No. I. — Account of Mount Vesuvius. 193 



cd the wall of the crater. It is generally alleged that the re- 

 maining portion of that ridge was actually the form of a seg- 

 ment of the original crater; yet even though we admit with Vis- 

 conti (who it is said measured it*) that the present crater 

 coincides with the centre of that circular segment, yet I can- 

 not enter into the adoption of so very enormous a crater as this 

 would imply, — certainly many miles in diameter. It seems to 

 me more probable that a part only of the Somma was the 

 wall of the existing crater ; but that by the tremendous (per- 

 haps unequalled) force of the eruption of 79, a longitudinal 

 rent was made, and a whole side of the hill thrown towards 

 the sea, where its debris formed the plain on which the new 

 cone rose. If we suppose a disposition of the volcanic agency 

 to work towards the sea, or a smaller resisting force to oppose 

 it on that side, the circular direction of the crack will be easi- 

 ly explained, as well as the subsequent change in position of 

 the crater. 



Some observations on that part of the mountain properly 

 called Vesuvius must next be made. Like all the higher 

 portions of volcanos, it is a cone covered on the exterior with 

 ashes, liable to change its height and form by different eruptions, 

 and having on its summit a deep chasm or crater of great size in 

 proportion to its height. The measurements of the absolute 

 altitude of the different parts of the mountain at successive 

 periods are of great interest, and, much as I wished to have 

 added some new facts on the subject myself, I am glad to find 

 that this problem has excited the attention of naturalists dur- 

 ing a series of years of some duration .-(• The imperfections 

 of barometrical measurement a century ago render the first 

 determinations very uncertain. The Abbe Nollet in 1749 made 

 it 3120 French feet, which probably approached the truth, 

 while three years after, Padre della Torre gave only 1677. 

 In 1772 Saussure found the height 3659 French feet; and af- 



* Daubeny on Volcanos. From the largest maps of the mountain I 

 have seen, I should not suspect this to be the case. 



f I had prepared and boiled a barometer for the express purpose of 

 measuring Vesuvius, but, being broke by an accident, I was compelled to 

 relinquish it. It was therefore with peculiar pleasure that I saw the ob- 

 servations of the Earl of Minto, in the Number of this Journal for July 

 1827, which formed a most valuable addition to my paper. 



