When we critically survey the face of the Moon with a good telescope, we see at once that her surface is broken up into a series of craters of various sizes, and that some very irregular formations are scattered here and there, which present a similar appearance to elevated mountain-ranges. The crateriform aspect of the Moon is perhaps the more striking feature, from its greater extent; and we recognize in the individual forms a _simile_ to the circular cavities formed in slag or some other hard substances under the action of intense heat. In certain regions of the Moon, especially those near the south pole, the disk is one mass of abutting craters, and were it not for the obvious want of symmetry in form and uniformity of size, the appearance would be analogous to that of a gigantic honeycomb. These craters are commonly surrounded by high walls or ramparts, and often include conical hills rising from their centres to great heights. While the eye examines these singular structures, and lingers amongst the mass of intricate detail in which the whole surface abounds, we cannot but feel impressed at the marvellous sharpness of definition with which the different features are presented to our view. It matters not to what district we direct our gaze, there is the same perfect serenity and clearness of outline. Not the slightest indication can be discerned anywhere of mist or other obscuring vapours hanging over the lunar landscape. _Absence of Air and Water._—Now it is palpable from this that the Moon has no atmosphere of sufficient density to render itself appreciable; for such an appendage, if it existed in any visible form, would at once obtrude upon the attention, and we should probably recognize some of the characteristics common to the behaviour of our terrestrial clouds. But nothing of the kind is apparent on the Moon: there is an unbroken transparency spread over the whole extent of the Moon’s scenery; whence we conclude that if any air exists on the surface it is of extremely attenuated nature, and possibly confined to the bottom of the craters and low-lying formations, which are arranged in such prolific manner on our satellite.