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

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

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

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

It looks like……..

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

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

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

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

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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