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The Roget Illusion and the Persistence of Vision by J. L. Hunt Dept. of Physics Univ. of Guelph

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Peter Mark Roget (1779-1869) the author of the famous Thesarus noticed an unusual illusion

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When a carriage wheel rolls behind A picket fence (palisade) it does NOT look like this

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It looks like……..

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Which is known as The Roget (Palisade) Illusion THIS!!!

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A simple apparatus demonstrates the illusion. An endless palisade Is turned by a crank and a fixed wheel rolls behind it.

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Here’s what you see looking at the rolling wheel through the palisade

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Let’s follow the intersection of a spoke and a slit as the wheel rotates and the array of slits moves across.

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This is one of the few illusions that can be analyzed mathematically. The x and y coordinates of the spoke and slit intersection are: x = r t y = x tan [2 n /N + x/r] Where r = radius of the wheel = angular velocity of the wheel N = number of spokes in the wheel n = 0……(N-1) is an index of a particular spoke.

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