168 COSMOS. 



of heat during the transition from fluidity to solidity. 

 The external strata were first cooled by radiation, and 

 were the first to become consolidated. The commotion is 

 occasioned by an unequal ascent of elastic vapours formed 

 (at the limit between the fluid and solid parts) either from 

 the fused terrestrial mass alone, or from the penetration 

 of sea-water into higher strata of rock, nearer to the sur- 

 face of the earth, the sudden opening of fissures, and by 

 the sudden ascent of vapours produced in the hotter and 

 consequently more elastic depths. The attraction of the 

 moon and sun 10 on the fluid, fused surface of the nucleus 



10 Hopkins has expressed doubts as to the action upon the fused 

 " subjacent fluid confined into internal lakes," at the Meeting of the 

 British Association for 1847 (p. 57), as Mallet has also done with regard 

 to "the subterraneous lava tidal wave, moving the solid crust above it," 

 at the British Association Meeting for 1850 (p. 20). Poisson also, with 

 whom I have often spoken regarding the hypothesis of the subterranean 

 ebb and flow, caused by the sun and moon, considers the impulse, 

 which he does not deny, to be inconsiderable, " as in the open sea the 

 effect scarcely amounts to 14 inches." Ampere, on the other hand, 

 says : " Those who admit the fluidity of the internal nucleus of the 

 earth, do not appear to have sufficiently considered the action which 

 would be exercised by the moon upon this enormous liquid mass ; an 

 action from which would result tides analogous to those of our seas, 

 but far more terrible, both from their extent and from the density of 

 the liquid. It is difficult to .conceive how the envelope of the earth 

 should be able to resist the incessant action of a sort of hydraulic 

 ram(?) of 1400 leagues in length" (Ampere, Theorie de la Terre, in Revue 

 des deux Mondes, July, 1833, p. 148). If the interior of the earth be 

 fluid, which in general cannot be doubted, as, notwithstanding the 

 enormous pressure, the particles are still displaceable, then the same 

 conditions are fulfilled in the interior of the earth that give rise on the 

 surface to the ocean tides; and the tide-producing force will con- 

 stantly become weaker in approaching the centre, as the difference of 

 the distances of every two opposite points, considered in their relation 

 to the attracting bodies, constantly becomes less in receding from the 

 surface, and the force depends exclusively upon the difference of the 

 distances. If the solid crust of the earth opposes a resistance to this 

 effort, the interior of the earth will only exert a pressure against its 

 crust at these points ; as my astronomical friend, Dr. Brunnow, ex- 

 presses himself, no more tide will be produced than if the ocean had an 

 indestructible covering of ice. The thickness of the solid unf used crust 

 of the earth Is calculated from the fusing points of the different kinds 

 of rock, and the law of the increase of heat from the surface into the 

 depths of the earth. I have already (Cosmos, vol. i, p. 26), justified 

 the assumption that, at somewhat more than twenty geographical 



