• 

  The Enigma Bulletin - Google Books

  http://books.google.de/books?id=K0QyAQAAIAAJ&q=Hans-Albrecht+Herzner&dq=Hans-Albrecht+Herzner&hl=de&sa=X&ei=4Bi7Ua-kJIqTswaqkYBo

  Keine Beschreibung vorhanden.

• 

  Codes, Ciphers and Secret Writing - Martin Gardner - Google Books

  https://books.google.de/books?id=y6Aw_ZTfpBAC&pg=PA46&dq=Charles%2BWheatstone#v=onepage

  "A fascinating, challenging book."―"A.L.A. Booklist"Learn to use the most important codes and methods of secret communication in use since ancient times. Cipher and decipher codes used by spies. Explore the famous codes that changed the fate of nations and…

---

---