PNEUMATICS. 307 



Tropics, or rather between 30 on the one side of 

 the Equator and 3C on the other. 



The Trade Wind declines somewhat from due east 

 toward the parallel to which the sun is vertical at 

 different seasons of the year. As the sun ap- 

 proaches the southern tropic, the Trade Wind is 

 directed somewhat to the south ; and as he ap- 

 proaches the northern, somewhat to the north. 



The cause usually assigned for the Trade Wind is 

 the constant motion, toward the west, of the spot 

 to which the sun is vertical, and where of course 

 the rarefaction is greatest. This, it is supposed, 

 draws along with it the air from the east. This, 

 however, is by no means a satisfactory explanation, 

 and it seems certain, that if the Trade Wind were 

 produced in that way, it must blow with great 

 force, instead of being a gentle breeze, moving at 

 the rate of seven or eight miles an hour. 



The opinion that the Trade Wind is produced by the 

 air, in its motion southward, falling back toward 

 the west, is mentioned, but rejected by H ALLEY. 

 It has since been espoused by FRANKLIN and LA 

 PLACE, and is, on the whole, less objectionable than 

 any other. 



The matter is here stated somewhat differently from 

 what is done by those authors, particularly the ef- 

 fect of the currents from the opposite hemispheres, 

 U2 in 



