The Moon 225 



with telescopes, and many details have been made out. 

 Prominent markings, like craters, supposed by some 

 observers to have been the vents of volcanoes long since 

 extinct, are numerous. Some of them are much larger 

 than any craters on the earth. From these radiate 

 straight lines, in some cases hundreds of miles long. 

 These " rays " are usually 5 to 10 miles wide and not 

 much higher or lower than the moon's surface on either 

 side. There are also " clefts," deep and narrow, run- 

 ning straight through mountain and valley for hundreds 

 of miles, and " rills " deep, narrow, crooked valleys. 

 It is not easy to explain the origin of all these markings. 



On the whole, the surface of the moon is much more 

 rugged than that of the earth. Mountains are more 

 common and some of them are higher than any on the 

 earth, excepting those of central Asia. This seems the 

 more remarkable when we consider that the moon is 

 very much smaller than the earth. Its whole area is 

 less than that of Asia. Its flat parts were named seas 

 at a time when they were supposed to be bodies of water ; 

 but we now know that water does not exist on the sur- 

 face of the moon unless it be in very small quantities. 

 The " seas " are really plains. Clouds are never seen. 



Part of the moon's surface never seen. Luna always 

 faces the earth as she goes around it. Therefore we 

 can never see her back, which is turned away. Forty- 

 one per cent of the moon's surface has never been seen 

 by any one on the earth. What that part is like we 

 may imagine, but we do not know. 



Conditions that would affect life on the moon. The 

 moon has no atmosphere surrounding it. How do we 



