IMPROVEMENTS IN THI DHONIA ADDADA
Year: 1881

page_text: LETTERS PATENT to Alfred Rosling Bennett, of 4, Talbot Road, Forest Gate,
London, in the County of Essex, Telegraphic Engineer, for an Invention of
"IMPROVEMENTS IN THI DHONIA ADDADA"
PROVISIONAL SPECIFICATION left by the said Alfred Rosling Bennett
at the Office of the Commissioners of Patents on the 11th October 1881.
ALFRED ROSLING BENNETT, of 4, Talbot Road, Forest Gate, London, in the
County of Essex, Telegraphic Engineer. "IMPROVEMENTS IN TELEPHONIC
APPARATUS."
My Invention has reference to the working of telephonic exchange systems and
to telephonic wires generally, and has for its objects (1), to enable the subscribers
of two telephonic exchange systems to converse together under the following
circumstances, vie, when the said subscribers are 'n communication with their
respective central exchange offices by ordinary wires joined to the earth at
their extremities, and when the said central ex age offices are connected with
each other by a double wire or metallic circuit, of which the earth forms no part;
and (2), to modify the inductive effects upon a telephonic wire of a neighbouring
conductor conveying telegraphic or other signals or currents.
To accomplish the first part of my Invention I provide at each central exchange
office an inductorium or induction coil, which may have a soft iron core of the
ordinary construction formed of two long layers of fine well insulated copper wire
wound side by side as closely as possible together. Wire of other metal than
copper may be employed, but not beneficially. To obtain the best effects the two
layers of fine wire should be of the same gauge and of the same length and
electrical resistance, but considerable variations in these respects may be made
without material sacrifice of efficiency. To suit varying circumstances the two
long layers of fine wire may with advantage be replaced by three, four, or more
layers of shorter lengths, provided with terminal screws or other means of joining
their extremities as may be required.
Induction coils of the ordinary construction, that is to say, consisting of two
separate layers of wire, one of high electrical resistance (termed the secondary wire)

page_text: superimposed upon another of low electrical resistance (termed the primary wire)
will not give good results; but this form of coil may be successfully employed. if
the primary and secondary wires are made both of long lengths of fine wire or of
high electrical resistance, and the effects will improve proportionally as the
primary and secondary wires approach each other in respect to gauge, length, and
electrical resistance.
The ends of one of the layers of a coil constructed as set forth, placed at the
central exchange office No. 1, are connected by means of a double wire or metallic
circuit with the ends of one of the layers of a similar coil placed at the central
exchange office No. 2. When a subscriber in communication with the central
exchange office No. 1 wishes to speak to a subscriber in communication with the
central exchange office No. 2, their respective single wires are connected to earth
through the second or disengaged layers of the two induction coils. The speaking
is then transmitted in the following manner-
1. The current arriving at the central exchange office No. 1 from the first sub-
scriber's wire passes through one of the layers of the coil at that office to earth,
and
*
2. Induces in the other layer similar currents which pass over the double wire
or metallic circuit to the central exchange office No. 2, and through one of the
layers of the coil there, and
3. Induces similar currents in the other layer of the coil at the central exchange
office No. 2, which currents pass away to the second subscriber's wire and to earth
through his telephone.
This part of my Invention likewise comprises the adaptation of my plan to
the switching apparatus now in use in telephonic exchanges; the insertion of
galvanic or magneto-electric batteries and keys at the central exchange offices
Nos. 1 and 2, in the metallic circuit connecting those offices, for the purpose of
transmitting call signals, and the utilizing of the induction coils and their soft iron
cores as electro-magnets for the purpose of receiving the said call signals in a
manner to be more particularly ascertained and described in the Final Specification
of these Letters Patent.
To accomplish the second part of my Invention I place an induction coil con-
structed as already set forth, midway, or as nearly midway as possible, in a
telephonic line liable to disturbance from telegraphic or other signals or currents
conveyed by a neighbouring wire or conductor, in such a manner that one half of
the telephonic line is connected directly to the earth through one of the layers of
the coil, and the other half of the telephonic line is similarly connected through
the other layer of the coil. The inductive effects upon the telephonic wire of the
currents conveyed by the neighbouring conductor will then be partially neutralized
by the induced currents in the opposite direction set up in the two layers of the
coil, and, as a consequence, in the halves of the telephonic line in connection with
them.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Alfred Rosling Bennett in the Great Seal Patent Office on the
11th April 1882.
