Toscanelli and Columbus
The Portuguese had, with slow persistency, devoted nearly a century to carrying out Prince Henry's idea of reaching the Indies by the eastward route. The ancients, had recognised the rotundity of the earth, and Eratosthenes had even recognised the possibility of reaching India by sailing westward. These views of the ancients came once more to the attention of the learned, owing to the invention of printing and the revival of learning, when the Greek masterpieces began to be made accessible in Latin, chiefly by fugitive Greeks from Constantinople, which had been taken by the Turks in 1453. Ptolemy's geography was printed at Rome in 1462, and with maps in 1478.
Christopher Columbus sailed on the hypothesis that the space to be traversed to reach the Indies by the west is neither great nor obstructed by any obstacle. These two ideas, though false, might, nevertheless, at the period have been considered important had they been new. But they were not.
The calculation which Ptolemy had made of the length of the known world tended to shorten the distance between Portugal and Farther India by 2500 miles. Since Ptolemy's time the travels of Marco Polo had added to the knowledge of Europe the vast extent of Cathay and the distant islands of Zipangu (Japan), which would again reduce the distance by another 1500 miles. As the Greek geographers had somewhat under-estimated the whole circuit of the globe, it would thus seem that Zipangu was not more than 4000 miles to the west of Portugal. As the Azores were considered to be much farther off from the coast than they really were, it might easily seem, to an enthusiastic mind, that Farther India might be reached when 3000 miles of the ocean had been traversed.
The notion of the possibility, and even the facility, of a passage to the Indies by leaving the coasts of Iberia or Africa was, so to speak, current in antiquity. Aristotle, Eratosthenes, Posidonius, Seneca, and others had expressed it, and it is no exaggeration to put forward the statement that it never ceased to be present to the minds of Greek and Latin thinkers. The educated Portuguese knew as well as Toscanelli of this opinion. The letter to Martins, therefore, added nothing to what they already knew respecting the theories put forward by the ancients as to the possibility of passing from Europe into Asia by crossing the Atlantic.
Aristotle speaks of the opinion of those who believed that the country situated near the Columns of Hercules stretches itself to meet those which are towards India, and says this supposition is not incredible, for it relies on the fact that elephants are found at the two extremities of this zone. According to Eratosthenes, the habitable zone of the earth formed a circle; "so that, if the extent of the Atlantic Ocean were not an obstacle, we might easily pass by sea from Iberia to India, still keeping in the same parallel" (Strabo, Book I., chap, iv., sect. 6; Hamilton's translation, page 101, London, 1854.—Bohn's Classical Library). Posidonius claimed that "Starting from the west, one might, aided by a continual east wind, reach India in so many thousand stadia" (Strabo, Book II., chap, iii., sect. 6, p. 154; Hamilton's translation).
It is the same with regard to the numerical ideas, that is to say, the information dealing with distances, found in this letter. These, like the others, were also borrowed from antiquity. From the point of view of length, that is to say, from east to west, the ancients generally considered that the habitable world occupied an extent corresponding to a third of its total circumference. This was the classical, the traditional, opinion. Eratosthenes was among the first to express it; Strabo adopted it, and for a very long while it prevailed. But as Eratosthenes gave 252,000 stadia to the circumference of the earth, and reckoned there were 70,800 stadia from the extreme west to the farthest east, following the parallel of greatest length through the habitable earth (which, according to the ancients, was the parallel of Athens, and in which Eratosthenes reckoned there were in all 200,000 stadia), his Atlantic on the great circle or equator measured 181,200 stadia.
Towards the end of the first century a cosmographer — not one of whose works has unfortunately survived, though from Ptolemy's writings Toscanelli would have been sufficiently acquainted with them — Marinus of Tyre introduced a considerable change into the measurements of Posidonius. He accepted the measurement of 180,000 stadia for the circumference of the globe, but extended considerably that of the known surface, which he increased to 225 degrees out of the 360, thus leaving to the unknown space occupied by the ocean only 135 degrees, and even this interval might be reduced to 130 degrees by checking Marinus' own calculations as reported by Ptolemy.
