234 COSMOS. 



of heat that lasts for many years ?* it is necessarily implied 

 that volcanoes must be connected with the existence of sub^ 

 stance^ capable of maintaining combustion, like the beds of 

 coal in subterranean fires. According to the different phases 

 of chemical science, bitumen, pyrites, the moist admixture of 

 finely pulverised sulphur and iron, pyrophoric substances, and 

 the metals of the alkalies and earths, have in turn been desig- 

 nated as the cause of intensely active volcanic phenomena. 

 The great chemist, Sir Humphrey Davy, to whom we are 

 indebted for the knowledge of the most combustible metallic 

 substances, has himself renounced his bold chemical hypo- 

 thesis in his last work (Consolation in Travel, and last Days of 

 a Philosopher] a work which cannot fail to excite in the 

 reader a feeling of the deepest melancholy. The great mean 

 density of the earth (5*44), when compared with the specific 

 weight of potassium (0-865), of sodium (0-972), or of the 

 metals of the earths (1'2), and the absence of hydrogen gas in 

 the gaseous emanations from the fissures of craters, and from 

 still warm streams of lava, besides many chemical consi- 

 derations, stand in opposition with the earlier conjectures 

 of Davy and Ampere. f If hydrogen were evolved from 

 erupted lava, how great must be the quantity of the gas dis- 

 engaged, when, the seat of the volcanic activity being very 

 low, as in the case of the remarkable eruption at the foot 

 of the Skaptar-Jokul in Iceland (from the llth of June to 

 the 3rd of August, 1783, described by Mackenzie and Soe- 

 mund Magnussen), a space of many square miles was covered 

 by streams of lava, accumulated to the thickness of several 

 hundred feet ! Similar difficulties are opposed to the assump- 

 tion of the penetration of the atmospheric air into the crater, 

 or as it is figuratively expressed, the inhalation of the earth, 

 when we have regard to the small quantity of nitrogen 

 emitted. So general, deep-seated, and far-propagated an 

 activity as that of volcanoes, cannot assuredly have its source 

 in chemical affinity, or in the mere contact of individual or 



* See the beautiful experiments on the cooling of masses of rock, in 

 Bisehofs Wdrmelelire, s. 384, 443, 500-512.,' 



: -f 1 See Berzelius and Wohler, in Poggend. Annalen, bd. i. s. 221, and 

 bd. xi. s. 146 ; Gay Lussac, in the Annales de Chimie, t. x. xii. p. 422; 

 and Bisehofs Reasons against the Chemical Theory of Volcanoes, in 

 the English edition of his Warmelehre 297-309. 



