oward the
jet, instead of being driven away from it. A well
known spraying device, called the "ball nozzle,"
is simply a ball on the end of a nozzle, and the
stream of water issuing is not effectual to drive
the ball away.

From the bird incident alluded to, a new theory
was propounded, namely, that birds flew because
of the aspirated action of the air, and the wings
and body were so made as to cause the moving air
current to act on it, and draw it forwardly.

OUTSTRETCHED WINGS.--This only added to the
"bird wing" theory a new argument that all flying
things must have outstretched wings, in order
to fly, forgetting that the ball, which has no
outstretched wings, has also the same "aspirate"
movement attributed to the wings of the bird.

The foregoing remarks are made in order to impress
on the novice that theories do not make
flying machines, and that speculations, or analogies
of what we see all about us, will not make an
aviator. A flying machine is a question of
dynamics, just as surely as the action of the sun on
the air, and the movements of the currents, and
the knowledge of applying those forces in the flying
machine makes the aviator.

THE STARTING POINT.--Before the uninitiated
should attempt to even mount a machine he should
know what it is composed of, and how it is made.
His investigation should take in every part of the
mechanism; he should understand about the plane
surface, what the stresses are upon its surface,
what is the duty of each strut, or brace or wire
and be able to make the proper repairs.

THE VITAL PART OF THE MACHINE.--The motor,
the life of the machine itself, should be like a
book to him. It is not required that he should
know all the theories which is necessary in the
building, as to the many features which go to
make up a scientifically-designed motor; but he
must know how and why it works. He should understand
the cam action, whereby the valves are
lifted at the proper time; what the effect of the
spark advance means; the throttling of the engine;
air admission and supply; the r