THE sea covers nearly three-fourths of the surface of the earth, and, until within the last few years, very little was known with anything like certainty about its depths, whether in their physical or their biological relations. The popular notion was, that after arriving at a certain depth the conditions became so peculiar, so entirely different from those of any portion of the earth to which we have access, as to preclude any other idea than that of a waste of utter darkness, subjected to such stupendous pressure as to make life of any kind impossible, and to throw insuperable difficulties in the way of any attempt at investigation.

Even men of science seemed to share this idea, for they gave little heed to the apparently well-authenticated instances of animals, comparatively high in the scale of life, having been brought up on sounding lines from great depths, and welcomed any suggestion of the animals having got entangled when swimming on the surface, or of carelessness on the part of the observers. And this was strange, for every other question in Physical Geography had been investigated by scientific men with consummate patience and energy. Every gap in the noble little army of martyrs striving to extend the boundaries of knowledge in the wilds of Australia, on the Zambesi, or towards the North or South Pole, was struggled for by earnest volunteers, and still the great ocean slumbering beneath the moon covered a region apparently as inaccessible to man as the 'mare serenitatis'.

A few years ago the bottom of the sea was required for the purpose of telegraphic communication, and practical men mapped out the bed of the North Atlantic, and devised ingenious methods of ascertaining the nature of the material covering the bottom. They laid a telegraphic cable across it, and the cable got broken and they went back to the spot and fished up the end of it easily, from a depth of nearly two miles.

It had long been a question with naturalists 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 question of a 'zero of animal life' and to determine with precision the composition and temperature of sea-water at great depths. An investigation of this kind is beyond the ordinary limits of private enterprise. It requires more power and sea skill than nuturalists can usually command. When, however, in the year 1868, at the instance of my colleague Dr. Carpenter and myself, with the effective support of the present Hydrographer to the Navy , who is deeply interested in the scientific aspects of his profession, we had placed at our disposal by the Admiralty sufficient power and skill to make the experiment, we found that we could work, not with so much ease, but with as much certainty, at a depth of 600 fathoms as at 100; and in1869 we carried the operations down to 2,435 fathoms, 14,610 feet, nearly three statute miles, with perfect success.

Dredging in such deep water was doubtless very trying. Each haul occupied seven or eight hours; and during the whole of that time it demanded and received the most anxious care on the part of our commander, who stood with his hand on the pulse of the accumulator ready at any moment, by a turn of the paddles, to ease any undue strain. The men, stimulated and encouraged by the cordial interest taken by their officers in our operations, worked willingly and well ; but the labour of taking upwards of three miles of rope coming up with a heavy strain, from the surging drum of the engine, was very severe. The rope itself, 'hawser-laid,' of the best ltalian 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 this extraordinary ordeal much longer.

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 improving machinery, and with ever-increasing knowledge. For the bed of the deep sea, the 140,000,000 of square miles which we have now added to the legitimate field of Natural History research, is not a barren waste. It is inhabited by a fauna more rich and varied on account of the enormous extent of the area, and with the organisms in many cases apparently even more elaborately and delicately formed, and more exquisitely beautiful in their soft shades of colouring and in the rainbow-tints of their wonderful phosphorescence, than the fauna of the well-known belt of shallow water teeming with innumerable invertebrate forms which fringes the land. And the forms of these hitherto unknown living beings, and their mode of life, and their relations to other organisms whether living or extinct, and the phenomena and laws of their geographical distribution, must be worked out.