Ayrtha: Hertha Ayrton, the Electric Arc and Sand Ripples
Electromagnetism & Plasma arc, page 89 of 193. Back to The Pixelated Physics Universe
Who they are
Ayrtha is a respectful pixel portrait of Hertha Ayrton, after a Bain News Service photograph of about 1900, holding a white-violet carbon arc above a basin of sand ripples.
Ayrtha is a character of the Electromagnetism & Plasma arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.
The physics
Hertha Ayrton (1854–1923) showed that the hissing and instability of carbon arc lamps came from oxygen reaching the hot crater of the positive carbon, and summed up her arc work in The Electric Arc (1902). There she gave an empirical law for the voltage across an arc, now called the Ayrton equation. Her ripple paper on how vortices build sand ripple marks, “The origin and growth of ripple-mark”, was read before the Royal Society on 16 June 1904. In 1906 she became the first woman to receive the Society’s Hughes Medal.V = a + b l + (c + d l) / I V: voltage across the arc (V) I: arc current (A) l: arc length, the gap between the carbons (m) a, b, c, d: empirical constants fitted for given electrodes (units V, V m⁻¹, W, W m⁻¹) The (c + d l)/I term makes V fall as I rises, a negative differential resistance, which is why an arc needs a series resistor to stay stable.
No single equation is shown for this character; the physics above is stated in words because it is an observation or a piece of history, and we do not invent formulas.
Honest caveat: The Ayrton equation is empirical, fitted to carbon arcs; it is not derived from plasma physics and does not hold for every arc. How sand ripples grow and choose their spacing is still studied.In characterThey said the arc hissed because it was fickle. It hissed because it was breathing oxygen. I listened until it told me why.
Crossovers
Ayrtha meets Remanenza (Magnetic Hysteresis Loop). Ayrtha studied the electric arc, whose voltage and current don't follow a simple straight-line law. Remanenza's hysteresis is another case where a material's response depends on its history, not just on the present input.
Ayrtha meets Tallywick (Thermionic Emission). Ayrtha's carbon arc runs hot enough that its electrodes emit electrons thermally. Tallywick's Richardson–Dushman law gives that emission current: J = AT²e^(−W/k_BT).
Ayrtha meets Kayella (Kaye Effect). Ayrtha also studied sand ripples formed by moving water. Kayella's shampoo stream leaping off its own heap is another fluid surprise, where the flow builds the shape that then redirects it.
Wear the lore
Concept keywords: Hertha Ayrton, the Electric Arc and Sand Ripples, Ayrtha, Electromagnetism & Plasma, physics lore, Pixelated Physics