Vlll PREFACE. 



In the chapters that foUow the psychological ones, I have 

 endeavoured to show how the science of history is capable 

 of being elucidated by the same principles which have thrown 

 so much light on the development of individual organisms 

 and of organic species. 



The subjects of the opening chapters are not in any obvious 

 way connected with the laws of life. But life is a manifesta- 

 tion of force, and cannot be defined, or accurately thought of, 

 except in relation to inorganic forces. For this reason I have 

 commenced the work with some general statements on the 

 subject of force and energy, and their relations to matter ; 

 and I have inserted a chapter on crystallization, for the purpose 

 of showing the remarkable general contrast, with still more 

 remarkable points of special resemblance, between the crystal- 

 line and the organic formative principles. 



I have prefixed to this work an Introduction, on the subject 

 of the historical tendency which all science is now so remark- 

 ably manifesting ; and I have concluded it with three chapters 

 containing some ideas on the classification, the history, and the 

 logic, of the sciences. 



I have throughout abstained as much as possible from 

 technical language and technical modes of statement. It has 

 been my aim to make the subjects treated of intelligible to 

 any intelligent man who is willing to give the necessary 

 attention, and to remove all difficulties except, such as are 

 inseparable from subjects which have not yet become familiar. 

 I have endeavoured to give my authority for all important 

 statements as to facts which are not matters of general noto- 

 riety; and when I have advanced any opinion of my own, 

 I have advanced it as such. 



In several places throughout this work, I have been brought 

 to the borders of a region external to that which is usually 

 regarded as the domain of science. Such subjects as the origin 



