TO this Place belongs the Solution of this Problem, viz. Having the difference of Time between the Sun's rifing (or setting) on the Top of a Mountain, and it's first Appearance to (or Occultation from) an Obferver at the Bottom, to find, if required, the Height of the Mountain; and converfly, having the Height of the Mountain, to find this difference of Time. Ariftotle and Pliny, have, by this Method of Calculation, fuppofed fome Mountains to be of incredible Altitudes, as appears from their Writings. However, fince the Solution of thefe Problems depends upon another, which we have referred to the fecond Part of this Work, we fhall refer them to Chapter xxx.

PROPOSITION VII.

The highest Mountains have no fenfible Proportion to the Semidiameter of the Earth; or fo little, that their Altitude no more affects it's Rotundity, than a Speck or particle of Duft upon the Surface of the artificial Globe does it's Rotundity.

WE have fhewed, that the Mountain in the Inland of Teneriff, called the Pike, is at moft no higher than a German Mile, or a German Mile and a half; and we are affured, that there are but few Mountains in the World higher than that: Therefore fince the Earth's Semidiameter is 860 fuch Miles, the Altitude of this high Mountain is to the Earth's Semidiameter as 1 to 860. But few Mountains are of this Height, moft of them not exceeding a quarter of a Mile; wherefore they no more obftruct the Earth's fpherical Figure, than the fmall inequality obferved in Globes turned artificially, does their Rotundity; and Nature hath not

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yet

yet been able to produce a Body of an exact Geometrical Roundness (d).

PROPOSITION VIII.

To explain the Origin of Mountains.

THIS is a great Question with fome Philofophers, but others think it fuperfluous, and not fit to be enquired into; because they fuppofe Moun tains to have had a Being ever fince the Creation. Nevertheless Hiftory acquaints us, that not a few Mountains have been undermined by interior Ruins, and funk down into fubterraneous Chafins and Receptacles, or wafted by fome other Means; fo that fince we can perceive a natural Decay and Corruption of them, we may judge they do not proceed from a fupernatural Origin. Moreover, that feveral Mountains were raifed fucceffively, and at feveral Times, is apparent from the Quantities of Sea-fhells that are found in fome of them, as in those of Gelderland, &c. Such Mountains as these seem to be generated by a rapid Wind, carrying Sand and Gravel by Degrees into the form of the Mountain, which is afterwards foaked and made solid by the Rain. This is to be understood in little Mountains, as to the very large ones it is probable, they

(d) Tho' the Body of the Moon be three times as little as the Earth, and the Protuberances or Mountains upon her Surface, three Times as high as the highest upon the Earth's Surface; yet when she is at the full, and obferved with the naked Eye, we cannot perceive that these vaft Mountains in the leaft obftruct, or deface her apparent Rotundity. On the contrary,

when she is viewed thro' a good Telescope, we can see the outward Edge of her Disk notched and made rugged, by the Tops of the Mountains rifing far above the other Parts of the Surface; which need not seem strange, when the best polished Globe that ever was male, being viewed thro' a good Microfcope, is found not to be free from fuch Rugofities. K 2

are

are of the fame Age and Origin with the Earth itfelf. They that argue more Theologically, fuppose the Globe of the Earth to have been at first created perfectly round, and with a foft Surface, without any eminent Parts or Mountains, without any Fiffures or Grottos; and afterwards, when GOD commanded the Waters to be gathered together in one Place, then there were Chanels made to receive the Waters, and the Earth that was removed out of these Chanels, was converted into Mountains. But we leave it to them to prove, whether the Mountains be fo many, and fo large, as to fill all the Chanels of the Sea (e).

PROPOSITION IX.

To explain the Caufes, why Rain, Mists, and Snows, are frequent upon the Tops of the Mountains; when in the neighbouring Vallies, the Air is ferene and calm without any fuch Meteors.

WE are informed by those, that have travelled over the Mountains of Afia, Peru, and other Countries,

(e) Dr Woodward, in his Effay towards a Natural Hiftory of the Earth, proposes · to prove, that the Strata at firft, whether of Stone, of Chalk, of Coal, of Earth, or • whatever other Matter they confifted of, (lying each upon other) were all originally parallel: that they were plain, even, and regular; and the Surface of the Earth likewife even and spherical: that they were continuous, and not interrupted or broken: and that the whole Mafs of the Water lay then above

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tries, that while they were on their Tops, they were frequently attacked with Showers of Rain, Snow, and thick Fogs; but defcending thence into the neighbouring Vallies, they observed no fuch Meteors, but enjoyed a ferene and pleasant Air. We also observe the fame in the Mountains of our own Country.

SOME fay, the Cause of this Phænomenon is owing to an occult Power that Mountains have of attracting Air, Clouds, and other Meteors; but fince they cannot explain this Power, they fay nothing to the Purpose (f). The following Explication feems to me the moft rational, viz. That Vapours and Exhalations being condenfed into fmall Drops, in the middle Region of the Air, (into which the Tops of feveral Mountains rife) begin to defcend and fall upon the Tops of the fubjacent Mountains which are nearer them than the Vallies, and coming there firft to Ground, they leave their Places in the Air, which are presently taken up by the small Drops that are next them; these being preffed and forced downwards by others, either to avoid a Vacuum, or because it is the Na

Agitation, and, in fome meafure, condensed by Winds, or other external Causes, they gather themfeves into Clouds and Mifts, and by their own specific Gravity, fall downwards, till they meet with fuch Air as is heavy and able to fupport them, with which they mix and swim about, and are every way difperfed in it, whereby the Sky is made ferene and clear: but if they meet not with fuch Air, or light upon the Top of a Mountain before they come at fuch Air, then they are formed into Drops, and fall down to the Ground.

ture of Water to flow to the lowest Place, or tỏ that Place where the Flux was first begun.

PROPOSITION X.

There bappen to Mountains, Ruins, Ruptures, Tranf pofitions, &c.

IT is but feldom fuch Accidents happen, yet fome Inftances are found in Hiftory, efpecially of Ruptures, whereof we fhall give fome Examples in the following Chapter.

PROPOSITION XI.

Whether the Superficies of a Mountain be more capacious than the Plane whereon it stands?

THAT it is larger is proved from Geometry: But whether it can fupport a greater Number of living Creatures, or produce a larger Quantity of Corn is another Queftion; to which I anfwer in the Affirmative. For tho' every thing placed upon the Surface of the Mountain, is fuppofed to ftand perpendicular to the fubjacent Plane, yet there is a greater Quantity of Earth, and a larger Superficies.