ANATOMY AND PHYSIOLOGY 63 
oscillation, the plane of the wing changes, as may be demon- 
strated by holding a detached wing by its base and blowing at 
right angles to its surface; the membrane of the wing then yields 
to the pressure of the air while the rigid anterior margin does 
not, to any great extent. Similarly, as the wing moves down- 
ward the membrane is inclined upward by the resistance of the 
air, and as the wing moves upward the membrane bends down- 
ward. Therefore, by becoming deflected, the wing encounters 
a certain amount of resistance from 
behind, which is sufficient to propel 
the insect. The faster the wings 
vibrate, the greater the deflection, 
TGs, 78% 
the greater the resistance from be- 
hind, and the faster the flight of the 
insect. 
The-path traced in the air by — Trajectory of the wing of an 
a rapidly vibrating wing may be oa 
determined by fastening a bit of gold leaf to the tip of the 
a wasp, for example—to vibrate 
wing and allowing the insect 
its wings in the sunlight, against a dark background. Under 
these conditions, the trajectory of the wing appears as a lumi- 
nous elongate figure 8. During flight, the trajectory consists 
of a continuous series of these figures, as in Fig. 73. 
Marey, the chief authority on animal locomotion, used 
chronophotography, among other methods, in studying the 
process of flight, and obtained at first twenty, and later one 
hundred and ten, successive photographs per second of a bee 
in flight. As the wings were vibrating 190 times per second. 
however, the images evidently represented isolated and not 
consecutive phases of wing movement. Nevertheless, the 
images could be interpreted without difficulty, in the light of 
the results obtained by other methods. At length he obtained 
sharp but isolated images of vibrating wings with an exposure 
of only 1/25,000 of a second. 
The frequency of wing vibration may be ascertained from 
the note made by the wing—if it vibrates rapidly enough to 
