Neighbourhood of the Lunar Spot, Mare Grisium. 863 



exhibiting itself, he says, in several other similar great plains, 

 especially Grimaldi. The wall is very broad, and tails on each 

 side in terraces — a mode of formation frequently recurring in 

 lunar rings, and worthy of careful attention : it reaches a height 

 on the W. side of about 8700 feet above the interior, rising 

 on the E. side nearly 1000 feet higher, and, dividing in its 

 course, encloses on the NE. a steep depression named Tralles, 

 lying no less than 13,700 feet beneath its E. boundary. Several 

 of the neighbouring smaller craters are also, as Schroter has 

 remarked in this and numerous other instances, deeper than 

 the principal cavity with which they appear to be connected. 

 It is a fact especially worthy of attention, that, as this observer 

 has pointed out, when one crater has encroached upon the 

 boundary of another, so as to be obviously of subsequent date, 

 the more recent is almost universally the smaller, as well as 

 the deeper, either absolutely, or at least in proportion to its 

 diameter. 



The area of Cleomedes contains several small objects. 

 Schroter at first saw three, a low hill in the centre between 

 two loftier objects, of which that to the S. might possibly be a 

 crater, all reflecting an ordinary light of about 4° of intensity. 

 Subsequently, under an angle almost precisely similar, he 

 found the N. spot changed from a longish ridge to a crater of 

 considerable size, and a brilliancy of not less than 7° or 8\ 

 approaching that of Aristarchus, the brightest spot on the 

 moon. In another lunation the ordinary-looking hill and its 

 shadow reappeared. On another occasion he saw in this place 

 both the ridge and two craters, the smaller of which had 6 3 of 

 light, close to it ; and subsequently he found the larger crater 

 grey instead of white, and a black shadow in both of them, 

 especially the smaller one, though 6' 40" to 7' removed from the 

 terminator, and though a neighbouring very deep crater (Ber- 

 nouilli) had lost nearly all its shade — thus indicating extraor- 

 dinary depth and steepness. He had been early persuaded, 

 from many such observations, that " the existence of real acci- 

 dental workings of nature, not dependent upon the different 

 reflection of light, lies so evidently before our eyes, that if any 

 one would desire a yet stronger conviction, he would do better 

 to give up altogether the closer investigation of the lunar 

 surface, since he (Schroter) did not believe that, with due 

 regard to our shortsightedness, more obvious proofs were pos- 

 sible;" and he thinks it hence certainly demonstrated that 

 these changes are partly atmospheric, depending upon the con- 

 densations and clearings up of different seasons, and partly 

 indicative of other unknown agencies working according to 

 the peculiar nature of the surface. In this respect he calls 

 attention to the variations in the colour of the area of Cleomedes, 



