pass in the 13th century. In the wake of its popularization,
the first known navigational book, Lo compasso di navi-
gare, began to circulate in 1296. Around the same time,
the Carta Pisana (Pisan chart) displayed the horizon in
terms of compass points, although directions, especially in
the Mediterranean area, were still mainly determined by
major winds. Also, early compasses were based on dead
reckoning, with no allowances for magnetic variation, the
principle of which was not understood until the mid-16th
century.
Along with instruments, CARTOGRAPHY flourished
during the Renaissance period. In the 15th century Por-
tuguese cartographers developed the use of latitude to
permit navigators unprecedented certainty in determining
their whereabouts; it was assessed by the position of either
the Pole Star or the midday sun. Various methods were
proposed to establish longitude; GEMMA FRISIUSsuggested
the use of a clock in 1530, but a sufficiently accurate time-
piece was not available until the chronometer was devel-
oped in the 18th century, and mariners until then had to
rely on very uncertain methods of dead reckoning.
Although navigational techniques improved through-
out the Renaissance period, most of the major gaps were
filled by instruments invented by German or Flemish sci-
entists, such as APIANand REGIOMONTANUSin the late 15th
and early 16th centuries. Improvements to ASTROLABESnnaavviiggaattiioonn 3 33377Navigation A woodcut from the Italian
translation (1537) of Sacrobosco’s
Tractatus de sphaera. It shows the author
with two globes, one of which includes
(South) America.