Page:Popular Science Monthly Volume 10.djvu/572

554 (which is less than a mile); that, whatever might be the age of the earth, we might be sure that it was solid in the interior—not through its whole volume, as there were spaces in volcanic regions occupied by liquid lava, but that this portion was small in comparison to the whole—and that any geological hypothesis must be rejected which assumes that the earth is a shell resting on a liquid mass. He also considered the question, first, of the accuracy of the earth as a timekeeper; and, second, the permanence of its axes of rotation. Since the first known observation of an eclipse of the moon at Babylon, on the 19th of March, 721 the earth has lost a portion of its velocity, and is now, as a timekeeper, going slower; and his observation upon the question of the earth's axis was, in effect, that if causes existed adequate to produce a change in the position of the axis by the upheaving of the surface, or otherwise, the result, even if sudden, would not be very great, or produce any extraordinary effect. Many important observations were made, at the same meeting, upon the tides, ocean temperature, and currents, and upon the physical geography of the sea, founded upon the results of the voyage of the Challenger."

Of this expedition Sir Wyville Thomson has given the general results. The superficial area of the world is 197,000,000 square miles, of which 140,000,000 are covered by the sea at an average depth of 15,000 feet. The floor of this region is, to a certain degree, comparable to the land. It has its hills, valleys, and great plains; its various soils; its climates, and its special races of inhabitants, depending on the conditions of climate and soil for their distribution.

"The vessel departed from England in December, 1872. She crossed the Atlantic four times in 1873, in a course of nearly 20,000 miles. In 1874 she went southward from the Cape of Good Hope, dipping within the antarctic circle as far as she could, and then traversed the Australian and New Zealand seas and the interior of the Malay Archipelago, arriving at Hong-Kong on November 10, 1874, after a run in that year of 17,000 miles. In 1875 she traversed the Pacific, in a course of about 20,000 miles, and then crossed the Atlantic for the fifth time, reaching England May 24, 1876. The three general results are—1. The knowledge obtained of the contour of the bottom, and the nature of the deposits now being formed. 2. The distribution of deep-sea climate. 3. The nature and distribution of the peculiar race of animals now found at the bottom of the sea. In the Pacific there is an enormous extension of water of great depth—in many cases beyond 18,000 feet. In the North Atlantic the greater portion has a depth of 12,000 feet; and in the South Atlantic, on each side of what is known as the Dolphin rise, there are troughs usually 18,000 feet deep, which form marked depressions roughly parallel with the arc of the South American and African Continents. The whole bottom of the sea is gradually receiving accumulations, giving rise to formations which must be regarded as the rocks of the future. The débris of