them lighter (after what manner foever it happens) gets an Opportunity of feparating itself from

them.

According to the firft manner, we fee in Diftillations from Retorts or Glafs Helms, when in the narrow Parts of their Necks, the Vapours are compreffed together, that they run into Watry Drops, and fo defcend; tho' juft before, having Room and Liberty, they did afcend, and would have rifen yet higher, without these narrow Paffages.

'Tis like wife well known to every one, that a hot Liquor in which there are many Particles of Fire, becomes colder by the Breath or Wind of Peoples Mouths. Now that this happens, becaufe the Fire-Particles are by fuch a Motion feparated from thence, feems probable for the following reafon; namely, that otherwife, if the greater Heat did confift only in a greater Motion of the famll Parts of a Liquid Matter, the fame, according to this Hypothefis, by the blowing, which encreases the Motion of the Liquor, would become hotter, and by no means colder, whereas common Experience teaches us the contrary.

SECT. XXIV. Vapours defcend by the Separation of the Particles of Fire from them.

II. IN cafe one only Wind be of so much Strength as to be able, by blowing from I to G, (Tab. XV. Fig. 1.) to drive forwards the Vapour or Cloud IG, in a ftreight Line IZ, and fo can protrude the whole or a part thereof to Z; it is plain, that the faid Cloud is higher from the Earth, at Z, and confequently in a thinner Air. From whence it will follow, according to the abovemention'd Experiments made upon hot Water and hot Lye, in the Air-Pump, that the Fire, which

by

by fticking to the Particles of Water render'd them lighter, will extricate itself from them, and afcending by its Lightness, the Water will become too heavy, not only to remain in this thin and light Air, but even in a thicker and a heavier near the Earth, and fo will be turned into a defcending Dew or Mift, or Rain, Snow, or the like, according as the Watry-Vapours are either rarified or comprefs'd.

SECT. XXV. Experiments, proving the Defcent of Vapours by the Air's becoming lighter.

III. Now, that the Air (which being near the Earth at P, is otherwife heavy enough to keep up the Vapours, and to cause them to float about F) is likewife frequently, for other Raafons, turned into a thinner and lighter Subftance, and fo gives an Opportunity to thefe Vapours to defcend, has been already fhewn in the preceding Contemplation, §. XVII, and XVIII. in the Glaffes of the AirPump; and the Barometers do upon many occafions, furnish us with Experimental Proofs thereof; in which the Quick filver defcending commonly upon the least Weight of the Air, does prognofticate, that the Watry-Vapours are about to defcend in Fogs or Vapours, or otherwife from the Air.

SECT. XXVI. Cold will produce the Same Effect: Shewn experimentally.

IV. BESIDES this, the fudden Ceffation of the Warmth of the Air feems to give an Opportu nity to the Vapours, which, by the faid Warmth, had been raised up in great Quantites, to be precipitated by the Cold, and to be turned into Fogs or Rain. Analogous Example thereof may be

feen

feen in Distillations that are performed by Spiral Pipes, or Worms; and fomiething like it is alfo found in Chymical Crystalizations; in which we fee, that the Salts that float and are diffolv'd in the Water, whilft warm, do coagulate and fubfide affoon as the fame becomes cold. But whether it happens fo in the Air, or after what other manner it is done there, fince the Nature of Cold is not yet fo fully known to us as many think, we fhalf not enquire farther here.

Now how many Caufes foever there may be, befides thofe that we have already mention'd, whereby the Watry-Vapours that are raised up in the Air may be made to defcend; this is certain, that both their Afcent and Defcent are owing to a wonderful Law of Hydroftaticks:

Now can any one imagine, that all this comes to pass without a wife Direction, and that it is by mere Chance that fo vaft an Army of Vapours in the great Space of the Air are every where fubjected to the moft exact Hydroftatical Rules, in fuch an infinite number of Occafions and Accidents? Is there no want of an Intelligent, Being to oblige fuch a prodigious Quantity of Waters, turned into Clouds, to remain floating in the Air, which are often obferved to descent in mighty in rainy Springs and Harvests, or other Seafons? To fay nothing now of the various Ways and Forms in which they defcend, and whereby formany Cifterns and other Recep tacles of Waters, as well as Ditches, Canals, and Ponds, are filled in fo fmall a time: But which is a great deal more, by which fuch vaft Rivers fwell fo fuddenly, and over-flowing their Banks, do frequently cover whole Diftricts of Land.

mig mall a time: But which

SECT.

1

d,

and

ich

ers

ks,

SECT. XXVII. The Motion of Vapours from one
Place to another, is neceffary.

BUT now if these Vapours had no other Quality or Property in them than barely an Afcent and Defcent to and from the fame Place, and that those, for inftance, represented in Tab. XV. Fig. 1. by F, having been exhaled from the Sea at P, fhould fall down again in the very fame Place; and that every Place were to be moiften'd only by no other Watry-Vapours than fuch as are drawn from its own Bofom, there would very little Advantage accrue to its Inhabitants from thence. How many Rivers would then be quite dried up, which at prefent have their Rife, or at least receive an abundance of Water from the Rains and Snows that defcend from the Mountains? How fhould the wild Beafts in Arabia, and fuch like Countries of Africa, which thro' their Drought afford no Water at all, affwage their burning Thirfts? What Fruits would the now moft fertile Places produce, in cafe none of the Water, which by the Heat of the Sun is exhaled in other Parts. of the World, were brought, and made to fall down upon them?

Can a miferable Philofopher think again, that he owes no Thanks to his Creator, that the Waters which are exhaled in the Torrid Zone, and other hot Countries, are, by the Winds that drive Clouds, brought home to him, yielding him Drink, and making fruitful that Part of the Earth where he inhabits?

SECT. XXVIII. An Experiment, fhewing that the Watry-Vapours leave their Salts behind them.

Now fince most of the Vapours that are fo beneficial to the whole World are chiefly exhaled from the Sea, and yet those Waters, by reafon of their Saltnefs, are unfit for the Purposes to which they are deftin'd; infomuch that Men would die of Thirst in the midst of the Sea, and no Herb or Plant, to which the Salt-Water fhould be applyed, could live and grow therewith, as by. fad Experience is but too well known in Lands that have been overflow'd by the Sea; Can any one again imagine, that it is by mere Chance or ignorant Caufes, that the Sun does only exhale the Fresh Watry-Vapours out of the Sea, and collect them into Clouds, whilft the Salt, with which they were at firft impregnated, by reafon of its being fo much heavier than Water, is left behind ?

That this is true, may be proved not only from the Freshness of Dew, Rain and Snow, but one may fee, whenever one will, a like instance, by fetting Salt-Water upon the Fire, and caufing it to exhale in Vapours, or by drawing them off in Distillation; in which Cafe you will find the Salt remaining at the Bottom. The fame we fee happen in Salt-works by the Sun's Heat, and in the Salt-works with our common Fires. So that after this manner two great Things come to pafs, without which the whole Race of Mankind would foon be extinct; namely, that Firft, Sea-Water is divested of its Salts, and render'd fit for Drink, and fo many other Ufes; and Secondly, that the faid Salt becomes very ferviceable to Men.

SECT.