An entire body of philosophy according to the principles of the famous Renate Des Cartes in three books, (I) the institution ... (II) the history of nature ... (III) a dissertation of the want of sense and knowledge in brute animals ... / written originally in Latin by the learned Anthony Le Grand ; now carefully translated from the last corrections, alterations, and large additions of the author, never yet published ... by Richard Blome.

CHAP. XXI. Of the State of Bodies; and first those that are Hard, Fluid, Frangible, Friable, Soft, Ductile, and such as may be cut or slit.

I. Whence the Hardness of Bodies proceeds. AMongst the Principles of Natural things, MOTION and REST only are op∣posed to each other, not privatively (as some would have it) but contrariously, as two Modes really distinct. For Rest or Quiet is not a Priva∣tion of Motion, but a true Form, whereby Stable and Hard Bodies are distinguish'd from such as are Fluid, and whence they receive the force of Acting and Resisting. For those Bodies are accounted Hard, whose Parts by a firm Union lye still toge∣ther; or whose Parts do so closely cleave toge∣ther, that they cannot without difficulty be sepa∣rated. Which close Union is perceptible to the Senses; for if we touch any of these Hard Bodies with our Hands, or any other part of our Body, they resist them, and oppose their entrance; as we see in Marble, Wood, Stone, &c. for if, when they are handled by us, they give way, we should per∣ceive no Sense of Hardness at all; as appears by the Air, which is not felt by us, because it gives way to our touch.

II. What is the Cause of the variety of Hard Bodies. The Hardness of Bodies is various, according to the variety of Rest; for wheresoever there is more of Rest, there also is more of Hardness; and so contrarily. Clay, when the Water is evaporated from it, grows hard, because the Rest of its Parts is by this means increased, its Earthy parts being delivered from the Agitation of the Fluid parts, interpos'd between them; whereas Wax being heated, becomes soft, because the Rest of its Parts is lessened, by reason of the Oily Par∣ticles, which being benum'd before, are by the Heat put in motion.

III. What Hardness is. When we say that Rest is the Cause of Hard∣ness, we mean the Formal, not the Efficient Cause; for the Efficient Cause of Hardness consists only in the force wherewith the Air, or other Subtil Matter, compresseth the Parts of Hard Bodies. To the end therefore that we may have a distinct Idea of Hardness, we must conceive it to be no∣thing else, but the Rest of many parts of Bodies, caused by the Pression of the Air, or the Subtil and Aethereal Matter, which acting from without, drives these parts inward in such a manner, that they cannot be separated afterwards, without making us sensible of their Resistance.

IV. What is the Cause of the Fluidity of Bodies. Fluid Bodies, on the contrary, readily yield to the motion of other Bodies, and therefore do not resist our Hands when we touch them, as appears in the Water and Air. The Cause of which diffe∣rence consists only in Rest and Motion: For if we enquire why some Bodies cannot but by force be thrust out of their places; whereas others without any difficulty yield the place they are in possession of, to others, we shall find that the Reason is, be∣cause their Parts, which resist those Bodies that approach to them, lye still and Rest; whereas the Parts of other Bodies, that without any force do leave their places, are in motion. So that Hard Bodies are such, whose Parts lye still and cohere together; but Fluid Bodies are divided into many little Parts, which are variously moved. For the Parts of Water, or any other Liquor, are agitated every way by the Subtil and Aethereal Substance: And accordingly those Bodies are called Fluid, whose Insensible parts have such various Motions.

V. How it ap∣pears, that the Parts of Fluid Bodies are agitated every wa••. Now that the Parts of a Fluid Body are moved, and that equally every way, appears from hence, that in what part soever of a Fluid Body we do move our Hand, or a Stick, it always goes on with the same easiness, which could never be, if the Determination were stronger one way, than it is another. Tho' it cannot be deny'd, but that some Resistance is found in a Fluid Body, if we swiftly lash any thing against the Parts of it; because a Body slowly moved, comes under the Notion of a Body at rest, when compared with a Body that is much more swiftly moved, and conse∣quently will resist it.

