'The moon has every month a winter and a
summer. And it has greater colds and greater
heats and its equinoxes are colder than ours!
Make glasses in order to see the moon large. c.a. 190 r. a
If you know the distance of a body you will know the size of the
visual pyramid if you take a section of it near the eye upon a wall and
then remove the line so far from the eye as to double the size of the
section. Then note the distance from the first to the second section and
ask yourself: — if within such a space the diameter of the moon in-
creases for me so much above the first section what will it do in the
whole space that is between the eye and the moon? It will form the
exact diameter of this moon.
Measure of the size of the sun, knowing the distance, c.a. 243 r. b
If the water of the moon had its centre of gravity at the centre of the
earth, it would strip the moon and fall upon us . . . suspended from
the centre of its sphere.
If you should be moving towards the sun along that line of water
which lies between this sun and its image, you will be sailing along a
continuous image which will be of the length of your movement.
Why the moon when surrounded by the luminous part of the sun in
the west has greater radiance in the centre of this circle than when there
is an eclipse of the sun. This comes about because as it eclipses the
sun it casts a shadow upon our ocean, and this does not occur when
it is in the west, for then the sun lights up this ocean.
Why in the eclipse of the sun the body of the moon when it is op-
posite to us shows itself in the middle of the sun with part of its ra-
diance somewhat like that of molten iron. This proceeds from the
moon which derives its radiance from the stars, and not from the earth,
because this is darkened. . . . c.a. 243 v. a
The image of the sun is all in all the water which sees it, and all ir
every minutest part of it.
This is proved because there are as many images of the sun as there
are positions of the eyes which see the water between themselves and
Moreover as the eye moves when carried along the line of the ship
it sees the image of the sun moving along the same line as that of the
movement of the eye; but it will not be parallel for as the sun moves
to the west the line of the images moves in a curve towards the sun,
in such a way as to seem finally to unite with the image of the sun
when it has reached the horizon.
If the ship's movement be to the south and the sun is in the middle
of the heaven the line of the image of the sun will be curved, and it
will always go on extending itself, so that at the last it will unite with
the sun on the horizon and the image will seem equal in size to this
sun. c.a. 243 v. b
How bodies send forth from themselves their form heat and potency:
When the sun during an eclipse assumes the shape of a crescent, take
a thin plate of iron and make a small hole in it, and turn the face of
this plate towards the sun, holding a sheet of paper behind it at a dis-
tance of half a braccio, and you will see the image of the sun appear
on this sheet in the shape of a crescent, similar in form and colour to
Quality of the sun:
The sun has substance, shape, movement, radiance, heat and genera-
tive power; and these qualities all emanate from itself without its
diminution. c.a. 270 v. b
The solar rays after penetrating the little holes which come between
the various rounded particles of the clouds take a straight and con-
tinuous course to the ground where they strike, illuminating with their
radiance all the air through which they pass. c.a. 297 v. a
It the moon is a mirror of our earth, when it is at the full the earth
will be half dark and half illuminated, or perhaps more than half dark.
And of dark things we cannot discern the shapes of the objects which
are within their boundaries.
The adversary says that the light of the moon illumines the portion
of the earth seen by it, and for this reason, as the earth is surrounded
by water, that only the water reflects the light of the moon, and the
earth as it is not smooth or polished in its surface as is the water, does
not transmit the image of itself to this water, and so it remains dark,
and thus our water shines in the moon with the darkness of the islands
which it surrounds. c.a. 300 r. b
The moon has every month a winter and a summer.
And it has greater colds and greater heats and its equinoxes are
colder than ours. c.a. 303 v. b
How it is possible for the quantity of the images of the sun to pass
through the indivisible point of the primitive into the derivative
The sun is composed of a very great number of indivisible parts; and
although this sun is possessed of bodily substance its powers are incor-
poreal consisting of heat and radiance; and since an incorporeal power
has no substance not having substance it does not occupy space, and
not occupying space it does not close the aperture, and consequently the
passage through this aperture to and fro is permitted to each spirit at
the same time.
It is possible that the solar rays reduced through a pyramid to a point
by the concave mirror is redoubled in warmth and radiance; as these
rays are in the derived pyramid they are thrown back by a similar mir-
ror to an equal distance from the point. c.a. 347 v. a
OF THE CIRCLES OF THE MOON
I find that those circles which at night seem to surround the moon,
varying in circumference and in their degree of redness, are caused by
the different degrees of thickness of the vapours which are situated at
different altitudes between the moon and our eyes. And the circle that
is larger and less red is in the first part lower than the said vapours; the
second, being less, is higher and appears redder, because it is seen
through two sets of vapours; and so the higher they are the smaller and
the redder will they appear, for between the eye and them there will be
more layers of vapours, and this goes to prove that where there appears
greater redness, there is a greater quantity of vapours. c.a. 349 v. e
BURNING MIRROR [sketch]
As many times as the point of the solar pyramid cut in any part what-
ever is contained in its base so many times is it hotter than this base.
a 54 r.
WHAT THE MOON IS
The moon is not luminous in itself, but it is well fitted to take the
characteristics of light after the manner of the mirror or of water or
any other shining body; and it grows larger in the east and in the west
like the sun and the other planets, and the reason of this is that every
luminous body grows larger as it becomes more remote.
