which, without question, the illuminating rayes of the Sun do come; yet neverthelesse, it appears not to us bright and shining, unlesse we set our eye in that particular place, where the reflection arriveth. Now let us consider what would succeed, were the glasse of a spherical figure; for without doubt, we should find, that of the reflection made by the whole surface illuminated, that to be but a very small part, which arriveth to the eye of a particular beholder; by reason that that is but an inconsiderable particle of the whole spherical superficies, the inclination of which casts the ray to the particular place of the eye; whence the part of the spherical superficies, which shews it self shining to the eye, must needs be very small; all the rest being represented obscure. So that were the Moon smooth, as a Looking-glasse,The Moon if it were smooth, like a spherical glasse, would be invisible. a very small part would be seen by any particular eye to be illustrated by the Sun, although its whole Hemisphere were exposed to the Suns rayes; and the rest would appear to the eye of the beholder as not illuminated, and therefore invisible; and finally, the whole Moon would be likewise invisible, for so much as that particle, whence the reflection should come, by reason of its smalnesse and remotenesse, would be lost. And as it would be invisible to the eye, so would it not afford any light; for it is altogether impossible, that a bright body should take away our darknesse by its splendor, and we not to see it.
Salv.Stay good Sagredus, for I see some emotions in the face and eyes of Simplicius, which are to me as indices that he is not either very apprehensive of, or satisfied with this which you, with admirable proof, and absolute truth have spoken. And yet I now call to mind, that I can by another experiment remove all scruple. I have seen above in a Chamber, a great spherical Looking-glasse; let us send for it hither, and whilest it is in bringing, let Simplicius return to consider, how great the clarity is which cometh to the Wall here, under the penthouse, from the reflection of the flat glasse.
Simpl.I see it is little lesse shining, than if the Sun had directly beat upon it.
Salv.So indeed it is. Now tell me, if taking away that small flat glasse, we should put that great spherical one in the same place, what effect (think you) would its reflection have upon the same Wall?
Simpl.I believe that it would eject upon it a far greater and more diffused light.
Salv.But if the illumination should be nothing, or so small, that you would scarse discern it, what would you say then?
Simpl.When I have seen the effect, I will bethink my self of an answer.
Salv.
