Archimedes Texts

50
illuminated parts of the Terrestrial superficies appear beheld from
the Moon, depends not on this alone, but on the divers aspects
which the Moon is still changing with the Sun; so that, if for in
stance, the Moon punctually followed the motion of the Sun, and
stood, for example, always in a direct line between it and the
Earth, in that aspect which we call Conjunction, it looking always
to the same Hemisphere of the Earth which the Sun looks unto,
she would behold the same all light: as on the contrary, if it should
always stay in Opposition to the Sun, it would never behold the
Earth, of which the dark part would be continually turn'd towards
the Moon, and therefore invisible. But when the Moon is in
Quadrature of the Sun, that half of the Terrestrial Hemisphere ex
posed to the sight of the Moon which is towards the Sun, is lumi
nous; and the other towards the contrary is obscure: and there
fore the illuminated part of the Earth would represent it self to the
Moon in a semi-circular figure.

SAGR. I clearly perceive all this, and understand very well,
that the Moon departing from its Opposition to the Sun, where it
saw no part of the illumination of the Terrestrial superficies, and
approaching day by day nearer the Sun, she begins by little and
little to discover some part of the face of the illuminated Earth;
and that which appeareth of it shall resemble a thin sickle, in regard
the figure of the Earth is round: and the Moon thus acquiring by
its motion day by day greater proximity to the Sun, successively
discovers more and more of the Terrestrial Hemisphere enlightned,
so that at the Quadrature there is just half of it visible, insomuch
that we may see the other part of her: continuing next to proceed
towards the Conjunction, it successively discovers more and more
of its surface to be illuminated, and in fine, at the time of Conjun
ction seeth the whole Hemisphere enlightned. And in short, I
very well conceive, that what befalls the Inhabitants of the Earth,
in beholding the changes of the Moon, would happen to him that
from the Moon should observe the Earth; but in a contrary order,
namely, that when the Moon is to us at her full, and in Opposition
to the Sun, then the Earth would be in Conjunction with the Sun,
and wholly obscure and invisible; on the contrary, that position
which is to us a Conjunction of the Moon with the Sun, and for
that cause a Moon silent and unseen, would be there an Opposition
of the Earth to the Sun, and, to so speak, Full Earth, to wit, all
enlightned. And lastly, look what part of the Lunar surface ap
pears to us from time to time illuminated, so much of the Earth
in the same time shall you behold from the Moon to be obscured:
and look how much of the Moon is to us deprived of light, so much
of the Earth is to the Moon illuminated. In one thing yet these
mutual operations in my judgment seem to differ, and it is, that it