It may be readily understood that every planet and star is farther
away from us when in the west than when it is overhead, by about
three thousand Rvt hundred [miles] according to the proof given at
the side [of the page]; 1 and if you see the sun and moon reflected in
water which is near at hand it will seem to be the same size in the
water as it does in the sky, while if you go away to the distance of a
mile it will seem a hundred times as large. And if you see it reflected in
the sea at the moment of its setting the image of the sun will seem to
you to be more than ten miles long, because it will cover in the reflec-
tion more than ten miles of sea. And if you were where the moon is, it
would appear to you that the sun was reflected over as much of the sea
as it illumines in its daily course, and the land would appear amid this
water like the dark spots that are upon the moon, which when looked
at from the earth presents to mankind the same appearance that our
earth would present to men dwelling in the moon.
1 Here the margin of the MS. contains a diagram representing the earth with the
sun shown in two positions.
OF THE NATURE OF THE MOON
When all that we can see of the moon is illumined it gives us its
maximum of light, and then from the reflection of the rays of the sun
which strike upon it and rebound towards us its ocean throws off less
moisture to us, and the less light it gives the more it is harmful.
a 64 r.
EXPLANATION OF WHY THE SUN SEEMS LARGER IN
Certain mathematicians contend that the sun grows larger when it is
setting, because the eye sees it continually through atmosphere of
greater density, alleging that objects seen through mist and in water
To this I reply that this is not the case, for the things seen through
ihe mist are similar in colour to those which are at a distance, but as
they do not undergo the same process of diminution, they appear
greater in size.
In the same way nothing seems larger in smooth water, and this you
may prove by tracing upon a board which is placed under water.
The real reason why the sun grows larger is that every luminous
body appears larger, as it is farther away. a 64 v.
PRAISE OF THE SUN
If you look at the stars without their rays, — as may be done by look-
ing at them through a small hole made with the extreme point of a
fine needle and placed so as almost to touch the eye, — you will perceive
these stars to be so small that nothing appears less; and in truth the
great distance gives them a natural diminution, although there are
many there which are a great many times larger than the star which is
our earth together with the water. Think, then, what this star of ours
would seem like at so great a distance, and then consider how many
stars might be set longitudinally and latitudinally amid these stars
which are scattered throughout this dark expanse. I can never do other
than blame those many ancients who said that the sun was no larger
than it appears, — among these being Epicurus; and I believe that such
a theory is borrowed from the idea of a light set in our atmosphere
equidistant from the centre [of the earth]; whoever sees it never sees
it lessened in size at any distance, and the reasons of its size and
potency I shall reserve for the Fourth Book.
But I marvel greatly that Socrates should have spoken with dis-
paragement of that body, and that he should have said that it resembled
a burning stone, and it is certain that whoever opposes him in such an
error can scarcely do wrong. I could wish that I had such power of
language as should avail me to censure those who would fain extol the
worship of men above that of the sun, for I do not perceive in the whole
universe a body greater and more powerful than this, and its light
illumines all the celestial bodies which are distributed throughout the
All vital principle descends from it, since the heat there is in living
creatures proceeds from this vital principle; and there is no other heat
or light in the universe as I shall show in the Fourth Book, and indeed
those who have wished to worship men as gods, such as Jupiter, Saturn,
Mars and the like, have made a very grave error seeing that even if a
man were as large as our earth he would seem like one of the least of
the stars, which appears but a speck in the universe; and seeing also
that these men are mortal and subject to decay and corruption in
The Spera, and Marullo, and many others praise the Sun.
f 5 r. and 4 v.
The stars are visible by night and not by day owing to our being
beneath the dense atmosphere which is full of an infinite number of
particles of moisture. Each of these is lit up when it is struck by the rays
of the sun and consequently the innumerable radiant particles veil these
stars; and if it were not for this atmosphere the sky would always show
the stars against the darkness. f 5 v -
Epicurus perhaps perceived that the shadows of columns striking the
opposite walls were equal in diameter to the column from which they
proceeded. As therefore the mass of the shadow from beginning to end
was a parallelogram he thought he might infer that the sun also was
opposite to this parallelogram and as a consequence would not be larger
than this column, not perceiving that such a diminution of the shadow
would be imperceptible on account of the great distance of the sun.
If the sun were smaller than the earth, the stars in a great part of our
hemisphere would be without light: this is contrary to Epicurus who
savs that the sun is only as large as it appears. f 6 r.
Epicurus says that the sun is as large as it shows itself; as therefore it
appears to be a foot we have to reckon it as such.
It would follow that when the moon obscured the sun the sun would
not surpass it in size as it does; therefore the moon being smaller than
the sun the moon would be less than a foot, and consequently when
our earth obscured the moon it would be less by a finger's breadth, see-
ing that if the sun be a foot across and our earth casts a pyramidal
shadow towards the moon it is inevitable that the luminous body which
is the cause of the shaded pyramid must be greater than the opaque
body which casts this pyramid. f 8 v.
A calculation of how many times the sun will go into its course in
twenty four hours:
Make a circle and set it to face south after the manner of sundials;
place a rod in the middle of it so that its length is pointing to the centre
of the circle and note the shadow made by the sun from this rod upon
the circumference of the circle, and let us say that the breadth of the
shadow is all a n (diagram). Now measure how many times this
shadow will go into this circumference of the circle, and this will be the
number of times that the solar body will go into its course in twenty
four hours. In this way one may see whether Epicurus was right in say-
ing that the sun is as large as it seems to be, for as the apparent diame-
ter of the sun is about a foot and as the sun would go a thousand times
into its course in twenty four hours, the length of its course would be
a thousand feet, that is five hundred braccia, which is the sixth of a
mile; so then the course of the sun between day and night would be
the sixth part of a mile, and this venerable snail the sun would have
travelled twenty five braccia an hour. nor.
