The route having been selected, the next work is to lay off
distances of 130 feet and drive a stake in the ground at the end of
each distance. Suppose that the problem is to lay out a pole line
along the road shown in Fig. 87, in which the road, more or less
crooked, is represented as crossing a river a. Suppose that the
x-marks with their accompanying numbers indicate the position of
the stakes. First of all, the curb line must be well defined, or else
a series of offsets must be taken from the building line to have
the poles properly located, just inside of the curb line. Except in
a few isolated cases the curb line is well enough defined for all
practical purposes. Supposing this to be the case, the start is
made at pole No. 1, presumably just outside of the office. A dis-
A
tance of 130 feet is measured off and at its extremity a second
92

TELEPHONY
83
X
* 29 30
х
31
32
х
33
x28
> 27
x 26
* 25
x24
*23
*22
21
x 20
x 19
x18
x 12
x 16
x 15
X14
x 13
x 12
stake is driven for pole No. 2. This process is continued until the
river is reached.
In approaching the stream great care should be taken to note
the condition of the bank.
If the bank be low and
34 35 36
marshy the last pole should
not be placed very near
the water. If, however,
the bank is high and firm,
the last pole may be placed
as near the edge as possible.
In approaching the river
bank, pole 6 bappens to be
so located that the space
between it and pole 8 is
greater than
130 feet.
Rather than have an extra
long span at this point, an
additional pole is placed at
x 7, midway between x 6
and x 8.
This arrange-
ment helps to support pole
6, which support is probably
needed in view of an extra
long span across the river.
When the river is very
wide, say from 250 to 400
feet, and is shallow in addi-
Fig. 87.
tion, a pole is sometimes
placed in the center if there is no navigation to be interfered with.
Single spans of more than 250 feet across a stream are not per-
missible, except with special construction to be described later.
Where the river is deep enough for navigation, it is best to use a
cable of special construction laid on or under the bottom. This
point will be dwelt on below.
In the straight reach between poles 8 and 16 care should be
taken to locate the intermediate poles in line. This can be done
by having a third man stationed at x 16 to sight back towards
x 11
x 10
x9
a
x8
a
*7
*6
x5
X4
х3
x2
X1
a

93
84
TELEPHONY
x 10 and keep in line the intermediate stakes. Wherever a sharp
turn occurs, as at pole 29, the pole should be placed at the point
of turning; where the turn is less abrupt, as between x 16 and
x 22, this practice is not necessary. Between x 33 and x 34 it
will be seen that the line crosses from one side of the road to the
other. This is often necessary, where it is impossible to secure a
continuous right of way on one side of the road. This crossing
over is sometimes done, also, to avoid trees or other obstructions.
A crossing should always be made at an angle of 45° with the
line of the road.
When the line is built beside a railroad track, the poles
should be set at a distance of at least 12 feet from the rail. If
there should be a clear space between the top of the rail and the
lowest cross-arm of 22 feet or more, the poles may be set at a dis-
tance of not less than 7 feet from the rail.
In cities, poles should be set at the corners of intersecting
streets so as to admit of guying. At road crossings the lowest
cross-arm should be at least 18 feet above the crown of the road.
No electric light or power wires should ever be placed above a
telephone line, as in case of breakage they would fall across the
latter and do serious damage. By placing them beneath the tele-
phone lines this danger is avoided, and the only way in which the
telephone lines can become entangled with the high-tension cir-
cuit is by themselves breaking. No power or trolley wire should
ever be nearer than 6 feet to the nearest telephone wire.
Before going into the method of setting poles, a word should
be said upon the subject of placing cross-arms and guying. On
straight runs, cross-arms are placed on alternate sides of the pole
as shown in Fig. 88. Starting with pole No. 1, the cross-arm is
placed on the side of the pole opposite to the direction of the line.
At pole 2, the cross-arm is placed on the opposite side. At pole
3 the position is again reversed, so that the cross-arm on this pole
and on pole 2 are placed on adjacent sides. This process is con-
tinued for straight runs. On long curves the cross-arms are
placed on the side of the pole facing the middle point of the
curve as shown at 6, 7, 8, 9 and 10, the middle point lying
between poles 7 and 8. At pole 10 a straight run begins again,
and the cross-arm is placed on the side opposite the direction of

94

TELEPHONY
85
b-
bon
the run.
At crossings, as between poles 11 and 12, the cross-arms
are placed on the sides facing the crossing. The point to be
aimed at in placing a cross-arm is to have the pole interposed
between the cross-arm and the point from which the strain comes.
On a straight run the pull comes from both ends,
so that the cross-arms must be placed on alternate o
sides. As soon as the line begins to curve, however, ,
the curved portion, from the fact that it changes its
direction at every point, ceases to be effective in pull- ļ
ing against the straight section, so that the strain at
the curve is toward the straight section.
As a re-
sult the cross-arm must be placed on the side of the
pole facing the middle point of the curve.
In addition to supporting the weight of the wires,
the pole must also withstand the horizontal strains,
and when these become excessive it must be rein-
forced or strengthened. This reinforcing is called
guying. The principle of guying will be touched
on here. If a curve is situated at the end of a straight
run, as between poles 5 and 10, the tendency of the
strain on the wires is to pull the poles on the curve
towards the center of the curve. A very simple
experiment will prove this fact. Set up three or four
Oa'
pins on the arc of a circle. Rigidly fasten one
end of a string and draw it around the pins,
bringing the end out straight. Grasp the end
Oa"
tou
8 do
d+
-oa
ОА

а
e
do
a
of
O"
124
a a
a
Fig. 88.
and pull. The string tends to assume a straight path between
the point where it is rigidly held and the hand, and in so doing it
will drag the pins over towards the center of the arc.
To over-
come this effect the poles on a curve, as 6, 7, 8, 9 and 10 in Fig.
88, are fastened by means of stout wire rope to anchor logs
95

86
TELEPHONY
shown at a', ah, ah, a" and b. These anchor logs are short
poles planted firmly in the ground. Pole 5 at the end of the
straight run is guyed to the anchor log A to prevent its being
pulled in the direction of the line. Pole 10 being at the begin-
ning of a straight run is guyed to the anchor log B, and, being
the last pole on the curve, is also guyed to the anchor log
b. At the crossing pole 12 is guyed to c, and pole 11 to d.
head guy is one placed so as to resist the pull towards pole 1.
A back guy is one so placed as to resist a pull in the opposite
A
16
2
3
4
Fig. 89.
direction, as at the beginning of long spans. Thus in Fig. 87
pole 7 and possibly pole 8 would be back-guyed to resist the
pull of the span across the river. A side guy is one so placed as
to resist a pull in a direction at right angles to the direction of
the line. Thus in Fig. 88 the guys on poles 6, 7, 8 and 9 are
side guys.
In passing througi hilly country care should be taken to
keep the tops of the poles as nearly level as possible, which is
accomplished by placing the longest poles in the lowest places,
and the shortest ones in the highest places. An exaggerated
example of this condition is shown in Fig. 89, where the figures
1, 2, 3, 4, etc., indicate poles placed in hilly ground. The tension
on the wires at the lowest pole a tends to lift them up in the air
and might under severe conditions pull the wires loose from their
fastenings. This effect is overcome by the arrangement shown in
Fig. 90, in which the poles increase in length as the hill is de-
scended, the wires themselves being run in a very nearly horizon-
tal direction. Under these conditions the poles should be so
spaced that the lowest point of the hollow comes in the middle of
a span.
In building a pole line through a very hilly country a profile
96

TELEPHONY
87
A
map of the country should be made or should be obtained from the
township authorities. A map that will suit the purpose can be
made by the use of a little superficial knowledge of land survey-
ing. All that is necessary in the way of apparatus is a surveyor's
theodolite and a leveling pole. They are used in the following
way: The theodolite is set up midway between stake No. 1 and
stake No. 2, and an assistant stations himself at the former with
the leveling pole. The leveling pole is sighted and the point of
intersection marked. The pole is then set up at stake 2 and
2
3
5
4
Fig. 90.
again sighted through the theodolite, the point of intersection
being again marked. The distance on the pole between these two
points gives the difference in level between stake 1 and stake 2.
This process should be repeated for all stakes lying within this
territory. The poles to be set are then graded in length to meet
the requirements. It is not necessary, and it would be impossible
in some localities, to maintain the tops of the poles at a constant
level; but sudden and very marked changes in level should be
avoided.
Setting and Equipping Poles. The line having been laid
out and the stakes driven, the next piece of work is to dig the
holes. The method of so doing depends upon the nature of the
ground. Where the ground is rocky, blasting must be resorted
to. If the line has been properly laid out, however, this
should very seldom be the case. Blasting is usually done
with a hand drill and a small charge of dynamite. The tools used
in digging are shown in Figs. 91, 92, and 93. In Fig. 93 is shown
a combined crow and digging bar, one end of which, b, is sharpened
for digging up the earth, and the other end, a, is broadened out for
tamping down the earth as it is being filled in around the pole.
In
digging, the earth is first loosened up with the sharp end of the
bar, and when this has been done sufficiently it is excavated by
1
97
88
TELEPHONY
means of the sharp-pointed shovel shown in Fig. 92. As the
hole becomes deeper the spoon-shaped shovel shown in Fig. 91 is
brought into play, as this is specially designed for lifting the earth

O
a
Fig. 91.
Fig. 92.
Fig. 93.
out of the hole. In diameter the hole should exceed that of the pole
by about 4 or 5 inches, and the depth should vary with the height
of the pole to be placed. The following table is a safe one to follow :
TABLE III.
a
Pole Setting
LENGTH OF POLE.
DEPTH IN GROUND.
66
25 feet.
30
35
40
45
50
55
60
65
70
75
80
85
90
5 feet.
57
6
6
61
7
71
8
87
9
97
10
101
11
66
66
66
98

TELEPHONY
89
The hole should be of the same diameter at the bottom as it
is at the top. Where the ground is very soft it is necessary to
construct an artificial foundation for
the pole to rest in. This is done in one
of three ways which are equally good,
and which are illustrated in Figs. 94,
95, and 96. In the method shown in
Fig. 94 the hole is dug with a diameter
of 3 feet. The butt of the pole is
equipped with a platform made of two
pieces of planking 33 inches long, 18
inches broad, and 2 inches thick, placed
at right angles, and nailed to the bottom
of the pole. The arrangement is shown
at a in the figure. The bottom of the
hole is covered to a depth of 12 inches
with a mixture consisting of 1 part
cement, 2 parts sand, and 5 parts stone.
When the pole is set, the platform rests
on this foundation, and rubble consist-
ing of the above mixture is fiiled in
around it to within 6 inches of the top
of the hole. Earth is then shoveled in
and packed down hard.
The second method, shown in Fig.
95, consists in fastening to the pole at a
point 2 inches above the surface of the
ground, two yellow pine planks 10 feet
long, 8 inches wide, and 2 inches thick.
They are placed parallel, and fastened
to the pole by means of a cross-arm bolt.
From the ends of these two planks four
others are brought up to the pole in
the manner shown. They are fastened
above and below by cross-arm bolts. To
the bottom of the horizontal planks are
nailed 8 others, 4 on each side of the pole, 3 feet long, 10 inches
broad, and 2 inches thick, making a platform for the pole to rest
O
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0
o
0
Fig. 94.
99

90
TELEPHONY
ممممممممممم
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upon. By this arrangement the pole is also braced against lateral
strains. The foundation shown in Fig. 94 is best adapted to
sandy soil, while that shown in Fig. 95 is more suited to muddy
or marshy ground.
Amore elaborate development of the framework scheme is shown
in Fig. 96, in which two chestnut
poles 10 inches in diameter at
009
the top are sunk into the earth,
one on each side of the main
pole, with their centers about 5
feet 2 inches from its center.
Two 8-inch by 2-inch planks,
shown at a, are fastened to the
tops of the two auxiliary poles,
being also fastened to the main
pole. The upright braces also
are fastened to the auxiliary
poles. As in the previous figure,
planks 3 feet long, 8 inches wide,
and 2 inches thick are nailed to
the bottom to make a platform.
The braces are fastened to the
main and auxiliary poles by
means of cross-arm bolts. Atb
is shown the method of cutting
out the tops of the auxiliary
poles to receive the braces.
The holes having been dug,
the next step is to erect the
poles. These should be dis-
tributed along the right of way,
the butts being placed at the
10'-0"
holes. Where possible, the poles
Fig. 95.
should lie with the top at a
greater elevation than the butt, for assistance in raising. When
poles of different lengths are used, they should be properly dis-
tributed along the right of way. Before the pole is raised it
should be moved so as to have the butt resting on the edge of
8'x 2"X14'-0
8'x 2'x12-0"
8 X 2"X10-0
-3'-0"
100

TELEPHONY
91
B
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กัน
0
a
II
ID
12-05-
Fig. 96.

101

92
TELEPHONY
the hole. For handling the poles properly a cant hook, shown
in Fig. 97, is used. It consists of a heavy ash handle a, to which
is fastened a wrought-iron spur b, pivoted at c. In using this
tool the pole is caught between the side of the handle, e, and
the spur, after which, by moving the handle upward, the pole is
a
+
C
C
D
Fig. 97.
rolled over.
The tongs shown in Fig. 98 are of wrought iron
fastened to a heavy ash handle.
When the pole has been properly placed, it is seized at the
top by the gang of linemen, usually from 5 to 8 men, and raised.
One man shown at a, Fig. 99, stands at the hole, and seizing the
pole in his arms directs the motion of the butt into the hole. The
&
Fig. 98.
tools used in pole raising are: a pike, shown in Fig. 100, and a
dead man, shown in Fig. 101. Pikes are made in lengths of from
8 to 14 feet, and consist of an ash pole a, Fig. 100, about 2 inches
in diameter, surrounded at one end by a wrought-iron ring b. Into
one end is driven a steel spike c. The dead man is made of a
heavy ash pole a, Fig. 101, with a U-shaped wrought-iron prong
at one end, equipped with a spur in the center, shown at c. This
implement is used to hold the pole in position from time to time as
it is being raised. This is being held by the man at b in Fig. 99.
As soon as the top of the pole is raised high enough to permit of it,
8
102

TELEPHONY
93
four linemen thrust into it the steel spurs of their pikes and are
thus enabled to raise it higher still. As the pole is raised nearer
and nearer to the perpendicular, the longer pikes come into play,
until, when the pole has been elevated to an angle of about 50°,
the butt slides into the hole. The pikes are then used to adjust it
عکس
h
a
Fig. 99.
bars.
to a perfectly vertical position. This having been done, the earth
is gradually filled in around the pole, being tamped down in the
meanwhile by two men using the end a (Fig. 93) of their tamping
Great care should be taken to pack the earth firmly as it is
being put in, and to this end only one shovel is allowed to be used
during the process. When the hole has been filled, the surplus
earth is piled up around the pole in the form of a mound.
In regard to the rate at which poles can be set by the average
gang of linemen, it may be said that this is governed by the num-
ber of holes that can be dug. Under ordinary conditions about 8
or 10 holes are all that one man can dig in one day. Where blast-
ing has to be resorted to, the rate is much lower. It rarely goes
above this. Eight or ten poles set is a good day's work for the
average gang.
The poles having been set, the next step is to set the cross-
arms.
For this purpose a lineman is sent up the pole, with a block
which he fastens at the top. A stout Manila rope is then rove
a
103
94
TELEPHONY
ft
La
C
through the block, and the cross-arm, being fastened to one end of
it, is hoisted to the top of the pole by the men on the ground.
The top cross-arm is always set first, the one just beneath it next,
and so on.
The reason for this arrangement is that poles
are not always equipped at once with their full capacity of
O
cross-arms, and frequently, after a line has been put into
working order, additional cross-arms have to be placed.
If the first cross-arms were placed in the bottom gains, not
only would the additional ones have to be carried over the
working wires, but the new wires, while being strung,
would be sure to hang down and to cause trouble on those
already in place. All this is avoided by beginning at the
top.
The cross-arm having been hauled up within reach
of the lineman, it is then seized, the rope is removed, and
the arm is placed in position in the top gain, being secured
by a cross-arm bolt driven first through the pole and then
through the cross-arm. The two cross-arm
braces are then fastened to the cross-arm by
means of two carriage bolts, which pass first
through the cross-arm and then through the
brace. The opposite ends of the braces are
then brought together and fastened to the
pole by means of a fetter drive-screw. If
more than one arm is to be placed, the suc-
Fig. ceeding ones are hoisted into position and
.
secured in the manner already described. On
terminal poles, on corner poles, and at the beginning
and end of long spans, back braces are used on the
cross-arms. The method of their attachment is
shown in Fig. 102, where the back braces are shown
at a and a'. They are fastened to the side of both
cross-arm and pole opposite that to which the regular
brace is fastened. When this work is finished, the
Fig. 101.
poles are ready for the reception of the wire. But
before a description of the method of stringing wires is given, it
will be necessary to say something about the nature of the
material used for wire.

100.
104

TELEPHONY
95
TELEPHONE WIRES.
o
2
a
a
use
Three kinds of material have been used in the manufacture
of wire for telephone use — namely, iron, steel, and copper. In
. -
the early days, learning their lesson from the telegraph men, tele-
phone engineers built their lines of iron wire, and it proved prac-
ticable for the short distances then in vogue. Steel wire was
next selected on account of its greater tensile strength. With
the advent of metallic circuits, 0 0 0 0 0
6
however, it was found that if
the telephone was to be suc-
cessful for transmission over
long distances, some better
conductor than iron must be
selected. Before discussing
at any great length the most
suitable metal to
in
line construction, it will be
necessary for us to understand
thoroughly the conducting
properties of the various
metals used in the mechanic
arts.
The measure adopted
for determining the relative
merits of different substances
as conductors of electricity,
is called Specific Resistance, which is the resistance between the
two opposite faces of a centimeter cube of the substance at a tem-
perature of 0° Centigrade. Table IV gives the resistances of
various metallic substances in microhms, or millionths of an ohm.
The Specific Conductivity of a substance is the reciprocal of
its
specific resistance. Substances are compared as to their con-
dueting qualities by what is called percentage of conductivity.
This is the ratio of the specific conductivity of the substance to
that of some standard substance. As a usual thing pure copper
is chosen as the standard substance, and the percentage of its con-
ductivity is taken to be 100. The percentage of conductivity of
a wire is the ratio that its conductivity bears to that of a pure
Fig. 102.

105
96
TELEPHONY
TABLE IV.
Relative Specific Resistances of Metals.

METAL.
RESIST-
ANCE.
METAL
RESIST-
ANCE.
Silver, annealed
Copper,
Silver, hard-drawn
Copper,
16
Gold, annealed
Gold, hard-drawn
Aluminum, annealed
Zinc, pressed
Platinum, annealed
1.504
1.598
1.634
1.634
2.058
2.094
2.912
5.626
9.057
Iron, annealed
Nickel,
Tin, pressed
Lead,
German silver
Antimony, pressed
Mercury
Bismuth, pressed
9.716
12.470
13.210
19.630
20.930
35.500
91.320
131.200
copper wire at the same temperature having the same area of
cross-section and the same length. In telephone practice it is
usually specified that a conductor shall have a conductivity equal
to 98 per cent of that of pure copper. The measure used for
determining the diameter of a wire is called the mil, and its mag-
nitude is doo inch. The unit of cross-sectional area of a con-
ductor is the circular mil, which means the area of cross-section
of a wire whose diameter is one mil. This forms a more conven-
ient measure than the square inch, since the area bears a very
simple relation to the diameter. The area of a circle in square
measure is equal to
a
T 02
πγ 2 -
4
in which r is the radius of the circle, and d its diameter. If d be
7 02
expressed in inches, the area
will be in square inches. If d
4
7 d2
be expressed in mils, the area
will be in square mils. Since d
.
4
T
is equal to 1, then 1 circular mil is equal to
sq. mil, and 1 sq.
4
4
mil is equal to
circular mils.
Therefore the area of a
T
circle in circular mils will be equal to the area of that circle in
square mils multiplied by the number of circular mils in one
106


G
BELL-EXPRESS TRANSFER OR MULTIPLE SWITCHBOARD
American Electric Telephone Co.
TELEPHONY
97
a
square mil. Thus, if a circle have a diameter d mils, its area in
circular mils will be
7 d2
A
4
x
TT
da,
-
4
which means that the area of a circle expressed in circular mils
equals the square of the diameter in mils. While the circular mil
is the measure of the cross-sectional area of a wire, and forms the
basis for figuring out the safe current-carrying capacity, wire is in
practice bought and sold according to arbitrary gauges adopted by
various manufacturers.
In America the Brown & Sharpe gauge is used almost uni-
versally, and was originated by the manufacturers of that name in
Providence, R. I. In this system the gauge number diminishes
as the diameter of the wire increases. The rule according to
which the change is made is a very simple one. If any gauge
number be taken as a basis of comparison, then by adding 3 to
the
gauge number there is obtained the number of a wire whose
area is about one-half that of the original. For example, one
No. 3 wire will have the same cross-sectional area as two No. 6
wires; and one No. 5 wire will have the same area as two No. 8
or four No. 11 wires. Again, by subtracting 3 from any gauge
number, a wire is obtained whose area is about twice that of the
original; thus a No. 1 wire has about twice the area of a No. 4.
The following course of reasoning deduced from the above-
mentioned facts, will enable the student to determine the factor
by which the area of a wire of any gauge number must be multi-
plied or divided in order to obtain the area of the next larger or
smaller wire. If the areas of any two consecutive sizes of wire
were in the ratio of 2 or 21, the factors which would be used to
determine the area of a wire three sizes larger or smaller would be
2 or I because the given area would have to be multiplied either
by 2 three times or by 1 three times. In other words, the factor
to be used in determining the area of the next consecutive size to
the given one, would be the cube root of that used to determine
the area of a wire three sizes removed. Now, since this latter
factor has been shown to be 2, it follows that the factor necessary
to determine the area of the next consecutive size is
1
1
which equals 1.26 or
1.26

3
♡ 2.
2 or 3
Ń 2,
107
98
TELEPHONY
a
For example, if the area of a No. 6 Brown & Sharpe gauge wire
were 26,250 circular mils, the area of a No. 5 wire would be
26,250 x 1.26 = 33,075 circular mils; and in like manner the
X
1
area of a No. 7 wire would be 26,250 X
1.26
20,834 circular
mils.
Again, since the ratio of the resistances of two wires varies
inversely as the ratio of their areas, it follows that the same two
factors can be used to determine the ratio of the resistances of any
two wires whose gauge number is known, if the resistance of one
of them is given. Thus, if the resistance of a foot length of No.
10 B. & S. gauge copper wire be .001 ohm, the resistance of a
No. 11 B. & S. gauge copper wire will be .001 X 1.26 = .00126
ohm. The ether wire gauges are the Washburn & Moen Manu-
facturing Co.'s gauge, the G. W. Prentiss gauge, the British
Standard gauge (abbreviated, S. W. G.), the Birmingham or
Stubs wire gauge (abbreviated B. W. G.), the Trenton Iron
Company's gauge, and the Old English gauge. A table of these
gauges will be given directly.
Copper as a Conductor. Reference to the table of relative
specific resistances given above will show that silver is the only
metal whose specific resistance is less than that of copper. Silver,
hewever, on account of its cost, is excluded from the metals
suited for telephone purposes. In looking farther down the list
it will be seen that iron is the only other metal that from a com-
mercial standpoint is suited for the manufacture. But the spe-
cific resistance of iron as compared with copper is as 6 to 1, which
means that of two wires of the same length, one iron and the
other copper, the former would have to possess 6 times the area
,
of the latter to have the same conductivity. As a result, if iron
a
wire were used in telephone line construction, it would have
to be of such large diameter to compete successfully with copper
in point of transmission, as to render the problems of line construc-
tion very much more difficult than they now are, and to adr very
materially to the cost of building.
Copper, when exposed to the air, forms on its surface an
oxide which is not soluble in water and which therefore presents a
protecting shield against further corrosion of the metal. The oxide

108

TELEPHONY
99
a
of iron, on the other hand, is readily soluble in water, and therefore
fresh surfaces of the iron are always presented to the atmosphere. For
this reason iron exposed to the weather is soon rusted away. The
requisite size of an iron wire, moreover, would preclude its use in
cables. Copper has therefore come to supplant iron in line con-
struction, and is now universally used by the leading companies.
Pure annealed copper has a specific gravity of 8.89 at 60°F. One
cubic inch weighs 0.32 lb. and the melting point of the metal is
about 2,100°F. Annealed copper does not possess sufficient ten-
sile strength to make it practicable for wire. The process of hard-
drawing it, however, has overcome this difficulty, and copper wire
used in line construction is manufactured in this way. Dr. Mat-
thiessen made a determination showing that a piece of soft copper
wire, one foot long and having a diameter of 1 mil, has a resistance
of 9.612 legal ohms at a temperature of 0° Centigrade. Tables
V and VI, which are based on Matthiessen's standard, give the
resistances and weights of all sizes of wire according to the B. &
S. and the B. W. G. gauges respectively.
In line construction the following sizes of wire are used :
For trunk and subscriber lines not over 50 miles in length - No. 12
N. B. S. G. hard-drawn copper.
For long-distance lines, 500 to 1,000 miles or over - No. 8 B. W. G.
hard-drawn copper.
For subscriber lines not over 3 or 4 miles in length - No. 14 B. & S.
hard-drawn copper.
NOTE. The above wires are all bare of insulation.
For bridle or drop wires - No.12 B. & S. hard-drawn copper, insulated.
Other sizes are sometimes used for special cases.
This point,
however, will be taken up later.
,
Iron wire, although largely superseded by copper, is still used
in country districts, where little long-distance business is done, and
where the subscribers have not yet been educated up to the point
where they are familiar with and demand the best transmission.
As iron rapidly corrodes, or “rusts," when exposed to the air,
the iron wire used in line construction is galvanized, which means,
covered with a film of zinc. This is accomplished in the following
manner: The iron wire, while hot, is drawn through a vat of
hydrochloric acid to render the surface perfectly clean. It is
immediately afterwards drawn through a vat of molten zinc, which
-
109
100
TELEPHONY

TABLE V.
Weights and Resistances of Wires, B. & S. Gauge.
Weights - Specific Gravity, 8.89.
Resistance at 68° F, in International Ohms,
Based upon Matthiessen's Standard.
Gauge No. B. & S.
Diameter,
Mils.
Area,
Circular Mils.
Area, Square
Inches.
Pounds
per
1,000 ft.
Pounds
per
Mile.
Feet
per
Pound.
Ohms
per
Pound
Annealed.
Ohms per 1,000 Feet. Ohms per Mile. Feet
per
Ohm
Pure Hard- Pure Hard- Annealed
Annealed. Drawn. Annealed. Drawn.
d
d2
12
0000 460.000
000 409.640
00
364.800
0 324.865
1 289.300
2 257.630
3 229.420
4 204.310
5 181.940
6 162.020
7 144.280
8 128.490
9 114.430
10 101.890
11 90.742
80.808
13 71.961
14 64.084
15 57.068
16 50.820
17 45.257
18 40.303
19 35.890
20 31.961
21 28.462
22 25.347
22.571
24 20.100
25 17.900
26 15.940
27 14.195
28 12.641
29 11.257
30 10.025
31 8.928
32 7.950
33 7.080
34 6.305
35 5.615
36 5.000
37 4.453
38 3.965
39 3.531
40 3.145
211600.00 .1661900000
167805.00 .1317900000
133079.40 .1045200000
105534.50 .0828870000
83691.20 .0657320000
66373.00 .0521280000
52634.00 .0413390000
41742.00 .0327840000
33102.00 .0259990000
26250.50 .0206180000
20816.00 .0163510000
16509.00 .0129670000
13094.00 .0102830000
10381.00 .0081518000
8234.00 .0064656000
6529.90 .0051287000
5178.40 .0040672000
4106.80 .0032254000
3256.70 .0025579000
2582.90 .0020285000
2048.20 .0016087000
1624.30 .0012757000
1288.10 .0010117000
1021.50 .0008023100
810.10 .0006362600
642.40 .0005045700
509.45 .0004001500
404.01 .0003173300
320.40.0002516600
254.10 .0001995800
201.50 .0001582700
159.79 0001255100
126.72 .0000995360
100.50 .0000789360
79.70 .0000625990
63.21 .0000496430
50.13 .0000393680
39.75 .0000312210
31.52 .0000247590
25.00 .0000196350
19.83 .0000155740
15.72 .0000123450
12.47 .0000097923
9.89 .0000077634
640.50000
508.00000
402.80000
319.50000
253.30000
200.90000
159.30000
126.40000
100.20000
79.46000
63 02000
49.98000
39.63000
31.43000
24.93000
19.77000
15.68000
12.43000
9.85800
7.81800
6.20000
4.91700
3.89900
3.09200
2.45200
1.94500
1.54200
1.22300
.96990
.76920
.61000
.48370
.38360
.30420
.24130
.19130
.15170
.12030
.09543
.07568
.06001
.04759
,03774
.02993
3381.400
2682.200
2126.800
1686.900
1337.200
1060.600
841.090
667.390
529.060
419.550
332.750
263.890
209.240
165.950
131.630
104.390
82.791
76.191
52.050
41.277
32.736
25.960
20.595
16.324
12.964
10.268
8.142
6.457
5.121
4.061
3.221
2.554
2.025
1.606
1.274
1.010
.810
.635
.504
.400
.317
.251
.199
.158
1.561
1.969
2.482
3.130
3.947
4.977
6.276
7.914
9.980
12.580
15.870
20.010
25.230
31.820
40.120
50 590
63.790
80.440
101.400
127.900
161.300
203.400
256.500
323.400
407.800
514.200
648.400
817.600
1031.000
1300.000
1639.000
2067.000
2607.000
3287.000
4145.000
5227.000
6591.000
8311.000
10480.000
13210.000
16660.000
21010.000
26500.000
33410.000
.00007639
.00012150
.00019310
.00030710
.00018830
.00077650
.00123500
.00196300
.00312200
.00496300
.00789200
.01255000
.01995000
.03178000
.05045000
.08022000
.12760000
.20280000
.32250000
.51280000
.81530000
1.29600000
2.06100000
3.27800000
5.21200000
8.28700000
13.18000000
20.95000000
33.32000000
52.97000000
84.23000000
133.90000000
213.00000000
338.60000000
538.40000000
856.20000000
1361.00000000
2165.00000000
3441.00000000
5473.00000000
8702.00000000
1387.00000000
2200.00000000
3498.00000000
.04893 .050036
.06170 .063094
.07780 .079558
.09811 .100330
.12370 .126490
.15600 .159530
.19670 .201140
.24800 .253610
.31280 .319870
.39440 .103320
.49730 .508540
.62710 .641270
.79080 .808760
.99720 1.019900
1.25700 1.285400
1.58600 1.621800
1.99900 2.044300
2.52100 2.577900
3.17900 3.250800
4.00900 4.099600
5.05500 5.169200
6.37400 6.518300
8.03800 8.219600
10.14000 10.372000
12.78000
16.12000
20.32000
25.63000
32.31000
40.75000
51.38000
64.79000
81.70000
103.00000
129.90000
163.80000
206.60000
260.50000
328.40000
414.20000
522.20000
658.50000
830.40000
1047.00000
.25835 .26419
.32577 .33314
.41079 .42007
.51802 .52973
.65314 .66790
.82368 .84239
1.03860 1.06210
1.30940 1.33920
1.65160 1.68890
2.08250 2.12950
2.62580 2.68500
3.31110 3.38590
4.17530 4.27690
5.26570 5.38480
6.63690 6.78690
8.37410 8.56330
10.55500 10.79400
13.31100 13.61200
16.78500 17.16500
21.16800 21.64600
26.69100 27.29400
33.65500 34,41600
42.44100 43.40000
53.53900 54.74900
67.47900
85.11400
107.29000
135.53000
170.59000
215.16000
271.29000
242.09000
431.37000
543.84000
685.87000
864.87000
1090.80000
1375.50000
1734.00000
2187.00000
2757.30000
3476.80000
4384.50000
5528.20000
20440.000
16210.000
12850.000
10190.000
8083.000
6410.000
5084.000
4031.000
3197.000
2535.000
2011.000
1595.000
1265.000
1003.000
795.300
630.700
500.100
396.600
314.500
249.400
197.800
156.900
124.400
98.660
78.240
62.050
49.210
39.020
30.950
24.540
19.460
15.430
12.240
9.707
7.698
6.105
4.841
3.839
3.045
2.414
1.915
1.519
1.204
.955
23
110

TELEPHONY
101
Diameter
in Mils, d.
Area in Cir-
cular Mils.
(C. M.=d.)
Ohms per
Pound
454
425
380
340
300
284
259
233
220
203
180
165
118
131
120
109
95
83
72
65
58
49
42
35
32
28
25
22
20
18
16
14
13
12
10
9
8
7
5
4
206116
180625
144400
115600
90000
80656
67081
56644
48100
41209
32100
27225
21904
17956
14400
11881
9025
6889
5181
4225
3364
2401
1764
1225
1024
78+
625
484
400
324
256
196
169
144
100
81
64
49
25
16
TABLE VI.
Weights and Resistances of Wires, B. W. G.
Weights.
Resistances in International
Ohms, Based upon Matthies-
sen's Standard at 68° F.
Gauge No.
B. W.G.
Pounds
per 1.000
Feet.
Pounds
per
Mile.
Ohms per
1,000 Feet.
0000
000
00
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
624.000
517.000
437.000
350.000
272.000
244.000
203.000
171 000
146 000
125.000
98.000
82.000
66.000
54.000
41.000
36 000
27.300
20 800
15.700
12.800
10.200
7.300
5.300
3 700
3.100
2 400
1.900
1.500
1.200
.980
.770
.590
.510
.440
.300
.250
.190
.150
,076
.018
3294 000
2887.000
2308.000
1847.000
1438 000
1289 000
1072.000
905.000
773.000
659.000
518.000
435.000
350.000
287.000
230.000
190.000
114 000
110 000
83.000
68.000
54.000
38.400
28.200
19.600
16.400
12.500
10.000
7 700
6.400
5.200
4.100
3.100
2.700
2.300
1.600
1.300
1.020
780
.400
.256
.05023
.05732
.07170
.08957
.11500
.12840
.15430
.18280
.21390
.25130
.31960
.38030
.47270
.57660
.71900
.87150
1.14700
1.50300
1.99700
2 45100
3.07800
4 31200
5.87000
8.45200
10.11000
13.21000
16.57000
21.39000
25.88000
31.96000
40.45000
52.83000
61.27000
71.90000
103.50000
127.80000
161.80000
211.30000
414.20000
647.10000
.00008051
.00010480
.00016400
.00025600
.00042230
.00052580
.00076010
.00106600
.00146000
.00201400
.00325800
.00461500
.00712900
.01061000
.01650000
.02423000
.04199000
.07207000
.12730000
.19160000
.30230000
.59330000
1.09900000
2.27900000
3.26200000
5.56500000
8.75600000
14.60000000
21.38000000
32.58000000
52.19000000
89.04000000
.119.80000000
165.00000000
342.00000000
521.30000000
835.10000000
1425.00000000
5473.00000000
13360.00000000
OT
111
102
TELEPHONY
is kept at a uniform temperature of 740° F. When the wire thus
coated is exposed to the atmosphere, an oxide of zinc is formed on
the surface. This oxide,
This oxide, however, not being soluble in water,
remains on the wire and protects it from further corrosion.
When galvanized iron is exposed to the action of sulphur or
chlorine, which occur in the exhausts of locomotives, in factory
chimneys, etc., zinc sulphate or zinc chloride is formed. Both of
TABLE VII.
Properties of Galvanized Iron and Steel Wires, B. W. G.

Weight, in
Pounds.
Breaking
Strengths in
Pounds.
Resistance per Mile
(International Ohms)
at 68° F.
Number, B.W.G.
Diameter in
Mils=d.
Area in Circular
Mils=d.
1,000
Feet.
One
Mile.
Iron.
Steel.
E. B. B.
B. B.
Steel.
O CON PO
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
340
300
284
259
238
220
203
180
165
148
134
120
109
95
83
72
65
58
49
115,600
90,000
80,656
67,081
56,644
48,400
41,209
32,400
27,225
21,904
17,956
14,400
11.881
9,025
6,889
5,184
4,225
3,364
2,401
304.0
237.0
212.0
177.0
149.0
127.0
109.0
85 0
72.0
58.0
47.0
38.0
31 0
24.0
18.0
13.7
11.1
8.9
6.3
1,607
1,251
1,121
932
787
673
573
450
378
305
250
200
165
120
96
72
59
47
33
4,821
3,753
3,363
2,796
2,361
2,019
1,719
1,350
1,134
915
750
600
495
375
288
216
177
141
99
9,079
7,068
6,335
5,268
4,449
3,801
3,237
2,545
2,138
1,720
1,410
1,131
933
709
541
407
332
264
189
2.93 3 42 4.05
3.76 4.40 5.20
4.19 4.91 5.80
5.04 5.90 6.97
5 97 6.99 8.26
6.99 8.18 9.66
8.21 9.60 11.35
10 44 12.21 14.43
12.42 14 53 17.18
15.44 18.06 21.35
18.83 22.04 26.04
23.48 27.48 32.47
28.46 33.30 39.36
37.47 43.85 51.82
49.08 57 44 67.88
65.23 76.33 90.21
80.03 93.66 110.70
100.50 120 40 139.00
140.80 164.80 194.80
these salts are soluble in water, so that the zinc coating is soon
eaten away, leaving the surface of the iron exposed. For this
reason iron wires that cross railroad tracks are soon eaten away,
and usually do not last more than six months or a year.
The three grades of iron wire used are designated by the terms
Extra Best Best, Best Best, and Best. These grades differ in
point of internal structure, and also in conductivity. Table VII
gives the properties of Extra Best Best, Best Best, and Steel wire
according to the Birmingham Wire Gauge.
Table VIII shows the tensile strength of various sizes of
copper wire.
112
TELEPHONY
103
TABLE VIU.
Tensile Strength of Copper Wire.

Breaking Weight
in Pounds.
Breaking Weight
in Pounds.
Number,
B. & S.
Gauge.
Number,
B. & S.
Gauge
Hard-
Drawn.
Annealed.
Hard-
Drawn.
An-
nealed.
0000
000
00
0
1
2
3
4
5
6
7
8
8310
6580
5226
4558
3746
3127
2480
1967
1559
1237
980
778
5650
4480
3553
2818
2234
1772
1405
1114
883
700
555
440
9
10
11
12
13
14
15
16
17
18
19
20
617
489
388
307
244
193
153
133
97
77
61
48
349
277
219
174
138
109
87
69
HOOO
43
34
27
Table IX gives the factors by which the resistance of a copper
conductor at an observed temperature must be multiplied to
determine its resistance at 75° F. Thus, if the resistance is 12.746
ohms at 88° F, the resistance at 75° F will be 12.746 X .9728, or
12.399 ohms.

TABLE IX.
Factors for Calculating Resistance of Copper Wire at 75° F.
Temperature, in
Degrees F.
Factor
Temperature, in
Degrees F.
Factor
Temperature, in
Degrees F.
Factor.
Temperature, in
Degrees F
Factor.
100
99
98
97
96
95
94
93
92
91
90
89
88
87
86
85
84
83
.9484
.9504
.9524
.9544
.9564
.9585
.9605
.9626
.9646
.9666
.9687
.9708
.9728
.9749
9769
.9790
.9811
.9832
82
81
80
79
78
77
76
75
74
73
72
71
70
69
68
67
66
65
64S2NS3&G86
.9853
.9874
.9895
.9916
.9937
.9958
.9979
1.0000
1.0021
1.0042
1.0064
1.0085
1 0106
1 0128
1.0149
1.0160
1.0193
1.0214
6+
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
48
47
1.0236
1.0258
1.0280
1 0301
1.0323
1.0345
1.0367
1.0389
1.0411
1.0433
1.0455
1.0478
1.0500
1.0522
1.0544
1.0567
1.0589
1.0612
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
1 0634
1.0657
1.0679
1.0702
1.0725
1.0748
1.0771
1.0793
1 0816
1.0839
1.0862
1 0885
1.0908
1.0932
1.0954
113
104
TELEPHONY
In recent years, with the great lowering in the cost of production
of aluminum, attempts have been made to use this metal in many
of the mechanic arts. Among the suggestions made is one for its
use in the manufacture of telephone wire. The great advantage
of this metal lies in its comparative lightness.
Table X gives the relative qualities of aluminum and copper.
TABLE X.
Properties of Aluminum and Copper.

ALUMINUM.
COPPER.
Conductivity (for equal sizes)
Weight (for equal sizes)
Weight (for equal length and resistance)
Price-Al. 29c., Cop. 160. (bare line-wire)
Price-(Equal resistance and length bare line-wire)
Temperature coefficient per degree F.
Resistance of mil-foot (20°C)
Specific gravity
Breaking strength (equal sizes)
.54 to .63
.33
.48
1.81
.868
.002138
18.73
2.5 to 2.68
1
1
1
1
1
1
.002155
10.5
8.89 to 8.93
1
Table XI gives the properties of the different grades of
aluminum wire manufactured by the Pittsburg Reduction Com-
pany.
To sum up, the only advantage to be gained by the use of
aluminum would lie in the fact that it is lighter than copper. To
offset this, however, the diameter of the wire would have to be
larger than that of a copper wire for the same conductivity, thus
offering a greater resistance to the wind. The greater surface of
the aluminum wire would cause a greater electrostatic capacity to
exist between it and the ground than would be the case with cop-
per wire. There would, moreover, be a greater difficulty in solder-
ing aluminum joints than copper joints. In view of these facts, it
does not seem possible that aluminum will ever supplant copper
in line construction.
Tie Wires. The line wires are tied to the insulators by
means of short pieces of wire called tie wires. The wire used
for this purpose should always be of annealed copper of the same
gauge as the wire to be tied. It should be cut into lengths of
about 18 inches.
Stringing Wires.
Wires. The poles having been erected and the
cross-arms fitted, the next piece of work to be done is to string the
114
TELEPHONY
105

TABLE XI.
Resistance, Tensile Strength, and Weight of Aluminum Telephone Wire.
Area in
Square
Inches
Area in
Circular
Mils.
Diameter
in Mils.
No., B. & S. Gauge.
Grade A o.
Grade A 75.
Grade A 2.
Pounds
per Mile.
Sp.Gr.2.68.
Tensile
Tensile
Tensile
Water,
Resistance Strength, Resistance Strength, Resistance Strength, 62.355 lbs.
per
Pounds per Pounds
per PoundsperCub.Ft.
1,000 Feet per Square 1.000 Feet per Square 1,000 Feet per Square
at 75° F. Inch. at 75° F.
Inch
at 75° F. Inch.
Having
Pounds per Mile of
Same Resistance as
Copper Wire of Size
Aluminum
Given.
d.
d2,
d2 X.7854
1,000,000
Grade
A 75.
4
5
6
7
8
9
10
11
12
13
14
204.31
181.94
162.02
144.28
128.49
114.43
101 89
90.74
80.81
71.96
64.08
417,420
331,020
262,505
208,160
165,090
130,910
103,810
82.340
65,299
51,784
41,068
.0327840
.0259980
.0206170
0163490
.0129660
.0102840
.0081532
.0064670
.0051286
.0040671
.0031469
.4012
.5058
.6380
.8044
1.6340
1 2780
1.6130
2.0330
2.5650
3.2330
4.1790
27,000
27,500
28,000
29,000
30,000
32,000
33.000
35,000
39,000
.4288
.5488
.6820
.8600
1.1050
1.3670
1.7240
2.1730
2.7410
3.4560
4 4670
33,000
34,000
35,000
36,000
37,000
39,000
40,000
41,000
42,000
.4605
.5818
.7325
.9235
1.1870
1.4680
1.8520
2.3350
3.0840
3.7120
4.7980
40,000
42,000
44,000
46,000
48,000
50,000
51,000
53,000
55,000
200.90
159.30
126.35
100.21
79.46
62.99
48.71
39.63
31.43
24.83
19.76
336.0
266.4
211.4
167.6
133 2
105.4
83.6
66.3
52.6
Conductivity.
(Pure Copper = 100.)
62.
58.
54.
Comparative Section of Equal Conductivity.
(Copper = 100.)
156.4
167
180.
Comparative Weight of Same Lengths of
Equal Conductivity.
(Copper=100)
47.
50 2
54.
115
106
TELEPHONY
wires. When only one or two wires are to be strung at a time,
the best method to pursue is to start from the first pole and unwind
the wire along the ground at the feet of the poles until the last
one has been reached. The wire is then made fast to the
proper
pins at the first pole, and is carried up over the cross-arm at each
succeeding pole. It is then tied to the proper pins.
When several wires are strung at once, as is usually the case,
a different method is pursued. As many coils of wire are provided
as there are lines to be run, and each coil is placed on what is
called a paying-out reel, Fig. 103. This consists of a horizontal

le
e
b
La
a
W
ht
h
9
V
Fig. 103.
wheel a on the spokes of which are placed four upright arms b, c,
d and e, which are bent over at the top to prevent the coil of wire
being pulled over their ends. The wheel is mounted on a pivot f,
the bearing of which g rests upon a four-legged truck h. The coil
of wire to be payed out is placed on the wheel, with the four
uprights projecting through the center of the coil. The end of the
wire is then seized, and, the wheel a revolving freely, the coil is
easily unwound.
The reel, or reels are placed in a convenient location near the
foot of the first pole. A piece of apparatus called a running board
is then provided. This consists of a heavy board, usually of oak,
of about the same length as the cross-arm, and having holes bored
through it, with the same spacing as that of the pins upon the
The ends of the wires are attached at these holes. A
stout rope, to be pulled by a horse, is run over the cross-arm, one
end of the rope being fastened to the center of the running board.

cross-arm.
116
TELEPHONY
107
The horse is then started, and the running board is dragged up
to the cross-arm on the first pole, over which it is lifted by a man
stationed there. It then passes on to the next pole, carrying the
wires after it, and is lifted over the cross-arm as before. As the
work progresses the rope is lifted over succeeding cross-arms so as
to keep the running board and the wires above them.
When all the wires on the reel have been played out, the ends
are fastened to their respective pins at the first pole, and the distant
ends of the wire are then grasped and pulled tight. Care must be
taken not to pull the wires too tight, as this would result in stretch-
ing and thereby materially weakening them. The best way to
measure the right amount of tension to exert on the wires is to
note the amount of sag in the spans between the poles. The
amount of allowable sag depends upon the length of the span,
and
the temperature of the air. It increases with the length of the
span, and decreases with the temperature.
Table XII is one largely used by telephone men in line
construction work.

TABLE XII.
Allowable Sag in Wires.

TEMPERA-
TURE
FAHREN-
HEIT.
SPAN 75 FT. SPAN 100 FT. SPAN 115 FT. SPAN 130 FT. SPAN 150 FT. SPÁN 200 FT
SAG.
SAG.
SAG.
SAG
SAG.
SAG.
27 inch
<<
66
66
8 inch
9
101
66
31
30°
10°
+10°
+ 30°
+ 60°
+ 80°
+100°
1 inch
11
11
2
21
3
41
2 inch
21
3
3
41
57
7
31 inch
4
41
51
7
2334579
--
CONN
41 inch
5
6
7
9
111
14
12
66
57
66
81
151
19
22
64
(
11
-
To illustrate the use of Table XII, take the case of the 75-
ft. span. If the wire be strung when the temperature is – 30° F,
it
may be pulled up until the sag is 1 inch, whereas, if the same
wire be strung when the temperature is 100°, a sag of 41 inches
will have to be allowed.
The next piece of work is to tie the wire to the insulators.
This is done in two ways, the first of which has passed out of use
with the most up-to-date companies. It is illustrated in Fig. 104,

117
108
TELEPHONY
where a represents the top of the insulator, d d the line wire, and
b the tie wire as it lies in the groove in the insulator. The ends
of the tie wire are wound around the line wire as shown at cc,
four and a half turns being taken. This method of tying was the
d
id
L6
O
Ornanso
Fig. 104.
Fig. 105.
one used altogether in connection with iron wire.
With the advent of copper wire, however, a different method
of tying was found necessary; and the one illustrated in Figs. 105,
105 A and 105 B, has come to be adopted. Looking at the last
.
figure, 105 B, it will be seen that the tie wire is passed around
the glass in one complete turn, one end being passed under, and
the other over the line wire. The ends are then wrapped around
the line wire in 5 complete turns, which are not laid as close
together as those of the old tie but are more spread out. The
completed tie is shown in Fig. 105 A, and the plan of it is seen in
Fig. 105.
There are two methods of making joints in the wires. One
of these, now passing out of use, is shown in Fig. 106, and is
called the Western Union splice. It is made by wrapping the
ends of the two wires about each other in the same manner as in


ig. 105 A.
Fig. 101 B.
the old form of tying. This joint should always be soldered, and
in so doing the heat should be applied at the center point, as the
solder takes hold best under these conditions. This form of joint
is being superseded by that made by the McIntire sleeve, which
118
TELEPHONY
109
is shown in Fig. 107, and which consists of two copper tubes a and
b sweated together. These sleeves are made in various sizes to
accommodate the different sizes of wire used. The two wires to
be joined are introduced into the holes c and d respectively. The
sleeve is then twisted through three turns as shown in Fig. 108, in
which a represents one of the wires entering one side of the sleeve,
and b the end of the same wire emerging from the sleeve. The
other wire c is brought in from the opposite direction, and its end
is shown emerging at d. The sleeve is given three turns, as already
La
MR MM.
d
16
Fig. 106.
Fig. 107.
-C
@

ter
Fig. 108.
said, and the short ends b and d are slightly bent over as a further
precaution against their pulling out. This class of joint need not
be soldered.
The line wires should always pass through the groove in the
insulator on the side facing the pole, except in the case of the
B two insulators nearest
the pole, which should
have the line wires tied
on the side away from
the pole. In turning a
corner the wires should be tied on the outside of the insulators so
that the tension will cause them to press against the glass.
In stringing wires the start is made from the central office,
and the work is carried on in the direction in which the line is to
Where the line wire is terminated on a cross-arm, it is
said to be dead-ended, which is
done in the manner shown in b a
d
Fig. 109. The line wire d is
passed around the insulator a as
Fig. 109.
shown at b b b and then through
a McIntire sleeve c. This sleeve is given one and a half turns.
-
The end of the wire is shown at e.
Guying. Under this heading is included all the work neces-
sary to make the line secure against extraordinary stresses such as
run.
Oldocon
a
119
110
TELEPHONY
have already been alluded to. The material used in fastening
the pole to whatever object has been selected with a view to
securing greater rigidity for the line, is called guy rope or guy

C
-b
-e
Fig. 110.
strand. The standard guy strand is made of seven steel wires,
each of a diameter not more than 111 inch nor less than 107
inch. Each wire must be free from scales, inequalities, and other
imperfections, must be of uniform diameter and be drawn in one
continuous length, and must be thoroughly galvanized. The wires
are twisted together, the length of the twist not to exceed 32 inches.
The strand must have a breaking weight of at least 6,000 pounds,
and must elongate not more than 17 per cent nor less than 11
per cent of its length before breaking.
One method of fastening the guy strand is shown in Fig. 110.
One end of the strand is wrapped twice around the pole at c,
being held in place by means of staples, and secured by a stand-
ard guy clamp. When the pole is equipped with more than one
cross-arm, the strand is attached just above the second arm.
When the pole is equipped with only one arm, the strand is at-
tached just below the second gain. To secure the other end of
the strand, a guy stub, shown at a, is sunk in the ground in the

120
TELEPHONY
111
manner depicted. The strand is wound twice around the stub,
being held in place by staples, and is secured by means of a stand-
ard guy clamp, shown at d.

b
Fig. 111.
There are two ways of setting guy stubs, both of which are
equally efficient. The method shown in the figure consists in
fastening to the stub two logs of chestnut, shown at
e and e'. These must be 5 feet long and 10 inches
in diameter, and fastened to the stub by cross-arm
bolts. The upper one e is placed on the side facing
the pole and at a depth of about one foot. The second
Fig. 112.
one e' is placed on the opposite side and at a depth
of about 6 feet. These two logs, acting together, pre-
vent the stub from being pulled into a vertical
position by the strain on the strand. It should
be observed that the earth is piled up around
the guy stub in the same manner as around the
pole.
When the above method is not used, a
separate anchor must be provided for the stub,
as shown in Fig. 111. In this case an anchor- =
rod, shown at a, is fastened to a chestnut log 6
5 feet long and 10 inches in diameter, sunk 6 feet in the earth
under a pile of rocks. The “eye” end of the rod projects about

Fig. 113.
121
112
TELEPHONY
one foot above the surface of the ground. One end of a piece
of guy strand is wrapped around the guy stub in the usual manner,
as shown at c, and is secured with a guy clamp. A standard
thimble, Fig. 84, is placed through the “eye” in the anchor-rod,
and the other end of the strand passed around it and secured with
a guy clamp.

York
.
Fig. 114.
In head guy-
The method of securing the guy strand to the pole or stub is
shown in detail in Fig. 112; and that used in fastening it to the
anchor rod, in Fig. 113.
The methods illustrated in Figs. 110 and 111 are applicable to
side guying and head guying at the end of a line. In head
ing and back guying, the guy strand is fastened to the next
adjacent pole at a point about 4 feet from the ground.
In Fig. 114 is shown another method of securing the guy
strand. A guy rod a is secured to an anchor-log b sunk 6 feet in
the ground. On the upper face of this log is secured a piece of
plank 2 feet by 2 inches and of the same length as the log. This
is done to afford additional resisting surface against being pulled
out. The “ eye” end of the rod is allowed to project about one
foot above the ground, and the guy strand is fastened to it in the
manner already described.
122

DC
ca
$
ma
DI FBBBBBBER
SO
UNIT TYPE SWITCHBOARD MAGNETO CALL 200 LINES
North Electric Co.
TELEPHONY
113
In Fig. 115 is shown the method of securing the guy strand
when the ground is rocky. A hole is drilled in the rock at the
angle shown, and the rock eye-bolt is driven into it, the strand
being attached to the “eye” end in the same manner as that de-
scribed for the guy rod. The hole in the rock should be of such
.

L
Fig. 115.
a size as to give the eye-bolt a binding fit. The detail of the eye-
bolt with the attached strand is shown to the right.
In addition to the directions for placing guys already given
under the heading of “Laying Out the Line,” the following
should be noted :
When a line turns a corner, both straight sections should be head-
guyed and side-guyed as shown in Fig. 116.
In crossing a road, each turning pole should be double side-guyed, or
guyed on both sides, and also head-guyed.
The two poles next to the turning poles should be head-guyed.
Terminal poles on long spans — 200 feet — should be head-guyed, and,
if possible, side-guyed in both directions.
The adjacent poles should be head-guyed to the terminal poles.
In passing through hilly country the poles should be head-guyed as
shown at a and b, Fig. 117, so as to overcome the downward strain.
Lines of four cross-arms or more should be double side-guyed every
quarter of a mile, and double head-guyed every half mile, in addition to
whatever other guying may be needed.
The method of guying in hilly country is shown in Fig. 117.
Here the downward strain would pull poles 2 and 3 over towards

123
114
TELEPHONY
pole 1 were it not for the guy a securing pole 2 to pole 3, and guy
b securing pole 3 to pole 4. In many cases it is convenient to
guy to trees. Particularly is this so in the case of side-guying.
When trees are used as guy stubs, the following precautions must


Б
e
Fig. 116.
be taken: A tree must be selected which is perfectly secure and
which is large enough in diameter to stand the strain. The bark
must be protected by means of lagging made of pieces of wood
124
TELEPHONY
115
about 1 foot long and 2 inches by 2 inches. These are placed
against the tree, the guy strand being wrapped around them and
secured in the usual manner. In guying it must be remembered
that the strain on the strand can be resolved into two components,
one vertical, or down the pole, and the other horizontal, or at
right angles to the pole. It is this latter that is useful; and to

6
3
5
Fig. 117.
make its amount as large as possible in proportion to the total
strain, the strand must be secured at a point as far from the foot
of the pole as possible.
TELEPHONE CABLES.
Types of Cable. There are three types of cable used in
telephone line construction, each one peculiarly suited to the con-
ditions it is called upon to meet. Considered with regard to the
nature of the insulating material, two of these classes may be
merged into one, leaving only two distinct kinds of cable when
classified in this way. The conductors of cables are insulated
either with paper or with a compound of rubber. When cables
were first introduced into telephone work, the conductors were in-
sulated with cotton braid saturated in rosin oil. It was found,
however, that a better insulation could be obtained by the use of
paper, besides securing the additional advantages of reduced cost
and reduced size of cable. Cotton insulation, therefore, so far as
cables used in line construction are concerned, is a thing of the
past.
Paper-insulated cables are made in several ways, but are com-
prised in two great classes, dry core cables and saturated core
cables. In the manufacture of dry core cables, as the name indi-
cates, the conductors are wrapped with dry paper, and are sub-
jected to no further treatment except baking. In the manufacture
of saturated core cables, the conductors, with their paper insula-

125
116
TELEPHONY
-
- or
tion, are saturated with melted paraffine. The advantage of the
latter treatment lies in the fact that, should the cable be subjected
to moisture, the paper will not absorb it as it does in the case of
dry core cables. As a general thing the dry core cable is used on
underground lines, while the saturated core cable is used on aërial
lines.
Paper-insulated cables “paper cables," as they are
called — are constructed in the following manner: The conduct-
ors, consisting of No. 19 B. & S. gauge soft-drawn copper, are
covered with a wrapping of Manila paper of about the thickness
used by shopkeepers in wrapping goods. In order to overcome
the mutual induction that would otherwise be present, each pair
of conductors forming a circuit are twisted together into a strand,
the length of the twist not exceeding 6 inches. These strands are
laid
up in layers around the center of the cable, each layer being
wound spirally around the center in the opposite direction to that
of the next adjacent layer. In order to distinguish one of the
conductors in a strand from its mate, the insulation on one of the
wires is marked in some peculiar way. The standard cables made
by the Western Electric Co., for instance, have one conductor
covered with red paper, and its mate covered with white. The
cable thus consists of a number of red covered conductors each
twisted with a conductor covered with white paper. Some manu-
facturers, notably the American Electric Works at Providence,
R. I., have a red thread in the paper on one conductor, and white
paper on its mate.
When the pairs of conductors have been arranged in layers as
described, the whole is bound with cotton thread saturated in
paraffine. If a dry core cable is intended, the whole is baked in a
suitable oven in order to expel all moisture from the paper; while,
if a saturated core is wanted, the cable is immersed in melted
paraffine.
This work having been finished, the cable is ready for the
lead sheath. This sheath consists of a lead pipe inch in thick-
ness and having an inside diameter equal to that of the cable. It
is forced on under pressure, cooling as it goes into place. When
the lead sheath has been placed, the ends, in case of a dry core
cable, are saturated in paraffine for a distance of 2 feet, to pre-
a
126
TELEPHONY
117
vent moisture entering. The sheath is then sealed up at both
ends, and the cable is ready for market. Standard lead cables of
both types are made in the following sizes and of the outside
diameters indicated in Table XIII :
TABLE XIII.
Sizes of Standard Lead Cables.

NUMBER OF PAIRS
OF CONDUCTORS.
SIZE OF WIRE.
B. & S. GAUGE.
OUTSIDE DIAMETER.
LENGTH
No. 19
66
2
5
10
15
25
50
100
150
200
1 inch
1} inches
13
13
17
ooolN00
1,000 feet
1,000
1,000
1,000
1,000
800
800
800
800
NNNN
66
21
23
23
wool
The New York Telephone Company have developed a cable
in which No. 22 B. & S. soft-drawn copper is used and which is
made in sizes of 300 and 400 pairs, each size having an outside
diameter of 24 inches. For underground lines in large cities, this
type of cable is especially well adapted.
In Fig. 118 is shown a typical paper cable, with part of the
sheath removed to show the successive layers, which appear at
a, b, c, etc., going from the center outwards.
A paper cable manufactured by the
ra b c
Felton-Guilleaume Company possesses
the same essential features as those
already described, but is more economical
in the use of insulating paper. It is
Fig. 118.
shown in section in Fig. 119, together
with a detail of the method of using the paper. It will be seen
that the conductors of a pair are placed on opposite sides of a
ribbon of insulating paper, and twisted together. A second ribbon
of paper is then wound around the pair to insulate it from the
other pairs. The whole is then bunched together, and covered
with a lead sheath in the manner already described.
When cables were first introduced, the great drawback to
their use lay in the high electrostatic capacity existing between

127
118
TELEPHONY
DO
the conductors. In the open-wire line this electrostatic capacity
is reduced to a minimum by the great distance existing between
the conductors. In the cable, however, where wires are bunched
together, this separation does not exist and special precaution must
be taken. Paper, on account of its porous texture, entraps within
itself a large amount of dry air — a substance which, with the single
exception of hydrogen gas, possesses the lowest electrostatic capac-
ity of all known bodies.
The specifications for
dry core 'cables call for
a capacity between each
conductor and its fellows
of .08 microfarad per
mile. In actual fact,
cables are constructed
Fig. 119.
with a capacity of .06
microfarad per mile and
even lower. Saturated core cables, for the reason that a great
deal of the dry air is excluded by the paraffine, have a somewhat
higher capacity. The specifications for these cables call for a
capacity between each conductor and its fellows of .175 micro-
farad per mile, which requirement is easily complied with by the
manufacturers. Each conductor should have a resistance of not
more than 47 ohms per mile at a temperature of 60° F, and the
insulation resistance of each conductor should be at least 500
megohms per mile. Cables of this type are made continually
whose insulation resistance is 1,000 megohms per mile and higher.
When lead-sheathed cables were introduced, the sheath was
made at first of pure metal. It was found, however, that when these
cables were laid in the creosoted duct tubing then in vogue, the
dead oil of tar corroded the lead. By an admixture of 3 per cent of
tin this liability to corrosion was found to be overcome, so that today
all lead sheaths are made with an admixture of 3 per cent of tin.
Some manufacturers go so far as to place a layer of tin outside the
lead, but this is not necessary. Lead-sheathed cables are always
constructed with two spare pairs to be used in case of emergency.

