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PROF. SAMUEL SHELDON 



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Telegraph Engineering 

A MANUAL FOR PRACTICING TELEGRAPH 

ENGINEERS AND ENGINEERING 

STUDENTS 



BY 

ERICH HAUSMANN, E. E., Sc. D. 

% 

Assistant Professor of Physics and Electrical Engineering 

at the Polytechnic Institute of Brooklyn, and 

Member of the American Institute 

of Electrical Engineers. 



WITH 192 ILLUSTRATIONS 




NEW YORK 

D. VAN NOSTRAND COMPANY 

25 PARK PLACE 

1915 



COPYRIGHT, 1915, 

BY 
D. VAN NOSTRAND COMPANY 



Stanbopc ipress 

F. H. GILSON COMPANY 
BOSTON, U.S.A. 



DEDICATED To 

Sorter 8>amu? 

IN APPRECIATION OF HIS INSPIRING INFLUENCE 



PREFACE 



THIS book is intended for electrical engineering students 
and as a reference book for practicing telegraph and tele- 
phone engineers and for others engaged in the arts of elec- 
trical communication. It presents in a logical manner the 
subject of modern overland and submarine telegraphy 
from an engineering viewpoint, its theoretical and practical 
aspects being correlated. No attempt is made to describe 
all telegraphic devices and to explain their operation, but 
rather to consider one or more representative types for the 
accomplishment of the various desired objects, thus per- 
mitting a presentation of the subject matter in proper per- 
spective. The book is the outgrowth of the course in 
Telegraph Engineering given by the author for a number 
of years at the Polytechnic Institute of Brooklyn. 

A knowledge of elementary electricity and magnetism 
is presupposed. For understanding the mathematical 
demonstrations a knowledge of algebra will in many cases 
suffice, but in other cases, appearing toward the latter part 
of the book, the calculus is a necessary adjunct, the study 
of which frequently precedes or accompanies the vocational 
studies of students and progressive telegraph workers. 
That the use of higher mathematics is important in the 
thorough pursuit of telegraph and telephone transmission 
studies is evident from an inspection of the writings of 
Lord Kelvin, Heaviside, Kennelly, Pupin, Campbell, Mal- 
colm and others. Those not versed in mathematical 

vii 



Viii PREFACE 

processes, however, may yet share in the value of the 
demonstrations by an analysis of their conclusions and an 
examination of the numerical illustrations based upon them. 
The solution of practical problems appended to each chap- 
ter will assist in a complete understanding of the principles 
presented. 

The author expresses his appreciation and thanks to Mr. 
Herbert W. Drake, Apparatus Engineer of the Western 
Union Telegraph Company, for making helpful suggestions 
and for reading the page proofs of the first six chapters. 
He also gratefully acknowledges the inspiration and en- 
couragement in the preparation of this work derived from 
his intimate association with Dr. Samuel Sheldon, Professor 
of Physics and Electrical Engineering at the Polytechnic 
Institute of Brooklyn. 

E. H. 

BROOKLYN, N. Y. 
January, 1915. 



CONTENTS 



CHAPTER I. 
SIMPLEX TELEGRAPHY. 

ART. PAGE 

1. Simplex Signalling i 

2. The Use of Relays 3 

3. Closed- and Open-circuit Morse Systems 5 

4. Telegraph Instruments 8 

5. Best Winding for Receiving Instruments 16 

6. Sources of Current 20 

7. Telegraph Codes 25 

8. Telegraph Lines 28 

9. Speed of Signalling 33 

10. Simplex Repeaters 35 

Problems 43 

CHAPTER II. 
DUPLEX TELEGRAPHY. 

r. Duplex Telegraph Systems 45 

2. The Differential Duplex 46 

3. Artificial Lines 51 

4. Polarized Relays 53 

5. The Polar Duplex 56 

6. Improved Polar Duplex 63 

7. Short-line Duplex 66 

8. The Bridge Duplex 67 

9. Advantage of Double-current Duplex Systems 74 

10. Duplex Repeaters 76 

11. Half-set Repeaters 80 

Problems , 83 

CHAPTER III. 
QUADRUPLEX TELEGRAPHY. 

1. Quadruplex Systems 85 

2. Operation of Quadruplex Systems 87 

3. Avoidance of Sounder-armature Release during Current Rever- 

sals in Neutral Relay 94 

ix 



X CONTENTS 

ART. PAGE 

4. The Postal Quadruplex 96 

5. The Western Union Quadruplex 98 

6. Quadruplex Repeaters 100 

7. Duplex-diplex Signalling 102 

, 8. Phantoplex System 103 

Problems 106 

CHAPTER IV. 
AUTOMATIC AND PRINTING TELEGRAPHY. 

1. Wheatstone Automatic Telegraphy 108 

2. Ticker Telegraphs. 115 

3. The Barclay Page-printing Telegraph System 121 

4. Other Printing Telegraph Systems 133 

Problems 134 

CHAPTER V. 
TELEGRAPH OFFICE EQUIPMENT AND TELEGRAPH TRAFFIC. 

1. Protective Devices 135 

2. Peg Switch Panels 136 

3. Main and Loop Switchboards 138 

4. Distributing Frames 143 

5. Instrument Tables 145 

6. Power Switchboards 146 

Traffic. 

7. Types of Messages 150 

8. Classes of Service and Tariffs 152 

9. Handling of Traffic 154 

10. The Telegraph in Railway Operation 157 

n. Telegraph Statistics 159 

Problems 161 

CHAPTER VI. 

MISCELLANEOUS TELEGRAPHS. 

1. Multiplex Telegraph Systems 162 

2. The Murray Multiplex Page-printing Telegraph 163 

3. The Pollak-Virag Writing Telegraph 167 

4. The Telautograph 170 

5. Telephotography 175 



CONTENTS xi 

ART - PAGE 

6. Television j8 2 

7. Military Induction Telegraphs 184 

Problems !88 

CHAPTER VII. 

MUNICIPAL TELEGRAPHS. 

1. Fire-alarm Telegraphy X 8g 

2. Fire-alarm Signal Boxes 192 

3. Public Alarms 200 

4. Fire-alarm Central Stations 202 

5. Signalling Devices at Apparatus Houses 210 

6. Operation and Routine of a Fire-alarm Telegraph System 212 

7. Police Patrol Telegraphs 217 

8. Statistics of Police and Fire Signalling Systems 221 

Problems 223 

CHAPTER VIII. 
RAILWAY SIGNAL SYSTEMS. 

1. Classes of Railway Signalling 224 

2. Types of Signals 225 

3. Manual Block Signal Systems 231 

4. Location of Automatic Block Signals 232 

5. Automatic Block Signalling 237 

6. Automatic Block Signals on Electric Railways 242 

7. Interlocking Plant Signals 247 

Problems 251 

CHAPTER IX. 
TELEGRAPH LINES AND CABLES. 

1. Aerial Open Lines 253 

2. Wire Spans 261 

3. Economical Span Length - 266 

4. Telegraph Cables 269 

5. Underground Cable Installation 273 

6. The Earth as a Return Path 279 

7. Electrical Constants of Telegraph Conductors 282 

8. Elimination of Inductive Interferences on Telegraph and Tele- 

phone Lines 288 

9. Simultaneous Use of Lines for Telegraphy and Telephony 293 

Problems 300 



Xli CONTENTS 

CHAPTER X. 



THEORY OF CURRENT PROPAGATION IN LINE CONDUCTORS. 

ART. PAGE 

1. The Transmission of Current Impulses along Telegraph Lines. . . 303 

2. Propagation of Alternating Currents along Uniform Conductors 

of Infinite Length 306 

3. Velocity of Wave Propagation over an Ideal Line 313 

4. Wave Propagation along Conductors of Finite Length 314 

5. Simplified Equations of Wave Propagation 321 

6. Current and Voltage Distribution on Lines for any Terminal Con- 

dition 324 

7. Effect of Impedance at Sending End 328 

8. Illustration of Sine-wave Telegraphic Transmission 330 

9. Current in Leaky Line Conductors 334 

10. Illustration of Direct-current Signalling on a Leaky Telegraph 

Line 338 

11. Simplex Signalling with Generators at Both Line Terminals 341 

12. Duplex and Quadruplex Signalling 344 

Problems 346 

CHAPTER XL 
SUBMARINE TELEGRAPHY. 

1. Theory of Cable Telegraphy 347 

2. Illustration of Current Growth at the Receiving End of a Cable. 354 

3. Transmission of Telegraphic Signals 355 

4. Speed of Signalling 363 

5. Picard Method of Signalling 367 

6. Gott Method of Signalling 369 

7. Duplex Cable Telegraphy 372 

8. Sine-wave Signalling 374 

9. Design of Submarine Cables 375 

10. Types of Cable Service and Tariffs 381 

Problems. 385 

APPENDIX. 
TABLES. 

I. Trigonometric Functions 388 

II. Exponential Functions 39 

III. Logarithms 39 2 

IV. Hyperbolic Functions 394 



TELEGRAPH ENGINEERING 



CHAPTER I 

SIMPLEX TELEGRAPHY 

i. Simplex Signalling. The transmission of intelligence 
between two points by means of electricity was accom- 
plished in 1837 by Professor Samuel F. B. Morse of New 
York University.* Seven years later he constructed the 
first telegraph line in this country (Baltimore to Washing- 
ton). The modernized system comprises a conveniently- 
operated switch called a key, for opening and closing the 
circuit at one place, a source of electric current, an electro- 
magnetic receiving device capable of producing an audible 
effect, called a sounder, at another place, and a line wire con- 
necting the two places or stations. Signals are transmitted 
over such a circuit by opening and closing the circuit by 
means of the key for long and short intervals in ac- 
cordance with a prearranged code, and are interpreted 
at the other station by the sounds produced by the move- 
ments of a pivoted spring-controlled lever actuated by an 
electromagnet which is traversed by the current pulses 
established by the key. In order to transmit messages in 
either direction, the apparatus mentioned is duplicated 
and connected with the single line wire as shown in Fig. i. 

The earth is generally utilized as the return path for the 

* Earlier electric telegraphs are described in J. J. Fahie's " A History of 
Electric Telegraphy to 1837." 



2 



TELEGRAPH ENGINEERING 



current, thereby saving the expense of another line wire 
and also avoiding the additional resistance introduced 
thereby. The resistance of the ground-return path GG is 
negligible in comparison with the resistance of the line wire, 
for in nearly all cases it is less than one ohm. This low 
resistance is due to the enormous cross-sectional area of the 
earth path, although the conductivity of the earth's crust is 
poor. Recent experiments, made by Lowy, indicate that 
the specific resistance of a variety of rocks is greater than 
io 5 ohms per centimeter cube, depending upon the amount 
of moisture in them. To attain low earth resistances it is 





=rB 



G 

Fig. i. 

essential that good connections be made between the line 
wire and earth, by iron pipes driven in damp ground or 
more usually by attachment to municipal water pipes. 

When the line is idle the circuit of Fig. i is kept closed 
by means of the circuit-closing switches s, 5 in parallel with 
the keys K, K, causing a current to flow continually from 
ground G at station A through switch s, battery (or 
generator) B, sounder S, line L, sounder 5, battery (or 
generator) B y and switch 5 to ground G at station B. When 
the operator at station A wishes to send messages, he 
interrupts the current by opening his circuit-closer s (as 



SIMPLEX TELEGRAPHY 3 

shown in Fig. i) and then establishes current pulses by 
depressing his key for long or short intervals producing 
respectively so-called dashes and dots, various combi- 
nations of which constitute the letters and numbers of a 
code. These current pulses flow through the windings of 
both sounders, causing the armatures on the levers to be 
attracted and released repeatedly and causing the other 
ends of these levers to strike against lower and upper 
stops, / and u. The long and short intervals between the 
two different sounds produced by striking the lower and 
upper stops are translated by ear as dashes and dots by 
both operators. The sending operator therefore hears his 
own message and is enabled to detect possible errors; it 
also serves as an indication that the line is not open-cir- 
cuited. When the operator is through sending signals, he 
again completes the circuit by means of the circuit-closer, 
thereby enabling the other operator to answer. 

The system described permits of signalling in only one 
direction at a time, and is therefore called a single Morse, 
or conveniently, a simplex telegraph system. It is still in 
use at present for short distances, and with more sensitive 
receiving instruments may be used for longer distances. 

2. The Use of Relays. The lever of a sounder must 
have a certain mass so as to produce loud and distinct 
sounds when striking the stops. A definite magnetizing 
force is required to move the lever with positiveness in 
opposition to its adjustable retractile spring. This mag- 
netizing force is measured by the product of the number of 
turns of wire on the sounder winding and the current 
traversing it. Sounders of the usual construction require 
from 150 to 500 ampere- turns for proper operation. 



4 TELEGRAPH ENGINEERING 

On long lines having high resistance the current is 
necessarily small for practicable voltages, and it would not 
be feasible to use ordinary sounders wound with a great 
many turns of fine wire to secure a proper magnetizing force 
because of the additional resistance introduced. Instead, 
more sensitive instruments, called relays, are used, which 
have light armatures with contact points that open and 
close local circuits containing sounders and local batteries. 
Such relays for simplex signalling require a magnetizing 
force of from 70 to 300 ampere-turns. 

For a given impressed voltage E on a perfectly insulated 
ground-return line of length / miles, having a resistance of 
R ohms per mile, with two receiving instruments each of 
R r ohms resistance, the steady current in the circuit is 



If 7 min be the minimum current which will actuate the 
receiver, the limit of transmission for a given voltage E is 

(i) 

If the electromotive force E be developed by N b series- 
connected primary batteries, each of voltage e and internal 
resistance R b , then replace E in the foregoing equations by 



Thus, if two 2o-ohm sounders requiring a current of 
5- ampere be the receiving instruments on a i2.4-ohm-per- 
mile ground-return line, the maximum length of line 
operated on 140 volts would be 



I2.4\0.20 



_ 2 x 20 



) = 52 miles; 

/ 



SIMPLEX TELEGRAPHY 



whereas if i5o-ohm relays requiring a current of 0.04 
ampere be the receiving instruments, the distance of trans- 
mission over this line would be 



12.4 



- 2 X 150 



J= 258 miles, 



a distance five times as great as before. By the use of 
lines of lower resistance per unit length, the distance of 
transmission can be increased in both cases. 

The voltage necessary for telegraphic transmission over 
a given distance can also be found from equation (i). 
Voltages over 200 are rarely employed in simplex signalling. 

The windings of relays and sounders are generally des- 
ignated by their resistance although the number of turns 
is the important consideration; this is done because of the 
ease in measuring the resistance of a finished instrument. 

3. Closed- and Open-circuit Morse Systems. The 

simple Morse circuit of Fig. i is normally closed, that is, 
it carries a current when no messages are transmitted, and 
is therefore called a closed-circuit system. The connections 









Fig. 2. 

of a closed-circuit system employing relays and local cir- 
cuits at the stations are shown in Fig. 2, which also includes 
an intermediate station. When the operator at station A 



6 TELEGRAPH ENGINEERING 

depresses his key the three relays R will be actuated and 
their armatures will be drawn from the rear stops r and 
strike the front contact screws /, thereby completing the 
three local circuits and permitting the local batteries b to 
operate the sounders. As many as thirty or forty inter- 
mediate stations may be connected in series on a single 
line, but only one operator can send at one time; all oper- 
ators, however, may receive the message whether intended 
for them or not. If another operator wishes to send he 
must wait until the line is idle, or else, if the urgency of 
his message warrants, he may interrupt traffic by opening 
the circuit at his station with the switch s, and then trans- 
mit. Such interruption also takes place when one oper- 
ator wishes to verify a portion of a message transmitted by 
another. 

The closed-circuit telegraph system is used throughout 
the United States. It is important that the relays on a 
circuit be of the same type, or, more specifically, that they 
have the same number of turns on their windings for the 
same core construction, so that the common current in the 
circuit will occasion the same magnetizing force in each 
relay and insure proper functioning of the armature. 

If primary or secondary cells are used as the source of 
current, they may be grouped together forming one bat- 
tery at one station, may be divided into two batteries 
located at the terminal stations, or may be apportioned 
among the various stations forming a number of separate 
batteries, care being exercised not to have some batteries 
connected in opposition to others. A single battery in a 
circuit conduces to uniform care of all cells and to economy 
of maintenance. On the other hand, should a circuit with 
a single battery at a terminal station become grounded, all 



SIMPLEX TELEGRAPHY 



stations beyond the ground would be rendered inoperative 
and unable to communicate with each other. A ground 
on a circuit with two terminal batteries prevents through 
operation, but the stations on each side of the ground can 
temporarily maintain local communication. 

Another simplex telegraph system is used extensively in 
Europe, namely the so-called open-circuit system, in which 
the main-line circuit is really normally closed but does not 
include a source of current when no messages are being 
transmitted. The system derives its name from the fact 
that all batteries are normally open-circuited. The con- 
nections of two terminal stations and one intermediate 
station using the open-circuit system are shown in Fig. 3, 





Fig. 3- 

the letters having the same significance as before. The de- 
pression of a key at a station introduces the source of 
current at that station into the circuit and causes the 
operation of the relays at all the other stations. These in 
turn operate the sounders through the local batteries, as 
before. 

In the open-circuit system the voltage of the batteries 
or generators at the various stations should be the same 
and sufficient individually to operate the entire circuit, 
whereas in the closed-circuit system the current sources 
may be subdivided arbitrarily so long as the aggregate 
voltage is sufficient to operate the entire circuit. Since 



8 TELEGRAPH ENGINEERING 

current flows when no messages are sent in the closed- 
circuit system, a greater amount of electrical energy is 
required for the operation of this system than the open- 
circuit system. When the connections of Fig. 3 are em- 
ployed, the sending operator does not hear the signals 
that he sends out on the line, but this disadvantage can be 
avoided by shifting the relays from their present position 
to the points on the line marked x and connecting the 
back key contacts directly with the points a. 

In the foregoing figures relays and sounders were rep- 
resented as having a single core, while in reality they have 
two cores connected at the rear with a soft iron yoke. 
The windings on the two cores are usually connected in 
series. This method of graphic representation will be re- 
tained for the sake of clearness. 

4. Telegraph Instruments. Keys. A key extensively 
used on closed-circuit systems is the Bunnell key illustrated 
in Fig. 4. It consists of a steel lever carrying a flat hard- 




Fig. 4. 

rubber knob at one end, and pivoted near the other end in 
trunnion screws that are mounted in uprights extending 
from the elliptically-shaped brass base. The movement 
of the lever is adjustable by the knurled screw at its rear 
end. The other end of the lever is kept up normally by 
means of the spring shown, the tension thereof being regu- 



SIMPLEX TELEGRAPHY 



lated by the knurled screw through the middle of the 
lever. When the knob is depressed a platinum point on 
the under side of the lever makes contact with a similar 
point fixed in a cone-shaped cap fastened to, but insulated 
from, the base. This latter contact point is connected 
by a brass strip to the front binding post, which is also 
insulated from the base; the other terminal is fastened 
directly to the base and therefore is in metallic connection 
with the contact point carried on the lever. An auxiliary 
lever, called a circuit-closer, carrying a taller knob, is 
pivoted on the base to move horizontally, so as to engage, 
when pressed toward the key lever, an extended clip on 
the fixed contact point, thereby short-circuiting the key. 

In holding the key for sending, 
the index finger should rest on the 
knob, with the thumb and second 
finger on its edge for steadying 
the motion of the key. Depres- 
sing the key closes or makes the 
circuit and releasing the key opens 
or breaks the circuit. 

Occasionally horizontally-oper- 
ated keys with double contacts 
are employed, requiring but half 
the motions in the formation of 
telegraphic characters that are 
necessary with the usual vertically- 
operated keys. Fig. 5 shows the 
BunneU " double-speed " key. The 
lever is attached to a post at the rear end of the key by 
means of a flat spring. It stands normally midway be- 
tween the two platinum contacts that are supported in a 




Fig. 5. 



10 TELEGRAPH ENGINEERING 

U-shaped piece, mounted on, but insulated from, the base. 
This connects with the binding post, the other terminal 
being the post which supports the lever. In operating the 
key, the knob should be allowed free play between thumb 
and finger, and the hand given a sidewise rocking motion. 
Moving the lever to the right or left closes the circuit. 

Many semi-automatic key transmitters, called vibroplex 
or mecograph transmitters, are used, and permit experi- 
enced operators to signal faster than with the keys already 
described. The horizontally-operated lever has a pendulum 
extension having an adjustable vibration rate. To form a 
dash the operator holds the key knob to the left for a suit- 
able length of time; to form dots the key is moved to the 
right and held there while the pendulum transmits auto- 
matically any desired number of dots. 




Fig. 6. 

Sounders. Fig. 6 shows a typical sounder. It consists 
of a horseshoe electromagnet with two series-connected 
coils protected by hard-rubber shells, and a pivoted brass 
or aluminum lever carrying a soft-iron armature properly 
placed with respect to the magnet poles. The lever is 



SIMPLEX TELEGRAPHY II 

pivoted near one end in trunnion screws mounted on an 
inverted U-shaped standard, this end being held down nor- 
mally by a spring whose compression is regulated by a 
knurled screw at the top of the standard. The motion of 
the lever is limited at the other upright by the two screws 
at the left, their adjustment being fixable by the locknuts. 
The parts mentioned are mounted on a brass surbase which 
is in turn mounted on the wooden base carrying the bind- 
ing posts that connect with the coil terminals. Perfect 
sounders produce a clear loud tone and act quickly. 

Sounders for main line use, that is for short lines without 
relays, are generally wound to have a resistance of 20 




Fig. 7. 

ohms, but many have resistances up to 150 ohms; for 
local circuit use they are usually wound to a 'resistance of 
4 ohms. 

For enhancing and concentrating the signals emitted by 
sounders, these instruments are encased in resonators, such 
as shown in Fig. 7. They are especially adapted for oper- 



12 TELEGRAPH ENGINEERING 

ators located in large offices or in noisy railway stations, 
and for operators using typewriters in recording received 
messages. The type illustrated is capable of being turned 
through three-fourths of a revolution, and is provided with 
a message clip. 

Relays. A relay widely used is shown in Fig. 8. It 
consists of a horizontally mounted electromagnet, the two 
cores of which are joined at the back by a soft-iron yoke. 
This electromagnet is movable longitudinally through the 
bobbin guide by means of the screw at the right, so as 
to vary the length of the gap between the magnet poles 




Fig. 8. 

and the armature, which is mounted in front of them. 
This armature is pivoted at the lower end, while the upper 
end or tongue plays between two adjustable screws, with 
locknuts, supported on the bobbin guide. An adjustable 
retractile spring suitably mounted keeps the armature 
normally away from the magnet poles and against the 
back stop screw which contains a small piece of insulating 
material. When the relay is energized the platinum con- 
tact on the tongue touches a similar contact in the front 
stop screw and thereby completes the local circuit which 
is joined to the left-hand binding posts. The right-hand 



SIMPLEX TELEGRAPHY 



binding posts are the terminals of the magnet winding, and 
connect with the lines. 

In practice, relays have resistances ranging from 20 to 
300 ohms, but i5o-ohm relays are the most extensively 
used. A i5o-ohm relay in considerable use consists of 
6500 turns of No. 30 B. & S. single-silk-covered copper 
wire and operates commercially on 0.05 ampere, although 
it can be adjusted to work reliably on a current as small as 
o.oio ampere. The average distance between the armature 
and pole faces of the magnets is about 0.03 inch. When 
traversed by a 25 cycle alternating current of 0.08 ampere 
the impedance of the relay is about 550 ohms. 

The number of turns of copper wire which can be accom- 
modated on any magnet bobbin may be quickly found by 
multiplying the length of the winding space in inches by the 
permissible depth of the winding in inches and dividing this 
result by a winding constant for the selected wire size, values 
of which constant are given in the following wire table: 



B.&S. 
gage 


Diameter 
of bare 
wire in 
mils 


Winding constants 


B.&S. 

gage 


Diameter 
of bare 
wire in 
mils 


Winding constants 


Single-silk- 
covered 
copper wire 


Enameled 
copper wire 


Single-silk- 
covered 
copper wire 


Enameled 
copper wire 


16 

I? 
18 

19 
2O 
21 
22 
23 
24 
25 
26 

27 
28 


50.82 
45-26 
40.30 

35-89 
31.96 
28.46 
25-35 
22.57 
2O. IO 

17.90 
15.94 

14.20 
12.64 


0.00267 
O.OO2I4 
0.00173 
0.00138 
O.OOIIO 

o . 000884 
0.000708 
0.000568 
0.000458 
0.000370 
0.000299 
0.000244 

0.000202 




29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 


11.26 
10.03 
8.928 
7-950 
7.080 

6.305 
5-6I5 
5-ooo 

4-453 
3-965 
3-531 
3-145 


O.OOOl68 
0.000142 
O.OOOI2I 
O.OOOIO5 

o . 0000889 

0.0000766 
0.0000658 
0.0000570 
0.0000497 
0.0000437 

o . 0000388 

0.0000348 


0.000137 
O.OOOII3 
0.0000928 
0.0000767 
. 0000645 
o . 0000484 
o . 0000398 
0.0000334 
0.0000268 
0.0000227 








o . 000845 
0.000673 
0.000534 
0.000413 
0.000327 
0.000267 
O.OOO2IO 
O.OOOI7O 






14 TELEGRAPH ENGINEERING 

When a constant electromotive force is impressed on the 
terminals of a relay or sounder the current does not in- 
stantly assume its ultimate value because of the inductance 
of the electromagnet. As the inductance of a winding 
surrounding iron depends on the current traversing the 
winding and the position of the armature, it is difficult to 
calculate the growth of current as a function of time for 
these telegraph instruments. The lower curve of Fig. 9 




Fig. 9. 

shows the growth of current strength in a typical relay as 
obtained experimentally by means of an oscillograph. Ab- 
scissas represent time one inch corresponds to 0.037 
second; ordinates represent current strength one inch 
corresponds to 0.030 ampere. The upper curve shows the 
current in the circuit controlled by the relay contacts. It 
will be observed that one-thirtieth of a second elapses after 
impressing voltage on the relay coils before armature chat- 



SIMPLEX TELEGRAPHY 15 

tering ceases and the local circuit is closed. This time, 
with different instruments, varies in some way with the 
ratio of the inductance to the resistance of the relay. 

When the impressed voltage is withdrawn the relay 
armature is not immediately drawn back by the spring be- 
cause of the residual magnetism in the cores. To attain 
quick release the armature when drawn toward the magnet 
poles should not quite touch them. This condition is ob- 
tained by the stop screws or else by the insertion of small 
non-magnetic pins in the pole faces so as to project about 
6*2 of an inch. 

Registers. Where it is desired to record automatically 
the received signals, as in small telegraph offices, or with 




Fig. 10. 



the District Telegraph Messenger Service, an ink-recording 
sounder or register may be used. A register consists of an 
electromagnet and a pivoted armature lever which presses 
a paper tape against an inked wheel when actuated. Spring- 



i6 



TELEGRAPH ENGINEERING 




driven clockwork moves the tape past the inked printing 
wheel, the motion beginning at the first current impulse 

and ending some seconds 
after the last impulse. Fig. 
10 shows a register and 
Fig. ii shows an automatic 
paper winder used with it 
for winding up the paper as 
it is delivered from the reg- 
ister. 

5. Best Winding for Re- 
ceiving Instruments. On a 
telegraph line the windings 
on the receiving instruments 
might have many turns of 

small wire or fewer turns of larger wire for the same wind- 
ing space. The former windings require a smaller current 
than the latter for a given magnetizing force, but at the 
same time have a greater resistance. On reflection it will 
be observed that a best, winding exists for each set of 
conditions, which winding results in the greatest transmis- 
sion distance for lines of given cross-section. The method 
of determining this ideal winding is given below. 

If A be the winding space on an electromagnet in square 
inches and d be the diameter of the wire over insulation in 
inches, the number of turns will be 

A 

n = -, (2) 

which takes no account of bedding of wires in preceding 
layers or of interleaving insulation. If D be the wire 
diameter in mils, and z be the mean length of a turn in 



SIMPLEX TELEGRAPHY 17 

inches, the resistance of the copper wire forming the wind- 
ing will be 

0.87 nz . , v 

Rr = jy- ohms (3) 

at 20 cent., where the constant 0.87 is the resistance of a 
copper wire i inch long and o.ooi inch in diameter. 

The steady current traversing the circuit of length / 
miles with N identical relays in series for an impressed 
unidirectional voltage E is 



where R is the line resistance per mile. The line is assumed 
perfectly insulated from ground. Therefore the ampere- 
turns are 

EA 

nl = 

from which 

l= Rd 2 (nJ~ 
Taking g as the thickness of insulation in inches, 

d = - - + 2 g inches, 





In order to find the maximum distance of transmission as a 
function of wire diameter, this equation is differentiated 
with respect to D and equated to zero. Whence 

^3 _ i.742JV(tt/) D _ irfiozgN (nl) = 
E E 



i8 



TELEGRAPH ENGINEERING 



which is of the form Z) 3 - PD - Q = o. The solution of 
this form is 



cos 



-cos 



-1 




\* 



mils. 



(6) 



This result gives the size of wire to be used in winding the 
coils of the receiving instrument, and substituting this 
value in equation (3) gives the instrument resistance. 

As a numerical illustration consider relays having the 
following constants: 

Sectional area of winding on both coils = A = i.o sq. in., 

Mean length of turn = z = 2.4 inches, 

Number of relays in circuit = N = 10, 

Impressed voltage = = 120 volts, 

Ampere-turns necessary for actuation = nl = 200, 

Thickness of silk insulation = g = o.ooi inch. 
For these values 



I.74ZJV (nl) 
E 



1.74 X 2.4 X 10 X 200 , , 
- = 69.6, 



1 20 



Q = 1000 gP = 1000 X o.ooi X 69.6 = 69.6, 
and consequently the wire diameter for the relay is 

69.6 



D 



cos 



-cos 



-1 




_ 

= 2 V23.2cos(| cos" 1 0.312) =9.632 cos 2357' = 8. 80 mils. 

* If the bracketed expression is greater than unity, hyperbolic cosines 
are taken. For cosine tables see the Appendix. 



SIMPLEX TELEGRAPHY 19 

The nearest standard wire size hereto is No. 31 B. & S. 
gage, for which D = 8.93 mils. Using No. 31 wire, the 
number of turns on both relay bobbins is 

_ i .00 _ _ o A 

(0.00893 + 0-002)2 - 

and the resistance of the instrument is 
0.87 nz 0.87 X 8360 X 2.4 

-- = 2I9 ohms - 



Thus the ideal relay winding for the given conditions 
would consist of 8360 turns of No. 31 copper wire having 
a resistance of 219 ohms. With 10 of these instruments 
the maximum distance of telegraphic transmission is such 
that the resistance of the whole line exclusive of relays is 
(from equation 4) 

En A7r> 120 X 8360 

-- NR r = - * -- 10 X 219 = 2826 ohms. 
200 200 

Using a i2.4-ohm-per-mile line, this means a transmission 

distance of -- = 228 miles. 
12.4 

The dependance of the ideal winding upon the impressed 
voltage and number of relays used in the circuit, for 
otherwise identical conditions assumed in the foregoing 
illustration, is shown in the table on the following page. 

The same method may be used in determining the most 
suitable windings for main-line sounders. 

In practice there are various standard relay and sounder 
'resistances, and for a given set of conditions, that type of 
instrument winding is selected which will approach closely 
to the ideal winding. Usual resistances of receiving instru- 
ments are 20, 50, 75, 100, 150, 250 and 300 ohms. Main- 



2O 



TELEGRAPH ENGINEERING 



line relays of 37.5 ohms resistance are also used on many 
commercial and railway telegraph lines. 





40 Volts 


80 Volts 


Number 
of 
relays 


Calcu- 
lated 
wire di- 
ameter, 
in mils 


Nearest 
B. &S. 
gage 
num- 
ber 


Relay 
resist- 
ance in 
ohms 


Maximum 
line resist- 
ance exclu- 
sive of 
relays 


Calcu- 
lated 
wire di- 
ameter 
in mils 


Nearest 
B. &S. 
gage 
num- 
ber 


Relay 
resist- 
ance in 
ohms 


Maximum 
line resist- 
ance exclu- 
sive of 
relays 


2 


6.QI 


33 


5 06 


1416 


S-oi 


36 


1700 


4760 


6 


11.67 


29 


94 


576 


8-37 


32 


334 


2036 


IO 


14.94 


27 


39-5 


367 


10.70 


29 


94 


1340 


is 


18.2 


25 


16.4 


2 5 8 


12.90 


28 


61 


949 


20 


2^.9 


24 


10.6 


198 


14.94 


27 


39-5 


734 


30 


25-5 


22 


4-36 


137 


18.20 


25 


16.4 


5i6 




120 VoltS 


160 Volts 


6 


6.91 


33 


5o6 ' 


4248 


6.04 


34 


762 


7028 


IO 


8.80 


3i 


219 


2826 


7.68 


32 


334 


4740 


13 


9-99 


30 


144 


2274 


8.70 


3i 


219 


384i 


16 


11.02 


29 


94 


1916 


9.60 


30 


144 


3224 


20 


12.28 


28 


61 


1576 


10.70 


29 


94 


2680 


30 


14-94 


27 


39-5 


IIOI 


12.90 


28 


61 


1898 



6. Sources of Current. In telegraphy the current for 
main and local circuits is furnished occasionally by primary 
batteries (such as Gravity, Fuller, Edison-Lalande, Dry, 
and Leclanche cells), more frequently by storage or second- 
ary batteries, but is furnished chiefly by dynamo electric 
machines. 

Primary Batteries. Primary cells consist of two dissim- 
ilar metals (or one may be carbon) immersed in an electro- 
lyte; and when these are connected externally by means of 
an electric circuit, the chemical energy of the cell is gradually 
converted into electrical energy, and a current is main- 
tained in the circuit. By this action one of the metal 
electrodes, the anode, is slowly consumed. To prevent 



SIMPLEX TELEGRAPHY 21 

the adhesion of liberated gas at the other electrode, or 
cathode, during current delivery, a depolarizer is em- 
ployed which combines readily with the gas evolved. In 
some cells, as in the Fuller and Leclanche types, the cathode 
and depolarizer are contained in porous cups. When com- 
mercial metals containing impurities are used, the anode is 
also consumed by local action without contributing to the 
production of current in the circuit. This deleterious proc- 
ess, which goes on whether the cell delivers current or not, 
is minimized by amalgamation of the anode. 

Cells such as the Gravity, Fuller and Edison-Lalande 
types are suitable for closed-circuit work, while the Dry 
and Leclanche cells are suitable for intermittent service. 

Of primary batteries the Gravity cell is the most exten- 
sively used in telegraphy. Fig. 12 shows the Crow-foot 
gravity cell, the copper being placed in 
the bottom of the jar and the zinc sus- 
pended from the upper edge. Zinc 
sulphate (ZnS0 4 ) is the electrolyte and 
copper sulphate (CuS0 4 ) is the depo- 
larizer of this cell, which yields a volt- 
age of about i.o, and has an internal 
resistance of approximately 2 to 3 ohms. 

When a battery furnishes current to 
several circuits, its internal resistance 
causes the current in each circuit to become less as the 
number of circuits connected in parallel to the same bat- 
tery increases. 

Storage Batteries. Storage or secondary batteries are 
reversible cells which can be charged from some source of 
direct current and later discharged. Charging increases 
the chemical energy of the cell, and this energy reverts to 




22 



TELEGRAPH ENGINEERING 



electrical energy during discharge. The usual form of 
storage battery consists of a lead peroxide (PbC^) positive 
grid and a spongy lead (Pb) negative grid in an electrolyte 
.of dilute sulphuric acid of specific gravity 1.2. During 
discharge these electrodes are gradually changed to lead 
sulphate (PbSC^), a poor conductor of electricity. Re- 
charge converts the electrodes to their initial states. The 
voltage of the cells when fully charged is 2.5, and the voltage 
beyond which it is inadvisable to discharge them, because 
of otherwise excessive sulphating, is 1.8. 

The rating of these storage bat- 
teries in ampere-hours is based on 
a uniform 8-hour discharge. A more 
rapid discharge results in a lowered 
ampere-hour capacity. The capacity 
of a cell depends primarily on the 
size and number of plates and their 
character, and is generally from 40 
to 60 ampere-hours for each square 
foot exposed surface of positive plate. 
Fig. 13 shows a 56o-ampere-hour 
storage cell made by the Electric 
Storage Battery Company. 
Fig * I3 * The Edison storage battery is also 

suitable for telegraphic purposes. Its positive electrodes 
consist of grids of nickel-plated steel supporting nickel 
oxide intermixed with flakes of pure nickel, and the nega- 
tive electrodes consist of similar grids containing iron 
oxide. The electrolyte is a 21 per cent solution of caustic 
potash in distilled water and is contained in a nickel-plated 
sheet-steel case. 
The ampere-hour capacity of these batteries is based on 




SIMPLEX TELEGRAPHY 



a 5-hour discharge rate. The voltage of a cell is 1.2 at 
normal discharge; for charging 1.85 volts are required per 
cell. Fig. 14 shows the appearance of an 8o-ampere-hour 





Fig. 14. 

Edison storage battery, and also the positive (at the right) 
and negative plates. 

Storage cells may be charged directly from direct-current 
service mains or through boosters and motor-generators. 
If only alternating current is available, it may be changed 
into direct current for the charging of storage batteries by 
means of electrolytic or mercury-vapor rectifiers, or by 
means of converters or motor-generators. 

Generators. Electric generators are extensively used in 
large telegraph offices for the operation of long lines and 
local instruments. They may be driven by steam or gas 
engines, but more generally by electric motors which re- 
ceive either direct or alternating current from service 
mains. For the operation of telegraph circuits of all types 
different voltages are required from about 25 to 400 volts. 

The voltages now considered standard for main-line 



TELEGRAPH ENGINEERING 



operation are 80, 160, 240 and 320 by the Western Union 
Telegraph Company, and 85, 125, 200 and 385 by the 
Postal Telegraph-Cable Company, while for local circuit 
operation they are 26 and 52 with the former and 40 volts 




Fig. 15- 

with the latter company. The generators for the two higher 
voltages are generally duplicated so as to permit of re- 
versal of potential, as necessary in duplex and quadruplex 
service (see Chapters II and III). With printing tele- 
graph systems no volts are generally used. 




Fig. 16. 



The arrangement of generators at a telegraph office is 
shown in Fig. 15, the voltages indicated being those of the 
Postal Telegraph-Cable Company. Protective resistances, 
r, in series with the generators, are used to prevent injury 
to the machines in case of line short-circuits, etc. Fig. 16 



SIMPLEX TELEGRAPHY 25 

shows the appearance of General Electric Company motor- 
generator sets each composed of a direct-current motor 
and generator. The 22O-volt 3 -wire direct-current system 
with neutral wire grounded is sometimes used, where avail- 
able, for telegraphic purposes. Dynamotors and mercury- 
vapor rectifiers are also frequently employed. 

It is common practice to have a source of electromotive 
force at both ends of simplex lines instead of a single 
source of equal total voltage at one end, because of better 
line operating characteristics during wet weather. 

7. Telegraph Codes. Telegraph codes consist of vari- 
ous combinations of dots, dashes and spaces for the rep- 
resentation of letters, numerals and punctuation marks. 
Two codes are in extensive use, the American Morse, or 
simply Morse, and the Continental Morse, or simply Con- 
tinental. The Morse code is used throughout the United 
States and Canada for overland signalling except in print- 
ing telegraphy. In punctuation, however, the Phillips 
Punctuation code has generally superseded it because of 
its greater completeness. The Continental, or so-called 
universal code, is in use throughout the world for sub- 
marine telegraphy and also in almost every country except 
those mentioned for overland signalling. The codes are 
given on the two pages following. 

In the code characters the length of a dot is taken as 
the unit of measurement of dashes and spaces. The ordi- 
nary dashes are three times as long as dots, the long 
dashes for letter / and cipher in the Morse code are re- 
spectively five and seven times as long as a dot, the spaces 
between the elements of letters are equal to dots, the 
longer spaces in the letters C, 0, R, Y, Z and & of the 



26 



TELEGRAPH ENGINEERING 



ALPHABET 



LETTERS 
A 
B 
C 
D 
E 
F 
G 
H 
I 

J 
K 
L 

M 
N 
O 
P 

Q 

R 
S 
T 
U 
V 
W 

x 

Y 
Z 

& 

FIGURES 
1 

2 
3 
4 
5 
6 
7 
8 
9 




MORSE 



CONTINENTAL 



MORSE 



NUMERALS 

CONTINENTAL 

- or 

or 



or - 



- - or 

or 

or 



SIMPLEX TELEGRAPHY 























fore words 
tter 
, repeat 


i. 1: 

r i 
ll h 

2, 2? 

II 






i 






i 


i 


i 






jS*' 


1 




PHILLIPS 


i 

1 

i i 
II 


j 


i i 

j 1 


i f i 

; ; i : 
!!;i 


i 
;i 


1 1 

i 1 


j! 


i 

1 

i 


1 1 

1' 1 

I 1 ' 
ll 1 

II 1 


' 

ii !: 

ii M 




1 


1 
i i 






::i: 


1 1 


: ! 


! i 


| 


II 1 
II 1 


ii n 




i 


1 1 


i 


i i 


I i i i 
i 1 i i i 


i i 
i i i 


1 ! 1 


1 1 


! 


111 


ii 1 1 
il ii 











i 


i 








i 
i 


1 




/ 


1VJLN3N 


i i 

1 1 


i 
I 


i 

: i 

i i 


jj 












i 

I 


SCTTJATIO 


1; 


i ! 
i i 


1 
i 

1 

i 


1 i 

1 1 
: i 


I :' 
1 i! 


i 
i 




I 
j 


i 
i 


1 


i 

i 





i 

i 


i 




i i 








I 




1 








1 i 


1 


ll 








I 










O 1 


1 i 


i 


i I 








i 




1 






1 


i ! 


1 

i 


i 1 

1 1 


1 






i 
, I 




1 


s-^>~~- 
















^ 




c 




co a 




T3 

.2 

& 


*J 

C <-> 

-2 -2'i 


Comma 


Interrogation 
Exclamation 


ijfj 

fa QE <Q 


#* 

~C d 

S 

CO 

bO 

c S 
C 3 =5 

v o *2 


Pence 
Capitalized lette 
Colon followed 
quotation 


Decimal point 
Paragraph 


1 

5 



M 



1 


Parenthesis 
Brackets 


Quotation mark 
Quotation withi 

quotation 
..< 



28 TELEGRAPH ENGINEERING 

Morse code are twice as long as dots, and the spaces be- 
tween letters and between words are respectively three and 
six times as long as dots. 

The Continental code, having more dashes than the 
Morse code, requires a little longer time in the transmission 
of any given message expressed in that code than when 
expressed in Morse code. 

A partial list of abbreviations used in commercial teleg- 
raphy follows: 

Scotus Supreme Court of the United States 

Bk Break 

Ck Check 

Fm From 

Ga Go ahead 

Min Wait a minute 

Nm No more 

No Number 

x (placed after check) Get reply to message 

x x x ... Omission 

4 Where shall I go ahead? 

8 Wait, I am busy 

Thus, in case of doubt as to the accuracy of a transmitted 
message, the receiving operator breaks and sends the let- 
ters bk, ga and the last word correctly received; whereupon 
the sending operator continues from that word. Abbre- 
viations used in differentiating the various classes of tele- 
graphic service are given in 8 of Chap. V, and of cable 
service are given in 10 of Chap. XI. 

'x 
8. Telegraph Lines. Galvanized iron, hard-drawn 

copper and occasionally steel wire are used for telegraph 
lines. The sizes generally employed on overhead lines are 



SIMPLEX TELEGRAPHY 



29 



from No. 9 to 14 B. & S. (Brown & Sharpe) gage copper 
wire and from No. 4 to 12 B. W. G. (Birmingham Wire 
Gage) iron wire. The increasing use of hard-drawn copper 
wire for telegraph lines is due to its having a lower resist- 
ance than iron for the same tensile strength, and to the 
fact that it is practically non-corrosive. Telegraph con- 
ductors in cables for transmission over relatively short 
distances are of from No. 14 to 19 B. & S. soft copper. 

The weights, diameters and resistances of telegraph line 
wires are given in the following table: 



Hard-drawn copper wire 


Galvanized iron wire (E. B. B. quality) 


B.&S. 
Gage 
No. 


Diameter 
in mils 


Weight in 
pounds per 
mile 


Resistance 
at 60 fahr. 
per mile in 
ohms 


B.W.G. 
No. 


Diam- 
eter in 
mils 


Weight in 
pounds per 
mile. 


Resistance 
at 60 fahr. 
per mile in 
ohms. 


9 
10 
II 
12 
13 
14 


114.4 
IOI.Q 
90.74 
80. 81 
71.96 
64.08 


208 

166 
132 
105 
83 
65 


4.22 
5-28 
6.6s 
8.36 

10.55 
13.29 


4 
6 

8 

9 
10 
ii 

12 


2 3 8 
2 2O 
203 

180 

165 

148 

134 
1 20 
109 


787 
673 
573 
450 
378 
305 
250 

200 
165 


5-97 
6.98 

8.20 

10.44 
12.43 
I5-4I 
18.80 
23-50 
28.48 


Soft copper wire 


14 

11 

17 
18 

19 


64.08 
57-07 
50.82 
45-26 
40.30 
35 89 


65 
52 
42 
32 
25.6 
20.7 


13.12 
16.54 
20.67 

26.55 
33-6o 
41.47 



Temperature rise increases the resistance of copper 
0.24 per cent per degree fahr. and increases that of iron 
0.35 per cent per degree fahr. reckoned from o fahr. 

Copper-clad or bimetallic wire is also used to some extent 
for telegraph lines. It consists of a steel core to which is 
welded a coating of copper, forming a wire of high tensile 



30 TELEGRAPH ENGINEERING 

strength and fairly low resistance. Several grades are 
available that differ in conductivity, depending upon the 
relative amounts of copper and steel used. 

Bare overhead conductors are supported by glass insu- 
lators mounted on wooden, or sometimes concrete and steel 
telegraph poles. These points of support offer leakage cur- 
rent paths from the conductor to ground. Even in dry 
weather the insulation resistance between the conductor 
and ground is not infinite, but of the order of 10 to 100 
megohms per mile of line, while in wet and foggy weather 
the insulation resistance may fall to a fraction of i megohm 
per mile. 

In the foregoing pages only perfectly insulated lines were 
considered. On actual lines, because of the distributed 
nature of the leakage paths, it is more difficult to determine 
the exact relation between the various factors involved. 
A rough- approximation on lines of short or medium length 
to the actual conditions is obtained by considering all the 
leakage paths to be grouped into one equivalent path at 
the middle point of the line, as shown in Fig. 17. 





Fig. 17. 

It is evident from the figure that even though the circuit 
is open at one station, current flows from the battery at the 
other station through the relay, part of the line, and the 
equivalent leakage path to ground. It follows, therefore, 
that at no time is the current flow in the receiving in- 



SIMPLEX TELEGRAPHY 31 

struments wholly interrupted; and consequently their re- 
tractile springs must be adjusted to release the armatures 
on a certain minimum current strength. In damp weather 
when the insulation resistance of the line is lowered the 
relays must be more delicately adjusted, because the 
currents flowing in the circuit when one switch and when 
both switches are closed are more nearly equal. 

Thus, on a 6oo-mile No. 9 B. & S. aerial copper line 
having a 25o-ohm relay and an 80- volt battery at each 
end, and having an insulation resistance of 10 megohms 
per mile, the steady current traversing the relay when one 
key is open is 

/ = = 0.0044 ampere, 

. 10,000,000 
250 + 300 X 4-22 + - 

ooo 
and when both keys are closed the current is 

7 = - = 0.0528 ampere. 

2 X 250 + 600 X 4.22 

On the other hand, if the insulation resistance be taken as 
one-half megohm per mile, the current when one key is 
open would be 

80 
7 = =0.034 ampere, 

250 + 300 X 4-22 + S 00 ? 000 
ooo 

showing that under these conditions the relay must be 
adjusted to operate on 0.0528 ampere and release the 
armature on 0.034 ampere. If so adjusted and if the in- 
sulation resistance falls still lower, the line would be ren- 
dered inoperative. 
With assigned insulation resistance, terminal resistance 



32 TELEGRAPH ENGINEERING 

and relay adjustment, it is possible, on the basis of the 
foregoing paragraphs, to determine the maximum permis- 
sible length of line for line conductors of any size. Let 

/ = maximum length of ground-return line in miles, 
R = line resistance per mile in ohms, 
R r = resistance of each relay in ohms, 
N number of relays in circuit (assumed uniformly 

distributed between terminal stations), 
R { = insulation resistance per mile in ohms, 
E = voltage impressed at each end of line, 
/! = current in amperes necessary to actuate relay, and 
7 2 = current in amperes which will just cause release 
of armature, 



r 4. -* 

I " [ 7 

2 2 / 



and 



Eliminating E from equations (7) and (8), and solving for I, 
there results, 



n, r 2 .. 

IT' -R(h-ij- 

from which the maximum transmission distance is 



an expression not involving the impressed voltage. 

As a numerical illustration, consider a No. 9 B. & S. 
copper conductor having a 25o-ohm relay at each end 
which is adjusted to operate on 0.06 ampere and .release 



SIMPLEX TELEGRAPHY 33 

on 0.04 ampere. For an insulation resistance of | megohm 
per mile, the maximum permissible length of line is 



// 250 \ 2 . 2 X 0.04 X 500,000 

V V 4.22 / 4.22 (0.06-0.04) 



2 X 4-22 

= - 59-3 + 691.0 = 631.7 miles. 
The voltage of the battery at each end should be 

E = ^ (NR r + Rl) = (2 X 250 + 4-22 X 631.7) 

2 2 

= 95 volts, 

as obtained by using equation (8). 

This approximate solution of the telegraph circuit will 
be referred to again because it is less involved than the 
exact solution which is considered in Chap. X. Experi- 
ence has proven that the maximum distance of trans- 
mission on long aerial lines is limited principally by line 
leakage. 

9. Speed of Signalling. The speed with which signals 
may be transmitted over a telegraph line depends upon 
three factors, namely the speed of the sending operator, 
the nature of the line, and the responsiveness of the receiv- 
ing instrument. 

An experienced operator can send from 30 to 40 five- 
letter words per minute by hand transmission. Semi- 
automatic devices may be availed of to raise this sending 
speed. Much higher speeds are attainable by automatic 
transmitters, as described later ( i, Chap. IV). 

It was pointed out in the last section that the current 
through the receiving device connected to a leaky line 
does not cease altogether upon opening one key. It is 



34 TELEGRAPH ENGINEERING 

evident that the greater the line insulation resistance the 
more rapid will be the current change in the relay coils 
with movements of the key, and consequently the quicker 
the actuation and release of the relay armature. On a 
long line with considerable leakage, rapid signalling may 
cause the duration of contact for dots to be so short as to 
prevent the current in the relay from attaining a value 
sufficient to attract its armature. More deliberate or 
"heavy " sending must then be resorted to, implying 
slower signalling speed. Thus, the shorter the line the 
higher may be the speed of signalling. 

Further, the line itself, especially if a cable, limits the 
speed of transmission. As most large telegraph offices are 
in the business centers of cities, short sections of nearly all 
long aerial lines are placed in cables under ground and there- 
fore the speed of signalling on these lines is limited by the 
cable sections. In cables a conductor is very near its 
return conductor or the grounded sheath, and conse- 
quently its electrostatic capacity is high. It will be 
shown in 4 of Chap. XI, that the signalling speed over 
cables (having negligible inductance and leakance) is in- 
versely proportional to the product of total line capacity 
and total line resistance. That is, if C be the capacity in 
farads per mile of conductor, and R be the resistance in 
ohms per mile, then 

V Signalling speed JL_ ^L., ( IO ) 



where / is the length of the cable in miles. This propor- 
tionality shows that for a given size of cable the signalling 
speed varies inversely with the square of its length. 
It is safe to say that the speed possibilities on long 



SIMPLEX TELEGRAPHY 35 

fairly well insulated aerial lines even with short cable sec- 
tions is greater than the operating speed of the receiving 
instruments. In 4 it was stated that the time of current 
growth in a relay depends upon the ratio of its inductance 
to its resistance. Rather than increase the relay resistance 
to obtain rapid response, it is more advisable to reduce its 
inductance. This may be done by decreasing the number 
of turns, by connecting the two coils in parallel instead 
of in series, by increasing the reluctance of the magnetic 
circuit either by removing the iron yoke or by lengthening 
the air gap between armature and magnet cores, and by 
using a shunting condenser. Some of these suggestions, 
however, conflict with the conditions for maximum mag- 
netization with a given current. 

The necessary mass of the relay armature should be 
apportioned in such a way as to possess the least moment 
of inertia about the pivots so as to acquire a high velocity 
under the action of a given force. The greater part of 
its mass should therefore be near the axis. The contact 
points, however, are preferably placed far from the pivots 
in order to reduce the angular motion of the armature and 
permit signals to follow each other in rapid succession. 
By embodying the features mentioned relays have been 
constructed which respond to signals sent at speeds as 
high as 400 words per minute. 

10. Simplex Repeaters. It was shown in 8 that 
leakage is the important factor in limiting the distance of 
telegraphic signalling. Using a No. 9 B. & S. copper con- 
ductor with two 25o-ohm relays with given adjustment 
(which implies a given signalling speed) it was found that 
the maximum permissible length of line is 631.7 miles 



36 TELEGRAPH ENGINEERING 

when the insulation resistance is assumed as J megohm 
per mile. If a No. 6 wire, which has double the cross- 
section (R = 2.09), were used instead, the maximum length 
of line under otherwise identical conditions would be 865.9 
miles. Thus, using a conductor of twice the size and 
costing twice as much would only increase the distance of 
transmission 37 per cent. It is apparent from this illus- 
tration that the cost of transcontinental telegraphy over a 
single continuous circuit would be prohibitive. 

If such long lines are subdivided into several shorter 
sections, say from 300 to 600 miles in length, each section 
terminating in a relay, signals may be automatically trans- 






Fig. 18. 

mitted thereby into the next section, and so on to the 
terminus of the line, without requiring unduly large lino 
conductors. The speed of signalling will then be that of 
the section which allows the slowest transmission less the 
speed loss in the relays. Two-line sections of such an 
arrangement are shown in Fig. 18, from which is seen the 
possibility of transmitting toward the right, but also the 
futility of endeavoring to transmit in the opposite direc- 
tion. In order to permit of signalling in either direction, 
the intermediate relays R^ R 3 . . . are replaced by re- 
peater sets. 
A repeater set consists of two relays and two transmit- 



SIMPLEX TELEGRAPHY 



37 



ters which are electrically and mechanically arranged to 
allow signalling in either direction and in such a way as 
to automatically prevent one transmitter breaking at the 
repeater station the line circuit which it controls when 
that circuit is repeating into the other. Two standard 
closed-circuit repeaters which accomplish these results will 
now be described. 

Weiny-Phillips Repeater. The connections of a Weiny- 
Phillips repeater set are shown in Fig. 19, in which T and T f 




are the transmitters, and R and R' are the relays. Each 
relay has an extra magnet, H or H' ', called a holding-coil, 
mounted above the ordinary magnets so as to act on the 
same moving element, as illustrated in Fig. 20. Its wind- 
ing has a tap at its middle point, so that if current enters 
at this point, it will traverse the two parts of the winding, 
a and b, in opposite directions, and consequently produce 
no magnetization in the core. The transmitter T has a 
small auxiliary lever m, insulated from and controlled by 
the main lever, each lever making contact with a platinum 



TELEGRAPH ENGINEERING 



contact point when the magnets of the transmitter are 
energized. The switches 5 and s' on the transmitters 




Fig. 20. 



enable an operator to sever the two circuits, leaving each 
complete in itself for simplex operation. Fig. 21 shows the 
Weiny-Phillips transmitter. 




Fig. 21. 



Normally, when both the eastern and western circuits 
are closed at the distant stations, current flows through all 
magnet windings of the repeater set. Thus, normally, 



SIMPLEX TELEGRAPHY 39 

current flows from the western station through the main- 
line coils of relay R, circuit-closing switch of the key K, 
and contact y' (which is closed) of the transmitter T", to 
ground at G '. Similarly, current flows from the eastern 
station through R', K' ', and y to G. Both relay armatures 
are therefore attracted and keep the. transmitter coils 
energized through the batteries B and B' '. The contacts 
x, y and x', y' are thus normally closed and currents from 
the batteries BI and J5 2 flow through both windings of the 
holding coils. Generators are very frequently used instead 
of batteries. 

When the western operator opens the circuit preparatory 
to signalling, the main-line coils of relay R are deprived of 
current and the armature is released, inasmuch as the hold- 
ing coil // exerts no attraction due to the neutralization of 
magnetizing forces developed in the two windings. This 
results in opening the circuit of the magnet of transmitter 
T and the release of its armature. The positions of the 
moving elements of the instruments at this instant are as 
shown in Fig. 19. The circuit of the winding b f of the 
holding coil H f is broken at x and consequently the un- 
interrupted current flowing through its associate winding 
a ! holds the tongue of relay R r against its contact stud 
irrespective of current condition in the main-line coils. 
This in turn maintains current flow through the winding of 
transmitter T' and prevents the opening of the western 
circuit at y r , and the opening at x' of coil b of the holding 
coil H, which is therefore not magnetized. In this way 
the continuity of the western circuit is preserved at the 
repeater while repeating eastward. A moment after 
breaking the circuit at x, the eastern circuit is broken at 
y and the distant relay releases its armature. 



40 TELEGRAPH ENGINEERING 

When the western operator depresses his key, relay R 
will be actuated, and then the transmitter T closes the 
eastern circuit at y, which is followed by the closing of 
coil b f at x. The distant eastern relay is thus energized. 
Signalling in the reverse direction is accomplished in the 
same manner. 

Atkinson Repeater. The Atkinson repeater set con- 
sists of two ordinary relays R and R', two transmitters T 
and T f similar in design to the Weiny-Phillips transmitters, 
and two repeating sounders S and S' which combine the 
functions of relay and sounder, the connections of the set 
being shown in Fig. 22. The contacts of the repeating 
sounders are shunted across the corresponding relay 
contacts. 

Normally, when no messages are being transmitted, 
the windings of all the repeater instruments carry current. 
Thus, the western line current traverses the contact x 
(which is closed) of the transmitter T and the winding of 
relay R' to ground. Similarly, the eastern line current 
traverses x' and R to ground. Both relay armatures are 
therefore in contact with their front connecting studs and 
keep the transmitter magnets energized by means of 
the batteries B and B' '. The contacts y and y' are 
thus normally closed and currents from the batteries b 
and V actuate the repeating sounders S and S' respec- 
tively. 

When the western operator opens the key prior to signal- 
ling, relay R' loses its magnetism and its armature falls 
back, thereby opening the circuit of the magnet of trans- 
mitter T f j inasmuch as sounder S' remains energized and 
does not short-circuit the relay contacts. The lever of 
this transmitter first opens a circuit at y' and immediately 



SIMPLEX TELEGRAPHY 41 

afterward opens a circuit at x'. The conditions are then 
as shown in Fig. 22. The opening of the circuit at y f 
causes the demagnetization of sounder 6* and the release 
of its armature. The magnet of transmitter T will thereby 
be kept energized regardless of the armature position of 
relay R. In this way the continuity of the western cir- 
cuit is preserved at x. The circuit opened at x' is the 
eastern line circuit. Thus, the relay at the eastern station 




Fig. 22. 

releases its armature as the distant western operator opens 
the circuit. 

As this operator then depresses his key, relay R' is 
energized and its armature closes the transmitter circuit 
at T', the result of which being the closing of the eastern 
circuit at #', followed by the closing of the circuit of re- 
peating sounder S. The actuation of the sounder, how- 
ever, does not open the circuit of the transmitter magnet 
T, because the relay R, energized by the eastern line 
battery (not shown) at the closing of contacts x', keeps its 
circuit closed. 



42 TELEGRAPH ENGINEERING 

Signalling in the reverse direction can be traced through 
the repeater in the same manner. 

Other Repeaters. Many other closed-circuit simplex 
repeaters are in use, among which may be mentioned the 
Milliken, Ghegan, Horton, Neilson and Toye repeaters.* f 
They all differ in the methods employed to prevent one 
transmitter breaking the circuit, that is repeating into the 
other circuit. Repeaters may also be arranged for re- 
peating into two or more circuits; the Maver multiple 
repeater* is one of this type. 

For the satisfactory operation of repeaters, attendants, 
each in charge of a certain number of sets, are required to 
supervise the working of the repeaters and make such ad- 
justments as are necessary to maintain uninterrupted 
service despite changes in weather conditions and irregu- 
larities in sending. With several types of self-adjusting 
repeaters, such as the Catlin and D'Humy repeaters,f this 
supervision may be dispensed with. 

There are various types of open-circuit repeaters, the 
simplest of which, employing only two double-contact re- 




Fig. 23. 

lays, is represented in Fig. 23. When no messages are 
being transmitted, no current flows through the line wires 
and repeater relays, and consequently both relay arma- 

* For description see Maver's "American Telegraphy." 
t Described in McNicoPs " American Telegraph Practice." 



SIMPLEX TELEGRAPHY 43 

tures rest against their upper contact studs. When the 
western operator depresses his key, relay R f attracts its 
armature, and current, supplied by battery B', flows over. 
the eastern line. At the same time the magnet circuit of 
relay R is broken at the upper contact point so that the 
continuity of the western circuit remains uninterrupted. 

PROBLEMS. 

1. How far would it be possible to telegraph over a perfectly 
insulated ground-return line having 8.36 ohms resistance per mile of 
length with an impressed voltage of 1 20, if the current necessary to 
actuate the two 75-ohm relays is 0.07 ampere? 

2. How many gravity cells, each having a voltage of i.o and an 
internal resistance of 2.5 ohms, would be required to transmit signals 
over an 8o-mile telegraph line which has a resistance of 5.28 ohms per 
mile and is equipped with two i5o-ohm relays requiring a current of 
0.04 ampere ? 

3. Three relays are adjusted to operate on 250 ampere- turns, 
and have the following constants: 

Relay No. i 20 ohms resistance 2400 turns, 

Relay No. 2 75 ohms resistance 4500 turns, 

Relay No. 3 150 ohms resistance 7500 turns. 

If these relays were connected in series across 2o-volt mains, which 
relays would operate ? What voltage would cause all three to oper- 
ate? 

4. What is the best winding for four main-line sounders operating 
on 400 ampere-turns when used on a telegraph line which requires 
40 volts? The sounders are of identical construction and have a 
winding cross-section of 0.9 square inch and a mean length of turn 
of 2.2 inches; double-cotton-insulated wire to be used, the insulating 
covering being four mils thick. 

5. Over how long a line, having 13.3 ohms resistance per mile, 
could the four sounders of the preceding problem operate when the 
impressed voltage is 40 volts ? 

6. Four separate telegraph lines, each having a total resistance of 
1000 ohms including receiving instruments, are supplied with cur- 
rent by one battery of 100 gravity cells, which has an internal re- 



44 TELEGRAPH ENGINEERING 

sistance of 220 ohms. Determine the current strength in a circuit 
when only one circuit is closed and also when all four circuits are 
closed. 

7. Decipher the following message: 



8. What would be the costs per mile of two telegraph lines of 
standard sizes having approximately 10.5 ohms resistance per mile, 
one constructed of galvanized iron and the other of hard-drawn 
copper wire? The costs of iron and copper may be taken as 4^ and 
1 6 cents per pound respectively. 

9. A 4oo-mile No. 6 B. W. G. aerial iron line, having a 25o-ohm 
relay and a 120- volt generator at each end, shows an insulation re- 
sistance of i megohm per mile in wet weather. What currents flow 
through one relay when the key at the other station is open and 
when closed? 

10. Calculate the maximum permissible length of a No. 10 B. & S. 
copper telegraph line having six 25o-ohm relays which are adjusted 
to operate on 0.05 ampere and release on 0.025 ampere, if the in- 
sulation resistance of the line be taken as \ megohm per mile. 'Com- 
pute the proper voltage to be impressed at each end. 

11. If the speed of telegraphic' signalling over a loo-mile cable 
of No. 1 6 B. & S. copper, having a capacity of 0.12 microfarad per 
mile, is 200 five-letter code words per minute, what would be the 
possible signalling speed over a 6o-mile cable of No. 19 B. & S. wire 
having a capacity of o.n microfarad per mile? 



CHAPTER II 

DUPLEX TELEGRAPHY 

i . Duplex Telegraph Systems. By duplex signalling 
is meant the simultaneous transmission of signals in oppo- 
site directions without interference over a single line. 
Four operators are required for each duplex circuit, one 
sending and one receiving operator at each station. The 
message capacity of a duplexed line is therefore twice that 
of the same line when operated simplex. When telegraphic 
traffic over a given line exceeds that which can be handled 
satisfactorily by simplex signalling, it is advisable to install 
the necessary apparatus at the terminal stations for duplex 
signalling, thereby avoiding the expense of erecting another 
line. Duplex telegraphy was first performed in 1853 by 
Dr. Wm. Gintl; its practical operation began about 1868. 

Duplex circuits do not permit of the intromission of inter- 
mediate stations, but. repeating stations may be inserted 
on long duplex lines. In telegraph systems intended for 
duplex signalling, the receiving instruments at both sta- 
tions must be in circuit at all times ready to respond to 
signals sent from the distant station, and yet so designed 
that the receiving instrument at each station will not 
respond to signals sent by that station. These condi- 
tions are met in various ways in the different duplex 
systems. 

There are three systems of duplex telegraphy: the dif- 
ferential duplex, the polar duplex and the bridge duplex 

45 



4 6 



TELEGRAPH ENGINEERING 



systems.* The first system, although now infrequently used 
for duplex signalling, is an essential part of the quadruplex 
telegraph system to be described in the next chapter, and 
consequently will be here discussed. Where it is advis- 
able to employ a battery at one end of the line only, a 
combination of the differential and polar duplex systems 
may be used for duplex operation over short distances. 

2. The Differential Duplex. The differential duplex, 
also known as the single-current duplex and as the Stearns 
duplex, utilizes a differential relay as the receiving instru- 
ment. This is a relay with two windings, identical as to 
number of turns and resistance, through which currents 





G' 



Fig. x. 



may flow in the same or in opposite directions around its 
iron cores. The corresponding turns of the windings are 
preferably wound side by side so as to avoid the formation 
of consequent magnetic poles. For clearness in diagrams, 
however, these windings will be shown as being adjacent. 
The scheme of connections of the differential duplex is 
represented in Fig. i, which shows a line L extending be- 
tween the two stations A and B, having a ground return 

* Early duplex schemes are described in Prescott's " Electricity and the 
Electric Telegraph." 



