Ocean's Story; or, Triumphs of Thirty Centuries / Maritime Adventures, Achievements, Explorations, Discoveries and Inventions; and of the Rise and Progress of Ship-Building and Ocean Navigation, from the Ark to the Iron Steamships

by Frank B. Goodrich

CHAPTER LVI.

DREDGING IN MODERN TIMES—WHAT IT HAS TAUGHT US—DEEP SEA SOUNDINGS—FIRST ATTEMPTS—IMPLEMENTS USED FOR IT—THE CHANCE FOR INVENTORS.

In modern times we have learned a great deal more of the ocean than the ancients knew, from dredging. By this means we have become acquainted not only with the outline of the bottom, but have also become acquainted with the temperature of deep seas, with the varied forms of animal and vegetable life which are present there, and have come to know, with far greater certainty and completeness than ever before, the part which the ocean has played and is still playing in the preparation of the land.

By sounding, the ancients, of course, knew the depths of the shallow waters along their coasts. It would be the most natural thing for a sailor to tie a stone to a string, and let it down into the water, when he wanted to know whether it was deep enough to float his vessel, and the same means would also be used to discover whether there were any sunken rocks in such harbors as he was frequenting. But the ocean, to all antiquity, was unfathomable; they dared not attempt to cross it, and of course did not think they could measure its depth. Long after the ocean had been crossed by ships the belief was still current that it was impossible to measure its depth, and this belief was made the stronger by the unsuccessful attempts made in mid ocean to obtain soundings with the ordinary lead and line.

Before we arrived at a positive knowledge of the depth of the ocean, scientific men attempted to calculate it by various methods. Laplace, calculating the mean elevation of the land, supposed the sea must be of about equal depth. Young, drawing his deductions from the tides, calculated the depth of the sea. This method has been recently used to calculate the depth of the Pacific. A wave of a certain velocity indicates water of such a depth. In the case of the earthquake of 1854, in Japan, which caused a wave that extended to California, the rate of its progress afforded an indication of the mean depth of the sea it passed over, and authentic soundings taken since have confirmed the general accuracy of the calculation.

The ordinary lead used for soundings is a pyramid of lead, the bottom of which has a depression in it, which is filled with tallow; on striking the bottom a little of the sand or mud adheres to this tallow and is brought up to the surface. In this way something is learned about the depth and bottom of the sea, but not enough to satisfy the naturalists, who inquired whether it might not be possible to dredge the bottom of the sea in the ordinary way, and to send down water bottles and registering instruments to settle finally the conditions of the deep waters, and determine with precision the composition and temperature at great depths.

An investigation of this kind is beyond the powers of private enterprise. It requires more power and sea skill than naturalists usually have. It is a work for governments. That of the United States has contributed fully its share. The coast survey has added a great deal to our knowledge of the deep sea, and the ships of the navy took part in the soundings by which the existence of the plateau across the bed of the North Atlantic, which has been used for the ocean telegraphic cable, was proved.

In 1868 the English government provided the vessels and crews for the purpose of conducting deep sea dredgings, under the direction of Dr. Carpenter and Mr. Wyville Thompson. These expeditions have found that it is quite possible to work with certainty, though not with such ease, at the depth of 600 fathoms, as at a depth of 100; and in 1869 it carried on deep sea dredging at a depth of 2,435 fathoms, 14,610 feet, or very nearly three miles, with perfect success. Dredging in such deep water is very trying. Each haul occupied seven or eight hours, and during the whole of this time the constant attention of the commander was necessary, who stood with his hand on the regulator of the accumulator, ready at any moment to ease an undue strain, by a turn of the ship's paddles. The men, stimulated and encouraged by the cordial interest taken by the officers in the operations, worked with a willing spirit; but the labor of taking up three miles of rope, coming up with a heavy strain, was very severe. The rope itself, of the very best Italian hemp, 2 1/2 inches in circumference, with a breaking strain of 2 1/4 tons, looked frayed out and worn, as if it could not have been trusted to stand such an extraordinary ordeal much longer.

The ordinary deep sea lead used for soundings weighs from 80 to 120 pounds. The samples of the bottom which it brings up are marked upon the charts as mud, shells, gravel, ooze or sand, thus 2,000 m. sh. s. means mud, shells and sand at 2,000 fathoms; 2,050 oz. st. means ooze and stones at 2,050 fathoms; 2,200 m. s. sh. sc. means mud, sand, shells, and scoriæ, at 2,200 fathoms, and so on. When no bottom is found with the lead it is entered on the chart thus:——3,200, meaning no bottom was reached at that depth.

This method of sounding answers very well for comparatively shallow water, but it is useless for depths much over 1,000 fathoms, or six thousand feet. The weight is not sufficient to carry the line rapidly and vertically to the bottom; and if a heavier weight is used, the ordinary sounding line is not strong enough to draw up its own weight, and that of the lead from a great depth, and so breaks. No impulse is felt when the lead touches the bottom, and so the line continues running out, and any attempt to stop it breaks it. In some cases the slack of the line is carried along by currents, and in others it is found that the line has been running out by its own weight and coiling in a tangled mass on top of the lead.