by Carl Sagan
Halley fulfilled his royal mandate by publishing “A New and Correct CHART Shewing the VARIATIONS of the COMPASS in the WESTERN AND SOUTHERN OCEANS as observed in ye YEAR 1700 by his Maties [Majesty’s] Command.” The map contained a dotted-line convention that Halley devised to indicate points of equal variation in the Earth’s magnetic field, the method that remains in use in magnetic maps today. Halley expanded his Atlantic chart to a world chart that remained in print, through many editions, for a century.
With the appearance of these magnetic charts and his already published work on the physics of wind, monsoons, and evaporation of seawater, Halley can truly be termed the founder of modern geophysics, a fact which was recognized by the Royal Society in 1957 during the International Geophysical Year, when it named its permanent scientific base in Antarctica Halley Bay.
—COLIN RONAN, EDMOND HALLEY: GENIUS IN ECLIPSE, 1969.
Note: The ominous and epochal finding of a hole in the ozone layer was made in 1985 by a British scientific team on the shores of Halley Bay.
Halley’s third and final voyage as Captain of the Paramour, in 1701, kept him closer to home. His purpose was to study the tides of the English Channel, although it has been suggested that his hidden agenda included a reconnaissance of the French coast on the eve of the War of the Spanish Succession. The following year, Queen Anne dispatched Halley on diplomatic missions to European monarchs.
When Halley returned to England he was, perhaps to his surprise, offered a Savilian Professorship at Oxford—but of geometry, not astronomy. Thirteen years after his vitriolic campaign against Halley’s appointment to another Savilian chair, Flamsteed wrote a carping letter to a mutual friend, denying both Halley’s suitability and his prospects for the chair, and complaining, “He now talks, swears, and drinks brandy like a sea captain.” But by now Halley was too well-respected for Flamsteed’s venom to do much harm, and in 1704 he was appointed.
His inaugural lecture was a loving tribute to the geometrical achievements of his colleagues. Newton, of course, was singled out for the most lavish praise. Halley dedicated much of his tenure as Savilian professor to a rediscovery of the ancient founders of geometry, among whom was one Apollonius of Perga, a mathematician and astronomer who flourished during the second half of the third century B.C. In the great city of Alexandria, Apollonius did for conic sections what Euclid had done for geometry: he was the first to describe the parabola, the hyperbola, and the ellipse. Halley, who used the properties of these curves to determine the orbits of the comets, wished to repay his debt to Apollonius by giving the work of the ancient mathematician new life. But no copies of Apollonius’ work survived in the original Greek—largely due to the burning of the Library of Alexandria. The only copies were in Arabic. So at age forty-nine Halley taught himself Arabic. He worked initially in collaboration with David Gregory, the man who had been given the Savilian chair in astronomy for which Halley had been passed over. When Gregory died soon after the Apollonius project had begun, Halley carried on alone in a task that had already defeated a number of full-time Orientalists. But Halley succeeded where they had failed, and he astonished the premier Orientalist of the day with his accuracy and insight. Knowing the geometry probably helped.
During this same period, he reedited the most interesting papers from the Philosophical Transactions into a three-volume work for a popular audience. He thought nonscientists might be curious about the physical and biological world.
Meanwhile, the miserable Flamsteed remained at the Royal Observatory at Greenwich in his capacity as Astronomer Royal, where he was expected to share his observations with the astronomical community. This he steadfastly refused to do. For years he was permitted this clear dereliction of duty, but by 1704 it had become intolerable. Newton, by now president of the Royal Society, visited him at Greenwich in an attempt to discover the state of the observations. After thirty years as Astronomer Royal, Flamsteed had hardly published a thing. Newton was given the impression that Flamsteed’s life’s work, The British History of the Heavens, was nearing completion, and Newton returned to London to arrange for publication. But Flamsteed was lying; he was years from finishing.
