204 



THE ZOOLOGIST. 



ADDITIONAL NOTES ON FLYING-FISH. 

 By Lionel E. Adams, B.A. 



Since a note of mine on the flight of Flying-Fish appeared 

 in 'The Zoologist' (1906, p. 145), Lieut.-Col. C. Durnford has 

 sent me copies of his two able and interesting papers on the same 

 subject.* As his observations differed slightly from my own, I 

 was glad of the opportunity of further careful and prolonged 

 observation on a recent voyage to the Plate. 



In describing the flight (as it appeared to me) in my previous 

 note, I said that the tail continues to vibrate during the whole 

 period of the flight, and that the extended wings have intervals 

 of rigidity alternating with vibratory motion. Col. Durnford 

 maintains that these intervals of apparent rigidity, which give 

 the flight the appearance of that of a bird sailing with outspread 

 motionless wings, are really periods of increased rapidity of 

 vibration, which my eye is unable to detect, and he points out 

 that the capacity for perceiving the vibrations differs in in- 

 dividuals. 



It has been ascertained that an impression lasts on the retina 

 from one-fiftieth to one-thirtieth of a second, so that a greater 

 number of vibrations than thirty to fifty per second would cause 

 the images to overlap and create the impression of a blur ; but 

 if the number of vibrations was exactly adjusted so as neither to 

 overlap nor to leave gaps, the result would be an image of the 

 vibrating object at rest. Thus it is quite possible for two 

 observers, whose visual capabilities vary, watching the same 

 flight to differ as to the vibration or rigidity of the wings. If 

 this is a correct explanation of the difference in opinions, it 

 would give the rate of vibration of the wings at not less than 

 thirty per second, since some observers (the aeroplanists) cannot 

 perceive any wing movement ; and not more than fifty per 



* ' Annals and Mag. of Nat. Hist.' January, 1906, and November, 1906. 



