LUNAR PHENOMENA. 387 



the remarkable appearances on the surface of the moon, chapter 

 in connexion with the Hght they seemed to throw on tiio -^•'^^'^'^- 

 study of geology, and he had procured some powerful Application 

 telescopes in order to observe them more particularly, in "^ ^^^'^^°v^ 

 addition to liiniself constructing one of great power, by 

 the aid of which many of his most valuable observations 

 have been made. He exhibited a variety of drawings 

 which have been taken by himself from what he observed. 

 The largest was a map, on a great scale, of the entire 

 lunar surface, on which was strikingly depicted the pe- 

 culiar nature of its surface, crowded with craterlike cups, 

 in some places so close as to overlie each other, and as it 

 were elbow each other out of the way. Other views in- 

 cluded various portions of the surface which had been se- 

 lected for more minute study. These representations have concinsiona 

 all been drawn from observations made in the most fa- established 

 vourable circumstances, and with great care, the result 

 of which is, that the conclusion is even stronger than in 

 the case of the earth, that it was once wholly in a molten 

 condition. The central cones seen in three-fourths of 

 the lunar mountains show plainly that the formation 

 observed is volcanic. These cones in the case of terres- 

 trial volcanoes are the result of the expiring action of 

 the volcano, after the eruptive energy has ceased to be 

 able to project the molten mass over the sides of the 

 crater, and the same thing has taken place in the moon. 

 Many of its volcanoes are 60 or 70 miles across the SizcoflunaT 

 crater — many times larger than those on the earth. But " "'^ 

 it is just because it is a very small body that it has very 

 large volcanoes. The force of gravitation is much less at 

 the moon, and hence the ejective force is able to expel 

 greater masses, and to act more uninterruptedly. The 

 crater of Etna is but a spot compared with some of those 

 in the moon. The proportional size of these lunar craters 

 may indeed be described as bearing in some degree an 

 inverse ratio to the relative size of the earth and moon. 

 The smallness of the moon, its mass being to that of 

 the earth as 1 to 64, and its surface as 1 to 16, is also 



