Marine archaeologists excavating a shipwreck off the coast of Oman have recovered the oldest known example of a type of maritime navigational tool. The archaeologists believed the object, originally discovered in 2014, to be an astrolabe, but they could not find any navigational markings on it.
The astrolabe was a very ancient astronomical instrument used to determine the latitude of a ship at sea by measuring the noon altitude of the Sun to determine their location during their voyages. The device has been used by mariners for around two thousand years.
Now, a later analysis has uncovered its hidden details. Laser scanning work carried out by scientists at the University of Warwick revealed etches around the edge of the disc, each separated by five degrees, which allowed the mariners to measure the height of the sun above the horizon.
The astrolabe was recovered from the Portuguese ship Esmeralda, which sank during a storm in the Indian Ocean in 1503. The ship was part of the fleet led by Portuguese explorer Vasco da Gama, the first person to sail directly from Europe to India. The recovered astrolabe is believed to date from between 1495 and 1500.1
The University of Warwick used laser scans to uncover etches on the astrolabe,
which helped navigators work out the height of the sun – source BBC.
Geoffrey Chaucer (c.1343 – 1400) wrote a medieval instruction manual on the astrolabe entitled 'A Treatise on the Astrolabe'. Chaucer's work is considered the "oldest work in English written upon an elaborate scientific instrument".
Chaucer wrote approvingly of Nicholas of Lynn's work, and made much use of it. The 16th century literary historian John Bale claimed Lynn became a Carmelite friar then moved to Oxford, where he studied at university and developed a significant reputation for his scientific work. In 1386 Nicholas published a Kalendarium of astronomical tables for the years 1387–1462.
The Astrolabe and the Discovery of the North
Early maps of the northern polar regions were based on information from the lost book Inventio Fortunata, of about 1363. Indeed, the 1507-08 map of Johann Ruysch explicitly claims such.
It seems likely this data had also influenced the early map of Claudius Clavus of 1431. Ruysch's map shows a ring of 18 islands surrounding the North Pole, nearby a marginal note claims the data came from the Inventio Fortunata.
Clavus's statement in the 'Vienna Texts' states that Norway had eighteen ice-bound islands, which suggests he also knew of this book. Gerard Mercator showed a version of these islands in his 1569 map.
|Mercator's 1606 map of the northern polar region|
"In the matter of the representation, we have taken it from the 'Travels' of Jacob Cnoyen of Buske who quotes certain historical facts of Arthur the Briton, but who gathered the most and the best information from a priest who served the king of Norway in the year of Grace 1364.....He related that in 1360 an English minor friar of Oxford who was a mathematician reached these isles and ..... measured the whole by means of an astrolable somewhat in the form hereunder which we have reproduced from Jacob Cnoyen."
The only knowledge we have today of the lost Inventio comes indirectly through another lost book, the 'Itinerary of all Asia, Africa and the North' by Jacob Cnoyen, probably written in the 14th century. Cnoyen's work contained a summary of part of the Inventio and extracts from another lost book, the Gestae Arthuri. Cnoyen seems to have gleaned his information from an intermediary source and may not have actually read the Inventio himself.
This intermediary was an unknown roving priest who claimed to have acquired an astrolabe directly from the unnamed author of the Inventio during face-to-face conversations.
Mercator also quoted parts of Cnoyen's work, now also lost, in a letter of 1577 to the Elizabethan mage John Dee. Mercator had wrote in response to questions from Dee concerning the source material for the "Septentrional Islands" on his map of the northern polar regions in 1569. Fortunately Dee had made a transcript of Mercator's letter after the original was lost. Dee's transcript is now slightly fire damaged but sufficient remains legible for the most part.
Dee's text included a description of eighteen to twenty islands, the "Septentrional Islands" adjacent the North Pole, separated from each other by nineteen "In-drawing channels" which would suck any ships in against the rocks.
Dee purpose was to assert British sovereignty over the north-western Atlantic during the Age of Discovery when he wrote:
"That all these Northern Isles and Septrentrional Parts are lawfully appropriated to the Crown of this Brytish Impire: and the terrible adventure and great loss of the Brytish people and other of King Arthur his subjects perishing about the first discovery thereof."
Dee's assertion is based on the account in the Gestae Arthuri which claims that the army of King Arthur conquered these Northern Islands. Dee also drew on the accounts of the Welsh Prince Madoc and Brendan the Navigator as evidence for British dominion over the New World.
According to Dee's translation of Cnoyen's summation of the Gesta Arthuri, found in Brytanici Imperii Limites (Limits of the British Empire, 1578), in 530 AD Arthur's great army had over-wintered in the northern islands of Scotland. The following May, part of this army crossed over into Iceland. Almost 4,000 men entered the in-drawing seas and never returned. Then four ships returned from the North and warned Arthur of the in-drawing seas. Arthur did not proceed any further, but colonised all of the islands between Scotland, Iceland, and Greenland.
In 1364 eight people claiming to be descendants of those who had penetrated the Northern Regions in the first ships, arrived at the King’s court in Norway. The delegation included two priests, one of whom possessed an astrolabe, and claimed to be descended in the fifth generation from a Bruxellensis.2
What are we to make of this odd account of the discovery of the North?
Clearly early depictions of the northern polar regions was based on mythical accounts that existed only in lost books. Most of the information we have about the contents of the Inventio comes indirectly from the priest with the astrolabe who reported to the Norwegian king as relayed by Jacob Cnoyen. The priest, based on time and date, has been identified as the Norwegian Ivar Bardarson or Nicholas of Lynn.
In response to a request from Richard Hakluyt in 1580, Mercator said he had borrowed the Gestae Arthuri from a friend in Antwerp. Mercator restored it and returned it, but when he required it again his friend had forgotten from whom he had lent it. We cannot rule out the likelihood that the Gestae, if it ever existed at all, was influenced by Geoffrey of Monmouth's Historia Regum Britanniae, c.1138, in which Arthur had become an emperor and conqueror of Northern Europe, including Iceland and Norway.
Indeed, the account of Arthur's deeds as reportedly found in the Gestae Arthuri may well be derived of Norse tales of Eirik the Red's 10th century adventures in the North Atlantic.3
However, we can be certain that the astrolabe is real enough.
Copyright © 2017 Edward Watson
Notes & References:
1. Astrolabe: Shipwreck find 'earliest navigation tool' - Rebecca Morelle, BBC News, Science &
2. James Robert Enterline, Erikson, Eskimos, and Columbus: Medieval European Knowledge of America, Johns Hopkins University Press, 2004.
3. Thomas Green, John Dee, King Arthur, and the Conquest of the Arctic, in The Heroic Age
A Journal of Early Medieval Northwestern Europe, Issue 15 (October 2012).
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