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 Dædalus. 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. But he did not foresee what was to come, both to himself or others.
His two books of a devotional character were, one on 'The Gift of Prayer,' a formal and elaborate treatise with many divisions and subdivisions, in spirit earnest and devout. Its companion treatise, 'Ecclesiastes; or the Gift of Preaching,' shows a high conception of the learning which he thought necessary for one who would preach well; knowledge of commentators; of preachers, especially of English sermon-writers; of works on Christian doctrine, on the history of Christianity; of all subjects which can be included in Theology. The list of books recommended is enormous, and beyond the reach of any man--even of Wilkins or Casaubon: it must have been intended to be a work of reference, a catalogue from which a student might select. It, like his 'Sermons Preached on Several Occasions,' is illumined by quaint utterances, humorous, sensible, and devout; qualities more frequently combined in those days than in our own, when the "dignity of the pulpit," a lamentable superstition, has weakened its influence, and has made religion appear to simple people remote from common life.