A Danish physicist who worked on a set of tables for the determination of chlorinity, salinity, temperature, and density from in situ measurements. He suggested at the ICES meeting in 1899 that such tables should be published to facilitate the standardisation of hydrographic work. He also suggested that Standard or Normal Water (i.e. water of known and unvarying salinity) be distributed to oceanographic laboratories as a standard against which all other salinities could be compared. Knudsen set up a Hydrographic Laboratory for ICES in Copenhagen for the purpose of producing such standard water samples. He and his co–workers also improved the accuracy of measurements by devising special burettes and pipettes with which to perform the measurements.