8 



THE AMERICAN NATURALIST 



[Vol. XL 



The difference in the rates of speed of wing-flapping on differ- 

 ent days is very marked. At times, and often for many successive 

 days, it is noticeable that, although the bodies of the fish as they 

 rise from under the steamer's bows are clearly and sharply defined 

 their supporting wings have a peculiar hazy and blurred look, with 

 a want of definition of outline which cannot be accounted for, for 

 they seem to be still. Then a day will come when the fish, still 

 fleeing in front of the ship, will move their wings less rapidly and 

 their motion will become plainly visible. There are still many 

 lookers-on who cannot pick it up, but for the rest the aeroplane 

 theory is exploded for ever, and when next the swifter-moving 

 wings are seen with the eye of knowledge the wonder is that there 

 had been any difficulty. The haze and blur are exactly what 

 should have been looked for under the circumstances. 



We have all of us watched sea-gulls soaring quietly in a certain 

 direction, but obliged to flap when they turn away, the vigor of 

 the flapping varying more or less regularly with the direction in 

 which they meet the wind. It is more than probable that the 

 change of wing-speed of the fish varies for similar reasons in degree 

 of rapidity, soaring being, as I have endeavored to show, quite 

 out of the question. From whatever cause, it certainly does so 

 vary. 



A curious thing about the "vibration" periods is that they seem 

 to offer fleeting glimpses of a satisfactory wing; for a moment, 

 now and again, the wings have outlines and edges, and will also 

 occasionally return a sun-glare to the eye from their wet glassy 

 surfaces, such as might be expected from them when not whirring. 

 Such a glare is also now and then momentarily to be seen when a 

 fish ceases flying, and just before it strikes the water, if it be in 

 the proper position with regard to the sun. There would, of 

 course, be many long periods of this glare were the wings really 

 still. 



One or two more prominent fallacies are handed on from writer 

 to writer, and often accepted as facts. One is that tli*^ fish are 

 helped in their flight by the distention of their air-hhui(UM-. If 

 such had any appreciable effect it would be that of impeding the 

 flight, for the contained air being under compression would be 

 denser and therefore heavier than the outside air, and the increased 



