INTRODUCTION. 73 



phases. It is not, however, in the definition given by Vale- 

 rius Flaccus,* but in the zoological writings of Aristotle, that 

 the word history presents itself as an exposition of the results 

 of experience and observation. The physical description of 

 the word by Pliny the elder bears the title of Natural His- 

 tory, while in the letters of his nephew it is designated by the 

 nobler term of History of Nature. The earlier Greek his- 

 torians did not separate the descriptions of countries from the 

 narrative of events of which they had been the theater. With 

 these writers, physical geography and history were long inti- 

 mately associated, and remained simply but elegantly blended 

 until the period of the development of political interests, when 

 the agitation in which the lives of men were passed caused 

 the geographical portion to be banished from the history of 

 nations, and raised into an independent science. 



It remains to be considered whether, by the operation of 

 thought, we may hope to reduce the immense diversity of 

 phenomena comprised by the Cosmos to the unity of a princi- 

 ule, and the evidence afforded by rational truths. In the 

 present state of empirical knowledge, we can scarcely flatter 

 ourselves with such a hope. Experimental sciences, based 

 on the observation of the external world, can not aspire to 

 completeness ; the nature of things, and the imperfection of 

 cur organs, are alike opposed to it. We shall never succeed 

 in exhausting the immeasurable riches of nature ; and no gen- 

 eration of men will ever have cause to boast of having com- 

 prehended the total aggregation of phenomena. It is only by 

 distributing them into groups that we have been able, in the 

 case of a few, to discover the empire of certain natural laws, 

 grand and simple as nature itself. The extent of this empire 

 will no doubt increase in proportion as physical sciences arc 

 more perfectly developed. Striking proofs of this advance* 

 ment have been made manifest in our own day, in the phe- 

 nomena of electro-magnetism, the propagation of luminous 

 waves and radiating heat. In the same manner, the fruitful 

 doctrine of evolution shows us how, in organic development, 

 all that is formed is sketched out beforehand, and how the 

 tissues of vegetable and animal matter uniformly arise from 

 the multiplication and transformation of cells. 



The generalization of laws, which, being at first bounded 



by narrow limits, had been applied solely to isolated groups 



of phenomena, acquires in time more marked gradations, and 



gains in extent and certainty as long as the process of reason- 



Aui. Gell., Noct. Alt., v., 18. 



VOL. I D 



