of Electricity in an Imperfect Insulator. 



425 



at once sets in, the rate of decay varying in different layers, 

 so that after a time the number of induction-tubes in conti- 

 guous layers will differ and there will be charges on the 

 separating surfaces. In those layers where the rate of decay 

 is most rapid, there will be negative charges on the surface 

 nearer the + plate, and + charges on the surface nearer the 

 — plate ; but still the induction in all is in the same direction. 

 Now let the two end plates be connected by a wire. At 

 once induction is propagated into the wire and transference 

 takes place from the space between the plates until they are 

 at the same potential, i. e. until the line-integral of the electric 

 intensity, or, since K is constant, that of the induction from 

 plate to plate is zero. The same number of tubes must have 

 entered all parts of the wire, otherwise there would be charges 

 at points along its length. Hence the same number of tubes 

 running in the positive direction must have passed out from 

 each of the layers. The result must be a reversal of the 

 induction of some of the layers, viz. those in which the induc- 

 tion decayed most rapidly. This, of course, means that after 

 their positive induction has all flowed out and they are quite 

 discharged, tubes from the other layers have bent round and 

 entered them, now charging them in the opposite direction. 

 We may imagine the process to be somewhat as in figs. 2 and 

 3, representing a condenser with three layers, A, B, C, the 

 decay having been most rapid in the middle one, so that it 

 has become completely discharged, while there is still positive 

 induction in A and C. 1, 2, 3, 4 (fig. 2) represent successive 



Fig. 2. 



positions of a tube moving out from A towards the wire : 

 1/, 2', 3', 4'' successive positions of a tube moving out from C, 

 When they have taken up the positions 4 4 / they come in 

 contact, and where they overlap they will neutralize each 

 other and break up into two portions, the outer part of each 



