'The air moves like a river and carries the 

clouds with it; just as running water carries 

all the things that float upon it! 

Surface is the name given to the boundaries of bodies with the air or I 
would rather say of the air with bodies, that is what is enclosed between 
the body and the air that surrounds it; and if the air makes contact with 
the body there is no space to put another body there; consequently it 
may be concluded that surface has no body and therefore no need of 

Surface is the name given to that which divides bodies from the air 
which surrounds them; or as you may prefer to say which divides or 
separates the air from the things which are located within it. 

And if the atmosphere and the bodies which are enclosed within it 
are in perpetual contact and there is not any space between them, the 
surface being that which shows the shape of the bodies this surface has 
existence of itself. And if the atmosphere and the body are touching 
each other no space will remain there, so we conclude that the surface 
has existence and not space. Consequently this surface is equal to noth- 
ing, and all the nothingness of the world is equal to the smallest part 
if there can be a part. Wherefore we may say that surface, line, and 
point are equal as between themselves, and each is of itself equal to the 
other two joined together. 

Surface is the name of that division which the body of the air makes 
with the bodies which are enclosed within it. And it does not partake 
of the body by which it is surrounded, nor of that which it surrounds; 
on the contrary it is the actual contact which these bodies make to- 

Therefore if these bodies are in continual contact it is necessary that 
nothing should interpose between them, and consequently the surface, 




which is enclosed there, is nothing. This surface has name and not 
substance because that which has substance has place. Not having place 
it resembles nothingness which has name without substance; conse- 
quently the part of nothing not having anything except the name and 
not the substance this part is equal to the whole; so that by this we 
conclude that the point and the line are equal to the surface. 

c.a. 68 v. a 


[With drawing] 

The atmosphere interposed between the fire and the water partici- 
pates in the water and the fire, but so much more in one than the other 
as it is nearer one than the other. It follows that the less it participates 
in each the more remote it is from them. And this remoteness occurs in 
the middle region of the atmosphere; therefore this middle region is 
in the first stage of cold. From which it follows that that part of the 
cloud which is in closest contact with the middle region becomes cold- 
est; consequently the warmth of the sphere of fire of this cloud which 
is the attracter and mover is of less potency, and from this it follows 
that the movements of the particles of moisture which form the clouds 
are slower; and from this it follows that, in the process of these par- 
ticles of moisture rising, the nearer they come to the vicinity of this 
middle region the slower the movement becomes, and the movement 
of that which follows is swifter than it, and consequently it overtakes 
it. And it often happens that it strikes underneath and mingles with it 
and thus increases its quantity and weight. The atmosphere in conse- 
quence not being able to support it makes way for it to descend, and 
in doing this it strikes all the drops which interrupt its course, and in- 
corporates many in itself, and acquiring weight it acquires velocity in 
its descent [. . . .]. And this is the reason why after it has penetrated 
the whole of the cloud in every stage of descent its pace will become 
slower, and there will be many occasions when these particles will not 
arrive at the ground. If then these particles at the highest part of their 
height acquire so much gravity that the weight produces a swift de- 
scent, then without doubt this movement will increase their size, inas- 
much as this speed will cause it to overtake the drops which are de- 



scending below it and incorporate them in itself, and this will bring 
about an increase of weight at every stage of its descent. 

The descent of the drops which strike together without wind will 
not be straight but at an angle. 

This is proved by the fact that if two bodies strike one another in 
the air the one which is less in bulk will be diverted more from its 

And if two particles of dew or of quicksilver varying in size become 
joined together each will be removed from its position and the propor- 
tion of their movements will be as that of their size. 

The drop of that liquid is of the most perfect roundness which is of 
less . . . 

Why if two spherical liquids unequal in quantity come to the be- 
ginning of contact with each other does the greater draw to itself the 
lesser and incorporate it immediately without destroying the perfection 
of its own roundness. 

It is difficult to give an answer; but I will not for this reason refrain 
from stating my opinion. Water clothed with atmosphere naturally 
desires to be united in its sphere, because in such a position it is de- 
prived of gravity, which gravity is double; for the whole has a gravity 
which depends on the centre of the elements, and there is a second 
gravity dependent on the centre of this watery sphere, for if it were not 
so it would form by itself a half sphere only which is that which stands 
from the centre upwards; and I do not perceive that the human in- 
tellect has any means of acquiring perception of this except by saying 
as one says of the action of the magnet when it draws the iron, that 
such virtue is a hidden property of which there are in nature an in- 
finite number. 

But it may be asked why there is greater perfection in the little 
sphere of the liquid than in the large one. To this the reply is that the 
little drop has a lightness which more resembles the atmosphere that 
surrounds it than the large drop has, and from the fact of this small 
difference it is more sustained from its centre downwards by this 
atmosphere than the large drop. And as a proof of this, one may take 
as an instance the little drops which are so small in shape as to be of 
themselves almost invisible but which are visible when there are a large 



quantity together; and these are the particles which go to form clouds 
and mist. 

Why the atmosphere when it has been submerged rises enveloped in 
a sheet of water. Which settles on its surface in the shape of a half 

And if it is slimy water it moves through the atmosphere in the form 
of a sphere. 
[Dm wing] Bubble or rather vesicle of water. 

You will make an experiment with these bubbles of water which 
over a little water set in a basin produce by means of the solar rays 
images of the form of a cross on the bottom of this basin. 

c.a. 75 v. a 

Air and fire are capable of an infinite amount of compression as is 
seen with mortar-pieces and thunderbolts. c.a. 97 v. a 

The body of the air is filled with an infinite number of radiant 
pyramids formed by the objects situated in it, and these pyramids inter- 
secting and interweaving without displacement one of another blend 
together in their separate courses throughout the whole of the sur- 
rounding air; and they are of equal power, and all have as much 
capacity as each one and each has as much as all; and through them 
the image of the body is carried all into the whole and all into a part, 
and each receives of itself in its every smallest part the whole cause. 

c.a. 101 v. b 

The movement of the thunderbolt which originates in the cloud is 
curved, because it bends from thickness to thinness, this thickness being 
occasioned by the fury of the aforesaid movement. For this thunderbolt 
not being able to extend in the direction in which it commenced, bends 
into the course that is freest and proceeds by this until it has created 
the second obstacle, and so following this rule it continues on to the 
end. c.a. 121 r. b 

Why flame does not occur except above some space where there is 
smoke, and why it does not strike except through its smoke. This hap- 
pens because the flames as they strike the air divide in pyramids, con- 
nected by ends which curve concavely and not convexly, and air within 
water does the same. c.a. 131 r. b 



That the atmosphere attracts to itself like a magnet all the images of. 
the things which surround it, and not only their bodily shapes but also 
their nature, is clearly to be seen in the case of the sun, which is a hot 
and luminous body. All the atmosphere which is exposed to its influ- 
ence is charged in all its parts with light and heat, and it all receives 
within itself the shape of that which is the source of this heat and radi- 
ance and does the same also in each minutest part. The north star is 
shown to do the same by the needle of the compass; and each of the 
planets does the like without itself undergoing any diminution. 

