1881.] 



Radiant Energy into Sonorous Vibrations. 



507 



light rays, are remarkably sensitive to this intermittent action. Dr. 

 Tyndall has more recently read a paper before the Society* proving 

 that these sonorous effects are a function of all gases and vapours 

 * absorbing radiant heat, and that the intensity of the sounds produced 

 is a measure of this absorption. 



The negative proof of Messrs. Bell and Tainter can be rendered 

 positive if it can be shown that ebonite is diathermanous. The author 

 provided himself with several sheets of different substances, and a 

 sensitive radiometer. A standard candle and a lime-light were used as 

 sources of energy, the former fixed four inches and the latter four 

 feet from the radiometer, which was carefully screened from all dis- 

 turbing influences but that of the source. The number of revolu 

 tions made by the radiometer per minute was counted, first without 

 any screen, and then with each sheet successively interposed ; and the 

 average of several observations was taken. The following is the result, 

 and the numbers indicate the relative diathermancy of the substances 

 used to the source of light used : — 



1. Experiments on Diathermancy. 



Material. 



Source of radiant energy. 



Candle, 4 inches. 



Lime-light, 4 feet. 





100 



100 



Ebonite, No. 1 ('4 millim.) .... 



60 



91 



„ „ 2 (-9 millim.) 



24 -3 



79-3 



„ 3 



24 3 



79-3 



„ 4 



24 3 



68 -2 



„ 5 



24-3 



68 -2 



„ „ 6 (*4 millim.) .... 







9 





44-3 



61 -4 





60 



54-5 



„ (vulcanized) 











„ (and ozokerit). . . . 







6-8 





0-14 



9 

























4-5 









4-5 













0-6 





Ebonite was, however, proved to be very variable, and while some 

 pieces proved to be as diathermanous as rocksalt, others of the same 

 thickness were found to be quite athermanous. 



Ebonite therefore, being sometimes diathermanous and opaque, it is 

 clear that the sonorous vibrations of Bell and Tainter are the result of 

 * " Proc. Roy. Soc," vol. 31, p. 307. 



