_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twisting or screw-like action of the wings at the shoulder, in which the pinions are alternately advanced towards and withdrawn from the head in a manner analogous to what occurs at the loins in skating without lifting the feet, birds of this order can not only maintain the motion which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 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 (_c d_). 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. [Illustration: 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.”[98] [98] “On some of the Birds inhabiting the Southern Ocean.”--Ibis, 2d series, vol. i. 1865. “Tranquil its spirit seem’d and floated slow; Even in its very motion there was rest.”[99] [99] Professor Wilson’s Sonnet, “A Cloud,” etc. As an antithesis to the apparently lifeless wings of the 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.