246 Aérial Locomotion. (April, 
of the wing increasing as the root of the wing is receded from.” . . . ‘* The 
small humming bird, in order to keep itself stationary before a flower, requires 
to oscillate its tiny wings with great rapidity, whereas the large humming bird 
can attain the same objec by flapping its large wings with a very slow and 
powerful movement.” ... ‘In the larger birds the movements are slower in 
proportion to the size, and more especially in proportion to the length, of the 
wing. This leads me to conclude that very large wings may be driven with a 
comparatively slow motion.” 
Professor Marey illustrates the same points as under 
(p. 224) :— 
“Tt is not immaterial whether the surface which strikes the air has its max- 
imum near the body or near the extremity ; these two points have very different 
velocities. For an equal extent of surface the resistance will be greater at the 
point of the wing than at its base.” 
Again (p. 226) :— 
“Tt can be proved that, if the strokes of the wing were as frequent in large 
as in smali birds, each stroke would have a velocity whose value would in- 
crease with the size of the bird; and as the resistance of the air increases, for 
each element of the surface of the wing, according to the square of the velo- 
city of that organ, a considerable advantage would result to the bird of large 
size, as to the work produced upon the air.” 
Dr. Pettigrew shows that the vigour with which the wing 
is propelled varies according as the bird is rising, falling, or 
progressing in a horizontal direction (Trans. Linn. Soc., vol. 
XRVi PPA s27. 200, 200). hile opseqves:—— 
‘“‘ All birds which do not, like the swallow and humming birds, drop from a 
height, raise themselves at first by a vigorous leap, in which they incline their 
bodies in an upward direction. By a few sweeping strokes, delivered down- 
wards and forwards, in which the wings are nearly made to meet above and 
below the body, they lever themselves upwards and forwards, and in a sur- 
prisingly short space of time acquire that degree of momentum which greatly 
assists them in their future career.” . . . ‘‘ The forward movement of the wing 
during the down or effective stroke is particularly evident in birds when rising, 
the wing on such occasions being urged with wnusual vigour.’’—(P. 227, op. cit.) 
“« When the bird has elevated itself to the desired height, the length of the 
downward stroke is generally curtailed, the mere extension and flexion of the 
wing, assisted by the weight of the body, in some cases sufficing for the ordi- 
nary purposes of flight. This is especially the case if the bird is advancing 
against a slight breeze.” —(Pp. 260 and 261.) ‘‘If birds wish to descend, they 
may reverse the direction of the inclined plane, and plunge head foremost 
with extended wings; or they may flex the wings, and so accelerate their 
pace ; or they may raise their wings, and drop parachute fashion ; or they may 
even fly in a downward direction—a few sudden strokes, a more or less abrupt 
curve, and a certain degree of horizontal movement, being in either case 
necessary to break the fall previous to alighting.”—(P. 262, op. cit.) 
Prof. Marey, as the annexed passages show, also adverts 
to the relative frequency and force with which the wing is 
urged in ascending, descending, and horizontal flight, though 
less fully than Dr. Pettigrew does :-— 
“The frequency of the strokes of the wing varies also according as the bird 
is first starting in full flight or at the end of its flight.”—(P. 228, ‘‘ Animal 
Mechanism.”’) 
