Hurroy.—On the Flight of the Black-backed Gull. 141 
hitherto proposed, but they also supply an explanation of many of the 
differences between other authors, and this curiously enough by showing that 
they are mistaken in the only point on which they are all agreed, viz., the 
folding of the wing during the up stroke. 
Before, however, describing my observations, I will mention some of the 
very interesting experiments made by Dr. Pettigrew on the flight of sparrows, 
with their wings cut in different ways, which, in my opinion, not only 
annihilate, as he says, Mr. Macgillivray’s theory, but his own also. 
From his experiments I pick out the following as the most decisive. 
1. Half of the secondary feathers of both pinions detached in the direction 
of the long axis of the wing, the primaries being left intact. Reswit.—Flight 
perfect. 
2. Half of the primary feathers in the long axis of either pinion detached, 
the secondaries being left intact. esw/t—When one wing only was operated 
on flight was perfect, when both were cut it was slightly laboured. 
3. Primary and secondary feathers from both wings removed alternately. 
Result.—Flight nearly perfect. 
4, Half the primary feathers from either wing removed transversely, 
Result.—When one wing only was operated on flight was but very slightly 
impaired, when both were cut the bird flew heavily and came to the ground at 
no great distance. 
These experiments prove that cutting the wings in the direction of the 
long axis interferes very little with flight, but that if the tips of the primaries 
are cut off transversely the effect is very evident. This, in other words, _ 
means that flight depends principally on the primary feathers of the wing, and 
not on the secondaries, while both Mr. Macgillivray’s and Dr. Pettigrew’s 
theories imply quite the reverse, for the former says that progression is 
obtained by the uplifting of the secondary feathers, and the latter by the 
secondary feathers forming a kind of funnel which compels the air to escape in 
a backward direction. Dr. Pettigrew himself (/.c., 245) says that “the 
bending up of the shafts of the feathers during the descent of the wing would 
impair its efficiency by permitting more air to escape along its posterior, or 
thin margin, than is necessary ;” much more, therefore, ought its efficiency to 
be impaired by cutting off the shafts of the feathers. But experiment proves 
clearly that such is not the case. 
There is no better time for observing the movements of the wings of a 
bird than when at sea, steaming against a fresh breeze, and surrounded by a 
flock of sea-gulls. Under these circumstances the birds often appear to be 
quite stationary, sometimes straight overhead, sometimes astern, and some- 
times on one or the other quarter, so that distinct views from below, from the 
front, or from one side, can be obtained, while the movements òf the wings of 
