HEYDON, John, who sometimes assumed the name of Eugenus Theodidactus, was a great pretender to skill in the Rosicrucian philosophy and the celestial signs, in the reign of King Charles I.; and wrote a considerable number of chemical and astrological works, with very singular titles. This ridiculous author was much resorted to by the duke of Buckingham, who was infatuated with judicial astrology. He employed him to calculate the king's and his own nativity, and was assured that his stars had promised him great things. The duke also employed Heydon in some treasonable and seditious practices, for which he was sent to the Tower. He lost much of his former reputation by telling Richard Cromwell and Thurloe, who went to him disguised like cavaliers, that Oliver would infallibly be hanged by a certain time; this period, however, he out-lived several years.