Among the earliest surviving treatises on the astrolabe, the treatise of Severus Sebokht (7th c. AD), written in Syriac, is included. This treatise was edited and translated into French in 1899 by M.F. Nau.
The first part of the treatise contains a description of the astrolabe, while the second part explains the use of the astrolabe in 25 chapters. The terminology used is the Greek one; the Greek terms are written in Syriac characters, but some terms are not used in the proper way.
Some chapters are similar to the respective ones of the treatise of Joannes Philoponus on the astrolabe (6th c. AD), but Severus Sebokht includes chapters on additional subjects.
Ya'qūbī (9th c. AD) ascribes to Ptolemy a treatise on the plane astrolabe and preserves its table of contents. Neugebauer, in The Early History of the Astrolabe (ISIS 40, 1949), comparing the table of contents preserved by Ya'qūbī to the treatise of Severus Sebokht, claims that “Sebokht has preserved a work of either Ptolemy or Theon", supposing that perhaps Ya'qūbī had replaced the name of Theon with that of Ptolemy.
The study of Sebokht’s treatise reveals at least two different sources. The first part contains two incompatible descriptions of the disks of the astrolabe: the rim of the disk coincides with the Tropic of Capricorn or with the greatest of the circles of perpetual occultation; the former appears in the treatise of Philoponus, while the latter is mentioned by Synesius (4th-5th c. AD).
Sebokht mentions Ptolemy and the Philosopher who constructed the astrolabe as two different persons and uses their results. In the last chapter of the treatise, we may also find traces of the Introduction to phaenomena of Geminus.
Although Sebokht’s treatise deals with some subjects not discussed in the treatise of Philoponus, the only complete surviving treatise on the astrolabe before Sebokht, it ranks at a lower scientific level because of the numerous errors that appear in it.