Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/83

 Why look you, there it is upon the opposite Wall, just as big as the Glasse, and little lesse bright than if the Sun had directly shined upon it.

Come hither therefore, and see from hence the surface of the Glasse, and tell me whether you think it more obscure than that of the Wall.

Look on it your self, for I have no mind at this time, to dazle my eyes; and I know very well, without seeing it, that it there appears as splendid and bright as the Sun it self, or little lesse.

What say you therefore, is the reflection of a Glasse lesse powerful than that of a Wall? I see, that in this opposite Wall, where the reflection of the other illuminated Wall comes, together with that of the Glasse, this of the Glasse is much clearer; and I see likewise, that, from this place where I stand, the glasse it self appears with much more lustre than the Wall.

You have prevented me with your subtlety; for I stood in need of this very observation to demonstrate what remains. You see then the difference which happens betwixt the two reflections made by the two superficies of the Wall and Glasse, percu•t in the self-same manner, by the rayes of the Sun; and you see, how the reflection which comes from the Wall, diffuseth it self towards all the parts opposite to it, but that of the Glasse goeth towards one part onely, not at all bigger than the Glasse it self: you see likewise, how the superficies of the Wall, beheld from what part soever, alwayes shews it self of one and the same cleernesse, and every way, much clearer than that of the Glasse, excepting only in that little place, on which the Glasses reflection reverberates, for from thence indeed the Glasse appears much more lucid than the Wall. By these so sensible, and palpable experiments, my thinks one may soon come to know, whether the reflection which the Moon sends upon us, proceed as from a Glasse, or else, as from a Wall, that is, from a smooth superficies, or a rugged.

If I were in the Moon it self, I think I could not with my hands more plainly feel the unevennesse of its superficies, than I do now perceive it, by apprehending your discourse. The Moon beheld in any posture, in respect of the Sun and us, sheweth us its superficies, touch't by the Suns rayes, alwayes equally clear; an effect, which answers to an hair that of the Wall, which beheld from what place soever, appeareth equally bright, and differeth from the Glasse, which from one place onely appeareth lucid, and from all others obscure. Moreover, the light which cometh to me from the reflection of the Wall, is tollerable, and weak, in comparison of that of the Glasse, which is little