Ideal, Simple Molecule

In 1890, Pieter Zeeman started a series of magneto-optic experiments that eventually showed that the application of a magnetic field caused emission lines to split.  Given the resolution available with his apparatus in 1896, the splitting looked like a widening of the emission lines in the spectrum.  In any case there was a shift in the wavelength (or “frequency”) of the emission.

Theodore Arabatizis, “The Zeeman Effect and the Discovery of the Electron” inHistories of the Electron, says:

In the same paper that contained Lorentz’s analysis, Zeeman confirmed that the polarization of the edges of the broadened lines followed the theoretical predictions. Lorentz considered the confirmation of his predictions as “direct proof for the existence of ions.” Furthermore, Zeeman estimated the order of magnitude of the ratio e/m. As we saw, the change in the period of vibration of an ‘ion’ due to the influence of a magnetic field depends on e/m. Thus, the widening of spectral lines, which is a reflection of the alteration in the mode of vibration of an ‘ion,’ is proportional to the ‘ionic’ charge to mass ratio. According to Zeeman’s approximate measurements a magnetic field of 10000 Gauss produced a widening of the D-lines equal to 2.5 percent of their distance. From the observed widening of the spectral lines, Zeeman calculated e/m, which turned out to be unexpectedly large. As he recalled, when he announced the result of his calculation to Lorentz, the latter’s response was: “That looks really bad; it does not agree at all with what is to be expected.” It should be noted that this was the first estimate of the charge to mass ratio of the ‘ions’ that indicated that the ‘ions’ did not refer to the well-known ions of electrolysis, but corresponded instead to extremely minute subatomic particles. J. J. Thomson’s measurement of the mass-to-charge ratio of the particles that constituted cathode rays was announced several months later and was in close agreement with Zeeman’s result.

I should note that what was surprising about the e/m ratio was that the mass was extremely small compared to the charge.  A mass close to the mass of an atom (“the well-known ions of electrolysis”) was what was expected and an electron’s mass is much smaller than that.  Both Larmor and Lorentz noted that if you knew how much the magnetic field of a given strength shifted the emissions, then you could derive the mass and electrical charge of the emitter.  Lorentz called this emitter the “ion” as did Larmor in 1897, though he noted it might be the same object as J.J. Thomson’s “electron”.  Lorentz assumed the emitter was “oscillating” in response to the magnetic field while Larmor described a more elaborate set of possibilities including rotations.

Earlier (December 1896), Larmor had reflected in a letter to Lodge before he undertook his more elaborate aetherial analyses:

in an ideal simple molecule consisting of one positive and one negative  electron revolving round each other, the inertia of the molecule would  have to be considerably less than the chemical masses of ordinary molecules, in order to lead to an influence on the period, of the order observed  by Dr. Zeeman.

This simple picture, of course, anticipates many aspects of Bohr’s model of the hydrogen atom, which would not see the light of day until almost 20 years later.  What were the problems that hindered looking at an ideal, simple model in 1896?  Several basic problems, I think:

  1. The need to relate every electromagnetic event to elaborate aether models
  2. The lack of a definite notion of a nucleus differing in mass (maybe or just being aetherial) and charge from the electron (Rutherford would eventually work that out – removing even the positive charge from the among the plum puddings of the aether)
  3. Related to problem 1 – no possibility of using quantum structures (in 1896 Planck’s constant had not yet been glimpsed and it would be almost two decades before the Bohr model of electrons at quantum energy levels and emitting as they made transitions between levels) so the aether models provided the only basis for any phenomenological descriptions of what was happening.

But what happened with the electron in the pre-quantum world?  Say from 1896 to 1913?  Again, several things, I think:

  1. A change in how the Maxwell equations were modelled as interacting with the aether
  2. A new type of models, where the electron formed material objects (“Atoms” and “molecules” and “corpuscles”)
  3. New dynamic models where the electromagnetic field formed the apparent mass of the electron (I’ll note again that for a time these models were seen as being better supported by experiment than models that used what was assumed to be the Einstein-Lorentz models using relativistic mass for the electron)
  4. Models of the electron itself (in terms of shape, self-energy, mass, size and deformability)

Meanwhile what about Larmor’s electron?  It changes the interaction of aether and matter and it solves aether-dragging by undergoing FitzGeraldian contraction:

Theodore Arabatizis, “The Zeeman Effect and the Discovery of the Electron” in Histories of the Electron, says:

Furthermore, he [Larmor] suggested that they were universal constituents of matter.  He had two arguments to that effect. First, spectroscopic observations in astronomy indicated that matter “is most probably always made up of the same limited number of elements.” This would receive a straightforward explanation if “the atoms of all the chemical elements [were] to be built up of combinations of a single type of primordial atom.” Second, the fact that the gravitational constant was the same in all interactions between the chemical elements indicated that “they have somehow a common underlying origin, and are not merely independent self-subsisting systems.” Larmor’s electronic theory of matter received strong support from experimental evidence. First, it could explain the Michelson-Morley experiment. Inspired by Lorentz, Larmor managed to derive the so-called FitzGerald contraction hypothesis, which had been put forward to accommodate the null result of that experiment. As he mentioned in a letter to  Lodge, “I have just found, developing a suggestion that I found in Lorentz,  that if there is nothing else than electrons—i.e., pure singular points of  simple definite type, the only one possible, in the aether—then movement  of a body, transparent or opaque, through the aether does actually change its dimensions, just in such way as to verify Michelson’s second order experiment.” Second, Fresnel had suggested that the ether was dragged by moving matter and had derived from this hypothesis a formula for the velocity of light in moving media. Larmor’s theory was able to reproduce Fresnel’s result: “The application [of electrons] to the optical properties of moving media leads to Fresnel’s well-known formula.” The introduction of the electron initiated a revolution that resulted in the abandonment of central features of Maxwellian electrodynamics.