492 COSMOS. 



upon mountain. 39 In the north-west region, two basins pre- 

 sent themselves as being more shut in and isolated, the Mare 

 Crisium (12,000 square miles), and the Mare Tranquillitatis 

 (23,200 square miles). 



The colour of these so-called seas is not in all cases grey. 

 The Mare Crisium is grey mixed with dark-green, the Mare 

 Serenitatis and Mare Humorum are likewise green. Near the 

 Hercynian mountains, on the contrary, the isolated circum- 

 vallation Lichtenberg presents a pale reddish colour, the same 

 as Palus Somnii. Circular surfaces, without central moun- 

 tains, have for the most part a dark steel-grey colour, border- 

 ing upon bluish. The causes of this great diversity in the 

 tints of the rocky surface, or other porous materials which 

 cover it, are extremely mysterious. While to the northwards 

 of the Alpine mountains, a large enclosed plain, Plato (called 

 by Hevel, Lacus niger major), and still more Grimaldus in 

 the equatorial region, and Endymion on the north-west edge, 

 are the three darkest spots upon the whole Moon's disc; 

 Aristarchus, with its sometimes almost star-like shining 

 points, is the brightest and most brilliant. All these alter- 

 nations of light and shade affect an iodized plate, and may be 

 represented in Daguerreotype by means of powerful magni- 

 fiers, with wonderful truthfulness. I myself possess such a 

 moonlight picture of 2 inches diameter, in which the so-called 

 seas and ring-formed mountains are distinctly perceptible ; it 

 was executed by an excellent artist, Mr. Whipple of Boston. 



If the circular form is striking in some of the seas ( Crisium, 

 Serenitatis, and Humorum), it is still more frequently, indeed 

 almost universally, repeated in the mountainous part of the 

 disc; especially in the configuration of the enormous moun- 

 tain-masses which occupy the southern hemisphere from the 

 pole to near the equator, where the mass runs out in a point. 



S9 Beer and Madler, p. 273. 



