'It is a remarkable fact how this proportion of wing-surface to
weight extends throughout a great variety of the flying portion
of the animal kingdom, even down to hornets, bees, and other
insects. In some instances, however, as in the gallinaceous
tribe, including pheasants, this area is somewhat exceeded, but
they are known to be very poor fliers. Residing as they do
chiefly on the ground, their wings are only required for short
distances, or for raising them or easing their descent from
their roosting-places in forest trees, the shortness of their
wings preventing them from taking extended flights. The
wing-surface of the common swallow is rather more than in the
ratio of two square feet per pound, but having also great length
of pinion, it is both swift and enduring in its flight. When on
a rapid course this bird is in the habit of furling its wings
into a narrow compass. The greater extent of surface is
probably needful for the continual variations of speed and
instant stoppages for obtaining its insect food.

'On the other hand, there are some birds, particularly of the
duck tribe, whose wing-surface but little exceeds half a square
foot, or seventy-two inches per pound, yet they may be classed
among the strongest and swiftest of fliers. A weight of one
pound, suspended from an area of this extent, would acquire a
velocity due to a fall of sixteen feet--a height sufficient for
the destruction or injury of most animals. But when the plane
is urged forward horizontally, in a manner analogous to the
wings of a bird during flight, the sustaining power is greatly
influenced by the form and arrangement of the surface.

'In the case of perpendicular descent, as a parachute, the