MECHANICS. 



13 



and B are two equal cylindrical weights 

 suspended from the ends of the thread, 



which rests in a groove on the edge of 

 the wheel bed. S is a small stage 

 which can be screwed upon the gradu- 

 ated shaft, at any particular division at 

 which it is designed to stop the descent 

 of the weight. G is a clock, attached 

 to the principal pillar, which beats se- 

 conds, in order to mark the rate of de- 

 scent. 



The weights A B are, commonly, so 

 adjusted, that, by placing on the top of 

 the cylindrical weight A a weight O of 

 a quarter of an ounce, the weight A will 

 descend through three inches in one 

 second. Thus we have obtained an 

 accelerating force, which is sixty-four 

 times less than that of gravity, and yet 

 which retains all the characteristic pe- 

 culiarities of that force. In fact it is 

 the force of gravity correctly represented 

 in miniature. 



(38.) We shall now show how this 

 machine is applied to establish by expe- 

 riment the laws which regulate the de- 

 scent of heavy bodies and which have 

 been already explained. 



Ex. 1. To establish these laws by 

 experiment, a ring R is provided, at- 

 tached to a block E, which can be fixed 

 by a screw to any division of the gradu- 

 ated shaft. A bar of metal /is also pro- 

 vided, weighing a quarter of an ounce, 

 and longer than the diameter of the ring 

 R. Let the ring R be fixed by the 

 screw to any division of the scale, and 

 let the stage S be so fixed, that when 

 the weight A rests upon it, the top of 

 the weight Will be six inches exactly 

 below the ring R. This done, let the 

 weight A be elevated by drawing down 

 the weight B until the top of the weight 

 A is exactly three inches above the 

 ring R. Holding the weight A in this 

 position, let the bar F be placed upon 

 it, and observing the beats of the clock, 

 let the weight A commence its descent 

 with any beat. It will be found that 

 the stroke of the bar F on the ring R 

 will exactly coincide with the next beat, 

 and that the stroke of the weight A on 

 the stage S will coincide precisely with 

 the succeeding beat. It will be observed 

 that the accelerated motion of the weight 

 A for the first second, and before the 

 bar strikes the ring, is entirely owing to 

 the action of the force of gravity on the 

 bar (36). When the bar is taken off 

 the weight A by the ring at the end of 

 the first second, this cause of accelera- 

 tion ceases, the action of gravity is sus- 

 pended, and the weight A moves on to 

 the stage S with the velocity which it 



