The monsoons or periodical winds of the Indian Ocean owe their origin to
the same cause which gives rise to the trade-winds, though they acquire
a different character in consequence of the proximity of the land. In
the southern portions of the ocean which are remote from this cause of
disturbance, the trade-wind blows with its wonted regularity; but in the
seas occupying the region between the eastern coast of Africa on the one
side, and the Malay peninsula and the island of Sumatra on the other,
the course of the trade-wind is reversed for half the year. This change
occurs from April to October; the sun at that period being vertical
north of the equator, and the land in the adjacent regions acquiring in
consequence a high temperature, and the air over the sea being cooler
than that over the land, a south-west wind prevails. This wind, called
the “south-west monsoon,” commences at about three degrees south of the
equator, and passing over the ocean arrives charged with moisture, and
accordingly usually deposits copious supplies of rain in India and some
of the adjoining territories. In the remaining half of the year, or from
October to April, the wind assumes the ordinary north-easterly direction
of the trade-wind.
Sea-breezes, which occur in regions bordering on the ocean in hot
climates, are produced by causes similar to those which give rise to the
south-west monsoon, but on a more limited scale of action, and changing
their direction daily.