The processes of natural development which we are now considering will at once elucidate and discredit the fashion of speculating on the attributes of _two_, _three_, and _four_ or more _dimensional_ space; but, in passing, it is worth while to point out the real significance of the sound, but incomplete, intuition that has prompted—among Spiritualists and Theosophists, and several great men of Science, for the matter of that(398)—the use of the modern expression, the “fourth dimension of space.” To begin with, the superficial absurdity of assuming that Space itself is measurable in any direction is of little consequence. The familiar phrase can only be an abbreviation of the fuller form—the “_fourth dimension of matter, in Space_.”(399) But even thus expanded, it is an unhappy phrase, because while it is perfectly true that the progress of evolution may be destined to introduce us to new characteristics of matter, those with which we are already familiar are really more numerous than the three dimensions. The qualities, or what is perhaps the best available term, the characteristics of matter, must clearly bear a direct relation always to the senses of man. Matter has extension, colour, motion (molecular motion), taste and smell, corresponding to the existing senses of man, and the next characteristic it develops—let us call it for the moment “Permeability”—will correspond to the next sense of man, which we may call “Normal Clairvoyance.” Thus, when some bold thinkers have been thirsting for a fourth dimension, to explain the passage of matter through matter, and the production of knots upon an endless cord, they have been in want of a _sixth characteristic_ of matter. The three dimensions belong really to only one attribute, or characteristic, of matter—extension; and popular common sense justly rebels against the idea that, under any condition of things, there can be more than three of such dimensions as length, breadth and thickness. These terms, and the term “dimension” itself, all belong to one plane of thought, to one stage of evolution, to one characteristic of matter. So long as there are foot‐rules within the resources of cosmos, to apply to matter, so long will they be able to measure it three ways and no more; just as, from the time the idea of measurement first occupied a place in the human understanding, it has been possible to apply measurement in three directions and no more. But these considerations do not in any way militate against the certainty that, in the progress of time, as the faculties of humanity are multiplied, so will the characteristics of matter be multiplied also. Meanwhile, the expression is far more incorrect than even the familiar phrase of the sun’s “rising” or “setting.”