The Notebooks of Leonardo Da Vinci, Complete by Leonardo Da Vinci

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The nerves with their muscles obey the tendons as soldiers obey the
officers, and the tendons obey the Common [central] Sense as the
officers obey the general. [27] Thus the joint of the bones obeys
the nerve, and the nerve the muscle, and the muscle the tendon and
the tendon the Common Sense. And the Common Sense is the seat of the
soul [28], and memory is its ammunition, and the impressibility is
its referendary since the sense waits on the soul and not the soul
on the sense. And where the sense that ministers to the soul is not
at the service of the soul, all the functions of that sense are also
wanting in that man's life, as is seen in those born mute and blind.

[Footnote: The peculiar use of the words _nervo_, _muscolo_,
_corda_, _senso comune_, which are here literally rendered by nerve,
muscle cord or tendon and Common Sense may be understood from lines
27 and 28.]

On involuntary muscular action.

839.

HOW THE NERVES SOMETIMES ACT OF THEMSELVES WITHOUT ANY COMMANDS FROM
THE OTHER FUNCTIONS OF THE SOUL.

This is most plainly seen; for you will see palsied and shivering
persons move, and their trembling limbs, as their head and hands,
quake without leave from their soul and their soul with all its
power cannot prevent their members from trembling. The same thing
happens in falling sickness, or in parts that have been cut off, as
in the tails of lizards. The idea or imagination is the helm and
guiding-rein of the senses, because the thing conceived of moves the
sense. Pre-imagining, is imagining the things that are to be.
Post-imagining, is imagining the things that are past.

Miscellaneous physiological observations (840-842).

840.

There are four Powers: memory and intellect, desire and
covetousness. The two first are mental and the others sensual. The
three senses: sight, hearing and smell cannot well be prevented;
touch and taste not at all. Smell is connected with taste in dogs
and other gluttonous animals.

841.

I reveal to men the origin of the first, or perhaps second cause of
their existence.

842.

Lust is the cause of generation.

Appetite is the support of life. Fear or timidity is the
prolongation of life and preservation of its instruments.

The laws of nutrition and the support of life (843-848).

843.

HOW THE BODY OF ANIMALS IS CONSTANTLY DYING AND BEING RENEWED.

The body of any thing whatever that takes nourishment constantly
dies and is constantly renewed; because nourishment can only enter
into places where the former nourishment has expired, and if it has
expired it no longer has life. And if you do not supply nourishment
equal to the nourishment which is gone, life will fail in vigour,
and if you take away this nourishment, the life is entirely
destroyed. But if you restore as much is destroyed day by day, then
as much of the life is renewed as is consumed, just as the flame of
the candle is fed by the nourishment afforded by the liquid of this
candle, which flame continually with a rapid supply restores to it
from below as much as is consumed in dying above: and from a
brilliant light is converted in dying into murky smoke; and this
death is continuous, as the smoke is continuous; and the continuance
of the smoke is equal to the continuance of the nourishment, and in
the same instant all the flame is dead and all regenerated,
simultaneously with the movement of its own nourishment.

844.

King of the animals--as thou hast described him--I should rather say
king of the beasts, thou being the greatest--because thou hast
spared slaying them, in order that they may give thee their children
for the benefit of the gullet, of which thou hast attempted to make
a sepulchre for all animals; and I would say still more, if it were
allowed me to speak the entire truth [5]. But we do not go outside
human matters in telling of one supreme wickedness, which does not
happen among the animals of the earth, inasmuch as among them are
found none who eat their own kind, unless through want of sense (few
indeed among them, and those being mothers, as with men, albeit they
be not many in number); and this happens only among the rapacious
animals, as with the leonine species, and leopards, panthers lynxes,
cats and the like, who sometimes eat their children; but thou,
besides thy children devourest father, mother, brothers and friends;
nor is this enough for thee, but thou goest to the chase on the
islands of others, taking other men and these half-naked, the ...
and the ... thou fattenest, and chasest them down thy own
throat[18]; now does not nature produce enough simples, for thee to
satisfy thyself? and if thou art not content with simples, canst
thou not by the mixture of them make infinite compounds, as Platina
wrote[Footnote 21: _Come scrisse il Platina_ (Bartolomeo Sacchi, a
famous humanist). The Italian edition of his treatise _De arte
coquinaria_, was published under the title _De la honestra
voluptate, e valetudine, Venezia_ 1487.], and other authors on
feeding?

