POWER THE GREAT ELEMENT.--Now, let us examine
the question of this power which is able to
set gravity at naught. The quality called energy
resides in material itself. It is something within
matter, and does not come from without. The
power derived from the explosion of a charge of
powder comes from within the substance; and so
with falling water, or the expansive force of
steam.

GRAVITY AS POWER.--Indeed, the very act of the
ball gradually moving toward the earth, by the
force of gravity, is an illustration of a power
within the object itself. Long after Galileo
firmly established the law of falling bodies it began
to dawn on scientists that weight is force.
After Newton established the law of gravitation
the old idea, that power was a property of each
body, passed away.

In its stead we now have the firmly established
view, that power is something which must have
at least two parts, or consist in pairs, or two elements
acting together. Thus, a stone poised on
a cliff, while it exerts no power which can be
utilized, has, nevertheless, what is called potential
energy. When it is pushed from its lodging place
kinetic energy is developed. In both cases,
gravity, acting in conjunction with the mass of
the stone, produced power.