THE AUTHOUR's PREFACE AND DECLARATION.

THEY that know how indispos'd I naturally am to Contentiousness, will, I presume, wonder to see me publickly engaged in two Controversies at once. But that I am still as averse as ever from entering into Disputes that may handsomly be declin'd, the way wherein I have managed the following Controversies will, I hope, evince. And the Inducements I now have to appear in publick are such, that it would be hard for me to resist the being prevail'd on by them.

For, in the first place, I was (by Name, as it were) challeng∣ed by a person, who undertook to disprove not one or two of my Conjectures, but as much of the whole Body of my Treatise as concern'd the Spring of the Air, which most of my Explications suppose. And this being done by a Learned Man, who writes very confidently of the goodness of his Hypothesis and Arguments, and his Book being soon after follow'd by another written by Mr. Hobbs, a man of Name in the World; there seem'd to be some danger that so early an Opposition might op∣press the Doctrine I had propos'd, before it was well understood and duly ponder'd. Wherefore I fear'd I might be wanting to the Truth and my self, if I should at such a time be altogether silent; especially since I might probably divert many who would otherwise be forward to appear against us, by letting them see how defensible our Doctrine is even against such Ad∣versaries as those I have reply'd to. And this course I the ra∣ther chose, that in case I should henceforward comply with those who would have me forbear to write any further of these Page  [unnumbered] Controversies, it might not be presently inferr'd from my si∣lence, that a good Cause cannot enable a Pen no better than mine to defend it.

But I scarce doubt but that intelligent Readers, especially those that are imbued with the Principles of the Corpuscularian Philosophy, will be much more apt to think that I had reason to write the following Discourses, than to think that I had any to make them so prolix: And especially ingenious men, that are accustomed to admit nothing that either is not intelligible, or is precarious, will think divers of the Objections I reply to have needed no Answers, or at least no solemn ones. But to these I have four things to represent.

And First, That which not a little swells the bulk of the fol∣lowing Treatises, is the incerting those passages of my Adversa∣ries that I examine in their own words: which being a Practice that I expect from any that shall think fit to animadvert upon any Opinion or Argument of mine; I thought it but equitable to do what I desir'd to have done to me, though oftentimes I could not do it in a little room.

Next, I was the more willing to prosecute some of Franciscus Linus his Objections, because the fear of being reduc'd to grant a Vacuum has so prevail'd with many eminent persons bred up in the received Philosophy of the Schools, that though they disagree both with him and among themselves about the parti∣cular manner of solving the Phaenomena of the Torricellian Ex∣periment; yet they agree in ascribing them to some extremely∣rarefi'd substance that fills up the space deserted by the Quick∣silver. So that this Opinion, as to the main, being approved by many eminent Scholars, especially of that most learned Or∣der of the Jesuites, (to whom perhaps its Congruity to some Articles of their Religion chiefly recommends it) I was willing to pay them that respect, as not to dissent from persons, divers of whom for their eminence in Mathematicks and other Learn∣ing I much esteem, without shewing that I do it not but upon Considerations that I think weighty.

Thirdly, though the Examiners Hypothesis have but few, Page  [unnumbered] and not very considerable, Arguments to countenance it; yet his Objections against our Doctrine (the Reply to which takes up the first Part of the following Treatise) are such, as though they may be solidly answered by any that throughly under∣stands our Hypothesis, yet they may chance puzzle such Readers as do not, and these possibly will prove more than a few

And, Lastly, because that sometimes when the Argument objected did not perhaps deserve to be much insisted on, the Argument treated of deserv'd to be considered; I thought it not amiss to make use now and then of some such opportuni∣ties to illustrate the matter it self under consideration: Which I the rather did for these two Reasons;

First, because I find that, except by some able Mathemati∣cians and very few other contemplative men, the Doctrine of the Spring of the Air, at least as I have proposed it, is not yet sufficiently apprehended, (and therefore needs to be inculcated.) Insomuch that through a great part of some late Discourses of men otherwise eminently learned, (written against other Ela∣terists, not me) there seems to run so great and clear a mistake, perhaps for want of skill in the Hydrostaticks, that I can scarce impute it to any thing, but to their not throughly under∣standing the Hypothesis they would confute.

