moving forwardly into the atmosphere in the
direction of the arrows B. The measurement
across the plane vertically, along the line B,
which is called the sine of the angle, represents
the surface impact of air against the plane.

In Fig. 8 the plane is at an angle of 27 degrees,
which makes the distance in height across the line
C just one-half the length of the line B of Fig. 7,
hence the surface impact of the air is one-half that
of Fig. 7, and the drift is correspondingly decreased.

_Fig. 7. Equal Lift and Drift in Flight._

_Fig. 8. Unequal Lift and Drift._


MOVING PLANES VS. WINDS.--In this way Boisset,
Duchemin, Langley, and others, determined
the comparative drift, and those results have been
largely relied upon by aviators, and assumed to
be correct when applied to flying machines.

That they are not correct has been proven by
the Wrights and others, the only explanation being
that some errors had been made in the calculations,
or that aviators were liable to commit errors
in observing the true angle of the planes
while in flight.