RADIATION. 19 



o 



tained a certain amplitude, the mutual jostling of the atoms 

 produces quicker tremors, and the light-giving waves fol- 

 low as the necessary product of the heat-giving ones. 



11. Absorption of Radiant Heat by Vapors 

 and Odors. 



We commenced the demonstrations brought forward in 

 this lecture by experiments on permanent gases, and we 

 have now to turn our attention to the vapors of volatile 

 liquids. Here, as in the case of the gases, vast differences 

 have been proved to exist between various kinds of mole- 

 cules, as regards their power of intercepting the calorific 

 waves. While some vapors allow the waves a compara- 

 tively free passage, the minutest bubble of other vapors, 

 introduced into the tube already employed for gases, causes 

 a deflection of the magnetic needle. Assuming the ab- 

 sorption effected by air at a pressure of one atmosphere to 

 be unity, the followng are the absorptions effected by a se- 

 ries of vapors at a pressure of one-sixtieth of an atmos- 

 phere : 



Name of vapor. Absorption. 



Bisulphide of carbon 4'7 



Iodide of methyl * 115 



Benzol 136 



Araylcne 321 



Sulphuric ether 410 



Formic ether 548 



Acetic ether 012 



Bisulphide of carbon is the most transparent vapor in 

 this list ; and acetic ether the most opaque ; one-sixtieth 

 of an atmosphere of the former, however, produces forty- 

 seven times the effect of a whole atmosphere of air, while 

 one-sixtieth of an atmosphere of the latter produces six 

 hundred and twelve times the effect of a whole atmos- 

 phere of air. Reducing dry air to the pressure of the acetio 

 



