INTRODUCTION. 7 



connected by some rational and speculative prin- 

 ciple, can only end in a practical acquaintance with 

 individual objects; the operations of the rational 

 faculties, on the other hand, if allowed to go on 

 without a constant reference to external things, can 

 lead only to empty abstraction and barren inge- 

 nuity. Real speculative knowledge demands the 

 combination of the two ingredients ; right reason, 

 and facts to reason upon. It has been well said, 

 that true knowledge is the interpretation of nature ; 

 and thus it requires both the interpreting mind, and 

 nature for its subject ; both the document, and the 

 ingenuity to read it aright. Thus invention, acute- 

 ness, and connexion of thought, are necessary on the 

 one hand, for the progress of philosophical know- 

 ledge ; and on the other hand, the precise and 

 steady application of these faculties -to facts well 

 known and clearly conceived. It is easy to point 

 out instances in which science has failed to advance, 

 in consequence of the absence of one or other of 

 these requisites ; indeed, by far the greater part of 

 the course of the world, the history of most times 

 and most countries, exhibits a condition thus sta- 

 tionary with respect to knowledge. The facts, the 

 impressions on the senses, on which the first suc- 

 cessful attempts at physical knowledge proceeded, 

 were as well known long before the time when they 

 were thus turned to account, as at that period. The 

 motions of the stars, and the effects of weight, were 

 familiar to man before the rise of the Greek astro- 



