1There was a young man of London named Edmond Halley, the son of a rich soap-maker, and he was everything the scholar of Woolsthorpe was not. He was cheerful, and liked company and wine. At twenty he left the university without waiting for his degree and sailed to a rock in the southern ocean. He lived there a year in the fog, mapping the stars that cannot be seen from Europe, the same strange stars that the hungry sailors had wondered at a hundred and fifty years before.
2By that time everyone who studied the sky had read Kepler. They knew that the planets go on long rounds with the sun to one side. What no one knew was why.
3Halley had worked out one thing for himself. If the sun pulls on the planets, then by Kepler's third rule that pull must weaken with distance in a certain way: twice as far, a quarter as strong. But he could not go the other way round. Suppose there is such a pull. What road will a planet then take? Will it be Kepler's long round, or something else? If it came out to the long round, the whole sky would be explained with one stroke. He could not do the sum.
4One winter afternoon he sat in a London coffee-house with two older men of the Royal Society. One was Sir Christopher Wren, who was building the city again after the fire. The other was Robert Hooke, a small, bent, quick man, the cleverest maker of experiments in England and the touchiest.
5Halley owned that the sum had beaten him. Wren said it had beaten him too. Hooke said that he had solved it, long ago.
6Wren asked to see it.
7Hooke said he would keep it back a while, so that others might try and fail, and then they would know how to value it.
8Wren had built enough to know a wall with nothing behind it. He offered a prize on the spot: a book worth forty shillings to whichever of them brought him the proof within two months.
9Two months went by. Hooke brought nothing.
10And in that same spring a grief fell on Halley. His father went out walking one morning and did not come home. Five weeks later his body was found beside a river, miles away. No one ever learned how he died.
11It was August before he was free. He took the coach to Cambridge, to ask the one man in England he thought might know.
12He had met Isaac Newton only once or twice. The man was forty-one now, a professor. He had built a new kind of glass for looking at the stars, with a mirror in it, and shown the world his work on colours, and Hooke had attacked it so sharply that Newton had sworn to print nothing more.
13Halley found him in his rooms by the college gate. Then Halley asked his question, as lightly as he could. Suppose the sun draws a planet with a force that weakens as the distance multiplied by itself. What curve would the planet follow?
14Newton said at once that it would be an ellipse: Kepler's long round.
15It is told, by one who had it from Newton in his old age, that Halley was struck with joy and amazement. He asked how Newton knew. Newton said that he had reckoned it out.
16Might Halley see the reckoning? Newton turned over the heaps on his table, and looked in a chest, and looked in another. He could not find it. He would work it again, he said, and send it.
17In November a messenger brought him nine sheets, written small.
18Halley read them standing up. It was all there. The pull, the long round, the sweeping line, the rule of the times: Kepler's three laws, not as three things found in the sky, but as one thing that had to be so.
19Now see what kind of man he was. He was twenty-eight and had a name to make. He had just been shown that another man, who cared nothing for being known, had done what he himself could not. He saw only that the thing must not be lost again in that room. He made Newton promise to set it down in full, and to let the Royal Society have it.
20That promise opened a door in the solitary man that had been shut since the plague year. He began to write, and could not stop.
21For eighteen months he hardly left his rooms. His servant told afterward how it was. He seldom went to bed before two or three in the morning. He forgot to eat; the dishes went back untouched, and if he was reminded he would take a bite or two standing.
22He took out the old box. He went back to the reckoning of the apple and the moon, the one that had answered only pretty nearly. There was a new measure of the earth now, made with care by a Frenchman. He put it in.
23The two numbers met. Not nearly. As exactly as any measure could tell.
24After that he seems to have gone at the world like a man who has found that one key opens every door in the house. He tried it on the moons of Jupiter that the Florentine had seen, and it fitted them. He tried it on the tides. Twice a day the sea rises at London Bridge and no one had ever known why; he showed it was the moon and the sun drawing the water, and reckoned how high.
25A cannonball, the tide, the moon, a wandering star. He weighed them all on the same scale.
26He sent it to Halley part by part, in Latin, and Halley read each sheet and corrected the printer's slips. It was to be three books in one, and the Royal Society voted, proudly, that it should be printed.
27Then it came out that the Royal Society had no money. It had lately spent all it had on printing a grand history of fishes, with fine pictures, and no one would buy it.
28So Edmond Halley paid. His father's death had left the estate in knots, and he had a wife and small children. He paid the printer out of his own pocket, for another man's book. The Society, in thanks, gave him his wages that year in unsold copies of the history of fishes.
29And then, with the first part at the printer, it nearly ended.
30Hooke stood up at the Society and said that the rule of the weakening pull was his. Newton had it from him, in letters, years ago, and ought to say so in print.
31There was a grain of right in it. Hooke had guessed the rule. But he had not been able to prove a line of it, and a guess is not a proof.
