The random motion of atoms, ions, and molecules has long been recognized as the microscopic explanation of heat. An overview will be given of how natural philosophers, chemists, and physicists understood and explained heat from the 17th through the 19th centuries. Mechanical corpuscular theories of the 17th century included an understanding of heat as motion. Because heat was obviously related to fire it could be understood in terms of the phlogiston theory while that theory held sway. Even while challenging the existence of phlogiston, Lavoisier explained heat in terms of another imponderable material, caloric. At the very end of the 18th century, experiments by Rumford and Davy supported the interpretation of heat as motion. During the 19th century the idea of heat as motion was developed into a quantitative dynamical theory of heat through the work of Carnot, Joule, Mayer, Clausius, Thomson, Maxwell, and Boltzmann among others.

HIST tutorial: Molecules in motion - the kind we call heat

246th National Meeting (2013)

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