5 
popular theory of the flight of birds ; and upon this fallacious basis it 
has long stood, undoubted and undisturbed by any one, so far as I 
know, besides myself. 
Now, I object to this manner of philosophizing on this subject, and 
along with the process ot reasoning, I also reject the hypothesis as 
alike untrue. For I am well assured of the soundness of my convic- 
tions, derived from long and careful observation and reflection, that 
gravity, instead of being an obstacle, is the true foundation and chief 
force by which flight proper, and all its modifications are effected. 
And, adopting an entirely different process of investigation ^from 
that just stated, I will now proceed to make a brief exposition of my 
new theory — based upon three leading propositions containing its 
principal elements, arranged in, what I consider, both their natural 
relation and logical dependence — and constituting the first part of it. 
They are as follows : 
First, That the injiuence of gravitation is the primary and efficient 
cause o f the progression of birds on the wing. 
Second, That the wings inflight are exerted vertically ^ the chisf ef- 
fect of which is, to raise and sustain the animal in the air. 
Third, That the velocity attained in flight proper, is incidental 
and that it equalizes the power exerted in imparling motion to the wings, 
in proportion to the weight carried, with that employed by all other ani- 
mals in their respective modes of locomotion on the earth and in the 
water. 
These propositions, according to my conceptions, embrace the three 
most important elements in the process of flight proper, and I will 
endeavor to elucidate them by the aid of such powers of reasoning as 
I can command, founded on the constant exhibitions of this motion as 
they usually appear among those species of the feathered tribe which 
fly the fastest and continue longest on the wing. 
During a period of twenty years, since my attention was first di- 
rected to this subject, I have constantly observed that, among those 
birds whose weight and area of wing bear such a relation to each 
other, as to require in the process of flight three or more strokes of 
the latter, per second of time, when one such is in the act of starting 
from the earth's surface, he makes a vigorous effort with both wings 
and legs, whereby he fairly launches himself, so to speak, within the 
aerial medium, and also imparts to his body considerable motion in 
