1881.] on the Conversion of Radiant Heat into Sound. 181 



fitting indiarubber stoppers, and permitted to remain undisturbed 

 tbrougliout the night. Tested after twelve hours, each of them 

 emitted a feeble sound, the flask last mentioned being the strongest. 

 Tested again six hours later, the sound had disappeared from three of 

 the flasks, that containing the phosphoric anhydride alone remaining 

 musical. 



Breathing into a flask partially filled with sulphuric acid instantly 

 restores the sounding power, which continues for a considerable 

 time. The wetting of the interior surface of the flask with the 

 sulphuric acid always enfeebles, and sometimes destroys, the sound. 



A bulb less than a cubic inch in volume, and containing a little 

 water lowered to the temperature of melting ice, produces very 

 distinct sounds. Warming the water in the flame of a spirit-lamp, 

 the sound becomes greatly augmented in strength. At the boiling 

 temperature the sound emitted by this small bulb * is of extraordinary 

 intensity. 



These results are in accord with those obtained by me nearly 

 nineteen years ago, both in reference to air and to aqueous vapour. 

 They are in utter disaccord with those obtained by other experi- 

 menters, who have ascribed a high absorption to air and none 

 to aqueous vapour. 



The action of aqueous vapour being thus revealed, the necessity 

 of thoroughly drying the flasks when testing other substances 

 becomes obvious. The following plan has been found effective ; — 

 Each flask is first heated in the flame of a spirit-lamp till every 

 visible trace of internal moisture has disappeared, and it is afterwards 

 raised to a temperature of about 400° C. While the glass is still hot 

 a glass tube is introduced into it, and air freed from carbonic acid by 

 caustic potash, and from aqueous vapour by sulphuric acid, is urged 

 through the flask until it is cool. Connected with the ear-tube, and 

 exposed immediately to the intermittent beam, the attention of the 

 ear, if I may use the term, is converged upon the flask. When tho 

 experiment is carefully made, dry air proves as incompetent to 

 produce sound as to absorb radiant heat. 



I also tried to extract sounds from perfumes, which I had proved 

 in 1861 to be absorbers of radiant heat. I limit myself here to the 

 vapours of pachouli and cassia, the former exercising a measured 

 absorption of 30, and the latter an absorption of 109. Placed in dried 

 flasks, and slightly warmed, sounds were obtained from both these 

 substances, but the sound of cassia was much louder than that of 

 pachouli. 



Many years ago I had proved tetrachloride of carbon to be 

 highly diathermanous. Its sounding power is as feeble as its 

 absorbent power. 



In relation to colliery explosions, the deportment of marsh-gas 



* In such bulbs even bisulphide of carbon vapour may be so nursed as to 

 produce sounds of considerable strength. 