THE ORDER OF PROVING THAT THE EARTH IS A STAR
First explain the mechanism of the eye, then show how the scintilla-
tion of each star originates in the eye, and why the scintillation of one
star is greater than that of another. And how the rays of the stars origi-
nate in the eye. I affirm that if the scintillation of the stars was as it
appears, in the stars, this scintillation would show itself as widely ex-
tended as the body of the star; and since it is larger than the earth this
movement made instantaneously would swiftly be found to cause the
star to seem double in size. See afterwards how the surface of the air
on the confines of the fire, and the surface of the fire at its boundary, is
that in which the solar rays penetrating carry the resemblance of the
heavenly bodies, large in their rising and setting and small when they
are in the centre of the sky. f 25 v.
AN EXPERIMENT IN ORDER TO SHOW HOW RAYS
PENETRATE LIQUID BODIES
Make two vessels each of parallel sides, the one four fifths of the
other and of equal height. Then Rx one within the other as you see in
the drawing, and cover outside with colour and leave an opening of the
size of a lentil, and allow a ray of the sun to enter there which makes
its exit through another dark hole or by the window. Then observe
whether the ray that passes within the water enclosed between the two
vessels keeps the direction that it has outside or no; and from this de-
duce your rule.
In order to see how the solar rays penetrate this curve of the sphere
of the air have two balls made of glass one twice as large as the other,
and let them be as round as possible. Then cut them in half, place one
inside the other, close them in front and fill them with water, then let
the solar ray pass within as you have done above, and observe whether
the ray is bent or curved and from this deduce your rule. And in this
way you can make an infinite number of experiments.
Observe as you place yourself with your eye in the centre of the ball
whether the light of a candle keeps its size or no. f 33 v.
OF THE SUN
Some say that the sun is not hot because it is not the colour of fire
hut is much paler and clearer. To these we may reply that when liqui-
fied bronze is at its maximum of heat it most resembles the sun in
colour, and when it is less hot it has more of the colour of fire.
The solar rays reflected by the surface of the undulating water cause
the image of the sun to seem continuous over all that water which is
between the universe and the sun. f 38 v.
Why the image of the sun is all in all the sphere of the water which
sees the sun and all in each part of the said water:
All the sky which sees the part of the sphere of the water seen by the
sun sees all this water covered by the image of the sun, and each part
of the sky sees all.
The surface of the water without waves lights equally the places
struck by the reflected rays of the image of the sun in the water.
The image of the sun is unique in the sphere of the water seen by
the sun, which shows itself however to all the sky that finds itself
before it, and every point of this sky itself sees an image, and that
which sees one in one position is seen by the other in another position,
in such a way that no part of the sky sees it all.
That image of the sun will cover a greater space in the surface of the
water which is seen from a place more distant from it. f 39 r.
How the earth is not in the centre of the circle of the sun, nor in the
centre of the universe, but is in fact in the centre of its elements which
accompany it and are united to it. And if one were to be upon the
moon, then to the extent to which it together with the sun is above us, 1
so far below it would our earth appear with the element of water, per-
forming the same office as the moon does for us. f 41 v.
All your discourse points to the conclusion that the earth is a star
almost like the moon, and thus you will prove the majesty of our uni-
verse; and thus you will make a discourse concerning the size of many
of the stars according to the authorities. f 56 r.
MS. sotto. I have followed M. Ravaisson-Mollien's rendering.
Whether the friction of the heavens makes a sound or no:
Every sound is caused by the air striking a dense body, and if it i
made by two heavy bodies one with another it is by means of the ai
that surrounds them; and this friction wears away the bodies that ar
rubbed. It would follow therefore that the heavens in their friction nc
having air between them would not produce sound. Had however thi
friction really existed, in the many centuries that these heavens hav
revolved they would have been consumed by their own immense spee<
of every day. And if they made a sound it would not be able to spreac
because the sound of the percussion made underneath the water is bu
little heard and it would be heard even less or not at all in the case c
dense bodies. Further in the case of smooth bodies the friction does nc
create sound, and it would happen in a similar manner that ther
would be no sound in the contact or friction of the heavens. And i
these heavens are not smooth at the contact of their friction it follow
that they are full of lumps and rough, and therefore their contact is nc
continuous, and if this is the case the vacuum is produced, which it ha
been concluded does not exist in nature. We arrive therefore at th
conclusion that the friction would have rubbed away the boundaries c
each heaven, and in proportion as its movement is swifter towards th
centre than towards the poles it would be more consumed in the centr
than at the poles; and then there would not be friction any more, am
the sound would cease, and the dancers would stop, except that th
heavens were turning one to the east and the other to the north.
f 56 v.
Whether stars have light from the sun or in themselves :
It is said that they have light in themselves, since if Venus and Mer
cury had no light of their own, when they come between our eye an<
the sun they would darken as much of the sun as they cover from ou
eyes. This however is false, because it has been proved how a dark ob
ject placed against a luminous body is surrounded and entirely covere<
by the lateral rays of the remainder of this luminous body, and so i
remains invisible. As is shown when the sun is seen through the rami
fication of leafless trees in the far distance these branches do not con
ceal any part of the sun from our eyes. The same thing happens witl
the above mentioned planets, for though they are themselves withou
li^ht they do not as has been said cover any part of the sun from our
It is said that the stars at night appear most brilliant in proportion as
they are higher up, and that if they have no light of their own the
shadow cast by the earth when it comes between them and the sun
would come to darken them, since these stars neither see nor are seen
by the solar body.
