Association, St. Louis, it was shown that electric motors and single-terminal incandescent lamps can be operated through a single conductor without a return wire. Although apparently lacking a complete circuit, such a topology effectively obtains a return circuit by virtue of the load's self-capacitance and parasitic capacitance.Experiments with Alternate Currents of High Potential and High Frequency, Institution of Electrical Engineers Address, London, February 1892. The final reference to "burning out" a machine was to emphasize the ability of such a system to transmit a large power given a proper impedance match, as can be obtained through electrical resonance. Theory This observation has been rediscovered several times, and described, for instance, in a 1993 patent. Single-wire transmission in this sense is not possible using direct current and totally impractical for low frequency alternating currents such as the standard 50–60 Hz power line frequencies. At much higher frequencies, however, it is possible for the return circuit (which would normally be connected through a second wire) to utilize the self- and parasitic capacitance of a large conductive object, perhaps the housing of the load itself. Although the self-capacitance of even large objects is rather small in ordinary terms, as Tesla himself appreciated it is possible to resonate that capacitance using a sufficiently large inductor (depending on the frequency used), in which case the large reactance of that capacitance is cancelled out. This allows a large current to flow (and a large power to be supplied to the load) without requiring an extremely high voltage source. Although this method of power transmission has long been understood, it is not clear whether there has been any commercial application of this principle for power transmission. Single conductor waveguides As early as 1899, Arnold Sommerfeld published a paper predicting the use of a single cylindrical conductor (wire) to propagate radio frequency energy as a surface wave. Sommerfeld's "wire wave" was of theoretical interest as a propagating mode, but this was decades before technology existed for the generation of sufficiently high radio frequencies for any such experimentation, let alone practical applications. What's more, the solution described an infinite transmission line without consideration of coupling energy into (or out of) it. Of particular practical interest, though, was the prediction of a substantially lower signal attenuation compared to using the same wire as the center conductor of a coaxial cable. Contrary to the previous explanation of the full'' transmitted power