to the practical needs of casting. Now it had reached an even grander
scale—a colossus that would require two hundred thousand pounds of
bronze! He recorded in his notes the very day that this work was
started, “On the twenty-third day of April 1490 I commenced this book
and recommenced the horse.” The “horse,” of course, was the monument and
“this book” referred to still another subject which had grown out of his
studies of anatomy and perspective.
The title of the proposed book was to be _Light and Shade_. It would
include the subject of optics or the mechanism of the eye, the problems
of reflection and refraction and it would lead him eventually to a
re-examination of his studies of the sun and moon.
In Leonardo’s day, and even for a long while afterwards, the popular
belief of vision was one that had originally been put forth by the
Platonic school and expanded by Euclid and Ptolemy. This belief was that
the eye sent forth rays that brought back the image to the soul.
Leonardo, in his younger days, had believed in the same theory. Not
content with what had been written on the subject, however, he began to
experiment for himself.
These experiments led him to an examination of the eye itself. He noted
the various parts of the eye—the optic foramen or opening, the pigment
layer, and the iris. These were already known by the Arabs. Leonardo
discovered, however, the crystalline area of the eye. He explained
binocular vision, or three-dimensional images, by correctly noting the
positions of the two eyes in the head. He described the variations in
the diameter of the pupil according to the surrounding light. Further
experiments with light brought him to the conclusion that light and
images are received by the eye. He took a piece of paper, for example,
and pierced it with a small hole. With this he looked at the source of
light. He noted the cone shape of the rays funneling into the tiny hole
and then when the paper was held next to a white wall he noted that the
rays spread out again. He established that light travels in straight
lines. He constructed the first “camera obscura”—a box with a small hole
in it. Inside the box an object was placed near the hole and behind that
a lighted candle. When the box was closed the image of the object was
cast on the wall. Leonardo was already acquainted with lenses, and he
placed a magnifying lens over the hole to create an enlarged image.
[Illustration: _Leonardo’s “camera obscura” which he used for
projecting an image of an object on a wall or screen._]
He also demonstrated various laws relative to optical illusion, such as
irradiation—when a metal rod is made red-hot at one end, that end seems
thicker than the other. A brightly lit object seems larger than one
exactly like it that is dimly lit; a dark object placed against a light
background seems smaller than it is; a light object seems larger than
its real size when placed against a dark background; and the illusion of
a light swung in a circle appears as a complete circle of light.
Many years before Newton, Leonardo described the experiment of breaking
up a ray of white light into the solar spectrum. Also he compared two
sources of light and measured their intensity by the depth of their
shadows accompanied by a drawing that was the forerunner of Rumford’s
photometer three centuries later! He stated the law of reflection—that
is, that the angle of reflection is always equal to the angle of
incidence.
About this time Leonardo left the studio of Ambrogio de Predis and moved
into the Sforza Castle. Ludovico had put at his disposal a studio in the
Corte Vecchia and the use of a room in one of the towers—which Leonardo
always kept locked. To his growing list of work, Leonardo now had to add
the preparations for the delayed wedding reception of Ludovico’s nephew,
Gian Galeazzo Sforza.
On a cold winter evening of January 1490 the guests assembled again.
Silks, satins and gold brocade, diamonds, rubies and pearls glittered in
the brilliant lights. Princes of the Church mingled with ambassadors of
foreign lands. Music and perfume filled the air and as the party quieted
down the entertainment began. There were dances in gay costumes. Poetry
was recited that flattered the bride and groom. There were allegorical
processions. The jokes and antics of the court jester made the audience
laugh.
Then, at midnight, the curtain that hung from wall to wall at the end of
the ballroom was raised. Applause and cries of delight greeted the
spectacle. The rising curtain revealed a room in which there was a
hemisphere surrounded by the signs of the zodiac and the planets. While
the planets in their niches flickered with concealed lights and the
signs of the zodiac glowed, lines were spoken in honor of the house of
Sforza to the accompaniment of a choir. The ancient gods swept down from
the heavens, and the Virtues and Graces moved across the scene with
nymphs waving lanterns. The music drowned out the sound of the
mechanism. This was the kind of mechanics that Ludovico could understand
and appreciate.
