8 PREFACE. 



language, my diffidence arises from a distrust in my own 

 abilities rather than from the deficient interest of the 

 subject itself, for the history of that literature has re- 

 peatedly proved that natural science can be made more 

 attractive than the products of fiction or mysticism — by 

 just as much as the resources of nature exceed the 

 resources of her rivals. 



Felix L. Oswald. 



Cincinnati, March, 1882. 



