Three Wimshurst pattern electrostatic generating machines, Unsigned, early 20th century The first with twin contra-rotating glass discs applied with brass lozenges centred with silvered metal buttons at regular intervals pivoted between two wooden uprights also supporting two pairs of nickel-plates electrostatic friction arms, flanked by comb pickups applied to insulated arms connected to Leyden jars at each end and with pivoted discharge arms above, the base with crank handle driving wooden drive pulleys, on bun feet (discs damaged), 46cm (18ins) wide; the other two smaller with Bakelite discs and cast iron frames, each approx. 25.5cm (10ins) wide. James Wimshurst (1832 - 1903) was an inventor and engineer who developed the type of contra-rotating disc design of electrostatic generator included in the present lot. Such machines operate by having two insulated discs and their metal sectors rotate in opposite directions passing the crossed metal neutralizer bars and their brushes. An imbalance of charges is induced, amplified, and collected by two pairs of metal combs with points placed near the surfaces of each disc. These collectors are mounted on insulating supports and connected to the output terminals. The positive feedback increases the accumulating charges exponentially until the dielectric breakdown voltage of the air is reached and an electric spark jumps across the gap.