CHAP. XXII. What Loose and Close, Rough and Smooth, Contiguous and Continuous Bodies are.
I. Whence proceeds the Loos∣ness or Closeness of Bodies. AS Stable and Fluid Bodies are constituted such by Rest and Motion; so Loose and Close Bodies are made such by their Figure and Situation, not outward, but inward. for the Loosness or Closeness of Bodies, is not to be con∣sidered according to the outward Space in which Bodies are dilated or contracted; seeing that a Body, whose Essence consists in three Dimensions, cannot take up a greater Space at one time, than at ano∣ther; but according to the Intervals which are understood to be betwixt their Parts; and which are said to be distended, when they are fill'd with any foreign Matter; or to be contracted, when by Removal of that Matter, they are either lessened, or quite taken away.
II. Loose Bo∣dies are made such, by the In∣gress of Matter; Close Bo∣dies by the Egress. For we must not imagin, as many do, that the parts of Loose Bodies are so separated from one another, that nothing extended comes between them; For no such Vacuum can be in Nature; but that the said Intervals are fill'd with other Bodies; as is apparent in New-bak'd Bread, which being put into Milk or VVine, presently swells up into a much greater bulk; because the Pores of the Bread are distended by the intruding particles of the VVine or Milk. So that all the New Exten∣sion we find here, is not to be attributed to the Substance of the Bread, but to the fluid Body that hath insinuated it self into the pores of it. Which is evident not only to Reason, but to the Senses them∣selves: For if a man behold the Steam that riseth out of a Pot of boyling VVater, or the Smoak that proceeds from a Torch at a distance, he will suppose the parts of them to be contiguous; but when he comes nearer, and views them more wish∣ly, he will find that there is neither Continuity nor Contiguity between the parts of them, but that they are separate from one another, by means of a foreign intervening Matter that divides them.
III. Examples of Loose and Close Bodies. A Body becomes close, when the parts of it being nearer together, leave few Intervals, or none at all. Of the first sort are Snow▪ Hay, and Wool, when they are compress'd, as also a Sponge, when the Water is squeez'd out of it; for then by the ex∣pulsion of the Liquor, its Pores are narrowed, and few Intervals are left in it, to receive any outward Bodies. Of the latter sort are those Bodies, which have no Pores at all into which any External Body can enter; and when it is so close, then it cannot be further condensed by any Power of Nature.
IV. What Rough and Smooth Bo∣dies are. As with respect to the Figure and Situation of its Inward parts, a Body is distinguish'd into Loose and Close; so with regard to their Outward figure and situation, Bodies are said to be Rough or Smooth. Which Modes are of great efficacy in Natural things; as appears in a Knife, wherewith the Hardest Bodies are cut; and in a Pen, with which an infinite variety of Characters may be made.
Rough Bodies are such whose superficial Parts are unequally disposed, so as that some are prominent and others deprest; as Rusty Iron. But Smooth or Polish'd Bodies are such, whose Extream parts are equally situated, as Ice, a Whetstone, &c. Smooth Bodies, because of their Surface, have more force to Act or Resist, than Rough Bodies. For a Sword, whose Edge and Extream parts are polish'd and even, cuts deeper than another Sword of the same bigness that is Rusty; and a Ball rebounds more strongly from polish'd Bodies, than from rough.
V. All Bodies are not Smooth, which ap∣pear to be so. Yet we are not to imagin, that all those Bodies in which neither our Touch nor Eyes can discover any inequality, are altogether smooth; forasmuch as even Glass and Crystal, which appears very smooth, have a rough Surface. For tho' Glass be made of Salts, which by Melting are resolved into very small Particles; yet because those Par∣ticles still retain their former figure, they can never make a polish'd Surface. What appears to our Eye more smooth than Paper? And yet by the help of a Magnifying-Glass, we perceive it to be very rough and uneven. Hence it is manifest, that in what part soever of the Medium the Eye be placed, it receives the various Rays, which come from and represent the Object.
What a Contiguous and Conti∣nuous Body is. The two Remaining Species of Bodies are Con∣tinuous and Contiguous. A Body is said to be Contiguous with respect to the situation it hath amongst other ambient Bodies. Thus a Tree sur∣rounded by the Air, is said to be Contiguous to it. And accordingly a Contiguous Body is thus defin'd by Plato in Parmenides: That which is to touch something, plac'd by it self, must be next to that which is to be touched; neither is there any Third thing that is a Medium between both these. A Continuous Body is that which besides the situation it keeps amongst Circum-ambient Bodies, becomes united to them, and by Rest is joyned with them. Thus a Stone is said to be a Continuous Body, being con∣sidered whole and undivided, and before any change happen to it by Motion. But this Conti∣guity of Bodies is not in all their parts, but only in those that are Insensible, since such only have an immediate Contact with one another.
VII. Wherein the Nature of Conti∣guity and Continuity consists. The Continuity therefore of Bodies consists in this, that their parts do cleave together by an Immediate Connexion, and rest together. So that Continuous Bodies cannot be dissolved, but by such a Motion as prevails over the Rest of their Parts. The Contiguity of Bodies consists in this, that their Extream parts lying still together, nearly touch one another, yet so as that a most thin subtil Matter flows and runs between them; and by reason of this Interfluent Subtil Matter, the parts of Contiguous Bodies are more easily separa∣ble.