^ EFFECTS OF HEAT* 



VIII. 



Experiments on the Ejects of Heat modified hy Comprejfion, hy 

 Sir James Hall, Ban, Read in the Royal Society of Edin- 

 burgh, Augnjl 30, 1 804-. Communicated by the Author, 



Experiments of ^ BEG leave to announce to this Society the refult of a feries 

 heat, modified of experiments which have occupied my attention almoft ex- 

 ycompre ion. (,iQfjygjy during feveral years. Thefe experiments relate to 

 the effe(5ts of heat modified by compreffion, and are intended 

 to inveftigate the peculiar and chara6leriflic principle of the 

 Huttonlan theory. 

 Dr. Huttrn's Dr. Hutton, in common with many former geologifts, has 



Smpo^nd^'n^* afcribed the formation of all mineral fubftances chiefly to fire. 

 turally produced But, according to him, the influence of this element has been 

 m this way. ^^^^ much modified by compreflion, occafioned by the weight 

 and flrength of a vaft fuperincumbent mafs, which then preflfed 

 upon what is now the furface of our globe. In this manner 

 he has anticipated the natural objedlion to all igneous theories 

 which muft arife from a comparifon of various mineral fub- 

 ftances with the produds of fire in our furnaces; for he con- 

 ceives that prefl'ure by repreflSng volatility would occafion the 

 prefence, in high temperatures, of many fubftances which 

 efcape in our fires, on a flight application of heat; and that 

 thefe by their chemical relations would give rife to a fiate of 

 things untried in any experiments hitherto publiftied, but fuch 

 as to afford a fatisfadory explanation of all the natural pheno- 

 mena upon his hypothefis, even of thofe which are the moft 

 incompatible with the common a6lion of fire. 

 Thefaftsare The two fundamental pojiulata required in this theory, 



^^^^ ^^^t has (o naniely, thea6tionof heat, and the prefence of a fuperincum- 

 globejbutthe bent mafs are certainly allowable; fince the volcanos furnifli 

 efFears have Hot yg ^jih a proof that internal fire does a6l occafionally and in 

 expenment. ^ the irregular manner which this fyflem requires; and fince th6 

 fragmented and perturbed fiate of our ftrata enables us to fay 

 with certainly that great changes have taken place, that enor- 

 mous mafles have been removed, and that what was once 

 placed at a great depth is now highly elevated. 



But a third pnpdaliun is involved in this theory, which feems 

 to be of more difficult admiflion. Granting that heat did a6| 



on 



