5-2 ELEMENTARY LESSONS ON [CHAP. I. 



machine is as follows. Suppose a small + charge to 

 be imparted at the outset to the right armature f ; this 

 charge acts inductively through the discs upon the 

 metallic comb, repelling + electricity and attracting - , 

 which is discharged by the points upon the front surface 

 of the movable disc ; the repelled + electricity passes 

 through the brass rods and balls, and is discharged 

 through the left comb upon the front side of the mov- 

 able disc. Here it acts inductively upon the paper 

 armature, attracting - electricity into that part of it 

 which is opposite itself, and repelling + electricity into 

 its farthest part, viz., into the tongue, which, being bluntly 

 pointed, slowly discharges a + charge upon the back of 

 the movable disc. If now the disc be turned round, this 

 + charge on the back comes over from the left to the right 

 side, in the direction indicated by the arrow, and, when 

 it gets opposite the comb, increases the inductive effect 

 of the already existing + charge on the armature, and 

 therefore repels more electricity through the brass rods 

 and knobs into the left. Meantime the - charge which 

 we saw had been induced in the left armature, has in 

 turn attracted + electricity into the left comb, which has 

 been discharged by the points upon the front of the disc, 

 and has repelled - electricity through the brass rods and 

 knobs in the opposite direction, discharging it through the 

 points of the right comb upon the front of the disc, there 

 to neutralise the + charge which is being conveyed over 

 from the left on the front of the disc. These actions 

 result in causing the top half of the moving disc to be 

 + ly electrified on both sides and the bottom half of the 

 disc to be -ly electrified. The charges on the front 

 serve as they are carried round to neutralise the electri- 

 cities let off by the points of the combs, while the 

 charges on the back induced respectively in the neigh- 

 bourhood of each of the armatures serve, when the 

 rotation of the disc conveys them round, to increase the 

 inductive influence of the charge on the other armature. 



