Leonardo da Vinci - Kathleen Krull [21]
He believed in a sixth sense, “common sense,” that ruled the other five senses. It was located, Leonardo said, in the center of the brain, “between sensation and memory.” Like others of his day, he speculated (wrongly) about which sections of the brain related to distinct skills, and thought that nerves from the brain led directly to all body parts.
He was the first person to depict correctly the relationship of the small and large intestines, but in general he failed to grasp the digestive process. He was clueless about peristalsis (rhythmic contractions of the esophagus that propel food along), believing instead that food moved because of intestinal gas. He thought the purpose of the appendix was to relieve gas pressure. (Actually, it has no known purpose.)
His drawings of the reproductive system, based on Galen, were imaginative, but more inaccurate than accurate. His knowledge of women’s anatomy lagged behind his knowledge of men’s. Doctors at the time believed that a woman’s uterus had seven chambers; Leonardo accepted this at first, though he soon realized it was false. But he never challenged the ancient belief that during pregnancy, a woman’s menstrual blood travels up the blood vessels to the nipples to become the mother’s breast milk.
Sometimes his theories were more poetry than science: “Tears come from the heart and not from the brain,” he once wrote. He believed that children who were born out of love and desire would become intelligent and beautiful, while “unworthy” children would result from relationships of reluctance or scorn.
Partly because he was so far ahead of his time, his descriptions of experiments and theories were sometimes confusing. The proper scientific vocabulary simply didn’t exist yet.
His desire to link things could lead him astray; he tried to make connections or parallels that didn’t exist. Leonardo believed that, just as the heart inside our body pumps blood, an “underground” heart was the source of rivers, instead of the water cycle we know today.
He was always stretching to formulate all-encompassing principles—“everything travels in waves,” “every natural phenomenon is produced by the shortest possible route,” “motion is the principle of all life.” Sometimes thinking big like this caused Leonardo to see patterns not always there. In his most famous drawing, the anatomically correct Vitruvian Man, he showed how the human body could be both a square and a circle. These shapes, he theorized, formed the basis of everything in the world. In this case, his theory was incorrect—another example of his seeing too much interconnection.
Sadly, he never gained mastery over mathematics, especially algebra. He even occasionally made basic mistakes in his arithmetic. He’d add up a list of numbers in his notebooks—and come up with the wrong total.
But in whatever he was investigating, Leonardo accepted nothing at face value. His theories were based on observation, documentation, and proof: “There is nothing more deceptive than to rely on your own opinion, without any other proof.”
In the thousands upon thousands of pages in the notebooks, he was thinking like a scientist.
CHAPTER TEN
“I Have Wasted My Hours”
FROM 1500, WHEN Leonardo turned orty-eight, until just before his death in 1519, he was essentially homeless. Without even a country to ground him, he lived at times from day to day. A steady, sympathetic patron was once again proving elusive.
Traveling about with his small household made up of Salai and Luca Pacioli, he tried, within his limited means, to act the part of a refined aristocrat. He had the best horses. His servants were always well dressed, and he himself wore brocade and other fine fabrics.
In his trunks were precious cargo, forty books and his secret notebooks, except when he thought he might be in personal danger. Then he would leave them in a monastery,