BARTLETT, William Hohns Chambers, mathematician, born in Lancaster, Pennsylvania, in 1809. He removed with his family to Missouri while yet an infant, and was appointed to the United States military academy from that state. During the last two years of his cadetship he served as acting professor of mathematics. He was graduated in 1826 at the head of his class, and was one of the few who have passed through the rigid course at West Point without any demerit marks. He was at once commissioned second lieutenant of engineers. For two years, 1827-'9, he was assistant professor of engineering at West Point. From 1829 till 1834 he was on engineering duty, constructing the principal coastwise fortifications. His permanent appointment as professor of natural and experimental philosophy at the military academy was made 20 April 1836. He received the honorary degree of A. M. from Princeton in 1837, and of LL.D. from Geneva, New York (now Hobart), College in 1847. He is the author of many contributions to " Silliman's Journal," and of an elaborate paper on rifled guns, published in the memoirs of the national academy of sciences, of which association lie was one of the original incorporators. In 1840 he was sent abroad to procure instruments for the astronomical observatory at West Point, and visited the principal observatories of the world. He was retired from military service at his own request in 1871, with the rank of colonel, and shortly afterward accepted the place of actuary for the Mutual Life Insurance county of New York. He prepared several textbooks for the use of the cadets, which have been adopted in many of the best Colleges. . Their titles are as follows : "Treatise on Optics" (New York, 1839) ; "Synthetical Mechanics" (1850), containing some of his original theorems, notably that of the conservation of work, applicable to all branches of scientific study; " Analytical Mechanics" (1853) ; and "Spherical Astronomy" (1855).