Oliver Lodge: Almost the Father of Radio
by James P. Rybak, W0KSD
Mesa State College
Grand Junction, CO 81501
B
y the year 1887, the 36-year-old
Oliver Lodge was already regarded in
Great Britain as a highly accomplished
scientist. A professor of physics at the
newly-established University College in
Liverpool, he was known for his brilliant
scientific mind and ability to explain
complex scientific principles in a manner
that could be understood by virtually
anyone. In 1887, the Royal Society of
Arts asked Lodge to prepare a series of
lectures, to be given the following year,
concerning how buildings might best be
protected from lightning damage.
[1]
The designers of the lightning protection
systems of that time assumed that
lightning was a continuous direct current
discharge. They believed that protection
from lightning could be obtained by
placing copper rods above the buildings
and connecting them to the earth by
means of heavy copper grounding
cables with a very low dc resistance.
[2]
The lightning protection "experts" could
not understand why lightning discharges frequently ignored the copper conductors
and chose what seemed to be higher resistance "alternate paths" to ground.
[3]
This
often resulted in great damage being done to the buildings. Such failures of the
lightning protection systems was typically blamed poor ground connections.
[4]
Lodge had had an interest in learning more about the subject for several years.
[5]
He now planned to conduct a series of experiments on electrical discharges prior to
giving the lectures. The scientist intended to learn why lightning often did not follow
the low-resistance path provided by the copper conductors.
[6]
He immediately
began a series of experiments to learn more about lightning protection.
These laboratory investigations proved to be extremely important. They would
contribute substantially to the development of wireless telegraphy and establish
Lodge's world-wide reputation as an outstanding scientist.
In addition to demonstrating the effects of inductance in circuits with time-varying
currents, the experiments ultimately resulted in Lodge establishing the existence of
electromagnetic waves independently of, but virtually simultaneously with, the
German scientist Heinrich Hertz. Lodge also discovered the phenomenon of
electrical resonance and found that the "coherer" effect provided a very useful
means for detecting the presence of electromagnetic waves.
[7]
It was commonly known in 1887 that a lightning discharge is produced when the
accumulation of electric charge in a cloud causes the potential difference between
that cloud and the earth to increase until the intervening air breaks down electrically
and becomes a conductor. Lodge visualized this as being much the same process
as when the voltage across a capacitor increases until the breakdown of the
dielectric occurs.
[8]
It also was well known that the discharge of a Leyden jar
(capacitor) produces an oscillatory current rather than a direct current.
[9]
Oliver
Lodge erroneously believed, therefore, that a lightning discharge also is
oscillatory.
[2]
The physicist decided to
perform some
preliminary "alternate
path" experiments to
attempt to confirm his
theories prior to giving
his first lecture on
lightning in March of
1888. He used Leyden
jar discharges to
simulate lightning. The
jars were usually
charged using a Voss
machine that generated
static electricity through
friction. One of the
experimental
arrangements used by
Oliver Lodge is shown
as Figure 1.
[4,6]
The Voss machine was connected to the terminals, A. These, in turn, were
connected to the inner conducting surfaces of two Leyden jars. The outer
conducting surfaces of the jars were connected to an adjustable spark gap, B. A
long loop of very low resistance copper wire, L, was connected across this spark
gap. The wire Lodge first used was approximately 12 meters in length but had a
resistance of only 0.025 ohm.
[4,6]
It wire closely simulated the characteristics of the
conductors normally connected to lightning rods.
The electrical charge stored in the Leyden jars could flow either through the very
low dc resistance path provided by the loop of wire or it could flow across the very
high resistance path through the air between the spark-gap terminals at B. It would
seem that the obvious path for the charge to follow would be through the low
resistance wire loop. Surprisingly, Lodge was able to produce very large sparks
across the spark-gap, B, even though the dc resistance of the wire across the gap
was only a fraction of an ohm.
[4]
When Lodge gave his first lecture on lightning to the Royal Society of Arts, he
argued that since (as he believed) lightning discharges have a very high oscillatory
frequency, it is necessary to take inductive reactance effects into account when
predicting which path the discharges will follow. Inductance was not a very well
understood or accepted concept in those days.
[6]
Michael Faraday in England and Joseph Henry in the United States, independently
but almost concurrently, had observed some effects of inductance almost sixty
years earlier. Sir William Thomson (Lord Kelvin) in 1853 had recognized the
influence which inductance (Thomson called it "electro-dynamic capacity") has in
causing the discharge of a Leyden jar to be oscillatory.
