ON SOME VOLCANIC FORMATIONS OF THE MOON. 469 



-which lies off in the direction of Gambart, and in a larger one to the north of 

 Copernicus, the circular zone around the central cavity is broader, clearer, and, 

 towards the outside, paler. Half a century ago, Gruithuisen discovered and re- 

 peatedly observed a similar object southward from the crater Hyginus. In this, 

 also, there was to be seen a tiny clear white crater in the middle of a roundish, 

 broad, grey patch. This tiny crater is in existence at the present day, and, in- 

 deed, is placed on the flat top of a very low ruined circular wall; but, in the 

 twenty years over which my observations have extended, I have never been able 

 to see it as a white speck. Neither do I find in Schmidt any mention of this cir- 

 cumstance. Now since Gruithuisen's observations are indisputable, it must be 

 concluded that that small crater has grown darker in the course of years. From 

 the agreement in the cases cited, but specially also from my rigorous examination 

 of the larger crater on the southwest of Theophilus, we must conclude that the 

 dark material which surrounds the bright shining crater was ejected from it. We 

 may look upon it as a species of lava, which becomes bleached in time, and then 

 -assumes that appearance which we perceive in many so-called "light-surrounded '» 

 craters. That the formation of the ring of dark material or, if you will, the 

 eruption, together with the aforesaid crater southwest of Theophilus, belong to 

 recent times is proved by the circumstance that this dark patch, which is so ob- 

 vious, and even appears in one of Rutherfurd's lunar photographs, was seen 

 neither by Lohrmann or Madler in the first third of our century. The conclu- 

 sion that it did not then exist receives complete confirmation from the observa- 

 tions of Gruithuisen. I have thoroughly examined the comprehensive journals 

 of this accurate and sharp-eyed selenographer, and have found that, on several 

 occasions, he specially explored the locality in which to-day that dark patch is so 

 plainly to be seen, without, however, having perceived it, although it was exactly 

 -^uch patches that Gruithuisen eagerly sought after. 



The intimate connection between the dark material and the bright crater in 

 its middle, as well as the inference that this mass was cast out lava-like from the 

 crater at a time long subsequent to its formation, I have proved from several 

 years' study of a similar crater which has been mentioned by no previous observ- 

 er. In this case, thanks to the configuration of the ground, the proof is so con- 

 vincing, that it could hardly be greater had it been afforded by a terrestrial vol- 

 cano directly accessible to our ascent. 



The object, concerning which I have now to report, lies in the inside of the 

 great walled plain Alphonsus. Madler has there described, out of several others 

 in the neighborhood of the slope of the east wall, a dark triangular spot, which at 

 at full Moon, when only little of the walls of Alphonsus is to be seen, stands out 

 with uncommon distinctness on account of its dark color and its regular form, 

 -According to Madler, this spot was only to be seen when the Moon stood high 

 over the lunal landscape referred to, and was neither sunk nor raised. The cir- 

 cumstance that, during my observations in the interior of this dark spot, I once 

 spied a bright point exactly similar to the central craters' in the above described 



VI-30 



