GEOPHYSICAL-CHEMICAL PROBLEMS SOSMAN. 233 



ti vely, with what results — whether rising or falling average tempera • 

 ture, increasing or decreasing volume, etc. — it is impossible now 

 to say. 



The preceding considerations apply also to the larger units of 

 structure of the interior — although what these units may be we can 

 only guess — and also to the earth itself as a unit. Complex mathe- 

 matical analysis is necessary in applying the data to the units of 

 structure as well as to the whole of a body as large as the earth, 

 where the force of gravitation is itself variable with depth. These 

 applications can in many cases be best made by those familiar with 

 the properties in question as measured in the laboratory. The course 

 of earthquake waves, to take an example of interest to the Section 

 of Seismology, is dependent both upon the elastic constants of the 

 earth's materials and the possible reflection and refraction of waves 

 at the boundaries of internal structural features. 



In this connection, the members of this Section could do a service 

 to the other Sections by making clearer the real meaning of some of 

 the physical concepts and physical constants involved in geophysical 

 problems. For instance, much confusion has been caused by the 

 fact that there is more than one kind of "rigidity." The geologist 

 to whom the statement that "the earth has the rigidity of steel" 

 is rather vague may take temporary comfort from the fact that the 

 statement also needs much qualification and explanation to the 

 physicist. 3 



General geophysics. — The physics of the earth considered as a unit 

 (the classical " geophysics ") is for the most part either covered by 

 other Sections of the Geophysical Union or is customarily considered 

 as a part of geology. Certain phases of geophysics, however, are 

 not thus assignable and may be mentioned here in order that all of 

 the groups of problems of the science may receive attention in this 

 assembly of surveys. 



The form and gravitation relations of our suspended spheroid, its 

 magnetic and electrical properties, its properties as a vibrating body, 

 and the physics of its air and water envelopes, are the obvious fields 

 of appropriate Sections. Hypotheses of its origin and the logical 

 deductions therefrom may confidently be left to the geologists, among 

 whose faults that of narrow-mindedness and lack of a broad outlook 

 in time and space have seldom been numbered. 4 Its properties as an 

 absorbing and reflecting body for external radiation are being well 

 handled by the astrophysicists and meteorologists. 



8 See Lambert, Journ. Wash. Acad. Sci., 10, 1920 (122-143). 



4 In this connection it is important that the study of the composition and probable 

 sources of the matter now being received by the earth, in the form of stony and metallic 

 meteorites, be continued and extended. 



