The plague year and the apple

Some discoveries are made by men sent into the world to make them. Others are made by a young man sent home from school because the city he lived in had begun to die. The great revolutions of thought rarely arrive in the lecture hall. They arrive in a kitchen garden, in a back orchard, in the long second summer of a quarantine, when a mind that has been crowded for a year is suddenly given a season of empty afternoons and the loan of its own attention.

THE COLLEGE SHUT

In the August of 1665 the plague that had taken London in the spring reached Cambridge by the carriers' road, and the Master of Trinity sent the undergraduates home. Isaac Newton, twenty-two years old, lately a sub-sizar, one year into the reading of mathematics, packed his Wallis and his Descartes and his Euclid and the half-written notebook he kept in a cipher his mother could not read, and took the road north to Lincolnshire. He went back to the stone farmhouse at Woolsthorpe where he had been born on Christmas morning of 1642, a child so small, his mother said in later years, that he could have been put into a quart pot. His father had been dead three months by then. The grandmother had reared him. The mother had remarried, gone away, come back widowed. The house at Woolsthorpe was a sheep farm and an orchard and a kitchen garden, and that summer it became, without anyone calling it so, the freest laboratory in England.

THE LONG QUIET

He stayed eighteen months. There were no lectures. There were no disputations. There were no fellows to write up to, no chapel bell, no terms. There was a south-facing room with a window that gave on the orchard, and a quill, and as much paper as Hannah Smith his mother would buy him from the chandler at Grantham. He read Wallis's Arithmetica Infinitorum in the spring and re-read it in the summer, and somewhere between the two readings he saw how to generalise the binomial expansion to fractional and negative exponents. He read Descartes's Geometria in the Schooten edition and put it down and began, by the autumn, to write his own. He bought a prism at the fair at Stourbridge and shut himself in the dark room and let a single thread of sunlight come through a hole the width of a pin, and watched the white thread come apart on the wall into a band of colours that no one before him had thought to call a spectrum. He gave the colours names. He counted them. He counted them again. The notebook filled.

AN AFTERNOON IN THE ORCHARD

It is the back end of summer, 1666. The apples are early, a Flower of Kent or a Pewsey, and a few are coming down ahead of season. The afternoon is hot in the way Lincolnshire afternoons are hot, dry on the high ground and slow over the valley. He is sitting against the south wall of the house with the notebook open on his knees. He is not, by his own later account to Stukeley, doing anything in particular. He is thinking, as he has been thinking on and off for a year, about the motion of the moon. An apple falls out of the tree above him. He hears it before he sees it. It lands in the grass a yard from his foot.

He looks up at the branch. He looks down at the apple. The branch is perhaps fifteen feet above the ground; the apple has come straight down. It has not gone sideways. It has not gone up. It has not hung in the air a moment and then chosen a direction. The earth has pulled it, and the pull is along the line that joins the apple to the centre of the earth, and the apple, having no power to resist, has come along that line. This is not new. Aristotle knew apples fall. What is new, what arrives in the back of the head as a small clean sentence and stays there, is the moon, hanging faint and white in the afternoon sky above the orchard wall. The moon is a body. The moon, by every property he can name, should fall as the apple falls. The moon does not fall. Or, he thinks, slowly, watching the pale disc above the chimney, the moon falls and does not arrive: it falls along a curve that is the same curve as its orbit, and the earth turns out from under the fall, and the fall and the turning together are what we have been calling the month. If the apple is drawn by the earth and the moon is drawn by the earth, they are drawn by one cause. The moon is further off. The cause is weaker. By how much weaker. He thinks, and the orchard is very quiet, and he thinks: by the square of the distance. He does not stand up. He does not call to anyone. He puts the apple on the bench beside him, opens the notebook to a clean page, writes the month in the corner because he has lost the day, and sets down one line in his own cipher. He underlines it twice. He sits in the orchard another forty minutes with the moon coming up, and does not write anything else.

THE WORK INDOORS

What follows that afternoon takes the rest of the year, and is done quietly, in the room with the south window, on rag paper bought a quire at a time. He works out the inverse-square law in the form that will, eighteen years later, become the third book of the Principia. He computes the period of the moon from the law and compares it with the figure Tycho left in the Astronomiae Instauratae Progymnasmata, and finds the two agree, by his own phrase in the memorandum of 1714, pretty nearly. He extends the binomial theorem. He sets out the method he calls fluxions and his successors call the calculus. He returns to the prism, and writes the experiment up in the form that will, five years later, scandalise Hooke before the Royal Society. He tells nobody. He puts the gravitation papers in a drawer in the press at Woolsthorpe and does not take them out again until Halley comes asking, in the August of 1684, what curve a planet would trace under an inverse-square force; and Newton, by Halley's account, answers without hesitation, an ellipse, and is asked how he knows, and says he has calculated it. He has, he says, mislaid the calculation. He will look for it.

THE COUSIN IN THE PARLOUR

Sixty years later, in April 1726, an antiquary named William Stukeley calls at the house in Kensington where Sir Isaac is living out his final spring. Newton is eighty-three. He is three months from his death. The day is warm and they take their dinner in the garden, under a lime tree, and Newton tells Stukeley, as we were drinking tea, the story of the orchard. It was occasion'd by the fall of an apple, as he sat in a contemplative mood. Why should that apple always descend perpendicularly to the ground, thought he to himself. Stukeley writes it down that night. The same story has been told already, in slightly different words, by Newton's half-niece Catherine Conduitt, who told it to Voltaire and to her husband John Conduitt and to anyone in the years after the funeral who came to ask. The apple is real. The tree is real. The orchard at Woolsthorpe has been replanted three times since and is still there. The tree fell in a storm in the 1820s and the gardener kept the stump, and the National Trust has taken grafts from the regrowth, and the grafts have been planted on every continent on which scientific men have wanted a relic.

THE RETURN

What is attested in the chronicle is leaner than the legend. A young man, sent home from a plague, spent eighteen months in his mother's orchard reading what he had brought with him and noticing what fell. By the end of the eighteen months he had, in the cipher notebook now in Cambridge University Library, the binomial theorem in general form, the method of fluxions, the decomposition of white light, and the inverse-square law of gravitation worked far enough to check it against the moon. He published none of it for nearly twenty years. Cambridge re-opened in the spring of 1667. He went back to Trinity, took his fellowship, took the Lucasian chair two years later, and the rest of the life is the life the world knows: the Principia, the Mint, the knighthood, the long presidency of the Royal Society, the quarrels with Hooke and Leibniz, the funeral at Westminster Abbey with the dukes carrying the pall. None of it would have happened in that shape if the colleges had not been shut for the plague, and the road north not been open, and the orchard at Woolsthorpe not been there waiting, with a south wall to lean against and a Flower of Kent in fruit a week ahead of season.

Fortune is said to favour the prepared mind. It is more honest to say she favours the unhurried one. The discoveries that change the shape of the world are not, as a rule, snatched in the corridor between two appointments. They are made by a young man with a quire of rag paper and eighteen months in which no bell is going to ring. The tree at Woolsthorpe still stands, or its grandchild does, leaning a little eastward on the same patch of ground, the apples coming down each August a week ahead of season into the same grass.