ADDITIONAL NOTES ON FLYING-FISH. 



205 



second, since Col. Durnford (and doubtless others) can perceive 

 vibration during the whole flight. 



Mr. F. M. Duncan, the cinematograph specialist, informs me 

 that " the number of separate images per second required to give 

 a non-jerky motion picture on the screen averages sixteen per 

 second ; that is the speed of all ordinary cinematograph pictures, 

 and is all right for general work of simply showing the picture as 

 a whole ; ... of course the number would be governed by the 

 speed of the movement. For the flight of a Flying-Fish you 

 would probably require from twenty-four to thirty-six pictures 

 per second." This, however, refers to the movement of the fish 

 as a whole, and not to the vibration of the wings, as Mr. Duncan 

 says further on in his letter : " Some four years ago I was able 

 to closely watch the movements of the Flying-Fish, and I came 

 to the conclusion that its 'flight' was very like that of a Swallow 

 skimming over a pool of water, i. e. a swift gliding motion, with 

 from time to time a vibratory movement of the wings of very 

 short duration, sufficient to produce an upward movement to 

 carry the fish over the crest of a wave." This is, of course, how 

 the aeroplanists see the flight. 



With the special object of examining what I have described 

 as " intervals of rigidity," I spent many hours daily watching 

 the flights with a good glass, and the result was a confirmation 

 of my previous experience ; that is to say, there were in most 

 flights short periods of soaring with motionless wings, but some- 

 times I could distinctly follow the vibration of the wings through- 

 out the whole of the flight. Possibly if Col. Durnford had been 

 with me he could have detected vibration during the periods 

 when I could not. I quote from my notes made at the time : — 

 " When the fish leave the water the flutter of their wings may be 

 seen very distinctly; this movement becomes more and more 

 rapid till it is often difficult, though not always impossible, to 

 distinguish movement. This movement, which is apparently a 

 mere shimmering, sometimes seems to cease altogether for a 

 second or two." This note relates to my experience of the 

 large " four-winged " species, which is the more common in 

 the Atlantic, and which is easier to observe than the " two- 

 winged." 



It may be as well to explain the terms " four-winged " 



