CALLENDAR, HUGH LONGBOURNE British physicist, was born at Hatherop :n Gloucestershire. He was educated at Marlborough and at Cambridge ; he held the post of professor of physics at McGill college, Montreal ; at University college, London (1898-1902) and at the Imperial College of Science.
His work in physics is mainly on heat and thermodynamics; he has been successful in devising and carrying out accurate methods of measurement and in designing new apparatus. The electrical resistance thermometer, with the Callendar-Griffiths bridge and various recording devices used with it, was the subject of papers published in 1886-87. This was followed by his work on the electrical continuous flow calorimeter, giving a new method of measuring specific heats of liquids, which eliminates the water equivalent of the apparatus and simplifies the radiation correc tion; the full description was given in 1902. In addition, Cal lendar is responsible for a compensated air thermometer (1891) and a radio-balance (1910).
His researches on steam led to the formulation of the Callendar steam equation and the publication of Callendar Steam Tables ; Properties of Steam and Thermodynamic Theory (1921) ; Abridged Callendar Steam Tables C. and F. Units (1922 and 1927), and Callendar Steam Diagram C. and F. Units (1922). The work on steam at high pressures and temperatures is still carried forward at the direct request of steam turbine manufac turers and the Electrical Research Association. In 1925 he pre sented a report to the latter association on the continuous flow method of measuring the total heat of steam at high pressures. Callendar is the author of a number of papers on various subjects such as internal combustion engines, thermometric scales, radia tion, vapour pressure, osmotic pressure of solutions, absolute expansion of mercury and the boiling point of sulphur. He is also responsible for Air Ministry reports and memoranda on work carried out by himself and colleagues on Dopes and Detona tion (1926) and on the effect of anti-knock compounds on en gine-knock (1927). He died in London on Jan. 21, 1930.
Callendar was a member and officer of many learned societies; he was awarded the Rumford Medal of the Royal Society in 1906 and the first Duddell Memorial Medal of the Physical Society in 1924; he received the C.B.E. in 1920.