IEEE Technology and Society Magazine - Spring 2014 - 15

required a circuit between the transmitter and receiver
to be completed by any means, whether grounded
or not. Clearly, there are no return currents in the
earth when terrestrial transmitters and receivers are
ungrounded, nor when signals are radiated from earth
to spacecraft, nor when radiated between two distant
spacecraft. Ground currents are indeed produced if
and when a source for electromagnetic radiation is
connected between an antenna terminal and ground,
but the ground currents are confined to the immediate vicinity of the antenna. They generally serve to
increase the effective length of an electrically short
antenna and thereby increase the radiated power,
something Marconi first demonstrated in 1895. (See [5].
For a more basic explanation, see [6].)
Carlson then describes Tesla's initial vision for
wireless transmission:
"... the transmitter sent an oscillating current
through the earth's crust to the receiver. The circuit was then completed by having electromagnetic waves flow through the atmosphere from
the receiver back to the transmitter."
However, Tesla did not believe that electromagnetic
radiation played a part in any of his approaches, and
no one believed that that the receiver emitted electromagnetic radiation. Tesla actually believed that it was
"practicable to disturb by large machines the electrostatic condition of the earth." He believed that ground
currents could be generated by electrostatic (capacitive) interactions between the transmitter and receiver
antennas and the "outer conducting air strata" [7]. As
Carlson correctly points out at the end of his discussion, Tesla later believed that conduction currents in

IEEE TECHNOLOGY AND SOCIETY MAGAZINE

SPRING 2014

the plasma formed in the rarefied atmosphere at high
altitudes by high voltages applied to his transmitter
antenna would generate large earth currents.
The key distinction between the two approaches is
that Tesla never believed that electromagnetic radiation played a role in transmitting power or intelligence
to distant points, and the early Hertzian investigators
never believed that ground currents flowed between
the transmitter and receiver to complete a circuit. By
claiming otherwise, Carlson has comingled the two
approaches, which are actually quite disparate.
In the end, the positive aspects of this book far
outweigh the occasional problems with factual
errors and inaccurate assertions. It is a very readable work and presents the whole picture of Tesla
both as an electrical wizard and as a human being
with all the associated foibles. I particularly liked
the way Carlson interspersed the narrative with
commentary on the inventive process, the role of
illusion, and the social implications of his technologies on bringing about positive changes in society
as a whole. If you wish to read a factual book about
Tesla, this is the one.

References

[1] N. Tesla, "The true wireless," Electrical Experimenter, vol. 7,
p. 87, May 1919.
[2] Elec. World & Engr., vol. 39, p. 675, Apr. 19, 1902.
[3] "Marconi Wireless Tel. Co. v. De Forest Wireless Tel., Co.," Federal
Reporter, 138F42, Apr. 11, 1905, p. 657
[4] R. Pocock, The Early British Radio Industry. Manchester, U.K.:
Manchester Univ. Press, 1988, p. 105.
[5] H. Aitken, Syntony and Spark. New York, NY: Wiley, 1976,
pp. 182-203.
[6] "Monopole antenna," Wikipedia, Feb. 10, 2014; http://en.wikipedia.
org/wiki/Monopole_antenna.
[7] N. Tesla, "On light and other high frequency phenomena, J. Franklin
Inst., pp. 268-271, July 1893.

http://www.en.wikipedia

Table of Contents for the Digital Edition of IEEE Technology and Society Magazine - Spring 2014