Entropy and The Second Law

The Finer Points of Heat

 By 1852, Thomson had come to believe that heat could be both transformed into work, as described by Joule’s theory, and free flowing to produce no work at all, as described by Fourier’s theory. In the latter, heat was simply dissipated, but not lost in accordance with the first law. Moreover, he distinguished between high quality and low quality energy and insisted that the universal tendency for energy is to dissipate as heat, making it unavailable for work. But Thomson wasn’t the only one thinking about the finer points of heat … so was Clausius.
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The Weight of Heat

The chemist Lavoisier actually tried to weigh heat; he found it was weightless.

The Imponderable Fluids

By the end of the eighteenth century, heat along with its cohorts light, magnetism and electricity were regarded as an imponderable fluid capable of flowing between the spaces assumed to be present in matter.

Heat as “Caloric”

Pierre-Simon Laplace (1749-1827) imagined heat to be a fluid composed of particles, deemed by Antoine Lavoisier (1743-1794) as “caloric”.