SOME CURIOSITIES.
Until within recent years it was never
supposed that a sunbeam would ever laugh except in
poetry. But the modern scientist has taken it
out of the realm of poetry and put it into the prosy
play of every-day life. The Radiophone, invented
by A. G. Bell, is an instrument by which articulate
or other sounds are transmitted through the medium
of a ray of light. It has as yet no practical
application and has never gone beyond the experimental
stage, but as a bit of scientific information it is
very interesting.
If we introduce into an electric circuit
a piece of selenium, prepared in a certain way, its
resistance as an electric conductor undergoes a radical
change when a beam of sunlight is thrown upon it.
For instance, a selenium cell, so called, that in
the dark would measure 300 ohms resistance, would
have only about 150 ohms when exposed to sunlight.
This amount of variation in a short circuit of low
resistance would produce a considerable change in
the strength of a current passing through it from
a battery of a given voltage.
If now we connect a selenium cell
to one pole of a battery, and thence through a telephone
and back to the other pole, we have completed an electric
circuit, of which the selenium cell is a part, and
any variation of resistance in this cell, if made
suddenly, will be heard in the telephone. Let
the diaphragm of a telephone transmitter have a very
light, thin mirror on one side of it, and a beam of
sunlight be thrown upon it and reflected from that
on to the selenium cell, which may be some distance
away. Then, if the diaphragm is thrown into vibration
by an articulate word or other sound, the light-ray
is also thrown into vibration, which causes a vibratory
change of resistance in the selenium cell in sympathy
with the light-vibrations; and this in turn throws
the electric current into a sympathetic vibratory
state which is heard in the telephone. So that
if a person laughs or talks or sings to the diaphragm,
the sunbeam laughs, talks and sings and tells its story
to the electric current, which impresses itself upon
the telephone as audible sounds articulate
or otherwise. Instead of the telephone, battery
and selenium cell, a block of vulcanite or certain
other substances may be used as a receiver; as a light-ray
thrown into vibration has the power to produce sound
or sympathetic vibration in certain substances.
Another curious application of the
selenium cell has been attempted, but has scarcely
gone beyond the domain of theory. This apparatus,
if perfected, might be called a Telephote. It
is an apparatus by which an illuminated picture at
one end of a line of many wires is reproduced upon
a screen at the other end. The light is not actually
transmitted, but only its effects. Suppose a
picture is laid off into small squares and there is
a selenium cell corresponding to each square and for
each selenium cell there is a wire that runs to a
distant station in which circuit there is a battery.
At the distant station there are little shutters,
one for each wire, that are controlled by the electric
current and so adjusted that when the cell at the
transmitting-end is in the dark the shutter will be
closed. Now if a strong light be thrown upon
the picture at the transmitting-end, and each square
of the picture reflects the light upon its corresponding
selenium cell, the high lights of the picture will
reflect stronger light than the shadows, and therefore
the wires corresponding to the high-light squares will
have a stronger current of electricity flowing through
them, because the resistance of the circuit is less
than the ones connected with the darker shadows.
So that the degree of current-strength in the various
wires will correspond to the intensity of light reflected
by the different sections of the picture. The
shutters are so adjusted that the amount of opening
depends upon the strength of current. The shutters
corresponding to the high lights of the picture will
open the widest and throw the strongest light upon
the screen, from a source of light that is placed
behind the shutters. The shutters that open the
least will be those that are operated upon by the
shadows of the picture. Inasmuch as a picture
thrown on a screen from a source of light is wholly
made up of lights and shadows, the theory is that
this apparatus perfectly constructed would transmit
any picture to a distance, through telegraph-wires.
It must not be understood that the rays of light are
transmitted through the wires as sound-vibrations are.
Light, per se, can be transmitted only through
the luminiferous ether, as we have seen in the chapter
on light in Volume II.
While we are talking about these curious
methods of telegraphic transmission, I wish to refer
to an apparatus constructed by the writer in 1874-5,
for the purpose of receiving musical tones or compositions
transmitted from a distance through a wire by electricity.
(A cut of this apparatus is shown on page 875 of “Electricity
and Electric Telegraph,” by Prescott, issued
in 1877.) It consists of a disk of metal rotated by
a crank mounted on a suitable stand. The electric
circuit passes through the disk to the hand of the
operator in contact with it, thence running through
the line-wire to the distant station. Now, if
a tune is played at that station, upon an electrical
key-board, as described in a previous chapter, and
the disk rotated with the fingers in contact with
it, the tune or other sounds will be reproduced at
the ends of the fingers. After the telephone was
invented and put into use I used this revolving disk
as a receiver for speech as well as music, and by
this means persons may carry on an oral conversation
through the ends of their fingers. This apparatus
has been confounded in the minds of some people with
Edison’s electromotograph. The phenomena
of the electromotograph were produced by chemical effects,
while that of the apparatus just described is electrostatic
in its action. The electrostatic disk was made
in the winter of 1873-4, while Edison’s electrochemical
discovery was made some time later.