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Operating Principles of the Wardenclyffe Apparatus 

Can you explain, within accepted laws of physics, what was Tesla was trying to accomplish at Colorado Springs and on Long Island?

This appeared in the Electrical Review - N. Y., Nov, 30, 1898, pp. 344, 345, "TESLA DESCRIBES HIS EFFORTS IN VARIOUS FIELDS OF WORK"

 . . . Starting from two facts that the earth was a conductor insulated in space, and that a body cannot be charged without causing an equivalent displacement of electricity in the earth, I undertook to construct a machine suited for creating as large a displacement as possible of the earth's electricity.

     This machine was simply to charge and discharge in rapid succession a body insulated in space, thus altering periodically the amount of electricity in the earth and consequently the pressure all over its surface. It was nothing but what in mechanics is a pump, forcing water from a large reservoir into a small one and back again.  Primarily I contemplated only the sending of messages to great distances in this manner, and I described the scheme in detail, pointing out on that occasion the importance of ascertaining certain electrical conditions of the earth.  The attractive feature of this plan was that the intensity of the signals should diminish very little with the distance, and, in fact, should not diminish at all, if it were not for certain losses occurring, chiefly in the atmosphere.  As all my previous ideas, this one, too, received the treatment of Marsyas, but it forms, nevertheless, the basis of what is now known as "wireless telegraphy."  This statement will bear rigorous examination, but it is not made with the intent of detracting from the merit of others.  On the contrary, it is with great pleasure that I acknowledge the early work of Dr. Lodge, the brilliant experiments of Marconi, and of a later experimenter in this line, Dr. Slaby, of Berlin. . . .

In 1899 Tesla arrived at the conclusion that he could periodically alter "the pressure all over [the earth's] surface."  This could not have been an idle prediction.  Real-world observations involving operating experimental apparatus must have played a role in the process.

I've read that,

in 1907 Jonathan Zenneck formulated a special surface wave solution to Maxwell's equations ["Uber die Fortpflanztmg ebener elektro-magnetischer Wellen langs einer ebenen Leiterflache und ihre Beziehung zur drahtlosen Telegraphie," Annalen der Physik, Vol. 23, September 20, 1907, pp. 846-866 and "Uber die Wierkungsweise der Sender fino gerichtete drahtlose Telegraphie," Physik. Zeitschrift, Vol. 9, 1908, pp. 50 and 553-556] that was fundamentally different from the free-space waves studied by Hertz in 1887. [Corum, K. L. and J. F. Corum, "The Zenneck Surface Wave," Appendix II of "Nikola Tesla, Lightning Observations, and Stationary Waves," 1994.]

And, in the 1916 interview Tesla said, ". . . the mathematical treatise of [Arnold] Sommerfeld, . . . shows that my theory is correct, that I was right in my explanations of the phenomena. . . ."  The paper, "Uber die Ausbreitlung der Wellen in der drahtlosen Telegraphie," ["Propagation of Waves in Wireless Telegraphy," Annalen der Physik, Vol. 28, March, 1909, pp. 665-736] contained a formal analytical solution for the radiation from a short vertical monopole over a finitely conducting ground, and was written within the context of Zenneck's 1907 formulation.  It posits,

     Two contrasting concepts arise which may be designated by the terms 'space waves' and 'surface waves.'  The Hertzian electrodynamic waves are [space waves].  Electrodynamic waves on wires are typical surface waves. . . . 

Then Sommerfeld goes on to ask,

     With which type are the waves utilized in wireless telegraphy to be identified?  Are they like Hertzian waves in air or electrodynamic waves on wires?

In his review of this paper the late James R. Wait points out that,

Sommerfeld obtained exact expressions for the field components in the form of integrals which were then evaluated asymptotically. . . . In an attempt to explain the physical nature of his solution, he divided the expressions for the field into a 'space wave' and a 'surface wave'.  Both parts, according to Sommerfeld, are necessary in order to satisfy Maxwell's equations and the appropriate boundary conditions.  He found that the 'surface wave' part of the solution had almost identical properties to the plane Zenneck surface wave.  The field amplitudes varied inversely as' the square root of the horizontal distance from the source dipole.  Furthermore it was a fast wave and it decayed exponentially with height above the interface. ["Electromagnetic Surface Waves," in Advances in Radio Research. J.A Saxton, editor, Academic Press, Vol. 1, 1964, pp. 157-217. (See Corrections in Radio Science, Vol. 69D, #.1, 1965, pp. 969-975.)]

