There, he recorded in his diary, he found “all the towne almost going out of towne, the coaches and waggons being all full of people going into the country.” He stopped awhile at the Cross Keys tavern—long enough to enjoy the company of the barman’s wife—but by the next day he was ready to decide “whether to send my mother into the country today.” She didn’t want to go, but “because of the sicknesse in the towne, and my intentions of removing my wife,” he finally managed to put her on a coach that would take her east, toward Cambridgeshire.

London’s exodus had the predictable result: refugees from the capital carried the contagion into the countryside. Some towns barred their gates to keep the disease at bay. It didn’t work. In Cambridge, the blow fell on July 25. John Morley, five years old, was found dead at his home in the parish of the Holy Trinity. There were dark spots on his chest. When the plague inspectors came, they found Morley’s younger brother already showing black irruptions on his face. The child was taken to the pesthouse, where he died ten days later.

Ann Fisher, a child from All Saints Parish, died on the same day, confirming that the disease had spread beyond a single neighborhood. More cases followed, more deaths, and from there Cambridge followed London’s pattern. Businesses shuttered. Stourbridge Fair, one of the greatest open-air markets in Europe, was canceled. The university scattered. On August 7, the College of the Holy and Undivided Trinity acknowledged the obvious and decided to pay its members an allowance whether or not they remained in residence after that date. No record for Isaac Newton appears in Trinity College’s accounts for the extra stipend. The newly passed bachelor of arts had already fled, traveling the sixty miles north and a little west to Woolsthorpe.

THERE HE REMAINED for almost two years, cut off from every other scholar or mathematician. The isolation suited him. “In those days,” he would recall half a century later, “I was in the prime of my age for invention & minded Mathematics & Philosophy more than at any time since.”

Those twenty months are now known as Newton’s annus mirabilis—his miracle year. In that brief time, he would solve several problems at the leading edge of contemporary mathematics. The decks thus cleared, he would go on to invent whole new ideas, laying the foundations of what we now call calculus, the mathematical tool used to analyze (among much else) change over time—where a cannonball might be at any instant, or a planet, for example. He then turned to what we now call physics, beginning with mechanics, the study of bodies in motion. Here too, before he could uncover specific results he had to work out fundamental concepts, mastering the first modern understanding of inertia, for example, an idea he first encountered in Descartes’s work, and thinking deeply about what it means to be a force—two ideas so essential to the future development of our understanding of the physical world that he in large measure had to construct them himself before he could go any further. Then came the first glimpses of what would become his theory of gravity and all that flowed from that epiphany. And, still not done, he dove further into an investigation of light, color, and optics that would yield his first great public triumphs. The record does not reveal when—or whether—Isaac Newton slept.

This seemingly superhuman accumulation of ideas during his plague-imposed exile has created a mythology of superhuman genius, conjuring worlds of thought out of country air. It’s not quite that simple, of course. Newton’s definitive biographer, Richard Westfall, points out that the program for the work to come was laid down in 1664, when Newton, just twenty-one, was still enrolled at Trinity College. That’s when he first dove into the mathematical inquiries that would dominate his first several months back home, and when he produced an extraordinary series of forty-five queries in which he grappled with fundamental issues of time, matter, motion, and much more. He didn’t need the plague, that is, to launch him into his comprehensive assault on the whole of natural philosophy. But it is true that when he reached the farm he was ready to move beyond anything Cambridge could teach him. He was “consistently concerned,” as Westfall wrote, “to develop general procedures” that would, in the end, produce not just new mathematics but a new way of thinking about how math insinuates itself throughout the material world.

One of the first problems to catch his eye was how to calculate the area marked out by a curve.

Who invented the stethoscope?