A new biography celebrates the great artist’s more scientific innovations. Illustration by Tamara Shopsin; engraving from Hulton Archive / Getty

In Renaissance Florence, a number of designated boxes placed throughout the city allowed citizens to make anonymous denunciations of various moral crimes—in 1461, for example, the artist-monk Filippo Lippi was accused of fathering a child with a nun. But the crime that the government was really trying to control was sodomy, so notoriously prevalent that contemporary German slang for a homosexual was Florenzer. The common nature of the offense did not erase the threat of serious consequences. In 1476, Leonardo da Vinci, on the verge of his twenty-fourth birthday, was named as one of four men who had practiced “such wickedness” with the seventeen-year-old apprentice of a local goldsmith. There is little doubt that Leonardo was arrested. Although any time he may have spent in jail was brief, and the case was dismissed, two months later, for lack of corroborating witnesses, he had plenty of time to ponder the possible legal punishments: a large fine, public humiliation, exile, burning at the stake. It is impossible to know if this experience affected the artist’s habit, later cited as a mark of his character, of buying caged birds from the market just to set them free. But it does seem connected with the drawings he made, during the next few years, of two fantastical inventions: a machine that he explained was meant “to open a prison from the inside,” and another for tearing bars off windows.

These drawings are part of a vast treasury of texts and images, amounting to more than seven thousand surviving pages, now dispersed across several countries and known collectively as “Leonardo’s notebooks”—which is precisely what they were. Private notebooks of all sizes, some carried about for quick sketches and on-the-spot observations, others used for long-term, exacting studies in geology, botany, and human anatomy, to specify just a few of the areas in which he posed fundamental questions, and reached answers that were often hundreds of years ahead of his time. Why is the sky blue? How does the heart function? What are the differences in air pressure above and beneath a bird’s wing, and how might this knowledge enable man to make a flying machine? Music, military engineering, astronomy. Fossils and the doubt they cast on the Biblical story of creation. “Describe,” he instructs himself, “what sneezing is, what yawning is, the falling sickness, spasm, paralysis, shivering with cold, sweating, fatigue, hunger, sleep, thirst, lust.” He intended publication, but never got around to it; there was always something more to learn. In the following centuries, at least half the pages were lost. What survives is an unparalleled record of a human mind at work, as fearless and dogged as it was brilliant. And yet, despite occasional jottings—a grocery list, a book to be borrowed—these notebooks were in no way a diary or a personal journal; they contain none of the self-exploration of Augustine or Thoreau. Consumed with the desire for knowledge, Leonardo told us more about the world than seems possible, and next to nothing about himself.

His biographers have a hard time, at once starved and overwhelmed, tasked with constructing a man around the spectacular evidence of this disembodied mind. The paintings offer little more in the way of knowledge. Arguments persist even about the identity of the woman known as Mona Lisa, or why Leonardo never delivered the portrait to the husband who commissioned it, if indeed it was her husband who commissioned it. Our deepest sense of this most famous artist remains subject to change. The systematic publication of the notebooks, beginning in the late nineteenth century, tipped our understanding of his goals from art toward science, and opened questions about how to square the legendary peacefulness of his nature with his designs for ingeniously murderous war machines. More recently, the sensationalizing notion at the center of Dan Brown’s mega-selling book “The Da Vinci Code”—that one of the apostles depicted in Leonardo’s “The Last Supper” is actually, and visibly, a woman—connects him with our current preoccupation with gender fluidity. And this sense of connection isn’t entirely imposed. Leonardo’s works do show a striking fixation on androgyny, a term often used about his figures—a fixation that became unignorable with the rediscovery, in the nineteen-nineties, of a long-lost pornographic drawing. Is there nothing in Leonardo that can’t be found once we start looking? Who will he be for us today?

Walter Isaacson, at the start of his new biography, “Leonardo da Vinci” (Simon & Schuster), describes his subject as “history’s consummate innovator,” which makes perfect sense, since Isaacson seems to have got the idea for writing his book from Steve Jobs, the subject of his previous biography. Leonardo, we learn, was Jobs’s hero. Isaacson sees a particular kinship between the men because both worked at the crossroads of “arts and sciences, humanities and technology”—as did Isaacson’s earlier subjects, Benjamin Franklin and Albert Einstein. For all the unfamiliar challenges this book presents, in terms of history and culture, Isaacson is working a familiar theme. As always, he writes with a strongly synthesizing intelligence across a tremendous range; the result is a valuable introduction to a complex subject. He states right off that he takes the notebooks, rather than the paintings, as his starting point, and it isn’t surprising that he has the most to say when he slows his pace and settles into a (still brief) discussion of optics, say, or the aortic valve. The most sustained and engrossing chapter is largely devoted to Leonardo’s water studies—vortices, floods, cloud formation—and depends on one of the remaining complete notebooks, the Codex Leicester. The codex is currently owned by Bill Gates, who (as Isaacson does not point out) had some of its digitized pages used for a screen saver on the Microsoft operating system.

Isaacson’s Leonardo is a comparably modern figure, not merely “human,” as the author likes to point out, but a blithe societal misfit: “illegitimate, gay, vegetarian, left-handed, easily distracted, and at times heretical.” True enough, although Isaacson sometimes strains the relatability. His Leonardo is lucky to have been born illegitimate—because he was not expected to follow his father into the notary business—and lucky, too, to have been only minimally educated, in math and writing, rather than schooled in the Latin authors reserved for youths of higher rank. Untrammelled by authority, he was free to think creatively. As for being easily distracted, Isaacson warns that a young Leonardo today might well be medicated out of his creative urges. Beneath its diligent research, the book is a study in creativity: how to define it, how to achieve it. Isaacson’s answer, repeated like a mantra, lies precisely in the Leonardesque (or Jobsian) refusal to distinguish art from science, observation from imagination, and to attain a “combinatory creativity.” And this goal isn’t just the prerogative of genius; we can all approach it.

“I’d hate to think there’s a national discussion I’m not part of.” Facebook

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The most up-to-date if occasionally dismaying aspect of the book is its framing as a self-help guide, along the lines of “How Leonardo Can Change Your Life.” Isaacson explains that, while working on the book, he taught himself to be more observant, and it isn’t hard to respect his good intentions—he mentions sunlight, eddying water—until he writes, “When I saw the hint of a smile come across someone’s lips, I tried to fathom her inner mysteries.” One hopes that she shook him out of it. Fortunately, the book contains several clear and absorbing pages about the “Mona Lisa” ’s famously mysterious smile, particularly in relation to Leonardo’s studies of lip muscles, which he dissected, and drew, alternately, with skin on and skin off. Most important, Isaacson tells a powerful story of an exhilarating mind and life, which is rewarding even if it doesn’t set you on the path to enlightenment.