32 CARNEGIE INSTITUTION 



One of the most hopeful resources for disclosing the constitution 

 and conditions of the interior is found in the transmission of earth- 

 quake vibrations directly through the body of the earth, such as are 

 now being recorded in different parts of the globe. These disclose 

 extraordinary elasticity in the center of the earth, but before this 

 fact can be safely interpreted the effects of pressure and heat on the 

 elasticity of different classes of earth material in its different 

 states need to be determined with the greatest practicable precision 

 for the greatest practicable range of pressures, temperatures, mate- 

 rials and states of materials. 



As a factor in the great problem of interior heat, the compressi- 

 bilit}^ of rock material, the amounts of heat developed in compres- 

 sion and recrystallizatiou need careful determination, and, if possi- 

 ble, also the question whether compressibility has definite limita- 

 tions or not. 



Intimately related to the problems outlined above, and to a great 

 extent doubtless entangled with them, are the problems of physical 

 geodesy and terrestrial magnetism. Important light on the distri- 

 bution of mass in the crust and nucleus of the earth must be derived 

 from an extended gravimetric survey of the earth's surface. The 

 various national geodetic surveys may be depended on to furnish an 

 increasing amount of data in gravimetric measures, but it ought to 

 be one of the functions of a geophysical laboratory to assist ac- 

 tively in such work, which is largel}^ incidental to the operations of 

 geodesy. 



Similarly the problem of terrestrial magnetism belongs rather with 

 geophysics than geodesy. It appears to be indeed, in some of its 

 aspects, a cosmological question, and should be studied as an impor- 

 tant problem in itself rather than as one incident to geodetic and 

 topographic work. 



3. The relation of the earth to neighboring bodies, its motions 

 and the modification of its form imposed by these, also constitute a 

 record of the earth's history, and a forecast of its future, since the 

 organization of a planet or a planetary system is as much the record 

 of past events as the organization of a rock or a system of sedi- 

 ments, but it is extremely difficult to read. It can only be deciph- 

 ered positively when the sign manual of planetary dynamics is 

 made as legible as that of the water sediments is now by critical re- 

 search, chiefly of a mathematico-pli3^sical type, aided by laboratory 

 verification. For example, the relations of the earth and moon and 

 their rotations undoubtedly record a history of tidal reactions and of 



