Caloric Theory - Later Developments

Later Developments

In 1798, Count Rumford published An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction, a report on his investigation of the heat produced while manufacturing cannons. He had found that boring a cannon repeatedly does not result in a loss of its ability to produce heat, and therefore no loss of caloric. This suggested that caloric could not be a conserved "substance" though the experimental uncertainties in his experiment were widely debated.

His results were not seen as a "threat" to caloric theory at the time, as this theory was considered to be equivalent to the alternative kinetic theory. In fact, to some of his contemporaries, the results added to the understanding of caloric theory.

Rumford's experiment inspired the work of James Prescott Joule and others towards the middle of the 19th century. In 1850, Rudolf Clausius published a paper showing that the two theories were indeed compatible, as long as the calorists' principle of the conservation of heat was replaced by a principle of conservation of energy. In this way, the caloric theory was absorbed into the annals of physics, and evolved into modern thermodynamics, in which heat may formally be put equivalent to kinetic energy of some particles (atoms, molecules) of the substance. However, there is a principal difference between the concept of heat and a mechanical movement of particles, which shows in spectroscopy. While sharp spectral lines correspond to mechanical movements of the particles, the heat shows spectroscopically as a noise with some spectral distribution.

In later combination with the law of energy conservation, the caloric theory still shows a very valuable physical insight into some aspects of heat. For example, the emergence of Laplace's equation and Poisson's equation in the problems of spatial distribution of heat and temperature. The caloric theory is now also remembered for the naming of the calorie.