166 REACTION OF THE INTERIOR OF THE EARTH 



and salses. Salsee sometimes show outbursts of flames, 

 visible to distances of very many miles, and rocks torn 

 from internal depths hurled into the air and scattered 

 around.( 229 ) These, as it were, prepare the way for the 

 grand phenomena of volcanoes proper, which in turn, 

 in the intervals between distant epochs of eruption, ex- 

 hale, like salses, .only aqueous vapours and gases from 

 fissures. Thus striking and instructive are the analo- 

 gies presented in different stages by the gradations of 

 volcanism. 



a. Earthquakes. 



(Extension of the Representation of Nature, in Kosmos, 

 Bd. I. S. 210225 ; Engl. Vol. I. p. 191205.) 



Since the publication of the first volume of the present 

 work (in 1845), and of the general description there 

 given of earthquake phenomena, the obscurity prevail- 

 ing respecting their seat and their causes has been but 

 little diminished ; but by the labours of ( 23 ) Mallet 

 (1846) and Hopkins (1847) some valuable light has 

 been shed on the nature of the movement, the connection 

 of operations apparently diverse, and the separation to 

 be made between physical and chemical processes, asso- 

 ciated or occurring simultaneously. Here, as elsewhere, 

 advantage cannot fail to be derived from the application 

 of mathematical reasoning, as in the precedent set by 

 Poisson. In theoretical considerations on the dynamics 

 of earthquakes, the analogies between the undulations 

 of solid bodies, and the atmospheric waves of sound, to 

 which Thomas Young had called attention, ( 231 ) are 

 particularly adapted to lead to more simple and more 

 satisfactory views. 



