Improvements in Telephones.
Year: 1898

page_text: Improvements in Telephones.
JOSEPH DEVONPORT FINNEY ANDREWS, 45, Fulham Park Gardens, Fulham,
London, S.W., Electrical Engineer, do hereby declare the nature of this invention
to be as follows:-
My invention relates to the improvement of electric telephones more especially
for the purpose of producing a louder transmission of speech. For the purpose
of transmitting I provide dust, shot, granules or powder of a conducting material
preferably carbon divided or dispersed by a soft or elastic material so that it
cannot collect in a mass such as by arranging it in cells or holes pierced through
a disc of soft or elastic material or within a single hole having radial arms project-
ing from the periphery or outside towards the centre but not meeting or within
pockets or tubes arranged together so as to constitute a disc or between pieces of
soft material such as a number of discs or pieces suitably supported but not neces-
sarily touching or left free to mix with the dust. Upon one side of the carbon
dust or granules I place a base preferably of carbon and upon the other side I
arrange a diaphragm or membrane preferably of carbon so that the carbon granules
or powder will touch both the membrane and the carbon base. I may stick the
soft or elastic material to the membrane and base with an adhesive substance.
I mount the membrane in a suitable frame so that it can vibrate with the vibra-
tions of speech or the like which will produce compression and relaxation on the
carbon dust or granules and when an electric current is passed from the membrane
through the carbon dust to the base variations in it will be produced in the known
manner. I may provide my membrane with carbon dust and a base on each side
of it. I sometimes mount the base with a spring behind it so as not to check the
amplitude of the vibration of the membrane or I may use a soft material instead
of the spring.
Instead of a base and a membrane on opposite sides of the carbon
dust I sometimes prefer to use two membranes with the carbon dust between
them and I may divide the carbon dust by two separators such as discs facing each
other and the membranes with a spring or soft or elastic material between them.
Both membranes would be arranged to vibrate simultaneously in opposite directions
and thus effect greater compression and relaxation than would be the case with a
single membrane. I may mix the carbon dust or granules with any suitable
material to form a paste or an elastic material. According to a modified form I
sometimes use solid pieces of carbon fixed in a soft material or network in the
place of dust and when I do so I need not use the base or second membrane, but I
would connect the solid pieces together as a whole and pass the current from them
to the disc or membrane. I may use dust and the arrangement of solid particles
in conjunction I may construct the membranes of any suitable material or of iron
or steel or other metal and I may attach carbon or other suitable discs to them
at the part where they meet the carbon dust or similar arrangement.
When I
construct the membranes of a magnetic metal I may use them also for receiving

page_text: soft material such as a number of discs suitably supported but not neces-
sarily touching or left free to mix with the dust. Upon one side of the carbon
dust or granules I place a base preferably of carbon and upon the other side I
arrange a diaphragm or membrane preferably of carbon so that the carbon granules
or powder will touch both the membrane and the carbon base.
I may stick the
soft or elastic material to the membrane and base with an adhesive substance:
I mount the membrane in a suitable frame so that it can vibrate with the vibra-
tions of speech or the like which will produce compression and relaxation on the
carbon dust or granules and when an electric current is passed from the membrane
through the carbon dust to the base variations in it will be produced in the known
manner. I may provide my membrane with dust and a base on each side
of it. Instead of a base and a membrane on opposite sides of the carbon dust I
sometimes prefer to use two membranes with the carbon dust between them and I
may divide the carbon dust by two separators such as discs facing each other and
the membranes with a spring or soft or elastic material between them. Both
membranes would be arranged to vibrate simultaneously in opposite directions and
thus effect greater compression and relaxation than would be the case with a
single membrane. I mix the carbon dust or granules with any suitable material
to form a paste or an elastic material. I may construct the membranes of any
suitable material or of iron or steel or other metal and I may attach carbon_or
other suitable discs to them at the part where they meet the carbon dust or similar
arrangement. When I construct the membranes of a magnetic metal I may use
them also for receiving speech by providing an electric magnet suitably arranged
with the membrane or membranes, such us by providing the two membranes
which would be arranged face to face with a magnetic rim common to both which
is so constructed as to form a bobbin or receive a bobbin containing
insulated wire. When a current is passed through the insulated wire
the membranes would be magnetised to opposite polarities and would attract
each other, and variations in the current would vary the degree of attraction
and speech would be produced by suitable variations. I may modify this
contrivance by making a bobbin containing the wire smaller than the
membranes and placing it near the centre of and between the membranes
and mounting each membrane in a suitably formed flange of the bobbin. The
body of the bobbin would be of iron and would effect attraction on the membranes
when a current is passed through the wire on the bobbin. Or instead of mounting
the membranes in the flanges of the bobbin or a frame or frames I
them by their centre to the poles of the electro magnet and allow the edges to be
free so that the attraction would be between the edges instead of between the
centres. Instead of winding the circuit wire on the bobbin forming the support to
the membranes I may mount the membranes in the same way and fix an electro
magnet between them with its poles presented one to each membrane. The
magnet may be of steel. I may construct the magnet with an outer envelope
of iron or steel. Instead of one of the membranes I may use a solid base prefer-
ably of iron and fix the magnet to it. In any form of my receiver I may provide
a permanent magnet to attract the membranes. I may use my combined receiver
and transmitter as a relay to introduce additional battery power and transmit
the message to another receiver or I may use the combination as a receiver
and transmitter for ordinary purposes when the receiver would react upon the
transmitter and intensify the result.
may attach
In Fig. 1, of the accompanying drawing I represent a disc of soft or flexible
material A shewn in section in Figure 2. Through this disc I pierce holes B in
which I would place granules of carbon when the dise is mounted between a
hase and a membrane or between two membranes as shewn in Figs. 5, 6, 7, & 8.
In Figs. 3, & 4, I show the flexible disc A with only one hole B provided however
with radial arms C to subdivide the dust. In Fig. 5, I show a section of a
transmitter in which A is the disc of flexible material provided with holes as in
Fig. 1, filled with carbon dust and fixed between a membrane M and a conducting

page_text: Figs. 1, 2, 3, 4, 5, 6, 7, & S, or in which the membranes or base and membrane
are separated by carbon dust dispersed in a soft or elastic material.
2. The construction of a microphone of two membranes with carbon dust
between them in cells the whole being mounted so that the air is caused to impinge
simultaneously on both membranes substantially as described, with reference to
Fig. 6.
3. The combination of a microphone and magnetic receiver for the purpose of
introducing a relay battery to augment the sound or re-transmit the current to
other receivers substantially as described and with reference to Fig. 14.
4. The construction of a transmitter with one membrane and compressible dust
on each side of it to act on two circuits.
5. The construction of magnetic receiver as described and illustrated in
Figs. 9, 10, 11, 12, & 15.