Aeroplanes and Dirigibles of War | Page 8

should be cut, it would fall to the earth,
for the reason that the attractive force of the great mass of the earth is
so much greater than the force of attraction in its companion ball.
INDESTRUCTIBILITY OF GRAVITATION.--Gravity cannot be
produced or destroyed. It acts between all parts of bodies equally; the
force being proportioned to their mass. It is not affected by any
intervening substance; and is transmitted instantaneously, whatever the
distance may be.
While, therefore, it is impossible to divest matter of this property, there
are two conditions which neutralize its effect. The first of these is
position. Let us take two balls, one solid and the other hollow, but of
the same mass, or density. If the cavity of the one is large enough to
receive the other, it is obvious that while gravity is still present the lines
of attraction being equal at all points, and radially, there can be no pull
which moves them together.

DISTANCE REDUCES GRAVITATIONAL PULL.--Or the balls may
be such distance apart that the attractive force ceases. At the center of
the earth an object would not weigh anything. A pound of iron and an
ounce of wood, one sixteen times the mass of the other, would be the
same,--absolutely without weight.
If the object should be far away in space it would not be influenced by
the earth's gravity; so it will be understood that position plays an
important part in the attraction of mass for mass.
HOW MOTION ANTAGONIZES GRAVITY.--The second way to
neutralize gravity, is by motion. A ball thrown upwardly, antagonizes
the force of 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
TANGENTIAL MOTION REPRESENTS CENTRIFUGAL PULL.--A

tangential motion, or a horizontal movement, seeks to move matter
away from the center of the earth, and any force which imparts a
horizontal motion to an object exerts a centrifugal pull for that reason.
In Fig. 1, let A represent the surface of the earth, B the starting point of
the flight of an object, and C the line of flight. That represents a
tangential line. For the purpose of explaining the phenomena of
tangential flight, we will assume that the missile was projected with a
sufficient force to reach the vertical point D, which is 4000 miles from
the starting point B.
In such a case it would now be over 5500 miles from the center of the
earth, and the centrifugal pull would be decreased to such an extent that
the ball would go on and on until it came within the sphere of influence
from some other celestial body.
EQUALIZING THE TWO MOTIONS.--But now let us assume that the
line of flight is like that shown at E, in Fig. 2, where it travels along
parallel with the surface of the earth. In this case the force of the ball
equals the centripetal pull,--or, to put it differently, the centrifugal
equals the 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