The North-West Lunar Limb. 207 



specified) c ' though there is none of these formations that might 

 not also be explained through the opposite assumption." 



The most conspicuous object in the neighbourhood of the 

 limb, as we proceed towards the pole, is the great wall-plain 

 Endymion, 78 miles in breadth : from its position it is much 

 affected by libration, which may carry it 180 miles from its 

 mean place towards the centre of the disc, or as much the other 

 way towards the limb. This has a great influence, not merely 

 upon the perspective of its form, but upon the tint of its 

 interior, which in the former case has but l-§° of light, in the 

 latter, at least 1° more. There is a space of nine or ten miles 

 broad all round the inside of the wall, which has, like the wall, 

 5° of light ; and the grey tone is always deepest, and this 

 border most distinct, on the side furthest from the limb. Such 

 remarks may at first appear unimportant, but in fact where we 

 know so little, we cannot tell what may ultimately prove worthy 

 of notice, and suspicions begin to be entertained, as we shall 

 find hereafter, that possibly markings of this nature may not 

 be in all cases invariable. Nothing further of interest is visible 

 in the interior. The wall is terraced on both sides, and is very 

 irregular in height. The highest summit towards the W. rises 

 to about 15,000 feet. I have seen the interior, near the ter- 

 minator in the crescent moon, crossed by a great pyramid of 

 shade, projected probably from this peak. 



On the E. and SE. of Endymion lies a tract of country full 

 of low hills, where a double parallelism may be distinctly 

 traced among all the details — the principal line of direction to 

 SSW. being crossed by another to SE. ; these lines, however, 

 though not far from perpendicular to each other, form but an 

 acute angle to the eye in perspective. 



Atlas (No. 4 in our map), together with its neighbour 

 Hercules (No. 5) form a noble pair. It is to be regretted that 

 the position which they occupy compels us to view them under 

 a great degree of foreshortening, but even as they lie they are 

 worthy of careful study. They afford a striking instance of a 

 peculiar arrangement noted by B. and M. that two considerable 

 ring-mountains, much resembling each other in form, size, 

 depth, steepness, and other particulars, frequently occur in 

 very close proximity, seeming to indicate similar and contem- 

 poraneous formation. Atlas is about fifty-five miles in diameter ; 

 its ring, which on the S. side is a portion of a somewhat 

 smaller circle than on the N., exhibits a lofty central ridge, 

 studded with peaks, and accompanied on either side by terraces, 

 buttresses, ravines, and basins, for a considerable distance. It 

 reaches its greatest height of nearly 11,000 feet on the N. side. 

 The grey interior contains a row of hills, of which the loftiest 

 occupies the centre. It is, perhaps, deserving of record that 



