THE GEOSPHERES 437 



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 denned 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 }^ou 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 b}' analysis, while its quality is improved! 

 by synthesis. 1 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. 



