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affirmed, unless he suppose the earth to be in the centre of the universe, which is the thing to be proved.
I would fain know from what grounds our adversaries can prove, that the descent of heavy bodies is to the centre; or the ascent of light bodies, to the circumference of the world. The utmost experience we can have in this kind, does but extend to those things that are upon our earth, or in the air above it. And alas! what is this unto the vast frame of the whole universe, but punctulum, such an insensible point, which does not bear so great a proportion to the whole, as a small sand does unto the earth. Wherefore it were a senseless thing, from our experience of so little a part, to pronounce any thing infallibly concerning the situation of the whole. The arguments from astronomy, are chiefly these four; each of which are boasted of to be unanswerable.
1. The horizon does every where divide all the great circles of a sphere into two equal parts; so there is always half the equinoctial above it, and half below. Thus likewise, there will constantly be six signs of the zodiac above the horizon, and other six below it. And besides, the circles of the heaven and earth, are each way proportionable to one another; as fifteen German miles on the earth, are every where agreeable to one degree in the heavens; and one hour in the earth, is correspondent to fifteen degrees in the equator. From whence it may be inferred, that the earth must necessarily be situated in the midst of these circles; and.so consequently, in the centre of the world.
I answer: this argument does rightly prove the earth to be in the midst of these circles; but we cannot hence conclude, that it is in the centre of the world: from which, though it were never so much distant, yet would it still remain in the midst of those circles, because it is the eye that imagines them to be described about it. Wherefore it were a weak and preposterous collection, to argue thus, that the earth is in the centre of the world, because in the midst of those circles; or because the parts and degrees of the earth are answerable in proportion to the parts and de
grees in heaven. Whereas, it follows rather on the contra, ry, that these circles are equally distant and proportional in their parts, in respect of the earth, because it is our eye that describes them about the centre of it.
So that though a far greater part of the world did appear at one time than at another, yet in respect of those circles which our eye describes about the earth, all that we could see at once, would seem to be but a perfect hemisphere; as may be manifested by this following figure.
Where if we suppose A to be our earth, BC D E one of the great circles which we fancy about it, F G H I the orb of fixed stars, R the centre of them: now though the ark GFI be bigger than the other G H I, yet notwithstanding, to the eye on the earth A, one will appcar a semicircle as well as the other; because the imagination does transfer all those stars into the lesser circle BCDE, which it does fancy to be described above that centre. Nay, though there were a habitable earth at a far greater distance from the centre of the world, even in the place of Jupiter, as suppose at Q; yet then also would there be the same appearance. For though the ark KFL in the starry heaven, were twice as big as the other K HL, yet notwithstanding at the earth Q they would both appear but as equal hemi
spheres, being transferred into that other circle MNOP, which is part of the sphere that the eye describes to itself about that earth.
From whence we may plainly discern, that though the earth be never so far distant from the centre of the world, yet the parts and degrees of that imaginary sphere about it, will always be proportional to the parts and degrees of the earth.
2. Another demonstration like unto this former, frequently urged to the same purpose, is this. If the earth be out of the centre of the world, then must it be situated in one of these three positions : either in the equator, but out of the axis; or 2dly, in the axis, but out of the equator; or 3dly, besides both of them. But it is not placed according to any of these situations, therefore must it needs be in the centre *.
1. It is not in the equator, and beside the axis: for then, 1st, there will be no equinox at all in some places, when the days and nights shall be of an equal length; 2dly, the afternoons and forenoons will not be of the same length; because, then our meridian line must divide the hemisphere into unequal parts.
2. It is not in the axis, but out of the equator; for then, first, the equinox would not happen when the sun was in the middle line betwixt the two solstices, but in some other parallel, which might be nearer to one of them, according as the earth did approach to one tropic more than another. Secondly, there would not be such a proportion between the increase and decrease of days and nights, as now there is.
3. It is not besides both of them: for then, all these inconveniencies, and sundry others must with the same necessity of consequence be inferred. From whence it will follow, that the earth must be situated there where the axis and equator meet, which is in the centre of the world.
To this we grant, that the earth must needs be placed
* Vid. Carp. Geog. I. I. c. 5.
both in the axis and equator; and so consequently, in the centre of that sphere which we imagine about it. But yet this will not prove, that it is in the midst of the universe : for let our adversaries
suppose it to be as far distant from that, as they conceive the sun to be; yet may it still be situated in the very concourse of these two lines; because the axis of the world is nothing else, but that imaginary line which passes through the poles of our earth, to the poles of the world. And so likewise the equator is nothing else but a great circle in the midst of the earth, betwixt both the poles, which by imagination is continued even to the fixed stars. Thus also, we may affirm the earth to be in the plane of the zodiac, if by its annual motion it did describe that imaginary circle: and in the plane of the equator, if by its diurnal motion about its own axis, it did make several parallels, the midst of which should be the equator. From whence it appears, that these two former arguments proceed from one and the same mistake; whilst our adversaries suppose the circumference and centre of the sphere, to be the same with that of the world.
Another demonstration of the same kind, is taken from the eclipses of the sun and moon; which would not always happen when these two luminaries are diametrically opposed, but sometimes when they are less distant than a semicircle, if it were so that the earth were not in the centre.
I answer: this argument, if well considered, will be found most directly to infer this conclusion; that in all eclipses, the earth is in such a strait line (betwixt the two luminaries) whose extremities do point unto opposite parts of the zodiac. Now, though our adversaries should suppose (as Copernicus does) the earth to be situated in that which they would have to be the sun's orb; yet would there not be any eclipse, but when the sun and moon were diametrically opposite, and our carth betwixt them; as may clearly be manifested by this figure, where you see the two luminaries in opposite signs: and according as any part of
our earth is situated by its diurnal revolution, so will every eclipse be either visible, or not visible unto it.
The last and chief arguinent, is taken from the appear. ance of the stars; which in every horizon, at each hour of the night, and at all times of the year, seem of an equal bigness *. Now this could not be, if our earth were sometimes nearer unto them by 2000000 German miles, which is granted to be the diameter of that orb wherein the earth is supposed to move.
I answer: this consequence will not hold, if we affirm the earth's orb not to be big enough for the making of any sensible difference in the appearance of the fixed stars.
Yea, but (you will say) it is beyond conceit, and without all reason, to think the fixed stars of so vast a distance from us, that our approaching nearer unto them by 2000000 German miles, cannot make any difference in the secming quantity of their bodies f.
I reply: there is no certain way to find out the exact distance of the starry firmament; but we are fain to con
* Arist. de cælo, lib. 2. c. 14.
† Copern. l. 1. cap. 5, 6.