blasting the rock, is universal in the Cornish mines. Indeed in all the mines situated in granite, almost the whole excavation of the galleries and shafts is effected by this agent. The operation is precisely the same as in quarries at the surface.
When the hole is charged and the match lighted, the operator and his immediate neighbours retire to a little distance until the explosion takes place, when they return almost immediately to remove the fragments and to resume their former labours in the inner extremity of the gallery, still filled with smoke and the sulphury vapours of the exploded powder. This operation is repeated in the same gallery, generally many times daily, insomuch that the sight and smell of the smoke is rarely not to be perceived, in some degree or other, throughout the whole period of excavating a gallery in a hard country. The extent of this practice in mining will be understood from the quantity of gunpowder consumed. In the six mines, the temperature of which is given above, and the far greater part of which are situated in the comparatively soft rock killas, the expenditure of gunpowder per month, in 1820, was 8,810 lbs.; the number of men employed underground being 2323. Each charge consists of from ¼ to ½ lb. of gunpowder. No means are taken to expel the smoke and irrespirable gases produced, which are left to find their way slowly to the outer extremity of the galleries and the shaft. They are certainly very offensive to the lungs, especially soon after an explosion, as I can myself testify from experience. The coloration of the sputa, from these fumes, is still more general and certain than from the inhalation of dust, and is
