Ferrel , William

(1817–1891) American meteorologist

Born in Fulton County, Pennsylvania, Ferrel moved with his family to farm in West Virginia in 1829. Receiving only the most rudimentary education, his early scientific knowledge was entirely self acquired. Despite this he developed an interest in mathematical physics and, after graduating from Bethany College in West Virginia in 1844, began to study the Principia of Isaac Newton and the Mécanique céleste (Celestial Mechanics) of Pierre Simon de Laplace. He earned his living as a school teacher from 1844 until 1857 when, having established his scientific reputation, he was appointed to the staff of the American Ephemeris and Nautical Almanac. He worked there until 1867 when he joined the US Coast and Geodetic Survey.

In 1856 he published his most significant work, Essay on the Winds and Currents of the Oceans. He showed that all atmospheric motion, as well as ocean currents, are deflected by the Earth's rotation. He went on in 1858 to formulate his law, which states that if a mass of air is moving in any direction there is a force arising from the Earth's rotation that always deflects it to the right in the northern hemisphere and to the left in the southern hemisphere. The air tends to move in a circle whose radius depends upon its velocity and distance from the equator. Ferrel went on to show how this law could be used to explain storms and the pattern of winds and currents. He was in some ways anticipated by Gustave-Gaspard Coriolis whose name is much better known.

Ferrel also did fundamental work on the solar system. He was able to correct Laplace and show that the tidal action of the Sun and Moon on the Earth is slowly retarding the Earth's rotation. In 1864 he provided the first mathematical treatment of tidal friction. His other works included his three-volume Meteorological Researches (1877–82). In 1880 he invented a machine to predict tidal maxima and minima.