The success of this entertainment so pleased Ludovico that Leonardo was
encouraged to present another amusing idea. This one was an “alarm
clock” and it utilized what we call today the mechanical relay
principle. When a small power is suddenly switched over, the power is
reinforced. The “alarm” clock worked by placing a shallow basin of water
at one end of a tubed lever. At the other end was another empty basin.
Water was led drop by drop into the second basin and as this slowly
filled the increasing weight lowered the lever. The shallow basin of
water at the first end was suddenly emptied and the immediate switch in
weight flipped the lever up and this in turn pushed up the sleeper’s
feet.
Leonardo decided to withdraw from the competition for the cathedral
dome. Although the cathedral authorities were pleased with his design,
they could not decide to whom the commission should be awarded. In the
summer of 1490 Ludovico was called upon to settle the issue and he
decided in favor of Antonio Amadeo from Milan. But the work that
Leonardo had done so impressed Ludovico that he sent him to Pavia in
company with an architect from Siena, Francesco di Giorgio Martini, to
inspect the work on the cathedral of that city. Leonardo, who had his
own workshop and apprentices now, took along one of them, Marco
d’Oggionno, a young boy of twenty.
In Pavia one of the greatest libraries in all of Italy was in the ducal
palace. Here Leonardo wandered among shelves of books and illuminated
manuscripts bound in rich velvets and gold-embossed leather all bound to
their places with silver chains. One book that he records in his notes
was written in the thirteenth century by Witelo, a Polish scholar, who
wrote extensively on perspective. Leonardo, by the necessity of his art,
had solved many problems in perspective. He had invented a pair of
proportional compasses, the forerunners of those used today for the
transfer of a drawing from one scale to duplicate the same drawing in a
larger scale. Leonardo had also designed in very careful detail a
parabolic compass for drawing a parabola in one continuous movement. He
now determined to write his own book on perspective and, as the subject
was so close to his studies of the eye, he would entitle it
_Introduction to Perspective, or the Function of the Eye_.
Leonardo submitted a number of plans for the completion of the cathedral
to the authorities in Pavia and then returned to Milan. He worked
through the rest of the summer on the equestrian statue and at the same
time he continued to expand his notes on anatomy, light and shade, and
perspective.
Late on a cold December night in 1490, Leonardo lit his lamp. This was a
very special lamp that he had invented. It had already created a great
deal of comment. It was so unusual, he had received an order from the
court for another which he made with a richly carved pedestal. Candles,
torches, and oil lamps, the only methods of artificial illumination in
those days, were poor substitutes for light. They flickered, smoked,
went out, and frequently caused damage with their hot drippings. As a
side result of his experiments in light, Leonardo had put a glass
cylinder in the middle of a larger glass globe. A wick in olive oil was
placed in the cylinder and the outside globe was then filled with water.
The result was a bright, steady light magnified by the water in the
globe.
He sat down by the small fire and arranged his papers in front of him.
Then, with a glance at his lamp, he picked up his goose-quill pen and
wrote, “No substance can be comprehended without light and shade; light
and shade are caused by light.”
7
_Success_
It was January of 1491, and a light snow had fallen in Milan, edging
with white all the roofs, the massive spires of the cathedral and the
red battlements of the Sforza castle. Soon Ludovico was to be married to
Beatrice d’Este of the ducal house of Ferrara.
Once more the streets of Milan echoed to the carpenters’ hammers.
Messengers rode to and from the castle and endless carts full of
provisions pushed through the crowded city. Guests began to arrive from
all the allied courts of Italy with their bodyguards and servants. The
rooms of the castle, the palaces of the nobles, and even the inns were
filling with the royal processions.
Leonardo was again summoned by the court to prepare the decorations, the
costumes for the masquerades, and the arena for the jousting
tournaments. An invitation had been sent to all the friendly courts to
attend these contests-at-arms. So, accompanying each new party’s arrival
was a band of armored knights, their breast-plates, helmets, and shields
glistening in the winter sun.
