334 



ON THE CONSERVATION OF FORCE. 



raised to the height A a. Hence my arm must exert a 

 certain force to bring the weight to a. Gravity resists 

 this motion and endeavours to bring back the weight to 

 M, the lowest point which it can reach. 



Now, if after I have brought the weight to a I let it 

 go, it obeys this force of gravity and returns to M, arrives 

 there with a certain velocity, and no longer remains 

 quietly hanging at M as it did before, but STK ings be- 



FIG. 43. 

 P 



yond M towards 6, where its motion stops as soon as it 

 has traversed on the side of B an arc equal in length to 

 that on the side of A, and after it has risen to a distance 

 B b above the horizontal line, which is equal to the height 

 A a, to which my arm had previously raised it. In b the 

 pendulum returns, swings the same way back through M 

 towards a, and so on, until its oscillations are gradually 

 diminished, and ultimately annulled by the resistance of 

 the air and by friction. 



