324 Observations on Subterraneous Heat, 



Nervations I have related appear to me to indicate that, at 

 the depth of 1 50 metres, the temperature is at Pouallouett 

 3° or 4 higher than at the surface of the ground. 



Observations made at Hnelgoat. 



The mine of Huelgoat is situated at 48° 1&' 17" latitude, 

 and 6° l' 4(3" of west longitude: i»$ orifice (the mouth of 

 the pit) is 173 metres above the level of the sea. It is situ- 

 ated upon a broad hill, which separates two valleys, the 

 depth of which is from 80 to 90 metres. 



From what we have said as to the latitude and elevation, 

 we may conclude that the mean temperature is 11°. 



The rock like that at Poullaouen is an argillaceous schist, 

 and also contains several strata of aluminous schist. 



The following are the Observations made by me on the 

 5th of September, being on the same day with those made 

 at Poullaouen. 



1 st, In a gallery about five metres below the one by which 

 the workmen generally enter the mine, which has no other 

 orifice but one, and which no person has entered for many 

 years, where there is no current of air, the thermometer 

 placed at its northern extremity marked in about 20 mi- 

 nutes,— -Temperature 11°* 



After having descended the pit called the Miners' pit, I 

 entered another pit which adjoined a gallery absolutely with- 

 out any communication with the rest of the mine, and in 

 which there was consequently no current of air. 



2d, The thermometer, when plunged into a little stag- 

 nant water upon the ground, rose to, — Temperature 12*2°. 

 Depth 70 m . 



3d, I reascended to the first gallery, and in the water of 

 a gutter, in a place through which a current of air passed, 

 the thermometer marked, — Temperature 13*7°- Depth 6o m . 



t then proceeded southward, to the spot where they were 

 then working. 



4tl\ In the second gallery, a little way from the pit by 

 which the produce of the mines is extracted, in a place where 

 there was a continual and strong current of air, a little stag- 

 nant water marked, — Temperature 1 5\ Depth 80 m . 



5th, 



