Hot and Thermal Springs. 34<1 



It has been found, from thermometrical observations, made in 

 various Prussian mining establishments, situated between 50'' 

 and 51°.5 N. Lat.,* that, notwithstanding the numerous precayt- 

 tions employed to isolate the thermometers placed at different 

 depths from the atmosphere, they still, in some cases, shewed 

 great irregularities of temperature, as will be seen from the fol- 

 lowing table ; 



From this we see, that in the temperate zones the influence of 

 the external temperature may be no longer perceptible at the 

 moderate depth of 27 feet ; but that, under less favourable cir- 

 cumstances, it may be more or less considerably felt at depths of 

 55 and 63 feet, or even more ; and, lastly, that at 155 and 159 

 feet it entirely disappears. 



In the years 1830-1832, observations were made with great 

 care in the mines of the Saxon Erzgehirge, on the temperature 

 of the rock at various depths.f In order, if possible, to avoid 

 the effects of a change of air, thermometers were used of such 

 a length, that the bulbs might be sunk 40 inches deep into holes 

 bored in the rock, whilst the scale might be observed from with- 

 out. The spaces between the thermometers and the sides of the 

 holes were filled with dry sand. The scales were divided to 

 tenths, by which the observations might be taken in hundredths 

 of a degree centesimal. The utmost care was bestowed on the 

 graduating and harmonizing of the thermometers. 



In choosing situations for the thermometers, points subject to 

 considerable draughts of air, and such as were occupied by 



• PoggenilorlFs Anual. vol. xxii. p. 520. 



t Beobachtungen ueber die Temperatur des Gesleins in verschiedenen 

 Tiefen in den Gruben dei Sachsischen Erzgebirges in den .Tahren 1830 bi 

 1832, znsaramengesteilt von F Reich. Freyberg. 1834. 



