Mechanism of Stromboli . 501 



Bunsen is of opinion that the above is simply the mechanism of the 

 Great Geyser ; but that to account for some of the minor phenomena of 

 the second, or Strokur Geyser, some additional mechanism, not widely 

 differing from that suggested by Herschel, may be necessary. Some of 

 the relations which subsist between geyser-phenomena, as thus explained, 

 and those which he supposes to occur at various depths in the tubes of 

 active volcanic vents, have been well discerned by Sir Charles Lyell, and 

 are described in his ' Principles of Geology,' 10th edit. vol. ii. p. 220 ; but 

 he has not applied them in explanation of the rhythmic recurrence of the 

 outbursts of Stromboli. From Bunsen's explanation, as above sketched, 

 it follows that the interval between two outbursts depends mainly on 

 three conditions the depth and capacity of the tube, the rate at which 

 the water that fills it is supplied, and the rate at which heat, from what- 

 ever source, is transmitted to the water. Were these three all perfectly 

 constant, the interval between two successive outbursts would be always 

 the same, but it must vary, more or less, as any one of these three conditions 

 may be altered. Again, the duration of the outburst, or time occupied 

 in the expulsion of the column of water, and the height to which it is 

 sent, as well as the volume of the jet, depend upon the capacity of the 

 tube and the height to which the water rises within it before the blow-out 

 commences, and must therefore vary in time with these conditions. The 

 depth and capacity of the tube may vary secularly or be deranged sud- 

 denly ; the temperature of the infiltrated water may vary, and therefore 

 the time of its boiling under given conditions may alter with the season ; 

 and the temperature of the sides of the tube, and of the steam blown into 

 it from fissures, must vary with the intensity of neighbouring volcanic 

 action whence these are drawn. 



Before proceeding to connect the circumstances presented by Strom- 

 boli with the above facts in relation to geysers, it will be necessary to 

 adduce some facts in relation to the former, derived from personal obser- 

 vation. 



In the latter part of the year 1864 I examined the whole of the Lipari 

 Islands, with the exception of Felicudi and Alicuda, which the lateness 

 of the season rendered impossible. Starting from Cape Mellazo (Sicily) 

 in a "well-found" speronala, with a crew of eight men, which I retained 

 throughout the voyage amongst the group of islands, I had the pleasure 

 and advantage of being accompanied for some days, and as far as Lipari 

 Island, Panaria, and Stromboli, by my friend Colonel H. Yule, B.E., well 

 known for his embassy to Siam, and recently for his noble edition of 

 Marco Polo's travels, and by various other works. Our landing at 

 Stromboli was difficult, from the high surf running in ; and after our 

 arrival the weather became so much more tempestuous as to detain 

 us there some time. "We enjoyed the hospitality of Padre Capellano 

 Giusseppe Eanza, whose house is situated not far from the central parts 

 of the island, and whence a steep but not difficult walk leads up to the 



2Q2 



