Leonardo da Vinci - Kathleen Krull [19]
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.
Leonardo grasped the principle that flooding water deposits layer upon layer of sediments (soil and sand), which turn into rock. At the same time, rivers erode rocks and carry their sediments to the sea, in a continuous cycle. He wrote, “The stratified stones of the mountains are all layers of clay, deposited one above the other by the various floods of the rivers.”
In Leonardo’s day, there were two theories about why fossils and shells were found in rocks on the tops of mountains. Some people believed the shells were carried there by the biblical Flood; others thought that