Physiologia Epicuro-Gassendo-Charltoniana, or, A fabrick of science natural, upon the hypothesis of atoms founded by Epicurus repaired [by] Petrus Gassendus ; augmented [by] Walter Charleton ...

CHAP. IX. Of Rarity, Density, Perspicuity, Opacity.

SECT. I.

* 1.1HAving thus steered through the dee∣pest Difficulties touching the pro∣per objects of the other Senses, the Chart of Method directs us in our next course to profound the parti∣cular natures of all those Qualities, which belong to the apprehensive jurisdiction of the Sense of TOUCH∣ING, either immediately, or rela∣tively. But, before we weigh Anchor, that we may avoid the quicksands of too General Apprehen∣sions, and draw a Map or Scheme of all the Heads of our intended En∣quiries; tha•• so we may praepare the mind of our Reader to accompany us the more easily and smoothly: it is requisite that we advertise,

* 1.2(1) That the Attribute of Touching is sometimes in Common to all Bodies, 〈◊〉〈◊〉 well Inanimate, as Animate, when their superficies or ex∣tremes ar•• Contingent; according to that Antithesis of Lucretius, Tactus Corporibus cunctis, intactus Inani. Sometimes in Common to all Sens••••, insomuch as all Sensation is a kind of Touching, it be∣ing necessa••••, that either the object it self immediately, or some sub∣stantial Em••nation from it, be contingent to the Sensory; as we have apodictically declared in our praecedent considerations of Visible, Au∣dible, Odo••••ble, and Gustable Species. Sometimes (and in praesent) Proper to th•• Sense of Touching in Animals; which, however it extend to the Per••••ption of Objects, in number manifold, in nature various and frequ••••••ly even repugnant (whereupon some Philosophers have contuma••iously contended for a Plurality of Animal Touchings; others gone so high as to constitute as many distinct Powers of Touch∣ing, as th••re are [〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉] Differences and 〈◊〉〈◊〉 of conditions in Tangibles) doth yet apprehend them all 〈◊〉〈◊〉 one and the same common reason, and determinate qualification, after the same manner, as the sight discernes White,

Black, Red, Green, &c. all sub communi Coloris ratione, in the common capacity of Colours.

And this is that fertile sense,* 1.3 to whose proper incitement we owe our Generation; for, had not the Eternal Providence endowed the Organs of∣ficial to the recruit of mankind, with a most exquisite and delicate sense of Touching, the titillation whereof transports a man beyond the severi∣ty of his reason, and charmes him to the act of Carnality; doubtless, the Deluge had been spared; for the First age had been the Last, and Huma∣nity been lost in the grave, as well as innocence in the fall of our first Parents. Quis enim▪ per Deum immortalem, concubitum, rem adeo fae∣dam, solicitaret, amplexaretur, ei indulgeret? quo Vultu Divinum illud Animal plenum rationis & consilii, quem vocamus Hominem, ob∣saenas mulierum partes, tot sordibus conspurcatus attrectaret, nisi incre∣dibili voluptatis aestro percita essent Genetalia? And let us but abate the temptation of this sense, and libidinous invitement of it praeambulous to the act of Congression; and we shall soon confess that so magnified delight of sensuality, to be no other than what the noblest of Stoicks, Marcus Antoninus defined it, 〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉, but the attrition of a base entrail, and the excretion of a little snivel, with a kind of convulsion, as Hippocrates describes it, This is that Fidus Achates, or constant friend, that conserves us in our first life, which we spend in the dark prison of the womb; ushers us into this, which our improvidence trifles away for the most part on the blandish∣ments of sensual Appetite; and never forsakes us, till Death hath trans∣lated us into an Eternal one. For when all our other unconstant senses perish, this faithful one doth not abandon us, but at that moment, which de∣termines our mortality. Whence Aristotle drew that prognostick (de Anim. lib. 3. cap. 13.)

that if any Animal be once deprived of the sense of Touching, death must immediately ensue; for neither is it possible (saith He) that any living Creature should want this sense, nor to the be∣ing of it is it necessary that it have any other sense beside this.

In a word, this is that persuasive sense, and whose testimony the wary Apostle chose to part with his infidelity, and to conclude the presence of his revived Lord. That painful sense, on the victory of whose torments the patient souls of Martyrs have ascended above their faith. That Virtual and Medical sense, by which the Great Physician of diseased na∣ture, was pleased to restore sight to the blind, agility to the lame, hear∣ing to the deaf; to extinguish the Feaver in Peters Mother-in-Law, stop the inveterate issue in his Haemorhoidal Client; unlock the adamantine gates of death, and restore the widows son from the total privation, to the perfect habit of life.

(2) That some Qualities are sensible to the Touch,* 1.4 which yet are common to the perception of other senses also; for no scholler can be ignorant of that Division of sensibles into Common and Pro∣per; and that among the Common are reckoned Motion, Quiet, Number, Figure, and Magnitude, according to the list of Aristotle (2 de Anim. cap. 6.)

