Night writing

Night writing, AKA sonography, was a system of code that used symbols of twelve dots arranged as two columns of six dots embossed on a square of paperboard, and is now remembered as the forerunner of Braille. It was designed by Charles Barbier in response to Napoleon's demand for a code that soldiers could use to communicate silently and without light at night. Called sonography, each grid of dots stands for a character or phoneme.

Barbier's system was related to the Polybius square, in which a two-digit code represents a character. In Barbier's variant, a 6×6 matrix includes most of the characters of the French alphabet, as well as several digraphs and trigraphs:

A character (or digraph or trigraph) was represented by two axes of dots, in which the first column had one to six dots denoting the row in the matrix, and the second had one to six dots denoting the column: e.g., 4–2 for "t" represented by

As many as twelve dots (two columns of 6) would be needed to represent one symbol.