By 1850 most of the basic electrical phenomena had been investigated. However, James Clerk Maxwell (1831-1879), Professor of Experimental Physics at Cambridge then came up with something entirely new. By some elegant mathematics he had shown the probable existence of electromagnetic waves of radiation. But it was twenty four years later (eight years after Maxwell's death) that Heinrich Hertz (1857-1894) in Germany gave a practical demonstration of the accuracy of this theory. He generated and detected electromagnetic waves across the length of his laboratory on a wavelength of approximately one metre. His own photograph of the equipment he had set up can be seen in the Deutsches Museum in Munich. To detect the electromagnetic waves Hertz employed a simple form of oscillator, which he termed a resonator. But it was not sensitive enough to detect waves at any great distance. Before wireless telegraphy could become practicable, a more delicate detector was necessary. Credit is due to Edouard Branly (1844-1940) of France for producing the first practical instrument for detecting Hertzian waves, the coherer. It consisted of two metal cylinders with leads attached, fitted tightly into the interior of a glass tube containing iron or steel filings. The instant an electric discharge of any sort occurred the coherer became conductive, and if it was tapped lightly its conducting property was immediately destroyed. In practice the tapping was done automatically by a tapper which came into action the moment the coherer became conductive. In Russia the physicist Aleksandr Popov (1859-1905) had used a coherer while engaged in the investigation of the effects of lightning discharges. He suggested that such discharges could possibly be used for signaling over long distances. Old timers may remember that about 50 years ago Russian amateurs used to send out a QSL card with a drawing of Popov and a caption which claimed that he was 'the inventor of radio'.