* 1.5(3 and principally) That the Qualities of Concretions, either Com∣monly or Properly appertaining to the sense of Touching, are to be con∣sidered in their several Relations to the Principles on which they depend. First, some result from the Universal matter, Atomes, in this respect, that they intercept Inanity, or space betwixt them; and of this original are Rarity and Density, with their Consequents, Perspicuity and Opacity. Se∣condly, Some depend on the Common Materials, in this respect, that they are endowed with their three essential Proprieties, Magnitude, Figure, Mo∣tion: and that either Singly, or Conjunctly. (1) Singly, and either from their Magnitude alone; of which order is the Magnitude o•• Quantity of any Concretion; and the Consequents thereof, Subtility and Hebetude: or from their Figure alone, of which sort is the Figure of every thing; and the Consequents thereof, Smoothness and Asperity, &c. or only from their Motiv•• Virtue, of which kind is the Motive Force inhaerent in all things in th•• General, and that which assisteth and perfecteth the same in most things, the Habit of Motion, and particularly Gravity and Levity. (2) Conjunc••ly, from them all; of which production are those common∣ly called the ••our First Qualities, Heat, Cold, Dryness, Moysture; as also those which ••r•• deduced from them, as Hardness, Softness, Flexility, Du∣ctility: and all others of which Aristotle so copiously (but scarce perti∣nently) treateth in his fourth book of Meteors: and lastly, those by vulgar Physiologist named Occult Qualities, which are also derivative from A∣toms, in res••••ct of their three essential Proprieties; and among these the most eminent and generally celebrated, is the Attractive Virtue of the Loadstone.

* 1.6Now on each of these we intend to bestowe particular speculation, al∣lowing it the ••••me order, which it holds in this scheme, which seems to be only a faithful Transsumpt of the method of Nature: and we shall begin at Rarity and Density. (1) Because nothing can be generated but of Atoms commixt, and that Commixture cannot be without more or less of the In∣ane space in••••rcepted among their small masses; so that if much of the Inane space 〈◊〉〈◊〉 intercepted among them, the Concretion must be Rare, if little, Dense, of meer necessity: (2) Because, the Four First reputed Qua∣lities, Heat, Cold, Dryness, Moysture, are posterior to Rarity and Density, as appears by that of Aristotle (physic 8. cap. 16.) where, according to the interpretation of Pacius, He intimates, that Heat and Cold, Hard∣ness and Sof••ness are certain kindes of Rarity and Density; and there∣fore we are ••o set forth from them, as the more Common in Nature, and consequently the more necessary to be known, a Generalioribus enim, tan∣quam notioribus ad minus Generalia procedendum, is the advice of Arist. (physic. 1. cap. 2.)

SECT. II.

COncerning the immediate Causes of Rarity and Density in Bodies,* 1.7 di∣vers Conceptions are delivered by Philosophers. (1) Some, ob∣serving that Rare bodies generally are less, and Dense more Ponderous, and that the Division of a body into small parts, doth usually make it less swift in its descent through aer or water, than while it was intire; have thereupon determined the Reason of Rarity to consist in the actual division of a body into many small parts: and, on the contrary, that of Density to consist in the Coadunation or Compaction of many small parts in∣to one great continued mass. But, These considered not, that Chrystal is not more rare, though less weighty (proportionately) than a Dia∣mond: nor that the Velocity of bodies descending, doth not encrease in proportion to the difference of their several Densities, as their inad∣vertency made them praesume; there being sundry other Causes, besides the Density of a body, assignable to its greater Velocity of motion in descent, as the Heroical pen of Galileo hath clearly demonstrated (in 1. Dialog. de motu.) and our selves shall professedly evince in convenient place.

(2) Others,* 1.8 indecently leaping from Physical to Metaphysical specu∣lations, and imagining the substance of a body to be a thing really di∣st••nct from the Quantity thereof; have derived Rarity and Density from the ••••veral proportions, which Quantity hath to its substance; as if in Ra∣refaction a Body did receive no mutation of Figure, but an Augmentation, and in Condensation a Diminution of its Quantity. But the excessive subtility, or rather absolute incomprehensibility of this Distinction, doth evidently confess it to be meerly Chimerical, as we have formerly inti∣mated, in our discourse concerning the proper and genuine notions of Corporiety and Inanity.

(3) A Third sort there are,* 1.9 who having detected the incompetency of the first opinion, and absolute unintelligibility of the Second; judiciously desume the more or less of Rarity in any body, from the more or less of Vacuity intercepted among the parts thereof; and on the contrary, the more or less of Density from the greater or less exclusion of Inanity, by the reduction of the parts of a body to mutual Contingency. And this is that opinion, which only hath subjugated our judgement, and which seems worthy our best patronage: in regard not only of its sufficiency to expli∣cate all the various Apparences among bodies, resulting from their seve∣ral Differences in Rarity and Density; but also of its exuperance of rea∣son above the F••rst, and of intelligibility above the second; it being the duety of a Philosopher, always to prefer Perspicuity to Obscurity, plain and genuine notions to such as are abstracted not farther from mat∣ter, than all possibility of Comprehension.

