IMPROVEMENTS RELATING TO TELEPHONIC AND TELEGRAPHIC APPARATUS AND CIRCUITS
Year: 1881

page_text: LETTERS PATENT to Sydney Pitt, of Sutton, in the County of Surrey, for
an Invention of "IMPROVEMENTS RELATING TO TELEPHONIC AND TELEGRAPHIC
APPARATUS AND CIRCUITS." A communication from abroad by William R.
Patterson and Charles E. Scribner, both of Chicago, Illinois, one of the
United States of America.
COMPLETE SPECIFICATION filed by the said Sydney Pitt at the Office of
the Commissioners of Patents on the 11th October 1881.
SYDNEY PITT, of Sutton, in the County of Surrey.
"IMPROVEMENTS RELATING
TO TELEPHONIC AND TELEGRAPHIC APPARATUS AND CIRCUITS." A communi-
cation from abroad by William R. Patterson and Charles E. Scribner, both of
Chicago, Illinois, one of the United States of America.
This Invention has for its object improvements relating to telephonic and
telegraphic apparatus and circuits.
An object of this Invention is to provide for each subscriber or member of a
telephone company a means of communication directly with the listening attendant
and central office at all times for the purpose of obtaining a connection or discon-
nection to enable the central office manager to regulate at will the number of
subscribers to be taken care of by a single attendant, and an improved method
of notifying the attendant of a call when he is not listening at his telephone.
Heretofore a given subscriber has signaled the central office over his individual
telephone line or by means of a separate circuit wire running from the central office
to all of the subscribers.
The objection to these systems is that if the circuit wire be broken none of the
subscribers on that particular circuit can communicate their wants to the central
office, nor can they obtain any service from the system until the damage is repaired ;
another objection is that the central office has no means of varying the number of
subscribers taken care of by a single attendant, and thus regulating the service at
the central office so as to correspond to the demands of business at different hours

page_text: of the day, which is necessary in case there are more calls from a group of
subscribers than one attendant can take care of.
By this Invention the subscriber's wires are grouped at the central office to a
common wire which connects to a listening operator's telephone and thence
to ground, as hereinafter shewn; and the terminals of subscribers' individual
wires are connected through call bells at subscribers' offices, and thence to a
common wire, said wire serving to group the outer ends of the telephone wires
together.
In the Drawing two groups of subscribers are shown connected with the central
office. The outfits of the subscribers S¹, S3, and Se are shown in detail. The outfits
of the other subscribers S2, S3, S4, S7, and SB are simply indicated.
The subscribers' lines a¹, a, a, a, are in one group and connected with jack-knife
switches b¹, 62, 63, 64, and to the common wire c of the listening operator's telephone
at the central office while their outer ends are connected by wire d.
The second group of telephone lines e¹, e, e³, and e¹ are connected in like
manner through jack-knife switches f', f, f³, and f' to common wire g of the
listening operator's telephone, and their outer ends are connected together by
wire h.
It will be seen that by means of the switch i the two groups may be united
and separated as occasion may require, and in like manner any number of groups
of wires may be combined or divided, so that the service at the central office may
be adjusted at different hours of the day and at different seasons in accordance
with the demands of the subscribers.
k and are peg switches, and m is an annunciator or bell in a line connecting
with line g through a battery.
When there are very few demands on the central office the attendant may change
the peg from switch k to switch 1, and take telephone n from his ear.
Now when
any subscriber of the group takes down his telephone the circuit will be closed to
ground through the battery o and annunciator m, and the listening operator will
change the peg back to switch k and answer the call.
An automatic switch operated by the weight of the operator's telephone may
be used instead of the peg switches k and l.
The battery o is used primarily for calling up the subscribers asked for, but may
be also used to ring bell m and thus notify the listening operator that a subscriber
has taken down his telephone. p is the listening operator's transmitter.
Each subscriber's outfit consists of a transmitter q, receiving telephone r,
telephone switch 8, call bell t, and open circuit contact or push key u.
On
When the telephone switch, say, of the outfit S¹ is depressed by the weight of
the telephone suspended upon, it the circuit of telephone line a¹ may be traced
from the lever of the switch 8 directly through the call bell t to wire d.
removing the telephone r from the hook the line a³ is changed and may be traced
from the switch lever 8 through the receiving telephone r and transmitter q to
ground.
