MITCHELL, William, astronomer, born in Nantucket, Massachusetts, 20 December, 1791; died in Poughkeepsie, New York, 19 April, 1868. He was fitted for college, and it was intended to send him to Harvard, but the war of 181.2 prevented. Subsequently he taught for several years and developed a fondness for astronomy, having only a rude telescope made by a clock-maker. He then became cashier of the Pacific bank in Nantucket, and, with a much better equipped observatory, made systematic determinations in connection with the United States coast survey. Investigations in astronomy and mathematics were the pastimes of his busy life, and were continued until his death. Mr. Mitchell received the degree of A.M. from Brown in 1848, and from Harvard in 1860, being also overseer of the latter university for some years, serving as chairman of the committee to visit the observatory in Cambridge. He was a member of scientific societies, and contributed astronomical articles to the " American Journal of Science " and other similar periodicals.--His daughter, Maria, astronomer, born in Nantucket, Massachusetts, 1 August, 1818, early made such progress in mathematical and astronomical studies as to be able to assist her father in his investigations, meanwhile acquiring her education under his tuition. Later she studied under Charles Peirce, becoming his assistant in the school at Nantucket. She was appointed librarian of the Nantucket athenwum, an office which she held for many years, and since she was seventeen years old she has regularly earned a salary. Her interest in astronomy was not relaxed, and she made many careful observations by herself, and devoted considerable time to the examination of nebuhe and the search for comets. Her efforts proved successful, and, besides finding small nebula, on 1 October, 1847, she discovered a comet, for which she received a gold medal from the king of Denmark, and also a copper medal struck by the republic of San Marino, Italy. When the publication of the American nautical almanac was begun she was employed on that work, which she continued until after her appointment at Vassar. She went to Europe in 1858 and visited the principal observatories of Great Britain and the continent. Miss Mitchell was the guest of Sir John Herschel and Sir George B. Airy during her stay in England, and also visited LeVerrier in Paris and Humboldt in Berlin. After her return from Europe she was presented with a telescope, much larger than any owned by her father, by the women of America, through the exertions of Miss Elizabeth Peabody, of Boston. In 1865 she was called to the professorship of astronomy at Vassar college, which, with the post of director of the observatory, she retained until January, 1888, when she offered her resignation, but the trustees refused to take any definite action, granting her, however, a leave of absence. In addition to her teaching she has in recent years specially studied the sun-spots and the satellites of Jupiter and Saturn. The degree of LL. D. was conferred on her by Hanover in 1852 and by Columbia in 1887. She is a member of various scientific societies, having been elected a member of the American association for the advancement of science in 1850, and a fellow of that organization in 1874. Miss Mitchell was the first woman to be elected to the American academy of arts and sciences, and she has been prominent in the movement tending to elevate woman's work, having held the presidency of the American association for the advancement of women at the Syracuse meeting in 1875 and at the Philadelphia meeting in 1876. Her published writings have been restricted to scientific papers.--William's son, Henry, hydrographer, born in Nantucket. Mass., 16 September, 1830, was educated at private schools, and turned his attention to physical hydrology as relating to rivers and harbors and their regimen and control under the action of tide-water and river currents. His earliest work was performed under the auspices of the United States coast survey, near the islands of Nantucket and Martha's Vineyard. Subsequently he made the waters of the vicinity, of New York the subject of his investigations, serving as assistant to the commissioners on harbor encroachments in 1859, and while thus employed first discovered the underflow of the Hudson, which has been since shown by him to be a restitution of equilibrium between river and sea waters of different densities, that changes with the seasons, in 1860-'7 he served as consulting engineer to the United States commission on Boston harbor, and later he became a member of the commission itself. He was called in as consulting expert by the National academy sent to investigate the causes of the decline of Greytown harbor, Nicaragua, in 1867, and the report contained a theory of the case that has since been confirmed by his later observations at Greytown. Mr. Mitchell has held government commissions to examine the principal harbors along the Atlantic coast, including Portland, Maine, Providence, Rhode Island, Norfolk and Portsmouth, Virginia, and Philadelphia, Pennsylvania, many of which he has been called to report on several times. In 1874 he was appointed to represent the United States coast survey in the board of engineers for the improvement of the mouth of the Mississippi, and was subsequently a member of the James B. Eads advisory board and of the Mississippi river commission. He was invited to take part in the Agassiz summer-school, and has also held the chair of physical hydrography in the Massachusetts institute of technology. He visited the Suez canal in 1879, and inspected it under the authority of Ferdinand de Lesseps, publishing a report in the "North American Review." Mr. Mitchell received the degree of A. M. from Harvard in 1867, is a member of the American society of civil engineers, and was chosen to the National academy of sciences in 1885. His scientific papers have been published principally in the United States coast survey reports. Among the most important are "Reclamation of Tide-Lands and its Relation to Navigation" (1869); "On an Inspection of the Terminal Points of the proposed Canal through Nicaragua and the Isthmus of Darien" (1874); "Notes concerning Alleged Changes in the Relative Elevations of Land and Sea" (1877); " Physical Hydrography of the Gulf of Maine" (1879) ; "The Estuary of the Delaware" (1883) ; and " On the Circulation of the Sea through New York Harbor" (1886).