Dr Hankin, The\soaring flight of drag on- flies 463 



The depressed position jyi the abdomen in continued flight is 

 seen only in the hotter months of the year and then only when 

 the sun is shining in full strength. 



V. Significance of the use of a hrake in continued flight . 



The interest of the above observations lies in their bearing on 

 the question whether the soaring flight of dragon-flies is due to 

 undiscovered wing movements. If this were the case, it may be 

 asked, why could not their flight be checked by cessation of such 

 movements and why should the use of a brake in continued flight 

 be necessary? 



These observations also furnish a proof of the dependence of 

 soaring flight in light winds on sunshine. It is remarkable that 

 the presence of an amount of thin cloud far too small to have 

 any known effect on the flight of birds should be able to influence 

 the flight of dragon-flies. 



VI. High speed soaring flight of dragon-flies. 



The first observation of high speed flight of dragon-flies was 

 made by Leeuwenhoek about 200 years ago. In discussing the 

 compound eyes of insects and as a proof of the quickness of sight 

 compatible with eyes of this description, he relates how he watched 

 a swallow chasing a dragon-fly over the surface of a large pond 

 and how the swallow was baffled by the speed and the unexpected 

 turns of the insect which kept it always several feet in front of 

 the enemy*. 



In my experience such high speed flight over water is due to 

 a combination of soaring w^th occasional flapping. This form of 

 rapid flight in which a dragon-fly can easily outdistance a swallow, 

 so far as I have seen, occurs only in the presence of sunshine and 

 wind. 



On rare occasions it has been my fortune to observe dragon- 

 flies in a strong wind and to be able to form a definite opinion as 

 to the absence or presence of flapping in their flight. The following 

 instance appears to be of sufficient interest to be worth transcribing 

 from my diary in detail: 



August 10th, 1915, at 10.05 a.m. on the Bharatpur Road, 

 22 miles from Agra. 



A strong wind that tended to blow off my hat. A cluster 

 of dragon-flies (Pantala) were gliding to leeward of a small 

 tree but generally remaining a little to one side of it so that 

 they met the full force of the wind. They were in continued 

 gliding flight. Long grass about 2 metres high was below 



* Miall, The Early Nnturalists, Their Lives ami Works (Macmillan and Co., 1912, 

 p. 206). 



VOL. XX. PART IV. 30 