Among the products of the earth the same is found to happen with 
musk and other scents. c.a. 138 v. b 

The cloud carried by the warmth which is shut up within it thrusts 
itself towards [....] disc of fire, comes to the cold region of the air, 
which is frozen on the outer side but is not frozen within, because the 
warmth which has carried it up there preserves it from such cold; and 
this brings to pass three circumstances, the first being the evaporation 
of the moisture which after being pent up through the cold separates 
and dissolves into vapour and produces a raging wind; the second is 
the rain that is produced by the accumulation of the particles of moist 
vapour, for those of swift movement driven by the heat clash against 
those which are moving more slowly, and as they encounter that part 
of the cloud which becomes cold towards its extremities the particles 
of the moisture fasten themselves together and acquire weight, and so 
it descends to earth in big drops; and on the very extremity of this 
cloud the particles of moisture are continually freezing into balls of 
various sizes, and these cannot expand because of the intensity of the 
cold, but come together with swift movement at the spot where the 
sphericity of the drop is produced, and therefore the hail is composed 
of [....] of many roundnesses which are joined together. 

c.a. 162 r. a 

The elements are changed one into another, and when the air is 
changed into water by the contact it has with its cold region this then 
attracts to itself with fury all the surrounding air which moves furi- 
ously to fill up the place vacated by the air that has escaped; and so 
one mass moves in succession behind another, until they have in part 



equalised the space from which the air has been divided, and this is 
the wind. 

But if the water is changed to air then the air which first occupied 
the space into which the aforesaid increase flows must needs yield place 
in speed and impetus to the air which has been produced, and this is 
the wind. 

The mist that is in the wind is produced by heat, and it is smitten 
and banished by the cold, and this cold drives it before it, and from 
where it has been driven the warmth is left cold. And because the mist 
which is driven cannot turn upwards because of the cold that presses it 
down, and cannot turn downwards because of the heat that raises it up, 
it therefore becomes necessary for it to proceed across, and I for my 
part consider that it has no movement of itself, for as the said powers 
are equal they confine the middle substance equally, and should it 
chance to escape the fugitive is dispersed and scattered in every direc- 
tion, just as with a sponge filled with water, which is squeezed so that 
the water escapes out of the centre of the sponge in every direction. 
So therefore does the northern wind become the producer of all the 
winds at one and the same time. c.a. 169 r. a 

[Of winds] 

The north wind comes to us from high and frozen places and there- 
fore it cannot give off moisture, and consequently it is pure and clean, 
because it is cold and dry, and for this reason it is very light in itself 
but its speed makes it powerful wherever it strikes. 

The south wind has not the same purity, and since it is warm and 
dry it dissolves the thicknesses of the watery vapours which the Medi- 
terranean Sea exhales, and these then follow in the wake of this wind 
and become dissolved in it; and so for this reason this wind as it strikes 
Europe comes to be warm and damp and heavy in its nature, and 
although its movement is sluggish its stroke is no less powerful than 
that of the north wind. 

Every wind is by nature cold and dry but it takes to itself as many 
different attributes as are those of the places through which it passes, 
leaving behind it in passing dampness and cold to the dry and hot 
places and taking from these same hot dry places their dryness and 
heat. So in its movement in each region it puts on different attributes, 



and in becoming warm and dry it weakens its power, and in resuming 
the things it had left behind it resumes the aforesaid forces together 
with them, for when there is the same swiftness of movement that 
thing which is of greater weight will give a greater percussion, and so 
conversely the lighter thing will give a less percussion. 

When in summer the sun returns to the parts of Africa the humidity 
which had been increased there by the winter becomes dissolved and its 
bulk increases, and it searches in fury for places to contain this increase. 
And this is the south wind, which in autumn drives the maritime 
vapours of the Mediterranean before it, and condenses them above our 
regions, until they fall down again through lack of power to maintain 

When many winds strive together then the waves of the sea have not 
a free course, but they clash together and raise themselves up and at 
times cause ships to founder; and in such a contest the stronger wind 
will be the victor through its being lighter and less interwoven or 
mingled with the other winds. c.a. 169 v. a 

All objects have all their images and likenesses projected and 
mingled together throughout the whole extent of the surrounding 
atmosphere. The image of every point of their bodily surfaces exists in 
every point of this atmosphere, and all the images of the objects are in 
every point of this atmosphere. The whole and a part of the likeness 
of the atmosphere exists in every point of the surface of the objects 
which are over against it. Therefore the part and the whole of the 
images of the objects appear in all and in each part of the atmosphere 
which is opposite to them; and the substance of the atmosphere is seen 
reflected in the whole and in each part of the surface of these objects. 
Therefore clearly we may say that the likeness of each object either 
whole or in part is interchangeably in each part and in the whole of the 
objects opposite to it, as is seen with mirrors when placed one opposite 
to another. c.a. 179 v. c 

Those winds which descending scour the parts of the mountains that 
lean towards the sea, penetrate to its bed and make waves, with sides 
that resemble the shores from which they descend, and these waves 
consequently have often deep narrow spaces between them, as I said 
in the book on the movement of water. And this tempest lasts only a 



short time after the stroke of the wind, lor alter it has struck it leaps 
hack into the air until it finds the other wind, and striking against this 
it compresses it and again leaps downward after the manner oi the 
rivers as they strike the shores. 

On the summits of the mountains the wind is of great density, and 
in the mouths of the valleys when the mountains which shut in these 
valleys are of great height. The entry of opposite winds one beneath 
the other with contrary movements may occur for two reasons, namely 
either through the reflex movement of the wind which turns back after 
having struck upon the mountains, or by the clashing together when 
the weaker parts of opposing winds strike against the stronger parts. 
The revolutions or eddies of the winds are born in the winds as they 
open out in the embrace of the mountains or of some building, and 
afterwards join together and strike with impetus; and their reflex 
movements are not made in a straight line, for it is checked in its own 
sphere, being moved by a substance like itself which has the power to 
check and bend its direct impetus. So therefore this wind not being 
able to extend proceeds to exhaust its impulse by a [curving] move- 
ment, and goes upwards in order to consume its impetus, this being 
necessary for three reasons; firstly because it cannot at once turn on 
the very lines of its descent, secondly because they strike at angles less 
than right angles, and because they cannot leap back on lines equal to 
those of their incidence. c.a. 180 v. a 

[Cloud, wind and thunderbolt] 

As water flows in different directions out of a squeezed sponge, or 
air from a pair of bellows, so it is with the thin transparent clouds that 
have been driven up to a height through the reflection occasioned by 
the heat, the first part which finds itself uppermost being that which 
comes first to the cold region, and here remaining through the cold and 
dryness awaits its companion. That part below as it ascends towards the 
part that is stationary treats the air which happens to be in the centre 
as though it was a syringe, and this then escapes crosswise and down- 
wards, not going upwards because it finds the cloud so thick that it 
cannot penetrate it. 

