DEPTH OF ZONE OF FLOW IN THE EARTH’S CRUST 105 
In every experiment a column of the rock, very accurately 
ground to the dimensions of .5 inch in diameter and 1.57 inch 
long, was taken and through it two holes were drilled. These 
holes were, as nearly as possible, .o5 inch in diameter. One of 
these passed through the vertical axis of the column from top to 
bottom. The other passed transversely through the middle of the 
column, being at right angles to the other hole but a little to one 
side of it, so that the two holes did not actually intersect. A wire 
was then drawn to fit the hole exactly, so that the slightest change 
in the diameter of the hole could be detected by passing the wire 
into it. 
A round bar of nickel steel, 34 inches long and 2% inches in 
diameter, was then taken and a hole very slightly smaller in diam- 
eter than the rock column was accurately drilled through it in 
the direction of the longitudinal axis. This bar was then heated 
slightly, and thus expanded just sufficiently to allow the column 
of rock to be slipped in so as to octupy a position in the middle of 
this bar or thick-walled tube. The tube was then allowed to cool. 
The perforated rock column enclosed in its steel tube is shown in 
Fig. 2. The rock was thus held firmly on all sides by the steel, 
but the size of the hole was such that the shrinking of the tube 
upon the column did not compress the rock more than was required 
to effect a perfect mechanical fit, and in this way to give the requisite 
lateral support to the rock when the latter was submitted to com- 
pression in a vertical direction. Preliminary experiments showed 
that this operation did not in the slightest degree affect the size 
of the holes which had been bored through the column, and also 
showed that if the latter were unsupported below, a load of 7,250 
Ibs. on its upper end would shove it down through the tube. 
If the experiment was to be conducted at ordinary tempera- 
tures, a disk of paper was then placed on either end of the column 
to equalize the pressure and two pistons of hardened “Novo” 
steel, ground so as to pass easily into the ends of the tube were 
inserted, by means of which pressure could be brought to bear 
upon the enclosed column. The whole was then placed in a power- 
ful press and the enclosed rock submitted to a pressure equivalent 
to any required depth beneath the surface of the earth for a period 
