Wimshurst machine

The Wimshurst machine, also called the Wimshurst influence machine, is an electrostatic generator that builds up very high voltages and releases them as a spark. The British inventor James Wimshurst developed it between 1880 and 1883. It is easy to recognise: two large insulating discs stand upright and turn in opposite directions, metal sectors are stuck to their surfaces, two crossed neutralizer bars carry small metal brushes, and a spark gap is formed by two metal spheres. The machine belongs to the class of influence machines, which separate electric charge by electrostatic induction instead of by friction. It improved on earlier machines by Holtz, Toepler and Voss, which were less efficient and tended to reverse their polarity unpredictably. Any small residual charge on a sector is enough to start it, and positive feedback then raises the voltage until the air breaks down and a spark jumps the gap. A pair of Leyden jars can be added to store more energy for each spark, and the machine works satisfactorily only in a dry atmosphere. In the nineteenth century it served in physics research and occasionally powered early X-ray tubes; today it is used mainly in science museums and classrooms to demonstrate electrostatics.