ON UNDERGROUND TEMPERATURE. 



31 



AU these temperatures, except tlie first two, were observed during the sink- 

 ing of the shaft, by drilling a hole with water to the depth of a yard in the 

 solid strata at the bottom. A thermometer was then inserted, the hole was 

 tightly plugged with clay so as to be air-tight, and was left undisturbed for 

 half an hour, at the end of which time the thermometer was withdrawn and 

 read — a mode of obsei-vation which appears well adapted to give reliable 

 results. With respect to the temperatures at 161 and 200 yards* (which I 

 have enclosed in brackets to indicate uncertainty), Mr.Bryham informs me that 

 he has some doubt as to the correctness of the thermometer with which they 

 were taken, and that they were not taken in the shaft at the time it was 

 sunk, but in the seams at the depths named. 



Assuming the surface-temperature to be 49°, we have, on the whole depth 

 of 815 yards or 2445 feet, an increase of 45°, which is at the rate of -0184 

 of a degree per foot, or a degree for every 54-3 feet. 



On plotting the temperature curve, including the two observations marked 

 as doubtful, we find that it naturally divides itself into four portions, which 

 are approximately straight lines. 



The most remarkable of these portions is the second from the top, extend- 

 ing from the depth of 161 yards to that of 605 yards. It embraces 1332 feet, 

 and shows an increase of only 1° for every 86 feet. 



The third portion, extending from the depth of 605 yards to that of 671 

 yards, covers only 198 feet, and shows an increase of 1° for every 33 feet. 



The lowest portion extends from the depth of 671 yards to 815 yards. It 

 covers 432 feet, and shows an increase of 1° in 54 feet. 



The topmost portion will be affected by the assumption we make as to 

 surface-temperature. Assuming this as 49°, it shows an increase of 1° in 

 31 feet. 



It is interesting to compare the Eose Bridge observations with those pre- 

 viously made by Mr. Fairbairn at Astley Pit, Dukenfield, Cheshire, which 

 have been described by Mr. Hull in 'The Coalfields of Great Britain,' 

 and by Mr. Fairbaim himself in the British Association Report for 1861. 

 The results have been thus summed up by Mr. Hull : — 



" 1. The first observation gives 51° as the invariable temperature through- 

 out the year at the depth of 17 feet. Between 231 yards and 270 yards, the 

 temperature was nearly uniform at 58-0. And the increase from the surface 

 would be at the rate of 1° F. for 88 feet. 



" 2. Between 270 and 309 yards, the increase was at the rate of l°for 

 62-4 feet. 



* Further inquiry has shown that these two temperatures must he rejected, as the 

 thermometer with which they were taken was afterwards found (by comparison with other 

 thermometers) to be in error by some degrees. No note was taken of the amount of the 

 error, and the thermometer itself is destroyed. 



Assuming the surface-temperature as 49°, we have an average increase downwards of 

 1° in 57-7 feet for the first 558 yards, and of 1° in 48-2 feet for the remaining 257 yards. 



