as well as thofe other Parts of the World, which for want of 'em would be uninhabitable, would each receive their Share; and it may be, thofe that least want them would enjoy the moft.

་

Once more, let thofe Philofophers with whom we have here to do, judge themselves, whether it be owing to mere Chance, that to the end, that those Countries which ftand in moft need of being water'd, may enjoy a greater fhare than others, fuch great Bodies as the Ridges of Hills and Mountains, are placed in or near the fame. The Ufe of which, as has been faid before, is to intercept the Watry Vapours floating in the Air, to collect them in a particular manner upon their Summits or Tops, to derive them down from thence, and fo to furnifh fuch a Quantity of Water as may compofe the requifite Brooks and Rivers which contribute fo much to the Benefit of the Earth and the Inhabitants thereof; and which running down from thefe Hills, from whence they derive their Source and Beginning, they moiften the furrounding Lands, which would otherwise be barren thro Heat and Drought, and render them fit to fupport their Inhabitants with Meat and Drink.

To fay nothing here of the number of Fifhes. and other Productions in thefe Waters, by the help of which the People, thro' whofe Countries they flow, can communicate their Fruits and Merchandizes to each other.

SECT. XXXVIII. The Mountains collect Watry Vapours, firft by the Winds.

HERE we feem to have a proper Occafion to inquire into the Manner and Caufes, how and why the Mountains are able to collect fuch a vaft Quantity of Waters, to the end, that what has

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been

been faid before upon this Subject, may be the more clearly understood.

How the Vapours are raised from the Sea, from P to g and F, Tab. XV. Fig. 1.) by the Warmth of the Sun (and under the Poles, by Cold too perhaps) has already, in fome manner, been endeavour'd to be fhewn; as alfo how they are enabled to float in thin Air, as in different Stages and De grees of Heighth, as g, K, d and F, I, G; and moreover, why the faid Vapours, being raised higher up to Z, by the Winds, or driven against one another by contrary Winds, and for other, Reasons, do defcend in Rain, Snow, and the like.

Dr. Halley, fubjoins another Manner to these namely, that a floating Vapour or Cloud in E, being driven against the Mountain QNR, by the Winds at E, afcends to the Top N, and there being got into a lighter Air, cannot be any longer. fuftain'd, but falls down in fmall Drops upon the Head of the Mountain, and from thence running down, fill the Cavities of the Mountains: (which are fupposed to be there, and fo are often found to be) with Water; which running continually thro the Orifice M, produces the little Brook Me T, or Me V; which joyning themfelves with others of the like Nature, form a large River.

It appears by this way, why the Waters are af fembled in greater Quantities upon the Mountains, forafmuch as oppofing their Tops from QR to N, against the Winds which drive the Clouds mE, Kd, &c. they ferve for Barricado's or Cross Trees, and fo do either force the Vapours to afcend into a Lighter Air, or forcing them against thofe Tops, fqueeze 'em together, whereby they, become heavy and fall down again.

SECT.

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SECT. XXXIX. Secondly, Vapours are collected by the Coldness of the Mountains and Superior

Air.

AND as it is credible, that this does often happen, it should seem that the Winds are neceffary thereto; and that in cafe they failed, fo great a Quantity of Water, according to all Appearance, would not be collected; whereas the above-mention'd Experiments teach us, that the Tops of the Mountains, even in hot Countries, are not only encompaffed by Winds at certain times, but continually with Fogs and Vapours; fo that befides this, it seems that a more fettled Caufe, and which does not always depend on the Motion of the Winds, must obtain here.

Now, whether this can be deduced from the Cold of the Mountains themselves, and of the Superior Air furrounding their Tops, and to which the Reflection of the Sum-Beams does not reach; or, whether it must be afcribed to their Heads being always hid in the Clouds, I leave to fuch as will enquire more ftrictly: This is certain, that by reafon ofthe Cold, they are often cover'd with Snow, and Varenius fays, that excepting in the Months of July and Auguft, there is always Snow upon the Pike of Teneriff; tho' none can be found in this and the other Canary in Islands.

SECT. XL. Thirdly, Vapours are collected by Shadows, fhewn Experimentally.

WE have not here undertaken to write largely upon Natural Knowledge, nor to repeat the whole Hiftory of Nature; but we cannot forbear obferving however, that the great Shadows which these Mountains produce, do occafion a continual

"

Cold

Cold Air about them. Thus we read in the Extract of the Hiftory of Bohemia, Act. Lipf. 1682. p. 244. That in a certain Valley of the GiantMountains, at the hottest Time of the Year, there are very deep Snows, and that they have lafted there for 16 Years together, the old being of brownish Colours, by which it is diftinguished from the latter Snows that are white and clear.

If then we fuppofe the Sun to be at O (Tab.XV. Fig. 1.) and a Mountain QNR, cafting its Shadow, as at QEX; where the Sun-Beams are hinder'd either by other Mountains lying about it, or, because the Sun feldom fhines upon that Side, from ever heating the Air to fuch a. Degree as is found in the next adjacent Air: It is plain, that the Air within the Shadow QEX, will be a great deal Colder than that which encompasses the Mountain out of the Shadow. Now it has been proved experimentally in the foregoing Contemplation, that a warmer Air having accefs to another which is Colder, if they be not of a too different Thicknefs, will be rarified and driven with a Wind and Stream towards the cold Air Now if this fhould be applied to the Air, which is here not only below, but alfo above, and on the Side, or rather round about the Shadow, we fhall fee how this Air, with all the Vapours in it, are driven to the Shadow: for that the Vapours floating in the Air do continually follow its Course, is plain, and will appear from a boiling and fteaming Pot of Water, fet in a place where there is no Wind; from whence then it may be concluded, that the Air with its Vapours, coming into fuch a Shadow, and being there deprived of its Elaftick Force by the Cold, will be immediately followed by more Air which is warmer, and confequently whofe Elafticity is stronger, and fo produce an entire and gentle Stream of Air and Va

pours,

Vapours, if not prevented by other Winds, and moiften those Places with continual Vapours.

SECT. XLI. Fourthly, Other Shadows likewife give occafion to the Concourse of Vapours, proved Experimentally.

Now, that this alfo, among other Reasons, must be laid down, why the Vapours seem to be drawn in a continual Stream to the Mountains (but really and properly are preffed thicker from all Sides) and why the Mountains are many times obferved to be clouded (of which we have given feveral Inftances above) every one that understands the Properties of the Air, may easily inferr from what has been faid. That in Shadows the Vapours of the Air are collected, does certainly appear from the Night, which is nothing but the Shadow of the Earth, and in which it is well known, that the Vapours and Dews fall thicker than in the Day-time. Thus we see the Defcent of Vapours in the Night-time was obferv'd by Dr. Halley, in the Ifland of St. Helena. And we find in the Memoirs of the Royal Academy of France, for the Year 1699. p. 128. a Method invented by Mr. de la Hire, to hinder the Dews of the Night from fticking to the Glaffes of the Telescopes. Now Experience teaches, that in the Mornings too, the Mountains are moiften'd with Vapours (fee Varenias's General Geography, Lib. 1. §. 5. p. 157.) because those Places that are within the Shadow of the Mountains, are much Colder at Night than other Places that are out of the Shadow. Thus we likewife fee from what has been faid, that in the lands of St. Thomas and Madegafcar, the Mountains which collect the Waters from whence the Rivers are produced, being cover'd with Woods, and confequently more fhady, do

make