RADIATION. 61 



13. Liquids and their Vapours in relation to 

 Radiant Heat. 



The deportment here assigned to atmospheric 

 vapour has been established by direct experiments on 

 air taken from the streets and parks of London, from 

 the downs of Epsom, from the hills and sea-beach of 

 the Isle of Wight, and also by experiments on air in 

 the first instance dried, and afterwards rendered arti- 

 ficially humid by pure distilled water. It has also 

 been established in the following way: Ten volatile 

 liquids were taken at random and the power of these 

 liquids, at a common thickness, to intercept the waves 

 of heat, was carefully determined. The vapours of the 

 liquids were next taken, in quantities proportional to 

 the quantities of liquid, and the power of the vapours 

 to intercept the waves of heat was also determined. 

 Commencing with the substance which exerted the 

 least absorptive power, and proceeding onwards to the 

 most energetic, the following order of absorption was 

 observed : 



Liquids Vapours 



Bisulphide of carbon. Bisulphide of carbon. 



Chloroform. Chloroform. 



Iodide of methyl. Iodide of methyl. 



Iodide of ethyl. Iodide of ethyl. 



Benzol. Benzol. 



Amylene. Amylene. 



Sulphuric aether. Sulphuric aether. 



Acetic aether. Acetic aether. 



Formic eether. Formic aether. 



Alcohol. Alcohol. 

 Water. 



We here find the order of absorption in both cases 

 to be the same. We have liberated the molecules from 

 the bonds which trammel them more or less in a liquid 

 -condition ; but this change in their state of aggregation 



