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this experiment, that a second expedition was arranged in 1869, and the government surveying-vessel Porcupine was assigned to the naturalists to carry on the work. This expedition was also so highly successful, that the ship Challenger has now started out on a four years' voyage around the world to carry out a comprehensive plan of deep-sea observations. We noticed very briefly last month the admirable work of Prof. Wyville Thomson on "The Depths of the Sea," giving a history of what has been lately done in the investigation of the subject. We propose now to lay Prof. Thomson's work under contribution for the benefit of our readers, and especially to give some account of the instruments of ocean-research, and the way the exploration is conducted.

It may be remarked, in passing, that, when the dredging of the deep seas was found to be feasible, questions of large scientific interest and moment, which had been hitherto regarded as inaccessible, were suddenly brought within the range of practical solution. It was a popular opinion, shared also by men of science, that the bottom of the sea was a dark and desolate waste, subject to such tremendous pressure as to render all life impossible. Prof. Thomson observes: "The enormous pressure at these great depths seemed at first sight alone sufficient to put any idea of life out of the question. There was a curious popular notion, in which I well remember sharing when a boy, that, in going down, the sea-water became gradually under the pressure heavier and heavier, and that all the loose things in the sea floated at different levels, according to their specific weight: skeletons of men, anchors, and shot, and cannon, and, last of all, the broad gold-pieces lost in the wreck of many a galleon on the Spanish Main, the whole forming a kind of false bottom to the ocean, beneath which there lay all the depth of clear, still water, which was heavier than molten gold. The conditions of pressure are certainly very extraordinary. At 12,000 feet a man would bear upon his body a weight equal to 20 locomotive-engines, each with a long goods-train loaded with pig-iron. We are apt to forget, however, that water is almost imcompressible, and that, therefore, the density of sea-water at a depth of 12,000 feet is scarcely appreciably increased."

Contrary to all anticipation, it was found that highly-organized representatives of all the invertebrate classes do live under these conditions of enormous pressure. The bottom of the ocean is, therefore, to be regarded as habitable, and is proved to be actually inhabited by numberless forms of animal life. A new world was thus opened to the naturalist, which, although difficult of access, was yet accessible and must be investigated. The pioneers in the exploration of course encountered very formidable obstacles; but the field was too vast and the promise too rich to be neglected, and how it was regarded by the devotees of research may be gathered from the following words of Dr. Thomson: