Caloric theory

The caloric theory is a superseded scientific theory that heat consists of a self-repellent fluid called "caloric" that flows from hotter bodies to colder bodies. Caloric was also thought of as a weightless gas that could pass in and out of pores in solids and liquids. The caloric theory was superseded by the mid-19th century in favor of the mechanical equivalent of heat, but nevertheless persisted in some scientific literature—particularly in more popular treatments—until the end of the 19th century.

Caloric theory held that heat was a conserved, weightless fluid called caloric that flowed from hotter objects to colder ones.