248 Aérial Locomotion. [April, 
Prof. Marey again corroborates Dr. Pettigrew’s original 
observations, as the subjoined extract from “ Animal 
Mechanism ” will show (p. 254) :— 
“The inspection of the curve shows us also that the pigeon’s wing was 
carried more especially in the direction of the upper parts, similar to the 
point A; in other terms, that the forward predominated over the backward 
movement.” 
Dr. Pettigrew describes and figures the body of the bird 
in flight as ‘alternately rising and falling in forward curves, 
the curves described by the body being the opposite of those 
described by the wing, those movements being due to a kite- 
like action of the wings (Trans. Roy. Soc. Edin., vol. xxvi., 
Pp- 343, 344). Thus Dr. Pettigrew remarks :— 
‘“Tt is a condition of natural wings, and of artificial wings constructed on 
the principle of living wings, that, when forcibly elevated or depressed, even 
in a strictly vertical direction, they inevitably dart forward. In both cases the 
wing describes a waved track, which clearly shows that the wing strikes 
downwards and forwards during the down stroke, and upwards and forwards 
during the up stroke. The wing, in fact, is always advancing, its under 
surface attacking the airy like a boy’s kite.” . . . . “As the body of the 
insect, bat, and bird, falls forward in a curve when the wing ascends, and is 
elevated in a curve when the wing descends, it follows that the trunk of the 
animal is urged along a waved line. I have distin&ly seen the alternate rise 
and fall of the body and wing, when watching the flight of the gull from the 
stern of a steamboat.” 
Professor Marey writes in a very similar strain. He asks 
(pp. 264, 265) :— 
“But do we find that the bird, when suspended in the air, keeps at a con- 
stant level, or does it pass through oscillations in the vertical plane? Do we 
not experience, by the intermittent effect of the flapping of its wings, rising 
and falling motions, of which the eye can detect neither the frequency nor 
extent ? Again, does not the bird advance in its onward course, with variable 
rapidity? Shall we not find in the action of its wings a series of impulses, 
which give to its advancing course a jerking motion? These queries can be 
answered experimentally.” ae - “To explain the ascent of the bird 
during the time of the elevation of the wing, it seems indispensable to refer to 
the effect of the child’s kite, to which we have before alluded. The bird, 
having acquired a certain velocity, presents its wings to the air as inclined 
planes.” > © . ‘Thus, by registering at the same time the two orders 
of oscillation in the flight of a buzzard, we find that the phase of depression 
of the wing produces at the same time the elevation of the bird and the accele- 
ration of its horizontal swiftness.” —(P.269). . . ‘‘ A part of this resistance, 
viz., that which is applied to the lower surface of the wing, is utilised to 
sustain the bird by the kind of action which we have compared to that of a 
child’s kite. It appears that this action is of primary importance in the flight 
of the bird.’—(P. 275). . . ‘Inthe bird, one of the phases of the move- 
ment of the wing is, to a certain extent, passive; that is to say, it receives 
the pressure of the air on its lower surface, when the bird is projected rapidly 
forward by its acquired velocity. Under these conditions, the whole bird, 
being carried forward in space, all the parts of the wing are moved with the 
same rapidity, to take advantage of the action of the air, “which presses on them 
as on a kite.’’—(P. 276). 
Dr. Pettigrew explains that the wing is a screw structurally 
and functionally ; that it revolves on two axes (the one 