But those who say this have not considered that the pyramidal
shadow of the earth does not reach many of the stars, and that in those
which it does reach the pyramid is so diminished that it covers little of
the body of the star, and all the rest is illuminated by the sun.
F 57 r.
Why the planets appear greater in the east than above us, though it
ought to be the opposite seeing that they are three thousand five hun-
dred miles nearer to us when they are in the middle of the sky than
when they are on the horizon:
All the degrees of the elements through which pass the images of
the celestial bodies which come to the eye are curved, and the angles by
which the central line of these images penetrates there are unequal,
and the distance is greater as is shown by the excess of a b over a d;
and by the Ninth of the Sixth the size of heavenly bodies on the hori-
zon is proved. f 60 r.
Explain the earth with its longer and shorter day in the north and
in the south, and do the same for the moon and define them accurately.
f 63 r.
DARKNESS OF SUN MOON AND EARTH
The moon has its days and nights as has the earth: the night in the
part which does not shine and the day in that which does.
Here the night of the moon sees the light of the earth, that is to say
of its water, grow dim — and the darkened water sees the darkness of
the sun, and to the night of the moon there is lacking the reverberation
of the solar rays which are reflected there from this earth.
In this other figure it is shown that the day of the moon is darkened
and the night of the earth remains deprived of the solar rays reflected
trom the moon.
When the moon is in the east and the sun in the west, all the day that
the moon enjoyed, such as it was with the sun in the west, is changed
Such day as has the moon which from the east looks at the sun in
the west will all be night when this moon is with the sun in the west.
f 64 v.
OF THE RAINBOW
Whether the rainbow is produced by the eye, that is its curve, or by
the sun by means of the cloud:
The mirror does not take any images except those of visible bodies,
and the images are not produced without these bodies; therefore if this
arch is seen in the mirror, and the images converge there which have
their origin in this rainbow, it follows that this arch is produced by the
sun and by the cloud.
The rainbow is seen in the fine rains by those eyes which have the
sun behind and the cloud in front, and a perpetually straight imaginary
line which starts from the centre of the sun and passes through the
centre of the eye will end in the centre of the arch.
And this arch will never be seen by one eye in the same position
as by the other eye; it will be seen in as many positions of the cloud
where it is formed as there are eyes that see it.
Therefore this arch is all in all the cloud where it is produced, and
all in each of the positions in which it may find itself, and so it will
appear larger or smaller, half, whole, double, triple.
If two spheres of metal transmit the solar rays into a dark place, as
the water is turned into vapour it will make the solar spectrum * long
This occurs also with the water turned into vapour when the solar
ray is passing into a dark place with the sun behind it, and also with
the light of torches or of the moon. f 67 v.
How the earth in performing the function of the moon has lost a
considerable amount of the ancient light in our hemisphere by the low-
ering of the waters, as is proved in Book Four 'Of the Earth and the
1 Thus Rav.-Moll. — 'le spectre solaire'. MS. 'arco iris'.
The earth is heavy in its sphere, but so much the more as it is in a
Fire is light in its sphere, and so much the more as it is in a heavier
No simple element has gravity or levity in its own sphere, and if a
bladder filled with air weighs more in the scales than an empty one,
this is because this air is compressed; and fire might be so compressed
that it would be heavier than the air or equal to the air, and perhaps
heavier than the water, and making itself equal to the earth, f 69 v.
This will follow the treatise on light and shade:
The extremities of the moon will be more illuminated and will show
themselves more luminous because nothing will appear in them except
the summits of the waves of its waters; and the shadowy depths of the
valleys of these waves will not change the images of those luminous
parts which from the summits of these waves come to the eye.
Omne grave tendit deorsum nee perpetuo potest sic sursum sustineri,
quare jam totalis terra esset facta spherica. 1
THE SPOTS ON THE MOON
Some have said that vapours are given ofi from the moon after the
manner of clouds, and are interposed between the moon and our eyes.
If this were the case these spots would never be fixed either as to posi-
tion or shape; and when the moon was seen from different points, even
although these spots did not alter their position, they would change
their shape, as does a thing which is seen on different sides, f 84 r.
OF THE SPOTS ON THE MOON
Others have said that the moon is made up of parts, some more, some
less transparent, as though one part were after the manner of alabaster,
and another like crystal or glass. It would then follow that when the
rays of the sun struck the less transparent part the light would stay on
1 Every heavy substance presses downwards, and thus cannot be upheld perpetually;
wherefore the whole earth has been made spherical.
the surface, and consequently the denser part would be illuminated,
and the transparent part would reveal the shadows of its obscure depths.
Thus then they define the nature of the moon, and this view has found
favour with many philosophers, and especially with Aristotle; but
nevertheless it is false, since in the different phases which the moon and
the sun frequently present to our eyes we should be seeing these spots
vary, and at one time they would appear dark and at another light.
