521 



VACUUM. 



VACUUM. 



we say a vacuum is full of nothing, and then arguing from the strict 

 meaning of the word " nothing," and denying that " nothing" can have 

 extension. It is not true, properly speaking, that there is " nothing " 

 in a vacuum, for the very notion of a vacuum is space void of matter. 



The idea of Descartes on the essence of matter was carried by hia 

 followers to the full extent of using matter as a synonyme for exten- 

 sion. Le Grand says that a vessel filled with gold has not more matter 

 than one filled with water. There is more weight, he says, more hard- 

 ness, &c., but not therefore more matter ; for the essence of matter is 

 not in weight, nor in hardness, c., but in extension. And he objects 

 to the adage that " Nature abhors a vacuum," because he considers 

 such an assertion merely to amount to saying that Nature abhors a 

 contradiction in terms. Newton (' Principia,' book iii., prop. 6, cor. '4) 

 expresses his opinion of the vacuum question in this way : " If all the 

 solid particles of bodies are of the same density, so that rarefaction 

 cannot take place without the creation of pores, there must be a 

 vacuum." Since matter is of different density in different substances, 

 and since the same substance may be compressed into smaller space or 

 expanded into larger, it must either be that the solid particles are 

 contracted or expanded, or that vacuous pores exist. This alternative 

 does not do much. A person trained in the sciences as they now exist, 

 think* the idea of toliil matter (that is, entirely solid, without any 

 vacuum) being compressed into more solid matter, to be most incon- 

 gruous and improbable ; but impressions derived from habits are not 

 arguments. The strong part of the Newtonian argument arises how- 

 ever from the results of the planetary theory. These celestial bodies 

 have moved, during two thousand years of recorded observations, with 

 exactly the same mean motions as at present, which they could not 

 have done if they had moved in a medium of any sensible resistance. 

 If then the celestial spaces be full of matter, it is matter of such a 

 degree of tenuity that two thousand years is not enough to make it 

 show any visible effect in altering the planetary motions'. But again, 

 though this argument has, almost up to the present time, induced astro- 

 nomers to suspect an absolute vacuum, yet very recently the feather 

 has shown a resistance which was not manifest against the guinea. A 

 comet has been strongly suspected all but proved to be undergoing 

 precisely the same sort of change in its mean motion which it is known 

 would result from a resisting medium. [CoMETS, col. 68.] The undu- 

 latory theory of light, moreover, which is now pretty generally received, 

 supposes the whole of the celestial spaces to be filled with the lumini- 

 ferous ether. The astronomical argument, therefore, in favour of 

 absolute vacuum has fallen ; but the views of the constitution of matter 

 which have grown with the riae of the molecular sciences of chemistry, 

 light, heat, electricity, &c., have supplied ita place with much more effect. 

 We cannot enter into the various probabilities in favour of the molecular 

 theory, which supposes matter to be atomic, the atoms being perhaps 

 separated by distances which are many times their own diameters. If any 

 one were to assert that the densest substance has in it many millions of 

 times more of vacuity than of solid matter, the assertion could not be 

 di -proved, nor even shown to be improbable. "There are difficulties," 

 said Dr. Johnson, " about a plenum, and there are difficulties about a 

 racuum, but one of them must be true ;" that ia, either all space is full 

 of matter, or there are parts of space which have no matter. The 

 alternative is undeniable, and the inference to which the modem phi- 

 losophy would give the greatest probability ia, that all rpace is full of 

 matter in the common sense of the word, but really occupied by par- 

 ticles of matter with vacuous interstices ; showing all degrees of density, 

 from that of the ether of light, which is wholly uuappreciable, to that 

 of hammered platinum, which is twenty-two times as heavy as water. 



Probably the manner in which the reader is most familiar with the 

 use of our leading word is in connexion ith what he may have seen 

 written on the maxim which we have already quoted "Nature abhors 

 a vacuum ;" a doctrine which, though common among the followers 

 of Aristotle, must not, any more than many others, be therefore taken 

 as emanating from that philosopher himself. This is usually cited as 

 a proof of the puerility of the ancient and middle philosophy we 

 think, somewhat unjustly. The personification of Nature is common 

 to all times, and we are in the habit of saying that Nature exhibits 

 phenomena, conceals her operations, uses the simplest means, &c. 

 Now Nature may as well abhor, as exhibit, conceal, or employ ; and 

 where intelligence ia understood, all who ue the word Nature mean 

 the <;<*! of Nature : while when the mere operations are referred to, 

 Nature ia only the personification of the collective body of second 

 causes. As the statement of a fact, it is true : Nature does, to the 

 beet of our knowledge, abhor a vacuum; she (if we may personify her) 

 never suffers it to exist to the extent of allowing any space which is 

 tible to our senses to be vacuous. But if the adage were meant 

 to supply a reason for the fact, those who used it were deceiving 

 themselves, but not so tliat the most of those who would laugh at 

 them would have any reason in their mirth. It ia the error of every 

 period to uae words expressive of a fact observed in the sense of 

 assignment of a reason for that fact ; and the centuries which have 

 always been ready with their fluids to stand for the causes of heat, 

 electricity, magnetism, &c., sho'uld not be too hard upon the pre- 

 ceding ages, which put the feelings of nature in the place which 

 they rather prefer to occupy by hypothetical gases. The very word 

 attraction [ATTRACTION], in the sense generally assigned to it, is pre- 

 cisely of the same nature aa the natural aMwmnce of the Aristotelians : 



namely, a word invented to supply the place of a cause. Those who 

 can use the former word in a really philosophical sense are precisely 

 those who can see that some of the ancients may have done the same 

 with the latter. 



