gravitational pull.

The constant tendency of the ball to fly off at
a tangent, and the equally powerful pull of
gravity acting against each other, produce a
motion which is like that of the earth, revolving
around the sun once every three hundred and
sixty-five days.

It is a curious thing that neither Langley, nor
any of the scientists, in treating of the matter of
flight, have taken into consideration this quality
of momentum, in their calculations of the elements
of flight.

_Fig. 2 Horizontal Flight_

All have treated the subject as though the
whole problem rested on the angle at which the
planes were placed. At 45 degrees the lift and
drift are assumed to be equal.

LIFT AND DRIFT.--The terms should be explained,
in view of the frequent allusion which
will be made to the terms hereinafter. Lift
is the word employed to indicate the amount
which a plane surface will support while in flight.
Drift is the term used to indicate the resistance
which is offered to a plane moving forwardly
against the atmosphere.