PRESENT PROBLEMS OF GEOPHYSICS 



BY GEORGE FERDINAND BECKER 



[George Ferdinand Becker, U. S. Geologist in charge of Division of Chemical 

 and Physical Researches, Geophysicist of Carnegie Institution, b. January 5, 

 1847, New York City. B.A. Harvard, 1868; Ph.D. Heidelberg, 1869; Mining 

 Engineer, Berlin, 1871. Instructor in Mining and Metallurgy, University of 

 California, 1875-79; Special Agent Tenth Census, 1879-83. Member of National 

 Academy; Geological Society of America; Washington Academy. Author of 

 numerous books and articles on geology.] 



ADVANCES in science are seldom made, without a view to the 

 solution of specific, concrete problems, even when the results of 

 investigation possess the widest generality. The history of science 

 is full of instances of the fruitfulness of researches the immediate 

 purposes of which were narrowly defined. Geophysics is only that 

 portion of general physics, including under that term physical 

 chemistry, which is applicable to the elucidation of the past history 

 and present condition of the earth. It is thus a very definite branch 

 of applied science, the exigencies of which call for the solution of 

 a group of related problems. These, however, possess great interest 

 apart from their application to the globe, while for the most part they 

 offer very serious experimental and theoretical difficulties. Had 

 they been easy, they might have been solved long ago, for many of 

 these problems have been propounded and more or less discussed 

 from the birth of modern science to the present day. Their difficulty, 

 not lack of recognition of their importance, has postponed their 

 solution. 



The main purpose of this paper is to deal with the order in which it 

 would be expedient to investigate the questions embraced under the 

 head of geophysics, but a brief and incomplete enumeration of the 

 problems from a geological standpoint will serve to lend a coherency 

 and a human interest to the subject which it would otherwise lack. 



Physical geology begins with the solar nebula and the genesis of 

 the earth-moon system. The harmonies of the solar system com- 

 pelled the immortal Kant and the ever-living Laplace to seek the 

 origin of the planets, the sun, and the other stars in heterogeneous 

 nebulas which they supposed to have condensed about one or several 

 nuclei. Every attempt to devise an essentially different hypothesis 

 has failed, and every history of the globe which begins after the birth 

 of the planet is unsatisfying. In the drama of the universe there 

 must have been pre-nebular scenes, but of these we have as yet no 

 inkling. The nebular hypothesis, as its authors propounded it, 

 explains the similarity in the composition of the members of the 

 solar system which is indicated by the analysis of meteorites and by 



