Newton · 1666
The plague year and the apple
In the summer of 1665 the plague took London and Cambridge in the same season, and the colleges sent the undergraduates home. Isaac Newton went back to his mother's house at Woolsthorpe in Lincolnshire, where he had been born in the year his father died, and stayed for most of two years. He was twenty-two. He had read mathematics for one year. In the orchard at Woolsthorpe, by the tradition his niece Catherine Conduitt told to William Stukeley in 1726, he watched an apple fall from a tree and asked himself, in earnest and not for a moment, why it should fall straight down rather than sideways or up. The notebook from those two years contains the binomial theorem, the method of fluxions, the first formulation of the inverse-square law of gravity and the decomposition of white light. Cambridge calls them the *anni mirabiles*. Stukeley's account is the only first-hand source for the apple, and Stukeley wrote it down sixty years after the fact.
It is the back of summer in the orchard at Woolsthorpe Manor. The afternoon is hot. The apples are early Pewseys and they are coming down a week ahead of season. He is twenty-three years old. He is sitting on a bench against the south wall of the house with a notebook on his knees and a quill in his right hand and the inkpot wedged between two stones at his feet. The college has been shut for the plague since the August of last year. He is supposed to be reading Wallis. He has been reading Wallis. He has been reading Descartes and Euclid and the De Analysi he has been writing himself for seven months in a cipher his mother cannot read.
An apple drops out of the tree above him onto the bench, six inches from his hand.
He does not move. He looks up at the branch. He looks down at the apple. He looks at the bench under the apple, and he looks at the ground under the bench, and he looks at the well in the kitchen yard and the wall and the roof of the house behind the wall and the moon, which is up in the afternoon sky, faint behind the heat.
He thinks: it has fallen straight down. It has not fallen sideways. It has not gone up.
He thinks: the moon is also a body and it does not fall.
He thinks: or it falls and it does not arrive.
He thinks: if the apple is pulled by the earth and the moon is pulled by the earth, they are pulled by the same thing. The moon is further. The pull is weaker. How much weaker. By the square of the distance.
He puts the apple on the bench beside him. He opens the notebook to a clean page. He writes the date in the corner, August or September, he does not bother with the day. He writes a single line of the cipher. He underlines it twice. He sits in the orchard for the next forty minutes without writing anything else, watching the moon come up.
By the end of the year he has the binomial theorem in general form, the calculus he calls fluxions, the prism experiment that takes white light apart into its colours, and the inverse-square law worked out far enough that he can compute the moon's orbit from it and check the answer against Tycho. He puts the inverse-square work in a drawer. He will leave it there for eighteen years.
The apple story has its first written telling in 1726, in William Stukeley's Memoirs. Stukeley is sitting under a lime tree at Newton's Kensington house, and Newton, eighty-three years old and three months from his death, is telling him about the orchard at Woolsthorpe and the afternoon the question opened up. Newton's niece Catherine Conduitt told the same story to Voltaire and to John Conduitt and to a half-dozen others in the years immediately after his death. The apple was a real apple from a real tree, a Pewsey or a Flower of Kent, in a real orchard that has been replanted three times since and is still there. The tree fell in a storm in the 1820s and the National Trust took grafts. What is attested in the chronicle is leaner than the legend: a man at the back of one summer in 1666 saw a thing fall, and asked the right question of it, and went indoors to do the arithmetic. The thread held.