Penny Blood: Serial Sensation and Working-Class Entertainment — page 286: what you’re looking at

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

CH. XXIlI.] SUMMARY. ) 269 thought that it is what has been called ‘potentially fluid,’ that 1s, wholly solid in consequence of the pressure to which the internal strata are subjected, but ready to become fluid, on account of its high temperature, whenever the pressure is relieved.. This is the great subject of controversy, towards the determination of which the present volume is intended as a contribution. The increase of temperature below the outer crust, which we know to be solid, will be governed by the laws of convection of heat if the interior is fluid, but by the laws of conduction if it likewise be solid. | The question whether the interior of the earth 1s at present solid or fluid, or partly solid and partly fluid, may, apart from geological considerations, be attacked in two ways. The first of these is by enquiring, what is the difference of effect that the moon and sun would have upon the: motions of the earth in these cases; and the other way is by considering the se- quence of events, according to which a molten globe may have passed into its present state. For the first, there are two kinds of effect produced by the attraction of the moon and sun upon the earth ; and these are precession and the tides. Mr Hop- kins, between 1839 and 1842, investigated the difference be- tween the precessional effects in the cases of a solid and of a fluid interior, and came to the conclusion that the crust of the earth could not be less than from 800 to 1000 miles thick. But the arguments of Mr Hopkins were, in 1876, abandoned by Sir Wiliam Thomson. With respect to the tides the case is different. The last- named eminent physicist says that unless the earth as a whole were extremely rigid, “the solid crust would yield so freely to the deforming influence of the sun and moon, that it would simply carry the water of the ocean up and down with it, and there would be no sensible tidal rise and fall of the water relatively to land.” It does not however appear necessary that the earth should be absolutely solid from the centre to the surface to satisfy the requirements of great rigidity as a whole, May this not be satisfied by the hypothesis of a rigid nucleus, nearly approaching the size of the whole globe, covered by a COMMUC NOO SS (CO)