Deciphering, or Decy-phering, the art, or act of disco vering the alphabet of a cypher, or of explaining a.letter written in cyphers, or secret characters.

Every language has peculiar rules of deciphering, which depend not only on the form of its characters, but also on the place, order, frequency, combination, and number of the letters. The importance of this science to politicians has long been acknowledged, and several ingenious philosophers of the 17th century, published profound treatises on this subject; but, as it would be deviating too widely from the avowed plan of this work, to enter into the theory of deciphering, we can only refer the curious, who desire farther information on this head, to the 12th volume of the Gentleman's Magazine for 1742, where they will find the art of deciphering deduced from principles, and explained by examples in several languages. It deserves to be remarked, that there is extant, in the library of Oxford, a collection of letters written in cypher, about the time of Charles the Second, and decyphered by Dr. Wallis, the most eminent scholar this country ever produced, in that branch of mystical grammar. Mr. W. Wal-lis, a descendant of that learned divine (whose "Life and Sermons" he has lately published), is in the possession of another volume of Decyphered Letters, with their keys in various cyphers and characters ; the whole of which contains much information relative to the transac tions of those times ; as the Doctor held the appointment of decypherer to that suspicious king.