436 Lunar Sketches. 



itself. Curious as to chronological sequence." It is just possi- 

 ble, however, that some process affecting the reflective power 

 of the surface may at this time be working here ; for B. and M. 

 say that this crater is cc in Full Moon not very distinct : we 

 only see a very undefined faint light spot in a vicinity almost 

 equally luminous." No mention is made of any darker portions, 

 or of their being so situated as to indicate the position of the 

 ring, and the description certainly does not tally well with 

 present appearances. This is a peculiarly suitable -spot for 

 examining the question whether the Full Moon markings are 

 unchangeable. Fixity, of course, if established by a long* 

 course of observation here, or anywhere else, would be no 

 argument for its universal prevalence, since a state of quies- 

 cence in this respect might be attained at very different epochs 

 in different regions ; but should the reverse be clearly ascer- 

 tained in a single well-marked, even though minute, case, it 

 need not be mentioned that one distinct, incontrovertible 

 affirmative weighs down any number of negative instances, and 

 merely throws back the date of their changes to a pre-historic 

 period. Sketches at the telescope, in lamp-black, Indian ink, 

 or sepia, if really careful and trustworthy, would be very valu- 

 able, and in some hands made with much facility. There is 

 this great convenience attending them — that the ground- 

 mai'kings they represent are much less fugitive than the actual 

 shadows indicating the relief of the surface, and that many 

 more opportunities are afforded in each succeeding lunation 

 for the production of such designs, than of delineations con- 

 taining ordinary effects of light and shade. And hence, by 

 the way, as regards that great desidei*atum, a good map of the 

 Full Moon, much more might be effected in a corresponding 

 time than in the case of the details of actual relief. Even a 

 single observer, possessed at once of accuracy of eye and 

 artistic training of hand, might make a great advance in the 

 right direction. To such an one (but more than one, we trust, 

 may be found) the experience of the Astronomer Royal for 

 Scotland (Piazzi Smyth), himself eminent alike as astronomer 

 and artist, may be acceptable. In sketching the Mare Crisium, 

 at the request of the former Lunar Committee of the British 

 Association, he found oil colours much preferable to water for 

 producing a likeness under the required conditions. It need 

 scarcely be added that a large scale would be required to follow 

 his example with success. But to return to our immediate 

 subject : 



Sinus JEsi 'num. — 1864. Dec. G. 5A-in. achr. " The entrance 

 of this dark plain is magnificent, and the curved banks lying 

 obliquely over one another, but with a general parallelism to 

 the mountain boundary, look like the rolliug waves of some 



