Page:Mathematical collections and translations, in two tomes - Salusbury (1661).djvu/99

 the wall hath it? The Sun shineth on that wall; from thence it is reverberated upon the wall of the Hall, from thence it's reflected upon that chamber, so that it falls on it at the third reflection: and I am very certain, that there is in that place more light, than if the Moons light had directly faln upon it.

But this I cannot believe; for the illumination of the Moon, especially when it is at the full, is very great.

It seemeth great by reason of the circumjacent dark places; but absolutely it is not much, and is less than that of the twilight half an hour after the Sun is set; which is manifest, because you see not the shadows of the bodies illuminated by the Moon till then, to begin to be distinguished on the Earth. Whether, again, that third reflection upon that chamber, illuminates more than the first of the Moon, may be known by going thether, and reading a Book, and afterwards standing there in the night by the Moons light, which will shew by which of them lights one may read more or less plainly, but I believe without further tryal, that one should see less distinctly by this later.

Now, Simplicius, (if haply you be satisfied) you may conceive, as you your self know very well, that the Earth doth shine no less than the Moon; and the only remembring you of some things, which you knew of your self, and learn'd not of me, hath assured you thereof: for I taught you not that the Moon shews lighter by night than by day, but you understood it of your self; as also you could tell me that a little Cloud appeareth as lucid as the Moon: you knew also, that the illumination of the Earth cannot be seen by night; and in a word, you knew all this, without knowing that you knew it. So that you have no reason to be scrupulous of granting, that the dark part of the Earth may illuminate the dark part of the Moon, with no less a light than that wherewith the Moon illuminates the obscurities of the night, yea rather so much the greater, inasmuch as the Earth is forty times bigger than the Moon.

I must confess that I did believe, that that secondary light had been the natural light of the Moon.

And this also you know of your self, and perceive not that you know it. Tell me, do not you know without teaching, that the Moon shews it self more bright by night than by day, in respect of the obscurity of the space of the ambient? and consequently, do you not know in genere, that every bright body shews the clearer, by how much the ambient is obscurer?

This I know very well.

When the Moon is horned, and that secondary light seemeth to you very bright, is it not ever nigh the Sun, and consequently, in the light of the crepusculum, (twilight?)