210 ANIMAL MIlrllAMSM. 



Conformation (>f the bird. By the simple inspection of a 

 bird's wing, it is easy to see that the im < -hanisia of its flight 

 is altogether different from that of an insect. From the 

 manner in which the leathers of its wing lie upon each other, 

 it is evident that the re>istance of the air cau only act from 

 below upwards, for in the opposite direction the air would 

 force for itself an easy passage by bending the long barbs of 

 the feathers, which would no longer sustain each other. This 

 well-kiio-.vu arrangement, so carefully de^-rilied by Prechlt,* 

 lias caused persons to suppose that the wing only needed to 

 oscillate in a vertical plane in order to sustain the weight of 

 the bird, because the resistance of the air acting from be- 

 low upwards is greater than that which it exerts iu the 

 opposite direction. 



This writer has been wrong in basing on the inspection of 

 the organ of tlight all the theory of its function. We shall find 

 that experiment contradicts in the most decided manner these 

 premature inductions. 



If we take a dead bird, and spread out its wings so as to 

 place them in the position represented in tig. 89, we see that at 



FIG. SO. Various curves of the wini; of u binl at different point;; in its 



length. 



different points in its length, the wing presents very remark- 

 able changes of plane. At the inner part, towards the body, 

 the wing inclines considerably both downwards and back- 

 wards, while near its extremity, it is horizontal and some- 

 times slightly turned up, so that its under surface is directed 

 .somewhat backward. 



Dr. Pettigrew thought that he roidd find in this curve a 

 sin-face resembling a lelt-handed screw propeller; struck with 

 the resemblance between ihe form of the wing and that of 

 the >i TCW u-ed in navigation, he considered the wing of a 



* Untersncliungeii i\\-i 'l-u Flu.:; <K-i Vu^.-l. Bvo \ .. mi.i 1S40. 