ALFRED ROSLING BENNETT, of 4, Talbot Road, Forest Gate, London, in the
County of Essex, Telegraphic Engineer. "IMPROVEMENTS IN TELEPHONIC
APPARATUS."
My Invention has reference to the working of telephonic exchange systems and
to telephonic wires generally, and has for its objects (1) to enable the subscribers
of two telephonic exchange systems to converse together under the following
circumstances, viz., when the said subscribers are in communication with their
respective central exchange offices by ordinary single wires joined to the earth at
their extremities, and when the said central exchange offices are connected with
each other by a looped double wire or metallic circuit, of which the earth forms no
part; and (2) to modify the inductive effects upon a single telephonic wire of a
neighbouring conductor conveying telegraphic or other signals or currents.
To accomplish the first part of my Invention I provide at each central exchange
office an induction coil, which may have a soft iron core of the ordinary con-
struction, formed of two long layers of well insulated copper wire wound side by
side as closely as possible together. Wire of other metal than copper may be
employed, but not beneficially. To obtain the best effects the two layers of wire
should be of the same gauge and of the same length and electrical resistance, but
considerable variations in these respects may be made without material sacrifice of
efficiency. To suit varying circumstances the two long layers of wire may with
advantage be replaced by three, four, or more layers of shorter lengths provided
with terminal screws or other means of joining their extremities, as may be
required.
With the view of obtaining the maximum inductive effect I prefer to make the
iron cores of the coils of unusual length and thickness, so that even the outermost
of the layers of wire may, when wound, be close to the core. With the same
object I wind one, two, or more iron wires, which may be either naked or covered,
side by side with the two insulated copper wires. The iron wire or wires act as
an extension of the iron core of the coil, and are not intended to serve as conductors
of current.
This part of my Invention may be given effect to by winding side by side upon
a soft iron core, one inch in diameter and thirteen inches long, two copper wires of
No. 30 (Birmingham wire gauge) insulated with silk, each one mile long, and one
naked soft iron wire of the same outside diameter as the silk covered copper
wires. The iron wire, instead of being continuous throughout, may be divided
into shorter or longer lengths. In winding the coil I prefer to alternate two copper
wires with one iron wire, as shown in Figure 1, in which J represents the core,
C, the copper, and I the iron wires; but this mode of construction may be varied,
as also may the above noted dimensions, gauges, and lengths.
Induction coils of the ordinary construction, that is to say, consisting of two
separate layers of wire, one of high electrical resistance (termed the secondary wire)
superimposed upon another of low electrical resistance (termed the primary wire)
will not give good results, but this form of coil may be successfully employed if
the primary and secondary wires are made both of long lengths of wire of similar
gauge, and the effects will improve proportionally as the primary and secondary
wires approach each other in respect to gauge, length, and electrical resistance.
The ends of one of the layers of a coil constructed as set forth, placed at the
central exchange office No. 1, are connected by means of a double wire or metallic

page_text: circuit, with the ends of one of the layers of a similar coil placed at the central
exchange office No. 2. When a subscriber in communication with the central
exchange office No. 1 wishes to speak to a subscriber in communication with the
central exchange office No. 2, their respective single wires are connected to earth
through the second or disengaged layers of the two induction coils. This arrange-
ment of connections is shown in Figure 2. The speaking is then transmitted in
the following manner :-
First. The current arriving at the central exchange office No. 1 from the first
subscriber's wire A passes through one of the layers B of the coil at that office,
and through A¹ to earth, and
Secondly. Induces in the other layer D similar currents which pass over the
double wire or metallic circuit E, E', to the central exchange office No. 2, and
through F, one of the layers of the coil there, and
Thirdly. Induces similar currents in the other layer G of the coil at the central
exchange office No. 2, which currents pass away to the second subscriber's wire H
and to earth through his telephone, the other end of the layer G of the coil being
also connected with earth by the wire H¹.
When the metallic circuit between the central exchange stations Nos. 1 and 2
is not quite free from disturbance due to induction from neighbouring wires, the
two branches of the metallic circuit E, E¹, should, by the insertion of artificial
resistances in one of them, be made of exactly the same electrical resistance, so that
the tension of the induced currents in each wire may fall regularly to the centres
of the coils.
