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Electromagnetic Things in 1890

So, by 1890, Hertz had found electromagnetic waves and noticed the photoelectric effect.  Phillip Lenard worked on the photoelectric effect and other cathode-ray-centric phenomena and won the Noble Prize for that work in 1905.  Here is his apparatus for producing photoelectric effects:

Definitely looks like it could have produced some rays.

Meanwhile, how was the world of electromagnetic theory – apparently fully “classical” by sometime in the late nineteenth century – doing?  I’ve already suggested that the whole fantastically elaborated aether thing was more a symptom of a prolonged crisis than the sign of any stable “classical” theory – but how was classical theory doing in 1890?

According to Buchwald (at around page 176 in From Maxwell to Microphysics) it was in its usual “classic” state of complete flux and total confusion.  Theorists outside of the Maxwellians in Great Britain had heard of Hertz’s “striking confirmation” of something Maxwellian with his waves, but (except for Willard Gibbs in the US and maybe August Otto Föppl in Bavaria) no one outside of the Maxwellians actually understood Maxwell because, for Maxwellians, electricity was a by-product of field processes and for other theorists the view (which had not changed since the 1840s) was that electricity was “not an epiphenomenon, but an entity in its own right.”

Still, by 1899, classical electromagnetic theory had attained a year of relative stability, based on the electron (which, as we will see had become necessary by 1894 before it was officially discovered as “corpuscular particles” by J. J. Thomson in 1897), the aetherial continuum for fields and some ways of connecting the aether and other things as well as accounting for why the aether was not very easy to evaluate or even define.  Even this limited stability was going to get wobblier very quickly since Planck was about to discover that the continuum fields had to support discontinuous energy states and Einstein was reading Föppl.

As Phillip Lenard perhaps groaned privately, “He who has not felt horror and vertigo when considering Classical Physics has not seriously looked at Classical Physics.”  Nevertheless, in his tubes of rays, Lenard had indeed seen something very strange and not very classical.  And something that still haunts us, maybe, sort of.

Here is a photo that seems to be of Föppl (or someone with a Föppl-esque beard) at the Technical University in Munich with some students:

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More Electrons

So, we left J.J. Thomson sort of dreaming of things a lot like electrons in some ways in 1881.  Historians of the electron tactfully note that the electron “has a complex prehistory” (as Helge Kragh says on page 38 of Quantum Generations).  Even in 1881 J.J. was not alone in his electrical dreams since Helmholtz was saying in that same year that he was looking for “atoms of electricity” – which – like Stoney’s “electron” of the same period – could be positive or negatively charged.  All of these particles or effects (except as we may see, those of Hertz and Thomson) were considered to be at least partly aetherial objects and not necessarily completely material things at all – or perhaps even totally aetherial.  The small charges envisioned by Weber, Larmor, Lorentz and others were devised so as to associate electrical effects directly with the aether and its fields.

When (to jump ahead a lot) in 1897, J.J. bent cathode rays with external charges and measured their energies, he claimed to have determined that the rays were material corpuscles or “primordial atoms” with negative charges and not aetherial entities at all.  He did not want to use the term “electron” because the prevailing theories of the “electron” at the time (those of Larmor and Lorentz) envisioned the electron as immaterial, aetherial objects and not ordinary material particles (Kragh, Quantum Generations, page 41).

But (to jump back to the early 1880s), what where these glowing rays inside of glowing cathode ray tubes that could be seen as electrons or corpuscles or aetherial events?  How were these rays and effects generated?

In Helmholtz’s lab in Berlin in 1883, Hertz set out to purify the rays of any electrical currents, and read, as it were, their own signatures as luminescences, or luminous essences, i.e. to see the rays as rays and nothing else.  To do this he put the Geissler tube (the glass vacuum tube) inside a metal case and used a brass tube and wire gauze to capture any stray currents from the Rühmkorff induction coil at the cathode end of the Geissler cathode ray tube.  The electrometer connected to the vacuum tube and the metal case would then detect only the effects of the rays and no contaminating currents.  This is how Buchwald summarizes Hertz’s experiment with cathode rays in his chapter on Hertz in Scientific Practice, 1995.  Hertz himself provided an illustration, which I have annotated:   

From Hertz 1883

As it happens, for one reason or another, this and the experiments that followed in 1883, convinced Hertz that the rays had no detectable charge.  There are (apparently) many ways of looking this apparatus and the question of what Hertz was trying to detect.  Thomson in 1897, looking at this experiment and that of Perrin that had (apparently) a similar aim, assumed that part of what was in question was the relation of currents and the aether in cathode rays.  From Thomson’s viewpoint, Hertz was looking for a pure aether effect since Thomson considered the rays to be material particles and he thought Hertz had gone badly wrong in his assessment of the characteristics of cathode rays.  And so it might have seemed in 1897.  However, in Berlin in the early 1880s, the general view was that the rays shot out of disturbances in the aether, so it is possible that what Hertz was hoping to do was quite the opposite:  to cancel the aetherial effects and release the rays from their proto-electronic aetherial bonds.

