212 Dr. J. Moser on the Microphonic 



lever. This would produce compensation by lengthening the 

 arm p c when the lever inclined downwards, and shortening it 

 when it inclined upwards. Another method would be to attach 

 one end of an independent string at the point B and the other 

 end to a point p, so that, if the arm A was deflected, a couple 

 would be introduced tending to keep it deflected. This method 

 would have the advantage of ready adjustment, by means of a 

 screw attached to the end of the compensating-spring. I do 

 not consider any of these methods so nearly perfect or so 

 simple as that which I have given prominence to in this paper; 

 but the main object has been to call attention to the principle 

 of compensation for such instruments. 



XXVL The Microphonic Action of Selenium Cells, 

 By Dr. James Moser*. 



WHEN I began these researches on the Transformation 

 of the Energy of Light into that of Sound by the 

 Photophone, I held the opinion which is still common, that 

 there are two kinds of photophones and three forms of light- 

 rays. My experiments led me to the conclusion that there 

 is only one way in which light acts photophonically. The 

 effect of radiation on selenium-cells is, in fact, the same as 

 that exerted on the majority of solid, liquid, and gaseous 

 bodies used as non-electric photophonic receivers. Though 

 rays may have different wave-lengths, all rays are the same 

 in kind. There are not three kinds — heating, luminous, and 

 chemical, but one and the same ray may have heating, che- 

 mical, and luminous effects. 



In February last, when I began these experiments, I 

 believed that the photophone could inform us as to the direct 

 correlation between light and electricity. A current cir- 

 culating around a beam of polarized light changes the plane 

 of its vibration. Hence we are led to conjecture that there 

 may exist further relations between light and electricity, and 

 that, as the electric current or lines of magnetic force affect 

 the beam, so, inversely, the beam may influence the electric 

 current or the magnetic lines of force ; and we may con- 

 jecture that such influence may manifest itself in the pho- 

 tophone. 



I therefore tried to change the magnetic condition of an 

 iron plate by light. I hoped, for instance, to get an electric 

 current in the coil of the telephone at the moment when 



* Communicated by the Physical Society, having been read June 25th, 

 188L 



