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.