362 KANSAS CITY REVIEW OF SCIENCE. 
The apparatus used to give the required undulatory character to light con- 
sists of a flexible mirror of silvered mica or thin glass. The speaker’s voice is 
directed against the back of this mirror, as against the diaphragm of a telephone, 
and the light reflected from it is thereby thrown into corresponding undulations. 
In his experiments, chiefly with sunlight, Mr. Bell concentrates upon the dia- 
phragm mirror a beam of light, which, after reflection, is again rendered parallel 
by means of another lens. 
The beam proceeding from the transmitter is received at a distant station 
upon a parabolic reflector, in the center of which is a sensitive selenium cell con- 
nected in a local circuit with a battery and telephone. In a recent experiment, 
Mr. Bell’s associate operated the transmitting instrument, which was placed on 
the top of the Franklin school house, in‘Washington, about eight hundred feet 
distant’ from the receiver, placed in a window of Mr. Bell’s laboratory. 
Through this distance messages were distinctly conveyed by means of light. In 
his laboratory experiments Mr. Bell finds that articulate speech can be transmit- 
ted and reproduced by the light of an oxyhydrogen lamp, and even by the light 
of a kerosene lamp. 
The rapid interruption of the beam of light by a 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 at the transmitter. 
The importance of these investigations 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 radical changes in military and other signaling opera- 
tions. The heliograph, which has proved so useful in recent campaigns in the 
Afghan country and elsewhere, can now be made to talk orally yet silently over 
the heads of an enemy or across impassable streams or other low barriers. For 
rapid communication between distant exploring or surveying stations, the photo- 
phone also promises to be serviceable. 
Another result of Mr. Bell’s researches in this connection is the discovery 
that many other substances are sensitive to light. He has found this property in 
gold, silver, platinum, iron, steel, brass, copper, zinc, lead, antimony, German 
silver, Jenkins’ metal, Babbitt’s metal, ivory, celluloid, gutta percha, hard rub- 
ber, soft vulcanized rubber, papar, parchment, wood, mica, and silvered glass. 
The only substances found insensible to light are carbon and thin microscopic 
glass. —Sczentific American. 
DEEP SEA RESEARCHES. 
Dr. Carpenter, the great English physicist, has recently published some re- 
markable results of his elaborate studies of the latest deep sea explorations. The 
work of the scientific circumnavigation expedition in the Challenger, though com- 
pleted in 1876, has not until within a few months, if even now, been fully re- 
