Penny Blood: Serial Sensation and Working-Class Entertainment — page 170: what you’re looking at

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

CH. XII. | THE THERMOMETER. 153 result is that the mean underground rates at all places at.the same height above the sea, and where the mean annual surface temperature is the same, ought to be equal, irrespectively of the nature of the rocks, provided only that the temperature at the bottom of the crust is the same. But if on the other hand the heights of two localities be different, the mean rates there ought to differ, not in inverse proportion to the heights above the sea, but approximately in inverse proportion to the total thicknesses of the crust, in- cluding the roots down to the molten substratum. Is there any reason to believe that this is the case? If we find it to be so, we shall have a presumption, in favour of our theory, not only that there is a downward protuberance of lighter material, as already shown to be corroborated by geodesy, but that this protuberance consists of unmelted crust projecting into molten fluid. Of course the above reasoning requires the state of tempe- rature to be sensibly permanent, and that a sufficient time should have elapsed, since the mountains were elevated, for the heat brought up from below along with the uplifted matter to have become so far dissipated, that the flow of heat through the crust has become steady. Mr Mallet, in his paper on Volcanic energy’, refers to a dissertation, which he considers “ the most complete and valua- ble collection and discussion of all the observations on record up to June, 1836,” by A. Vrolik, who, he states, “believes it proved, that 1n general the rate of increment is greater in plains and valleys than in mountains.” The great engineering achievements of the present time have afforded exceptional facilities for testing this question ; and the above statement has been found to be strictly true. An extensive series of observations was carried out more especially in connection with the construction of the tunnel through the Alps at Mont St Gothard, by Dr F. M. Stapff, geological engineer 1 Phil. Trans. Royal Soc., Vol. 163, p. 158. The title of the dissertation is “Disputatio physica Inauguralis de Calore telluris infra superficiem augescente.” 4to., 101 pages, Miller, Amsterdam, 1836, COLA @ NOO (CO)