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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 whose 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 Eratosthenes's Mensuration, these Things are to be observed. 1. He did not add 15 min. (for the Angle made by the Sun's apparent Ray xz 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 same Meridian. 3. The Termination of Shadows cannot be accurately observed ; and also 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 seldom exact ; neither do we certainly know the Length of his Furlong.

IN Posidonius's Method these Errors may be objected. 1. He supposed 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 Guess, and computed Voyages. 3. The Length of his Furlong is not truly stated. 4. It may be doubted whether Alexandria and Rhodes.

Jie under the same Meridian, &c. 1. IN the Terrestrial Methods there are these De.

fects. I. An Error is easily committed in taking the exact Altitude of any Mountain. 2. The extream Point of Vision cannot be exactly determined, by reason of the Refraction and the Weakness 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

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

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

IN Geography, not only the greater Circles, as the Equator, &c. are to be considered, but also the lesser are of Use, that are parallel to the Equator, viz. how many Miles, or Perches, make a Degree in such or such a Parallel ? Therefore we bave 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 shewing the Extent of one Degree in the seve

ral Parallels.

The Latitude of the Place, or the Distance of each Parallel from the Equator.

Perches in
i Degr.

Equ.

60

alitwinni

28500 28496 28483 28461 28431 28392 28344 28288

Holland German | Italian

Miles Miles Miles Miles Perch. Miles Min. Miles Min. 19

15 0
18 1496 14 59 59 59
18 1483 14 59

59 58 18 1461 14 58

59 54 18 1431 14 57 59 51 18 1392 14 56 59 45 18 1344 14 55 59 41 18 1283 | 14 53 1 59 34

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Lati. Perches in Holland German | Italian tudel i Degr. Miles | Miles Miles

| Miles Percb. Miles Min. Miles Min. 2822

18 1223 14 51 59.25 28149 18 1149 14 48

59 16 28061 18 1067

14 46

59 6 27976

14 43
27877
18 877

14 40

58 42 27769

14 37

58 29 27653

14 33 27526

529 14 29 27396

14 25 27255 18 255 14 21 27105

57 4 26947 17 1447

14 II

56 44 26781 17 1281 17 1107

56 o 17 925 13 54 55 36 17 734

55 12 26036 17 536

13 42

54 48 25830 17 330

54 24 25616

17 116 13 29 25394 16 1394 13 22 | 25164 16 1164

15 15 53 0 24927

16 927 13 7. 52 28 24681 16 681 13 59 51 96 24429 | 16 429 12 511 51 24 24169 1.16 169

50 52 23902

15 1402
15 1128

49 -44 15 846

12 17
23057
15 557

12 8
22761 15 261

11 59 22458 14 1458

47 16 39 22149 14 1149

46 39 21832 14 832

Il 29

46 0 21509 14 509 IL 19 21180 14 180 II 9 44 36 20843 13 1343

10 58 20501 13 1001 10 47

43 8 20152 13 652

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Lati-| Perches in i Holland German
Degr. Miles 1 Miles

Miles Perch: | Miles Min
18698. 12 698
18319 12 319
17936 u 1436
17546

Il 1046
17152

652 16752 Il 252 16347

10 1347
15937

10 937 8 23
15522 10 522
15103

10 103 7 57
14679

9 1179 7 44
14250 9 750
13817 9 317
13380

8 1380
12939

8 939 12494

8 494 12045

8 45 11592 7 1092 11136 7 639 10676 7 176 10213 6 1213

6 748 9279

6 279 8807 5 1307 8333 5 933 7846

5 346

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CH A P. V.
Of the Motion of the Earth.

THE Pythagorean Motion or Circumvolution

T of the Earth (not a Nutation or Quaking) is according to the Copernicans the Cause of most of the Changes in the Celestial Appearances, which would otherwife be constantly the same in every Place (a). Tho' indeed there is not any Property

of

(a) This System was not in- parent, arising from the Movented by Pythagoras, as some tion of the Earth round it's imagine, for Diogenes Laërtius Axis. expressly faith, that Pythago. The next Person who made ras's Opinion was, That tbe a considerable Figure this way, World was round, containing was Ptolemy with his Cycles, the Earth in the middle of it; Epicycles, and Eccentrics, he and that Philolaus, the Pythago- quite burthened Nature, and his rean, was the first that said the Hypothesis shews too much of Earth moved in a Circle : But Art; these are all now explosome say Hercetas the Syracu- ded, and his solid Spheres broke fian. Derham's Aftro-Theology. to pieces; he left behind

Pythagoras, who lived in So- him a Work entitled Almageft, ciety with the Egyptian Priests or the great Construction, seven Years, and was initiated which was founded on the into their Religion, carried Observations of Hipparchus. home from thence, besides se. Copernicus had the Honour veral Geometrical Inventions, to restore the ancient Pytha. the true System of the Uni- gorean System, notwithstanding verse, and was the first that the Prepossession the Ptolemaic taught in Greece, that the had gained in the World. Earth and Planets turned round To these succeeded the Nothe Sun, which was immovea- ble Dane, Tycho Brahe, whose ble in the Center; and that the Hypothesis in a great Measure Diurnal Motion of the Sun and is compounded of the other two, fixed Stars, was not real but ap- and seems designed to account

for

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