James Prescott Joule, a British physicist, was born in Salford on December 24, 1818, into a wealthy brewing family. He received some formal education in mathematics, philosophy, and chemistry but was in large part self-educated.
Joule's most active research period, from 1837 through 1847, led to the establishment of the principle of conservation of energy and the equivalence of heat and other forms of energy. His study of the quantitative relationship between the electrical, mechanical, and chemical effects of heat culminated in his announcement in 1843 of the amount of work required to produce a unit of heat:
First: that the quantity of heat produced by the friction of bodies, whether solid or liquid, is always proportional to the quantity of energy expended. And second: that the quantity of heat capable of increasing the temperature of water . . . by 1° Fahr requires for its evolution the expenditure of a mechanical energy represented by the fall of 772 lb through the distance of one foot.