128

OK
1
O
Stromberg Carlson
Tel: Mig.co
ROCHESTER.N.Y. CHICACO.ILL:
GALUME SA DRUGELIA DRY CELE
DRY BATTERY TYPE BRIDGING TELEPHONE.
Stromberg-Carlson Telephone Mfg. Co.
TELEPHONY
PART III.
TELEPHONE LINES.- (Continued.)
16
Rubber-insulated cables, with the exception of submarine
work, are used exclusively for aërial work. They comprise two
classes known as bridle cables and tree cables, which differ but
slightly. For local work, the sizes of the wires are No. 18 B. & S.
and No. 16 B. & S. The Long Distance Company use No. 12 B.
& S. The copper is hard-drawn and covered with a coating of
tin. The insulation consists of a rubber compound 3 inch in
thickness, which is covered with a layer of tape. In some rubber
cables the conductors of a pair are covered with differently col-
ored insulation, one conductor, for example, being covered in red
and the other in a drab color. It has been found, however, that
coloring matter injures the texture of the compound, rendering it
so soft as to be easily peeled off with the finger nail. Its use,
therefore, is not to be recommended. The pairs are twisted
together, and laid up around a central core of jute, called the
filling. The whole is then bound together with a winding of jute,
called the serving, and is saturated with rosin oil. Over the
serving are wound two layers of heavily tarred tape. In the case
of the tree cable, an additional covering of heavily tarred cotton
braid is placed outside of the tape. The conductors of these
cables should have an insulation resistance of 250 megohms per
mile after being immersed in water for 48 hours at a tempera-
ture of 60° F. This requirement is easily met by the manufac-
turers. The electrostatic capacity of this class of cable is very
high, but as it is used only in very short lengths, this feature is of
no material importance. Rubber cables are made in the following
sizes : 3-pair, 6-pair, 11-pair, 15-pair, 20-pair, and 25-pair. Their
diameters vary from about į inch to 14 inches.
a
131
120
TELEPHONY
5
Stringing Aerial Cables. Aërial lead-covered cables are
strung on the poles in connection with the open wires, to increase
the capacity of the line. The method of construction consists in
hanging the cable to a suspension wire supported upon the poles.
There are many ways of supporting the suspension wire or mes-
senger wire, as it is sometimes called. The most approved method
will be described. The suspension wire is constructed of galvan-
ized steel wires twisted together in the same manner as that
described for guy rope. Three sizes are used in standard con-
struction, which are of the following diameters and weights :
4-inch diameter, having a weight of 113 lbs. per 100 feet; Po-inch
16
diameter, having a weight of 21 lbs. per 100 feet; l-inch diameter,
having a weight of 51 lbs. per 100 feet. The first has a breaking
weight of 1,750 lbs.; the second, a breaking weight of 3,300 lbs.;
and the third breaks at 8,320 lbs. For special work, such as
,
supporting extra large cables, or on extra long spans, special sizes
of suspension wire must be used. The above sizes are standard.
The first method adopted for supporting suspension wire was
next to the pole, and to lash it
to rest it upon the cross-arm,
firmly with marlin as shown
in Fig. 120, where the pole is
shown at a, the cross-arm at
b, and the suspension wire at
The marlin lashing is
shown at d, and is wrapped
around the cross-arm and sus-
pension wire and secured to
the pole. This construction,
however, was found to be
rather crude. Not only did
Fig. 120.
the suspension wire cut into
the cross-arm, but an addi-
tional disadvantage lay in the fact that the arm was subjected
to too great a load.
The next method devised was to drive a pole step securely
into the pole just below the bottom gain, rest the suspension wire
on it, and securely fasten the wire with marlin, as shown in Fig.

d
b
c.
a
hahaah
132
TELEPHONY
121
121. While this change was a step in the right direction, there still
remained the disadvantage of having the suspension wire resting
on so small a bearing surface as the pole step. An improved
method is to drill out the center hole of a guy clamp to a suffi-
mamo

b
ZZ
с
a
Fig. 121.
Fig. 122.
a
manner.
Db
Q
C
it
cient size to take a cross-arm bolt, and to secure the clamp to the
pole by means of such a bolt driven through the pole in the usual
The suspension wire is then passed through the upper
groove, and securely held in place by the
muuw
muy
two end bolts. This construction is shown
in Fig. 122, where a represents the pole, b
the suspension wire, c the cross-arm bolt
passed through the center hole of the guy bel
clamp, and d d' the two end bolts securing
the suspension wire.
A special form of hanger has been de-
vised to take the place of the guy clamp. It
is shown in Fig. 123. It consists of a flat
hook a made of 2-inch galvanized wrought
iron about 4 inches wide. It is fastened to
the pole by means of a cross-arm bolt b b.
Fig. 123.
The suspension wire is shown in section at d;
and the retaining bolt, which prevents the wire from getting out
of place, is shown at c. On account of the strength, simplicity,
and cheapness of these hooks, this method is the one most to be
recommended. A more elaborate method, and one to be recom-

wwwww

133
122
TELEPHONY
mended where a large number of cables are to be supported on one
pole, is to have a specially designed cable cross-arm. One of these
is shown in Fig. 124, and consists of a steel angle 4] inches by 3
inches, constructed of 4-inch stock. The 42-inch face is set in the
gain and is fastened to the pole and braced in the usual manner.
The horizontal face is for the support of the suspension wire, and
in it are drilled holes, a, b, etc., the extreme one being 4 inches from
the end of the beam on each side. The other holes are spaced 6
-34
20"
fhole for
a stock
Fig. 124.
inches, with the exception of the two holes nearest the pole,
which are 20 inches apart. The holes on the horizontal face are
of the proper size to take a 5-inch bolt of special length to secure
the guy clamp to the arm. The guy clamps are secured to the
arm by this special bolt passed through their center holes, and
the suspension wires are passed through one of the grooves in
each clamp and secured by the two end bolts. The suspension
wire should never be spliced; but when the end is reached it
should be secured to the nearest pole in the same manner as that
adopted for guy strand, and a new run begun. Suspension wire
is usually furnished in lengths of 1,000 feet, and when it is to be
strung it is run off on the ground, and then hoisted up at each
pole. The suspension wire having been strung, pulled tight with
a block and fall, and fastened, the work of running the cable
should be started. Great care must be taken to protect the
sheath from abrasions or kinks.
There are several good ways of stringing cable, but probably
the best method to adopt is to mount the reel on a stout truck in
such a manner as to allow it to unwind and let the cable run off.
One end of the cable is fastened securely to the terminal point,
and the truck is driven slowly ahead. A man seated in a boat-
swain's chair, which is mounted on wheels on the suspension wire,
raises the cable up to the wire as the cable unwinds, and secures
it temporarily at intervals of about 50 feet. As the cable un-
winds, the truck is driven ahead so that it is always about 50 feet
134
TELEPHONY
123
in advance of the man in the boatswain's chair. When the cable
is very heavy, and therefore difficult of manipulation by the man
in the boatswain's chair, a better method is to follow that shown
in Fig. 125. The reel is mounted as shown, so that it unwinds
from the upper side. The suspension wire is carried down to the
ground at an angle of about 45°, as shown at a, and is securely
fastened. It is better, but not necessary, to have two rollers 68'
over which the cable runs as it passes off the reel. A rope strung

BRESSE
6.
Fig. 125.
over the cross-arms in much the same manner as that described
for stringing open wires, is attached to the end of the cable and
serves to drag it along. As the cable begins to ascend, a man
stationed at that point attaches it to the suspension strand by
means of suitable hangers, which move along the suspension
strand with the cable. As the cable reaches the cross-arm, a man
on the pole lifts the rope off and guides the hangers past the point
where the suspension wire is fastened. At the next pole the same
process is repeated, this being continued until the cable has been
strung. One disadvantage in this method lies in the fact that it
requires the services of a man constantly at each pole.

135
124
TELEPHONY
Another method, and probably the best of all, is to carry the
cable in a stirrup attached to a wheel that runs along the suspension
wire. The wheel is guided around the point of support at each pole.
Cable Hangers. The old method of supporting cables was
to wrap a stout marlin string around the cable and the suspension
wire. This was done by an instrument called a spinning jenny,
consisting of a hollow cylinder made in two halves. The section
is shown at a, Fig. 126, and the end view at c. Attached to one

6
a
Fig. 126.
end of the cylinder is a lug b, to which is attached the rope by
means of which it is drawn along. The hole through the center
of the cylinder is large enough to accommodate the cable and the
suspension wire. The marlin is wound in layers on the jenny,
which is placed over the cable and the suspension wire, the two
halves being held together by a suitable device. One end of the

un
Fig. 127.
marlin is fastened securely and the jenny is pulled forward. As
it moves, the marlin is unwound, and wraps itself around the sus-
pension wire and the cable, thus holding the two together. The
action is shown in Fig. 127. Recently, however, this method has
been superseded by using some form of metallic hanger. The
most approved type of this style of hanger is shown in Fig. 128.
It is made of sheet iron tinned, and is called the metropolitan
clamp.
The cable sheath should be specially protected from abrasions
at points where it passes poles. During high winds the cable
136
TELEPHONY
125
sways to some extent, and a certain amount of rubbing between
the cable sheath and the pole takes place. The necessary pro-
tection from abrasion is given by fastening wooden lagging about
the cable with marlin, as shown in Fig. 129, where a denotes the
O
C
Fig. 128.
ia
76
suspension wire, 6 and b' the hangers, and c and c' two wooden
strips fastened on opposite sides of the cable by the marlin. A
better way is to give the cable at this point a heavy wrapping of
marlin wound close together and in several layers. This is more
flexible than the wood, and forms a better cushion.
Underground Cable Lines.
more on the evening
In large cities and in many
towns, laws exist against the
building of aërial lines, whether
open-wire or cable. In many
13
6
residential suburbs, the inhabi-
tants object to the building of
aërial lines on account of the un-
sightly appearance of the poles.
The number of underground
lines in use is accordingly in-
huuhn
creasing at a very rapid rate
Fig. 129.
from day to day. While under-
ground wires are much more costly to build than aërial lines,
they are proof against injury by storms.
When telephone cables were first put underground, an open
trench was dug and the cable was laid in, being surrounded with
a mixture of cement and sand. The trench was then filled. It
was found, however, that if a cable became defective, the whole
trench had to be dug up in order to replace it. The necessity for
some form of duct into which the cables could be drawn was


137
126
TELEPHONY
apparent. Disregarding the experimental work that proved
worthless, the first form of duct used was constructed of creosoted
pine in the shape of an open trough. This trough was laid in
the trench, the cable being laid in it and the earth then filled in.
This construction proved to be equally defective with the open
trench in the fact that the cable could not be drawn out without
opening the trench. The next method devised was to construct a
circular duct of the form shown in Figs. 130 and 130 a. The stand-
ard size consists of a stick of timber 8 feet long, sawed square,
with edges 47 inches. Through the axis is bored a hole 3 inches
in diameter. One end of the stick is cut with a tongue, shown at


T
e
-10
p-
-45
-4
Fig. 130 a.
Fig. 130.
á, Fig. 130; while the other end is cut with a recess, shown at b,
Fig. 130 a. In construction the tongue of one log fits into the
corresponding recess in the next succeeding log, and the joint is
made secure by pouring in hot pitch. These logs, or ducts,
called pump logs by some, are impregnated with creosote in the
same manner as the cross-arms. The method adopted in con-
structing subways with this form of duct tubing, is illustrated in
Fig. 131. A trench is first dug, varying in depth from 3 to 6
feet according to the grade of the street. Creosoted planks 2
inches thick, shown at a a', are laid in the bottom of the trench
for a foundation, upon which is placed the duct tubing. In the
present case there are 12 ducts being laid, 3 rows of 4 ducts each.
On top of the upper layer is laid a roofing of creosoted planking;
and between the sides of the ducts and the trench are placed
joists, one of which is shown at c, to prevent lateral motion.
The earth is then filled in and packed down. One of the men on
a
138

VIEW OF THE TUNNELS OF THE CHICAGO SUBWAY COMPANY.
Showing Manner of Hanging Automatic Telephone Cables.
TELEPHONY
127
top of the ducts will be seen with a hammer, in the act of driving
home a joist. The creosoted ducts about to be used are shown
piled up at the side of the excavation at b. The depth of the
trench should be so regulated that the top planking is at least
from 21 to 3 feet below the surface of the road.
Another form of duct tubing which has come into use since

L
Fig. 131.

a
the introduction of the pump log, is the cement-lined iron pipe.
The method of constructing it is shown in Fig. 132. It consists
of a tube 8 feet long constructed of wrought iron .018 inch thick,
the seam being fastened by rivets placed 2 inches on centers as
shown at a a'. The tube is lined with a wall of Rosendale
cement about 5 inch in thickness, shown at d. Into one end of
the tube is fitted a casting of the form shown at b; while into the
other end is inserted a casting of the form shown at c. The cast-
139
128
TELEPHONY
ing c fits securely into the opening at b. The standard size of
this tube has a 3-inch hole.
In setting this conduit the ends are butted together, the

Q
Fig. 132.

sockets making secure joints, and yet allowing enough play for
slight bends. When short curves have to be made, bent tubes
must be used. This conduit is laid in a trench, in the bottom of
which is placed a bed of concrete about 6 inches thick. The first
DODO
ALL....
Fig. 133.
layer of tubes is covered with a layer of cement mortar, reaching
to the height of about 1 inch above the top of the tubes, the
second layer being laid upon this. This process is repeated for
each succeeding layer. In Fig. 133 is shown the method of con-
structing a subway with this form of duct. It will be seen that
140
TELEPHONY
129
the sides of the trench are walled in with rough planking, which
acts as a retaining wall for the mortar and the concrete. On the
top of the upper layer of ducts is laid a layer of concrete from 4
to 6 inches in depth. The earth is then filled in and packed
down tightly.
The two forms of conduit just described have been largely
superseded by those made of vitrified clay or terracotta. The


Fig. 134.
Fig. 135.
vitrified duct has the advantages of cheapness, ease of construc-
tion, and high insulation, besides being absolutely proof against
all forms of chemical action. One form of this duct is shown in
Fig. 134. It is made in sections 2 feet in length. The edges of
the hole are beveled to facilitate the drawing in of the cable.
Another and better form of this class of conduit is shown in
Fig. 135. It consists of sections of 4 ducts of the size indicated.
The great advantage of this conduit lies in the fact that with it 4

Fig. 136.
ducts can be laid with the same amount of labor that would other-
wise be necessary in laying only one. This duct is laid in a bed
of concrete as is the case with the cement-lined pipe, and a
cement casing is built all around. In laying the duct a mandrel,
shown in Fig. 136, is used. It is of wood, 3 inches in diameter and
30 inches long. At one end is attached an iron eye a, and at the
other end is a rubber gasket b whose diameter slightly exceeds
that of the interior of the duct. One of these mandrels is placed
in each duct as the work of laying is begun; and as successive
141
130
TELEPHONY
sections are laid around it, it is drawn forward so that ſ of its
length is constantly projecting beyond the end of the last duct
laid. By this means good alignment is secured, and whatever
dirt may have accumulated in the ducts during the process of con-
struction is swept out. In Fig. 137 is shown the process of con-
struction as followed with this class of duct.
On first consideration it might seem advantageous to con-
struct subways that would be continuous from the point of start-
ing at the exchange to the point of termination, wherever that
might be. Such a course, however, would necessitate hauling the

Fig. 137.
cables in in one piece, which, even if it were possible, would be
difficult and very costly. It has been found best to break the
subway every 350 to 400 feet by a suitable chamber dug in
the earth, called a manhole. The manhole also serves to furnish
a point of inspection. Still another advantage gained by having
a manhole lies in the fact that should a cable become defective at
any point, it is necessary to remove only the section between the
two adjacent manholes. If the cable were laid in one piece, it
would be necessary to remove the whole cable. The construction
of manholes is very important, and should be done in the follow-
ing manner:
The size of the manhole depends upon the number of ducts,
142
TELEPHONY
131
but it should be large enough to allow a man to work with advan-
tage. The usual form is that of a rectangle 8 feet by 4 feet, and
about 6 feet deep. The walls are made of brick. In Fig. 138.is
shown the elevation of a manhole, in which a a' denote the brick
wall. The bottom of the manhole, in the best construction, is
made of cement and concrete mixed in the following proportion:
a
Good Cement.........
Sand ...
Broken Stone
1 part.
2 parts.
.5 parts.

b
b
a
०२
m
n
m
a'y
&
L
TO SEWER
Fig. 138.
This is laid to a depth of 8 inches. In some cases the man-
hole is drained off by a pipe connection to the sewer, having the
usual trap to prevent the entrance of the sewer gases. The con-
crete foundation and the sewer connection are not absolutely neces-
sary. On top of the brick work is placed a cast-iron manhole
head shown at b b. The bottom of this casting is equipped with
a circular flange e e', which, when in place, lies up against the
sides of the brick wall and prevents lateral motion. The casting
is reinforced by two flanges c d'. A second circular flange d d',

143
132
TELEPHONY
projecting upwards, serves as a rest for the inner cover m, whose
edge is grooved to fit. A circular rubber gasket is placed in this
flange, making, when the cover is in place, a water-tight joint. In
the center of the cover is a cup-shaped depression n, into which
fits, the bolt p of the locking bar o, which is itself held in place by
,
a groove in each side of the casting. The outer cover, shown at
s, fits on a seat at the top of the casting. This cover is heavier
than the inner one, being strong enough to bear the weight of
heavy trucks; it should fit securely on the seat and not rattle.
The ducts are shown coming through the side of the wall.

S
0
an
Fig. 139.
In Fig. 137 is shown in the foreground a manhole in course of
construction. Where the manhole is large, as in the case shown
in the figure, it would be impossible to corbel the brick work suf-
ficiently to make the opening at the top small enough to support
the manhole head. In this case two iron girders are laid across
the top, and the head is supported on them, the open spaces being
filled in with flat brick arch work. Fastened to the sides of
the hole through which there are no ducts penetrating, are two
stout planks to which are attached several wrought-iron hooks for
supporting the cables. These are not necessary, but usually
accompany the best construction.
Manholes are sure to collect more or less gas, which is drawn
144
TELEPHONY
133
a
in through the ducts. Gas and sewer pipes sometimes pass through
the manholes, and the gas escapes into them in this way. Before
any work is done in a manhole, therefore, it should be allowed to
stand open for a while in order that the gas, if there be any, may
escape. The gas can be removed with a pump, or by means of a
contrivance like an umbrella with a string attached to the handle.
This is lowered into the hole and then pulled up smartly, the
resistance of the atmosphere opening it and thus enabling the gas
to be drawn out. A very good method of securing good ventila-
tion in a manhole during the process of work, is to erect one end
of a long, narrow sheet about 6 feet above the side of the hole
opposite that from which the wind is blowing, and to allow the
other end to hang down into the hole. The wind, striking this
sheet, is deflected downward into the hole, and forming an eddy
forces up the gases that may be lodged inside. To guard as much
as possible against the collection of gases in manholes, the ducts
not in use have their ends closed with wooden plugs.
The subway is brought into the cellar of the building used
for the central office, in order that the lines may be brought in a
suitable manner to the switchboard. In doing this the ducts are
either terminated in a vault under the sidewalk, or are carried
through the cellar wall itself. In Fig. 139 is shown the method of
laying the ducts into the exchange building. They come from
both directions, bend at right angles, and pass through the founda-
tion wall directly under the hall door. In large exchanges where
a great number of ducts terminate, the construction necessary for
the proper handling of the cables is sometimes very elaborate. In
Fig. 140 is shown a system of piping devised for continuing the
ducts from their point of termination in the cellar wall to the
place where the cables are to be distributed, and for arranging
them in the proper order to facilitate this work. It consists of a
number of iron pipes a a' a" etc., which run from the cellar wall c
to the point of distribution. They are supported upon two brick
piers, one of which is shown at b, and the other at b'. The cables
emerging from these tubes are shown at e e' etc.; and the plugged
ends of those not in use, at m m' etc. This system has been in-
stalled in one of the largest exchanges in New York City.
Drawing in Cables. The subway being constructed, every-

145
134
TELEPHONY
thing is in readiness for the drawing-in of the cables. The first
step in this direction is to carry a rope through the duct into
which the cable is to be drawn, from one manhole to the other.
The old way of doing this work was called rodding, and consisted
in pushing a number of rods through the duct, the end of each
being screwed into the end of the one directly in front of it, until
enough had been introduced to reach from one manhole to the
other. A string was then attached to the last rod, and the rods
were pulled out of the duct and unscrewed at the opposite man-

e
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Fig. 140.
hole. When the last rod was reached, the string was untied. To
the opposite end of the string was then fastened a stout rope,
which was in turn pulled through. A better way, and one now
practiced altogether, is to thread a string through each duct as it
is being laid, and fasten the ends in each manhole so that they
cannot be accidentally pulled out. A stout rope is then attached
to the end of one of these strings and pulled through. The cable
is in turn pulled through by means of this stout rope, in the fol-
lowing manner:
The reel containing the cable to be drawn in is mounted on
the edge of the manhole, as shown in Fig. 141, in such a manner as
to allow the cable to unwind from the bottom. Care must be
taken to keep the sheath from touching the sharp edge of the hole
146
TELEPHONY
135
at ay
, and for this purpose a man must stand in the hole and “ feed”
the cable in. The stout rope is fastened to the end of the cable in
one of several ways, all of them good and yet all of them possess-
ing disadvantages. One method, illustrated in Fig. 142, consists

0 0 0
с
Fig. 141.
o
o
o
in fastening over the cable-end a wrought-iron clamp such as that
shown in the figure, by means of screws passed through the holes
and driven into the cable. The rope is fastened to the eye-piece
a, and the cable is then drawn through the duct. Another method
is to cut away the
sheath for a length
of two feet, and,
bunching the con-
ductors together,
bend them back in
the form of an eye,
Fig. 142.
fastening them to
the sheath, as shown in Fig. 143. Still another way is to wind
around the sheath a network of iron wire, leaving an eye at the
end for the attachment of the rope. All these methods require a
good deal of time, and the first two necessitate wasting about 2
feet of the cable.
The rope being fastened to the cable, the latter is drawn
through the duct by means
of the capstan d, Fig. 141
mounted on the shaft c that
carries the drum m about
Fig. 143.
which the rope is wound.
The capstan is turned by men pushing on the capstan bars, two of
which are shown at e and e'. Sometimes horse-power is used to


147
136
TELEPHONY
с
turn the drum, and one company has used a portable engine to
perform this work. There seems, however, to be no indication of
these methods coming into general use. In pulling in the length of
the cable in the section between the central office and the first
manhole, the reel is mounted in the central office and the pulling
is done at the manhole.
Splicing. It has already been said that cables, whether un-
derground or aërial, are strung in sections. Aërial cables are
furnished in lengths of 1,000 feet, while underground cables are
furnished in lengths corresponding to the distances between the
manholes along the line of subway, so that each section of cable
stretches only from one manhole to the next. In order, therefore,
that the conductors may furnish contin-
uous circuits, those of one section of cable
must be joined properly to those of the
next adjacent section ; and in order that
moisture may not attack the cable at these
points of junction, the lead sheath must
be made continuous throughout the whole
length of the cable. This work is called
splicing, and is done in the following
manner:
In stringing aërial cables, the ends of
adjacent sections are allowed to overlap
about 18 inches. In pulling in under-
ground cables enough slack is left in each
manhole to allow the cable to be placed on
its proper supporting hook, or, wanting
Fig. 144
these, to lie loosely on the floor; also, as in
the case of aërial cables, the ends of adja-
cent sections are allowed to overlap about 18 inches. In making
a splice, the lead sheath on the two adjacent ends is cut away
for about 2 feet, exposing the conductors. This work must
be done very adroitly, so as not to cut the cotton wrapping or
injure the paper insulation in any way. The tools needed for this
work comprise a chipping knife and a hammer. The chipping
knife, shown in Fig. 144, is a blunt heavy knife of wrought steel,
with an edge a a, a broad back b, and a handle c. The method of

a
148
TELEPHONY
137
cutting off the sheath is shown in Fig. 145. At a point about 2
feet from the end of the sheath, a groove a in depth about half
the thickness of the sheath is cut all round. Starting at the end
of the cable, holding the chip-
ping knife as shown, and striking
with the hammer in the direction
shown by the arrow c, a longi-
tudinal groove is cut to meet a.
The arrow b shows the direction
in which the knife blade is driven
under the blows of the hammer,
and it will be seen to be tan-
gential to the conductors, so that,
should the knife be driven too
Fig. 145.
deeply, the insulation will not be
injured. The lead sheath being thus removed, the cotton binding
is wound tightly, and tied at a point about half an inch from its

b
C
6
6
6"
Fig. 146.

end, as shown at a, Fig. 146. The conductors are then spread out
as shown at 6 6'6" etc. Both ends are treated in this manner.
A lead sleeve about 2 feet long, whose diameter exceeds that of the
cable by from 1 to 2 inches according to the size of the cable, is
6
a
5 Τα
Fig. 147.
then slipped over one of the ends, after having its edges tapered
off with a file as shown at c in the figure. The two cable-ends are
then brought near enough together to make the distance separating
the ends of the sheaths about 18 inches. A pair from each cable
is then taken, and the insulation is removed from the wires in such
149
138
TELEPHONY
a manner that when the wires are placed as shown at a and b,
Fig. 147, the ends of the insulation come together. A paper
sleeve 24 inches long is then slipped over each conductor of each
pair in one of the cables, as shown at c d d". The red-covered
wires are then joined together as shown at a' b', the joint being
bent flat as at a" 6", after which the cotton sleeve is moved over
the joint as at c''. The two white covered wires are then treated
in the same manner, and this process is repeated until all the pairs
of one cable have been joined to those of the next, red to red, and
white to white. The appearance will be as shown at a b c etc.,
Fig. 148. Care should be taken not to have all the joints situated
in the same locality. They should be spread out over a distance
about 12 inches long.
To make a splice of this sort properly, the two cables should
a
6
с
Fig. 148.
be laid horizontally and at the same level. Aërial cables naturally
assume this position, and the cable splicer sits in a boatswain's
chair hung from the suspension wire. In the case of underground
cables, the best way is to place the end of each on a box or barrel.
.
The conductors having been spliced as shown in Fig. 148, the next
process is that of boiling out. For this purpose paraffine is heated
in a metal trough over a portable furnace such as plumbers use.
The paraffine should be thoroughly heated to expel whatever
moisture may be contained therein, and in order to determine
when it is hot enough the following points may be observed :
When paraffine becomes thoroughly melted it emits a light-
colored smoke, which assumes a dark hue just before the paraffine
bursts into flame. It is just when the dark smoke is first seen
that the paraffine is at the right temperature to be used. A very
simple and absolutely reliable test — one resorted to by cable
-
splicers — is to spit into the paraffine. When the paraffine is hot
enough the saliva is instantly thrown off.
When the paraffine is of the proper temperature it is poured
over the splice with a ladle, and permeates all the spaces between
-
a
150
TELEPHONY
139
the wires, making them air-tight and driving out whatever
moisture may be contained in the insulation. It also saturates
the cotton sleeving. When sufficient paraffine has thus been
poured on, the conductors are bound together as tightly as pos-
sible with cotton thread, and the lead sleeve is moved up into
place. The ends of the sleeve are hammered down to make a a
binding fit on the sheath, and a joint is wiped at each end. To do
this a quantity of hard solder is melted in a pot over a plumber's
furnace.
The bent surfaces of the sleeve are rubbed with tallow,
as are also the two sheaths, to a point one inch from the edges of
the sleeve. The metal is then poured over the joints, and rubbed
into place with a cloth pad, until a sufficient amount has been
made to adhere to the two surfaces. It is then allowed to cool.
At the completion of the work, the joint is as shown at a b c, Fig.
149, where the space occupied by the wires is shown between the
lines x x x etc., f, and fl. The sheath underneath the joint is
9'
9
α
х
х
h
х
Fig. 149.
enclosed in the lines g'flh' and g, f, and h. The edges of the
sleeve are denoted by the lines e e'; and the spaces m n m'n'
are filled with the wiping metal.
In splicing cables it is advantageous to preserve the position
of the pairs throughout; that is to say, the middle pair in the
first section is spliced to the middle pair in the second section,
which in turn is spliced to the middle pair in the third section,
etc. The first pair in the outer layer of the first section is spliced
to the corresponding pair in the succeeding section, and so on.
Observance of this rule facilitates the work of testing out after
the cable has been finished.
In making a wiped joint the principal point to be guarded
against is to keep the wiping metal from running under the
sleeve onto the conductors, burning off the insulation, and ruining
the cable. To this end the work must be done as quickly and
adroitly as possible.
At the two terminating points of the cable — the central

151
140
TELEPHONY
a
office and the end of the line the conductors are spliced to wire
having some form of waterproof insulation, or to a cable made up
of such wires. The ends of the lead cable are then sealed up
hermetically so that no moisture can enter. Such an arrangement
is called a pot-head, and is made in the following manner:
The waterproof wire used for splicing to the conductors of
the lead cable is No. 19 B. & S. gauge tinned, and has rubber
insulation. The insulation is not covered with braid, as there
is slight chance of mechanical injury. This wire is usually made
into a cable, the pairs being bound together with waxed thread.
Such a cable is called a pot-head cable, and the number of its
pairs must always correspond to the number of pairs in the lead
cable to which it is to be spliced.
The method employed in making the splice is the same as
that already described. The lead sleeve is wiped at one end to
the cable sheath in the usual way; the other end projects above
the end of the sheath about 18 inches. After the splice has been
boiled out in the usual manner, and the joint wiped, the space be-
tween the wires and the sleeve is filled with a compound of rosin
and oil, which is heated into liquid form so that it fills not only
space between the wires and the sheath, but also that between
the wires themselves. A sufficient quantity of the compound is
poured in to fill the space up to the top of the sleeve. It is then
allowed to cool, and in doing so hardens, and forms a solid mass
that prevents any moisture from entering the cable.
Submarine Cables. As their name implies, submarine cables
are used where it is necessary to carry the line underneath water,
as, for example, in crossing navigable rivers when the presence of
overhead lines would interfere with traffic. The usual construction
of a submarine cable calls for each conductor to be made of three
strands of No. 24. B. & S. gauge copper wire tinned, rubber insula-
tion being used. The conductors forming a pair are twisted to-
gether, the length of the twist not exceeding 6 inches. The pairs
are bound together with cotton thread saturated in paraffine, and
the whole is incased in a lead sheath of the usual construction.
Over the lead sheath, steel wires of a diameter of .2 inch are wound
helically. These steel wires constitute the armor, and are provided
to protect the cable against mechanical injury. Over this armor is
the space

a
152
TELEPHONY
141
C
6
wound very tightly a layer of tarred oakum, to protect the wires
from the action of the water. In Fig. 150 is shown the cross-section
of an armored submarine cable, in which the conductors are shown
at a a' a," etc., with their rubber insulation. The paraffined cotton
binding is shown at b, and the lead sheath at c. At d d d', etc., are
seen the armor wires, with the marlin binding at e. This form of
cable, owing to the use of rubber for insulation and to the fact that
the armor wires surround the whole, has a very high static capacity,
which is increased when the cable is laid, because of the presence of
the water in such close proximity. The use of the stranded con-
ductors is to give the cable increased flexibility, enabling it better to
conform to the contour of the bottom upon which it is laid.
In order to reduce the capacity
of the cable as much as possible, the
Long Distance Company are using
a submarine cable in which the in-
sulation is of paper saturated with
asphalt. The armor wires are re-
placed by a second lead sheath
placed outside of the first one. This
style of cable gives good satisfaction
for short lengths, but is much more
easily injured by mechanical shocks than the other described. For
long spans — 200 feet and more —
-
the armored cable is to be
preferred.
In terminating rubber-insulated submarine cables it is not
necessary to make a pot-head, as the nature of the insulation itself
precludes the entrance of moisture. In terminating the asphalt-
filled cable, the usual pot-head must be made.

d
din
Fig. 150.

-
-
TRANSPOSITION.
a
It is a well-known fact following from the laws of self-induc-
tion and mutual induction, that if two wires be placed parallel to
each other, an alternating current flowing in one wire will induce
similar and opposite currents in the other. These induced currents
may be caused by the presence of the magnetic field set up around the
first wire, or may be due to the electric stress set up between
the two wires. The first is called electro-magnetic induction, and
153
142
TELEPHONY
the second electrostatic induction. Electro-magnetic induction is
illustrated in Fig. 151. Suppose that in the line a b an alternating
current is flowing, and that the alternating magnetic field set up
thereby is represented by the concentric circles. As these magnetic
lines cut the telephone circuit c carrying the two receivers e and d
an induced current will be set up in the telephone circuit, which
either opposes or agrees in direction with that of the current flowing
at that instant in the first circuit. This induced current will mani-
au
nel mono- 6
b
1.
d
Fig. 151.
fest itself by the presence of noise in the two receivers. As the cur-
rent in the wire a b increases, the induced magnetic field, becoming
therefore stronger, will cut across the wire c, and the induced cur-
rent will be in the opposite direction to that which induces it. As
the current in a b decreases, the induced field will contract towards
the wire cutting the line c in the reverse direction, and inducing a
current therein, which is in the same direction as that in the line
ab.
b
+
+ 1
+
+
+
+1
+
1 +
+ 1
1 +
+
+
+
+1
c
d
e
Fig. 152.
In Fig. 152 is illustrated the nature of electrostatic induction.
Suppose the line a b again to be the disturbing wire carrying an
alternating current. Under these conditions the medium around it
will receive alternate positive and negative charges. Consider the
instant when it receives a positive charge, as shown in the diagram.
The medium surrounding the telephone wire will by static induction
receive a negative charge; the positive charge, being repelled by that
on the disturbing wire, will flow to ground in the direction indi-
cated by the arrows. With each alternation in the disturbing cur-
rent, the direction of flow of this repelled current is changed, with


154

AMERICAN EXPRESS CABINET.
American Electric Telephone Co.
TELEPHONY
143
the resultant noise in the receiver. Such a disturbance would be
produced by the proximity of electric light and power wires running
parallel to the telephone lines. This kind of disturbance will be
treated in greater detail later on. It will be evident that the
same effect will also be produced by two telephone lines running
parallel and in close proximity. In this case the effect of the
induced currents would be not merely to produce noise, but to
repeat on one line, more or less distinctly, the conversation carried
on over the other. Such an effect is called cross-talk.
Mr. J. J. Carty, chief engineer of the New York Telephone
Company, carried on a series of experiments to prove that cross-talk
bolile

a
5
+
+
+
+ +
+
+
+
-
-
1
1
1
产 ​。
d
Fig. 153.
was not the result of electro-magnetic induction, but wholly due to
electrostatic induction. In Fig. 153 is shown his method of experi-
mentation. The line a b, one end a being open, had the other end
grounded through the secondary winding of an induction coil. The
primary winding was connected through a transmitter to a battery.
A constantly vibrating tuning fork placed in front of the transmitter
caused an alternating current to be induced in the line a b. Since
one end of this line remained open, the only current that could flow
was that necessary to charge the line up to the potential of the im-
pressed E. M. F. Therefore the electro-magnetic induction was
negligible. At the moment when a positive charge was held on the
line a b, a negative charge was induced on the other line, the posi-
tive charge, as already explained, being driven to earth in the direc-
tion shown by the arrows. As the charge on the wire a b changes
from positive to negative, that on the other line changes from nega-
tive to positive. the negative charge being released and driven to
155
144
TELEPHONY
earth by the path already described, and its place being taken by
the positive charge which flows up from the earth at both ends of the
line. As a result the current flow in this line was either from
the center toward both ends, or from both ends toward the center.
The lines used by Mr. Carty were each 200 feet long, and separated
from each other by inch. The nature and direction of current
}
1
flow was proven by the fact that a receiver d placed in the center of
the line gave perfect silence, while noise was heard in the other two.
The proof was made still stronger by the fact that when the wire
was opened at its center point noise was still heard in the two
receivers c and e.
When the line between Boston and New York was built, and
telephone communication first established between these two cities,
it was found that cross-talk was very marked, and in some cases so
6
-

+
+
+
+
+
+
+
+
+
+ + + +
d
с
e
改
​Fig. 154.
serious as to interfere with conversation. It was this fact that
started Mr. Carty on his series of experiments, with the results
already given.
So far, grounded circuits only have been considered. If the
telephone circuit is metallic, and the disturbing wire is placed so as
to be at equal distances from the two conductors of the telephone
circuit, no induced current will be produced in the latter, since, if
the disturbing wire has a positive charge at any time, the surfaces of
the two telephone conductors nearest to it will have a negative
charge, while those most remote will have a positive. As the
charge on the disturbing wire changes to negative, that on the
adjacent surfaces will change to positive, while that on the remote
surfaces will become negative. Since the telephone circuit is not
grounded, it is obvious that the only way for this change to take place,
is by the current flowing across the wire, which produces no noise.



156
TELEPHONY
145
When the two conductors of the telephone circuit are at un-
equal distances from the disturbing wire, a different condition pre-
vails. This is shown in Fig. 154. At the instant that the disturbing
wire receives a negative charge, a positive charge is induced on the
adjacent surface of the nearest telephone conductor, the negative
charge being repelled to the remote conductor, causing a flow of
current away from the receiver c towards the receiver f, in the
direction indicated by the arrow, with a resultant noise in the
receivers e and d.
It will now be apparent that if two metallic telephone lines
are placed side by side, the conductors of the circuits not being dis-
posed symmetrically with respect to each other, an effect similar to
that illustrated in Fig. 154 will be produced and cross-talk will re-
sult. This condition is overcome by transposing the conductors of
one of the circuits at certain intervals as shown in Fig. 155, where
a a' is one circuit and 6 b' the other. At c and d the position of
the conductors of the latter circuit is reversed so that both are
6
b
Fig. 155.
equally exposed to the effect of the circuit a a'. As a result, any
disturbing influences coming from a d' are felt equally by both con-
ductors of the circuit b b', the induced current in one conductor bal-
ancing that in the other, with the result that no current flows.
This is called transposition, and is resorted to on all open-wire
lines to prevent cross-talk. Quite an elaborate scheme has been
worked out for transposing the conductors on lines carrying several
cross-arms. The scheme is shown in Fig. 156, and is described as
follows:
Starting from the first pole, a distance of 1,300 feet is measured
off, and the pole nearest to this point is marked A. From the pole
A, a second 1,300 feet is measured off, and the pole at this point
marked B. Another 1,300 feet is measured off, and the pole at this
point marked C. The distance is again measured, and the correspond-
ing pole marked B. This process is continued, the transposition poles

157
146
TELEPHONY
being marked as shown by the capital letters in the diagram.
Referring to the top arm, at the A poles the wires on pins 1 and 2,
3 and 4, 9 and 10, are transposed. At the B poles the wires on
pins 7 and 8 are transposed; while at the C poles those on pins 3 and 4,
5 and 6 are transposed. Referring to the second arm, on the A poles
the wires on pins 15 and 16, 17 and 18 are transposed; while on
the B poles the wires on pins 13 and 14 are transposed. On the
C poles the transpositions are made in the wires on pins 11 and 12,
17 and 18, 19 and 20.

7
OOONO MN-
TOP ARM.
A B C B A B C B A B C B A B C B A B
20
19
18
17
16
X
15
14
13
12
11
SECOND ARM
Fig. 156.
When a third arm is placed, the wires on this are transposed
the same as those on the first; and should a fourth arm be used its
wires would be transposed similarly to those on the second. The
method of cutting in the transpositions is shown in Fig. 157 and
Fig. 158.
The former is applicable to the case where the insulators
are on the same side of the pole, while the latter is used when the
pole lies between the two insulators. Referring to Fig. 157, the wire
a, being one conductor of the pair, is brought around the top glass of
a transposition insulator x, and secured by a McIntire sleeve b.
The free end is run through a second sleeve c. The wire a', being
that to which a is to be transposed, is cut through the sleeve d',
the short end being wound around the upper glass of the transposi-
tion insulator ac', brought through the sleeve b', and ended in
the sleeve c. The wire a', being the mate of a, is brought round the
lower glass of the transposition insulator X', passed through the
sleeve b', the free end being terminated in the sleeve c. The wire a,
being that to which a' is to be transposed, is cut through the sleeve

158
TELEPHONY
147
d, the short end being wound around the lower glass of the transpo-
sition insulator x, passed through the sleeve b, and terminated in the
sleeve c'.

a
d
6
هه
Srecs
ad
ja
දර
5
b
Fig. 157.
It will be observed that the transposing wires run between the
two
upper and the two lower glasses respectively, so that there is
no chance for them to come in contact. In Fig. 158 the pole is
represented at P, and to avoid it the transposing wires are carried

d
ib
Р
6
Fig. 158.
around the insulators before crossing over. Otherwise the method is
the same as that shown in Fig. 157. This is called a transposition.
TERMINAL POINTS.
The terminal points of a line, as the name indicates, are the
points in which the line terminates. In the case of trunk lines the
terminal points are the two exchanges that the lines connect. In
the case of subscriber lines, one terminal is the exchange, and the
other the subscriber telephone. The term is also used to denote the
point where a certain class of line ends, the circuits being continued
by another class of line — for example, the point where a cable line
159
148
TELEPHONY
8
b
e
ca
30
is connected to an open-wire
line, or where a submarine
& & &
cable line ends.
The method of terminat.
ing lines in an exchange, con-
C
sists, in the case of cables, in
d''
making a pot-head in the man-
ner already described, and con-
necting the conductors of the
pot-head cable to a piece of
apparatus called the
« main
distributing frame.” This sub-
ject will be described in detail
under the heading of “Tele-
phone Exchanges," where it
properly belongs. Where the
line approaching the exchange
is of the open-wire type, it is
connected to a bridle cable at
the point nearest the exchange,
the bridle cable being carried
inside. The manner of termi-
nating open-wire lines outside
of an exchange consists in
simply dead-ending them on
the insulators in the way al-
ready described, terminal cross-
arms being used.
The terminating of a cable,
whether aërial, underground, or
submarine, is a more elaborate
affair and needs to be done
with great care.
In this case
a piece of apparatus called a
Fig. 159.
cable box is used. A cable box
is a box made of pine, strongly put together and of sufficient size
to enable all the conductors in the cable to be arranged in order
and permanently terminated within the box.
It should be per-

1515-15-
1,9,2

160
TELEPHONY
149
de
o
fectly water-tight, and the door should be so constructed as to
prevent the rain from entering on being opened in wet weather.
In Fig. 159 is shown at a, a cable box mounted on a pole.
The roof b is made to slant towards the pole, and projects suffi-
ciently over the side and at the front to throw off water. The
arrangement of the apparatus inside of a cable box is shown in Fig.
160. The underground cable or submarine cable, as the case may
be, is brought up through a hole in the center of the box, the pot-
head being shown at a in the figure. The pot-head cable is fanned
out, or formed, in the manner shown, and its conductors are
attached to the binding-posts arranged on two strips d and d'. At
e, e', h, and h' are four strips of maple cleats with holes bored
through them horizontally, as
shown by the dotted lines.
ih ed
hi
These cleats and the strips of
binding-posts are firmly screwed
to the back of the cable box.
At the left-hand side of the
box, at b, is shown a bridle
cable, which comes down from
the cross-arm, where it takes
the open wires.
wires. It is formed
as shown, and is connected to
6
the strip of binding-posts i'.
At the right-hand side of the
box, at c, is seen an aërial lead
cable, which comes down from
above, and which, being formed,
Fig. 160.
is connected to the binding-
posts on the strip i. Referring to the two strips d and d', and beginning
at the top of the latter, the binding-posts are numbered downward in
series from 1. For example, the top post is No. 1, the second No. 2,
the third No. 3, etc. Assuming that there are 50 binding-posts on
each strip, the bottom one on strip d' would be No. 50. The post at
the top of strip d would be No. 51, and the bottom one on this
strip No. 100. In connecting up the cable conductors to these
posts, the first pair is placed on posts Nos. 1 and 2, the second
pair on posts Nos. 3 and 4, and so on. The binding-posts on the

o
o
d

161
150
TELEPHONY
a
strips i and i' are also numbered from the top downward in series;
that at the top of strip i is No. 1, as is also that at the top of strip
i'. The wires in these two cables are connected in pairs exactly
similar to those of the underground type. The pairs in the under-
ground cable are connected to those in the bridle and aërial lead
cables by what is known as cross-connecting. By means of a
piece of twisted pair wire No. 19 B. & S. gauge, rubber-insulated, and
braid-covered, the proper connections can be made. One end of each
wire of the pair is connected to the proper binding-post of the
underground cable, the other ends being connected to the proper
binding posts of the bridle or the aërial lead cable, as the case may
be. The cross-connecting wire is
d'
ď passed through the holes in the
e cleats as shown. Should it be neces-
sary to connect a pair of the under-
ground, terminating on the left-hand
strip of binding-posts, with a pair
in the aërial lead cable, the cross-
connecting wire, after being passed
through the hole in the cleat e', is
carried to the top of the box and is
passed through two japanned iron
Fig. 161.
rings to the right-hand side of the
box, to the proper point. The same
practice would be resorted to if it were desired to connect a pair
on the strip d with one on the strip i'.
Whenever an aërial lead cable runs for any considerable length,
say 200 feet or over, the conductors should be protected at the cable
box by fuses suitably mounted. A strip of these arresters is shown
in Fig. 161. They are mounted in the box and take the place of
the binding-posts. The strip consists of a block of wood a, on the
top of which are securely fastened brass lugs, one of these being
shown at e. These lugs are bent as shown, and are slotted at one
end and nicked at the other. To the bottom of the block are
fastened a second row of brass lugs f, etc., through the center of
which a hole is drilled and tapped. The tubular fuses are shown at
6 b' 6", etc. They consist of a fiber tube, to the bottom of which is
fastened a brass cap with a projecting screw that fits into the hole

b

162
TELEPHONY
151
in the bottom lug. The top of the tube is equipped with a cap
and hollow screw, over which fits a ring-nut c. This nut is slotted
at d d so that it can be set with a screw-driver. The fuse, which
has a capacity of 7 amperes, is soldered to the bottom cap, passed
up through the center of the tube, and soldered to the edge of the
hollow nut. The conductors in the cable to be protected are
soldered to the bottom lugs, while the cross-connecting wire is
soldered to those at the top.
Returning again to Fig. 159, it will be seen that the cable box
is mounted by fastening two boards, the ends of which are shown at
o c' and d d', to the back of the box, and bolting these with cross-
arm bolts to the pole. The cable-box door is shown closed, and
should always be secured with a padlock. At is shown a pole
seat, which is placed on the pole to afford a seat for the lineman
while working. The method of bringing a lead aërial cable into the
box is also shown; and it will be seen that the cable is given a bend
at e, called a drip loop, which prevents water from following the
cable down to the box. The underground cable is brought from the
nearest manhole to the bottom of the pole, through an iron pipe laid
in the earth. The pipe is bent and runs up the side of the pole to
the height of 15 feet. From this point to the cable box, the cable is
protected with a covering of sheet iron.

TEST POINTS.
Test points are placed here and there in a long line, to afford
means of opening the line for the purpose of testing.
purpose of testing. Such points
are necessary on toll trunks only. In many cases, toll trunks pass
,
through several exchanges before reaching their destination, and
under these conditions test points are not usually needed. The
necessary number of test points on a line has never been definitely
figured out. The Long Distance Telephone Company formerly
placed test points at about every 50 miles. More recently, however,
this distance has been reduced to 30 miles. The point to be
considered in locating test points is the amount of ground that the
lineman can cover in clearing trouble. In flat country traversed by
good roads, the lineman can take care of a longer stretch of line
than in rough country where movement from point to point is not
so easy. He is at still better advantage at points where the line
163
152
TELEPHONY
runs parallel to a railroad track, for in this case he can make use of
the train service in clearing trouble.
The test point is located in a convenient building, which
usually becomes the lineman's home. The method adopted for
bringing the wires into this building is the same as that described
for connecting a bridle cable to an open-wire line. The other end of
the cable, instead of going into the cable box, is cut into the build-
ing. In Fig. 162 is shown the standard form for cutting the con-
ductors of the bridle cable onto the open wires. The line wires
at this pole are dead-ended both ways as shown, transposition insu-
lators being used. The free end of the line wire, after being passed
through the McIntire sleeve, is bent down at right angles, and the
conductor of the bridle cable is soldered to it. These conductors
pen

Fig. 162.
are brought down beneath the cross-arm, and are passed through
wooden cleats to prevent the insulation from touching the creo-
soted arms, as it has been found that creosote has a deteriorating
effect upon the insulating material.
In Fig. 163 is shown the method of wiring a test pole. It
will be seen that the wires are dead-ended both ways, the short ends
being brought over the top of the insulator and placed in a clip a, a
firm connection being made by means of the thumb-screw b. In
making the test, the lineman opens the line by removing the clip,
and is thus enabled to connect himself with either end of the line
independently
The method of wiring up a test house is shown in Fig. 164, in
164
TELEPHONY
153
which a b, a' b' represent the top and bottom glasses respectively of
two transposition insulators, the method of cutting in the bridle
cable at the pole having been 'already shown. At c d e c"" are
shown four pieces of apparatus called jacks. Each one consists of a
brass ring e, e', etc., a German silver spring 1, 2, etc., and a contact
point shown by the arrow. When a properly shaped plug is intro-
duced into the ring e, the plug is held firmly, and its end makes
contact with the end of the
b
spring 1, pushing it to one side
and in so doing breaking con-
tact with the contact point
When the jacks are without
plugs, the two conductors from
a a', being wired to the two
springs 1 and 2 of the two jacks
c and c', form a connection
through the arrow points to the springs 3 and 4 of the jacks c" and
c'", thence passing out to the line wires at the transposition glasses b
and b. By introducing a plug into each of the jacks e and e', the line

Fig. 163.
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Fig. 164.
is opened towards the west, and communication is established with
the east. If on the other hand a plug is introduced into each of the
jacks e" and e'', the line is opened towards the east and communica-
tion is established with the west.
DISTRIBUTING POINTS.
As the name indicates, these are points where the line wires
are distributed to the subscribers' telephones. The simplest method
165
154
TELEPHONY
of distribution is from an open-wire line by means of twisted-pair
wire. This case is illustrated in Fig. 165, which will be recognized
as exactly similar to that of cutting in
for a test station. The line is dead-ended
in the usual manner, the twisted-pair
wire being brought down to the bottom
of the arm and passed through cleats to
preserve the insulation, and springing
away from the cross-arm at the point
nearest to the location of the subscriber's
station.
In residential districts where the
running of overhead lines must be re-
O
stricted as far as possible, it is often
most convenient to run the underground
Fig. 165.
cable into the rear yard of some house, in
which permission has been granted to erect a distributing pole.
The cable is carried to the top of this pole and terminated in a pot
head, the conductors being fastened to binding posts. One such pole
is shown in Fig. 166. The pole
6
is of the box-girder type, made
of steel, and equipped with steps
for the use of the lineman in
climbing. At the top is a flat
ring, on which are mounted the
binding-posts. On the bottom of
this ring are mounted porcelain
insulating knobs, shown at a
etc. in the illustration, and to
which are securely fastened the
distributing wires. The pot
head is covered with a sheet-
iron hood for protection against
the weather. Distributing
wires will be seen at b. In
Fig. 167 is shown a rather more
Fig. 166.
elaborate type of distributing hood. It consists of a sheet-iron
cylindrical box a surmounted by a hood b. This box contains the


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166
TELEPHONY
155
binding-posts and protecting fuses at which the cable is terminated.
The cable can be seen fastened against the pole by an iron pipe c,
with the pot head at d. The flat distributing ring can be plainly seen,
and is equipped with small hard-rubber-covered rings, one of which is
shown at e, which are used to secure the distributing wires. The
distributing wires also can be plainly seen. They are No. 14 B. & S.
gauge, tinned, covered with rubber insulation and heavy braid. The
copper is hard-drawn, and has a breaking weight of 200 lbs.
The conductors forming a pair are twisted together, the length of the
twist not exceeding 3 inches. The hood is shown mounted on a
wooden pole, but it can also be used on an iron pole.

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​Fig. 167.
The New York Telephone Company has developed a system of
distribution called the "block” system, which is used exclusively in
the down-town districts. The features of this system are as follows:
The underground cable from the exchange terminates in the
cellar of one of the buildings in a block, in the regulation cable box,
Fig. 159. In this box terminate also one or two other cables,
called block cables, which have their other terminals in the cellars
of the various buildings in the block. These cables are usually
bridging cables. From each of the terminals of the block cables,
run house cables — one cable for each building - which have ter-
minals on each floor. If a subscriber is to be given service any-
-
167
156
TELEPHONY
where within this block, all that is necessary is to make the proper
cross-connection between the underground cable and the block
cable, and between the block-cable terminal and the house cable.
The only wire that need be run is that from the telephone instru-
ment to the house-cable terminal on the same floor. The wire used
for this purpose is called house wire. It is No. 19 B. & S. gauge
&
tinned wire, soft-drawn, and covered with rubber insulation 1 inch
}
in thickness. Over the insulation is woven a cotton braid, which is
colored to imitate oak, mahogany, or cherry finish. The conductors
are twisted together, the length of a twist not exceeding 2 inches.
LINEMEN'S TOOLS.
5
"
Climbers. A word should be said here about the nature of the
tools used by the lineman, and the method of using them. The first
requisite in the lineman's kit of tools is the climbing irons, or spurs, as
they are called. These are worn to assist in climbing up and down
the pole. They are made in two forms as shown in Figs. 168 and 169.
Both types are made of wrought iron, with a steel spur welded on.
In Fig. 168 is shown what is termed the “Western” spur
from the fact that it is used more
in that part of the United States
than in the East. It consists of
a wrought iron strip a, the upper
e end being shaped into an "eye'
c, while the other end is bent at
d right angles to pass under the
instep, curving upward slightly to
Fig. 168.
give the foot a firm hold. At the
extremity is the wrought steel
spur b, which bends downward —- so that it can be jabbed into the
pole by an inward and downward motion of the foot. The device is
held in place by a strip passing through its “eye,” and around the
upper part of the thigh of the climber. The strip a is on the out-
side of the leg when in place.
In the Eastern type shown in Fig. 169 the strip is equipped
with an "eye” at the upper and also at the lower end, the former
being shown at b and the latter at c. The spur d is welded to the
lower part of the strip. When in place the strap a is on the inside


Fig. 169.

168
TELEPHONY
157
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of the leg, and is held in place by two leather straps, one passing
through the eye c and the other passing through the eye
b.
One of these types is about as good as the other, the Western
being somewhat simpler in construction and easier of adjustment.
In climbing, the pole is grasped with the fingers and lower part
of the palms of the hand, and
the spurs are jabbed into the a abb
side of the pole with a down-
ward thrust. Care should be
taken not to “hug” the pole
Fig. 170
but to hold on at arm's length.
To be a good climber requires a cool head and strong muscles, and it
is well for a beginner to practice at moderate heights — say 15 feet
in order to accustom himself to the work before he attempts to
climb higher.
Pliers and Wrenches. In addition to the ordinary pliers
used, the lineman carries a wrench, shown in Fig. 170. It is made
in the form of ordinary 9-inch pliers, but is equipped with two sets
of circular jaws shown at a a' and b b', the former being for No. 8
wire and the latter for No. 12.
The wrench is held closed by a
lock C, which holds the two
handles together. This wrench
is used to twist McIntire sleeve
joints. Two such wrenches
b
are used together, one being
clasped over one end of the
sleeve and held rigid, while
the other is clasped over the opposite end of the sleeve and rotated
until the requisite number of twists have been made.
Come Alongs. This term is used to denote the mechanism
used to pull up open wires to the proper tension. The device is shown
in Fig. 171. It consists of a set of jaws a and b, which are pivoted
to two links at e' and e' respectively. These links are strapped
together by pivoted joints at e and e", so that by pulling on the “eye”
c the jaws are brought together, always maintaining a parallel posi-
tion. The wire to be pulled up is placed between the two jaws as
shown at d, the whole being drawn up by a rope attached to c.

