1 877.] 
On Underground Temperature. 
*77 
water in the bore-hole correctly gave the temperature of the 
rock, its temperature would be likewise represented by the 
same straight line A C. But since it is affeCted by convec- 
tive currents this cannot be the case : for they tend to warm 
the upper portions of the column of water, and to cool the 
lower. Hence, so far as we have gone, the water in the 
upper part of the bore-hole will be warmer than the body of 
the rock, and in the lower part it will be cooler ; and in our 
diagram we must draw a line to represent its temperature, 
more distant from O X in the upper part, and nearer to it in 
the lower. It need not, however, be a straight line, the law 
of increase of temperature being possibly altered. Suppose, 
then, D E to be this line, or the curve of temperature of the 
water on the supposition now made. It will be seen that it 
must intersect the line A C. 
There is a further consideration to be taken into account. 
If the bore-hole is nearly full of water, and of considerable 
dimensions, it will present a considerable surface to the 
atmosphere. At Sperenberg the water stood 7 feet from the 
stage of the bore-pit, and the bore-hole was afoot in diameter. 
The consequence would be that the open surface of the water 
would be cooled, sensibly to the temperature of the air. 
This would bring the curve of temperature of the water at the 
surface nearly to the same point as the temperature line of the 
rock there, and it would also have the effedt of reducing the 
temperature of the water throughout the column, below 
what it would be if it had not this extrinsic cause o f cooling. 
The ultimate result would be that the temperature curve of 
the water would assume some such form and position as AF. 
It will be observed that this line also intersects A C ; and the 
signification of this is, that the water in the bore-hole is 
warmer than the rock mass in its upper portion, and cooler 
than the rock mass in its lower portion ; or, in other words, 
the water tends to warm the rock in the upper portion, 
and to cool it in its lower portion. Consequently, if the 
circulation of the currents be interrupted, the water im- 
vol. vii. (n.s.) n 
