THE STORY OF EDMUND HALLEY
The great French astronomer Lalande considered Halley the greatest astronomer of his time. This opinion is still held. Halley’s “time” means the age of Kepler, Sir Isaac Newton, Flamsteed, Hevelius, and Leibnitz, all of whom achieved first rank in Astronomy.
Halley’s greatest achievement in Astronomy was the discovery that our solar system was but an atom in immeasurable space whence wandering stars could be caught within the influence of our Sun, our Earth and the other Planets swinging around our Sun.
Halley was the first to discover and to prove that the Comets that come within the vision of man have fixed periods of return. He made this discovery during the appearance of the great Comet of 1682, which has since been known by his name.
In his studies of the motions of Comets, of which Halley computed the orbits of twenty-four, he observed that a Comet of similar phenomena, recorded by Appian in 1531 and by Kepler in 1607, had swung through the same orbit as the Comet under his observation in 1682. Halley surmised from this that these Comets might be one and the same, whose intervals of return appeared to cover a period of seventy-five or seventy-six years. Halley’s surmise seemed to be confirmed by the recorded appearance of similar bright Comets in the years 1456, 1378, and 1301, the intervals again being seventy-five or seventy-six years.
Halley was deeply imbued with Newton’s new discovery of gravitation, for the publication of which Halley paid the expenses, so he brought the principles of Newton’s theory of gravitation to bear on his own new theory of the motions of Comets. He rightly conjectured that Comets were drawn to our Sun across the disturbing orbits of our planetary system, and that the comparatively small differences of one or two years in the recorded intervals of this one Comet (Halley’s Comet) were due to the attraction of the larger planets.
During the previous year, 1681, Halley computed that the Comet had passed near the planet Jupiter, the attraction of which must have had a considerable influence on the Comet’s motion. Making due allowance for this disturbing influence of Jupiter, he computed that the Comet would return to the vicinity of our Sun about the end of 1758 or beginning of 1759.
Halley did not live to see his prediction fulfilled (he died in 1742), but he wrote shortly before he died: “If this Comet should return according to our predictions about the year 1758, impartial posterity will not refuse to acknowledge that this was first discovered by an Englishman.”
All through the year 1758 the most noted astronomers of Europe were on the lookout for the return of the predicted Comet. One of these astronomers, Messier, looked for it through his telescope at the Paris Observatory every night from sunset to sunrise throughout that whole year. On Christmas night, 1758, the Comet was first seen by a German peasant near Dresden, who had heard about the Comet and was looking for it. He was a man of unusually good eyesight, yet his discovery was doubted until Messier, nearly a month afterward, at Paris, “picked up” the Comet with his telescope.
From that time forth this Comet, which returned in 1835, and is reappearing in this year (1910), has been known as Halley’s Comet.
EDMUND HALLEY.
Besides this achievement, Halley accomplished many other noteworthy feats in astronomy, such as his discovery of the proper motions of the fixed stars; his detection of the “long inequality” of Jupiter and Saturn, and of the acceleration of the moon’s mean motion; his theory of variation, including the hypothesis of various magnetic poles, with his suggestion of the magnetic origin of the aurora borealis; and his indication of a method still used for determining the solar parallax by means of the transits of Venus.
On the strength of these achievements, Halley for many years was elected to serve as secretary to the Royal Society. Commissioned as a Captain in the Royal Navy, he also commanded a vessel on a long cruise of exploration, and late in life he was made Astronomer Royal.
Although in his sixty-fourth year, he then undertook to observe the moon through an entire revolution of her nodes (eighteen years), and actually carried out his purpose. To appreciate the full significance of so painstaking an achievement it should be borne in mind that astronomical observations must be made in a temperature equal to that of the open air. Observatories cannot be heated because the heat would impair the accuracy of the instruments.
Great astronomers, like poets, are born, not made. Edmund Halley was one of these. At the age of seventeen he had already observed the change in the variations of the compass. At nineteen he was recognized as an astronomer of reputation, having supplied a new and improved method of determining the elements of the planetary orbits. His detection of considerable errors in the tables then in use led him to the conclusion that a more accurate determination of the places of the fixed Stars was indispensable to the progress of astronomy. With this end in view he set out on a voyage to the other side of the globe, St. Helena, where he undertook the task of making complete new observations of the entire Southern Hemisphere. Though the Heavens proved clouded he succeeded within two years in registering three hundred and sixty stars, a colossal achievement which won for him the title of the “Southern Tycho.” This was when Halley was barely of age.
