PREFACE. Xi 



single organ, of themselves alone invariably produce 

 an artificial system. Nor ought it indeed to excite 

 surprise, that a definite truth can rarely be obtained 

 by reasoning on solitary data; because we are usually 

 in such cases forced to call in some hypothesis to our 

 aid in order to arrive at a conclusion. Yet thus it 

 is that the habit of reasoning on single facts has been 

 the bane of the study of nature, that it has led many 

 of us totally away from the true path, and created 

 such a delusion that we often imagine the most to 

 be known when in reality we know nothing. 



Were the planets to be arranged in a table ac- 

 cording to any one of their properties, — as for 

 instance, the period of rotation on their several 

 axes, — such a system would be artificial, and only 

 useful in that, having observed the length of a ro- 

 tation, a reference to the table would be a conve- 

 nient mode of determining the name of the planet. 

 But no one would ever think of confounding this 

 artificial table or system with the system of the 

 universe; although an error exactly similar is every 

 day committed in natural history, when a person 

 who may by the mere exercise of his memory have 

 become acquainted with an artificial table, fancies 

 that he must therefore be a profound naturalist. 



If it should be asked what is here meant by 

 an artificial table in natural history, the author 

 would reply, that such in his opinion is that rather 



