Friday, January 28, 2011

Mark Twain has some fun with extrapolation

In chapter 14, "Cutoffs and Stephen," of Life on the Mississippi, Twain explains how the river has shortened itself. This happened when the river cut across various bends in its course, creating a new island, creating new riverfront property, and taking a more direct course south. In fact, the river was thus shortened more than once intentionally by landowners who wanted their property to front the river itself, by simply digging a ditch to start the course going, and once it began, there was no stopping it. This also often resulted in ill-will, to say the least, not excluding actual killing because of it.

But then he goes off on a slight tangent to show the dangers of extrapolation:
In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old O├Âlitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing rod. And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three quarters long, and Cairo and new Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

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