ELASTIC CONSTANTS OF ROCKS. 19 
investigators to be "preliminary," can as yet hardly be taken as of general 
application to all rocks, even if correct for the specimen of sandstone examined. 
In our own investigations the laboratory was maintained at a temperature 
of from 63 to 68 F. (17.2 to 20 C.), and a thorough investigation into 
the effect of temperature was not undertaken, as this would be very difficult 
to carry out when employing the method of direct compression used, the diffi- 
culty consisting in heating the specimen itself without in any way affecting 
the measuring apparatus attached to it. 
It seemed, however, possible to ascertain whether any serious change in the 
elastic constants of the massive crystalline rocks employed in the present 
investigation would result from a moderate change of temperature. For 
purpose of trial the rock selected was the Sudbury diabase, a typical fine-grained 
plutonic rock. A column of it was placed by Mr. McKergow in a small test- 
ing machine having a capacity of 50 tons, and the temperature of the room in 
which the machine was set up having been lowered to -I- 10 F., a cycle of 
compression readings were taken in the usual way adopted when Young's 
modulus is to be determined. The temperature of the room was then raised 
by about 10 and another cycle of readings were taken. It was then raised 
another 10 and a third series of readings were obtained, and so through suc- 
cessive stages of 10 until the normal temperature of the room (about 65 F.) 
was reached. The initial reading of the instrument before the application of 
pressure was of course different in each case, owing to the expansion of the rock 
which followed from heating. These initial points were plotted on a line, 
and the results obtained when the specimen was subjected to a certain 
maximum load, together with the increase of temperature at each stage, were 
plotted on a second line. If the compression was greater at 65 than at 10 for 
the same load these two lines should have diverged, but as a matter of fact 
they were practically parallel. The differences between the readings given by 
the same load at different temperatures were no greater than those obtained by 
different measurements under the same load at the same temperature. The 
conclusion therefore seems to be indicated that a change of temperature made 
no perceptible difference within the range of temperatures employed, although 
a difference of 0.5 percent for each degree centigrade, which was Nagaoka's 
result, would mean a difference of about 25 per cent in range of temperature 
employed by Mr. McKergow. 
While, therefore, this experiment can not be considered as supplying accurate 
information concerning the effect produced by a rise in temperature on the 
elastic constants of rocks, for the instruments themselves are in some measure 
affected by the same changes of temperature, they serve to show that in the 
case of the massive crystalline rocks the influence of temperature is probably 
not very great. The subject is one which requires further investigation. 
