An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction (1798), which was published in the Philosophical Transactions of the Royal Society, is a scientific paper by Benjamin Thompson, Count Rumford that provided a substantial challenge to established theories of heat and began the 19th century revolution in thermodynamics.
Rumford was an opponent of the caloric theory of heat which held that heat was a fluid that could be neither created nor destroyed. He had further developed the view that all gases and liquids were absolute non-conductors of heat. His views were out of step with the accepted science of the time and the latter theory had particularly been attacked by John Dalton and John Leslie.
Rumford was heavily influenced by the argument from design and it is likely that he wished to grant water a privileged and providential status in the regulation of human life.
Though Rumford was to come to associate heat with motion, there is no evidence that he was committed to the kinetic theory or the principle of vis viva.
In his 1798 paper, Rumford acknowledged that he had predecessors in the notion that heat was a form of motion. Those predecessors included Francis Bacon, Robert Boyle, Robert Hooke, John Locke, and Henry Cavendish.
Rumford had observed the frictional heat generated by boring cannon at the arsenal in Munich. Rumford immersed a cannon barrel in water and arranged for a specially blunted boring tool. He showed that the water could be boiled within roughly two and a half hours and that the supply of frictional heat was seemingly inexhaustible. Rumford confirmed that no physical change had taken place in the material of the cannon by comparing the specific heats of the material machined away and that remaining were the same.
Rumford argued that the seemingly indefinite generation of heat was incompatible with the caloric theory. He contended that the only thing communicated to the barrel was motion.
Rumford made no attempt to further quantify the heat generated or to measure the mechanical equivalent of heat.
Most established scientists, such as William Henry, as well as Thomas Thomson, believed that there was enough uncertainty in the caloric theory to allow its adaptation to account for the new results. It had certainly proved robust and adaptable up to that time. Furthermore, Thomson, Jöns Jakob Berzelius, and Antoine César Becquerel observed that electricity could be indefinitely generated by friction. No educated scientist of the time was willing to hold that electricity was not a fluid.
Ultimately, Rumford's claim of the "inexhaustible" supply of heat was a reckless extrapolation from the study. Charles Haldat made some penetrating criticisms of the reproducibility of Rumford's results and it is possible to see the whole experiment as somewhat tendentious.
However, the experiment inspired the work of James Prescott Joule in the 1840s. Joule's more exact measurements were pivotal in establishing the kinetic theory at the expense of caloric.