196 Physical Notices on the Bay of Naples. 



as a very general fact in geology" says the able author of the 

 article Physical Geography in the Edinburgh Encyclopaedia *, 

 " that the most elevated volcanic mountains have the smallest 

 craters at their summits, had it not been ascertained by Hum- 

 boldt that the crater of the colossal volcanos of Cotopaxi and 

 Ruen Pichincha are nearly a mile in diameter. 11 Vesuvius 

 now exceeds even these. Etna, which is about 11 ,000 feet high, 

 had a crater estimated by Sir William Hamilton f in 1769 at 

 only 2J miles in circumference, three quarters of a mile smal- 

 ler than Vesuvius, which is but 3400 feet high. The peak 

 of Teneriffe, which is above 12,000 feet in height, has a crater 

 only 300 by 200 feet, and 100 deep +. 



In the proportion which the cone of ashes bears to the total 

 altitude, Vesuvius is also remarkable, as the following compa- 

 rison made by the indefatigable Humboldt § proves. 



Total height, 



Toises. 



Vesuvius, 606 



Peak of Teneriffe, 1904 



Pichincha, 2490 



The mean slopes of volcanic cones, according to the same 

 author, are from 32° to 40°, and the steepest parts either of 

 Vesuvius, Teneriffe, Pichincha, or Jorullo, from 40° to 42°. 

 I have been at some pains to estimate the existing slope of 

 Vesuvius by the comparison and careful measurement of a 

 great number of eye sketches of Vesuvius made by different 

 persons, so as to eliminate as much as possible the errors of 

 such a vague observation, though the eye is not liable, as far 

 as I know, to any particular misjudgment in taking profile 

 views, such as it experiences in looking down a rapid descent. 

 From a mean of a considerable number of angles thus taken 

 for the northern acclivity, and by several observers, in the close 

 of 1 826 or the following spring, I deduce 41 f ° as a probable 

 mean, from which the extreme differences are not so consider- 

 able as we might have expected. This represents nearly the 

 angle of ascent by the usual path from the hermitage of St 

 Salvador, and the line whose angular elevation is measured ex- 



* Vol. xvi. p. 487. t Daubeny on Volcanos, p. 25. 



J Campi Phlegrcei, i. 47. $ Pers. Nar. i. 207. 