So for this reason all the winds that make war upon the earth's sur- 
face come down from above, and as they strike upon the resisting earth 



they produce a movement of recoil, and this as it desires to raise itself 
up again to a height finds there the other wind, which descends and 
subdues its ascent, whereby the said upward movement is constrained 
to break its natural order, and taking a transverse route it pursues a 
violent course which grazes incessantly the surface of the earth. 

And when the aforesaid winds strike upon the salt waters the form 
is clearly visible, in the angle that is created by the line of incidence 
and that of the recoil from which proceed the proud menacing and 
engulfing waves, of which the one for the most part is the cause of 
the other. 

Here someone perhaps may think to censure me by putting forward 
as against my contention as to the winds the argument that these can- 
not be produced by the clouds because then it would be necessary for 
one to remain stationary and give movement to another, and this does 
not appear to be so, because when the north wind blows the clouds all 
collect together and fly before it. The reply to this is that when the air 
is still and a full company of clouds have risen to a height, and there 
above as has been said press themselves together, they squeeze out so 
much air from themselves, which through the violence exerted creates 
such movement in the air, that as you may see it communicates its 
movement to the other lesser clouds. And as they also drive the air 
forwards in the same way they even furnish themselves with a reason 
for greater flight; for when a cloud either finds itself in the midst of 
others or apart from them, if it produces the wind behind itself that 
air which is between it and its neighbour following comes to multiply, 
and by multiplying acts in the same way as the powder does in the 
mortar, for this expels from the position near to it the less heavy body 
and the lighter weight. And this being the case it follows that the 
cloud in driving the wind towards the others which offer resistance is 
the cause of putting these themselves to flight. And by sending this 
vanguard of the winds before itself it also adds volume to the rest. And 
if it should send them crosswise it would form a kind of rotatory circle 
around some cloud and then return in concert with the others. 

As the natural warmth spread through the human limbs is driven 
back by the surrounding cold which is its opposite and enemy, and 
flowing back to the lake of the heart and the liver fortifies itself there, 
making of these its fortress and defence, so the clouds being made up 



of warmth and moisture, and in summer of certain dry vapours, and 
finding themselves in the cold dry region, act after the manner of cer- 
tain flowers and leaves which when attacked by the cold hoar-frost 
press themselves close together and offer a greater resistance. 

So these in their first contact with the cold air commence to resist 
and not to wish to pass farther forward; the others below continue 
constantly to rise, the part above being stationary proceeds to thicken, 
the warmth and dryness recede to the centre, the part above abandoned 
by the warmth commences to freeze or to express it more exactly to 
dissolve, and as the clouds below continue to rise their warmth is 
brought nearer to the cold and so being constrained to reduce itself to 
its primary element is suddenly transformed into fire, and this twines 
itself among the dry vapour and in the centre of the cloud makes a 
great increase, and as it kindles itself within the cloud which has be- 
come cool it makes a noise that resembles that of water falling on boil- 
ing pitch or oil, or of molten copper when plunged into cold water. 
Even so driven forth by its opposite it shatters the cloud that would 
withstand it, and hurtling through the air breaks and destroys every- 
thing that opposes it, and this is the thunderbolt. c.a. 212 v. a 

The air is compressible to infinity, and this is shown by the extremely 
swift movement of the radiance which produces the mighty thunder 
of the heavens, which bends and twists itself in different directions so 
much the more as the air and cloud before it is compressed and . . . 

Example of thunder 

The process of evaporation of water thrown upon burning coals is 
as that of the fire when kindled among the clouds which evaporate 
with such fury as to restrict the course of the brightness that has been 
created; that is to say that as the water is changed into vapour and 
becomes steam as it increases so the cloud evaporates and becomes 
changed into air, which by its increase hems in and restricts the flame 
which is produced in it. c.a. 213 r. a 

Flame has its beginning and end in smoke. 

The smoke out of which the flame is produced is of much greater 
heat than the smoke in which this flame ends, because in the first 



smoke there is the nascent power of the flame, and the last is the dying 
away of the same flame. 

Wood that is young and dry will produce smoke of a more intense 
blue than wood that is old and damp. 

The blue flame which is midway between the darkness and the light 
comes into being between the nutritive portion of the candle and its 
flame, and is of greater heat and radiance than the smoke and of less 
heat and radiance than its flame; and the vapour cannot transform 
itself into flame, without first becoming changed to this blue colour, 
and this is known in the case of smoke. 

Flame is condensed smoke, formed out of the meeting together of 
the air that is in this blue smoke, which . . . 

The blue smoke is the transit of the material nutriment that is the 
grease that is in the candle. The white smoke that surrounds the vestige 
of the flame is the spiritual transit of the flame of this candle, which in 
its lowest part is mingled with the topmost part of the aforesaid blue 
smoke, and in the upper part is mingled with the smoke which pro- 
ceeds from the flame of the candle. c.a. 237 v. a 

Write why the campanile shakes at the sound of its bells. 

c.a. 242 v. a 

The southern winds are more powerful in the northern than in the 
southern regions and in summer than in winter; and this is because 
the sun dissolves all the moisture that rises from the Mediterranean 
Sea, which cannot dissolve during the cold of winter, and of these 
vapours few rise and these few are dissolved in water. But when the 
sun passes beyond the circle of the equinox, and it is winter here at 
hand and summer over yonder the sun dissolves all the vapours as 
they rise, so that they glide in aerial waves as far as the chief [moun- 
tains] of Europe, and there coming upon the cold in the autumn they 
turn into rain, and in the winter they are knit together in snow, and 
fall in snowstorms and so proceed little by little to stifle the breath of 
the aforesaid winds. c.a. 246 v. a 

Where flame cannot live no animal that draws breath can live. 
Excess of wind puts out flame, moderate wind nourishes it. 



I Of flame and wind] 

The bottom part of the flame is the first beginning of this flame 
through which passes all its nutriment of fat; and this is of so much 
less heat than the rest of the flame as it is of less brightness; and it is 
blue in colour and is the part in which its nutriment is purged and 
disposed of. 

