and that, if they did not shine of
themselves, the shadow cast by the earth between them and the sun would
darken them, since they would not see nor be seen by the sun. But
these have not taken into consideration that the conical shadow of the
moon does not reach many of the stars, and even for those it does reach
the shadow is diminished to such an extent that it covers very little
of the star, and the remaining part is illumined by the sun.

{158}

[Sidenote: On the Nature of the Moon]

40.

The moon having density and gravity, how does it stand?

41.

i. No very light object is opaque.

ii. Nothing light can remain beneath that which is heavier.

iii. Whether the moon is the centre of its elements or not. And if it
has no fixed position like the earth in the centre of its elements, why
does it not fall to the centre of our elements? And if the moon is not
in the centre of its elements and does not fall, it must then be
lighter than any other element. And if the moon is lighter than the
other elements, why is it opaque and not transparent?

42.

No body which has density is lighter than the air. Having proved that
the part of the moon which shines consists of water which mirrors the
body of the sun and reflects for us the splendour it receives from the
sun, and that if there were no waves in these waters, it would appear
small, but almost as bright as the sun--it must now be shown whether
the moon is a heavy or a light body; if it is a heavy body--admitting
that from the earth upwards with every grade of distance lightness must
increase, so that water is lighter than earth, air is lighter than
water, and {159} fire lighter than air, and so on in succession--it
would seem that if the moon had density, as it has, it must have
gravity, and if it has gravity the space in which it lies could not
contain it, and consequently it would fall towards the centre of the
universe and be joined to the earth, or if not the moon itself, its
waters would fall from the moon and strip it and fall towards the
centre, leaving the moon bare and lustreless; whence, as this could not
happen, as reason would tell us, it is manifest that the moon is
surrounded by its elements, that is to say, water, air and fire, and
thus it sustains itself by itself in that space as our earth is
suspended with its elements in this part of space; heavy bodies act in
their elements there just as other heavy bodies act in ours.

[S