Johanne and Matilda Hertz, daughters of Heirnrich and Elizabeth Hertz, c 1889.

Photograph. Hertz (1857-1894) discovered 'Hertzian waves' (electromagnetic waves) and discovered that they behaved like light waves except for their wavelength. He was reputedly the first person to transmit and receive radio waves and the unit of frequency of radio waves is named after him.