472 DOMAIN XII. TOLCANIC. 



edly, have been much beneath the level of the 

 sea*. Had the grottoes then been visited, what 

 a fund of knowledge might not have been ac- 

 quired ! 



Vapours. When the volcano is at rest, vapours ar 

 seen to arise from the cauldron's brim, or front 

 the interior of its sides, which are very percepti- 

 ble. It would be difficult to conceive it possible 

 that they should proceed from the internal fur- 

 nace ; that they should, by tortuous and hidden 

 conduits, penetrate from such a profound depth 

 to the summit of the cone : for all confined va- 

 pour seeks for liberation by the shortest road ; 

 and, consequently, were these derived from a 

 source so low, they would issue from the bottom 

 of the cauldron, which presents them an easier 

 passage with a smaller mass of matter to tra- 



* " If the angle of descent, during the distance of the three miles, 

 was 60 from vertical, or 30 from an horizontal line, the perpendi- 

 cular depth, by a plain trigonometrical problem, will be found to 

 have been 7Q20 feet ; if, however, the steepness of the declivity be 

 reduced to form an angle of no more than 22j, the perpendicular 

 depth will yet have been 6o60 feet ; and, as the height of Vesuvius, 

 according to our author (tome ii. p. 43), is only 3Q22 English feet, 

 allowing the statement of the length of the descent to the plain, as 

 stated by Braccini, to have been correct, viz. three English miles, , 

 or 5280 yards, that plain must have been at least 2000 feet below the ' 

 level of the sea, even with a slope of descent of only 22j; but if & 

 slope of 30 be allowed, it will have been 4000 English feet below 

 the level of the sea ! TRANSL." 



