|A possible depiction, drawn by D. Dumon (Ѻ), of Benjamin Thompson (Count Rumford) in 1798 describing his cannon boring experiment at the Munich Arsenal in Germany, in which water was made to boil (heat was generated) without the use of fire.|
Thompson gives an account of his interest in discovering the “hidden nature of heat” during his years, early circa 1790s, at the military arsenal at Munich, as follows: 
“Being engaged, lately, in superintending the boring of cannon, in the workshops of the military arsenal at Munich, I was struck with the very considerable degree of heat which a brass gun acquires, in a short time, in being bored; and with the still more intense heat (much greater than that of boiling water, as I found by experiment) of the metallic chips separated from it by the borer.
The more I meditated on these phenomena the more they appeared to me to be curious and interesting. A thorough investigating of them seemed even to bid fair to give a farther insight into the hidden nature of heat; and to enable us to form some reasonable conjectures respecting the existence, or non-existence, of an igneous fluid: a subject on which the opinions of philosophers have, in all ages, been much divided.”
When he did actually get around to conduct his experiment in 1798, he showed that the "work" expended by a team of two draft horses (a 2 horsepower engine), turning a cannon boring drill bit at a rate of thirty-two revolutions per minute, inside of a cannon barrel, which itself was submerged in a tank of water, will generate "heat" in the cannon barrel to the effect that it caused the water to boil at 2 hours and 30 minutes. 
The following is a reconstruction (Ѻ) of Thompson’s cannon boring experiment, showing the mechanical work of the horses, in turning the bore, converting into heat, as evidenced by the boiling of water in the tub in contact with the cannon being bored:
The following are other details and renditions of the experiment:
|Left: a rendition of Thompson’s cannon boring experiment from Elmer Burns’ illustrated 1910 book The Story of the Great Inventions.  Right: diagram of some of Thompson's 1798 cannon boring experimental equipment.|
Rumford states, in reaction to this un-explained phenomenon of the production of heat without fire, that “it would be difficult to describe the surprise and astonishment expressed in the countenances of the bystanders, on seeing so large a quantity of cold water heated, and actually made to boil, without any fire.”  The following is an alternative color rendition of Thompson’s cannon boring experiment: 
● Paddle wheel experiment
● Ice-rubbing experiment
● Double-slit experiment
1. (a) Thomson, Benjamin. (1798). “An Inquiry Concerning the Source of Heat which is Excited by Friction”, read before the Royal Society of London, Jan 25, Philosophical Transactions. Vol. XVIII, pg. 286.
(b) Thomson, Benjamin. (1798). “An Inquiry Concerning the Source of Heat which is Excited by Friction” in The Complete Works of Count Rumford (pgs. 469-93). Oxford University Press, 1870.
2. Count Rumford on Heat (1798) – a short excerpt.
3. Baeyer, Hans C. von (1999). Warmth Disperses and Time Passes - the History of Heat, (pg. 6). New York: The Modern Library.
4. Burns, Elmer E. (1910). The Story of the Great Inventions (fig 20). Harper & Brothers.
5. Rumford – DavidDarling.info.