54 The Lunar Arctic Region. 



branches off from the S.W. part of the wall, and runs along 

 the W. side of the interior, leaving a very narrow, but gradually- 

 widening trench between itself and the main wall, and vanish- 

 ing in a most minute point : it is less conspicuous for height, 

 not exceeding 1400 feet, than for sharpness of contour. Schro- 

 ter has not represented it very well. The interior is but 

 slightly uneven : it contains a small but deep crater, Posidonius 

 A, the definition of which, as of most of the objects connected 

 with this great ring, is peculiarly clear. It is more remarkable 

 in another point of view. 1 791, November 1, Schroter saw and 

 represented it as a pretty flat depression or ring-plain, its interior 

 being merely grey, without any dark shadow, while seven 

 other small craters in the immediate vicinity had a very obvious 

 black shade within. On referring to a previous drawing, made 

 1788, August 19, he found that he had then seen it as an or- 

 dinary crater, and so it appeared on the following evening 

 (1791, November 2), as a pretty deep hollow with a black 

 shadow like its neighbours, although of course under a con- 

 siderably greater angle of illumination than twenty-four hours 

 before. Hence he concluded that on November 1, the shadow, 

 which must have not merely existed but been more exten- 

 sive, had been concealed by the intervention of something 

 giving the crater a grey aspect ; and this again would infer 

 the presence of a lunar atmosphere, however subtle and limited 

 in depth. The valley of Lilienthal in which he lived would 

 present, he thought, a similar aspect, if similarly viewed, when 

 during the month of June the moors were set on fire for agri- 

 cultural purposes. As an analogous indication he remarks 

 that the careful observer will often perceive, in localities in the 

 Moon where mountains have never been noticed, something 

 like very flat hillocks that seem to come into existence under 

 the eye, and again disappear : and if they should be caught up 

 on future occasions, are always found in some altered form. 

 Some such minute variations he noted in the interior level of 

 Posidonius, and thought it possible that they might be connected 

 with the assembled habitations of intelligent beings, "who there, 

 as well as we here, praise the goodness and wisdom of their 

 Maker : at least this hypothetical supposition is not unworthy of 

 the greatness of the Creator of the universe ; and appearances 

 which vary in such manifold ways admit of being very well recon- 

 ciled with it.-"* Such changes, however, he admits, might be 

 equally referred to clouds, or rather their analogues. And if so, 



* It is worthy of note that Herschel I. in his early days, when alone he seems 

 to have paid attention to the moon, expressed his conviction as to " the great 

 probability, not to say almost absolute certainty, of her being inhabited." This 

 impression appears, however, to have been merely the result of her general 

 aspect. 



