326 POPULAR LECTURES AND ADDRESSED. 



figure would become unstable, and the small sphere 

 A would take the position A' or A", in either of 



Fir,. 7. 



which two cases the configuration would be again 

 stable. 



Look now at Fig. 2 and suppose the outer circle 

 to represent the section of a globe 8,000 miles 

 in diameter, and let the inner circle represent 

 the section of an enclosed globe 2 miles less in 

 diameter. Suppose the outer envelope to be 

 water, and the inner globe to be solid matter, of 

 density equal to or greater than that of water, 

 then the configuration of Fig. 2 would evidently 

 be stable. On the other hand, if we suppose the 