Thus, fourteen centuries before Toscanelli, a cosmographer, whom Ptolemy has made known by discussing his views at length, had given to the ancient world the same extension towards the east as the author of the letter to Martins, and had reduced, exactly as he had done, the space which divides the two extremities of this Continent. This is not a mere coincidence. The writer of this famous letter has evidently reproduced the system of Marinus of Tyre, just as he has reproduced the notions current in antiquity on the proximity of the regions of Eastern Asia with those of Western Europe, and the opinions held during the Middle Ages concerning the islands of the Atlantic.
It was not until 1475 that a Latin translation of Ptolemy's work, done by Jacopo Angelo, was printed at Vicenza; the Greek text only appeared still later. Angelo's translation dates, it is true, from 1409 or 1410; and, as this Hellenist dwelt at Florence, it is quite possible Toscanelli may have known ot his work; there were, moreover, Greek manuscripts ot Ptolemy at Florence. Anyway, it was only through some manuscript of Ptolemy that Toscanelli could have known, in 1474, the opinions of Marinus of Tyre reproduced in the letter to Martins.
Even before 1474, the Portuguese were thinking of reaching by sea the eastern shores of China and Japan. The Florentine astronomer, Toscanelli, is supposed to have written to a councillor of King Alfonso, recommending to that prince the route to the Indies by the west, a copy of which letter was found among the papers of Columbus. The Lisbon Canon, Fernam Martins [Fernan Martinez de Roriz], who entertained friendly relations with Toscanelli, and who filled an important personal post near King Alfonso V, had been commissioned by this monarch to obtain some information from his friend as to the possibility of reaching the East Indies by sailing to the west. This matter led to an exchange of views between Martins and Toscanelli, and that the latter represented the western route to be much shorter than the one by the south-east.
In order to encourage Alfonso V in the undertaking he was contemplating, he describes the countries and cities that are sure to be found at the end of the journey: the great province of Cathay, the usual residence of the Great Khan, supreme emperor of tributary kings; that of Mangi, which lies adjacent; the wealthy city of Zayton, and the beautiful city of Quinsay. Now, all these denominations belong to the period of the Mongol power in China, founded by Chinghis Khan in 1206, and ended in 1368 by the advent of the Ming dynasty.
The learned astronomer observed that, though he well knows the practicability of the route he suggests is demonstrated by the sphericity of the earth, he will make the matter clearer by means of a map, on which he has marked the coasts of Portugal and the islands whence one must sail directly west to the point of arrival, as also the route to follow, the distances to be covered, and the places where the ship may put in.
The most important part of this letter is the Postscriptum, which indicates the distance to be traversed going from Portugal to the land of spices. From Lisbon to the superb city of Quinsay, in the province of Mangi [Southern China], there are, going directly west, 26 spaces marked on the map, each space comprising 250 miles, or 6500 miles in all, making about one-third the circumference of the globe. But as from the isle of Antilia to the famous isle of Cipangu [Marco Polo's Japan] there are only 10 spaces, the unknown portion of the ocean to be crossed is not great; therefore, by bringing up at Antilia the Asiatic coast is easily reached. Thus, on these indications, the maritime space separating the two extremities of the world is far less in extent than the terrestrial space; in other words, by taking the ocean-way westward to the Indies the journey is much shorter than by the overland route eastward, or by the sea route to the south-east, for the first road extends to but 26 spaces — a third of the sphere — while the others comprise 52 spaces.
It is supposed Columbus wrote several times to Toscanelli; at any rate a letter attributed to the Florentine master is considered to be a reply to another communication from Columbus. In it Toscanelli rejoices that his map has been understood; he repeats that the projected voyage is certain to succeed; and he persuades Columbus to persevere, by laying stress on the commercial advantages which will result from the undertaking, and on the desire the princes of the rich countries to which he is going have to enter into relations with the Christian nations. Aristotle did not think the maritime space separating the two ends of the habitable world was considerable; but he does not say, as Ferdinand Columbus makes him, that the space can be traversed in a few days. It was reckoned in those days that a ship on an average could make four knots an hour, dead reckoning, which would give about 100 miles a day, so that Columbus might reckon on passing over the 3100 miles which he thought intervened between the Azores and Japan in about thirty-three days.
