Ask Ethan: How do we know the Earth isn’t flat?
Ethan Siegel

Great article, but maybe it would be better if you have added the last piece of information. 
The greek experiment was great, but the problem is that the conclussion might as well be that the Earth is a semisphere, or a piece of a sphere, or maybe it was stil flat but the places where the shadow was meassured were part of a giant semispheric hill, like a bump on a flat Earth. 
There was also an observation about how the liquids behaved and how the ships, instead on just getting smaller in the horizon, seemed to sink until they dissapeared, which could only be explained with a curved Earth.

That’s why it was so important when Juan Sebastián el Cano completed the first circumnavigation of the Earth: it was the scientific demonstration that the Earth should be round (assuming our universe’s geometry is euclidean, etc). Anything until then, was also relevant and very interesting, and maybe necessary to make people think in that direction, but precisely not a demonstration.

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