TRUE VOLCANOES. 251 



its solitary position, at a distance from all roads of commu- 

 nication. It was only in December, 18 19, that an adven- 

 turous and highly informed traveler, Sebastian Wisse, after 

 a sojourn of five years on the chain of the Andes, ascended 

 it, and nearly reached the extreme summit of the snow- 

 covered, precipitous cone. lie not only made an accu- 

 rate chronomctric determination of the wonderful frequency 

 of the eruptions, but also investigated the nature of the 

 trachyte which, confined to such a limited space, breaks 

 through the gneiss. As has already been remarked,* 2G7 

 eruptions were counted in one hour, each lasting on an 

 average 13" -4, and, which is very remarkable, unaccom- 

 panied by any concussion perceptible on the ashy cone. The 

 erupted matter, enveloped in much smoke, sometimes of a 

 gray and sometimes of an orange color, is principally a mix- 

 ture of black ashes and rapilli, but it also consists partly of 

 cinders, which rise perpendicularly, are of a globular form 

 and a diameter of 15 or 1G inches. In one of the more vio- 

 lent eruptions, however, Wisse counted only fifty or sixty 

 red-hot stones as being simultaneously thrown out. They 

 usually fall back again into the crater, but sometimes they 

 cover its upper margin, or, visible by their luminosity at a 

 distance, glide down at night upon a portion of the cone, 

 which, when seen from a great way off, probably gave origin 

 to the erroneous notion of La Condamine, " that there was 

 an effusion of burning sulphur and bitumen." The stones 

 rise singly one after the other, so that some of them are fall- 

 ing down while others have only just left the crater. By 

 an exact determination of time, the visible space of falling 

 (calculated, therefore, to the margin of the crater) was ascer- 

 tained to be on the average only 78G feet. On JEtna, ac- 

 cording to the measurements of Sartorius von Waltershau- 

 sen and the astronomer D. Christian Peters, the ejected 

 stones attain an elevation of as much as 26G5 feet above 

 the walls of the crater. Gemellaro's estimates during the 

 eruption of JEtna in 1832 gave even three times this eleva- 

 tion ! The black, erupted ashes form layers of three or four 

 hundred feet in thickness upon the declivities of the Sangay 

 for a circle of nearly fourteen miles in circumference. The 

 color of the ashes and rapilli gives the upper part of the 

 cone a fearfully stern character. We must here again call 

 attention to the colossal size of this volcano, which is six 

 times greater than that of Stromboli, as this consideration is 



* Cosmos, see page 175. 



