gravity during the period of its ascent. In like
manner, when an object is projected horizontally,
while its mass is still the same, its weight is less.

Motion is that which is constantly combating
the action of gravity. A body moving in a circle
must be acted upon by two forces, one which tends
to draw it inwardly, and the other which seeks to
throw it outwardly.

The former is called centripetal, and the latter
centrifugal motion. Gravity, therefore, represents
centripetal, and motion centrifugal force.

If the rotative speed of the earth should be retarded,
all objects on the earth would be increased
in weight, and if the motion should be accelerated
objects would become lighter, and if sufficient
speed should be attained all matter would fly off
the surface, just as dirt dies off the rim of a
wheel at certain speeds.

A TANGENT.--When an object is thrown horizontally
the line of flight is tangential to the earth,
or at right angles to the force of gravity. Such
a course in a flying machine finds less resistance
than if it should be projected upwardly, or directly
opposite the centripetal pull.

_Fig 1. Tangential Flight_