BUYS BALLOT'S LAW, in meteorology, the name given to a law which may be expressed as follows :—"Stand with your back to the wind; the low-pressure area will be on your lef t hand." This rule, the truth of which was first recognized by the American meteorologists J. H. Coffin and W. Ferrel, is a direct consequence of Ferrel's Law (q.v.). It is approximately true in the higher latitudes of the northern hemisphere, and is reversed in the southern hemisphere, but the angle between barometric gradient and wind is seldom a right angle in low latitudes. The law takes its name from C. H. D. Buys Ballot, the chief of the Dutch Meteorological Services from 1854-89, who introduced a new instrument called the aeroclinoscope which indicated the position of the centre of a depression and the barometric gradient. The original formulation of the law was modified later, but an early form of it appears in the Jaarboek of the Meteorological Institute of the Netherlands for