Richard Tetley Glazebrook

“ Joule's earlier experiments had shown that when air is allowed to expand into a vacuum there is on the whole neither loss nor gain of heat. According to these more accurate investigations there is a very slight cooling effect produced by the expansion of both air and carbonic acid, while with hydrogen a slight heating effect is observed. ”

“ For this purpose a new electric current meter was invented, which consisted of a coil of wire suspended from the arm of a balance between two fixed coils (Collected Papers, i. 584) . The same principle is adopted at present in Sir William Thomson's balance instruments and in the standard Ampère meter of the Board of Trade. When using the tangent galvanometer to measure a current, an accurate value of the magnetic force due to the earth is required, and this led Joule to examine the methods ordinarily employed, and to suggest modifications and improvements. ”

“ On his return to Manchester, encouraged, no doubt, by the reception of his work at Oxford, and aided by the generous enthusiasm of Thomson, Joule set himself to repeat his experiments on the production of heat by friction. The results were communicated to the Royal Society by Faraday on 21 June 1849, and printed during the following year in the paper ‘On the Mechanical Equivalent of Heat’ (Phil. Trans. 1850, pt. i.; Collected Papers, i. 298) . The introduction to the paper contains a very fair account of the labours of others in the same field. ”

“ This remarkable paper describes a number of experiments in which a small electro-magnet was rotated in water in a magnetic field produced either by permanent magnets or by a fixed electro-magnet. The current induced in the moving coils, the total heat generated, and the energy used in maintaining the motion were all measured, and it was shown that the energy used and the heat produced were both proportional to the square of the current. ”

“ He regularly attended the society's meetings, and throughout his life found there his most congenial society.
In a paper ‘On the Production of Heat by Voltaic Electricity’ (Proc. R. S. 17 Dec. 1840) the first of the great laws with which Joule's name is imperishably connected was announced. The experiments are given in detail in the ‘Philosophical Magazine’ (xix. 260) . Ohm in his work ‘Die galvanische Kette,’ 1827, had introduced and defined the accurate notions to which we now give the names of electro-motive force, current, and resistance, and had stated the law which goes by his name. ”

“ Various other papers on magnetism and electro-magnetism followed; one of these, ‘On Electro-magnetic Forces’ (ib. 1840) , describes almost the earliest attempt known to measure an electric current in terms of a unit. A unit current is defined by Joule as one which, if allowed to pass for an hour through a water voltameter, will decompose nine grains of water. In a lecture delivered at Manchester in February 1841 (ib. vol. viii.) Joule showed that the efficiency of the most nearly perfect electro-magnetic motor that he had contrived was, per lb. ”

“ In 1852 a Royal medal was awarded by the council of the Royal Society to Joule for his researches. He had been elected a fellow on 6 June 1850, and in 1860 he received the Copley medal from the hands of Sir Edward Sabine for the same experiments. In presenting this Sir Edward said: ‘The award of two medals for the same researches is an exceedingly rare proceeding in our society, and rightly so. ”

“ The experimental question referred to in No. 5 was soon submitted to further test, and on 21 Aug. 1843 a paper, the first of a long series on the subject, ‘On the Calorific Effects of Magneto-Electricity and on the Mechanical Value of Heat,’ was read before the British Association at Cork (Phil. Mag. 3rd ser. vol. xxiii.; Collected Papers, i. 123) . ”

“ Trans. 1859; Collected Papers, i. 413) , in which, at the suggestion of Sir William Thomson, the changes in temperature produced by longitudinal extension and compression of various solids were examined; the anomalous behaviour of indiarubber had already been noted by Gough, and careful experiments were made on this point. In 1860 a paper was read ‘On the Surface Condensation of Steam’ (Phil. Trans. 1861; Collected Papers, i. 502) .
The experiments on the value of J., as determined by the heating of a wire, required for their completion an accurate means of measuring an electric current. ”

“ In 1872 his health gave way, and from that time till his death on 11 Oct. 1889 he lived quietly at his residence, 12 Wardle Road, Sale, pursuing his studies so far as his health permitted. His modesty was always notable. ”