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169
158
TELEPHONY
TELEPHONE EXCHANGES
The subject to be studied now is the method employed to so
terminate telephone lines, that the proper connection can be made
when one subscriber wishes to converse with another. This sub-
ject naturally divides itself under two heads: first, the terminating
lines as they enter the exchange building; and second, the arrange-
ment of these terminals, so that the proper connections can be
made. To accomplish the desired results, two pieces of apparatus
are necessary: that used in properly terminating the lines is called
The Distributing Board. That used in properly arranging the ter-
minals so that connections may be made, is called The Switchboard.
Auxiliary apparatus is also needed, but it should be remembered,
that the two principal pieces of apparatus in a telephone exchange
are the distributing board, and the switchboard. In dealing with
the subject of telephone exchanges, the terminating of the lines
will be considered first, and later the distributing board will be
described in detail.
The design and use of a distributing board is based upon the
following principles. All wires entering an exchange, whether of
the open-wire or cable type, must be permanently connected to
fixed terminals. All wires running between the distributing board
and the switchboard, must be permanently connected at the for-
mer end to fixed terminals. These two sets of terminals must be
so arranged with respect to one another as to be really connected
together, or disconnected according to the needs of the case.
By this means, the two systems of wiring — that entering the
exchange from without, and that between the switchboard and the
distributing board - are entirely independent of one another, and
either one can be changed without necessitating a change in the
other.
Numbering. All conductors entering an exchange are num-
bered according to some system, and the numbers are placed op-
posite the terminals on the distributing board. The conductors
on an open-wire line, are numbered to correspond with the pins on
which they are placed. The pins are numbered in the following
manner: standing with the back to the exchange, and facing the
direction in which the pole line runs, the left-hand pin on the top


170

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SWITCHBOARD OF AUTOMATIC EXCHANGE OF TELEPHONE DEPARTMENT,
CHICAGO SUBWAY CO.
Automatic Electric Co.
TELEPHONY
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arm is No. 1; that to the right of it, No. 2; and so on till the
right-hand pin on the top arm is reached, which is No.10. The
left-hand pin on the second arm is No. 11; and the right-hand pin
on the same arm, No. 20, and so on to the right-hand pin on the
bottom arm. This system is maintained whether or not wires are
attached to the pins in consecutive order. For example, suppose
that pins Nos. 1, 2, 3 and 4 have wires attached and that the rest
of the pins are vacant to pin No. 15, the wire on this pin would
still be No. 15.
All cables entering an exchange are numbered consecutively.
In cities having more than
one exchange, cables enter-
ing one exchange are distin-
guished from those entering
another by a different hun-
dred. For example,
the
cables entering the Broad St.
Exchange in New York are
numbered from 1 to 99;
those entering the Cortlandt
St. Exchange in the same city
are numbered from 100 to
199. Those entering the
John St. Exchange are num-
bered from 200 to 299, etc.
Fig. 172.
The conductors in the cable
are numbered from 1 up, each one taking its number from that
of the binding post in the cable box to which it is attached. The
wires running to the switchboard are numbered in an alto-
gether different manner, which will be explained.
Main Distributing Board. The style of the distributing
board varies with the size of the exchange, and also with the ideas
of the designer. For small exchanges, in which 100 or 200 lines
terminate, it is a very simple affair. In Fig. 172 is shown one
type of this piece of apparatus used with small exchanges. It
consists of a board a of maple. The size of this board depends
upon the number of lines to be handled. For 100-line capacity it
is about 3 feet by 2 feet, while for 200 lines it is about 4 feet by

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171
160
TELEPHONY
y
3 feet. Two maple cleats b and b' are fastened to the board, and
have holes bored in them, shown at c, c', c", etc., and d, d', d", etc.
These holes are for the accommodation of the cross-connecting
wires. The cleats are similar to those used in cable boxes which
have already been described. Fastened to the face of the board
by small screws e, e', e", etc., are brass clips, one of which is shown
in detail at x. The hole through which the screw passes is shown
at y. There is a nick in each end of the lug for the wire; one of
them being shown at 2.
The lugs in each group correspond in number to the number
of conductors handled; the one shown in Fig. 172 having a capac-
ity of 50 lines.
The lines coming in from the outside, are brought to the back
of the board and soldered to the lugs, being passed through holes
for the purpose. The conductors from the switchboard are treated
in a similar manner and soldered to the bottom row.
The cross-
connecting wire is run on the face of the board, and is passed
through the proper holes in the cleats, and soldered to the oppo-
site side of the lug. Referring to the detail, the outside wire
would be soldered at 2, and the swichboard wire at w.
For cross-
connecting purposes, the wire is the same as that used in cable

boxes.
This form of distributing board is very compact and admits
of the connection being established between any switchboard wire
and any pair of wires coming in from outside.
There are certain essential features which this form of board
does not possess, and which are absolutely necessary in a distribut-
ing board in an exchange of any considerable size. First, this
arrangement of terminals is not the most economical as regards
space. Second, it does not make provision for protecting the
switchboard from lightning or foreign currents. Third, it is very
difficult to get at the inner lugs for soldering wires or breaking
connections. Fourth, it does not afford an easy way of opening a
line for testing. While it is not essential to have the high-poten-
tial protecting apparatus mounted on the distributing board, and
while many excellent boards have been designed without this
feature, it is absolutely necessary that a distributing board for a
large exchange should possess the other features.
172
TELEPHONY
161
a
Hibbard Distributing Board. In Fig. 173 is shown a distrib-
uting board designed by Mr. Hibbard, which, although now out-
of-date, was formerly extensively used. It consists of an iron rack
upon one side of which are fastened wooden horizontal strips
shown at a, a', etc. On the opposite side, the same kind of
strips are fastened vertically as shown at e, e', e", etc. Down the
a'

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Fig. 173.
center of the rack run horizontal iron rails d, d', d," etc. to which
are fastened rings. The wooden strips have holes bored through
the center, and on opposite sides are mounted brass punchings as
shown in the detail, where the hole is at x, and the punchings at
y, y'. Two of these punchings are shown at c and c'.
The method of using this rack is as follows: The cables from
outside are formed upon the inside of the vertical strips, the con-
ductors being passed through the holes. Pairs are connected to
the lugs on the opposite sides of a hole. The conductors from
the switchboard are formed upon the inner side of the horizontal
rails, and connected in the same manner as described for the cable
173
162
TELEPHONY
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conductors. The cross-connecting wires are brought over the
edges of the rail and soldered to the outside ends of the lugs.
The cross-connecting wires are passed from the horizontal rail
diagonally to the ring opposite the proper vertical strip, and
thence through the ring to the proper lug. With this form of
distributing board, the cable conductors are soldered to the lugs
on the horizontal rails, while the switchboard wires are soldered
to those on the vertical rails.
As has already been stated, this form of distributing board
does not provide for the proper protection of the wires, so that
additional facilities for furnishing protection must be at hand.
The standard method of accomplish-
ing this is to terminate the cable
in what is known as a cable head
which contains the desired protecting
apparatus. One form of cable head
is shown in Fig. 174, where a repre-
sents a cast-iron box, equipped at the
back with lugs b,6', 6", b!", for fasten-
ing it securely to some suitable sup-
port. Over the front of the box fits
&
a lid c, which, by means of a rubber
6" gasket x, forms an air-tight cover.
It is held in place by means of screws,
d, d', d", etc. which fit into holes
Fig. 174
drilled and tapped into the edge of
the box. Projecting from the bottom
of the box, and secured to it by means of a lock-nut, is a brass sleeve
e, to which, by means of a wiped joint, the sleeve of the sheath
is attached. Projecting through the sides of the box, as shown at
f, f', f", etc. are the connectors. They consist of hollow tubes of
fiber held in place by lock-nuts. At the inner end of each is a
binding post for attaching the cable conductors, while at the outer
end is a larger one for attaching the cross-connecting wire. Run-
ning through the fiber tube and attached to both binding posts is
a fuse, for protection against an abnormally large current.
When a cable terminates in a cable head, it is not necessary
to make use of a pot head ; it is sufficient to wipe the sheath to

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the brass sleeve as already explained. The cross-connecting wire
running from these terminals is soldered to the lugs on the hori-
zontal rails of the distributing board. After the cable conductors
have been properly fastened to the binding posts, hot paraffine is
poured into the cable head several times, and while the inside is
still hot, the lid is securely fastened.
The numbering of the binding posts begins on the left-hand
side of the box at the top. The
top front binding post is No. 1;
that slightly lower and to the
rear of the box is No. 2 ; that
directly under No. 1 is No. 3,
etc. This system is continued
on the opposite side of the box
beginning at the top and ending
at the bottom.
The disadvantages of this
method of terminating a cable
are the extra cost of the box,
and the extra run of cross-
connecting wire from the cable
terminal to the distributing
board. While the fuse is a suit-
able protection against abnormal
currents, it is not sufficient pro-
tection against the damage due
to a sudden charging of the line
with a high potential as in the
case of thunder storms.
Fig. 175.
Ford-Lenfest Distributing Board. To do away with the
cable terminal, and to place the necessary protecting apparatus in
the most convenient place the form of distributing board shown in
Fig. 175 was devised. It consists of a series of vertical iron
beams of which two are shown at a and a'. They are held
securely together by flat iron bars d, d', d", etc. These horizontal
bars are fastened to the angles by bolts. Running at right angles
to d, d', d", etc. is a second set of flat iron bars c, d, and c", etc.,
which are bolted to the verticals, and which carry at one end a

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175
164
TELEPHONY
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heavy, vertical iron strip g, g', and at the other end, wooden chan-
nel pieces f, f', f", etc. These channel pieces, which are of maple,
,
carry a series of brass lugs arranged in groups, each group taking
up the space between two consecutive horizontal supports. Each
group consists of 20 pairs of lugs.
The end view of one of these channel pieces is shown at a in
Fig. 176. Mounted in the channel is a hard-rubber strip c, into
b
which slots are cut for the accommodation of the
lugs. These slots are of sufficient depth to allow
the top of the lug to project about to of an inch.
On top of this is placed a second hard-rubber
id
strip d' which is securely bolted to the first one
and to the maple strip by brass bolts, one of which
is shown at d. The lugs are made with two ears,
6
e and e'. Two holes b and b' are bored through
Fig. 176.
the channel piece opposite each pair of lugs for
the accommodation of the wires. To the vertical
iron strips g and g', Fig. 175, are attached the protecting device
to be described directly. Rings e, e', etc., Fig. 175, are fastened to
the horizontal braces at each section for the accommodation
of the cross-connecting wires.
This form of main distributing frame is used exclusively by
the Bell Companies, and is made in two forms, known as the 4a
and 4b frame. In the 4a frame, the cable conductors are attached
to the lugs on the horizontal channel pieces; while in the 4b frame,
the cable conductors are connected to the protecting apparatus on
the vertical side. In the 4a frame, the switchboard wires are at-
tached to the protecting apparatus, while in the 4b frame, they are
attached to the lugs on the horizontal side. In Fig. 175, a cable
is shown at o, coming up through a hole in the floor. It is fanned
out at the rear of the strip, and its conductors are brought through
the bottom row of holes and soldered to the lugs. A cross-con-
necting wire is shown at m; it is soldered to the upper ears of the
lugs, and brought through the ring e" to the vertical side.
The only difference in the make-up of the 4a and 4b frames
lies in the style of protecting device. The 4a protection is shown in
Fig. 177. At a is shown in cross-section the iron strip g' in Fig.
175. Mounted on this strip is the protection which consists for

176
TELEPHONY
165
a
each line of the following apparatus : On two hard-rubber blocks
c d' are placed two German-silver springs d d', with the ends bent
up into lugs as shown. The opposite ends are slightly bent, one
rests on the carbon block g, and the other on the carbon block g'.
Firmly attached to each spring by rivets is a flexible strip of
German silver, one of which is shown at e, and the other at e'.
Resting on the two hard-rubber blocks r and r' are the two springs
i and i' shaped as shown. Fitting into a hole drilled through r, c,
a, d' and r', are two hard-rubber sleeves n and m, the latter being'
provided with a shoulder which rests against the spring i.
Through the center of these tubes
passes a brass bolt l. It is held
in place by a nut p resting on the
lug o and one at the opposite end
resting against the end of the
short, hard-rubber sleeve q. In
this way the lug o is in electrical
contact through the bolt I and the
BP
nut P, with the spring d' while
the three remaining springs are
insulated from one another. is
Fastened to the end of a is a Ger-
man-silver strip f, against which
rest the two carbon blocks h and
h', which in turn rest against &
and g’ respectively. The spaces
'
between g and h, and j' and k'
g
are filled with a thin sheet of
Fig. 177.
mica.
At s and s' are shown two pieces of apparatus called heat
coils, shown in detail in Fig. 178. A heat coil consists of a fiber
shell a, with a brass pin c passing through its center; soldered to
this pin is a brass sleeve d so placed that there is an interval of
about 1 inch between its upper end and the top of the fiber shell.
16
A coil of very fine wire, insulated with silk and cotton covering,
,
is wound around this sleeve, one end being soldered to the sleeve,
and the other to a brass plate placed on top of the shell. At o is
shown a small fiber projection. Returning to Fig. 177; the heat

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177
166
TELEPHONY
coil is so placed that the fiber projection o fits into a slot in the
spring i or i' and the pin c passing through a hole in d or d' rests
on the German-silver strip e or é' as the case may be. The sleeve
d, Fig. 178, rests on the edges of the hole and with the tension of
the outer springs holds the heat coil in place. Starting from the
lug o, Fig. 177, a circuit is formed through the brass bolt l to the
spring d', and thence to the sleeve of the heat coil s'. Through
the winding of this coil it passes to the brass cap which rests
against the spring i', and thence to the lug at its end. Starting
from the spring d, a circuit is made through the heat coil to the
spring i, and thence to the lug i. The cross-connecting wire,
'
coming from the lugs at the horizontal side of the frame to which
the underground conductors are also attached, is connected to the
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Fig. 178.
Fig. 179.
lugs о and d, while the switchboard wire is connected to the lugs
i and i'.
The carbon plates are shown in detail in Fig. 179. It will
be seen from the end view that the upper plate g is slotted at b, so
that the springs d or d' will hold it securely and not allow it to
fall out of place. The lower carbon has a depression a in its up-
per surface which is filled with solder, care being taken to have
the surface of the solder flush with that of the carbon. The mica
separating the carbons is shown at c. It is about 4 inch in thick-

ness.
The action of the arrester is as follows: A high potential
coming in on the line, as for example a charge of lightning, would
pass over the springs d and d', called the ground springs, and
reaching the carbons g and g' would arc across the spaces between
them and the other carbons h and h', through the gap in the micas.
This arc would melt the fuse a, Fig. 179, forming a permanent con-
nection between the two carbons. The iron strip a, Fig. 177, being
178
TELEPHONY
167
permanently grounded, a path is afforded directly to earth, thus
saving the exchange wiring and apparatus from destruction. When
the discharge has taken place all that is necessary is to replace the
carbon plates by new ones, and blow away whatever carbon dust
may have accumulated.
Should an abnormal current come in on the line of a poten-
tial not sufficient to arc between the carbons, it will pass through
the heat coils, and fuse the wire, opening the circuit toward the
exchange. The heat produced would, in addition to fusing the
wire, melt the solder which holds the sleeve d, Fig. 178, in place ;
and as a result, the pressure of the outer spring would push the

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Fig. 180.
Fig. 181.
heat coil down till the pin, driving before it the strip e, Fig. 177,
would press it against the strip f, thereby grounding the line, and
affording a safe path for the current.
In Fig. 180 is shown the 4b arrester, and it differs from the
4a only in the method of mounting the springs. It will be seen
that the lug o is electrically connected through the bolt ? to the
spring i', while the remaining springs are insulated from one an-
other. The wires of the outside cable are soldered to the lugs d
and d', while the cross-connecting wire is fastened to the lugs o
and i. In every other respect, and in the action, this style of
179
168
TELEPHONY
arrester is identical with that already described. In Fig. 181 is
shown part of a vertical fanning strip, not shown in Fig. 175, but
which is mounted on the horizontal flat irons e, c', etc. This con-
sists of two parts, one shown at a, being comparatively wide, and
having recesses cut in it for the iron braces to pass through. A
second narrow strip b, is screwed on to the side of a, and serves to
hold the latter rigidly. In a are drilled two rows of holes, e, f, g,
h, etc., and e', f', g', h', etc. They are about į inch in diameter. In
bis drilled a row of holes i, i', 3", i"', etc., of a diameter of 1 inch.
In a 4a frame, the wires from the switchboard are passed through
the smaller holes, while the cross-connecting wire is passed through
the larger. The vertical spacing between the holes is 1 inch, the
same as that between the arrester springs. In the 4b frame, the
conductors of the cable pass through the small holes, but the cross-
connecting wire passes through the large ones. In Fig. 177, the
plan of the fanning strip is shown at x, the hole for the cross-con-
necting wire at y, and that for the switchboard wires at z and z'.
In Fig. 180, the cable conductors pass through the holes z and z',
while the cross-connecting wire passes through the hole y.
a

SWITCHBOARD.
The switchboard is that piece of the apparatus in which the
lines are so arranged that the proper connections can be made.
In the most simple form of switchboard, all the lines termi-
nate within reach of one operator who is thus enabled to handle
all the business. The essential parts of such a switchboard may be
defined as follows: First — the line terminals, designed and
placed to enable the operator to connect herself with each and all
of the circuits. Second the line signals, constructed and placed
to give notice to the operator when the subscriber wants attention.
Third — the necessary connecting circuits, for establishing the
proper connections between the line terminals, and also to enable
the operator to connect herself with any line terminal to learn the
wish of the subscriber. Fourth - a key wired to each connecting
cord circuit, to enable the operator to cut in her telephone circuit
on the connecting circuit for the necessary conversation with the
subscriber. Fifth — a signal placed on each connecting-cord
circuit to enable the subscribers to signal the operator upon
180
TELEPHONY
169
a
the completion of a conversation, in order that the connection may
be taken down. Sixth — an additional key placed on each con-
necting-cord circuit to enable the operator to cut in on it and an
alternating current of suitable potential to enable the operator to
call the subscribers.
The line terminals are called jacks. They are made of brass
of various designs, and so constructed as to be placed in rows.
The line signals take the form of magnetic drops, and are called
line drops. The connecting-cord circuit is wired permanently to
the switchboard, and terminates at both ends in a flexible cord and
plug for inserting into the jack. The circuit of a switchboard is
shown in Fig. 183. Two subscriber lines are shown, and for con-
venience, one is shown terminated on a 4a distributing board,
while the other is shown terminated on a 4b board. Referring to
the upper one; the cable conductors terminate on the horizontal
side, the wavy lines denoting the cross-connecting wires. At band
b' are shown the carbon-block lightning arresters, and at c and d
the heat coils. Referring to the lower line, the cable conductors
are terminated on the vertical side of the distributing board, the
lightning arresters being shown at b,b', and the heat coils at c, and
c'. As before, the wavy lines denote the cross-connecting wires.
The two line jacks are shown at d and d', and are constructed as
follows: Referring to the upper one e is a brass ring shown in
section 1, a German-silver spring, which normally makes contact
with the point indicated by the arrow. To this contact is wired
one side of the drop, the other side being permanently connected
to the ring. The drop is shown at x and consists of the ordinary
form of electro-magnet, with a pivoted armature and a brass shut-
ter, which is allowed to fall when the former is attracted to the
pole pieces. The two plugs of the operator's cord circuit are
shown at p and p. Each one consists of two metallic parts insu-
'
lated from one another (called the tip) shown at 3 and 5. The
shank or sleeve is shown at 4 and 6. The two flexible cords
tend from the two plugs to the connectors w and w', and w 19 and
W'1, respectively
At R and R" are shown the two ringing keys, used for throwing
the alternating current onto the line to call the subscriber. Each
one of these keys consists of two normal German-silver springs 9

ex-
181
170
TELEPHONY
and 10, which with the key in the position shown, make contact
with the points 11 and 12 respectively. This circuit is connected
to the outer spring 7 and 8. At m is shown the clearing-out drop,
or drop connected to the connecting-cord circuit to give the signal

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Fig. 183.
to the operator upon the completion of the conversation. The
drop is permanently bridged across the circuit, and must be of
high impedance. It is wound to a resistance of 500 ohms.
At l is shown the listening key. This differs from the ring-
ing key in that there are no inner contacts. The normal springs
are bridged across the line, and the outer ones are connected to
the operator's telephone circuit. The ringing current generator is
shown at s. The method of operating is as follows: One of the
subscribers, for example the one whose line is connected to the
jack d, desiring to converse with another one, rings with the gen-
erator at his telephone and throws the shutter of the drop x. The
operator upon seeing the drop fall, introduces the plug p' into the
jack, the tip 5 touching the spring 1, while the shank 6 makes
contact with the ring 2. The spring 1 is raised, breaking con-
tact with the drop at the arrow point. The drop is thus cut off.
This is necessary, otherwise the presence of the drop bridged

182
TELEPHONY
171
across the line would seriously reduce transmission as has already
been explained in connection with the series bell. A circuit is
now formed from the jack through the tip and sleeve of the plug
and the cord, to the normal contacts of the ringing key R', thence
through the inner contacts 11 and 12 to the cord circuit wiring.
The operator, by adjusting her listening key l, cuts her telephone
in on this circuit and communicates with the subscriber. Upon
learning that the calling subscriber wishes to communicate with
the subscriber whose line is connected to jack d', she introduces
the plug p into the jack, thereby cutting off the drop x as already
described. The ringing key R is then depressed with the result
that the ringing current is thrown on the line, thus ringing the bell
at the called subscriber's telephone. It should be observed that
when the bell at a subscriber's station is rung, the cord circuit is
open towards the other one. The reason of this is that the call-
ing subscriber who is waiting with the receiver at his ear would
otherwise receive the very unpleasant sensation of having the ring-
ing current pass through its coils when held in that position.
Again the presence of the calling subscriber's receiver bridged
across the line would shunt so much current that the called sub-
scriber's bell would ring very faintly if at all.
During the conversation the two-line drops x and x' are cut off
from their respective lines, and the only signal within reach of
either subscriber is the clearing-out drop m. Upon the completion
of the conversation the act of one or more of the subscribers ring-
ing, throws the clearing-out drop, thus giving the signal to the
operator that the connection must be taken down. The operator
can, by means of her listening key 1, listen in on the circuit. The
operator can establish as many simultaneous connections as she
has cord circuits. The number varies from 5 to 12 according to
the magnitude of the business to be handled.
With the exception of the ringing-current generator, and the
operator's telephone circuit, each cord circuit is made up of the
apparatus shown in Fig. 183. The ringing generator and the
operator's telephone circuit are common to all the cord circuits.
When the telephone business started, there were many differ-
ent systems of operating, each requiring its peculiar form of ap-
paratus. None of these systems are now in use. Only two of

183
172
TELEPHONY
them will be mentioned here. They are the Chinnock System, and
the Law System. In the former, the line signals were placed
together in an annunciator box, and one of the operators was de-
tailed to watch them. Sitting at a table were a number of oper-
ators, who switched in on the subscriber line whose number was
called out by the annunciator operator, and ascertained the num-
ber required. The operator then gave the calling and the called
numbers to an operator placed at the switchboard, termed the
switching operator, who established the connection. This system
more than any other prepared the way
for those now in use.
The Law system, although now obsolete, proved very success-
ful for the uses to which it was adapted. In outline the system
was as follows: All the subscribers' telephones were placed on
one wire, known as the calling wire. When the subscriber
wished to call the operator, he went in on the calling wire.
Since all subscribers were on the same calling-wire, the party
calling had to give his number and that of the party required.
Upon so doing the party would establish the connection. The
principal feature of this system was the fact that a very small
switchboard was needed. When, however, the volume of business
became heavy, it was found to be inadequate and went out of use.
Switchboards in use to-day, may be divided into two classes :
Standard and Multiple. The former board is so made up that
each line entering the exchange has one terminal, or jack, and only
The multiple system is based on the fact that every line en-
tering the exchange has a jack within reach of every operator.
Before taking up in detail the method of construction of the
standard switchboard it will be necessary to say something about
the nature of the construction of the essential pieces of apparatus
of a switchboard. Let us take them in the order named: The
type of jack used in the standard switchboard is constructed as
shown in Fig. 183a. It consists of a brass casting shaped cylindri-
cally at a, and cut out in the middle
with a rectangular enlargement b at the
opposite end. The cylindrical end is
.b
slightly hollowed out in the center, and
the extremities are neatly turned as
Fig. 183a.
shown at x and ad'; by means of the
hole through the lug i the jack is screwed to the switchboard.

one.
х
e
9
184
TELEPHONY
173
Fastened to b, but insulated therefrom by the hard-rubber strip
c, is the German-silver spring e the end of which is bent as shown
to make contact with the tip of the plug. A second spring g,
fastened to 6 but insulated therefrom by the hard-rubber strip d,


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Fig. 184.
is provided with a point h, which passes through a hole in the
casting and makes contact with e.
The two conductors of the subscriber's circuit are soldered
to the punchings e' and f. One side of the drop circuit is
soldered to f and the other to g. These jacks are usually
mounted in a hard-rubber panel called the jack panel, which
forms part of the face of the switchboard. Next the line signal
or drop is shown in Fig. 184, where the two magnet coils are
shown at a and b, and the plate upon which they are mounted, at
This plate is equipped with two projections e' e' from which

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Fig. 185.
is pivoted the armature d. This armature has attached to it a
stiff steel wire f, the other end of which is shaped to hold the
drop g in place. When the magnet coils are energized, the
185
174
TELEPHONY
a
a
armature is attracted to the poles, lifting the steel rod f and
allowing the shutter to fall. The face of the drop is shown at a
and the shutter in the fallen position, at y. The ringing and
listening keys are shown in Figs. 185 and 186 respectively. The
ringing key consists of a brass frame a at the bottom of which is
mounted a hard-rubber strip 6. Upon this strip are mounted the
b
contact points i i with their respective lugs i' and i, to which the
wires are soldered. Mounted on 4 hard-rubber blocks h, h', h,
and h, are 4 springs K, ), K' and ;', with their respective lugs K',
j', K, and ; Each one of these springs is insulated from its
fellows. A brass plunger c passes through holes in a and b, and
screws into a hard-rubber wedge d. A hard-rubber button e is
screwed to the top of this plunger; a spiral spring f which is
1
1

m

z

Fig. 186.
Fig. 187.
wound around c has one end butting against e, and the other
against a. The brass sleeve g prevents the button e from being
depressed too far. The action of the key has already been
explained.
Ringing keys are usually mounted in a row, the two on each
cord circuit being placed as shown in the right-hand figure. The
listening key is shown in Fig. 186 and its construction will
readily be understood from what has been said about the ringing
key.
There remains to be described, the signals on the operator's
cord circuits called the “clearing-out drops.” One of these is
shown in Fig. 187. It differs in construction from the line drop,
in that it has only one core, which is considerably longer than
those of the line drop. By actual measurement, the cores of the
186

100
LIGHTNING ARRESTER CABINET-NARROW TYPE
Stromberg-Carlson Telephone Mfg. Co.
TELEPHONY
175
line drop are an inch and a half long while that of the clearing-
out drop is 24 inches long. The magnetic coil is encased in an
iron shell a, terminating at one end in a shoulder with lugs shown
at m and m'. From these lugs is pivoted the ar-
mature d. Two circular holes are cut into the X
armature, through which are brought the terminals
of the coil, shown at o and o'. To prevent the
coil terminals making contact with the armature,
these two holes are bushed with hard-rubber rings
e and e'. The face of the drop is shown at b,
e
while the shutter is seen at c. The steel wire
holding the shutter in position is shown at n.
The catch at the end of this rod, called the arrow,
is shown more clearly at x, the face of the drop
9
being shown at z and the shutter at y. Since
these drops are always in the circuit, and since
several of them are placed side by side, it is neces-
S
sary to equip each one with an iron shell a to pre-
Fig. 188.
vent cross talk by their mutual electro-magnetic
induction. The action of the shell is to short circuit the lines of
force, emanating from the coil so that no field will be present in
the surrounding space to affect the coils of the adjacent drops.
The plugs which form the terminals of the cord circuits,
deserve notice. One of them is shown in Fig. 188. It consists
of a hollow brass cylinder a turned down at one end into a shank.
Placed inside of this is a hard-rubber sleeve e. Through the
center of the sleeve is a steel bolt b enlarged at one end as shown

a


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b
Fig. 189.
Fig. 190.
at d. Onto the opposite end is screwed a brass ball, called the
tip and shown at f. Fitting over the brass cylinder is a fiber
One conductor of the cord circuit is connected to the
sleeve g.

187
176
TELEPHONY
tip of the plug by a screw fitting into the hole t; while the
other conductor is connected to the shank by a screw fitting into
the hole s. It will be seen that the tip is completely insulated
from the shank by means of the hard-rubber sleeve e. The fiber
sleeve g is provided to afford an insulated handle for the operator
to take hold of. At x and y are shown the spring contact and
the ring of the jack respectively, thus illustrating the condition
when the plug is introduced into the jack.
In Fig. 189 is shown a flexible cord, which, as has been
stated, forms part of the connecting circuit. It consists of two
strands a and b, each made up of many fine copper threads so as


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Fig. 191.
Fig. 192
to be very flexible. The straining cord is shown at g. They are
covered with two windings of cotton braid shown at c and d.
Over the two is wound a brass spiral e, which protects the strands
from mechanical injury, and yet retains the flexibility. Over
this spiral are wound three layers of heavy cotton braid shown at
f. One end of the cord is shown entered into the plug, which,
while it is of a somewhat different design from that shown in Fig.
188, yet retains the same essential features. The opposite end of
the cord is shown frayed out. In actual fact, each strand termi-
nates in some form of terminal to enable it to be readily connected
to and disconnected from the ends of the cord circuit wiring.
One method of terminating the strands is shown in Fig. 190.
It consists of soldering the ends of the two strands to two spirals
made of brass wire and shown at a and b; the soldering portions
being shown at m and o. These spiral springs are quite flexible,
and in addition form good electrical contact. The method of

188
TELEPHONY
177
using them is shown in Fig. 191, where a peculiarly shaped brass
punching shown at b is screwed to the upper surface of the board
c, called the cord shelf. To the short lug of this punching is
soldered the wire of the connecting circuit. The long lug is per-
forated by two holes through which is threaded the spiral, in the
manner shown at a. The two punchings forming the terminals of
the two sides of cord-circuit wiring are placed side by side on the
cord shelf as shown in Fig. 192, the long lugs being shown at a
and b, and the portions of the spirals threaded through the holes
at cc and d d.
189

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KELLOGG HARMONIC FOUR-PARTY SYSTEM.
TELEPHONY
PART IV.
TELEPHONE EXCHANGES. (Continued.)
Switchboard Cable and Switchboard Wire. It has already
been shown that the lines are brought from without to the main
distributing board either in lead-covered or braid-covered cables,
and that they are brought across to the switchboard side of this
piece of apparatus by cross-connecting wires.
All lines running from the main distributing board to the
switchboard, with the exception of those carrying the transmitter
battery current, ringing current, and whatever other comparatively
heavy current may be provided, are carried in what is known as a
switchboard cable. This cable is made up in various sizes, the
number of pairs of conductors varying with the work required.
For standard boards, the cable is made up of 20 pairs for working
purposes, and one or two extras called spare pairs, to be used in
the event of the failure of any of the regular pairs. The wire used
is No. 22 B. & S. gauge, tinned; the insulation consists of a layer
of silk thread wound over the wire, and a superimposed layer of
cotton thread. This insulation is technically known as double
silk and cotton. The pairs are bound together by two layers of
dry paper, over which is wrapped a layer of tin foil. The outside
cover consists of two layers of heavy cotton braid saturated with
powdered soapstone and painted. One conductor of each pair is
covered with colored cotton thread while its mate is white.
In all switchboard cables used by the Bell companies, and in
those used by the large independent companies, a system of color-
ing is maintained, to assist in distinguishing the pairs. The
arrangement of the colors is as follows: Blue, Orange, Green,
Brown, Drab or Slate, Blue and White threads mixed, Blue and
Orange mixed, Blue and Green, Blue and Brown, Blue and Slate,
Orange and White, Orange and Green, Orange and Brown, Orange

191
180
TELEPHONY
ot
a
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and Slate, Green and White, Green and Brown, Green and Slate,
Slate and White. The colors for the two extra, or spare, pairs are
usually Red and White, and Solid Red. These cables are oval in
cross-section, the longer diameter being about an inch, and the
shorter about 3 inch. In order to make the proper connections,
the cable must be fanned out or formed, as it is called, and before
this is done the location of the
lugs or terminals to which the
wires are to be attached must
be known.
In making a cable, the follow-
ing points of information should
be obtained, as shown in Fig.
193. The distance between the
highest and the lowest lugs; the
distance from the surface on
which the cable is to rest, to the
line of lugs farthest removed.
In the illustration, the first dis-
tance is that between the lines a
and b; and the second distance,
that between c and d. To the
sum of these two distances is
added two inches, which gives
the distance from the end of the
cable to which the lead and braid
6
covering is to be removed. This
distance is called the 6 skinning
Tape length”. This having been done
to expose the conductors, the
edge of the braid covering is
bound tightly with cotton tape as
Fig. 193
shown. This point is called the
butt of the form. The opposite end a is called the tip. Wire
nails about two inches in length are then driven into a board in a
line, with a spacing equal to that between consecutive lugs. The
nail heads should be allowed to project about one inch. The cable
is then laid down on the board, with the stripped portion against


Cotton
192
TELEPHONY
181
a
Х
the nails, the butt being one inch from the first nail. It is then
securely held in place by two or three leather strips placed over the
unstripped portion and fastened
with screws. There are two
ways of forming a cable—one is
6
to have the blue wire at the tip,
and the other is to have it at the
butt. This latter form is resorted
to only for special purposes.
Assuming the blue wire to
be at the butt, the blue wire with
its mate is drawn out, and bent
around the first nail, as shown at
No. 1, Fig. 194. The orange
wire with its mate is bent around
nail No. 2; green around No. 3;
brown around No. 4, etc., until
all wires have been so treated.
It should be noticed that if the
form is to be that shown in Fig.
193, and the spacing of the nails
equal to that between consecutive
lugs, as a d', the blue wire will be
Slate 5
bent around the first nail, and
the second around No. 2; the
orange wire around No. 3 and
Brown 44
its mate around No. 4, etc. The
Green
wires having been all thus treat-
ed, the wires are held in position
Orange 2
by a linen thread wound around
the cable to bind it at the points Blue & Mate î
where the wires bend at right
angles. For this purpose, the
best quality linen thread should
Fig. 194.
be used, and it should be thor-
oughly saturated with melted
crude beeswax before using.

3
2
193
182
TELEPHONY
In Fig. 195 are shown two methods of winding on this thread.
That at the top is the better for giving a binding hold. The form
having been thus securely bound together, a distance is measured
off along the wires from the line of nails at right angles to the
cable, equal to the distance from the surface on which the cable is
to rest to the line of lugs. In Fig. 194 this distance is shown be-
tween the lines a b, and at this point the insulation is cleaned off
each wire. In the case of the form shown in Fig. 193 two dis-
tances must be measured alternately, first to the farthest line of
lugs, and second, to the nearest line. The wire is cut off, one inch
from the point where the insulation ends, to allow for working.
The form is then saturated in melted wax, in the same manner as
that adopted in connection with paper cables. The form having
been saturated, it is given a coat of shellac and allowed to dry.
Fig. 195.
The cable is then ready for placing, and in so doing it is laid in
place and securely held by pieces of leather, such as is used for
belt lacing, placed around the form at intervals of about 15 inches
and held to the wood by screws. The wires are then drawn through
the holes in the lugs, bent over sharply, and soldered. When the
solder is cool, the free ends of the wires are cut off close to the
lug, and the job is finished.
In soldering, great care should be taken to have the soldering
iron thoroughly heated. It should then be placed on the lug at
the point where the wire passes through the hole, until the lug
itself becomes hot enough to make the solder run.
In making a form for the end of the cable that is to be con-
nected to the jacks, the same method is adopted. The nails are
driven in at intervals equal to the spacing of the jacks as they are
placed in the switchboard, and the pairs are formed together. In
wiring between the jacks and the drops, or between any two points
194
TELEPHONY
183
a
not far removed, it is often most economical and convenient to
make a cable out of switchboard wire. It is done as shown in Fig.
196. The wire used is No. 22 B. & S. gauge, double silk and
cotton insulation, two conductors twisted together to form a pair.
The two conductors are distinguished from one another by the
different coloring of the insulation. In making a form of this
kind, both ends must be done at the same time, and at each form
two rows of nails must be driven in. These two rows at one end
are denoted by the numbers 1 to 5, for the inner row, and 1' to 5,
for the outer. At the other end they are called by the numbers
1 to 51 for the inner and 11, to 54, for the outer. The distance be-
tween the two rows is one inch in excess of ab in Fig. 194. The

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end of the twisted pair is wound around nail No. 1', so as to be
held securely, and brought around No. 1, thence to No. 11 to 1',,
to No. 21, to No. 21, to No. 2, to No. 2, to No.3, to No. 3, to No.
3', to No. 3',, to No. 4',, to No. 4', to No. 4, to No. 4, to No. 51,
to No. 5, to No. 51, ending at No. 57. The form is then sewed
up in the manner already described, except that the sewing extends
the whole length of the cable. By cutting the wire between nails
2, and 3, 4, and 5,, 1, and 2, 3', and 4', there remains a made-
up cable having 5 pairs. A cable of this kind can be made with
a capacity of almost any number of pairs. It is seldom made,
however, with a capacity larger than 20 pairs. From this point
the treatment of the cable is identical with that already described.
Switchboard cables, or cables made up of switchboard wire,
should never be placed in damp places, or where water is liable to
195
184
TELEPHONY
Dannii ilit
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reach them. In small exchanges, the best method is to build a
false floor upon the real one; the false floor being of sufficient
height to accommodate beneath it all the cables necessary. Per-
haps a safer method is to construct a galvanized sheet-iron duct,
made water-tight and placed beneath the floor. This need not be
done, however, except when the exchange is damp, or where it is
impossible to construct a false floor.
In
Fig. 197 is shown the end elevation of a standard section
of switchboard. The framework
is made of mahogany, the height
over all being about 6 feet. The
portion of the framework en-
closed in the bracket a is called
the face of the board, and on it
are mounted the line drops i,
Hх
the clearing out drops 8, and
the jacks o.
Of the horizontal
n
portion that marked 6 is called
the plug shelf. It is about six
inches wide and covered with sole
W
2
leather, shown by the shaded
portion. It is drilled for two
inih
rows of holes through which the
cords pass, and against the edges
of which the plugs rest when the
cords are not in use. The two
plugs on the same end circuit are
placed on a line; the one nearest
the face of the board (usually re-
Fig. 197.
ferred to as the answering plug)
is for answering calls; the one farthest from the face (referred to
as the calling plug) is for calling subscribers. The answering
and calling plugs are placed on two lines parallel to the face of the
board. The cords are shown by dotted lines at g g' and hh'.
Each one passes through a pulley attached to a weight which
ensures the plug returning to its position on the plug shelf. The
two cord weights are shown at t and t'. The cords are shown
attached to their respective fasteners 1 and 2 placed on the cord

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i
6211
gig

196
TELEPHONY
185
shelf. These fasteners are placed in two rows parallel to the face
of the board, one row for the answering and the other for the
calling cords. The portion of the board d is called the keyboard,
from the fact that the listening and ringing keys are mounted
thereon. One listening key is shown at e, and a ringing key at f.
The listening key is placed directly in front of the pair of cords to
which it connects the operator's telephone circuit. The ringing
keys are placed, one just to the right and one just to the left of

Fig. 198.
the two plugs to whose circuit they are wired. The ringing keys
and the listening keys are each placed in a line parallel to the face
of the switchboard. The keyboard is hinged to the plug shelf at
n so that it can be raised to give access to the keys and wiring.
It closes down on a wooden trough w. The transmitter x is sus-
pended by the two transmitter cords which form the circuit, and
which are similar in construction to, but lighter than, the cords

197
186
TELEPHONY
00
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​月​月​月​月​月​月​月​月​月
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JAAA AAA
used on the connecting circuits. The cords run over two weighted
pulleys, one of which is shown at y.
Fig. 198 is the rear view of the same board. Near the bottom
is seen the cord shelf with the two rows of cord fasteners to which
the cords are attached. The cords
are also seen passing through the
cord shelf from below. Some of
them are knotted—a practice
resorted to when the cord is too
long to keep the weights from
striking against the floor when
the plug falls into its seat on
the plug shelf.
A short distance above the
cord shelf is seen the hard-rub-
ber jack panel. This panel is
drilled for 120 jacks, but is
equipped with only 80. The
bottom row of vacant holes can
be seen. The switchboard cables
carrying the lines rise on the
right-hand side of the board,
and bend horizontally to take the
jacks. The forms and the sew-
ing are shown. The clearing-
out drops are in a row just above
the line jacks. These are 12 in
ÜÜD
number. The line drops are
placed above the clearing-out
drops. The board has a capacity
of 10 rows of 10 drops each, 8
rows only having been placed.
Fig. 199.
The hand-made cable, rising
from the jacks to the line drops,
can be seen on the left-hand side. The cord circuit wiring from the
cord fasteners is placed on the under side of the cord shelf, and
is therefore invisible. The hand-made cable from the keys to the
clearing-out drops, rises in the forward corner of the left-hand side

17
198
TELEPHONY
187
Pe
of the board. In the upper left-hand corner is the operator's
-
induction coil, and the wiring to it is seen in the foreground on
the left-hand side. The transmitter cords are attached to binding
posts screwed to the roof of the
boards; and the transmitter
cords with their weights.
At the right-hand side of
the line-drop panel, and passing
down to the clearing-out drops,
is what is known as the night-
bell circuit. It is of compar-
atively heavy wire, and soldered
to lugs opposite each row of
drops. From these lugs the
circuits are continued to small
contacts placed on each drop
just beneath the shutter, so that
when a shutter falls this cir-
cuit is closed, and a buzzer,
which is wired in series, caused
to sound.
It should be observed that,
though the switchboard is only
partially equipped with jacks
and drops, wiring has been
placed for the accommodation
of the full number of circuits.
This is done as a measure of
economy; if an increase in the
equipment is desired at some
future time, all that is neces-
sary is to place the additional
jacks and drops and solder the
Fig. 200.
connections.
In Fig. 199 is shown a slightly modified form of this type of
board in which the full length of the framework is seen. In addi- .
tion to the apparatus already shown, the ringing current hand
generator is seen on the left-hand side. In Fig. 200 is shown the

199
188
TELEPHONY
same switchboard with the rear shutter in place. This shutter is
provided to keep out the dust.
The forms of switchboards already shown have a capacity of
100 lines. This number is about all that one operator can handle.
In fact, when the calling rate exceeds 4 calls per day per line, one
operator cannot successfully handle more than 80 lines. Therefore
when more than 80 to 100 lines have to be brought into a switch-
board, a new section must be placed beside the first, and the addi-
tional lines connected thereto. Under these conditions, should a a
call from a subscriber, whose line terminates on one section, be
received for a line which terminates on the other section, the opera-
tor can easily complete the connection by reaching across to the
required switchboard.
Office Trunks. When it becomes necessary to place a third
section of switchboard to handle the increased business, a new con-
dition presents itself. Calling the first or original section A, the
second B, and the one last installed C, it will be evident that the
operator at A, can make connections between lines whose jacks are
on the A and B sections respectively, but cannot complete a con-
nection between a line whose jack is on A section, and one whose
jack is on C section. The operator sitting at the B section can,
however, complete connections between any lines in her section,
and any other one in either A or C. The operator at the C section
is similarly situated to the one at the A section, and her work is
similarly limited. To sum up, each operator, in addition to being
able to complete connections between lines the terminals of which
are on the board before which she sits, is also able to complete
connections between lines, one of which has its terminal on her
section, and the other on an adjacent section. It must become
evident that some means must be provided for the operators to
complete connections between two lines, which under the present
conditions are not accessible. If, for example, the operator sitting
at the A section were provided with one or more circuits, running
between her section and C, then these circuits could be used to
establish connections between the two boards. This is the method
used in overcoming this difficulty.
As has been stated, trunk lines are those running between
two exchanges. It is necessary here to expand the term to include

200
TELEPHONY
189
lines joining non-adjacent sections of switchboard in the same
exchange. This class of trunk is referred to as office trunk or
stripping trunk. With the office trunk, the number of sections of
switchboard in an exchange can be increased indefinitely, as far as
the practicability of establishing connections is concerned. There
comes another limitation, however, which will be discussed later.
These office or stripping trunks, when they were first introduced,
were wired like a subscriber line, with a drop placed on each one
of the two sections that they connected, as shown in Fig. 201. A
trunk wired in this manner can be used for calls in both directions.
For example, should the operator at A receive a call for a sub-
scriber whose line terminates at C, she would introduce her calling
plug into the trunk jack, thereby cutting off the drop at that end,
and ring down the drop at C. The operator at C, upon plugging,
would cut off the drop at her end. The operator at A having in-

a

UTO
A
C
Fig. 201.
formed the one at C of the connection required, the latter, leaving
the answering plug in the trunk jack, introduces the plug of the
calling cord into the jack on the called subscriber's line and rings
in the usual manner. Upon the called subscriber answering, a
circuit is established through his line to the operator's cord circuit
at C, through this to the office trunk, thence through the cord cir-
cuit at A to the calling subscriber's line. Should the call originate
at C, for a line terminating at A, the same process is gone through,
but in the opposite direction.
In Fig. 202 is shown a complete connection established in
this manner. The details can be readily followed. It will be seen
that there are two clearing-out drops bridged across the circuit;
one at the A section, and the other at the B section. This condi-
tion is not desirable as it tends to cut down transmission, and
therefore attempts were made to change the wiring of the office
trunk. A further reason for desiring to make a change, was due

201
190
TELEPHONY
to the fact that the number of calls that can be handled on a trunk
of this type is limited; and therefore if the business is heavy, the
number of such circuits will necessarily be excessive. The change
adopted was to divide the number of such trunks in two, using one
half for handling calls from A to C, and the other half for calls
from C to A. The drops were removed and the incoming end
wired to cords and plugs. The drops being removed, it was neces-
sary to provide some other means of transmitting the information
concerning the call, from one operator to the other. To this end a
special circuit called an order circuit, order wire, or call circuit
was provided. Experience soon proved that it was advantageous

A
B
DO
LT
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mma
ima
Loule
Fig. 202.
to have two such circuits, one for transmitting information from
A to C, and the other for transmitting it from C to A. At the
sending end, the circuit is wired to a key, which acts in the same
manner as the listening key. The other end is wired directly to
the telephone circuit of the operator. Thus by depressing the key
at the sending end, the operator at that point puts herself into
direct communication with the operator at the distant point.
The trunks in each group are numbered from one up. At
the sending end these numbers are stamped in the hard rubber
beside the jack, and at the incoming end, they are stamped in the

202

DOOR
WWW
SWITCHBOARD OF AUTOMATIC EXCHANGE OF NORTHEASTERN TELEPHONE CO.,
PORTLAND, ME.
Automatic Electric Co.
TELEPHONY
191
leather of the plug shelf directly in front of the trunk plug. Sup-
pose that the operator at A has a call for a line terminating on C.
After answering the subscriber, she would depress the key of the
order wire and say to the operator at C, "give me 250”, that being
the number of the called subscriber's line. The operator on C
would answer, “Take it on 1”, 1 being the number on the trunk
,
assigned, and taking up the plug on trunk No. 1 would introduce
it into the jack of the called subscriber's line. The operator at A,
having received the assignment, introduces the plug of the calling
cord into the jack of trunk No. 1, thus completing the circuit.
Had the call come first to the operator at C, for a number on
a

А
С
sh
una
to telephone circuit
of operator at C.
4ool
Fig. 203.
the A section, she would depress her order-circuit key, connecting
herself with the operator's circuit at A and say: “Give me 15”, 15
being the number called for. The operator A would then answer,
“ Take it on No. 1", No. 1 being the number of the trunk assigned
and introduce the plug of that trunk into the called subscriber's
jack. The operator at C would then plug with the calling cord
into the jack on trunk No. 1, thus completing the circuit.
It must be remembered that the order circuit used by the
operator at A to transmit calls to C is separate and distinct from
that used by the operator at C to transmit to A. Also the set of
203
192
TELEPHONY
trunks used for completing connections from A to C is separate
and distinct from that used for completing connections from C
to A. The No. 1 referred to in the first case is therefore not iden-
tical with that referred to in the second.
In Fig. 203 is shown a connection established between a sub-
scriber's line on the A section and one on the C section. Here,
the trunk jack at A is wired without a drop, while at the C end,
the trunk ends in a cord and plug which is in the subscriber's
jack. The order circuit key is shown at b; the normal contacts
being bridged to the outer contacts of the listening key, while the
outer contacts are wired to the telephone circuit of the operator
at C. Upon the completion of the conversation on a connection
which is completed over a ring-down trunk, both the clearing-out
drop at A and C are thrown by the ring-off, so that both the opera-
tors receive the signal signifying that the connection is to be
taken down.
Where a circuit trunk is used, however, the operator at one
end only, receives the ring-off signal, and the operator on whose
section the trunk plug is situated receives no signal whatsoever
when the connection is thus taken down. In order to prevent the
trunk plug being left in the subscriber's jack, thereby preventing
the subscriber from calling central, and also keeping the trunk out
of service, the operator upon taking down the connection, goes in
on the order circuit again and orders the other operator to discon-
nect the trunk. This system can be readily extended to take in 4,
5, 6, 10, and more sections. When more than three sections exist,
each section is equipped with a group of trunks and an order
circuit to every other section except the adjacent one.
The number of sections that can be successfully handled with
the above mentioned system depends upon another point which
will be taken up directly. Reference to what has already been said,
and to the circuits will show that every time a connection is handled
over a trunk circuit, the work of two operators is required, which
necessarily takes up more time than would be necessary if the work
were done by one operator. When a connection is required be-
tween two lines whose jacks are within reach of one operator, the
time required is that of plugging into the calling jacks, ascertain-
ing the number desired, and then plugging into the jack on the

204
TELEPHONY
193
line called for, ringing the subscriber and waiting for him to
answer. When a call is trunked, the additional time taken is that
necessary to reach the second operator, and to get her to make the
assignment. If the second operator puts the trunk plug into the
jack of the line called for at the same time that the first operator
plugged into the trunk jack, no additional time would be taken up
beyond that already noted. In actual fact there is always a little
loss here, which further retards the completing of the connection.
Again, the fact that upon the completion of the conversation,
the trunk must be ordered to be cleared causes an additional delay.
The operator whose duty it is to order the trunk cleared, may at
that moment be busy attending to the wants of some other sub-
scribers, so that the trunk will remain idle, together with the sub-
scriber line into which it is plugged. All of which tends to slow
down the service. The result is that with this system an operator
cannot handle as many lines as would be possible, were the necessity
for trunking reduced to a minimum or eliminated altogether.
А
B
с
D
E
Fig. 204.
However, before this point is followed out in detail, it will be
well to consider the condition arising when an additional exchange
is opened. If a call from a subscriber in one of the exchanges is
sent for a subscriber in the other exchange, obviously, the connec-
tion must be completed over a trunk between the two switch-
boards. Since all operators are likely to have a connection of this
sort, the trunks between the two exchanges must be within the
reach of all the operators. A little thought will show that the
trunks between exchanges must be of the ring-down type, because
if they were of the circuit type, they could be used only on con-
nections that lay within reach of the section at which they termi-
nated in cords and plugs.
It might be urged that a group of trunks could be provided
for each non-adjacent section of switchboard at the other office.

205
194
TELEPHONY
This, however, would be too wasteful of trunks. It is advisable
to divide the ring-down trunks into two groups: one for sending
calls from one exchange to the other, and the other for sending
them in the reverse direction. Each group of trunks should, at
the sending end, be placed within reach of every operator and this
is done by wiring them to jacks placed in every
alternate section
as shown in Fig. 204, where the straight lines placed above the
letters A, B, C, etc., denote the sections of switchboard. Two
trunks will be seen wired to jacks placed at A, C, and E. The
operator at B can reach the trunk jacks at A or C, and the one at
D, can reach those at C or E, so that they are within reach of
every operator in the office.
At the incoming end, each trunk terminates in a jack and

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HC
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E
Holulu
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​Fig. 205.

drop, and these jacks with their accompanying drops are distributed
evenly among the sections. The calls handled over these trunks,
are dealt with in the same manner as described in connection with
office trunks. Let an extreme case be taken. Suppose that a call
originates in one office which shall be designated by No. 1 for a
connection with a subscriber's line terminating in another exchange
known as No. 2, the method of completing it is shown in the
following figure.
In Fig. 205 is shown a connection established over a ring-
down trunk between the two exchanges. The portion on the left-
hand side of the dotted line represents 'one exchange, No. 1, and
a
206
TELEPHONY
195
that on the right-hand side the other exchange, or No. 2. Assum-
ing that the call originates in exchange No. 1, the call is answered
in the usual manner, and the operator at No. 1 upon learning what
is required, plugs with the calling cord into trunk jack a, placed
on or adjacent to the section at which she is sitting. The jacks
denoted by b and c represent those on the same trunks placed on
the other section of the same exchange, as already described. This
trunk being rung on, the drop e at exchange No. 2 falls, and the
,
operator sitting at the section upon which it is placed answers.
Unless the number called for happens to be on the same section as
the trunk jack and drop, this latter operator must make use of an
office trunk to complete the connection. This is the condition
shown in the figure, where f denotes the office trunk jack and g
the plug of this trunk introduced into the subscriber jack.
In putting through this connection, the order must be sent,
first from the operator at exchange No. 1 to the operator at No. 2
who answers the trunk. Second, from this operator to the other
one in the same exchange who has access to the called subscriber's
jack. This process entails a loss of time and slows down the
service. Again, the condition of two clearing-out drops being
bridged across the circuit is met with.
Subdivided Multiple. To do away with the necessity for re-
peating the call to a third operator, and also cutting out one clear-
ing-out drop, a scheme was devised which is called a subdivided
multiple. Some one section, usually one of the two end sections,
is set aside for a trunk section, and on it are placed a sufficient
number of jacks to have one connected to every line entering the
exchange. When a trunk is called for from some other exchange,
this operator answers it, and having the terminals of all the lines
in the exchange within reach, is able to complete the connection
herself. This was the first step towards the introduction of a full
multiple switchboard.
Multiple Switchboard.
The full multiple switchboard, or
multiple switchboard as it is more commonly called, does away
altogether with the use of the office trunks, and when the business
is heavy enough it is the most economical system. For example,
suppose that there are 1,000 lines to be handled in an exchange,
and one operator is able to handle 100 only. With the standard
a

207
196
TELEPHONY
system 10 sections and 10 operators would be required. If a
multiple switchboard be substituted, the time saved in doing away
with the use of the stripping trunk will be sufficient to enable each
operator to handle maybe 200 lines, thus cutting down the num-
ber of operators necessary to handle the business by one half.
The principle of the multiple switchboard is as follows: Each
line is wired to a jack and drop, placed on the section at which the
operator sits whose duty it is to answer calls. This jack is called
the answering jack. In addition to this jack, there appears in
each section one additional jack, wired to this line. These latter
are called multiple jacks, and are used by the operators in calling
subscribers.
Multiple switchboards are divided into two classes: Series
and Bridging, Series and Switchboard. In the former, the line
runs through the multiple and answering jacks in series. In Fig.

2
3
5
own
H
率​。
Fig. 206.
206 is shown a subscriber's line multipled through a series board.
The sections are denoted by the numbers 1, 2, 3, 4, etc., and are
separated from one another by the dash lines. The multiple jacks
are shown at a, b, c, d, and e, one in each section; and the answering
jack and drop are shown at f and g respectively. They are placed
on the fifth section. It will be observed that the jack is of the
same type as that already shown. One side of the line is wired
through the contact spring and the contact point of each jack in
series, so that when a plug is introduced into any one of the jacks,
the drop is cut off. Hence the name series. The two sides of the
main distributing board are shown at o and m.
In Fig. 207 is shown a connection established between two
lines a and b, both of which are multipled in sections 1, 2, 3, 4,
and 5. The multiple jacks of the line a are shown at j, k, l, m,
208
TELEPHONY
197
and n, and the answering jack and drop, at o and p respectively,
on the “5” section. The multiple jacks on the line b are shown

b
Z
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no
nde
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Fig. 207.
N
P 4
no
no
ho
nos
3
at c, d, e, f, and g, with the answering jack and drop at h and i
respectively, on the first section. The subscriber on line a has
209
198
TELEPHONY
called and was answered by the operator at the “5” section by
introducing the answering plug into the answering jack o, thereby
cutting off the dropp. The subscriber on the line b was called by
the operator pushing the calling plug into the multiple jack g,
thereby cutting off the drop i, and ringing. Had the call come in
the reverse direction, that is, had the party on line b called, the
operator at section No. 1 would have answered by pushing her
answering plug into the answering jack h, and calling the sub-
scriber on line a by going in with the calling plug at the multiple
jack ;, thereby cutting off the drop p.
It must be remembered that there may be anywhere from
1,000 to 8,000 lines in the switchboard, all wired as those shown
at a and b. It will be evident that with this system, connections
can be established and cleared in much less time than where a
second operator is necessary. Furthermore, the service receives an
additional impetus from the fact that the operators being relieved
of the necessity of making trunked connections, have nothing else
to do but to attend to the wants of the subscribers whose answer-
ing jacks are placed before them.
One feature, however, of this system is absent from the stand-
ard board. Take the case shown in Fig. 207. Suppose that, while
the conversation is going on between the two parties on the lines
a and b, a call comes in for either one of them from a line x whose
answering jack is situated on section 3.
Now the operator at
section 3 not being able to see section 5, and not having the time
to look, if she were able to see, would complete the connection by
plugging into the jack l or e as the case might be, thus connecting
x with the two parties who are already talking. This condition
would, of course, be very undesirable.
Το prevent this, some form of signal must be given to the
other operators that these two lines are in use. The signal used
in this work is called the busy test and is established in the follow-
ing manner: First consider the operator's cord circuit shown at
section 5. It consists of the two plugs and cords, the two ringing
and one listening keys, and the clearing-out drop; but the wiring
is different from anything yet seen.
The shanks of the plugs are
connected through the middle and inner contacts on one side of
each of the two ringing keys r and r'. The listening key t is of
a

210
TELEPHONY
199
special design and is equipped with a special spring 1, which, when
in the position shown, makes connection with an inner contact
point. This spring, although insulated from 2 and 3, is mechanic-
ally connected to them, so that when the key is depressed the con-
tact is broken. Following the cord circuit from the tip of one plug
to that of the other, it will be seen that after passing through the
opposite side of the ringing key r it passes to the spring No. 1 of
the listening key. Suppose this key depressed and the contacts at
1, 2, and 3 broken in consequence, and that between 3 and 4 made.
The spring 1 being wired, or strapped, to the spring 4, the circuit
therefore follows this path to the spring 3, thence to the point 7,
from whence it passes through the ringing key r to the tip of the
plug at o. The clearing out drop is bridged across this circuit
at 8 and 7.
Suppose now the operator, in order to listen, adjusts her key
as shown in the figure. The connection between 3 and 4 is broken
and those between 3 and 6; 2 and 5, and 1 and 9 are made. Fol.
lowing the circuit now from the shank of the plug to the point 8,
it runs from there through the contacts 1 and 5 to one-half w' of
the secondary coil winding. Thence through the operator's re-
ceiver u to the other half w of the winding, to the condenser x, to
the contacts 9 and 1, and back to the tip of the plug. A bridge
is formed through the condenser x, and the contacts 6 and 3, the
point 7 to the tip of the plug at o. Returning from the shank,
the bridge is completed at 8. Thus the operator's circuit is bridged
to both subscribers.
The coil of the operator's receiver is split, the middle point
being carried to ground at q. Wired to the shank of each plug is
a battery-one shown at 2 and the other at z', the circuits passing
through a retardation coil, one of which is shown at v and the
other at v'. When a plug is introduced into a jack, this battery
is thrown on the rings of all the jacks on that line.
Under the condition shown in Fig. 207, the potential of the
battery 2 would be thrown on the rings of the jacks o, n, m, 1, k,
and j; and that of the battery z', on the rings of the jacks g, f, e, d, c,
and h. The retardation coils r and peach consist of an electro-
magnet with a soft-iron core, the coils having a resistance of 600
ohms. Their action is to retard or choke off the talking current,

a
211
200
TELEPHONY
a
to
so that transmission will not be reduced or the line made noisy,
while the direct current from the battery is allowed to flow when-
ever a path is offered. Remembering that every operator is
equipped with cord circuits identical to that shown, suppose that
the operator at section 2, for example, receives a call for the line a.
By touching the tip of the calling plug to the ring of the jack, k,
the following path will be afforded the current, which will be traced
out on the cord circuit shown to save confusion by drawing another
cord circuit on section 2. From the ring of the jack to the tip of
the plug, thence through the ringing key to the spring 1, thence
to 9, to the opposite side of the condenser x, through w to the
receiver u. Passing through one-half of the coil on u it goes
ground at q. Every time the tip of the plug is touched to the
ring of the jack, a rush of current flows to ground through this
circuit causing a “click” in the operator's receiver. The pres-
“
ence of this click informs the operator that the line is busy.
The connection being taken down, the battery potential is
moved from the rings of the jacks, so that upon an operator touching
the tip of a calling plug to any of them, no current flows through her
receiver to ground, and consequently no “click” is heard.
The condenser x, which has a capacity of 2 M.F., is needed
for the following reason: When the operator tests for a busy
line, the answering plug is always in some answering jack. There-
fore when the tip of the calling plug is touched to the ring of the
jack called for, the current would flow down to the condenser x,
as described, and wanting its presence, some of it would pass
through the listening key, out on the line of the party calling.
This would result in the subscriber getting an unpleasant noise in
his ear, and in reducing the strength of the busy test by shunting
too much current.
The great disadvantage of the series multiple switchboard lies
in the fact that on one side of the line there is a series contact at
each jack, and the number of such contacts increases with the
number of sections. In the series switchboard in use a short
while
ago at the Courtland St. exchange in New York, there were
44 sections, and consequently 44 series contacts on one side of
each line. The smallest amount of dust settling on these contacts
gives them an appreciable resistance, which increases with the
212
TELEPHONY
201
number of jacks, and this resistance is all thrown in on one side
of the line. The result is that the line becomes unbalanced and
noisy. Furthermore, if the dust deposit is the least bit exagger-
ated, as for example from sweeping the floor carelessly, the resist-
ance at the contacts often becomes so high as to render conversation
impossible. A practical example will illustrate: In the Courtland
St. exchange above referred to, the resistance between the first and
the 44th section of that side of the line which passed through the jack
contacts, was normally 13 ohms. At times it went as high as 50
ohms, and even to an open circuit. To overcome this defect, the
idea was conceived of bridging the multiple and answering jacks
across the line, and this gave use to the bridging multiple board.
Bridging Switchboard. In Fig. 208 is shown the wiring of
a subscriber line passing through a bridging board. As before,
the main distributing board is seen at a. At b is a new piece of

11 12
1 ² 3
re
vi
Sm
n
T
m
1
//
IV
V
Fig. 208.
apparatus which came into use in connection with this type of
switchboard, although it is also used with the series board. It is
called the intermediate distributing board and its use will be
described directly. There are five sections of switchboard denoted
by the Roman numerals, and in each one is shown a multiple jack
bridged to the line. This jack is of a different design from that
previously shown. Referring to the one shown in section I, it will
be seen to be made up of three springs and two rings. The
springs are shown at c, d, and d', and the two rings at e and f.
The spring c forms one of the contacts of the talking circuit, the
other contact being the ring e. A battery n grounded at m is con-
nected to the spring d' on all the jacks; while the spring d is
strapped to the outer ring f, and is connected to a third wire which,
e.
213
202
TELEPHONY
с
-e
for the multiple jacks, runs to the contact 3 on the intermediate
distributing board, and for the answering jack g which is shown
on the third section it is run to the contact 3'. The contacts 3
and 3', 2 and 2', and 1 and 1' are cross-connected as shown. The
drop is shown at h, and is of a special design introduced with this
type of switchboard.
The drops shown in connection with the standard and series
multiple boards, are so constructed that the shutters, upon being
rung down, must be restored by hand. This work naturally takes
up a large percentage of the operator's time and also necessitates
the placing of the drops in such a manner that they shall be within
easy reach. In the design of the drop used in connection with
bridging boards two points are brought out:
First, the drop being permanently bridged across the line, like the
clearing-out drop, must be of high
impedance and proof against cross
d
9 talk. To this end it is wound to a
resistance of 600 ohms and is in-
cased in an iron shell.
Second, the drop must be so con-
structed that it will be restored by
the introducing of the plug of the
Fig. 209.
operator's cord circuit either into the
multiple or the answering jacks.
To accomplish this, a second coil is wound around the surface
of a second core, which, when energized, attracts the armature,
which acts as the drop back to its original position. In Fig. 209
is shown this style of drop in section. The cores are shown at a
and d' and are of the usual form, covered with the insulating
material b. The line coil or that which is bridged to the line, and
operates to throw the drop, is shown at c. The armature actuated
by this coil is shown at f, and is pivoted at the top in the usual
Attached to this is the stiff wire with the catch
g.
The
second armature, which acts as the drop, is shown at e, and is piv-
oted at the bottom.
A stop is provided so that it cannot fall
through a greater angle than that shown. The second, or restoring
coil, is shown at d, it being separated from the line coil by a par-
tition. It is wound to have a resistance of about 50 ohms. Both
the armatures e and f have a hollow depression in the center into
which fits the end of the core, when they are drawn close up

manner.
214
TELEPHONY
203
against the magnets. The catch is of a peculiar design, having a
notch into which fits the upper edge of the armature e when the
latter is restored. The smaller projection in the rear of the notch
keeps the armature from being attracted any nearer to the core,
which would result in its failing to fall by gravity when released.
The terminals of the two coils are brought out through holes f in
the armature.
Fig. 210 shows the general appearance of the drop. Here
the armature f is shown in the foreground, with the four hard-
rubber-bushed holes for the coil terminals. Terminals Nos. 1 and
2 are for the line coil and Nos. 3 and 4 for the restoring coil. The
other armature or drop is shown at e. The line number is painted
on this armature, and an aluminum shutter corresponding in size
normally covers it. When the drop is rung down, this shutter
swings up exposing the number, and falls into place again when
the drop is restored. The drop
is mounted on the plate X, which
separates the two halves. Since
these drops need not be placed
within reach of the operator they
are mounted over the multiple
jacks. Turning again to Fig. 208
it will be seen that the section of
the drop enclosing the line coil is
shown at i, while that enclosing
Fig. 210.
the restoring coil is shown at 0.
Before going into the details of the design of the operator's
cord circuits let us consider what would be the effect of introducing
the plug into a jack after the drop has been rung down. Let the
jack on section I be considered. Plugging into the jack, the tip,
to which is connected one side of the talking circuit, makes contact
with the spring c. The other side of the talking circuit is con-
nected to the shank of the plug, and makes contact with the ring
of the jack e.
The shank is protected with a hard-rubber collar,
so that it will not make contact with the outer ring f. The plug
is so constructed that, when in place, a brass ring makes contact
between the springs d and d', closing the circuit and allowing cur-
rent from the battery n to flow from one to the other. When this

X
2
3
4
215
204
TELEPHONY
happens, the potential of the battery is thrown on the outer rings
of all the jacks for the busy test, and also from the answering jack
through the restoring coil of the drop to ground, thus restoring the
drop. Analysis of the circuit will show that this action will take
place, no matter in what jack the plug is placed.
In Fig. 211 is shown the detail of the wiring of the operator's
cord circuit. The tip of the plug is shown at a. The brass ring
to which no wire is connected, but which serves to close the con-

a
b
offe
9
ch
EK
helen
Fig. 211.
nection between the two jack springs, is seen at b. The shank of
the plug is shown at c and the two hard-rubber rings insulating a
from b and from c, at f and e respectively. At d is seen the
,
hard-rubber collar insulating the shank from the outer ring of the
jack. Both plugs are identical. The listening key is shown at g
and is of peculiar design; it consists of four springs 6, 5, 2, and 7.
The springs 2 and 7 are electrically insulated, but mechanically
connected by the hard-rubber block h. There are three contact

216
TELEPHONY
205
points 1, 3, and 4. The springs 5 and 7 are bridged across the
cord and the contact points 3 and 4 are connected to the operator's
telephone circuit. One terminal of the line coil of the clearing-
out drop, shown at i is connected to 6, while the other terminal is
connected to 7. One terminal of the restoring coil j is connected
to the spring 2, while the other terminal is grounded at l.
Grounded battery K, is connected to the contact point 1.
In the position shown, the operator is able to listen in. Sup-
pose the key depressed, so that contact with the points 1, 3, and 4
is broken, and contact made between the springs 5 and 6. The
line coil of the clearing-out drop is now bridged across the cord.
When, upon completion of the conversation it is rung down, the
operator adjusts her key as shown, opening one side of the line
coil, cutting in her telephone set, and by closing the contact be-
tween the point 1 and the spring 2, throws the current from the
battery K through the restoring coil j. The clearing-out drop is
identical with the line drop in design and construction.
The system just described is an improvement over the series
switchboard, because it is perfectly balanced throughout, and the
drops are self restoring. It gives excellent satisfaction for local
work. The fact that the two line drops and the clearing-out drop
are bridged across the line during conversation, tends to reduce the
efficiency of transmission. On very long lines this reduction would
be serious, and therefore the Long Distance Company cut the drop
off by a special form of wiring which will be described later.
Intermediate Distributing Board. It has already been said
that the introduction of the bridging board brought into use the
intermediate distributing board. It must be remembered that all
lines entering a switchboard, are not equally busy. It may happen
that the operators on section I find that the lines assigned to them
are so busy that the calls can be handled with difficulty, if at all,
while those assigned to the operators at section IV are not busy
enough to make the operators work up to their full capacity. A
remedy that suggests itself as obvious, would be to transfer some
of the answering jack circuits from section I to section IV. It
must be remembered that in making this transfer, the call number
cannot be changed, so that it cannot be made at the main dis-
tributing board. What is wanted is to connect that row of multi-
217
206
TELEPHONY
ple jacks to an answering jack and drop placed on section IV. At
the intermediate distributing board this change can be readily made
by cross-connecting the given multiple wiring to an answering
jack and drop placed on the required section.
The intermediate distributing board has also another use.
Though the growth of the telephone business is steady, subscribers
often give up service from one cause or another. From an oper-
ating standpoint, it is not good practice to use the call number of
the disconnected line for a new subscriber within three months of
the date of disconnection. A new connection being established, it
is cross-connected to a new set of multiple jacks, but by means of
the intermediate board, the old answering jack can be used, and
this particular operator retain the same number of lines to handle
as she had originally.
In designing, the intermediate frame resembles the main dis-
tributing frame, the difference being that no protecting apparatus
is used. The multiple-jack wiring is connected to the horizontal
side, while the answering-jack wiring is connected to the vertical
side. The cross-connecting wire used is triple-conductor twisted
wire, two conductors for the talking circuit, and the third for the
busy test and restoring battery.

