Penny Blood: Serial Sensation and Working-Class Entertainment — page 261: what you’re looking at

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

244 THE VOLCANO IN ERUPTION. [cH. XIX. There is however to guide us the consideration, that the quantity of water, which is given off along with the lava, will bear a ratio to the quantity of the lava depending upon the value of V. If it be true, as we have seen reason to think to be the case, that the water-substance in the lava must be of the same density as the rocky matter with which it is combined, then the proportion of water-substance to rocky matter being 1—V: YV, the proportion of ordinary water to the lava in the erupted matters will be nearly o (1— V): V. Thus if V were 0°9, or the compressed water-substance occupied one-tenth of the volume of the magma, and if o were 2°96, the water given off would bear to the lava given off the ratio of 2°96 x 0°1: 0°9, or about 0°3: 1; that is the volume of the lava stream would be about three times the volume of the water; which does not appear improbable. When we take into account the passage of the vesicles of water-substance through the lava in their ascent towards the surface, we cannot doubt that this takes place with greater rapidity than the ascent of the lava itself, and the exhaustion of water in the column goes on much more rapidly than diffusion can repair it. Consequently the lava in the upper part of the column at last becomes so deficient in vesicles of water-sub- stance, that its weight balances the expansive force beneath it. The vesicles beneath it will then cease to expand, and their upward motion will be checked, and the evolution of steam gradually almost cease. But the column of lava has been for some while rising in the vent, and at this juncture the forces which press it upwards are just in equilibrium with those that - keep it down. The ws viva which it already possesses will be only gradually destroyed, and it will continue to well forth steadily and without much evolution of vapour for a little while and then sink back into the vent. In this manner the eruption will be brought to a close’. 1 Instances are recorded in which an eruption of lava has been followed by a great evolution of steam and ashes. It is conceivable that vapour may accumu- late in parts of the chasm which are closed above, and when the level of the lava which confined it there has sunk sufficiently, steam may find an exit by the open vent, rushing with violence through the lava, now no longer deep enough to restrain its escape, and blowing it into dust; the mode of action being some- COLA @ NOOKS ACO @\