* 1.10According to this Hypothesis, therefore, of Vacuities interspersed (of which ••pecurus seems to have been the Author) we understand, and dare define a Rare Body to be such, as obtaining little of Matter, possesseth much of Place; and on the contrary, a Dense one to be that, which obtaining much of Matter, possesseth little of Place: intending by Place, all that space circumscribed by the superfice of the Ambient, such as is the space in∣cluded betwixt the sides, or in the concave of a vessel.

* 1.11For, supposing any determinate space to be one while possessed by Aer alone, another while by Water alone; the Aer therein contained cannot be said to be Rare, but only because though it hath much less of matter, or substance, yet it takes up as much of space, or room as the Water: nor the Water to be Dense, but only because though it hath much more of matter, yet doth it take up no more of space, than the Aer. Whence it is purely Consequent, that if we conceive that Water to be rarified into Aer, and that Aer to be condensed into Water; the Aer made of the Water re••ifi∣ed, must replenish a vessel of capacity not only ten-fold, as Aristotle inconsi∣derately conjectured, but a hundred-fold greater, as Mersennus by stalick experiments hath demonstrated: and transpositively, the Water made by the Aer condensed, must be received in a Vessel of capacity an hundred-fold less; when yet in that greater mass of Aer, there can be no more of Mat∣ter, or Quantity, than was in that smaller mass of Water, before its Rare∣••action; nor in that smaller mass of Water less of Matter, or Quantity, than was in that greater mass of Aer, before its Condensation. Evident it is, therefore, that by those, contrary motions of Rarifaction and Conden∣sation, a Body doth suffer no more than the meer Mutation of its Figure, or the Diffusion and Contraction of its parts: its Quantity admitting no Augment••tion in the one, nor Diminution of the other.

* 1.12This being Apodictical, the sole Difficulty that requires our Enodation, is only this; Whether a Rare Body possessing a greater space, than a Dense, proportion••tely to its Quantity, doth so possess all that space circumscribed by its superfice, as to replenish all and every the least particle thereof, not leaving any space or spaces, however exile, unreplenisht with some adae∣quate particle of its matter? Or whether there are not some small parts of space, in••••rmixt among its diffused or mutually incontingent particles, in which no particles of its matter are included, and so there remain small Vacuola, or Empty spaces, such as we have formerly more than twi••e described, in our Chapter of a Disseminate Vacuity in Nature?

And this descends into another Doubt, whose clear solution is of so much importance, as richly to compensate our most anxious En∣quirie; viz. Whether Rarity be caused from the interception of much Inanity, when the parts of a Body, formerly Adunate, are separated each from other (at least, in some points of their superfices) and so the Body become so much more Rare, by how much the more, or more ample empty spaces are intercepted among its incontingent particles: or Wheth••r Density and Rarity depend on any other possible Causes besides th••s, i. e. without the intermistion of inane spaces among ••he 〈◊〉〈◊〉 of Bodies? And this we conceive to be the whole

and true state of that Controversie, which hath so perplexed the minds of many the most eminent Philosophers in the world.

That the Rarity and Density of Bodies can arise from no other Cause immediately,* 1.13 but the more or less of Inanity intercepted among their particles; may be thus Demonstrated.

If in a Rare body there be admitted no Vacuola, or small emp∣ty spaces, but it be assumed, that the particles of Matter are adae∣quate both in Number and Dimensions to the particles of space, wherein it is contained; then must it necessarily follow, that in Con∣densation many particles of Matter must be reduced into one particle space, which before Condensation was adaequate onely to one particle of Matter: and, on the contrary; in Rarefaction, one and the same particle of matter must possess many of space, each whereof, be∣fore Rarefaction, was in dimensions fully respondent thereto. For Example; in Aer condensed into Water, an hundred particles of Aer must be reduced into one particle of space: and in Water rarified in∣to Aer, one particle of the matter of Water must possess an hundred particles of space. Again, according to the Assumption of no Va∣cuity, since in a Vessel replete with Aer, the parts of Aer must be equal in number and dimensions to the parts of space, thereby circum∣scribed, none the least particle of space being admitted to be Inane; if you fill the same Vessel with Water, or Lead, or Gold, it must follow, that the parts of the matter of Aer, and the parts of the matter of Water, Lead, or Gold, shall be equal in number, because Quae sunt uni tertio aequalia; aequalia sunt etiam inter se: and if so, needs must Aer be aequally Dense with Water, Lead, or Gold, which all men allow to be the most dense and compact body in Nature in regard it transcends all others in weight and difficulty of Solution, or Division;

(2) All bodies in the Universe must be equally Dense, or equally Rare;

(3) And so nothing can be capable of Condensation or Rarefaction. The least of which unconcealable Absurdities, (not to enumerate any o∣thers of those many that depend on the same Concession of an absolute Plenitude, or no Vacuity) is great enough to render those Heads, which have laboured to destroy the Vacuola of Epicurus, strongly suspected of Incogitancy, if not of stupidity.

