James Joule was a brewer by trade and a keen physicist. In 1843 he published the results of some experiments, which proved that heat was produced by mechanical movement. This contradicted the prevailing theory that heat could be neither created nor destroyed. His identification of the relationship between mechanical work and heat enabled the theory of the conservation of energy, and thus eventually led to the first law of thermodynamics.
Editors. "Mechanical equivalent of heat found by James Joule". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6288, accessed 04 July 2015.]