Dr Edmund, an eminent astronomer, was the only son of a soap-boiler in London, and was born in 1656. He first applied himself to the study of the languages and sciences, but at length gave himself up wholly to that of astronomy. In 1676, he went to the island of St Helena to complete the catalogue of fixed stars, by the addition of those which lie near the south pole; and having delineated a planisphere in which he laid them all down in their exact places, he returned to England in 1678. In the year 1683, he took what is called the grand tour, accompanied by his friend the celebrated Mr Nelson. In the midway between Calais and 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 now hastened to complete his observations upon it, in 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 returned to England. 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 a great magnet, with four magnetical poles, or points of attraction: but afterwards thinking that this theory was liable to great exceptions, he procured an application to be made to King William, who appointed him commander of the Paramour pink, with orders to seek by observations the discovery of the rule of variations, and to lay down the longitudes and latitudes of his majesty's 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 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 Verd, Barbadoes, the Madeiras, the Canaries, the coast of Barbary, and many other latitudes, arrived in September 1700; and the next year published a general chart, showing 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 British 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 King George I, then electoral prince, 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 and added new fortifications to those of Trieste. Mr Halley returned to England in 1703; and the same year was made professor of geometry in the university of Oxford, in the room of Dr Wallis, and had the degree of doctor of laws conferred on him by that university. He is said to have lost the professorship of astronomy in that city, because he would not profess his belief of the Christian religion. He was scarcely settled at 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. Afterwards he had a share in preparing for the press Apollonius's Conics; and ventured to supply the whole eighth book, the original of which is also lost. He likewise 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. In 1713, he was made secretary of the Royal Society; in 1720, he was appointed the king's astronomer at the royal observatory at Greenwich, in the room of Mr Flamstead; and, in 1729, was chosen as a foreign member of the Academy of Sciences at Paris. He died at Greenwich in 1742. His principal works are, 1. *Catalogus stellarum australiwm*. 2. *Tabulae astronomicae*. 3. An abridgment of the astronomy of comets, &c. We are also indebted to him for the publication of several of the works of the great Sir Isaac Newton, who had a particular friendship for him, and to whom he frequently communicated his discoveries.

**HALLEY'S Quadrant.** See Quadrant.