# Dictionary of National Biography, 1912 supplement/Joly, Charles Jasper

​JOLY, CHARLES JASPER (1864–1906), royal astronomer of Ireland, born at St. Catherine's rectory, Tullamore, on 27 June 1864, was eldest son in the family of three sons and two daughters of John Swift Joly, successively rector of St. Catherine's, Tullamore, and of Athlone, by his wife Elizabeth, daughter of the Rev. Nathaniel Slator. His father's family, of French origin, settled in Ireland in the eighteenth century. After a short attendance at school at Portarlington, and nearly four years at Galway grammar school, Joly in October 1882 entered Trinity College, Dublin, where he won a mathematical scholarship. He graduated in 1886 with the first mathematical honour of his year—the 'studentship,' candidates for which were required to offer a second subject in addition to mathematics. Joly chose physics, the experimental side of which so much interested him that he went to Berlin in order to work in Helmholtz's laboratory. The death of his father in 1887 rendered it needful for him to seek a competency without delay, and abandoning a design of devoting himself wholly to experimental science, he returned to Ireland to read for a fellowship in Trinity College. The conditions of the examination discouraged strict specialism in mathematics or science, and Joly failed to win election till 1894. He then engaged in tuition at the college, and was junior proctor in 1896.
Joly's career as a productive mathematician began almost as soon as he was admitted to a fellowship. In his first paper, on 'The theory of linear vector functions,' which was read to the Royal Irish Academy on 10 Dec. 1894, he proved his discipleship to Sir William Rowan Hamilton [q. v.], the discoverer of quaternions, and first applied the quaternionic analysis to difficult and complex problems of geometry, using it as an engine for the discovery of new geometrical properties. The properties of linear vector functions were further studied in 'Scalar invariants of two linear vector functions' (Trans. R.I.A. 1896, xxx. 709) and 'Quaternion invariants of linear vector functions' (Proc. R.I.A. 1896, iv. 1), while the extension of the quaternion calculus to space of more than three dimensions was discussed in 'The associative algebra applicable to hyperspace' (Proc. R.I.A. 1897, v. 75); the algebras considered are those that are associative and distributive, and whose units satisfy equations of the same type as the units of quaternions. Other more purely geometrical investigations were published about this time under the titles 'Vector expressions for curves' (Proc, R.I.A. 1896, iv. 374) and 'Homographic divisions of planes, spheres, and space' (Proc. R.I.A. 1897, iv. 515).
In 1897 Joly resigned his work at Trinity College on his appointment as royal astronomer of Ireland at Dunsink observatory, where the rest of his life was spent. In this quiet retreat Joly devoted himself to advanced study and research. From 1898 to 1900 he was engaged in editing Hamilton's 'Elements of Quaternions,' originally published shortly after its author's death in 1865, and now out of ​print. Joly made considerable additions, including an appendix of 114 pages; the first volume of the new edition was published in 1899, and the second in 1901. While occupied with this work, Joly communicated several memoirs to the Royal Irish Academy: 'Astatics and quaternion functions,' 'Properties of the general congruency of curves,' and 'Some applications of Hamilton's operator in the calculus of variations' were all read in 1899; in the first, quaternions are applied to the geometry of forces, in the second to pure geometry, and in the third to some of the equations of mathematical physics. Early in the following year he presented a paper 'On the place of the Ausdehnungslehre in the general associative algebra of the quaternion type,' in which he showed that Grassmann's analysis for n dimensions, which is distributive but only partially associative, may be regarded as a limited form of the associative algebra of n + 1 dimensions. In the course of the following five years Joly continued his labours in such memoirs (in the publications of the Royal Irish Academy or the Royal Society) as 'Integrals depending on a single quaternion variable'; 'The multilinear quaternion function'; 'The interpretation of a quaternion as a point symbol'; 'Quaternion arrays'; 'Representation of screws by weighted points'; 'Quaternions and projective geometry'; 'The quadratic screw-system'; 'The geometry of a three-system of screws,' and 'Some new relations in the theory of screws.' Finally in 1905, the centenary year of Hamilton's birth, he brought out 'A Manual of Quaternions,' which at once superseded all other introductory works on the subject. During Joly's tenure of the office of royal astronomer he directed much observational work, the fruits of which appeared in the 'Dunsink Observations and Researches.' In 1900 he accompanied an eclipse expedition to Spain, and obtained some excellent photographs of totality; an account of the results was published in 'Trans. R.I.A.' xxxii. p. 271. He also edited Preston's 'Theory of Light' (3rd edit. 1901). He was elected F.R.S. in 1904, and was a trustee of the National Library of Ireland and president of the International Association for Promoting the Study of Quaternions. Of outdoor sports he was fondest of climbing, being a member of the Alpine Club from 1895 to death. In literature he was well versed in Dante's work. Joly died at the observatory of pleurisy following typhoid fever on 4 Jan. 1906; he was buried at Mount Jerome cemetery, Dublin. On 20 March 1897 Joly was married to Jessie, youngest daughter of Robert Warren Meade of Dublin. His wife and three daughters survived him.
[Personal knowledge; private information from the surviving relatives of Dr. Joly; Proc. Roy. Soc. 78A; Monthly Notices Roy. Astronom. Soc. lxvi. 177; Alpine Journal, 1906.]
E. T. W.