ers which are its effects. The human
mind is not satisfied with observing and studying any natural occurrence
alone, but takes pleasure in connecting every natural fact with what has
gone before it, and with what is to come after it. Thus, when we enter
upon the study of rivers, our interest will be greatly increased by
taking into account, not only their actual appearances but also their
causes and effects.

Let us trace a river to its source. Beginning where it empties itself
into the sea, and following it backwards, we find it from time to time
joined by tributaries which swell its waters. The river, of course,
becomes smaller as these tributaries are passed. It shrinks first to a
brook, then to a stream; this again divides itself into a number of
smaller streamlets, ending in mere threads of water. These constitute
the source of the river, and are usually found among hills. Thus, the
Severn has its source in the Welsh Mountains; the Thames in the Cotswold
Hills; the Rhine and the Rhone in the Alps; the Missouri in the Rocky
Mountains; and the Amazon in the Andes of Peru.

But it is quite plain, that we have not yet reached the real beginning
of the rivers. Whence do the earliest streams derive their water? A
brief residence among the mountains would prove to you that they are fed
by rains. In dry weather you would find the streams feeble, sometimes
indeed quite dried up. In wet weather you would see them foaming
torrents. In general these streams lose themselves as little threads of
water upon the hillsides; but sometimes you may trace a river to a
definite spring. You may, however, very soon assure yourself that such
springs are also fed by rain, which has percolated through the rocks or
soil, and which, through some orifice that it has found or formed, comes
to the light of day.

But we cannot end here. Whence comes the rain which forms the mountain
streams? Observation enables you to answer the question. Rain does not
come from a clear sky. It comes from clouds. But what are clouds? Is
there nothing you are acquainted with, which they resemble? You discover
at once a likeness between them and the condensed steam of a locomotive.
At every puff of the engine, a cloud is projected into the air. Watch
the cloud sharply: you notice that it first forms at a little distance
from the top of the funnel. Give close attention, and you will sometimes
see a perfectly clear space between the funnel and the cloud. Through
th