166 GENERAL VIEW AND BASIS OF SCIENTIFIC RESEARCH. 



difficult paths, seek the easiest methods of accomplishing 

 their objects ; particular* trades and manufactures flourish 

 in the most favourable localities, &c. Even the gradual 

 civilisation and development of the human race is largely 

 dependent upon the unequal action of causes. Man is the 

 most differentiated of all organisms, is still differentiat- 

 ing, and appears destined to do so as long as he may exist. 

 Adaptation, natural selection, and evolution of living 

 things also depend upon the operation of this principle. 1 ' 

 This chapter might be very considerably extended, so 

 as to fill a volume, and exhibit a comprehensive scheme of 

 all the chief principles, not only of energy in general, but 

 also of all its forms, and all the sciences ; but as this book 

 is not intended to be an exposition of scientific knowledge, 

 I must refer the reader for further information and addi- 

 tional illustrations to the various works published on the 

 subject, amongst which may be mentioned Grrove's ' Corre- 

 lation of the Physical Forces ; ' ' Principles of Science,' 

 by S. Jevons ; 'First Principles,' by H. Spencer, 1876; 

 6 The Conservation of Energy,' by B. Stewart ; ' Eecent 

 Advances in Physical Science,' by P. Tait ; ' The Unseen 

 Universe,' by Stewart and Tait ; ' The New Chemistry,' 

 by Cooke, &c. 



1 For illustrations of the action of the principle of exciting causes 

 and of latent causes, see Chapters XL VI. and XLVII. 



