(b. Aillant-sur-Milleron, France, 29 December 1843; d. Vincennes, France, 16 October 1918)
Seldom mentioned in English chronologies, Deprez was a major innovator in many fields of technology. After graduating from the National School of Mines, he served as the school’s secretary from 1866 to 1872. In this period he invented improved valve and indicator mechanisms for steam engines. During the 1870 siege of Paris he conducted pioneer researches, using instruments of his own creation, on the instantaneous gas pressure, metal strain, projectile velocity, and recoil motion produced in the firing of mortar cannon. For this work and for the invention of a railway dynamometer car he received two prizes from the Académie des Sciences.
Deprez was an early promoter, after 1875, of employing electric power in industry, and he collaborated with d’Arsonval and J. Carpentier in the design and manufacture of a wide variety of direct-current measuring instruments, and adapted small motors to manufacturing and domestic uses. He invented compound winding for voltage and speed stabilization in d.c. machines and showed how the operation of such machines could be fully determined from “opencircuit” and “short-circuit” characteristics.
Convinced of the commercial importance of transmitting power electrically, Deprez presented four dramatic and historic public demonstrations of d.c. electric power transmission, the first at Munich in 1881 and the last in 1886 when he sent seventy-five kilowatts over fifty kilometers of line from Creil to Paris. The 5,800-volt dynamo used was of his own design. He and Carpentier foresaw the advantages of high-voltage a.c. power transmission using transformers and patented the principle in 1881, but they did not develop it commercially.
Deprez was elected to the Académie des Sciences in 1886. In 1890 he was appointed professor of electrotechnology at the Conservatoire des Arts et Métiers. Deprez’s work in the areas cited and on other topics, such as the laws of friction, the mechanical equivalent of heat, planimeters, and electric clocks, is described in more than sixty scientific papers, mainly in the Comptes rendus de l’Académie des sciences.
Deprez’s works are listed in Poggendorff. Revue générale de l’élctricité published a special issue (Paris, 1935) commemorating the fiftieth anniversary of Deprez’s powertransmission demonstration at Creil. Two obituaries appear in Comptes rendus de l’Académie des sciences, 167 (1918), 57–574; and Electrician (17 Jan. 1919).
Robert A. Chipman