# Dictionary of National Biography, 1885-1900/Molyneux, William

​MOLYNEUX, WILLIAM (1656–1698), philosopher, was born at his father's house in New Row, Dublin, on 17 April 1656. He was the eldest surviving son of Samuel Molyneux (1616–1693) by Margaret, daughter and coheiress of William Dowdall, esq., of Dublin. The family was descended from Sir Thomas Molyneux [q. v.], chancellor of the Irish exchequer in 1590. The father, a gentleman of property in several counties, had acquired considerable fame as a master-gunner during the rebellion, particularly at the battle of Ross in 1643 (Carte, Life of Ormonde, i. 405), and afterwards as an experimentalist in the science of gunnery, on which subject he published a treatise when seventy years of age; he died on 23 Jan. 1693. A younger son, Sir Thomas Molyneux (1661–1733), is separately noticed. After receiving a good elementary education, William entered Trinity College, Dublin, on 10 April 1671, and was placed ​under the tuition of Dr. William Palliser [q. v.], afterwards archbishop of Cashel (Taylor, Dublin Univ. p. 377). Having graduated B.A. he quitted the university with credit, and proceeding to London entered the Middle Temple as a student of law on 23 June 1675. The heir to an easy fortune, and having no particular predilection for law, he devoted himself chiefly to philosophy and applied mathematics. In June 1678 he returned to Dublin, and with his father's consent married, on 19 Sept., Lucy, youngest daughter of Sir William Domvile, attorney-general of Ireland. Mrs. Molyneux was a lady of remarkable beauty and of an amiable disposition, but unfortunately, only three months after her marriage, she was attacked by an illness which not only deprived her of sight, but until her death, thirteen years later, caused her intolerable pain. Molyneux himself suffered from an hereditary affection of the kidneys, which seriously interfered with his enjoyment of life, and was eventually the cause of his premature death.
After some time spent in England in the vain endeavour to obtain medical relief for his wife, Molyneux settled down in Dublin. He resumed his philosophical studies, and during the winter of 1679 he made an English version of Descartes's 'Meditations,' which was published in London in April 1680. His interest in optics and astronomy was stimulated by a correspondence which he opened with John Flamsteed [q. v.], astronomer royal, in 1681. This intercourse continued till 1692, when, according to Molyneux, Flamsteed broke off relations with him owing to some offence Molyneux had given him in his 'Dioptrica Nova.' In the summer of 1682 he was engaged in collecting materials for a 'Description of Ireland,' to form part of Moses Pitt's 'Atlas;' it was never published owing to Pitt's failure to carry out his project. Among others with whom he in this way became acquainted was Roderick O'Flaherty [q. v.], whom he assisted in the publication of his 'Ogygia,' and Peter Walsh [q.v.], to whom he owed an introduction to the Duke of Ormonde. His interest in science, and the example furnished by the Royal Society, led him to take an active part in the foundation in 1683 of the Dublin Philosophical Society, the precursor of the Royal Irish Academy, of which he was the first secretary, and Sir William Petty [q. v.], the first president.
By the influence of the Duke of Ormonde Molyneux was in 1684 appointed, jointly with (Sir) William Robinson, chief engineer and surveyor-general of the king's buildings and works, in which capacity he built that part of Dublin Castle which stands upon the Piazza, with the turrets to the south; but he was ejected from office in 1688 by Tyrconnel on account of his religion. In 1685 he was elected a fellow of the Royal Society; and it being his intention that summer to visit his brother, Thomas (afterwards Sir Thomas) Molyneux [q. v.], at Leyden, he received a concordatum of 100l. from the Irish government to enable him to view and make draughts of the principal fortresses in Flanders. He left Dublin on 13 May, and meeting at Calais Viscount Mountjoy he travelled with him through the Netherlands and parts of Germany and France, including Paris, where, by means of letters of recommendation from Flamsteed, he made the acquaintance of the astronomer Cassini and other eminent men of science.
