IMPROVEMENTS IN TELEPHONE CIRCUITS
Year: 1884

page_text: PROVISIONAL SPECIFICATION.
We, SILVANUS PHILLIPS THOMPSON of University College, Bristol, in the County
and City of Bristol, Doctor of Science and Professor of Experimental Physics, and
PHILIP JOLIN of 2 Elmdale Road, Redland, in the aforesaid County and City,
Engineer, do hereby declare the nature of our invention for IMPROVEMENTS IN
TELEPHONE CIRCUITS to be as follows :-
Our invention consists in winding the electromagnet with a double or divided
coil so arranged that the magnetising current in traversing the two branches or
parts or divisions of the coil produces no magnetic effect until the current in one
branch or division of the coil is stopped by the complete rupture or by the partial
opening of that branch or division. To accomplish this end it must be arranged
that the windings of the two branches or divisions of the coil shall be so wound
around the core and so connected together and to the circuit that the currents
shall circulate around the core in opposite directions. When such a method of
winding is applied we find that great improvement results in the working of
induction coils and in telephonic circuits.
Our
Our improved method of winding when applied to the primary circuit of an
induction coil entirely prevents the sparking at the break which has hitherto been
a source of trouble in those instruments; and when applied to the primary circuits
of induction-coils as used in conjunction with telephonic transmitters we find that
it prevents almost completely the occurrence of the stray noises and rattling sounds
which occur when the transmitter receives by accident a sudden jar or agitation,
and which are almost wholly due to the occurrence of minute sparks.
invention by minimising sparking increases the efficiency of those induction coils
and telephonic circuits to which it is applied. In common electro magnets the
magnetism is excited when the circuit is made, and ceases or is discharged when
the circuit is broken; and in consequence at the breaking there is a self-induced or
extra-current spark due to the discharge of the magnetism of the magnet. In our
improved method of winding with two opposing sets of coils, when both branches
or divisions of the circuit are closed the magnet remains unmagnetised. On
breaking the circuit in either branch or division the whole current is thrown round
the other branch or division of the circuit and the magnet is magnetised without
any spark of self-induction occurring. When the circuit is again made through
this branch or division the magnetism is discharged from the iron core, because the

page_text: current now circulates in two opposing senses in the two branches, but there is
again no spark for the circuit is closed before the discharge current or extra-current
of self-induction is set up. The branches or divisions of the circuit may be wound
in several ways: the two wires may be wound on simultaneously side by side in
the same direction (but with reversed connexions) or they may be wound on
separately beside or between or above one another, or the two windings may be
put on in alternate layers or in alternate cells or sections along the core. All that
is necessary is that they should be so wound and connected that the current in one
branch or division completely neutralises the magnetising effect of the current in
the other section or branch. The wires may be of equal length if wound side by
side. If one is wound outside the other it is advisable to give to the outer one
more turns on account of its greater distance from the coro. A double or divided,
or branched coil such as described we propose to call a balanced winding. Our
balanced electromagnet may be substituted for the primary of any ordinary
induction coil, the break-piece being inserted in one of the two branches and
reversed so that when attracted by the core it makes the circuit instead of breaking
it as usually arranged in. induction coils. When our balanced electromagnet is
substituted for the primary of a telephonic transmitting system using an induction
circuit the transmitter is introduced into one branch of the circuit and it is convenient
to introduce also a compensating resistance coil into the other branch. In those
cases where telephones are worked in direct circuits the transmitter may be
included in one branch of a balanced coil and the battery may be in the other or
in the united circuit; or the receiver may be included in one branch and the
transmitter in the other or in the united circuit. Where more than one primary
circuit or battery is employed, each branch or division may be made up of two or
more wires laid beside or twisted round one another. Where two separate cores
are used for the two branches of the balanced coil the cores must be so juxtaposed
that the magnetism of either can affect that of the other.

page_text: WE SILVANUS PHILLIPS THOMPSON of University College Bristol in the County
and City of Bristol, Doctor of Science and Professor of Experimental Physics, and
PHILIP JOLIN of 2 Elmdale Road Redland in the aforesaid County and City
Engineer do hereby declare the nature of said Invention for "IMPROVEMENTS IN
TELEPHONE CIRCUITS" and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement :-
Our Invention relates to electromagnets or coils used in Telephone circuits and
having double or divided convolutions or windings so arranged that the magnetising
current in traversing the two branches or parts or divisions of the coil or circuit
produces no magnetic effect until the current in one branch or division is diminished
or stopped by the partial opening or complete rupture of that branch or division,
such an arrangement as is set forth in this Specification we will hereinafter
denominate a compensated circuit.
To accomplish this end it must be arranged that the windings of the two
branches or divisions of the coil or circuit shall be so wound round the core and so
connected together, and to the circuit, that the currents shall circulate around the
core or through the branches of the circuit in opposite directions.
Windings of a kind analogous to those herein before mentioned have already been
used or described in connection with certain branches of electrical technology, for
example one of us namely the said Silvanus Phillips Thompson has described in
Specification of Letters Patent N° 1639 of 1883 as applied to Electric Motors an
analogous method of winding. We find that great improvement results whon such
a method of winding is applied in the working of Telephonic circuits-This method
of winding is designed to prevent the sparking which would otherwise occur at the
break of contact in the circuit which has been a source of trouble-When applied
to the primary circuits of induction coils as used in conjunction with telephonic
transmitters we find that the occurrence of the stray noises and rattling sounds
which often occur when the transmitter receives by accident a sudden jar or
agitation and which are almost wholly due to the occurrence of minute sparks are
prevented or in great part prevented-The arrangement as hereinafter described
increases the efficiency of those telephone circuits to which it is applied.
In ordinary coils with iron cores such as are used in the primary circuit of an
ordinary induction coil the magnetism is excited in the iron core when the circuit
is made, and ceases or is discharged when the circuit is broken, and in consequence
at the breaking of the circuit there is a self induced or extra-current spark due to
the discharge of the magnetism of the core-Even in those cases where the circuit
is partially interrupted by a rapid increase of resistance, there is a sudden flow of
self-induced electricity tending to set up a spark-In the arrangement herein
described of winding with two opposing sets of coils, when both branches or
divisions of the circuit are closed the core remains unmagnetized. On breaking
the circuit in either branch or division the whole current is thrown round the other
branch or division of the circuit and the core is magnetised without any spark of
self induction occurring. When the circuit is again made through this branch or

