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 and Ireland, and in 1782 he supported Grattan's motion for an address to the king in favour of legislative independence.

In spite of his advocacy of the popular cause, O'Brien was defeated at Clare in 1783 by an unknown man (ib. i. 119); he was, however, returned for Tuam, which he represented until 1790. In 1787 he was sworn a privy councillor, and appointed clerk of the crown and hanaper in the high court of chancery. He took a prominent part in the debates on Pitt's proposals for removing the restrictions on Irish trade, and also on the regency question of 1788. In 1790 he was returned for Ennis, and he represented it until his death. In 1791 he moved a resolution for the more satisfactory trying of election petitions, and his last recorded speech in parliament was made in March of the same year on the subject of India trade. Arthur Young [q. v.] acknowledges his indebtedness to O'Brien, at whose house he stayed, and who was indefatigable in procuring materials for Young's ‘Tour in Ireland.’ O'Brien died on 15 Jan. 1795 at Dromoland.

He married, on 26 May 1768, Nichola, daughter of Robert French of Monivea Castle, co. Galway. By her he had six daughters and five sons, of whom the eldest, Edward, succeeded him, and became the father of William Smith O'Brien [q. v.], and of Edward O'Brien [q. v.]

 O'BRIEN, MATTHEW (1814–1855), mathematician, was born at Ennis in 1814, the son of Matthew O'Brien, M.D. He entered Gonville and Caius College, Cambridge, as a scholar in 1834, and graduated third wrangler in the mathematical tripos of 1838 (M.A. 1841). He became junior fellow of his college in 1840, but resigned his fellowship in the following year. He was moderator in the mathematical tripos for 1843 and 1844. He was lecturer in practical astronomy in the Royal Military Academy, Woolwich, from 10 Jan. 1849 till his death, and professor of natural philosophy and astronomy in King's College, London, from 8 March 1844 to 17 Aug. 1854. He died in Petit Ménage, Jersey, on 22 Aug. 1855. He was the author of two elementary text-books—on ‘Differential Calculus’ (1842), and on ‘Plane Co-ordinate Geometry’ (1844). In the former of these he makes exclusive use of the method of limits. He published ‘Solutions to the Senate-House Problems for 1844;’ ‘Lectures on Natural Philosophy,’ given at Queen's College, London (1849); and ‘A Treatise on Mathematical Geography,’ being part i. of ‘A Manual of Geographical Science’ (1852). He also wrote some tracts on mathematical questions connected with astronomy, in which he claimed a certain latitude in the symbolic use of divergent series.

 O'BRIEN, MURROUGH, first (d. 1551), lineal descendant of  (Boroimhe) [q. v.], king of Ireland, was third or fourth son of Turlough O'Brien, lord of Thomond (d. 1528), and Raghnailt, daughter of John MacNamara. On the death of his brother, [q. v.], in 1539, he succeeded by custom of tanistry to the lordship of Thomond and the chieftainship of the Dal Cais. Conor had made a vain endeavour to divert the succession to his children by his second wife, Ellen, sister of James Fitzjohn Fitzgerald, fourteenth earl of Desmond, and there had been, in consequence, much dissension between the brothers.

O'Brien's first step on attaining the chieftainship was to join [q. v.] and [q. v.] in a confederacy against the English government. Their scheme, however, was frustrated by the vigilance of Sir William Brereton; and on the arrival shortly afterwards of Sir Anthony St. Leger as viceroy, O'Brien expressed a wish to parley with him. Early in 1541 O'Brien met the lord-deputy at Limerick. Conditions of peace and submission were propounded to him; but, as these included the restriction of his authority to the west of the Shannon, and other stipulations affecting his clan as well as himself, he asked time for deliberation. He made, however, no difficulty about acknowledging Henry VIII as his sovereign or renouncing the supremacy of the pope, and was represented in the parliament which in that year conferred on Henry the title of king of Ireland. On the adjournment of the parliament to Limerick on 15 Feb. 1542, he repaired thither. The recent submission of Con O'Neill in December 1541 exercised a profound effect upon him, and he not only consented to the curtailment of his authority to the west of the Shannon, but expressed his intention of personally renew-