MECHANICAL PARADOXES. 



wings seems appropriate enough for keeping 

 up, if that were all that had to be done. But 

 it is at least equally important to move rapidly 

 forward. How is this accomplished without 

 backward beats upon the air ? 



First look at a diagram of the flying bird, 

 as seen from straight in front, Fig. 19, A and 



C V D 



FIG. 19. POSITION AND ACTION OF WINGS IN FLYING. 



B, in which the front edges of the wings are 

 shown with continuous lines, their rear edges 

 with dotted lines, and the upper surface on the 

 left side, and the lower on the right side, by 

 parallel bars. 



In the position A it is seen that the reaction 

 from the down-beat, which is nearly finished, 

 has caused the body to rise. At B the up-beat 

 is nearly finished, and while lifting the wings 

 up, the body, unsupported, has fallen. There 



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