the moment he pauses gravitation exercises a force much greater that when he glides.
While hovering there are several forces balanced: first, the original impetus onwards; secondly, that of the depressed tail dragging and stopping that onward course; thirdly, that of the wing beating downwards; and fourthly, that of the wing a very little reversed beating forwards, like backing water with a scull. When used in the ordinary way the shape of the wing causes it to exert a downward and a backward pressure. His slip is when he loses balance: it is most obviously a loss of balance; he quite oscillates sometimes when it occurs; and now and then I have seen a kestrel unable to catch himself, and obliged to proceed some distance before he could hover again. Occasionally, in the slip he loses a foot or so of elevation, but not always. While actually hovering, his altitude does not vary an inch. All and each of these movements and the considerations to which they give rise show conclusively that the act of hovering is nothing more or less than an act of balancing; and when he has his balance he will rest a moment with outstretched wings kept still. He uses his wings with just sufficient force neither to rise nor fall, and prevents progress by a slightly different stroke.
The next point is, Where does he hover? He hovers any and everywhere, without the slightest choice. He hovers over meadows, cornfields; over the tops of the highest downs, sometimes at the very edge of a precipice or above a chalk quarry; over gardens, waste ground; over the highway; over
