18 



Prof. J. Prestwich. 



reduce the temperature of the body from which it escapes, though 

 here again no special experiments have been made to ascertain the 

 exact loss of heat from this cause. I find, however, one of the wit- 

 nesses* on the Coal Commission remarking that in a pit the depth of 

 which had been increased from 830 to 1588 feet, the temperature of 

 the coal was lower at the greater than at the lesser depth, and he 

 attributed this to a strong blower of gas issuing from the coal, which 

 at that point was sensibly cooler to the touch. 



On a Table also put in by Mr. Elliot, and referring apparently to 

 the same case, it is stated that, — 



In the Lower Duffryn Mine at a depth of 1588 feet, 



— and distant from shaft 1850 yards, 



the temperature of coal in a wet hole with a blower of gas was 62° P., 

 whereas it was found that — 



At a depth of . . , 1269 feet, 



Distance from shaft 1020 yards, 



the temperature in a dry hole with little gas was 74° F. 



At the Cym Neol Colliery, at depths of 990 and 1150 feet, and 

 1350 and 1070 yards distant from shaft, the temperature was re- 

 spectively 62° and 65°, which is abnormally low, but it is stated that 

 the observations were made in wet holes with bloivers. 



This escape of gas from the body of the coal may account for the 

 observation of another witness to the effect that " the coal gives out 

 heat quicker than the rock," and that the temperature of the coal is, 

 on the whole, less than that of the associated rocks. In several cases 

 observations have been made in the same pit, both on the coal and on 

 the underlying shale, and generally the temperature of the rock has 

 been found to be higher than that of the coal. In the Earns Mine, 

 Pendleton, for example, the temperature of the coal in a hole 3 feet 

 deep was 82° F., and in the floor 83° F. ; in the Crumbouke Mine the 

 coal was 80° F., and the floor 82° F. ; and in other levels it was 80° 

 and 80°, and 78° against 82° F. In one of the Ruabon collieries the 

 relative temperatures varied as follows : — 



Depth 1002 feet; temperature = 60° F. in coal, and 67° F. in floor. 

 „ 1503 „ „ 70i „ 68 



„ 1605 „ „ 73 „ 77 



„ 1770 „ „ 78 „ 74 



As the conductivity of the coal (0*00068) is less than that of sand- 

 stone (0'00672) or shale (0*00235), the coal should retain its heat 

 longer than the rocks. If the coal is cooler than the rock, it must 



* Mr. Winner : " Coal Commission," p. 118. 



