minutes. Whereas on the contrary that apparent motion of the Sun is really greater at the beginning of Pisces than at the beginning of Virgo, as experience teftifies; and therefore the earth is fwifter at the beginning of Virgo than at the beginning of Pifces. So that the hypothefis of vortices is utterly irreconcileable with aftronomical phænomena, and rather ferves to perplex than explain the heavenly motions. How thefe motions are performed in free fpaces without vortices, may be understood by the first book; and I shall now more fully treat of it in the following book of the System of the World monté OF THE SYSTEM OF THE WORL D. I BOOK III. puesto derribar. N the preceding books I have laid down the principles of philofophy; principles, not philofophical, but mathematical; fuch, to wit, as we may build our reafonings upon in philofophical enquiries. Thefe principles are, the laws and conditions of certain motions, and powers or forces, which chiefly have respect to philofophy. But left they fhould have appeared of themfelves dry and barren, I have illuftrated them here and there, with fome philofophical fcholiums, giving an account of fuch things, as are of more general nature, and which philofophy feems chiefly to be founded on; fuch as the denfity and the refiftance of bodies, leidg bodies, fpaces void of all bodies, and the motion of light and founds. It remains, that from the fame principles, I now demonftrate the frame of the Syftem of rusthur the World. Upon this fubject, I had indeed compos'd vevida deva the third book in a popular method, that it might be juneda read by many. But afterwards confidering that fuch per as had not fufficiently enter'd into the principles, could not, eafily difcern the ftrength of the confequences, nor frida lay afide the prejudices to which they had been many years accuftomed; therefore to prevent the disputes acostumbrad which might be rais'd upon fuch accounts, I chose to reduce the fubftance of that book into the form of propofitions (in the mathematical way) which fhould be read by thofe only, who had firft made themselves mafters of the principles eftablifh'd in the preceding books. Not that I would advise any one to the pre-acti vious study of every propofition of those books. For today they abound with fuch as might coft too much time, even to readers of good mathematical learning. It is enough if one carefully reads the definitions, the laws of motion, and the firft three fections of the first book. He may then pafs on to this book, of the Syftem of the World, and confult fuch of the remaining propofitions tantes of the first two books, as the references in this, and his occafions, fhall require. - {{} the ت las luzes del movimient, "y prieures seccions del libro I erdemas las vistente. Consubstant 1 We are to admit no more caufes of natural things, than fuch as are both true and fufficient to explain their appearances. To this purpose the philofophers fay, that Nature do's nothing in vain, and more is in vain, when lefs will ferve; For Nature is pleas'd with fimplicity, and affects not the pomp of fuperfluous causes. RULE II. Anima Therefore to the fame natural effects we must, (as far as poffible, affign the fame causes. As to refpiration in a man, and in a beaft; the defcent of ftones in Europe and in America; the light of our culinary fire and of the Sun; the reflection of light in the Earth, and in the Planets. RULE 7 RULE III. идина tension. tensidad The qualities of bodies, which admit neither in- nunca рез -in pertenecer estimada I ས completamente For fince the qualities of bodies are only known to miert. etrus by experiments, we are to hold for univerfal, all t fuch as univerfally agree with experiments; and fuch to as are not liable to diminution, can never be quite taken away, We are certainly not to relinquished the evidence of experiments for the fake of dreams and vain fictions of our own devifing; nor are we to recede from the analogy of Nature, which ufes to bexortumb Timple, and always confonant to it felf. We no other cou foíma ways know the extenfion of bodies, than by our +tamen consideracion fenfes, nor do thefe reach it in all bodies; but becaufe alcanzar we perceive extenfion in all that are fenfible, therefore we afcribe it univerfally to all others alfo. That t abundance of bodies are hard we learn by experience. And because the hardness of the partnefs of the whole arifes from the mist arts, we therefore juffly infer the hardprecisament. nefs of the undivided particles not only of the bodies we feel but of all others. That all bodies are im- Toranis penetrable, we gather not from reafon, but from fenfa- col tion. The bodies which we handle we find impene-alpotis trable, and thence conclude impenetrability to be an univerfal property of all bodies whatfoever. That all bodies are moveable, and endow'd with certain powers eve (which we call the vires inertia) of perfevering in their motion or in their reft, we only infer from the like properties obferv'd in the bodies which we have feen. are wel The extenfion, hardness, impenetrability, mobility, and vis inertia of the whole, refult from the exten |