CHAPTER XIV 



AERIAL LOCOMOTION 



The Flight of Insects 



Summary. — Frequency of tlie movements of insects' wings as estimated 

 by the sound produced in flying — Mechanical registration of the 

 movements of the wings ; frequency among different species — 

 Synchronous movements of the wings — Changes in inclination 

 of the wing surface — Trajectory of an insect's wing — Its inter- 

 pretation— Experiments to demonstrate the direction of move- 

 ment of the wins:, and its variations in plane — The artificia 1 

 insect — Theory of the flght of insects — Photography as applied 

 to the study of insect flight— Lendenfeld's experiments — Trajec- 

 tory of the wing as the insect advances — Photography on moving 

 films — Arrangement of the experiment— Different types of flying 

 insects. Bees, flies, tipulae — Substantiation of the mechanical 

 theory of flight. 



Frequency of the Movements of Insects' Wings as es- 

 timated by the Sound produced in Flying. — The flight of 

 insects is accompanied by a humming sound, which is 

 of somewhat low pitch in the larger species, and of 

 very high pitch in some of the smaller insects, such as 

 mosquitoes. The wings of insects may be regarded 

 simply as vibrating wires, and hence the frequency of 

 their movements can be calculated by the note pro- 

 duced. But then it must be taken for granted that 

 the four wings of an hymenopterous, or the two wings of 

 a dipterous insect vibrate in perfect unison. In calcu- 

 lating the frequency of the movement of the wings 

 by this method, the following difficulty may be met 

 with. If we listen to a fly on the wing, it will be 



