HOPKINSON, JOHN (1849-1898), English engineer and physicist, was born in Manchester on July 27, 1849. After a brilliant career at Cambridge and London universities, he became a pupil in the engineering works in which his father was a partner. In 1872 he undertook the duties of engineering manager in the glass manufactories of Messrs. Chance Brothers and Company at Birmingham. Six years later he removed to London, where he established a most successful practice as a consulting engineer. His work was mainly electrical, and his services were in great demand as an expert witness in patent cases. In 1890 he was appointed director of the Siemens laboratory at King's college, London, with the title of professor of electrical engineering. His death occurred prematurely on Aug. 27, 1898, when he was killed, together with one son and two daughters, by an accident while climbing the Petite Dent de Veisivi, above Evolena. Hopkinson presented a rare combination of practical with theoretical ability. His name is best known in connection with electricity and mag netism. He worked out the general theory of the magnetic circuit in the dynamo (in conjunction with his brother Edward), and the theory of alternating currents, and conducted a series of observa tions on the phenomena attending magnetization in iron and nickel and the curious alloys of the two which can exist both in a magnetic and non-magnetic state at the same temperature. By the application of the principles he elucidated, he furthered to an immense extent the employment of electricity for the purposes of daily life. He made great improvements in the design and efficiency of the dynamo. Hopkinson took a leading part in the development of the three-wire system and the closed-circuit transformer used in the distribution of electric current and he introduced the series parallel method of working motors. During his work with Messrs. Chance, Hopkinson turned his attention to problems of lighthouse illumination, and he was able to devise improvements in both the catoptric and dioptric methods for concentrating and directing the beam. He was a strong advocate of the group-flashing system as a means of differentiating lights, and invented an arrangement for carrying it into effect optically. He further undertook researches on electrostatic capacity, the phenomena of the residual charge, and other problems arising out of Clerk Maxwell's electromag netic theory.
His original papers were collected and published, with a memoir by his son, in 1901.