James David Forbes, a Scottish physicist, horn in Edinburgh, April 20, 1809, died at Clifton, Eng., Dec. 31, 1868. He was educated at the university of Edinburgh, and at the age of 17 he began a correspondence on scientific matters with Dr. (afterward Sir David) Brewster, which continued for some years, and Forbes's papers were published in Brewster's "Journal." In the summer of 1826 he visited the continent; he ascended Vesuvius, publishing his observations, and during this tour made his first visit to Chamouni. In June, 1830, he passed as an advocate, but immediately abandoned the bar to devote himself to scientific pursuits. In the ensuing winter he became a member of the royal society of Edinburgh. In September, 1831, he assisted in founding the British association. In January, 1833, at the age of 24, he was elected professor of natural philosophy in the university of Edinburgh, and entered upon the duties in November following. In 1837 he was appointed dean of the faculty of arts. His summer vacations were devoted to travel.

He passed the summers of 1837 and 1838 in an extended tour through north Germany and Austria; from May to August, 1839, he was in the south of France, and was more or less among the Alps; and in July, 1841, in company with Prof. Agassiz, he ascended the Jungfrau. His first Alpine experiences appeared in an article on glaciers in the Edinburgh Review," April, 1842, though the year before he had published in the proceedings of the royal society his views on the peculiar structure of the ice in glaciers, and in August, 1840, he had crossed the southern spurs of Monte Rosa from valley to valley, exploring the glaciers as he went. In September, 1842, he was again at Chamouni, and numerous geological excursions to Vesuvius in the vicinity of Naples occupied him till the end of the year. In 1843 he published "Travels through the Alps of Savoy," and in April of that year he visited Mt. Etna. The summers of 1844 and 1846 he devoted to the measurement of the rate of motion in the Swiss glaciers. In the summer of 1845 he made a tour of the western highlands, explored Coolin mountain in the isle of Skye, in company with M. Necker, and found indisputable traces of glaciers. In September of that year Sir Robert Peel conferred upon him a government pension of £200 a year.

He passed his vacation in 1850 at Chamouni, not specially occupied with glacier observations, but correcting and extending his survey. He crossed from the Glacier du Tour, descending into the Swiss Val Ferret by the Glacier de Salena, making the most interesting, most difficult, and last of his expeditions among the higher glaciers of the Alps. His survey of the Mer de Glace was the last of his Alpine work. His last scientific journey was in June, 1851, to Bergen, Norway, to observe an eclipse of the sun visible only in northern latitudes; and on his way to Christiania he visited the glaciers of the Hardangertield. In 1853 he published "Norway and its Glaciers," and in 1855Tour of Mont Blanc and Monte Rosa." In December, 1859, he succeeded Sir David Brewster as principal of the United college in St. Andrews, and in April following he resigned his chair at Edinburgh. His health had been failing since 1852, and he resigned his principalship in October, 1868, two months before his death. He had received the degree of I). C. L. from Oxford university in 1855. Besides the works above enumerated, Dr. Forbes printed from 1827 to 1867 in the"Edinburgh Journal of Science the proceedings of the royal society of Edinburgh and of the British association, the "Edinburgh New Philosophical Journal," and other publications, more than 100 important scientific papers on geology, meteorology, electricity, magnetism, refraction and polarization of heat, volcanic formations, temperature and conducting powers of different strata, excessive rainfall, and many other subjects.

Among his original contributions to physical science is the polarization of radiant heat, which he confirmed by a variety of ingenious experiments. Besides his works on the Alps and Norway, he published 15 letters and several papers on glaciers. He claimed the discovery of the real structure of glacier ice; the treatment of glacier motion as a problem of mechanical forces and its examination as such; and, generally, the first attempt to explain the leading phenomena of glaciers. These claims involved him in a controversy with Prof. Tyndall and others.-See his "Life and Letters," by Shairp, Tait, and Adams-Reilly (London, 1873).