Leonard B Loeb

Leonard B. Loeb
Leonard B. Loeb
Born	September 16, 1891; Zürich, Switzerland
Died	June 17, 1978 (aged 86); Monterey, CA, United States
Nationality	USA
Known for	Streamer theory of spark discharge, electrical coronas, gaseous electronics
	Scientific career
Fields	Physicist
Institutions	University of California, Berkeley

Leonard Benedict Loeb (16 September 1891 – 17 June 1978) was an American physicist at the University of California, Berkeley, and the principal architect of the streamer theory of spark discharge — the account of electrical breakdown that displaced the reigning Townsend theory at atmospheric pressure and now underlies the physics of lightning, sprites, plasma medicine and high-voltage engineering.

His presence on this wiki calls for an explanation, and it is given below: he was not a dissident in the sense of the wiki's other subjects, and the "antigravity" label formerly attached to this page was an error. But he is worth having here for a better reason. In the late 1930s Loeb argued that a forty-year-old theory taught everywhere, framed by a distinguished elder, simply could not account for what was observed — and he was contradicted in print for a decade afterwards. He turned out to be right.

Biography

Loeb was born in Zürich, where his father — the mechanist physiologist Jacques Loeb — was then working; his mother, Anne Leonard Loeb, held a doctorate in philology from the same university. His brother Robert Frederick Loeb became a distinguished physician at Columbia and a member of the National Academy of Sciences. His daughter Anne Loeb Bredon was the Berkeley folk musician who wrote "Babe I'm Gonna Leave You".

He took a bachelor's degree in organic chemistry at the University of Chicago in 1912 and switched to physics after hearing Robert A. Millikan lecture; he completed his doctorate under Millikan at Chicago in 1916 on the mobility of gaseous ions in high electric fields — the thread he would pull on for the next sixty years. After a year at the Bureau of Standards he went overseas in January 1918 with the American Expeditionary Force, working on spark plugs for aircraft, and then in laboratories in Paris and Manchester.

He joined Berkeley as assistant professor in 1923, became associate professor in 1925 and professor in 1929, and retired as emeritus in 1959 — though he continued to publish and take students, and his last major book appeared in 1965. With Raymond T. Birge he made the February 1928 offer that brought Ernest O. Lawrence from Yale to Berkeley. His doctoral students included Norris Bradbury, who directed Los Alamos for twenty-five years after Oppenheimer, and G. W. Trichel, for whom Trichel pulses are named.

Loeb was commissioned in the U.S. Naval Reserve in the early 1920s and eventually held the rank of captain. During the Second World War the Navy assigned him first to the Naval Proving Ground at Dahlgren, Virginia, where he set up the research laboratory in 1941 to work on armour plate and projectiles, and then to the Degaussing School at San Francisco, where he organised degaussing for the 12th Naval District. He was a Fellow of the American Physical Society. He was interviewed by Thomas S. Kuhn in August 1962 for the Archives for the History of Quantum Physics, and his papers are held at the Bancroft Library.

The streamer theory, and the challenge to Townsend

What was wrong with the accepted theory

From about 1900, electrical breakdown of gases was explained by J. S. Townsend's avalanche theory: electrons accelerated by the field ionise gas molecules, the resulting positive ions strike the cathode and liberate fresh electrons, and successive generations of avalanches build until the gap breaks down. At low pressures the theory works, and it is still correct there.

At atmospheric pressure it did not fit, and Loeb catalogued the ways. The theory predicted formative time lags of order 10⁻⁵ s where 10⁻⁸ s were measured — a discrepancy of a thousandfold. It predicted a diffuse glow filling the gap, where photographs showed a thin, branching filament. It made breakdown depend on gap geometry and pressure separately, in violation of Paschen's law. And it required a cathode to supply the secondary electrons, which lightning conspicuously does not have.

The alternative

Loeb's proposal, developed at Berkeley from corona-discharge work with Arthur F. Kip, was that a single avalanche can become self-propagating. Once the space charge at the avalanche head is dense enough, its own field rivals the applied field, and photoionisation ahead of the head seeds new avalanches that feed into it. The result is a self-guiding filament — a streamer — that crosses the gap at a fraction of the speed of light and needs no cathode at all.

The idea arrived twice at once. Heinz Raether reached it in Germany in 1939 from cloud-chamber photographs of avalanches; Loeb reached it independently from corona measurements. What turned the picture into a theory was John M. Meek's quantitative criterion of April 1940, giving the condition on the integrated ionisation coefficient at which an avalanche converts to a streamer. Loeb and Meek published the two-part "The Mechanism of Spark Discharge in Air at Atmospheric Pressure" in the Journal of Applied Physics in 1940 and the book The Mechanism of the Electric Spark with Stanford University Press in 1941. A 1943 review in Nature put the division of labour precisely: Meek's criterion, applied to "Prof. Loeb's qualitative streamer theory of spark discharge, converted an interesting speculation into a quantitative theory of great power."

The decade of objections

The claim was not accepted quietly. John Zeleny of Yale found an error in Meek's derivation of the radial field and argued in 1942 that the physical significance attached to it was misplaced. Fisher and Weissler reported "the apparent breakdown of Meek's streamer criterion" in 1944, and Fisher published "An Attempt to Verify the Theory of the Long Spark of Loeb and Meek" in 1947; Loeb answered in the Reviews of Modern Physics in 1948. Through the 1950s and 1960s the Swansea school under Frank Llewellyn-Jones argued that a generalised Townsend mechanism could cover the whole range, including exactly the conditions where Loeb said it could not.

