C 137 ] 
ward the fun. For here we mu ft confefs, that the 
fun is the great agent in detaching vapour and exha- 
lation from their maffes ; whether he ads immedi- 
diately by himfelf, or by his rendering the eledric 
fire more adive in its vibrations : but their fubfe- 
quent afcent I attribute intirely to their being ren- 
der’d fpecifically lighter than the lower air, by their 
conjundion with this eledrical fire. The fire, which 
furrounds the vapour, beginning to condenfe, and the 
vapour to fubfide, in paffing the tropics, becomes a 
greater prefTure on the air beneatli, and by that 
means forces fome part back into the tropics, in the 
place of that air protruded by the afcent of the va- 
pour, ^c. and the remainder in a diredion toward 
tire poles. The common rotation of the air in 
coming in below, to fupply the place of that part 
carried up by any fire, may explain this motion. To 
fhew, how this motion muft tend to the weft, we 
muft confider, that the column of air, raifed by the 
afcending vapour, &c. is at its greateft altitude to 
the eaft ; and thdefore muft prefs that air to the 
weftward, which is continually protruded by the va- 
pours, beginning to afcend from eaft to weft ; 
and the comprefiTed air at the tropics muft tend to 
the weftward, till their forces meeting make the mo- 
tion intirely to the weft. The air itfelf being rare- 
fied, and carried up by the refledion of the intenfe 
heat of the fun (for heat, in flying off from all bo- 
dies, does afcend through the air with great velo- 
city), may be a confiderable additional caufe of thefe 
trade winds ; but never can be the foie caufe of all 
the erratic winds. As I am not fufficiently inform’d 
of the particular formation of the globe, to account 
VoL. 4p. T for 
