HALLEY (Dr. Edmund)

, a most eminent English mathematician, philosopher and astronomer, was born in the parish of St. Leonard, Shoreditch, near London, Oct. 29, 1656. His father, a wealthy citizen and soap-boiler, resolving to improve the promising disposition observed in his son, put him first to St. Paul's school, where he soon excelled in all parts of classical learning, and made besides a considerable advance in the mathematics; so that, as Wood observes, he had perfectly learnt the use of the celestial globe, and could make a complete dial; and we are informed by Halley himself, that he observed the change of the variation of the magnetic needle at London in 1672, one year before he left school. In 1673 he was sent to Oxford, where he chiefly applied himself to mathematics and astronomy, in which he was greatly assisted by a curious apparatus of instruments, which his father, willing to encourage his son's genius, had purchased for him. At 19 years of age he began to oblige the world with new observations and discoveries (which he continued to do to the end of a very long life), by publishing “A Direct and Geometrical method of finding the Aphelia and Excentricity of the planets.” Besides various particular observations, made from time to time upon the celestial phenomena; he had, from his first admission into college, pursued a general scheme for ascertaining the true places of the fixed stars, and so to correct the errors of Tycho Brahe. His original view in this was, to carry on the design of that first restorer of astronomy, by completing the catalogue of those stars from his own observations; but upon farther enquiry, finding this province taken up by Hevelius and Flamsteed, he dropped that pursuit, and formed another; which was, to perfect the whole scheme of the heavens, by the addition of the stars which lie so near the south pole, that they could not be observed by those astronomers, as never rising above the horizon either at Dantzick or at Greenwich. With this view he left the University, before he had taken any degree, and embarked for the island of St. Helena in Nov. 1676, when he was only 20 years of age, and arrived there after a voyage of three months. He immediately set about his task with such diligence, that he completed his catalogue, and, returning home, landed in England in Nov. 1678, after an absence of two years only. The university of Oxford immediately conferred upon him the degree of A. M. and the Royal Society of London elected him one of their members.

In 1679 he was pitched upon by the Royal Society to go to Dantzick, to endeavour to adjust a dispute between Hevelius and Mr. Hooke, concerning the pre-| ference as to plain and glass sights in astroscopical instruments. He arrived at Dantzick the 26th of May, when he immediately, in conjunction with Hevelius, set about their astronomical observations, which they closely continued till the 18th of July, when Halley left Dantzick, and returned to England.

In the year 1680 he undertook what is called the grand tour, accompanied by his friend the celebrated Mr. Nelson. In the way from Calais to Paris, Mr. Halley had a sight of a remarkable comet, as it then appeared a second time that year, in its return from the sun. He had the November before seen it in its descent; and he now hastened to complete his observations upon it, by viewing it from the royal observatory of France. His design in this part of his tour was, to settle a friendly correspondence between the two royal astronomers of Greenwich and Paris; and in the mean time to improve himself under so great a master as Cassini. From thence he went to Italy, where he spent great part of the year 1681; but his affairs calling him home, he then returned to England.

Soon after his return, he married the daughter of Mr. Tooke, auditor of the exchequer, and took up his residence at Islington, where he set up his tube and sextant, and eagerly pursued his favourite study: in the society of this amiable lady he lived happily for five-andfifty years. In 1683 he published his Theory of the Variation of the Magnetical Compass; in which he supposes the whole globe of the earth to be one great magnet, having four magnetical poles or points of attraction, &c. The same year also he entered upon a new method of finding out the longitude, by an accurate observation of the moon's motion. His pursuits it seems were now a little interrupted by the death of his father, who having suffered greatly by the fire of London, as well as by a second marriage, into which he had imprudently entered, was found to have wasted his fortunes. Our author soon resumed his pursuits however; for in the beginning of 1684 he turned his thoughts to the subject of Kepler's sesqui-alterate proportion; when, after some meditation, he concluded from it, that the centripetal force must decrease in proportion to the square of the distance reciprocally. He found himself unable to make it out in any geometrical way; and therefore, after applying in vain for assistance to Mr. Hooke and Sir Christopher Wren, he went to Cambridge to Mr. Newton, who fully supplied him with what he so ardently sought. But Halley having now found an immense treasure in Newton, could not rest, till he had prevailed with the owner to enrich the public with it; and to this interview the world is in some measure indebted for the Principia Mathematica Philosophiæ Naturalis. That great work was published in 1686; and Halley, who had the whole care of the impression, prefixed to it a discourse of his own, giving a general account of the astronomical part of the book; and also a very elegant copy of verses in Latin.

