The new knowledge gained by European peoples about the
land routes of Asia was accompanied by much progress in the art of ocean
navigation. First in importance came the compass to guide explorers across the
waters of the world. The Chinese appear to have discovered that a needle, when
rubbed with a lodestone, has the mysterious power of pointing to the north. The
Arabs may have introduced this rude form of the compass among Mediterranean
sailors. The instrument, improved by being balanced on a pivot so that it would
not be affected by choppy seas, seems to have been generally used by Europeans
as early as the thirteenth century. It greatly aided sailors by enabling them
to find their bearings in murky weather and on starless nights. The compass,
though useful, was not indispensable; without its help the Northmen had made
their distant expeditions in the Atlantic.
NAUTICAL INSTRUMENTS
The astrolabe, which the Greeks had invented and used for
astronomical purposes, also came into Europe through the Arabs. It was employed
to calculate latitudes by observation of the height of the sun above the
horizon. Other instruments that found a place on shipboard were the hour-
glass, minute-glass, and sun-dial. A rude form of the log was used as a means
of estimating the speed of a vessel, and so of finding roughly the longitude.
