Sadi Carnot
Can heat be turned fully into work?
That time, that place
France after Napoleon's fall. Sadi Carnot was a soldier and an engineer, and what gripped him was a galling fact: Britain, not France, was building far better steam engines.
Why this question
Engine improvement then was trial and error: widen this, narrow that, keep what works. No one knew why anything worked.
Carnot's question was more fundamental. However well you build it, is there a limit you cannot pass?
What was found
There was — and the answer was unexpected.
An engine's maximum efficiency has nothing to do with what it is made of, what gas it uses, or how it is built. It depends only on the temperature difference between the hot side and the cold side.
He likened it to a waterwheel. Water turns the wheel by falling from high to low; heat does work by flowing from hot to cold. So there must be somewhere cold for it to flow to — which means some of the heat is necessarily discarded.
An engine that turns heat entirely into work is impossible, however well made.
Build an engine well enough and it can always be improved
The argument that the same temperature difference gives the same limit regardless of material or design
He died of cholera at thirty-six and most of his belongings were burned. His book, which had barely sold, was rediscovered twenty years later and became the seed of the second law of thermodynamics