Penny Blood: Serial Sensation and Working-Class Entertainment — page 208: what you’re looking at

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

cH. xv.} COMPRESSION AND VOLCANIC ACTION. IQI a fissure should commence to be formed at any place in the bottom of the crust, some portion of. the water-substance would escape from the magma into it, its place in the magma being partially supplied from the magma in the vicinity. By the continuation of this process the fissure would become filled by what we have called vapour, at the elastic pressure due to the temperature*. The case would be analogous to that of a liquid confined in the presence of its own vapour. The upper portion of the lava in the fissure would retain only so much water as the pressure of the vapour upon its surface would enable it to keep in solution. But at lower levels, where the pressure would be increased by the weight of the superincum- bent lava, it would retain more water. Suppose then that at the depth 2 below the surface of the crust the volume of a certain mass of lava is V +v, where V is the volume of the rocky matter which we suppose in- compressible and v is the volume by which it is increased owing to the water-substance which is combined with it. We have no means of knowing what law connects » with the’ pressure p; but we feel assured that it diminishes as the @ @ a @ pressure is increased, If we assume v=-—, a is probably some function of p; but for want of a better hypothesis we will sup- pose a constant, and then v becomes subject to Boyle's law. The rocky matter may itself contain water as one of its chemical constituents, which we leave out of the question. Let » be the mean density of the mixture and 8 the mass under consideration. Then our hypothesis gives the relation p=, V+— P The temperature is taken as constant. 1 Richthofen (p. 56, note) refers, though not without hesitation, to a calcu- lation by G. Bishof that ‘‘the elastic force of steam is at its maximum when it has the same density as water.” This appears to imply that at temperatures above the critical it becomes more compressible. *“ Natural System of Volcanic Rocks,” California Academy of Sciences, Vol. 1., Part u. San Francisco, 1868. CONNEC OOO @ (CO)