TOLCANOES. 235 



merely locally distributed substances. Modern geognosy* 

 rather seeks the cause of this activity in the increased tem- 

 perature with the increase of depth at all degrees of lati- 

 tude, in that powerful internal heat which our planet owes to 

 its first solidification, its formation in the regions of space, 

 and to the spherical contraction of matter revolving ellipti- 

 cally in a gaseous condition. We have thus mere conjecture 

 and supposition side by side with certain knowledge. A phi- 

 losophical study of nature strives ever to elevate itself above 

 the narrow requirements of mere natural description, and does 

 not consist, as we have already remarked, in the mere accu- 

 mulation of isolated facts. The enquiring and active spirit of 

 man must be suffered to pass from the present to the past, to 

 conjecture all that cannot yet be known with certainty, and 

 still to dwell with pleasure on the ancient myths of geognosy 

 M-hich are presented to us under so many various forms. If 

 we consider volcanoes as irregular intermittent springs, emit- 

 ting a fluid mixture of oxidised metals, alkalies, and earths, 

 flowing gently and calmly wherever they find a passage, or 

 being upheaved by the powerful expansive force of vapours, 

 we are involuntarily led to remember the geognostic visions of 

 Plato, according to which hot springs, as well as all volcanic 

 igneous streams, were eruptions that might be traced back to 

 one generally distributed subterranean cause, Pyriplileyethon.\ 



* [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 relat- 

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

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

 enters 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 relating 

 to volcanoes ; amongst others, an interesting notice of Professor Bischof 's 

 views " on the origin of the carbonic acid discharged from volcanoes," 

 as enounced in his recently published work, Lehrbuch der chemischen 

 und physikalischen Geologic.] Tr. 



*h According to Plato's geognostic views, as developed in the Phcedo* 

 Pyriphlegethon plays much the same part in relation to the activity of 

 volcanoes, that we now ascribe to the augmentation of heat as we descend 

 from the Earth's surface, and to the fused condition of its internal strata. 

 PJicedo, ed. Ast. p. 603 and 607 ; Annot., p. 808 and 817.) " Within 

 the earth, and all around it, are larger und smaller caverns. Water flows 



