o 



72 Lunar Details. 



Copernicus, with a smaller one on its W. edge — to Euler (36) ; 

 others pass through the Oceanus Procellarum to meet the 

 narrow and not easily distinguishable streaks of Aristarclms 

 (43), and run into a great spot of light between both. Others, 

 shorter and less distinct in appearance and direction, are found 

 S. of Mayer. On the side of Kepler (41) they are more clear 

 and decided : several, nearly parallel, run E. to that crater, 

 and enter its " nimbus," thus uniting the two main streak- 

 systems of the N. hemisphere. These details are so far worthy 

 of record, as the suspicion of change in the reflective power of 

 portions of the lunar surface, if not yet warranted, is not un- 

 reasonable. The streaks are of course best seen in Full Moon, 

 very little of them being visible if the terminator has not 

 passed Mayer in the increase, or reached Eratosthenes in the 

 wane, and that little being masked by the opposite direction 

 of the mountain ridges. 



Copernicus and its nimbus can be clearly made out on the 

 night-side before the First, not so readily after the Last 

 Quarter. 



We now come to a very singular region, more than once 

 adverted to in our previous paper, and certainly in its own 

 way one of the most remarkable in the Moon; — the Crater - 

 chains, as we may term them, between Copernicus and Eratos- 

 thenes. Here' we find the greatest and strangest contrast to 

 the neighbouring Sinus JEstuum. There, craters are all but 

 invisible, even after the strictest search : here they exist in 

 such profusion that it is doubtful whether any really level sur- 

 face intervenes. The sixty-one shown in the map, of which 

 the greater part lie in a line between Pytheas (a moderate- 

 sized crater two-thirds of the way from Copernicus to Lambert) 

 and Stadius, are probably not the half that are perceptible, 

 but past delineation. They are not scattered at random 

 through the plain, but lie behind one another in rows, in some 

 places closely compressed, in others wider apart at nearly 

 equal distances, and. but few seem entirely insulated. Though 

 the majority are very minute, and only a few exceed 1" in 

 diameter, B. and M. cannot give them, like Gruithuisen, a width 

 of only 500 (French) feet, but would estimate most of them at as 

 many toises (3200 feet). The closely compressed rows, they 

 observe, assume easily the aspect of a connected cleft ; and, in 

 fact, the two forms are neai-ly interchangeable ; we only need 

 imagine the absence of a common and usually very low parti- 

 tion, to convert the one into the other. Kt the N. end of the 

 landscape, for the length of a lunar degree, there is such a 

 cleft, with a distinct embankment on either side, and four of 

 the smallest craters in its depth, with which the next three 

 craters S. of it often seem to form a whole. At a distance of 



