Theories of Aether and Electricity (Part 1)

I’ve been reading an amazing book, a little bit every night in bed:

• Edmund Whittaker, A History of the Theories of Aether and Electricity, Two Volumes Bound As One. Volume I: The Classical Theories. Vol. II: The Modern Theories, 1900-1926. Dover, 1989, 753 pages.

How in the world did our species figure out the laws governing the electric field, magnetic field, and charged particles? A lot started with pure luck. Two unusual stones played a key role: amber and lodestone.

The first, really fossilized tree sap, easily acquires an electric charge if you rub it against wool or silk. This was one of human’s introductions to the electric field, and electrons. Indeed, the ancient Greek word for amber was ēlektron. The second, called magnetite, is naturally magnetic.

How odd that of all the minerals in nature, there were two with peculiar abilities to attract and repel! This duality foreshadowed the duality between electric and magnetic fields, now understood mathematically using the Hodge star operator. Who could have guessed that a pair of stones would eventually lead to such deep discoveries?

Isaac Newton caught a glimpse of it. In the early 1700s he commented about both amber and lodestones in the third book of his Opticks, called simply The Queries. He was imagining challenging someone skeptical of the existence of aether:

Let him also tell me, how an electrick Body can by Friction emit an Exhalation so rare and subtile, and yet so potent, as by its Emission to cause no sensible Diminution of the weight of the electrick Body, and to be expanded through a Sphere, whose Diameter is above two Feet, and yet to be able to agitate and carry up Leaf Copper, or Leaf Gold, at the distance of above a Foot from the electrick Body? And how the Effluvia of a Magnet can be so rare and subtile, as to pass through a Plate of Glass without any Resistance or Diminution of their Force, and yet so potent as to turn a magnetick Needle beyond the Glass?

While these are brilliant questions, he and some later thinkers had to struggle for a long time to sort out the relation between what we’d later call electrons and the electric field. It’s easy to see why, since they’re so intimately related.

As it turns out, electrons are not emitted but absorbed by amber when it rubs against wool. Later there were long arguments about whether there were two kinds of ‘electrical fluid’, positively and negatively charged, or just one. But maybe the ‘exhalation’ he mentions is really the electric field, just as the ‘effluvia’ of a magnet are the magnetic field.

There is a lot more to say about all this, but I think I’ll do it in short bits, to avoid writing a 753-page tome like Whittaker’s.

8 Responses to Theories of Aether and Electricity (Part 1)

  1. You meant that amber acquires a negative charge, right?

    Triboelectricity, as this effect is called, took a lot longer to explain than Maxwell’s equations. I think Feynman comments somewhere on the irony.

    • John Baez says:

      Whoops! Yes. I deleted that bit because it’s not the main point. By the way, Benjamin Franklin is responsible for the unfortunate convention of calling the charge of an electron ‘negative’. I’m not sure why. You can blame my slip on him.

      Why do the electrons move to the amber instead of the other way around? You can read a completely useless answer here:

      Why do electrons move from amber to wool during static electricity charging?, Physics Stack Exchange.

      and likewise here:

      What happens when amber is rubbed with silk? Physics Stack Exchange.

      where when the questioner persists, the answerer replies “Your question is no longer related to physics but has more to do with organic chemistry still I’ll answer it…” before coughing up something slightly more useful.

      • Well, Franklin had a 50-50 chance of getting it “right”; in an antimatter universe, he would be right. I guess he’s also right in P-type semiconductors. Of course Franklin wasn’t talking about electrons, just the current.

        Triboelectricity, like ferromagnetism and the friction force, belong to the “messy” branches of physics. As I understand it, real progress in the theory of these phenomena has occurred only in the last couple of decades.

        Faraday apparently thought the electric current was a tension rather than a flow. (Or so I recall from L. Pearce William’s bio.)

  2. Stasheff, James says:

    Wow! Thanks
    Hope your little bits will come without too much delay between

  3. Supernaut says:

    When we think of Newton we think about his seminal work on dynamics and perhaps also optics, not necessarily E&M but of course he was very curious about everything. The author you mention (Edmund Whittaker) is also the author of the classic text ‘A Treatise on the Analytical Dynamics of Particles and Rigid Bodies’ (I have the 2nd Ed., 1917…but unfortunately it’s just a pdf!).

  4. Bruce Smith says:

    Lodestones had a crucial practical application (navigation) which undoubtedly contributed to the scientific interest in how they worked. Is anything like that also true of amber?

    • John Baez says:

      I don’t know of any practical application like that for amber. So I guess magnetism took the lead for practical applications at first!

      I’d heard the lodestone compass was invented in China, but I see now that happened long ago:

      The compass was invented more than 2000 years ago. The first compasses were made of lodestone, a naturally magnetized stone of iron, in Han dynasty China (20 BC – 20 AD). The compass was later used for navigation during the Chinese Song Dynasty (960–1279 AD), as described by Shen Kuo. Later compasses were made of iron needles, magnetized by striking them with a lodestone. Magnetized needles and compasses were first described in medieval Europe by the English theologian Alexander Neckam (1157–1217 AD). Dry compasses begin appearing around 1300 in Medieval Europe and the Medieval Islamic world.

      • Wikipedia, History of the compass.

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