ON THE RATE OF INCREASE OF UNDERGROUND TEMPER ATURE. 91 



this last station being relatively hotter than any of the others. Though 

 only 24 feet deeper than Station VI., it is 3-2° warmer ; and Station VI. 

 was itself exceptionally warm. 



It is evident that there are local sources of distui-bance which render 

 this spot unsuitable for obtaining average results. The observation itself 

 may be relied upon as correct, having been made by the captain of the 

 mine, Mr. J. Lean, who assisted Mr. Strahan in last year's observations. 



Mr. E. Garside, engineering student. Queen's College, Belfast, has 

 continued his observations in the East Manchester coal-field. 



In Ashton Moss Colliery, the temperature was observed on June 27 at 

 the depth of 930 yards, and found to be 85-3°, the thermometer being 

 inserted in a hole 2 inches in diameter and 3^ feet deep, drilled for the 

 purpose in hard blue shale which lies below the Great Mine coal seam, 

 being newly-opened ground, dry, and free from cracks. The hole was 

 allowed to stand ten or fifteen minutes, that the heat of drilling might 

 partially escape, and one of the Committee's slow-action thermometers 

 was then inserted with proper plugging, and left in for six hours. It 

 was not considered advisable to leave it longer, as, ' owing to the great 

 crush and unsettled state of the ground,' there might have been difficulty 

 in extracting it. Up to the time at which the thermometer was withdrawn, 

 no disturbance of the solidity of the ground had occurred. The tunnel, 

 and especially this part of it, was free from the action of any strong air- 

 current. 



Assuming 49° as the surface-temperature, we have here an increase of 

 36-3° in 2,790 feet, which is at the rate of 1° in 76-9 feet. 



Earlier observations were taken, at the depths of 871 and 897 yards, 

 by the colliery engineer ; but Mr. Garside reports that the thermometer 

 with which they were taken was an ordinary cheap one with wood scale, 

 and that on examination the tube was found to be a little loose in the 

 scale. It seems best therefore to neglect them as unreliable. 



^ In reference to an apprehension which was expressed that the heat of 

 drilling had not had sufficient time to escape, Mr. Garside writes that he 

 has on several occasions made a second observation in the same hole in 

 places where he knew that the strata would stand and not crack, and he 

 has always found the temperature unchanged ; but that it is impossible to 

 repeat the observation at such great depths as that of Ashton Moss, as in 

 a few hours the holes became crooked. 



Mr. Garside's next observation was at Bredbnry Colliery (in the 

 county of Cheshire), at the depth of 340 yards. A hole was drilled, as 

 before, in dry warren earth (an argillaceous rock) free from cracks or 

 water, in New Mine south level ; and the temperature, observed as before, 

 was 62°. 



Assuming (as above) 49° as the surface-temperature, we have here an 

 increase of 13° in 1,020 feet, which is at the rate of 1° in 78-5 feet. 



The distance from Ashton Moss Colliery is three or four miles, and 

 the two shafts are sunk through the same coal-measures, one being near 

 the outcrop, and the other more on the deep. 



Making no assumption as to surface-temperature, but comparing the 

 two observations with each other, we have an increase of 23-3° in 1,770 

 feet, which is at the rate of 1° in 760 feet. The consistency of these 

 results is eminently satisfactory. 



On a subsequent date, July 19, Mr. Garside took the temperature at 

 Nook Pit, belonging to the Broad Oak Colliery Company, at the depth of 



