66 



ON THE OKIGIN AND NATUBE OF 



It will be observed that in this table we presume that in 

 clear and undisturbed air the temperature at the surface is at 

 zero, which is found only in very cold localities ; and as the 

 temperature is presumed to be lower after the rate of 1° for 

 every one hundred yards of ascent, at the height of ten 

 thousand yards it will be 100*^ below zero. But as we 

 presume that the heat liberated by condensation and freezing, 

 as just explained, keeps the column in which these processes 

 are taking place for some time at S2°, the difference between 

 the two columns at the full height named must be for that 

 time 132°. In so very cold a locality as that of which we are 

 now treating, we know that any vapour which escaped from 

 the surface of the earth and passed into the atmosphere, 

 would be soon condensed ; but the heat that would then be 

 liberated would keep the product of that condensation in a 

 liquid state for some certain time, however short it might be, 

 yet in such a part that heat would pass rapidly away, and the 

 liquid would be frozen. The liberated heat of liquidity 

 would, however, now preserve the cloud of liquid and frozen 

 particles for some further time at 32° ; and then two pro- 

 cesses, first, condensation of vapour, and secondly', congelation 

 of water, being successively and rapidly repeated in a column 

 ascending to a great height, would keep the whole mass at 



