PREFACE. 



This reproduction of four lectures, delivered be- 

 fore the members of the Detroit College Alumni 

 Association, and published by the same gentlemen 

 during the winter of 1888-89, * s respectfully dedi- 

 cated to the cultured classes of the community, 

 and to the advanced students in colleges and acad- 

 emies, who frequently ask what line of theoretic 

 truth is to be followed, in the midst of so much 

 scientific research. If we would not lose the best 

 part of the practical results which science offers us, 

 we must keep scrupulously to the line of truth 

 which sound logic requires us to follow. 



The Author. 



New York, July 31st, 1890. 

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