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instant of sunrise on the central meridian line of the basin, these 

 points would have stood up on the soft edge of the light and shade, 

 as bright as the Swiss mountains at sunrise or sunset, but not like 

 them reddened by the optical property of the atmosphere. Gassendi 

 has at least two (I have somewhere a memorandum of more) small 

 craters within the central plain. None such appear in this drawing of 

 Copernicus. In many other lunar mountains the centre is occupied 

 by a crater-formed hill, as Vesuvius stands within Somma ; in 

 others the hill remains a smooth rounded mass, but its crater is 

 lost ; and a further stage of decay seems to be seen in Gassendi and 

 Copernicus, where the central mass is broken into fragments and 

 sculptured by ramified hollows. May we ascribe these effects to 

 the former action of a lunar atmosphere, now absorbed in the oxi- 

 dated crust of the moon ? If so, the lunar mountains have a history 

 of water, as well as records of fire, and we must look on the sinuous 

 ridges of the Mare Humorum with eyes accustomed to the gravel 

 mounds of Norway and Ireland ; study the degraded craters after 

 the models of the Eifel ; and map the 'rillen*' with reference to 

 valleys of erosion as well as of eruption. 



In questions of this kind we shall find such drawings as this of 

 the Roman astronomer of priceless value. Studied, scrutinized, 

 enriched with new discoveries, it may be the model for all time to 

 come in this line of research. It may be followed by two other 

 drawings of the same mountain, one at the moment when the sun 

 is on the meridian of the central hillocks, to show the light streaks, 

 which hide themselves when the sun is low, and another in the 

 clear afternoon of the lunar day (as much after midday, as this 

 drawing was taken before noon), when every little crack and cavity 

 becomes again distinct, but greatly altered in aspect, and the whole 

 landscape changes under the eye of the observer ; the plains grow- 

 ing grayer and softer, and revealing many minute low undulations ; 

 the hills looking more and more rugged, and burning with narrower, 

 brighter and more angular tracts of silvery light. 



* I have some curious results regarding these beautiful objects. 



