Page:Popular Science Monthly Volume 57.djvu/486

476 flap with the base forming the front edge of the wing and the apex lying in the elbow joint.

The wing of the frigate bird, too, is quite the opposite of that of the hummer, for it is the inner portion of the wing, the upper arm and forearm, which is elongated, and instead of the six feeble secondaries of the humming-bird there are no less than twenty-four; instead of a short, stiff, rounded wing we have one that is long, flexible and pointed. Instead of a wing driven at the rate of several hundred strokes a minute there is a wing that may be held outstretched and apparently motionless for minutes at a time, the muscles of the frigate bird being almost as constantly in repose as those of the other are perpetually in motion.

If the frigate bird represents the highest type of soaring flight two more familiar birds, the turkey buzzard and albatross, are not far behind, and these represent two methods of sailing flight and two distinct modifications in the type of wings. The albatross is continually on the move, ever quartering the water as a well-trained setter does the ground, and yet with all this movement rarely mounting higher than fifty feet above the water and never wheeling in great circles in mid-air. This bird has that type of wing which best fulfills the conditions necessary for an aeroplane, being long and narrow, so that while a fully grown albatross may spread from ten to twelve feet from tip to tip, this wing is not more than nine inches wide. This spread of wing, like that of the frigate bird, is gained by the elongation of the inner bones of the wing and by increasing the number of secondaries, there being about forty of these feathers in the wing of the albatross.

The turkey buzzard is emphatically a high flyer, wheeling slowly about, half a mile or a mile above the earth, while his cousin, the condor, so Humboldt tells us, has been seen above the summit of Chimborazo. If any bird knows how to utilize every breath of wind to the utmost that bird is the albatross, and it is equally a delight and a marvel to see this bird apparently setting at naught all natural laws as he sails with outstretched pinions almost into the eye of the wind or hangs just off the lee quarter of a ship reeling off ten or twelve knots an hour. In this last trick, however, the gull is almost equally expert, evidently making use of the draft from the sails as well as of the eddies caused by the passage of the vessel.

It has long been evident that if man is to navigate the air it must be done after the method of the albatross rather than that of the humming-bird, by the aeroplane and not by any device to imitate the strokes of a bird's wings, for not only do the largest birds and those of the longest flight for the most part sail or soar, but it is apparent that the limit of size in a vibrating wing must soon be reached, since in a strong wind with its varying eddies it would be quite out of the question to manipulate such a piece of mechanism.