206 



THEORY OF CENTRAL HEAT. 



C^-' 



[Ch. XXXII. 



n 



At Naples, according to Mr. Mallet, tlie water in th.e Artesia 

 well at tlie Eojal Palace, at the depth of 1,460 feet, has a 

 temperature of only 68° Fahr,, which, deducting for the 

 mean temperature of the surface soil, 61° Fahr., gives an 



r" 



increment of only 1° Falir. for every 208 feet in depth. 

 Another well in the same city, only a mile distant from the 

 former and 909 feet deep, gives 1° Fahr. for 83 feet in depth. 

 It is conjectured that the low temperature of the well first 

 mentioned may be due to the cooling influence both of fresh 

 and sea water which may be filtered through porous beds of 

 tufa. 



Some writers have endeavoured to refer these phenomena 

 (which, however discordant as to the ratio of increasing heat 

 appear all to point one way) to the condensation of air con- 

 stantly descending from the surface into the mines. Tor the 

 air under pressure would give out latent heat, on the same 

 principle as it becomes colder when rarefied in the higher 

 ons of the atmosphere. But, besides that the quantity 

 of heat is greater than could be supposed to flow from this 

 source, the argument has been answered in a satisfactory 



^ 



manner 



Mr 



Cornwall the ascending have generally a higher temperature 

 than the descending aerial currents. The difl^erence between 

 them was found to vary from 9"" to 17° Fahr. : a proof that, 

 instead of imparting heat, these currents actually carry off a 

 large quantity from the mines. "^ 



If we adopt the mean increase of 1° Fahr. for every 65 feet 

 of depth, and assume, with the advocates of central fluidity, 

 that the increasing temperature is continued downwards for 

 an indefinite distance, we should reach the ordinary boiling 



more 



and at the depth 



miles should arrive at the 



m 



pyrometer, a heat sufiicient 



ti 



stance. 



diairram 



miles 



** 



the 2 circles, together with the lines themselves, represents a 



in depth. If, therefore, the heat Avent on 



miles 



* Phil. Mag. and Ann. Fob. 1830. 



incr 

 not 



stall 

 befo 



iiit€ 



ceiv 



face 



(les( 



stai 

 isr 



dep 

 an 



en 

 sti 

 cr 

 lo 

 ci 

 m 

 If 



of 



ten 



J. 

 in] 



ac( 



tad 



oft 

 oft 





