VACUUM
, in Physics, a space empty or devoid of all matter.
Whether there be any such thing in nature as an absolute Vacuum; or whether the universe be completely full, and there be an absolute plenum; is a question that has been agitated by the philosophers of all ages.
The Ancients, in their controversies, distinguished two kinds; a Vacuum coacervatum, and a Vacuum interspersum, or disseminatum.
Vacuum Coacervatum, is conceived as a considerably large space destitute of matter; such, for instance, as there would be, should God annihilate all the air, and other bodies, within the walls of a chamber.
The existence of such a Vacuum is maintained by the Pythagoreans, Epicureans, and the Atomists or Corpuscularians; most of whom assert, that such a Vacuum actually exists without the limits of the sensible world. But the modern Corpuscularians, who hold a Vacuum coacervatum, deny that appellation; as conceiving that such a Vacuum must be infinite, eternal, and uncreated.
According then to the later philosophers, there is no Vacuum coacervatum without the bounds of the sensible world; nor would there be any other Vacuum, provided God should annihilate divers contiguous bodies, than what amounts to a mere privation, or nothing; the dimensions of such a space, which the Ancients held to be real, being by these held to be mere negations; that is, in such a place there is so much length, breadth, and depth wanting, as a body must have to fill it. To suppose then, that when all the matter in a chamber is annihilated, there should yet be real dimensions, is to suppose, say they, corporeal dimensions without body; which is absurd.
The Cartesians however deny any Vacuum coacervatum at all, and assert that if God should immediately annihilate all the matter, for example in a chamber, and prevent the ingress of any other matter, the consequence would be, that the walls would become contiguous, and include no space at all. They add, that if there be no matter in a chamber, the walls cannot be conceived otherwise than as contiguous; those things | being said to be contiguous, between which there is not any thing intermediate: but if there be no body between, there is, say they, no extension between; extension and body being the same thing: and if there be no extension between, then the walls are contiguous; and where is the Vacuum?—But this reasoning, or rather quibbling, is founded on the mistake, that body and extension are the same thing.
Vacuum Disseminatum, or Interspersum, is that supposed to be naturally interspersed in and among bodies, in the interstices between different bodies, and in the pores of the same body.
It is this kind of Vacuum which is chiefly contested among the modern philosophers; the Corpuscularians strenuously asserting it; and the Peripatetics and Cartesians as tenaciously denying it. See Cartesian and Leienitzian.
The great argument urged by the Peripatetics against a Vacuum interspersum, is, that there are divers bodies frequently seen to move contrary to their own nature and inclination; and that for no other apparent reason, but to avoid a Vacuum: whence they conclude, that nature abhors a Vacuum; and give us a new class of motions ascribed to the fuga vacui or nature's flying a Vacuum. Such, they say, is the rise of water in a syringe, upon the drawing up of the piston; and such is the ascent of water in pumps, and the swelling of the flesh in a cupping glass, &c.—But since the weight, elasticity, &c, of the air have been ascertained by sure experiments, those motions and effects are universally, and justly, ascribed to the gravity and pressure of the atmosphere.
The Cartesians deny, not only the actual existence, but even the possibility of a Vacuum; and that on this principle, that extension being the essence of matter, or body, wherever extension is, there is matter; but mere space, or vacuity, is supposed to be extended; therefore it is material. Whoever asserts an empty space, say they, conceives dimensions in that space, i. e. he conceives an extended substance in it; and therefore he denies a Vacuum, at the same time that he admits it.—But Descartes, if we may believe some accounts, rejected a Vacuum from a complaisance to the taste which prevailed in his time, against his own first sentiments; and among his familiar friends he used to call his system his philosophical romance.
On the other hand, the corpuscular authors prove, not only the possibility, but the actual existence, of a Vacuum, from divers considerations; particularly from the consideration of motion in general; and that of the planets, comets, &c, in particular; as also from the fall of bodies; from the vibration of pendulums; from rarefaction and condensation; from the different specific gravities of bodies; and from the divisibility of matter into parts.
1. First, there could be no linear or progressive motion without a Vacuum; for if all space were full of matter, no body could be moved out of its place, for want of another place unoccupied, to move into. And this argument was stated even by Lucretius.
2. The motions of the planets and comets also prove a Vacuum. Thus, Newton argues, “that there is no such fluid medium as æther,” (to fill up the porous parts of all sensible bodies, and so make a plenum), seems probable; because the planets and comets proceed with so regular and lasting a motion, through the celestial spaces; for hence it appears that those celestial spaces are void of all sensible resistance, and consequently of all sensible matter. Consequently if the celestial regions were as dense as water, or as quicksilver, they would resist almost as much as water or quicksilver; but if they were perfectly dense, without any interspersed vacuity, though the matter were ever so fluid and subtle, they would resist more than quicksilver does: a perfectly solid globe, in such a medium, would lose above half its motion, in moving 3 lengths of its diameter; and a globe not perfectly solid, such as the bodies of the planets and comets are, would be stopped still sooner. Therefore, that the motion of the planets and comets may be regular, and lasting, it is necessary that the celestial spaces be void of all matter; except perhaps some few and much rarefied effluvia of the planets and comets, and the passing rays of light.”