Twere good manners in us to praesume, that no man can be so Facile,* 1.14 as to conceive, that Aristotle hath prevented these Exceptions, by that Distinction of his, de Actu & Potentia: but, because Praejudice may do much, we judge it expedient a while to insist upon the Examination of the importance and congruity thereof. He ratiocinates (4▪ physic. cap. 9.) that the matter of Contraries, E. G. of Heat and Cold, Rarity and Density is one and the same; so that as the same matter is one while Actually Hot a∣nother while Actually Cold, because it is both Hot and Cold Potentially: so is one and the same matter now Actually Rare, now Actually Dense, be∣cause it is both Rare and Dense Potentially. But, in strictness of Lo∣gick, all that this Argument enforceth, is only that the same matter

is Capable of Rarefaction and Condensation; which no man ever di∣sputed. The Quaestion is, Whether the same Matter, when Actu∣ally Rare, hath its parts dissociated and diffused into a greater space, than what they possessed while it was onely Potentially Rare, and that without the intermixture of Inanity among them? And all that can be collected from his discourses touching that, is no more than this; that as a matter or substance actually Hot, doth become more Hot, without the Emersion, or Accession of any new part, which was not actually Hot before: so likewise doth the same matter actually Extense, be∣come more Extense, without the Emersion, or Accession of any new part, which was not actually Extense before. But this Arrow was shot at random, not directly to the mark, nor hath it attained the Difficulty▪ For the Quaestion again is not, Whether in Rarefaction, any part of the matter were not formerly Extense: but, Whether that matter, which was formerly Extense, can be made more Extense without the Dissociation of its particles▪ and whether the particles of it can be actu∣ally Dissociated, without the interception of Inanity among them? Besides, His Comparison is as incongruous, as his Argument is weak; for (1) His Assumption concerning Heat is not only Precarious, but false, as shall be demonst••••ted, in suo loco: (2) were it true, yet doth that part of mat∣ter, which is actually Hot, remain indivulse or indistracted; otherwise than a part of matter, which being actually Extense, becomes more Extense, and therefore the Analogy faileth.

In conclusion, to mend the matter, He recurrs to that similitude of a Circle, which though contracted into a less, hath yet none of its parts more incurvate than they were before: But, alas the Quaestion still remains untoucht, ••nd (that we may not stay to impeach him of indecorum, in making an ••ndecent transition from a Physical to a Mathematical subject; contrary to his own Dialectical institutes) his similitude will bear no more of inference but only this, that a thing may be made more Dense, which is 〈◊〉〈◊〉 and Lax; which is impertinently disputed, when all men concede it.

* 1.15The Ad••ocates of Aristotle generally alleage in his Defense, that He supposed a certain Aethereal, or as some have called it, Animal sub∣stance, which inexistent in all Bodies, doth replenish their pores, and more espe••••••lly if their Contexture be Rare; and that when a Dense Bo∣die is rarified, there are no small Inane spaces intercepted among its Disso∣ciated parti••les, but that the spaces betwixt them are immediately posses∣sed by that subtile Aethereal substance: and that when a Rare Body is Con∣densed, th••t Aethereal substance, which did replenish its pores, is exclu∣ded.

But th•••• supposition, though it come neerer to the Quaestion, or cen∣ter of the Difficulty, is yet far short of solving it. For, take we (for Ex∣ample) •• C••b••cal foot of Aer, and insomuch as the substance of the Aer is more 〈◊〉〈◊〉, or less exile, than the substance of the supposed Aether, therefore 〈◊〉〈◊〉 it consist of fewer particles, than the Aether: and upon con∣sequence▪ 〈◊〉〈◊〉 the whole Cubical foot of Aer there are not more particles of Matte•• 〈◊〉〈◊〉 the Aereal and Aethereal ones being conjoyned, than if it consisted o••••y of Aereal particles. Now we enquire of Aristotles Cham∣pions,

Whether or no in that Cubical foot consisting of the Aggregate of both sorts of particles, there are as many particles of Matter, as are in a Cubical foot of Water, Lead, or Gold▪ The Affirmative is more than they dare own; nor can they deny, but that the space possessed by one foot containeth as many small parts of space, respondent to the par∣ticles of matter, as the other: and if so, must not there be in the Foot of Aer, many particles of space, which are possessed neither by the Aereal nor Aethereal particles, and are not those unpossessed particles of space abso∣lutely Empty? If you undertake the Negative, you insnare your self in this Absurdity, that the particles of a Cubical Foot of Aer and Aether conjoyn∣ed, must be equal in number to the particles of a Cubical foot of Water, Lead, or Gold.

