16 Professor BisclioPs Reasons ajainst 



other hand, that the advocates of the hypothesis presented, 

 allow the existence of a central heat supporting chemical ac- 

 tions, it would not be difficult to conceive the melting of 

 lavas. 



I shall not pass from this subject without adding, that this 

 hypothesis does not necessarily require the volcanic actions 

 at very considerable depths below the surface of the earth, 

 but merely where the earthy and alkaline metals were pre- 

 sent. This circumstance may perhaps be viewed as more fa- 

 vourable to the hypothesis in question than to the other, which 

 assumes a central heat, and consequently considerable depths, 

 for volcanic actions. But are there grounds for supposing that 

 the place where these actions are developed is near the sur- 

 face of the earth ? On the contrary, all volcanic phenomena, 

 both the eruptions themselves and earthquakes, afford de- 

 cided proofs that volcanic actions are peculiar to a spot very 

 deep below the surface. As to this subject I refer to my for- 

 mer publications. 



The theory of Professor Daubeny supposes the existence, 

 near and about the focus of a volcano, of vast caverns, caused 

 originally by the heaving up of the softened rocks, owing to 

 the elastic vapours disengaged, and consequently filled in the 

 first instance by these matters. Granting the passages be- 

 tween these caverns and the external atmosphere not to be 

 hermetically sealed during the state of rest of the volcano, 

 air must enter into them. But it is obvious that, on the be- 

 ginning of the volcanic action, particularly on the heaving up 

 of the lava, those passages must be completely interrupted ; 

 therefore, only that air which formerly entered the cavities 

 can act on the earthy and alkaline metals supposed to be in 

 their vacuity. This effect will consequently be limited, and 

 finished as soon as the oxygen of this air is consumed. In 

 order to gain a distinct notion of the quantity of air requisite 

 to produce a certain quantity of lava by oxidation of the earthy 

 and alkaline metals, let us make the following calculation : 

 Let us take, like Professor Daubeny, for instance, the analysis 

 of the lava from Etna given by Dr Kennedy. According to 

 the calculation given by the former, 58 parts of the metallic 

 bases of this lava require 42 parts of oxygen to give 100 parts 



