A Method of and Apparatus for Transmitting Sounds to a Distance by Means of Light.
Year: 1888

page_text: A Method of and Apparatus for Transmitting Sounds to a Distance
by Means of Light.
I, LEON JULES LE PONTOIS, of No. 95 Boulevard Beaumarchais, Paris, in the
Republic of France, 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 relates to means of transmitting articulate and other sounds over great
distances by means of light rays, without requiring an electric conductor or other
communication between the transmitting and the receiving stations.
For this purpose at the transmitting station I convert sonorous waves into luminous
vibrations of intensities proportional to the amplitudes of the sound waves. I direct
these luminous vibrations towards the receiving station, where I reconvert them into
sonorous waves of proportional amplitude, thus reproducing the sounds emitted at the
transmitting station. The transmitting and receiving apparatus which I employ may
be varied in form and construction. I will describe several forms of these referring to
the accompanying drawings.
Fig. 1 is a diagram of transmitting apparatus used for light made to vibrate at its
source by means of apparatus such as is shewn in Fig. 4 which I will first describe.
A is a lamp of great illuminating power having a central air supply through a
pipe F which communicates with a speaking instrument consisting of a chamber
divided by a diaphragm B, of celluloid or other suitable material, into two compart-
ments the one Ca segment of a sphere the other D of paraboloid form provided with a
small valve G opening inwards.
When speech or other sound is directed into a mouth piece E communicating with C,
the diaphragm B is caused to vibrate as indicated by the dotted lines B' B' and thus
air is forced out of D to the lamp or drawn into D through the valve G. The
amplitude and rapidity of the vibrations of the diaphragm B being proportional to
those of the sound waves, the pulses of air transmitted to the lamp cause proportional
vibrations of the light.
Referring now to Fig. 1, the light thus caused to vibrate is situated at F the focus
of a parabolic reflector H by which most of the emitted rays are reflected parallel to
the axis.
Those rays that could not be caught by the reflector are passed through a lens T

page_text: giving them parallel direction, and in order to give this direction to such of the rays
as after reflection would pass through the lens, the vertex of the paraboloid H is curved
into two parabolic segments J and K which cause those rays to undergo two
reflections. In front of the reflector is a glass L of spherical form and of red colour,
which rectifies the directions of the rays and suppresses the other colours. A colour
other than red may be employed, provided that at the receiving station it is treated, as
will hereafter be described, with the complementary colour.
Instead of employing a light which vibrates at its source, vibrations may be imparted
to the rays from a steady light as shewn in Fig. 2, where F is a steady light situated
as in Fig. 1 within a parabolic reflector, arranged as already described, but faced with
a lens M causing the reflected rays to converge. These converging rays are received
on a mirror P which is supported on light springs R in front of a diaphragm B to
which it is connected by a small magnet and armature Q. The diaphragm B fronts
a chamber N communicating with a mouthpiece E. A mirror S is fixed parallel to P,
and near the focal intersection of the rays reflected from T is fixed perpendicular to S
and Pa screen V with a hole through it allowing all the rays to pass through it
when P is in reposo.
As the mirror P is caused to vibrate by the sound pulses, the
number of rays passing through the hole of V is made to vary, and these reflected
from S are transmitted parallel through a Tresnel lens T and a red glass U.
According to another arrangement shewn in Fig. 3, the fixed light F is situated in
a focus of an elliptical reflector H causing the rays to converge to the other focus F¹,
beyond which are fixed the Tresnel lens T and the coloured glass U. In the course
of the rays towards these is interposed the vibratory apparatus X Y shewn to an
enlarged scale in vertical sectional elevation and horizontal section by Fig. 5. Of
two gratings X and Y having coincident openings between their bars, the one Y is
fixed, the other X is free to slide in a guide ¹ and is connected by a magnet and
armature Q to a diaphragm B fronting the chamber C communicating with the
mouthpiece E. As the diaphragm B is caused to vibrate by sound waves, the
grating X is caused to move, obstructing more or less the passages between the bars
of Y, and so producing vibrations of the light transmitted from the apparatus shown in
Fig. 3.
The varying beam of light proceeding from any of the transmitting apparatus
above described may have great penetrating power so as to be visible at a great
distance or through fog, especially when such arrangements as those shown in Figs. 2
and 3 are adopted, employing at F a powerful electric lamp. Even when the
transmitting apparatus is somewhat below the horizon of the receiving station, or
beyond a rising ground, aerial refraction may render the light visible.
The receiving apparatus, like the transmitting apparatus may be varied in form
and construction. Fig. 6 shews one form adapted for making the varying light act
on a telephonic receiver. A dark chamber a is provided with a finder telescope c.
and is mounted so that it can be directed vertically or horizontally so as to receive
the parallel transmitted rays on its lens 6 by which they are converged. The rays
diverging beyond the focus of b are again converged by an achromatic lens d adjustable
in position, and thrown on the face of a prisme which is blackened except in one
place for their reception and is provided with a sliding screen f. In order to render
more effective the rays falling on e, they are reheated by combining them with hot
rays of their complementary colour which do not affect the amplitude or rapidity of
their vibrations.
For effecting this reheating, I employ a lamp g within a reflecting case through
an opening i of which the rays pass to a lens J rendering them parallel. In front of
this lens is a circular screen k, shewn in front view in Fig. 6, having through it
several openings k fitted with green glasses of various depths of tint.
A
By turning round one or other of these glasses may be brought in line for the
rays to pass through it to a reflector by which they are thrown upon the prism e.
small telescope m enables the observer to see the incidence of the rays on e and to
make the necessary adjustments to bring the green and red rays together on e, as he
can notico by sliding the screen f forwards to receive them.

