Great Scientific Theories - flat Earth

JETfri has started a project to illustrate great scientific theories, with a touch of humor. Let's start with the flat Earth theory. Contrary to what many believe, in western civilization a belief in a flat Earth was dispelled a few centuries BC. This was probably first noticed by sailors leaving port and seeing their point of origin drop below the horizon due to the curvature of the earth. As early as 240 BC Eratosthenes measured the circumference of the Earth by comparing the shadow cast by the sun in two different locations. From this point on all educated people knew that the Earth was round (uneducated people probably never considered the matter). For instance, if you read Dante's Divine Comedy, he travels down into the Earth through Hell, and climbs up a tunnel on the other side to find Mount Purgatory (he even describes the flip in the pull of gravity as he passes through the center of the Earth). When Columbus proposed to sail around the Earth to reach China, the objection was not that the Earth was flat and that he would sail over the edge, instead it was that the Earth was way too large and he would run out of supplies before ever reaching China. Indeed his detractors were correct - Columbus vastly underestimated the size of the Earth. It was only the placement of the Americas that saved his journey from disaster - If there were just ocean all the way from Spain to China his men would have died of thirst long before they made it there.