32Newton did not see the grain. When the word reached Cambridge he fell into one of the cold furies that frightened those who knew him. He wrote to Halley that he would hold back the third book altogether. That was the book that showed the plan of the whole world.
33Halley had put his savings and two years of his life into this. He sat down and wrote the most careful letter of his life. He told Newton, gently, that no one of sense believed him; that the whole Society was waiting for the third book, and it would be a great pity to lose it. He did not once say, I have paid for this.
34The third book came. But Newton went through his pages first and struck out Hooke's name nearly everywhere it stood. The man who weighed the moon could not weigh a rival fairly.
35Yet years before, in a milder season, he had written to this same Hooke a line that has outlived both their quarrels. It is in a letter that can still be read:
36"If I have seen further it is by standing on the shoulders of giants."
37He knew who they were. The old canon, who moved the earth and feared to say so. Tycho, with his metal nose and thirty years of cold nights. Kepler, who would not round off the truth. The Florentine with his glass and his rolling bronze balls. And behind them the measurers of Alexandria and the lamp-keepers of Baghdad, whose books the goldsmith's presses had saved. Each had handed up one stone. He was the first who stood high enough to see over the wall.
38The book came from the press in the summer, three years after the visit to Cambridge. It had a long Latin name that means the mathematical beginnings of the knowledge of nature. Halley wrote a poem for the front of it.
39Few could read it. Those few could check it, line by line, and they did, in every country, and it stood.
40And hear what Newton did not claim. He had shown how the drawing between bodies acts, and by what measure. He did not say what it was. He wrote plainly that he had not been able to find its cause, and that he would not make one up. He left that door standing open with a sign on it, for whoever came after. And being a believer to the bone, he added that so fair an order of sun and planets and comets could only have come from the counsel of a wise and mighty Being. He did not think he had put God out of the sky. He thought he had read a little of His handwriting.
41Now hear the end of Halley's part, for he has one more thing to do.
42Comets had always been the terror of the heavens. They came from nowhere, with their tails like swords, and went into nowhere, and kept no times. Kepler's mother had led him up a hill to see one.
43But if the one rule held for everything, it must hold for them too. When he was past forty, Halley went through all the old records of comets he could find and reckoned the road of each by Newton's way.
44Three of the roads were the same road. The comet he had seen with his own eyes as a young man. One that Kepler had watched from Prague. And one before that, seen in the time of the old canon. They lay about seventy-six years apart.
45So it was not three comets. It was one, going round the sun on a long round so stretched that it was out of sight for a lifetime at a time. And if it had come three times, it would come a fourth.
46He printed the year. It would be back, he said, about the end of the year fifty-eight.
47The year he named was fifty-three years off. He knew he would not see it. He wrote only that if it came back as he said, he hoped those who lived then would remember it was an Englishman who first told of it.
48He set down a date on the far side of his own Last Door, where anyone could hold him to it. If he was wrong, his name would be a joke. If Newton was wrong, the whole great book would fall with him. He staked it all on a point of light that no living person would see until both of them were dust.
49Newton died, an old man full of honours. Halley died, at eighty-five, in his chair, having asked for a glass of wine and drunk it. Sixteen more years went by.
50In the winter of the year he had named, the astronomers of Europe were searching the sky with the best glasses made. They did not find it. It was found by a farmer in a village of Saxony named Palitzsch, who had taught himself the stars after his day's work. He went out to his field on Christmas night, the feast on which Newton had been born, and there in the Fishes was a small smear of light that had not been there before.
51It had kept the appointment. A dead man had told the heavens where to be, and they were there. No one was afraid of it. People stood in the cold streets of every city and pointed, and called it by his name, and they call it so still.
52Go back now to the summer the book was printed, for there is one thing left to tell.
53Halley sent copies out as fast as the binder could finish them. Some he had carried across the narrow sea to Holland. For in those days Holland was the one corner of Europe where a book was simply a book. The old Florentine's last work had been printed there when no Catholic land dared. In Amsterdam alone there were more presses than in all of some kingdoms, and no one stood over them.
54In that city a child had been born the very year the Florentine's forbidden book came out. He grew up to make his living grinding lenses, such lenses as the blind glass-master of Murano would have passed with his thumb. His own people cast him out for the questions he asked, and he answered no one in anger, and went on asking. He died of a sickness of the lungs, in a rented room in another Dutch town, ten years before Newton's book was printed.
55He never saw the book of Newton. But he had come by his own road to the question that it leaves a careful reader holding.
56If one law runs through the apple and the moon and the tide, where does it stop? Is there a wall somewhere, with the law on this side and something else beyond? Or is there no outside at all?
57The friar of Nola had asked whether the sky has an edge. The lens-grinder asked whether nature has one. He wrote down his answer in a book that his friends printed in Amsterdam the year he died, with no name on it, for it was more dangerous than anything in this one.
58A crate of Newton's book came up the canal in the autumn rain and was opened in a bookseller's back room. The lamp was lit. Someone cut the first pages.
59One fire, many hands. Now hear what came after.