Mare Vaporum and the Lunar Clefts. 5S 



groove. Its adoption, however, by ourselves, though sanc- 

 tioned by some great names, does not seem free from objection, 

 on account of the existence of a similar, but by no means equi- 

 valent English word, the derivation of which, from the Latin, 

 rivulus, and its meaning as given by Johnson, " a small brook, 

 a little streamlet/' refer unequivocally to the presence of water. 

 It is, however, frequently easier to find a fault than to mend it ; 

 and in the present instance {furrow having been rejected, on 

 high authority, as not sufficiently comprehensive), if the em- 

 ployment of the term cleft is suggested, it need only be looked 

 upon as a provisional arrangement, till something more appro- 

 priate has been brought forward in its stead. It would indeed 

 be a gain to selenography, if the whole subject of lunar ter- 

 minology were to undergo a careful revision at the hands of 

 those whose geological as well as astronomical acquirements- 

 would enable them to frame such a nomenclature as would 

 command universal acceptance. 



But, to proceed from the name, to the objects which it 

 designates. The lunar clefts are characterized by B. and M. 

 as very narrow and long depressions either in a straight or 

 moderately curved direction ; occasionally serpentine or hooked 

 in form : with very steep,* parallel sides, and usually without 

 any external rampart : in Full Moon they appear as delicate 

 white lines ; near the terminator usually as black ones, as we 

 perceive only the shaded interior. They sometimes pass 

 through or close by small craters, or come to an end in them ; 

 at others they lie isolated in level surfaces, without any marked 

 termination; in fact, one of their frequent characteristics is 

 this want of apparent object, as we might speak with reference 

 to the handywork of intelligent beings. They are frequently 

 hemmed in by mountains, but do not appear to run straight 

 over them ; occasionally they are found to unite like veins, and 

 even to intersect one another. Their individual breadth varies- 

 but little ; if there is any enlargement, it is somewhere in the 

 middle, never at the end [rather an inattentive assertion, by 

 the way] . They occur in every kind of surface, excepting on 

 lofty summits, or in the centre of the great plains ; being of 

 course less distinguishable towards the limb. A few of them 

 are only from 9 to 14 miles in length ; the generality 45 to 

 70; some, again, reach a maximum of 115 to 140 m. : their 

 breadth is in places not inconsiderable, a mile or upwards ; but 

 they may be traced down to \ of that size.f Connecting links 

 with other formations may often be perceived : the enlarge- 

 ments occasionally noticed take the form of longish craters, or 

 if these are frequent, the whole cleft appears almost like a chain 



* Schmidt considers them not extremely steep. 



t Schmidt gives their depth from 100 yards to \ mile. 