VI. Fluid Bo∣dies hav no certain figure, as Hard Bo∣dies have. Hence it is that the Figure of Fluid Bodies is undetermin'd, because they are so easily divided and diffus'd, that they cannot keep themselves in their own bounds. But Hard and Stable Bodtes being hard to be divided, easily retain their Figure, and are easily comprehended within their own limits; as appears in Lead, Iron, Silver, Gold, Wood, Marble, &c. which according to their several de∣grees of Solidity preserve their figure and Bulk. That therefore we call a Fluid Body, whose Parts being divided into many small Particles, and these again into less Indefinitely, are variously agitated. But that is called a Hard Body, whose Parts by Rest do so closely cleave together, that they cannot be separated, but by a Force sufficient to overcome their coherence.

VII. The vari∣ous kinds of Fluid Bodies. The smaller and lighter the Parts of any Fluid Body are, the greater is its Fluidity; and the thicker and more Branchy they are (if Contact doth not hinder) so much the less is it. Hence arise the diverse kinds of Fluid Bodies, according as by the lightness and smalness of their Particles, they are more, or according to the Thickness and Branchiness of them, less yielding to the Caelestial Matter, which is the Cause of their Fluidity. Upon this account it is that the Air is more fluid than the Water; because the Parts of Water, tho' they be smoother, yet are thicker than those of the Air. And Water is more fluid than Oil, because the Parts of Oil are more thick and branchy: Lastly, Oils are more or less fluid, as their Particles are more or less thick and branchy.

VIII. How Fluid Bodies are said to be in Motion. When I say that the Nature of Liquid Bodies consists in Motion, it is not so to be taken, as if the whole Liquid Body were moved out of one place to another, for this happens also to Hard Bodies: For a Bowl of Brass is easily rowl'd from one end of a Table to the other, and for all that persists to be a Hard Body; but in this, that the Particles into which they are divided, are moved and variously agitated, some of them being tost to the Right, others to the Left; some upwards, others down∣wards; some forwards, and others backwards: Which Motions of the Particles must be different. For if they were all of them carried one way, they would in a short time cling together, and make up a stable or hard Body.

IX. Why Ice is carried with a greater Force, than the Water. And tho' the Course of a River be directed to one particular part of the Land, it does not there∣fore lose the Name or Nature of a Fluid Body; forasmuch as the various Motion of the Particles of the Water is preserved, notwithstanding the

said Course of the River, as much as in a still standing Water. Hence it comes to pass, that Ice driving on the top of the Water, because of the firm clinging together of its Parts, doth with a greater force pursue its way, and with more vio∣lence set against the Banks, than the Water it self which carries it; because the Parts of Water being tost with various Motions, weaken the force of it, and therefore cannot tend with that vehemence to one part, as the Ice, which is a solid Body, doth. By which Example it is evident, why Fluid Bodies easily give way to other Bodies, but solid Bodies not; because Fluid Bodies are always in Motion, and therefore do not oppose the entring of other Bodies into the places they are in, but readily and easily quit them. Whereas Hard Bodies rest, and according to the Law of Natures immutability, strive to continue in the state of Conjunction, except they be disturbed by some strong Motion.

X. How the Parts of Solid Bo∣dies are joyned to∣gether. This Sentiment will not please some Philosophers, who suppose no two Bodies can be joyned without some intervening Third, distinct from them both; which they imagine to be as the Glew that holds the parts together, that the Union may be the more firm: But since nothing is to be admitted in Natural Philosophy, which we are not convinc'd of by Reason, we must consider first, what kind of Glew this can be, before we appropriate it to this use. Without doubt it must be either a Substance, or the Mode of a Substanee, seeing that amongst Natural things nothing else is to be found besides Substances and their Affections. If it be supposed to be a Substance, it cannot be understood why the Parts, which because they are Substances, cannot be united by themselves, should yet stand in need of an adventitious Substance to unite them. If it be a Mode, then without doubt none can be more pro∣perly assign'd to this purpose than Rest, since that which makes the Parts to be united together, must be most opposed to Motion, by which they are di∣vided from one another. For opposit Things must have opposit Principles; but nothing is more con∣trary to Motion than Rest, as being the contrary Affections of Material Substances.

XI. The Motion of the Particles of Fluid Bodies, is discernible from their Effects. You'l say, How may we know that the Parts of Fluid Bodies are in continual Motion? I answer, That tho' the smalness of those Particles doth not permit us to discern their Agitation, yet may the same be easily discovered by the Effects. There is no body but perceives, that some parts of VVater, evaporate in boyling, and that in the Summer time Ponds are lessen'd or dryed up, which could not be, but that some Parts of the Water, being separated from one another by Motion, steam away into the Air. Moreover, how else comes it to pass that the Particles of VVater, do so readily mix together? Or, how could they insinuate themselves into the Pores of thick Bodies, if their Parts did cling together by mutual Rest?

