ON UNDERGROUND TEMPERATURE. 



131 



The springs which -wore met ■with in the tertiary strata correspond to 

 those found in other parts of the basin in which Paris is situated, and 

 have not sufficient strength to spout above the surface of the ground at 

 this elevation. They were encountered at the depths of 19"2 metres, 

 34-5 metres, 86 metres, and 97 metres, and the water now stands in 

 equilibrium in the central tube at 16-5 metres below the surface of the 

 ground. 



It was not practicable to take observations of temperature during the 

 regular progress of the boring ; but an interruption occurred on the 12th 

 of June, and the tool was not at work from this date till after both sets 

 of observations were finished. In reference to this point, Messrs. Mauget 

 and Lippmanu say, under date April 29, " To obtain the natural temperature, 

 it will be necessarj' to select a time when the work has been interrupted for 

 several days ; for the boring being executed by the full of a heavy tool upon 

 the bottom of the well, the percussion developes a considerable amount of 

 heat, as we perceive by the mud (Jes boues) which we extract, and which 

 in coming to the surface is found to have still a temperature of from 48° 

 to 90° C. (118° to 194° F.)." In their letter of June 19, containing the 

 report of the observations, they remark : — 



" You will observe that though the water at the bottom of the well is 

 still some degrees above its natural temperature owing to the action of 

 the drill {trepan), the latter has not been in operation since the 12th of 

 the month. At a convenient time, we intend to observe the temperature 

 of the mud as it lies at the bottom of the well, immediately after the 

 withdrawal of the drill, wfien the latter has been working constantly, a 

 temperature which will probably be found to depend upon the hardness of 

 the rock." 



The following Table exhibits the successive increments of temperature 

 shown in the second series, which purports to be the more accurate : — 



The last two columns of this Table show that the rate of increase is about 

 four times as rapid in the last 60 metres as in the rest of the well, a circum- 

 stance which naturally suggests the explanation given by Messrs. Mauget 

 and Lippmann. There are, however, some difficulties in the way of accepting 

 this view. Comparing the two sets of observations, one taken on the second 

 and third day after the withdrawal of the tool, and the other on the fifth and 

 sixth day, we have precisely the same temperature at the bottom of the well 

 on both occasions, although the olaservatious were sufficiently precise to 

 detect a difference of a tenth of a degree where such ditference existed. It 

 seems difficult to believe that a temperature 2g degrees above the normal 



