Pet-Names—"Jack."

Perhaps one of your many readers, erudite in etymologies, will kindly explain how "Jack" came to be used as the *diminutive* for John. Dr. Kennedy, in his recent interesting disquisition on pet-names (No. 16. p. 242.), supposes that Jaques was (by confusion) transmuted into "Jack;" a "metamorphosis," almost as violent as the celebrated one effected, some two centuries ago, by Sir John Harrington. "Poor John," from being so long "Jack among his familiars," has been most scurvily treated, being employed to form sundry very derogatory compounds, such as, Jackass, Jackpudding, Jack-a-dandy, Jackan…