The Book of Soyga, also known as Alderaia is a 16th century treatise on magic.

One copy is known to have been owned by John Dee.

The book was thought to have been lost, until 1994, when two manuscript copies located in the British Library (Sloane MS. 8) and the Bodleian Library (Bodley MS. 908), under the title Aldaraia sive Soyga vocor by Dee scholar Deborah Harkness (Wikipedia page [1]). The Sloane 8 version is also described as Tractatus Astrologico Magicus.

Elias Ashmole recorded that the Duke of Lauderdale owned a manuscript titled Aldaraia sive Soyga vocor that had formerly belonged to Dee. The manuscript was sold at auction in 1692 and is now probably Sloane MS. 8

Jim Reeds in 'John Dee and the Magic Tables in the Book of Soyga' has analysed the documents - a PDF can be found here [2]. He notes a proclivity to record words backwards in the MS, citing as examples Lapis reversed as Sipal, Bonum reversed as Munob, and the title of the MS, Soyga, as Agyos, literis transvectis, revealing a practice which sought to obscure some of the works cited. 'Soyga' is ‘Agios’ (Greek for “Holy”) spelled backwards.

More information on the Wikipedia page [3].

The Clavis article on the Book is [4]. Another site is [5]. Jane Kupin has edited and translated it here [6] (Checked October 2017)