That has the brighter flame, and this is the first to come into exist- 
ence when the flame is created, and it comes into existence in spherical 
shape, and after a span of life produces above itself a very small flame, 
radiant in colour and shaped like a heart with its point turned to the 
sky, and this proceeds to multiply continuously on towards infinity, 
by means of its acquiring possession of the substance that feeds it. 

The blue flame is formed of spherical shape because it is not of such 
great heat as exceeds the lightness of the air; and for this reason it 
does not in itself form a pyramidal figure, but remains in spherical 
shape until it has warmed sufficiently the air which surrounds it, and 
because the chief warming of the air is above the principal heat of this 
blue flame, this heat being produced by that part where the natural 
desire of the flame is to move itself, that is to the sphere of fire by the 
shortest way. Therefore the fire comes into existence in the upper part 
of the blue spherical flame, in a small round figure, the roundness of 
which immediately undergoes some extension and assumes the shape 
of a heart, of which the point is turned towards the sky. And this shape 
immediately and with swift dilation overcomes the power that feeds it, 
and penetrates the air which serves it as a covering. But this blue colour 
remains in the base of this flame as may be seen in the light of the 
candle; and this comes to pass because in this position the flame is 
always less warm than elsewhere, because there is the first encounter 
which provides the nourishment of the flame with this flame, and it 
is there that the first heat is produced, and this is feebler and causes 
less warmth because it is only the commencement of the heat. . . . 

That wind will be of briefer movement which is of more impetuous 
beginning; and this the fire has taught us as it bursts forth from the 
mortars, for it shows us the form and speed of the movement in the 
smoke as it penetrates the air opposite to it in brief and spreading 



But the impetuosity of the wind is fitful, as is shown by the dust that 
it raises in the air in its various twists and turns. One perceives also 
in the chains of the Alps how the clashing together of the winds is 
caused by the impetus of various forces. One sees also how the flags 
of ships flutter in different ways; how on the sea one part of the water 
is struck and not another; and the same thing happening in the pi- 
azzas and on the sandbanks of the rivers, where the dust is swept 
together furiously in one part and not in another. And since these 
effects give us experience of the nature of their causes we can say with 
certainty that the wind which has the more impetuous origin will have 
the briefer movement, from the experience that has been referred to 
above as to the brief movement of the smoke from the mouth of the 
mortar. And this arises from the resistance that the air makes on being 
compressed by the percussion of this smoke, which also itself, as has 
been seen clearly shows compression when it offers resistance to the 
wind. But if the wind is of slow movement it will extend a long way 
in a straight course, because the air penetrated by it will not become 
condensed opposite to it and thus thwart its movement, but will readily 
expand spreading its course over a very great space. 



When a wind has been divided by mountains or other erections, if 
on coming together again it should assume the shape of a rectangle, the 
movement which it makes after this reunion will be of a rotatory nature 
in the shape of a twisted column; and if the winds which are thus re- 
united should be equal then this column will not change its position; 
but if the winds are unequal the column will move in the direction of 
the weaker wind. c.a. 270 v. a 

Fire or other heat lightens moisture and makes it lighter than the 
air; for which cause this moisture rises to the middle region of the air, 
and finding there the maximum cold of the air, the fire or heat infused 
through this cloud flies towards the centre, and there becoming strong 
separates the moist vapour from the dry, and it is for this reason that 
the fire becomes kindled there and turns into steam a great part of the 
moisture which is round about this fire. And this process of vaporisa- 


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lion as it increases restricts the fire, and the fire thus restricted acquires 
potency and bursts through the cloud in the part in which it is weakest, 
and forms a gate tor the movement of the thunderbolt and the wind. 

Whether the wind is caused amid the air, and cannot make any move- 
ment unless it is supported in the place where it resists by the opposite 
side of the movement, as is seen to be the case with the rays driven by 
the fire, for through the percussion that the fire makes in the air which 
offers some resistance to it, these fly more slowly than this fire; and if 
this were not the case such ray would be without movement. 

Further we may say: the wind moves in a straight line and not as 
Aristotle would have it in a circular line; and this we learn from the 
movement of a storm at sea when there is no wind, for it is a sign that 
such wind follows its straight line leaving below it the curve of the sea. 

Why the clouds are formed with various round shapes which are 
separated at different spaces one from another: 

The movements of the air spring from the dispersal and collection 
of moisture. 

Heat separates and disperses and cold assembles and freezes or 
condenses. c.a. 279 r. b 



Drops are formed in the air through the mists or clouds by various 
movements, as when they encounter each other and become condensed 
or unite in the movement of the same cloud in the same direction, 
when one part of the cloud is swifter or slower than the other; for as 
the swifter part is behind the slower it conquers it in its course and 
overtakes it, and condenses it and out of many small drops makes one 
large one, and this acquires weight and falls. But unless the drops are 
so formed as to be of considerable size they are consumed by the fric- 
tion they make with the air as they traverse it. c.a. 292 r. a 

The moist wind which is found in the caverns that have both en- 
trance and exit can produce water, and this especially when these 
caverns have twisted and shapeless sides; but this production of water 
is not permanent in its effect for when the wind is lacking the supply 
ceases, and if a contrary wind should enter by the opposite mouth of 



this cavern the water which bathed its walls will become evaporated 
and changed into air; and if this cavern have an entrance but no exit 
the moist wind which strikes its mouth could not enter there unless 
the air within that filled it were expelled. And since two opposite 
movements cannot penetrate each other it must needs be that the air 
that dwells within the cavern will find it easier to be condensed than 
to escape, and for this reason it will resist the entrance of the wind 
which beats upon it. c.a. 296 v. b 

The images of every visible object are all infused in all the air over 
against them, and are all separated in every part of the same air. 

The images of objects which confusedly as they mingle fill with 
themselves the air over against them are all in all this air and all in 
every part of it. c.a. 345 r. b 

Every body situated within the luminous air fills the infinite parts of 
this air circle-wise with its images, and it is all in all and all in the part, 
and goes lessening its images throughout the equidistant surrounding 
space like a . . . 

Of the four elements and two . . . 

1. The stone thrown into the water becomes the centre of various 
circles, and these have as their centre the spot which has been struck. 

2. And the air in the same way is filled with circles, the centres of 
which are the sounds and voices formed within them. 

How the various circles of the water form round the spot which has 
been struck by the stone. 

The stone where it strikes the surface of the water creates circles 
round itself which proceed to expand so much that they die away; and 
the air also when struck by a voice or a noise departing circle-wise in 
the same way proceeds to lose itself so that the nearest perceives better, 
and the more distant hears less. 


