Hertz demonstrated that electromagnetic radiation could be emitted from a spark gap in an induction current, thereby giving evidence supporting the Maxwell theory. Then, Marconi (1895) invented wireless communication by means of electromagnetic waves at radio frequencies and opened the modern era of telecommunication technology. Using an antenna, electromagnetic waves can be transmitted through open space, and detected by another antenna at a distant location. Although not clearly established in Hertz’s experiment, the spark gap played the role of an antenna for emitting a high-frequency radiation. Further, he demonstrated a persistent oscillation is required for continuous radiation from the antenna.