Sosman — Work of the Geo physical Laboratory. 255 



Art. VIII A. — The Work of the Geophysical Laboratory 

 of the Carnegie Institution of Washington; by R. B. 



SoSMAX. 



There are three methods of approach to the great 

 problem of rock formation. The first undertakes to 

 reproduce by suitable laboratory experiments some of 

 the observed changes in natural rocks. The second seeks 

 to apply the principles of physical chemistry to a great 

 body of carefully gathered statistics. The third method 

 of attack is like the first in being a laboratory method, 

 and like the second in seeking to apply existing knowl- 

 edge to the association of minerals as found in rocks, but 

 in its procedure differs widely from both. It consists of 

 bringing together pure materials under measurable con- 

 ditions, and thus in establishing by strictly quantitative 

 methods the relations in which minerals can exist 

 together under the conditions of temperature and pres- 

 sure that have the power to affect such relations. 



It is to this third method of investigation of the prob- 

 lems of the rocks that the Geophysical Laboratory has 

 been devoted since its establishment in 1905. It has 

 proved entirely practicable to make quantitative studies 

 of the relations among the principal earth-forming 

 oxides (silica, alumina, magnesia, lime, soda, potash, and 

 the oxides of iron) over a very wide range of tempera- 

 tures. The resources of physics have proved adequate 

 to establish temperature with a high degree of precision 

 and to measure the quantity of energy involved in the 

 various reactions. The chemist has been able to obtain 

 materials in a high degree of purity, and to follow out in 

 detail the chemical relationships that exist among the 

 earth-forming oxides. The petrographic laboratory has 

 been available for the comparison of synthetic laboratory 

 products with the corresponding natural minerals. 



It has als-o proved entirely practicable to extend the 

 same methods of research to some of the principal ore 

 minerals such as the sulphides of copper. Other infor- 

 mation which is certain to be of ultimate economic value 

 has also come out of the thorough study of the silicates, 

 which are basic materials for the vast variety of indus- 

 tries which are classed under the name of ceramic indus- 