(The famous astronomer Tycho Brahe, long before this had won his fame by mapping the stars of the Northern Heavens.)
No one could well have begun with prospects more remote from so high a career, for Edmund Halley was born in 1656, the son of a soap boiler in a shabby London suburb. From the refuse of rancid fat and lye the boy was rescued by friends, who procured for him a scholarship at Saint Paul’s school. By his brilliant attainments in mathematics he won another scholarship to Oxford University.
While at Oxford the youth published a treatise on the planetary orbits and argued the Sun’s axial rotation.
On his graduation from Oxford, the young would-be astronomer conceived the project of turning his attention to the southern Stars, of which no good observations had been made. Shortly before this time a Dutch astronomer, named Houtman, had observed these Stars in the island of Sumatra; and Blaeu, the best globe maker of the age, had used these new observations in the correction of his celestial globes. Halley, on examining these corrections, came to the conclusion that he himself could do better. He also concluded that the Island of St. Helena might be a better point for southern observations. His father, unable to pay the expenses of so long a trip, broached the project to some friends. The young astronomer was recommended to King Charles II. by Williamson and Jones Moore, and the King in turn recommended the youth to the Indian Company, which then had control over the island of St. Helena.
After this all was plain sailing. The India Company placed a ship at his disposition and promised him all the assistance he required. Young Halley provided himself with telescopes, and micrometers, and other instruments of the latest approved pattern. In November, 1666, at the age of twenty, he sailed for St. Helena. Among his luggage was a sextant of five and a half feet and a telescope twenty-four feet in length constructed under the supervision of Flamsteed, the Astronomer Royal.
Halley was disappointed in the climate of St. Helena. Frequent rains and a constantly hazy sky scarcely permitted any observations in the months of August and September. Notwithstanding these difficulties, he succeeded in observing and cataloguing some 360 Stars.
In addition to his work on the Stars, Halley made some investigations on the Moon’s parallax, combining his observations at St. Helena with those made in northern skies. He also evolved a new theory of the Moon’s motion, which proved of great aid in the determination of longitudes.
On November 7, 1677, Halley observed a transit of Mercury which suggested to him the important idea of employing similar phenomena for the calculation of the Sun’s distance.
Halley returned to England in November, 1678, and was hailed by his fellow astronomers as the “Southern Tycho.” He was elected a fellow of the Royal Society, and by the King’s command the degree of Master of Arts was conferred upon him by the University of Oxford.
Six months later Halley set out for Dantsic for a personal conference with Hevelius, the Polish astronomer. Halley wanted to satisfy himself as to the accuracy of observations claimed by Hevelius without the aid of a telescope. Halley convinced himself that the errors of the observations made by Hevelius were less than had been supposed, and did not exceed a minute of an arc. The two became life-long friends. Halley proceeded to other cities of Europe where there were observatories. In Paris he observed with Cassini the great Comet of 1680. This was the beginning of Halley’s special study of Comets.
Returning to England, the young astronomer married the daughter of Mr. Tooke, auditor of the Exchequer, with whom he lived harmoniously until her death, fifty-five years later. The young couple settled at Islington, where Halley erected an observatory of his own and engaged in constant lunar observations with a view toward finding a method for computing longitudes at sea.
Halley’s mind at the same time was busy with the momentous problem of gravity, upon which Isaac Newton was working then. Independently of Newton, Halley reached the conclusion that the central force of the Solar System must decrease inversely as the square of the distance. Having applied vainly to his fellow astronomers, Hooke and Wren, Halley in August, 1684, made a special journey to Cambridge to consult Isaac Newton, who confirmed his conjectures.
Halley and Newton became life-long friends. Halley had Newton elected to the Royal Society, and when Newton became too poor to pay his quarterly dues, Halley, through his influence with the leading members of the Society, had them remitted. It was Halley who encouraged Newton to put his momentous discovery and elucidation of the forces of gravity into permanent form in his “Principia,” the first volume of which, “De Motu,” was presented to the Royal Society at Halley’s suggestion.
