<a href="https://en.wikipedia.org/wiki/British_Post_Office" class="extiw" title="en:British Post Office">British Post Office</a> engineers inspect <a href="https://en.wikipedia.org/wiki/Guglielmo_Marconi" class="extiw" title="en:Guglielmo Marconi">Guglielmo Marconi</a>'s <a href="https://en.wikipedia.org/wiki/wireless_telegraphy" class="extiw" title="en:wireless telegraphy">wireless telegraphy</a> (radio) equipment, during a demonstration on <a href="https://en.wikipedia.org/wiki/Flat_Holm" class="extiw" title="en:Flat Holm">Flat Holm</a> island, 13 May 1897.  This was the world's first demonstration of the transmission of radio signals over open sea, between Lavernock Point and Flat Holm Island, a distance of 3 miles.<br><br>
In the background is the <a href="https://en.wikipedia.org/wiki/spark-gap_transmitter" class="extiw" title="en:spark-gap transmitter">spark-gap transmitter</a>, an <a href="https://en.wikipedia.org/wiki/induction_coil" class="extiw" title="en:induction coil">induction coil</a> <i>(right)</i> that generates high voltage pulses that create sparks between the balls of the Righi spark gap <i>(left)</i>, which excites oscillating currents in a wire <a href="https://en.wikipedia.org/wiki/antenna" class="extiw" title="en:antenna">antenna</a> suspended aloft by the pole seen in the center, ratiating radio waves.  Information is transmitted by switching the transmitter on and off rapidly using a switch called a <a href="https://en.wikipedia.org/wiki/telegraph_key" class="extiw" title="en:telegraph key">telegraph key</a> <i>(not visible)</i>, spelling out text messages in <a href="https://en.wikipedia.org/wiki/Morse_code" class="extiw" title="en:Morse code">Morse code</a>.
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