BOX 1.1 Henry the Navigator

Early in the 15th century, interest in exploration had awakened in many European nations, owing to the discovery and translation into Latin of Ptolemy’s second-century Geography, wide publicity of Marco Polo’s earlier journeys, and increasing trade with Asia via Arab middlemen. Portugal’s Henry the Navigator (Prince Henry, 1394-1460) foresaw that the discovery of a maritime route to India could dramatically lower the cost of trade and thus gain Portugal a dramatic trading advantage vis-à-vis its European rivals, including Spain and Venice.

At the time, European knowledge about Africa was essentially limited to the Mediterranean coast and the lower Nile, and European sailors rarely entered the Atlantic Ocean. When they did, the ships that navigated along the shores of the African coast risked running aground, while those who attempted to steer into open waters could stray too far and be lost, since open-water navigation in that era was mostly guesswork. To measure latitude they used the star Polaris, which is not visible in the Southern Hemisphere. The furthest south anyone had sailed was Cape Bojador (at the southern end of the Atlantic coast of modern-day Morocco). No one knew whether Africa continued all the way to the mythical “Southern Continent” of Ptolemy or if one could sail around it. Ship technology was primitive and ill suited to the demands of long voyages, which often involved long passages against prevailing winds.

To overcome these technical challenges, Henry founded a multidisciplinary community of scholars—the School of Navigation at Sagres, at the southern tip of Portugal. Here, Abraham Zacuto published the first accurate solar ephemeris and improved the astrolabe for measuring the positions of heavenly bodies. These two advances enabled accurate determination of latitude far out to sea. Cartography improved, and a new type of ship was designed, the caravel, that could sail close to the wind. A series of ocean voyages that probed ever southward culminated in Vasco da Gama’s sailing around Africa to India in 1498. The sea route to India had been discovered, 38 years after Henry’s death and almost 70 years after Portugal’s maritime quest had begun. These maritime advances enabled Portugal to establish dominance over the sea lanes to the east that would go unchallenged for nearly a century.

In the mid-18th century, John Harrison’s invention of the chronometer completed the technological picture of that era by enabling accurate determination of time, and thus longitude, at sea.

SOURCE: “The European Voyages of Exploration,” University of Calgary Applied History Research Group, <>.

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