DUPLEX TELEGRAPHY 47 

path. The relays R and R r have two windings each (a, b 
and a' , b'), the common terminal being joined to the levers 
of keys K and K r respectively. The similar batteries 
B and B f are connected with like poles to the front con- 
tacts of the keys, while resistance coils d and d> ', having a 
resistance equal to the internal battery resistance, are con- 
nected to the rear key contacts. In this way the resistance 
of the circuit is unaltered whether the keys are on the front 
or the rear contacts. The resistance coil r is adjusted to 
have a resistance equal to that of the line xy plus the 
resistance from the point y to ground at G' and the ground 
resistance G' to G, and similarly the coil r' to have a re- 
sistance equal to that of the line plus that from the point 
x to ground at G and back to G' (the ground resistance 
being usually neglected). With this adjustment, if a cur- 
rent enter either relay at the junction of its two coils, it 
would divide equally between the two paths to ground 
presented to it, each path including one of the relay coils. 
The equal components of this current in the two coils 
circulate around the core in opposite directions and 
consequently the magnetomotive force developed by one 
is neutralized by that developed by the other, thereby 
exerting no attractive force on the relay armature. 

The resistances of the coils r and r' are experimentally 
adjusted in practice so that the home relay is not affected 
by movements of the keys. The resistances may, however, 
be determined as follows: The resistances of the two bat- 
teries will be assumed equal and of value R b ohms each," 
the resistances of the two relays likewise of R r ohms each; 
then from the symmetry of the circuit the two coils r 
and r' will also have equal resistance, say r ohms. The 
line will be assumed perfectly insulated from ground and 



48 TELEGRAPH ENGINEERING 

of resistance Rl ohms. For exact neutralization of mag- 
netizing forces in the two relays, the resistance of the 
one path, 

f + r + * (i) 

must equal that of the other path, which is 



2 _!_ I 

* & 

2 



+ ^ + r) = R, (^ + r ) 



Whence 



(r> 2 1? i;>7\ 
# r # 6 + R b Rl + ^ + 42] = o. 
4 2 / 

Therefore the resistance of each coil is 



r = + - V(Rl+R r )(Rl+R r + 4R*). (3) 

2 2 

Thus, if 2oo-ohm relays are connected to the ends of a 
20oo-ohm line and if a 2oo-volt gravity battery having 250 
ohms internal resistance be employed at each end, then 
the resistance coils r and r' would each have a resistance of 



_ 2 OOP 



+ - V(20oo + 200) (2000 + 200 + 4 X 250) 



2 2 

= 2327 ohms. 

These values are indicated in Fig. 2, and it may be verified 
that the resistances of the four paths: m, n, p, m (2, p t 
m, q, G f G', /, q, m, G g, s, t, q, are all equal and have a 
resistance of 2677 ohms. 



DUPLEX TELEGRAPHY 49 

An inspection of Fig. i will reveal the principle of opera- 
tion of this system. If neither key be depressed, no cir- 
cuit containing an E.M.F. is closed and therefore no relay 
is actuated. The depression of only one key at either 
station will fail to actuate the relay at that station because 
of equal and oppositely directed currents in the halves of 



100 -J- 100 





Rj = 260 



Fig. 2. 

its relay coils, but will actuate the relay at the remote sta- 
tion because of the additive action of these currents. The 
depression of both keys connects both batteries in opposi- 
tion and, since no current then flows in the line wire nor in 
the line coils b, a f , of the relays, both relays are actuated 
by the currents flowing in their other coils. Although a 
key has no control over the home relay, it will be ob- 
served that when both keys are depressed each relay is 
operated by current from the home battery. 

Thus in this system a relay is properly actuated when- 
ever the key at the other station is depressed regardless of 
the position of the other key. 

In the numerical illustration, the steady currents in 
milliamperes traversing the relay coils under the various 
conditions, are readily seen to be those given in the follow- 
ing table. The figures following the braces give the 
equivalent currents through one coil and the stars indicate 
the operation of the relays. 



TELEGRAPH ENGINEERING 



CURRENTS IN RELAY COILS 



Relay 


Coil 


Neither 
key de- 
pressed 


Key K only 
depressed 


Both keys 
depressed 


Key K' only 
depressed 


R 


a 
b 


j| 


si? 


7 *}75* 


JJ* 


R' 


a' 
b' 


o| 


11 * 


IS* 


21* 



In the manipulation of the two keys as shown, there are 
constantly recurring intervals during which the key levers 
are in an intermediate position, touching neither contact 
stud. This condition is apt to cause confusion of signals, 
especially on leaky lines. In differential duplex circuits 
where primary cells are used, this confusion of signals may 
be avoided by the employment of transmitters so designed 
that contact is made with one stud an instant before con- 
tact is broken with the other. The appearance of such 
continuity- preserving transmitters, operated magnetically by 
means of a local circuit, is shown in Fig. 3. 




Fig. 3. 



The connections of one station of a duplex circuit using 
this transmitter, are shown in Fig. 4, wherein T is the 
transmitter, and j and k are the contact studs, the other 



DUPLEX TELEGRAPHY 



letters having the same significance as before. The trans- 
mitter has an auxiliary spring lever, insulated from the 
main lever, which may make contact either with the fixed 




study or with the stud k attached to the main lever. When 
the key is depressed the contact aty is made before that at 
k is broken, and when the key is released, the contact at k 
is made before that aty is broken. In this way the circuit 
from m to ground is always complete. The momentary 
short-circuits of the line battery during the excursions of 
the transmitter lever do not prove injurious to the battery. 

3. Artificial Lines. The resistances r and r' of Fig. i, 
each possessing a resistance equal to that of the line plus 
that of the terminal apparatus at the remote station, are 
aptly termed artificial lines. But, since actual telegraph 
lines have electrostatic capacity with respect to ground, 
for more exact imitation the artificial lines should also 
have capacity. When the artificial line has the same 
capacity as the line wire, then the currents through them 
and through the relay coils will rise and fall at the same 
rate. That this result is essential is evident from the fact 



TELEGRAPH ENGINEERING 



that if the current should rise more quickly to its ultimate 
value or decay more rapidly to zero in one relay coil than 
in its companion coil, the armature would give a momen- 
tary kick and produce a false signal upon each depression 
or release of the home key. When the resistance and 
capacity of the artificial line in a duplex circuit are so 
adjusted that the depression of a key produces no effect 
upon the home relay, the circuit is said to be balanced. 

The arrangement of an artificial line which is used by 
the Postal Telegraph-Cable Company for duplex telegraphic 








Fig- 5- 



signalling is given in Fig. 5. The resistance between the 
terminals A and B can be varied from 10 to 11,100 ohms, 
and each of the two condenser sets can be adjusted from o.i 
to 3.0 microfarads. This wide adjustment permits of its 
use on lines of different lengths, resistances and capacities. 
Parts of the 400- and i6oo-ohm resistances are connected in 
series with the two condenser sets in order to vary the time 
of their charge and discharge to approximate the cor- 
responding times for the line. 
The design of the Western Union artificial line is shown 



DUPLEX TELEGRAPHY 



53 



in Fig. 6. The resistance between the terminals " Ground" 
and " Relay" can be varied from 25 up to 11,000 ohms, 
and each of the two condenser sets can be adjusted from 
i to 3! microfarads. One of the resistances connected in 
series with the condensers can be varied from 100 to 500 




10 W| lyi i i l MI i ii i 



* X 



1 2 | 2 I J$ X Ji 

Fig. 6. 

ohms while the other adds from 200 to 1000 ohms. When 
a line becomes leaky in wet weather, the resistance of its 
artificial lines must be lowered for balance. 

4. Polarized Relays. The polar duplex telegraph 
system depends for its operation upon reversals in the 
direction of current flow. In this system, the function of 
the key is not to make and break the circuit as in the 



54 



TELEGRAPH ENGINEERING 



Stearns duplex, but instead to present alternately the 
positive and negative poles of the battery to the line. 
Obviously the receiving instrument employed must oper- 
ate upon current reversals, and such an instrument is 
called a polarized relay. 

The principle of the simple polarized relay may be ex- 
plained with the aid of Fig. 7. A U-shaped permanent 
magnet magnetized to have two equal South poles as indi- 
cated at (a) has pivoted at its mid-point a soft iron arma- 
ture which projects upward and plays between two pole 
pieces that are attached to the ends of the magnet, as 
shown at (b). The North magnetic pole is then shifted 
to the position shown, and it is evident that the armature 



SL 




(a) 



(6) 



s ",LU n 
W) 



Fig. 7. 



will remain against whichever pole piece it is placed, for no 
retractile spring is used. A winding surrounds each pole 
piece and the two windings are connected in series. Re- 
membering that a current traversing a winding around an 
iron core will cause the formation of magnetic poles as 
shown at (d), it will be evident that if a current traverses 
the windings as indicated by the arrows at (c) the mag- 
netization due to the permanent magnet in the left-hand 
pole piece will be partially neutralized while that in the 
other pole piece will be strengthened. Consequently the 
armature will be drawn over toward the stronger right- 
hand pole piece, and make contact with the right contact 



DUPLEX TELEGRAPHY 



55 



screw. If the direction of current flow be reversed, the 
left-hand pole piece will be the stronger and therefore the 
armature will make contact with the left-hand contact 
stud. Thus, every time the direction of current changes, 
the armature will move from one contact screw to the 
other. 

The windings of the polarized relay may also be wound 
differentially in the same way as with the ordinary or neu- 
tral differential relays, already described. 
Each coil contains an equal number of 
turns belonging to the two windings. To 
avoid complicated diagrams, differentially- 
wound relays will be represented as in 
Fig. 8, with a tap m at the middle point 
of the winding. When current is sent through the coils 
differentially in either direction the armature will not move 
from the position previously assumed. 




Fig. 8. 




Fig. 9. 

Fig. 9 shows one form of differentially-wound polarized 
relay. The armature is pivoted in a brass casing just 



TELEGRAPH ENGINEERING 



below the upper end of the semicircular-shaped permanent 
magnet and extends between the adjustable pole pieces of 
the electromagnet coils that are mounted on the other end 
of the permanent magnet. The post supporting the con- 
tact points is shown at the left. 

In practice polarized relays usually have resistances of 
from 50 to 500 ohms, and will operate satisfactorily on 
currents of from 5 to 200 milliamperes. When traversed 
by currents of from 10 to 15 milliamperes, the inductances 
of such relays are from 1.5 to 6 henrys when the air gap 
between armature and pole faces is about 0.02 inch. 

5. The Polar Duplex. The connections of the ap- 
paratus used on a polar duplex line for primary battery 
operation are shown in Fig. 10. The pole-changing trans- 





Fig. 10. 

mitters, represented by C and C', consist of double arma- 
ture relays, each armature playing between two contact 
studs. When the key K is not depressed, retractile springs 
hold the armatures x and y respectively in contact with 
the positive and negative terminals of the battery B, but 
when the key is depressed the armatures are attracted 



DUPLEX TELEGRAPHY 57 

and x and y are respectively in contact with the negative 
and positive poles of the battery. In other words, depres- 
sion of the key reverses the polarity of the home battery 
with respect to the circuit. 

The differentially-wound polarized relays are shown at 
P and P f and control the operation of the local sounders 
S and S r respectively. The letters 5 and n on the relay 
poles represent the South and North poles due to the 
permanent magnets alone. The properly-balanced arti- 
ficial lines are shown at AL. The proper resistance of 
the artificial line may be calculated similarly to the method 
given in 2. 

When both keys are open, it is seen that the negative 
terminals of both main batteries are connected to the 
mid-points of the relay windings, and that therefore no 
current traverses the line coils a, ai and e, ei of the relays. 
Currents, however, will flow in the artificial line coils 6, 61 
and /, /i, and these are in such direction as to strengthen 
the left-hand poles of the polarized relays and weaken their 
right-hand poles, and consequently both armatures will 
be drawn to the left and away from the sounder contacts. 
Hence both sounders are idle when both keys are open. 

If only key K be depressed, the positive pole of battery 
B is connected to the line and the conditions are exactly 
as represented in the figure. About twice as much cur- 
rent flows through the line coils of the relays as through 
the artificial line coils, so that the operation of the relays 
depends upon the direction of current in the line coils. 
The current in the coils a and a\ strengthens the left-hand 
pole and weakens the right-hand pole of relay P } and con- 
sequently the armature stays away from its sounder con- 
tact. At the other station the current in the line coils 



58 TELEGRAPH ENGINEERING 

e and e\ strengthens the right-hand pole and weakens the 
left-hand pole of relay P', and therefore the armature 
closes the local circuit and the sounder S' responds. In 
like manner the depression of key K' only will operate 
the sounder S. Thus, the manipulation of one key 
controls the operation of the distant sounder, but does not 
control the home sounder. 

When both keys are simultaneously closed, no current 
again flows over the line, because the positive poles of 
both batteries are in contact with the line. The currents 
in the artificial line coils are now in such a direction as to 
weaken the left-hand poles and strengthen the right-hand 
poles of both relays. Both armatures are then held against 
the local circuit contacts and both sounders operate. In 
this way signalling can be carried on in opposite directions 
over a single wire. If relays are used that have their 
armatures magnetized South, reversal of the batteries will 
cause the system to operate in the same way. 

Continuity-preserving pole-changers may be used with 
polar duplex systems if current is supplied by primary 
batteries, but their use is not so important as the use of 
continuity-preserving transmitters with differential duplex 
systems. For, assume key K to be depressed while key K' 
is open, and consider the instant when the armatures of 
the pole-changer C are midway between their contacts. 
The battery B is then completely cut off from the circuit 
and the line circuit is completed to ground at G only 
through all coils of the relay P and the artificial line. The 
line current from battery B' flowing through these coils of 
the home relay strengthens the left-hand pole and weakens 
the right so that sounder S does not operate. At the other 
station more current traverses the coils /, /i than the coils 



DUPLEX TELEGRAPHY 59 

e, e\ and consequently the left-hand pole of relay P f is 
strengthened and the other is weakened, so that sounder S f 
is not operated until the armatures of the distant pole- 
changer touch their front contacts. Conversely, sounder 
S' will release its armature at the instant when armatures 
x and y leave their front contacts. Again, assume that key 
K is held down, as in Fig. 10, which means that the relay 
armatures of P and P' are respectively on their left and 
right contact studs, and that sounder 5" is actuated. If 
now key K f is also depressed the pole-changer C' operates, 
and its armatures will be drawn toward their front stops. 
Consider the instant when these armatures are in their 
intermediate positions, touching neither contacts. The 
battery B f is then completely isolated, and the only path 
for the line current at station B is through all four coils 
of relay P' and through the artificial line to ground at G '. 
The current supplied by battery B enters the relay P at 
junction y and divides between the line and artificial line 
coils. The current through the coils of relay P' keeps the 
right-hand pole magnetized stronger than the left so that 
sounder S f will remain actuated. At the other station 
more current flows through the coils b and b\ than through 
the others, and is in such direction as to magnetize the 
right-hand pole stronger than the left and consequently 
the sounder S will operate as soon as the armatures x' and 
y' leave their rear contacts. Conversely, sounder 5 will 
remain actuated until these armatures again touch their 
rear contacts. Thus false signals can hardly ensue with 
the polar duplex if properly balanced. 

A polar duplex circuit is balanced in practice by first 
adjusting the polarized relays, with all current cut off, so 
that the armatures will move with equal force from their 



60 TELEGRAPH ENGINEERING 

intermediate positions to either stop and remain there. 
Then connect the relays in circuit. At one station alter- 
nately depress and release the key while varying the re- 
sistance of the artificial line until such manipulation of the 
key does not alter the behavior of the home relay. The 
capacity of the artificial line is adjusted by first moving 
back that magnet pole piece which is on the side away 
from the local circuit contact, and then, starting with all 
the condensers in circuit, gradually diminish the capacity 
and alter the resistances in series with the condensers, 
while depressing and releasing the key at intervals, until 
the relay armature will not kick with every movement of 
the key. This adjustment signifies that the current grows 
and decays simultaneously in both relay windings. Then 
restore the pole piece to its proper position, and the balance 
is complete. The other station is adjusted similarly. 

A single-armature pole-changer, such as illustrated in 
Fig. n, is extensively used with duplex telegraph circuits 




Fig. ii. 

when operated by generators. The armature moves be- 
tween two contacts, one being connected to the positive 
terminal of one generator and the other contact to the 
negative terminal of another similar generator, the two 



DUPLEX TELEGRAPHY 



6l 



other generator terminals being grounded as shown in 
Fig. 12. Another generator supplies current to the local 
pole-changer circuit. The same generators may furnish 




Fig. 12. 

current to other duplex circuits, by connecting these cir- 
cuits, each with protective fuses, /, /, /, to the positive and 
negative bus-bars. 

This figure shows the transmitting arrangement used by 
the Postal Telegraph-Cable Company. At the instant of 
transferring contact from one stud to the other a spark is 
produced and drawn across the air gap, thereby bridging 
the two 2oo-volt generators through the 3oo-ohm protec- 
tive resistances. These resistances (usually in lamp form) 
protect the machines in cases of accidental short-circuit. 
This spark is effectively quenched by the provision of a 
discharge path to ground through a ^-microfarad con- 
denser, for each machine, as shown. Three-hundred ohm 
or 6oo-ohm protective resistances are usually connected in 
series with the generators. 

In order to find the current strength in the various por- 
tions of a polar duplex circuit let R p , R b , Rl and r be re- 
spectively the resistances of the polarized relays, battery or 
protective resistance in series with generator, perfectly in- 



62 TELEGRAPH ENGINEERING 

sulated line, and artificial line, let 7, 7i and 7 2 be respectively 
the current supplied by each battery or generator, current 
in artificial line and current in line wire, and let E be the 
voltage of each battery or generator. Then, when both 
keys are open or both closed 

p 
I = I\ = = - and 7 2 = o; (4) 



2 

when one key is closed 

E-RJ 2 (E - RJ) 



,. 

2, (5) 



2 



E (2 R p + Rl + 2 r) 
whence 7 = - 

4- 



In order to have 7 2 twice as great as I\, the artificial lines 

p 
should have a resistance of r = 2 + -K/. 

2 

Where only generators of higher voltage are in service, 
as necessary for the operation of long quadruplex telegraph 
circuits (see next chapter), the potential may be reduced 
to values sufficient for duplex operation by the intro- 
duction of a leakage path to ground. The connections of 
one station of such a leak duplex circuit, as used by the 
Postal Telegraph-Cable Company, are shown in Fig. 13. 
Fourteen-hundred-ohm resistances are in series with the 
generators, and 22oo-ohm shunt or leak paths are provided 
to ground. The difference of potential between the point 



y and ground does not exceed - - X 380 or 233 

1400 + 2200 

volts and this occurs when the armature is midway between 



DUPLEX TELEGRAPHY 



the pole-changer contacts. Assuming that each winding of 
the polarized relay has a resistance of 150 ohms and that 




the artificial line has a resistance of 1700 ohms, this poten- 
tial difference would fall to 



380 1400 



380 



or 159 volts, 



1400 



(1700 + 15) 22QQ 

22OO + I7OO + 150 

when the armature makes contact so that no current flows 
over the line. In this way the voltages available at the 
pole-changer contacts are rendered materially less than the 
terminal voltages of the generators. 

6. Improved Polar Duplex. The arrangement of the 
improved polar duplex circuit due to Davis and Eaves and 
now employed by the Postal Telegraph Company is shown 
in Fig. 14. The principle of operation is identical with 
that already described in connection with Fig. 10, and it 
will be observed that the transmitting arrangement used 
is that of Fig. 12. The additional features of this duplex 
circuit are the resistances g, h, j, k, I and m and the con- 
densers c, c f , Ci and c^ the functions of which will be ex- 
plained presently. 

It was pointed out in the last section in describing the 
polar duplex circuit, that with the home key open, (i) the 



TELEGRAPH ENGINEERING 



home sounder is not operated until the distant pole-changer 
armature touches its front contact and (2) that it will 
cease to operate at the instant this armature leaves this 
front contact. Also, that with the home key closed, 
(3) the home sounder will operate as soon as the distant 
pole-changer armature leaves its rear contact and (4) will 
remain actuated until this armature again touches its rear 
contact. Thus, conditions 2 and 3 permit of faster trans- 
mission of signals than the others. The introduction of 
the non-inductive resistances g, h, j and k, each of 500- 
ohms resistance and the 12 -microfarad condensers c and c f 





Fig. 14. 

is for the purpose of quickening transmission for the slow 
conditions (i) and (4). 

When both keys are open the negative generator termi- 
nals touch armatures y and y f of the pole-changers and no 
current traverses the line, line coils of both relays, or re- 
sistances g and j. Currents, however, flow from the gen- 
erators to v ground, through the artificial lines, lower relay 
windings and resistances h and k back to their respective 
generators. As a consequence the condensers c and c' will 
be charged respectively to the potential differences exist- 
ing across the resistances h and &, the plates w and z being 
charged positively. If, now, key K is depressed, the 
armature y of pole-changer C travels from the rear to the 
front contact. In its intermediate position, the armature 



DUPLEX TELEGRAPHY 65 

isolates the generators D. A current 'now flows from the 
generator D f to ground, through the left-hand artificial line, 
relay P, resistances h and g, line, upper coils of relay P' and 
resistance j back to the generator; and this current is 
about one-half that which flows from the same generator 
through the right-hand artificial line, lower coils of relay 
P r and resistance k back to the generator. The charge on 
condenser c remains practically unchanged because its 
potential difference, that across coils g and h, is due to a 
current of approximately half the initial strength though 
double the initial resistance. This condenser will produce 
no appreciable discharge. 

At the other station, however, the potential difference of 
condenser c' is now that across coil k minus that across 
coil 7, and is therefore approximately half that possessed 
before and in the same sense. This condenser will then 
discharge partially and a current pulse flows from q through 
the lower coils of relay P', both artificial lines, relay P, 
resistances g and h, line, upper coils of relay P f to the other 
condenser terminal at p. This current does not affect the 
relay P, but it does tend to operate the relay P' momen- 
tarily. This discharge current through all coils of P' is in 
the same direction as that which will flow through its 
upper coils when the pole-changer armature y reaches the 
front contact. Thus the condenser discharge begins the 
operation of the home relay at the instant the distant 
pole-changer armature leaves the rear contact, and this 
operation is completed by the generators as this armature 
reaches its front contact. The improvement for the fourth 
condition can be traced similarly. 

The function of the four 6oo-ohm non-inductive resist- 
ances /, /', m and m' ', with the four i-microfarad condensers 



66 



TELEGRAPH ENGINEERING 



Ci> Ci, 2 and 2', shunted around the relays is to provide an 
auxiliary path to ground, for inductive 'disturbances from 
neighboring telegraph, telephone or high-tension transmis- 
sion lines, which does not include the relay windings, thereby 
eliminating such interference with the operation of the 
duplex circuit. The shunt circuits offer a further advantage 
in that the first portion of the current pulse for each 
signal over this home shunt path reaches the other end of 
the line a little in advance of the current which passes 
through the home relay windings. This action assists in 
attaining a high signalling speed. 

7. Short-line Duplex. The circuit of the Morris 
duplex, which system is successfully employed by the 
Western Union Telegraph Company on many short lines, 
is shown in Fig. 15. It utilizes a neutral relay at one sta- 




Fig. 15. 

tion and a polarized relay at the other, and employs main- 
line generators at one station only. The artificial line has 
a resistance equal to the resistance from the point x to 
ground at G '. The resistance of the compensating rheo- 
stat r\ is adjusted so that three times as much current flows 
through the line when the key K' is depressed as when K f 
is open. These conditions are: 

r = SI + R r + r lt (7) 



DUPLEX TELEGRAPHY 67 



where R p and .R r are the resistances of the polarized and 
differential neutral relays respectively, R^ is the resistance 
in series with the generator, RL is the resistance of the 
assumedly perfectly-insulated line and r is the resistance 
of the artificial line. Thus, if Rl = 1000 ohms, R b = 300 
ohms, R r = 200 ohms and R p = 400 ohms, then 

r = ri + 1400, 

600 (200 -f 2 r) 
ri= 800+ ,r 

whence r = 4966 ohms and r\ = 3566 ohms. 

The function of the repeating sounder RS is to eliminate 
false signals when key K is depressed while the other key 
is held down. The reversal in magnetization of relay R 
takes place quickly and before its armature has an oppor- 
tunity to fall back to its rear contact and open the circuit 
of sounder S. In view of the foregoing descriptions, the 
operation of this duplex system may be readily understood 
without further comment, by tracing the conditions when 
no keys, either of the two keys, and both keys are depressed. 

8. The Bridge Duplex. The form of the bridge duplex 
circuit resembles that of the Wheats tone bridge, in having 
four arms with the home receiving instrument connected 
across opposite arm junctions, as shown in Fig. 16. For 
the station A the bridge arms are: winding a of the re- 
tardation coil /, line xy plus the paths from y to ground at 
the right-hand station, artificial line A LI, and the winding b 
of the same retardation coil. The arrangement for station 
B is identically the same. The simple polarized relays are 



68 



TELEGRAPH ENGINEERING 



connected across the junctions x, w and y, z. The artificial 
line at each station is adjusted to equal the resistance of 
the line and the apparatus at the distant station, and the 
resistances of the two coils of each retardation coil are equal. 
When both keys are idle, the armatures of the pole- 
changers C and C' rest against their rear stops which are 
joined to the positive generator terminals, and therefore 
no current traverses the line wire. At station A a current 
divides at the point m, one part traversing winding a and 
relay P, and the other part traversing winding bj both 




Fig. 16. 

currents then combining at the point w to flow through the 
artificial line A LI to ground and back to the other generator 
terminal; while at station B, a current divides at the 
point n, one part traversing winding c and relay P' ', and 
the other part traversing winding d, both currents then 
combining at the point z to flow through the artificial line 
ALz to ground and back to the other generator terminal. 
It will be observed that the direction of the currents through 
the two relays is such that the relay armatures touch their 
idle contacts and therefore do not close tjie local sounder 
circuits, as indicated in the figure. 

When the key K is depressed, the armature of pole- 
changer C touches the negative generator terminal, and 
consequently more current flows over the line than through 
either artificial line, and this current flows from y to x. 



DUPLEX TELEGRAPHY 69 

The line current entering at the point y is made up of the 
current coming through the coil c and that coming from z 
through the relay P f . The direction of this current is 
such that the right-hand pole of the relay will be more 
strongly magnetized than the left and consequently its 
armature closes the sounder circuit. At station A the 
arriving current divides at the point x, and that part 
which traverses the relay P is in such direction as to mag- 
netize the left-hand pole more strongly than the right, so 
that this relay will not close the sounder circuit. Thus, 
the depression of one key controls the operation of the 
distant relay and sounder. 

If both keys are closed, both pole-changer armatures 
will be in contact with the negative generator terminals, 
and again no current will flow over the line. Currents will 
now flow through relay P' from z to y, and through relay 
P from w to x, and their direction is such as to magnetize 
the right-hand poles stronger than the others and con- 
sequently the relay armatures will close both sounder cir- 
cuits. Although each relay is caused to operate by its 
home battery, yet its action is controlled entirely by the 
distant key. 

It will be noted that each receiving instrument is always 
shunted, so that only a part of the generator current can 
flow through the relay. The magnitudes of the currents 
in the various paths can best be compared by means of a 
numerical illustration. 

Using 8oo-ohm polarized relays, 3oo-ohm resistances in 
series with each generator, and retardation coils with 500 
ohms resistance per winding, at the ends of a i poo-ohm 
perfectly-insulated line, requires that the artificial lines be 
adjusted to have a resistance of 2500 ohms. The joint re- 



70 TELEGRAPH ENGINEERING 

sistance of the paths from the points x or y to ground at 
the corresponding station is then 600 ohms (calculated 
according to equation (9) following); thus the resistances 
of the artificial lines are correct, viz. 1900 + 600 = 2500 
ohms. The steady currents, in milliamperes, flowing 
through these paths for various sending conditions with 
1 50- volt generators, are given in the following table, and 
their directions are indicated by + and in connection 

a = 600 Rl = 1900 C = 500 




ffcov. 



Fig. 17- 

with the scheme of Fig. 17, the + sign signifying a cur- 
rent flowing upwards or toward the right, while denotes 
a current flowing downwards or toward the left. The stars 
represent the operation of relays. 

CURRENTS IN BRIDGE DUPLEX CIRCUIT 





3 






ft, 








fc 






a? 


Condition 


'a) 


s 


g 


I 


^ 


O 

c 


^ 


1 

a 








1 




ft 




















$ 


Neither key depressed 


+48 


+13 


+35 


-13 


-48 





-48 


-13 


-13 


-35 


+48 


Key K depressed 


120 


71 


49 


13 


_j_ ^ 


-81 


-tf 


+n* 


71 


49 


+120 


Key K' depressed 


+120 


+71 


+ 10 


+13* 


36 


+81 




13 


+ 7 T 


+ 10 


I2O 


Both keys depressed . ... 


- 4 8 


-13 


-35 


+13* 


+48 





+48 


+13* 


+13 


+35 


-48 





fBy equation (80) of Chap. X. 



DUPLEX TELEGRAPHY 71 

The resistance of the terminal apparatus when a = b is 
calculated from the equation 

R _ aP (2 R b + g) + RbAL (2 a + P) + all (a + P) , , 



which is obtained by an application of Kirchhoff's laws. 
Since, for a perfectly insulated line 

AL = Ro + Rl, 

by combining with equation (9) there results that the 
proper resistance of the artificial line should be 



where p _*( + 2*) 



The bridge-duplex arrangement used by the Western 
Union Telegraph Company embodies various improve- 
ments on the system described, and will now be considered. 

The retardation coil comprises two 5oo-ohm coils wound 
upon a circular core of rectangular cross-section, made up 
of soft iron wires. The core has an inside diameter of 3! 
inches, an outside diameter of 5! inches, and is if inches 
wide; it is composed of about 6000 turns of No. 26 B. & S. 
annealed iron wire. Each winding has 7900 turns of No. 29 
B. & S. double-cotton-covered copper wire and has a re- 
sistance of about 400 ohms. Its resistance is brought up 
to 500 ohms by adding approximately no turns of No. 28 
german silver wire wound back on themselves, to render 
this compensating winding non-inductive. 

Each 5oo-ohm coil possesses considerable inductance, 
and consequently a current coming over the line wire meets 
at first with great opposition in traversing the retardation 



72 TELEGRAPH ENGINEERING 

coil, because of the counter electromotive force of self-in- 
duction which is developed in it. This electromotive force 
is in such direction as to assist in the rapid growth of cur- 
rent in the polar relay to a value momentarily greater 
than the steady value. This initial pulse of current 
through the relay causes its armature to be moved from 
stop to stop with great rapidity. The retardation coils do 
not hinder outgoing currents very much because differing 
currents pass through the two windings of the coils differ- 
entially, and the magnetism developed in the core by one 
winding is neutralized to some extent by that developed 
by the other, and hence the coils for this condition are less 
inductive than before. 

In order that the speed of pole-changer armatures shall 
be. high, two series-connected electromagnets are provided 
on each instrument, one on either side of the armature. 
The iron cores of the front magnet are laminated while 
those of the rear magnet are solid and surrounded by 
copper sleeves, thereby causing the magnetism to be es- 
tablished much more rapidly in the front than in the rear 
magnets. Light retractile springs hold the armatures 
against their back contacts when the keys are elevated. 
When the key is depressed, current flows through both 
pole-changer electromagnets, but the armature is drawn 
toward the front contact because sufficient attraction is 
first exerted by the front magnet. As the armature is 
now further from the rear magnet, subsequent full magneti- 
zation of this magnet cannot cause its return. However, 
when the key is released, the rear magnet retains its mag- 
netism much longer than the other, and consequently the 
armature is brought over to its rear contact far more 
rapidly than if the spring alone were acting. For 26-volt 



DUPLEX TELEGRAPHY 73 

local-circuit operation each electromagnet has a resistance 
of 4 ohms, while for 52-volt operation each has 13 ohms 
resistance. 

A milliammeter, reading to 50 milliamperes in either 
direction, is placed in series with the polarized relays to 
measure the current flowing and to facilitate line balancing. 
When the artificial line resistance and capacity are so ad- 
justed that the milliammeter needle is practically unaffected 
by the manipulation of the home key, a good working 
balance is established. 

For increasing the resistance of short lines for operation 
at the voltages usually employed in duplex signalling, a 
line-resistance box is used at each station. It contains 
two separate and identical sets of resistances (five 25o-ohm 
resistances in each set) simultaneously adjustable by means 
of a double lever. These resistances are interposed in the 
real and artificial lines at the points w, x, y and z, Fig. 16. 
The variation of each line resistance, requires an adjust- 
ment of the distant artificial line. The insertion of this re- 
sistance, which is almost perfectly insulated from ground, 
in the line circuit during wet weather, raises the apparent 
insulation of the whole line, that is the insulation resist- 
ance per ohm of line is greater than before. 

The method of quenching the sparks produced at the 
pole-changer contacts is similar to that shown in Fig. 12, 
but the ground connection at the point x is replaced by a 
2o-ohm resistance lamp connected in series with the con- 
densers; or a single \ mf. condenser may be used instead 
of the two J mf. series-connected condensers. In practice 
non -ad jus table i mf. condensers are also connected to the 
points m and n of Fig. 16, their other terminals being 
grounded. 



74 



TELEGRAPH ENGINEERING 



9. Advantage of Double-current Duplex Systems. It 
has been stated that the differential or single-current 
duplex is infrequently used because of the superiority in 
practice of the polar- and bridge-duplex systems, these 
latter being called double-current duplexes. Considerable 
difficulty is experienced in maintaining operation over 
single-current duplex lines when the weather is unfavor- 
able, because the line insulation is poor. That this is the 
case can be seen from the following illustration. 

In 2 a 474-mile, 2ooo-ohm differential duplex line with 
two 2oo-ohm relays was considered. A 2oo-volt gravity 
battery having an internal resistance of 250 ohms and a 
23 2 7 -ohm artificial line was employed at each end. The 



2827 





Fig. 18. 

table in that section shows the current strengths in the 
relay coils when the line is perfectly insulated. If the in- 
sulation resistance should fall to i megohm per mile, and 
considering the distributed leakage to be concentrated at 
the middle of the line, the conditions are representable by 
Fig. 18. 

It can readily be verified that the currents then travers- 
ing the relay coils, under otherwise identical conditions, 
will be as shown in the following table. The figures fol- 
lowing the braces give the equivalent currents through one 
relay coil. 



DUPLEX TELEGRAPHY 



75 



CURRENTS IN NEUTRAL RELAY COILS, EXPRESSED IN 
MILLIAMPERES 



Relay 

R 


Coil 


Neither 
key de- 
pressed 


Key K only 
depressed 


Both keys 
depressed 


Key K' only 
depressed 


a 
b 


:l 


SH 


III- 


Jfsr 


R f 


a' 
b' 


:} 


5 sl" 


Z\* 


SH 



To assure satisfactory operation under these conditions the 
relays must be adjusted so that they will not operate on 
18 milliamperes through one coil, but will operate on 40 
milliamperes. For longer lines or for poorer insulation this 
margin of 22 milliamperes will be reduced and operation 
rendered unsatisfactory. 

Consider a polar duplex line to have the same constants. 
When this line is perfectly insulated, the currents travers- 
ing the relay coils are as tabulated below, the values being 
computed in accordance with equations (4), (5) and (6). 

CURRENTS IN POLARIZED RELAY COILS, EXPRESSED IN 
MILLIAMPERES 



Relay 


Coil 


Both keys 
raised or de- 
pressed 


One key only 
depressed 


R 


a 
b 


7 Sh 


ih 


R' 


a' 
b' 


nfr 


} 



When the line is poorly insulated, and the multitude of 
leakage paths be considered grouped at the middle point q 
of the line, and one key be depressed, this point q, being 
midway between + 200 and 200 volts, will be at zero 
potential with respect to ground, and consequently leak- 



7 6 



TELEGRAPH ENGINEERING 



age will cause no alteration in current distribution, and the 
current values in the last column still apply. The follow- 
ing table shows the currents then traversing the relay 
windings for all key positions. A margin of at least 40 

CURRENTS IN POLARIZED RELAY COILS, EXPRESSED IN 
MILLIAMPERES 



Relay 


Coil 


Both keys 
raised or de- 
pressed 


One key only 
depressed 


R 


a 
b 


Sir 


wf 


R' 


a' 

b' 


f> 


"El" 



milliamperes is effective for operating the relays. Of course, 
if these leakage paths were considered uniformly distrib- 
uted along the line, the tabulated values would be altered 
somewhat, but it is clear that the double-current duplex 
systems are not as sensitive to weather variations as is the 
single-current system and consequently excel it in operation. 

10. Duplex Repeaters. Duplex repeaters are not as 
complicated in theory as simplex repeaters, for it is only 
necessary to connect the magnet of the pole-changer that 
controls one circuit with the contact points of the receiving 
relay of another line. A still simpler arrangement, dis- 
pensing with pole-changers, and called a direct-point re- 
peater, is widely used. 

Polar Direct-point Repeater. The schematic diagram 
of the polar direct-point repeater is given in Fig. 19. The 
repeating station is equipped with four generators, D\ and 
A, two differentially-wound polarized relays, P\ and P 2 , 
and two artificial lines. The elements of the originating 
and receiving stations A and B are also shown. When 
both keys K and K' are elevated they rest on the rear con- 



DUPLEX TELEGRAPHY 



77 



tacts which are connected to the negative generator termi- 
nals. For this condition all four relay armatures will rest 
against their left contacts, as indicated in the figure. The 
armatures of repeater relays PI and P 2 will be against the 
negative contacts of generators D\ and Z> 2 , no current will 
flow over either line wire, and sounders S and S' will not 
be actuated. 

The depression of key K causes a greater current to flow 
over the western line and line coils of relays P and PI 
than through their artificial line coils, and its direction 
will be such as to move only the armature of relay PI to 
the right, thereby touching the positive generator termi- 




Fig. 19. 

nal .of DI. A greater current will then flow over the 
eastern line and line coils of relays P 2 and P' than through 
their artificial line coils, and its direction is such as to 
move only the armature of relay P' ', which then closes the 
local sounder circuit. Thus key K controls the operation 
of repeater relay PI, of relay P' and of sounder 5" at the 
remote station. In the same way key K' controls the 
operation of repeater relay P 2 , relay P and sounder S. 

When both keys are depressed it will be seen that all 
relay armatures press against their right-hand contacts, no 
current flows over either line, and both sounders are oper- 
ated. Thus messages being transmitted in opposite direc- 



78 TELEGRAPH ENGINEERING 

tions over a single wire are simultaneously repeated without 
interference. 

Fig. 20 shows the connections of the direct-point duplex 
repeater used by the Postal Telegraph-Cable Company. 
The principle of operation is identical with that just de- 
scribed, but there are several additional features. For the 
operation of reading sounders Sz and S^ at the repeating 
station, the leak relays LI and LZ in series with 2o,ooo-ohm 




Fig. 20. 

resistances r, r (shunted by i-mf. condensers) are bridged 
from ground to the armatures of the repeater relays PI 
and PZ- The transmission of signals from one station to 
the other through the repeater for the various positions of 
the keys can readily be traced, the pole-changers C and C r 
remaining in the positions shown. 

This repeater arrangement permits of separation, by 
the upward movement of the switches a and a', into two 
polar-duplex sets. Thus duplex signalling may be effected 
between the left-hand station and the repeater station by 
manipulating the key K\ and the distant key, and also 
distinct duplex signalling may be carried on between the 



DUPLEX TELEGRAPHY 



79 



repeater station and the right-hand station by manipulat- 
ing the key K 2 and the distant key. These sets differ from 
those described in connection with Figs. 10 and 12 only in 
the introduction of the leak relays. The unmarked coils 
are 3Ooohm protective resistances. 

Bridge Direct- point Repeater. The arrangement of the 
repeater used with the bridge duplex by the Western 
Union Telegraph Company is shown in Fig. 21. The in- 
strument positions represented are for the normal con- 
dition, that is, no signals being sent in either direction, 
the positive generator terminals being connected to the 




Fig. 21. 

line at both stations. Reference to the explanation of the 
bridge duplex and Fig. 16 will indicate that the armatures 
of the two repeater relays PI and P% and Consequently 
those of the leak relays LI and L% rest against their left- 
hand contacts. Further, no current traverses the two 
line wires, and the two reading sounders 63 and S 4 at the 
repeating station are not actuated. 

When the key at the western station is depressed, 
thereby bringing the line in contact with the negative 
terminal of the home generator, current will flow through 
the repeater relay PI from the point x to y, and conse- 
quently its armature will be drawn over to the right. 



80 TELEGRAPH ENGINEERING 

This will cause the operation of sounder 5 3 through the 
leak relay LI, and the negative generator terminal will be 
in contact with the junction n of the right-hand retardation 
coil. Current will then flow over the eastern line and 
through the relay P% from the point y' to x' so that the 
armatures of relays P% and Z^ will remain as shown. The 
eastern line current is in such direction as to operate the 
polarized relay and sounder at the eastern station (see 8). 

The depression of both keys will cause all armatures to 
rest against their right-hand contacts, thereby actuating 
the sounders Sz and ,4 and also the sounders at the termi- 
nal stations. 

When the double-throw triple-pole switches a and b are 
moved to the left, the repeater is separated into two dis- 
tinct bridge-duplex sets that differ from that already de- 
scribed only in the addition of the leak relays. It can be 
seen, then, that the western and repeating stations and 
that the repeating and eastern stations can engage in 
separate duplex signalling, both the repeater and leak re- 
lays being in use in this divided service. The resistances 
r are adjustable to have the following values: 8,000, 12,000, 
16,000 and 20,000 ohms. 

ii. Half-set Repeaters. Where it is found desirable to 
join a duplex line with a simplex line for through simplex 
operation in either direction, a half-set repeater is used. 
One-half of the apparatus necessary for a simplex repeater 
of any type will serve as a half-set repeater. 

The connections oi a Weiny-Phillips half-set repeater 
joined between a simplex line and a polar-duplex circuit 
are shown in Fig. 22. The repeater apparatus is shown 
between the two broken lines, while the simplex and 



DUPLEX TELEGRAPHY 



8l 



duplex receiving apparatus are shown respectively on the 
left and right sides as A and B. This apparatus is usually 
interconnected at a switchboard by means of flexible 
double-conductor cords equipped with plugs or wedges 
which fit into appropriate jacks, these cords being repre- 
sented, for the sake of simplicity, by dotted lines. 

The operation of the repeater transmitter T is con- 
trolled by the armature of the polarized relay P, and the 
operation of the pole-changer C is controlled by the arma- 
ture of the repeater relay Ri. The function of the differ- 



(S) 




Fig. 22. 

ential holding coil H of the Weiny-Phillips relay has been 
explained in 10 of Chap. I. 

In the normal condition, when the distant keys on both 
lines are depressed (or circuit-closers closed) current flows 
over the simplex line, distant relay and relays R and RI, 
and the duplex line will be in contact with the negative 
generator terminal. The armature of relay P will rest 
against the right-hand contact regardless of the position of 
the armature of the pole-changer C (because the distant 
pole-changer makes contact with the negative generator 
terminal), and consequently the armatures of sounder $3 
and of transmitter T will be attracted. Equal and oppos- 



82 TELEGRAPH ENGINEERING 

ing currents traverse the windings of the holding coil H 
so that its core is not magnetized; nevertheless the arma- 
ture of the repeater relay will be attracted owing to the 
current in the main coil RI. The attraction of this arma- 
ture closes the magnet circuit of pole-changer C and its 
armature places the negative generator terminal in con- 
tact with the junction m of the relay windings. This 
action does not affect relay P, but the distant polarized 
relay on the duplex line responds and operates its local 
sounder. 

When the key at the distant office on the simplex line 
is raised, no current flows through this line and relays R and 
RI, and, therefore, their armatures will be released. The 
armature of the repeater relay opens the circuit of the 
pole-changer magnet which causes the positive battery 
terminal to be placed on the junction m. The relay P 
will not be affected, but the distant relay on the duplex 
line will open the home sounder circuit. In this way 
signals formed by the key on the simplex line are repeated 
to a distant station on a duplex line. 

If, instead, the distant key on the duplex line be raised, 
the armature of relay P will be drawn over to the left- 
hand side, causing the magnet of transmitter T to be de- 
energized. This action opens the simplex line at x, and 
consequently the distant sounder on the simplex line re- 
leases its armature. Although no current flows through 
the relay RI the magnetism developed in the core of the 
holding coil H by current in one of its coils is sufficient to 
hold over the armature, which action keeps the distant 
sounder on the duplex line energized. When the key at 
the remote end of the duplex line is again depressed, the 
armature of relay P is drawn to the sounder contact and 



DUPLEX TELEGRAPHY 83 

the armature of the transmitter is again attracted, thereby 
closing the simplex line at the repeating station. Thus 
the composite circuit operates as a closed-circuit simplex 
line. 

Some important duplex circuits are operated simplex 
through half-set repeaters by current reversals instead of 
ordinary Morse simplex operation, because of higher speed 
possibilities and lesser dependence upon weather con- 
ditions. The Associated Press leased wire is operated in 
this way, the signalling being carried out by mecograph 
transmitters. 

PROBLEMS. 

1. A perfectly-insulated differential duplex line has a resistance of 
1500 ohms and is equipped with a i4o-ohm differential relay at 
each end. If the battery resistance is 200 ohms, calculate the proper 
resistance of the artificial lines. 

2. When one key of the circuit of Prob. i is closed, thereby in- 
troducing a 1 60- volt battery, how much current flows through the 
line and through each artificial line ? 

3. A 2000-ohm polar-duplex line has a 3oo-ohm polarized relay, 
and a 2644-ohm artificial line at each end. Using 6oo-ohm re- 
sistances in series with the 2oo-volt generators, determine the current 
strength in each relay coil for the various positions of the signalling 
keys. 

4. If the line of the preceding problem be operated on 380 volts 
as a leak duplex with 22oo-ohm leak paths, compute the current 
strengths in the relay coils when one key is depressed and when both 
keys are either raised or depressed. 

5. A Morris duplex line, having 800 ohms resistance, employs a 
3oo-ohm polarized relay at one end and a i4o-ohm differential neutral 
relay at the other end. Using 6oo-ohm protective resistances in 
series with the generators, determine the proper resistance values of 
the artificial line and compensating rheostat. 

6. Derive equation (9) for the terminal resistance of a bridge- 
duplex circuit. 



84 TELEGRAPH ENGINEERING 

7. What should be the resistance of the artificial lines used with 
a perfectly-insulated bridge-duplex circuit having a looo-ohm line, 
when using 6oo-ohm polarized relays, 2oo-ohm protective resistances 
and 5oo-ohm (each winding) retardation coils? 

8. If in unfavorable weather conditions the line of Probs. i and 2 
has a total leakage resistance to ground of 1500 ohms, considered 
concentrated at the mid-point of the line, determine the relay ad- 
justment that will cause satisfactory operation. 



CHAPTER III 

QUADRUPLEX TELEGRAPHY 

i. Quadruplex Systems. A quadruplex telegraph sys- 
tem provides for the simultaneous transmission of two 
groups of signals in one direction and also two groups of 
signals in the opposite direction without interference over 
a single telegraph line. When in full use, eight operators 
are required for each quadruplex circuit, two receiving 
and two sending operators being located at each terminal 
station. Quadruplex signalling was devised by Thomas 
A. Edison, and was first placed in operation in 1874 by the 
Western Union Telegraph Company. It is now employed 
on many lines over distances up to 500 miles. 

Quadruplex systems are generally based on a combi- 
nation at each station of the single-current and double- 
current duplex systems, which have been described in the 
foregoing chapter. The single-current, or Stearns duplex, 
permits of the simultaneous transmission of one message 
in each direction through changes in current intensity, and 
the double-current system, either the polar or bridge 
duplex, permits of the simultaneous transmission of one 
message in each direction through changes in current 
direction. When these duplex systems are combined to 
form a quadruplex circuit, the latter is called the polar 
side, or first side, of the system, and the former is called the 
neutral side, or second side, of the system. 

The manner in which these systems are combined is 

85 



86 TELEGRAPH ENGINEERING 

illustrated in Fig. i, which shows one station A equipped 
with apparatus only for sending and the other station B 
equipped with apparatus only for receiving messages. 
This circuit permits of the simultaneous transmission of 
two independent messages over one wire in the same 
direction, which transmission is called diplex signalling. 
Key K is a form of continuity-preserving pole-changer, 
which, when depressed, causes its lever contact a to raise 
the upper spring u away from the fixed contact b, and per- 
mits the lower spring / to follow until it strikes against this 
fixed contact. The key K f is a transmitter which changes 
the number of cells of the battery B which is included in 




Fig. i. 

the circuit. Both keys are normally held in their upper 
positions by retractile springs. Relay R is a neutral relay 
which has its spring so adjusted that the armature will not 
be attracted when the small current, supplied by the left- 
hand part, or short end, of the battery traverses the relay 
winding, but will be attracted when supplied with current 
from the entire, or long end, of the battery. Instantaneous 
reversal of current direction has no effect upon this relay 
(see 3). The polarized relay P responds only to cur- 
rent reversals and is not influenced by changes in current 
intensity, so long as this intensity exceeds 3 to 5 milli- 
amperes. 
When neither key is depressed the short end of the 



QUADRUPLEX TELEGRAPHY 87 

battery is in circuit and key contacts a and b are re- 
spectively connected to the negative and positive battery 
terminals. It will be seen that the current then flowing is 
not strong enough to operate the neutral relay R and is 
in the wrong direction to operate the polarized relay P. 
When key K is depressed (as shown in the figure) the cur- 
rent flowing is not altered in intensity, but is reversed in 
direction, and consequently relay P responds and causes 
the actuation of its sounder 6*2 through the local battery 
B f . When key K' is also depressed the direction of current 
flow remains unaltered but its intensity is now sufficient to 
operate neutral relay R, which in turn operates sounder Si. 
Thus, pole-changing key K controls the polarized relay, 
and the transmitting key K' independently controls the 
neutral relay, thereby enabling the simultaneous trans- 
mission of two messages from one station to another over 
a single wire. 

2. Operation of Quadruplex Systems. By duplicating 
the apparatus necessary for the diplex circuit just de- 
scribed and employing differentially-wound relays and an 
artificial line at each end of the line wire, as in the duplex 
systems, it is possible to send two messages in each direc- 
tion at the same time, thereby affording quadruplex tele- 
graphic signalling. Such a quadruplex circuit extending 
between two stations A and B, and operated by batteries, 
is shown in Fig. 2. It will be observed that the pole- 
changers C and C' are electromagnetically controlled by the 
keys K and K'j and that the transmitters T and T are 
similarly controlled by the keys K\ and K z . The short 
ends of the main batteries B and B f are connected in circuit 
when the keys KI and K 2 are open, and the entire batteries 



88 



TELEGRAPH ENGINEERING 



are in circuit when these keys are depressed. The figure 
shows the long-end battery to have three times as many cells 
as the short-end battery. The positive and negative ter- 
minals of these batteries are connected to the line junctions 
x, y, when the keys K and K' are raised and depressed 
respectively. 

The figure represents the condition when the circuit is idle, 
all four keys being in the raised position. In this condition 
the positive terminals of the short ends of both main-line 
batteries are joined to the junctions x and y, consequently no 
current flows through the line coils of all relays nor through 
the line wire. A current will flow, however, from each 




Fig. 2. 

main battery through the artificial line coils of both re- 
lays, through the artificial line, and back to the other 
battery terminal. These currents are too weak to oper- 
ate the neutral relays R and R', and they are in the wrong 
direction to operate the polarized relays P and P'. Con- 
sequently the armatures of all sounders, S, S', Si and 62, 
will remain drawn up by their retractile springs. 

When key K is depressed the armatures of pole-changer 
C will be attracted and the negative terminal of the home 



QUADRUPLEX TELEGRAPHY 89 

battery will be connected to the junction x, and the posi- 
tive terminal will be grounded. The main-line batteries 
are now cumulatively connected, and more current traverses 
the line and line coils of all relays than flows through the 
artificial lines and artificial line coils of these relays. For 
ease in presentation, let the current traversing the artificial 
lines be considered of unit intensity, and let the adjust- 
ment of these lines be such that the current in the line 
wire when either key K or K' only is depressed be 2 
units. Currents, then, of i unit intensity flow through 
the artificial line coils of all relays, and opposing currents 
of 2 units intensity flow through their line coils. The 
surplus of i unit current through all the line coils of the 
relays is insufficient to actuate the neutral relays R and 
R'\ it is in the proper direction to operate polarized relay 
P', but is in the wrong direction to operate polarized re- 
lay P. In the same way, the depression of key K f only 
causes the operation of relay P. Thus the depression of 
a pole-changing key causes the operation of the distant 
polarized relay and the actuation of the sounder con- 
trolled by it. 

The depression of both pole-changing keys places the nega- 
tive battery terminals to the junctions x and y, and, since 
the two identical main-line batteries are opposed to each 
other, no current flows over the line wire. Currents of 
unit intensity flow through the artificial line coils of all 
relays, and, as before, are too weak to operate the neutral 
relays R and R' . The direction of these currents is such 
as to operate both polarized relays. 

The closing of key KI, all other keys being open, intro- 
duces the long end of battery B into the circuit. Its 
voltage being assumed three times that of the short-end 



90 TELEGRAPH ENGINEERING 

battery B', the opposing line currents will not neutralize, 
but a current of 2 units will flow from station A to sta- 
tion B and through the line coils of all relays. At station 
A a current of 3 units intensity flows through the arti- 
ficial line coils of the relays and artificial line, while at 
the other station a current of i unit intensity flows through 
the corresponding circuit. The currents through the two 
coils of relay R are in opposite directions around the core 
and, consequently, partially neutralize each other, the 
surplus of i unit current being insufficient to operate this 
instrument. This surplus current in the artificial line coils 
of the relay P is in such direction as to hold its armature 
away from the sounder contact. The currents through 
the two coils of relay R f are in the same direction around 
the core and are equivalent to a current of 3 units travers- 
ing a single coil. This current is strong enough to operate 
relay R' } for this instrument is so adjusted. The currents 
flowing through the coils of polarized relay P' are both 
in the wrong direction to operate this instrument. Thus, 
the depression of key K\ causes the operation of neutral 
relay R'\ similarly the closing of key KZ causes the opera- 
tion of neutral relay R. 

The depression of both keys KI and K 2 connects the long 
ends of both batteries to the circuit. No current flows 
over the line wire, but currents of 3 units intensity traverse 
the artificial line coils of all relays. These currents are 
sufficiently strong to operate the neutral relays R and R' ', 
but are in the wrong direction to operate the polarized re- 
lays P and P' . Sounders S and 5", therefore, respond to 
the depression of both transmitting keys KI and K z . 

When keys K and KI are closed, the negative terminal of 
the long-end battery B is joined to the point x, while the 



QUADRUPLEX TELEGRAPHY 91 

positive terminal of the short-end battery B f is joined to 
the point y. A current of 4 units intensity will flow over 
the line from the right toward the left, a current of 
3 units will flow through the artificial line circuit at the 
left and a current of i unit will flow through the artificial 
line circuit at the right. It will be seen that the relays 
P' and R f respond, thereby operating sounders S 2 and S'. 

In the same manner, the currents in the various portions 
of the circuit and the relays affected, for the remainder of the 
16 possible combinations of key positions, may be traced. 
Having given the constants of any circuit, the currents 



r 3 <0oo 




Fig. 3. 

traversing the various relay coils can be determined in the 
usual manner. 

The main-circuit connections of one station of a quad- 
ruplex circuit, using the Field key system with a single 
generator instead of the battery, are shown in Fig. 3. The 
function of the pole-changer C is the reversal of the gen- 
erator Dj while that of the transmitter T is the variation 
of available potential difference by means of the resist- 
ances r-i and r 3 . When the armature of the transmitter is 



92 TELEGRAPH ENGINEERING 

attracted, the added resistance r 2 is short-circuited and the 
resistance from the point x to ground at G is 2 X 300 or 
600 ohms, and when this armature is released the resist- 

. ooo (1200 + 600) , , 

ance is ^ or 600 ohms, as before. The 

900 + 1 200 + 600 

terminal resistance therefore remains unaltered regardless 
of the position of the transmitter armature. 

To consider the variation in current produced by the 
movements of the transmitter armatures, let, as in the 
preceding chapter: 

R p = resistance of polarized relays, 

R r = resistance of neutral relays, 

R b = resistance of protective coils in series with 

generators, 

r = resistance of artificial lines, 
and E = voltage of generator. 

Then, if the apparatus at the distant station is also as 
shown in Fig. 3 (that is, all keys open), the line current is 
zero and the current supplied by each generator is 

7 = _ E _ , . 

' 







of which, the part that traverses the artificial line circuit is 

E-I(R b + r a ) . 



the remainder traversing the leak resistance r 3 . When the 
armatures of both transmitters are attracted, the current 
flowing through the artificial line circuit is 



QUADRUPLEX TELEGRAPHY 93 

Thus, if the resistances of the various paths are as indi- 
cated in the figure, the currents traversing the artificial 
line circuit when the transmitter armatures are both re- 
leased and when both attracted are respectively 35.3 and 
106 milliamperes. The attraction of the armatures thus 
triples the current flowing and this larger current is sufficient 
to operate the neutral relays. The currents for other key 
positions might be similarly determined. 

At times it is feasible to raise the current ratio from 3 to 
i up to 4 to i, which may be done by changing the added 
resistance to 1800 ohms and altering the leak resistance to 
800 ohms, if the resistance in series with the generator 
remains the same. For any other current ratio r, or 
other series generator resistance R b , the added and leak 
resistances should be respectively 

r z = R b (r- i) (4) 

and 

. ,-. (5) 



^ 

In practice two generators at each station are more fre- 
quently employed in quadruplex service than one gener- 
ator. The connections of one station, according to the 
Field key system with two generators, are shown in Fig. 4. 
Its similarity to the preceding figure will be noticed, and 
consequently the foregoing equations apply to this ar- 
rangement also. The relay contacts marked S are those 
against which the armatures must rest in order to operate 
the sounders. 

To balance a quadruplex circuit the distant generators 
may be disconnected from the circuit while the resistance 
of the home artificial line is adjusted to equal the resist- 
ance of the line plus the terminal apparatus at the other 



94 



TELEGRAPH ENGINEERING 



end. In order that the removal of the distant generators 
will not alter the terminal resistance, a switch, Si, is ar- 




Fig.4- 

ranged to introduce a resistance r g from the junction x to 
ground which equals the resistance connected in series 
with the generators. 

3. Avoidance of Sounder-armature Release During 
Current Reversals in Neutral Relay. When a neutral re- 
lay of a quadruplex circuit is actuated, and the position of 
the pole-changing key at the other station is altered mean- 
while, the magnetism in the core of this relay is reversed. 
This means that the magnetism falls to zero and then 
rises to the same intensity in the opposite direction. As a 
consequence the attracting force also passes through zero, 
and a moment exists when the relay armature is not held 
against its front contact point. During this brief interval 
the local sounder circuit is opened and the sounder armature 
is momentarily released. In the operation of a quadruplex 
system such periods of zero magnetism in the neutral 
relay cores are constantly recurring, and result in false 
signals. 



QUADRUPLEX TELEGRAPHY 



95 




Fig. 5. 



Various methods have been adopted for avoiding the 
release of the sounder armature during these short non- 
magnetization periods of the neutral relay. One method 
has already been mentioned in connection with the Morris 
duplex system, described in 7 of the fore- 
going chapter; namely, the insertion of a 
repeating sounder. The connections of the 
local-sounder and repeating-sounder cir- 
cuits are illustrated in Fig. 5. The repeat- 
ing sounder RS has a heavy armature lever 
so as to render its action slow. It is evi- 
dent that when the magnetism of the neu- 
tral relay R passes through its zero value, 
the relay armature would have to be drawn against its 
rear contact before the sounder S would release its arma- 
ture. Since, in practice, the relay armature falls back but 
a small distance before magnetism of sufficient intensity 
in the opposite direction is again established to attract the 
armature, it follows that no false signals will arise. 

Another device, for accomplishing 
this result, now extensively used on 
the quadruplex circuits of the Postal 
^ Telegraph- Cable Company, is the Diehl 
relay arrangement, which is shown in 
Fig. 6. It will be observed that the 
sounder 5* is actuated as long as the 
armature of relay R is away from its 
rear stop. When this armature touches 
its rear contact, the local battery, which supplies current 
to the relay R', is short-circuited through a protective re- 
sistance, and consequently neither this relay nor the 
sounder is energized. 




Fig. 6. 



9 6 



TELEGRAPH ENGINEERING 




Neutral relays equipped with an extra coil, which re- 
ceives current during the period of current reversal in the 
other coils from a condenser or from a reactor, are also 
used in order to avoid false signals. The arrangement 
used by the Western Union Telegraph Company with its 
quadruplex circuits is shown in Fig. 7. Each winding of 

the main relay has a resistance 
of 350 ohms while the extra or 
holding coil H has a resistance 
of 225 ohms. The condenser 
C has a capacity of about 3 
microfarads. As the condenser 
is charged to the difference of 
potential across the points a 
and b, the instant the dis- 
tant pole-changer armature leaves either contact in the 
act of reversing the polarity of the distant generator, 
the condenser immediately discharges through the hold- 
ing coil, thus keeping the armature attracted during 
the interval that the current reverses in the main relay 
coils. The Freir self -polarizing neutral relay also gives 
satisfaction with quadruplex systems. 

In order that the period of current reversal be as short 
as possible the movements of the pole-changer armatures 
between their contacts should be reduced as much as prac- 
ticable. Quick reversals of magnetism in the relay cores 
are made possible by the use of relays possessing little 
inductance and having laminated cores. 

4. The Postal Quadruplex. The Davis-Eaves quad- 
ruplex is now largely used by the Postal Telegraph-Cable 
Company, and is illustrated in Fig. 8, which shows the ap- 



QUADRUPLEX TELEGRAPHY 



97 



paratus at one station. This arrangement is modelled 
after the improved polar duplex described in 6 of the fore- 
going chapter. The functions of the bridge coils g and h 
with the bridged condenser c, and the shunt paths con- 
taining the resistances / and /' and the condensers Ci and 
cij have there been explained. The operation of the 
transmitter T in varying the available potential by means 
of the leak resistance r 3 and the added resistance r z has 
been considered in connection with Figs. 3 and 4. The 
condenser c 3 curbs the sparking at the transmitter contacts. 
The pole-changer C and the transmitter T are equipped 
with permanent magnets, />/>, so arranged as to hasten the 




return of their armatures to the rear contact points. 
Neutral relay R controls the operation of sounder Si 
through the Diehl relay R' ', as explained by means of 
Fig. 6. A high-resistance leak path to ground is provided 
by closing a switch introducing resistance r' . Four local 
generators are shown in order to avoid complication of 
the diagram, but in practice only one generator is em- 
ployed. The constants of the main circuit are: resistances 
of g = h = 500 ohms, of / = /' = r^ = 600 ohms, of r$ = 450 
ohms, of R 60 ohms, of P = 200 ohms, and of r' 25,000 
ohms; capacities of c\ = c\ = c$ = i microfarad, and of 



9 8 



TELEGRAPH ENGINEERING 



c = 1 2 microfarads. The generator voltage should be from 
250 to 385 volts. 

5. The Western Union Quadruplex. The quadruplex 
circuits, now the standard of the Western Union Telegraph 
Company, embody the principles of the bridge duplex, 
already considered in 8 of Chap. II. The connections of 
the apparatus at one station of the Western Union quad- 
ruplex are shown in Fig. 9. The retardation coil 7, 
the milliammeter A, the pole-changer C, the line resist- 
ance box, and the method of quenching the sparking at 
the pole-changer contacts have already been described 
in connection with the bridge duplex. The variation in 




Fig. 9. 

available potential is again effected by the Field system, T 
being the transmitter and rz and r$ being respectively the 
added and leak resistances. Both the repeating sounder 
and neutral-relay holding-coil methods (see 3) are utilized 
in tiding over the period of zero magnetization in the 
neutral relay core. Each artificial line is adjusted to 
equal, in resistance and capacity, the main-line wire plus 
the apparatus at the distant station. The ground resist- 
ance r g facilitates line balancing. This resistance is also 
contained in the artificial line box, as shown in Fig. 6 of 
the preceding chapter, and connects with the terminal 
marked "Ground Balance." 



QUADRUPLEX TELEGRAPHY 99 

When the distant pole-changer places the negative gen- 
erator terminal to the line, the armature of the polarized 
relay at the home station will close its local sounder circuit, 
but when it places the positive terminal to the line the 
polarized relay will not operate its sounder. An alteration 
in current intensity from a minimum to a maximum value, 
or vice versa, does not affect the polarized relay whether 
it be against one contact or the other. Each polarized re- 
lay is unaffected by the movements of the home pole- 
changer. 

The neutral relay is connected in the circuit exactly as 
in Fig. 2, that is, one winding is connected in series with 
the line wire while the other is connected in series with the 
artificial line. Each neutral relay operates only on the 
attraction of the armature of the distant transmitter, for 
the current then traversing this receiving instrument is 
three times as great as when the transmitter armature is 
not attracted, and because the retractile spring on the re- 
lay is adjusted so that its armature will not be attracted 
when the relay is traversed by the weaker current. 

The charge residing in the condenser c, bridged across 
the line and artificial line through the holding coil of the 
neutral relay, will be relieved whenever the distant pole- 
changer armature leaves either contact. This discharge 
causes a pulse of current to traverse the holding coil, 
which pulse is sufficient to hold the armature of the neutral 
relay (if attracted prior to current reversal), against the 
front contact while the reversal of magnetism takes place 
in the main cores of the relay. As a further safeguard 
against the development of false incoming signals on the 
second side of the quadruplex the repeating sounder RS 
is used. 



100 



TELEGRAPH ENGINEERING 



The constants of the main circuit are: resistances of 
coils a = b = 500 ohms, of resistance lamps in each main 
potential lead = 600 ohms, of r? = 1200 ohms, of r$ = 
900 ohms, P = 600 or 800 ohms, R = 700 ohms and 
r g = 600 ohms; capacities of c' = i microfarad, and of 
c = i to 3 microfarads. The generator voltage should be 
sufficient to develop a current of from 0.09 to 0.15 am- 
pere in the line wire when both transmitters and one pole- 
changer are closed. 

When extremely bad weather renders the second side of 
the quadruplex inoperative, the quadruplex circuit may 
be used as a duplex circuit by keeping the two trans- 
mitters closed. 

