316 Scientific Intelligence. 



recent studies to be mentioned later these views may be too 

 extreme. In regard to the question of vegetable life upon the 

 moon it is very properly stated that other possible explanations 

 should be sought to account for the darkening of certain areas at 

 lunar midday in preference to believing them due to vegetable 

 growth. Against the existence of even vegetable life upon the 

 moon it is urged that no terrestrial life exists upon mountain 

 slopes 20,000 feet or more above the sea under atmospheric and 

 thermometric conditions which must be vastly more favorable 

 than those to be found upon the moon. Furthermore, whatever 

 were the circumstances, as yet unknown, which led to the beginning 

 of life upon this earth, they were evidently of rare occurrence. 

 "The fate of our satellite was probably in large part determined 

 by the ratio between its gravitative force and the energy of the 

 kinetic movement of the gases such as constitute the atmosphere. 

 If that energy had been sufficient to retain them on the satellite, 

 there is no reason, at least so long as the original rotation on its 

 axis continued, why it should not have had the history of a min- 

 iature earth." 



The plates are from photographs in the possession of the 

 Smithsonian Institution and have been taken at the Lick, Paris, 

 and Yerkes Observatories. They are all extremely fine repro- 

 ductions on several different scales selected with reference to the 

 questions discussed in the text and may be considered as a sepa- 

 rate contribution by the Smithsonian Institution to Selenography. 



•' The Moon," by Professor Pickering, although written in a 

 popular manner, is issued as a scientific book intended for an 

 intelligent class of readers who are not astronomers, and it must 

 be criticized on that basis. 



The first three chapters present the commonly accepted views 

 as to the origin of the moon, the data in regard to its distance, 

 rotation, etc., and views arrived at within a few years by the 

 writer and others regarding the density and temperature of a 

 lunar atmosphere. 



In another chapter under the subject of artificial craters, the 

 author cites the blow holes formed on the surface of pots of 

 solidifying slag, and also gives the results of experiments upon 

 paraffin, especially where a pumping motion was given to the 

 still molten portions beneath the solidifying crust to simulate 

 subcrustal tidal waves. By this means he was able to obtain the 

 appearance of lunar craters. It may be remarked, however, that 

 even if the craters were all made during that distant time when 

 the moon still retained an axial revolution faster than its orbital 

 revolution about the earth, a conclusion which Pickering himself 

 apparently does not accept, it would be impossible for a solid 

 crust to maintain such rigidity that the lava communicating with 

 a molten interior could rise and fall to an appreciable extent 

 through tidal action. On the contrary, as in the case of the 

 earth, the whole spheroid would yield. This weakness is pointed 

 out by Professor Shaler. The hypothesis is furthermore based 



