Volcanoes in the different regions of' the Earth. tSl 



neriffe as one to twenty-two. Vesuvius, therefore, has the cone 

 of ashes proportionally higher, probably because, as a volcano of 

 little height, it has acted principally by its summit. I succeed- 

 ed lately not only in repeating my barometrical measurements on 

 Vesuvius, but also in ascending that mountain three times, in 

 order to take a complete survey of all the edges of the crater. 

 This undertaking is perhaps deserving of some interest, because 

 it embraces the period of the great eruptions from 1805 to 1822 ; 

 and because it affords, perhaps, the only measurement of the 

 volcano, made with reference to all its parts, that has hitherto 

 been published. It shews that the edges of the crater, not only 

 in the places where they are visibly composed of trachyte, as in 

 the Peak of Teneriffe, and in all the volcanoes of tlie chain of 

 the Andes, but also every where else, present a phenomenon 

 much more constant than had previously been supposed from ob- 

 servations hastily made. Simple angles of height, determined from 

 the same point, answer much better for researches of this kind 

 than trigonometrical and barometrical measurements, otherwise 

 very complete. According to my last determination, the north- 

 west edge of Vesuvius has not perhaps undergone any diminu- 

 tion of height since the time of Saussure, that is to say for the 

 last forty-nine years, and the south-east edge, on the Bosche Tre- 

 Case side, which, in 1794, was 400 feet lower than the preced- 

 ing, has undergone a diminution of 10 toises. 



If the public journals, in describing the great eruptions, very 

 frequently relate that the form of Vesuvius has totally changed, 

 and if these assertions are confirmed by the picturesque views 

 of that mountain which are painted at Naples, the cause of 

 error exists in the circumstance that the contour of the edges of 

 the crater is confounded with those of the heaps of scoriae which 

 are accidentally formed in the centre of the crater, on the bot- 

 tom of the ignivomous mouth raised up by vapours. One of 

 these heaps, consisting of rapilli and scoriae, became gradually 

 visible in 1816 and 1818, above the south-east edsre of the 

 crater. The eruption of February 1822 increased it to such a 

 degree, that it even exceeded the Rocca del Palo, or the north- 

 west edge of the crater, by 100 or 110 feet. In the last erup- 

 tion, the remarkable cone, which was usually considered as the 

 true suunnit of Vesuvius, fell down with a terrible noise, so that 



