VII 



FLIGHT '93 



sault. Then put in the pin with its head near B and 

 drop it as before, but make B the lower end. It will 

 glide by a steep descent to the ground. It is worth 

 while improving the cut and balance of these little toys 

 till they behave properly, for they admirably illustrate 

 gliding flight : when A leads, a bird with wide-spread 

 wings is represented ; when B, a bird with wings 

 partly flexed. 



Before closing this subject I must refer to the old 

 fallacy that the bird, owing to its hollow bones, is 

 like a balloon. This has been already dealt with in 

 the previous chapter (see p. 105). 



The General Shape of the Bird. 



If a ship were built on absolutely perfect lines, when 

 she lay at anchor and swung to the tide, the pressure 

 of the stream upon the bows would be exactly balanced 

 by the closing of the waters again at the stern, so 

 that the only force straining at the cable would be due 

 to friction. The case would be far differrent if the 

 vessel presented a flat surface to the current at right 

 angles to it. The lines on which a bird is built are 

 first-rate : its body is not unlike in shape to that of a 

 fish, and investigations have shown that fish are con- 

 structed so as to meet the minimum of resistance in 

 passing through a fluid. 



