1881.] 



of Radiant Heat upon Gaseous Matter. 



315 



term, is converged upon the flask. When the experiment is carefully- 

 made, dry air proves as incompetent to produce sound as to absorb 

 radiant heat. 



In 1868, I determined the absorptions of a great number of 

 liquids whose vapours I did not examine. My experiments having 

 amply proved the parallelism of liquid and vaporous absorption, I 

 held undoubtingly twelve years ago that the vapour of cyanide of 

 ethyl and of acetic acid would prove powerfully absorbent. This 

 conclusion is now easily tested. A small quantity of either of these 

 substances, placed in a bulb a cubic inch in volume, warmed, and 

 exposed to the intermittent beam, emits a sound of extraordinary 

 power. 



I also tried to extract sounds from perfumes, w T hich 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 

 was of special interest. Professor Dewar was good enough to furnish 

 me with a pure sample of this gas. The sounds produced by it, when 

 exposed to the intermittent beam, were very powerful. 



Chloride of methyl, a liquid which boils at the ordinary temperature 

 of the air, was poured into a small flask, and permitted to displace the 

 air within it. Exposed to the intermittent beam, its sound was similar 

 in power to that of marsh-gas. 



The specific gravity of marsh-gas being about half that of air, it 

 might be expected that the flask containing it, when left open and 

 erect, would soon get rid of its contents. This, however, is not the 

 case. After a considerable interval, the film of this gas clinging to 

 the interior surface of the flask was able to produce sounds of great 

 power. 



A small quantity of liquid bromine being poured into a well-dried 

 flask, the brown vapour rapidly diffused itself in the air above the 

 liquid. Placed in the intermittent beam, a somewhat forcible sound 

 was produced. This might seem to militate against my former ex- 

 periments, which assigned a very low absorptive power to bromine 

 vapour. But my former experiments on this vapour were conducted 

 with obscure heat ; whereas, in the present instance, I had to deal 

 with the radiation from incandescent lime, whose heat is, in part, 

 luminous. Now the colour of the bromine vapour proves it to be an 



