166 COSMOS. 



tion of chemical and physical processes, which may accom- 

 pany it or occur simultaneously with it. Here, as elsewhere, 

 a mathematical mode of treatment, such as that adopted by 

 Poisson, may have a beneficial effect. The analogies between 

 the oscillations of solid bodies and the sound-waves in the 

 ordinary atmosphere to which Thomas Young 7 had already 

 called attention, are peculiarly adapted to lead to simpler 

 and more satisfactory views, in theoretical considerations 

 upon the dynamics of earthquakes. 



Displacement, commotion, elevation, and formation of fissures 

 indicate the essential character of the phenomenon. We 

 have to distinguish the efficient force, which, as the impulse, 

 gives rise to the vibration ; and the nature, propagation, in- 

 crease or diminution of the commotion. In tiie Picture of 

 Nature I have described what is especially manifested to the 

 senses ; what I had myself the opportunity of observing for 

 so many years on the sea, on the sea-bottom of the plains 

 (Llanos), and at elevations of eight to fifteen thousand feet ; 

 on the margin of the craters of active volcanos, and in re- 

 gions of granite and mica schist, twelve hundred geographical 

 miles from any eruptions of fire \ in districts where at cer- 

 tain periods the inhabitants take no more notice of the num- 

 ber of earthquakes, than we in Europe of that of the showers 

 of rain, and where Bonpland and I were compelled to dis- 

 mount, from the restiveness of our mules, because the earth 

 shook in a forest for 15 to 18 minutes without intermission. 

 By such long custom, as Boussingault subsequently expe- 

 rienced even in a still higher degree, one becomes fitted for 

 quiet and careful observation, and also for collecting varying 

 evidence with critical care on the spot, nay, even for ex- 

 amining under what conditions the mighty changes of the 

 surface of the earth, the fresh traces of which one recognises, 

 have taken place. Although five years had already elapsed 



] 850, pp. 1 89 ; also Manual of Scientific Inquiry for the Use of the 

 British Navy, 1849, pp. 196 223. William Hopkins, On the Geological 

 Theories of Elevation and Earthquakes, in the Report of the British Asso~ 

 ciation for 1847, pp. 33 92. The rigorous criticism to which Mr. 

 Mallet has subjected my previous work in his very valuable memoirs 

 (Irish Transactions, pp. 99 101, and Meeting of the British Association 

 at Edinburgh, p. 209), has been repeatedly made use of by me. 

 7 Thomas Young, Lectures on Natural Philosophy, 1807, vol. f, 

 717. 



