MAHAN, Dennis Hart, engineer, born in New York city, 2 April, 1802; died near Stony Point, New York, 16 September, 1871. He spent his boyhood in Norfolk, Virginia, and was appointed from that state to the United States military academy, where he was graduated in 1824, at the head of his class. During his third year he was appointed acting assistant professor of mathematics at the academy, and he continued as such after his promotion as 2d lieutenant into the corps of engineers until 1825, when he became principal assistant professor of engineering. In 1826 he was sent abroad, by order of the war department, to study public engineering works and military institutions, and he spent some time, by special favor of the French government, at the Military school of application for engineers and artillerists in Metz. While in Paris he was frequently the guest of Lafayette. He returned to West Point in 1830, and resumed his duties as acting professor of engineering, which chair he accepted permanently in 1832, vacating his commission in the corps of engineers. This office he continued to hold, with that of dean, after 1838, until his death, which was by suicide during a fit of insanity that resulted from his distress on learning that the Board of visitors had recommended that he be put on the retired list, although assured by the president that he should be retained. Professor Mahan was appointed in l850 by the governor of Virginia a member of the board of engineers to decide the controversy between the city of Wheeling and the Baltimore and Ohio railroad company as to the proper route of the railroad to Wheeling. He received the degree of LL. D. from William and Mary in 1852, from Brown in 1852, and from Dartmouth in 1867, and, besides being a member of many scientific societies in the United States, was one of the corporate members of the National academy of sciences in 1863. As an engineer he acquired a world-wide reputation by his text-books, which were used in the military academy and in many universities. They include "Treatise on Field Fortifications" (New York, 1836) ; "Elementary Course of Civil Engineering" (1837 ; rewritten in 1868) ; "Elementary Treatise on Advanced Guard, Outposts, and Detachment Service of Troops" (1847 ; improved ed., 1862); "Elementary Treatise on Industrial Drawing" (1853); "Descriptive Geometry, as applied to the Drawing of Fortifications and Stereometry" (1864); and " Military Engineering," including "Field Fortifications, Military Mining, and Siege Operations" (1865); and "Permanent Fortifications" (1867). He also edited, with additions, an American reprint of Mosely's "Mechanical Principles of Engineering and Architecture " (1856). See the sketch by General Henry L. Abbot in vol. ii. of the "Biographical Memoirs " of National academy of sciences (Washington, 1886). His portrait, painted by Robert W. Weir, is included in the collection of professors to be seen in the library of the United States military academy.--His son, Frederick Augustus, engineer, born in West Point, New York, 28 March, 1847, was graduated at the United States military academy in 1867, and promoted into the corps of engineers as 2d lieutenant, becoming 1st lieutenant in 1869 and captain in 1881. He has served principally on engineering work and on duty as instructor at the military academy. Captain Mahan was associated in the editorship of the latest edition of his father's "Civil Engineering" (1880), and has translated from the French Krantz's "Study on Reservoir-Walls" (New York, 1882).--Dennis Hart's brother, Milo, clergyman, born in Suffolk, Virginia, 24 May, 18"19 ; died in Baltimore, Maryland, 3 September, 1S70, was educated at St. Paul's college, Flushing, L. I., and took orders in the Protestant Episcopal church in 1845. He became rector of Grace church, Jersey City, New Jersey, in 1848, and two years later assistant in St. Mark's church, Philadelphia. He was professor of ecclesiastical history in the General theological seminary, New York city, from 1857 till 1864, and was then called to the rectorship of St. Paul's church, Baltimore, Maryland, where he remained until his death. He received the degree of D. D. from William and Mary in 1852. Dr. Mahan published "The Exercise of Faith" (Philadelphia, 1851) : " History of the Church during the First Three Centuries" (New York, 1860; new ed., enlarged to include seven centuries, 1872);"Reply to Colenso" (1863); "Palmoni, a Free Inquiry" (1864) ; and "Comedy of Canonization" (1868). His works. have been collected, with a memoir, by the Reverend John II. Hopkins, Jr. (a vols., New York, 1872-'5)