THE MOON IN MASQUERADE 123 



the snowfall radius to, say, a thousand feet, for we 

 must, not overlook the quiescent nature of the moon's 

 atmosphere, on account of which the snows spread but 

 slightly. 



Now until the water in the cistern has evaporated 

 down to the level of the first tread (beginning from the 

 top) the falling snow cannot gain a footing on the 

 water surface, but must settle only on the brim and 

 beyond. Us depth gradually decreasing to our pre- 

 scribed snowfall limit. A yard's depth of water, area 

 for area, being equivalent, to ten times that heighth of 

 snow, we shall have gained by the evaporation of the 

 first yard a snow rampart all around the brim, say 

 five feet high, .sloping gradually backward to nothing. 

 I have just stated that the snow could settle only on 

 the brim, but this is not precisely true, for we must 

 not forget, the tallest, of the granite blocks, which for 

 one third of this time has been exposed. It too is 

 capped with snow, say to the depth of two feet. 



Now suppose another equal period to elapse, and 

 the cistern's depth reduced to the level of the second 

 tread. This time the brim's cap has increased by 

 another live feet in heighth, and the slope behind it in 

 slightly less proportion, because the rising xnow brim 

 //r/.s- /// a in ''aw re Mocked the spread of tfic SHOW. Again, 

 the first tread having all this time been clear of the 

 water, it too is covered, and to a depth of five feet; the 

 tallest granite island has also gained six more feet in 

 heiiiht; and the second one of eight feet, having been 

 above water two thirds of the period, disports a snow 

 cap of four ft*et. Thus the process goes on till we reach 

 the circular area at the bottom. Tn this area we have 

 finally four islands standing in a shallow pool of water 

 less than a yard deep. l>ut note that the first block 

 uncovered is not the tallest now, for its pinnacle being, 

 let us say, only two feet square, lacks tire area ueces- 



