Year: 1887

page_text: I, ALFRED ROSLING BENNETT of 90 George Street, Edinburgh, Telegraph
Engineer, do hereby declare the nature of this invention to be as follows:-
My invention consists of a method of transmitting several telephonic messages
simultaneously and independently over a single pair of conductors.
There being two telephone stations A and B, several miles apart, I erect two wires
or conductors between them, Y and Z, which two wires owing to the transfer of speed
by induction cannot be used as two independent conductors in the usual way. At
cach station I join in the circuit of each wire a resistance, which may conveniently
consist of a bobbin of wire. This resistance may be of 1000 ohms, but I do not confine
myself to that amount. After passing through their respective resistances I join the
wires Y and Z, together at their extremities. At this stage, the two wires Y and Z,
form a metallic circuit, each side or half of the circuit passing through two resistances,
one resistance at station A, the other at station B.
I then join a set of telephonic instruments at each station so as to form a bridge
between the two sides of the metallic circuit, the said bridge being made between the
resistances and the wires going away to the other station. At this stage, conversation
may be carried on between the stations A and B by means of these instruments.
I then, from the points at which the two wires are joined together to form the
metallic loop, take two branches, one at station A, the other at station B, to the earth,
and insert in each of the two earth wires so formed, another set of telephonic
instruments.
There are now two sets of instruments at station A, and two sets at station B, one
set at each station forming a bridge between the two sides of the metallic loop on the
line side of the resistances, and the second set at each station being joined in the earth
wire on the earth side of the resistances.
The two resistances employed at station A, should be of exactly equal value, and
the two resistances at station B, should be of exactly equal value. The two wires
joining the stations A and B, should be as nearly of the same resistance and insulation
as possible.

page_text: If these conditions are complied with, the two sets of instruments in the earth wires
may be used for conversing without interfering with the two sets of instruments
which form bridges between the two sides of the metallic loops; and vice versa.
In telephone exchange practice, the two instruments in the earth wires may be
replaced by apparatus such as is employed in telephone exchanges for connecting
the wires of the various subscribers together according to the requirements of the
service; and the instruments which form bridges between the sides of the metallic
loop may be replaced by translators or repeating coils in accordance with the invention
described in the Specification of my Patent No. 4428 of 1881, or by equivalent
apparatus.
The resistances at station A and B, may be resistances variable at will, so that
differences of resistance existing between the two wires Y and Z, may be com-
pensated by altering the resistances at the stations. It is desirable that the wire Y,
together with its resistances be equal in resistance to the wire Z, together with its
resistances; and the nearer this condition is approached the better will be the
results obtained. This plan is shown in figure 1 of the annexed diagrams. R, R, are
resistances, T, T, the telephones and E, E, the earth connections.
If the stations A, and B, are connected by four wires, these four wires may be
caused to give four independent services by a development of the invention which is
shown in Figure 2. As thus developed the four wires are formed into two metallic
loops each as already described. At each station these two metallic loops are after
the junction of their component wires, each continued through a resistance and meet
at the further sides of those resistances. A set of telephonic instruments is placed
in a bridge at each station between the two sides of the greater metallic loop formed
by these continuations.
The point of junction of the continuations at each station is then connected
through a set of telephonic instruments to earth.
When the resistances are approximately equal each telephone will operate with the
corresponding one at the one station independently of all the others.
In telephone exchange practice switching apparatus or translators may be sub-
stituted for the various sots of telephones.
By multiplying the wires connecting the two stations further developments may
be similarly arrived at.
Dated this Eleventh day of January 1887.
CRUIKSHANK & FAIRWEATHER,
62, Saint Vincent Street, Glasgow,
Agents.

