AND GEOLOGICAL RELATIONS OF CERTAIN HOT SPRINGS. 
611 
temperature near the edge of the pool. What is the amount of discharge, or where 
the exit of the water, I do not know. So far as I know it has not been analysed. Its 
complete insulation in the heart of the hill, and its high temperature, renders it a 
most interesting subject for the experiment on constancy of temperature ; though we 
must not forget its near approximation to active volcanoes. There are various other 
passages in the rock which are used for vapour baths. I am glad to have this oppor- 
tunity of reproducing a curious and apparently accurate plan of these by Bulifon, 
published in Sarnelli’s Guida dei Forestieri, Napoli, 1688, and not, so far as I know, 
copied or superseded by later authors, whose works indeed are generally full of 
blunders on this subject. 
C. Temperature. — The elevation above the Mediterranean is, I believe, about 30 feet. 
Almost all authors have stated that the water boils. My observation was made with 
much care, though the difficulty of observing was so great that it may be doubtful to 
half a degree. The thermometer employed was one by Cary. I have already stated 
in the introduction the satisfaction which I had in recovering it after nine years, and 
thus rendering this observation available to science, by comparing it with my standard 
thermometer. 
Cary. Reduced. 
1826, December 11. — Baths of Nero or Sudatorij di Tritoli 183°*5 182°-2 
VI. La Pisciarella , near Naples. 
A. Geological Position.— This spring rises from the exterior of the cone of the Sol- 
fatara amidst decomposed volcanic rocks. It is within a short distance of the lake 
Agnano. 
B and C. Specialties and Temperature. — La Pisciarella rises from the ground under 
cover of a small hut. It contains sulphate of alumina, sulphuric acid, sulphur, and 
much sulphate of iron. To judge by the evidence of authors its temperature must 
be subject to extraordinary alternations. Sir William Hamilton declares that he saw 
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