Bartolomeu Dias Museum Complex

(29.03.2001 , South Africa, Mossel Bay )
Research Information: NAVIGATIONAL METHODS

The scientific and technical developments which took place in sixteenth-century Portugal had their roots in the Atlantic navigation of the previous century or, to be more precise, in the conditions created by ocean navigation and the new possibilities it opened up.

Around the middle of the fifteenth century, navigators began to study sea currents and wind directions as a first step towards understanding the geography of the great oceans. Improvements were also made in shipbuilding techniques, and in the accuracy of navigational instruments. The art of cartography developed in Portugal during the early years of the century, initially inspired by Mediterranean (Italian and Majorcan) models, but eventually acquiring an originality of its own and gaining acceptance in other countries, especially France and Japan. Ptolemy's geographical theories, which enjoyed a revival of popularity from the second decade of the century, were soon being revised in the light of new information.

The study of currents and winds and their variations began when Portuguese merchant and exploratory ships ventured ever further south along the west coast of Africa. The outward voyage was not particularly difficult, but the winds and currents encountered on the return journey frequently slowed down the ships or brought them to a complete halt. The efforts made to overcome these obstacles had three important consequences. Initially, a technique was evolved for dealing with a head or beam wind by going about or tacking, then a lighter vessel better suited to this type of navigation was designed - the caravel. Eventually, returning sailors realized that they would reach their destination more quickly by heading out into the open sea to avoid the problem zones. This manoeuvre, which no doubt accounted for the frequent stops in the Azores, is referred to by modern historians as "the return by the open sea", whereas in the fifteenth and sixteenth centuries it was called the "Guinea return'' or the "Mina return". (On the way back from Sao Jorge de Mina, the Portuguese trading-post on the Gold Coast, now Ghana, ships would change course and head northwest until they reached the approximate latitude of Lisbon.)

These navigational tactics, which obliged ships for the first time to take to the open sea, were bound to confront pilots with unexpected problems. Even when Mediterranean ships sailed beyond the Strait of Gibraltar to the Channel or North Sea ports, they hugged the coastline and could check their position virtually every day by reference to a point on land. On the other hand, the return voyage by the high seas from Guinea, and later from the Gold Coast, to Lagos (in Portugal) or Lisbon, involved sailing "blind" for anything from three weeks to two months. The best moment to change course and head eastwards towards the Portuguese coast could be indicated by the winds, the currents, the colour of the water, or the sea-birds, but this kind of "natural" indication could be extremely unreliable. A means had, therefore, to be found to check the ship's position every day in the absence of any landmark.

The cross-staff was used to observe stars directly and the syn by reflection.
The astrolabe was used mainly to observe the sun's altitude.
The quadrant was the first instrument used by the Portuguese to determine latitude.

At first pilots calculated the meridian altitudes of the stars (the Pole Star and certain others, and also the sun). Then, at some point in the ocean, with the aid of sextant or astrolabe (later replaced by the quadrant), they compared these celestial observations with the altitudes of the same stars at their meridian transit above Lisbon or some other fixed point of reference.

Initially this procedure was nothing more than an adaptation of a method which John of Hollywood had recommended in his thirteenth-century treatise Sphaera mundi, for measuring the length of one degree of a meridian. This technique was a major innovation in the history of navigation, in that it enabled latitude to be determined almost daily on board ship. However, early-sixteenth-century navigators still lacked a means of determining longitude, which would have made it possible to fix the ship's exact position. If some of them came up with the wrong solutions in their experiments, others would point out their errors, thus enabling different problems to be solved.

Even erroneous calculations were put to immediate use. Convinced that longitude was in direct linear relation to the Earth's magnetic declination, the Portuguese navigators of the sixteenth century noted all the values of this declination (which they would later use as "sightings" or indicators of their position). These accumulated data would prove useful to the English pioneer researcher into magnetism, William Gilbert, and the Flemish mathematician Simon Stevin, when, towards the end of the century, they were studying phenomena connected with the Earth's magnetism, theories regarding which were still at a rudimentary stage.

The art of navigation had made rapid strides in the second half of the fifteenth century. Pilots had quickly learned to determine latitude from the altitude of stars, or from that of the sun using daily declination tables (showing the distance of the sun's zenith north or south of the Equator on any given day). Apart from these basic data, they possessed readings of the number of leagues covered by different wind-zones (from one compass point to another) and by one degree of latitude, as well as timetables of tides at various points along the coast. The earlier navigational techniques, improved and adapted to the new methods, were also still in use.

All this information was recorded in the navigation manuals and charts known as portolans. The first two of these anonymous guides were published at Lisbon in 1509 and 1516, with some differences between the two editions. Based on sailing experience, they contained the data already mentioned, together with the latitudes of the places most frequented by navigators and an occasionally inaccurate translation of John of Hollywood's treatise, in which pilots learned the rudiments of cosmography.

Despite some inconsistencies, these innovative works, the oldest of their kind, gained widespread acceptance and were wholly or partially imitated until the sixteenth century. Some extracts from them were even translated into French, English, Italian and German.

