THE MOON AND LUNAR PHENOMENA. 83 



waxes. Here we have a clear indication of elevations. The portions of the dark part of 

 the moon which thus stand out into the light are plainly eminences, their summits catching 



the illumination of the sun's rajs before the adjacent plains 

 below, exactly as the summit of Mont Blanc is enlightened 

 whilst the valley of Chamouni at his foot is in darkness. 

 But we have further evidence of the existence of lunar 

 mountains and valleys. It is obtained from the fact that 

 what are considered elevations project shadows in a direction 

 opposite to that of the sun, while the depressions are dark 

 on the side nearest to him, and illuminated on the opposite 

 one. These shadovts are observed to shorten as the sun's 

 rays become more direct, and they proportionably lengthen 

 as his beams fall more obliquely. This is so answerable to 

 the phenomena which the action of sunlight upon hills 

 and valleys will yield, and so consistent with what takes 

 place on our own globe, as to place the conclusion of the 

 moon's irregularity of surface beyond all doubt. 

 A remarkable appearance may perhaps be explained by the inequalities of the lunar 

 superficies. It has repeatedly been observed in the case of an occultation, that a star has 

 advanced actually upon and within the edge of the moon's disk before its disappearance 

 behind the lunar body. Captain Smyth remarks : " October 15, 1829. I saw Aldebaran 

 approach the bright limb of the moon very steadily. It kept the same steady line to 

 about f of a minute inside the lunar disk, where it remained, as precisely as I could 

 estimate, two seconds and a quarter, when it suddenly vanished. In this there could be 

 no mistake, because I clearly saw the bright line of the moon outside the star, as did 

 Dr. Lee, who was with me." The same accurate observer, on the 18th of December 1831, 

 saw the star 119 Tauri pass over the disk, and disappear between two protuberances on 

 the moon's bright edge ; and on the same night Sir James South observed the star 120 

 Tauri accomplish the same achievement. Sir John Herschel never witnessed this 

 singular phenomenon, but it rests on the best evidence, and has been usually considered 

 an optical illusion, the cause of which is obscure. The latter, however, throws out the 

 conjecture that possibly a star may shine on such occasions through deep fissures in the sub- 

 stance of the moon. The rim being jagged and uneven, owing to elevations and depressions, 

 a star, in the process of occultation, may obviously pass into one of the cavities, and be 

 actually within the disk before its complete obscuration by the general body of the moon. 

 We have now large and accurate maps of the lunar superficies. The average aspect of 

 our attendant planet is minutely exhibited in the map of MM. Baer and Madler of 

 Berlin, which has a diameter of three feet. A reduction of this will appear in connection 

 with the present work. Prominent lunar peculiarities have their respective names, taken 

 from those of places on the earth, or from eminent men, chiefly astronomers, as Plato, 

 Tycho, Keppler, and the Apennines. 



The dark and dusky patches apparent upon the moon's face, which remained constantly 

 obscure, were supposed by the early observers to be seas, owing to water reflecting less 

 light than land. Hence the names applied to them, as Mare Tranquillitatis, Mare 

 Imbrium, and Oceanus Procellarum, which are still retained. The supposition, 

 however, of any quantity of fluid at the surface is plainly precluded by the fact of 

 there being little or no atmosphere. These parts have all the appearance of being 

 enormous spaces of lunar depression, their obscurity arising from being below the general 

 level. They are not, however, depressed uniformly. The intermingling of light and 

 dark shades, with the occurrence of districts as luminous as any portion of the lunar disk, 



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