[9]
Oliver Heaviside later demonstrated the importance of inductive effects in the
transmission of signals along long telegraph lines and undersea telegraph cables.
The concept of inductance, however, did not receive general acceptance or
understanding until Sir William Thomson (Lord Kelvin) publicly endorsed
Heaviside's inductance theories in 1889. Lodge's lectures on lightning, however,
occurred prior to Thomson's endorsement.
[2]
Lodge maintained that, at the frequencies involved in the oscillatory lightning
discharge, the inductance of the conducting cables resulted in a very high
opposition to current flow. Therefore, the alternate path actually followed by a
lightning discharge did indeed exhibit the lowest total opposition or impedance to
the current flow even if its dc resistance was not the lowest.
[6]
Those in attendance who did not subscribe to Lodge's inductance theories were
quick to question the accuracy of simulating lightning with Leyden jar discharges.
Particularly questionable, they argued, was the idea that a lightning discharge is
oscillatory.
[1]
Years later, Lodge realized that lightning is not an oscillatory discharge but is
actually a rapidly pulsating unidirectional (dc) discharge.
[2]
However, the effects of
the inductive reactance on the flow of these pulsating lightning currents is the same
as Lodge predicted for
oscillatory currents.
[6]
The issue could not be
resolved satisfactorily at
the March lectures, and
the critics wanted more
convincing experiments
to be performed. Further
discussions on lightning
were scheduled for the
September 1888
meeting of the British
Association to be held at
Bath, England.
[1]
Oliver Lodge continued
his "alternate path"
experiments during the
spring and summer of 1888 with the purpose of investigating the behavior of the
electrical oscillations produced by the Leyden jar discharges. He now replaced the
loop of wire he had been using with a pair of long wires, each approximately 29
meters in length (Figure 2). The wires, L and L', were terminated in spark-gaps.
[4,6]
He found that the Leyden jars discharged in the usual manner at spark-gap A, but
that a simultaneous spark was produced at spark gaps B1, B2, or B3.
Oscillatory currents were produced in the part of the circuit consisting of the Leyden
jars and the spark-gap at A. The capacitance of the jars together with the
inductance of the spark-gap wires at A determined the frequency of the
oscillations.
[4]
Every time a spark occurred at A, however, Lodge found that a longer
spark occurred at B1, B2, or B3. The spark at B3 always was the longest.
The electrical waves produced by the oscillations at A traveled along the wires and
were reflected at the far ends. Lodge knew that the longer spark at B3 was due to
what he called the "recoil impulse" or "recoil kick" at the end of the wires where the
waves were reflected.
[4]
At spark gap B3 both the incident wave and the reflected
wave had their maximum values and were in phase. This produced a voltage twice
as large as the voltage at spark gap A.
More importantly, Lodge determined that the discharge at B3 was the most intense
when the lengths of the two wires L and L' were one-half wavelength (or an integral
multiple of one-half wavelength) for the oscillations produced.
[4,8]
Under these
conditions, a maximum coupling of the oscillations produced at A was occurring in
the wires. Oliver Lodge had discovered electrical resonance (or "syntony" as he
later would call it
[6]
) between the two parts of the circuit.
[4,8]
In addition, the scientist was able to demonstrate that standing waves existed along
the wires. In a darkened room, he observed a visible glow along the wires at one-
half wavelength intervals corresponding to the voltage peaks. He also performed a
number of other experiments concerning the characteristics of discharging Leyden
jars during that spring and summer of 1888.
[11]
Oliver Lodge clearly knew that he had produced and detected the electromagnetic
waves predicted some twenty-four years earlier by James Clerk Maxwell.
[3]
Before
he presented these observations as part of the findings in his study of lightning
conductors, however, Lodge went on vacation in that summer of 1888. It was while
on vacation that Lodge read of Hertz's similar work with electromagnetic waves.
[6,10]
Lodge then added a postscript to his own paper acknowledging Hertz's work in an
extremely positive way. He concluded the postscript by saying: "The whole subject
of electrical radiation seems working itself out splendidly."
[8]
Lodge presented his findings to the British Association meeting in Bath in
September of 1888. The well known theoretician, G. F. FitzGerald, who reported on
the results Hertz recently had published, chaired the meeting. Interestingly enough,
FitzGerald had told Lodge in 1878 that it never would be possible for anyone to
produce the electromagnetic waves predicted by James Clerk Maxwell. By 1882,
however, FitzGerald had corrected his erroneous belief.
