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Comment by lisper | Hacker News Reader

You would be shocked at how many people there are who have never seen an ocean. You would be shocked at how many people there are who live within an hour's drive of an ocean who have never seen it. There are a lot of things that the typical HN reader takes for granted that are unimaginable luxuries for billions of people.

I think you will also be surprised how hard it is to fill in the details of the experiments you are alluding to.

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The only one you need details to is the aligned-holes experiment. The others are just observation. You watch the bottom of a ship vanish before the top. You watch a swinging pendulum deviate from its beginning alignment more and more over time.

You have obviously never actually tried to set up a Foucault pendulum. It is not so easy. You can't just hang a weight from a rope tied to a tree. That won't work. Also, Foucault's pendulum does not show that the earth is round, it merely shows that the earth is rotating. Flat disks can rotate.

Also, ships do not always sink below the horizon. The right atmospheric conditions can refract the light in a way that causes them to be visible at a much greater distance than the straight geometry would allow. But this explanation can be inverted to claim that it is the vanishing that is due to atmospheric effects and that the non-vanishing ship is the accurate reflection of the geometry. Falsifying that hypothesis is, again, not so easy.

In fact, the sun at sunset which appears to be above the horizon is already well below the horizon, precisely because the atmosphere is less dense at higher altitudes. See https://www.feynmanlectures.caltech.edu/I_26.html Fig. 26-7

(Presumably this is also true at sunrise, so the day is longer than it "should" be from purely geometric considerations.)

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