backward from an observation car register the train's motion.
In the air there are no stones or trees or telegraph poles—no milestones for the eye, to act as speed indicators. Only a somewhat flattened countryside below, placidly slipping away or spreading out. Even when the plane's velocity is greatly altered no noticeable change in the whole situation ensues—80 miles an hour at several thousand feet is substantially the same as 140, so far as the sensations of sight and feeling are concerned.
Piloting differs from driving a car in that there is an added necessity for lateral control. An automobile runs up and down hill, and turns left or right. A plane climbs or dives, turns, and in addition, tips from one side to another. There is no worry in a car about whether the two left wheels are on the road or not; but a pilot must normally keep his wings level. Of course
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