HASSLER, Ferdinand Rudolph, surveyor, born in Aarau, Switzerland, 6 October, 1770; died in Philadelphia, Pennsylvania, 20 N o v., 1843. He received a scientific education in Europe, and was for some time connected with the trigonometrical survey of Switzerland. Subsequently he emigrated to the United States, and through the influence of Albert Gallatin secured an appointment at the United States military academy as acting professor of mathematics, which he held in 1807-'10, and in 1810-'11 he served in a similar capacity in Union college. He was then selected to direct the United States coast survey, and sent on a mission to France and England to procure instruments and standards of measurement. He was detained in England as an alien enemy till 1815, and on his return was formally appointed superintendent of the coast survey, but did not begin his field work until 1817. During the following year the work was discontinued, and was not resumed until 1832. After this he was the active head of the survey until his death. During his administration a base line had been measured in the vicinity of New York. The triangulation had been extended as far east as Rhode Island and south to the head of Chesapeake bay. The topography had kept pace with the triangulation, and the hydrography of New York bay, of Long Island, of Delaware bay and river, and the off-shore soundings from Montauk point to the capes of the Delaware, were substantially completed. The triangulation covered an area of 9,000 square miles, furnishing determinations of nearly 1,200 stations for the delineation of 1,600 miles of shore line. Professor Hassler was also for many years chief of the bureau of weights and measures. He was a fellow of the American philosophical society, and contributed papers to its "Transactions" pertaining to his work on the survey. Besides his annual reports of the coast survey, and as superintendent of the fabrication of standard weights and measures (Washington, 1837-'42), he published "Analytical Trigonometry" (New York, 1826); "Elements of Geometry" (Richmond, 1828); " System of the Universe," with plates and tables (2 vols., New York, 1828); "Logarithmic and Trigonometric Tables" (1838); and "Elements of Arithmetic" (1843).