Sir H. Davy on the Phenomena of Volcanoes. 91 



edge of the stream ; they proved to be the same in the nature 

 of their constituent parts as those of the lava of the 26th of 

 January, but with a larger proportion of sulphate of soda, and 

 a smaller proportion of muriate of iron ; and I have no doubt 

 that the dense white smoke which was emitted in immense 

 columns by the lava during the whole of its course, was pro- 

 duced by the same substances. 



I shall now mention the state of the volcano at some other 

 periods. 



When I was at Naples in May 1814, the crater had the ap- 

 pearance of an immense funnel, closed at the bottom, with 

 many small apertures emitting steam ; and on the side towards 

 Torre del Greco, there was a large aperture from which flame 

 issued to a height of at least 60 yards, producing a most 

 violent hissing noise. This phenomenon was constant during 

 the three weeks I remained at Naples. It was impossible to 

 approach sufficiently near the flame to ascertain the results of 

 the combustion ; but a considerable quantity of steam ascended 

 from it. When the wind blew the vapours upon us, there was 

 a distinct smell both of sulphurous and muriatic acids. There 

 was no indication of carbonaceous matter from the colour of 

 the smoke ; nor was any deposited upon the yellow and white 

 saline matter which surrounded the crater, and which I found 

 to be principally sulphate and muriate of soda, and muriate of 

 iron : in some specimens there was a considerable quantity of 

 muriate of ammonia. 



In March 1815, the appearances presented by the crater 

 were entirely different. There was no aperture in the crater ; 

 it was often quiet for minutes together, and then burst out into 

 explosions with considerable violence, sending fluid lava and 

 ignited stones and ashes to a considerable height, many hun- 

 dred feet, in the air. 



These eruptions were preceded by subterraneous thunder, 

 which appeared to come from a great distance, and which 

 sometimes lasted for a minute. During the four times that I 

 was upon the crater in the month of March, I had at last learnt 

 to estimate the violence of the eruption from the nature of the 

 sound : loud and long continued subterraneous thunder indi- 

 cated a considerable explosion. Before the eruption the cra- 

 ter appeared perfectly tranquil ; and the bottom, apparently 

 without an aperture, was covered with ashes. Soon, indistinct 

 rumbling sounds were heard as if at a great distance; gra- 

 dually the sound approached nearer, and was like the noise of 

 artillery fired under our feet. The ashes then began to rise 

 and to be thrown out with smoke from the bottom of the crater ; 

 and lastly, the lava and ignited matter was ejected with a most 



N 2 violent 



