The distance of one place from another, east or west of a meridian, was obtained by ascertaining the difference of time at the two points; the difference of time being one hour to each space of fifteen degrees of longitude. Although a navigator in the latter part of the fifteenth century could determine with his astrolabe the time of the place where he was in port, from the altitude of the sun or other heavenly bodies, the want of an accurate chronometer made it impossible for him to know the exact time of a place elsewhere. Pigafetta, who sailed round the world in 1519-1522, says in his treatise on navigation: “Pilots now are satisfied with knowing the latitude, and are so presumptuous that they refuse to hear longitude mentioned.”—MS. in Ambrosian Library, Milan.
To obtain a practical solution of the difficulties which perplexed seamen in determining the longitude of places, the Spanish government offered a thousand crowns, in 1598, for an accurate method of ascertaining the time of distant places. Not long afterward the government of the United Provinces of the Netherlands offered ten thousand florins for similar information, and, in 1714, the parliament of Great Britain passed an act proffering a gift of money to any person who should discover the best means of ascertaining longitude.
[99] Joam II. of Portugal reigned from 1481 to 1495.
“Astrolabes designed for the determination of time and geographical latitudes by meridian altitudes, and capable of being employed at sea, underwent gradual improvement from the time that the astrolabium of the Majorican pilots was in use, which is described by Raymond Lully, in 1295, in his Arte de navegar, till the invention of the instrument made by Martin Behaim, in 1484, at Lisbon, and which was, perhaps, only a simplification of the meteoroscope of his friend Regiomontanus.”—Humboldt: Cosmos. Otté’s trans. vol. ii. pp. 630, 631.
[100] Martin Behaim was born in Nuremberg about the year 1459. His commercial business induced him to visit Portugal about the year 1480, where, it is said, he became a pupil of Johann Müller, known as Regiomontanus. He accompanied Diogo Cam to the Congo, in 1484. He afterward resided on the island of Fayal, one of the Azores, for a number of years. His celebrated terrestrial globe was constructed by him, at Nuremberg, about the year 1492. He died at Lisbon, on the twenty-ninth of July, 1506.
[101] Asia de Joam de Barros dos fectos que os Portugueses fizeram no descobrimento & conquista dos mares & terras do Oriente. Impressa per Germao Galharde em Lixboa: a xxviij. de Junho anno de m. vᶜ. lij. dec. i. lib. iv. cap. ii.
[102] Arte de nauegar. Por el maestro Pedro de Medina. Valladolid. 1545.
[103] “I find the first mention of the application of the log in a passage of Pigafetta’s journal of Magellan’s voyage of circumnavigation, which long lay buried among the manuscripts in the Ambrosian Library at Milan. It is there said that in the month of January, 1521, when Magellan had already arrived in the Pacific, ‘Seconda la misura che facevamo del viaggio colla catena a poppa noi percorrevamo da 60 in 70 leghe al giorno,’ [following the measure which we made of our progress with the chain at the stern, we ran from sixty to seventy leagues a day]. (Amoretti. Primo Viaggio intorno al Globo terracqueo ossia Navigazione fatta dal Cavaliere Antonio Pigafetta sulla squadra del Magaglianes, 1800. p. 46.) What can this arrangement of a chain at the hinder part of the ship (catena a poppa), ‘which we used throughout the entire voyage to measure the way,’ have been except an apparatus similar to our log?”—Humboldt: Cosmos. Otté’s trans. vol. ii. p. 633.
[104] The Cape of Good Hope is in 34° 22´ south latitude.
It is said that Dias found by the astrolabe that the cape was in 45° south latitude, and that it was 3,100 leagues distant from Lisbon. This distance, it is related, Dias set down, league by league, on a marine chart, which he presented to King John II. Historia General de las Indias. Bartolomé de las Casas. lib. i. cap. vii.