The operating principle of the machine is based on two counter-rotating discs made of insulating material. Each disc has several metal segments attached to it, called sectors. As the sectors pass, they induce a charge imbalance on another. This imbalance is drained to the collecting electrodes. Set the gaps between the two electrodes to about 1-2 inches. Turn the handle slowly at first and increase the rotation speed gradually. Once the voltage of the capacitor is sufficient to overcome electrostatic breakdown at the electrodes, discharge occurs and a spark is seen or heard. Size: 33*10.5 cm. Material: Wood + metal. Color: Silver. Package Contents: 1 * Electrostatic Generator. Only the above package content is included; other products are not included. Note: Light and different displays may cause the color of the item in the picture to be slightly different from the real thing. The measurement allowed error is +/- 1-3 cm.