And, Next, because I was willing to lay down in my Answer to the Objections I examin'd, the grounds of answering such other Arguments as may be built upon the same or the like Principles. And perhaps I may truly enough say, that in the following Treatise I have already in effect answered several dis∣courses, written some before and some since mine, by learned men, about the Torricellian and other new Experiments relating to a Vacuum, though I forbore to mention the names or words of the Authors, because I found not that my Writings or Experi∣ments were as yet known to them. To these things I may adde, that I thought the Discourses of Linus the fitter to be insisted on, because he seems to have more diligently than some others, (who yet venture to dispute against it) enquired into our Do∣ctrine. And I shall not scruple to say thus much of an Adversa∣ry, Page  [unnumbered] (and one to whom I gave no provocation to be so) that though I dare not speak in general of those that have written ei∣ther about the Weight of the Air, or else For or Against a Va∣cuum, because (as I acknowledge in the first Chapter following) I cannot yet procure the Books of divers learned men, especial∣ly of those great Personages, Robervall, Balianus and Casatus; yet among the Writers I have hitherto met with, who have re∣course to the Aristotelean Rarefaction and Condensation in the Controversies under debate, scarce any seems to have contrived his Hypothesis better than our Linus. Not that I think his Prin∣ciple is either true, or (at least to such as I) intelligible; but that the Funiculus he assumes being allow'd him, he may, for a Reason to be touch'd a little below, make out, though not all the Phae∣nomena of my Experiments, yet many more of them than most other Plenists, that deny the Spring of the Air, can deduce from their Hypotheses if granted. And in regard that, whereas we ascribe to the Air a Motion of Restitution outwards, he attri∣butes to it the like Motion inwards, it cannot but happen that, though the Principles cannot both be true yet many of the Phae∣nomena may be explicable by which of them soever is granted: because of this, I say, it is not so easie as many ingenious Rea∣ders may be apt to think, to draw pertinent Objections from Ex∣perience against the Adversary I have to deal with. Which I re∣present, lest, as some may think I have employ'd more Argu∣ments than I needed, so others should think I have omitted ma∣ny; as indeed I have omitted some, that I might pertinently have employ'd.

But there is another sort of Persons besides those I mention'd at the beginning of this Preface, to whom I must address the remaining part of it; namely, to those who seem troubled, that I suffer my self to be diverted either by Linus or Mr. Hobbs from perfecting those Ex∣perimental * Treatises that are lying by me, al∣most promis'd by the learned Publisher of the Latine Edition of my Essays; and from prosecuting those wayes of enquiry into the Nature of things, Page  [unnumbered] wherein they are pleas'd to think I may be more serviceable to real Learning and the Lovers of it. And I confess that these Mens Reasons and Perswasions have so far prevailed with me, that after what I have done in the two following Treatises, to Vindicate my Writings from the Objections made against them by two Learned men of very differing Hypotheses, and thereby to shew in some measure that I am not altogether unacquainted with the way of defending oppos'd Truths, I have laid aside the thoughts of writing any more distinct or entire Polemical Trea∣tises about the Subjects already disputed of. And to this I am invited by several other Reasons (besides what I have newly intimated.)

For first, as I elsewhere declare, it was not my cheif Design to establish Theories and Principles, but to devise Experiments, and to enrich the History of Nature with Observations faith∣fully made and deliver'd; that by these, and the like Contribu∣tions, made by others, men may in time be furnish'd with a suffi∣cient stock of Experiments to ground Hypotheses and Theories on. And though in my Physico-Mechanical Epistle and my Spe∣cimens I have ventur'd some Conjectures also at the Causes of the Phaenomena I relate, lest the Discourse should appear to in∣quisitive Readers too jejune; yet (as I formerly said) I pro∣pos'd my Thoughts but as Conjectures design'd (though not onely, yet chiefly) to excite the Curiosity of the Ingenious, and afford some hints and assistance to the Disquisitions of the Speculative. And accordingly I have not forborn to mention divers things, which judicious Readers may easily perceive I foresaw that many would think unfavourable to the Opinions I inclin'd to. So that for me to leave Experimental for Contro∣versial Studies, were a course unsuitable to the principal scope of my Writings.

Next, though I have adventur'd to improve the Doctrine of the Spring and Weight of the Air by some Supplements where I found it deficient, and to recommend it by some new Illustra∣tions and Arguments deduc'd from my Experiments: yet the Hypotheses themselves (for the main) being the Opinions also of Page  [unnumbered] far learneder Men than I, it might be thought injurious both to them and to our common Cause, if I should needlesly go about to hinder them from the Honour of Vindicating the Truths we a∣gree in; especially, some of them being Excellent Mathematici∣ans, and others Eminent Naturalists, whose Concern to maintain the Hypotheses against Objections, if any shall arise, is equal to mine, and whose leisure and abilities far exceed those of a Per∣son who both is sickly, and hath other employments enough, and who (if he were far better skil'd in Geometry than he pretends to be) hath such a weakness in his Eyes, as makes him both un∣willing and unfit to engage in any Study where the conversing with Mathematical Schemes is necessary.

