was rushing upon the trees. Swinging his rudder in a panic, he attempted to turn. But the pace of the machine had lessened; and, there being no motive-power behind it, the abruptness of the turn robbed it suddenly of its forward speed. It wavered, came to a standstill in the air, and then side-slipped heavily, falling upon one wing-tip, and becoming an almost total wreck. But the pupil, although shaken, was not injured. A novice, in landing from a flight, has not only to gauge just where his machine will touch ground, but must estimate also how far the craft will roll upon its running wheels before it comes finally to a standstill. One beginner, alighting correctly but rather too near the rails of an aerodrome, found that his machine ran forward till it struck them, and then turned a somersault, pinning him down within his machine, but not causing him any injury. On some aircraft nowadays, so as to control this movement over the ground after alighting, a form of brake is fitted between the landing-wheels, which can be lowered by the pilot from his seat, and digs a steel prong into the ground, bringing a powerful checking influence upon the machine. A device of this kind is illustrated in Fig. 95. Such a means of stopping a machine is often very necessary, particularly in cross-country flying, for a pilot may land, say, upon a sloping field, and find that his craft is running downhill quite beyond his control, and threatening to collide either with a wall or fence. [Illustration: FIG. 95.--Ground-brake for aeroplane. A.A. Running wheels of chassis; B.B. Axle-rods; C. Brake; D. Prong which plunges into the ground; E. Wire which operates brake.]