One point of the push key u is connected with the common line d, the other
point with the line by which the circuit of the line a' is completed from the switch
to the receiver. Ordinarily a subscriber has simply to take down his receiver
and speak directly to the listening operator. Thus S is connected directly with
telephone n at the central office.
Suppose however that the line a¹ were open at the central office.
S¹ by pressing on push key u would immediately connect his telephone and
transmitter with the listening operator by a circuit passing from the common
line d over the individual telephone lines a² and a³ of the group, or so many of
the group, whether one or a hundred, as might happen to be connected at the
time, with the common line d.
Any subscriber may thus talk directly to the listening operator over a circuit
consisting of many telephone lines connected at their outer ends with a common
wire, and at the central office with the common line of the listening operator.

page_text: Each subscriber is thus provided with two circuits, first, his individual telephone
line; second, the lines of his group that happen to be connected with the common
line at their outer ends when he connects with the said common line. S¹ and S
are shown in private communication, connected through the central office by their
telephone lines a' and e¹ and the flexible cord v, which with the plugs connects
their respective switches b¹ and f¹. The central office calls the subscriber asked
for by the following means:-
The telephone circuits are normally closed to ground.
The normally open
circuit of the battery o is connected with points l*, m*, n*, &c., so that when a
plug is inserted in any spring jack the switchman, by crowding the plug clear in
or crowding it to one side, as is seen at f, or in other like suitable manner, may
connect the calling battery with the circuit of the subscriber, connected with the
spring jack. Switch is shown thus connected to calling battery o, and by
line through the call bell of Ss. (The telephone of S8 is supposed to be hung
on the switch), and thence to common line h, and by lines e² and e³ of the group,
or such lines as happen to be connected with line h, whether few or many, back
to the central office to line g, to which the other pole of the battery is
connected.
Heretofore the spring jack and plug have been used simply to take off the ground
and connect the subscribers.
The improvement consists in connecting the calling battery with a point near
the lever of each spring jack, and so constructing the plug that the switch man may
by means of the plug, connect any subscribers line with a contact point connecting
with the calling battery and thus signal the subscriber.
In practice there will be many lines in the return circuit, so that the current
dividing through the call bells of the return wires will not be sufficient to ring the
bell of a given line.
As the current passes in one direction through the bell of the subscriber called,
and in the opposite direction through the bells of the wires of the return circuit,
the bells may be polarized to respond only to the current passing out from the
central office, and thus the possibility of false signals being caused by the return
current may be effectually prevented, even though there might be but a single
wire of the group in the return circuit.
When the subscribers are through talking either one may close his push key, and
thus connect his outfit with the listening operator through the wires of his group
that are at the time connected with the common wire of that group, or one
subscriber may wait till the other hangs up his telephone and then talk to the
listening operator by a circuit composed of the two connected telephone lines, and
the other wires of the group of the subscriber who has hung up his telephone to
the listening operator. Suppose S¹ and S³ to have been in conversation and that
S has hung up his telephone, S¹ may then talk to the listening operator at
telephone n by the following circuit. Beginning at ground as indicated by G at
station of S', and thence as shown through the transmitter and telephone to the
telephone switch, and thence by telephone line a¹' to switch b', and thence by cord
vto switch fand by line e¹ to the switch of S, and thence through the call bell
of S to common line h, and thence through the call bells of S6, S7, &c., and their
lines e, e, &c., to the common line g which passes through the listening operators
telephone n and his transmitter p to ground as shown. By this latter method the
system may be worked successfully without the push keys.
It will be seen that two subscribers of the same group may be connected in the
same manner, and that the number of subscribers in a group may be varied in
accordance with the demands of the business. A subscriber at all times has two
chances of getting the central office. He has his individual line which he will
ordinarily use in the first instance. But if this line is not connected with the
listening operator, by closing his push key he has another circuit at his command.
For containing the line wires, cables have sometimes been used, which consist of
a core of conductors enclosed within a pipe and insulated by some substance which.

page_text: is turned in in the liquid state and allowed to cool and become more or less
solidified.
