in a hundred there will be a planet in the habitable zone fulfilling all the other conditions of habitability, of size, mass, inclination of axis, circular orbit, and rotation? Of these ten thousand earths which may be made fit for the habitation of Man, can we assume that even one in a hundred is now at that epoch in its history when it is no longer "without form and void," when a division has been made between the waters under the firmament and those that are above the firmament; when the waters under the heaven have been gathered into one place, and the dry land has appeared, and when the earth and the waters have brought forth life abundantly? Out of a hundred million of planetary systems throughout the depths of space, can we suppose that there are even one hundred worlds that are actually inhabited at the present moment? These numbers and proportions certainly are not, and cannot be, based on knowledge; they are given as illustrations only; but, vague as they are, they suggest that our Earth may be neither one of many inhabited earths, nor yet unique, but one of a few--indeed of a very few. And then the objection is raised: "If our own Earth is but one of, perhaps, two inhabited worlds in the solar system; and of perhaps one or two hundred inhabited worlds throughout the furthest space that we can scan; why is all this waste?" Of all the countless millions of stellar systems without living organisms as inhabitants, we cannot tell the purpose for the simple reason that we do not know it; but of "waste" in the solar system, there is no question. Relatively speaking, this is quite insignificant, for we cannot consider that as "waste material" which is useful and, indeed, essential to existence. For, consider first the material in the Earth itself. Its total volume is 260,613,000,000 cubic miles, but man only lives _upon_ its surface of less than 200 million square miles in extent, and he can not probe down as far as ten miles below it, through the depths of ocean or by his deepest mine. Thus we are left with over 258 thousand million of cubic miles that man, or plant, or beast can never make direct use of. But without this 258 thousand million cubic miles that he can never sow nor reap, the overlying platform on which he dwells would be useless for retaining the air or the water by which he lives. No less essential is the Sun; its vast bulk of 2,000,000,000,000,000,000,000,000,000 tons can, in no single unit, be counted "waste," for it is from this that the heat and light necessary for life on the Earth is derived. But the tonnage of all the planets combined is but 0·13 per cent of the Sun alone; and a wastage, if such it is, like this is insignificant from a material point of view.