Optical illusions play an important role in magic performances. Most stage illusions depend on the limitations of our visual perception. The Jastrow illusion, known to magicians as the boomerang illusion, is a well-known deception that can be used in close-up magic. The basic principle is simple. Two boomerang shaped arches seem to be of different sizes, but are in actual fact identical.
Magicians tend to underestimate the power of this simple trick, but a recent viral video shows that its deceptive power is as strong as it was when first discovered almost 150 years ago.
My toddler's train track is freaking me out right now. What is going on here?! pic.twitter.com/9o8bVWF5KO
— marc blank-settle (@MarcSettle) April 6, 2016
The Jastrow Illusion as a Magic Trick
Performing the Jastrow Illusion as a magic trick successfully requires it to be turned to theatre. Simply showing the arcs to be swapping relative size will render it a ere puzzle. Many different variations on this theme have been published and marketed over the decades. The trick can be performed with boomerangs, fish, card fans, mud flaps or anything else that resembles an arch. Magic routines using this principle can use two, three or even four arches, adding an additional layer of deception. When using small arcs there are also possibilities to deploy slight of hand for additional complexity. The video below shows the Sakkaku Scale, a very deceptive version with three arches.
You can read more about the Jastrow Illusion and how it can be used in magic in my upcoming e-book. This book describes the science behind the illusion. It describes a large number of published and marketed routines and provides suggestions to develop your own routines.
The lists below provide an overview of marketed tricks and publications about the Jastrow illusion and magic tricks that use this principle.
Marketed Tricks
Adair, Ian (n.d.). Monkey Puzzle.
Adair, Ian (n.d.). Fishy Tale.
Adair, Ian (n.d.). Butterfly Puzzle.
Anonymous (n.d.). Donkey-Monkey Competition.
Anonymous (2009). Baffling Boomerangs. Magic Makers.
Franke, Harry G. (n.y.). Fish Tales. Daytona Magic.
Leach, Chuck (2006). Boomerang Cards Across. Chazpro Magic.
Murray, George and Jorgenson, Tom (1990). Magic Color Changing Boomerangs. Nielsen Magic.
Rogers, Terri (2000). Top of the Bill. A Close-Up Illusion. Martin Breese International.