That the moon is a planet similar to our earth, is a sentiment very early adopted. Orpheus is the most ancient author, whose opinion on this subject has come down to us. Proclus presents us with three verses of that philosopher, wherein he positively asserts, that the moon was another earth, having in it mountains, vallies, &c. Pythagoras, who followed Orpheus in many of his opinions, taught likewise, that the moon was an earth like ours, replete with animals, whose nature he presumed not to describe, though he was persuaded they were of a more noble and elegant kind than ours, and not liable to the same infirmities. Stobæus gives us the opinion of Democritus about the nature of the moon, and the cause of those spots which we see upon its disk. That great philosopher imagined, that “those spots were no other than shades, formed by the excessive height of the lunar mountains,” which intercepted the light from the lower parts of that planet, where the valleys formed themselves into what appeared to us as shades or spots. Plutarch went further, alleging, that there were embosomed in the moon, vast seas and profound caverns: he says, those deep and extensive shades which appear upon the disk of that planet, must be occasioned by _the vast seas_ it contains, which are incapable of reflecting so vivid a light, as the more solid and opake parts; “or by caverns extremely wide and deep, wherein the rays of the sun are absorbed,” whence those shades and that obscurity which we call the spots of the moon. And Zenophanes said, that those immense cavities were inhabited by another race of men, who lived there just as we do upon earth. “And oft I think, fair planet of the night, That in thy orb the wretched may have rest.” [The height of the moon’s atmosphere is supposed to be 1.622 miles; or a little more than a mile and a half. The observations on the moon have been so accurate, and so often repeated, by means of the best glasses, that the _map of the moon_ is now considered nearly perfect. On this map is laid down the position of _spots_, _cavities_, and _mountains_, representing their _size_, _height_, _depth_, and _peculiarities_. They are very numerous. Some of these mountains are full _five miles high_. They descend in height, from the highest to small elevations. Several astronomers, particularly Herschell, has distinctly observed and described _volcanos_ in the moon, _actually flaming_; and others in an _expiring state_. _Craters_ of extinct volcanos are visible, and so numerous as to indicate very clearly, that volcanic action was once very extensive and powerful in the moon. Some of the _cavities_ are more than _three miles and a half deep_, and sixteen broad at the surface. _Ferguson’s Astronomy, additional chapters by Dr. Brewster._]