202 



MB. T. HOPKINS ON THE INFLUENCE OF SUN-HEATED L^ND 



the fact ; for in the Persian deserts to the south, as well as 

 across the arid country of Beloochistan, the wind continues 

 to blow from the heated north during the whole summer, 

 producing the great dryness that is found there. At Bagdad 

 and Bushire the thermometer sometimes stands as high as 

 135*^, yet no fact can be traced in the locality to counte- 

 nance the idea that any atmospheric current ascends from 

 the part. 



The great desert of Arabia, a considerable portion of which 

 is west of Persia, but a large part south of it, and much of it 

 lying within the northern tropic, presents the same general 

 features as the more northern and eastern deserts just spoken 

 of. It is not however to be supposed that the winds, as they 

 pass over these extensive and rugged countries, are never to 

 any extent disturbed in their courses by local influences. 

 Mountains and hills, there is no doubt, do and will more or 

 less affect them, and cause local deviations from their general 

 course. But the powerful cause that produces the great 

 general wind, seems to have sufficient force to overcome 

 these partial influences, and to determine the motion of the 

 aggregate mass of the atmosphere. 



The land in the broad expanse of the desert of Arabia is 

 probably raised to as high a temperature by the direct action 

 of the solar rays as any extensive portion of the surface of the 

 earth ; and if the mass of air resting on it could be raised and 

 made to overflow by mere surface heating, it would most 

 undoubtedly here ascend energetically and flow away in the 

 upper regions, leaving other air to come in below from any 

 contiguous part, but particularly from the comparatively cool 

 adjoining Arabian Sea. What, however, are the facts of the 

 case? Why, the general wind continues to blow over the 

 heated surface until it reaches and then passes over the 

 Arabian Sea ; that is, it moves from a hot surface to a cool 

 one. This large mass of air, coming from the heated lands 

 already described, makes its way over the hot deserts and 



