The Ocean and its Wonders | Page 4

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 them, which, by compression, would show the aqueous
pressure to which they had been subjected; but the trial proved to be
more than the instrument could stand.
Captain Maury, of the American Navy--whose interesting book has
been already referred to--invented an instrument for sounding the deep
sea. Here is his own description of it:--"To the lead was attached, upon
the principle of the screw-propeller, a small piece of clock-work for
registering the number of revolutions made by the little screw during
the descent; and it having been ascertained by experiment in shoal
water that the apparatus, in descending, would cause the propeller to
make one revolution for every fathom of perpendicular descent, hands
provided with the power of self-registering were attached to a dial, and
the instrument was complete. It worked beautifully in moderate depths,
but failed in blue water, from the difficulty of hauling it up if the line
used were small, and from the difficulty of getting it down if the line
used were large enough to give the requisite strength for hauling it up."
One eccentric old sea captain proposed to sound the sea with a torpedo,
or shell, which should explode the instant it touched the bottom.
Another gentleman proposed to try it by the magnetic telegraph, and
designed an instrument which should telegraph to the expectant
measurers above how it was getting on in the depths below. But all
these ingenious devices failed, and it is probable that the deepest parts
of the ocean-bed still remained untouched by man.

At last an extremely simple and remarkably successful deep-sea
sounding apparatus was invented by Mr Brooke, an American officer.
It consisted of nothing more than thin twine for a sounding-line, and a
cannon ball for a sinker. The twine was made for the purpose, fine but
very strong, and was wound on a reel to the extent of ten thousand
fathoms. The cannon ball, which was from thirty-two to sixty-eight
pounds' weight, had a hole quite through it, into which was fixed a
sliding rod, the end of which, covered with grease, projected several
inches beyond the ball. By an ingenious and simple contrivance, the
cannon ball was detached when it reached the bottom of the sea, and
the light rod was drawn up with specimens of the bottom adhering to
the grease.
With this instrument the Americans went to work with characteristic
energy, and, by always using a line of the same size and make, and a
sinker of the same shape and weight, they at last ascertained the law of
descent. This was an important achievement, because, having become
familiar with the precise rate of descent at all depths, they were enabled
to tell very nearly when the ball ceased to carry out the line, and when
it began to go out in obedience to the influence of deep-sea currents.
The greatest depth reached by Brooke's sounding-line is said to have
been a little under five miles in the North Atlantic.
The value of investigations of this kind does not appear at first sight, to
unscientific men. But those who have paid even a little attention to the
methods and processes by which grand discoveries have been made,
and useful inventions have been perfected, can scarcely have failed to
come to the conclusion that the search after TRUTH, pure and simple,
of any kind, and of every kind, either with or without reference to a
particular end, is one of the most useful as well as elevating pursuits in
which man can engage.
All truth is worth knowing and labouring after. No one can tell to what
useful results the discovery of even the smallest portion of truth may
lead. Some of the most serviceable and remarkable inventions of
modern times have been the result of discoveries of truths which at first
seemed to