6. Quadruplex Repeaters. In general, any two quad- 
ruplex sets can be connected together to form a quadruplex 
repeater. The scheme of connections of a quadruplex 



WEST 
LINE 




Fig. 10. 

repeater is shown in Fig. 10. The polarized relays PI and 
Pz control the operation of pole-changers C\ and Cz re- 
spectively, and the neutral relays RI and R 2 control the 
operation of transmitters T" 2 and T\ respectively. It is 
possible also to have the pole-changers controlled by the 



QUADRUPLEX TELEGRAPHY ibl 

neutral relays and the transmitters by the polarized re- 
lays. For more satisfactory operation repeating sounders 
may be interposed between each neutral relay and its 
corresponding transmitter, as already explained. 

The armature positions indicated in the figure are for 
the normal condition, that is, when all keys at both eastern 
and western stations are open. This means that the 
positive terminal of the short-end battery or generator is 
joined to the line at each station as well as at the repeat- 
ing station. The generators at the repeating station are 
not shown, but the pole-changer contacts are marked to 
show their respective polarities (the other generator termi- 
nals are grounded). 

When the pole-changing key at the western station 
is depressed, twice as much current flows (toward the 
western station) through the line coils of relays Ri and PI 
as through their other coils. This causes the operation of 
relay PI but not of relay R lm The armature of pole-changer 
Ci is attracted, thereby placing the negative generator 
terminal to the eastern line. This action does not affect 
the repeater relays R 2 and P 2 nor the distant neutral re- 
lay, but only the eastern polarized relay. 

If, instead, the transmitter key at the western station 
be depressed, the long end of the home battery or gener- 
ator will be joined to the line. Twice as much current 
flows (toward the repeating station) through the line coils 
of relays RI and PI as through their artificial line coils. 
This causes the operation of relay RI but not of relay PI. 
The attraction of the relay armature energizes the trans- 
mitter T 2 , which impresses the greater generator voltage at 
the repeating station on the eastern line. This causes 
more current to flow through the artificial line coils of 



102 TELEGRAPH ENGINEERING 



relays R 2 and P 2 than through their other coils. The 
surplus current is insufficient to operate relay R% and in 
the wrong direction to operate relay P 2 - The distant neu- 
tral relay only responds to the depression of the western 
transmitter key. 

In the same way the conditions may be traced, for 
other key positions at the two terminal stations, through 
the repeating station. 

It is practicable to secure quadruplex operation over a 
portion of a line that at other portions is operated duplex. 
Thus, a number of lines between New York and Chicago 
are operated polar duplex between these terminal sta- 
tions, and are also simultaneously operated differential 
duplex between New York and Buffalo. Such a circuit 
requires repeating apparatus at Buffalo that is formed by 
combining a direct-point duplex repeater with a quadru- 
plex set. 

7. Duplex-diplex Signalling. A system of telegraphy 
that permits of duplex or diplex transmission, but not 
both simultaneously as in quadruplex signalling, is called 




ll|c 



Fig. ii. 



a duplex-diplex system. One such system, devised by 
Crehore, utilizes both an alternating current and a direct 
current, these currents being separated by means of in- 
ductances and condensers. Fig. n shows the schematic 



QUADRUPLEX TELEGRAPHY 103 

arrangement of apparatus at one station for an open- 
circuit duplex-diplex system. 

Continuity-preserving keys KI and K 2 respectively con- 
trol the currents supplied by the battery B and alternator 
A. The neutral relay R and the polarized relay P are in 
parallel with each other, and in series with the line. The 
inductance of the polarized relay is neutralized by the 
properly-adjusted condenser C. The key K 2 is shunted by 
a reactor / which has large inductance but little resistance. 

If key KI is depressed, a direct current flows through 
relay R and no current flows through relay P because of 
the presence of condenser C. Thus relay R as well as the 
distant neutral relay will operate on the depression of the 
direct-current key KI. 

Depression of key K% introduces the alternator into the 
circuit, as shown. Because of the high inductance of re- 
lay R, only a small current will flow through it, and its 
retractile spring is adjusted so that the armature will not 
be attracted on this weak current. Polarized relay P as well 
as the distant polarized relay will, however, be actuated. 

In this way either duplex or diplex transmission may be 
effected, the corresponding home instruments being also 
responsive to the outgoing signals. In duplex signalling 
one direct-current key and one alternating-current key 
must be used. Alternating currents of fifty to one hun- 
dred and fifty cycles may advantageously be employed. 
A quadruplex system may also be built up on the fore- 
going principles by applying alternating current to the 
ordinary duplex systems. 

8. Phantoplex System. To increase the message- 
carrying capacity of simplex, duplex or quadruplex lines by 



104 



TELEGRAPH ENGINEERING 



additional superimposed channels, the so-called phanto- 
plex system is employed by the Postal Telegraph-Cable 
Company. The arrangement of this system adapted to a 
quadruplex circuit and thereby affording sextuplex signal- 
ling, that is, the transmission of three messages in each 
direction simultaneously without interference, is shown in 
Fig. 12 for one station. The quadruplex connections will 
be recognized as those of the Field key system and ex- 
plained with the aid of Fig. 4, the local circuits being 
omitted for simplicity. 




Fig. 12. 

The secondary winding of a sending transformer, /, is 
introduced between the armature of 'the transmitter and 
the junction of. the neutral relay windings. The primary 
winding of this transformer receives current from the 
alternator A (frequency from 60 to 125 cycles) when 
the armature of the transmitter T' rests against its rear 
stop, the transmitter being actuated by the current from 
battery b through the key K. The two primary windings 
of the receiving transformer t' are connected in the line 
and artificial line circuits, their secondary windings being 
properly connected in series to the phantoplex relay X, 
and through the condenser c. This phantoplex relay oper- 



QUADRUPLEX TELEGRAPHY 105 

ates a sounder (not shown) when its armature rests against 
its rear stop. 

When the key K is raised, as shown, an alternating 
electromotive force is induced in the secondary winding of 
the sending transformer, thereby superimposing an alter- 
nating current upon whatever steady currents traverse this 
winding. When no alternating current is superimposed on 
the main circuit at the other station by its sending trans- 
former (that is, the distant key corresponding to K is 
closed), then the alternating current developed at / divides 
equally between the line and artificial line circuits. The 
voltages induced in the secondary windings of the home- 
receiving transformer oppose each other, and do not cause 
the attraction of the armature of phantoplex relay X. Its 
local circuit will be closed and the sounder actuated the 
proper condition, for the distant key is closed. The alter- 
nating current that traverses the line wire also flows 
through one primary winding of the distant receiving 
transformer, no current flowing through its other primary 
winding. As a result the distant phantoplex relay will be 
energized, thereby opening its local circuit. Thus the dis- 
tant phantoplex sounder will not be energized when key K 
is raised. Repeating sounders are used so that the flutter- 
ing of the armatures of the phantoplex relays, due to the 
alternating currents traversing their windings, will not 
affect their local sounders. 

Condensers ci, c% and c$ provide a direct path past the re- 
sistances and relay windings for the alternating currents. 
The alternating currents are of an intensity insufficient to 
energize the quadruplex relays. 



io6 



TELEGRAPH ENGINEERING 



PROBLEMS. 

1. In the battery quadruplex circuit of Fig. 2, the long-end 
battery has 300 volts and the short-end has 100 volts, the internal 
resistance being 2 ohms per volt. Taking the resistance of the 
assumedly perfectly-insulated line as 2000 ohms, and the resistances 
of the polar and neutral relays as 400 and 200 ohms respectively, 
calculate according to the method of 2, Chapter II (using R r = 600), 
the proper resistance of the artificial line when both short ends of 
the battery and when both long ends of the battery are in circuit. 

2. With the artificial lines adjusted to 2800 ohms calculate the 
currents, in milliamperes, traversing the relay coils of the quadruplex 
circuit of Prob. i for all key positions, and record the results in 
tabular form as indicated below. In the last column for each relay 
should be placed the equivalent current in one coil, and if this cur- 
rent is of sufficient intensity or of the proper direction to operate the 
particular relay, this figure should be starred. The neutral relays 
are adjusted so that a current greater than 0.050 ampere is necessary 
for their operation. 



Keys closed 
(Fig. 2.) 



none 
K 

K' 



KK' 
KK* 



KK'K 2 



Relay P 



Relay R 



ll 

2 






Relay P' 



Relay R' 



QUADRUPLEX TELEGRAPHY 107 

3. If the two 3Oo-ohm protective resistances of the single-gen- 
erator quadruplex circuit shown in Fig. 3 are replaced by 2oo-ohm 
resistances, determine the proper values of the added and leak re- 
sistances necessary for a 3 to i current ratio. 

4. Calculate the strengths of the currents in the artificial line 
circuit of Prob. 3, when both transmitter armatures are released and 
also when both are attracted. 

5. Compute the terminal resistance of the Postal Quadruplex, 
the constants of which are given in 4, if the artificial line has a 
resistance of 2000 ohms. 

6. Develop the diagram of connections of a telegraph line circuit 
that extends from city A, through city B, to city C, which simulta- 
neously affords two channels of communication (differential duplex) 
between cities A and B and two channels (polar duplex) between 
cities A and C. 



CHAPTER IV 

AUTOMATIC AND PRINTING TELEGRAPHY 

i. Wheatstone Automatic Telegraphy. When rapid 
or accurate telegraphic signalling is to be accomplished, 
automatic transmitting and receiving devices are availed of, 
and consequently such rapid telegraphs are usually called 
automatic telegraph systems. The Wheatstone automatic 
system has been most extensively used and permits of 
satisfactory telegraphic transmission at speeds up to 400 
words per minute. The messages to be transmitted are 
perforated in specially prepared oiled or parchmentized 
paper tapes in accordance with the Morse code, and these 
tapes are then automatically propelled through a transmit- 
ter, which is really a high-speed pole-changer, driven by 
springs or weights, or, more modernly, by electric motors. 
The Wheatstone transmitter is connected in the line circuit 
in the same way as is the pole-changer of a duplex circuit. 
The messages are received at the distant station by an 
inking polarized relay, called a Wheatstone recorder, which 
records the message in the Morse code on a tape, as is done 
by a register. 

The transmitting tapes are prepared by means of three- 
key mallet perforators or keyboard perforators, and appear 
as in Fig. i, which shows the punching for the word " relay. " 
The Morse characters are also shown, the letter / in auto- 
matic telegraphy being written: dot, dash, dash, dash 
(Postal), or dot, dot, dash, dash (Western Union), instead of 

108 



AUTOMATIC AND PRINTING TELEGRAPHY 



109 



a long dash. The size of standard perforator tape is 0.47 
inch wide and from 4 to 5 mils thick. The center line of 
holes, or guide holes, are o.i inch apart when the perforator 



O 00 O 00 O C OO OO OO 
ooooooooooooooooooooooooooo 
O OO O O O O O O O OO OO 



Fig. i. 

is properly adjusted. A dot appears as three holes in a 
vertical line, a space appears as one guide hole, and a dash 
appears as four holes: two guide holes and two others, one 
above the first guide hole and the other below the second 
guide hole. Longer spaces are allowed between words, 
sentences and messages. 

A mallet perforator with interchangeable punch-blocks 




Fig. 2. 



and removable punch-ends is shown in Fig. 2. The de- 
pression of the left plunger punches a dot, the center plunger 
punches a space, and the right plunger punches a dash. 



no 



TELEGRAPH ENGINEERING 



The punching operator uses a rubber-tipped mallet in 
each hand for depressing the plungers. The plungers are 
restored by springs to their normal position after each de- 
pression, which action advances the tape one space after 
the depression of the dot or space plungers, and two spaces 
after depression of the dash plunger, the tape feeding being 
accomplished by a small spur-wheel which engages in the 
guide holes. 

The principle of operation of the Wheatstone high-speed 
transmitter can be explained with the aid of Fig. 3, which 
illustrates simplex transmission from the left-hand to the 




right-hand station. Only those mechanical features of the 
transmitter are shown which serve directly in the capacity 
of pole-changer. The transmitting tape / is moved along 
over a slotted platform, in the direction indicated by the 
arrow, by means of the spur-wheel w which engages in the 
guide holes. Another wheel, not shown, is mounted above 
the spur-wheel and serves to press the tape against the 
platform. Rods / and b pass freely through a guide plate 
g so that they remain respectively in ; line with the front 
and back rows of holes, and are spaced longitudinally so 
that their distance apart equals the distance between two 
adjacent guide holes. The rocking beam r carries out- 



AUTOMATIC AND PRINTING TELEGRAPHY III 

wardly-projecting pins p, p, which limit the upward 
motion of the rods against the tendency of the spring s. 
The eccentric gear-wheel k, driven at any desired speed 
by clockwork, or by an electric motor, causes the rocking 
beam to oscillate through a small arc around its central 
pivot. With each downward movement of the rod b the 
tape moves forward one space or the distance between two 
successive guide holes. The motions of the rods / and b 
are transmitted to the pole-changer C by means of the 
cranks, rods and the ivory collets c, c. The function of the 
jockey-roller / is to hasten the movements of the pole- 
changer and to insure steady contacts. 

If the transmitter is set in operation without carrying a 
tape, the rise and fall of the rods will be unhindered, and 
every time the front rod / is in its upper position, the posi- 
tive terminal of the battery B is connected to the line 
while its negative terminal is grounded, and every time 
the back rod b is in its upper position (as in Fig. 3) the 
negative battery (or generator) terminal is joined to the 
line. Thus the battery is reversed with every half oscil- 
lation of the rocker arm when the transmitter is operating 
idly. 

These current reversals cause the armature of the polar- 
ized relay P to oscillate simultaneously, which motion is 
translated to the printing wheel shaft a that is kept re- 
volving by means of the gear-wheel d. Whenever the 
positive battery terminal is joined to the line at the trans- 
mitter, the direction of the current through the polarized 
relay is such as to hold the printing wheel i against the 
inking wheel h which dips in the ink reservoir e. And 
when the negative battery terminal is connected to the 
line, the current direction is such as to press the inking 



112 TELEGRAPH ENGINEERING 

wheel almost against the moving receiving tape t r . These 
currents are called spacing and marking currents respec- 
tively. Thus, when the transmitter operates without tape, 
a succession of dots appears on the receiving tape. 

At the instant represented in the figure rod b has passed 
through the tape, thereby sending a marking current and 
causing the printing wheel to press almost against the 
receiving tape and leave an ink mark thereon. The rock- 
ing beam then draws down rod b and allows rod/ to rise; 
meanwhile the tape has moved forward one space. In 
this case the signal is a dot, and consequently rod / in its 
upward motion meets the front or lower hole and so passes 
through it. The complete transit of this rod causes the 
shifting of the pole changer C and the sending of a spacing 
current; consequently the printing wheel i is withdrawn 
from the receiving tape to the inking wheel. A dot is 
printed on the receiving tape. 

If, instead, the signal were a dash, the upward movement 
of rod / would be arrested by the tape, because in a dash 
perforation there is no lower hole in line with the upper 
hole. As a consequence, the pole-changer would not be 
operated. Tracing the operation further, the upward 
movement of rod b would also be restricted, but the next 
upward movement of the other rod / would cause it to pass 
through the lower hole, which movement reverses the pole- 
changer. The time elapsing since the last reversal is 
sufficient to form a dash signal on the receiver tape. It 
will be observed that the current pulse for a dash signal 
is of the same direction as for a dot signal, but three times 
as long. For relatively low transmission speeds the signals 
may be read from a sounder connected to the local-circuit 
contacts of the receiving relay. 



AUTOMATIC AND PRINTING TELEGRAPHY 113 

Fig. 4 shows an automatic transmitter made by Muir- 
head & Co., Ltd., for cable signalling. It is provided with 
a local pole-changer, speed regulator, speed indicator, and 
a switch for shifting connections from transmitter to hand- 
key sending, which at the same time lifts the paper wheel 
off the spur-wheel. The mechanical devices of the trans- 




Fig. 4- 

mitter are somewhat different from those shown in Fig. 3, 
but have the same function. 

The connections of the Wheatstone automatic system for 
duplex operation are indicated in Fig. 5, which shows only 
the electrical features at one station. The connections are 
those of the polar duplex, already described, with a choice 



TELEGRAPH ENGINEERING 



of pole-changers. When the switch S is to the left as 
shown, the automatic transmitter C is in circuit, and when 
this switch is shifted to the right, the pole-changer Ci con- 
trolled by the key K is in circuit. The Wheatstone recorder 
P is immune from the movements of the home transmitting 
devices C or Ci and will only respond to the operation of 




either the distant automatic transmitter or the distant 
manually-operated pole-changer. The Wheatstone system 
is almost invariably operated duplex. 

Repeaters for use with the Wheatstone automatic system 
resemble polar direct-point duplex repeaters ( 10, Chap. II) 
thereby dispensing with automatic transmitters at the 
repeating station for through operation. A Wheatstone 
recorder may be introduced at the repeater as a leak relay 
to enable the attendant to discern the character of the 
signals passing through the repeater. 

The system described has been used by the Western 
Union Telegraph Company for many years. The auto- 
matic system used by the Postal Telegraph- Cable Company 
differs herefrom in the reception of the signals. It em- 
ploys instead of the inking Wheatstone recorder, an elec- 
tromagnetic punch, or reperforator, invented by d'Humy. 

The reperforator punches characters in a moving tape 
somewhat similar to those of the transmitting tape. If the 



AUTOMATIC AND PRINTING TELEGRAPHY 115 

completed receiving tape be passed slowly through a repro- 
ducer, whose speed is in control of the receiving operator, 
the messages can be read by ear and simultaneously copied 
by hand or on a typewriter. The punches of the reper- 
forator are adjusted to travel over a very short distance, 
and their motion is rendered rapid by strong retractile 
springs and by a series condenser in the punch magnet cir- 
cuits. Such small and rapid motion of the punches com- 
bined with a tape take-up device are the essential features 
of the reperforator, for they shorten the time of tape 
stoppages during punching and compensate for these stop- 
pages respectively, thereby preventing tearing of the tapes. 

2. Ticker Telegraphs. A ticker telegraph system com- 
prises a transmitter and a number of receiving instruments, 
called tickers, which print the messages in ordinary type 
on paper tape as they are received. The various ticker 
systems for the dissemination of news and stock quotations 
differ widely in the mechanical construction of instruments, 
but the fundamental operating principles are not very 
different. 

A schematic diagram of a transmitter with one ticker 
of such a tape-printing system is given in Fig. 6. The 
transmitter consists of a shaft 5 driven by a constant- 
speed motor M through a friction clutch k. Mounted on 
this shaft is a current-reversing commutator c, formed by 
a pair of metal crown-shaped wheels which are fitted 
into but insulated from each other. The wheels connect 
through brushes with the negative and positive terminals 
respectively of generators D and Z>', the other generator 
terminals being grounded. The shaft also carries an 
escapement wheel e, and a contact arm a which passes 



n6 



TELEGRAPH ENGINEERING 



over the contact points located on the contact disk C. 
The escapement is controlled by an electromagnet m 
through the keyboard K. Upon the depression of any 
key no current from the battery B will flow through the 
electromagnet until the contact arm a reaches the contact 
stud corresponding to the key depressed. At that instant 
the armature of magnet m will be attracted, thereby 
arresting the rotation of the shaft and commutator. Thus 
the shaft is stopped at a particular place for each depressed 
key. 

At the receiver the type-wheel T is rotated by clock- 




Fig. 6. 



work through the gear-wheel g, but this rotation is con- 
strained by means of the escapement wheel w. The arma- 
ture of polarized relay P controls this escapement wheel. 
The rear end of the armature of printing relay R, when 
this instrument is operated, presses the tape, which moves 
over the armature, against the type-wheel; consequently 
that letter will be printed on the tape which, at the mo- 
ment of operation of the relay R, is in the lowest position. 
If n characters are to be employed in transmission, there 
must be n keys on the keyboard, n notches on the escape- 



AUTOMATIC AND PRINTING TELEGRAPHY 117 

ment wheel e, n contact studs on C and n segments on the 
commutator c\ the commutator brushes and the contact 
arm a being properly aligned with respect to the notches 
on the escapement wheel. Thus, depressing any given key 
will always stop the shaft at the same place. At the 
receiver there are also n characters on the type-wheel and 
n teeth on the escapement wheel. 

In operation, when no keys are depressed, the trans- 
mitter shaft revolves uniformly and the current supplied 
to the line is periodically altered in direction by the com- 
mutator. This reversal of polarity occurs so rapidly that 
the current in relay R never reaches a value sufficient to 
cause the attraction of its armature before the next re- 
versal takes place, consequently the rear end of this 
armature does not press the tape against the type-wheel. 
However, the alternating current traversing the sensitive 
polarized relay P causes its armature to shift its position 
with each reversal in polarity, thereby operating the escape- 
ment. One revolution of the transmitter shaft produces 
n current reversals and the escapement wheel at the re- 
ceiver moves through n notches, or one revolution. It is 
evident, then, that if the type-wheel is started with its 
characters in a certain position, it will always remain 
during proper operation in the same relative position with 
respect to the transmitter shaft. The proper position of. 
the type-wheel is such that the letter a will be in the 
printing position when the a-key of the transmitting key- 
board is depressed. 

Upon the depression of any key the motion of the shaft 
and commutator will be momentarily arrested. This 
stopping is permitted by the friction clutch without affect- 
ing the rotation of the motor. During this instant the 



Il8 TELEGRAPH ENGINEERING 

current ceases to alternate in direction, and relay R is 
enabled to attract its armature. This action presses the 
tape against the type-wheel, thus printing the character 
corresponding to the key that is depressed at the trans- 
mitter keyboard. As the armature resumes its former 
position through the intervention of spring s, the tape is 
moved forward one space by clockwork and is ready for 
the printing of the next character. 

The system just described is known as a single- wire and 
single type-wheel ticker system. To avoid spelling figures, 
which occur very frequently in stock quotations, figures 
and fractions should also be provided on the keyboard 
and type-wheel. Adding to the 26 letters of the alphabet 
10 figures and say 7 fractions would increase the size of 
the wheel and would materially decrease the speed of oper- 
ation. Instead, it is customary to use two type- wheels 
on the same ticker-shaft and adjacent to each other, one 
containing letters and a couple of dots, and the other con- 
taining figures and fractions. As the numbers of charac- 
ters on both type-wheels should be identical, the fractions 
may be repeated and the still-existing deficiency may be 
made up by dots. A ticker so equipped is called a two- 
wheel ticker. 

In two-wheel tickers provision must be made for shifting 
either the type-wheels or the tape in order to print from 
either wheel. This shifting is accomplished electromag- 
netically in a variety of ways in the various ticker systems. 
For fast working an additional wire is generally used for 
the current which actuates the shifting magnet, thus neces- 
sitating two line wires to each ticker. 

Should, for any reason, the type-wheel of a ticker be 
thrown out of step with the transmitter, as may occur 



AUTOMATIC AND PRINTING TELEGRAPHY 119 

upon sticking of the escapement wheel or momentary inter- 
ruptions of the line wire, a jumble of letters on the tape will 




Fig. 7. 



result. Automatic devices, termed unison devices, are availed 
of to bring the tickers back into step whenever desired. 




Fig. 8. 



Generators are now more frequently employed in the 
operation of ticker systems than batteries, the generator 



I2O 



TELEGRAPH ENGINEERING 



leads being provided with fuses and protective resistances. 
Condensers are also used in these systems for the elimina- 
tion of sparking at the transmitter contacts. 

The appearance of the ticker used by the Stock Quota- 
tion Telegraph Company in New York is shown in Fig. 7. 




Fig. 9. 

It has 8 ohms resistance and requires about 0.65 ampere 
for operation. Figs. 8 and 9 show respectively the key- 
board and motor-driven transmitter used at the central 
station of a ticker system. The cost of ticker service is 
about $20 per month. Fac-simile reproductions to full 



.SUPREME. COURT. OF. THE. U.S. 



.80 



SP 



U 



.9! | 


.700.833 


.147 



Fig. 10. 



scale of the received tapes of a news ticker and a stock 
quotation system are given in Fig. 10; the significance of 



AUTOMATIC AND PRINTING TELEGRAPHY 121 

the stock abbreviations on the lower tape being BO = Balti- 
more & Ohio, SP = Southern Pacific, and U = Union 
Pacific. 

3. The Barclay Page-printing Telegraph System. - 

The Barclay printing telegraph system is now extensively 
used by the Western Union Telegraph Company, and com- 
prises a keyboard perforator, an automatic transmitter, 
and a receiving polarized relay which repeats the arriving 

BARCLAY PRINTING TELEGRAPH CODE 

A ^_. O 9 _ - _ 

B @ - _ P O _ __ _ 

C : _ - _ Q I _ _ _ 

D$ _ __ R 4 p. _ _ 

E 3 ___ S # __ - 

T X __ - T 5 ... 

G& __ _ u T _-_ 

H * -__ V J _ . 

I 8 ___ W 3 _ .__ 

J ' . -- - XI _ . - 

Kf --- Y6 _._ 

L) . __ Z " __ _ 



ce 
Type Shift __ - ^^ Carriasre Return ^ ^^ mm ^ 



--- , 

Space -. . Paper Feed. 



signals into a set of local relays which control the opera- 
tions of the printing magnets, the received message being 
directly printed in page form on message blanks. This 
system may be operated successfully through several re- 
peaters. Its capacity is about 100 words per minute over 
lines 1000 miles long. 

Transmitting Apparatus. Messages to be transmitted 
are first perforated in prepared paper tapes, exactly as 



122 TELEGRAPH ENGINEERING 

in the Wheatstone automatic telegraph system described in 
i, only a different code is employed. The code used in 
the Barclay system has three elements for each character 
and these are separated from each other by short or long 
spaces, as shown on the preceding page. The spaces be- 
tween the various words, figure groups, etc., are formed 
by three closely-spaced dots. Thus, the perforations in 
the transmitting tape for the word " relay" would appear 



>oo oo o oo o o oo o oo o o o ooo 

lOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 

>OO O O O O OO OOO OOO OOO OOO 



RELAY 
Fig. II. 

as in Fig. n (compare with Fig. i showing perforations 
according to Morse code). 

The Kleinschmidt perforator, now largely used with the 
Barclay page-printer, is shown in Fig. 12, and is a purely 
mechanical device for punching the tape, but derives its 
motive power from an electric motor. All the perforations 
representing a letter, figure or other character on the tape, 
as well as their proper spacing, are produced by a single 
depression of the key. After this depression, the tape is 
advanced a distance commensurate with the space occupied 
by the letter or figure. After about 60 letters are punched 
an indicator lamp illuminates giving a warning that the 
end of a line (on the receiving page) is approaching. The 
pointer, which indicates the number of letters perforated, 
is returned to zero by the depression of the indicator key 
before the limiting number of 75 characters have been 
prepared. 

The automatic transmitter used with the Barclay print- 



AUTOMATIC AND PRINTING TELEGRAPHY 123 




Fig. 12. 



ing system is a Wheatstone transmitter, or high-speed pole- 
changer, as described in i. A front elevation of the upper 
portion of this transmitter is shown in Fig. 13, wherein 
most of the letters refer to the same parts as in Fig. 3. 




Fig. 13. 



124 TELEGRAPH ENGINEERING 

The pole-changer contacts are shown at k and fe, and con- 
nect respectively with the negative and positive terminals 
of the generators. In operation the adjustment of the 
rods / and b must be very precise, and is effected by the 
screws e and e' '. When the switch 5 is thrown to the left 
the paper wheel P, which is shown bearing upon the tape, 
is raised out of engagement with the spur-wheel w, thereby 
halting the progression of the tape. A local pole-changer 
for hand signalling is located in the base of the automatic 
transmitter. In practice, when the transmitter operates 
without tape, from 40 to 70 current reversals take place per 
second. 

When the front rod / is at the upper end of its travel the 
positive generator terminal is joined to the line, and when 
the other rod is in a similar position the negative generator 
terminal connects to the line. Thus, for each letter there 
are six current pulses, three positive and three negative, 
and the code is so arranged that there is at least one long 
current pulse among the first five, either positive or nega- 
tive, per character. In the letter R ( "), for example, 
these current pulses have the following sequence: short 
negative, short positive, long negative, long positive, short 
negative, long positive, the last pulse corresponding to the 
space between this and the next following letter. The 
significance of the code elements are therefore: 

dot = short negative current; 

dash = long negative current; 

short space = short positive current; 
long space = long positive current. 

Receiving Apparatus. The current impulses sent out 
by the transmitter are received by a differentially-wound 



AUTOMATIC AND PRINTING TELEGRAPHY 



125 



polarized relay of special construction to render it quick 
acting. To attain this end, its magnetic circuit has several 
air gaps, the moving element has a small moment of 
inertia, and the two coils of each winding are connected in 
parallel. The series resistance of each winding is 150 ohms. 
A top view of this relay is shown in Fig. 14, in which a is 




Fig. I4 . 

the armature tongue, e is the separately-excited energizing 
coil which takes the place of the usual permanent magnet, 
m, m are the main winding bobbins with the pole-pieces p, 
p] c, c are the platinum contacts, and k is the knurled 
screw which moves the bridge b carrying these contacts. 

The connections of the main line and artificial line cir- 
cuits of automatic duplex apparatus as arranged in the 



126 



TELEGRAPH ENGINEERING 




Fig. 15. 



Barclay printing telegraph system are shown in Fig. 15 
for one terminal station. In the figure, C is the pole- 
changer, D, D are the generators, P is the polarized relay 

with its coils connected in 
parallel, AL is the artificial 
line, and g is a differential 
galvanometer which aids in 
line balancing. Repeaters 
for use with this system re- 
semble polar duplex direct- 
point repeaters. 

The main-line' relay con- 
trols through the intervention of a " printer relay," a " sepa- 
rator relay," an " escapement magnet" and a " sunflower" 
distributing switch, the operation of five " distributing 
relays" with multiple contact points, which in turn control 
the operation of 32 "printer" magnets. The actuation of 
the distributing relays, as dependent upon the nature of 
the received current impulses, may be studied with the 
aid of diagram Fig. 16, in which the various intermediate 
devices mentioned are indicated. 

The separator relay is a neutral relay which is adjusted 
to be responsive only to long current impulses in either 
direction. The escapement magnet is a polarized relay 
which controls the movement of the escape wheel. This 
wheel has 45 teeth and is mounted on the same shaft as 
the unison wheel with 15 teeth, the shaft tending to rotate 
under the influence of an electric motor. The six current 
pulses of each letter or character, alternately negative 
and positive, that traverse the escapement magnet cause 
the escape wheel to turn through a distance corresponding 
to 3 teeth and the unison wheel through a distance of one 



AUTOMATIC AND PRINTING TELEGRAPHY 127 

tooth. As the unison wheel turns, its teeth successively 
butt against the toes of the six pivoted levers marked 
i, 2, 3, 4, 5 and 6; thereby establishing connections with 
the five distributing relays and the sixth pulse or " final" 
relay. However, the circuits of the five distributing relays 
are only completed when the armature of the separator relay 
is on its front contact, which occurs only when a long cur- 
rent pulse traverses its winding. 

Suppose the letter R is being received; the impressed 
pulses are: short , short +, long , long -f, short, 
and long +. Fig. 16 shows the armature positions during 
the first pulse. The armatures of the line and printer 
relays are respectively on their right and left contacts, the 
armature of the separator relay is not attracted, and the 
armature of the escapement magnet is toward the right. 
The unison wheel has turned through one-sixth the distance 
between two teeth, thereby causing a tooth to engage the 
toe of pivoted lever i. But inasmuch as the circuit of 
distributor relay i is interrupted at the separator relay 
armature, the closing of its circuit at the sunflower does 
not cause the operation of relay i, which remains inop- 
erative until the end of the cycle of current pulses for the 
selected letter. During the second pulse the armatures of 
the line and printer relays and of the escapement magnet 
will be in their opposite positions, and the armature of the 
separator relay will still remain unattracted. Therefore the 
completion of the circuit of relay 2 at the sunflower does 
not cause the operation of relay 2. The third pulse is of 
dash duration, so the separator relay is capable of attract- 
ing its armature by current supplied by generator D. The 
escape wheel has moved another half notch, bringing a 
tooth of the unison wheel in engagement with the toe of 



128 



TELEGRAPH ENGINEERING 




SEPARATOR 
RELAY 



IT T 



ESCAPEMENT 
MAGNET 




5 32 PRINTERS MAGNETS 



Fig. 16. 



AUTOMATIC AND PRINTING TELEGRAPHY 129 

pivoted lever 3. Relay 3 will therefore be operated and 
remain so until the expiration of* the remaining three- 
current pulses. The fourth pulse likewise causes the oper- 
ation of distributor relay 4. As the fifth pulse is of short 
duration, relay 5 will not be actuated. Thus for the letter 
R, relays 3 and 4 are operated and close local circuits (not 
shown in this figure) which hold all printer magnets open 
except that which prints the letter R, as will be described 
subsequently. The closing of sunflower contact 6 causes a 
current pulse always of long duration, since it represents 
the interval between letters, to flow from the generator D r 
through the rear spring contact of the final relay, through 
the particular printer magnet corresponding to the letter 
R, which places this letter in the printing position, and 
through the trip magnet which causes the type-wheel to 
come in contact with the message blank. Since the estab- 
lishment of this sixth pulse the armature of the final mag- 
net has been moving forward due to the current through 
its winding. This movement soon opens the circuit of 
the printer and trip magnets, but is adjusted not to do so 
until the proper printing of the desired letter is accomplished. 
Immediately after opening this circuit, the armature comes 
in contact with its front stop, thereby establishing a current 
through the left-hand or " reset" coils of the five distribut- 
ing relays, which is in a direction to cause the armatures 
of the relays previously energized to resume their normal 
position on the left, in readiness for the next letter. 

The distributing system, whereby a particular printer 
magnet out of thirty-two is selected by means of the five 
distributing relays, is shown in Fig. 1 7 . Relay i is equipped 
with two contacts, relay 2 with four contacts, relay 3 with 
eight contacts, relay 4 with sixteen contacts, and relay 5 



130 



TELEGRAPH ENGINEERING 



with thirty-two contacts. The small contact levers shown 
in the figure are insulated from each other. 
The sequence of the long-current pulses in any letter or 




Fig. 17. 



character determines the relay or group of relays that will 
be operated in the selection of the particular printer mag- 
net. In the transmission of letter R the third and fourth 
relays are operated, causing their armatures to move to- 



AUTOMATIC AND PRINTING TELEGRAPHY 131 

ward the right. This condition is represented in Fig. 17, 
and it is evident that the only printer magnet circuit that 
is closed is that which places the letter R in the printing 
position, the direction of current flow being indicated by 
the arrows. Current simultaneously traverses the trip 
magnet which urges the type-wheel, now rotated to its 
proper position, against the paper, causing the printing 
of the letter R thereon. In a similar manner the selection 
of the printer magnet for any other letter or character is 
accomplished. 

The printing of the " upper-case" characters, given in 
the second column of the Barclay printing code, is accom- 
plished by raising the type- wheel, which carries 56 char- 
acters grouped in two rows, so that the upper-case letters 
are brought into the printing line. Raising the type- 
wheel is done by the type-shift magnet T and its assisting 
magnet A, and the type- wheel remains raised until a 
" space" is transmitted, which lowers the type-wheel (if 
raised) through the operation of the type-release magnet 
R, as shown also in Fig. 17. As the sixth current pulse is 
of insufficient duration to cause the proper actuation of 
the type-shift magnet T, the assisting magnet A keeps the 
circuit of the other closed until the type-wheel is raised. 
Since magnets T and A are connected in parallel, both 
will be magnetized when the sixth current pulse of the 
type-shift group passes through their coils. Magnet A 
attracts its armature and causes current to flow from gener- 
ator D through the coils of the type-shift magnet until 
the armature of this magnet is at the end of its travel. 
When this occurs the windings of both magnets are short- 
circuited, the assisting magnet releasing its armature, 
thereby opening the circuit of generator D. The armature 



132 TELEGRAPH ENGINEERING 

of the type-shift magnet is held down by the catch c engag- 
ing the pin p; consequently the type-wheel is maintained 
in its upper position for the printing of upper-case letters 
until released by the attraction of catch c by the type- 
release magnet R, which operates on the reception of the 
" space" character. 

Shifting of the paper for line spacing is accomplished by 
the paper-feed magnet which is actuated by the sixth pulse 
following 5 dash current pulses. Its operation is identical 
with that of the type-shift magnet, being assisted also by 
an auxiliary magnet, not shown in the diagram. 

The carriage, holding the paper upon which the message 
is printed, is returned to the starting position by means 
of the carriage-return magnet, the mechanism, as before, 
not being shown in the figure. When the armature of this 
magnet is attracted, causing the return of the carriage, 
the circuit of the final relay is opened at the normally- 
closed contacts m. As a result, the current through the 
final relay is interrupted before its armature spring breaks 
contact with its rear stop, through which current continues 
to flow from generator D f to energize the carriage-return 
magnet. The instant the carriage arrives at its starting 
position, the circuit-breaker B opens the circuit of the 
carriage-return magnet, which in releasing its armature, 
completes at m the circuit of the final relay, thereby per- 
mitting this relay to reset the distributing relays. 

Reverting to Fig. 16, the lever of the synchronizing mag- 
net is seen to act upon the unison wheel. The function of 
this magnet is to restore f the unison wheel to the zero 
position, if, for any reason, it gets out of step with the in- 
coming current pulses. The winding of this instrument, 
which is of the polarized type, is such that its permanent 



AUTOMATIC AND PRINTING TELEGRAPHY 133 

magnetization is opposed by negative current pulses and 
assisted by positive current pulses. Since the armature 
of this magnet is adjusted not to operate on short-current 
pulses, only long positive current pulses bring the synchro- 
nizer into action. Such pulses occur in some letters, and 
occur invariably at the end of each letter or character. 
In proper operation, the hook on the synchronizer lever 
rests in spaces between the teeth of the unison wheel, and 
would interfere with its motion at the end of each letter 
were not the synchronizer magnet energized at that instant 
by a long positive pulse. Should any pulses of a letter be 
lost, this magnet would restore synchronism upon the 
reception of the next following long positive current pulse. 

4. Other Printing Telegraph Systems. The Mor- 
krum page-printing telegraph system is also used at 
present both by the Western Union Telegraph and Postal 
Telegraph-Cable Companies. The Baudot tape-printing 
system is extensively used abroad, the system being 
operated simplex, duplex or multiplex. The Hughes tape- 
printing system is largely employed in Europe, about 3000 
instruments being now in use. The Rowland multiplex 
and the Wright page-printing systems were for a time used 
on some circuits of the Postal Company. The Burry page- 
printing telegraph is used by the Stock Quotation Tele- 
graph Company for disseminating general and financial 
news in New York City and vicinity. 

Many other systems have been invented and are now 
used more or less here and abroad for the direct printing 
of the received messages, among which may be mentioned 
the systems of Munier, Murray, Essick, Dean, Creed, 
Siemens, Kinsley and Buckingham, the last being the fore- 



134 TELEGRAPH ENGINEERING 

runner of the Barclay printing system, herein described. 
Multiplex page-printing telegraph systems will be consid- 
ered in Chap. VI. 

PROBLEMS 

1. Show the appearance of a transmitting tape for automatic 
telegraphic transmission with perforations representing the word 
"Wheatstone." 

2. How many words may be telegraphically transmitted in one 
direction over a wire by the Wheatstone automatic system in 6 hours 
if the perforated tape is passed through the transmitter at the rate 
of 4 words per second? Allow two per cent for idleness in changing 
tapes. 

3. Fill out the letter designations of the blank printer magnet 
circles of the Barclay printer shown in Fig. 17. 

4. When the speed of the Barclay transmitter is such that forty 
current reversals take place per second when running without tape, 
and considering the length of the average letter to be the average 
of the characters of the Barclay code, how many five-letter words 
could be transmitted per minute in each direction with this printing 
system? 



CHAPTER V 

TELEGRAPH OFFICE EQUIPMENT AND TELEGRAPH TRAFFIC 

i. Protective Devices. Fuses are used in telegraph 
circuits to protect these circuits from damage which might 
result from an excessive flow of current through them. 
They are made of fusible material, generally of lead or of 
an alloy of tin and lead, and assume the form of wire or 
strips provided at each end with a copper terminal which 
engages the contacts of the fuse receptacles. With en- 
closed fuses the fusible material is surrounded by a finely- 
divided non-combustible powder that is contained in an 
insulating casing. All fuses are placed at accessible places, 
generally in telegraph offices, so as to facilitate replacement 
in case of their melting. 

Fuses are rated at 80 per cent of the greatest current 
they can carry indefinitely without melting. Thus, a 
fuse would carry a current 25 per cent greater than the 
normal rated current strength. For telegraph service 
fuses of ^-ampere capacity and upward are used. Line 
fuses also offer protection to terminal apparatus when the 
lines are crossed with electric distributing and other high- 
voltage lines. 

Lightning arresters are employed at telegraph offices 
and also on lines, as a protection against injury to terminal 
apparatus and attendant operators, that would otherwise 
result from lightning strokes or relieved abnormal induced 
charges. These arresters provide a short path to ground 

135 



136 



TELEGRAPH ENGINEERING 



through a small insulating gap, generally of air, that is 
readily broken down and rendered conductive by such 
discharges. The length of these gaps is such that the oper- 
ating voltages in telegraph service cannot initiate arcs 
across the spark gaps. 

In practice, satisfactory fuses and lightning arresters for 
telegraph circuits assume a variety of forms, concededly 
more or less familiar. The type of protector now used by 
the Western Union Telegraph Company is shown in Fig. 8. 

2. Peg Switch Panels. A switching arrangement 
adapted for use at intermediate stations on simplex lines 




Fig. i. 

is shown in Fig. i, and is called a peg switch panel or a strap 
and disc switch panel. The wall panel shown is used where 
two-line wires pass through an intermediate office, and pro- 
vides means for introducing either set of receiving instru- 
ments into either line, for cross connecting, for looping 
these lines with or without introducing home instruments, 
and for cutting off one side of a line. 

This panel consists of four brass straps and two rows of 
discs, five in each row. The line terminals are on the 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 137 

upper ends of the straps, and the instrument terminals 
are along the left edge of the panel. The latter terminals 
are in line horizontally with the discs, and each terminal is 
in electrical connection with the discs located in the same 
horizontal row. The plate g is placed transversely over 
the straps and over the two upper discs, but is insulated 
from the vertical straps by a small air gap, thereby 
serving as the ground plate of a lightning arrester. Any 
disc may be connected to either of the straps between 
which it is located by means of a brass plug or peg, which 
fits in the holes formed between the discs and straps. These 
holes are in five horizontal rows numbered i, 2, 3, 4 and 5, 
and in four vertical rows lettered a, b, c and d, so that any 
one of the 20 holes may readily be referred to. Two re- 
ceiving sets, each consisting of relay and key, are also 
shown connected to the panel terminals. The insertion 
of a plug in any of the four upper holes grounds the corre- 
sponding strap. 

When it is desired to insert receiving set i into line A, 
plugs are inserted in holes 02 and d $ (or 3 and d 2). 
If, at the same time, it be desired to complete line B with- 
out a receiving set, plugs are inserted in holes a 4 and b 4 
(or a 5 and 5). To cross connect the two lines with 
receiving instruments in each circuit, plugs are placed in 
holes a 2 and d 3, and b 4 and c 5. Instead, to cut off the 
western section of line A, leaving receiving set i in its 
other section, insert plugs in holes c i, c 2 and d 3. In 
order to loop the two eastern wires together with or with- 
out intermediate set i, insert plugs respectively in holes 
b 2 and d 3 or in holes b 2 and d 2. 

For the accommodation of additional lines at inter- 
mediate or terminal offices, peg panels having a corre- 



TELEGRAPH ENGINEERING 



spondingly greater number of straps and discs may be 
used. A combination of the peg-switch panel and the 
spring-jack device, the latter shown in Fig. 2, forms a 




Fig. 2. 

widely used panel. The insertion of a wedge, as shown, 
raises the shank away from the fixed shoe and introduces 
into the line whatever apparatus is connected with the 
wedge cord. Single- and double-conductor wedges are used 
for various purposes, and more than one wedge may be in- 
serted in a spring jack, thus meeting a variety of telegraph- 
circuit requirements. 

3. Main and Loop Switchboards. In large telegraph 
offices the switching arrangements for the interconnection 
of all classes of circuits are located at switchboards. Usu- 
ally these switchboards are divided into two parts: the 
main switchboard, at which terminate the incoming line 
wires, each wire being equipped with a group of pin-jacks; 
and the loop switchboard, at which the local office circuits 
or loops may be connected from one circuit to another. The 
pin- jacks on both switchboards are so connected that each 
line or local circuit is complete for normal operation. 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 139 



Changes in these normal conditions are effected by single 

or double flexible conductors or patching cords having plug 

terminals which fit into the jacks. Fig. 3 shows the type 

of pin- jacks and plugs 

now extensively used on 

telegraph and telephone 

switchboards. 

Main Switchboards. 
All line wires terminate 
at the main switchboard 
which is equipped with Fi - 3. 

properly connected jacks for the establishment of any 
desired connections with these wires. 

A main switchboard comprises a variety of circuits. A 




. BUSY TEST KNOBS 




TO LOOPP 
VIA DI8TRIB 



40 - 3 LOOP SIMPLEX MORSE WIRE 



Fig. 4- 



typical panel of the Western Union main switchboard 
for terminal offices contains nine types of circuits, five of 
which are shown in Fig. 4, the number of circuits of each 



140 



TELEGRAPH ENGINEERING 



type being indicated. The remaining four types are 
shown as circuits A, D, E and F in Fig. 6 in connection 



RESISTANCE 

LAMP3 

CABLE FROM LAMPS 
TO LOCAL BATTERY FUSES 

a 




REAR VIEW OF 
CABLING FOR 
FLOOR DUCTS 



SECTION 
Fig. 5- 



FRONT VIEW 



with the loop switchboard, twenty A, four D, ten E and 
twenty F circuits being employed. Circuits for combined 
telegraphy and telephony are also provided where necessary. 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 141 



RESISTANCE LAMP (3 - 12 OHMS PER VOLT) 

~ 



20 TWO-WIRE TRUNKS (FROM ONE 
' END OF BOARD TO OTHER ) 




fr-^"- 

*-^~l SOUNDE 




10 - DUPLEX OR QUAD. SETS AND REGULARLY 
ASSIGNED LOOPS 



RESISTANCE 
LAMPS 



80- DUPLEX LOOPS WITHOUT REGULAR ASSIGNMENT 



POLE CHANGE 



TO MAIN SWITCH- ) 
BOARD JACKS OR >- 

REPEATERS VIA I 

DISTRIBUTING FRAME )~ 



(D 



'II 



64 - TWO WIRE TRUNKS TO MAIN SWITCH B'D. 
20 - HALF-REPEATER LOOPS <2 FOR EACH ) 
20 - FULL-REPEATER LOOPS ( 2 FOR EACH ) 
24- DOUBLE LOOP REPEATERS (3 FOR EACH) 




16 -DUPLEX OR HALF-QUAD. REPEATER LOOPS. 



8-TE8TING8ET8 



Fig. 6. 



142 TELEGRAPH ENGINEERING 

Referring to Fig. 4; circuit B is used for simplex service 
which may require three loops or sets each, the loops being 
included by inserting the plugs of patching cords in jacks 
7-8, 9-10 and 11-12; circuit C is used on multi-section 
switchboards for extending loops and other circuits from 
one section to another; circuit G is used in cases of loop 
failures and circuit H is used for testing purposes where 
it is required to ground a line. For duplex or quadruplex 
circuits it is only necessary to connect the line through 
three jacks to the corresponding set via the loop switch- 
board and distributing frame, as indicated by circuit /. 

The design of this switchboard is shown in Fig. 5, the 
jacks bearing numbers corresponding to those in Fig. 4. 

Loop Switchboards. A loop switchboard is generally 
installed at large telegraph offices to provide facilities for 
conveniently changing local circuit connections of duplex 
and quadruplex sets from one operating table to another 
at the main office or for distributing these connections to 
subscribers or branch offices, so as to take care of varying 
traffic requirements. The terminals of such local circuits 
extend to pin jacks on the loop switchboard, the board cir- 
cuits being so arranged that the local apparatus regularly 
assigned to the same circuit is normally conriected thereto, 
changes in these connections being made with flexible 
patching cords. 

A loop switchboard includes a variety of circuits. A 
typical panel of the Western Union one-section loop switch- 
board comprises the eleven types of circuits shown in 
Fig. 6, the number of circuits of each type being indicated. 

Circuit A is used in the testing of simplex circuits; cir- 
cuit B is used in testing, or in case of failure of the resist- 
ances or contacts of an office loop, it replaces the lower 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 143 

jack of circuit G; circuits C and D enable simplex apparatus, 
loops, repeaters, etc., to be readily joined in series, the 
former including a current source; circuit E permits of the 
interconnection of apparatus terminating at remote por- 
tions of the board by means of two short patching cords 
instead of one long one; the jacks of circuit F connect 
with receiving sets, repeaters, half -repeaters, etc., or extend 
to jacks on the main switchboard; circuits G and H con- 
nect the apparatus of a duplex or quadruplex set for 
normal operation, the latter circuit being used where an 
outside loop is regularly assigned to the set; circuit / is 
used for branch office loops that are not regularly assigned 
to any particular duplex set, and may replace those nor- 
mally assigned in circuits G and H; circuit / normally 
joins the two duplex or half -quadruplex sets that constitute 
the duplex repeater; circuit K serves as a testing set for 
making any desired tests on duplex or quadruplex sets. 

4. Distributing Frames. Before telegraph aerial or 
underground lines reach the main switchboard at an office 
they pass through a distributing frame generally placed 
in back of the switchboard. Office cables extend from this 
frame to the main and loop switchboards and to the instru- 
ment tables on- which repeater, duplex and quadruplex 
apparatus are located. Fig. 7 shows three units of a 
Western Union distributing frame. The right or " hori- 
zontal" side has 8 horizontal strips which carry terminal 
blocks for connection, say, to office apparatus, while the 
left or " vertical" side has 3 vertical strips which may 
carry similar terminal blocks or office protectors and con- 
nect with the incoming line cables. Each horizontal seg- 
ment accommodates 20 terminal clips for an equal number 



144 



TELEGRAPH ENGINEERING 




Fig. 7. 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 145 



of wires and each vertical strip accommodates 100 pro- 
tectors. These connections to terminal clips and pro- 
tectors are permanent. Any desired connection may be 
made between the different pieces of apparatus in the 
office, or between such apparatus and entering lines, by 
cross-connecting or " bridle" wires at the distributing 
frame. Switchboard rearrangements or changes in traffic 
requirements are, therefore, readily met by shifting the 
bridle wires without altering the apparatus and line wiring 
to the distributing frame. 

The type of protector used comprises a one-half ampere 



^AMPERE FUSE 




RELAXED SPRING INDICATES 
BLOWN FU6E 



| | LIGHTNING ARRESTER 



GROUND PLATE 



Fig. 8. 

indicating fuse and a lightning arrester formed by two 
carbon blocks separated by a thin strip of mica, and is 
shown in Fig. 8. 

5. Instrument Tables. Telegraph apparatus at large 
telegraph offices is arranged in a very compact form on 
instrument tables. One general form of instrument table 
construction is shown in Fig. 9, which shows that portion 
of one side of a long table occupied by the apparatus of 
one quadruplex set. A duplex set requires about 13 inches 
and a duplex repeater set about 33 inches of table length. 

The location of the apparatus of a Western Union 
quadruplex set on this table is generally as indicated in 



146 



TELEGRAPH ENGINEERING 



the figure, the upper shelf being reserved for signalling 
purposes. The unit-section instrument tables used by the 
Postal Telegraph Cable Company are constructed of angle 
and sheet iron with apparatus located on four narrow tiers, 
each unit accommodating two quadruplex sets, or four 
duplex sets, or four repeater sets. 

/ 



< , - SIGNAL ,. SIGNAL 

' SIGNAL * -~MAMP '' SIGNAL ' /--IrAMP 

^'____RELAY_^ X __)LAMP ^. RELA_Y_^' (-LA.MP, 



_ _ S.WITCHE8 
PLATE ' 





''''-lwNtt^/^&''' -~ '}^ P P~?' ^l'j^^~*-'?. E J--,/'s' 

tsxH**-af 4 

NEUTRAL s' 

RELAY S ' 




X^O 



Attendants constantly oversee the operation of such 
duplex, quadruplex and repeating apparatus, each attend- 
ant having supervision of a certain number of sets. 

6. Power Switchboards. A switchboard for a tele- 
graph power plant should comprise the necessary switching 
facilities, measuring and regulating devices for the placing 
of the desired potentials of correct polarity on the terminals 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 147 

of the distributing panel from which conductors lead to the 
main switchboard. As most telegraph power plants con- 
sist of motor-generator units, which alter the voltage of 
the available commercial current supply to values suitable 
for telegraphic purposes, switchboards for such plants 
should also include motor-starting switches and rheostats. 
To maintain continuity of service in case of shut-down of 
the commercial current supply, arrangements are made if 
possible, for break-down connection with another source, 
or, if the available current sources are not dependable, 
a storage battery or, where practicable, a steam, gas or 
oil engine and generator, is installed. 

The appearance of a typical power switchboard now used 
by the Western Union Telegraph Company for a motor- 
generator plant is shown in Fig. 10, scale gV- The board is 
mounted directly over the machines, each panel controlling 
the motor-generators below it. The left-hand panel con- 
trols three machines, one generator having its positive ter- 
minal permanently grounded, another its negative terminal 
grounded, and the middle generator serves as a spare unit 
which may replace either of the others by shifting the re- 
versing switch. The smaller switchboard panel is intended 
for two machines, one delivering current to the local cir- 
cuits and the other a spare unit. All generator and motor- 
starting switches and the voltmeters are provided with 
enclosed fuses on the face of the board. 

The connections of this power board for motor-generators 
with direct-current motors are shown in Fig. n. Three 
1 60- volt and two 2 6- volt motor-driven . generators are 
shown, the outer i6o-volt machines and the left-hand 
26-volt machine being in service. When the middle 
i6o-volt generator is to replace its left neighbor, it is 



148 



TELEGRAPH ENGINEERING 




TELEGRAPH OFFICE EQUIPMENT TRAFFIC 149 




150 TELEGRAPH ENGINEERING 

started and brought up to proper voltage by means of its 
field-regulating rheostat RR and placed in parallel with 
its neighbor by throwing switch E to the left and closing 
switch B. Thereafter switches A and then F are opened. 
In the figure V and A indicate voltmeters and ammeters 
respectively, / indicates fuses and SR represents motor- 
starting rheostats with no-voltage release, the terminals 
marked M, A and F connecting with the service main, 
motor armature and motor field respectively. The gener- 
ator leads go to a distributing panel which provides con- 
venient means for distributing the proper current to the 
various classes of circuits. This panel also includes the 
main service switch and instruments. 

Switchboards for motor-generators, having alternating- 
current single-phase, two-phase or three-phase motors, 
differ slightly from the board described in that different 
starting devices and motor switches are employed. 

TRAFFIC 

7. Types of Messages. Messages for telegraphic 
transmission may be written in plain language, be expressed 
in code words, or be couched in cipher. Code words are 
actual or artificial pronounceable words having not more 
than 10 letters. The object of employing code words is 
the saving of telegraph tolls, inasmuch as a single word is 
given a meaning expressible in plain language only by 
several words or even a sentence. A few code words with 
their interpretation according to the Western Union 
Travelers' code are given below: 

ALLAH Arrived all right, address letters to care of 

BALMY Are very busy. Please return soon as possible. 

BRING There is no occasion for alarm. 

COVER Can you send me letter of introduction to ? 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 151 



ENTER Arrangements are progressing satisfactorily. 

LUNAR I (or ) do not wish to take responsibility for deciding. 

You (or ) know all the circumstances and must 

decide what shall be done. 
PEGGY Market very strong. Prices have advanced since last 

advice. 

PUNCH Please accept my heartiest congratulations. 
SPIKE Have sent telegraphic money order as requested. 
SCORN We wish you all a Happy New Year. 

Cipher messages are used solely for secrecy. Such 
messages consist of unpronounceable groups of letters or 
of groups of figures, or both. They can be read only by 
the sender and recipient, in accordance with some pre- 
arranged scheme. Considerable time is necessary for 
couching and deciphering such cipher messages. As an 
illustration, the Confederate cipher used during the Civil 
War will be cited, the keywords employed by the Confed- 
erates being "Complete Victory," ^Manchester Bluff" 
and later " Interest. " The cipher is made up by giving 
numbers to the letters of the alphabet as below: 

abcdef ghi j k 1 mnopqrstuvwxyz 
I 2 3 4 5 6 7 8 9 10 n 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 
27 28 29 3 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 

To write a cipher message add the respective numbers 
corresponding to the letters of the keyword and of the 
message (letter for letter, repeating the keyword if neces- 
sary), subtract the index number i, and the corresponding 
letters will yield the cipher message. Thus to write 
" Reach Richmond to-day," using the keyword " Interest," 
proceed as below: 

R I CHMOND 
18 9 3 8 13 15 14 4 
E S T I N T E R 
5 19 20 9 14 20 5 18 



REACH 
185 i 3 8 

INTER 

9 14 20 5 18 

Sum minus one 26 18 20 7 25 

Z R T G Y 



22 2? 22 l6 26 34 18 21 

VAVPZHRU 



TODAY (message) 
20 15 4 i 25 
E S T I N (keyword) 
5 19 20 9 14 

24 33 23 9 38 

X G W I L (cipher) 



The last line is the appropriate cipher message. 



152 TELEGRAPH ENGINEERING 

To decipher a message according to this cipher, subtract 
numbers corresponding to keyword from number corre- 
sponding to cipher (letter for letter), add the index num- 
ber i, and the corresponding letters will yield the message. 
By varying this scheme and using different keywords, an 
infinite variety of cipher codes may be developed. The 
characters of cipher words are transmitted with double 
spacing as a safeguard for avoiding errors. 

8. Classes of Service and Tariffs. Several classes of 
telegraph service are rendered by the large telegraph com- 
panies. The overland services offered by the Postal and 
Western Union Companies are: telegrams and night letters; 
the latter company also offers day letters. 

Present rates (1914) for commercial telegrams from New 
York City to the capitals of the states and territories in 
the United States and of some of the provinces in the 
Dominion of Canada, are given in the table on the follow- 
ing page, which includes also the rates to Mexico City and 
Dawson City, Yukon. Day rates apply to messages in- 
tended for immediate delivery whereas night rates apply to 
telegrams for delivery the following morning. The number 
before the dash is the rate in cents for telegrams of 10 words 
or less (address and one signature free), and the number 
following the dash is the charge for each additional word. 

Night letters containing 50 words (or less) may be sent 
at the lo-word day message rate, one-fifth of this rate being 
charged for each additional group of 10 words; and day 
letters of 50 words (or less) may be sent at ij times the 
night letter rate. Day letters are forwarded as promptly 
as the facilities of the company permit only in subordination 
to the full-paid telegrams, and night letters are trans- 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 153 





RE 


ites 


Citv 


Ra 


tes 




Day 


Night 




Day 


Night 




60-4 


5O-3 


Carson City, Nev. 


100-7 


100-7 


Juneau, Alaska 
Phoenix Ariz. 


260-23 
100-7 


260-23 
100-7 


Fredericton, N. B 
Concord, N. H. 


50-3 
35-2 


40-3 
25-1 


Little Rock Ark 


60-4 


50-3 


Trenton, N. J. 


25-2 


25-1 


Victoria, Brit. Col 


100-7 
100-7 


100-7 
100-7 


Santa Fe*. N. Mex 
Albany, N. Y. 


75-5 
25-2 


60-4 
25-1 


Denver, Col 
Hartford Conn. 


75-5 
25-2 


60-4 
25-1 


Raleigh, N. C 
Bismarck, N. Dak. 


50-3 
75-5 


40-3 
60-4 


Dover, Del 
Washington, D. C. 


30-2 
30-2 


25-1 
25-1 


Halifax, N. S 
Columbus, Ohio 


50-3 
40-3 


40-3 . 
50-2 


(National capitol) 
Tallahassee, Fla. 


60-4 


50-3 


Oklahoma City, Okla. . . 
Ottawa, Ont. . 


75-5 
50-3 


60-4 
4O-3 


Atlanta, Ga 
Boise, Id 
Springfield 111. 


60-4 
100-7 
50-3 


50-3 
100-7 
40-3 


(Capitol of Dominion) 
Toronto, Ont 
Salem, Ore. 


50-3 

100-7 


40-3 
100-7 


Indianapolis, Ind 
Des Moines, la. 


50-3 
60-4 


40-3 
50-3 


Harrisburg, Pa 
Charlottetown, P. E. I.. 


30-2 
75-5 


25-1 
65-5 


Topeka, Kan 
Frankfort, Ky. 


60-4 
50-3 


50-3 
40-3 


?uebec, Quebec 
rovidence, R. I. 


50-3 
30-2 


40-3 
25-1 


Baton Rouge, La 
Augusta, Me. 


60-4 
40-3 


50-3 
30-2 


Columbia, S. C 
Pierre, S. Dak.. 


60-4 
75-5 


50-3 
60-4 


Winnipeg Manitoba 


75-5 


60-4 


Nashville Tenn. 


50-3 


40-3 


Annapolis, Md 
Boston, Mass. 


30-2 
30-2 


25-1 
25-1 


Austin, Tex 
Salt Lake City, Utah. 


75-5 
75-5 


60-4 
60-4 


Mexico City, Mexico 
Lansing, Mich. 


175-12 
50-3 


175-12 
40-3 


Montpelier, Vt 
Richmond, Va. 


35-2 
40-3 


25-1 
30-2 


St. Paul Minn 


60-4 


50-3 


Olympia Wash 


100-7 


100-7 


Jackson, Miss 
Jefferson City, Mo. 


60-4 
60-4 


50-3 
50-3 


Charlestown, W. Va 
Madison, Wis. 


40-3 
60-4 


30-2 
50-3 


Helena, Mont 
Lincoln, Neb -. . . . 


75-5 
60-4 


60-4 
50-3 


Cheyenne, Wyo 
Dawson City, Yukon. . . 


75-5 
425-29 


60-4 
425-29 



mitted sometime during the night at the convenience of 
the company and are delivered the following morning. 
Such deferred service is offered at attractive rates in order 
to keep the equipment effectively busy at all hours, or in 
other words, to keep up the load factor of the equipment. 

Day and. night letters must be written in plain English 
and must not contain code words. The letters BLUE, 
NL or NITE are prefixed to a message and transmitted 
to inform the receiving operator as to the class of service 
desired, whether day letters, night letters or night-rate 
telegrams respectively. The indication DH (representing 
dead head) is used on unpaid messages for company matters, 
etc. When a group of messages of one class is transmitted, 



154 



TELEGRAPH ENGINEERING 



a single indication on the first message of a group suffices 
for successive messages until a different indication is re- 
ceived. 

A message blank bearing a message for transmission 
should contain the following information: 



ITEM No. ITEM 

1 Originating city 

2 Date 

3 Addressee (name and address) 

4 Message 

5 Signature 

6 Indication as to class of service 

(Different blanks are used for the 
various classes.) 

7 Telegraph clerk's number 

8 Time of filing 

9 Check of number of words 

10 Wire number 

11 Office call letter at destination 

12 Sending operator's sign 

13 Time of transmission 

14 Receiving operator's sign 



BY WHOM WRITTEN 



Sender or telegraph 
clerk. 



Telegraph clerk. 



Sending operator. 



The first six, the ninth, tenth, thirteenth and fourteenth 
items as well as the call-letter of the originating office are 
transmitted and appear upon the received message blank 
that is delivered to the addressee. If a reply is to be pre- 
paid the letters RP followed by the number of words pre- 
paid are transmitted and also appear upon sending and 
receiving message blanks. 

9. Handling of Traffic. The methods employed in 
handling commercial telegraphic traffic depends largely 
upon the volume of incoming and outgoing traffic. In a 
large center the handling of this traffic at the main office 
must be fully systematized in order to facilitate prompt 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 155 

transmission and delivery of messages. Somewhat differ- 
ent methods of handling traffic are naturally employed at 
different places; that used in a large city will here be out- 
lined. 

The telegraphic stations of a city for the reception and 
transmission of messages comprise a main office and many 
branch offices distributed throughout the city. The Wes- 
tern Union Telegraph Company has about 200 branch 
offices in New York City. Messages for transmission may 
reach these branch offices either by submission in person 
or by representative, or may be collected by messenger 
upon call, no charge being made for this service. Messages 
may also be telephoned from telephone subscribers' stations 
to the main office by requesting the telephone operator 
for "Western Union" or for "Postal," and upon connec- 
tion, dictating the message to the answering telegraph 
clerk. The tolls for a message so sent will either be col- 
lected upon delivery or will be charged to the sender on 
his telephone bill. Messages received at branch offices 
are sent to the main office in two ways : the blanks may be 
carried by pneumatic tube carriers from those offices that 
are connected with the main office by such tubes, or else 
the message is telegraphed to the main office. 

The messages arriving at the main office for telegraphic 
transmission are sorted at a central distributing place or 
routing room and are distributed by mechanical carriers 
to division stations, each division being a portion of the 
operating floor seating operators who transmit on lines 
terminating in some geographical division of the country. 
Check boys or girls carry the message blanks from the 
division stations to the proper operators. After the oper- 
ators have transmitted a message, they indorse the blank 



156 TELEGRAPH ENGINEERING 

(by inscribing items 10-14 of the scheme given in foregoing 
section) and place it in a message clip. Check boys pass 
up and down the aisles and remove the blanks from the 
clips and take them to the division stations from whence 
they are carried mechanically to a searching room. Here 
the blanks are examined as to the indorsement and are 
filed away and preserved for a reasonable length of time. 

Incoming messages are typewritten upon suitable blanks 
by the receiving operators or are automatically printed by 
the printing telegraphs. These incoming messages are 
carried by check boys and mechanical carriers to the 
routing room, where they are sorted. Such messages re- 
quiring retransmission are carried to the proper sending 
operator in the same way as originating messages. The 
remaining messages are for local distribution within the 
city confines. These city messages are sorted and may 
be telephoned directly to the addressee if he be a telephone 
subscriber, or else sent to his nearest branch office either 
by pneumatic tube or by wire, and from there delivered 
by messenger to the addressee. 

