268 BENJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 293. 



d, about seven inches therefrom ; under or at the side of one 

 of the balls, d, is a hook ; the other ball, e, has at its side a 

 brass rod, c e, with upright arm, c f, about four inches long, 

 each having balls, c f, at their ends ; the rod is about seven 

 inches long, extending in a direction opposite to the insulated 

 ball with a hook ; also connected by a brass tube about four 

 inches long with another ball, b, formed of two hemispheri- 

 cal brass cups, the one fitting within the other, and within 

 this is balanced a brass rod, g h, about fourteen inches long, 

 with a knife edge centre in the middle, placed a little below 

 the centre of gravity, and equally balanced with a hollow 

 brass ball, g h, at each end, the centre or axis resting upon 

 a proper shaped piece of brass fixed in the inside of the ball, 

 each part of the hemisphere being cut out to permit the end 

 towards the insulated brass ball to descend, and the other to 

 ascend ; to the arm is attached a small slider moving freely 

 over a line divided into 60 grains, the slider to be set at the 

 number of grains the experiment requires. 



To use the instrument ; suppose the slider to be set at 15 

 grains, it will cause the arm, g h, bearing the slide, to rest 

 on the ball,/, beneath, with a pressure equal to that weight ; 

 as the charge increases in the jar, or battery, the balls be- 

 come more and more repulsive to each other, and when the 



