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 (au inferior) limit to its expansibility.
But, on the other band, 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 plee —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 e1 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 certain that the awakening of the attention of philosophers to the trim condition of the subject involved, dates from about that time* This result is of course f dal to the admission of a true physical vacuum. It is remarkable that this result had been clearly anticipated by Newton himself, who held that the planetary spaces could not really be vacuous because they were traversed by the force of gravity. This remarkable expression of Newton's sagacity and power of thought has had a siugular fate. Recorded in 1693, it remained unpublished for nearly a century, when it appeared (in I 783) in Horsley's edition of his works. But it seems to have remained unregardeel until it was brought forward by the celebrated Professor Mayfair, so late as the year 1819—more than • century and a quarter after its original enunciation—and that merely for the purism of proving " that Newton did not consider gravity m a property inherent in matter." But even Mayfair did not perceive the entire force of the passage, and, indeed, the light which electricity was destined to throw on all branches of molecular physics had not then been received ; Faraday had not yet replied to Playfair's question, " it is not quite clear in what manner the interposition of a material substance can convey the action of distant bodies to one another." t A third part more of at century was destined to elapse, when Faraday cited Newton's expression, to the general surprise of the scientific world, in one of his discourses at the Royal Institution, in 1853, in order to show that Newton " was an unhesitating believer in physical lines of gravi tating force," and must be ranked "amongst them who sustain the physical nature of the lines of magnetic and electrical force.": The irreconcilability of the conception of lines of physical force with that of an absolute vacuum, identifies the subject now reviewed with that of the present article.