They would be dark when the sun is in the west and the moon in the
centre of the sky, because the transparent hollows would then be in
shadow, as far as the tops of their edges, since the sun could not cast
its rays into the mouths of these same hollows; and they would appear
bright at full moon, when the moon in the east faces the sun in the
west; for then the sun would illumine even the lowest depths of these
transparent parts, and in consequence as no shadow was created, the
moon would not at such times reveal to us the above-mentioned spots,
and so it would be, sometimes more sometimes less, according to the
change in the position of the sun to the moon, and of the moon to our
eyes, as I have said above. f 84 v.
It has also been said that the spots on the moon are created in the
moon itself, by the fact of it being of varying thinness or density. If this
were so, then in the eclipses of the moon the solar rays could pierce
through some part where it is thin, as has been stated, but since we do
not see this result the aforesaid theory is false.
Others say that the surface of the moon is smooth and polished, and
that, like a mirror, it receives within itself the reflection of the earth.
This theory is false, since the earth, when not covered by the water,
presents different shapes from different points of view; so when the
moon is in the east it would reflect other spots than when it is overhead
or in the west, whereas the spots upon the moon, as seen at full moon,
never change during the course which it makes in our hemisphere. A
second reason is that an object reflected in a convex surface fills only a
small part of the mirror, as is proved in perspective. The third reason is
that when the moon is full it only faces half the orb of the illuminated
earth, in which the ocean and the other waters shine brightly, while the
land forms spots amid this brightness; and consequently the half of our
earth would be seen girded round about by the radiance of the sea,
which takes its light from the sun, and in the moon this reflection
would be the least part of that moon. The fourth reason is that one
radiant body cannot be reflected in another, and consequently as tin sea
derives its radiance from the sun, as does also the moon, it could not
show the reflected image of the earth, unless one also saw reflected
there separately the orb of the sun and of each of the stars which look
down upon it. f 85 r.
The solar rays pass through the cold region of the air and do not
change their nature. They pass through glasses filled with cold water
and lose nothing of their nature thereby; and whatever may be the
transparent place through which they pass it is as though they passed
through so much air.
And if you maintain that the cold rays of the sun are clothed with
the heat of fire as they traverse its element, just as they assume the
colour of the glass they penetrate, it would follow that in penetrating
the cold region they put on this mantle of cold after they have already
put on the said mantle of heat, and thus the cold would counteract the
heat, and therefore the solar rays would come to us deprived of heat,
and as this is not confirmed by experience such method of reasoning as
to the sun being cold is vain.
But if you were to say that the cold through which the fiery rays of
the sun pass somewhat modifies the excessive heat of these rays it
would follow from this that one would feel greater heat on the high
peaks of the Caucasus the mountain of Scythia than in the valleys,
because the mountain towers above the middle regions of the air, and
no clouds are found there nor anything that grows.
And if you say that these solar rays thrust towards us the element of
fire from whence they pass by local movement, this cannot be admitted
because the local movement of such [a volume of] air cannot occur
without the passing of a period of time, and this is greater in propor-
tion as the sun is more on the horizon, for when there it is 3,500 miles
farther away from us than when it is in the centre of our heaven. If it
acted thus it would cool the part of our horizon opposite to it, because
it would carry away in its rays such part of the element of fire opposite
to it as it penetrated.
If the lesser fire is attracted to and deflected by the greater fire as one
sees happen by experience, it must needs be that the sun draws the
element of fire to itself rather than that it banishes it from itself and
drives it towards us.
And the heat of the fire does not descend unless it follows burning
matter, and in acting thus it is material and in consequence it is visible.
f 86 r.
How if the moon is polished and spherical the image of the sun upon
it is powerfully luminous, and is only on a small part of its surface:
You will see the proof of this by taking a ball of burnished gold and
placing it in the darkness and setting a light at some distance from it.
Although this illuminates about half the ball, the eye only sees it re-
flected on a small part of its surface, and all the rest of the surface
reflects the darkness which surrounds it. For this reason it is only there
that the image of the light is apparent, and all the rest remains invisi-
ble because the eye is at a distance from the ball. The same thing
would happen with the surface of the moon if it were polished, glitter-
ing and solid, as are bodies which have a reflecting surface.
Show how if you were upon the moon or upon a star our earth
would appear to you to perform the same function for the sun as now
the moon does. And show how the reflection of the sun in the sea
cannot itself appear a sun as it does in a flat mirror. f 93 r.
My book attempts to show how the ocean with the other seas makes
our world by means of the sunshine after the manner of a moon, and
to the more remote worlds it appears a star; and this I prove.
Moon cold and moist.
Water is cold and moist.
Our sea has the same influence on the moon as the moon has on us.
f 94 v.
EXPLANATION OF THE MOON WITH THE IMAGE
OF THE SUN
If the sun / reflected in the surface of the water n m should seem to be
at d (that is to say seems to be as far below the water as it is above), and
to the eye b appears to be of the size a, and this image doubles itself
as the eye is removed from b to c\ how much would this Image grow it
the eye were removed Erom c to the moon?
Work with the rule of three and you will see that the light which
there is in the moon on its fifteenth day can never be the light that this
moon receives from it being spherical; therefore it is necessary that this
moon contains water. c 20 r.
