318  Tainter and Bell—Production of Sound by Light. 
Photophonic Transmitters. 
We have devised upwards of fifty forms of apparatus for 
varying a beam of light in the manner required, but only a few 
typical varieties need be described. 
(1st.) The source of light may be controlled, or (2nd) a steady 
beam may be modified at any point in its path. 
In illustration of the first method we have devised several 
and Dr. : 
Let a polarized beam of light be passed through a solution 
of bisulphide of carbon contained in a vessel inside a helix of 
insulated wire, through which is passed an undulatory current 
of electricity from a microphone or telephonic transmitter op- 
erated by the voice of a speaker. 
e passage of the polarized beam should be normally par- 
tially obstructed by a Nicols prism, and the varying rotation 
of the plane of polarization would allow more or less of the 
light to pass through the prism, thus causing an undulatory 
beam of light capable of producing speech. 
he beam of polarized light, instead of being passed through 
a liquid could be reflected from the polished pole of an electro- 
magnet in circuit with a telephonic transmitter. 
5. 
a municated to the gas or liq- 
uid, thus causing a vibrato 
change in the convexity of the glass surfaces and a correspond- 
ing change in the intensity of the light received upon the sen- 
sitive selenium. We have found that the simplest form of 
apparatus for producing the effect consists of a plane mirror 
observe that a lens of similar construction has been invented in France by 
Dr. Cusco, and is described in a recent paper in ature.” See, also, Scien. 
Amer., Aug. 28, 1880, xliii, 131. Mr. Tainter and I have used such a Jens in our 
experiments for months past. 
