Christophorus Henricus Diedericus Buys Ballot (also Christoph Heinrich Diedrich Buys Ballot) (October 10, 1817-February 3, 1890) was the third professor (after Haring and Mulder) to be appointed at Utrecht University.
He's most known for his accomplishments in the field of meteorology, specifically the explanation of the direction of air flow in large weather systems. Furthermore he founded the Royal Dutch Meteorological Institute (KNMI) in 1854. He was one of the first to see the need for international cooperation, and in 1873 became the first chairman of the International Meteorological Committee, a precursor of the World Meteorological Organization (WMO).
Also well known is Buys-Ballot's law, which states that if a person stands with his back to the wind, the low atmospheric pressure is found to his left in the Northern Hemisphere.