Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/89

 solar rays come: but it is true that by the vivacity of the light, the said image will appear fringed about with many rays, and so will seem to occupie a far greater part of the plate, than really it doth. And to shew that this is true, when you have noted the particular place of the plate from whence the reflection cometh, and conceived likewise how great the shining place appeared to you, cover the greater part of that same space, leaving it only visible about the midst; and all this shall not any whit diminish the apparent splendor to one that beholds it from afar; but you shall see it largely dispers'd upon the cloth or other matter, wherewith you covered it. If therefore any one, by seeing from a good distance a small gilt plate to be all over shining, should imagine that the same would also even in a plate as broad as the Moon, he is no less deceived, than if he should believe the Moon to be no bigger than the bottom of a tub. If again the plate were turn'd into a spherical superficies, the reflection would be seen strong in but one sole particle of it; but yet by reason of its liveliness, it will appear fringed about with many glittering rays: the rest of the Ball would appear according as it was burnished; and this also onely then when it was not very much polished, for should it be perfectly brightned, it would appear obscure. An example of this we have dayly before our eyes in silver vessels, which whilst they are only boyl'd in the Argol and Salt, they are all as white as snow, and do not reflect any image; but if they be in any part burnish'd, they become in that place presently obscure: and in them one may see the representation of any thing as in Looking-glasses. And that chanto obscurity, proceeds from nothing else but the smoothing and plaining of a fine grain, which made the superficies of the silver rough, and yet such, as that it reflected the light into all parts, whereby it seemed from all parts equally illuminated: which small unevennesses, when they come to be exquisitely plained by the burnish, so that the reflection of the rays of incidence are all directed unto one determinate place; then, from that same place, the burnish'd part shall shew much more bright and shining than the rest which is onely whitened by boyling; but from all other places it looks very obscure. And note, that the diversity of sights of looking upon burnish'd superficies, occasioneth such difference in appearances, that to imitate and represent in picture, v. g. a polish'd Cuirace, one must couple black plains with white, one sideways to the other, in those parts of the arms where the light falleth equally.

If therefore these great Philosophers would acquiese in granting, that the Moon, Venus and the other Planets, were not of so bright and smooth a surface as a Looking-glass, but wanted some small matter of it, namely, were as a silver plate, onely boyled