President's Address. 309 



recognised through a powerful telescope at an elevation of 

 four miles ! passing the disc of the moon, on a clear star-lit 

 night ; and even the species was recognised, — if I remember 

 aright, the Curlew {Nimienius arqvMd). 



(■<3.) Birds in passage over Heligoland have often been ob- 

 served by the veteran ornithologist of that island — Herr 

 Oaetke (than whom, I presume, no man in Europe knows 

 more of his subject) — to pass for hours and hours of daylight, 

 in uninterrupted flights, high overhead, from E. to W. Then, 

 with one of these sudden changes of temperature peculiar, 

 possibly (?), to the North Sea and British coasts, a dense fog, 

 11 Scotch mist, a Danish " haar," quickly covers sea and land 

 as night sets in. Almost simultaneously with it come 

 myriads and legions of migrants, lured by the intense white 

 rays of the lighthouse. Herr Gaetke says: "A rapid de- 

 scent from the higher altitudes, at which previously they 

 were travelling, takes place, because, mist or fog beneath 

 blotting out their bird's-eye landmarks, yet indicate resting- 

 places and LAND in the midst of ocean." What does this 

 prove % That in clear, bright weather^even at vast altitudes 

 — the birds' vision maps out beneath them vast tracts of land 

 and ocean, by which visual guidance they proceed ; but that 

 when haze and mist obscure and blot out the land and sea 

 beneath them, a sudden descent takes place in search of these 

 blotted- out landmarks; and the vivid rays of lighthouses 

 and lightships lure them in multitudes, to rest, or to destruc- 

 tion ! Even our modern balloonist knows that earth^viewed 

 from heaven, as it were— is a vast bird's-eye view. If a 

 mariner, from his crow's-nest on his mast-head, can see twelve 

 to fifteen miles of distance between his ship and the horizon, 

 tell me how many more miles will a bird see at an elevation 

 of four miles' altitude ? To what extent the power of vision 

 of many birds amounts to must remain still undefined ; but 

 it may yet be discovered to be so intense as greatly to relieve 

 students of migration of one of their chief and most intricate 

 and difacult subjects, by accounting, in part at least, for one 

 of the more obscure phenomena. 



One other point we will mention here, which we consider 



