PREFACE. V 



know everything under the sun. There is not and 

 there never was a student of Nature so perfectly 

 gifted and equipped that he could master all the 

 branches of his profession. Practical and theoretical 

 knowledge are rarely, if ever, fully and equally de- 

 veloped. The patience and ability to pursue a thor- 

 oughly systematical course of investigation is pos- 

 sessed by very few; a penetrative mind may be 

 greatly hampered in the search for truth by an im- 

 perfectly developed sense of tone and color. So far 

 as tone and color are concerned, there are very few 

 people, anyway, who can hear and see with absolute 

 accuracy. How many are there who, without in- 

 strumental aid, can whistle with perfect pitch the 

 key of C ? How many can remember a given color 

 and match it by memory months later ? Yet the 

 ability to do either of these things unquestionably 

 belongs to the perfectly gifted and equipped student 

 of Nature; but even with this ability, there is still 

 nearly everything for the student to master if he 

 would really know Nature. There are a thousand 

 facts never to be learned from books, which only 

 grassy meadows and dimly lit forests can teach ; yet 

 it is quite as true that one may live under the shadow 

 of the forest for a lifetime, and through lack of 

 interest never learn the secret of its hidden life. 



So it happens that a fullness of wisdom can never 



