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



region of contracting crust, and that the heat under the 

 crust sufficed for the vaporisation of a considerable portion 

 of the underlying parts of the moon's substance, we might 

 find an explanation of the great craters like Copernicus, as 

 caused by true volcanic action. The masses of vapour 

 which, according to that view, sought an outlet at craters 

 like Copernicus must have been enormous however. Almost 

 immediately after their escape they would be liquefiedV, and 

 flow down outside the raised mouth of the crater. According 

 to this view we should see, in the floor of the crater, the 

 surface of what had formerly been the glowing nucleus of 

 the moon : the masses near the centre of the floor (in so 

 many cases) might be regarded as, in some instances, the 

 debris left after the great outburst, and in others as the signs 

 of a fresh outburst proceeding from a yet lower level : while 

 the glistening matter which lies all round many of the 

 monster craters would be regarded as the matter which had 

 been poured out during the outburst. 



We need not discuss in this connection the minor phe- 

 nomena of the moon's surface. It seems evident that the 

 rillcs, and all forms of faults observable on the moon's surface, 

 might be expected to result from such processes of contraction 

 as Mallet's theory deals with. 



It is, in fact, the striking features of the moon's disc — 

 those which are seen when she is examined with compara- 

 tively low telescopic powers — which seem to tax most 

 severely every theory which has yet been presented. The 

 clustering craters, which were compared by Galileo to ''eyes 

 upon the peacock's tail," remain unaccounted for hitherto ; 

 and so do the great dark regions called seas. Mallet's 

 theory explains, perhaps, the varieties of level observed in 

 the moon's surface-contour, but the varieties of tint and 

 colour remain seemingly inexplicable. 



There is one feature of the lunar globe which presents 

 itself to us under a wholly changed aspect if we adopt 

 Mallet's theory. I refer to the radiations from certain great 

 craters, and especially those from Tycho, Copernicus, 

 Kepler, and Aristarchus. The reader is doubtless aware 

 that an attempt has been made to explain these radiations 

 by comparing them to the fissures produced when hollow 

 globes are burst by pressure from within. It is in "this way 

 that Mr. Nasmyth accounts for these striking features of the 

 moon's disc. But it has been objected that if such fissures 

 were formed and filled up by matter extruded from the 

 interior of the satellite, it could not but happen that along 

 some portions of the length of each fissure the original 