The dispute was settled in a way that vindicated Loeb without discrediting Townsend. Hodges, Varney and Riley located the transition experimentally in 1985 and constructed a unified breakdown-probability theory in which the Townsend and streamer mechanisms appear as limiting cases — the Townsend mechanism below roughly 1000 torr·cm in uniform fields, the streamer mechanism above it and in non-uniform fields. Both are right in their domains.

It is worth recording that the resistance documented in print came from the Townsend school and from other physicists, not demonstrably from Townsend himself, who lived until 1957. No published rebuttal by him has been located.

What became of it

Streamer physics is now a large and active field, and Loeb, Meek and Raether are named as its founders in the modern reviews. The Meek criterion — often the Raether–Meek criterion — is still in daily use and still being refined. Its reach has turned out to be much wider than spark gaps: it governs the initiation of lightning and the streamer-to-leader transition; sprites and other transient luminous events in the mesosphere have been shown to be the same physical object as laboratory streamers, related by a density scaling; and streamer discharges are the working mechanism in plasma medicine, ozone generation, air purification and plasma-assisted combustion.

Loeb's name has largely fallen off the criterion, which is generally credited to Meek and Raether. The concept is his.

Other work

Ion mobility ran through his whole career, from the 1916 thesis onward. He established that Trichel pulses require electronegative gases and gave the successive-avalanche account of them, and his Electrical Coronas (1965) remains a standard reference on corona discharge. He wrote extensively on the kinetic theory of gases and on static electrification, and late in life turned to atmospheric electricity, proposing an "ionising wave of potential gradient" mechanism for the stepped leader of lightning — not the accepted account today, though the stepped leader remains an unsolved problem.

On one fringe-adjacent question he took the sceptical side: he published a critical comment in 1966 on a proposed energy source for ball lightning, to which the author replied in the same issue.

Books

The Kinetic Theory of Gases — McGraw-Hill, 1927; 2nd ed. 1934; Dover reprint 1961.
The Nature of a Gas — Wiley, 1931.
Fundamentals of Electricity and Magnetism — Wiley, 1931; 3rd ed. 1947; Dover reprint 1961.
The Development of Physical Thought: A Survey Course of Modern Physics, with Arthur S. Adams — Wiley, 1933.
Atomic Structure — Wiley, 1938.
Fundamental Processes of Electrical Discharge in Gases — Wiley, 1939.
The Mechanism of the Electric Spark, with John M. Meek — Stanford University Press, 1941.
Basic Processes of Gaseous Electronics — University of California Press, 1955; 2nd revised ed. 1960.
Static Electrification — Springer-Verlag, 1958.
Electrical Coronas: Their Basic Physical Mechanisms — University of California Press, 1965.

Fundamental Processes and Static Electrification were both translated into Russian; several titles have been reissued, Basic Processes and Electrical Coronas as recently as 2022.

Why he appears on this wiki

This page previously recorded Loeb as known for antigravity and filed him under that category. That was wrong, and it has been corrected. Loeb never worked on gravity, published no criticism of relativity or quantum mechanics, and left no polemical or philosophical writing of any kind.

The label came from how the record was created. The single item catalogued here, The Streamer Theory of Spark Discharge, is dated 2006 — twenty-eight years after Loeb's death. It is a posthumous reprint of the 1940–41 work in issue 40 of the Electric Spacecraft Journal, an amateur experimenters' magazine, alongside articles on lifters, Tesla coils and pulse generators. The whole run of that journal was harvested into the paper archive issue by issue, and this entry came in with it, acquiring the surrounding issue's subject tags. The title appears to be the journal editor's rather than Loeb's; no publication under that exact title exists from 1940 or 1941. The co-author John M. Meek was dropped in the process.

There is nonetheless a reason to keep him here, and it is not a grudging one. Loeb is a worked example of the thing this wiki is interested in: a researcher who told a settled field that its foundational theory failed on four independent counts, was argued against in the journals for a decade, and was eventually shown to be right — with the added grace that the resolution preserved his opponent's theory in the domain where it worked. Successful heterodoxy is rarer than the unsuccessful kind and rather more instructive.

Papers on this wiki

Loeb and John M. Meek, The Streamer Theory of Spark Discharge — Electric Spacecraft Journal 40 (2006), reprinting work of 1940–41.

Selected publications elsewhere

L. B. Loeb, "The Problem of the Mechanism of Static Spark Discharge", Reviews of Modern Physics 8, 267 (1936).
L. B. Loeb and J. M. Meek, "The Mechanism of Spark Discharge in Air at Atmospheric Pressure", Parts I and II, Journal of Applied Physics 11, 438 and 459 (1940).
L. B. Loeb, "Statistical Factors in Spark Discharge Mechanisms", Reviews of Modern Physics 20, 151 (1948).
L. B. Loeb, "The Mechanism of Lightning", Scientific American, February 1949.

External links

Leonard Benedict Loeb Papers, 1916–1970 — Bancroft Library, University of California, Berkeley.
Oral history interview with Leonard B. Loeb by Thomas S. Kuhn, 7 August 1962 — American Institute of Physics.
Robert N. Varney, "Leonard B. Loeb", Physics Today 31(12), 70–71 (December 1978).