HOMOLOGIES. 201 



CHAPTER XIII. 



HOMOLOGIES. 



IT may seem to some of my readers that 1 

 have wandered from my subject and forgotten 

 the title of these articles, which purport to be a 

 series of papers on " Methods of Study in Natu- 

 ral History." But some idea of the progress of 

 Natural History, of its growth as a science, of 

 the gradual evolving of general principles out of 

 a chaotic mass of facts, is a better aid to the stu- 

 dent than direct instruction upon special modes 

 of investigation ; and it is with the intention of 

 presenting the study of Natural History from 

 this point of view that I have chosen my title. 



I have endeavored thus far to show how scien- 

 tific facts have been systematized so as to form a 

 classification that daily grows more true to Na- 

 ture, in proportion as its errors are corrected by 

 a more intimate acquaintance with the facts ; but 

 I will now attempt a more difficult task, and try 

 to give some idea of the mental process by which 

 facts are transformed into scientific truth. I fear 

 that the subject may seem very dry to my read- 



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