oduction of the
same currents in a globe by the circular currents of Ampere, that the
globe is magnetized, and the needles made to dip.

CHAPTER VIII.

It is exceedingly desirable, in a practical point of view, to understand
the precise character of the reciprocal action which takes place between
the earth and the counter-trade, and produces the varied phenomena which
mark our climate. We have seen that the same laws, other things being
equal, operate every where, and that analogies may be sought in the
character of those phenomena elsewhere, under the same, or different,
modifying circumstances. Looking, therefore, at the magneto-electric
movable machinery as a whole, and its influence upon the atmospheric
circulation and conditions, we find many facts which point to a primary
action in the counter-trade, and others that point as significantly to a
primary local-inducing-action in the earth. Let us briefly review those to
which we have alluded, and advert to some others, and see what solution of
the question they will justify:

The belt of inter-tropical rains appears to be, in width, and amount of
precipitation, and annual travel north and south, proportionate to the
volume of trades which blow into it, the quantity of moisture they
contain, and the elevation of the surface over which they meet.

South America is the most thoroughly-watered country within the tropics,
except, perhaps, portions of Hindoostan, Burmah, Siam, etc., on
south-eastern Asia. The contrast between both, and Africa, as far as
explored, and as shown by its rivers, is most obvious. The Amazon, alone,
delivers more water to the ocean than all the rivers of Africa.

Of the width of the belt of rains over Africa, in the interior, we know
little. Its northern extension is less, by from 7 deg. to 10 deg., than the same
belt over South America, the West Indies, and Mexico. Probably its
southern is also. Upon South America, the southern edge is carried down to
Cochabamba, in latitude 18 deg., and probably to 25 deg., to the northern edge of
the coast-desert of Peru, while it is rarely, if ever, found over the
Atlantic below 7 deg., a difference of 12 deg. to 20 deg.. Over South America, too,
the quantity of water which falls is also vastly in excess of that which
falls upon the Atlantic. The main cause of these differences is obvious.
The N. E. counter-trades which blow over Africa, originate on a surface
which is rainless, as eastern Sahara,