by alternate expansions and contractions of the entire masses, which in the long run of ages must bring about dislocations or dislodgments of matter that might considerably affect the surface features from a close point of view, but which can hardly be of sufficient magnitude to be detected by a terrestrial observer whose best aids to vision give him no perception of minute configurations. And it must always be borne in mind that changes can only be _proved_ by reference to previous observations and delineations of unquestionable accuracy. Speaking by our own lights, from our own experience and reasoning, we are disposed to conclude that in all visible aspects the lunar surface is unchangeable, that in fact it arrived at its terminal condition _eons_ of ages ago, and that in the survey of its wonderful features, even in the smallest details, we are presented with the sight of objects of such transcendent antiquity as to render the oldest geological features of the earth modern by comparison. CHAPTER XIII. THE MOON AS A WORLD: DAY AND NIGHT UPON ITS SURFACE. A wide interest, if not a deep one, attaches to the general question as to the existence of living beings, or at least the possibility of organic existence, on planetary bodies other than our own. The question has been examined in all ages, by the lights of the science peculiar to each. With every important accession to our astronomical knowledge it has been re-raised: every considerable discovery has given rise to some new step or phase in the discussion, and in this way there has grown up a somewhat extensive literature exclusively relating to mundane plurality. It will readily be understood that the moon, from its proximity to the earth, has from the first received a large, perhaps the largest, share of attention from wanderers into this field of speculation: and we might add greatly to the bulk of this volume by merely reviewing some of the more curious and, in their way, instructive conjectures specially relating to the moon as a world—to imaginary journeys towards her, and to the beings conjectured to dwell upon and within her. This, however, we feel there is no occasion to do, for it is our purpose merely to point out the two or three almost conclusive arguments against the possibility of any life, animal or vegetable, having existence on our satellite.