434 Volcanoes. 



ence as a confined elastic fluid, rend tlie rocks, and burst into 

 a flame upon exposure to the atmosphere. There is certainly 

 a great degree of plausibility about this hypothesis, and it is 

 not altogether unphilosophical ; but Davy was, from some 

 cause, induced to renounce it, and give preference to an ex- 

 planation founded on the doctrine of central heat. Dr. 

 Daubeny, who has adopted Davy's discarded child, suggests 

 that it is not inconsistent with what we know of Davy's cha- 

 racter to suppose that he acquired a distaste for the theory in 

 question, when he found it an object of admiration among an 

 humbler class of enquirers. This observation may be correct ; 

 but perhaps a better reason may be given for Davy's want of 

 confidence in his own theory. 



If the assumption of a number of unproved statements as 

 facts afford any argument against the correctness of a theory, 

 this one of Davy's must stand very low in our estimation. 

 But, lest we should be charged with arrogance in thus speak- 

 ing of that which was proposed by Davy, and is still sup- 

 ported by an acknowledged scholar, we will give our reasons 

 for the statement. Two admissions are required by this 

 theory, and they appear to draw largely upon the faith of the 

 reader, but it is absolutely necessary that he should admit 

 the probability of the existence of a metallic nucleus, and its 

 inflammability, or he must at once give up the theory itself. 

 We must first allow the existence of a metallic nucleus. It 

 is possible that the interior of our world consists of metallic 

 alloys, but we have as much reason to believe that it consists 

 of water or of stone. We will, however, grant, for the sake 

 of the argument, that the earth, beneath its superficial cover- 

 ing, consists of metals, for it is only a matter of opinion, 

 and we may imagine it one substance as well as another; all 

 that is required by ascertained facts is, that we should fix upon 

 some heavy body. We are next required to admit that this 

 metallic nucleus is of such a character that it is oxidised by 

 the presence of water, the hydrogen being liberated and 

 ignited. To determine the nature of the metallic nucleus, we 

 must examine the character of the lava that is ejected, or of 

 the earths composing the crust of our globe, which are sup- 

 posed by this theory to have been at some former period a 

 part of the metallic globe. Dr. Daubeny accurately states 

 that silica, alumina, lime, and iron are the chief constituents 

 of volcanic products. The metallic alloy, therefore, must be 

 composed of silicon, aluminum, calcium, and iron. Now, of 

 all electro-positive substances, silicon is the most incom- 

 bustible : it may be made white hot in the open air without 

 evincing any tendency to burn ; and, so far from decomposing 



