them about this time may be mentioned transmission and absorption dynamometers, and a dispersion photometer. Apart from specific inventions of apparatus and instruments the two men carried out investigations into almost every branch of electric engineering and the branches of mechanical engineering specially useful to the electrical engineer.
In 1891 Ayrton and Perry published their last joint paper, in which, together with one of Ayrton's pupils, Dr. W. E. Sumpner, they showed that the theoretical law previously worked out for quadrant electrometers was not valid. From 1891 onwards Ayrton worked mainly in collaboration with Mr. Thomas Mather, F.R.S. (first his assistant and later his successor), with Dr. Sumpner, and with others of his pupils, past and present. Among his later researches of importance are those on accumulators, on Clark cells, on galvanometer construction, on glow lamps, on non-inductive resistances, on the three voltmeter method of determining the power supplied to a circuit (devised jointly with Dr. Sumpner), on the very ingenious 'universal shunt box' and electrostatic voltmeters, invented jointly with Mr. Mather, work on alternate-current dynamos, on ampere-balances and on transformers, an elaborate determination of the ohm in conjunction with Principal John Viriamu Jones [q. v. Suppl. II], and an investigation of the phenomena of smell, dealt with in Ayrton's presidential address to the mathematical and physical section of the British Association in 1898. An address on 'Electricity as a Motive Power' delivered to working men at the Sheffield meeting of the British Association, 23 Aug. 1879, put forward for the first time the important suggestion that power could be distributed at once most economically and safely by means of high tension currents of relatively small quantity 'transformed down' at the distant end of the transmission system. In the lecture delivered at the Johannesburg meeting of the British Association on 29 Aug. 1905, Ayrton pointed to the fulfilment of his prophecies ; and at the same time discouraged the project for utilising the Victoria Falls on the Zambesi as a generating station, on the ground that the plan proposed was inefficient and that their beauty would be spoilt to no purpose.
Research work was only one side of Ayrton's many activities ; he was employed as a consulting electrical engineer by government departments and by many private firms, and took part as an expert in many important patent cases. He invariably declined to act in legal cases unless a preliminary investigation had convinced him of the soundness of the cause for which he was to appear.
Ayrton was elected fellow of the Royal Society in 1881, and was awarded a royal medal in 1901. In the Institution of Electrical Engineers (founded in 1871 as the Society of Telegraph Engineers and Electricians) Ayrton took a special interest, and the development of the institution, which he joined in 1872, was largely due to his energetic support. From 1878 to 1885 he acted as chairman of the editorial committee and as honorary editor of the 'Journal.' In 1892 he was elected president and from 1897 to 1902 acted as honorary treasurer of the institution. He was president of the Physical Society from 1890 to 1892.
For the admiralty Ayrton carried out important investigations on the heating of cables used in the wiring of warships, on searchlights (in conjunction with his second wife), on sparking pressures, and other matters, and he was a member of the committee appointed in 1901 to consider and report upon 'the electrical equipment of His Majesty's ships.' He served on the committee appointed in 1889 to advise the board of trade on electrical standards, of which the report led to the formation of the present board of trade testing laboratory; and he also served on the general board of the national physical laboratory and on juries of several international exhibitions, including that of Chicago in 1893 and of Paris in 1900. He acted in 1903 as a member of the educational commission organised by Mr. Alfred Mosely, C.M.G., to visit the United States and report on American education.
Above all Ayrton threw himself heart and soul into his teaching. The laboratories, which he created at Finsbury and South Kensington, turned out hundreds of electrical engineers, and by his stirring addresses on technical education, he played an important part in the technical development of the country. His public lectures were elaborately prepared, abounded in striking illustration, and were delivered with the skill and fire of an accomplished advocate. In the laboratory he taught each student to carry out every experiment 'as if he were the first who had ever investigated the matter,' and criticised the work that came to his notice in the most minute detail, and on any indication of want of energy or thoroughness he was mercilessly severe.
