Abstract
In 1612, the Jewish polymath David Gans (1541-1613) published a prospectus for his astronomical-cosmological work Magen David in the Prague printing press of Moses ben Joseph Betsalel Katz. The prospectus is preserved as a slightly damaged unicum in the Bodleian Library of Oxford (Opp. 4o 417 [4]).
Gans died almost exactly one year after the prospectus was published, before he could have the entire work printed. A comparison of the list of chapters in the prospectus with the surviving earlier version of the work (MS Hamburg, Cod. hebr. 273) on the one hand and with the later printed version (Jessnitz 1743 as Neḥmad we-naʿim) on the other hand allows us to reconstruct with some exactitude how Gans proceeded with his work on the book in the years before and after the prospectus was published.
It appears that during the last year of his life Gans expanded his Magen David with additional chapters, some of which were incongruous with the original focus of the work and the origin of which was probably in Migdal David. Gans already suspected that he would not have time to publish his other writings.
The analysis of the position of Magen David among Gansʼs other known writings, including those that have not survived, suggests that Magen David, together with the historical Ṣemaḥ (Prague 1592) and the mathematical and geometrical Migdal David (lost), formed the trio of works that Gans valued most highly. This is why he gave them titles that contained an allusion to his own name (the title Neḥmad we-naʿim, under which Magen David was later printed, is most likely not authentic).
The text of the prospectus contains a commendation from Yom-Ṭov Lipmann Heller, approbations of three Prague rabbis and a preface by Gans, which allows us to clarify his attitude towards theoretical astronomy. The publication of a modern complete edition of the prospectus will therefore hopefully be a contribution to the study of Jewish science at the turn of the 17th century.