Four chapters of Gemirme' astronomical treatise, the Isagoge, were excerpted probably in the first half of the fifteenth century and later mistakenly attributed to the neoplatonist Proclue under the title Sphaera. This opueculum became a popular handbook of elementary astronomy in the sixteenth century. There were over sixty editions between 1499 and 1620, a period in which there was only one edition of the Isagoge, Edo Hilderich's (first published in 1590). Apart from establishing a stemma codicum, the present analysis of the ten earliest manuscripts of the Sphaera has as its main conclusions : (1) that the ediüo princeps, the Aldine edition of 1499, used a separate source from Thomas Linacre's Latin translation that accompanies it ; (2) t...