288 STUDY OF NATURAL HISTORY. 



instance, differing in some essential respects from 

 that already before us ; so that, from the various 

 lights of different facts, concentrated in the point in 

 question, we may form a correct judgment, whether 

 the conclusion obtained from the first instance be a 

 real principle of nature. If, for instance, any truth of 

 anatomical science, collected from observation of our 

 own species, were discerned also in the structure of 

 most of the vertebrated animals, we should be almost 

 sure that it was a general principle in that division of 

 nature ; but if, pursuing our examination into the 

 invertebrated animals, we discovered the same prin- 

 ciple under a different modification, and were en- 

 abled to trace all the intermediate steps of gradation 

 between the two extremes, we should then be sure 

 that the principle was a general law of nature ; since 

 we found that it held also where the peculiar cir- 

 cumstances, in which it was first observed, were 

 wanting. 



(199.) The variety which is introduced into any 

 subjects by analogical argument, is in itself greatly 

 serviceable to the business of instruction ; it throws 

 over the subject an inviting garb of attractiveness, 

 thus alluring the attention of the general reader, and 

 keeping alive the interest of the student. For ex- 

 ample, in the analogy just quoted, what a pleasing 

 and delightful illustration is given — by the circular 

 progression of the seasons — of the circular pro- 

 gression of beings in nature ! both exhibited in 

 friendly contrast with some of the greatest truths of 

 the material and the spiritual world. How different 

 are the analogical instances ! and yet how harmoni- 

 ous ! The mind, thus led to the acknowledgment of 



