INTRODUCTION. 



scientific solution; indeed only by means of correct induction, by the 

 exclusion of all speculation, to which the seeming „Mystery", the so- 

 called „Wonderfulness" or „lnexplicableness" opens so wide a field. 



The power of flight is certainly also an essential condition to 

 Migration on the part of Birds, but considered in itself, it is not a 

 special characteristic of this class. As a peculiar power and in its 

 manifold changes, we find it not only among highly developed 

 Vertebrata, but also in the Insect class, and here just as in the case 

 of Birds we find it to be not only a means of locomotion, but far 

 more an essential condition of life, without which the species and the 

 individual cannot acquire the food necessary for their existence. 



We can easily understand that this regularly recurring Phenomenon 

 of Migration, even in antiquity, attracted the curiosity of mankind in gene- 

 ral, but particularly that of the scientist. The Phenomenon which in 

 its course avoided and still avoids the rational observation of man, 

 remained enveloped in mysterious darkness. This darkness affected, and 

 still affects, not so much the intellect as the imagination of man, and 

 to some extent also that of the investigator. But imagination is known 

 to be a very bad adviser and the most unreliable guide conceivable in 

 cases, where we must stand solely on the firm ground of facts. 



As far as the Phenomenon of Migration is concerned. Bacon 

 of Verulam has in many respects lived in vain. From a few data dealing 

 with a small area, to draw conclusions which extended to, and em- 

 braced zones, and, where neither data nor conclusions were or are to 

 be had, to put forward the „Mysterious" and then draw inferences, was 

 then and is often now even „Method" ! ! 



The only change is the call for „Facts" ! The records dealing with 

 the day, hour, direction, course of the wind and weather chosen 

 for the Migration and the manifestations of life among Birds; the sort- 

 ing of these data according to locality, time and species; such and 

 other calculations are worked out with little or no coherence. They 

 are then published as „Treatment-', though strictly speaking they are 



