European longitude prizes. I: longitude determination in the Spanish empire

Following Columbus’ voyages to the Americas, Castilian (Spanish) and Portuguese rulers engaged in heated geopolitical competition, which was eventually reconciled through a number of treaties that divided the world into two unequal hemispheres. However, the early-sixteenth-century papal demarcation line was poorly defined. Expressed in degrees with respect to a vague reference location, determination of longitude at sea became crucial in the nations’ quest for expanding spheres of influence. In Spain, King Philip II and his son, Philip III, announced generous rewards for those whose solutions to the longitude problem performed well in sea trials and which were suitable for practical implementation. The potential reward generated significant interest from scientist-scholars and opportunists alike. The solutions proposed and the subset taken to sea provided important physical insights that still resonate today. None of the numerous approaches based on compass readings (‘magnetic declination’) passed the exacting sea trials, but the brightest sixteenth-century minds already anticipated that lunar distances and the use of marine timepieces would eventually enable more precise navigation. With most emphasis in the English-language literature focused on longitude solutions developed in Britain, France and the Low Countries, the earlier yet ground-breaking Spanish efforts have, undeservedly, largely been forgotten. Yet, they provided a firm basis for the development of an enormous ‘cottage industry’ that lasted until the end of the eighteenth century.