Set of Knochenhauer spirals, replica of originals in Deutsches Museum, made by the Science Museum, South Kensington, London, England1963.

Set of Knochenhauer spirals, replica of originals in Deutsches Museum, made by the Science Museum, South Kensington, London, England, 1963.

Knochenhauer or Riess spirals are flat double wound wire coils of copper wire, insulated with sealing wax. While experimenting with a pair of Knockenhauer spirals in his laboratory at the Technical High School in Karlsruhe in spring 1886, Hertz observed that the discharge of even a small Leyden jar through one of the coils was enough to produce sparks between the terminals of the other. It was this observation that proved to be the starting point of Hertz's work on electro-magnetic waves between 1886 and 1888, and his demonstration that such waves possessed all the properties normally associated with lightwaves.