The names of the spots were first given by itiecioli, and his nomen clature is still generally followed, although with very numerous additions. The spots are distinguished by tho names of eminent astronomers, philosophers, and mathematicians, both ancient and modern, as Eratosthenes, Plato, Pythagoras, Archimedes, Tycho, Coper nicuts, Kepler, &c. Many .of these spots deserve a more particular notice. Thus Tycho, the large crater in the centre of the lower part of the cut, is remarkable, not only ou account of its brilliancy and size, (being 54 miles in diameter, and in depth 16,600 feet,) but also for the radiating streaks, which proceed from it in all directions, some of which extend into the opposite hemisphere. Copernicus, a con spicuous spot to the left of the cut. and about half way to the top, presents an immense crater, 56 miles in diameter, in the centre of which he a mountain having six peaks, of which two are very con spicuous. It is surrounded by a ring composed of successive terraces, ending in a narrow ridge, and rising to the height of 11,000 feet from the bottom of the crater Aristarchus, the spot still mire to the left above Copernicus, is the brightest crater in the moon ; it is so brilliant as to be quite dazzling in a large telescope. It is this spot that was supposed by Sir William Herschel to be a volcano in eruption. Plato, a large dark oval spot in the upper portion of the cut, is remarkable for having the bottom of the crater striped, which is also the case with Archimedes, a large oval spot at no great distance from Plato, in which seven nearly parallel stripes may be easily distin guished. Near Plato is a remarkable insulated pyramidal mountain or rock called Pico, rising from a narrow base to about 7000 feet above the surrounding plain, from which it must present a most magnificent appearance. Eratosthenes, a crater situated near a ridge of lofty mountains called the Apennines, is also a very brilliant object, and Stadius, a neighbouring crater, is one of those to be seen only under peculiar illumination, being absolutely invisible at the time of full moon.
The surface of the moon exhibits a very large number of moun tains " almost universally of an exactly circular or cusp shaped form, foreshortened however into ellipses near the limb ; but the larger have for the most part flat bottoms within, from which rises centrally a small, steep, conical hill. They offer in short, in its highest perfection, the true volcanic character, as it may be seen in the crater of Vesuvius.
And in some of the principal ones, decided marks of volcanic stratification, arising from successive deposits of ejected matter, may be clearly traced with powerful telescopes. What is moreover ex tremely singular in the geology of the moon is, that although nothing having the character of seas can be traced (for the dusky spots which are commonly called seas, when closely examined, present appearances incompatible with the supposit on of deep water) yet there are large regions perfectly level, and apparently of a deeded alluvial character." (Sir J. Herschel, ' Astronomy,' p. 229.) The mountains are known by their shadows, which are perfectly visible, and which are long when they are new the boundary of light and darkness, or when the sun is By the help of thole shadows, as well by other means, the heights of many of the lunar mountains have been measured, and some have been found whose heights exceed a mile and a half.
From the manner In which the moon is seen, as well as from the stars, when she approaches near them, undergoing no refraction what ever, it is certain that she has either no atmosphere, or one of a degree of tenuity which must exceed, perhaps, that of the best exhausted receiver. From this it has been inferred that there are no fluids at the surface of the moon, since, if there were, an atmosphere must be formed by evaporation. It is however enough to say that the fluids, if such there be, must be very different from those which abound at the surface of the earth. Since the moon has a day (with reference to the sun) of a whole sidereal month in duration, each part is 142 daye in sun light, and 142 days without it. The intense heat and cold which must thus alternate would destroy human life, even on the supposition that terrestrial vegetation could be maintained. The fluid on the warm side if any) must be constantly evaporating and passing off to the colder side. " The consequence must he absolute aridity below the vertical sun, constant accretion of hoar frost in the opposite region, and perhaps a narrow zone of running water at the borders of the enlightened hemisphere. It In possible, then, that evaporation on the one howl, and oondensetion on the other, may, to a certain extent, perserve en equilibrium of temperature, and mitigate the extreme severity of both climates" (Sir J. Herschel, ' Astronomy,' p. 230.) The mass of the moon, as determined from her effect upon the earth's motion, is about one.elghtleth (or .01252) of that of the earth, her volume Is one forty-ninth of that of the earth, and the average density of her material .815, or about six-tenths, of that of the earth. A body weighing six pounds at the earth, would weigh one pound at the moon, if tried against weights which retained their terrestrial gravity. Travelling 10 miles an hour on the surface of the moon would enable a person to keep up with the sun ; so that it is not at all im possible that animal life may be maintained by constant migration, keeping always near the boundary of light and darknests.
It might be supposed that nothing could ever be known of the figure of the moon, sinus we can only see one aide. But this very circum stance hauls us to some knowledge on the point. It is impossible to believe that the moon should revolve on her axis precisely in the same average time as she revolves round the earth, without half a second of difference, and not to suppose that there in some mechanical connec tion between the two revolutions, so that either one is a consequence of the other, or both aro consequences of some common cause. As this subject is rarely elucidated in elementary treatises, we have somewhat abridged several of those topics which are usually treated, in order to supply considerations fur which we could only refer to treatises of the most mathematical character.