TRUE VOLCANOES. 365 



Kliutschewsk had great igneous eruptions from 1727 to 

 1731, as also in 1767 and 1795. On the llth of September 

 1829, Erman performed the hazardous feat of ascending the 

 volcano, and was an eye-witness of the ejection of red-hot 

 stones, ashes, and vapour from the summit, while at a great 

 distance below it an immense stream of lava flowed from 

 a Assure on the western declivity. Here also the lava is rich 

 in obsidian. According to Erman (Beob., vol. i, pp. 400 

 403 and 419) the geographical latitude of the volcano is 56 D 4', 

 and its height in September 1829 was, on a very accurate 

 talculation, 15,763 feet. In August 1828 ; on the other hand, 

 Admiral Liitke, on taking angles of altitude at sea, at a 

 distance of 160 knots (40 nautical miles) found the summit 

 of Kliutschewsk 16,498 feet high (Voyage,*, iii, p. 86; 

 Landgrebe, Vulkane, Bd. i, s. 375386). This measure- 

 ment, and a comparison of the admirable outline drawings. 

 of Baron von Kittlitz, who accompanied Lutke's expedition 

 on board the Seniawin, with what Erman himself observed 

 in September 1829, led the latter to the conclusion that, in 

 this short period of thirteen months, great changes had taken 

 place in the form and height of the summit. "I am of 

 opinion," says Erman (Reise,vol. iii, p. 359), "that we can 

 scarcely be wrong in assuming the height of the summit in 

 August 1828, to have been 266 feet more than in September 

 1829, during my stay in the neighbourhood of Kliutschi, 

 and that therefore its height at the former of these periods 

 must have been 16,029 feet." In the case of Vesuvius I 

 found, by my own calculations (founded on Saussure's 

 barometrical measurement in 1773), of the Rocca del Palo, 

 the highest northern margin of the crater, that up to the 

 year 1805, that is to say, in the course of thirty-two years, 

 this northern margin of the crater had sunk 35 \ feet, while 

 from 1773 to 1822, or forty-nine years, it had risen (appa- 

 rently) 102 feet (Views of Nature, 1850, pp. 376378). In 

 the year 1822, Monticelli and Covelli calculated the Rocca 

 del Palo at 3990 feet, and I at 4022 feet ; I then gave 

 3996 as the most probable result for that period. In the 

 spring of 1855, thirty -three years later, the delicate baro- 

 metrical measurements of the Olmutz astronomer, Julius 

 Schmidt, again brought out 3990 feet (Neue Bestimm. am 

 Vesuv. 1856, s. i, 16 and 33). It would be curious to 



