On Miiscidar Motion and Animal Spirits 301 



which they are until their state is changed by some 

 external cause. As to the impetus with which a 

 stone from a sling or a ball from a gun is projected, 

 we can suppose it to be nothing else than the very 

 rapid motion in which the projectiles were when 

 they emerged from the sling or the gun. But to give 

 an instance of what has been said, let us suppose a 

 pendulum let go at any point of the circle, while it 

 descends to the lowest point of the circle it does not 

 remain there at rest but mounts up to almost the 

 same height on the opposite side of the circle. But 

 what is it that causes this ascent of the pendulum ? 

 For as to gravity, it is not its character to cause the 

 ascent but on the contrary the descent of things ; 

 and yet in this case the gravity of the pendulum is 

 the cause of its ascent ; in so far as the pendulum 

 when it has come to the lowest point of the circle 

 has acquired, on account of the continued impulse of 

 its own gravity, a so much accelerated motion that it 

 can carry itself up : for so much higher as is the 

 point from which the pendulum is let go, so much 

 higher does it ascend on the other side ; and that 

 happens only because the pendulum, let fall from a 

 higher point, acquires, at the lowest point of the 

 circle, a more rapid motion and thence also a greater 

 impressed force. Nor is the case otherwise when a 

 ball is discharged from a longer gun ; for so it gains 

 a much accelerated motion, and in consequence also 

 a very great impressed force. Obviously the ac- 

 celerated motion or the impressed force of a stone 

 descending from on high, and of a ball shot out of a 

 long gun, are increased for quite the same reason, 

 because, as the stone descends or the ball passes along 

 the gun, the impetus of gravity, or the impelling force, 

 is renewed every moment. 



