Ellicott. I. Andrew, an American astronomer and civil engineer, born in Bucks co., Pa., Jan. 24, 1754, died at West Point, N. Y., Aug. 28, 1820. His father, a Quaker, having united with a brother in the purchase of a large tract of wild land on the Patapsco river, in 1774 founded the town of Ellicott's Mills (now Elli-cott City), in Maryland, where the younger days of his son were devoted to the study of the sciences and practical mechanics. His scientific attainments early attracted attention, and he enjoyed the friendship and confidence of Washington, Franklin, and Rittenhouse. At various times he was appointed commissioner for marking parts of the boundaries of Virginia, Pennsylvania, and New York. About 1785 he removed to Baltimore, and represented that city in the state legislature. In 1789 he was appointed by Washington to survey the land lying between Pennsylvania and Lake Erie, and during that year he made the first accurate measurement of the Niagara river from lake to lake, with the height of the falls and the descent of the rapids. In 1790 he was employed by the government to survey and lay out the federal metropolis.

In 1792 he was made surveyor general of the United States, and in 1795 he superintended the construction of Fort Erie at Presque Isle (now Erie, Pa.), and was employed in laying out the towns of Erie, Warren, and Franklin. In 1796 he was appointed by Washington commissioner on behalf of the United States, under the treaty of San Lorenzo el Real, to determine the southern boundary separating the United States territory from the Spanish possessions. The results of this service, embracing a period of nearly five years, appear in his "Journal" (4to, with 6 maps, Philadelphia, 1803). Upon the completion of this service he was appointed by Gov. McKean of Pennsylvania secretary of the state land office, from which he retired in 1808, and in 1812 he became professor of mathematics at West Point, a post which he occupied till his death. In 1817, by order of the government, he went to Montreal to make astronomical observations for carrying into effect some of the articles of the treaty of Ghent. He was an active member of the American philosophical society, and maintained correspondence with the learned societies of Europe; but with the exception of his " Journal," contributions to philosophical societies, and a few other writings, his works are yet in manuscript.

II. Joseph, brother of the preceding, born in Pennsylvania, died in Batavia, N. Y., in 1826. In 1790 he assisted his brother Andrew in laying out the city of Washington, and in 1791 was appointed to run the boundary line between Georgia and the Creek Indians; and for a long period, embracing the most active portion of his life, he was engaged in the service of the Holland land company. He was identified with the great public improvements of the state of New York.