Waves propagated through them' (Trans. Royal Irish Academy, vol. xxii.) ; ' On the Original and Actual Fluidity of the Earth and Planets' (ib.), and various papers on the reflection and refraction of polarised light, which were published chiefly in the 'Philosophical Magazine' and 'Philosophical Transactions.' For the first-mentioned paper he obtained the award of the Cunningham medal from the Royal Irish Academy.
Concurrently with this work he was engaged in the study of geology, and in 1851 was appointed professor of geology in the university of Dublin. This chair he held until 1881, when he resigned it on being co-opted a senior fellow.
His geological papers cover a very wide range. Most of them are to be found in the 'Journal' of the Dublin Geological Society, the 'Proceedings ' of the Royal Irish Academy, and the 'Proceedings' of the Royal Society of London. They deal, among other subjects, with the mineralogy of Ireland and of Wales, they include an exhaustive study of Irish granites, and a laborious investigation, carried on in conjunction with Professor Edward Hull, of the composition of the lava of Vesuvius from 1631 to 1868. But perhaps his most important contributions to this science are his studies of the cleavage and joint planes of the old red sandstone of co. Waterford (Dubl. Geol. Soc. Journal, viii. 1857 ; Phil. Trans. 1858).
In physical geology Haughton studied the effect on the position of the earth's axis of elevations and depressions caused by geological changes, with the resulting changes of climate (Proc. Roy. Soc. 1877). His final conclusion on the length of geological time, based on the probable rate of formation of stratified rock, was that the whole duration was about two hundred millions of years. He also investigated the question of geological climate in connection with Rossetti's law of cooling, and arrived at the conclusion that the secular cooling of the sun has been the chief factor in the changes of geological climate.
In connection with this and other geological questions Haughton undertook a laborious series of calculations on solar radiation, the object of which was to determine the effects on terrestrial climates of alterations in the temperature of the sun and in the constitution of the atmosphere. He also made a research on the effect of the great ocean currents on climate (Trans. Roy. Irish Acad. xxviii. 1881 ; Cunningham Memoir, 1885).
In 1854 Haughton commenced the work of reducing and discussing the tidal observations which had been carried out in 1850-1 at various stations on the coast of Ireland under the direction of the committee of science of the Royal Irish Academy. The results of this work are to be found in numerous papers published in the 'Transactions' of the Royal Irish Academy, the 'Proceedings' of the Royal Society, and the 'Philosophical Magazine.' In consequence of this work he was entrusted with the reporting of the observations made on the tides of the Arctic seas by the expedition in the yacht Fox under Sir Leopold McClintock, which went in search of the Franklin expedition, as well as those made on board H.M.S. Discovery (Proc. Roy. Soc. 1875-8). His final papers on this subject appeared in 1893-5 {Trans. Roy. Irish Acad. xxx.)
Haughton's studies on fossils in the course of his geological work led him to desire a closer acquaintance with anatomy, and it was in this way that in 1859, at the age of thirty-eight, he came to enter the medical school of Trinity College as a student. He passed through the full course, and graduated in medicine in 1862. He was appointed medical registrar of the school, and applied himself to the work of reform, which at that time was sadly needed, and the high position attained by the school subsequently was mainly due to his energy and determination. He subsequently became chairman of the medical school committee and university representative on the General Medical Council.
In the cholera epidemic of 1866 Haughton organised from among the students a volunteer nursing staff, the ordinary nursing arrangements being quite insufficient to cope with the epidemic. The fearlessness and energy with which he threw himself into that work was the means of saving many lives. But Haughton's medical course had also a directing influence on his scientific work. He commenced a series of observations on the mechanical principles of muscular action, which were published between 1865 and 1873, chiefly in the 'Proceedings' of the Royal Society and 'Transactions' of the Royal Irish Academy. They were finally condensed and arranged in his book on 'Animal Mechanics,' which appeared in 1873. The object of this volume is to show that the muscular mechanism is so arranged that the work required of it is done with a less expenditure of muscular contraction than would result from any other configuration. This he calls 'the principle of least action.' His opposition to the doctrine of evolution, which was probably largely due
