Hugh Longbourne Callendar (18.04.1863—21.01.1930) was an English experimental physicist and a Fellow of the Royal Society (1894). He was born in Hatherop. He graduated from the University of Cambridge (1885), where he then worked. In 1888 —93 he was professor at the college in Egham, in 1893 —98 at McGill University (Montreal) and in 1898 — 1902 at the University of London. From 1902 he was professor at the Imperial College of Science and Technology in London.
His research concerned heat, thermometry and molecular physics. He developed accurate methods of thermometric measurement and accurate instruments; in particular, he developed the method of continuous electrical calorimetry, built a calorimeter and improved the platinum resistance thermometer (the Callendar thermometer), which came into wide use. He proposed a temperature scale based on this thermometer. He studied the thermal properties of water, gases and steam. He developed a method of determining the coefficient of expansion of liquids (the Callendar — Moss method). He built a compensated air thermometer. He gave an equation of state for moderate pressures (the Callendar equation).
The B. Rumford Medal (1906).