r, and makes it light; cold at the
poles chills it, and makes it heavy. Hot water, being light, rises;
cold water, being heavy, sinks.

Here, then, is a sufficient cause to produce the effect of currents in
the sea.

But there are other causes at work. Excessive evaporation at the
equator carries off the water of the sea, but leaves the salt behind,
thus rendering it denser and heavier; while excessive influx of fresh
water at the poles, (from rain and snow and melting ice), renders the
sea light;--in addition to which corallines and shell-fish everywhere
abstract the lime that is in the sea, by secreting it on their bodies in
the form of shells, and thus increase the lightness of those particles
of water from which the lime has been abstracted. The other particles
of water being generous in their nature, hasten to impart of their lime
and salt to those that have little or none.

Here, then, we have perpetual motion rendered absolutely certain, both
as to continuance and direction.

But the latter causes which I have named are modifying causes which tend
to counteract, or rather to deflect and direct currents in their flow.
Besides which, the rotation of the earth, the action of the winds, and
the conformation of continents and islands, have a powerful influence on
currents, so that some flow at the bottom of ocean, some on the surface,
some from east to west or west to east, or aslant in various directions,
while, where currents meet there is deflection, modification, or
stagnation, but there is no confusion; all goes on with a regularity and
harmony which inconceivably excels that of the most complex and
beautiful mechanism of man's constructing, although man cannot perceive
this order and harmony by reason of his limited powers.

Now, these are facts, not theories founded on speculation. They have
been arrived at by the slow but sure method of induction. Hundreds of
thousands of practical men have for many years been observing and
recording phenomena of every kind in connexion with the sea. These
observations have been gathered together, collated, examined, and deeply
studied by philosophers, who have drawn their conclusions therefrom.
Ignorance of these facts rendered the navigation of the sea in days of
old a matter of uncertainty and great danger. The knowledge of them and
of other cognate facts enables man in these days to map out the
so-called trackless ocean into districts, and follow its well-known