A NEW CRATER IN THE MOON. 103 



in such sort as either to throw shadows or to lie in shadow 

 when surrounding regions are in sunlight. But when the 

 moon approaches her full illumination, the radiating regions 

 come into view, as bright streaks bright even on the light- 

 tinted lunar uplands. A mighty system of rays can be seen 

 extending from the great crater Tycho in all directions. 

 Other systems, scarcely less wonderful, extend from the 

 battlemented crater, Copernicus, the brilliant Aristarchus, 

 and the solitary Kepler. One ray from Tycho can be 

 traced round nearly an entire hemisphere of the moon's 

 surface. It is specially noteworthy of this great ray that, 

 where it crosses the lunar Sea of Serenity, that great plain 

 seems to be divided as by a sort of ridge line, the slope of 

 the plain from either side of the ray's track being clearly 

 discernible when the moon is near her first quarter. 



What are these mysterious ray systems ? How are we to 

 explain the circumstance that though only the most tremen- 

 dous forces seem competent to account for bands such as 

 these, many miles broad and many hundreds of miles in 

 length, there are yet none of the usual signs of the action of 

 volcanic forces ? If mighty rifts had been formed in the 

 moon's crust by the outbursting action of a hot nucleus, or 

 through the contraction of the crust on an unyielding 

 nucleus (for the effect would be the same in either case), we 

 should scarcely expect to find that after such rifts had formed 

 no signs of any difference of level would appear. If lava 

 flowed out all along the rift, one would imagine that it would 

 form a long dyke which would throw an obvious shadow, 

 except under full solar illumination. If the rift were not 

 filled with lava, the bottom of the rift would certainly remain 

 in shadow long after the surrounding region was illuminated. 

 That lava should exactly fill the rift along its entire length 

 seems incredible. This might happen by a strange chance 

 in the case of a single rift, but not with all the rifts of a ra- 

 diating system, still less with all the rifts of all the radi- 

 ating systems. Yet I believe that neither astronomers 

 nor geologists can form any other opinion respecting these. 



