(^86) THE WEALTH AND POVERTY OF NATIONS
against southing ships, and the coasdine is dreary-arid. Once one gets
past the Cape Verdes, moreover, one finds littie in the way of harbor
and refreshment between Guinea and the Cape. Time-honored tech
niques of coasting, then, highly effective in the North Atlantic,
Mediterranean, Indian Ocean, and China seas, do not work here. This
is high-seas navigation.^3 (See Maps 1,2, and 3.)
Here the earlier experience of the Portuguese in using the trade winds
to ease their return home from the islands paid off, but in a different di
rection. After decades of beating and tacking their way south, they filled
their sails and took the audacious step of swinging well out to the west,
clear across the ocean to Brazil, before turning back to the southeast.
This added hundreds of leagues to the route and meant weeks, even
months out of sight of land; but the effect was to shorten the voyage
and give them clear sailing around the point of Africa into friendlier seas.
One must not think of this as luck. The Portuguese could do this be
cause they had learned to find the latitude. In the North Atlantic,
sailors had always read their location north-south by the height of the
Pole star. As they approached the equator, however, the Pole star stood
too low in the sky, and they had to rely on the sun for guidance. Here
the problem was complicated by the changing position of the sun in
the sky: in European summer, it stood farther north, hence higher; in
winter, farther south. This variance in position, known as declination,
had to be taken into account in reading the sun's altitude as the mea
sure of latitude. Here Iberia's position as frontier and bridge between
civilizations paid off. In the fourteenth and fifteenth centuries, Arab
and Jewish astronomers there (the key figure was Abraham Zacut) pre
pared convenient tables of solar declination for the use of navigators.^4
Once one could find the latitude, both at sea and on land, one had
the key to the oceans; for now one could know position north-south;
and if one also knew the latitude of the destination, one could get
there by sailing to and then following the parallel. (Occasional prob
lem: should one turn east or west?) The most important information
that Bartolomeu Dias brought back from his voyage (1488) was the
coordinate of the southern tip of Africa. Knowing that, the Portuguese
could find their way there from any part of the South Atiantic.
These explorations had taken the Portuguese the better part of a
century. Some of this was the work of the Portuguese crown and its de
vout, single-minded prince (we are told that he died a virgin) come
down to us as Henry the Navigator, who built a marine research station
at Sagres on a promontory overlooking the ocean and directed decades
of inquiry into the science and technique of steering and sailing on the
nora
(Nora)
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