64 



ON THE ORIGIN AND NATURE OF 



Here we see that at the height of ten thousand yards from 

 the surface of the earth, the difference of temperature between 

 the clear and the clouded atmospheric columns produced by 

 condensation of vapour, is no less than 50^ ; and with a 

 force proportioned to that difference would the former column 

 be disposed to press up the latter, whilst the pressure upwards 

 at the various intermediate heights would be as the numbers 

 expressing the difference of temperature. 



So far we have treated of the condensation of vapour 

 carrying high temperature to great elevations ; but at a certain 

 stage of the process a new power comes into action. The 

 undisturbed atmosphere was presumed to be of a lower 

 temperature than S2°, above the height of four thousand 

 eight hundred yards ; any vapour, therefore, ascending above 

 that height and entering the cold air that existed there, would 

 be liable to be not only condensed into water, but to be 

 frozen into snow! And were it not for the heat that is 

 liberated by condensation, the vapour that penetrated this 

 lofty region would be not only condensed, but frozen. And 

 further, although condensation liberates much heat and keeps 

 the temperature in the ascending column above the freezing 

 point to a considerable height, yet at some greater elevation 

 that point will be reached even within the comparatively 

 warm ascending column. When this takes place and freezing 

 commences within the column, we have a result differing from 

 that which has been pointed out, as a new law then comes 

 into operation. 



When, through reduction of incumbent pressure, the 

 ascending mass cools down to a temperature below 32°, the 

 particles of water that had been formed by condensation are 

 frozen ; and in freezing, the liquid water gives out the latent 

 heat that is always liberated when water is converted into 

 ice. Now this liberated heat will have a tendency to keep up 

 the temperature of the ascending column, and of the w^ter 

 and ice that are in it, and to prevent that temperature from 



