Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/104

 of the Sun capable to penetrate the substance of the Moon, he makes her in part diaphanous, as is v. g. the transparence of a cloud, or crystal: but I know not what he would think of such a transparency, in case the solar rayes were to passe a depth of clouds of above two thousand miles; but let it be supposed that he should boldly answer, that might well be in the Cœlestial, which are quite other things from these our Elementary, impure, and feculent bodies; and let us convict his error by such wayes, as admit him no reply, or (to say better) subter-fuge. If he will maintain, that the substance of the Moon is diaphanous, he must say that it is so, whilest that the rayes of the Sun are to penetrate its whole profundity, that is, more than two thousand miles; but that if you oppose unto them onely one mile, or lesse, they should no more penetrate that, than they penetrate one of our mountains.

You put me in mind of a man, who would have sold me a secret how to correspond, by means of a certain sympathy of magnetick needles, with one, that should be two or three thousand miles distant; and I telling him, that I would willingly buy the same, but that I desired first to see the experiment thereof, and that it did suffice me to make it, I being in one Chamber, and he in the next, he answered me, that in so small a distance one could not so well perceive the operation; whereupon I turn'd him going, telling him, that I had no mind, at that time, to take a journey unto Grand Cairo, or to Muscovy, to make the experiment; but that, if he would go himself, I would perform the other part, staying in Venice. But let us hear whither the deduction of our Author tendeth, and what necessity there is, that he must grant the matter of the Moon to be most perforable by the rayes of the Sun, in a depth of two thousand miles, but more opacous than one of our mountains, in a thicknesse of one mile onely.

The very mountains of the Moon themselves are a proof thereof, which percussed on one side of the Sun, do cast on the contrary side very dark shadows, terminate, and more distinct by much, than the shadows of ours; but had these mountains been diaphanous, we could never have come to the knowledg of any unevennesse in the superficies of the Moon, not have seen those luminous montuosities distinguished by the terms which separate the lucid parts from the dark: much lesse, should we see this same term so distinct, if it were true, that the Suns light did penetrate the whole thicknesse of the Moon; yea rather, according to the Authors own words, we should of necessity discern the passage, and confine, between the part of the Sun seen, and the part not seen, to be very confused, and mixt with light and