VI. 



migration, than the veteran author ; and the results of his 

 fifty years or more of labour, as now presented to the notice 

 of the ornithological world, are eloquent testimony to the untiring 

 zeal and energy of an accomplished field naturalist. 



The opinions he expresses, on the special department of 

 ornithological science, for the study of which Heligoland is so 

 pre-eminently adapted, will naturally have the greatest weight 

 with all, and some in their admiration for the veteran observer 

 have formed the opinion, that all, or nearly all of our previous 

 conceptions, as to the direction, attitude and velocity of the 

 migratory flight, will have to be greatly modified or altogether 

 abandoned in favour of those he sets before us. 



In the study of so complex a subject as the why and whither 

 of the migration of birds in general, much diversity of opinion 

 is naturally to be expected, and whilst the views of Herr Gatke 

 are entitled to the respect his long experience demands, it will 

 not be surprising perhaps, if others find, in the observations 

 which he presents to our notice in support of the conclusions 

 at which he has arrived, evidence which may just as readily be 

 urged in favour of results quite as different. 



In estimating the value of his various theories, it must not be 

 forgotten that they are based on observations conducted in 

 a very limited and somewhat exceptionally situated area ; outside 

 this area his personal experience seems to have been very small. 



