3 oo THE POPULAR SCIENCE MONTHLY. 



at the bottom, 116 metres, 3. It was thus seen that, whereas the rate 

 of increase from the surface to 60 metres in depth was 6*4, for the 

 remainder of the depth, 56 metres, it was only 1*8. 



The experiments made in artesian wells have given analogous 

 results that is, wholly irregular as regards the rate of increase of 

 temperature. The mean of 27 observations in Vienna is, according to 

 Spasky, 1 to 20 metres. The very accurate experiments of Magnus, 

 in 1831 at Rudersdorf, near Berlin, on the occasion of the boring of 

 an artesian well, yielded the same result, but at Pregny, near Geneva, 

 Messrs. Rieve and Marcet found the depth corresponding to an increase 

 of 1 Cent, to be 32 metres. The well was sunk 220 metres. This 

 figure represents sufficiently exactly the average rate of increase of 

 temperature resulting from thermometric soundings made in artesian 

 wells. Walferdin found an increase of 1 to 31 metres in the arte- 

 sian wells of the Military School at Paris, in that at St. Andre (Eure) 

 and in the well of Grenelle ; and many others have given figures com- 

 prised between 30 and 35 metres for the difference of level represent- 

 ing a difference of 1 in temperature. The temperature of the water 

 of the Grenelle well, 548 metres deep, and of the Passy well, 570 

 metres deep, is 28, while the mean temperature of Paris is 10-6. 

 These waters, therefore, receive from the deep strata an addition to 

 their temperature of a little more than 17 ; i. e., a little more than 1 

 to each 32 metres of depth. The much deeper borings of Musalweek, 

 near Minden in Prussia, 700 metres, and of Mondorf in the grand duchy 

 of Luxemburg, 730 metres, show a difference of 1 to 30 or 31 metres. 



From a comparison of the temperatures observed by Walferdin 

 near Creuzot, at the bottom of a boring 816 metres deep, and in a neigh- 

 boring well 554 metres deep, it also appears that at these depths the 

 heat increases more rapidly than at the surface. But wells situated 

 very near each other may give widely varying results. Thus at Na- 

 ples, according to M. Mallet, in two very deep artesian wells, distant 

 from each other 1,600 metres, the depths corresponding to 1 of addi- 

 tional heat were 45 and 109 metres respectively. 



The observations of M. Mohr, in 1876, in a well 4,000 feet deep, 

 pierced through a salt-rock at Speremberg, near Berlin, led this phys- 

 icist to believe that the rate of progression sensibly slackens as we 

 descend below the surface a conclusion agreeing with Fox's deduc- 

 tions from observations in the English coal-mines. M. Mohr remarked 

 that from 700 feet, where the glass marked 19-6 Cent., to 3,300 feet, 

 where it marked 46, the difference in temperature corresponding to 

 a difference of 100 feet, diminished in a regular ratio, so that, continu- 

 ing the sounding, beyond 5,000 feet only a barely perceptible increase 

 could be observed. But M. A. Boue, who warmly contested M. Mohr's 

 conclusions, has observed with reason that percolated water will fre- 

 quently lower the temperature of these deep beds, and this would ex- 

 plain the diminution observed by M. Mohr. 



