Tainter and Bell— Production of Sound by Inght. 321 
Kaperiments to ascertain the nature of the rays that affect 
uM, 
We have made experiments with the object of ascertaining 
the nature of the rays that affect selenium. For this purpose 
we have placed in the path of an intermittent beam various 
absorbing substances. 
Prof. Gross has been kind enough to give his assistance in 
ete these experiments. 
hen a solution of alum, or bisulphide of carbon, is em- 
ployed, the loudness of the sound produced by the intermit- 
tent beam is very slightly diminished, but a solution of iodine 
in bisulphide of carbon cuts off most, but not all, of the audi- 
ble effect. Even an x neice opaque sheet of hard rubber 
does not entirely do t 
This observation, at was first made in Washington, D. C., 
by Mr. Tainter and myself, is so curious and suggestive that I 
give in full the ant for studying the effect. 
9. 
hen a sheet of hard rubber, A, was held as shown in the 
diagram (fig. 9) the rotation of the disc or wheel B interr upted 
what was then an invisible beam, which passed over a space of 
several meters before it reached the lens C, which finally con- 
centrated it upon the selenium cell, - 
A faint but perfectly perceptible musical tone was heard From the 
telephone connected with the selenium that could be a 
at will by placing the hand in the path of the invisible bea 
It wou . be piston without further experiments to ipho- 
ulate too much concerning the nature of these invisible rays 
but it is difficult to believe that they can be heat rays, as the 
effect is produced through two sheets of hard rubber having 
between them a saturated solution of alum 
Although pe a are produced, as above ‘shown, by forms of 
radiant energy w are invisible, we have named the appara- 
tus for the production and reproduction of sounds in this way 
“the Photophone,” because an ordinary beam of light con- 
— the rays which are operative. 
M. Jour. Sct. Siar” mapa, Vou, XX, No, 118.—Ocr., 1880. 
