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 blished by these researches the identity of thermal and luminous radiations.’ Professor P. G. Tait, in his survey of the scientific work of Forbes, observes that his ‘discovery of the polarisation of heat will certainly form an epoch in the history of natural philosophy.’ At a later stage Forbes determined the thermal conductivity of trap-tufa sandstone and pure loose sand, and finally obtained quantitative measurements of the absolute thermal conductivity of iron at various temperatures, and showed that this is diminished (contrary to the assumption of Fourier) by increase of temperature, thus following the known laws of electrical conductivity.

But Forbes is equally well known by his glacier theory, which he summed up in the statement that ‘a glacier is an imperfect fluid or viscous body which is urged down slopes of a certain inclination by the mutual pressure of its parts.’ The analogy between glaciers and viscous bodies had been vaguely noticed by previous observers, such as Bordier (1773), Basil Hall, and especially Bishop Rendu of Annécy. Forbes was undoubtedly the first to obtain accurate measurements, and to establish a definite base for future theories. He was, as Professor Tait says (ib. p. 511), ‘the Copernicus or Kepler of this science.’ He announced facts, though he did not properly give a physical theory. The facts were sufficient to explode the so-called gravitation and dilatation theories previously current, and they have been partly explained by theories of W. Hopkins, Faraday, James and Sir William Thomson, and Professor Tyndall. Forbes's substantial originality is unquestionable, and Professor Tyndall says that his book was ‘worth all other books on the subject taken together.’ Some unfortunate discussions arose as to his relations to other inquirers. His first observations were made during a visit to Agassiz's hut on the lower Aar glacier in 1841. Forbes claimed to have been the first to notice the ‘veined structure’ in glaciers, and it seems that he was certainly the first to recognise its importance and publish an account of it. Professor Guyot of Neufchatel had noticed it previously, but his notes remained in manuscript. Agassiz had also apparently seen it, but without attaching importance to it. Two honourable men were alienated by the discussions arising out of this, and by an alleged want of recognition on Forbes's part of Agassiz's previous work. Professor Tyndall, in his ‘Glaciers of the Alps’ (1860), gave an account of Rendu's speculations, which Forbes and his friends considered to attribute too much to the earlier inquirer. Forbes wrote a ‘reply,’ now appended to his ‘Life.’ He had certainly himself called attention to Rendu's work in his first book, and Rendu afterwards wrote to him in the friendliest terms, showing no sense of injury. He must be acquitted of any intentional unfairness, and may fairly claim to have founded the scientific study of the phenomena. Full information may be found in Forbes's ‘Life’ and in the papers there referred to, with which should be compared Professor Tyndall's ‘Principal Forbes and his Biographers’ (1873). Forbes's chief work, ‘Travels through the Alps of Savoy and other parts of the Pennine Chain, with Observations on the Phenomena of Glaciers,’ appeared in 1843. It is the most charming, as well as most scientifically important of all books of Alpine travel. A list of 149 publications of various kinds, chiefly papers in the ‘Proceedings’ of the Royal Society of Edinburgh, is appended to his ‘Life,’ besides which he contributed articles to the ‘Quarterly,’ ‘Edinburgh,’ and other reviews upon scientific subjects.

The Royal Society of London awarded to Forbes the Rumford medal for his discovery of the polarisation of heat, and the royal medal for a paper on the influence of the atmosphere on the sun's rays. The Keith medal of the Royal Society of Edinburgh was thrice presented to him, and he occupied the post of secretary to that society from 1840 till the failure of his health in 1851. Besides being a fellow of the Royal Societies of London and Edinburgh, and of the Geological Society, he was corresponding member of the Institute of France, and associate or honorary member of the Bavarian Academy of Sciences, of the Academy of Palermo, of the Dutch Society of Sciences (Haarlem), of the Helvetic Society, of the Pontifical Society, of the Pontifical Academy of Nuovi Lincei at Rome, and of the Natural History Societies of Heidelberg, Geneva, and Vaud; and honorary member of the Royal Medical Society of Edinburgh, of the Cambridge, Yorkshire, St. Andrews, and Isle of Wight Philosophical Societies, and of the Plymouth and Bristol Institutions.

[Forbes's Life and Letters, by Principal Shairp, Professor P. G. Tait, and A. Adams-Reilly, 1873; Professor Forbes and his Biographers, by Professor Tyndall, 1873; Chambers's Encyclopædia, 1874; Encyclopædia Britannica (ninth ed.), art. ‘Forbes,’ 1879; Waller's Imperial Dict.; Forbes's Scientific Writings.] 

FORBES, JAMES OCHONCAR, seventeenth (1765–1843), colonel, was the eldest son of James, sixteenth baron, by Catherine, only daughter of Sir Robert Innes, bart., of Ortoun. The lands of Forbes in Aberdeenshire, still in their possession, have been held by this ancient family since the