THE MOON 337 



and later appearance, and from the other spots about it. Its 

 color becomes decidedly bluish, and the fog or mist in a thin 

 transparent stream is swept off across the mare to the south, as 

 indicated in Figure 9. The action becomes less violent about 

 colongitude, 90, and by 95 has ceased altogether, as a usual 

 thing, although it was observed on one occasion at the base of d 

 as a very faint haze as late as 115. All the spots have occa- 

 sionally been recorded as slightly hazy at about this time, but none 

 of the others are at all comparable in this respect to d. At co- 

 longitude 76.8 the ridges of Teneriffe have been recorded as 

 steaming from end to end. In the meantime neighbouring bright 

 spots were perfectly sharp and distinct. This steaming might be 

 either a case of melting snow or of volcanic activity, the steam 

 condensing into ice crystals and falling as snow. The writer 

 rather favors the latter view, since the other spots do not exhibit 

 it. * * * 



That certain bright spots such as Linne are always hazy is 

 well known. The peculiarity of Pico d is that it is hazy only at 

 specified seasons on the moon, when other neighboring and simi- 

 lar spots are sharp. * * * 



Turning now to quite a different type of formation, we find 

 scattered over the moon's surface, but especially in the equatorial 

 regions, a series of small craterlets whose interior walls under 

 all illuminations are of dazzling brilliancy. The floors of the 

 smaller ones are also bright. One of the best known of these is 

 Mosting A, some 5 miles in diameter, 3000 feet deep, and situated 

 in longitude 5, latitude 3. On January 27, 1915, at colongi- 

 tude 56.3 the shadows still showed within the crater, but had 

 entirely cleared the center of the floor, which appeared of a uni- 

 form brilliant white, without detail. On March 19, 1913, 6i.o, 

 a minute black dot was detected at the center, of less than half a 

 mile in diameter. It was also observed Feburary 18, 1913, 66 .o. 

 On January 28, 1915, 70.!, the dot was clearly seen, was about 

 a mile in diameter, and was of the same darkness as the region 

 surrounding the crater. Accompanying the dot, and reaching 

 from it towards the north, three-quarters of the way up to the 

 rim, was a faint dark band one mile in breadth. * * * 



The point of first interest perhaps in this investigation is to 

 find when the spots reach their minimum size. Within the 

 craters, the dark areas appear and disappear at about the same 

 interval before and after midday, which therefore seems to be 

 the time when the snow presents the smallest area. In the case 

 of Linne, Professor Barnard and the writer agreed that the mini- 

 mum occurred one terrestrial day after the lunar midday. * * * It 

 would certainly be of interest to prepare a series of drawings of 

 the craterlet near Littrow B, and determine when its minimum 



