A classic demonstration of the curvature of the Earth was performed by Alfred Russel Wallace in 1870: http://blogs.scientificamerican.com...modern-biology-got-suckered-by-flat-earthers/ Put more simply, we have: A) A telescope (which we would replace with a digital camera with powerful zoom lens) B) A target 3 miles away C) A target 6 miles away, in line with A and B. A,B, and C are all the same height above the waterline. So you just look from A towards B and C, and if B is visually higher than C then the water surface is curved up in the middle. Rather surprisingly I can't find any well documented recreations of this experiment. It seems like it would be an ideal science project. There are significant difficulties though as you need a suitable stretch of water, the targets are 12 feet above the water, and the six mile distance makes it difficult to coordinate. But it's really a very straightforward demonstration. So what I'd like to do in this thread is discuss places where the experiment might best be carried out, and what procedures could be used to make the execution of the experiment as straightforward and foolproof as possible.