PROFESSOR F. D. ADAMS AND DR. J. T. NICOLSON 
steady for weeks at a time when necessary by means of a small spring relief valve (a) 
with an adjusting screw, so that the water from the mains is allowed to overflow at 
any desired pressure, which thus cannot he exceeded. A recording gauge ( b ) attached 
to cylinder (C) registers the history of the experiment throughout its course. The 
allowance to be made for the friction of the 20-inch diameter cup leather was care¬ 
fully determined, so that a close estimate of the pressure to which the rock is sub¬ 
jected can be formed. This was done by observing the amounts of compression of a 
specimen of hard steel due to various loads applied by a Buckton testing machine, 
and then inferring the loads to which it was afterwards subjected in the actual press 
from the compressions to which these gave rise. The compressions were measured by 
means of a Martens’ mirror extensometer reading to the l/l00,000th of an inch; and 
any possible difference in the Young’s modulus of the steel in two successive loadings 
was got rid of, after the manner of Bauschinger, by first alternately stretching and 
compressing it, and so reducing it to a “ state of ease.” In this way the cup leather 
friction was found to be approximately constant in quantity (■ i.e ., independent of the 
pressure) within the limits of pressure employed, and to amount to about 400 lbs. 
Thus, if p be the gauge-pressure in the 20-inch cylinder, and P the pressure per 
square inch on the rock, of area a, we shall have - 
p _ 3 1-p; - 400 |^ e ’ n g j n g q_ inches). 
Cl 
We may tabulate the values of P for the three sizes of rock cylinder employed, 
viz., 1 inch, 0‘8 inch, and 0’4 inch diameter, corresponding to various values of p, 
from 50 lbs. to 300 lbs. per square inch in the cylinder (C). (The latter was the 
greatest pressure allowable in the 20-inch cast-iron cylinder as designed.) 
p- 
Rock 1 inch dia. 
Rock ‘8 inch dia. 
Rock "4 inch dia. 
P., lbs./sq. in. atm. 
lbs./sq. in. 
atm. 
lbs./sq. in. 
atm. 
50 
19,500 1330 
31,300 
2130 
125,300 
8530 
100 
39,500 2680 
63,400 
4320 
253,500 
17,200 
200 
79,500 5400 
127,600 
8700 
510,300 
34,700 I 
300 
119,500 8150 
191,800 
13,050 
767,100 
52,100 ! 
It having been ascertained that columns of the Carrara marble, 1 inch in diameter 
and 1'585 inch high, crushed at a pressure of from 11,430 to 12,026 lbs. to the square 
inch when free from any lateral support, the column enclosed in its wrought-iron tube 
in the manner above described was placed in the machine and pressure applied 
gradually, the exterior diameter of the tube being accurately measured at frequent 
intervals. No effect was noticeable until a pressure upon the marble, varying of 
course with the thickness of the enclosing tube, but ordinarily about 18,000 lbs. to 
