206 
MR, ROBERT MALLET ON VOLCANIC ENERGY. 
But we have already found that the heat developed by the crushing to powder of 
1 cubic foot of mean rock is =6472 British units of heat. 
Hence a cubic foot (or cubic mile) of ice requires 1*27 cubic foot or mile of crushed 
rock to liquefy it. 
Therefore, if the total amount of all the heat annually lost by the earth were pro- 
duced from crushed rock in the contracting crust (which it certainly is not), it would 
only require 777 xl'27 = 987 cubic miles of such crushed rock to produce it. 
180. This seems a large amount; but it is as nothing compared with the mass of the 
globe. 
If, for example, we suppose it all crushed within a shell of solid crust whose volume 
is but one fourth that of the entire globe, it is less than the one 65 millionth part of 
the volume of that spherical shell, and if spread over the earth’s surface would form a 
mere film. There would therefore he nothing incredible were we to suppose that 
nearly the whole of the heat annually lost by the entire globe was equalled by that pro- 
duced by the crushing of its crust by the contraction of the entire globe. Nor, as it 
appears to the writer, would the annual amount of contraction necessary to account for 
that amount of heat be inadmissible. It is certain, however, that the whole of the heat 
lost annually by the globe cannot come from such a source, but only a very small pro- 
portion of it, because the lost heat is the source of the contraction. 
181. We appear obliged by the phenomena of hypogeal increase of temperature (per- 
plexing as they are) to conclude that by far the largest proportion of the heat annually 
lost reaches the surface from a cooling nucleus, which surface, though in various degrees, 
it everywhere reaches ; whereas volcanic activity is confined to narrow lines spread widely 
apart over the surface and parting with very little heat by lateral conduction. 
The spheroidal wave of heat constantly passing upwards from the nucleus to the 
surface everywhere must be dissipated from the dry land by radiation, consumed in 
heating the water of the ocean and helping in the production of its currents, and is 
partly brought up by thermal waters which have infiltrated cold from the surface (see 
Appendix A). 
182. Contraction due to this constant cooling (and that greatest in the nucleus, which is 
hotter and contracts most for given amount of cooling) is the necessary result, and with 
it crushing together of the crust as it follows down after the shrinking nucleus, and 
through the work expended in that crushing the production of a distinct source of heat, 
the amount of which must be demonstrably sufficient if it be the true source of vulca- 
nicity. 
Let us then attempt to estimate, so far as our knowledge of the amount of volcanic 
action going on upon our globe may enable us, whether it be sufficient or not. 
183. Volcanic energy as witnessed on our globe is mainly expended in three ways: — 
1. Heat converted into work of elevation and ejection. 
2. Heat employed in fusing or heating solid ejecta. 
3. Heat wasted and dissipated in steam &c. at volcanic vents. 