TRUNKING.
The subject of trunking has already been touched on in con-
nection with standard and subdivided multiple boards. It will
now be desirable, in connection with full multiple switch boards, to
go into the subject rather more in detail. In connection with
ring-down trunks nothing additional need be said, as the multiple
switchboard introduces no new features, so that the discussion
will be given up entirely to circuit trunks. The following points
are essential:
In operating with circuit trunks the following events occur in order:
The subscriber operator having received a request for a connection neces-
sitating the use of a trunk to a distant exchange, puts herself in communi-
cation with the trunk operator at the distant exchange by means of the
order circuit, and requests the desired connection; or, to use technical lan-
guage, passes the call. The trunk operator, having received the call, as-
signs the trunk to be used and after testing the subscriber line called for
and finding it not in use, plugs into it with the trunk plug. This interval
is called that required to put up the connection.

218

EZE
MONARCH
TELE
3189
MEMARCHEZ MEG.CO
TELEPHO CESAROUSA
BRIDGING
COMPACT TYPE TELEPHONE -SERIES AND
Monarch Telephone Mfg. Co.
TELEPHONY
207
Upon the completion of the conversation, the subscriber operator at
the first exchange withdraws the plug from the answering jack, and again
going in on the order circuit orders the trunk operator at the distant ex-
change to withdraw the trunk plug from the called subscriber's multiple
jack or to clear the trunk as it is called. The trunk operator thereupon
does as directed. The interval from the time that the conversation is fin-
ished and the ring-off signal given, up to the time that the trunk is cleared,
is called the time required to clear the connection. The first interval is
shorter than the second and is almost a minimum; there is no possible
way in which its length can be materially reduced.
The history of trunk development is connected with the de-
velopment of the switchboard, so that the trunks first considered
will be those between two exchanges equipped with series boards.
In order that the trunk operator may have no other class of
business to handle, the trunk plugs are placed together at one end
of the switchboard. The number of sections thus occupied will
depend altogether on the number of trunks handled. In Fig. 212
B
w

A
t
[os
UN
wody
AD>
un
Yr I
5
K'
Ki
42
rapport rap rap rap
0
b
с
e
Fig. 212.
is shown the wiring of a circuit trunk between two series switch-
boards. One exchange is shown at B and the other at A. The
multiple jacks are shown at 1, 2, 3, 4, and 5; one jack within
reach of each operator. The trunk jacks are placed in a group
separate from those on the subscriber lines, and are called the out-
going trunk multiple. In general, trunks used for completing
connections from an exchange B to another exchange A are called,
with reference to B, outgoing or sending trunks; while those used
for completing connections from another exchange are called in-
coming trunks. Thus the trunk shown in Fig. 212 with reference
to B is an outgoing trunk, and with reference to A, an incoming
trunk. The plug in which the trunk ends at the incoming ex-
tremity is shown at f and is of the same type as that used on the
subscriber's cord circuit. Ats and p are shown the secondary and

219
208
TELEPHONY
primary windings of the trunk operator's induction coil, while the
head telephone is seen at t, one terminal of the coil being grounded
at g. For the opposite terminal of the receiver, runs a single con-
ductor cord which terminates in a plug i. The order wire is a
grounded circuit running from the trunk operator's head receiver
to one of the outer springs on each one of the order wire keys K,
K', K", etc. The other outside spring of these keys is grounded;
the two inner springs of each key are wired to the subscriber oper-
ator's telephone circuit as shown in Fig. 203, and at a, b, c, etc., in
Fig. 212. The order wire is thus a grounded circuit.
It should be observed at the outset that the trunk operator
cannot communicate to the subscriber operator, unless the latter
has his key depressed. Suppose a call comes in at the exchange
B for a party whose line terminates at A, and that it is answered
by the operator stationed at the jack 5. This operator after learn-
ing the subscriber's wish depresses the order key K" and trans-
mits the call to the trunk operator at A. Before the latter puts
up the connection, she must ascertain whether or not the sub-
scriber line called for is busy. To do so she touches the ring of his
multiple jack with the tip of the single plug i. As she does this
she calls back to the subscriber operator at B the number of the
trunk that she is going to use, the latter operator waiting with the
key depressed for the receipt of this information.
Assuming that the line called for is not busy, the trunk oper-
ator plugs into it, and the subscriber operator at B rings. As has
already been stated, the trunk operator is altogether unable to listen
in on the connection, and must depend on the order coming over
the order circuit as to when the trunk shall be cleared. The con-
versation being completed, and the ring-off being received by the
subscriber operator, she again goes in on the order circuit and
directs the trunk operator to clear the trunk.
While this method seems very simple, and while it seems
that the trunk operator should be just as diligent in clearing con-
nections as she is putting them up, such is not the case. It must
be remembered that at the instant when the subscriber operator
comes in to order down a connection, another may come in to
order one up. In fact, two or more operators may order up con-
nections at the same instant. In such a case, the trunk operator

220
TELEPHONY
209
will always pay more attention to orders to make connections than
to those to clear. So that the trunk operator often puts off clearing a
connection until she has forgotten about it. In the meantime, the
subscriber operator at B, has cleared that end of the connection so
that the called for subscriber is left connected to the trunk without
any means of signaling either one of the exchanges.
This condition has two results: First, the called subscriber
cannot signal the exchange to get a connection, and, second, no-
body can call him because the trunk plug being in his jack, his
line will be reported busy. All this necessitates a second request
from the subscriber operator to clear the trunk, which multiplies
the work done over the order wire, which tends to confuse the trunk
operator and delay her work.
It was found also that a grounded order wire was liable to
become noisy, causing the transmission to become poor, and neces-
a

S
K
K
"
I op lot lop) (fp) Lip
In
Color
Fig. 213.
sitating the repetition of orders over it, to the further detriment of
the service. Two changes were made in the wiring, which are
shown in Fig. 213. The first was to use a metallic order circuit
as shown, the busy test being obtained for the trunk operator
through her split receiver to ground at g. The second change con-
sisted of wiring a drop a to the trunk at the outgoing end. This
was called the safety drop, and its use was calculated to prevent
the called subscriber from being “hung up” on the trunk, by
affording him a means of signaling in. This drop was wired in
the usual manner, so that when the outgoing end of the trunk was
taken up it was cut off.
The method of the operation was as follows: The subscribers
having rung off and the connection having been cleared at the out-
going office, if the trunk operator fails to clear the connection, the
221
210
TELEPHONY
called subscriber, upon ringing, will throw the safety drop, thereby
attracting an operator's attention. This operator will plug into
the trunk jack, learn the subscriber's wish, and going in on the
order circuit again, order the trunk operator to clear the connection.
While the scheme prevented the called subscriber from being
indefinitely hung up, it did not reduce the work over the order cir-
cuit, nor help out the trunk operator. To this latter end, a prac-
tice was introduced about this time called testing down. It
worked as follows: Inspection of the operator cord circuit shown
in Fig. 207 reveals the fact that there is a battery on the shank of
both plugs. Now when one of these plugs is placed into the trunk
jack, this battery being thrown on the ring, current flows along one
side of the trunk to the shank of the plug at the other office.
Therefore, if the trunk operator touches the shank of the plug with
qoz

100
3
Typy lyp lap lap lap
(
bolum
2
3
4
Too
d
Fig. 214.
the test plug i, a click will be heard in her receiver, due to this
current flowing to ground through the split receiver. This “test”
will be heard so long as the subscriber operator has a plug in the
trunk jack. Upon her clearing the connection, however, the cur-
rent will be received and the test will disappear.
To facilitate the clearing of trunk connections, the trunk
operator was required to touch, from time to time, the shanks of
the trunk plugs upon connections, with the test plug, and to clear
all that did not give the test. It being assumed that if the sub-
222
TELEPHONY
211
scriber operator had removed her plug, that the conversation was
completed. While this scheme, together with the safety drop,
reduced the chances of a subscriber being hung up, and therefore
increased the efficiency of the trunks, it did not lessen the work of
the trunk operator. In fact, it increased it, as she was compelled
to be continually, when not otherwise occupied, reaching over the
face of the board to test the trunk plugs. To overcome this diffi-
culty, test buttons were introduced. These consisted of brass but-
tons about the size of a copper cent, placed on the plug shelf, each
one directly in front of the plug to which it is wired. One of these
is shown at a, Fig. 214. To test down, the operator need only touch
these buttons, which saved her the time and trouble of reaching all
through the multiple, wherever the plugs happened to be.

o
ALU
10
Y
Gps GP
lyps lips
fotolar
Fig. 215.
So far, the condition of the called-for subscriber's line being
busy has not been considered. With the circuits heretofore de-
scribed, if this condition obtained, the trunk operator would have
to wait till the subscriber operator again came in on the circuit
before she could be informed of the fact. To save this delay, the
busy-back was devised. It consists of a series of jacks placed
within reach of all trunk operators, and shown at 1, 2, 3, and 4.
To these jacks is wired a small alternating-current machine shown
at d, giving a potential of 75 volts and having two lamps 6 and c
in series, to reduce the current to the proper amount. If the
trunk operator finds the line called for to be busy, she plugs the
trunk into the nearest of the busy-back jacks. The subscriber
operator plugging into the trunks, hears the hum of the alternator,
and knowing what is meant, reports busy to the calling subscriber.
In order to test the subscriber's lines, the trunk operator had
to make use of a third plug as has been shown. Now, the trunk

223
212
TELEPHONY
operator is often busy with both hands, so that to carry a test plug
was a source of great inconvenience, and a material hindrance to
her work. To overcome this defect, the trunks were so wired that
the testing could be done with the trunk plug, as shown in Fig.
215. The tip side of the trunk plug is wired to the middle spring
of a key a. The same side of the trunk, coming from the other
exchange, is connected to the outer spring 3 of the same key, and
the inner contact point 2, to the operator's induction coil. With
the key in the position shown, the test can be obtained through the
tip of the plug. When the plug is placed in the jack, the key is
depressed, cutting off the circuit through the operator's receiver,
and closing the trunk through the springs 1 and 3 of the key.
This circuit represents the highest development of trunking
between series switch boards.
SoQ
ਉੱਥੇ ਹੀ

bart
nh
Typ lap laptop
meg
Fig. 216.
With the introduction of the bridging board, there came a
necessary change in the wiring of the trunks. Fig. 216 shows the
earliest form of trunk used with this system. It is wired at the
outgoing end in the same manner as the subscriber line, the safety
drop 6 taking the place of the line drop. This drop is slightly
different in action from that used with the series board. Here,
when the subscriber operator plugs into the trunk, current is sent
through the restoring coil and the drop is sealed. Upon being
cleared at the sending end, however, this current is removed, and
the drop is free to be rung down. With this system, since no
224
TELEPHONY
213
battery is connected to the shank of the subscriber operator's cord
circuits, the scheme of testing down cannot be resorted to. It will
be observed that a ringing key a is wired to the trunk cord, to
enable the trunk operator to
ring the called subscriber.
006
In order to do away with
the necessity of ordering the
trunk to be cleared over the
order wire, upon completion of
the conversation, a scheme was
brought out in connection with
this form of trunk.
It con-
sisted of a disconnect signal,
placed at the incoming end,
and so wired that it would give
notice to the trunk operator
automatically, upon the con-
nection being taken down by
the subscriber operator.
The wiring of this signal,
as first introduced, is shown in
Fig. 217. Here, the springs
on the opposite side of the test-
ing key are used. The outer,
No. 2, is wired to one side of
the trunk, while the middle
one, No.1, is wired to one ter-
minal of the coil of a relay,
shown at a, the other terminal
being permanently connected
to the opposite side of the line.
This relay consists of an elec-
tromagnet of high impedance, ob
,
with a pivoted armature c,
which, when the relay is ener-
gized, is drawn up against a contact point d. Since this relay is
permanently bridged across the trunk, and since several are likely
to be mounted together, each one is encased in an iron shell to

Fig. 217.
To Operator
Split Receiver
225
214
TELEPHONY
prevent cross talk. Wired to the armature of this relay is a bat-
tery, and to the contact point is connected a small lamp b, the other
terminal of which is grounded. At the outgoing end is another
relay e, which is similar in construction to the restoring end of a
bridging drop. The armature f, to which is connected one ter-
minal of a small 20-volt direct-current generator h, rests normally
against the contact point g, which is permanently connected to one
side of the line.
The method of using this trunk is as follows: When the
trunk operator plugs into the subscriber jack, and adjusts the key
to cut off the test, the relay a is bridged across the line through
the springs 1 and 2. The current from the direct-current machine
h flows out over the trunk, through the armature f and the con-
tact g, and energizes the relay a. Its armature c, being drawn up
9
against the contact d, closes the battery circuit through the lamp,
with the result that it is illuminated.
Upon the subscriber operator plugging into the trunk jack,
current is sent through the relay e and as a result the armature is
from the contact g, cutting off the current from the
machine h. This current failing, a ceases to be energized, its
armature c falls away from the contact d, and the lamp 6 is ex-
tinguished. At the completion of the conversation, the subscriber
operator removes the plug from the trunk jack, with the result
that current is cut off from the relay e, whose armature therefore
falls against g, thereby again cutting the current from h on the
trunk. The relay a, therefore, again becomes energized, the lamp
circuit closed, and the lamp lighted. The trunk operator, upon
seeing the illumination, instantly clears the trunk without waiting
for further orders.
This device is by far the most useful ever invented for expe-
diting the work of the trunk operator. By doing away with the
necessity of ordering down connections, half the business was
removed from the order wires, so that orders for connections could
be transmitted with much greater dispatch and clearness, and the
trunk operators having only orders to establish connections trans-
mitted to them could listen with undivided attention, and therefore
do better work.
drawn away

226
TELEPHONY
215
One more change was necessary to bring the trunk up
to
per-
fection, as far as it could be obtained with the bridging-board
system, and that was to save the trunk operator the time taken to
adjust the testing key. This was accomplished by placing a relay
on the trunk, the contacts of which would do automatically what
those of the manual key did. The wiring of this trunk is shown
in Fig. 218. The manual key is replaced by a relay a which is
wired to the brass ring of the trunk plug so that when it is pushed
into the jack on the subscriber line, the current used for the busy
test also flows through the coil of the relay, causing it to be ener-
gized. The armature of this relay actuates two springs. b and c,
to which it is rigidily attached. The armature is insulated from
the two springs, and the two springs are insulated from one an-

200
Holly
6
5
Holole
1
On
vos
3A
K4
ab
Fig. 218.
other. The relay is equipped with two inner contact points, 2 and
3, and two outer ones, 1 and 4, so that in action it is identical with
the manual key. The circuit passing through the operator's receiver
to give her the busy test, is wired to contact 1, and the tip of the
trunk plug, to the spring c. One terminal of the coil of the relay
actuating the signal lamp, is connected to contact 3. The spring b
is wired to the opposite side of the trunk and contact 4 is spare.
The other terminal of relay d is wired to the trunk at s.
When the relay a is energized, the springs c and b are drawn away
from the contacts 1 and 4 respectively, and brought up against
contacts 2 and 3.
At the outgoing end, the trunk is wired in the same manner
as that previously shown, except that the direct-current generator
227
216
TELEPHONY
m gives a potential of 75 volts instead of 20, and two lamps p and
n are used for reducing the current to the amount requisite to
operate the relay d, which is about .08 ampere.
It was found more convenient to use a higher potential, for
by using lamps of proper resistance the system could be made to
work on trunks varying greatly in length. The necessary resist-
ance of the lamps will depend altogether on the resistance of the
trunk on which they are used.
The operation of this trunk is the same as that previously
described. When the trunk plug is pushed into the subscriber
jack, the relay a is energized and contacts are made between c and
2, and b and 3, so that the tip side of the trunk is cut through,
and the relay d bridged across. Current from the generator m
energizes d, closing the lamp circuit and lighting the lamp. When
the subscriber operator plugs into the trunk, the relay at that end
is energized, cutting off the current from the machine, causing d
to “release ”, thereby putting out the lamp. Upon the subscriber
operator clearing out, current from the machine m is again cut in,
d is again energized, lighting the lamp, thus signaling the oper-
ator to clear out.

AUXILIARY APPARATUS,
The auxiliary apparatus used in a telephone exchange can be
classed under two headings. First, Power Apparatus ; second,
Protection Apparatus.
Power Apparatus. There are two kinds of power apparatus
used: Dynamos or Dynamotors, and Batteries. Two classes of
dynamos are used—direct and alternating. The first-named type
is employed to charge the storage batteries, and for operating the
lamp signal on the trunks. The second type is provided to furnish
the ringing current and that for the busy-back jacks. The nature
and size of the ringing-current machine depend upon the size of
the exchange and the volume of business handled. In small ex-
changes equipped with two or three standard boards, and in which
the number of calls handled is not as great as to require the oper-
ator to put forth her utmost efforts, hand generators, similar to
those used in telephone instruments, are employed. They are
placed in the keyboard with the handle projecting through the
228
TELEPHONY
217
front of the trough, one being provided for each section. Where
the number of sections is in excess of three, or where the business
is heavy, some form of power generator must be installed. Where
water power is available, the usual practice is to use a water motor
belted to a small but powerful magneto generator; if there is no
water power, a small electric motor is used, to which the generator
is belted.
One type of magneto generator is shown in Fig. 219. It is
of the same general make-up as that used in the subscriber tele-
phone. It is larger and more powerful, and differs in a few details:
It consists of five permanent magnets bolted to two pole pieces. One
terminal of the armature coil is connected to an insulated collar s on the
a

a
b
b
e
Ad
S
C
m
m'
Fe
Fig. 219.
Fig. 220.
shaft, the other is connected to the shaft. There are two copper brushes,
one bears on s and the other on the shaft, from the two terminals a and b.
Two oil cups c and d are provided for lubricating the bearings. The oppo-
site end of the shaft is equipped with a pulley e, over which is placed the
belt. The flat pulley is often replaced with a grooved one, for the accom-
modation of a cylindrical belt. The whole machine is mounted on a
wooden base, upon which are placed the two line binding posts m and m'.
The armature of this type of the machine is wound to give a potential of
from 75 to 80 volts.
In Fig. 220 is shown a very compact and convenient form of
water motor for use in small exchanges. - It consists of a turbine
encased in an iron chamber a. To the shaft is attached a pulley b,
the whole being supported on a stand c, through the center of
a
229
218
TELEPHONY
which passes the discharge pipe e. The supply pipe is shown at
d. This supply pipe terminates inside of the motor in a nozzle
about 16 inch in diameter, through which the water is forced, to
impinge against the buckets of the wheel.
The discharge pipe should have a diameter of about 11 inches
and should run straight for a distance of 20 feet from the motor.
This type of machine can be used successfully in localities where
the water pressure is at least 40 pounds per square inch. It runs
noiselessly and requires very little attention.

2
a
-6
JU
070
Fig. 221.
In Fig. 221 is shown one of the most approved types of in-
duction motors used for operating magneto generators. The motor
is shown at b. It is of the usual type of induction motor made to
operate on single-phase alternating circuits. It is made self-start-
ing by dividing the stator winding into two halves, one of which
has a choke coil in series with it, and the other a non-inductive
resistance. A push button 3 mounted on top of the case, serves
to make the necessary connections when starting, by simply depress-
ing it. The terminals are shown at 1 and 2.
The magneto generator is shown at a and is mounted, together
with the motor, on the same wooden base c.
This unit gives very
good results and is used very extensively.
Even when some form of power generator is used in smaller
exchanges, hand generators are supplied to be used in the case of
the failure of the former. In larger exchanges, motor generators

230
TELEPHONY
219
are used, and the motor end is wound for direct or alternating cur-
rent as the case may require. In Fig. 222 is shown a motor gen-
erator used for charging storage batteries. It is built by the
Crocker-Wheeler Co. and is self-contained and very compact. The
motor end (which in this case is direct current) is shown in the
с
5

b,
TE
b'
a
I
6'
A
C
Ő
Fig. 222.
foreground, and the dynamo end, in the background. The base
of the machine forms the yoke, upon which are mounted the field
coils. The pole pieces are at the top, one being shown at A. The
starter is shown mounted on the side of the pole piece, and is con-
trolled by the handle H, which actuates a contact moving between
four upright clips. The motor side is wound to the potential of the
mains on which it is to operate, and the dynamo side delivers current
at a potential slightly in excess of that of the battery it is to charge.

231
220
TELEPHONY
a
One very important point about a charging dynamo is that it
should have an automatic cut-out, which opens the circuit, when
the current delivered by the dynamo falls below a certain fixed
amount. This is to prevent the battery from discharging through
the armature should the motor slow down or stop from failure of
the current supply in the mains. A very ingenious form of cut-
out is used in this type of machine. It is mounted on top of the
pole pieces. The front pole piece A is hinged so as to swing out,
and is held in place by the attractive force of the magnetic field.
A spiral spring S is securely fastened to the back pole piece and
rests against a block on the front one. When the strength of the
magnetic field is of the proper amount, the tension of this spring
is overcome and the pole piece held in place. When the field is
in place, two brass clips b and b' close the circuit to the battery,
which is carried by the leads a a' through the back brass block c.
Should the field weaken sufficiently, so that the dynamo is unable
to develop a potential sufficiently high to feed the batteries, the
tension of the spring will then overcome the attractive force, A
will be swung forward, and the circuit to the battery through the
clips broken.
Ringing-current machines are built according to the design
shown, only there is no automatic cut-out present, and the dynamo
side is wound for alternating current at a potential of 75 volts.
The two commutators are shown at C and C'.
Batteries. Two types of batteries are used in telephone
exchange work: Primary and Secondary or Storage. The choice
between the two depends altogether upon the amount of current
needed, the cost of charging, and the cost of the electrolyte and
elements in the case of the primary cell. In general, in small
exchanges, consisting of three sections of standard board or less,
primary cells are used, while in larger exchanges, storage cells
find favor.
Of the various types of primary batteries, either gravity or
Fuller cells are used. The maintenance of the former type is less
than that of the latter; but, on the other hand, the cost of the
former is greater than that of the latter. So that where a great
number of cells are needed, the Fuller batteries are used, and
when a small number are required the gravity cell comes into



232
TELEPHONY
221
play. Three gravity cells in series are placed on each operator's
transmitter circuit, while two Fuller cells are usually deemed suffi-
cient. The wire used for battery leads is No. 14 B. & S. gauge
soft-drawn copper with rubber insulation protected by heavy
braid. The conductors of a pair are twisted together, so that a
number of leads may be sewed up together in cable form without
producing cross-talk.
Mr. J.J. Carty, Chief Engineer of the New York Telephone
Company, conceived the idea of feeding a bank of transmitters
from one storage battery. He realized that on account of the ex-

i
> 2
3
a
-
wo
omto
ca 4
5
omwa
o
ol
6
9
a
ol
+
2
71 72
h
ادمی |
3
TOMI
HE
Hali
d
α
Fig. 223.
ceedingly low internal resistance of this type of cell, no cross-talk
would be produced by so doing. The reason was as follows: After
two or more transmitters, each taking normally .20 amperes, be
connected to the same battery, the fluctuation in the internal fall
of potential due to the fluctuations in the current furnished to one
transmitter upon its being talked into, is of infinitesimal amount
owing to the very low internal resistance, so that the other trans-
mitters are furnished with a steady current. This condition would
be impossible with any form of primary cell. Two cells are re-
quired in series, and the number of elements in each will depend
upon
the number of transmitters to be fed.
Fig. 223 shows the method of connecting up the batteries.
The mains coming from the charging machine pass through two
fuses a and b, and thence to two knife switches c and c'. Each of
233
222
TELEPHONY
+
a
6
these switches is equipped with three pairs of contacts 1, 2, 3, 4,
5, and 6. The switch is pivoted to 3 and 4. The charging leads
are wired to 1 and 2, and the battery leads to 3 and 4. The trans-
mitter leads are connected to 5 and 6.
The switch d' is thrown into the position to charge the battery
d', the current passing from the contacts 1 to 3, and 2 to 4 through
the battery, the transmitter leads being at 5 and 6. The switch c
is thrown into the position to discharge the battery d into the trans-
mitters, the current passing through the contacts 3 and 4 to 5 and
6 and thence to the transmitter bus-bars g and g'. The charging
leads are open at 1 and 2. The trans-
mitter leads are fused at e and f. The
bus-bars are made of copper rods, drilled
and tapped for machine screws to hold
the fuses for the various transmitter
circuits. The wooden strips h and h'
are placed on opposite sides of the bus-
bars, equipped with binding posts for
the accommodation of the fuses and the
transmitter wires, the latter being shown
at 1, 2, 3, 4, and 5.
Fig. 224.
In connecting up the charging leads,
the utmost precaution must be taken to
properly adjust the polarity, so that the positive lead of the charg-
ing circuit will be connected to the positive pole of the battery.
A very convenient method of finding the positive pole of the charg-
ing circuit is to dip the two terminals in a jar containing water
made slightly acid or water into which has been thrown a pinch
of salt. This point is illustrated in Fig. 224 at a and b. Upon
so doing, bubbles will be seen to rise from the two leads, but much
faster from one than the other. The one from which they rise the
faster is the negative lead. This experiment is rather dangerous
and should be performed with great care.
Another simple method, and one not attended with so much
danger, is to allow current to flow through the leads while an ordi-
nary compass is held under one of them. The point to remember
is that when a current flows over a magnetic needle from north to
south, the north pole of the needle is deflected to the east.



234

Mall
HUU
C
CENTRAL ENERGY VISUAL SIGNAL SWITCHBOARD
Stromberg-Carlson Telephone Mfg. Co.
TELEPHONY
223
The success of the scheme of feeding a bank of transmitters
from a storage battery rests on the fact that the resistance of the
leads to the bus-bars must be as small as possible. Therefore
great care must be taken to make the leads as short as possible,
and of sufficiently heavy wire. In general, it might be said that
the battery should have a capacity of 50 amperes for small ex-
changes, and the total resistance, including the battery to the bus-
bars, should not be over .006 ohm. A great deal of troublesome
cross-talk has been caused by overlooking this fact, in exchanges
that are otherwise installed with the utmost care; and unless one
is familiar with this point, such cross-talk is very difficult to locate.
Protection Apparatus. This subject has already been touched
on in connection with the main distributing board. It will now
be necessary to go into it a little more in detail in connection with
power wiring. Reference to Fig. 223 will show that fuses are

G
ón
6
Fig. 225.

placed in the charging circuit, and in the discharge circuit to the
bus-bars, and on each individual transmitter lead. The best plan
to follow in exchange wiring is to place the necessary knife
switches, fuses, bus-bars, etc., on a slate power switchboard, upon
which are mounted also an ammeter in the charging circuit, a
voltmeter on the same circuit, and also one to measure the poten-
tial of the battery. In Fig. 225 is shown the style of fuses used
on the charging and discharging mains. It consists of a strap of
fuse metal c attached at either end to two copper lugs a and b.
These copper lugs are slotted to fit over studs, and are held in
place by nuts. The fuse metal is made of the requisite size to
carry the current required. The type of fuse used on the leads to
the transmitter bus-bars is shown in Fig. 226, and consists of a
hollow cylindrical fiber tube a fastened to two German-silver slips
d and e, by two brass screws 6 and c. Through the center of the
b
tube runs the fuse which is soldered at each end to the brass col-
lars m n.
The lugs are fastened to the power board by means of
the screws s s'.
235
224
TELEPHONY
Switchboard Construction. Fig. 227 shows the rear view
of the multiple switchboard, in which will be seen the con-
struction of the framework and the placing of the cable and the
wiring. At A and B are shown the multiple cables for the sub-
scribers' lines and the outgoing trunks. It will be seen that they
rest upon a shelf running along the length of the board. The five
bottom rows are for the outgoing trunks, and the remainder are
for the subscriber lines. Running in a trough at C, are seen the
answering jack cables which turn up at their respective sections;
they are formed out and take the answering jacks at D, D', and D".
Just below these forms is seen the wiring of the operator's circuits.
It should be noticed that these switchboards are built in sec-
tions, each accommodating 3 operators. This is the usual con-
m
aj
n
b
مه
d
Fig. 226.
struction. Every multiple jack is within reach of every operator;
the operator sitting in the center position, can reach everything
on her own section, while the operators occupying the end posi-
tions, can reach on the adjacent sections everything that is inac-
cessible on their own.
COMMON BATTERY SYSTEM.
The desire to centralize power has permeated even the tele-
phone practice, and within the past five or six years various sys-
tems have been introduced with this end in view. It was supposed
that if the batteries could be removed from the subscriber tele-
phones, the cost of their maintenance would be entirely wiped out.
If the batteries were all concentrated in the exchange, and the cur-
rent fed out over the line during conversation, they could be
maintained in better shape and at a lower cost than when scattered
about the district at each subscriber station. Again, the current
may be used for automatic signals which would accelerate the
service. These considerations led to the development of the so-
called common battery, or central energy systems that have come
rapidly to the front in the past three years.


236
TELEPHONY
225
The earliest and simplest method for using a common bat-
tery is shown in Fig. 228. In this case, the receiver and trans-
mitter of both subscriber instruments are connected in series with
the battery a in the middle. Grounded circuits are used. This
method of connecting up telephones is known as direct transmis-
sion and operates as follows: Let the right-hand telephone be used
for transmitting and the left-hand one for receiving. The trans-
mitter e upon being spoken into will cause a variable current to
flow over the line, and this passing through the receiver b will

」
B
o
D?
D
C
Fig. 227.
reproduce the sound in the usual manner. Transmission is car-
ried on in the opposite direction in the same manner.
As has already been pointed out, this direct transmission is
not sensitive, because the resistance of the line forms too great a
ratio to that of the transmitter. For short lines it does very well,
but for general use it does not give good results. The operatoris
cord circuits have each an independent battery so that cross-talk
.
may not result
237
226
TELEPHONY
The Stone System. Probably the first system devised
whereby one common battery was made to feed all the cord circuits
was that devised by Stone. The plan of wiring is shown in Fig.
229 where a and 6 represent the receiver and transmitter at one
station, and c and d those at the other. The battery g is connected
across the line through the retardation coils e and f. A metallic
O
a
Hulle
d
To
с
e
12
f
Fig. 228.

circuit is used throughout. The action of this system is as follows:
Current flows from the positive pole of the battery g through
the retardation coil e to the point o where it splits, one portion
going through the receiver a and transmitter back to o'; the
other portion flowing from o through the receiver c and the trans-
mitter d goes back to o'. This current divides itself in proportion
to the resistance of the two circuits. The retardation coils e and f
are wound with comparatively heavy wire, so that while the ohmic
resistance is low the impedance is very high. As a result they
.
o
a
를 ​9
6
If
ta
pe
Fig. 229.
offer very little resistance to the flow of the direct current of the
battery, but entirely choke out the rapidly varying current pro-
duced by talking
Since the current in the two branches divides itself in the in-
verse ratio of the resistance of the two circuits, the flow of cur-
rent through the retardation coils is practically constant. The
talking current flows around the circuit through the two receivers
and transmitters. On short lines this system works well, giving
better results than the one previously described.
238
TELEPHONY
227
It has been said that this system renders it possible to use one
common battery for all the cord circuits, and that with the use of
the retardation coils cross-talk is done away with. The method in
which this is accomplished is shown in Fig. 230, in which two con-
nections each between two subscriber lines are shown. At a and
b are shown the two retardation coils on one pair of cord circuits,
and at c and d those on the other. To illustrate this action, let us
suppose that conversation is being carried on over the other con-
nection. As the transmitters are talked into, a variable current
flows out from the battery over the circuit. It might seem at first
sight that this current upon reaching the points 1 and 2 would

量
​to
I b
for
2
IC
d
of
Fig. 230.

divide, part flowing through the lower connection. This is pre-
vented by the retardation coils in the following manner:
First, it has been shown that the variable talking current is
nearly all confined to the circuits joining the two subscriber tele-
phones, and that the current flow through the retardation coils is
nearly obstructed. Whatever variable current does pass through
these two coils would, upon reaching the points 1 and 2, have two
paths, the one through the retardation coils c and d, and the other
through the battery. The first possesses high induction, the sec-
cond almost none, so that this variable current would all flow
through the battery, thus preventing cross-talk.
Hayes System. A modification of this system, gotten out
,
by Mr. Hammond V. Hayes, is shown in Fig. 231.
retardation coils of the Stone system are replaced by a repeating
coil having four windings a, b, c, and d. Suppose that station
Here the
239
228
TELEPHONY
No. 1 is transmitting to station No. 2, a variable current will be
set up through this station which will pass through the windings
a and c of the repeating coil. In consequence, an alternating cur-
rent will be induced in the windings b and d of the coil, which
will flow through station No. 2, reproducing the sound.
Should station 2 wish to transmit to station 1 by talking into
the transmitter a variable current is set up through the windings

a
6
2
C
d
to
of
Fig. 231.
b and d of the repeating coil, with the result that induced currents
are set up in the windings a and c, which reproduce the sound at
,
the other end. The repeating coil thus acts as an induction coil.
When station 1 transmits to station 2, the windings a and c are
the primary, and b and d the secondary. When transmission is
carried on the other way the reverse is the case.

1
b
с
d
2
e
مد
1
to
9
h
Fig. 232.
With this system, as with the one previously described, a
common battery is used on all the cord circuits, and cross-talk is
kept out in much the same manner. This point will be illustrated
by reference to Fig. 232, in which two connections are again

240
TELEPHONY
229
shown. If conversation is being carried on over the upper connec-
tion, the variable current, through what happens to be the primary
winding, and the induced current, through what happens to be the
secondary winding, upon reaching the points 1 and 2, have a choice
of two paths, one through the battery and the other through the
retardation coils in the lower circuit. The battery, however, hav-
ing practically no self-induction, prevents any of this current from
reaching the lower circuit and producing cross-talk. This system
gave better results than that invented by Stone, because the cur-
rent from the battery is used only to feed the transmitter, the

S
C
b
p
7. 2
臺​。
a
Fig. 233.
repeating coil in the exchange acting like an induction coil. In
other words, it is one step removed from direct transmission.
The next step in the development of this system was to place
an induction coil in each of the subscriber telephones, and to this
end the Dean system was introduced. The plan of wiring is
shown in Fig. 233. A grounded battery a is connected to the
center point of a retardation coil 6 which is bridged across the
line. A second retardation coil c is placed at each subscriber sta-
tion and from its center a connection is made to point No. 1 in
the transmitter circuit of the telephone. Point No. 2 at the oppo-
site side of this circuit is grounded. The current from the battery,
upon reaching the middle point of the retardation coil 6, splits,
one half following one side of the line and the other half following
the other side. Upon reaching the subscriber station, these two
halves flow through the retardation coil c, uniting at the middle
point and flowing to point No. 1. Here the current again divides,

241
230
TELEPHONY
one half going through the primary winding of an induction coil,
and the other half passing through the transmitter. They again
unite at 2 and flow to ground.
It should be observed that the arrangement of the transmitter
circuit is somewhat different from anything yet shown. Instead
of the current flowing through the primary coil and transmitter in
series, the one is shunted onto the other, which gives a more sen-
sitive arrangement. The transmitter current flowing out over both
sides of the line in parallel has no inductive effect, providing the
resistances of the two sides of the circuit are equal. The talking
current, induced in the secondary
a
winding of the induction coil, flows
over the line in the usual way, and
on account of the high self induc-
tion, does not pass through the re-
tardation coils. As far as trans-
d
mission is concerned this is a better
6
arrangement than any previously
described.

AUTOMATIC SIGNALS.
ng bf
h
f
H00
In addition to gaining the ad.
vantages already mentioned in con-
nection with the maintenance of the
apparatus, the current from the
common battery is made use of to
operate automatic signals so that
the service may be expedited by
Fig. 234.
their greater reliability and quick-
ness of action. The scheme adopted
for working this automatic signal, is to provide a lamp so wired to
each subscriber line, that when the receiver is lifted from the hook
at the subscriber station, it will be lighted.
The plan first adopted was to equip each subscriber telephone
with a bell, the resistance of whose coils was 6,000 ohms instead
of the usual 1,000. The wiring was as shown in Fig. 234 in which
a represents the bell coils having a resistance of 6,000 ohms, 6 the
receiver, c the transmitter, and d the hook switch. One side of
242
TELEPHONY
231
the line runs through the retardation coil h to the common battery
g, while the other side passes through the lamp f and the contact
point 1 of the jack e. The battery g is continually on the line, and
current flows constantly through the bell coils. On account of
their high resistance, however, the volume of the current flow is
not sufficient to illuminate the lamp.
Upon the receiver being removed from the hook, the bell coils
are shunted by the circuit through the hook switch, transmitter,
and receiver, and the current flow is thereby sufficiently increased
to light the lamp. As far as the operator is concerned, this lamp
answers the purpose of the drop, and upon seeing it light, she
plugs into the jack to answer. When the plug enters the jack,
the contact is broken between the upper jack spring
and point 1, cutting off the portion of the circuit con- a е
taining the lamp and putting it out.
001
oft
The talking battery is connected to the operator's
cord circuits in a manner to be described later. The
retardation coil h is used for preventing cross-talk.
It must be remembered that the battery g is common
to all lines, and while the resistance of the bell coils
B
of one subscriber telephone is sufficiently high to pre-
vent an appreciable amount of current from flowing, Fig. 235.
yet when several such bells are bridged to this battery,
the resistance of the combined circuit is very much less, and as a
result, a large leakage from the battery takes place.
For example, suppose that there were 100 subscriber tele-
phones bridged to one battery in an exchange, which figure is
very
small. If each bell had a resistance of 6,000 ohms, the combined
resistance of the whole bridge would be 60 ohms, which would
allow of a very serious drain on the cells. To overcome this
defect, a condenser was made use of, and the wiring of the telephone
was as shown in Fig. 235, in which a again represents the bell
coils, 7 the receiver, c the transmitter, and d the hook switch.
At
e is shown a condenser which is cut in series with the bell coils.
This condenser presents an open circuit to the direct current from
the battery, although it allows the alternating current from the
ringing machine to pass through readily.
d

243
232
TELEPHONY
2
α 9
With this style of wiring, while the receiver is on the hook
there is absolutely no current passing through the telephone, so
that there is no drain upon the battery.
The telephone wiring shown thus far, included no induction
coil. A further step was necessary to provide for this piece of
apparatus. When this was done, the instrument was brought to
its present condition. The plan of the wiring of the fully developed
common battery telephone is shown in Fig. 236. As in the other
form, the bell a, wound to the usual resistance of 1,000 ohms, is
bridged across the line in series with the condenser g whose capacity
is 2 M.F. Connected to the No. 1 side of the line
is one terminal of the primary winding e of the in-
duction coil, while the other terminal of this coil is
connected to the contact point. The transmitter e
od
is connected to the hook switch and to the No. 2
side of the line. The secondary winding d of the
induction coil has one terminal connected to the
contact point and the other to one terminal of the
6
receiver b. The other terminal of the receiver is
connected between the bell a and the condenser g.
The action of this telephone is as follows: The
receiver being on the hook switch, the line is open
through the condenser to the direct battery current,
but the alternating ringing current can readily pass
through so that the subscriber can be rung in the
Fig. 236.
usual manner. When the subscriber removes the
telephone from the hook switch, a circuit is formed
from the No. 1 side of the line through the primary winding of the
induction coil to the hook switch, thence through the transmitter to
the No. 2 side of the line. When the transmitter is spoken into,
a variable current flows over the line from the battery in the ex-
change, passing through the primary winding e. An alternating
current is thereby induced in the secondary coil d, which flows
through the receiver 1, the condenser g, the No. 2 side of the line,
to the transmitter, through which it passes back to d.
After much experimenting, the wiring of the subscriber's
line shown in Fig. 237 has been adopted by the Bell companies as
the best suited for general use. The subscriber telephone is shown
www
on
244
TELEPHONY
)
233

u
at the left-hand side, and the
line is seen running between
it and the main distributing
frame w. The multiple jacks
are seen at a, b, and C,
and
the answering jack at d. So
far, the arrangement is very
similar to that of the bridg-
ing board. The jack used
here is of simpler design
d
than that of the bridging
board. It is made up on two
contact springs 1 and 2 and
HOH
the ring 3. The contact
spring 2, when the plug is in
the jack, touches the tip.
The spring 1 touches a brass
ring on the plug, while its
shank makes contact with
the ring of the jack. The
al
jacks are bridged across the
line in the same manner as
in the plain bridging system.
The horizontal side of
the intermediate distribut-
ing board x = has three lugs
7, 8, 9, and the vertical side
is equipped with four, 7, 8,
9, and 10. The two sides of
the talking circuit are con-
nected to lugs 7 and 8 on
both sides of the board, while
the wiring running from the
Foogle
ring of the jack is soldered
to lug No. 9.
www.
On the vertical side of
the board is seen a fourth lug
10, to which is connected a wire running from the line lampe. Two
618
o
45
Fig. 237.
245
234
TELEPHONY
relays are seen. The one marked A is known as the cut-off relay;
it has one terminal of its coil connected to lug No. 9, and there-
fore to the wire running from the rings of the jacks. The other
terminal of this coil is grounded at m. Attached to the armature
of this relay are two springs 1 and 2, which are insulated both
from each other and from the armature. When the relay is not
energized, these two springs make contact with the two points 3
and 4, to which are connected the two sides of the talking circuit,
No. 4 being connected to that side of the line that touches the tip
of the plug. Spring No. 1 is grounded at m, while No. 2 is con-
nected to one terminal of the line relay o. The other terminal of
the coil of the relay is connected to the grounded battery f. This
relay has one armature 5 grounded at m, and one contact point 6,
which is connected to lug 10, and therefore to the wire running to
the lamp e.
The action of this circuit is as follows: When the receiver is
on the hook at the subscriber station, the line is open through the
condenser. Upon the receiver being removed from the hook and
a path formed through the primary coil and transmitter, the cur-
rent flows from the battery f in the direction indicated by the
The line relay will therefore become energized and its
armature 5 drawn against the contact point 6. A second circuit
is now formed from the battery f through the lamp e to the lug
10, to the contact point 6, to the armature 5, and to ground at m.
The lamp becomes lighted. The subscriber operator upon seeing
the lamp become illuminated, plugs into the answering jack d.
For the present all that will be necessary to know is that on
the shank of the plug is a battery and upon touching the ring of the
jack, current flows along the wire to lug No. 9, thence through
the coil of the cut-off relay A to ground at m. This relay being
energized, the two springs are pulled away from their respective
contacts, and the current is cut off from the line. As a result, the
,
relay o ceases to be energized, its armature 5 falls away from the con-
tact 6, opening the circuit through the lamp e, and putting it out.
We may sum up the conditions under which this circuit works
as follows: The potential of the common battery f is on the line
constantly. Owing to the presence of the condenser in the bell
circuit, however, no current flows. Directly the receiver is removed
arrows.

246
TELEPHONY
235
from the hook switch, current flows through the line relay to the
subscriber telephone and back, lighting the line lamp and giving
the operator the signal that attention is required. The operator,
upon plugging in to answer, energizes the cut-off relay which
operates to disconnect the battery from the line, breaks the circuit
through the line lamp and puts it out.
The wiring of the operator's cord circuit should be understood
next. The plan of the wiring is shown in Fig. 238, and the simi-

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larity will at once be seen between this arrangement and that of
the outline circuit shown in Fig. 231. A repeating coil having
four windings is connected to the common battery as shown. The
windings 1 and 2 are connected to the calling plug a, those marked
3 and 4 are connected to the plug b. The common battery (one
side being grounded) is connected to the junction between 1 and
3 and 2 and 4. Wired in series with the side of the cord circuit
leading to the ring of the plug are two relays d and d'. From the
point m two battery leads run, one to each of the two lamps e and
é'. In series with these two lamps, and between them and the
shank of the plug, are two German-silver resistances f and f'.
From the point o two leads run to the armatures h and h' of the
relays d and d'. Two other resistances g and g have one terminal

247
236
TELEPHONY
connected to the contacts i and i' respectively, and the other ter-
minals to f and f'. The listening key is shown at k, and acts in
the usual way to bridge the operator cord circuit across the cord
circuit. It will be observed that a condenser n is cut in between
the receiver l and the secondary winding q. This is done to pre-
vent the current from the battery c from flowing through the
receiver when the operator listens in. The primary circuit con-
tains in addition to the transmitter and receiver, a retardation coil
u and a condenser s. It must be remembered that the battery c is
common to the exchange, and furnishes all the current used; that
on the line circuit, that on the cord circuits, and that on the oper-
ator's transmitters.
When the common battery system was introduced it was
thought best to provide a separate battery for the line signals, a
separate battery for the operator's transmitters, and a separate
battery for the cord circuits. The potential used for the first was
6 volts, that for the second was 4, and that for the cord circuits
24. It was soon discovered that everything could be run off the
24-volt circuit, so that this potential was adopted as standard for
the common battery system. The proper understanding of this
point is essential to the thorough comprehension of the subject.
Returning to the operator's transmitter circuit, the retardation
coil u is placed in circuit to guard against cross-talk. Its resist-
ance is about 100 ohms, which serves to reduce the current fur-
nished to the transmitter, down to the proper amount. The con-
denser s, having a capacity of 2 M.F., being bridged across the
transmitter and primary coil, assists the retardation coil in keeping
out cross-talk; for if any of the talking current from some other
operator's set, should leak past the retardation coil, it will be
absorbed by the condenser rather than pass through the transmitter
and primary coil, which is possessed of high self-induction.
248

KELLOGG CHARGING AND RINGING MACHINE.

TELEPHONY
PART V.
AUTOMATIC SIGNALS.(Continued.)
Returning to the cord circuit—it will be seen that current is
furnished to both the answering and calling plugs through the re-
tardation coil. Following the wiring of the shank of the plug, it
will be seen that, when the plug is inserted into the jack, current
is sent from the battery through the lamp and resistance to the
shank, thence through the shank wire to lug 9, Fig. 237. From
this point it passes through the coil of the cut-off relay A to ground
at m energizing the relay and cutting off the direct battery from
the line. The resistance of the lamp, the coil in series, and the
cut-off relay are so proportioned that sufficient current is allowed
to flow to energize the relay and to light the lamp. When the re-
lays d and d’, Fig. 238, are energized, their armatures are drawn
up against the contact points, and shunt circuits, through g and g',
are placed on each lamp. These shunt resistances are so propor-
tioned that the current flowing through the lamp is reduced suffi-
ciently to prevent illumination. Using the 24-volt battery, the
cut-off relay A is wound to a resistance of 30 ohms, and the series
resistances f and f' each have a resistance of 831 ohms. The
lamps e and e' are designed to operate on a potential of 12 volts,
so that a resistance equal to their own must be placed in series,
thus the combined resistance of the cut-off relay and coil f or f
is 1134 ohms, which equals the resistance of the lamp.
The resistance of the shunt coils g or g'must be of the proper
magnitude to reduce the current flow through the lamp to prevent
it from being illuminated. When the shunt circuit is open the
total resistance of the circuit on the shank is 1131 + 1131 = 227.
24
The E.M.F. being 24, the current flow
.105 amperes,
227
which amount is sufficient to illuminate the lamp. This lamp will
just glow very faintly with .06 ampere.

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It has been found by experiment rather than the result of cal-
culation that a shunt resistance of 40 ohms will sufficiently reduce
the brilliancy of the lamp to produce the desired effect. Suppose
the resistance of the shunt coil to be 40 ohms, and suppose its cir-
cuit to be closed. The total resistance of the shank circuit will
then become
1
30 + 834 +
143 ohms.
1
1
113] + 40
The total flow of current in this circuit will be given by the
24
expression
= 17 ampere.
143
The current will divide itself between the lamp and shunt resist-
ance in inverse ratio to the two resistances, or as 40 : 113, which
proportion gives a current flow of .06 amperes, which is sufficient
for the purpose.
The relays d and d deserve special mention. Since they are
both placed in the talking circuit, some device must be used for
rendering them as feeble a barrier to transmission as possible.
They must also be proof against cross-talk. The first point is
accomplished by providing each relay with two windings—one hav-
ing a resistance of 10 ohms and being wound inductively, the
other having a resistance of 100 ohms and being wound non-induct-
ively. The direct current from the battery selects the low resist-
ance inductive path of 10 ohms, because this current sets up little
or no counter E.M.F. of self-induction. The talking current
which is alternating, and therefore capable of setting up a counter
E.M.F., chooses the high resistance non-inductive path.
HANDLING A CONNECTION.
Before giving a more thorough explanation of the manner in
which transmission is carried on over this circuit, it will be neces-
sary to explain the method of handling a connection. This will
be done by reference to Fig. 239. Suppose a and b to be two sub-
scribers' telephones. The multiple jacks connected to a's line
being shown at f,g, and h, and the answering jack and line lamp at
e and i respectively. The multiple jacks on b's line are shown at j,
253
240
TELEPHONY
k, and l, and the answering jack and line lamp at m and n respec-
tively. Suppose that a, desiring to call, raises the receiver from
the hook, thereby lighting the line lamp i in the manner already
shown. The operator, sitting before the answering jack, plugs in-
to the answering plug with the result that current is sent through
the shank wire of the plug to the ring of the jack, and thence
through the cut-off relay d' to ground, thereby cutting off direct
battery and putting out the line lamp. The receiver being off the
hook at a, current flows out on the line through the windings 1
and 2 of the repeating coil. Therefore, the supervisory relay o is
energized and the shunt circuit being closed, the lamp p does not
glow. At this stage, the subscriber's transmitter is fed by current
sent out through the repeating coil, direct battery is cut off the
line, the line lamp circuit is opened, and the supervisory lamp
shunted out.
Suppose that the call is for subscriber 6. The calling plug is
pushed into the multiple jack j of b's line and the ringing key de-
pressed. The condition shown in the illustration is that existing
before 6 has removed the receiver from the hook switch to answer.
The calling plug being in the jack j, the cut-off relay cis energized,
and the direct battery cut off the line. The receiver at b being on
the hook, the line is open at the condenser, so that no current flows
through the supervisory relay o'. Therefore, the shunt around the
lamp p' is opened and the lamp illuminated. Directly b removes
the receiver from the hook to answer, the line is closed through the
primary coil and transmitter, current flows from the battery,
through the windings 3 and 4 of the repeating coil to the tele-
phone, the relay o' is energized, with the result that the shunt
around p' is closed, and p' dimmed And this is the state of things
during conversation.
At the completion of the conversation, both telephones are
hung up, and both lines again opened. Current therefore ceases
to flow through o and o', and as a result, the shunt circuits around
p and p' are opened, and both lamps become illuminated. Upon
seeing this the operator instantly clears the connection.
It will be observed that these supervisory signals are much
more efficient than the ring-off drop since they are independent
and automatic. The clearing-out drop necessitates the additional
3


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254
TELEPHONY
241
work on the part,of the subscriber of the ringing, upon the com-
pletion of the conversation, a thing which took time and was often
forgotten, and when forgotten the operator either left the connec-
tion up or was put to the necessity of listening in to find out
whether or not conversation was going on.
With the signal sys-
tem just shown the case is different. The proper operation of the
signals depends only upon the act of hanging up the receiver, a
thing not so likely to be forgotten as the additional work of ring-
ing off. While subscribers do sometimes forget to hang up, it is
not probable that both will forget to do so, and since the super-
visory signals work independently, the action of one subscriber
hanging up, lights the signal on his side of the cord circuit. The
operator seeing this would clear the connection.
The connection being cleared, the cut-off relays are released,
direct battery is thrown in on the line, and the original condition
is again established. In Fig. 239 the ringing current generator
is not shown wired to the key for the sake of clearness.
It will now be time to say a word more on the subject of the
method of transmission. Suppose the subscriber at a to be trans-
mitting to the party at b. In speaking into the transmitter, a
variable current is made to flow from the common battery through
the windings 1 and 2 of the repeating coil, over the line to and
through the primary coil and transmitter at the telephone. This
variable current does two things. At the telephone end, it sets up
a talking current in the secondary winding of the induction coil,
which flows through the receiver, condenser, transmitter and back
to the coil again. This is side tone. At the repeating coil, this
variable current sets up a talking current in windings 3 and 4
which flows over the other line—the receiver supposed to be off
the hook—and passing through the primary winding, receiver
secondary winding and condenser, reproduces the sound. The
windings 1 and 2 act as the primary of an induction coil, while 3
and 4 act as the secondary. When b transmits to a, the action is
the same but in the reverse order. The windings 3 and 4 then
become the primary, and 1 and 2 the secondary.
While the common battery system is excellent for rapid
service, and while it tends towards a better and cheaper mainten-

255
242
TELEPHONY
-test,
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ance, the transmission is not so good as that of the local battery
system under the best conditions.
The line and cut-off relays
are mounted upon a separate
rack, and the line lamp only is
on the face of the board in addi-
tion to the jack. The line lamps
are mounted in the same strip
with the answering jack, each
lamp being directly below the
jack to which it is attached. The
sections, as is the case with all
multiple boards, both series and
bridging, are made to accommo-
date three operator positions
each. The supervisory relays
and the 831- and 40-ohm resist-
ance coils are mounted in the
rear of the switchboard. The
supervisory lamps p and p' etc.,
are mounted in the keyboard in
two rows directly in front of the
cords.
Trunking. With the intro-
duction of the common battery
Halala
system came additional changes
in the trunking systems, which
reduced the time of making and
clearing a connection to a mini-
mum. In Fig. 240 is shown
the wiring of a trunk from a
magneto switch board to one
operating under the common
battery system.
switchboard selected is of the
t H
bridging type, but the method
of operating is the same for the
series board.
At the outgoing

Fig. 240.
The magneto
PAS
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TELEPHONY
243
end is a relay a wired in series with the busy-test battery. To the
two contact springs is wired a retardation coil 6 of high impe-
dance, and having a resistance of 600 ohms. When a plug is
inserted into a jack this retardation coil is bridged across the line.
Its center point is grounded at m. At the incoming end is the
repeating coil with the four windings 1, 2, 3, and 4. The first
two are strapped together, and the battery is wired between the
other two. The wire running to the shank of the trunk plug
passes through a relay d and a lamp l'. The upper spring of this
relay is wired to the tip of the plug, while the lower spring is
wired to the lamp l", the other terminal of which is connected
through a resistance h of 100 ohms to ground. Wired to one side
of the battery is the relay c, called the trunk-line relay, whose
resistance is 25 ohms. The other terminal of this relay is wired
to the strap on the repeating coil.
The armature of the relay c is wired to the battery, while the
contact is wired through a 30-ohm coil i to the junction of l" and h.
The inner contact for the lower spring of the relay d is wired to
the battery, while the outer contact is wired through a 25-ohm
coil g to ground. The relay e, which is of the same type as that
on the operator's cord circuit shown in Fig. 239, has the armature
connected to the shank wire of the plug, and the contact, through
a resistance k of 30 ohms to the coil of the relay f, a strap being
extended to the left-hand inner contact. The left-hand spring of
the relay f, is wired to the battery through the resistance j of 60
ohms, and the right-hand inner contact is strapped across. The
right-hand spring is connected to one terminal of the lampl, the
other terminal of which is wired to the shank of the plug.
It will be seen at a glance that the upper spring of the relay
d performs the functions of an automatic testing key. The method
of handling connections over this trunk is the same as that already
described. The trunk operator having received the call in the
usual way tests the line called for in the manner already described,
and assuming the line not busy, plugs in. A circuit is instantly
formed along the wire to the shank of the plug, thence through the
cut-off relay on the called subscriber's line to ground. The relay
d is energized, the trunk closed through at the upper side, and
current sent through the lamp l" and resistance h to ground on the
257
244
TELEPHONY
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lower side. The trunk operator rings the subscriber. When the
subscriber operator plugs into the trunk jack, the relay a is ener-
gized and the grounded retardation coil 6 bridged across the line.
Current then flows through the trunk line relay c along both sides
of the trunk in parallel to the
ground at m, energizing the re-
lay c and closing the armature
against the contact. Directly
this happens the resistance coil ;
is connected in shunt across the
lamp l', making its illumination
invisible, or “shunting it out”,
as it is called. When the called
subscriber removes the receiver
from the hook, current is sent
,
out to him through the relay e
energizing it and closing the
armature against the contact,
with the result that current is
sent through the resistance k and
the relay f forming a shunt
around the lamp l'. The current
passing through f energizes it
and the two springs are closed
against their respective contacts.
On the left-hand side current
passes through the resistance j,
the contact and coil of the relay
f, thus causing the coil j to be
shunted around k. Sufficient
current is drawn from l' to
shunt it out. The spring and
contact close the circuit through
the lampl; but this lamp is also
shunted out by the same circuit.
Upon the completion of the con-
versation and the consequent hanging up of the receiver by the
called party, the relay e is released, its armature falls away from the

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Fig. 241.
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258
TELEPHONY
245
contact and the circuit through k is opened. The relay f, however,
does not release because it is locked through its left-hand spring
and contact, and the lamp l' still remains shunted out. The lampl,
however, being of a lower resistance than 1', lights up the instant
that the circuit through k is opened, and therefore serves as a
signal to the trunk operator that the called party has hung up.
Upon the subscriber operator clearing the connection, the
ground is taken off the outgoing end of the trunk, the trunk line
relay cis therefore released, and the shunt through the coil i removed
from the lamp l", which instantly lights up. The trunk operator
clears the connection either upon seeing the lamp l or the lamp l"
light up, according to instructions. As a usual thing the lamp
l" is taken as the signal, which means that the trunk operator waits
for the subscriber operator to clear out, before doing so herself.
The lamp ?" also serves as a guard lamp against cut-offs.
Should the trunk operator through carelessness or other cause
clear the trunk during the process of conversation, the lamp l" will
instantly light up, because the connection being up at the outgoing
office the ground m is still on the trunk, and the trunk line relay
energized. The trunk plug being removed from the subscriber
jack, the relay d is released, and the lower spring leaves the inner
contact and touches the outer one. A circuit is therefore formed
through the resistance i, the lamp l" and the resistance g to ground.
The coil h becomes a shunt on the lamp but its resistance is too
high to shunt the lamp out.
In Fig. 241 is shown a trunk between two common battery
offices. It will be seen to be much simpler than the one previously
shown. A condenser c is cut in between the windings 1 and 2 of
the repeating coil. From the point 1 a wire extends to the con-
tact on the supervisory relay g, the spring of which is grounded.
The trunk line relay e is wired to the point d. With the exception
of the ringing key, the rest of the wiring is the same as that already
shown. The wiring of the ringing key is for what is known as
machine ringing. The ringing key is provided with a catch,
which, when the key is depressed, holds the contacts in the position
to allow the ringing current to flow over the line. Wired in series
with the ringing machine is a magnetic clutch k which is so ad-
justed that, when the called subscriber removes the receiver from

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259
246
TELEPHONY
the hook to answer, it is energized sufficiently to trip the catch and
cut off the ringing current. This arrangement saves a good deal
of the trunk operator's time, and prevents ringing in the called sub-
scriber's ear.
The best feature of this circuit lies in the fact that by means
of it the subscriber operator has her supervisory signal controlled
by the called subscriber's hook switch. Referring to the outgoing
end of the trunk, the ring of the jack is wired to ground through

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a coil a having a resistance of 36 ohms, so that the shank circuit
of the operator's cord circuit will be completed. A plug being
inserted into the trunk jack, the supervisory lamp lights. The
ring of the plug sends current out through the jack spring o over
one side of the trunk to the point b, and thence to the contact
point of the supervisory relay g. The tip of the plug, touching
the jack spring o' puts a ground on it because it is connected to
the grounded side of the battery, and therefore a current flows
through the trunk line relay e to the point d and thence over the
opposite side of the trunk to ground through the tip of the plug.
The relay f and the lamp l" work exactly the same as shown in
Fig. 240. The called party taking the receiver from the hook
energizes the relay g, closing the spring against the contact. Cur-

260
TELEPHONY
247
rent now flows through the supervisory relay on the subscriber
operator's cord circuit to the jack spring o to the ground, energizing
the relay and shunting out the lamp. When the called subscriber
hangs up upon the completion of the conversation, the relay g is
released, the ground taken off the contact, and therefore the circuit
over which flowed the current through the subscriber operator's
supervisory relay is broken. The shunt on the supervisory lamp
being thus removed, the lamp lights, just as if the called sub-
scriber's line had terminated in the same exchange as the calling
line. This form of trunk circuit is the most efficient ever devised.
There are three weak points about the common battery line
and operator's cord circuits that have been shown so far, and
they are:
First, when the operator plugs in to answer a call the subscriber
hears a painful click in the ear, caused by the direct battery being sud-
denly cut off the line through the cut-off relay. Second, during conver-
sation current is required to keep the cut-off relay energized. Third, the
presence of a relay in the talking circuit.
In Fig. 242 is shown a very simple circuit which does away
with the click in the ear upon the operator answering. In this
circuit the battery is permanently connected to the subscriber lines
through the relays a and a'. The armature of the relay rests nor-
mally against the outer contact point, the inner contact being con-
nected to the lamp d, whose other terminal is connected to the
grounded side of the battery. The armature itself is connected to
through the resistance b to the free side of the battery. The tip
and ring of the plug form the connections of the talking circuit,
the two shanks being connected together through the lamps e and
e', one side of each being grounded. Two condensers f and f" are
cut into the talking circuit.
Referring to the left-hand line, when the subscriber removes
the receiver from the hook switch current flows through the relay
The armature is pulled against the inner contact, and current
flows through the resistance b and the lamp d to ground. The
lamp becomes illuminated. The operator plugging in to answer,
throws a ground on the ring of the jack through the shank of the
plug, which shunts the lamp e across the lamp d. The resistances
and current-carrying capacities of these two lamps are so propor-
tioned that both are shunted out.
a.
261
248
TELEPHONY
When the subscriber hangs up, the relay a ceases to be ener-
gized, the armature falls against the outer contact opening the
circuit through the lamp d. The two coils c and b are connected
together through the lamp e with the result that the latter lights
as the shunt has been removed.
Since the battery is permanently connected to the line, the
click in the ear is done away with, as is the presence of the relay
in the talking circuit. The current passing through the two lamps
in multiple is fully equal to that taken by the cut-off relay, so that
no saving is accomplished in this manner. This circuit with some
modifications may be provided with a busy test and is in commer-
cial use by one of the independent telephone companies.

