Isabella's musings were not, however, all so piously confined. She wrote to Columbus from Segovia in August, requiring him to make provisions for bringing back to Spain specimens of the peculiar birds of the new regions, as indications of untried climates and seasons.
Astronomy and navigation.
Again, in writing to Columbus, September 5, she urged him not to rely wholly on his own great knowledge, but to take such a skillful astronomer on his voyage as Fray Antonio de Marchena,—the same whom Columbus later spoke of as being one of the two persons who had never made him a laughing-stock. Muñoz says the office of astronomer was not filled.
Dealing with the question of longitude was a matter in which there was at this time little insight, and no general agreement. Columbus, as we have seen, suspected the variation of the needle might afford the basis of a system; but he grew to apprehend, as he tells us in the narrative of his fourth voyage, that the astronomical method was the only infallible one, but whether his preference was for the opposition of planets, the occultations of stars, the changes in the moon's declination, or the comparisons of Jupiter's altitude with the lunar position,—all of which were in some form in vogue,—does not appear. The method by conveyance of time, so well known now in the use of chronometers, seems to have later been suggested by Alonso de Santa Cruz,—too late for the recognition of Columbus; but the instrumentality of water-clocks, sand-clocks, and other crude devices, like the timing of burning wicks, was too uncertain to obtain even transient sanction.
Astrolabe.
The astrolabe, for all the improvements of Behaim, was still an awkward instrument for ascertaining latitude, especially on a rolling or pitching ship, and we know that Vasco da Gama went on shore at the Cape de Verde Islands to take observations when the motion of the sea balked him on shipboard.
THE CLOCK-MAKER.
[From Jost Amman's Beschreibung, Frankfort.]
Cross-staff and Jackstaff.