the more effectually to betray and wound it. Mr Halley continued in his secretaryship to the Royal society only seven years. In 1692 he resigned it for the office of comptroller of the mint at Chester, which was one of the five different mints appointed for the recoinage of the silver specie. He remained in this situation, residing at Chester, two years; but continued his philosophical studies, and communicated their results regularly to the Royal society. In 1698 he procured a vessel from King William, and set out to make observations on the needle, and to determine latitudes and longitudes for our American settlements; but was obliged to return home on account of the sickness and untractableness of his men. In a few months he set sail with two ships under his command, and traversed the vast Atlantic ocean from one hemisphere to the other, as far as the southern ice would allow. He returned in the year 1700, and published a chart showing at one view all the variations of the compass in those seas known to British navigators. Soon after, he received a commission to observe the course of the tides in the British channel, and to lay down the latitudes and longitudes of all the head lands. This task he executed with eminent ability and despatch. He was subsequently employed by the emperor of Germany in some surveys for ports, and received marks of high respect from several foreign courts. In 1703 he returned to England, and was chosen, the same year, to the office of Savilian professor of geometry in Oxford. There he was created doctor of laws. Speedily he entered upon a new work. He undertook to translate, out of the Arabic, Apollonius de Sectione Ratione.' This work he undertook when he was wholly unacquainted with Arabic. In 1706 the whole was published by him at Oxford, notwithstanding the imperfections and mutilations of the manuscript which he had to decypher and translate. This was followed by several other learned works on mathematics. In 1713 he was appointed secretary to the Royal society, and in 1719 astronomer royal at Greenwich. Two years after, he gave up his secretaryship, that he might appropriate his whole time to the studies suited to his new office, particularly to the completion of his theory respecting the moon's motion. He was now in his sixty-fourth year, yet he performed all the business of the observatory himself, without an assistant, for the space of eighteen years. In 1729 he was admitted a member of the academy of sciences at Paris. He continued his laborious pursuits almost without interruption, till the year 1737, when a paralytic affection seized his right hand. From this period he gradually sunk under the influence of disease, though for several years he continued to enjoy the society of his friends, and usually came to London every Thursday, prior to the assembling of the Royal society, to meet the club, known yet by the name of Dr Halley's club. He died in his chair without a groan, January 14th, 1741-2, in his eighty-sixth year. Dr Halley was a thin and rather tall man, of a lively disposition, and of a warm, though not hot or violent temper. He is said to have preserved much gaiety and good humour throughout life, and to have been exceedingly warm and sincere in his friendships. He preserved his faculties to the last, though these were gilded by none of those rays, falling from another world, which have gilded the last hours of philosophers not less eminent than Halley, who thought it no degradation to profess their faith in brighter revelations than any philosophy had ever

made to them. Dr Halley's works, distinct, were numerous, and his papers in the Philosophical transactions, still more so. found from volume xi. to volume lx.

Abraham Sharp.

BORN CIRC. A. D. 1651.-DIED A. D. 1742.

They are to be

сара

THIS distinguished mathematician and astronomer was born at Little-Horton, near Bradford, in Yorkshire, about the middle of the 17th century. His father was nearly related to Archbishop Sharp. His mother was a sister of the celebrated nonconformist divine, David Clarkson. Abraham was at first apprenticed to a merchant at Manchester; but, on his discovering a decided taste and bent for mathematical studies, his master consented to release him from his indenture. In early life we find him supporting himself by keeping a school for writing and accounts in Liverpool. His spare hours at this time were exclusively devoted to the pursuit of his favourite science. An accidental circumstance having introduced him to a London merchant then visiting Liverpool, in whose house the astronomer Flamsteed then resided, young Sharp, in the hope of gaining the acquaintance of so great a man, eagerly embraced the merchant's offer to take him to London in the city of a clerk. Having been thus introduced to Flamsteed, the astronomer soon discovered the merits and acquisitions of the young mathematician, and engaged his assistance in completing and arranging the astronomical apparatus of the Royal observatory at Greenwich. In this situation he assisted the astronomer royal in his observations on the meridional zenith distances of the heavenly bodies, also in making a catalogue of the fixed stars. The tables in the second volume of the Historia Cœlestis' were principally drawn up by Mr Sharp, together with the explanatory charts and drawings annexed, and which, though engraved by a superior artist in Amsterdam, were much exceeded in elegance and graphic beauty by the originals furnished by Mr Sharp. These exertions, however, soon told upon a constitution at no time strong; and Sharp was compelled to retire to his own house at Horton, where he fitted up an observatory of his own. His mechanical skill was nowise inferior to his mathematical; for most of his instruments were of his own constructing, and even the lenses of his telescopes, as well as the exterior parts, were prepared and adjusted by himself.

In 1699 Mr Sharp, for his own amusement, undertook an approximation to the quadrature of the circle deduced from two different series, which he proved to seventy-two places of figures. Mr Smeaton regards Mr Sharp as the first person that brought the hand-division of mathematical instruments to any degree of perfection.1 The celebrated mural arc, erected by Flamsteed at Greenwich, owed its superiority over all other instruments of the kind which had yet been produced, chiefly to the accurate hand of Mr Sharp. His accuracy and application as a computer rendered him for many years the constant resource of Mr Flamsteed, Sir Jonas Moore, Dr Halley, and others, in all sorts of

1 Phil. Trans. for the year 1786.

troublesome and delicate calculations. He also numbered among his correspondents Sir Isaac Newton, Mr Wallis, Mr Hodgson, and Mr Sherwin. Mr Sharp, although he had come to the possession of a patrimonial estate which greatly removed him above want, led a very retired life at Horton. He was a bachelor himself, and the only company which he solicited was that of his pastor Oliver Heywood, and another pious friend who lived in the neighbourhood. He was remarkably abstemious in his habits; and would sometimes continue his calculations for whole days without tasting food. He was a man of sincere piety, and remarkable for his strict observance of religious duties. He died on the 18th of July, 1742.

END OF VOL. IV