Of all birds, the albatross has, perhaps, the most extended powers of flight. It has been known to follow a vessel for several successive days without once touching the water except to pick up floating food; and even then it does not rest. In describing the flight of this bird from personal observation, Captain Hutton writes as follows: "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 the 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 crests of the waves as he skims over them. 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. 'Tranquil its spirit seemed and floated slow; even in its very motion there was rest.'" But these birds and the frigate bird are sea and ocean species, and, with rare exceptions, are able to rest upon the waters. This, however, cannot be said of many of the land birds, and here observation is easier. As an antithesis to the apparently lifeless wings of the albatross, Pettigrew compares the ceaseless activity of those of the humming-bird. In these delicate and exquisitely beautiful birds, the wings, according to 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 the bird is all that is perceptible. When a humming-bird flies in a horizontal direction, it occasionally proceeds with such velocity as altogether to elude observation. Mention of the calm majestic flight of the albatross suggests the possibility of birds resting on the wing. An American naturalist asserts that birds of prey and some others have the power to lock securely together those parts of the wing holding the extended feathers, and corresponding to the fingers of the human hand. The action of the air on the wing in this condition extends the elbow, which is prevented from opening too far by a cartilage, and the wings may keep this position for an indefinite length of time, with no muscular action whatever on the part of the bird. While resting in this way, the bird cannot rise in a still atmosphere; but if there be a horizontal current, it may allow itself to be carried along by it, with a slight tendency downward, and so gain a momentum by which, with a slight change of direction, it may rise to some extent, still without muscular action of the wings. This same naturalist also believes it quite possible for birds to sleep on the wing. As bearing on this subject, Professor J. S.