INTRODUCTION 



in the latter part of the chapter, gives some ac- 

 count of the relation of this hypothesis to lunar 

 phenomena, and here, as throughout the chapter, 

 touches upon matters of detail which he would 

 frequently have had to express with some modi- 

 fications, in view of the later advances of know- 

 ledge, had he been able to revise his book. 



17. Chapter vi., on "The Evolution of the 

 Earth," is brief, and touches upon matters which 

 Spencer has occasion to treat, in passing, in the 

 illustrative paragraphs of the text of the "First 

 Principles," even while he is stating the gen- 

 eral characteristics of evolution. Fiske's chap- 

 ter vii., on " The Sources of Terrestrial En- 

 ergy," stands in a comparatively free relation 

 to the order of Spencer's exposition. It corre- 

 sponds most of all to the chapter on " The 

 Transformation and Equivalence of Forces," 

 chapter viii. of Part II. of the " First Princi- 

 ples." Fiske's chapter contains a summary of 

 well-known portions of the modern theory of 

 energy. Significant here is especially Fiske's 

 statement of the relation of the doctrine of en- 

 ergy to nervous and mental phenomena. Here, 

 in fact, we come upon one of Fiske's most im- 

 portant lines of thought. He carefully avoids 

 saying that physical energies are transformed at 

 any point into mental processes. The passage 

 in Fiske's text corresponds, however, in the 

 Iviii 



