In ancient times the Earth appeared round to the observant. Some learned the world’s shape by watching ships disappear over the horizon from the bottom up, then return mast first. Others followed the globe’s curved shadow as it crept across the Moon during lunar eclipses. The notion that people deemed the world flat until Columbus proved otherwise is a clever fiction hatched by Washington Irving in the nineteenth century. As early as 240 BC, Eratosthenes had estimated the earth’s circumference with nothing more than the shadow cast by a stick and the basic theorems of geometry.
However, finding the true measure of the Earth’s roundness – whether it was perfectly spherical, or flattened at the poles to bulge at the equator, or elongated at the equator to resemble an egg on end – proved far more difficult. In 1735, the quest to determine the