4 PAUL WEAVER 
physics, including geophysics, unless he needs them to solve a geo- 
logical or a mechanical problem not readily understood by his former 
teaching and its interpretation of his former experience. 
Geophysics, like geology and like chemistry, began with the find- 
ing of novelties. For example, the first chemists mixed together vari- 
ous combinations of substances and observed that, although usually 
the substances preserved their identity, and could subsequently be 
separated, in some cases, substances were changed by juxtaposition, 
and lost their identity, so that new names were necessary for the 
resultant new substances. Chemistry of twenty-five years ago was 
principally a memorizing of names of the substances which were 
formed by the juxtaposition, technically called a “‘reaction,”’ of other 
substances. Now, however, chemistry not only foretells the products 
of a reaction, under different environments, but calculates numerically 
the rate at which the reaction is carried out and the heat evolved dur- 
ing the process. 
In geology, both applied to mining and to oil, pioneers were look- 
ing for novel structures, such as anticlines and faults, which they had 
found to be present where known commercial deposits existed. Now, 
however, a change similar to that of chemistry has come in geology. 
In geology we now talk about the amount of closure on the surface 
beds of an anticline, the number of feet of throw and of hade of a 
fault. 
Our latest development in geophysics has been an endeavor to 
give profiles and contour maps to the anomalies which we discover. 
Now this advance in geophysics requires very accurate measurements, 
which means a very careful calibration of the measuring device, espe- 
cially in view of the fact that these measurements are carried on in 
the field and can not be exempt from the effects of variations in 
temperature and in other factors of operating environment. 
Although further improvements are constantly being made, the 
instruments now available for geophysical measurements in most 
cases already have the precision necessary for the present state of the 
art. 
It is also generally agreed that the technique of operation is ad- 
vancing equally with the instrumental precision and is already being 
handled satisfactorily by the experienced operators. 
The present high specialization in instruments and technique is 
gratifying, but does not insure that geophysics can successfully solve 
all the problems which it is now attempting. We must find out whether 
the problems are theoretically capable of solution, and I must assume 
in the discussion which follows, on the part of the geologists, a certain 
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