Penny Blood: Serial Sensation and Working-Class Entertainment — page 182: what you’re looking at

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

CH. x11] THE THERMOMETER. 105 With the values hitherto used for o and p, k=c—TO. If we now give to 5 any value approaching to that of the mean depth of the ocean, this will make the mean thickness of the crust very much less than it can be in fact. Indeed if c be less than about 25 miles, with the usual value 3°5 for 6, k& would be negative. It 1s evident therefore that this assumption cannot be cor- rect, and that the relative densities of the crust and fluid beneath the oceanic areas cannot be the same as beneath the continents. We must therefore examine this point. Now it is certain that, whatever be the form or law of density of the nucleus of the earth which is believed to be solid, in any fluid strata which may occur above it, surfaces of equal density will be also surfaces of equal pressure ; for this is always true of a fluid in equilibrium under the action of such forces as existin nature. This therefore must be the case within the fluid substratum. Let us then suppose that the depth measured from the bottom of the crust to such a couche de niveau, not far below the place A at the sea-level, is z, and that the depth of the same couche below the bottom of the crust under the ocean, where the crust has the mean thickness, is «. And because the surface is one of equal pressure it will be also one of equal density, and o will be the same at both these places. But the crust, being solid, may differ in density at the two places. Let its density then be p below the ocean, where its thickness has the mean value k. The surface of the ocean is likewise a couche de niveau. In order therefore that the hydrostatic pressure may be the same at the two places, taking the density of the ocean as unity, we must have, considering gravity constant for a depth so small compared to the radius, 6+pk+oax’=pcet+ox. But these couches de niveau may be considered parallel, §6+k+a2’=ct+a, whence (o —1)84+(o —p)k=(o — p)e......080000(1). COLA @ NOO (CO)