Os Pneufnatics . 107

The pressure of the air being equal on ali sides of a body expofedt® it, the Tostest bodies Tustain this pressure without Tussering any changein their figure; and To do the most brittle bodies without being broke»

The air is rarefied, or made to Twell with heat; and of this pro-perty, wind is a necessary confequence. For, when any part of the The caufe <jsair is heated by the Tun, or otherwife, *it wiil Twell, and thereby affect cwlnds -the adjacent air: and To, by various degrees of heat in different places,there will arife various winds.

When the air is much heated, it will aTcend towards the upper partof the atmofphere, and the adjacent air will rush in to fupply its place jand therefore, there will be a stream or current of air from ali partstowards the place where the heat is. And hence we Tee the reasonwhy the air ruflies with Tuch force into a glaTs-houTe, or towards anyplace where a great sire is made. And also, why Tmoke is carried upa chimney, and why the air rufhes in at the key-hole of the door, orany fmall chink, when there is a sire in the room. So we may take itin general, that the air will preis towards that part of the world whereit is most heated.

Upon this principle, We can easily account for the frade~winds x which The tradt-blow constantly from east to west about the equator. For, when the rwinduTun sliines perpendicularly on any part of the earth, it will heat the airvery much in that part, which air will therefore rise upward, andwhen the Tun withdraws, the adjacent air Will rufh in to sili its place;and confequently will caufe a stream or current of air from all parts to-wards that which is most heated by the Tun. But as the furi, Withrefpect to the earth, moves from east to west, the common courfe ofthe air will be that way too; continually presiing aster the Tun : andtherefore, at the equator, where the Tun Ihin'es strongly, there will bea eontinual wind from the east; but, on the riorth side, it will incline alittle to the north, and on the fouth side, to the fouth.

This general courfe of the wind aboüt the equa tot, is chariged infeveral places, and upon feveral accounts as, 1. By exhalations thatrise out of the earth at certain times, and from certairi places; in earth-quakes, and from volcaho’s. 2. By the fallirig’bf great quantities ofrain, causing thereby a sodden' conderifatiort 'or coritraction of the air.

3. By burning Tands, that ofteh retain the solar heat to a- degree incre-dible to thofe who have not feit' it, causing a more than ordinary rare-•faction of the air contiguous to them. 4. By high mouritäins, that alterthe direction of the winds in striking against them. 5. By the declina-tion of the Tun towards the north or fouth, healirig the air on the northor fouth side of the equator. *• K -

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