Molyneux, Sir Thomas (1661–1733), physician, natural historian, and antiquarian, was born 14 April 1661, near Gormond's (Ormond, Wormwood) Gate on Cook St., Dublin, second son among five sons and two daughters of Samuel Molyneux (d. 1693), lawyer, landowner, and army captain, and his wife Margaret Anne, daughter of William Dowdal of Mount Town, Co. Meath. Only he, his two sisters, and one of his brothers, William Molyneux (qv), survived childhood. The family – descended from William Des Molines (Molineus or Molyneux), who is reputed to have accompanied William, duke of Normandy, to England in 1066 – began their association with Ireland in 1576 with Thomas's great-grandfather Sir Thomas Molyneux (qv) (1531–97), whose sons, Daniel Molyneux (qv) and Samuel Molyneux (survegor-general of the works in Ireland), were prominent in Dublin life; his daughter Catherine married Sir Robert Newcomen. Daniel's son Samuel Molyneux (1616–93), known as ‘Honest Sam’, trained as a lawyer, but was a skilful artillery officer during the rebellion; he distinguished himself at the battle of New Ross (1643), wrote a book on gunnery, and was appointed ‘master gunner in Ireland’. He engaged in some legal practice, but his private income from investments in several estates around the country supported his family in relative wealth. In 1664 he bought the 6,000-acre Castle Dillon estate, Co. Armagh, which became the family seat. Prudent management by his wife is said to have improved the family's fortune. As master gunner, he received nominal pay, and spent more than he received on firearms experiments. He had interests in mathematics and philosophy and acquired a large library. A skilled surveyor, he turned down an offer by William Petty (qv) to participate in the Down Survey of Ireland. In 1665 he built a large house in New Row (latterly St Augustine St.), off Thomas St., which, with his county estates, eventually became the property of his elder son, William. One daughter, Jane, married Anthony Dopping (qv), bishop of Meath; another, Mary, married Dr John Madden, a member of the Dublin Philosophical Society, and father of the more famous Samuel Madden (qv).
Thomas, the second son, was educated by Dr Henry Ryder (later bishop of Killaloe), at St Patrick's grammar school, Dublin. His mother, an accomplished musician, is said to have had a key role in influencing the development of both her sons’ intellectual interests. Thomas entered TCD (1676) at the age of 15, graduating BA (1680) and MA (1683). There being no school of medicine in Ireland at the time, he left (1683) to further his medical studies in Leiden, the Netherlands, then one of the best medical centres in Europe. En route he spent some months in London, and visited Oxford and Cambridge, where he met many eminent scientists and members of the Royal Society, including William Petty, Robert Boyle (qv), and John Flamsteed, the astronomer royal, and was able to listen to such notables as John Evelyn (1620–1706), Robert Hooke (1635–1703), and Isaac Newton (1642–1727).
Throughout his travels he wrote regularly to his brother William, with whom he shared interests in science and philosophy. William was the founder (1683) and main initiator of the Dublin Philosophical Society, which sought to emulate the Royal Society. The society played a leading role in the intellectual life of Dublin and was an important forum for new scientific thinking, influenced by advances in Britain and Continental Europe. Thomas's detailed letters (summarised by Sir William Wilde (qv) in the Dublin University Magazine, xviii (1841)) were read out at society meetings, kept members informed of scientific developments abroad, and included colourful comments on some of the personalities he met. His first public scientific article, concerning the dissolution of heavy bodies in menstruum, appeared in French in Nouvelles de la République des Lettres (August 1684).
In 1685 Thomas undertook a three-month tour of Europe with his brother, visiting several scientists and astronomers in the Netherlands and Germany. In Leiden he became friendly with the philosopher John Locke, who had sought asylum there from the hostility of James II (qv), who had just acceded to the throne. Not knowing the family connection, Locke later became a close friend of his brother William. Thomas visited libraries and hospitals in Paris and intended travelling on to Montpelier and Italy, but political instability in Ireland persuaded his father to recall him home. Travelling to London (1686), he renewed his acquaintances with scientists and was elected a fellow of the Royal Society (November 1686) before returning to Ireland (April 1687), where he took his MD (1687). The political situation had become more serious when the viceroy of Ireland, Henry Hyde (qv), earl of Clarendon, was recalled to England and the catholic Richard Talbot (qv), earl of Tyrconnell, took over his position in February 1687. Rumours of a possible repeal of the act of settlement provoked great anxiety among protestants. Rents became difficult to collect on Molyneux estates in the catholic-dominated counties of Limerick and Kildare. Mass emigration of protestants began and Thomas eventually left (1689) for Chester, England, where he set up a medical practice. His brother and family soon joined him. The success of William of Orange (qv) at the battle of the Boyne (1 July 1690) removed the threat to protestants and allowed the return of the Molyneux brothers to Dublin.
Thomas lived in his father's house at New Row, and quickly built up a lucrative and successful medical practice. He became one of the wealthiest medical practitioners of Dublin, if not of Ireland, and bought an estate in 1693 worth £100 a year. He became a fellow (1692) of the RK&QCPI under the royal charter of William and Mary, when the college was reconstituted. The college became a dominant force in medical education and reform in Ireland. He was elected president four times (1702, 1709, 1713, 1720) and acted as treasurer until his resignation (1728). From 1695 to 1699 he represented Ratoath in the Irish parliament.
