The material behind the ninety-one Parts of the Earth comes from a specific, well-dated series of sessions. Between 1583 and 1587 the mathematician and royal adviser John Dee worked with the scryer Edward Kelley in a sustained attempt to obtain instruction from angels. Kelley looked into a crystal and reported what he saw and heard; Dee sat with pen and paper and wrote it down, asked questions, and occasionally argued.
The portion relevant here belongs to the work of 1584, much of it conducted in Cracow and Prague under the patronage of the Polish nobleman Albert Laski and later at the imperial court. The angel named Nalvage introduced it by telling Dee that thirty Calls remained to be delivered, and that those thirty were the Calls of ninety-one Princes and Spiritual Governors, to whom the earth was delivered as a portion. The stated purpose was practical and political: these were the powers that bring in and dispose kings and governments, and the Calls were the means of reaching them.
The delivery of this body of material was completed on 13 July 1584, with the final portion of the Call of the Aethyrs and the names of the thirty Aethyrs themselves. Dee then compiled the results into a book, Liber Scientiae Auxilii et Victoriae Terrestris, the Book of Knowledge, Help and Earthly Victory, which he dated 2 May 1585. That book is a table. For each of the ninety-one Parts it gives the name, the Aethyr the Part belongs to, the Zodiacal King that governs it, and a count of the ministers said to dwell there.
Everything else attached to the Parts in modern practice was added later, and in most cases much later. The tabulation itself is short, dry and administrative, and reads far more like a register than like a revelation.