|Salusbury, Thomas Mathematical collections and translations 1667|
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 refle
cted 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.
The third resle
ction of a Wall illu
minates more than
the first of the
SIMPL. But this I cannot believe; for the illumination of the
Moon, especially when it is at the full, is very great.
SAGR. 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, be
cause you see not the shadows of the bodies illuminated by the
Moon till then, to begin to be distinguished on the Earth. Whe
ther, 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.
The light of the
Moon weaker than
that of the twi
SALV. 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 can
not 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 scru
pulous of granting, that the dark part of the Earth may illuminate
the dark part of the Moon, with no less a light than that where
with 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.
SIMPL. I must confess that I did believe, that that secondary
light had been the natural light of the Moon.
SALV. 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 conse
quently, do you not know in genere, that every bright body shews
the clearer, by how much the ambient is obscurer?
appear the brighter
in an obscurer am
SIMPL. This I know very well.
SALV. When the Moon is horned, and that secondary light
seemeth to you very bright, is it not ever nigh the Sun, and con
sequently, in the light of the crepusculum, (twilight?)