eldest daughter of George Wauchope, on 4 July 1843. In consequence of ill-health Forbes was compelled to spend the winter of 1843 and the summer of 1844 in Italy, returning to Edinburgh in September of the latter year. The summer of 1845 was spent with his wife in the west highlands, in a tour ranging from Bute to Skye. In the latter island he explored the Cuchullin mountains with M. Necker, finding ‘amidst the splendid hypersthene formation indisputable traces of glaciers.’ These explorations were afterwards embodied in a paper on the geology of the Cuchullins. In September 1845 a pension of 200l. per annum was conferred upon him for the services he had rendered to science. In 1846 he visited the Alps, and again for the last time in 1850. In 1850 he put the finishing touches to his survey of the Mer de Glace, which for some years was the only correct Alpine map in existence.
The last scientific expedition undertaken by Forbes was a journey to Norway at the close of the university session of 1850–1. He went to see the total eclipse of the sun, and to examine the Norwegian glaciers. The tour was a very fatiguing one, and Forbes returned home with his health greatly impaired. He began his classes in November 1851, but was attacked by hæmorrhage, which proved to be the precursor of a long and dangerous illness. In the succeeding January he moved from Edinburgh to Clifton, which was his headquarters for two years. His enforced leisure was employed in the composition of his ‘Dissertation on the Progress of Mathematical and Physical Science,’ principally from 1775 to 1850, for the eighth edition of the ‘Encyclopædia Britannica,’ and in preparing for the press a work on ‘Norway and its Glaciers,’ similar in character to his ‘Glaciers of the Alps.’ The university of Oxford conferred the honorary degree of D.C.L. on Forbes in June 1853. He resumed his class work in the session of 1854–5, and continued it, with but little interruption from illness, until 1859, being latterly assisted by Dr. Balfour Stewart. The foundation of the Alpine Club in 1858 was regarded by Forbes with keen interest, and he was elected an honorary member.
In 1859 Brewster resigned the principalship of the United College, St. Andrews, on becoming principal of Edinburgh University. Forbes offered himself for the vacancy, with the recommendation of Sir G. Cornewall Lewis, the Duke of Argyll, and Mr. Gladstone. He received the appointment on 2 Dec. 1859, and resigned his professorship at Edinburgh University in the following April, when he received the honorary degree of LL.D. The Scottish University Commission was sitting, and Forbes had to supply it with information and suggestions. He proved himself to be an able and a fearless reformer, and the college was also indebted to him for a laborious examination and classification of its ancient charters. The collegiate church of St. Salvator was in great part restored by his action. He gave lectures on glaciers, climate, heat, and the history of discovery, and endeavoured to complete his researches on the conductivity of iron. In consequence of continued weak health Forbes was obliged to decline the presidency of the British Association in 1864. From this time forward there was no recovery in his condition. The last public act he performed was to preside at the ceremonial of the laying of the foundation-stone of the new college hall at St. Andrews—a building which owed its existence entirely to his own exertions. By September 1867 he had to go to the Riviera for his health. His weakness obliged him to decline an offer of the presidency of the Royal Society of Edinburgh. In the summer he returned to Clifton, to be under the care of Dr. Symonds. He lingered for eight months, and died on 31 Dec. 1868.
Forbes, though somewhat cold in manner, united to a very sensitive nature a high moral courage, while his domestic affections were unusually warm. He was methodical and persevering, and his cousin, Bishop Forbes, says that his ‘sense of right amounted to chivalry.’ He was a strict disciplinarian, and somewhat over-sensitive about his claims to scientific reputation (Life, p. 467), but he was universally respected, and was beloved by his intimate friends. He left a great mass of correspondence, which is said to be of much interest, but too much concerned with personal controversy to be published at present. He was an attached member of the episcopal church of Scotland. Forbes had two sons, Edward Batton and George, and three daughters, one of whom died before, and the others soon after him.
An original experimenter upon heat, Forbes, beginning with Melloni's thermo-multiplier, measured the refractive index of rock-salt with heat from various sources, luminous and non-luminous, and was led in early life to his most brilliant discovery, viz. the polarisation of heat, by transmission through tourmaline and thin mica plates, and by reflection from the latter. ‘By employing mica for depolarisation, he succeeded in showing the double refraction of non-luminous heat—a fact of which this experiment remains the only proof. He also produced circularly polarised heat of two internal reflections, using Fresnel's rhombs made of rock-salt. He thus esta-
