ON TIIK EATE OF INCEEASE OF UNnERGEOUND TEMPERATDEE. 77 



since our present patterns of instrument came into use. The questions 

 for discussion are thus confined to those which relate to possible diiferences 

 between the temperature of the point at which the thermometer was 

 placed and the normal temperature at the same depth in its vicinity. 



1. The heat generated by the action of the boring tool will vitiate the 

 observation if snfScient time is not allowed for its escape. 



A very full discussion of this subject in connection witli the great 

 artesian well at La Chapelle will be found in reports V., VI., and VII., 

 clearly establishing the fact that the temperature at the bottom both on 

 the third and the sixth day after the cessation of boring opei'ations, was 

 7j° F. higher than after the lapse of four months, though the water had 

 been left to itself during this interval. Further evidence showing that 

 the temperature in the lower part of a bore full of water may thus be 

 raised several degrees, is furnished by the Snb-Wealden bore (VI. 255). 



The heat generated by boring will increase with the hardness of the 

 rock, and Mr. Garside, in report XIV., testifies that he has found two 

 hours a sufiScient time to give the permanent temperature in holes 3^ feet 

 deep and 2 inches in diameter drilled in the sides of a deep mine in the 

 East Manchester coalfield. 



2. The generation of heat by local chemical action is well known to 

 be a powerful disturbing cause when pyrites is present. In the tentli 

 report, the observers in the mines of Schemnitz say, ' Pyrites and also 

 decaying timber were avoided, as being known to generate heat.' In the 

 uinth report, p. 210, the observations in the coal mines of Anzin show 

 a temperature of 70f ° F. in shaft IV. (a very dry one) at the depth of 

 21'2 metres, or less than 70 feet. This must be about 15° F. above the 

 normal temperature. In shaft II. the observer mentions that there was at 

 a depth of 90 m. a seam of coal in which heat was generated by oxidation. 



At Talargoch lead mine in Flintshire (XIII., XIV.), the discrepancies 

 between the temperatures at the six observing stations are suggestive of 

 local chemical action. 



3. Convection of heat has proved a very troublesome disturbing cause. 

 As to convection of heat by air in a shaft or well not filled with water, 



evidence will be found in the second report, both in the case of Mr. 

 Hunter's observations in the shafts of two salt mines at Carrickfei'gus, 

 having the depths of 570 and 770 feet respectively, and in the case of 

 Mr. Symons' observations at Kentish Town, where the first 210 feet of the 

 well are occupied with air. At the depth of 150 feet the temperature was 

 52'1 in January and 54'7 in July. 



Convection of heat by water in old shafts whicli have heen allowed to 

 become flooded, is very manifest in some of the observations communicated 

 by Mr. Burns in the second and fourth reports. In Allendale shaft 

 (Northumberland), 300 feet deep, with about 150 feet of water, the 

 temperature was practically the same at all depths in the water, and this 

 was also the case in Breckon Hill shaft, where the observations extended 

 from the depth of 42 feet to that of 350 feet. A similar state of things 

 was found in a shaft at Ashburton (Devon), by Mr. Amery (III. 7), who 

 observed at every fiftieth foot of depth down to 350 feet. 



Convection by water in the great well at La Chapelle, 660 m. (2,165 

 feet) deep, and 1 35 m. (4 feet 5 inches) in diameter at the bottom, 

 appears probable from the following comparisons. 



Very concordant observations (communicated by M. Walferdin to 

 Compies Bendus for 1838) at three different wells in the Paris basin of 



