THE PAST HISTORY OF OUR MOON. 83 



to the difficulty of interpreting the problems she presents to 

 us. For we have manifestly to differentiate between the 

 effects due to the moon's relative smallnesson the one hand, 

 and those due to her great age on the other. If we could 

 believe the moon to be an orb which simply represents the 

 condition to which our earth will one day attain, we could 

 study her peculiarities of appearance with some hope of 

 understanding how they had been brought about, as well as 

 of learning from such study the future history of our own 

 earth. But clearly the moon has had another history than 

 our earth. Her relative smallness has led to relations such 

 as the earth never has presented and never will present. If 

 our earth is, as astronomers and physicists believe, to grow 

 dead and cold, all life perishing from her surface, it is 

 tolerably clear, from what we already know of her history, 

 that the appearance she will present in her decrepitude will 

 be utterly unlike that presented by the moon. Grant that 

 after the lapse of enormous time- intervals the oceans now 

 existing on the earth will be withdrawn beneath her solid 

 crust, and even (which seems incredible) that at a more 

 distant future the atmosphere now surrounding her will have 

 become greatly reduced in quantity, either by similar with- 

 drawal or in any other manner, yet the surface of the earth 

 would present few features of resemblance to that of the moon* 

 Viewed from the distance at which we view the moon, 

 there would be few crateriform mountains indeed compared 

 with those on the moon ; those visible would be small by 

 comparison with lunar craters even of medium dimensions ; 

 and the radiated regions seen on the moon's surface would 

 have no discernible counterpart on the surface of the earth. 

 The only features of resemblance, under ^the imagined 

 conditions, would be probably the partially flat sea bottoms 

 (though these would bear a different proportion to the 

 more elevated regions) and the mountain ranges, the only 

 terrestrial features of volcanic disturbance which would be 

 relatively more important than their lunar counterparts. 

 I do not purpose, however, to discuss the probable, future 



