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and anatomy—he was doing the first of his amazing drawings of the human body. The notebooks show the birth and development of Leonardo the natural philosopher, Leonardo the scientist.
    Leonardo did not compartmentalize his interests. To him, all knowledge was related. What he could learn in one field would help shed light on others. This attitude allowed him to cross-fertilize ideas in unusually creative ways. He thought of architecture, for example, as related to human anatomy. Buildings resembled bodies; the more he could learn about anatomy, the better an architect, or “building doctor,” he would be.
    In his notebooks, Leonardo’s goal was the direct study of nature. “Nothing can be found in nature that is not part of science,” he wrote. “Science is the captain, and practice the soldiers.”
    He decided early on that firsthand experience—using the five senses—was the means of discovering scientific truths. Experience to confirm theories was absolutely crucial: “The greatest deception men suffer is from their own opinions.” And direct experience was certainly more important than reading about others’ experience: “The grandest of all books, I mean the Universe, stands open before our eyes.”
    Leonardo valued knowing what great minds before him had thought, hence his ongoing self-education. But he didn’t necessarily accept their views. He called some scholars “stupid fools” for relying solely on the works of other men, for not thinking for themselves—investigating, questioning.
    The people who impressed him most were those inventors who discovered ways to control nature.
    In these new notebooks, Leonardo was thinking about science, and he was really thinking big. Inspired by Aristotle perhaps, he planned eventually to publish them as a grand encyclopedia of scientific knowledge, a system for understanding everything. His research and writing would occupy him for the next thirty-seven years. Like many of his projects, this one was never finished.
    But what he did accomplish was beyond magnificent. The result was thirteen thousand pages that scholars have divided into ten assortments.
    Leonardo was out to question everything. Like others during the Renaissance, he was discovering he could think for himself: “Anyone who argues by referring to authority is not using his mind but rather his memory.” He was taking the first steps—baby steps—toward the methods of modern science.

CHAPTER SEVEN
    Citizen of the World
    THE HEAVENS—or what we call outer space—were one of Leonardo’s obsessions in his notebooks, and his next job for Duke Sforza appealed to this interest.
    In 1490, the duke invited all of Italy’s elite to Milan for a great spectacle designed by Leonardo: the Feast of Paradise. The theme was to be astrology. Leonardo’s task was to create the party’s climax, a pageant called The Masque of the Planets. Perhaps it seems surprising to us that someone with such a critical mind accepted some of the ideas of astrology. But he did. Everyone did. However, Leonardo did scorn astrologers who made money by preying on foolish people. (He thought they should be castrated.) The visual possibilities of the astrological theme excited him to outdo himself. Hundreds of workers carried out his plans for the masque.
    At the stroke of midnight, after the dancing and feasting, the duke stopped the music. He raised the curtain on Leonardo’s latest creation: a gigantic revolving stage shaped like an enormous half-egg. Inside floated models of what were then considered the seven planets—Mercury, Venus, Mars, Jupiter, Saturn, the sun, and the moon. Earth was not considered a planet, and Uranus, Neptune, and Pluto hadn’t been discovered yet.

    Each planet revolved in its orbit, along with the signs of the zodiac illuminated by torches behind colored glass. Other torches flamed bright yellow, representing the stars. The effect was outrageous.
    At age thirty-eight, Leonardo had arrived. By now