which being of a spherical figure, if its superficies were smooth, as this paper, the parts of its hemisphere illuminated by the Sun, which are towards its extremity, would receive much less light, than the middle parts; the rays falling upon them most obliquely, and upon these at right angles; whereupon at the time of full Moon, when we see almost its whole Hemisphere illuminated, the parts towards the midst, would shew themselves to us with more splendor, than those others towards the circumference: which is not so in effect. Now the face of the Moon being represented to me full of indifferent high mountains, do not you see how their tops and continuate ridges, being elevated above the convexity of the perfect spherical superficies, come to be exposed to the view of the Sun, and accommodated to receive its rays much less obliquely, and consequently to appear as luminous as the rest?
Sagr.All this I well perceive: and if there are such mountains, its true, the Sun will dart upon them much more directly than it would do upon the inclination of a polite superficies: but it is also true, that betwixt those mountains all the valleys would become obscure, by reason of the vast shadows, which in that time would be cast from the mountains, whereas the parts towards the middle, though full of valleys and hills, by reason they have the Sun elevated, would appear without shadow, and therefore more lucid by far than the extreme parts, which are no less diffused with shadow than light, and yet we can perceive no such difference.
Simpl.I was ruminating upon the like difficulty.
Salv.How much readier is Simplicius to apprehend the objections which favour the opinions of Aristotle, than their solutions? I have a kind of suspition, that he strives also sometimes to dissemble them; and in the present case, he being of himself able to hit upon the doubt, which yet is very ingenious, I cannot believe but that he also was advis'd of the answer; wherefore I will attempt to wrest the same (as they say) out of his mouth. Therefore tell me, Simplicius, do you think there can be any shadow, where the rays of the Sun do shine?
Simpl.I believe, nay I am certain that there cannot; for that it being the grand luminary, which with its rays driveth away darkness, it is impossible any tenebrosity should remain where it cometh; moreover, we have the definition, that Tenebræ sunt privatio luminis.
Salv.Therefore the Sun, beholding the Earth, Moon or other opacous body, never seeth any of its shady parts, it not having any other eyes to see with, save its rays, the conveyers of light: and consequently, one standing in the Sun would never see any thing of umbrage, forasmuch as his visive rays would evergo
