On the Migration of Birds. 167 



tion-routes and to schematize thein, even before they were 

 corroborated, on maps. If we draw the most important of 

 these migration-routes on a map of the eastern section of the 

 Northern Hemisphere, an entanglement of lines is obtained. 

 If all the routes indicated by the authors are indicated, we 

 get a Grordian knot. "We are overcome by the feeling that it 

 is impossible for the birds to pass along these routes. 



Some ornitho-cartographs, instead of migration routes, 

 draw, so to say, only lines of stupendous boldness over points 

 where no human being has ever set his foot. 



I do not want to enter here into a critical discussion of the 

 subject. I take the facts as they exist authorizing us to 

 continue our investigations on this basis, and therefore in an 

 inductive way. In order to do this, we must proceed in a 

 strictly methodical manner. 



I shall now, in brief outline, elucidate the principles of the 

 method. 



The migration of birds is a phenomenon of movement 

 from one zone to the other, and vice versa. It follows 

 therefrom that space and time are the basis of the phenomenon, 

 and that the question cannot be solved from the phenomena 

 of one locality or point only, even if this be a whole country. 



The solution is only possible elucidating the phenomenon 

 along its whole course. 



From the nature of the subject it follows that the task can 

 only be accomplished by a division of labour, which labour 

 ought to be evenly divided, as far as possible, over the whole 

 area. 



The migration of birds corresponds in the main with the 

 seasons of the year and is thus, as a phenomenon, phaeno- 

 logically connected with the subject we call Meteorology. 



Meteorology owes its great success to the networklike 

 division of the areas, to the uniformity of observation and 

 of working out of the data. 



The migration of birds ought to be treated exactly in the 

 same way, viz., in organical connection with Meteorology. 



The short space of time at my disposal prevents me from 