The Difficulty of understanding the Formal and Immediate Reason of Rarity and Density in Bodies,* 1.16 by that so popularly applauded Hypo∣thesis of an Aethereal substance (imagined to maintain an absolute Pleni∣tude, and so a Continuity through the whole vast Body of Nature) being thus evinced; let us a while consider, how easily even the meanest Capaci∣ty may comprehend the full Nature of those Primary and Eminent Affe∣ctions, from the concession of small Vacuities. We have formerly ex∣plicated the matter, by the convenient similitude of an Heap of Corn, or Sand; which being lightly and gently poured into a Vessel, takes up more room then when prest down: and we shall yet more facilitate the Conception thereof by another simile, somewhat more praegnant, be∣cause more Analogous. When a Fleece, or Lock of Wool is deduced, or distended, we say, it is made more Rare; and when Compressed, more Dense: now the Rarity thereof consisteth only in this, that the Hairs, which were formerly more Consociate, United, or at closer Or∣der among themselves, are Dissociated, Dis-united, or reduced to more open Order, and the spaces betwixt them, become either more, or larger, in which no particle of Wool is contained: and on the con∣trary, the Density thereof consisteth onely in this, that the Particles or Hairs, which were before more Dissociated, or at open order, are by Compression brought to more Vicinity, or to closer order, and the spa∣ces betwixt them become fewer and lesser. And thus are we to con∣ceive, how the same Matter, without Augmentation or Diminution of Quantity, may be now Rarified into Aer, and anon Condensed into Water; for, instead of the Hairs in the Fleece of Wool, we need only put the Particles of the matter, which in Rarifaction are Dissociated, in Condensation Coadunated. And this Conception may be exten∣ded also to a Spunge, Flaxe, or any other Porous and Lax bodie▪ be∣cause they are capable of Expansion and Contraction onely in this re∣spect, that the small spaces intercepted in the incontiguities or distan∣ces of their particles, are now enlarged, now contracted. We con∣fess, this similitude is not adaequate in all points, there being this Difference, that when a Fleece of Wool is expansed, the ambient Aer doth instantly insinuate into the small spaces intercepted betwixt the dissociated particles of it, and so possess them▪ but▪ nothing of Aer, or Aether, or other substance whatever doth insinuate it self into the small spaces intercepted betwixt the dissociated particles or Aer▪ or Water, when either of them is Rarified: we say, notwithstanding this

Disparity, yet doth it hold thus far good and quadrant, that as no∣thing of Wool possesseth those spaces, which would therefore re∣main absolutely Empty, in case the sociable Aer did not instantly succeed in possession of them; so, since the parts of the matter of Water are Expansed or Dissociated after the same manner, as are the Hairs of Wool, and after the same manner Contracted or United; and certain small Loculaments are likewise intercepted betwixt the parti∣cles of that matter, in which nothing of Water can be contained, during the state of Rarifaction, and which no other substance can be proved to possess; it must thence follow, that those deserted small spaces, or Loculaments remain absolutely Empty. And more than that, our similitude is not concerned to impart.

* 1.17But, that we may make some farther advantage thereof, we ob∣serve; that as when a Fleece of Wooll is expansed, it is of a great∣er circumference, and so includes a greater Capacity therein, than when it is compressed; not that the single Hairs thereof take up a greater space in that capacity, for no Haire can possess more space, than its proper bulk requires, but because the inane spaces or Locu∣laments intercepted betwixt their divisions are enlarged: exactly so, when the same Matter is now Rarified into Aer, anon Condensed into Water, the Circumference thereof becomes greater and less, and the Capacity included in that circumference is augmented and di∣minished accordingly; not that the single Particles of the Matter possess a greater part of that capacity in the state of Rarifaction, th•••• in that of Condensation, because no particle can possess more of space than what is adaequate to its dimensions; but only because the Inane spaces intercepted betwixt their divisions are more ample in one case, than in the other. And hence it is purely consequent, that the mat∣ter of a Body Rarified can not be justly affirmed to possess more of true or proper Place, than the matter of the same body Condensed; though, when we speak according to the customary Dialect of the Vulgar, we say, that a Body Rarified doth possess more of space, than when Condensed: insomuch as under the terme Place is comprehended all that Capacity circumscribed by the extremes or superfice of a Body; and to the Matter, or Body it self are attributed not onely the small spaces possessed by the particles thereof, but also all those inane spa∣ces interjacent among them, just as by the word City, every man understands not only the dwelling Houses, Churches, Castles, and o∣ther aedifices, but also all the streets, Piazzaes, Church-yards, Gar∣dens, and other void places contained within the Walls of it. And in this sense onely are our praecedent Definitions of a Rare, and Dense Body to be accepted.

