… enormously at variance with truth

Annie

I repeat, then, that I speak of these things only as of coincidences. And further: in what I relate it will be seen that between the fate of the unhappy Mary Cecilia Rogers, so far as that fate is known, and the fate of one Marie Rogêt up to a certain epoch in her history, there has existed a parallel in the contemplation of whose wonderful exactitude the reason becomes embarrassed. I say all this will be seen. But let it not for a moment be supposed that, in proceeding with the sad narrative of Marie from the epoch just mentioned, and in tracing to its dénouement the mystery which enshrouded her, it is my covert design to hint at an extension of the parallel or even to suggest that […] measures found in any similar ratiocination, would produce any similar result. 

[…] it should be considered that the most trifling variation in the facts of the two cases might give rise to the most important miscalculations, by diverting thoroughly the two courses of events; very much as, in arithmetic, an error which, in its own individuality, may be inappreciable, produces, at length, by dint of multiplication at all points of the process, a result enormously at variance with truth.

From “The Mystery of Marie Rogêt” (1842), Edgar Allan Poe (1809 – 1849)

Poe discusses error propagation and the sensitive dependence on initial conditions in nonlinear systems to make clear that even parallels of seemingly “wonderful exactitude”, such as the cases of Mary Cecilia Rogers and Marie Rogêt, may considerably diverge from each other in the long run due to initial “inappreciable” discrepancies.

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