ON UNDERGROUND TEMPERATUHE. 253 



falls ia a week was 15x60x100=90,000, representing 401,000 kilo- 

 gramme degrees Fahr. Now, the sectional area of the well being 1'43 sqnare 

 metres, and a cubic metre of water being 1000 kilogrammes, the weight of 

 water in each vertical foot is 1430 kilogrammes. The heat generated in one 

 week's woi-k would therefore heat, by 1° Fahr., as much water as occupies a 

 height of ^^i^§-g-^= 280 metres, and the heat generated in one day would 

 heat a column of the height of 40 metres to the same extent. A large 

 portion of this heat is removed by the extraction of the mud, which, on 

 coming to the surface after its three hours' passage through the water, is 

 found (as stated in last Report) to have a temperature of from 118° Fahr. to 

 194° Fahr. ; but the quantity of heat remaining must assuredly bo sufficient 

 to keep the bottom of the well higher by some degrees than its natural 

 temperature. The temperature actually observed on June 15, three days 

 after the cessation of the boring operations, was about 2|° greater than the 

 natural temperature as computed fi-om the observations at other depths in 

 the well ; and the temperature observed on June 18 was exactly the same 

 as on the 15th ; whereas the temperature at a point 60 metres higher had 

 fallen by "4 of a degree. These circumstances were mentioned in last year's 

 Report as difficult of interpretation, since one would have expected to find 

 the greatest change at the bottom, where the artificial disturbance of the 

 temperature had been greatest. 



It must, however, be borne in mind that the operations of boring, including 

 the raising to the surface and reloweriug of the boring tool and the extracting 

 cylinder, both of which are nearly as large in section as the well itself, have 

 a tendency to mix together the waters at different levels, and to prevent a 

 sudden increase of temperature in approaching the bottom. Judging from 

 the temperature of the mud, as above stated, it is probable that, during 

 the boring operations, the solid rock surrounding the miid had, to the thick- 

 ness of a few inches, a temperature not less than 100° Fahr. The 

 temperature observed at the bottom on June 15, was 83:]^° Fahr., which, 

 though exceeding by 7|° the temperature of the water 60 metres higher, must 

 have been lower than the temperature of the rock immediately surrounding 

 the bottom. It is therefore quite possible that after three more days of 

 stagnation, the water at the bottom, situated between these two opposing 

 influences, may have retained its temperature unchanged, while the water 

 60 metres higher showed a fall of temperature, from the discontinuance of the 

 stirring processes which had previously enabled it to borrow heat from below. 



It would appear, then, that, in computing the mean rate of increase down- 

 wards, the temperature (75°-4) observed at the depth of 600 metres (June 18), 

 is to be preferred to the temperature observed at the bottom. Employing 

 as the other term of comparison, the temperature 58° observed at 100 

 metres from the surface, the rate of increase obtained is 1° Fahr. in 28*7 

 metres, or in 94-3 feet. If, however, instead of the temperature at 100 

 metres, we employ the permanent temperature of the caves iinder the Paris 

 Observatory, which is ll°-7 Cent, or 53°- 1 Fahr., -with a depth of 28 metres, 

 we obtain a rate of 1° Fahr. in 25-6 metres, or 84 feet. 



A few months after the observations above discussed, the boring was again 

 interrupted by caving in, and has not yet been resumed ; but preparations 

 are being made for tubing the well through its whole depth, the previous 

 tubing having been carried only to the depth of 139 metres. In the mean 

 time M. Mauget has promised to take another set of observations before the 

 water is disturbed. 



[This promise has been redeemed, since the reading of the Report, by the 



