Berend Wilhelm Feddersen (1832-1918) was a German physicist. In his experiments with the Leyden jar, he was able to demonstrate that electrical oscillations occur in a circuit consisting of a coil, capacitor, and resistor. Now largely forgotten, the insights Feddersen gained from his experiments with the Leyden jar are still considered a cornerstone for the work of Marconi, the pioneer of wireless telecommunications. This is a carefully edited reprint of the original edition from 1908.