152 COSMOS. 



selves AS being more shut in and isolated, the Msre Crisiiirtk 

 (12,000 square miles) and the 3Iare Tranquillitatis (23,200 

 square miles). 



The color of these so-called i>tas is not in all cases gray. 

 The Mare Crisium is gray mixed with dark green ; the Mare 

 Serenitatis and Mare Humorum are likewise green. Near 

 the Hercynian mountains, on the contrary, the isolated cir- 

 cumvallation Lichtenherg presents a pale reddish color, the 

 same as Palus Somnii. Circular surfaces, without central 

 mountains, have for the most part a dark steel-gray color, 

 bordering 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 northward 

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

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

 the equatorial region, and Endymion on the northwest edge, 

 are the three darkest spots upon the whole Moon's disk, Aris- 

 tarchus, with its sometimes almost star-hke shining points, is 

 the brightest and most brilliant. All these alternations of 

 light and shade affect an iodized plate, and may be repre- 

 sented in Daguerreotype, by means of powerful magnifiers, 

 with wonderful truthfulness. I myself possess such a mooji- 

 light picture of two inches diameter, in which the so-called 

 ieas 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 s,ea$ ( Cris- 

 ium, Serenitatis, and Humorurri), it is still more frequently 

 — indeed, almost universally, repeated in the mountainous 

 part of the disk, especially in the configuration of the enor- 

 mous mountain-masses which occupy the southern hemisphere 

 from the pole to near the equator, where the mass runs out 

 in a point. Many of the annular elevations and inclosed 

 plains (according to Lohrmann, the largest are more than 

 4000 square miles in extent) form connected series, and, in- 

 deed, in the direction of the meridian, between 5° and 40° 

 south latitude.* The northern polar region contains cpm- 

 paratively few of these crowded mountain circles. In the 

 western edge of the northern hemisphere, on the contrary, 

 they form a connected group between 20° and 50° north 

 latitude. The North Pole itself is within a few degrees of 

 the Mare Frigoris, and thus, like the whole level northeast- 

 ern space, including only a few isolated annular mountain? 

 {Plato, Mairan, Aristarch, Copernicus, and Kepler), pre 

 * Schumacher's Jahrbuch for 1841, p. 270. 



