Plate 4 from Americae Retectio
by Johannes Stradanus

Navigational Manual of Cortés


Beginning in the early fifteenth century, the Portuguese explorations of the Atlantic and of the arts of navigation went hand-in-hand, and most other European states learned to navigate the oceans from the manuals that the Portuguese and the Spanish eventually published as a product of their experiences. In 1519, for instance, Martín Fernández de Enciso published the first geographical treatise that included the Old and New Worlds together, the Suma de Geografia que trata de todas las partidas del mundo. In 1535, Francisco Faleiro, a Portuguese cosmographer, published the Tratado del Esphera y del arte de marear con el regimiento de las alturas, con algunas reglas nuevamente escritas muy necesarias. In 1545, Pedro de Medina published the Arte de navegar, which was translated into Italian (three editions in 1554, 1555, 1609), French (15 editions between 1554 and 1633), Dutch (five editions between 1580 to 1598), and English (two editions in 1581 and 1595).

The Spanish royal cosmographer Martín Cortés de Albacar belongs to that first generation of cosmographers and pilots who sought to establish an instrumental method of transatlantic navigation and to make that method available to other pilots. In 1551, Cortés—who had been teaching cosmography and the art of navigation to pilots in Cádiz since 1530—published his Breve compendio de la sphera y de la arte de navegar, con nuevos instrumentos y reglas, exemplificado com muy subtiles demostraciones. In this practical book, Cortés clearly discussed matters of navigation and cosmography and included illustrations and models for making instruments. His became the standard navigational textbook.

In his letter of dedication to Charles V, Cortés claims to have been the first person to "condense the navigational art into a small manual: establishing infallible principles and evident demonstrations; writing the practice and theory of the art; providing true rules to sailors; showing the paths to the pilots, making instruments to take the solar altitude; . . . discovering the secret property of the magnet; . . . [With this treatise], those who are alive and those who will succeed us will see and understand that the world owes more to V.M [Charles V] than the Egyptians to Isis, for she gave them letters to read their charts, but V.M gave [the world] rules and method to navigate the oceans. The benefits of Isis was for only one province; the benefits of Charles are for the whole universe, for all provinces, for all oceans, to go to places already discovered and to go to places not yet discovered" (author's translation; folios IIIv.-IIIIr.).

The treatise was not only very popular with Spanish sailors but also for mariners from other countries. It became, for instance, the foundational text for England's long tradition of sea-dominance and colonization. Stephen Borough, the chief pilot of the English Muscovy Company, brought back to England a copy of the Breve Compendio from his visit to the navigational school in Seville, where it was a textbook. Borough had his copy translated by Richard Eden and published as the Art of Navigation in 1561. In the sixteenth century alone, there were seven English editions. The pirates Martin Frobisher and Francis Drake were among the Englishmen who enjoyed and used Corté's book. Robert Norman in his The Newe Atractive (1581) and William Gilbert in his De magnete (1600) discussed Cortés's magnetic theories.

Cortés's manual is filled with practical instructions. Even the illustrations in the book are meant to be used by the reader, as they not only accompany precise instructions for the making of nautical instruments but also demonstrate their working in simplified form. The text contains several volvelles, for instance, a term derived from the Latin "to turn." These are devices, such as the one here, that contain several layers of movable paper parts affixed to a central point with thread (as here) or perhaps a pin or some other mechanism that will allow the parts to rotate around a central turning point. The instrument illustrated here helps a navigator find the declination of the sun as well as the place of the moon-important in the determination of latitude.

The Breve compendio also provided the earliest descriptions of the method of making, graduating, and using the astrolabe. An astrolabe is a two-dimensional model of the celestial sphere in relation to the earth. The instrument had many applications, but for a navigator was most useful in finding the sun's altitude. If a pilot knew the altitude of the sun at, say, noon in Seville, once he found the altitude of the sun at noon in the middle of the ocean he could find the ship's position in the Atlantic relative to Seville. Such calculations were critical if explorers were to be able to ascertain their location when out of sight of land and to mark a landfall in a distant place so as to be able to return to it.

Antonio Barrera
Colgate University

Suggested Reading

Piñero, J. M. López. Ciencia y Técnica en la Sociedad Española de los Siglos XVI y XVII. Barcelona: Editorial Labor, S. A., 1979.

Waters, David. The Art of Navigation in England in Elizabethan and Early Stuart Times. London: Hollis and Carter, 1958.