COSMIC PHILOSOPHY 



But when it becomes solid, the rearrangements 

 which occurred latest become permanent, and 

 further rearrangements cannot be produced save 

 by a fresh supply of molecular motion. In like 

 manner, when we come to study planetary evo- 

 lution, we shall find strong reasons for believ- 

 ing that on small bodies, like the moon and the 

 asteroids, which have rapidly lost their internal 

 heat, there has been but little chance for such 

 complex secondary rearrangements as have oc- 

 curred upon our relatively large and slowly cool- 

 ing earth. 



Even after the attainment of solidity, how- 

 ever, a new supply of motion from without may 

 cause some further redistribution without caus- 

 ing the body to relapse into fluidity. Thus a 

 wrought-iron rail, which when new is tough and 

 fibrous, gradually acquires the brittle crystalline 

 texture of cast-iron, under the influence of the 

 vibrations communicated by the cars which pass 

 •bver it. And the magnetization of steel rods, 

 when fastened in the meridian and frequently 

 jarred, is cited by Mr. Spencer as a fact of 

 like import. Many other excellent illustrations, 

 gathered from physics and chemistry, may be 

 found in the thirteenth chapter of the second 

 part of " First Principles." ! 



If now we contemplate in a single view the 



1 Throughout this work, reference is made only to the sec- 

 ond and rewritten edition of First Principles, London, 1867. 

 2IO 



