them, more efl'ectually than those who with greater pretensions attempt to build 

 up theories, which, at best, can have no other object than as means of classify- 

 ing facts and guiding observers to the fittest objects of examination. 



OF VOLCANIC THUNDER-CLOUDS. 



The clouds of ashes, smoke, and vapor, which issue from volcanoes, exhibit 

 i IK- phenomena of thunder and lightning. All observers, ancient and modern, 

 concur in their evidence on this question. Pliny the younger, in his celebrated 

 letters to Tacitus, speaks of the lightning that issued from the clouds in the 

 eruption of Vesuvius, in the year 79 of the Christian era, in which his uncle, 

 Pliny the naturalist, lost his life. Delia Torre gives the same evidence respect- 

 ing the eruption of 1182 ; and Bracini states that the column of smoke which 

 issued from the same volcano in the eruption of 1631, and which spread in the 

 atmosphere to a distance of forty leagues, was attended by lightning, by which 

 many persons and animals were killed. The lightning in all these accounts 

 is described as being tortuous and serpentine. The same description is given 

 by Giovanni Valetta of the appearance of the eruption of 1707. 



The inhabitants of the foot of the mountain assured Sir William Hamilton 

 that, in the eruption of 1767, there were more terrified at the lightning which 

 fell among them than at the burning lava and other fearful circumstances at- 

 tending the eruption. 



Sir William Hamilton states, that in the eruption of 1779 there issued from 

 the crater of Vesuvius, together with the red-hot fluid lava, constant puffs of 

 black smoke, intersected by serpentine lightning, which appeared at the mo- 

 ment it escaped from the crater. 



In 1779 the lightning was not attended by audible thuwder. It was othef- 

 wi.se in the eruption of the 16th of June, 1794, of which an account has been 

 supplied by the same observer. During the latter eruption, the loudest and 

 mu -it-continued claps of thunder were heard. The lightning was in this case 

 productive of the usual effects. Houses stricken by it were destroyed, and the 

 clouds of ashes, from which these lightnings issued, were carried by the wind 

 as i';ir as Tarentum, a distance of one hundred leagues from Vesuvius, where 

 the lightning struck a building and destroyed a part of it. The ashes of which 

 this cloud was composed were as fine as common snuff. 



According to Seneca, a great eruption of Etna, in his own time, was accom- 

 panied by similar effects, and the same phenomena are recorded by the Abbe 

 .Francesco Ferrara of the eruption of 1755. 



When the island called Sabrina, in the neighborhood of the Azores (which 

 has since disappeared), rose from the sea in 1811, columns of intensely black 

 smoke, composed of dust and ashes, ascended from the bosom of the deep, and 

 wern intersected in their darkest and most opaque parts by vivid lightnings. 



The same appearances were observed in *he small volcano which, in July, 

 1831, appeared between Sicily and Pantellaria. 



It would be natural to ascribe the electricity of volcanic clouds to the aque- 

 ous vapor which is ejected, mixed with the dust, ashes, and lava, in great quan- 

 tities from the crater ; but this supposition is not so free from difficulties as to 

 be admitted without some hesitation. In the eruption of Vesuvius, in 1794, it 

 is hard to conceive that the vapor should be carried uncondensed from Vesu- 

 vius to Tarentum ; nor was there anything in the appearances on thayjccasion 

 which indicated the presence of any other substance in the cloud save a fine 

 dust ; yet the lightning struck a building at that place. According to the nar- 

 rative of M. Tellard, who witnessed the phenomenon, columns of black smoke 

 rose from the ocean before the island of Sabrina was formed. In this case, 