[12]
The following year,
FitzGerald suggested that electromagnetic waves might be produced by
discharging a capacitor through a very small resistance.
[3]
Those in attendance and, later, other knowledgeable people, recognized that
Lodge's findings were equivalent to those of Hertz and had been arrived at
independently of, and virtually simultaneously with, Hertz's.
[3,6]
Heinrich Hertz,
however, would always receive the world's principal acclaim and recognition
because his work was published slightly before that of Lodge.
The electromagnetic waves generated by Hertz were radiated into space whereas
those generated by Lodge were guided by wires. Consequently, the work of each
man helped confirm the validity of what the other had done. Lodge and Hertz
corresponded and exchanged scientific papers. They always maintained great
respect and regard for each other as scientists and as human beings.
[3]
Lodge
never resented the fact that Hertz's work received greater acclaim.
[6]
When Hertz
died in 1894, Lodge wrote a magnificent tribute to his achievements.
[13]
In 1894, Lodge discovered that a nonconducting tube containing metal filings
(Figure 3) could be used to detect the presence of electromagnetic waves. His
findings were based on an observation made in 1890 by Edouard Branly (1846-
1940). Branly had discovered that the resistance measured across the ends of a
such a tube normally was very high. However, if an electromagnetic wave was
generated nearby, the metal particles became fused together and the resistance
dropped to a low value. The resistance remained low until the tube was tapped and
the fused particles returned to their original, separated condition.
[14]
Earlier, Lodge
had observed the
same fusing
effect between
metal spheres in
light contact with
each other when
an
electromagnetic
wave was produced. He called the fusing of the metal produced by the
electromagnetic wave, the "coherer effect." Similarly, he called any detector of
electromagnetic waves based on this effect, a "coherer." He quickly realized that
the "filings tube coherer" represented the most convenient form for utilizing the
coherer effect to detect electromagnetic waves.
[15]
Perhaps Lodge's most important improvements to the filings tube coherer were the
evacuation of the air from the tube and the development of an automatic "tapping
back" device which utilised a rotating spoke wheel driven by a clockwork
mechanism. The mechanical impulses provided by the tapping back device
restored the filings tube coherer to its non-conducting state at regular intervals,
independent of the detection of electromagnetic waves. This filings tube coherer
detector was considerably more sensitive than was the simple wire loop "resonator"
with a spark gap that Heinrich Hertz had used as the detector of electromagnetic
waves in his experiments. It also was more convenient to use than was the metal-
sphere coherer detector Lodge had previously developed.
[15]
Lodge used his improved filings tube coherer, together with a Hertzian wave
oscillator, as part of a demonstration for a commemorative lecture entitled "The
Work of Hertz" given in London at a meeting of the Royal Institution in June of
1894. A sensitive mirror galvanometer was connected to the coherer so that the
detection of the electromagnetic waves was visible to the audience in the form of a
moving beam of light.
[6,16]
Later that same month, Lodge used a small portable
receiver based on similar equipment to demonstrate the detection of
electromagnetic waves at the annual "Ladies' Conversazione" of the Royal Society
in London.
[6,17]
He also demonstrated essentially the same apparatus at a meeting of the British
Association held at Oxford in August of 1894. In that demonstration, however, he
replaced the mirror galvanometer with a more sensitive marine galvanometer of the
type normally used for the detection of submarine cable telegraphy signals. Lodge's
source of electromagnetic waves, located in another building some 55 meters
away, consisted of a Hertzian oscillator energized by an induction coil. A telegraph
key connected to the primary winding of the induction coil was used by Lodge's
assistant to send both long and short duration trains of waves, corresponding
somewhat to Morse code dots and dashes.
[6]
Those in attendance witnessed
Lodge's receiving equipment detecting electromagnetic waves that had traveled the
55 meter distance.
Lodge clearly had all the necessary elements of an elementary wireless telegraphy
system. While it could be argued successfully that Lodge did indeed achieve
signaling of a sort in all three of these demonstrations, there is no indication that the
sending of any true messages was accomplished or even attempted with this
apparatus. It was not his intent to do so. Oliver Lodge never considered using his
equipment for communicating, although the idea of wireless telegraphy had been
suggested two years earlier by William Crookes.
[18]
The first two demonstrations were performed simply to show that electromagnetic
waves can be generated and detected. The purpose of Lodge's demonstration at
Oxford was to propose that perhaps there exists an analogy between the way a
coherer responds to electromagnetic waves and the way the eye responds to
light.
