De Gravitatione
principles, sufficiently well known to the student, strictly and geometric- ally. Since this doctrine may be judged to be somewhat akin to natural philosophy, in so far as it may be applied to making clear many of the phenomena of natural philosophy and in order, moreover, that its useful- ness may be particularly apparent and the certainty of its principles perhaps confirmed, I shall not be reluctant to illustrate the propositions abundantly from experiments as well, in such a way, however, that this freer method of discussion, disposed in scholia, may not be confused with the former, which is treated in lemmas, propositions and corollaries. The foundations from which this science may be demonstrated are either definitions of certain words, or axioms and postulates no one denies. And of these I treat directly. Definitions The terms ‘quantity’, ‘duration’, and ‘space’ are too well known to be susceptible of definition by other words.1 1 Cf. Newton’s discussion in the Scholium to the Pr