Dr. Armitage consulted the Poligraphia at Miskatonic University's library. Poligraphia, by Johannes Trithemius (1462-1516), is a work about the cabala, an occult theosophy based on an esoteric interpretation of the Hebrew Scriptures, which was a popular subject in medieval Europe. Trithemius is elsewhere in Lovecraft's fiction mentioned as the author the De Lapide Philosophico of which Joseph Curwen owned a copy.
("The Case of Charles Dexter Ward," "The Dunwich Horror," "The Evil Clergyman")
See also: Trithemius and De Lapide Philosophico