56 FRAGMENTS OF SCIENCE. 



and the light-giving waves follow as the necessary 

 product of the heat-giving ones. 



11. Absorption of Radiant Heat by Vapours and 

 Odours. 



We commenced the demonstrations brought forward 

 in this lecture by experiments on permanent gases, and 

 we have now to turn our attention to the vapours of 

 volatile liquids. Here, as in the case of the gases, 

 vast differences have been proved to exist between 

 various kinds of molecules, as regards their power of 

 intercepting the calorific waves. While some vapours 

 allow the waves a comparatively free passage, the 

 faintest mixture of other vapours causes a deflection of 

 the magnetic needle. Assuming the absorption effected 

 by air, at a pressure of one atmosphere, to be unity, 

 the following are the absorptions effected by a series of 

 vapours at a pressure of -^th of an atmosphere : 



Name of vapour Absorption 



Bisulphide of carbon 47 



Iodide of methyl 

 Benzol . 

 Amylene 

 Sulphuric ether 

 Formic ether. 

 Acetic ether . 



115 

 136 

 321 

 440 

 548 

 612 



Bisulphide of carbon is the most transparent vapour 

 in this list ; and acetic ether the most opaque ; -g^th of 

 an atmosphere of the former, however, produces 47 

 times the effect of a whole atmosphere of air, while -^th 

 of an atmosphere of the latter produces 612 times the 

 effect of a whole atmosphere of air. Eeducing dry air 

 to the pressure of the acetic ether here employed, and 

 comparing them then together, the quantity of wave- 



