662 THE UNIVERSE. 



Another pliilosoplier, tlie illustrious Sir Humphry 

 Davy, also proposed a very ingenious chemical theory, too 

 ingenious perhaps, for which reason it came less into 

 favour than that of Leniery. Having discovered certain 

 metals, potassium and sodium, which have the singular 

 property of taking fire so soon as they are brought into 

 contact Avith Avater, the English chemist supposed that the 

 flames which issue from volcanoes are only the j^roduct of 

 the combustion of these metals taking place in the dejDths 

 of the globe when the Avater reaches them. 



NotAvithstanding the great celebrity of its author, this 

 hypothesis had only a very brief existence : phenomena so 

 l^OAverful and general could not have their source in local 

 chemical reactions. The geologists of our epoch are 

 almost unanimous in admitting that all volcanic pheno- 

 mena are to be attributed solely to the central fire of the 

 globe making greater or less efforts to project outAvards 

 the superfluity of its incandescent materials. It is certain 

 that this theory explains easily and better than any other 

 Avhat happens during eruptions, and all those Avho have 

 visited volcanoes admit it Avithout hesitation. 



Earthquakes are essentially imited to volcanic phe- 

 nomena, and often accompany them. They apparently 

 result from the effort Avhich the igneous materials of the 

 globe make to launch themselves from their furnace. In 

 countries Avhere there are volcanoes they are looked upon 

 as being in some measure safety- A^alves ; so long as they 

 are in full activity, and the centre, Avhen overfilled, 

 empties itself by the fire-spouting mouth, the country is 

 trancjuil. 



No 2:)henomenon offers such a dreadful spectacle as the 

 earthquake. The naturalist Avho explores a dangerous 

 volcano arrives at it armed with patience and courage. He 



