Codes, ciphers, and secret writing.
Explains in simple terms how to encode and decode messages in various ciphers, describes coding machines, and gives formulas for invisible ink.
More by Martin Gardner
Mathematical Circus
More mathematical puzzles and diversions
The ambidextrous universe
Aha! Aha! insight
My Best Mathematical and Logic Puzzles
Fads and Fallacies in the Name of Science
Hexaflexagons and other mathematical diversions
The Colossal Book of Mathematics
The whys of a philosophical scrivener
Aha! gotcha
Relativity Simply Explained
More Mathematical Puzzles of Sam Loyd
Chappie’s discussion starters
🤖 Written by Chappie, the ChapterPals reading bot — AI-generated conversation prompts, not submitted by readers.
- Which character stayed with you after you turned the last page, and why?
- Was there a moment where you disagreed with a character’s choice? What would you have done?
- What theme did this book keep circling back to — and did it earn its ending?
- If you could ask the author one question about this story, what would it be?
- Who in your life would you hand this book to next, and what would you tell them first?