22 SECTIONAL ADDRESSES • 



title. Applied geophysics may clearly be taken to include certain aspects 

 of meteorology or oceanography or, indeed, any branch of knowledge in 

 which physics is applied, in the service of mankind, to the elucidation of 

 the properties of the earth. I propose to deal with what is in fact only 

 a limited field of work. Put briefly, it covers the application of physical 

 methods to the examination, without digging or boring, of what lies 

 beneath the surface of the earth at relatively shallow depths of less than 

 a few thousand feet. The apphcation is more particularly directed to 

 the discovery of deposits of economic importance, such as minerals or oil, 

 or the structural formations with which they are likely to be associated. 



Truly this is a subject as different as it could very well be from those 

 flights of theoretical physics — relativity, quantum theory, wave mechanics 

 and the like — which those of us with slower minds and more pressing 

 other occupations try so desperately to follow. In our admiration and, 

 perhaps, envy of the apparent ease with which the pioneers in these new 

 fields make progress, we are inclined, wrongly, I think, to allow it to be 

 assumed that modern physics and atomic physics are one and the same 

 thing. It should not be overlooked that physics is making rapid strides 

 forward also in other directions. Much that is new in the precision of 

 measurement, in the choice of methods, and in the invention and design 

 of physical tools for the attack on old problems hitherto unsolved, has 

 become in recent years added to our knowledge. This is true with regard 

 to the particular branch of physics we are now to consider. Its funda- 

 mental basis is not new. It involves no appeal to, let us say, wave 

 mechanics ; the old gravitational theory of Newton and the electro- 

 magnetic theory of Maxwell serve well enough our purposes. Yet its 

 successful application continues to demand the highest experimental skill 

 that training in physics can provide, and initiative ability equal to that 

 more frequently directed in less practical channels. 



My subject is also a border-line one, and, perhaps for that reason, has 

 not received as much attention as it deserves, at any rate in this country. 

 Its practice involves the co-operation of geologists with physicists, except 

 in those rare examples of the same person being expert in both branches 

 of knowledge. This co-operation is desirable for many reasons, and 

 essential for others. The geologist, if I may say so, is more practically- 

 minded than the physicist. He puts a higher monetary value upon his 

 work, and he is bolder in the expenditure of money upon exploratory 

 investigations. His experience in the field accustoms him to the rigours 

 of work out of doors as compared with the calm of a laboratory, and he 

 is more ready to attack problems at first sight unlikely to be soluble. 

 He has a keener eye, too, regarding the economic results of his field work. 

 As illustrating these points I can do no better than relate the fact that it 

 was a famous geologist, the late Prof, de Bockh, who suggested to the 

 equally famous physicist. Baron von Eotvos (whose work we shall con- 

 sider more fully later), that the Eotvos torsion balance should be used to 

 locate and delineate buried salt domes — geological features with which 

 oil is frequently associated. Prof, de Bockh once told me that at first 

 Eotvos was horrified at the idea. He regarded the use of his instru- 

 ment for such an economic purpose as debasing science, and it was only 



