“Looping the loop,” which has made so great a sensation, has taught airmen one definite lesson; and it is this: no matter how their machines may be beaten and tossed by the wind, they need not fear a fall--provided they are high enough above ground. The movements of a machine, as it makes a series of “loops,” are shown in Fig. 57. The pilot reaches a high speed before he rears up his machine to begin the “loop,” and this downward velocity is attained by diving; then, when he estimates his pace sufficient, he pulls his elevating-lever back and the machine leaps upward, rearing itself vertically towards the sky, turning over on its back, then diving again and coming right-side-up--thus achieving a complete somersault. A skilled trick-flyer, also, will allow his machine to drop sideways or tail first, deliberately working the controls so that it shall do so. Then, just as it seems to spectators that he is falling to destruction, he will dive or twist, regain the mastery of his machine, and descend in a normal glide. An airman, flying in a wind, is rather in the position of a man who puts to sea in a small boat when waves are high. Once he can clear the shore, the boatman feels at ease; but should a breaker catch him before he reaches the smooth, rolling billows a little distance from the beach, his craft may be overturned and dashed to pieces. So with the airman; his moments of peril, when flying in a gusty wind, come just as he is soaring from the ground, and when descending from a flight. Then an air-wave, like a sea-wave, may lift his craft and drive it with a crash to earth. [Illustration: FIG. 57.--Looping the loop.] And there is the peril, when near the ground, of a down-rush of wind caused by hills or woods. More than once, when making a landing near trees, a pilot has found his machine swept in a descending current. What happens, in such a case, is that the wind curls over the wood or hill that may form the obstruction, and sends a strong eddy downward; should a machine be caught in such a trend, it may be carried to earth, pell-mell, before the pilot can check its dive. Again--as another unseen danger--there are “holes in the air.” The atmosphere is in constant movement, it must be remembered; currents of warm air ascending and currents of cold air descending; and sometimes, between a layer of warm air and a layer of cold, there may be violent swirls and eddies. An aeroplane may fly into such a disturbed area and fall suddenly a distance of many feet, through being caught and swept earthward in a rapidly descending current.