64 JOURNAL OF THE 



thought this was produced by unsteady currents of wind. It is 

 probable, however, that this slow rocking, which I have noticed 

 is quite common with the Turkey Vulture, gives the needed 

 additional force, in many instances, required to ascend. The 

 rocking is equivalent to a slow flapping of the wings. 



To show how beautifully the wing is adapted to utilize to the 

 best advantage all of the compressed air, I wish to call attention 

 to a use of the primaries of a bird's wing, which up to this time 

 seems to have been overlooked. Indeed, in some cases the special 

 structure which I wish to point out has been regarded by some 

 eminent men as detrimental to the bird, so that they have, in 

 some cases, conceived that the bird resorts to some mechanical 

 contrivance to give to the wing the form which nature neglected 

 to give ! 



In looking up this question it has surprised me to see how 

 near the Duke of Argyll was to the truth in regard to the use 

 of the primaries, and yet missed it at last ! 



He says : *" Round-ended wings are also almost always open- 

 ended, that is to say, the tips of the quills (primaries) do not 

 touch each other, but leave interspaces at the end of the wing, 

 through w r hich, of course, a good deal of air escapes. Since 

 each single quill is formed on the same principle as the whole 

 wing — that is, with the anterior margin stiff and the posterior 

 margin vielding — this escape is not useless for progression ; but 

 the air acts less favorably for this purpose than when struck by a 

 more compact set of feathers." 



The italics are my own. I wish to emphasize the fact that he 

 concludes a compact set of primaries would be more useful than 

 the natural separation of the primaries. I contend that the con- 

 verse is true, namely, that the natural separation of the prima- 

 ries, of a round-ended wing, is more useful for progression than a 

 compact set of feathers would be. Else, why did nature make 

 them so? 



A careful examination of the structure of the primaries of the 

 Turkey Vulture's wing, and the length of the separated portion 



-Reign of Law, 5th Ed., pp. 156-157. 