On the 19th April 1492 articles were signed, by which Columbus received from the Spanish monarchs the titles of Admiral and Viceroy of all the lands he might discover, as well as one-tenth of all the tribute to be derived from them; and on Friday 03 August 1492, he set sail in three vessels. On 12 October 1492 [after a voyage not of 33 days but of 40 days] they landed on an island, called by the natives Guanahain, and by Columbus San Salvador. A second voyage with a much larger fleet of seven vessels started from Cadiz, 25 September 1493, and ended with Columbus's return to Spain in chains and disgrace. In his third voyage, in 1498, he touched on Trinidad, and saw the coast of South America, which he supposed to be the region of the Terrestrial Paradise. This was placed by the mediæval maps at the extreme east of the Old World. Only on his fourth voyage, in 1502, did he actually touch the mainland, coasting along the shores of Central America in the neighbourhood of Panama. After many disappointments, he died, 20th May 1506, at Valladolid, believing, as far as we can judge, to the day of his death, that what he had discovered was what he set out to seek—a westward route to the Indies.
Determination of Longitude
Mariners could determine their latitude using Polaris, but only in the Northern Hemisphere. More importantly, there was no known way of measuring longitude other than by estimating speed, direction, and time from a known starting point, a technique known as dead reackoning. Both dead reckoning and celestial navigation resulted in considerable error due to measurement technique and infrequency of determination. These errors led to countless ship wrecks, loss of precious cargo and lives. While dead reckoning was suited to measuring location north and south or east and west, it proved useless over large distances where precision of several miles was needed.
In consequence of these errors, the lands discovered by the Magellans, the Mendanas, the Quiros, were so ill placed in longitude, that geographers had great difficulty to ascertain them. Solomon's isles, so remarkable for their beauty and riches, and for the detailed description of them by their first discoverer Mendana, floated through near a quarter of the circumference of the globe. None of the navigators who went over these parts after him, beginning with Quiros, his companion, and who followed him immediately, could break the charm which seemed to forbid to mankind the access to a land which the imagination, stimulated by obstacles, clothed in the most brilliant colors. More sober minds began to doubt their existence; when Dalrymple and Fleurieu showed, that they must be identical either with the New Britain of Dampier, or with the land of the Arsacides, and the adjacent isles visited by Bougainville and Surville.
Though the use of coarse celestial navigation proved useful in measuring latitude (north-south mapping), it offered little in measuring longitude (east-west mapping). These factors led to the unique reward offered for a longitude measuring solution. Simply dividing the circumference (approximately 25,000 miles at the Equator) by the unit of longitude (degree) gives a measure of approximately 1,000 miles at the Equator per 15 degrees of Earth's rotation. It is known that the 360 degrees of longitude divided into the 24 hours of the day means that each hour is equivalent to 15 degrees of longitude. Thus, if the time at a known point could be maintained on a ship at sea, longitude could be calculated based on the time difference as established locally from the occurrence of the noon Sun. The problem was that no clock was able to retain its accuracy under the difficult conditions of a sea voyage.
A cash purse of 10,000 to 20,000 British pounds (depending on accuracy of thesolution) was offered in 1714 for the determination of longitude at sea. After receiving incremental financial support from the Board of Longitude to develop and improve increasingly accurate timepieces of decreasing sizes, the prize was finally won by John Harrison, a working class man with little formal education, for his invention of H4 (a marine chronometer) in 1761. The first half of the prize purse (10,000 pounds) was made to Harrison in 1765, but ultimate public recognition as having solvedthe longitude problem and the remainder of the prize purse (8,750 pounds) was not made until 1773. In 1884 an international conference recommended that the meridian of Greenwich, England be the standard reference meridian for longitude and time. Until radio signals were available in the early 1900’s, navigation at sea was totally dependent upon good clocks.
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