Effects of Heat modified hy Compression. 1 95 



answer to an argument lately urged against the Huttonian 

 theory, founded on the waste of heat which must have taken 

 place, as it is alleged, through the surface. For if, after 

 absolute cessation, a power of renewal exists in nature, the 

 idea of waste by continuance is quite inapplicable. 



The external phsenomena of volcanoes are suhiciently well 

 known; but our subject leads us to inquire into their in- 

 ternal actions. This we are enabled to do by means of the 

 foregoing experiments, in so far as the carbonate of lime is 

 concerned. 



Some experiments, which I formerly* laid before this so- 

 ciety and the public, combined with those mentioned in this 

 paper, prove that the feeblest exertions of volcanic lire are 

 of sufficient intensity to perform the agglutination, and even 

 the entire fusion, of the carbonate of lime, when its carbonic 

 acid is effectually confined by pressure ; for though lava, 

 after its fusion, may be made, in our experiments, to con- 

 geal into a glass in a temperature of 16° or 18° of Wedge- 

 wood, in which temperature the carbonate would scarcely 

 be affected, it must be observed that a similar congelation 

 is not to be looked for in nature ; for the mass, even of the 

 smallest stream of lava, is too great to admit of such rapid 

 cooling. And, in fact, the external part of a lava is not 

 vitreous, but consists of a substance which, as my experi- 

 ments have proved, must have been congealed in a heat of 

 melting silver, that is, in 22° of Wedgewood ; while its in- 

 ternal parts bear a character indicating that they congealed 

 in 27° or 28° of the same scale. It follows, that no part of 

 the lava, while it remained liquid, can have been less hot 

 than 22° of Wedoewood. Now, this happens to be a heat 

 in which I have accomplished the entire fusion of the car- 

 bonate of lime under pressure. We must therefore con- 

 clude, that the heat of a running lava is always of sufficient 

 intensity to perform the fusion of limestone. 



In every active volcano a communication must exist be- 

 tween the summit of the mountain and the unexplored re- 

 gion, far below its base, where the lava has been melted, 



* 1 dinburgh Traauctions, VOL v. part i. p. 60 — 60 



N B and 