[Of the nature of the suns heat]
OF THE PROOF THAT THE SUN IS HOT BY NATURE
AND NOT BY POWER
That the sun is hot in itself by nature and not by power is shown
very distinctly by the radiance of the solar body on which the human
eye cannot continue to look. And this moreover the rays reflected by
concave mirrors show very clearly, for when their percussion is of such
radiance that the eye cannot endure it, this percussion will have a radi-
ance resembling that of the sun in its own position. And the truth of
this is proved by the fact that if such a mirror has such a concave sur-
face as is required in order to produce this ray, no created thing will
be able to support the heat of such percussion of ray reflected from
any mirror. And if you say that the mirror also is cold and yet throws
warm rays, I say in reply that the ray comes from the sun and will
have to pass through the mirror in order to resemble its cause and can
pass through whatever medium it wishes. . . .
The ray of the concave mirror having passed across the windows of
the furnaces where are cast . . . has not great heat nor any longer has
whiteness. g 34 r.
THE SOLAR RAYS
Where there is the finer and more rarefied medium the solar rays
meet with a less resistance and where there is the less resistance it is
less permeated by the nature of the agent. Consequently for this reason
one may infer that where the air is more rarefied the percussion of the
said solar rays transmits less radiance, and as a consequence it is darker ,
and so also conversely. k 118  r.
A proof how the nearer you are to the source of the sun's rays the
greater will the sun appear when reflected upon the sea:
If the sun produces its radiance from its centre fortified by power
from the whole body it must needs be that the farther its rays proceed
from it the more they go on separating. This being so when you have
your eye near water that reflects the sun, you see a very small part of
the sun's rays carrying upon the surface of the water the form of the
sun reflected; and if you are nearer to the sun as would be the case
when the sun is at the meridian and the sea is to the west, you will see
the sun reflected in the sea of very great size, because as you are nearer
to the sun your eye as it takes the rays near to the point takes in more
of them and so greater radiance ensues. For this reason it might be
proved that the moon is another world similar to ours, and that the
part of it which shines is a sea that reflects the sun and the part which
does not shine is earth. ms. 2038 Bib. Nat. 16 v.
If you keep the details of the spots of the moon under observation
you will often find great differences in them, and I have myself proved
this by making drawings of them. And this comes about because the
clouds rise from the waters of the moon and come between the sun and
this water, and with their shadows cut off the rays of the sun from it,
and consequently it remains dark because it cannot reflect the solar
body. b.m. 19 r.
OF THE MOON
As wishing to treat of the nature of the moon it is necessary in the
first place that I should describe the perspective of mirrors, whether
flat concave or convex, and first of all what is meant by a luminous ray
and how it is refracted by various kinds of media. Then whether the
reflected ray is more powerful if the angle of incidence be acute or a
right angle or obtuse, or if the surface be convex or flat or concave,
or the substance opaque or transparent. Furthermore how it is that the
solar rays which strike the waves of the sea show themselves of the
same width in the angle close to the eye as in the farthest crest of the
waves on the horizon, notwithstanding which the solar radiance re-
flected by the waves of the sea is of the shape of a pyramid, and as a
consequence at every stage of distance acquires an access of breadth,
although to our sight it may appear parallel.
Nothing extremely light is opaque.
Nothing that is lighter remains below what is less light.
Whether the moon has its station in the midst of its elements or no.
If it has not a particular station as has the earth in its elements why
it does not fall to the centre of our elements.
And if the moon is not in the midst of its elements and does not
descend it is therefore lighter than the other element.
And if the moon is lighter than the other element why it is solid and
Of things of different size which when placed at different distances
show themselves equal, there will be the same proportion between
their distances as there is between their sizes. b.m. 94 r.
OF THE MOON
The moon has no light of itself but so much of it as the sun sees, it
illuminates. Of this illuminated part we see as much as faces us. And
its night receives as much brightness as our waters lend it as they reflect
upon it the image of the sun, which is mirrored in all those waters
that face the sun and the moon.
The crust or surface of the water of which the sea of the moon and
the sea of our earth are composed is always wrinkled whether little or
much or more or less; and this ruggedness is the cause of the expansion
of the innumerable images of the sun which are reflected in the hills
and valleys and sides and crests of the innumerable furrows, that is in
as many different spots in each furrow as there are different positions
of the eyes that see them. This could not happen if the sphere of water
which in great part covers the moon were of uniform roundness, be-
cause then there would be an image of the sun for every eye, and its
reflection would be distinct and the radiance of it would always be
spherical in shape, as is clearly shown in the gilded balls placed on the
summits of lofty buildings. But if these gilded balls were furrowed or
made up of many small globules like mulberries, which are a black
fruit composed of minute round balls, then each of the parts of this
rounded mass visible to the sun and to the eye will reveal to the eye
the radiance produced by the reflection of the sun. And thus in the
same body there will be seen many minute suns and very often on
account of their great distance they will blend one with another and
The lustre of the new moon is brighter and more powerful than
when it is full; and this is due to the fact that the angle of its incidence
is much more obtuse in the new moon than in the full moon, where
the angles are extremely acute, and the waves of the moon reflect the
sun both on their hollows and on their crests, and the sides remain
dark. But at the sides of the moon the troughs of the waves do not see
the sun, for it only sees the crests of these waves, and in consequence
the reflections are less frequent and more mingled with the shadows of
the valleys. And this intermixture of shaded and luminous images all
blending together comes to the eye with only a moderate amount of
radiance, and at its edges it will be even darker, because the curve of
the side of these waves will be insufficient to reflect the rays which it
receives to the eye.
