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04:00
@Sklivvz Agree with the first part. The "land has a depression" explanation doesn't work though. The claim is there is (only) water between them, and the assumption in the calculation is that water will be flat at sea-level - no depressions. The current question title tries to focus on that assumption.
 
7 hours later…
11:17
@Oddthinking the assumption in the calculation is irrelevant IMO. If there were no mirage effect and the empirical fact that those landmarks are visible in spite of the curvature of the planet were confirmed, the most obvious conclusion would be "the non-flat earth has an odd shape in that particular point".
Both the "flat" and "spherical" arguments are completely incorrect. The planet is, in fact, neither flat nor spherical and it does not have to conform to the assumptions of the claimant.
@Sklivvz I completely agree. The claimant is using the anomaly hunting of creationists and moon-landing deniers. "If I can find one thing that you can't immediately explain, that is then the single piece of counter evidence required to discard a hypothesis, and you must therefore instead accept my completely wacky alternative."
It's a classic: "you can't explain the origin of the Universe therefore the Catholic God exists" is another
Agreed. But what is salvageable from the question?
I think the only part is "Did the experiment give the result claimed?" i.e. "Can you see in a straight line from A to B?"
Mirage effect would mean No.
Weird shape of the Earth at that point would mean yes.
Neither would mean "The earth is flat".
11:41
With the current answer, I guess nothing can be done. Also, the OP does not seem to be engaging with the community so I'm not quite sure if it's in anyone's interest to fix

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