The traffic manager at a large telegraph office is kept 
constantly informed regarding the amount of traffic over 
the various interurban and important lines, so that if 
necessary he may alter the customary routing of messages 
in order that telegraphic business at all centers may be 
adequately disposed of with the available existing facilities. 
Thus, if an unusual amount of traffic has accumulated at 
Philadelphia for transmission to Chicago via New York, 
and if the traffic from Philadelphia to Boston, and from 
Boston to Chicago is light, the traffic manager would 
direct the operators at Philadelphia to send some of the 
messages to Chicago via Boston. In the event of severe 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC 157 

storms felling pole-lines between important centers, the 
traffic manager endeavors to re-establish service between 
these points over another route even if very circuitous. 

Records of the amounts of traffic accommodated on the 
various line circuits are kept for the information of tele- 
graph engineers who determine the necessity for additional 
lines and equipment or suggest rearrangements of existing 
facilities for improving the service. 

10. The Telegraph in Railway Operation. The hand- 
ling of steam trains in accordance with telegraphic orders 
began in 1851, and since that time has been rapidly ex- 
tended to all railroad systems. Since 1907 the telephone 
' is also used in train dispatching and in the directing of train 
movements; at present, about 70,000 miles of railroad in 
this country are telephonically handled. 

A large majority of all telegraph offices in the United 
States are located in railway stations, and large amounts 
of commercial and especially railway telegraph traffic are 
handled through them. Railway telegraph traffic may 
deal with inter-departmental business or with train move- 
ments, the latter traffic being usually urgent and requiring 
immediate attention. Such traffic on a railroad division 
includes the progress of passenger and freight trains, 
attendance to emeVgencies as they arise, information on 
the location of rolling stock, messages concerning ship- 
ments, and so on. 

The use of the telegraph for issuing and receiving such 
information generally requires two local single-wire circuits 
linking the principal office of the division with its various 
local offices. One of these circuits, termed the train wire, 
is used by the train dispatcher, and the other, termed the 



158 



TELEGRAPH ENGINEERING 



message wire, is used for transmission of commercial and 
railway telegrams. On unimportant branch roads both ser- 
vices are sometimes handled over a single circuit, whereas 
on long or busy railway divisions the more important 
offices may be connected to a special circuit to relieve con- 
gestion of traffic on the other circuits. Between the 
principal division offices of a system and the general offices 
or administrative center of the railroad are a series of 
circuits, which may be operated simplex, duplex or quad- 
ruplex, with or without repeaters, as the traffic or length 
of the circuit may warrant. Thus, an idea of the extent 
of the telegraph circuits of the Northern Pacific system 
(which operates over 6000 miles of main-line track) may be 
gained from the following list of principal circuits now 
operated out of the St. Paul, Minn., general office. This 
list, given by M. H. Clapp, does not include some local 
circuits operating out of St. Paul to points in the direct 
vicinity of the Twin Cities. There are four repeating 
stations on the St. Paul-Tacoma line, at which traffic is 
also relayed to different offices to which direct wires are 
not provided. 



Circuit from St. Paul to 


Circuit 
operated 


Distance 
in miles 


Tacorna Wash . ... 


Quadruplex 


1900 






1250 






1650 


Helena, Mont 




1130 


Billings and Livingston, Mont. 




1008 


Dickinson N. D. and Glendive, Mont .... 




667 


Fargo N D and Dilworth Minn. 




252 


Duluth Minn 


Duplex 


152 


Winnipeg, Man. Local 32 offices 


Simplex 


483 


Fargo, N. D. Local 41 offices 




252 


Duluth Minn. Local 40 offices . 





152 


St Paul Division. Local 30 offices 





170 









TELEGRAPH OFFICE EQUIPMENT TRAFFIC 159 



ii. Telegraph Statistics. The United States censuses 
of electrical industries show the following statistics of the 
domestic telegraph industry in the years 1880, 1902, 1907 
and 1912: 

COMMERCIAL LAND AND OCEAN TELEGRAPH SYSTEMS 





1880 


1902 


1907 


1912 


Number of companies or sys- 
tems 


77 


25 


25 


27 


Nautical miles of ocean cable. . 
Miles of single wire owned and 
leased 
Number of messages 
Number of telegraph offices 
Dollars total income 


(a) 

291,213 
31,703,181 (d) 
12,510 
16,696,623 


16,677 

1,318,350 (b) 
91,655.287 
27,377 
40,930,038 


46,301 

1,577,961 
103,794.076 
29,056 
51 583 868 


67,676 

1,814,196 (c) 
109,377,698 
30.864 
64 762 843 


Average number of employees(e) 
Employees salaries and wages 
(dollars) (g) 


14,928 
4,886,128 


27,627 
15,039,673 


28,034 (/) 
17,808,249 


37,295 
24,964,994 













(a) Not separately reported. 

(b) Includes miles of wire operated by W. U. Tel. Co. outside of the United States. 

(c) Exclusive of 314,329 miles of wire wholly owned and operated by railway companies 
for their own business. 

(d) For 54 companies out of 77. 

(e) Does not include railway operators also doing work for telegraph companies. 
(/) For 23 companies out of 25. 

(g) Two companies in 1907 and one in 1902 did not separate salaries and wages from oper- 
ation expense. The wages of persons enumerated above spending a part of their time 
in telegraph service are those received for telegraphic service only. 

The large decrease in the number of separate companies 
from 1880 to 1902 was due to numerous consolidations of 
formerly competing companies. Far more than one-half 
of the number of telegraph offices tabulated are located 
in railway stations, and these offices are not used exclu- 
sively for the transmission of messages for the general public. 

The extent to which the telegraph industry is controlled 
by a few companies is indicated by the fact that the six 
largest companies reported 99 and 97.7 per cent of the total 
tabulated income in the years 1902 and 1907, respectively. 



i6o 



TELEGRAPH ENGINEERING 



The 1907 census also shows that 625 railway companies 
in the United States, operating 225,059 miles of single track, 
owned 383,833 and leased 423,991 miles of telegraph wire, 
and sent 258,589,333 telegraph messages for railroad busi- 
ness during the year. 

Comparative telegraphic statistics of various countries 
selected from Senate Document No. 399, dated 1914, for 
the year 1910 (except where otherwise stated) are tabu- 
lated below: 

TELEGRAPH STATISTICS OF DIFFERENT NATIONS 



Country 


Population 


Annual 
telegrams 
per capita 


Average 
receipt per 
domestic 
telegram 
in cents 


Telegraph 
offices 


Miles of 
telegraph 
wire 


Per 10,000 of population 


Austria 
Belgium 


28,571,934 
7,074,91 
2,585,660 
38,961,945 
63,886,000 
41,976,827 
20,886,487 
32,475,253 
49.732,952 
246,455 
5,591.701 
1,062,792 
2,240,032 
152,009,300 
5,294,885 
3,315,443 

95.410,503 


0.73 
1.25 
1. 31 
1.65 
0.92 
2.18 
0.59 
0.55 
0.60 
0.84 
1.19 
8.09 
1.48 
0.24 
0.80 
1.75 

1.09 


22.4 
14.2 

14.0 

12. 1 

18.0 
17.2 
25.1 
19-3 (a) 
12.3 
9-0 
15-0 
15-7 
I3.4(a) 
42.0 
15 3 
17.2 

45.0 


1.58 
2.31 
2.17 

5-21 

7.06 
3-33 

2.20 
2.36 

0.86 
13.16 
2.49 
18.51 
7.08 
0.55 
5-39 
7.13 

3-42 


50 
36 
34 
108 
175 
135 
42 
38 

20 
29 
40 

357 
142 
28 
37 
48 

190 


Denmark 


France 


Germany 
Great Britain 
Hungary 


Italy 


Japan 
Luxemburg (1905) . . . 
Netherlands . 


New Zealand 


Norway 


Russia 
Sweden 


Switzerland 


United States (1912) 
(b) 





(a) Minimum message rate. 

(b) Statistics computed from preliminary report on Land Telegraph Stations: 1912, 
issued Feb., 1914. 

It will be observed that of the countries tabulated, the 
average cost per telegram is least in Luxemburg and most 
in the United States, and that the yearly telegrams per 
individual is most in New Zealand and least in Russia. 



TELEGRAPH OFFICE EQUIPMENT TRAFFIC l6l 



PROBLEMS 

1. How are the two lines passing through a four-strap peg switch 
panel (see Fig. i) interconnected at this panel without introducing 
intermediate receiving instruments into either line? 

2. How may a simplex line having three loops at the main switch- 
board give service to three additional subscribers or brokers' offices? 

3. Show the connections at one end of a duplex line through the 
main and loop switchboards and through the distributing frame, 
when the operators are stationed at an office some distance away 
from the main telegraph office. (Refer to circuit I of Fig. 4, circuit G 
of Fig. 6 and Fig. 16 of Chap. II.) 

4. How may the duplex line of the preceding problem be tempor- 
arily assigned to some' other branch telegraph office? 

5. Using the Confederate cipher, the key word "Manchester 
Bluff," and the index number i, decipher: YCPNLPDTRTPXCSL. 



CHAPTER VI 

MISCELLANEOUS TELEGRAPHS 

i. Multiplex Telegraph Systems. Multiplex teleg- 
raphy means the simultaneous transmission, without 
interference, of a plurality of messages in either or both 
directions, over a single line. The duplex, quadruplex, 
duplex-diplex and phantoplex systems already described 
and also the alternating-current systems of Picard and 
Mercadier may be considered multiplex systems, but in 
practice this name is applied to those systems utilizing 
synchronous rotation of contact distributors located at the 
two terminal stations. Inasmuch as the maximum speed 
of hand transmission is only about 40 words per minute, 
it is evident that the speed possibilities of telegraph lines 
even with short cable sections are not being utilized. With 
the automatic telegraph the lines are more effectively 
used, for speeds of 250 to 400 words per minute in each 
direction are maintained. Multiplex telegraphs also con- 
duce to better utilization of the lines and permit of signalling 
at rates up to about 200 words per minute in each direction. 

In the Delany multiplex system the line is successively 
assigned for short intervals to several pairs of operators 
by means of synchronously revolving distributors, the 
intervals being so short that during the hand transmission 
of a dot signal by one operator, he has exclusive momen- 
tary use of the line several times. Thus, if one pair of 
operators receive the line 36 times per second and assum- 

162 



MISCELLANEOUS TELEGRAPHS 163 

ing the average word to have the equivalent of 18 dots, 
signalling at the rate of 40 words per minute indicates 
3 contacts per dot. Between these contacts the line is 
periodically assigned to about five other pairs of operators. 
Thus, each telegraphic character is made up of short im- 
pulses rather widely separated as compared with their 
duration. Such signals are rendered intelligible when 
transmitted by pole-changing keys and received by polar- 
ized relays, as in the polar or bridge-duplex systems. 

The Delany system, adapted for hand signalling, was 
used for a number of years but has gradually given way 
to the more accurate printing multiplex systems. The 
Rowland multiplex page-printing telegraph, which affords 
octuplex signalling as a quadruple duplex, was for a time 
used on some circuits of the Postal Telegraph-Cable Com- 
pany and is now being further improved. The Baudot 
tape-printing and the Murray page-printing multiplex 
systems are at present considerably used abroad, being 
operated as double or quadruple duplex systems. The 
Murray multiplex ( 2) has also begun its operation in this 
country, affording a speed of 40 words per minute in each 
of eight channels over a single wire between two cities 
250 miles apart. A quicker telegraph service is possible 
with multiplex printing telegraphs than with ordinary 
automatic transmission because of the direct printing of 
the received messages. 

2. The Murray Multiplex Page-printing Telegraph. - 

The principal instruments used in the Murray multiplex 
telegraph are keyboard tape perforators, automatic trans- 
mitters, distributors and electromagnetically-operated 
printers. 



164 TELEGRAPH ENGINEERING 

The tapes are perforated according to a special 5-unit 
code, the units for each letter, figure or other character 
being arranged transversely to the tape. The alphabet 
perforations are shown in Fig. i to correct size, the letters 
being separated by the space character which consists 
of one perforation immediately below the guide hole. The 
tape passes directly through a constant-speed automatic 
transmitter, patterned after the Wheatstone transmitter, 
and is then wound in rolls by an automatic tape-winder. 
The transmitter is provided with a starting and stopping 

abcdefahi'jklm 



o o o o o o o 
o o o o o o o 

ooooooooooooooo oooooooooooooooo 
O OOO O OOO OOOOO 000 OO 
OOO OO OO O 
O O O O O 



O O O 0000 
OOO OOO 
ooo oooooooooooooooooooooooooooo 
OO OOOOO OOO OOOOO OOOOO 

o o o oo 

OOO O OOOOO 



n o p q r s t u v w x y z 
Fig. i. 

lever for use in case the transmitter overtakes the perfor- 
ating operator. 

The function of the distributors is evident from Fig. 2, 
wherein a single line provides four channels of communi- 
cation in either direction by means of the distributor arms 
D and D', sweeping over the contacts a, b, c and d at 
stations A and B respectively. By joining duplex term- 
inal apparatus to the contact points at both ends of the line 
quadruple duplex or octuplex signalling is rendered possible. 
Only one artificial line is used at each station. The con- 
tacts are preferably multipled so that a distributor arm con- 



MISCELLANEOUS TELEGRAPHS 



nects with one duplex set several times in one revolution, 
thereby reducing the rotational speed of these arms. 

It is absolutely essential that both contact arms occupy 
the same relative positions at all times, that is, they must 
rotate synchronously. Such rotation is secured by the 



a 
b 

c0 
i $ 




D' 



Fig. 2. 



use of manually-started motors having tooth-wheel iron 
armatures and periodically excited field magnets, the con- 
tact arms being mounted directly on the motor shaft. 
Periodic field excitation is obtained by the use of reeds 
which are kept vibrating at their natural frequency. To 
maintain synchronism the distributor at one station sends 




DISTRIBUTING 



Fig. 3- 



to that at the other station one or more governing impulses 
during each revolution of the arm, which impulses control 
the speed of the distant motor. 

The circuit arrangements for securing synchronous rota- 
tion of the distributors and for signalling over one of the 
communicating channels are schematically shown in Fig. 3, 



l66 TELEGRAPH ENGINEERING 

the groups of contacts for the other channels (that is, the 
return over a and duplex over b, c and d of Fig. 2), as 
well as the vibrating reed and distributor motor at station 
A, being omitted for the sake of clearness. The toothed 
wheel w of the distributor motor, when once set in rotation, 
will advance one tooth every time the vibrating reed r 
makes one complete vibration due to the impulsive currents 
reaching the magnet M every time the reed touches its 
front contact. The reed is kept in vibration electromag- 
netically in the usual manner, that at station B being 
adjusted to operate one or two per cent faster than that 
at A. Thus if distributor arm D' reaches the contact 
marked while the other arm D is still on the contact 
marked +, a current pulse from battery B will flow over 
the line and through the polarized relay P in such direc- 
tion as to close the contact of this relay. This momentary 
contact enables battery B f to actuate the governing relay 
R and open the vibrator circuit for an instant, thereby 
retarding slightly the vibration of the reed and the rota- 
tion of the distributor arm D'. If both arms were to pass 
over the contacts simultaneously, the contact of the 
polarized relay would be open and no governing impulse 
would reach relay R. 

Thereafter, the two distributor arms pass together succes- 
sively over the main contacts i, 2, 3, 4 and 5, and then over 
similar sets of contacts for the other transmitting chan- 
nels (not shown). The polarity of the five current pulses 
sent out jipon the line at station A depends upon the 
positions 'of the rocking pins which, in turn, depend upon 
the tape perforations, as in the Wheatstone transmitter, 
the various permutations of positive and negative pulses 
corresponding to the various letters and other characters to 



MISCELLANEOUS TELEGRAPHS 167 

be transmitted. At station B the five main contacts are 
connected to an equal number of distributing relays which 
select the particular printer magnets in a manner very 
similar to that explained with the aid of Fig. 16 of Chap. IV. 
As the contact arm passes over the contact x, the print- 
ing magnet is energized, causing the printing on the receiver 
message blank of that letter whose printer magnet was se- 
lected by the distributing relays. 

From the foregoing it will be understood how this method 
of signalling can be extended to give quadruple-duplex or 
possibly even sextuple-duplex transmission over a single- 
line wire, the received characters over each communicating 
channel being directly printed. Messages requiring retrans- 
mission to remote places may be directly perforated in 
tapes at the intermediate station, the five magnets that 
set the punches of the receiving perforator being connected 
in series with the corresponding distributing relays of the 
printer. 

3. The Pollak-Virag Writing Telegraph. The Pollak- 
Virag rapid telegraph system has been installed on a num- 
ber of European telegraph lines and affords signalling at 
rates up to 700 words per minute over two-wire lines. 

Tape transmission is utilized in the Pollak-Virag writing 
telegraph, the perforations for the various characters being 
of various sizes and located in one or more of six rows. 
The paper tape is prepared on a keyboard perforator, all 
the perforations for a letter or other character being made 
by a single depression of a key. The tape is passed over 
a motor-driven drum D, Fig. 4, which is formed of six 
electrically-distinct rings. Two brushes, b and &', each 
spanning three rings, press the tape against the drum and 



i68 



TELEGRAPH ENGINEERING 



make contact with its rings through the perforations, 
the duration of contact depending upon the size of the 
perforation. Rings i, 2 and 3 connect to battery B so 
that brush b and the upper line wire may have a potential 
with respect to the other line wire of say + 50, + 30 or 

30 volts respectively. Similarly, rings 4, 5 and 6 con- 
nect to battery B f so that brush b f and junction x may have 
a potential with respect to ground of say -f 30, 30 and 

50 volts respectively. Combinations of contacts of 
different durations and in correct sequence with these six 
rings occasion current pulses in the line which actuate a 



RECEIVER 




Fig. 4 . 

specially-designed receiver to produce in script the various 
letters and figures. 

The receiving instrument resembles two telephone re- 
ceivers (R and R f , Fig. 4) whose diaphragms are placed 
in one plane. In front of the diaphragms is mounted a 
permanent magnet, from the center and ends of which 
project soft iron strips with forwardly-extending pointed 
tips. A small soft iron sheet carrying the mirror m (shown 
in the lower right corner) is magnetically held against the 
three tips. The motions of the two diaphragms of re- 



MISCELLANEOUS TELEGRAPHS 169 

ceivers R and R f are transmitted by means of links to the 
tips t and /' respectively, which are located i mm. above 
and to the left of the center tip c respectively. Therefore, 
if the diaphragm of receiver R vibrates the mirror will 
rotate about a horizontal axis, and if the other diaphragm 
vibrates the mirror will rotate about a vertical axis. If 
both vibrate, the mirror will describe the motion of the 
resultant vibration. 

A small pencil of light issuing fr6m an electric light / 
impinges upon the mirror and is reflected as a spot of light 
upon a band of photographic paper p. A revolving 
opaque hood H having a helical slit encloses the lamp so 
that the spot of light will advance from one side of the 
paper to the other, and then jump to the next line, and so 
on. If the mirror vibrates in accordance with transmitted 
impulses, its motions will be properly recorded. After 
exposure, the sensitive paper travels down through solu- 
tions which develop and fix the paper in about 15 seconds, 
revealing legible script. 

The two-line wires join with the terminals of the winding 
of receiver R, which is actuated by portions of the battery 
B, this receiver forming all vertical components of the 
transmitted characters. Both line wires are used as a 
single conductor for the other receiver circuit by means 
of the neutral points x t formed by a high-resistance shunt 
at the transmitter, and y, the mid-point of the winding of 
receiver R. In this way battery B' actuates receiver R' 
(ground being the return path), this receiver forming all 
horizontal components of the characters. In order to 
abolish the disturbing influences of. resistance, inductance 
and capacity when signalling over long lines, various con- 
densers and reactors may be introduced at particular places 



iyo 



TELEGRAPH ENGINEERING 



in the circuit. Condensers connected in parallel with 
the receivers R and R f are introduced to soften the action 
of the currents. Synchronous rotation of the hood at 
the receiver and the drum at the transmitter is not neces- 
sary in this system. 

The nature of the perforations and the corresponding 
received script is indicated in Fig. 5 for the word " message. " 
The direction and relative magnitudes of the impressed 
voltages are indicated at the left, and the received graph 
for only the vertical components is shown immediately 



o o 

1 " -" -t "- ~ ~ " 



__/lA/l/^j/l^^ 



i i i 

Fig. 5. 

below the tape. The actual received trace, which corre- 
sponds to both vertical and horizontal movements, is 
shown at the bottom. 

4. The Telautograph. The telautograph is an instru- 
ment for the electrical reproduction of handwriting at a 
distance, invented by Prof. Elisha Gray and perfected by 
Geo. S. Tiffany, and consists of a transmitter and a receiver. 
The appearance of the instrument made by the Gray 
National Telautograph Company is shown in Fig. 6. These 



MISCELLANEOUS TELEGRAPHS 



171 



devices may be operated singly over a private line or con- 
nected through a switchboard so as to enable any two 
instruments to be used together. Also, a single transmitter 
may be arranged to operate a number of receivers simul- 
taneously. 

At the transmitter the pencil is attached by a system 
of levers to two contact rollers which bear against the inner 




Fig. 6. 

surfaces of two curved rheostats, which are connected across 
direct-current supply mains, usually of 115 volts. The 
potential difference between either end of each rheostat 
and the accompanying roller varies with the position of 
this roller, which position changes in writing. These vary- 
ing voltages are impressed on circuits which extend to the 



172 



TELEGRAPH ENGINEERING 



receiver, where they terminate in coils wound on copper 
bobbins and arranged to move horizontally within intense 
magnetic fields against the action of springs. In operation 
the two coils are displaced in proportion to the forces acting 
on them, which forces are proportional to the currents 
traversing the coils, which currents vary with the im- 
pressed voltages, and which, in turn, depend upon the dis- 
placements of the transmitting rollers from their zero 
positions, thereby rendering the displacement of each coil 
proportional to that of the corresponding roller. The coils 
at the receiver are connected by a system of levers which 
actuates the recording pen, the lever system being similar 
to that at the transmitter. Thus, the motion of the pen 
is the resultant of the motions of the two coils, which mo- 
tions are proportional to those of the transmitting contact 
rollers, and they are the component motions of the trans- 
mitting pencil; therefore, the receiving pen duplicates 
the motions of the transmitting pencil. 

The simplified scheme of connections of the improved 
transmitter and receiver is shown in Fig. 7, which also 



PAPER SHIFTER 

So 




PAPER M 8 rd F N T ET R RECEIVER 



TRANSMITTER 



Fig. 7. 



indicates the various auxiliary devices utilized in realizing 
commercial practicability. The apparatus used for the 
transmission of the writing motions is apparent, the left 



MISCELLANEOUS TELEGRAPHS 173 

and right rollers on the transmitter rheostats connecting 
directly with the two corresponding receiver coils that are 
located in separate annular air gaps of one magnetic cir- 
cuit. The two pairs of power terminals connect to com- 
mercial electrical supply mains. 

The functions of the auxiliary devices are as follows: - 
The master switch controls the paper shifter magnet which 
operates a clamp that pulls the paper through one line 
space over the transmitter platen. Shifting of the receiver 
paper is similarly accomplished, the shifting magnet being 
locally energized through the contacts of the relay which 
is included in one of the two line wires and which is like- 
wise under the control of the master switch. 

This relay also serves to complete the circuit of the elec- 
tromagnet which develops the magnetic field for the 
receiver coils. It will be observed that the winding on 
the lower bobbin may be periodically short-circuited by the 
spring armature of a vibrator. This action causes the 
intensity of the magnetic field to flicker rapidly and pro- 
duces a minute vibration in the receiver coils. Friction of 
the pen on the paper and in the moving parts of the re- 
ceiver is greatly reduced by this vibration, and conse- 
quently the pen is very sensitive to small changes in the 
line currents. Although small alternating currents are in- 
duced in the coils by this vibratory motion, the pen-lifting 
relay bridged across the line wires will not operate, because 
of the equality of these opposing currents. 

Pen lifting is accomplished at the receiver by means of 
a locally-operated magnet- placed back of the receiver 
writing platen, the armature carrying a rod adapted to 
move the pen arms and lift the pen away from the paper 
when the magnet is energized. This pen-lifter magnet is 



174 TELEGRAPH ENGINEERING 

controlled by a pen-lifting relay that has a peculiarly 
constructed armature which is set into violent vibration 
and makes imperfect contact with its contacts points 
when alternating current passes through the relay winding, 
but which armature is quiescent and makes good contact 
with its contact points when no current traverses the 
winding. At the transmitter the secondary winding of 
a small induction coil is bridged across the line wires through 
two condensers, and the primary winding derives its 
energy from the power mains through a vibrating armature. 
A contact beneath the writing platen is arranged to short- 
circuit the vibrator when the platen is not depressed. 
Thus, during intervals when no characters are written 
no electromotive force is induced in the secondary winding 
of the coil, no current traverses the pen-lifting relay and 
consequently the circuit of the pen-lifter magnet is closed, 
thereby lifting the pen away from the paper. Depression 
of the platen by the transmitter pencil in writing, per- 
mits operation of the vibrator and occasions an alternating 
electromotive force in the secondary winding of the coil. 
This induced voltage develops a current that traverses the 
two-line wires simultaneously with the "writing" currents 
and also traverses the pen-lifting relay. The armature of 
this relay is thereby agitated so that the pen-lifter magnet 
is effectively open-circuited, and the release of its armature 
permits the receiving pen to touch the paper. 

Ink for the receiving pen is contained in a small stoppered 
bottle with an orifice near the bottom, the ink being re- 
tained by atmospheric pressure. When the telautograph 
is idle, retractile springs hold the pen in the ink at this 
orifice. In order to close the master switch it is necessary 
to bring the transmitting pencil to a position corresponding 



MISCELLANEOUS TELEGRAPHS 



175 



to that of the pen and to press the pencil on a button there 
located, thereby releasing a catch that holds the master 
switch. This process is repeated for each paper-shifting 
operation so that sudden large movements of the receiving 
pen are avoided. 

5. Telephotography. The electrical transmission of 
photographs from one place to another, called telephotog- 
raphy, may be accomplished 
by utilizing the property of 
the element selenium by vir- 
tue of which it varies its 
electrical resistance under 
the influence of light. The 
lowering of selenium resist- 
ance with increasing inten- 
sity of white light is shown 
in Fig. 8 for three different 



160 



120 



80 



40 




80 



160 



240 



320 



Fig. 8. 



"cells," which are metallic 
grids properly coated with selenium. Intensity of illumi- 
nation is expressed in luces (sing, lux), the lux being the 
intensity of light at one meter's distance from a standard 
candle. The resistance R of a cell under illumination / 
can be conveniently expressed as 



where c is a constant depending upon the selenium cell, 
and n is an exponent whose value depends upon the dura- 
tion of exposure and wave-length of light, and lies between 
0.25 and i.o. The resistance change in selenium with light 
variation is not instantaneous, but most of this change 



i 7 6 



TELEGRAPH ENGINEERING 



occurs during the first few instants, as indicated in Fig. 9, 
which represents a three minutes exposure of cell B to 
light of ico luces intensity, with subsequent recovery. 

Dr. Korn has perfected telephotographic apparatus 
which is in successful practical operation over several long 
distance lines. 

The complete apparatus for a station consists of a trans- 
mitter and a receiver mounted together, each having a 
long tube through which light from the lamps at one end, 
passes to the rotating cylinders at the other. The princi- 




pal details of the improved Korn transmitter and receiver 
are shown in Figs. 10 and 1 1 respectively. 

In the transmitter the Nernst lamp L sends out, through 
lens A, a beam of light which is received upon the dia- 
phragm g, after passing through lens G. The diaphragm 
serves to concentrate the light to a point upon the glass 
cylinder, around which is placed the photograph in the 
shape of a positive film, the cylinder being mounted upon 
the rotating shaft V. The beam of light passes through 
the photographic film and is reflected upward within the 



MISCELLANEOUS TELEGRAPHS 



177 



cylinder by the prism P and impinges upon the selenium 
cell Si. The cylinder T, in addition to its rotary motion, 
has an axial movement, so that all parts of the photo- 




TRAN8MITTER 




Fig. 10. 



graph successively pass the point of light. As the cylinder 
revolves, the illumination on the selenium cell will change, 
thus sending a current of variable intensity to the receiver. 




Fig. xz. 

The receiver, Fig. n, is provided with a Nernst lamp L f 
which sends out a beam of light through the galvanometer 
shutter b. This galvanometer, called a light-relay, con- 
sists of an electromagnet d, provided with long perforated 



178 TELEGRAPH ENGINEERING 

pole-pieces pp, between which is placed the moving ele- 
ment M. This consists of a double fine platinum wire 
under tension, carrying a small sheet of aluminium foil b. 
When a current flows through the wire, the electromagnet 
being separately excited, the aluminium sheet is deflected 
to one side and the amount of the deflection is propor- 
tional to the current flowing. Thus, the intensity of the 
beam of light which passes through the light-relay to the 
cylinder R depends upon the current in the line. The 
cylinder is mounted on a revolving shaft W, which has 
also an axial movement, so that all parts of the cylinder 
surface are brought successively under the point of light 
emerging from the diaphragm. Thus, the variable current 
coming from the transmitter causes a corresponding varia- 
tion in the amount of light incident upon the receiving 
cylinder, and an exact reproduction of the original photo- 
graph may be obtained upon developing the received 
image. 

It is necessary for the proper operation of this apparatus 
that the resistance change of the selenium cell be rapid 
so that it will respond almost immediately to the variations 
of light incident upon it. Such quick action is secured by 
the use of a second selenium cell connected with the cell of 
the transmitter, so that the resultant conductivity-time 
curve of both rises quickly at the start and falls quickly 
upon darkening the cell. As the receiver of a station is 
not in use when sending, the light-relay of the receiver can 
be employed in this connection, as shown in Fig. n. In 
the bottom of the vertical mirror-lined chamber is the cell 
S z , which receives illumination from the lamp L' by means 
of the reflecting prism P' . To secure a diffused light upon 
this selenium cell, a series of glass cylindrical rods is inter- 



MISCELLANEOUS TELEGRAPHS 



179 



posed at r. When the transmitter cell 6*1, Fig. 10, is illu- 
minated, a current flows through the home light-relay 
deflecting its shield, and thus gives the compensating cell 
62 a corresponding illumination. The two cells are con- 
nected in opposition, and the resulting current variation 



s, 



s, 



LINE TO 

LIGHT RELAY 

OF DISTANT 

RECEIVER 



Fig. 12. 

corresponds very closely with the variations of light, 
owing to the fact that the two cells are selected to give dif- 
ferent resistance changes under the same illumination. 
The method of connecting the selenium cells is shown in 




Fig. 12. The shape of the differential current which flows 
between x and y is shown in Fig. 13, in which the con- 
ductivity-time curve of each cell is indicated, one above 
and the other below the datum line. As cell 5 2 is not 
illuminated as soon as cell Si, its curve will begin shortly 



l8o TELEGRAPH ENGINEERING 

after that of the latter. As will be observed, the time of rise 
and decay of current are practically identical, and the rate 
of change is exceedingly rapid. The use of the compensat- 
ing cell results in a considerable gain in photographic detail. 

As the normal swing of the light-relay is from o.oi to 
0.02 second, a rapid variation of current is permissible, 
and the cylinder at the transmitting end can, therefore, 
be rotated very rapidly. At present a photograph 9 inches 
by 6 inches can be reproduced in less than 12 minutes, the 
size of the received image being 4 inches by 2^ inches. 

It is obvious that the cylinder at the transmitting station 
and that at the receiving station must revolve at the same 
speed, otherwise, no image reproduction could be obtained. 
The speed of the receiving cylinder is adjusted to be 
about one per cent faster than that of the transmitter. 
The former is brought to a stop at the end of each revolu- 
tion, and when the transmitter cylinder has finished its 
revolution, a current impulse of the reverse direction is 
sent to the receiving station actuating a relay there and 
releasing the cylinder. Both cylinders then start up 
together upon the next revolution. 

A modification of the light-relay has lately been intro- 
duced by Korn, called a step-relay, for controlling weak 
high-frequency currents which serve to initiate high-tension 
arcs. The currents so started are either sent directly over 
the line to affect the receiver, or are used to furnish a per- 
forated tape corresponding to the picture for affecting its 
transmission at suitable speed. He has also devised an- 
other transmitting method which dispenses with selenium 
cells and thereby permits of larger line currents. This 
method employs a photographically-prepared copper sheet 
upon which are formed parallel striations of gelatin in 



MISCELLANEOUS TELEGRAPHS 



181 



greater or less widths depending upon the darkness or 
brightness of the various parts of the image to be trans- 
mitted. This sheet is placed around a metal cylinder, and 
as it revolves and also advances axially, a metal stylus trav- 
erses the striations and causes contact to be broken for long 
or short intervals in accordance with the width of the stria- 
tions. The resulting intermittent currents pass through the 
light-relay at the receiver and reproduce the image as before. 
Marino has developed a system of color telephotography 
which utilizes the sustained high-frequency electrical 
oscillations derived from three direct-current arcs that are 
shunted by condensers and inductances. These Thomson 




arcs are arranged to produce oscillations of different fre- 
quencies whose amplitudes are controlled by seven sele- 
nium cells, every cell being most sensitive to one of the 
seven primary colors. At the receiver these oscillations 
control other arcs connected in circuits that are tuned to 
the respective frequencies. The manner in which color 
variations are transmitted in this system is indicated in 
Fig. 14. 

A long opaque diaphragm d, with properly placed aper- 
tures of about i mm. diameter, passes uniformly in front 
of an illuminated plate P bearing the picture to be trans- 
mitted. These apertures are spaced transversely about 



182 TELEGRAPH ENGINEERING 

i mm. apart and longitudinally a distance equal to the 
width of the plate, therefore light from every point of the 
picture, after passing through a lens, falls successively 
on the prism p. Each ray is dispersed by the prism, and 
impinges upon the set of selenium cells S located so that 
each cell receives light of one color, thereby actuating one 
or more of the cells according to its constituent colors. 
These cells are in three groups, each group with a battery 
being bridged across the inductance (L, U or Z/') connected 
in the supply circuit of the arc (a, a' or a"\ Variations 
in the resistances of the selenium cells modulate the voltages 
across the arcs and consequently affect the amplitudes of 
the oscillations that are developed in the three condensive 
circuits. These oscillations induce corresponding currents 
in the line coils /, and are superimposed upon each other 
to form the line current. 

At the receiver the three component oscillations of the 
line current are sorted out by means of the tuned oscillatory 
circuits c, c' and c", and are rectified by audion or crystal 
detectors D, D' and D" . The detectors vary the potential 
difference of the three receiving arcs A, A' and A", and 
consequently vary their brilliancy. In front of the arcs 
are colored screens s, a mixture of red and orange; s', a 
mixture of yellow, green and blue; and s", a mixture of 
indigo and violet the emitted rays from all three arcs 
being recombined and focussed upon a particular point of 
the receiving plate R. Each resulting beam is therefore 
rendered identical in color variations and intensity with 
the original. 

6. Television. The property of selenium of varying 
its resistance under the influence of light is also utilized 



MISCELLANEOUS TELEGRAPHS 183 

in experiments to attain a practical method of seeing at 
a great distance by means of a connecting wire or wires. 
Numerous such systems of television have been patented; 
indeed elementary geometrical patterns have been success- 
fully transmitted by Ruhmer between Brussels and Liege, 
a distance of 72 miles, his transmitter consisting of 25 sele- 
nium cells, each about 5 centimeters square. 

Rignoux and Fournier have developed a system of 
television, involving the employment of a multitude of 
cells but employing only two connecting wires between 
the stations. The currents from the various circuits are 
taken successively by a rapidly rotating collector arm at 



<k 



^^ *-&- -> 



LINE 
WIRES 








Fig. 15. 



the transmitting station and supplied to the two-line wires. 
The principle of the receiving device is based upon the 
Faraday effect. The arrangement of the apparatus at 
this station is shown in Fig. 15, in which L is a source of 
light whose rays are polarized by the prism P and then 
traverse . a tube T containing water, or better, carbon 
bisulphide. A second Nicol prism P' is so rotated about 
the direction of the light ray as an axis that the polarized 
light cannot pass through it, and is then fixed in this 
position. If a current flows through the electromagnet E 
which surrounds the tube filled with liquid, the angle of 
polarization changes and the prism P' no longer prevents 



1 84 TELEGRAPH ENGINEERING 

the light from passing through it. Thus, a beam of light 
of varying intensity, corresponding to the illumination of 
the particular selenium cell connected at that instant 
with the line wires, falls upon the cylinder C, which rotates 
in synchronism with the collector arm at the transmitting 
station. This cylinder carries a number of small mirrors 
m, which are so arranged that the light reflected from each 
falls on a particular part of the screen S. On this screen 
is therefore formed a picture, consisting of patches of 
various degrees of brightness, of the object exposed at the 
transmitter. The different parts of the picture, although 
projected successively, will appear simultaneous, if the 
entire picture is produced within a fraction of a second. 
An indefinite repetition of this process yields a persistent 
picture. 

In Low's system of television the received currents mag- 
netically control the positions of slots which admit light 
to squares on the receiving screen that are located in the 
same positions as the corresponding selenium cells at the 
transmitter. 

7. Military Induction Telegraphs. In times of war 
crudely-constructed pole lines and often short lines of bare 
wire laid on the ground are utilized in the telegraphic trans- 
mission of military information. Because of the low insu- 
lation resistance of such lines, and because of the difficulty 
of transporting means for the production of electricity, the 
ordinary simplex signalling methods are not used, but, in- 
stead, signalling by means of induced currents at high 
voltage is employed. Such induction telegraphy permits 
of signalling over distances of about 300 miles with only 
3 to 6 dry cells. 



MISCELLANEOUS TELEGRAPHS 185 

The circuit of an induction telegraph includes the sec- 
ondary winding of an induction coil at each station, the 
primary winding being joined to a local circuit with a key 
and battery. A current pulse is induced in the secondary 
coil whenever the primary circuit is made or broken, but 
no steady current is induced either when the key is kept 
open or when kept closed. Since the direction of the sec- 
ondary momentary current when the primary circuit is 
broken is opposite to that when the primary circuit is 
closed, it will be observed that a polarized receiving in- 
strument is essential for the operativeness of this type of 
telegraph circuit. Using step-up induction coils, high line 
voltages may be availed of with few cells, thereby render- 
ing induction telegraphs admirably suited for military pur- 
poses even for fairly long lines. 

The United States army induction telegraph field kit 
includes a polarized receiving instrument, a key, several 
dry cells and an induction coil, mounted in a portable 
box. The induction coil has 100 times as many turns on 
the secondary as on the primary winding, and takes about 
12 watts at 4 volts. The circuit of a simplex induction 
telegraph is shown in Fig. 16, in which P, P f are polarized 
relays, 5, S f are sounders, B, B' are local batteries, K, K' 
are keys, and p and s are respectively the primary and sec- 
ondary windings of the induction coils /, /'. Upon de- 
pressing the key K, an induced current of momentary 
duration will be produced in the secondary winding of in- 
duction coil /, flowing, say, upward, which current in flow- 
ing through the two polarized relays to ground G' at the 
distant station causes their armatures to touch the sounder 
contacts. Both sounders will operate as the result of the 
completion of their local circuits. Although the current 



i86 



TELEGRAPH ENGINEERING 



pulse over the line is of very short duration, the polarized 
relay armatures will remain against their sounder contacts 
until the key is released. The subsequent opening of key 
K produces a reverse current pulse through the line and 
the relay windings, which causes the relay armatures to 
open their respective sounder circuits. Signalling in the 
opposite direction may be accomplished similarly. 

To reduce further the impedimenta during warfare, the 
polarized relay and local sounder are replaced by a polar- 
ized sounder in induction telegraph sets devised by G. R. 





Fig. 16. 



Guild for use by the United States Signal Corps. Such 
sounders resemble those of the usual type except in that 
the soft-iron yokes joining the lower ends of the magnet 
cores are replaced by permanent horseshoe magnets, 
thereby giving a definite polarity to the poles of the electro- 
magnet cores. A current through the coils will cause the 
armature to be more or less strongly attracted according 
as the electromagnetization assists or opposes that of the 
permanent magnet. The retractile spring of the polarized 
sounder is adjusted so that reversal of current direction 
will effect its proper operation with currents as small as 
10 milliamperes. Inasmuch as these instruments may be dif- 



MISCELLANEOUS TELEGRAPHS 



I8 7 



f erentially wound (shown at PS in Fig. 1 7) , they may be used 
advantageously for duplex induction telegraphic signalling. 
Induction telegraph repeaters are used for repeating into 
simplex closed- or open-circuit lines or into another induc- 
tion telegraph circuit. Fig. 17 shows the arrangement for 
repeating from an induction telegraph to a closed-circuit 
simplex line, and vice versa, using polarized and polarized- 
repeating sounders. The position of the armatures corre- 
sponds to the normal condition for no transmission of mes- 
sages. The arrows a and a' indicate the direction of the 
induced currents in the line circuit on the closing of the 
local circuits including batteries B and b f respectively. 
The armature of the polarized repeating sounder PR 2 is 
biased to remain on its lower contact except when a current 
flows through either of its coils. The letters n and s indi- 
cate the polarity of the polarized sounders which is occa- 
sioned by their permanent magnets. The opening of the 




Fig. 17. 

armature contact of the other repeating sounder PRi re- 
moves the short-circuit from the left-hand coil of repeater 
PR 2 , thereby energizing this coil, but at the same time the 
introduction of its resistance reduces the current strength 
in relay R to a value insufficient to keep its armature at- 
tracted. The repeating of signals in either direction may 
readily be traced (see problem 5). 



l88 TELEGRAPH ENGINEERING 



PROBLEMS 

1. Decipher the tape shown below, which represents part of a 
message transmitted by the Murray multiplex telegraph. 

2. If operators can perforate transmitting tapes at the rate of 
only 4 letters per second, how many operators would be required to 
keep the transmitters at one station of the Murray quadruple-duplex 
and of the Pollak-Virag writing telegraphs supplied if their trans- 
mitters are operated at 40 and 700 words (each of 5 letters) per 
minute respectively? 



O O OO CO O O O OOOO OOOO OO 
O O O OO OO OO OO 

OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO 

OOO O O OOOOO OO O OOOO OOO O O 
OOO OOOOO O OOO 

O OO OO O O OOO 



3. The rheostats of the telautograph are not of the same width 
from one end to the other, but have a width that is calculated to 
compensate for the variation of the line resistance occasioned by the 
inclusion of more or less of the resistance of these rheostats. Formu- 
late an equation giving the resistance from one end to any point 
on the rheostat so that the line current will be strictly proportional 
to the distance of that point from the reference end. 

4. The resistances of a selenium cell are 30,000 and 20,000 ohms 
under illuminations of 20 and 100 luces intensity. Calculate its 
resistance under an illumination of i lux. 

5. With the aid of Fig. 17 describe the operation of the instru- 
ments for repeating from a closed-circuit to an induction telegraph 
line, and vice versa. 



CHAPTER VII 

MUNICIPAL TELEGRAPHS 

i . Fire-alarm Telegraphy. Signalling systems are in- 
stalled in cities and towns to enable the inhabitants to 
notify the fire-fighting force promptly of the discovery and 
location of a fire. The facts that a fire in its incipiency is 
more readily subdued than after it has made considerable 
headway, and that the loss of human life and property is 
always imminent, render it imperative that the fire-fighting 
force reach the scene of the fire and begin its activities in 
the shortest possible time. Fire-alarm telegraph systems 
should have street signalling stations or fire-alarm signal 
boxes at convenient points throughout the territory served 
that are capable of being operated by any one when an 
occasion demands. In villages and towns where the 
fire-fighting force is composed of volunteers, the operation 
of a signal box sounds a public alarm which indicates the 
location of the signal box operated, and the volunteers 
hasten to their quarters for the fire apparatus and then 
proceed therewith to the fire. In cities maintaining paid 
fire departments, the operation of a signal box sends a 
distinctive signal to a central station which is equipped 
with facilities for disseminating this information to the 
firemen stationed at the apparatus houses of the fire depart- 
ment. 

The time interval between the discovery of a fire by 
an individual and the arrival of the firemen at a fire in a 

189 



IQO TELEGRAPH ENGINEERING 

city may be divided into three periods. First, the time 
required for the individual to reach the nearest street 
signal box after his discovery of fire; second, the time 
taken between the sending of the signal, usually called 
" turning in the alarm " or " pulling the box," and the 
repeating of this signal in the apparatus houses of the fire 
department; and, third, the time elapsing from the recep- 
tion of the signal at apparatus houses to the arrival at 
the scene of the fire of those fire-fighting companies that 
are expected to " turn out " or answer the particular 
signal. 

Of these periods, the first depends largely upon the prox- 
imity of the nearest fire-alarm box; thus, in the Borough 
of Manhattan of New York City the distribution of boxes 
is such that the nearest box is anywhere from 100 to upward 
of 800 feet from a building, depending to a certain extent 
upon the nature of the businesses or residences of the 
various districts. This time period is frequently reduced 
by the use of supplementary or auxiliary boxes installed 
in buildings and leased from private concerns, which are 
designed when operated to trip automatically the nearest 
street fire-alarm box, and also by the use of thermostatic 
devices located in buildings and operated by the fire itself 
to send signals to the office of the company giving the 
service, from which point the alarm is telegraphically 
transmitted to the central station. The second time period 
comes within the province of municipal fire-alarm tele- 
graphs, and depends upon the signalling speed of the fire- 
alarm boxes, of central station repeating, and of the 
signal-receiving devices at apparatus houses. Alarm trans- 
mission in New York City requires, on the average, some- 
what less than 50 seconds from the pulling of the box to the 



MUNICIPAL TELEGRAPHS IQI 

last stroke of the gong at apparatus houses. The third 
time period depends upon the rapidity with which the 
apparatus is turned out, its speed in advancing to the 
fire and the distance it must traverse. The increasing 
use of motor-propelled fire-fighting apparatus within recent 
years has materially diminished the duration of this time 
period. 

It is apparent that the fire-alarm boxes of a municipal 
fire-alarm telegraph system might be individually con- 
nected to the central station by electric circuits, each ter- 
minating in an annunciator drop which bears the number 
of the box associated with it, and that the signalling de- 
vices at the apparatus houses might also be connected to 
the central station by separate circuits, thereby enabling 
operators to signal particular fire companies that a fire 
exists within their districts. The great cost of a large 
number of such diverging circuits located on poles or in 
underground conduits renders such a system prohibitive. 
Instead, in fire-alarm systems, a number of signal boxes 
are connected in series on one circuit, and similarly the 
signalling devices at a number of apparatus houses are 
connected to one circuit; in small municipalities both 
types of devices are frequently joined to a single circuit. 
In Manhattan there are approximately 40 box circuits 
averaging 26 fire-signal boxes per circuit. While such 
series-circuit systems introduce more elaborate fire-alarm 
boxes, in that each must send a distinctive signal and should 
be immune from interference by the simultaneous . actua- 
tion of other boxes on the same circuit, the reduction of 
the cost of line material and its installation renders such 
systems far more economical than the individual-circuit 
arrangement mentioned above. 



IQ2 TELEGRAPH ENGINEERING 

2. Fire-alarm Signal Boxes. The fire-alarm boxes that 
are distributed throughout a city are usually mounted 
on posts located near the curb of sidewalks so 
as to be conspicuous. One style of fire-alarm 
post, with a glass globe for illumination at 
night, is shown in Fig. i. 

The turning in of an alarm necessitates 
the opening of key boxes in order to expose the 
"hook," the pulling of which starts the 
mechanism for transmitting the alarm. Some 
key boxes have trap locks on their outer 
doors, and when a key is inserted it cannot 
be withdrawn until released by a fire depart- 
ment officer with his " release " key. Keys 
to such boxes are customarily distributed to 
responsible citizens of a town, each key being 
numbered for identification. Other boxes have 
keys permanently trapped in the locks and 
covered with key guards consisting of an iron 
casing with a glass cover. Breaking the glass 
leaves the key accessible. With keyless boxes, 
a handle protrudes from the front of the box, 
as shown in Fig. i. In one type of keyless 
box, turning the handle opens the door to 
expose the hook for pulling, and also sounds a 
local alarm on a large gong within the box 
for attracting the attention of persons in the 
vicinity, thereby discouraging the sending of 
false alarms. With the other type of keyless box, the 
turning of the handle sounds the local alarm as well as 
operates the signalling mechanism without opening the box. 
Fire-alarm boxes are generally designed to operate on 



MUNICIPAL TELEGRAPHS IQ3 

normally-closed circuits. Each signal box is equipped 
with a spring-driven mechanism which, when set in motion 
by pulling the hook, revolves a signal wheel that causes 
the circuit to be opened a definite number of times with 
definite time intervals between, thereby transmitting 
to the central station a code signal indicating the number 
and thus the location of the particular box operated. 
Two such signal wheels located in different fire-alarm boxes 
are shown in Fig. 2 at A and B. Each wheel has groups 
of projections, one group representing units, another tens, 
and so on, and when it revolves the projections suc- 

Central Station 
Signal Boxes 




Fig. 2. 

cessively touch a contact spring, thereby closing the circuit 
which extends to the receiving relay R situated at the 
central station. The normal position of the two signal 
wheels is indicated in the figure, one wheel having 3 and 5 
projections and the other 2 and 4 projections in its two 
groups. When wheel A is set in motion, the circuit is 
opened 3 times and after a pause is opened 5 times, which 
action causes the bell at the central station to strike 3 
times and then 5 times, a signal interpreted as 35. The 
mechanism is arranged to rotate the signal wheel a certain 
number of times, usually four, with one depression of the 
hook, consequently transmitting 4 rounds of number 35 
in a complete signal. The signal boxes are designed so 



IQ4 TELEGRAPH ENGINEERING 

that the mechanism when once started cannot be interfered 
with by subsequent pulling of the hook, thus guarding 
against mutilation of the transmitted signals by excited 
persons who do not heed the usual directions appearing 
on the inner cover of signal boxes to " pull the hook down 
once and let go." 

With signal boxes connected in series and having the 
parts indicated in Fig. 2, it is possible that two boxes on 
the same circuit might be pulled at about the same time, 
and as both signal wheels would then revolve, the signal 
transmitted by each would be mutilated by that sent by 
the other, and both would be lost. Such interference 
might arise, not only because of the breaking out of two 
fires at almost the same time in districts served by one 
circuit, but also because of two individuals seeing the same 
fire from different points and turning in alarms from differ- 
ent signal boxes. The latter condition is often minimized 
by interlacing the signal-box circuits, so that alternate 
boxes in both directions are joined to different circuits. 
Both of these causes of signal interference, however, may 
be eliminated by the use of signal boxes arranged so that 
a box cannot transmit its signal while an alarm, originating 
at another box, is being transmitted over the same circuit. 
Such non-interfering signal boxes first came into use in 
1870 through the invention of Game well, and have since 
been perfected by Crane, Gardiner, Ruddick and others. 

Ruddick, in 1889, introduced features in signal boxes 
whereby, if two boxes were pulled simultaneously, neither 
would interfere with the other, but both would transmit 
their signals properly, one after the other, or successively. 
Thus, if a box is pulled while another is transmitting, 
the mechanism of the -former would operate without 



MUNICIPAL TELEGRAPHS 1 95 

affecting the circuit until the line is again free, and then 
this box would automatically assume control of the circuit 
and send its signal. 

Fire-alarm signal boxes may, therefore, be grouped into 
three types in accordance with the foregoing description, 




Fig. 3. 



namely: plain boxes, which are devoid of the non-inter- 
fering and successive features, non-interfering boxes, which 
have not the successive feature, and successive boxes, which 
are also non-interfering. The successive non-interfering 
type of fire-alarm box represents the highest development 
of signalling devices on series fire-alarm circuits. 

Fig. 3 shows the interior of the positive non-interfering 



196 TELEGRAPH ENGINEERING 

successive fire-alarm signal box made by the Gamewell 
Fire Alarm Telegraph Company. These boxes are pro- 
vided with a mechanism capable of giving 16 rounds 
at one operation of the starting device, a single-stroke 
bell for striking at the box the signal that is being trans- 
mitted, a signal key for transmitting code signals, a test 
switch for keeping the circuit closed while electrical or 
mechanical tests are being made on the box, a protector 
against abnormal currents, a lightning arrester and a 
plug switch for including either the signal key or the signal 
wheel in the circuit or for grounding the circuit at the box 
during tests. The outer dimensions of this signal box are 
18 by 13 by 6 inches. 

The scheme of the mechanism and connections of a 
Gamewell successive signal box is indicated in Fig. 4. 
The line wires terminate at the outer plates of the plug 
switch, the inner plate being grounded. The electrical 
devices in the box are kept normally short-circuited by 
the contacts C, which are kept closed by the door of the 
signal box, and by the contacts C", which are kept closed 
except when the box is actuated. When contacts C' or 
C" are open, the line circuit includes the rear key contact, 
the bell magnet, the "succession" magnet, and the signal 
contacts C. The opening and closing of the signal con- 
tacts is under the control of signal lever L, pivoted at h, 
which carries a small roller R for riding over the teeth of 
signal wheel W. The movements of lever L are limited 
by the actions of locking lever B, pivoted at e, by catch T, 
pivoted at a, and by controlling lever , pivoted at d. 
Signal wheel W and gear wheel G are mounted on the same 
shaft and are driven by the main driving wheel D under 
the influence of the spiral spring S, the signal wheel mak- 



MUNICIPAL TELEGRAPHS 



IQ7 



ing 8 revolutions during one revolution of the driving wheel, 

at a speed governed by an escapement and fan, not shown. 

When the mechanism is at rest, the driving wheel is 

locked by pawl P, which is attached to lever B, because 




Fig. 4. 



the pawl rests in slot p or p' of the upwardly-extending 
flange of driving wheel D. When the hook H is pulled, the 
locking lever B is raised, carrying with it insulating block 
/, thereby opening contacts C". At the same time the 
pawl is raised out of slot p and the mechanism is set in 



1 98 TELEGRAPH ENGINEERING 

motion, the pawl then slides over the periphery of the 
flange on D. Signal lever L does not fall immediately, 
because it is momentarily held by pin b or b' carried on the 
driving wheel. If during this short test interval the line 
circuit is uninterrupted, a current will flow through the 
succession magnet and its armature A will be attracted, 
consequently keeping locking pin / to the left and clear of 
signal lever L. As pin b passes the downwardly-projecting 
hook of the signal lever, this lever will fall and the roller 
R will engage the teeth of the signal wheel, since catch T is 
pushed to the left when the first tooth on the signal wheel 
reaches roller 7?, and is kept in this position until the com- 
plete signal is transmitted by means of the notched wheel 
beneath W and, for a time during each revolution, by lever 
L itself. While the signal lever is in its lower position, 
pin / banks against its left end in order to keep lever E 
clear of the signal lever during the intervals when the line 
circuit is opened at C and the succession magnet is de- 
prived of current. After the signal wheel has revolved 
four times slot p' will be in position for pawl P to fall into 
it, which action arrests the motion of the mechanism. 
The engagement of pin b' with the right-hand end of the 
signal lever raises roller R from the signal wheel and causes 
the contacts C to be closed. 

If, when the signal box is pulled, another is transmitting 
its signal over the same line, the succession magnet will be 
deprived of current at some instant during the brief period 
that the signal lever is held up by pin b or b f , and conse- 
quently, spring ^ is enabled to pull lever E away from the 
magnet. Locking pin I then prevents the signal lever 
from bearing on W, and causes contacts C to be kept 
closed. As the normal line current, when traversing the 



MUNICIPAL TELEGRAPHS 199 

succession magnet, is not sufficiently strong to enable this 
magnet to attract its armature when retracted to the full 
extent, contacts C will be kept closed. Restoring pin r 
bears against the shoe at the lower end of lever E once in 
each revolution of the signal wheel, and moves this lever 
clockwise so as to bring armature A close to the magnet. 
This movement, which carries pin / clear of the signal lever, 
does not cause this lever to drop, because catch T has 
moved to the right during this interval, since its lip has been 
pressed into the recess of the notched wheel beneath the 
signal wheel W. After 4 revolutions of the signal wheel 
the pawl P will drop into the slot of the flange on Z>, but 
only partially, because the downward movement of lever 
B is checked by pin q striking the shoulder m. In conse- 
quence, the pawl is forced out of this slot, and the mecha- 
nism continues in operation. At the next instant lever E 
is moved by the restoring pin r so as to bring armature A 
close to the magnet. If, while the armature is in this 
position, it is kept attracted by the magnet, the signal 
lever will fall after engaging pin b or b', and roller R will 
ride on the signal wheel. The box now has control of the 
circuit, and will transmit the box number. But if, while 
the armature was close to the magnet, it was not kept at- 
tracted, lever E would be pulled back by spring s, and the 
signal key would be kept up by the locking pin /. Thus, 
the box " looks in" on the circuit every little while, and 
if it finds the circuit idle it assumes control of the circuit. 
Should the circuit still be open after the signal wheel has 
revolved 16 or 20 times, the mechanism is automatically 
stopped by a ratchet-lever (not shown) and the box number 
will not be transmitted. 
The appearance of the non-interfering successive signal 



2OO 



TELEGRAPH ENGINEERING 



box made by the Star Electric Company is shown in Fig: 5. 
This box is equipped with a mechanism capable of repeat- 
ing its signal number forty times with one winding of the 
spring, a single-stroke bell, a signal key, a test switch for 
testing the operation of the mechanism by the response 
of the bell without sending any signals to the receiving 




devices on the box circuit, a protector against abnormal 
currents, a lightning arrester and a grounding switch. 

Fire-alarm boxes that are wound by the act of pulling 
the starting lever, termed sector boxes, are also used, the 
mechanisms being driven either by springs or weights. 

3. Public Alarms. In villages or towns having volun- 
teer fire brigades, the volunteers are called by the sounding 
of a public alarm which is operated by electromechani- 
cal devices connected in the same circuit as the signal 
boxes. Fig. 6 shows a Game well electromechanical whistle- 



MUNICIPAL TELEGRAPHS 



201 



4 




Fig. 6. 



Fig. 7. 



202 TELEGRAPH ENGINEERING 

blowing machine with a two-bell steam gong. This type 
of public alarm gives satisfactory results where a steam 
pressure of 80 pounds per square inch is maintained. 
The weight-driven mechanism opens the whistle valve 
simultaneously with the circuit openings, and returns to 
its normal position every time the circuit is closed, thus 
rendering the signal blasts sharp, and distinct. Com- 
pressed air is also used for blowing horn alarms, the oper- 
ation being effected in the same way as with steam gongs. 
Electric horns are now being introduced for public fire 
alarms. 

Bells are frequently used for sounding public alarms in 
cases of fire. A bell with its electrically-controlled strik- 
ing mechanism is illustrated in Fig. 7. Bell-striking and 
whistle-blowing machines may be wound up manually 
or by automatic motor-driven machines called electrolifts. 

4. Fire-alarm Central Stations. The central stations 
of fire-alarm telegraph systems comprise apparatus for 
receiving, recording, and transmitting signals and fire 
alarms, which devices may be designed for manual, semi- 
automatic or automatic operation. Manually-operated 
stations are frequently equipped also with facilities for 
semi-automatic and automatic transmission of signals. 
The gravity or storage battery for operating all the cir- 
cuits of the system is located at the central office. The 
size and character of fire central-station equipments for 
cities and towns naturally depend upon local conditions 
and upon the scope of the fire- signalling system. Typical 
installations for central stations will now be considered. 

At a manual central station, each signal-box circuit ter- 
minates in a visual drop and a relay; the latter actuates 



MUNICIPAL TELEGRAPHS 203 

a bell and one pen of a multiple-pen register, Fig. 2. In- 
coming alarms are received by one or more operators, 
who are on duty at all times. Having heard the bell 
signal and seen the record on the register tape, an operator 
proceeds to transmit the alarm to the apparatus houses. 
As the receiving instruments at these houses are usually 




Fig. 8. 

grouped on several circuits, it is necessary to transmit 
the signal over all apparatus-house circuits simultaneously. 
This is accomplished by fire-alarm transmitters, three 
types of which are illustrated in Figs. 8, 9 and 10. 

Fig. 8 represents a spring-driven detachable signal- 
wheel transmitter with signal wheels that are cut to cor- 
respond with those in all the fire-alarm boxes of the system. 
These wheels are orderly arranged on pegs as shown, or, 



204 TELEGRAPH ENGINEERING 

if numerous, are placed in accessible drawers. Upon 
receiving an alarm, the proper signal wheel is selected 
and placed in position on the mechanism, and then the 
handle is drawn to start the mechanism and transmit the 
signal. 

Fig. 9 shows a Gamewell one-dial four-number adjus- 




Fig. 9. 

table-speed weight-driven transmitter. The box number 
to be transmitted is set on the dial at the front by moving 
the four slotted disks relative to each other. The number 
of rounds transmitted may be varied by drawing a lever 
toward the right to the positions marked i, 2, 3 or 4. 
This movement causes the multiple contacts at the rear 



MUNICIPAL TELEGRAPHS 205 

to be opened the proper number of times and at the correct 
intervals, thereby transmitting the box number simul- 
taneously over all the apparatus-house circuits. 

The Star Electric Company's one-dial four-number 
transmitter is illustrated in Fig. 10. Each digit is set by 
moving a lever down to the desired number, and the num- 
ber is then displayed near the top of the instrument. 




Fig. 10. 

These transmitters may be equipped with speed-changing 
devices so that one or more rounds of signals may be 
transmitted over one class of circuits at a certain speed 
and then, by an automatic shifting of the mechanism, the 
remaining rounds of the signals may be transmitted over 
another class of circuits at a different speed. 

Some circuits extending to the apparatus houses also 
have a key and a relay at their central station ends, the 



206 



TELEGRAPH ENGINEERING 



relay with a local bell enabling the reception of signals 
originating at the apparatus houses. 

Automatic central stations are used principally where a 
fire-alarm system requires two or more circuits but is not 
large enough to warrant the attendance of operators. 
Automatic repeaters are used in such stations for repeating 
signals that come in on any one circuit over all the other 
circuits. These repeaters should possess non-interfering 
features in order to avoid confusion of signals transmitted 
by two or more boxes located on different circuits when 
pulled at the same time. Such non-interfering repeaters 




Fig. zi. 

have been devised by Skelton, Kirnan, Cole and others. 
Fig. ii shows an 8-circuit automatic repeater made by the 
Gamewell Fire Alarm Telegraph Co. 

The operation of a Gamewell repeater will be under- 
stood by a consideration of Fig. 12, which shows the re- 
peating arrangement and one box-circuit magnet with 
auxiliary devices in the normal condition. The weight- 
driven transmitting cylinder D is mounted eccentrically 



MUNICIPAL TELEGRAPHS 



207 



on shaft S so as to move contact rollers R and R' against 
or away from their respective contact springs in the proc- 
ess of repeating alarms over box and gong circuits other 
than that over which an alarm is being transmitted. As 




Fig. 12. 

many contacts may be provided as there are gong and 
signal-box circuits in the fire-alarm telegraph system. 
The transmitting cylinder makes one complete revolution 
every time a box circuit is opened. Shafts E, F, G 1 P and 
Q extend to the right in front of other repeater magnets, 
and carry levers before each magnet precisely as illustrated 
for the one box-circuit magnet. 



208 TELEGRAPH ENGINEERING 

When the current through magnet M is interrupted, 
armature A is drawn back by spring s, carrying lever B 
back with it. This movement of B raises lever L and with- 
draws pin p from the path of detent K, which is rigidly 
attached to shaft S. As a result, cylinder D with its cams 
C, C f and C" is set in rotation. Gam C then acts upon 
roller r to depress lever L, thereby restoring armature A 
and resetting pin p to obstruct detent K at the end of its 
revolution. Cam C' depresses lever T, which through shaft 
F and spring b lowers locking lever / so as to engage and 
hold armature A against the action of spring s while no 
current traverses the electromagnet. Cam C" slowly lowers 
the right-hand end of lever N, and as the opening o 
reaches tip / of detent K' ', this tip is forced through the 
opening by clockwork. Shaft G makes only a half revolu- 
tion because tip t' ', when it reaches its upper position, is 
held against the face / of lever N. After roller r' of lever 
N reaches its highest position it is gradually lowered by 
clockwork to its normal position, in the process of which 
tip /' escapes through opening 0, thus permitting another 
half revolution of shaft G. A series of latches #, one for 
each repeater magnet, is mounted loosely on eccentrics on 
shaft Gj so that the first half revolution of this shaft 
lowers the latch, and the second half revolution restores 
it. With those magnets whose armatures are kept at- 
tracted because of the normal current traversing them, the 
downward movements of latches H cause locking levers 
I to. move down and hold the armatures, and also effect 
the opening of contacts c by means of the pins p f . But 
with the electromagnet of the box-circuit over which a 
signal is being transmitted, the latch H was pushed back 
by the outward movement of the armature so that its 



MUNICIPAL TELEGRAPHS 2OQ 

downward movement does not affect the corresponding 
contacts c. This latch H is kept back by pin p" on H 
engaging with latch H' during the further excursions of the 
signalling armature. Every time the circuit is closed at 
the signal box the armature is drawn up close to the cores 
of the electromagnet, thereby releasing the locking lever 
by the overbalancing effect of weight W. When signalling 
ceases all devices are automatically restored to the normal 
position. A break in any circuit will cause that circuit to 
be automatically locked out by the locking lever until the 
disabled circuit has been repaired. The circuit on which a 
signal originates is indicated at the repeater by the drop /, 
which is thrown back by the armature when the circuit is 
first opened. All alarms transmitted by the repeater are 
usually recorded on a register. 

With systems arranged for semi-automatic operation, 
incoming signals are received and recorded at the central 
station, but after one round of a box number has been 
signalled, the operator may cause the remaining rounds to 
be transmitted directly to the apparatus houses of the fire 
department. 

The signal-box and apparatus-house circuits of a fire- 
alarm telegraph system generally terminate at a switch- 
board in the central station, upon which is located the 
various devices associated with these circuits. Where 
storage batteries are used for operating the circuits, a bat- 
tery switchboard is installed for enabling the charging of 
the cells in series, multiple, or series-multiple as may be 
necessary, for switching from one battery to a reserve 
battery, and for testing purposes. Such a switchboard 
is shown in Fig. 10, located behind the fire-alarm 
transmitter. 



2IO 



TELEGRAPH ENGINEERING 



5- Signalling Devices at Apparatus Houses. In fire- 
alarm signalling systems having automatic central stations 
or having manual stations employing a single method in 

transmitting alarms, the sig- 
nalling equipment at apparatus 
houses comprises electrome- 
chanical gongs and frequently 
registers or visual alarm indica- 
tors. The gongs have spring- 
driven mechanisms and strike 
one blow every time the circuit 
is closed. The usual sizes of 
gongs are 6, 8, 9, 10, 12, 15 and 
1 8 inches in diameter. The 
indicators are spring-driven 
electromechanical devices for 
displaying the box numbers in 
large figures, being operated 
only by the first round of 
signals. Such indicators are 
designed for showing either 
three or four digits, each digit 
being brought into view by a 
wheel bearing the numbers 
from i to 9 on its periphery. 
The mechanism is of the step- 
by-step type, and is manually 
restored by the pulling of a 

cord. Both gong and indicator may be combined into one 
instrument as shown in Fig. 13, which depicts a 1 5-inch 
electromechanical gong with a three-digit indicator. 