page_text: COMPLETE SPECIFICATION.
Improvements in Multiplex Telephony.
I, ALFRED ROSLING BENNETT of 904 George Street Edinburgh, Telegraph
Engineer 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 of a method of transmitting several telephonic messages
simultaneously and independently over one or more pairs of wires or conductors.
There being two telephonic stations A and B joined by two or more wires or
conductors, so circumstanced that independent telephonic correspondence cannot be
maintained along them without inductive disturbances, either originating in the wires
themselves or in neighbouring wires, being experienced I arrange the wires or con-
ductors according to one or other of the methods hereinafter set forth, with the
object of obviating such disturbing inductive effects.
:-
When there are only two wires between the stations, I arrange them as follows:-
At each station I join in the circuit of each wire a resistance which may con-
veniently, but not necessarily consist of a bobbin of wire. Each resistance may be
of from 1000 to 3000 ohms, but it may be varied within much wider limits and I do
not confine myself to any specific resistance. After passing through their respective
resistances I join the two wires at their extremities. At this stage, the two wires
form a metallic circuit, each side or half of the circuit passing through two resistances.
one resistance at station A the other at station B.
I then join a set of telephonic instruments at each station so as to form a bridge
between the two sides of the metallic circuit the said bridge being made between the
resistances and the wires going away to the other station. At this stage, conversation
may be carried on between the two stations by means of these instruments.
I then, from the points at which the two wires are joined together to form the
metallic circuit as already described, take two branches one at station A the other at
station B to the earth and insert in each of the two earth wires so formed another set
of telephonic instruments.
There are now two sets of instruments at station A and two at station B one set at
each station forming a bridge between the two sides of the metallic circuit on the
line side of the resistances, and the second set at each station being joined in the
earth wire on the earth side of the resistances.
The two resistances employed at station A should be of exactly equal value and
the two resistances at station B should be of exactly equal value. The two wires
joining the stations A and B should be as nearly of the same resistance and insulation
as possible.
If these conditions are complied with the two sets of instruments in the earth
wires may be used for conversing without interfering with speech between the two
sets of instruments which form bridges between the two sides of the metallic circuit
and vice versa.

page_text: In telephone exchange practice the two instruments in the earth wires may be
replaced by apparatus such as is employed in telephone exchanges for connecting
the wires of the various subscribers together according to the requirements of the
service; and the instruments which form bridges between the sides of the metallic
circuit may be replaced by translators or repeating coils in accordance with the
invention described in the Specification of my Patent No. 4428 of 1881 or by
equivalent apparatus.
This plan is shown in Figure 1 of the annexed diagrams in which T1, T2, T³, T', are
telephones or switching apparatus, R1, R2, R3, R', the resistances and Y, Z, the line
wires. D1 D2 D3 D' are the indicators for calling attention between T¹ and T³, and
between T2 and T the said indicators being of any efficient type and actuated by
voltaic or magneto currents, as is well understood.
If the stations A and B are connected by four wires these four wires may be
arranged to give either three or four independent telephonic services by developments
of the invention which are shown in Figures 2 and 3.
Figure 2 shows the four wires arranged for three independent services. The four
wires are formed into two metallic circuits, each as already described. At each
station these two metallic circuits are, after the junction of their component wires
connected together through a set of telephonic or switching apparatus. T³, T'
represent the third sets of telephonic or switching apparatus and D Do the indicators
for signalling between T and T. The two metallic loops Y, Z and Y, Z are worked
exactly like the single metallic loop Y Z of Figure 1.
Figure 3 shows the four wires arranged for four independent services, the fourth
sets of apparatus T7 D7 and T D³ being placed in continuations through resistances to
the earth of the system shown in Figure 2, R7 R7, R³, R³ being the additional
resistances.
When the resistances are approximately equal each set of apparatus will operate
with the corresponding one at the other station without disturbing the others.
In telephone exchanges, switching apparatus or translators may be substituted for
the various sets of telephones.
It is best to make the resistances variable at will, so that differences of resistance
existing between the line wires may be compensated by varying the resistances at the
stations.
Further developments may be made similarly when the stations are joined by eight
or more wires as will be well understood by electricians.
:-
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 :-
The method and means herein described for transmitting several telephonic
messages simultaneously and independently over one or more pairs of wires or
conductors.
Dated this Eleventh day of October 1887.