Willem Hendrik Keesom (/ˈkeɪsoʊm/) (21 June 1876, Texel – 24 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 dipole–dipole interactions in 1921. Thus, dipole–dipole 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.