ON UNDERGROUND TEMPERATURE. 197 



Matthew Heckels, Manager of Boldou Collier)-, between Newcastle and 

 Suuderl and, in holes bored upwards to a distance of 10 feet from some of the 

 deepest seams. The mine is doscribed as " perfectly dry," and those parts of 

 it in which these observations were made are quite free from currents of air. 

 The surface of the ground is tolerably level, and is 07 feet above Trinity high- 

 water mark. 



Hole No. 1 is bored up from the roof of the Bensham seam. The thermo- 

 meter (one of the new slow-action instruments, not self-registering) was 

 placed at the end of the hole, so as to be 10 feet within the rock, and pro- 

 tected by air- tight plugging. The surrounding strata consist of arenaceous 

 strata known as " grey metal." The distance of the thermometer from the 

 surface of the ground overhead was 1365 feet. 



The hole had been standing idle for some time when the thermometer was 

 inserted, April 5, 1876. The first reading was taken April 26, and was 75°, 

 the surrounding air being at 75|° and almost stagnant. The readings were 

 repeated during four consecutive weeks, without change of the indications. 



Hole No. 2 is in the same vertical with No. 1, and is bored up (also to the 

 height of ] feet) from a deeper scam — the Hutton seam. The same thermo- 

 meter was employed and in the same manner. The surrounding strata con- 

 sist of a close compact sandstone known as " hard post." The distance of 

 the thermometer from the surface of the ground overhead was 1514 feet. 



Immediately after the drilling of the hole, June 6, 1876, the thermometer 

 was inserted, and on July 4 the first reading was taken, namely 81°. On 

 July 24 it had fallen to 791°, and on August 1 to 79°. Readings taken 

 August 15 and 29 and September 1 also showed 79°, the surrounding air 

 having never altered from the fixed temperature 78|°. It would therefore 

 appear that the first observation in this hole was 2° too high, owing to the 

 remains of the heat generated in boring, notwithstanding the lapse of 4 weeks 

 which had intervened. Four readings have since been taken at regular in- 

 tervals, endiug with July 1877, and the same temperature, 79°, continues to 

 be shown. 



Assuming 4S° as the mean annual temperature of the surface, we have the 

 following data for calculating the rate of increase downwards : — 



Surface 48° F. 



1365 feet 75 



1514 feet 79 



For the interval of 149 feet between the two holes we have an in- 

 crease of 4° F., which is at the rate of 1° F. in 37 feet. 



For the whole depth of 1514 feet, from the surface to the lower hole, we 

 have an increase of 31°, which is at the rate of 1° F. in 49 feet. 



In explanation of the length of time required for the heat of boring to 

 disappear in the second hole, Mr. Heckels remarks that " it required two men 

 sixteen hours with a hand boring-machine to drill this hole, so hard is the 

 stratum." He further says, " the tool by which this hole was bored, on 

 being drawn out, was too hot to allow of it being touched with the hand, so 

 that the temperature of the hole, on being fiuished, must have been con- 

 siderable ; and no doubt it would be, when we consider the immense pres- 

 sure required to bore holes in such strata as this." "With respect to the per- 

 manent temperature (781°) of the surrounding air, Mr. Heckels remarks — ■ 

 " The air of this district is almost stagnant, and what circulation there is will 

 have travelled a distance of three miles underground, and hence it may be 



