ON THE KATE OF INCREASE OF UNDERGROUND TEMPERATURE. 43 



On Saturday, July 27, by a mistake, the hole was bored in the duns 

 20 feet behind the coal. This point had been exposed for a week or two, 

 and the temperature indicated, 69'2, is therefore rejected by Mr. Wethered. 



On Saturday, August 3, another hole was bored in the coal, and gave 

 on Monday the same temperature, 68 - 5, which had been observed in the 

 first hole in the duns. Another hole in the duns gave, a week later, the 

 same temperature, 68 - 5. Mr. Wethered adopts this as the true tempera- 

 ture at the depth in question (1367 feet). 



The thermometer was now removed to the Speedwell pit, the shaft of 

 which is distant about half a mile from the Deep pit, and observations 

 were commenced in a cross-measure branch, which shortly afterwards 

 cut the Two-feet seam of coal. 



On Saturday, August 17, the thermometer was inserted in a hard 

 arenaceous stone, and on Monday the temperature 69 • 7 was read, depth 

 1439 feet. This reading was confirmed from the following Saturday to 

 Monday. 



On Saturday, October 12, the Two-feet seam of coal having been cut, 

 the thermometer was inserted in it, and on Monday gave a temperature 

 of 69 - 7, the same as in the stone further back in the branch in August. 

 The depth was the same within 2 feet. 



On Saturday, October 26, a hole was bored in the duns under the 

 Two-feet coal, which again gave 69'7. 



The next observation was made in the Great Seam coal of the Speed- 

 well pit, in an advanced level head, opening out new ground, depth 1232 

 feet. The thermometer was placed in a hole bored in the coal on Saturday, 

 November 2, and on Monday the temperature was 667. The same 

 reading was obtained the following week in the duns under the coal. 



This was the last of the observations deemed reliable. Two other 

 observations were made, the first in ground from under which coal had 

 been worked, and the second in strata disturbed by faults, but in neither 

 case could reliable results be obtained. 



The following is a summary of the temperatures, arranged in order of 

 depth, omitting those which are doubtful. 



Temperature. Fahrenheit 

 48-7 

 54-7 

 66-7 

 68-5 

 69-7 

 74-7 



with the next, we have the following 



1° for 67 feet 

 1° » 69 „ 



1° „ 75 „ 

 1° „ 60 „ 

 1° „ 66 „ 



a remarkably regular progression, especially for observations taken in 

 different parts of a colliery. Comparing the surface with the lowest 

 depth, we have an increase of 26 o- in 1769 feet, which is at the rate of 

 1° in 68 feet ; and comparing the depth of 402 feet with the lowest depth, 

 we have an increase of 20 o- in 1367 feet, which is at the rate of l o- for 

 68-35 feet. 



