FLIGHT 8i 



angles to the plane of its surface is very greatly increased 

 if it be made to move at the same time through the air 

 rapidly in a direction parallel with its surface." The sup- 

 porting force, which is the thrust upwards on the bird's 

 wings and body, increases with the square of the velocity, 

 and varies also with the surface of the bird and with the 

 density of the air. The precise formula is given in Professor 

 Roy's article in Newton's " Dictionary of Birds." 



It seems safe to say that some common birds, like the 

 starling, readily attain for a short time to a velocity of 

 over 40 miles an hour. A carrier pigeon can keep up 

 40 miles an hour for a considerable time, but this will be 

 halved against the wind and nearly doubled with the wind 

 in the bird's favour. Hilzheimer cites the case of a swallow 

 which flew along with carrier-pigeons from Compiegne to 

 Antwerp, a distance of about 140 miles. It accomplished 

 this in I hour 8 minutes, reaching its nest a long time 

 before the first pigeon. This is a well-known case, often 

 cited, but von Lucanus (1921) points out that it is not above 

 criticism. It seems very doubtful if sufficient care was 

 taken in the marking of the swallow (" un peu de couleur ") 

 and in making quite sure that the swallow seen entering the 

 nest at Antwerp was the identical swallow that left Compiegne 

 a little over an hour before. 



§ 7. General Biological Significance of Flight 



The Vertebrate transition from water to dry land was 

 made by Amphibians. From some Amphibian stock there 

 probably evolved the race of Reptiles, partly terrestrial, 

 partly aquatic, and, in the case of Pterodactyls, aerial. 

 From a bipedal terrestrial race of Reptiles, probably the 

 Dinosaurian Ornithischia, arose the Birds. 



The problem of true flight has been solved four times — 

 by Insects, Pterodactyls, Birds, and Bats — and the four 

 solutions are very different. In insects the lightly built 

 body, containing a good deal of air in the much branched 

 tracheze, is sustained and propelled by the extremely rapid 



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