* 1.18The Reasons of Rarity and Density thus evidently Commonstrated, the pleasantness of Contemplation would invite us to advance to the ex∣amination of the several Proportions of Gravity and Levity among Bodies, respective to their particular Differences in Density and Rarity; the several ways of Rarifying and Condensing Aer and Wa∣ter; and the means of attaining the certain weights of each, in the several rates, or degrees of their Rarifaction and Conden∣sation;

according to the evidence of Aerostatick and Hydrostatick Expe∣riments: but in regard these things are not directly pertinent to our present scope and institution, and that Galilaeus and Mersennus have enriched the World with excellent Disquisitions upon each of those sublime Theorems; we conceive ourselves more excusable for the Omissi∣on, than we should have been for the Consideration of them, in this place. However, we ask leave to make a short Excursion upon that PROBLEM, of so great importance to those, who ex∣ercise their Ingenuity in either Hydraulick, or Pneumatick▪ Mecha∣nicks: viz.

Whether may Aer be Rarified as much as Condensed; or whether it be capable of Rarifaction and Condensation to the same rate, or in the same proportion?

That common Oracle, for the Solution of Problems of this abstruse nature, Experience hath assured, that Aer, may be Rarified to so great a height, in red-hot Aeolipiles, or Hermetical Bellows, that the 70 part of Aer formerly contained therein, before rarifaction, will totally fill an Aeolipile upon extreme Rarifaction thereof. For, Mersennus, using an Aeolipile, which being Cold, would receive exactly 13 ounces, one Drachm and an half; and when Hot, would suck in only 13 ounces: found, that the whole quantity of Aer ignified, and replenishing the same Aeolipile, when glowing Hot, being reduced to its natural state, did possess only the 70. part of the whole Capacity, which was due to the Drachm and half of Water. We say, upon Extreme Rarifaction; because this seems to be the highest rate, to which any Rarifaction can attain, in regard the Metal of the Aeolipile can endure no more violence of the Fire, with∣out Fusion.

As for the Tax, or Rate of its utmost Condensation; though many are persuaded, that Aer cannot be reduced, by Condensation, to more than a Third part of that Space, which it possesseth in its natural state; because they have observed, that Water infused into a Vessel of three He∣minae, doth not exceed two Heminae, in regard of the Aer remaining within: yet certain it is, that Aer may be Condensed to a far high∣er proportion. For, Experience also confirms, that into the Cham∣ber of a Wind-Gun (of usual Dimensions) Aer may be intruded, to the weight of a Drachm, or sixty Grains: and that in that Capa∣city, which contains only an ounce of Water, it may be so included, as that yet a greater proportion of Aer may be injected into it. Now, therefore, insomuch as the Aer in ••ersennus his Aeolipile amounts to four Grains (at least) or sixe (at most) which number is ten times multiplied in sixty; and that the Concave of the Aeolipile is to the Concave of the Pipe of the Wind-Gun, in proportion sesquialteral: by Computation it appears, that the Aer condensed in the Chamber of the Wind-Gun must be sufficient to fill the Aeolipile ten times over, or the same Chamber 15 times over, if restored to its natural te∣nour. And hereupon we may safely Conclude, that Aer may be Compressed in a Wind-Gun, to such a rate, as to be contained in a space 15 times less, than what it possessed during its natural Laxity; and that by the force only of a Mans hand, ramming down the Embol••s, or

Charging Iron: which Force being capable of Quadruplication, the Aer may be reduced into a space subquadruple to the former. If so, the rate of the possible Condensation of Aer, will not come much short of that of its extreme Rarefaction: at least, if a Quadruple Force be sufficient to a Quadruple Condensation; and Aer be capable of a Quadruple Compressi∣on: both which are Difficulties not easily determinable.

SECT. III.

PERSPICUITY and OPACITY we well know to be Qualities not praecisely conformable to the Laws of Rarity and Density;* 1.19 yet, insomuch as it is for the most part found true (caeteris paribus) that every Concretion is so much more Perspicuous, by how much the more Rare; and è contra, so much the more Opace, by how much more Dense; and that the Reason of Perspicuity can hardly be understood, but by assuming certain small Vacuities in the Body interposed betwixt the object and the eye, such as may give free passage to the visible Species; nor that of Opacity, but by conceding a certain Corpulency to the space or thing therein inter∣posed, such as may terminate the sight: therefore cannot this place be judged incompetent, to the Consideration of their severall originals.

By a Perspicuum [〈 in non-Latin alphabet 〉〈 in non-Latin alphabet 〉] we suppose, that every man un∣derstands that Body,* 1.20 or Space, which though interposed betwixt the Eye and a Lucid, or Colorate Object, doth nevertheless not hinder the Transition of the Visible species from it to the Eye: and by an Opacum; that which obstructing the passage of the Visible Species, terminates the sight in it self.

We suppose also, that (according to our praecedent Theory) the Spe∣cies Visible consist of certain Corporeal Rayes emitted from the Object,* 1.21 in direct lines toward the Eye; and that where the Medium, or inter∣jacent space is free, those Rayes are delated through it without impediment; but, where the space is praepossessed by any solid or Impervious substance, they are repercussed from it toward their Original, the Object. And hence we inferr, that because the total Freedom of their Transmission depends only upon the total Inanity of the Space intermediate; and so the more or less of freedome trajective depends upon the more or less of Inanity in the Space intermediate: therefore must every Concretion be so much more Perspicuous, by how much the more, and more ample Inane Spaces it hath intercepted among its Component particles; which permit the Rayes freely to continue on their progress home to the Eye.