At the end of the seventeenth century, hospital care was limited in Ireland, and in 1699 Thomas attempted to redress this when he requested Dublin corporation to respond generously to the offer of £2,000 from a private benefactor for the construction of a hospital for 'aged lunatics and diseased persons'. A site was selected but the plans came to nothing. In 1711 he was nominated by Grizel or ‘Madam’ Steevens (qv) (sister of Richard Steevens (qv)) as one of her trustees for the building of Steevens’ Hospital, and was later nominated a governor (1730). In 1711 he built a handsome mansion at 34 Peter St. at a cost of £2,310, which he furnished lavishly (£2,341). He built up a large collection of rare specimens of natural history, and a collection of ancient and modern paintings. On hearing reference to the large estate of Dr Steevens, he once boasted that he ‘had spent more than Steevens ever made’. He was the first state physician in Ireland (1715–30), and succeeded Steevens as professor of physic in the University of Dublin (1717–33), where his portrait by Sir Godfrey Kneller now hangs. He was made physician general to the army in Ireland (1718–25) and in 1730 became the first medical baronet in Ireland, having been knighted in 1715.
Thomas became a formal member of the Dublin Philosophical Society in 1693, on his return to Dublin. It was an exciting period for scientific advancement in Europe. Attempting to establish experimental science in Ireland, members of the society were encouraged to carry out investigations and experiments on natural phenomena. Thomas wrote several detailed and descriptive papers on a number of subjects, many published in the Philosophical Transactions of the Royal Society (listed in Lyons, Brief lives). His medical writings included a description of an epidemic of coughs and colds (1694) and the extraction of a stone from the bladder (1698). Like many medical practitioners of the time, he had a wide interest in many aspects of natural science and culture: botany, zoology and geology, antiquities (archaeology), and the classics. His general writings include the first anatomical account of the structure of the sea mouse (a marine polychaete worm) Scolopendra marina (later renamed Aphrodita aculeata), essays on Lough Neagh and its fish, the Irish elk, the Irish wolf-dog, swarms of insects, the Aurora borealis, and the ancient Greek and Roman lyre. He was a keen plant collector, and his records of plants in Ireland were included in an appendix to Synopsis stirpium Hibernicarum (1727), by Caleb Threlkeld (qv). Molyneux was the first to argue (1694) that the Giant's Causeway, Co. Antrim, developed by natural processes rather than human action. His most notable antiquarian publication was ‘A discourse concerning the Danish mounts, forts and towers in Ireland’ as an appendix in the 1725 edition of Gerard Boate's Natural history of Ireland, where he fervently argued that most of the archaeological remains known to be of Celtic origin were in fact the work of the Danish invader, a popular belief at the time. His interest in economics was displayed in his unpublished essay ‘Some observations on the taxes paid by Ireland to support the government’ (1727). He made a number of tours in Ireland, of which he kept a detailed account in manuscript form. Some of these were later published in the Belfast Natural History and Philosophical Society, the Journal of the Kilkenny Archaeological Society, and the Shamrock.
After the early death of his brother William (1698), Thomas Molyneux reared and educated William's son Samuel Molyneux (qv), according to methods prescribed by Locke. Samuel was educated at TCD, and as a young man tried in 1707 to revive the flagging Dublin Philosophical Society, which had gone into abeyance after the death of his father. Thomas was one of the only members who maintained contact with the Royal Society and British scientists during those years. The revival was short-lived, though Thomas contributed a number of papers and became curator. Samuel moved to England (1712), becoming secretary to the prince of Wales (later George II). The revived Dublin Philosophical Society collapsed in 1708 and it was not until 1731 that certain of its interests were taken up by a new Dublin Society (later the RDS), which applied science to the cause of improving agriculture, manufactures, and other aspects of Irish life. Thomas was one of its early members. After Samuel's death, he inherited the family estates, except Castle Dillon, in which Samuel's wife had a life interest.
Thomas died 19 October 1733, aged 72, and was buried in the family vault at St Audeon's church. A statue of him by Louis François Roubilliac (1695–1762) in Armagh cathedral includes an elaborate description of his honours and genealogy. Commissioned by his son Capel Molyneux, the statue was originally meant to stand as a memorial in the grounds of Castle Dillon, but was given by his grandson Thomas Molyneux to Armagh cathedral, after its restoration by Archbishop John George de la Poer Beresford (qv). On the plinth is a relief, which shows Molyneux tending a patient, a rare representation of a doctor at work at the time. Sir William Wilde wrote of him: ‘He was a man of uncommon skill and ability in his profession, well acquainted with several branches of polite literature, a good linguist and a deeply read classic scholar. He was for forty years the leading physician in Ireland and it is not without reason that John Locke chose him as his friend and advisor’ (DUM, xviii, 764). Elsewhere he has been described as the ‘father of Irish medicine’ (Cameron, History, 11).
Thomas married (1693) Catherine, daughter of Dr Ralph Howard of Shelton, Co. Wicklow, grandfather of Ralph Howard, 1st earl of Wicklow. They had between eight and sixteen children, some of whom died in childhood. His daughter Jane married (1730) the dean of Ross, Dr Arthur St George; his daughter Dorothea married (1754) Dr John Garnett (bishop of Clogher 1758–82). In his will Thomas left his house to his wife. His estates were to pass to his sons in succession, and each of his daughters was to receive £1,000.