⚫therto discover'd. Sendivogius maintain'd it openly, that there lies hid in the air, the occult Food of Life; and other Chymifts have afferted the fame: But what that is, or how it acts, or what is the proper effect ⚫ of it, is a matter ftill in the dark, Happy the • Perfon that fhall happen to discover it. Let • this hint fuffice for Perfons that are ignorant of it, Is it not the elaftic Part of the Air ⚫ alone?' 46. For my own part, I confefs, I cannot apprehend, that either the natural Philofophers, or Physicians, have yet difcover'd the phyfical cause of this wonderful quality of air. I have feen indeed a great many conjectures upon it; but they have almoft all fallen • of themselves.' Dallow's Translation of Boerhaave's Theor. of the Art of Chym. p. 292. 00000000000 CHAP. II. PART I. SECTION 47. Sir Ifaac Newton's Rules of Reafaning in Philofophy. And, the Author's Firft Principles. A FTER having confulted those refpectable Authors, mentioned in the preceding Chapter, upon Air, and throughly and ftrictly examined the electrical Fluid, by means of the most effectual Experiments, that I could either meet with or invent, and varied and changed them into many different forms, I diligently compared the electrical fluid with the defcription that had been given of air; and confidering the whole with the utmost attention and accuracy, I was convinced of the truth of many things, which they had advanced, fince it was no more than I myself saw verified at the electrical apparatus. 48. When a Writer undertakes to explain and fettle any important point, which before was doubtful, his First Principles should be rational, and his Method perfpicuous: In order to which, I fhall lay down my firft and funda mental mental Principles in fuch a manner, as to ferve for fo many Heads of a Theory of the Air; which Theory I fhall inveftigate by a kind of Practice, i. e. Experiments: And this I fhall endeavour to effect with fuch clearness and plainness, that those Heads, or first Principles may supply the place of a Criterion, or Touchftone, whereby to prove the validity of my Conclufions; and if they be thought unfatisfactory, or infufficient, by any of my Readers, let them be tried by Sir Ifaac's excellent Rules of Reafoning, which are as follow: 49. Rule I. 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 does nothing in vain, and more is in vain, when lefs will ferve. Rule II. Therefore, to the fame natural effects, we muft, as far as poffible, affign the fame causes. Rule III. The qualities of bodies, which admit neither intenfion nor remiffion of degrees, and which are found to belong to all bodies within the reach of our Experiments, are to be efteem'd the univerfal qualities of all bodies whatsoever. Rule Rule IV. In experimental Philofophy we are to look upon Propofitions, collected by general Induction from Phenomena, as accurately or very nearly true, notwithstanding any contrary hypothefes that may be imagined, till fuch time as other Phenomena occur, by which they may either be made more accurate, or elfe liable to exceptions. Princip. Book 3d. p. 202. To thefe Rules, I have fubjoin'd those Heads, or Syftem of my First Principles, that both may be the more eafily referr❜d to. F SECTION 50% IRST, That in the beginning, the ed an univerfal ætherial Fluid or primary Air, endued with the utmost purity, fubtilty, and rarity; and in fine, a perfectly fubtile elaftic Fluid. Secondly, That the whole Universe is replete with it; for otherwife a Fluid fo perfectly fubtile and elastic would be perpetually petually expanding, till all parts were equally full; and then neither the whole nor its parts could remain endued with that perfect elasticity, which was at first Suppos'd, and at prefent appears. Thirdly, That this Æther or pure Air is universal, not only in all open spaces, but in the minuteft vacuities of the most compact Bodies by reafon of its being compofed of almost infinitely finer Particles than thofe of grofs Matter, which renders it capable of permeating the fmalleft Pores and Interfices of the hardest and clofeft Subftances. Fourthly, Since the Earth is endued with a property of transpiration or of breathing forth the most volatile parts of it to a confiderable height from its Jurface; thofe Effluvia become blended, incorporated, and most intimately mixed with Particles of the univerfal pure Ether or primary Air, and by that means conftitute a fecondary Air*, ог *The Atmosphere. |