1867.] The Ventilation of Coal Mines. 189 



of a shaft, the temperature increases, and it increases in some 

 ratio with, the depth. Mr. Edward Hull has given, as the result 

 of observations made in the Duckinfield colliery in Cheshire, an 

 increase of 1 J Fahr. for every 83*2 feet in depth. Professor 

 Phillips obtained results in Monkwearmouth colliery which 

 appeared to show an increase of 1° F. for every 60 feet of depth. 

 The results arrived at by Mr. Eobert Were Fox, in the deep mines 

 of Cornwall were, that for the first hundred fathoms, the increase 

 of temperature was 1° F. for every 50 feet ; in the second hundred 

 fathoms, 1° F. in every 60 feet ; and for the third hundred fathoms, 

 1^ F. in every 75 feet: thus showing that the increase was in a 

 constantly diminishing ratio. In addition to the natural heat in a 

 mine, the temperature is increased by the lights employed and by 

 the breathing of the men and horses. Therefore the air, after it 

 has passed through a mine, is of a higher temperature than when 

 it entered. Such heat acting upon the air of a mine rarefies it, 

 and passing into the "upcast" shaft presents a column of air 

 specifically lighter than that in the " downcast " shaft. Thus a 

 continual current of air is produced down one shaft, it travels 

 around the workings, and up another shaft j this constitutes what 

 is called natural ventilation. Mr. Nicholas "Wood has shown 

 that at Seaton pit, the shaft, having a diameter of 14 feet, equally 

 divided by a timber brattice, airtight from top to bottom, and a 

 depth of 1,560 feet, the length of the air courses being 3,036 feet, 

 by merely natural ventilation 7,002 cubic feet of air passed out of 

 the upcast side of the shaft per minute, the temperature of the air 

 entering the mine, at the top of the downcast, being 47" F., and of 

 that leaving the mine, at the top of the upcast shaft, 62 * 5° F. It 

 will be evident to any reflecting mind that the greater the difference 

 between the temperature of the air entering a mine and on leaving 

 it, the more powerful will be the mechanical force exerted by the 

 heat. Hence in winter natural ventilation is far more effective than 

 in the summer, at which season the surface temperature is so 

 slightly different from the subterranean, that very little movement 

 takes place. 



It being a necessity to secure a constant motion of the air 

 through every portion of a colliery's workings, and for this motion to 

 be of sufficient rapidity to carry off, as quickly as it is evolved, the 

 gas from the coal, an artificial system must be established. The 

 first obvious method would clearly be, to heat the air in one of 

 the shafts, or in one division of the shaft, where one only existed ; 

 hence the introduction of furnace- ventilation. The ventilating 

 current is produced by the difference of density between the air 

 passing down one shaft, or one side of a shaft, and that passing 

 up ;< — the amount of current varying with the square root of the 

 difference of temperature between the columns respectively; so 

 that if it were necessary to double an air-current, the difference 



