EARTHQUAKES. 165 



in the fused mass of the interior (even though, according to 

 Lenz and Kiess, iron, in the fused state, may be capable of 

 conducting an electrical or galvanic current), produces evolu- 

 tion of light in the magnetic poles of the earth, or at least 

 usually in their vicinity. We concluded the first section of 

 the volume on telluric phenomena with the luminosity of the 

 earth. This phenomenon of a luminous vibration of the ether 

 by magnetic forces is immediately followed by that class of 

 volcanic agencies, which, in their essential nature, act purely 

 dynamically, exactly like the magnetic force : causing move- 

 ment and vibrations in the solid ground, but neither produc- 

 ing nor changing anything of a material nature. Secondary 

 and unessential phenomena (the ascent of flames during the 

 earthquake, and eruptions of water and evolutions of gas* 

 following it) remind one of the action of thermal springs and 

 salses. Eruptions of flame, visible at a distance of many 

 miles, and masses of rock, torn from their deep seats and 

 hurled about, 6 are presented by the salses, which thus, as it 

 were, prepare us for the magnificent phenomena of the true 

 volcanoes; which again, between their distant epochs of erup- 

 tion, like the salses, only exhale aqueous vapour and gases 

 from their fissures. So remarkable and instructive are the 

 analogies which are presented in various stages by the grada- 

 tions of vulcanism. 



a. Earthquakes. 



(Amplification of the Picture of .Nature. 

 Cosmos, vol. i. pp. 199213). 



Since the appearance in the first volume of this work 

 (1845) of the general representation of the phenomena of 

 earthquakes, the obscurity, in which the seat and causes of 

 these phenomena are involved, has but little diminished ; 

 but the excellent works 6 of Mallet (1846) and Hopkins 

 (1847) have thrown some light upon the nature of concussions, 

 the connection of apparently distinct effects and the separa- 



4 Cosmos, vol. i, p. 214. 



6 Cosmos, vol. i, p. 222. Compare Bertrand-Geslin, " Sur les roches 

 lancges par le Volcan de bouedu Monte Zibio pres du bourg de Sassuolo," 

 in Humboldt, Voyage aux Regions Equinoxiales du Nouveau Continent 

 (Relation ffistorique), t. iii, p. 566. 



'Robert Mallet, in the Transactions of the Royal Irish Academy , 

 vol. xxi (1848), pp. 51113, and First Report on the Facts of Earth- 

 quake Phenomena, in the Report of the Meeting of the British A ssociatior^ 



