A few months ago I ran across a historic magic trick in our collection: the Mystic Oracle, ca. 1825.
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| Mystic Oracle. EL3 .A1my The Rosenbach of the Free Library of Philadelphia |
As the package states, the trick consists of a set of cards which allow you to guess a person’s age, or any other number they choose. You ask them to think of their age or to pick a number between one and sixty. You then offer them the following set of six cards.
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| Mystic Oracle. EL3 .A1my The Rosenbach of the Free Library of Philadelphia |
You ask them to hand you all the cards which contain their number. You then triumphantly announce their number to your astounded audience. How did you do it? You just add the numbers in the upper right corner of the cards they give you and that will be their number. As the instructions in the set point out, if they give you the correct cards, then the method is foolproof. If you’d like to try it for yourself, you can print out a PDF of the cards and give it a shot.
The mathmaniacs website explains that the reason the trick works has to do with binary numbers and powers of two–note that the number in each of the upper right corners is a power of two. Dr. Mike’s Math Games for Kids extends the trick with a set of cards that work for numbers up to 1000. Interestingly, nearly two hundred years after the Mystic Oracle, commercial versions of the trick are still popular today–check out the boards at the lower right of this Melissa and Doug magic set on Amazon.
I guess a good trick has a long shelf life.
Kathy Haas is the Associate Curator at The Rosenbach of the Free Library of Philadelphia and the primary poster at the Rosen-blog.