TROWBRIDGE, William Petit, engineer, born in Oakland county, Michigan, 25 May, 1828. He was graduated at the United States military academy in 1848 at the head of his class, and promoted 2d lieutenant in the corps of engineers. During the last year of his course he acted as assistant professor of chemistry, and after graduation he spent two years in the astronomical observatory at West Point, preparing himself for duty in the United States coast survey, to which he was ordered at his own request. In 1852 he was assigned to duty under Alexander D. Bathe in the primary triagulation of the coast of Maine, which in 1852 was placed under his immediate charge. Later he executed surveys of Appomattox river, in Virginia, with a view to the improvement of its navigation, and also similar surveys of James river near Richmond. He also surveyed the Dutch gap, and recommended the "cut-off," or canal, that was subsequently constructed. In 1853 he was sent to the Pacific coast, where he conducted a series of tidal and magnetic observations extending through a period of three years along the coast from San Diego to Puget sound. He became 1st lieutenant, 18 December, 1854, returned from the west in 1856, and resigned from the corps of engineers on 1 December to accept the professorship of mathematics in the University of Michigan, which chair he held for a year. At the solicitation of Supt. Alexander D. Bache he accepted the permanent appointment of assistant on the coast survey, and was engaged in preparing for publication the results of the Gulf stream exploration. In 1860 he was sent to Key West to superintend the erection of a permanent self-registering magnetic observatory, and in 1861 he prepared minute descriptions of the harbors, inlets, and rivers of the southern coast, for the use of the navy. Later he was ordered to execute a hydrographic survey of Narragansett bay, where there was a design to erect a navy-yard, but the results of the survey were not favorable to the project. Soon after the beginning of the civil war he was placed in charge of the engineer office in New York city, where his duties included the supply of materials for fortifications and other defences, and the construction and shipping of engineer equipage for armies in the field. He also was superintending engineer of the constructing of the fort at Willett's point, New York, of repairs of Fort Schuyler, New York, and in charge of works on Governor's island in New York harbor. In 1865 he became vice-president of the Novelty iron-works in New York city, with direction of their shops, where he remained for four years. He was then elected professor of dynamical engineering in the Sheffield scientific school of Yale until 1876, when he was called to take charge of the engineering department of the School of mines of Columbia, which place he now holds. Professor Trowbridge held various state offices while he was in New Haven, notably that of adjutant-general with the rank of brigadier-general on the governor's staff in 1872-'6. The degree of A.M. was conferred on him by Rochester in 1856 and by Yale in 1870, that of Ph. D. by Princeton in 1879, and that of LL.D. by Trinity in 1880, and the University of Michigan in 1887. He is a member of scientific societies, and vice-president of the New York academy of sciences, was vice-president of the American association for the advancement of science, presiding over the section of mechanical science in 1882, and in 1878 was elected to the National academy of sciences. In addition to many papers in scientific journals and the transactions of societies of which he is a member, he has published "Proposed Plan for building a Bridge across the East River at Black-well's Island" (New York. 1869) ; "Heat as a Source of Power" (1874) ; and "Turbine Wheels" (1879).