He returned to Ireland at the end of September, and was almost immediately prostrated by a severe illness. Early in the following year (1686) he published his 'Sciothericum Telescopicum: or, A New Contrivance of adapting a Telescope to a Horizontal Dial,' with a dedication to the lord-lieutenant, the Earl of Clarendon, in which he raised the question 'whether the natural philosophy formerly professed in the schools or that which is at present prosecuted by the societies lately instituted in several of the most noted parts of Europe be the true philosophy or method of investigating nature?' The telescopic dial itself never came into general use, and was practically condemned by Flamsteed. On the appearance of Sir Isaac Newton's 'Principia' in 1687 Molyneux candidly admitted that his knowledge of mathematics was not sufficient to enable him to understand it. Becoming alarmed at the policy of proscription pursued by Tyrconnel, and dreading a repetition of the horrors of 1641, he retired on 31 Jan. 1689, with his wife, to Chester, where he resided in a little house outside the north gate for nearly two years. There he wrote the greater part of his 'Dioptrica Nova,' in which he was assisted by Flamsteed. The book, which was for a long time the standard work on optics, was published at London in 1692, the sheets being revised by Edmund Halley [q. v.] the astronomer, who, at Molyneux's request, allowed his celebrated theorem for finding the foci of optic glasses to be printed in the appendix. A passage in the Epistle Dedicatory in warm commendation of Locke's 'Essay on the Human Understanding' obtained grateful acknowledgment from that philosopher, and was the beginning of a long and friendly correspondence between them (see Some Familiar Letters between ​Mr. Locke and several of his Friends, London, 1708).
Immediately after the battle of the Boyne (1 July 1690) Molyneux paid a hurried visit to his old father, who had persisted in remaining in Dublin. On his return through Wales he was mistaken by the Denbighshire militia for William Molyneux, eldest son of Lord Molyneux, for whose apprehension 500l. reward had been offered ; but having proved his identity he was, after a brief detention, allowed to proceed on his journey. In December 1690 he was suddenly recalled to Dublin by the news that he had been placed on a commission for stating the accounts of the army. He was shortly afterwards rejoined by his wife and infant son, but recent events had proved too much for her delicate constitution, and on 9 May 1691 she died. A parliament, the first with the exception of Tyrconnel's convention that had met for twenty-six years, having been summoned for October 1692, Molyneux was returned as one of the representatives of Dublin University. In the discussion on the right of the commons to originate money bills Molyneux appears to have played a neutral part, for shortly before the dissolution he was nominated a commissioner of forfeited estates, with a salary of 400l. a year. But the ill reputation of the commissioners with whom he was to act induced him to decline the appointment, and his conduct, which was highly applauded, led to a reconstitution of the board. In July 1693 Trinity College conferred on him its honorary degree of LL.D., and in 1695 he was again chosen to represent the university in parliament. He was assiduous in his attention to his parliamentary duties, and during the absence of the lords justices Galway and Winchester in the winter of 1697-8 he shared the responsibility of government with the lord chancellor, John Methuen [q. v.], and the lord mayor, Mr. Van Homrigh.