[6]
Oliver Lodge later admitted that, at the time, he had not seen any advantage in
using the relatively difficult process of telegraphing across space without wires to
replace the well developed and comparatively easy process of telegraphing with the
use of connecting wires.
He, like virtually all of his contemporaries, believed at the time that electromagnetic
waves travel only in straight lines as does light. (Maxwell, after all, had shown that
light is nothing more than electromagnetic waves with very short wavelengths.)
Consequently, Lodge assumed that the maximum possible range attainable using
wireless signaling would be very limited. These reasons help to explain why, in
Lodge's own words, ". . . stupidly enough no attempt was made to apply any but the
feeblest power so as to test how far the disturbance could really be detected."
[19]
As
a result, Lodge was one of several electrical experimenters who, had they
recognized what they had in their hands, might have earned the principal credit for
the development of wireless telegraphy.
In all fairness, however, one should never think that Lodge was lacking in either
insight or in astuteness. His exceptional perceptiveness and keenness of mind
when conducting experiments had been demonstrated time and time again. But he
was first and foremost a scientist and teacher, more concerned with theory than
commercial applications.
[6]
While Oliver Lodge is remembered for numerous significant scientific
achievements, including his contributions to the development of wireless
telegraphy, it might be said that he let "the two big ones" slip through his fingers.
Had he proceeded with his alternate path experiments a little more rapidly, Lodge
might be the one whom we today credit with having experimentally verified
Maxwell's predictions. Similarly, if Lodge had realized the potential of wireless
communication, Marconi might have had to share with him the unofficial but
commonly used title "Father of Radio."
Those wishing to read about other aspects of Oliver Lodge's life are referred to the
author's earlier, less specialized article.
[20]
References
[1]
Jolly, W.P.; Sir Oliver Lodge, Fairleigh Dickinson University Press, Rutherford,
NJ, 1974.
[2]
Lodge, Oliver; Advancing Science, Harcourt Brace, New York, 1932.
[3]
Lodge, Oliver; Past Years, Hodder and Stoughton Ltd., London, 1931.
[4]
Lodge, Oliver; Lightning Conductors and Lightning Guards, Whittaker Ltd.,
London, 1892.
[5]
Rowlands, Peter; Oliver Lodge and the Liverpool Physical Society, Liverpool
University Press, Liverpool, 1990.
[6]
Aitken, Hugh G.J.; Syntony and Spark, Princeton University Press, Princeton,
NJ, 1985.
[7]
Lodge, Oliver; "The History of the Coherer Principle," The Electrician, vol. 40,
November12, 1897, pp. 86-91.
[8]
Lodge, Oliver; "On the Theory of Lightning Conductors" The London, Edinburgh,
and Dublin Philosophical Magazine, Series 5, vol. 26, August, 1888, pp.217-230.
[9]
Thomson, William; "On Transient Electric Currents," The London, Edinburgh,
and Dublin Philosophical Magazine, Series 4, vol. 5, June, 1853, pp. 393-405.
[10]
Hertz, Heinrich; "On Electromagnetic Waves in Air and their Reflection,"
Wiedemann's Annalen, vol. 34, July 1888, p. 610.
[11]
Lodge, Oliver; "Experiments on the Discharge of Leyden Jars," Proceedings of
the Royal Society, vol. 50, January, 1892, pp. 2-39.
[12]
Lodge, Oliver; Talks About Radio, Doran Inc., New York, 1925.
[13]
Lodge, Oliver; "The Work of Hertz," The Electrician, vol. 33, June 8, 15, 22,
and July 6, 27, 1894, pp. 153-155, 186-190, 204-205, 271-272, 362.
[14]
Branly, Edouard; "Variations of Conductivity under Electrical Influence", The
Electrician, vol. XXVII, June 26 and August 21, 1891, pp. 221-2 and 448-9.
[15]
Lodge, Oliver; "The History of the Coherer Principle", The Electrician, vol. XL,
November 12, 1897, pp. 86-91.
[16]
Lodge, Oliver; The Work of Hertz and Some of His Successors, London, 1894,
p. 24.
[17]
Unsigned and untitled article, Nature, vol. L, June 21, 1894, pp. 182-183.
[18]
Crookes, William; "Some Possibilities of Electricity," The Fortnightly Review,
February 1,1892, pp. 173-181.
[19]
Lodge, Oliver; Signalling through Space Without Wires, (3rd edition), London,
1908, pg. 84.
[20]
Rybak, James; "Radio's Forgotten Pioneer," Popular Electronics, July 1990,
pp. 62-66 and 95.
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