CLIMATE

349

be imagined. The explanation of the natural phenomena
which precede and accompany the monsoon are simple
enough. During the winter months, when the meridional
sun is low, the surface of the earth throughout the
Southern Asiatic continent cools down by the radiation
of its heat into space until its temperature is below that
of the adjoining sea. Atmospheric pressure rises over the
scean and falls over the land ; but after March, as the
sun strikes with more direct rays, and the daily period
to which the earth is exposed to them grows longer, this

JUNE=~OCT.
“WW. MONSOON

NOV.~ DEC.
RC REATING S.W.
MONSOON

A

Fig. 106.

jifference in temperature is reversed. The land speedily
becomes hotter than the ocean, and the falling pressure of
the atmosphere above it induces strong moisture-laden
currents to set towards India from the seas south of the
equator, where the pressure is rising under the influence
of their winter's sun. Thus is originated the south-west
monsoon, which usually reaches the west coast of India
about the end of May, and is fairly established through
‘he Northern Provinces by the end of June. Its action
on the interior of the country is modified by the resistance
that it encounters on its course, and this resistance is
chiefly found in mountain altitudes, which arrest the
currents, and lead directly to the condensation of the
wind-borne vapour and the precipitation of rain.