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# The Horizontorium: A Nineteenth-Century Optical Illusion

Here’s one for history buffs and optical illusion lovers: The Horzontorium, the once popular 3D illusion invented by William Shires in 1821. I’m all for bringing this back, so who wants to give it a try?

## The History of Horizontoriums

According to an 1835 issue of Mechanics’ Magazine, a British mathematical tutor named William Shires invented the optical illusion known as “The Horizontorium” in 1821. Horizontoriums typically depicted a distorted building or monument, which when placed horizontally on a flat surface, would appear to leap into perspective as a miniature 3D model when viewed through a pea-sized hole at the appropriate distance and height. Horizontoriums were apparently so popular that they were copied by a number of different individuals who spuriously claimed to have invented them. The print below is the only known American-made Horizontorium. It depicts the Philadelphia bank building designed by Benjamin Latrobe, once located at Fourth and Chestnut Streets, in 1832.

## Using a Horizontorium

Now for the fun part. If you want to view the illusion for yourself, print out the image above and place it flat on a table, preferably with the sideways “D” toward the edge for maximum maneuverability of the viewing piece. Next, you’ll want to cut a strip of paper. Poke a hole roughly the size of a pea in one end. This is your viewing piece; close one eye and place the strip with the hole over the open eye. Find the sidewise “D” and look through the strip just above that mark. Move your head vertically until the bank pops into perspective.

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