were
required to make such a navigator as Columbus._

[Illustration: MAP OF ANTONIO DE HERRERA, THE HISTORIAN OF COLUMBUS.
(See page 220.)]

The first necessity for a pilot who conducts a ship across the ocean,
when he is for many days out of sight of land, is the means of checking
his dead reckoning by observations of the heavenly bodies. But in the
days of Columbus such appliances were very defective, and, at times,
altogether useless. There was an astrolabe adapted for use at sea by
Martin Behaim, but it was very difficult to get a decent sight with it,
and Vasco da Gama actually went on shore and rigged a triangle when he
wanted to observe for latitude. If this was necessary, the instrument
was useless as a guide across the pathless ocean. Columbus, of
course, used it, but he seems to have relied more upon the old
quadrant which he had used for long years before Behaim invented his
adaption of the astrolabe. It was this instrument, the value of which
received such warm testimony from Diogo Gomez, one of Prince Henry's
navigators; and it was larger and easier to handle than the astrolabe.
But the difficulty, as regards both these instruments,[49] was the
necessity for keeping them perpendicular to the horizon when the
observation is taken, in one case by means of a ring working freely, and
in the other by a plummet line. The instruction of old Martin Cortes was
to sit down with your back against the mainmast; but in reality the only
man who obtained results of any use from such instruments was he who had
been constantly working with them from early boyhood. In those days, far
more than now, a good pilot had to be brought up at sea from his youth.
Long habit could alone make up, to a partial extent, for defective
means.

Columbus regularly observed for latitude when the weather rendered it
possible, and he occasionally attempted to find the longitude by
observing eclipses of the moon with the aid of tables calculated by old
Regiomontanus, whose declination tables also enabled the Admiral to work
out his meridian altitudes. But the explorer's main reliance was on the
skill and care with which he calculated his dead reckoning, watching
every sign offered by sea and sky by day and night, allowing for
currents, for leeway, for every cause that could affect the movement of
his ship, noting with infinite pains the bearings and the variation of
his compass, and constantly recording all phenomena on his card and in
his j