ON SUBT^ERRANEAN IIEAT. - l4g 



, and I shall now give some othei-s noticed last summer in 

 Brittany. The habit of making aiinilar experiments, and 

 the knowledge" I had of the places, enabled me to choose 

 with some disdimination the points of which I ascertained 

 the temperature; so that I trust the facts I have recorded 

 will not be uninteresting to those, who make our Earth an 

 objeQt of their study. . 



The thermometer I employed was of mercury, and di- Thermometer 



y.yided into eighty degrees from the freezing to the boiling "^^ * 

 ppint of water. It was enclosed in a tube. 1 found by trial, 3'or 4'toalter 

 that when it indicated a given temperature, and was made ^^° ^- ^'^ ^'^^' 

 to deviate from this about a dozen degrees, it required thr^e 

 or four minutes to bring it back to the former point by \va- 

 mersing it in water of that temperature, and eleven or twelve ^ i' or 12' in 

 minutes if kept in the open air. Hence, whenever I was the air. 

 desirous of ascertaining the temperature of a body of water 

 in the mines, I immersed the thermometer in it entirely,- 

 and left it there five minutes; and when I took the temper- 

 ature in the air, I let it remain a quarter of an hour. All 

 the observations were afterward reduced to degrees of the 

 centigrade thermometer. Notwithstanding all the care and 

 patience I employed however, I cannot answer for their ex- 

 actness to less than a quarter of a degree. 



Observations made at Poullaouen. 



THE mine of Poullaouen is in latitude 48° I7' 49''' N., Situation and 

 and lon-itude 5° 06' ^l" West of Paris. Its mouth, that PoSuel^'^ 

 of St. George's pit, is lOGmet. [347| feet] above the, level 

 of the sea. It is 4 myriam. [25 miles"| from the seacoast of 

 Brittany on the north, and 6 [SyJ miles] from that on the 

 south and that on the west. It is in that tongue of land, 

 which advances into the ocean under the form of a roof, 

 raised in its centre about 260 met. [853 feet] above the level 

 of the sea, and constitutes Brittahny. The country round 

 the mine, to the distance of near 6 miles, is about 150 met. 

 [490 feet] above the level of the sea; and is intersected in 

 eveiy direction by valleys, one of which is an almost circu- 

 lar basin about a millimetre [IO93 yards] in diameter, that 

 forms the roof of the mine. 



k 



According 



1 



