So much for the appearance of hawks when standing at ease on the block or perch. As soon as they are put on the wing the task of distinguishing between them in point of merit becomes very much more easy. The good hawk, when in good condition, has a buoyancy in the air which is wanting in the other. She flies with less effort, and as if she liked the exercise. It seems as natural to her to fly in a slanting line upwards as on a level. When she spreads her wings and sails along they are held out to the very farthest possible extent, and kept "flat": that is to say, the tips are on a level with the back of the head, or even a little above it. The fast flier does not usually go along steadily through the air, moving, as a boating man would say, on an even keel. On a windy day one wing is often higher than the other, and her course swerves more or less from time to time as she utilises or counteracts with a marvellous art, not understood of men, the wayward pressure of the disturbed air. If you have to choose between a hack hawk, which makes her way along with regular beats of beautifully even wings, like a heron or a dove, and one which hurls herself forward in unexpected lines like a lapwing, by all means choose the latter. Do not suppose that either lapwings or haggard peregrines go crooked by accident, or because they know no better. They can go straight enough if they choose, and will do so if it happens to be their game to play. But just as a skater, having only one skate on the ice, can go along if he moves in divergent lines but not if he attempts to keep a straight line, so it seems that by a sort of zigzaggy course more pace can be got up than by mere plodding straight-forward work. It is only after watching many hundreds of flights that a man can hope even to begin to understand how birds, both pursuer and pursued, manoeuvre in the air, trimming their sails, so to speak, so as to increase to the utmost, the one the momentum of her stoop, and the other the speed and suddenness of its shift.