Have you ever watched a ship disappear when it sailed away?

It is one of the most discussed subjects in the flat earth debate. Do you watch it disappear because it gets smaller, or because of the curve of the earth.

But seeing is one thing, discerning the truth is something else.

This has a lot to do with the limit's of how far we can actually see (because of the haziness (water vapour, pollution) of the air), perspective (things look smaller over greater distances) and then there is this thing called refraction (caused by layers of air of different temperature), it messes with light going in a straight line.

My guess (I cannot proof it) is, that is actually harder to see at sea. This is because refraction get worse when the difference in temperature increases. Water has a great capacity to store heat, and takes longer to get warmer than land. In winter the sea is warmer, in summer colder. This creates a big difference in temperatures between the surface and the air.

So lets get into some 'evidence'.

 And there are other examples in the list under the hamburger. What you see is that only the top of the object is visible and the lower part is hidden by the water.

 This video shows a different view for the same phenomenon. At first glance the lower part disappears. Zooming in though reveals the whole boat again. It is not clear though how far this will go. At one point the magnification becomes the problem itself.

So...hard..to..tell isn't it?

So these videos do not proof a thing, it only makes it clear that relying on you eyes, or camera, alone is not enough.

So thinking about this I thought: 'We need bigger things' and we need to get rid of the shimmering effect of refraction. So like a mountain. This would show it in a better way.

And luckily some people did exactly that.

For example

 Next part where flat earthers (sort of) agree A further explanation by greatersapien about how this cannot be caused by perspective and what perspective is about

What is explained here is that taking into account the perspective (both in flat and round) a mountain that is higher but further away, should still be visible above the mountain in front. However it is not. And atmospheric disturbance could never account for that. Actually the people defending the flatearth model agree on this particular example (well not directly, but still (See 'next part').
So is this proof the earth is round? No, because that is not how science works. It is a whole lot harder to proof something, than it is to disproof something. Sorry.

This one video is showing the same thing. Again, the refraction is (as far is I can tell) taken off the table. And again it shows something opposite of what you would expect on a flat earth.
I have not seen a video that shows the same thing and show the flat earth model works.

An interesting observation though is the appearance of the Canigou mountains

 This is Canigou mountain appearing silhouetted at sunset,when it was not visible just before. However this can be explained by refrection.And this video shows only the top of the mountains are visible not the whole.

So on itself this is tough. but do try it yourself and see.

 A very nice video explaining a lot of things is this one on the right. It is nice because the tone is professional.

 On the right a video taken with a telescope of a smoke stack vanishing bottom first from the horizon.

On the page To prove or not to prove I will show you an example of a test, which seemed legitimate on first glance, but which proved to be wrong later on.

Together with other subject though it might become more... clear?

If you are interested in things like refraction