Fifteenth- and sixteenth-century navigation had an equally strong impact on shipbuilding. When the first forays took place beyond Cape Bojador, there was as yet no typical vessel, as different designs were being experimented with. But once voyages of coastal reconnaissance, or the exploration of river estuaries, became more frequent, the caravel (or rather caravels, as there was never a standard model) became the type of vessel preferred by explorers, because it was fast and light - qualities which shipwrights were determined to maximize.

Caravels still formed part of the first fleets to reach India in the early sixteenth century, but they were gradually replaced by the larger, heavier carracks and galleons which could transport more cargo. However, caravels continued to be built in the Portuguese shipyards, not only for the reconnaissance missions begun in the Atlantic in the fifteenth century, but also, owing to their lightness, to provide fast connections between the forts scattered along the route to India.

Around this time also, ships began to be equipped with a superstructure which enabled cannon to be mounted in them. The oldest treatises on shipbuilding that have come down to us, by Fernando Oliveira, Joao Baptista Lavanha and Manuel Fernandes, are documents of inestimable value for the history of naval architecture.

Two significant events sum up the contribution that the transoceanic voyages made to scientific geography. Firstly, about a year after Bartolomeu Dias completed the voyage which virtually proved that the Atlantic and Indian oceans were connected, the German cartographer Henricus Martellus drew a map of the African coast as far as the Rio Infante (not far from the Cape of Good Hope, which Dias had named the Cape of Storms), based upon the data collected by Dias and his predecessors. For the areas beyond the Gulf, the Red Sea and Ceylon (present-day Sri Lanka) Germanus relied on the Ptolemaic model.

Equally important was the publication in the fifteenth century of a Latin translation of Ptolemy's Guide to Geography, which had been forgotten throughout most of the Middle Ages. Reprinted in 1475, the Geography reached its seventh edition in 1490. It reappeared in 1507, and the eleventh edition, published in Strasbourg in 1513, included new maps, the tabulae novae, which showed the configuration of all the lands and inhabited islands which had been recorded by navigators up to that time.

A planisphere included in the Strasbourg edition is modelled on the anonymous Portuguese map of the world, the so-called Cantino map (after Alberto Cantino, the Italian who purchased it in Lisbon). Although not dated, it was probably made in the early autumn of 1502.

The Equator and the two Tropics are represented for the first time on this map. Later, on a map of the Atlantic which has been dated at 1504, Pedro Reinel incorporated a scale of latitudes - the first in the history of cartography. Portuguese sixteenth-century cartography won wide recognition, not because of its revolutionary nature, but because it showed with some degree of accuracy many parts of the world which were previously unknown, or little known, in Europe. Portuguese cartographers were also to be found at this period in Spain (Jorge Reinel and Diogo Ribeiro), France (Lopo Homem and Bartolomeu Velho) and England (Diogo Homem), where their work was generally very well paid.

Dutch engraved cartography of the late sixteenth century also made occasional use of the services of Portuguese cartographers such as Luis Teixeira, founder of a dynasty of map-makers which flourished until the end of the seventeenth century.

The achievements of the Portuguese voyages of exploration were to culminate in the discovery of Brazil, the opening of a complex network of maritime routes in the Indian Ocean, the occupation of Malacca and the penetration of the western Pacific, followed by the Portuguese arrival in China and the Molucca Islands and finally in Japan. Many men, driven by the pursuit of wealth and profit, no doubt, but also curious and observant, travelled through previously unknown lands and cities, cast anchor in faraway ports, mixed with peoples who differed from them in language and customs, and discovered many kinds of fauna and flora. All these discoveries were passed on in works that are remarkable for the accuracy of their information and the understanding and respect they show for people's myths and beliefs.

Around 1513, for example, A Suma Oriental by Tomi Pires, an apothecary who died in China, provided not only botanical observations but a veritable commercial guide to the Orient. Duarte Barbosa produced a similar work in 1518, and Francisco Alvares wrote a monograph on Abyssinia which was published in 1540. In 1587, Gabriel Soares de Sousa completed a wide-ranging treatise on the Indians of the Brazilian coast, the scientific rigour of which would do credit to a modern ethnologist. Father Gaspar da Cruz wrote about China and Hormuz, an anonymous author left a description of the Moluccas, and Garcia da Orta and Cristovao da Costa produced excellent studies of the medicinal plants of the East.

If we add to this list, which is far from exhaustive, the texts on the art of navigation which were written in the same period, if we think of the role played by the portolans, travelogues and, especially, the innumerable marine charts, and if we point out that some of these works, in translation, found their way into the priceless collections of the Italian geographer Giovanbattista Ramusio and of other scholars, we gain at least some idea of how a small country, with a population of less than two million, participated in the birth of the modern era and in the irresistible European expansion that was destined to last for four centuries. The Portuguese and their cultural and geographical neighbours thus contributed to the construction of the world in which we live.

- Kindly sponsored by SAMWEB Creations (information obtained from various historical sources: Bartolomeu Dias Museum Complex)

copyright © gmbh. all rights reserved.
copyright policy