Physical geography. By Mary Somerville ...

294 PHYSICAL GEOGRAPHY. CHAP. XXII.
the sun passes the zenith in his progress to the nearest tropic, and
the other at his return, but in the latter the rains are less violent
and of shorter duration. Although the quantity of water which
falls between the tropics in a month is greater than that of a whole
year in Europe, yet the number of rainy days increases with the
latitude, so that there are fewest where the quantity is greatest.
Neither does it fall continually during the rainy season between the
tropics, for the sky is generally clear at sunrise, it becomes cloudy
at ten in the morning, at noon the rain begins to fall, and, after
pouring for four or five hours, the clouds vanish at sunset, and not a
drop falls in the night, so that a day of uninterrupted rain is very
rare.
At sea within the region of the trade-winds it seldom rains,2 but
in the narrow zone between them known as the Variables, in both
the great oceans, it rains almost continually, attended by violent
thunder and lightning.
Throughout the whole region where the monsoons prevail, it is
not the sun, directly, but the winds, that regulate the periodical
rains. That region extends from the eastern coasts of Africa and
Madagascar across the Indian Ocean to the northern districts of Australia, and from the tropic of Capricorn to the face of the Himalaya,
the interior of China, and even to Corea, inclusive. In these countries the western coasts are watered during the south-west monsoon,
which prevails from April to October; and the eastern coasts are
watered during the north-east monsoon, which blows from October
to April. For example, the south-west wind condenzes the vapour
on the summit of the Ghauts, and violent rains fall daily on the
coast of Malabar, while on the Coromandel coast the sky is serene.
Exactly the contrary takes place during the north-east monsoon; it
rains on the coast of Coromandel, while there is fair weather on the
Malabar coast, and the table-land of the Deccan partakes of both.
In the southern hemisphere the rainy season corresponds with the
south-west monsoon, and the dry with the south-eastern.
Between the tropics it rains rarely during the night, and for months
together not a drop falls; 3 while in the temperate zone it often rains
in the night, and rain falls at all seasons, though more abundantly
in some than in others. It seldom rains in summer throughout the
north of Africa, Madeira, the southern parts of Spain and Portugal,
At Demerara six inches have been known to fall in 12 hours. The
quantity that falls in Italy is sometimes very great; at Rome half the
yearly average quantity fell in 15 hours.
[I Showers and squalls of rain occur frequently in the regions of both
the N.E. and S.E. trade-winds.]
a [According to the experience of the writer, derived from cruising several years within the tropics, rain is most frequent at night. It is certainly
the case in the Chinese Seas, and in the vicinity of Sumatra and Java.]