? of Underground Temperatures. 455 



Depth InBhenish 



teebt 



700 



17-275 

















23-277 





24-741 







2,100 



37-23 6 8 



Assuming, with Herr Dunker, the mean temperature of the 

 arface to be 718, which is the mean annual temperature of 

 le air at Berlin, we have the following increments of tempera- 

 ire with depth : 



Depth in Rhenish 



Increment 



increment o, 



p£Sft& 



Inc ^ a rfer 













to 700 



700 



10095 



1-442 



3.94 







1-505 







700 to 1,100 















0-363 











1-767 





1-99 



















•882 



1-98 



1,900 to 2,100 





2-164 





243 





1,290 









to 3,390 



3,390 



30-058 



•887 



2-00 



The mean rate of increase found by comparing the tempera- 

 tures at the surface and 3.390 feet is exactly 1° Fahr. for 50 

 Rhenish or 51/5 English feet. 



The numbers in tbe last two columns exhibit upon the whole 

 a diminution with increase of depth ; in other words, the tempe- 

 rature increases less rapidl v as we go deeper down. As regards 

 the first 700 feet, which exhibit a decidedly more rapid rate 

 than the rest, it must be remembered that nearly half of this 

 distance was in a different material from the rest of the bore, 

 being in gypsum with some anhydrite, while all the rest was in 

 rock salt. ' Prof. Herschel has f< irnents not 



yet published, that the conductivity of rock salt is exceedingly 

 high; and theory shows that the rates of increase, in superim- 

 posed strata, should be inversely as t leir c< n<\ ictivities. We 

 may, therefore, fairly attribute the rapid increase in the first 

 700 feet to the relatively small conductivity of the portion (283 

 feet) which is not rock salt. The slow rate of increase observed 

 Qg interval between the depths of 2,100 and 3,390 feet 

 is not so easily accounted for; we can only conjecture that this 

 and the other inequalities which the above table prea 

 depths exceeding 700 feet, are due to fissures and other inequali- 

 ties in the rock which have not been put in evidence. 



