444 Obscuration of a Lunar Crater. 



OBSCURATION OF A LUNAR CRATER. 



BY W. R. BIRT, F.R.A.S. 



Although the disappearance of a crater on the moon's surface 

 may tiot possess such an amount of interest as the sudden out- 

 break of a star, or a shower of meteors, as the earth plunges 

 into a congeries of minute bodies, circulating around the sun — • 

 the two leading astronomical facts of the year 1866 — yet, as 

 giving us, inhabitants of the earth, intelligence that some 

 change is taking place on the surface of our nearest celestial 

 neighbour, every circumstance indicating that a portion of 

 that surface is not in precisely the same condition as it was a 

 few months since, must be regarded as extremely interesting ; 

 especially when we consider that " change " is the principal 

 means by which we become acquainted, in a more intimate 

 manner, with the physical constitution of bodies. 



On the extensive lunar plain known as the Mare Serenitatis 

 (Intellectual Observer, vol. viii., p. 292) stands a crater 

 named « Linne/'in W. longitude, 1 1° 32' 28" and N. latitude, 

 27° 47' 13". The crater, which is 5*6 English miles in diameter, 

 is situated upon one of those low ridges, described by Mr. 

 Webb, and is perfectly isolated, according to our maps; neither 

 Lohrmann, nor B. and M. give any other in its locality, nor 

 does Schroter ; but it is not a little remarkable, that when ob- 

 serving the Mare Serenitatis, on the 5th of November, 1788, he 

 saw in the place of " Linne •" a dark diffused, but not sharply 

 bordered spot, of not more than 4° of light. Lohrmann saw 

 the crater very distinctly, and measured its position. B. and M. 

 also saw it distinctly, and made seven measurements for posi- 

 tion. The indefatigable astronomer Herr Julius Schmidt, the 

 Director of the Observatory at Athens, who has devoted much 

 of his attention to the study of the lunar surface, for more than 

 a quarter of a century, has known the crater since the year 

 1841, and never found it difficult until October, 1866, when 

 instead of seeing the well known object, he could perceive 

 nothing but a glimmer, a small whitish cloud in its place, and 

 this was repeated in November, so that for upwards of one 

 month, this somewhat conspicuous object must have been 

 under a cloud. 



It is hardly likely that this phenomenon can be any other 

 than a concealment, and it would be interesting to know, if 

 such were the case, when Schroter recorded the dark Bpot in 

 its place. This is very probable, as the crater is distinctly 

 shown on the ridge in Ricicoli's map, published 1653. The 

 most recent observations, December, 1866, show that the 



