ABSTRACT
Manuscript Escorial 939 contains the only extant copy of a short work on the tasytr (progression) and the projection of rays by Abu Marwan ‘Abd (or ‘Ubayd) Allah Khalaf al-lstijjl. Said praised very highly the competence of al-lstijjl as an astrologer and the importance of his risala. He said that he was ‘one of those who have a sound knowledge of astrology and who has read the books on this subject of both ancient and modern authors. Such is the case of Ptolemy’s Tetrabiblos and of an unnamed book of one of the Hermes where a method for the tasytr and the projection of rays was described: the identification is easy, for Said attributes, to Hermes the Babylonian, methods for the projection of rays and for the division of the houses of the horoscope.
