144 THE RIDDLE OF MIGRATION 



matter nothing to him whether the results are 

 positive or negative. Even the latter are valuable 

 in the controlled elimination of observable factors. 

 Repeated failure may lead to ultimate success. A 

 problem as wide in its scope as the migration of 

 birds involving, as it does, many branches of 

 biological science, will inevitably take many years 

 of patient effort to analyse on an experimental basis. 

 But the mere fact that one is dealing with animal 

 behaviour is an incentive with a deep and lasting 

 appeal. One feels continually that one may some 

 day encounter something that will not only provide 

 a key to the migrations of birds, wonderful per- 

 formances, in many cases (e.g., young birds) 

 achieved with neither thought nor forethought, but 

 also to those curious streaks of thoughtless be- 

 haviour that so frequently reveal themselves in 

 man himself. 



