English: The first spark gap radio transmitter with a monopole antenna invented by radio pioneer Guglielmo Marconi in 1895 and patented 1896 (US patent 586193, G. Marconi, Transmitting electrical signals, filed 7 December 1896, granted 13 July 1897) during his development of the first radiotelegraphy communication system. It is a modification of Heinrich Hertz's dipole transmitter to give greater range. The invention of the monopole antenna was the breakthrough that enabled Marconi to transmit long distances, making radio practical. The short horizontal dipole antennas Marconi had been using, invented by Heinrich Hertz, generated radio waves in the very high frequency range which were limited to line of sight propagation. Marconi replaced one side of the dipole with a connection to ground and the other side with a metal plate "capacity area" suspended high above the ground. The lower frequency vertically polarized waves which this antenna produced propagated as ground waves which followed the contour of the Earth, so they could travel beyond the visual horizon. The four balls are called a Righi spark gap, invented by Marconi's mentor Augusto Righi, which was designed to reduce the energy lost in the spark.