UNDERGROUND TEMPERATURE. 
13 
first sight, to give the most reliable results, and possibly some good 
ones may have been so obtained. But it frequently happens that 
a considerable amount of water flows down the sides of the shaft 
from springs cut through during the sinking, and varying in tem- 
perature : this water then, must have some effect on the strata at 
the bottom of the shaft ; and to obtain accurate observations under 
such conditions is difficult, and may perhaps account for the 
discrepancy in results so obtained. 
Then again, old shafts, partly filled with water, have been utilized 
for observations, it being assumed that the column of water would 
attain the temperature of the earth, but these, I consider, to be 
open to great objection, owing to the inflow of water of various 
temperatures (termed convection), which, in some instances, would 
vary with the seasons. A good illustration of this is shown in the 
observations made by Mr. David Burns, H.M. Geol. Survey, in 
a shaft at Allandale, near Carlisle. The shaft was over 50 fathoms 
deep, and was about half-full of water. The result was as follows : 
i. a period of drought. 
Depth, 160 feet. Temperature, 47°' 5 
„ 200 ,, ,, 47 *0 
250 
300 
47 7 
47°7 
ii. Shortly after heavy rain. 
Depth, 160 feet. Temperature, 47° 
200 
250 
300 
47 '5 
47°’3 
47°-3 
Another discrepancy, which I think may be ascribed to the 
same cause, was in the case of a well at Kentish Town, where, for 
the depth of 210 feet, a second series of observations gave an 
e^^cess above the first of from 2° to 5®. 
