_The Wing acts as an Elevator, Propeller, and Sustainer, both during extension and flexion._--The wing, as has been explained, is recovered or drawn off the wind principally by the contraction of the elastic ligaments extending between the joints, so that the pinion during flexion enjoys a certain degree of repose. The time occupied in recovering is not lost so long as the wing makes an angle with the horizon and the bird is in motion, it being a matter of indifference whether the wing acts on the air, or the air on the wing, so long as the body bearing the latter is under weigh; and this is the chief reason why the albatross, which is a very heavy bird,[95] can sail about for such incredible periods without flapping the wings at all. Captain Hutton thus graphically describes the sailing of this magnificent bird:--“The flight of the albatross is truly majestic, as with outstretched motionless wings he sails over the surface of the sea--now rising high in air, now with a bold sweep, and wings inclined at an angle with the horizon, descending until the tip of the lower one all but touches the crest of the waves as he skims over them.”[96] [95] The average weight of the albatross, as given by Gould, is 17 lbs.--Ibis, 2d series, vol. i. 1865, p. 295. [96] “On some of the Birds inhabiting the Southern Ocean,” by Capt. F. W. Hutton.--Ibis, 2d series, vol. i. 1865, p. 282. _Birds of Flight divisible into four kinds:--_ _1st._ Such as have heavy bodies and short wings with a rapid movement (fig. 59, p. 126). _2d._ Such as have light bodies and large wings with a leisurely movement (fig. 60, p. 126; fig. 103, p. 186). _3d._ Such as have heavy bodies and long narrow wings with a decidedly slow movement (fig. 105, p. 200). _4th._ Such as are intermediate with regard to the size of body, the dimensions of the wing, and the energy with which it is driven (fig. 102, p. 183; fig. 106, p. 203; fig. 107, p. 204). They may be subdivided into those which float, skim, or glide, and those which fly in a straight line and irregularly. The pheasant, partridge (fig. 59, p. 126), grouse, and quail, furnish good examples of the heavy-bodied, short-winged birds. In these the wing is rounded and deeply concave. It is, moreover, wielded with immense velocity and power. The heron (fig. 60, p. 126), sea-mew (fig. 103, p. 186), lapwing (fig. 63, p. 138), and owl (fig. 104), supply examples of the second class, where the wing, as compared with the body, is very ample, and where consequently it is moved more leisurely and less energetically. [Illustration: FIG. 104.--The Cape Barn-Owl (_Strix capensis_, Smith), as seen in full flight, hunting. The under surface of the wings and body are inclined slightly upwards, and act upon the air after the manner of a kite. (Compare with fig. 59, p. 126, and fig. 102, p. 183.)--_Original._]