Just as the air struck by the voice, the water by the stone proceed 
in circular movement revealing their cause, and these circles make their 
centre in the place which has been struck, and the farther away they 
proceed from it . . . c.a. 373 r. b 



The fifth essence is infused through the air as is the clement of fire, 
although each of these may have its reason in itself or through itself; 
and since each particle is supplied with nutritive matter it acquires 
growth and increase of form; and if the nourishment be taken away 
from them they suddenly abandon this body and return to their first 
nature. c.a. 393 v. a 

The air is all in all and all in its image in the part set over against it. 

If within the air there be no opaque body the whole of it has a 
capacity which extends over the whole and over the part, and the part 
has a capacity which extends over the part and over the whole. 

Therefore we may say that the air is all entwined in all of it, and is 
filled with the infinite rays of the images of the bodies which are 
situated within it, and this air is full of an infinite number of points, 
and every point is indivisible, and the parts of this indivisibility of all 
the images of the parts of bodies set over against them have capacity, 
and in these points they are entirely united and entirely divided and 
separated without confusion the one from the other. 

And the pyramids of the images are spread throughout the whole of 
this air without occupation of space the one of the other, and each for 
itself, and are all divided through all and united through all. 

And although the images approach the eye in the form of pyramids 
the eye is not conscious of this unless it forms a pyramid opposite to the 
thing seen. c.a. 396 r. b 

Just as the stone thrown into the water becomes the centre and cause 
of various circles, and the sound made in the air spreads itself out in 
circles, so every body placed within the luminous air spreads itself out 
in circles and fills the surrounding parts with an infinite number of 
images of itself, and appears all in all and all in each smallest part. 

a 9 v. 


I say that cold proceeds from two causes; the first is from the air 
being deprived of heat; the second is from the movement of the air. 
The air of itself is cold and dry and it is void of all matter or vapours, 
and it changes readily or to put it more exactly steeps itself in the 
nature and image of the things which touch it and which it has oppo- 



site to it. As regards things that touch it, when a pungent thing such 
as musk or sulphur or some other powerful odour touches it it in- 
stantly permeates it; also if a luminous body be placed within it the 
whole of the surrounding air will be lit up. 

Now to return to this question of cold I say that just as the many 
rays of a concave mirror converging at one point produce an extreme 
of heat even so many bellows blowing on the same point produce an 
extreme cold. a 20 r. 

[ Concerning visibility ] 

Men naturally if they wish to know whether the rain has com- 
menced look in the air that is between the eye and some dark place; 
and then the fine threads which the minute drops of water cause to 
appear in the air being lighted up are easily visible against a dark 
background. But men reckon the threads which are near at hand and 
first as though they were the last and almost touched the dark place, 
not perceiving that this dark place is sometimes so remote that it 
would not be possible to be able to see a neighbouring tower there. 

c 5 v. 

The colours of the middle of the rainbow mingle with each other. 

The bow itself is neither in the rain nor in the eye that sees it, al- 
though it is produced by the rain, the sun, and the eye. 

The rainbow is invariably seen by the eye which is situated between 
the rain and the body of the sun, and consequently when the sun is in 
the east and the rain in the west the rainbow is produced upon the 
western rain. e cover 1 v. 


I saw at Milan a thunderbolt strike the Torre della Credenza on its 
northern side. It travelled along it with a slow movement and then all 
at once parted from the tower and carried with it and tore away a part 
of the wall, three braccia in breadth and length and two in depth. The 
wall was four braccia in width and was built of old bricks which were 
thin and small. It was torn away through the vacuum caused by the 
flame of the thunderbolt. I have found traces of the same power in the 



rocks of the high Apennines and especially in the rock of La Vernia. 
The same thing occurs with a cannon in the vacuum left by the flame. 

e 1 r. 

Which will darken the earth more? A thick dark cloud that comes 
between the earth and the sun, or a quantity of water equal in bulk to 
the said cloud, the cloud touching the ground as does the water? 

f 46 v. 

[Of fire and light] 

Fire would increase to infinity if the wood were indefinitely in- 

The light of the candle will be proportionately less as it is placed 
in a colder spot. f 56 r. 


The air moves like a river and carries the clouds with it; just as 
running water carries all the things that float upon it. This is proved 
because if the wind were to penetrate through the air and drive the 
clouds these clouds would be condensed between the air and the mov- 
ing force and would take a lateral impress from the two opposing 
extremities, just as wax does when pressed between the fingers. 



Air moves when it is drawn away to fill a vacuum, or driven by the 
rarefaction of the humidity of the clouds. g 10 r. 

[Reflex course of wind and water] 

The reflex wind as it turns back upon its course subdues the oncom- 
ing wind until this reflex wind becomes enfeebled, and then it regains 
its force when it becomes joined with the falling movement; and such 
power springs from its condensation acquired at the place of the per- 
cussions, which condensation always penetrates into the falling wind 
up to the point at which it becomes separated and its speed of move- 
ment becomes less. 

The water does the same; not however by condensation but because 
it rises in the air and acquires weight. g 69 r. 



Why do the northern winds commence to blow at the winter solstice, 
and continue until melancholy January? 

At the winter solstice, that is at the middle of December, the north- 
ern winds are at their maximum strength. g 91 r. 



If the wind strikes the cloud on one side only, then although its 
opposite side, that is of the clouds, is in the motionless air, this cloud 
will be driven forward and turned round, and it will make a circular 
movement like that of the wheel of a mill turned by the water. 



When the movement of two contrary winds brings two clouds to 
strike together these clouds then become incorporated in each other, 
and not being able either to expand or lower themselves because of the 
wind passing beneath them, these clouds extend in that direction in 
which their passage is least impeded, that is upwards. 



When with the same wind two clouds meet together, the greater in 
order to have part of the more powerful wind covers the smaller; and 
the two become condensed at their common contact, and this causes 
rain. c 91 v. 

If the wind is created by excess or dearth the southern parts which 
separate the humidity drawn to them come to condense themselves, 
and not being able to receive such multiplication they drive it back; 
it is then drawn by the vacuum created in the cold region where this 
humidity becomes contracted in forming clouds, or in the southern 
parts where the other clouds are formed 




The course of the cloud is less swift in itself than its shadow which 
moves over the earth. This is proved: — Let e be the solar body, a the 
cloud, and c its shadow: then as the cloud moves from a to b the 
shadow will move from c to d> from which it follows that as the 
shadows that pass from the earth to the cloud are made by lines that 
converge in the centre of the sun,, we may say by my fourth [rule] 
that what is set forth is true, for this fourth says : — the equidistant sec- 
tions at the angle of the two converging lines will be so much less as 
they are nearer the place of meeting; therefore as the clouds are nearer 
the sun than their shadow there can be no doubt that the shadow will 
travel a greater distance over the earth than the cloud does through the 
air in the same time. g 92 v. 

The atmosphere is blue because of the darkness which is above it, 
for black and white together make blue. h 77 [29] v. 

