1881.] 



Radiant Energy into Sonorous Vibrations. 



517 



into the interior of the tubes, which were always considerably in- 

 tensified by blackening their interiors, and closing the open end with 

 a glass plate. 



45. Since the sounds varied considerably in intensity, according to 

 the number of intermittences per second transmitted, white and ruby 

 glass plates were used, and it was found that the maximum effect 

 (60) was produced when the note corresponding to the intermittences 

 was — 



With white glass d/=297 vibr. per sec. 



With ruby „ & =247 „ 



This showed that the element of time was a function of the amount 

 of radiant energy transmitted through the plate. 



46. The two cases, which possessed air-cavities of different dimen- 

 sions, were tried with white glass : 



Case 1 gave 5 = 247 vibr. per sec. 

 Case 2 „ <Z'=297 „ 



Hence it is evident that there is a time element, and that the loud- 

 ness of the note emitted depends upon the rapidity with which the 

 contained air not only absorbs the degraded energy, but upon the 

 rapidity with which it gives up its heat to the sides of the case and 

 -the exits open to it. Though the pitch of the maximum note varied 

 with the cavity and the amount of radiant heat transmitted, its quality 

 never varied, notwithstanding the great diversity of materials used as 

 diaphragms. 



47. Since these sonorous effects are due to the expansions of 

 :absorbent gases under the influence of heat, and since wires are heated 

 by the transference of electric currents through them, it seemed pos- 

 sible that if we inclosed a spiral of fine platinum wire P (fig. 7) in a 

 dark cavity, abed, well blacked on the inside, and sent through it, 

 by means of the wheel-break W, rapid intermittent currents of elec- 

 tricity from the battery B, heat would be radiated, the air would 

 expand, and sounds would result. This was done, and the sounds 

 produced were excellent. In fact, with four bichromate cells, sounds 

 more intense than any previously observed were obtained. 



Furthermore it was evident that if the wheel-break (W) were re- 

 placed by a good microphone transmitter, articulate speech should be 

 heard in the case abed. This was done, and an excellent telephone 

 receiver was the consequence, by means of which speech was per- 

 fectly reproduced. 



The explanation of these remarkable phenomena is now abundantly 

 clear. 



It is purely an effect of radiant heat, and it is essentially one due to 

 the changes of volume in vapours and gases produced by the degrada- 

 tion and absorption of this heat in a confined space. The disks in Bell 

 t YOL. xxxi. 2 o 