In 1687 he undertook to explain the cause of a natural phenomenon, which had till then baffled the researches of the ablest geographers. It is observed that the Mediterranean sea never swells in the least, although there is no visible discharge of the prodigious quantity of water that runs into it from nine large rivers, besides several small ones, and the constant setting in of the current at the mouth of the Streights. His solution of this difficulty gave so much satisfaction to the Society, that he was requested to prosecute these enquiries. He did so; and having shewn, by accurate experiments, how that vast accession of water was actually carried off in vapours raised by the action of the sun and wind upon its surface, he proceeded with the like success to point out the method used by nature to return the said vapours into the sea. This circulation he supposes to be carried on by the winds driving these vapours to the mountains; where being collected, they form springs, which uniting become rivulets or brooks, and many of these again meeting in the valleys, grow into large rivers, emptying themselves at last into the sea: thus demonstrating, in the most beautiful manner, the way in which the equilibrium of receipt and expence is continually preserved in the universal ocean.

He next ranged in the field of speculative geometry, where, observing some imperfections in the methods before laid down for constructing solid problems, or equations of the 3d and 4th powers, he furnished new rules, which were both more easy and more elegant than any of the former; together with a new method of finding the number of roots of such equations, and the limits of the same.

Mr. Halley next undertook to publish a more correct Ephemeris for the year 1688, there being then great want of proper ephemerides of any tolerable exactness, the common ones being justly complained of by Mr. Flamsteed.—In 1691 he published exact tables of the conjunctions of Venus and Mercury; and he afterwards shewed one extraordinary use to be made of those tables, viz, for discovering the sun's parallax, and thence the true distance of the earth from the sun.—In 1692, our author produced his tables for shewing the value of annuities on lives, calculated from bills of mortality; and his universal theorem for finding the foci of optic glasses.

But it would be endless to enumerate all his valuable discoveries now communicated to the Royal Society, and published in the Philos. Trans. of which, for many years, his pieces were the chief ornament and support. Their various merit is thrown into one view by the writer of his eloge in the Paris Memoirs; who, having mentioned his History of the Trade-winds and Monsoons, proceeds in these terms: “This was immediately followed by his estimation of the quantity of vapours which the sun raises from the sea; the circulation of vapours; the origin of fountains; questions on the nature of light and transparent bodies; a determination of the degrees of mortality, in order to adjust the valuation of annuities on lives; and many other works, all the sciences relating to astronomy, geometry, and algebra, optics and dioptrics, balistics and artillery, speculative and experimental philosophy, natural history, antiquities, philology, and criticism; being about 25 or 30 dissertations, which he produced during the 9 or 10 years of his residence at London; and all abounding with ideas new, singular, and useful.”

In 1691, the Savilian professorship of astronomy at Oxford being vacant, he applied for that office, but without success. Whiston, in the Memoirs of his own Life, tells us from Dr. Bentley, that Halley “being thought of for successor to the mathematical chair at| Oxford, bishop Stillingfleet was desired to recommend him at court; but hearing that he was a sceptic and a banterer of religion, the bishop scrupled to be concerned, till his chaplain Bentley should talk with him about it, which he did. But Halley was so sincere in his insidelity, that he would not so much as pretend to believe the christian religion, though he thereby was likely to lose a professorship; which he did accordingly, and it was then given to Dr. Gregory.”

Halley had published his Theory of the Variation of the Magnetical Compass, as has been already observed, in 1683; which, though it was well received both at home and abroad, he found, upon a review, liable to great and insuperable objections. Yet the phenomena of the variation of the needle, upon which it is raised, being so many certain and indisputed facts, he spared no pains to possess himself of all the observations relating to it he could possibly come at. To this end he procured an application to be made to king William, who appointed him commander of the Paramour pink, with orders to search out by observations the discovery of the rule of variations, and to lay down the longitudes and latitudes of the English settlements in America.— He set out on this attempt on the 24th of November, 1698: but having crossed the line, his men grew sickly; and his first lieutenant mutinying, he returned home in June 1699. Having got the lieutenant tried and cashiered, he set sail a second time in September following, with the same ship, and another of less bulk, of which he had also the command. He now traversed the vast Atlantic ocean from one hemisphere to the other, as far as the ice would permit him to go; and having made his observations at St. Helena, Brazil, Cape Verde, Barbadoes, the Madeiras, the Canaries, the coast of Barbary, and many other latitudes, he arrived in England in September 1700; and the next year published a general chart, shewing at one view the variation of the compass in all those places.

