Notebooks of Leonardo da Vinci

a small size. If the eye were as large as the sun it would see the
image of the sun in water of the same size as the real body of the
sun, so long as the water is smooth. 

891. 

A METHOD OF SEEING THE SUN ECLIPSED WITHOUT PAIN TO THE EYE. 

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. 

And, if it has no proper place of its own, like the earth, in the
midst of its elements, why does it not fall to the centre of our
elements? [Footnote 26: The problem here propounded by Leonardo was
not satisfactorily answered till Newton in 1682 formulated the law
of universal attraction and gravitation. Compare No. 902, lines
5-15.] 

And, if the moon is not in the centre of its own elements and yet
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? 

When objects of various sizes, being placed at various distances,
look of equal size, there must be the same relative proportion in
the distances as in the magnitudes of the objects. 

[Footnote: In the diagram Leonardo wrote _sole_ at the place marked
_A_.] 

893. 

OF THE MOON AND WHETHER IT IS POLISHED AND SPHERICAL. 

The image of the sun in the moon is powerfully luminous, and is only
on a small portion of its surface. And the proof may be seen by
taking a ball of burnished gold and placing it in the dark with a
light at some distance from it; and then, although it will
illuminate about half of the ball, the eye will perceive its
reflection only in a small part of its surface, and all the rest of
the surface reflects the darkness which surrounds it; so that it is
only in that spot that the image of the light is seen, and all the
rest remains invisible, the eye being at a distance from the ball.
The same thing would happen on the surface of the moon if it were
polished, lustrous and opaque, like all bodies with a reflecting
surface. 

Show how, if you were standing on the moon or on a star, our earth
would seem to reflect the sun as the moon does. 

And show that the image of the sun in the sea cannot appear one and
undivided, as it appears in a perfectly plane mirror. 

894. 

How shadows are lost at great distances, as is shown by the shadow
side of the moon which is never seen. [Footnote: Compare also Vol.
I, Nos. 175-179.] 

895. 

Either the moon has intrinsic luminosity or not. If it has, why does
it not shine without the aid of the sun? But if it has not any light
in itself it must of necessity be a spherical mirror; and if it is a
mirror, is it not proved in Perspective that the image of a luminous
object will never be equal to the extent of surface of the