Look at this VIDEO to see what is supposedly happening:
A Wimshurst machine is a seemingly simple device consisting of two plastic wheels with embedded metal plates on the rim. The wheels spin in opposite direction, facing each other. Two metal bars, one on each side, span the device: They are at an angle of 90°, but separated by the two discs spinning between them. At the end of the bars, metal brushes touch the plates spinning underneath them. A slight initial charge imbalance on one of the plates (which necessarily exists) causes the bar brushing against it to polarize along its length, so the metal plate on the other end of the same disc is charged oppositely and retains that charge when the brush disconnects during the spinning. As this two-plate "dipole" spins past the bar located behind the other disc, it induces an opposite dipole in its opposing plates on the other disc, which, in turn, polarizes the bar brushing against them. The charged metal plates give off their charges to two Leyden jars which connect to the plates with brushes of their own.
However, why do the Leyden-jar-brushes collect the charges? They tend to get very negative/positive, so why don't they push the electrons/holes away instead of collecting them? Wouldn't the brushes charge the passing plates which then travel around to the other Leyden brush, and get discharged there?