This we affirm not Universally, but under the due limitation of a Caeteris Paribus, as we have formerly hinted. Because, notwith∣standing a piece of Lawn is more or less Perspicuous, according as the Contexture of its Threads is more or less Rare; and the Aer in like man∣ner is more or less pellucid, according as it is perfused with more or fewer Vapours: yet do we not want Bodies, as Paper, Sponges, &c. Which though more then meanly Rare, are nevertheless Indiaphanous; and on the

contrary, we see many Bodies, sufficiently Dense, as Horn, Muscovy-glass, common glass, &c. which are yet considerably Diaphanous.

Now, that you may clearly comprehend the Cause of this Difference, be pleased to hold your right hand before your eye, with your fingers somewhat distant each from other; and then looking at some object, you may behold it through the chinks or intervals of your fingers:* 1.22 this done, put your left hand also over your right, so as the fingers of it may be in the same position with the former; and then may you perceive the ob∣ject, at least as many parts of it as before. But, if you dispose the fingers of your left hand so as to fill up the spaces or intervals betwixt those of your right; the object shall be wholly eclipsed. Thus also, if you look at an object through a Lawn, or Hair Sieve, and then put another Sieve over that, so as the holes or pores of the second be parallel to those of the first; you may as plainly discern it through both as one: but, if the twists of the second sieve be objected to the pores of the first, then shall you per∣ceive no part of the object, at least so much the fewer parts, by how much greater a number of pores in the first are confronted by threads in the se∣cond. And hence you cannot but acknowledge that the Liberty of in∣spection doth depend immediately and necessarily upon the Inanity of the pores; the Impediment of it upon the Bodies that hinder the trajection of the Rayes emitted from the Object: and yet that to Diaphanity is required a certain orderly and alternate Position of the Pores and Bodies, or Particles. This considered, it is manifest, that the Reason why Glass, though much more Dense, is yet much more perspicuous than Paper, is only this; that the Contexture of the small filaments, composing the substance of Paper, is so confused, as that the Pores that are open on one side or superfice thereof, are not continued through to the other, but variously intercepted with cross-running filaments: as is more sensible in the Co••texture of a Spunge, whose holes are not continued quite thorow, but determined at half way, (some more, some less) so that frequently the bottome of one hole is the cover of another, as the Cells in a Hony-comb: but, Glass, in regard of the uniform and regular Contexture of its particles, which are ranged as it were in di∣stinct ranks and files, with pores or intervals orderly and directly remaining betwixt them; hath its pores not so soon determined by particles opposite∣ly disposed, but continued to a greater depth in its substance.

Though this make the whole matter sufficiently intelligible, yet may it receive a degree more of illustration,* 1.23 if we admit the same Conditions to be in the substance of Glass, that are in a Mist, or Cloud; through which we may behold and object, so long as the small passages or intervals be∣twixt the particles of the Vapours, through which the rayes of the visi∣ble species may be trajected, remain unobstructed: but yet perceive the same so much the more obscurely, by how much the more remote it is; because, in that case, more impervious particles are variously opposed to those small thorow-fares, that obstruct them, and so impede the progress of most of the rayes. For, thus also Glass, if thin, doth hinder the sight of an object very little, or nothing at all; but if very thick, it wholly termi∣nates the progress of the species: and, by how much the thicker it is, by so much the more it obscures the object. And this, only because Glass, con∣sisting of small solid Particles, or Granules, and insensible Pores alternately situate, hath many of its pores running on in direct lines through its sub∣stance

to some certain distance; but sometimes these; sometimes those are obturated by small solid particles succedent, when at such a determinate Crassitude, it becomes wholly opace.

* 1.24And this gives us an opportunity to refute that vulgar Error, That the substance of Glass is totally Diaphanous, or that all and every Ray of the the Visive Species is trajected through it, without impediment. To demon∣strate the contrary, therefore, we advise you to hold a piece of the finest and thinnest Venice Glass against the Sun, with two sheets of white paper, one betwixt the Sun and the Glass, the other betwixt the Glass and your Eye: for, then shall all the Trajected Rayes be received on the paper on this side of the glass, and the Reflected ones be received on that beyond it. Now, insomuch as that paper, which is betwixt your eye and the glass, doth receive the Trajected rayes, with a certain apparence of many small shadows intercepted among them; and that paper beyond the glass, doth receive the Reflected rayes with an apparence of many small lights: therefore we de∣mand (1) from whence can that species of small shadows arise, if not from the Defect of those rayes, that are not transmitted through the Glass, but averted from it? (2) Whence comes it, that in neither paper the Bright∣ness or Splendour is so great, as when no Glass is interposed betwixt them; if not from hence, that the reflected rayes are wanting to the nearest, the tra∣jected ones to the farthest? (3) Whence comes it that some rayes are refle∣cted, others trajected; if not from hence, that as a Lawn sieve transmits those rayes, which fall into its pores, and repercusseth others that fall upon its threads: so doth Glass permit those rayes to pass through, that fall into its pores; and reverberate those, that strike upon its solid particles? And what we here say of Glass, holds true also (in proportion) of Aer, Water, Horn, Vernish, Muscovy-glass, and all other Diaphanous Bodies.

