14 



Prof. J. Prestwich. 



a hole 3 feet deep was 76°, and at a distance of 930 yards 82°, while 

 in a hole 7 J feet deep the temperature was 84°. The general opinion 

 amongst the witnesses seemed to be that the effect of ventilation was 

 to reduce the temperature of the pits some 9° to 10° F., though some 

 estimated it at as much as 15° to 20°. 



The effect of exposure is well shown in the following records from 

 one of the pits at Ruabon. 



Temperature 



t -* N 



Temp, of air in holes 3 feet deep 



at date f * ^ 



on surface. Depth. of air in gallery, of coal. of bed below coal. 



60° 1002 feet 58-0° 60-0° 67° 



62 1503 „ 58-5 70*5 68 



57 1605 „ 71-0. 73-0 77 



65 1770 „ 71-0 78-0 74 



No other particulars are given. The rate of increase here for the 

 first 1000 feet is 1° for every 95 feet, whilst for the whole 1770 feet 

 the rate of increase is 1° for every 61 feet. This is clearly due to 

 the circumstance that the shaft had long been sunk to 1004 feet and 

 the mine cooled, and only recently opened to 1770 feet. 



Mr. Lupton mentions that in a pit 1425 feet deep, the fresh cut 

 coal had a temperature of 73°, whereas at the end of six months it 

 had fallen to 64°. In another case a period of three months had 

 sufficed to reduce the temperature 11°. 



After the air in the pits has circulated a certain distance (estimated 

 by one of the witnesses at one mile), it may become in the face of the 

 workings hotter than the rock ; while the difference, which arises from 

 the heat of the lights and the men in an instance given, does not exceed 

 + 2°. 



The extent to which the temperature of the air affects that of the 

 coal is also shown in the table of experiments, given on next page, 

 made by Mr. Wood in another Durham Colliery (No. Report, p. 140). 

 Here the difference between the coal and the air in the part of the 

 pit through which the intake air circulates, is from 4° to 6^-°, or an 

 average of 5° ; whereas in the return air at the same distances from 

 the shaft, the differences are reduced to an average of 1 



In the Crumbouke mine the face of the coal which had been worked 

 two years had, according to Mr. Dickinson, lowered 4°. A similar 

 loss was shown at the Rosebridge Colliery, but after a longer 

 interval. In an adjoining pit, the difference between the temperature 

 of the air in the galleries and of the coal varied from 10° to 12^° F. 



At the Rosebridge Colliery other observations made three, four, and 

 nine years after opening the colliery showed, that at 1410 feet deep, 

 and 200 yards from shaft, the temperature of the coal was = 66° F., 

 and at 360 yards = 70° F., while at 1800 feet deep and 215 yards 



