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1665 to 1666Reputable source · 2 sourcesWell documented

Newton's Plague-Year Annus Mirabilis

Cambridge closes for the plague and a 23-year-old works out gravity, optics, and calculus at home

On the timeline · around 1665 to 1666 · Institutions and InstrumentsNew Bodies, New MethodInstitutions and InstrumentsNewton's Plague-Year Annus Mirabilis16581662166416661668167016721674

Quick facts

Scientist
Isaac Newton, 1643 to 1727
Location
Woolsthorpe Manor, Lincolnshire
Period
1665 to 1666, during the Great Plague closure of Cambridge
Key insight
Inverse-square law of gravitational attraction

What happened

Isaac Newton earned his bachelor's degree from Trinity College, Cambridge, in April 1665, just as an outbreak of plague forced the university to close. Newton returned to his family's farm at Woolsthorpe in Lincolnshire, and over roughly two years there, still under 25, he made foundational advances across four fields at once. He worked out early versions of his three laws of motion and the law of centrifugal force for circular motion, and in 1666 had the insight that the same force pulling an apple to the ground might extend far enough to hold the Moon in orbit around the Earth, counterbalancing its centrifugal tendency to fly outward. Combining this idea with Kepler's third law, he deduced that this force must weaken with the square of the distance, the inverse-square law. In the same period he developed his method of fluxions, his version of calculus, and began the experiments on light and prisms that would become his later work on optics.

Why it matters

Newton kept almost none of this to himself for two decades, mentioning fragments in letters but publishing nothing comprehensive until the 1680s. The delay meant that when Gottfried Leibniz independently developed his own version of calculus in Paris in the 1670s, publishing it before Newton published his own, the stage was set for a bitter priority dispute that would consume the last decades of both men's lives.

How we know

Newton's own later recollections of the plague years, along with surviving notebooks and manuscripts from Woolsthorpe, document the sequence of discoveries; MacTutor's biography of Newton traces the timeline of the inverse-square deduction and the early laws of motion to this 1665 to 1666 period from these primary sources and subsequent scholarly reconstruction.

Sources

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