" The question of the existence of vacuum, in its strict and absolute 

 sense," to repeat the designation given in the preceding portion of this 

 article, which is reprinted as it originally appeared, on account of its 

 historical and philosophical value, is inseparable from that of the 

 nature of space. If space, as suggested in a former article [PHYSICAL 

 FORCES, CORRELATION OF, col. 496], be " the extension of material 

 substance, the resultant of its dimensions, and mere consequence of 

 its existence," an absolute vacuum is iu the nature of things impos- 

 sible. But the admission of the existence of space distinct from 

 matter is equivalent to affirming the existence of an absolute vacuum. 

 Space distinct from matter is nothing else. This subject, however, 

 resembles others of what may be termed transcendental natural 

 philosophy, such as the (alleged) infinite divisibility of matter or of 

 space, the absolute-zero of heat, &e. The affirmative of each is purely 

 imaginary, being something which is mentally conceived to be 

 abstractedly and intrinsically possible, without any reference to known 

 physical facts, which are gratuitously assumed, not in reality to 

 deBne and limit the subjects, but to depend altogether, in relation to 

 them, on the necessary imperfections of the senses and of our finite 

 condition. But neither by observation or experiment, nor by mathe- 

 matical reasoning from either, do we know anything about space 

 distinct from matter, about the infinite division of matter, or about the 

 existence of anything but at some temperature or amount of heat in the 

 state or condition in which it causes expansion. (The calculations which 

 have been made as to the number of thermometric degrees between some 

 known temperature and the supposed absolute zero are entirely nugatory, 

 and unworthy of attention. There is no more reason to believe in the 

 existence of an absolute zero than in absolute rest, or in a limit to space, 

 or than to believe, for philosophical reasons, in the cessation of pheno- 

 mena, or in the beginning or the end of time.) And these three subjects 

 the alleged absolute vacuum, infinite division of matter or of space, 

 and absolute zero or its converse are as inseparably connected in mental 

 conception, as are the physical types of which they are abstractions iu 

 observed fact. 



To divest the subject of a notion introduced we think unneces- 

 sarily into modern discussions on the divisibility of matter, we must 

 here premise that absolute vacuum and empty space, or space distinct 

 from matter, being the same thing, it is clear that there can be no 

 infinite division of space ; while, by hypothesis, so far as our argument 

 has yet advanced, there may be infinite division of matter. But admit- 

 ting space to be the property of matter, its divisibility is the same 

 thing as that of matter, and the possibility of that divisibility must 

 depend on that of matter itself. 



This being premised, we return to the main union of subjects before 

 us. The mental conception of an absolute vacuum is in reality incom- 

 patible with that of the infinite division of matter and of the absolute 

 privation of heat ; though, remarkably, some philosophers, and even 

 modern men of science, have affirmed the second and third (the two 

 latter) and denied the first, while others, also, have denied the first 

 and third but admitted the second. If, again, matter be infinitely 

 divisible, there can be no absolute zero, since everything must exist at 

 some temperature, which, in fact, is as inseparable from material 

 existence as space and time themselves. If there were an absolute 

 zero, matter could not be infinitely divisible, for there would be (an 

 inferior) limit to its expansibility. 



But, on the other hand, the idea of the only finite divisibility of 

 matter does not imply that of an absolute zero, though it is the only 

 notion of divisibility compatible with it ; because the finite particles of 

 matter, like the masses they compose, must be susceptible of indefinite 

 reduction of temperature, if they retain the character of matter. 



We must descend, however, from these views to the observed facts 

 from which we believe they are necessary inferences. The sum of our 

 actual knowledge, whether exclusively experimental or also inductive 

 or deductive, is, that something (but not everything) exists everywhere ; 

 that everything exists in some place that is, in, or is, some part 

 of space, is of some magnitude and of some temperature, and that 

 nothing is at rest that is, that the place of everything is always 

 changing. In absolute truth these are, we believe, if not identical 

 propositions, yet such as involve each other, though to prove this would 

 require greater length than we can now command. 



In the present era of physical science, that inaugurated, iu certain 

 directions, by the successive labours of Volta, Davy, Oersted, Seebeck, 

 and Faraday, a belief that the intervention of material particles is 

 necessary for the transmission of any kind of force, and therefore that 

 no force does or can operate through unoccupied space or vacuum, has 

 gradually, but, until a comparatively late period, as it were silently, 

 grown up. The force of the evidence which had accumulated, however, 

 appears not to have been recognised until after the appearance (in the 

 ' Philosophical Transactions ' for 1835-1838) of Dr. Faraday's experi- 

 mental researches on electrical induction. We have been of opinion, 

 from the time of their publication, that these in reality involve the 

 demonstration of the impossibility of distant action, and therefore of 

 the necessity of the intervention of particles by which the action may 

 be and is transmitted from one acting body to a distant one ; and it is 



