Oil Sal Nitrum and Nitro- Aerial Spirit 175 



the tongue, the taste of vitriol will be manifest 

 enough. Indeed nitro-aerial spirit, after a lapse of 

 time, unites and effervesces with the metallic mineral 

 or saline-sulphureous marchasite (such as vitriol is 

 usually made from) which is mixed in the said sand, 

 and at last turns it into vitriol in the manner 

 described in another place. 



Let us next consider how not only the hot springs 

 of Bath but all thermal springs acquire their heat. 

 With regard to the heat of thermal springs, I cannot 

 agree with those who maintain that their heat is due 

 to warmth communicated by subterranean fire. For 

 if any fire of this sort burned in the bowels of the 

 earth, it would certainly betray itself by its flame 

 bursting out somewhere ; since indeed a continual 

 influx of air is absolutely necessary for the mainten- 

 ance of fire. But granting that there are subterranean 

 fires, how is it, I ask, that they are not extinguished 

 by the waters which they are supposed to heat ? 

 And whence should the material be supplied for 

 maintaining a fire so vast and enduring ? 



Wherefore, since it is not probable that the hot 

 springs are heated by subterranean fires, we may 

 maintain with our learned countryman, Jordan, that 

 the warming of the hot springs originates in 

 fermentation excited somewhere in the bowels of the 

 earth. But to understand how this fermentation is 

 produced the following must be premised. 



In the first place, then, it may reasonably be 

 supposed that at any rate most fountains derive their 

 origin from rain-water. For it is not probable that 

 any o f them are derived, as is generally believed, 

 from the sea ; for who can entertain the idea that the 

 gushing waters which burst forth from the summits 

 of the loftiest mountains have their origin in the 



