1818-1889

English physicist who investigated the equivalence of mechanical, electrical, and heat energy, and who is often credited (together with Joseph Mayer) with formulating the law of conservation of energy. The unit of energy in the international system is named after Joule. Joule's family had acquired substantial wealth through a family-owned brewery, leaving him free to devote his time to scientific experiments, generally involving careful measurement of the heat energy released by different physical processes.