James Prescott. 1818–89, English physicist, who evaluated the mechanical equivalent of heat and contributed to the study of heat and electricity

the derived SI unit of work or energy; the work done when the point of application of a force of 1 newton is displaced through a distance of 1 metre in the direction of the force. 1 joule is equivalent to 1 watt-second, 107 ergs, 0.2390 calories, or 0.738 foot-pound