Penny Blood: Serial Sensation and Working-Class Entertainment — page 180: what you’re looking at

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

CH. XII] THE THERMOMETER. 163 geologists as the probable temperature below the solid crust, whence the usual estimate for the thickness of the crust has been derived of about 20 mules. But there is reason to think that the crust may be some- what thicker, and consequently the temperature somewhat higher than we have just estimated them, even on the showing of our own formule,.and that for the following reason, The value of c in equation (4) is increased if the ratio of o : p is made more nearly one of equality. We have taken this ratio to be that of basalt to granite, viz. 2°96 : 2°68; and the reason why we have done so is because the denser eruptive rocks are of the basaltic type, so that we may reasonably infer that the heavier fluid substratum 1s, as regards mineral character, a basic magma. But it by no means follows that, while not yet erupted, it should be as dense as basalt. Indeed the probability is in the other direction; because if, as we believe, it is in a condition of igneo-aqueous solution, its high temperature may diminish its density. Whether the water-substance combined with it will have such an effect will be hereafter discussed’. There is yet another reason, though perhaps a less cogent one, to lead us to suppose that we are taking the density of the substratum too great, rf we assume it equal to that of basalt; for it has been already pointed out’ that, according to Laplace’s law, the density of basalt would be found at the depth of 100 miles, which is much more than that, at which we should expect the temperature of fusion to commence. It seems therefore almost certain that the value of o is nearer to that of p than it has been assumed to be, and the resulting value for the thickness of the crust greater, and the tempera- ture higher than those found; while the downward protu- berance below the mountains will be also greater than estimated. It is probable that the water, which is believed to be pre- sent, will render the rocks fusible at a lower temperature, and increase the liquidity of the magma. Again we see, from the difference in the results for the thickness and melting temperature according as we take ,, or . 1 p. 190. 2 See note, p. 118. 11—2 CONNEC OOO @ (CO)