Paraffin, resin, beeswax, and other similar substances alone and in combination,
have been used as an insulating substance. These substances, as is well known,
sbrink on becoming cold. Thus cavities have been left within the pipe which have
caused great trouble. Among the difficulties experienced on account of this
shrinkage may be mentioned the increased liability of moisture to penetrate
through flaws or joints in the pipe on account of the vacuum thus formed, and
also the liability of water to penetrate the cavities to a considerable distance in
case a cable should be broken under water.
In order to compensate for this shrinkage I charge the melted paraffin or other
insulating substance with carbonic acid gas or other suitable gas or mixture of
gases, and force the liquid thus prepared into the heated pipe around the core,
allowing the air to escape from the other end of the pipe through a small orifice so
that the pressure will not be removed from the charged paraffin and allow the gas
and paraffine to separate.
When filled the pipe is closed and allowed to cool.
The gas is held in very minute bubbles hardly visible to the naked eye. As the
substance cools and contracts these bubbles expand, and the pipe is thus kept
entirely full.
These bubbles are isolated from each other and uniformily diffused throughout
the mass of solid substance. The insulating substance is thus formed into a light
porous homogeneous mass.
The gas may be generated and forced into the insulating substance in any well
known way, but should be dried so as not to injure the insulating qualities of the
paraffin.
The higher the degree of heat to which the substance is raised the more will the
substance shrink in cooling and the greater will be the pressure required to keep it
charged with gas, I therefore prefer to charge the substance and force it into the
cable at a temperature but little above the melting point.
If the core of conductors consist of insulated wires they should be dried and
soaked in an insulating substance like paraffin, after which the core should be
compressed in any well known way, so that the insulating substance may thoroughly
fill the pores of the fibrous covering, otherwise air would be left in the cable and
in case of injury to the cable water might penetrate to a considerable distance.
As to the pipe to be employed the objections to using iron are its rapid
oxidation unless galvanized or protected in some way, and its inflexibility. When
galvanized the tools used in laying are liable to abraid the zinc.
Lead pipe is preferable on account of its flexibility, and also on account of its
durability as compared with iron pipe when exposed to moisture. Lead however
in itself is not tenacious enough to withstand the wear and tear to which telegraph
cables are exposed, and is more flexible than is desirable.
As an improvement on these forms of pipes I propose to use a lead pipe covered
externally with a sheath or armour of galvanized wires of either iron or steel
wrapped helically about the pipe, and by the means employed in the manufacture
of gutta-percha cables.
The diameter of the lead pipe is determined by the number of wires desired in
the core, and the size of the wires of the protecting armour by the weight of the
pipe, and the tensile strain to which it is to be subjected.
After being thus prepared the pipe, by which I mean the lead tube and its iron
armour, may be laid in position under ground or under water and the core of
conductors drawn in; or in case a solid insulating substance is desired the core may
be drawn in and the cable coiled up and heated in an oven or by other suitable
means, and when thus heated filled with melted insulating substance; after it has
cooled the cable is ready to be laid in place.
The pipe combines the durability of lead and the tensile strength of iron or
steel. There are no tools used liable to abraid the zinc coating of the wires, and it

page_text: is not necessary to drag the pipe over the ground as its flexibility permits of its
being coiled upon a reel and uncoiled in place.
Two lengths of lead pipe may be united by an ordinary wipe joint before the
armour is applied.
Telegraph cables protected in this manner may be drawn within sewer pipes in
long lengths, and in case of injury through accident or otherwise may be withdrawn
for repairs and replaced without disturbing the pavements.
Light aerial cables may be protected with light armour so as to be drawn over
buildings without injury to the pipe.
To neutralize induction in telegraph cables I combine a circuit of low resistance
with the telephone line circuits in such manner as to neutralize the effect of the
secondary currents.
The establishment of a current in any conductor causes an induced current in the
opposite direction in all the other circuits, including the low resistance circuit.
It follows from Ohm's law that the current being equal to the electro motive
force divided by the resistance that a much greater tertiary current will be induced
from the current of low resistance than from any of the others.
I find that when the resistance of this circuit is very low in comparison with
that of any of the others, say, from one tenth to one fifteenth, or less, this tertiary
current will practically neutralize the secondary currents in the small conductors.
