1. An early type of static-electricity generator or an apparatus that produces electric charges from the friction between a disk and a metal plate.
2. A generator which produces small amounts of static electricity by induction.
3. An instrument used to produce electric charges by induction.

It consists of a hard-rubber disk, that is negatively charged by rubbing with fur, and a metal plate, held by an insulating handle, which is placed on the disk.

The plate is then touched with a grounded conductor, so that the negative charge is removed and the plate has a net positive charge.