454 On the Bate of Increase of Underground Temperatures. 



tubes, between which the water had the opportunity of circula- 

 ting even when the innermost tube was plugged, hence the 

 observations taken in this part were rejected. 



All the successful observations are given in the third column 

 of the following table, subject to a correction for pressure; and, 

 for frhe sake of showing the error due to convection in the ordi- 

 nary mode of observing, the temperatures observed at the same 

 depths when no plugs were used, are given in the second 

 column : 



Deptbiu 



Temperature Reaumur. 



















700 



1608 



17-06 



0-98 



1,100 



17-18 



20-8 



1*32 



1,300 





21-1 





1,500 



22-9 



24-1 



0-72 





24-8 



25-8 









27-1 













These temperatures are 

 are corrected for rise of : 

 this last circumstance explains the difference of 0*4 between the 

 temperature 36 - 15 here given and 36*55, which is the mean of 

 the above-mentioned observations at the depth of 3,390 feet. 



Another proof of the injurious effect of convection was ob- 

 tained by comparing the observed temperatures (without plug- 

 ging) in the first 400 feet of the great bore, designated Bore I, 

 with the temperatures observed at the same depths during the 

 sinking of another bore, designated Bore II, near it; the ob- 

 servations in this latter being always taken at the bottom. 

 The following were the results : 



Deothin 



Temperature. 





Borel. 



Bore II. 



200 



11-0 

 13-6 



12-5 



The temperature at the depth of one hundred feet in the 

 great bore thus appears to have been raised about 2° B. by 



i table of the successful observations, cor- 



