Willem Hendrik Keesom () (21 June 1876, Texel – 3 March 1956, Leiden) was a Dutch physicist who, in 1926, invented a method to freeze liquid helium. He also developed the first mathematical description of dipoleâÂÂdipole interactions in 1921. Thus, dipoleâÂÂdipole interactions are also known as Keesom interactions. He was previously a student of Heike Kamerlingh Onnes, who had discovered superconductivity (a feat for which Kamerlingh Onnes received the 1913 Nobel Prize in Physics).
He also discovered the lambda point transition specific-heat maximum between helium-I and helium-II in 1930.
In 1924 he became member of the Royal Netherlands Academy of Arts and Sciences. In 1966, the minor planet ' was named after him.