With the exception of the difference in the wings mentioned above, the structure of the eagle and falcon is very similar, and as has been pointed out, the larger of two birds of similar structure once it gets going is almost invariably faster, owing no doubt to its superior muscular power and driving force. In comparing the downward flight of the eagle and falcon it is also necessary to recollect the advantage which the former has by reason of its much greater weight. It is difficult to obtain thoroughly reliable records of the weights of the golden eagle and the different falcons; but so far as I can ascertain, the weight of the eagle varies from 8½ to 12½ lb., that of the gyr-falcon from 3 to 3¾ lb., and that of the peregrine from 2 to 3 ounces under 2 lb. to 2¾ lb., in each case of course the female bird being heavier than the male. But for the resistance of the air, all bodies, light or heavy, small or large, would fall at the same rate. In fact, however, as velocity increases a notable air resistance is set up which increases rapidly. The velocity of a body falling freely _in vacuo_ is over forty miles per hour at the end of two seconds, over sixty at the end of three seconds, and so on. We all know by experience the great force exerted by a wind of a velocity even as low as thirty miles an hour, which most people would call a hurricane. But it is not perhaps so generally known that in proportion to its weight, other things such as shape and specific gravity being similar, a small body experiences much greater resistance than a large body. The resistance of the air to the fine particles of vapour which constitute a cloud is such that they only fall at the same rate of a few feet per hour. And in the case of two birds of similar shape and specific gravity, but one eight times the weight of the other, the larger bird would ultimately attain a velocity roughly twice as great as the other, if both fell for a sufficient distance to attain their limiting velocities, _i.e._ the velocity at which the resistance offered by the air is equal to the attraction of gravity. Similarly if the one bird were four times the weight of the other, the velocity ultimately attained under the conditions mentioned would be roughly one and a half times as great as the other. In “Notes by an Old Stalker” in the _Field_ for September 9, 1922 (p. 370) there appears the following interesting account of a duel between a golden eagle and a peregrine which the writer himself witnessed: