442 Lunar Sketches. 



slope just above its junction with the floor ; they are readily 

 seen N. and S., but are most evident on the former side : land- 

 slips from above may probably explain them. — As to Full 

 Moon markings, I find only the following: 1855, Aug. 27, 

 cc The appearance of the ring is encroached upon by a grey bay 

 on S.S.W. side." — 1855, Oct. 24 (a little before total eclipse), 

 " While none of Tyclio's streaks reach the foot of his wall, it is 

 remarkable that Copernicus is penetrated even to the centre by 

 several of his : two distinctly on the W. side, and one or two, 

 not so well made out, on the N. The former look almost like 

 a prolongation of the system of Kepler, as if Copernicus had 

 pierced through, or been pierced through by it." (From some 

 such observations, of which he has given no detail, Nichol 

 assigned the chronological sequence, Copernicus, Aristarchus, 

 Kepler. However this may be, it is not easy to interpret the 

 development of a different shading, frequently taking the appear- 

 ance of a definite patch or stain, among matter not only forced 

 from beneath, but subjected to the most violent dislocation. 

 If not due to original difference of material, it points to subse- 

 quent modification either from within or without. There seem 

 reasons for doubting the former cause, as well-defined dark 

 spots are occasionally met with where, as we suppose, the 

 materials have been so dislocated that any original distinction 

 could not have been so clearly maintained.) 



The bare results of these rough studies might have been 

 given in a briefer compass, but, in the original form, there 

 may be some interest and. some advantage to the inexperienced 

 student. He may thus perceive what apparent variations may 

 be produced by a slight difference in illumination, how unsafe 

 are inferences from single observations, and how discrepancies 

 are to be reconciled, if at all, by repeated examination. With 

 a little more of the advantges of leisure, these memoranda 

 might have been presented in a less fragmentary form, espe- 

 cially since the mirror now in my possession gives results far 

 in advance of almost any hitherto published (and indeed the 

 same might be said of smaller apertures of the same accurate 

 workmanship). But even these may answer a good end by 

 stimulating curiosity, and showing in what direction it may be 

 suitably exercised. 



Before finally quitting the neighbourhood of Copernicus, 

 it may be well to make some addition from the observations 

 of B. and M. The next crater of any size S.S.W. of the 

 mighty monarch of the district, is Gambart, a circle, 16 miles 

 across, but neither high nor deep. In this direction lies a 

 large insulated accumulation of short ridges, trending the same 

 way, the highest lying in a line from Copernicus to that crater. 

 They are more connected, but less elevated, on the W. of the 



