Dr Daubeny on the Spring at Torre del Annwiziata. 229 



air only in consequence of being heated, did not rccorabine with 

 it upon becoming again cool. 



The expulsion of air from water in a retort by ebullition does 

 not seem a strictly parallel case, because the whole body of the 

 liq^uid is here kept at an high temperature ; whereas, we know 

 that the upper strata, at least, of the sea-water, remained in the 

 neighbourhood of the volcano at the same point of heat as in 

 other parts of the Mediterranean. But, in the case of a thermal 

 spring, where the whole body of the liquid has its temperature 

 raised considerably, there is no difficulty in conceiving that its 

 gas may have been expelled, and that it may pass upwards 

 through the several strata of the fluid, until it reaches the air, 

 without meeting with any capable of dissolving it. 



Even the large quantity of gas disengaged at Bath may per- 

 haps be attributed to the source itself, without resorting to any 

 such theory as that by which, in my paper in the Philosophical 

 Transactions in 1834, I was led to account for it, although in 

 this case the carbonic acid with which the water is found im- 

 pregnated, would have assisted in promoting its expulsion. 



To those, however, who refuse to admit volcanic action to 

 be a process of oxygenation, such a mode of explaining the 

 emission of nitrogen would seem to remove the difficulty only 

 one step farther, since it still remains to be shewn, why spring- 

 water, which is in general impregnated more fully with oxygen 

 than with nitrogen gas, should in these cases disengage chiefly 

 the latter. 



I ought also in candour to acknowledge, that, in none of the 

 warm springs in the neighbourhood of Naples (for that of Ca- 

 stellamare is scarcely thermal), did nitrogen appear to be evolved 

 in any such notable quantity, as happens amongst the extinct 

 volcanos of Auvergne, in the thermal springs at the base of the 

 Alps, and in other localities less obviously connected with vol- 

 canic agency. 



The warm springs we meet with between Puzzuoli and Naples 

 occur in wells which afford no opportunity for examination, but 

 the mineral ones in Ischia, all of which I have visited, seem 

 totally destitute, not only of this, but of every other gaseous im- 

 pregnation. 



Whilst admitting, therefore, that the hot springs of Campania 



