Forbes was born on 20 April 1809 at 86
George Street in Edinburgh, the fourth son of Sir
William Forbes, 7th Baronet, of
Monymusk and
Pitsligo (1773–1828) and Williamina Belches of
Invermay. His brothers were the advocate and agriculturalist Sir
John Stuart Hepburn Forbes of Fettercairn and Pitsligo and the banker Charles Forbes. He entered the
University of Edinburgh in 1825, and soon afterwards began to contribute papers to the
Edinburgh Philosophical Journal anonymously under the signature "Δ". At the age of nineteen he became a fellow of the
Royal Society of Edinburgh, and in 1832 he was elected to the
Royal Society of London. At this time he maintained correspondence with Sir
David Brewster, who encouraged him to pursue an original research in science. A year later he was appointed professor of natural philosophy at the University of Edinburgh in succession to Sir
John Leslie, and during his tenure of that office, which he did not give up until 1860, he not only proved himself an active and efficient teacher, but also did much to improve the internal conditions of the university. In 1859 he was appointed successor to Brewster in the principalship of the United College of St Andrews, a position which he held until his death at Clifton in 1868. As a scientific investigator he is best known for his researches on heat and on glaciers. Between 1836 and 1844 he published in the
Trans. Roy. Soc. Ed. four series of "Researches on Heat," in the course of which he demonstrated that
tourmaline would
polarise infrared thermal radiation, by transmission through a bundle of thin mica plates inclined to the transmitted ray, and by reflection from the multiplied surfaces of a pile of
mica plates placed at the polarising angle, and also its
circular polarisation by two internal reflections in
rhombs of
rock salt. His work won him the
Rumford Medal of the Royal Society in 1838, and in 1843 he received its
Royal Medal for a paper on the "Transparency of the Atmosphere and the Laws of Extinction of the Sun's Rays passing through it." He invented an inverted pendulum
seismometer in 1842. In 1846 he began experiments on the temperature of the earth at different depths and in different soils near Edinburgh, which yielded determinations of the thermal conductivity of trap-tufa,
sandstone and pure loose
sand. Towards the end of his life he was occupied with experimental inquiries into the laws of the conduction of heat in iron bars, and his last piece of work was to show that the thermal conductivity of iron diminishes with increase of temperature. His attention was directed to the question of the flow of glaciers in 1840 when he met
Louis Agassiz at the Glasgow meeting of the British Association, and in subsequent years he made several visits to Switzerland, where he was particularly impressed by
Bernhard Studer's theories, and also to Norway for the purpose of obtaining accurate data. His observations led him to the view that a glacier is an imperfect fluid or a viscous body which is urged down slopes of a certain inclination by the mutual pressure of its parts, and involved him in some controversy with Tyndall and others both as to priority and to scientific principle. A notable defender of Forbes in this controversy was
John Ruskin, the two having first met by coincidence in 1844 during a study tour of the
Alps. During these expeditions, he made many measurements of the
boiling point of water at various altitudes. This data set, published in 1857, is often known in statistics as ''Forbes's data'', its utility being that: • It illustrates how a
curvilinear relationship between a
dependent and
independent variable can be transformed into a
linear model by knowledge of the
physical phenomenon observed. • It emphasises the importance of
residuals analysis in
linear regression as the residuals manifest an
outlier that is not apparent in a visual inspection of the raw data. Forbes was also interested in geology, and published memoirs on the thermal springs of the
Pyrenees, on the extinct volcanoes of the Vivarais (
Ardèche), on the geology of the Cuchullin and Eildon hills, etc. In addition to about 150 scientific papers, he wrote
Travels through the Alps of Savoy and Other Parts of the Pennine Chain, with Observations on the Phenomena of Glaciers (1843);
Norway and its Glaciers (1853);
Occasional Papers on the Theory of Glaciers (1859);
A Tour of Mont Blanc and Monte Rosa (1855). He was also the author (1852) of the "Dissertation on the Progress of Mathematical and Physical Science," published in the eighth edition of the
Encyclopædia Britannica. The
Forbes River,
Mount Forbes, and
Forbes Glaciers in New Zealand are named after him as is Aiguille Forbes between the
Glacier de Saleina and the Glacier du Tour in the
Mont Blanc massif. James David Forbes was a devout Christian, as can be seen in the work "
Life and Letters of James David Forbes" (1873), a compilation of personal letters written by Forbes, co-authored by
John Campbell Shairp and Forbes's student
Peter Guthrie Tait. He died on 31 December 1868 and is buried in
Dean Cemetery in
Edinburgh. The grave is marked by a simple but large grey granite
Celtic cross and lies on the south side of the main path just west of the roundel. His wife, Alicia Wauchope (1824–1885), is buried with him. His cousins were
Scottish Episcopal Church leaders
Alexander Penrose Forbes and
George Hay Forbes. His son was the scientist
George Forbes. ==Selected publications==