Dr Hanhin, The Problem of Soaring Flight 227 



active air movement which, so far as is yet known, must have been 

 the effect rather than the cause of the bird's progress. 



10. Conclusions. 



This brief summary of the facts observed by me during the last 

 ten years amply supports the view that soaring flight is inexplicable 

 in the light of existing knowledge. 



In the case of soaring flight at slow speed a proof exists that 

 the energy involved is derived from the sun's rays. But the mode 

 by which it becomes available to the soaring animal is, as yet, a 

 complete mystery. Direct observation having failed to point the 

 way to a solution, it is to be hoped that the subject will be attacked 

 with the aid of an experimental investigation. It is only in this way 

 that an explanation of the problem is likely to be attained. 



REFERENCES. 



(I) "The flight of birds." i^%H August to December 1911. 



(II) "Development of Animal Flight." Aeronautical Journal, Jan. 1912, 



p. 24. 



(III) "Soaring flight of birds." Aeronautical Journal, April 1912, p. 70. 



(IV) Animal Flight. Iliffe and Sons, London, 1914. 



(V) "On the flight of pterodactyls" (with Dr D. M. S. Watson). Aero- 



nautical Journal, October 1914, p. 324. 



(VI) "Atmospheric rotary movements of small extent." Aeronautical Journal, 



Oct. 1914, p. 344. 



(VII) "On the flight of albatrosses and gannets." Aeronautical Journal, Jan. 



1915, p. 22. 



(VIII) " On the flight of seaguUs." Aeronautical Journal, Sv^y-^Q'^t. 1915, p. 84. 



(IX) "Observation of transiently visible movements." Aeronautical Journal, 



July^ept. 1915, p. 104. 



(X) "On the flight of locusts." Aeronautical Journal, April-June 1916, p. 56. 



(XI) "Observations on the flight of Ajdng-fishes." Proceedings of the Zoological 



Society of London, 1920, No. xxxii, p. 467. 



(XII) "Observations on the flight of dragon-flies" (presented to the Royal 



Meteorological Society, November 1920). 