[Footnote: We are led to believe that Leonardo himself was a
vegetarian from the following interesting passage in the first of
Andrea Corsali's letters to Giuliano de'Medici: _Alcuni gentili
chiamati Guzzarati non si cibano di cosa, alcuna che tenga sangue,
ne fra essi loro consentono che si noccia ad alcuna cosa animata,
come il nostro Leonardo da Vinci_.

5-18. Amerigo Vespucci, with whom Leonardo was personally
acquainted, writes in his second letter to Pietro Soderini, about
the inhabitants of the Canary Islands after having stayed there in
1503: "_Hanno una scelerata liberta di viuere; ... si cibano di
carne humana, di maniera che il padre magia il figliuolo, et
all'incontro il figliuolo il padre secondo che a caso e per sorte
auiene. Io viddi un certo huomo sceleratissimo che si vantaua, et si
teneua a non piccola gloria di hauer mangiato piu di trecento
huomini. Viddi anche vna certa citta, nella quale io dimorai forse
ventisette giorni, doue le carni humane, hauendole salate, eran
appicate alli traui, si come noi alli traui di cucina_ _appicchiamo
le carni di cinghali secche al sole o al fumo, et massimamente
salsiccie, et altre simil cose: anzi si marauigliauano gradem ete
che noi non magiaissimo della carne de nemici, le quali dicono
muouere appetito, et essere di marauiglioso sapore, et le lodano
come cibi soaui et delicati (Lettere due di Amerigo Vespucci
Fiorentino drizzate al magnifico Pietro Soderini, Gonfaloniere della
eccelsa Republica di Firenze_; various editions).]

845.

Our life is made by the death of others.

In dead matter insensible life remains, which, reunited to the
stomachs of living beings, resumes life, both sensual and
intellectual.

846.

Here nature appears with many animals to have been rather a cruel
stepmother than a mother, and with others not a stepmother, but a
most tender mother.

847.

Man and animals are really the passage and the conduit of food, the
sepulchre of animals and resting place of the dead, one causing the
death of the other, making themselves the covering for the
corruption of other dead [bodies].

On the circulation of the blood (848-850).

848.

Death in old men, when not from fever, is caused by the veins which
go from the spleen to the valve of the liver, and which thicken so
much in the walls that they become closed up and leave no passage
for the blood that nourishes it.

[6]The incessant current of the blood through the veins makes these
veins thicken and become callous, so that at last they close up and
prevent the passage of the blood.

849.

The waters return with constant motion from the lowest depths of the
sea to the utmost height of the mountains, not obeying the nature of
heavier bodies; and in this they resemble the blood of animated
beings which always moves from the sea of the heart and flows
towards the top of the head; and here it may burst a vein, as may be
seen when a vein bursts in the nose; all the blood rises from below
to the level of the burst vein. When the water rushes out from the
burst vein in the earth, it obeys the law of other bodies that are
heavier than the air since it always seeks low places.

[Footnote: From this passage it is quite plain that Leonardo had not
merely a general suspicion of the circulation of the blood but a
very clear conception of it. Leonardo's studies on the muscles of
the heart are to be found in the MS. W. An. III. but no information
about them has hitherto been made public. The limits of my plan in
this work exclude all purely anatomical writings, therefore only a
very brief excerpt from this note book can be given here. WILLIAM
HARVEY (born 1578 and Professor of Anatomy at Cambridge from 1615)
is always considered to have been the discoverer of the circulation
of the blood. He studied medicine at Padua in 1598, and in 1628
brought out his memorable and important work: _De motu cordis et
sanguinis_.]

850.

That the blood which returns when the heart opens again is not the
same as that which closes the valves of the heart.

Some notes on medicine (851-855).

851.

Make them give you the definition and remedies for the case ... and
you will see that men are selected to be doctors for diseases they
do not know.

852.

A remedy for scratches taught me by the Herald to the King of
France. 4 ounces of virgin wax, 4 ounces of colophony, 2 ounces of
incense. Keep each thing separate; and melt the wax, and then put in
the incense and then the colophony, make a mixture of it and put it
on the sore place.

853.

Medicine is the restoration of discordant elements; sickness is the
discord of the elements infused into the living body.

854.

Those who are annoyed by sickness at sea should drink extract of
wormwood.

855.

