the Prussian Coal-Mines. 191 



\T to 22^ R. (70 .25 to 81^50 F.). In a pit lying not far to 

 the north, sunk in a newer stratum, I found the high tempe- 

 rature of 30^ R, (99°.50 F.). Nearer to the reported burning 

 bed, the temperature was probably 40° R. (122° F.) It was 

 not possible for me to advance farther. I have hitherto 

 omitted to measure, on the plans of the Mining Office, how 

 far that place is distant from the bed which is supposed to be 

 ignited. The superintendent who conducted the formation 

 of the bore, told me that it was carried four feet into the coal, 

 and that here the borer fell down one foot. He gave me 

 some specimens which had been taken thence, and they were 

 completely converted into coke. Mr Sello informed me, 

 that in the old plans of the mines, several places are indicated 

 by flames, to which our forefathers reached while approaching 

 the burning strata, but which they were obliged to forsake 

 and stop up. There cannot, therefore, be a doubt that at 

 an early period the stratum really was on fire, and probably 

 at that time the products of a dry distillation also made their 

 appearance. From the reasons, already stated, however, I 

 must doubt their still being in a state of ignition. Two 

 causes may be conceived, which caused the high temperature 

 that is still observable ; either the rocks of the coal-formation 

 preserve the high temperature caused by the actual burning 

 of the stratum, or the oxidation goes on, which was formerly 

 commenced) of the sulpluu* in the alum-slate. Streams of 

 lava prove that a rocky mass, enclosed in a circulai* manner, 

 and surrounded by bad conductors, which formerly acquired 

 a vei'y high temperature by means of the burning of a stra- 

 tum, retain their original heat for a long time. I have treated 

 of this subject in my " Wdrmelehre^^ p. 493, &c. The greatest 

 loss of heat to which the burning mountain is exposed, is from 

 the quantity carried away by the water which penetrates into 

 tlie interior, and which becomes heated, and then issues through 

 fissui'es in the form of vapour. The quantity of suck vapour is 

 very considerable. In wet weather, when the vapours cannot so 

 well escape into the atmosphere, the whole basin of the burn- 

 ing mountain is enveloped in mist. The atmospheric air, 

 which probably flows in through the old deserted mining works, 

 also carries off much warmth. I found two fissures in slate- 



