Pierre Prévost


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(1751–1839) Swiss physicist

Born in Geneva, Switzerland, Prévost was professor of physics at Berlin and then at the university in his native city. In 1792 he published his Sur l'equilibre du feu (On the Equilibrium of Heat), which did much to clarify the nature of heat.

If, as was widely believed at the time, heat was a fluid, called caloric, which flowed from hot bodies to colder ones, then it was reasonable to suppose that cold was also a fluid, ‘frigoric’, which flowed from cold bodies to warmer ones. In favor of the existence of frigoric was a body of experimental work that dated back to the 17th century. Thus it was known that if a piece of ice was placed near a thermometer in a room of constant temperature then the temperature of the thermometer would fall. More impressively, if two concave mirrors are arranged so that they face each other and a piece of ice is placed at one focus and a thermometer at the other, then the indicated temperature will fall. Experiments like this readily lent themselves to the interpretation that the fluid frigoric can be emitted and reflected.

Prévost argued in 1791 that there is but a single fluid involved. Snow melting in the hand was a case of heat flowing from the hand to the snow rather than conversely. He introduced the idea of dynamic equilibrium in which all bodies are radiating and absorbing heat. When one body is colder than another it absorbs more than it radiates. Its temperature will rise until it is in equilibrium with its surroundings. At this point, it does not stop radiating heat but absorbs just as much as it loses to remain in equilibrium. The idea is known as the Prévost theory of exchanges.

Although Prévost was a supporter of the caloric theory of heat, his views influenced a later generation of physicists who introduced the kinetic theory of heat on a quantitative basis toward the end of the 19th century.

Subjects: Science and Mathematics.

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