Leonardo Da Vinci by Kathleen Krull Page B

made from silk and reeds, wings with all combinations of strings and pulleys, and even a sort of helicopter with a whirling spiral of fabric above it. He puzzled about the best shape—should the flying object be a butterfly with four wings, a canoe with attachments, or more like a windmill’s sails? Whatever the shape, his flying devices anticipated sophisticated principles of aerodynamics, the branch of physics having to do with motion of the air.
    His ideas were the results of years of observing birds and sketching them. “The bird is an instrument operating through mathematical laws,” he believed—laws that could be figured out and applied to human flight. “As much pressure is exerted by the object against the air as by the air against the body,” he wrote—a startling observation not fully developed until Isaac Newton in the seventeenth century. He observed bats and flies equally, and was a great admirer of the aerial techniques of bees. He borrowed ideas from everyone before him who had ever contemplated flying.
    Historians agree that his contraptions were probably not technically workable, but they disagree as to whether he actually made or tested any flying machine himself. If he did, we have no record of it.
    Leonardo wasn’t always right. For example, he was intrigued by the study of physiognomy, the “science” of evaluating a person’s character by his or her facial features. Like everyone in his time, he believed that a person’s inner value was reflected on the outside. That is, good-looking people were virtuous, and ugly ones were bad. (Physiognomy was all the rage until completely debunked well after Leonardo’s day.)
    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