452 frade Winds. [BookV. 



-generally run down their eafting on the parallel of 

 36' fouth *. 



Navigators have given the appellation of tradc- 

 winds to thefe general winds. 



Thofe winds, which blow in a certain direction for 

 a time, and at certain dated fcafons change and blow 

 for an equal fpace ef time from the oppofite point of 

 the compafs, are called monfoons. During the months 

 of April, May, June, July, Auguft, and September, 

 the wind blows from the (buthwara over the whole 

 length of the Indian Oevanj viz. between the parallels 

 of 28 N. and 28 S. lac. and between the eaftern coaft 

 of Africa and the meridian which pafles through the 

 weftern part of Japan , but in the other months, Octo- 

 ber, November, December, January, February, and 

 March, the winds in all the northern parts of the 

 Indian Ocean fhift round, and blow directly contrary 

 to the courle they held in the former fix months. 

 For fome days before and after the change, there are 

 calms, variable winds, and tremendous dorms, with 

 thunder, &c. 



Philofophers differ in their opinions refpecting the 

 caufe of thefe periodical winds ; but a moil probable 

 theory of the general trade-winds is, that they are oc- 

 -cafioned by the heat of the fun in the regions about the 

 equator, where the air is heated to a greater degree, and 

 confequently rarefied more than in thofe parts of the 

 globe which are nearer the poles. From this expanfion 

 of the air in thefe tropical regions, the denfcr air, in 

 higher latitudes, rufhes violently towards the equator 

 from both fides of the globe. By this conflux of the 

 denfer air, without any other circumftances intervening, 

 a direct northerly wind would be produced in the noi th- 



* See Nicholfon's Phil. vol. ii. p. 56. 



crn 



