The laws of optics, which are founded upon the nature of things, have ordained that, from this small globe of earth on which we live, we shall always see the material heaven as if we were the centre of it, although we are far from being that centre; that we shall always see it as a vaulted roof, hanging over a plane, although there is no other vaulted roof than that of our atmosphere, which has no such plane; that our sun and moon will always appear one-third larger at the horizon than at their zenith, although they are nearer the spectator at the zenith than at the horizon.

Such are the laws of optics, such is the structure of your eyes, that, in the first place, the material heaven, the clouds, the moon, the sun, which is at so vast a distance from you; the planets, which in their apogee are still at a greater distance from it; all the stars placed at distances yet vastly greater, comets and meteors, everything, must appear to us in that vaulted roof as consisting of our atmosphere.

The sun appears to us, when in its zenith, smaller than when at fifteen degrees below; at thirty degrees below the zenith it will appear still larger than at fifteen; and finally, at the horizon, its size will seem larger yet; so that its dimensions in the lower heaven decrease in consequence of its elevations, in the following proportions:
At the horizon     100
At fifteen degrees above       68
At thirty degrees       50
At forty-five degrees       40

Its apparent magnitudes in the vaulted roof are as its apparent elevations; and it is the same with the moon, and with a comet.

It is not habit, it is not the intervention of tracts of land, it is not the refraction of the atmosphere which produces this effect. Malebranche and Régis have disputed with each other on this subject; but Robert Smith has calculated.

Observe the two stars, which, being at a prodigious distance from each other, and at very different depths, in the immensity of space, are here considered as placed in the circle which the sun appears to traverse. You perceive them distant from each other in the great circle, but approximating to each other in every circle smaller, or within that described by the path of the sun.

It is in this manner that you see the material heaven. It is by these invariable laws of optics that you perceive the planets sometimes retrograde and sometimes stationary; there is in fact nothing of the kind. Were you stationed in the sun, we should perceive all the planets and comets moving regularly round it in those elliptical orbits which God assigns. But we are upon the planet of the earth, in a corner of the universe, where it is impossible for us to enjoy the sight of everything.

Let us not then blame the errors of our senses, like Malebranche; the steady laws of nature originating in the immutable will of the Almighty, and adapted to the structure of our organs, cannot be errors.

We can see only the appearances of things, and not things themselves. We are no more deceived when the sun, the work of the divinity — that star a million times larger than our earth — appears to us quite flat and two feet in width, than when, in a convex mirror, which is the work of our own hands, we see a man only a few inches high.

If the Chald?an magi were the first who employed the understanding which God bestowed upon them, to measure and arrange in their respective stations the heavenly bodies, other nations more gross and unintelligent made no advance towards imitating them.

These childish and savage populations imagined the earth to be flat, supported, I know not how, by its own weight in the air; the sun, moon, and stars to move continually upon a solid vaulted roof called a firmament; and this roof to sustain waters, and have flood-gates at regular distances, through which these waters issued to moisten and fertilize the earth.

But how did the sun, the moon, and all the stars reappear after their setting? Of this they know nothing at all. The heaven touched the flat earth: and there were no means by which the sun, moon, and stars could turn under the earth, and go to rise in the east after ............