  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
groundbreaking 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.
