42 
ITS VARIOUS EVOLUTIONS. 
time witli a simultaneous downward and 
backward motion, lus body is propelled in 
advance. A Frencli observer — M. Marcy — 
has ascertained that the force which sustains and 
directs the bird in the realms of air is wholly created 
during the lowering of the arm ; and that the wing- 
tip in the movements of translation describes a series 
of continuous curves. According to this authority, 
the sparrow makes thirteen evolutions of the wing 
per second, the wild duck nine, the 
pigeon eight, the barn-owl only five, 
the buzzard three ; and, contrary to 
the opinion of most observers, the 
duration of the lowering movement 
of the wing exceeds that of the 
LEAKNINO TO n,Y. 
movement of elevation. The wing- 
strokes succeed one another, some- 
times slowly, sometimes rapidly ; the anterior margin is some- 
times raised, sometimes depressed, accoi'ding as the bird flies 
swiftly or slowly, hovers, or describes a circular flight. When 
he wishes to sink to the ground, he folds them up completely. 
The bend of the arch of the wing indicates that the bird is 
flying against the wind ; the air-current which strikes it in 
front raises the wing, and the bird with it; while that from behind 
ruffles and disarranges the feathers, and considerably impedes progres- 
sion. In guiding his flight, the bird uses his tail as a rudder : when he 
would rise, he raises it ; when he would sink, he lowers it ; and when 
he would go sideways, he moves it diagonally. 
The rapidity, nature, and type of the bird's flight vary with the 
conformation of the wing and of the plumage generally. Long, 
pointed, acuminated wings, with resistent pens and short feathers, 
