Radiant Heat, and its Conversion thereby into Sound. 503 



same diameter, but furnished with circumferential teeth and 

 interspaces. The disk was mounted vertically on a whirling- 

 table, and caused to rotate across the beam near the focus of 

 the concave mirror. Immediately behind the disk was placed 

 the flask containing the gas or vapour to be examined, while 

 an india-rubber tube, ending in a hollow cone of ivory or box- 

 wood, connected the flask with the ear. With this arrange- 

 ment, simple as it is, sounds of surprising intensity were 

 obtained with all those gases and vapours which my previous 

 experiments with the experimental tube and thermopile had 

 proved to be powerful absorbers of radiant heat. The final 

 arrangement was that shown in fig. 6. 



The source of heat is the carefully worked and centred 



lime-cylinder L, heated by the oxyhydrogen flame. The 



rays from this source are received by the concave mirror R, 



and converged upon the bulb B, which contains the substance 



° ^ 2P2 