For which reason the new moon by its nature reflects the solar rays
more towards the eye through these last waves than through any other
place, as is shown by the figure of the moon striking with the rays a on
the wave b and reflected in b d where the eye d is situated. And this
cannot happen at full moon, where the solar ray standing in the west,
strikes the last rays of the moon in the east from n to m, and does not
reflect towards the eye in the west; but leaps back to the east, slightly
bending the direction of this solar ray; and so the angle of the incidence
is very great.
The countless images which are reflected by the innumerable waves
of the sea from the solar rays that strike upon these waves, cause a
continuous and far reaching splendour upon the surface of the sea.
The moon is an opaque and solid body, and if on the contrary it
were transparent it would not receive the light of the sun. b.m. 94 v.
You have to prove how the earth performs all those same functions
towards the moon which the moon does towards the earth.
The moon does not shine with its reflected light as does the sun,
because the moon x does not receive the light of the sun on its surface
1 MS. has 'il lume della luna'.
Continuously, but in the crests and hollows ot the waves ot its waters,
through the sun being indistinctly reflected in the moon through the
mingling of the shadows which arc above the waves that shed the radi-
ance. Its light therefore is not bright and clear as is that of the sun.
b.m. 104 r.
To observe the nature of the planets have an opening made in the
roof and show at the base one planet singly: the reflected movement
on this base will record the structure of the said planet, but arrange
so that this base only reflects one at a time. b.m. 279 v.
The circles of the celestial spheres together with the elements equally
drive and thrust away from themselves everything that has weight,
whence for this reason it must be confessed that it is necessary for the
centres of these spheres to meet and become stationary.
Whence through this it is necessary to confess that the things falling
towards the centre are rather thrust from above than drawn by this
centre downwards; because if it were possible that this earth should
be withdrawn in part in such a manner that the space occupied by the
position of the earth were filled with air, you would see a stone thrown
off from our world into this air become stationary in the centre of the
two elements and of the spheres. Forster 111 6 v.
The centre of the world cannot be the centre of the universal circles
made by the course of the glittering stars, because in a like position it
cannot be taken for granted that the universal parts of the earth, the
encompasser and enveloper of this centre, are not of equal weight when
removed at an equal distance from this centre.
Naturally every heavy thing is thrust towards the centre because the
centre is farthest removed from these expelling and rotatory forces.
I conclude: the centre of the weight of the earth with the water is
the centre of the spheres and not the centre of the mass of this world.
Forster m 7 r.
These heavy parts which were thrust down from there above, have
of themselves already created bodies which always stand in continual
desire of returning there above. Forster in 8 r.
The sun does not move. Quaderni v 25 r.
Between the sun and us there is darkness, and therefore the air
appears blue. Windsor mss. r 868
If you wish to prove that the moon appears larger than it is when it
reaches the horizon, you take a lens convex on the one side and concave
on the other and place the concave side to your eye and look at the
object beyond the convex surface; and by this means you will have
made a true imitation of the atmosphere which is enclosed between the
sphere of fire and that of water, for this atmosphere is concave towards
the earth and convex towards the fire. Windsor: Drawings 12326 v.
Memorandum that I have first to show the distance of the sun from
the earth and by means of one of its rays passing through a small hole
into a dark place to discover its exact dimensions, and in addition to
this by means of the sphere of water to calculate the size of the earth.
And the size of the moon I shall discover as I discover that of the
sun, that is by means of its ray at midnight when it is at the full.
Leic. 1 r.
Reply to Maestro Andrea da Imola who said that the solar rays
reflected by the surface of the convex mirror intermingled and became
lost at a short distance, and that for this reason it is altogether denied
that the luminous side of the moon is of the nature of a mirror, and
that in consequence this light is not produced by the innumerable muL
titude of the waves of that sea, which I have demonstrated to be that
part of the moon which is illuminated by the solar rays. Leic. 1 v.
OF THE MOON
No solid body is lighter than air.
As we have proved that the part of the moon which shines consists
of water and it serves the body of the sun as a mirror which reflects the
radiance it receives from it; and that if this water were without waves
it would show itself as small but of a radiance almost equal to that of
the sun, it is necessary now to show whether the moon is a heavy or
light body. Thus if it were a heavy body — considering that in progres-
sion upwards from the earth at every stage of altitude there is an
accession of lightness, inasmuch as water is lighter than earth, air than
water and fire than air and so continuing in succession — it would set m
that if the moon had density, as it has, it would have weight, and that
having weight the space in which it finds itself would not be able to
support it, and as a consequence it would have to descend towards the
centre of the universe and to join itself to the earth; or if not the moon
itself its waters at any rate would fall away and become lost to it and
would fall towards the centre leaving the moon stripped of them and
devoid of radiance. The fact however that these events do not occur
as might with reason have been anticipated is a clear sign that the
moon is clothed with her own elements, namely water air and fire and
so sustains itself by itself in that part of space as does our earth with
its elements in this other part of space; and that the heavy bodies per-
form the same function in its elements which the other heavy bodies
do in ours.
[Diagratn] sun, moon, earth.
When the eye in the east sees the moon in the west near the setting
sun it sees it with its shaded part surrounded by the luminous part; of
which light the lateral and upper portions are derived from the sun
and the lower portion from the western ocean, which still receives the
solar rays and reflects them in the lower seas of the moon, and more-
over it imparts as much radiance to the whole of the shaded part of
the moon as the moon gives to the earth at midnight, and for this
reason it does not become absolutely dark. And from this some have
believed that the moon has in part a light of its own in addition to that
which is given it by the sun, and that this light is due to the cause
already mentioned, namely that our seas are illumined by the sun.
