Improved Signalling Apparatus for Telephones.
Year: 1892

page_text: Date of Application, 21st Sept., 1892
Complete Specification Left. 20th June 1893-Accented 22nd July, 1893
PROVISIONAL SPECIFICATION.
Improved Signalling Apparatus for Telephones.
Sir CHARLES STEWART FORBES Baronet, 28 Queen's Gate Terrace, London,
S.W. East India Agent, do hereby declare the nature of this invention to be as
follows:-
My invention consists in the employment of an induction coil for producing the
call signal, whereby I am able to dispense with the alternating bell and generator
usually employed for this purpose. To this end I construct the induction coil with
a make and break, which is put in operation by a push button or ringing key, the
interrupted primary current induces a similar current in the secondary wire and
line circuit, to which the telephone responds, producing a loud hum or buzz.
Included in the primary circuit of the induction coil is a microphone which is
thrown in or cut out by suitable switching gear.
Dated September 21st. 1892
F. M. ROGERS,
Agent.
COMPLETE SPECIFICATION.
Improved Signalling Apparatus for Telephones.
I, Sir CHARLES STEWART FORBES, Baronet, 28 Queen's Gate Terrace,
London, S.W. East India Agent, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
My invention consists in the employment of an induction coil for producing the
call signal, whereby I am able to dispense with the alternating bell and generator
usually employed for this purpose. To this end I construct the induction coil with
a make and break, which is put in operation by a push button or ringing key, the
interrupted primary current induces a similar current in the secondary wire and
line circuit, to which the telephone responds, producing a loud hum or buzz.
Included in the primary circuit of the induction coil is a microphone which is
thrown in or cut out by suitable switching gear.
To enable my invention to be better understood I will now describe the same more
particularly by means of the accompanying drawing in which :-
Fig. 1, is a part sectional side view of my invention, on line A. B.
Fig. 2, is a front view of same, part being in section and the lid of case
removed.
In the drawing, 1, is a wooden, ebonite, or equivalent spool having a cylindrical
hole 2, bored longitudinally through it which is fitted with a sliding core of
annealed iron wires 3, of suitable size. A soft iron cap 4, is fastened upon one end
of the wires by soldering or equivalent means while the other end is sweated with
solder or secured by any suitable means to the metallic fork 5. A metal spring 6,
surrounds the part of the core 3, between the spool 1, and fork 5, as shewn. The
primary wire 7, is wound next the core, 5 or 6 turns of say No. 24 or No. 26 B.W.G.,
or thereabouts usually sufficing with the battery ordinarily used to operate the
microphone to effect the double purpose of speaking and calling. The secondary
wire s, consists of a great number of turns of fine well insulated silk covered wire
and is wound on in the manner well understood over but well insulated from the
primary coil, the number of turns will of course vary in a manner depending upon
the length and resistance of the line, but I have found that excellent results over

page_text: ordinary distances are obtainable when the electrical resistance of the secondary
wire is 500 times the resistance of the primary. The ends of the secondary
wires, are connected to the terminals. S, S, and to line and earth through the
telephone T.
Pivotted to the metallic bracket 8 screwed or otherwise fastened to the spool 1,
is a metal lever 9, which is also pivotted to the sliding core 3, by a pin 10, passing
through the fork 5, the lower end of this lever is preferably fastened by a screw or
equivalent means to an ebonite, ivory or other insulating button 11, which protrudes
through the wall of the case in the manner shewn. The head of screw 12, or its
equivalent is silvered or platinized so as to make good electrical contact with the
platinized adjustable screw 13, mounted in cock 14, screwed to case, which is in
metallic connection with one side of the battery B, by terminal P. This screw is so
adjusted as to cause the current circulating round the primary wire to be interrupted
before contact could be made between the cap 4, and hammer 17. The battery B,
is connected on the other side to the pillar 15, which carries an adjustable platinized
contact screw 16, which when the instrument is inoperative, presses against the
platinum or other plate upon spring hammer 17, electrically connected by wire w,
with one end of the primary wire 7, the other end of which is soldered or otherwise
secured to the metallic bracket 8.
The operation of this part of my invention is as follows: When it is desired to
call up the person at the exchange or other end of the line wire, the button 11, is
pressed in until the primary circuit is closed by the contact made between the
screw head 12, and contact 13, a current now flows round the primary wire
surrounding the annealed iron wire core 3, and converts the ends of it into a
powerful magnet, the spring hammer 17, the head of which is formed of soft iron
is attracted and pulled away from contact 16, thereby breaking the circuit, a
*succession of rapid makes and breaks follow so long as the circuit is closed by
pressing in the button 11, the primary current being thus rapidly interrupted
induces a like current in the secondary wire s, surrounding it, and in the line circuit
to which the telephone T, responds producing a loud hum or buzz. The same
induction coil may be used for speaking purposes by including a microphone in the
circuit. In Fig. 1, I have shewn a microphone of ordinary form; and in Fig. 2,
the lid of the case being removed, I have shewn the same diagrammatically. By
means of wire w', one end of the microphone M, is connected to the bridge 20 of
spring switch 18, the tongue of which may be operated by means of the telephone T,
attached to the hook 19, or by any equivalent means, the tail of switch 18, is
connected by wire w" with one side of the battery and the other side connected
through the pillar 15, contact 16, and wire w, with the primary wire 7, passing round
the coil and terminating in bracket 8, which is also connected by wire wl, with the
other end of microphone M.
When the telephone T, is removed from the hook 19, the spring switch 18,
closes the battery circuit through the microphone and primary coil, conversation
can now be carried on over the line by the current induced in the secondary wire
and line in the manner well understood. The flow of current round the iron core
tends to magnetize the same, but owing to the action of spring 6, surrounding
moveable core 3, the soft iron cap 4, is withdrawn sufficiently from the hammer 17,
to prevent any motion in the same by the attraction set up.
It will be seen that by the employment of my improved apparatus the magneto
or ordinary type of bell used for signalling can be dispensed with as well as the
switching gear employed for operating the same.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is-
1st. For telephonic signalling purposes the use and employment of an induction
coil having a sliding core and otherwise so constructed and arranged as herein
described as to serve the double purpose of signalling and speaking.

page_text: 2nd. In signalling apparatus for telephones the combination of the induction coil
having a primary and secondary wire with the sliding core 3, and spring 6, thereon,
the lever 9, pivotted as described for operating said core and closing the battery
circuit through the contacts 12, 13, and pillar contact 16, hammer 17, and
bracket 8, and circuit connections therewith when the button 11, is pressed inwards
as described.
3rd. In signalling apparatus for telephones having an induction coil and moveable
core with make and break as described in Claim 2, the combination of the
microphone M, for speaking purposes operated by the means and in the way and
manner set forth.
D
COLL 1909
FRANCIS M. ROGERS,
Agent.