THE MOON. 



22. The visible hemisphere of our satellite has, within the 

 last quarter of a century, been subjected to the most rigorous 

 examination which unwearied industry, aided by the vast im- 

 provement which has been effected in the instruments of telescopic 

 observation, rendered possible ; and it is no exaggeration to state 

 that we now possess a chart of that hemisphere, which in 

 accuracy of detail far exceeds any similar representation of the 

 earth's surface. 



Among the selenographical observers, the Prussian astronomers, 

 MM. Beer and Madler, stand pre-eminent. Their descriptive 

 work, entitled " Der Monde," contains the most complete collec- 

 tion of observations on the physical condition of our satellite, and 

 the chart, measuring 37 inches in diameter, exhibits the most 

 complete representation of the lunar surface extant. Besides this 

 great work, a selenographic chart was produced by Mr. llussel, 

 from observations made with a seven-foot reflector, a similar 

 delineation by Lohrmann, and, in fine, a very complete model 

 in relief of the visible hemisphere by Madame Witte, a Hanove- 

 rian lady. 



23. The surface of the visible hemisphere is thickly covered 

 with mountainous masses and ranges of various forms, magni- 

 tudes, and heights, in which, however, the prevalence of a 

 circular or crater-like form is conspicuous. The various tints of 

 white and gray which mark the lineaments observed upon the 

 disk arise partly from the different reflecting powers of the matter 

 composing different parts of the lunar surface, and partly from 

 the different angles at which the rays of the solar light are incident 

 upon them. The more intensely white parts are mountains of 

 various magnitude and form, whose height, relatively to the 

 moon's magnitude, greatly exceeds that of the most stupendous 

 terrestrial eminences ; and there are many characterised by an 

 abruptness and steepness which sometimes assume the position of 

 a vast vertical wall, altogether without example upon the earth. 

 These are generally disposed in broad masses, lying in close con- 

 tiguity, and intersected with vast and deep valleys, gullies, and 

 abysses, none of which, however, have any of the characters which 

 betray the agency of water. 



24. There are circular areas, varying from 40 to 120 miles in 

 diameter, enclosed by a ring of mountain ridges, mostly con- 

 tinuous, but in some cases intersected at one or more points by vast 

 ravines. The enclosed area is generally a plain on which moun- 

 tains of less height are often scattered. The surrounding circular 

 ridge also throws out spurs, both externally and internally, but 

 the latter are generally shorter than the former. In some cases, 

 however, internal spurs, which are diametrically opposed, unite 



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