574 USE OF THE ELECTROSCOPE. 



an electroscope by induction, only a small portion of the two elec- 

 tricities which the electroscope contains in the neutral state are 

 actually separated. Hence if, for example, the electroscope be 

 charged negatively, and a strongly charged positive body be brought 

 near to the knob, a further separation of the two electricities in the 

 instrument takes place, and since all free negative electricity is 

 attracted to the knob, there will be no electricity in the leaves 

 when the body has reached a certain distance from the electroscope ; 

 the leaves now collapse. But when the body is brought still 

 nearer, the positive electricity which is repelled to the leaves will 

 cause them to diverge again. It is obvious that corresponding 

 effects are produced in a positively charged instrument by a body 

 with a strong negative charge. 



By means of the electroscope it may easily be proved 

 that two bodies which are rubbed together assume 

 opposite electrical states. A round stick of sealing- 

 wax, 12 or 15 mm thick, and from 15 to 18 cm long, is 

 pushed with one end into a little bag of chamois leather 

 6 or 8 cm long, into which it fits exactly. To the closed 

 end of the bag a thread of common sewing silk is 

 fastened, which is about two decimetres long. Holding 

 the bag in the left hand and turning the sealing-wax 

 with the fingers of the right hand, the leather becomes 

 positively charged, and the sealing-wax negatively. 

 The bag is now pulled off by seizing the thread at the 

 end of it and holding it suspended by the thread it is 

 allowed to touch an uncharged electroscope. The in- 

 strument will become immediately charged as seen by 

 the divergence of the leaves. If now, the charged 

 sealing-wax be brought near the instrument, the leaves 

 collapse, that is, the electricity of the sealing-wax 

 attracts that of the leaves, which is identical with that 

 of the leather bag, hence both are of opposite kind. 



If after being rubbed the sealing-wax is left in the 

 bag and both together brought near the instrument, no 



