84 M. L. Cordier, Examination of recent Experiments 



that would be deduced from them would be affected with too 

 much uncertainty to be usefully consulted, even as approxima- 

 tive documents, with reference to the object in view. 



2. The water of engine-pits commonly possesses a very com- 

 pound temperature, and which could only represent exactly 

 that of the surrounding rock in very rare cases, resulting from 

 compensations which it would be impossible to appreciate. In 

 fact, this temperature depends upon the original heat of all the 

 rilis of water which flow from different levels, upon that of the 

 rock forming the basin, which may have been more or less modi- 

 fied, on the time during which the water has remained in it, and 

 on the influence of the ventilation, which is commonly very active. 

 Further, if an engine-pit have a great depth, such as 150 or even 

 300 feet, which may take place, the temperature could scarcely 

 be uniform in it in the vertical direction ; the water at the bot- 

 tom would be sensibly colder than that of the surface. From 

 these considerations, and from those which were previously 

 mentioned, we are authorised to believe, that the results of the 

 indications collected in puisards are generally inferior to those 

 which it is our object to obtain. I shall mention an example. 



At Decise (at the new shaft) I took the temperature of an en- 

 gine-pit, which was in commimication with a great extent of old 

 works that were inundated, and had been abandoned for a very 

 long time, and from which, for a year back, 4240 cubic feet 

 had been taken in the twenty-four hours. The level of the 

 water was at 434 feet 8 inches from the surface ; the thermo- 

 meter marked 61°.02, a quantity much superior to the mean 

 temperature of the country, but lower by 7°.6 than the proper 

 temperature which the rock ought to have at this level, accord- 

 ing to the experiments which I shall relate. The water ex- 

 tracted presented a circumstance which I regard as foreio-n to 

 the result of the experiment. It disengaged a weak smell of 

 sulphuretted hydrogen, as is generally the case with water that 

 has accumulated in old coal- works. 



With the above considerations in view, the following table 

 may be consulted with advantage, as giving a general vidimus ; 

 it contains the results of twelve observations made in England, 

 Saxony, and Bretagne. 



