Preface. xv 



stop with ascertained facts. When it has reached 

 the limit of the known it will push on, as best it 

 may, into the region of the unknown. No harm 

 can be done, if the writer fairly states where he is, 

 and relies upon facts alone for proof. 



In treating of Chemistry and other Sciences, the 

 common language and most familiar formulas 2nd 

 theories have been adopted. As the facts will 

 always remain the same, no advantage would be 

 gained by introducing into a work on Natural The- 

 ology discussions on the nature of force, and on 

 the constitution of matter, or the language and for- 

 mulas that have come into partial use in conse- 

 quence of new theories. 



The Theory of Development has not been at- 

 tacked directly. In fact, those who hold to' that 

 theory present so many phases of belief, that it is 

 difficult for one to refer to it at all, without being 

 liable to the charge of unfairness. The learning 

 and the labors of the men who hold to it, in some 

 form, entitle it to respectful consideration. Its 

 leading principles, grounds of proof, and theological 

 tendencies, are evidently misunderstood by many 

 who oppose it. It is believed, however, that the 

 arguments from the final cause of varieties and 

 from the chemical relation of the elements to each 



