Illustration depicting Heinrich Hertz's oscillator. The terminals of an induction coil (top) were connected to condenser consisting of two metal plates each 40cm square set 60cm apart in the same plane. Initial spark passing between metal balls at the centre formed a path for subsequent oscillations which were measured. Heinrich Hertz (1857-1894) a German physicist who first conclusively proved the existence of the electromagnetic waves theorised by James Clerk Maxwell's electromagnetic theory of light. Dated 20th century.