1877 •] 
On Underground Temperature . 
179 
The second column gives the temperatures observed at 
the respective depths when the convention currents were 
stopped by the use of the geo-thermometer. 
The third column gives the temperature of the water in 
the bore-hole when the convention currents were allowed to 
circulate. 
The fourth column gives the alteration of temperature at 
each depth which arose from stopping the convention 
currents — minus when the temperature fell, phis when it 
rose. 
The fifth column gives the increase of temperature at 
each depth over that at the previous one, as taken from the 
second column. 
The sixth column gives the rate of increase at each 
depth, measured by the number of feet which it would be 
required to descend to gain an increase of 1 degree Reaumur, 
on the supposition that the increase per foot remained con- 
stant throughout that depth ; consequently large numbers 
show a proportionately slow increase. 
The seventh column, like the fifth, shows the increase of 
temperature at the depth against which the number stands, 
over that at the depth at which the previous number 
stands ; the objedt of this column being to obtain averages 
at longer distances apart. 
The eighth column, like the sixth, shows the rate of in- 
crease of temperature with longer averages, measured by 
the number of feet of descent for i° Reaumur. 
The ninth gives the same increase when measured in feet 
of descent for T F. 
The difference between a Prussian and an English foot is 
so small that, for the purpose in hand, they may be consi- 
dered equal. 
In discussing this table the first point to be noticed is that 
the rate of increase is by no means so equable as, from the 
homogeneity of rock, it might have been expected to have 
been. In order to obtain anything like a general law of 
increase, it is necessary to take the average of the increase 
at considerable distances apart. 
The second point has been already adverted to, viz., that 
the shutting off of the convention currents caused an increase 
of temperature in the upper part of the bore-hole, and a dimi- 
nution of it in the lower. This shows clearly that the tempera- 
ture of the rock was altered temporarily, by the adtion of the 
convention currents, to some distance away laterally from the 
bore-hole. The hole was lined with three tubings, one behind 
another, for the upper 440 feet, and, on account of the pre- 
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