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Fig. 243.
Another form of circuit is shown in Fig. 243 which aims at
reducing the amount of current used up in shunting out signals
during conversation. As in the previous one, the battery is per-
manently connected to the line through a retardation coil. When
the subscriber removes the receiver from the hook the relay a be-
comes energized closing the lamp circuit b. Referring to the cord
circuit, the talking contacts here are the tip and the shank and
upon the plug being inserted into the jack, current flows along the
wire from the ring through the supervisory relay d to the tip of
the plug and thence out on the line. The relay is energized, and the
armature pulled away from the contact. The current through the
relay a is so far shunted as to cause it to release, and open the line
262

TELEPHONY
249
lamp circuit. When the subscriber hangs up, the relay d is
released, the armature falls against the contact and lights the su-
pervisory lamp. This circuit has some good features, but it is
very problematical whether or not it is more economical of current
than the one originally shown. In Fig. 244 is shown the general
appearance of an exchange switchboard. The one shown is of the
common battery type with a capacity of 5,400 lines. The girl seen
standing up is called a supervisor, and her duty is to see to it that
the operators attend properly to their work and also to assist them

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Fig. 244.
out of any difficulty that they might get into from time to time.
The chief operator sits at a desk and has direct charge of all the
operators. The whole force is presided over by a manager.
TOLL BOARDS.
e
Long toll lines, upon which a mileage rate is charged, are
handled over a special board placed in the most convenient ex-
change. In cities having only one exchange, and in which the
toll business is large, each exchange has a toll board. Toll boards
are equipped, in addition to the toll line multiple and answering
jacks, with a multiple of the outgoing trunks to other exchanges.
For example, the toll board in the Courtland St. exchange, for
e
263
250
TELEPHONY
handling calls to points in Jersey City and Long Island, is equipped
in addition to the toll trunks, with outgoing trunks to every other
exchange in the city, and also with outgoing trunks to the local
switchboard in the Courtland St. exchange. The calls for toll
points are handled over what is known as a recording circuit. This
is simply a sending order circuit from all the local exchanges to a
special operator set aside to receive calls. The calls are written
upon tickets, and passed to the toll operators for completion. The
toll operator times and supervises every connection. The method
of procedure is as follows. Suppose that No. 76, 38th St. calls for
.
No. 56 Paterson, N.J. The subscriber operator at 38th St. answer-
ing the call would go in on the recording circuit, to the recording
operator at the New Jersey toll board at Courtland St. and say:
No. 760, 38th St. wants No. 56 Paterson. The recording oper-
ator would note the facts on a slip and pass it to the toll operator
handling the Paterson toll trunks. This operator would go in on
the order circuit to the incoming trunk operator at 38th St. and
order up No. 760. She would then go in on a Paterson trunk
and having gotten the Paterson operator ask her for No. 56. This
line having been plugged up the connection would be established.
The conversation having been completed, the toll operator would
disconnect the circuit trunk to 38th St. thus giving the trunk oper-
ator there the signal to clear out, and she would ring on the Pater-
son trunk, and when the Paterson operator answered, she would
direct her to clear the connection. Long Distance connection
being in substance, toll connections are handled in this manner.
Toll boards are used for two purposes. First, to establish
connection between two toll trunks. Second, to establish connec-
tion between a toll trunk and a subscriber's line. This type of
switchboard, therefore, is equipped with two classes of trunks, viz.,
toll trunks and trunks to local exchanges. The operator cord cir-
cuits must be, therefore, of two classes. That suited for connect-
ing two toll trunks, and that suited for connecting a toll trunk and
a trunk to a local exchange. With the magneto system, since both
the toll trunks and those to the local exchanges are wired sub-
stantially in the same manner, one set of cord circuits will do for
both purposes. But with the introduction of the common battery
system, where the wiring of the trunks to the local exchanges takes

264
TELEPHONY
251
a
-
-
a new form, a corresponding change must be made in the wiring
of a portion of the cord circuits. Toll boards are designed on the
multiple type, but differ in construction from the local switch-
boards in the fact that the sections are built to accommodate only
two operator positions instead of three. The reason for this change
lies in the fact that greater ease is given to the operator thereby,
to reach all the jacks in the multiple. With large multiples in
use in the local switchboards this device cannot be resorted to on
account of the extra expense. For example, suppose that a switch-
board is equipped with 5,000 subscriber multiple jacks, and that
the calling rate is such that only 50 answering jacks are assigned
5,000
to each operator. The number of sections needed would be
50 X 3
which is approximately 34. The number of multiple jacks would
be, therefore, 5,000 X 34 = 170,000. If now these sections were
designed for two operators' positions instead of three each, the total
5,000
number of sections needed would be
50 and the total
50 X 2
number of subscriber multiple jacks would become 5,000 X 50
250,000 or an increase of 80,000 jacks. Assuming the cost of a
jack to be $0.25 the increase in cost due to this change would be
80,000 X .25 $20,000.00, which would be much in excess of
the money saved from better operating.
With the toll board the case is different. Here the multiple,
counting the toll trunks and those to local exchanges seldom
reaches 700 jacks, so that the extra cost of the jacks is not of
so much importance. Again, since in the case of connections over
toll trunks a rate is charged which is in proportion to the length
of the trunk used, and the length of time during which the
conversation is carried on, the return to the company in money is
higher per call, than in the case when the connection is handled
exclusively over a local board. A toll connection requires more
time to establish, for reasons that will be seen directly, than a
local connection. The above two facts make it necessary to give
the toll operators every advantage.
The trunks to local exchanges are of the same type as
those in the local board, and are wired in the same general
way. The toll board is situated in the same room, or at any
-
265
252
TELEPHONY
rate, in the same building with one of the local switchboards.
For example, the toll board for handling the toll lines to the
suburbs of Philadelphia and surrounding towns, is situated in
the same building as the local exchange known as No. 2. The
toll board for handling the toll trunks to the northern suburbs
of New York, throughout the district known as the Bronx, and
the outlying towns, is situated in the same building as the local
switchboard known as Melrose. The outgoing trunk multiple
of the toll board is made up of an extension of the outgoing
trunk multiple of the local board, and in addition, a set of

f
6
с
d
WA
WWW
b'
d'
9
h
Fig. 245.
trunks to one of the incoming trunk positions of the local board
in the building in which it is situated. Thus, at Melrose, the out-
going trunk multiple in the local board is extended through the
toll board, and in addition there is a set of trunks to the local
board at Melrose. The toll board is thus equipped with trunks to
each one of the local exchanges. These trunks are either circuit
or ring-down as the case may be.
In Fig. 245 is shown the wiring of a ring-down trunk,
the jacks in the local board being shown at a b c and d, and
those in the toll board at a' ' ' and d'. The lugs on the
intermediate distributing board are shown at f and f', and the
repeating coil at e.
In the toll board each multiple jack is
266

HHA
it
711
were
MANZ
CHICAGO
COMPLETE COMMON BATTERY SYSTEM.
Installed in the Kellogg Switchboard and Supply Co. Factory.
TELEPHONY
253
accompanied with an automatic signal called a busy visual.
This signal is of the magnetic type, to the armature of which
is attached a light aluminum shutter which, when the coil is
energized, is pulled over the face of the magnet so as to be in
plain view of the operator. When a plug is inserted in a jack,
either on the local or toll board, the relay g is energized, and its
armature drawn against the contact point. Current then flows
from the battery h, through the coils of the busy visuals in series,
energizing them and making the shutters show busy. By this
means the toll operators are relieved of the necessity of testing the
trunks to find one that is not in use, which tends to save time.

e
a
b
с
d
www
www
ww
a'
b'
с
d
Fig. 246.

In Fig. 246 is shown the wiring of a circuit trunk, the jacks
in the local board being shown as before at a b c and d, and those
in the toll board at a' l' c' and d'. The 36 ohm coil is shown at e.
In this case, the multiple through the toll board consists merely
of a duplicate of that through the local board. The wiring of a
toll trunk is similar to that of a ring-down trunk shown in Fig.
245, with the exception that it does not appear in the local switch-
board, and that there is an answering jack wired to it and placed
on the toll board. It is shown in Fig. 247. The repeating coil is
.
removed and a drop g is wired across the trunk. The multiple
jacks are shown at a b c and d and the answering jack and lamp
at e and f respectively. A relay h, having two windings i and i',
is so wired that one of the windings is connected to the restoring
coil of the drop, while the other winding is connected to the arma-
The opposite terminal of the lamp is wired to the contact

ture.
267
254
TELEPHONY
point of the drop to which is also connected one terminal of the
resistance coil o. The opposite side of the busy visuals is wired
to the contact point of the relay, and the armature is grounded.
The action is as follows: The trunk being rung on from the
distant end, and the armature falling, current flows through the
lampf and the resistance o, through the winding i' of the relay h,
0
energizing it and closing the circuit through the busy visuals.
The trunk is thus shown busy the instant it is rung upon, pre-
venting any operator taking it up before the proper operator
answers at the answering jack.

g
6
1
e
9
k
k
K
k"
VAN h
H0001116
Fig. 247.
When the plug is pushed into the jack, current is sent
through the restoring coil of the drop, and the coil i of the relay.
Therefore, although the circuit through the coil i' is broken, that
through the coil i keeps it energized so that the busy visual circuit
remains closed. The resistance o, which is 600 ohms, is shunted
around the lamp so that, should the latter become open, the busy
visuals will be energized when the trunk is rung upon.
In Fig. 248 is shown the wiring of a cord circuit to connect
together two toll trunks. It differs in no very essential feature
from that of an ordinary bridging board. The clearing out drop
268
TELEPHONY
255
f is not placed on the board in view of the operator, but a lamp g
actuated by its armature is placed in the keyboard and acts as the
supervisory signal. The resistance h, which is in series with the
lamp, is 120 ohms, while that of j, in series with the restoring coil,
is 190 ohms. The resistances of i and k are 200 ohms each. The
wiring of the operator's transmitter circuits is identical with that
already shown for a common battery office.
In Fig. 249 is shown the circuit for connecting together a toll
trunk and one to a local office. One half is the same as that shown
6

voon
k
19
e
w
h
1
wwww
i
w
00001
I
Fig. 248.
in Fig. 248, while the other half is that of local subscriber's oper-
ator's cord circuit. Here the left-hand plug a is for the toll-trunk
jack, while the right-hand plug 6 is for the trunk to the local
switchboard. In this cord circuit a repeating coil is used, and the
windings 1 and 2 are strapped together on the left-hand side of the
cord, while the battery is connected between 3 and 4 for the right-
hand side in the usual manner. A toll board position is usually
equipped with 12 cord circuits, and of these 4 are of the type
shown in Fig. 248, and the remainder, of that shown in Fig. 249.
269
256
TELEPHONY
LONG-DISTANCE SWITCHBOARDS.
The business done by the Long Distance Company is essentially
a toll business, and the switchboards used are, therefore, of the toll
board type. They differ, however, in many respects from the toll
boards used by the local companies. The types of switchboard used
in a Long Distance exchange consist of: Toll boards, Through
boards, and Recording boards. The toll boards are those at which

oopa
toon
www
k
h
www.
wwww
Hullut
HI
ám to
m
Fig. 249.
the toll lines terminate, and are equipped in the larger offices
with the toll line answering jacks, line drops, outgoing trunk mul-
tiple to the local exchanges, and circuits to the chief operator's
board. The through boards are used to complete connections from
one point to another, when the line to these two points passes
through the office. For example, if a connection is wanted between
Boston and Philadelphia, there being no direct trunks between these
two points, the connection would have to be handled through New
York. Boston would call New York, and ask for Philadelphia.
New York would then raise Philadelphia, and connect the two
270
TELEPHONY
257
m
hi
168
1
trunks together. This would be done at the through board. The
recording board is used for handling calls from local subscribers
to Long Distance points. The
through boards are equipped with a
multiple of the toll lines, a multiple
of the trunks to local offices, and a
4
multiple of the trunks to the chief
operator's board.
The wiring of a toll line is
shown in Fig. 250. The main rack
Hoopla
is shown at x ac', and in this connec-
tion it should be said that the main
rack of the Long Distance Com-
pany is not equipped with protect-
ing devices. The lines after enter-
ing the office are equipped with the
regular carbon sandwich protector
for lightning, as shown at o and o'.
The jack a is in the chief operator's
board, which contains a bridge on all
lines entering the office. The jacks
b, c, d represent the multiple in the
through boards, while at e is shown
the answering jack. After passing
the answering jack, the line runs
through the contacts of the relay in
which has a resistance of 90 ohms,
and thence through the line coil of
the drop h. One terminal of the
coil of the relay is connected to the
ring of the jacks and the other is
wired to the restoring coil of the
drop. The lamp g is the answering
lamp, and those marked f,f", F", and
f'' are the busy lamps. The oper-
HH
ation of the circuit is as follows:
The trunk being rung open the
drop is thrown and the lamp g lighted. The operator plugging

Fig. 250.
Da
mo
x x
O'
HH
271
258
TELEPHONY
into the jack e to answer, restores the drop, putting out the light g.
At the same time the relay i is energized and the drop cut off.
Also a path is made between the lower spring and inner contact of
the relay i for the common return of the busy lamps f, f',f",
and f'', lighting these lamps and giving the signal that the line is
in use. It will be observed that the heat coils m and m' are placed
in series with the drop to protect it against sneak currents. The
busy lamp f'' is placed above the answering jack to notify the
operator at that point when the trunk is taken up at any other
section of the board.
In Fig. 251 is shown the operator's cord circuit that is used

7
O
1
un
150 W
150 w
www
190 W
20οω
www
HE
Fig. 251.
a
on the toll board and through board. The wiring of the trunks to
local offices is shown in Fig. 252, and is of a design different from
that used between the exchanges of a local company. It is so
wired that the long distance operator does all the ringing, and to
this end a special relay is placed at the incoming end, which is
actuated by the alternating current from the ringing key of the
long distance operator. At the long distance office the trunk is
wired in the usual manner with the ring of the jacks connected to
ground through a coil of 90 ohms resistance.
At the incoming
end is the regulation repeating coil a wired up in the regulation
manner, with the exception that the relay above mentioned is
bridged around the condenser, with another condenser in series.

272
TELEPHONY
259
The outside contacts of a second relay b are also bridged across the
terminals of the first condenser, the upper swinging contact of this
relay being wired through the coil of a third relay c to ground,
and the lower swinging contact of this relay being connected to
the contact point of the relay e. The two inner contacts of the
relay b are strapped together. The armature of the relay a is con-
nected to battery, and its contact point is wired through the coil of
the relay d and the coil of the relay b to ground, through a resist-
ance of 170 ohms. To this wire is also strapped the contact of the
relay e, its armature being connected to that of the relay c. The auto-

0
ringing
key
를
​m40w
х
30w
0°
300w
w
с
5οοω
170 W
Fig. 252.
matic testing key is wired in the usual manner, with the exception
that the lower inner contact is connected to battery, and the lower
swinging contact is connected to the contact point of the relay c.
The working of this trunk is as follows: The trunk operator
at the local office taking up the called subscriber's line, the auto-
matic key is energized, and battery is thrown out on one side of
the line to the long distance office, where the keyboard signal is
energized. The supervisory lamp o is lighted. The Long Dis-
tance operator upon ringing, energizes the relay a, closing the
armature against the contact, and throwing battery through the
relay with the result that it in turn becomes energized, cutting in
the ringing current and calling the subscriber. This current
flows also through the relay b energizing it, breaking the contacts
between the middle and outer, and making them between the
273
260
TELEPHONY
middle and inner points, with the result that current is now sent
from the lower contacts on the automatic testing key through the
strap on the relay b and the coil of relay c to ground. The relay
c becomes energized and its armature is closed against the contact
point, thus closing the shunt circuit around the lamp through the
resistance coil m, shunting out the lamp. When the called sub-
scriber removes the receiver from the hook, the supervisory relay
e is energized, and current flows through the lamp, and the resist-
ance coil m, the armature and contact point of the supervisory
relay, and the coil of the relay b to ground. The relay b again
being energized, current is sent through the relay c energizing it,
and current is again allowed to flow through the lower contacts of
the automatic testing key, to the point X, where it splits; one por-
tion passing through the coil m, again shunting out the lamp.
The other portion flows through the armature and contact of the
supervisory relay, the coil of the relay b to ground, thus keeping
6 and the relay c energized. No disconnect signal is placed at the
long distance end of the trunk, as the long distance operator is
required to supervise the connection.
When the conversation is completed, the operator at the dis-
tant office rings on the toll trunk, thus throwing the clearing-out
drop. The long distance operator then clears the connection, and
the lamp at the incoming end again lights up. The recording
boards are used to record calls from local exchanges to long dis-
tance points, and to transmit the information to the proper toll
operator in order that the required toll point may be reached.
These boards are equipped with a multiple of the outgoing
trunks to local offices. The operator's cord circuit is the same as
that of a toll board, with the exception that it has only one cord
and plug, is used to hold the trunk, until the toll operator takes
up the connection. Each recording operator position is equipped
with a set of sending order wire keys to the local offices. A
special operator, called a receiving operator, is equipped with a
telephone circuit at which terminates an order circuit from each
of the local exchanges. All calls coming from the local exchanges
are received over this order circuit by the receiving operator, who
writes the details on a ticket and passes it to one of the recording
operators. This operator goes in on the order circuit to the trunk

274
TELEPHONY
261
orders up
operator in the exchange from which the call originated and
the calling subscriber's line, which is done in the
regular circuit trunk manner. The ticket is then sent from the
recording operator to the toll line operator, who proceeds to get
the called subscriber at the toll point required. Upon the toll
line operator plugging into the trunk to the local exchange upon
which the calling subscriber's line is being held, the recording
operator withdraws her plug and has nothing more to do with the
connection.
a
TELEPHONE OPERATING.
The work of establishing connections in a telephone exchange
is called operating. The department that handles the operating is
called the Traffic Department. The force in a telephone exchange
is made up as follows: Each exchange is in charge of a manager,
whose business it is to see that the operating force properly attends
to the work of handling connections. He should have full authority
over his force, being free to make whatever change he may deem
to be necessary. In large exchanges his efforts are seconded by
one or more assistant managers. These are usually men, although
the position of assistant manager is sometimes filled by a woman.
The official who comes in the most direct contact with the operators
is the chief operator. This position should always be filled by a
The force of operators is assisted by one or more super-
visors, whose duty it is to watch closely the manner in which the
operators directly under her charge attend to business, and to help
them out of any difficulties into which they may from time to time
fall. Each supervisor is assigned a certain number of sections to
patrol, and she walks continually to and fro watching the work.
She should watch the manner in which the operators answer the
subscribers, insisting that it be done promptly, and that the sub-
scribers be carefully listened to so that their wishes may be
prop-
erly recorded.
The supervisor should see that the subscriber
always gets courteous treatment. Each supervisor is equipped with
a telephone placed conveniently on the wall so that the operators
may be readily able to communicate with her. It is part of her
duty to give the operators all the assistance necessary in the per-
formance of their work.
woman.
275
262
TELEPHONY
Next to the supervisor in authority comes the monitor. This
official sits at a desk so as to be in constant communication with
the switchboard. She is required to take up all matters of com-
plaint by the subscribers, to furnish any information that may be
required by the subscriber, and to complete connections that the
operators have found impossible to complete. The number of
monitors required varies with the size of the office, but is seldom
over four, and usually two.
Next highest in authority is the chief operator, already re-
ferred to, who is somewhat analogous in her relations to the oper-
ating force as the first mate of a ship is to the sailors. She sits
at a desk somewhat similar to that of the monitor, so as to be in
constant touch with the operating force. Her duties are many and
various. First of all, she is the person to whom the force report
directly. She watches the work, and is the first to note any defects
therein. She receives the reports from the supervisors and moni-
tors and acts on them. She is directly responsible to the manager
for the manner in which the traffic of the office is carried on. All
calls for the manager are given to her, and it is her duty to deter-
mine whether to handle them herself or turn them over to the
manager for his action.
The night force is presided over by a night manager who has
the rank of chief operator. The night force is not so large as that
employed in the day, and as a result no night supervisors are
needed. Only one night monitor is required and no night chief
operator. The manager should see to it, first of all, that he
pro-
vides himself with the proper kind of a chief operator. This done,
one half of the battle for good operating is won. He should then
supervise carefully the work of the chief operator, in selecting the
proper operators, supervisors, and monitors. He should select such
assistants as will best help him in his work.
The hours of the operating force are divided as follows: Half
of the day force reports at 7 A. M. and the other half at 8 A. M.
The half that report at 7 A. M. are relieved at 5 P. M. The sec-
ond half is split up, the majority reporting at 8 A. M., but a small
number reporting at 9 A. M. and remaining till 7 P. M. The
hours for reporting usually change every week so that those oper-
ators who, during the first week, report at 7 A. M. will, during
a
276
TELEPHONY
263
the second week, report at 8 or 9 A. M. The new operators are
formed into a relief squad which reports at 4 P. M. and remains
till 9 P. M. As the operators in this squad show increased pro-
ficiency they are promoted to the regular force. In some exchanges
the night force consists of boys from 16 to 21 years of age. But
it has been found after repeated trials that girls give better results
than boys, as they are more tractable, so that they are being used
more and more every year. The night force reports at 7 P. M.,
and remains till 7 A. M.
These hours seem very long, and are in actual fact. But a
great deal of time during the middle of the night is given to the
operators to sleep so that the strain is not as great as would seem
at first sight. The telephone companies select these long hours so
that the girls will not be compelled to be on the street at any un-
seasonable hour.
The operators are divided into two groups. Those that an-
swer the subscriber lines, called subscriber or “A” operators, and
those that handle the incoming trunks, called the trunk or “B”
operators. In offices where there is situated a toll board, there
exists a third group called the toll operators. The work per-
formed by each of these groups differs in detail from that performed
by the others. The subscriber operators have to deal with the
public, and therefore must be well schooled in soothing ruffled
tempers and the like. They must also be instructed in the proper
method of answering questions. In answering calls a certain formula
must be gone through with, which will be described directly. In
the early days the operator used to answer the subscriber's call by
saying "Hello". But within the past five or six years this custom
has been discontinued, and the operators instructed to substitute the
word “Number", so that to-day, in all well regulated exchanges the
operator answers the subscribers call by saying “ Number” with a
rising inflection. The operator then gives the number required.
There are two methods of operating, one used with the mag-
neto system, and the other with the common battery system. That
used with the magneto system will be explained first. In explain-
ing the various methods of operating, the multiple board only will
be considered, since all methods applicable to this are also applica-
ble to the standard or subdivided board.
a
66
277
264
TELEPHONY
FROM -
TO__
TIME DISCONNECTED
There are in all five classes of calls: First, those for sub-
scribers in the same exchange as the calling subscriber. Second,
those for subscribers in other exchanges reached over a ring-down
trunk. Third, those for subscribers in other exchanges reached
over a ring-down trunk through some intermediate exchange.
Fourth, calls for subscribers in other exchanges reached over
circuit trunks. Fifth, calls for subscribers reached through the
tall board. A system followed now by nearly every telephone
company is to give three classes of service. First, flat rate, ac-
cording to which the subscriber is charged a fixed rate per year for
unlimited service. Second, message rate,
according to which the subscriber is charged
a fixed rate per year which is regulated by
the number of calls made. Third, pay sta-
tion, according to which the subscriber pays
TIME CONNECTED
for each call made at the time of making the
call. It is obvious that a record must be
kept of all message-rate and pay-station calls
made, while no record need be kept of the flat
rate calls. The method of keeping record of
Fig. 253 the calls is by filling out a ticket such as
shown in Fig. 253, on which opposite the
word “From” is written the number of the calling subscriber's
line; and opposite the word “To” is written the number of the
line called for. Pay station calls are limited in time to five min-
utes, so that two additional blanks on the ticket, one headed “Time
Connected”, and the other “ Time Disconnected”, have to be filled
out in this case.
Consider now the first case in which the called subscriber is
in the same exchange as the subscriber calling. The operator
having plugged into the answering jack, and said "Number" with
a rising inflection as already described, listens intently to the re-
quest of the calling party. Assume that 500 calls for 4930. The
operator takes
up the calling plug and touches the rim of the
multiple jack on 4930. If the busy test is obtained, the operator
says to 5002 They are busy". If upon touching the jack no
busy test is obtained the plug is pushed into the jack and 4930 is
rung up. The listening key can be adjusted all this while so as to


278
TELEPHONY
265
66 Are you
cut in the operator's telephone, but the operator must be very
careful not to have more than one listening key so adjusted at the
same time, else the two cord circuits will be connected through her
telephone and cross-talk will result. When the called party has
answered the operator says:
4930 ?”, and upon receiving
the affirmative answer says: “Go ahead," and the two parties begin
conversation. The operator should supervise the connection from
time to time in order to see that the subscribers are able to con-
verse properly, and also to determine whether or not they have
finished. This latter point is made necessary by the possibility of
the subscribers forgetting to ring off. This supervising consists
merely of temporarily throwing the listening key on each cord
circuit upon which there is a connection. If the operator in so
supervising should happen to listen in on a connection over which
there is no conversation she should ask: “ Are you waiting?” and
after a pause “Are you through ?" If no response is obtained
66
she should then take down the connection.
It often happens that the operator has to answer several calls
at once. In doing so she should answer each calling subscriber in
turn, before making any attempt to raise any of the subscribers
called for. When the last subscriber has been answered, she should
then start in and raise the subscribers called for in the order in
which she has received the calls. When the party called for does
not answer the telephone, the call is reported as a “Don't An-
swer”, and given to the monitor for further trial. If the called
subscriber's line is out of order so that he cannot be raised, the
fact is so reported to the calling subscriber. All cases of " Don't
Answer” or “Out of Order” are reported as lost calls, and the
ticket marked with a cross. One of the greatest problems in oper-
ating is to reduce the percentage of lost calls. Should the operator,
through confusion or any other cause, plug into the wrong jack
and call the wrong party, she should allow the plug to remain in
the jack until the called subscriber answers, and then say: “ Ex-
,
cuse that, please”, after which she is free to withdraw the plug and
call on the proper line.
The next case to be considered is that in which the called-for
subscriber is in another exchange reached over a ring-down trunk.
The subscriber operator, having answered the call, tests with the
:
279
266
TELEPHONY
tip of the calling plug of a different pair of cords, usually the one
adjacent to that used for answering, the rings of all the jacks on
the trunks to the required exchange, until one is found that is not
occupied. The calling plug is inserted into this jack and the
trunk rung on. When the operator at the distant exchange an-
swers, the first operator asks for the required number, and if the
line is not in use the connection is plugged up and the called sub-
scriber rung up by the operator at the distant exchange. When
the called subscriber answers, the operator at the originating office
asks: “What number"; and upon learning that it is the one re-
quired, quickly substitutes for the calling plug then in the trunk
jack, that one forming the mate to the answering plug in the call-
ing subscriber's jack, thus giving him a connection through. This
method of using the cords is called : “Using split cords”, and is
done to prevent the calling subscriber from hearing the connection
put through to the distant office, which would tend to confuse him.
This connection is supervised by the operator at the originating
office in the manner already described. When the conversation is
completed and the calling subscriber rings off, the originating oper-
ator goes in and
says " Are you waiting ?” “ Are you through ?”
and upon hearing no response, pulls out the answering plug from
the answering jack and rings on the trunk. When the operator at
the distant office answers she is told to clear the connection, which
she promptly does.
One great defect in the ring-down trunk system, when a large
number of trunks are required between two offices, lies in the fact
that it is often very difficult for an operator to secure an unoccupied
trunk. Say, for example, there are ten trunks to the required ex-
change, and that she starts testing at the first one and finds it
busy; she then passes to the next one and finds that busy, and so
on. By the time she has reached the eighth jack the first one may
be cleared. But if upon reaching the tenth and finding that busy,
she starts over again, the first trunk may have been taken up before
she again tests the jack, so that when she does it for a second time,
she again finds it busy. It has been known that operators have
tested over a strip of jacks in this way three or four times before
an idle trunk is found.
66
a
280
TELEPHONY
267
The third case is that in which the called-for subscriber must
be reached over ring-down trunks through an intermediate ex-
change. Call the exchange in which the call originates A; the
intermediate exchange, B; and the exchange in which the required
subscriber's line terminates, C. From A there are direct ring-
down trunks to B, and also from B to C. But there are no direct
trunks to Ofrom A. The subscriber operator at A, having an-
swered the call and ascertained the required number, plugs in on
a trunk to B, after having tested as already described. A split
cord is used. When the operator at B answers, the one at A says:
“Give me a wire to C”. The operator at B thereupon tests over
the trunks to C in the manner already described and finding one
unoccupied, plugs in and rings. Split cords are not used. When
the operator at C answers she finds herself in direct communica-
tion with A and receives her request for the number required
The other details of the connection are identical with those already
described. When the conversation is completed, the operator at A
rings on the trunk, and when the operator at B answers, directs
her to clear the connection. This operator thereupon rings on the
trunk to C and directs that operator to clear the connection. This
is called the tandem trunk method and is used very much in toll
business to small towns and villages. It is also used a great deal
by the Long Distance Company.
The fourth case is that which is universally used in all large
cities, on account of the rapidity with which business can be
handled by it. It covers the condition in which the called-for
sul scriber is in a distant exchange reached over a circuit trunk.
The subscriber operator as usual, having answered the calling sub-
scriber and learned his wish, throws the listening key so as to cut
herself off from his line and goes in on the order key to the re-
quired exchange and asks for the number required. Suppose that
the subscriber at No 750 Courtland wishes to talk to the subscriber
at No 5760 38th St, the subscriber operator at Courtland St. hav-
ing answered and learned the request, would go in on the order
circuit to 38th St and say “ 5760 for Courtland St.” The trunk
operator at the latter exchange would then assign the trunk by
calling back over the circuit “ Number 5," or " Take it on Num-
ber 5," Number 5 being the trunk that she is going to use. After
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TELEPHONY
assigning the trunk, the trunk operator touches the ring of the
multiple jack on line No 5760 to see whether or not it is in use.
Assuming that the line is not busy, she pushes the plug into the
jack In the meantime the A operator at Courtland St plugs into
the multiple jack on trunk No. 5, using a split cord. When the
incoming trunk cords are equipped with ringing keys, the trunk
operator rings the called subscriber. But when these are wanting
the A operator does the ringing. In either case when the called
subscriber answers, the A operator assures herself that he is the
right party by asking his number and then, quickly replacing the
plug in the trunk jack with the mate to the one in the answering
jack, completes the connection. The connection is cleared in the
manner already described.
The A operator in ordering up the connection should be very
careful and listen on the circuit before passing the call, to ascertain
whether or not any other call is being passed at the same time. If
this be neglected, she might interrupt some other call on the same
circuit. Under these conditions the result would simply be con-
fusion to the trunk operator, and both calls would have to be
repeated.
Where the trunks are not equipped with disconnect signals,
the same precaution should be observed by the A operator in order-
ing down connections, and for the same reason, Where the dis-
connect signals are in use, the circuit is used only for ordering up.
,
The fifth case is that in which the called subscriber is at a
toll point and must be reached over the toll board. There are two
conditions: First, where the call originates at a local office for
the toll point; and, second, where the call originates at the toll
point for the subscriber-at the local exchange. The method of
operating under the first condition is identical, whether the calling
subscriber is in the same exchange as that in which the toll board
is placed, or whether he is in a different exchange. It is as follows:
The subscriber having given the call to the A operator who answers
him, she goes in on an order circuit to a special operator called the Record-
ing Operator, and placed in the exchange with the toll board. The duty
of this operator is to receive the calls for toll points and to make out tickets
The call having been passed, the A operator withdraws the answering plug
from the answering jack and attends to other business The recording
operator, in the meanwhile, having entered on the ticket the number of the
a
282

(
ENORTH ELECTED
OLIVEIRA
RURAL TELEPHONE TYPE K
North Electric Co.
TELEPHONY
269
calling subscriber's line and the number of the called subscriber's line at the
toll point, passes the ticket to the toll operator who handles the toll trunks
to this point This operator goes in on the order circuit to the exchange
at which the call originated, and orders up the calling subscriber's line,
which is done in the manner already described for circuit trunk operation.
The toll operator plugs the answering cord into the trunk jack. While
the connection over the circuit trunk is being made, the toll operator plugs
the calling cord into the jack of the first unoccupied toll line, and ringing,
calls the operator at the toll point. When this operator answers, the called
subscriber's number is given and the connection put through in the usual
way The toll operator thus handles the call throughout, noting the time
during which conversation is held.
When the conversation is completed, the toll operator withdraws the
plug from the local trunk jack, thus giving the disconnect signal to the
trunk operator at that point, if the trunks are so equipped. If not she
must go back on the circuit and order the connection cleared. She then
rings on the toll line and when the operator at the distant point answers,
orders the connection cleared.
From the foregoing it will be evident that from the time that
the A operator, after having transmitted the call over the record-
ing circuit, withdraws her answering plug from the answering
jack, up to the time that the trunk operator takes up the calling
subscriber's line, this line having no plugs in either the multiple
or answering jacks, would not show busy to any other operator
who tested it. If, therefore, during this period, a call comes in
for the calling subscriber's line, it will be taken up by either an A
or B operator as the case may be. So that when the trunk
oper-
ator receives the call from the toll operator to put the connection
up, she will report the line busy As a result of all this, the
calling subscriber, instead of getting hold of the toll point required,
gets the subscriber who is calling for him This period, during
which the calling subscriber's line is unprotected, is called the
unguarded interval.
With the introduction of the common battery system, a device
was introduced with a view towards protecting the calling sub-
scriber's line during the unguarded interval. Though common
battery operating has not yet been touched on, this device will be
explained here for convenience.
It consists of a specially designed cord-circuit, the plug of
which is introduced by the A operator, as she transmits the call
over the recording circuit, into the answering jack, and is not

283
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TELEPHONY
removed until the trunk operator takes up the connection. This
circuit is called the Tone test circuit, and is wired as shown in
Fig. 254. The tip and ring of the plug are connected to battery
through the retardation coil, the ring strand having a relay, of the
type used on the A operator's cord circuit, in series. The shank
of the plug is connected to battery through the secondary winding
of a transformer, a 140-ohm resistance coil, the 15-ohm coil of a dif-
ferentially wound relay, and the coil of a second supervisory relay.
a

M
llit
Fig. 254.
The primary winding of the transformer is connected through a
150-ohm resistance to the terminals of an alternating machine a.
When the A operator has received the call from the calling
subscriber, and just before withdrawing the answering plug, she
directs him to hang up the receiver, so that when the tone test plug
is inserted, the receiver is on the hook. No current, therefore,
flows through the retardation coil Current flows, however, through
the 140-ohm resistance, the 15-ohm winding of the differential
relay, and the coil of the 6-ohm supervisory relay, to ground
through the cut-off relay on the calling subscriber's line. The 6-
ohm relay becomes energized, and a path is formed through its

284
TELEPHONY
271
armature and contact for the current to pass through the 130-ohm
coil of the differential relay to ground. The two coils of this relay
being in opposition, it is not energized. The direct current from
the battery, passing through the transformer becomes alternating,
and therefore, when the tone test plug is inserted in a jack, this
alternating current being thrown on the ring, any operator, touch-
ing the ring to get the busy test, will, instead of getting the usual
click, hear the humming noise produced thereby.
All operators are instructed to regard this “ tone test” in the
same light as the busy test, with the exception of the trunk oper-
ator who receives the call from the toll board. She recognizes in
it the fact that the line is being held up for the toll call and intro-
duces the trunk plug into the jack. When the trunk operator
thus takes up the line, the current from the shank of the trunk
plug flows along the wire attached to the rings of the jacks, till it
reaches the one in which is inserted the tone test plug. From
here it flows down the shank wire, through the 6-ohm relay to the
common terminal of the two windings on the differential relay,
thence through the 130-ohm coil to ground through the armature
and contact of the 6-ohm relay.
Since the current flowing through the 15-ohm coil must still
flow through the 130-ohm coil to ground, it remains the same in
amount as before. The current passing through the 6-ohm relay
is greater in amount and, therefore, the magnetizing effect of the
130-ohm coil becomes greater than that of the 15-ohm, hence the
relay becomes energized. When this happens, the armature, touch-
ing the contact, forms a circuit through the lamp marked - Disc.
Sig.”, which lights. Upon seeing this the A operator removes the
tone test plug. Should the calling subscriber require attention
during the unguarded interval, he has only to remove the receiver
from the hook, and the 120-ohm supervisory relay is energized,
closing the circuit through the lamp marked "Sub. Sig." Upon see-
ing this lamp light, the A operator removes the tone test plug, and
again answers the subscriber with the ordinary answering plug.
With the introduction of the common battery system and the
resultant system of automatic signals, the methods of operating
were changed in some cases. In a general way, the operators were
relieved largely of the necessity of supervising calls, and the work

285
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TELEPHONY
was in many instances considerably expedited. The principal
change has taken place in the work of the A operator. This should
be divided into three classes:
First, calls in which the calling and called subscriber's lines are in
the same exchange. Second, those in which the called subscriber's line
is in a different exchange of the magneto type, reached by circuit trunks.
Third, those in which the called subscriber's line is in a different ex-
change of the common battery type reached over circuit trunks.
The ring-down trunk operation and the toll operation are the
same as already described.
Taking the first case, the operator answers the calling sub-
scriber with the answering cord, which action automatically puts
out the line lamp as has been shown previously. Upon the sub-
scriber giving his call, the ringing plug on the same cord circuit is
inserted in the called subscriber's multiple jack, after it has been
tested for busy, and the subscriber rung up. When the plug is
inserted into this jack, the receiver being on the hook, the supervis-
ory lamp lights. When the called subscriber answers, this lamp is
shunted out. During the conversation the two supervisory lamps
are out. When the subscribers hang the receivers up after com-
pleting their conversation the supervisory lamps light, each one
independent of the other. Should one of the subscribers wish to
call the attention of the operator so that another call might be put
through, it is done by merely moving the hook up and down, when
the supervisory lamp on the cord connected with his line is flashed,
thus calling the attention of the operator. When the two super-
visory lamps light at the completion of the conversation, the oper-
ator clears the connection, without listening in to inquire whether
the parties are through.
The second case is that in which the called subscriber's line
is in a different exchange of the magneto type, reached over circuit
trunks. The method of putting up the connection is identical
with that already described except that split cords are not used.
When the conversation is completed and the subscribers hang up,
the supervisory lamp on the answering cord lights, but the super-
visory signal on the calling cord remains shunted out on account
of the fact that the trunk is closed through the repeating coil at
the incoming end. When the first supervisory lamp lights the A


286
TELEPHONY
273
a
operator takes down the connection, thus giving the disconnect
signal to the trunk operator who clears also.
The third case is that in which the distant office is of the com-
mon battery type and reached by circuit trunks. Here the con-
nection is put up in the manner already described. At the com-
pletion of the conversation, when the subscribers hang up, both
supervisory lamps light just as if both subscribers' lines terminated
in the same office. When the A operator clears out, the discon-
nect signal is given on the trunk and the trunk operator clears also.
Before closing the subject of operating in a local exchange a word
should be said relative to the duties of the trunk operator.
In one respect the duties of a trunk operator are easier to per-
form, than those of the subscriber operator; in another respect
they are the opposite. The trunk operator does not deal with the
subscriber, and is therefore free from the nervous strain consequent
upon this class of work. On the other hand, in exchanges in which
the percentage of trunked calls is above forty, the trunk operator
is required to work more rapidly than the subscriber operator.
Again, the trunk operators have to receive the calls from the sub-
scriber operators who are always in a hurry to complete the con-
nection. As a result they must be very careful to receive the call
correctly, which is made all the more difficult from the fact that
the numbers are called off very fast, and different calls come in, in
rapid succession.
It often happens that two or more A operators go on the same
order circuit at the same instant to order up different connections,
with the result that the trunk operator is able to hear only a con-
fused jumble. She must remain cool under these trying conditions,
and be ready to put up the first intelligible order that comes.
Wrong connections are sometimes put up, either because the A
operator has made a mistake or because the trunk operator has
heard wrongly. The result is that the A operator, after finding
the mistake, has to go back on the circuit a second time, usually
in a not very pleasant frame of mind, and order
up
the
proper
connection.
The frame of mind above referred to is usually vented at the.
trunk operator, but she must remain a perfect automaton, as far
as temper is concerned, and attend strictly to business. Lastly,
a



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TELEPHONY
where the percentage of trunked calls is above 50, the trunk oper-
ators must work faster than the A operators.
Long-Distance Operating partakes of some special features
which will be mentioned directly. Calls handled by the Long
Distance operating department are divided into three classes.
First, calls from local subscribers to long-distance points. Sec-
ond, calls from long-distance points to local subscribers. Third,
through calls. Calls from local subscribers to toll points are, as
far as the subscriber operators are concerned, handled in the same
manner as those to local toll points. The A operator, after having
answered the subscriber, passes the call over a special order circuit
to the receiving operator in the long-distance exchange, plugs the
tone test into the subscriber's multiple and withdraws the answer-
ing plug. The receiving operator, whose duties are the same as
those of the recording operator at a local toll board, makes out a
ticket with the number of the calling subscriber's line, his name
and the name of the party called for, together with his telephone
number and the town in which it is situated. This ticket is passed
to one of the recording operators, who, upon its receipt, goes in on
an order circuit to the proper local exchange trunk operator and
orders up the calling subscriber's number. The connection is put
up in the manner already described for local toll connections, the
recording operator plugging the trunk jack assigned by the local
trunk operator.
She then records the number of the trunk used on the ticket,
which is passed to the toll board operator who handles the lines, to
the long-distance point required. The toll operator rings on one
of the unused toll lines to the point required, and raises the long-
distance operator at that point. This latter operator proceeds to
get the called subscribers in the manner that will be described for
incoming calls from toll points.
In the meantime, the calling subscriber's line, together with
the trunk to the local exchanges, is held by the recording operator.
When the called subscriber has been reached by the toll line
operator she plugs the answering plug into the local trunk whose
number has been written on the ticket, and rings the calling sub-
scriber, who in the meantime has hung up his telephone. Upon
the subscriber again answering he finds himself in communication
288
TELEPHONY
275
with the point required. When the toll line operator plugs into
the trunk which is being held by the recording operator the visual
on the latter's cord circuit is shown, whereupon the recording oper-
ator withdraws the plug from the trunk jack. When the conver-
sation is completed, the visual is thrown on the toll line operator's
cord by the calling subscriber hanging up. The toll line operator
then releases the local trunk, and ringing on the toll line, directs
the operator at the distant end to clear the connection.
Calls from toll points to local subscribers are handled as fol-
lows: It must be remembered that the call is handled in the origi-
nating exchange in the manner already described. When the toll
trunk is rung upon at the distant exchange, the toll operator an-
swers, and upon learning the number required, goes on the order
circuit to the proper exchange and orders the trunk operator to
put up the connection, which is done in the regular way. The toll
operator plugs into the trunk assigned and the connection is com-
plete. The connection is cleared in the manner already described.
Through calls are handled in the following manner: Suppose
that a call from a toll point M comes in for a toll point N, which
has to pass through the exchange in question. The operator at M
rings on a toll trunk and is answered by the proper operator. .
After learning the details of the call, a ticket is made out with the
called and calling points, and passed to the through board operator.
The ticket also contains the number of the toll trunk upon which
the call has come in. The through board operator selects an idle
trunk to N and rings. When the operator at N answers, the de-
tails of the call are given. The through board operator then plugs
the answering plug into the assigned toll trunk from M, com-
pleting the circuit. When the trunk to M is taken up at the
through board, the visual is thrown on the cord circuit of the toll
operator holding it, who thereupon clears out.
a
TELEPHONE SYSTEMS.
Under this heading is included all methods of wiring tele-
phone circuits which possess special features, distinct from the
general features of telephone wiring. Some of these systems are
simple, and some of them are very complex.- Some concern only
the wiring of the subscriber's telephone, and some of them concern
289
276
TELEPHONY
the wiring of the whole exchange. Of the vast number of tele-
phone systems that have been introduced from time to time, only
those will be considered that possess distinctive features and that
have proven themselves by experience to possess decided advantages.
The origin of the telephone system seems to have been the
desire to connect two or more subscribers on the same line. The
first step in this direction was taken when the bridging bell was
invented, as has already been explained. The system which pro-
vides for the wiring of two or more telephones to the same line is
called a Party Line System; and a line which carries two or more
telephones is called a Party Line.
The simplest party line system that can be devised is that in
which the telephones are bridged across the same line. In Teleph-
ony,
Part I, it was shown what was the limit to the number of
bells that could be successfully bridged to the same line, looked at
from the standpoint of the electrician. It will now be necessary
to inquire what are the limits, if any, other than electrical, govern-
ing the number of telephones that can be successfully used on a
party line. In this discussion the party line circuits in Telephony,
Part I, should be referred to. It will be evident that when any one
subscriber calls the operator, or when the operator calls any one sub-
scriber, all the remaining subscriber telephone bells ring. Therefore,
a system of signaling has to be used, in order that when the oper-
ator rings, each subscriber will know when his attention is required.
The form of signal used is a given number of rings of the bell.
For instance, the first subscriber's signal will be two rings of the
bell; the second, three rings; the third, four rings; the fourth, five
rings, etc. Sometimes the duration of the “ring” is varied. For
instance, the signal for the first subscriber may be two short rings;
the second, one long and one short ring; the third, two long rings;
the fourth, one short and one long ring. As the number of sub-
scriber's telephones on the line increases, the number of signals
must increase, until a point is reached at which the signals have
either become so complex that the operator has difficulty in remem-
bering them, or else they take so long to ring that a serious loss of
time results, or the subscriber has difficulty in recognizing them.
Experience has shown that in large cities, and generally where
the calling rate is above three per day, four telephones is all that

a
290
TELEPHONY
277
а
can be bridged on one line, consistent with good results. It should
be remembered that during the time that any one subscriber is
using the instrument, the other subscribers cannot get service. So
that the greater the number of subscribers on a line, the larger will
be the interval during which any one of them will be denied the use
of the line.
With this system the different stations are denoted by letters
of the alphabet. The first station is denoted by A, and the second
by B. With the object of selecting a letter which has a different
vowel sound from either A or B, the third station is denoted by F,
and the fourth by I.
The usual code of signals made use of is as follows:
When the operator wishes to call A, two rings are used. Three
rings call B; four rings, F; and five rings I. When any one of the sub-
scribers wishes to call the operator, one ring is used.
The great disadvantage of this system lies in the fact that,
when any one subscriber is wanted, the bells are rung at all the
remaining stations, and also is this the case, when any one sub-
scriber wishes to call the operator. This condition, while never
pleasant, becomes a source of serious annoyance when one of the
stations requires all-night service, and the others are situated in
private houses.
Recognizing this point, telephone engineers set to work some
time ago to devise some system whereby each station could be rung
independently of the others, and the operator could be called with-
out disturbing the remaining subscribers. It was further recognized
as an additional disadvantage that when the various stations were
merely bridged across the line, each subscriber was free to listen to
the conversations of the others by merely lifting the receiver from
the hook and holding it to the ear. Of the many systems developed
to overcome the first mentioned disadvantage, the most elaborate,
and at the same time the only one that overcame the second defect
was that known as the B. W. C. system.
It is so named from the fact that these three letters represent
the first letters of the names of the three inventors, Messrs. Barrett,
Whittemore and Craft, at that time in the engineering department
of the American Telephone and Telegraph Co. The principle upon
which it worked consisted of the fact that the telephone bells were

291
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TELEPHONY
so wired that each one would respond only when the ringing cur-
rent was passed through the coils in the proper direction. The
system accommodated six telephones on a line. In the center of
the door of the bell box was a circular opening about 1 inch in
diameter. When any one of the telephones were in use a white
disc with the words: "Line in Use” was automatically displayed in
front of this opening on the remaining five instruments. When
the receiver was hung up, the signal on the others disappeared
This was called the lockout signal, and when it was displayed the
hook switch was automatically held down, so that the conversation
could not be listened to.
The wiring of the bells is shown in the following figures: In
Fig. 255 is shown the outline of the system, illustrating the prin-
a
с
b
Fig. 255.
е
ciples upon which the operation is based. Here a and b represent
two sides of the line, which are known as the a and b side; cand
d represent the coils of two polarized relays, the middle point being
grounded. At e is the battery which may be connected to the line
in any one of the following ways:
The positive pole to the a side of the line, and the negative pole to
ground, causing the current to flow through the coil c to ground. The
negative pole to a and the positive pole to ground, causing the current to
flow in the same circuit, but in the opposite direction. The positive pole
of the battery to the b side of the line and the negative to ground,
causing the current to flow over the b side of the line and through the coil
d to ground. The negative pole of the battery to the b side of the line,
and the positive to ground, causing the current to flow over the same cir-
cuit, but in the opposite direction. The positive pole of the battery to the
a side of the line and the negative to the b side, causing the current to flow
through the two coils in series. The negative pole to the a side of the line
and the positive to the b side, causing the current to flow over the same
circuit, but in the opposite direction.
By properly connecting the two relay coils together and also
to line, the bell may be made to respond to any one of these com-

292
TELEPHONY
279
binations. There are other combinations that could be made, but
these six are all that are used in connection with this system.
The battery used for ringing consists of three banks of 80
volts of Leclanche battery each; the first one having the negative
pole grounded, the second having the positive pole grounded, and
the third connected metallic. The keyboard circuit is so wired
that any one of these banks can be cut in at will.
The wiring of the bells will next be considered. From the
nature of the combinations, the same bell wiring will answer for
stations 1 and 3. The same wiring for stations 2 and 4 and the
same for stations 5 and 6. So that only 3 different forms of bell
wiring are required for six stations.
Figure 256 shows the wiring for stations 1 and 3. The bell
box is equipped with three binding posts; the two outside ones
being for the line and the center one for the ground connection.
From the right-hand binding post the line passes down through
the upper hinge of the door, to and through the right-hand 200-
ohm coil, to the upper magnet coil; thence through the upper 500-
ohm coil to the left-hand upper contact at the heel of the switch.
The receiver being on the hook, contact is made at this point
with the switch, from which the current passes through the 200-
ohm coil to the middle binding post, and thence to ground. The
armature of the magnet and the contact point, when touching, form
a short circuit around the upper magnet coil. When no current is
following, the polarized relay attracts the armature away from the
contact, so that this shunt circuit is open.
When the operator rings No.1, the current is sent out over the
a side of the line to the right-hand binding post, and thence to
ground through the circuit already traced. The action of the cur-
rent passing through the upper magnet coil, repels the armature
till it touches the contact, closing the short circuit and drawing all
the current from the coil. The electromagnetic field is therefore
reduced to zero, and the armature, acting under the influence of
the permanent field is again attracted away from the contact point.
Directly this happens, current again flows through the upper coil,
and the same process is repeated. In short, the armature acts like
a buzzer and rings the bell.
293
280
TELEPHONY
When current is passed through from the left-hand binding
post, it follows the internal wiring through the lower coil to
ground. The action of this coil is to keep the armature away
from the contact, thus preventing the bell from ringing. This
would be the condition when No.3 was rung. When No. 2 is rung,
the current is passed through the upper coil in the opposite direc-
tion, with the result that the armature is kept away from the con-
tact and the bell does not ring. The same conditions prevail
when No.4, No.5 and No. 6 are rung, so that it will be seen that the

F
conden
ser
500
ohms
2000
Tohms
MWM
200
500 ohms
O200 ohms
ohms
TE
telephone trans- second-
mitter ary
Fig. 256.
bell at No. 1 responds only to its proper current. By connecting
the a side of the line to the left-hand binding post, the bell re-
sponds to the combination for No. 3.
The wiring of the bell used at stations 2 and 4 is identical with
that of No. 1 and No. 3, with the exception that the magnet coils
are wound in the opposite direction. When the bell is used for
station No. 2, the a side of the line is connected to the right-hand
binding post, thus causing the current to flow through the upper coil,
which makes the bell ring in the manner already described. Thus
the bell is irresponsive to the ringing current for any other station.
In Fig. 257 is shown the wiring of the bell used for stations 5
and 6. It will be seen that the wiring is different from that already
294
TELEPHONY
281
described. It will be remembered that the ringing circuit for these
two stations is metallic. From the right-hand binding post, the
circuit goes to the upper hinge on the door, and from thence through
the upper 900-ohm coil, the right-hand 200-ohm coil to the right-
hand magnet winding, through which it passes to the hook switch.
Passing through the switch, it runs through the left-hand contact
to the left-hand magnet coil, the left-hand 200-ohm coil, the lower
900-ohm coil, the lower hinge and out at the left-hand binding post.
Current passing through the magnet coil in this direction, rings
the bell in the manner already described. When the current is
passed through in the opposite direction, the magnet armature is
attracted and the bell does not ring.

condenser
900
Ohms.
2000
Ohms.
WW WWW
200
200
Ohms. Oohms
HP
900 Ohms.
Fig. 257.
When this bell is used for station No. 6, the a side of the line is
connected to the left-hand binding post. It will now be necessary to
describe the manner in which the subscribers call the central office.
In Fig. 258 is shown the wiring of a line entering the exchange.
A 4-volt battery is connected to the line drop, which is differentially
wound. The current passes out through one winding of the drop,
through the bell circuit at the instruments, and returning on the
opposite side, passes through the other winding. The two wind-
ings of the drop being opposed to each other, the magnetic effect
of one is neutralized by that of the other, so that the drop is not
thrown. When the receiver is removed from the hook, however,
at any one station, the hook switch in moving upward makes rub-
bing contact with two springs. Directly this happens, the current
295
282
TELEPHONY
from the 4-volt battery passes through one side of the drop and to
ground, through the middle binding post, the circuit being
made through these contacts. When the hook switch reaches its
highest point, this contact is again broken, and remains so during
the conversation. The current passing in this way through only
one winding of the drop, the differential effect is lost, and the shut-
ter thrown. The drop is self-restoring.
In Fig. 259 is shown the wiring of the operator cord circuit,
where the a and b sides of the line are shown at a and b.
The B.W.C. System has some advantages and many disadvan-
tages, some of which were supposed to be especially strong features
4volts.

d
c drop
W wb
1
2
a
to subscriber telephones.
by jack
Fig. 258.
by the inventors. Among the advantages may be mentioned--First:
Selective ringing. This feature has been shown to be the strong-
est one that the system possesses, and it paved the way for the
inventions in this direction. Second: in small towns and villages,
it gives a cheap and comparatively good service.
Among its disadvantages may be mentioned-First: The
apparatus both of the telephone and switch board are very compli-
cated, and it is impossible to obtain inspectors with sufficient edu-
cation to properly maintain either for the pay that the companies
are willing to give. Second: The keyboard wiring is so compli-
cated that only one set of keys is provided for each operator,
with which she is compelled to ring on all cords. This necessarily
tends to slow up the service, Third: The complicated keyboard

296
TELEPHONY
283
wiring makes it impossible to provide incoming trunk sections, as
with only one set of keys to a trunk operator, this would have to
be used on all the trunk cords in this position, which would be
prohibitive.
The switchboards are therefore made up into standard sections
of from 80 to 100 lines each, and the system of operating is iden-
tical with that employed in connection with the standard switch-
board. This feature limits the capacity of the office to 600 lines 6
sections. As a result in large cities the system is not at all applicable.
a
Fourth: The “Lock-out” device which was supposed to be the
b

다​.
a
M21 131 2 Mol MAI 14,411
5
6
7
8
Fig. 259.
strong point, proved to be directly the opposite, and for the follow-
ing reason:
When the lock-out signal is destroyed, the subscriber, should he
desire to use the telephone, has no means of listening on the line to
assure himself that the line is actually in use. He must wait until the
signal disappears. His natural suspicion of corporations leads him to
believe that the company has devised some scheme to prevent him using
the line according to the contract, and he therefore writes a letter of
complaint to that effect.
So serious a source of complaint has this become in some cases,
that the lock-out device had been abandoned, and the subscribers
allowed to listen in at will. Experience has shown therefore that
while the selective feature of the system is a success, the other
features are not, and as a whole the system does not seem to have
a very bright future.
The selective systems to be described directly have retained
the selective feature, but discarded the others. A very simple and
efficient selective system is one which provides for two parties on
a line, and is wired up as shown in Fig. 260. Each cord circuit
297
284
TELEPHONY
both for the A operators and B operators is equipped with a special
ringing key which throws the free side of a grounded alternating
machine on either side of the line. This system was introduced
contemporaneously with the common battery system. The diagram
shows the regulation cord circuit plugged into a jack on a subscrib-
er line, to which is wired two stations; for simplicity the line and
cut-off relays are not shown, as they play no part in the operation
of the system. The ringing key will be seen to be made up of two
halves, each one a duplicate of the other. The ringing current
generator a, one side of which is grounded, is wired to the outside
contacts of both halves. The inner points of the right-hand half
are strapped to the opposite middle contacts of the left-hand half.

