MOLYNEUX (William)

, an excellent mathematician and astronomer, was born at Dublin in 1656. After the usual grammar education, which he had at home, he was entered of the university of that city. Here he distinguished himself by the probity of his manners, as well as by the strength of his parts; and having made a remarkable progress in academical learning, and particularly in the new philosophy, as it was then called, after four years spent in this university, he was sent over to London, where he was admitted into the Middle Temple in 1675. Here he spent three years, in the study of the laws of his country. But the bent of his genius lay strongly toward mathematical and philosophical studies; and even at the university he conceived a dislike to scholastic learning, and sell into the methods of lord Bacon.

Returning to Ireland in 1678, he shortly after married Lucy the danghter 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; in which astronomy having the greatest share, he began, about 1681, a literary correspondence with Mr. Flamsteed, 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 imitation of the Royal Society at London; and, by the countenance and encouragement of Sir William Petty, who accepted the office of president, 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 great duke of Ormond, then lord-lieutenant of Ireland; by whose influence chiefly he was appointed that year, jointly with sir William Robinson, surveyor-general of the king's buildings and works, and chief engineer.

In 1685, he was chosen fellow of the Royal Society at London; and that year he was sent by the government to view the most considerable fortresses in Flanders. Accordingly he travelled through that country and Holland, with part of Germany and France; and carrying with him letters of recommendation from Flamsteed to Cassini, he was introduced to him, and others, the most eminent astronomers in the several places through which he passed.

Soon after his return from abroad, he printed at Dublin, in 1686, his Sciothericum Telescopium, containing a Description of the Structure and Use of a Telescopic Dial, invented by him: another edition of which was published at London in 1700.

In 1688 the Philosophical Society of Dublin was broken up and dispersed by <*>e confusion of the times.| Mr. Molyneux had distinguished himself as a Member of it from the beginning, and presented several discourses upon curious subjects; some of which were transmitted to the Royal Society at London, and afterwards printed in the Philosophical Transactions. In 1689, among great numbers of other Protestants, he withdrew from the disturbances in Ireland, occasioned by the severities of Tyrconnel's government; and after a short stay at London, he fixed himself with his family at Chester. In this retirement, he employed himself in putting together the materials he had some time before prepared for his Dioptrics, in which he was much assisted by Mr. Flamsteed; and in August 1690, he went to London to put it to the press, where the sheets were revised by Dr. Halley, who, at our author's request, gave leave for printing, in the appendix, his celebrated Theorem for finding the Foci of Optic Glasses. Accordingly the book came out, 1692, in 4to, under the title of “Dioptrica Nova: a Treatise of Dioptrics, in two parts; wherein the various effects and appearances of spherical glasses, both convex and concave, single and combined, in telescopes and microscopes, together with their usefulness in many concerns of human life, are explained.” He gave it the title of Dioptrica Nova, both because it was almost wholly new, very little being borrowed from other writers, and because it was the first book that appeared in English upon the subject. The work contains several of the most generally useful propositions for practice, demonstrated in a clear and easy manner, for which reason it was for many years used by the artificers: and the second part is very entertaining, especially in the history which he gives of the several optical instruments, and of the discoveries made by them.

Before he left Chester 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 her marriage; from which time she had been very sickly, and afflicted with great pains in her 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 lately 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 5001. a year; but looking upon it as an invidious office, he declined it.

In 1698, he published “The Case of Ireland stated, in regard to its being bound by Acts of Parliament made in England:” in which it is supposed he has delivered all, or most, that can be said upon this subject, with great clearness and strength of reasoning.

Among many learned persons with whom he maintained correspondence and friendship, Mr. Looke was in a particular manner dear to him, as appears from their letters. In the above mentioned year, which was the last of our author's 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, he was seized with a fit of the stone, which terminated his exist- ence.

Besides the three works already mentioned, viz, the Sciothericum Telescopium, the Dioptrica Nova, and the Case of Ireland stated; he published a great number of pieces in the Philosophical Transactions, which are contained in the volumes 14, 15, 16, 18, 19, 20, 21, 22, 23, 26, 29, several papers commonly in each volume.

Molyneux (Samuel), son of the former, was born at Chester in July 1689; and educated with great care by his father, according to the plan laid down by Locke on that subject. When his father died, he fell under the management of his uncle, Dr. Thomas Molyneux, an excellent scholar and physician at Dublin, and also an intimate friend of Mr. Locke, who executed his trust so well, that Mr. Molyneux became afterwards a most polite and accomplished gentleman, and was made secretary to George the 3d when prince of Wales. Astronomy and Optics being his favourite studies, as they had been his father's, he projected many schemes for the advancement of them, and was particularly employed in the years 1723, 1724, and 1725, in perfecting the method of making telescopes; one of which instruments, of his own making, he had presented to John the 5th, king of Portugal.

Being soon after appointed a commissioner of the admiralty, he became so engaged in public affairs, that he had not leisure to pursue those enquiries any farther, as he intended. He therefore gave his papers to Dr. Robert Smith, professor of astronomy at Cambridge, whom he invited to make use of his house and apparatus of instruments, in order to finish what he had left imperfect. But Mr. Molyneux dying soon after, Dr. Smith lost the opportunity; he however supplied what was wanting from M. Huygens and others, and published the whole in his “Complete Treatise of Optics.”