Two books have been particularly important in his research: Francis Bacon’s scientific publication “The Advancement of Learning” and Gustavus Selenus: “Cryptomenytices et Cryptographiae. Libri IX”.

 

“The Advancement of Learning” from 1623 produces a description of the famous bi-literal cipher, which Petter made use of in his attempt on deciphering William Shakespeare’s original gravestone. The first English edition of this book was published in 1640, several years after Francis Bacon’s death. Bacon wrote that he had invented this code-system in his youth, while being in Paris.