Me
52
A
9.
9
thi
B
OO
Oo!
wwy
wy
中​。
th
Fig. 260.
If the right-hand half of the key is used, the free side of the gen-
erator is thrown out on the ring of the plug, while if the left-hand
half of the key is used, the free half is thrown out on the left tip
of the plug. In both cases the opposite side of the line is grounded.
At A and B are shown two telephones, the former having the
condenser wired to the ring contact line of the jack, and the latter
having the condenser wired to the tip contact of the jack.
Suppose that the right-hand half of the ringing key is depressed.
The free side of the generator being thrown on the ring of the plug,
the current therefrom passes out on that side of the line, and upon
reaching the telephone at A, flows through the condenser and bell
coils to ground at g ringing the bell. Passing on to B the current
finds an open circuit at the hook switch. If the left-hand half of
298

so B
대
​HOLTZER-CABOT
MULTICYCLE RINGING SET WITH SPEED CONTROLLER AND BUSY-BACK ATTACHMENT
Holtzer-Cabot Electric Co.
TELEPHONY
285
the key is used, the current flows out on the tip side of the line,
and upon reaching B, flows through the condenser and bell coils to
ground at g, thus ringing the bell. This current upon reaching A,
finds an open circuit at the houk switch. The bells are thus rung
selectively.
A very good form of party selective system has been devised,
which is more complicated than that already described, and oper-
ates upon a somewhat different principle. That this principle may
be understood properly, it will be necessary to return for a moment
to the consideration of the nature of an alternating current.
An alternating current is usually defined as one that rises from
zero to a maximum in one direction, then dies away gradually to
zero; it then increases gradually in the opposite direction to a
maximum, after which it again gradually dies away till zero is
reached. That is, if one of the terminals of an alternating current
generator is regarded at the instant of the beginning of the cycle,
the current will begin to flow with a gradually increasing density
from the machine out on the line. After the instant of maximum
flow has been passed, the current density gradually diminishes,
until it dies out, but still continues to flow in the same direction.
When the instant that the current density reaches zero has been
passed, it starts to flow in the opposite direction, that is, from the
line towards the machine, until its density has again reached a
maximum, after which it dies away until it again reaches zero.
This fluctuation from zero through a maximum back to zero
again, in one direction, and from zero through a maximum to zero
again, in the other direction, constitutes one wave or cycle.
This wave may be regarded as made up of two impulses: The
one flowing from the generator terminal to the line and the other
flowing from the line towards the generator. The first is called
the positive impulse; the second, the negative impulse.
The operation of this four-party selective system consists in
providing a bell that will be responsive to one of these impulses
and irresponsive to the others. In looking over the situation it
will be seen that four combinations can be made.
First: Positive impulse on the ring of the plug with the tip grounded.
Second. Negative impulse on the ring of the plug with the tip grounded.
Third: Positive impulse on the tip of the plug with the ring grounded.
Fourth: Negative impulse on the tip of the plug with the ring grounded.
299
286
TELEPHONY
8
In order that these combinations can be effected, the gener-
ator must be so constructed that one brush collects positive
impulses only, and the other negative impulses only. This can
readily be accomplished with the usual form of magneto generator
by making one half of each collector ring out of some non-con-
ducting material such as hard rubber as shown in Fig. 261, where
6b' represents the armature coil. Regarding the side 6, assume
that the direction of the magnetic flux and the direction of rota-
tion cause the current to flow in the direction of the arrow; then
the direction of the flow in the side b' will be as indicated by the
other arrow. Then in the position shown, the left-hand brush will
be positive and the right-hand one negative. If the collector
rings were made up wholly of conducting material, then when the
armature rotates through 90° the right-hand brush will become
positive and the left-hand neg-
ative. But if one half of each
ring is made of hard rubber as
shown by the shaded portions
on the diagram, then when the
armature coil has revolved far
enough to change the direction
of current flow in the side 6, the
brush will be resting upon the
insulated portion and no cur-
rent will flow through it. Sim-
Fig. 261.
ilarly, when the direction of cur-
rent flow in the side b' changes,
the left-hand brush will be resting on the insulating portion. As a
result the left-hand brush will receive positive impulses only, while
the right-hand brush will receive nothing but negative impulses.
The ringing key used in connection with this system is so arranged
that the positive or negative terminal is connected to either side
of the line while the opposite side is grounded. The wiring of the
operator's cord circuit is shown in Fig. 262.
AUTOMATIC SYSTEMS. .
Under this heading is included all the systems whereby the
subscriber is enabled to provide the proper connections without

+
leer
موقفف
300
TELEPHONY
287
use.
جی
the assistance of an operator. Systems of this type have been
largely used for some years for what is known as house service,
which means interconnection between offices in the same building
or the like. Automatic systems have also been devised for general
In this connection the exchange is equipped with the auto-
matic switching device, and no operators are required. These
latter systems do not give much promise, as the cost of the instal-
lation is away beyond that of the ordinary type of switch-
boards; while the cost of maintenance is also excessive. For ex-
ample, the cost of a 50-line
switchboard installed with
auxiliary apparatus is about
0
$500.00, while the cost of an
automatic switchboard of
the same capacity is about
$3,000.00. The annual
charge against an exchange,
including operator's salaries,
Suva
heat, supplies, maintenance,
but not rent, is about
$1,000.00. The automatic
system has not been in use
long enough to enable one
to get a very correct idea
of the cost of maintenance.
But experience, shows that
it is fully equal to the above-
mentioned figure, and may,
Fig. 262.
in some cases, even exceed
that. For house service,
however, the automatic system is very successful and is used ex-
tensively.
Among the best adapted systems of this class is the one which
is shown in Fig. 263. Here are shown four instruments connected
together. The wiring of the telephone is the same as that of those
designed for general use. Each instrument is equipped with a
series bell and magneto generator. One side of all the instruments
is wired to a common return wire, in addition to which there

-
ad
+
301
288
TELEPHONY
extends between each one and its fellows, the same number of
wires as there are instruments, and each one terminates in the
contact of the switch placed at each station. These contacts are
arranged on the circumference of a circle, over which the switch
lever passes. The heel of the switch lever is permanently con-
nected to the opposite terminal of the instrument. These contact
points are numbered to correspond with the number of the station
with which they connect. When the telephone is not in use,
the
switch lever should be left on the contact whose number corre-
sponds with that of the instrument.
Referring to the figure. Suppose that station No. 1 wishes
to call station No. 2. The switch lever at station No. 1 is moved
from contact No. 1 to contact No 2 and the generator turned.
16
still

2
46
Thooth
♡
Hooli
Toollh
b
b'
3
b'
3
B'
O
4
1.23
4
2A
3
2
4
2
നുപ
2
3
4
SIWN
common return
Fig. 263.
The ringing current flows from the generator at No. 1, along the
common return to station No. 2, thence through the generator and
bell to the opposite side of the lever. Passing through the switch
lever which rests on contract point No. 2, the current flows along
wire No. 2 to the No. 2 contact at switch No. 1, and through the
switch lever through the bell back to the generator. Transmission
is carried on over the same circuit. If the party at No. 1 desires to
communicate with station No. 3, the switch lever is moved to con-
tact No. 3 and the party rung up. The circuit is made up of the
common return wire to station No. 3, thence through the instru-
ment to the switch lever. Passing through the switch lever to
302
TELEPHONY
289
contact No. 3, it follows the line to contact No. 3 at station No.
1, from which it passes through the switch lever to the opposite
side of the telephone. By the same method each one of the other
stations can call any of the others. In the figure No. 1 is in posi-
tion to call up No. 4.
From the nature of the wiring, it will be seen that when a
telephone is not in use, the switch lever must be always left on the
contact whose number corresponds to that of the station. That is,
at station No. 1, the switch lever must be left on contact No. 1,
while the instrument is not in use; at station No. 2 the switch
lever must be left on No. 2, etc.
Consider what would happen if this were not done. Suppose
that through carelessness or other cause, the switch at No. 1 were
left on contact No. 4, and that station No. 4 wished to call up No.
1. The party at No. 4 would move the switch lever to contact
No. 1 and ring, but under these conditions the circuit would be
open at the contact at station No. 1, so that this station could not
be called. It is, however, possible to arrange the wiring so that a
station will get a ring even if his switch is not on the home station
point, although it must be placed there before conversation can be
carried on.
One defect of this system lies in the contact buttons of the
switches. Being exposed to the air, they are apt to become cov-
ered with dust, and thereby the electrical contact is made very
poor, in fact, it sometimes happens that the dirt accumulation is so
thick as to prevent contact from being made at all. To overcome
this defect, the switches are sometimes replaced by jacks and plugs.
Under these conditions each station is equipped with a small box
containing the same number of jacks as there are stations. Each
jack is numbered to correspond to the number of the station to
which it is wired. To call, the plug is inserted into the proper
jack and the generator turned. When the telephone is not in use
the plug is left in the jack corresponding to the number of the
station. This jack is called the home jack.
Various devices have been brought forward from time to time.
with the object of doing away with the necessity of returning the
switch to the home contact, or placing the plug in the home jack.
The most successful of these is the one put forth by the Holtzer-
303
290
TELEPHONY
PA
0
Cabot Company, of Boston, Mass. The feature of this system
consists of an automatic mechanism which causes the switch lever
to return to the home button or contact, when the receiver is hung
up. In addition it also makes use of a common signaling wire.
.
The mechanism of the apparatus is shown in Fig. 264. The hook
switch and the switching
mechanism are contained in a
d box, on the outside of the door
of which is placed the switch
lever and the contact buttons.
Outside of the latter and in-
sulated from them is a metal
arc-shaped piece, which the
end of the lever does not nor-
mally touch; but by pressing
the lever, electrical contact
can be made between the two.
To this arc is connected the
common call wire. Fastened
to the shaft of the switch
lever, and placed inside of the
box is a ratchet wheel a into
which fits a pawl 1, held in
place by a spiral spring c.
switch
The hook switch is shown at
lever
d and has its heel equipped
with a hard steel dog e pivoted
at f. This dog is brought
metal arc
back by the spiral spring g to
the position shown. The
Fig. 264.
ratchet wheel a is, when left
free, rotated clockwise by a coiled spring (not shown).
The receiver being on the hook, the party wishing to call
moves the lever till it touches the proper contact button, and press-
ing it till it makes contact with the arc, calls the desired party. .
As the lever is rotated so is the ratchet wheel, and the pawl retains
it in the proper position. When the receiver is hung up again, as
the heel of the switch moves up, the dog e engages in a notch at



contact
109
8
buttons.
765
304
TELEPHONY
291
its top, and lifts it clear off the ratchet teeth. The ratchet wheel
thus being set free is rotated under the action of the coiled spring
towards the home position. Since the dog e engages the notch in
the pawl only momentarily, as the heel of the switch passes upward,
it would slip back and engage the ratchet teeth before the wheel
had returned to the home position, were not some means taken to
prevent it. To this end the pawl is provided with a pin h, which
as it passes upward engages with a second dog i, preventing it
from again returning to its downward position. This second dog
is tripped by the ratchet wheel just as it reaches the home position,
allowing the pawl to fall at the proper time.
MAINTENANCE.
General Remarks. The general plan of organization followed
by the majority of the telephone companies at the present time,
calls for the following departments:
The Engineering Department, whose business it is to design
the plant to be used and to supervise its construction. The Con-
struction Department, which has to do with the building of the
plant. The Traffic Department, which has to do with the opera-
tion of the plant. The Maintenance Department, which has to do
with keeping the plant in condition necessary for its proper
operation. The Supply Department, which is concerned with the
feeding of the plant.
There are two other departments which are found to be nec-
essary in all large companies, and they are, the Contract Depart-
ment and the Right of Way Department. The functions of these
two latter are indicated by their titles. It is not the purpose of this
article to discuss the subject of organization, but to prefix a treatise
on the subject of maintenance, by a few general remarks on the
duties performed by each department of a well organized company.
THE MAINTENANCE DEPARTMENT.
The Maintenance Department has been defined as that
which has to do with the keeping of the plant in such shape that it
can be properly operated. It will now be necessary to learn the
method of organization and the nature of the work to be per-
formed, in order that the plant may be so maintained.
305
292
TELEPHONY
The subject of maintenance is best studied under the follow-
ing heads: Exchange Maintenance, Line Maintenance, and Sta-
tion Maintenance. The first, as its name indicates, treats of the
maintenance of the central office apparatus; the second treats of
the maintenance of the line; while the third relates to the main-
tenance of the subscriber telephone.
It should be mentioned here in passing that line maintenance does
not include the maintenance of cables; this work being done by the con-
struction department for reasons which it is not necessary to state.
The subject of central office maintenance will be taken up
first, and in this connection it will be learned how and where the
trouble is first reported; to whom the trouble reports are sent; how
they are recorded and the trouble tested, and what steps are neces-
sary to be taken to clear the trouble, whether it be in the exchange,
on the line or at the station,
METHOD OF REPORTING TROUBLE.
From the fact that the traffic department operates the plant,
it would be the first to note any defect in its condition, and so all
trouble reports originate in this department. Besides the cases of
actual trouble, there is a second class of irregularity called “Don't
Answer", which, as the name indicates, refers to all cases in which
the operator is unable to make the called subscriber answer the
telephone. These “ Don't Answers”, as they are called, are re-
ferred to the monitor in the exchange into which the called sub-
scriber's telephone line runs. If after trial this official is unable
to obtain a response from the called party, the case is referred,
together with the actual trouble, to the maintenance department.
A record of all trouble reported is kept by the traffic department.
ORGANIZATION OF MAINTENANCE DEPARTMENT.
The method of organization of the maintenance department
will depend largely on the nature of the territory to be covered
and the volume of business to be handled. A typical system of
organization will be given, however, which will cover all the
essential features.
The department is presided over by a superintendent, who in
addition to the necessary clerical force, should have the following

306
TELEPHONY
293
a
lieutenants: A district inspector, a foreman of instrument set-
ters, and a foreman of inspectors. Reporting to the district in-
spector, there should be in each exchange a wire chief, whose duty
it is to test all trouble reported, to direct the force of men who
clear the trouble, and to see that the central office is kept in proper
condition. The size and nature of the force reporting to the wire
chief will depend on the size of the exchange, and the extent of
territory covered by the district. In the large exchange, it will be
found necessary to provide an assistant wire chief in addition to
the inside trouble men. Where there is an assistant wire chief,
he is the man who does the actual testing; the wire chief having
enough to occupy his time in the general supervision and care
of the office.
The duty of the inside trouble men is to clear whatever trouble
occurs to the switchboard and central office apparatus. The requi-
site number of these men will depend altogether on the size of the
office and the volume of business handled. For the purpose of
clearing line trouble a force of outside trouble men is needed.
These men must be linemen, and capable of handling all trouble
that occurs to the open-wire lines.
The instrument or subscriber station trouble is handled by a
force of inspectors who are familiar with the method of operation
of the various telephone instruments, and are therefore able to
keep them in proper working order.
The usual arrangement is to have the outside trouble men,
together with the central office force, report to the wire chief, while
the inspectors report to their foreman This plan is considered to
be the best practice, but is not always followed.
The Foreman of Inspectors has under him his force of in-
spectors, who keep constant watch over the subscriber stations.
The usual method is to divide the territory into “Routes”, assign-
ing an inspector to each route. The inspector visits constantly
the telephones on his route, taking each in its turn, repairing what-
ever defects he notices, and keeping them in first-class general
working order. He is also called upon from time to time, as
occasion arises, to clear whatever trouble may occur to the telephones
under his jurisdiction. To this end he is required to keep in con-
stant touch with the wire chief of the exchange, within the district
307
294
TELEPHONY
of which his route lies. In cases where Leclanche batteries are
used, he is required to carry in his satchel, in addition to the
necessary tools, a supply of sal ammoniac and battery zincs. Where
Fuller batteries are used, he carries in connection therewith only
a small bottle of mercury.
The work of renewing the batteries is here delegated to a sep-
arate force of " battery men,” who are provided with wagons, car-
rying battery acid, zincs, carbons, and jars, and who are assigned to
routes similar to but larger than those assigned to the inspectors.
These men are also required to clear special battery troubles, and
are therefore required to report regularly to some one delegated to
receive reports of this nature. Where the battery route lies wholly
within one exchange district, the battery man reports to the wire
chief. Where the route lies within the districts of more than one
exchange, the wire chiefs of these exchanges report their battery
troubles to an assistant to the foreman of inspectors, and the bat-
tery men are required to keep in touch with this official. Usually
the battery men come under the jurisdiction of the foreman of
inspectors Where the work is very heavy, however, a special
foreman is assigned to look after this work. Where the common
battery system is used, the battery renewal work is eliminated.


308

000
OOK
QOROS
CENTRAL ENERGY SWITCH BOARD WITH TOLL ANNEX POSITION.
Stromberg-Carlson Telephone Mfg. Co.
TELEPHONY
PART VI.
MAINTENANCE.- (Continued.)
The Foreman of Instrument Setters has under his direction
the force of men who equip the subscriber stations with the neces-
sary telephones. Their work consists, in addition to placing new
telephones, of renewing and replacing working telephones, upon
the subscribers changing their addresses. Upon the completion of
such work they are required to call the wire chief of the district
in which this work is done, in order to keep him posted and assist
him in making whatever tests he deems necessary. The organiza-
tion of the maintenance department having thus been treated in
outline, it will now be necessary to take up each sub-department
in detail, and follow closely the work performed. It will be
assumed that the student is familiar with the nature of a modern
telephone plant, both in regard to circuits and apparatus used.
Wherever it becomes necessary to refer to circuits or apparatus de-
signed for maintenance purposes, these will be given in fullest detail.
The District Inspector. This official is the one to whom the
wire chiefs report. He should be a thorough maintenance man,
and is usually graduated from the position of wire chief. He is
responsible for the condition of the exchanges and the lines. He
receives monthly reports from each wire chief, which show the
number of troubles reported; the number of such cases in which
actual trouble was found upon testing; the number of such cases
which were found to be without actual trouble upon testing; the
number of " Don't Answers” reported, and the number of these
reports that proved upon test to be cases of actual trouble. A
report is also sent in from each exchange showing the number of
troubles cleared by each trouble man, and the average time occu-
pied in so doing
311
296
TELEPHONY
These reports form a basis for a monthly report which the
District Inspector is required to forward to the Superintend-
ent. The reports above referred to, are useful not only in de-
termining the character of the employes' work, but also in deter-
mining which portion of the circuit or apparatus is most apt to
get into trouble. From these reports also, the requisite informa-
tion is obtained for determining the size of force necessary for
the proper maintenance of the plant. It is in the analysis of
these reports that the experience of the district inspector becomes
useful, in rendering him able to compare the actual conditions
with those which should obtain in an ideal plant. In addition to
.
the handling of reports, the district inspector is called upon to
transmit all necessary orders to the wire chiefs, and to see that
they are properly carried out. The duty of ordering supplies,
and extra apparatus for maintenance purposes also devolves upon
him, and he is the sole judge of the amount of such material nec-
essary to be kept on hand
The Wire Chief. The duties of the district inspector having
been described, it now becomes necessary to take up those of the
man who has in hand the actual maintenance of the plant, the
Wire Chief. He is the officer on the firing line as it were, and he
is directly responsible for the condition of the district. Every-
thing depends on the wire chief. If this official is of the right
caliber, he will see to it that he has the right sort of assistance,
and that his force, both within the exchange and without, attend
properly to their duties, under his direction. He should be a man
who is not only thoroughly familiar with the details of the plant,
both within and without the exchange, but also with the habits of
the men of the class whom he has to direct. He must be able to do
all the necessary testing with the utmost dispatch, and to properly
direct the men in clearing trouble. An exchange maintenance
force with a poor wire chief is like a ship without a rudder.
The following routine business passes through the wire
chief's hands :
Testing and clearing all cases of trouble within the exchange dis-
trict. Giving the construction gangs and the instrument setters, O.K.
reports when their work is properly done. Receiving the reports of the
inspectors and battery men. Supervising the renewal of lines that have
been discontinued.

312
TELEPHONY
297
At this point it will be well to follow the course of some of
the orders which reach the wire chief for final action. The order
for a new line will be taken as an example.
The new-line orders are made out in the General Superin-
tendent's office and are then sent to the construction department for
the proper assignment of conductors. The conductor assignment
having been placed upon the order, it is then sent to the mainten-
ance department, after the requisite information has been taken off
to enable the construction gang to build the line. Upon its receipt
at the maintenance-department office a duplicate is made out for the
foreman of instrument setters, the original being sent to the wire
chief, within whose district the new line is to lie. Upon receipt
of this order the wire chief has the cross connection properly run on
the main distributing frame, and sends the order to the exchange
manager for his information, and for the purpose of enabling him
to enter upon the order the answering jack assignment. The order
is then returned to the wire chief, who has the proper cross con-
nection made on the intermediate distributing frame, and where
the magneto system is used, the line drop is placed with the new
line number and whatever symbol is used to denote the particular
class of service. Where the common battery system is used, in
addition to running the cross-connection at the intermediate jack,
the
proper number plate must be placed over the answering jack,
and a lamp cap, marked to denote the particular class of service,
placed over the line lamp.
In the meantime, when the construction gang which has been
busy building the line, finishes its work, the wire chief is called
and a thorough test made to determine whether or not the proper
conductors have been used, and of proper continuity and insulation
resistance. The construction foreman is then given an O.K., and
this is recorded on the order, together with the time of day and the
name of the foreman. The line is now ready for the instrument
setter, and when he finishes his work he calls the wire chief and
the line is given a complete test.
Nature of Tests and Testing Apparatus. The nature of the
tests made, and the nature of the testing apparatus used in the
routine work of central office maintenance, will now be described.

313
298
TELEPHONY
Leaving out of consideration for the present the subscriber
station, the troubles to be cleared by the maintenance force are
classified under the following heads:
1. Crosses, in which one or both sides of two metallic circuits come
into electrical contact, so that conversation on one can be heard on the
other.
2. Opens, in which one or both sides of a circuit become electrically
discontinuous.
3. Short circuits, in which one side of a circuit comes in contact with
the other side, thereby cutting out or isolating the terminal apparatus.
4. Grounds, in which one or both sides of a circuit form electrical
contact with the earth, rendering the line more or less noisy, and the con-
versation indistinct.
The introduction of the common battery system, has introduced a
fifth class of trouble called “low insulation”, which refers to the condition
where the insulation of the line has become so low that, while it does not
interfere with conversation, it prevents the proper working of the line
and supervisory signals.
With the magneto system, the following conditions obtain
on the subscriber—sending, ring-down, and common trunks. A
metallic circuit closed at the distant end through the bell at the
subscriber telephone, or drop in the case of a trunk, and at the ex-
change end, closed through a drop in the first and last named cir-
cuits, or standing open through the multiple in the case of a
sending ring-down trunk. All circuit trunks, whether incoming
or outgoing, are closed through repeating coils at both exchanges,
so that under normal conditions all circuits show closed towards
the foreign end, and all circuits except sending circuit trunks and
sending ring-down trunks, show open towards the home exchange,
if the test is made inside of the repeating coil. With the common
battery system, on the other hand, the subscriber lines test open
towards the telephone, or distant end, and open towards the ex-
change when the cut-off relay is energized. The outgoing ring-
down trunks show closed as before, as do the outgoing circuit
trunks to magneto offices. The outgoing trunks to relay offices, on
the other hand, show open under normal conditions, owing to the
presence of the condenser cut into the repeating coil at the distant
end. All circuits except the incoming ring-down trunks, if there
bo
any,
show closed towards the home exchange, if the test is made
inside of the repeating coil.

314

AUS
***
TELEP
(MONARCH
DOUBLE BATTERY BOX TELEPHONE
Monarch Telephone Mfg. Co.
TELEPHONY
299
The tests made by the wire chief are by no means as elaborate
as those used by the cable maintenance department in locating
faults. They are such as can be made very rapidly, and yet are suf-
ficiently accurate to enable the wire chief to determine where to
look for the trouble. Before going into the details it will be neces-
sary to consider the general plan followed in locating trouble; after
which the detail tests, with the apparatus used for both the mag-
neto and common battery system, will be followed out.
When a trouble is reported to the wire chief, his first duty is
to determine whether it lies within the exchange or without. Any
trouble which is located on the main distributing frame, or in the
office wiring between this point and the last section of switchboard,
is said to be an inside trouble. But if it is located in the wiring
anywhere between the main frame and the subscriber station, it
is said to be outside trouble. Some troubles are of such a nature
that their location can be determined without any special test,
while others necessitate a succession of tests before the requisite
knowledge is determined. A trouble being reported, the line in
question is first taken up at the main frame and a test made
between this point and the switchboard. If this portion of the
line is found to be in good working order, a test is then made
between the main rack and the subscriber station, and the trouble
will be found to be located in this portion of the wiring. The
portion of the line in which the trouble is located, must next be
determined, and the method of so doing will be described later.
Should the trouble be located in the exchange wiring, the line is
again tested between the main and intermediate frames. If this
portion proves to be in proper condition, it is tested between the
intermediate frame and the first section of switchboard, then
between the first and last sections of switchboard, the process being
repeated until the defective portion has been found.
The apparatus used for testing in connection with the com-
mon battery system differs materially from that used with the mag-
neto system, and the nature of the tests used differs also, on account
of the difference in the natures of the circuits used in the two sys-
With the magneto system all circuits, with the exception
of the incoming end of circuit trunks, are normally closed. With
the common battery system on the other hand, all circuits test
tems.
315
300
TELEPHONY
normally open. Again, the presence of current on the line continu-
ally, in the case of the common battery system, gives an additional
means of testing, which is not present in the magneto system.
In connection with the magneto system, the circuit shown in
Fig. 265 is the one made use of by the wire chief. It consists of
the following: A plug a is wired to a ringing key b, the gener-
ator being shown at c. The listening key is seen at d, the wires
leading to the wire chief's telephone being shown at k. At e is
seen a battery of 3 Fuller cells, which is wired to a telegraph relay
f, so that when the plug a is inserted into a closed line, current
flows through the relay, energizing it and drawing the armature i

a
lo
b
с
g
m
17
h
n
d]
е
f
K
Holole
Fig. 265.
up against the contact point h, closing the auxiliary circuit contain-
ing the battery and the telegraph sounder g. The sounder is used
to intensify the noise made by the closing of the relay, thus giving
the wire chief an oral test. At l is shown another plug wired to a
reversing key m which is grounded at n, so that this ground can
be thrown on either the tip or ring, as desired. This circuit is used
in testing crosses, as will be explained later.
This circuit is placed on the wire chief's desk, which is wired
like the operator's keyboard. A second class of circuits must now
be provided for use in enabling the wire chief to get access to the
line to be tested. These latter circuits are called “the wire chief's
trunks”. The following trunks are usually provided: One or
more to the first section of switchboard; one or more to the last
316
TELEPHONY
301
section; one or more to the main distributing frame, and one to
each one of the incoming trunk positions. The wire chief's desk
is lastly equipped with lines to the switchboard for use in ordinary
conversation.
In Fig. 266 is shown the wiring of a line to first and last
sections of switchboard. It consists of a cord and plug a, placed
on the switchboard and wired to a jack b placed on the wire chief's
desk, there being no drops placed at either end.
6
Fig. 266.
In Fig. 267 is shown the wiring of a line to the trunk posi-
tions. It consists of a jack a placed in the multiple, and wired to
a jack b placed at the wire chief's desk.
b
Fig. 207.
In Fig. 268 is shown the wiring of a line to the main distrib-
uting board. It is rather more complicated than any of the others,
and is arranged to cut off one part of the line while the other part

d
3
'De
6
there
6_6
де?
2
с
o
al
Fig. 268.

is being tested. Two special jacks d and d' are placed on the wire
chief's desk. Their sleeves e and e' are not connected. The spring
5 of d, is wired through the contact points to the spring 7 of d';
and the spring 6 of d is similarly wired to the spring 8 of d'. At
a and a' are shown two hard rubber plugs with one face bevelled.
The face of each of these plugs is equipped with a German silver
clip b and b', while the two bevelled faces are equipped with two
German silver clips c and c'. Following out the circuits, it will
be seen that the spring 5 is wired to b; the spring 6 to b'; the
317
302
TELEPHONY
occupy the
,
spring 7 to c, and the spring 8 to c'. At 1 and 2 are shown the
heat coil springs of a line on the main distributing frame; and at
3 and 4 are shown the ground springs. The heat coils are sup-
posed to occupy spaces 1 and 3, and 2 and 4; while the carbon
plate arresters fit in between 3 and 4.
When a line is to be tested, the heat coils are removed from
the springs, and the plug a is inserted between 1 and 3, and the
plug a' between 2 and 4. When in position the spring 1 makes
contact with the clip c, and the spring 3 makes contact with the
clip b. Turning to the other plug, the clip b' makes contact with
the spring 4, and the spring 2 with the clip c'. Under these con-
ditions, the line coming in from outside passes from the spring 3
to the clip b, thence to the jack spring 5, and through the con-
tacts to the jack spring 7. Thence to the clip c and the heat coil
spring 1 to the switchboard. Returning to the heat coil spring 2,
it passes through the clip o' to the jack spring 8, thence through
the contacts to the jack spring 6, to the clip b', the ground spring
4 and out. If a plug be inserted into the jack d, the contacts at 5
and 6 being broken, the switchboard end of the line is cut off, and
communication is established with the outside portion. On the
other hand, when a plug is inserted into the jack d', the contacts at 7
and 8 are broken, the outside end of the line is cut off and commu-
nication is established with the switchboard. In addition to the
above circuits, the wire chief's desk is equipped with an order circuit
to the first section, and one to the last section of the switchboard
and one to each incoming trunk operator.
The next point to be considered is the method adopted by the
wire chief for testing the troubles that are reported to him. In
this connection, it will be well to go over the nature of the troubles
that he may be called upon to test.
TESTING FOR TROUBLES.
Troubles may be divided into three classes:
(1) Those situated in the wiring of the line, whether within the ex-
change or without.
(2) Those in the apparatus of the exchange, such as the drop
or jack.
(3) Those in the apparatus of the subscriber telephone.
318
TELEPHONY
303
a
The first class are called wiring troubles, the second, appara-
tus troubles, and the third, station troubles. The wiring troubles
are the only ones which the wire chief is able to test out with the
apparatus described. Wiring troubles are divided into five classes:
(a) Opens; (6) Grounds; (c) Short circuits; (d) Crosses; (C) Es-
capes. Opens are caused by a parting of the wire on one or both
sides of the line. Grounds are caused by one or both sides of the
line coming in electrical contact with the earth. Short circuits
are caused by the two sides of a circuit coming in electrical con-
tact. Crosses are caused by one or both sides of one circuit com-
ing in electrical contact with one or both sides of another circuit.
Escapes are nothing more than high resistance grounds.
Opens are detected by the fact that the subscriber cannot be
rung over the line. If a long line made up largely of cable con-
ductors be open on one side it is often possible to carry on conver-
sation over it. But the alternating current used for ringing is not
of sufficient frequency to pass the gap, therefore the signal cannot
be transmitted.
Grounds are detected by the fact that the line becomes noisy,
and when the ground is heavy on both sides, it amounts to a short
circuit and the subscriber is cut off from
cut off from all communication
whatsoever.
Short circuits are detected by the subscriber being thus cut off.
Crosses between two lines are detected by the fact that a per-
son conversing over one line can be heard on the other line
Escapes are detected by the presence of noise, when the line
is connected to a long-distance trunk.
When an open is reported to the wire chief, his first duty is
to determine whether or not it is situated outside of the exchange.
To this end he removes the heat coils from the arrester springs and
inserts the plugs a and a', Fig. 268, in the manner already shown.
The plug a of the testing circuit, Fig. 265, is inserted into the
jack d, Fig. 268, thus cutting off the switchboard end of the line.
If the open is located outside of the exchange, the relay f, Fig.
265, will not be energized when the plug is so inserted; for the
circuit being open, no current can flow through it. If the open
is
located within the exchange, on the other hand, the relay will be
energized when the plug is so inserted, and the click of the sounder
319
304
TELEPHONY
will be heard. If this latter condition obtains, the plug is then
inserted into the jack d', Fig. 268, thus cutting off the outside
portion of the line, and establishing communication with the
switchboard. The presence of an open is detected in the same man-
ner as before. The plugs a and a', Fig. 268, are then removed, and
the heat coils are replaced, care being taken to test both of them
for opens before doing so. The wire chief then goes in on the
order wire to the operator at the last position of switchboard, and
directs her to place one of the plugs a, Fig. 266, into the multiple
jack of the line in question. The test plug is then introduced into
the jack b, Fig. 266, and an inside man is directed to short circuit
the line on the main distributing frame with his pliers. Should
the line show open still it is cleared at the last section, and the
operator at the first section is directed to plug it up, using a sim-
ilar circuit, while the short circuit is maintained on the main rack.
Should the line show closed from the first section, the open is
located in the switchboard wiring somewhere between the first and
last section.
Assuming that such is the case, the inside man removes the
short circuit from the main rack, and going to the switchboard,
sticks a plug, the ring and tip of which are short circuited, and
which he carries in his pocket for the purpose, into the multiple
jack on the second position. If the line then shows closed, he
removes the plug and places it in the multiple jack on the third
position. He continues this process until the line again shows
open. When this occurs, he knows that the open is located between
the section where it last showed closed and the section where it
first showed open.
Again, if when the line is tested from the first section of
board, the short circuit being placed on the main frame, and it
shows open, it will prove that the trouble is located between these
two points. Under these conditions, the inside man is directed to
short circuit the line at the intermediate distributing board, and if
upon so doing, it tests short circuited, the open will be located
between the intermediate and main distributing boards. This
method of testing will be understood more easily by referring to
Fig. 269, which shows in outline, the circuit in question from the
main frame to the last section of switchboard. Suppose that a and

320
TELEPHONY
305
7
C,
represent the main and intermediate frames respectively, and
d, e, f, g, and h, the multiple jacks. Let a be the point where the
9,
line is open; let 1 and 2 be the tip and ring of the testing circuit,
which is shown much simplified. The test battery is at i and the
relay at j. With the conditions shown, if the line be short cir-
cuited at the main frame, it will nevertheless test open as one
side is open at a. If now the test plug be placed in the jack c,
the line will test short circuited, because the open is beyond the
testing point. Leaving the testing plug at c, removing the short
circuit from a, and putting a short circuiting plug in d, the line
will again show closed, as it will if the plug be placed at e. But
when the plug is placed at f, the line will test open, because the

h
9
f
e .
d
с
0
d
1
12
N
Holde
Fig. 269
open lies between the testing point and the place where the line is
short circuited. The test could also be made by placing the plug
at j, removing the short circuit from a, and placing the short cir-
cuiting plug successively at 9, f, and e. In this case the
open
lies
between the jack where the line first showed open and the last
jack, where it showed closed.
Trouble located between the first and last section of switch-
board, is said to be in the multiple and is usually found at the point
where the cable conductors are soldered to the jacks. It should
be remembered that in the case of a bridging board, a separate
test must be made on the answering jack wiring, and the answer-
ing jack wiring must be cut off when a test is made on the mul-
tiple. This is accomplished by unsoldering the wires at the inter-
mediate distributing board.
On very rare occasions the cable conductors open in the
cable. When this happens the defective pair is unsoldered from


321
306
TELEPHONY
the jacks at the two sections between which the break is located
and a spare pair, with which the cable is equipped, is substituted.
As a parting remark, when a line is tested at the main rack, great
care must be taken to test the heat coils for continuity before
they are replaced. For should the open be located at this point,
the line will test O. K. when taken up at the main rack, but will
immediately show open when the heat coils are replaced. This
combination will cause the wire chief a great deal of trouble
before the defect is located.
The method employed for testing heat coils is to use two or
three dry cells connected in series with a buzzer. The two
terminals of the circuit are soldered to two clips, one shaped like
the heat coil spring and the other like the ground spring of the
arrester. They are also separated by the same distance as these
springs. The heat coil to be tested is placed between these two
clips, closing the circuit and sounding the buzzer if it is in proper
condition. If the buzzer fails to sound, it shows that the heat
coil is open.
ear.
As has been already stated, a ground is caused by one or
both sides of the circuit coming into electrical contact with the
earth. When a line is grounded on both sides, the effect is
similar to a short circuit. The characteristic effect of a ground is
to throw noise on the line due to the presence of the earth currents
on the line. The wire chief, in testing, therefore, has to locate
the point at which the noise originates. He is assisted by the
relay and sounder, but the final adjustment must be made by the
The routine adopted in making the test is the same as that
employed in testing opens.
The line is first taken up at the main rack, the testing circuit
being inserted into the jack d, Fig. 268, thus cutting off the
switchboard end. If the line be grounded outside, the relay f,
Fig. 265, will be closed by the current from the battery e, flowing
over the line to the grounded point, and returning through the
ground x to the relay. But since the same condition will prevail
on a normal circuit as on a grounded one, the only way to differ-
entiate is to feel with the finger the pull on the relay armature.
In the case of a normal circuit, the line is closed through the
1,000-ohm bell, and the current flow through the relay is deter-
322
TELEPHONY
307
mined by the E.M.F. of the battery divided by the resistance of
the line and bell together. When the line is grounded, however,
the return circuit is made through the earth, if the battery is con-
nected to the grounded side of the line, and the bellis cut out. The
resistance of the circuit carrying the testing battery is reduced by
this amount, and the current flowing through the testing relay is
proportionately greater, so that the pull on the testing relay arma-
ture is greater under these conditions, than is the case with a normal
line. To ensure the testing battery being cut in on the grounded
side of the line, the relative position of the testing plugs a and a',
Fig. 268, must be reversed. This point will be understood better
by referring to Fig. 270, where 1 and 2 represent the two sides of
a line with the telephone bell at a. The tip of the testing plug,
a
e
음
​1
7 g 7 g
g
Lilitoa
f
2
с
b
Fig. 270.
Fig. 265, is shown at c, and the shank of the plug at e, the relay at
,
b, the battery at f, and the two grounds on the testing circuit at g'
and g". The trouble is located at g. With the conditions as shown
in the figure, the battery is on the side of the line opposite to the
ground, so that the testing battery must flow through the bell coils
to reach g. The portion of the line between g and e is the only
portion cut out, and the resistance cut out of the circuit thereby
bears such a small proportion to the resistance of the whole line,
that the current through b is not increased sufficiently to make
any material difference in the pull of the relay armature. If now,
the relative positions of cand e are changed, so that the testing
battery is sent out on the No. 1 side of the line, the bell coils are
cut out, and the pull on the relay armature increased sufficiently
to be readily detected.
The above conditions hold good whether the ground is located
within or without the exchange, for in the former case, the drop
coil takes the place of the bell coil, and the circuit tests out the
same way. Assuming that the trouble is located in the exchange,
.
the same process is carried out as in the case of an open, with the
323
308
TELEPHONY
exception that the defective portion of the lire must be cut off in
every case.
The defective line being ordered up on the last sec-
tion, it is opened at the main intermediate distributing board. If
under these conditions the line clears, the trouble will be located
between the main and intermediate distributing boards. If on the
other hand the line still shows trouble, the wire chief knows that
the defective point lies between the intermediate board and the last
section of switchboard.
If the switchboard is of the series type, and the ground be on
the spring side of the jack, the ground can be located by using a
투​g
i

T
m
e
с
b
[T
g'
Fig. 271.
not.
plug made of hard rubber, or an ordinary plug to which nothing is
attached. Because plugging into the jack opens the line, so that
by plugging on each section the defective portion of the line is cut
off until the section on which the ground is located is passed. The
ground will be located between the last section on which the trouble
was cut off on plugging in, and the first section on which it was
Since it is not practicable to unsolder the multiple jack wir-
ing, some other device must be resorted to in the case of a bridg.
ing switchboard, or a series board, when the trouble is on the ring
side of the jack.
Such a device is shown in Fig. 271, and depends for its action
on the ability of the ear to detect the diminution of the flow of
current in a receiver, caused by the resistance of the switchboard
wiring. It has proven to be very useful and saves a great deal of
time that would otherwise be wasted in searching through the
switchboard wiring. Here the multiple jacks are shown at a, b, c,
d, and e; the trouble being located at g, between b and c. The
answering jack is shown at f and the drop at h. At k is shown a
battery of dry cells, one pole of which is wired to a receiver 1,
324
TELEPHONY
309
whose other terminal is grounded at g'; and the other pole is wired
to the tip of a plug m. The intermediate distributing board is
shown at i, and the answering jack wiring is thrown off at this
point. The plug m is then inserted into the jack e, a circuit being
made for the battery k through the ground g. As a result, a click
is heard in the ear, directly the contact is made. The plug is then
inserted at d. This time the resistance of the circuit is reduced by
the amount of resistance in the wiring from d to e, which makes
an appreciable effect in the distinctness of the click. At c the
click is still louder and of equal intensity to what is experienced
at b. At a it is again diminished. Should the ground be located
on the opposite side of the line, it will be detected by the fact that
the line will show open when the plug is inserted. Under these
conditions, the tip strand of the cord is removed from k and the
ring strand substituted. If the trouble be located in the answering
jack wiring, it will disappear when the latter is disconnected.
The next class of troubles to be considered is the short circuit,
in which both sides of the line come into electrical contact. The
method of handling this trouble is identical with that described
for grounds, with the exception that in making the receiver test,
the battery and receiver are wired to the ring and tip of the
testing plug.
The class of troubles known as crosses, necessitate the use of
an auxiliary testing circuit, but in other respects they are handled
just like the grounds and crosses. The auxiliary circuit made use
of has already been shown in Fig. 265, where the plug / is wired
to a reversing key m, one side of which is grounded. In testing
for crosses, the two lines in trouble are taken up on the main dis-
tributing board by means of two testing circuits, one of which is
shown in Fig. 267. The plug a, Fig. 265, is inserted into the jack
e, Fig. 268, while the plug l of the auxiliary testing circuit, Fig.
Z
265, is inserted into the corresponding jack on the other testing
circuit similar to Fig. 268. The switchboard portions of both the
lines in trouble are thus cut off.
The principle of locating a cross depends upon the fact that
if two lines are connected together, a ground thrown on one line
will ground the other also, and the location of the cross will be
determined by the pull, on the relay armature, as in the case of a


325
310
TELEPHONY
simple ground This will be illustrated by reference to Fig. 272.
Here let 1, 2, 3, 4 be the conductors of two subscribers' circuits,
each with the bell bridged across, and let conductors 2 and 3, be
crossed at d. Let a, b, and c be the tip of the testing plug, the
relay and grounded battery respectively; and a' be the plug of the
auxiliary circuit. Let the former be connected to the No. 2 side
of the line, and the latter to the No. 3 side of the line. It is plain
that a path for the current from cis formed through the cross at x,
back over conductor No. 3, to the auxiliary test plug, and thence
to ground at g'. The resistance of the telephone bell and a portion
of the line being cut out, the pull of the relay armature will be
much stronger than normally. The relative positions of a and a'
с
15
2
Loo
2
b.
a
-0-0
o colle
lily
Х
3
35
4인
​9
Fig. 272.
must be reversed in order to determine on which side the cross is
located. In other respects, the location of a cross is determined in
the same manner as a short circuit.
There remains to be discussed one more class of trouble, the
escape. As has already been explained, the escape is a high resist-
ance ground, and its presence is felt through the line becoming
noisy, due to the presence of induced earth currents. With the
magneto system, escapes were tested by means of the ear only,
and when the trouble was located outside of the exchange, it was
as it is to-day, turned over to the cable maintenance department.
When an escape occurs in the switchboard wiring, it is usually
due to the fact that dampness in the air has saturated the cables
and wire. This is apt to occur in the damp warm days of summer,
and along the seashore. It can be remedied only by thoroughly
heating the atmosphere of the exchange, and by the application of
chloride of lime around the cables and wiring. Switchboard cords
are very apt to saturate from this cause and have to be changed
very frequently
326
TELEPHONY
311
CLEARING OF TROUBLE.
So far nothing has been said of the clearing of trouble that is
located on the line outside of the exchange, as this work is attended
to by a force of men different from that mentioned above. The
outside force is divided into two groups. Inspectors who clear
the station troubles, and troublemen who clear the troubles located
on the lines. The inspectors also perform routine inspection of
the telephones, and maintain them in good working order. It will
be evident from an inspection of the telephone wiring, that all of
the above-mentioned troubles may be located in this apparatus,

L
2
g
5
Б
C
d
H
Fig. 273.
and the wire chief often has nothing but his experience to guide
him in determining whether the case requires the office of an
inspector or troubleman. The trouble being located on the line,
however, the wire chief sends out a troubleman, giving him the
number of the cable in which the conductors are located, together
with the numbers of the conductors and the location of the dis-
tributing point. If the line is made up wholly or in part of
open
wires, the pole numbers and wire numbers are also given. The
troubleman is equipped with a pair of spurs and a lineman's test-
box, which is nothing more than a portable magneto telephone
wired as shown in Fig. 273, where 1 and 2 are binding posts to
which the line is attached; a, a switch pivoted at 5, and playing
over the points 3 and 4. At d is a receiver which is also used as
a transmitter; at b is a buzzer and at c, a series generator. One
327

312
TELEPHONY
pole of the receiver is wired to the switch point 3, while the other
pole is wired to the binding post 2. One terminal of the buzzer is
wired to the switch point 4 and the other terminal to the gener-
ator. With the switch in the position shown, the test set is ready
to receive or transmit a signal; while with the switch thrown to
point 3, the buzzer and generator are cut out, and the receiver cut
in for talking
Equipped as described, the troubleman goes to the distrib-
uting point, cuts in on the given conductors by means of a
flexible cord equipped with two clips for holding to the lugs in
the cable box. Assuming the trouble to be an open, he rings,
and if the trouble lies between himself and the exchange, he will
raise the subscriber but not the operator. If on the other hand
he is unable to raise the subscriber, but the operator answers, he
knows that the trouble lies between himself and the subscriber.
If the trouble lies between the distributing point and the exchange,
the wire chief is called and a new pair of conductors is taken to
carry
the line. Should the trouble be located between the sub-
scriber and the distributing point, this portion of the line is gone
over very carefully and the fault remedied. It may be that
through mechanical injury a portion of the distributing or drop
wire has been broken. If so this must be spliced temporarily, so
as to get the subscriber working as quickly as possible. If need
be, the line will be permanently repaired at a later date.
These breaks are very apt to take place where the line passes
through trees, as under the influence of high wind, the swaying
of the branches is apt to break the wire. Where such conditions
exist, or where from any one cause or another, the line is apt to
be again thrown into trouble, a report of the fact should be made
by the troubleman, so that the conditions may be permanently
bettered. The largest percentage of line troubles will be found to
be located in the contacts of the cable box.
The station trouble consists almost altogether of parts of the
apparatus getting out of repair, and the work of the inspector is
that of either repairing or replacing them. About 80% of the
transmission troubles are found to be due to weak batteries.
When Leclanché cells are used the inspector replenishes them
328
TELEPHONY
313
himself. When Fuller batteries are used he directs the battery
man to perform the work.
With the introduction of the common battery system, a more
elaborate testing circuit was devised for the wire chief, and a volt-
meter was introduced. The lines to the first and last sections of
switchboard were also wired more elaborately. In considering the
subject of testing trouble with the common battery system, it must
be remembered that in this case the subscriber lines test normally
open, which is not the case with the magneto system. Further-
,
more, battery being on the line continually, it can always be used

L24 Phy or
dillite
Dim
W
0
n
S
o
wwwm ?
9 "p
att du
х
www
K
Fig. 274.
to test with. This feature makes it, in some respects, easier to
locate trouble on the common battery system than on the magneto
system. In Fig. 274 is shown the wiring of the wire chief's test-
ing circuit used in connection with the common battery system.
To a cord and plug a are wired ten keys, designated by the letters
of the alphabet. The key b is called the reversing key, because, as
will be seen, current coming from the battery r can be thrown
either on the ring or tip of the plug. At c is the ringing key, the
ringing generator leads being connected to the two outer points.
At d is the grounding key for throwing ground on one side of the
testing circuit. This side is always opposite to that on which the


329
314
TELEPHONY
battery is connected. By means of the key e, the voltmeter l of
special design, with the battery r in series, is thrown on one side
of the line. At f is the ammeter key, by means of which the
ammeter m with the battery r in series is thrown on one side of
the line. For the safety of the ammeter, a resistance n of 100
ohms is connected in series with it. This may be short circuited
by the key g if so desired. At h is a key for cutting in a telegraph
relay o, the same as the one shown in the magneto testing circuit.
To the armature of this relay is wired a sounder not shown in the
diagram. At i is the holding key, which is thrown across the cir-
cuit, to hold a line, should the wire chief desire to talk on some
other line for a moment. The talking key is at j and deserves

/
,
4oo
b
a
х
2
g'
g
Fig. 275.
special mention. At æ is a repeating coil wired as a retardatiou
coil, battery coming through the inner points and swinging con-
tacts of the key k. The receiver q of the wire chief's telephone
circuit is bridged across the circuit with a 2 M.F. condenser P,
and the secondary winding of the induction coil in series. The
key k has its outer springs strapped together, so that by throwing
it, the two halves of the repeating coil winding are strapped
together and battery cut off. The above circuit gives a very elab-
orate means of testing, and is used as follows:
The line to be tested being taken up in one of the ways already de-
scribed, the grounding key d, is thrown, thus grounding one side of the
line. The voltmeter key is then thrown, so that this instrument with
grounded battery in series is connected to the opposite side of the line. If
the circuit is in normal condition, it will be open to direct battery at the
subscriber bell, so that the needle of the voltmeter I will not be perma-
nently deflected. The condenser in series with the bell, will however be-
come charged. If the reversing key b be thrown, thereby changing the
direction of the battery potential on the line, the condenser will be dis-
charged, and then charged in the opposite direction, which action causes
the voltmeter needle to make an excursion, depending in magnitude upon
330

6
4
:13
P
COMMON BATTERY TELEPHONE
COMMON BATTERY TELEPHONE-OPEN
Dean Electric Co.

TELEPHONY
315
the capacity of the line, and to again return to zero. Should the line be
open between the point where it is tested and the subscriber station, there
will be no excursion of the needle when the voltmeter is thrown This
excursion, therefore, is the indication of a normal condition of the line
Should the line be short circuited, the condenser will be strapped out, and
the circuit will be closed to direct current, so that under the proper condi-
tions there will be a permanent deflection of the voltmeter needle, when
that instrument is thrown on to the line.
This point will be understood better by reference to Fig. 275,
where the testing circuit and the line to be tested are shown in
outline. Let 1 and 2 be the two sides of the line to be tested; and
let c, d, and g be the voltmeter, battery and ground respectively;
,
while g' is the ground thrown on the opposite side of the line by
the grounding key. Let the line be short-circuited at x, then un-
der the conditions shown, current will flow from d through the
/
4600
х
2
9
Fig. 276.
voltmeter c to No. 1 side of the line, returning through the short
circuit x to the No. 2 side of the line to the ground at g'. If the
ground at g' is removed, which is equivalent to releasing the
grounding key d, Fig. 274, the voltmeter circuit would be opened
and the needle would return to zero. Therefore, if when the volt-
meter key and grounding key are both thrown, a deflection is ob-
tained, and if the needle returns to zero when the grounding key
is released, the line tested is shown to be short circuited.
Suppose, now the line to be grounded, the conditions shown
in Fig. 276 will obtain. Suppose that the line to be tested is
grounded at x, the testing circuit being connected up as in the
previous figure, the same letters of reference being used. With
the conditions as shown the line will test normal, because the
ground x being on the opposite side of the testing battery, the cir-
cuit will test open through the condenser b, and the ordinary
swing of the needle will be obtained. Should, however, the ground
g' be removed by releasing the grounding key d, Fig. 274, the line
331
316
TELEPHONY
will still test normal, for the return circuit will be made through
the ground at to the ground at g. Therefore, should a swing
of voltmeter not be obtained when the grounding key is released,
the line tested will prove to be grounded on the side opposite to
that on which the voltmeter is connected.
If the reversing key b, Fig. 274, is so adjusted that the volt-
meter and battery are connected to the No. 2 side of the line,
while the grounding key is connected to the No. 1 side of the line
as shown in Fig 277, then a steady current would flow through
the voltmeter out on the No. 2 side of the line, to ground at x and
return, and the voltmeter would be permanently deflected. This
current flow would be altogether independent of the presence of
the ground g'. Therefore, should the voltmeter needle be perma-

1
b
4600
Eg'
2
Х
с
9
Fig. 277.
nently deflected when the grounding key is released, the line
tested will prove to be grounded on the same side as that on
which the voltmeter is connected. If the voltmeter used on the
testing circuit is of the proper sensitiveness the insulation of the
line can be measured. Referring to Fig. 275, it will be seen that
any leakage current, either from the line to ground, or from one
side of the line to the other, will flow through the voltmeter, and if
the instrument be sensitive enough, the magnitude of the insula-
tion resistance can be determined by means of the following
considerations:
Let E denote the E.M.F. of the battery used for testing;
denote the reading on the voltmeter for any given leakage cur-
rent; let R denote the insulation resistance, and r the resistance of
the voltmeter.


332
TELEPHONY
317
In Fig 278, let 6 be the testing battery, a the voltmeter, and
the lines 1, 2, 3, 4, etc., denote the leakage. The current flowing
through the voltmeter is given by the expression
e
I=
1
r
where I denotes the flow of current.
Again, the current flow is denoted by the following different
expression
E
2
I=
R+r
Placing the right-hand member of 1 equal to the right-hand mem-
w
ES
Iue
wo
ww
wo
mo
Em
Nw
11 10 9 8 7 6 5 4 3 2 1
9
4 -
Fig. 278.
ber of 2, we get

E
e
=
3
R+1
r
Er
Er
or
Clearing fractions (R + ) e =
Re + re =
from which
Re
Simplifying
Re
4
5
6
7
= Er
re
r
(E - e)
E-e
Solving for R.
R
=
r
8
e
Equation 8 gives the insulation resistance of the line in terms of
the voltage of the battery and the resistance of the voltmeter, so
that the sensitiveness of the apparatus will increase with the poten-
tial of the battery used and the resistance of the voltmeter coil.
At first thought it might seem as if the sensitiveness could be
increased without limit, by increasing the potential of the testing
battery. The limit to which this voltage can be increased is gov-
333
318
TELEPHONY
-
E-c
е
е
erned by the fact that the higher the voltage used, the greater the
strain upon the insulation. In the testing of cables, the usual
practice is to test with 100 volts of chloride of silver battery, as
this potential is considered to be high enough to give sufficient
sensitiveness and not high enough to subject the insulation to
undue strains. In connection, however, with such testing as the
wire chief does, it is not essential to get as high a sensibility and
for the sake of economy, the same battery is used for testing as is
used for operating the station, so that the value E, in the above
equations is given at 24 volts. It therefore becomes necessary to
increase the other quantity as much as possible. The highest
resistance of voltmeter winding used for this purpose is 40,000
ohms, so that the highest insulation resistance that can be read
with this combination is given by the following expression: Let
E = 24 andr 40,000, and e = 1, the smallest reading on the
24 - 1
voltmeter. Then R
pa becomes R = 40,000
1
23 x 40,000 920,000 ohms, almost 1 megohm. Lines having
an insulation resistance equal to this figure are in good condition,
and unless this quantity decreases from day to day no attention
need be paid to it The smallest insulation resistance that can be
measured on this instrument is given by the following expression:
Let E= 24 volts as before, r = 40,000, and e = 23, the maxi.
mum reading of the instrument next to a dead ground. Then
E-
24 - 23
R =
p becomes R =
40,000 40,000 : 23
23
1,740 ohms.
Lines having as low an insulation resistance as the above need
attention immediately. Roughly speaking, when the insulation
resistance falls below 40,000 ohms the line needs attention.
In speaking of the testing circuit, Fig. 274, an ammeter m
controlled by a key f was referred to. This ammeter, or rather
milliammeter, is used to measure lower resistance than 1,740 ohms,
and is useful in locating crosses, short circuits, and dead grounds.
The milliammeter used has a reading of 0 to 500 milliamperes or
ampere. The expression used to determine resistance by this
instrument is derived from Ohm's law :
=
e
-
e
1

334
TELEPHONY
319
E
I
; R
E
I
9
R
where R is the resistance to be measured, E the potential of the
testing battery, and I, the current density flowing through the
ammeter. The highest resistance that can be measured with this
combination is determined in the following manner: Let E= 24
volts and I :.001 or novo ampere. Then equation 9 becomes
24
R
= 24,000 ohms. Likewise the smallest resistance that
.001
can be measured is given by the following, assuming that E = 24
06
b

с
9
e
use.
Fig. 279.
24
and I = 500 milliamperes or .5 ampere.
= 42 ohms.
.5
While high resistance can be measured with the ammeter, it
is not as sensitive for the purpose as the voltmeter, so that the
latter instrument is always used. For low resistances, the ammeter
covers a field that cannot be reached by the voltmeter, hence its
The method pursued by the wire chief in the use of these
instruments is as follows: The voltmeter is first used, and if the
resistance is so low that a full reading is obtained, the ammeter is
then thrown on. A record is kept by the wire chief of the normal
resistance of each line with the receiver at the subscriber station
removed from the hook. This, of course, refers to the metallic
resistance of the line and not to the insulation resistance. By this
means when a short circuit or dead ground occurs on any one of
these lines it can be determined by comparison.
The telegraph relay is used in the same manner as described
for the magneto circuit, and therefore needs no special mention.
335
320
TELEPHONY
The battery key k is used when the wire chief is talking to a line-
man with a test box, as under these conditions it is not necessary
to throw battery on the line. In all other respects, the locating of
.
trouble is performed in the same manner as that described for the
magneto system. The lines to the main distributing board possess
no new features, but the lines to the first and last sections of switch-
board are characteristic and are shown in Fig. 279, where f denotes
the plug at the switchboard, and the jack on the wire chief's
desk. To the points of the jack is connected the drop a with a
condenser h in series. The drop is provided for the convenience
of the line men in calling up. Wired to the shank of the plug f
is a lamp c, the battery lead being run through a key g. When
the plug is introduced into the subscriber jack, the battery e is
grounded through the cut-off relay, and current, therefore, flows
through the lamp, thus indicating to the wire chief by its illumi-
nation that the line has been taken up by the operator. By de-
pressing the key g this lamp circuit is opened, and current removed
from the cut-off relay of the line being tested, so that this relay
being released, direct current is thrown on the line. Under these
conditions when the wire chief throws the listening key on his test-
ing circuit, the line lamp becomes illuminated. This affords the
wire chief a means of quickly testing the answering-jack wiring
While the use of the voltmeter affords a great help to the
wire chief in detecting and locating trouble, he must possess a
trained ear, and be thoroughly familiar with the nature of the con-
,
struction of the line both inside and outside of his exchange. He
must also possess executive ability in a high degree to successfully
deal with the large volume of business that is transacted at his
desk in the course of the day.

CABLE MAINTENANCE.
The clearing of trouble in cables is a much more elaborate
piece of work than that of clearing trouble in open-wire lines,
bridle wires, or drop wires, since it always necessitates the opening
of old splices and the making of new ones.
The work of locating
trouble, too, necessitates the use of delicate scientific instruments
and more or less complicated mathematical formulae. This work,
therefore, cannot very well be handled by the force under the wire
336
TELEPHONY
321
chief, and in the larger companies is performed by the construc-
tion department, a sub-department being provided for this purpose.
The force of men employed in this work consists of a gang of
cable splicers and a gang of galvanometer men with their assist-
ants. The size of these two gangs depends on the size of the
cable plant, and the volume of business to be done. Large com-
panies that have a great number of underground cables, find that
they are getting out of order all the time, so that these two forces
are continually employed in locating and clearing cable trouble.
All reports of cable trouble come to the construction depart-
ment from the wire chief, who, by the methods already described,
locates the trouble in the cable. The work of clearing the trouble
is divided into two distinct heads: First, locating trouble.
second, clearing trouble. The work of locating trouble is per-
formed by the galvanometer man, and for this purpose he is
equipped with a galvanometer of one of the portable types, a
battery of 100 chloride of silver cells, a battery reversing switch,
and a capacity switch. A standard megohm coil should also be
provided. Some form of lamp stand and scale will also be
necessary
Lead cables are thrown into trouble from three causes: Me-
chanical injury, deterioration of the lead sheuth due to electroly-
sis, and the burning of the.conductors and sheath by accidental
contact with high foreign potentials, such as lightning, trolley cur-
rent and the like. The fact that a cable is deteriorating is made
known by the increasing number of troubles that are found to be
located in it, and when such a condition prevails the galvanometer
man is sent out to locate the trouble. As a usual thing the galva-
nometer man makes his test from the exchange, and to this end sets
his instruments at this point. Except in the case of mechanical in-
jury, or injury due to lightning, the trouble from which cables are
most likely to suffer is grounding. In the case of mechanical injury,
or lightning, grounds, short circuits, crosses, and opens are apt to
be encountered. The nature of the trouble with which a cable is
afflicted is usually reported by the wire chief, but the galvanometer
man, while he uses the wire chief's report as a guide, must never-
theless make a thorough determination as to whether or not any
other trouble exists.

