ME. ROBERT MALLET ON VOLCANIC ENERGY. 
207 
184. Had the writer been fortunate enough to have completed his projected pyro- 
metric determination of the actual temperature deep in the V esuvian crater (which the 
Royal Society aided some years back, but which the sudden alteration of the state of 
that volcano prevented), we should have been better prepared to make the following 
estimation. 
185. All the volcanic cones upon our globe may be averaged as each equal in volume 
to a solid cone of one mile in height above the base Fig. n. 
of five miles in diameter ; for while many are far 
below this height, and the majority of those mea- 
sured do not reach this elevation, all the loftiest 
cones (above sea-level), such as Cotopaxi, &c., stand 
upon elevated tablelands or plateaux not volcanic 
or but covered skin deep with volcanic matter, and so have only a real elevation as 
volcanic cones of about 5000 feet. Thus Cotopaxi stands on the plain of Quito, 9000 
feet above the sea. Antisana and two or three others only upon the whole globe 
appear to be exceptions; but it is very doubtful whether any of these cones really rise 
from sea-level; and the number is so small of these cones reaching 10,000 feet and 
upwards as not materially to affect the result. 
186. The volume of one such cone (5 miles base xl mile high) is 6 *54 cubic miles. 
As all volcanic cones are mere “ cinder tips,” masses of dust, lapilli, and scoriae, to which 
the volume of solid lava beds bears a very small proportion, so we cannot take the 
average specific gravity of their materials at probably more than 2’0, or CM)5 of a ton 
per cubic foot; so that in one such cone we have 48,133,730,304 tons, to elevate 
which to the height of the centre of gravity of the cone 0'25 mile above its base requires 
63,536,524,001 foot-tons; and as there are 2°*9 or nearly 3 British heat units in a foot- 
ton, dividing the above we obtain 21,178,841,333,760 British units of heat equivalent to 
the work. But we have found that one cubic foot of crushed (mean) rock evolves 6472 
such units, dividing by which we obtain 3,272,370,686 cubic feet of such crushed rock 
to perform the work, which is or less than of a cubic mile of crushed rock 
to perform the lifting work from base of the cone; or if we suppose it lifted from 10 
miles deep below the base of the cone, then , or less than 1 cubic mile of crushed 
rock. 
187. As respects the heating and fusing work, the observations made everywhere on 
volcanic cones indicate that but a very small proportion of their total mass has been 
fused, the rest having been merely heated. It is probably below the truth to assume 
that there is twenty volumes of such heated matter (dust, lapilli, scoriae, &c.) to one of 
fused lava. 
The whole of this material, before being exposed to volcanic heating, exists at the 
hypogeal temperature due to its depth. 
We may assume this temperature as above 300° Fahr., or that due to from fifteen to 
twenty thousand feet depth, that the heated material is raised to 1000° Fahr. (the 
