Fhtnomena i7i the Solar System, 451 



these figures, which we have adopted to render the demonstration 

 more clear, the interest and importance of this inquiry is evident. 



I am convinced that the ultimate complete cooling of the in- 

 terior of the earth is inevitable. We may affirm on general prin- 

 ciples, that between two media of different temperatures, sepa- 

 rated by a layer of rock which is a conductor of heat, an equili- 

 brium will at length be established. It is probable that this 

 cooling is however to a great extent effected by the innumerable 

 currents of water and gases which circulate in every direction 

 through the interior of the globe, and of which volcanic eruptions, 

 hot springs and suffioni are only the more violent manifestations 

 attaining the earth's surface. The recent ingenious experiment 

 of Daubree has shown us that water may be drawn by capillary 

 force towards spaces heated much above its boiling point. The 

 water thus conveyed, in passing into the state of vapour does not 

 everywhere produce volcanic phenomena, for these probably 

 require the concurrence of conditions which are not often found* 

 The aqueous vapour will ordinarily ascend to colder portions of 

 the earth's crust, and there yielding its heat to the walls of the 

 fissures, will flow back in the liquid state to the source of heat, to 

 repeat the same process, while on the other hand currents of cold 

 water will absorb the heat thus conveyed to the rocks and bring 

 it to the surface by thermal springs. 



The general permeability of rocks is so well admitted by most 

 geologists that I have not thought it necessary to seek for proof 

 of it in the discussions of the present question ; the briUiant con- 

 ception of the metamorphism of rocks by the humid way, which 

 has been, so well maintained by the ablest chemists, is only pos- 

 sible on this condition. The permeability of rocks also explains 

 in a satisfactory manner the formation of agates, and of zeolites, 

 arragonite and other minerals in the midst of the most compact 

 basalts, and of geodes of quartz in the Norwegian granites. We 

 may also recall the artificial colours which are given to agates. 

 Mr. Damour has even shown by a series of curious experiments 

 that the water which is ordinarily considered as chemically com- 

 bined in certain hydrated silicates, such as zeolites, may be in 

 part extracted from them, and again restored, without any appa- 

 rent alteration in these minerals. 



