WALKING, SWIMMING, AND FLYING. 



533 



ments ; and, in human locomotion, the same phenomenon is observed. 

 The diagram, Fig. 5, shows the curved track made by man walking. 

 The accuracy of this is easily verified by observation. As the limbs 

 swing forward, they move in the arc of an ellipse ; that is, in a slight 

 curve outward, and. with the arms form the double curves, as shown 

 in the figure. In the movement of the horse, walking or trotting, the 

 same phenomenon appears, as the figure shows. 



Fig. 6. 



Horse in the Act op trotting. — In this, as in all the other Daces, the body of the horse is 

 levered forward % a diagonal twisting of the trunk and extremities, the extremities describing 

 a figure-of-8 track (s, u, r, t). 



The wings of birds, bats, and insects, describe similar curves. They 

 are produced by the rotation of the wing, as it rises and falls, so that 

 it twists, screw-like, on its long axis, one-half of the figure being formed 

 in the ascent, the other in the descent of the wing. 



Fig. 7. 



Imitation or Wing Movement bi a Reed with Flexible Sail moving on a Ball-and- 

 Socket Joint, showing the Double Curves. 



The double curves or figure-of-8 lines which thus occur are not 

 mere coincidences, nor in any sense accidental, but the expression of a 



