(N/A) Benjamin Thomson,also known as Count Rumford,conducted a famous experiment in $1798$ while observing the boring of cannons.
$1$. He observed that when a blunt drill was used to bore a cannon,a significant amount of heat was generated,which could boil water.
$2$. He noted that the heat production continued as long as the mechanical work of turning the drill was performed.
$3$. Since the heat did not seem to come from the metal itself (as the chips of metal produced were not significantly different in heat capacity),he concluded that heat is not a fluid (caloric) but is instead a form of energy generated by mechanical work.
$4$. This experiment provided early evidence that mechanical work can be converted into heat,laying the groundwork for the first law of thermodynamics.