What caused the caloric theory to be abandoned?

The caloric theory came under attack soon after its introduction. It maintained

that heat is a substance that could not be created or destroyed. Yet it

was known that heat can be generated indefinitely by rubbing one's hands together

or rubbing two pieces of wood together. In 1798, the American Benjamin

Thompson (Count Rumford) (1753-1814) showed in his papers that

heat can be generated continuously through friction. The validity of the caloric

theory was also challenged by several others. But it was the careful experiments

of the Englishman James P. Joule (1818-1889) published in 1843 that

finally convinced the skeptics that heat was not a substance after all, and thus

put the caloric theory to rest.