The Ikhwân al-safâ', or The Brothers of Purity, was a group of au¬
thors whom wrote a compendium of all the sciences known in the Xth cen¬
tury. Also, this compendium is the first complete exposition of the Ismaciti
philosophical system. This encyclopedia contains a great number of textual
material taken by the arabs from greek-helenistic sources. In this paper we
give a translation of some chapters of the arabic text concerning the
Aristotle's cosmological model of celestial spheres. More exactly, the revision
to this philosophical system done by the Neoplatonism in Hellenistic times.