110 PHOTOGRAPHY OF THE LUNAR SURFACE. 



themselves to the study of those concerning the existence of which 

 there can be no doubt. Their efforts have been directed to obtain exact 

 images of them and to compare their present state with previous 

 descriptions. In the absence of precise ideas in regard to the physical 

 constitution of the moon, they flattered themselves to have encountered 

 traces of an evolution as active as that of which our globe is the seat; 

 of having seen manifestations of the circulation of water, of vegeta- 

 tion, and of life. This hope appeared at first justified by the results. 

 Discrepancies, which were revealed in large numbers, were interpreted 

 as indications of probable changes. We shall briefly point out those 

 which appear most worthy of attention. 



At the bottom of the gulf, situated between the Caucasus and the 

 Lunar Alps, we find Oassini, a crater 60 kilometers in diameter, whose 

 ramparts rise 1,000 meters above the surrounding plain and above the 

 interior floor. This formation, which the smallest telescope at the 

 present day clearly reveals, is wanting on the maps of Hevelius and of 

 Eiccioli, who have represented many other objects in its neighborhood 

 much less visible. It was first mapped in 1680 by Dominique Cassini, 

 the author justly celebrated for the discovery of the laws of libration. 



At the present day we see in the southern part of the " Sea of Bains," 1 

 two twin craters very close together nearly equal in every respect, 

 having a diameter of 20 kilometers and a depth of more than 1,000 

 meters. These two have been named Helicon and Leverrier. Hevelius 

 and Eiccioli again agree in mapping at this point only a single circle. 



Cichus, a crater of a considerable circumference, forming part of the 

 southern border of the " Sea of Clouds," 2 has a paracitic crater which 

 interrupts the regularity of its contour. On three different maps of 

 Schroter, made between 1784 and 1802, this object is represented rela- 

 tively one-half as large as it now appears. 



In the same region all modern photographs show in the neighborhood 

 of the crater " Hell" a very bright spot, in which are assembled several 

 craters. Cassini assures us that he observed this region covered by a 

 temporary white cloud, which disappeared to give rise to a new formation. 



We actually see in the dark part of the " Sea of Clouds " a round 

 bright spot called Alpetragius d., about 20 kilometers in diameter, with- 

 out any appreciable relief. Madler represents at this point a crater 8 

 kilometers in diameter, of which not the least trace can at present be 

 found. 



In the middle of the " Sea of Fertility" 3 there arise a pair of craters 

 named after Messier. They attract attention by the straight white 

 bifurcated trail which extends from them in an easterly direction, and 

 resembles in a most remarkable manner the tail of a comet. These 

 two circles, so close together, appeared exactly similiar to Beer and 

 Madler. Their attention having been attracted to this point by a 

 remark of Schroter, they submitted them to a continuous examination 



*Mare Imbrium. 2 Mare Nubium. ' 3 Mare Fcucunditatia. 



