CHAP. I.

The Introduction, containing the order of the ensuing Enquiries.

AMong the many Experi∣ments of latter Ages, there hath been invented that Engine that commonly goes under the name of the Torricellian Experiment, which is but this: A Glass-Tube of three foot or more long, closed at one end, and then filled with Mercury or Quick∣silver, and then the open end stopped with the finger, and inverted into a vessel of restagnant Mercury & and when the end is sufficiently immersed, then the finger nimbly removed so that Page  2no Air get in, the Mercury will subside in the Tube to the height of 29 Inches, and half an inch, or near thereabout; but infallibly between 27 and 30 Inches, leaving the residue of the upper end of the Tube emptied of the Mercury.

This Experiment, and the solution of it, hath exercised the Tryals and Wits, and Invention of very many excellent Persons, such as were Helmont, Gassen∣dus, Kircherus, Shottus, Dr. Carleton, Mr. Hobbs, Mr. Sinclere, Monsieur Pec∣quett, Monsieur Pascall, Magnanus, Mr. Boyle, Linus, Honeratus, Fabri, and divers others; who though men of great Learning and Industry, have run into several Parties, and given Soluti∣ons, and raised Conclusions from it, extreamly contradictory the one to the other.

And although this seems but a very trifling and ludicrous Experiment, yet almost all dissenting Parties have made it to suffragate to their several precon∣cerned Sentiments, and Perswasions, and that in Philosophical Points of as great moment and importance per∣chance Page  3as most to be found in na∣tural Inquiries. Some from hence con∣firm themselves in their Perswasion, that there are both interspersed and coacervated Vacuities or Spaces, empty of any corporeal substance in the Uni∣verse; others again as confidently con∣cluding the untruth of that Opinion, and that from the same Experiment. Others again from hence confirming themselves in the Cartesian suppositi∣on of his Tria Principia, and especially of that Materia Subtilis, which cannot be excluded from pervading the most contumacious and solid body: Others attributing the same Power to the more subtil parts of the aerial consistence; some from hence concluding an actual pressure and gravitation of the Air up∣on all subjected bodies, and that there∣by the Mercury is susteined by way of Pressure, and Trusion, and Counterpoys, and have substituted thereupon as an undoubted Hypothesis, a world of admi∣rable consequences in natural appea∣rances, not only in the greater World, but also in the lesser World the humane Page  4structure. Others again have hereupon maintained their opinion of Attraction as the necessary effect of Tension, and resolve this suspension of the Mercury unto the force of attraction and suction, occasioned by that Catholick Law of Nature for preservation of the conti∣nuity of the Universe, and all its parts, and the Fuga Vacui, and are no way satis∣fied with that confidence that decryes it.

From this diversity of Judgments of Learned men, we may learn, first, how little it is in natural Effects that we re∣ally and truly know and understand, when so trivial an Experiment that we have so easie an access unto, and handle with our hands, and perceive by our sight its motion, which yet so gravels, or at least divides men of great Parts, Judg∣ment, Learning and Experience. 2. How strangely partial men are to those Sentiments that they have once enter∣tained, and perchance taken much pains to mould and fashion, or have even publickly engaged unto or for; whereby it comes to pass that men are not wil∣ling Page  5impartially to consider what makes against their opinion, and frame a thousand imaginations to evade the strength of the opposite reasons, and to construe all appearances (as melan∣cholick persons do the sound of Bells) to speak what they fancy; And possi∣bly all the opposite Opinators in this business are under the like partiality and unindifferency.

There is a great odds between a Mat∣ter propounded only as an Hypothesis, and propounded as a real truth. In the former there is nothing more required than a true understanding of the Phae∣nomena, and a ready Wit to contrive some Model, and to dress it up so hand∣somly, that it may answer the Phaeno∣mena, and to fit up such expedients as may meet with and stop the Leaks that otherwise would happen in the Hypo∣thesis: And such a man tells us not so much what the truth of Nature is, as what he thinks he could have made it, if he had had the handling of it; such may be the Systemes of Ptolomy, Copernicus, and Tycho Brahe, Page  6which cannot be possibly all true, though possibly they may be all false. And yet every of them is so fitted and accommodated by the Wit, Invention, and Industry of the Authors, that they solve the Phaenomena very near equally: And thus if I remember aright des Cartes fairly propounds his tria Principia's; and some other parts of his New Philoso∣phy.

