' I 



CONCERNING THE CAUSE OF THE GENERAL TRADE 



WINDS 



BY GEO. HADLEY, ESQ., F. R. S. 

 [Phil. Trans. Vol. XXXIX, London, 1735-36, p. 5S] 



I think the causes of the General Trade Winds have not been 

 fully explained by any of those who have wrote on that subject, 

 for want of more particularly and distinctly considering the share 

 the diurnal motion of the earth has in the production of them. 

 For although this has been mentioned by some amongst the causes 

 of those winds, yet they have not proceeded to show how it 

 contributes to their production; or else have applied it to the 

 explication of these phenomena, upon such principles as will appear 

 upon examination not to be sufficient. 



That the action of the sun is the original cause of these winds, 

 I think all are agreed ; and that it does it by causing a greater 

 rarefaction of the air in those parts upon which its rays falling 

 perpendicularly, or nearly so, produce a greater degree of heat 

 there than in other places ; by which means the air there becoming 

 specifically lighter than the rest round about, the cooler air will 

 by its greater density and gravity, remove it out of its place to 

 succeed into it itself, and make it rise upward. But it seems, 

 this rarefaction will have no other effect than to cause air to rush 

 in from all parts into the part where 'tis most rarefied, especially 

 from the north and south, where the air is coolest, and not more 

 from the east than the west, as is commonly supposed: so that, 

 setting aside the diurnal motion of the earth, the tendency of 

 the air would be from every side towards that part where the 

 sun's action is most intense at the time, and so a NW. wind be 

 produced in the morning, and a NE. in the afternoon, by turns, 

 on this side of the parallel of the sun's declination, and a SW. 

 and SE. on the other. 



That the perpetual motion of the air towards the west, cannot 

 be derived merely from the action of the sun upon it, appears 

 more evidently from this: If the earth be supposed at rest, that 



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