In the proceedings of the Royal Society for December, 1684, there is an entry that “Mr. Halley had lately seen Mr. Newton at Cambridge, who had told him of a curious treatise ‘De Motu,’ which at Mr. Halley’s desire he promised to send to the Society to be entered upon their register. Mr. Halley was desired to put Mr. Newton in mind of his promise for the securing this invention to himself, till such time as he could be at leisure to publish it.”
Early in the following year Newton sent his treatise to the Society, to whom it was read aloud by Halley. This treatise “De Motu” was the germ of the “Principia” and was intended to be a short account of what the greater work was to embrace.
During the next two years Newton was hard at work on his “Principia,” while Halley was equally hard at work on his computations of the Comet of 1682, and on his theory of the orbits and the periodical returns of Comets which grew out of his observations.
On April 21, 1686, Halley read to the Royal Society his own “Discourse Concerning Gravity and its Properties,” in which he stated that his “worthy countryman, Mr. Issac Newton, has an incomparable treatise on Motion almost ready for the press,” and that the law of the inverse square “is the principle on which Mr. Newton has made out all the phenomena of the celestial motions so easily and naturally that its truth is past dispute.”
Shortly afterward Newton sent in the manuscript of his great work. The Society voted “that a letter of thanks be written to Mr. Newton and that the printing of his book be referred to the consideration of the council and that in the meantime the book be put into the hands of Mr. Halley.”
The truth was that the Royal Society, at that time, did not have money enough to print the book. The Society went through the empty form of “ordering” that the book be printed “forthwith,” but no printer was forthcoming until Halley himself undertook the publication of the great work at his own expense.
The delicacy of Halley’s feeling is revealed by his correspondence with Newton, in which he informed Newton that the book had “been ordered to be printed at the Society’s charge.” The preliminary delay about printing he explained to Newton “arose from the President’s attendance on the King, and the absence of the vice-presidents, whom the good weather had drawn out of town.”
Later Newton came to realize how much he owed to Halley in this matter. In his letters to Halley henceforth he always referred to his book as if it had been Halley’s book. When the great work was finished at last Newton wrote to Halley under the date of July 5, 1687: “I have at length brought your book to an end, and hope it will please you.”
The finished work contained a note to this effect: “The inverse law of gravity holds in all the celestial motions, as was discovered also independently by my countrymen Wren, Hooke, and Halley.”
The book was dedicated to the Royal Society, and to it was prefixed a set of Latin hexameters addressed by Halley to the author, ending with the well known line:
“Nec fac est propius mortali attingere divos.”
(“It is not given to a mortal to get in closer
touch with the gods.”)
Halley was fifty years old when he made his famous prediction of the return of the Comet of 1682. This was in his “Synopsis of Comet Astronomy,” which ended with these words: “Hence I may venture to foretell that this Comet will return again in the year 1758.”
Besides being an astronomer of the first class, Halley was also a good navigator. In 1698 he was commissioned a captain in the Royal Navy and was put in command of the King’s ship, “The Paramour Pink.” With this vessel he set out on a long cruise to the Pacific for the purpose of making observations on the laws which govern magnetic variations. This task he accomplished in a voyage which lasted two years and extended to the fifty-second degree of southern latitude, when the ice compelled him to turn back. On the return voyage his crew mutinied and his lieutenant sided with the mutineers. Halley quelled the mutiny by sheer force of personality, and returning to England got rid of his lieutenant. The results of his voyage were published in his “General Chart of the Variation of the Compass” in 1701. Immediately afterwards Halley set out on another King’s ship and executed by royal command a careful survey of the tides and coasts of the British Channel, an elaborate chart of which he published in 1702.
Next Halley was sent by the King to Dalmatia, for the purpose of selecting and fortifying the port of Trieste.
On Halley’s return to England, he was made Savilian professor of geometry at Oxford, and received an honorary doctor’s degree. He filled two terms of eight years each as secretary to the Royal Society, and early in 1720 he succeeded Flamsteed as Astronomer Royal.
He died on January 14, 1742, at the age of eighty-five in the full possession of his faculties, the foremost astronomer of the day and a man universally beloved and respected. His gravestone stands at the Greenwich Observatory.
Halley’s works fill several shelves in the library of the Royal Society. His fame is kept green by the periodical return of the wandering star known by his name.