OBSERVATIONS OF LUNAR OBJECTS. 95 



tion fair, -with boiling. * * Plato is a grand and striking sight. Tint of 

 floor medium. More than half the floor in shadow. Terminator just in- 

 cluding the W. rim. The rim of the crater on the N. exterior slope finely 

 seen. In three parts the rim appeared hrolcen down to Uvd of floor — close 

 to m, opposite to c, and nearly so at W. II E"/'^ [the hreaks at m and op- 

 posite c are in the line of the well-known fault crossing Plato from N.W. 

 to S.E.]. ^ was throwing a long spire of shadow the full length of the 

 floor at 11" 40°'. That part of the floor contiguous to the W. and S.W. 

 rim was deeply shaded, with streaks of shade running towards the centre of 

 the floor. Between the break near c and the shadow of '( a straight shading 

 as of a narrow valley was weU seen. [These shadings appear to be roughly 

 coincident with the dark spaces on the floor as seen under high illumination, 

 the straight shading being, as Mr. Pratt suggests, between the "sector" and 

 the E. arm of the " trident." Is there really a valley here running inta 

 the central depression between 1 and 4, seen by Mr. Elger in January, 1870, 

 and observed much earlier by Schrbter?] Between these shadings and the 

 shadow of the E. rim were three roundish lighter regions, the higher parts of 

 the floor giving the appearance of a strongly marked convexity." 



" A strong suspicion arises that the apparently higher portions of the 

 floor are the light streaJcs usually seen, and the highest parts are spots 1, 17 

 and 5." Mr. Pratt further suggests that the light streaks are coincident 

 with formations analogous to " spurs "' from the chief centres of the residual 

 activity on the floor. 



It is not a little remarkable that on the occasion of such a very favoiirable 

 oblique illumination the craterlets 1 and 17 should not have been detected 

 by Mr. Pratt ; both have raised rims of the nature of true volcanic cones, 

 and 1 has been seen, and I believe 17 also, with interior shadows and bright 

 interiors facing the sun. Mr. Pratt does not appear to have seen even the 

 remotest semblance of a shadow. The spots properlg so called do not appear 

 generally iintil the sun has attained an altitude of 20°. If craterlets are 

 recorded as spots earlier, it is probably in consequence of bad definition 

 confusing the crater-form appearance. Is it possible that on the two 

 occasions mentioned by Mr. Pratt, Oct. 17 and Nov. 1, the craterlets 1, 17, 

 3, and 4 were by some means concecded? As regards Nov. 1, the observation 

 of the crater-cones as the shadows gradually recede from E. to W. is very 

 frequent ; indeed the surface of Plato as it just emerges out of night ajjpears 

 to be in a very different state to what it is about mid-day ; objects are much 

 sharper, and it is difficult to conceive of any agency so affecting such visible 

 objects as to render them invisible at a time when they are generally most 

 conspicuous. So far as contemporaneous observations are capable of throwing 

 light on this phenomenon, three spots only were recorded on the same even- 

 ing ; No. 1 by Mr. Elger, who noticed it from 9'' to 9** S", near the shadow 

 of the summit of the middle peak of the W. wall, three hours later than 

 Mr. Pratt's observation. Mr. Gledhill at 6"*, same as Mr. Pratt, says, " Moon 

 so low and air so thick that very little light from moon can reach us ;" he 

 says also, " I sec 3 as double elevated cones [i.e. 3 and 30]. No other objects 

 can be seen." Mr. Neison, 5.10 to 8.15 [probably 8.10 to 8.15] succeeded 

 in seeing 3 only, which he records as very faint. He does not give the state 

 of the atmosphere as to definition ; but from his remarking that " a deep cleft 

 in west edge of wall was very distinctly seen," I should suppose that it was 

 pretty good. Taking the four sets of observations it would appear that at 

 sunrise on Plato Nov. 1, 1870, some ageney was in operation capable of 

 concealing the craterlets ; and combining these observations with those of 



