AEKIAL LOCOMOTION 249 



track that the insect was made to fly. A needle stuck 

 perpendicularly in the middle of the disc served as an 

 axis for a revolving beam and its counterbalance. This 

 beam consisted of a straw, and at the end of it was 

 fixed a light pair of surgical forceps to hold the insect 

 by a part of its abdomen. When thus fastened, the 

 dragon-fly was left to its own devices. It then com- 

 menced flying at rather a rapid rate round the track, 

 drawing the straw after it, the movement often per- 

 sisting for some considerable time. The gold spangle 



Fig. 175.- Photographic trajectory of ihe wing of a dragon-fly. 



fastened to its wing described a trajectory which is 

 reproduced in Fig. 175. 



The lemniscate described by the insect during its 

 flight in captivity, is no longer to be seen, but in its 

 place there is an undulating curve which presents at 

 different stages of its course a greater or less degree 

 of brightness, according as the inclination of the wing 

 is favourable for the reflection of light or the reverse. 



Chronophotography of Insects on Moving Films. — The 

 series of proofs which we have just given appear to 

 us to leave no doubt as to the correctness of our views 

 on the flight of insects. 



