294 The Lunar Mare Serenitatis. 



subterranean galleries by which the common mcle unites his 

 more serious and massive upheavings. Schr. was in fact 

 disposed to refer their origin to the working of an elastic force 

 beneath the surface of the moon, which, in regions where the 

 crust of the globe was of great tenacity, and offered a propor- 

 tionate resistance, would thus slightly elevate it in making its 

 way laterally till it reached a more penetrable spot, where it 

 would protrude a lofty mountain mass, or explode in a crater. 

 Whatever may be thought of the probability of the explana- 

 tion, the fact is unquestionable that these ridges generally 

 begin and end, like terrestrial highways, in something of more 

 importance than themselves, and that this is of such continual 

 occurrence in every part of the moon that we can hardly be 

 mistaken in ascribing it to the operation of some general law. 

 In the plain which we are now studying, the most remarkable 

 of these ridges lies not far from its W. side, and in a general 

 sense parallel to it. Including its curvatures it measures nearly 

 500 miles in length, while it is but 400 or 500 feet high 

 towards its S. extremity, and rises only to 700 feet in one part 

 near its opposite end, its slope never exceeding 10°, and its 

 base of 7 miles, as Schr. observes, giving a proportion of 

 only -^rd for its altitude. In one place it bears a minute 

 crater, precisely where a similar ridge runs into it, in accordance 

 with Schroter's hypothesis. B. and M. have not drawn atten- 

 tion to the very curious appearance which this great serpent 

 exhibits near the terminator. This has been well though 

 rudely delineated by its discoverer Schr., who points out its 

 connection with the ring of Posiclonius at its N. extremity. 

 The student will find it worth watching for, and will notice 

 how its strong dark shadow close to the terminator demon- 

 strates the visibility of very slight elevations in that position. 

 In the E. side of the plain the ridges are less considerable, and 

 B. and M. remark that in no portion of the lunar hemisphere 

 is the terminator of so regular an elliptical curve as when it 

 passes through part of this district. 



A good many craters lie scattered throughout the level, 

 but generally of minute dimensions. The most important by 

 far is Bessel, which though but 14 miles in diameter, is the 

 most conspicuous object in the interior, lying, not indeed cen- 

 trally, but far out at sea, and on the brightest part of the long 

 bisecting streak. B. and M. make the depth of its interior 

 4000 feet below the W. wall, and the height of its E. wall 

 1600 feet from the plain. Schr. gives a depth of about 3400 

 feet, but observes that in such minute measures an error of j 

 might easily occur; the height of the E. wall he states at 900 

 feet, with two peaks of 1000 feet, casting a cone of shade at each 

 extremity. I think I have remarked a singular form in the 



