150 ON SUBTERRANEAN HEAT. 



Mean temper- According to tlie law of the temperature from th« equatotf 



lation, ^^ ^^^^ pole, the mean temperature of the surface at Poul- 



laouen should be 1^2-4® [5^-5° F.]*. The elevation of the 



soil requires near 1® [l'8° of diminution, so that the mean 



temperature may be estimated at 11*5"^ [50*9° F.] 



Observations My observations were made the 5th of September, 1806^. 



gept. Day fine. I^y^>"g the whole day the weather was fine, and but few 



clouds were seen. The temperature in the shade, in the 



middle of the day, was 19° [64*4° F,]. In reporting my 



observations I shall mention the situation of the places where 



they were made, as well as whatever appeared to me capable 



of influencing the temperature. Opposite each expression 



of the temperature I shall note the depth of the place below 



the surface of the ground, 



Tempe- 

 Tabulated !• I" the first gallery, called fifty foot /e- rature Depth 



temperatures ve/, near the shaft, in a place where there was ^ . ^ ' '"§ 1^^^ 



and depths renn ri. in. 



with remarks. ^"* ^ slight current of air, a little water that thermo 



lay on the ground indicated 53*8° 52* »3 



2. In St. George's gallery, under the inter- 

 section of three branches of the vein, in a kind 

 of cul de sac, very remote fora the places 

 where the miners were at work, in which there 

 was no current of air, but a lar^e quantity of 



water filtered from the roof : this water' was • • 51*6° 127* '4 



3. The ^ater that thus filtered into the gal- 

 lory,' when it reached the well from which it 



was raised, was- • • . • 52^ ]27* '4 



4. Thirty six metres lower, at the level of 

 Boullaye, toward the end of a long gallery, 

 where tliere was no current of air, and no per- 

 son at work, under very strong percolations 



lind in the water 1 had 5r6<^ 244.10 



* Theory and observation have led me to a very simple expression of 



the iheriuQinetrical terjijperature of z, place, the latitude of which is 



known. This expression is 30-7° [85 4^ F.]. cps. ^'zs latitude j or 



"with sufficient exactnes&in the temperate zone 28® [80 6° F ]. cos. * 



:iat. ' • ■' 



•\ In the atmosphere the temperature diminishes 1° [18* F ] fs)r 

 every 175 met. [I9l yardc] in height. , 



'■■■"" •• • 5. At 