Registers yield a record of received alarms either by 




Fig. 13. 



MUNICIPAL TELEGRAPHS 211 

ink marks or perforations in paper tapes. Fig. 14 shows 
a punching register, paper take-up reel and an automatic 
time and date stamp which prints on the register tape the 
exact time that alarms are received. 

With systems having manual central stations and em- 
ploying two different methods in transmitting alarms to 
apparatus houses, two circuits enter each of these houses 
from the central station, and these are called " gong cir- 





Fig. 14. 



cuits " and " joker circuits." The gong circuits terminate 
at apparatus houses in electromechanical gongs and some- 
times also in indicators, as described above. The joker 
circuits terminate in single-stroke electric bells, or tappers, 
having 5- or 6-inch gongs, and also frequently in registers. 
With such systems one or more rounds of signals may be 
transmitted at high speed over the joker circuits and then 
the remaining rounds transmitted over the gong circuits 
at the necessarily slower speed suitable for electromechan- 
ical gongs, or vice versa. 

Where routine telegraphic communication is desirable 
between the central office and the apparatus houses, joker 
circuits are also equipped with relays, -sounders and keys 
at all stations. These circuits may be used for routine 
instructions and messages when no alarms are being trans- 



212 



TELEGRAPH ENGINEERING 



mitted, but as soon as alarm transmission commences, 
telegraphic communication ceases. Such circuits, enabling 
both telegraphic and alarm signalling, are called combina- 
tion circuits. A scheme of connections of a signal equip- 
ment at apparatus houses for use on gong and combination 
circuits is represented in Fig. 15, the gong circuits being 
normally open and the combination circuit normally 
closed. Relay armature a, controlling the telegraphic 



Gong Circuit 




Sounder 



Fig. 15- 



apparatus, is attracted when the small normal currents 
traverse the combination circuit, but armature b, con- 
trolling the tapper, is attracted only when a larger current 
is sent out on the line, which function is performed by 
the central station transmitter in the process of trans- 
mitting alarms. 

6. Operation and Routine of a Fire-alarm Telegraph 
System. The operation of municipal fire departments 
in receiving and responding to alarms is obviously different 
in the various cities. A particular fire department, that 
of Brooklyn, N. Y., which serves a population of 1,800,000 
inhabitants and protects an area of 71 square miles, will 
here be considered. 



. MUNICIPAL TELEGRAPHS 213 

There are 1800 fire-alarm boxes included in 40 circuits 
which lead to the manual central station on Jay St., and 
there are 4 combination and 7 gong circuits extending 
from this central station to the 91 apparatus houses of the 
department. Each box circuit terminates at the central 
office in a relay, which controls one pen of a 3o-pen register 
and a tapper. Each of these box circuits passes through 
one or more apparatus houses for affording convenient 
places for line testing. Two rounds of an alarm are trans- 
mitted over the gong circuits by means of a four-dial 
four-number transmitter, and then two rounds are trans- 
mitted manually over the combination circuits by means 
of a multiple key. A three-position telephone switch- 
board at the central station is connected to the " Main " 
exchange of the New York Telephone Company through 
10 trunk lines, for receiving calls for fire-fighting apparatus 
by telephone. Each apparatus house is joined to this 
private branch telephone switchboard by a direct or a 
party line. 

An area of 4.8 square miles of Brooklyn is protected by 
high-pressure service, supplied by two pumping stations. 
Alarms of fire are received at these stations simultaneously 
with the apparatus houses and a water pressure of 75 
pounds per square inch is immediately applied to the water 
mains. There are 215 telephone boxes connected directly 
with the pumping stations for enabling fire department 
officers to call for increased pressure or order the system 
shut down. 

The duties of fire companies and officers are largely 
directed by an assignment book. Upon the pulling of a 
box (or sending a first alarm) and the subsequent receipt 
of the number of that box at the apparatus houses, certain 



214 TELEGRAPH ENGINEERING 

engine companies, hook and ladder companies, and chiefs 
immediately respond to the alarm. Upon the receipt 
of a second, third and fourth alarms from the same signal 
box, other companies respond without other notification 
than the receipt of the particular alarm, and further, 
still other companies move from their own quarters into 
those made vacant by companies responding to earlier 
alarms. If more apparatus is needed than available on 
the fourth alarm, special calls are made by the central 
station operator. Such calls are also made in order to 
supply a substitute for any company that for various 
reasons may be prevented from answering an alarm sent 
from a box to which that company is regularly assigned. 
The operator must, therefore, be kept constantly informed 
upon the preparedness of all companies and officers to 
respond to immediate' call. 

To illustrate the use of this method of answering alarms 
upon signal, consider that box 93, located at Borough Hall, 
be pulled. The location of this signal box and that of 
the various fire companies in this section of Brooklyn are 
indicated in Fig. 16 by small circles bearing the proper 
numbers of the companies. Numbers between 30 and 
50 represent battalion chiefs, numbers between 100 and 200 
represent hook and ladder companies, numbers over 200 
represent engine companies, numbers preceded by S rep- 
resent fire insurance salvage corps, numbers 10 and n 
represent deputy chiefs, C represents the chief of the depart- 
ment, 6 represents a water tower, SI represents a search- 
light engine and numbers preceded by FB represent fire 
boats. The assignments for box 93 follow, the first line 
gives the numbers of the companies and officers responding 
to the first alarm from this box, the second line those for 



MUNICIPAL TELEGRAPHS 



215 




2l6 



TELEGRAPH ENGINEERING 



the second alarm, etc., the sequence of the numbers of each 
group being the order in which the companies are expected 
to arrive at the signal box. These assignments are also 
shown in Fig. 16 by the light dotted lines marked I, II, 
III and IV which are drawn to include the locations of all 
companies and officers that are assigned to answer the first 
second, third and fourth alarms respectively sent from 
box 93. The changes of company locations on the third 
and fourth alarms are also indicated. 



Station 


Engine companies 


Hook 
and 
ladder 
com- 
panies 


Dep- 
uty 
chief 


Bat- 
talion 
chiefs 


Water 
tower 


Companies to change 
locations 


Engine 
companies 


H. &L. 
Go's. 


93 

Joralemon 
and Court 
Streets 


205, 224, 207 
226, 204, 206, 256 SI 

203, 208, 210 
219, 279, 202 


118, no 

103 

105 


10 


31,. 33 
32 

34 






119 to 118 


6 


( 209 to 226 ) 
( 251 to 206 J 
(235 to 219 ) 
(239 to 204 ) 











Alarms beyond the first are sent to the central station 
by officers of the fire department or their aids by trans- 
mitting, with the telegraph key at any signal box near the 
fire, the numbers 2, 2 and the box number for the second 
alarm, or 3, 3 and the box number for the third alarm, etc. 
Any engine company may be ordered by the central-station 
operator to respond to a box to which it is not regularly 
assigned by transmitting over the apparatus-house circuits 
the number 5, the box number and then the company 
number in close succession. Such special calls may also 
be made for hook and ladder companies by transmitting 
the number 7, the box number and then the company 
number. On their return from a fire, engine companies 
and hook and ladder companies signify their preparedness 



MUNICIPAL TELEGRAPHS 



217 



to answer another call by transmitting respectively to the 
central office over the combination circuits the numbers 
4, 4, 4 and the company number, and 4, 4, 4, 7 and the com- 
pany number, the operator answering this signal by the 
numbers 2, 3. Should a company be called out on a " still 
alarm," one of its firemen informs the central operator 
to this effect by transmitting 2, 2, 2, the company number 
and then the number of the box nearest the scene of the fire. 
In all five boroughs of New York City (280 square 
miles) there are 13 deputy chiefs, 43 battalion chiefs, 181 
engine companies, 93 hook and ladder companies, 10 fire- 
boats and 8 hose companies; the personnel totals 6740 
individuals. The number of fires and false alarms and the 
resulting loss to buildings and contents in this city during 
the first nine months of 1913 are given below; the average 
loss per fire during this period is found to be $542. 



1913 


Number of 
fires 


Number of 
false alarms 


Loss in dollars 


Total (Jan.-Sept.) 


9660 


I2Q3 


"?,2it;,o87 


Average per day 


7C 


c 


19,103 











7. Police Patrol Telegraphs. Signalling systems are 
installed in cities for enabling policemen to transmit code 
signals for summoning assistance, calling ambulances or 
patrol wagons, and informing headquarters that they are 
on duty, and to communicate with their superior officers 
by telephone. Such police-patrol signal systems have 
many features in common with fire-alarm signal systems, 
already described. Means for transmitting signals from 
headquarters to convenient points in the city, for calling 
any or all patrolmen to their nearest street stations for 



2l8 TELEGRAPH ENGINEERING 

the purpose of receiving instructions, may be incorporated 
in police signal systems. In some cities police signal 
systems utilize telephone instruments exclusively. 

Police signal boxes resemble fire-alarm boxes in that 
they include a mechanism for transmitting the box number 
by means of a signal wheel, a telegraph key and a single- 
stroke bell. In addition, police signal boxes have a tele- 
phone receiver, a telephone transmitter and an induction 




Fig. 17. 

coil, properly connected together to form a telephone set. 
Fig. 17 represents a Gamewell y-call police signal box 
with its outer door open, and Fig. 18 shows the same box 
with both outer and inner doors open to exhibit the various 
parts. 

When a policeman has occasion to send any one of the 
seven code signals, he moves a pointer to the proper posi- 
tion as indicated by the plate on the inner cover (Fig. 17) 



MUNICIPAL TELEGRAPHS 



219 



and then pulls the crank located just below the pointer. 
Thus, if the pointer of box 34 is placed in the second 
position corresponding to " ambulance," the mechanism 
would transmit 2 dots at slow speed followed after a short 
pause by the box number 3, 4 at faster speed. If a patrol- 
man transmits an " on duty " code signal and the cen- 
tral station attendant wishes to converse with him, the 




Fig. 18. 

attendant depresses a key a prearranged number of times 
immediately after receiving the code signal, which act 
causes the bell at the signal box to sound accordingly, 
thereby notifying the patrolman to use the telephone. 

Numbered keys may be given to responsible citizens 
with which they can operate the police signal boxes when 
in need of police assistance without opening the outer door, 
such keys when used being trapped in the locks for iden- 
tifying the possessors. 

Incoming signals are usually received at the precinct 



220 TELEGRAPH ENGINEERING 

headquarters by a tapper and a register. Calls for patrol 
wagons are transmitted by the operator to the police 
stables and garages, the number of the signal box being 




Fig. 19. 



sent out by detachable signal-wheel or special dial trans- 
mitters. The equipment at the stables and garages usually 
includes an electromechanical gong and indicator as illus- 



MUNICIPAL TELEGRAPHS 221 

trated in Fig. 13, a register with take-up reel as indicated 
in Fig. 14, a tapper and a telephone set. Upon the receipt 
of a call for a patrol wagon at these places, a wagon is 
dispatched from the stable nearest the signal box from 
which the call originated. 

Fig. 19 shows the Star Electric Company's unit- type 
central-office police desk with the necessary devices for 
receiving code or telephone calls over box circuits, for 
transmitting calls for patrol wagons and ambulances, 
for calling one or more patrolmen on duty by flashlight 
or bell signals to proceed to their nearest signal boxes 
for receiving orders, for controlling and charging the 
storage battery which supplies current to the signal cir- 
cuits, and for testing the continuity and insulation of 
the circuits. This cabinet is arranged for 3 box circuits, 
2 flashlight circuits, i chief's circuit, i stable circuit and 
i test circuit. 

8. Statistics of Police and Fire Signalling Systems. - 
The latest published census statistics of fire-alarm and 
police-patrol telegraph systems in the United States are 
for the year 1907. The following table gives data selected 
from this census on signalling systems used for fire alarms 
exclusively, those used jointly for fire alarm and police 
signal service, and those used for police patrol signalling 
exclusively, the various systems being grouped according 
to population of the cities wherein installed. 

Of the 38 cities with a population in excess of 100,000, 
there are 28 + 8 or 36 having fire-alarm systems; the re- 
maining 2 cities, Kansas City and St. Joseph, Mo. depended 
entirely upon the telephone for transmitting alarms of fire. 
Of the 40 cities having from 50,000 to 100,000 inhabitants, 



222 



TELEGRAPH ENGINEERING 



39 have fire-alarm systems and Kansas City, Kans. de- 
pended upon telephonic fire-alarm transmission. The cities 
of Quincy, 111. and Chester and Williamsport, Pa. of 
36,000, 34,000 and 29,000 inhabitants respectively, were 
reported as having no fire-alarm systems. 



Fire-alarm signal systems 



Cities having populations of 





100,000 

and 
over 


50,000 
to 

100,000 


25,000 
to 
50,000 


10,000 
to 
25,000 


Less 

than 
10,000 


Total 


Number of cities in group * 
Fire-alarm systems 
Fire alarms received in 1907 
Signal boxes 


38 
28 
39.581 
12,151 


40 
35 
10,700 
4,268 


82 
69 
14,372 
5.387 


281 
231 

17,688 
8,700 


'"568 
14,175 
9,895 


"931 
96,516 
40,401 


Telephone boxes 
Miles of single wire 


216 
17,218 


3,377 


37 
3,447 


112 

5.322 


131 

5,973 


496 
35.337 


Manual transmitters 
Automatic transmitters 


30 

24 


16 
34 


14 
52 


46 
IO3 


58 
73 


164 
286 


Receiving circuits 
Transmitting circuits 


584 
332 


265 
182 


368 
196 


712 
366 


880 
394 


2,809 
1,470 

















Combined fire-alarm and police-patrol signal systems 


Combined systems 
Fire alarms received in 1907 


8 
19.832 
8,118 
i,9i5 
19,223 
17 
8 
356 
108 


4 
959 
669 
127 
1. 154 

2 

4 
34 
20 


10 
1,848 
93i 

& 
1 

74 

52 


14 

109 
601 
6 
3 
81 
35 


12 
6l9 
338 
10 
156 
2 
I 

27 
13 


48 
24,203 
10,721 
2,192 
21,897 
31 
24 
572 
228 


Signal boxes t 
Telephone boxes 


Miles of single wire 


Automatic transmitters 


Transmitting circuits 



Police-patrol signal systems 



Police signal systems 
Signal boxes t 


27 

3,758 


29 

1,204 


39 
1,020 


$ 


& 


178 
6,999 


Telephone boxes 
Miles of single wire 


1,054 
8,788 


no 
1.543 


153 
1,601 


226 
1,148 


152 

498 


1.695 
13.578 


Transmitters 


107 


12 


21 


31 


3 


174 


Receiving circuits 


358 


117 


181 


136 


96 


888 


Transmitting circuits 


191 


75 


1 20 


76 


29 


491 

















* Population based on 1900 census. 

t Combined signal and telephone boxes were in most cases reported as signal boxes. 



MUNICIPAL TELEGRAPHS 223 

PROBLEMS 

1. Explain that if two successive fire-alarm boxes are pulled simul- 
taneously, that box whose number has the lowest first digit will as- 
sume control of the circuit before the other signal box. 

2. Show the scheme of connections at the central office of 3 
fire-alarm box circuits, each terminating in a relay and a drop, 
the relays controlling the operation of a common tapper and a 
3 -pen register. 

3. Formulate the assignments of fire-fighting companies and 
officers for signal box number 234 located at Fulton St. and Hudson 
Ave., Brooklyn. The location of this box and of the various com- 
panies and officers is shown in Fig. 16, the same number of com- 
panies being assigned to this box as to box 93. 



CHAPTER VIII 

RAILWAY SIGNAL SYSTEMS 

i. Classes of Railway Signalling. Railway signals for 
the conveyance of information to those engaged in running 
trains or cars fall into the following classes: (a) block 
signals which indicate whether or not a train may proceed 
into the next track section or block; (b) train-order signals 
for advising engineers when train-dispatcher's orders are 
to be given them; (c) route or switch signals for authorizing 
the passage of trains over junctions, crossings, drawbridges, 
etc. ; (d) other signals, such as flags, lanterns and torpedoes, 
for the warning of temporary dangers, and fixed signs for 
indicating speed limits, location of water tanks, etc. 
Classes b and d lie outside the scope of electric signalling, 
the former class always being manual signals operated by 
the telegraphers who take the train orders. 

Block signals are used on lengths of track devoid of 
switches and crossings for limiting the space between two 
trains on the same track to an amount affording a proper 
braking distance for those trains running over this track 
at maximum speed. On single-track roads, block signals 
also give proceed and stop indications to trains advancing 
in opposite directions. Block signals may be manually 
operated, manually controlled, or automatic. Manually- 
operated block signals are operated either by engine drivers 
or motormen upon reaching a block, or by attendants 
stationed along the roadway who set their signals in accord- 

224 



RAILWAY SIGNAL SYSTEMS 225 

ance with information of train movements received by 
telegraph or telephone from their neighboring attendants. 
Manually-controlled block signals are set by attendants, the 
action of one in operating signals being under the control 
of another; thus, two attendants, one at each end of a 
block, must act in setting a signal. Automatic block signals 
are actuated by track or trolley attachments, or are oper- 
ated through an electric track circuit, the train movements 
governing the signals in both cases. These arrangements 
control either a local electric circuit which operates the 
signal, or a valve which allows compressed air or gas to 
move the signal. 

Route or switch signals are the signals of interlocking 
plants which comprise groups of switches and signals that 
govern the movements of trains at crossings, junctions, 
terminal yards, etc. The switches and signals of inter- 
locking plants may be moved manually or by means of 
compressed .gas or of electricity under the control of lever- 
men, the individual movements for establishing a track 
route following each other in a predetermined order. These 
signals also act in conjunction with the block signals just 
beyond interlocked territories. 

2. Types of Signals. Signals for block systems and 
interlocking plants may be electric lights, semaphores 
(with lights as night signals), or enclosed disk signals (with 
lights as night signals) . These signals indicate in different 
ways the commands: Stop danger, proceed with caution, 
and clear proceed. With light signals, these commands 
are displayed by utilizing a distinctive color for each : thus, 
red is used as the danger signal, green generally as the clear 
signal, and orange-yellow usually as the caution signal. 



226 



TELEGRAPH ENGINEERING 



Semaphores are either of the two-position or three-posi- 
tion type, the blade positions for the various indications 
being shown in Fig. i. A high three-position semaphore 
is shown at A } this signal being mounted on iron masts 
placed beside the tracks or on signal bridges. A dwarf 



DANGER 




CAUTION 



\CLEAR 



Fig. i. 



three-position signal is shown at B, and is mounted directly 
alongside of the tracks, usually at interlocking plants. 
These three-position upper-quadrant signals indicate by 
their blade positions: danger when horizontal, caution 
when inclined upward at 45 degrees, and clear when vertical. 
Two two-position semaphore signals mounted on the same 
mast are shown at C, the upper serving as the home blade 



RAILWAY SIGNAL SYSTEMS 227 

and the lower as the advance or distant blade of a block 
signal. Both blades horizontal signify " stop," the upper 
inclined downward 60 degrees and the lower horizontal 
mean " proceed with caution," and both inclined down- 
ward 60 degrees signify "clear." Spectacles carrying col- 
ored glasses are fastened rigidly to the semaphore blades so 
as to move in front of lamps, thereby displaying at night 
colored light signals corresponding to the blade positions. 

Enclosed disk signals consist of an electromagnet whose 
armature controls the position of a wire hoop covered with 
colored bunting, all enclosed in a glass-covered case. When 
the magnet is energized, the colored disk is drawn away 
from the aperture and a white background is visible; when 
released, the disk falls into position and its color is dis- 
played. Colored glass disks, similarly controlled and mov- 
ing before a lamp, serve as the night signals. Such enclosed 
signals, while once widely used, are now infrequently 
employed. 

Electric light signals assume a variety of forms depending 
upon the conditions of use; three styles made by the Union 
Switch and Signal Company are shown in Fig. 2. The 
block signal used by the Interborough Rapid Transit 
Company in the New York Subway is shown at A. The 
upper or home signal displays either a red or a green light, 
and the lower or distant signal shows either a yellow or a 
green light, both being provided with an auxiliary miniature 
semaphore signal immediately below the lenses for use in 
case of lamp failures. Colored glass disks supported in 
vertical sliding frames move in front of the lamp apertures 
by means of compressed air, the valves being controlled by 
electric track circuits (5). The block signal used in the 
Pennsylvania Railroad Tubes under the Hudson and East 



228 



TELEGRAPH ENGINEERING 



Rivers is shown at B, the three upper lights performing the 
same function as a three-position semaphore, since only one 
can be illuminated at a time. The lower lamp always 




Fig. 2. 



remains lighted and serves as a fixed signal. Similar 
signals with an additional lower lamp are used as inter- 
locking signals. At C is shown a type of signal for daylight 
service used by the Indianapolis, Columbus & Southern 



RAILWAY SIGNAL SYSTEMS 22Q 

Traction Company and by other electric railway com- 
panies. 

Semaphores for block and interlocking signals are some- 
times distinguished from each other by their color or by the 
shape of the ends of their blades. The indications of sema- 
phores used with automatic block signal systems may be 
normally danger or clear. A normal danger signal ordi- 
narily stands at " danger," but goes to " clear " as a train 
approaches it if the block governed by the signal is clear, 
returning to " danger " when the train enters the block. 
A normal clear signal stands at " clear " except when a 
train occupies the block governed by the signal. Normal 
clear signals are now preferred by signal engineers. 

Mechanical, electric, electro-pneumatic and electro-gas 
devices are used for actuating the semaphores and switches 
of interlocking plants, and (excepting the first), for operat- 
ing the semaphores of automatic block signal systems. 
Electric-motor semaphores &re now more frequently in- 
stalled than semaphores actuated in other ways. 

The mechanism of the Style B upper-quadrant two- 
position direct-current semaphore, manufactured by the 
Union Switch & Signal Company, is shown in Fig. 3. The 
track circuit is arranged so that the motor A and the holding 
magnet B receive current while the block governed by the 
signal is being cleared. When the signal subsequently 
indicates " clear " the motor is open-circuited but the flow 
of current through the holding magnet remains uninter- 
rupted. The holding magnet is fixed to the " slot arm " 
C which rocks around pivot D. This slot arm carries the 
rod E which connects with the semaphore blade, and also 
carries a system of links terminating in the cam piece F 
which may engage the trunnions of the chain G. The 



230 



TELEGRAPH ENGINEERING 




Fig. 3. 

passing of a train out of the block causes the operation of 
the semaphore motor, the rotation of which produces an 
upward movement of the chain through the gear-wheels 
H and /. Simultaneously, the armature of the holding 
magnet is attracted, thereby holding the system of links 



RAILWAY SIGNAL SYSTEMS 



2 3 I 



and the cam F rigid. This cam, consequently, engages a 
trunnion of the upwardly-moving chain, and the -slot arm 
is carried to its upper position, corresponding to the clear 
position of the semaphore. At this position, the circuit of 
the motor is automatically opened at / by the slot arm, 
this arm remaining in its upper position as long as the 
holding magnet is energized. 

The presence of a train in the block causes the release of 
the holding-magnet armature and the loosening of cam F, 
this action allowing the slot arm to descend by gravity to 
the position shown in the figure. The pneumatic buffer 
K, connected to the right-hand end of the slot arm, permits 
the gradual return of the semaphore to this danger position. 
Series-wound or induction alternating-current motors may 
also be used with this mechanism. By the addition of 
another slot arm, the same motor may operate the other 
position for a one-blade three-position signal or the second 
blade of a two-arm (home and distant) signal. 

Trolley Wire 



Signal Wire 





Fig. 4. 

3. Manual Block Signal Systems. The scheme of a 
manually-operated block signalling arrangement, frequently 
used on single-track electric railways operating relatively 
few cars, is shown in Fig. 4. A signal box, having three 
electric lights, L\ y L 2 and Z, 3 , and a two-point switch S, is 
located at each end of a block. No illuminated lamp at 



232 TELEGRAPH ENGINEERING 

either end indicates that the block is clear, and illuminated 
lamps at either end denote that the block is occupied by 
a car and that no other car may enter until these lights are 
extinguished. A motorman, reaching signal box A and 
finding no lamps lit, moves switch Si to the right, thereby 
causing lamps L, L 2 , Z, 3 , L\ and L 2 ' to be illuminated, and 
proceeds into the block toward signal box B. The lights 
now displayed by both signal boxes permit no other motor- 
man, advancing from either direction, to enter this occupied 
block. The lamp L, joined in the signal wire, indicates to 
the motorman in the block that the signals are still set 
against advancing cars. Upon reaching signal box J5, the 
motorman moves switch 6*2 to the left, thereby extinguish- 
ing all lamps" and clearing the block. It will be observed 
that irrespective of the positions of switches Si and S 2 , if no 
lamps are lit, a movement of either switch will light the 
lamps at each box, or, if lamps are illuminated, a movement 
of either switch will extinguish them. With 5 50- volt trolley 
circuits, five no- volt lamps are connected in series when 
illuminated. 

With manually-controlled block signal systems, arrange- 
ments are utilized whereby each operator stationed along 
the roadway cannot clear his own signal for an approaching 
train until it is unlocked through electrical means by the 
operator located at the other end of the block, his own 
signal thereby displaying the danger signal to trains ad- 
vancing in the opposite direction. 

4. Location of Automatic Block Signals. A home signal 
is one showing the condition of the track directly in front 
of a train, and which, if in the stop or danger position, is 
not to be passed except as governed by the rules of the 



RAILWAY SIGNAL SYSTEMS 233 

railway company. A distant signal shows the condition 
of the track some distance ahead of a train, and, if in the 
caution position, may be passed if the train is brought under 
control, prepared to stop at the next home signal. Distant 
signals should be placed a distance in advance of the home 
signals permitting the fastest trains to be brought to stand- 
still without overrunning the corresponding home signals. 
This braking distance may be from 1000 to 3000 feet, 
whereas the length of blocks is usually from 2500 to 8000 
feet; the two distances depending upon traffic, train speed 
and roadway conditions. 

An automatic overlap system without distant signals is 
indicated in Fig. 5. Each home signal controls a block 

Block 1 Block 2 



Fig. 5. 

plus an overlap equal to a braking distance beyond the next 
signal (as indicated by the dotted lines), thereby insuring 
that a stopped car is always protected by a signal located 
at least a braking distance behind it. The two-position 
semaphores HI and #3 are shown held in the clear position, 
while Hz is in the stop position owing to the presence of the 
car in block 2. The objection to this overlap system is that 
an engine driver or a motorman, knowing that at times 
there are two signals at " stop " between him and the train 
ahead, may be careless and overrun a stop signal without 
speed diminution on the belief that he will have ample time 
to stop, thereby courting danger. 

Because of this objection, the automatic block systems 



234 TELEGRAPH ENGINEERING 

represented in Figs. 6 and 7 are preferred and generally 
employed for double-track signalling. In Fig. 6, distant 
signals D z and A give advance indications of the positions 
of home signals Hz and HZ respectively. When at " cau- 
tion/' a distant signal signifies to an approaching train: 



Block 1 Block 2 
_J\ A_ 



l fl I i fl Car i -*> i r7? 

D H^P oT^ H7!f___ 

Fig. 6. 

expect to find the next home signal at " danger." For the 
position of the car shown in the figure, signals HI, D 3 and 
Hz are in the clear position, A is in the caution position, 
and H-i is in the stop position. 

In Fig. 7, shorter blocks are represented wherein a distant 
signal is mounted on the same mast with the home signal 

Block 1 Block 2 Block 3 



2-Position 
Two*8.rm o \ r v o * ^^ o i M u r* 

g!l 8A C. j^V J 3 v ^ 4 V_ 

3 S!f 1?L V JV^ JvL * V 

Fig. 7- 

of the preceding block. The track length controlled by 
each home signal is shown by the dotted lines. The 
indications of the two-position two-arm semaphore signals 
while a car is in block 3 are: Si and 5 4 at " clear," 5 2 at 
"caution," and 3 at* " stop." The corresponding indica- 
tions of three-position semaphores are shown at the bottom 
of the figure. 

The foregoing double-track signal systems are not 



RAILWAY SIGNAL SYSTEMS 235 

applicable to single-track roads, because they afford no 
protection against oppositely-moving cars, but a number 
of automatic block-signal systems have been devised and 
installed for single-track railway operation. One such 
system, called the TDB (Traffic Direction Block) System, 
has been recently introduced by the Union Switch & Signal 
Company, and is now in operation on a number of inter- 
urban electric railways. In this automatic block system, 
the distance between adjacent sidings is a block for oppo- 



PTr-x 



Fig. 8. 

sitely-moving cars, called an opposing block, and half of this 
distance is a block for cars moving in the same direction, or 
a following block. Thus, each opposing block forms two 
following blocks. : 

Fig. 8 shows the location of semaphore signals in two 
opposing blocks of this signal system and gives the indica- 
tions of these signals as one or more cars proceed through 
the blocks. Each opposing block is equipped with four sig- 



236 TELEGRAPH ENGINEERING 

nals, two being located at its ends and the other two being 
located a distance of 500 to 1000 feet on either side of its 
middle point. Each signal at a siding governs the track 
to the signal at the next siding in the case of opposing car 
movements, but only to the next signal in the case of 
following car movements; whereas the intermediate signals 
govern the track to the next signal for following car move- 
ments. The track sections controlled by each signal are 
indicated at A by broken lines for following movements and 
by dotted lines for opposing movements. The signals may 
be of either the light or the semaphore types, the latter, 
with two-position indications in the upper left-hand quad- 
rant, are represented in the figure. This type of semaphore 
is widely adopted on electric roads, because the motorman's 
view of them is not obstructed by the poles which support 
the trolley wire. 

An eastbound car R is approaching siding X at B, Fig. 8, 
and, consequently, signal 2 is in the stop position. At C, 
this car has passed out of the block to the left, thereby 
clearing signal 2 and setting at stop signals i, 4 and 6. 
A second car S is approaching siding X at D while the first 
car R is approaching signal 3. It is seen that signal i 
protects the rear of the first car and signals 4 and 6 protect 
this car against opposing car movements. At E, car R, 
having passed signal 4, causes signal i to clear for the 
following car S. At F, car S has entered the first following 
block while car R is in the second following block; con- 
sequently, signals 4 and 6 still protect the cars against 
opposing car movements and signals i and 3 protect against 
following car movements. The first car has passed siding 
Y at G into the next opposing block, it being observed 
that both cars are protected from both directions. The 



RAILWAY SIGNAL SYSTEMS 



237 



signal indications for westbound cars may similarly be 
traced. 

The four remaining diagrams, H, I, J and K, show the 
signal indications for two cars R and T approaching siding 
Y from opposite directions. At /, the eastbound car has 
taken the siding, and does not affect any signals while off 
the main track. 



Trolley Wire 



5. Automatic Block Signalling. Automatic block sig- 
nal systems may be divided into two groups: first, those 
wherein trains or cars affect signal apparatus on arrival at 
definite places along the roadway and, after passing these 
points, leave the apparatus wholly 
beyond their control while pro- 
ceeding through the block, and 
subsequently, when leaving the 
block, again affect the apparatus 
to restore it to its normal condi- 
tion; and second, those wherein 
the train or car is itself continu- 
ously in direct control of the 
signal for the block over which it 
is passing, through the medium 
of a track circuit. While cheaper to install, the first 
group does not afford such thorough and continuous 
protection as does the second group of signal systems. 
Block signals of the first group were formerly used 
on some steam railways, and are now giving marked 
satisfaction on a number of interurban electric railways, 
the latter permitting better signal actuation. 

Fig. 9 shows the apparatus at one end of a block for an 
automatic signal system of the first group as applied to an 




Fig. 9. 



238 TELEGRAPH ENGINEERING 

electric railway. The arrangement is similar to the manual 
block signal described in 3, except that the switch S, 
Fig. 4, is moved automatically when the car passes the 
block limits. This action is accomplished when the trolley 
wheel reaches the signal contactor C, Fig. 9, for the wheel 
then touches the spring contacts of C and the trolley wire 
simultaneously and causes a momentary current to flow 
from the trolley wire through the switch-controlling magnet 
M to ground at G. The consequent attraction of armature 
A of this magnet permits the campiece c to turn the ratchet 
wheel R through a distance of one tooth. This causes the 
notched wheel N, having half as many crests as the ratchet 
wheel has teeth, to turn an amount equal to the distance 
from a hollow to a crest. A projection of the switch arm 
S carries a small wheel W which rides on the notched wheel. 
When wheel W rests in a hollow (as shown), switch S closes 
its left contact, and when it rests on a crest, switch S closes 
its right contact. 

When both signal sets of a block are in the position 
illustrated, no current traverses the signal wire with its 
lamps L, thereby giving the indication that the block is 
clear. When a car enters the block, the magnet is momen- 
tarily energized and the attraction of its armature causes 
a limited rotary movement of wheels R and N. Switch 5, 
in consequence, moves. to its opposite position and closes 
the right and opens the left contact. This action illumi- 
nates lamp L and the other lamps connected in the signal 
wire, thereby giving the stop indication to other cars ad- 
vancing in the same or in the opposite direction. As the 
car moves out of the block, the switch at the other signal is 
similarly moved and the lamps are extinguished, thus again 
clearing the block. 



RAILWAY SIGNAL SYSTEMS 239 

The Chapman Automatic Signal System employs con- 
tactors which are returned by a spring to their normal 
position after they have been moved in either direction 
by a trolley wheel. The signals used with this system are 
of the semaphore type and are actuated by electromagnets. 
There are three magnets in each signal, two for controlling 
the indication of the semaphore arm, and the third for 
closing certain contacts upon momentary actuation as a 
car enters a block section. The three positions of the 
semaphore blade indicate : horizontal car approaching in 
opposite direction, inclined downward 45 degrees clear, 
vertically downward car in block receding from you. 

Insulating 
Track Joints 

j Track Rails t 

* 




Fig. 10. 

The principle of all automatic block signal systems of the 
second group is the operation of a relay whenever a pair of 
wheels with their connecting axle enters or leaves a block. 
The scheme of such systems for steam railroads is illustrated 
in Fig. 10. A battery is located at one end of a block and 
connected across the two track rails of a section, which are 
separated from the rails of the adjacent sections by insulat- 
ing joints. The rails serve as conductors for the current 
from battery b to a track relay R, which is located at the 
other end of the block and likewise connected across the 
track rails. The relay controls through its contact points 
the local circuit of battery B and the semaphore signal S. 
When no car is in the block, relay R is energized and the 



240 



TELEGRAPH ENGINEERING 



local circuit is closed, thereby holding the signal at clear. 
When a car enters the block, the battery b is short-circuited 
by the car wheels and axles, and the relay is deprived of 
current. The consequent opening of the local circuit at 
the relay sets the signal in the danger position. The 
battery and relay are placed at opposite ends of a track 
section, because this arrangement protects against broken 
rails and also indicates open bonds between rail-lengths. 
Either primary or storage batteries are used, and these 
are located in battery wells or chutes beside the tracks. 
When distant signals are used with the scheme repre- 
sented in Fig. 10, polar-neutral track relays are employed, 



Block 2 



Block 1 




Fig. ii. 

their neutral armatures controlling the home signals and 
their polarized armatures controlling the distant signals; 
the operation of a home semaphore blade moving a pole- 
changer for reversing the current in the relay of the pre- 
ceding block. This system is called the polarized or 
" wireless " automatic block signal system. 

Each signal may be controlled by any number of track- 
circuit relays, and each relay may have a plurality of 
contacts. Thus, Fig. n shows the scheme of connections 
for normally-clear two-arm semaphores (located as in 
Fig. 7) for two blocks of a track intended for traffic in one 
direction only. Each block is shown divided into two track 



RAILWAY SIGNAL SYSTEMS 



241 



sections a and b, so as to increase the reliability of the track 
circuits by reducing the effect of current leakage from one 
rail to the other along ballast and ties. Track relays RI 
and R 2 control the home blade HI of block i, relays R 3 and 
RI control the home blade H 2 of block 2, and relays RI, R 2 , 
R 3 and R control the distant blade D 2 . The operation 
of the signals for indicating the track conditions with the 
passage of a train can be understood readily from an 




Fig. 12. 

examination of the diagram, if it be remembered that each 
semaphore blade assumes the horizontal position whenever 
its local circuit is opened at a relay contact. For the 
position of the train indicated, the contacts of relay RI are 
open and, therefore, home blade HI and distant blades A 
and DZ will be horizontal. 

A large variety of track circuits is utilized in practice 
for different types of automatic block signalling, using 



242 



TELEGRAPH ENGINEERING 



normally-clear or normally-danger signals on single- or 
double-track steam and electric roads in connection with 
overlap, non-overlap or preliminary-section systems. 

The appearances of two .types of direct-current track 
relays manufactured by the General Railway Signal Com- 
pany are shown in Figs. 12 and 13. That shown in Fig. 12 
is the Taylor tractive-type relay and has 4 contacting fin- 




r 



Fig. 13- 

gers, each with front and back contacts ; that shown in Fig. 
13 is a three-position mo tor- type relay also with 4 contact- 
ing fingers, the closing of one or the other sets of contacts 
being accomplished by a partial rotation of the motor 
armature through the medium of an eccentric link. 



6. Automatic Block Signals on Electric Railways. 
Signalling on electric railways is accomplished in a some- 



RAILWAY SIGNAL SYSTEMS 243 

what different manner from that employed on steam rail- 
roads as just described, because the track rails are utilized 
as a return path for the current required in car propulsion. 
One-rail Block Signal System. Where it is possible to 
spare the conductivity of one track rail in the return of the 
propulsion current, as on elevated roads where the support- 
ing structure serves also as a return path, one track rail is 
sectionalized and used for block signalling. Alternating 
current is now usually employed for signalling with this 
arrangement, requiring the use, on direct-current railways, 
of relays that are responsive to alternating current but not 
to direct current, and, on alternating-current railways, of 
relays that are responsive only to alternating current of 
higher frequency than the propulsion current. 

Return Rail for Propulsion Current 




A. C. Signal Mains 
Fig. 14. 

Fig. 14 shows the scheme of connections of the one-rail 
automatic block signalling system. The transformers T 
supply alternating current to the " exit end " of each track 
section from the alternating-current supply mains. The 
alternating-current relays Rj connected at the opposite end 
of the track sections, control the operation of signals 5 
through the local batteries B, as before, or through alter- 
nating-current motors fed by transformers joined to the 
signal mains. Each relay is shunted by an impedance to 
keep direct currents from the instrument. Usual trans- 
mission voltages are from 2200 to 4400, and at each block 



244 



TELEGRAPH ENGINEERING 



are stepped down to 220 or no volts for the operation of 
alternating-current semaphore motors, and to 6 to 15 volts 
for the operation of the track circuits and lamp signals. 

This system is used in the New York Subway, where 
approximately 700 signals, 500 track circuits and 40 inter- 
locking plants are used. During the morning and evening 
rush hours 150 subway trains per hour pass g6th Street, 
this heavy traffic demanding blocks as short as 1500 feet. 
The signal mains supply 6o-cycle current at 500 volts to the 
block transformers, each having two secondary windings, 
one which feeds the track circuit at 10 volts, and the other 
which feeds the lamp signal circuits at 50 volts. The valve- 
Track Rail 




A. C. Signal Mains 
Fig. 15. 

controlling magnets of the electro-pneumatic signal mecha- 
nisms are operated by direct current at 16 volts supplied 
by storage batteries. 

Two-rail Block Signal System. Both track rails of an 
electric railway may be used simultaneously as a return for 
the propulsion current and as conductors for the signalling 
current by the employment of impedance bonds placed 
between and connected across the track rails at both ends 
of each track section. These bonds are shown at I in 
Fig. 15, the middle points of the windings of adjacent bonds 
being connected together. In other respects, the one-rail 



RAILWAY SIGNAL SYSTEMS 



245 



and two-rail signal systems are identical; compare the 
schemes of Figs. 14 and 15. 

The impedance bonds have little resistance but large 
inductance, for they consist of heavy windings of copper 
around massive laminated-iron cores as illustrated in Fig. 
1 6. For 600- volt railways the resistance of a bond may 




PLAN VIEW-COVER REMOVED. 




SECTIONAL SIDE VIEW 

Fig. 1 6. 

be from 0.0004 to 0.0015 ohm. The propulsion current, in 
being carried around the insulating joints which separate 
the track signal circuits from each other, flows differentially 
through the bonds and, consequently, does not magnetize 
their cores. Therefore, the propulsion current will not 
affect the signalling apparatus. The impedance of the 
bonds to the alternating current used for signalling is so 



246 TELEGRAPH ENGINEERING 

great in comparison with that of the relays that the 
presence of the bonds will not affect the operation of the 
alternating-current track relays. 

The two-rail block signal system is installed on a number 
of direct-current railways, a few of which are: the West 
Jersey and Seashore Railroad, the Washington, Baltimore 
& Annapolis Electric Railroad, the Hudson and Manhattan 
Railroad, and in the electrified zones of the New York 
Central, the Pennsylvania, and the Southern Pacific 
Railroads. 

This block signal system is also used on alternating- 
current electric railways, the relays being designed not to 
respond to the propulsion currents, but to respond to cur- 
rents of a higher frequency used in signalling. Thus, on 
25-cycle electric railways the signalling is usually accom- 
plished by currents of 6o-cycle frequency. Signal installa- 
tions of this type include the New York, Westchester and 
Boston Railway, the Chicago, Lake Shore & South Bend 
Railway, and the electrified zone of the New York, New 
Haven and Hartford Railroad. 

Alternating-current Track Relays. The vane- type al- 
ternating-current relay, shown in Fig. 17, made by the 
Union Switch & Signal Company is widely used with one- 
rail block signal systems. It consists of a C-shaped 
laminated core carrying two field coils, one on either side of 
the core air-gap. The pole-pieces of the core are provided 
with single turns of wire short-circuited upon themselves, 
called shading coils. An aluminum vane, pivoted in jewel 
bearings, is arranged to move up and down in the air-gap. 
When an alternating current traverses the field coils, a 
shifting magnetic flux is established at the air-gap with the 
aid of the shading coils, which flux causes an upward 



RAILWAY SIGNAL SYSTEMS 



247 



movement of the vane. Contact fingers mounted on the 
shaft carrying the vane are thereby brought against sta- 
tionary contacts connecting with the terminals on the cover. 




Fig. 17. 

Fig. 1 8 shows the appearance of the centrifugal frequency 
track relay made by the same concern and used on alter- 
nating-current electric railways employing the two-rail 
block signal system. Other types of alternating-current re- 
lays for both one-rail and two-rail automatic signal systems 
are available. 

7. Interlocking Plant Signals. Track switches and 
signals at railroad crossings, junctions, crossovers, draw- 
bridges and terminal yards are operated mechanically, 
electrically or electro-pneumatically and are actuated by 
the levers of interlocking machines under the control of 
levermen. An interlocking machine is usually placed as 
close as possible to the devices which it controls, but 
numerous such machines are in use which are 6000 feet 






248 



TELEGRAPH ENGINEERING 



distant from some of the devices controlled. The use of 
mechanical interlocking machines is restricted to short 
distances, say up to 1000 feet; but the electric and electro- 
pneumatic machines may be used for controlling devices 
at great distances. Fig. 19 shows the Unit Lever type 
Electric Interlocking Machine, in combination with the 




Fig. 18. 

operating switchboard and indicator groups, made by the 
General Railway Signal Company. This machine has 
38 levers for operating switches and signals and has 14 
indicators. Such indicators are used for checking the 
correspondence of movement between the lever and the 
device which it operates, the indications being received 
after the operation of the device has been properly com- 
pleted. The movement of a lever locks all levers conflicting 
with its new position and operates the device which it 



RAILWAY SIGNAL SYSTEMS 



249 



controls. This interlocking of levers is performed at the 
" locking bed " located at the front of the machine, by 
horizontal locking bars carrying V-shaped dogs which en- 
gage notches in vertical tappet bars. Upon moving a lever, 
its tappet bar is moved vertically and one or more locking 
bars are moved by the dogs which engage them, and the 




Fig. 19. 

dogs carried by these bars move into the notches on cer- 
tain tappet bars, thus locking their corresponding levers. 

A simple illustration of the function of an interlocking 
machine will be considered in connection with Fig. 20 
which represents the position of signals and derails at a 
single-track railway crossing. In this diagram i, 6, 7 and 
12 are distant signals, 2, 5, 8 and n are home signals, and 
3, 4, 9 and 10 are derails, all devices being represented in 
their normal positions, that is, the derails open and sema- 
phore blades horizontal. To permit a train to pass from 



2 5 



TELEGRAPH ENGINEERING 



A to B requires that derails 3 and 4, and signals i and 2 
must be reversed, and for proper protection to this train 
while on the crossing, derails 9 and 10, and signals 5, 6, 7, 
8, ii and 12 must be held normal. This is accomplished 
by the levers of the interlocking machine, which bear the 
same numbers as their corresponding devices. Therefore, 



^ an. 



10 



B 
Fig. 20. 



derail levers 3 and 4 when reversed should each lock derail 
levers 9 and 10 normal, and conversely. Further, to pre- 
vent levers 8 and n being reversed before levers 9 and 10 
are reversed, it is necessary that levers 8 and n when 
reversed should each lock levers 9 and 10 reversed. Each 
distant signal when reversed locks its home signal reversed. 
Finally, lever 2 when reversed should lock lever 5 normal, 
and lever 8 when reversed should lock n normal. These 
operations may be tabulated in the form of a chart as shown 
on the next page, thus forming the locking sheet for the 



RAILWAY SIGNAL SYSTEMS 



25 1 



interlocking machine. It will be observed that converse 
lockings are not duplicated, for it is understood that if one 
lever locks another lever normal, the opposite is also true, 
that is, the latter lever locks the former normal. 



Lever 


When reversed locks 


Reversed 


Normal 


I 


2 




2 


3 4 


5 


3 




9 10 


4 




9 10 


5 


3 4 




6 


5 




7 


8 




8 


9 10 




9 






10 






ii 


9 10 


8 


12 


ii 





PROBLEMS 

1. At what minimum separation may two cars travelling m the 
same direction be operated at full speed over a track with the signal 
arrangements shown in Figs. 5, 6, 7 and 8? Express the result in each 
case in terms of block lengths. 

2. Describe the operation of the relays and semaphore signals of 
the automatic block signal system illustrated in Fig. n as a train 
advances from one track section to another. 

3. A 1.3 volt primary battery supplies 0.5 ampere to one end of 
a track circuit 3600 feet long, at the other end of which is a 3.5 ohm 
track relay. The voltage measured from rail to rail at frequent 
intervals along this track section showed a drop of 3.5 millivolts for 
each 3o-ft. track length, this being due to resistance of track and 
bonds, and to leakage across ballast and ties. What percentage of 
the battery current traverses the relay? 



252 TELEGRAPH ENGINEERING 

4. Draw up the locking sheet for an interlocking machine to be 
installed at a single-track railway junction at which the signals and 
switches are located as shown below. The distant signals i, 2, 8 and 
ii show the indications of the home signals 3, 4, 7 and 10 respectively; 




12 34 

signals i and 3 apply to route AC, and signals 2 and 4 apply to route 
AB. Switch 5 is shown normally open, and the derails 6 and 9 are 
normally set to derail. It should be noted that lever 5 of the machine 
is under the immediate control of either lever 6 or 9, for lever 3 (or 4) 
cannot be reversed until lever 9 (or 6) has been reversed. 



CHAPTER IX 

TELEGRAPH LINES AND CABLES 

I. Aerial Open Lines. Line conductors for telegraphic 
signalling may be: bare wires mounted overhead at some 
distance from each other on poles or towers; insulated 
wires grouped together, forming a cable, and usually en- 
closed in a lead sheath, either suspended at short intervals 
from a steel cable fastened to poles or else drawn into 
underground conduits; or cables comprising one or more 
well-insulated conductors surrounded by a waterproof 
covering and steel armor, as in submarine cables. These 
types will be considered in the order mentioned. 

For overhead telegraph lines galvanized iron of various 
grades, hard-drawn copper and sometimes steel or copper- 
clad steel wire are employed. The sizes, weights and re- 
sistances of the conductors generally used are given in 8 
of Chap. I. The increasing adoption of copper for tele- 
graph lines is due to its low resistance (about one-sixth 
that of iron), its high tensile strength (45,000 to 68,000 
pounds per square inch) and its non-corrosion under ordi- 
nary atmospheric conditions. 

Joints. Lengths of iron line wire are usually joined by 
placing the two ends side by side and winding half the 
overlap of each wire spirally around the other; this is 
called the Western Union joint. For joining copper line 
wires the Mclntyre connector is widely used, which con- 
sists of a double copper tube, of correct size to fit the line 

2 53 



254 TELEGRAPH ENGINEERING 

wire. The ends of the wires are inserted from opposite 
ends, one through each of the twin tubes, and the sleeve 
is then twisted through three complete turns. Such joints 
do not require soldering. 

Insulators. The insulators f6r supporting bare overhead 
telegraph lines in this country are generally constructed of 
glass, and sometimes of porcelain. The design of the stand- 
ard form of insulator is shown at the left of Fig. i, the 
dimensions in inches being indicated thereon. Its small 
diameter, coupled with the relatively large distance along 
the surface from the wire groove to the insulator pin, con- 
duces to the maintenance of high-insulation resistance 
despite accumulations of dirt and other foreign matter on 
the insulator surface. The insulator at the right of Fig. i 
shows the standard form of two-piece transposition insu- 
lator. Insulators having double flanges or " petticoats " at 
the bottom are sometimes used when greater insulation 
resistance is desired. 

The line wire when attached to the insulators is not 
passed around the insulator but is laid in the groove at 
one side and is tied in this position by short pieces of 
wire of the same size as the line wire and which pass around 
the insulator. The middle portion of Fig. i shows the 
standard type of insulator pin for supporting the insu- 
lators on the pole cross-arms. They are commonly made 
of chestnut, locust or oak, both the shank and thread being 
tapered. Wood-top steel pins and wood bracket-pins are 
also used, the latter being fastened directly to the pole 

(Fig. 4). 

Poles. Wooden poles are most generally used for sup- 
porting aerial telegraph or telephone lines, except where 
unusually large spans demand strong towers of steel or re- 



TELEGRAPH LINES AND CABLES 



255 



inforced concrete. In this country white cedar, chestnut, 
cypress, pine and redwood poles are principally used for 
this purpose. These poles are from 20 to 80 feet in height, 
but those from 25 to 40 feet are the more usual. The 
height of poles to be used in a given locality is governed 
by several conditions, such as ordinances requiring a 
minimum distance of the lowest wire above the ground, 




non-interference of the wires with the possible activities of 
the fire department, clearance at trolley and railway cross- 
ings, etc. The poles are from 5 to 8 inches in diameter at 
the top, with an increase in diameter of about one inch in 
every 10 feet toward the bottom. Poles are set from 5 
to 10 feet into the ground, according to the height of the 
pole and the nature of the soil. In many cases it is de- 
sirable to treat the lower ends of the poles so as to mini- 
mize decay where they are embedded in the ground. This 



256 TELEGRAPH ENGINEERING 

treatment consists of applying a preserving fluid, such as 
creosote or carbolineum oil, applied by pressure, dipping or 
by brush. Poles decayed at the ground may be repaired 
by placing a rigid collar v of reinforced concrete around the 
decayed portion of the poles. 

The size of the poles should be selected so that the 
transverse forces, due to the tension in the wires at turns 
in the line and to wind pressure on poles and wires, do not 
exceed the breaking stress of the pole. The pull, exerted 
at the center of load at a point L c feet above the ground, 
that will break a circular-sectioned pole having a diameter 
d feet at the ground line, may be expressed as 

F = -S pounds, (i) 



where A is the cross-sectional area of the pole at the ground 
in square inches and S is the tensile strength in pounds 
per square inch. Accepted values of the maximum fibre 
stress S for some woods are given below: 



Chestnut 6,000-10,000 

Cypress 5,ooo- 8,000 

White cedar 4,000- 8,000 

Yellow pine 4,000- 8,000 



pounds per sq. in. 



In proper designs much lower values of this maximum 
fibre stress are employed, thereby allowing a considerable 
factor of safety. 

At a turn in the line, if the horizontal angle between the 
directions of the wires at either side of the pole be 6, and 
the tension in each of N wires be T pounds, then the trans- 
verse force acting on the pole at a height L c feet above the 
ground is 

F = 2 NT cos - pounds, (2) 



TELEGRAPH LINES AND CABLES 257 

which assumes that the tension in the wires is the same on 
both sides of the pole. The wind pressure on the pole, 
having an average diameter of d a feet and a height of H 
feet above the ground, will be equivalent to a force of 
KdaH pounds acting at the center of the pole, where K is 
the wind pressure per square foot of projected pole area, 
usually taken as a maximum of 8 pounds. This force act- 
ing at the center of the pole may be replaced by a force 
at the center of load of, say, 0.6 Kd a H pounds acting at a 
point distant L c or f of the pole height from the bottom. 
If the wind blows in the direction of the resultant trans- 
verse force F', the wind pressure on the wires will be 

! sin-, where / is the distance between poles in feet, 
12 2 

and di is the diameter of each conductor over a possible 
ice coating, in inches. Therefore the maximum wind 
pressure on the pole and wires which may assist the trans- 
verse force on the pole at a turn in the line is 

F" = K (0.6 dJI + 0.0833 Nidi sin -} pounds, (3) 

and consequently a pole should be selected so that 
F>F' + F" 

with a considerable factor of safety. If this requirement 
demands a pole of unusually large diameter for an assumed 
factor of safety and for a given angular change in the direc- 
tion of the pole line, a smaller pole may be used if rein- 
forced by the use of guy wires or braces of suitable types. 
Such reinforcement is generally utilized with terminal 
poles, with poles at the ends of long wire spans or with 
poles near a curve or corner. Fig. 2 indicates the method 
of guying a line at a road crossing. 



TELEGRAPH ENGINEERING 



To consider a specific example, assume a bend of 160 
degrees in a 24-wire, 3-arm pole line of No. 9 B. & S. gage 
copper wire, supported on white-cedar poles projecting 30 
feet above the ground and spaced 130 feet apart. If the 
maximum fibre stress be taken as 6000 pounds per square 
inch, and the diameter of the pole at the ground is i foot, 
and at the top is 8 inches, the transverse force on the 




Fig. 2. 

corner pole acting at the center of load (say at a point 25 
feet from the ground) necessary to break the pole is 

IT (6) 2 X i, 

F = a s/ r 6oo = 3390 pounds. 

o A 25 

If the tension of each wire be 200 pounds, the transverse 
force due to wire tension at the corner pole is 

F f = 2 X 24 X 200 cos - = 1670 pounds, 

and if the outside diameter of the ice-covered wire be 
taken as 1.114 inches, thereby allowing \ inch of ice all 



TELEGRAPH LINES AND CABLES 259 

around the conductors, the transverse force due to wind 
pressure is 

F" = 8(0.6^30 + 0.0833 X 24X130X1.114 sin) 

\2Xl2 2 / 

= 2376 pounds. 

Thus, the total transverse force that may act on the pole 
under consideration is 1670 + 2376 = 4046 pounds, a 
force greater than the assumed breaking stress of the pole, 
or 3390 pounds. Therefore this corner pole must be 
firmly guyed or braced in order to maintain telegraphic 
service over this line in times of severe wind and sleet. 

Cross-arms. The cross-arms for a telegraph pole are 
made of sound, thoroughly seasoned straight-grained tim- 
ber, either creosoted or painted. The standard cross-arms 
measure 3^ by 4^ inches, and may vary in length from 3 
to 10 feet, depending upon the number of wires accom- 
modated. These cross-arms are attached to the poles by 
placing them in gains or slots cut in the poles and securing 
them in position either by lag-screws or by bolts which 
pass through the pole. 

The strength of standard cross-arms is indicated in 
the following table, which gives the results of recent 
tests conducted by the Forest Service on 6-foot, 6-pin 
cross-arms : 

Average maximum downward 
load in pounds 

Longleaf pine (75 per cent heart) 10,180 

Longleaf pine (100 per cent heart) 9,?8o 

Longleaf pine (50 per cent heart) 8,980 

Shortleaf pine 9,260 

Shortleaf pine (creosoted) 7,650 

Douglas fir 7,590 

White cedar 5,200 



260 



TELEGRAPH ENGINEERING 



Cross-arms are further secured by iron or steel braces, as 
indicated in Fig. 3, which also shows the usual spacing in 
inches of insulators and cross-arms. 

Poles at line terminals or at the ends of long spans are 




g a a a 




9 9 a 




Fig. 3. 

usually provided with double cross-arms, placed on op- 
posite sides of the poles and bolted together. 

Lightning Arresters. To protect pole lines against de- 
struction by lightning, it is common practice to lead a 
ground wire to the top of at least every tenth pole. Fig. 4 
shows one arrangement employing a double-grooved in- 



TELEGRAPH LINES AND CABLES 



261 



sulator mounted on a bracket pin. It will be observed 
that a small gap is formed between the ground wire and 
the line wire, over which a lightning discharge may take 
place and pass to ground. The 
lower end of the ground wire usually 
connects with an iron pipe driven 
into the ground at least two feet 
away from the pole. 




WIRE 



2. Wire Spans. In suspending 
wires from pole cross-arms, the ten- 
sion of the wire should be such that 
at the lowest attainable temperature 
the tension due to the weight of 
the wire with possible coverings of sleet and snow and 
due to wind pressure must not exceed a predetermined 
value. The physical constants of various sizes of hard- 



Fig. 4- 




Fig. 5. 

drawn copper and galvanized iron wire are given in the 
following table. The values of tensile strength given 
in this table should not be used directly in determining 
the proportions of wire spans, but should be divided by a 
proper factor of safety, say 2 to 4, so that the wire may 



262 



TELEGRAPH ENGINEERING 



withstand excessive momentary loads to which the line 
may be occasionally subjected. 



Hard-drawn Copper 

Modulus of Elasticity = 16,000,000 pounds 
per sq. in. 

Coefficient of Expansion = 0.0000095 per deg 
fahr. 



Galvanized Iron Wire 

Modulus of Elasticity = 26,000,000 pounds 

per sq. in. 

Coefficient of Expansion = 0.0000067 per deg. 
fahr. 



B.&S. 
Gage 
No 


Diam- 
eter in 
inches 


Area 
in 
square 
inches 


Tensile 
strength 
in 
pounds 


Weight 
in 
pounds 
per 
foot 


S.W.G. 
No. 


Diam- 
eter in 
inches 


Area 
in 
square 
inches 


Tensile 
strength 
in 
pounds 


Weight 
in 
pounds 
per 
foot 


9 


O.II4 


0.01028 


630 


o . 0396 


4 


0.238 


0.0445 


2I2O 


0.1490 


10 


0.102 


0.00815 


525 


0.0314 


5 


O.22O 


0.0380 


1820 


0.1275 


ii 


O.OQI 


. 00646 


420 


0.0249 


6 


0.203 


0.0324 


*55 


0.1085 


12 


O.oSl 


0.00513 


330 


0.0198 


7 


0.180 


0.0254 


I2IO 


0.0853 


13 


0.072 


. 00407 


270 


0.0157 


8 


0.165 


0.0214 


IO2O 


0.0716 


14 


0.064 


0.00323 


213 


O.OI24 


9 


0.148 


0.0172 


820 


0.0578 












10 


0-134 


0.0141 


670 


0.0474 



In determining the proper sag of a wire span, the maxi- 
mum weight of the wire with sleet or ice loads must be 
known. In view of the variation of climatic conditions, it 
is usual to assume an ice coating of f inch thickness all 
around the wire as the severest load, the weight being 
0.033 pound per cubic inch. Wind pressure must also be 
considered, this force being assumed horizontal and per- 
pendicular to the wire. The maximum wind pressure may 
be taken as 8 pounds per square foot of projected area of 
the wire or of the ice cylinder; this value corresponds ap- 
proximately to a wind velocity of 60 miles per hour. The 
minimum temperature may be considered as 20 deg. fahr. 
and the maximum temperature as 120 deg. fahr., these 
temperatures being reasonable values for the northern 
part of this country. 

Let wi = weight of wire and ice per foot of wire length, 



TELEGRAPH LINES AND CABLES 263 

and w<t = wind pressure per foot of wire length, then the 
resultant force per foot will be 



W = Vwi 2 + Wi 2 , (4) 

and the wire will assume the position indicated in Fig. 5. 
With relatively small spans, the curve assumed by a wire 
suspended between two insulators approximates with suf- 
ficient accuracy to a parabola. On this assumption the sag 
in feet at the lowest probable temperature will be 

= rr w 

where w is the resultant force in pounds per foot of wire 
length, / is the distance between the supporting insulators 
on the same horizontal level in feet, and T is the maximum 
allowable tension in the wire in pounds (assumed uniform 
throughout the length of the wire). 
The length of the wire in feet may be expressed as 

(6) 

If this wire were removed from the supports and laid on 
the ground its length would be 

L -- ^' (7) 



where L u is the unstressed length of the wire in feet, A is 
the area of the wire cross-section in square inches and E 
is the stretch modulus of elasticity of the wire material in 
pounds per square inch. 

Inasmuch as wires are strung without ice- coverings and 
usually in fair weather on other than the coldest days, it is 



264 TELEGRAPH ENGINEERING " 

desirable to know what sags to allow at the higher tempera- 
tures so that, with the severest external loading at lowest 
temperature, the tension will not exceed the maximum 
allowable value. The increase of the unstressed length L u 
due to a temperature rise of / fahr. degrees above the former 
temperature is L u kt, where k is the temperature coefficient 
of linear expansion per fahr. degree reckoned from the for- 
mer temperature. Therefore the total unstressed length of 
the wire at the higher temperature will be 

L t -L.(i+kt); (8) 

but when strung its length will be 



where T 1 is the tension of the wire at the higher tem- 
perature. Also by analogy with equations (5) and (6), the 
sag at this temperature is 



do) 
and the length of the wire is 



r ;j_ ( \ 

L st =l-\ -- -> (n) 

3 ' 33 

where w is the resultant force per foot of wire length with 
no ice covering. 

In order to find the sag D t of the wire without ice at 
any temperature in terms of the unstressed length L u at 
the lowest temperature, eliminate L tj L 8t and T r from equa- 
tions (8) to (n), and there results, 



TELEGRAPH LINES AND CABLES 265 

This cubic equation is of the form 

Df -3 PD t -2Q = o, (12) 

where P = l -[L u (i + kt) - 1} (13) 

_ 



The solution of equation (12) is 

(15) 



when P z > Q 2 , but when P 3 < Q* hyperbolic cosines must 
be used. 

As an illustration, consider a No. 9 B. & S. gage hard- 
drawn copper wire suspended between insulators 130 feet 
apart, the factor of safety being taken as 2. From the 

foregoing table, T = -*- =315 pounds, A =0.01028 square 

inch, the wire diameter = 0.114 inch and the weight of 
copper per foot = 0.0396 pound. The outer diameter of 
an ice coating ^ inch thick all around the wire would be 
1.114 inch, and the weight of this covering would be 

X 12 X 0.033 = 0.382 pound per foot. 
4 

The wind pressure would be - - = 0.743 pound per 

linear foot. Whence 



w = V(o.o396 + 0.382)2+ (0.743)2 = 0.854, 

and the sag at the lowest temperature (say 20 deg. fahr.) 
becomes, from equation (5), 



266 TELEGRAPH ENGINEERING 

The length of the wire when unstressed is therefore 



- = 13067,4 = feet> 
j. + 315 1-0019 

0.01028 X 16,000,000 
To iind the sag at 120 deg. fahr., substitute the foregoing 

t T i// A\2 / 8 XO.II4\ 2 

value of L M , w = V 0.0396 + - - = 0.0857, 

\ / \ 12 / 

and / = 140 in equations (13) and (14). Thus, 

P = ^p[ I 343 + 0.0000095 X 140) - 130] = 9.75, 

and 

Q _ 3 X 130.43 (i +0.0000095 X 140) 0.0857 (i3o) 3 _ 
128 X 0.01028 X 16,000,000 

Since P 3 > Q 2 , the sag at this temperature, from equation 
05)> is 

/ - /i ^ Si 

D t = 2 V975 cos ( - cos" 1 , 

\ V- 



3 
= 6.24cos2747' = 5.52 feet, 

and its vertical component is 



For unusually long spans, such as river crossings, wire of 
steel or copper-clad steel are more suitable than of hard- 
drawn copper or galvanized iron. 

3. Economical Span Length. To determine the pole 
spacing conducive to a minimum annual maintenance 
charge on the supporting structures of an aerial line, let 



TELEGRAPH LINES AND CABLES 267 

n = economic number of poles per mile, 

h = minimum required distance of wires above 

ground in feet, 

H = height of pole above ground in feet, 
Ci = cost of cross-arms, insulators and pins per pole 

in dollars, 
r = average interest and depreciation rate on poles, 

insulators, etc., 
Wi = weight per foot of wire in pounds at maximum 

sag, 

T = tension in conductor in pounds at maximum sag, 
and D' = maximum vertical sag in feet. 

Assume that the cost of the line wire will not vary 
with the pole spacing, and that the cost of the poles ready to 
set varies as the square of their height, or C p = aH 2 dollars, 

where a is a constant. Then the pole spacing is / = - - 

n 

feet, and the height of the poles is (see 2) 



The cost of line material per mile, exclusive of conductors, 
is 

C = n (Ci + Cp) dollars; 

consequently the annual expense per mile for maintaining 
the pole line is 



C a = m | C, + a [h + H ff 9 ) 2 ] 2 j dollars. (17) 

To determine the minimum annual expense equate to zero 
the differential coefficient of C a with respect to n. Then 



268 TELEGRAPH ENGINEERING 

dC* _ vC 7 2 arw 1 h($28o) 2 sarw? (528o) 4 _ 

dn~~ 4 Tn* 64 TV ' 

or 

4 aWjh&So) 2 g 3<m>i 2 (528o) 4 , 

- * " = 



This equation is of the form x 2 px q = o, and when p 
and q are positive quantities the solution may be written 



as * = + y + q. If w 2 = x, 



(528o) 2 , , 

' 



and q = 64 p (c v : ..^' M 

then 




As an illustration, consider the following values sug- 
gestive of the order of magnitude of the cost constants 
for a 3-arm 24-wire pole line with poles 6 inches in diameter 
at top: 

a = 0.006, 
Ci = 1.50, 
r = 0.15. 

