I grew up on Kenneth Roberts’s historical-fiction novels set in the Revolutionary War era. Arundel, A Rabble in Arms, Northwest Passage. Each included historical figures, such as Major Robert Rogers, Benedict Arnold, and Philip Schuyler. His Oliver Wiswell introduced me to Benjamin Thompson, a man born in Woburn, Massachusetts, who dabbled in science, married into wealth, and opposed the Revolutionary uprising. His loyalist stance won him no favors with the rebels and he eventually fled to the British lines, leaving his wife behind, and sailed to London at the end of the war.

I encountered Thompson again, years later, during my research into the history of thermodynamics. I just didn’t realize it at the time for his scientific achievement was done under a different name: Count Rumford.

Context: a short review on the history of heat

The rise of energy was as much about the fall of caloric as anything else. 

In the late 1700s physicists viewed heat as some kind of invisible, indestructible fluid.  Lavoisier named this fluid caloric, although the name arrived without a strict definition, and gave it prominence by placing it on his list of elements.  It was generally thought that, among other properties and characteristics, caloric was conserved, just as any element was, and that caloric was released by friction and hammering.  But no quantified proof accompanied these thoughts.

Entering the 1800s, the caloric theory pervaded science and stood as the sole hypothesis to explain much but not all of the phenomena related to heat.  For those phenomena it couldn’t explain, its adapting nature gave rise to ad hoc corrections that provided explanations and thus gave scientists a certain peace of mind that the theory was good enough.

But to some, the caloric theory made no sense

To some, however, the caloric theory just didn’t make sense.  In addition to the fact that, as indicated above, the theory lacked quantitative predictive power, the theory also couldn’t address the following question:  If caloric was indeed conserved, then how could a constant source of friction continually generate unlimited caloric in the form of heat when caloric itself was limited?  Such questions, in addition to questions addressing the fact that the caloric theory fundamentally offered no quantitative predictive power, led to demonstrative experiments that directly challenged caloric.  Complete refutation should have resulted except for one problem.  There was no alternate hypothesis waiting to replace caloric. 

Early 1800s provided new evidence challenging the caloric theory

In the ideal world, the scientific method would have been used to generate a range of hypotheses to explain the range of heat-related phenomena and then an experimental program would have been executed to systemically challenge and eliminate each hypothesis until only one was left standing.  The early 1800s was not this ideal world.  The scientific method was still in its infancy and there was no coordinated effort to employ it to solve the heat problem, thus leaving one hypothesis alive but on shaky and unconvincing ground.

Count Rumford – The Most Interesting Man in the World

The story of Count Rumford (1753-1814) is one I can’t do justice to.  How can one capture in anything other than a full book the very colorful story of Benjamin Thompson?  Continuing with his story, after Thompson fled overseas, he somehow ended up marrying (and later separating from) Lavoisier’s widow and eventually became Count of the Holy Roman Empire in Bavaria.  It was during this latter event that Thompson adopted the name, Count of Rumford, based on the former name of Concord, New Hampshire, site of his early home.

Count Rumford – The Scientist

Thompson/Rumford showed early aspirations toward science in the colonies and continued to do so in Europe. In particular, the caloric theory never captured his attention. He doubted it as early as 1778 when he observed that gun barrels were hotter when firing without the bullet.  How insightful!  How many others had conducted the same experiment but never made this observation?  While folks then didn’t understand the reason behind this phenomenon, today we do.  Without having to do any work to accelerate the bullet, the hot air produced by the combustion didn’t cool off and so remained hot.  It’s interesting that it was this concept involving the transformation of work done by an expanding gas against a resistant force into a cooling effect on the gas that was the basis for Mayer’s subsequent calculation of the mechanical equivalent of heat.

Rumford bores a cannon and so boils water

Rumford continued to doubt the caloric theory when in 1789 he observed a cannon manufacturing process in the Munich arsenal.  As a new brass cylinder was being bored out to form the cannon barrel, Rumford noted that the barrel and metal chips all became very hot.  While he was surely not the first to notice this, he was the first to think about what it meant for he simply could not walk away from such an observation without thinking about its cause.  Inspired by his inquiry, Rumford proceeded to conduct one of the most illuminating and legendary experiments in the history of physics.  He set up a boring process with an intentionally dull drill bit pressed hard against the bottom of the bore of the cylinder.  As the cylinder was turned by the efforts of two walking horses, the temperature of the brass cannon rose.  Figuring that the best way to share this finding was to show it to people, Rumford encased the barrel with a box filled with water and then waited.  Sure enough, after awhile, the water began to boil, a true “ooh” and “ahhh” moment for the crowd that gathered since there was no fire there to do the boiling, making it one of the most famous public-demonstration experiments ever.

Why this was such a big deal

But why?  Why was this such a big deal?  We easily grasp the concept of friction today.  Rub two objects together, hard, and then touch them afterwards.  They’re hot.  We now know this to be true.  We know that atoms interacting with each other during such contact is what hinders motion and so causes friction and so causes heat.  Friction moves atoms out of their normal resting place.  When they snap back, like a stretched rubber band that’s released, potential energy is converted into kinetic energy.  But back in the late 1700s, the phenomena called friction was very baffling, especially in the context of the caloric theory of heat since this theory couldn’t explain it.  Nothing was really happening in Rumford’s experiment other than the rubbing together of two pieces of metal.  And yet water boiled.  How?  To the calorists, the heat was produced by squeezing caloric out of the metal.  But to Rumford, this could not be true, for how could a conserved material like caloric be continuously squeezed from a body without limit?  This simply did not make sense to him, especially in light of the belief that caloric was conserved.  The only thing that did make sense to him was that motion caused the heat.

Rumford: heat is caused by motion

From this demonstration and other supporting evidence, Rumford became convinced that heat is caused by motion—“heat is merely the vis viva of the constituent atoms of all material bodies”[1] —and shared his results and views in a public forum called the Royal Institution of London, which he himself founded in 1800.  (I told you that his life was interesting!)  While historians acknowledge that Rumford’s demonstration revealed weakness in the caloric theory, they hesitate to acknowledge beyond this.[2] Rumford proposed to jettison caloric but offered no principle to replace it with, as he really didn’t have any concept of energy, and his famous experiment became famous in retrospect.  But his work did inspire others, especially Humphrey Davy, Thomas Young, and later James Joule, and because of this, Rumford belongs in this history.

Explore more!

Explore more about why it took so long to kill the caloric theory of heat in my book Block by Block – The Historical and Theoretical Foundations of Thermodynamics. Thank you for listening! .

[1] Cardwell, D. S. L. 1971. From Watt to Clausius; the Rise of Thermodynamics in the Early Industrial Age. Ithaca, N.Y: Cornell University Press. p. 103.

[2] Cardwell, 1971. pp. 95-107. Brush, Stephen G., 2003a. “Introduction.” In The Kinetic Theory of Gases: An Anthology of Classic Papers with Historical Commentary, edited by Stephen G. Brush and Nancy S. Hall, 1–42; 179–96. History of Modern Physical Sciences 1. London : River Edge, NJ: Imperial College Press ; Distributed by World Scientific Pub. p. 10.  Fox, Robert. 1971. The Caloric Theory of Gases: From Lavoisier to Regnault. Clarendon Press. p. 4.  Fox suggested that Rumford’s work was a “red herring for the historian.”