COSMIC PHILOSOPHY 



the lunar atmosphere. The moon is indeed 

 subjected at each rotation to the fierce noontide 

 heat sent from the sun ; but however this may 

 scorch and blister the rocky surface, it can exer- 

 cise but little melting power. An atmosphere, 

 as Mayer has happily observed, is like a valve 

 which lets water run through in one direction, 

 but not in the other. Through an enveloping 

 atmosphere the solar rays easily pierce, but re- 

 turn with difficulty. But from the airless surface 

 of the moon the solar radiance must be imme- 

 diately reflected into space, as from the surface 

 of a polished mirror. Just as on the summits 

 of the Himalayas, where the atmosphere is so 

 rare, the huge snow masses remain through cen- 

 turies unmelted, in spite of the sun's blazing 

 heat ; so on the surface or in the deep abysms 

 of the moon, the air and water once frozen must 

 remain frozen forever. 



We have not yet, however, reached a satis- 

 factory interpretation of the original disappear- 

 ance of the lunar atmosphere. Granting the 

 disappearance of the atmosphere, the mainte- 

 nance of a more than arctic cold in spite of the 

 utmost intensity of solar radiation may readily 

 be admitted. But in this explanation the ab- 

 sence of a surface atmosphere is presupposed 

 rather than accounted for. Yet I have thought 

 it worth while to introduce the case in this 

 way, as we thus get a more vivid impression of 

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