ME. EOBEET MALLET ON VOLCANIC ENEEGY. 
185 
13. Syenite. — Mount Sorrel, Leicestershire. 
14. Blue granite. — Aberdeenshire. 
15. Grey granite. — Aberdeenshire. 
16. Porphyry. — Furnace Quarry, Inverary, Scotland. 
108. Of each of these sixteen species of rock, half a dozen cubes, each as nearly as 
possible 1-5 inch on the edge, were prepared. Each set of cubes was roughed out from the 
same selected block of stone, and brought to the exact cubic form and size by grinding by 
Messrs. Field and Co., of Westminster, by whose care, with the help of their fine stone- 
working machinery, the work was done in a very excellent manner. 
A larger-sized cube than 1'5 inch on the edge could scarcely have been employed, as 
respects the harder rocks, with safety to the testing-machine ; but it is believed that no 
series of crushing experiments on rocks has previously been conducted on cubes so 
large. 
109. The cubes could not be produced of precisely the same dimensions; hut all were 
accurately measured before crushing by the instruments described, and the results reduced 
to a common standard. 
110. The most scrupulous care, however, was taken to secure two opposite faces in each 
cube rigidly parallel to each other, so as to avoid unequal hearing when being crushed ; 
and this result was fully attained by cementing the whole of the cubes down upon a flat 
metallic plate, and grinding off the uppermost faces simultaneously by another like plate, 
and then reversing the cubes and cementing them down again by the last ground face, 
repeating the process. 
The experiments were conducted at Crewe works in August 1870, Mr. Moorsom, C.E., 
assisting at all of them. Three good experiments were obtained for each description of 
rock, in some instances more. 
111. Each experiment was conducted in the following manner: — 
The testing-lever being raised by the hydraulic press, the crushing-plunger was raised, 
by a small hand lever of wood, from the base-plate of the cage sufficiently to admit of 
placing the cube. 
The cube was then placed on the base-plate centrally, or with its centre of figure truly 
under the axis of the plunger. 
A square piece of the thinnest and most Aarc?-pressed letter-paper was placed upon 
the top and bottom faces of the cube, the size of the squares of paper being (h20 inch 
less than the edge of the cube, so as to allow a free margin of OTQ inch all round each 
of these faces, the object being by this very thin film of more compressible material to 
neutralize any residual departure from absolute parallelism between the upper and lower 
faces, and so secure perfect uniformity of bearing, a method which was found to succeed 
perfectly. 
112. The cube being in place, the plunger was gently and without shock lowered upon 
it ; and in like manner the lever itself, by aid of the hydraulic press, was lowered so as 
to bear upon the head of the plunger. The weight of the unloaded lever was then per- 
