Penny Blood: Serial Sensation and Working-Class Entertainment — page 211: what you’re looking at

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

194 COMPRESSION AND VOLCANIC ACTION. {cu. xv. In the equation which connects the pressure p of the lava at the surface of the crust with V the proportion of rock substance in the magma, if we assume one of the quantities we can find the other, but we have no sure guide to lead us to the choice of either of them. We will assume V=0°9, and it will hereafter appear when we are treating more particularly of volcanic action that this assumption is not unreasonable. If we put a =n in the equation for the pressure at the surface and assume the usual values for p and a, then with the above value for V it may be put into the form n (log n — 2°044) = Using a table of hyperbolic logarithms we find by trial that the value 14°4 substituted for n gives 8°97 and the value 14:5 gives 9:13. Hence 14-4 is a near approximation, and the pressure of the lava at the level of the surface of the crust would be that due to a column of the crust 7 or 17 miles high. The weight of a column of vesicular lava would not be so great as that of a column of solid crust of equal height. We see then that if ~,th of the volume of the magma consisted of water- substance it would be sufficient to produce an overflow of lava from a lofty crater, or to raise a range of mountains consisting of eruptive rocks above an elongated fissure. The relation _ 2p enables us to find the whole horizontal pressure upon the sides of a fissure which is filled with lava under the conditions implied by it. For 7g ("p+a) dp = pao; Cr r ap) = | pao. But | pda taken from the surface to the bottom of the crust is the whole pressure upon a vertical section of the side of COMIC OOOKS.EO _—_ & =» .