100 The Lunar Clefts — Mare Vajoorum. 



curious objects, I shall beg permission to add a few observations 

 of my own ; they are indeed of a very fragmentary character, 

 but may perhaps be useful to those who are disposed to make 

 out the whole detail of this interesting region, which, after all 

 the attention given to it, is still but imperfectly known. My 

 excellent 5-^- in. object-glass carried me, of course, considerably 

 further than B. and M., and my 9|- in. C( With " speculum, 

 would have made a much greater advance, but for the long 

 continuance of unfavourable weather. 



Beginning, as at first, at the widened extremity of the Hygi- 

 nus cleft, where it lies like a long pool under a bank of some 

 height on the left-hand, I find that in the middle of this part 

 it sends out a narrow continuation towards the E., which 

 having cut through a low dark mass of hills, is soon lost in the 

 plain on the other side of them ; beyond this, at a short distance, 

 its direction is carried on by the N. edge of a mountain mass, 

 but I could not trace any cleft there. Less than half-way from 

 this "pool" to Hyginus, an insulated hill stands close above it 

 on the right, after passing which it becomes convex towards 

 the W., and evidently broader, contracting, however, suddenly, 

 and turning more to the left a little way before reaching Hygi- 

 iius. In this broader part, it would seem that the three first 

 craters of B. and M. must be placed (including the two which 

 L. has so exaggerated in size), and I might have detected them 

 at this time in steadier air. Hyginus itself I have repeatedly 

 seen without a wall, though possibly it might come out close 

 to the terminator, where I have never observed it. Schm. 

 doubts whether any actually ringless craters exist on the moon, 

 but they are known on the earth, the " explosion-craters " of 

 Humboldt ; cavities surrounded by inconsiderable margins of 

 ejected fragments only; such are the Maars of the Eifel, and 

 several in Auvergne and Java. I have never seen the two 

 bright lines crossing the floor, as described by B. and M. 

 Once I detected one of them, corresponding with the S. edge 

 of the cleft, very narrow, but obvious, and cut off by a narrow 

 black space from the E. slope of the crater ; but I have more 

 frequently seen the whole cleft entering the crater as a broader 

 line of light. On one occasion, an indistinct uncertain shading 

 led me to suspect that its level was somewhat depressed as it 

 passed through the crater's edge, and I have never been able 

 to trace it beyond -§- the breadth of the floor, nor to ascertain 

 how this white stripe comes to an end, though once I thought 

 there was a slight shadow there. The two accompanying 

 sketches, taken (1) 1861, April 18; (2) 1867, Feb. 7, will give 

 some idea, though a very rough one, of the object. They 

 show also the cavity which encroaches on the N. edge of 

 Hyginus, and which has been given, though too small, by L., 



