S36 COSMOS. 



substances, has himself renounced his bold chenacal hypothcsij 

 in his last work ( Cojisolation in Travel, and last Days of a 

 Philosopher) — a work which can not fail to excite in tlic 

 reader a feehng of the deepest melancholy. The great mean 

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

 weight of potassium (0-86o), of sodium (0'972), or of the 

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

 the ofaseous emanations from the fissures of craters, and from 

 gtill warm streams of lava, besides many chemical considera- 

 tions, stand in opposition with the earlier conjectures of Davy 

 end Ampere.* If hydrogen were evolved from erupted lava, 

 how great must be the quantity of the gas disengaged, 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 11th of June to the 3d of August, 1783, 

 described by Mackenzie and Soemund Magnussen), a space of 

 many square miles was covered by streams of lava, accumu- 

 lated to the thickness of several hundred feet I Similar diffi- 

 culties are opposed to the assumption of the penetration of the 

 atmospheric air into the crater, or, as it is figuratively ex- 

 pressed, the inhalatio7i 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, 

 can not assuredly have its source in chemical affinity, or in 

 the mere contact of individual or merely locally distributed 

 substances. Modern geognosyt rather seeks the cause of this 

 activity in the increased temperature with the increase of 

 depth at all degrees of latitude, in that powerful internal heat 

 which our planet owes to its first sohdification, its formation 

 in the regions of space, and to the spherical contraction of 



* See Berzelius andWohler, in Poggend., Annalen, bd. i., s. 221, and 

 l)d. xi., s. 146 ; Gay-Liissac, in the Annales de Chimie, t. x., xli., p. 422 ; 

 and Bischof s Reasons against the Chemical Theory of Volcanoes, in the 

 English edition of his IVdrmelehre, p. 297-309. 



t [On the various theories that have been advanced in explanation of 

 volcanic action, see Daubeney On Volcanoes, a work to which we have 

 made continual reference during the preceding pages, as it constitutes 

 the most recent and perfect compendium of all the important facts re- 

 lating to this subject, and is peculiarly adapted to serve as a source of 

 reference to the Cosmos, since the learned author in many instances en- 

 ters into a full exposition of the views advanced by Baron Humboldt. 

 The appendix contains several valuable notes with reference to the 

 most recent works that have appeared on the Continent, on subjects re- 

 lating to volcanoes ; among others, an interesting notice of Professor 

 Bischof's views "on the origin of the carbonic acid discharged trom 

 volcanoes," as enounced in his recently published work, Lehrbuck def 

 Chemischcn tmd Physikalischcn Geologie.'\ — Tr. 



