light in the extremities, than in the middle parts.
Salv.The doubt is ingenious and worthy of consideration; and as it but just now came into your mind unawares, so I will like wise answer with what first comes into my thoughts, and it may happily fall out, that by thinking more upon it, I may stumble upon a better reply. But before, that I labyrinth my self any farther, it would be necessary, that we assure our selves by some experiment, whether your objection prove in effect, what it seemeth to conclude in appearance; and therefore taking once more the same paper, and making it to incline, by bending a little part thereof upon the remainder, let us try whether exposing it to the Sun, so that the rayes of light fall upon the lesser part directly, and upon the other obliquely; this which receiveth the rayes directly appeareth more lucid; and see here by manifest experience, that it is notably more clear. Now if your objection be conclusive, it will follow, that stooping with our eye so, that in beholding the other greater part, less illuminated, in compression or fore-shortning, it appear unto us no bigger than the other, more shining; and that consequently, it be not beheld at a greater angle than that; it will necessarily ensue, I say, that its light be encreased, so that it do seem to us as bright as the other. See how I behold, and look upon it so obliquely, that it appeareth to me narrower than the other; but yet, notwithstanding its obscurity, doth not to my perceiving, at all grow clearer. Try now if the same succeed to you.
Sagr.I have look't upon it, and though I have stooped with my eye, yet cannot I see the said superficies encrease in light or clarity; nay me thinks it rather grows more dusky.
Salv.We are hitherto confident of the invalidity of the objection; In the next place, as to the solution, I believe, that, by reason the Superficies of this paper is little lesse than smooth, the rayes are very few, which be reflected towards the point of incidence, in comparison of the multitude, which are reflected towards the opposite parts; and that of those few more and more are lost, the nearer the visive rayes approach to those lucid rayes of incidence; and because it is not the incident rayes, but those which are reflected to the eye, that make the object appear luminous; therefore, in stooping the eye, there is more lost than got, as you your self confesse to have seen in looking upon the obscurer part of the paper.
Sagr.I rest satisfied with this experiment and reason: It remains now, that Simplicius answer to my other question, and tell me what moves the Peripateticks to require this so exact rotundity in the Cœlestial bodies.
Simpl.The Cœlestial bodies being ingenerable, inalterable, im-passible,
