Currents of air moving from about the 30th degree of latitude towards the equator. The diurnal motion of the earth makes them incline from the eastward, so that in the northern hemisphere they are from the N.E., and in the southern hemisphere from the S.E. Their geographical position in latitude varies with the declination of the sun. In some parts of the world, as the Bay of Bengal and China Sea, the action of the sun on the neighbouring land has the power of reversing the trades; the winds are there called monsoons.