page_text: division the magnetism is discharged from the iron core, because the current now
circulates in two opposing senses in the two branches, but there is again no spark,
for the circuit is closed before the discharge-current or extra-current of self-
induction is set up. The branches or divisions of the circuit may be wound in
several ways, the two wires may be wound on simultaneously side by side in the
same direction (but with reversed connexions) or they may be wound on separately
beside or above or between one another or the two windings may be put on in
alternate layers or in alternate cells or sections along the core-All that is
necessary is that they should be so wound and connected that the current in the
one branch or division completely neutralises the magnetising effect of the
current in the other section or branch, otherwise the tendency to spark will not bo
neutralized. The wires may be of equal length if wound side by side. If one bo
wound outside the other it is advisable to give to the outer one more turns on
account of its greater distance from the core. When our compensated coil is
substituted for the primary wire of a telephonic transmitting system using an
induction circuit, the transmitter is introduced into one branch of the circuit, and
perfect compensation is not obtained unless we introduce also a small fixed
compensating resistance coil into the other branch. Where more than one primary
circuit or battery is employed each branch or division may be made up of two or
more wires laid beside or twisted round one another. In these cases where
telephones are worked in direct circuits it is convenient to include the transmitter
in one branch of a compensated circuit and to insert the battery either in the other
branch or in the united circuit; or the receiver may be included in one branch and
the transmitter in the other or in the united circuit.
In the accompanying drawings Figure 1 illustrates in diagrammatic form a
winding suitable for application to the circuits according to our Invention. The
current from the battery divides at A, part flowing through the portion of the
circuit shewn by the black line, part flowing through the portion of the circuit
shewn by the dotted line. These portions of the current circulate around the
iron core C. C' in Figure 1 in opposite directions and reunite at B. the circuit
between A and B being in this manner branched or divided into two branches or
sections which neutraliso each other's action when the current flows through both.
In one of these two branches we introduce the transmitter T which may be any
suitable microphone or preferably the "valve" transmitter described in the Speci-
fication of our application for Letters Patent No 8524 the position of the
transmitter being indicated in Figure 1 by a cross.
In Figure 1 the two separate branches are represented as being wound side by
side in the same way (both being right-handed helices) round the core and then
BO connected that the currents in the two branches circulate in reverse ways around
the core, as shewn by the arrows. The same end is accomplished in another manner
as shown in Figure 2 to which the same lettering applies, but here the two branches
aro wound in opposite directions round the core, one being a right handed the other
a left handed helix. The two coils or branches of the circuit may also be wound as
shewn in Figure 3 in alternate sections or colls along the core, or in any equivalent
manner which will cause them to tend to neutralise each other's magnetising effect.
We do not confine ourselves to the individual methods of coiling the wires or
arranging the circuits shewn in the drawings, as any method of winding or con-
necting the circuit which produces the same result of balancing the magnetic effects
of the two parts or branches of the circuit may be used. Such balanced windings
may be applied simply in place of the usual primary coil of the induction coil of
a telephonic system. As there will be nothing unusual in the secondary coil of the
induction coil we have not deemed it necessary to illustrate it in Figures 1 to 4.
Figure 4 shews the transmitter T introduced in one branch and a small fixed
resistance W, preferably a coil of German Silver wire doubled upon itself to prevent
induction in it, is introduced in the other branch to compensate for the average
resistance of the transmitter T and equalize the currents in the two branches. Ŏr
a transmitter may be included 'in each branch provided the transmitter be sq

page_text: arranged with respect to the air-waves of the speakers voice that the motion of
the one tends to open the one branch of the circuit at the same time as the motion
of the other tends to close the other branch of the circuit.
Figure 5 exhibits one way of carrying out our Invention in a telephonic system
which is worked in an induction circuit, L L' represents the line wire or main
circuit of the system which in this Figure passes through a battery Z Y and then
enters the induction coil at S, traverses the secondary coil S. S' then passes to the
receiver R and thence to earth. The primary circuit is that part to which our
Invention in this case applies. The current is taken preferably from the battery
in the line wire and divides at A into two parts or branches. One part of the
current flows through the transmittor V preferably the "valve" transmitter herein-
before mentioned and thence through one branch P¹ P¹ of the primary coil of the
induction coil. The other part of the current on leaving A passes through the
compensating resistance (indicated by the zigzag line at W) and the other branch
PP of the primary and so forth to B where both branches unite and return to
the battery.
We do not claim in general the winding of an electromagnet with two opposing
coils or circuits, nor do we claim the use of such winding as applied to induction
coils.
Having now particularly described and ascertained the nature of our said
Invention and in what manner the same is to be performed, we declare that what
wo claim is
A Telephone apparatus with a compensated circuit, substantially as described
having a transmitter in one branch and a compensating resistance included in the
other branch of the circuit substantially as set forth with reference to Figures 4
and 5 of the accompanying drawings.
Dated the 10th day of March 1885,
J. HENRY JOHNSON,
Agent for the said Silvanus Phillips Thompson
and Philip Jolin.