IMPROVEMENTS IN ARRANGEMENTS OF TELEPHONIC APPARATUS
Year: 1885

page_text: WIH DELE
"
I, SILVANUS PHILLIPS THOMPSON of University College, Bristol Doctor of
Science and Professor of Experimental Physics do hereby declare the nature of my
invention for "IMPROVEMENTS IN ARRANGEMENTS OF TELEPHONIC APPARATUS
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
1
My Invention consists in the arrangement of telephonic circuits in the manner
hereinafter described and illustrated by the Drawings.
In electro magnetic telephone instruments that is to say instruments in which
the voice currents influence the armature by means of an electromagnet instead of
a permanent magnet, the difficulty found hitherto in working, arises from the lack
of sensitiveness of the instrument, and this in turn is chiefly due to the high
resistance of the wire ordinarily used on the line, the effect whereof is to diminish
the initial current in the receiver coil, which current should be sufficient to
magnetise the core of the Electro magnet somewhat strongly. To obviate this
difficulty and obtain the requisite sensitiveness of the instrument without being
obliged to use an inordinate number of cells. I connect with the line-wire & loop
or shunt circuit (as shewn in Figure 1) extending from a point P in the line
anterior to the line battery Z. Y through an Electro-magnet S to a point Q.
posterior to the receiving telephone R.
If this shunt circuit were merely a shunt with a resistance of more or less value
or amount, it would not satisfactorily serve the purpose of my invention; for,
although it would by reason of its greater or less resistance allow a considerable
part of the battery current to run through it, thereby causing an increased current
through the receiver and ensuring an adequate magnetization of the core of its
Electro-magnet, yet it would not attain my purpose, because the "working
currents" or "voice currents" coming through the main line would be partially
diverted into the shunt and would without passing through the receiver, leak
through the said shunt to earth-This method of working, that is to say, by
shunting or diverting a portion of the current from the Receiver is altogether
distinct and different from, and would prevent the attainment of the object of my

page_text: invention, which is based upon the principle of blocking the loop or shunt circuit
against the rapidly fluctuating voice-currents or telephonic currents coming along
the main line, while allowing the steady flow of the Battery current through the
said loop.
For this purpose it is necessary to interpose in the loop or shunt circuit, a device
or organ which, while having very little resistance, possesses great electric inertia,
or in other words has a high co-efficient of self induction.
I therefore insert in this loop circuit, an Electro magnet S constructed with a
large number of turns of wire surrounding an iron core to ensure the required
co-efficient of self-induction, in order that by its great Electric inertia, it will block
or "plug" the loop or shunt circuit with respect to the rapidly fluctuating
telephonic currents, and ensure their traversing the main line, the Battery in the
line and the Receiver which is also in the main line-The Electro-magnet which,
for the purpose of my invention must, in all cases have a high co-efficient of self-
induction relatively to its Electrical resistance, I call an "induction plug" because
of the well known property of such an Electro-magnet of obstructing, by its great
Electro-magnetic inertia-The passage of rapidly fluctuating currents-An Electro-
magnet so constructed and arranged will prevent the rapidly fluctuating currents
from being diverted through the shunt circuit to earth, and will force them almost
entirely to traverse the main line through the receiving telephone.
I have hereinabove stated that this plugged loop line is not a mere shunt through
which the voice currents would leak away, furthermore I wish it understood that
my invention is distinct from any system of simultaneous telegraphy and telephony
in which an Electro magnet or coil is used for the purpose of separating the
telephonic from the telegraphic currents. For my purpose the resistance should be
as small as possible, and it would best answer my purpose to have (if practicable)
an Electro magnet without any resistance, the wires that connect the electro
magnet with the main circuit should also have an inappreciably small resistance.
In some instances I adopt the arrangement shown in figure 2, that is to say,
I extend a loop line or shunt circuit from a point P on the main line anterior to the
line battery, and connect it through an electro magnet or induction plug S of great
electric inertia to the earth at E
In figure 3 I have illustrated an arrangement of the circuit which may advan-
tageously be adopted when this Invention is used in connection with the valve
telephones described in the Specification of Letters Patent granted to myself and
P. Jolin No 8254 in the year of Our Lord 1884.
In the drawings which I have herein above partly described figure 1 shews a
portion of the main line wire at L L with the battery Z Y included therein. The
loop or shunt circuit is shewn extending from the point P, anterior to the battery to
the point posterior to the instrument R which is between the point Q and the
battery. S is the electro magnet or induction plug in the said loop or shunt
circuit. The end of the main line below or posterior to the point Q is connected
to earth as shewn at E or to a return wire.
The arrangement shewn in figure 2 differs from that in figure 1 only, in respect
of the direction of the loop or Shunt circuit which extends from the point P to earth
as above described.
In figure 3 the main circuit or line wire L, the position of the battery Z Y and
the connection of the loop or shunt circuit with the point P are the same as in
figures 1 and 2. C is an induction coil,-V is the transmitter, The line circuit is
through the battery Z. Y. The receiver R and the secondary wire c, c. of the said
induction Coil to earth. The transmitter circuit starts from the battery Z, Y, (part
of which is utilized for the primary circuit) and divides preferably into two branches,
one branch extends through p, p, and through the transmitter V. The other branch
extends through p, p, and through a compensating resistance W. These two
branches which form.a double primary of the induction Coil C reunite at A. whence
the circuit returns to the battery.

page_text: Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is
First, The improved arrangement of Telephonic circuits hereinbefore described.
Second, The combination of an Electro magnetic telephone instrument with an
induction plug which permits a steady battery current to flow through the electro
magnet of the telephone instrument by means of a shunt circuit, but prevents the
fluctuating voice currents from passing round the shunt circuit.
Dated this eighteenth day of March 1885.
SILVANUS PHILLIPS THOMPSON.