The Wimhurst machine is an historical electrostatic machine, a form of electrical generator for generating high voltages. It has a distinctive appearance, with two large contra-rotating discs mounted in a vertical plane, and a spark gap formed by two metal spheres. It was invented by James Wimshurst in 1883.
The machine belongs to a class of generators called influence machines. This means that they separate electrical charges by electrostatic induction, or influence. Earlier machines in this class were developed by Wilhelm Holtz (1865 and 1867), Toepler (1865), and Voss (1880). They were more efficient than the earlier machines that worked by friction.
The machine is self-starting, meaning that it requires no electrical power supply to create the initial charge. It does, however, require mechanical power to turn the discs. The output of the machine is a constant current. The spark energy can be increased by adding a Leyden jar, which is an early type of capacitor suitable for high voltages.