[Diagram] moon, solar body, earth.
Further it might be said that the circle of radiance which the moon
shows when it is in the west together with the sun is derived entirely
from the sun, when its position with regard to the sun and the eye is
as is shown above.
Some might say that the air which is an element of the moon as it
catches the light of the sun as does our atmosphere was that which
completes the luminous circle on the body of the moon.
Some have believed that the moon has some light of its own, but this
opinion is false, for they have based it upon that glimmer which is
visible in the middle between the horns of the new moon, which ap-
pears dark where it borders on the bright part, and where it borders
on the darkness of the background seems so bright that many have
assumed it to be a ring of new radiance which completes the circle
where the radiance of the tips of the horns illuminated by the sun
And this difference in the background arises from the fact that the
part of it which borders on the illuminated portion of the moon, by
comparison with that brightness shows itself darker than it is, and in
the part above where appears a portion of a luminous circle of uniform
breadth it comes about that there the moon being brighter than the
medium or background upon which it finds itself, in comparison with
this darkness shows itself on that extremity brighter than it is, this
brightness at such a time being derived from our ocean and the other
inland seas, for they are at that time illumined by the sun which is
then on the point of setting, in such a way that the sea then performs
the same office for the dark side of the moon as the moon when at the
full does for us when the sun is set, and there is the same proportion
between that small quantity of light on the dark side of the moon and
the brightness of the illuminated part, as there is between . . .
If you want to see how much brighter the shaded part of the moon is
than its background, cover from your eye with your hand or with some
other object farther away the luminous part of the moon, so that . . .
Leic. 2 r.
I say that as the moon has no light of its own, but is luminous, it
must needs be that this light is caused by some other body: this being
so it is of the nature of a spherical mirror; and if it is spherical it takes
the light pyramid-wise; and of this pyramid the sun is the base, and its
angle ends in the centre of the body of the moon, and it is cut by the
surface of this body, and only takes as much as corresponds to the
section of this pyramid on its surface. And to the human eye this moon
would only seem the size of this section of the pyramid. Whence there
would follow from the light of the moon the contrary effect to that
which experience shows us; for this is that as the moon turns it has its
whole orb luminous as is shown us by this; for this clearly shows us
that this lunar body has more than half its orb illuminated. But this
would not happen if it were a polished body like the mirrors; conse-
quently for this reason we are constrained to admit, by my fifth [rule],
that the surface of the moon is furrowed; and this muchness only
exists in liquid bodies when they are stirred by the wind, as we have
seen with the sea how the sun is reflected by tiny waves near to the
eve, and stage bv stage over a distance of more than forty miles these
illuminated waves grow larger. Wherefore we conclude that the lumi-
nous part of the moon is water, which if it were not in movement
would not be luminous to the same degree; but by the movement of
this water which has been stirred up by the winds it becomes filled
with waves; and every wave takes the light from the sun; and the
great multitude of waves beyond number reflect the solar body an
infinite number of times; and the sun thus reflected will be as bright
as the sun, for as is seen when the water does not move it gives back
the sun to the eye in the pristine splendour that it has by nature.
But the shadows also are beyond number as well as the waves, and
these are interspersed between the waves; and their shapes blend with
the shapes of the images of the sun, which are upon the waves; and
each shadow shape becomes blended with a luminous shape and so
they come to obscure the luminous rays and make them weak, as is
clearly shown us by the light of the moon. And when the sea of the
moon is stirred to tempest by the winds the waves are larger and the
lights less frequent and the enlarged shadows intermingle more with
the sparse images of the sun upon the waves, and for this reason the
moon becomes less luminous. But when the moon is in its circle and
has a position at about the centre of our hemisphere, each wave shows
the reflection of the sun both in the centre of the valleys interposed
between the waves and in the summits of these waves; and for this
reason the moon shows itself more luminous than ever, through hav-
ing the number of the parts in light doubled.
It shows itself also strongly luminous a short time after its turn,
because the sun which stands beyond the moon, striking the waves
upon their summits, when these summits are near together and seem
almost to clash one against another when the eye is on this side, causes
the shadows which come between the waves not to transmit to the eye
their images mingled with the luminous images; and for this reason the
light of the moon is more powerful.
And what is proved of one luminous body holds true of all the rest.
Leic. 30 r.
Of the moon: all the objections of the adversary, to say that in the
moon there is no water.
Objection: Every body thicker than the air is heavier than this air
and cannot be supported upon it without other cause; and the more it
rises the less it is resisted by its medium: therefore, if there were water
in the moon, it would despoil the moon of itself, and would come to
cover our earth, because in this moon the water would be above its air.
Here the answer is that if there is water in the moon there is also earth
there upon which this water supports itself, and consequently the other
elements: and water is supported up there among the three other ele-
ments, as down here our water is among its accompanying elements;
if however as the adversary holds the water had to fall from the moon,
it would rather be that the moon would have to fall as being a body
heavier than the water; therefore not falling it is a clear proof that the
water up there and the earth are supported with their other elements
just as the heavy and light elements down here are supported in space
that is lighter than themselves.
The adversary says that the light of the moon, if not the whole of
it, is the same in itself; and that it shows itself more or less illuminated,
according as the eye sees more or less of its shaded part, that is, if it is
more in the east than the west.
Here, at this point, one replies, that if the . . . Leic. 36 v.