EXPLANATORY ADDITIONS. 



(I) p. 303. — " A more complete determination of the margins 

 of the Crater of Mount Vesuvius.'' 

 My astronomical fellow-labourer, Oltmanns, who was im- 

 happily too early lost to science, has re-calculatccl the baro- 

 metric measurements I made on Mount Vesuvius (from the 

 2 2 iicl to the 25th of November, and on the 1st of December, 

 1822), and compared the results with those yielded by the 

 measurements given to me in manuscript by Lord Minto'; 

 Visconti, Monticelli, Brioschi, and Poulett Scrope. 



A. liocca del Palo, the highest northern margin of the Crater 

 of Vesuvius, was estimated hy — 



Saussure, in 1773, barometrically; probably according Feet. 



to Deluc's formula . .... 3894 



Poli (1794), barometrically 3875 



Breislak (1794), barometrically, although, as in the 



case of Poli, it is uncertain what formula was used . 3920 

 Gay-Lussac, Leopold von Buch, and Humboldt (1805), 

 barometrically, according to the formula of Laplace, 



as in all the folio wins; barometric results . . 3856 



Brioschi (1810), trigonometrically . . . . 4079 



Visconti (1816), trigonometrically . . . . 3977 



Lord Minto (1822), barometrically, and frequently re- 

 peated ........ 3971 



Poulett Scrope (1822). This calculation is somewhat 

 uncertain, owing to the unknown relation of the 



diameters of the tubes to those of the cistern . . 3862 



Monticelli and Covelli (1822) 3990 



Humboldt (1822) 4022 



The most probable final result is 2026 feet above the 

 hermitage, or 3996 feet above the level of the sea. 



B. The lowest south-eastern margin of the Crater, opposite 



Bosche Tre Case. 



After the eruption of 1794, this margin was 426 feet 

 lower than the Rocca del Palo, consequently, if the 

 latter be estimated at 3996 feet, it would be . . 3570 



Gay-Lussac. Leopold von Buch, and Humboldt (1805), 



barometrical! v . . . • • . .3414 



Humboldt (1822), barometrically . . . .3491 



