53

the uninsulated plate, s, is brought into close contactwith the insulated plate, p, and afterwards withdrawn

Fig. 16.

a little, so as' just to discern an opening betweenthem. The plates of the condenser are now parallelto each other, with an exceedingly thin plate of airbetween them. The copper and zinc discs are thentaken by their glass handles, one in each hand, andbrought into contact with each other, as representedby fig. 17. They are afterwards suddenly separated,

Fig. 17.

and one of them made totouch the cap of the elec-troscope. This operation isto be repeated six or eighttimes with the same disc-—suppose the zinc, for in-stance. On withdrawingthe plate, s, of the con-denser from the other, thegold leaves diverge with electro-positive action.When the experiment is repeated, and the copperdisc is made to touch the cap of the electroscope, thegold leaves diverge as before, when the uninsulatedplate of the condensor is withdrawn, but they nowshow an electro-negation. When the single gold-leafelectroscope is employed, no condenser is necessary,