58 : THE ZOOLOGIST. 
move against the bird. The maximum velocity of this meeting 
of bird and air is unknown to me. I have timed the flight of 
Frigate-birds through calm air on fixed wings at 100 miles per 
hour, and their velocity seems to depend on their wishes more 
than on any limitation of the powers of translation. The minimum 
speed, however, can be approximated. For the Frigate-bird it is 
about two miles per hour, three for the Buzzards, and five for the 
Gannets. The heavier the bird the greater is the minimum 
velocity required, and a gorged Vulture cannot range itself with 
a flock of hungry ones, which are sporting in their minimum, 
without repeatedly flapping its wings. 
As soaring is a phenomenon dependent entirely on bird and 
air, which are not connected with the earth, to avoid confusion it 
is best to pay no attention to the latter. For instance, a bird 
motionless in regard to a point on the earth facing a five-mile-per- 
hour breeze; the same bird moving in calm air at the rate of five . 
miles per hour, or going with the wind at the rate of ten miles 
per hour, are identical in character so far as soaring is concerned. 
In each case the wind is meeting the bird at the rate of five miles 
per hour, and the differences of translation over the earth are 
accidental, not connected with the mechanical activities of flight. 
A bird resting in a minimum breeze cannot fall to the rear 
without descending; neither can it rise vertically nor at any 
angle obliquely to the rear. It can draw forward on the air at 
any speed, and, when the minimum is exceeded, can then fall to 
the rear or rise until the minimum is once more reached. At the 
minimum velocity the bird’s wings are stretched to their extreme 
limit, and the angle of inclination is the greatest. As the breeze 
stiffens, the bird, if it remains in the same place, flexes its pinions 
and reduces its incline. The Frigate-bird will float in a storm 
with not more than one-quarter of its wing-surfaces exposed. 
Sometimes it bends the points of its wings downwards until they 
meet underneath. 
The positions of the stretched wings in regard to a level with 
the body of the bird also varies. Those of the Frigate-bird will 
average level, the Buzzards will be above, and the Gannets below 
a level. 
For at least three hundred days in the year these birds could 
be observed in the air, and when the attention was given to their 
actions for a considerable time, at all seasons, and in the various 
