Callendar, Hugh Longbourne (1863–1930)

English physicist and engineer. He carried out fundamental investigations into the behaviour of steam, resulting in the compilation of reliable steam tables that enabled engineers to design advanced steam machinery.

Callendar, born in Gloucestershire, studied classics, mathematics, and physics at Cambridge, then medicine and law. He was professor of physics at the Royal Holloway College, Egham, Surrey, 1888–93, at McGill College, Montréal, 1893–98, at University College, London, 1898–1901, and at the Royal College of Science, London, from 1902. During World War I Callender was a consultant to the Board of Inventions, which received more than 100,000 ‘war-winning’ ideas.

While he was at Cambridge, Callendar's main research was on the platinum resistance thermometer, with which he obtained an accuracy of 0.1°C in 1,000°C – about 100 times better than previous results. In 1927 the method was adopted as an international standard. This work led to recording temperatures on a moving chart, a principle now fundamental to any branch of science or industry that requires a continuous record of temperature.

Callendar's research topics were varied, most of them connected with thermodynamics. He carried out experiments on the flow of steam through nozzles, producing much information of great value to steam turbine designers. In 1920 he published The Properties of Steam and Thermodynamic Theory of Turbines. He also worked on antiknock additives for fuels.