148 



THE BIRDS OF HELIGOLAND 



Both in regard to this question as to the immediate cause of the 

 departure of birds on their migTations, as well as ih reference to 

 that propounded in the previous chapter, we are coiafronted with 

 a riddle which has hitherto defied everj' attempt at a solution, and 

 which indeed we may hardly expect will ever be likely to receive 

 a final explanation. 



Long and profound study has been devoted to this subject in 

 many quarters, and has residtcd in the enunciation of several verj- 

 ingenious and plausible hypotheses. None of these, however, will 

 stand their ground when the actual facts, which the life of birds in 

 Nature presents in such abundance, are marshalled against them. 



In one way or another, however, almost every attempt at an 

 explanation admits that migrants, with regard to the time and 

 direction of their movements, act with a means to an end, but 

 unconsciously, or, in other words, by instinct. 



In treating of the various momenta of the migratory flight, we 

 have striven as much as possible to place before the reader only 

 such facts as are beyond question or criticism, but no attempt has 

 been made to furnish a solution of the wide j^roblems which they 

 involve. 



In thus abstaining from setting forth new theories, I have been 

 guided by the conviction, rendered firmer mth increasing know- 

 ledge of the phenomena, that what at present has been ascertained 

 in reference to the migration of birds furnishes us with no clue, 

 by the aid of which we are enabled to penetrate the depths of 

 this wondrous myster^^ The life of a man is too short for the 

 complete exploration of this inexhaustible field, and one can only 

 regret that one is unable to start afresh with observations and 

 inquiries from the standpoint which one has reached at its close. 