Notes

• * 1.1

  Art. 1. This Chapters right of suc∣cession to the former.
• * 1.2

  Art. 2. The Dive•••• accep••ation of the term, — Touching.
• * 1.3

  Art. 3. A pertinent (though short) Panegyrick on the sense of Touching.
• * 1.4

  Art. 4. Some Tactile Qualities, in common to the perception of other senses al∣so.
• * 1.5

  Art. 5. A Scheme o•• all Qualities, or Commonly, or Properly ap∣pertaining to the Sense of Touching; as they stand in their several Relations to, or Dependen∣cies on the U∣niv••••s••l Mat••er, Atoms: and so, of all the sub••e∣quent Ca••ital A••guments to be treated of, in this Book.
• * 1.6

  Art. 6. The right of Rarity and D••n∣sity, to the Pri∣ority of cons••∣deration.
• * 1.7

  Art. 1. The Opinion of those Philo∣sophers, who place the Rea∣son of Rarity, in the actual Di∣vision of a Body into small parts; and the brief Refutation th••reof.
• * 1.8

  Art. 2▪ A second Opi∣nion, deriving Ra••ity and Density from the several pro∣portions, which Quantity hath to its substance; convicted of i••compre••ensi∣b••lity, and so of insatisfacti∣on.
• * 1.9

  Art. 3. A Third, desu∣ming the more and less of Ra∣rity in Bodies, from the more and less of VA∣CUITY inter∣cepted among their particles: and the Advan∣tages thereof a••ove all o∣t••ers, concer∣ning the same.
• * 1.10

  Art. 4. The Definitions o•• a Rare, and of a Dense Bo∣dy; according to the assum¦pti••n of a Vacu¦ity Disseminate.
• * 1.11

  Art. 5. The Con••rui••y of those D••fi∣nitions, de∣monstrated.
• * 1.12

  Art. 6. 〈…〉〈…〉 of Diff••••ulties, wherein the thoughts of Physi••logists have so long wandered; ••e∣duc••d to a p••int, the ge¦nuine state of the 〈◊〉〈◊〉.
• * 1.13

  Art. 7. That Rarity and Density can have no other Causes imme∣diate, but the more and less of Inanity inter∣spersed among the particles of Concretions; DEMON∣STRATED
• * 1.14

  Art. 8. Aristotles Ex∣ceptions, a∣gainst Dissemi∣nate Inanity; neither impor∣tant nor com∣petent.
• * 1.15

  Art. 9. The Hypothe∣sis of a certain 〈◊〉〈◊〉 sub∣stance, to re∣p••enish the pores of Bo∣dies, in Ra••i∣faction▪ de∣monstrated in∣sufficient, to s••l••e the Diffi∣culty, or demo¦l••••h the Epicu∣••••a••▪ 〈…〉〈…〉 Vacu••••e:
• * 1.16

  Art. 10. The 〈…〉〈…〉 understand••ng t••e Reason•• a••d Manner of ••a∣••i action and C••ndensation, from the 〈…〉〈…〉
• * 1.17

  Art. 11. PARADOX. That the Mat∣ter of a Body, when Rarified, doth possess no more of true Place, than when Conden∣sed, and the Conciliation thereof to the praeposed Defi∣nitions of a Ra••e and of a Dense Body.
• * 1.18

  Art. 12. PROBLEM. Whether Aer be capable of Condensation to so high a rate as it is of Rari∣faction: and the Apodictical solution thereof.
• * 1.19

  Art. 1. The opportunity of the present speculation, concerning the Causes of Perspicuity and Opacity.
• * 1.20

  Art. 2. The true No∣tions of a Per∣spicuum and Opa••um.
• * 1.21

  Art. 3. That every Concretion is so much the more Diapha¦••ous, by how much the more & more ample Inane Spaces are in∣tercepted a∣mong its par∣ticles; caeteris pa••ibus.
• * 1.22

  Art. 4. Why Glass, though much more Dense, is yet much more Diaphanous, than Paper.
• * 1.23

  Art. 5. Why the Dia∣phanity of Glass is gradually diminished, ac∣cording to the various de∣grees of its Cra••••••tude.
• * 1.24

  Art. 6. An Apodicti∣cal Confutati∣on of that po∣pular Error, that Glass is to∣tally, or in every particle, Dia∣phanous.