still kept on the stretch, it will be observed that it has been made to
move in a curved line away from the earth's attracting mass, and that
the pull of the attraction is then to a certain extent taken off from
the string and transferred to the supporting hand; the force of the
attraction consequently becomes then sensible as the weight of the body
that is upheld. If in this state of affairs the supporting hand is taken
away, the body at once rushes down sideways to the position it before
occupied, with a pace accelerating considerably as it goes; for the
earth continues to attract it during each instant of its descent. When
it has reached the second stage of its journey, it is moving with a
velocity that is caused by the addition of the attraction exercised in
that stage to the attraction that had been exercised in the first stage;
and so of the third, fourth, and other successive stages. It must go
quicker and quicker until it comes to the place which was before its
position of absolute repose.

But when it has at last arrived at this place, it cannot rest there, for
during its increasingly-rapid journey downwards, it has been
perseveringly acquiring a new force of its own--an onward impulse that
proves to be sufficient to carry it forward and upward in spite of the
earth's pressing solicitation to it to stay. Moving bodies can no more
stop of their own accord than resting bodies can move of their own
accord. Both require that some extraneous force shall be exerted upon
them before the condition in which they are can be changed.

Now, in the case of the vibrating pendulum, it is the downward pull of
the earth's attraction that first causes the stationary body to move,
and as this commencing motion is downwards, in the direction of the
pull, it is also an accelerating one. As soon, however, as this motion
is changed by the resistance of the string into an upward one, it