Marvels of the Universe 



145 



the outset was possessed of 

 both water and air, but she 

 has not retained them. Her 

 volume is only a fiftieth part 

 of that of the earth, her mass 

 only an eighty-first part and 

 the weight of her surface about 

 one-sixth. A pound of matter 

 transported from the earth 

 would weigh no more than two 

 and four-fifths ounces in the 

 moon. So her feeble powers 

 of attraction have not been 

 able to retain an atmosphere, 

 for she allows every molecule 

 thrown up vertical!}- to escape 

 at a speed of at least one and 

 a half miles per second ; and, 

 further, according to the kinetic 

 theory of gas, this speed is 

 frequently surpassed by the 

 majority of gaseous particles. 



As to the waters which first 

 covered her mass, they have 

 been quickly absorbed by the 

 soil, which is as porous as a 

 sponge. 



Owing to its small size, the 

 moon has cooled much more 

 rapidly than the earth, and 

 possessed a soHd crust long 

 before the latter body. The 

 gases and vapours enclosed be- 

 neath this crust have played 

 dire havoc with the walls of 

 their prison. Under the enor- 

 mous pressure of their expan- 

 sive force, the surface of the 

 moon has^suffered the extremes 

 of tension, to which the ap- 

 pearance of lunar territories 

 to-day bears ample witness : 

 the ground bristles with moun- 

 tains, whose summits are worn 

 away by the agency of the 

 contraction of ages ; there are 

 numerous deep beds of rock, 

 landslips of various natures, 

 and corresponding upheavals. 



Pholo hyl 



[O. E. Hale. 



THE MOON'S SURFACE. 



Showing the innumerable craters which witness to the vast disturbances 

 that have befallen our satellite. 



