324 



THE POPULAR SCIEXCE MONTHLY. 



rr.ODUCTiox of sound by eadiant energy.^ 



By ALEXANDER GKAIIAM BELL. 



AT the time of my communication to the American Association f 

 the loudest effects obtained were produced by the use of sele- 

 nium, arranged in a cell of suitable construction, and placed in a gal- 

 vanic circuit with a telejihone. Upon allowing an intermittent beam 

 of sunlight to fall upon the selenium, a musical tone of great intensity 

 was produced from the telej^lione connected with it. 



But the selenium Avas very inconstant in its action. It was rarely, 

 if ever, found to be the case that two pieces of selenium (even of the 



same stick) yielded the same 



Fig. 7. ... 



results under identical cir- 

 cumstances of annealing, etc. 

 While in Europe last autumn, 

 Dr. Chichester Bell, of Uni- 

 versity College, London, sug- 

 gested to me that this incon- 

 stancy of result might be due 

 to chemical impurities in the 

 selenium used. Dr. Bell has 

 since visited my laboratory in 

 Washington, and has made a 

 chemical examination of the 

 various samples of selenium I 

 had collected from different 

 parts of the world. As I un- 

 derstand it to be his intention to publish the results of this analysis 

 very soon, I shall make no further mention of liis investigation than to 

 state that he has found sulphur, iron, lead, and arsenic in the so-called 

 " selenium," with traces of organic matter ; that a quantitative exami- 

 nation has revealed the fact that sulphur constitutes nearly one per 

 cent, of the whole mass ; and that when these impurities are eliminated 

 the selenium appears to be more constant in its action and more sen- 

 sitive to light. 



Professor W. G. Adams \ has shown that tellurium, like selenium, 

 has its electrical resistance affected by light, and we have attempted 

 to utilize this substance in place of selenium. The arrangement of 

 cell (shown in Fig. 7) was constructed for this purpose in the early 



* Continued from paae 197. 



f "Proceedings of American Association for the Advancement of Science," August 27, 

 1880 ; see, also, "American Journal of Science," vol. xx, p. 305 ; " Journal of the American 

 Electrical Society," vol, iii, p. 3 ; " Journal of the Society of Telegraph Engineers and 

 Electricians," vol. ix, p. 404 ; " Annales dc Chimie et de Physique," vol. xxi. 



\ "Proceedings of the Royal Society," vol. xxiv, p. 163. 



