540 DISSOLUTION. 



inorganic aggregate, along with all undissipated remnants 

 of organic aggregates, must be reduced to a state 

 of gaseous diffusion, and so complete the cycle of its 

 changes. 



§ 181. For the Earth as a whole, when it has gone 

 through the entire series of its ascending transformations, 

 must remain, like all smaller aggregates, exposed to the 

 contingencies of its environment ; and in the course of those 

 ceaseless changes in progress throughout a Universe of 

 which all parts are in motion, must, at some period be- 

 yond the utmost stretch of imagination, be subject to forces 

 sufficient to cause its complete disintegration. Let us glance 

 at the forces competent to disintegrate it. 



In his essay on " The Inter-action of Xatural Forces," 

 Prof. Helmholtz states the thermal equivalent of the Earth's 

 movement through space, as calculated on the now received 

 datum of Mr. Joule. " If our Earth," he says, " were by a 

 sudden shock brought to rest in her orbit, — which is not to 

 be feared in the existing arrangement of our system — by 

 such a shock a quantity of heat would be generated equal 

 to that produced by the combustion of fourteen such Earths 

 of solid coal. Making the most unfavourable assumption 

 as to its capacity for heat, that is, placing it equal to that 

 of water, the mass of the Earth would thereby be heated 

 11,200 degrees; it would therefore be quite fused, and for 

 the most part reduced to vapour. If then the Earth, after 

 having been thus brought to rest, should fall into the 

 Sun, which of course would be the case, the quan- 

 tity of heat developed by the shock would be 400 times 

 greater." Now though this calculation seems to 



be nothing to the purpose, since the Earth is not likely 

 to be suddenly arrested in its orbit and not likely there- 

 fore suddenly to fall into the Sun; yet, as before pointed 

 out (§ 171), there is a force at work which it is held must 

 at last bring the Earth into the Sun. This force is the re- 



