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counted 4000 Cubits according to Alfraganus) is not well known to us. 2. They do not shew us the Situation of the Places whofe Latitude they took; neither can we be certain of their Diligence in taking them. 3. Nor do they tell us by what Method they measured their Distances.

IN Eratofthenes's Menfuration, thefe Things are to be obferved. 1. He did not add 15 min. (for the Angle made by the Sun's apparent Ray Z and the true central Ray) (Fig. 7.) to the Arch found B Z 7 degr. 12 min. 2. He did not prove Syene and Alexandria to lie under the fame Meridian. 3. The Termination of Shadows cannot be accurately obferved; and alfo a Style at any other Place within 150 Furlongs of Syene would have been without a Shadow. 4. He took the Distance between Syene and Alexandria from common Computation which is feldom exact; neither do we certainly know the Length of his Furlong.

IN Pofidonius's Method thefe Errors may be objected. 1. He fuppofed Canopus not to rise above the Horizon of Rhodes; tho' it is known to be elevated two Degrees there: however, he could not be sure it exactly touched it. 2. He determined the Distance between Rhodes and Alexandria by Guefs, and computed Voyages. 3. The Length of his Furlong is not truly stated. 4. It may be doubted whether Alexandria and Rhodes lie under the fame Meridian, &c.

IN the Terreftrial Methods there are thefe Defects. 1. An Error is eafily committed in taking the exact Altitude of any Mountain. 2. The extream Point of Vifion cannot be exactly determined, by reafon of the Refraction and the Weaknefs of the Sight.

THUS far concerning the Dimensions of the Earth's Perimeter, it's Semidiameter, Superficies, and Solidity; from whence we might compute it's Solidity

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Solidity or Weight: but because it's Parts are of different Gravities and Textures unknown to us, we cannot fo well determine it's Weight but by Suppofition.

IT must be remember'd that the Semidiameter of the Earth is the Model of all Celestial Dimenfions, both in determining the Distances of the Planets from the Earth, and from one another, and in computing their Magnitude. Thus we fay, the Sun is diftant from the Earth 1200 Semidiameters, and the Moon 59, &c.

IN Geography, not only the greater Circles, as the Equator, &c. are to be confidered, but also the leffer are of Ufe, that are parallel to the Equator, viz. how many Miles, or Perches, make a Degree in fuch or fuch a Parallel? Therefore we have taken the following Table out of Snellius, and have added to his Measure of a Degree in Perches, the fame in German, Dutch, and Italian Miles.

A Table fhewing the Extent of one Degree in the feveral Parallels.

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TH

СНАР. V.

Of the Motion of the Earth.

HE Pythagorean Motion or Circumvolution of the Earth (not a Nutation or Quaking) is according to the Copernicans the Caufe of moft of the Changes in the Celestial Appearances, which would otherwise be conftantly the fame in every Place (4). Tho' indeed there is not any Property

of

parent, arifing from the Motion of the Earth round it's Axis.

The next Perfon who made a confiderable Figure this way, was Ptolemy with his Cycles, Epicycles, and Eccentrics, he quite burthened Nature, and his Hypothefis fhews too much of Art; these are all now exploded, and his folid Spheres broke to pieces; he left behind him a Work entitled Almagest, or the great Conftruction, which was founded on the Obfervations of Hipparchus.

(a) This Syftem was not invented by Pythagoras, as fome imagine, for Diogenes Laertius exprefsly faith, that Pythagoras's Opinion was, That the World was round, containing the Earth in the middle of it; and that Philolaus, the Pythagorean, was the first that faid the Earth moved in a Circle: But fome fay Hercetas the Syracufan. Derbam's Aftro-Theology. Pythagoras, who lived in Society with the Egyptian Priests feven Years, and was initiated into their Religion, carried home from thence, befides fe. veral Geometrical Inventions, the true Syftem of the Univerfe, and was the first that taught in Greece, that the Earth and Planets turned round To these fucceeded the Nothe Sun, which was immoveable Dane, Tycho Brahe, whose ble in the Center; and that the Diurnal Motion of the Sun and fixed Stars, was not real but ap

Copernicus had the Honour to restore the ancient Pythagorean Syftem, notwithstanding the Prepoffeffion the Ptolemaic had gained in the World.

Hypothefis in a great Measure is compounded of the other two, and feems defigned to account

for

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