Telephonic Communication.
Year: 1886

page_text: Telephonic Communication.
I ALFRED JULIUS BOULT of 323 High Holborn, in the County of Middlesex
Engineer, do hereby declare the nature of this invention (a communication from
William Marshall of New York United States of America) and in what manner
the same is to be performed, to be particularly described and ascertained in and by
the following statement:-
This telephone receiver may be used with the ordinary transmitter, is constructed
on the general plan of what is known as a condenser, and consists of a pile of
leaves of tin foil or other suitable substance with insulating material interposed;
the whole preferably perforated and in the middle, and placed in layers pressed
together at the outer edge.
Reference being had to the accompanying drawing in which Figures 1, 2 and 3
are diametrical sections of the various forms which I have given to this invention
-Figures 4, 5 and 6 are diagrams showing the circuits in which this improved
receiver is preferably used and Figures 7, 8, 9, 10 and 11 are views of details of
construction.
Figure 1 shows one form consisting of a case A provided with perforated covers B,
the covers having screw threads which construction serves to regulate the amount
of compression brought to bear upon the outer part of the condenser pile.
Every second leaf of the tin foil is connected to the binding post c and every
other leaf to the binding post d. Above and below the condenser pile are placed
washers K. All the parts being introduced into the case, the cover B is put in
place and screwed down by turning it until a degree of compression is produced
at the circumference of the condenser pile to produce a sufficient bulging of the
middle part of the condenser to be relieved from pressure, when its speaking powers
will be clear. Instead of washers the cover may have an annular projection
2

page_text: around its inner face shown in Figure 11. To further improve its speaking
powers, I sometimes cause more than one hole to be made extending through the
substance of the pile that is not under pressure. In the drawings Figures 1, 2,
and 3, one such hole is shown in the centre and extending quite through the pile.
To prevent contact between the alternating sheets of tin foil I also generally make
the holes in them a little larger than the corresponding holes in the paper and
make the discs of tin foil smaller than the discs of paper as shown in Figures 7
and 8.
Figure 2 shows a telephone receiver the condenser of which is constructed of two
long pieces of tin foil or other suitable conducting material shown by the full
lines a a, with paper or corresponding insulating material, shown by the cross-
hatched lines b b, interposed between them. The leaves of foil are connected at
their opposite ends to four binding posts c, d, e f. At the bends of the condenser
the insulator and plates are nearer together than at the middle from the bends, and
this acts as if it were under greater pressure at the edge.
g
Figure 3 shows the receiver provided with a resistance coil C, contained within
the case and provided with binding posts 9 h. The terminals of the resistance coil
can be connected to posts dc for the purpose of shunting the condenser especially
when used on single or ground lines. One form of such resistance coil is shown
in Figures 9 and 10.
In Figure 4 the receiver is connected in multiple arc in the primary circuit.
Here, D indicates a transmitter, F the receiver, G a battery and E a resistance coil.
The circuit may be grounded at x. Figure 5 shows another way of shunting the
receiver with a resistance coil instead of putting the resistance coil or shunt in the
receiver case proper. Figure 6 shows a circuit analogous to that shown in Figure 4
except that a local microphonic circuit is introduced and the receiver F is placed in
multiple arc upon the secondary circuit. Here, G represents a battery on the
primary circuit, G a battery on the secondary circuit or lino E a resistance coil, and
Da transmitter, x shows where the line may be grounded if desired.
The resistance coils or shunts used for shunting the receiver should have a high
resistance and the resistance should be proportionate to the resistance of the line-
for instance on a line of two thousand ohms the shunt may have five thousand to
six thousand ohms.
When a proper amount of pressure is brought to bear on any one part of the
condenser pile leaving the other part very loose, and especially those parts near the
perforation, the condenser speaks the best because the condenser plates being
statically charged by the line battery they are able to vibrate when an extra or
secondary current is induced in the line and modifies the static charge of the
condenser.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed as communicated to
me by my foreign correspondent I declare that what I claim is :-
1. The receiving telephone herein described consisting of a condenser perforated
through its leaves with a shunting in the said receiver.
2. A receiving telephone consisting of a shunted condenser, which is normally
charged by a constant current on line, and current varying devices located at the
transmitting station in a primary or transmitting circuit and adapted to vary
the statical condition of the normally charged receiver and thereby reproduce
articulate speech and other sounds which actuate the transmitter.
3. A receiving condenser telephone located in a normally charged secondary
circuit extending to a transmitting station in combination with a high resistance
shunt around said condenser a local primary circuit to said secondary circuit located
at the transmitting station and containing current varying devices substantially as
described.

page_text: 4. A condenser telephone located in a normally charged secondary circuit
extending from the transmitting to the receiving station in combination with a
shunt around said condenser and current varying devices located in an independent
circuit at the transmitting station whereby any variation in the current in said
independent circuit creates a change of statical condition in the receiver and causes
it to reproduce the sounds which cause said current variation substantially as
described.