140 Capt. F. W. Hutton on the Flight of Birds. 



wiugs^ show that progi-ession is not obtained by the uplift- 

 ing of the free ends of the feathers ; for their flight was 

 apparently in no way impaired when the free ends of the 

 feathers were cut off. 



Dr. Pettigrew, in his admirable paper on the subject (Trans. 

 Linn. Soc. xxvi.), asserts that the effective stroke is downward 

 and forward, and that by a peculiar twisting or screwing 

 motion of the wing (which I am bound to confess I do not quite 

 understand) the air is forced to escape near the root of the 

 pinion, between the secondary and the tertiary feathers, in a 

 downward and backward direction, and that the reaction thus 

 produced supports the bird and drives it forward. Dr. Pettigrew^s 

 own experiments, however, hardly support his theory ; for both 

 No. 12 and No. 13 (p. 220) show that the feathers forming the 

 funnel by which the air is supposed to escape, are not necessary 

 for flight, while No. 18 proves that, although the secondaries 

 may be complete, flight is prevented by cutting off the ends 

 of the primaries ; that is to say, his experiments show that flight 

 in reality depends principally upon the primary feathers, while 

 his theory makes it depend principally upon the secondary ones. 

 Both Dr. Pettigrew and Mv. MacgiUivray consider that the 

 wing is extended during the down-stroke, and more or less folded 

 during the up-stroke; and Dr. Pettigrew and the Duke of Argyll 

 agree that the wings during progression describe a "wave- 

 track," or undulating line in the air. But the ingenious ex- 

 periments of Prof. Marey (Ibis, April 1870) appear to show 

 that during the down-stroke the wing moves first slightly 

 forward, then more and more backward — and in the up-stroke, 

 at first backward and then forward into its original place again, 

 thus describing, during progression, a cycloidal curve in the air ; 

 also that during the greater part of the down-stroke the wing, 

 by turning on its axis, slopes forward and downward, while 

 during the up-stroke it slopes forward and upward — thus 

 being, on this point, quite opposed to Dr. Pettigrew, who states 

 distinctly (p. 255) that during the down-stroke no depression of 

 the anterior margin and elevation of the posterior one takes 

 place. Under these circumstances a few observations that I 

 have made on the motion of the wings of the Sea-gull during 