The Astronomer Royal’s procrastination and arrogance brought out the worst in Newton. There is plentiful evidence in the correspondence of both men attesting to an active mutual hatred. Nor were they each other’s only enemy. There were legitimate grievances on both sides, but Newton had the upper hand and used it shamefully. For the next ten years he seemed to derive an ugly pleasure from torturing Flamsteed, who was by this time ill and desperate.
Halley was now presented with the perfect opportunity to avenge himself against the man who had, through unreasoning malevolence, campaigned to harm him. But vengeance was one of the few subjects that failed to engage Halley’s interest. Indeed, at Newton’s request, he worked on the manuscript of The British History of the Heavens himself, correcting errors, making many needed calculations, and helping to see the book through publication—but all this against Flamsteed’s explicit wishes. In June 1711, Halley wrote to him,
… Pray govern your passion, and when you have seen and considered what I have done for you, you may perhaps think I deserve at your hands a much better treatment than you for a long time have been pleased to bestow on
Your quondam friend, and not yet profligate enemy (as you call me),
Edm. Halley
The book extended the map of the northern skies from 1,000 to 3,000 stars, including many too faint to be seen without a telescope, and was prized by astronomers for centuries. Nevertheless, Flamsteed was enraged by Halley’s version of the Historia Coelestis, which appeared in 1712. By 1714 he had managed to burn nearly every copy in existence. The official version, with the word Britannicae appended to the title, was not published until 1725, in a posthumous edition.
Despite Flamsteed’s contrary opinion, a review of the correspondence suggests that Halley had remained circumspect toward Flamsteed until the latter’s death in 1719. Then fate intervened to thrust on Halley a kind of satisfaction that he had denied himself, appointment as Flamsteed’s successor. Halley became Astronomer Royal. But when he arrived to take over his duties, he found the Royal Greenwich Observatory denuded of astronomical instruments; they had all been Flamsteed’s personal property, his widow said. It was true. He had bought every last sextant and quadrant with his own money.
Halley was now sixty-three years old and as curious and passionate about science as ever. To read his paper, An Account of the Extraordinary METEOR seen all over England on the 19th of March 1719, is to encounter a kind of naked enthusiasm which has been effectively eliminated from the literature of science today. He begins by announcing “This wonderful luminous Meteor,” which, he laments, “it was not my good Fortune to see.” But others saw it and he gives their accounts. Sir Hans Sloan, vice-president of the Royal Society, was one of the lucky ones. Without warning, he sees something in the night sky much brighter than the Moon, first near the Pleiades, and then down below Orion’s Belt. It was so bright that Sir Hans is forced to avert his eyes. He estimates that it moved across 20 degrees of the sky in about half a minute or less. All in all, pretty thorough testimony from a man unprepared for astronomical observation. But Halley is dissatisfied: “It were to be wished,” he chides, “that Sir Hans had more especially regarded the Situation of the Track of this Meteor among the fixt stars, and let us know how much it past above the Pleiades and how much under the Belt of Orion.… ” Halley cannot help himself; he is desperate to know, and his desire is even greater than his celebrated kindness. He wants to know everything about the meteor: its altitude, velocity, what sound it made, how big it is, of what it is made. We feel privileged today to know the answers to his questions (Chapter 13) and wish it were possible to share them with him.
At the age of sixty-five, in an act of consummate optimism, Halley undertook an ambitious study of the eighteen-year cycle of solar eclipses. Halley, the inventor of the actuarial table, coul
d not have been unaware of the improbability that he would live long enough to complete the project. He confounded the odds, and finished when he was eighty-four.
His productivity and his longevity were extraordinary in another respect. Physicists are sometimes said to be like mayflies, with only a brief creative period; indeed, a strikingly large fraction of major discoveries are made before the age of thirty-five. This is more true for theoretical than for experimental physics, and more true for physics than for astronomy. Perhaps past thirty, the mind loses some of its capacity to conceptualize on a grand scale. But in the last decades of Halley’s life, he made major theoretical advances in our understanding of nature on its grandest scale: the universe. He discovered that the so-called fixed stars actually moved with respect to one another. The discovery may have been stimulated by his work on Flamsteed’s book. It took another hundred years of instrumental development in astronomy before Halley’s discovery of stellar proper motion could be confirmed. In another paper of his last years, he anticipated the discoveries of a much later time, arguing for a limitless universe without a center. Halley was, at last, guilty of believing in infinity.
