1:0 PEOGRESS: ITS LAW AND CAUSE. 



There is every reason to believe that at an extreme heat 

 the elements cannot combine. Even under such heat aa 

 can be artificially produced, some very strong affinities 

 yield, as for instance, that of oxygen for hydrogen; and 

 the great majority of chemical compounds are decomposed 

 at much lower temperatures. But without insisting upon 

 the highly probable inference, that when the Earth was in 

 its first state of incandescence there were no chemical com- 

 l>iuations at all, it will suffice our purpose to point to the 

 unquestionable fact that the compounds that can exist at 

 the highest temperatures, and which must, therefore, have 

 been the first that were formed as the Earth cooled, are 

 those of the simplest constitutions. The protoxides — in- 

 cluding under that head the alkalies, earths, &c. — are, as a 

 class, the most stable comj^ounds we know : most of them 

 resisting decomposition by any heat we can generate. 

 These, consisting severally of one atom of each component 

 element, are combinations of the simplest order — are but 

 one degree less homogeneous than the elements themselves. 

 More heterogeneous than these, less stable, and therefore 

 later in the Earth's history, are the deutoxides, tritoxides, 

 peroxides, &c. ; in which two, three, four, or more atoms 

 of oxygen are united with one atom of metal or other ele- 

 ment. Higher than these in heterogeneity are the hydrates ; 

 in which an oxide of hydrogen, united with an oxide of 

 some other element, forms a substance whose atoms sever- 

 ally contain at least four ultimate atoms of three different 

 kinds. Yet more heterogeneous and less stable still are 

 the salts ; which present us with compound atoms each 

 made up of five, six, seven, eight, ten, twelve, or more 

 atoms, of three, if not more, kinds. Then there are the 

 hydrated salts, of a yet greater heterogeneity, which un- 

 dergo partial decomposition at much lower temperatures. 

 After them come the further-complicated supersalts and 

 double salts, having a stability again decreased : and so 



