Leonardo Da Vinci (6 page)

His text, although precise, witty, and often poet ic, was there to explain the elegant artwork, not the other way around. He was of the “one picture is worth a thousand words” school, and no one who has ever seen one of his notebook pictures could argue against that. To Leonardo the key to everything was
saper vedere
—“knowing how to see.” He wanted to be a sort of camera; he referred to “becoming like a mirror.” The way he illustrated anything was always clear, dramatic. He observed, then recorded.

Whether he was studying the mysteries of flight; the relationship of the sun, moon, and stars; or the formation of fossils, he followed a pattern: recording ideas, doing experiments, and confirming or changing his ideas. It was a pattern revolutionary for its day—Leonardo was working his way toward the scientific method.

CHAPTER NINE

The Fabulous Notebooks, Part 2

THE CRUMBLING PAGES of Leonardo’s otebooks are now five hundred years old. Ancient. How could they possibly be relevant to anything today?

Prepare to be surprised.

Leonardo was deeply interested in just about every area of science, but the three subjects he got the furthest on were anatomy, optics, and anything to do with water.

Medicine then was dominated by the twenty-two volumes of the ancient Greek Galen—who lived in the second century—and his theories about complexion and humors. The body had its own normal balance of four fluids, or “humors,” as they were called: blood, phlegm, yellow bile, and black bile. Each of the four humors could be reduced to its basic qualities: hot, cold, wet, and dry. People’s “complexions,” or temperaments, could be classified the same way: sanguine (optimistic), phlegmatic (low in energy), choleric (easily angered), and melancholy (sad). So could organs—phlegm was associated with the brain, black bile with the spleen, and so forth.

Disease was a result of a person’s “humors” getting out of balance for some reason. Diagnosis was a matter of doctors looking at the patient’s urine and deciding which humor was out of balance, with bloodletting and vomiting as the usual recommended remedies. The heavens affected the humors, so astrology played a vital part in diagnosis. Almost any symptom—and cure—could be connected to the alignment of the planets on that particular day. There was no need to know the actual structure of an organ or how it functioned.

Leonardo, inspired by painting people from the outside, was determined to understand exactly what went on inside. There are plans in his notebooks for a whole book based on his drawings, to be called
On the Human Body.
Incredibly ambitious, it was to deal with how the body worked from the time it was a fetus right up until the moment of death. He wanted to explain the nervous system, the muscles and veins and capillaries, how the five senses worked, the flow of blood, each bone of the skeleton, every organ . . . everything. He wanted to
see
, in detail, how it all worked so he could
understand
how it all worked.

He had been able to dissect some animals, but he was itching to do the real thing—human dissections. In anatomy classes at medical schools, cutting into a human body—even a dead one—was considered repugnant. Human dissections were rare and generally done on the bodies of recently executed criminals. It was more important to read Hippocrates (the “father of medicine,” born around 460 B.C.) and Galen (born in A.D. 129). Galen had dissected only dogs, pigs, and monkeys, yet his findings were applied to humans.

Historians disagree about exactly when Leonardo began dissecting human corpses. It’s possible he may have started in the 1460s while still at Verrocchio’s workshop, to satisfy the master’s demand for accuracy in painting. A famous professor of medicine, Marcantonio della Torre, may have smuggled Leonardo into a hospital in Florence and gotten him going on cadavers. (Some historians think Leonardo actually lived at the hospital for a time.)

After 1487, however, he became much more systematic and skilled in his study of human anatomy. He worked alone, by candlelight and only at night, to avoid prying eyes. In total, he dissected some thirty dead bodies, most of recently executed criminals or homeless beggars.

The more he learned, the more amazed he was at the intricacies of the human body: “I do not think that rough men, of bad habits and little intelligence, deserve such a fine instrument.”

It is hard to exaggerate the creepiness of Leonardo’s anatomy studies. There was no refrigeration or formaldehyde, so a corpse would have started to decay immediately. For his own sanity, Leonardo had to work as quickly as possible. But to get the information for his notebooks—the structure of the heart, for example, drawn from several different angles, and with the layers peeled back like the skin of an onion—he had to be on intimate terms with a corpse for as long as a week. Presumably he tried to schedule dissections for the colder winter months.

Here was an artist who didn’t like getting paint under his fingernails; how did he deal with being up to his elbows in guts and gore? He described it in his notebooks as disturbing, “living through the night hours in the company of quartered”—cut into pieces—“and flayed corpses fearful to behold.”

A serene person in general, Leonardo was cool, calm, and collected about witnessing what most people today could not bear to watch. Besides dissecting, he observed prisoners being tortured (he sketched their facial expressions) and executed. He did a quick but extremely realistic drawing of a nobleman’s corpse dangling from a noose. People with amputated or deformed limbs—anyone who “broke the rules” of proportion—fascinated him.

Saws and scalpels were his tools, some of them his own inventions. After separating the organs, he washed them thoroughly in water and a solution of calcium oxide, or caustic lime. Now, how to get them to keep their shape long enough for him to draw everything from three different angles? He came up with his own method: he injected the organs with wax.

For eyeballs (notoriously squishy and hard to cut), he had the brainstorm of coating them with egg white first. Then he boiled them, to make them firmer, like hard-boiled eggs.

He didn’t discard the bones and, in fact, was the first person to describe the human skeleton correctly. To discover how the parts of the body worked together, he would take a skeleton, insert copper wires where the muscles would go, and study how the contraction or relaxation of the wires caused different movements.

He once befriended a one-hundred-year-old man in a hospital, chatting for hours about his unusual longevity. Then the man died, and Leonardo immediately dissected his body to find out the cause of death. In describing the shriveled “artery that feeds the heart,” he may have written the first description of arteriosclerosis (the hardening of the arteries) in history. A short time after dissecting the old man, he dissected the body of a two-year-old child. He noted all the differences between the healthy young organs and those he found in the body of the old man.

More than a century ahead of his time, Leonardo theorized that the heart was a thick muscle that pumped blood. The heart, according to Galen, was not even a muscle at all, but some unique tissue unlike anything else in the body. And in Leonardo’s day, medical schools were teaching that blood came from two places—the liver as well as the heart.

Scientists then, and for centuries before, believed the valve to the heart to be a passive one. To test this, Leonardo created a glass model of the human aortic valve, inserting it into a cow’s heart filled with water. He then poured water into the valve with bits of paper mixed in so that he could follow the movement of this new water. With this experiment, he demonstrated the correct motions of the valve opening and closing: he proved the valve was active.

Leonardo was the first person known to make a drawing of a baby inside a womb, although it wasn’t entirely accurate. (The sacklike placenta was the wrong shape; it looked more like a cow placenta.) He was also one of the first to state that the mother and father have equal influence on an embryo—the belief of the day was that all characteristics of a baby came from the father.

Leonardo distilled his anatomy research into some 1,500 three-dimensional, multilayered drawings—again, he not only wanted to see but to record what he saw. The results were the first attempts at accurate depiction of human organs, muscles, and bones in history. His drawings have influenced medical textbooks to this day. There are cutaways and cross sections to show layers of an organ from various angles, as well as see-through images and sketches that portray as much motion as possible. His goal was to show the parts of the body in three dimensions. Five hundred years later, the drawings appear perfectly at home on the Internet.

Anatomy led to studies about vision and eyes, and Leonardo tried to break new ground in optics, although his knowledge was often primitive. In his day, many accepted Plato’s belief that we see because our eyes project rays of light onto objects, then the rays are reflected back to the eye in an image. But Leonardo questioned Plato: how could this be true? If it were, wouldn’t we see objects closer to us before we see ones farther away? But we don’t. Our eyes take in a scene all at once.

Leonardo observed that when a knife stuck in a table was made to vibrate, it gave the illusion of two knives. For Leonardo, this was more evidence that the eye receives images. It also told him that the eye finds it hard to distinguish images in quick succession.

As another test, Leonardo put a glass of water on a windowsill so that sunlight struck it. He observed that sunlight penetrated the glass and separated into different colors. His conclusion: the colors—the changes in the light—were a result of the water in the glass, not of what the eye was “projecting.” In this and other experiments, he was influenced by the eleventh-century Arab philosopher Alhazen, who wrote a collection of essays on optics called
Opticae Thesaurus.

Having mastered linear perspective as an artist also helped Leonardo develop his theories about vision. The principles of perspective set out by his old friend Alberti (who in turn stood on the shoulders of Brunelleschi) contained their own optical theories. But no artist was exploring vision as thoroughly as Leonardo was.

He kept revising his ideas until he came up with his own, simpler theory about light. From watching ripples made by stones tossed in a river, he leaped to the theory that light traveled in waves, and many believe he was the first person to realize this.

He was the first to write about the difference between peripheral (on the edge) and central vision. Also, he understood that a pair of eyes gathers information stereoscopically; the image seen by the left eye blends with the same image as seen by the right eye, allowing for depth perception. He discovered the reasons for farsightedness, and the principle behind the contact lens. He accurately listed the conditions under which the pupil of the eye changes in size. And he created a variety of optical devices, including what some believe was an early form of the telescope.

Leonardo had no great wealth to finance a laboratory; indeed, he brought the humblest of tools to his experiments. To test theories in optics and other fields, he used buckets, funnels, the eye of a needle, the ends of candles, metal boxes, sheets of paper pierced with holes, and the strings of a lute.

As with anatomy and optics, his notebook studies about water were breathtaking in their ambition. Pages had titles like “How to deal with rivers,” “Of the flow and ebb,” “Of what is water,” and “Of the sea, which to many fools appears to be higher than the earth which forms its shore.”

He studied all aspects of hydraulics (how to control water and use its power). He devised a scheme to divert rivers into canals and to reroute the Arno River, and invented various ingenious machines, among them drawings for an underwater vehicle resembling a submarine. He would spend hours on the banks of a river with his ear to a submerged tube, learning about how sound travels in water. Perhaps at some point he fell in—he even wrote swimming instructions and what to do if you were caught in a whirlpool.

Ripples and waves—how did they move? Leonardo dropped different-shaped objects into a bucket of water and saw that the ripples always formed in a circular pattern. He dropped in two objects at the same time to record the effect of merging ripples. His powers of observation were so keen that what he could see with the naked eye requires high-speed photography to record.

Watching waves—and depicting them in beautiful, curling drawings—led him into areas such as meteorology and geology. He seemed to have understood the principle of erosion, describing the way waves carry sand away and the way water “gnaws at mountains.” He learned the effect of the moon on the tides, speculated about continent formation, and analyzed the nature of fossil shells found on moun taintops. One would think that, with his artistic eye, he would have been most interested in the beauty of shells and fossils—their forms and patterns. But he was after something else: to understand why they were there at all.