Penny Blood: Serial Sensation and Working-Class Entertainment — page 20: what you’re looking at

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

CH. 1.| ON UNDERGROUND TEMPERATURE. 3 in deep mines is due to the pressure of the overlying strata or “cover.” We may unhesitatingly dismiss this hypothesis. Pressure by itself cannot develop heat. Where motion is destroyed as motion, there it 1s that it 1s converted into heat. Thus the motion which is destroyed when a hammer strikes upon an anvil will develop heat that can explode fulminating powder, or heat a nail red-hot. So, also, the bearings of a wheel become heated by friction, which gradually destroys its motion. But though mountains rise on mountains, there will be no heat produced unless motion of some kind is destroyed. In deep coal-mines an effect called “creep” is caused by the enormous pressure upon the sides of a passage, or upon the pillars left to support the roof, causing the floor of the excava- tion to swellup. In this case there is immense friction between the particles of the rock, were it not for which the passage would become instantaneously closed. It has been remarked that considerable heat sometimes accompanies this creep, in which, be it observed, we have not pressure alone, but motion destroyed by friction and converted into heat. Sir Humphry Davy ascribed the volcanic fires to the oxida- tion of earthy and metallic bases, supposed by him to exist low down in the interior of the earth. Since water is everywhere present in the crust, if it be dissipated by the abstraction of its oxygen when it encounters the bases, and by the blowing-off from volcanic vents of the equivalent hydrogen, then its place must be continuously supplied by the percolation downwards of fresh accessions ; and thus a generally diffused increase of tem- perature was supposed to arise, and to manifest: itself by its escape towards the surface. A very fascinating theory, which has met with support among many scientific men, has of late years been promulgated by Mr Mallet, who considers the heat of volcanic action to be derived from the transformed work of crushing the rocks of the earth’s crust, owing to the contraction of its interior through long-sustained cooling. The cause of evolution of the volcanic heat under this theory is of the same kind as that alluded to above, in the case of creeps; while the ubiquitous increase of temperature in descending into the earth is looked 1—2 GONG oOo SS cof