would be inevitably opened, and the integrity of the wing impaired by a downward and backward movement. 5th. The disposition of the articular surfaces of the wing (particularly that of the shoulder-joint) is such as to facilitate the downward and forward movement, while it in a great measure prevents the downward and backward one. 6th and lastly. If the wing did in reality strike downwards. and backwards, a result the converse of that desired would most assuredly be produced, as an oblique surface which smites the air in a downward and backward direction (if left to itself) tends to depress the body bearing it. This is proved by the action upon the air of free inclined planes, arranged in the form of a screw. 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,1 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." Birds of Flight divisible into four kinds :— 1st. Such as have heavy bodies and short wings with a rapid movement (fig. 59, p. 126). 1 The average weight of the albatross, as given by Gould, is 17 lbs.-Ibis, 2d series, vol. i. 1865, p. 295. 2 "On some of the Birds inhabiting the Southern Ocean," by Capt. F. W. Hutton.-Ibis, 2d series, vol. i. 1865, p. 282. 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. 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. The albatross (fig. 105, p. 200) and pelican afford instances of the third class, embracing the heavy-bodied, longwinged birds. The duck (fig. 107, p. 204), pigeon (fig. 106, p. 203), crow and thrush, are intermediate, both as regards the size of the wing and the rapidity with which it is made to oscillate. These constitute the fourth class. The albatross (fig. 105, p. 200), swallow, eagle, and hawk, provide instances of sailing or gliding birds, where the wing is ample, elongated, and more or less pointed, and where ad vantage is taken of the weight of the body and the shape of the pinion to utilize the air as a supporting medium. In these the pinion acts as a long lever, and is wielded with great precision and power, particularly at the shoulder. The Flight of the Albatross compared to the Movements of a Compass set upon Gimbals.-A careful examination of the movements in skimming birds has led me to conclude that by a judicious twisting or screw-like action of the wings at the shoulder, in which the pinions are alternately advanced towards and withdrawn from the head in a manner analogous to what occurs at the loins in skating without lifting the feet, birds of this order can not only maintain the motion which they secure by a few energetic flappings, but, if necessary, actually increase it, and that without either bending the wing or beating the air. The forward and backward screwing action of the pinion referred to, in no way interferes, I may remark, with the rotation of the wing on its long axis, the pinion being advanced and screwed down upon the wind, and retracted and unscrewed alternately. As the movements described enable the sailing bird to tilt its body from before backwards, or 1 Advantages possessed by long Pinions.-The long narrow wings are most effective as elevators and propellers, from the fact (pointed out by Mr. Wenham) that at high speeds, with very oblique incidences, the supporting effect becomes transferred to the front edge of the pinion. It is in this way "that the effective propelling area of the two-bladed screw is tantamount to its entire circle of revolution." A similar principle was announced by Sir George Cayley upwards of fifty years ago. "In very acute angles with the current, it appears that the centre of resistance in the sail does not coincide with the centre of its surface, but is considerably in front of it. As the obliquity of the current decreases, these centres approach, and coincide when the current becomes perpendicular to the plane; hence any heel of the machine backwards or forwards removes the centre of support behind or before the point of suspension."-Nicholson's Journal, vol. xxv. p. 83. When the speed attained by the bird is greatly accelerated, and the stratum of air passed over in any given time enormously increased, the support afforded by the air to the inclined planes formed by the wings is likewise augmented. This is proved by the rapid flight of skimming or sailing birds when the wings are moved at long intervals and very leisurely. The same principle supports the skater as he rushes impetuously over insecure ice, and the thin flat stone projected along the surface of still water. The velocity of the movement in either case prevents sinking by not giving the supporting particles time to separate. the converse, and from side to side or laterally, it may be represented as oscillating on one of two centres, as shown at fig. 105; the one corresponding with the long axis of the body (fig. 105, a b), the other with the long axis of the wings (cd). Between these two extremes every variety of sailing and gliding motion which is possible in the mariner's compass when set upon gimbals may be performed; so that a skimming or sailing bird may be said to possess perfect command over itself and over the element in which it moves. с ს -d FIG. 105. Captain Hutton makes the following remarkable statement regarding the albatross :-"I have sometimes watched narrowly one of these birds sailing and wheeling about in all directions for more than an hour, without seeing the slightest movement of the wings, and have never witnessed anything to equal the ease and grace of this bird as he sweeps past, often within a few yards, every part of his body perfectly motionless except the head and eye, which turn slowly and seem to take notice of everything.' "1 "Tranquil its spirit seem'd and floated slow; Even in its very motion there was rest."2 As an antithesis to the apparently lifeless wings of the 1 "On some of the Birds inhabiting the Southern Ocean."-Ibis, 2d series, vol. i. 1865. 2 Professor Wilson's Sonnet, "A Cloud," etc. albatross, the ceaseless activity of those of the humming-bird may be adduced. In those delicate and exquisitely beautiful birds, the wings, according to Mr. Gould, move so rapidly when the bird is poised before an object, that it is impossible for the eye to follow each stroke, and a hazy circle of indistinctness on each side of the bird is all that is perceptible. When the humming-bird flies in a horizontal direction, it occasionally proceeds with such velocity as altogether to elude observation. The regular and irregular in Flight.—The coot, diver, duck, and goose fly with great regularity in nearly a straight line, and with immense speed; they rarely if ever skim or glide, their wings being too small for this purpose. The woodpecker, magpie, fieldfare and sparrow, supply examples of what may be termed the "irregular" in flight. These, as is well known, fly in curves of greater or less magnitude, by giving a few vigorous strokes and then desisting, the effect of which is to project them along a series of parabolic curves. The snipe and woodcock are irregular in another respect, their flight being sudden, jerky, and from side to side. Mode of ascending, descending, turning, etc.—All birds which do not, like the swallow and humming-birds, drop from a height, raise themselves at first by a vigorous leap, in which they incline their bodies in an upward direction, the height thus attained enabling them to extend and depress their wings without injury to the feathers. By a few sweeping strokes delivered downwards and forwards, in which the wings are made nearly to meet above and below the body, they lever themselves upwards and forwards, and in a surprisingly short time acquire that degree of momentum which greatly assists them in their future career. In rising from the ground, as may readily be seen in the crow, pigeon, and kingfisher (fig. 102, p. 183), the tail is expanded and the neck stretched out, so that the body is converted into an inclined plane, and acts mechanically as a kite. The centre of gravity and the position of the body are changed at the will of the bird by movements in the neck, feet, and tail, and by increasing or decreasing the angles which the under |