Geology. 317 



upon the old idea, of an outer crust and a fluid interior, though 

 it has never yet been proved that at any time in the cooling of a 

 planet would such conditions exist. 



As it would appear impossible, therefore, to account for the 

 lunar craters by a hypothesis of tidal action upon a fluid interior, 

 it must be confessed that their fundamental differences point to 

 an origin unlike any volcanic features of the earth, and we are 

 still far from an understanding of them. 



Under the subject of active lunar craters and river beds, the 

 author describes changes which have been observed in certain 

 lunar craters, which have led him to the belief that volcanic 

 activity has not ceased upon the moon, and that water vapor 

 which immediately turns into clouds of hoar frost is given off 

 from certain craters. In the following chapter it is maintained 

 that the greater brightness of many crater rims and likewise the 

 bright streaks radiating from a number of the principal craters 

 consist of snow. 



In the earlier chapter upon the lunar atmosphere, water, and tem- 

 perature, the author gives good observational grounds for believ 

 ing that an atmosphere exists at the moon's surface, comparable in 

 density to that of the earth at a height of from 40 to 45 miles 

 above the surface. In addition, a haze appears to rise to a 

 height of from three to four miles upon the sunlit side of the 

 moon, but is absent from the unilluminated portion. 



Accepting the facts of observation, the extremely questionable 

 side is in the interpretations given them. It has been shown by 

 Stoney that water vapor would escape with great rapidity from 

 the moon and carbon dioxide somewhat more slowly. It would 

 seem extremely improbable, therefore, that these two gases should 

 at the present time be undergoing elimination from the body of 

 the moon, at such a rate as to constitute even such a rare atmos- 

 phere as is found or permanent snow fields. Such a hypothesis, 

 while explaining with apparent satisfaction the observed enlarge- 

 ment of the white spots of Linne toward lunar sunset and during 

 a lunar eclipse, as due to a sublimation of hoar frost, is peculiarly 

 difficult of application to the system of rays, and both the atmos- 

 phere and rays may consist of some other substances. Until 

 some means is found of proving their nature, some of the sugges- 

 tions offered by Professor Shaler would appear more reasonable. 



Finally in the chapter upon " Vegetation: the Lunar Canals" 

 the writer gives his reasons for believing that a luxuriant vegeta- 

 tion exists upon the moon. The evidence for this extreme view 

 is based entirely upon the darkening of certain areas, and their 

 increase of size during the lunar morning, and their disappear- 

 ance shortly before the time of sunset. 



Since conditions so unfavorable to life exist upon the moon, 

 the hypothesis of vegetation should apparently be the last to be 

 sought as an explanation for these mystifying phenomena. An 

 outline of Professor Shaler's criticisms has already been given, 

 and it may be said in addition that for any form of lunar life to 



