Ashtabula weekly telegraph. (Ashtabula, Ohio) 1880-1886, 1880-10-08
The Pnotophone.

In May, 1873, Mr.. Alexander Graham
Bell, well known in connection with the
telephone, announced before a scientific
society Of London his belief that it would
be possible 10 hear a shadow by inter-
rupting the action Of light upon seleni-
UNI. At the recent meeting of the
American Science Association in Bos-
ton, Mr.. Bell read paper describing at
length his experiments in the prOduc-
tiOn and reproduction of sound by light,
and the invention by Mr.. Summer Tain
ter and himself of an instrument for the
purpose.
The influence of light upon the cleo
trio conducting power of selenium is
well known. Mr.. Bell found the electric
resistance of some selenium cells of pecu-
liar construction only one-ffteenth as
much in the light as in the dark. 1t oc-
Cured to him that all the audible effects
obtained in the telephone by variation
of the electric current by sound waves,
could also be produced by variations of
| light acting upon selenium; and that
with suitable transmitting and receiving
apparatus voices might be conveyed
without a wire along line of light.
The fundamental idea on which rests
/ the possibility of producing speech by
the action of light is the reception of
| what Mr.. Bell terms an undulatory beam
| of light in contradistinction to an inter-
rupted beam; meaning by the former a
beam that shines continuously, but is
subject to rapid changes of intensity.
The apparatus used to give the re-
quired undulatory character to light
consists of a flexible mirror of dlvered
mica or thin glass. The speakers voice
is directed against the back of this mir
ror, as against the diaphragm of tele-
phone, and the light reflected from it is
thereby thrown into corresponding un.
dulations. In his experiments, chiefly
with sunlight, Mr.. Bell concentrates upon
the diaphragm mirror beam of light,
which, after reflection, is again rendered
parallel by another lens.
The beam proceeding from the trans
mitter is received at a distant station
upon parabolic reflector, in the center
of which is a sensitive selenium cell con-
nected in a local circuit with q battery
and telephone. In a recent expert
ment, Mr.. Bells associate operated the
transmitting instrument, which was
placed on the top of the Franklin school.
house, in Washington, about eight hum
dred feet distant from the receiver,
placed in window of Mr.. Bells labora.
tory. Through this distance messages
were distinctly conveyed by means OF
light. In his laboratory experiments
Mr.. Bell finds that articulate speech can
be transmitted and reproduced by the
light of an oxyhydrogen lamp, and even
by the light of a kerosene lamp.
| Trno MD nj of tho hoo ~, ~
light by perforated disk gives rise to
musical tones, siren fashion. With this
apparatus silent motion produces sound,
loud musical tones being emitted from
the receiver when no sound is made al
the transmitter.
The Importance of these investiga.
tiOns it is impossible now to estimate,
That the photophone can practically
take the place of the telephone is not
likely, though it is likely TO work radi,
cal changes in military and other sig
mailing operations. The heliOgraph,
which has proved so useful in recent
campaigns in the Afghan country and
elsewhere, can now be made TO talk or.
ally yet silently over the heads of an en-
emy or across impossible streams OF
other low barriers. For rapid cOmmu,
nication between distant exploring OIL
surveying stations, the photophone also
promises to be serviceable.
Another result of Mr.. Bell sresearche'
in this connection is the discovery thai
many other substances are sensitive to
light He has found this property il
60 d, silver, platinum, iron, steel, brass
copper, zinc, lead. anlimony, German
silver, Jenkins metal, Babbitt's metal
ivory, celluloid, gutta percha, hard rub
Der, soft vulcanized rubber, paper
parchment, wood, mica, and silveret
glass. The only substances found in
sensible to light are carbon and thir
, microscopic glass.-Scientifc american