Leonardo enjoyed designing mechanical toys and entertaining the guests
with them. One of these was a mechanical drum. Ordinarily most of the
entertainment began with normal drum rolls, but Leonardo’s rolls were
made on a kind of wheelbarrow. On it was mounted an enormous drum. When
the “wheelbarrow” was pushed, it put into motion a cogged wheel geared
to the axle. This wheel in turn was geared to two rotary cylinders with
pegs mounted around the top. The pegs moved against five drumsticks on
either side of the drum and thumped out a rhythm according to the
position of the pegs.
Ludovico’s marriage to Beatrice d’Este, a girl of little more than
fifteen years, further isolated Leonardo from the court. Being almost a
child, Beatrice loved parties and festivities, and she surrounded
herself with people who catered to her frivolous whims. As a result so
serious a man as Leonardo was forced into the background of the court
life. He was called upon more and more to act as stage-designer while
his more important work went unnoticed. Because these entertainments
were easy for Leonardo to design, they did give him more time to work on
his giant equestrian monument of Francesco Sforza. Working one day on
the scaffolding surrounding the clay figure of his statue, Leonardo
heard a knock at his studio door.
“Come in,” he shouted as he climbed down. “The door’s open.”
Three peasants cautiously entered the room and quickly took off their
caps. One of them was holding a carefully wrapped bundle.
“Master Leonardo, we have brought you some shells we found on a ridge of
Monferrato. Remember, you asked us to bring anything we found that was
unusual?”
“Yes, Pietro. Thank you. Put them here on the table.”
Leonardo opened the bundle. He smiled when he saw the shells. He
remembered how, as a young boy, he had found seashells like these high
in the mountains. Leonardo questioned Pietro and his companions as to
where they had been found and under what circumstances. He gave them
some coins and, when they had gone, he looked among his growing
collection of notes and drawings on the shelves. It took some time for
him to find what he wanted, for the pages were in such confusion.
Finally, he sat down at the table with several of the sheets and,
putting the seashells in front of him, he began to make notes.
The shells were fossil shells but, thought Leonardo, their presence on
the high mountains of Lombardy could hardly be attributed to the great
flood as described in the Bible. In his notes, Leonardo cited the case
of the cockle which, out of water, is like the snail. It makes a furrow
in the sand and can travel in this furrow about three to four yards a
day. By such means, he calculated, it could not possibly have reached
Monferrato from the Adriatic in forty days (which was supposed to have
been the duration of the flood)—a distance of 250 miles. Nor were these
simply dead shells deposited by the waves—for the living creatures are
recognized by being in pairs, and these in front of him had certainly
been traveling in pairs. Consequently, they could have been left there
only when they were alive and the mountains were covered by the primeval
oceans. Moreover, Leonardo also described how living matter in
prehistoric times fell into the mud and died, and how this mud, as the
waters receded and years had passed, was changed into rock forming a
mold about the fossil—literally making a cast of its original living
appearance.
By such deductive reasoning and the testing of the evidence before him
against the common beliefs, Leonardo struggled to free the minds of men
from medieval superstitions and beliefs. Indeed, these medieval
superstitions existed everywhere. Astrologers, or men who told fortunes
by the position of the stars at a given moment; and necromancers, those
who by tricks of magic claimed to be able to talk to departed
spirits—these men profited from the ignorant. The Church, with its
preaching of devils and hells, provided the background against which
these fakers flourished.
Ludovico Sforza was himself a believer in such things. His own physician
and astrologer was a man by the name of Ambrogio da Rosate, who had such
influence over the court that he was given a post in the University of
Pavia, and his fame was so great that he was called upon to predict the
future of Pope Innocent VIII! Leonardo’s dislike of these men was
intense. He scorned the supernatural and asked men to look about them at
the real world and the real heavens. Observation and experiment—these
were Leonardo’s key words. But he was a lonely figure in his
thinking—like a man awake while the rest of the world slept.
