Structured Table of Contents for John Wilkins' Mercury

In 1641, just before the outbreak of the English Civil War, John Wilkins (1614-1672) published Mercury or the Secret and Swift Messenger, the first book on cryptology written in English. As noted in the title page, the book shows "how a man may with privacy and speed communicate his thoughts to a friend at any distance."

What is commonly called cipher/code today is described in chapters 6-9 and 11. While politicians and diplomats at this tumultuous age used numerical ciphers that represent letters or words by two- or three-digit figures (see Ciphers during the Early Reign of Charles I before the Civil War for ciphers in 1630s and King Charles I's Ciphers and Codes and Ciphers of Thurloe's Agents for 1640s-1650s), Mercury is not directed to such actual ciphers then in practice. While numerical ciphers may in principle belong to substitution ciphers described in Chapter 7 or 11, Mercury does not mention them.

Besides such orthodox ciphers, known seventeenth century ciphers include "Trevanion's cipher" (whose principle is mentioned in Chapter 8; see another article) and "Argyll's cipher" (whose principle is mentioned in Chapter 6; see another article), though there is no evidence that these ciphers were taken from Mercury.

Text of Mercury:
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Structured Table of Contents

• Authors, ancient and modern, who addressed communication (Chapter 1)

1. Secrecy

• Cryptologia (secrecy of speech)
  • "In the matter" ... expression of other matter than intention ... metaphor, allegory, etc. (Chapter 2)
  • "In the words" (Chapter 3)
    • Inventing new words ... canting of beggars, conjuring (charms of witches), etc.
    • Changing the known language
      • Inversion ... letters or syllables are spelled backwards
      • Transmutation (substitution) (cf. Chapter 7)
      • Diminution ... leaving out part of words
      • Augmentation ... adding letters
• Cryptographia (secrecy of writing)
  • Secrecy of conveyance ... secret conveyance of written messages by land, water, air (Chapter 4)
  • Secrecy of writing
    • In materials (Chapter 5)
      • Paper ... scytale
      • Ink ... secret ink
      • Drawing a string through holes; divers knots tied upon a string
    • In form (ciphers in the narrow sense)
      • Secret writing with common letters
        • With the same number of signs
          • Changing places (transposition cipher) (Chapter 6)
          • Changing powers (substitution cipher) ... ATBASH; Caesar cipher; Switching alphabets by lines, words, or letters according to a keyword (Chapter 7)
        • With more signs ... only particular letters are significant; Cardan grille (concealment cipher) (Chapter 8); expressing any letter by combinations of five, three, or two letters (binary, ternary, quinary coding); a double alphabet, wherein each letter has two styles; Francis Bacon's biliteral cipher (Chapter 9)
        • With fewer signs ... abbreviations (Chapter 10)
      • Secret writing with invented notes and characters
        • Signifying letters. Deciphering by frequency analysis; expressing letters by points, lines, or figures (Chapter 11)
        • Signifying words. Stenography or short-hand (Chapter 12)
        • Signifying things and notions. Hieroglyphics and emblems (ornamental designs) (Chapter 12)
        • Universal characters (Chapter 13)
• Semaeologia……signs and gestures (Chapter 14)
  • "Ex congruo" ... actions resembling the thing to be expressed
  • "Ex placito" ... signs with signification from use and mutual compact

2. Swiftness

• Spiritual ... by angels or spirits (Chapter 15)
• Corporeal ... by bodies inanimate as arrows, bullets or animate as men, beasts, birds (Chapter 16)

3. Joining secrecy and swiftness

• by species of sound ... imaginary recording tube; code communication by loud sounds (two bells of different notes etc.) (Chapter 17); expressing letters by a single sound according to tone (pitch) and length; expressing letters by musical notes (Chapter 18)
• by species of sight
  • Fabulous ... sympathy of magnetism (Chapter 19)
  • Magical ... Projection of letters by mirror; Enchanted glasses that answer any enquiry (Chapter 19)
  • Natural and true ... Use of fire and smoke; Polybius' coordinate cipher; Expressing any letter by only two torches (Chapter 20)