Nikola Tesla Books
[Sec. 5., cont.]
a. Use of resonating earth to obtain high voltages Tesla's concept of the the Magnifying Transmitter operation was analogous to the operation of Helmholtz resonators, where spheres respond at their fundamental resonance mode to sounds of that frequency. Tesla's further extension of this concept is discussed in his article "The True Wireless," Electrical Experimenter, May 1919, pp. 28-30, 61, in association with Fig. 6 on page 29. Before going to Colorado Springs, Tesla pondered the question whether the earth had a static charge. If it did, then he believed that it might be possible, with suitable apparatus, to oscillate the charge between an elevated sphere of large radius of curvature and the earth, causing an enormous current to flow between the two sphere capacitors. This was the principle of operation of the Magnifying Transmitter in Tesla's words.
In attempting to examine the Helmholtz sphere analogy in electrical terms, this writer is not aware of an analysis of the manner in which a wavefront would propagate over a charged, conducting sphere, together with an analysis of the resulting free, damped oscillations, when the charge on the sphere is altered. It is possible that such an oscillation could be sustained in the manner of Tesla's concept, but if the earth is not sufficiently conductive a charge disturbance would only result in localized effects.
Some years ago this writer discussed in correspondence with Harold Barlow the "surface wave" propagation mode for currents produced by Tesla's Magnifying Transmitter (refer to the work Radio Surface Waves, Oxford University Press, London, 1962, co- authored with John Brown). Barlow was of the opinion that the earth's surface would not be sufficiently smooth to support surface-wave propagation of kilohertz waves. This writer is not certain that sufficient examination has been made of this propagation mode for the earth, considering that the earth reduced to the size of a ball one foot in diameter would have an irregularity of only 0.008 inch for Everest's peak--a rather respectable smoothness.
b. Patent No. 787,412 remarks on requirement for persistence of wave train Tesla's Patent No. 787,412 ("Art of Transmitting Electrical Energy Through the Natural Mediums," granted April 18, 1905), referred to above as containing data on observations of wavelengths of sferics, also contains the following interesting disclosure (at p. 3, lines 52-57):
"The most essential requirement is, however, that irrespective of frequency the wave or wave-train should continue for a certain interval of time, which I have estimated to be not less than one-twelfth or probably 0.08484 of a second and which is taken in passing to and returning from the region diametrically opposite..."
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