28 CAXNKGIE INSTITUTION 



other celestial bodies. The earth presents the grandest concrete ex- 

 ample, and the grandest congeries of concrete examples, of the 

 properties of matter available to us. The phenomena presented by 

 the earth are the historical products of chemical and physical forces. 

 From the phenomena we infer the nature of the chemical and phy- 

 sical forces which produced them. Howe\'er, these inferences re- 

 quire confirmation or refutation by special chemical and pliysical 

 tests. Usually the phenomena are complex, and it is impracticable 

 to decide between a number of hypotheses as to the manner in 

 which the chemical and physical forces have accomplished the 

 results. In such cases experimental work is absolutely essential in 

 order to make correct inferences as to the nature and manner of 

 work of the forces which have produced the phenomena observed 

 Moreover, the history of the earth, in large part well preserved in the 

 rocks, is undoubtedly typical of the history of the other x^l^iuets of 

 the solar system, and hence affords a key to the problems of stellar 

 systems in general. 



Geophysics, using the term broadly to include geochemistry and 

 related sciences, is founded on pure physics and chemistry ; its data 

 are supplied chiefly by geology : and the ramifications of its super- 

 structure extend into astronomy and astrophysics. 



The principles of physics have been demonstrated experimentally 

 for only a very limited range of conditions. The experiments of 

 physical laboratories usually relate to small masses only, under ordi- 

 nary pressures and moderate temperatures, with brief time limits. 

 The problems of the earth involve immense masses, extraordinary 

 pressures, very high temperatures and enormous lapses of time. 

 Before the results of ordinary experiments can be safely applied to 

 the great earth problems, they must be tested for the most extreme 

 ranges of mass, pressure, temperature and time that can be com- 

 manded. It is quite certain that nearly all the deductions from 

 experiments under common surface conditions are subject to modifi- 

 cation under the extraordinary condition? of the earth's interior, and 

 the nature of these modifications must be determined before safe 

 application of the deductions can be made. It is obvious that the 

 determinations reached by such geophisical researches will be con- 

 tributions of a high order of value to the science of physics itself. 



(b) The province of laboratories of geophysics. There are three 

 great fields which should be embraced within the researches of the 

 laboratory These blend into each other and embrace tnany minor 

 fields and the researches in each will contribute to those of the oth- 



