In 1638 he published his first work, an Astronomical treatise, the fruit of his studies at Oxford and at Fawsley. It is entitled 'The Discovery of a World in the Moone, or a discourse tending to prove that there may be another habitable World in that Planet': in the third impression, issued in 1640, is added a "Discourse concerning the Possibility of a Passage thither." Like Lucian he imagined a voyage to the moon, though he admits that the journey through the air was a formidable difficulty. He successfully defended his views against an objection raised by the Duchess of Newcastle. That clever and eccentric lady, the authoress of many "fancies," philosophical and poetical, asked him where she was to bait her horses if she undertook the journey. "Your Grace could not do better," he replied, "than stop at one of your castles in the air." In his treatment of the difficulties caused by the apparent conflict between certain passages of Scripture and the conclusions of Astronomical Science, which he accepts, he anticipates in a remarkable way that explanation of them which rests on the understanding of the meaning of the Bible and of the nature of inspiration. The book was parodied in the story of 'Peter Wilkins' Journey to the Moon,' which even usually well-informed persons have been known to attribute as a _jeu-d'esprit_ to the Warden of Wadham. It was written by Robert Paltock, and published in 1751. His next production was 'Mercurie; or the Secret and Swift Messenger,'--a treatise on Cryptography or ciphers; curious contrivances whereby A can communicate with C without B's suspecting or understanding, by signs, gestures, parables, and transpositions of the alphabet: such as the writer looked at seemed to confirm the view that every cipher which depends on system, and not on an arrangement of a capricious kind, can be interpreted by an expert, a title to which he lays no claim. The book was meant perhaps for use in the Civil War, as was the system of Wilkins' friend, Dr Wallis, who could both invent and solve such puzzles, and distinguished himself by deciphering the letters of the king which fell into the hands of the Parliamentarians at Naseby. There is also among the "Tracts of Bishop Wilkins," a treatise dated 1648, entitled 'Mathematical Magic; or, the Wonders worked by Mechanical Powers and Motions,' subdivided, according to that distinction, into two books, styled Archimedes and Daedalus. The names are quaint, and the classical illustrations are very numerous. The work is a kind of handbook for engineers, enlivened by quotations, not always apposite, from ancient authors, as was the fashion when high literary culture and science could be more easily combined than in our days of ruthless specialism. It is dedicated in very courtly language to the Prince Elector Palatine. Wilkins looks forward to the Prince's restoration to his dominions--a curious aspiration to be professed by a man who did not, then at least, put his trust in princes.