First to devise an absolute scale of temperature and argued that an air-thermometer scale provided ‘an arbitrary series of numbered points of reference sufficiently close for the requirements of practical thermometry’. Also devised the second law of thermodynamics: ‘it is impossible, by means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the temperature of the coldest of the surrounding objects’. Pioneered electrical standards and submarine telegraphy Invented the Kelvin Compass.