3. The same great author also deduces a Vacuum from the consideration of the weights of bodies; thus: “All bodies about the earth gravitate towards it; and the weights of all bodies, equally distant from the earth's centre, are as the quantities of matter in those bodies. If the æther therefore, or any other subtile matter, were altogether destitute of gravity, or did gravitate less than in proportion to the quantity of its matter; because (as Aristotle, Descartes, and others, argue) it differs from other bodies only in the form of matter; the same body might, by the change of its form, gradually be converted into a body of the same constitution with those which gravitate most in proportion to the quantity of matter: and, on the other hand, the heaviest bodies might gradually lose their gravity, by gradually changing their form; and so the weights would depend upon the forms of bodies, and might be changed with them; which is contrary to all experiment.”
4. The descent of bodies proves, that all space is not equally full; for the same author goes on, “If all spaces were equally full, the specific gravity of that fluid with which the region of the air would, in that case, be filled, would not be less than the specific gravity of quicksilver or gold, or any other the most dense body; and therefore neither gold, nor any other body, could descend in it. For bodies do not descend in a fluid, unless that fluid be specifically lighter than the body. But by the air-pump we can exhaust a vessel. till even a feather shall fall with a velocity equal to that of gold in the open air; and therefore the medium through which this feather falls, must be much rarer than that through which the gold falls in the other case. The quantity of matter therefore in a given space may be diminished by rarefaction: and why may it not be diminished ad infinitum? Add, that we conceive the solid particles of all bodies to be of the same density; and that they are only rarefiable by means of their pores; and hence a Vacuum evidently follows.”
5. “That there is a Vacuum, is evident too from the vibrations of pendulums: for since those bodies, in places out of which the air is exhausted, meet with no resistance to retard their motion, or shorten their vibrations; it is evident that there is no sensible matter in those spaces, or in the occult pores of those bodies.” |
6. That there are interspersed vacuities, appears from matter's being actually divided into parts, and from the figures of those parts; for, on supposition of an absolute plenum, we do not conceive how any part of matter could be actually divided from that next adjoining, any more than it is possible to divide actually the parts of absolute space from one another: for by the actual division of the parts of a continuum from one another, we conceive nothing else understood, but the placing of those parts at a distance from one another, which in the continuum were at no distance from one another: but such divisions between the parts of matter must imply vacuities between them.
7. As for the figures of the parts of bodies, upon the supposition of a plenum, they must either be all rectilinear, or all concavo-convex; otherwise they would not adequately sill space; which we do not find to be true in fact.
8. The denying a Vacuum supposes what it is impossible for any one to prove to be true, viz, that the material world has no limits.
However, we are told by some, that it is impossible to conceive a Vacuum. But this surely must proceed from their having imbibed Descartes's doctrine, that the essence of body is constituted by extension; as it would be contradictory to suppose space without extension. To suppose that there are fluids penetrating all bodies and replenishing space, which neither resist nor act upon bodies, merely in order to avoid admitting a Vacuum, is feigning two sorts of matter, without any necessity or foundation; or is tacitly giving up the question.
Since then the essence of matter does not consist in extension, but in solidity, or impenetrability, the universe may be said to consist of solid bodies moving in a Vacuum: nor need we at all fear, lest the phenomena of nature, most of which are plausibly accounted for from a plenum, should become inexplicable when the plenitude is set aside. The principal ones, such as the tides; the suspension of the mercury in the barometer; the motion of the heavenly bodies, and of light, &c, are more easily and satisfactorily accounted for from other principles.
Vacuum Boileanum, is used to express that approach to a real Vacuum, which we arrive at by means of the air-pump. Thus, any thing put in a receiver so exhausted, is said to be put in vacuo: and thus most of the experiments with the air-pump are said to be performed in vacuo, or in vacuo Boileano.
Some of the principal phenomena observed of bodies in vacuo, are; that the heaviest and lightest bodies, as a guinea and a feather, fall here with equal velocity: —that fruits, as grapes, cherries, peaches, apples, &c, kept for any time in vacuo, retain their nature, freshness, colour, &c, and those withered in the open air recover their plumpness in vacuo:—all light and fire become immediately extinct in vacuo:—little or no sound is heard from a bell rung in vacuo:—a bladder half full of air, will distend the bladder, and lift up 40 pound weight in vacuo:—most animals soon expire in vacuo.
By experiments made in 1704, Dr. Derham found that animals which have two ventricals, and no foramen ovale, as birds, dogs, cats, mice, &c, die in less than half a minute; counting from the first exsuction: a mole died in one minute; a bat lived 7 or 8. Insects, as wasps, bees, grasshoppers, &c, seemed dead in two minutes; but after being lest in vacuo 24 hours, they came to life again in the open air: snails continued 24 hours in vacuo, without appearing much incommoded. —Seeds planted in vacuo do not grow: Small beer dies, and loses all its taste, in vacuo: And air rushing through mercury into a Vacuum, throws the mercury in a kind of shower upon the receiver, and produces a great light in a dark room.
The air-pump can never produce a perfect Vacuum; as is evident from its structure, and the manner of its working: in effect, every exsuction only takes away a part of the air; so that there is still some left after any finite number of exsuctions. For the air-pump has no longer any effect but while the spring of the air remaining in the receiver is able to lift up the valves; and when the rarefaction is come to that degree, you can come no nearer to a Vacuum; unless perhaps the air valves can be opened mechanically, independent of the spring of the air, as it is said they are in some new improved air-pumps.
Torricellian Vacuum, is that made in the barometer tube, between the upper end and the top of the mercury. This is perhaps never a perfect and entire Vacuum; as all fluids are found to yield or to rise in elastic vapours, on the removal of the pressure of the atmosphere. See Torricellian, and Barometer.
