ical belt of rains, which travels _down from
the north_, and covers it in winter. Northern Mexico and the adjoining
regions west of the 100th meridian are between the limits of the two, and
neither travels far enough to reach them, except for brief and uncertain
periods; they are comparatively rainless; while the eastern portion of
the continent, _in all latitudes_, unlike the others, is without a
distinctly marked dry season, or a rainless region, and with the exception
of occasional droughts, is abundantly supplied with rain at all seasons of
the year.

And now, what is the explanation of all this? What produces the
extra-tropical belt of regular rains surrounding the earth, north of the
parallel of 30 deg. north, in some places, and 35 deg. in others, extending to the
pole, with its southern edge traveling up ten or more degrees in summer,
leaving large portions of the earth subject to a dry season; and back
again in the winter to give them a rainy one? What produces the narrow
belt of inter-tropical rains, encircling the earth; traveling up and down
every year over an average of 35 deg. of latitude, supplying every portion of
it alternately with rain? And what connects the two together over the
eastern portion of North America, so as to leave no distinctly marked wet
and dry season, and no rainless and sterile portion there? Are all these
the result of simple evaporation, ascent to a colder region, condensation,
and descent again? Demonstrably not. Of the forty inches which fall
annually upon the middle and eastern portions of the United States, an
average probably of one-half or twenty inches, runs off by the rivers to
the ocean, or is carried away eastward by the westerly and north-westerly
evaporating winds. The same is true, in degree, of the rain which falls
upon the other portions. Evaporation, therefore, could not keep up the
supply. From whence, then, does it come? this twenty inches, thus lost by
the rivers and winds, and with such wonderful regularity every year.

"All the rivers run into the sea, yet the sea is not full. _Note the place
whence the rivers come, hither they return again._"

But how is it that they thus return with such wonderful regularity, in a
narrow traveling belt of daily rains within the tropics, and a movable
belt of irregular rains without the tropics, extending to the poles,
leaving a space on each side of the equator encircling the earth in like
manner (except at two points, _viz.