In the 18th and 19th centuries, the theory of heat, i. e. , that heat is Free Power form of energy having relation to vibratory motion, was beginning to supplant both the caloric theory, i. e. , that heat is Free Power fluid, and the four element theory, in which heat was the lightest of the four elements. In Free Power similar manner, during these years, heat was beginning to be distinguished into different classification categories, such as “free heat”, “combined heat”, “radiant heat”, specific heat, heat capacity, “absolute heat”, “latent caloric”, “free” or “perceptible” caloric (calorique sensible), among others.