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 and original character and high desert of Mr. Joule's discovery.’

The summary already given is not by any means a complete account of Joule's activity. In 1848, in a paper entitled ‘Some Remarks on Heat and on the Constitution of Elastic Fluids’ (Phil. Mag. 4th ser. vol. xiv.; Collected Papers, i. 290), he determined, according to the molecular theory of gases, the velocity of a molecule of hydrogen under a pressure of one atmosphere, and about the same time he calculated the ratio in which, according to the theoretical correction of Laplace, Newton's value for the velocity of sound required to be increased. The result of this calculation (‘On the Theoretical Value of Sound,’ Phil. Mag. 3rd ser. vol. xxxi.; Collected Papers, i. 282) was to bring up Newton's theoretical value from 943 to 1095 feet per second. The value given by Newton's measurements was 1130.

The results of some experiments on the air-engine (Phil. Trans. 1852, pt. i.; Collected Papers, i. 331) were communicated to the Royal Society on 19 June 1851, and about the same time the important series of papers ‘On the Thermal Effects experienced by Air in rushing through Small Apertures’ (Phil. Mag. 4th ser. Suppl. vol. iv.; Collected Papers, ii. 216) and ‘On the Thermal Effects of Fluids in Motion’ (Phil. Trans. 1853; Collected Papers, ii. 231) was commenced in conjunction with Sir William Thomson. 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. These results are in satisfactory accord with Thomson's thermo-dynamic reasoning, as developed in his paper already referred to. The experiments were carried out in part in one of the cellars of his house in Acton Square, Salford, and afterwards in a large yard attached to his father's brewery, New Bailey Street, Salford.

This series of papers was followed by an investigation into ‘Some Thermo-dynamic Properties of Solids’ (Phil. 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. 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. These are contained in papers ‘On an Apparatus for determining the Horizontal Intensity in Absolute Measure’ (Proc. Manchester Lit. and Phil. Soc. vi. 129; Collected Papers, i. 561), and ‘On a New Magnetic Dip Circle’ (Proc. Manchester Lit. and Phil. Soc. viii. 171; Collected Papers, i. 575), with experiments on magnets (ib. i. 589).

In his earlier years Joule made various experiments on magnetism with Dr. Scoresby, while about 1845 he was engaged with Dr. (now Sir) Lyon Playfair in various researches on the change of volume occurring on solution, and the relation in volumes between simple bodies, their oxides and sulphurets (Memoirs of the Chemical Society, vols. i. ii. and iii.; Collected Papers, ii. 11, 117, 173, 180). The third of the above papers contains the account of his experiments on the temperature at which the density of water is a maximum.

Joule's work sufficiently indicates the breadth of his interests and the greatness of his powers. His papers were collected by the Physical Society of London, under his own editorship, and appeared in two volumes; the first contains his own papers, the second those published by him jointly with others (, Scientific Papers, vol. i. 1885, vol. ii. 1887). He was to have been president of the British Association at the Bradford meeting in 1872, and again at the Manchester meeting in 1887, but ill-health prevented his attendance on both occasions. 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. ‘I believe,’ he told his brother on 14 Sept. 1887, ‘I have done two or three little things, but nothing to make a fuss about.’ During the later years of his life he received many distinctions both English and foreign. He was created LL.D.