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.