THESES FROM LITERATURE. 



7. During the dark phases of the moon many Birds, attracted by 

 the light of Lighthouses or Lightships, perish by collision with 

 the lanterns. 



8. Migration by moonlight is not excluded, but then the light of 

 Lighthouses is avoided. 



9. The losses through Lighthouse-lanterns are most numerous 

 in autumn, on account of the longer duration of the nights, 

 and the much greater number of individuals, among which are 

 many inexperienced ones. 



LuCANUS, F. von: „Die Hohe des Wanderfluges auf Grund aero- 

 nautischer Beobachtungen". Journ. f. Ornith. 1902. 

 \. Birds of Migration generally pass lower than 1000 Metres 

 relative height. 



2. They always migrate below the lowest clouds. 



3. Only within sight of land are Birds able to find the proper 

 direction. 



4. A very high altitude is unnecessary for Birds, because according 

 to aeronautical observations at an altitude of above 1000 Metres 

 the perspective (Fernsicht) lessens. 



Before proceeding to group the Theses taken from Literature, I 

 have to make somere marks on those of Barrington. This author keeps 

 strictly to positive data, and if, here and there, he does go in for conclu- 

 sions, he is very cautious. His Theses are therefore inductive and in this 

 respect valuable. However I cannot suppress one remark and that refers 

 to the predominance of observations which are made on Lighthouses, 

 not only by BARRINGTON but by the English in general and lately 

 elsewhere too. 



The proper meaning of paragraph 8 with Barinqton is that the 

 light of the Lighthouses attracts migrating Birds only on dark nights, 

 but that migration by moonlight is not excluded; only the migrants 

 avoid the light of Lighthouses and go on in their own direction, in which 



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