Then for No. 9 B. & S. gage hard-drawn copper wires 
covered with ice J inch thick all around and suspended 
with a factor of safety of 3, at the minimum distance of 
20 feet above the ground, 

T = 210 pounds, 
and wi = 0.422 pound per foot (page 265). 



TELEGRAPH LINES AND CABLES 269 

For these constants 

0.006 X 0.422 X 20 (5280)2 
4 X 210 (1.50 + 0.006 X 2O 2 ) 

3 X 0.006 (0.422)2 (528o) 4 

and q = - ^ = 226,000; 

64 (2io) 2 (1.50 + 0.006 X 20 ; 

whence from equation (21) the economic pole spacing is 
n = V 215 -f V(2i5) 2 + 226,000 = 27 poles per mile. 

The height of towers to be used, and the annual mainte- 
nance of the supporting structure for the wires, may now be 
found from equations (16) and (17) respectively, yielding 
H = 29.5 feet above ground, and C a = 27 dollars per mile. 

4. telegraph Cables. Aerial and underground tele- 
graph cables are formed of any desired number of annealed 
copper wires, from No. 14 to No. 19 B. & S. gage, indi- 
vidually insulated with prepared paper, fibre or sometimes 
rubber. These conductors are assembled in layers, form- 
ing a cylindrical group or core and held in shape by one or 
more spiral coverings of paper, and the whole is then en- 
closed in a lead sheath or else is covered with tarred jute 
and is surrounded by a cotton braid saturated with water- 
proof compound. Lead-covered paper-insulated cables are 
now principally used in telegraphy, and are called saturated- 
core cables if the paper insulation is saturated with an in- 
sulating compound, or dry-core cables if the insulation is 
untreated. The saturated-core cables excel the dry-core 
cables in the protection afforded in case of mechanical 
injury, but have a higher electrostatic capacity, due to 
the larger specific inductive capacity of the insulating com- 
pound. Low capacity is especially desired in telephonic 



270 



TELEGRAPH ENGINEERING 



transmission and therefore dry-core cables with somewhat 
smaller wires (usually of No. 19 to No. 22 B. & S. gage for 
local distances) are considered standard practice. In order 
to exclude moisture from dry-core cables, the ends of sec- 
tions when supplied by manufacturers, are always satu- 
rated with paraffin or other insulating compound for a 
distance of about two feet, and the lead sheath is then 
hermetically sealed. The sheaths for cables may be of 
pure lead, lead and antimony composition, or lead with 
a small percentage of tin; their minimum thicknesses are 
outlined in the following table. 



Number of 
conductors 


Thickness of 
sheath 




Inch 


10 tO 100 


Ji- 


IOO tO 2OO 


/z 


200 tO 400 


A 



The conductors of a paper-insulated cable may have a 
single, double or triple wrap of manila rope paper spirally 
applied, the thickness of each being from 0.004 to 0.008 
inch. The thickness of the insulation around the con- 
ductors of a rubber-insulated aerial or underground tele- 
graph cable varies from 20 to 60 mils. 

Telegraph companies usually specify that the individual 
rubber-insulated conductors for a telegraph cable be im- 
mersed in water for 24 hours and thereafter while still 
immersed be able to withstand an alternating electro- 
motive force of looo volts, applied for one minute be- 
tween the conductor and the water. With dry-core cables 
the finished lead-covered cable is subjected to a similar 
test. The insulation resistance of each conductor is then 



TELEGRAPH LINES AND CABLES 



271 



measured by an application of 100 volts for one minute 
across this conductor and all the other wires and the 
sheath, the reference temperature being 60 deg. fahr. A 
table showing the variation of the average insulation re- 
sistance with temperature is usually supplied by the cable 
manufacturer. 

Cables are also used where telegraph lines extend across 
rivers, lakes and bays, or from the mainland to islands. 
Such submarine cables are formed of either rubber- or 
paper-insulated conductors within a lead sheath, this 
sheath being covered with several layers of jute thoroughly 
saturated with a waterproof compound. Cables to be 
installed on rocky river-beds or in waters having rapid 
currents are provided in addition with an armor of galva- 
nized iron wire, which is surrounded by jute servings sat- 
urated with a compound of pitch and fine sand. 

The telegraph cable mileage in the United States in 1907 
is tabulated below: 



Location 


Miles of cable 


Miles of single 
wire in cables 


Average num- 
ber of wires per 
cable 


Overhead 


2 ego 


40,066 


ie e 


Underground 


1130 


37,727 


33.4 


Submarine* 


7760 


7.7,82 


2 O 










Total 


7488 


8<?,i7<; 













* Exclusive of ocean cables. 

The weights and prices of the Standard Underground 
Cable Company's telegraph cables, composed of No. 14 
B. & S. gage conductors with fibre or paper insulation 
measuring / 2 inch in diameter over insulation, are given 
in the following table: 



272 



TELEGRAPH ENGINEERING 



Number of 
conductors 


Diameter over 
sheath in 
inches 


Weight in 
pounds per 
foot 


Catalog price 
in cents per 
foot 


5 


0.76 


I.4I 


25-1 


10 


0.97 


1-93 


33-9 


20 


1.16 


2,. 55 


45-7 


50 


1.63 


4-23 


81.2 


100 


2.18 


6-54 


133-9 


150 


2-55 


8.45 


181.5 



Aerial Cable Installation. In supporting overhead 
cables on pole lines it is necessary to provide supports be- 
tween poles because the cable itself does not possess suf- 
ficient strength to sustain its own weight over ordinary 
pole spans. The required support is furnished by solid or 
stranded galvanized steel messenger wires of proper size, in 
accordance with the weight of the cable and length of 
span, to which the cable is fastened- by means of appro- 
priate hangers at intervals of about 2 feet. The messenger 
wire is fixed to the sides of poles or to their lower cross- 
arms by means of suitable messenger supports. The sizes 
and breaking stresses of various grades of steel messengers 
are given in the following table: 



Diameter 




Weight in 




Breaking st 


ress in pounc 


Is 


in inches 




pounds per 
100 feet 


Besse- 
mer 


Siemens- 
Martin 


High- 
strength 


Plow 


Solid | 


0.192 
0.225 


9.8 
13-4 


.... 


2,500 
3.500 


4,300 
5.900 


6,000 
8,000 


Stranded 


0.250 
0.312 
o 37"? 


13.0 
22.0 

30 o 


2,500 
4,200 

r 700 


3,060 
4,860 
6,800 


5,100 
8,100 
1 1 , 500 


7,600 
12,100 
17,250 




0-437 
0.500 


4O.O 
52.0 


7,600 
9,8OO 


9,000 
1 1 ,000 


15,000 
18,000 


22,500 
27,000 



TELEGRAPH LINES AND CABLES 



273 



The sags of messengers at different temperatures and 
the transverse stresses on aerial 
cable pole lines may be deter- 
mined in the same manner as 
shown in 2. One type of cable 
hanger, known as the metro- 
politan, is represented in Fig. 6. 




5. Underground Cable In- 
stallation. --In densely-popu- 
lated localities it is customary to place telegraph and 



Fig. 6. 




Fig. 7. 



other electric cables underground. These cables are not 
buried in the ground, but are drawn into finished ducts 



274 



TELEGRAPH ENGINEERING 



or conduit from one manhole to another. When laid, 
conduit having a sufficient number of ducts to allow 
for future growth is placed in a trench and is partially 
or entirely surrounded with concrete. Fibre and vitrified- 
clay conduits are those principally installed, but ducts may 
also be formed in concrete directly. Fig. 7 illustrates the 
single-duct and multiple-duct types of vitrified clay con- 
duit manufactured by the H. B. Camp Company. The 
lengths of multiple-duct conduit are held in alignment by 
dowel pins and each joint is wrapped with a layer of wet 
muslin or burlap and thereafter plastered with cement 
mortar. The top of conduits should not be less than 20 
inches below the street surface. 

The arrangement of a six-duct conduit of concrete, fibre, 
multiple-duct clay and single-duct clay is shown in Fig. 8, 
with dimensions in inches. The total costs per trench 
foot of these types of conduit construction installed, in- 
cluding repaving but exclusive of manholes, as estimated 
by W. N. and C. L. Matthews, for various numbers of 
ducts, are given in the following table: 



Num- 


Costs per trench foot in dollars 


ducts 


Concrete 


Fibre 


Multiple 
clay 


Single 
clay 


I 




O 44 




5 1 


2 


0.56 


0.67 


0-73 


0.76 


3 


0-73 


0.88 


1.03 


1.05 


4 


0.83 


0.91 


0.98 


1.09 


6 


0.97 


1.22 


1-37 


1 .46 


8 


I.I7 


i-SS 


1.64 


1.92 


12 


1 .40 


1.98 


2. II 


2.45 


16 


l.6 7 


2.42 


2.72 


3.01 


20 


I-9S 


2.94 


3-22 


3563 



TELEGRAPH LINES AND CABLES 



275 



This table is based upon the spacings shown in Fig. 8, 
but with multiple-duct vitreous clay conduit i inch of 
concrete is allowed between the sections, and it assumes 
that the conduit is laid in streets with granite or equivalent 
paving. Oftentimes the concrete at the sides of the con- 






4. 






m 



f!X 4>U O'l I t?. : 

I3CK1 

.--. 




FIBRE TUBE 




MULTIPLE CLAY 




Fig. 8. 



duit is dispensed with, thereby reducing the cost of in- 
stallation. 

Manholes, or conduit-openings, are located along the 
conduit line at suitable distances apart, rarely greater than 
700 feet, to facilitate the installation, repair and removal 
of cable sections. The manholes are constructed of brick 
or concrete, in sizes of 3 ft. by 3 ft. and upwards, depend- 
ing on the number of cables to be accommodated. Fig. 9 



276 



TELEGRAPH ENGINEERING 



shows a section of an oval manhole whose inside dimen- 
sions are 7 ft. by 3! ft. The costs of manholes of either 
construction vary from about $60 to $150 according to 
their size and the nature of the ground where they are 
installed. 



GRADE LINE \ 




Fig. 9. 

Cable Splices. Aerial and underground cables are al- 
most invariably spliced near poles or in manholes respec- 
tively. The method of making splices in multi-conductor 
paper-insulated cables is indicated in Fig. 10. Two cables 
to be spliced are placed in position so that their conductors 
overlap from 12 to 24 inches, depending on the number of 
conductors. The corresponding innermost conductors of 
the two cables are then twisted together as shown at A, 
and a paper or cotton tube is placed over the joint as 
shown at B. All others are similarly spliced with the 
joints staggered (C, Fig. 10), and then the entire splice 
is boiled out with paraffin and wrapped with muslin or 
linen. A lead sleeve, whose inside diameter exceeds the 



TELEGRAPH LINES AND CABLES 



277 



outside diameter of the cable sheaths by i or i| inches, 
is then placed over the splice and is joined to the sheath 
by means of wiped soldered joints. 





Fig. 10. 

Cable Pole Boxes. At suburban points beyond which it 
is not deemed necessary to extend underground cable lines, 
and at water crossings, cables are brought to the tops of 
poles and terminated in cable pole boxes, as shown in Fig. 
ii. Combined fuses and lightning arresters are located 
within this cable box, as shown at /, and are interposed 
between the bare aerial wires and the cable conductors. 

Electrolysis of Underground Cable Sheaths. If stray 
electric currents of an electric railway system, in wending 
their way back to the generating station, flow out of cable 
sheaths in moist locations at certain places, electrolytic de- 
composition of the sheaths occurs at these places, for the 
sheaths there behave as anodes in electrolytic cells. Con- 
tinued electrolytic decomposition, or electrolysis, causes 
the pitting of the cable sheath, and the consequent ad- 
mission of moisture to the insulation around the con- 
ductors within the protecting sheath. The extent of 



2 7 8 



TELEGRAPH ENGINEERING 



electrolysis depends upon the number of ampere-hours 
conducted, since, according to t araday's Law, one ampere 
flowing out of a lead sheath into an electrolyte for one hour 
would dissolve 3.87 grams of lead. 




Fig. ii. 

In order to locate the regions where this rapid corrosion 
of cable sheaths takes place, tests are made at manholes 
to determine the potentials of the sheaths with respect to 
the adjacent ground, and the amounts of current carried 
by them. By thus observing the direction and value of 
the stray currents at a number of manholes, the places 
where currents leave the cables and pass to the moist 
ground are readily determined. Where a cable sheath is 
found by test to be decidedly positive with respect to 



TELEGRAPH LINES AND CABLES 279 

ground or to the railway track, a temporary connection of 
heavy copper wire including an ammeter may be made 
from the sheath to a suitable ground, to the track, or to 
a neighboring negative feeder. Readings at other places 
where the sheath was positive to earth may then be re- 
peated, and if conditions are improved, a permanent 
soldered bond is installed so that the current may flow 
from the cable along a wire instead of into an electrolyte. 
Where several cables pass through a manhole it is good 
practice to bond all of them together. After such bonds 
are in place, another complete and final survey is made. 
The use of negative track feeders of proper copper dis- 
position, and possibly with negative boosters in these 
feeders, reduces the stray railway currents to a large 
extent.* 

6. The Earth as a Return Path. Professor Steinheil 
in 1837 made the discovery that the earth may be used as 
a portion of an electric circuit. It has been stated that 
the resistance of the earth when used as a return circuit 
for a telegraph line is very small if the line terminals are 
properly grounded. To verify this statement, consider a 
hemispherical ground electrode of radius a centimeters to 
be buried a short distance below the earth's surface. The 
resistance of the earth outward from this electrode to a 
distance d centimeters is 

pdr xv 



- 



as expressed by Heaviside, where p is the specific resist- 
ance of the earth, assumed uniform, in ohms per centi- 

* See Sheldon & Hausmann's "Electric Traction and Transmission 
Engineering," p. 157; G. I. Rhodes' paper, A.I.E.E., Trans. 1907, p. 247. 



280 



TELEGRAPH ENGINEERING 



meter cube, and r and r + dr are the radii of concentric 
hemispherical equipotential surfaces, in centimeters. The 
distribution of resistance outward from this electrode may 
be calculated from equation (22) by considering the resist- 
ances over the distances, say a to 2 a, 2 a to 4 a, and so on. 
Thus 



2irJa 
P 



871-0 



ohms, etc. 



The following table shows the resistance values for the 
various distances from the electrode, and Fig. 12 shows 
the total resistance outward from the electrode for a par- 
ticular case in which p = 800 ohms per centimeter cube and 
a = i foot = 30.5 centimeters. 



Distance in 
centimeters 


Resistance 
in ohms 


a to 2 a 


o . 07958 p/a 


2 a to 4 a 


o. 03979 p/a 


4 a to 8 a 


0.01989 p/a 


8 a to 16 a 


0.00994 p/a 


16 a to 32 a 


0.0049 7 p/a 


32 a to 64 a 


0.00248 p/a 


64 a to 128 a 


0.00124 P/ a 



It is seen that the greater share of the ground resistance 
is very near the electrode, consequently good conductivity 
of the soil near the electrode is essential, but with greater 
distances from the electrode the earth's conductivity be- 
comes of less importance. It is also to be noted that the 
resistance varies inversely with the size of the electrode, 
whence the desirability of utilizing available extensive 
municipal water pipes as ground electrodes. 



TELEGRAPH* LINES AND CABLES 



28l 



Inasmuch as the resistance between two electrodes is 
principally in the neighborhood of these electrodes, the 
total resistance between them might be expressed as 



2 7T 



(23) 



20 40 60 80 

DISTANCE FROM GROUND 

ELECTRODE IN FEET 

Fig. 12. 



where a and a' are the radii of the two electrodes respec- 

tively, it being understood that one electrode is not perfectly 

insulated from its mate. Some instances of almost com- 

plete electrical isolation 

of the ground at a local- 

ity from the earth have 

been observed. Thus, to 

secure telegraphic com- 

munication with Nash- 

ville, Tenn., it was found 

necessary to extend a 

ground-wire from that 

city to an effective ground 

at a point several miles distant. On the other hand, large 

sections of the earth between two widely-separated stations 

may be perfectly insulating without materially increasing 

the resistance of the ground return. 

When the pipes of a community's water supply are not 
available as a ground electrode, satisfactory ground con- 
nections may be made by driving two or more iron pipes 
about 2 inches in diameter into moist earth in the basement 
of the telegraph office. Line and office connections with 
such pipe grounds are of copper wire, usually larger than 
No. 9 B. & S. gage, well soldered to the pipes. 

In the practical measurement of ground resistance either 
another permanent electrode presenting a known ground 



282 TELEGRAPH ENGINEERING 

resistance or two auxiliary temporary ground electrodes 
or grounds are used, these test grounds being at least 15 
feet distant from each other and from the permanent 
main ground whose resistance is to be measured. In the 
first case the series resistance of the two grounds minus 
the resistance of the known ground gives to a fair degree 
of accuracy the resistance of the desired ground. In the 
second case, employing two auxiliary grounds in the 
measurement of the main ground, the resistance between 
each pair is observed. Then, if RI be the series resistance 
between the main and first auxiliary grounds, R% that 
between the main and second auxiliary grounds and RZ 
that between the two auxiliary grounds, it follows that 
the earth resistance at the main ground is 

R = *i + fr-ft. ( 24 ) 

2 

The resistance of a ground will vary from time to time, de- 
pending upon the amount of moisture in the soil in the 
immediate neighborhood of the electrode. In practice 
these resistance measurements are made periodically, at 
least once a year. 

The Western Union Telegraph Company specifies that 
the resistances of various classes of grounds should not in 
general exceed the following values: 

Central office battery grounds o . i ohm, 

Small office and test station grounds 5 ohms, 

Lightning arrester grounds 15 ohms, 

High-potential protection grounds 25-100 ohms. 

7. Electrical Constants of Telegraph Conductors. The 
four electrical constants of a line conductor are : resistance, 
inductance, capacity and leakance. 



TELEGRAPH LINES AND CABLES 283 

Resistance. The resistance to direct currents of a wire 
of area A square inches, at any temperature / degrees cent., 
expressed in ohms per mile, is 

R = 0.02495 . (i + at), (25) 

where p is the specific resistance in microhms per centi- 
meter cube of the material at ocent., and a is the mean 
temperature coefficient of electrical resistance per centi- 
grade degree reckoned from o cent. Accepted values of 
these constants for copper and iron follow: 



Material 


P 


a 


Annealed copper (stand.) 
Hard-drawn copper 
Galvanized iron 


1.587 
1.631 
9.69 


0.00427 
O.OO4I4 
0.0058 



Tabulated values of the resistances of standard sizes of 
telegraph wire are given in Chap. I. The conductivity of 
commercial copper and bimetallic wire is usually specified 
as a percentage of that of standard annealed copper. 

Inductance. The self-inductance of a single linear cylin- 
drical wire, mounted at a height h above the ground which 
serves as the return path, is 

. r. 

L = 0.000741 logio ^ + 0.0000805 n (26) 

henrys per mile, where D is the diameter of the conductor 
and p. is its permeability. A short table of logarithms 
appears in the appendix. The mutual inductance between 
two parallel ground-return wires, mounted at the same 
height above the ground and separated by a distance d, in 
henrys per mile, is 



,, , N 

M = 0.000741 logio - * --- (27) 



284 



TELEGRAPH ENGINEERING 



In these expressions, h, D and d must be expressed in the 
same units. Therefore the total inductance of the two 
similar wires for equal currents in the same direction is 

L. = i(L + aO, (28) 

while for equal currents in opposite directions is 



2 d 
or 0.00148:2 logio 



0.000161 ju. (29) 



Equation (29) indicates that the inductance of wires 
within a grounded conducting sheath is very small, inas- 
much as the sheath, which may be considered as the return 
path, is very near the conductors. 

For compound conductors consisting of a steel core sur- 
rounded by a copper shell, the factor /z in the foregoing 
equations is replaced by the values given in the following 
table for various ratios n of the conductivity of the com- 
pound wire to that of a solid copper wire of the same 
outside diameter, // being the permeability of the steel core. 



n 


Factor to replace n 


O. 2 

0-3 
0.4 

o-5 


o.2g8fjL f +0.1292 
o. 1012/1' + o. 204 
0.0416 M' + o. 294 
o. 0185 M' + 0.386 



This table, derived from that given by Fowle,* assumes 
steel to have 12 per cent of the conductivity of copper. 

Capacity. The capacity of a single overhead wire 
utilizing ground as its return, in microfarads per mile, is 



C = 



0.0894 



,t 



(3) 



cosh" 1 






* Electrical World, v. 56, p. 1474. 

f Sheldon and Hausmann's " Electric Traction and Transmission Engi- 
neering," p. 230. 



TELEGRAPH LINES AND CABLES 285 

the symbols having the same significance as above. For 
large values ot , it is more convenient to use the very 
approximate equation 




where is the base of Napierian logarithms and is equal to 
2.7183. Logarithms to the base e may be obtained by mul- 
tiplying the corresponding logarithms to the base 10 by 
2.3026; that is, log e x= 2.3026 logio %> 

When a number of overhead wires are located near each 
other, the capacity of each wire is increased by the pres- 
ence of the others. For two parallel ground-return wires 
suspended at the same height above the ground and sepa- 
rated a distance d from each other, Heaviside gives as the 
capacity of each wire in microfarads per mile: 

0.0894 log^ -=- 

(a*) 



Their mutual capacity in microfarads per mile is 
0.0894 log 






As the number of wires in close proximity to each other 
increases, the formulae for their individual and mutual 

* Sheldon and Hausmann's " Alternating Current Machines," p. 313. 



286 TELEGRAPH ENGINEERING 

capacities become more and more unwieldy for numerical 
computation.* 

Thus, for a single No. 9 B. & S. gage wire, suspended 25 
feet above the ground, the capacity is 

n 0.0894 



2.3026 log 10 



0.00966 mf. per mile. 



O.II44 



If another similar ground-return wire be placed hori- 
zontally i foot distant from the first, then 



A , 
= 9.25 and log e - '^ L - = 3.91; 

therefore the capacity of each wire, as obtained from 
equation (32), is now 

0.0894 X 9.25 or M 

C = - -- X V / NO = 0.01178 mf. per mile. 
(9.25)2- (3.91)2 

The mutual capacity of the wires is found to be 
C m = 0.0050 mf. per mile. 

The capacity of a single-conductor cable within a con- 
centric metallic sheath, in microfarads per mile, is 

; . (34) 



where k is the specific inductive capacity or permittivity 
of the homogeneous separating medium or dielectric, d is 
the inside diameter of the conducting sheath and D is the 
diameter of the conductor. If the dielectric consists of n 

* Refer to Oliver Heaviside, "Collected Papers," v. i, p. 45; Louis 
Cohen " Calculation of Alternating Current Problems," p. 97. 



TELEGRAPH LINES AND CABLES 



2 8 7 



cylindrical layers having different specific capacities fe, 
& 2 , , k n , and of outer diameters di t d%, . . . d respec- 
tively, the capacity of the conductor in microfarads per 
mile is 



C = 



0.0894 



D 



d 



(35) 



The capacity of multi-conductor dry-core paper-insulated 
aerial or underground cables, in microfarads per mile, are 
usually as follows: 



B. & S. gage number 




Mutual capacity 


Grounded capacity 


| 


14 


O. IOO 




Telegraph cables < 


16 


O OQ2 




* 


18 


O.O8O 












Telephone cables \ 


13 

16 


O.O72 
O.O72 


0.108 
0.108 




iQ 

22 


o . 074-0 . 080 

0.070-0.083 


O.III-O.I2O 
O.IOS-O.I25 



The mutual capacity is that of a conductor with respect 
to its mate of a twisted pair, all the other wires being 
grounded to the sheath. The grounded capacity is that of 
one wire against all the others grounded to the sheath. 

Leakance. The reciprocal of the insulation resistance 
of a line, when expressed in ohms, is called the leakage con- 
ductance or leakance of the line and this constant may be 
expressed in terms of a unit which is often called the mho. 

The insulation resistance of a well-constructed open line 
fastened to insulators that are mounted on poles or towers 
may be from about 50 to 100 megohms per mile in clear 
weather, but will drop to a fraction of a megohm during 



288 TELEGRAPH ENGINEERING 

prevailing wet and foggy weather. Thus, the leakance of 
the wire at insulators, at places where the wire touches 
trees, etc., due to moisture and dirt, is of the order of 
from io~ 5 to io~ 8 mhos. 

The insulation resistance of a rubber- or paper-insulated 
wire within a sheathed cable is usually over 200 megohms 
per mile (at 60 fahr.) when laid, spliced and connected 
to terminals, each wire being measured against all the 
rest and the sheath. Submarine cables generally have an 
insulation resistance of over 1000 megohms per mile. The 
leakance of a properly-installed cable is not affected by 
weather conditions unless moisture enters as the result of 
mechanical injury to the cable sheath. 

8. Elimination of Inductive Interferences on Telegraph 
and Telephone Lines. Whenever direct currents are 
established, changed in intensity and stopped, or when- 
ever alternating currents are maintained, in an electric 
circuit, electromotive forces are induced in all neighboring 
conductors (a) due to the varying magnetic field, the in- 
duced voltages being dependent upon the time-rate of 
change of current in the inducing circuit and the proximity 
of the wires to this circuit, and (b) due to the varying 
electrostatic field, the resulting current flow being depend- 
ent upon the time-rate of change of voltage in the inducing 
circuit and the proximity of the wires to this circuit. 
Thus, when telegraph and telephone circuits are located 
in parallel proximity to the lines of large alternating- 
current railway and power-transmission systems, the 
latter operating at voltages up to 150,000 volts, these 
circuits derive by electromagnetic and electrostatic in- 
duction sufficient voltages to interfere seriously with their 



TELEGRAPH LINES AND CABLES 289 

proper transmission of signals. Fig. 13 shows the disturb- 
ing effect on a ground-return telegraph line AB during the 
brief time that the alternating current in the disturbing 
wire CD is growing from zero to its positive maximum 
value, the full and dotted arrows on the telegraph line in- 
dicating respectively the currents produced electromag- 






Fig. 13. 



netically and electrostatically. The directions of these 
currents change repeatedly in unison with the current in 
the disturbing wire. With metallic circuits having the out- 
going and return conductors close together, which is the 
almost universal arrangement of telephone lines, electro- 
magnetic disturbances may be eliminated so far as the 
terminals are concerned by transposing the two wires of 
the telephone line at the center of exposure to the dis- 



A o" 



Fig. 14. 

turbing wire, as shown in Fig. 14, for the same conditions 
as in the preceding figure. However, electrostatic dis- 
turbances, while reduced, are not eliminated, but it is 
evident that such disturbances may be minimized by fre- 
quent transposition of the two-line wires. When numer- 
ous aerial telephone lines are mounted on the same poles a 
careful consideration will yield a satisfactory arrangement 
of transpositions for the elimination of mutual disturbances 



290 



TELEGRAPH ENGINEERING 



as well as those occasioned by adjoining power circuits. 
Fig. 15 shows a single aerial transposition made at a trans- 
position insulator of the type represented at the right of 
Fig. i. 

Simple expedients for the elimination of small inductive 
interferences on earth-return telegraph lines have been de- 




Fig. 15. 

vised and usually involve: the addition of inductance and 
resistance to the line, shunting of relays with resistances or 
condensers, or the provision on each relay of a neutralizing 
winding which connects with one coil of a transformer 
whose other coil is inserted in the line wire. Severe in- 
ductive disturbances on grounded lines, however, require 
better neutralization. Conductors within metallic sheaths 

are shielded from electrostatic 
but not from electromagnetic 
induction. 

Fig. 1 6 indicates one method 
for diminishing electrostatic 
and electromagnetic disturb- 
ances on a ground-return line. 
At frequent intervals along the line one coil of current 
transformers S is bridged across a resistance R in the 
telegraph line AB, the other coil being properly joined 
in series with a neutralizing wire NN, or, if practicable, 
with the disturbing wire itself. Also a potential trans- 
former P has one coil included in the neutralizing wire, 
and its other coil with a condenser C of proper capacity is 




Fig. 16. 



TELEGRAPH LINES AND CABLES 2QI 

bridged from the telegraph wire to ground. This"neutraliz- 
ing wire is placed parallel and close to the telegraph line 
or lines and inasmuch as it is subject to the same magnetic 
effects as the signal wires, the currents developed in it are 
arranged to oppose by transformer action those developed 
in the telegraph lines, thereby neutralizing electromagnetic 
disturbance. Electrostatic induction is neutralized by the 
potential transformer P in a similar manner. 

Another method * particularly suitable for single-phase 
alternating-current railway systems and not requiring an 
additional conductor is shown in Fig. 17. The telegraph 




Fig. 17. 

wire AB parallels the sectionalized overhead trolley wire 
which has alternate sections of opposite polarity, as indi- 
cated, in order to minimize electrostatic induction. Each 
section is fed at both ends from adjacent substations by 
.means of the secondary windings s of the transformers 
T, whose primary windings p are connected across the 
high-tension transmission line, not shown. A car located 
between substations draws some current from each sub- 
station depending upon its distance therefrom, and these 
currents flow in opposite directions, the greater current 
over the shorter distance, and vice versa. Electromagnetic 
induction is neutralized by this arrangement. 

The present method of overcoming the detrimental 

* Taylor's " Telegraph and Telephone Systems as Affected by Alternating- 
current Lines," Trans. A.I.E.E., v. 28, p. 1202. 



2Q2 



TELEGRAPH ENGINEERING 



effects of induction on the telegraph and telephone lines 
paralleling the single-phase lines of the New York, New 
Haven & Hartford Railroad, recommended by a com- 
mittee including Mr. G. M. Yorke, is giving marked satis- 
faction in practical operation. The generator voltage of 
11,000 volts is stepped up to 22,000 volts by means of 
auto- transformers A, Fig. 18, situated in the power station; 




Fig. 18. 



one terminal of each transformer joins with the contact 
conductors or trolleys, the other joins with feeders which 
extend along the roadway, and the mid-point connects to 
the rails. The arrangement is similar to three-wire direct- 
current distribution systems except that the direct load is 
on one side of the circuit, the other side receiving its share 
through the sectionalizing auto-transformers T, T situated 
on sectionalizing bridges at frequent intervals over the 
roadway. It will be seen that any train draws its current 
from the auto- transformers on either side, the directions 
of the currents in the n,ooo-volt and 2 2,000- volt circuits 
being indicated by full and dotted arrows respectively. 
Inasmuch as the two parts of the current taken by a train 
flow in opposite directions toward this train, electromag- 
netic effects on adjacent telegraph and telephone lines are 



TELEGRAPH LINES AND CABLES 



293 



neutralized. Since the feeders may be placed in the same 
general direction as the contact conductors with respect 
to neighboring lines, electrostatic disturbances may also 
be neutralized, although such disturbances were inap- 
preciable along the electrified zone of the New Haven 
Railroad. 



9. Simultaneous Use of Lines for Telegraphy and Teleph- 
ony. A pair of line wires forming a metallic telephone 
circuit may be utilized at the same time as one or two 
ground-return telegraph lines, without interference be- 
tween the two classes of service. A single telegraph line 
may also be used simultaneously as a grounded telephone 




SUBSCRIBER 1 



SUBSCRIBER 2 



Fig. 19. 



COMMON-BATTERY TELEPHONE 

CB 




line. Such combined working is extensively employed for 
gaining increased earning capacity of the wire plant. 

Telephone Circuits. Figs. 19 and 20 show respectively 
the connections of the telephonic apparatus for the inter- 
communication of two subscribers joined to a magneto and 
a common-battery telephone system. Sound waves imping- 



294 TELEGRAPH ENGINEERING 

ing upon the diaphragm of a telephone transmitter vary 
its electrical resistance and consequently vary the current 
in the corresponding line circuit; the varying current flow- 
ing through the magnet of the telephone receiver produces 
a varying attraction for the iron diaphragm, the motions of 
which set up sound waves in the air which are similar to 
those incident on the transmitter diaphragm. 

Each subscriber's set of a magneto telephone consists 
of a telephone transmitter T, telephone receiver R, hand- 
driven magneto or alternating-current generator G (open- 
circuited normally), polarized bell P, induction coil /, local 
battery B and receiver hook switch H. A subscriber's set 
of a common-battery exchange does not include a gener- 
ator and local battery, but has a condenser C which keeps 
the set open-circuited to direct current when not in use; 
the circuit for such current is closed by the hook switch 
when the receiver is lifted therefrom in the act of calling 
and when conversing with another subscriber. Electrical 
energy for the operation of the common-battery telephone 
circuit is supplied by the battery CB located at the central 
office, this battery also supplying current to numerous 
other similar circuits, each circuit having its own repeat- 
ing coil 5. The apparatus at the central office used in the 
establishment and in the supervision of the connection be- 
tween the two subscribers is not shown in the figure. 

The repeating coil S is similar in design to the retarda- 
tion coils used with the bridge duplex telegraph circuits 
(p. 71), except that the resistance of each of the four 
windings is usually from 20 to 40 ohms. Coils b and c 
form the primary winding, and coils a and d form the 
secondary winding of a transformer when subscriber i is 
talking, the reverse being true when subscriber 2 is talking. 



TELEGRAPH LINES AND CABLES 295 

Variations in current magnitude in one subscriber's circuit 
are thus inductively transferred to the circuit of the other 
subscriber. 

Simplex Signalling over Telephone Lines. The simplex 
simultaneous signalling system affords the transmission of 
one telephone and one telegraph message over one pair of 
wires, as indicated in Fig. 21. The two wires are used as 



TO CENTRAL JVV-^O fr~^<\_ T CENTRAL 

OFFICE OF CTT S Ifa 1 1 LTT S ID OFFICE OF 

SUBSCRIBER 1 X>-O / d JC^X/T SUBSCRIBER 2 





Fig. 21. 

a metallic telephone circuit, and both wires in parallel are 
used as the line wire of a ground-return telegraph line. 
The junctions between the coils b and d of the two re- 
peating coils 5,5 connect with the usual telegraphic ap- 
paratus at single Morse stations. When the lines and 
repeating coils are properly balanced, the current for 
actuating the telegraph relays divides equally between the 
two-line wires in flowing from station B to A, and these 
portions flow in opposite directions around the iron cores 
of the repeating coils, thereby contributing no magnetiza- 
tion to the cores. Consequently the telegraph currents 
will not affect the telephone instruments which connect 
with the repeating coil windings a and c. Inasmuch as 
the points of attachment of the telegraphic apparatus are 
neutral points of the telephone line, the telephone voice and 
ringing currents will not affect the telegraph relays. The 
simultaneous transmission of both messages is improved 



296 



TELEGRAPH ENGINEERING 



by the shunting of condensers C around the key contacts. 
It is evident that the resistance of the telegraph line cir- 
cuit is only half that of one of the telephone lines. 

Intermediate telegraph stations may be readily intro- 
duced into the circuit of Fig. 21 by inserting two retardation 
coils and joining the mid-points of their coils to the tele- 
graph apparatus at the intermediate office. 

In telephony, an extension of the circuit arrangement, 
shown in Fig. 2 1 , whereby two telephone circuits each with 
two repeating coils permit of the establishment of a third 
telephone circuit, is much used for long-distance trans- 
mission. This third, or so-called phantom circuit, utilizes 
the two conductors of one of the side or physical circuits 
as the outgoing conductor, and the two conductors of the 
other physical circuit as the return (see Fig. 24), with an 
obvious gain in transmission efficiency. 




TO R 
TELEPHONE 
APPARATUS R 






Fig. 32. 

Composite Signalling. Composite simultaneous signal- 
ling secures the transmission of one telephone and two 
telegraph messages over one pair of wires, each telephone 
wire serving as a ground-return telegraph line. Pioneer 
work in this field was done by Van Rysselberghe. Fig. 22 
shows a modernized arrangement of the composite system, 



TELEGRAPH LINES AND CABLES 297 

and it will be observed that impedance coils and condensers, 
for opposing respectively the alternating telephone and the 
direct telegraph currents, are the principal features. 

It is seen that the upper and lower telegraph currents 
are confined to their respective line wires because of the 
condensers c\. The condensers &i eliminate sparking at 
the key contacts and also take care of the rise and fall 
of the current in the telegraph circuit so as not to influence 
the telephone instruments. The telephone circuit includes 
both line wires and the four condensers c\. Because of the 
high impedance of the retardation coils Z to alternating 
currents of high frequency (telephone currents are often 
considered to have a representative frequency of 800 cycles 
per second), the telephone cur- 
rents are prevented from enter- 
ing the telegraph circuits. The 
function of the retardation coils 
R and condensers c is to balance 
the telephone line and guard 
against mutual interferences be- 
tween the telephone and tele- 
graph circuits. The two coils 

Fig. 23. 

R at each end may also be 

replaced by a repeating coil of the type shown in 

Fig. 21. 

The following numbers indicate the order of magnitude 
of the condenser capacities: c = 2 mf., c\ = 2 mf. and 
c 2 = 6 mf . The impedances Z and R are windings on soft 
iron cores of the closed type (Fig. 23) and possess large 
inductance; their resistances are respectively 50 and 30 
ohms. 

Telephone ringing over composited lines by the usual 




298 



TELEGRAPH ENGINEERING 



low-frequency generators (about 16 cycles) is unsatisfactory 
because the impedance of the retardation coils Z is small 
to these ringing currents, resulting in chattering of the 
relay armatures. Instead, calling is accomplished by 
means of weak high-frequency currents (about 300 cycles) 
over the lines which actuate suitable relays that control 
the operation of local low-frequency ringing devices. 

Phantom Circuits with Simplexed and Composited Tele- 
phone Lines. Two telephone circuits, each adapted for 
simplex telegraphic signalling, as shown in Fig. 21, may 
also simultaneously serve as the conductors of a phantom 





Fig. 24. 

telephone circuit, as shown schematically in Fig. 24. The 
location of the simplex telegraphic apparatus is indicated 
by the letters A, B, C and D. In a similar manner, two 
telephone circuits, each adapted for composite working as 
shown in Fig. 22, may also simultaneously serve as the 
conductors of a phantom telephone circuit, thereby secur- 
ing 4 telegraphic and 3 telephonic channels over 4 wires. 

Railway Composite Signalling. Telephonic and tele- 
graphic communication may also be effected simultaneously 
over a single line, both services utilizing the ground as the 
return path. Such telephonic transmission over existing 



TELEGRAPH LINES AND CABLES 



299 



telegraph lines is possible over distances up to say 200 
miles, and is therefore useful principally in supplementing 
telegraphic signalling on railway telegraph lines. 

The arrangement of the apparatus at a terminal station 

for such composite signalling differs from that used with 

magneto or common-battery systems, and is shown in 

Fig. 25. Several intermediate telegraph and intermediate 

z 




Fig. 25. 



telephone sets may be operated on a line, code signalling 
being utilized for telephonic calling. Portable telephone 
sets may be carried on the trains so that in cases of emer- 
gency one may be bridged from the line to ground at any 
place, enabling prompt requests for directions or assist- 
ance. At intermediate telegraph stations a condenser and 
a resistance bridge the telegraph set so as to maintain the 
continuity of the line for telephonic currents, and to pre- 
vent the high-frequency signalling current affecting the 
telegraph relay. 

Referring to Fig. 25, the presence of the impedance 
coil Z prevents telephone currents passing through the re- 
lay, as before ; also the presence of the condenser C hinders 
the telegraph currents from entering the telephone circuit. 
The signalling current is produced by an induction coil / 



300 TELEGRAPH ENGINEERING 

with a vibrator, the coil also serving for transmission pur- 
poses when talking. The signal-receiving device is a 
special telephone receiver or howler h, with a heavy dia- 
phragm, which is responsive to incoming high-frequency 
signalling currents. 

To signal another telephone station the keys K\ and KI 
are depressed; in reality both keys are combined so they 
will open and close together. The closing of key K\ sets 
the armature of induction coil / in vibration, and the core 
is repeatedly magnetized and demagnetized. The alter- 
nating current induced in the other winding thereby flows 
from ground, through the lower contacts of hook-switch 
H and key K 2 , through coil / and condenser C to the line. 
At the other stations this signalling current flows through 
the condenser C, howler h, upper contact of key K 2 and 
lower contact of hook-switch H to ground, thus operating 
the howler. 

Having secured the distant station attendant, the keys 
are released and the receiver R is lifted from the hook. 
The local transmitter circuit is now completed and the 
receiver is placed in connection with the line through the 
condenser C and the secondary winding of the induction 
coil. 

PROBLEMS 

1. For a factor of safety of 5 against wind pressure, what should 
be the diameter of poles at the ground line for supporting 10 No. 6 
B. W. G. iron wires at intervals of 100 feet along a straight path? 
The poles project 25 feet above the ground and the center of load 
may be considered as 5 feet from the pole-tops. Allow 8000 pounds 
per square inch as the breaking fibre stress of the poles, and assume 
an ice coating \ inch thick all around the conductors. 

2. What sag should be allowed in zoo-foot spans of No. 9 B. & S. 
gage hard-drawn copper wires while being strung at a temperature 



TELEGRAPH LINES AND CABLES 



3 OI 



of 80 degrees fahr., so that the tension in the wires with a -inch ice 
coating at 20 degrees fahr. will not exceed 300 pounds ? 

3. Determine the economic pole spacing for a pole line with 
No. 12 B. & S. gage hard-drawn copper wires in which the maximum 
allowable tension is specified as 100 pounds. The wires are to have 
a minimum clearance of 20 feet above ground, the cost of cross- 
arms, insulators, pins, etc., is $2.00 per pole, and the pole cost- 
constant is a = 0.005. 

4. Estimate the cost per mile installed of two zoo-conductor (No. 
14 B. & S.) lead-covered telegraph cables located in a clay under- 
ground conduit, with manholes 440 feet apart, each costing $75.00. 
The cost of drawing the cables in the conduit and splicing the con- 
ductors may be assumed as 7 cents per foot of cable. 

5. Millivoltmeter readings over 6-foot lengths of a lead-sheathed 
cable, taken at two successive manholes, were i.o and 0.25 milli- 
volts. If the outside diameter of the sheath is 2.5 inches and the 
thickness of its wall is inch, determine the current leaving the 
cable-sheath to ground between the manholes, the resistivity of lead 
being taken as 8 microhms per inch cube. 

6. Two auxiliary grounds were employed in the measurement of 
the ground resistance at a newly-constructed permanent ground, 
and a battery in series with an adjustable resistance of r ohms was 
successively bridged from one ground electrode to each of the. others. 
The voltage V across the battery, the voltage drop V over the re- 
sistance r and the earth potential difference E volts were observed 
for each case with a voltmeter, resulting in the following data: 



Quantity 


From perma- 
nent to first 
auxiliary 
ground 


From perma- 
nent to second 
auxiliary 
ground 


Across the two 
auxiliary 
grounds 


r 


70 


50 


110 


V 


10.3 


IO.O 


II. 


V 


6.8 


7.2 


7.8 


E 


0-3 


-O.I 


O. 2 



The ground resistance of each path is 



V - V + E 
V 



r, whence the 



resistance of the permanent ground may be computed. 



302 TELEGRAPH ENGINEERING 

7. Two No. 9 B. & S. gage copper wires one foot apart hori- 
zontally are suspended 25 feet above the ground. Calculate the 
total inductance per mile of both wires for currents in the same and 
in opposite directions. 

8. A single conductor 0.30 inch in diameter is surrounded by two 
concentric layers of insulating material each 0.25 inch thick, the 
inner and outer layers having specific capacities of 3 and 2 respec- 
tively, and these are surrounded by a metallic armor. Compute the 
capacity of this cable per' mile of length. 

9. Draw a scheme of connections for compositing two telephone 
circuits which serve simultaneously as the physical circuits of a 
phantom telephone circuit. 



CHAPTER X 

THEORY OF CURRENT PROPAGATION IN LINE 
CONDUCTORS 

i. The Transmission of Current Impulses along Tele- 
graph Lines. The currents at any instant that pass 
different points of a line conductor differ from each other, 
and become less and less the more remote the point of 
consideration is from the generator end of the line con- 
ductor. This is due to the distributed nature of the four 
line constants: resistance, inductance, capacity and leak- 
ance. In determining the effect at any place on a telegraph 




Fig. i. 

line of impressing an electromotive force at one or both 
of its terminals, it is necessary to consider the conditions 
existing in telegraphic transmission. The nature of the 
impulses to be transmitted by a telegraph line may be 
inferred from graph (a), Fig. i, which indicates the sequence 
and duration of the voltage applications to the line for 
the -word "thumb." It is seen from this figure that 
telegraphic transmission involves the propagation of long 

303 



304 TELEGRAPH ENGINEERING 

and short unidirectional impulses of constant magnitude 
hj which are variously grouped and spaced. The theory 
of propagation of such irregular impulses may be con- 
sidered in the following ways: 

a. The impulses may be considered as made up of a 

continuously applied direct current of magnitude -, upon 
which is superposed an alternating current of rectangular 
wave-shape of amplitude - . While this rectangular wave- 

2 

shape is susceptible to resolution into a Fourier's Series of 
sine curves whose relative frequencies are the successive 
odd numbers, it is much more convenient in the theory 
of telegraphic transmission to consider a single equivalent 
sine-wave alternating current rather than such a multiplicity 
of harmonics which together constitute the actual impulse. 
Graphs (b) and (c), Fig. i, reveal the approximation of 
" equivalent" sine curves to dot and dash wave-shapes 
respectively, the amplitude being conveniently taken as 

2 

- h. The frequencies of the equivalent alternating cur- 

o 

rents in the two cases correspond respectively to the number 

of dots and to the number of T's which may be sent out on 
the line per second, the latter frequency being ^ of the 
former or dot-frequency. Neither frequency prevails for 
more than several cycles, but nevertheless this alternating- 
current theory of transmission leads to an approximate idea 
of the propagation of telegraphic characters, especially 
when the speed of signalling approaches the theoretically 
attainable limit imposed by the conductor. It may be re- 
marked that a somewhat similar condition exists in teleph- 
ony, for in practical telephonic transmission calculations a 



CURRENT PROPAGATION IN LINE CONDUCTORS 305 

"representative " frequency of 800 cycles per second is 
considered appropriate for a single equivalent sine-wave 
alternating current, which is recognized in preference to 
a constantly-varying series of complex wave-shapes that 
actually constitute articulate speech. The frequency of 
the equivalent telegraphic alternating current to be used in 
any particular calculation depends upon the speed of sig- 
nalling, the dot-frequency varying possibly from 15 cycles 
or less with hand transmission to 125 cycles with automatic 
transmission. The computed sinusoidal current wave-shape 
at any point of the line may then be reduced to its corre- 
sponding rectangular wave-shape. 

0. If the speed of telegraphic signalling over a line is 
much below that theoretically attainable thereon, the time 
of growth and fall of the unidirectional current impulse 
will be short in comparison to the duration of a dot signal, 
and consequently the steady value of the current at every 
place on the line will be reached within every signal. There- 
fore the magnitude of the received impulses may be ascer- 
tained on the basis of a maintained direct current flowing 
over the line, the effects of inductance and capacity being 
ignored because these constants influence only the growth 
and fall of the current value. This method of treatment 
may be termed the direct-current theory of transmission. 

7. On the contrary, if the speed of signalling is such that 
the current at any place does not nearly assume the ulti- 
mate value that accompanies slower signalling during the 
time of dot or dash signals, then a consideration of the 
growth and subsequent fall of the current alone is of im- 
portance. This consideration of occurrences during the 
repeated transitional periods of application and with- 
drawal of voltage on the line may be called the transition 



306 TELEGRAPH ENGINEERING 

theory of transmission, and is utilized chiefly in the treat- 
ment of submarine cable telegraphy for computing the 
shape of arrival current curves. 

The transmission theories just enumerated will be con- 
sidered in the order named, the first two being developed 
in the present chapter while the third is discussed in the 
following chapter devoted to submarine telegraphy. 

Alternating-current Transmission Theory 

2. Propagation of Alternating Currents along Uniform 
Conductors of Infinite Length. The impression of a 
sinusoidal or harmonic alternating E.M.F. upon a localized 
circuit, having resistance R, inductance L and capacity C, 
initiates three reactions of the circuit as follows: (a) re- 
sistance reaction (RI f ), the overcoming of which produces 

heat; (b) inductance reaction (I,-), the overcoming of 

\ at J 

which develops a magnetic field; (c) capacity reaction 
[ / I'dt\ the overcoming of which forms an electrostatic 

field; where I' is the instantaneous current value, and / 
represents time. With long line circuits the electrical 
constants of the circuit are distributed in space, and con- 
sequently the current, while everywhere sinusoidal, has not 
the same value or phase throughout the circuit. 

The simplest case of alternating-current wave propa- 
gation is that on conductors of infinite length, since on 
such lines the effect of reflection of the waves at the distant 
end can be ignored. Consider the element ds of an infinitely 
long uniform line with a perfectly-conducting ground re- 
turn, at a distance s from the end upon which a simple 
harmonic electromotive force is impressed, as shown in 



CURRENT PROPAGATION IN LINE CONDUCTORS 307 

Fig. 2. A current will flow through the conductor, and at 
the instant t at the element ds it may be represented by 
/', and that in the adjacent elements by I' + dl' and 
/' dl 1 ', the latter referring to the element more remote 
from the generator. Let E', at this instant, be the poten- 
tial of the line with respect to the earth at the element ds 
and let the potentials of the adjacent elements above that 
of the earth be E' + dE f and E' - dE' respectively. Let 
R, L and C in homologous units represent respectively the 

i i' i i-ai' 




Ground 



Fig. 2. 

uniformly distributed resistance, inductance and capacity 
of the line per unit length. 

The difference of potential between the two ends of the 
element ds is dE' and this must be equal to the sum of the 
resistance and inductance reactions of the elementary cir- 
cuit occasioned by the current /'. As only the reactions 
of the conductor need be considered, there results for this 
element 



*f+ -f- ,-. <-> 

Since the line has capacity with respect to earth, it takes 
a charging current; and since the line is not perfectly 



308 TELEGRAPH ENGINEERING 

insulated from ground, a slight leakage current will flow. 
Therefore the current which does not continue beyond the 
element ds, but which flows from the line to ground under 
the voltage E', is 



where g, the leakage conductance or leakance, is the recipro- 
cal of the apparent insulation resistance per unit length of 
line. Then 

_<^-C d -^ + E'z (2) 

ds~ ' dt * g ' 

Differentiating (i) with respect to time, there results 



^ dt* dt dt\ds 

and differentiating (2) with respect to distance, there results 

Substitution of the former in the latter equation gives 

dl' dE' 



and replacing the last term by its equivalent from (i) there 
is obtained the equation of propagation of current along a 
uniform line, as 



the solution of which shows the current value at the point s 
of the line at the time t in terms of the line constants 
R, L, C and g. 



CURRENT PROPAGATION IN LINE CONDUCTORS 309 

Similarly, by differentiating (i) with respect to distance, 
and (2) with respect to time, and then combining the re- 
sulting expressions, there is obtained 

dE' d 2 E' 



Equations (3) and (4), for current and voltage distribution 
respectively, are true for any length of line, and are identi- 
cal, so that the solution of one of them suffices. 

Since the magnitude of the current must decrease in re- 
ceding from the generator end of the infinitely long line, 
and since the current is simple harmonic when the impressed 
electromotive force is such, and differs in phase therefrom 
more and more as s increases, the following representation 
of the current at any point s of the infinitely long line at the 
time / suggests itself: 

/'=/-* cos (#- as), ( 5 ) 

where 7 is the maximum value of the current at the genera- 
tor end of the line, p is 2 T times the frequency of the im- 
pressed harmonic electromotive force, e~^ is the diminution 
in magnitude of the wave over unit length of circuit, a is the 
phase retardation per unit distance which in degrees is 

, j8 and a being constants which depend upon the 

resistance, inductance, capacity and leakance of the line, 
and c being the base of Napierian logarithms. 

The substitution of this assumed expression for the cur- 
rent I' with proper values of a and /3 in (3) will satisfy this 
equation and permit of the evaluation of the constants a 
and /3. Thus, differentiating (5) with respect to time, 

' = - pi - S in ( P t - s), 



310 TELEGRAPH ENGINEERING 

and again, 

rPJ' 

- --#*/-* COS (#- as) j 



and differentiating with respect to distance, 
sin (pt - as) - ftle^* cos (pt 
a sin (pt -as) -ft COS (pt -as)}, 



JTf 

= air* 8 sin (pt - as) - ftle^* cos (pt - as) 



and again, 

J2Tt 

= / Hfc{ - a* cos (pt - as) - aft sin (pt - as) } 
- Pie'? 8 { a sin (pt - as) - ft COS (pt - as) } 
= 7e-^[(/3 2 - a: 2 ) COS (pt - as) - 2 aft sin (pt - as)]. 

Substituting these values in equation (3), there results, 

^cos (pt - as) - (RC + gL) pie-** 3 sin (pt - as) 
* COS (pt - as) - le-P* [(ft 2 - a 2 ) COS (pt - as) 
2 aft sin (pt as)] = O, 
or 

p 2 CL cos (pt - as) + p (RC + gL) sin (pt - as) 
- Rg COS (pt - as) + (ft 2 - a 2 ) COS (pt - as) 
2 aft sin (pt as) = O. 

This expression can only be true if 

fCL -Rg = -(0*- 2 ) = c? - p, (6) 

and if 

p (RC + gL)=2 aft. (7) 

These are simultaneous equations which can be solved for 
a and ft. Thus, substituting the value of a from (7) in (6) 
gives the following biquadratic: 

= o, 



CURRENT PROPAGATION IN LINE CONDUCTORS 311 
whence 



(RC- 

p*L 2 C 2 -p 2 LC + Rg]. 
Therefore, 

(8) 



and similarly 

(9) 



The constant /3 is called the attenuation coefficient, and a 
is called the wave-length constant. Having determined the 
values of a and 0, the current at any point on the line dis- 
tant s from the generator at the time t may be determined 
when the maximum current value is known at the end upon 

which the electromotive force of frequency -2- is impressed. 

At some other point on the line distant r from the genera- 
tor end, the current value at the instant / is 

// = / -* cos (pt - or). 

If this more distant point r be chosen so that the current 
there will be in phase with that at the point s at that in- 
stant, then 

cos (pt as) = cos (pt or). 

Between these points r and s there is an integral number of 
complete waves, n; therefore, the wave-length is 



n 



Since the phase retardation can be considered over this 
distance as 2 irn, 

as + 2 irn = ar: 



312 TELEGRAPH ENGINEERING 

consequently, 



r s _ 



a n 

As the frequency of the impressed electromotive force is 
cycles per second, the velocity of wave propagation 
will be 

v = --\ = > (10) 

27T a 

In cables, because of the close proximity of the conduc- 
tors to one another, the inductance is little and the capacity 
large. Since 2 irf times the inductance is small compared 
with the resistance of the conductors, and, in good telegraph 
and telephone cables, as the conductance of the insulation is 
small compared with 2 irf times the capacity, the attenua- 
tion constant of such cables may be expressed in a more 
convenient form by expanding the factors \^R 2 + P 2 L 2 and 
^/p 2 C 2 + g 2 of equation (8) by the binomial theorem and 
disregarding terms of higher order than the second as being 
too small to make any appreciable difference. Then 



*(>+m^(>+^] 

PCR(* -i-^-i 4 f?-\ 




Neglecting the last term for similar reasons, the attenuation 
constant becomes 



CURRENT PROPAGATION IN LINE CONDUCTORS 313 
If the inductance be entirely ignored, there results herefrom 



by disregarding g 2 This expression is convenient in 

considering wave transmission over cables. If the leakage 
conductance be taken as zero, it reduces to 



3. Velocity of Wave Propagation over an Ideal Line. - 

An ideal line may be considered a perfectly insulated one 
employing conductors of zero resistance, for then the at- 
tenuation would be nil. Thus, by substituting in (8) and 
(Q)> g = an d R = o, there results 

= o and a = p VZC. 
Therefore, the velocity of wave propagation on such a line 

would be v = - - (n) 

VLC 

The inductance of a straight conductor due to the mag- 
netic flux surrounding the conductor, in electromagnetic 
units per centimeter length, is 

d-D 



and the capacity thereof in electrostatic units per centi- 
meter length is ^ 

d-D* 



where D is the diameter of the wires and d is their inter- 
axial separation. 



314 TELEGRAPH ENGINEERING 

As there are 9 X lo 20 electrostatic units in one electro- 
magnetic unit of capacity, the square root of the product of 
these expressions in electromagnetic units is 



3 X io 10 

Therefore, the velocity of electric wave propagation, when 
the resistance and leakance of the conductors are neglected, is 

3 X io 10 
v = ^ centimeters per second. (12) 



With conductors in a medium like air, for which both the 
permeability /* and the permittivity k are unity, the velocity 
of propagation is 300,000 kilometers per second (186,000 
miles per second), which is identical with the velocity of 
light. For actual lines the velocity of wave propagation 
is somewhat lower than this value. 

4. Wave Propagation along Conductors of Finite Length. 

In the foregoing discussion of wave propagation on in- 
finitely long lines, no cognizance was taken of reflection 
of the outgoing waves upon arrival at the distant terminal 
of the circuit. Voltage and current waves, which together 
constitute an electromagnetic wave, when traversing rela- 
tively short circuits having distributed capacity and induc- 
tance, are partially reflected at both ends thereof with or 
without phase reversal, total reflection taking place only 
when the impedances at the terminals of the lines are either 
zero or infinity (that is, short-circuited or open-circuited). 
If a single impulse be impressed upon the circuit, a wave will 
travel back and forth along the line, until it is attenuated 
to practically nothing. If such waves continually depart 



CURRENT PROPAGATION IN LINE CONDUCTORS 315 

from one end of a line, and each wave is reflected a great 
many times, alternately at the other and initial ends of the 
circuit, before extinction, the current and voltage every- 
where on the line will be gradually built up and ultimately 
assume their final values. This steady state is approached 
by successive jumps and not uniformly, although attained 
in a very short time perhaps a second. After the steady 
state is reached, all the outgoing waves may be considered 
together as a single resultant wave-train, and all the re- 
turning waves as another single wave-train. The following 
method of deriving the equations of current and voltage 
distribution on lines of finite length for the steady state 
displays the results physically as two oppositely moving 
wave-trains, each of definite initial amplitude. By not con- 
sidering the short, unsteady period immediately following 
the voltage application, a simplification of operations may 
be effected over the foregoing method of treatment by intro- 
ducing the complex quantity, inasmuch as one independent 
variable that of time is eliminated thereby. The 
resulting expressions are complex quantities and their in- 
terpretation must be made accordingly. 

Harmonically varying quantities can be represented by 
vectors. The length of such a vector shows the maximum 
value of the quantity, and its direction indicates the phase 
of that quantity. Each vector may be resolved into two 
rectangular component vectors, say, one horizontal and the 
other vertical. To distinguish vertical from horizontal 
components, a symbol, usually^', is placed before the verti- 
cal component. Thus, the expression a + jb means that b 
is to be added vectorially at right angles to a. Obviously 
the magnitude of the resultant vector is Va 2 -{- b 2 , and 
the angle it makes with the horizontal component is 



316 TELEGRAPH ENGINEERING 

tan" 1 - The interpretation of this quadrantal operator or 
a 

neomony isj = V i. 

By applying the operator to equations (i) and (2) and 
counting the distance s positive from the receiving end of 
the line, it follows that for the steady state 



(13) 
and 

(14) 



which are relations independent of time, wherein E m and 
I m represent the maximum values of electromotive force 
and current respectively at any point on the circuit. The 
factor (R -\-jpV) may be called the conductor impedance, 
and (g -\-jpC) the dielectric admittance. Differentiating 
these expressions and substituting gives respectively 



and 

^=(R+jpL)(g+jpC)I m . 

For convenience, let (R + jpL)(g + jpC) = y 2 , then the 
equations of wave propagation along conductors become 

;, .,' f-^ ' ;< 

and 

^df = y2Im ' (l6) 

These are identical differential equations of electromotive 
force and current which differ in the terminal conditions 



CURRENT PROPAGATION IN LINE CONDUCTORS 317 

only, and consequently the solution of one of them will 
suffice. 

Choosing the latter expression and multiplying through 

by 2 - j there results 

d*I m dl n dl m 

2 ~7~z --- T~ = 2 r lm ~T~' 
ds 2 ds ds 

which, when integrated, becomes 



Replacing the constant of integration c\ by 7 2 c 2 2 , where c^ is 
also a constant, and separating the variables, there obtains 

dl m 



= yds. 



V/ ro 2 

Integration gives 

log e [C 3 (l m + 

where c 3 is another constant of integration. Writing in 
exponential form, this equation becomes 



Squaring, 



or - T -c 2 2 = 2/ ro J 

C 3 2 C 3 

whence 

/ _ *" _ tfc* 

2C 3 26^' 

Choosing constants A and B so that 

A = and B = ^ 



318 TELEGRAPH ENGINEERING 

the expression for the maximum value of the current at a 
distance s from the receiving end of the line becomes 

I m = Ae^ 8 - B*", (17) 

where the two constants must be evaluated from the termi- 
nal conditions. 

Since the exponential coefficient 7 is the square root of 
the product of two complex numbers, it is also a complex 
quantity, and may be written 

7 = +ja, 
where a and are its two rectangular components. Then 

08 +ja) = (R +jpL)(g +jfQ, (18) 

or 

2 + 2ja0 +JW = Rg +jgpL +jpRC + 

and remembering that j = V i, this becomes 
(0 2 - a 2 ) + 2ja0 = (Rg - P 2 CL) +j (gpL + 
This equation can only be true if 

c?-f? = fCL - Rg, 
and if 

2a(3 = p(RC + gL). 

These expressions are identical with equations (6) and (7), 
and, therefore, the components of 7 have the same signifi- 
cance as before; namely, is the attenuation coefficient and 
a is the wave-length constant, the values of which are given 
by equations (8) and (9) respectively. The quantity 7 is 
called the propagation constant of the line. 

The maximum current value at a point on the line distant 
s from the receiving end may now be indicated as 



Writing for the exponential function with the imaginary 
exponent the equivalent trigonometric expression e :>as = 



CURRENT PROPAGATION IN LINE CONDUCTORS 319 

cos as 7 sin as, the equation for I m becomes 

I m = A<? 8 (cos as +j sin as) Bt~v* (cos as j sin as), (19) 

the first term of which, since it increases as 5 increases, may 
be considered the main current wave, and the second term 
may be called the reflected current wave. The amplitudes 
of these waves at the receiving end are respectively A and B. 
The maximum value of the voltage at the same point on 
the line can be obtained by differentiating (19) or (17) and 
substituting in equation (14), 

E m = , /" [A f 9 (cos as + j sin as) 

g+jpc 

+ Be~ 08 (cos as j sin as)]. (20) 

To evaluate the constants A and B, two conditions must 
be known, as current and voltage at one end of the line, or 
current at one terminal and voltage at the other terminal 
of the line; thus, at the receiving end s = o, and equations 
(19) and (20) give the maximum current and voltage values 
respectively at this point as 

Ir = A-B, 

and 



The fraction & +ja + g +jpC is frequently called the 
surge impedance or characteristic impedance of the line. 
Then 



and 

' (22) 



The ratio of the amplitude of the reflected wave to that 
of the main wave arriving at the receiving end, that is, the 



320 



TELEGRAPH ENGINEERING 



ratio of B to A , will depend upon the character of the termi- 
nal apparatus, and may be called the coefficient of reflec- 
tion. This coefficient is 



A Lf fS | J**. 

^R+jJi + " 
Representing the impedance of the terminal apparatus by 
Z r , this expression becomes 

Z r (p+ja)-(R+jpL) ,x 
Z F &+ja) + (R+jpL) 



Z r = 



T R+jpL 




For total absorption of the wave, m = o, and the receiver 
impedance should be 

R +jpL 
ft +j<* ' 

Substituting the values of A and B in equations (19) and 
(20), the complete equations for the maximum values of 
current and voltage at any point of the line at a distance s 
from the end to which the receiver is connected, become 
respectively 



as +j sin as) 



-* ( cos <* s -J sin *) (*4) 




(25) 



CURRENT PROPAGATION IN LINE CONDUCTORS 321 

If it be desired to reckon the distance in the opposite 
direction, that is, from the generator to the receiving ends 
of the line, the sign of s must be reversed in equations (13) 
and (14), and there result for the current and voltage at 
any point distant s from the generator end of the line, 
respectively, 



(26) 
and 



E m = i E. + 7. ~ -* (cos a* -j sin as) 




where and / are the maximum voltage and current 
values at the generator end of the circuit. 

The terminal conditions in any given problem are usually 
specified, the voltage being considered the standard phase. 
In the present notation for vector rotation a current lead- 
ing the voltage in phase is written i\ + ji^, and a lagging 
current is represented by i t ji^. 

The foregoing equations may also be employed with 
equal relevancy to calculations involving effective current 
and voltage values instead of the maximum values of these 
quantities. Short tables of exponential and trigonometric 
functions appear in the Appendix. 

5. Simplified Equations of Wave Propagation. The 

solution of the equations of wave propagation can be trans- 
formed into a more convenient form, as shown by Kennelly, 



322 TELEGRAPH ENGINEERING 

by expanding the factors e 7S of equation (17). Thus, by 
Maclaurin's series 



l [3 [4 



that is, e 7S can be expanded into two series, one containing 
even powers of ys and the other having odd powers thereof. 
From hyperbolic trigonometry, these series are called re- 
spectively the hyperbolic cosine and hyperbolic sine, and 
are written 



Therefore, 



i + - = cosh 7*, 

[4 

XK 

... =sinh7 , 



Equation (17) for the current on the line at a point dis- 
tant s from the receiving end may thus be written 

I m = A (cosh ys + sinh 75) B (cosh ys sinh 75), 
or I m = (A - B) cosh ys + (A + ) sinh 7*. (28) 

The maximum value of the voltage at the same point 
can be found by differentiating (28) and substituting in 
equation (14). 

Since cosh ys = 7 sinh 75, 

as 

and sinh ys = 7 cosh 75, 

as 

there results 

(g +JPC) E m = (A-B}y sinh 7* + (A + B) 7 cosh 7*, 



CURRENT PROPAGATION IN LINE CONDUCTORS 323 

whence 

E m = ^^\(A - S) sinh 7* + (A + B) cosh ys\ (29) 
g+jpCl J 

The constants A and of expressions (28) and (29) may be 
determined from the conditions at the receiving end of the 
line. Let E r and I r be maximum values respectively of 
the voltage and the outgoing current at this terminal. 
Then, for s = o, since cosh (o) = i and sinh (o) = o, 

Ir=A -B, 

and B ' 

Substituting these values yields 

I m = I r cosh 7S + E r / {" sinh ys, (30) 

K + jpL 

and 

E m = I r ft *? a ~ sinh 7* + E r cosh 75. (31) 



The hyperbolic functions of the propagation constant 7 
may be written, since 7 = + y, 
cosh 75 = cosh (0j +y5) = cosh /3s cos as +j sinh /3s sin as, 

and 

sinh 75 = sinh (3s cos as -\-j cosh /3s sin as. 

