A small, beautiful centenary

Electron
April 11, 1997

Textbooks have drilled into successive generations of physics students that J. J. Thomson's beautifully simple series of experiments, first reported in April 1897, convinced the world that the "cathode rays" were a stream of particles which came to be called electrons. This discovery, if an single discovery, deserves to be seen as the birth of modern technology - which, after all, we call "electronics" - as well as one of the seminal events at the foundation of modern physics. As such it deserves all the commemoration anyone chooses to give it, including the present volume from Cambridge University Press, celebrating this achievement of the first of the remarkable series of five successive Nobelist Cavendish professors of "experimental" physics (a sobriquet which, happily, is often taken very loosely by the electors).

The first chapter, by Brian Pippard, deals with the history of the electron's discovery and the early years, and we learn unsurprisingly that it was not all that simple. The word electron had been coined six years before by one G. J. Stoney to designate something quite different, a hypothecated atomic unit of charge. J. J. Thomson adopted the name late and reluctantly, preferring "corpuscle"; luckily "corpuscle" lost out, otherwise we might have "protuscles" and "photuscles" or "positive heavy corpuscles" to deal with. More or less simultaneously; E. Wiechert in Germany was independently doing experiments similar to Thomson's, but for various reasons he was not able to follow up, and the popular assignment of credit is, unusually, for all practical purposes, fair. The value of the ratio e/m of charge to mass which Thomson originally published was not very accurate (not as good as Wiechert's, for instance) but, with further improvements around such as a better vacuum, he came within a year or so to a pretty good one. Since Thomson could only exert force on his corpuscles with electric and magnetic fields, all forces being proportional to e and velocities to e/m, he had no direct handle on the mass, which had to wait for a gravitational experiment like Michelson's in the next decade. Yet the physics of the time had a rough idea of the charge e from galvanic phenomena, so Thomson knew that the electron was very light; he estimated 1/1000 of an atom - not bad at all.

After the first, historical chapter, the book consists of a series of chapters about technical subjects involving the electron, bearing such names as the "The isolated electron" and "The electron glue". Each is written by an authority in the respective field, almost all British or associated with Britain. Except in the first chapter, there is no mention of the immense body of technology involving the manipulation of electrons, first in vacuum and gases, later in semiconductors, ie vacuum tubes, cathode-ray scopes, transistors and their descendants. This is true even when the experimental apparatus is a direct descendant of technological breakthroughs in the electronic world, as in the chapters on the "composite electron" by R. J. Nicholas or that on the "coherent electron" by Y. Imry and M. Peshkin. The physics is chosen, I surmise, to emphasise the most recently active fields and, to an extent, the interests of the community, rather than with an eye to historical or technological significance. For instance, there is much of interest still in the physics of electrons in semiconductors, relevant to new types of lasers and light emitters, but no "electron in semiconductor" chapter is included.

The reader will find a considerable difference in level between the various chapters. The book is unlikely to attract the coffee-table book crowd of Hawking or Barrow readers. The cover, in fact, recommends it to "advanced students and researchers interested in advances in their fields", and I go along with that. For the intelligent undergraduate or the nonspecialist I would recommend: Pippard's history, A. D. Cottingham's "Isolated electron", D. Olive's outstanding little essay "The relativistic electron", Piers Coleman's "Introduction to the electron fluid" - ie, interacting electrons in metals - and, in a somewhat different mode, M. S. Longair's "Electron in the cosmos", which more than the others touches on historical background. These chapters deal with relatively straightforward subjects and go to considerable effort to explain them. The remainder of the chapters are at Physics World level or tougher. "The electron glue" by B. L. Gyorffy is a manly effort to explain and to proselytise for the modern methods of band theory for calculating and, he argues, for understanding the bonds between atoms. The former one must, in most cases, concede, but the latter is marred by the existence of cases where the former does not work - but in any case, this structure is immensely useful and deserves to be understood by those workers in other fields. "The composite electron" by Nicholas is a good introduction to the weird and wonderful world of the quantum Hall effects, but I think eventually gets beyond the abilities of the nonspecialist, and much the same may be said for "The heavy electron", by the editor himself.

The remaining chapters, on superconductivity, on magnetism, and on coherence and mesoscopics, in each case seem to me to have delved too deeply into their subjects to be recommended for the nonspecialist. The chapters on coherence and superconductivity suffer considerably from an attempt to describe coherence between quantum fields without ever biting the bullet and introducing the electron as a quantum field. One might as well try to describe a laser without mentioning the electric field. A few of these authors seem to have taken as their task to produce a full scholarly review rather than a nonspecialist description.

Finally, let me relieve myself of a few quibbles. I believe that a commemorative volume such as this should get the history as straight as possible. Admittedly, Pippard's excursion into the early history of the vacuum tube amplifier was an afterthought, but this discussion should have included how the audion became the radio tube at the hands of H. H. Arnold and the then Western Electric Laboratory in the United States. A second bit of history which bothered me - possibly because of personal involvement - was Springford's "awarding" K. G. Wilson the Nobel prize for his numerical renormalisation group for the Kondo effect; Wilson's finely crafted method is very special to that problem, but he was not the first to use the RG to solve the Kondo effect, nor was his prize given for that work. M. Springford also does not credit T. H. Geballe for the first "heavy" electrons in SmB6, six years at least before the papers he quotes. In A. J. Leggett's chapter on superconductivity, "The paired electron", unfortunately the link via Nambu to the particle physics concept of broken symmetry goes unmentioned.

The history of superconductivity is a hopelessly layered subject; the chips are not down yet, and perhaps an historic overview is not yet appropriate, especially of the high Tc cuprates. But even for the conventional superconductors one would like to hear from some of the other actors.

Another cavil is that Cottingham's chapter, "The isolated electron", while giving an outstanding account of precision measurements of the Bohr magneton and e/m on trapped, isolated electrons, could not somehow be coordinated with the precision measurement of other electronic properties which were only briefly mentioned in the Nicholas and the Imry-Peshkin chapters; h/e by Josephson effect, and e2/h from quantum Hall effect.

This is an excellent book for its declared purpose of providing collateral reading at the Physics World level to those who already have a background in modern physics. There is more than enough here to allow the electron to consider its birthday suitably celebrated.

P. W. Anderson, Nobel laureate, is professor of physics, Princeton University.

Electron: A Centenary Volume

Editor - Michael Springford
ISBN - 0 521 56130 2
Publisher - Cambridge University Press
Price - £37.50
Pages - 330

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