The Notebooks of Leonardo Da Vinci — Complete
It is impossible that at any distance the image of the sun cast on
the surface of a spherical body should occupy the half of the
sphere.
Here you must prove that the earth produces all the same effects
with regard to the moon, as the moon with regard to the earth.
The moon, with its reflected light, does not shine like the sun,
because the light of the moon is not a continuous reflection of that
of the sun on its whole surface, but only on the crests and hollows
of the waves of its waters; and thus the sun being confusedly
reflected, from the admixture of the shadows that lie between the
lustrous waves, its light is not pure and clear as the sun is.
[Footnote 38: This refers to the small diagram placed between _B_
and _B_.--]. The earth between the moon on the fifteenth day and the
sun. [Footnote 39: See the diagram below the one referred to in the
preceding note.] Here the sun is in the East and the moon on the
fifteenth day in the West. [Footnote 40.41: Refers to the diagram
below the others.] The moon on the fifteenth [day] between the earth
and the sun. [41]Here it is the moon which has the sun to the West
and the earth to the East.
898.
WHAT SORT OF THING THE MOON IS.
The moon is not of itself luminous, but is highly fitted to
assimilate the character of light after the manner of a mirror, or
of water, or of any other reflecting body; and it grows larger in
the East and in the West, like the sun and the other planets. And
the reason is that every luminous body looks larger in proportion as
it is remote. It is easy to understand that every planet and star is
farther from us when in the West than when it is overhead, by about
3500 miles, as is proved on the margin [Footnote 7: refers to the
first diagram.--A = _sole_ (the sun), B = _terra_ (the earth), C =
_luna_ (the moon).], and if you see the sun or moon mirrored in the
water near to you, it looks to you of the same size in the water as
in the sky. But if you recede to the distance of a mile, it will
look 100 times larger; and if you see the sun reflected in the sea
at sunset, its image would look to you more than 10 miles long;
because that reflected image extends over more than 10 miles of sea.
And if you could stand where the moon is, the sun would look to you,
as if it were reflected from all the sea that it illuminates by day;
and the land amid the water would appear just like the dark spots
that are on the moon, which, when looked at from our earth, appears
to men the same as our earth would appear to any men who might dwell
in the moon.
[Footnote: This text has already been published by LIBRI: _Histoire
des Sciences,_ III, pp. 224, 225.]
OF THE NATURE OF THE MOON.
When the moon is entirely lighted up to our sight, we see its full
daylight; and at that time, owing to the reflection of the solar
rays which fall on it and are thrown off towards us, its ocean casts
off less moisture towards us; and the less light it gives the more
injurious it is.
899.
OF THE MOON.
I say that as the moon has no light in itself and yet is luminous,
it is inevitable but that its light is caused by some other body.
900.
OF THE MOON.
All my opponent's arguments to say that there is no water in the
moon. [Footnote: The objections are very minutely noted down in the
manuscript, but they hardly seem to have a place here.]
901.
Answer to Maestro Andrea da Imola, who said that the solar rays
reflected from a convex mirror are mingled and lost at a short
distance; whereby it is altogether denied that the luminous side of
the moon is of the nature of a mirror, and that consequently the
light is not produced by the innumerable multitude of the waves of
that sea, which I declared to be the portion of the moon which is
illuminated by the solar rays.
Let _o p_ be the body of the sun, _c n s_ the moon, and _b_ the eye
which, above the base _c n_ of the cathetus _c n m_, sees the body
of the sun reflected at equal angles _c n_; and the same again on
moving the eye from _b_ to _a_. [Footnote: The large diagram on the
margin of page 161 belongs to this chapter.]
Explanation of the lumen cinereum in the moon.
902.
OF THE MOON.
No solid body is less heavy than the atmosphere.
[Footnote: 1. On the margin are the words _tola romantina,
tola--ferro stagnato_ (tinned iron); _romantina_ is some special
kind of sheet-iron no longer known by that name.]
Having proved that the part of the moon that shines consists of
water, which mirrors the body of the sun and reflects the radiance
it receives from it; and that, if these waters were devoid of waves,
it would appear small, but of a radiance almost like the sun; --[5]
It must now be shown whether the moon is a heavy or a light body:
for, if it were a heavy body--admitting that at every grade of
distance from the earth greater levity must prevail, so that water
is lighter than the earth, and air than water, and fire than air and
so on successively--it would seem that if the moon had density as it
really has, it would have weight, and having weight, that it could
not be sustained in the space where it is, and consequently that it
would fall towards the centre of the universe and become united to
the earth; or if not the moon itself, at least its waters would fall
away and be lost from it, and descend towards the centre, leaving
the moon without any and so devoid of lustre. But as this does not
happen, as might in reason be expected, it is a manifest sign that
the moon is surrounded by its own elements: that is to say water,
air and fire; and thus is, of itself and by itself, suspended in
that part of space, as our earth with its element is in this part of
space; and that heavy bodies act in the midst of its elements just
as other heavy bodies do in ours [Footnote 15: This passage would
certainly seem to establish Leonardo's claim to be regarded as the
original discoverer of the cause of the ashy colour of the new moon
(_lumen cinereum_). His observations however, having hitherto
remained unknown to astronomers, Moestlin and Kepler have been
credited with the discoveries which they made independently a
century later.
