RADIATION. 61 



13. Liquids and their Vapours in relation to 

 Radiant Heat. 



The deportment here assigned to atmospheric va- 

 pour 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 artificially 

 humid by pure distilled water. It has also been es- 

 tablished 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 quan- 

 tities of liquid, and the power of the vapours to inter- 

 cept the waves of heat was also determined. Com- 

 mencing 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 ether. Sulphuric ether. 



Acetic ether. Acetic ether. 



Formic ether. Formic ether. 



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 



