VOLCANOES. 235 



Tlie greater part of the ascending vapor is mere steam. 

 When condensed, this ibrms springs, as in Pantellaria,=^ where 

 they are used by the goatherds of the island. On the morn- 

 mg of the 26th of October, 1822, a current was seen to flow 

 from a lateral fissure of the crater of Vesuvius, and was long 

 supposed to have been boiling water; it was, however, shown, 

 by Monticelh's accurate investigations, to consist of dry ashes, 

 which fell like sand, and of lava pulverized by friction. The 

 ashes, which sometimes darken the air for hours and days to- 

 gether, and produce great injury to the vineyards and olive 

 groves by adhering to the leaves, indicate by their columnar 

 ascent, impelled by vapors, the termination of every great 

 earthquake. This is the magnificent phenomenon which 

 Pliny the younger, in his celebrated letter to Cornelius Tacitus, 

 compares, in the ca.se of Vesuvius, to the form of a lofty and 

 thickly branched and foliaceous pine. That which is de- 

 scribed as flames in the eruption of scoriee, and the radiance 

 of the glowing red clouds that hover over the crater, can not 

 be ascribed to the efi'ect of hydrogen gas in a state of combus- 

 tion. They are rather reflections of light Avhich issue from 

 molten masses, projected high in the air, and also reflections 

 from the burning depths, M^ience the gloAving vapors ascend. 

 We will not, however, attempt to decide the nature of the 

 flames, which are occasionally seen now, as in the time of 

 Strabo, to rise from the deep sea during the activity of littoral 

 volcanoes, or shortly before the elevration of a volcanic island. 



When the questions are asked, what is it that burns in the 

 volcano ? what excites the heat, fuses together earths and 

 metals, and imparts to lava currents of thick layers a degree 

 of heat that lasts for many years?! it is necessarily in:iplied 

 that volcanoes must be connected with the existence ot sub- 

 stances capable of maintaining combustion, like the beds of 

 coal in subterranean fires. According to the diflerent phase* 

 of chemical science, bitumen, pyrites, the moist admixture of 

 finely-pulverized sulphur and iron, pyrophoric substances, and 

 the metals of the alkalies and earths, have in turn been desig- 

 nated as the cause of intensely active volcanic phenomena. 

 The great chemist, Sir Humphrey Davy, to whom we are in- 

 debted for the knowledge of the most combustible metallic 



* [Steam issues from many parts of this insular mountain, and sev- 

 eral hot sj)rings gush forth from it, which form together a lake 6000 feet 

 in circumference. Daubeney, op. cit.] — Tr. 



t See the beautiful ex[)eriuieuts on the cooling of masses of rock, iu 

 Bischof's Wdrmtlehrc, s. :384, 443, 500-5 12. 