Captain Halley, as he was now called, had been at home little more than half a year, when he was sent by the king, to observe the course of the tides, with the longitude and latitude of the principal head-lands in the British channel; which having executed with his usual expedition and accuracy, he published a large map of the channel.

Soon after, the emperor of Germany resolving to make a convenient harbour for shipping in the Adriatic, captain Halley was sent by queen Anne to view the two ports on the coast of Dalmatia. He embarked on the 22d of November 1702; passed over to Holland; and going through Germany to Vienna, he proceeded to Istria: but the Dutch opposing the design, it was laid aside; yet the emperor made him a present of a rich diamond ring from his finger, and honoured him with a letter of recommendation, written with his own hand, to queen Anne. Presently after his return, he was sent again on the same business; when passing through Hanover, he supped with the electoral prince, who was afterward king George the 1st, and his sister the queen of Prussia. On his arrival at Vienna, he was the same evening presented to the emperor, who sent his chief engineer to attend him to Istria, where they repaired the fortifications of Trieste, and added new ones.

Mr. Halley returned to England in Nov. 1703: and the same year he was made professor of geometry in the university of Oxford, instead of Dr. Wallis then just deceased, and he was at the same time honoured by the university with the degree of doctor of laws. He was scarcely settled in Oxford, when he began to translate into Latin, from the Arabic, Apollonius de Sectione Rationis; and to restore the two books De Sectione Spatii of the same author, which are lost, from the account given of them by Pappus; and he published the whole work in 1706. He afterwards had a share in preparing for the press Apollonius's Conics; and ventured to supply the whole 8th book, the original of which is also lost. To this work he added Serenus on the Section of the Cylinder and Cone, printed from the original Greek, with a Latin translation, and published the whole in folio 1710. Beside these, the Miscellanea Curiosa, in 3 volumes 8vo, had come out under his direction in 1708.

In 1713, he succeeded Doctor, afterwards Sir, Hans Sloane, in the office of Secretary to the Royal Society. And, upon the death of Mr. Flamsteed in 1719, he was appointed to succeed him at Greenwich as Astronomer Royal; upon which occasion, that he might be more at leisure to attend the duties of this office, he resigned that of secretary to the Royal Society in 1721. Although he was 63 or 64 years of age when he entered upon his office at Greenwich, for the space of 18 years he watched the heavens with the closest attention, hardly ever missing an observation during all that time, and, without any assistant, performed the whole business of the observatory himself.

Upon the accession of the late king, his consort queen Caroline made a visit at the Royal Observatory; and being pleased with every thing she saw, took notice that Dr. Halley had formerly served the crown as a captain in the navy: and she soon after obtained a grant of his half-pay for that commission, which he accordingly enjoyed from that time during his life. An offer was also made him of being appointed mathematical preceptor to the duke of Cumberland; but he declined that honour, on account of his advanced age, and the duties of his office. In 1729 he was chosen a foreign member of the Academy of Sciences at Paris.

About 1737 he was seized with a paralytic disorder in his right hand, which, it is said, was the first attack he ever felt upon his constitution: however, he came as usual once a week, till within a very short time of his death, to meet his friends in town on Thursdays, before the meeting of the Royal Society, at what is yet called Dr. Halley's club. His paralytic disorder increasing, his strength gradually wore away, till he expired Jan. 14, 1742, in the 86th year of his age; and his corps was interred in the church-yard of Lee near Blackheath.——Beside the works before mentioned, his principal publications are, 1. Catalogus Stellarum Australium. 2. Tabulæ Astronomicæ. 3. The Astronomy of Comets. With a great multitude of Papers in the Philos. Trans. from vol. 11 to vol. 60.

HALIFAX (John). See Sacrobosco.