286 M. L. Cordicr on the Temperature of 



This is not the place for developing the purely ihermometri- 

 cal hypothesis which I propose for explaining volcanic pheno- 

 mena, and shewing with what success it may be applied to all 

 the details of these phenomena. I shall content myself with re- 

 marking, that it accounts for the identity of circumstances by 

 which the manifestation of volcanic action, in all parts of the 

 world, is characterised, for the prodigious reduction which the 

 number of volcanoes has undergone since the commencement of 

 things, for the diminution that has been effected in the quantity 

 of matters ejected at each eruption, for the nearly similar com- 

 position of the products of each geological epoch, and for the 

 small differences that exist between the lavas which belong to 

 different epochs. Lastly, in this hypothesis, the most usual di- 

 rections of earthquakes announce the thinnest zones of the earth's 

 crust ; and the volcanic centres, as well ancient as modern, con- 

 stitute, at the same time, the points at which this crust has the 

 least thickness, and presents the smallest resistance. 



In the above I have not calculated upon the gaseous matters 

 which each eruption produces, because, supposing them reduced 

 to the state of liquidity which they originally had in the mixture 

 from which they have been disengaged, their volume would be 

 very inconsiderable, and because the mean of one cubic kilo- 

 metre, which I have adopted, is much above the real mean. 



21. The greater part of the substances contained in mineral 

 and thermal waters being analogous to those which are exhaled by 

 craters during and after eruptions, and by currents of lava when 

 they crystallize, as well as by solfaterras, it must be supposed 

 that they come from a common reservoir. Their emission occa- 

 sions continual losses to the internal gaseous charge. These 

 losses, which, however, are incessantly repaired by new subter- 

 raneous products, take place in virtue of an expansive power, 

 which is immense, and through a succession of extremely narrow 

 ' fissures. The water is furnished by the superficial causes which 

 feed common springs. The alteration of certain parts of the 

 canals, especially near the surface, may sometimes occasion 

 the substitution of certain principles by others. In this systeitt 

 of explanation, it is easy to conceive the permanence of the 

 springs, their nearly invariable temperature, and the singular 

 nature of their principles. Several phenomena appear to me to 



