Penny Blood: Serial Sensation and Working-Class Entertainment — page 265: what you’re looking at

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

248 THE VOLCANO IN ERUPTION. (cH. xrx. The mode of action suggested appears competent to account easily for the eruption of steam and lava in a case where a chan- nel of communication has been freshly opened between the liquid substratum and the surface. There is more difficulty in under- standing how, when an eruption has taken place, and the water- substance has been exhausted to that degree at which the lava becomes too dense to rise any longer, the action can be after a period renewed. And as there is a difficulty in understanding the process, so also is there evidently a difficulty in the process itself, otherwise the periods of repose would not be so long and so irregular as they are, and sometimes perpetual. The comparison between the geyser and the volcano is no new one. Bunsen’s explanation of the former turns upon the temperature at each depth in the column of water becoming raised above the boiling point for the pressure there. Our account of a volcanic eruption is somewhat similar, except that the boiling point of the lava depends, not so much on the tem- perature, which we have regarded as constant (although that cannot be strictly so), but upon the presence of a sufficient quantity of water mingled with the lava, to cause the requisite expansion of volume under the pressure at each depth. What will be required therefore to repeat the eruption, will be the diffusion afresh of sufficient water into the column for this purpose, and it seems that the escape of vapour from the surface becoming reduced below the supply gained by diffusion from below, must be the requisite condition. This may be perhaps caused by the cooling of a plug of lava at the top of the column, except a narrow passage through which what escape there is takes place, and which serves as the leading channel for the next eruption. Or else, when the period of repose has been protracted until this channel has become blocked with cooled lava, some fresh movement of the crust may open the necessary communication between the surface and the fluid substratum. COMIC OOOKS.EO