(1818-1889) English physicist whose work on the relations between electrical, mechanical, and chemical effects led to the discovery of the first law of thermodynamics.
He determined the mechanical equivalent of heat (Joule's equivalent) 1843, and the SI unit of energy, the joule, is named for him. He also discovered Joule's law, which defines the relation between heat and electricity; and with Irish physicist Lord Kelvin in 1852 the Joule–Kelvin (or Joule–Thomson) effect.
Joule was born in Salford, Lancashire, and educated by private tutors, including scientist John Dalton. Having a private income, he dedicated his life to precise scientific research. Until neighbors protested, he kept a steam engine in his house in Manchester.
Joule showed experimentally that the ratio of equivalence of the different forms of energy did not depend on how one form was converted into another or on the materials involved.

ETYM From the distinguished English physicist, James P. Joule.
(Homonym: jewel).
A unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second; SYN. J, watt second.
SI unit of energy (or work or heat) equal to one newton-meter.
Unit of energy or work: equal to work done when force of one newton moves its point of application one meter.
SI unit (symbol J) of work and energy, replacing the calorie (one joule equals 4.2 calories).
It is defined as the work done (energy transferred) by a force of one newton acting over one meter and equal to 107 ergs. It can also be expressed as the work done in one second by a current of one ampere at a potential difference of one volt. One watt is equal to one joule per second.