XII. T•••• Motion 〈◊〉〈◊〉 Parts 〈◊〉〈◊〉 their Di∣vision. For the Division of Parts depends on their Motion, Agitation being that which separates one thing from another. This is very evident in Flesh, which is soon corrupted by the Air, the Particles whereof being agitated either by the Sun, or some other way, thrust themselves into the Pores of Flesh, and by dilating of them and spoiling their Natural situation, do at last dissolve and putrifie it. The ready and thorough mingling of Liquors dis∣covers the same thing, it being evident that this easie mingling cannot be done without Motion, whereby the Parts of two Liquors, as for Examples VVater and VVine, run together.

XIII. Bodies would not be distin∣guish'd from one another, if some were not moved. Besides, what diversity would there be amongst Bodies, if all their Parts lay still together, and were equally united? Cold water would not differ from Ice; Crystal and Milk would be the same thing; nor would any Cause be assignable, why Crystal resists our touch, or why Milk yields to the approach of Hard Bodies.

XIV. Parts of a twofold sort are found in Liquid Bodies. Wherefore we may conceive twofold Parts in Liquid Bodies; some at it were flying, by reason of their swiftness, such as the Parts of Smoak, the Steam of boyling VVater, and Flame are, which are tost so forceably that our Senses can discern their motion: And others, as it were, creeping, because of the slowness of their motion; as the Particles of Oil, Milk and VVine, whose motion is so slow and leisurely, that our Senses cannot perceive it. So that when it happens that one Liquid Body is not sufficient to dissolve another, or that it can exercise its force more upon one Body than another; the Reason thereof chiefly is, because its Parts are more or less agitated, or because the Pores of those Bodies are not open alike.

XV. What Soft Bodies ar••▪ Soft Bodies approach to the Nature of Liquid, and are such whose Particles do not cling so close and firmly together, as the Parts of Hard Bodies, nor are agitated with so swift a motion as Fluid Bodies, but partake of both their Natures, being middle things between fluid and stable Bodies, such as are Sand, VVax, &c. The softness of Sand is caused, for that something intervenes betwixt their separated Parts: And VVax is soft, because its Particles terminate in flexible branches, which twisting together lightly, joyn the said Parts.

Frangible, are rec∣kon'd a∣mongst Hard Bo∣dies. Of Hard Bodies some are Frangible, others Friable. For whatsoever can be broken must have such a degree of stiffness, that its outward Parts when struck, may be neither dilated, nor admit any ingress of parts into parts; but that the sur∣faces being broken, the inward parts likewise be divided and broken asunder. Of which Nature are Flints, Earthen Pots, Stones, and the like, which according to the diversity of their contexture, are more easily or hardly broken.

XVII. Friable Bodies. Thus Friable Bodies must have so much stiffness, that they cannot be stretched or bended; but upon any force pressing upon them, do crumble into Dust. Of which Nature is the Sand-stone, which is easily dissipated into small parts, and those again easily crumbled to Dust.

XVIII. Ductil Bo∣dies resort under Soft Bodies. Amongst Soft Bodies are reckoned those that are commonly called Ductil (that is, Bodies that suffer Drawing or Extension) such as Gold is, one grain whereof may be drawn into a Thred of four hundred Foot long; and consequently one Ounce to the length of 230400 Foot. The Cause of which vast discussion is commonly attributed to its extream Compactness, the Thinness of its Parts, and their intimate Union and Connexion. Of which we shall speak more at large hereafter.

XIX. Bodies that may be cut or slit, be∣long to Soft Bodies. Some reckon Bodies that may be cut or slit, also amongst Soft Bodies; because whatsoever is cut, must have so much flexibility, that the Part which is prest (suppose with an Ax) can give way downwards, at the same time that the Collateral parts yield to the dividing Instrument. And what∣soever can be slit, must be so flexible or bending,

that when the Parts in a certain place, begin to be pull'd asunder, a Compression may be successively made, in whatsoever places the rest are to be gra∣dually separated from each other. VVood is said to be Cut, when it is divided Cross-wise; but to be slit, when divided Long-ways, or with the Grain.