140 Transactions. 
Art. XVI.—On the Flight of the Black-backed Gull (Larus dominicanus). 
By Captain F. W. Hurtron, C.M.Z.S. 
[Read before the Auckland Institute, 19th August, 1872. ] 
THE phenomenon of flight has of late years attracted considerable attention, 
and the subject has been very fully and ably discussed, especially by Dr. 
Pettigrew, of London (Trans. Lin. Soc., 1868, p. 197), and Professor Marey, 
of Paris (Smithsonian Report, 1869, p. 226). Both these authors have been 
very successful in explaining the flight of insects, but considerable obscurity 
seems still to exist as to the actual movements of the wings of birds when 
flying. Mr. Macgillivray (British Birds, Vol. L., p. 34) said that the effective 
stroke of the wing is delivered downward and backward, and suggested that 
during the down stroke the resistance of the air bends upward the free tips of 
the feathers, and the reaction thus produced gives a forward impulse to the 
bird. The Duke of Argyll (Reign of Law, p. 132, 1867) and Professor 
Marey both hold a similar view, but while the former maintains that the 
effective stroke is delivered directly downward, the latter says that his 
experiments prove 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 position again. Dr. Pettigrew 
on the other hand asserts that the effective stroke is delivered downward and 
forward, and that by a peculiar twisting or screwing motion of the wings, 
which I confess I do not quite understand, the air is forced to escape near the 
root of the pinion, between the secondary and tertiary feathers, in a downward 
and backward direction, thus by its reaction supporting the bird and driving 
it forward. 
Professor Marey again says 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 that during the down stroke 
no depression of the anterior margin and elevation of the posterior one takes 
place. Dr. Pettigrew, and the Duke of Argyll also, both say that during 
flight the point of the wing describes a “wave track,” or simple undulating 
line through the air, while Professor Marey says that his experiments show 
conclusively that it describes a more or less regular cycloidal curve, or looped 
line. All four authors, however, agree that the wing is extended during the 
down stroke, and more or less folded during the up stroke. Under these 
circumstances a few observations that I have made on the movements of the 
wings of the common black-backed sea-gull during flight may prove of interest, 
_ for not only do they point to a theory of progression much simpler than any 
