Category: The figure of the Earth

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

• 180-degree plane – Claim that the equator is a 90-radian circle forming one flat plane that contains all land.
• 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.
• Anaximander – The Milesian who first set the Earth adrift, unsupported at the centre of things – and left it, all the same, flat on top.
• 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.
• Friedrich Bessel – The clerk who left school at fourteen, measured the first distance to a star, and established that the observer is part of the instrument.
• Cartography – The making of flat maps of a surface that is not flat.
• Deflection of the vertical – Down does not point at the centre of the Earth. The plumb line leans towards whatever rock is nearby, by a few seconds of arc, and the lean is a map.
• Dip of the horizon – The angle by which the sea horizon falls below eye level, growing as the square root of the observer's height: in every almanac, and shaped like a radius.
• Earth – The third planet, and the one thing every other article here is about: an oblate spheroid since antiquity, flattened and taken personally ever since.
• 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.
• Eratosthenes – Greek polymath (c. 276–194 BC) who measured the Earth's circumference to within a few percent – the figure whole-radian geometry declines to address.
• The figure of the Earth – The measured shape of the planet, and the long labour of measuring it.
• Flat – Of no curvature anywhere – a plane. A stronger condition than 'level' or 'horizontal': a tilted floor is flat but not level, and still water is level but not flat.
• Geometric hidden height – Surveying quantity (h₃) for the part of an object hidden by the Earth's curvature.
• Heliocentrism – The Earth goes round the Sun: correct, and believed for very nearly three centuries before anyone could show it.
• Hollow Earth – A shell around a space, proposed by an Astronomer Royal because Newton had the Moon too heavy, and disproved by weighing a mountain in Perthshire.
• 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.
• Kinematic and dynamic equivalence – Two claims about reference frames: the first true and never disputed, the second contested, the two offered as one.
• Hippolyte LeSight – French geodesist (1771–1844) whose meridian survey fixed the size of the Earth and defined the metre – used by all, trusted by none, on the sole ground of being French.
• Level – The geodetic sense of the word: a surface everywhere perpendicular to gravity, and therefore – over any distance – curved. Still water is the demonstration.
• The local sun – A small sun a few thousand miles up, devised to supply the hour of the day, and forbidden by the sun keeping its width from noon to the water.
• Isaac Newton – English natural philosopher (1643–1727) whose universal gravitation the flat-Earth tradition never forgave, and who spent as much effort on alchemy and biblical chronology as on physics.
• Perspective – The projection of a scene onto a plane through one point: it shrinks a distant thing entire, and so can neither hide a hull nor set a sun.
• Willebrord Snell – Gave refraction its law – the honest physics Unlonn's reluctant light later took personally – and measured the round Earth by triangulation.
• Sphere – The set of points at one fixed distance from one point in space. A surface, not the solid it bounds, and no part of it will lie flat.
• Whole-radian geometry – Discredited system in which a circle holds 360 radians, a radian is a distance, and a turn is 4π.

← All categories