Penny Blood: Serial Sensation and Working-Class Entertainment — page 205: what you’re looking at

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

188 § COMPRESSION AND VOLCANIC ACTION. {cu. xv. while the horizontal pressure at a depth z below the same surface will be t = gpk — goh+ goz. At the same time the vertical pressure upon an élement of the rock in the crust near the chasm at a height y above the bottom of it will be p=gp (k—y). Hence the difference between the horizontal and vertical pressures on such an element situated above the level to which the magma rises in the chasm, will be t— p= gpy —goh. And the like difference below that level will be t — p= gpy— gah + gaz. The excess of the horizontal over the vertical pressure, which is the force that will cause lateral compression, increases as y in- creases, and also increases as fh diminishes. This force will therefore be greater towards the upper part of the chasm, and it will also be greater the greater the tension of the vapour, which will tend to decrease h by preventing the magma rising. If the rock should allow the vapour only slowly to escape, and if the magma below the chasm can supply fresh vapour sufficiently rapidly to keep up the temperature, it is conceivable that the tension of the vapour in the chasm may be nearly equal to gpk, in which case fA will be nearly. evanescent, and the horizontal pressure much greater than the vertical especially in the upper part of the chasm where y is nearly equal to k. We can there- fore understand how a chasm, commencing below, may be rent open upwards, and at last reach the surface of the ground. When that occurs, vapour at a high tension will escape at what- ever point is first broken through, and after issuing at a diminish- ing pressure for a certain timé, it will be followed by the magma itself, which will overflow at the surface because the water-sub- stance in the upper part of the column, expanding owing to the diminished pressure there, will render the whole column of less weight than an equal column of crust. This appears to be the mechanism required to explain the formation of a volcano, and of the earthquakes which precede its appearance. COMIC OOOKS.EO Cy ee a ay ny Vy. a | ne ene et A ee ae eaenee “> eee” amen ‘ * oe” | ee a - —_——seeeM |