The part of the cloud which is nearest to the eye will seem swifter 
than that which is higher; and for this reason they often appear to be 
moving in contrary directions, one to the other. h 89 [41] r. 

Of the shapes that one element assumes as it penetrates into another : 

Air falling from fire will turn the mill as fire issuing from air will, 

and in the same way air falling from water as water from air, and as 

earth falling from water; and you should describe the equality of the 

powers and resistances and the shapes that they assume as they pass. 

1 76 [28] v. 

[Compressed air in rose-water at barber's] 

Whether air can be compressed in itself is shown by the barber's 
vessel for supplying rose-water, in which it is doubled. 

Fire is quadrupled by the force of the place where it cannot increase. 

1 133 [85] r. 


Every movable thing continues its movement in the shortest way 
and either shuns the obstacle or is bent by the obstacles; therefore the 



wind curves in penetrating the thick air, and bends upwards towards 
the light air. k 113 [33] v. 


Air that moves with impetus within the other air is compressed 
within itself as is shown in the expansion of the solar rays; for if the 
wind moves their atoms in various revolutions you see these atoms 
form themselves into marbled waves after the manner of watered silks 
or camlets (gianbellotti) ; and that which you see done to these atoms 
is done by the air which bears them shut up within itself. 

The water in such cases cannot become compressed, and having all 
these like movements in its body it is necessary for it to drive the other 
water from its place, so that they may all appear on the surface. 

l 78 r. 

When the sun strikes upon concave mirrors and leaps back from 
them with pyramidal course, that part of the pyramid will be propor- 
tionately as much warmer than its base as it is less in size, and it does 
so in as much as its moisture becomes restricted. The hot steam which 
is mingled with it becomes so much more powerful as it is more united, 
and as it is confined within a less space it generates more heat. Conse- 
quently it often catches fire and increases, forming itself into a thun- 
derbolt out of the cloud; and so it bursts the cloud with devastating 
lightning and thunder. The little particles of water, when the cloud 
has been contracted by the cold, fasten themselves together and fall by 
reason of their weight. And in this way the clouds break up, and so 
they return in rain to the low position. b.m. 57 r. 

The surfaces of transparent and polished bodies always mirror the 
objects which look upon their surfaces and are looked upon by them. 

Therefore that which stands underneath the water is mirrored in the 
surface of the air which borders upon this water, and that which is in 
the air is mirrored in the surface of the water which borders upon 
this air. b.m. 196 r. 

The course of the winds changes and follows the movement of some 
other wind by reason of the mouths of the valleys which it enters and 
issues forth from, and this happens more with the low winds than with 



the high ones, and this it docs 1mm its being flexible and able to be 
bent in any direction except that directly opposite to its course. And 
desiring to move and to give place to the new wind it has to do as does 
the water that enters a pool by a line and then turns in various chan- 
nels, but more by the line that follows that of the movement it makes 
at its entrance, and less by that farthest away from this entrance. 

The wind is condensed above the places where it strikes, and more 
in the summits of the mountains than on the sea coasts visited by it; 
for there gather all the reflex winds, that is on summits of the straight 
sides of the mountains where these winds strike; for they do not ex- 
tend all crosswise following the shape of the summit of the mountain, 
but many proceed up in a straight line and especially those that strike 
nearest the bases of the mountains, although after they are above the 
summit of the mountain they describe a curve, and after such process 
of curving straighten themselves into the course of the other wind which 
struck them and which first made them describe a curve. b.m. 276 r. 



Many are the times when the course of one wind is diverted into 
that of another, and this arises from the percussion which they make 
at the meeting of their courses when as they are not able to penetrate 
one into the other necessity constrains them to leap back in opposite 

If however the said winds are not of equal power one with another 
their reflex movements will not follow the movement of their striker, 
but the angle of percussion of the more powerful will be as much 
greater than that of the less powerful as is the excess of the greater 
power over the lesser. 

Winds which blow in the same direction may be simple or mixed 
with other winds, that is along one part of its side the wind may be all 
taut because the free wind strikes it and leaps back at equal angles, 
but never opposite to its source because it would have to re-enter into 
itself and the movement of two bodies cannot penetrate within them- 
selves. Therefore it follows that the part of the greater wind which is 
struck by the lesser wind would turn backwards and follow the course 
of the lesser wind which has struck it, but it encounters it along the 



remainder of its width and this causes it to curve gradually until finally 
it has changed back to its former course. 

The same wind therefore in striking produces within itself different 
movements and different degrees of power, for the part of its breadth 
before mentioned which drives before it the part which flies away also 
takes a reflex movement upon the wind which it strikes, and so after 
it does the part which when struck puts to flight the second; and the 
fourth which strikes the third in such a way that in these parts it 
becomes denser. But the first density is greater than the last, after the 
manner of two streams of water striking together, as I have demon- 
strated in the fourth of the seventh of the elements of mechanics, for 
there is an angle formed at the place of the first percussion which 
makes the water that first strikes leap up more than any other part of it. 

b.m. 276 v. 

[Movement of the winds] 

If the movement of the winds proceeds from Jupiter the cause of 
the wind must be in the twenty-four hours during which the move- 
ment of Jupiter is from the east to the west and not from the north 
to the south; and this arises from the fact that a thing moved by some- 
thing else has the form and time of the movement of its mover. 

Quaderni 11 20 v. 



If (the wind) is a vapour of the earth and of cold and dryness, and 
is carried by heat, it rises to the cold region of the air, and, abandoned 
by heat, its conductor, it remains there. Such is the reason why the 
vapour, being similar to the vapours in that place, that is to say cold 
and dry, leaves the place and vapour, and flies from its similar; and 
this, indeed, having ceased its upward movement and entering a place 
entirely similar to itself is free to remain without motion. And yet if 
you concede it its movement, it must still move in the cold region by 
itself. But we shall say that such a vapour being cold and dry in its 
slow and late birth, becomes successively mixed with the hot, and so 
with a gradual expansion it generates an almost imperceptible motion 
in proportion to this expansion. But the motion of the heat which car- 



ries it upward is swift and SO conducts it as far as the cold region oi 
the air, where, having expelled the first part, the heat which conducts 
it there leaves it there, and so diminishes the vapour, which being with- 
out wind by the same amount as that of the heat which was mixed 
with it, being thus diminished in quantity, grows in weight above the 
air which sustains it, and so descends below the other vapour, and hav- 
ing descended there the heat which is divided from it is reunited with 
the heat and with the other vapour; and this giving it an upward 
movement and so raising all the vapour little by little it chills the upper 
part which penetrates the cold; and so little by little it falls back 
through the weight it has acquired, in such a way that the whole is 
composed of a greater weight than it was formerly. Hence it descends 
in the form of clouds, and approaching the heat refracted by the earth 
warmed by the sun, it becomes dissolved and dilates with great move- 
ment; and this is the wind. 