337
322
TELEPHONY
k
Thompson Galvanometer.
In Fig. 280 is shown one of the
best adapted forms of the Thompson galvanometer for cable-testing
work. It consists of 4 coils, two of which are shown at a and a
mounted on two ebonite pillars b and b', which in turn are sup-
ported on an ebonite base c.
This base is equipped with three
leveling screws d, d', and d".
The terminals of the coils are
brought out to binding posts
placed on the ebonite base, four
of which are shown at e, e', e",
c". The system is suspended by
an unspun silk thread, which is
fastened to the milled-head screw
f. The upper magnet of the
system having the mirror at-
tached is shown at g, while the
m lower one is shown at h. The
.
coils are enclosed in a cylindrical
glass case i, upon the metal top
of which is mounted the vertical
rod j carrying the control mag-
net k. The bottom of the rod is
equipped with a worm wheel
into which meshes a screw l with
a milled head m. The control
16
magnet makes a binding fit over
the rod, and coarse adjustment
can be made with the hand.
Fine adjustment is made with
the screw and worm wheel. The
Fig. 280.
glass case fits air-tight, so as to
exclude the dust.
In Fig. 281 is shown the plan of wiring the coils and method
of bringing the terminals to the binding posts. By following the
direction of the arrows, it will be seen that by properly connecting
together the binding posts 2, 3, 4, 5, 6, and 7, the coils can be
connected in series or multiple as desired, and that any one of the

0
60
a
а.
et
e
nd
e
e
DODD
с
可​品
​90
10
END
338
TELEPHONY
323
7
6
5
4
Bottom
Coil
Top
Coil
Bottom
coil
Top
Coil
Level
a
coils can be cut out at will. A leveling glass, shown at a, is
pro-
vided by means of which the instrument can be accurately ad-
justed in this respect.
D'Arsonville Galvanometer. While this type of instrument
gives very good results, and is the best form of the Thompson
type for portable work, it is not
as good as the D'Arsonville gal-
vanometer, a very excellent form
of which is shown in Fig. 282.
This instrument is as sensitive as
the Thompson, but is much
more easily set up and adjusted,
and is absolutely unaffected by
fluctuations in the earth's field.
The permanent magnet is lam-
inated, thus ensuring a high de-
gree of magnetic saturation in
the iron. The system is sus-
pended top and bottom in the
metal tube, which can readily be
placed in position and secured
with a screw. By means of a
small nut at the bottom of the
tube, the system can be held rig-
Fig. 281
idly, when the tube is being car-
ried about, thus preventing mechanical injury.
Battery reversing keys are made up in several forms, one of
the most approved being that shown in Fig. 283. Here six bind-
ing posts E, E', E”, D, F, and F', are mounted on ebonite pillars
to ensure good insulation. These columns are mounted on an
ebonite base. To the binding posts E' and E' are attached two
springs which carry at their opposite ends two ebonite buttons A A
and C. Each one of the binding posts F and F' is equipped with
a short strap at the end of which is a set screw. The ends of these
two screws are platinum-pointed, and touch two platinum projec-
tions on the springs when the latter are in the normal position.
The two binding posts E and D are connected by two copper rods
to two posts H and H' respectively, each mounted on an ebonite

339
324
TELEPHONY
post. Two keys G and G'are mounted on ebonite pillars, by
means of which the springs are depressed, so that they break con:
tact with F and F and make it with H and H'. Each one of these
keys can be operated independently of the other. Whenever it is
desired to depress either spring momentarily, the finger is pressed
on either one of the buttons A or
C. The method of connecting up
this switch will be shown a little
later.
Capacity Key. The most ap-
proved type of capacity key is
shown in Fig. 284, where mounted
on an ebonite base is an ebonite
pillar bearing a binding post a.
To this post is attached a spring
b, carrying at the other end an
ebonite button c. Two other bind-
ing posts d and d' each mounted on
an ebonite column, are provided.
Each binding post is equipped
with a stout copper strap, the one
attached to d, bending up and over
the spring b; while the one at-
tached to d' bends down and under
b. Each strap is equipped at the
end with a set screw, whose end
is platinum-pointed. When the
spring is in the upper position it
makes contact with the upper set
screw, and when it is in the lower
position it makes contact with the
bottom set screw, breaking its
Fig. 282.
contact with the top one. Two
keys e and e', each equipped with an ebonite button, are so con-
structed as to catch the spring b when it is depressed, and hold
it firmly. When, after the spring 6 has been depressed, the key
marked discharge is tripped, it flies upward until it strikes against
the upper set screw. When, however, the key marked insulate is

$
e
340
TELEPHONY
325
depressed, the spring b flies upward until it strikes against the
tooth of the discharge key, which holds it in a mid position insu-
lated from both the upper and lower set screws.
The method of

D
E
E
F
a'
ನಿನ್ನಾ
E
DD)
g
A
с
-H'
I
a
B
H
Fig. 283.

e
connecting up will be described later. The standard megohm
resistance used to get a constant is one of the many forms gotten
out for this purpose, as is the standard condenser.
The method of wiring up the galvanometer, battery key, bat-
tery, and standard resistance to get a constant is shown in Fig. 285.
Here a denotes the battery, m the battery reversing key, b a tapper
key to short circuit the gal-
vanometer, d the galvanom-
eter, c the shunt, and f the
standard megohm resist-
If the spring 2 is in
its normal position, and
spring 3 depressed, the cur-
3
rent flowing from a will pass
Ydischarge
from contact 1 to spring 2
Fig. 284.
and thence through the gal-
vanometer and shunt, when 6 is depressed, to the spring 3, from
this point, to the contact e, through the megohm f, returning to
the battery. If spring 2 is depressed and 3 normal, the direc-
tion of current flow through the galvanometer will be reversed.
ance.
insulate
341
326
TELEPHONY
When a constant has been obtained, the standard megohm is
reversed and the negative pole of the battery connected to the wire
to be tested, the positive pole of the battery being grounded as
shown in Fig. 286, where n represents the joint between the cable
conductor and the test wire, the insulation on the conductor being
shown at p, and the sheath of the cable at o. The terminal e is
grounded. By means of the key m, either pole of the battery can
be connected to the line and double readings taken. The magni-
tude of the deflections should be the same in both cases.
е

d
min
b
a
3
2
LE
m
Fig. 285.
Measurement of Capacity. There are many methods adopted
for measuring capacity, but the one oftenest employed by the
galvanometer man is that of proportional deflections, and consists
of charging the cable at a given potential, and noting the magni-
tude of the deflection at discharge, then comparing it with that
obtained by discharging a condenser of known capacity that has
previously been charged. The method of connecting up for this
purpose is shown in Fig. 287, in which the standard megohm is
replaced by a standard condenser c and the capacity key k is in-
troduced. This key k is depressed, causing current from the
battery to charge the condenser. The key k is then released, flies
to its upper position and discharges the condenser through the

342
TELEPHONY
327
galvanometer. When a constant deflection has been obtained the
condenser is removed, and one terminal is connected to the con-
ductor to be tested, and the other to ground, as shown in Fig.
288, where the contact e of the battery switch and one terminal of
the battery are connected to the conductor at с, the insulation
being shown at a and the sheath at b. The spring of the capacity
key is grounded. With the key k in its lowest position the cable

d
min
b
a
3
2
m
은
​p
Fig. 286.
is charged. But when it is allowed to fly up, the battery is cut
off and the cable discharged through the galvanometer.
Murray and Varley Loop Tests. The galvanometer man
uses these two tests, to determine the insulation resistance and
capacity of each conductor of the cable. The defective conductors
are thus picked out and the next piece of work to perform is to
locate the trouble found. There are two methods employed of doing
this, each one having its peculiar advantages; and both having in
common the advantage of simplicity. They are known as the
Murray Loop Test and the Varley Loop Test. With both of
these tests the Wheatstone bridge method is employed. The scheme
of connection for the former is shown in Fig. 289. One terminal
343
328
TELEPHONY

of the battery is grounded, and the other one is connected to the
junction of b and d, or what is the same thing, between the rheo-
stat and one arm of the bridge. The other arm of the bridge is
plugged up as shown. Let f be the location of the ground located
on conductor No. 1 and let conductor No. 2 be any other good con-
ductor in the same cable, and suppose that their ends are joined

с
k 소
​Fig. 287.
at p. The resistances at b and d are adjusted until a balance is
reached and no current flows through the galvanometer. Denot-
ing by r, the resistance of the conductor from C to the fault, and
by y, that from E to the fault, we have
b xy = d xa
10
Denote by L the resistance of the whole loop, and we have
x + y = 1
11
y
12
Substituting for y in equation 10 its value found from equation 12,


L - 30
2C
we get
(L - x) = d x 20
7.
L
6 td
13
X
344
TELEPHONY
329
which gives the resistance of the conductor from the exchange to
the fault in terms of the two known resistances of the bridge, and
that of the whole loop.
Knowing the gauge of the conductor the location of the fault
can be determined from the resistance. To get the loop condition,

2
ויויויויויויו
LLLLLLLL
n
K
섬
​Fig 288.
all that is necessary is for the galvanometer man to send his
assistant out to the cable box, at which point the defective con-
ductor and a good one selected at random are joined. If more
than one conductor be found defective, a test is made on each one,
or on a sufficient number to determine that they are all defective
at the same point.
In Fig. 290 is shown the scheme of wiring for the Varley
Loop Test. Here B C and A B are the two bridge arms and A E
is the adjustable resistance. The defective conductor is shown at
No. 2 and the good one at No. 1 They are joined at p. The
fault is at f. The resistance d is adjusted until balance is estab-
lished, when we have
a (d +-x) = by
14
where the symbols denote the same quantities as in the previous



345
330
TELEPHONY
case
-
Letting as before the total resistance of the loop be denoted
by L, we have
2 + y = L
y = L - ac
Substituting a (d + x) = 6 (L - x)
15
7 L - ad
16
bt a
L-d
If
7 = a then x =
17
2
which gives the resistance to the fault in terms of the total resist-
ance of the loop and the adjustable resistance.
X =
-

X
6
99
a
wwwy
2
d
2
e
4
DDDDD
Fig. 289.
Cable faults are usually located in the splices, and are due to
more or less careless work on the part of the cable splicer, in either
not properly making the joints, or not properly placing the insu-
lating sheeving, or not properly boiling out the splice after it has
been made. Again, when the joint in the cable sheath has not been
properly wiped, moisture is apt to leak in to the conductors, thus
causing grounds. When the trouble has been located in the splice,
the cable man is sent out to open it, examine its condition, prop-
erly re-make it and wipe it over again, after which it is again tested
out to make sure that the trouble has been cleared. When the
trouble is located in the cable between splices it is usually due to
mechanical injury or to the fact that the cable has not been prop-
346

MOTOR GENERATOR WITH BUSY-BACK ATTACHMENT FOR TELEPHONE SIGNALING
Holtzer-Cabot Electric Co.
TELEPHONY
331
erly constructed. When, however, this condition obtains, the only
thing to do is to replace the defective section, and this work is
per-
formed in the following manner :
Let a and 6 in Fig 291 represent two manholes, and let 1, 1,

y-
P
un
2
www
B
A d E
2
Fig. 290.
a
2, 2, 3, 3, etc., represent the conductors of a cable that has become
defective at the point x between the two manholes. A new cable
c o is run in a spare duct between the two manholes, the lead sleeve
on the old cable is removed in the manhole a, and the conductors
of the new cable are joined to those of the old one at random.
This having been done the lead sleeve is removed from the old
b
X
23.45
с
Fig. 291.
cable and the conductors of the new cable are spliced to those of
the old in the following manner:
In Fig. 292 let 1, 2, 3, etc., represent the conductors as before,
only three conductors being shown for simplicity. A telegraph
relay d has one terminal connected through a battery c to one of
the conductors selected at random as No. 1. The other terminal
of the relay is grounded at g. To the local of the relay is connected
the battery d' and the buzzer f. The lineman is equipped with a
347
332
TELEPHONY
at g
pair of shears e, which he always uses to skin off the insulation
and to cut the wire. To these shears is attached a wire grounded
With these shears he cuts through the insulation of all the
conductors so as to touch the wire, and when the conductor to
which No. 1 has been joined is reached, a circuit will be found
through the shears and wire to ground, causing current to flow
through the relay d and the buzzer f to ground The
ductor having been thus located, it is cut, and the end of the por-
tion from 7 on is spliced to No. 1 conductor in the new cable,
while the portion running between a and b is left open. The cir-
cuit is thus made over the conductor in the new cable between the
two manholes. The relay is then connected to another conductor
in the new cable selected at random, and the conductor to which it
proper con-
b

3
3
9
95
de
Fig. 292
has been attached, found as in the previous manner, and a joint
made. This process is continued until all the conductors in the
new cable have been joined to those in the old.
The condition at this stage is that shown in Fig. 293, where
the conductors of the new cable are shown connected to those
in the old cable at c, d, and e, in manhole b, while the conductors
in the old cable are shown dead between the two manholes. Care
must be taken not to short circuit or cross the free ends of these
conductors in manhole b, as they are still connected to working
wires. The lineman then goes to manhole a and cuts off the old
conductors running between the two manholes, after which the
new splices at a and b are boiled out and the joints wiped. The
length of old cable between the two manholes is then pulled out
and the work is completed.
348
TELEPHONY
333
THE PUPIN SYSTEM OF LOADED CIRCUITS.
The subject of increasing indefinitely the long-distance limit
of transmission, is one which has interested telephone engineers
ever since the beginning of the art. With the best possible con-
struction, and the most improved apparatus, the limit of transmis-
sion over open wires is about 1,200 miles. When cables are used
to make up portions of the line, this figure is materially reduced;
the amount of reduction depending upon the percentage of cable
with which the line is made up. This loss of transmission current
is due to three factors, disregarding the leakage through the insu-
lation resistance; and they are: Resistance of the line, Capacity
of the line, and Self induction of the line.
The resistance factor can be reduced by increasing the size of
the conductor; but this increase is limited, as has already been
a
b
ร์
w
Fig. 293.
shown, by practical line construction considerations. The capacity
factor cannot be affected, as in the best construction, it is already
reduced as low as possible. The one remaining factor, that of self
induction, seems to be the only one that can be looked to for aid in
increasing the limit of transmission. This point was grasped by
the pioneer writers in this field, and during the World's Fair in
Chicago, Ill., the English scientist, Sylvanus P. Thompson, advo-
cated the construction of a cable that should have electromagneto
or retardation coils placed at intervals throughout its length, so
that by increasing the self induction, the effect of the static capacity
might be overcome and the limit of transmission thereby increased.
This scheme was subsequently tried several times, but so far
from meeting with success, it was found that the transmission was
not as good under these conditions, as with the circuit in normal
condition. It was found that the presence of the magnetic coils on
the line produced electric “echoes,” which made the transmission
very indistinct. The experiment showed that while increasing the

349
334
TELEPHONY
self induction of a line uniformly throughout its length increased
the distance over which transmission could be carried on, the
presence of increased self induction at points along the line had the
opposite effect. At this point the matter was allowed to rest, until
Professor M. I. Pupin discovered in a very ingenious manner, the
proper intervals at which the points of high self induction must be
placed, in order that the effect would be the same as if the increased
self induction were distributed uniformly throughout the length of
the line. His method of reasoning was as follows:
To start with, the electrical energy in the talking current is
transmitted from one end of the line to the other in wave motion.
The amplitude and wave length depend upon two factors: First,
the intensity and law of variation of the impressed E.M.F. at the
transmitting end, and Second, the nature of the reactions of the
circuit. The intensity and variation of the impressed E.M.F. at
the transmitting end, will follow exactly the intensity and law of
variation of the exciting force, which in the case under discussion
is the energy of the sound waves. This quantity being easy of
determination, nothing further may be said on the subject. The
quantities to be considered are the reactions which take place in
the circuit. It will be of material assistance to the proper under-
standing of the subject, if the analogous case of wave transmission
over a cord, be considered first.
Suppose that in Fig. 294, one end a of the string a b be agi-
tated backward and forward in the direction of the arrows by a
simple harmonic motion. A wave of decreasing amplitude will be
transmitted along the string from the point a towards the point b.
That the amplitude decreases is shown by the fact that the ordinate
1-2 is greater than 3-4, which in turn is greater than 5-6, etc. The
wave motion dies out before b is reached, so that no energy is felt
at this point. Let us consider now the reaction that takes place
in the string
First, there is the inertia reaction, which is due to the kinetic energy
stored up in the mass of the string.
Second, there is the elasticity reaction, due to the tension existing
between the particles of the string when distorted.
Third, there is the frictional reaction, due to the production of heat.
Of these three reactions, the first and second are useful in
propagating the wave motion through the length of the cord. The
350
TELEPHONY
335
2
2
3
4
3
4
6
5
inertia of the cord acts like the inertia of the fly-wheel of an
engine to absorb the energy given out by the piston rod, and give
it out again to the machinery. The elasticity reaction being due to
increased tension between the particles of the cord, tends to make
it return to its original position.
The method of procedure is somewhat as follows: The end of
the string a having been displaced to the right by the disturbing
force, the inertia of the cord tends to transmit this motion to the
remaining portion, and in so doing transforms itself into elastic
energy or tension between the particles. When this tension has
become equal to the energy of in-
ertia, its reaction brings the string
to rest, and causes it to move back
to its original position. When the
original position has been reached,
this elastic energy has been re-
transformed into energy of inertia
which carries the string past the
original position to some point on
the opposite side. As the string
passes the original position, its
energy of inertia is again trans-
formed into elastic energy, till,
when this transformation is com-
pleted, the cord again comes to rest.
The elastic energy again causes the Fig. 294.
Fig. 295.
string to return to its normal posi-
tion, and when this point is reached, the inertia again carries it to
the other side. The frictional reaction tends to produce heat only,
and is, therefore, useless in propagating the wave motion along the
cord. Now, this motion will continue to be propagated along the
cord until the successive losses due to the frictional reaction have
become so great as to absorb all the energy, whereupon the string
comes to rest.
From these conditions it will be apparent that there are three
methods by which the distance over which the wave motion can be
propagated, may be increased:

5
6
7
8
7
8
10
9
b
b.
336
TELEPHONY
First, by the reduction of the frictional reaction.
Second, by increasing the elastic reaction.
Third, by increasing the inertia reaction.
It is a well known principle of Mechanics that, all motion is
attended by friction; so that while, with properly designed mech-
anism friction may be reduced materially, it can
never be
eliminated. Supposing that in the case of the cord just consid-
ered, the friction to be reduced as far as possible, the next thing,
to do is to consider the effects of increasing the inertia reaction
and the elastic reaction. If the inertia of the string be increased
by making it of heavier material, the inertia reaction will be in-
creased correspondingly, and the ratio of the frictional reaction to
the inertia reaction will be reduced so that the wave motion will
be transmitted to a greater distance before the useful energy is ab-
sorbed, as shown in Fig. 295, and if the inertia is sufficiently
increased some energy may be transmitted to b.
Again, should the elastic reaction be increased, by increasing
the tension of the string, the distance over which the wave mo-
tion can be propagated will also be increased, as shown in Fig.
296. In this case, however, it will be noticed that the wave length
,
is increased. So far the method of increasing the inertia consid-
ered has been by increasing the mass of the string uniformly
throughout its entire length. The next method of increasing the
inertia of the cord is by attaching weights to the string at inter-
vals. If the intervals at which these weights are attached be
properly selected, the result will be that the distance over which
the wave motion is propagated will be equal to that of a cord of
uniform mass, whose inertia is the same as that of the loaded cord.
This point is illustrated in Fig. 297, where 1, 2, 3, 4, etc., repre-
sent the weights attached to the cord. It being assumed that the
distance between the weights, a-1, 1-2, 2-3, etc., is the proper one,
the mass of the cord plus the weights must be the same as that
of the uniform cord shown in Fig. 295 in order to have the condi-
tions of wave transmission the same in both cases.
It can be shown readily by experiment, that even if the mass
be retained constant, and the weights be not placed at the proper
intervals, the resultant wave transmission, so far from being im-
proved by their presence, will be decreased, as shown in Fig. 298,


352
TELEPHONY
337
1
1
1
1
2
2
3
4
6
where 1 and 2 represent two weights whose combined mass is
equal to that of the weights shown in Fig. 297.
It will be seen then, that as far as the capacity for trans-
mitting wave motion is concerned, a loaded string can be made
equal to a uniform unloaded string, if sufficient mass be added to
the former, to make the two strings equal in this respect, pro-
vided this added mass is subdivided and each portion placed at
the proper interval along the string, .
We are now prepared to con-
sider the analogy existing between
the case of wave motion being
transmitted over a string, and
electrical wave motion being trans-
mitted over wire. When an alter-
nating current is transmitted over
a circuit, three reactions take place.
First, inductance reaction, called
ordinarily the counter E.M.F. of
self induction, and which corre-
sponds to the inertia reaction. Sec-
ond, capacity reaction, which cor-
responds to the elastic reaction.
Third, resistance reaction, which
b
corresponds to the frictional reac-
b
tion. Denote the inductance re-
Fig. 296.
Fig. 297.
action by Ri; the capacity reaction,
by Re; and the resistance reaction, by Rr. Reaction as used in this
discussion is defined as that quantity which, multiplied by the cur-
rent flow, gives the rate at which energy is given out. Denoting
therefore by I, the current flow, we have the following equations:
R; I= Energy expended in overcoming the inductance reaction.
RI= Energy expended in overcoming the capacity reaction.
RI= Energy expended in overcoming the resistance reaction.
Denoting the total energy delivered to the circuit by E. we
have E. = Ri I + RI+ Rr I, which is a statement in mathe-
matical form of the law that action and reaction are equal. The
first two reactions are called conservative reactions and are useful
in transmitting energy over the circuit. The last is used up in
4
3
7
8
-
-


353
338
TELEPHONY
0
20
generating heat only, and represents lost energy. The first two
correspond to the inertia and elastic reactions in the case of the
cord; and the last to the resistance reaction. The first, or in-
ductance, reaction represents the energy utilized in producing a
magnetic field around the wire. This magnetic field is capable of
returning its energy back to circuit in the form of current. The
capacity reaction represents the energy utilized in establishing an
electrical stress between the conductor and its sur-
rounding medium. This electrical stress is capable
of returning its energy to the circuit in the form of
current flow.
From mathematical considerations of the propa-
gation of electrical energy along circuits, we have the
following:
Ri = a L where a is a constant and L the coef-
ficient of self induction of the circuit. From the ex-
pression, it is apparent that the inductance reaction
varies directly with the self induction of the circuit,
so that the greater the self induction the greater will
be its reaction.
Again we have
Rc =b.
b
where b is another constant, and the reciprocal of
Fig. 298.
the capacity of the line. From this expression it will
be seen that the capacity reaction varies inversely
with the capacity of the circuit; so that, the greater the capacity
the less will be its reaction.
Again,
Rr = R I?, where R denotes the resistance of the circuit and I
the strength of current flow, this latter expression being well known.
From the above considerations it is evident that there are three
ways of increasing the transmission limit: First, by increasing
the self induction. Second, by decreasing the capacity. Third, by
decreasing the resistance. The limit to which the resistance of the
circuit can be decreased has already been discussed under Line
Construction, so that this discussion will be limited to what can be
done with the other two. With the use of the present paper insu-
-
354
TELEPHONY
339
lated cables and open wire line construction, the capacity has been
reduced to a point beyond which there does not seem to be any
chance of progressing. Therefore, the only reaction that can be
improved is the inductance reaction. As stated above, this point
had already been recognized, but all attempts to make use of it led
to failure, due to the fact that the points of increased self induction
were not properly selected. These results were similar to those
obtained when the vibrating cord was improperly loaded, as shown
in Fig. 298. Professor Pupin's discovery consists in determining by
mathematical considerations the proper intervals at which the points
of increased self induction should be located. This interval varies
with the capacity of the line, and for open wire lines has been estab-
lished at 23 miles, while for cables the interval is about 1,000 feet.
The scheme adopted is to cut into the line at the intervals
mentioned, a retardation coil, thus producing a point of high self
induction. These coils, called loading coils, are encased in iron
boxes, made perfectly water tight, and so constructed as to be
mounted on the pole. For cable work, they are placed in manholes,
the case being so constructed as to be capable of being mounted on
the side of the manhole.
For cable work, the loading coil has proved very successful;
but in connection with open-wire lines, there has been experienced
considerable trouble due to lightning. This difficulty will no doubt
be overcome. Transmission is increased by the use of the load
coil about 25 per cent.
PRIVATE BRANCH EXCHANGES.
Certain classes of subscribers, such as hotels, factories, and
corporations located in the large modern office building, often
require an extension of telephone service beyond that given under
ordinary conditions. This arises from the fact that the number of
calls per day for this class of subscriber is very high, and because
a local service is required in addition. For example take the case
of an insurance company occupying many rooms in an office build-
ing, and being subdivided into many departments, say ten. The
head of each department requiring telephonic communication in
his own office, it will be necessary, unless some other plan be
devised, to place in each office at least one telephone connected to
355
340
TELEPHONY
a direct wire to the telephone exchange. This arrangement would
call for ten direct lines. Now the necessity for these ten lines
arises from the fact that a telephone must be placed in each office,
and not because this number is required to handle the business.
It follows, therefore, that each line will be operated far below its
normal capacity of calls.
To illustrate the above, suppose the total number of calls sent
and received by the company per day to be 100. Assuming that
the business is equally divided among the various offices, the total
number of calls handled by each line would be ten, which does not
approach the capacity of a telephone circuit.
Again, in addition to the calls to and from other companies,
there would often be occasion for one department to hold com-
fanna
6
a

3
2
4
1.
6
5
Fig. 299.
munication with another, which under the existing conditions could
be done by establishing the connections through the exchange in
the regular manner. This means that for these inter-department
communications, lines to and from the exchange must be main-
tained, whereas short lines extending only between the various
departments are all that is required.
To handle this class of business on a more economical basis
the private branch exchange was devised. The private branch
exchange is nothing more than a switchboard placed in some con-
venient locality within the offices of the subscribing company. To
this switchboard are run from the exchange a sufficient number of
lines to handle the total number of calls for outside points. From
this switch board also extend lines to each one of the telephones
placed in the department offices. The lines to the exchange are
called trunks, while those to the telephones are called auxiliary
lines, or extension lines.

a
356
TELEPHONY
341
The size of the switch board required depends upon the neces-
sary number of lines of these two classes. For example, if there
are ten extension lines and two trunks required, the switch board
must have a capacity of 12 lines. Since telephone business grows,
as a general thing, it is well to look to the future and provide a

ㅁ
​ron
va
Fig. 300.


switchboard with a capacity somewhat in excess of the actual
requirements. This practice allows of this class of switchboard
being made in standard sizes, which are usually of 5, 10, 20, 40, 50
and 100-line capacities.
In design and construction these switchboards are of two
classes. Those in which the connections are made by means of the


357
342
TELEPHONY
usual connecting cords, called cord boards, and those in which the
connections are established by means of keys, called cordless boards
The 5 and 10-line brand are usually of the latter class, while those
of larger capacities are of the former type, on account of the ex-
cessive number of keys required were they constructed in this
manner. The cord boards are of the type of the standard switch-
board, but made of various sizes to meet the requirements of sub-
scribers and with a view toward economy of space.

w
h
b
[Q)
9
k
anno
Tm
m'
n
©
Hulp
KO
Hole
Fig. 301.
In Fig. 299 is shown the circuit of a trunk line terminating in
a private branch exchange board; and in Fig. 300 is shown the
wiring of the cord circuit and operator telephone set.
Referring to Fig. 299, the trunk is shown entering the office at
It is wired in the same manner as an ordinary subscribers' line
in every particular, and in the exchange is connected in the usual
way to the proper subscriber multiple and answering jacks. At 6
is shown a small cross-connecting board, which is mounted in the
rear of the private branch exchange switchboard. This cross-con-
a.
358
TELÉPHONY
343
necting board is constructed in a similar manner to that shown in
Fig. 172. It is equipped with two rows of lugs, as 1 and 2, and 3
and 4. To the bottom row the wires from the outside are soldered
while the line jacks, such as 5, are permanently wired to the other
row, the circuits being completed by the cross-connecting wire
shown by the broken lines. It will be seen that the circuit is the
same as that of a subscriber line entering a standard switch board.
Referring to Fig. 300, it will be seen that the cord circuit also
is the same as that used on a standard switchboard. The ringing
current generator is of the same type as that used on a subscriber
telephone and is turned by hand. The transmitter battery is usu-
ally made up of two Fuller cells. The switchboard is designed for a
capacity of 10 pairs of cord circuits; but where the full capacity is
not needed, is only partially equipped. In private branch exchanges
where the business is so heavy that it would be inconvenient for
the operator to ring with a hand generator, ringing current is sent
from the exchange over special conductors, and wired to the ringing
keys of the private branch exchange switchboard. The extension
lines are wired at the private branch switchboard end, as shown
in Fig. 299.
In Fig. 301 is shown a complete connection between the
exchange, and an extension station at a private branch exchange.
Here the multiple jacks in the exchange are shown at a, b, c, and
d; while the answering jack is shown at e, the drop at f, and the
busy-test and restoring battery at g. The intermediate distribut-
ing board is seen at h and the main distributing board at i. The
type of switchboard here shown is bridging, but might just as
well be series. At j is shown the trunk to the private branch ex-
change, and it will be seen to be terminated at the connecting
board k. The jack is shown at l' and the drop at m'. The exten-
sion telephone is shown at n, and it will be seen that the exten-
sion line is wired to the connecting board k as already described.
The jack is shown at 1 and the drop at m. The connection is
shown completed through the cord circuit. The connection at
the exchange is put through in one of the many ways already
described.
A connection between two extension stations is shown in Fig.
302, where it will be seen that the conditions are identical to that
359
344
TELEPHONY
of a connection between two subscriber lines made over a stand-
ard switchboard.
In the case of a connection as shown in Fig. 301, the clearing
out is simultaneous at the exchange and at the private branch.
Both subscribers ringing off, throw the clearing out drops at the
main exchange and also at the private branch. The operator at
the private branch disconnects the extension line, while the oper-
ator at the main exchange supervises and asks: "Are you

Holo
4ole
o
to
Hole
Fig. 302.
through ?” The private branch operator who is listening in says
“Yes," and clears the trunk. The connection is then cleared in
the main exchange.
One of the most approved types of cordless private branch
exchange boards is shown in Fig. 303. Here the lines are shown
at 1, 2, 3, 4, and 5; they are wired to the middle contacts of the
keys h, h', 7", hilt, and respectively. These keys are con-
structed on the same principle as the ringing key, but are
equipped with cams which normally keep the middle springs
away from both the inner and outer contacts. When they are
thrown one way, contact is made between the inner points and
360
TELEPHONY
345
middle springs; and when thrown the opposite way, contact is
made between the middle and outer springs. The outer springs of
these keys are bridged together as are the inner contacts, so that

2
3
5
o
-b
d
Не
Sh
Non Non
pet meg Mit Motion
Net
nes non non non non
m
Fig. 303.
by wiring the cams of any two keys in the same direction the
two lines wired to them are connected together, either through the
inner or outer contacts. Bridged to each line is the line drop
shown at a, b, c, d, and e. They are of the same construction as

e
d
h
с
b
b
α
k
ha
m
Fig. 304.

those used as clearing out drops, having a resistance of 500 ohms,
and being surrounded with iron shells to prevent cross-talk. Also
bridged to each line is a listening key l, l', 2", 211, and 71, all con-
nected to the operator telephone set m.

361
346
TELEPHONY
The method of operating this board is as follows: Suppose
that the subscriber on line No.1 wishes to be connected to line No. 2.
The line is rung on and the drop a thrown. The operator throws
the listening key l and communicates with the calling party. To
make the connection, keys h and hII are adjusted to make contact
on the outer contacts, and the circuit is established between the
two. If while this connection is being maintained, and additional
connection is required between line No. 2 and line No.5, the keys h'
and h' are adjusted to make contact at the inner points, thus
cutting the circuit through. Considering the number of keys re-
quired, this type of board is not flexible, as only two connections
can be established at the one time. The advantages, however,
lie in the small amount of space occupied by the board, and the
ease with which it can be operated.
In Fig. 304 is shown a general view of this type of board
The drops and keys are mounted in the face of a neat cabinet a.
The drops are shown at b, c, d, e, and f, the connecting keys at g,
h, i, j, and k, and the listening keys at l, m, n, o,
and
p.
The
cabinet is designed to be mounted on a desk, and the wires are
brought up through a hole in the bottom. The lid is hinged so
as to lift up and give access to the inside.

362

LLLL
INT
LLLL
1ST
133
11
IIIIIIII
INTERIOR OF THE AUTOMATIC TELEPHONE EXCHANGE, LINCOLN, NEBRASKA.
Showing the Power Plant of the Exchange.

AUTOMATIC TELEPHONY.
The spirit of the present age is not better shown forth than
by the ever-increasing demand which industry, pressed by the
keenness of competition, is making upon genius for the invention
of labor-saving and time-saving machinery; and nothing pays
higher tribute to the breadth of the human intellect than the char-
acter of the machinery which has been evolved as the result of this
insistent call. Indeed, we are sliding
rapidly into an automatic age. The
work that once was done by hand, then
by hand-guided machines, is now done
by automatic devices. Scarcely a large,
up-to-date factory but has in one or more
of its departments a battery of automatic
machines busily engaged in turning out
such things as screws, buttons, tin cans,
cloth, shoes, or a thousand other varieties
of useful articles from the raw material,
with surprising nicety and tremendous
speed, reducing the cost of manufacture
to a minimum and widening the field
of sale. We have wondered at the in-
genuity of these machines and marveled
at their cleverness, but we have looked
upon
their invention and introduction as something that was bound
to come, as only another step in the logical order of things. We
have waited for them, and have not, therefore, been surprised at
their successful advent.
Few of us, however, as we have stood before a telephone box,
wiggling a switch hook, or whirling the crank of a hand generator,
and impatiently waiting for time and the “Hello girl” to bring
us our connections, have ever gone so far as to hope, or even con-
ceive the idea, that this genius who had so long presided over the

Desk Telephone.
a
365
2
AUTOMATIC TELEPHONY
central office, would ever be unseated and her place occupied by an
iron machine whose speed and accuracy would discount her best
performances, and yet that day is here. The States are already
dotted with automatic telephone exchanges, which are giving serv-
ice to thousands and thousands of subscribers, and with such
success that it is not hazarding anything to predict that a few

Automatic Telephone Exchange, Dayton, Onio.
years will see the absolute divorce of the operator from the ex-
change room—except, of course, for long-distance calls, for which
her services will probably always be needed.
Historical Retrospect. The application of the automatic idea
to telephony is not new. It is considerably more than a decade
since Strowger, an obscure Chicago engineer, brought out the first
automatic telephone. The Strowger Automatic Telephone Com-
pany and the installation of a number of small exchanges résulted.
These exchanges were successful, not so much in what they actually
accomplished in the way of improved service, as in the promise they
366
AUTOMATIC TELEPHONY
3
gave of future development in that direction. The apparatus was
crude, imperfect, and complex; but the fundamental ideas involved
were right and required only better expression.
Ten years passed, ten years of experiment and persistent
effort. Strowger died. The Automatic Electric Company was
organized to take over the Strowger patents. Further experi-
menting was done, and greater capital expended. The result has
been a system from which the im-
perfections have been eliminated,
a system which is scarcely more
complex than the manual switch-
boards now in general use.
The
limit of capacity is no longer
reached at 1,000 staticns. In fact,
the business of the very largest
city can be handled as efficiently
and conveniently as that of a town
which requires but a hundred tele-
phones. In Chicago to-day an au-
tomatic exchange of 10,000 sta-
tions is aiready in operation, and
others will be added as occasion
demands, the ultimate purpose
Wall Telephone.
being to handle the business of Showing Method of Operating Dial
and Making Call.
the entire city.
The Automatic Mechanism, A study of the apparatus which
has made all this possible, will, no doubt, be interesting and in-
structive. The telephone itself resembles, in many particulars,
the manually operated telephones with which we are so familiar.
It consists of the usual transmitter, receiver, bells, battery, and
induction coil, adding only a calling dial, a circular metal piece,
on the periphery of which are ten finger holes numbered 1-2-3-4-
5-6-7-8-9-0. A stop is provided at the lower of the holes to limit
the distance which the dial may be made to revoive.
How a Call is Made. The method of calling is very simple.
To secure a number, say 761, the subscriber first takes the receiver
from the hook; then placing his finger in hole number 7, pulls the
dial around to the stop above mentioned. When released, the dial

367
4
AUTOMATIC TELEPHONY
is instantaneously restored to its normal position. The subscriber
is now connected to a trunk line leading to the seventh group of
so-called “ connector” switches, which we may call the “seven
hundredth” group. In the same manner he calls 6 and 1 in this
group. Having turned the number desired, he presses a button
underneath the dial, which
rings the bell of the person
wanted, and the connection is
completed. In the event that
the 'phone of the subscriber
called is busy at the time of
the call, a vibratory sound in
the receiver of the caller noti-
fies him that such is the case.
The keyboard or internal
mechanism of the telephone,
occupies a space 5 X 3X2 in-
ches, and consists of an im-
pulse-sending mechanism,
which, in response to the ro-
tations of the dial, communi-
cates to the subscriber's switch
a number of impulses corre-
sponding to the number of the
hole in which the finger is
placed, lifting the shaft which
occupies the central position
of the switch, up to the proper
row of contacts, and bringing
the “wiping fingers” fastened
thereto, into connection with
Automatic Telephone Switch.
the proper contact in that row.
It should be understood
that, when the call is made, no impulses are sent over the line on
the down movement of the dial, but on the return. This is arranged
for the protection of the instrument against careless or hasty sub-
scribers. The return of the dial is regulated by a governor which
always insures proper speed.

REA
Front View.
368
AUTOMATIC TELEPHONY
5
The calling mechanism may be said to be perfect. It is sim-
ple, and works with remarkable accuracy, speed, and precision.
The Switch. The switch, shown in the accompanying illus-
trations, is a device about 13 inches in height, 41 inches in depth,
and 4 inches in breadth. The upper half of this device consists
of two relays and three pairs of
magnets mounted on a solid cast
metal base. These relays and
magnets, together with the
proper springs, wires, etc., oper-
ate a vertical rod in the center, in
obedience to the impulses sent
from the subscriber's telephone,
and bring the three pairs of
“wiping fingers” attached there-
to, into connection with the brass
contacts, which, arranged in three
semicircular banks, constitute
the lower half of the switch.
The upper of these banks,
known as the “busy bank”,
serves to indicate busy lines in
the automatic selection of
trunks. The lower two are line
banks”, to which the line wires
connect, and over which the con-
versation is held.
Two classes of switches are
employed, one known as "select-
ors”, of which there is one for
every telephone connected with
the exchange, and the other as
Automatic Telephone Switch.
“connectors”, of which there are
Side View,
ten for every hundred selectors
and which are in groups each capable of connecting one hundred
telephones. The function of the selector is to connect the calling
telephone with the connector in the proper group, which in turn
connects with the telephone desired in that group. This is the


369
6
AUTOMATIC TELEPHONY
case in exchanges of one thousand capacity or less.
In larger
exchanges a second connector is employed. This is an intermediate
switch, and divides the work of selection with the first selector.
Trunk-Selecting System. The trunking system employed is
very much akin to that now generally used in manual practice and,
therefore, needs no description here. It may be said, however, that
the selection of trunks is automatically accomplished, the “wiping
fingers” on the shaft of the selector
switch passing over all busy contacts
and stopping at the first idle point.
Accessories. The accessorial
equipment consists of a 52-volt
storage battery, which furnishes.
the current for operating the
switches; a cross-connecting board
or distributing rack, equipped with
carbon lightning arresters and beat
protectors; a ringing machine with
- busy back” and “howler” at-
tachment; charging machines; pow-
er board, on which are mounted the
usual knife switches, circuit-break-
Interior of Wall Telephone.
ers, voltmeters, ammeters, etc.,
necessary for controlling and meas-
uring the current; and a tell-tale” board.
This last consists of a number of 8-candle-power lamps
mounted on a marble panel, together with a magneto bell. In
case of a short circuit or “ground” on any line, the bell rings and
the lamp on the panel glows. The position of this lamp instantly
indicates to the attendant the exact location of the trouble, and
oft-times enables him to rectify it before the subscriber is aware
that there has been any trouble.
The automatic switches are mounted on steel shelves, twenty-
five to the shelf, each board containing four shelves of first selectors,
and one shelf of connector switches. This is the arrangement for
a system of 1,000 stations. In a 10,000-station system, the board
is made up of six shelves, four of first selectors, one of second
selectors, and one of connector switches. The floor space occupied

"
a
370
AUTOMATIC TELEPHONY
7
by such a switchboard is 11 feet 6 inches by 12 inches. The
switchboard is made of steel angles and is rigidly braced.
A very important feature of the automatic switchboard is that
it can be increased to any capacity by simply adding new sections
with the desired number of switches
mounted thereon, without in any
way interfering with existing con-
ditions. Ninety-five per cent of
the electric contacts and connec-
tions are made at the factory; con-
sequently better results are secured,
as well as time and expense saved
in installation.

Advantages of the Automatic
System. 1. A switchboard has no
operators; and thus one of the large
fixed charges incident to manual-
exchange operation is eliminated.
2. There being no operators, the
automatic exchange can be located in
less expensive quarters than the man-
ual. No reading or retiring rooms are
needed, no lockers, no lavatories; and
the cost of fuel and lighting is reduced.
3. One switchboard attendant,
for testing and keeping apparatus in
order for 1,000 subscribers, is all that is
needed in the automatic practice.
4. The cost of maintenance and
interior equipment is no greater, and
in large exchanges is less than in the
manual exchange.
5. The service which the auto-
matic system gives, unlike that of the
manual system, is absolutely secret,
each subscriber having a "private
wire" on which to transmit his com-
munication-an advantage that cannot
Automatic Telephone Switch.
be overestimated by the general busi-
Rear View.
ness man, as well as by the broker,
the lawyer, and the physician.
6. The subscriber himself instantaneously connects with the person
he wishes to call; and the apparatus is so constructed that it is an impos-
sibility for another subscriber to "cut in” or in any way interfere with
the line he is using.
371
8
AUTOMATIC TELEPHONY
7. The frequent delays and mistakes which the manual board
causes are entirely unknown to users of automatic telephones. The
switches do not make errors nor gossip; are never weary or sleepy; are
not interested in subscribers' affairs; and are not impudent.
8. The complexity of the automatic exchange does not increase
proportionately to the increase of size, as is the case with manual ex-
changes, where the cost of giving service is much more per subscriber in
large than in small exchanges. The cost of operation in the automatic
exchange is fixed. An increase is merely a matter of adding new tele-
phones and switches, the cost of operation being the same per subscriber.
9. The automatic switch is thoroughly cosmopolitan in its nature,
no interpreter being needed by the foreigner in a country where the auto-
matic exchange is located, any person being able to secure the desired con-
nection by simple rotations of the dial.
10. The same number of automatic switches are always at work,
night and day.
11. Quick connections, instantaneous accommodations, prompt
answers, accuracy, and promptness, with the busy signal given when
the subscriber called is busy.
372

3
f
1
SENDING AND RECEIVING A MESSAGE. COLLINS' SYSTEM.
WIRELESS TELEPHONY.
The transmission of intelligence by electricity has reached, in
its broadest sense, its final stage of development.
Intercommunication by means of an electrical disturbance set
up for the purpose of propagating energy representing the alpha-
betic code or articulate speech, may be divided into four general

8
Fig. 1.
classes, namely, telegraphy with wires, telephony with wires,
telegraphy without wires, and telephony without wires.
These principal classes may, it is evident, again be subdivided
into many branches, but there can be no further evolution in the
arts of sending and receiving messages by electrical methods, where
instruments are interposed between those who are to be brought
into mental relationship with one another.

5
6
3.
X7
8
6
Fig. 2.
This is not to say that each of the forenamed systems approxi-
mate in their present state anything like perfection, for all are more
or less crude in practice if not in theory, but any improvements
that may be made in the future must be in degree and not in kind.
Hence the raison d'être for the numerous arrangements of both
wire and wireless systems of telegraphy and telephony is obvious.
When wireless telegraphy made its spectacular début a few
375
2
WIRELESS TELEPHONY
years ago, to the casual observer there seemed no good and valid
reason why speech propagation and reception without wires were
not already at hand, but to the investigator it was soon revealed
that history was repeating itself and that wireless telegraphy and
telephony were as different in all their phases as were their pre-
decessors which utilized the connecting wire. A brief analysis of
these differences that mark so clearly the dividing line between the
four great classes enumerated, will assist materially in an under-
standing of the final principles of wireless telephony.
5
6
110
20
8
을
​6
Fig. 3.
When Morse took up the study of telegraphy a working knowl-
edge of the laws of electricity had not as yet been very accurately
deduced. Induced and alternating currents had been explained by
Henry and Faraday, but their usefulness remained to be indicated.
It was well known, however, that a direct current traversing a wire
was capable of energizing an electromagnet, and from this fact
Morse conceived the idea of the relay--the device that made
telegraphy a commercial factor.
Although nearly half a century elapsed before Bell made his
successful essay to produce a speaking telephone, electricity had not
made as much progress as might have been expected; Reis had
attempted to construct a telephone by utilizing a rapidly inter-
mittent current, and these futile trials led Bell to believe that such
a method was impractical; experimenting with steel reeds vibrating
over magnets he produced currents of varying strengths, termed
undulatory currents, in virtue of their wave-like characteristics, and
this formed the basic principle of the telephone.
In Marconi's wireless telegraphy any kind of a low-voltage
current may be transformed into one of high potential and frequency,
but the oscillations of such a transmitter emit their energy in the
form of a train of waves with long intervals of time between them,
and these are not, therefore, at all adapted to the transmission of
376
WIRELESS TELEPHONY
3
voice undulations. There are several methods whereby articulate
speech may be transformed into electric current waves which may,
in turn, be propagated through the ether of the air, earth, or water.
The first of these methods consists of a battery and a telephone
transmitter connected in series, with the terminals which are embed-
ded in the earth or immersed in the water, thus forming a circuit;
when the undulatory current flows through it, the larger portion of
the energy is dissipated, flowing out in curved stream lines, owing
to the great cross-section of the earth, and extending to consider-

LA
Ruhmer Photo-Electric Telephone. The Transmitter.
Fig. 4.
able distances. Now if a complementary equipment consisting of
a telephone receiver is likewise in contact with the earth by having
its terminals similarly grounded, when the energy impinges upon
these the current then flows through the receiver and speech may
be accurately reproduced.
A second method, ideal in its simplicity, is accomplished by
electromagnetic induction; everyone knows that when a current
flows through the primary of an induction coil alternating currents
are set up in the secondary coil by what is called induction, but
everyone does not know that these coils may be widely separated
before the limits of the inductive influence will be reached. If, for

377

hannon
Ruhmer Photo Electric Telephone. The Receiver.
Fig. 5.
378
WIRELESS TELEPHONY
5
a
а.
а
instance, a telephone transmitter and a source of electromotive
force approximating 25 volts are included in the circuit of a coil of
wire having, say, 25 turns and a diameter of 5 feet, and a telephone
receiver is included in a coil of
wire having 60 turns and a diam-
eter of 3 feet, words spoken into
the transmitter may be distinctly
heard in the receiver when the
two instruments are separated a
distance of 100 feet, providing,
of course, that the coils have
their planes parallel with each
other. This is the inductivity
method and like the one previ-
ously described, it is operated by
a low-voltage direct current.
The invention of the tele-
phone receiver led to many inter-
esting experiments and to many
curious discoveries. Bell in
working with his new telephone
devised an apparatus for tele-
phoning on a beam of light.
This instrument, which he
named the radiophone, also in-
volved the use of selenium, a
substance that possesses the
very remarkable property of
varying in its electrical resist-
ivity and its reciprocal when
fused in between two connect-
ing wires of platinum or silver.
This apparatus is shown in Fig. 6. Herr
Ruhmer Receiving a Photo-
Electric Message.
the diagram, Fig. 1; the trans-
mitter used by Bell was not electrical, for the transmitter as we
know it had not been invented; it comprised the mouthpiece 1 and
shell 2 for supporting a thin metal diaphragm 3; to the latter was
attached a small concave mirror 4, a plane mirror 5, convex con-

379
6
WIRELESS TELEPHONY
densing lens 6, and projecting lens 7, all of which, suitably mounted
on a frame, completed the apparatus for transforming the air
vibrations produced by the voice into light variations of the pro-
jected beam.
The receiver was formed of a parabolic mirror 8 of large
diameter and in the focus of this a selenium cell 9 was adjusted;
nnnn ro
Fig. 7.
the terminals of the conducting wires or electrodes of the cell led
through insulated bushings in the reflector to the back where they
were connected in series with a battery 10 and a telephone receiver
11. When in operation the successive transformations take place
in the following manner—the light from the sun is reflected by the
plane mirror 5 to the condensing lens 6 where its rays are focused
on the concave mirror 4. From the latter the light is reflected to
the lens 7 where it is propagated through the intervening space to
the large parabolic reflector 8, where its diffused waves are col-
lected and concentrated to a pencil point on the selenium cell 9. It
is evident that any changes in the intensity of the light will change
а
Fig. 8.
the resistance of the selenium cell, varying in consequence the
current from the battery 10 and finally affect the telephone 11.
When words are spoken into the transmitter this is precisely
what takes place, for the movements of the diaphragm of the trans-
mitter cause the concave mirror to vibrate in unison with it and
every change is thus indicated at the receiving end in virtue of
these fluctuations. While the distance to which Bell was able
to propagate the light variations representing the human voice was
probably less than one hundred feet, recent improvements in the
system by Herr Ernest Ruhmer have resulted in the transmission
of speech a distance of several miles.
This was made possible through the remarkable advance of
electro-physics during the past few years. Prof. H. T. Simon
380
WIRELESS TELEPHONY
7
ascertained that an ordinary arc light could be made to reproduce
articulate speech more clearly and distinctly than any phonograph
by superimposing a feeble alternating current upon a heavy direct
current. The diagram, Fig. 2, illustrates one form of the method by
which this may be accomplished.
An ordinary telephone transmitter 1 and battery 2 are con-
nected in series with the primary of a small induction coil 3; the
secondary coil 4 leads through the condensers 5, 5 to the opposite
carbons 6, 6, forming the electrodes for the arc light 7; the latter
is produced by a direct 50-volt current from a generator 8 or, what is
yet better, a storage battery. When the speaking arc or arcophone
a
a

al
RIDGETOLLE
ERIE
Ferryboat Ridgewood Equipped With Collins' Wireless Telephone.
Fig. 9.
is operated, the voice causes the air waves to vary the resistance
of the transmitter 1 in the usual manner; the current from the bat-
tery 2, thus varied, energizes the primary coil 3, setting up alter-
nating currents in the secondary coil 4; the condensers 5, 5 pro-
duce no appreciable effect on the wave form of the current which is
superimposed upon the current from the generator flowing through
the circuit formed of the carbons 6, 6; arc light 7, and generator 8.
The object of the condensers, however, is to prevent the direct
current from backing up into the transmitter and burning it out.
The superimposed currents, however feeble, vary the resistance of
the arc, and this produces a change in its temperature which gives
rise in turn to sound waves. Another important function of the
speaking arc is that there is also a variation of the intensity of the
light which it emits.

381

8
WIRELESS TELEPHONY
no
Fig. 10. Collins Wireless Telephone.
382
WIRELESS TELEPHONY
9
It is this by-product, as it were, of the speaking arc that Ruh-
mer employed in his photo-electric telephone which, in all other
respects, is based upon the original Bell photophone. In Ruhmer's
system the speaking arc is placed in the focus of a parabolic
reflector whence its rays are directed to the distant receiver, and
when the two are in perfect alignment the voice into the one will
be distinctly audible in the other. The arrangement then takes the

JOHN
Upper Deck of John G. McCullough, Showing Aerial Wires Used in Collins System.
Fig. 11.

form shown schematically in Fig. 3, and with the description of the
speaking arc and the selenium cell that have gone before, its action
will be readily apparent. Figs. 4, 5, and 6 are photographs of the
Ruhmer apparatus.
The writer, A. Frederick Collins, in endeavoring to bring about
the advent of a commercial wireless telephone that would not be
interfered with by fogs or other conditions and would not require
either alignment or a direct visual line, investigated the several
schemes of dispersion, inductivity, and electromagnetic wave meth-
ods. The latter is the most interesting since it partakes of the
383
10
WIRELESS TELEPHONY
a
nature of the wireless telegraph as well as of the wire telephone,
yet it will do that which is not possible with either of the latter,
i.e., it will transmit articulate speech wirelessly.
In the beginning of this article it was pointed out that electric
waves, when emitted by a high frequency and potential oscillation
equalized through a spark gap, were periodic as indicated in the
diagram, Fig. 7, the current strength decreasing in geometric pro-
gression like the vibrations of a straight steel spring. In wireless
telephony an undulatory oscillation is required, and this may be
obtained by loading the radiating circuit with large inductances
and capacities whose coefficients possess the properties of slowing
down each oscillation until a more or less perfect sine wave results
as indicated in Fig. 8.
When this point is reached the striking effect of the oscillatory
discharge on the ether is greatly weakened, but at short distances
the telephone will respond audibly without the usual coherer inter-
vening; some of the most recent work by the writer though, has
shown that a liquid detector, made by immersing a platinum point
and a platinum plate in an alkaline solution, increases the volume
of sound to an appreciable extent.
The first series of tests with this type of apparatus was made
at Rockland Lake, N. Y., a distance of a mile, while articulate
speech has been transmitted and received under very favorable
conditions a distance of three miles and a half. Tests were also
carried out between the ferry boats John G. McCullough and
Ridgewood, plying between New York and Jersey City.
Its final adoption will prevent collisions of vessels in harbors,
while telephone communication between docks and vessels will
facilitate transportation, saving time and money as well as insuring
the safety of the passengers and crews. It is another step in the
march of human progress.
a
384

LIGHTNING ARRESTER RACK NO. A-1878
Stromberg-Carlson Telephone Mfg. Co.
COMMERCIAL ASPECTS OF TELEPHONE
LINE PROTECTION*.
The problems involved in telephone line apparatus and protec-
tion are numerous and varied because of the widely different con-
ditions which may, and often do arise to make protection necessary.
To-day the protective apparatus used in a telephone plant forms an
important part of the entire equipment, as on it depends not only
the safety of the lives of the operators and users, but of the physical
property of the telephone company and that of its customers.
The presence of the street railway and electric lighting and other
systems in the allied fields of electrical engineering, and the advent of
the common battery system now largely used in the telephone industry
itself, has placed before the telephone engineer more and more com-
plex conditions.
There are broadly three elements against which apparatus must
be protected: lightning, high-tension currents, such as may be caused
to flow on a telephone line by a cross with electric light or power wires;
and sneak currents, which are currents too small to do instantaneous
damage, but which, if they persist, may, by the accumulation of heat,
cause damage to the apparatus. Unless danger from consequent fire
be taken into account, only the first two causes need be considered in
regard to the danger to human life.
The types of apparatus for protecting against one or all of these
sources of danger are well known. It is the purpose of this article to
consider where and under what conditions protection should be given,
and under what conditions it is better to take some risk and give only
partial protection or none at all.
Carbon-block arresters, wherein two carbon blocks separated by
a thin air-gap are used as a “safety valve” for high potentials, are now
almost universally employed for protection against lightning, and
against all currents such as might produce potentials, of, say, 350 volts
or over between the line and ground. With a distance of .005 of an
* By Kempster B. Miller. Reprinted from Electrical Review, December 10, 1904, by
permission.

a
387
2
TELEPHONE LINE PROTECTION
a
inch between the carbon blocks a pressure of 350 volts across the
blocks will break down the insulation of the air-gap between them.
This kind of an arrester, of course, operates by grounding the
line either temporarily or permanently; and in the case of a lightning
discharge, which persists for only a minute period of time, no other
protection is necessary. However, a high potential current due to a
cross with a high tension wire is likely to persist after being grounded,
and thus cause a very large current to flow over the conductor so
grounded, which may be injurious to the line wire or cable itself.
For this reason it becomes desirable to provide some means for open-
ing the circuit after it has been grounded in case the current allowed
to flow on account of the grounding is of sufficient magnitude to be-
come dangerous. The most simple means of accomplishing this
consists of a fuse wire of limited carrying capacity.
Sneak currents may be caused by low potential crosses somewhere
on the line, or of comparatively high potential crosses through a high
resistance. In common battery work still another very common cause
of sneak currents is due to the grounding of one of the telephone wires
or the crossing of two wires, in which cases, even though the lines are
not subjected to any outside electromotive force, the current flowing
from the common battery may, in some systems, persist to such an
extent as to cause ultimate damage to the apparatus.
The most simple means of protection against these small currents
is to employ a fuse wire of very small carrying capacity, mounted on
mica strips to which they are secured. These are not very efficient
forms of sneak-current arresters, for the reason that they can not be
depended upon to open the circuit when traversed by current of
pre-
determined strength. Another disadvantage is that, on account of
their small size, they are very frail and liable to mechanical injury.
The well-known heat coil is the most effective sneak-current arrester
yet put into extensive use.
For protection against heavy currents such as may be caused to
flow in the line after the heat coil has operated and grounded the line
conductor, comparatively heavy fuses—five to ten amperes—usually
mounted in wooden or fibre tubes are found most desirable. These
are not so much subject to the frailties of mechanical construction as
the mica fuses, and may, therefore, be used on outside construction
with considerable freedom.
388
TELEPHONE LINE PROTECTION
3
By the judicious use of all of these general types of protectors, a
degree of protection that is well-nigh absolute, may be attained; but
there is a difference of opinion as to whether or not absolute protection
is at all desirable. Under conditions made necessary for absolute
protection the heat coils, on account of their extreme sensitiveness,
may be frequently operated by the normal currents of the exchange;
again, if the line fuses are made of too low carrying capacity very
slight currents which might injure nothing would also cause their
operation. If the gaps in the carbon arresters are made too small,
the liability of short-circuiting the line to ground by the accidental
contact between the carbons, or the presence of a small amount of
carbon dust, would exist.
The blowing of a heat coil or the short-circuiting of the carbon
arrester at the exchange is not a matter of much importance, because
it is
easy to replace them quickly, men being always present in the
exchange for that purpose. However, all such unwished-for occur-
rences at the office arrester, even though remedied within a few mo-
ments, are likely to cause interruption in the service which, from the
subscriber's standpoint, is not desirable. The blowing of a fuse or
the operation of a carbon arrester or heat coil at some point in the
outside construction or at the subscriber's station is, however, much
worse, as the interruption to the service is of longer duration and the
cost of repairing is much greater.
It seems evident that there is such a thing as overdoing protec-
tion, as too perfect a system, considered from the standpoint of pro-
tection alone, brings about an increased cost for maintenance and
frequent interruptions of service. If the cost of protection, due to
added maintenance and service interruption, is greater than the gain
due to the saving afforded by the protection, then there is too much
protection. For this reason a middle course is usually pursued, aim-
ing to give sufficient protection to the apparatus and property to pre-
vent the possibility of any far-reaching disastrous results, at the same
time keeping in mind the minimizing of the cost of maintenance and
of service interruption.
A typical telephone line for this discussion may be taken as one
extending from the central office to a subscriber's instrument, this
line passing directly from the office through a section of underground
cable, thence through a section of overhead cable, and thence through

389
4
TELEPHONE LINE PROTECTION
a
bare wires on poles to the subscriber's premises. The underground
cable, it is understood, runs directly into the central office, being ter-
minated either in potheads or equivalents, or directly on the line side
of the distributing frame, so that there are practically no points, be-
tween the place where the cables enter the underground conduits and
the inside wiring of the central office, at which the conductors are
liable to become crossed with wires charged to dangerous potentials.
This portion of the line, therefore, may be fairly assumed to offer no
points of exposure to danger, although, of course, danger may be
transmitted to it from other portions of the line.
At the point in the office where the conductor emerges from the.
cable, it is common practice to provide a combined carbon and heat-
coil arrester. The coil is so arranged that when released it will allow
the line spring to make contact with the ground connection, grounding
the line and opening the circuit to the switchboard.
That the central office protection on the line in question should
consist of a heat coil and carbon arrester is a matter concerning which
there is a little dispute. There are those who maintain that a line
when entirely underground from the central office to the subscriber's
premises has no need of any protection whatever.
The degree of sensitiveness of the heat coil can not be specified
for all cases, as the apparatus of some switchboard systems is very
much more susceptible to damage by excessive currents than others.
In other words, currents which would be excessive for the electro-
magnets of some systems would be carried readily without danger of
harm by those of others. It may be said in this connection that the
best switchboard designers are making the coils of electromagnets,
as far as possible, self-protecting; so that they would not be damaged
current due to the voltage of a central office battery which
might flow through them, even on a short circuit. With such appa-
ratus there seems no doubt that an all underground line may be left
without protection.
The electromagnets of some switchboards are wound with such
fine wire as to render the following requirements of the heat coil
necessary: that it shall carry 0.1 ampere indefinitely and operate
on 0.2 ampere within five minutes. To meet these requirements
the heat coil is generally wound to about twenty-ohms resistance.
In other cases the requirements are that the coil shall stand 0.2 ampere
by any
390
TELEPHONE LINE PROTECTION
5
indefinitely and that it must operate on 0.25 ampere within three
minutes, and that the resistance of the coil shall not be more than
seven and one-half ohms. These latter figures are now perhaps the
most commonly adopted, and with such a coil when the current is in
excess of one-quarter of an ampere but less than 0.4 of an ampere
the coil will operate in from one to one and one-quarter minutes;
and with currents in excess of 0.4 of an ampere they are operated
practically instantaneously.
The air-gap between the arrester blocks at the central office is
now fairly well standardized at 0.005 inch, and with such an air-gap
and with carbon of ordinary grade the insulation between the blocks
will break down when subjected to a tension of about 350 volts.
The question as to whether a fuse should be placed at the point
where an underground cable joins an aerial cable is a mooted one.
It is probably true that as in many other disputed questions there
are good reasons on both sides and that under some conditions a
fuse should be placed at this point, while under others it should not.
Pure logic certainly brings us to the conclusion that a fuse should be
placed at a point on the line where the exposed construction begins.
This being true, the placing of fuses in the conductors at the point
where the aerial cable passes to the underground cable, depends on
whether or not the aerial cable may be considered as, within itself,
exposed. Clearly, a high-tension wire falling across or in any other
way coming in contact with an aerial telephone cable, is a possible
occurrence. It is also clear that such a cross might cause the speedy
disintegration of the sheath of the cable and thus direct exposure to
the conductors within. In this sense the aerial cable is exposed to
danger and to protect the underground conductors from damage due
to such a contingency, it would be necessary to place fuses at the outer
end of the underground cable.
While every telephone man who has had experience with out-
side construction will probably call to mind one or a few cases where
damage to aerial cables—and through them to underground cables
-has occurred, due to exposure at some point within the aerial
cable, it is probably true that the cases that one man is able to cite
Certainly aerial cables are often damaged, due to high-
tension crosses or to lightning, but in many of these cases of damage
the doubt exists as to whether the trouble originated at some point
.

are few.
391
6
TELEPHONE LINE PROTECTION
along the line of the aerial cable or whether it originated elsewhere
and was brought into the aerial cable conductors through the lines
leading to those conductors. Many cases of damage to aerial cables,
and through them to underground cables, which at first sight appeared
to be clearly due to some conditions along the line of the aerial cable,
have afterwards proved to be due to conditions existing beyond it,
where the conductors of the circuits were more exposed to trouble.
Perhaps the best answer to the question arising as to the loca-
tion of fuses at the outer end of the underground construction is that
unless the aerial cable traverses a route such that high-tension crosses
are very likely to occur along the line of the cable, the aerial cable
may
be fairly considered as an unexposed portion of the lines; and this con-
clusion brings us unalterably to the conclusion that the fuse should
be at least carried to the outer end of the aerial cable. In those
special cases where the danger arising along the line of the aerial
cable seems great, then only should a fuse be inserted between the
underground and overhead cables.
We have now arrived at the conclusion that in most cases the
line fuse should be moved at least as far from the central office as
the end of the aerial cable. What should be done at this point ?
Cleariy the bare wire joining the aerial cable and the drop wires
serving the subscribers are exposed portions of the circuit. To
provide, therefore, against heavy currents due to crosses being car-
ried into the cable conductors, a fuse should be placed at the outer
end of the aerial cable. If the line be such a one that the underground
cable joins directly to the bare wire, then the fuse should be placed
at the end of the underground cable. We may say, therefore, that
,
-a fuse always should be placed between the exposed and unexposed
portions of the circuit.
The fuse at such point provides only for the interruption of
strong currents. It does not provide against static discharge. For
this reason it follows that in the case of all long aerial lines, such as
toll lines, country lines and long bare city lines, a carbon arrester
should be added as a protective means at the point where the bare
wire arrives at the outer end of the cable. These carbon arresters,
owing to their comparative inaccessibility, should be provided with
a wider air-gap than is used in the central office arresters, and proba-
bly from 0.01 to 0.015 inch represents about the best practice in this
392
TELEPHONE LINE PROTECTION
7
respect. The question as to the relative position of the fuse and the
carbon arresters now arises. It is evident that if the fuse were placed
in the circuit between the carbon arrester and the central office, a
high-tension cross on the exposed portion of the line beyond the car-
bon arrester might cause an arc in the arrester which would persist,
if the cross persisted, and gradually consume the carbons and perhaps
incidentally also the cable box, pole fixture and pole. The fuse, there-
fore, should be placed between the carbon arrester and the outer end
of the line and never between the carbon arrester and the cable.
The carbon arrester in such cases protects the cable from
lightning and other high-tension crosses, while the fuse not only
prevents a heavy current from entering the cable conductors, but
also prevents the continuance of arcing at the arresters which might
lead to the damage of the equipment at that point.
We may then decide that at least a fuse is required at the point
where the overhead cable joins the bare wire or where an under-
ground cable is connected to a bare wire without the intervention
of an aerial cable. Also, wherever a long open wire line joins a
cable at such a point, a carbon arrester also should be employed.
Some engineers use a carbon arrester as well as a fuse at all
points of juncture between open wire and cable regardless of the
length of line. This seems poor policy and one that is productive
of excessive maintenance expense. In other words, practice has
proven in general that the occasional loss due to damaged cables
caused by the omission of carbon blocks, where the open-wire lines
are short, is of less importance than would be the maintenance of
such blocks at all points where the open wire joins the cable.
Probably all telephone engineers agree that a fuse should be
placed at the points where the line wire enters the subscriber's prem-
ises. Many complete telephones are now equipped with fairly
efficient forms of carbon lightning arresters, these latter forming
integral parts of the telephone as produced. The combination of
the fuse and the arresters, therefore, forms a very efficient protection
for the instrument, the premises, and in fact for the line conductor
itself. The carbon blocks under any circumstances should never be
used without the fuse outside, as a dangerous fire may result from
arcing. For this reason the indiscriminate placing of carbon arresters
on telephone instruments by the manufacturers is to be deplored.
393
8
TELEPHONE LINE PROTECTION
Some companies add a heat coil to the protective device at the
subscriber's premises, but this is thought not to be in accordance
with the best practice. The cost of burnt-out telephones which
may be saved by the presence of a heat coil probably would prove
much less than the cost of time and labor of replacing heat coils at
the subscriber's stations.
394

MAGNETO MULTIPLE SWITCHBOARD
American Electric Telephone Co.
THE QUALITY OF TELELPHONE SERVICE*.
Telephone service wholly between people in the same town or
between correspondents in separate towns is subject to variations
of quality in two principal ways. One of these is a variation in the
goodness of the actual transmission of speech, and the other is a
variation in the excellence of the steps required to get the lines con-
nected for the conversation, and disconnected after it.
Excellence of service and clearness of transmitted speech are
of the highest importance in long-distance work, and it has been
suggested by a prominent engineer in a discussion upon this subject
that with the best conditions of to-day, operated in the best known
way, the possible radius for long-distance talking from any point
is definitely limited, and on the edge of the area indicated by this
radius is a zone in which successful talking is likely to be out of the
question at one time or another. In such long-distance work, there-
fore, the more important problem is that the lines, instruments and
switching appliances be such as to enable the conversation to be
commercially satisfactory, and the questions having to do with the
speed of connection and disconnection are relatively of smaller
importance.
In local telephone service, however, making up by far the greater
bulk of telephone activity, it is now relatively a simple matter to
provide and keep in order satisfactory conditions for uniformly suc-
cessful commercial conversation. As it is possible wholly to eliminate
primary batteries at the subscribers' stations, and to supply current
for transmission from a central point, the old difficulty of transmitter
current supply has ceased to be a bugbear. The market is full of
transmitters of designs good enough to ensure acceptable local trans-
mission. The real problem, therefore, is that of getting the con-
nections made and unmade at a rate of speed high enough to satisfy
all reasonable expectations of the subscribers, and at the same time
keep reasonably reduced the expense of switching.
* By Samuel G. McMeen. Reprinted from Electrical Review, December 17, 1904, by
permission.

