Take a piece of paper and pierce holes in it with a needle, and look at the sun through these holes.
III.
THE MOON.
On the luminousity of the moon (892-901).
892.
OF THE MOON.
As I propose to treat of the nature of the moon, it is necessary that first I should describe the perspective of mirrors, whether plane, concave or convex; and first what is meant by a luminous ray, and how it is refracted by various kinds of media; then, when a reflected ray is most powerful, whether when the angle of incidence is acute, right, or obtuse, or from a convex, a plane, or a concave surface; or from an opaque or a transparent body. Besides this, how it is that the solar rays which fall on the waves of the sea, are seen by the eye of the same width at the angle nearest to the eye, as at the highest line of the waves on the horizon; but notwithstanding this the solar rays reflected from the waves of the sea assume the pyramidal form and consequently, at each degree of distance increase proportionally in size, although to our sight, they appear as parallel.
1st. Nothing that has very little weight is opaque.
2dly. Nothing that is excessively weighty can remain beneath that which is heavier.
3dly. As to whether the moon is situated in the centre of its elements or not.