In the past decades, a mid-1830s two-page paper by Carl Gustav Jacob Jacobi on the use of elliptic and Abelian integrals in Diophantine analysis has offered a well-known case in point of conflicting interpretations in twentieth-century historiography. Hardly more than a note taking stock of a shifting mathematical landscape, this paper was originally meant as breaking new ground in mathematics at its peak, rather than shedding light on its remote past. And yet, it was much later used (and sometimes misused) as allegedly providing evidence that could be read both ways, whether as prefigurative of modern standard algebraic geometry, or as providing presumably convenient tools for making sense of Diophantus’ ancient methods. As a rule, though, the current historiographic consensus notoriously warns against unchecked anachronistic reconstructions, which in turn prompts new questions.
This contribution aims at analyzing and contextualizing C. G. J. Jacobi’s late engagement with Diophantus’ text against the backdrop of his previous mathematical work. Trained in mathematics and classical philology, Jacobi turned indeed to carefully reading Diophantus in the 1840s, chasing Greek manuscripts in European libraries from the Vatican to Wolfenbüttel. His approach, however, strictly complied with prevailing philological standards, never mixing higher mathematics with source criticism. At Alexander von Humboldt’s pressing request, Jacobi jotted down some thoughts on ancient mathematics in general, and Diophantus in particular. These reflections, it will be shown, not only bear witness to Jacobi’s involvement in current debates but also reveal his debt to Georg Heinrich Ferdinand Nesselmann, a Diophantus scholar and a former Königsberg student of his. They also cast light on the way Jacobi conceived the relationship between ancient and modern methods.