The Longitude Problem: Print, Mathematics, and Geolocation in Nineteenth Century China

In nineteenth-century China, longitudinal coordinates were widely understood conceptually. From the end of Qianlong’s reign, but during the Jiaqing-Daoguang period especially, the idea of a spherical earth divided into 360 degrees spread to remote places across China, as evidenced by local gazetteers describing a county’s longitude. Though ultimately derived from Jesuit translations of the previous two centuries, this idea circulated independently within China, through imperially-endorsed court texts and the movement of bureaucrats around the empire. But a problem emerges from these passages: they provide little evidence that longitude was actually being measured and calculated on the ground. Rather, these passages indicate that estimates of longitude were being derived from early eighteenth-century Jesuit gazetteers. The idea was there, but not the practice. Why? This talk will introduce the evidence, and offer some preliminary speculation about this puzzling absence.