A first version of it was invented in 1762 by Swedish professor Johan Carl Wilcke. It is a simple manual capacitive generator used to produce electrostatic charge via the process of electrostatic induction.
The electrophorus consists of a dielectric plate (originally a ‘cake’ of resinous material such as pitch or wax, but in modern versions plastic is used) and a metal plate with an insulating handle.The dielectric does not transfer a significant fraction of its surface charge to the metal because the microscopic contact is poor. Instead the electrostatic field of the charged dielectric causes the charges in the metal plate to separate. It develops two regions of charge — the positive charges in the plate are attracted to the side facing down toward the dielectric, charging it positively, while the negative charges are repelled to the side facing up, charging it negatively, with the plate remaining electrically neutral as a whole. Then, the side facing up is momentarily grounded (which can be done by touching it with a finger), draining off the negative charge. Finally, the metal plate, now carrying only one sign of charge, is lifted.