55+ THE POPULAR SCIENCE MONTHLY. 



(which is less than a mile) ; that, whatever might he the age of the 

 earth, we might he sure that it was solid in the interior not through 

 its whole volume, as there were spaces in volcanic regions occupied 

 by liquid lava, hut that this portion was small in comparison to the 

 whole and that any geological hypothesis must he 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 time- 

 keeper; 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 b. c, 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 up- 

 heaving of the surface, or otherwise, the result, even if sudden, would 

 not be very great, or produce any extraordinary effect. Many impor- 

 tant 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, compar- 

 able to the land. It has its hills, valleys, and great plains; its vari- 

 ous 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, dip- 

 ping 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 debris of 



