Radiant Heat, and its Conversion thereby into Sound. 499 



liquid followed its vapour in absorptive energy when the 

 quality of the heat was changed. On Monday the 31st, ac- 

 cordingly, the rays from the spiral being rendered parallel by 

 a rock-salt lens, the absorption of sulphuric ether was deter- 

 mined, and found to be 



6 6* 7 per cent.; 

 while the absorption of the liquid was 

 67-2 per cent., 

 which again gives a difference of only 05 per cent. 



On another occasion I found the absorption by sulphuric 

 ether to be : — 



Vapour . . . . 71 per cent. 

 Liquid .... 70 „ 

 On the 1st November I checked the result obtained with 

 the lime-light and mirror, by using the lime-light and rock- 

 salt lens. Here are the absorptions of the vapour and liquid 

 respectively : — 



Vapour . . . » 83*3 per cent* 

 Liquid .... 33*3 „ 



The absorptions are identical ; while the result agrees closely 

 with that obtained with the concave reflector. 



When the requisite quantity of sulphuric-ether vapour, viz. 

 7*2 mercury inches, was in the experimental tube, 1 tried 

 whether the radiation from a Leslie's cube, coated with lamp- 

 black and filled with boiling water, could pass through the 

 vapour. About 14 per cent, of the incident heat was trans- 

 mitted. Had I been asked at the time whether a liquid layer 

 of sulphuric ether 1 millimetre thick was pervious to the heat 

 of the cube, I should have replied with some confidence in the 

 negative. Hence, for the moment, I thought the experiment 

 opposed to the law that vapour absorption and liquid absorp- 

 tion, when equal quantities of matter are compared, are the 

 same. On actually testing a layer of the liquid ether 1 milli- 

 metre thick, the transmission of upwards of 6 per cent, of the 

 incident heat was observed. So that in this case also we have 

 harmony of deportment between liquid and vapour. The 

 absorption of the vapour exceeds that of the liquid, because the 

 heat from the cube radiated freely against the interior silvered 

 surface of the experimental tube, and by its reflection from 

 that surface had its path through the vapour augmented in 

 length. This augmentation naturally carried with it an in- 

 crease of the absorption. 



The next substance examined was hydride of amyl, the 

 boiling-point of which is 30° Fahr., or 5° lower than that of 