At last the full-size model of the Sforza monument was nearing
completion. Ludovico had ordered it ready for exhibition in the
courtyard of the castle for yet another marriage festival that was soon
to take place. This time it was the marriage of his niece Bianca Maria
to Maximilian I of Germany. Leonardo and his assistants were busy with
the finishing touches on the monument, and with building a wagon on
which to carry it from the studio to the courtyard.
During these last months Leonardo had had to struggle with all kinds of
heavy loads. Already he had improved on pulleys by inventing a new kind
of tackle, and he also had utilized many kinds of levers. One of his
simpler discoveries for raising heavy weights was a jack which, in
appearance and principle, was the forerunner of our own automobile jack.
In 1493 when the clay model of the Sforza monument was completed, it was
put on the cart and wheeled to its place of exhibition where a curtain
was thrown around it. Again Milan was the host to a gathering of noble
courts, and this time Ludovico outdid himself in the display of luxury.
Tapestries hung from the buildings and rich carpets were laid down the
steps of the cathedral. Everything that Milan had to show was on
exhibition—even a crocodile.
But the most impressive sight of all was the unveiling of Leonardo’s
colossal statue. It rose in majesty against the red walls of the castle.
The name of Leonardo da Vinci was suddenly on everyone’s lips. As the
word of his artistic achievement spread from city to city, messages of
praise came pouring in. And, for a while the years of frustration and
failure to gain recognition melted away. Leonardo at forty-one had at
last achieved some success.
Now there was a breathing spell, and Leonardo returned to some of his
own projects. For a long time he had continued his observations of his
two favorite elements—air and water. To him they were related in their
movements. The birds flying in the currents of air and the fish swimming
in the flow of water seemed very similar to him. He had already designed
various instruments to tell him about the direction of wind and its
velocity, and he had also commenced to analyze the wing structure of
birds and bats. To soar through the air like a bird was an ancient dream
of man, yet for Leonardo it had become a passion. Ceaselessly, he
sketched the flights of birds, the flutterings of butterflies and
analyzed their flying patterns.
But to Leonardo, understanding the _dynamics_, or motion, of air was the
most important thing. He built an _anemoscope_, an instrument like a
weather-vane for telling the direction of the wind; and, he also
constructed several types of _anemometers_ for measuring the velocity or
force of the wind. One of these latter consisted of a thin rectangle of
metal hanging straight down in front of an upward-curving wooden arc.
This arc was marked off in units of measurement. When the wind blew, it
pushed the thin rectangle up the arc; thus, by noting at which gradation
it stopped, Leonardo could tell the velocity.
In addition, Leonardo at this time constructed a device which has been
compared to the modern instrument used for testing the weight-carrying
capacity of airplane wings. He fashioned a wing resembling a bird’s wing
and attached it to a lever so that it would be possible to lower the
wing by pushing rapidly down on the lever. This wing in turn was mounted
on a plank that was in weight equal to that of a human being. He then
calculated that two wings of this kind would have to be about twelve
meters wide and twelve meters long to raise a man and his machine
together. Another device resembling those found in airplanes today that
Leonardo constructed was an inclination gauge. He made this by
suspending a heavy ball on a cord within a glass bell. This ball was
then supposed to guide the flyer by telling him whether he was flying
level, diagonally, up, or down.
[Illustration: _One of Leonardo’s anemometers. The wind blew against
the strip of metal, pushing it up the curved gauge and thereby
measuring the force of the wind._]
[Illustration: _Leonardo’s inclination gauge, designed to guide a
man in flight. The ball in the glass cylinder was supposed to tell a
“flyer” whether or not he was flying level or tipped._]
To Leonardo, water was also a phenomenon that from his youth never
failed to excite his curiosity. The use of water power to run machines,
to irrigate fields and to carry boats inland was a subject that he never
ceased investigating. Out of his experiments at this time he constructed
a device for raising water to high levels. It was based on the geometric
spiral of Archimedes. He took a piece of gut, inflated it, and let it
dry. Then, covering it with a coat of wax to make it waterproof, he
wound it around a thin staff in a spiral. He put one end in a stream and
attached it by gears to a cogged water wheel; this set the long screw to
turning, and he was able to raise water from a low level to any height
he desired. With a multiple system of these screws he could raise water
in continuous circulation to the reservoirs on the highest towers.
