cession to James David Forbes [q. v.] The candidates included Clerk Maxwell and Edward John Routh [q. v. Suppl. II]. Tait's prochvity lay towards physical rather than purely mathematical work. On his arrival in Edinburgh he was elected a fellow of the Royal Society, and four years later became one of its secretaries. Henceforth his spare time was divided between literary work and criticism, and experimental research of exceptional note in the university laboratory, the results of which were presented to the Royal Society of Edinburgh or published in Journals of other societies. Unusual thoroughness characterised all his scientific work, whether expository or experimental. He was a good linguist, French, German, and Italian being equally at command, and he was quickly conversant with the scientific work of the continent. He contributed to British scientific journals translations of valuable foreign papers, including Helmholtz's famous papers on ' Vortex Motion' (Phil. Mag. 1867) and F. Mohr's 'Views on the Nature of Heat' (ibid. 1876).
Tait early came into contact with (Sir) William Thomson (afterwards Lord Kelvin) [q. v. Suppl. II], who had become fellow of Peterhouse in 1845, but had left Cambridge next year to become professor of natural philosophy at Glasgow. In that capacity Thomson first made Tait's acquaintance. In 1861 Tait was engaged on a book on mathematical physics, and had nearly completed arrangements for publication with the Cambridge firm of Macmillan, 'when Thomson to my great delight offered to join.' The result was Thomson and Tait's Natural Philosophy.' Two books were at first intended: a handbook for students and another, 'Principia Mathematica,' which Tait referred to as 'quite unique in mathematical physics,' and 'our great work'; but Thomson's other engagements threw the bulk of the writing on Tait, and only a single 'first' volume came to birth late in 1867. The earlier portion was written by Tait. Thomson's hand is more apparent in the later portion. The work was epoch-marking, and created a revolution in scientific development. For the first time 'T & T,' as the authors called themselves, traced to Newton (Principia, Lex iii.. Scholium) the concept of the 'conservation of energy' which was just then obtaining recognition among physicists, and they showed once for all that 'energy' was the fundamental physical entity and that its 'conservation' was its predominating and all-controlling property. In Tait's words, 'Thomson and he had rediscovered Newton for the world.' Their treatise takes rank with the 'Principia,' Laplace's 'Mecanique Celeste,' and Clerk Maxwell's 'Electricity and Magnetism.' A second edition of 'Thomson and Tait' appeared in two parts, issued respectively in 1879 and 1883. No further opportunity of collaboration offered. The material which Tait had collected for the second section of the joint original design he worked up independently into volumes for students on 'Heat' (1884; new edit. 1892), 'Light' (1884; last edit. 1900), and 'Properties of Matter' (1885; 5th edit. 1907). In these educational handbooks Tait presented each subject as a connected whole, avoiding all examination methods of presentation, carrying on the student logically by experiment and general reasoning to the main truths, and only introducing mathematics when really necessary or useful to shorten some process of reasoning. 'Heat' and 'Properties of Matter' were soon translated into German.
Tait was a strenuous controversialist, especially where his friends were concerned. He actively defended his predecessor, James David Forbes, in his struggle with Tyndall, who asserted his priority to Forbes in his theory of the motion of glaciers. In Tait's second important work, 'Thermodynamics' (1868; 2nd edit. 1877), which still enjoys authority, he established against Julius Robert Mayer, the German physicist, the claim of James Prescott Joule [q. v.] to have first determined strictly the relationship between heat and work. Tait similarly defended Thomson (Lord Kelvin) against Clausius's claim in 1854 to prior discovery, both theoretically and experimentally, of the fact that Carnot's function was inversely proportional to the temperature as measured on the absolute dynamic scale (Knott's Life of Tait, p. 223).
In the spring of 1874 Tait lectured before the Edinburgh Evening Club, a gathering of congenial friends, on 'Recent Advances in Physical Science.' Tait spoke from notes, but a shorthand transcript was published in 1876 (3rd edit. 1885). The book, which holds a high place in scientific literature, was translated into French, German, and Italian. Subsequently Tait, whose religious sentiment was always strong, joined his colleague Balfour Stewart [q. v.] in an endeavour 'to overthrow materialism by a purely scientific argument.' The result, 'The Unseen Universe, or Physical Speculation on a Future State,' appeared anonymously
