If, however, the suspended body be raised up from its position of forced repose by any interference that draws it to one side, the string being 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 becomes a retarded one from the same cause.  The body is now going upwards, away from the earth, and the earth’s attraction therefore drags upon it and keeps it back instead of hastening it.  As it travels up in its curved path, more and more of its weight is taken off the string, and thrown, so to speak, upon the moving impulse.  In the descending portion of the vibration the weight of the body increases its movement; in the ascending portion it diminishes its movement.  At last the upward movement becomes so slow, that the impulse of momentum is lost, and the earth’s attraction is again unopposed.  The body then begins to retrograde, acquires progressively increasing velocity as it descends, overshoots the place of its original repose, and once more commences the ascent on the opposite side.