Then the equations of current and voltage at any point on 
a line at a distance 5 from the receiving end thereof are 
I m = I r (cosh 0s cos as -\-j sinh 0s sin as) 

+ E r p ?" (sinh 185 cos as +y cosh /3s sin as), (32) 
K -rJpL 

and 

m = E r (cosh /3s cos as +j sinh /3s sin as) 

+ I r ." (sinh /3s cos as +j cosh /3s sin as). (33) 



324 TELEGRAPH ENGINEERING 

When 5 is measured from the generator toward the re- 
ceiving end of the line, equations (30) and (31) become 

I m = I g cosh ys - E g R j" sinh js, (34) 

and 

E m = E g cosh ys - I g * ?" sinh 7$. (35) 



From equation (34) is seen that for an infinitely long line, 
on which the current at the inaccessible end is 



/.cosh (oo) = g sinh (oo), 
whence 



0+ja , . 

(36) 



By substituting this value in the same expression, the cur- 
rent at a distance s from the generator end of such a line 

becomes 

I m = I g (cosh ys - sinh ys) = I g ~ ys } (37) 

which shows that the entering current decreases logarith- 
mically to zero as s increases to oo . This expression is 
analogous to equation (5). Similarly, on an infinitely 

long line 

E m = E g e^ s . (38) 



Tabulated numerical values of the hyperbolic sines and 
cosines appear in the Appendix. The hyperbolic functions 
of complex quantities may be obtained directly from tables 
and charts prepared by Prof. Kennelly. 

6. Current and Voltage Distribution on Lines for any 
Terminal Condition. The current and voltage relations 
in circuits having distributed capacity and inductance with 



CURRENT PROPAGATION IN LINE CONDUCTORS 325 

given terminal conditions under a given impressed electro- 
motive force will now be considered. Three cases arise, 
namely: a, line open-circuited at receiver; 6, line short- 
circuited at same place; and c, apparatus of given impedance 
connected to the receiving end of the line. 

(a) When the line is open-circuited at the receiving 
end (I T = o), the current I g , entering it at the other end, 
is obtained from equation (34) by placing I m = o. Since 

sinh ys 



cosh 75 
there results 



= tanh ys, 



where Si represents the total length of the line conductor. 
Upon substitution in equations (34) and (35), there re- 
sults respectively the values of current and voltage at 
any point distant 5 from the generator end of the line, 
when the other end is open-circuited, as 

7 m = Eg _ , -?L (cosh ys tanh 7*1 - sinh 75), (40) 
K +JPL, 

and 

E m = Eg (cosh ys sinh ys tanh 751). (41) 

When 5 = si y these equations reduce respectively to the 
current and voltage at the open end, viz: 

Ir= O, (42) 

and E -- I" = E, sech >*,, (43) 

cosn ySi 

since cosh 2 7^1 sinh 2 7^1 = i. 

(b) The current and voltage relations at any point of a 
line which is short-circuited at the distant end are easily 



E 



326 TELEGRAPH ENGINEERING 

obtained, since the voltage at that end, E r , is zero. By 
placing E m = o when s = si, in equation (35), there results 
the current entering the circuit as 

I " j*/~* 

+ a 

The current and voltage at any place are, therefore, respec- 
tively, from equations (34) and (35), 

J 



(cosh ys coth 7*1 - sinh ys), (45) 



E m '= Eg (cosh ys sinh ys coth 7^1). (46) 

The conditions at the short-circuited end are obtainable 
herefrom by replacing s by si, whence 



CSCh 7*1, (47) 
| a 

and E r ' = o. 

(c) When the character of the receiving apparatus is 
specified, that is, when its impedance, 




is known, the voltage and current at any point of the line 
may be determined in terms of the impressed electromotive 
force. By placing 5 = Si, equations (34) and (35) give the 
current and voltage at the receiving apparatus; and divid- 
ing the latter by the former, there results 

E cosh 7*1 - I ?" sinh 7*1 



_ __ _ 

11 j<f ~~- ^ 

I cosh ysi - E a p ? " sinh 751 
K -\-jpL 



CURRENT PROPAGATION IN LINE CONDUCTORS 327 

from which 

Z r p ? " sinh ysi + cosh 7^ 

' = E jp & + ja -- (48) 

Z r cosh ysi + - ^ sinh 7*1 

g+jpc 

By substituting this value in the same equations there 
results respectively as the current and voltage at a point on 
the line distant s miles from the generator: 

0+ja 
E 'R+JPL* 



Z r sinh 751 H --- -* cosh 



/3 i ^ 

Z r cosh 7*1 + , r " sinh 7*1 

g+jpc 



cosh 75 sinh 75 



, (49) 



and E m = E g X 

Z r sinh 7$! H 7 cosh 



Q | " 

Z r cosh ysi + T^T; sinh 



sinh 75 



(50) 



These equations may be more conveniently expressed by 
choosing an angle such that 



= 

R +jpL 

and they assume the following forms: 

I m = E _f "^ [coth ( T 5i + 0) cosh 7^ - sinh 75], (51) 
/t -\-jpL 

and 
w = ff [cosh 75 coth (7^1 + 0) sinh 75]. (52) 

These general expressions are similar in form to those 
derived under case (b) . 



328 TELEGRAPH ENGINEERING 

At the terminal apparatus of impedance Z P , the current 
and voltage in terms of the impressed electromotive force 
Eg may be obtained from equations (49) and (50) by putting 
$i for S whence 



Z r cosh ysi + , . 

8+JpC 



(53) 



and 

? 

(54) 




cosh ~ 

Z r 

The general expressions (49) to (54) reduce to those 
derived under cases (a) and (b) for lines open- and short- 
circuited at the distant end by placing Z r equal to infinity 
and zero respectively. 

7. Effect of Impedance at Sending End. In the fore- 
going expressions the impedance, Z t , of any apparatus which 
might be connected to the generator end of a line, such as 
a relay on a telegraph line, has been ignored. The in- 
fluence of such impedance can be taken into account by 
replacing E in equations (49) to (54) by 

E a >- I.[R, +j(pL t - ^-)]= /- I,Z t , (55) 

where R t , L t and C t are respectively the resistance, induc- 
tance and capacity of the transmitting device, Fig. 3, and 
I a is the current entering the line. 

This current value, from (51) by placing 75 = o, is 



CURRENT PROPAGATION IN LINE CONDUCTORS 329 
where 



which, when substituted in equation (55), yields 

p r 

= 



"R+jpL 

By replacing the value of E g in equations (51) and (52) by 
this quantity, there result respectively the complete and 

Im 





^////////////////^^^^^ w/////////////////^^^^^ 

Fig. 3. 

general expressions for the current and voltage values at 
any point on the line distant s miles from the generator 
as 

r J7'JL+1^_ cosh ys coth (7^1 + </>)- sinh 7* 

lm = tig p -- - - 



and 

^ = / cosh 75 - sinh 75 coth (7*1 + 0) / v 

' 



By placing 5 = Si in the foregoing general expressions 
for current and voltage distribution on lines, the condi- 



33 TELEGRAPH ENGINEERING 

tions at the receiving end of the circuit are obtained; 
namely, 



/= 

' 



and (58) 

T? _ _____ Eg Z r 

" 




(59) 

These equations are together represented by the determi- 
nantal expression 

' Z7 
g J^ r , , N 

1 - - - -=- (ooj 

Z r 




I O 

i sinh 75 1 



The equations derived in 4-7 are applicable to all 
alternating-current circuits having distributed resistance, 
inductance and capacity in the steady state, and with any 
terminal condition at either end. They are extremely use- 
ful in solving transmission problems not only in teleg- 
raphy, but also in telephony and power transmission. In 
applying the equations to circuits employing two or more 
line conductors, the significance of the symbols must be 
properly interpreted. 

8. Illustration of Sine-wave Telegraphic Transmission. 

Consider a 150- volt (effective value) alternating-current 
generator to be connected to one end of a 6oo-mile simplex 
ground-return aerial telegraph line of No. 10 B. & S. gage 



CURRENT PROPAGATION IN LINE CONDUCTORS 331 

copper wire, the line having a 3oo-ohm relay at each termi- 
nal. Determine the current and voltage relations in the 
circuit for a signalling speed yielding a dot-frequency of 
15 cycles per second. 

The maximum value of the impressed harmonic voltage 
is 150 ^fi or 212.2 volts, which may be considered the 
equivalent of a unidirectional voltage of 320 volts, as out- 
lined in i. The electrical constants of the line per mile 
will be taken as follows: 

R = 5.28 ohms, (page 29) 

L = 3.10 X io~ 3 henrys,! For a single wire 25 feet 
C = 9.54 X io~ 9 farads, J above ground (page 283) 
and g = 2. co X io~ 6 mhos. 

While the inductance of the relays depends upon several 
conditions, its value in this calculation will, however, be 
considered constant at 5 henrys; whence the impedance of 
each relay at 15 cycles is 

Z r = Z t = R r +jpL r = 300 + 2 TT 15 X 5.7 = 300 + 
ohms, and the absolute value is 



VR r * + p*L? = v^ 2 + ^ = 558 ohms. 

The attenuation and wave-length constants of the line are 
respectively obtained from equations (8) and (9) as 

j8 = 0.00331, 

and a = 0.000808. 

The velocity of propagation and the wave-length are re- 
spectively 



and 



1 TT T ^ 

V = 88 = II ^5 n 1 ^ 68 P er second, 



. 27T .. 

X = r-r = 7770 miles. 

0.000808 ' ' ' 



332 TELEGRAPH ENGINEERING 

Further, since 

Si = 600 miles, 

E a ' = 212.2 VOltS, 

+JpC = (2-0 + 0.8997) iQ- 6 mhos, 
R + jpL = 5.28 + 0.2927 ohms, 



g+jpc 






ySi = fa +jaSi = 1.986 + 0.4848^*, 
sinh 7^1 = sinh 1.986 cos 0.4848 +j cosh 1.986 sin 0.4848 * 

= 3.163 + 1.7307, 
and cosh 7^1 = 3.284 + 1.6667, 

it follows from equation (58) that the maximum value of 
an alternating current arriving at the remote end of the 
6oo-mile telegraph line is 

2 (300 + 4717) (3.284 + 1.6667) + [iS 2 ^ 
I r =212.2 -^- - 2837 + (300 + 471 7') 2 (635 + n87')io- 6 ] 

(3.163 + 1.7307) 

212.2 , . 

= - - - . = 0.0169 0.02067 ampere, 
5070 +61577 

or I r = 16.9 20.67* rnilBamperes. 

The absolute value of this maximum alternating-current 
value is V(i6.9) 2 + (20.6) 2 = 26.7 milliamperes, and the 
corresponding unidirectional current of rectangular wave 
shape is | X 26.7 = 40.1 milliamperes. 
The potential difference across the distant relay is 

E r = IrZ r = (0.0169 - 0.02067) (300 + 4717) 

= 14.77 + i -7^y v its. 

* See tables in Appendix. 



CURRENT PROPAGATION IN LINE CONDUCTORS 333 



Equation (30) now enables the determination of the current 
and voltage values at the other end of the line. Thus 

I g = (0.0169 0.0206 7) (3. 284 + 1.6667) + ( I 4-77 + I -7^y) 

(635 + 1187) (3.163 + 1.730^') io-* 
= 0.1138 0.01457 ampere. 

The potential difference across the relay at the generator 
end of the line is 

IgZt (O.II38 0.01457*) (3OO + 4717') 

= 41.0 + 49.37 volts, 
and, therefore, the voltage impressed upon the line is 

Eg = Eg - IgZt = 212.2 - (41.0 + 49-37) 

= 171.2 - 49.37 volts. 

This value may be verified by means of equation (31). 
The foregoing results are displayed graphically in Fig. 4, 

V 



49.8 



Fig. 4. 

which shows the harmonic alternating-current quantities 
as vectors, the generator voltage E g f being the datum phase. 
The scale of the receiving-end quantities is 5 times as large 
as that of the sending-end quantities, all current Values 
being expressed in milliamperes. Absolute values and 
phase relations are also indicated. 



334 TELEGRAPH ENGINEERING 

Effect of Employing Higher Signalling Speeds. If instead 
of 15 cycles, the speed of signalling in the foregoing example 
had been ten times as great as before, making the dot- 
frequency of the equivalent alternating current 150 cycles, 
then under otherwise identical conditions: 

P = 942.5, 

/3 = 0.00446, 

a = 0.00597, 

v = 157,900 miles per second, 

X = 1052 miles, 
Z r = Z t = 300 + 47107 ohms, 
ysi = 2.676 + 3.5827, 

and the current traversing the remote relay is found to be 
I r = i. 08 0.4577 milliamperes. 

The absolute value of this received current is 1.17 milli- 
amperes, and the corresponding unidirectional current of 
rectangular wave-shape is f X 1.17 = 1.75 milliamperes. 
This value is only 4.3 per cent of that obtainable when the 
signalling speed is one-tenth as great. The influence of 
signalling speed upon the magnitude of the received im- 
pulses is, therefore, evident. 

Direct-current Transmission Theory 

9. Current in Leaky Line Conductors. When a uni- 
directional electromotive force is impressed upon a line 
conductor, the current at every point of the line assumes a 
steady value. Ignoring the short unsteady period of cur- 
rent growth, the steady current value at any point on the 
line distant 5 from its generator end may be determined 
without considering the effects of inductance and capacity 
of the line conductor. The current and voltage equations 



CURRENT PROPAGATION IN LINE CONDUCTORS 335 

to be satisfied are obtained by placing L = o and C o in 
equations (i) to (4) ; whence for a leaky line 

^H=-RI, (61) 

I 

T=~SE, (62) 



-** 



and 



(64) 

where R is the conductor resistance per mile, and g is the 
leakage conductance per mile of conductor length. Equa- 
tions (63) and (64) are identical equations which differ only 
in the terminal conditions, and, therefore, the solution of 
one will suffice. 

Choosing the former equation and multiplying both sides 

by 2 , there results 
as 

d?I dl 
2 d?-ds = 
which, when integrated, becomes 



Replacing the constant of integration c\ by Rgof, where c z 
is also a constant, and separating the variables, there re- 
sults 

dl 



336 TELEGRAPH ENGINEERING 

Another integration yields 

log e [c 8 (/ + VP + tf)] = VRg.s = 0s, 

where c 3 is another constant of integration and 

is the attenuation constant. In exponential form, this 

equation becomes 



Squaring, and solving for 7, gives 



For convenience let - = A + B and c 2 2 c 3 = A B\ fur- 

3 

ther, let the exponential terms be replaced by their equiva- 
lent hyperbolic functions, viz. : 

c 0* = cosh/35 sinh/Ss. 
Then / = A sinh 0s + B cosh 0j. (65) 

Differentiating this expression with respect to distance 
and substituting the result in equation (62), there results 

E=--(A cosh 0s + B sinh $s) . (66) 

o 

Equations (65) and (66) are the expressions for current and 
voltage respectively at any point of the line, but the con- 
stants A and B are still to be evaluated from the terminal 
conditions. 

If one source of electromotive force supplies current to 
the line and this source be located at one terminal, then the 
constants A and B may be determined by placing 5 = 
and representing the current and voltage at this end by I 



CURRENT PROPAGATION IN LINE CONDUCTORS 337 

and E Q respectively. Since cosh (o) = i, and sinh (o) = o, 
it follows that 



A - 77 



" 



and B = I g . 

Substituting these values in equations (65) and (66) yields 
the current and voltage respectively at any point on the 
line distant 5 from its generator or sending end as 

/ = / cosh /3s - ^ E g sinh /3s, (67) 

P 

and E = E g cosh 0s - - I g sinh 0s. (68) 

g 

Connecting a receiving instrument of resistance R r to 
the far end of the line which has a length s\ t the current 
traversing this instrument would be 



I r = I cosh fa -E sinh fa, (69) 

p 

and the voltage across its terminals would be 

/3 

E r = E cosh fa -Ig sinh fa. (70) 

o 

E 

Since R r = -p , it follows that the current entering the line 

will be 

R r & sinh fa + cosh fa 
I.-E.-B. - - - . (71) 

R r cosh fa + - sinh fa 
g 

If, as is usual, there is a resistance at the sending end also, 
then Eg in the foregoing should be replaced by Eg 



338 



TELEGRAPH ENGINEERING 



where / is the voltage of the generator, and R t is the total 
resistance at the generator end of the line. Whence 



R r sinh fa + cosh fa 

P 



(R r + Rt) cosh fa + f- + RrRt f ) sinh /toi 
\g /v 



(72) 



Substituting this value in equation (69) gives the current 
traversing the remote receiving instrument in terms of the 
generator voltage as 

EJ 



(R r +Rt)coshfa 



(73) 



R r R t -)smhpsi 



Ayrton and Whitehead have shown that the best re- 
sistance of a receiving instrument on a leaky telegraph line 

is Q 

R r ' = - tanh fa 
g 

irrespective of the relation between the torque exerted and 
the ampere-turns applied. 

10. Illustration of Direct-current Signalling on a Leaky 
Telegraph Line. Consider a simplex telegraph circuit 

Rr 





Fig. S. 

with a 320-volt direct-current generator at one terminal, 
as shown in Fig. 5. The line wire is 600 miles long of No. 



CURRENT PROPAGATION IN LINE CONDUCTORS 339 

10 B. & S. gage copper wire, and a 3oo-ohm relay is con- 
nected at each end. To determine the currents traversing 
the relays for various positions of the keys K and K', 
when the insulation resistance is 0.5 megohm per mile. 
In this example 

Eg =320 volts, 
R t = R r = 300 ohms, 
R = 5.28 ohms, 
g = 2.00 X IO" 6 mhos, 
and Si = 600 miles; 



therefore, ft = ^5.28 X 2.00 X icr 6 = 0.00324, 

0si = 1.944, 
sinh /3$i = 3.422, 
cosh/3^ = 3.565, 

| = 0.000617, 

* = 1620. 
g 

When both keys, or their circuit-closing switches, are closed, 
the current entering the line is obtained from equation 
(72) as 

300 x 0.000617 x 3-422 + 3-565 

600 X 3.565 + (1620 + 300 2 X 0.000617) 3.422 

320 X 4.108 
* -- y = 0.1706 ampere, 

2139 + 5734 

or 170.6 milliamperes; and the current that reaches the 
other end of the line is obtained from equation (73) as 

T 3 20 

/ = - t - = 0.0406 ampere, 
2139 + 5734 

or 40.6 milliamperes. 



= 



340 TELEGRAPH ENGINEERING 

The closeness of this result to that obtained in 8 by 
means of the alternating-current method for the same con- 
ditions and a 15 cycle frequency justifies the use of the 
direct-current method whenever the speed of signalling is 
much below the theoretically attainable speed 1 on the line, 
as with hand signalling on open wire lines. The alternat- 
ing-current method excels when dealing with long aerial 
and underground cables. 

When key K f is opened, no current traverses the home 
relay, but the current flowing through the relay at the 
generator end of the line is obtained from equation (69) by 
placing I r = o and replacing E g by E g f I R t ', 

thus I g cosh to = & (E g f - IgRt) sinh to, 
P 

whence 7." = E.' 



R t sinh to + cosh to 
g 

or 7 f = -& . (74) 

R t + -cothto 
g 

Substituting the numerical values herein gives 

T O 32O 

I B = = 0.161 ampere. 

300 + 1620 X 1.042 

For satisfactory operation, therefore, the relay at the 
generator end of the line must be very closely adjusted, 
for it should attract its armature on 170.6 milliamperes 
and release it on 161 milliamperes; thus giving a margin 
of 9.6 milliamperes. This condition is improved by the 
use of generators at both ends of the line, as will now be 
considered. 



CURRENT PROPAGATION IN LINE CONDUCTORS 341 

ii. Simplex Signalling with Generators at Both Line 
Terminals. If two equal cumulatively-connected sources 
of current be located one at each terminal of a line, as in 
the usual simplex Morse telegraph circuit, then the con- 




Fig. 6. 

stants ^4 and B of equations (65) and (66) are evaluated 
upon a consideration of the conditions shown in Fig. 6. 
Herein E g ' is the electromotive force of each generator, R r 
is the total resistance at each terminal station, E g and E r 
are the potentials with respect to ground of the line wire 
at the stations i and 2 respectively, and I g and I r are the 
currents at these stations respectively. 

When both keys are closed as shown, the current and 
line voltage at station i are obtained by placing s = o in 
equations (65) and (66) respectively, whence 



and E =-*-A = E g f - I R r . 

g 

Similarly the current and line voltage at station 2 are 
obtained by placing 5 = Si in the same equations, thus 

I r = A sinh fa + B cosh fa, 
and E r = - - (A cosh fa + B sinh fa) = - (/ - 

o 



342 TELEGRAPH ENGINEERING 

The constants A and B are ascertainable from these four 
equations, and are 

at \ 

R r - ( i cosh fa \ sinh fa 

A = EO/ : /v 5\ ' ^ 

2 R r cosh to + ( * Rr 2 + - J sinh to 
and 

cosh to + R r - sinh fa + i 

B = Ea ' 77 T\ (76) 

2 R r cosh to + ( - -# r 2 + ~ ) sinh to 



Substituting these values in equations (65) and (66) results 
in the current and voltage equations for any point on the 
line distant s from one end, when equal generators are 
connected to both ends of the line wire. 

The current traversing the relays at stations i and 2 are 
respectively 

I g = B, 
and I r = A sinh fa + B cosh fa 

as already indicated. Upon replacing A and B herein by 
their equivalents given in equations (75) and (76), these 
currents are found to be equal, as might be inferred from 
the symmetry of the line and terminal conditions, and have 
the value 

cosh fa + R r - sinh fa + i 

(77) 



2 R r cosh fa + ( lR r 2 + - ) sinh fa 
\p gl 



When one of the keys is opened the current traversing the 

relay at the other terminal station is given by equation (74). 

To illustrate the advantage of dividing the total voltage 



CURRENT PROPAGATION IN LINE CONDUCTORS 343 



on a telegraph line, one-half being impressed at each end, 
consider the same circuit as was discussed in the preceding 
article. In this case a 1 60- volt generator is located at each 
end of the 6oo-mile line. 

The current traversing each relay when both keys are 
closed is given by equation (77) as 

I _/ r -i6o 3-565+300X0.000617 X 3422 + i 

2X300X3. 565 + (0.00061 7X30? +1620)3.422 
= 0.1056 ampere = 105.6 milliamperes, 

while the current traversing a relay when the key at the 
opposite station is opened is given by equation (74) as 

r o 160 

ig = ~ - = 0.0805 ampere 

300 -f 1620 X 1.042 

= 80.5 milliamperes. 

The comparison of the two generator arrangements for 
the line under consideration is revealed in the following 
table, the current values being expressed in milliamperes. 
It is seen that with a generator at each end the operating 
margin is 25.1 milliamperes, as against 9.6 milliamperes 
at the home relay for a single generator of double voltage 
at the home end of the line. 



Key positions 


32O-volt generator 
at home end 


i6o-volt generators 
at both ends 


Current 
through 
relay at 
generator 
end 


Current 
through 
relay at 
distant 
end 


Current 
through 
relay at 
home 
end 


Current 
through 
relay at 
distant 
end 


Both keys closed 


170.6 

161 




40.6 
O 

o 


105.6 
80.5 
o 


105.6 
O 

80.5 


Distant key open 


Home key open 




Operating Margin 


9.6 


40.6 


25-1 


25-1 





344 TELEGRAPH ENGINEERING 

12. Duplex and Quadruplex Signalling. The theory 
of signalling on leaky lines discussed in the preceding pages 
is also applicable to duplex and quadruplex telegraph cir- 
cuits if the terminal conditions are properly deduced. 
The general expressions for current and voltage are equa- 
tions (65) and (66), wherein the constants A and B depend 
upon the conditions existing at the ends of the line wire. 
The values of these constants with duplex and quadruplex 
signalling are different from those pertaining to simplex 
signalling, already considered. 

In a polar duplex circuit, let R p = entire resistance of 
each polarized relay, R b = resistance of each battery or of 




Relay 
Fig. 7. 

the protective resistance in series with each generator, and 
r = resistance of each artificial line, as indicated in Fig. 7 
for one station. Placing s = o in equations (65) and (66), 
there results 



and E= -.A = 



. 

where - - = q for simplicity. The current and 



CURRENT PROPAGATION IN LINE CONDUCTORS 345 

voltage conditions at the other end are obtained by placing 
s = Si, whence 

I r = A sinh 0Si + B cosh Qsi, 

and r = --U cosh fa + 5 sinh 0*)= (qE g f - I r 

the plus sign being taken when the two batteries or genera- 
tors oppose each other as when both pole-changers are 
either idle or energized, and the negative sign being taken 
when the two current sources assist each other as with only 
one pole-changer energized. These expressions assume the 
current traversing the artificial lines to remain constant 
irrespective of key movements. 

Solving for A and B from the preceding four equations, 

yields R q 

- cosh Qsi db 2 - sinh fa i 

B = * E ''l - \R - 2 / z R 2 8\ - ' (78) 
[ i - i.pcoshto +(f .* -eWnhto 
V / 2 \ 4 gl 

and A=B-qE ' (79) 



The upper signs in equation (78) are employed when the 
generators oppose and the lower signs are used when the 
generators assist each other. Substitution of these values 
in equations (65) and (66) gives the final expressions for 
current and voltage in the case of a polar-duplex telegraph 
circuit. 

The bridge duplex and the quadruplex terminal condi- 
tions may be similarly analyzed and the current and voltage 
equations formed.* It is to be noted that the current 
passing through the relay of a bridge duplex circuit ex- 

* An excellent treatment 'of these conditions appears in a paper by 
F. F. Fowle on "Telegraph Transmission," Trans. A.I.E.E., v. 30, p. 1683. 



346 TELEGRAPH ENGINEERING 

pressed in terms of the current I g at the end of the line 
wire and the voltage Eg' of the generator is 

T aE g f -aI g (2R b + r + a) ( . 

^- 



where P is the resistance of the relay, a = resistance of 
each half of the retardation coil, r = resistance of artificial 
line, and R b = resistance in series with generator. 

PROBLEMS 

1. Determine the attenuation and wave-length constants of a 
perfectly-insulated ground-return line having the following constants 
per mile, when the frequency of the impressed electromotive force is 
50 cycles: R = 4.25 ohms, L = 0.002 henry, and C = 0.016 micro- 
farad. 

2. Compute the current and voltage at both ends of an 8oo-mile 
line of No. 10 B. & S. gage copper wire and having a 3oo-ohm relay 
at each end. A 150- volt i5-cycle alternating-current generator is 
to be considered connected in one terminal of this simplex circuit in 
place of a 3 20- volt direct-current generator. The constants of the 
relay and line are those given in 8. Construct the vector diagram 
of currents and electromotive forces. 

3. Verify the value of I r given in 8 for signalling on a particular 
line at a speed corresponding to a dot-frequency of 150 cycles. 

4. For different key positions, determine the. unidirectional cur- 
rents traversing the 25o-ohm terminal relays on a 4oo-mile simplex 
telegraph line of No. 9 B. & S. gage copper wire. Assume the line to 
have an insulation resistance of 0.5 megohm per mile, and that a 
single i6o-volt direct-current generator located at one terminal 
station supplies current to the circuit. 

5. Calculate the currents traversing the relays of the line men- 
tioned in the preceding problem when the 1 60- volt generator is re- 
placed by two 8o-volt generators, one at each line terminal. 

6. Solve Problem 3 of Chap. II, taking into account a uniformly 
distributed leakance of io~ 6 mhos per mile for this 475-mile polar 
duplex circuit. 



CHAPTER XI 

SUBMARINE TELEGRAPHY 

i. Theory of Cable Telegraphy. Because of the large 
capacity and small leakance of submarine telegraph ca- 
bles, the direct-current transmission theory 'discussed in 
the foregoing chapter is inapplicable to signalling over 
cables. However, the alternating-current transmission 
theory already considered may be utilized for cable teleg- 
raphy if the speed of signalling is such that a steady state 
is constantly approached within a reasonable margin. For 
practicable speeds on commercial cables this theory is 
limited to cable sections of moderate length. When the 
steady state is not nearly approached during each signal, 
then the growth and fall of the direct-current accompany- 
ing the application and withdrawal of constant voltage to 
one end of the cable are alone of importance. The con- 
sideration herein presented of these transitional states on 
long cables, conveniently called the transition theory of 
transmission, will reveal the nature of the current which 
reaches the distant terminal of the cable. 

If a steady voltage E is applied to one end of a perfectly- 
insulated cable of length /, while the other end is grounded, 
the potential at each point gradually rises until its value 
at any poiht distant 5 from the sending end is 

* ... ; EJ = E 1 -^, \ (i) 

347 



348 TELEGRAPH ENGINEERING 

which indicates that the voltage-distance graph for the 
steady condition is a straight line falling from E to zero, 
as shown in Fig. i. Should this condition be altered, say 




IB 
i 



Fig. i. 

by grounding the sending end, then the voltage there at 
that instant would be zero, but at other places in the cable 
would be as indicated by equation (i). The subsequent 
voltage at any point is found by drawing an image of AB 
toward the left, forming a curve DAB, and considering 
this curve to represent a periodic function of distance; 
which is, therefore, expressible by a Fourier's series of the 
form 

Em = F 4-Fisin0 + F 2 sin20 + . . . +F n sinnO + 
GI cos + Gz cos 20 + . . . + G n cos nO, 

where 6 = and n is any integer. To evaluate the co- 
efficients, multiply both members by sin nO times the width 
ds of the element and summate these elementary areas over 
the distance DB, and there results 

ri /2J (*1l 

E m f sin nO ds = F I sin nS ds + FI I sin sin n0 ds 
Jo Jo 

(*2l 

+ + F q I sin qB sin nB ds + - 
Jo 

ri rzi 

sin 2 ndds + GI I cos - sin nB ds + 
Jo 

X2l f*2l 

cos q6 sin nd ds + + G n I cos nB sin nd ds. 
Jo 



SUBMARINE TELEGRAPHY 349 

Since E m r = E - E, dO = y ds, and when s = 2 1 then = 2 TT, 
I I 

E I smnedO -- I 6 sin nd dO = F Q I sin n6 d0 

J Q ffJ JQ 

X27T /*2tr 

sin sin w0 </0 + + F q I sin g0 sin w0 d0 
t/O 

+ . - - +F n l&xPntidO + Gi / cos0-sinw0</0 + - - 
Jo Jo 

+ G q I *cosq0 smn8dO+ +G n I cos n6 sin nd d6. 
The terms of this expression are integrated as follows: 



T 2 ' . 

I sin n0 dO = \ = o. 

Jo \_ n J 



rif Tj Q ~|2ir 2 

^ sin w^ c?0 = -r sin w^ -- cos w^ = --- 
L^ 2 w Jo - n 

I sLnqO'SmnOdO = - I cosfg n\B cos(q + n\d \dO 

= i fsin (q - n) _ sin (q + n) 0"] 2y 
2L g g + w Jo 

When q and w are different integers, substitution of the 
limits reduces this expression to zero. 

rsin 2 nBde = - I (i cos 2 n0 } dd 
2 J o V / 

i f\ sin 2 w^1 2T 

= - \e -- = TT. 

2[_ 2W Jo 

I cosqO 'SmnddO = - I Isinln + qjd + smln q\6 \dO 

_ _ i fcos (^ + q) , cos (n q) 0"[ 2r 
2L w + g w- 1 



350 TELEGRAPH ENGINEERING 

This expression is zero whether the integers q and n are 
equal or unequal. Therefore, by substitution, 

2E 2E 

= irF n or F n = , 
n irn 

and consequently the potential at any point of the cable 
distant s from the sending end where E volts are impressed, 
reaches the maximum value of 

E m f = ( Sm + - Sin 2 + + - 

TT \ 2 n 

n f 2 j 

or E m = 

This equation represents the voltage distribution at the 
instant of grounding the sending end of the cable. 

If, now, the potential distribution be left to itself, then 
the diminishing voltage all along the cable must satisfy 
the differential equation of propagation over a uniform line, 
namely, equation (4) of Chap. X, which is 



where C, L, g and R are the cable constants per unit length. 
But in submarine telegraphy the inductance of cables is 
very small and the leakage conductance is very low, that 
is, L and g are negligibly small; so that the equation to be 
satisfied reduces to 



dt 

the so-called "telegraph equation." 
A solution of this equation suggests itself of the form 



SUBMARINE TELEGRAPHY 351 

where E' is the voltage at the point distant s from the send- 
ing end at a time / after grounding that end. Differenti- 
ating this expression twice with respect to distance there 






results jsT^'j an( ^ differentiating with respect to time 

there results - n 2 bE'. Substituting these values in (4) 
yields 

' =-RCn 2 bE': 



whence b = . (6) 



With this interpretation of the exponential constant, 
equation (5) is a solution of equation (4), for it reduces to 
equation (2) when / = o, is zero when / = <x> , and is zero 
when s = o or s = I. 

The fall in voltage at the point of reference during the 
time / elapsing since suppression of voltage E at sending 
end by grounding is 



<> 



On the other hand, if the origin of time were taken at the 
instant when the voltage E is applied, the rise in voltage 
during the time / at the point of reference is also given by 
equation (7). This expression also satisfies equation (4) 
since it is the difference of two expressions which satisfy 
it separately. 

The growth of current in the cable at the point under 
consideration is obtained by differentiating (7) with respect 
to distance, and using de' = R ds /'. Thus, the current 



35 2 TELEGRAPH ENGINEERING 

value at a time / after applying the voltage E to the sending 
end is 



At the receiving end s = /, and the current is 

// = T < 2 COS HIT 2J ( ~ n26 ' COS WTT J > 

But 2/cosw7r= i + i i + i ; 

transposing the first term of the right hand member, there 
results 

i + 2 cos HTT = i i + i i+ , 

and adding these two series term by term it will be found 
that 



cos rnr = . 

n=l 



Consequently, the instantaneous current at the grounded 
receiving end is 



when both ends of the cable are without sending or receiving 
instruments. The series 



and when t is zero, the sum is i + i i + = J 
as before, and therefore // is zero when time begins. 

As the foregoing expression for // is slowly convergent 
for small values of / it is more convenient, for purposes of 



SUBMARINE TELEGRAPHY 



353 



evaluating the received current at first, to alter its form into 
a rapidly-converging series by means of an equality due to 
Fourier that 



oo n^r 

2"?cos^ 

n=l 



8000 
7500 



7000 
6500 



6000 
6500 



5000 
E4500 



3500 
3000 



2500 
2000 



1500 
1000 



ARRIVAL CURVES 

on 
2500 Mile Cable 



\ 



500 



0.2 0.4 0.6 0.8 1 



2 

Seconds 



Fig. a. 



Taking bt = ^ and " = i, equation (9) becomes 



* Sir WiUiam Thomson, " Collected Papers," V. 2, p. 48; 1884 ed. 



354 TELEGRAPH ENGINEERING 

then using equation (6), there results 

oo - (2 m + 1) V 2 

"' <> 



If the key be kept depressed, the current at the receiving 

jy 

end will grow from o for / = o to the value , as obtained 

Kl 

from (9) by placing / = oo . The graph of current growth 
will resemble curve 7, Fig. 2. When the battery is re- 
moved and the sending end grounded, the current at the 
other end will decay as shown by curve II, which is the 
same as curve / drawn downward from the steady current 
value as axis. 



2. Illustration of Current Growth at the Receiving End 
of a Cable. As an example of the growth of the current 
at the receiving end of a cable, consider a 25oo-mile cable 
having a total resistance of 5000 ohms and a total capacity 
of 987 microfarads to have 40 volts impressed upon the 
sending end. Thus, Rl = 5000 ohms and Cl = 0.000987 

7T 2 

farad; therefore b = = 2.00, and the 

5000 X 0.000987 

ultimate current value -at the grounded receiving end of the 
cable is 0.0080 ampere. Values of // to an accuracy of a 
fraction of one per cent can be obtained by using only the 
first terms of equations (9) and (10), if the latter be used 
for time intervals up to one second, say, and the former 
for longer intervals. For the conditions of this example, 
the equations utilized are 

// = aE\f^.~&.?2^e~^empeatoit< i, 

f 7T/U V t 



SUBMARINE TELEGRAPHY 



355 



and 

// = 7T 7 (i - 2 e~ bt } = 0.008 (i - 2 ~ 2t ] amperes for/ > i. 
Rl \ I \ I 

The values of current at the receiving end of this cable as 
calculated from these expressions (see table of exponential 
functions in Appendix) for different values of t are given in 
the following table, and are also shown by curve 7 of Fig. 2. 
It will be observed that the application of voltage to one 
end of a cable produces an instantaneous effect at the other, 
but the growth of current at first is so extremely slow as to 
give rise to the impression that there is at first a " silent 
interval." 



t 

seconds 


// 
microamperes 


t 
seconds 


IT 

microamperes 


O 


O 


0.8o 


4794 


0.05 


0.0000017 


0.90 


5357 


0.10 


0.279 


I.OO 


5835 


0.15 


14.96 


1 .20 


6548 


O.2O 


93-6 


1-50 


7204 


0.25 


288 


1.70 


7466 


0.30 


599 


2.OO 


7707 


0.40 


1457 


2.50 


7892 


0.50 


2401 


4.OO 


. 7995 


O.6O 


3302 


10.00 


7999 


0.70 


4112 


00 . 


8000 



3. Transmission of Telegraphic Signals. The alpha- 
betic code used generally for cable telegraphy is the con- 
tinental Morse Code, comprising for its characters various 
combinations of dots and dashes as tabulated in 7 of 
Chap. I. The transmission of a letter is usually accom- 
plished by repeated applications of constant potential for 
equal intervals of time to one end of the cable, the potential 



TELEGRAPH ENGINEERING 

differing in direction for dots and for dashes. With this 
method of signalling over cables the code for alphabet and 
figures is better represented as below, dots and dashes being 
indicated respectively by upwardly and downwardly pro- 
jecting rectangles of equal length. 



c ~d e f 



T -I M - Hi M M 



o P Q r s t 



Dashes 
v w x y z 



12 34 



5 6 7 



9 or 



Taking T seconds as the duration of a dot or dash element, 
the interval between elements is generally r, that between 
letters 3 r, and that between words 7 T . By an analysis 
of traffic matter it is found that the average letter contains 
7.2 elements, including space between letters, and hence 
requires 7.2 r seconds for transmission. 

Signals are usually sent, therefore, as a succession of 
equal rectangular voltage-time pulses differing in direction 
and spaced irregularly. If the alternating-current theory 
of wave propagation were applied to cable signalling, two 
hypothetical frequencies for an equivalent sine wave would 
be recognizable, namely: the dot-frequency, as outlined 
in the foregoing chapter, and the reversal-frequency, as 



SUBMARINE TELEGRAPHY 



357 



indicated in Fig. 3; the former being twice as high as the 
latter. Kennelly* has considered both frequencies in 
ascertaining the best resistance of receiving instruments 
on cables, and the influence of terminal apparatus upon 
signalling speed. He has shown that the receiving instru- 



J. 




\ 


Seconds 


/ 


f 


*\ 


\ 


r 



Fig. 3- 

ment for greatest sensitiveness should have a resistance 
equal to the resistance component of the surge impedance 
of the cable plus the resistance component of reactive 
apparatus, if any, in the receiving circuit. The surge 
impedance, from 4 of Chap. X, being in general 

f~+ja 



g +JPC 



or 



v/f 



+JPL 

g+jpc' 



rjr 

becomes y ohms for highly insulated cables, where 

p = 2 TT times the frequency (dot- or reversal-frequency as 
selected) of the equivalent alternating current. Thus, 
taking a reversal-frequency of 4 cycles per second in the 
numerical illustration of 2, and with no reactive apparatus 
at the receiver, the best resistance of the winding of the 
receiving instrument, as found by this method, is the re- 
sistance component of 

* " Hyperbolic Functions applied to Electrical Engineering," 1912, Chap. 9. 



358 TELEGRAPH ENGINEERING 



2 7T 



= V 202 ,ooo (90) =449 (45) 



2500 

or is 449 cos 45 = 317 ohms. 

Reverting to the transition theory of cable transmission, a 
dot or dash may be transmitted by applying a unidirectional 
voltage at the sending end of the cable for T seconds, 
thereafter grounding that end; consequently the equation 
for a dot or dash is obtained by subtracting from equation 
(9) a similar equation in which the time / is replaced by 
t T whence 



COS HIT - 



In other words, a dot is transmitted by the maintenance 
of voltage at the sending end for an infinite time, and after 
T seconds the application of an equal opposite potential 
also maintained indefinitely. The subtraction indicated 
in equation (n) is most conveniently done graphically. 
The curve of arrival of a dash element for a contact lasting 
o.i second on the cable considered in the foregoing numeri- 
cal illustration is shown by curve 7 of Fig. 4 as the sum of 
curves a and b. An enlarged view of this curve is shown 
by curve T, the multiplier being 5. It will be evident that 
the shorter the contact the lower and flatter will be the 
curve of received current for a dot or dash element. 

By applying the foregoing method it is a simple matter 
to construct a curve showing the received instantaneous 
current for any combination of dots and dashes. It is only 
necessary to plot the same dash arrival curve in the proper 
places and with proper direction and then add the ordinates. 



SUBMARINE TELEGRAPHY 



359 



Thus in Fig. 4 are also shown the forms of received signals 
on this cable for the letters E, N, D, B and BT, the lower 
dotted lines representing the nature of the impressed elec- 




0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1JL 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 
Seconds 

Pig. 4. 

tromotive force. Curve II exhibits the cumulative action 

of successive like signals for a signalling speed of 

7.2 X o.i 

= 83.3 letters per minute and the result is apparently 
undecipherable, but still it would be legible to an expert 
recorder attendant. 
In Fig. 5 is shown the received current curve for the 



3<5 



TELEGRAPH ENGINEERING 



same letters BT sent at the same speed on a shorter cable 
having the same constants per unit length as that pre- 
viously considered. The variations in this curve are very 
prominent and are easily interpreted. 



10000 
8000 
6000 
4000 
2000 

2000 
4000 
6000 
8000 

( 










































1 




^ 


\ 


LETTERS BT Received 
on 
1250 Mile 
Cable 














1 


\J 




\ 








2 


\J 








\ 


















/ 












\ 































\ 










\ 




/ ^ 


^ 


*.~ 










\ 








s* 


\ 




P 
















\ 




7 






\ 


f 


















\ 


/ 








t- 


/ 


















\> 












- 


















Dots 














V 
















Dashes 








T 


) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1. 
Seconds 



Fig. 



The receiving instrument used in cable telegraphy over 
relatively short distances (several hundred miles) is the 
ordinary sensitive relay, while over long distances the 
siphon recorder is used. The siphon recorder, devised by 
Lord Kelvin in 1867, traces on a paper tape the curve 
of current which traverses the instrument winding. This 
recorder is a D'Arsonval galvanometer, the movements 
of the coil of which are transmitted by means of two silk 
fibres to an extremely small glass siphon. As one end of 
this siphon passes transversely to and fro across the slowly- 



SUBMARINE TELEGRAPHY 



361 



moving tape, it takes ink at the other end from a small 
reservoir and exudes it upon the paper in the form of a 
wavy line. To eliminate friction, the siphon is kept vibrat- 
ing rapidly, by means of an electromagnetic vibrator, so 
as to oscillate perpendicularly to the paper, thereby form- 
ing a trace that really consists of a succession of closely 




Fig. 6. 

spaced dots. Fig. 6 shows a siphon recorder made by 
Muirhead & Co., Ltd. The suspension piece with vibrator 
is shown in Fig. 7. 

Fig. 8 is a reproduction to exact size of a portion of a 
message which was transmitted over the Bay Roberts, N. F.- 
New York i6io-mile cable at a speed of 200 letters per 



362 TELEGRAPH ENGINEERING 

minute ( r= = 0.0416 second V The dotted neu- 

' V 200 X 7.2 / 

tral line shows that the siphon recorder in practice does 
not behave as a fixed-zero instrument. 

The resistance of siphon recorders is usually between 300 
and 800 ohms, and their inductance about 0.2 to 0.3 henry. 




Fig. 7. 

The recorder will operate satisfactorily on a current as 
small as 20 to 40 microamperes. 

Signals are sent either manually or by means of auto- 
matic transmitters such as described in i of Chap. IV. 
Fig. 9 shows a cable key with removable contact levers. 
Automatic transmission by means of perforated tapes 
results in greater speed and more regularity in the signals 
than is possible with hand transmission; it is the method, 
therefore, chiefly employed in cable telegraphy. 



SUBMARINE TELEGRAPHY 



363 



4. Speed of Signalling. From the foregoing expres- 
sions it will be seen that the received current is a function 
of bt, consequently the time required to establish a given 
current at the far end varies inversely with b or directly 




One hund red f orty th ree 



hr^M\r^^r^^^ 




Federal St. Boston Mass 

Fig. 8. 

CRF 
with . Since the speed of signalling varies inversely 

with the time required for establishing the necessary cur- 
rent, this speed varies directly with , or it varies in- 




Fig. 9. 



versely with the product of the total resistance and total 
capacity of the cable. Also, when C and R are kept con- 
stant, the speed of signalling varies inversely with the square 
of the cable length. 



364 TELEGRAPH ENGINEERING 

Accordingly, the speed of signalling over a given distance 
may be increased by decreasing the total capacity or the 
total resistance or both. The capacity depends upon the 
conductor diameter, upon the distance between conductor 
and metallic sheath and upon the dielectric constant of the 
cable insulation. Greater separation between conductor 
and armor and the use of larger wire are accompanied by an 
increase in cost. Further, with very few exceptions, no 
insulating material having a lower dielectric constant than 
gutta percha compound has been successfully used up to 
the present time in submarine cables. 

The statement that the speed of signalling varies inversely 
with the product of total resistance and total capacity of a 
cable is called the "CR Law " and was announced by Lord 
Kelvin. In other words, two cables of length /i and k 
having the constants Ci, RI and C 2 , R?. respectively will be 
similar (that is, yield the same arrival curves "under identi- 
cal conditions) when 

CM? = cAif. (12) 

This is only true when the cable is entirely devoid of in- 
ductance and leakance, has no terminal apparatus, and 
is earthed at both ends. Malcolm has shown that two 
cables having the constants Ci, Zi, RI, gi and C 2 , 2, R^ 2 
and with terminal apparatus of impedances Z t i, Z r i and Z <2 , 
Zr2 at transmitting and receiving ends respectively will be 
similar when 

gih _ Zti _ Z r i __ / x 

gili Zt2 Zrf 

and the size of the signals will be in the ratio of rj to i. 
This generalized expression may be appropriately called 
Malcolm's law. It reduces to equation (12) when the 



SUBMARINE TELEGRAPHY 365 

cable inductance and leakance and the terminal apparatus 
are ignored. 

Fig. 4 shows the graph of current received over a 2500- 
mile cable without terminal apparatus for the letters BT 
with contacts of o.i second. Taking 7.2 elements for an 
average letter including space, the number of five-letter 
words transmitted per minute over this cable, having 
CRl 2 = 4.935 ohm-farads or seconds, under these conditions 

60 
would be - = 15. Signalling at this speed 

gives legible results, as evinced by the figure. The greater 
legibility for the same signalling speed over a shorter cable 
is manifest from Fig. 5 for CRl? = 1.234 seconds. The 
maximum speed of signalling over any cable is determined 
by constructing arrival curves of various words using dif- 
ferent values of r and submitting these to an experienced 
operator to determine the limit of legibility. On short 
cables the inertia of the receiving instrument prevents the 
attainment of the theoretically possible speed of trans- 
mission. 

The use of condensers in series with a cable at one or 
both of its ends affords better definition in the received 
signals. The curves of Fig. 10, calculated according to a 
method given by Malcolm,* show the arrival curves for the 
same cable considered in the foregoing numerical illustra- 
tion, with terminal condensers. Curve / represents the 
received current curve when a condenser of gV the capacity 
of the cable is connected in series with the cable at one end. 
Curve // represents the current curve when a condenser of 
-j 1 ^- the capacity of the cable is connected at each end. This 
curve is considerably lower than the first but its decay is 
* The Electrician, V. 69, pp. 315-318 and 981. 



3 66 



TELEGRAPH ENGINEERING 



much more rapid. The advantage of introducing a con- 
denser of ^ the capacity of the cable in series with it at 
its middle point, if possible from a practical viewpoint, is 
shown by curve ///. The ultimate steady current value 
for all of these conditions is zero. 



800 
720 
640 
560 

r 

E 400 
| 320 
240 
160 
80 






































^ 


>, 
^ 


X 










ARRIVAL CURVES 
on 2500 Mile 
Cable with 
Terminal 
Condensers 










V 




\ 


X 


L 




















\ 




XJ 


^v,^ 








1 










\" 




^ 


\ 














1 










\ 


\ 








\ 


^ 






/ 


S" 


^s 










^ 


\ 










"^ 




// 






X 


s^ 










\ 












1 










^ 


Ss^ 








^ 


^x 


. 




V 


1 
















** . 


~ 


~ 


- 


, 






0.2 0.4 0.6 0.8 1.0 



Seconds 
Fig. 10. 



2.0 



3.0 



By subtracting from curve II a similar curve following 
the first at an interval of o.i second, the received current 
curve for a dot of that duration will result, and is shown in 
Fig, 1 1 by curve 7. A comparison of this curve with curve 
T of Fig. 4 dispjays the fact that the maximum current is 
attained sooner with condensers than without them, but 
this maximum is very much lower; and further that the 
positive current lobe is followed by a negative pulse when 
using condensers. 

When the letters BT are transmitted over this cable with 
condensers of 98.7 microfarads at each end, the received 



SUBMARINE TELEGRAPHY 



367 



current appears as in Fig. n, curve //, when the time of a 
dot or a dash is o. i second. The result is more legible than 
the curve of Fig. 4 for the same signalling speed without 



LETTERS BT . 

Received on 2500 

Mile Cable with 

Terminal Condensers 




120 



0.1 0.2 0,3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 

Seconds 

Pig. n. 

condensers, and, consequently, the speed with condensers 
might be increased for the same degree of legibility. The 
use of condensers at the ends of cables also serves to stop 
earth currents and to facilitate duplex cable operation ( 7). 

5. Picard Method of Signalling. In transmitting 
signals over great distances through several cables con- 
nected in series the speed of signalling is very low, but if 
messages are repeated at intermediate stations the speed 
of signalling is higher and is limited by the speed on that 



368 TELEGRAPH ENGINEERING 

cable section having the largest value of CRl 2 . This re- 
peating of messages has been done manually, but from time 
to time schemes have been devised and placed in operation 
to utilize automatic retransmission in order to avoid error 
and loss of time. When the received signals are such that 
if a straight zero line of some width be drawn on the tape 
all of the lobes which correspond to dots or dashes still 
project on their respective sides of this zero line, then the 
retransmission of these signals may be accomplished auto- 
matically by the use of suitable relays, such as the Brown 
drum relay or the Muirhead gold-wire relay. 

The signalling systems of Picard and Gott, using modi- 
fications of the ordinary Morse code, are arrangements for 
permitting the automatic retransmission of messages, even 
on cables having a large value of CRl 2 . 

In the Picard method, the signals are formed by the time 
interval between two momentary oppositely-directed equal 
impulses, a dash being distinguished from a dot by a longer 
interval between these impulses. Thus, the impressed 

I I I I J 



Fig. 12. 

impulses for the letters BT are roughly shown in Fig. 12. 
These impulses are impressed upon the cable by means of 
two polarized relays P, P' and a local condenser C, con- 
nected as shown in Fig. 13. A depression of the key K 
causes a momentary kick of the right-hand relay armature 
against its contact stud and connects the positive pole of 
the main battery B to the cable for an instant. When the 



SUBMARINE TELEGRAPHY 



3 6 9 



key comes to rest after each dot or dash signal the other 
relay armature shifts and causes the negative pole of the 
battery to be connected momentarily to the cable. Be- 
tween these cable impulses the sending end of the cable is 
open-circuited, and the impressed charge passes through 



Cable 




Fig. 13. 

the receiver. The receiving device is a suspended-coil 
relay which has no retractile springs and is free to respond 
to cable impulses. This system has been used for many 
years on the three Marseilles-Algiers cables (560 miles) 
belonging to the French government for Morse signalling 
and also for Baudot printing telegraphy from Paris to 
Algiers with automatic translating relays at Marseilles. 

6. Gott Method of Signalling. The method of cable 
signalling devised by Gott utilizes the Morse code of short 
applications of potential for dots and longer applications 
for dashes, with successive elements in opposite directions, 
and employing a sensitive relay at the receiver. Inasmuch as 
a relay of definite and sufficient sensibility connected to the 
far end of a long cable operated at high speed in the ordinary 
way (3) could not properly automatically retransmit unidi- 
rectional impulses into another cable owing to the spreading 
out of the signals received by it, the message in the Gott 



370 



TELEGRAPH ENGINEERING 



system consists of an assemblage of lobes, alternately posi- 
tive and negative, one lobe for each dot and one for each 
dash, and the latter distinguished from the former by their 
greater length. Fig. 14 shows the results obtained by using 



280 
240 
200 
160 
120 
80 
|40 

1 
|40 

80 
120 
160 















































































































































/ 


f 


\ 






GOTT SYSTEM 
of Signalling 
Letters BT on 
2500 Mile Cable 








/~* 


















\ 










/ 


/ 


\ 












1 




] 










/ 




\ 










/ 








\ 


















/ 






\ 








/ 








\ 
















/ 








\ 






/ 










\ 

















/ 










\ 














\ 




/ 




\ 






/ 


/ 










\ 
















\ 


/ 




\ 






/ 




























^/ 








V 


S 




































































\ 




1 


II 


i 






3 











































n 













0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 

Seconds 
Fig. 14. 

this method over a long cable. The upper line shows 
the impressed voltage on the 25oo-mile cable previously 
considered with terminal condensers, for the letters BT, 
having dashes three times as long as dots; the curve shows 
the current form received at the end of this cable and 
traversing the relay; and the lower line shows the voltage 
impressed upon the second cable by the relay, which is as- 
sumed to respond to currents as small as 30 microamperes. 
The curve is constructed by the addition of properly placed 
dot arrival curves of the type shown by curve 7 of Fig. n, 
and dash arrival curves obtained by adding two curves 



SUBMARINE TELEGRAPHY 



37 1 



(the latter reversed) of the type shown by curve II of Fig. 
10 with an interval of 0.3 second between them. It will 
be observed that the second dot in Fig. 14 is very short 
while the third dot is almost as long as the dashes. This 
distortion of signals may render deciphering difficult, but 
the method can be improved upon by giving each im- 
pressed letter its theoretically best shape. Much better 
results are attained over shorter cable sections. 

One arrangement for automatically reversing the direc- 
tion of the voltage impressed upon the cable is shown in 




Fig. 15. 

Fig. 15. The outer terminals of the split battery B connect 
with the contacts of the polarized relay P, and the middle 
tap is grounded through the primary winding of trans- 
former T. The secondary winding of this transformer con- 
nects with the coils of the relay. Depressing the key K 
charges the cable with a polarity depending upon whichever 
contact stud the relay armature is touching. Permitting 
the key to resume its normal position will cause the cable 
to be grounded at the sending end after each signal. 

The function of the transformer is to control the relay 
armature so that successive impulses will always be of 
different polarity. Assuming the armature to rest against 



372 TELEGRAPH ENGINEERING 

its left contact, depression of the key will cause a current 
to be produced in the secondary of the transformer and in 
the relay coils in such direction as to hold the armature to the 
left contact, thereby securing firm contact. Releasing the 
key causes a current of opposite polarity to flow through 
the relay coils, consequently the armature will move against 
the opposite contact stud in readiness for the next signal. 
For automatic retransmission, from an overland line to a 
submarine cable or from one cable to another, the key may 
be replaced readily by the armature of a relay. 

The receiver employed with this system is a recorder 
with a contact-making tongue attached to the moving coil. 
This tongue plays between two contacts, alternately touch- 
ing one and then the other. These contacts are connected 
together and lead to a battery and sounder (or relay) and 
back to the tongue, thus forming a local circuit for the read- 
ing of the received Morse dot and dash characters. 

7. Duplex Cable Telegraphy. In modern practice 
telegraph cables are generally duplexed so that messages 
may be sent in both directions simultaneously. This 
practice involves the use of an artificial cable equivalent 
in capacity and resistance to the actual cable arranged at 
each end of the submarine cable, as shown in Fig. 16. 
Artificial cables may be constructed in a variety of ways. 
The Muirhead artificial cable is widely used and consists 
of zigzag tinfoil sheets, connected in series, separated by 
means of paraffined paper from other sheets of tinfoil. The 
latter sheets are grounded, or may be grounded through 
resistances, while the zigzag sheets are so proportioned as 
to have the requisite resistance and also the proper capacity 
with respect to the grounded sheets. 



SUBMARINE TELEGRAPHY 



373 



The real and artificial cables may be considered as form- 
ing two arms of a Wheatstone bridge, the other arms being 
formed by two nearly equal condensers C\ and 2 of from 
30 to 80 microfarads capacity each, arranged in the so- 




Artificial 
Cable 



Fig. 16. 

called double block. One of these condensers should be 
slightly adjustable in capacity so that with the variable 
resistance, r, an accurate balance may be secured. The 
siphon recorder, R, provided with an adjustable inductive 
shunt, 5, is connected across the bridge, while the reversible 
battery is connected from r to ground through the double 
key K. The function of the inductive shunt is to make 
up the deficiency in recorder inductance for maximum 
arrival current, so that, according to the alternating-current 
transmission theory already mentioned, the receiving circuit 
reactance neutralizes the reactance component of the cable 
surge-impedance. Another arrangement employs a con- 
denser in series with the recorder and shunted by a resist- 
ance, the inductive shunt being bridged across both 
condenser and recorder. 

When balance is procured, depression of one of the keys 
establishes a current which divides equally in the two cir- 
cuits, one through the condenser C\ and the cable and the 
other through the condenser Ci and the artificial cable. 
Hence the terminals a and b of the recorder have the same 



374 TELEGRAPH ENGINEERING 

potential and, consequently, no current flows through this 
instrument. Thus, manipulation of the key does not affect 
the home recorder. 

If, however, a current arrives at this end of the cable, 
part passes through the recorder to ground jointly through 
the artificial cable and condenser Ci, while the remainder 
passes through the condenser Ci directly to ground. Thus 
the key at one end controls the operation of the recorder at 
the other end of the cable. In this way signals may trav- 
erse the cable in opposite directions at the same time 
without interference. The Gott signalling method is also 
applicable to duplex cable operation. Considerable care 
must be exercised in adjusting the artificial lines to secure 
a good balance, and such adjustment is always made with 
the distant end of the cables open-circuited. 

8. Sine -wave Signalling. A method of signalling on 
cables was devised by Crehore and Squier which employs 
a tape transmitter for impressing half sine waves of electro- 
motive force upon the cable instead of the usual rectangular 
wave-forms. The battery ordinarily employed is, therefore, 
replaced in this system by a low-frequency alternator. The 
tape has three lines of holes, the upper for dots, the lower 
for dashes, and the center line of guide holes engages with 
a toothed wheel driven by the alternator shaft so that the 
tape travels a definite distance for each revolution of the 
alternator armature. The tape passes beneath two rollers 
attached to levers, which close a local circuit at their other 
ends whenever perforations move under a roller. Two 
relays in this local circuit connect the alternator to the 
cable in the proper way and for a proper time. The ap- 
pearance of the tape and the corresponding form of the 



SUBMARINE TELEGRAPHY 375 

impressed voltage for the letters cab are shown in Fig. 17. 
The mechanical and electrical features of the transmitter 
excel those of the Wheatstone automatic transmitter. 




; o o o coo 

\oooooooooooooo 

o o o o 



This system of signalling was operated experimentally 
by its inventors over actual submarine cables and resulted 
in a higher signalling speed than afforded with the usual 
battery system under like conditions. Recently, Malcolm* 
has published the results of his analytical investigation of 
this sine-wave system of cable signalling, in which he con- 
cludes that (a) the received signals resulting from short 
applications of any symmetrical electromotive force are 
independent of the shape of the voltage wave and dependent 
only upon its mean value, and (b) the impressed sine-wave 
voltage produces less shock at the sending end of the cable 
than the abrupt battery wave-shapes. It is not unreason- 
able to expect the commercial application of this sine-wave 
signalling system. 

9. Design of Submarine Cables. A submarine cable 
consists of a copper conductor surrounded by a tube of 
gutta-percha insulation, all of which is protected by jute 
coverings and by spirally-laid metallic armor. It has been 
pointed out that the speed of signalling on such cables 
(ignoring terminal apparatus, inductance and leakance) 
varies inversely with the product of the conductor resistance 
and the capacity of the conductor with respect to the sheath. 

* The Electrician, v. 72, pp. 14-17, 50-52, 131-134, 245-247. 



376 TELEGRAPH ENGINEERING 

A large conductor surrounded by a thin tube of insulation 
may have the same product of capacity and resistance as a 
small conductor surrounded by a thick tube of insulation, 
but the cost will be different. To find the sizes of conduc- 
tor and insulation which yield the minimum cost of cable 
of given length for a specified signalling speed (that is, for a 
given value of CR), the expression of total cost in terms of 
conductor diameter is differentiated and equated to zero. 
No cognizance will be taken of the armor and other pro- 
tecting coverings as these items do not affect the electrical 
characteristics of the cable, but they may be included in 
determining the economic cable, if desired, without altering 
the method of procedure. 

The weight of a copper wire one mile long and having a 

cross-section of one circular mil is 0.016 pound. If c\ be 

the cost of copper in dollars per pound, then the cost of a 

stranded conductor / miles long and D mils in diameter is 

0.016 sD 2 ki dollars, (14) 

where s is the stranding factor or the ratio of the copper 
cross-section in circular mils to the cross-section of the 
circle of diameter Z); thus, for a seven-strand conductor 
having strands of equal size, s = ^. 

If d be the diameter in mils over the insulation, the vol- 
ume of insulation will be 

12 X 528 / (d 2 - D 2 ) = 0.0497 1 (^ - D 2 ) cu. in., 
1,273,240 

where 1,273,240 is the number of circular mils in a square 
inch. Taking 8 as the density of the insulating material 
in pounds per cubic inch, and c 2 as the cost in dollars per 
pound of this material, its cost will be 

0.0497 / (d 2 - D 2 ) 5^2. (15) 



SUBMARINE TELEGRAPHY 377 

As the capacity of two concentric cylinders i mile long, 
the inner of diameter D and the outer of diameter d, sepa- 
rated by a medium of uniform specific indue tivity k, is 

^ 0.0804 k . . j 
C = - ^ microfarads 




( 7, Chap. IX), and as the resistance of the stranded con- 
ductor, having a resistivity of p ohms per circular-mil mile 
at sea temperature, is 



it follows that the product is 

0.0894 P k 



K_ 

whence d = De D *, (16) 

r. 



Substituting this value of d in equation (15) and com- 
bining with^(i4), the total cost of the cable exclusive of 
armor and other coverings is 

(2K \ 

c^-l). (17) 

Differentiating and equating to zero, there results 

/ *K\ .?* 

0.032 sDld + 0.0497 Ifa f 2 D - ^ J e D * - 0.0994 /5Z>C2 = o 

IlK \ ^ 0.03 2 Ci5 

or ( -rrr- i j " = - - i = /^ for convenience. 

V D* / 0.0994 ^5 



378 



TELEGRAPH ENGINEERING 



It is possible to determine D from this expression in terms 
of the known factors K and F, and this is best done graphi- 
cally. Fig. 1 8 shows the relation of -= - to F. 



1.4 

1.3 
1.2 

1.1 

D 2 " 
0.9 

0.8 

0.7 
0.6 
0.5 

-: 
























^ 




















^ 




















/ 




















/ 


^ 




















/ 






















7 






















/ 






















/ 
























7- 






















-0.8 -0.6 -0.4 -0.2 0.2 0.4 0.6 0.8 l.O 1.2 1. 



Fig. 18. 

As a numerical illustration, let it be required to design 
the most economical 25oo-mile seven-strand submarine 
cable for a value of CR = 0.6 ohm-mf. per mile (that is 
CR/ 2 = 3.75 seconds). Let 

Ci = 0.16 
c 2 = 0.80 
6 = 0.037 
k = 3.04 
p = 51,000, 

then F = 0.032X0.16X0.778 
0.0994 X 0.80 X 0.037 



SUBMARINE TELEGRAPHY 379 



and g = o.o8 94 X ,V4 X 5 = 
0.6 X 0.778 

From Fig. 18, for F = 0.354, = 1.115 and, therefore, the 
diameter of the stranded conductor is 



~ /20,7OO X 2 ., 

D = \ V;/ - = 231 mils, 
V i. nc 



and the diameter over insulation is 

29,700* 

d = 231 e (231)1 = 403 mils. 

The total cost of the conductor and insulating material 
as determined from equation (17) is 265,000 + 401,000 = 
666,000 dollars. 

Had the conductor been a single wire (i.e., 5 = i) the 
cost would be less for the same signalling speed. Its diam- 
eter would then have been 196 mils and its diameter over 
insulation 358 mils (no correction being made for increase 
in resistance due to stranding) . The cost would be $5 76,000. 
Solid conductors, however, are not frequently used because 
of the greater liability of fracture in laying the cable. 

To make certain that the stranded cable has sufficient 
insulation resistance, the foregoing diameters are sub- 
stituted in the following equation: 
' i 

Insulation resistance = I = log e (18) 
2 irJo x 2 TT D 

2 

megohms per mile, where a is the resistance in megohms 

between opposite faces of a cube of the insulation one mile 

on a side when at sea temperature but at atmospheric 

* See Table of Exponential Functions in Appendix. 



380 TELEGRAPH ENGINEERING 

pressure. Taking o- = 28,000 in the numerical illustration, 
the insulation resistance will be 2480 megohms per mile. 
Under the enormous pressures existing at great depths under 
water, the insulation resistance of the cable when laid is 
greater than when tested in the factory. Taking 0.05 per 
cent increase per fathom (i fathom = 6 feet) the insula- 
tion resistance at a depth of 1500 fathoms will be 4340 
megohms per mile, which is adequate. The design of 
cables for specified insulation resistance is of secondary 
importance to signalling speed, inasmuch as leakance rel- 
atively affects the shape or amplitude of the arrival current 
curve but little, so long as it remains constant. 
The weight of conductor and insulation is 



0.016 sD 2 + 0.0497 (<P ~ D 2 )* <. 

