Bacon's cipher

Type on the left and each letter comes back as a group of five As and Bs. Swap the boxes to decode. Anything that isn't an A or a B is ignored on the way back, so you can paste in groups separated however you like.

Alphabet picks between the 24 letters Bacon actually wrote, where I covers J and U covers V, and a modern 26-letter table that gives every letter its own code. Pick 24 letters (Bacon's own) for historical text.

Five slots, two choices each, gives 32 combinations. That's more than enough for 24 letters. A is AAAAA, B is AAAAB, and the pattern counts upward in binary with A standing for 0 and B for 1.

Bacon's own alphabet ran to 24 because Elizabethan English treated I and J as one letter, and U and V as another. The 26-letter version is a later tidy-up. The two agree from A to I and part company at J, so a message encoded with one won't decode cleanly with the other.

Francis Bacon mentioned it in passing in The Advancement of Learning in 1605 and set it out properly in De Augmentis Scientiarum in 1623. He called it a biliteral cipher, and the As and Bs weren't supposed to appear anywhere.

The point was to hide them. Write a harmless cover message in two slightly different typefaces, one standing for A and one for B, and the five-letter groups disappear into the shapes of the letters. Bacon's phrase for the goal was writing "omnia per omnia", anything by means of anything. That's steganography. What it hides is the fact that there's a message at all.

That idea attracted cranks. Ignatius Donnelly claimed in 1888 to have found a cipher in Shakespeare's plays, and in 1899 Elizabeth Wells Gallup claimed to have found Bacon's own biliteral cipher in the typefaces of the First Folio, proving Bacon wrote them. William and Elizebeth Friedman, who had met while working on Gallup's claims, published the demolition in 1957. The Folio's printers mixed type haphazardly, as printers of the time did, and a determined reader can find any message in noise.

Binary does the same counting with 0 and 1 and eight slots instead of five. Morse also builds letters from two symbols, but its codes vary in length so common letters stay short.

For a scheme that numbers the alphabet rather than encoding it, try A1Z26.