Martin Hans Christian Knudsen

Born Feb. 15, 1871, in Hansmark, island of Fyn; died May 27, 1949. Danish physicist and oceanographer. Member (1909) and secretary (1917–46) of the Danish Academy of Sciences.

Knudsen graduated from the University of Copenhagen in 1906. He was a professor at the university from 1912 to 1941 and its rector in 1927–28. One of the founders of the International Council for Exploration of the Sea (1899), he was also president of the International Association of Physical Oceanography (1930–36).

Knudsen is the author of works on the kinetic theory of gases. He theoretically and experimentally demonstrated that a departure from Poiseuille’s equation is observed at low pressures, in particular, molecular flow takes place. He also studied the thermal conductivity of rarefied gases and the radiometric effect. Knudsen invented the precision manometer and proposed a number of physicochemical methods of studying seawater. He also invented the bathometer, an automatic pipette for determining the salinity of water, and other instruments. He established the constancy of the ratios of components of saline composition and developed a technique for determining the chlorine content in seawater and calculating the water’s salinity according to its chlorine content.