Have you seen this puzzle that’s been making its way around the net lately? Count the number of men, wait for them to shift, and then count them again. Confused? Or did you spot the secret? As it turns out, this little brain-teaser is based on one that’s over a century old. The genius behind it is a man named Sam Loyd.
I remember seeing a similar “vanishing person” puzzle at a science museum when I was young and when my family started sending this one around via e-mail, I remembered vaguely how it worked. Thanks to the magic of the internet, I tracked down a fantastic detailed explanation of the solution over at Defective Yeti.
But what’s even better, Defective Yeti had a link to the Sam Loyd website, where I learned about a truly old-school GeekDad, sort of a 19th-century Will Shortz. Samuel Loyd, born in 1841, started off as a chess player who loved to devise chess-related puzzles. He became the editor of the Chess Monthly at age sixteen; then by age 30 he had shifted into mathematical puzzles and toys. He’s the one responsible for the “trick donkeys” puzzle, later sold to P. T. Barnum himself.
In 1896 he created the “Get Off the Earth” puzzle, in which a man vanishes when you turn a disc in the center. This is the puzzle that inspired the Twelve/Thirteen Man problem, and Loyd made several variations on it later, including one featuring Teddy Roosevelt and some lions. Loyd continued to devise puzzles and riddles, publishing a monthly magazine and a book of puzzles for children. After his death, his son Walther actually changed his name to Sam and continued his father’s work. (Think any of your kids will do the same?)
The Sam Loyd website is a great source of brain-teasers for both adults and kids. The Flash-based interface is a little clunky, but there’s a section on puzzles for kids (with answers), and a downloadable “Cyclopedia” of 5,000 puzzles. (Click on “Sam Loyd’s Store” and then the image of the Cyclopedia.) There’s even a section on how to use Sam Loyd puzzles for education, classroom activities, and a free Sam Loyd School Pack if you’re an educator.
If you like puzzles, riddles, and brain-teasers, the Sam Loyd website is definitely worth a visit.
Click for the explanation of the Twelve or Thirteen Man puzzle.