On Underground Temperatures. 



19 



arise from an independent source of cooling in the coal, such as that 

 just mentioned which would be caused by the escape of gas condensed 

 under great pressure. It is an effect important to notice, inasmuch as 

 not only is the discharge of gas from coal of frequent, and often con- 

 stant occurrence, but also from the circumstance that it affects espe- 

 cially the fresh opened surfaces of coal in which the temperature 

 observations have so commonly been made. 



The Effects of Irregularities of the Surface. — Although it was known 

 that the underground isothermals under mountain masses are not 

 prolonged in horizontal planes, but follow in a certain ratio the curves 

 of the ground above, little was known to what extent mines were 

 affected by the smaller irregularities of the surface until Mr. George 

 Elliot, M.P.'s experiments in coal pits in Glamorganshire, showed that 

 there is a sensible increase of heat with an increase in the mass of 

 the superincumbent strata. This important point has been rarely, or 

 never sufficiently, taken into consideration in any of the underground 

 temperature observations. 



The following observations and sections of Mr. Elliot* laid before 

 the Coal Commission were mostly made in abandoned parts of the 

 pits, so as to avoid as far as possible both the effects of ventilation and 

 of working, and the holes, in which the thermometers were placed, 

 were 4 feet deep. Only the depths and temperature of the coal are 

 given in the original sections. I am responsible for the isothermal 

 lines which I have plotted on these data, for the purpose of showing 

 the more precise manner in which the temperature at depths is 

 influenced by the surface heights. 



At Upper Duffryn Colliery, in South Wales, the top of the shaft is 

 400 feet above the sea level, and the shaft 360 feet deep. The seam 

 of coal has been followed southward for a distance of 2327 yards, at 



Fia. 1. — Section at Upper Duffryn, Aberdare District. 



which point it is 190 feet lower in respect to the sea level than at the 

 entrance. This difference might account for a lowering of 3° to 4° 

 in the temperature, but not for the difference of 14°, which is due to 



* " Coal Commission Eeporls," vol. ii, p. 105 — 111. 



c 2 