The winds descend from above to below at various angles, and, 
striking the water or the earth, set up lateral movements along various 
lines, as does the water which penetrates other water. 

You say that the movement of an effect follows the movement of its 
cause; and then say that the twelve signs of the Zodiac are the cause of 
the motion of winds, and that the three fiery signs, the Ram, the Lion 
and the Archer are of the east and move the eastern winds; and that 
the three cold and dry signs, the Bull, the Virgin and the Goat move 
the southern winds, and the other three signs move the western winds. 
This theory leaves the inventor of such causes in confusion from the 
first proposition which you agreed on, viz. that all bodies in motion 
follow the movement of their motive force. Now these signs of the 
Zodiac are moving from east to west and go round the world in twenty- 
four hours. How then do you account for the fact that these signs 
which move towards the west will move the western winds; and yet 
these winds should move towards the east which would be contrary to 
the motion of their motive force? This is contrary to your first assump- 
tion, which is true, but your consequent theory is false. 

You say that the vapour which generates the wind is carried upwards 
by heat and pressed down again by cold; which having been said, it 
follows in course that this vapour, finding itself between two contrary 
motions, escapes to the sides; and this lateral movement is the wind, 



which has a tortuous movement because it cannot descend to the earth 
because the heat pushes it up, and it cannot move very high up because 
the cold presses it down; hence this necessity gives it a latitudinal and 
tortuous movement. Now many drawbacks will follow from this the- 
ory of yours, of which the first is that the wind will never descend to 
the plain, and secondly that the cold in being driven down by such a 
vapour would be acting contrary to its inert nature. 

Windsor: Drawings 12671 r. 

Then again, it is possible that the vapour which collects in the cold 
region, through being abandoned by the heat which conducts it there, 
comes to be compressed and makes itself larger (heavier?); and the 
air which formerly sustained it no longer resists it, and in consequence 
gives place to it; and this vapour being heavy descends rapidly into 
the hot region near to the earth. There it is entirely permeated with 
heat and in consequence completely dilated and resolved, and moves 
in every direction which is round about it, and strikes the sea on its 
surface. And here one can see the cause of the origin of such wind as 
makes the movement of the sea, for it is flying from the first place it 
struck. And in this cause (case?) the courses of the parts of this wind 
are not parallel because they move from the centre to the circumference 
in direct lines. 

The congregation of humidity scattered through the air, which comes 
together for the creation of clouds, creates wind in the air. And simi- 
larly the breaking up of the clouds makes the fine and penetrable 
humidity through the air; and this is the wind. The proof: one may 
see the water churned up on a fire which makes a wind in the chimney 
that is above this fire; and again, boiling water which is shut into vases 
escapes through little vents of such a vase with great force in the man- 
ner of wind. And again, fires made in small rooms suck in the air 
through little cracks in the windows with great force and noise. 

Windsor: Drawings 12671 v. 

The force inherent in moving bodies has the result that movement 
is often contrary to the nature of the thing moved. 

You say that the vapour of the wind is driven up by the heat which 
lifts it and is then pushed down again by the cold which joins with 



it; and yet necessity gives it a lateral and a curved movement, since 
being enclosed between two contrary forces it flies out sideways all 
over the earth. 

But this theory denies that the vapour which has been mixed in the 
cold region of the air is pushed down by this cold, because it is neces- 
sary to say either that the vapour flies before the cold from its nature, 
or that the cold really removes it of itself, which is being contrary to 
the nature of the vapour. And if such a vapour moves of itself, it does 
so after it has increased and not before, because at first it is the power 
of the heat pressing it down which makes itself greater than the power 
of the vapour which wishes to descend. Here it must be confessed that 
such a vapour in increasing acquires weight, and that with this weight 
it overcomes the force of the heat which sustains it, and that here cold 
does not press it down because, if it were natural to such cold to press 
it down, it would have been easier to expel it when the vapour was 
small in quantity and weak than when it was increased in quantity and 
in force. And so here we shall say that the vapour of the wind, having 
reached the cold region, stops there, because the heat which has con- 
ducted it to this place becomes consumed in cold; and the heat being 
consumed the vapour remains without motive force, and so it stays 
there and awaits the parts which succeed and adjoin it. And these not 
being at such an altitude are not yet completely deprived of heat and 
in consequence of movement; and so not being stationary they move 
until at last they arrive at the same altitude as the part which has been 
chilled and they penetrate this and unite with it, and the heat being 
there condensed leaves it [the vapour]. And so subsequently rising, 
one part after the other, and penetrating the higher part, they are pre- 
vented from condensing, and from that weight of such a nature that 
the lower region cannot sustain it above itself. Hence by necessity it 
descends united with it until the heat makes it light and again lifts it 
upwards, and does the same as it did the first time, and so once more 
joining with the cold part it again acquires weight and again sinks 
down and again turns to vapour in the upper air. And so this would 
go on continually and from this arises the motion of the wind spread- 
ing itself from high to low and not from here to there [vertically and 
not horizontally]. Well then this theory given above is false, because 
experience shows itself in disagreement. 



You say that the winds begin by being weak and go on growing in 
strength, because in the beginning there was a small quantity of vapour 
generated by a small blast; but when such a vapour was increased in 
a greater quantity, being struck by the cold, it descends with greater 
force and from this arises the growth of wind. To this we answer that 
any movement is born of a void or a deficiency. If vapour which is 
raised by the heat, which though it penetrates the said heat, dissolves 
such a vapour and makes a movement sideways or rather upwards 
because that is the true [direction] of the movement of fire, and when, 
the more this evaporation rises the more it is pressed in, its exterior 
moves itself inwards towards the centre of the bulk. And this second 
movement is contrary to the first, because the first moved from the 
centre to the extremities and the second movement is from the ex- 
tremities to the centre, and from one to the other the movement is more 
rapid in proportion as it is more remote from the centre, because the 
extremities are more affected by heat and cold than are the parts which 
are near the middle. But to return to the matter in hand; the more the 
vapour rises the more it is pressed in because it grows nearer to the 
cold, the exact opposite of the heat which conducts such a vapour and 
presses it in. 

This cannot make wind which flows from it, but can make it if it 
runs contrary to it because it does not allow a vacuum, and the place 
from whence its parts are flying would remain a vacuum if the air did 
not fill them up, and this air rushes to fill up [the vacuum] with the 
same speed as the vapour when it is rushing away from the cold. And 
since the material joined with the motive force which moves it, moves 
itself in the same amount of time as the movement made by this motive 
force, therefore here the vapour will move itself in such time as the fire, 
its first motive force, accompanies it, and when the fire is parted from 
it the vapour loses its movement which [movement] the cold does not 
give it if it is not against the half of its quantity (?), or it may be that 
that part of the vapour which touches the cold first of all is the first to 
rush backwards towards the centre, but one cannot classify this as 
actual flight but as the loss of its elevation. 

