treated it on somewhat original lines. One of his first papers explained by geometrical reasoning the conditions of the propagation of undulations of plane waves in media {Trans. Roy. Irish Acad. vol. 24, 1861). Late in life he pursued the subject in his ’Monograph on Microscopic Vision' (Phil. Mag. Oct.-Dec. 1896), in which he analysed and proved the fundamental proposition — first enunciated by Sir George Stokes in 1845 — that 'the light which emanates from the objective field may be resolved into undulations, each of which consists of uniform plane waves,' suffering no change as they advance. This theme was pursued after the close of his official life in several papers and memoirs in the 'Philosophical Magazine,' the last being a monograph on 'Telescopic Vision' (Aug.-Dec. 1908), in which he discussed among other matters the possibility of seeing very small markings on the planet Mars.
Valuable as these optical researches are, Stoney' s work in molecular physics and the kinetic theory of gases proved more important. An early paper on Boyle's law (Proc. Roy. Irish Acad. vol. vii. 1858) was followed ten years later (in Phil. Mag. Aug. 1868) by his paper ' On the Internal Motions of Gases compared with the Motions of Waves of Light,' in which he estimated the number of molecules in a gas at standard pressure and temperature. There followed inquiries into the conditions limiting planetary atmospheres. As early as 1868 he published a long paper 'On the Physical Constitution of the Sun and Stars' (Proc. Roy. Soc. 1868), in which he first suggested limits of atmospheres. Stoney considered this paper one of his chief achievements. In a very valuable contribution, 'On Atmospheres of Planets and Satellites' (Trans. Roy. Soc. Dublin, 1897, vi. 305), Stoney afterwards explained from inductive reasoning the absence of hydrogen and helium from the atmosphere of the earth, and the absence of an atmosphere from the moon and from the satellites and minor planets of the solar system. This paper was reprinted in the 'Astrophysical Journal' (vii. 25), and gave rise to controversy, but Stoney's position was unshaken. His investigations as to helium are of great importance in view of recent inquiries into the length of geological epochs, and mto the past history of the radio-activity of the materials of the earth's crust.
To Stoney was due the introduction of the word 'electron' into the scientific vocabulary. In a paper 'On the physical units of nature,' which he read before the British Association at Belfast in 1874 (printed in Phil. Mag. May 1881), he pointed out that 'an absolute unit of quantity of electricity exists in that amount of it which attends each chemical bond or valency.' He proposed that this quantity should be made the unit of electricity, and for it subsequently suggested the name 'electron' in place of the old name 'corpuscle' proposed by Prof. J. J. Thomson (cf. Phil. Mag. Oct. 1894). Stoney worked with admirable results on the periodic motion of the atom and its connection with the spectrum (Proc. Roy. Irish Acad. Jan. 1876 ; Trans. Roy. Soc. Dublin, May 1891). To the units of physical science and their nomenclature Stoney devoted much of his attention. He served on the committee of the British Association for the selection and nomenclature of dynamical an^ electrical units in 1873, which adopted the C[entimetre] G[ramme] S[econd] system of units in England. He did much work in physical mensuration, and strove to facilitate the introduction of the metric system into England. In 1888 Stoney entered upon a study of the numerical relations of the atomic weights (see Proc. Roy. Soc. April 1888). His versatihty was also illustrated by papers on 'The Magnetic Effect of the Sun or Moon on Instruments at the Earth's Surface' (Phil. Mag. Oct. 1861) ; 'On the Energy expended in driving a Bicycle' (Trans. Roy. Dublin Soc. 1883, with his son) ; 'On the Relation between Natural Science and Ontology' (Proc. Roy. Dublin Soc. 1890), and many papers on abstract physics. In bacteriology he suggested that the source of the life energy in bacteria was to be found in their bombardment by the faster moving molecules surrounding them, whose velocity is great enough to drive them well into the organism, and carry in energy, of which they can avail themselves (Phil. Mag. April 1890). Music also claimed his attention, and he wrote papers on musical shorthand and on echoes (Proc. Roy. Dublin Soc. 1882), and did much for the advance of musical culture in Dublin by inducing the council of the Royal Dublin Society to inaugurate chamber music concerts by leading European musicians.
During the twenty years that he was hon. secretary of the Royal Dublin Society he zealously fulfilled the duties of the office at a period when the affairs of the society demanded much attention. He was afterwards vice-president till 1893, and to its
