In the history of
science, the
theory of heat or
mechanical theory of heat was a theory, introduced in 1798 by
Sir Benjamin Thompson (better known as 'Count Rumford'), and developed more thoroughly in 1824 by the French physicist
Sadi Carnot, that
heat and
mechanical work are equivalent. It is related to the
mechanical equivalent of heat. Over the next century, with the introduction of the
second law of thermodynamics in 1850 by
Rudolf Clausius, this theory evolved into the science of
thermodynamics. In 1851, in his "On the Dynamical Theory of Heat",
William Thomson outlined the view, as based on recent experiments by those such as
James Joule, that “heat is not a substance, but a dynamical form of mechanical effect, we perceive that there must be an equivalence between mechanical work and heat, as between cause and effect.”