To keep in health, this rule is wise: Eat only when you want and
relish food. Chew thoroughly that it may do you good. Have it well
cooked, unspiced and undisguised. He who takes medicine is ill
advised.

[Footnote: This appears to be a sketch for a poem.]

856.

I teach you to preserve your health; and in this you will succed
better in proportion as you shun physicians, because their medicines
are the work of alchemists.

[Footnote: This passage is written on the back of the drawing Pl.
CVIII. Compare also No. 1184.]

_XV_.

_Astronomy_.

_Ever since the publication by Venturi in_ 1797 _and Libri in_ 1840
_of some few passages of Leonardo's astronomical notes, scientific
astronomers have frequently expressed the opinion, that they must
have been based on very important discoveries, and that the great
painter also deserved a conspicuous place in the history of this
science. In the passages here printed, a connected view is given of
his astronomical studies as they lie scattered through the
manuscripts, which have come down to us. Unlike his other purely
scientific labours, Leonardo devotes here a good deal of attention
to the opinions of the ancients, though he does not follow the
practice universal in his day of relying on them as authorities; he
only quotes them, as we shall see, in order to refute their
arguments. His researches throughout have the stamp of independent
thought. There is nothing in these writings to lead us to suppose
that they were merely an epitome of the general learning common to
the astronomers of the period. As early as in the XIVth century
there were chairs of astronomy in the universities of Padua and
Bologna, but so late as during the entire XVIth century Astronomy
and Astrology were still closely allied._

_It is impossible now to decide whether Leonardo, when living in
Florence, became acquainted in his youth with the doctrines of Paolo
Toscanelli the great astronomer and mathematician (died_ 1482_), of
whose influence and teaching but little is now known, beyond the
fact that he advised and encouraged Columbus to carry out his
project of sailing round the world. His name is nowhere mentioned by
Leonardo, and from the dates of the manuscripts from which the texts
on astronomy are taken, it seems highly probable that Leonardo
devoted his attention to astronomical studies less in his youth than
in his later years. It was evidently his purpose to treat of
Astronomy in a connected form and in a separate work (see the
beginning of Nos._ 866 _and_ 892_; compare also No._ 1167_). It is
quite in accordance with his general scientific thoroughness that he
should propose to write a special treatise on Optics as an
introduction to Astronomy (see Nos._ 867 _and_ 877_). Some of the
chapters belonging to this Section bear the title "Prospettiva"
_(see Nos._ 869 _and_ 870_), this being the term universally applied
at the time to Optics as well as Perspective (see Vol. I, p._ 10,
_note to No._ 13, _l._ 10_)_.

_At the beginning of the XVIth century the Ptolemaic theory of the
universe was still universally accepted as the true one, and
Leonardo conceives of the earth as fixed, with the moon and sun
revolving round it, as they are represented in the diagram to No._
897. _He does not go into any theory of the motions of the planets;
with regard to these and the fixed stars he only investigates the
phenomena of their luminosity. The spherical form of the earth he
takes for granted as an axiom from the first, and he anticipates
Newton by pointing out the universality of Gravitation not merely in
the earth, but even in the moon. Although his acute research into
the nature of the moon's light and the spots on the moon did not
bring to light many results of lasting importance beyond making it
evident that they were a refutation of the errors of his
contemporaries, they contain various explanations of facts which
modern science need not modify in any essential point, and
discoveries which history has hitherto assigned to a very much later
date_.

_The ingenious theory by which he tries to explain the nature of
what is known as earth shine, the reflection of the sun's rays by
the earth towards the moon, saying that it is a peculiar refraction,
originating in the innumerable curved surfaces of the waves of the
sea may be regarded as absurd; but it must not be forgotten that he
had no means of detecting the fundamental error on which he based
it, namely: the assumption that the moon was at a relatively short
distance from the earth. So long as the motion of the earth round
the sun remained unknown, it was of course impossible to form any
estimate of the moon's distance from the earth by a calculation of
its parallax_.

_Before the discovery of the telescope accurate astronomical
observations were only possible to a very limited extent. It would
appear however from certain passages in the notes here printed for
the first time, that Leonardo was in a position to study the spots
in the moon more closely than he could have done with the unaided
eye. So far as can be gathered from the mysterious language in which
the description of his instrument is wrapped, he made use of
magnifying glasses; these do not however seem to have been
constructed like a telescope--telescopes were first made about_
1600. _As LIBRI pointed out_ (Histoire des Sciences mathematiques
III, 101) _Fracastoro of Verona_ (1473-1553) _succeeded in
magnifying the moon's face by an arrangement of lenses (compare No._
910, _note), and this gives probability to Leonardo's invention at a
not much earlier date._

I.

