the cask, where it was condensed into water, minus
the saline particles, which, not being evaporable, were left behind in
the pitch-pot. In less than an hour a quart of fresh water was thus
obtained; which, though not very palatable, was sufficiently good to
relieve the thirst of the ship's crew. Many ships are now regularly
supplied with apparatus for distilling sea water; and on the African
coasts and other unhealthy stations, where water is bad, the men of our
navy drink no other water than that which is distilled from the sea.

The salts of the ocean have something to do with the creating of oceanic
currents; which, in their turn, have a powerful influence on climates.
They also retard evaporation to some extent, and have some effect in
giving to the sea its beautiful blue colour.

The ocean covers about two-thirds of the entire surface of the Earth.
Its depth has never been certainly ascertained; but from the numberless
experiments and attempts that have been made, we are warranted in coming
to the conclusion that it nowhere exceeds five miles in depth, probably
does not quite equal that. Professor Wyville Thompson estimates the
average depth of the sea at about two miles.

Of the three great oceans into which the sea is naturally divided--the
Atlantic, the Pacific, and the Arctic--the Atlantic is supposed to be
the deepest. There are profundities in its bosom which have never yet
been sounded, and probably never will be.

The difficulty of sounding great depths arises from the fact that, after
a large quantity of line has been run out, the shock of the lead
striking the bottom cannot be felt. Moreover, there is sufficient force
in the deep-sea currents to sweep out the line after the lead has
reached the bottom so that, with the ordinary sounding-lines in use
among navigators, it is impossible to sound great depths. Scientific
men have, therefore, taxed their brains to invent instruments for
sounding the deep sea--for touching the bottom in what sailors call
"blue water." Some have tried it with a silk thread as a plumb-line,
some with spun-yarn threads, and various other materials and
contrivances. It has even been tried by exploding petards and ringing
bells in the deep sea, when it was supposed that an echo or
reverberation might be heard, and, from the known rate at which sound
travels through water, the depth might thus be ascertained. Deep-sea
leads have been constructed having a column of air in