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Jefferson wheel

Six rings of letters threaded on a pencil, invented by Thomas Jefferson and used by the US Army a century later.

about 40 minutes the most impressive one makes a working machine

What you need

The printed template
Card
Scissors
Sticky tape
A pencil to thread them on

How to build it

Cut out the six stripsEach strip is one ring, and each has a different scrambled alphabet on it.
Roll each strip into a ringTape the ends so the letters run all the way round with no gap.
Thread them onto the pencilIn any order you like. That order is your key, and it must be written down.
Spell your message along the ringsTurn each ring until your letters line up in one straight row across all six.
Now copy a different rowAny other row. That row of six letters is your cipher text.
Send the row and nothing elseYour friend threads their rings in the same order, spells out your row, and looks round the wheel for the line that makes sense.
Number the rings on the inside before you thread them. Once they are on the pencil they all look the same, and the order is the key.

The template

Print this at 100 per cent, not fit to page, or the sizes will be wrong. The ruler line below tells you whether it printed correctly.

10 cm1QWERTYUIOPASDFGHJKLZXCVBNM2IOPASDFGHJKLZXCVBNMQWERTYU3GHJKLZXCVBNMQWERTYUIOPASDF4CVBNMQWERTYUIOPASDFGHJKLZX5ERTYUIOPASDFGHJKLZXCVBNMQW6PASDFGHJKLZXCVBNMQWERTYUIOcut into six strips, roll each into a ring, thread onto a pencil in any order you like
The bar above should measure exactly 10 centimetres. If it does not, your printer has shrunk the page.

Now send something

Six letters at a time is the whole message length, so start with SIXTHS or PENCIL and work up.

Where it comes from

America, the 1790s
Invented by a president, and forgotten twice

Thomas Jefferson designed a stack of lettered discs while he was Secretary of State, then set it aside. It was reinvented independently in France a century later, and again by the American army, which used a version as the M-94 into the 1940s. Jefferson's own description was found in his papers long after.

Why it works

Each disc is a different scrambled alphabet, so a letter is enciphered differently depending on which disc it lands on. The key is not a word but the order you thread the discs, which is why they must be numbered before you build it.

When it goes wrong

It usually does, the first time. Almost always one of these.

You cannot decode itThe discs are in a different order. Number them on the inside before threading, because once on the pencil they all look alike.
The rings will not turnToo tight on the pencil. Roll them a fraction looser and re-tape.

Where to go next

Lewis Carroll’s tableBack to Make