THE EARTH AS A PLANET.

The earth's place in the universe (857. 858).

857.

The equator, the line of the horizon, the ecliptic, the meridian:

These lines are those which in all their parts are equidistant from
the centre of the globe.

858.

The earth is not in the centre of the Sun's orbit nor at the centre
of the universe, but in the centre of its companion elements, and
united with them. And any one standing on the moon, when it and the
sun are both beneath us, would see this our earth and the element of
water upon it just as we see the moon, and the earth would light it
as it lights us.

The fundamental laws of the solar system (859-864).

859.

Force arises from dearth or abundance; it is the child of physical
motion, and the grand-child of spiritual motion, and the mother and
origin of gravity. Gravity is limited to the elements of water and
earth; but this force is unlimited, and by it infinite worlds might
be moved if instruments could be made by which the force could be
generated.

Force, with physical motion, and gravity, with resistance are the
four external powers on which all actions of mortals depend.

Force has its origin in spiritual motion; and this motion, flowing
through the limbs of sentient animals, enlarges their muscles. Being
enlarged by this current the muscles are shrunk in length and
contract the tendons which are connected with them, and this is the
cause of the force of the limbs in man.

The quality and quantity of the force of a man are able to give
birth to other forces, which will be proportionally greater as the
motions produced by them last longer.

[Footnote: Only part of this passage belongs, strictly speaking, to
this section. The principle laid down in the second paragraph is
more directly connected with the notes given in the preceding
section on Physiology.]

860.

Why does not the weight _o_ remain in its place? It does not remain
because it has no resistance. Where will it move to? It will move
towards the centre [of gravity]. And why by no other line? Because a
weight which has no support falls by the shortest road to the lowest
point which is the centre of the world. And why does the weight know
how to find it by so short a line? Because it is not independant and
does not move about in various directions.

[Footnote: This text and the sketch belonging to it, are reproduced
on Pl. CXXI.]

861.

Let the earth turn on which side it may the surface of the waters
will never move from its spherical form, but will always remain
equidistant from the centre of the globe.

Granting that the earth might be removed from the centre of the
globe, what would happen to the water?

It would remain in a sphere round that centre equally thick, but the
sphere would have a smaller diameter than when it enclosed the
earth.

[Footnote: Compare No. 896, lines 48-64; and No. 936.]

862.

Supposing the earth at our antipodes which supports the ocean were
to rise and stand uncovered, far out of the sea, but remaining
almost level, by what means afterwards, in the course of time, would
mountains and vallies be formed?

And the rocks with their various strata?

863.

Each man is always in the middle of the surface of the earth and
under the zenith of his own hemisphere, and over the centre of the
earth.

864.

Mem.: That I must first show the distance of the sun from the earth;
and, by means of a ray passing through a small hole into a dark
chamber, detect its real size; and besides this, by means of the
aqueous sphere calculate the size of the globe ...

Here it will be shown, that when the sun is in the meridian of our
hemisphere [Footnote 10: _Antipodi orientali cogli occidentali_. The
word _Antipodes_ does not here bear its literal sense, but--as we
may infer from the simultaneous reference to inhabitants of the
North and South-- is used as meaning men living at a distance of 90
degrees from the zenith of the rational horizon of each observer.],
the antipodes to the East and to the West, alike, and at the same
time, see the sun mirrored in their waters; and the same is equally
true of the arctic and antarctic poles, if indeed they are
inhabited.

How to prove that the earth is a planet (865-867).

865.

That the earth is a star.

866.

In your discourse you must prove that the earth is a star much like
the moon, and the glory of our universe; and then you must treat of
the size of various stars, according to the authors.

867.

THE METHOD OF PROVING THAT THE EARTH IS A STAR.