Thirdly, nor do I see much cause to doubt that the things I have deliver'd will notwithstanding my silence be left undefended: The forwardness I have already observ'd in divers Vertuosi to Vin∣dicate those Writings, which they are pleas'd to say have con∣vinc'd them, and to save me the labour of penning the following Treatises, scarce permitting me such an Apprehension. Especi∣ally since there are some things that will much facilitate their Task, if not keep men from putting them upon it. For though Mr. Hobbs and Linus have examin'd my Writings upon Princi∣ples wherein they differ as much from each other as from me; yet neither have they seen cause to deny any thing that I deliver as Experiment, nor have their Objections been considerable, whether as to Number or to Weight, against the Applications I have made of my Principles to solve the Phaenomena. So that usually without objecting any Incongruity to my particular Ex∣plications, they are fain to fall upon the Hypotheses themselves: in whose Defence I think I may with the more Reason expect to be seconded, because not onely I have endeavour'd, as I formerly noted, to lay the grounds of answering such Objections as I fore∣saw might arise; but I have also, to prevent or ease their labour, written the two first Parts of my Defence against Linus, without being oblig'd to do so for the Vindicating of my Explications, which are particularly maintain'd in the third Part.

I know not whether I may venture to adde on this occasion, Page  [unnumbered] That those who have taken notice of the usefulness of Experi∣ments to true Philosophy, and have observ'd that nevertheless the Difficulty, Trouble, and Charge of making them is such, that even in this Learned Age of ours there are very few Bacon's or Mersennus's to be met with, and those who have either made themselves, or at least seen others make Experiments, even such as those I have publish'd, with the care I am wont to think my self oblig'd to employ on such Occasions; will perhaps not onely believe that they cost me far more time and pains than they that have not made nor seen such tryals are apt to imagine, but will possibly think it enough for a Person that is not by Profession a Scholar, to make them carefully, and set them down faithfully, and will allow him to let others Vindicate the Truths he may have the good fortune to discover, especially, when there are so many fitter for it than he, who have (as well as his Adversaries) more leisure to write Disputations than opportunity to prose∣cute Experiments; the latter of which to be perform'd as it ought to be, doth in many cases, besides some Dexterity scarce to be gain'd but by practice, require sometimes more Diligence, and oftentimes too more Cost, than most are willing, or than ma∣ny are able, to bestow upon them.

To be short, though if any thing very worthy to be taken no∣tice of by me be suggested against any of my cheif opinions or Explications, I may either take an occasion to say somewhat to it elsewhere, or at least have an opportunity to consider it in a Review, wherein I may alter, mend, supply, vindicate or retract divers Passages of my other Writings: yet I would not have it expected that I should exchange a Book with every one that is at leisure to write one against a Vacuum, or about the Air. Which Declaration I make, not that I think it will or ought to hinder any man from making use of his liberty to express a dis∣sent, if he sees cause; but for these two Reasons.

The one, That my silence might not injure either the Truth or my self, by tempting men to think, that whatever I do not an∣swer, I cannot; but might give unbiass'd and judicious Readers a Caution to allow as little of Advantage to the Writings of my Page  [unnumbered] adversaries upon the account of their being unanswer'd by me, as if I were no longer in the World. And the other, That I may not hinder those who would reply to such Adversaries by leave∣ing them an apprehension that either I may prevent them, or they me. To conclude, I see no cause to despair, that whether or no my Writings be protected, the Truths they hold forth will in time in spite of opposition establish themselves in the Minds of men, as the Circulation of the Bloud, and other former∣ly much contested Truths have already done. My Humour has naturally made me too careful not to offend those I dissent from, to make it necessary for any man to be my Adversary upon the account of Personal Injuries or Provocations. And as for any whom either Judgment or Envy may invite to con∣tend, that the things I have communicated to the World deser∣ved not so much Applause as they have had the luck to be en∣tertain'd with; that shall make no Quarrel betwixt us: For per∣haps I am my self as much of that mind as he; and however I shall not scruple to profess my self one of those who is more desirous to spend his time usefully, than to have the Glory of leaving nothing that was ever written against him unan∣swer'd; and who is more solicitous to pursue the wayes of discovering Truth, than to have it thought that he never was so much subject to Humane Frailties as to miss it.