20 
AN INVESTIGATION INTO THE 
THE METHOD OF MEASUREMENT. 
In carrying out the measurements, prisms of the rock approximately i inch 
square and 3 inches long were usually employed (see fig- 4). These were 
cut and ground with smooth faces, but were not polished. In these two 
small round holes were drilled in the medial line of each vertical face for the 
purpose of attaching the instrument, when Young's modulus was to be 
measured. These holes were made by means of a small diamond drill and 
were perfectly round and smooth. They were each 0.05 to 0.08 inch in dia- 
meter and 0.125 inch deep and 1.25 inches apart, lying at equal distances 
above and below the center of 
the prisms. These holes were 
champfered at the outer end, 
as shown in figure 4, and were 
found to afford the most per- 
fect attachment which could 
be secured for the points of 
the instrument. By means of 
these prisms two sets of meas- 
urements of the vertical com- 
Detail of hole 
Hole 
1 
1 
FIG. 4. Square test specimen of rock. 
FIG. 5. Round test specimen, 
showing position of holes. 
pressiori could be made with each prism, by attaching the instrument 
first to one pair of opposite faces and then to the other._ 
In some cases round columns were used (see fig. 5) . These were approxi- 
mately i inch in diameter and 3 inches in length. With these it was possible 
to make four sets of measurements in compression with each column, by drill- 
ing eight pairs of holes, as above described, whose planes intersected at 
angles of 45 instead of 90 as in the square prisms. 
It was of course necessary in every case, whether prisms or columns were 
employed, to exercise great care to have the ends of the test pieces very 
