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 are 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 are 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 
