Ferrel, William

Ferrel, William (1817–91) meteorologist; born in Fulton County, Pa. Largely self-taught, he is credited with moving meteorology from a descriptive science to a quantitative science. He was the first to describe mathematically the significance of the earth's rotation on its surface bodies. Known as Ferrel's Law, it states, "if a body is moving in any direction, there is a force, arising from the earth's rotation, which always deflects it to the right in the northern hemisphere and to the left in the southern hemisphere." He taught school in the midwest before joining the American Ephemeris and Nautical Almanac in Cambridge, Mass., in 1857. From 1867–82 he worked on the U.S. Coast and Geodetic Survey. As a member of the Signal Service (1882–86), he invented a tide machine, the first to predict maximum and minimum tides. His publications include Popular Essays on Movement of the Atmosphere (1882).