[a] Although the Terraqueous Globe be of an orbicular Figure, yet it is not strictly so, 1. On account of its Hills and Vallies. But there are inconsiderable to the Earth’s Semidiameter; for they are but as the Dust upon a common Globe. But, 2. Our modern Astronomers assign a much greater Variation from a globous Form, namely, that of a prolate Sphæroid, making the Polar about 34 Miles shorter than the Equatorial Diameter. The Cause of which they make to be the centrifugal Force of the diurnal Rotation of the Globe.
This Figure they imagine is in Jupiter, his Polar being to his Equatorial Diameter, as 39⅗ to 40⅗. But whether it be so or no, I confess I could never perceive, although I have often viewed that Planet through very good, and long Glasses, particularly a tolerable good one of 72 Feet in my Hands: And although by Reason of cloudy Weather, and (at present) Jupiter’s Proximity to the Sun, I have not been of late able to take a review of that Planet; yet Saturn (so far as his Ring would permit,) and Mars appear perfectly round thro’ Mr. Huygens’s long Glass of 126 Feet, which by Will he bequeathed, with its whole Apparatus, to our R. S. by whose Favour it is now in my Hands. And moreover, I believe it difficult, next to impossible, to measure the two Diameters to a 40ᵗʰ Part, by reason of the smallness of Jupiter’s apparent Diameter, and by reason he is moving all the time of measuring him.
As to what is alledged from lengthening the Pendulums of Clocks, to make them keep the same Time under the Equator, as they do in our Climes; I have shewn from the like Variations in the Air-Pump, that this may arise from the rarity of the Air there, more than here. V. Phil. Trans. Nᵒ. 294. But if the Degrees of a Meridian grow larger, the more we go towards the Line, (as Mr. Cassini affirms they do, by an 800ᵗʰ Part in every Degree, in Phil. Trans. Nᵒ. 278.) then there is great reason to conclude in behalf of this Sphæroidal Form.
The natural Cause of this Sphericity of our Globe, is (according to Sir Isaac Newton’s Principles) that Attraction, which the infinite Creator hath stamp’d on all the Matter of the Universe, whereby all Bodies, and all the Parts of Bodies mutually attract themselves and one another. By which means, as all the Parts of Bodies tend naturally to their Center, so they all betake themselves to a globous Figure, unless some other more prevalent Cause interpose. Thus Drops of Quick-silver put on a spherical Form, the Parts thereof strongly attracting one another. So Drops of Water have the same Form, when falling in the Air; but are Hemispherical only when they lie on a hard Body, by reason their Gravity doth so far over-power their self-attracting Power, as to take off one half of their Sphericity. This Figure is commonly attributed to the Pressure of the circumambient Air: But that this can’t be the cause, is manifest from the Air-Pump; the case being the very same in an exhausted Receiver, as in the open Air, and not any the least Alteration of the Figure that I could perceive, in all the Trials I have made.
[] It would be frivolous as well as endless to reckon up the various Opinions of the Ancients about the Figure of the Terraqueous Globe; some of them may be seen in Varen. Geogr. l. 1. c. 3. init. or Johnston’s Thaumat. c. 1. Artic. 3. But among the variety of Opinions, one of the principal was, That the visible Horizon was the Bounds of the Earth, and the Ocean the Bounds of the Horizon, that the Heavens and Earth above this Ocean, was the whole visible Universe; and that all beneath the Ocean was Hades, or the invisible World. Hence, when the Sun set, he was said tingere se Oceano; and when any went to Hades, they must first pass the Ocean. Of this Opinion were not only the ancient Poets, and others among the Heathens, but some of the Christian Fathers too, particularly Lactantius, St. Augustine, and others, who thought their Opinion was favoured by the Psalmist, in Psal. xxiv. 2. and cxxxvi. 6. See Bp. Usher’s Ans. to a Jes. Chall. p. 366. &c.
[c] Neither do these constant Trade-Winds usually blow near the Shore, but only on the Ocean, at least 30 or 40 Leagues off at Sea, clear from any Land; especially on the West Coast, or Side of any Continent: For indeed on the East Side, the Easterly Wind being the true Trade-Wind, blows almost home to the Shore, so near as to receive a check from the Land-Wind. Dampier’s Winds, Ch. 1.
And not only the general Trade-Winds, but also the constant coasting Trade-Winds, are in like manner affected by the Lands. Thus, for Instance, on the Coast of Angola and Peru. But this, saith the curious Captain Dampier, the Reader must take notice of, That the Trade-Winds that blow on any Coast, except the North Coast of Africa, whether they are constant, and blow all the Year, or whether they are shifting Winds, do never blow right in on the Shore, nor right along Shore, but go slanting, snaking an acute Angle of about 22 Degrees. Therefore, as the Land tends more East or West, from North or South on the Coast; so the Winds do alter accordingly. Ibid. Ch. 2.
CHAP. II.
Of the Bulk of the Terraqueous Globe.