[ 5 1 1 ] 
Wind is a Stream of Air ; Air an unmixed Fluid 
encompafling our Globe, with a Shell of at leaft 6o 
Miles thick. Every Particle of Air gravitates equally 
towards the Centre of the Earth. Air is capable of 
being comprefled and expanded : The more Air is 
compreffed, the heavier it is ; the more it is expanded, 
the lighter. Cold and Heat, whatever they be, or 
however they ad, produce thefe contrary Effeds in 
the Air: That is, Cold doth comprefs the Air, and 
Heat expands it : Therefore Cold and Heat, in different 
Parts of the Air, will make it flow : For Cold making 
the Air heavy, and Heat making it light, the lighter 
muft, of courfe, give Way to the heavier; as, in a 
Balance, a greater Weight makes a fmaller rife. We 
daily fee a Proof of this in a Stove. 
The Sea and Land-breezes, and the Trade-wind, 
owe their Original to thefe Caufes. The Sea-breeze, 
when regular, begins at Nine o’Clock in the Morn- 
ing, approaches the Shore gently, at firft ; increafes 
till Twelve; retains its full Strength till Three; then 
gradually decreales till Five, when it dies away. At 
Six in the Evening the Land breeze begins, and con- 
tinues till Eight next Morning : The Interval be- 
tween thefe Two Breezes, at Morning and Evening, 
are the hotteft Parts of the Day. It is faid, that thefe 
Winds vary in their Periods; which not being to my 
Purpofe, I take no Notice of. 
The way of accounting for this Viciflitude of Sea 
and Land-wind, is thus : The Sun, as it afcends, fheds 
its Heat equally on the Land and Sea; but the Earth 
receives the Heat fooner than the Water, or elfe 
refle&s it ftronger. For one or both of thefe Reafons, 
the Air that hangs over the Land, is heated more 
X x x than 
