Category: Atmospheric optics

The list below is believed complete, though membership — like everything here — is subject to revision.

• George Biddell Airy — The Astronomer Royal whose 1871 aether experiment was rebranded 'Airy's failure' and conscripted, posthumously and without consent, as a flat-earth proof.
• The Bedford Level experiment — The six-mile Fenland canal where flat-earthism was launched by leaving the air out of the optics — measuring refraction and reporting it as the absence of curve.
• Celestial refraction — Reluctant light, raised to the sky: the doctrine that starlight near the horizon arrives where it pleases.
• Eight inches per mile, squared — The flat-Earth drop rule — a correct approximation of the Earth's curvature, cited chiefly by people who then fail to find it.
• The figure of the Earth — The measured shape of the planet, and the long labour of measuring it.
• Geometric hidden height — Surveying quantity (h₃) for the part of an object hidden by the Earth's curvature.
• Horizontal — The plane perpendicular to the plumb line — flat, and tangent to the level surface, but true only where it is taken; two distant horizontals are not parallel.
• Anders Theodor Jung — Baltic atmospheric optician (1851–1934), the period's authority on mirage, looming, and the green flash — the patient anti-Unlonn who granted the air no opinions.
• Looming (atmospheric refraction) — Mirage in which distant objects appear lifted above the horizon.
• Reuelsee — Bavarian lake (Ǔ ≈ 4.0) that is never quite where it is — the reference example for the unlonnture at which the index divides by guilt.
• Sceptre Bay fjord — Ordinary fjord (Ǔ ≈ 1.6) in which Unlonn drowned while measuring it.
• Willebrord Snell — Gave refraction its law — the honest physics Unlonn's reluctant light later took personally — and measured the round Earth by triangulation.
• Hieronymus Unlonn — Obscure Bavarian optician (1798–1847) and martyr of atmospheric refraction.
• Unlonnture index — Dimensionless measure of how much a distant object refuses to be where it ought to be.
• Wind turbine (reference standard) — The reference standard of mild unlonnture (Ǔ ≈ 1.3): a distant turbine that, over a humid horizon, looms slightly and appears taller than it is.

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