GEOLOGICAL CLIMATE. 



those carried by ocean currents, from temperate to 

 polar regions. Think of a south wind of 15 

 nautical miles per hour through a space 2300 feet 

 above the surface. The air thus in motion will be 

 T T T of the whole of the atmosphere over the region, 

 and will therefore be equal in weight to 3 fathoms 

 of water, and equal in thermal capacity to f of a 

 fathom of water. This, if at the same temperature 

 as our previously supposed current of water of 

 three quarters of a mile per hour will carry as 

 much heat as 15 fathoms deep of the water 

 current ; without taking into account the latent 

 heat of aqueous vapour condensed into liquid 

 water in the air as it cools, which gives a large 

 addition to the heat carrying capacity of wind in 

 ordinary atmospheric conditions. For example 

 air at 15 Cent, saturated with aqueous vapour 

 must have twice as much heat taken from it as dry 

 air at the same temperature, to cool it to o Cent. 



According to my brother Prof. James Thomson's 

 theory of the great primary and secondary 

 circulations of the atmosphere, the earth's surface 

 in the temperate and circumpolar regions must 



VOL. II. U 



