ON THE MIGRATION OF BIRDS. 245 



The prevalence of the speculative tendency in endeavouring 

 to explain the movement led many authors to assume migration 

 routes, and to schematize them, even before they were corro- 

 borated, 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 entered, we get a Gordian 

 knot. We are overcome by the feeling that it is impossible for 

 the birds to pass along these routes. Some orni-chartographers, 

 instead of migration routes, draw, so to say, only stupendously 

 bold lines over points where no human being has ever set his 

 foot, still less birds under observation ! 



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

 subject. I take the facts — they exist, and authorize us to continue 

 our investigations on the basis of facts, therefore in an inductive 

 way ; and, in order to do this, we must proceed in a strictly 

 methodical manner. 



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

 method. The migration of birds is a phenomenon of movement 

 which leads 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 possible only if we elucidate the pheno- 

 menon in its whole course, or, to express it concisely, if we 

 endeavour to grasp and clear it up. 



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

 only be accomplished by a division of labour, which 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, connected with the 

 subject we call meteorology. Meteorology owes its great success 

 to the network- like division of its areas, to the uniformity of 

 observation, and of working out of the data. The migration of 

 birds, as " ornitho-phaenology," 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 

 entering on a detailed exposition of the method. I shall there- 

 fore only touch on the essential points. We must work out the 



