Physiognomy of the MoorCs Surface. 4S 



we should say that they occupied about one-eighth of the sur- 

 face, whilst in the other they occupy one-fourth. There are cer- 

 tain districts, as for example one situated round the large spot 

 called Tycho^ where the surface is so studded with these kinds 

 of appearances that it is impossible to find a level which may 

 serve as a base by which to measure the neighbouring heights. 

 Innumerable circular hollows of smaller dimensions occur up- 

 on the moon's surface. These may be distinguished into craters 

 and pits ; confining this latter term to those small cavities con- 

 nected with which we do not perceive an elevated zone, either 

 because none really exist, or because the size is so inconsider- 

 able that it cannot be recognised. In the craters, central moun- 

 tains are perceived, and by an attentive examination often a 

 smaller crater may be found placed within the large one. 

 Sometimes, again, two are found so closely approximated that a 

 part of their boundaries is common to both, and it also some- 

 times happens that, at the point of contact, the zone is inter- 

 rupted, and there is a passage which unites the two interiors. 

 There are circles of mountains which are in part margins of 

 craters ; and, lastly, we may observe that very small craters 

 may be distinguished on the moon's surface, even on those por- 

 tions which are most uniform. 



When the craters are situated at a considerable distance from 

 the limits of the light, and when they are not very steep, their 

 depth cannot be very accurately ascertained. It follows, that, 

 when under a direct light, many of them present luminous and 

 bright spots ; whilst on the other hand a certain number of great 

 annular mountains are recognised with great difficulty, and some 

 not at all. Small craters are also seen with much difficulty near 

 the margin of the moon; their rim can then be seen only in profile; 

 their far side is hid as well as the interior, and it is often very 

 difficult to determine whether we are examininc: a mountain or 

 a crater. It sometimes even happens, that in regions much 

 nearer the centre, a crater exists where we had supposed there 

 was a mountain, and a mountain where we had concluded there 

 was a crater. 



It hence results, that it is only by confining ourselves to the 

 examination of regions which are not farther removed from the 

 middle of the moon than 45° or 50", that we can satisfactorily 