From his correspondence with Locke it appears that Molyneux was at this time engaged in investigating the effect that the recent legislation of the English parliament was having on the linen and woollen industries of Ireland. His interest in the matter moved Molyneux to publish early in 1698 the work by which he is best known—viz. 'The Case of Ireland's being bound by Acts of Parliament in England stated.' It was, he admitted to Locke (Familiar Letters, p. 269), ' a nice subject,' but he thought he d treated it with discretion, and consequently had not hesitated to put his name to it and even to dedicate it to his majesty. None the less, he thought it prudent, till he saw how it was taken by the English parliament, not to cross the Channel, for though 'not apprehensive of any mischief from them, yet God only knows what resentments captious men may take on such occasions.' In substance the book is based on the treatise, 'A Declaration setting forth how and by what means the Laws and Statutes of England from time to time came to be in force in Ireland,' attributed by some to Patrick Darcy [q. v.] and by others to Sir Richard Bolton [q. v.] But Molyneux's effort has special value of its own as an attempt to prove the legislative independence of the Irish parliament. It made an immediate sensation, and two replies were at once forthcoming viz. 'A Vindication of the Parliament of England,' &c., by John Cary [q. v.], London, 1698, and 'The History and Reasons of the Dependency of Ireland,' &c., by William Atwood [q. v.], London, 1698. The Irish government was supposed to have given some encouragement to its publication, and Methuen, as if to divert responsibility from the Irish ministry, himself introduced it to the notice of the English House of Commons on 21 May 1698 (Vernon, Letters, ii. 83). The business was referred to a committee. On 22 June the committee reported, and it was unanimously resolved 'that the said book was of dangerous consequence to the crown and parliament of England' (Parl. Hist. v. 1181). An address embodying the resolution was presented to the king (Journals, House of Commons, xii. 337) ; but there appears to be no ground for Macaulay's opinion (Hist, of England, v. 60) that Molyneux himself stood in any personal danger, or for the general belief that the book was condemned to be burnt by the common hangman. About the beginning of July Molyueux went to England in fulfilment of a longstanding promise to visit Locke. ' I reckon it the happiest scene of my whole life,' he wrote (Familiar Letters, p. 272), in reference to his meeting with Locke and to the time he spent with him at Oates and in London. He reached Dublin again on 15 Sept., but shortly afterwards he was attacked with a severe fit of the stone. He died on 11 Oct. 1698, and was buried beside his wife, in the tomb of his great-grandfather, Sir William Ussher, in the north aisle of St. Audoen's ; Church, Dublin, where a monument with a long Latin inscription (cf. Gilbert, Hist. of Dublin, i. 283) was erected to his memory. The monument was removed by his grandnephew, Sir Capel Molyneux, in order to be repaired, but owing to Sir Capel's death soon ; afterwards it was never replaced. In 1869 a tablet was fixed in the church on its site ​by a niece of Sir Capel's wife, the widow of the Hon. Henry Caulfeild (Notes and Queries, 4th ser. v. 291). The new inscription describes Molyneux as one 'whom Locke was proud to call his friend.' In appearance Molyneux was said somewhat to have resembled Locke (Familiar Letters, p. 172), and whom in his will, by a clause written with his own hand, he bequeathed 'the sum of five pounds to buy him a ring, in memory of the value and esteem I had for him ' (ib. p. 292).
A portrait of Molyneux hangs in the examination hall, Trinity College, Dublin, beside that of Archbishop King. There is also an engraved portrait by Simms prefixed to 'The Case of Ireland,' Dublin, 1725.
Molyneux had two sons, of whom Samuel Molyneux [q. v.] survived him. In addition to the works already mentioned, Molyneux contributed some papers to the Royal Society, which were printed in the 'Philosophical Transactions,' 1686-9. 'A Journal of the Three Months' Royal Campaign of His Majesty in Ireland; with a Diary of the Siege of Lymerick,' London, 1690, is wrongly attributed to him.
[The chief authority for the life of Molyneux is a short account written by himself in 1694, at the request of his brother Thomas, edited and printed for private circulation at Evesham in 1820 by Sir Capel Molyneux. The best life, and that on which the life in the Biographia Britannica is based, was contributed by the Rev. John Madden in 1738 to Bayle's General Dictionary (English translation, with additions, London, 1734–41), where also is an interesting series of letters between Molyneux and Flamsteed, communicated by James Hodgson [q. v.], who married a niece of Flamsteed. The originals of these letters, with others of Samuel Molyneux, subsequently found their way into the possession of the corporation of the town of Southampton (Hist. MSS. Comm. 11th Rep. App. iii. p. 31). See also Molyneux's correspondence with Locke, now in the possession of Alfred Morrison, esq. (Hist. MSS. Comm. 9th Rep. App. p. 409), but printed in Some Familiar Letters between Mr. Locke and several of his Friends, London, 1708; Letters to Sir H. Sloane, in Sloane MS. 4053, ff. 175, 177, 181, 183; Molyneux's own works, particularly Dioptrica Nova; Birch's Hist. of the Royal Society, London, 1756–7, vol. iv.; Weld's History of the Royal Society; James Vernon's Letters, illustrative of the reign of William III; Notes and Queries, 1870.]
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