[ 5 11 ] 
than the Sea-air, it becomes thereby more rarefied* 
and confequently lighter 5 and therefore the Sea-air, 
with its fuperior Weight, flows in upon it every 
W ay. The Intervals between are owing to the Air 
of both Places being in an equal Degree of Heat, and 
confequently of equal Weight. 
The Trade- wind never varies, which is thus ac- 
counted for: The Air juft under the Sun is the 
hotteft : The cold Air prefieth upon the hot, as the hot 
Air follows the Sun ; and therefore it makes a perpe- 
tual Flow of Wind between the Tropics from Africa 
to America , and from thence to the Eaft-Indies. 
With regard to the Wind influencing the Wea- 
ther ; 1 find that though Air be an unmixed Fluid, yet 
it is capable of receiving many Vapours, which float 
in it, as we fee other Bodies float in Water. Some- 
times the Vapour afeends, and fometimes it falls to 
the Ground. All which I take to be effefted by 
Heat and Cold in this Manner : Heat feparates Water 
into fmall Particles, and the incorporated Air, rare- 
fied by the fame Heat, blows up thofe Particles into 
Bubbles 5 by which means the fwoln Vapour be- 
coming fpecifically lighter than a like Space of am- 
bient Air, afeends, fwift, at firft, (which affords a 
pleafant Sight in a warm Summer's Day) and then 
gradually flower, till it gets up to that Part of the 
Air which is of equal Lightnefs withitfelfj and there 
it remains, as long as the Air continues in the fame 
State : But whenever the Air cools, in which thefe 
watery Bladders float, the Cold contracts the Bladder, 
which becoming thereby fpecifically heavier than the 
Air, down it falls in Dew, or Rain. A common 
Alem- 
