ME. EOBEET MALLET ON VOLCANIC ENEEG-Y. 
181 
evolved is almost precisely the equivalent of the work expended in deformation. No 
experiments (except those now to be detailed) have been made, however, so far as the 
writer knows, upon rigid bodies, such as rocks &c., to determine whether this is likewise 
true of them, although a priori the fact could scarcely be doubted. 
99. A few preliminary experiments were made to ascertain if this was the fact. A short 
cylinder of thin iron (a a, fig. 8) was lined with hard wood ( c c), an iron plunger ( b ) was 
fitted to the interior, the diameter of which just admitted, 
without touching at the arrises (e), a cube of 1 inch on the 
side. The cylinder placed on a plate of iron (f) had a cir- 
cularpiece of moderately thick paper gun-wadding dropped 
into it; upon this the cube to be crushed was placed ; upon 
the top of the cube another piece of gun-wadding, and then, 
the plunger (b) being inserted and made to bear firmly on 
the matters below it, a known weight (25 lbs.) was dropped 
from a known and constant height upon the plunger so as 
to crush the cube to powder. The height necessary was 
fixed by trial, so that very little more work should be em- 
ployed than was just necessary to crush the cube. 
The material operated on was statuary marble, whose specific gravity was 2-710 and 
its specific heat 0-205. The apparatus, it will be seen, admitted of rapidly shaking out 
the powder of the crushed marble into a small known weight of water at a known tem- 
perature, from the rise in temperature of which the heat developed in the crushed 
material was inferred. The wood lining to the cylinder and the paper above and below 
prevented any very sensible loss of heat by conduction. 
Eight good experiments were obtained with this little apparatus, the details of which 
it is needless here to give, as they do not pretend to any great exactness, the paper gun- 
wadding having in every instance to be thrown into the water with the crushed rock, 
and there being some little loss by conduction to the cylinder, and, indeed, the apparatus 
being on too small a scale. The results, however, showed that, on a mean of the whole 
eight, the heat produced was the equivalent of the work expended within about of 
the whole. 
100. Prior to making these few preliminary experiments, the writer consulted his friend 
the late Professor Eankine, and found that the views of that competent authority agreed 
with his own — that in the crushing of rigid material, such as rock, almost the entire mecha- 
nical work reappears as heat , the extremely small residue of external work being employed 
in producing vibrations of sound (or analogous to those of sound, though perhaps not 
affecting the ear) in the apparatus used for crushing or in the air around. Thus, even in 
the most rigid bodies, crushing begins by compression and deformation, however small ; 
the mass then cracks, and then the discontinuous and irregular prisms and wedges soon 
suddenly and finally crush to powder. We hear when it cracks, and work is consumed 
in the little impulse that originates the sound; but its amount, as compared to the totality 
2 b 2 
Fig. 8. 
