CHAP. X. What Rarefaction is, and how it is per∣formed.
I. Rarefacti∣on cannot be per∣formed without the entrance of new Mat∣ter. IT appears from what goes before, that Exten∣sion is something that is not distinct from Matter, and that the one cannot be encreased, but the other must be so likewise. Hence it follows, that in Rarefaction and Condensation the Constitutive Quantity of Bodies, is neither encreased nor dimi∣nished; but only that in Rarefaction, the parts that were before United, are distended, so as some intervals are left between them, which are fill'd up by the entring in of some fluid and moveable Body; as is manifest in a Spunge swell'd with VVater; and that on the contrary in Condensation, the se∣parated parts are more closely united, by expul∣sion of those Bodies that fill'd up the Intervals; as appears in a Spunge out of which the VVater is squeez'd.
II. What a loose and, what a close Body is. A Thin or Loose Body is that whose parts are intercepted by Spaces fill'd with some forein Mat∣ter, which afterwards may become a Close Body again by expulsion of the more subtil Matter, en∣tred from without, by which means the parts come close together. Thus Boiling VVater is rarefied in a Pot over the Fire; for we find that when it be∣gins to boil, it swells up into Bubbles, which could not be, but by the entrance of some External Matter, causing them to swell and be extended: and the same is the case with VVater, when it is turned into a Vapour.
III. An Objecti∣on rais'd from the Rarefaction of Water. You will say, that in this case of a Vapour we perceive indeed that Extension is encreas'd, but no access of any new Matter: Wherefore it is with∣out ground to say that Rarefaction is performed by the addition of some other Body.
IV. Answer. I answer, that in a Vapour there is no more Exten∣sion or Quantity perceived, than there was in the VVater before its Resolution, because in this change nothing else happens but a Solution, Division and Separation of those parts, which before were more closely joined together; For he who at a distance beholds the Vapours that rise from boiling water, takes them to be a continuous Body; but if he take a nearer view of them, he will find them to be nothing else, but a crowd of innu∣merable small Particles, which separate and come between many other Heterogeneous Bodies. Where∣fore where we find any Body dilated, we must con∣clude that it is by the access of some new Mat∣ter.
V. The Bodies which enter the Pores of Bodies are of the same ma∣ture with those that strike our Senses. But what kind of little Bodies are these, which enter the Pores of Rarified Bodies, and which are expell'd when they become close and hard again?
I answer that they are the same in Substance with those Bodies which are seen and felt by us; save only that they are more subtil and fluid, and so are fit to penetrate and fill the Pores of other Bodies. For according to our Hypothesis, there are some Particles in the Air and other Bodies so subtil, as to be able to pierce Gold, Diamonds and the most Solid Bodies that are.
VI. There are Bodies that are not per∣ceptible by the Senses. You will say, that we do not find that the Pores are dilated in Rarefaction, nor that any New Bo∣dies enter into them. But to this I answer, that all Bodies do not affect our Senses, by reason of their extream littleness. We know that a Vine in the Spring grows, and becomes extended to a further Length; which Extension could not be, but by an addition of Bodies, which dilate and stretch out the Substance of the Vine. And yet no Man ever perceiv'd these Bodies. We never saw the Air, and yet know that it is extended throughout the whole World. Wherefore neither in Rare∣faction are we to deny Bodies to enter into the Pores, because we do not see them; but are to judge of what happens in these little Bodies, by what we see happens in the greater.
VI. Why Metals are not ra∣refied. From this Explication of Rarefaction it is evi∣dent, why Metals and other Hard Bodies are not rarified without difficulty, but soft Bodies very easily, because the parts of them are readily sepa∣rated and admit other Bodies, whereas hard Bodies, as Iron, &c. are not without great violence dissol∣ved, and by that means hinder other Bodies from entring between their parts, wherein the Nature of Rarefaction doth consist.
VIII. It is not necessary that all the Parts of Matter be rarefied. You'l say that in Rarefaction not only that Body is rarefied whose Pores are dilated; but also all the subtil Matter that enters them, which cannot be without the introduction of other Bodies, and these again by the Introduction of others, and so to infi∣nity, which is not to be admitted in Natural Causes.
IX. There are some Par∣ticles that do not ad∣mit Rare∣faction. I answer, there is no inconvenience to say that Bodies that have Pores, become rarefied by the In∣tromission of others, and these again by the Intro∣mission of other lesser Bodies, so we do but admit that there are some Bodies, which because they have no Pores cannot receive other Bodies, and that there are such is not to be doubted, especially by them who hold Quantity to be indefinitely extend∣ed: For they must acknowledge that the Parts of Matter may by Division be made so small, that they cannot be further divided but by our Thought.
X. The Di∣stinction be∣tween a Pure and a Rarefied Body. You'l say that the more loose or Rarefied a Body is, the more Pure it is also; as the Air is, when it is free from Clouds and Vapours: But now the Purer any Body is, the less it admits the mixture of any External Bodies; therefore Rarefaction is not made by the Introduction of other Bodies.
XI. Answer. The Major of this Argument is to be deny'd; for Pure and Rarefied are not one and the same thing: That is Pure which is free from any mixture of forein Matter: As the Air is said to be pure, when it is not obscur'd by Clouds or Exhalations. But a loose or Rarified Body involves the mixture of External Bodies, and cannot be understoood with∣out it; as a Spunge that is swell'd with the Intro∣mission of Water.
XII. Fire is the ordinary Cause of the Rare∣faction of Bodies, whether they be li∣quid or solid. The ordinary Cause of Rarefaction is Fire; for the subtil Particles whereof it consists, being in continual Motion, easily enter the Pores of other Bodies, and dilate them. Hence it comes to pass that Water, which hath long boiled over the Fire, is more easily congeal'd than cold Water newly taken out of a Well or River, because the most subtil parts of it, which by their Agitation and Motion hinder'd Congelation, are evaporated in the Boiling. Neither are liquors only, but Metals, and other solid Bodies somewhat distended by Heat. Thus we find that melted Metals swell somewhat;