 Nevertheless, Hume’s interpretation of the status of “principles” makes him deviate from Newton’s methodology in a fundamental fashion. In the Treatise, he uses the “science of man” to claim it is “beyond the reach of human understanding” to “penetrate into the nature of bodies, or explain the secret causes of their operations”. He cannot “approve” of the ambition to go beyond knowing bodies by their external properties (THN 1.2.5.25). This contradicts the final paragraph of the “General Scholium” of the Principia, where Newton promises a program of research, perhaps inspired by the success of Francis Hauksbee’s electrical experiments, to penetrate into the nature of matter. Although this program was by no means finished by the time of Newton’s death, Newton’s optical research had revealed, for example, that light has an internal constitution characterized by the proportions, in it, of the distinct homogeneal (or “uniform”) kinds, which have different degrees of refrangibility (Schliesser 2004).