OF THE RARTH's ROTATION ON WINDS. 25 1 



in order to account for unexplained facts. But if no in- 

 fluence of the kind can be traced in parts near to the polar 

 circles,, say from 74° of latitude, are we at liberty at once 

 to assume, without any attempt at proof, that that in- 

 fluence is great within the tropics ? It appears an unwar- 

 ranted assumption. 



Even within the tropics, however, there is strong evi- 

 dence to show the fallacy of the assumption that is here 

 combated. Over the eastern side of the Atlantic Ocean, 

 from Sierra Leone, in west longitude 15°, a wind generally 

 blows with considerable force towards the east, in the Gulf 

 of Guinea, to beyond the meridian of Greenwich; and 

 therefore the air constituting the wind moves eastward 

 faster than the surface over which it is passing ; and there 

 is good reason for presuming that it continues its eastern 

 course far into the interior of the continent of Africa. 

 The whole of this part is near to the equator, and the 

 comparative increase of rotatory velocity is therefore not 

 considerable ; but the positive rotation here is very rapid, 

 say, in round numbers, 1000 miles an hour. And yet, so 

 far from the air being left behind by the surface, it moves 

 so much faster as to make it a wind of considerable 

 strength. 



In like manner, on the eastern side of the Tropical Pa- 

 cific Ocean, winds blow from the west towards the east, 

 and of course the air in them must move eastward faster 

 than the surface of the globe on which it presses. One 

 of them blows with considerable constancy, another is in- 

 termitting in its action, but both are illustrative of the 

 subject under consideration. 



The former wind is generally found blowing from the 

 west of California, in about latitude 30° north, to the 

 equator in the Gulf of Panama ; and therefore it passes 

 eastward over about 40° of longitude faster than the sur- 

 face of the earth does on which it presses. The other 



