If the discharger is used again a short time after a jar has been discharged, a second and much fainter discharge takes place. This could not be the case if the charge were located in the conducting coatings, as they would be discharged at once.
Procure a Leyden jar with movable coatings, which consists of a cone-shaped glass jar, А in Fig. 1, having two conical tin coatings, one, B, fitting the inside, the other, C, the outside of the glass. Put the parts together and charge the jar. Remove the inner coating with a glass rod and bring it near an electroscope. It will be found to have no charge. Remove the outer coating and test in the same way. It has no charge. Now put the jar together again, and a spark can be taken from it by connecting the inner and outer coatings.
These results prove that the coatings act simply as a means for collecting the charge, and that the seat of the charge is in the glass. As the glass is a poor conductor, the charge does not all pass into the coatings at once, when the jar is discharged. This explains the second spark, which is called the residual discharge.
