400 FROM NEBULA TO NEBULA 



cannot arise directly from a crystalline surf ace, but must 

 first pass through the detached liquid stage. Until a 

 blanket of snow is reduced to at least the condition of a 

 very shallow slush, it will never give off '^ steam ". On 

 ,J;he moon there is ^^indee4 j( ^p. ii^n>jens,e r^n^Q^n|t p^ tawing 

 $oing on during the day, but the %id r ^ft% t; w4eTje { ^ im- 

 $iediate contact ^wit^ c^ysjt.aJiic ice, preseryep it^Uqui4ity 

 and seeps down into and through the . porous, spongy 

 snow underneath. Not only this, but such little vapor as 

 does form obviously becomes quickly frosted by the "air" 

 and settles immediately. Either of these explanations 

 alone, or at .least the two acting combinedly, sufficiently 

 explain the anomaly of the moon's cloudlessness as well 

 as the minor fact that the snow peaks are oftentimes per- 

 ceptibly whiter than their lower, water-soaked slopes. 



ALBEDO. Were the surface of the moon perfectly 

 smooth and covered with new-fallen snow, her albedo (i. 

 e., her general brightness) would far surpass the actu- 

 ality. The deficiency is due to several things, for in- 

 stance ; first, the strong shadows thrown upon her by her 

 own hills, secondly, the slushiness of certain regions, 

 thirdly, the seaming and corrugating of her snow sur- 

 faces due to repeated sopping and irregular settling, and, 

 finally, the darkness of her maria. Paradoxically, her 

 dark side is intrinsically whiter than her illuminated face, 

 for then her frozen-over maria and pools are universally 

 covered over by fresh sprinkles of snow. 



ABSENCE OF ATMOSPHERIC REFRACTION. This pecu- 

 liarity has heretofore very properly been attributed to a 

 paucity of air ; some saying that this was carried off by a 

 passing comet; some that it was probably absorbed by 

 porous volcanic rocks ; some that it may have been drawn 

 into the moon's interior by causes unknown ; some that its 

 lighter molecules escaped into space, and still others that 

 the satellite never had any more atmosphere than it has 

 just now. As the reader has already learned, my own 

 view is, that it has been almost totally absorbed by union 

 with the water in the manufacture of snow crystals. 



