10 
AN INVESTIGATION INTO 
Of these marbles No. 1 1, if a mean of the two readings be taken, has about the 
same modulus as the average of those on our list, while No. 12 is very much 
lower. The highest value given for any granite in Nagaoka's list, viz, No. 69, is 
somewhat higher than that of the lowest of the granites in our series, that from 
Stanstead. The other granites examined by Nagaoka have values for E 
assigned to them which are so low that they are comparable only to that of 
the sandstone in our series. Of the three sandstones included in Nagaoka's 
list the Izumi sandstone of the Mesozoic has modulus of 1,322,000, while 
the other two, which belong to the Diluvium, have values for E of 587,500 
and 583,000, respectively. 
And so when an attempt is made to calculate the cubic compression D 
from the values given in Nagaoka's list and obtained by his method, it is 
found that a negative value is actually obtained in about one-third of the rocks 
which he has examined. His figures, however, were intended chiefly for the 
purpose of calculating the velocity of the propagation of earthquake shocks. 
FIG. i. Instrument for determining the modulus of a simple strain. 
In consequence of the somewhat unsatisfactory results obtained in our pre- 
liminary experiments with this method, as well as the facts with regard to 
Nagaoka's figures just mentioned, it was decided to adopt a somewhat 
different method and one which avoided both torsion and flexure and depended 
simply on strain produced by simple compressive stress. This will be termed 
the "method of simple compression. " 
Among the possible indirect methods, this seems to be the most satisfac- 
tory, as the assumptions necessary in the calculation of compressibility are 
reduced to a minimum, and the range of stress for which the ratio of stress 
to strain is practically constant is great. We were able to measure the 
strains obtained very accurately, by means of an apparatus forming part 
of the equipment of the testing laboratory of McGill University, for the 
use of which we are indebted to Dean Bovey . 
This is an instrument designed by Professor Bwing, and of which a diagram- 
matic representation is given in figure i , in which A is a specimen of the rock 
