National Geographic : 1898 Oct
THE GEOSPHERES matter, which it is convenient to call the lithosphere-the third of the four geospheres. While observation of terrestrial things ends with the atmos phere and hydrosphere and lithosphere, definite thinkers find it necessary to form some idea of the constitution of the interior portions of the planetary mass at depths below the reach of di rect vision. Now knowledge of the earth's interior is gained not through geology but through the sister science, astronomy. You are aware that within recent years astronomers have re duced to system our sun, the planets and asteroids which circle about it, the satellites which follow the planets, and the long mysterious rings of Saturn-the various constituents of our solar system ; and the paths of the planets and satellites have been surveyed, while each of the bodies has been measured and weighed, so that their volumes and densities are known with considerable accuracy. Let me indicate the accuracy with which this astronomical work has been done by saying that sun, planet, and satellite have been weighed with an accuracy no less than that of the grocer in dealing out sugar and tea, and that the orbits of planets, satellites, and asteroids have been surveyed as accurately as the roadways and even the railways of the earth's surface. The earth itself has been weighed, with somewhat less accuracy than the other planets, it is true, yet with sufficient accuracy to indicate that its mean density is nearly six times that of water (5.6 ±), or more than twice that of the known lithosphere. Accordingly it is known beyond peradventure that the earth has an interior portion much denser than the known exterior; and this somewhat vaguely defined part of the earth may conveniently be called a centrosphere-the innermost of the four geospheres. In the light of these definitions, you will understand that my object in coming before you is not so much to say new things as to try to establish a new point of view. Knowledge pro gresses in two ways which are interrelated yet fairly distinct; the first is analysis and the second is synthesis; the sum of knowledge is increased by analysis, while its quality is improved by synthesis. I am now attempting, not to bring new facts be fore you, but to put old facts together in a new way, and thus to carry you to a higher plane in the synthesis or generalization of a wide range of observations; and I am seeking to do this in such manner as to reflect the workings of another man's mind the mind of the real author of this address.