Each coil may be made to transmit the call signals and the speech necessary for
the transaction of business between the central exchange offices, Nos. 1 and 2, by
the addition of a system of permanent magnets shown at I, in Fig. 3, the alter-
nating poles of opposite name of which are revolved by a hand crank, as closely as
possible without actual contact, to one end of the iron core J, the other end of the
core being fitted with a circular iron disc K, in every respect similar to the discs
employed in the construction of electro-magnetic telephones, as is well understood,
the said disc being mounted in a suitable frame N rising from the baseboard of
the instrument, and having a permanent polarity communicated to it by contact at
one part of its circumference with one end of a bar magnet M. The centre of the
iron core and of the iron dise, which should exactly face each other, and be almost
but not quite touching, are provided with small contact pieces L, L, of some
inoxidable metal, as is also the centre of the outer side of the iron disc, which
faces a small contact stop O supported on a suitable pillar or bracket P rising from
the base board. The distance of this contact stop O from the disc K should be
adjustable by means of a screw. The disc is in communication with one pole of
a voltaic battery, and when the system of permanent magnets at the distant
station corresponding with that shown at I is revolved closes a local bell circuit by
oscillating between and touching the contact pieces fixed to the core J and the
contact stop O, both of which are connected to the other pole of the battery
through the bell. The play of the disc must be so regulated that its vibrations
when transmitting or receiving speech will not close the local circuit.
arrangement is shewn in Figures 3 and 4, in which I represents the system of
revolving magnets; J, the iron core; K, the telephonic disc; N, the disc frame;
M, the permanent bar magnet communicating polarity to the disc; L, L, the
contact stops; B, the bell; and C, Z, the local battery.
This
To accomplish the second part of my Invention I place an induction coil con-
structed, as already set forth, midway, or as nearly midway as possible, in a
telephonic line liable to disturbance from telegraphic or other signals or currents
conveyed by a neighbouring wire or conductor, as shewn in Fig. 5, in such a
manner that one half of the telephonic line A is connected directly to the earth
through one of the layers B of the coil and the wire A, and the other half of the
telephonic line H is similarly connected through the other layer D of the coil to
earth through H¹. The inductive effects upon the telephonic wire of the currents

page_text: conveyed by the neighbouring conductor will then be partially neutralized by the
induced currents in the opposite direction set up in the two layers of the coil,
and as a consequence, in the halves of the telephonic line in connection with
them.
Instead of joining the two halves of the severed line wire to earth through the
two layers of the coils, as described, one half A may be connected, as shown in
Fig. 6, to the first end of one of the layers B of the coil. The second end of this
layer is then joined to the first end of the remaining layer D, the second end of
which is in communication with the second half H of the severed line wire. Then
the disturbing currents will pass in the same direction through both layers, and
set up induced currents in opposition to themselves in each layer, the effect of
which will be the partial neutralization of the disturbances due to induction from
neighbouring parellel telegraphic or other wires.
may here state that the induction coils are to be constructed as hereinbefore
described, and are indicated in the Drawings by conventional diagrams which show
their position and connections.
Having ascertained to the best of my ability the nature of my Inventions, and
the means of giving them practical effect, I claim,―
(1.) The construction of induction coils containing two conducting wires of the
same gauge and length, or approximately so, and their use and application as
translators between single and double telephonic circuits, substantially as herein
described and shewn in the Drawings.
(2.) The combination therewith of one or more iron wires serving to extend the
area of action of the iron core as described.
(3.) The utilization of the coils not only as translators, but as transmitters and
receivers of call signals and speech between the central exchange offices by
means of apparatus, substantially as herein described and as shewn in Figures 3
and 4.
(4.) The insertion of induction coils, of whatsoever construction, midway, or as
nearly midway as possible, in a telephonic line, with the view of neutralizing
induction from neighbouring wires, substantially as herein described.
In witness whereof, I, the said Alfred Rosling Bennett, have hereunto set
my hand and seal, this Tenth day of April, in the year of our Lord One
thousand eight hundred and eighty two.
DAGEN
(87)
TTTATC
ED ROSLIN
DEN