The Turkey Vulture 



turns and sweeps about in stately curves, or glides swiftly off at will 

 in any direction. How does he do it! It is easy to see how a bird, 

 moving with the wind and falling sharply, may wheel and breast the 

 wind more sharply still, using his acquired momentum to gain a greater 

 height than the one originally occupied. In this the momentum is like 

 the pull of the string which 

 enables the kite to shoot 

 rapidly upward through the 

 air. But what shall we say 

 of a bird which, without 

 momentum, but still on mo- 

 tionless wing, rises steadily 

 against the wind? Not only 

 rises, but makes rapid prog- 

 ress forward, as well, in a 

 direction contrary to the 

 wind. Ascending air-cur- 

 rents, the engineers say; but 

 it seems to me that they are 

 only masking their ignorance 

 or begging the question. As- 

 cending air currents are un- 

 doubtedly an important 

 modifying factor operative 

 near inequalities of the land's 

 surface; but it yet remains 

 to be proved that the mere 

 radiation of heat from the 

 earth's surface is sufficient to 

 sustain a weight aloft. It 

 will not do so on a perfectly 

 calm day, however intense 

 the radiative action. I stub- 

 bornly believe, therefore, that 

 the configuration of a bird's 

 wing is such that it is enabled 

 to play gravity as if it were 

 a kite string, and to resolve 

 the thrust of the wind into 

 its two elements of drift and 

 lift, neutralizing the one and 



... ° Taken near Santa Barbara 



utilizing the other to any re- an ancient model 



Photo by the Author 



1739 



