FIRST PRINCIPLES OF AERIAL TRANSIT. 
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have declared that, in straight flight it apparently never moves 
its wings at all — at least, in the rapid flapping manner of 
smaller birds — and this seems to crown the mystery; for if 
there is mechanical force exerted, it shonld be indicated by some 
form of motion. But the term 44 stationary wings ” must be 
taken in a modified sense in this case, for the strokes may be 
too slow to be perceptible. It cannot be supposed that a few 
deliberate strokes, a foot or so in extent each minute, will 
propel the bird with a force not much exceeding that exerted 
by a lady’s fan in still air ; but the conditions are in reality 
widely different. If the bird, as a fixture in still air, were to 
wave its wings slowly in a stroke of twelve inches, the power 
and also the effect would be inappreciable, not greater than the 
fan ; but when the bird is traversing the air, say at the rate of 
thirty miles per hour, instead of exerting a trifling force on one 
foot perpendicular of air, during a rate of ten waves per minute, 
each stroke passes over a stratum of two hundred and sixty - 
four feet of air, and this, having its momentum undisturbed 
from the same law of reaction that applies to the support, must 
also give nearly a solid abutment for propulsion. 
Taking the albatross as a model for the utmost perfection in 
the principle of animal flight, the question of the possibility of 
imitation has to be considered. The mechanical action of the 
wing is not complicated. This bird does not find support upon 
the air by a series of downward impulses by means of any wing 
action or mechanism that gives a bearing only during the down 
stroke, and without resistance in the upward one, for the weight 
of the bird is equally sustained during the time of both the 
rise and fall — the wing, in both cases, being inclined upwards 
so that the rush of air against the inclined plane represented by 
the under surface causes a continuous and equable support. 
This is regulated by the sense of feeling of the bird, which, 
conscious of its own weight and the proper movement required 
for support, is able instantly to adapt the position of its wings, 
under all conditions of flight, so as to carry it securely. The 
faculty of propulsion requires no particular muscles for its 
performance, as it is an inherent property in the formation of 
the wing itself — the fore edge being in all cases rigid, and the 
backward part consisting of the elastic ends of a row of feathers, 
which, in slightly yielding, acts upon the air as a propeller, like 
the waving tail of a fish in water. This action may be seen, 
and the effect felt, by waving the dried extended wing of a 
large bird. 
The foregoing theory fully accounts for the necessity of lateral 
extension of wing in all birds of prolonged flight ; and in all 
attempts at imitation, where economy of motive force is a chief 
desideratum, the principle must be borne in mind. If the 
