Sound by Radiant Energy. 525 



Upon the Nature of the Rays that produce Sonorous Effects 

 in Different Substances. 



In my paper read before the American Association last 

 August, and in the present paper, I have used the word "light " 

 in its usual rather than its scientific sense ; and I have not 

 hitherto attempted to discriminate the effects produced by the 

 different constituents of ordinary light — the thermal, luminous, 

 and actinic rays. I find, however, that the adoption of the 

 word "photophone" by Mr. Tainterand myself has led to the 

 assumption that we believed the audible effects discovered by 

 us to be due entirely to the action of luminous rays. The 

 meaning we have uniformly attached to the words " photo- 

 phone " and " light " will be obvious from the following pas- 

 sage, quoted from my Boston paper : — 



"Although effects are produced as above shown by forms of 

 radiant energy which are invisible, we have named the appa- 

 ratus for the production and reproduction of sound in this way 

 the ' photophone,' because an ordinary beam of light contains 

 the rays ivhich are operative." 



To avoid in future any misunderstandings upon this point, 

 we have decided to adopt the term "radiophone" proposed by 

 M. Mercadier, as a general term signifying an apparatus for 

 the production of sound by any form of radiant energy, limit- 

 ing the words thermophone, photophone, and aciinophone to 

 apparatus for the production of sound by thermal, luminous 

 or actinic rays respectively. 



M. Mercadier, in the course of his researches in radiophony, 

 passed an intermittent beam from an electric lamp through 

 a prism, and then examined the audible effects produced in 

 different parts of the spectrum (Comptes Rendus, Dec. 6th, 

 1880). 



We have repeated this experiment, using the sun as our 

 source- of radiation, and have obtained results somewhat dif- 

 ferent from those noted by M. Mercadier. 



(1) A beam of sunlight was reflected from a heliostat (A, 

 fig. 12) through an achromatic lens (B), so as to form an image 

 of the sun upon the slit (C). 



The beam then passed through another achromatic lens (D) 

 and through a bisulphide-of-carbon prism (E), forming a spec- 

 trum of great intensity, which, when focused upon a screen, 

 was found to be sufficiently pure to show the principal absorp- 

 tion-lines of the solar spectrum. 



The disk interrupter (F) was then turned with sufficient ra- 

 pidity to produce from five to six hundred interruptions of the 

 light per second, and the spectrum was explored with the 



Phil, Mag. S. 5. No. 71. Suppl. Vol. 11. 2P 



