Against this, some may object that what we call “vacuum” may be full of imponderable matter, say, of ether, the presence of which cannot indeed be detected by the balance, but is well proved by the phenomena of heat, electricity, etc. To which we answer, that the presence of ether between the molecules of bodies does not exclude vacuum; for ether itself is subject to condensation and rarefaction, as is manifest by its undulatory movements; and no condensation or rarefaction is possible without vacuum, as we have already explained.
Another objection against our conclusion may be the following: Simple elements, if they be attractive, can penetrate through one another, as we infer from the Newtonian law of action. Hence, the possibility of movement does not depend on the existence of vacuum. We answer, that the objection destroys itself; for whoever admits simple and unextended elements, must admit the existence of vacuum, it being evident that no space can be filled by unextended matter. We may add, that natural bodies and their molecules do not exclusively consist of attractive elements, but contain a great number of repulsive elements, to which they owe their impenetrability.
The ancients made against the existence of a vacuum another objection, drawn from the presumed necessity of a true material contact for the communication of movement. Vacuum, they said, is contra bonum naturæ—that is, incompatible with the requirements of natural order, for it prevents the interaction of bodies. This objection need hardly be answered, as it has long since been disposed of by the discovery of universal gravitation and of other physical truths. As we have proved in another place that “distance is an essential condition of the action of matter upon matter,”[120] we shall say nothing more on this point.
Objective Reality of Vacuum.—The second thing we must ascertain is whether space void of matter be a mere nothing, or an objective reality. Though Balmes and most modern philosophers hold that vacuum is mere nothingness, we think with other writers that the contrary can be rigorously demonstrated. Here are our reasons.
First, nothingness is not a region of movement. But vacuum is a region of movement. Therefore, vacuum is not mere nothingness. The minor of this syllogism is manifest from what we have just said about the impossibility of movement without vacuum, and the major can be easily proved. For, the interval of space which is measured by movement may be greater or less, whilst it would be absurd to talk of a greater or a less nothing; which shows that vacuum cannot be identified with nothingness. Again, void space can be really occupied, whilst it would be absurd to say that nothingness is really occupied, for occupation implies the presence of that which occupies in that which is occupied; hence, the occupation of nothingness would be the presence of a thing to nothing. But presence to nothing is no presence at all, just as relation to nothing is no relation. And therefore, the occupation of void space, if vacuum were a mere nothing, would be an evident contradiction. Moreover, nothingness has no real attributes, whereas real attributes are predicated of void space. We find no difficulty in conceiving void space as infinite, immovable, and virtually extended in all directions; whilst the conception of an extended nothing and of an infinite nothing is an utter impossibility. Whence we conclude that space void of matter is not a mere nothing.
Secondly, a mere nothing cannot be the foundation of a real relation: space void of matter is the foundation of a real relation; therefore, space void of matter is not a mere nothing. In this syllogism the major is quite certain; for all real relation has a real foundation, from which the correlated terms receive their relativity. Now, all real foundation is something real. On the other hand, nothingness is nothing real. Therefore, a mere nothing cannot be the foundation of a real relation. The minor proposition is no less certain, because space founds the relation of distance between any two material points, which relation is certainly real. In fact, that on account of which a distant term is related to another distant term, is the possibility of movement from the one to the other—that is, the possibility of a series of successive ubications between the two terms, without which no distance is conceivable. But the possibility of successive ubications is nothing else than the successive occupability of space, or space as occupable. And therefore, occupable space, or space void of matter, is the foundation of a real relation, and accordingly is an objective reality.
Thirdly, if vacuum were mere nothingness, no real extension could be conceived as possible. For, since all bodies are ultimately composed of elements destitute of extension, as has been demonstrated at length in our articles on matter, and since the primitive elements cannot touch one another mathematically without compenetration, the extension of bodies cannot be accounted for except by the existence of void intervals of space between neighboring elements. But, if vacuum is a mere nothing, all void intervals of space are nothing, and nothing remains between the neighboring elements; and if nothing remains between them, all the elements must be in mathematical contact, and therefore unite in a single indivisible point, as even Balmes concedes. Whence it is evident that the existence of real extension implies the objective reality of vacuum. We conclude, therefore, that space void of matter is not a mere nothing, but an objective reality.
Against this proposition some objections are made by the upholders of a different doctrine. In the first place, distance, they say, is a mere negation of contact; and since a mere negation is nothing, there is no need of assuming that vacuum is a reality.
We answer, that, if distance were a mere negation of contact, there would be no different distances; for the negation of contact does not admit of degrees, and cannot be greater or less. Distances may be, and are, greater or less. Therefore, distance is not a mere negation of contact. The negation of contact shows that the terms of the relation are distinct in space; for distinction in space is the negation of a common ubication. But the distinction of the terms, though a necessary condition for the existence of the relation, does not constitute it. Hence, the relation of distance presupposes, indeed, the distinction of the terms and the negation of contact, but formally it results from a positive foundation by which the terms are linked together in this or that determinate manner. If the interval between two material points were nothing, a greater interval would be a greater nothing, and a less interval a less nothing. We presume that no philosopher can safely admit a doctrine which leads to such a conclusion.
A second objection is as follows: It is possible to have distance without any vacuum between the distant terms. For, if the whole space between those terms were full of matter, their distance would be all the more real, without implying the reality of vacuum.