80 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
over a large space of the ocean. It has no room for escape but 
in the upward direction 105). It expands as it ascends, and 
becomes cooler ; a portion of its vapor is thus condensed, and 
comes down in the shape of rain. Therefore it is that, under 
these calms, we have a region of constant precipitation. Old 
sailors tell us of such dead calms of long continuance here, of 
such heavy and constant rains, that they have scooped up fresh 
water from the surface of the sea. 
116. The conditions to which this air is exposed here under the 
equator are probably not such as to cause it to precipitate all the 
moisture that it has taken up in its long sweep across the waters. 
Let us see what becomes of the rest ; for Nature, in her economy, 
permits nothing to be taken away from the earth which is not to 
be restored to it again in some form, and at some time or other. 
Consider the great rivers — the Amazon and the Mississippi, for 
example. We see them day after day, and year after year, dis- 
charging an immense volume of water into the ocean. 
" AH the rivers run into the sea, yet the sea is not full." — Ecc, 
i., 7. Where do the waters so discharged go, and where do they 
come from ? They come from their sources, you will say. But 
whence are their sources supplied ? for, unless what the fountain 
sends forth be returned to it again, it will fail and be dry. 
117. We see simply, in the waters that are discharged by these 
rivers, the amount by which the precipitation exceeds the evapor- 
ation throughout the whole extent of valley drained by them ; and 
by precipitation I mean the total amount of water that falls from, 
or is deposited by the atmosphere, whether as dew, rain, hail, or 
snow. ' 
The springs of these rivers 87) are supplied from the rains 
of heaven, and these rains are formed of vapors which are taken 
up from the sea, that " it be not full," and carried up to the mount- 
ains through the air. 
" Note the place whence the rivers come, thither they return 
again." 
118. Behold now the waters of the Amazon, of the Mississippi, 
the St. Lawrence, and all the great rivers of America, Europe, 
and Asia, lifted up by the atmosphere, and flowing in invisible 
streams back through the air to their sources among the hills 
(§ 87), and that through channels so regular, certain, and well de- 
