510 Prof. A. G. Bell on the Production of 



volt. The reversal of the rods again produced a reversal of 

 the deflection. 



In corroboration of the theory above stated, it should be 

 borne in mind that the chlorides of silver, copper, zinc, and 

 iron, when fused, are electrolytes. The liquid chloride of tin 

 is not an electrolyte ; and it was found that on immersing tin 

 in this liquid no deposition of crystals was observed when it 

 was so arranged that one part of the liquid was kept at the 

 heat of boiling water and another at the ordinary temperature 

 for two days ; nor was there the least action on a galvanometer 

 when arrangements were made for testing by that instrument. 



These experiments form a good lecture-table illustration of 

 the conversion of heat into electricity and chemical force. 

 They also seem to have a bearing on the theory of voltaic 

 action, since, from the nature of the substances employed, it 

 is difficult to imagine that chemical action in any way initiates 

 the current. 



LXVIII. Upon the Production of Sound by Radiant Energy. 

 By Alexandek Graham Bell *. 

 [Plates X. & XI.] 



IN a paper read before the American Association for the 

 Advancement of Science last August, I described certain 

 experiments made by Mr. Sumner Tainter and myself which 

 had resulted in the construction of a " Photophone" or ap- 

 paratus for the production of sound by light f ; and it will be 

 my object today to describe the progress we have made in the 

 investigation of photophonic phenomena since the date of this 

 communication. 



In my Boston paper the discovery was announced that thin 

 disks of very many different substances emitted sounds when 

 exposed to the action of a rapidly-interrupted beam of sunlight 

 The great variety of material used in these experiments led me 

 to believe that sonorousness under such circumstances would 

 be found to be a general property of all matter. 



At that time we had failed to obtain audible effects from 

 masses of the various substances which became sonorous in the 

 condition of thin diaphragms ; but this failure was explained 



* From advance proofs of a paper read before the National Academy 

 of Arts and Sciences, April 21, 1881, communicated by the Author. 



t. Proceedings of the American Association for the Advancement of 

 Science, August 27th, 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 ; 

 Annates de Chimie et de Physique, vol. xxi. 



