MR. ROBERT MALLET ON VOLCANIC ENERGY. 
21 
2ndly. The volume of matter that must be annually crushed and extruded from the 
shell of 800 miles in thickness in order to admit of its following down after the con- 
tracting nucleus, being 0-758199 of a cubic mile, which, if measured in terms of mean 
crushed rock, amounts to xrr6 °f the heat annually dissipated. The former of these 
quantities is comprised within the second as its source of supply, which, as we observe, 
exceeds the annual demand necessary for existing volcanic energy by about one half. 
Srdly. The volume of material heated or molten annually blown out of all the volcanic 
vents of our globe, as based upon the estimates made in the author’s original paper 
(paragraphs 195 to 197), which amounts to 0-1486 of a cubic mile, a quantity probably in 
excess of the truth. The first of these quantities, upon the data assumed in this paper, 
would be produced by a thickness of the solid shell of our earth of more than 400 but 
less than 800 miles. The third of those quantities might be accounted for by a shell 
of more than 200, but less than 400 miles in thickness. If the shell be actually less than 
the smallest of these thicknesses, it follows either that the annual dissipation of heat 
from our globe greatly exceeds that due to 777 cubic miles of melted ice, or that the 
coefficient of contraction for the nucleus here employed and based on experiment is 
below the truth, neither of which suppositions is improbable. It will be remarked that 
the results in this paper have been obtained by an independent and different method of 
investigation from that employed in the author’s original paper (Philosophical Trans- 
actions of 1873), and that they coordinate to such an extent as to support the proba- 
bility of the truth of the views enunciated in both papers. 
In conclusion I wish to acknowledge the efficient aid I have received from my assistant 
Mr. W. Worby Beaumont, Assoc. Inst. C.E., in completing the laborious calculations 
involving a mass of figures of which the results only are here seen. 
MDCCCLXX V. 
G 
