ASTRONOMY WITH AN OPERA-GLASS. 489 



center of the moon contains some of the grandest of these strange 

 configurations of conjoined mountain, plain, and crater. The names 

 of the principal ones can be learned from the map, and the reader will 

 find it very interesting to watch them coming into sight about first 

 quarter, and passing out of sight about third quarter. At such times, 

 with a field-glass, some of them look like enormous round holes in the 

 inner edge of the illuminated half of the moon. Theophilus (23), 

 Cyrillus (24), and Catharina (25), are three of the finest walled plains 

 on the moon Theophilus, in particular, being a splendid specimen of 

 such formations. This chain of craters may be seen rapidly coming 

 into sunlight at the edge of the Sea of Nectar, in our second illustra- 

 tion. The Altai Mountains (26) are a line of lofty cliffs, two hundred 

 and eighty miles in length, surmounting a high table-land. 



The Caucasus Mountains (38) are a mass of highlands and peaks, 

 which introduce us to a series of formations resembling those of the 

 mountainous regions of the earth. The highest peak in this range is 

 about nineteen thousand feet. Between the Caucasus and the Apen- 

 nines (44) lies a level pass, or strait, connecting the Sea of Serenity 

 with the Sea of Showers. The Apennines are the greatest of the lunar 

 mountain - chains, extending some four hundred and sixty miles in 

 length, and containing one peak twenty-one thousand feet high, and 

 many varying from twelve thousand to nearly twenty thousand. It 

 will thus be seen that the Apennines of the earth sink into insignifi- 

 cance in comparison with their gigantic namesakes on the moon. As 

 this range runs at a considerable angle to the line of sunrise, its high 

 peaks are seen tipped with sunlight for a long distance beyond the 

 generally illuminated edge about the time of first quarter. Even with 

 the naked eye the sun-touched summits of the lunar Apennines may 

 at that time be detected as a tongue of light projecting into the dark 

 side of the moon. The Alps (41) are another mountain-mass of great 

 elevation, whose highest peak is a good match for the Mont Blanc of 

 the earth, after which it has been named. 



Plato (42) is a very celebrated dark and level plain, surrounded by 

 a mountain-ring, and presenting in its interior many puzzling and ap- 

 parently changeable phenomena which have given rise to much specu- 

 lation, but which, of course, lie far beyond the reach of opera-glasses. 

 Plato is seen in our third illustration, being the second ring from 

 the top. 



Copernicus (46) is the last of the lunar formations that we shall 

 describe. It bears a general resemblance to Tycho, and is slightly 

 greater in diameter ; it is, however, not quite so deep. It has a cluster 

 of peaks in the center, whose tops may be detected with a field-glass, 

 as a speck of light when the rays of the morning sun, slanting across 

 the valley, illuminate them while their environs are yet buried in 

 night. Copernicus is the center of a systeni of light-streaks some- 

 what resembling those of Tycho, but very much shorter. 



