against the air. Consequently Birds with very long wings have this great advantage, that with pre-acquired momentum, they can often for a long time fly without flapping their wings at all. Under these circumstances, a Bird is sustained very much as a boy's kite is sustained in the air. The string which the boy holds, and by which he pulls the kite downwards with a certain force, performs for the kite the same offices which its own weight and balance and momentum perform for the Bird. The great long-winged oceanic Birds often appear to float rather than to fly. The stronger is the gale, their flight, though less rapid, is all the more easy--so easy indeed as to appear buoyant; because the blasts which strike against their wings are enough to sustain the bird with comparatively little exertion of its own, except that of holding the wing vanes stretched and exposed at proper angles to the wind. And whenever the onward force previously acquired by flapping becomes at length exhausted, and the ceaseless inexorable Force of Gravity is beginning to overcome it, the Bird again rises by a few easy and gentle half-strokes of the wing. Very often the same effect is produced by allowing the Force of Gravity to act, and when the downward momentum has brought the Bird close to the ground or to the sea, that force is again converted into an ascending impetus by a change in the angle at which

the wing is exposed to the wind. This is a constant action with all the oceanic Birds. Those who have seen the Albatross have described themselves as never tired of watching its glorious and triumphant motion :--

"Tranquil its spirit seemed, and floated slow;
Even in its very motion there was rest.” 1

Rest-where there is nothing else at rest in the tremendous turmoil of its own stormy seas! Sometimes for a whole hour together this splendid Bird will sail or wheel round a ship in every possible variety of direction without requiring to give a single stroke to its pinions. Now, the Albatross has the extreme form of this kind of wing. Its wings are immensely long-about fourteen or fifteen feet from tip to tip-and almost as narrow in proportion as a riband.2 Our common Gannet is an excel

1 Professor Wilson's Sonnet, "A Cloud," &c.

2 The mechanical principle involved in the sufficiency of very narrow wings has, I believe, been adequately explained in a very ingenious paper read before the Aeronautical Society, by Mr. F. H. Wenham, C.E. It is the same mechanical principle which accounts for the narrow blades of a Screw Propeller having a resisting force as great as would be exerted upon the whole area of rotation by a solid Disc. In the case of a flat body, such as the wing of a bird, being propelled edgeways through the air, nearly the whole resisting and sustaining force is exerted upon the first few inches of the advancing surface.

lent, though a more modified, example of the same kind of structure. On the other hand, Birds of short wings, though their flight is sometimes very fast, are never able to sustain it very long. The muscular exertion they require is greater, because it does not work to the same advantage. Most of the Gallinaceous Birds (such as the common Fowl, Pheasants, Partridges, &c.) have wings of this kind; and some of them never fly except to escape an enemy, or to change their feeding-ground.

The second fact observable in reference to Birds of easy and powerful flight-namely, that their wings are all sharply pointed at the end-will lead us still further into the niceties of adjustment which are so signally displayed in the machinery of flight.

The feathers of a Bird's wing have a natural threefold division, according to the different wing-bones to which they are attached. The quills which form the end of the wing are called the Primaries; those which form the middle of the vane are called the Secondaries; and those which are next the body of the Bird are called the Tertiaries. The motion of a Bird's wing increases from its minimum at the shoulder-joint to its maximum at the tip. The primary quills which form the termination of the wing are those on which the chief burden of flight is Each feather has less and less weight to bear, and less and less force to exert, in proportion as it lies nearer

cast.