Connect the leads from the large gang capacitor to the electroscope as shown.  Do no use the ball on the electroscope as this will drain charge off the capacitor.  Charge the positive terminal of the capacitor with negative charge using the PVC rod and Cat's fur until there is a good deflection shown on the electroscope.  Turn the uncharged gang into the charged gang and observe that the electroscope deflection decreases.  Turn the uncharged gang back to the zero position and the electroscope deflection will return to the original position.

Caution: Repeating this demonstration several times in a row will lead to charges leaking onto the uncharged gang, and therefore no deflection of the electroscope.  It is recommended you discharge the uncharged gang to a large ground between each demonstration.