years, where they had hoped to sell their services to the emperor. However, this sale seems quite unlikely, according to John Schuster, because Dee's meticulously kept diaries do not mention it. If Bacon did not create the Voynich manuscript, a supposed connection to Dee is much weakened. It was thought possible, prior to the carbon dating of the manuscript, that Dee or Kelley might have written it and spread the rumor that it was originally a work of Bacon's in the hopes of later selling it. Fabrication by Voynich Some suspect Voynich of having fabricated the manuscript himself. As an antique book dealer, he probably had the necessary knowledge and means, and a lost book by Roger Bacon would have been worth a fortune. Furthermore, Baresch's letter and Marci's letter only establish the existence of a manuscript, not that the Voynich manuscript is the same one mentioned. These letters could possibly have been the motivation for Voynich to fabricate the manuscript, assuming that he was aware of them. However, many consider the expert internal dating of the manuscript and the June 1999 discovery of Baresch's letter to Kircher as having eliminated this possibility. Eamon Duffy says that the radiocarbon dating of the parchment (or, more accurately, vellum) "effectively rules out any possibility that the manuscript is a post-medieval forgery", as the consistency of the pages indicates origin from a single source, and "it is inconceivable" that a quantity of unused parchment comprising "at least fourteen or fifteen entire calfskins" could have survived from the early 15th century. Giovanni Fontana It has been suggested that some illustrations in the books of an Italian engineer, Giovanni Fontana, slightly resemble Voynich illustrations. Fontana was familiar with cryptography and used it in his books, although he did not use the Voynich script but a simple substitution cipher. In the book Secretum de thesauro experimentorum ymaginationis hominum (Secret of the treasure-room of experiments in man's imagination), written c. 1430, Fontana described mnemonic machines, written in his cypher. That book and his Bellicorum instrumentorum liber both used a cryptographic system, described as a simple, rational cipher, based on signs without letters or numbers. Other theories Sometime before 1921, Voynich was able to read a name faintly written at the foot of the manuscript's first page: "Jacobj à Tepenece". This is taken to be a reference to Jakub Hořčický of Tepenec, also known by his Latin name