Analytically, the issue arose as follows:

     After Somrnerfeld formulated the wave function for a vertical infinitesimal dipole as an infinite integral and noted that the integral around the pole of the integrand is the wave function for a surface wave, which at great distances is identical with the Zenneck wave, no one questioned the reality of Zenneck's surface wave. [Wise, W.H, "The Physical Reality of Zenneck's Surface Wave," Bell System Technical Journal, Vol. 16, January, 1937, pp. 35-44.]" [Corum and Corum, 1994, loc cit.]

Getting back the original "mathematical treatise," Sommerfeld concluded,

     Zenneck surface waves appear as an important and occasionally predominant component of the electromagnetic field accompanied by space waves, which on their part predominate under certain other conditions.

How might the surface-wave be made to predominate?  For one, significant presence of this component appears to be very much frequency dependent.  Tesla asserted, "I only used low [frequency] alternations, and I produced 90 percent in current energy and only 10 percent in electromagnetic waves . . . and that is why I got my results."


Zenneck wave field strength decrease for around-the-world propagation as a function of frequency in kHz.

Another condition is the physical geometry of the launching structure.  After a series of experiments performed in 1937, Charles Burrows of Bell Labs concluded, "The surface wave component of Sommerfeld is not set up by simple [monopole] antennas on the surface of the earth. . . ." such as modeled by Sommerfeld in his analysis. [Burrows, C.R, "The Surface Waves in Radio Propagation Over Plane Earth," Proceedings of the IRE, Vol. 25, No.2, February, 1937, pp. 219-229].

A paper by Yu. V. Kistovich, "Possibility of Observing Zenneck Surface Waves in Radiation from a Source with a Small Vertical Aperture" [Soviet Physics Technical Physics, Vol. 34, No.4, April, 1989, pp. 391-394] appears to shed further light on what an appropriate geometry for launching the Zenneck surface wave might be.

Kistovich notes that it is known that the asymptotic expansion of the field of a vertical electric dipole does not manifest a Zenneck wave, ". . . and it is inferred from this result that a Zenneck surface wave is never generated by sources with a small vertical aperture.  This opinion is widely held in radiophysics at the present time."  However, he and his colleagues have found, both analytically and experimentally, that it is possible to use small "resonators" to excite a Zenneck wave that is observed to be 10-20 dB stronger than radiation fields.  They also found that both traveling and standing Zenneck waves can be excited.  [Schelkunoff and Friis clearly delineate the distinction between a quarter wave resonator and a quarter wave radiator in terms of the in-phase "feed current" (which supplies the radiated power) and the "quadrature current" (which supplies the resonant oscillations of the structure) [Schelkunoff, S., and H.T. Friis, Antennas: Theory and Practice, Wiley, 1952, pp. 352-353].  Without the "feed current" component, the base impedance of an ideal lossless series-resonant quarter wave monopole would drop to zero at resonance despite the fact that the reactive "quadrature current" would be infinite [Schelkunoff and Friis, ibid, pg. 252.]]. . .

As it turns out, the Zenneck wave is generally difficult to excite with a realistic source because it has a rather slow decay with height above the earth's surface.  But there is still an open question whether other types of sources may not be more favorable. . . .  An infinite vertical aperture with a height variation corresponding to that of the Zenneck wave will excite only the Zenneck surface wave with no radiation field. . . .  The infinite Zenneck aperture excites no radiation field and the pure Zenneck surface wave is the expected result. . . ." [Hill, D. and J.R Wait, "Excitation of the Zenneck Surface Wave by a Vertical Aperture," Radio Science, Vol. 13, No.6, November-December, 1978, pp. 969-977.]  This analysis examined the fields produced by a vertical sheet of horizontally directed magnetic current with an exponential variation in [a] vertical aperture. . . called an 'infinite Zenneck aperture,' and such a source truly "excites a pure Zenneck wave with no radiation field." [Corum and Corum, 1994, loc cit.]

Furthermore, it should be remembered that in Colorado Springs Tesla was at times using frequencies in the area of 5 kHz and below, well below those to be expected from any realistically sized helical resonator by itself.  The extra coil of his large 1899 oscillator vibrated at about 100 kHz which suggests that Tesla had developed a technique for producing a very low frequency (VLF) output from this low frequency (LF) machine.

See also "Rediscovering the Zenneck Surface Wave."

Revised: 02/14/2003 

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