Phileas Fogg's Lost Day

The climax of Around The World In Eighty Days is an unexpected, but logically sound, argument: that if you travel in the same direction as the Earth is turning, you'll eventually 'lap' the planet and gain a day.  It turns out that somebody went through the mathematical effort to prove that Phileas Fogg didn't really gain a day, so Passepartout's watch didn't really mess up the plan.  Blame Poe, though: a short story of his, no doubt, planted the seed in Verne's mind of this date conundrum.