PREFACE. 



These little essays, now specially addressed to 

 an American public, are mostly endeavors to place 

 before American readers some of the latest results 

 of modern science, in simple, clear, and intelligible 

 language. M^'self born in America, I am glad 

 thus on a return visit to my native land to contri- 

 , bute somewhat to the formation of that great 

 mass of thought which must ultimately quicken 

 and inform the whole world of civilization. Dat- 

 ing as I do from Thoreaii's town, I trust I may 

 have caught some slight echo of Thoreau's inspi- 

 ration. 



Concord, Mass., June, 1886. 



