42 Condition of the Moon's Surface. [January, 



once gave countenance to that somewhat bizarre theory ; 

 but he admitted in a letter addressed to myself, that the 

 objection I had based on the circumstances of libration was 

 sufficient to dispose of the theory. The hypothesis that a 

 comet had whisked away the lunar oceans and atmosphere 

 does not need serious refutation ; and it is difficult to see 

 how the theory that lunar seas ar>d lunar air have been 

 solidified by intense cold can be maintained in presence of 

 the fact that experiments made with the Rosse mirror in- 

 dicate great intensity of heat in the substance of those 

 parts of the moon which have been exposed to the full heat 

 of the sun during the long lunar day. 



If there ever existed a lunar atmosphere and lunar seas, 

 then Prof. Frankland's theory seems the only available 

 means of accounting for their disappearance. Accordingly 

 we must recognise the extreme interest and importance of 

 telescopic researches directed to the inquiry, whether any 

 features of the moon's surface indicate the action of pro- 

 cesses of weathering, whether the beds of lunar rivers can 

 anywhere be traced, whether the shores of lunar seas can be 

 recognised by any of those features which exist round the 

 coast-lines of our own shores. 



One circumstance may be remarked in passing. If the 

 multitudinous lunar craters were formed before the withdrawal 

 of lunar water and air into the moon's interior, it is some- 

 what remarkable that the only terrestrial features which 

 can be in any way compared with them should be found in 

 regions of the earth which geologists regard as among those 

 which certainly have not been exposed to denudation by the 

 action of water. Thus Sir John Herschel, speaking of the 

 extinct volcanoes of the Puy de Dome, remarks that here 

 the observer sees " a magnificent series of volcanic cones, 

 fields of ashes, streams of lava, and basaltic terraces or 

 platforms, proving the volcanic action to have been continued 

 for countless ages before the present surface of the earth 

 was formed ; here can be seen a configuration of surface 

 quite resembling what telescopes show in the most volcanic 

 districts of the moon ; for half the moon's face is covered 

 with unmistakable craters of extinct volcanoes." But 

 Lyell, speaking of the same volcanic chains, describes them 

 as regions "where the eruption of volcanic matter has taken 

 place in the open air, and where the surface has never since 

 been subjected to great aqueous denudation." If all the 

 craters on the moon belonged to one epoch, or even to one 

 era, we might regard them as produced during the with- 

 drawal of the lunar oceans within the still heated substance 