^^ - tons per mile, 
2000 

which weight is generally less than one-fifth of the total 
weight of the cable. The amount of protection on cables 

depends on the depth of sub- 
mergence, and is light on deep- 
& compound sea cable sections and heavy 
~ 7 st conductor ^ or ^ ne shore-end sections of 
-jute Yam cables. In order to facilitate 
the k^ and ^covering of 
cables they should be as light 
as is consistent with the stresses 

to which they are subjected. Weights of galvanized iron 
or steel cable sheaths for various depths of cable sub- 
mergence are indicated roughly by 

- - r^ ; - ^rz tons per mile. 
(depth in fathoms) ' 8 




SUBMARINE TELEGRAPHY 



381 



The weight of jute, tape and preservative compound may 
be from 40 to 100 per cent of the weight of the metallic 
sheath. Fig. 19 shows to proper size the cross-section of 
the 25oo-mile cable considered in this article, well pro- 
tected for a depth of 1500 fathoms. 

The electrical constants of a few long cables are given 
below : 



Cable 


Length in 
miles* 


Total re- 
sistance in 
ohms 


Total ca- 
pacity in 
microfarads 


Anglo-American Atlantic (Valentia 
to Heart's Content) . . . 


2I2O 


7,288 


776 


Second German Atlantic (Borkum to 
Fayal) 


22O7 


^218 




Pacific (Fanning Island to Fiji). . . . 
Atlantic (Canso to Waterville) 
Commercial Pacific (San Francisco 
to Honolulu) 


2354 
2493 

2622 


10936 
4895 

4O7 ^ 


746 
914 

87< 











* Distances over sea are more frequently expressed in nautical miles (nauts); i naut = 
1.152 miles. 

The cost of laying a cable is generally estimated as half 
of the cost of the cable. The life of a submarine cable is 
variously estimated as from 30 to 40 years; in fact, por- 
tions of cables laid from 1851 to 1854 from England to 
neighboring countries are still in use. 

The commercial status of submarine telegraphy is indi- 
cated by the fact that in 1911 there were over 2000 cables 
in the world aggregating 314,000 miles of cable and repre- 
senting an estimated investment of 350 million dollars. 

10. Types of Cable Service and Tariffs. There are 
two types of cable service rendered at present by some of 
the large telegraph companies, namely: full-rate service for 
code and urgent messages requiring prompt transmission 
and delivery, and deferred service to many countries for 



382 TELEGRAPH ENGINEERING 

messages in plain language not requiring the greatest ex- 
pedition and involving transmission within 24 hours. In 
addition the Western Union Telegraph Company renders 
cable letter service and week-end letter service across the At- 
lantic for less important communications in plain language 
which should not be subjected to the delay of over-sea 
mails. The following conditions and rates apply at present 
(July, 1914) to the various types of service. 

All Classes. Addresses and signatures are counted and 
charged for, but no charge is made for name of originating 
city and date. In addresses, the names of delivery offices, 
countries, provinces, states, etc., are each counted as one 
word regardless of the number of letters employed. The 
cost of full addresses may be avoided by using code ad- 
dresses, which are permitted by all governmental adminis- 
trations upon payment of a fee. In plain language, words 
of 15 letters or less are counted as one word. Abbreviated 
words and illegitimate combinations of words are inadmis- 
sible. Every isolated character counts as one word, and 
words joined by a hyphen or separated by an apostrophe 
are counted as separate words. Punctuation marks are 
only transmitted upon the expressed desire of the sender, 
and then charged for as one word each. 

Full-rate service. Full-rate messages may be in code or 
cipher language or in any plain language expressible in 
Roman letters. Code messages, formed of regular or arti- 
ficial words not making intelligible phrases, must be pro- 
nounceable and must not contain more than 10 letters. 
Cipher messages, formed of either unpronounceable groups 
of letters or of groups of figures, are counted at the rate of 
5 characters, or fraction thereof, to a word. The presence 
of a code word in an otherwise plain language message 



SUBMARINE TELEGRAPHY 



383 



subjects the entire message to the lo-letter code count, but 
plain language words in cipher messages are reckoned 15 
letters to a word. If unpronounceable groups of letters 
appear in code or plain language messages, such groups are 
subject to the 5-letter cipher count. Fraction bars, periods, 
commas and decimal points grouped with figures count as 
figures. Replies to a message may be prepaid by writing 
before the name and address the letters RP followed by the 
figure showing the number of words prepaid (this indica- 
tion is charged as one word). The following table shows 
the rates per word to points in some of the principal coun- 
tries from New York City. 

Present cable rates in cents (July, 1914) 



'Argentine Republic 


65 






'Australia 


66 






'Austria-Hungary 


32 






'Belgium 


25 






Bermuda 


42 




61 


'Brazil '. 


70-249 






Bulgaria! 


35 




AC 


'Cape Colony 
'Chili 


86 
65 


Philippine Islands 
Porto Rico 


112-136 


JChina (except Macao =127) 


122 


'Portugal 




Cuba (except Havana =15) 


2O 


Roumaniaf. . . 




'Denmark 


ir 






'Egypt 


50-58 


'Serviaf 


43 


'France 


25 


Siam 




'Germany 


25 


'Spain 




'Great Britain and Ireland 


25 


'Sweden 


38 


'Greece 


36 


'Switzerland 




'Holland 


25 


'Transvaal 


86 


Honduras 


55 


Turkey (in Europe)f 




'India 


74 


'Uruguay 


6< 


Italy 


31 


Venezuela 













* Countries to which Deferred Service may be utilized at present, 
f Secret language prohibited. 

J Deferred service only to Pekin, Hankow, Tientsin, Amoy, Chefoo, Foochow, Shang- 
hai, Tsingtau, Weihaiwei, Hong Kong, and Macao. 

It is of historical interest to recall that in the early pioneer days of transatlantic te- 
legraphy the minimum tariff was 20 ($100) for 20 words and i for each additional word. 



384 TELEGRAPH ENGINEERING 

Deferred service. Deferred messages must be written in 
one language which may be that of the country of origin 
or of destination or may be in French, the letters LCO, 
LCD or LCF respectively being prefixed to the address as 
indicative of the type of service and the language used 
(one word is charged for this indication or prefix). The 
text of the message must be entirely in plain language, 
numbers, except in addresses, being also written in words. 
The rates for deferred service is one-half those shown in 
the foregoing table to the countries therein starred, except 
to Great Britain and Ireland where the rate is 9 cents per 
word. Replies may be prepaid as in full-rate service but 
the instruction as to the number of words prepaid must be 
expressed in terms of full rates. 

Cable and Week-end letter service. Cable and week-end 
letters must be written in plain language of the country of 
origin or of destination, the indication CLP or CLT and 
WLP or WLT respectively being prefixed to the address as 
indicative of the type of service and the method of delivery 
beyond London or Liverpool, whether by post or telegraph. 
Cable letter tolls are based on an initial charge of 75 cents 
for 12 words (13 including indication) and week-end letters 
on an initial charge of $1.15 for 24 words (25 including 
indication), plus 5 cents for each additional word in both 
cases. These charges cover cable transmission only and do 
not include terminal telegraphic charges. The letters may 
be mailed to the New York Western Union Cable Office, the 
week-end letters being sent in time for mail delivery at this 
office on Saturday evenings. The charges cover delivery 
in London or Liverpool and mail delivery to all other places 
abroad. With telegraphic delivery beyond these cities cable 
letters are deliverable during the day following their date 



SUBMARINE TELEGRAPHY 385 

and week-end letters on Monday forenoon ; and the follow- 
ing additional charge per word is made to points in : Great 
Britain and Ireland i cent, Holland and Belgium 2 
cents, France yi cents, Italy 6 cents, Germany 9 cents, 
and in other countries at the regular foreign rates. Figures 
when not used as cipher are counted each group of 5 or less 
as a word. Replies may be prepaid as in deferred service. 
Cable letter service is likewise in operation with Cuba, 
the rate between New York and Havana being one dollar 
for 20 words (including prefix), plus 5 cents for each addi- 
tional word. Double this rate applies to letters for other 
points in Cuba. Week-end letter service is in operation 
with Argentine Republic, Chili and Peru, and the tariff 
between New York and these countries is $4.85 for 24 
words (25 including prefix) plus 20 cents for each additional 
word, the letters being delivered on Tuesday mornings. 

PROBLEMS 

1. Compute the values of the current received at one end of the 
2129-mile Anglo-American Atlantic cable, having R = 1.591 ohms 
per mile and C = 0.3645 microfarad per mile, at instants respectively 
of 0.2, 0.4, 0.6, 0.8, i.o, 1.4, 1.8, and 2.5 seconds after impressing 30 
volts on the cable; also plot a curve showing these values co-ordi- 
nated to time. 

2. From the curve of the preceding problem construct graphically 
the curve of arrival on this Atlantic cable of a dot element for a con- 
tact on 30 volts lasting 0.05 second. 

3. Using the dot arrival curve of the foregoing problem as a 
basis, construct the shape of signals received over the cable for any 
three-letter word. 

4. What may be the signalling speed in terms of 5 -letter code 
words on a icoo-mile cable having a total resistance of 3000 ohms and 
a total capacity of 350 microfarads for the same legibility of received 
signals as represented by Fig. 4. 



386 TELEGRAPH ENGINEERING 

5. Plot the received signals for the letters HE (for T = o.i second 
with 40 volts) sent^through the 25oo-mile cable considered in 2 to 
4 according to the Gott system. Curve I of Fig. n shows the 
magnitude and shape of the dot element. Show the type of signals 
retransmitted into another cable if the receiving relay is actuated by 
a current of 40 microamperes. 

6. Determine the economic dimensions of the conductor and 
insulation of the cable considered in 9 if the cost of insulation be 
taken as 55 cents per pound, other constants remaining unaltered. 

7. Calculate the weights per mile and the total cost of 7-strand 
conductor and insulation for a looo-mile cable having a value of 
CR = 1.05 X io~ 6 seconds. The cost of copper is 17 cents and the 
cost of insulation is i dollar per pound. Take k = 3.1. 

8. What would be the possible maximum annual net income of a 
duplexed cable when continuously used for automatic transmission 
of code messages averaging 8.5 letters to the word and 9 words to the 
message, if the dot element T is 0.05 second and the space between 
messages is 12 T (the symbol " understand" 3 dots, dash, dot, is 
frequently used between messages); the apportioned revenue over 
this cable section being 8 cents per word ? Two operators prepare 
tapes and feed the transmitter and two decipher the received mes- 
sages; they work in 8 hour shifts and receive an average weekly 
salary of 26 dollars. Allow 3 per cent depreciation on the cost of 
the cable installed and terminal apparatus, which was $1,000,000. 

9. How much would it cost to send the following cable letter: 

CLT-RP 10 Instrument Cambridge 

Give price and delivery spectrophotometer and radio-micrometer 
with scale Richardbrown Brooklyn. 

10. Decipher the message reproduced below which was received 
over a i6oo-mile cable. 



nf-AT^AAAM 



f\A /VA/^V^ 



APPENDIX 

TABLES OF TRIGONOMETRIC FUNCTIONS, 

EXPONENTIAL FUNCTIONS, LOGARITHMS AND 

HYPERBOLIC FUNCTIONS 



387 



3 88 



TELEGRAPH ENGINEERING 



TABLE I. TRIGONOMETRIC (CIRCULAR) FUNCTIONS 





H 








u 






Degrees 


Radians 






Degrees 


Radians 









o 


o 


I OOOO 


13.5 




o 2334 


o 9724 


o 5 




o 0087 


I OOOO 




o 24 


2377 


9713 




O.OI 


OIOO 


0.9999 


14.0- 




2419 


97O3 


I O 




0175 


0008 








0680 


1-5 


02 


O20O 
O262 


9998 

9997 


14-5 


26 


2504 
2571 


9681 
9664 




03 


O3OO 


9996 


15.0 




2588 


9659 


2.O 




O349 


9994 




27 


2667 


9638 




04 


O4OO 


9992 


15.5 




2672 


9636 


2.5 




0436 


9990 


16.0 




2756 


9613 








0088 




28 




96ll 


3-0 
3-5 


06' 


0523 
O6OO 
o6lO 


9986 
9982 
9981 


16.5 

17 o 


29 


2840 
2860 
2924 


9588 
9582 
9563 


4.0 




0698 


9976 




30 


2955 


9553 




07 


0699 


9976 


17.5 




3007 


9537 


4.5 




0785 


9969 




3i 


3051 


9523 




08 




0068 










. S.o 




0872 


9962 




32 


3146 


9492 




09 


0899 


9960 


18 5 




3173 


9483 


5-5 




0958 


9954 




33 


3240 


9460 


















6.0 




IO45 


9945 




34 


3335 


9428 




ii 


1098 








\r*8 


9426 


6.5 




1132 


9936 


20 o 




3420 


9397 


7.0 


12 


"97 
1219 


9928 
9925 


20 5 


35 


3429 
3502 


9394 
9367 




13 








o(j 


1C2"* 


9359 


7-5 




1305 


9914 


21 O 




3584 


9336 


8.0 




1392 


9903 




37 


36l6 


9323 




14 


1395 


9902 


21 5 




3665 


9304 


8.5 




1478 


9890 




38 


37O9 


9287 




It; 




9888 










9-0 




1564 


9877 




39 


3302 


9249 




16 


IITQ-I 


0872 






7827 


9239 


9-5 




l65O 


9863 




40 


3894 


9211 




17 


1692 


9856 


23.O 




3907 


9205 


10. 




1736 


9848 




41 


3986 


9171 




18 


I79O 


9838 


23 5 




3987 


9171 


10.5 




1822 


9833 


24 o 




4067 


9135 


II. 

II. 5 


19 

20 


1889 
1908 
1987 
1994 


9820 
9816 
9801 
9799 


24-5 
25 o 


42 
43 


4078 
4147 
4169 
4226 


9131 

9100 
9090 
9063 


12.0 




2O79 


9781 








9048 


12.5 


21 


2085 
2164 


9780 


25.5 




4305 


9026 


13.0 


22 


2182 


9759 


26.0 


^6 


4384 


8988 
8961 





23 


2280 


9737 


26.5 




4462 


8949 



















APPENDIX 



389 



TABLE I. TRIGONOMETRIC (CIRCULAR) FUNCTIONS (Continued) 





u 








U 






Degrees 


Radians 






Degrees 


Radians 






27 o 


0.47 


0.4529 
4540 


0.8916 
8910 


37-5 


o 66 


0.6088 
6131 


0.7934 
7900 


27-S 
28 o 


'"48" 


4617 
4618 
4695 


8870 
8870 
8829 


38.0 
38 5 


67 


6i57 
6210 
6225 


7880 
7838 
7826 




49 


4706 


8823 




68 


6288 


7776 


28.5 
29.0 


50 
51 


4772 
4794 
4848 
4882 


8788 
8776 
8746 
8727 


39-0 
39-5 

40.0 


'"69" 


6293 
6361 
6365 
6428 


7771 
7716 
7713 
7660 


29.5 




4924 


8704 




70 


6442 


7648 


30 o 


52 


4969 
5000 


8678 
8660 


40.5 


71 


6494 
6518 


7604 
7584 




53 


5055 


8628 


41 o 




6561 


7547 


30.5 

31.0 


54 


5075 
5141 
5150 


8616 
8577 
8572 


41-5 


72 
73 


6594 
6626 
6669 


75i8 
7490 
7452 


31 5 




5225 


8526 


42 o 




6691 


7431 




55 


5227 


8525 




74 


6743 


7385 


32.0 
32.5 


56 


5299 

5312 

5373 


8480 

8473 
8434 


42.5 

43 o 


75 


6756 

6816 
6820 


7373 

7317 
7314 




57 


5396 


8419 


43 5 




6884 


7254 


33.0 




5446 


8387 




76 


6889 


7248 


33.5 


58 


548o 
5519 


8 3 6S 
8339 


44.0 


77 


6947 
6961 


7193 
7179 




59 


5564 


8309 


44 5 




7009 


7133 


34.0 




5592 


8290 




78 


7033 


7109 




60 


5646 


8253 


45.O 




7071 


7071 


34-5 




5664 


8241 




79 


7104 


7O39 


35-0 
35- 5 

36.0. 
36.5 
37-0 


61 

62 
'"63" 
64 
' 6s" 


5729 
5736 
5807 
5810 
5878 
5891 
5948 
5972 
6018 
6052 


8197 
8192 
8141 
8i39 
8090 
8080 
8039 
8021 
7986 
796l 





80 
85 
90 
.00 
.10 
.20 
30 
.40 
50 
.60 


7174 
7513 
7833 
8415 
8912 
9320 
9636 
9855 
9975 
9996 


6967 
6600 
6216 
5403 
4536 
3624 
2675 
1700 
0707 
.0292 



The functions of larger angles are: 



Function 


When angle u lies between 


45 and 90 


90 and 180 


180 and 270 


270 and 360 


sin u = 
cos = 


cos (90 M) 
sin (90 ) 


sin (180 u) 
cos (180 M) 


cos (270 u) 
sin (270 ) 


sin (360 u) 
cos (360 M) 



390 



TELEGRAPH ENGINEERING 



TABLE II. EXPONENTIAL FUNCTIONS 






e* 


e- u 


u 


e" 


-* 


u 





r" 





I. 0000 


I. 0000 


0.50 


1.6487 


0.6065 


I.OO 


2.7183 


0.3679 


0.01 


OIOI 


0.9901 


51 


6653 


6005 


02 


7732 


3600 


02 


O2O2 


9802 


52 


6820 


5945 


04 


8292 


3535 


03 


0305 


9704 


S3 


6989 


5886 


06 


8864 


3465 


04 


0408 


9608 


54 


7160 


5827 


08 


9447 


3396 


OS 


0513 


9512 


55 


7333 


5769 


10 


3.0042 


3329 


06 


O6l8 


9418 


56 


7507 


5712 


12 


0649 


3263 


07 


0725 


9324 


57 


7683 


5655 


14 


1268 


3198 


08 


0833 


9231 


58 


7860 


5599 


16 


1899 


3135 


09 


0942 


9139 


59 


8040 


5543 


18 


2544 


3073 


10 


1052 


9048 


60 


8221 


5488 


20 


3201 


3012 


II 


Il63 


8958 


6l 


8404 


5434 


22 


3872 


2952 


12 


1275 


8869 


62 


8589 


5379 


24 


4556 


2894 


13 


1388 


8781 


63 


8776 


5326 


26 


5254 


2837 


14 


1503 


8694 


64 


8965 


5273 


28 


5966 


2780 


IS 


1618 


8607 


65 


9155 


5220 


30 


6693 


2725 


16 


1735 


8521 


66 


9348 


5169 


32 


7434 


2671 


17 


1853 


8437 


67 


9542 


5117 


34 


8190 


2618 


18 


1972 


8353 


68 


9739 


5066 


36 


8962 


2567 


19 


2093 


8270 


69 


9937 


5016 


38 


9749 


2516 


20 


2214 


8187 


70 


2.0137 


4966 


40 


4.0552 


2466 


21 


2337 


8106 


71 


0340 


4916 


42 


1371 


2417 


22 


2461 


8025 


72 


0544 


4868 


44 


2207 


2369 


23 


2586 


7945 


73 


0751 


4819 


46 


3060 


2322 


24 


2712 


7866 


74 


0959 


4771 


48 


3929 


2276 


25 


2840 


7788 


75 


1170 


4724 


50 


4817 


2231 


26 


2969 


7711 


76 


1383 


4677 


52 


5722 


2187 


27 


3100 


7634 


77 


1598 


4630 


54 


6646 


2144 


28 


3231 


7558 


78 


1815 


4584 


56 


7588 


2101 


29 


3364 


7483 


79 


2034 


4538 


58 


8550 


8000 


30 


3499 


7408 


80 


2255 


4493 


60 


9530 


2019 


31 


3634 


7334 


81 


2479 


4449 


62 


5.0531 


1979 


32 


3771 


7261 


82 


2705 


4404 


64 


1552 


1940 


33 


3910 


7189 


83 


2933 


436o 


66 


2593 


1901 


34 


4049 


7118 


84 


3164 


4317 


68 


3656 


1864 


35 


4191 


7047 


85 


3396 


4274 


70 


4739 


1827 


36 


4333 


6977 


86 


3632 


4232 


72 


S84S 


1791 


37 


4477 


6907 


87 


3869 


4190 


74 


6973 


1755 


38 


4623 


6839 


88 


4109 


4148 


76 


8124 


1720 


39 


4770 


6771 


89 


4351 


4107 


78 


9299 


1686 


40 


4918 


6703 


90 


4596 


4066 


80 


6.0496 


1653 


41 


5068 


6637 


91 


4843 


4025 


82 


1719 


1620 


42 


5220 


6570 


92 


5093 


3985 


84 


2965 


1588 


43 


5373 


6505 


93 


5345 


3946 


86 


4237 


1557 


44 


5527 


6440 


94 


5600 


3906 


88 


5535 


1526 


45 


5683 


6376 


95 


5857 


3867 


90 


6859 


1496 


46 


5841 


6313 


96 


6117 


3829 


92 


8210 


1466 


47 


6000 


6250 


97 


6379 


3791 


94 


9588 


1437 


48 


6161 


6188 


98 


6645 


3753 


96 


7.0993 


1409 


49 


6323 


6126 


99 


6912 


37i6 


98 


2427 


1381 



APPENDIX 



391 



TABLE II. EXPONENTIAL FUNCTIONS (Continued) 



u 


t 


_u 




u 


t 


*-" 


2.OO 


7.3891 


0.13534 


4-50 


00.017 


O.OIIIOO 


05 


7679 


12873 


55 


94.632 


010567 


10 


8.1662 


12246 


60 


99.484 


010052 


IS 


5849 


11648 


65 


104.585 


009562 


20 


9 . 0250 


11080 


70 


109.947 


009095 


25 


4877 


10540 


75 


H5.584 


008652 


30 


9742 


10026 


80 


I2I.5IO 


008230 


35 


10.4856 


09537 


85 


127.740 


007828 


40 


11.0232 


09072 


90 


134-290 


007447 


45- 


11.5883 


08629 


95 


I4LI75 


007083 


50 


12.1825 


08209 


S.oo 


I48.4U 


006738 


55 


12.8071 


07808 


05 


156.022 


006409 


60 


13.4637 


07427 


10 


164.022 


006097 


65 


14.1540 


07065 


IS 


172.431 


005799 


70 


14.8797 


06721 


20 


181 . 272 


005517 


75 


15.6426 


06393 


25 


190.566 


005248 


80 


16.4446 


06081 


30 


200.337 


004992 


85 


17-2878 


05784 


35 


210.608 


004748 


90 


18.1741 


05502 


40 


221 . 406 


004517 


95 


19.1060 


05234 


45 


232.758 


004296 


3.00 


20.086 


04979 


50 


244.692 


004087 


05 


21.115 


04736 


55 


257.238 


003888 


10 


22.198 


0450S 


60 


270.426 


003698 


15 


23.336 


04285 


65 


284.291 


003518 


20 


24-533 


04076 


70 


208.867 


003346 


25 


25.790 


03877 


75 


3I4.I9I 


003183 


30 


27.113 


03688 


80 


330.300 


003028 


35 


28.503 


03508 


85 


347-234 


002880 


40 


29.964 


03337 


90 


365.037 


002739 


45 


31.500 


03175 


95 


383.753 


002606 


50 


33-115 


03020 


6.00 


403.43 


0024788 


55 


34.813 


02872 


7.00 


1,006.6 


0009119 


60 


36.598 


02732 


8.00 


2,98l.O 


00033546 


65 


38.475 


02599 


9.00 


8,103.1 


00012341 


70 


40.447 


02472 


10.00 


22,026 


000045400 


75 


42.521 


02352 


11.00 


59,874 


000016702 


80 


44-701 


02237 


12. OO 


162,754 


000006144 


85 


46-993 


02128 


13.00 


442,413 


0000022603 


90 


49-402 


02024 


14.00 


1,202,600 


00000083153 


95 


51-935 


01925 


15.00 


3,269,000 


00000030590 


4.00 


54.598 


01832 


16.00 


' 8,886,100 


00000011253 


05 


57-397 


01742 


17.00 


24,155,000 


000000041399 


10 


60.340 


01657 


18.00 


65,660,000 


000000015230 


IS 


63.434 


01576 


19.00 


178,482,000 


0000000056028 


20 


66.686 


01500 


20.00 


485,165,000 


0000000020612 


25 


70.105 


01426 


21.00 


1,318,800,000 


00000000075826 


30 


73-700 


OI3S7 


22.00 


3,584,000,000 


00000000027895 


35 


77.478 


01291 


23.00 


9,744,800,000 


00000000010262 


40 


81.451 


01228 


24.OO 


26,489,100,000 


00000000003775 


45 


85.627 


01168 


25.00 


72,004,800,000 


00000000001389 



39 2 



TELEGRAPH ENGINEERING 



TABLE III. LOGARITHMS TO BASE 10 



No. 





I 


2 


3 


4 


5 


6 


7 


8 


9 


10 


00000 


00432 


00860 


01284 


01703 


02119 


02530 


02938 


03342 


03743 


ii 


04139 


04532 


04922 


05307 


05690 


06070 


06446 


06819 


07188 


07555 


12 


07918 


08279 


08637 


08990 


09342 


09691 


10037 


10380 


10721 


11059 


13 


1 1394 


11727 


12057 


12385 


12710 


13033 


13354 


13672 


13988 


14301 


14 


14613 


14922 


15229 


15533 


15836 


16137 


16435 


16732 


17026 


I73I9 


IS 


17609 


17898 


18184 


18469 


18752 


19033 


I93I2 


19590 


19866 


20140 


16 


20412 


20683 


20952 


21219 


21484 


21748 


2201 1 


22272 


22531 


22789 


17 


23045 


23300 


23553 


23805 


24055 


24304 


24551 


24797 


25042 


25285 


18 


25527 


25768 


26007 


26245 


26482 


26717 


26951 


27184 


27416 


27646 


19 


27875 


28103 


28330 


28556 


28780 


29003 


29226 


29447 


29667 


29885 


20 


30103 


30320 


30535 


30749 


30963 


3H75 


31386 


31597 


31806 


32015 


21 


32222 


32428 


32633 


32838 


33041 


33244 


33445 


33646 


33846 


34044 


22 


34242 


34439 


34635 


34830 


35025 


352i8 


3541 1 


35603 


35793 


35984 


23 


36173 


36361 


36549 


36736 


36922 


37107 


37291 


37475 


37658 


37840 


24 


38021 


38202 


38382 


38561 


38739 


38916 


39094 


39270 


39445 


396i9 


25 


39794 


39967 


40140 


40312 


40483 


40654 


40824 


40993 


41162 


41330 


26 


41497 


41664 


41830 


41996 


42160 


42325 


42488 


42651 


42813 


42975 


27 


43136 


43297 


43457 


43616 


43775 


43933 


44091 


44248 


44404 


44560 


28 


44716 


44871 


45025 


45179 


45332 


45484 


45637 


45788 


45939 


46000 


29 


46240 


46389 


46538 


46687 


46835 


46982 


47129 


47276 


47422 


47567 


30 


47712 


47857 


48001 


48144 


48287 


48430 


48572 


48714 


48855 


48996 


31 


49136 


49276 


49415 


49554 


49693 


49831 


49969 


50106 


50243 


50379 


32 


50515 


50651 


50786 


50920 


51055 


5H89 


51322 


51455 


51587 


51720 


33 


5I85I 


51983 


52114 


52244 


52375 


52504 


52634 


52763 


52892 


53020 


34 


53148 


53275 


53403 


53529 


53656 


53782 


53908 


54033 


54158 


54283 


35 


54407 


54531 


54654 


54777 


54900 


55022 


55145 


55267 


55388 


55509 


36 


55630 


55751 


55871 


55991 


56110 


56229 


56348 


56467 


56585 


56703 


37 


56820 


56937 


57054 


57I7I 


57287 


57403 


57519 


57634 


57749 


57863 


38 


57978 


58093 


58206 


58320 


58433 


58546 


58659 


58771 


58883 


58995 


39 


59106 


59218 


59328 


59439 


59550 


59660 


59770 


59879 


59989 


60097 


40 


60206 


60314 


60423- 


60531 


60638 


60745 


60853 


60959 


61066 


61172 


41 


61278 


61384 


61490 


61595 


61700 


61805 


61009 


62014 


62118 


62221 


42 


62325 


62428 


62531 


62634 


62737 


62839 


62941 


63043 


63144 


63246 


43 


63347 


63448 


63548 


63649 


63749 


63849 


63949 


64048 


64147 


64246 


44 


64345 


64444 


64542 


64640 


64738 


64836 


64933 


65031 


65128 


65225 


8 


65321 
66276 


65418 
66370 


65514 
66464 


65609 
66558 


65706 
66652 


65801 
66745 


65896 
66839 


65992 
66932 


66087 
67025 


66181 
67117 


47 


67210 


67302 


67394 


67486 


67578 


67669 


67761 


67852 


67943 


68034 


48 


68124 


68215 


68305 


68395 


68485 


68574 


68664 


68753 


68842 


68931 


49 


69020 


69108 


69197 


69285 


69373 


69461 


69548 


69636 


69723 


69810 


50 


69897 


69984 


70070 


70157 


70243 


70329 


70415 


70501 


70586 


70672 


Si 


70757 


70842' 


70927 


71012 


71096 


71181 


71265 


71349 


71433 


7I5I7 


52 


71600 


71684 


71767 


71850 


71933 


72016 


72009 


72181 


72263 


72346 


53 


72428 


72509 


72591 


72673 


72754 


72835 


72916 


72997 


73078 


73159 


54 


73239 


73320 


73399 


73480 


7356o 


73639 


73719 


73799 


73 fl 8 


73957 


55 


74036 


74H5 


74194 


74273 


74351 


74429 


74507 


74586 


74663 


74741 


56 


74819 


74896 


74974 


75051 


75128 


75205 


75282 


75358 


75435 


755U 


57 


75587 


75664 


75740 


75815 


75891 


75967 


76042 


76118 


76193 


76268 


58 


76343 


76418 


76492 


76567 


76641 


76716 


76790 


76864 


76938 


77012 


59 


77085 


77159 


77232 


77305 


77379 


77452 


77525 


77597 


77670 


77743 


60 


77815 


77887 


7796o 


78032 


78104 


78176 


78247 


78319 


78390 


78462 



APPENDIX 



393 



TABLE III. -LOGARITHMS TO BASE 10. - (Continued) 



No. 





I 


2 


3 


4 


5 


6 


7 


8 


9 


61 


78533 


78604 


78675 


78746 


78817 


78888 


78958 


79029 


79099 


79169 


62 


79239 


79309 


79379 


79449 


79518 


79588 


79657 


79727 


79796 


79865 


63 


79934 


80003 


80072 


80140 


80209 


80277 


80346 


80414 


80482 


80550 


64 


80618 


80686 


80754 


80821 


80889 


80956 


81023 


81090 


81158 


81224 


65 


81291 


81358 


81425 


81491 


81558 


81624 


81690 


81757 


81823 


81889 


66 


81954 


82020 


82086 


82151 


82217 


82282 


82347 


82413 


82478 


82543 


67 


82607 


82672 


82737 


82802 


82866 


82930 


82995 


83059 


83123 


83187 


68 


83251 


83315 


83378 


83442 


83506 


83569 


83632 


83696 


83759 


83822 


69 


83885 


83948 


84011 


84073 


84136 


84198 


84261 


84323 


84386 


84448 


70 


84510 


84572 


84634 


84606 


84757 


84819 


84880 


84942 


85003 


85065 


71 


85126 


85187 


85248 


85309 


85370 


85431 


85491 


85552 


85612 


85673 


72 


85733 


85794 


85854 


85914 


85974 


86034 


86094 


86153 


86213 


86273 


73 


86332 


86392 


86451 


86510 


86570 


86629 


86688 


86747 


86806 


80864 


74 


86923 


86982 


87040 


87099 


87157 


87216 


87274 


87332 


87390 


87448 


75 


87506 


87564 


87622 


87680 


87737 


87795 


87852 


87910 


87967 


88024 


76 


88081 


88138 


88196 


88252 


88309 


88366 


88423 


88480 


88536 


88593 


77 


88649 


88705 


88762 


88818 


88874 


88930 


88986 


89042 


89098 


89154 


78 


89209 


89265 


89321 


89376 


89432 


89487 


89542 


89597 


89653 


89708 


79 


89763 


89818 


89873 


80927 


89982 


00037 


90091 


90146 


90200 


00255 


80 


00309 


90363 


90417 


90472 


90526 


00580 


90634 


90687 


90741 


90795 


81 


90848 


90002 


90956 


91009 


91062 


91116 


91169 


91222 


91275 


91328 


82 


9I38I 


91434 


91487 


91540 


91593 


91645 


91698 


9I75I 


91803 


91855 


83 


91908 


91960 


92012 


92065 


92117 


92169 


92221 


92273 


92324 


92376 


84 


92428 


92480 


92531 


92583 


92634 


92686 


92737 


92789 


92840 


92891 


85 


92942 


92993 


93044 


93095 


93146 


93197 


93247 


93298 


93349 


93399 


86 


93450 


93500 


93551 


93601 


93651 


93702 


93752 


93802 


93852 


93902 


87 


93952 


94002 


94052 


94IOI 


94I5I 


94201 


94250 


94300 


94349 


94398 


88 


94448 


94498 


94547 


94596 


94645 


94694 


94743 


94791 


94841 


94890 


89 


94939 


94988 


95036 


95085 


95U4 


95182 


95231 


95279 


95328 


95376 


90 


95424 


95472 


95521 


95569 


95617 


95665 


95713 


95761 


95809 


95856 


91 


95904 


95952 


95999 


96047 


96095 


96142 


96190 


96237 


96284 


96332 


92 


96379 


96426 


96473 


96520 


96567 


96614 


96661 


96708 


06755 


96802 


93 


96848 


96895 


96942 


96988 


97035 


97081 


97128 


97174 


97220 


97267 


94 


97313 


97359 


97405 


97451 


97497 


97543 


97589 


97635 


97681 


97727 


95 


97772 


97818 


97864 


97909 


97955 


98000 


98046 


98091 


98137 


98182 


96 


98227 


98272 


98318 


98363 


98408 


98453 


98498 


98543 


98588 


98632 


97 


98677 


98722 


98767 


98811 


98856 


98900 


98945 


98089 


99034 


99078 


98 


99123 


99167 


9921 1 


99255 


99300 


99344 


99388 


99432 


09476 


99520 


99 


99564 


99607 


99651 


99695 


99739 


99782 


99826 


99870 


99913 


99957 



Characteristics of Logarithms: 
log 4030 =3.6053 
log 403 =2.6053 
log 40.3=1.6053 



log 4.03 =0.6053 
log 0.403 =1.6053 
log 0.0403 =2.6053 
log 0.00403 =3. 6053 



Useful Constants: 



= 2.7182818 

IT = 3.1415927 

i radian 57.29578 degrees. 
i degree = 0.0174533 radian. 



394 



TELEGRAPH ENGINEERING 



TABLE IV.-HYBERBOLIC FUNCTIONS 



M. 


sinh u. 


cosh . 


. 


sinh w. 


cosh . 


. 


sinh . 


coshw. 


o.oo 


0.0000 


I .OOOO 


0.50 


0.5211 


I .1276 


i .00 


1.1752 


I-543I 


OI 


0100 


OOOI 


51 


5324 


1329 


05 


2539 


6038 


02 


O2OO 


OOO2 


52 


5438 


1383 


10 


3356 


6685 


03 


0300 


OOO5 


53 


5552 


1438 


15 


4208 


7374 


04 


O4OO 


. 0008 


54 


5666 


1494 


20 


5095 


8107 


05 


0500 


OOI3 


55 


5782 


1551 


2 5 


6019 


8884 


06 


O6OO 


OOl8 


56 


5897 


1609 


30 


6984 


1.9709 


07 


O7OI 


OO25 


57 


6014 


.1669 


35 


7991 


2-0583 


08 


080I 


0032 


58 


6131 


1730 


40 


1.9043 


1509 


09 


OQOI 


OO4I 


59 


6248 


1792 


45 


2.0143 


2488 


10 


1002 


0050 


60 


6367 


1855 


50 


1293 


3524 


II 


1 102 


006l 


61 


6485 


1919 


55 


2496 


4619 


12 


1203 


0072 


62 


6605 


1984 


60 


3756 


5775 


13 


1304 


0085 


63 


6725 


2051 


65 


5075 


f 

6 995 


14 


1405 


0098 


64 


6846 


2119 


70 


6456 


8283 


IS 


1506 


OII3 


65 


6967 


2188 


75 


7904 


2.9642 


16 


1607 


OI28 


66 


7090 


2258 


80 


2.9422 


3.1075 


17 


I 7 08 


0145 


67 


7213 


2330 


85 


3-IOI3 


2585 


18 


1810 


Ol62 


68 


7336 


2402 


90 


2682 


4177 


19 


1911 


0181 


69 


7461 


2476 


95 


4432 


5855 


20 


2013 


O2OI 


70 


7586 


2552 


2.00 


6269 


7622 


21 


2115 


O22I 


7i 


7712 


2628 


05 


3-8196 


3-9483 


22 


2218 


0243 


72 


7838 


2706 


10 


4.0219 


4-1443 


23 


2320 


0266 


73 


79 66 


2785 


15 


2342 


3507 


24 


2423 


0289 


74 


8094 


2865 


20 


4571 


5679 


25 


2526 


03M 


75 


8223 


2947 


25 


6912 


4.7966 


26 


2629 


0340 


76 


8353 


3030 


30 


4-9370 


5-0372 


2? 


2733 


0367 


77 


8484 


3114 


35 


5.I95I 


2905 


28 


2837 


0395 


78 


8615 


3199 


40 


4662 


5569 


29 


2941 


0423 


79 


8748 


3286 


45 


5-7510 


5-8373 


30 


3045 


0453 


80 


8881 


3374 


50 


6.0502 


6.1323 


31 


3 J 5o 


0484 


81 


9015 


3464 


55 


3645 


4426 


32 


3255 


0516 


82 


9150 


3555 


60 


6.6947 


6 . 7690 


33 


336o 


0549 


83 


9286 


3647 


65 


7.0417 


7.1123 


34 


3466 


0584 


84 


9423 


3740 


70 


4063 


4735 


35 


3572 


0619 


85 


956i 


3835 


75 


7.7894 


7-8533 


36 


3678 


0655 


86 


9700 


3932 


80 


8.1919 


8.2527 


37 


3785 


0692 


87 


9840 


4029 


85 


8.6150 


8.6728 


38 


3892 


0731 


88 


0.9981 


4128 


90 


9.0596 


9.1146 


39 


4000 


0770 


89 


I. 0122 


4229 


95 


9.5268 


9-5791 


40 


4108 


0811 


90 


0265 


433i 


3-00 


10.0179 


10.0677 


4i 


4216 


0852 


9i 


0409 


4434 


05 


10.5340 


10.5814 


42 


4325 


0895 


92 


0554 


4539 


10 


11.0765 


11.1215 


43 


4434 


0939 


93 


0700 


4645 


15 


11.6466 


11.6895 


44 


4543 


0984 


94 


0847 


4753 


20 


12.2459 


12.2866 


45 


4653 


1030 


95 


0995 


4862 


25 


12.8758 


12.9146 


46 


4764 


1077 


96 


1144 


4973 


30 


13-5379 


13.5748 


47 


4875 


1125 


97 


1294 


5085 


35 


14-2338 


14.2689 


48 


4986 


"74 


98 


1446 


5199 


40 


14.9654 


14.9987 


49 


5098 


1225 


99 


1598 


5314 


45 


15-7343 


15.7661 



APPENDIX 



395 



TABLE IV. HYPERBOLIC FUNCTIONS. (Continued) 



. 


sinh . 


cosh M. 


u. 


sinh u. cosh u. 


3.50 


16.5426 


16.5728 


6.00 


201.7132 


201.7156 


55 


I7-3923 


17.4210 


05 


212.0553 


212.0577 


60 


18.2855 


18.3128 


IO 


222.9278 


222.9300 


65 


19.2243 


19.2503 


15 


234.3576 


234.3598 


70 


20.2113 


20.2360 


20 


246.3735 


246.3755 


75 


21.2488 


21.2723 


25 


259.0054 


259.0074 


80 


22.3394 


22.3618 


30 


272.2850 


272.2869 


85 




23.5072 


35 


286.2455 


286.2472 


90 


24.6911 


24.7113 


40 


300.9217 


300.9233 


3-95 


25-958I 


25-9773 


45 


316.3504 


316.3520 


4.00 


27.2899 


27.3082 


So 


332.5700 


332.5716 


5 


28 . 6900 


28.7074 


55 


349.6213 


349.6228 


IO 


30.1619 


30.1784 


60 


367.5469 


367.5483 


15 


31.7091 


31.7249 


65 


386.3915 


386.3928 


20 


33-3357 


33-3507 


70 


406 . 2023 


406.2035 


25 


35-0456 


35.0598 


75 


427.0287 


427.0300 


3 


36-8431 


36.8567 


80 


448.9231 


448.9242 


35 


38.7328 


38.7457 


85 


471-9399 


471-9410 


40 


40.7193 


40.7316 


90 


496.1369 


496.1379 


45 


42.8076 


42.8193 


6-95 


521.5744 


521.5754 


50 


45.0030 


45.0141 


7.00 


548.3161 


548.3170 


55 


47.3109 


47-3215 


5 


576.4289 


576.4298 


60 


49-7371 


49.7472 


IO 


605.9831 


605.9839 


65 


52.2877 


52.2973 


15 


637.0526 


637.0534 


70 


54.9690 


54.9781 


20 


669.7150 


669.7157 


75 


57.7878 


57.7965 


25 


704.0521 


704.0528 


80 


60.7511 


60.7593 


30 


740.1497 


740.1504 


85 


63.8663 


63.8741 


35 


778.0980 


778.0986 


90 


67.1412 


67.1486 


40 


817.9919 


817.9925 


4-95 


70.5839 


70.5910 


45 


859.93I3 


859.9318 


5-oo 


74.2032 


74.2099 


50 


904.0210 


904.0215 


05 


78.0080 


78.0144 


55 


950.37H 


950.3716 


10 


82.0079 


82.0140 


60 


999.0976 


999.0981 


IS 


86.2128 


86.2186 


65 


1050.323 


20 


90.6334 


90.6389 


70 


II04.I74 


25 


95-2805 


95.2858 


75 


1160.786 


30 


100.1659 


100.1709 


80 


1220.301 


35 


105.3018 


105.3065 


85 


1282.867 


40 


110.7009 


110.7055 


90 


1348.641 


45 


116.3769 


116.3812 


7-95 


1417.787 


5 


122.3439 


122.3480 


8.00 


1490.479 


55 


128.6168 


128.6207 


05 


1566.698 


60 


135-2114 


135.2150 


10 


1647 . 234 


65 


142.1440 


142.1475 


IS 


1731.690 


70 


149.4320 


149-4354 


20 


1820.475 


75 


157-0938 


157.0969 


25 


I9I3.8I3 


80 


165.1482 


165.1513 


30 


2011.936 


85 


173.6158 


173.6186 


35 


2115.090 


90 


182.5173 


182.5201 


40 


2223.533 


95 


191.8754 


191.8780 


45 


2337-537 



INDEX 



Abbreviations on ticker tapes, 121. 
used in telegraph transmission, 28. 
Added resistance of Field quad., 93. 
Admittance, dielectric, 316. 
Advantage of double-current duplex, 

74- 
using two generators on simplex 

lines, 342. 
Aerial cables, 269. 

installation of, 272. 
lines, 253. 

Alarm indicators, 210. 
Alarms of fire, transmission of, 189. 

public, 200. 
Alphabets, telegraph, 26, 121, 164, 

356. 
Alternating-current track relays, 

246. 
transmission theory, 304. 

illustration of, 330. 
Armor on cables, 380. 
Arresters, lightning, 135, 260. 
Arrival curves on cables, 353. 
Artificial cables, 372. 
lines, 47, 51. 

calculation of, 47, 62, 67, 71. 
Atkinson, Richard L., repeater, 40. 
Attenuation coefficient, 311. 
Automatic block signals, 225. 
fire-alarm repeaters, 206. 
repeaters, 37. 

retransmission over cables, 368. 
telegraphy, 108. 
transmitter, no, 122. 



Auto-transformers in eliminating 

line induction, 292. 
Ayrton, Prof. William E., receiver 

resistance, 338. 

Balanced circuit, conditions of, 52. 
Balancing polar duplex, 59. 

quadruplex, 93. 
Barclay, John C., printing telegraph, 

121. 

Batteries, location on lines, 6. 
primary, 20. 
secondary, 21. 

Baudot, Jean M.E., printer, 133, 163. 
Bell-striking machines, 202. 
Block signals, automatic, 237. 
for electric roads, 231. 
for steam roads, 239. 
location of automatic, 232. 
manual systems, 231. 
one-rail system, 243. 
TDB system, 235. 
two-rail system, 244. 
types of, 224. 

Bonding of cable sheaths, 279. 
Bonds, impedance track, 244. 
Boxes, cable pole, 277. 
fire-alarm, 192. 
police signal, 218. 
Bridge duplex, 67. 

current in relay of, 345. 
direct-point repeater, 79. 
Wheatstone, 67, 373. 
Brooklyn fire-alarm system, 212. 



397 



398 



INDEX 



Brown, Sidney G., drum relay, 368. 
Buckingham, Charles L., printer, 133. 
Bunnell keys, 8. 
Burry, John, printing telegraph, 133. 

Cable keys, 363. 

letters, 382. 

service, 381. 

splices, 276. 

tariffs, 381. 

telegraphy, theory of, 347. 
Cables, artificial, 372. 

attenuation constant of, 312. 

capacity of, 287. 

constants of some, 381. 

design of submarine, 375. 

installation of, 272. 

telegraph, 269. 
Capacity of cables, 287. 

line wires, 284. 
Catlin, Fred, repeater, 42. 
Cells, voltaic, 20. 
Central stations, fire-alarm, 202. 
Chapman, Winthrop M., block sig- 
nals, 239. 
Characteristic impedance of line, 

3 r 9- 

Cipher messages, 151. 
Circuits on Northern Pacific, 158. 
Clapp, Martin H., statistics, 158. 
Closed-circuit Morse system, 2, 5. 
Code, Barclay printing, 121. 

cable, 356. 

Continental, 25. 

Morse, 25. 

Murray multiplex, 164. 

Phillips punctuation, 25. 

words, 150. 

Cole, Frederick W., repeater, 206. 
Combination fire-alarm circuits, 212. 
Common-battery telephone, 293. 



Composite signalling, 296. 

railway, 298. 
Condensers in series with cables, 365. 

with artificial lines, 52. 
Conductance, leakage, 287. 
Conductors, constants of, 262, 282. 
Conduit, underground, 274. 
Continental telegraph code, 25, 356. 
Continuity-preserving pole-chang- 
ers, 58. 

transmitters, 50. 
Copper-clad wire, 29. 
inductance of, 284. 

line wire, 29, 262. 
Corrosion of cable sheaths, 277. 
Cosines, table of, 388, 394. 
Crane, Moses G., fire-alarm box, 194. 
Creed, Frederick G., printer, 133. 
Cr chore, Dr. Albert C., cable signal- 
ling, -3 74. 

duplex-diplex, 102. 
CR Law, 364. 
Cross-arms, pole, 259. 
Current distribution equations, 308. 
general, 329. 

in duplex circuits, 50, 62, 69, 75. 

in leaky lines, 334. 

propagation over lines, 303. 

ratio in quadruplex, 93. 

received over cable, 352. 

sources, 20. 

variation in quadruplex, 92. 

D'Arsonval, Dr. Arsene, galvanome- 
ter, 360. 
Davis, Minor M., duplex, 63. 

quadruplex, 96. 
Day letters, 152. 
Dean, Robert L., printer, 133. 
Deferred cable service, 381. 

overland service, 152. 



INDEX 



399 



Delany, Patrick B., multiplex tele- 
graph, 162. 

Desk, police central-office, 221. 
D'Humy, Fernand E., repeater, 42. 

reperforator, 114. 

Diehl, Clark ., relay scheme, 95, 97. 
Dielectric admittance, 316. 

permittivity, 286. 
Differential duplex, 46. 

neutral relay, 46. 

polarized relay, 55. 
Diplex signalling, 86. 
Direct-current transmission theory, 

305 334- 

illustration of, 338. 
point repeaters, 76. 
Disk railway signals, 227. 
Distance of transmission over leaky 

lines, 32. 

over perfectly-insulated lines, 4. 
Distributing frames, 143. 
Distributors, synchronous, 164. 
Disturbances, inductive, 288. 

elimination of, 290. 
Dot-frequency, 304, 356. 
Double-block condenser scheme, 373. 

current duplex, 74. 
Dry-core cables, 269. 
Duplex automatic telegraphy, 113. 
balancing, 59. 

Barclay, printing telegraph, 126. 
bridge, 67. 

cable telegraphy, 372. 
Davis and Eaves, 63. 
differential, 45. 
diplex signalling, 102. 
double-current, 74. 
leak, 62. 
Morris, 66. 
polar, 56. 
improved, 63. 



Duplex, Postal Telegraph Co., 63. 

repeaters, 76. 

short-line, 66. 

signalling, theory of, 344. 

single-current, 46. 

Stearns, 46. 

switchboard circuits, 142. 

telegraphy, 45. 

Western Union Co., 71. 
Dwarf railway signals, 226. 

Earth as return path, i, 279. 

resistance, 280. 
Eaves, Augustus J., duplex, 63. 

quadruplex, 96. 
Economic cable determination, 376. 

span lengths, 266. 
Edison, Thomas A., battery, 20, 22. 

quadruplex, 85. 

Electric railways, signals for, 231, 
237, 242. 

telegraphy, see Telegraphy. 
Electrolysis of cable sheaths, 277. 
Electromagnetic induction, 288. 
Electrostatic induction, 288. 
Equivalent sine curves, 304. 
Essick, Samuel V., printer, 133. 
Exponential functions, 390. 

Faraday, Prof. Michael, law of, 278. 

polarizing effect, 183. 
Fibre stress in poles, 256. 
Field, Stephen D., key system, 91. 
Fire-alarm boxes, 192. 

central stations, 202. 

devices at apparatus houses, 210. 

repeaters, 206. 

systems, operation of, 212. 
statistics of, 221. 

telegraphy, 189. 

transmitters, 203. 



4oo 



INDEX 



Fourier, Jean B. /., series, 304, 348. 
Fournier, Prof., television, 183. 
Fowle, Frank F. , copper-clad wire, 2 84. 
Freir, Samuel P., neutral relay, 96. 
Frequency, dot-, 304, 356. 

reversal-, 356. 
Fuller, John, battery, 20. 
Fuses, 135. 

Galvanized iron wire, 29, 262. 

Gamewell, John N., fire-alarm box, 
194. 

Gardiner, James M., fire-alarm box, 
194. 

General equations of line current 
and voltage, 329. 

Generators, 23. 

Ghegan, John /., repeater, 42. 

Gintl, Dr. Wilhelm, duplex, 45. 

Gong circuits, fire-alarm, 211. 
electromechanical, 210. 

Gott, John, cable signalling, 369. 

Gravity battery, 20. 

Gray, Prof. Elisha, telautograph, 170. 

Ground as return path, i, 279. 
connections, 281. 
resistance, 2, 280. 

Grounded capacity of cables, 287. 

Growth of current in cables, 351. 
in relay, 14, 35. 

Guild, George R., induction tele- 
graph, 186. 

Guying of aerial lines, 257. 

Half-set repeaters, 80. 
Handling of telegraphic traffic, 154. 
Hangers, cable, 272. 
Hard-drawn copper wire, 29, 262. 
Heaviside, Oliver, earth resistance, 

279. 
wire capacity, 285. 



High-potential leak duplex, 62. 
Horton, Lewis, repeater, 42. 
Howler, telephone, 300. 
Hughes, Prof. David E., printer, 133. 
Hyperbolic functions, table of, 394. 
use of, 18, 265, 284, 322. 

Ideal line, velocity of wave propaga- 
tion on, 313. 
Impedance at ends of line, 326. 

characteristic, of line, 319. 

conductor, 316. 

of relays, 13. 

surge, 319, 357. 

track bonds, 244. 
Indicators, fire-alarm, 210. 
Inductance of line wires, 283. 
Induction repeaters, 187. 

telegraphs, 184. 
Inductive line interference, 288. 

shunt for recorders, 373. 
Installation of aerial cables, 272. 
Instrument tables, 145. 
Insulation resistance of cables, 270, 

288, 379. 
of lines, 30, 287. 
Insulators, 254. 
Interlacing of circuits, 194. 
Interlocking machines, 247. 

plant signals, 225, 247. 
Intermediate offices, 6. 
Iron line wire, 29, 262. 

Jacks, pin-, 139. 

spring-, 138. 
Joints in line wire, 253. 
Joker fire-alarm circuits, 211. 

Kelvin, Lord (Wm. Thomson), CR 

law, 364. * C 
recorder, 360. 



INDEX 



401 



Kennelly, Dr. Arthur E., hyperbolic 

functions, 321, 324. 
receiver resistance, 357. 
Keyboard, ticker, 119. 
Keys, 8, 363. 

Kinsley, Carl, printer, 133. 
Kirnan, William H., repeater, 206. 
Kleinschmidt, Edward E., perforator, 

122. 
Korn, Dr. Artur, telephotography, 

175- 

Lalartde, F. de, battery, 20. 
Leak duplex, 62. 

relays, 78. 

resistance of Field quad., 93. 
Leakage, line, 30. 
Leakance of lines, 287. 
Leclanche", Georges, battery, 20. 
Legibility of recorder tapes, 359. 
Letters, cable, 382. 

day and night, 152. 
Light-relay, 177. 

signals on railways, 225. 
Lightning arresters, 135, 260. 
Lines, aerial open, 253. 

artificial, 47, 50. 

capacity of, 284. 

inductance of, 283. 

inductive interference on, 288. 

leakance of, 287. 

resistance of, 29, 283. 

telegraph, 28. 
Local circuits, 4. 

duplex and quadruplex, 141. 
Locking sheet, 250. 
Logarithms, table of, 392. " 
Loop switchboards, 141. 
Low, A. M., television, 184. 
Lowy, Heinrich, earth resistance, 



Maclaurin, Colin, series, 322. 
Magnet bobbins, windings of, 13. 
Magneto telephone circuit, 293. 
Main switchboards, 139. 
Malcolm, Dr. Henry W., law, 364. 
Mallet perforator, 109. 
Manholes, 275. 

Manual block signals, 224, 231. 
Marino, Algeri, telephotography, 

181. 

Marking current, 112. 
Matthews, W. N. and Claude L., con- 
duit costs, 274. 

Maver, William, Jr., repeater, 42. 
Mclntyre, C., connector, 253. 
Mecograph transmitting key, 10. 
Mercadier, Prof. Ernest J. P., tele- 
graph system, 162. 
Messages, telegraph, types of, 150. 
Messenger wires, 272. 
Military induction telegraphs, 184. 
Milliken, George F., repeater, 42. 
Morkrum printer (Chas. L. Krum 

and Jay Morton), 133. 
Morris, Robert H., duplex, 66. 
Morse, Prof. Samuel F. B., code, 25. 

telegraph system, i. 
Motor-generator sets, 24. 

switchboard connections of, 147. 
Muirhead, Dr. Alexander, artificial 
cable, 372. 

relay, 368. 

Multiplex, Murray, page printer, 
163. 

telegraphy, 162. 
Municipal telegraphs, 189. 
Munier, Claude J. A., printing 

telegraph, 133. 

Murray, Donald, printer, 133, 163. 
Mutual capacity of wires, 285. 

inductance of wires, 283. 



402 



INDEX 



Neilson, Hugh, repeater, 42. 
Neomon, interpretation of, 316. 
Nernst, Dr. Wallher, lamp, 177. 
Neutral relays, construction of, 12. 

differential, 46. 

effect of current reversals in, 94. 

with extra coil, 96. 
Nicol, William, prism, 183. 
Night letters, 152. 
Non-interfering repeater, 206. 

signal boxes, 194. 

Open-circuit Morse system, 5. 
Oscillogram of current growth, 14. 
Overlap railway signal system, 
233- 

Paper winder, 16^ 211. 
Patching cords, 139. 
Peg-switch panel, 136. 
Perforator, keyboard, 122. 

Kleinschmidt, 122. 

mallet, 109. 

Permittivity of dielectric, 286. 
Phantom telephone circuit, 296. 
Phantoplex system, 103. 
Phillips, Walter P., punctuation 
code, 25. 

repeater, 37, 80. 

Photographs, transmission of, 175. 
Physical telephone circuits, 296. 
Picard, Pierre, cable signalling, 367. 

telegraph system, 162. 
Pins, insulator, 254. 
Plugs for pin jacks, 139. 
Polar direct-point repeater, 76. 

duplex, 56. 
Polarized block-signal system, 240. 

relays, 53, 125. 

sounder, 186. 
Polar-neutral track relay, 240. 



Pole boxes, cable, 277. 
changer, 56. 

Western Union, 72. 
spacing, economic, 266. 
telegraph, 254. 
Police patrol boxes, 218. 
central offices, 220. 
telegraphs, 217. 

statistics of, 221. 

Pollak, Dr. Anloine, writing tele- 
graph, 167. 
Postal polar duplex, 63. 

quadruplex, 96. 
Power switchboards, 146. 
Primary batteries, 20. 
Printing telegraph, Barclay, 121. 

various, mention of, 133. 
Printing telegraphy, 115. 
Problems, 43, 83, 106, 134, 161, 188, 

223, 251, 300, 346, 385. 
Propagation constant of line, 318. 
Protective devices, 135. 

resistances, 24, 6 1. 
Protectors, 145. 
Public fire alarms, 200. 

Quadrantal operator, 316. 
Quadruplex, Davis-Eaves, 96. 

Field key system, 91. 

Postal Telegraph Co., 96. 

repeaters, 100. 

signalling, theory of, 344. 

switchboard circuits, 141. 

systems, operation of, 87. 

telegraphy, 85. 

Western Union, 98. 

Railway composite signalling, 298. 
interlocking signals, 247. 
operation, the telegraph in, 157. 
signal systems, 224. 



INDEX 



403 



Receiver, Barclay printing, 126. 

Korn telephotographic, 177. 

Pollak-Virag, 168. 

Receiving instruments, best resist- 
ance of, 357. 
best winding for, 16. 
Recorder, siphon, 360. 

Wheatstone, 108, 114. 
Reflection coefficient, 320. 
Registers, 15, 210. 
Relay current in bridge duplex, 

345- 
Relays, ampere-turns for, 4. 

cable, 368. 

construction of neutral, 12. 

current growth in neutral, 14. 

design of, 35. 

Diehl arrangement of, 95, 97. 

differential neutral, 46. 
polarized, 55, 125. 

leak, 78. 

light-, 177. 

phantoplex, 104. 

polarized, 53. 

resistance of, 13, 19, 56. 

step-, 1 80. 

track, 240, 246. 

use of, 3. 

windings, 16. 
Repeaters, Atkinson, 40. 

closed-circuit, 37. 

direct-point, 76. 

duplex, 76. 

fire-alarm, 206. 

half-set, 80. 

induction, 187. 

open-circuit, 42. 

quadruplex, 100. 

simplex, 35. 
various, mention of, 42. 

Weiny-Phillips, 37, '80. 



Repeating coil, 294. 

sounders, 40, 67, 95. 
Reperforator, 114. 
Resistance of artificial lines, 52. 

of Field quadruplex, 93. 

of grounds, 2^2. 

of polarized relays, 56. 

of relays, 13. 

of selenium, 175. 

of siphon recorders, 362. 

of sounders, n. 

of telegraph lines, 29. 

of the earth, 279. 

of wires, 283. 

Resonators for sounders, n. 
Retardation coils, 67. 

construction of, 71. 
Retransmission over cables, 368. 
Reversal-frequency, 356. 
Rheostats, artificial line, 52. 
Rignoux, television, 183. 
Ringing over composited lines, 297. 
Rowland, Prof. Henry .4. /printing 

telegraph, 133, 163. 
Riiddkk, John /., fire-alarm box, 194. 
Ruhmer, Ernst, television, 183. 

Sags of wires, 262. 
Saturated-core cables, 269. 
Secondary batteries, 21. 
Sector signal boxes, 200. 
Seeing at a distance, 183. 
Selenium resistance as affected by 

light, 175. 

Self-inductance of wires, 283. 
Semaphores, 225. 

operation of, 229. 
Semi-automatic transmitters, 10. 
Sextuplex signalling, 104. 
Shading coils on relay, 246. 
Shunt, inductive, 373. 



404 



INDEX 



Side circuit, 296. 

Siemens, Dr. E. Werner, printer, 133. 
Signal boxes, fire-alarm, 192. 
Gamewell Company, 196. 
police, 218. 
successive, 195. 
Signalling speed on cables, 363. 

types of, see Telegraphy. 
Signals, railway, 224. 
Silent interval in cable operation, 355. 
Simplex instruments, 8. 

repeaters, 35. 

signalling on telephone lines, 295. 
with one generator, 336. 
with two generators, 341. 

switchboard circuit, 142. 

telegraphy, i. 

Simultaneous telegraphy and teleph- 
ony, 293. 

Sines, table of, 388, 394. 
Sine- wave cable signalling, 374. 
equivalent, 304. 

transmission, illustration of, 330. 
Single-current duplex, 46. 

line repeaters, 35. 

Morse circuit, 2. 
Siphon recorder, 360. 
Skelton, Francis A., repeater, 206. 
Sounders, ampere-turns for, 3. 

construction of, 10. 

polarized, 186. 

repeating, 67, 95. 

resistance of, n. 

windings of, 16. 
Spans, economic length of, 266. 

wire, 261. 

Spark quenching at contacts, 61, 73. 
Specific inductive capacity, 286. 
Speed, effect of signalling, 334. 

of cable signalling, 363. 

of signalling, 33. 



Splices, cable, 276. 
Spring jacks, 138. 

Squier, Col. George 0., cable signal- 
ling, 374. 
Statistics of cables, 271, 381. 

of telegraph systems, 159. 
Steam railways, signals for, 239. 
Stearns, Joseph B., duplex, 46. 
Steinheil, Prof. Karl A. von, earth 

return, 279. 
Step-relay, 180. 
Storage batteries, 21. 
Strap and disc switch, 136. 
Stresses in poles, 256. 
Submarine cables, design of, 375. 

telegraphy, 347. 
Successive signal boxes, 195. 
Sunflower distributor, 126. 
Surge impedance, 319, 357. 
Switchboards, fire-alarm, 209. 

police telegraph, 220. 

power, 146. 

telegraph, 138. 
Synchronous distributors, 164. 

Tape, perforated transmitting, 108, 
122, 164, 167. 

siphon recorder, 361. 

ticker, 120. 
Tariffs, cable, 381. 

telegraph, 152. 
Taylor, John D., relay, 242. 
Telautograph, 170. 
Telegrams, 152. 
Telegraph cables, 269. 

equation, 350. 

induction, 184. 

in railway operation, 157. 

lines, 253. 

current propagation in, 303. 

municipal, 189. 



INDEX 



405 



Telegraph statistics, 159. 
Telegraphy, automatic, 108. 

cable, 347. 

duplex, 45. 
cable, 372. 

fire-alarm, 189. 

multiplex, 162. 

police-patrol, 217. 

printing, 115. 

quadruplex, 85. 

simplex, i. 

simultaneous telephony and, 293. 

submarine, 347. 

synchronous, 162. 

writing, 167. 
Telephone circuits, 293. 
Telephoning of messages, 155. 
Telephony on telegraph lines, 298. 

simultaneous telegraphy and, 293. 
Telephotography, 175. 

color, 181. 
Television, 182. 
Test grounds, 282. 
Theory of current propagation, 303. 
Thomson, Prof. Elihu, arcs, 181. 
Ticker telegraphs, 115. 
Tiffany, George S., telautograph, 170. 
Time stamp, automatic, 211. 
Timing of condenser discharge, 52. 
Toye, Benjamin B., repeater, 42. 
Track circuits, 239. 

relays, 240, 246. 
Traffic-direction-block system, 235. 

telegraph, 150. 

handling of, 154. 
Transformers, use of, in eliminating 

inductive interference, 290. 
Transition theory of transmission, 

305, 347- 

Transposition insulator, 254. 
of line wires, 289. 



Transmission distance on leaky lines, 

3 2 - 

on perfectly-insulated lines, 4. 
of current over line, 303. 
of signals over cables, 355. 
theory, alternating-current, 306. 

direct-current, 334. 

transition, 305, 347. 
Transmitters, automatic, no, 122. 
continuity-preserving, 50, 58. 
fire-alarm, 203. 
Korn telephotographic, 176. 
pole-changing, 56. 
Pollak-Virag, 167. 
repeater, 38, 40. 
semi-automatic, 10. 
ticker telegraph, 115. 
Wheatstone, 108. 
Trigonometric functions, 388. 

Underground cables, 269. 

installation of, 273. 
conduit, 274. 

Uniform lines, current distribution 
on, 306. 

Van Rysselberghe, Prof. Francois, 
composite signalling, 296. 

Vector representation, 315. 

Velocity of wave propagation, 312. 

Vibrator, siphon recorder, 361. 

Vibroplex transmitting key, 10. 

Virag, Josef, writing telegraphs, 167. 

Voltage distribution equations, 309. 

general, 329. 
on cables, 350. 

Voltages, standard, in telegraphy, 24. 

Wave-length constant, 311. 

propagation, theory of, 306. 
Wedges for spring jacks, 138. 



406 



INDEX 



Week-end letters, 382. 
Weights of cable, 271, 380. 

sheaths, 380. 
of line wire, 29, 262. 
Weiny, Roderick H., repeater, 37, 

80. 

Western Union bridge-duplex, 71. 
quadruplex, 98. 
switchboards, 139. 
Wheatstone, Sir Charles, automatic 

telegraph, 108. 
bridge, 67, 373. 

Whistle-blowing machine, 200. 
Whitehead, Charles S., receiver re- 
sistance, 338. 



Winding constants of magnets, 13. 

for receiving instruments, 16. 
Wire, bimetallic, 29. 

capacity of line, 284. 

leakance of line, 287. 

inductance of line, 283. 

resistance of line, 29, 283. 

sizes of line, 29. 

spans, 261. 

tensile strength of, 262. 

weights of line, 29, 262. 
Wright, John E., printer, 133. 
Writing telegraphs, 167. 

Yorke, George M., line induction, 292. 



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