born Dec. 24, 1818, Salford, Lancashire, Eng.
died Oct. 11, 1889, Sale, Cheshire
English physicist.
After studying under work required to produce a unit of heat, called the mechanical equivalent of heat, and established that heat is a form of energy. He established that the various forms of energy are basically the same and can be changed from one into another, a discovery that formed the basis of the law of conservation of energy, the first law of thermodynamics. In his honour, the value of the mechanical equivalent of heat is usually represented by the letter J , and a standard unit of work is called the joule.