9 
It is known to all persons informed on general subjects of natural 
philosopliy, that all birds of extensive flight, such as the eagle, wild 
goose and duck, usually progress at the rate of from seventy-five to 
one hundred miles per hour in a still atmosphere ; and, at this velocity, 
(as may be ascertained by a simple calculation,) they traverse the 
space of from one hundred and twenty to one hundred and forty-five 
feet per second of time. Hence, from this simple statement it is 
evident that those animals cannot exert their organs of motion in the 
manner stated, with sufiicient celerity to act upon the air to any use- 
ful purpose, whilst being borne along at such a rate by the body. 
Such an eff'ort made by the bird, with the design of propelling 
himself while contniuing on a horizontal line, would be similar to that 
of a person endeavoring to row a boat against a current of water 
which moved by him with greater velocity than that he could impart to 
the oars. At each dip of the paddles into the water, instead of effect- 
ing the desired object, those instruments would be dashed out of his 
hands by the rushing stream. And so in flight ; each turn of the 
wings, whether intentional or incidental, would only result in ob- 
structing the velocity of the animal, by presenting their broad sur- 
faces, or portions of them, to the force of the impinging atmosphere, 
which would instantly dash the parts thus exposed down to a level posi- 
tion, and to that extent disturb his equilibrium and impede his motion. 
And finally, the peculiar form of the wings being concave on one 
side and convex on the other ; strong and unyielding in the greater 
portions of their front, and attenuate and elastic throughout the back 
outlines ; their relation to, and position upon the body when spread, 
and their vertical action in flight — the latter being so easily observed 
and obviously necessary, it is remarkable that men of science especially, 
should have so long failed to discover the inevitable effect resulting 
therefrom ; the constant influence of gravity upon all bodies in motion 
on the earth and in the air alike ; and the great and uncontrollable 
velocity of winged animals whilst traversing the latter gaseous field 
of nature on a horizontal line, all of which, to a greater or less extent, 
are concerned in this process, when wisely considered, unitedly concur 
in establishing the truth of my second proposition : " That the wings 
in flight are exerted vertically^ the chief effect of which is, to raise 
and sustain the animal in the air." 
I now come to consider the effect of the velocity in flight proper, 
upon the weight of the animal, with reference to the amount of power 
2 
