152 ' ON SUBTERRANEAN HEAJ. 



increases with lower parts of the niiue is ijaore> considerable than that of 

 * ' the upper parts. If in the cjeptbs the air a])pear hotter than 

 the water, it is probably because it has retained a part of 

 the heat it possessed wKen.it. enter^gl the mine. I have al- 

 ready pointed oui the reason why in 7, 8, and 9, the heat 

 was less than the depth requires. 



Pyrites do not > Experiments 10 and 11 ,sl^oiy, that there are circum- 



ahvays occa- stances in which the presence of pyrites does not occasion 

 sioa heat. i . i i • ,. V 



heat. That which they indicated was not occasioned by 



them, for in St. George's shaftj. where there was none, the 

 -.temperature was the same. 

 Heat increases Thus, setting aside every extraordinary cause, the ob- 

 ^d° fV"th^ servations I have reported appear to me to indicate, that at 



the depth of 150 met. [iCS yards] the temperature at Poul- 



laouen is 2° Qr 3° [3*6° or ^?4J JF,,] ^ore^ than at the siir- 



fiace. 



Observations made at Huelgoat. 



Huelgoat THE mine of Huel is in latitude 48° 18' J?"' N., lon^. 



iniae. go j/ 45'/^ ^][^he opening of its shaft is 173 met. [188 yards] 



above the level of the sea ; and is on a large hill, that sepa- 

 rates two valleys, the depth of which is 80 or <)0 met. [87 or 

 97 yards]. 



Me^n temper- From this latitude and elevatioJi we may infer the mean 



Tatlon^' ''•'"" temperature to be 1 1° [50° F.] 



Insciiist. '^^^ rock, like that of PouUaouen, is an argillaceous 



schist, but it likewise contains some strata of aluminous , 

 schist. 



Observations The following are the observations I made on the 5th of 



the same day. September, the same day as those at PouUaouen. 



Tabulated 1» In a gallery about 16 yards below that Tempe- 



^17.T ^ ^^[''^ the workmen commonly enter the "'^l ^^ ' 

 ^ith remarks, mine, into which no person had been for se- renh. Ft. In. 

 veral years, which has no other outlet, and in ' 

 . which there was no current of air, a therna^)- 

 nieter at its northern end after twentyminutes 



indicated 50^ 



After having descended the shaft called the 

 miners, and goiie a few dozen yards into Jthe 



gallery 



