112 ANIMAL LOCOMOTION. 



Weight contributes to Horizontal Flight. — Tliat the weight of 

 the body plays an important part in the production of flight 

 may be proved by a very simple experiment. 



Fig. 55. 



If I take two primary feathers and fix them in an ordinary 

 cork, as represented at fig. 55, and allow the apparatus to 

 drop from a height, I find the cork does not fa>ll vertically 

 downwards, but downwards and forwards in a curve. This 

 follows, because the feathers a, I are twisted flexible inclined 

 planes, which arch in an upward direction. They are in fact 

 true wings in the sense that an insect wing in one piece is a 

 true wing. (Compare a, I, c of fig. 55, with g, g\ s of fig. 82, 

 p. 158.) When dragged downwards by the cork (c), which 

 would, if left to itself, fall vertically, they have what is vir- 

 tually a down stroke communicated to them. Under these 

 circumstances a struggle ensues between the cork tending to 

 fall vertically and the feathers tending to travel in an upward 

 direction, and, as a consequence, the apparatus describes the 

 curve d ef g before reaching the earth h, i. This is due to 

 the action and reaction of the feathers and air upon each 

 other, and to the influence which gravity exerts upon the 

 cork. The forward travel of the cork and feathers, as com- 

 pared with the space through which they fall, is very great. 

 Thus, in some instances, I found they advanced as much as a 

 yard and a half in a descent of three yards. Here, then, is 



