The Milan exchange. (Milan, Gibson County, Tenn.) 1874-1978, 1880-09-30
The PhOtOphone---Sound Reproduced by /
Light.

The latest marvel in applied science
is the discovery by the inventor of the
Bell telephone and Sumner TaintOr of
|. Watertown, Mass, that Is sounds can
be produced by the action of "a variable
light from substances of all kinds, when
in the form of thin diaphragms.n In
other words, ray oflight is substituted
for the connecting wire, and sounds at
one station are reproduced ut another.
As is well known the action of the tele-
phone is due to variations in an electric
current, caused by diaphragm set in
vibration byit voice, the current thus
modified reproducing its variations on
a sensitive diaphraghm at the other end
OF the circuit. In the photophone,"
as the new invention is called, the
changes in the electric current are made
during its passage through selenium, a
substance heretofore known only as
chemical curiosity, but with the strange
property of conducting electricity more
easily when exposed to light than when
in the dark. A steady light allows a
current to pass through an even resist
ance; varied light varies the resist
ance, so that the current is stronger or
weaker after passing through the
selenium, and its variations are easily
turned, in telephone, into vibrations
of sound. Professor Bell and Mr..
Taintor have already spoken between
points about six hundred feet apart,
and they believe that the result can be.
obtained as far as beam of light can
be flashed. The simplest apparatus of
many devised consists of plane mirror
,f Hox-ihlo ol OilvraroH
scope glass or mica, which will CULVER
with vibrations of sound. On this is
gathered through lens beam of light
from any source, success having
been found with kerosene or can
die flame. The parallel beam re-
iected from the plane mirror is thrown
to distant concave mirror and focused
on piece of selenium, electrically
connected with telephone. The
voice throws the plane mirror into vi
brations which modify in intensity the
ray of light, which rapidly changes the
resistance of the distant selenium, this
varying the electric current in the tele-
phone as the voice now does directly.
Another means of affecting the beam of
light is by disk, perforated with Sits,
which is rapidly turned, producing in
the selenium continuous musical tone, .
whose pitch varies with the rapidity of
the disks rotation, silent motion thus
producing a sound. A strange thing is
that some substances placed in the beam
of light do not cut off the sound. A
sheet of hard rubber, for instance,
made the beam invisible, but the mu-
steal note was still heard. Other exper-
iments suggest the possibility of doing
entirely without the electric current in
the telephone at the receiving station.
MANY other substances were substituted
for selenium, the affected ray of light
focused upon them and the musical
note was heard without the aid of a
telephone or battery. Only carbon and
thin glass failed to give sound. Some
minor details of the difficulties encoun-
tered and overcome in using selenium
in the apparatus for speaking from
distance are of interest. A small bar of
selenium has resistance to electricity
equivalent TO that offered BY q telegraph
wire long enough to reaeh from theearth :
to the sun. Even the cold light of the
moon lessons this resistance and such
q brilliant light as that of burning mag
nesium wire halves it. But Bel and
Sumner had to work long to reduce this
resistance within. manageable limits
No selenium crystal was ever known to
measure less than 100000 ohmes of re-
sistance in the dark They have made
cells measuring only 800 ohmes in the
dark and 155 ohmes in the light, by
melting seleDium to brass conductors. . /.
chemical union being formed less
ers the resistance at the point of con-
tact of the two substances. Their fifty
forms of apparatus are based on one,of
two principles, --either to control the
source of light or to modify the beam
tsef, the. second being the most prsc-a
icaL--Sprinqffcld Mass. Repub Iicdn.
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