470 i)R. E. II. IJANKIN ON THE 



3. Speed of flight of flying-fishes. 



During my recent voyage a flying-fish was seen flying on a 

 course parallel with the ship and at the same apparent speed. 

 During eight seconds, timed with a stop-watch, it remained fixed 

 in position relatively to the ship. The latter was travelling 

 through the water at 15g knots or 7| metres per second. The 

 direction of the real wind was learnt by noting the movement of 

 the waves, that of the apparent wind by the position of the line 

 of smoke from the funnel. From these data it was calculated 

 that the velocity of the wind was 4 metres per second and that of 

 the flying-fish through the air was 10 metres per second. This 

 estimate involves the assumption that the wind-velocity was the 

 same near water-level as at the level of the top of the funnel. 



A similar observation on another flying-fish gave an identical 

 i-esult. Later in the day the wind decreased, and then flying- 

 fishes travelling on the same course as the ship were seen to move 

 distinctly faster than the latter. 



These flying-fishes were all gliding with tails hanging down and 

 wings " up." That is to say they were in slow-speed flight. In 

 ' Animal Flight ' reasons have been brought forward for believing 

 that, when in high-speed flight (wings flat and tail up on a level 

 with the body), flying-fishes may attain speeds of more than 20 

 metres per second. 



Flapping sometimes occurs at starting, especially in the 

 presence of wind and in the colder months of the year. The 

 above- described observations of the position of the wing-tips, and 

 also the sharp-cut appearance of the wings in species whose 

 wings are opaque, definitely prove that flapping does not occur 

 when once the fish is well under way. Hence flapping cannot 

 be invoked as an explanation of the speed maintained during 

 flight. 



Sometimes — when it may be supposed that the air is not fully 

 suitable for flight, or perhaps if the fish is exceptionally frightened 

 by the ship — during its flight the fish lowers its tail into the water 

 at intervals of about two seconds and wags it to and fro for a 

 fraction of a second with a resulting increase of speed. 



4. Comparison with the speeds attained by vidtures 

 in horizontal soaring flight. 



That the speed of flight of flying-fishes is similar to that of 

 soaring vultures when in horizontal flight is shown by the 

 following figures : — 



During April 1920, I made several measurements, in Agra, of 

 the apparent speed of vultures with the help of a Souchier 

 telemetre by the method described by me in 'Animal Flight.' 

 Information as to the velocity of the wind in which the vultures 

 were gliding was obtained from measurements made with the help 

 of balloons sent up by Mr. J. H. Field (to whom I owe my thanks) 



