ON UNDJCRGKOUND TEMPERATURK. 



205 



pluggiug, it gave on the same day 33°-9. It thus appears that the effect of 

 convection was to render the temperature in the advance-bore 3° R. too low. 



Apparatus was then employed for isolating any portion of a bore by means 

 of two plugs at a suitable distance apart, with the thermometer between them. 

 This operation was found much more difficult than that above described ; but 

 in several instances it gave results which were deemed quite satisfactory ; 

 while in other instances the apparatus broke, or the plugging was found im- 

 perfect. The deepest of the successful observations by this method was at 

 2100 feet, and the shallowest was at 700 feet. The first 444 feet of the bore 

 were lined with iron tubes, between which the water had the opportunity of 

 circulating 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 follow- 

 ing Table, subject to a correction for pressure ; and, for the sake of showing 

 the error due to convection in the ordinary mode of observing, the tempera- 

 tures observed at the same depths when no plugs were used are given in the 

 second column : — 



These temperatures are not corrected for pressure, but they are corrected 

 for rise of zero in the normal thermometer ; and this last circumstance 

 explains the difference of 0-4 between the temperature 36°-15 here given and 

 36'-'-o5, which is the mean of the above-mentioned observations at the depth 

 of 3390 feet. 



Another proof of the injurious effect of convection was obtained by com- 

 pariug the observed temperatures (without plugging) 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 observations in this latter being always taken at the bottom. The fol- 

 lowing were the results : — 



Depth in 

 feet. 

 100 . 

 200 . 

 300 . 

 400 . 



The temperature at the depth of 100 feet in the great bore thus appears 

 to have been raised about 2' R. by convection. 



The following is a Table of the successful observations, corrected for 

 pressure : — 



