12 
longing the time of his fall, while progressing on the line of motion 
at the rate of one hundred miles per hour, produced alone by this 
irregular tendency downward and acceleration, and controlled entirely 
by the resistance of the medium through which he moves, and which 
necessarily involves a large portion of his weight in his velocity, and 
thereby reduces the amount of power required in this process, com- 
pared with what was necessary to overcome his inertia on starting 
from the earth, so far as to enable him thus to continue as long as 
bone and muscle can endure this kind of gentle exercise — during a 
whole day, or even to the extent of making a great circuit around the 
earth — yes, and forever, if it were pos^ble to continue the required 
celerity of wing. 
But usually, when coming within sight of the place of destination, 
this species of birds effect their descent by merely relaxing their 
muscular exertion, and thus, under a corresponding reduced action of 
the organs of motion, the weight soon brings them to the earth. And 
it may as well be said here, as elsewhere, that those birds whose 
organs of motion are very large in proportion to their weight, always 
descend on the motionless wings which, from their greatly extended 
surfaces, sufficiently resist the influence of gravity as to make the 
fall gradual ; while at the same time, from the flexibility of the back 
portions of them, they assume the form of two inclined plans between 
which the body smoothly and gracefully glides towards, and when 
coming near the earth, it often occurs that the force of the velocity 
is broken by one or more cycloid movements. 
I will now offer an explanation of the manner in which some of 
those large-winged birds, just alluded to, ascend by gyratory move- 
ments on the motionless wings, and which exhibitions occur almost 
daily throughout the southern portion of the United States. But, in 
the first place, I will here state the converse of the rule above laid 
down, with reference to the best adaptation of the organism of birds 
for easy-going and long-continued flight ; namely : when the wings 
are greatly enlarged without a proportionate increase of the weight of 
the animal, the number of strokes of the former is correspondingly 
reduced within a given time, and the capacity for rapid progression 
(except along with the currents of high winds ^ is equally lost. 
And this peculiarity is strikingly exhibited in that species of the 
falcon commonly called the buzzard, the true process of whose grace- 
ful and noiseless gyration.^ on the wing I will now unfold. 
