BIRDS CLIMBING THE AIR.
Two hawks come over the trees, and, approaching each other, rise higher into the air. They wheel about for a little without any apparent design, still rising, when one ceases to beat the air with his wings, stretches them to their full length, and seems to lean aside. His impetus carries him forward and upward, at the same time in a circle, something like a skater on one foot. Revolving round a centre, he rises in a spiral, perhaps a hundred yards across; screwing upwards, and at each turn ascending half the diameter of the spiral. When he begins this it appears perfectly natural, and nothing more than would necessarily result if the wings were held outstretched and one edge of the plane slightly elevated. The impulse of previous flight, the beat of strong pinions, and the swing and rush of the bird evidently suffice for two or three, possibly for four or five, winding movements, after which the retarding effects of friction and gravitation ought, according to theory, to gradually bring the bird to a stop. But up goes the hawk, round and round like a woodpecker climbing a< tree; only
