Note 98 — Chapter II · 1295-1487.

The distance of a place, north or south of the equator, was determined by ascertaining with the astrolabe the elevation of the pole of the heavens above the plane of the horizon.

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.