[ I9I ] 
-may be another caufe of our general north- weft 
winds, which blow off to fea at right angles from 
our North American coaft ; the warm light fea 
air rifing, the heavy cold land air preffing into its 
place. 
Heavy fluids defcending frequently form eddies, 
or whirlpools, as is feen in a funnel, where the water 
acquires a circular motion receding ev'ery way from 
a centre, and leaving a vacancy in the middle, greateft 
above, and leflening downwards, like a fpeaking 
trumpet, its big end upwards. 
^ i\.ir defceriding, or afcending, may form the fame 
kind of eddies, or whirlings, the parts of air ac- 
quiring a circular motion, and receding from the 
fiddle of the circle by a centrifugal force, and leav- 
ing theie a vacancy, if defcending, greateft above, 
and leflening downwards; if afcending, greateft be- 
low, and leflening upwards, like a fpeaking trumpet, 
ftanding its big end on the ground. 
When the air defcends with violence in fome 
places, it may rife with equal violence in others, 
and form both kinds of whirlwinds. 
The air in its whirling motion receding every way 
from the centre, or axis, of the trumpet, leaves there 
a vacuum, which cannot be filled through the fides, 
the whirling air as an arch preventing ; it muft then 
prefs in at the open ends. 
The greateft preffure inwards muft be at the lower 
end, the greateft weight of the furrounding atmo- 
fphere being there. The air entering rifes within, 
and carries up duft, leaves, and even heavier bodies 
that happen in its way, as the eddy or whirlpool 
paffes over land. 
If 
