38 Mr. Moyle on the Temperature of Mines. [Jan. 



ature of the same spot in a deep and confined part of a mine at 

 work, in summer or winter ; or at least the miners are not sensi- 

 ble of any. Capt. W. Teague assures me, that he has often met 

 with ice in great abundance in Tin-Croft mine, at the depth of 

 318 feet below the surface ; and in such quantities that the lad- 

 ders have been impassable ; deep crevices in the walls have been 

 completely filled, and icicles hanging abundantly around him. 



As liquid and aeriform bodies convey heat on a different prin- 

 ciple from that observed in solids, viz. by an actual change in the 

 situation of their particles, instead of an augmentation of their 

 bulk, as in solids, in proportion to the absorption of caloric, it 

 may not be deemed irrelevant to explain this principle, and apply 

 it to the circumstances of the water in a relinquished mine, and 

 show how the whole water becomes of an uniform temperature. 



Supposing the greatest temperature is at E, the bottom A 

 of the mine, and the whole becomes filled with water by — 

 infiltration from the surface. This water must bring with B 

 it a medium temperature of the surface, and the different — 

 strata of earth through which it has passed, which, if of C 

 less heat than that possessed by the earth at the bottom, — 

 will of course become heated to the same degree; it, D 

 therefore, is expanded, and, becoming specifically lighter, — 

 ascends to the surface, and is replaced by a colder portion E 

 from above. This, in its turn, becomes heated and dilated, — 

 and gives way to a second colder portion ; and thus the 

 process goes on as long as the fluid is capable of imbibing heat. 

 Therefore, whether the thermometer is sunk to A, B, C, D, or E, 

 in an old mine, it must be found of an equable degree. 



M. de Mairan asserts, that the rigour of the cold of winter is 

 tempered by the heat imparted to the atmosphere by the earth 

 itself, which heat, probably possessed from its origin, is pre- 

 served and renewed by the incessant influence of the sun, to 

 which one half of its surface is constantly exposed. 



Admitting this fact, the temperature of the atmosphere must 

 depend on the capacity of the earth for receiving and retaining 

 heat, and for communicating it to the surrounding medium. 

 But as the earth is composed of land and water, it should be 

 considered that the capacities of these constituent parts, for 

 receiving heat are very different. Land, particularly when 

 dry, receives heat from the sun's rays very readily, but 

 transmits it through its own substance to great depths very 

 slowly ; and, on the other hand, water, by reason of its transpa- 

 rency, receives heat very slowly, but diffuses what it receives 

 more readily. 



Dr. Hales found, that in the month of August, 1724, when the 

 air and the surface of the earth were both at 88°, a thermometer 

 placed only two inches below the surface of the earth stood at 

 85° ; another, 16 inches under the surface, indicated 70° ; and a 



