184 
MB, EOBEBT MALLET ON* VOLCANIC ENEEGY. 
shown in Plate IX. fig. 2, was prepared to receive each cube when exposed to pressure, 
which was applied by a cylindrical steel plunger moving freely in a deep cylindrical 
hole bored in the upper part. The lower part of the cage consisted of a flat steel plate 
upon which the cube of stone was placed, when the lower end or opposite face of the 
plunger applied itself to the top of the cube. 
Thus the pressure upon the cube was preserved rigidly in the one vertical direction, 
whatever might be the motion (through a small arc) of the bearing edge of the lever 
itself upon the summit of the plunger. A small hydraulic press fixed between the 
fulcrum of the lever and this cage enabled the lever (and load if required) to be raised 
off from the head of the plunger at any time, and also enabled the cube about to be crushed 
to be conveniently placed between the faces of the crushing-cage without shock or any 
pressure acting upon it, except the small weight of the plunger itself; after which, by 
letting the water slowly out of the hydraulic-press cylinder, the bearing edge of the lever 
was brought gently and without jar or shock upon the head of the plunger, and the 
successive increments of load thereon then proceeded with. 
The crushing-cage admitted of very precise measurements of the vertical distance 
between the crushing faces (?'. e. that of the plunger and of the plate on which the cube 
was placed) at any instant. 
Those distances from the commencement to the conclusion of each experiment were 
measured with great exactness by means of “ distance callipers,” with multiplying arms 
(on the same principle as “ proportional compasses ”) increasing the indication tenfold, 
and provided with graduated arcs and verniers made by Becker (now Elliott Brothers), 
the indications being controlled by ordinary beam-calliper measurements read off from 
a steel diagonal scale. These measurements admitted of being made within less than 
UToW °f an inch. 
107. The following selection of rocks was made as tolerably well representing litho- 
logically the whole series in depth of the earth’s known crust from the least to the most 
rigid and coherent formations, viz. : — 
Rocks experimented on. 
1. Oolite. — Caen and Normandy. 
2. Oolite. — Portland stone. 
3. Dolomite. — Magnesian limestone, Yorkshire. 
4. Sandstone. — Bradford, Yorkshire. 
5. Sandstone. — Ayre Hill, Yorkshire (fine texture). 
6. Sandstone. — Bramley Fall (hard millstone-grit). 
7. Carboniferous limestone. — Devon marble. 
8. Cambro-Silurian. — Conway slate (North Wales). 
9. Cambro-Silurian. — -Bangor slate (North Wales). 
10. Basalt (greenstone). — Rowley Bag, Staffordshire. 
11. Bed granite. — Dartmoor, Devon. 
12. Grey granite. — Guernsey. 
