HOW THE SEA-DEPTHS ARE EXPLORED.
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"Still the thing is possible, and it must be done again and again, as the years pass on, by naturalists of all nations working with improved machinery and with ever-increased knowledge. For the bed of the deep sea, the 140,000,000
Fig. 1.

There are two principal operations in exploring the bottom of the ocean: first, sounding to ascertain depth; and, second, dredging to bring up materials. Although much ingenuity has been expended in devices to bring up samples of the sea-bottom by the sounding-apparatus, yet dredging contrivances are now mainly relied upon for that purpose. To determine the depth with a sounding-line, it is customary to graduate it by attaching slips of different-colored cloths or leather which mark it off into sections, and give the means of determining the distance to which