Marine current power the rotation of the earth. The sun acts as the primary driving force, causing winds and temperature differences. Because there are only small fluctuations in current speed and stream location with minimal changes in direction, ocean currents may be suitable locations for deploying energy extraction devices such as turbines. Other effects such as regional differences in temperature and salinity and the Coriolis effect due to the rotation of the earth are also major influences. The kinetic energy of marine currents can be converted in much the same way that a wind turbine extracts energy from the wind, using various types
Winds in the Age of Sail them where they wanted to go. During the age of sail winds and currents determined trade routes and therefore influenced European imperialism and modern political geography. For an outline to the main wind systems see Global wind patterns. Pilotage or cabotage, in one sense, is the art of sailing along the coast using known landmarks. Navigation, in one sense, is the art of sailing long distances out of sight of land. Although the Polynesians were able to sail the Pacific (with great difficulty) and people regularly sailed north and south across the Mediterranean, before the time of Columbus nearly all