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.