MOLYNEUX (William), an excellent mathematician and astronomer, was born at Dublin in 1656, and admitted into the university of that city; which when he left, he carried with him a testimonial drawn up in an uncommon form, and in the strongest terms, signifying the high opinion conceived of his genius, the probity of his manners, and the remarkable progress he had made in letters. In 1675, he entered in the middle-temple, where he spent three years in the study of the laws of his country; but the bent of his genius lay strongly toward mathematics and philosophical studies; and even at the university he conceived a dislike to scholastic learning, and fell into the methods of Lord Bacon. Returning to Ireland in June 1678, he shortly after married Lucy the daughter of Sir William Domville the king's attorney-general. Being master of an easy fortune, he continued to indulge himself in prosecuting such branches of natural and experimental philosophy as were most agreeable to his fancy; wherein astronomy having the greatest share, he began, about 1681, a literary correspondence with Flamstead the king's astronomer, which he kept up for several years. In 1683, he formed a design of erecting a philosophical society at Dublin, in imita-
Molyneux, tion of the Royal Society at London; and, by the countenance and encouragement of Sir William Petty, who accepted the office of president, they began a weekly meeting that year, when our author was appointed their first secretary.
Mr Molyneux's reputation for learning recommended him, in 1684, to the notice and favour of the first and great duke of Ormond, then lord-lieutenant of Ireland; and chiefly by his grace's influence he was appointed, that year, with Sir William Robinson, surveyor general of his majesty's buildings and works, and chief engineer. In 1686, he was sent abroad by the government to view the most considerable fortresses in Flanders. He travelled, in company with Lord Mountjoy, through that country, Holland, part of Germany, and France. Upon his return from Paris to London, in April 1680, he published his Scotoberricum Telecopium, containing a description of the structure and use of a telescopial dial invented by him. The fevers of Tyreconnel's government forced him, with many others, into England, where he spent two years with his family, his place of residence being at Chester. In this retirement he wrote his Dioptrics, dedicated to the Royal Society. Here he lost his lady, who died soon after she had brought him a son. Illness had deprived her of her eye-sight 12 years before, that is, soon after she was married; from which time she had been very sickly, and afflicted with extreme pains of the head. As soon as the public tranquillity was settled in his native country, he returned home; and, upon the convening of a new parliament in 1692, was chosen one of the representatives for the city of Dublin. In the next parliament, in 1695, he was chosen to represent the university there, and continued to do so to the end of his life; that learned body having, before the end of the first session of the former, conferred on him the degree of doctor of laws. He was likewise nominated by the lord-lieutenant one of the commissioners for the forfeited estates, to which employment was annexed a salary of 500l. a-year; but looking upon it as an invidious office, he declined it. In 1698, he published "The Case of Ireland stated, in relation to its being bound by Acts of Parliament made in England;" in which he is supposed to have delivered all, or most, that can be said upon this subject, with great clearness and strength of reasoning. Among many persons with whom he maintained correspondence and friendship, Mr Locke was in a particular manner dear to him, as appears from their letters. In the above year, which was the last of his life, he made a journey to England, on purpose to pay a visit to that great man; and not long after his return to Ireland was seized with a fit of the stomach, of which died. Besides the works already mentioned, he published several pieces in the Philosophical Transactions.