THOSE who have treated of natural pilosophy, may be nearly reduced to three classes. Of these some have been attributed to the several species of things, specific and occult qualities; on which, in a manner unknown, they make the operations of the several bodies to depend. The sum of the doctrine of the Schools derived from Aristotle and the Peripatetics is herein contained. They affirm that the several effects of the bodies arise from the particular natures of those bodies ariſe from the particular natures of thoſe bodies. But whence it is that bodies derive thoſe natures they don't tell us; and therefore they tell us no thing. And being entirely employed in giving names to things, and not in ſearching into things themſelves, we may lay that they have invented a philoſophical way of ſpeaking, but not that they have made known to us true philoſophy.
Others therefore by laying aſide that uſeleſs heap of words. thought to employ their pains to better purpoſe. Theſe ſuppoſed all matter homogeneous, and that the variety of forms which is ſeen in bodies arifes from ſome very plain and ſimple affections of the component particles. And by going on from ſimple things to thoſe which are more compounded they certainly proceed right; if they attribute no other properties to thoſe primary affections of the particles than Nature has done. But when they take a liberty of imagining at pleaſure unknown figures and magnitudes, and uncertain ſituations and motion of the parts; and moreover of ſuppoſing occult, freely pervading the pores of bodies, endued with an all-performing fubtilty, and agitated, with occult motions; they now run out into dreams and chimera's, and neglect the true conſtitution of things; which certainly is not to be expected from fallacious conjectures, when we can ſcarce reach it by the moſt certain obſervations. Thoſe who fetch from by hypotheſes the foundation on which they build their ſpeculations, may form indeed an ingenious romance, but a romance it will ſtill be.
There is left then the third claſs, which proſeſs experimental philoſophy. Theſe indeed derive the cauſes of all things from the moſt ſimple principles possible; but then they assume nothing as a principle, that is not proved by phenomena. They frame no hypotheses, nor receive them into philosophy otherwise than as queftions whose truth may be disputed. They proceed therefore in a two-fold method, fynthetical and analytical. From some select phænomena they deduce by analysis the forces of nature, and the more simple laws of forces; and from thence by fynthelis shew the constitution of the rest. This is that incomparably best way of philosophizing, which our renowned author most justly embraced before the rest; and thought alone worthy to be cultivated and adorned by his excellent labours. Of this he has given us a most illustrious example. by the explication of the System of the World, most happily deduced from the Theory of Gravity. That the virtue of gravity was found in all bodies, others suspected, or imagined before him; but he was the only and the first philosopher that could demonstrate it from appearances, and make it a solid foundation to the most noble speculations.