AN INVESTIGATION INTO THE ELASTIC CONSTANTS OF ROCKS, 
MORE ESPECIALLY WITH REFERENCE TO CUBIC 
COMPRESSIBILITY. 
INTRODUCTION. 
The question as to the amount of cubic compression which rocks may 
undergo under the stresses to which they are subjected in the earth's 
crust is one which has a direct bearing on many very important problems 
in geophysics. It is, however, a subject which has been but little investi- 
gated as the experimental difficulties connected with it are very considerable. 
The importance of a series of determinations of the cubic compressibility 
of a few typical plutonic igneous rocks was some time since impressed 
upon the authors by Mr. G. K. Gilbert, with a request that if possible they 
should make such determinations in connection with the researches on rock 
deformation which are now being carried out at McGill University under 
the auspices of the Carnegie Institution of Washington. An examination 
of all the direct methods proposed or adopted for the measurement of the cubic 
compressibility of solids showed that none of these could be satisfactorily 
applied to such materials as rocks, but the indirect methods based on Hook 's 
law and which have been applied to metals and other compact iso tropic bodies 
having an approximately perfect elasticity promised to give satisfactory re- 
sults if applied to certain rocks, more especially to the class of rocks referred 
to above, viz, the acid and basic plutonic rocks, which form the greater 
part at least of the outer portions of the earth's crust. The present paper 
sets forth the methods adopted and the results obtained. 
The work which was carried out in the laboratories of McGill University was 
commenced by the authors whose names appear on the title page, and was 
carried well towards completion when Dr. Coker was called to take the 
professorship of mechanical engineering in the Finsbury Technical Institute 
of I/ondon, England. He was accordingly obliged to give up the work of 
the research and his place was taken by Mr. Charles McKergow, lecturer 
in mechanical engineering in McGill University, but who immediately on 
the completion of the work was appointed to the professorship in mechanical 
engineering in the University of Virginia. A large number of the very care- 
ful measurements of elastic constants which are given in the paper were 
made by the latter gentleman. 
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