244 On the Mean Temperature of the 



We may from this law calculate the temperature of the earth 

 at Bogoslowsk, although we possess no direct observation ; for, 

 after the most diligent search, we found no spring fitted for the 

 purpose. As we have here determined the temperature of the 

 earth from that of springs whose temperature is almost uni- 

 form, and as this property is not found in all springs, but only 

 in those which arise from a certain depth ; so it is not properly 

 the temperature of the level of the soil, of which we have been 

 hitherto speaking, but that of a shaft, which is continued to a 

 considerable, but very uniform, distance from the level of the 

 earth. If we, therefore, wish to calculate the temperature of 

 the earth from that of great depths, in the above sense, we 

 must first of all determine at what depth the bed may be, 

 from which rise the springs which possess a nearly uniform 

 temperature throughout the whole year. This question cannot 

 be answered with precision, yet this depth may be fixed at 

 nearly 25 metres. This estimate does not appear too large; 

 for, at Paris, the oscillations of the temperature of the earth do 

 not quite cease at 28 metres ; and it is probable, that, in high 

 latitudes, where the maxima and minima are farther removed 

 from one another than at Paris, the oscillations of the deeper 

 points are as observable as was the case with the springs which 

 were examined. 



Deducting, now, 25 metres from the first station, 31 metres 

 remain, as its depth below the bed, to which we have referred 

 all the temperatures of the earth. But 31 metres give, accord- 

 ing to the foregolngj 2°. 7, as the difference of temperature. 

 But as the temperature of the upper station was found to be 

 38°.07, the temperature of the soil at Bogoslowsk must be placed 

 about 35°.37. 



In Bogoslowsk, in some places, after hard winters, the soil at 

 the end of summer is still frozen some feet below the surface. 

 We see from this, that we are justified in referring the tem- 

 perature of the earth to a deeper level, and that, in inconsider- 

 able depths, the mean temperature of the year is very change- 

 able, and may sink below 22°. When the oscillations of the 

 earth's temperatui'e are so great, that the formation of ice is 

 possible, it may happen that the succeeding warmth is not able 

 to melt it ; and thus we easily explain the existence of ice on 

 ground where the mean temperature is certainly above 32°. 



