FOREWORD 



Before the manuscript of this book had been sent to the 

 publisher, the author had gone to France in the American 

 Ambulance Service. The proof, therefore, has not had 

 the advantage of the author's revision. The undersigned 

 was familiar enough with his general purpose, however, 

 to undertake the final reading and to make such minor 

 modifications as seemed desirable. The field covered is 

 so broad that no one could be expected to have a critical 

 knowledge of all the facts presented, but they have been 

 obtained from the most reliable sources. 



It is to be expected that each specialist will be most 

 critical in reference to his own subject, but the chief mo- 

 tive of the book is to develop some appreciation of nature 

 as a great synthesis and of our relation to it. To present 

 so general a picture with the least confusion involves the 

 omission of many details. Perhaps no two independent 

 teachers would agree exactly upon the selection of ma- 

 terial, but this is of minor importance as compared with 

 the purpose in view. 



The colloquial method of presentation, accompanied 

 by more or less repetition, was adopted because it had 

 proved to be the most effective as tested by many trials 

 with classes. Even here it is recognized that much de- 