Some disconnected notes treat of the same subject in MS. C. A. 239b;
718b and 719b; "_Perche la luna cinta della parte alluminata dal
sole in ponente, tra maggior splendore in mezzo a tal cerchio, che
quando essa eclissava il sole. Questo accade perche nell' eclissare
il sole ella ombrava il nostro oceano, il qual caso non accade
essendo in ponente, quando il sole alluma esso oceano_." The editors
of the "_Saggio_" who first published this passage (page 12) add
another short one about the seasons in the moon which I confess not
to have seen in the original manuscript: "_La luna ha ogni mese un
verno e una state, e ha maggiori freddi e maggiori caldi, e i suoi
equinozii son piu freddi de' nostri._"]
When the eye is in the East and sees the moon in the West near to
the setting sun, it sees it with its shaded portion surrounded by
luminous portions; and the lateral and upper portion of this light
is derived from the sun, and the lower portion from the ocean in the
West, which receives the solar rays and reflects them on the lower
waters of the moon, and indeed affords the part of the moon that is
in shadow as much radiance as the moon gives the earth at midnight.
Therefore it is not totally dark, and hence some have believed that
the moon must in parts have a light of its own besides that which is
given it by the sun; and this light is due, as has been said, to the
above- mentioned cause,--that our seas are illuminated by the sun.
Again, it might be said that the circle of radiance shown by the
moon when it and the sun are both in the West is wholly borrowed
from the sun, when it, and the sun, and the eye are situated as is
shown above.
[Footnote 23. 24: The larger of the two diagrams reproduced above
stands between these two lines, and the smaller one is sketched in
the margin. At the spot marked _A_ Leonardo wrote _corpo solare_
(solar body) in the larger diagram and _Sole_ (sun) in the smaller
one. At _C luna_ (moon) is written and at _B terra_ (the earth).]
Some might say that the air surrounding the moon as an element,
catches the light of the sun as our atmosphere does, and that it is
this which completes the luminous circle on the body of the moon.
Some have thought that the moon has a light of its own, but this
opinion is false, because they have founded it on that dim light
seen between the hornes of the new moon, which looks dark where it
is close to the bright part, while against the darkness of the
background it looks so light that many have taken it to be a ring of
new radiance completing the circle where the tips of the horns
illuminated by the sun cease to shine [Footnote 34: See Pl. CVIII,
No. 5.]. And this difference of background arises from the fact that
the portion of that background which is conterminous with the bright
part of the moon, by comparison with that brightness looks darker
than it is; while at the upper part, where a portion of the luminous
circle is to be seen of uniform width, the result is that the moon,
being brighter there than the medium or background on which it is
seen by comparison with that darkness it looks more luminous at that
edge than it is. And that brightness at such a time itself is
derived from our ocean and other inland-seas. These are, at that
time, illuminated by the sun which is already setting in such a way
as that the sea then fulfils the same function to the dark side of
the moon as the moon at its fifteenth day does to us when the sun is
set. And the small amount of light which the dark side of the moon
receives bears the same proportion to the light of that side which
is illuminated, as that... [Footnote 42: Here the text breaks off;
lines 43-52 are written on the margin.].
If you want to see how much brighter the shaded portion of the moon
is than the background on which it is seen, conceal the luminous
portion of the moon with your hand or with some other more distant
object.
On the spots in the moon (903-907).
903.
THE SPOTS ON THE MOON.
Some have said that vapours rise from the moon, after the manner of
clouds and are interposed between the moon and our eyes. But, if
this were the case, these spots would never be permanent, either as
to position or form; and, seeing the moon from various aspects, even
if these spots did not move they would change in form, as objects do
which are seen from different sides.
904.
OF THE SPOTS ON THE MOON.
Others say that the moon is composed of more or less transparent
parts; as though one part were something like alabaster and others
like crystal or glass. It would follow from this that the sun
casting its rays on the less transparent portions, the light would
remain on the surface, and so the denser part would be illuminated,
and the transparent portions would display the shadow of their
darker depths; and this is their account of the structure and nature
of the moon. And this opinion has found favour with many
philosophers, and particularly with Aristotle, and yet it is a false
view--for, in the various phases and frequent changes of the moon
and sun to our eyes, we should see these spots vary, at one time
looking dark and at another light: they would be dark when the sun
is in the West and the moon in the middle of the sky; for then the
transparent hollows would be in shadow as far as the tops of the
edges of those transparent hollows, because the sun could not then
fling his rays into the mouth of the hollows, which however, at full
moon, would be seen in bright light, at which time the moon is in
the East and faces the sun in the West; then the sun would
illuminate even the lowest depths of these transparent places and