You say that the wind does not blow continuously, but with various 
gusts divided one from the other; and the cause of this is the vapour 
which rises to the cold carried by heat in various quantities. Here one 



may answer that the cold does not expel the vapour but (that this is 
produced); but that the heat which is escaping from the cold brings 
back the vapour which it formerly carried with it to the cold regions. 
And again one may say that the heat, in the first contact which it 
makes with the cold, warms this cold in proportion as it touches it 
[the cold]; and similarly the cold chills the heat in proportion as it 
receives it [the heat] into itself. Hence there arises a storm; which has 
the result that the heat and cold lose some of their original force; and 
in this case the way is prepared for the transformation into vapour 
which succeeds, together with the heat, in penetrating more deeply into 
the cold and warming it to a greater altitude. And so the vapour pene- 
trates farther in such a way that it passes through the cold region and 
penetrates towards the element of fire [the source of heat]; and being 
united with it the vapour makes a great outburst through all the sur- 
rounding regions, which outbursts are rapid movements in direct lines 
and result in a flood of air which [strikes] the sea above the horizon 
and proves to be the cause of your solution. 

Windsor: Drawings 12672 


I say that the blue which is seen in the atmosphere is not its own 
colour, but is caused by the heated moisture having evaporated into 
the most minute imperceptible particles, which the beams of the solar 
rays attract and cause to seem luminous against the deep intense dark- 
ness of the region of fire that forms a covering above them. And this 
may be seen, as I myself saw it, by anyone who ascends Mon Boso 
(Monte Rosa), a peak of the chain of Alps that divides France from 
Italy, at whose base spring the four rivers which flow as many different 
ways and water all Europe, and there is no other mountain that has 
its base at so great an elevation. 

This mountain towers to so great a height as almost to pass above all 
the clouds; and snow seldom falls there, but only hail in summer when 
me clouds are at their greatest height; and there this hail accumulates, 
so that if it were not for the infrequency * of the clouds thus rising and 

1 MS. has reta which Dr. Richter reads in sense of 'malanno'. I have adopted Dr. 
Solmi's suggestion 'rarita'. (Note, Dec. 1929. Calvi reads [rajreta.) 



discharging themselves, which does not happen twice in an age, there 
would be an enormous mass of ice there, built up by the various layers 
of the hail; and this I found very thick in the middle of July. And I 
saw the atmosphere dark overhead, and the rays of the sun striking 
the mountain had far more brightness than in the plains below, be- 
cause less thickness of atmosphere lay between the summit of this 
mountain and the sun. 

As a further example of the colour of the atmosphere, we may take 
the case of the smoke produced by old dry wood, for as it comes out 
of the chimneys it seems to be a pronounced blue when seen between 
the eye and a dark space, but as it rises higher and comes between the 
eye and the luminous atmosphere, it turns immediately to an ashen 
grey hue, and this comes to pass because it no longer has darkness 
beyond it, but in place of this the luminous atmosphere. But if this 
smoke comes from new green wood, then it will not assume a blue 
colour, because, as it is not transparent, and is heavily charged with 
moisture, it will have the effect of a dense cloud which takes definite 
lights and shadows as though it were a solid body. 

The same is true of the atmosphere, which excessive moisture renders 
white, while little moisture acted upon by heat causes it to be dark 
and of a dark blue colour; and this is sufficient as regards the defini- 
tion of the colour of the atmosphere, although one may also say that if 
the atmosphere had this transparent blue as its natural colour, it would 
follow that wherever a greater quantity of atmosphere came between 
the eye and the fiery element, it would appear of a deeper shade of 
blue, as is seen with blue glass and with sapphires, which appear 
darker in proportion as they are thicker. The atmosphere, under these 
conditions, acts in exactly the opposite way, since where a greater 
quantity of it comes between the eye and the sphere of fire, there it is 
seen much whiter, and this happens towards the horizon; and in 
proportion as a lesser amount of atmosphere comes between the eye 
and the sphere of fire, of so much the deeper blue does it appear, even 
when we are in the low plains. It follows therefore, from what I say, 
that the atmosphere acquires its blueness from the particles of mois- 
ture which catch the luminous rays of the sun. 

We may also observe the difference between the atoms of dust and 
those of smoke seen in the sun's rays as they pass through the chinks 



of the walls in dark rooms, that the one seems the colour of ashes, and 
the other — the thin smoke — seems of a most beautiful blue. We may 
see also in the dark shadows of mountains far from the eye that the 
atmosphere which is between the eye and these shadows will appear 
very blue, and in the portion of these mountains which is in light, it 
will not vary much from its first colour. 

But whoever would see a final proof, should stain a board with 
various different colours, among which he should include a very 
strong black, and then over them all he should lay a thin transparent 
white, and he will then perceive that the lustre of the white will 
nowhere display a more beautiful blue than over the black, — but it 
must be very thin and finely ground. Leic. 4 r. 

Smoke is swift at its beginning and becomes slower at every stage of 
its ascent, because it becomes colder and heavier, owing to the fact 
that a great part of it is condensed through the parts striking against 
each other and being pressed together and made to adhere one to an- 
other; and water does the same for it is swift at the beginning of its 
movement. Leic. 12 v. 

Air even if it changes its position preserves the impression of its 
eddies more than water does, from the fact of it being swifter and 
thinner. Leic. 30 v. 

An excess of smoke acts as a veil, a small quantity of it does not 
render the perfection of this blue: it is by a moderate admixture of 
smoke therefore that the beautiful blue is created. 

Experience it is that shows how the air has darkness behind it and 
yet appears blue. 

Make smoke of dry wood in a small quantity; let the rays of the 
sun fall upon this smoke, and behind it place a piece of black velvet, 
so that it shall be in shadow. You will then see that all the smoke 
which comes between the eye and the darkness of the velvet will show 
itself of a very beautiful blue colour; and if instead of the velvet you 
put a white cloth, the smoke will become the colour of ashes. 

How water blown in the form of spray into a dark place, through 
which the solar rays pass, produces this blue ray; and especially when 
this water has been distilled; and how the thin smoke becomes blue. 



This is said in order to show how the blue colour of the atmosphere 
is caused by the darkness that is above it; and the above-mentioned 
instances are offered for the benefit of anyone who cannot confirm 
my experience on Mon Boso. 1 Leic. 36 r. 

1 See Leic. 4 r. in which Leonardo refers to his ascent of Mon Boso (Monte Rosa) 
in the month of July and the atmospheric conditions which he found prevailing.