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The Plot Liquifies

I’ll get back to the Kerr Effect soon.

Meanwhile, a closer look at one of the themes of this blog: the fading away of the aethers.  (The other themes on the way to Mesons would be – defining the Electron, resolving the Photon, something about the positron and then dealing with Mesons).

One thing that emerges as one looks at notebooks and articles and letters from the late nineteenth century, is that there was no stable imagery for the aethers or their possible substitutes in electromagnetic theory.  Rowland, for example (Henry Augustus Rowland, 1848-1901), first thought of electrical currents as waves in materials (notebooks of 1868), and then as fluid blobs (while talking to Maxwell and Helmholtz and experimenting with the effects of convection currents in the 1870s) and eventually (1880s and after) as “the wonderous aether.”  Rowland’s imagery and his Maxwellian experiments and phenomenological theories as reported in the work of John David Miller (Isis, 1972) and Jed Z. Buchwald (From Maxwell to Microphysics, 1985) were not fixed on a definite vision of the aethers, though eventually he hoped the aether thing would all work out.

From a contemporary perspective, we might think his aetherial hopes were doomed to disappointment, since we know that Special Relativity was just around the chronological corner in 1905, but, as I hope to illustrate in this blog, the aethers actually took at least a few decades after 1905 to fade even from the techniques of experimental phenomenology – which is (at first glance) surprising until one looks into how the aethers actually came up in the phenomenology of electromagnetism and allied branches of microphysics.  On the other hand, the case of Rowland, who did not use the aethers phenomenologically in his work until around 1880, show that the aethers did not become embedded in all electromagnetic explanations except for a relatively brief time from around 1880 to 1905.

Rowland would later be most famous for the unprecedented precision of his diffraction gratings (says Abraham Pais in Inward Bound), but in the late 1870s he was known for having shown experimental evidence for charge convection – the effect of moving electrical charges on magnetic fields.  Maxwell wrote a poem about Rowland as a brave knight from Troy (New York — with echoes of Roland it would seem) making a needle move with charge convection.

And now we make our first dive into the weirdness of nineteenth-century experiments.

Later versions of Rowland’s experimental devices are preserved in the Smithsonian.  Miller’s 1972 article shows a picture of one of the devices but notes that you can’t see the needle that was supposed to be moving.  In practice (to quote Miller describing the Berlin 1876 version of the experiment – the first):

…Rowland employed a single gilded ebonite (vulcanite) disk 21 centimeters in diameter, revolved about a vertical axis at 60 times a second.  His method was to reverse the polarity of the electrification of the disk while at the same time observing the reflection of a beam of light from the mirror of his static needle system.

Once he learned to spot the deflection of several millimeters, he was able to get three series of quantitative readings that indicated the generation of a magnetic force one fifty-thousandth of that of the Earth’s magnetic field in Berlin.

In calculating this force, Rowland used a constant v (little v as opposed to big V, the velocity of light) – the ratio of Maxwell’s electrostatic to electromagnetic units, of which Maxwell had noted the “agreement or disagreement of the values of V and of v furnishes a test of the electromagnetic theory of light.”  Which is to say that by the mid-1870s, measurements of V and v were getting closer and closer, suggesting that Maxwell’s theoretical exposition of light as an electromagnetic phenomenon was likely to contain some measurable fundamental truths.

Rowland used Maxwell’s suggested value for v in his comparison calculations and found that his sixty-two readings of the magnetic force on the needle were closer to the values for v expected from computations based on Maxwell’s v than the other five possibilities for V and v (3 based on the velocity of light and 2 based on v).  But, based on the series of readings that resulted in the closest correspondence between the observed values and the computed Maxwellian values, Rowland thought that 300,000,000 meters a second was the most likely value for V and v – which is significantly closer to the modern accepted value than any of the other estimates of V or v in the 1870s.

Weirdly enough, these apparently very accurate readings of the magnetic force produced by electrical currents that Rowland made in Helmholtz’s laboratory in Berlin, were very hard to confirm – even for Rowland himself.  Part of the problem seems to have been the growth of electric streetcar lines and the electromagnetic interference they produced in the big cities where electromagnetic experimentalists were concentrated.  Another problem may have been a change in materials and power sources used in the experiments.  The Maxwellian George Fitzgerald suggested moving to the country and using induction coils, and some experimentalists did, but the general confirmation of Rowland’s 1876 experimental findings was not even completed by an experimental face-off in 1902 and 1903 in Paris between Pender (for confirmation) and Crémieu (against) under the supervision of Jules Henri Poincaré.