LAWS OF HEAT. AIR. 99 



would be perpetually displaced below by the 

 denser portions which belonged to cooler lati- 

 tudes. We should have a current of air from 

 the equator to the poles in the higher regions of 

 the atmosphere, and at the surface a returning 

 current setting towards the equator to fill up the 

 void so created. Such aerial currents, combined 

 with the rotatory motion of the earth, would pro- 

 duce oblique winds; and we have in fact instances 

 of winds so produced, in the trade winds, which 

 between the tropics blow constantly from the 

 quarters between east and north, and are, we 

 know, balanced by opposite currents in higher 

 regions. The effect of a heated surface of land 

 would be the same as that of the heated zone of 

 the equator, and would attract to it a sea breeze 

 during the day time, a phenomenon, as we also 

 know, of perpetual occurrence. 



Now a mass of dry air of such a character as 

 this, is by far the dominant part of our atmos- 

 phere ; and hence carries with it in its motions 

 the thinner and smaller eddies of aqueous vapour. 

 The latter fluid may be considered as permeating 

 and moving in the interstices of the former, as 

 a spring of water flows through a sand rock.* 

 The lower current of air is, as has been said, 

 directed towards the equator, and hence it resists 

 the motion of the steam, the tendency of which is 



* Daniell. p. 129. 



