Sky & Telescope March 1986 [antikvár]

Newton, Halley, and the CometOwen Gingerich, Harvard-Smithsonian Center for AstrophysicsIN 1696 Britain faced a coinage crisis.For years the irregular edges of hand-struck coins had been systematically clipped by thieves, who made a precarious living by selling the tiny silver chips. Finally, the government introduced a new style of machine-pressed coin, which on larger denominations included a legend around the edge: DECUS ET TUTA-MEN, "a decoration and a protection." The letters and mill marks prevented the edges of the coins from being trimmed.Naturally, it was very difficult to get enough new change into circulation at the beginning of the coinage reform. Yet one reason why the new system finally succeeded was that the newly appointed Warden of the Mint took the work very seriously. He did not accept the post merely as a well-deserved sinecure.The new officer was none other than the former Cambridge University professor, Isaac Newton. His great Principia and the invention of calculus behind him, the eminent mathematician-physicist had apparently tired of science, university politics, and life in a provincial college town. He was ready for a change of pace and threw himself into the work at the mint, then located in the Tower of London. There his day began at 4 a.m. with a mighty din when horse-powered presses began stamping out 50 coins per minute.Yet it was during those years at the mint that two interesting Newtonian scientific achievements occurred. The first concerned a challenge problem issued by the Swiss mathematician Johann Bernoulli in June, 1696. Later called the brachisto-chrone problem, the challenge was to find the curve by which a bead, sliding down a frictionless wire, would get from point A to point B in the shortest time (see illustration on facing page). Its solution requires what is now termed the calculus of variations, and Bernoulli and his friend Leibnitz supposed that only their form of the newly invented calculus was powerful enough to find the solution. Although Bernoulli addressed the test problem "to ail the mathematicians of Europe," the real quarry was apparently Newton himself. Perhaps Bernoulli and Leibnitz doubted that the strange man who had abandoned science to run the mint was really such a genius after all.230 Sky Telescope, Aiarc/i, 7955Left: Sir Isaac Newton graces the frontispiece of the third edition of his Principia a masterpiece that might never have been written had it not been for Edmond Halley. Illustration courtesy of the author. Right: Halley as depicted in the frontispiece of his Astronomical Tables. Reproduced courtesy Cambridge University Observatories.Newton received his copy of the challenge from the Royal Society on January 29th. That day, recounted his niece, "Sir I. N. was in the midst of the hurry of the great recoinage [and] did not come home until four from the Tower very much tired, but did not sleep till he had solved it." The next morning her uncle sent the solution to the society, and it was printed anonymously. When Bernoulli saw the solution he exclaimed, "Ex ungue leo-nem!" "By the claw, the lion is revealed." There was no question as to the author's identity.In the same year that Newton became Warden of the Mint and in which Bernoulli issued the challenge, another Newtonian triumph was in the making. At the Royal Society meeting of June 3, 1696, member Edmond Halley produced the results of a calculation on the comets of 1607 and 1682, "which are in all respects alike, as to the place of the Nodes and Perihelia, their Inclinations to the plain of the Ecliptick and their distances from the Sun, whence it was highly probable, not to say demonstrative, that these were but one and the same Comet, having a period of about 75 years, and that it moves in an Elliptick Orb about the Sun."Newton and Halley were stamped out of widely different molds. The former was an absent-minded professor, a near recluse, with (in Wordsworth's lines) "a mind forever voyaging through strange seas of thought, alone." The other was a congenial bon vivant and an astronomer who, in the opinion of straitlaced John Flamsteed, the Astronomer Royal, "swore like a sea captain." What course of events brought these gifted geniuses together?Newton was born at Woolsthorpe Manor near Grantham on December 25, 1642. At age 18 he entered Trinity College in Cambridge, where he was what we might today call a work-scholarship student. Then came the plague year, when the university shut down, and during that enforced 18-month vacation Newton planted all the seeds of his future fame: mechanics, optics, the calculus, and gravitation. '*I was in the prime of my age for invention," he later said, "and minded Mathematics and Philosophy more than any time since."When the university reopened, Newton returned to Cambridge and began a swift climb up the academic ladder. First he was elected a fellow at Trinity College;