Depth of the Ocean All measurements of depth, by which we ascertain the relief of that part of the earth’s crust covered by water, are referred to the sea-surface; the measurements of height on the land are likewise referred to sea-level.
It is admitted that the ocean has a very complicated undulating surface, in consequence of the attraction which the heterogeneous and elevated portions of the lithosphere exercise on the liquid hydrosphere.
Our knowledge of the ocean is still very incomplete.
So much has, however, already been acquired that the historian will, in all probability, point to the oceanographical discoveries during the past forty years as the most important addition to the natural knowledge of our planet since the great geographical voyages associated with the names of Columbus, Da Gama, and Magellan, at the end of the fifteenth and the beginning of the sixteenth centuries.
Wireline sounding had been invented by Sir William Thomson, steel cable for dredging operations and other oceanographic purposes had been introduced, and great strides had been made in biological, chemical, geological and physical oceanography. A great many sciences were enriched by a grand accumulation of new facts.
Dominating this new science of the sea was Sir John Murray of the Challenger Expedition. Large collections were sent and brought home, and were subsequently described by specialists belonging to almost every civilised nation.
In the following essay, Sir John Murray describes the then state of knowledge of the oceans of the world; and like Edward Forbes, many years before, ends his essay with a plea for funding, both from the government and private individuals for, not oceanic exploration, but the exploration of the Antarctic regions. Since the Challenger Expedition there has been almost a revolution in the methods employed in deep-sea observations.
Down to that time there had been no systematic attempts to ascertain the physical and biological conditions of those regions of the earth’s surface covered by the deeper waters of the ocean; indeed, most of the apparatus necessary for such investigations had not yet been invented. This section of the map shows the Mid-Atlantic Ridge as well as all areas of the Atlantic Ocean and eastern Pacific Ocean where depths greater than 3,000 fathoms (deeps) had been discovered. It was the desire to establish telegraphic communication between Europe and America that gave the first direct impulse to the scientific exploration of the great ocean-basins, and at the present day the survey of new cable routes still yields each year a large amount of accurate knowledge regarding the floor of the ocean.
In that very able and detailed review there is no reference whatever to the work of the numerous expeditions which had been fitted out by this and other countries for the exploration of the depths of the sea, nor is there any mention of the great advance in our knowledge of the ocean during the period of sixty-five years then under consideration.
The most profound abysses of the ocean are now being everywhere examined by sailors and scientific men with increasing precision, rapidity, and success.