Mary Halley died when Halley was eighty years old. Shortly after, he suffered a stroke and the loss of his son. Despite these blows, he continued making astronomical observations and attending scientific meetings until a few weeks before his death on January 14, 1742, at the age of eighty-six. His last words were a request for a glass of wine. He drank it while sitting in a chair. When the glass was drained, he died without a sound.
He had wished to lie next to Mary forever. His daughters had this tribute (translated here from its original Latin) engraved on their parents’ tomb:
Under this marble peacefully rests, with his beloved wife, Edmond Halley, LL.D., unquestionably the greatest astronomer of his age. But to conceive an adequate knowledge of the excellencies of this great man, the reader must have recourse to his writings; in which almost all the sciences are in the most beautiful and perspicacious manner illustrated and improved. As when living, he was so highly esteemed by his countrymen, gratitude requires that his memory should be respected by posterity. To the memory of the best of parents their affectionate daughters have erected this monument, in the year 1742.
Edmond Halley was not just a man who discovered a comet. In fact, discovering a comet was one of the few things he never did.
There is a widely held belief that the price of deeply understanding the complexities of nature is paid out in the currency of alienation. Something like an inverse square law exists, it is said, between scientific genius and the capacity for love. If the life of Isaac Newton is pointed to as the most dramatic illustration of this theorem, then the life of his friend Edmond Halley, who more than anyone else made manifest Newton’s genius, may be offered as its most inspiring exception.
He seems to be not one but all mankind’s epitome.
—HERBERT DINGLE, THE HALLEY LECTURE, OXFORD UNIVERSITY, 1956
*Although some hint of this idea can be found in the writings of Aristotle (who firmly rejected it) and Seneca (who, as we have seen, embraced the suggestion of Apollonius of Myndos that comets move as the planets do).
*A cloth imbued with wax, and used as a bandage.
*Richard S. Westfall, Never at Rest (Cambridge University Press, 1980).
*Cassini had suggested something similar, but, as we now know, for apparitions of quite different comets, which have not, at least so far, returned.
*i.e., both clockwise and counterclockwise as seen from a vantage point high above the North Pole.
†In fact, because he fit the orbits to open parabolas, the aphelia were effectively at infinity.
*Or Paramour. Spelling conventions were less rigid in Halley’s time.
CHAPTER 4
The Time of the Return
Guardian and friend of the moon, O Earth, whom the comets forget not,
Yea, in the measureless distance wheel around and again they behold thee!
—SAMUEL TAYLOR COLERIDGE, HYMN TO THE EARTH, 1834
China invaded Tibet and Turkestan; French troops seized the Ohio Valley; Britain declared war on France; Prussia defeated Austria, whereupon Austria defeated Prussia; a Russian army occupied Germany; and an Indian revolution against the British army of occupation was ruthlessly suppressed. In such respects, the decade of the 1750s was almost indistinguishable from many others. But it was also a time of enlightenment. Diderot’s Encyclopaedia was published in France and Samuel Johnson’s Dictionary in England; Hume, Rousseau, and Voltaire wrote seminal works; Bach died and Mozart was born. Lomonosov founded the University of Moscow. The Prussian Academy of Sciences in Berlin and the first mental asylum in London both opened their doors; Tristram Shandy was being written; Hokusai was born in Tokyo; and an obscure Virginia surveyor named George Washington married a widow named Martha Custis.
In science, this was the decade that would end with the return of a comet—if Edmond Halley’s prediction could be believed. In the first half of the decade, two extraordinary scientific works were published, each bearing on the nature of comets, and each presenting a view of the universe surprisingly in advance of its time.
Drawing of the nucleus, coma, and tail of the Great Comet of 1680, and the nuclei of the Earth and four other comets. From Thomas Wright of Durham, An Original Theory or New Hypothesis of the Universe, ed. by Michael A. Hoskin (London, 1750, and New York, 1971). Courtesy Michael A. Hoskin.
Thomas Wright of Durham was an astronomer by temperament, although entirely self-taught. Born in 1711, in the north of England, the son of a carpenter, he was prevented from continuing his early schooling “by a very great impediment of speech.” He also seems to have been expelled from school on account of his behavior. He described himself as “very wild and much addicted [to] sport.” Following the practice of the time, at age thirteen he was apprenticed—to a clockmaker, where he spent so much of his time poring over the astronomical literature that his father thought him mad. Unlike Edmond Halley’s father, Wright’s apparently attempted to influence his son’s course of study by burning his books. Shortly after, the young man was dismissed from his apprenticeship, the culmination of a considerable scandal; fell in love with a clergyman’s daughter, but discovered his plans for a secret marriage “prevented, and Miss lock’d up”; and arranged, in his anguish, a passage to the West Indies, but was prevented from embarking by his outraged father.
Thomas Wright of Durham as depicted in an engraving in Gentlemen’s Magazine, January 1793. The portrait is circumscribed by a serpent with its tail in its mouth, symbolizing eternity. Ann Ronan Picture Library.
With this promising start, he taught himself surveying and navigation, became a tutor to the children of the aristocracy, turned down a professorship at the Russian Imperial Academy in St. Petersburg, and began writing books on astronomy. The most extraordinary of them, called An Original Theory of the Universe, was just that. Published in 1750, it is the first modern statement of the true nature and geometry of the Milky Way—not a road of the gods, not divine milk splashed across the heavens, not an architectural support holding up the sky, but a flat disk of stars each like the Sun, all suspended in the ocean of space. From the time of Democritus, there had been a few people who had guessed that the Milky Way was made of individual stars too faint and distant to be seen individually; and this notion had been vindicated by Galileo with the first small telescope. So by Milton’s time it was possible for a poet to describe the Milky Way as a Galaxy, “powder’d with stars.” But the idea of the Milky Way as a flattened concentration of stars in which the Sun is embedded was first proposed by Wright. He even imagined that the stars revolved about the center of the Galaxy “as do the planets around the Sun.”
While there are mystical elements in Wright’s writings, and certainly not all that he proposed in his Original Theory has stood the test of time, his vision of the Milky Way is a landmark in the history of astronomy. The work is the more remarkable
since its author had never acquired a formal education. This vision—a galaxy full of moving stars—turns out, as we shall see later, to be central to any understanding of the nature and origin of comets.
But comets were discussed in their own right in An Original Theory. Using his talents as draftsman and surveyor, Wright designed elegant diagrams of the solar system, with comets much in evidence. He delighted in showing the cometary orbits tabulated by Halley in their correct sizes and orientations (see this page), providing many readers with a jolting first look at the comparatively small scales of the planetary orbits.
With this fine beginning, he attempted to draw the comets to scale as well, from the observations available in his time. The result is shown on this page. For scale, A represents the Earth; and C, D, E, and F, the nuclei of the comets of 1682, 1665, 1742, and 1744, respectively. In fact, what was being measured in Wright’s day—and this is still largely true in our own—was not the nucleus of the comet, but the coma. The nucleus—Wright used the term—is the bright solid object at the center of the comet, the presumed source of the fine particles or gas that constitute the comet’s tail. But the coma, the cloud of matter around the nucleus, shields it from our view. The almost total absence of detail in Wright’s drawings of cometary “nuclei” could have provided a hint that the nucleus is surrounded by coma. The nucleus might also be much smaller than the coma; it might even be too small to make out any details on, even if it were not enveloped in a shroud of matter. As the figure indicates, the comas of comets in the vicinity of the Earth can be as large as the Earth, or even larger.