90 ROUGH WAYS MADE SMOOTH. 



whence it would continue to pour out so long as this process 

 of contraction continued. All round the borders of the 

 aperture the crust would be melted, and would continue 

 plastic long after the matter which had filled the fissures and 

 flowed out through them had solidified. Thus there would 

 be formed a wide circular orifice, which would from the be- 

 ginning be considerably above the mean level of the moon's 

 surface, because of the manner in which the liquid matter 

 within had been gathered there by the pressure of the sur- 

 rounding slopes. 1 Moreover, around the orifice, the matter 



1 I have occasion to make some remarks at this stage to avoid 

 possible and (my experience has shown me) not altogether improbable 

 misconception, or even misrepresentation. The theory enunciated 

 above will be regarded by some, who may have read a certain review of 

 my Treatise on the Moon, as totally different from what I have advo- 

 cated in that work, and, furthennore, as a theory which I have borrowed 

 from the aforesaid review. I should not be particularly concerned if I 

 had occasion to modify views I had formerly expressed, since I appre- 

 hend that every active student of science should hope, rather than dread, 

 that as his work proceeds he would form new opinions. But T must 

 point out that earlier in my book I had advocated the theory urged above. 

 After describing the radiations from Tycho and other craters, I proceed 

 as follows in chapter iv. * It appears to me impossible to refer these 

 phenomena to any general cause but the reaction of the moon's interior 

 overcoming the tension of the crust, and to this degree Nasmyth's 

 theory seems correct ; but it appears manifest, also, that the crust 

 cannot have been fractured in the ordinary sense of the word. Since, 

 however, it results from Mallet's investigations that the tension of the 

 crust is called into play in the earlier stages of contraction, and its 

 power to resist contraction in the later stages, in other words, since 

 the crust at first contracts faster than the nucleus, and afterwards not 

 so fast as the nucleus, we may assume that the radiating systems were 

 formed in so early an era that the crust was plastic. And it seems 

 reasonable to conclude that the outflowing matter would retain its 

 liquid condition long enough (the crust itself being intensely hot) to 

 spread widely, a circumstance which would account at once for the 

 breadth of many of the rays, and for the restoration of level to such a 

 degree that no shadows are thrown. It appears probable, also, that not 

 only (which is manifest) were the craters formed later which are seen 

 around and upon the radiations, but that the central crater itself acquired 

 its actual lorm long after the epoch when the rays were formed.' 



