ELECTRICAL INDUCTION. 



567 



The electricities separated by induction manifest a 

 very different behaviour when the conductor in which 

 the separation has taken place is touched by the finger, 

 or is, by means of a wire or otherwise, conductively con- 

 nected with the ground. When a conductor is charged 

 by simple contact with a rubbed glass rod, it loses its 

 electricity immediately when placed in conducting com- 

 munication with the ground. Electricity which can 

 thus be removed from a body is called i free/ On the 

 other hand, of the two electricities induced in a con- 

 ductor by induction, only the electricity of the same 

 kind as that of the inducing body can be removed while 

 the influence of the inducing body lasts; the electricity 

 which is of the opposite kind cannot be removed by 

 conduction, and is said to be ' disguised ' or ; bound/ 



Let an excited glass rod 

 be brought near to the disc, 

 which is fastened to the top 

 of the stick of sealing-wax 

 on the wooden support. 

 The electrical separation 

 which takes place in that 

 case is shown at A in fig. 

 306. If, while the glass rod 

 is near, the disc be touched 

 by the finger the free posi- 

 tive electricity is discharged 

 as represented at jB, while 

 the negative electricity is in 

 the bound state and remains in the disc. If now the 

 glass rod is taken away, the attraction between the 

 positive electricity of the rod and the induced negative 



