ESHS/HSS Annual Meeting

Theoretical Success, Practical Superfluity: The Trajectory of Mercury’s Epicyclic Center in al-Kāshī’s Equatorium

• In Event: Contested Success and Celebrated Failure: The Practice of Mathematical Instruments in Varied Settings II

English Abstract

In his Nuzhat al-ḥadāʾiq, Jamshīd al-Kāshī (d. 1429) primarily discusses the construction and operation of an equatorium. He provides detailed instructions for constructing the instrument, marking points, and drawing planetary orbs on its plate. For many of these steps, he offers alternative procedures: some simplify the construction or use of the equatorium, while others present mathematically equivalent but more demanding solutions with no clear practical advantage. A striking example is his discussion of various methods for drawing the trajectory of Mercury’s epicyclic center. In this paper, I examine in detail the options al-Kāshī offers instrument makers for representing this trajectory on the main plate of the equatorium, and I argue for their theoretical significance in contrast to their practical insignificance for the functioning of the instrument. Nuzhat al-ḥadāʾiq thus appears as a treatise in which al-Kāshī privileges the display of geometrical rigor and mastery of planetary theory over the instrument’s practical simplicity and ease of use. In this context, although al-Kāshī was an influential figure in the Islamicate mathematical sciences, the equatorium described in this work appears to have attracted limited scholarly attention and practical use and can therefore be regarded as a type of “failure” in use, even as it succeeds as a vehicle of mathematical sophistication. I use this example to explore how different actors — authors, makers, users and patrons — could value an instrument for its conceptual ambitions as much as for its practical performance.

Author

• Hamid Bohloul, Postdoctoral Fellow, ASTRA Research Group, Max Planck Institute for the History of Science (MPIWG), Berlin, Germany