4 CLIMATE AND EESOUECES OF 



As Upper India lies between the parallels of 25 and 33 N., 

 and the north-east trade-winds extend as far north as 80, 

 the prevalent winds to that degree of latitude should be east, 

 and not west, were there not local causes at work acting ad- 

 versely; and the winds north of the parallel of 30 should 

 be more variable, and not so persistently from the west as 

 they now are. 



The fact of these hot west winds getting up daily shortly 

 after sunrise, their period of greatest intensity being about 

 2 or 3 P.M., and their gradual decrease after that time till 

 about sunset, when they die away, points to solar heat as the 

 cause of their origin. 



Solar heat is considered to be the primary cause of all 

 winds, and we have merely to consider the causes which in 

 Upper India tend to make the wind a west wind, and thus 

 contrary to the direction of the trade- winds, in whose course 

 Upper India lies. 



We know that heated air expands and ascends, and its room 

 is taken up by cooler, denser air, which rushes into its place 

 to preserve an equilibrium, and to fill what would otherwise 

 be a vacuum ; or it may be that the cooler, denser air, by its 

 greater specific gravity, sinks and spreads over the ground, 

 forcing the lighter air to ascend. The result is the same, a 

 rush of air, i.e. a wind. The draught in an ordinary fire- 

 place is caused by the expansion and ascension of the air over 

 the fire as it becomes heated. The ascension is due to cooler, 

 denser air sweeping along the floor, and displacing by its 

 greater gravity the air over the fire as it becomes heated and 

 is lighter. The histories of all large fires, from that of London 

 to that of Chicago, state that there has been a wind during 

 the time the fire was raging; but it is not always clear that 

 there was a wind previous to the breaking out of the fire. 

 The ascension of the heated air in these cases, or rather the rush 



