Capt. F. W. Hutton on the Fl'ujht of Birds. 141 



flight may perhaps prove of interest ; for I think that they will 

 reconcile many of these discrepancies, as well as explain all the 

 anomalies observed by Dr. Pettigrew in his experiments with 

 sparrows, and at the same time will supply a theory of flight 

 much simpler than any of those hitherto proposed. My observa- 

 tions were made on the Black-backed Gull of the southern 

 hemisphere {Larus dominicanus) ; but doubtless they will apply 

 to all other Gulls, and probably even to all other birds. 



No better opportunity occurs of observing the movements of 

 the wings of a living bird in a free state than when on board 

 a steamer steaming head to wind, and surrounded by a flock 

 of Gulls. The Sea-gull is a bird that moves its wings so slowly 

 that their movements can be followed by the eye ; and under 

 the conditions just mentioned they can be seen in all positions, 

 either vertically or horizontally, the bird apparently remaining 

 stationary for several minutes together, although in reality flying 

 just as fast as the steamer is going. When a Gull is viewed 

 from the side, it is easily seen that the stroke of the wing, from 

 the shoulder, is vertically up and down, or very nearly so ; and 

 when observed directly over head, it is still more easily seen 

 that, at each downward stroke, the primary feathers from the 

 carpal or wrist-joint are moved backward, slightly closing the 

 wing, but without any perceptible bending of the elbow-joint. 

 I cannot, of course, say exactly at what time the backward stroke 

 begins, only that it is principally delivered during the downward 

 stroke, which agrees fai^^-ly enough with Prof. Marey^s experi- 

 ments, which show that the back-stroke commences soon after 

 the down-stroke has begun, and finishes soon after the up- 

 stroke has begun. The mechanical principles here employed 

 are obvious. The support of the bird in the air is partly ob- 

 tained by the concave under surface of the wing off"ering more 

 resistance to the air during the downward stroke than the 

 convex upper surface does during the upward stroke. The rise 

 of the bird during the down-stroke, and its fall during the up- 

 stroke are quite perceptible when viewed horizontally ; its flight, 

 however, would be nothing more than a series of tremendous 

 jerks upward and downward, which, even with immense exer- 

 tion, would hardly raise it in the air, if it were not that by far 



SER. III. VOL. II. M 



