Pierre Prévost

1751-1839

Swiss Physicist

Pierre Prévost is best known for his theory of exchanges, which he articulated in 1791. Whereas scientists in his time postulated the existence of cold as a substance or phenomenon all its own, Prévost correctly stated that bodies radiate only heat. When a person's warm hand becomes cold because of touching snow, it is not because coldness passed from the snow to the hand, but because the difference in temperatures resulted in a transfer of heat from the hand to the snow. This would prove to be a crucial principle in the soon-to-emerge science of thermodynamics.

Prévost was born in Geneva—now the leading city of French-speaking Switzerland, but then an independent city-state—on March 3, 1751. His father was a Calvinist minister, and ensured that Prévost and his siblings received classical educations. As a college student, Prévost studied theology and later law, receiving his doctorate in 1773. Immediately he went to work as a teacher and tutor, a profession that took him to various parts of Holland and France.

His early career was consumed with the classics, and during his years as a tutor, Prévost focused on translating the works of Euripides. In 1778, he published Orestes, which won him acclaim among classical scholars, and later that year he was invited by King Frederick the Great of Prussia to join the Academy of Sciences and Belles-Lettres in Berlin. There he continued to pursue his already established interests, publishing works of moral philosophy and poetry; but he also met Joseph-Louis Lagrange (1736-1813), who encouraged him to engage in scientific studies.

Prévost published a number of scientific papers in Berlin, but was forced to return home when in 1784 his father died. He took the chair of literature in Geneva for a year, then moved to Paris, where he continued to occupy himself with the classics. He soon became involved in politics, serving as a member of Geneva's Council of Two Hundred upon his return to the city in 1786.

During the late 1780s and early 1790s, Prévost again became intrigued with scientific questions. This led to his publication of De l'origine des forces magnétiques (1788), a work on magnetism that won him attention among physicists. Soon he shifted his focus to the matter of heat phenomena, thanks to the 1790 publication of Essai sur la feu by Marc Auguste Pictet, also of Geneva. Pictet maintained that heat was a fluid in material form, and that radiations of heat were the result of expansions and contractions of this fluid in various bodies.

In "Sur l'équilibre du feu" (1791), Prévost maintained that heat was a "discrete" if material fluid composed of widely spaced particles that pass continuously between two bodies. His conviction of heat's materiality may have been incorrect, but his theory of exchanges—the idea that all temperature changes are a matter of heat loss and gain obtained through transfer between bodies of differing temperature—was revolutionary.

Prévost took the chair of philosophy and general physics at Geneva in 1793, and remained there until his retirement 30 years later. He wrote extensively, corresponded with a number of scholars throughout the continent, and translated a number of important works such as Adam Smith's Wealth of Nations. In 1796, he became a member of the Royal Society of Edinburgh, and in 1801 was invited to join the Royal Society of London and the Institute of France.

In his later decades, political involvements overshadowed much of Prévost's work. After the outbreak of the French Revolution, he argued strongly that Geneva should remain separate from France, and this led to a brief imprisonment by zealots in 1794. Ironically, when it became clear that Geneva was about to unite with France, as it briefly did in the Napoleonic era, Prévost was named to the commission that regulated this union. In 1814, with Napoleon all but defeated, Geneva returned to the status of a republic, and Prévost served on its representative council. He spent his last years studying the effects of aging, both on humans in general and on himself in particular, and died in Geneva on April 8, 1839.

JUDSON KNIGHT