After 1513, and so on to the middle of the century, it was to the north of the Alps that the cosmographical students turned for the latest light upon all oceanic movements. The question of longitude was the serious one which both navigators and map makers encountered. The cartographers were trying all sorts of experiments in representing the converging meridians on a plane surface, so as not to distort the geography, and in order to afford some manifest method for the guidance of ships.
Lunar observations.
Chronometers.
These experiments resulted, as Nordenskiöld counts, in something like twenty different projections being devised before 1600. For the seaman the difficulty was no less burdensome in trying to place his ship at sea, or to map the contours of the coasts he was following. The navigator's main dependence was the course he was steering and an estimate of his progress. He made such allowance as he could for his drift in the currents. We have seen how the imperfection of his instruments and the defects of his lunar tables misled Columbus egregiously in the attempts which he made to define the longitude of the Antilles. He placed Española at 70° west of Seville, and La Cosa came near him in counting it about 68°, so far as one can interpret his map. The Dutch at this time were beginning to grasp the idea of a chronometer, which was the device finally to prove the most satisfactory in these efforts.
Earliest sea-atlas.
Reinerus Gemma of Friesland, known better as Gemma Frisius, began to make the Dutch nautical views better known when he suggested, a few years later, the carrying of time in running off the longitudes, and something of his impress on the epoch was shown in the stand which a pupil, Mercator, took in geographical science. The Spieghel der Zeevaardt of Lucas Wagenaer, in 1584 (Leyden), was the first sea-atlas ever printed, and showed again the Dutch advance.
There were also other requirements of sea service that were not forgotten, among which was a knowledge of prevalent winds and ocean currents, and this was so satisfactorily acquired that the return voyage from the Antilles came, within thirty years after Columbus, to be made with remarkable ease. Oviedo tells us that in 1525 two caravels were but twenty-five days in passing from San Domingo to the river of Seville.
Two of the duties imposed by the Spanish government upon the Casa de la Contratacion, soon after the discovery of the New World, were to patronize invention to the end of discovering a process for making fresh water out of salt, and to improve ships' pumps,—the last a conception not to take effective shape till Ribero, the royal cosmographer, secured a royal pension for such an invention in 1526.