 You can practice geometry and metaphysics as much as you like; but I, who am a physicist and a chemist, who take bodies in nature and not in my mind, I see them as existing, various, bearing properties and actions, as agitated in the universe as they are in the laboratory where if a spark is in the proximity of three combined molecules of saltpeter, carbon and sulfur, a necessary explosion will ensue. (PPMM; DPV XVII: 34)