“Light rays, as well as sound rays, are each formed of a continuous series of globules constantly in vibration.

“This subtle transpiration is radiant because the expansion which provokes it is an equal, uniform Force. It is thus, by radiating, that globes of very large dimensions like the sun, the stars, transpire their light, and globes of small dimensions such as the Earth, having much more condensed envelopes, transpire a more subtle fluid, the caloric. 

“Finally, each terrestrial body, each man, each animal, each plant, each fragment of rock or metal, enjoys the transpiring faculty. Each projects a subtle fluid which, according to the circumstances, remains homogeneous, caloric, or splits into two fluids of different subtlety which balance each other and which constitute it in the magnetic or electric state.”

Pierre Hyacinthe Azaïs, 1831