In the Drawing z represents an insulated wire passing through the cable and
connected to earth at each of its ends, so forming a circuit of low resistance.
When a telephone line is closed to battery secondary currents are thus induced
in the other lines that are closed, and also in the low resistance conductor z.
The currents induced in conductor z will tend to induce tertiary currents in the
telephone lines which will practically neutralize the secondary currents induced in
the same lines.
I claim,―
First. The combination of telephone line a¹, switch 64, ground line c, telephone r,
switch 8, signal instrument t, and common line d with a return circuit of such
lines of the group as
are at the time connected with line d, substantially as
described.
Second. The circuit consisting of two subscribers' telephone lines connected
through the central office, one line being grounded at its terminal station, the
other line connecting from the telephone switch of its subscribers station to a line
common to the group, and one or more lines of the group connecting said common
line with the line of the listening operator.
Third. The circuit of the telephone line beginning at the common line of the
listening operator and passing through a switch to a subscriber's line, and thence
to the telephone switch of said subscriber's station, and thence normally through
the call bell to a line common to the group of telephone lines, and thence by
one or more of said group to the said common line of the listening operator in
combination with a calling battery in said circuit, substantially as shown and
described.
Fourth. Two or more groups of telephone lines, each group in combination with
an outer common line, and at the central office with a listening operator's telephone,
and one or more switches whereby the groups may be united or separated as
occasion may require, substantially as and for the purpose specified.
Fifth. The key u combined with the circuit connecting subscriber's telephone
with common line d, whereby the subscriber may close a circuit over the lines of
the group connected with line d to the ground wire of the listening operator.
Sixth. The method of grouping the individual lines of a telephone exchange
system by connecting their outer ends with one or more common lines and
providing switches so that each subscriber has at his command a circuit over one
or more lines of the group other than his own line to the central office, substantially
as and for the purpose specified.
Seventh. The combination of the switches 8 and u under the control of the

page_text: subscriber with circuits, substantially as shown, whereby the subscriber may
converse with the central office over his individual line, or by a circuit over one
or more lines of the group to which his line belongs.
Eighth. The combination of three circuits under the control of the subscriber,
first through signal apparatus to common line, second through telephone to earth,
and third through the telephone connected directly with the common line.
Ninth. The combination of a group of telephone lines with a common line
connecting their outer ends and polarized bells, one at each subscriber's station
responding to currents in but one direction.
Tenth. The combination of a contact point of the calling battery with the spring
jack and plug so that the switch man may signal by moving the plug, thus throwing
the calling battery to line.
Eleventh. The method of filling telegraph cables with an insulating substance,
consisting of pouring into the pipe around the conductors melted paraffin or its
equivalent charged with gas, whereby the shrinkage of the insulating substance
resulting from cooling is distributed through its mass, substantially as and for the
purpose specified.
Twelfth. The telegraph cable consisting of a pipe and core of conductors in
combination with an insulating substance charged with gas, substantially as and
for the purpose specified.
Thirteenth. The combination of galvanized or other wires with the lead pipe
of a telegraph cable, said wires being wound helically about the pipe so as to
cover its exterior and form a flexible armour of great tensile strength, substantially
as and for the purpose specified.
Fourteenth. The method of neutralizing induction in telegraph cables, which
consists in the use of tertiary currents in the conducting wires opposed in direction
to the secondary currents in said conducting wires, said tertiary current being
produced by one of the secondary currents flowing through a special circuit of low
resistance.
Fifteenth. The combination of a circuit of low resistance with a primary circuit
and several secondary circuits, whereby the effects of induction are overcome,
substantially as and for the purpose specified.
Sixteenth. In a telegraph cable, the combination of separately insulated
conducting wires with a special conductor of low resistance, the circuit through
said special conductor being completed by a conductor of equally low resistance
exterior to the cable.
Seventeenth. In a telegraph cable, one or more of the telegraph or telephone
circuits closed to battery, and one or more of said circuits acting as secondaries to
said battery circuits in combination with a low resistance secondary circuit whereby
tertiary currents are induced, as and for the purpose set forth.
In witness whereof, I, the said Sydney Pitt, have hereunto set my hand and
seal, this Twenty second day of September, in the year of our Lord One
thousand eight hundred and eighty one.
SYDNEY PITT. (L.S.)