Penny Blood: Serial Sensation and Working-Class Entertainment — page 174: what you’re looking at

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

CH. x11.] THE THERMOMETER. 157 neighbouring crust, because the isogeotherm is plane, It is obvious therefore from geometry, the rates beneath the moun- - tain and at any place in the neighbourhood being both of them uniform yet not the same, that this plane isogeotherm cannot be elsewhere than at the bottom of the crust, unless the isogeo- therms beneath the mountain become concave upwards after the plane isogeotherm is passed. Suppose then the former to be the case, and that & is the mean average thickness of the crust, and k’ its thickness beneath the mountain; at which re- spective depths (if the isogeotherms beneath the mountain do not become concave) the temperatures become equal. Then we must have, k or i But observation shows that 7 is about $7, or the height of the mountain above the mean level of the crust would in such case be equal to the thickness of the crust. This would make the crust far thinner than it can be admitted to be; and therefore shows that the isogeotherms below the plane one must have a convexity downwards, answering to their convexity upwards in the upper portion. There must therefore be a protuberance of solid crust below corresponding to the elevation of the mass above. We see then that we have here an additional proof of the existence of roots to the mountains derived from thermal phenomena. The downward protuberance will be much greater than the upward elevation, and therefore we perhaps ought not to assume that the extreme value of the ratio of A : S will be so nearly one of equality below the plane isogeotherm as above it. But it is probable that the downward protuberance, although it may be ten times as deep as the other is high, will be very much wider, because the St Gothard mountain is only a remnant, carved by subaerial denudation out of a much more extended elevated tract, with which the root was originally conterminous: and whatever denudation, or what may be analogous to it, the roots of the mountain range may have undergone, it is not likely COLA @ NOO (CO)