First describe the eye; then show how the twinkling of a star is
really in the eye and why one star should twinkle more than another,
and how the rays from the stars originate in the eye; and add, that
if the twinkling of the stars were really in the stars --as it seems
to be--that this twinkling appears to be an extension as great as
the diameter of the body of the star; therefore, the star being
larger than the earth, this motion effected in an instant would be a
rapid doubling of the size of the star. Then prove that the surface
of the air where it lies contiguous to fire, and the surface of the
fire where it ends are those into which the solar rays penetrate,
and transmit the images of the heavenly bodies, large when they
rise, and small, when they are on the meridian. Let _a_ be the earth
and _n d m_ the surface of the air in contact with the sphere of
fire; _h f g_ is the orbit of the moon or, if you please, of the
sun; then I say that when the sun appears on the horizon _g_, its
rays are seen passing through the surface of the air at a slanting
angle, that is _o m_; this is not the case at _d k_. And so it
passes through a greater mass of air; all of _e m_ is a denser
atmosphere.

868.

Beyond the sun and us there is darkness and so the air appears blue.

[Footnote: Compare Vol. I, No. 301.]

869.

PERSPECTIVE.

It is possible to find means by which the eye shall not see remote
objects as much diminished as in natural perspective, which
diminishes them by reason of the convexity of the eye which
necessarily intersects, at its surface, the pyramid of every image
conveyed to the eye at a right angle on its spherical surface. But
by the method I here teach in the margin [9] these pyramids are
intersected at right angles close to the surface of the pupil. The
convex pupil of the eye can take in the whole of our hemisphere,
while this will show only a single star; but where many small stars
transmit their images to the surface of the pupil those stars are
extremely small; here only one star is seen but it will be large.
And so the moon will be seen larger and its spots of a more defined
form [Footnote 20 and fol.: Telescopes were not in use till a century
later. Compare No. 910 and page 136.]. You must place close to the
eye a glass filled with the water of which mention is made in number
4 of Book 113 "On natural substances" [Footnote 23: _libro_ 113.
This is perhaps the number of a book in some library catalogue. But
it may refer, on the other hand, to one of the 120 Books mentioned
in No. 796. l. 84.]; for this water makes objects which are enclosed
in balls of crystalline glass appear free from the glass.

OF THE EYE.

Among the smaller objects presented to the pupil of the eye, that
which is closest to it, will be least appreciable to the eye. And at
the same time, the experiments here made with the power of sight,
show that it is not reduced to speck if the &c. [32][Footnote 32:
Compare with this the passage in Vol. I, No. 52, written about
twenty years earlier.].

Read in the margin.

[34]Those objects are seen largest which come to the eye at the
largest angles.

But the images of the objects conveyed to the pupil of the eye are
distributed to the pupil exactly as they are distributed in the air:
and the proof of this is in what follows; that when we look at the
starry sky, without gazing more fixedly at one star than another,
the sky appears all strewn with stars; and their proportions to the
eye are the same as in the sky and likewise the spaces between them
[61].

[Footnote: 9. 32. _in margine:_ lines 34-61 are, in the original,
written on the margin and above them is the diagram to which
Leonardo seems to refer here.]

870.

PERSPECTIVE.

Among objects moved from the eye at equal distance, that undergoes
least diminution which at first was most remote.

When various objects are removed at equal distances farther from
their original position, that which was at first the farthest from
the eye will diminish least. And the proportion of the diminution
will be in proportion to the relative distance of the objects from
the eye before they were removed.

That is to say in the object _t_ and the object _e_ the proportion
of their distances from the eye _a_ is quintuple. I remove each from
its place and set it farther from the eye by one of the 5 parts into
which the proposition is divided. Hence it happens that the nearest
to the eye has doubled the distance and according to the last
proposition but one of this, is diminished by the half of its whole
size; and the body _e_, by the same motion, is diminished 1/5 of its
whole size. Therefore, by that same last proposition but one, that
which is said in this last proposition is true; and this I say of
the motions of the celestial bodies which are more distant by 3500
miles when setting than when overhead, and yet do not increase or
diminish in any sensible degree.

871.

_a b_ is the aperture through which the sun passes, and if you could
measure the size of the solar rays at _n m_, you could accurately
trace the real lines of the convergence of the solar rays, the
mirror being at _a b_, and then show the reflected rays at equal
angles to _n m_; but, as you want to have them at _n m_, take them
at the. inner side of the aperture at cd, where they maybe measured
at the spot where the solar rays fall. Then place your mirror at the
distance _a b_, making the rays _d b_, _c a_ fall and then be
reflected at equal angles towards _c d_; and this is the best
method, but you must use this mirror always in the same month, and
the same day, and hour and instant, and this will be better than at
no fixed time because when the sun is at a certain distance it
produces a certain pyramid of rays.