No, that’s not a typo in the title. Caloric was a kind of infinitesimally subtle fluid substance, believed by many prominent scientists in the late eighteenth century to be the source of heat when it flowed. This may sound like just another example of a now-debunked belief that many clever and educated people had in the distant past, to be put up there alongside the longstanding
"Caloric" is very similar to what we now call "thermal energy". It acts like thermal energy acts, e.g., goes from hotter to colder, so it's not surprising that Carnot and others came to correct conclusions from incorrect premises. Caloric was matter not energy, but it was "a kind of infinitesimally subtle fluid substance" that acted like thermal energy, so there was little practical difference.
Right. What's interesting, I think, is how caloric ended up being removed from the standard narratives of how the science progressed - or at the very least downplayed as a kind of blip. It seems this was because Kelvin, Joule and others whose ideas became dominant after the 1850s were all in favour of the heat-as-motion theories, so had to reintegrate caloric theory's insights into their systems. I find it so interesting how the foundations can be faulty, but still be enormously practiclally useful. (Incidentally, Carnot's notes reveal that after publishing his work he ended up rejecting caloric theory!)
What is the most interesting to me is how little science mattered for the technological advances of the Industrial Revolution. High-pressure steam engines were moving trains, ships, pumps, millstones and industrial machinery before scientists started to figure out thermodynamics, the same way people had been using yeast to ferment, brew and bake for millennia before we figured out it's a living thing.
I really enjoyed reading this, thank you for posting. I am the opposite of scientifically inclined, but it occurred to me that Carnot's premise, that heat flowed like water, begged an obvious question: if water is impelled to motion through gravity, what force would 'impel' heat to flow?
Great question. Caloric was seen as a self-repelling kind of matter, able to move through all substances by filling the gaps between atoms, while also being attracted to ordinary atoms. The self-repulsion explained why gravitational force did not result in all particles of matter creating a single homogeneous mass. It also explained why heating a body (adding caloric) made most bodies expand in volume, as well as why sensible heat seemed to increase when a body was put under pressure or when bodies collided - these actions squeezed the self-repelling caloric surrounding atoms closer together than their mutual repulsion would allow, forcing caloric to be released.
"Caloric" is very similar to what we now call "thermal energy". It acts like thermal energy acts, e.g., goes from hotter to colder, so it's not surprising that Carnot and others came to correct conclusions from incorrect premises. Caloric was matter not energy, but it was "a kind of infinitesimally subtle fluid substance" that acted like thermal energy, so there was little practical difference.
Right. What's interesting, I think, is how caloric ended up being removed from the standard narratives of how the science progressed - or at the very least downplayed as a kind of blip. It seems this was because Kelvin, Joule and others whose ideas became dominant after the 1850s were all in favour of the heat-as-motion theories, so had to reintegrate caloric theory's insights into their systems. I find it so interesting how the foundations can be faulty, but still be enormously practiclally useful. (Incidentally, Carnot's notes reveal that after publishing his work he ended up rejecting caloric theory!)
What is the most interesting to me is how little science mattered for the technological advances of the Industrial Revolution. High-pressure steam engines were moving trains, ships, pumps, millstones and industrial machinery before scientists started to figure out thermodynamics, the same way people had been using yeast to ferment, brew and bake for millennia before we figured out it's a living thing.
Yeast is another great example - would be interesting to trace the theories of what it was at some point.
I really enjoyed reading this, thank you for posting. I am the opposite of scientifically inclined, but it occurred to me that Carnot's premise, that heat flowed like water, begged an obvious question: if water is impelled to motion through gravity, what force would 'impel' heat to flow?
Great question. Caloric was seen as a self-repelling kind of matter, able to move through all substances by filling the gaps between atoms, while also being attracted to ordinary atoms. The self-repulsion explained why gravitational force did not result in all particles of matter creating a single homogeneous mass. It also explained why heating a body (adding caloric) made most bodies expand in volume, as well as why sensible heat seemed to increase when a body was put under pressure or when bodies collided - these actions squeezed the self-repelling caloric surrounding atoms closer together than their mutual repulsion would allow, forcing caloric to be released.
I would have loved these pieces added throughout my physics undergrad for fun