Sears Cook Walker, an American mathematician, born in Wilmington, Mass., March 28, 1805, died in Cincinnati, Jan. 30, 1853. He graduated at Harvard college in 1825, taught school for several years near Boston and in Philadelphia, and actively engaged in scientific labors. His parallactic tables, first prepared in 1834 for the latitude of Philadelphia, greatly reduced the time needed for computing the phases of an occultation. In the " Memoirs of the Philosophical Society" (new series, vol. i.) he published a long series of observations of occupations. In 1837 he prepared a plan for the organization of an observatory in connection with the Philadelphia high school, which was one of the earliest built in America. (See Observatory, vol. xii., p. 567.) In 1841 he published a valuable memoir on the periodical meteors of August and November. In 1845 he received an appointment in the Washington observatory, where on Feb. 2, 1847, four months after the detection of the planet Neptune, he made the discovery that a star observed by Lalande in May, 1795, must in fact have been this planet.

The prediction consequently made, that the recorded star would not be found in the heavens, was confirmed by Prof. Hubbard. The same discovery was made independently in Europe a few weeks later by an actual examination of the heavens through 270 square degrees, and confirmed by an examination of the original manuscripts of Lalande. From 1847 till his death Mr. Walker had charge of the longitude computations of the United States coast survey. With Prof. Bache he developed the method of determining differences of longitude by telegraph, which was put into successful operation in 1849.