It is generally thought that the concept of a round Earth is a principle that was hard-won by science in the face of stiff opposition. There is a well-known image of Cristopher Columbus (1451-1506) holding up an egg to illustrate the roundness of the Earth to sceptical onlookers. However, the truth is that most educated people since the days of the Greek were convinced that the world is round.
It is said that Pythagoras was the first to suggest that the Earth is round about 525 BC. The suggestion was made on philosophical grounds — the sphere was considered to be the perfect shape. Later, Aristotle had convincing evidence that the Earth is round. He noted that as one travelled north or south while observing the night sky, visible stars disappeared beneath the horizon behind and new stars appeared over that horizon ahead. He also noted that when ships sailed out to sea, regardless of the direction, they always disappeared from sight hull first. On the other hand, ships heading towards land always showed their masts first as they came over the horizon. All of these observations could be explained only by assuming that the earth was a sphere.
The idea of a rotating Earth was much less easily established. The Greek philosopher Heraclides of Pontus suggested in 350 BC that the Earth rotates on its axis but most ancient and medieval scholars refused to accept this idea.
The Copemican model of the solar system (1543), in which the Earth revolves around the sun, made the idea of a non-spinning Earth illogical, and slowly the idea that the Earth rotates on its axis was accepted by all. However, it was not until 1851 that the Earth’s rotation was experimentaly demonstrated by the French physicist Jean Bernard Foucault ( 1819-1868). The Earth is not a perfect sphere. Centrifugal forces tend to push material away from the centre of rotation.
