250 



Mr W. J. Henwood on the Temperature 



TABLE IV. 



ileal. Temperature?, at nearlj/ equal depths, in tke lodes which contain ores of 

 different metals. 



The following table (viz. Table V.) indicates the respective 

 ratios of increase in temperature, expressed in fathoms of de- 

 scent requisite to produce an elevation of one degree. The 

 columns 2 and 3 are formed from Table 11. ; 4, 5, and 6, from 

 Table III. ; 7, 8, and 9, from Table IV. ; and the last is the 

 arithmetical mean of all the others. The eight columns are 

 therefore deduced from the same facts, grouped in three dif- 

 ferent ways ; it may therefore be anticipated that there will be 

 considerable resemblance — between some of them, at least. 



The temperature of the air at Plymouth and Penzance, 

 which are near the eastern and western limits of the mining 

 districts of Devon and Cornwall, has been very accurately * 

 determined ; and the observations made at several interme- 

 diate spots-f* may, perhaps, be equally relied on. 



Rut this temperature, though affecting the rock to the depth 



* The mean temperature of Plymouth is stated, by Mr Han-is, at 52°. 081 ; 

 Reports of tlie Britibh Association, vii. p. 24 : that of Penzance, at 52'.0, by 

 Mr Giddy, Phil. Mag. and Annals, iii. p. 182. 



t Observations on the Temperature of Truro are recorded in the Reports 

 of the Royal Institution of Cornwall ; and of Falmouth, in the Reports of 

 the Roval C'oiawall Pohtechuic Society. 