In the year 1494, King Charles VIII of France crossed the Alps at the
head of an army of twenty-five thousand men. Now Ludovico, by a series
of diplomatic maneuvers, had allied himself with Charles and had, by
secret negotiation, actually invited the invasion. By such an alliance
he hoped to use Charles’ army to overcome the forces of the Pope which
stood in the path of Ludovico’s ambition to become the most powerful
ruler in Italy. Outwardly Charles was asserting his rights to the
Kingdom of Naples, but inwardly he dreamt of leading a crusade against
the infidels in the Holy Land. At the same time young Gian Galeazzo
Sforza, Duke of Milan, was dying. Ludovico desired this title for
himself; however, until Galeazzo was out of the way, he could not have
it. There were ugly rumors that young Sforza had been poisoned.
Moreover, in 1494, the Medicis—another powerful obstacle—were expelled
from Florence, and a republic was established.
Soon young Gian Galeazzo died, leaving a son, Francesco. This son was
the rightful heir to the Dukedom of Milan but Ludovico usurped the boy’s
claim and declared himself Duke of Milan. Now Ludovico was in a position
to await the impending battle between Charles and the Pope.
With such military and political ambitions in mind, Duke Ludovico now
assigned Leonardo the task of reviewing Milan’s defenses. Again Leonardo
submitted to Ludovico his plans for strengthening fortresses and designs
for new ones. The great architect Bramante was also assigned the task of
seeing to the city’s defenses, and for some time the two brilliant men
worked together.
Then, in the spring of 1494, Leonardo was sent to Vigevano where
Ludovico’s young wife was staying. This town was also the birthplace of
Ludovico, and Leonardo was given the job of designing and building a
small summer house and garden there for Beatrice. In addition, Leonardo
built a kind of “air conditioner” for her bedroom. It consisted of a
large waterwheel that cooled the air circulated into her room. Although
this ancient device had long been known to the Greeks and Romans,
Leonardo was the one who succeeded in perfecting it.
During this time Leonardo’s highly original mind was also at work on
other devices. One of these was an _odometer_, an instrument for
measuring the distance traversed by a vehicle. Dials, turned by a system
of gears attached to the wheel of a wheelbarrow, measured the distance
traveled as the barrow was pushed along the ground. In addition,
Leonardo conceived a kind of odometer to be used at sea; this consisted
essentially of a spinner that was towed by a ship which registered its
speed. Leonardo even invented an automatic spit operated by metal vanes
mounted in the chimney that revolved with the pressure of the hot air
rising from the fire—and a pair of large floating shoes for walking on
water!
In the meantime, Charles VIII of France had marched through Rome and
entered Naples. The conquest was without opposition. Charles was then
crowned King of Naples and all Italy was at his feet. Yet his triumph
was a short one. Ludovico, having used the king to get rid of his
enemies, now plotted against the king himself. He formed an alliance
with the Pope, Venice, Spain, and the German emperor. Charles, faced
with this league, hastily beat a retreat to France. Fighting his way to
the border, he there signed a peace treaty. Thus Ludovico had swept
Italy clean of all opposition and was now the most powerful prince in
the land.
Yet Ludovico was quick to realize that his position could only be held
by force and he set about strengthening himself and his allies. To
provide for more cannons, a hundred and fifty thousand tons of bronze
were sent to manufacturing works in Ferrara. This, however, included the
very bronze Leonardo needed for the casting of his equestrian statue,
and this is why the statue was never cast. Years of Leonardo’s work now
seemed to vanish overnight. Ludovico also needed large sums of money to
secure friends in high places and Leonardo’s own payments were suddenly
dropped. Forced again to worry about paying for his daily bread and for
his household and apprentices, he wrote letters to Ludovico complaining
of his lack of funds and asking for money that was owed him for work
done. He looked about for other commissions, but none were available.
Moreover, because he was still court painter to Ludovico, he was ordered
to paint the decorations of some rooms in the castle. But this was more
than Leonardo could take—he walked off the job without finishing it.