Cipher methods Symbols
Moon alphabet (W. Moon, 1845)
The Moon alphabet is a tactile writing system for blind readers, invented by William Moon (1818-1894) in Brighton (UK) in 1845, twenty years after Louis Braille’s system (1825). Moon, blind since age 21, observed that adults who lose their sight later in life struggled to learn braille — a fully abstract system based on raised dots.
His answer: preserve the shape of Latin letters but simplify them so they remain readable by touch. An arc for C, a diagonal for A, a crossed stroke for T — each letter keeps a recognisable feature of its printed form. The system is still in limited use in the UK, notably in publications by the Royal National Institute for the Blind (RNIB). 26 Latin letters, no digits in the standard table.
How does the alphabet work?
The cipher relies on a graphical monoalphabetic substitution: each cleartext letter is replaced by its simplified Moon shape (arc, diagonal, crossed stroke). Same principle as the Caesar cipher (~50 BC), except the “key” is a silhouette table instead of a numeric shift.
The table holds 26 glyphs for the 26 Latin letters (no digits in the standard version). Several letters reuse the printed letter’s silhouette (C, L, O, V), others are a further simplification (A, B, F).
Cryptographic strength: low. Like any monoalphabetic substitution, frequency analysis breaks it in a few dozen words. But Moon was never used cryptographically: it’s an accessibility system, presented on CipherChronicle as a historical testament to reading ergonomics in the 19th century.
Historical and modern usage
- Royal National Institute for the Blind (RNIB) — specialised publications.
- Tactile reading — adults who became blind later in life.
- History of accessibility — historical alternative to braille.
- Pedagogy — illustrates keeping a familiar silhouette to ease learning.
Related variants
- Braille (1825) — see our entry, the contemporary dot-based alternative.
- Nyctography (Lewis Carroll, 1891) — see our entry, another night-writing system.
- Tifinagh — see our entry, an alphabet of geometric silhouettes.
What are the weaknesses?
- Monoalphabetic substitution — frequency analysis is immediate.
- Recognisable silhouettes — several letters stay visually close to Latin.
- No digits — the standard version doesn’t cover 0-9.
The 26 glyphs
