ON SOARING PLIGHT. 



By E. 0. HUPFAKER. 



With an introduction by S. P. Langley. 



INTRODUCTION. 



It is generally known that birds sustain themselves in the air in two 

 distinct ways: 



First. By the direct exercise of mechanical iDower, as in a large class 

 3f birds that flap their wings. Although the exact motions and power 

 Df the wing have not yet been studied exhaustively, there is nothing 

 in this method of support, considered as a mechanical contrivance, in 

 apparent contradiction to known principles. 



Second. Another and important class of birds, including the largest, 

 can fly without flapping the wings, and are able to glide over the laud- 

 scape (sometimes from horizon to horizon), on nearly motionless pinions, 

 in a manner and with an effect which is not easily explained on known 

 mechanical principles, and which is in striking contrast with the labored 

 way of other birds. This manner, which has never yet been completely 

 accounted for, and which is called ^'soaring flight," forms the special 

 subject of the following article. 



In this latter case the bird is in some way held up, as though by an 

 invisible hand, upon the thin and yielding air, on which it seems to 

 float almost like a ship, although its specific gravity is nearly a thou- 

 sand times as great as that of the air, far greater, in proportion, than 

 that of a ship of solid lead or gold would be to water. 



There is no obvious explanation of this soaring flight, nor has any 

 yet been offered which is not open to some objection. Passing by the 

 childish idea of the support being derived from the lightness of the 

 birds' hollow bones, or quills, we find ourselves restricted to a very 

 few hypotheses indeed. 



Perhaps the first of these is that the bird is everywhere upborne by 

 invisible ascending currents. Without in any way denying that such 

 currents exist or that the bird may frequently utilize them, it seems 

 almost superfluous to enter upon a refutation of the idea that these are 

 universally present, even if we allow that they can have ascensional 

 force sufficiently to sustain such masses in the air. "What goes up 



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