On Underground Temperatures. 



27 



perature of the air at different levels varied very little, and was higher 

 in the third level than in one lower. 



Depth. 

 480 to 540 feet 

 600 „ 780 „ 



Temp, of air. 



.. 69° 

 .. 70 



Depth. 



780 to 840 feet 

 840 „ 900 „ 



Temp, of air. 

 . 73° 

 70 



That the temperature of the air does influence that of the rocks is 

 shown by another series of experiments made by him in holes in the 



rock in Dolcoath Mine with the following results : — 



Eate 







Temperature 



of increase 





Depths. 



of rock. 



per 1° F. 



I, , 



, 240 to 300 feet 



58° 



34 feet 



II 



. 540 „ 600 „ 



58 



71 „ 



III 



. . 720 „ 780 „ 



63 



57 „ 



IV.. . 



. . 1140 „ 1200 „ 



64 



83 „ 



V , 



. . 1320 „ 1380 „ 



78 



. 48 „ 



Mr. Fox does not give the temperature of the air, but states that 

 the abnormally low temperatures of Stations II and IV arose from the 

 passage of strong currents of air. The effect of these conditions, in 

 estimating the rate of increase of temperature with depth, is clearly 

 shown in the last column which I have added for this purpose. 



But although there maybe extreme cases, it is probable, as a general 

 rule, that the ventilation does not produce the extent of difference 

 between the temperature of the air and of the rock that it does in coal 

 mines. Mr. Fox who, to avoid the effects of ventilation, always, if 

 possible, made his observations near the ends of the levels, states that 

 in those cases there is little difference between the temperature of the 

 air and the rock. At the same time it is possible that, even then, the 

 uniformity may be owing to the rock having permanently cooled down 

 to the temperature of the air — though it may not be much. The 

 following are cases in which the temperatures of both are given. 



Temperature. 



Depth. 



No. 71. Par Consols 1248 feet. 



No. 72. Botallock 1128 „ . 



No. 77. Levant 1530 „ . 



No. 79. Tresavean 2112 „ . 



Ait. 



82° 

 81 

 85 

 91-5 



Eock. 

 84° 

 79 

 85 



90 -5 



Eate 

 of increase 

 per 1° F. 

 38 feet 

 40 „ 

 45 „ 

 52 „ 



Here it will be observed that there is only a difference of 1° to 2° 

 between the temperature of the air and the rock, and that the rate of 

 increase with depth is, with one exception, much more uniform. 



May not circumstances such as these account for the marked dis- 



