THE MOON'S HISTORY. 69 



in contact with it, the moon coursed around our globe, the 

 period of its revolution being shorter to such an extent 

 that the satellite completed its circuit in the same time as 

 the earth required for one turn round its axis. We cannot 

 indeed say that the earth and the moon in this wonderful 

 condition bore much resemblance to the earth and the 

 moon as we now know them. Even if the bodies had by 

 that time assumed the globular form, it seems certain that 

 they must have been composed of wholly or partially 

 molten material, very unlike the rigid globes that the 

 earth and moon now appear to be. 



Up to this point our reasoning has been based on the 

 results of mathematical investigation. It is characteristic 

 of such investigations that they leave no loop-hole for 

 error when the conditions have been properly stated. We 

 are naturally anxious to push the research one step farther 

 and to learn how it was that the moon happened to 

 be found in such a remarkable situation in the immediate 

 vicinity of the earth. At this critical stage mathe- 

 matics seems to withhold its guidance, but at the same 

 time does not forbid an attempt to penetrate the mystery 

 of the moon's origin. The reasoning that has hitherto 

 guided our inquiries becomes no longer available, and any- 

 thing which we can add to the sketch already given of 

 earth-moon history must therefore be received on authority 

 possessing a different value from that which has charac- 

 terized the former stages of the inquiry. It is, how- 

 ever, almost impossible to resist the conjecture which 

 naturally arises when we endeavour to form a mental 

 picture of the condition of the earth and moon at this 

 most interesting epoch. 