But to propound a thing as really a truth in Nature, is another kind of bu∣siness, and requires not so much a dex∣trous Invention, but an impartial in∣spection into the things themselves, and examination how all things stand one with another, as we truely find them, and not as we mind to make them: For the Laws of Nature are stable, and setled, and regular, and not like the Laws of Men, or the fashions of our Cloaths, mutable, according to new Modes, or devices of Fancy.

Therefore the bare accommodation of Hypotheses to the Solution of the most obvious Phaenomena is not always the measure of its truth, for that may Page  7be but the product of Invention and Wit. For it is apparent, that though it is impossible that all the varying So∣lutions of this trifling Experiment can be all true, yet they are all so dressed and pieced up, that they do solve the most obvious Phaenomena in this Experiment, well near equally each with other.

But on the other side, if any Phaeno∣mena happen cleerly either in this or any other instance, that do cross and thwart that which is taken up as a necessary postulatum in any of these Solutions; it is if not an undeniable, yet a great and possibly a clear demonstration, that the Hypothesis its self is false, and ill Founded, especially if it be the great Basis upon which such Hypothesis is bottomed and built.

And if the foundation of a Hypothe∣sis, or the general postulatum upon which it is bottomed, be false, or only imagi∣nary, although the Inferences and Con∣clusions made upon such a Basis be de∣duced with all the fineness and subtilty imaginable, and such (as were the postula∣tum it self true, upon which they are bot∣tomed) Page  8would be as necessary and consequential, as the Demonstrati∣ons of Euclide, yet the whole fabrique will fail when it comes to tryal, and be∣come like the Astrological Predictions Calculated with Art enough upon a false Ephemerides.

I that come after the Labours and Scrutinies of so many Excellent Men that have gone before me upon this Subject, cannot promise my self or others that I shall say much in this Matter that hath not been said before; and the ne∣cessity of a free Discourse requires that I should take in somewhat of other mens Labours. But I shall avoid, as much as I can, the imputation of a Plagiary, by mentioning the Authors as I have oc∣casion: But yet, though somewhat that I shall say hath been said before, especi∣ally by Linus, and Fabri, yet somewhat will be new, although the most I shall do herein will be to make the Me∣thod and manner of Explication of it as much my own as I can, which I shall do in this order.

First, I shall explain some Termes Page  9which I shall have occasion to use, that so I may write intelligibly according to that sense I gave my words; though it may be possibly not according to the sense wherein others have used them.

Secondly, as preliminary to what I shall say touching this Experiment, I shall set down some Statical Observati∣ons, that may be useful to me upon this inquiry, not that I shall ingage my self in the whole Theory of Statical Principles and conclusions; this hath been done already by those worthy Per∣sons that have ex professo handled this Subject, as Archimedes, Steving, Mr. Boyl, and others; but only shall glean up some general Observations therein ne∣cessary to this inquiry.

Thirdly, I shall set down what it is not, that may be supposed in the space derelicted by the Mercury, namely, it is not Nothing, nor Ayre, nor Aether, nor any Body that comes from without.

Fourthly, I shall set down what I think it is that possesseth the place de∣relict by the Mercury.

Fifthly, I shall set down what I think Page  10is not the cause that suspends the Cylin∣der of Mercury, in the Tube to that Altitude of 29 Inches, or thereabouts; namely, not the Gravitation or pressure of the impending Ayr, nor its Ela∣stricity.

Sixth, I shall set down what I think is the cause, that suspends the column of Mercury from subsiding in the Tube be∣low Twenty nine Inches, or thereabouts.

Seventhly, I shall set down those ob∣jections, that seem of the greatest force against the last supposition.

Eighthly, I shall take a particular ex∣amination of some other Experiments, as touching the cohesion of Polished Marbles, and the Magdeburgh Hemi∣sphere, and the rising of Water in the common Pumps.

And this Order I shall as near as I can observe in the ensuing Chapters.