395
2
TELEPHONE SERVICE
It has often been suggested that the operation of a telephone
exchange for the production of local service is nothing more nor
less than a manufacturing problem, the product in such a work being
local telephone service. In a very large degree this analogy is
exact, and so far as it is so there seems to be no reason why the accu-
mulated experience of manufacturers of other commodities should
not be utilized by the maker of telephone service. It requires but
little close observation of the daily methods of telephone exchanges
to find opportunity for applying the experience of other manufac-
turers to the result of an improvement in local service, and a reduction
of its cost. One of the most illuminating results of such a study is
to reach a simple understanding of what local telephone service
really is and what are the elements of which it is composed.
Without attempting too great a refinement, it may be said that
the following items represent the elements which operators in manual
exchanges must contribute to the making of the service:
1. Prompt answering.
2. Prompt disconnection.
3. Freedom from errors in connecting with the called line.
4. Promptness in connecting with the called line.
5. Courtesy and the use of form.
6. Freedom from failure by busy lines and failure to reply.
7. Clear enunciation.
8. Team work.
It is to be admitted that there is some interrelation between these
elements, as for example, that of the last assisting to accomplish the
first. It is also to be commented that in an effort to determine
the quality of the service made, many managers are content if the
answering service is prompt. We have long been accustomed to
hearing the quality of service measured in terms as to the number of
seconds required to answer the subscriber's signal, and if such a
standard were sufficient, exchanges giving quick answering would be
found to give the best service in other ways. Only a little enquiry
and service are necessary to show that this is rarely true; so that if
we are to know the real quality of the service manufactured, we
must have more definite information and it must be such as is col-
lected by patient and systematic work.

396
TELEPHONE SERVICE
3
The best method of determining the speed of answering is by
recording the results of a long series of observations on actual calls
made by the observers, and making an accurate analysis of the
results. To enable the performance of a given operator to be
studied with relation to the performance of others, and in comparison
with a standard, the clearest and most truthful statement is found
by dividing the test calls upon that operator into groups, of various
numbers of whole seconds each, and comparing the percentages
of these with the whole number of tests. For example, assume
each of the calls to a given position to have been answered in ten
seconds or less, in which:
One hundred per cent are answered in ten seconds or less.
Eighty per cent in eight seconds or less.
Sixty per cent in six seconds or less.
It is probable that a reasonably uniform service will show only
a small percentage answered in three seconds or under.
It is
very simple to draw these percentages in the form of a
curve, and to see at a glance the value of an operator with reference
to her skill in prompt answering, while the average time of answer-
ing and the number of calls in the busiest hour might not give any
such clearness of understanding.
Prompt disconnection where relay boards are used is possible
to an astonishingly greater degree than before the introduction of
lamp signals. Observations made in New York City before the
installation of any relay boards showed an average time required
to disconnect of over seventeen seconds. Five years later, after
the completion of a relay switchboard equipment throughout
Manhattan Island, the average time taken to disconnect was some-
thing under three seconds. The excellence of relay apparatus in
this particular has led subscribers to a larger traffic, and to the mak-
ing of calls which come close upon the heels of one another. A most
important rule is that a signal for disconnection shall be given
prompt attention either by the operator who made the connection
or by a monitor who may be assisting; and another, still more im-
portant, is that in the case of a flashing lamp, indicating a recall,
such a signal shall be given precedence over all others.
It goes without saying that items 3 and 4, covering the prompt-
ness and accuracy of connecting with the called line, are vital, and
397
4
TELEPHONE SERVICE
yet that a large percentage of errors in these elements might exist
in an exchange having a very high average speed of answering the
originating call. Indeed it seems quite the rule that where the
effort of the management is devoted toward securing and maintain-
ing extreme speed of original answering, all the other elements suffer
in due proportion.
As to item 5, it goes without saying, of course, that operators
should be courteous; but it is necessary to say it, and keep saying
it in the most effective form, in order to prevent human nature under
the most exasperating circumstances from lapsing a little from the
standard, however high. The use of form assists both the operators
and the subscribers, because in all matters of strict routine it is
much easier to secure high speed and great accuracy by making as
many as possible of the operations automatic. The use of the word
"number” and other well accepted formalities has assisted greatly
in securing speed, clear understanding, and accurate performance.
The simple expedient of spelling numbers by repeating the figures
in a detached form (as “1-2-5'' for 125) has taught subscribers the
same expedient, and the percentage of possible error is materially
reduced by going one step further and having the operator, in repeat-
ing, use always the opposite form from that spoken by the calling
subscriber.
The old impression of the public to the contrary notwithstand-
ing, the operator has no control over the “busy line” and “don't
answer” situation. It is, however, of high importance that the man-
agement should know by the analysis of repeated and exhaustive
tests of the service, to what extent these troubles are degrading it.
In addition to improving the service by the elimination of busy reports,
there is no means of increasing revenue which is so easy and so uncer-
tain as that which comes from following up the tabulated results of
busy calls.
It must be remembered that clear enunciation for telephone
purposes is a matter wholly relative, and the ability of an operator
in this regard can be determined only by a close analysis of many
observations from the standpoint of a subscriber. A trick of speech
rather than a pleasant voice and an easy address has made the
answering ability of many an operator captivating to a group of
satisfied subscribers.
398

13
12
|
JOHNSTOWN, PA., SWITCHBOARD.
Kellogg Switchboard and Supply Co.
TELEPHONE SERVICE
5
By team work is meant the ability of a group of operators,
seated side by side, to work together as a unit in caring for the service
brought to them by the answering-jacks within their reach. In
switchboards of the construction usual to-day, a call before any oper-
ator may be answered by her, or by the operator at the right or the
one at the left of her position. In many exchanges this advantage
is wholly overlooked. In the period of general re-design of central-
office equipments about eight years ago, a switchboard was installed
with mechanical visual signals and answering-jacks on a flat top
board, and an arrangement of operators such that the signal of any
call was extremely prominent, and in easy reach of each one of four
or possibly five operators Associated with the line signals within
the reach of such a group was an auxiliary lamp signal which would
light when a call was made by any of the lines so terminating. It
was found that with this arrangement the calls were answered in a
strictly even manner, special rushes being cared for by the joint
efforts of the group rather than serving to swamp the operator who
happened to be in charge of the particular section affected by the rush.
This principle has been tried out in so many ways that it is
astonishing that it is not recognized as being a vital one. The
whole matter is accomplished by impressing upon each operator
that it is her duty not to answer the calls of a specific number of
lines before her, but to answer with such promptness as is possible
any call which is within the reach of her answering equipment.
All that is required to be known concerning the form of address
and courtesy may be learned by a close observation of the operators'
work by the chief operators and monitors, and by the use of listen-
ing circuits permanently connected to the operators' sets. It is
naturally necessary that the use of these listening circuits by the
chief operator or her assistants must not be known to the operators
at the times of use, even though they may know of the existence of
such facilities.
Fig. 1 illustrates a simple schematic arrangement of such circuits,
the chief operator's set being marked CO, and the subscribers opera-
tor's set marked A. By opening the contact at the key K associated
with the chief operator's set, all sounds from her transmitter are kept
from the listening circuit. The fact that the primary winding of the
induction coil is in open circuit while this key is open, increases the
399
6
TELEPHONE SERVICE
impedance of the secondary of the induction coil to a considerable
degree. The condenser C in series with the listening circuit assists
this high impedance in keeping the current taken by the listening
circuit from becoming noticeable in the operator's set. If desired,
the condenser C may be replaced by a high resistance, as R. With
such an arrangement, or one similar to it, it is quite impossible for an
operator to know when such listening-in occurs.
For the purpose of carrying on the routine tests, it is of course
possible to have an observer walk about the town, call upon sub-
scribers, and make calls from their telephones. This for many years
was the accepted method, and it had the real advantage of bringing
a representative of the operating company into contact with the sub-

WW
To Listening
Keys
K
Chief Operator's Listening Circuit.
Fig. 1.
scribers. Experience has shown, and good judgment indicates, that
this is not the best way to get good results. Visits upon the subscrib-
ers are important and necessary, but ought to be devoted to the pro-
motion of acquaintance, and to finding out what needs the subscriber
has which remain unfulfilled, as well, of course, as to promoting his
education in the use of the telephone service. For the making of test
calls
upon
the operators, other expedients are available. If the office
in which the tests are to be made is provided with an incoming trunk
switchboard, or even an incoming trunk position co-operating with
the tollboard, a trunk may be chosen at such a position and devoted,
part of the time at least, to the making of test calls. Wires should be
led from this trunk plug to a desk located outside of the operating
room, and having facilities for testing the called line after the plug is
inserted, and listening upon it without closing it, so as to place a call
before the operator if it is not in use. A condenser in series with the
a
400
TELEPHONE SERVICE
7
conductors will accomplish this, and a key to short-circuit that con-
denser will place a call when desired. A stop-watch and record
sheets will complete the equipment for testing originating calls.
It is often necessary to supervise the line of a given subscriber
for a long enough time to enable it to be determined whether his com-
plaints are well founded or not. A service-testing desk, or the service-
testing part of the chief operator's desk, should be provided with

Multiple Jack
Au
Answering Jack
Line Lamp
Service
Testing Set
1
Chief Operator's Supervising Circuit.
Fig. 2.
equipment enabling every call from such a line to be set in duplicate
upon such a position. The equipment also should include means for
knowing when a call is made for such a line.
Fig. 2 illustrates one possible form of such an arrangement.
When it is remembered that a plug in any jack of the line at the
switchboard proper will operate the cut-off relay C, and that three of
the heavy dotted lines leading to the service testing set are merely
attached to the line under test at the intermediate distributing board,
it will be seen that all calls, whether incoming or outgoing, may be
observed, and that the operation and character of the connection may
be determined by listening with such a set as is shown in Fig. 1.
All that is required is that the signal at the service-testing desk
be such as to respond to calls for or calls from the central office; and
with this in mind it should be found easy to design similar and simple
circuits to co-operate with any form of common battery switchboard.
For observation upon magneto lines, a simple jack and bridging drop
401
8
TELEPHONE SERVICE
are all that are required, because the signal to the central office and
the signal from it are electrically alike.
There are exchanges of considerable size in which private branch
exchanges have not been installed to a sufficient number to make that
phase of the business a real problem in itself. These exchanges are
rapidly dropping into the minority, as it is more and more generally
recognized that the private branch exchange is a phase of telephone
working which is equally essential to the success of general business
and the telephone traffic as well. In one district of a large city there
are more operators working at private branch exchange switchboards
than are working in the central office which receives the trunk lines
from them. Some such result is sure to occur in every exchange.
Because the private branch exchange operators are not under the
attention of skilled supervisors, and often because they have other
duties than the care of the small switchboard to perform, it is possible
for them to degrade the general character of telephone service in a
marked degree. At any reasonable sacrifice, the duty of the operating
company is clear in that it should secure and retain a fair degree of
control over private branch exchange operators, and should co-
operate with employers to the fullest extent in the education of the
local operator and the principal users of the local service.
402
THE AUTOMATIC v. THE MANUAL TELE-
PHONE EXCHANGE.*
There are two general methods of giving telephone service to
a community
1. By what is commonly called the “ Manual” system, be-
cause of the fact that the switchboards employed at the central
office require manual operation.
2. By the so-called “ Automatic” system, wherein the cen-
tral office operator is dispensed with, switches being so arranged
that they will, without the aid of human hands, perform the neces-
sary act of connecting lines for conversation, and afterward discon-
necting them at the will of the subscribers.
In the manual system in its highest development, the telephone
user has only to place his receiver to his ear and make his wants
known, the desired connection being made at the central office by
operators. This system may be assumed to be highly developed,
as it has been almost universally used since the advent of telephony,
a period of nearly thirty years. The manual system, in its present
form, represents the consecutive work of a large number of men in
a field of the most intense and constantly increasing activity, all
these men striving for the best possible means of accomplishing a
desired result.
In the automatic system, the central office switches are gov-
erned in their movements by the actions of the subscribers or users
who desire connections and subsequent disconnections. The sub-
scriber does his own work, manipulating the apparatus before him
in such a way as to cause the switches at the central office to select,
connect with, and afterward disconnect from, the line of the sub-
scriber desired.
Unlike the manual system, the automatic cannot be assumed
at the present time to have reached a relatively high development.
* Presented at the International Electrical Congress of St. Louis, 1904, by Kempster
B. Miller.
403
2
TELEPHONE EXCHANGES
While the automatic switchboard has been in the minds of inventors
since the year 1879, it is not true that it has been put into con-
siderable use until very recently. Instead, therefore, of its develop-
ment being paramount in the minds of a large number of practical
telephone workers, it has been fostered till lately by but few men,
some of whom were unfamiliar broadly with the details of the tele-
phone business. With a courage that must excite the admiration
of all, a very few of these men have persisted, and as a result, the
telephone engineer, the operator of telephone companies, and last
but most important, the general public, are confronted with what
I think is the greatest problem that has been recently before the
telephone world: The problem of the automatic v. the manual
switchboard.
It is not the purpose of this paper to attempt to solve this
problem. The unequal degree of development of the two systems
makes impossible a final satisfactory solution at the present time.
It is rather to state some of its phases as they appear to me; and
to make comment on them wherever my study of the situation has
led to more or less positive convictions, that this paper is offered.
A fundamental question affecting the entire problem is this:
Is it possible to make a machine serve to effect the electrical con-
nection of any line, in a large or small group, with any other line
in the group, for the purpose of telephonic communication, and
afterward to effect a disconnection when required? There can be,
even at the present early stage of development, but one answer
to this question. That it is. The automatic switchboard at Grand
Rapids, Mich., recently selected for me 100 different lines chosen
at random from among approximately 5,000 lines centering in that
office. Some of the subscribers called did not respond, which will
occur in any system; and some of the lines were automatically
reported busy, which is to be expected; but in no single case was
the wrong line chosen, and in but one case was the disconnection
improperly secured. The verdict of a large number of the sub-
scribers interviewed by me in that city is practically unanimous to
the effect that they uniformly secure their connections and discon-
nections promptly, accurately and satisfactorily.
I conclude, then, in view of present achievement, and of that
future progress which this must stimulate men to make, that it is
a
404
TELEPHONE EXCHANGES
3
possible for the automatic switch to perform these functions satis-
factorily.
If, then, the automatic switchboard may be made to accomplish
the commonplace connection and disconnection of lines, which
forms the great bulk of the work in a telephone exchange, is not
the system so inflexible in its method of operation as to preclude
the possibility of its performing the great multitude of special
duties which, while not constituting the main bulk of the work,
are nevertheless of constant occurrence and of hardly less im-
portance? I refer to such matters as toll connections, private
branch exchange work, and to a number of less important but
nevertheless necessary class of service.
A prominent telephone engineer has recently remarked to the
effect that if some of the people enthusiastic on the subject of
automatic switching in telephone exchanges were to visit the school
for telephone operators maintained by the New York Telephone
Company, they would be discouraged in their efforts, as no machine
could ever be made to perform the many and varied functions that
it was necessary to teach these young ladies before they became
proficient telephone operators. This seems to be a statement that
has very little to do with the real automatic problem. It should
never be required that the machine shall do the same work that is
required of the girl, nor do it in the same way. That is manifestly
impossible, for no machine can ever be endowed with intelligence.
(It may be that some will say that there are some telephone girls
similarly affected.) Since the very reason for the existence of the
automatic exchange is to do away largely with the operator, it
follows logically that whatever intelligence is to be applied to the
making of the ordinary connection between two lines shall be
that with which the 'subscriber desiring to make the connection
is endowed. Here is a fundamental difference between the two
systems which must always lead to different modes of operation.
The real functions that the automatic switchboard should be
required to do automatically are those relating to the ordinary
routine work of connecting and disconnecting subscribers' lines
under the control of the calling subscriber. When some act need-
ing intelligence at the central office is required, then let an operator
supplement the work of the machine. To condemn the automatic
405
4
TELEPHONE EXCHANGES
switch because it will not perform all of the special requirements
without the aid of human intelligence is just as unfair as to con-
demn as valueless a linotype machine because it cannot digest
one of Steinmetz' equations. My mind has gradually changed upon
this point until the doubt now exists as to whether the automatic
system, wisely supplemented by operators, is not even more flexible
than the manual. It is the ease with which the personality of the
operator may be introduced into the automatic system as a whole,
and also the ease with which certain of the purely automatic
functions may be varied by mere changes in the circuit, or in the
mechanical relation of the parts, that make this doubt exist.
Of course, there are many problems concerning traffic and service
that are yet to be worked out for the automatic system, but ap-
parently the longer one studies the automatic problem the more
nearly he becomes convinced that the automatic system is suffi-
ciently flexible, with the interjection of human intelligence when
necessary, to make possible the solution of practically all of the
problems of service.
So far as I am aware, the selective signal party line working
has never been accomplished commercially with automatic systems.
I believe that the reason for this is solely the fact that automatic
telephony is yet new. I have recently seen a plan whereby any
ordinary number of stations can be selectively operated on a party
line with practically no other added complication either at the
central office or at the subscribers stations, than that which is
added to the apparatus of an individual line manual system, to
adapt it to the same class of party line work. I can say, therefore,
that the solution of the party line problem, while not yet reached to
the extent of being actually introduced into commercial use, is
entirely feasible and will not be one of the controlling factors in
solution of the problem: automatic v. manual.
I have looked into the subject enough to believe that the same
thing that is true of the party line problem is true of the common
battery problem, and also of the measured service problem, whether
the measuring of the service is accomplished by collecting coins
or tokens at the subscribers stations, or by operating counting
devices ether at the sub-stations or at the central office. There
is undoubtedly a vast amount of work yet necessary before they
406

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​CELLANEOUS LINCS
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UNIT TYPE SWITCHBOARD MAGNETO CALL 100 LINES-REAR VIEW
North Electric Co.
TELEPHONE EXCHANGES
5
are commercially incorporated in working apparatus in an entirely
satisfactory manner. I merely say that my study has shown me
that no insurmountable obstacles exist that would prevent the suc-
cessful establishment of party line, common battery and measured
service working
These statements do not greatly help the man who is to-day
casting about in making a choice between the automatic or the
manual system for present use. It is not, however, with the
pres-
ent alone that we are concerned. We must plan and build for the
future; and the remarks just made are given merely as little bits
of contributory evidence as to what developments may be expected
in the future.
Having seen that the thing is possible, that it seems from a
technical standpoint to be able to do what is wanted, another ques-
tion is: Do the subscribers like it?
The evidence all seems to point in one direction. They do.
At Grand Rapids, Mich., 95 per cent of a large number of sub-
scribers interviewed by me liked it better than common battery
manual service; 4 per cent did not care much one way or the other,
and 1 per cent liked the manual system better. At Fall River,
Mass., where the system has been in use for a much longer period,
the verdict was quite the same in effect. Evidence from other
cities where automatic service is being tried seems to agree. It
must be said in fairness, however, that at Grand Rapids, the mass
of subscribers is leavened by the presence of a large number of
stockholders in the local company. Again, there is in that city
much civic pride in the system. Telephone people come from all
parts of the country to inspect the plant. Still again, the delight
of the subscribers may be similar to that of a child with a new
toy, but this can hardly be true, because of the fact that the ex-
change at Grand Rapids has been in service for a period of nearly
nine months, and is carrying a very large business load, so that
if the people were not actually getting satisfaction, they would
probably know it
The new toy idea is also apparently disproven
by the condition at Fall River and New Bedford, where the service
has been maintained for several years, and seems to be much liked.
The question also naturally arises: Is not the automatic switch-
board and necessary subscribers' mechanism too complex to be
407
6
TELEPHONE EXCHANGES
maintained in proper working order without undue cost? It is
perhaps too early to decide this question. There is not enough
evidence one way or the other. Judging from the past, however,
the tendency of the industrial achievement seems to be to do things
automatically. As examples, take the arts of printing, of weaving,
and use of automatic machine tools.
Summing up, therefore, the statements already made, the auto-
matic system is not only a possibility, but is actually here. With
the interjection of human intelligence to supplement it in per-
forming certain functions, it seems to be as flexible as the manual.
Party line, common battery, and measured service working, while
not yet achieved commercially, so far as I am aware, seem to be
well within the grasp of those who are doing the development
work. The public seems to like it, and we do not know whether
.
it is too complex or not.
It will be noted from the foregoing that the idea of having the
central office apparatus perform all the phases of telephone service
is apparently not tenable. Many of those who have advocated it
in the past have abandoned it, and are introducing human aid in
the performance of some of the functions. This being true, a
certain number of operators will be, and are, needed in automatic
exchanges. This tends to destroy in some degree the primary
object of the automatic system the doing away with operators.
We have seen many papers bearing on each side of this question,
to the effect that the salaries of the operators were or were not to
be eliminated; that retiring-rooms, matrons, operators' luncheons,
etc., were or were not to be done away with. These items of ex-
pense will probably exist to some degree in all large automatic
exchanges. That they will be greatly reduced is without question,
but whether or not they are reduced to such an extent as to offset
other sources of expense introduced by the employment of auto-
matic apparatus is a problem yet to be solved.
What are some of these sources of expense that tend to offset
the reduction in operators’ salaries and expenses coincident there-
with? Taking the system as a whole, we find that the present
automatic system is considerably higher in first cost than the
manual system, and assuming that interest and depreciation are at
the same rate in each case, this shows to considerable disadvantage
-
408
TELEPHONE EXCHANGES
7
against the automatic system in the annual charges due to these
items alone.
For an exchange of 5,000 lines served by one office, the cost of
automatic equipment including telephones may be taken at $35.00
for each individual line. In manually operated exchanges the cor-
responding cost is not far from $25.00 per line. The difference
becomes greater, that is, more in favor of manual, for smaller
offices, and smaller or less favorable to the manual in larger offices.
Whether or not the depreciation on automatic apparatus should
be taken at a higher rate than that on the manual is a question
that we have not at present sufficient data or information to
determine. It is true that in the present manual switchboard the
flexible cord nuisance found in all present forms of manual switch-
board apparatus is largely eliminated. It is also true that the
automatic apparatus is more complicated, and requires greater
care in its maintenance; but whether, if both systems are main-
tained with reasonable care, the automatic will show a much
greater rate of depreciation than the manual, I am not at all
certain. Much of the depreciation in manual telephone apparatus
is due, not to the fact that the apparatus wears out, but rather to
the fact that the apparatus is rendered obsolete by new inventions.
That the same will be true in the case of automatic apparatus can-
not be doubted, but it is a good point to bear in mind that if
telephonic development should point toward automatic apparatus
to the exclusion of manual, and should prove the superiority of
automatic, then the highest developed and newest manual apparatus
will depreciate greatly in value by that fact alone. It does not seem
unreasonable, therefore, to place the rate of depreciation on both
manual and automatic apparatus at about the same figure.
In point of maintenance the advantage must be conceded to the
manual. This is certainly true at present with regard to both the
central office and the subscriber's station apparatus. No good
reason is apparent why it should not always be true. Automatic
apparatus is especially at a disadvantage at the subscribers' stations
and it is really at this point that the automatic system seems to
involve a poor engineering feature. The tendency of telephone
development in regard to sub-station apparatus has been until
lately along what seemed to be unquestionably good engineering

409
8
TELEPHONE EXCHANGES
lines. The sub-station apparatus has been gradually simplified,
the battery has been removed, as has also the magneto generator,
and the instrument has been reduced to the simplest fundamental
parts.
Automatic telephony as at present developed for large work takes
a step backward by reintroducing the local battery. That this is
disadvantageous no one can deny, but on the other hand it must
be pointed out that the disadvantage is by no means as great as
it would have been several years ago because of the fact that dry
batteries have recently come into almost universal use for this
kind of work and are far superior, all things considered, to any-
thing heretofore available.
The disadvantage of local batteries, while mitigated, is still
present, and is real; but, taking the automatic system as we have
reason to believe it will exist in the future with no local batteries,
it will still possess, as far as we are able to see, a more or less
complicated impulse transmitting device, by means of which the
subscriber will be able to direct the movements of the switches at
the central office. Complexity not only of mechanism, but of
function, is thus introduced at the subscriber's instrument, and
this seems to be an inherent disadvantage to all present schemes
of automatic exchange working. This, of course, is another factor
that must be weighed in considering the relative economies of
the two proposed methods.
There is a point that I have not yet seen mentioned in print,
which under certain cases seems to be of great importance. This
is the matter of trunking between two or more automatic offices
in such cities or communities as naturally demand, by the distribu-
tion of their subscribers, more than one office. It is true that the
present automatic switchboard seems to be capable of properly
handling this condition if the requisite number of trunk lines
between the two offices are provided. At first thought it seems that
the number of trunks required between offices for a given amount
of traffic might be somewhat less in the case of the automatic than
in the case of the manual system, on account of the immediate
disconnection and release of the trunks, in the automatic, upon
the hanging up of the receiver of the calling subscriber. Further
consideration, however, will show that there is very little difference
410

ANGLE VIEW OF REAR OF CALLING DEVICE ON TELEPHONE.
Automatic Electric Co
TELEPHONE EXCHANGES
9
in the time the trunk is held busy in the two systems, the length
of actual conversation being assumed to be the same in each case.
The reason for this is that, while the automatic gains in this respect
in the release, it loses something in the making of the connection,
because in the case of the automatic the trunk is selected with the
first movement of the dial by the subscriber, and the length of time
that the trunk is held busy, therefore, must in the case of the
automatic include the time during which the subscriber is setting
up his own connection; whereas, in manual boards a trunk line
begins to be busy at the time when the B operator picks up the in-
coming trunk and designates its number to the A operator.
So far there seems to be little difference between the systems in
this respect.

per cent
The bearing on the trunking problems of the relative efficien-
cies of different sized groups of trunks between offices does not,
however, seem to have been considered by many in considering the
question of automatic v. manual exchanges. When sufficient trunks
are provided between offices to handle business on the so-called
66
“no delay” basis, it is known that a large group of trunks will
handle very much more business per trunk line than a small group.
For instance, when there are only 10 trunks in a group between
offices, it is a well-established fact that slightly less than 80 calls
per trunk per day may be handled. If, however, the group is in-
creased to 100 trunks, as many as 145 calls per trunk per day may
be bandled. This is an increase of considerably over 80
in actual trunk efficiency. In the present automatic system, group
the trunks as you may, it is inherently true that the efficiency of
the trunks is reduced to that of a group of 10. I do not mean by
this that it is not possible to place as many trunks as desired be-
tween any two offices, but that any subscriber has access to 10
trunks only in order to secure a connection to any other office. It
is true that some other subscriber may have access to another 10,
or to the same 10, but no one subscriber can reach more than 10.
This seems to be a grave objection to the use of automatic systems
as at present developed, in those communities where several offices
must be employed and where traffic is such as to demand a large
number of trunks between offices. The remedy to this is obviously
that of giving the subscriber the chance to select his trunks from

411

10
TELEPHONE EXCHANGES
larger groups. This, I take it, is one of the problems that need
serious consideration in adapting the automatic system to very large
communities. It does not enter seriously in single office work.
In all that I have said I have attempted to take the very prac-
tical view of the engineer, and fundamentally that view must
always compare systems with the intent of selecting a means of
doing what is required well enough for the smallest price. From
the strictly engineering view one does not take into account relative
popularities of mere ways of accomplishing results. But this is
necessary in such a case as this, for there are features of the auto-
matic system which may make it so popular as to force upon the
owners or prospective owners of telephone industries a serious con-
sideration of the doctrine of expediency. This is by no means the
least of the important things to consider.
I expect to be criticized because I have not solved the prob-
lem. It cannot now be solved any more than the question of alter-
nating v. direct-current transmission could be decided when we
first were brought to realize that there was an alternating v. direct-
current transmission problem. My object has been to state the
problem as I see it, and I hope that in doing this, something may
have been accomplished toward clarifying it.
KEMPSTER B. MILLER.
412
REVIEW QUESTIONS.
PRACTICAL TEST QUESTIONS.
In the foregoing sections of this Cyclopedia
numerous illustrative examples are worked out in
detail in order to show the application of the various
methods and principles. Accompanying these are
examples for practice which will aid the reader in
fixing the principles in mind.
In the following pages are given a large number
of test questions and problems which afford a valu-
able means of testing the reader's knowledge of the
subjects treated. They will be found excellent prac-
tice for those preparing for College, Civil Service,
or Engineer's License. In some cases numerical
answers are given as a further aid in this work.



REVIEW QUESTIONS
ON THE SUBJECT OF
TELEPHONY.
PART I.
1. What is the best feature in an induction coil, clearness
or intensity ?
2. Describe the nature of the alternating current.
3. Describe by means of a diagram the action of a Bell
telephone.
4. Draw the circuit of a bridging telephone.
5a. Why cannot the transmitter be used directly on the line?
Explain fully.
6. How did Edison overcome the difficulty ?
6. For commercial purposes what law does the fluctuation of
current follow ?
7. What are the actions that take place when sound is trans-
mitted by the electric telephone ?
8. What is a simple vibration? Complete vibration? Ampli-
tude ?
9. Draw the circuit of a telephone line equipped with four
bridging instruments, and describe fully the method of operation.
10. What should be the shape and resistance of the coils of
a receiver ?
11. In an induction coil 10 c.m in length containing 50 turns
of wire in the primary winding, how many lines of force would be
produced by passing a current of 2 ampere if p.=60.
12a. What limits the distance over which sound can be trans-
mitted by the Bell telephone ?
6. What instrument was devised to increase this limit, and
upon what principle did it work?
13. What is the resistance of a series bell?
415

TELEPHONY
14. Describe the “chloride” storage battery.
15. Sketch and describe some form of transmitter.
16. For telephone purposes what is the best construction for
an induction coil and why?
17. Which would give the best results, a transmitter whose
resistance varied from 10 to 5 ohms, working on a transmitter
circuit of a resistance of 10 ohms; or the same working on a circuit
of 100 ohms, the current in both cases being furnished by two
Fuller batteries? Give comparative figures.
18. What is meant by magnetic lag and how does it affect
an induction coil ?
19. Give wiring diagrams of telephone.
20. What is meant by Pitch ? Intensity ? Character ?
21. Draw the circuit of a series telephone.
22. Describe the automatic shunt, and automatic circuit
closer, and give the reasons for their use.
23. What is gained by having the permanent field stronger
than that produced by the induced currents in the coil ?
24. Discuss the relative merits of the Gravity, Fuller,
Leclanche and dry batteries, for use with transmitters.
25. What is meant by packing?
26. What is the resistance of a bridging bell ?
27. Sketch and describe the Edison transmitter.
28. How does the local action announce itself at the receiy.
ing end?
29. What limits the size of the diaphragm of a receiver ?
30. In the City of New York, assuming that 15 per cent of
the calls sent by the telephones are for long distance points, what
form of cell should be used on the transmitter batteries? Why?
31. When and where should Gravity batteries be used ?
32. On a line 500 feet long, equipped with a telephone at
each end, what type of cell should be used on the transmitters ?
33. What should be the thickness of the diaphragm of a
receiver ?
34. When should Leclanche batteries be usea on transmitter
circuits ?
35. Describe the styles of hook switch used in connection
with the American Bell Telephone Co’s. bridging and series bell.
416
REVIEW QUESTIONS
ON THE SUBJECT OF
TELEPHONY.
PART II.
a
a
a
1. Draw the diagram of a pole showing the typical equip-
ment.
2.
How are telephones classified ?
3. How should poles be guyed in passing through hilly
country?
4. What is meant by distribution?
5. Of what material are insulators made?
6. Draw a standard pin, for standard and terminal cross-
arm. Also draw a transposition pin, for standard and terminal
cross-arm.
7. What is a terminal cross-arm? Give drawing.
8. Draw a standard pole.
9. Describe fully the method of stringing wires.
10. What is a McIntire sleeve?
11. Give a table of allowable sag.
12. Describe in detail the method of setting a pole.
13. Is a pole ever placed in the center of a stream? If so,
when ?
14. What is a cable line, when should it be used, and what
are the advantages it
possesses ?
15. Describe fully the method of placing cross-arms, giving
diagrams.
16. Discuss fully the relative merits of iron, copper, and
aluminum for use in the manufacture of telephone wire.
17. What is meant by an open-wire line?
18. What is the reason for creosoting wood ?
19. Discuss fully the subject of pole fittings, giving dia-
grams.

417
TELEPHONY
20. What precaution must be taken crossing a river?
21. What is a Western Union splice?
22. How are calls between two towns best handled ?
23. What points must be observed in the construction of a
telephone line?
24. Describe fully the method of fastening cross-arms.
25. What is meant by back-guying, side-guying, and head-
guying?
26. In going through hilly country, how should the line be
graded ?
27. What is the difference between subscriber lines, trunk
lines, and toll lines?
28. Why is it not possible to connect all telephones in a
district to one line? Explain fully.
29. What is the minimum allowable height of the lowest
wire above the ground?
30. What kind of wood has superseded cedar, and why is it
used ?
31. What kind of a splice is used in line construction ?
Describe fully.
32. How should guying be done when the pole is equipped
with two or more arms ?
33. Discuss fully the method of calculating the area of a
wire section in circular mils.
34. When are back braces used, and how are they placed ?
35. Describe fully the method employed in crossing roads.
36. Describe fully the manufacture of a standard cross-arm.
Give drawing.
37. What advantage is gained by placing the guy stub near
the foot of the pole? Explain this point fully.
38. What is meant by an exchange, and how is it used?
39. Draw a standard insulator and a transposition insulator.
Describe fully.

a
418
REVIEW QUESTIONS
ON THE SUBJECT OF
TELEPHONY. ,
PART IIL
1. Explain the process of transposing the lines of a tele-
phone circuit.
2. What is a drip loop, and what is its purpose ?
3. What precautions should be taken in climbing a pole?
4. Describe the action of a come-along.
5. What is a chipping knife? Describe its use with
sketch if necessary.
6. How does the 4a type of main distributing frame differ
from the 4b type ?
7. About how far apart should the manholes be in a
subway?
8. Why does transposing reduce cross-talk?
9. Into what two classes may rubber-insulated cables be
divided ?
10. Describe the most approved method of stringing cable.
11. Describe the so-called pump-log type of duct.
12. What is a spinning jenny, and why is it going out of
use?
13. Without referring to the text make a sketch of a
scheme for transposition.
14. What do you consider a good method of fastening a
rope to the end of a cable which is to be drawn in ?
15. What are test points, and how frequently should they
be placed on a line?

419
TELEPHONY
16. How would you tell when paraffine is at the proper
temperature?
17. What is a jack ?
18. Describe a method of numbering the conductors enter-
ing an exchange.
19. Why cannot a subway be continuous from start to
finish?
20. What is a manhole ? Describe with sketch.
21. What do you understand by a cable box ? Describe its
construction.
22. Describe with sketch the method of drawing in cables.
23. What is meant by cross-talk ?
24. What means have been devised for supporting the
messenger wire of an aërial cable ?
25. Describe with sketch the effect of electrostatic induc-
tion on a telephone wire of a neighboring wire carrying an alter-
nating current.
26. Which do you consider to be the cause of cross-talk,
electrostatic or electromagnetic induction ?
27. In making a wiped joint what precautions should be
taken?
28. Describe fully the effect of magnetic induction of a
wire carrying an alternating current upon a neighboring tele-
phone wire.
29. How did the Chinnock and Law systems differ?
30. What are the advantages and disadvantages of under-
ground cable lines?
31. What is meant by a pot head?
32. What is the usual construction of a submarine cable ?
33. Describe with sketch the wiring of a test pole.
34. In laying underground cables, why was it necessary to
draw them into some form of duct?
35. Describe the mandrel used in laying ducts for under-
ground cable work.
36. How does a clearing-out drop differ from a line drop?

a
420
REVIEW QUESTIONS
ON THE SUBJECT OF
TELEPHONY.
PART IV.
1 What is meant by a full multiple switchboard ?
2. Why were primary batteries superseded by storage bat-
teries?
3. How are calls handled in a standard board ?
4. What is the standard potential for the common battery
system?
5. What are stripping trunks and how are they used ?
6. In the manufacture of switchboard cables, how are the
wires distinguished ?
7. What is the use of a self-restoring drop ?
8. Of what two classes are multiple switchboards?
9. Draw and describe the operator's cord circuit.
10. What is meant by a disconnect signal ?
11. How is a cable formed ?
12. What is a multiple switchboard ?
13. What kind of a drop is used on a bridging board and
how is it wired ?
14. What are circuit trunks?
15. What points should be observed in soldering wires ?
16. Draw and describe the most advanced type of trunk
between bridging boards.
17. What is the use of the condenser in the subscriber tele-
phone?
18. What are the two types of switchboards?

421
TELEPHONY
.
19. What are ring-down trunks?
20. What is meant by the common battery system?
21. What is a standard switchboard ?
22. What piece of apparatus was brought out in connection
with the bridging board ?
23. What two types of power apparatus are used in a tele-
phone exchange?
24. What is gained by the use of the common battery system?
25. What is a subdivided multiple board and what advantages
does it possess ?
?
26. How does the operator make use of the busy test?
27. What are the requisites of a charging dynamotor?
28. What is gained by using circuit trunks?
29. How was transmission carried on with the Stone system?
30. Describe fully the method of trunking between standard
boards.
31. What is meant by a busy test, and what is the necessity
of it?
a

422
REVIEW QUESTIONS
ON THE SUBJECT OF
TELEPHONY.
PART V.
every
1. What two types of circuit have been devised to overcome
the click heard in the ear when the operator answers a call ?
2. Why are outgoing local trunks and toll trunks multiplied
five panels in the toll board ? Explain the point fully.
3. What three classes of boards are used in a long-distance
office?
4. What is meant by shunting out a lamp ?
5. What are the duties of the recording operator?
6. Describe fully the method of handling a call between two
subscribers whose lines are in the same exchange both with the
magneto and with the common battery system.
7. What are the duties of a supervisor ?
Describe fully the method of handling a call with the
common battery system.
What two purposes are toll boards used for?
10. What is meant by operating?
11. How many kinds of service do telephone companies give
and what are they?
12. What three classes of calls are handled in a long-distance
exchange?
13. Describe the method followed in putting a call through
the recording board.
14. Draw and describe fully a trunk from a magneto to a
common battery office.
8.
9.
423

TELEPHONY
15. What is the nature of the business done by the Long-
Distance Company?
16. How is the force in a telephone exchange made up ?
17. In connection with what classes of calls are tickets used &
18. What is meant by a “ lost call”, and how can the percent-
age of lost calls be reduced ?
19. What is the trunk line relay?
20. Why are not subscribers' lines multiplied every five panels
in the subscriber board ?
21. What are the duties of the monitor?
22. What is meant by the tandem trunk method ?
23. On all trunks from local battery to common battery ex-
changes, what is the method used at the sending end, to properly
work the signal at the incoming end ?
24. What is the circuit trunk equipment of a toll board ?
25. How would a call from Washington to Boston be put
through New York ?
26. What are the duties of the manager?
27. What point is gained in a trunk between two common
battery exchanges ?
28. Are busy visuals used on circuit trunks? Give the
reasons fully.
What are the duties of the chief operator? Explain this
point fully.
30. How are the hours of the operators arranged, and why?
29.
424
REVIEW QUESTIONS
ON THE SUBJECT OF
TELEPHONY.
PART VI.
1. What did Pupin's discovery consist of ?
2. What general plan is followed by the wire chief in
making tests?
3. How do the subscribers call the operator?
4. What two forces of men are occupied in the work of
cable maintenance ?
5. If the wire chief should receive a report that the operator
could not ring a subscriber, but that conversation could be carried
on over the line, what kind of trouble would he expect to find,
and how would he make his test?
6. What analogy exists between the transmission of wave
motion over a cord, and the transmission of electrical wave motion
over a conductor ?
7. In regard to a private branch exchange what is meant
by a trunk
8. What are the Murray and Varley loop tests and when
are they used ?
9. What is meant by the term “party line”?
10. How are load coils connected to a line ?
11. How can you determine with the voltmeter, the presence
of a ground?
12. Describe in detail the nature of the tests used by the
galvanometer man in determining the capacity and insulation
resistance of a cable.
13. What is meant by “ load coils”?
14. What two types of private branch exchange switchboards
are there?

425
TELEPHONY
15. What is the best type of galvanometer for the use of the
galvanometer man?
16. How are heat coils tested ?
17. Define capacity reaction, inductance reaction, and re-
sistance reaction.
18. What points limit the number of instruments that can be
successfully operated on one line?
19. How does the galvanometer man proceed in locating
trouble?
20. What three reactions are set up in a circuit over which
an alternating current is flowing ?
21. How is a ground in the multiple located ?
22. What does the work of the galvanometer man consist of ?
23. Suppose that a kite tail fell across the two conductors of
an open-wire line, on a foggy day, what would be the nature of the
trouble caused ? Give reasons for your
decision.
24. How is a cross detected and how is it located ? Describe
fully the method of testing.
25. What is a private branch exchange?
26. Describe in detail the method of locating

an open.

426
INDEX
Page
160
88
76
58
64
76
Aerial cables, stringing
Allowable sag, table of
Alternating current
Aluminum and copper, table of
Aluminum wire, table of
American Electric Works' cable
Anchor-rod
Answering plug
Apparatus, power
Apparatus, protection
Arrester
Arrow
Automatic mechanism
Automatic signals
Automatic systems

213


Page
132
117
34, 299
114
115
126
121
196
228
235
178
187
367
242
300
371
301, 365
advantages of
Automatic telephone system
Automatic v. manual telephone
exchange
Automatie telephony
B. & S. gauge, weight of
B. W. C. telephone system
B. W. G. wire, table of
Back guy
Battery
connecting up
dry
gravity
secondary
storage
telephone
transmitter
Battery men
Battery reversing keys
Bell
Bell, Alexander Graham
Bell, bridging
Bell telephone
early type of
Berliner transmitter
Blake transmitter
Block cables
Board, main distributing
Boards, toll
Boiling out conductors
Bolts, carriage
Bolts, cross arm
Box, cable
Braces, cross arm
Branch, bridging
Bridging bell
Bell Cos.
Bridging branch
Bridging switchboard telephone
exchange
Bridging telephone
Bridle cables
Brown & Sharpe gauge
Burnley cell
Busy-back
Busy test
Busy visual
Buttons, test
Cable for telephone exchange
Cable box
Cable conductors
Cable faults
Cable hanger
Cable lines
underground
Cable maintenance
Cables
aerial, stringing of
block
bridle
drawing in
dry core
paper
paper-insulated
pot-head
rubber-insulated
saturated core
sizes of lead, table of
splicing
stringing
submarine
telephone
termination of
tree
types of
underground
Call
classes of
how made
57
131
107
24
223
210
267
223
191
160
125
346
136
77
137
336
170-275
301, 365
110
292
111
96
233
24
19
26
26
232
66
308
339
54
36
58
54
37
45
44
167
171
263
150
88
87
132
167
131
145
125
126
126
152
131
125
127
148
134
152
125, 336
160
131
125
137
278
367
Note.-For page numbers see foot of pages.
427
2.
INDEX
Page
Page
319
218
289
196
342
340
88
58
23
34
57
339
119
102
82
60
97
237
225
30
24
25
23
22
19
21
236
29
263
312
184
246
202
106
Call
passes
through
Calling plug
Capacity, measurement of
Capacity key
Carriage bolts
Carty, J. J.
Cassner cell
Cells
arrangement in batteries
Burnley
Cassner
Edison-Lalande
Fuller
gravity
Leclanche
Central energy telephone system
Charging storage batteries
Chief operator
Chief, wire
Chinnock system
Circuit
action of
order
Circular mill
Clamps
guy
metropolitan
Clear the trunk
Clearing of trouble
Clearing-out drop
Climbers
Coils
heat
induction
loading
Come alongs
Common battery telephone system
weak points about
Conductivity
percentage of
specific
Conductor, copper
Conductors, numbering
Conduit
terra cotta
vitrified clay
Connection, handling
Connecting up batteries
Copper as conductor
Cord shelf
Creosoting
Cross-arm
175
173
217
171
165
71
311
145
163
89
221
24
125
33
168
42
23
77
181
170
18
20
154
153
100

90
136
218
327
182
168
177
35, 48
355
169
236
261
105
105
108
170
355
170-275
90
196
346
127
89
87
278
175

141
141
253
233
Crosses
Current
alternating
talking
D'Arsonval galvanometer
Dead-ended
Dead man
Decaying of poles
Desk cabinet telephone
Digging bar
Direct transmission
Disconnect signal
Distributing board
Ford-Lenfest
Hibbard
intermediate
main
Distributing points
Distribution
District inspector
Drawing in cables
Drip loop
Drive-screws, fetter
Drop, safety
Dry battery
Dry core cables
Dynamotors
Eastern climbers
Edison
Edison-Lalande cell
Electric line construction
Electric line, terminals for
Electrical conductors, numbering of
Electricity, nature of
Electrolyte
Electrostatic inducticn
Electromagnetic induction
Erecting poles
Exchange
private-branch
telephone
Eye-bolts, rock
Face of the board
Faults, cable
Felton-Guilleaume Cos.' cable
Fetter drive-screws
Fittings, pole
Flat rate
Ford-Lenfest distributing board
Framing
Fuses
Gains
Galvanometer
D'Arsonval
Thompson
Gauge, Brown & Sharpe
Generator
Glass insulators
Gravity battery
Gravity cell
Grey, Elisha
81
235
81
108
189
82
bolts
braces
standard
telephone pole
terminal
Cross bar
Cross-connecting
87
88
83
82
83
97
162
339
338
107
53
86
19
19
36
Note.-For page numbers see foot of pages.
428
INDEX
3
Page
Grounded circuit
Grounds
Guy clamps
Guy rods
Guy rope
Guy stub
Guying
Handling a connection
Hangers, cable
Hayes system
Page
71
319
90
89
120
120
119
253
136
238
96
177
18
173
36
36
276
168
44
46
219
Head guy
153
154
35, 48
36
50
311
308
311
86
86
Lines
open-wire
77
party
290
rules for laying out
123
telephone
71, 131
Lines of rest
14
Listening key
182
Loading coils
355
Logs, pump
138
Long distance limit of transmission 343
Long distance switchboard
270
Long distance switchboard exchange 270
Loop, drip
163
Loudness of sound
17
Machine ringing
259
Magnetizing effect of coil
48
Magnetism
31
Magneto generator
229
Main distributing board
171
Maintenance, cable
336
McIntire sleeve
118
Measurement of capacity
342
Message rate
278
Messenger wire
132
Metallic circuit
72
Metropolitan clamp
136
Microphone
42
Mil
106
Multiple switchboard
184
principle of
208
Multiple switchboard exchange
207
Murray and Varley loop tests
343
Musical sound
16
Negative impulse
299
Night-bell circuit
199
Night force
276
Numbering conductors
170
N. Y. Telephone Cos.' cable
127
Office trunks
200
Open-wire lines
77
Opens
319
Operating force, hours of
276
Operating telephone
275-303
Operator's cord circuit, wiring of 216
Order circuit
202
Order wire
202
Organization, telephone
307
Out-going trunk multiple
219
Paper cables
126
Party line
290
Passes the call
218
Pay station
278
Paying-out reel
116
Pike
102
Pins
84
standard
84
transposition
84
Pitch
17
Pliers
169
Plug shelf
196
Heat coils
Helmholz
Hibbard distributing board
History of the telephone
Hooke, Robert
Hours, operating force
House wire
Hughes transmitter
Hunnings transmitter
Incoming trunks
Induction
electromagnetic
electrostatic
Induction coils
design of
table of
Inspectors
district
telephone
Instrument setters
Insulators
glass
porcelain
transposition
Intermediate distributing board
Iron wire
Jacks
Keys
battery reversing
listening
ringing
Law system
Laying out pole line
Lead cables, sizes of
Lead-sheathed cable
Leclanche cell
Limit of transmission
Line, electric
construction
telephone
terminals for
Line protection, telephone
Line terminals
Linemen's tools
climbers
come alongs
pliers
wrenches
Lines
cable

86
87
217
109
165
339
182
181
184
91
127
128
21
349

77
71, 131
181
387
181
168
168
169
169
169
77
Note.-For page numbers see foot of pages.

429

4
INDEX
Page
395
97
98
96
52
242
225
380
127
192
118
194
16
17
16
11
15
Page
Points, distributing
165
Polarization
20
Pole fittings
87
Pole line, laying out
91
Pole steps
89
Poles
artificial foundation for
99
artificial treatment of
81
decaying of
82
dimensions of
80
erecting
100
rate of setting
103
setting of
97
telephone
78
weight of
81
Porcelain insulators
86
Positive impulse
299
Pot-head cable
152
Power apparatus
228
batteries
232
dynamos
228
Power for telephone
228
Private branch exchange
355
Protection apparatus
233
Protection for telephone
235
Pump logs
138
Pupin
330
Pupin system
349
Rate
flat
278
message
278
Receivers, telephone
38, 56
Receiving operator
274
Recording operator
282
Reel, paying-out
116
Reporting telephone trouble
306
Resistance, specific
105
Resistance of wires
110
Right of way
92
Ring down system, defect of
280
Ring-down trunk, wiring of
266
Ringing, selective
296
Ringing current machines
232
Ringing keys
181
Rock eye-bolts
90
Rodding
146
Rods, guy
89
Rubber-insulated cables
131
Ruhmer
380
Running board
116
Safety drop
221
Sag, allowable, table of
117
Saturated core cables
125
Secondary batteries
26
Section of circuit
246
Selective ringing
296
Selectors
369
Series multiple switchboard, disadvan-
tage of
212
Series telephone
51
105
10.3
136
148
148
83
84
184
89
238
26
28
27
132
134
114
201
207
207
152
263
369
369
180
213
270
184
184
236
16
18
18
115
49
112
50
127
80
Service, telephone
Setting poles
table of
Side guy
Side tone
Signal
automatic
disconnect
Simon
Sizes of lead cable, table of
Skinning length
Sleeve, McIntyre
Soldering
Solid-back transmitter
Sound
character of
musical
nature of
Sound waves, nature of
Specific conductivity
Specific resistance
Spinning Jenny
Splicing
Splicing cables
Standard cross-arm
Standard pins
Standard switchboard
Steps, pole
Stone system
Storage batteries
action in
forming
Stringing aerial cables
Stringing cable
Stringing wires
Stripping trunk
Subdivided multiple exchange
Subdivided multiple switchboard
Submarine cables
Supervisor
Switch
automatic telephony
telephone
Switchboard
bridging
long-distance
multiple
standard
Switchboard construction
Sound
rate of travel
timbre
Sound tint
Tables
aluminum wire
coil test data
galvanized wire
induction coil
lead cable
pole dimension
Note. For page numbers see foot of pages.
430
INDEX
5
57
50
36
55
Page
Tables
pole setting
98
resistance factor
113
sag in wire
117
specific resistance of metal
106
tensile strength of wire
113
weights of wire
110
Talking currents
Tandem trunk method
281
Telegraph relay
335
Telephone, complete
Telephone, history of
Telephone cables
125
Telephone line distribution
71
Telephone operating
275
Telephone poles
78
Telephone receiver
56
Telephone switch
Telephone transmitters
Berliner
45
Blake
44
Hughes
44
Hunnings
46
solid-back
46
Telephone trunks
200, 218, 256
Telephone wires
105
Telephony
11-379
auxiliary apparatus
228
batteries
232
power
228
protection
235
bridging
57
cables
125
exchanges
170-275
automatic v. manual
403
bridging switchboard
213
cable and wire for
191.
intermediate distributing board 217
long-distance switchboard 270
multiple switchboard
207
office trunks for
200
private branch
355
subdivided multiple
207
history of
36
line protection
387
lines
71, 131
maintenance
305, 347
apparatus used
313
cables
336
inspectors
308
crganization
307
reporting trouble
306
tests for troubles
313
wire chief
312
operating
275-305
long-distance
288
poles
78
Pupin system of loaded circuits
349
receivers
38
service, quality of
395
Page
Telephony
transmitters
42
wireless
375
wires
103
Telephony systems
236, 290
automatic
301, 363
B. W. C.
292
central energy
236
common battery
236
automatic signals
242
handling a connection
253
Hayes system
239
Stone system
238
toll boards
263
trunking
256
party line
290
private branch exchange
355
Pupin
349
Tensile strength of wire, table of 113
Terminal cross-arm
83
Terminal points
159
Terminals for electric line
181
Terra cotta conduit
141
Test
busy
210
telephone trouble
313
Test buttons
223
Test house, wiring of
164
Testing circuit auxiliary
323
Testing down
222
Testing heat coils
322
Thimbles
89
Thompson galvanometer
338
Through calls
289
Tie wires
114
Timbre
18
Toll boards
263
uses of
264
wiring of
271
Toll lines
75
Tone test circuit
284
Tools, linemen's
168
Transmission
limit of
349
method of
255
Transmitter batteries
66
Transmitters
Berliner
45
Blake
44
Hughes
44
Hunnings
46
solid-back
46
telephone
42
Transposition
153
Transposition insulator
87
Transposition pins
84
Tree cables
131
Trouble reported
315
Trunk between common battery offices 259
Trunk lines
75


约
​Note.-For page numbers see foot of pages.
431

6
INDEX
Page
219
370
Page
126
118
Trunk multiple, outgoing
Trunk-selecting system
Trunks
incoming
tandem
telephone
Underground cable lines
Unguarded interval
Vitrified clay conduit
Wall cabinet telephone
Wasteless zinc
Wave length
Weights of wires
B. & S. gauge
B. W. G., table of
219
281
200, 218, 256
137
283
141
60
25
16
Western Electric Cos.' cable
Western Union splice
Wire
aluminum, table of
resistance of
telephone
tensile strength of
tie
weights of
Wire chief
Wireless telephony
Wiring test house
Wrenches
Zinc. wasteless
115
110
103
113
114
110
312
375
164
169
25
110
111
Note.--For page numbers see foot of pages.

432
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