1881.] Radiant Energy into Sonorous Vibrations. 



513 



vibrations of the disk itself, or of the air in which the microphone was 



15. If the lens d, fig. 5, were removed, and the disk left supported 

 without any air cavity, either behind or in front of it, no perceptible 

 sound could be obtained, proving that the effects were really due to the 

 vibrations of the confined air, and not to those of the dish. It was 

 therefore determined to dispense with the disk altogether. 



' 16. Case (No. 1) similar to fig. 5 was taken, and the disk removed, 

 but the lens remaining, the sonorous effects were nil. 



17. Another case (No. 2), also similar to fig. 5, was taken under 

 similar circumstances, i.e., without the dish, but the effects were 

 very loud — 60 ; in fact, the best results which had yet been obtained. 

 Now, the only difference between the one case or cup and the other, 

 was that the one was blacked in the interior, and the other was not. 



18. Hence Case No. 1 was again taken without the disk, and though 

 when clean it gave no effect, when its interior was blacked by camphor 

 smoke, it gave sounds as strong as those in Experiment 17, viz., 60. 

 It was thus evident that the sonorous effects were materially assisted 

 by coating the sides of the containing vessel with a highly absorbent 

 substance, such as the carbon deposited by burning camphor. It re- 

 mained to be seen how far the lens played a part in this phenomenon. 



19. The lens was now removed from the front of the case, and it 

 was replaced by a moveable glass plate (1*5 millims. thick) (e) fig. 6 ; 

 the sounds were the same, but they gradually ceased on gradually un- 

 covering the front opening of the case, so as to give the air room to 



placed, was doubtful. 



expand. 



20. The glass plate e was replaced by a heavy rigid plate of rock- 

 salt 13 millims. thick, and the sounds were equally loud, namely, =60. 



