BIRDS OF PREY IN SUCCESSIVE LAYERS. 337 



in a short time the signal being thus communicated 

 from one tribe to another, the air is full of a great com- 

 pany of gigantic birds, wheeling rapidly in circles over 

 the fallen dead. Even then the highest birds are often 

 seen sailing at such an altitude that though the spread 

 of their wings may be something like 6 feet from tip to 

 tip, they appear as mere specks balanced upon the azure 

 depths of space. 



It has moreover been remarked that the different 

 kinds of vultures follow each other in regular succes- 

 sion, showing that these various species have arrived 

 from different distances. This circumstance is not one 

 of occasional, and perhaps accidental occurrence ; but is a 

 regular rule, which may be said to be always followed. 

 This therefore affords strong circumstantial evidence 

 of the truth of the theory, that these birds float in 

 distinct layers throughout the atmosphere, at different 

 elevations above the earth, and consequently they thus 

 follow each other in their arrivals in regular order of 

 sequence. The late Sir Samuel Baker, than whom there 

 was no more acute or careful observer of all matters 

 connected with the hunter's craft and life in the wil- 

 derness, has expressed himself most clearly and strongly 

 as entirely of this way of thinking and in what, now 

 that he is gone, we shall perhaps be pardoned for 

 indicating, as being in our opinion the best written 

 and most interesting book of travel and sporting 

 adventure that has ever been published, he has stated 

 his experiences of these matters as follows: 



" Throughout all the countries that I traversed, these birds 

 (vultures) were in enormous numbers." * "I have paid much 



* The Nile Tributaries of Abyssinia, by Sir Samuel White Baker, 

 1867, p. 491. 



VOL. III. 22 



