From T?n to Torun: The Twists and Turns of the Tust-Couple

In discussions of the possible connections between Copernicus and his Islamic predecessors, the "Tusi-couple " has often been invoked by both supporters and detractors of the actuality of this transmission. But as I maintained in an earlier article, the "Tusi-couple ", as well as other mathematical devices invented by Islamic astronomers to deal with irregular celestial motions in Ptolemaic astronomy, may be of secondary importance when considering the overall significance of Islamic astronomy and natural philosophy in the bringing forth of Copernican heliocentrism.1 Nevertheless, the development and use of Tusi's astronomical devices does provide us with important evidence regarding the transmission of astronomical models and lessons about intercultural scientific transmission. So in this article, I will attempt to summarize what we know about that transmission, beginning with the first diffusion from Azerbaijan in Iran to Byzantium and continuing to the sixteenth century. Though there are still many gaps in our knowledge, I will maintain, based on the evidence, that intercultural transmission is more compelling as an explanation than an assumption of independent and parallel discovery.