h
topics as the angle of attack of the cellule, the incidence of the
wings, and the carrying power of the tail-plane. More than any other
science aviation has a vocabulary of its own, and a peculiarly
cosmopolitan one drawn from all tongues, but with the French
predominating. America gave the airplane to France, but France has
given the science its terminology.

The maps of the battlefields of this war are the marvels of military
science. Made from the air they show every road and watercourse,
every ditch and gully, every patch of woodland, every farmhouse,
church, or stonewall. Much of the early work of the aviator is in
learning to make such maps, both by sketches and by the employment
of the camera. It is no easy task. From an airplane one thousand
feet up the earth seems to be all a dead level. Slight hills, gentle
elevations, offer no contrast to the general plain. A road is not
easy to tell from a trench. All these things the aviator must first
learn to see with accuracy, and then to depict on his map with
precision. He must learn furthermore to read the maps of his
fellows--a task presupposing some knowledge of how they had been
made. He must learn to fly by a map, to recognize objects by the
technical signs upon it, to estimate his drift before the wind
because of which the machine moves sidewise _en crabe_--or like a
crab as the French phrase it.

His first flight the novice makes in a machine especially fitted for
instruction. The levers are fitted with double handles so that both
learner and tutor may hold them at once. If the greenhorn pushes
when he should pull the veteran's grip is hard on the handle to
correct the error before it can cost two lives--for in the air there
is little time to experiment. Either set of controls will steer the
machine. The pupil grasps his levers, and puts his feet on the
pedals. At first the instructor will do the steering, the pupil
following with hands and feet as the motions made by the instructor
are communicated to him by the moving levers. For a time the two
work together. Then as the instructor senses that the student
himself is doing the right thing he gradually lessens his own
activity, until after a few days' practice the student finds that he
is flying with a passenger and directing the machine himself. In
France, at any rate, they teach in brief lessons. Each flight for
instruction is limited to about five minutes. At first the student
operates in a "penguin"--a