PREFACE. XI 



If a book like this, guiding the unlearned to the 

 fountain-head of science — nature itself — shall help 

 to break down the artificial barrier between oriofinal 

 research and popular information , between study and 

 pleasure, aye, between fact and imagination, I shall 

 feel "that my labor has not been in vain" — words 

 quoted from a humility praiseworthy though quaint. 



E. I. 



Washington^ April, 1882. 



