second or two after it is exerted, while the action of the
motor is prolonged.

Another Simple Illustration.

Another simple means of illustrating the principle of
flying machine operation, so far as sustentation and the
elevation and depression of the planes is concerned, is
explained in the accompanying diagram.

A is a piece of cardboard about 2 by 3 inches in size.
B is a piece of paper of the same size pasted to one edge
of A. If you bend the paper to a curve, with convex
side up and blow across it as shown in Figure C, the
paper will rise instead of being depressed. The dotted
lines show that the air is passing over the top of the
curved paper and yet, no matter how hard you may
blow, the effect will be to elevate the paper, despite the
fact that the air is passing over, instead of under the
curved surface.

In Figure D we have an opposite effect. Here the
paper is in a curve exactly the reverse of that shown in
Figure C, bringing the concave side up. Now if you
will again blow across the surface of the card the action
of the paper will be downward--it will be impossible to
make it rise. The harder you blow the greater will be
the downward movement.

Principle In General Use.