]

1. _The Equatorial Belt._--Within a few degrees of the equator, and when
not interfered with by other controls, the annual curve of temperature
has two maxima following the two zenithal positions of the sun, and two
minima at about the time of the solstices. This _equatorial_ type of
annual march of temperature is illustrated in the three curves for the
interior of Africa, Batavia and Jaluit (fig. 4). The greatest range is
shown in the curve for the interior of Africa; the curve for Batavia
illustrates insular conditions with less range, and the oceanic type for
Jaluit, Marshall Islands, gives the least range. This double maximum is
not a universal phenomenon, there being many cases where but a single
maximum occurs.

[Illustration: FIG. 5.--Annual march of rainfall in the tropics.

S.A, South Africa.
Q, Quito.
S.P., Sao Paulo.
M, Mexico.
H, Hilo.
P.D., Port Darwin.]

As the belt of rains swings back and forth across the equator after the
sun, there should be two rainy seasons with the sun vertical, and two
dry seasons when the sun is farthest from the zenith, and while the
trades blow. These conditions prevail on the equator, and as far north
and south of the equator (about 10 deg.-12 deg.) as sufficient time
elapses between the two zenithal positions of the sun for the two rainy
seasons to be distinguished from one another. In this belt, under normal
conditions, there is therefore no dry season of any considerable
duration. The double rainy season is clearly seen in equatorial Africa
and in parts of equatorial South America. The maxima lag somewhat behind
the vertical sun, coming in April and November, and are unsymmetrically
developed, the first maximum being the principal one. The minima are
also unsymmetrically developed, and the so-called "dry seasons" are
seldom wholly rainless. This rainfall type with double maxima and minima
has been called the _equatorial_ type, and is illustrated in the
following curves for South Africa and Quito (fig. 5). The monthly
rainfalls are given in thousandths of the annual mean. The mean annual
rainfall at Quito is 42.12 in. These double rainy and dry seasons are
easily modified by other conditions, as by the monsoons of the
Indo-Australian area, so that there is no rigid belt of _equatorial
rains_ extending around the world. In South America, east of the Andes,
the distinction between rainy and dry seasons is often much confused. In
this equatorial