IT belongs to this Place to explain this Theorem ; that the Distances of the fixed Stars, and fuperior Planets, Mars, Jupiter, and Saturn, are fo great from the Earth that it's Semidiameter hath no fenfible Proportion thereto; tho' it is not fo in the Distance of the Moon, Mercury, and Venus : And if there is any Proportion between the Earth's Semidiameter, and the Sun's Distance, it is fo very fmall that we are still not able fenfibly to difcover it ().

THIS Theorem is thus demonftrated. 1. The fixed Stars, and fuperior Planets appear to rife the very fame Moment in our fenfible Horizon, that they are found by Calculation to do, if we were at the Center of the Earth; therefore our Distances from the Center (or the Earth's Semidiameter) hath no Proportion to the Distance of the fixed Stars. 2. If we take the Meridian (or other) Altitude of a fuperior Planet, or any of the fixed Stars, with an Inftrument, we find it the fame as if we had obferved it at the Center of the Earth: Therefore the Semidiameter of the Earth is nothing in respect of their Distance. 3. If there were any fuch Proportion, the Distance of two fixed Stars would appear lefs near the Horizon than at the Meridian, where they are nearer the Earth by almost it's Semidiameter.

THIS alfo is true in the Sun, whofe apparent Diameter is not perceived greater in the Meridian than in the Horizon.

(1) The quantity of the Parallax of Mars is determined, by M. Caffini's and Flamsteed's Obfervations, to have been fcarce 30 Sec. when in Oppofition to the Sun, and alfo in his Perihelion; from whence having the true Proportions of the

Distances of the Planets from the Sun, we have, in effect, acquired the Parallax of the Sun itfelf, and of the rest of the Planets, and alfo their Diameters and Distances from the Sun and the Earth; of which fee the Note at the end of this Chapter. G 3 BUT

BUT the apparent Diameter of the Moon is found to be fomewhat enlarged in the Meridian ; becaufe fhe is there nearer us, than when he is in the Horizon, almoft a whole Semidiameter of the Earth (m). CHAP.

CHAP. VII.

Of the Subftance and Conftitution of the Earth.

I

N the preceding Chapters we have confidered Four general Properties of the Earth, without Regard to it's Substance or Constitution: it will therefore be here proper to confider what kind of Body the Earth is, that we may not be ignorant how it's Parts cleave or are cemented together : which tho' it seem more to belong to Phyfics; nevertheless because it renders the Knowledge of the Earth more perfect, we fhall here briefly difcufs it; leaving the accurate Theory thereof to Natural Philofophers.

PROPOSITION I.

To fhew of what fimple or fimilar Bodies the Earth may confift, or be compounded.

THERE are feveral Opinions of Philofophers concerning this matter. The Peripatetics reckon four Elements in the Earth and the whole Sublunary World, fufficiently known to every one viz. Fire, Air, Water, and Earth. Many of the Ancients, as Democritus, Leucippus, &c, were of Opinion, that the whole World confifted of very small folid Particles, which only differed in Magnitude and Shape. Which Opinion is followed by feveral of the Moderns; and fome time fince, des Cartes endeavoured to account for all the Phænomena of Nature upon this Hypothefis,

THE Chymifts imagine that there are three Principles of Nature, viz. Salt, Sulphur, and Mercury, to which fome reasonably add Caput Mortuum. But there feems to me upon a thorough Confideration of the Matter (to drop all ambiguous terms and quibbles), to be five fimple Bodies which are the first Elements or Principles of all things, viz. Water, Oil or Sulphur, Salt, Earth, and a fixed Spirit; which fome call an Acid, and is perhaps like the Mercury of the Chymifts (a). For

may

it is plain that all Bodies, and Parts of the Earth, be refolved into these five elementary Subftances. Nevertheless I do not suppose them to differ fo much in their particular Effences, as in the Variety of their feveral Shapes and Magnitudes.

OF thefe Bodies, mixed after different manners, is the whole Earth compofed; from which proceeds fuch a furprising Variety in the Nature of Bodies; tho' they are apparently fimilar (b). But fince the more accurate Explication of these things belongs to Phyfics, we fhall fay no more to them here; but handle them at large in another Place.

PROPOSITION II.

The Earth is divided into dry and moist Parts, or into Land and Water; to which fome add the Atmosphere.

THIS is the common Divifion of Geography. But then Water is taken, in a large Senfe, for all forts of Liquids and Fluids; and Land for the whole dry and confiftent Parts of the Globe: whilst

to divide what God himself made one in the firft Crea⚫tion. While the Particles

continue entire, they may compofe Bodies of one and the fame Nature and Texture in all Ages: But should they ❝ wear away, or break in Pieces, the Nature of Things ⚫ depending on them would be changed. Water and Earth compofed of old worn Particles, and Fragments of Particles, would not be of the fame Nature and Texture now, with Water and Earth compofed of entire Particles in