Penny Blood: Serial Sensation and Working-Class Entertainment — page 244: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

cH. xvi.) THEORY OF VOLCANIC ENERGY. 227 considerable favour by many. Impressed with the necessity of admitting the doctrine of a solid earth upon the authority of the highest masters of physical science, they saw in Mr Mallet’s hypothesis a way.of escape from the difficulty in which they were placed. If the earth be a solid body cooling by conduction, and if the corrugations upon its surface are caused by the con- traction of the mass and consequent compression of the super- ficial layers, what, it has been thought, can be more. in accord- ance with probability, than that the work of compression should be converted into heat, and that volcanic energy should be its manifestation, and have its seat no deeper than the compressed crust. Like many simple explanations, the only wonder was that no one had suggested it before. Yet how often had been long delayed the discovery of some theory, which when once proposed seems simplicity itself. If Mr Mallet’s theory be true, it 1s obvious that that now propounded must be untenable, It will therefore be necessary to examine it. The theory is enunciated in the following terms*:— “The heat from which terrestrial volcanic energy 18 at present derived 1s produced locally urthin the solid shell of our globe by transformation of the mechanical work of compression or of crushing of portions of that shell, which compressions and crush- angs are themselves produced by the more rayd contraction, by eooling, of the hotter material of the nucleus beneath that shell, and the consequent more or less free descent of the shell by grav- tation, the vertical work of which rs resolved into tangenival pres- sures and motion within the thickness of the shell.” As regards the lateral pressure to which Mr Mallet appeals as the cause of compression, and of crushing portions of the shell, there can be no doubt that, if there were a continual contraction of the interior and subsidence of the shell going on, the pressure arising from the descent of the shel] would be per- fectly adequate to produce the crushing attributed to it. _ We have however, as we believe, seen grave reason to doubt 1 Op. cit. § 67, p. 167. 15—2 GONG oOo SS (CO)