History of Navigation - Age of Exploration

Age of Exploration

Further information: Age of Discovery

The commercial activities of Portugal in the early 15th century marked an epoch of distinct progress in practical navigation. These trade expeditions sent out by Henry the Navigator led first to the discovery of the Porto Santo (near Madeira) in 1418, rediscovery of the Azores in 1427, the discovery of the Cape Verde Islands in 1447 and Sierra Leone in 1462. Henry worked to systemize the practice of navigation. In order to develop more accurate tables on the sun's declination, he established an observatory at Sagres. Combined with the empirical observations gathered in oceanic seafaring, mapping winds and currents, Portuguese explorers took the lead in the long distance oceanic navigation.

Henry's successor, John II continued this research, forming a committee on navigation. This group computed tables of the sun's declination and improved the mariner's astrolabe, believing it a good replacement for the cross-staff. These resources improved the ability of a navigator at sea to judge his latitude.

In the 15th and 16th centuries, Spain was in the vanguard of European global exploration and colonial expansion. Spain opened trade routes across the oceans, specially the transatlantic expedition of Christopher Columbus in 1492. The Crown of Spain also financed the first expedition of world circumnavigation in 1521. The enterprise was led by Portuguese navigator Ferdinand Magellan and completed by Spaniard Juan Sebastian Elcano. The trips of exploration led to trade flourishing across the Atlantic Ocean between Spain and America and across the Pacific Ocean between Asia-Pacific and Mexico via the Philippines.

The compass, a cross-staff or astrolabe, a method to correct for the altitude of Polaris and rudimentary nautical charts were all the tools available to a navigator at the time of Christopher Columbus. In his notes on Ptolemy's geography, Johannes Werner of Nurenberg wrote in 1514 that the cross-staff was a very ancient instrument, but was only beginning to be used on ships.

Rabbi Abraham Zacuto perfected the astrolabe, which only then became an instrument of precision, and he was the author of the highly accurate Almanach Perpetuum that were used by ship captains to determine the position of their Portuguese caravels in high seas, through calculations on data acquired with an astrolabe. His contributions were undoubtedly valuable in saving the lives of Portuguese seamen, and allowing them to reach Brazil and India. While in Spain he wrote an exceptional treatise on astronomy/astrology in Hebrew, with the title Ha-jibbur Ha-gadol. He published in the printing press of Leiria in 1496, property of Abraão de Ortas the book Biur Luhoth, or in Latin Almanach Perpetuum, which was soon translated into Latin and Spanish. In this book were the astronomical tables (ephemerides) for the years 1497 to 1500, which were instrumental, together with the new astrolabe made of metal and not wood as before, to Vasco da Gama and Pedro Álvares Cabral in their voyages to India and Brazil respectively.

Prior to 1577, no method of judging the ship's speed was mentioned that was more advanced than observing the size of the vessel's bow wave or the passage of sea foam or various floating objects. In 1577, a more advanced technique was mentioned: the chip log. In 1578, a patent was registered for a device that would judge the ship's speed by counting the revolutions of a wheel mounted below the ship's waterline.

Accurate time-keeping is necessary for the determination of longitude. As early as 1530, precursors to modern techniques were being explored. However, the most accurate clocks available to these early navigators were water clocks and sand clocks, such as hourglass. Hourglasses were still in use by the Royal Navy of Britain until 1839 for the timing of watches.

Continuous accumulation of navigational data, along with increased exploration and trade, led to increased production of volumes through the Middle Ages. "Routiers" were produced in France about 1500; the English referred to them as "rutters." In 1584 Lucas Waghenaer published the Spieghel der Zeevaerdt (The Mariner’s Mirror), which became the model for such publications for several generations of navigators. They were known as "Waggoners" by most sailors.

In 1537, the Portuguese cosmographer Pedro Nunes published his Tratado da Sphera. In this book he included two original treatises about questions of navigation. For the first time the subject was approached using mathematical tools. This publication gave rise to a new scientific discipline: "theoretical or scientific navigation".

In 1545, Pedro de Medina published the influential Arte de navegar. The book was translated into French, Italian, Dutch and English.

In the late 16th century, Gerardus Mercator made vast improvements to nautical charts.

In 1594, John Davis published an 80-page pamphlet called The Seaman's Secrets which, among other things describes great circle sailing. It's said that the explorer Sebastian Cabot had used great circle methods in a crossing of the North Atlantic in 1495. Davis also gave the world a version of the backstaff, the Davis quadrant, which became one of the dominant instruments from the 17th century until the adoption of the sextant in the 19th century.

In 1599, Edward Wright published Certaine Errors in Navigation, which for the first time explained the mathematical basis of the Mercator projection, with calculated mathematical tables which made it possible to use in practice. The book made clear why only with this projection would a constant bearing correspond to a straight line on a chart. It also analysed other sources of error, including the risk of parallax errors with some instruments; and faulty estimates of latitude and longitude on contemporary charts.

In 1631, Pierre Vernier described his newly invented quadrant that was accurate to one minute of arc. In theory, this level of accuracy could give a line of position within a nautical mile of the navigator's actual position.

In 1635, Henry Gellibrand published an account of yearly change in magnetic variation.

In 1637, using a specially built astronomical sextant with a 5-foot radius, Richard Norwood measured the length of a nautical mile with chains. His definition of 2,040 yards is fairly close to the modern International System of Units (SI) definition of 2,025.372 yards. Norwood is also credited with the discovery of magnetic dip 59 years earlier, in 1576.