3562 Mr Forbeis's Physical Notices of the Bay of Naples. 



lower. Delia Torre* found it to be 68° R. = 185° Fahr. 

 From my own very careful observations, which were made in 

 the month of December 1826, when the temperature of the air 

 was 48°.5, the interior of the hut was 70°.5, and the warmest 

 part of the spring 11£°.5. The Abbe Giraud Soulavief stated 

 it so low as 1 01° Fahr. Humboldt, in his Personal Narra^ 

 tive^X states the Pisciarelli of the Lake Agnano to have a tem- 

 perature of 93° Cent. = 199°.4 Fahr. At the same time there 

 seems to be some mistake in this part of Humboldt's work ; 

 for a few pages farther on, when speaking of the hot springs 

 of Nueva Valencia in South America, one of which has the 

 temperature of 90°.3 Cent. = 194.5 Fahr. he considers it the 

 warmest in the world, except that of Urijno in Japan, said to 

 be pure water at 100° Cent. Humboldt seems to be too gene- 

 ral in this assertion, not only in the example he himself gives 

 of the Pisciarella, but Dr Webster || has found the tempera- 

 ture of several springs in St Michael's, one of the Azores, to 

 be 207°, 203°, and 200° respectively. The Pisciarella, how- 

 ever, probably never attains now the temperature at which Ha- 

 milton and others observed it. Breislak§ notices some changes 

 which it seems to have experienced towards the close of the 

 last century, apparently by the falling in of the soil, which may 

 have materially affected it. It would appear, however, to have 

 been always very sensible to the effects of the weather, and par- 

 ticularly to the percolation of rain water. 



The water of this spring contains sulphate of alumina, some 

 uncombined sulphuric acid, a little sulphur, and sulphate of 

 iron in great abundance. So predominant is the last salt, that, 

 if the water be mixed with galls, it immediately becomes black, 

 and by evaporation forms very tolerable writing ink, as I 

 proved experimentally. The origin of these ingredients is 

 easily pointed out. The alumina and vitriol it derives from 

 the decomposed volcanic strata of the hill from which it issues, 

 appropriately named Monte Secco ; and the abundant streams 

 of sulphuretted hydrogen gas which rise through the water, 

 and give it the appearance of ebuUition, by uniting with the 



• Storia del Vesuvio, 4to, Napoli. 



+ In his notes to the French edition of Hamilton's works, 8vo, p. 445. 

 + Vol. iv. p. 171. II Edtn. Phil. Joum. vi. 308. § Campanie, ii. 66. 



