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I. INTRODUCTION
Everything we know about the observatory in Tabriz founded by Ghazan Khan (r. 12711304), the seventh ruler of the Ilkhänid dynasty of Persia (1295-1304), was published by Aydin Sayili some fifty years ago.1 Relying on primary historical sources, he presented an adequate description of its astronomical activities and of the many skills of Ghazan Khan in the field of observational instrumentation.2 Sayili also presented a good overview of the Marägha observatory from 1260-1283, 3 but due to a lack of reliable evidence for the period after ca. 1280, he made some statements - especially concerning Ghazan Khän's astronomical innovations - that could not be substantiated. A recently discovered treatise has now revealed the exact type and location of Ghazan Khän's innovations, which we enumerate below. Our treatise begins where Sayili left off and appears to give dependable information that we can use to illuminate the later period at the Marägha observatory, during which very little is known concerning the type and extent of astronomical activity.
We begin by introducing Rashïd al-Dïn Tabïb's claim as to Ghäzän Khän's astronomical activities and innovations. We then examine the validity of the claim with the help of the newly discovered treatise, as well as verify the reliability of the information in the treatise as to the type, structure, and location of Ghäzän Khän's newly made instruments. For this purpose, it was necessary to examine Ghäzän Khän's innovations both in the context of the Marägha astronomical tradition (as the dominant tradition of the time) and in the context of medieval observational instrumentation in general. We follow with a general classification of the instruments and argue their possible relation to later Western models; and we conclude by describing the instruments in the order in which they appear in the treatise.
II. HISTORICAL BACKGROUND
According to his vizier, Rashïd al-Dïn Tabïb (d. 718/1318), Ghäzän Khan was a prominent artisan, an alchemist, an expert in medicine and botany (he invented a new antitoxin called tiryäq-i ghäzäni), and a mineralogist, as well as being interested in theology. 4 In his youth he was taught by Mongol Buddhist monks, but he later converted to Islam.5 Upon his victory over the Mamluk army...