482 THE POPULAR SCIENCE MONTHLY. 



Rainbows," or the " Lake of Dreams," or the " Sea of Tranquillity," if 

 for no other reason than a curiosity to know what could have induced 

 men to give to these regions in the moon such captivating names ? 

 Or who would not desire to visit them if he could ? though no doubt 

 we should find them, like the " Delectable Mountains " in the " Pil- 

 grim's Progress," most charming when seen from afar. 



The limited scale of our map, of course, rendered it impossible to 

 represent upon it more than a comparatively small number of the lunar 

 mountains that have received names. In selecting those to be put in 

 the map, I have endeavored to choose such as, on account of their size, 

 their situation, or some striking peculiarity, would be most likely to 

 attract the attention of a novice. The observer must not expect to 

 see them all at once, however. The lunar features change their ap- 

 pearance to a surprising extent, in accordance with the direction of 

 their illumination. Some great mountain-masses and ring-plains, or 

 craters, which present scenes of magnificence when the sun is rising or 

 setting upon them, disappear under a perpendicular light, such as they 

 receive at full moon. The great crater-plain, known as Maginus, num- 

 bered 10 in our map, is one of these. The broken mountain-wall sur- 

 rounding this vast depressed plain rises in some places to a height of 

 over fourteen thousand feet above the valley within, and the spectacle 

 of sunrise upon Maginus, seen with a powerful telescope, is a most im- 

 pressive sight, and even with a field-glass it is very interesting. Yet, 

 a few days later, Maginus vanishes, as if it had been swallowed up, 

 and as Beer and Madler have expressed it, " the full moon knows no 

 Maginus." The still grander formation of mountain, plain, and crater, 

 called Clavius (11 in the map), disappears almost as completely as Ma- 

 ginus at full moon, yet, under the proper illumination, it presents a 

 splendid pageant of light and shadow. . 



On the other hand, some of the lunar mountains shine vividly at 

 full moon, and can be well seen then, though, of course, only as light 

 spots, since at that time they cast no shadows. Menelaus (36 in the 

 map), Aristarchus (51), Proclus (30), Copernicus (46), and Kepler (52), 

 are among these shining mountains. Aristarchus is the most cele- 

 brated of them all, being the brightest point on the moon. It can 

 even be seen glimmering on the dark side of the moon that is to 

 say, when no light reaches it except that which is reflected from the 

 earth. With a large telescope, Aristarchus is so dazzlingly bright un- 

 der a high sun, that the eye is partly blinded in gazing at it. It con- 

 sists of a mountain-ring surrounding a circular valley, about twenty- 

 eight miles in diameter. The flanks of these mountains, especially on 

 their inner slopes, and the floor of the valley within, are very bright, 

 while a peak in the center of the valley, about as high as Storm King 

 Mountain on the Hudson, shines with piercing brilliancy. Sir William 

 Herschel mistook it for a volcano in action. It certainly is not an ac- 

 tive volcano, but just what makes it so dazzling no one knows. The ma- 