page_text: According as the red rays are stronger or weaker he uses a glass k¹ of more or less
deep tint of green. The directions of the two sets of rays relatively to the prism
are such that the angle which the ray of each colour makes with the prism corre-
sponds with the angle at which it would be refracted by the prism from a pencil of
white light.
When this condition is observed the two sets of rays become combined in the prism
forming white light.
The variations in the rays of one of the colours modifies the whiteness of the com-
bined rays and consequently modifies the heat rays which pass through a lense W
beyond the prism, its diathermic power varying with the colour. It thus results that
the heating of the varying red rays by the hot green rays is proportional after their
passage through W to their intensity.
Obviously the reflector might be dispensed with, the heating lamp 9 taking its
place and sending rays directly upon e.
In what precedes I have spoken of red and green rays, but it is to be understood
that rays other than red might be transmitted and heated by rays of the suitable
complementary colour instead of
green.
The combined rays transmitted through W are made to act on a transformer in
which is utilised the peculiar property that selenium has of varying its electrical
resistance under variations of temperature, in the following manner.
A conductor n from a battery p having in its course a telephonic receiver t, has part
of its circuit q formed wholly or partly of selenium.
g
As this is acted on by the varying heat rays from W causing variations of its
electrical resistance, these variations are converted by the telephonic receiver into
sound waves corresponding with those which acted on the transmitter.
The selenium resistance 9 may be constructed as follows.
On a strip of brass covered with parchment paper is coiled helically a brass wire,
and the whole is covered with a thin layer of selerium which is coated in part with
lampblack to receive the heat rays.
The two ends of the wire are connected to the conductor n.
Instead of employing selenium and its electrical action as above described, the rays
proceeding from the prism e may be made to act on apparatus such as is shewn in
section by Fig. 7.
This consists of a parabolic reflector 9 internally coated with lamp black or lined
with other heat absorbent such as coloured woollen texture.
The reflector q is fronted by a very thin parabolic glass r and is provided with an
ear tube s.
9.
The vibratory rays pass through and are absorbed by the lining of the reflector
This absorption has the effect of producing sonorous vibrations within the interior of
the apparatus, and these are reflected by r to the ear applied to s.
In order to prevent the reflector from becoming overheated by the absorption of
heat by its lining it is covered outside with metal or other good heat conducting and
radiating material.
I have described the use of a prism e for combining the red and green rays, but this
might be dispensed with, these rays being directed together on the transforming part
of the apparatus.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The herein described method of transmitting sounds by means of light, that is
to say, by means of a transmitting instrument transforming sound waves into luminous
vibrations of proportional intensity and rapidity, and directing these upon a receiving
instrument by which the vibratory rays are heated and retransformed into sound
waves corresponding to those which act on the transmitter.
2. Transmitting apparatus, substantially as described with reference to Figs. 1
and 4, wherein sound waves acting on a diaphragm cause variations in the air

page_text: supply and illuminating power of a lamp, and the rays of the lamp thus varied are by
a reflector and lens transmitted parallel through a coloured glass.
3. Transmitting apparatus, substantially as described with reference to Fig. 2,
wherein constant rays converged by a reflector and lenses are, by a mirror moved by a
diaphragm acted on by sound waves, reflected through an orifice, on a second mirror,
and thence by a lens and coloured glass transmitted parallel, with variations resulting
from the movements of the former mirror.
4. Transmitting apparatus, substantially as described with reference to Figs. 3
and 5, wherein constant rays converged by a reflector and lens are passed through a
double grating one member of which is moved by a diaphragm acted on by sound waves,
and the rays varied by passing through the openings thus varied are transmitted
parallel through a lens and coloured glass.
5. Receiving apparatus substantially as described with reference to Fig. 6 wherein
the varying coloured rays arriving from the transmitter, converged by lenses and
combined with hot rays of complementary color are directed, with or without inter-
vention of a prism, upon selenium in an electric circuit causing variations of resistance
which act on a telephonic receiver in the circuit.
6. Receiving apparatus substantially as described with reference to Figs. 6 and 7,
wherein the varying colored rays arriving from the transmitter, converged by lenses
and combined with hot rays of complementary colour, with or without the inter-
vention of a prism, are directed on the heat absorbent lining of a covered reflector
causing therein sonorous vibrations which are reflected by the cover to an ear tube.
Dated this 7th day of April 1888
ABEL & IMRAY,
Agents for the Applicant.