It was this unknown element that made voyages of exploration so dangerous. Before the end of the 15th century, European sailors had never crossed the oceans or encountered the mighty ocean currents, mountainous rollers and violent storms
Facts which Geographers Did not Know
The geographical knowledge of the time was unsuited to world exploration. In the first place, no one knew for certain that the world was round. The Polish astronomer Niklaus Copernicus said it was and Columbus himself believed it. Nevertheless, many people thought the world was flat, and some sailors imagined they would fall over the edge if they sailed too far out to sea
There were several important facts geographers did not know. How wide was the Atlantic Ocean? Until he crossed it, not even Columbus knew for certain. How wide was the Pacific? Again, no one knew until the ships of Ferdinand Magellan’s fleet traversed it in 1520-1522.
How long was the coast of Africa? Vasco da Gama had no idea when he set out from Portugal in 1497 to sail the sea route from to Asia. Da Gama did not know, either, how far away India was
Mercator’s Map for Ocean Sailing
Explorers also set out into the unknown oceans without proper sea charts or navigational equipment. The charts used for sailing around Europe and in the Mediterranean were plane charts on which the meridians were mainly shown as parallel to each other.
Over short distance this did not matter very much. It was very different, though, when explorers embarked on voyages lasting many weeks and covering very long distances out of sight of land
This was because the parallel meridians on the plane chart made east-west distances seem much greater than they really were. For instance, on the plane chart, the distance between the Lizard Point in southwestern England and the Azores Islands in the Atlantic was shown as 1,703 miles when it was actually 1,261 miles
These problems were not solved until the Flemish geographer Gerhardus Mercator provided sailors with a chart especially designed for ocean voyaging. But Mercator did not produce his map until 1569, long after the voyages Columbus, Magellan, Vasco da Gama and other early explorers took place
The Chronometer for Reckoning Longitude
Another dangerous disadvantage they suffered was their inability to reckon longitude accurately. It was 1761 before the first instrument for calculating longitude properly was perfected. This was the chronometer, a special clock for use at sea, developed by the British watchmaker John Harrison
Once again, this was long after the days of the early explorers, whose methods of reckoning longitude could be inaccurate. One method, known as dead reckoning, was more like guesswork than mathematics. Dead reckoning was based first on the course a ship had already steered and the distance it had sailed. Adjustments were made to allow for the tides and currents at sea, mistakes in steering or speed and other factors
Calculating Position by the Moon
Another method used lunars. This was based on observing the positions of the Moon. A comparison was then made with tables showing where the Moon was at a known place at the same time
Dead reckoning, lunars and similar methods were not completely useless. However, not all sallors had the talent for mathematics they required to use them accurately. So, during the great voyages of exploration to America, India and around the world and the long, hard weeks explorers spent in the open ocean, there were times when they did not know precisely where they were
Sources
Fritze, Ronald H. New Worlds: The Great Voyages of Discovery 1400-1600 (Santa Barbara, California, Praeger Publishers, 2003) ISBN-10: 0275979822/ ISBN-13: 978-0275979829
Short, John Rennie, by John Rennie Short (Tonawanda, New York, Firefly Books 2003) ISBN-10: 1552978117/ISBN-13: 978-1552978115
Website: European Voyages of Exploration - Home Page
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