# Dictionary of National Biography, 1885-1900/McCullagh, James

James MacCullagh in the ODNB.
​McCULLAGH, JAMES (1809–1847), mathematician, son of a poor farmer, was born in 1809, at Glenellie, in the parish of Upper Badoney, co. Tyrone. He entered Trinity College, Dublin, as a pensioner, November 1824, became sizar June 1825, scholar 1827 (the examination being purely classical), and fellow in 1832. He was befriended in his college course by Provost Lloyd, to whom some of his geometrical discoveries were communicated during this period. In 1836 McCullagh was elected professor of mathematics and in 1843 professor of natural philosophy in the university of Dublin. He threw himself into his duties as a teacher with an ardour which communicated itself to his pupils, and gave a powerful stimulus to mathematical and physical studies in the university. He introduced the studies of electricity and galvanism, heat and terrestrial magnetism into the fellowship course.
As secretary of council to the Royal Irish Academy from 1840 to 1842, and as secretary to the Academy from 1842 to 1846, he rendered that institution valuable service. His liberality and influence secured for the museum some of its most precious archæological treasures. Shortly before his death he unsuccessfully contested Dublin University in the nationalist interest. He died by his own hand in October 1847, in a fit of temporary insanity. Dyspepsia and overwork appear to have intensified a mental disorder of which he had shown slight symptoms long before. He was unmarried.
Of the voluminous manuscript investigations, geometrical and physical, which he was known to have had by him ready for the press shortly before his death, no trace could afterwards be found, though careful search was made. Such of them as had already appeared in the transactions of the Royal Irish Academy, the ‘Philosophical Magazine,’ and elsewhere, have been collected in a volume by Drs. Jellett and Haughton (Dublin Univ. Press). To them are added notes of his lectures on the rotation of a solid body round a fixed point, and on the attraction of ellipsoids, and also two short papers on Egyptian chronology, which remain to attest his interest in archæological studies.
By far the most important of McCullagh's scanty remains is the memoir on surfaces of the second order, read to the Royal Irish Academy on 30 Nov. 1843. His geometrical work is characterised by an elegance and power which might have placed him beside Chasles and Poncelet had he lived to finish his work. His numerous papers on the wave theory of light contain ingenious attempts to construct a dynamical theory of the luminiferous ether. His geometrical work was in the first instance undertaken as subsidiary to his physical investigations; but, though the geometrical methods and results are of permanent value, his physical theory retains only an historical interest, being vitiated by erroneous fundamental assumptions. It was then a moot point whether the vibrations of plane polarised light are parallel or perpendicular to the plane of polarisation. Fresnel thought they were perpendicular, McCullagh differed from him, and assumed they were parallel. Subsequent researches have proved that Fresnel was right.
[Manchester Examiner, 6 Nov. 1847; Nation, 30 Oct. (p. 889) and 20 Nov. (p. 939) 1847; information supplied by Dr. Ingram, F.T.C.D.]
C. P.