Illustration of a <a href="https://en.wikipedia.org/wiki/Lecher_lines" class="extiw" title="w:Lecher lines">Lecher line</a>, an experimental method of measuring the wavelength of radio waves developed by <a href="https://en.wikipedia.org/wiki/Ernst_Lecher" class="extiw" title="w:Ernst Lecher">Ernst Lecher</a> in 1888. The <a href="https://en.wikipedia.org/wiki/spark-gap_transmitter" class="extiw" title="w:spark-gap transmitter">spark-gap transmitter</a> <i>(right)</i>, a primitive <a href="https://en.wikipedia.org/wiki/transmitter" class="extiw" title="w:transmitter">radio transmitter</a> consisting of a <a href="https://en.wikipedia.org/wiki/dipole_antenna" class="extiw" title="en:dipole antenna">half-wave dipole antenna|</a> <i>(A1, A2)</i> with a spark gap between the elements excited by an <a href="https://en.wikipedia.org/wiki/induction_coil" class="extiw" title="en:induction coil">induction coil</a>,  produced radio waves which were coupled into the parallel-wire  <a href="https://en.wikipedia.org/wiki/transmission_line" class="extiw" title="w:transmission line">transmission line</a> <i>(D1, D2)</i> through the capacitors <i>(A1, B1)</i> and <i>(A2, B2)</i>.  They travelled down the line and were reflected back by the open circuit <i>(E2)</i> at the end.  The returning reflected waves interfere with the outgoing waves to create <a href="https://en.wikipedia.org/wiki/standing_wave" class="extiw" title="w:standing wave">standing waves</a> along the line.  At intervals of one-half wavelength the waves interfere destructively to create a node, a point where the voltage goes to zero.  By sliding a thin <a href="https://en.wikipedia.org/wiki/Geissler_tube" class="extiw" title="w:Geissler tube">Geissler tube</a> (neon light) along the wires until its light went out, the location of the nodes could be determined, and by measuring the distance between them and multiplying by two the wavelength of the radio waves could be found.  The frequency of the waves could be found by dividing the speed of light by the wavelength.  Lecher lines were a common method of measuring frequency up until World War 2.
Брокгауз и Ефрон
<a rel="nofollow" class="external text" href="http://dic.academic.ru/dic.nsf/brokgauz_efron/146322"><i>Brockhaus and Efron Encyclopedic Dictionary</i>, Moscow, ~1905</a>