CHAPTER VII 



FLIGHT 

 The Wings as Levers, the Air as Fulcrum 



ARCHIMEDES was prepared to move the world if 

 he could find a fulcrum for his lever. The problem of 

 flight seems almost equally difficult : the body must 

 be lifted by levers, and the fixed points on which they 

 are to work must be found in the air. But before I 

 show how the bird surmounts this great difficulty, a 

 word about levers is necessary. Levers arc rigid 

 rods resting on a fulcrum or fixed point ; at another 

 point in the rod is the weight to be moved, and at a 

 third point the power is applied. There arc three 

 kinds of levers, the difference lying in the relative 

 position of the three points mentioned. In the first the 

 fulcrum is in the middle, in the second the weight, in 

 the third the power. Of the first we have an example 

 when a poker, rested on the bar of the grate, raises 

 the coal. An oar is an instance of the second ; the 

 boat is the weight, the fulcrum is the water upon 

 which the oar works. And this makes clear an im- 

 portant fact, viz. that the fulcrum is not always an 



